For my last project in microbiology this term, we were to select a microbe, or microbial phenomenon and give a short presentation. Being interested in anaerobic digestion, I chose the process of methanogenesis, the process during anaerobic digestion which produces methane. Anaerobic digestion is the broad term for turning organic waste into natural gas, including all the stages that material goes through before methane is produced as a byproduct of microbial metabolism, which is the process of methanogenesis.
After realizing that anaerobic digestion is nearly identical to the process of fermentation (with some notably different byproducts…), I decided to use my brewing equipment and the organic waste collected over one week in my Green Bin to see if I could producemethane at home.
Methanogenic archaea (microbes that produce methane as a product of metabolism) require an intermediary step before methane is produced from organic waste, just as brewers yeast requires enzymes to break down starch molecules into simple sugars during the mashing process. For the methanogenic microbes, this intermediary step is the decomposition of larger organic molecules such as proteins, cellulose and carbohydrates into smaller molecules by naturally occurring microbes. These are the same microbes that produce acetic acid (vinegar) from wine in the presence of oxygen. Once the material is sufficiently decomposed, oxygen levels are depleted by microbial activity and carbon dioxide concentration is high, only then will the methanogens begin producing methane. The chemical equation is as follows:
CO2 + 4 H2 → CH4 + 2H2O
The first step in my home anaerobic digestion experiment was to grind the organic material into a uniform pulp and mix it with oxygenated water to kick start the decomposition process.
Currently the mixture is working through the primary stages of decomposition, releasing carbon dioxide through the airlock. Hopefully, in a week or so the methanogenic microbes will get to work and methane capture can begin!
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