MUNICIPAL WASTEWATER TREATMENT IN A MEMBRANE BIOREACTOR

ABSTRACT A membrane bioreactor (MBR) with a submerged membrane was used for the treatment of municipal wastewater from the city of Zagreb, Croatia, in a continuous mode for 123 days. The MBR was very efficient in organic matter removal (92.3 and 98.5 % for COD and BOD, respectively) for the entire duration of the experiment. Nitrification was established after 20 days remaining stable and efficient with a low concentration of ammonia and nitrite in the effluent. On average, 87% of ammonia was converted to nitrate. Biomass concentration, measured as MLSS, was dependant on the organic loading rate (OLR) and food to microorganism ratio (F/M), and its growth could be stopped or its concentration reduced by setting OLR and F/M to appropriate values, thus reducing the excess sludge production. Throughout the range of hydraulic retention times from 2.6 to 5.9 h, the efficiencies of organic matter removal and nitrification were not affected