Anaerobic membrane bioreactor treatment of domestic wastewater in Tunisia

An anaerobic cross-flow ultrafiltration membrane bioreactor was investigated for municipal wastewater treatment at 37 degrees C. The removal of the total suspended solid, the soluble chemical oxygen demand and the biochemical oxygen demand were respectively 100%, 90% and 88%. Less than 85 mg l(-1) of soluble chemical oxygen demand in the effluent was obtained by ranging the organic loading rate from 0.23 to 2 g COD l(-1) d(-1). The biomass accumulated in the reactor reached 4.3 to 4.9 g l(-1) in terms of MLVSS in the last month of the treatment. The biogas production increased with the increase of the loading rate to reach an average of 281 after 140 days. The average content of the biogas in methane was practically constant at 70%. The treated wastewater could be considered non phytotoxic since the germination index of Lepidium sativum ranged between 60 and 87%. The quality of the treated wastewater fits largely with Tunisian norm NT 106.03 and World Health Organization Guidelines for the microbiological quality of treated wastewater used in agriculture. However, this treated wastewater should undergo further processes to reduce its contents in residual nitrogen and phosphate and thus to conform with the Tunisian standards NT 106.02, a requirement for acceptance in hydraulic public domain.