Food Organics Review

Food Organics Processing Options for New South Wales

2007Second Edition

Recycled Organics Unit Food organics processing options for New South Wales Page 2 2nd Edition 2007

Recycled Organics Unit PO Box 6267 The University of New South Wales Sydney Australia 1466 Internet: http://www.recycledorganics.com Contact: Angus Campbell Copyright © Recycled Organics Unit, 2001. Second Edition. First Published, 2001. This document is and shall remain the property of the Recycled Organics Unit. The information contained in this document is provided by ROU in good faith but users should be aware that ROU is not responsible or liable for its use or application. The content is for information only. It should not be considered as any advice, warranty, or recommendation to any individual person or situation.


Table of Contents

FOOD ORGANICS PROCESSING OPTIONS FOR NEW SOUTH WALES 1

EXECUTIVE SUMMARY 5

SECTION 1 INTRODUCTION 9 1.1 Background................................................................................................................... 9 1.2 Scale of technology reviewed..................................................................................... 10 1.3 Objectives ................................................................................................................... 11 1.4 Terminology................................................................................................................ 11 1.5 Food organics material description............................................................................. 11

SECTION 2 ECONOMIC ISSUES CONCERNING THE REPROCESSING OF FOOD ORGANICS 13

SECTION 3 ENVIRONMENTAL LICENSING AND PLANNING REQUIREMENTS 14 3.1 Licensing issues ......................................................................................................... 14 3.2 Planning issues........................................................................................................... 14 3.3 Siting of facility............................................................................................................ 15 3.4 Environmental issues with regard to food organics processing ................................. 16

SECTION 4 IN-VESSEL COMPOSTING SYSTEMS 18 4.1 Introduction ................................................................................................................. 18 4.2 Generic description of technology .............................................................................. 18 4.3 Quality issues relating to the technology.................................................................... 25 4.4 Environmental impacts and licensing requirements ................................................... 26 4.5 Economics .................................................................................................................. 26 4.6 List of manufacturers .................................................................................................. 28

SECTION 5 WINDROW-BASED COMPOSTING SYSTEMS 35 5.1 Introduction ................................................................................................................. 35 5.2 Generic description of technology .............................................................................. 35 5.3 Quality issues relating to the technology.................................................................... 44 5.4 Process control and infrastructure upgrades.............................................................. 45 5.5 Environmental impacts and licensing requirements ................................................... 45 5.6 Economics .................................................................................................................. 45 5.7 List of manufacturers (composting facilities) .............................................................. 46

SECTION 6 ANAEROBIC DIGESTION SYSTEMS 51 6.1 Introduction ................................................................................................................. 51 6.2 Generic description of technology .............................................................................. 51 6.3 Quality issues relating to the technology.................................................................... 59 6.4 Environmental impacts and licensing requirements ................................................... 60 6.5 Economics .................................................................................................................. 60 6.6 List of manufacturers .................................................................................................. 61

SECTION 7 FOOD ORGANICS USE IN ANIMAL FEED PRODUCTION 67 7.1 Introduction ................................................................................................................. 67 7.2 Generic description of processes ............................................................................... 67 7.3 Quality issues relating to the technology.................................................................... 71 7.4 Environmental inputs and licensing requirements...................................................... 73 7.5 Economics .................................................................................................................. 74 7.6 List of manufacturers .................................................................................................. 75


SECTION 8 DIRECT SOIL INJECTION OF FOOD ORGANICS 80 8.1 Introduction ................................................................................................................. 80 8.2 Generic description of technology .............................................................................. 80 8.3 Quality issues relating to the technology.................................................................... 83 8.4 Environmental impacts and licensing requirements ................................................... 84 8.5 Economics .................................................................................................................. 89 8.6 List of manufacturers .................................................................................................. 89

SECTION 9 CONCLUSIONS 94

SECTION 10 REFERENCES 95

SECTION 11 GLOSSARY 99


Executive Summary The majority of food organics materials generated in the Greater Sydney Region are sent to landfill

sites. This practice is inconsistent with the principles of the Waste Hierarchy (Waste Minimisation and

Management Act, 1995) and principles of Ecologically Sustainable Development (ESD) as there are a

range of alternatives that offer improved environmental and resource conservation outcomes.

Diverting food organics from landfill sites will reduce pressures on limited landfill space, while at the

same time diverting valuable resources from landfill to a range of higher resource value applications.

This review identifies a number of commercial scale technologies or systems that can process food

organics and convert these materials into valuable, safe and useful end-products (Table 1).

Technologies considered include, in-vessel aerobic composting, windrow composting, anaerobic

digestion, stock food manufacture, and direct soil injection of food organics. Each system is reviewed

in detail and its associated costs and benefits are highlighted. Please note, this is not a comparative

study; the suitability and associated benefits of these systems is dependent upon regional and site

specific variables.

Table 1 Summary of technologies reviewed.

Technology Technology price range Processing speed Direct animal feeding Very low, no processing of feedstocks.

Transport costs are perhaps the most significant expense associated with direct feeding.

No processing time, as food organics are fed directly to livestock.

Direct soil injection Very low processing costs. Application machinery adds considerable establishment costs to an operation, ranging from $80 000 for tractor drawn injectors to $310 000 for specialised sludge injection trucks. Other expenses include tractors, storage tanks and pumps.

Very little processing time if feedstock is received in liquid form. Short processing time for liquefaction.

Windrow composting $100 000 - $300 000+ depending upon the equipment purchased (e.g. windrow turners) and associated infrastructure. Establishment costs are higher if specialised windrow turning machinery ($500 000+) is purchased.

3-5 weeks (though some companies have reported processing times of up to 4.5 months). Additional processing time (several weeks) is required if products are matured.

Processed animal feed Dependent upon the technology used. Processes can cost up to $1 000 000+ depending upon the processing capacity of a facility.

Several hours to several days.

In-vessel composting Technologies range in price from $70 000 to $1 000 000+ depending upon the processing capacity and number of vessels purchased.

1-3 weeks depending upon the process used + 2-4 weeks maturation (if required).

Anaerobic digestion This is the most expensive technology, costing well above $1000 000+ for most commercial scale facilities.

10-20 days depending upon the process used. Additional processing (several weeks to months) is required if solid digestate is composted).


In general, establishment and running costs are related to the processing capacity of a technology and

the level of sophistication employed. Of the recycling approaches reviewed, the direct feeding (to

livestock) of unprocessed food organics is the cheapest technology/approach available for the re-use of

food organics. Of the other processing technologies, direct soil injection, windrow composting and

smaller in-vessel composting systems are the next cheapest option. Larger scale, more complex in-

vessel composting systems and anaerobic digestion systems add considerable expense to the

establishment cost of a facility. However, at the same time, larger systems have greater processing

capacities and better process control than alternative cheaper technologies (Table 2). The adoption of

these technologies may require operator compliance to NSW Acts and Regulations. These are

summarised below.

Table 2. General (generic) comparison of different food organics processing systems. Note: system suitability is dependent upon regional and site specific factors.

System1 Infrastructure cost2

Additives for processing Products Space required3

Direct animal feeding Very low Oats; other cereals

Stock food (high risk) Very small

Direct injection Low Generally none Liquid soil additive

Very small for storage; Very large for application

Windrow composting Low Garden organics Composted material Large

In-vessel composting Medium Garden organics Composted material Medium–large

Processed animal food High–very high Generally none Stock food Medium

Anaerobic digestion Very high Garden organics Electricity, composted

product Medium–large

1 Systems arranged in order of generic infrastructure cost – this arrangement does not indicate quality or suitability of systems in different situations. 2 Infrastructure cost is dependent upon the scale of an operation – these estimates should only be used as a general guide. 3 The space required for the different systems is dependent upon the amount of feedstock a system processes – estimates of size should only be used as a general guide.

Acts and Regulations

In NSW, the establishment of a food organics re-processing facility/operation requires that the facility

conforms to certain Acts, Regulations and guidelines. Some of these include:

• Protection of the Environment Operations Act (1997) • Environmental Planning and Assessment Act (1979) • Environmental Planning and Assessment Regulation (2000) • Clean Air (Plant and Equipment) Regulation (1997)


Other legislation that is relevant to the reprocessing of food organics into stock food include:

• Stock Foods Act (1940) • Stock Foods Regulations (1997) • Stock Diseases Act (1923) SECT 20FB • Stock Diseases (General) Regulation (1997).

Although there are no guidelines for the direct injection of food organics to land, companies practicing

direct injection generally follow the biosolids guidelines by the NSW Environment Protection

Authority.

Aerobic in-vessel composting systems

Aerobic in-vessel composting systems range in price from several thousand dollars for a specific

technology to over one million dollars for a large number of composting vessels, or one large

processing system. These technology types are often more space efficient than alternative windrow

composting operations. However, establishment costs can be significantly higher depending upon the

technology used and processing capacity required. In-vessel systems allow for better process control

than windrow composting, and may have fewer labour requirements. In-vessel systems can cater for a

range of food organics, but usually require mixing with other complementary bulking agents in order to

facilitate effective composting. Pasteurised or composted soil conditioners or mulches are the main

products generated by these systems.

Aerobic windrow composting

Windrow composting (turned, aerated or passive) generally requires lower establishment costs than

aerobic in-vessel composting systems, but may have higher labour requirements and higher running

costs. The type of composting operation used (e.g. turned v’s forced aerated), will impact upon the

labour requirements and establishment costs. Costs are also dependent upon the size of a facility,

infrastructure and machinery used. Prices range from $60 000-300 000+ for passively or forced aerated

systems to well over $300 000 for systems using specialised machinery such as windrow turners.

These systems also have greater space requirements than in-vessel systems and offer lower levels of

process control. Windrow composting facilities may require improved receival and short term storage

systems for food organics feedstocks to suppress odours. Windrow composting produces similar end-

products to in-vessel systems, but processing times are longer due to the use of less efficient and less

complete methods of composting.

Anaerobic digestion

Anaerobic digestion is perhaps the most expensive technology that can be used to process food

organics. These systems are generally much more complicated that other processing systems and have

greater space requirements than equivalent in-vessel composting systems. Commercial scale facilities

generally cost well in excess of $1 000 000, depending upon the size and complexity of the system

used. Anaerobic systems generate methane, which can be used to produce electricity to run a facility.

Solids are also produced, which are usually composted aerobically to produce soil conditioner


products. Anaerobic systems therefore do not displace or replace aerobic composting systems. On an

energy budget basis, studies have shown that anaerobic digestion facilities are less energy intensive

than equivalent in-vessel composting systems, due to the generation of methane (and electricity) during

the digestion process.

Stock food

Food organics can be converted into or used as stock food. The level of processing the food organics

undergo ranges from no processing (direct feeding) to considerable processing using processes such as

fermentation. The length of time required to convert food organics into stock food (where processing

is used) ranges from several hours to several days. The quality of stock food produced is dependent

upon the process used and the quality of feedstock. Stock food generated from poor quality or meat

based feedstocks carry the greatest risks, as they may have pathogens or residual chemicals, which are

harmful to livestock. More sophisticated processes (fermentation, pasteurisation, sterilisation etc.) can

be used to address these pathogenic or chemical risks, but processing time and expense will increase.

Some of these processes (e.g. fermentation) cost well in excess of $1 000 000.

Direct soil injection

The direct injection of liquefied food organics in soil has very low processing requirements or costs,

but may require considerable capital expenditure to establish an operation. This form of food organics

recycling may carry some risks (as identified in scientific literature), as the food organics are not

processed, pasteurised or treated in any way. This may contribute to phytotoxic effects on plants and

the contamination of nearby waterways and ground water if the food organics are not applied in

suitable locations or in appropriate quantities. However, if operators follow the environmental

guidelines for biosolids, runoff and contamination issues should be minimised. Research has shown

that the direct soil injection of liquefied food organics (at suitable application rates) increases organic

matter and soil nutrient levels. Applications may also enhance microbial activity in soil, contributing

to improved soil stability.

General

This review provides a basis for increasing knowledge and awareness of food organics processing

options in industry and government, supporting informed decision making within an Environmentally

Sustainable Development (ESD) framework across New South Wales.

It is not within the scope of this review to recommend any of the technologies covered, as their

suitability for application is dependent upon regional and site specific variables. For a more detailed,

situation specific evaluation of food organics processing options, further research is required.


Section 1 Introduction 1.1 Background

Highly putrescible food organics material makes up a high percentage of the waste stream produced by

the municipal and commercial and industrial sectors (EPA, 1998). Current practices of disposing of

food organics into solid waste class 1 (putrescible) landfill sites (EPA, NSW, 1999b) are inconsistent

with the principles of the Waste Hierarchy (Waste Minimisation and Management Act, 1995), as there

are alternative management strategies which realise a higher net resource value of these materials. The

reprocessing or re-use of food organics will help alleviate increasing pressures on landfill sites, while at

the same time utilising materials that have been considered ‘waste’ as a resource.

In total, 440 000 tonnes/annum of food organics are produced in the Sydney Metropolitan Area (SMA)

(Waste Enquiry, 2000). The commercial and industrial sector (C&I) currently produces 160 000

tonnes/annum of food organics, whereas the municipal sector produces 280 000 tonnes/annum across

the SMA. Food organics comprise approximately 10% by weight of all waste landfilled by the C&I

sector, whereas this increases to approximately 21% by weight of all waste landfilled by the municipal

sector (Waste Enquiry, 2000).

It is important to note that no new class 1 landfills are planned for putrescible waste generated in the

SMA, and that current putrescible landfill capacity is expected to be exhausted by 2011 based on

current levels of putrescible waste generation and recycling/reprocessing rates (Wright, 2000).

Opportunities for maximising the diversion of food organics from landfill must be secured to conserve

remaining putrescible waste landfill capacity available to the SMA.

Diversion of food organics from landfill not only conserves finite landfill space, but is also associated

with a number of environmental benefits. As food organics are very high in moisture and nutrients,

these materials generate considerable quantities of methane during decomposition, contributing to

global warming. Food organics are the second largest source of methane generated by landfills (EPA,

US, 1997a). The nutrients present in food organics also contribute to the high nutrient loadings in

landfill leachate – a major contributor to groundwater and surface water contamination in regions with

unlined landfills (Russel and Higer, 1988; Borden and Yanoschak, 1990; Assmuth and Strandberg,

1993).

At present, only 3.1% of food organics produced by the C&I sector is recycled, while no food organics

collected from municipal sources are recycled (Waste Enquiry, 2000). Although there are a number of

obstacles to be overcome – such as collection, transportation, storage and processing (Farrell, 1998) –

there are many processing opportunities and technologies currently available to divert these highly

putrescible materials from the waste stream. This review details reprocessing approaches relevant to

the Greater Sydney Region, including the use of in-vessel aerobic composting systems, windrow

systems, anaerobic digesters, animal feed production systems and direct soil injection of food organics.

Each process is described and case studies from within Australia and internationally are presented.


1.2 Scale of technology reviewed

This review focuses on large-scale technologies/systems capable of processing in excess of 250 kg/day

of food organics (Table 1.1). In some instances, smaller (mid-scale) technologies can be used in series

to process a large-scale quantity of food organics (Rynk, 2000a). Consequently, the division between

mid and large-scale processing technologies may be unclear (Recycled Organics Unit, 2000).

Large-scale processing systems predominantly consist of technologies with the ability to process

between 250 and 5000+ kg of food organics per day. Procedures involved in the management of these

processing systems are usually automated or carried out with industrial machinery (Recycled Organics

Unit, 2000).

Table 1.1 Processing technology options (adapted from Recycled Organics Unit, 2000).

Category Processing range (kg d-1) a Technology options

Technology specific processing range per unit (kg/d) a

(manufacturer data)

Indicative investment

cost (AUS$)

Mid-scale 20–250

• In-vessel, induced and/or forced aeration, continuous- or batch-flow composting units,

• Windrow composting, • Animal feed production.

20–250 $10 000–$100 000

• In-vessel, forced and/or induced aeration, batch-flow, modified roll-off containerised composting units,

• Windrow composting. • Direct soil injection

250–1000 $100 000–$300 000+

Large-scale 250–5000+ • In-vessel, passive-or forced aeration, continuous-flow, batch-flow, vertical loading composting systems,

• Windrow composting, • Direct soil injection • Anaerobic digestion, • Fermentation processors, • Animal feed production

250–5000+ $75 000–$1 000 000+

a Processing range based on a given mass of compostable organics processed seven days a week.

Investment costs associated with the purchase and installation of processing technologies depend upon

the size and complexity of the technology type, and/or whether the system is purchased or leased from

a supplier. Figures quoted in Table 1.1 are indicative only, and they will vary considerably with system

and manufacturer. Investment costs quoted do not include those associated with collection, process

management, labour, site-works (particularly with large-scale on-site systems) and on-going

maintenance. Furthermore, the cost estimates do not include ancillary equipment, such as that

employed for size reduction, blending, screening etc.


1.3 Objectives

This review has addressed the following objectives:

1.3.1 Primary objective

To inform the identification and subsequent development of appropriate and cost effective food

organics infrastructure and practices by reviewing documented international and national experience.

With this information, relevant bodies can make informed decisions regarding the suitability of

different food organics processing technologies for the GSR.

Briefly, the review consists of:

• A (generic and brief) process-based review of food organics processing systems;

• Detailed coverage of in-vessel aerobic systems, windrow-based aerobic systems, anaerobic

digestion systems, animal feed processing systems, and direct soil injection;

• A listing of current food organics processing facilities and related installations in Australia and

internationally, and

• Case studies of current food organics processing facilities and related installations in Australia and

internationally.

1.4 Terminology

The terminology in this package is consistent with that officially adopted by the NSW Waste Boards in

July 2000. That is, compostable organic materials (including garden organics, food organics, wood and

timber) are processed by the recycled organics industry into a range of recycled organics products. The

Recycled Organics Unit has submitted a range of compostable organics material description sub-

categories for inclusion in the Australian Waste Database. These material descriptions have already

been adopted as a standard by the NSW Waste Boards (Recycled Organics Unit, 2000c). “Food

organics” material (formerly “food waste”) is defined by its component parts, as detailed in Section 1.5

below.

Terminology used in this report is consistent with that documented in the Recycled Organics Unit

Dictionary and Thesaurus: standard terminology for the NSW recycled organics industry (Recycled

Organics Unit, 2000a). This document has undergone national peer review, and is freely downloadable

from http://www.rolibrary.com

1.5 Food organics material description

Food organics is a generic expression that covers all food residuals regardless of whether they are

derived from domestic or commercial kitchens, special events, or from commercial food processing

operations (Recycled Organics Unit, 2000b).


Where greater detail in food organics material categorisation is required, the consistent application of

standard (and relevant) sub-categories within composition studies is essential. Standard material

description sub-categories have been developed by the ROU in consultation with recycled organics

industry and waste management sector stakeholders for garden organics, food organics, and for

residual wood and timber. These standard material description sub-categories for food organics

material are detailed in Table 1.2.

Table 1.2 Range of materials categorised as food organics (Recycled Organics Unit, 2000).

Material description Material description subcategory

Food organics • fruit and vegetables

• meats and poultry (including bones <15mm),

• fats and oils

• seafood (including crustaceous seafood material)

• recalcitrants (bones >15mm, oyster shells, coconut shells)

• dairy products (solid and liquid)

• bread, pastry and flours (including rice and corn flours)

• food soiled paper products (hand towels, butter wrap)

• biodegradeables (cutlery, bags, polymers)1

• contaminants - typically plastic, stainless steel and other cutlery, ceramics, aluminium foil

1 These are included here for the purpose of auditing, where material description subcategory level of detail is required. The definition here does not imply that these materials are food based.


Section 2 Economic issues concerning the reprocessing of food organics

Although there are many benefits associated with the reuse or reprocessing of food organics, there are

also a number of constraints that may influence the economic feasibility of such practices; these

include:

• Cost of collection and transport;

• Processing costs;

• Marketing costs and market potential, and

• Institutional constraints – separation, refrigeration, frequency of pick up and storage.

Other issues impacting upon the reprocessing of food organics are feedstock volume and quality. In

some instances, the quantity of food organics may not be sufficient for economic reprocessing (Farrell,

M., 1998). As sources of food organics become smaller or less consistent, costs will increase.

Similarly, as supply per source is less, the cost of collection will increase (Derr and Dhillon, 1997).

These issues must be considered when selecting an appropriate reprocessing approach or technology.

The various sources of food organics, if separated and handled properly, have the potential to reduce

disposal costs and produce valuable end-products. In a review of processing approaches, Derr and

Dhillon, (1997) suggested that composting is the most feasible option for these materials. However, for

some types of food organics, which are generated in sufficient quantity and have a value added

potential, other reprocessing options (e.g. digestion or fermentation) should also be considered.

There are several options available for the processing of food organics that are consistent with the

principles of the waste management hierarchy (EPA, 1997b). These include:

• Aerobic in-vessel or windrow composting;

• Anaerobic digestion;

• Re-use or reprocessing into stock food, and

• Direct soil injection.

Reprocessing opportunities produce valuable products from food organics materials. However, if the

cost of processes used to create an end-product are too high, then non-recycled alternatives may be

favoured by the market. This is particularly important in situations where food organics are converted

into animal feed using expensive processing procedures. Alternative products such as grain (e.g. oats

or corn) may be preferred by landholders if they are cheaper (Glen, 1997).


Section 3 Environmental licensing and planning requirements

3.1 Licensing issues

The establishment of food processing facilities within NSW may require that they comply with

Schedule 1 of the Protection of the Environment Operations Act (1997) (Table 3.1). Proposed

developments that meet any of the conditions listed in Table 3.1 are considered to be scheduled

activities in terms of the Act and require an environment protection licence from NSW Environment

Protection Authority to operate. Note that non-scheduled activities may still require a permit or licence

to operate from a consent authority (usually a local council).

Table 3.1 Extract from Schedule 1 of the Protection of the Environment Operations Act (1997).

Conditions that classify a reprocessing activity a scheduled activity

Reprocessing or treatment facilities (including facilities that mulch or fermentorganic residuals, or that are involved in the preparation of mushroom growing substrate, or in a combination of any such activities) that:

(1) receive over 200 tonnes per year of animal waste, food waste, sludge orbiosolids, or

(2) receive over 5,000 tonnes per year of wood waste, garden waste, or naturalfibrous material, or

(3) receive any organic waste and are located within 500 metres of anyresidentially zoned land, or within 250 metres of a school or hospital or adwelling not associated with the facility.

Information about licensing and associated costs may be found in “Guide to Licensing under the

Protection of the Environment Operations Act 1997”, published by the EPA.

3.2 Planning issues

The (Environmental Planning and Assessment Act, 1979) and the (Environmental Planning and

Assessment Regulation, 2000) require developers of new facilities to lodge development applications

to an appropriate consent authority. Facility development proposals will fall into a number of possible

categories under this Act, and may be (Recycled Organics Unit, 2000b):

• Local development (refer s. 76A ss. 4); • Advertised development (refer s. 79A); • Integrated development (refer s. 90-93B). • Designated development (refer s. 77A-79 and Schedule 3 of Environmental Planning and

Assessment Regulation, 2000). • State significant development (refer s. 88-89A).

These different categories result in different assessment processes, particularly related to different

levels of public advertising and appeal rights. However, they also affect which level of government has


the decision-making responsibility and the degree of scrutiny and review by other State Government

authorities such as the Environment Protection Authority (Inner Sydney Waste Board, 2000).

In general, almost all commercial developments require a development application be prepared and

development consent be obtained before any developments can proceed. In some cases, developments

may contravene a local environmental planning instrument (e.g. a local environmental plan, LEP). A

LEP is a legally binding policy document, which sets out a strategic planning framework for a part of,

or for an entire local council area. These documents are made under the Environmental Planning and

Assessment Act (1979).

The purpose of an LEP is to:

• define zonings, permissible land uses and control development; • reserve land for public purposes; • control advertisements; and • provide for the protection of trees, vegetation, native animals and plants (Farrier et al., 1999).

Where a proposed facility contravenes a LEP, rezoning of an area may need to be performed. The

likelihood of achieving this will depend on the nature of the development and the strategic planning

goals a local council has for a particular area (Recycled Organics Unit, 2000b).

The performance based development process assesses proposals based on their likely impact —

sometimes referred to as Environmental Impact Assessment (EIA). The suitability of a particular

proposal is judged not on arbitrary and inflexible legal definitions, but rather on the anticipated impact

the development will have on its built and natural environment and the amenity of its neighbours (Inner

Sydney Waste Board, 2000).

3.3 Siting of facility

During initial site identification, attention must be given to how a facility may affect the environment,

in terms of (Recycled Organics Unit, 2000b):

• air quality; • water quality; • soil quality; • transport and traffic; • noise; • energy needs; • social issues; • public health; • visual issues; • flora and fauna; • associated hazards; • heritage issues, and • economic issues (Department of Urban Affairs and Planning, 1996).

Appropriate siting of a facility is, perhaps, the most effective way of dealing with potential negative

impacts on local amenity, followed closely by careful design and selection of process components and

equipment and by good operating techniques, procedures and staff training. While operational and


market considerations are important factors when selecting sites, a high priority must be given to the

environmental and social characteristics of the location. Appropriate site selection can avoid or reduce

many of the environmental problems inherent with proposals, and (Recycled Organics Unit, 2000b):

• reduce the need for technically based environmental mitigation measures and ongoing management measures;

• result in substantial savings in establishment and operation; • reduce levels of public concern, and • avoid potential delays in approval processes (Department of Urban Affairs and Planning, 1996).

3.4 Environmental issues with regard to food organics processing

Through environmental management plans, facilities need to adopt strategies that meet the

environmental performance objectives identified in Table 3.2. These strategies allow the consent

authority and government regulating authorities to consider the likely impacts of a development on the

environment, and whether development consent and an environmental protection licence (if needed)

should be issued to the proponent, subject to conditions if necessary. Proponents should consult the

[draft] Environmental Guidelines: Composting and Related Facilities (EPA, NSW, 2000) for detailed

information on how these performance objectives may be achieved (Recycled Organics Unit, 2000b).

Of the issues identified in Table 3.2, water pollution and air pollution are often identified as the main

issues affecting facilities. These are described in greater detail below.

Table 3.2. Environmental performance objectives required in an environmental management plan (Recycled Organics Unit, 2000b).

Performance Objective Outcome

Prevent water pollution Surface or underground discharges of leachate and water from the facility must not pollute groundwater and/or surface waters at or near the processing facility.

Minimise methane gas emissions and explosion hazards

Minimise emissions of methane to air and ground and the risk of explosions.

Minimise nitrogen oxide and non methane organic compound emissions

Minimise emissions of nitrogen oxides and non-methane organic compounds whenever using biogas combustion processes.

Minimise odour emissions Minimise odour emissions. Minimise bioaerosol emissions Minimise bioaerosol emissions. Ensure suitability of incoming feedstock Incoming feedstocks must not create negative environmental or amenity impacts. Ensure environmental quality of reprocessed products and stabilised wastes

Ensure that the output of products from the facility can be beneficially and sustainably used, and that any stabilised wastes are suitable for disposal at the facility that receives the waste.

Ensure safe storage and disposal of residual wastes and contaminated materials

Process residues and contaminated products must be stored appropriately and disposed of lawfully.

Minimise stockpiling Stockpiles of raw materials and finished products must be kept as small as practicable to avoid potential negative environmental impacts.

Prevent unauthorised entry Prevent unauthorised entry to the site Minimise noise emissions Noise emissions must not be intrusive or detract from the local amenity. Minimise dust emissions Minimise dust emissions from the facility.

Prevent proliferation of pests and vermin Prevent pests and vermin from proliferating at and/or near the facility to avoid health risks to facility personnel and the local community.

Prevent proliferation of weeds Prevent weeds from proliferating to preserve local amenity and to prevent their propagation via compost, soil conditioner and mulch products.

Minimise litter Litter and site materials are effectively controlled and retained on the facility.

Ensure adequate fire fighting capability Adequate fire prevention measures are in place and that fire fighting equipment can be accessed and staff are trained and able to manage fire outbreaks at any part of the processing facility.


3.4.1 Water pollution

Leachate may be generated from food organics during storage and processing. These leachates can be

acidic (e.g. from anaerobic conditions), and can therefore contribute to the dissolution of metals and

metallic compounds from within the feedstock material. Alkaline leachates can also be formed in

materials with a low carbon to nitrogen ratio under normal aerobic conditions. Consequently,

leachates from food organics processing facilities (regardless of technology type) have the potential to

pollute ground and surface waters. The high nutrient content of these liquids is utilised by bacteria and

other microorganisms, resulting in high biological oxygen demand. In addition, runoff from a facility

may contribute to increased sediment loads in adjacent waterways.

To prevent water pollution, facilities should comply with the design and operating requirements of the

NSW Department of Housing guideline “Managing Urban Stormwater: Soils and Construction” (NSW

Department of Housing, 1998).

3.4.2 Air pollution

The release of excessive quantities of atmospheric pollutants such as bioaerosols, methane and carbon

dioxide and odours (from the ammonia, volatile amines, hydrogen sulphide and volatile organic

compounds) are not acceptable from food organics processing facilities. Process control and the use of

appropriate infrastructure is therefore important to minimise the release of these pollutants. Developers

must comply with NSW Acts, regulations and licensing conditions if food organics processing facilities

are to be established.

Gas emission concentrations from a facility must comply with the limits prescribed in the Clean Air

(Plant and Equipment) Regulation 1997 or specific licence conditions. In addition, the Protection of

the Environment Operations Act 1997 prohibits the emission of offensive odours (as defined in that

Act) from scheduled facilities unless:

• the occupier can establish that the emission was identified in the facility licence as a potentially offensive odour, and

• that it was emitted in accordance with licence conditions directed at minimising the odour, or the only people affected by the odour were facility staff.

Food organics processing facilities will generally be identified as generators of potentially offensive

odours on an EPA licence, and they will therefore have licence conditions directed at minimising the

odour emissions outside the facility.


Section 4 In-vessel composting systems 4.1 Introduction

Aerobic decomposition is a naturally occurring process involving the biological breakdown of organic

materials in the presence of oxygen. This process encourages the development of colonies of bacteria,

and is characterised by the generation of heat (Gottas, 1956). This decomposition mechanism is used

by aerobic in-vessel technologies to treat different compostable organics material.

In-vessel composting systems differ in their scale of application. Some are designed to compost small

volumes of material from such places as schools, restaurants, cafeterias and local produce markets,

while others are designed to be used in centralised facilities to receive feedstock materials from a

number of sources. Many of these systems are modular, allowing for the addition of individual

containers/units as feedstock volumes increase (Rynk, 2000a). Large scale systems (individual or

modular) can manage feedstocks from multiple generators at a central location. Compared with small

scale systems, large scale systems utilise larger (and/or more) containers, have more sophisticated

processes and incur greater capital expenses (Tardy and Beck, 1996).

4.2 Generic description of technology

Digestion of feedstocks in aerobic in-vessel systems is achieved through careful monitoring and control

of the composting process. Although the specifications for in-vessel systems vary widely, they

commonly comprise fixed augers or agitated beds to promote mixing. Moisture and temperature levels

are closely monitored and most systems use forced aeration technologies (Tardy and Beck, 1996).

These systems are usually:

1. Insulated to retain heat and to provide uniform temperature distribution; 2. Enclosed to prevent pest/vermin access and contain odours, and 3. Designed to contain and/or manage leachate.

A process flow diagram for an in-vessel system is shown in Figure 4.1. More detailed descriptions of

the process stages are described below.

4.2.1.1 Size reduction/initial screening/bulking agents

Most processes may require an initial size reduction and screening phase for the removal of physical

contaminants which may interfere with operations and to facilitate more rapid decomposition and

processing of feedstocks. Although source separated materials should be relatively free of

contaminants, it may still be necessary to screen the feedstock material and size reduce depending upon

the material type (Curzio et al., 1994). The addition of bulking agents to the food organics material is

often necessary to help maintain or increase porosity of the compost mixture and to adjust the carbon to

nitrogen ratio for optimal decomposition. Woodchips or garden organics are typically used for this

purpose.


4.2.1.2 Composting process

Material is usually fed into the top of a composting vessel. Depending upon the type of process used,

the material in the vessel may be static, turned by mechanical devices or aerated. In aerated systems,

fresh air is drawn into the supply fans and exhaust air is recirculated into the mass when necessary,

either to control temperature or oxygen levels. Temperatures of 50-60ºC and oxygen levels of >10%

(v/v) are usually maintained in such systems to maximise the rate of decomposition and to minimise

odour production. Use of aeration systems allows for very close control of the composting process,

with minimal temperature variations between the inlets and outlets of vessels (Stentiford, 1996). In

completely enclosed systems, leachate from the vessels is recycled and used to control moisture levels

in the vessels and also to inoculate fresh feedstock material. The composting process lasts for several

days to a number of weeks depending upon the technology used and the desired quality of the

discharged product (See Section 4.2.2).

4.2.1.3 Biofilters

Although most aerated in-vessel processes recycle the air used for process control, there is an amount

of air that is eventually discharged from the system. This air may carry odours and other larger

particulates (bioaerosols). To address this pollution issue, most systems contain a biofilter component,

which is used to clean the air discharged from a composting vessel. Biofilters may be present in a

number of forms, depending upon the manufacturer and processing system used. One type of biofilter

used by containerised in-vessel systems comprises small containers adjacent to larger composting

vessels, containing mixtures of mature compost and wood chips (Block and Farrell, 1998).

Microorganisms within the water film on compost particles breakdown odorous compounds (such as

organic sulfides), rendering the process air relatively odour free (Haug, 1993).

Figure 4.1 In-vessel aerobic composting system flow chart (Adapted from Waste Enquiry, 2000). Dotted lines indicate a by-product of the main process.

Enclosed composting

Biofilters

Water treatment

Food organics

Screening Compost

Inert residues/ physical

contaminants

Cleaned air for atmospheric discharge

Odours

Polluted runoff

Cleaned for discharge or

re-use

MaturationShredding/ screening

Feedstock blending

with bulking agents


4.2.1.4 Maturation

Although most in-vessel processes effectively pasteurise feedstock materials, the end-product is

usually not fully stabilised and matured. Therefore, in most instances, materials produced by in-vessel

systems require further composting or maturation in windrows or piles under aerobic conditions

following the initial period spent in the container. This stage is required for the production of

composted products as defined in Australian Standard AS 4454 (Standards Australia, 1999). If

composted products are not required or demanded, then the pasteurised product may be sufficient to

meet the minimum standards outlined in AS 4454 (1999).

4.2.2 Range of commercial processes

There are many facilities around the world that have utilised in-vessel composting technologies to treat

food organics. The main processes used are summarised in Table 4.1.

Table 4.1 Types of in-vessel aerobic composting systems.

Process name Description Forced aerated containers (Rynk, 2000a)

Enclosed systems that use fans for aeration and process control without internal agitation.

Tunnel composters (Rynk, 2000b)

Aerated tunnel style composting containers, commonly used by the mushroom industry, but also being considered for on-site composting of food residuals.

Rotating drum composters (Rynk, 1992)

Horizontal rotary drum, which mixes, aerates and moves feedstock material.

Agitated-aerated containers (Rynk, 2000a)

Feedstock materials are placed in beds contained by long channels with concrete walls. Feedstocks are agitated periodically by machinery. Air may be forced through material from the underside of the beds.

Passively aerated bins (Rynk, 2000a)

Composting feedstocks are contained in narrow wire mesh cages, arranged in series.

Different processes are used to achieve similar end-results. The above processes may operate on a

batch or continuous flow basis. In addition they may be modular on non-modular in design. Each is

described in greater detail below.

Batch or continuous flow?

In-vessel composting processes may utilise either batch or continuous flow technologies. Batch-flow

type units, such as the Biobox® by Spartel Pty. Ltd. and the Containerized Composting System™

developed by Green Mountain Technologies Inc., have feedstocks loaded into the top of the vessel, and

then after a certain period of time (after the last load of material is deposited into the unit), pasteurised

materials are harvested from a door from the bottom in a single batch.


Other systems, such as the Vertical Composting Unit™ (VCU), developed by VCU Technology Ltd. or

the Wright Environmental Management Inc. composter, operate on a continuous flow basis, where

material is continually fed into the top of a vessel (at a specified rate for different feedstocks), and is

then removed from the bottom after a certain period of time (dependant upon retention time required to

decompose the feedstock material). In general, batch flow technologies are less efficient than their

continuous flow equivalents, and consequently may not be able to process as much feedstock material.

(a) (b)

Modular or non-modular units?

In-vessel aerobic processes may be of a modular design, allowing commercial facilities to add

additional containers to a system to cater for the amount of feedstock received. Examples of modular

systems include the 10 Cell VCU™ in New Zealand (J. Kater pers. com.), the Biobox® by Spartel Pty.

Ltd., the Containerised Composting Process™ developed by Green Mountain Technologies Inc. (P.

Bernard pers. comm.) in the United States and the 13.8 m3 Stinnes-Enerco Inc. containers in Colchester

County in Canada (Anonymous, 1999a).

Some modular processes are based on roll-off transport containers. These containers are completely

enclosed with stainless steel perforated floors through which air is supplied. These modular designs

give facilities the opportunity to expand processing capacity as feedstock supply increases.

Plate 4.2 Examples of batch-type and modular containerised composters. The photograph on the right shows how the containers are transported and unloaded, with the assistance of a roll-off truck.

Plate 4.1. The Biobox® batch-type composting unit by Spartel Pty. Ltd. is a modified transportcontainer that houses a removable vessel which contains the compostable organics. The transportcontainer is fitted with an aeration fan, biofilter and temperature monitoring unit (Figure 4.1a). Process control is similar to other systems manufactured in the United States. Figure 4.1b shows how theinternal vessel is positioned inside the transport container with the assistance of a mobile carriage.


Many of these modular processes are quite mobile and may be of use in situations where a centralised

facility is not viable (Block and Farrell, 1998). Other systems such as the Tunnel Composting System

of Brentwood Recycling Systems or the concrete vessels developed by Natural Recovery Systems Pty.

Ltd. are not designed to be mobile. These processes are fixed at the point of their installation.

4.2.2.1 Forced aerated containers

Large scale aerated containers use control devices, loading equipment and leachate and odour

management processes. Aerated container processes include those developed by Spartel – Biobox®;

Green Mountain Technologies Inc. – the Containerized Composting Process™ and others from

NaturTech™, Stinnes Enerco Inc. and Ag-Bag Technologies Inc. These systems are similar in concept

and are made from or modelled on steel solid waste roll-off containers. This type of container provides

a durable enclosure that is modular and moveable. These systems have provisions for leachate

collection with the option for leachate reuse. Many containers are served by single central air delivery

systems and comprise process control and biofilter systems. The containers are filled via a door at the

side or top and processed as batch systems (Rynk, 2000a).

A number of 30 m3 containerised composters from NaturTech™ are being used in Minnesota, USA to

collect and process food organics from supermarkets, businesses and households. The food organics

feedstocks are mixed with wood chips and cardboard as bulking agents to facilitate the in-vessel

composting process. After mixing the feedstocks, a loader is used to deliver the compost mixtures into

a top-loading door on a NaturTech™ vessel. Following a 21 day composting cycle, the material is

removed through a swing door on the back of the unit and placed in static curing piles (Riggle, 1997).

Similarly, the University of Massachusetts has a centralised in-vessel composting facility, which

receives food organics from a number of sources including on-campus sources, local businesses and

off-campus organisations. The facility has 7 indoor roll-off containers with 23 m3 capacity.

Feedstocks are processed in the containers for approximately 18 days and then placed in windrows for

a further 10 days (Chaves, 1998).

As these systems are modular, additional units can be added to the system depending upon the amount

of material processed by a facility. The total throughput of a system is determined by the volume and

number of containers plus retention time (typically within 2-3 weeks) (Rynk, 2000a). In most

instances, the containers are only used for the first stage of a composting process, followed by a second

composting stage in windrows or aerated piles.

Containerised composting units are suitable for the treatment of a wide range of compostable organics

materials, including food organics. Large scale operations, municipalities, universities, large schools

and correctional institutions use containerised composting units for converting compostable organics

into saleable recycled organics products (Goldstein, 1998).


4.2.2.2 Passively aerated in-vessel systems

Passive aeration involves the natural ventilation of a container of composting material. Air required by

the process occurs by diffusion and convective mechanisms. Examples of passively aerated systems

include the VCU™ (see Case Study 4.2 for details) and the TEG Environmental PLC™ silo-cage. The

PLC™ silo cage contains the composting feedstocks in tall, narrow wire mesh cages, arranged in series

of modular units. A 10 cm gap separates adjacent cages and provides a channel for air flow and

oxygen diffusion. Cages are approximately 4 m high, 6 m long and 1.2 m wide, allowing for the core

of the mass to be at the most 60 cm from the airspace surround the cage. This continuously fed system

has a cycle time of 8 to 24 days depending upon the feedstock used. The manufacturer recommends an

additional 14-21 days for the composting/maturation of the pasteurised product (Rynk, 2000a).

4.2.2.3 Rotating drums and agitated-aerated containers

Aerated rotating drums are manufactured by a number of companies including BW Organics Inc. and

Environmental Products and Technologies Corporation in the United States of America (Rynk, 2000a).

Rotating drum-based processes are applicable at a range of scales, from small on-site situations to large

scale centralised processing facilities. Horizontal rotary drums mix, aerate and move feedstock

material through a system. Drums are usually mounted on large bearings and turned by a bull gear.

Air is supplied through the discharge end and is incorporated into the material is it tumbles.

Decomposition in a drum is rapid, however further composting/maturation is required in windrows. A

number of commercial-scale drums have been developed over recent years that are suitable for

composting food organics and other materials. The largest drums range from 2.5-3 m in diameter and

9-15 m in length (Rynk, 2000a).

Agitated-aerated containers include those developed by Wright Environmental Management Inc. (see

Case Study 4.3 for details), Global Earth Products Inc. and Resource Optimization Technologies Inc.

Agitated containers compost materials contained in long channels with concrete walls (Rynk, 1992). A

turning machine, which travels on top of the beds, agitates and moves the materials. Most, but not all

systems provide forced aeration through the floor of the channel. The agitated bed is usually contained

within a larger facility. Channel length and the turning frequency influence the composting period in

the channel (generally 10-28 days). Channel lengths typically range from about 60-90 m. Most

facilities use multiple channels and a single turning machine. Agitated beds are currently being used to

process large quantities of food organics at a number of prisons in the United States of America (Rynk,

2000a). For example, a correctional facility in Travis County, Texas, USA uses Wright Environmental

Management Inc. technology to process food organics. Using this in-vessel technology, the facility

composts approximately 500 kg of food organics on a daily basis. Wood chips are blended with the

food organics, comprising 40% of the feedstock mix. Following a 28 day processing period, the

compost is placed in windrows to mature for an additional 2 week period. The final compost is used in

the gardens within the correctional facility.


4.2.2.4 Tunnel composting system

Although tunnel composting systems are predominantly used in the mushroom industry, a number of

facilities are starting to use this technology to compost food organics (Manser and Keeling, 1996;

Rynk, 2000a). Examples include the Natural Recovery Systems Pty. Ltd. facility in Melbourne (see

Case Study 4.1 for details) and Brentwood Recycling Systems. Brentwood Recycling Systems in

Unanderra, New South Wales constructs tunnel composting facilities. They utilise a GICOM

Composting Systems tunnel process to convert a variety of feedstock materials including garden and

food organics into compost. Compostable organic material is fed into a tunnel and then air is

circulated within the tunnel to control temperature, humidity, oxygen content and pressure. Compost

temperature is measured at several points within the tunnel. These systems are similar to forced

aerated containers with a processing period of between 14 to 21 days. Products should be effectively

pasteurised through this process. Further composting/maturation may be required to produce a stable

and matured end-product.

4.2.3 Energy budgets

Curzio et al., (1994) indicated that the use of composting-based technologies to process food organics

resulted in a net energy deficit, as the process itself does not produce energy. This is particularly true

for facilities where forced aeration and turning processes are utilised. The use of other processing

machinery also adds to the overall energy requirements for the production of an end-product.

4.2.4 Input feedstock requirements

In-vessel technologies are capable of processing a wide range of compostable organic materials. Food

organics in particular are easily processed in these systems, as these feedstock types are highly

putrescible. However, it may be necessary to mix other feedstocks with these materials in order to

achieve optimum carbon-nitrogen ratios and to also improve the porosity of the compost mixture (Gies,

1995). The mix is dependent upon the particular food organics used, the process and the material used

as bulking agent in the compost mixture.

In a 1997 survey, Goldstein, (1997) concluded that in terms of food organics, fruit and vegetable

trimmings “are by far the most common feedstock composted” in the United States of America. In

addition, garden organics are the most frequently used amendments to adjust the physical and chemical

characteristics of the food organics feedstock to produce a suitable compost mixture. Woodchips and

sawdust are also used by many food organics composters (Goldstein, 1997).

4.2.5 Processing capacity and land requirements

Processing facility size varies with the type of technology used and also the number of vessels utilised

in an operation. The additional composting/maturation (e.g. windrowing) required to produce a more

mature product adds to the space requirements of a facility. However, the area required for the

windrowing or maturation of in-vessel composted materials is significantly less than that required in


facilities where an initial in-vessel composting phase is not used. This occurs because the overall

volume of feedstock material is usually reduced by up to 50 % through the size reduction and in-vessel

composting stages of processing.

The processing capacity of large-scale in-vessel composting technologies ranges from 1-4 m3 per day

to in-excess of 50 m3 per day depending upon the type of process and number of modules used (for

modular systems).

4.2.6 Processing time

This is dependent upon the process used and also on the characteristics of the feedstocks. In most

instances, processing time for primary decomposition is quite short for food organics. On average,

processing time ranges from a few days to several weeks. If an additional maturation/composting

phase is implemented by a facility, this will generally add another 2-4 weeks to the total processing

time of food organics – depending upon the product quality requirements of the market to which the

products are sold.

4.2.7 Outputs and products

Soil conditioners and mulches are the main products manufactured from in-vessel composting systems.

Although discharged material from these systems is usually pasteurised, it may still be immature and

relatively unstable. In these instances, further maturation via composting in windrows is required in

order to produce higher quality stable and mature products suitable for a wide range of applications.

Such products can then be utilised for various purposes in a range of situations, including:

• Potted plants • Home gardens • Commercial landscaping • New housing developments • Parks, gardens, playgrounds and other community open spaces • Roadside applications • Forestry and agricultural applications • Mine site applications

4.3 Quality issues relating to the technology

Although there is no state or federal legislation controlling the quality of material produced by the

processing of food organics using in-vessel composting technologies, manufacturers of compost should

be aware of some relevant Australian Standards that identify minimum quality levels for different

compost based products.

Composts generated from aerobic composting processes should be compliant with the guidelines

described in Australian Standard 4454 (1999). Although in-vessel systems produce pasteurised

products, it may be necessary for a product to be composted/matured in windrows/static piles if a stable

and matured compost is to be manufactured. This will add to the overall processing time of the


feedstock, but should result in the production of higher value soil conditioner and mulch products.

Products that do not comply with Australian Standards risk spreading weed seeds and plant/animal

pathogens, which can impact on the environmental health of animals and humans. Immature products

can also have phytotoxic effects on plants if applied incorrectly. Such risks are greatly reduced if

mature composted products are used.

4.4 Environmental impacts and licensing requirements

General environmental impacts and licensing requirements are summarised in Section 3. The reader is

directed to this section for relevant details.

Emissions from in-vessel aerobic composting processes are usually limited to carbon dioxide, water

vapour and occasional traces of ammonia. In addition, emissions of volatile organic compounds and

leachate are also possible. In order to minimise such outputs process control is essential. Facilities

operating within NSW must comply with the conditions of their environment protection license in

accordance with the Protection of the Environment Operations Act (1997). Key process control

features required at a facility to minimise impacts on the environment are documented in “Establishing

a licensed Composting Facility” by the Recycled Organics Unit (2000b).

Some in-vessel composting facilities are established at existing council-owned waste management

centres for processing food organics. As these facilities are licensed, well managed in-vessel

composting facilities can be easily established. The provision of council support for the development

of high performing in-vessel composting facilities at existing waste management centres is a novel

concept, effectively overcoming many of the delays normally experienced in developing a composting

facility. This is currently occurring in the Wingecarribee Shire Council area (south-west of Sydney),

with assistance of Macarthur Waste Board (M. Jackson pers. comm.).

4.5 Economics

In-vessel composting systems are commercial systems, which may be purchased or licensed for use,

and/or specially designed by consultants. They usually carry high capital costs compared with

windrowing (see Section 5), but lower costs than anaerobic digesters (see Section 6). The operation

and maintenance of in-vessel systems generally requires greater expense and a higher level of

knowledge and skill than windrow and aerated pile technologies. In-vessel systems, however, offer

several potential advantages, including reduced labour, fewer weather problems, potentially better

odour control, closer process control, faster composting, reduced land area, and consistent compost

quality (Rynk, 1992).


Table 4.2 Cost of processes on a capacity basis.

Company Name Capital cost ($ AUD) Volume of in-vessel chambers (m3)

Capital cost/ chamber capacity ($AUD/m3)

VCU™ Technology Pty. Ltd., 10 chamber

$1 400 000 250 $5600/m3

VCU™ Technology Pty. Ltd., 1 chamber

$198 000 25 $7920/m3

Green Mountain Technologies Inc., Earth Tub™/CompTainer™

$13 000/Earth Tub™ $70 000/ CompTainer™

2.9

30 $4820/m3

$2333/m3

NaturTech, Containerized Composting Process™

$400 000/ container 15 $26 667/m3


4.6 List of manufacturers

The Recycled Organics Unit does not endorse any of the manufacturers listed in the Table 4.3. The

generic technology profiles presented in the previous sections (or in the case studies) do not directly

reflect the performance of specific proprietary technologies.

Table 4.3 Manufacturer contact details.

Company Name Contact details

Natural Recovery Systems

15 Berends Drive Dandenong, Vic. 3175 Email: [email protected] Tel: 03 9706 5557 Fax: 03 9706 5559

VCU Technology Pty. Ltd.

11 Newman St Newtown Sydney NSW 2042 E-mail [email protected] Internet: www.vcutechnology.com Ph. +61 2 95573487 Fax +61 2 95573453

Wright Environmental systems Inc.

9050 Yonge Street, Suite 300, Richmond Hill, Ontario, Canada L4C 9S6

Spartel Pty. Ltd. PO Box 1097 Wester Leederville, WA, 6007 Australia Tel: 08 93606699 Fax: 08 93107334

Global Earth Products Inc.

R.R. #2 Utopia, ON L0M 1T0 Canada

TEG Environmental PLC

TEG Environmental PLC Crescent House, 2-6 Sandy Lane Leyland, Lancashire PR5 1EB, United Kingdom Email: [email protected] TEL: +44 (0)1772 422220

Stinnes Enerco Inc. (Canada)

Sheridan Science & Technology Park 2800 Speakman Drive Mississauga, Ontario, Canada, L5K 2R7 Internet: http://www.stinnesenerco.com

Green Mountain Technologies Inc.

East Coast Office PO Box 560 Whitingham,Vermont 05361 Internet: http://www.gmt-organic.com

Brentwood Recycling Systems

238 Berkeley Rd Unanderra NSW 2526 Tel: 02 42 717611 Fax: 02 42 729339


Introduction

The Natural Recovery Systems in-vessel composting facility is located in the south-eastern suburbs of Melbourne at Dandenong. It is situated in an industrial area of Dandenong and is surrounded by a wide variety of industries. The closest residential areas/ dwellings are approximately 1500 m from the site. Although the facility commenced operations in September 1999, it was only officially opened on the 28 March 2001 (C. Hudson pers. com).

Process description

Currently the facility uses 3 x 200 m3 vessels constructed of concrete walls and base. The base houses a series of plenums to supply air evenly into the bottom of the composting bed through a network of holes in the floor of the vessel.

The feedstock is loaded into a concrete vessel by travelling conveyors. The container is then hermetically sealed and air

is drawn from within the top of the vessel via a fan and directed back into the distribution chamber at the bottom. The continual recirculation of air through the compost bed serves to equalise temperature and oxygen and moisture content. In addition, the constant upflow of air helps maintain the bed in a porous state and prevent excessive compaction.

The in-vessel composting cycle is controlled by a Citect, System Control and Data Acquisition (SCADA) computer package. This system controls temperature, oxygen, differential pressures, air velocities, fan motor power consumption, damper positioning and cycle times.

Composted material from the vessels is placed in outdoor windrows on maturation pads. The moisture content of the windrows is monitored during maturation and water is added when required. The windrows are also turned when required.

The Natural Recovery Systems in-vessel composting facility can process 35 000 tonnes of food organics every year when operating at full capacity. Feedstocks Source separated fruit and vegetable material blended with bulking agents Facility size 2000 m2 Process 3 x 200 m3 in-vessel containers with a separate aeration system Processing time 7 days in-vessel composting and 2-3 weeks windrow composting Outputs Pasteurised soil conditioner and mulch Installations Melbourne, Victoria Cost Information not supplied Status Commenced operations

Case study 4.1 Natural Recovery Systems (Melbourne) – In-vessel composting of food organics

Plate 4.3 Concrete vessel used for composting food organics at the Natural Recovery Systems facility in Dandenong, Victoria. Photo on the left is an open vessel, and closed on the right.


Input feedstock requirements

This in-vessel system is capable of processing a range of compostable organic materials from a range of sources including: supermarket produce, food processing residuals, industrial food manufacturing sludges, out-of-date products, produce market wastes, fish wastes, sawdust and shavings, straw wastes, garden organics, waste paper fibre and sewage sludge. However, the primary feedstock is fruit and vegetable residuals from supermarket chains. At present, their main customer is the Coles Supermarket group. Food organics from this supermarket chain are source separated for collection.

Drier materials including saw dust and garden organics are mixed with the food organics in order to achieve the optimum carbon to nitrogen ratio and to help maintain required porosity in the compost mixture.

Processing capacity and land requirements

The facility is designed to process 35 000 tonnes of food organics every year. It is situated on two adjacent allotments (approximately 0.4 ha each). One allotment has a 2000 m2 building in which all feedstock is received, handled and in-vessel composting operations are conducted. The second allotment houses the compost maturation pad, which is fully bunded and sealed. The area is equipped with leachate collection and recycling facilities.

Processing time

The compost mixture undergoes 7 days in-vessel composting and 2-3 weeks windrow composting.

Output

This facility produces pasteurised soil conditioner or mulch that complies with the requirements identified in Australian Standard AS 4454 (1999).

Existing installations

Currently there is only one facility located in the Dandenong area of Melbourne.

Costs

Information not provided.

Source

C. Hudson pers. comm.

Contact details

Natural Recovery Systems 15 Berends Drive Dandenong, Vic. 3175

Email: [email protected]

Tel: 03 9706 5557 Fax: 03 9706 5559


Introduction

A 10 module VCU was purchased by the Waitakere City Council in Auckland City. The facility was established at the council’s waste transfer station, which accepts 7500 tonnes per annum of municipally collected garden and food organics.

A single VCU (25 cubic metre chamber size) was initially used for a three month trial in mid-2000. The single unit had a throughput of 2.4 tonnes per day (on a 7-day continuous cycle). At this time tub-ground garden organics were processed and pasteurised. VCU Technology Ltd. expect that a 7-day cycle with food organics on a woodchip matrix will increase processing capacity to between 3.75 and 4 tonnes per day per chamber.

As a result of this trial, Waitakere City Council placed an order for a 10 chamber system, ie. 250 cubic metres of chamber space with a capacity of 24+ tonnes per day. The throughput can be increased with shorter cycle periods, but with an increase in the odour of

the immature pasteurised product. VCU Technology Ltd. does not recommend cycle periods less than 7 days.

Process description

The VCU 250 is a group of two rows of five 25 m3 modules fed by a shared blender feed system. The VCU is an insulated tower in-vessel composting system. Material is fed via elevator and distribution systems approxi-mating continuous-flow, with the harvest of product from the base of each chamber. Product is conveyed to one end and elevated for skip loading.

VCU uses plug-flow movement of composting material, and is passively aerated. Air is passively drawn in via the base and exits the top of the system. Exhaust gas is released at the top of the chamber after condensing out much of the moisture. Condensation combined with an 8 m release height render most of the odour undetectable at the base of the VCU.

Temperatures within each unit stratify into thermophilic

The VCU Technology Ltd. 10 module unit is capable of processing 20-40 tonnes of material a day to produce coarse mulch. Feedstocks Food organics, garden organics Facility size The VCU chambers occupy an area of 132 m2. The complete facility occupies several hectares Process 10 chamber Vertical Composting Unit with a total volume of 250 m3 and a throughput of 20-40 tonnes/day Processing time Feedstock is put through a 7 day in-vessel cycle. Additional time is required for further composting and maturation in static piles Outputs Pasteurised coarse mulch or composted coarse mulch if further composting is employed Installations Australia, New Zealand and the United Kingdom Cost $1.4 million for 10 units $198 000 for 1 unit Status Operational commercial facility

Case Study 4.2 VCU Technology Ltd. (New Zealand)– 10-module Vertical Composting Unit (VCU)

Plate 4.4 The 10-cell vertical composting unit at Waitakere in New Zealand has the capacity to process 20-40 tonnes per day.


(lower, 40-50ºC) and extreme thermophilic (upper, >70ºC) zones with distinct resident organism groups populating each temperature zone, and degrading different substrate components. Compost is discharged through a roller grid onto a conveyor.


Feedstock is shredded through a hammer mill prior to being added to a VCU unit. Material received by the facility is generally source separated, allowing for a reduction in contaminants. Contaminants are manually removed from incoming feedstocks prior to being put through the shredder.


The 10 chamber VCU can process between 20 to 40 tonnes per day of organic material. The VCU modules occupy an area of 132 m2, while the complete facility occupies several hectares.

Processing time

The continuous flow VCU has a cycle time dependent on the daily volume fed into the chambers. Therefore, as the input volume changes, the cycle speed (retention time) will vary. On average, however, a 7 day cycle is used. Market demand is used to determine whether further composting and maturation is required for the pasteurised material discharged from the VCU.

Output

This facility produces pasteurised coarse mulch or composted coarse mulch if further composting and maturation is applied.


VCU Technology Ltd. has developed a number of facilities in Australia and internationally. Facilities that have been developed or are in the process of being developed include:

• Lord Howe Island (NSW) • Compaq Computer

(Sydney) • Waitoa rendering plant

(New Zealand) • Unitec (Auckland) • Chemwaste (Auckland) • University of NSW • University of Auckland

(Tamaki) (planned) • Bromley Council in

London (planned) • Sheffield transfer station,

London (planned) • Camden Soil Mix (under

development)

Costs

The cost of the 10 chamber system in New Zealand is $1.4 million. The cost of a single chamber unit is $198 000.

Source

J. Kater pers. comm.

Contact details

11 Newman St Newtown Sydney NSW 2042 E-mail: [email protected] Internet: www.vcutechnology.com Ph. +61 2 95573487 Fax +61 2 95573453


Introduction

Wright Environmental Management Inc. have developed a continuously loading, fully enclosed, flow-through process that is used to convert food organics into “compost” in a 14-28 day period. The end-product is a pasteurised soil conditioner suitable for agricultural and horticultural purposes.

The composting vessel can be custom designed by Wright Environmental Management to handle different feedstock quantities. A modular stainless steel construction allows outdoor operation and continuously composts from hundreds of kilograms to hundreds of tonnes per day.

The unit can be located indoors or outdoors in any environment, with only a small shed needed to contain the loading zone, and can be used as an on-site or as a centralised composting facility.

Process description

This system uses computer control of temperature, oxygen

and moisture.

The in-vessel composter located at the Ontario Science Centre presently handles food organics from seven Provincial Government facilities. A schematic of the process is shown in Figure 4.1.

Food organics are mixed with an equal volume of amendment material, including wood chips, paper sludge and cardboard, which increase the bulk and porosity of the compost mixture. The residuals are mixed with the bulking agent by a drag chain mixer, which has two opposed two-speed augers. The mixture is then fed into the composter via a conveyer and enters the unit through a hydraulic door.

Bacterial activity begins almost immediately and air is continuously circulated around and through the composting material. As the waste travels inside the vessel, it passes through three composting zones and two mixing zones. The temperature and humidity levels are monitored within each zone and airflow rates are controlled to optimise composting conditions.

This Canadian company uses an in-vessel, horizontal, continuous flow system for composting a range of organic materials Feedstocks Food organics including: • meats, fats and seafood • pulp sludge • garden organics Facility size This technology can process several hundred kilograms to several tonnes of food organics every day. Process Completely enclosed stainless steel modular construction with odour control and continuous loading processes. Processing time 14-28 days Outputs Pasteurised soil conditioner. Installations Several in Canada, the USA and Britain. Cost Cost not available Status Operational commercial facility

Case Study 4.3 Wright Environmental Management Inc. (Canada) – In-vessel continuous flow system

Figure 4.1 The composting vessel is a double-walled horizontal tunnel (stainless steel interior, burnished steel exterior) insulated to control the heat produced when organic materials decompose. Temperature and moisture levels inside the vessel's seven air zones are monitored constantly, and air flow is independently controlled in the three composting zones (shown) to assure optimum composting conditions. The mixing zones (between each composting zone) assure proper mixing and aeration for bacterial growth.


Oxygen in the vessel is maintained at 17%, and the manufacturer claims that the process is very water efficient. In the mixing zones, specially designed spinners throw the residuals forward to ensure they are well mixed and aerated. Air is continuously drawn out of the composter in order to maintain a negative pressure. This prevents air from escaping from the vessel and ensures that the majority of exhausted air is passed through a biofilter to remove particulates and odours.

After spending approximately 28 days in the vessel, the finished compost is removed from the vessel and filtered on a shaker screen. Larger pieces are removed and then recirculated through the composter as amendment. The finished product can be used without further maturation.


Wright Environmental Technology accept all compostable organics, including: food organics (e.g. meats, fats, seafood), pulp

sludge, packing and food processing facility residuals, garden organics, and contaminated soils from bioremediation projects.


Depending upon the quantity and type of material to be treated, composting units can be custom designed for capacities from 136 kg/day to several tonnes/day; requiring between 7 - 140 m² of area for operation.

Facilities using the Wright technology and their associated processing capacities are listed below.

• Ontario Science Center North York, Ontario 1.4 tonnes/day

• Department of National Defence HQ Ottawa, Ontario 340 kg/day

• Ste. Anne des Plaine Institution Laval, Quebec 9 tonnes/day

• Mountain Institute Agassiz, B.C. 680 kg/day

• Atlantic Institute Renous, N.B. 680 kg/day

• Jasper National Park Jasper, Alberta 900 kg/day

• San Francisco State University California 453 kg/day

• Belfast Northern Ireland, UK 453 kg/day

Processing time

The processing time for the Wright composting system ranges from 14 to 28 days (depending upon the desired product quality).

Output

This technology can produce high quality compost, suitable for marketing in agricultural, horticultural and other markets.


As identified above, Wright composting units are installed throughout North America and in Europe.

Costs

Cost not available.

Source

Internet: http://www.oceta.on.ca/profiles/wright/wright.html

Contact details

Wright Environmental Management Inc.

9050 Yonge Street, Suite 300, Richmond Hill, Ontario, Canada L4C 9S6

Tel: (905) 881-3950 Fax: (905) 881-2334

Plate 4.5 In-vessel composting units at the Wright Environmental Technology facility in Ontario, Canada.


Section 5 Windrow-based composting systems 5.1 Introduction

Aerobic decomposition occurs when organic material is decomposed in the presence of oxygen. In

aerobic decomposition, living organism which utilise oxygen, feed upon organic matter and develop

cell protoplasm from nitrogen, phosphorus, some carbon, and other nutrients. Much of the carbon

serves as a source of energy for the organisms and is burnt up and respired as carbon dioxide (Gottas,

1956). This is the main process used in windrow composting systems. As with other compostable

organic materials, highly putrescible food organics can usually be processed in windrows.

In brief, a windrow is a pile of organic material subjected to aerobic decomposition. The pile must be

aerated, through forced or passive aeration systems or via mechanical agitation (Manser and Keeling,

1996). Although windrow composting of food organics is not commonly practiced in Australia, it is

commonly used in North America. Facilities such as prisons (Allen, 1994; Allen, 1997; Marion, 2000),

farms (Anonymous, 1999b), colleges (Seif, 1999) and other centralised commercial facilities use

windrow-based composting processes for food organics and other complementary feedstock materials.

Windrow composting utilises different equipment and infrastructure to that used by in-vessel

composting (as described in Section 4). Equipment includes front-end loaders or windrow turning

machines, shredding and screening equipment, perforated piping (for passive and forced aerated

systems), blowers (for forced aerated systems), and bunded pads for windrow placement (Rynk, 1992).


These systems are considerably simpler than other food processing systems such as in-vessel

composters (Section 4), anaerobic digesters (Section 6) or fermentation processors (Section 7).

Consequently, establishment costs for facilities using windrow technology types may, in some

instances, be considerably less than for alternative technology types. The generic stages in a

composting process are identified in Figure 5.1.

Figure 5.1 Windrow based aerobic composting flow chart. Dotted lines indicate a by-product of the main process.

Odours

Polluted runoff to leachate

management system

Food organics

Windrow composting

Product blending/

formulation

Bulking agent

Size reduction and removal of contaminants

Screening/ removal of

contaminants

Product maturation


The main types of windrow composting systems to be reviewed in this section are (see Section 5.2.2 for details):

• Turned windrows • Aerated static piles/windrows • Passively aerated piles/windrows

5.2.1.1 Initial odour control, size reduction, removal of contaminants and addition of bulking agent

Food organics may pose considerable odour problems if not properly received and stored by a facility.

In some instances, facilities bury feedstock material directly into woodchip ‘baths’ in order to suppress

potential odours. More sophisticated (and expensive) approaches involve the storage of material in

negative pressure containers (e.g. the CompTainer™ by Green Mountain Technologies Inc.), in order

to suppress odours. In these instances, air is drawn from the containers, and filtered prior to release,

reducing or eliminating odours. In other cases, specialised receival bays that are completely enclosed

under negative pressure (with biofiltration of odours) are used to receive and temporarily store food

organics before being blended with bulking agents and then composted.

An initial size reduction process may be used prior to placing feedstock material into a windrow/pile.

Size reduction of feedstocks to between 10 and 30 mm is beneficial to promote the composting process.

This stage also allows for the removal of physical contaminants such as plastic, metal and glass from

the feedstock material. This contaminant removal phase may use mechanised systems with magnets

and metal detectors to remove metal contamination, air blowers to remove plastic, and crushers to

reduce the size of glass. Manual labour is also used for the removal of visual contaminants from

feedstocks.

Bulking agents, such as wood chips or shredded garden organics, are usually added to food organics to

create a compostable mixture of suitable porosity (at least 20 % v/v) and carbon to nitrogen ratios (30-

40:1) that promote the composting process. The ratio of food organics to bulking agent varies

according to the composition of the food organics and the type of bulking agent used.

5.2.1.2 Windrow composting

After the initial mixing process, the compost mixture is formed into piles or windrows using equipment

such as front-end loaders. Windrows are often placed on bunded concrete or asphalt pads (improving

leachate control), but this may not be necessary in all instances. In turned windrow systems, feedstock

material is turned on a regular basis or as required to achieve effective decomposition. This is often

based upon windrow temperatures, moisture content, and the odours from composting material. If

aeration systems (forced or passive) are used, perforated pipes or specialised concrete pads with

aeration channels generally underlie the feedstock material in the windrows. In some instances, wood

chips or similar materials are placed underneath the main feedstock material to act as a sponge to

absorb any leachate. Facilities may have other runoff control infrastructure, such as sloped pads that

redirect leachate to a drain basin or water storage area (Marion, 2000). This leachate is sometimes re-


used by a facility when mixing fresh feedstock materials in a compostable mixture, and to maintain

moisture levels in compost windrows/piles.

Different levels of labour are required depending upon the process used to maintain a windrow. For

example, if turned windrows are used, regular turning of the composting material is required,

contributing to greater labour requirements. Forced aerated or passive windrow processes do not

require this level of maintenance following the initial establishment process (Manser and Keeling,

1996).

5.2.1.3 Final screening and maturation

Composted products are usually screened with trommels or similar equipment to remove remaining

oversized materials that have not been properly decomposed or to remove any remaining contaminants.

Some facilities re-process the oversized materials by incorporating them into new feedstocks.

Following screening, pasteurised products are often composted/matured for several weeks to several

months, depending upon the process used. This phase helps to produce stable and mature end-products

(Anonymous, 1999b).

5.2.1.4 Covering of windrows/piles

Windrow covers or burial-bath

In some instances composting facilities cover food organics with woodchips or similar materials in

order to suppress the emission of odours from a pile. Other facilities use mature compost or manure to

cover fresh feedstock, suppressing odours and to insulate the composting material. Another approach

is to create a channel in the middle of a woodchip or sawdust pile and place fresh feedstock material

into the ‘bath’. The feedstock is then enclosed within the bath by more woodchips or sawdust. Saw

dust is particularly effective for organics of high liquid content (e.g. milk and dairy material).

Plastic covers

Plastic covers over windrows are used to help maintain more consistent temperatures throughout the

feedstock, by reducing heat loss from the outer layers of a windrow/pile. The use of covers also helps

protect composting material from climatic forces such as wind and rain. This is particularly important

if food organics are used, as these materials may become very wet and dense if exposed to rainfall.

These covers are generally used in passively or forced aerated systems, where windrow turning does

not occur. Some cover materials may allow for the diffusion of air from and into the feedstock

material, while suppressing odours.


There are a number of windrow/pile technologies that are available to process food organics. These

technologies include those identified in Table 5.1. In most instances, turned windrows are the favoured

method for processing food organics. However, forced or passively aerated systems are also used, as

they may be more space efficient and less labour intensive than turned windrows.


(Manser and Keeling, 1996) noted a number of difficulties associated with the use of aerated systems

compared with turned systems. Similarly, in a comparative study in Laem Chabang, Thailand, (Brown

and Chalermwat, 1998) showed that turned windrow composting was more effective than passive

aeration, as there was evidence of anaerobicity in some passively aerated piles. In this study, the turned

windrow systems were also shown to decompose food organics more quickly than the aerated piles.

These findings differ from the experiences of others such as Seif, 1999, where passively aerated

windrows were found to be more suitable for composting food organics than turned windrows due to

better odour control (see Section 5.2.2.3 for details). This is plausible as mechanical turning of piles

often releases odours into the atmosphere.

Table 5.1 Types of processes used in windrow systems.

Process name Description Mechanically turned windrows (Rynk, 1992)

The absence of any enclosure, ventilation and odour control characterise these processes. The simplest facilities may utilise front-end loaders to pick up residuals. These systems are compatible for use with food organics.

Aerated static piles (Manser and Keeling, 1996)

A pile of food organics is placed over a perforated pipe on a prepared base. Air from a fan is blown or sucked down a pipe, delivering or drawing oxygen through the material.

Passively aerated windrows (Rynk, 1992)

A pile of material is positioned over perforated pipes that extend to the outside of a pile. Outside air then enters the pipe in a natural slow aeration process. This has lower running costs than forced aeration systems, but may not be efficient enough to aerate some food organics.

5.2.2.1 Mechanically turned windrows

Windrow composting consists of placing a mixture of raw feedstock materials in long narrow piles or

windrows, which are agitated or turned on a regular basis. They are typically 1 to 3.6 m in height

depending upon the density of the compost mixture. As food organics are of a relatively high density,

windrows incorporating these feedstocks are usually lower in height, averaging 1 to 1.5 m. The width

of windrows varies between 3 to 6 m. The equipment used in the turning process determines the size,

shape and spacing of windrows (Rynk, 1992).

Windrows are aerated by natural or passive air movement (convection and gaseous diffusion) between

turnings. The rate of air exchange depends on the porosity of the windrow. Therefore, the size of a

windrow that can be effectively aerated is determined by its porosity. A low density windrow (e.g.

comprising coarsely shredded garden organics), can be much larger than a wet dense windrow

containing food organics. If a windrow is too large, anaerobic zones may result near its centre, which

release odours when the windrow is turned. At the same time, small windrows lose heat quickly, and

may not achieve required thermophilic temperatures to effectively pasteurise composting material

(Rynk, 1992). Consequently, a balance must be reached in order to optimise composting conditions.


The turning procedures used in mechanically turned windrows help:

• mix the feedstock materials; • rebuild the porosity of the windrow, and • release trapped heat, water vapour and gases.

An important effect of the turning process is to rebuild windrow porosity, which in turn improves

passive air exchange. The turning process exchanges the material at the windrow’s surface with

material from the interior. This exposes all material equally to the air at the outer surface and to the

high temperatures inside the windrow, helping materials to decompose evenly while eliminating most

weed seeds and pathogens (Rynk, 1992).

A food organics processing facility was established at a correctional centre in Connecticut, USA using

windrow turning processes. The facility processes in excess of 1 tonne of food organics every day.

The food organics materials comprise bread, fruits, vegetables and pastas, which are bulked with

garden organics to form a compost mixture. The compost-mix is formed into windrows on a covered

concrete pad using a small front-end loader. Feedstocks are composted for a period of 5-6 weeks, and

turned when required. Following composting, the product is screened to remove woodchips, which are

then mixed with new feedstocks and reprocessed. The screened compost is placed in maturation

windrows on asphalt pads and are covered and left to cure until the material is deemed mature. The

finished compost is used as mulch and soil conditioner on the prison grounds (Anonymous, 1997).

Other facilities, such as Seacoast Farms Compost Products Inc. process their food and garden organics

mixes for 4.5 months, with additional maturation periods of 6 weeks (Anonymous, 1999b) (see Case

Study 5.1 for details).

Turning equipment

For smaller scale operations (processing 1-2 tonnes/day), turning can be accomplished with a front-end

loader or a bucket loader on a tractor (e.g. Anonymous, 1997). However, for larger operations,

specialised machines for turning windrows may be necessary. These machines greatly reduce the

processing time and labour requirements, size reducing and mixing feedstocks thoroughly to produce a

Plate 5.1 Front-end loader used for turning windrows in smaller scale commercial operations.


more uniform compost, but require significant capital expenditures (Rynk, 1992). Importantly,

effective turning processes may be difficult to achieve using less specialised equipment, contributing to

incomplete composting/pasteurisation of some feedstock material.

The California Waste Recovery Systems Inc. composting facility in Lodi, California use a mechanical

agitator, which travels along rows and lifts the compost mixture. Aerated material is then dropped onto

a discharge conveyor and restacked approximately 5 m to the left of its original location. This facility

composts on average 110 tonnes of food and garden organics every day (Masoud et al., 1996).

Prices for turning equipment are dependent upon the type of technology used and the processing

capacity of the equipment (Table 5.2). General prices range from over $100 000 to over $500 000 for

the different types of windrow turners.

Table 5.2 Approximate costs associated in purchasing windrow turners with a range of capacities.

Equipment Capacity Cost (Australian Dollars)

Mobile self-propelled windrow turner

(m3/hour data not available) 9.5 m width

$540 000


(m3/hour data not available) 7 m width

$360 000


(m3/hour data not available) 3.5 m width

$146 000

Tractor with loader (m3/hour data not available) 1.4 m3 bucket

$130 000

5.2.2.2 Aerated static piles

Aerated static piles use a similar piping system to that used in passively aerated windrows. In their

simplest form, these systems comprise a pile of compostable materials placed over a perforated pipe on

a prepared base. Air from a fan (blower) is blown or sucked down the pipe, delivering air or drawing

Plate 5.2 Specialised (straddle) self-propelled windrow turner used for processing large volumes ofmaterial.


air through the composting material (Manser and Keeling, 1996). The blower provides direct control of

the process and gives an operator the flexibility to use larger piles than in passively aerated windrows

(see Section 5.2.2.3). No turning or agitation of composting materials occurs once the pile is formed.

Depending upon the feedstock characteristics, the active composting period is usually completed in 3 to

5 weeks (Rynk, 1992).

These systems suffer from a number of practical disadvantages, such as the need for a power supply for

fans and a control system to regulate the operation of the fans. In addition, harvesting of composted

product is complicated by the presence of the air pipes, and processing can sometimes be erratic.

However, this can be simplified if a permanent concrete slab with aeration channels is used.

Drawbacks include (Manser and Keeling, 1996):

• Piles drying out too quickly due to rising warm air;

• Excessive settlement of feedstock (due to a lack of mechanical agitation), which creates voids and fissures – allowing air to pass through channels without penetrating the majority of the feedstock;

• Inadequate aeration leading to pockets of anaerobicity (as was the case in the Brown and Chalermwat, (1998) study);

• Feedstocks on the outer surface may not reach pasteurising temperatures, meaning that weed seeds and pathogens may survive and carry-over into the finished product, and

• Material near the ground may never be aerated, simply because the heat in a pile tends to make the air from pipes rise away.

An example of a facility using aerated static piles to process food organics is Ithaca College in New

York, USA. This facility processes food organics from on-campus sources. The food organics

materials are bulked with wood chips and formed into 1.8 m high static piles. Fans are used to blow air

through perforated pipes into the piles when required. In this instance, the composted product is left to

cure for a very long period (2 years) (Anonymous, 2000a), though this is generally not required.

Plate 5.3 Aerated static piles using blowers to force air through the feedstock material.


5.2.2.3 Passively aerated windrows

Passively aerated windrow systems eliminate the need for turning by supplying air to the composting

materials through perforated pipes embedded within each windrow. The pipe ends are open, allowing

air to flow into them and through the windrow. Windrows should be 90-120 cm in height, with a

covered top of matured compost, wood chips or some other material to absorb moisture, odours,

ammonia and to insulate the windrow (Rynk, 1992). These systems have similar if not more

pronounced problems to those identified in aerated static pile systems. The diffusion of air in passively

aerated windrows is significantly less efficient than in equivalent aerated static pile systems. In

particular, the use of these systems for food organics may be inappropriate due to the moisture content

and density of food organics feedstocks.

Although there are appear to be a number of disadvantages or difficulties associated with the use of

passively aerated systems to process food organics, the Middlebury College, Vermont, USA utilise this

technology to process approximately 1 tonne/day of food organics. Their success is attributable to the

use of a large number of perforated pipes and the establishment of low pile heights (see Plate 5.4). The

college collects food organics from on-campus food halls, dining facilities, a golf course and ski area, a

satellite campus, and from special events (note that significant physical contaminant removal is

required). The feedstock material is then stored in a Green Mountain Technologies Inc. CompTainer™

until the container is full. The material is then emptied onto a concrete pad and the food organics are

mixed with wood chips and manure. The compost mixture is then placed on a bed of manure and wood

chips, which act as a sponge to absorb any moisture leakages from the bottom of the piles. The

compost pile is formed over numerous perforated pipes and a 15 cm layer of dry manure is then placed

on top of the feedstock in order to seal the odours in a 1 m high pile. The composting period runs for

12 to 16 weeks, followed by a number of weeks in 3.6 m high maturation piles. The finished product is

used as soil conditioner for on-campus landscaping purposes (Seif, 1999).

Plate 5.4 Passively aerated windrow in Vermont, USA. Open ended perforated pipes are placed at regular intervals perpendicular to the windrow to aerate the food organics feedstock. Although the operator claims that this is a well managed facility, the photograph shows that it is not a good example of a well managed passively aerated pile composting process. Note the numerous plastic contaminants in the feedstock material.



Whilst almost any compostable organic material can be windrowed, many materials, including food

organics, need to be mixed with complementary bulking materials to form a suitable compostable

mixture. Due to the moisture, chemical and physical attributes of food organics, it is necessary to mix

them with wood chips or other bulking agents to facilitate the composting process. Work in Northern

America indicates that the addition of bulking agents at a ratio of 2 parts bulking agent to 1 part food

organics (by volume) gives a reasonable mixture for aerobic decomposition to occur (Brown and

Chalermwat, 1998). However, different mix proportions are used depending upon the process and the

facility in question. The addition of bulking agents is necessary to maintain feedstock porosity and

aeration during the composting process.

5.2.4 Advantages and disadvantages of these systems

Turned windrows

The turned windrow method is more common in areas where space is not the primary limiting factor,

e.g. farms. Turning processes used in turned windrows help to mix, pulverise and aerate the

composting material. This produces a more uniform compost and reduces the need for further

processing such as, screening and grinding. A major disadvantage of turned windrow composting is

that it is at the mercy of the weather, as most facilities are outdoors. Paved surfaces and open-sided

buildings have been used to better cope with adverse weather, but add to the overall establishment cost

of a facility (Rynk, 1992). Turning often releases odours, so the appropriate siting of facilities that

intend to process food organics is important to minimise impacts on surrounding environments and

land uses. Further details regarding the siting and establishment of composting facilities can be seen in

“Establishing a Licensed Composting Facility” by the (Recycled Organics Unit, 2000b).

Aerated static piles

In general, aerated static piles provide for a more concentrated (space efficient) method of composting.

Higher, broader piles can be used than in either turned or passively aerated windrows. This makes it

easier to cover these processes with a roof or to enclose them within a building. Forced aeration makes

automation easier, permits closer process control and shortens the composting period. In addition, the

insulating layer of compost and the larger pile size reduce temperature variations. This improves

conditions for destroying pathogens and weed seeds. The insulation layer and lack of turnings

conserve nitrogen and limit the release of odours. Nearly all the nitrogen can be conserved within

aerated static piles, whereas over one-third may be lost in windrow composting (Rynk, 1992).

Passively aerated windrows

Passively aerated windrows share features of both turned windrows and aerated static piles. Like the

turned windrow method, it is more land-intensive. Unlike aerated static piles, passively aerated

windrows do not require electricity for running aeration fans, and therefore have lower running costs.


As with aerated static piles, passively aerated windrows conserve nitrogen, maintain even temperatures

and minimise the release of odours (Rynk, 1992). However, if aeration is not sufficient (not enough

perforated pipes or piles that are too high) all material may not be effectively composted or pasteurised.


Processing time ranges from 3 to 16 weeks depending upon the type of process used and also the

composition of the feedstock. An additional period of 2 to 3 weeks is often used by facilities to mature

and stabilise their composted product.


Products manufactured from windrow systems are similar to those generated from in-vessel aerated

composting systems (i.e. soil conditioners and mulches are produced). If correct procedures are

followed, the feedstock material should be pasteurised. For stable and mature products, additional

maturation is required.

5.3 Quality issues relating to the technology Windrow facilities face similar issues to those identified in Section 4 for in-vessel aerated composting

systems. These issues are described below.

5.3.1 Australian standards

Although no state or federal legislation controls the quality of end-products produced by

windrow composting, manufacturers should be aware of some relevant Australian

Standards that identify minimum quality levels for different compost-based products.

Composts generated from composting processes should be compliant with guidelines set

out in Australian Standard 4454 (1999). For compliance to be achieved, it is necessary for the end-

product to be pasteurised. If a composted product is to be produced, additional processing is required

for a mature end-product. Products that do not comply with this Australian Standard risk spreading

weed seeds and plant/animal pathogens.

5.3.2 Pasteurisation

If pasteurisation is to be achieved during the windrow/static pile composting, feedstocks should be

subjected to thermophilic temperatures for the minimum period specified in Australian Standard AS

4454 (1999). Thermophilic temperatures are achieved when feedstock is exposed to temperatures in

excess of 55ºC. All windrow-based systems risk incomplete pasteurisation of feedstock material due to

intrinsic difficulties associated with turning and making sure all the material is exposed to pasteurising

temperatures. Therefore, greater risks may be associated with end products originating from windrow

composting, due to less process control compared with in-vessel composting systems. The use of

specialised windrow turning equipment reduces the risk of incomplete or inconsistent pasteurisation of

feedstocks. This, however, will add to the establishment cost of an operation.


5.4 Process control and infrastructure upgrades

To facilitate the transition from composting garden organics to composting food organics, it may be

necessary for a facility to adopt one or a number of the following changes (depending upon the nature

of the feedstock material, existing processes and infrastructure, and site specific issues):

• Efficient and well designed receivals process:

• Enclosed receivals area – delivery vehicles enter a dock area that is enclosed and held under negative pressure (the food organics material is unloaded directly into the receivals area and exhaust air is treated through biofilters to remove odours);

• Establishing a receival system in which food organics are placed directly into enclosed food organics storage infrastructure (e.g. Biobox®) and/or immediate incorporation to address odour, vermin and leachate issues;

• Immediate incorporation - mixing food organics with bulking agents immediately upon receival prior to completing compost mixture and forming windrow;

• Immediate formation of windrow (e.g. incorporation into a woodchip bath)

• Improved blending practices to account for the different physical and chemical properties of food organics (e.g. creating compost mixes with higher proportions of bulking agents – comprising high carbon contents, low bulk densities and low moisture contents);

• Improved aeration to facilitate effective composting;

• Use of specialised windrow turners for improved size reduction of food organics; • Use of specialised windrow turners for more effective aeration of food organics; • Lower windrow heights (3 m or less) to account for the denser nature of food organics

compared with garden organics;

• Improved leachate control on composting pads;

• Use of windrow covers for improved moisture control, and

• It will be necessary for a facility to apply for a variation of their environment protection license, as food organics.



directed to this section for relevant details. Environmental protection licences are specific to the

feedstock type received by a facility. If facilities are currently processing class 1 feedstocks (e.g.

garden organics) and want to process food organics (class 2/3), they will need to upgrade their site and

operating license (EPA, 2000). In some instances, facilities cannot be upgraded to process food

organics due to site limitations and related licensing requirements. The only other strategy in such

situations may be to use in-vessel technologies to store and process food organics.

5.6 Economics Operating and establishment costs for windrow-based facilities are dependent upon many variables.

These include, machinery requirements (e.g. windrow turners, front-end loaders, aeration fans),

methods in which the feedstock material is stored (e.g. use of containers, covered pads, sheds),

infrastructure housing the composting material (e.g. covered enclosures), surfacing used for windrows

and static piles (e.g. cement, asphalt), and other control measures used to minimise leachate loss from a

facility. In general, turned windrow composting is more labour-intensive than equivalent aerated pile

composting, requiring some activity to be performed on a site almost daily. By contrast, aerated static


piles and passively aerated windrows have labour peaks that occur when piles are constructed and

removed. Although aerated windrows have reduced machinery requirements, operational costs may

still be high due to increased electricity requirements.

General cost estimates for a number of systems reviewed by Marion, (2000) are summarised in Table

5.3. These figures can vary significantly if processing capacities are changed. For example, if

specialised equipment is purchased for windrow turning, a facility will be able to process more material

more effectively over a shorter period of time, reducing operating costs.

Table 5.3 Costs associated with the establishment of different facilities and processes in the United

States (adapted from Marion, 2000). Note prices will vary markedly depending upon the type and

processing capacity of equipment used by a facility, site lining, site office, sheds/technologies used for

receival and storage and other processing equipment used (e.g trommel screens).

Process type Capacity(tonnes/day food organics)

Establishment cost ($AUD) Processing cost/tonne

Turned windrow 3 $192 000 (excludes the price of a dedicated windrow turner)

$12

Passively aerated windrows (covered)

2 $356 000 $24

Covered aerated static pile 1 $344 000 $72 5.7

5.7 List of manufacturers (composting facilities)

Table 5.4 presents a list of composting facilities that utilise a number of the food organics processing

methods identified in this section. The Recycled Organics Unit does not endorse the systematic

operation of any of the facilities listed in the Table 5.4 as being replicable and appropriate within the

NSW context. The equipment referred to in this section is readily available through many suppliers,

advertising in industry journals such as BioCycle (http://www.biocycle.com )

Table 5.4 Facility contact details.

Company Name Contact details

Seacoast farms compost products – turned windrow

59 COLUMBUS AVE, EXETER, NH 03833, United States of America Phone: +(603)772-6490

Middlebury college – passive aeration

HANCOCK, VT 05748, United States of America Phone: +(802)388-4356

Adirondack Correctional Facility – aerated static piles

Box 110 Ray Brook, New York 12977-0110 +(518) 891-1343

Ithaca College – aerated static piles

ITHACA, NY 14850, United States of America Phone: +(607)255-2000


Introduction

Seacoast Farms diversified their original wood recycling business into a windrow composting operation in 1995.

Process description

Seacoast Farms collects and composts food and garden organics that are generated locally. At their source, the food organics are placed in 280 litre wheeled carts, which are then collected by a Seacoast Farm truck.

Currently, the facility uses a front-end loader to turn their windrows, to blend food organics with garden organics, to load a screener and to load trucks with finished composted product. However, the facility owners plan to purchase specialised windrow turning equipment in the near future.

On average the facility composts food and garden organics in ten windrows, averaging 2-3 m in height. The windrows are formed using a front-end loader.

Once established, windrows are turned using the front-end

loader on average once a week, or when required. The composting process proceeds for a period of 4.5 months, with an additional maturation period of six weeks.

The facility uses a large trommel screen to remove wood and plastic contaminants from the final composted product.


Seacoast farms process a total of 30 000 m3 of food and garden organics every year. The food organics originate from a local college, a hospital and local businesses including delis, bakeries and a number of supermarkets. Seacoast farms process garden organics from towns in central and eastern New Hampshire.

In general, compost windrows are a mixture of food organics and garden organics. Horse and cow manure is also composted by this facility.


Seacoast Farms can process in excess of 30 000 m3 of food and garden organics every year.

Seacoast Farms process in excess of 30 000 m3 of food and garden organics every year Feedstocks Food organics, garden organics, horse and cow manure Facility size 1.5 ha Process Turned windrows Processing time 4.5 months in windrows and 6 weeks maturation Outputs Soil conditioner and mulch Installations Exeter, New Hampshire, USA Cost Not available Status Operational commercial facility

Case study 5.1 Seacoast Farms Compost Products Inc., USA – turned windrow process

Plate 5.5 Unloading food residuals at the Seacoast Farms compostingfacility in New Hampshire, USA.


This process is achieved on a 1.5 ha block of land.

Processing time

This facility processes its feedstocks for a period of 4.5 months in windrows. An additional period of 6 weeks is used to mature and stabilise the composted product.

Output

The facility produces compost that can be used as soil conditioner or mulch. The material is usually sold in bulk to local nurseries.


The Seacoast farms facility is located on a farm in Exeter, New Hampshire, USA.

Costs

Not available

Source

Anonymous, 1999b.

Contact details

59 COLUMBUS AVE, EXETER, NH 03833, United States of America Phone: +(603)772-6490

Plate 5.6 Using a front-end loader to turn windrows are the Seacoast Farms composting facility in New Hampshire, USA.


Introduction

A composting operation located within the Adirondack Forest Preserve, USA was established to receive food organics feedstocks from the Adirondack Correctional facility. The site was developed in response to an initiative by the New York State Department to divert organic residuals from landfill sites.

In order to meet park regulations, site limitations and be in close proximity to the security compound, an aerated static bay design was used.

Process description

The facility comprises a 700 m2 structure over a concrete pad. Integrated within this structure is a bulking agent bunker, where food organics are mixed with chipped garden organics. The bunker is also used to store materials in the short term and to minimise the release of odour from the fresh feedstock.

The facility has a trommel screen, curing area and stationary agricultural mixer.

The concrete pad is drained directly to the municipal wastewater system.

The facility handles materials with a 75 HP skid steer loader.

The structure has a covered concrete access ramp, which allows unloading of food organics from trucks directly into the mixer.

The 2.5 by 3 m compost bays are aerated by individual wall mounted blowers through 10 cm perforated PVC pipes. An electronic timer control allows automated blower intervals for each bay.

Following composting, the end-product is put through a trommel screen to remove any remaining contaminants and oversized materials. The screened product is then matured for several weeks in the curing area of the building.


This facility receives food organics from the Adirondack Correctional facility on a daily

The Adirondack Correctional facility diverts one tonne/day of food organics to its composting operation within Adirondack Forest Preserve Feedstocks Food organics, garden organics Facility size Aerated static bay occupies an area of 700 m2 Process Forced aeration- aerated static piles Processing time 5 weeks + several weeks maturation Outputs Soil conditioner and mulch Installations Adirondack, USA Cost $344 000 Status Operational commercial facility

Plate 5.7 The 20 by 35 m pole structure at the Adirondack Correctional facility houses aerated static piles, a bulking agentbunker, trommel screen, curing area and stationary agricultural mixer.

Case study 5.2 The Adirondack Correctional facility, USA – covered aerated static piles


basis. These food organics are mixed with garden organics to facilitate the composting process.


The composting facility processes 1 tonne of food organics per day. The composting structure occupies a 20 by 35 m area.

Processing time

Feedstocks are processed in the composting bays for a period of 5 weeks. The pasteurised product is then matured for several more weeks in a curing area within the structure.

Output

The facility produces compost that can be used as soil conditioner or mulch.


Only one facility is currently operational within the Adirondack Forest Preserve, USA.

Costs

Capital construction and equipment expenditure was $344 000.

Source

Marion, 2000.

Contact details

Adirondack Correctional Facility Box 110 Ray Brook, New York 12977-0110 United States of America

Phone: +(518) 891-1343


Section 6 Anaerobic digestion systems 6.1 Introduction

In the absence of oxygen, the conversion of complex organic materials by bacteria to simple stable end-

products forms the basis of all anaerobic digestion systems (Davies et al., 1997). Although the bacteria

used in these systems are similar to those in aerobic systems, the process does not generate as much

heat (Manser and Keeling, 1996) and may require heating to facilitate digestion (Mata-Alvarez et al.,

2000). Food organics materials are readily digested in anaerobic processes to produce methane

(biogas) for electricity generation or substitute natural gas, and solid residues for use as fertiliser or soil

conditioner (after further processing e.g. composting ) (Goldstein, 2000).

Although anaerobic technology has traditionally been used in the waste water industry to treat liquid

wastes (Manser and Keeling, 1996) and dilute slurries of organic materials (Davies et al., 1997), it is

also used to treat garden organics and food organics (Goldstein, 2000). A large number of facilities

have been established in Europe and Northern America for the treatment of residuals from municipal

sources using anaerobic digestion technologies. In fact, Mata-Alvarez et al., (2000) identified that

there were over 36 000 anaerobic digestion facilities in Europe in 2000 processing a range of materials

(including food organics). In Australia, there is only one facility specifically being used to process

food organics, the Atlas Group Inc. plant in Stirling, Western Australia (see Case Study 1 for details).

This plant is currently closed, but is expected to re-open in the near future. Another anaerobic

digestion facility is currently being constructed by EarthPower Technologies Pty. Ltd. at Camellia in

Western Sydney (see Case Study 2 for details).


6.2.1 Process description

Anaerobic digestion is a controlled process in which organic materials are degraded by a large number

of bacteria in the absence of oxygen. The digestion process is described by the following equation:

Organic material → Stable organic material(s) + CO2(g) + CH4(g) + traces of H2S(g) + H2(g)

Where CO2(g) is carbon dioxide; CH4(g) is methane gas; H2S(g) is hydrogen sulfide; and H2(g) is hydrogen.

The anaerobic digestion process produces a number of by-products including methane, carbon dioxide,

trace amounts of hydrogen and hydrogen sulfide and solid organic residues (Malina and Pohland, 1992)

(Figure 6.1). Anaerobic living organisms break down the organic compounds in digestion vessels by a

process of reduction. As in aerobic processes, the organisms use nitrogen, phosphorus, and other

nutrients in developing cell protoplasm, and reduce the organic nitrogen to organic acids and ammonia

(Malina and Pohland, 1992). The carbon from the organic compounds, which is not utilised in the cell

protein, is released mainly in the form of reduced methane and carbon dioxide (Gottas, 1956).


1. Removal of contaminants

Organic material utilised by a digester should consist predominantly of easily biodegradable material

and be free of contaminants. To achieve this objective, facilities require effective pre-sorting systems

to remove contaminants. This is particularly important if the feedstock material (e.g. food organics) is

not source separated. Even if the feedstock is source separated, contaminants may still be present in

the material. For example, the Atlas Group Pty. Ltd. facility in Western Australia uses automated

machinery to separate organic materials from non-organic contaminants in source separated food

organics. Other companies such as Canada Composting Inc. use a patented process called

hydropulping to achieve a similar end result. This process separates organics from contaminants

(plastic, glass, and metals) in mixed residuals or source separated organic residuals, producing an

organic suspension in water. Canada Composting Inc. use an additional patented process –

hydrodynamic de-gritting – to remove any shards of glass, small stones or sand remaining in the

organic suspension.

Both the Atlas Group Pty. Ltd. (Davies et al., 1997) and Canada Composting Inc. (Goldstein, 2000a)

redirect contaminants to recycling markets after further sorting or to landfill for materials that cannot

be recycled.

2. Addition of feedstock to digestion tanks

The next stage of the process is the addition of the feedstock to digestion tanks in a facility. Depending

upon the process used, these tanks may be stirred (see Table 6.1 for the range of technology types

Feedstock preparation/ contaminant

removal

Biofilters

Inert residues

Food organics Anaerobic

digestion

Digestate dewatering

Cleaned air for discharge

Water treatment

Heat, electricity, vehicle fuel, or natural

gas substitute.

Water for discharge

Biogas (Methane, carbon dioxide, hydrogen and

hydrogen sulfide)

Methane purification

Solids/ biosolids

Composting

Soil conditioner

Figure 6.1 Generic anaerobic digestion system flow chart (adapted from Curzio et al., 1994). Dotted lines indicate a by-product of the main process.

Digester heating


used). In general, this equipment is of a batch design. However, in some instances continuous flow

digesters are used (e.g. the Atlas Group Pty. Ltd. facility in Western Australia – see Case Study 6.1 for

details). Some processes use co-digestion processes to help increase bacterial activity in the digesters

and increase the processing speed. Co-digestion processes involve mixing of highly degradable

feedstock (e.g. food organics) with feedstock that is not as easily degraded (e.g. sewage sludge) (Mata-

Alvarez et al., 2000). Water is usually added to the feedstocks to increase moisture content, and in

some instances, the feedstock material may be inoculated with bacteria to facilitate the digestion

process (Curzio et al., 1994). Feedstocks are processed in the digestion tanks for between 10-20 days,

depending upon the technology used. Biogas is usually drawn directly from the digestion tanks during

digestion process (see case Study 6.2 for details).

3. Purification of biogas

The biogas (~60 %methane and ~30-40% carbon dioxide) produced during a digestion process can

have a number of applications (See Section 6.2.6). Depending upon the application, this by-product of

the digestion process may need to undergo purification procedures. In some instances, biogas can be

used with little or no purification (e.g. for heat generation purposes-combustion), or may require

significant purification, (e.g. electricity generation), to upgrade the gas to pipeline quality or for use as

a substitute for natural gas. Where purification is required, contaminants such as water, hydrogen

sulphide, and carbon dioxide are removed. This improves the calorific or heating value of the biogas,

making it a more effective combustive heat source. Some existing biogas cleaning technologies

include (Curzio et al., 1994):

i) Absorption in water, methanol or an amine solution; ii) Membrane permeation; iii) Absorption on zeolites, and iv) Methane-enrichment digestion (involves carbon dioxide absorption/desorption using the

digesting liquid as the carrier–used for pipeline quality gas).

4. Dewatering of digestate (solids) and composting processes

Anaerobic digestion systems have dewatering phases where water is drained from digester effluent.

After draining, digested material is dewatered using centrifuges and/or filters. The waste water is often

reused for feedstock preparation and/or digestion. Dewatering the digester effluent and recycling the

resulting filtrate helps to preserve water, heat, nutrients, inoculum and alkalinity (Curzio et al., 1994).

In some instances, e.g. EarthPower Technologies Pty. Ltd., the treated residual water is sold as a liquid

ammonium or nitrogen-based fertiliser.

Solid organic materials remaining after anaerobic digestion are usually contaminated with plant

phytotoxins (e.g. unstable fatty acids) and with methane and hydrogen sulfide residues. Before these

materials can be used in the environment to improve plant growth and soil conditions, they must be

dried and/or matured (usually for a number of months) to permit the breakdown of the phytotoxins

(Manser and Keeling, 1996). To address this issue, windrow composting procedures are used by the


Atlas Group Inc. in Western Australia to produce soil conditioner that complies with Australian

Standard AS 4454 (1999) (See Case Study 6.1 for details).

The Ellert Inc. facility in Germany sends digestate to a nearby aerobic composting facility, where it is

mixed with bulking agent (e.g. garden organics). This material is then placed in enclosed drums, and

composted for a period of 7 days. After this, the material is removed from the drums and cured in a

covered area. The end-product is sold as high quality soil conditioner (Anonymous, 2000).


High solids versus low solids systems

There are a large number of anaerobic digestion systems that have been developed for different waste

streams (solid and liquid) (Table 6.1). These may be either low-solids based processes or high-solids

systems (Manser and Keeling, 1996).

Low-solids systems usually treat sewage effluent, comprising 10% or less total solids. In these

processes the organic mass is suspended in water and may be digested in enclosed vessels or in ponds

fitted with some means of continuous stirring. For enclosed vessels, it is common to provide some

heating to maintain the mixture at either a mesophilic (15-35ºC) or thermophilic (45-60ºC) temperature

range (Manser and Keeling, 1996).

High-solids systems have only recently been developed in the past 20 years (Converti et al., 1999). It

has been suggested that high solids systems can process a maximum practical solids concentration of

approximately 40%, although the rate of digestion begins to decrease at concentrations above 32.5 %

(Manser and Keeling, 1996). This is perhaps due to the fact that high-solids systems have less free

water, thereby reducing the rate of anaerobic bacterial colonisation of the solid feedstock materials.

Multistage systems versus single stage systems

Single stage systems involve no pre-treatment (e.g. hydropulping, see Case Study 6.2 for details) of

feedstock prior to digestion. Multistage systems, by contrast, may involve the physical or chemical

treatment of feedstock prior to the main digestion process. Following the initial physical or chemical

treatment, feedstocks in multistage systems undergo hydrolytic processes and anaerobic decomposition

in digestion tanks. Multistage treatments increase the volatile solids content of organic residuals,

which results in the production of more biogas, making the process more efficient than single stage

processes (without the pre-treatment of feedstocks) (Mata-Alvarez et al., 2000). For example, woody

materials comprised mainly of cellulose breakdown slowly. When this material is physically broken

down – by shredding – anaerobic bacteria can gain better access to the cellulose and covert this partly

to methane. Manser and Keeling, (1996) suggest that the end product of multistage systems “is also

likely to be more suitable for use as a soil ameliorant, being [less contaminated with] glass, metals and

plastics”. Although multistage systems have advantages over older single stage processes, the pre-

treatment of feedstocks, either chemical or physical, adds cost and energy consumption to the process.


The additional cost can only be justified if it also boosts methane production and/or adds considerable

value to the end-product.

Table 6.1 Anaerobic digestion processes and descriptions.

Technology Description Pond (lagoon) based systems (uncovered or covered) (Goldstein, 2000)

This is the simplest form of anaerobic digestion, which usually does not involve any mixing. Covered systems (i.e. floating covers) may be utilised for the collection of biogas (methane) for the generation of electricity. Uncovered lagoons are normally not used, as the methane cannot be captured.

Completely-mixed stirred tank systems (Anonymous, 1996)

Contains a mixer to maintain good contact between biomass (containing anaerobic bacteria) and the organic material to be digested. This system has a post clarification step with biomass re-use to ensure a steady quantity of mixed liquid suspended in a solids reactor. Clarification is a primary waste water treatment process to remove suspended solids by settling.

Anaerobic filter (Anonymous, 1996)

Relies on a media substrate to retain the biomass within the reactor vessel. Different types of substrate material can be utilised for this purpose. Generally only used for liquid feedstocks.

Upflow anaerobic sludge blanket (Anonymous, 1996)

This technology combines the mixing attributes of the “Completely-mixed stirred tank” system with an internal gas separation and clarification mechanism. The mixing within the reactor results from the gassing which occurs as the organic components are distributed within the biomass bed at the bottom. The reactor contains no mechanical components, but does have mechanisms, which separate the gas, liquid and solid phases.

Upflow fluidised bed (Anonymous, 1996)

These processes reduce feedstock loading rates and reactor sizes. The reactor maintains a fluidised or expanded bed to facilitate biomass contact.

Dry continuous digestion (Anonymous, 1996)

Involves a continuously fed digestion vessel with a digestate (feedstock) dry matter content of 20 to 40%. These systems rely on the external recycling of a proportion of the outgoing digestate to inoculate incoming raw feedstock. As this process type only requires minimal water additions, feedstock material generally reaches thermophilic digestion temperatures.

Dry batch digestion (Mata-Alvarez et al., 2000)

In this process, feedstock added to containment vessels is inoculated with digestate from another reactor. It is then sealed and left to digest naturally. During this closure period, leachate from the base of the vessel is recirculated to maintain a uniform moisture content and to redistribute soluble substrates (volatile fatty acids) and methane bacteria throughout the mass of feedstock within the vessel.

Leach-bed processes (Mata-Alvarez et al., 2000)

Similar to dry batch digestion, except that the leachate from the base is exchanged between established and new batches to facilitate the inoculation and removal of volatile acids in the active reactor.

Wet continuous digestion (Anonymous, 1996)

Involves mixing with a large proportion of water to provide a dilute feedstock than can be fed into a conventional completely-mixed stirred tank system. Effective removal of physical contaminants (glass and stones) is required in the feed preparation stages to prevent their rapid accumulation in the bottom of digestion tanks. Involves a continuously fed digestion vessel with a digestate (feedstock) dry matter content of 10 to 15%.

Multistage wet digestion (Manser and Keeling, 1996)

Includes a range of proprietary multistage wet digestion processes where feedstocks are mixed with water (fresh or recycled) and fermented with hydrolytic and fermentative bacteria to release volatile fatty acids which are then converted to biogas in a specialist high rate industrial anaerobic digester.

Lafitte-Trouque and Forster, (1999) looked at the co-digestion of sewage sludge and confectionary

residuals in dual anaerobic digestion systems. In this study, it was found that the dual system operating

at thermophilic temperatures in the first stage and mesophilic temperatures during the second stage was


significantly more efficient at processing the combined feedstock that the use of a single phase

digestion process.

Thermophilic versus mesophilic

Research indicates that in general, thermophilic anaerobic digestion results in more rapid digestion and

an increase in methane production than equivalent mesophilic digestion. For example, Converti et al.,

(1999) compared the efficiency of thermophilic to mesophilic anaerobic digestion processes for the

vegetable fraction of municipal solid waste (MSW). This work suggested that moving from mesophilic

to thermophilic digestion conditions was responsible for a dramatic increase in both methane yield and

methane content (60%) of biogas. As most anaerobic digestion processes (excluding dry batch

digestion) do not naturally operate at thermophilic temperatures, additional energy is required to

increase digestate temperature to the thermophilic temperature range. This will add to the operating

cost of a facility and also to the cost of the end-product. However, this is often achieved by using some

of the methane produced by the system for digestion heating. This reduces the amount of methane

available for sale.


Traditionally, anaerobic digestion systems were designed to process sewage and waste water (Mata-

Alvarez et al., 2000). The use of such technologies to process solid residuals including garden and

food organics has only recently been considered an option. Depending upon the type of process used

by a facility and the type of feedstock received, feedstock materials may need to be treated in different

ways. In all cases, inorganic contaminants need to be removed from feedstock material. In most

instances, to facilitate the digestion process, water (new and/or recycled) needs to be added to the

feedstock. This water is used to facilitate the digestion process, by preserving heat, nutrients, inoculum

Plate 6.1 Canada Composting Inc. anaerobic digestion facility in Newmarket, Canada. This facilityprocesses 150 000 m3 of food organics per year on a 2.2 ha site. The food organics are processed for 14-16 days in the facility’s anaerobic digestion tanks. The facility generates 60 000 tonnes of compost and 5000 kW of electricity every year.


and digestate alkalinity (Curzio et al., 1994). The amount of water used is dependent upon the process

utilised, however, even ‘dry’ digestion processes use water. In general, all anaerobic digesters capable

of processing solid residuals can treat food organics feedstocks. In fact, as food organics naturally

contain a high percentage of water (approximately 80%), they are a more suitable feedstock than other

compostable organic materials (such as garden organics) or paper.


These processes usually require considerably larger areas than equivalent in-vessel aerobic processes.

This is related to larger digestion tanks requirements compared with those used by aerobic composting

facilities. In addition, they may require space for the aerobic composting and maturation of the solid

digestate produced by the anaerobic digestion process. Depending upon the number of digestion tanks

used and the size of digestion tanks, facilities may range in size from several thousand square metres

(e.g. the Atlas Group Inc. facility in Western Australia) (Davies et al., 1997) to many hectares (e.g. the

Hyperion Inc. digester complex in Los Angeles, United States) (Haug et al., 2000).


Total processing time for anaerobic digesters is usually longer than that for aerobic processing systems,

as solid digestate usually requires additional aerobic composting and maturation before it can be used

as a composted product. This will add to the overall cost of the end product. The digestion processing

cycle can run from approximately 10-20 days (Anonymous, 2000) or longer (e.g. for ponded systems).


6.2.6.1 Electricity generation

Electricity may be generated from refined biogas produced during anaerobic digestion (Goldstein,

2000). The gas is usually combusted in a generator or turbine to produce electricity and heat (Plate

6.2). The electricity and heat may then be used to run a facility and to promote the digestion process.

Research indicates that electricity produced from conventional sewage-based feedstocks is usually

sufficient to make a contribution to the overall electricity requirements of a facility. In most instances,

additional sources of electricity are, however, still required to run a facility (Riggle, 1996). This is

related to the low energy output of biogas compared with more traditional fuels such as natural gas or

coal (Manser and Keeling, 1996). For example, the calorific value of biogas is approximately 20.5

MJ/m3 compared with 37–43 MJ/m3 for natural gas and 26–30 MJ/kg for coal. The deficiency in

electricity generation is also related to the relatively small amount of biogas produced by sewage

sludge. Nevertheless, even though biogas has a lower calorific value than coal or natural gas, it is a

clean burning fuel, producing only carbon dioxide as a by-product. In addition, the use of biogas as a

source of electricity reduces pressures on our limited natural resources.


The production of biogas from food organics has been shown to be up to 10 times higher than that

obtained from sewage sludge (Jewell, 1999). This should compensate for the low calorific value of

biogas to some extent, allowing for the production of more electricity by facilities using food organics

than those using traditional sewage-based feedstocks (Chandler et al., 1980). Some facilities such the

Atlas Pty. Ltd. facility in Western Australia (See Case Study 6.1 for details) and Canada Composting

Inc. (Goldstein, 2000a) claim that their digestion processes can generate enough electricity to run the

facility, in addition to producing surplus electricity. This is related to the high proportion of food

organics received by these facilities, thus allowing them to generate more methane per tonne of

feedstock used. Research indicates that approximately 150 m3 of biogas is generated from every (wet)

tonne of food organics processed.

6.2.6.2 Compost

The anaerobic digestion process creates solid by-products, which, given further processing, can be of

value as an organic fertiliser or soil amendment. Anaerobic digestion residues are generally not

suitable for direct application onto land, as they are too wet and/or contain a significant amount of

volatile fatty acids (cause phytotoxic effects to plants). Moreover, if digestion has not occurred within

the thermophilic range of temperatures, these products will not be pasteurised. Therefore, post-

treatment after anaerobic digestion is required to obtain a high quality finished product that is not

contaminated with weed seeds or contains microbial pathogens, which can impact on human and

animal health (Mata-Alvarez et al., 2000).

The amount, quality and nature of these products largely depends upon the quality of the feedstock

used, the method of digestion (thermophilic or mesophilic) and the extent/type of the post-treatment

refining processes used. The main product of a digestion process is a solid digestate, which can be

matured into a composted product. Unlike most aerobic composting systems, the ammonia from the

anaerobic feedstock may not be completely volatilised in an anaerobic digestion process. This may

Plate 6.2 Photograph of an 820 kW cogeneration engine installed at the Canada Composting Inc.Newmarket facility. The generator can produce almost 5 mW of electrical power from 150 000 tonnes of food organics every year. The facility uses 2 mW of electricity and sells the surplus 3 mW to the electricity grid, which is enough for the annual electrical needs of approximately 3,000 homes.


give the final product a higher nitrogen content compared with aerobic composts (Riggle, 1996).

Similarly, this may contribute to phytotoxic effects if the final product is not properly matured or is

inappropriately used.

6.2.6.3 Solid fuel

Work at the University of California suggests that in high solids digestion systems (e.g. dry batch

digesters), the final dry residual product can have a calorific value of up to 14.8 MJ/kg, and can

potentially be used as a solid or granulated fuel following drying (Manser and Keeling, 1996).

Unfortunately the process to convert the solid digestate into a suitable fuel is time consuming and

requires the addition of heat or an additional aerobic digestion phase for the removal of excess water.

On a dry solids basis, it has been estimated that the combined calorific value of both solid residue and

methane gas could be as high as 31 MJ/kg of feedstock material (Manser and Keeling, 1996).

6.2.6.4 Methane for vehicle fuel

In an analysis and comparison of recycling methods, Sonesson et al., (1999) suggested that the use of

biogas as bus fuel has certain advantages when compared with diesel. This would require considerable

refinement of the biogas to produce methane, but would have the added advantage of decreasing

vehicle emissions and reducing demand for non-renewable fossil fuels. The combustion process is

described by the following:

CH4(g) + 2O2(g) CO2(g) + 2H2O

where CH4 is methane; O2 is oxygen; CO2 is carbon dioxide; H2O is water; and ∆ is heat.

6.2.6.5 Pipeline quality gas

In the United States and Europe, biogas is upgraded to pipeline quality gas (substitute natural gas) by

removing contaminants such as carbon dioxide. Unfortunately, existing gas cleanup processes are

expensive and energy-intensive. In addition, they may also be associated with significant methane loss

(up to 10%) (Curzio et al., 1994). However, this may be a viable option for facilities located near gas

distribution systems. In Australia, the EarthPower Technologies Pty. Ltd. Camellia plant (when

completed) should generate pipeline quality gas for use at a nearby food processing facility.


The quality of material generated from anaerobic digestion processes is dependent upon the quality of

feedstock used and the level/type of processing it is subjected to. Solid recycled organics products

such as soil amendments or conditioners should comply with relevant Australian Standards (see

below).

6.3.1 Relevant Australian Standards

Although there is no state or federal legislation controlling the quality of recycled organics products

manufactured from anaerobic digestion systems, manufacturers should be aware of some relevant


Australian Standards (e.g. Australian Standard 4454, 1999) that identify minimum quality levels for

different compost-based products. It should be recognised that the adoption of a relevant Australian

Standard is on a voluntary basis.

Composts generated from anaerobic composting processes should be compliant with guidelines set out

in Australian Standard 4454 (1999) to minimise risks associated with use in the environment and to

maximise market value. To comply, it may be necessary for the solid residue/digestate to be aerobically

composted and matured. This will add to the overall processing time of the feedstock, but should result

in the production of high-value composted products. Importantly, products that do not comply with a

minimum quality standard (such as AS 4454, 1999) risk spreading weed seeds and plant/animal

pathogens, which can have deleterious effects on the environment and on animal/human health.

6.3.2 Pasteurisation

Depending upon the process used to anaerobically digest food organics (thermophilic or mesophilic),

the final product may not be pasteurised and hence free of weed seeds and plant/animal pathogens. If a

product has not been processed at a thermophilic temperature for the minimum period specified in

Australian Standard AS 4454 (1999), or if a product is not composted/matured followed digestion, then

the end product may not comply with the Standard and may have detrimental effects on soil, plants,

animals and humans. To avoid problems, facilities such as the Ellert Inc. plant in Germany pasteurise

their solid digestate at temperatures greater than 70ºC for a period of two hours. The facility owners

consider the material to be pathogen free following this period (Anonymous, 2000). Other facilities,

such as the Atlas Group Pty. Ltd. plant in Western Australia, aerobically compost their solid digestate

in windrows following anaerobic digestion (Davies et al., 1997).




Modern anaerobic digestion facilities generally have little to no environmental impacts associated with

odour, noise, and leachate, as they are tightly controlled processes.

To gain approval for development, large facilities such as the EarthPower Technologies Pty. Ltd.

facility in Camellia are required to submit Environmental Impact Statements to a relevant consent

authority (usually the local council). In addition, anaerobic digestion facilities may require Dangerous

Goods Licenses for the storage of chemicals on site. Other permits such as a tradewaste permit from

Sydney Water are also required for the discharge of wastewater.

6.5 Economics

Mata-Alvarez, J. et al., (1999) suggested that the overall investment cost of anaerobic digestion may be

1.2 to 1.5 times higher than that for equivalent aerobic composting. In brief, the operating expenses of


an anaerobic digestion facility may include, labour, operation and maintenance, residue/ash landfilling,

and debt service. Revenue elements include: the sale of electricity, gas, compost, recyclables and gate

fees (Curzio et al., 1994).

An anaerobic process requires larger and structurally stronger digesters than those used for aerobic

composting. While most basic designs do not require an aeration plant, they do need gas cleaning and

compressing equipment if the biogas is to be used for production of electricity. They also require

sludge de-watering plants to restore the residues to a manageable condition and large maturing areas if

solid digestate is to be processed into a soil conditioner. All these components add to the initial capital

cost of a facility and also to the running costs. (Manser and Keeling, 1996).

Table 6.2 Cost of facility on a processing capacity basis.

Facility Cost ($AUD) Processing capacity Cost of facility per processing capacity

($AUD/m3)

EarthPower Technologies, Camelia plant

$19 000 000 4 x 4500 m3 digestion tanks (82 000 tonnes/year)

$1056

Canada Composting Inc - Newmarket facility

$50 000 000 (150 000* tonnes/year)

$217

Atlas Pty. Ltd Not available 3 x 1500 m3 digestion tanks

Not available

Hyperion $250 000 000 38 x 9600 m3 digestion tanks

$685

* Assuming the bulk density of food organics received is ~650 kg/m3, annual processing of food organics is estimated to be ~ 230 770 m3.

Anaerobic facilities recover at least some (if not all) energy used, whereas aerobic composting facilities

are net energy consumers. However, at the same time, anaerobic technology requires larger capital

investments, highly engineered capital infrastructure, and more complex operations (Mata-Alvarez et

al., 2000), all of which contain significant embodied energy.


The Recycled Organics Unit does not endorse any of the manufacturers listed in the table below. The

generic technology profiles presented in the previous sections do not directly reflect the performance of

specific proprietary technologies.


Table 6.3 Company contact details.

Facility Contact details

EarthPower Technologies Pty. Ltd.

35 Grand Avenue, Camellia Mr Ron Mendelsohn, EarthPower Technologies Sydney Pty Ltd, Ph. (03) 9654 6799 Email: [email protected]

Atlas Group Pty. Ltd. (digestion plant is temporarily closed)

Stirling, Western Australia Ph. (08) 9249 1422 Fax (08) 9249 3575 Web: http://www.atlas-group.com.au

Canada Composting Inc

Canada Composting In. 390 Davis Drive, Suite 301 Newmarket, Ontario L3Y 7T8 Ph. (0011) 905 830 1160 Fax (0011) 905 830 0416 Kevin Matthews, President Email: [email protected] Web: http://www.canadacomposting.com/


Introduction

In 1996, the Atlas Group Pty. Ltd. constructed a materials recovery facility (MRF) and anaerobic digestion plant at their landfill site near Stirling (Western Australia). This plant can process up to 60 000 tonnes per year of MSW (municipal solid waste) from the 186,000 residents of Stirling. The plant is currently closed, but is expected to open again in the near future.

Process description

The anaerobic digestion plant is designed to process compostable organics in three enclosed, vertical cylindrical digesters. MSW entering the MRF is mechanically sorted to recover recyclable materials and to separate the organic fraction of the waste stream for processing in the digester vessels. As hand sorting is not required in this separation process, direct exposure of staff to the MSW is kept to a minimum.

The Atlas Group Pty. Ltd. digesters operate in the thermophilic range of temperature scale. However,

unlike aerobic composting, anaerobic processes are only weakly exothermic, so the digesters must be heated and also insulated to minimise heat loss.

Compostable organics are conveyed to the top of the sealed reactor vessels and removed from the bottom after a digestion period of 20 days. The fermentation process within the digesters stabilises the solids to produce biogas (60% methane and 40% carbon dioxide) and solid digestate.

The solid digestate is dewatered and the excess water re-used in the digestion vessels. The digestate is then transported to a nearby aerobic composting facility (also owned by Atlas Group Pty. Ltd.) to manufacture composted soil conditioner in aerobic windrows. The digestate is combined with other complimentary feedstock materials to form a compostable mixture and is composted for a period of 10-12 weeks.


The Atlas Group Pty. Ltd. facility receives MSW from

The Atlas Group Pty. Ltd. MRF processes up to 60 000 tonnes of MSW per year from the city of Stirling in Western Australia– separating and processing the organic fraction via an anaerobic digestion plant Feedstocks Compostable organic material (food organics and garden organics) separated post collection from mixed MSW collection Facility size 3000 m2 + additional space for aerobic composting facility Process 3 continuously fed 1500 m3 anaerobic digester tanks; multistage technology + aerobic windrow composting of solid digestate Processing time 20 days Outputs Electricity and soil conditioner Installations Stirling, Western Australia Cost No information Status Currently closed – expected to open again in the near future

Case study 6.1 Atlas Group Pty. Ltd. (Perth) – Thermophilic anaerobic digestion of food and garden organics

Plate 6.3 Model of the Atlas Group Pty Ltd plant in Stirling, Western Australia. This facility processes source separated MSW inthree continuously fed anaerobic digestion tanks to produceelectricity and soil conditioner.


municipal Mobile Garbage Bin (MGB) collections in Stirling. The material is then mechanically sorted to separate the organic fraction (including food organics and garden organics) from the mixed solid waste stream.

The sorting system developed by the Atlas Group Pty. Ltd. uses ‘soft sorting’ technologies, which are designed to non-violently size reduce MSW material so that anaerobic process contaminants can be separated effectively from the organic fraction.


The organic fraction is digested in 3 x 1500 m3 digester tanks. The Atlas Group Pty. Ltd. anaerobic digestion facility occupies an area of 3000 m3. Additional space is occupied by the aerobic composting facility.

Processing time

The MRF facility can receive up to 60 000 tonnes/year of municipal solid waste, operating 5 days per week. The anaerobic digestion process for the organic fraction takes approximately 20 days. The de-watered digestate is

composted for 10-12 weeks.

Outputs and products

Electricity and soil conditioner products are produced. The electricity is used to power the facility.

This company claims that its soil conditioner fully complies with AS 4454 (1999).


The Atlas Group Pty. Ltd. has a facility located near the city of Stirling in Western Australia.

Costs

Information not provided.

Sources

Davies et al., 1997 http://www.atlas-group.com.au

Contact details

Ph. (08) 9249 1422 Fax (08) 9249 3575 Web: http://www.atlas-group.com.au

Plate 6.4 Pelletised soil conditioner produced from anaerobicdigestion and aerobic composting processes at the Atlas Pty. Ltd.facility in Western Australia.


Case study 6.2 EarthPower Technologies Pty. Ltd., Camellia – Anaerobic digestion of food organics

Introduction

EarthPower Technologies is in the process of developing an anaerobic digestion facility in Camellia, western Sydney. The facility will use BTA digestion technologies (a European-based company). Similar plants have been constructed in Europe and Northern America.

Process description

The western Sydney facility will consist of four main operations, including biomass reception and preparation, anaerobic digestion, sludge dewatering, fertiliser drying and steam generation.

When construction of the facility is completed, food organics materials will be unloaded into a below ground 160 m3 bunker. From here the material will be mechanically fed into a screw feeder for size reduction.

The size reduced food organics will then be mixed with water and anaerobically digested. A series of anaerobic digesters process the material for a

period of 10-12 days or more if required. As the operating temperature of this system is mesophilic (33-37ºC), a boiler will be used to provide heat to the digesters.

Solid digestate is dewatered and further processed to produce a liquid fertiliser and a pelletised solid fertiliser.

The liquid from the dewatering process will contain a high amount of nitrogen. This water is directed to a reverse osmosis process, where two materials, one clean water and the other containing 12% ammonia liquid fertiliser will be produced. Both products will be sold, making the process zero discharge.

The dewatered solids are sent to a fertiliser drier to further reduce the moisture content to 20% and to sterilise the product. This product can then be sold as a nitrogen rich organic fertiliser.

The gas produced by the digestion process leaves the digester via a 200m3 capacity

When completed the EarthPower Technologies Pty. Ltd. Camellia plant will process in excess of 82 000 tonnes/year of food organics Feedstocks Food organics Facility size 13 000 m2 Process BTU anaerobic digestion process- multistage technology. 2-4 x 4500 m2 digestion tanks Processing time 20 days Outputs Methane, organic fertiliser, liquid inorganic fertiliser Installations Camellia, western Sydney Cost $19 000 000 Status Currently being built

Plate 6.5 Overhead view of the proposed EarthPower Technologies anaerobic digestion facility to be constructed in Camellia, Sydney.


gas bladder, which is required to deliver gas at a constant pressure via pipeline to a nearby (800m) food processing company, where it will be used for fuel.


When operational, the Camellia facility will process food organics, which are predominantly generated in the Western Sydney region.


It is expected that the first stage of the facility will process up to 82 000 tonnes/annum of food organics.

Processing time

Digestion processing time ranges from 10-12 days, but can be extended if required.

Output

It is anticipated that this facility will produce approximately 10 000 tonnes/year of organic fertiliser, 12.4 million m3/year of biogas (60% methane), 4000 tonnes/year of liquid inorganic fertiliser, and reusable clean water 310 m3/day.


The BTU technology used at this facility has been used in several facilities in Europe and Northern America. EarthPower will construct one facility in Camellia, western Sydney.

Costs

The cost of this facility is $19 million.

Contact details

35 Grand Avenue, Camellia EarthPower Technologies Sydney Pty Ltd,

Ph. (03) 9654 6799 Email: [email protected]


Section 7 Food organics use in animal feed production

7.1 Introduction

Livestock have the ability to eat plant materials or foodstuffs that humans cannot consume. Because of

this capability, source separated food organics (processed or unprocessed) can be used as animal food

(Westendorf and Zirkle, 1997). Importantly, however, the level of preparation food organics receive

may directly limit the type of animal that can consume the food. For example, chickens have strict

dietary requirements, which limits their ability to consume unprocessed food organics due to the high

moisture content (in excess of 80%) and variability of these products. By contrast, if food organics are

processed in an appropriate manner, and the end product is of an acceptable moisture and nutrient

content, then food organics may be suitable for consumption by animal types with more specific dietary

requirements. Alternatively, animals with less stringent dietary requirements may be receptive to less

processed food organics. However, due to the lack of pasteurisation or sterilisation, the use of

unprocessed food organics may carry risks such as pathogen transfer, which can significantly affect

animal production systems.

There are several problems relating to the production and use of quality animal feed from food

organics. These include:

• Regulatory issues • Collection methods • Procuring adequate quantities of food organics • Minimising variability in product quality, toxicity, composition and characteristics • Competing with traditional disposal methods • Competing with non-recycled stock food equivalents (e.g. oats, formulated dry feeds etc.) • Food safety and risk

Processing facilities must address these issues as a means of establishing viable operations. 7.2 Generic description of processes

Food organics can be either processed or unprocessed depending upon the targeted animal group the

food is to be consumed by. As processing levels become more complicated, establishment costs,

operating costs and the cost of the end product will also increase.

Some methods used for processing food organics include:

• Pressing/compaction • Shredding/grinding/screen separation • Dehydration • Activated sludge processes • Sodium hydroxide treatments (Glen, 1997) • Organic acids treatment with as propionic or formic acid (Glen, 1997) • Fermentation processes



7.2.1.1 Unprocessed animal feeds (direct feeding)

At a very basic level, all that is required to recover food organics as animal feed is a source of

uncontaminated material, a truck and a farm (Figure 7.1) (Glen, 1997). Market Management Services’

in the United States of America transport 55 tonnes of unprocessed fruit and vegetables to a farm in

New Jersey every day- where they are mixed with other feeds and given to cattle. Similar approaches

are used by Organics Recycling Systems (OCR) – to divert pre-consumer food organics from grocery

stores and institutions to nearby farms (Anonymous, 1999). 80% of the materials received by OCR

comprise of green vegetable material. The material is stored in 230–760 litre containers at supplier

locations. Collected material is taken to nearby farms and mixed with silage and fed to heifers. The

majority of this material is unprocessed, and comprises of vegetable and fruit materials. Meat and

other animal materials are usually avoided or limited.

7.2.2 Processed animal feeds

Fermentation/sterilisation/dehydration procedures

The development of new technologies to process food organics into drier, less variable products and

using them as components of commercial stock diets is gaining wider acceptance in the United States

and Europe. To reduce variability, processing systems may involve the size reduction or shredding of

food organics followed by pasteurisation or sterilisation processes, which involve the application of

heat to remove pathogenic organisms.

Some processes involve the controlled fermentation of liquefied food organics in insulated vessels.

This process generates heat through microbial activity, and can pasteurise the liquefied food organics.

Fermentation processes allow for a variety of food organics to be used from vegetables and fruits to

grease trap waste (Anonymous, 1999). The food organics treated by these systems may also be

dehydrated and pelletised for use as feed in chicken batteries or piggeries.

BW Feeds Inc. in Portland, United States uses dehydration processes to produce pelletised stock food.

The company collects approximately 40 000 tonnes of source separated bakery residuals on an annual

Odours/leachate

Selected/sorted food organics

collection systems

Transport to nearby farms

Mixing with other feedstocks- e.g.

grain

Product given to animals

Figure 7.1 Non-processed stock food flow chart. Dotted lines indicate a by-product of the main process.


basis. They pulverise material and then remove any shredded plastic and paper contaminants. Air is

used to blow off the lighter plastic fraction, and the crushed food is separated from the paper with a

screen. After separation, the material is put through a 12 m rotary dehydrator. The material is then

pelletised using two types of binding agents- lignin and water (Anonymous, 1999).

Australian Dehydration Technologies (ADT) Pty. Ltd. in Toowoomba, Queensland uses dehydration

technologies to create stock food from food organics. The company claims that it’s process produces

products that are free from such diseases as bovine spongiform encephalophathy (BSE) and Salmonella

spp. (see Section 7.3.2 for details). The ADT process uses a hydrolytic reaction to breakdown the

primary structure of organic compounds, including the prion proteins responsible for BSE. This

approach uses desiccants to sterilise the feedstock material at relatively low temperatures.

Liquefaction

The liquefaction of food organics for use a liquid pig feed is still prevalent in many parts of the world.

Food organics that are simply liquefied undergo minimal processing and present many quality

problems, as there may be pathogenic and other chemical problems with the end product (see Section

7.3). The use of liquefied food organics without additional heat treatment is not permitted in many

areas, including the United States of America and Britain.


Food organics that are utilised as stock food originate from a number of sources and may be exposed to

different levels of processing (Table 7.1). Feedstock type and processing systems constrain the

potential end-use of animal food products. In general, pre-consumer food organics are used for the

manufacture of stock feed. This is required to maintain feedstock consistency and quality and to

minimise physical and chemical contaminant levels.

In the United States of America and Europe, food organics residuals from the food processing industry

have been a source of stock food particularly in grain based food processing. Food organics processors

often locate themselves near cereal, snack or baked food producers (Anonymous, 1999).

Selected/sorted food organics

collection system

Size reduction with macerator type equipment

Dehydration, Fermentation,

other processes

Product given to animals

Removal of contaminants

Figure 7.2 Processed stock food flow chart (adapted from Waste Enquiry, 2000) Dotted lines indicate a by-product of the main process.


Table 7.1 Stock food feedstock sources and technology types.

Material description Processing or technologies used

Feedstock sources

• Bakery (bread, pastry, flour)

• Fruit • Vegetables • Meat

• No processing • Shredding • Compaction • Dehydration • Fermentation • Acids or hydroxide

• Supermarkets • restaurants • Fruit and vegetable

outlets • Bakeries • Food processing and

manufacturing facilities *Columns are independent of one another.


Size of facilities and equipment are dependent upon the amount of feedstock to be processed and the

processing technologies used. For example, the Lammas Resources Ltd. facility processes up to 50

tonnes of food organics every day in two 20 000 litre digestion tanks (see Case Study 7.1 for details).

By contrast Thermo Tech™ Technologies Inc. builds facilities that can process in excess of 1200 tons

per day (see Case Study 7.2 for details). However these large Thermo Tech™ Technologies Inc.

facilities are significantly more expensive and have greater space requirements than the Lammas

Resources Ltd. facility. Land area occupied by facilities is dependent upon the number and size of

digestion tanks used, water storage tank requirements, and feedstock stock pile/containment areas used.

In general facilities occupy an area of several thousand metres squared.


This is dependent upon the technology used. Processing times can range from 1-2 hours if material is

simply boiled, to 48 hours for some fermentation procedures.


Dry or wet stock foods can be generated by the processes described in Section 7.2. The application of

these stock foods is dependent upon the requirements of the animals consuming the food.

Plate 7.1 Example of a smaller scale fermentation facility build by Thermo Tech™ Technologies Inc.in Corinth, New York, United States of America.



There are important quality issues that may impact upon the production and application of stock food

generated from food organics. These issues are outlined below.

7.3.1 Nutritional value

Westendorf and Zirkle, (1997) suggested that “food residuals from a number of different sources [in the

United States] have excellent nutritional quality”. Food organics usually comprise in excess of 20%

protein and 20% fat, with a mixture of vitamins and minerals. When compared on a moisture free

basis, food organics derived stock food contains nutrients that should give nutritional values similar to

many non-recycled foodstuffs fed to animals. Similarly, Myer et al., (1999) found that dehydrated

food organics from restaurants “have potential to produce a nutritious feedstuff for pigs while offering

a viable solid waste disposal option”. In this study, food organics (60 to 75 % moisture) from

restaurants were blended and mixed with dry feedstock (soy hulls and wheat flour), resulting in a blend

with approximately 40% moisture. The blend was then pelleted and dried at temperatures of between

150-200ºC for 4 to 7 minutes, giving a final moisture content of 8.4-11.4%. The study found that the

average fat content (amongst other parameters) of pigs eating the food organics-based stock food was

the same as those eating standard pig feed. Although these findings suggest that food organics are

beneficial to pig production, stock food for livestock will only be of significant value to intensive

animal production systems if the nutritional content of the food is known and within desirable

nutritional parameters.

For unprocessed stock food, the high moisture content (in excess of 80%) and variability in nutrient

content is a major limiting factor affecting stock food value and quality. The high moisture content

limits the shelf life of a product to only a few days, and product variability makes these products

difficult to use as stock food in any intensive animal production system. Even if a product is dried

(moisture content 10-15%), there are potential problems with product variability (Glen, 1997). A

highly variable product – in terms of chemical composition –may not meet the specifications required

for commercial stock diets. In many instances, this has limited the use of food organics in the United

States to pigs (Westendorf and Zirkle, 1997). In NSW, however, limitations also extend to pigs, as

unprocessed food organics cannot be fed to cattle or pigs under any circumstances (L. Cook pers.

comm.) (see Section 7.4). The risks are related to the transference of viruses (e.g. foot and mouth

disease). Only sterilised (i.e. rendered) food organics may be fed to pigs.

7.3.2 Food born animal pathogens

7.3.2.1 Protein based diseases

Diseases such as bovine spongiform encephalophathy (BSE) in meat and bonemeal material can

potentially be transferred to other animals if the material has not been effectively sterilised. BSE is a

degenerative infection of the brain that affects cattle, sheep and in some instances people. Studies have

shown that standard heat-based sterilisation or pasteurisation procedures are not sufficient to eliminate


this disease. This occurs because proteinaceous infectious particles (prions), thought to be responsible

for BSE, are extremely resistant to heat and chemicals. Prions are misfolded versions of a protein

(known as the cellular prion protein) that cells make all of the time. When present in a brain, prions

alter the way normal cellular prion proteins fold, so that they too become misshapen. If enough

misshapen proteins form, the infected subject dies (Anonymous, 1998). Although some companies

claim to have processes that eliminate prions, there is still little scientific evidence suggesting that this

will work 100 % of the time.

7.3.2.2 Other microorganism, bacterial and viral diseases

Other diseases such as foot and mouth, E. coli, Salmonella typie, Cysts and tapeworms also present

significant health risks in the application of food organics. Some companies claim to eliminate these

pathogens using hydrolytic processes, but solid scientific evidence is still required.

Recent outbreaks of foot and mouth disease in Europe may be linked to the presence of meat in animal

feed. The dangers of this disease in unprocessed meat products have been recognised for some time.

For example, (Cole, 1979) suggested that foot and mouth disease “is present in uncooked or partially

cooked meat from infected animals, which allows it to be easily transmitted from one country unto

another if, for example, the meat eventually finds its way into feed for pigs”.

To address these problems, it may be necessary for processing technologies to pasteurise food organics

feedstocks or even sterilise the product to eliminate more virulent varieties of pathogens. In the United

States, there are strict Federal regulations that require food residuals containing meat be boiled to a

temperature of 100ºC for at least 30 minutes prior to being fed to animals such as pigs (Westendorf and

Zirkle, 1997). Although such requirements do not exist in New South Wales, there are regulations

regarding the composition of stock food that must be adhered to (see Section 7.4).

7.3.3 Residual chemicals on food organics

In many instances, the leaves and other outer surfaces of fruit and vegetables may be contaminated

with herbicide or pesticide residues. Stock foods containing a disproportionate concentration of such

residues may comprise unacceptable or inappropriate levels of chemicals for feeding to livestock and

can be a stock contamination risk (Blackwood and Byrne, 2000). Chemical residue contamination of

food organics originates from (Blackwood and Byrne, 2000):

• Chemicals from pre-planting to harvest • Chemicals used for insect control in storage • Storage facilities previously treated with organocholorine pesticides • Spray drift from neighbouring crops • Other accidental contamination during storage or transport • Inappropriately applied chemicals

These residue-related risks apply to unprocessed and processed stock foods. However, some

manufactured stock foods are supported by chemical residue quality assurance programs for raw


product purchases. These aim to minimise the risk of acquiring raw ingredients which exceed the

maximum residue limit (Blackwood and Byrne, 2000).

Continued consumption of stock food contaminated with residual chemicals may contribute to an

accumulation of these chemicals in the animals over time. This accumulation can have an adverse

effect upon the health of the animals, or make the animals unfit for human consumption. It is therefore

important that residual chemical levels be monitored in stock food products in order to avoid possible

health problems. The use of more extensive processing procedures such as fermentation may also help

with the biological breakdown of these chemicals. However, if feedstock material undergoes little or

no processing, then the risks associated with using such materials as stock food will be significant.

Knowing the source of the food organics materials will help identify and minimise chemical

contamination risks if sources of contamination are avoided.

7.4 Environmental inputs and licensing requirements



7.4.1 NSW State Acts and Regulations

Producers and users of stock foods should be aware of the Stock Foods Act (1940), Stock Foods

Regulations (1997), and the Stock Diseases Act (1923) s.20FB. These Acts and Regulations provide

legal requirements for stock food composition, application, labelling, packaging and testing. The NSW

Department of Agriculture enforces these Acts and Regulations by way of an on-going audit program

(L. Cook pers. comm.).

The Stock Foods Act and Regulations only apply to stock foods that have undergone a manufacturing

process (e.g. products manufactured by Australian Dehydration Technologies Pty. Ltd.), are identified

as stock food, and are in a form to be fed directly to livestock. Due to current definitions of stock food

in the NSW legislation, residual food organics that are supplied in either raw or processed form and are

not specifically identified as stock food are not covered by this legislation (Cook, 2000).

7.4.1.1 Packaging and labelling

Section 6A of the Stock Foods Act (1940) states that a person who supplies stock food in bulk must at

the time of delivery provide a written statement about the product that complies with the relevant

regulations about the stock food. If the stock food is not sold in bulk and is packaged, then the package

must be clearly labelled according the relevant regulations within the Stock Foods Act. The written

statement or package label needs to make it clear that the food contains mammalian material (meat

meal) and that it may not be fed to ruminants. In the case of mammalian material, an alternative

statement should indicate that the animal feed (must be sterilised – see Section 7.3.1) must only be fed

to non-ruminants such as pigs and poultry (Cook, 2000).


7.4.1.2 Foreign ingredients

Manufactured stock food must comply with the Schedule 1 of the Stock Foods Regulations (1997).

This regulation prescribes the proportion or amount of any foreign ingredient that may be contained in

stock food. A detailed list of foreign ingredients that are either prohibited or can only be present in

limited amounts is given. In some instances, the limitations are animal specific and may not apply to

all livestock. Relevant limitations for the production of stock foods from food organics include (see the

Schedule 1 of the Stock Foods Regulations (1997) for a complete list):

1. Prohibited substances

• Hormones of any kind, natural or synthetic, including dienoestrol diacetate, diethylstilboest rol, medroxyprogester one acetate, trenbolone, zeranol;

• Mammalian material manufactured stock food for ruminants. Note: this is currently being changed to all animal or bird material, including fish and feather meals (L. Cook pers. comm.).

2. Toxic compounds

• Aflatoxin B1 peanut meal, linseed meal, lupin meal, pea meal, rapeseed meal, safflower meal, soybean meal, sunflower meal is limited to 0.1 grams per tonne;

• Varying low levels of aflatoxin B1 (produced by moulds on decaying vegetation) for different stock types are allowed;

• DDT (1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane), TDE (1,1'-(2,2-dichloroethylidene) bis(4-chloro)-benzene) and DDE(1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene) in manufactured stock foods are limited to 0.05 grams per tonne;

• Dieldrin in manufactured stock foods is limited to 0.01 grams per tonne;

• Mercury fish meal for pigs or poultry is limited to 0.4 grams per tonne.

3. Antioxidants

• Ethoxyquin blood meal, meat meal, meat and bone meal, bone and meat meal or fish meal are limited to 800 grams per tonne;

• Butylated hydroxytoluene (BHT), Butylated hydroxyanisole (BHA), Isopropyl gallate or Lauryl gallate blood meal, meat meal, meat and bone meal, bone and meat meal or fish meal 200 grams per tonne.

Section 20FB of the Stock Diseases Act (1923) places some responsibility on the buyer of stock food to

be aware of prohibited/limited-content substances and not use inappropriate products accordingly. It is

illegal to feed “mammalian” (soon to be restricted animal) material to ruminants, and labels/dockets

must say if it does or does not contain such material. In addition, it is illegal to feed (raw, pasteurised

or sterilised) food organics/swill to pigs under any circumstances. Any products that may contain meat

in any form is illegal to feed to pigs (and will soon be for cattle and other livestock) (L. Cook pers.

comm.).

7.5 Economics

As with other technologies, the costs associated with stock food generation from food organics is

dependent upon the technology used, the processing capacity of the technology and the type of


feedstock used. Low technology options, where feedstocks undergo limited or no processing cost the

least amount of money. In these instances, the main costs will be transport from the source to the user,

possible liquefaction of feedstocks and heating (pasteurisation and sterilisation) followed by mixing

with other feedstocks. More sophisticated technologies (e.g. fermentation processes), which

significantly reduce the risks of feeding contaminated food organics to animals cost considerably more

(see case studies for details).

The recent outbreaks of foot and mouth disease and BSE in Europe highlight the risks associated with

food organics that are not properly processed. Therefore, although low technology options are cheaper

than fermentation procedures for example, it may be necessary for facilities to adopt some kind of

sterilisation procedure. This of course will add to running costs and the overall establishment cost of a

facility. Notably, even with sterilisation procedures in place, there are still risks associated with using

meat to produce stock food.


The Recycled Organics Unit does not endorse any of the manufacturers listed in Table 7.2. The



Table 7.2 Company contact details.


Australian Dehydration Technologies

PO Box 123 Toowoomba Qld 4350 Tel: 617 46679123 Fax: 617 46679178 Internet: http://www.adtpl.com.au

Lammas Resources Limited

Maylan Road Earltrees Industrial Estate Corby, Northlands NN17 4DR, Unit Kingdom Tel: 01536443998 Fax: 01536 206640 Internet: http://www.lammasresources.co.uk

Thermo Tech™ Technologies Inc.

Corporate Head Office: Thermo Tech™ Technologies Inc. 204 - 195 County Court Blvd Brampton, Ontario Canada L6W 4P7 Tel: (905) 451-5522 Fax: (905) 451-5833 Internet: http://www.ttrif.com/


Introduction

Lammas Resources Ltd. uses a patented aerobic fermentation system (Biotel™) to produce liquid pig feed from surplus vegetable and fruit matter produced by local supermarket chains.

Process description

The raw materials used to make the liquid pig feed are size reduced using a large macerator. The pulp is then transferred to digestion tanks, where it is inoculated with thermophilic bacteria to facilitate feedstock breakdown. Heat released by bacteria during the breakdown process causes temperatures to rise above 65ºC. The feedstock is maintained at temperatures above 60ºC for a period of 12 hours. This is presumed to be sufficient time to pasteurise the material.

Although this company claims that this is sufficient to remove pathogens – by heat deactivation – different feedstocks may require longer processing times to eliminate more resilient contaminants/pathogens.

The Biotel™ process is designed, built, erected and operated by Lammas Resources Ltd. They are responsible for the day to day running of a licenced facility. This company has constructed a pilot size Biotel™ test facility at Corby, alongside another full-size commercial Biotel™ Facility. The Biotel™ test facility offers companies that generate food organics the opportunity to have representative samples of their organic residuals bio-processed to determine their suitability as feedstock material for the Biotel™ system.

In addition to identifying the suitability of a material to the Biotel™ process, Lammas provides clients with cost information and associated benefits of recycling their material for use as animal feed.

Lammas Resources Ltd. makes a number of claims regarding the benefits of the Biotel™ processing system. These include: disease control; weed control; hazardous waste control; odour control and health risk control. The feedstock type affects the full effectiveness of these processes,

Lammas Resources Ltd. uses thermophilic fermentation processing technology to convert food organics into liquid pig feed. Feedstocks Vegetable and fruit material Facility size This facility can process up to 50 tonnes/day of food organics, using two 20 000 litre digester tanks Process Fermentation Processing time 16 hour fermentation process Outputs Liquid pig feed Installations Corby, United Kingdom Cost No information Status Commercial facility

Case study 7.1 Bio-digestion of food organics into liquid pig feed: Lammas Resources Ltd. (United Kingdom)

Plate 7.2 Digesters used in the Lammas Resources Ltd. Biotel™processing system in the United Kingdom.


and therefore processing regimes are sometimes altered to produce safe stock food products. This is particularly important given the outbreak of such diseases as bovine spongiform encephalophathy (BSE) and foot and mouth disease in Europe.

Feedstock types

Appropriate feedstocks utilised in the Biotel™ process include cabbage and cabbage cores, peppers, coleslaw, potatoes, onions, kiwi fruit and apples. The company claims that all food organics used can be traced to their source. No meat is processed in this system.

Size and area requirement

This facility uses two 20 000 litre digester tanks. The facility occupies an area of 3000 m2.

Processing time and throughput

Lammas Resources Ltd. claims that the complete processing

time, from source of feedstock to pig is 48 hours. Feedstock is processed for a period of 16 hours during the fermentation process, and the facility is capable of processing up to 50 tonnes/day of food organics.


Currently Lammas Resources Ltd. has a prototype and a full working facility in Corby, United Kingdom.

Costs

Cost of facility is dependent upon number and size of digesters.

Sources

R. Dwyer pers. comm. www.lammasresources.co.uk

Contact details

Lammas Resources Limited Maylan Road Earltrees Industrial Estate Corby, Northlands NN17 4DR, Unit Kingdom Tel: 01536443998 Fax: 01536 206640 www.lammasresources.co.uk

Plate 7.3 Transporting the liquidpig feed end-product followingfermentation at the Lammas facility.The facility uses a patented Bioteltechnology, which pasteurises fruitand vegetable feedstocks during a 16-hour thermophilic fermentationprocess.


Introduction

The Canadian based Thermo Tech™ Technologies Inc. company uses similar thermophilic fermentation processes to those used by Lammas Resources Ltd. in the United Kingdom.

Process description

Initially, material entering a facility is inspected and then processed using a ‘hydropulper’. Packaged food is put through a shredder and a crusher that separates the food from the packaging. After the feedstock is ground, the resulting slurry is stored in raw material tanks. From these tanks, the material is fed into continuous two–stage fermenting units, where it is maintained under aerobic conditions and reaches temperatures of 73 ºC.

Thermo Tech™ Technologies Inc. claims that the fermenting process provides a number of benefits, including increasing the protein content of a product to about 20 percent. In addition, they suggest that the fermenting

process does not require as much energy as other systems since it produces its own heat. It is also claimed that the fermenting process helps to predigest some of the fats, making the resulting product more valuable as feed.

After fermentation, the resulting slurry is sent to a holding tank and then into a centrifuge where the moisture content is reduced from 85 to 60%. The extracted liquid is directed back to a receiving area where it is reused in the process. The moisture reduced product is put through a final drying and extrusion process and formed into pellets. Air from a plant is contained within a facility and exits only after scrubbing (removes small particulates) and treatment with a thermal oxidiser, which destroys odours.

Feedstock requirements

A large range of food organics can be processed by the Thermo Tech™ Technologies Inc. system, including: residuals from bakeries, restaurants, grocery stores and food

Thermo Tech™ Technologies Inc. processes food organics using thermophilic fermentation technologies. Facilities using their technology have been licensed around the world. Feedstocks All food organics Facility size Variable Process Fermentation Processing time 48 hours Outputs Dry animal feed Installations North America, Europe and South-East Asia Cost $2 000 000 license fee + cost of installation Status Commercial facility

Case study 7.2 Two stage aerobic fermentation process- dry stock food: Thermo Tech™ Technologies Inc. (Canada)

Plate 7.4 Thermo Tech™ Technologies Inc. food organics fermentation facility. This facility processes a variety of food organics (including grease trap waste) from several sources inCanada. The fermentation and dehydration process used producesdry animal feed, which should be free of pathogens.


processing facilities. The system can also process grease trap waste.

Size and area requirement

Facility sizes vary according to the processing requirements.

Processing time and throughput

Thermo Tech™ Technologies Inc. facilities can process up to 1100 tonnes/day. The entire process takes approximately 48 hours.

For every 270 tonnes of material received, a facility can produce approximately 40 tonnes of animal feed, with 10% moisture content.


Thermo Tech™ Technologies Inc. has facilities in Canada, the United States, Europe and South East Asia. It is in the process of licensing facilities in New Zealand.

Costs

Thermo Tech™ Technologies Inc. licenses its technology for use in Thermo Master™ plants. The company also enters into master license agreements with other parties that are ready to open facilities around the world. Each requires a one time licence fee of $2 000 000. Thereafter, the company receives a royalty of 5% on gross revenue plus a further royalty of 10% on the net income generated by a plant.

Sources

Internet: http://www.ttrif.com/ Glen, (1997)

Contact

Corporate Head Office: Thermo Tech™ Technologies Inc. 204 - 195 County Court Blvd Brampton, Ontario Canada L6W 4P7 Tel: (905) 451-5522 Fax: (905) 451-5833

Internet: http://www.ttrif.com/

Plate 7.5 Food organics based stock food pellets produced byThermo Tech™ using fermentation and drying processes.


Section 8 Direct soil injection of food organics 8.1 Introduction

Direct soil injection practices involve the application of liquefied food organics beneath the soil

surface. Research indicates that this process helps increase soil organic matter and the availability of

nutrients in soil and may also increase soil microbial activity. However, as the food materials are not

pasteurised or processed in any way, there is potential for the transfer of pathogens to plants and

animals, and for phytotoxic effects to plants and/or the attraction of flies and vermin to application

sites.

At present, most research describes the application of wastewater solids or biosolids to land.

Therefore, where appropriate, some of the information in this section has been derived from research

on the land application of wastewater solids or biosolids.

Although there are no direct guidelines or legislation controlling the land application of food organics,

companies in New South Wales follow the biosolids guidelines for land application, as identified in

“Environmental Guidelines: Use and Disposal of Biosolids Products” (EPA, NSW, 1997). Licensing

requirements for applying food organics to land are contained in Schedule 1 of the Protection of the

Environment Operations Act (1997).


The generic process involved in the direct soil injection of food organics is summarised in Figure 8.1.

Food organics that are used for land application undergo minimal processing prior to being applied to

land. In most instances, facilities receive food organics that are already in liquid form (e.g. ice cream

and chicken manufacturing sludge). If materials are not in a liquid form to begin, operators may

liquefy the food organics (e.g. macerate and mix feedstock with water) prior to injecting them into soil.

This, however, may add considerable expense and processing time to an operation.

Following delivery, material is usually stored in sealed containers in order to contain odours. However,

for smaller operations, the material may be pumped directly into liquid sludge injection vehicles or

similar equipment. In some instances the material is passed through a metal grate to remove metal and

plastic contaminants. Storage of the food organics material is usually quite short due to their

putrescible nature. Therefore, the material is usually applied to soil at the time it is received or within

1-2 days of being received.

Liquefied material is transferred to agricultural injection machinery (e.g. sludge injection vehicles,

tractor drawn injectors or vacuum trucks) and applied directly to soil. The material is usually

incorporated into the soil at the time of application with tines, discs or similar equipment. However, if

the injection machinery does not have tines or discs attached, operators may have to pass over the

treated soil a second time with a tractor and appropriate tillage equipment to facilitate incorporation.


Following application, the material is simply left to decompose in the soil. The site is usually left in

fallow for a minimum period of 1 week prior to being used for cropping purposes. For beef and dairy

cattle grazing, treated soil is left for 30 and 90 days respectively, as specified in “Environmental

Guidelines: Use and Disposal of Biosolids Products” by the Environment Protection Authority of

NSW.


In some instances, non-liquid food organics are added to soil. For example, farmers in New Jersey,

USA apply food organics from food processors directly to their land. The food organics are usually

transported to farms in a raw form and then loaded onto manure spreaders and applied to soil surfaces

directly without any further processing (Anonymous, 1997a) (Plate 8.1). Application of solid food

organics to soil surfaces is unlikely to meet EPA approval due to the environmental and public health

risks associated with odour and attraction of pests (Plante and Voroney, 1998).

Odours

Polluted runoff

Food organics Storage, and liquefaction if

required

Soil injection/land application

Breakdown of waste by soil

bacteria

Some runoff

Physical contaminants/ Phytotoxicity

Figure 8.1 Generic process used in the land application food organics. Dotted lines indicate a by-product of the main process.

Plate 8.1 Example of a manure spreader (attached to a tractor) used for the direct application of solid food organics to soil


Operators such as L.V. Rawlinson and Associates (Appin, Australia) accept liquid food organics from a

number of food processing companies in NSW (See Case Study 8.1 for details). After a short storage

period in sealed metal containers, the unprocessed food organics are injected directly into soil using an

AgChem™ 11 000 litre capacity sludge injection vehicle. L.V. Rawlinson and Associates also use a

14 000 litre capacity tractor drawn Marston™ sludge injector (Plate 8.2). The AgChem™ vehicle was

imported from the United States of America, while the Marston™ sludge injection was imported from

the United Kingdom. Although the food organics material applied by L.V. Rawlinson and Associates

generates considerable odour, they do not consider it to be a major problem as the storage tanks and

application sites are usually located in isolated areas without residential housing (L. Rawlinson pers.

comm.).

A farm in Toronto, Canada, stores its liquid food organics in concrete manure storage tanks. Prior to

application, a mixing prop attached to a tractor is used to stir the food organics to homogenise the

material, as it separates into layers during storage. The material is then transferred to a vacuum truck

and broadcast onto the soil surface. Immediately after application, the oily food organics are

incorporated into the soil using a disc plough. The operator claims that there are only minimal odour

problems during storage. However, once the material in the storage tank is stirred, odour problems

become more apparent. The incorporation process after application of the food organics to the soil

helps reduce odours and the attraction of pests (e.g. flies, mice, birds etc.) (Plante and Voroney, 1998).

Plate 8.2 Photograph of the tractor drawn Marston™ sludge injector used for the direct injection of liquid food organics into soil. Note the tines at the rear of the machinery are used to incorporate thefood organics to a depth of 15-20 cm.



Food organics used in direct soil injection operations include: fermentation residues from food

processing operations, chicken sludge, ice cream, grease trap waste and other residual fruit and

vegetable material. Although these food organics are directly injected/applied to soil, they are in some

instances combined with other materials e.g. garden organics or lime to suppress odours. For example,

L.V. Rawlinson and Associates sometimes combine their grease trap waste with lime in order to

suppress odours (L. Rawlinson pers. comm.). This material is then land applied with a manure

spreader and incorporated into the soil.


The processing capacity of these systems is related to the number and capacity of storage tanks used by

a facility. In addition, the processing capacity is related to the capacity of the machinery used during

an operation and the rate at which the food organics can be applied to soil, and the area of land

available for direct injection applications. As there is very little or no processing involved, direct

injection infrastructure has minimal land requirements, requiring only space for food organics storage

tanks and application machinery.


As food organics materials received by facilities operating in NSW for direct land application are in a

liquid form no processing time is required, as the liquid is directly injected into the soil.


The direct injection process does not produce any products. The raw liquid food organics are applied

directly as liquid soil amendments, which can increase soil organic matter and nutrient levels and

improve soil structural stability. These benefits are particularly important in the Australian context due

to weathered and nutrient deficient nature of many of our soils. Improving soil nutrient and organic

matter levels through direct soil injection may translate to such benefits as improved crop growth and

emergence, fertility, increased soil porosity and water holding capacity, decreased bulk density and

increased soil stability.


As the food organics in direct injection operations are untreated, the decomposition of this feedstock

material could contribute to plant phytotoxicity in some instances. In addition, food organics risk

spreading weed seeds and pathogens due to their unpasteurised condition, as well as attracting flies and

vermin if materials are not properly incorporated into the soil. Phytotoxicity and pasteurisation issues

are addressed in previous sections. The reader is directed to Sections 4.3, 5.3 and 6.3 for further

information.


Although the direct application of food organics material presents many potential benefits, the

management of nutrients such as nitrogen and phosphorus is important to avoid water contamination

problems (from surface and subsurface water movement) (Epstein, 1998). Applications of organic

wastes to soils in excessive quantities can cause potential ground water pollution with nitrate (Chang et

al., 1973). Therefore, rates of application must be carefully assessed to obtain the desired soil benefits

from the added nitrogen and yet prevent excessive leaching of nitrate to ground waters (Wright, 1978).

Other relevant issues pertaining to the direct injection of food organics include: the release of

bioaerosols and contamination from other toxic compounds (Epstein, 1998).


8.4.1 Licensing requirements


directed to this section for relevant details. The licensing requirements for applying food organics to

land are contained in Schedule 1 of the Protection of the Environment Operations Act (1997). For the

purposes of this Schedule, food organics can be applied to land for agricultural purposes only if:

(a) the agricultural purpose is the dominant purpose of applying the waste, and

(b) the application of the waste supplies nutriment (whether directly or indirectly) to the land and so maintains or improves (and is not likely to harm) the productivity, quality, development or reproductive capacity of vegetation on the land, and

(c) the application of the waste (taking into account the manner of its application) does not, and is not likely to, result in the deterioration of the land (for example, through soil structure degradation, salinisation, waterlogging, erosion or the build-up of heavy metals or other contaminants), and

(d) the application of the waste does not, and is not likely to, constitute a risk to public health.

Similarly, food organics are applied to land for environmental rehabilitation purposes only if:

(a) the environmental rehabilitation purpose is the dominant purpose of applying the waste, and

(b) the application of the waste improves the ability of the soil to sustain vegetation on the land by directly or indirectly improving soil characteristics, and

(c) the application of the waste (taking into account the manner of its application) does not, and is not likely to, result in the deterioration of the land (for example, through soil structure degradation, salinisation, waterlogging, erosion or the build-up of heavy metals or other contaminants), and

(d) the application of the waste does not, and is not likely to, constitute a risk to public health.

In most instances an Environmental Protection License will be required by a operator (see Section 3 for

details.

8.4.2 Environmental effects

A field and laboratory scale experiment by Plante and Voroney, (1998) in Toronto, Canada, examined

the decomposition of oily food organics applied to agricultural land. This study found that soil


microbial biomass carbon in the field increased by up to five fold compared with control plots. The

aggregate stability of the soil also increased following the addition of food organics and was

maintained over the course of the growing season.

Laboratory incubation studies examining the biodegradation of rapeseed oil and oily food organics

showed that the oily fraction of the material was not rate limiting. Both substrates degraded rapidly

with initial decomposition half-lives of 40-45 hours and 70-94 hours for rape oil and oily food organics

respectively (Plante and Voroney, 1998). The longer lasting binding abilities of microbial products and

bodies are the major contributing factors for the increased soil aggregation. This study concluded that

the land application of oily food waste is agronomically beneficial by increasing soil microbial activity,

and in turn improving soil structure through increased aggregate stability. Similar results were

obtained by Smith, (1974) in a study examining the decomposition in soil of waste cooking oils from

potato processing facilities. Application rates examined ranged from 2.2 tonnes/ha to 112 tonnes/ha.

The food organics were found to decompose at a rate of between 2.5 and 8 tonnes/ha/week depending

upon the initial quantity of food organics applied. It was concluded that “there was no evidence for

toxicity to the decomposition systems with the high application of oil and no evidence that difficulty

would develop with land disposal of wastes containing edible cooking oils”.

Other studies by Brown et al., (1998) and Lehrsh et al., (1994) examined the effects of incorporating

cottage cheese whey into soil. These studies found that erosion was reduced on treated soils, and

infiltration rate of water into the soil was also increased. As with the findings of Plante and Voroney,

(1998), Lehrsh et al., (1994) found that the aggregate stability of the soil improved following the

incorporation of cottage cheese whey. Interestingly, work by Lehrsch and Robbins, (1996) indicates

that when the cottage cheese whey is not incorporated into the soil (i.e. surface applied), soil infiltration

rates do not increase.

Although studies such as Plante and Voroney, (1998) indicate that food organics can have beneficial

effects upon soils, other work highlights potential problems. For example, in a field study, Cockborne

et al., (1999) identified the environmental risks and the main biochemical processes involved when

apple residuals were applied to farmland in France. It was found that soil pH decreased significantly

and nitrate depletion in the soil was noted. The deficiency in nitrate was attributed to nitrogen

immobilisation and denitrification (i.e. the conversion of soil nitrogen (nitrate) required for plant

growth to gaseous nitrogen gas). This process occurs under low oxygen (anaerobic) conditions by

some soil bacteria. The creation of anaerobic conditions (which leads to denitrification) is caused by

the consumption of soil oxygen by bacteria when they break down the food organics. This could be

due to excessive food application and/or lack of air exchange within the soil injection zone and the

atmosphere.

Similar denitrification effects where found by Rice et al., (1988) examining the decomposition of soil

injected fermentation residues. These studies highlight the possible negative impacts different types of

food organics or excessive application rates could have on soil chemical and physical properties.


8.4.3 Biosolids guidelines

Currently there is no direct legislation in NSW controlling the direct injection of food organics into

soil. However, commercial companies involved in the direct injection of food organics contacted in the

preparation of this report follow the guidelines described in “Environmental Guidelines: Use and

Disposal of Biosolids Products” (EPA, NSW, 1997) by the NSW Environmental Protection Authority.

In most instances, food organics are applied to agricultural lands. Therefore classification and

application issues identified for agricultural applications in the guidelines are described below.

Biosolids (and hence food organics) are given a number of classifications according to their

contamination potential and stability. The contaminant grade describes the quality of a biosolids

product based on the concentration of its constituent contaminants (e.g. heavy metals and chlorinated

hydrocarbons). Grades are assigned from A (high quality) to E (low quality). The stabilisation grade is

based on product pathogen reduction, vector attraction reduction and odour reduction. Stabilisation

grades are assigned from A (high quality) to C (low quality). Based upon these parameters, a product

is given an overall classification that provides guidelines for the application of the product in different

situations (Table 8.1). In most instances, food organics feedstocks fall into the unrestricted

classification or restricted use 1 and 2 classifications (L. Rawlinson pers. comm.). In instances where

restrictions apply, operators should follow the application guidelines for restricted use (Table 8.2).

The biosolids guidelines also provide information about the maximum allowable soil contaminant

concentrations for agricultural land after the application of a product (Table 8.3). It is therefore

important for operators to determine initial soil properties and the composition of the food organics

used, as this will help them determine maximum amounts of food organics that can be applied to soil

without increasing soil contaminant concentrations above prescribed levels.

For Restricted Use 1 and 2 biosolids, operators should comply with the management practices for

restricted use biosolids products in agriculture as identified in the biosolids guidelines. Operators need

to consider storage issues such as: site drainage; odour impacts on neighbours, and storage period of

the feedstock. Other issues to consider include

• Incorporation of biosolids: biosolids (hence food organics) should be incorporated into soil within 36 hours of spreading;

• Frequency of application (applies if feedstock is not Contaminant Grade A); • Soil pH adjustment [use of a liming agent if feedstock reduces soil pH (in CaCl2 solution) to below

5.5] (applies if feedstock is not Contaminant Grade A), and • Water sampling may be required – where application rates exceed 1200 kg total nitrogen/ha


Table 8.1. Classification of biosolids products, these guidelines also apply to liquefied food organics subject to soil injection (EPA, NSW, 1997).

Biosolids classification

Allowable land application use

Minimum quality grades

Contaminant grade

Stabilisation grade

Unrestricted use i) Home lawns and gardens ii) Public contact sites iii) Urban landscaping iv) Agriculture v) Forestry vi) Soil and site rehabilitation vii) Landfill disposal viii) Surface land disposal2

A A

Restricted use 1 i) Public contact sites ii) Urban landscaping iii) Agriculture iv) Forestry v) Soil and site rehabilitation vi) Landfill disposal vii) Surface land disposal2

B A

Restricted use 2 i) Agriculture ii) Forestry iii) Soil and site rehabilitation iv) Landfill disposal v) Surface land disposal2

C B

Restricted use 3 i) Forestry ii) Soil and site rehabilitation iii) Landfill disposal iv) Surface land disposal2

D B

Not suitable for use i) Landfill disposal ii) Surface land disposal2

E1 C1

Notes: 1. Biosolids products which are not contaminant or stabilisation graded are automatically

classified Not suitable for use. 2. To be applied within the boundaries of sewage treatment plant site.


Table 8.2 Site characteristics of agricultural land where Restricted Uses 1 and 2 biosolids application should be avoided (EPA, NSW, 1997).

Site Characteristics Restrictions:

Maximum slope Land with a slope in excess of 10% (6º)

Areas of undesirable drainage characteristics

Waterlogged soils slowly permeable soils Highly permeable soils

Depth to bedrock Land where depth to bedrock is less than 60 cm

Surface rock outcrop Land with >10% rock outcrop

Vegetation Native forests and significant native vegetation

Buffer zones1 Land within the following buffer zones:

Protected areas Minimum width of buffer zones (m)

Flat (<3% or <2º)

Downslope2 (>3% or >2º)

Upslope2

Surface waters 50 100 5

Farm dams 20 30 5

Drinking water bores3

250 250 250

Other bores 50 50 50

Farm driveways and fence lines

5 5 5

Native forests and other significant vegetation types

10 10 5

Animal enclosures 25 50 25

Occupied dwelling 50 100 50

Residential zones 250 500 250

Notes: 1. All buffer zones must be stable and covered with suitable vegetation to limit the transfer of

biosolids from the application area to neighbouring areas. 2. Downslope refers to the situation where the Protected Area is below the biosolids application area.

Upslope refers to the situation where the Protected Area is above the biosolids application area. 3. The depth to watertable can either be assessed by a suitably qualified professional using standard

hydrogeological techniques (soils, geology, topography, local information and the States Groundwater Database) or, if insufficient information exists, a shallow drill hole will be required.


Table 8.3 Maximum allowable soil contaminant concentrations for agricultural land following biosolids application.

Contaminant Maximum allowable (mean) soil contaminant concentration (mg/kg weight of soil)

Arsenic 20 Cadmium 1 Chromium 100 Copper 100 Lead 150 Mercury 1 Nickel 60 Selenium 5 Zinc 200 DDT/DDD/DDE 0.5 Aldrin 0.02 Dieldrin 0.02 Chlordane 0.02 Heptachlor and Heptachlor epoxide 0.02 Hexachlorobenzene 0.02 Lindane 0.02 Benzene hexachloride 0.02 PCBs 0.3

8.5 Economics

As the food organics feedstocks in these systems require very little processing, most of the expenses

associated with this method of food organics recycling comes from the initial capital expense of

purchasing application machinery such as sludge injectors, storage tanks, pumps and tractors. In

general, costs could range from $80 000 for tractor drawn sludge injectors to over $300 000 for

specialised sludge injecting machinery. The overall cost of a facility is dependent upon the number of

injectors and storage tanks used (Table 8.4). There may be additional costs associated with

constructing a bunded pad for storage of the liquid food organics.

Table 8.4 Capital cost and processing capacity of direct soil injection operations in NSW.

Facility Capital cost Processing capacity

L.V Rawlinson and Associates $700 000 40 000 tonnes/year

Applied Soil Technology Pty. Ltd.

Information not provided 52 000 tonnes/year


The Recycled Organics Unit does not endorse any of the manufacturers listed in Table 8.5. The




Table 8.5 The following companies direct inject food organics in New South Wales. Note: they do not necessarily supply equipment related to the establishment of such operations. This list does not represent all soil injectors across New South Wales.


L V Rawlinson and Associates Pty. Ltd.

Lisa Rawlinson PO Box 255 Berry NSW 2535 Australia Tel: 02 4464 1657 Fax: 02 4464 2248 E-mail: [email protected]

Applied Soil Technology Pty. Ltd.

Simon Leake Scientific Director Applied Soil Technology Agricultural Division “Shannongrove” Silverdale NSW 2752 Australia Tel: 61-2-9980 6554 Fax: 61-2-9484 2427 E-mail: [email protected] Internet: http://sesl.com.au


Introduction

Case Study 8.1 L. V. Rawlinson and Associates – Direct injection of liquid food organics


L. V. Rawlinson and Associates lease several properties in the Appin area. These properties are used as their base for the direct soil injection of liquid food organics to nearby agricultural land. On average, this company treats 100-200 ha/year of land with the liquid food organics.

Process description

This operation utilises two 11 000 litre liquid sludge injection vehicles, a 14 000 litre tractor drawn sludge injector, a tractor and a pump. Tines have been attached to the rear of the sludge injection vehicles.

Liquid food organics are stored in two 45 000 litre mobile storage tanks. These mobile tanks give the company the flexibility to store their feedstocks close to application sites.

Cleanaway and other companies transport liquid food organics in 14 000 to 25 000 litre trucks to L.V. Rawlinson and Associates. The food organics are pumped through a metal grate into sealed storage tanks.

The food organics are usually transferred to a liquid sludge injector vehicle or trailer within

1-2 days of delivery. The feedstock is then incorporated into the soil to a depth of 15-20 cm with the sludge injection machinery at an approximate rate of 200 tonnes/ha (dependent upon feedstock used and soil characteristics).

After application, the treated soil is left for a period of 30 or 90 days before grazing beef or dairy cattle respectively. Cropping of soil following application is dependent upon the requirements of the landholder. However, the soil is usually cropped within 1-2 weeks of application.

The company claims that all odours from the injected food organics disappear within 1-2 days of application.

L. V. Rawlinson and Associates directly injects food organics onto 100-200 ha of agricultural land at an average rate of 200 tonnes/ha/year Feedstocks Chicken sludge, ice cream residuals and fermentation residues from yogurt manufacturers Facility size No central processing facility Process Liquid food organics are directly applied to soil using sludge injection machinery Processing time 0 days Outputs Unprocessed liquid food organics applied to 100-200 ha/year Installations (sites) Appin, NSW Cost Machinery and storage costs: $733 000 Status Commercial operation

Plate 8.3 Sludge injection vehicle used to apply liquid food organics to agricultural soils. The food organics are incorporated into the soil using tines attached at the rear of the vehicle.



This company receives food organics from food processing manufacturers. Food organics materials include chicken sludge, ice cream residuals, fermentation residues from yogurt production and grease trap residuals. The material is passed through a metal grate in order to filter out any contaminants such as metal or plastic.

In some instances, the chicken or grease trap residuals are mixed with garden organics or lime and composted in order to reduce odour problems. However, as the material is usually applied and stored in isolated locations, odour does not generally pose any problems.


The facility can store a maximum of 90 000 litres in its metal storage tanks. A very small land area is required for the storage tanks and vehicles.

Processing time

No processing of the food organics materials (other than the direct soil injection process). Materials are, however, passed through a metal grate to remove plastic and metal contaminants.


Appin, NSW. Location of storage tanks varies depending upon the area in which the food organics are to be injected.

Costs

Machinery costs associated with the land application of the feedstocks are significant. The two soil injection vehicles cost $310 000 each. The tractor drawn sludge injector is worth $80 000. Additional machinery expenses include a tractor and

manure spreader. The storage tanks cost approximately $5 000 each and the pump cost $28 000.

Contact details

Lisa Rawlinson

PO Box 255 Berry NSW 2535 Ph: 02 44 641657 Fax: 02 44642248 [email protected]

a)

b)

c)

Plate 8.4 a) Delivery of liquid food organics to L.V. Rawlinson and Associates by Cleanaway. b) Feedstocks are usually pumped through a metal grate to remove metal and plastic contaminants. c) Feedstocks are temporarily stored in sealed metal storage tanks.


Section 9 Conclusions This review provides a basis for increasing knowledge and awareness of food organics processing

options in industry and government, supporting informed decision making within an Environmentally

Sustainable Development (ESD) framework across New South Wales.

It is not within the scope of this review to recommend any of the technologies covered, as their

suitability for application is dependent upon regional and site specific variables. For a more detailed,

situation specific evaluation of food organics processing options, further research is required.


Section 10 References Allen (1994) Composting food scraps at Georgia prison. BioCycle 35:4, 90.

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EPA, NSW (2000) Environmental Guidelines: Composting and Related Facilities. Draft for Community Consultation. EPA, Chatswood, NSW.

EPA, US (1997a) Greenhouse Gas Emissions from Municipal Waste Management. Report prepared for the Office of Policy, Planning and Evaluation, U.S. Environmental Protection Agency.

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Section 11 Glossary Aerobic In the presence of, or requiring, oxygen.

Anaerobic In the absence of oxygen, or not requiring oxygen. Composting systems subject to anaerobic conditions often produce odorous compounds and other metabolites that are partly responsible for the temporary phytotoxic properties of compost. Anaerobic conditions are important for anaerobic digestion systems.

Carbon to nitrogen ratio The ratio of the weight of organic carbon (C) to that of total nitrogen (N) in an organic material.

Compostable organics Compostable organics has been adopted by NSW Waste Boards as the generic term for all organic materials that are appropriate for collection and use as feedstocks for composting or in related biological treatment systems (e.g. anaerobic digestion). Compostable organics is defined by its material components: residual food organics; garden organics; wood and timber; biosolids, and agricultural organics.

Feedstock Organic materials used for composting or related biological treatment systems. Different feedstocks have different nutrient concentrations, moisture, structure and contamination levels (physical, chemical and biological).

Fluidised Having liquid added – in a semi-liquid form.

Food Organics Food Organics includes organics generated by any one of the following activities: the manufacturing, preparation or consumption of food (including beverages); the processing of meat, poultry or fish, and the manufacturing of edible grocery products. Such materials may be derived from domestic or commercial and industrial sources. The definition does not include grease trap waste. Food organics is one of the primary components of the compostable organics stream, see Compostable Organics.

Foreign ingredient Any substance, or other thing, that is prohibited from use or can only be present in specified amounts in stock foods.

Garden organics

Any garden derived organic (plant) materials generated by domestic, C&D and C&I sources. Garden Organics is defined by its component materials including: putrescible garden organics (grass clippings); non-woody garden organics; woody garden organics; trees and limbs, and stumps and rootballs. Garden organics is one of the primary components of the compostable organics stream, see Compostable organics.

Hermetically Made air-tight.

Inoculum Plural inocula. Living organisms or material containing living organisms (such as bacteria or other microorganisms) which are added to initiate or accelerate a biological process.

In-vessel System of composting involving the use of an enclosed chamber or vessel in which (in most cases) the composting process is controlled by regulating the rate of mechanical aeration. Aeration assists in heat removal, temperature control and oxygenation of the


mass. Aeration is provided to the chamber by a blower fan which can work in a positive (blowing) and/or negative (sucking) mode. Rate of aeration can be controlled with temperature, oxygen or carbon dioxide feedback signals.

Maximum residue limit The maximum level of an agricultural or veterinary chemical allowed in a particular agricultural commodity or food (Blackwood and Byrne, 2000).

Mesophilic A temperature range of 20-45ºC. Mesophilic microorganisms grow well at these temperatures and are also important for decomposition during the cool-down or maturation stage of composting. Most pathogenic microorganisms grow in this temperature range, and are thus destroyed under high temperature (thermophilic) conditions during composting.

Pasteurise The process whereby organic materials are treated to kill plant and animal pathogens and weed propagules.

Phytotoxic Toxic to plants. Partially decomposed organic materials or immature composts are often phytotoxic, but this usually decreases with time. Such products may be phytotoxic due to a number of factors, including: low nutrient content; high oxygen consumption; presence of fatty acid or alcohol metabolites formed by microorganisms under anaerobic conditions; or due to excessive concentrations of salts, heavy metals and other organic compounds.

Plenum A container of air, or other gas, under greater than the surrounding pressure.

Sterilise A method for killing all microorganisms using heat and moisture. Sterilisation occurs quickly at temperatures above the boiling point of water (100°C). Sustaining very high temperatures (>75°C) for long periods during composting increases the risk of sterilisation and system failure. It is a different process to pasteurisation, which occurs at 55-70°C and kills only the unwanted pathogenic microorganisms.

Stock food Stock foods are foods for farm animals that have undergone a manufacturing process (Cook, L., 2001).

Thermophilic Temperatures above 45ºC. Used to describe a stage of composting in which high temperatures are sustained resulting in high rates of decomposition and pasteurisation of the organic material. Heat tolerant microorganisms survive well in these conditions.

Waste As defined in the Waste Minimisation and Management Act (1995) to include:

any substance (whether solid, liquid or gaseous) that is discharged, emitted or deposited in the environment in such volume, constituency or manner as to cause an alteration in the environment, or any discarded, rejected, unwanted, surplus or abandoned substance, or any otherwise discarded, rejected, unwanted, surplus or abandoned substance intended for sale or for recycling, reprocessing, recovery or purification by a separate operation from that which produced the substance, or any substance prescribed by the regulations to be waste for the


purposes of this Act.

A substance is not precluded from being waste for the purposes of this Act merely because it can be reprocessed, re-used or recycled.

Waste stream A general term used to denote all waste material placed out for removal, either by the recycling or garbage contractor.

Zeolites Any of various hydrous silicates that are analogous in composition to the feldspars, occur as secondary minerals in cavities of lavas,

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Food Organics Review