Re: DIG-L: Anaerobic digestion

[Roos.Kurt@epamail.epa.gov]

Doelle is really refering to an "Energy" balance of the system based on costing
of the systems MEASURED operating parameters.

Kurt Roos
AgSTAR Program


|--------+----------------------->
|        |          doelle@ozemai|
|        |          l.com.au     |
|        |                       |
|        |          02/13/00     |
|        |          04:07 PM     |
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   >----------------------------------------------------|
   |                                                    |
   |       To:     h2osmart@ix.netcom.com               |
   |       cc:     digestion@crest.org                  |
   |       Subject:     Re: DIG-L: Anaerobic digestion  |
   >----------------------------------------------------|




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I totally disagree with you saying that mesophilic anaerobic digestion is
obsolete, when we have more than 6 million mesophilic digesters working in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
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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