[Digestion] Fwd: The biology of biogas production

Thu Jun 30 00:44:29 CDT 2011

 I have shared my thoughts on the matter earlyer with dr. Karve, and as this
debate has gotten some mettel on this list, I am posting my reply here,
likewise.

The biochemistry of biogas production dictates that CO2 and CH4 must be
produced simultaneously to achieve stable operation. The product CO2/CH4
ratio is governed by the type of substrates used. There are two main
pathways (also some others that are currently regarded as exceptions & less
important) of biochemical pathways, that result in biogas:

- acetoclastic pathway (acetic acid is decarboylized to methane and carbon
dioxide)
- hydrogenotrophic pathway (hydrogen and carbon dioxide are utilized to form
methane alone)

As both these processes are are mutually dependable on the other one, CH4
and CO2 must be formed together, or none at all. An disturbance in
theeither one of these processes results in
the condition which I'm sure we are all familiar with, t.i. theacidification of
the reaction. The amount of H+ in the broth becomes easily toxic to
acetoclastic methanogens, therefore in a stable process, all the H+ must
react with the dissolved carbonate, and the carbonate that remains is
therefore the source of final CO2 in the biogas.

Further on, regarding the CO2 fixation from the gas phase above the
fermentation broth (e.g. in digesters equipped with  floating drum,
inflatable cover and similar); the methane ration in the "headspace" does
not affect the level of methane production, as the amount of the methane
that is made is governed by the biochemical properties of the substrate.
Also, methane is poorly soluble in water , so there is no physiochemical
mechanisma that would neable the microorganisms to "know" what the methane
content in the produced biogas is.

Interesting mechanism described by Khrishna, are you refering to the CO2
fixation from the gas phase (biogas) or from the liquid phase (fermentation
broth itself)?

I remember some systems were proposed, where the CO2 formed due to methane
combustion in the cogeneration plant would be purged through the
fermnetation broth to achieve higher methane yields, but I have no knowledge
if any commercial applications of this exist.

Also, I think, there is the general problem of carbon dioxide that must be
addressed, as we must start to view the produced CO2 as a product and not as
an impurity. A vast amount of biochemical energy is used to produce carbon
dioxide in the biological process, so by utilizing the produced CO2 rather
than discarding it, the energy efficiency of such processes could be
considerably increased. E.g. the  biogas plants can be could be coupled to
greenhouses to enhance the productivity of plants. Similarly, there are
attempts being made, to flue gases from biogas co-generation units to feed
the algae plantations. Further on, a wast scientific community is quite
successful in researching new ways to catalytically transform ch4 and co2 to
synthesis gas or similar intermediates, that can be further transformed to
various high-value chemicals.

BR from SI, Gasan

------------------------------
From: Gasan Osojnik <gasan.osojnik at gmail.com>
Date: 16 May 2011 09:17
Subject: Re: Digestion Digest, Vol 7, Issue 13
To: digestion at lists.bioenergylists.org

Dear David and Melvin,

I apologize for not responding sooner, a lot of things were prioritized.
Here is the full sources list for the basic anaerobic degradation described
on 23 Mar 2011 in the topic "The biology of Biogas Production".

(i) As already mentioned, basic biology for engineering purposes (encluding
the biochemisty of the biogas formation from various sources) is explained
in:*
Deublein & Steinhauser's Biogas form waste and renewable resources (Willey,
2009))* and many other pollution engineering handbooks.

(ii) The microbial syntrophism explained (interspecies hydrogen transfer),
essential for biogas production, is explained in e.g.:
*Schink, B (1997) Energetics of syntrophic cooperation in methanogenic
degradation. Microbiology and Molecular Biology Reviews, 61 (2), 262-280*,
(an example was explained already in 1967 by *Bryant et al., Methanobacillus
omelianskii, a symbiotic association of two species of bacteria.
Arch. Microbiol. 59:20.*)

(iii) Regarding the biodiversity in the reactor, the number 800 species was
given recently at a lecture from prof. Romana Marinsek-Logar from UL. In a
recent publication, *Jaenicke et al (2011), Comparative and Joint Analysis
of Two Metagenomic Datasets from a Biogas Fermenter Obtained by
454-Pyrosequencing,* the taxonomic profile of the biogas producing community
is updated with several new genera (s.a. *Streptococus* and genera in
the*Firmicutes
* phylum), altogether 40 genera was identified. Furthermore, I'm am anxios
to see the outcome of the biogas-producing microbial community sequencing
(Martin Wu, UC Davis & DOE JGI), a project which is bound to produce
interesting results.

(iv) General facts about *Archaea* etc. can be found in *Brock's Biology of
Microorganisms** *and in *Bergey's Manual* .

(a.d.) Also, i have come across an interesting educational cartoon
describing the biological process of biogas formation . It is informative
and has one or two slips (e.g. in the animation water is added after the
hydrolysis, where in fact it has to be present before the process for the
decay of complex molecules), but still very nice to see.

http://www.youtube.com/watch?v=bUBAndojs50&feature=player_embedded

BR, Gasan Osojnik

------------------------------
>
> Message: 3
> Date: Wed, 29 Jun 2011 12:14:39 +0930
> From: "Paul Harris" <paul.harris at adelaide.edu.au>
> To: "'For Discussion of Anaerobic Digestion'"
>        <digestion at lists.bioenergylists.org>
> Subject: Re: [Digestion] Fwd:  The biology of biogas production
> Message-ID: <00fb01cc3606$7e81c800$7b855800$@harris at adelaide.edu.au>
> Content-Type: text/plain; charset="iso-8859-2"
>
> G'day A.D. Karve et al,
>
> This post from a while back prompted an interesting thought - if you are
> right we may be able to acclimate a digester to using just CO2 as the
> carbon
> source, so we could convert CO2 back to methane and solve both CO2
> emissions
> and "peak oil".
>
> The quality ratio of CH4 to CO2 does vary a bit, sometimes being less than
> 50% methane and sometimes claims of over 90% methane, but David Fulford has
> shown that sugar and starch give 50% methane so any improvement is due to
> some methanogens using CO2 produced earlier in the sequence and H+ from
> water and acids to make CH4 and H2O.
>
> Happy digesting,
>
> HOOROO
>
> Mr. Paul Harris, Room 202 Charles Hawker Building, Faculty of Sciences, The
> University of Adelaide, Waite Campus, PMB 1, Glen Osmond SA 5064 Ph    :
> +61
> 8 8303 7880      Fax   : +61 8 8303 4386
> <mailto:paul.harris at adelaide.edu.au> mailto:paul.harris at adelaide.edu.au
> <http://www.adelaide.edu.au/directory/paul.harris>
> http://www.adelaide.edu.au/directory/paul.harris
>
> From: digestion-bounces at lists.bioenergylists.org
> [mailto:digestion-bounces at lists.bioenergylists.org] On Behalf Of Anand
> Karve
> Sent: Thursday, 2 June 2011 12:50 PM
> To: digestion at lists.bioenergylists.org
> Subject: [Digestion] Fwd: The biology of biogas production
>
>
> ---------- Forwarded message ----------
> From: Anand Karve <adkarve at gmail.com>
> Date: 2011/6/2
> Subject: Re: [Digestion] The biology of biogas production
> To: Gasan Osojnik <gasan.osojnik at gmail.com>
>
> Dear List,
>
>  Irrespective of the substrate, design of the system or the temperature of
> the reaction, the proportion of methane to carbon dioxide in the biogas
> seems to be constant all over the world. Is there an equilibrium between
> these two gases that keeps this proportion constant? Because in that case,
> one might introduce carbon dioxide from outside into the biogas plant and
> see if the organisms in the digester produce more methane to reach the
> euilibrium constant. I shall be grateful to get your reaction on this.
>
> Yours
>
> A.D.Karve
>
> ------------------------------
>
> Message: 9
> Date: Wed, 29 Jun 2011 22:23:27 +0800
> From: Anand Karve <adkarve at gmail.com>
> To: paul.harris at adelaide.edu.au, For Discussion of Anaerobic Digestion
>        <digestion at lists.bioenergylists.org>
> Subject: Re: [Digestion] Fwd: The biology of biogas production
> Message-ID: <BANLkTi=iCPU9n=ULeu9W-5JM6+MNCXWAMQ at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-2"
>
> Dear Paul,
> The text book opinion is that methanogens are helped by a large number of
> other bacteria in the process of methanogenesis. Some time ago I had posed
> a
> question to Gasan that if there are so many different organisms involved in
> this process, why we did not get a lot more carbon dioxide in our biogas
> than the 40% that everybody reports.  He wrote that the organisms that
> associated themselves with the methanogens used the carbon dioxide as the
> source of carbon. Gasan may elaborate this point.
> Yours
> A.D.Karve
>
> ------------------------------
>
> Message: 11
> Date: Wed, 29 Jun 2011 21:55:08 +0530
> From: Murali Krishna <bmkrishna6 at gmail.com>
> To: For Discussion of Anaerobic Digestion
>        <digestion at lists.bioenergylists.org>
> Subject: Re: [Digestion] Fwd: The biology of biogas production
> Message-ID: <BANLkTimK=jpAkgRjbfxa+HJbdpnncQV2RA at mail.gmail.com>
> Content-Type: text/plain; charset="iso-8859-2"
>
> Good day Paul,
>
> CO2 is isolated and streamed into a separate chamber.  Carbonic Anhydrase
> enzymes are used to isolate CO2 from the digester. Carbonic anhydrase,
> rapidly converts carbon dioxide to bicarbonate. Thus CO2 is efficiently
> removed  from the solution in the digester. The product of this reaction,
> bicarbonate, can then be reacted with sodium to form NaHCO2, baking soda.
> By this process CO2 emission into atomosphere is reduced substantially and
> there is more space in the digester. There is a patent on this.
>
> The isolated CO2 after modifications is sent back into the digester and
> Methane is generated.  (This second part I need to yet confirm). I shall
> come back to you soon on this.
>
> Krishna
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.bioenergylists.org/pipermail/digestion_lists.bioenergylists.org/attachments/20110630/0ee97185/attachment.html>