The organic fraction (wet fraction) is made up of food scraps and residues, mowing and pruning and residues from the maintenance of ornamental greenery. In general, this type of waste is “digested” by microorganisms. In aerobic conditions (i.e. in the presence of oxygen), the organic fraction of waste is used as food by aerobic microorganisms which transform it into carbon dioxide and water vapor. Bacteria eat waste, and produce just water and a gas.
Under anaerobic conditions (i.e. without oxygen), the biodegradable organic substance is converted, by other anaerobic microorganisms (different from the previous ones), into a gaseous mixture consisting meanly of methane and carbon dioxide. Both biochemical degradation processes (aerobic and anaerobic) give rise to a solid matrix. In summary: aerobic degradation generates water and carbon dioxide (one liquid and one gas); anaerobic degradation generates methane and carbon dioxide (both gases).
Why do we use this degradation process (both aerobic and anaerobic)? We use it to obtain a very useful material called “compost”, through the “composting process”. Look at this video to better understand the production of compost: