DIG-L: Thermophilic vs. Mesophilic (was: Anaerobic digestion)

[Brian Smyla <ssg@vnet.net>]

Greetings, all!

I am currently exploring the benefits of AD, and would like to build a
test digester using the litter from a poultry farm.  I've
located a farm that seems to be interested in working with me on the
project.  I'm leaning towards a continuous flow digester,
although I'm not sure whether to use the thermophilic or mesophilic
model.  Here are some of  the requirements:

Replacement of LP gas (200 gallons / month average) with biogas for
heating of the poultry houses.
Enough effluent to provide fertilization for the farm's cattle grasses.
Minimal time spent maintaining the digester.

Optional:
Enough biogas for continuous operation of the farm's existing 100 kWh
gasoline backup generator.


Farm Information:
The amount of poultry litter produced by the farm is about 2000 Tons
annually.  This litter is currently collected from the
houses every 10 weeks, piled outside in the open and spread entirely on
the fields as time allows throughout the year.  Our
average annual temperature is 59 degrees F.

My preliminary calculations indicate that if digested, this amount of
litter should generate enough biogas to equal the energy in
36,000 gallons of LP gas or about 90,000 cubic meters of biogas.

My questions are these:
Are my calculations remotely accurate?
Is there a possibility of meeting the listed requirements with the
current volume of litter production?
What size and type digester should I be looking at?
Between thermophilic or mesophilic digestion, which would be the better
choice for this application?
What would be the best method of mixing and introducing the feedstock to
the digester?

As for the debate between Horst Doelle and Chuck Steiner, I'd be
interested to see data from actual test results in support of
your claims.

I'm new to AD, and I've found this list and its archives to be very
informative.  I'd also like to thank Paul Harris of the
University of Adelaide for his web site and the information therein.  As
my AD project takes shape, I'll be setting up and
maintaining a web site to track its progress.  I'll post the URL to the
list when it becomes available.  Thanks in advance for
any help or information.

-brian smyla




doelle wrote:

> 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is obsolete, when we have more than 6 million mesophilic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.
>



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