[Digestion] food waste better as biogas?

Thu Nov 1 10:42:21 EDT 2007

Hello everybody

This last message from William Brinton is very interesting. Figures of gas
production per kg of VS are not often declared. Usually, when you ask owners
of digestion plants, you get information on gas yield per ton of waste
material but no information on water content nor on how much of the dry
substance or the volatile substance that is biodegradable by digestion. Also
they do not have good information on how much of the biodegradable substance
that is actually converted to biogas or to methane. Actually quite a few do
not seem to know what they put in and what they get out. I have not yet seen
a good energy balance for a digestion plant where the energy content (upper
heating or calorimetric heating value) of the waste matter going in is
declared. (The same accounts for mass balance.) It is also very difficult to
get information on how much electricity the plant is using for the operation
and how much of the produced gas is used for the pasteurisation of the raw
material in cases where this is necessary or required by authorities. These
things are necessary if you want to make good feasibility studies of new
plants and compare digestion with alternative methods.

Not considering any inert ash-forming material, the higher heating value of
starch and cellulose is around 4,3 kWh/kg TS, the same for vegetable oils
and fatty tissues around 12,7 and for meat remnants (mixture of fat and
proteins) around 8. The protein rich material requires much longer digestion
time if digested alone. So there is a scope in higher heating value of the
dry substance (often the same thing as VS) ranging from 4,3 up to 12,7
kWh/kg VS. That is why it is necessary to know what actually goes into the
plant if you want to know how it is performing. You also need to know the
composition of what is actually going out. 

The fact that manure from for instance cattle is beneficial for the process
we know. It doesn't give as much gas as food remnants as it has already been
digested in the rumens of the cattle but it stabilises the process.

In Sweden there are four groups who are interested in the digestion of
waste. The waste producers who want to get rid of the stuff, the
municipalities who are more interested in the gas for bustraffic and service
vehicles, the farmer who are more interested in the nitrogen (but some what
reluctant) and the environment authority who seems to be more interested in
the phosphorous content. Several plants have been built and more are
planned, but inspite of all these interest there is still a lack of
important scientific information.

Sometimes things seem to run away too fast.

I would be happy for comments.

Regards too all in the network

-----Ursprungligt meddelande-----
Från: digestion-bounces at listserv.repp.org
[mailto:digestion-bounces at listserv.repp.org] För Will Brinton
Skickat: den 31 oktober 2007 17:15
Till: digestion at listserv.repp.org
Ämne: Re: [Digestion] food waste better as biogas?

We routinely measure biogas yield potential from various wastes , and 
food scraps
are among the highest ( ~ 500 liter methane / kg VS ). They can not be 
easily digested
alone, but in combination with and already buffered substrate as in 
dairy manure, are excellent additives
and farmers are reporting a synergistic effect- net increase of total 
methane when added appropriately.

In contrast composters are frequently using inappropriate methods and 
end up making lots of fatty acids- spoilage types - that cause odor 
complaints and are plant toxic in growing media. Why bother?

I consider the feeding option for food scraps not really viable as it is 
unsafe and, with the requirements to heat-treat, probably not  
economically viable .. unless we use some biogas boiler to do the heat 
treating at the same facility- safety issues aside.

William F Brinton jr President
Woods End Laboratories, Inc.

Today's Topics:

   1. Re: Digestion Digest, Vol 16,	Issue 20  consumption of waste
      products by hogs (Jim and Amy Rankin)
   2. Re: Digestion Digest, Vol 16,	Issue 20  consumption of waste
      products by hogs (Dick Gal lien)
   3. Re: Digestion Digest, Vol 16,	Issue 20  consumption of waste
      products by hogs (Katahdin Energy Works)

----------------------------------------------------------------------

Message: 1
Date: Tue, 30 Oct 2007 18:23:09 -0500
From: "Jim and Amy Rankin" <ajrankin at westal.net>
Subject: Re: [Digestion] Digestion Digest, Vol 16,	Issue 20
	consumption of waste products by hogs
To: <digestion at listserv.repp.org>
Message-ID: <22A9DA14B8294E68820B9970622247E1 at RankinPC>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
	reply-type=original

The practice of garbage/food waste feeding (on production agricultural
scale) is regulated because of the potential for disease transmission.

Tapeworm and Trichinosis are the classical parasitic concerns, but probable
transmission of foot and mouth disease and possibly other viruses have
happened in the past.

In reality, no one is ever sure what actually was in the food waste/garbage,
when an outbreak occurs, and if no other source is identified, food waste
gets the blame.  So the regulations are written to ban feeding outright or
require cooking the food waste to temperatures sufficient to inactivate
parasites and viruses.

In the US, you will find that states with a large swine population (and
others) are especially cautious of anything which might allow a small amount
of diseased material to be multiplied/disseminated through the swine
population.  Nationwide, even in states where it is allowed, feeding food
waste is regulated by USDA because of regulations prohibiting feeding of
bovine products back to cattle among other concerns.

Regulation of garbage/food waste feeding adds another layer of defense
against importation by normal trade (foreign grown food products), and other
accidental or deliberate introduction of infectious disease into a country.
And it makes it less likely for there to be spread of the disease even if it
makes it across the borders.  After all, if some bit of disease containing
material is "wasted" in a landfill or digested in a thermophilic digester,
it is unlikely to ever be near enough to another live animal who might
contract the disease for tramsission to occur.

James R Rankin, DVM
Cedarcrest Farms Inc
Faunsdale, AL USA

------------------------------

Message: 2
Date: Wed, 31 Oct 2007 06:35:16 -0500
From: "Dick Gallien" <dickgallien at msn.com>
Subject: Re: [Digestion] Digestion Digest, Vol 16,	Issue 20
	consumption of wsste products by hogs
To: <digestion at listserv.repp.org>
Message-ID: <BLU107-DAV1046441D10E0B3A7BC9CD8A4930 at phx.gbl>
Content-Type: text/plain; format=flowed; charset="iso-8859-1";
	reply-type=original

Jim--thanks for the response.  If a state decides to allow foodwaste 
feeding, then it is evidently up to the state to enforce the fed. 
regulations.  In 10 yrs. of feeding I have never seen anyone from USDA, only

the state ag. inspector.  He mentioned being at lunch with a Tx. inspector, 
while at a conference there and the Texan mentioned there were over 6,000 
feeding in Tx..  Later we checked and there are only 2,000 some licensed in 
Tx..  We mentioned that on his next visit and he said there are that many 
licensed but the Tx. inspector estimated over 6,000 were feeding food waste.

He also said food waste feeding has always been big in the se states and the

Mob controls it in NJ..  Knowing how difficult this law is to enforce, it is

suprising there aren't more desease outbreaks, especially with so much food 
being imported.

Dick Gallien
22501 East Burns Valley Road
Winona  MN  55987
dickgallien at msn.com  [507]454-3126

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