Abstract: A process for the treatment of wastewaters heavily polluted by fats, proteins and/or carbohydrates of vegetable or animal origin or their processing products by degradation by microorganisms in a continuous flow reactor without separation of fats and/or sludges, comprising passing the wastewasters through a first part of a reactor containing aerobic and anaerobic microorganisms to consume the free oxygen present in the water, with at least partial degradation of the pollutants to fermentation products, and on flowing through another, adjoining part of the reactor, the fermentation products and any pollutants still present are coverted in the presence of the anaerobic microorganisms into--predominantly--digester gas and biomass. Optionally, fertilizing and/or pH-stabilizing substances or other auxiliaries are added in order to reduce the susceptibility of the system to failure.