Anaerobic fermentation is a process which takes part in a natural circle of the organic matter. This process was used for sewage water purification and biogas production for illumination in Exeter, England, since 1895. A bigger development for this process was the period before the Second World War especially in Germany, where the biogas was utilized as a tractor fuel. Investigations were advanced in direction to find alternative energies after the petroleum crisis, during the 1970’s. For this purpose, biogas, as a product of anaerobic fermentation was considered to be a proper solution. Anaerobic fermentation in mesophylic conditions (36C) is complementary process in aerobic purification of wastewater for sludge treatment in methane tanks, etc. Thus, this process was developed parallel with the aerobic one. The first bio filters - combination between bioreactor and later bio filters - were built in France and in Spain, in wine industry and with complete automation of the working parameters.

Keywords : Waste Water Treatment Plant, Retention Time, Anaerobic Fermentation, Continuously Bio Filtration, Fixed Bacterial Film.