Bioconversion is a process involving a microbial and enzymic reaction to decompose biomass.

Thus, anaerobic digestion, or methanisation, is the transformation of biomass into biogas (methane and Carbon dioxide) by a natural complex microbial community present in organic waste. These bacteria react in three steps: Hydrolysis of the macromolecules, acido-genesis and methanogenesis. One tonne of biomass typically produces 4.2 GJ, or 0.2 TOE. The residue, called digestat, is recovered in agriculture in the form of compost.

The alcoholic fermentation of the carbohydrates (sugars, starch) by yeasts contained in the biomass produces bio-alcohol (used pure or mixed in fuels), and Carbon dioxide.