[Digestion] Digestion Digest, Vol 11, Issue 10 --- AD and how it works.
Len Walde
sigma at ix.netcom.com
Tue May 15 19:49:39 CDT 2007
Hello to all:
The following may shed some light on the general subject of AD. This is
from an unpublished "White Paper" that is still under development, and
because of that, I am not prepared to enter into any further discussion or
answer any questions. By searching many of the key words herein, one should
be able to find your own answers. This is a very basic description of the
process. Good luck as you explore the Learning Curve.
Len Walde, ,P.E.
Sigma Energy Engineering, Inc.
Creative Problem Solving & Process Engineering
Serving Agriculture, Mining, Industry & Commerce
through "Symbiotic Recycling" tm
Est. 1985
Ph: 925-254-7633
E-mail: sigma at ix.netcom.com
5.2 Brief Introduction to Anaerobic Digestion
Methane production by anaerobic digestion is formed solely through the
activity of bacteria, unlike composting in which fungi and lower creatures
are also involved in the degradation process. Microbial growth and methane
production is very slow at ambient temperatures. They tend to occur
naturally wherever high concentrations of wet organic matter accumulate in
the absence of dissolved oxygen, most commonly in the bottom sediments of
lakes and ponds, in swamps, peat bogs, intestines of animals, and in the
anaerobic interiors of landfill sites.
This process involves the biological conversion of the organic components of
biomass into simple products by various reactions and interactions that take
place among the bacteria known as methanogens and non-methanogens and the
substrates fed into the digester as inputs. This is a complex
physio-chemical and biological process involving different factors and
stages or steps of change. This process of digestion (methanization) is the
breaking down of inputs that are complex organic materials and is achieved
through three steps.
Anaerobic Digestion occurs through the symbiotic action of a complex
consortium of bacteria. Hydrolytic microorganisms, including common food
spoilage bacteria, break down complex organic wastes. These sub-units are
then fermented into short-chain fatty acids, carbon dioxide, and hydrogen
gases.
Very specialized microorganisms then convert the complex mixture of
short-chain fatty acids to primarily acetic acid - (in fact, a combination
of 7 acids) with the release of more carbon dioxide, and hydrogen gases.
Finally, methanization produces biogas from the acetic acid, hydrogen and
carbon dioxide. Biogas is a mixture of methane, carbon dioxide, a small
amount of hydrogen sulphide and numerous trace elements.
According to some, the two key biological issues are determining the most
favorable conditions for each process stage and how non-optimal
circumstances affect each process stage as a whole, and the governing role
of hydrogen generation and consumption.
Step 1. Hydrolysis: The waste materials of plant and animal origins consist
mainly of carbohydrates, lipids, proteins and inorganic materials. Large
molecular complex substances are solubilized into simpler ones with the help
of extracellular enzyme released by the bacteria. This stage is also known
as the polymer breakdown stage. For example, the cellulose consisting of
polymerized glucose is broken down to dimeric, and then to monomeric sugar
molecules (glucose) by cellulolytic bacteria.
Step 2. Acidification: The monomers such as glucose which are produced in
Step 1 are fermented under anaerobic condition into various acids with the
help of enzymes produced by the acid forming bacteria. These acidogenic
bacteria are robust, hardy microorganisims which can double their population
every few hours, if properly fed. At this stage, the acidogenic or
acid-forming bacteria break down molecules of six atoms of carbon (glucose)
into molecules of less atoms of carbon (acids) which are in a more reduced
state than glucose. The principal acids produced in this process are acetic
acid, propionic acid, and butyric acid.
Step 3. Methanization: The principle acids produced in Step 2 are processed
by methanogenic bacteria to produce methane. The reaction that takes place
in the process of methane production is called Methanization and is
expressed by the following equations.
CH3COOH à CH4 + CO2
Acetic acid Methane Carbon dioxide
2CH3CH2OH + CO2 à CH4 + 2CH3COOH
Ethanol Carbon dioxide Methane Acetic acid
CO2 + 4H2 à CH4 +
2H2O
Carbon dioxide Hydrogen Methane Water
These equations show that many products, by-products and intermediate
products are produced in the process of digestion of inputs in an anaerobic
condition before the final product (methane) is produced. Obviously, there
are many facilitating and inhibiting factors that play their role in the
process.
Methanogenic bacteria develop slowly, taking 3 days to double their
population numbers, and are sensitive to a sudden change in physical and
chemical conditions. For example, a sudden fall in the slurry temperature
by even 2 deg. C may significantly affect their growth and the gas
production rate.
Conventional anaerobic digesters are commonly designed to operate in either
the mesophilic temperature range (95°-105°F) or thermophilic temperature
range (125°-135°F).
6. About Sigma Energy Engineering, Inc.
Sigma Energy Engineering Inc. a closely held California "S" Corporation, was
established in 1985. Sigma is a Consulting and Process Engineering Company,
specializing in recycling research and the development of technologies to
recycle "difficult-to-recycle" waste materials, and resource recovery. They
are presently focusing on the research and development of technologies to
recycle animal and agricultural waste into renewable energy and value-added
bio-products and commodities. The company is one the most experienced
California consulting and process engineering firms in their field. They
concentrate their research on the solution of diverse industrial, commercial
and agricultural waste management and recycling problems.
----- Original Message -----
From: "Mike Walter" <sailingmike50 at hotmail.com>
To: <digestion at listserv.repp.org>
Sent: Tuesday, May 15, 2007 3:53 PM
Subject: Re: [Digestion] Digestion Digest, Vol 11, Issue 10
> Hi,
> In reply to Mel's response about the diversity of a general culture, I
> "googled" the word co-fermentation and found that by adding 10% fat of
> some sort (up to 30%) could double the gas output of a culture.
> Considering the bulk one deals with doubling this sounding promising.
> Mike Walter
>
>
>
>> From: digestion-request at listserv.repp.org> Subject: Digestion Digest, Vol
>> 11, Issue 10> To: digestion at listserv.repp.org> Date: Tue, 15 May 2007
>> 13:00:06 -0400> > Send Digestion mailing list submissions to>
>> digestion at listserv.repp.org> > To subscribe or unsubscribe via the World
>> Wide Web, visit>
>> http://listserv.repp.org/mailman/listinfo/digestion_listserv.repp.org>
>> or, via email, send a message with subject or body 'help' to>
>> digestion-request at listserv.repp.org> > You can reach the person managing
>> the list at> digestion-owner at listserv.repp.org> > When replying, please
>> edit your Subject line so it is more specific> than "Re: Contents of
>> Digestion digest..."> > > Today's Topics:> > 1. Re: Digestion Digest, Vol
>> 11, Issue 5 (Carolyn Henri)> >
>> > ---------------------------------------------------------------------->
>> > Message: 1> Date: Mon, 14 May 2007 17:07:24 -0700> From: "Carolyn
>> Henri" <Carolyn at ResourceConsulting.us>> Subject: Re: [Digestion]
>> Digestion Digest, Vol 11, Issue 5> To: <digestion at listserv.repp.org>>
>> Message-ID: <029f01c79685$0458be50$0201a8c0 at OFFICE>> Content-Type:
>> text/plain; format=flowed; charset="iso-8859-1";> reply-type=original> >
>> Don't be dismayed, Steve. There is no such thing as a stupid question. I
>> > am also not a digestion expert, but have learned a great deal from this
>> > forum and made several good contacts who have been helpful in directing
>> me > towards information.> Carolyn Henri> >
>> **************************************************> Carolyn J. Henri,
>> Ph.D.> Resource Consulting Service, LLC> 4805 Belvedere Ave.> Everett, WA
>> 98203> > Phone: (425) 290-3181> Fax: (425) 290-7586> Cell: (425)
>> 308-1634> E-Mail: Carolyn at ResourceConsulting.us> Website:
>> www.ResourceConsulting.us> >
>> **************************************************> ----- Original
>> Message ----- > From: <digestion-request at listserv.repp.org>> To:
>> <digestion at listserv.repp.org>> Sent: Friday, May 04, 2007 10:00 AM>
>> Subject: Digestion Digest, Vol 11, Issue 5> > > > Send Digestion mailing
>> list submissions to> > digestion at listserv.repp.org> >> > To subscribe or
>> unsubscribe via the World Wide Web, visit> >
>> http://listserv.repp.org/mailman/listinfo/digestion_listserv.repp.org> >
>> or, via email, send a message with subject or body 'help' to> >
>> digestion-request at listserv.repp.org> >> > You can reach the person
>> managing the list at> > digestion-owner at listserv.repp.org> >> > When
>> replying, please edit your Subject line so it is more specific> > than
>> "Re: Contents of Digestion digest..."> >> >> > Today's Topics:> >> > 1.
>> An apology...and an excuse (Steve Verhey)> > 2. Re: An apology...and an
>> excuse (finstein at envsci.rutgers.edu)> >> >>
>> > ---------------------------------------------------------------------->
>> >> > Message: 1> > Date: Fri, 04 May 2007 07:44:17 -0700> > From: "Steve
>> Verhey" <verheys at hotmail.com>> > Subject: [Digestion] An apology...and an
>> excuse> > To: finstein at envsci.rutgers.edu, duncanjmartin at eircom.net> >
>> Cc: digestion at listserv.repp.org> > Message-ID:
>> <BAY133-F10A55ED1E41C782C76038CA9400 at phx.gbl>> > Content-Type:
>> text/plain; format=flowed> >> >> > There's been talk in the media here
>> about what constitutes a good apology,> > so I know this one will be of
>> low quality, but I am sorry for asking such > > a> > simple question. I
>> do have access to reasonable online sources, but not a> > good physical
>> library, and I don't actively work in this field -- I'm just> >
>> interested in it, and in energy issues in general. I'm pretty sure it > >
>> would> > take me longer than 10 minutes to answer my question. My
>> background is in> > molecular biology and biochemistry, not all that
>> useful. This relatively> > quiet forum seemed a reasonable place to ask
>> the question, which I didn't> > think was off-topic.> >> > That said, the
>> question was my ignorant response to the difficulty/large> > uncertaintly
>> in estimating methane output, which must be mostly due to> >
>> digester-to-digester variability of microbial communities. My impression
>> > > is> > that AD is done with whatever organisms happen to be present,
>> but it > > seemed> > to me that (as some products claim to do with
>> composting) it might be> > possible to inoculate with a particularly
>> enthusiastic microbial > > community,> > or even engineer better
>> methanogens. Apparently this is either not > > possible,> > or is not
>> considered worth thinking about.> >> > Thanks for your patience,> >> >
>> Steve> >> >>From: finstein at envsci.rutgers.edu> >>To: "Duncan Martin"
>> <duncanjmartin at eircom.net>> >>CC: "Steve Verhey" <verheys at hotmail.com>,
>> digestion at listserv.repp.org> >>Subject: Re: [Digestion] Calculating
>> methane production> >>Date: Fri, 4 May 2007 07:32:55 -0400 (EDT)> >>>
>> >>Duncan -> >>> >>As you say (in effect): one man's junk (one microbe's
>> metabolic waste) is> >>another man's treasure (another microbe's
>> substrate). But questioning the> >>complexity of the metabolic web
>> terminating in methane was not what> >>started the thread. Rather, the
>> question asked was - how to estimate> >>methane production.> >>> >>Mel>
>> >>> >>> >> > Come on lads!!> >> >> >> > I might speak only for myself but
>> I think it's an abuse of a forum like> >> > this> >> > for folk to use it
>> as a replacement for ten minutes work in a> >>half-decent> >> > public
>> library or on the internet. I'm more tolerant when the enquiry> >> >
>> comes> >> > from somewhere remote. But I don't think the USA qualifies!>
>> >> >> >> > For info, Steve, yes there is a mass of research and "a
>> particularly> >>good> >> > methanogenic microbial community" is
>> characterized by a great diversity> >>of> >> > species, very many of
>> which are not methanogens. Now, go read!> >> >> >> > Fraternally yours>
>> >> >> >> > Duncan J Martin> >> >> >> > Chair> >> > Republic of Ireland
>> Centre> >> > Chartered Institution of Wastes Management> >> >> >> >
>> ================================> >> > CONTACT DETAILS> >> > Duncan J
>> Martin, PhD, CEng, CSci, MIEI, MCIWM, MIChemE> >> > 24 Townsfield,
>> Cloughjordan, N Tipperary, Ireland> >> > Mobile: +353 86 8377 906> >> >
>> Home: +353 505 42087> >> > Email: duncanjmartin at eircom.net> >> >
>> ================================> >> >> >> >> >> >> >> >> >> > -----
>> Original Message -----> >> > From: "Steve Verhey" <verheys at hotmail.com>>
>> >> > To: <finstein at envsci.rutgers.edu>; <digestion at listserv.repp.org>> >>
>> > Sent: Thursday, May 03, 2007 11:13 PM> >> > Subject: Re: [Digestion]
>> Calculating methane production> >> >> >> >> >> >>> >> >> Presumably not
>> all organisms in an anaerobic environment are> >> >> methanogens.> >> >>
>> Is> >> >> there research on what a particularly good methanogenic
>> microbial> >> >> community> >> >> looks like? Maybe it's even possible to
>> make an inoculum that would > >> >> get> >> >> things started off in the
>> right direction?> >> >>> >> >> Steve Verhey, Ph.D> >> >> Biologist at
>> Large> >> >> Ellensburg, WA USA> >> >>> >> >
>> _________________________________________________________________> >
>> Exercise your brain! Try Flexicon.> >
>> http://games.msn.com/en/flexicon/default.htm?icid=flexicon_hmemailtaglineapril07>
>> >> >> >> >> > ------------------------------> >> > Message: 2> > Date:
>> Fri, 4 May 2007 11:14:03 -0400 (EDT)> > From:
>> finstein at envsci.rutgers.edu> > Subject: Re: [Digestion] An apology...and
>> an excuse> > To: "Steve Verhey" <verheys at hotmail.com>> > Cc:
>> finstein at envsci.rutgers.edu, digestion at listserv.repp.org> > Message-ID:>
>> > <50830.72.84.59.43.1178291643.squirrel at webmail.envsci.rutgers.edu>> >
>> Content-Type: text/plain;charset=iso-8859-1> >> > Not a problem, Steve ->
>> >> > Your background in molecular biology and biochemistry is actually
>> central> > to the matter. But - and a big but it is - not in the clean
>> context of> > pure culture systems being fed nice uniform substrates.
>> Think of the vast> > range of substrates in garbage, and the vast array
>> of organisms and enzyme> > systems needed to transform that mess to CO2,
>> H2O and CH4! The idea of> > adding some special inoculum or biocatalyst
>> to bring it about - or even to> > accelerate it - becomes absurd. Same
>> for composting, sewage treatment, etc> > etc. Think nature guided by
>> appropriate technology.> >> > Mel> >> >> >> >> There's been talk in the
>> media here about what constitutes a good > >> apology,> >> so I know this
>> one will be of low quality, but I am sorry for asking > >> such> >> a> >>
>> simple question. I do have access to reasonable online sources, but not
>> a> >> good physical library, and I don't actively work in this field --
>> I'm > >> just> >> interested in it, and in energy issues in general. I'm
>> pretty sure it> >> would> >> take me longer than 10 minutes to answer my
>> question. My background is in> >> molecular biology and biochemistry, not
>> all that useful. This relatively> >> quiet forum seemed a reasonable
>> place to ask the question, which I didn't> >> think was off-topic.> >>>
>> >> That said, the question was my ignorant response to the
>> difficulty/large> >> uncertaintly in estimating methane output, which
>> must be mostly due to> >> digester-to-digester variability of microbial
>> communities. My impression> >> is> >> that AD is done with whatever
>> organisms happen to be present, but it> >> seemed> >> to me that (as some
>> products claim to do with composting) it might be> >> possible to
>> inoculate with a particularly enthusiastic microbial> >> community,> >>
>> or even engineer better methanogens. Apparently this is either not> >>
>> possible,> >> or is not considered worth thinking about.> >>> >> Thanks
>> for your patience,> >>> >> Steve> >>> >>>From:
>> finstein at envsci.rutgers.edu> >>>To: "Duncan Martin"
>> <duncanjmartin at eircom.net>> >>>CC: "Steve Verhey" <verheys at hotmail.com>,
>> digestion at listserv.repp.org> >>>Subject: Re: [Digestion] Calculating
>> methane production> >>>Date: Fri, 4 May 2007 07:32:55 -0400 (EDT)> >>>>
>> >>>Duncan -> >>>> >>>As you say (in effect): one man's junk (one
>> microbe's metabolic waste) is> >>>another man's treasure (another
>> microbe's substrate). But questioning the> >>>complexity of the metabolic
>> web terminating in methane was not what> >>>started the thread. Rather,
>> the question asked was - how to estimate> >>>methane production.> >>>>
>> >>>Mel> >>>> >>>> >>> > Come on lads!!> >>> >> >>> > I might speak only
>> for myself but I think it's an abuse of a forum> >>> like> >>> > this>
>> >>> > for folk to use it as a replacement for ten minutes work in a>
>> >>>half-decent> >>> > public library or on the internet. I'm more
>> tolerant when the enquiry> >>> > comes> >>> > from somewhere remote. But
>> I don't think the USA qualifies!> >>> >> >>> > For info, Steve, yes there
>> is a mass of research and "a particularly> >>>good> >>> > methanogenic
>> microbial community" is characterized by a great> >>> diversity> >>>of>
>> >>> > species, very many of which are not methanogens. Now, go read!> >>>
>> >> >>> > Fraternally yours> >>> >> >>> > Duncan J Martin> >>> >> >>> >
>> Chair> >>> > Republic of Ireland Centre> >>> > Chartered Institution of
>> Wastes Management> >>> >> >>> > ================================> >>> >
>> CONTACT DETAILS> >>> > Duncan J Martin, PhD, CEng, CSci, MIEI, MCIWM,
>> MIChemE> >>> > 24 Townsfield, Cloughjordan, N Tipperary, Ireland> >>> >
>> Mobile: +353 86 8377 906> >>> > Home: +353 505 42087> >>> > Email:
>> duncanjmartin at eircom.net> >>> > ================================> >>> >>
>> >>> >> >>> >> >>> >> >>> > ----- Original Message -----> >>> > From:
>> "Steve Verhey" <verheys at hotmail.com>> >>> > To:
>> <finstein at envsci.rutgers.edu>; <digestion at listserv.repp.org>> >>> > Sent:
>> Thursday, May 03, 2007 11:13 PM> >>> > Subject: Re: [Digestion]
>> Calculating methane production> >>> >> >>> >> >>> >>> >>> >> Presumably
>> not all organisms in an anaerobic environment are> >>> >> methanogens.>
>> >>> >> Is> >>> >> there research on what a particularly good methanogenic
>> microbial> >>> >> community> >>> >> looks like? Maybe it's even possible
>> to make an inoculum that would> >>> get> >>> >> things started off in the
>> right direction?> >>> >>> >>> >> Steve Verhey, Ph.D> >>> >> Biologist at
>> Large> >>> >> Ellensburg, WA USA> >>> >>> >>> >>
>> _________________________________________________________________> >>
>> Exercise your brain! Try Flexicon.> >>
>> http://games.msn.com/en/flexicon/default.htm?icid=flexicon_hmemailtaglineapril07>
>> >>> >> >> >> >> > ------------------------------> >> >
>> _______________________________________________> > Digestion mailing
>> list> > Digestion at listserv.repp.org> >
>> http://listserv.repp.org/mailman/listinfo/digestion_listserv.repp.org> >>
>> > End of Digestion Digest, Vol 11, Issue 5> >
>> ****************************************> >> > > > > > >
>> > ------------------------------> >
>> _______________________________________________> Digestion mailing list>
>> Digestion at listserv.repp.org>
>> http://listserv.repp.org/mailman/listinfo/digestion_listserv.repp.org> >
>> End of Digestion Digest, Vol 11, Issue 10>
>> *****************************************
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