[Digestion] Pressure

[David]

Dear Dr. Fulford and others,

On 11/20/2010 9:22 AM, David Fulford wrote:
> David and listers, Hello,
>
> The microbes do not seem to be affected significantly by pressure, 
> at least up to the 1 atmosphere found in small dome plants as used 
> in India, Nepal and China. In the 1970s there were reports of some 
> earlier work in India that suggested less gas was generated at 
> higher pressures; but gas analysis demonstrated that the reduction 
> in volume at higher pressures was mainly due to carbon dioxide 
> dissolving in the slurry.... So, [perhaps] the answer is that the 
> relationship between pressure and biogas production seems rather 
> complicated.

It seems to me, then (all things considered) that pressure in the 
great majority of situations is not worth any attention. Three things 
lead me to this conclusion. First, most applications and appliances 
that use biogas are satisfied with pressures that are measured in 
inches of water, not feet, and second very few digesters are likely to 
be built that exceed 30 feet in depth, at which point the pressure is 
doubled. (The majority of those deep digesters-- which after all would 
have to be quite large and which would therefore generally tend to be 
fairly sophisticated-- would almost certainly be agitated, not 
plug-flow.) Finally, since long experience, even if not multiple 
studies, confirm that the effect even of a doubling of standard 
atmospheric pressure tends to be so slight as to avoid notice, most of 
us will never need to consider it as a factor.

I would still love to find some studies that discuss the matter, but 
for the time being the sole driver is now simple curiosity, and no 
longer the potential for practical impact.


d.

-- 
David William House
"The Complete Biogas Handbook" |www.completebiogas.com|
/Vahid Biogas/, an alternative energy consultancy |www.vahidbiogas.com

|
"Make no search for water.       But find thirst,
And water from the very ground will burst."
(Rumi, a Persian mystic poet, quoted in /Delight of Hearts/, p. 77)

http://bahai.us/
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