Re: DIG-L: Anaerobic digestion

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

Dear Lisa,

In a cold climate like Europe I would never recommend a thermophilic digester, particularly if you require the by-products.
As I mentioned in an earlier message, mesophilic digesters reduce pathogens significantly and as you know, also the BOD by approx. 60%. Thus you have enough nutrients left in the solid and liquid effluents to compost or use it as an excellent resource for aquaculture, eg algae and fish. Also the biogas requirement to keep your temperature all year round at 35-37C is far lower and you can sell the rest or use the rest of the energy for other purposes.

In the case of a thermophilic digestion, it has been claimed that the BOD can be reduced by 80% +, pathogens are of course further reduced, biogas yield is higher, BUT you require a much higher amount of biogas for heating your digester. Your by-product opportunities are significantly reduced, since the solid and liquid effluents are much poorer in nutrients.

Both types have their place. I prefer the mesophilic one because the economics appear to be much better, IF you believe in an integrated biosystem. Thermophilic digesters are good if you do not believe in an integrated biosystem.

I hope this helps.
Best regards
Horst Doelle


At 11:51  12/02/00 +0000, you wrote:
>Dear all,
>
>My name is Lisa Pritchard and I currently work for a company called
>GreenfinchLtd based in Shropshire, UK.  Our demonstration plant is a 20m3
>anaerobic digester which treats  5-7 tonnes of source-separated household
>kitchen waste (biowaste) each week  from approximately 1500 households.  
>
>One of our objectives is to recycle and reuse of by-products of the AD
>process.  This does not include agricultural land application.  As you
>know regulations are getting tighter so we do not want to rely on land
>application to reuse the nutrients effectively.  Hence we are reusing our
>by-products through various processes including aquaculture and
>vermiculture.
>
>Our digester is mesophilc. Do you see any clear advantages for running our
>digester at thermophilic temperatures, bearing in mind our climate and
>need to reuse all by-products?
>
>Thankyou and look forward to any replies,
>
>Lisa Pritchard
>
>
>   
>*** greenfinch@burford.co.uk using SmartMail v4.00.15 ***       
>--------------------------------------------------
>
>
>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
>
>
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