biogas carbon fixation

markh at sonic.net markh at sonic.net
Thu Nov 14 01:24:56 EST 1996


I'm interested in small scale methane digesters as a means to cycle nutrients contained in human and 
animal wastes, in a manner which does not contribute to public health problems.  I'm especially focusing 
on basic technologies which could be effective/practical in rural locations (primarily small farms) in 
developing countries.

I want to make the most efficient use of these nutrients without compromising human health.  The 
anaerobic methane digester seems like a very practical means of processing these wastes.  One 
concern I have is that I would like to use the digester wastes as an ammendment to compost.  
However I beleive that very little carbon remains in the sludge it has been lost in the CO2 and Methane 
from the digestion process.  

Is it feasible to develop a biological scrubber (containing carbon fixing bacteria) which could remove the 
CO2 (and fix it as calcium carbonate/limestone, which could be used as a soil ammendment), this would 
also  increase the caloric value of the biogas?  What species of microbes would you suggest for such 
an application?  What holdfast mechanism would be useful in which to manifold and capture the 
effluent gases.  I've heard that such a scenario, on a much bigger scale is being contemplated by 
chinas coal burning power plants.  Would such an effort be worthwhile in the long term, if we 
considered that fertilizers become much more expensive?

I'm also interested in the most efficient, yet safe utilization of the digester sludge.  I've heard it can be 
used to raise algae or aquatic plants or fishes.  Could this algae (aquatic biomass)  say be fed by the 
sludge( from human and animal wastes) and then be fed to say chickens and/or pigs?  Would this pose 
a health risk at this point?

I've heard of pig manure being fermented for about one week with an unknown microorganism and 
then feeding the high protein microbes back to the pigs.  How can I find out more about such a 
system?  Is it advisable?

Any ideas and feedback would be greatly appreciated.

Mark Harrington

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