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Why doesn't methane form in a MFC ? PDF Print E-mail
Written by Bynge   
Tuesday, 12 May 2009

Hi,

 I am a studnet doing some research on MFCs. I came across the process and found that anaerobic digestion takes place in the anode chamber.

 My question is does methane form in the anode chamber like in usual anaerobic digestion by methanogenesis. If not, then why ?

 Also if methane is a product in MFC too, then does it simply mean that MFCs are better than conventional Anaerobic Digestors.

Why is everyone talking only about the hydrogen produced not even mentioning about methane ? 

 Thanks in advance for the help.

 

» 3 Comments
3Comment
at Wednesday, 27 May 2009 01:05by kike
I think that if you have a cathode chamber that uses oxigen as final aceptor of electrones you produce CO2 but if there's no oxigen then the final aceptor will mainly be the carbon molecule and the protons from the media, and therefore you produce methane and hidrogen. Anaerobic metabolism is slower and because of this many people prefer to work with aerobic cathode chambers. The problem with MFC is the cost, I think it hasnot been a good busines to use them yet as the benefits should be less than the costs. 
 
That is my idea but your question is very good and it would be better to have a coment from an expert.
2Comment
at Monday, 18 May 2009 08:13by bachmann
Methane production in an MFC is undesirable because it reduces the efficiency of electricity production from organic matter by producing an energy-rich by-product which cannot be used (e.g. combusted) because of its low concentration in the gas produced (mainly CO2). 
Perhaps, in order to avoid growth of methanogens which like to grow at pH 7.3 +/- 0.3 (roughly), one could lower the pH to pH 6.5.
1Comment
at Monday, 18 May 2009 07:12by bachmann
Based on Rozendal et al. (2008; doi:10.1016/j.tibtech.2008.04.008) electrochemically active microorganisms at an anode can outcompete methanogens for acetate (non-fermentable) as an electron donor, however the use of fermentable glucose and ethanol, for example, leads to notable amounts of methane production. Rozendal et al. (2004) suggest that methanogens, in contrast to electrochemically active microorganisms, are 
not dependent on close, electrical contact with the electrode. Microorganisms can grow on the anode in multilayered aggregations that are referred to as biofilms.nMethanogens can colonize the top of anodic biofilms, where they scavenge the hydrogen at the place it is formed in the fermentation process before it can reach the electrochemically active microorganisms deeper in the biofilm. From an operational perspective, this implies that when fermentable substrates are present in the wastewater, pre-fermentation might be required before bioelectrochemical ww treatment.
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