The combined UASB and MBR system to COD and TSS removal and excess sludge reduction for the treatment of high strength wastewater in various operational temperatures

There are many activated sludge plants (ASP) in Iran. Most of them are overloaded and as a result their efficiency is very low. A combined laboratory-scale system (5 L reactors) consisting of an up-flow anaerobic sludge blanket (UASB) and aerobic membrane bioreactor (MBR) was operated at 20 and 30°C with pH between 7.6 and 8.4. The experiment was run to optimize treatment of high-strength enriched municipal wastewater of the Ekbatan treatment plant located in west Tehran. The chemical oxygen demand (COD) of the wastewater was enriched due to the addition of molasses and milk powder. To prevent pH fluctuation of the influent, NaHCO3 and K2HPO4 were added to the wastewater. The excess sludge from the MBR was recirculated into the UASB. The system treated fortified municipal wastewater with a volumetric COD loading rate of 600, 1,200, 1,800, and 2,400 mg/L, and temperatures at 20 and 30°C. The results of the present work indicate an optimum organic loading (7.2–10.8 kg m−3 d−1) with COD removal efficiency (RE) between 74 and 85% in both examined temperatures in UASBR. The total combined system efficiency was, approximately, 98% in COD removal and 100% in total suspended solids removal. Furthermore, the nitrate RE was about 80%. Also, excess sludge reduction was over 90%, and the optimum hydraulic retention time for influent COD concentration of 1,200 mg l−1 is shown to be 4 h. This upgraded system increases the treatment capacity by factor of 5.