I have been anaerobically fermenting biomass for a week and measuring the pressure in the bottles every day. Over the first couple of days pressure increased due to hydrogen production - but now the pressure is decreasing each day, why is this?
Thank you.
Hydrogen is usually only co-products in AD. Methanogens can utilize it following this scheme: CO2 + 4H2 -> CH4 + 2H2O
As you can see, from initial 5 molecules, you will have just 3, and H2O will probably be condensed to liquid additionally. So the drop in pressure is totally fine and logical. To be sure, if this is the explanation, you can use any gas analyzer to check how the composition of the gas is changing with time.
Finally - the most natural product in fermentation is methane. Stopping the process on hydrogen is tricky, and require specific microbiome, induced by correct inoculum. That's why most of the articles focusing on AD process, consider methane production.
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