anaerobic digesters for food waste

[Lynne Pledger]

I'd like to hear more from Craig and others about tonnage needed for
anaerobic digestion. It was my understanding that this method is
viable on a very small scale. I've seen photos of very small digesters
in use in Asia. Thanks.
--Lynne Pledger

[Craig]

Lynne is right about small scale digesters in Asia. The Australian
Institute for Energy notes there are about 5 million in use in rural
China, providing biogas for one or two homes each. There are larger-
scale units in operation in China and in Korea. Small scale units are
in place in the U.S. for handling animal manures on-farm, where on-
farm heating needs (think vegetable greenhouses) utilize the biogas.

Problems with digesting food waste were encountered in the pilot
testing of 40 tons/day in the biosolids anaerobic digesters of the
East Bay Municipal Utility District in Oakland. The plastic
contaminants and grit in the food waste damaged the rotors of the
pumps used to feed the sludge to the digesters. I understand those
problems have been fixed, but the long-term viability of that program
is in jeopardy, as I understand it. The Central Vermont Solid Waste
Management DIstrict is doing a project this summer to look at how food
waste should be pre-processed to make it a suitable feedstock for a
planned digester at Vermont Tech College.

My comment was not to say that small scale is not possible, just that
the American society and our waste management infrastructure does not
lend itself to small-scale digesters and biogas utilization schemes
(yet). Look how hard it is to get individual homes to practice
backyard composting! Still, I can see potential for a combined
digester-composter backyard unit at a scale that would handle a
family's waste, produce biogas usable for helping with heating demand
and produce compost for use in the garden for growing the family's
food.

Craig



On Apr 15, 8:55 am, Lynne Pledger <pled...@hardwickpostandbeam.com>
wrote:

[TO SSO]

There are lots of anaerobic digesters used to process food waste all
over the world, both large scale and small scale. Toronto has been
collecting food waste from single family homes for several years now
and generally collects 110,000 tonnes per year. They operate an AD
facility located in the middle of the city which this year will
process close to 40,000 tonnes of this material. Toronto is very
happy with this 'demonstration' facility and has now issued a 'Request
for Proposals' to build it's first full scale facility which will be
designed to process up to 75,000 tonnes of SSO (source separated
organics) per year (300 tonnes per day). The plant will generate bio-
energy (not determined yet whether electrical power, pipeline gas or
biofuel). The city plans to build two such facilities in the next 3
to 4 years.

Toronto's SSO is considered high in 'contamination'. In order to
promote high levels of participation in the program, Toronto allows
households to collect the food waste in non-biodegradeable film
plastic bags. They also collect pet waste, diapers and as likely in
any large city get glass jars, tin cans and other assorted
contamination.

The process used in Toronto strips out the contamination,
anaerobically digests the organic portion in a mesophilic, fully mixed
digester. The finished, digested solids are shipped out to composters
outside the city to be aerobically 'finished'. The material produced
at this facility has been tested hundreds of times over several years
now and easily meets the provinces quality standards allowing it to be
converted to the highest grade of compost. Ontario has one of the
highest 'compost' standards in the world.

The 'demonstration' plant was designed for 25,000 tonnes per year but
has operated at much higher levels (up to 200%)due to the shortage of
processing capacity in our area. The process is reliable, generally
operates at 96 to 100% online time, 24 hours per day, 5 days per
week. The digester has operated 7 years without interuption. The
plant had two odour complaints in 2008, not entirely related to
facility operations.

An interesting site to visit is http://www.german-biogas-industry.com
as many of the AD technologies have originated in Germany. There is
almost unlimited information available on the subject of AD.

Europe is way ahead of North America in farm and food AD projects.
The US has lots of farm based digesters. I believe Toronto will have
the first large scale AD system in operation processing SSO in North
America if it moves ahead with it's current plans.

Info on the Toronto AD project is available at:
https://wx.toronto.ca/inter/pmmd/calls.nsf/0/4675E7B6479787AA8525758A005C2704?OpenDocument
Unfortunately, to get the complete document they charge $75. The full
document runs to several hundred pages and is a complete record of the
entire history of Toronto's development program to collect and process
SSO. The document goes into great detail regarding the required
design of the proposed facility.

On Apr 15, 8:55 am, Lynne Pledger <pled...@hardwickpostandbeam.com>
wrote:

[Neil Tangri]

Hi Doug,

Thanks for this information. I am surprised to hear that
highly-contaminated SSO still results in high-quality compost. Can you
tell us how the SSO is "cleaned"? Also, how does the current facility
handle the biogas? Is it scrubbed prior to burning? Are there emission
controls on it? All of these are the devils in the details in moving to
commercial-scale AD.

best,

Neil

[Terrence83]

I am totally appalled to see discussion on AD of food waste when it
has been applied for over 15 years in Switzerland. Yes they had
(Kompogas) to work hard to reach the public and public policy to
encourage the AD treatment of organics, due to their federal organics
landfilling ban and interest in composting. Yes Kompogas (W. Schmidt)
fiddled since the 80'ies with his reactors. We are VERY far away from
this in North America in terms of public policy and public conscience.
But we don't need to fiddle again with systems that are not
approprietly applied. It's bad publicity for people who know what they
are doing.

Kompogas plants from Switzerland has the required equipment to process
high quality compost on site. Design of each SS cylinders can
accommodate 10'000 t/yr of fresh material, able to function with
medium contamination (they have their own proprietary sorting
equipment).

Now talking about Toronto. Okay, BTA is an not so bad system, but has
not been designed for poorly sorted SSOFMSW (source seperated organic
fraction of municipal waste). If the system doesn't work, its the
fault of the people responsible to distribute the proper sorting
information. Dont really like to "soup" concept of similar
technologies. I prefer the dry AD technology, but only Kompogas knows
what they are doing (and they are to busy to come over here). It uses
less energy to process the waste, and its a single stage system (less
pumps to fix, no centrifuges that jams up, etc...). Also there is less
rejects and all the solids are available to the digestion (no phase
separation like in the Dufferin station, and it produces more biogas).
Okay, phase separation removes most of the plastics that float and
settles some of the grit and glass. But I think it is just idiotic to
accept diapers! Oh well, it will be sorted by the screens... Oh, and
Kompogas is thermophilic (most of their plants), one other main
advantage of producing a higher quality compost (grade A MOE compost)
and kills more pathogen (with the added benefit of higher kinetic
rates of organics degradation

This is a free, but old report from Toronto. There are others out
there:
http://www.nerc.org/documents/toronto_report.pdf
Yes the report (Request for proposal) from Conestoga&Rovers would be
more interesting to read. However, Toronto still wants to go ahead
with a wet based system, hydropulper and all...

I was always in the impression that there was a ~100'000 t/yr BTA
plant in operation in Toronto (besides the Dufferin demonstration
plant). Was it ever built? (Oh yeah, since 2000) Is it running? Is the
Newmarket BTA plant still broken? I dont know the proper answer to
these questions, but it shows that the technology used in the
Newmarket plant also is not appropriate:
http://www.jgpress.com/archives/_free/000508.html

It also shows that you cannot learn how to operate these machines with
a course taken from a "Craker Jack" box. It is a must to learn from
the experienced in EU.

I would also add as a general comment that is has been shown in the
past that systems that do not sell well in EU are the first systems
being exported to the international market. They end up here and are
most of the time a flop due to improper engineering and operation/
maintenance. I am not saying that is a good thing to reinvent the
wheel in North America with goods and equipment from here, just saying
that we could 'copy' the systems here with proper patents or trade
secrets agreements.

Humm, looks like Montreal is also in the run for the first full scale
AD plant of SSO in North America? (Sorry, french only!)
http://ville.montreal.qc.ca/portal/page?_pageid=916,18089594&_dad=portal&_schema=PORTAL

The info is out there, just go and GRAB IT!
http://www.jgpress.com/archives/_free/001406.html

Sorry for the rant.
I am always surprised to explain to my friends and family that I study
in systems producing methane from organic waste (and manure) with low
inputs of energy. Not a lot of people understands!

Have a good day everyone.

> An interesting site to visit ishttp://www.german-biogas-industry.com

> as many of the AD technologies have originated in Germany.  There is
> almost unlimited information available on the subject of AD.
>
> Europe is way ahead of North America in farm and food AD projects.
> The US has lots of farm based digesters.  I believe Toronto will have
> the first large scale AD system in operation processing SSO in North
> America if it moves ahead with it's current plans.
>

> Info on the Toronto AD project is available at:https://wx.toronto.ca/inter/pmmd/calls.nsf/0/4675E7B6479787AA8525758A...

[TO SSO]

Interesting rant but not too useful. In the EU there are a number of
different technologies being used to treat Municipal Source Separated
Organics. Some systems are also used to treat what is called
'Residuals' in the EU which is the remaining organic material left
after extracting recyclable materials (they call these MBT plants for
Mechanical Biological Treatment). This waste stream still contains
material which will over time break down in landfills to cause
environmental problems such as leachate and air emmissions. Some
countries do more or less recycling and still use MBT but follow up by
incinerating whatever they can. Overall not a great way to go.

There are some basic trends which have taken place in the EU, we see
happening Canada and will almost certainly happen in the US.

Waste in North America is largely controlled by a relatively small
number of large companies with a large stake in landfill operations
which generate very nice profits. They resist any change in the
status quo but slowly adapt to some of the changes, especially if they
can make money at it.

Coming Trends (in some areas they have already arrived):
1) Awareness of the environmental issues associated with landfilling
grows.
2) Focus on the need to reduce landfilling.
3) Recycling of materials of higher value to reduce landfilling
(aluminum, other metals mainly tin cans, plastic containers, glass
bottles, paper and cardboard, and various other materials).
4) Focus on GHG issue brings more focus on organics (food and yard
wastes).
5) After lots of research in each country they rediscover that source
separation yields a higher value use for these wastes.
6) Traditional (and cheapest) way to recover organics is through
composting. Traditionally this is done in 'windrows' or in piles
outdoors.
7) Existing outdoor composting facilities in operation for years get
overwhelmed by large volumes and run into operational problems
resulting in odour complaints and poor process control (resulting in
methane and other emmissions from large piling operations). The more
odour complaints the less they turn the compost piles because turning
the pile causes complaints.
8) The composting industry evolves to more sophisticed and usually
indoor or containerized systems. These systems are more expensive to
build and operate and as they evolve end up costing as much as a well
designed AD system.
9) As awareness increases regarding the need for renewable energy
sources AD becomes of greater interest.
10) AD technologies develop to fill this need.

As companies see the need for AD technologies, many jump into the
business starting with the 'consultants'. Lots of money to be made
here. Many companies jump into the market with new processes, most of
them unproven (and many will fail).

The big waste companies are generally slow to move since profits in
landfills are so good and it's a real simple process. They hesitate
to move to AD since they don't fully understand the technology and
aren't sure of the profit margins.

A great deal of money and research effort has gone into AD in Europe.
Many plants have failed over the years in the EU for many different
reasons. Often it is as simple as not enough food waste (the waste
companies control the waste).

In the EU there are some rivalries between countries (such as
Switzerland (Kompogas) and Germany (BTA and others). I am sure that
for the 'surviving' technologies they must offer benefits if they have
survived.

After many years of research, Toronto's waste management engineers
chose the BTA AD process since it is very efficient at removing
contaminants. High solids AD systems have more difficulty removing
contamination such as film plastic and small shards of glass and
metal. Toronto know it's SSO waste would have a 'high' level of
contamination since this is generally the case in very large cities.
Smaller communities are sometimes able to limit contamination.

Mechanical equipment has a problem trying to sort small bits of metal
and glass from small bits of dry compost. Screening is not efficient
since much of the 'good stuff' may get screend out as well. In a
liquid phase, due to differences in weight it is simple to remove even
very small bits of metal and glass. Some technologies simply use
settling tanks.
I think I'm likely getting into too much technical 'stuff'?

The BTA plant in Newmarket (25 miles North of Toronto) is still in
fact being operated. Over the years, this plant which is privately
owned and operated has suffered from commercial problems largely
related to access to food waste. Remember the waste companies!

In terms of 'learning the technology', AD is not a terribly difficult
technology to learn. In fact it is a very simple process to operate.
Mostly it is a process of mixing and pumping. Some very basic tests
are used to monitor the anaerobic digesters such as pH, temperature,
volatile fatty acid level (at test done by the plant operators) and
methane content of the gas. It's really not all that difficult, not
certainly rocket science or anywhere near it.

If you're ever up in the area of Toronto, call ahead and we can see if
we can arrange a tour of the SSO facility.

I hope I'm not ranting through all this! Someone should write a book
on all this 'stuff', it's really quite interesting.

Cheers

> AD plant of SSO in North America? (Sorry, french only!)http://ville.montreal.qc.ca/portal/page?_pageid=916,18089594&_dad=por...
>
> The info is out there, just go and GRAB IT!http://www.jgpress.com/archives/_free/001406.html

> > > --Lynne Pledger- Hide quoted text -
>
> - Show quoted text -

[TO SSO]

Sorry Neil,
As I was scanning back over messages I realized I had not answered
you.
Toronto's SSO 'appears' highly contaminated since it is collected in
plastic, non-biodegradeable bags. The total contamination level is
under 10% dry weight. Film plastic covers everthing but relative to
the weight of food scraps is only a tiny part by weight. The SSO is
treated by mixing with reclaimed water in a 9500 us gallon tank. The
food is broken down to a pulp and pumped out of the bottom of the tank
through a screen. The pulp is then stripped clean of small bits of
bone, glass and metal using centrifugal force in a piece of equipment
called a 'hydro-cyclone', a rather simple process. Atter this, the
pulp is pumped to the anaerobic digester.

The contaminants (mostly large bones, tin cans, broken glass, ect..)
left back in the mixing tank are then removed from the tank and water
is hydraulically pressed out of the plastic bags.

Unfortunately, in Toronto the biogas is simply burned in a flare. The
facility built in Toronto was only designed to demonstrate that it was
possible to efficiently clean the SSO, that the resulting pulp would
digest without problems and that it would produce a grade A compost
(called un-restricted use in Ontario). All this has been proven as
the plant, originally designed to process 25,000 tonnes per year is
now operating at roughly 40,000 tonnes per year.

The biogas has a small tank to remove free water droplets but is not
scrubbed before going to the flare. The flare has been tested and
meets all of the requirements of our regulatory bodies. Typically,
before using the biogas to produce energy (boiler for heat, co-
generation engines for electrical power and heat, or conversion to
pipeline quality gas or to fuel) it does have to be scrubbed,
primarily to remove sulphur containing compounds which occur at very
low levels. The sulphur typically comes from protein based foods.

Hope this answers some of your questions...

> > An interesting site to visit ishttp://www.german-biogas-industry.com

> > as many of the AD technologies have originated in Germany.  There is
> > almost unlimited information available on the subject of AD.
>
> > Europe is way ahead of North America in farm and food AD projects.
> > The US has lots of farm based digesters.  I believe Toronto will have
> > the first large scale AD system in operation processing SSO in North
> > America if it moves ahead with it's current plans.
>
> > Info on the Toronto AD project is available at:

> >https://wx.toronto.ca/inter/pmmd/calls.nsf/0/4675E7B6479787AA8525758A...

> > Unfortunately, to get the complete document they charge $75.  The full
> > document runs to several hundred pages and is a complete record of the
> > entire history of Toronto's development program to collect and process
> > SSO.  The document goes into great detail regarding the required
> > design of the proposed facility.
>
> > On Apr 15, 8:55 am, Lynne Pledger <pled...@hardwickpostandbeam.com>
> > wrote:
> >> I'd like to hear more from Craig and others about tonnage needed for  
> >> anaerobic digestion. It was my understanding that this method is  
> >> viable on a very small scale. I've seen photos of very small digesters  
> >> in use in Asia. Thanks.

[phil fredericks]

Is Waste to Energy the best and highest value use of this material? Please look at http://www.youtube.com/user/MicrobeClean. 4 short videos Be sure to view all four and let's discuss pros and cons.

Phil Fredericks

[Toni Stein]

Phil:

Great work!!

You appeared to want some constructive feed back and to have intellectual dialogue so I'll offer my perspectives regarding issues of "sustainability" to discuss.  

I have two comments:

1.  The operations shown in the videos document operations that generate local concentrations of "particulate matter" from grinding.  Only one shot showed the worker with a respirator on.  It appeared that future improvements to the operations may be of interest to reduce the PM releases and to ensure that the workers are fully geared and protected from any PM intakes.  For example the grinder could be enclosed and the PM near it scrubbed with some filtration devices.  And all the workers could have nose and mouth protection.  

2.  No doubt the creation of humus and compost for use in agriculture is an honorable activity that we need more of.  The climate change issues that get mixed up surrounding  WTE concerns "methane" and NOX generation from composting or natural degradation processes in a landfill.  The question that leans away from some forms of  composting and of course land filling is and may be that anaerobic digestive systems that includes  "burning" of the gaseous methane production may be thought of in a positive light because it converts the methane to CO2 and avoids methane releases.   There is always interest to reduce or minimize methane releases and by some perspectives anaerobic activities with the WTE burn integration converts the methane to CO2 eliminating the release of methane.

The question is how much methane is released from the windrows and is there methods to aerobically minimize it to a level that is acceptable.  It seems that the WTE process involves high temperatures and may create more NOx issues then the composting .  What are your thoughts?   Additionally you show the trucks and heavy equipment and these things all still run on petroleum based products and still involve GHG productions.  I'm against WTE for many reasons including the fact that the ash generated has high toxics in it and what do you do with it?  Similarly what do you do with the plastics that you sieve out of the ground up bio MSW that you are processing??  It did not look like there were many electronics in those streams in the videos in that country but in the US and elsewhere the MSW is much more mixed with more chlorine containing and metal containing waste that creates a mess with it is burned for WTE.  

 

Best, 

Toni Stein PhD

Berkeley CA

650-823-7662

[Jewell, Rebecca]

The description provided for Toronto's facility seems to be similar to a waste-water treatment facility which seems to require a lot of pre-processing, grinding, slurry-ing.

 

I'm hearing a lot about "dry fermentation," lately, which takes organics, food scraps, yard debris, etc, and puts it into a garage-type space under negative pressure, circulate its own liquids over it. During 60-90 days, pull off the methane and other gasses, for use in typical bio-gas facilities and at the end there's compost left in the garage.

Here is the entity working to site a facility here in the SF Bay area; www.pacificbiogasenergy.com.

 

Thoughts?

[Richard Anthony]

Now your talking.
These need to be fed only compostable organics but have a dual purpose, making compost and capturing the by product gas.  I have toured operating facilities in Zurich 

---

Green cleaning products -- do they work as well? Find out now!

[Terrence83]

Richard, what was the name and location of the facilities you mention
in Zurich? Was it an organics sorting plant?

In reply to Rebecca, the "batch" systems she must be referring to must
be similar to the system by BEKON in Germany. There is actually a
conference by the German Chamber of Commerce close to Montreal on May
4. The North American representative present there is Jean-Claude
Corbeil. As far as I know, these systems are not very popular in
Germany. The push from the government in the recent years was axed
towards green energy crops, mainly corn silage on farm digesters,
which is far from AD of food wastes.

http://kanada.ahk.de/index.php?id=78&no_cache=1&L=15&tx_mjseventpro_pi1[showUid]=192&cHash=d2a0346779&recentView=listView

My thoughts to these batch systems:
More capital investment necessary than single stage continuous dry-
fermentation, more land base required to store organics while one of
the 'garage' is being filled, digested, or vented. Think of a SBR for
aerated wastewater treatment, reaction time for SBR is much quicker
here (typically 4 to 6 hrs) compared to 60-90 days with anaerobic
treatment with this type of system. How much of these 'garages' are
required?
Biogas quality is a severe issue if you rely on the biogas as a steady
source of revenue to run a generator or a biogas scrubber. Once a
scrubber is set at a specific flow rate, it is very tricky to change
it. You might consult Questair regarding biogas quality issues. They
participated in an important feasibility project in British Columbia.

And remember that even if it requires less pre-treatment to treat
organics in batch systems, as in software engineering: Garbage in =
Garbage out.
Compost quality will be an issue if insufficient pre-treatment is
used, specifically if you wish to market the compost after AD or wish
to meet compost quality criteria like the USEPA Biosolids guidelines,
or like in Ontario, grade "A" compost (I wish I would find the link to
the regulations...).
Or you can go with a continuous, plug flow, thermophilic dry-AD
system, with a retention time of 15-20 days like systems in
Switzerland:
http://www.youtube.com/watch?v=ksX3gCR6klw (sorry, in German)
or like the one in Toronto, which I believe is a continuous,
completely mixed, mesophilic slurry (8-12% TS) AD system, with a
retention time of at least 30 days or less (I wish someone from CCI
would chip in on this topic!)

You also have to look at how you will manage your rejects and
wastewater from the process and if you have any odor issues which will
require negative pressure buildings with a biofilter.

And the list goes on...

On Apr 24, 4:39 pm, Richard Anthony <ricanth...@aol.com> wrote:
> Now your talking.

> These need to be fed only compostable organics but have a dual purpose,?making compost and capturing the?by product gas.? I have toured?operating facilities in Zurich?
>
> -----Original Message-----
> From: Jewell, Rebecca <RJew...@wm.com>
> To: Toni Stein <tw...@igc.org>; phil fredericks <philfrederi...@pgtc.com>
>
> Cc: TO SSO <dougwil...@msn.com>; GreenYes <Gree...@googlegroups.com>

> Sent: Fri, 24 Apr 2009 11:57 am
> Subject: [GreenYes] Re: anaerobic digesters for food waste
>
> The description provided for Toronto's facility seems to be similar to a waste-water treatment facility which seems to require a lot of pre-processing, grinding, slurry-ing.
>

> ?

>
> I'm hearing a lot about "dry fermentation," lately, which takes organics, food scraps, yard debris, etc, and puts it into a garage-type space under negative pressure, circulate its own liquids over it. During 60-90 days, pull off the methane and other gasses, for use in typical bio-gas facilities and at the end there's compost left in the garage.
>
> Here is the entity working to site a facility here in the SF Bay area;www.pacificbiogasenergy.com.
>

> ?

>
> Thoughts?
>
> -----Original Message-----
> From: Gree...@googlegroups.com [mailto:Gree...@googlegroups.com]On Behalf Of Toni Stein
> Sent: Friday, April 24, 2009 8:05 AM
> To: phil fredericks
> Cc: TO SSO; GreenYes
> Subject: [GreenYes] Re: anaerobic digesters for food waste
>
> Phil:
> Great work!!
>

> You appeared to want some constructive feed back and to have intellectual dialogue so I'll offer my perspectives regarding issues of "sustainability" to discuss. ?
>
> I have two comments:
>
> 1. ?The operations shown in the videos document operations that generate local concentrations of "particulate matter" from grinding. ?Only one shot showed the worker with a?respirator?on. ?It appeared that future improvements to the operations may be of interest to reduce the PM releases and to ensure that the workers are fully geared and protected from any PM intakes. ?For example the grinder could be enclosed and the PM near it scrubbed with some filtration devices. ?And all the workers could have nose and mouth protection. ?
>
> 2. ?No doubt the creation of humus and compost for use in agriculture is an honorable activity that we need more of. ?The climate change issues that get mixed up surrounding ?WTE concerns "methane" and NOX generation from composting or natural degradation processes in a landfill. ?The question that leans away from some forms of ?composting and of course?land filling?is and may be that anaerobic?digestive systems that includes ?"burning" of the gaseous methane production may be thought of in a positive light because it converts the methane to CO2 and avoids methane releases. ? There is always interest to reduce or minimize methane releases and by some perspectives anaerobic activities with the WTE burn integration converts the methane to CO2 eliminating the release of methane.
>
> The question is how much methane is released from the windrows and is there methods to aerobically minimize it to a level that is acceptable. ?It seems that the WTE process involves high temperatures and may create more NOx issues then the composting . ?What are your thoughts? ? Additionally you show the trucks and heavy equipment and these things all still run on petroleum based products and still involve GHG?productions. ?I'm against WTE for many reasons including the fact that the ash generated has high toxics in it and what do you do with it? ?Similarly what do you do with the plastics that you sieve out of the ground up bio MSW that you are processing?? ?It did not look like there were many electronics in those streams in the videos in that country but in the US and elsewhere the MSW is much more mixed with more chlorine containing and metal containing waste that creates a mess with it is burned for WTE. ?
>
> ?
>
> Best,?

>
> Toni Stein PhD
>
> Berkeley CA
>
> 650-823-7662
>
> On Apr 24, 2009, at 6:50 AM, phil fredericks wrote:
>

> Is Waste to Energy the best and highest value use of this material? Please look athttp://www.youtube.com/user/MicrobeClean. 4 short videos Be sure to view all four and let's discuss pros and cons.

> On Apr 22, 11:22?am, Neil Tangri <n...@no-burn.org> wrote:
>
> Hi Doug,
>
> Thanks for this information. I am surprised to hear that
> highly-contaminated SSO still results in high-quality compost. Can you
> tell us how the SSO is "cleaned"? Also, how does the current facility
> handle the biogas? Is it scrubbed prior to burning? Are there emission
> controls on it? All of these are the devils in the details in moving to
> commercial-scale AD.
>
> best,
>
> Neil
>
> TO SSO wrote:
>
> There are lots of anaerobic digesters used to process food waste all

> over the world, both large scale and small scale. ?Toronto has been

> collecting food waste from single family homes for several years now

> and generally collects 110,000 tonnes per year. ?They operate an AD

> facility located in the middle of the city which this year will

> process close to 40,000 tonnes of this material. ?Toronto is very

> happy with this 'demonstration' facility and has now issued a 'Request
> for Proposals' to build it's first full scale facility which will be
> designed to process up to 75,000 tonnes of SSO (source separated

> organics) per year (300 tonnes per day). ?The plant will generate bio-

> energy (not determined yet whether electrical power, pipeline gas or

> biofuel). ?The city plans to build two such facilities in the next 3
> to 4 years.
>
> Toronto's SSO is considered high in 'contamination'. ?In order to

> promote high levels of participation in the program, Toronto allows
> households to collect the food waste in non-biodegradeable film

> plastic bags. ?They also collect pet waste, diapers and as likely in

> any large city get glass jars, tin cans and other assorted
> contamination.
>
> The process used in Toronto strips out the contamination,
> anaerobically digests the organic portion in a mesophilic, fully mixed

> digester. ?The finished, digested solids are shipped out to composters
> outside the city to be aerobically 'finished'. ?The material produced

> at this facility has been tested hundreds of times over several years
> now and easily meets the provinces quality standards allowing it to be

> converted to the highest grade of compost. ?Ontario has one of the

> highest 'compost' standards in the world.
>
> The 'demonstration' plant was designed for 25,000 tonnes per year but
> has operated at much higher levels (up to 200%)due to the shortage of

> processing capacity in our area. ?The process is reliable, generally

> operates at 96 to 100% online time, 24 hours per day, 5 days per

> week. ?The digester has operated 7 years without interuption. ?The

> plant had two odour complaints in 2008, not entirely related to
> facility operations.
>
> An interesting site to visit ishttp://www.german-biogas-industry.com

> as many of the AD technologies have originated in Germany. ?There is

> almost unlimited information available on the subject of AD.
>
> Europe is way ahead of North America in farm and food AD projects.

> The US has lots of farm based digesters. ?I believe Toronto will have

> the first large scale AD system in operation processing SSO in North
> America if it moves ahead with it's current plans.
>
> Info on the Toronto AD project is available at:https://wx.toronto.ca/inter/pmmd/calls.nsf/0/4675E7B6479787AA8525758A...

> Unfortunately, to get the complete document they charge $75. ?The full

> document runs to several hundred pages and is a complete record of the
> entire history of Toronto's development program to collect and process

> SSO. ?The document goes into great detail regarding the required

> design of the proposed facility.
>
> On Apr 15, 8:55 am, Lynne Pledger
>

> ...
>
> read more »

[Nancy Poh]

When I read about that there are 5 million digesters in use in rural
China, I did a search and discovered that the women who started the
project won an Ashden Award for Sustainable Energy in 2006.

I am actually researching for a suitable model for our neighbourhood
park. I hope it will help eradicate the problem with dumping of green
waste by house owners living near it. I think that if it can generate
income through sales of the compost created, the fund can also be used
to add value to the neighbourhood by beautifying the park and setting
it up to be a gated and guarded community.

Nancy

[TO SSO]

Toronto's AD system is a mesophilic, fully mixed anaerobic digester
with a capacity of 3600 m3 (about 950,000 usg). It generally operates
at 6 to 7% total solids operating at 37 to 39 deg. C. (98 to 100 deg
F.). Retention time in this type of digester can vary depending on
needs from one week to four or more. Gas quality (and volume
produced) in any AD system is highly dependant upon the quality of
input material.

Anaerobic, (meaning in the absence of oxygen) requires that the
process takes place in a closed system. This makes the job of
containing odours a little simpler. Anyone with any experience in
processing food waste or for that matter, any organic material will
tell you that odour control is a very large part of the solution.

Many traditional composting sites across Canada have been closed due
to odour complaints and the technology is 'morphing' to closed, indoor
systems requiring much higher energy consumption. Energy is required
to blow air through the piled organics as well as to ventilate the
building and/or containers, generally through a 'biofilter'.

Biofilters are actually wonderfully, simple devices to operate.
Basically, the smelly airstream is exhausted through a bed of
composting wood (companies use different woods, some use inorganic
media). Aerobic microbes living on the surface of the wood (in the
moist layer between wood and air) digest the odour as it passes
through pile. Secret to operating successfully is to keep the bed
moist. Like any aerobic composting process, it doesn't work if it
dries out. Secret to design is retention time in the bed. Some
odours need longer to allow the microbes to get their work done.

Cheers!

> ...
>
> read more »- Hide quoted text -

[TO SSO]

A link to Canadian compost regs...

Link to Canadian compost 'guidelines': http://www.ccme.ca/assets/pdf/compostgdlns_1340_e.pdf
Compost quality is a provincial matter so the 'feds' have a process to
develop suitable guidlines which are generally adapted by the
provinces.

On Apr 25, 6:05 pm, Terrence83 <terrence.sa...@gmail.com> wrote:

> ...
>
> read more »- Hide quoted text -

[TO SSO]

Maybe not practical for your neighborhood but an interesting
experiment on small scale AD carried out in the Phillipines:
http://www.habmigern2003.info/biogas/Baron-digester/Baron-digester.htm

Generally, manure based digesters are much simpler to operate than
food waste systems. Manure has been prepared for digestion and
partially digested so all we do is continue the process. Food waste
generally requires work to prepare it for digestion or alternatively a
relatively slow dogestion process in order to break down the larger
pieces of material.

Food waste comes with various levels of contamination which will have
to be removed either before or after the digestion process. Even a
very 'clean' source of food waste contains materials that will have to
be removed such as bones for example.

In a liquid digestion process this contamination is generally removed
before digestion. If not removed, particles of bone, glass, metal
will tend to settle to the bottom of the anaerobic digestion vessel
and sometimes can quickly fill the vessel to a point that it needs to
be shut down and cleaned out (never a fun process). In a high solids
digestion process the contamination can be removed after digestion
takes place but it can be more difficult to remove small particles of
things such as glass since the physical properties of a small particle
of glass are similar to a small particle of compost.

Automatated, large scale systems (of either type) are able to
accomplish the cleaning process very efficiently.

> >> --Lynne Pledger- Hide quoted text -