Re: DIG-L: Re:'Understanding Anaerobic Treatment' - longish message

[doelle <doelle@ozemail.com.au>]

Dear Chuck,
In answer to your long elaboration of trying to tell me as microbiologist what anaerobic digestion, I just like to tell you the following:
1. Anaerobic digestion has 4 different types of phases:
a) liquefaction, where the polymers are degraded into monomers
b) fermentation, whereby fermentative microorganisms convert all the monomers into CO2, and volatile fatty acids. In this process, carbohydrates are converted into acetate and CO2 and H2, whereas the proteins and fats are forming predominantly the higher volatile fatty acids.
c) the acidogenic microorganisms are those, which convert the higher volatile fatty acids into acetate and CO2 and H2 
d) the methanogenic phase, whereby the methanogenic bacteria convert the acetate, CO2 and H2 into methane and CO2.

If you like I can also provide you with the name of all the individual bacteria involved in the process together with the detailed biochemistry, which I have taught for 30 years at University.

Thus I do understand very well what is going on and know what I am talking about.
If C/N ratoi is in favour of carbohydrates, more acid is formed and you are getting problems as you said. This is the reason why I strrongly emphasize the proper C/N ratio in order to get a balanced digestion without any need for pH adjustment.
Because the methanogenic bacteria work best in the presence of acidogenic and fermentative bacteria is due to the interspecies hydrogen transfer, which keeps the redoxpotential so low that methanogens can properly and efficiently function.

Thermophilic digestion is absolutely nothing new and has been known for donky days, but has only been scarcely used in 1-stage fermentation systems , as they work excellent in that system.

Your company obviously separated the stages, which s never recommended by us because of the increased problems you can have. It is ludicrous from you, in my opinion , to say that there are no problems and that  we stick to old methodology. 

That shows me that you do not want to understand the fact that mesophilic anaerobic digestion is cheaper and you can make more money in rural areas. This has proven over and over again in developing countries.

As I said before and say it now again. Both technologies are known for ages and botrh technologies have been improved out of sight, but which one is appropriate in a specific case depends on the Region, Society and local resource availability.

I think in this discussion we should stop accusing each other being deterimend that "my technology is best". What a lot of nonsense. Let us work together to make as many nw advances as possible and then see which one is the better one in the particular circumstances.

I certainly strongly object to your accusations and do not think that that brings us very far.

In the hope we continue rationally
with best regards
Horst Doelle
Horst W.Doelle, D.Sc., D.Sc. [h.c.]
Chairman, IOBB
Director, MIRCEN-Biotechnology
FAX: +617-38783230
Email: doelle@ozemail.com.au DIGESTION List Sponsors, Archive and Information http://www.crest.org/renewables/digestion-list-archive http://www.crest.org/renewables/biomass-info/ Beginners Tour of Biogas http://WWW.roseworthy.adelaide.edu.au/~pharris/biogas/beginners