Proposed bio-conversion technologies for food waste ...€¦ · Proposed bio-conversion technologies for food waste recycling in Singapore Hsien H. KHOO, Reginald B.H. TAN Institute

1

Proposed bio-conversion technologies for

food waste recycling in Singapore

Hsien H. KHOO, Reginald B.H. TAN

Institute of Chemical and Engineering Sciences (ICES)SINGAPORE

• Singapore is a densely populated island with high standards of living and large food consumption and waste

• Total agriculture and farming occupies a total of 1500 hectares (1.6% of Singapore land area)

• Food is mostly imported (~ 97.6%) from neighboring countries, (for example, rice, vegetables, fruits, fish, meat from Malaysia, Indonesia, Thailand, Japan, etc), as well as other types of meat-products and fruits from Australia, New Zealand, U.S., etc

• As most of the “beginning” part of the food chain are imports, the focus of this presentation is on the “end”of the chain, e.g. food wastes

Introduction

2

Singapore food global supply chain (imports)

Some import items include:

- Rice and other agriculture products from Malaysia, Thailand, Myanmar, Cambodia, Indonesia-Vegetables/tropical fruits/meats from Indonesia, Philippines, Malaysia, Thailand- Vegetables/fruits/meat from China, Japan- Wheat products, cereal, meat from Australia, New Zealand- etc..

Waste disposal statistics for year 2005

• Food waste accounts for 20% of Singapore waste stream

• Food waste in year 2005 totaled 531,500 tons

Food waste

3

End-of-food chain disposal• Incineration and landfilling are the most

common methods for food waste management• Landfilling of food causes foul air, bad odor,

and increase of pathogens in soil and water• Total food waste recycled (converted into

animal feed) in 2005 was only 7%• Singapore Green Plan 2012Green Plan 2012 targets 30% for

food recycling and the aim for zero landfill• Food waste is a biodegradable material for

which alternative recycling options exists• Two examples proposed: Aerobic CompostingAerobic Composting

and Anaerobic DigestionAnaerobic Digestion

Current food management for the “End” stage of food chain

4

Treatment/recycling of food waste

• New and innovative bio-technologies are required for promoting food recycling

• Proposal: Anaerobic and Aerobic treatment of waste food

Food waste

Food waste

Composts Bio-Fertilizers

Aerobic Composting• Aerobic composting is the transformation of organic

wastes (food) into biologically stable, humus substances suitable for soils and plant use

• New developments in bio-technology have emerged for composting processes due to increase in landfill costs and decrease in landfill space

• For aerobic composting to take place, the following environmental conditions are required: Air (oxygen), organic matter, minerals, water, microorganisms

Organic matter

Microorganisms

Minerals

Water Compost pile

Heat Water

CO2

O2

5

Aerobic Composting• An aerobic composting system was developed at

the Nanyang Technological University of Singaporefor waste food bioconversion to bio-fertilizers

• Pilot-scale reactor consisting of a steel cylinder (500 L volume)

• Temperature in reactor maintained at: 55 – 65 °C• Moisture content: 75 – 80% to prevent drying• To maintain pH, 5% of CaCO3 was added to the

food waste solids• Time taken for full conversion food waste into bio-

fertilizers: 10 days

Ref: Stabnikova et al. (2005), Biotechnology for aerobic conversion of food waste into organic fertilizer, Waste Management and Research, 23, 39 – 47.

Schematic diagram of Aerobic Bioconversion (Composting) system for food waste

Heating Plate

Air Outlet

Air Inlet

Output GateCooling

Tower

Blower & Motor Chamber

6

Anaerobic food conversion• Anaerobic digestion (AD) is a biochemical

degradation process that converts complex organic materials into biogas in the absence of oxygen

• Biogas is composed of methane, carbon dioxide and trace amounts of hydrogen sulfide

• Food wastes, mostly generated from food processing, food service and re-tail establishments, are excellent feedstock for AD

• Food wastes typically have high ratios of volatile solids/total solids (VS/TS), which indicate high energy content

Anaerobic food conversion• A two-phase anaerobic digester system was

designed, also by Nanyang Technological University, to produces organic residue that can be used as soil conditioners or fertilizers

• The system was designed to minimize the amount of food waste for disposal in Singapore

• Apart from fertilizers, bio-gas is also produced as a new source of energy

7

Anaerobic food conversion• The two-phase digester system was called: Hybrid Hybrid

Anaerobic SolidAnaerobic Solid––Liquid (HASL) systemLiquid (HASL) system

• In the HASL system, organic matter is degraded to volatile fatty acids (VCA) by hydrolytic and acidogenic bacteria in an acidogenic reactor

• The laboratory-scale HASL system consists of acidogenic and methanogenic cylindrical reactors

• Volume of reactors: 5.4 dm3 and 3.0 dm3

• Operating conditions are: 70 °C for 1 hr or 150 °Cfor 2 hrs

Ref: Wang et al. (2006), Digestion of pre-treated food waste in a hybrid anaerobic solid-liquid (HASL) system, J Chem Tech & Biotech, 81, 345-351.

Anaerobic Digestion: Two-phase digester system (HASL) for waste food conversion

8

Proposed food waste management

Zero landfill

Life cycle assessment• LCA is carried out for waste food management in

Singapore• Objective: Investigate alternatives for increasing

food waste recycling to 30% by alternate bio-conversion methods; and compare with the present incineration / landfill practices

• Scope: Only the main emissions of the processes will be taken into consideration

• System boundary: from waste generation to final conversion (due to unavailable data, conversion of food waste to animal feed is not included)

• Functional Unit: Total annual amount of food waste Total annual amount of food waste

generated in the countrygenerated in the country

9

Food waste management system(Reference caseReference case)

93% Dispose

93% Dispose

90%Incinerate

90%Incinerate

10%Landfill10%

Landfill

Food waste

(531,500 tons)

No Other Recycling Scheme

No Other Recycling Scheme

7% (fixed)Animal feed7% (fixed)

Animal feed

LCA System Boundary (Base Case)

Alternative system IAlternative system I

70% Dispose

70% Dispose

100%Incinerate

100%Incinerate

zeroLandfillzero

Landfill

Food waste

(531,500 tons)


Animal feed

23% Recycle

23% Recycle

50%Aerobic

Composting

50%Aerobic

Composting

50%Anaerobic Digestion


Propose

LCA System Boundary (I)

SGP 2012

Increase food recycling to 30%, and zero landfill

SGP 2012SGP 2012

Increase food Increase food recycling to 30%, recycling to 30%, and zero landfilland zero landfill

10

Alternative system IIAlternative system II

70% Dispose

70% Dispose

100%Incinerate

100%Incinerate

zeroLandfillzero

Landfill

Food waste

(531,500 tons)

23% Recycle

23% Recycle

100%Aerobic

Composting

100%Aerobic

Composting




Animal feed

Propose

LCA System Boundary (II)

SGP 2012


SGP 2012SGP 2012


Alternative system IIIAlternative system III

70% Dispose

70% Dispose

100%Incinerate

100%Incinerate

zeroLandfillzero

Landfill

Food waste

(531,500 tons)

23% Recycle

23% Recycle

0% Aerobic Composting0% Aerobic Composting




Animal feed

Propose

LCA System Boundary (III)

SGP 2012


SGP 2012SGP 2012


11

Global Warming Potential

0.0E+00

5.0E+07

1.0E+08

1.5E+08

2.0E+08

2.5E+08

3.0E+08

Referene I II III

kg-C

O2-

eq

Landfill IncinerateAnaerobic Digestion Aerobic Composting

Results: Global Warming

Acidification Potential

0.0E+00

5.0E+04

1.0E+05

1.5E+05

2.0E+05

2.5E+05

3.0E+05

3.5E+05

4.0E+05

4.5E+05

Referene I II III

kg-S

O 2-e

q

Landfill Incinerate

Anaerobic Digestion Aerobic Composting

Results: Acidification Potential

12

Nutrient Enrichment Potential

0.0E+00

5.0E+04

1.0E+05

1.5E+05

2.0E+05

2.5E+05

3.0E+05

3.5E+05

Referene I II III

kg-N

O 3-e

q


Results: Nutrient Enrichment

Photochemical Oxidation Potential

0.0E+00

5.0E+03

1.0E+04

1.5E+04

2.0E+04

2.5E+04

3.0E+04

3.5E+04

4.0E+04

4.5E+04

I II III

kg-E

then

e-eq


Results: Photochemical Oxidation

13

Final Weighted Scores

0.00E+00

7.50E+00

1.50E+01

2.25E+01

3.00E+01

3.75E+01

4.50E+01

5.25E+01

6.00E+01

6.75E+01

7.50E+01

Reference I II III

AerobicComposting

AnaerobicDigestion

Incinerate

Landfill

Overall environmental impacts

Up to 45% reduction in environmental impacts with 30% food recycling

Discussions and Conclusions• For many years, the easiest way to get rid of organic

wastes is either by dumping them in landfills or by mass burning (incineration)

• However, since food waste is a biodegradable material, better options exists

•• Aerobic CompostingAerobic Composting and Anaerobic DigestionAnaerobic Digestion are two methods presented for food waste recycling

• Both bio-conversion processes can offer environmental benefits of reducing negative environmental impacts, as well as, economic benefits of producing useful products such as compost or bio-fertilizers

• An added advantage is the generation of bio-gas by Anaerobic Digestion (AD)

14

• Steps to promote food recycling should be introduced at a regional level

• Involve the participation of communities and general public by creating awareness and neighborhood projects to facilitate waste food collection

• Some of the suggestions include: - Collection of food scraps from their source (restaurants, food stalls, canteens, etc)- Provide the use of Separate waste bins- Set schedule for collection- Provide information on what are the allowable contaminants that may be mixed with the food waste fractions

Discussions and Conclusions

Documents

Proposed bio-conversion technologies for food waste ...€¦ · Proposed bio-conversion technologies for food waste recycling in Singapore Hsien H. KHOO, Reginald B.H. TAN Institute