[USCC] Compost Digest Vol 29 # 6- Response to Craig CH4

[David Schellinger]

Edo,
In theory, composting is an aerobic process, and loss of methane emitted
from properly composted sewage sludge would be reduced significantly from
the emissions from raw biosolids.  The redox potential (Eh) required for
methane generation is around -200mv or lower, while aerobic composting
should occur at +250mv or above.  Under truly aerobic conditions methane
generation should not be possible, and methane should be biologically
oxidized rapidly in a biofilter.  It may be possible for some methane
generation in microsites within the composting materials, but most of it
should be consumed before exiting the composting materials.  It appears that
we are mixing apples and oranges again, because composting biosolids and the
biosolids of which you speak are probably not the same materials, and I too
have a hard time believing that composting biosolids could generate the 34.5
lbs of methane per ton of a biosolids mix.  Aerated systems are a sink for
methane while anaerobic systems generate methane.

Dave Schellinger
W. A. Callegari Environmental Center

-----Original Message-----
From: compost-bounces at composter.com [mailto:compost-bounces at composter.com]
On Behalf Of Edo McGowan
Sent: Tuesday, July 11, 2006 9:03 PM
To: compost at composter.com
Subject: [USCC] Compost Digest Vol 29 # 6- Response to Craig CH4

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Re: Compost Digest, Vol 29, Issue 6. Methane emissions from composting
(Craig Coker)


If one were to pull up the following and refer to Appendix F, the data on
conversions are presented. Loren Faundahl of EPA and I spoke some weeks ago
about this. Her office supplied me with the following: each ton of sewer
sludge will produce somewhere between 2,000 and 4,000 cu ft of CH4. The
average is about 3,000 cu ft. Using the data in Report#:EIA/DOE-0573(98),
November 5, 1999, 

1 thousand cubic feet of methane = 42.28 pounds. 

Thus using the data supplied by Loren and her office, and assuming the 3,000
cu ft average, the product is 127.28 pounds, the 34.5 supplied by Maureen is
thus a substantial under estimate. Since CH4 eventually shifts to CO2 at a
conversion of about 21X, the average ton of sewer sludge when land applied
or composted warrants more attention. If however, this material is used as a
fuel source, the evolution of greenhouse gasses is essentially eliminated.

Assume, for example the roughly one half million tons that are moved out of
the LA Basin into the closed and over subscribed air basin around
Bakersfield. Doing the math assuming the above, we obtain the following

3,000 cu ft/ton X 500,000 tons yields 1,500,000,000 cuft CH4 or 3.15 x
10/10th cuft CO2. I think my math is valid, but the data are available to
recalculate independently. See what you come up with. You may also compute
BTUs and kWh to see what is being thrown away.

Cheers----------------Edo


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