Re: DIG-L: Anaerobic digestion

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

Would you please also compare the cost factor ?
I totally disagree with you saying that mesophilic anaerobic digestion is obsolete, when we have more than 6 million mesophilic digesters working in excellent conditoins with excellent results all over the world.
Please let us be rational and not push one's own pet.
If thermophilic digestion produces double the amount of biogas, with which I fully agree, you probably use more than you gain of the biogas in heating a thermophilic digester.
It is also not true that the liquid and solid effluent of mesophilic digestion has low nutrient value, since it has been used extremely efficiently for aquaculture. If BOD is 10% less in thermophilic effluent, how can nutrient content be higher ? Please give some comparative data. I learned that thermophili digestion removes 80% of the BOD compared with 60% of the mesophilic, thus nutrients must be much more in the effluent of the mesophilic. 
Please make a cost analysis of your claim and then we can much more reasoanably compare both systems.
best regards
Horst Doelle
At 09:20 13/02/00 -0600, you wrote: 
>>>>
> Dear All:
>   
> To justify mesophilic over thermophilic digestion because of its claimed better process stability and beneficial nutrient yield represents
> incorrect thinking.  The principal purpose of treatment is to maximize the removal of pollutants by conversion to solids.  It goes without
> saying that the less the resulting solids the greater the efficiency of treatment.  Biosolids and liquid effluents from mesophilic
> treatment can hardly be thought of as a useful source of nutrients as the nutrient concentrations are very low and both the solids 
> and liquids still contain pathogens.  While traditional single-phase themophilic treatment is indeed difficult if not impossible to control, 
> two-phase thermophilic digestion can be very easy to control.  At this higher temperature (60 degrees C) pathogens are virtually 
> eliminated from both the treated solids and liquids. The solids remaining are perhaps 5-10% of those left over after mesophilic 
> treatment.  These few solids can, however, still be safely used as a soil conditioner or amendment, not a fertilizer.  For those still interested
> in fertilizer values, the liquid effluent from thermophilic digestion contains far greater levels of ammonia-nitrogen than mesophilic treatment 
> as this specific nutrient is generated during anaerobic digestion.  As such the liquid effluent from thermophilic digestion is a splendid 
> candidate for irrigation water so long as the ammonia-nitrogen nutrient uptake of the crop or grassland is equal to or exceeds the application loading to prevent nitrate contamination of groundwater.  
>   
> It is true that thermophilic treatment requires greater heating than mesophilic treatment.  Two-phase thermophilic digestion generates 
> twice the quantity of methane as mesophilic because of its ability to achieve twice the level of volatile solids reduction.  This greater 
> gas production easily produces the additional energy required to heat the digester.  Additionally, there should be no credible concern 
> over the higher operating temperature because of the ease of capturing the vast majority of the exit heat through the use of heat exchangers.
>   
> In short, mesophilic digestion represents obsolete technology compared with the far greater efficiencies and associated pathogenic 
> destruction resulting from two-phase thermophilic digestion.  As an example, a two-phase thermophilic digester utilizing fixed growth 
> bacteria can successfully treat at least ten (10) times the organic loading of a traditional high rate single phase mesophilic digester.   
> The good news is that most mesophilic digesters can generally be converted or upgraded to this type of a treatment dynamo.  The true
> potential of anaerobic digestion if far greater than most of us realized a few short years ago.  Eliminating thermophilic digestion is but
> a technology step backwards regardless of how its justification is formulated.  Regards-Chuck Steiner, WaterSmart Environmental, Inc.  
>   
> > ----- Original Message ----- 
> > From: <mailto:doelle@ozemail.com.au>doelle 
> > To: <mailto:greenfinch@burford.co.uk>greenfinch@burford.co.uk 
> > Cc: <mailto:digestion@crest.org>digestion@crest.org 
> > Sent: Sunday, February 13, 2000 4:55 AM
> > Subject: Re: DIG-L: Anaerobic digestion
> >
> >
> > 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 *** 
> > >--------------------------------------------------
> > >
> > >
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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
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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