Application Of A~2/O+MBR Process In Municipal Wastewater Treatment Engineering

With the increase of municipal water resource shortage and wastewater pollution,the wastewater discharge standard will be more strictly. As a result, the deepwastewater treatment technologies develop rapidly. Membrane bioreactor （MBR）,which is considered as an efficient new wastewater treatment technology, has a godapplication future in wastewater treatment and reuse area and has been a investigatedhotspot in the field of water pollution and control so far. Therefore, it is important todeeply investigate the MBR technique and the combination of MBR and otherprocesses, for the studies are beneficial to its widespread application.The aim of this study was to treat a full-scale municipal wastewater. Thecombination technologies of anaerobic/anoxic/oxic and MBR （A²/O+MBR） wereselected as the key process based on the comparisons of the multi-wastewatertreatment process. First, the whole process flow of this process was introduced, andthe technical index and design parameter of each unit were determined according tothe1A discharge standard of “Discharge Standard of Pollutants for MunicipalWastewater Treatment Plant”（GB18918-2002）. Then, the optimal operationalparameters of the A²/O+MBR were obtained. Finally, to ensure the efficiency andstability of these processes, the evaluation on membrane contamination and cleaningwas performed. The studies presented here would provide some experiences for thedeep treatment of municipal wastewater treatment operation.The results showed that A²/O+MBR could achieve high efficiencies of mainpollutants removal under the optimal operation. The highest sludge concentration inMBR reactor could achieve at8.2g/L, and the average concentration was usuallymaintained5⁶g/L. Under this operational condition,93.0%of CODcr,78.5%oftotal nitrogen and94.7%of ammonia were removed. The result showed that theoptimal sludge return ratio was4, and the highest total nitrogen removal efficiencywas gained at this operation. Experimental results also showed that comparableefficiencies of nitrification and denitrification could be achieved under the lowtemperature condition, suggesting that the lower impact of temperature on nitrogenremoval. Phosphorus removal could be enhanced via the combination of chemical andbiological means, which was realized by adding aluminium trichloride into the MBRreactor. The optimal addition was measured at20mg/L which could ensure theeffluent TP concentration to meet the1A discharge standard. During the two and half year’s operation, the average removal efficiencies of COD_Cr, TP and TN were reached93.4%,79.1%and93.9%, respectively, which implied that these removalperformances kept stably and meet the1A discharge standard.The results of membrane pollution control displayed that aeration strength couldobviously affect the degree of membrane pollution, and the optimal value was foundto be110¹20m³/（m²·h）. This study selected low concentration of sodiumhypochlorite to clean the membrane. When0.015MPa of pressure difference wasmeasured higher than the initial pressure differential, in situ chemical cleaning wasconducted probably once per three months. When the above two kinds of cleaningmethod could not reach the expected effect, a conversion elixir dipping was thenperformed approximately once per eight months. With increase of the operation, insitu chemical cleaning and conversion elixir dipping might be performed morefrequently.