Biogas is a clean and renewable fuel source produced by the breakdown of organic matter by particular microorganisms.It is primarily composed of methane, carbon dioxide and water vapour.Biogas can be produced from a variety of sources of biomass – including manure, sewage, agricultural waste or food scraps
The production of biogas involves two groups of microorganisms – eubacteria and archaeans (methanogens).
Bacteria first convert the organic material into organic acids and alcohol.Other bacteria convert these products into acetate, carbon dioxide and hydrogen gas.Archaeans then create methane, either via breakdown of acetate or via a reaction between carbon dioxide and hydrogen gas.
The production of biogas can occur in small-scale fermenters under anaerobic conditions.The fermenter needs to be maintained at a neutral pH (~ 7) and constant temperature (~ 35ºC) to maximise yield.Small-scale biogas fermenters are air-tight containers that anaerobically break down kitchen and garden wastes to produce biogas.The fermentation process produces a digested slurry (digestate), which can be used as a fertilizer.The biogas forms within the slurry and collects at the top of the chamber, where it can be transported for use via an outlet. The main design elements of a biogas fermenters are an air-tight chamber, an inlet and a vessel for biogas collection.A small-scale fermenter can also be directly linked to toilets for the additional treatment of human excreta.Small-scale biogas fermenters are typically used by households or communities in rural areas as a supplementary fuel source.