Small scale FOOD/Kitchen Waste

On – Site Treatment Units (Reactors)

A. Review

Prepared by A. Brazas, July 2014

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8th July, 2014

I think that everyone involved in Food Waste Recycling business should have

understanding what there are differences between:

1) DEHYDRATORS / DRYERS, very often so-called „high-speed composting

machines“, but using heaters/boilers for biomass heating(?!))

2) LIQUID Food DIGESTORS / Wet BIOREACTORS / BIO-LIFUEFACTION

machines and Food/kitchen waste DISPOSERS

3) Real COMPOSTERS / DECOMPOSERS - composting machines

(BIOSTABILISATORS) and ATAD (Autothermal Thermophilic Aerobic Digestion)

machines

Small scale FOOD/Kitchen Waste On – Site Treatment Units

(reactors):

1) DEHYDRATORS / DRYERS – physical process of heating and dehydration

dominate, and biological – composting process presence only as secondary

(accessory).

Manufacturers and/or equipment name: GAIA corp., EcoVim, Somat,

BioGreen360 (dry), and also ERS-machine, Hungry Giant, Oklin International

(Green Good), Biomax RTDS (Biomax International Pte Ltd) and many others - who

there are advertising its as so-called „high-speed composting machines“.

In the Dehydrators / Dryers biological process does not occur in practice (well,

it only happens at the very beginning, a couple of hours after load of food

waste - then food waste (biomass) become too dry and the composting process

is interrupted (optimum moisture content for composting should be 50-60%)).

Heating of biomass to > 70 °C (and often at a higher temperature) kill all

thermophilic bacteria from exponentially grew (at operating temperature of

40-65 °C) and the resulting destruction of (produced) enzymes...

Conclusion - actually in the dehydrators / dryers going on (obviously dominates)

only physical drying process. Therefore, a "product" can’t possibly be a bio-

stable (biologically degraded - decomposed (rotten)). Also this “product”

couldn’t be mature (non-toxic for plans and/or soil microbes.

This is by no means the compost.

In addition, Dehydrators / Dryers big disadvantage - an expensive operation

(due to heating, etc.). Also Dehydrators / Dryers there are expensive, and

exist a number of cheaper Food/Kitchen Waste Dewaterers... (?!)

The apparatus advantage over the other 2 (4) types of machines - that it is

possible to produce feed for animals!

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2) LIQUID Food DIGESTORS / Wet BIOREACTORS/ BIO-LIQUEFACTION

machines – water adding and biological liquefaction process (very often in

anaerobic conditions – microbial hydrolysis / anaerobic fermentation) occure.

Manufacturers and/or equipment name: Eco-Save Digestor (Bio Hitech

America), EnviroPure (EPW), ECO-Wiz® Wet System, BioGreen360 (wet),

Green Key biodigestor, Power Knot, ORCA GreenTM Machine (Totally Green),

ecoWater digester (Greentail Invironmental Inc.), Tidy Planet and others.

In the liquefied (by adding water) food / kitchen waste bioreactors (liquid

digesters)/ Liquefication machines (actually going microbial hydrolysis /

anaerobic fermentation machines) the good/kitchen waste is converted into a

variety of liquids (grey water) after all spent down the drain! A result an

increased loadings of BOD, and TSS to the WWTP, increased loads of organic

carbon that reaches water treatment plant, which in turn increases the

consumption of oxygen.

Also what to buy these expensive machines, if there are various cheap food /

kitchen waste Disposers (Macerators, Grinders/Shredders) positioned just

under the sink?

DISPOSERS of Food/kitchen waste

Manufacturers and/or equipment name: IMC Ltd., InSinkErator, Fowex,

EcoFast, Disperator and others, and a dozen of China and South Korea

companies.

A food/kitchen waste disposal unit is a device, usually electrically

powered, installed under a kitchen sink between the sink's drain and the

trap which shreds food waste into pieces small enough—generally less

than 2 mm —to pass through plumbing.

Food/kitchen waste disposers are widely used in North American

households, but far less commonly used elsewhere.

The most common argument against food waste disposers is that the

capacity of WWTPs is not sufficient.

Yes, wide using of Food/kitchen waste disposers increased loadings of

BOD and TSS to the WWTP. Food/kitchen waste disposal units increase

the load of organic carbon that reaches water treatment plant, which in

turn increases the consumption of oxygen.

A result od disposers using - increased energy consumption for both

disposer use and WWTP aeration.

The most common conclussion made that in order to allow the use of

food/kitchen waste disposers and also food/kitchen waste liquefaction

machines - in particular, should be reconstructed wastewater treatment

facilities ...

Is it true?

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Please, look „Regarding the Environmental Efficacy of Food Waste Disposers. Summary prepared by: Michael Gitter, P.E. Senior Environmental Engineer, InSinkErator. Last revised: October 27, 2006“ (remark - and a number of other reports prepared).

The main conclusions of this summary report:

Food Waste Disposer (FWD) Life Cycle Analysis show that the FWD/WWTP has the

lowest municipality cost (system cost due to disposer cost, which is paid by the

homeowner); least air emissions; converts food waste to a recycled resource; is the

most convenient system of food waste disposal; is the most likely system for organic

source separation; and overall is the most environmentally friendly and sustainable

option.

Reduced (food waste) transportation emissions and costs.

As food waste is 60-70% water, the WWTP is a more natural system of Waste

processing than hauling the waste to a “solid waste” facility.

The effect of disposers on WWTP processes is very limited.

Additional average pollutant loading due to disposer use is 66 g/person/day BOD, 60

g/person/day TSS, 2.1 g/person/day TKN, 0.3 g/person/day P, and 2.5-5% biosolids.

Up to a 15% disposer market share, the use of disposers in multi-unit dwellings would

have a very small impact on sewage treatment systems.

No operational problems are expected for market levels up to 15% in regard to BOD

and O&G loadings, or up to 20% market for additional TSS loadings.

At a 15-20% disposer market share, loadings do not result in significant variations in

the characteristics of sewage.

At a 25% disposer market share, influent BOD would increase 12%, TKN and P would

increase 2%.

At a 20-35% disposer market share, an increased WWTP system energy consumption

is observed due to greater respiration of the active biomass and a larger production

of excess biosolids.

Beyond a 35-40% disposer market share, additional works must be done at the WWTP.

Beyond this figure are increasing impacts, with potentially significant impacts at a

50% market share.

However, this level of market share is unlikely in the near future.

European Union (EU) market levels will not exceed 15% in 25-30 years, thus, normal

WWTP upgrades will allow for an accommodation of increased disposer loading.

The additional soluble food waste fraction will lead to higher BOD/COD loading within

the biological treatment steps, which on one hand will cause a higher oxygen demand,

but on the other can serve as a cheap and continuously available carbon source (for

nutrient reduction).

The food waste disposer has to be considered an addition rather than a competitor to

the current system for the collection of kitchen, food, and garden waste.

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3) COMPOSTERS / DECOMPOSERS – real composting machines: biological

(aerobic digestion - composting) process occure, and per long time mix of

food/kitchen wastes + structural C rich materials become BIO-STABILE.

Manufacturers and/or equipment name: JORAform, HotRot, Rocket,

Rotoposter, Big Hanna, CITYPOD (Vertal, Inc.), AEL TUBES, Biovator, Eco

Values Technology, XACT systems and others.

On-site (home) Composting has the smallest environmental impacts, and On-site

Composting is the least expensive option for multi-unit residents.

Short remarks concerning BIOSTABILITY and MATURITY, and etc. I don't like to be involved into discussions about microbiology of these processes, because I

am engineer, and because microbiology isn't a subject of this discussion.

For me it is clear that if process of decomposing (decay, rotting) / composting –

biostabilisation happen (expired), microorganisms have nothing to eat, and they die (intense

biological processes stops held, and bio-waste turned into bio-stabile product COMPOST.

Generally it is considered that this is already occurring when the Static Respiration Index

(AT4 or BOD4) is < 10 mg O2 / g DM or Dynamic Respiration Index (DRI) < 1000 mg 02/ kg

VS / hour.

Moisture of compost isn't very important. Whether the compost will be wetter or drier -

intensive biological processes will still be ended...

Meanwhile, after the dehydration / drying obtained "product" is not a bio-stable.

We're just getting him humidity and under favorable temperatures - biological processes

begins again be intense....

This is because this "product" is full of food (nutrients) for microbes - because in reality no

decay / rotting (decomposing) process happened during dehydration / drying.

Composting - a biological decomposition of organic matter (biodegradation) in controlled

aerobic conditions caused by rapidly multiplying organisms (microbes and also soil

invertebrates, and protozoa), which generates heat and to form water, carbon dioxide and

mineral nitrogen compounds - organic matter is stabilized (mineralized and partly

humificated) - produced humus enriched with organic compost product.

The process of MINERALIZATION (ammonification and nitrification) - organic nitrogen

compounds transformation in mineral under the influence of micro-organisms it is very

important.

MATURITY is the main condition for describing the usability of compost - compost is mature

when it becomes non-toxic for plants, i.e. when it never (no longer) contain toxic compounds

for plants and / or microbes or these are negligibly small, as phytotoxic compounds and

microbes inhibits plant growth.

And I'm not sure what to have add something more...

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Autothermal Thermophilic Aerobic Digestion (ATAD) process it

is well known technology, which is widely used for sewage sludges (biosolids)

treatment.

Autothermal means Self-heating or Exothermic process (but all

Composting processes there are Exothermic (i.e. Self-heating)).

Now it is used so named 2nd generation ATAD technologies - usually using

2 stages ATAD process: 1st sage from 40 °C up to 60 °C temperatures,

and 2nd stage up to 75+ °C temperatures (so named hyper - thermophilic

process, when act hyper – thermophilic microbes).

Normally process takes from a few days up to 2 weeks.

It is well known Fuchs ATAD process, and VERTAD™ (Noram Engineering

and Constructors Ltd) process, and exist also a few other companies

supplying this technology.

ThermAer ™ 2 stages process state that 24 hours there are enough (?).

The same ATAD process principles there are used for food/kitchen

waste treatment.

The key element - very intensive mixing inside reactors.

There exist a number of so-called „high-speed composting machines“

(which never use heaters / boilers for biomass heating) most probaly

using some version of ATAD process : EcoHERO digester (ASM Organic

Recyclates), EnviroPure (EPD), ECO-Wiz® Dry System, Biotel ATAD unit

and other.

Many (but not all) of these „high- speed composting machines“ require enzymes to speed up the rate of the fermentation process. The cost of these enzymes is normally high.

EcoHERO digester (ASM Organic Recyclates and Greentail Environmental

Inc. - ecoOrganic™) never use expensive enzymes or chemical additives

to accelerate the process, and converts food waste into organic fertiliser

in 3 days.

EnviroPure (EPD) systems use EP BioMix™, a proprietary blend of all

natural organic nutrients. These nutrients are utilized by the naturally

occurring bacteria present in the food waste to increase the metabolic

efficiency and accelerate the biochemical reactions involved in the de-

composition process.

EnviroPure (EPD) systems general turnaround time for producing

ferlilizers from food waste is between 24-48 hours.

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ECO-Wiz® Dry System work with a microbial additive that is specially

designed and produced.

This additive contains a powdered blend of organisms blended with crude

enzymes and emulsifiers specifically designed to digest and deodorise

organic wastes.

Eco-Wiz® Dry System uses a natural process to decompose food waste at

the highest speed (most probably per 24 hour).

Biotel ATAD (Autogenous Thermophilic Aerobic Digestion) technology

unit (PMA Biotel Ltd.) state that 24 hours it is enough to digest

food/kitchen waste never using enzymes and to produce high quality

organic fertilizers.

But I always there are asking „high-speed composting machines“ suppliers

- what it is a bio-stability of "product" made?

Is it really bio-stable and mature product - compost - or not?

Short remarks concerning BIO-DRYING process It seems that Bio-drying pricess presence in these ATAD machine, and also in

DEHYDRATORS/dryers.

Biodrying (autothermal drying process) is the process by which biodegradable waste

is rapidly heated through initial stages of composting to remove moisture from a bio-

waste stream and hence reduce its overall weight.

In biodrying processes, the drying rates are augmented by biological heat in addition

to forced aeration. This heat generation assists in reducing the moisture content of

the biomass without the need for supplementary fossil fuels, and with minimal

electricity consumption.

But biodrying does not however greatly affect the biodegradability of the bio-waste

and hence is not bio-stabilised. Biodried bio-waste will still continue to be (stay) non

bio-stable, i.e. potentially biodegradable…

Prepared by Alfonsas Brazas -------------------------- Managing Director Atlieku tvarkymo konsultantai, UAB P. Luksio str. 7, LT-08221, Vilnius, LITHUANIA E-mail: a.brazas@zebra.lt, atk@zebra.lt Skype a.brazas Mobile: +370 687 76633 ___________________