Re: DIG-L: a note on "philosophical" vs. "technical" discussi

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

Dear Les,
I am not going so far to fine and lock up farmers who use raw manure. Many thanks for your detailed outline on the European condition. Also remember I am probably a bit overcautious having worked extensivly in developing countries.
The problem is that European and US experts recommend the use of raw manure also in these countries, which are hygenically not as advanced in their control systems as Europe. Also in many countries, antibiotics and sometimes hormones are still fed to so-called chicken farms and piggery farms and feedlots. Furthermore, many of these countries, in particular the tropical islands live on bore water. You would be scared to drink it if you see the E.coli counts.
I realise that one should not generalise, but simply warn that AD is better in regard to pathogens. The danger of antibiotic resistancy is great.
In regard to viruses I fully agree. They are very hard to kill and one of my old colleagues works on that issue still here in Australia, which keeps me well informed.
Best regards
Horst Doelle


At 05:15  22/02/00 +0000, you wrote:
>>Subject:     Re: DIG-L: a note on "philosophical" vs. "technical"   discussi
>>Sent:        27/2/20 1:21
>>Received:    22/2/0 14:56
>>From:        doelle, doelle@ozemail.com.au
>
>
>>Of course, liquid and solid fuel from anaerobic digesters is a much safer 
>>biofertiliser than straight manure. Organic farming using manure is 
>>criminal and should not be allowed. It is an enormous potential health 
>>hazatrds.
>
>Dear Dr Doelle and the group, 
>
>According to your statement Dr., all the Northern Ireland farmers I know 
>should be locked up or fined!   The biological arguement for 
>pasteurisation or hygenisation by AD is not so clear as you make out. The 
>problem appears to me to be in the details of the ratios.
>
>Take ecoli for example.  A manure might contain 5 log ecoli per 100ml, a 
>mesophilic digester may kill 3 log as long as the digester is not fed 
>continously and well stirred (as with a good CSTR) since in a well 
>stirred CSTR with a 20 day RT it is axiomatic that 5% of the fresh input 
>is expelled with the digested output.  The infectivity level of 
>ecoli(157) is I believe 25 colony forming units in 100 mls  or just over 
>1 log.  The output from the digester is at least 2 log and may contain 
>3-4 log  - which is quite enough to kill children working with the 
>material.
>
>So why digest for pathogen control.
>
> In Denmark the best scientists and vets have approved of AD with various 
>caveats.
>
>1.  If the digestion of wastes is 'hygenic' then all the farms that 
>receive the waste may be regarded for veterinary purposes as separate 
>farms.
>
>2.  If the digestion of wastes is not 'hygenic' then the farms that 
>receive the waste are regarded as one farm and therefore if one farm 
>supplying waste to the digester is infected with an outbreak of say 
>salmonella, then all the farms are quarrantined.
>
>3. 'Hygenic' digestion is clearly defined as a digestion without short 
>circuiting in the digester for a minium of 8 hours at a minimum 
>temperatue of 53 degrees C. That is to say the minimum temperature must 
>never fall below the set limit. Graphing recorders are required to prove 
>the point.
>
>So far (a decade) this has worked well in practice and has enabled many 
>Centralised AD units to be built and operated economically.
>
>In the UK:
>
>The best recent summary of the AD industry in recent years has been 
>written by 27 AD companies and consultants co-ordinated by the UK's 
>environment council.  The issue of pathogen control by digesters has been 
>very carefully researched. The pathogen kill conclusions appear in 
>appendix 7 of the "Good Practice Guidelines - Anaerobic Digestion of farm 
>and food processing residues - the development of a sustainable 
>industry."  Published by ETSU, Harwell.
>
>APPENDIX 7  -------snip 
>
>PARASITES
>Anaerobic digestion at 35 degrees C (known as mesophilic digestion used 
>by the vast majority of farm digesters), has been shown to reduce the 
>numbers of viable lavae and eggs of some parasitic worms to undetectable 
>levels after one week although there is generally poor control of 
>'Ascaris', 'Tacnia' (sic), and 'cryptosporidium'.  However the oocysts (a 
>type of egg) of these worms, which can infect any animal ingesting them, 
>remain viable after 50 days at 35 deg.C.  Digestion at 55 deg. C 
>significantly reduces the number of oocysts, but many viable units still 
>persist, even after digestion for extended periods of time.  Mesophilic 
>anaerobic digestion will not significantly reduce the infectivity of 
>slurry contaminated with parasites.
>
>PATHOGENIC BACTERIA
>Experiments with pig slurry have shown that mesophilic digestion for four 
>days will destroy 90% of a population of Salmonella bacteria, although 
>low levels of the bacteria will persist even after 70 days digestion.  
>This persistence may be due to poor mixing within the digester, allowing 
>pockets of bacteria to survive in a crust on the surface.  Properly 
>managed, thermophilic digestion can reduce bacterial levels by an even 
>greater factor, but again low levels may persist due to poor mixing.  
>Mesophilic anaerobic digestion will significantly reduce the levels of 
>pathogenic bacteria, but will not eliminate them completely from the 
>waste and so the COSSH [ Control of Subtances Hazardous to Health 
>regulations 1994 -LKG] assessment will determine the measures required to 
>control the potential damage to human health. 
>
>VIRUSES
>Research findings have shown that mesophilic anaerobic digestion reduces 
>virus numbers in sewage samples, but viable virus units may still be 
>found to be present, even after extended periods of digestion.
>
>-----snip
>
>
>There is much work to be done in this important area - I am collecting 
>papers on the subject and would be grateful for any references from 
>readers.
>
>
>
>
>
>Best Regards
>
>
>
>
>Les. Gornall
>Director
>Practically Green 
>Environmental Services
>Solar House
>Magherafelt
>BT45 6HW
>Northern Ireland
>+44 1648  32615 Tel./Fax
>
>http://www.practicallygreen.com
>
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>
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>
>
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