[Digestion] Mixing in digesters?

[Katahdin Energy Works]

Let me refine those comments a bit more.

Carbon is the major chemical element in manure that is digested by bacteria
to produce biogas. In order to do that, nitrogen must be available in the
raw manure. The RATIO OF CARBON TO NITROGEN in the raw manure is critical to
efficient digestion.

"A high C/N ratio means that the nitrogen will be exhausted before the
carbon is digested...a low C/N ratio or too much nitrogen in relation to
carbon results in high ammonium concentrations which may become toxic to the
anaerobic bacteria"..Penn State monograph on THE ANAEROBIC DIGESTER SYSTEM.

Blending feedstock's with a high C/N ratio like sawdust with another that
has a low C/N ratio like chicken manure is a consideration where different
feedstock's are used. As expected, Dairy manure has a C/N ratio just
slightly below that required by the bacteria.

Incoming manure should be in a hot- 95-100 degrees F. slurry with a pH of
around 7.0. "Under normal conditions, the digestion process balances excess
acidity or alkalinity on its own" ibid.

We are considering a bio-gas bubbler, taking gas from the top of the primary
digester and pumping it in the bottom. There are some circumstances where a
crust could form or solids settle on the bottom. Aeration would help prevent
this. 

Frank J. Heller, MPA
KATAHDIN ENERGY WORKS
12 Belmont St.
Brunswick, ME 04011-3004
207.729.6090
http://mysite.verizon.net/fjheller/

-----Original Message-----
From: digestion-bounces at listserv.repp.org
[mailto:digestion-bounces at listserv.repp.org] On Behalf Of frank
Sent: Wednesday, September 12, 2007 4:58 PM
To: fjheller at verizon.net
Cc: Digestion at listserv.repp.org
Subject: Re: [Digestion] Mixing in digesters?



Katahdin Energy Works wrote:

><snip>
>
>Can the pH be used to control the CO2 given off?....depends on the microbe
>strain, I think?
>
>Higher pH to keep the CO2 in solution , perhaps adjusting at the end?  to
>reduce the CO2 in 
>the out gas. Good question; really haven't adjusted the pH levels to
account
>for CO2; we are mostly seeking to shorten the digestion cycle so we can
>process more manure with a smaller tank faster; and to increase gas yields.
>We are trying to sell the CO2 to a greenhouse or it is just scrubbed out. ?
>Are you going for REC's?
>
>
>  
>
I am thinking if CO2 in with the methane is a problem (?) that it could 
be removed by capture in a caustic solution like a Conway Diffusion, or 
(perhaps) removed using Teflon tubing, or perhaps adjusting the pH of 
the solution. Is ammonia  a problem in the gas?

I work in a lab and have set up  an anaerobic digester that will capture 
and measure the methane, CO2 and ammonia in the gas. We want to 
formulate the right mix to produce the cleanest gas.



>>Hope this helps.
>> 
>>
>>    
>>
>It helps a lot as I am on a steep learning curve.
>And the top of Mt Katahdin is my favorite place on Earth.
>
>It is nice; and the trail has been improved. Really haven't be up it, in
>years. Thanks for reminding me!
>  
>
Its been years for me too - I would be a little slower now. I did the 
Northern section of the AMT back in the late 60's. and climbed Mt 
Katahdin several more time since.





>Thanks
>Frank
>
>
>
>  
>
>>Frank J. Heller, MPA
>>KATAHDIN ENERGY WORKS
>>12 Belmont St.
>>Brunswick, ME 04011-3004
>>207.729.6090
>>http://mysite.verizon.net/fjheller/
>>
>> 
>>
>>    
>>
>
>  
>

-- 
Frank Shields
Soil Control Lab
42 Hangar way
Watsonville, CA  95076
(831) 724-5422 tel
(831) 724-3188 fax
frank at compostlab.com
www.compostlab.com




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