Commonly, for determining the activity of acetoclastic methanogens from anaerobic seed sludge (with low remaining carbon source), I use sodium acetate as main carbon source and analyse the max slope for methane production to get the value of its activity. However, I have problem to determine the activity of acetoclastic methanogens from the microbial sample with high remaining carbon source (such as starch and fibers). The remaining carbon source from this sample can also be used by microorganisms to produce acids then methane. The separation (centrifugation) of starch and fiber from microbial sludge is also difficult, since they have similar density. The control test shows similar methane production with experiment test (+sodium acetate). Would you like to give me some suggestions for this test?
Thank you very much
I understood your question till you said "The remaining carbon source from this sample can also be used by microorganisms to produce acids then methane."
I didn't really understand this what you mean by that?
You can always try to wash your biomass. But, if understood correctly, the remaining carbon source is non-soluble. So, this should not affect the value of the SMA. In the time in which the test will be performed, few hydrolysis should be expected.
Abhijeet Singh. Thank you very much for your reply. I am sorry that I response very late due to no notification.
The acetoclastic methanogens activity is determined based on methane production from acetate (addition into vial). Since the microbial sample contains the other substrate (starch and other). The remaining substrate (starch) in sample can be utilized by hydrolytic, fermentative to produce acetate which then finally used by methanogens for methane production. Therefore, the remaining substrate can interfere the result of activity test.
Victor S Garcia-Rea. Thank you very much for your response. Yes, I commonly washed to remove the remaining substrate which is soluble, such as VFAs. In case of insoluble substrate, such as starch, it is difficult to remove because it settle with microorganisms after centrifugation.
So, yes, I agree for determining the SMA based on complex microbial community in the system. It is quite difficult to determine the activity of acetoclastic methanogens (specific microbes) when the remaining insoluble substrate still in the microbial sample.
The SMA is not going to be modified. As mentioned in the name, you are measuring the maximum activity so if you have more acetate it won't disturb your results. Of course this considering that there will be no inhibitory concentrations of, for example, VFA. The hydrolysis is not going to be fast enough to add more COD. You can double check it by a COD balance. Regards.
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