A Study On Hybrid Membrane Bioreactor Process For Municipal Wastewater Treatment

Based on its characteristics, municipal wastewater is treated by hybrid membrane bioreactor, a pilot-scale device. Hybrid membrane bioreactor process combines both suspended growth activated sludge process and attached grow biofilm process in one bioreactor by adding suspended carriers into conventional activated sludge reactor, and sets a submerged MF membrane in the bioreactor for solid/liquid separation.The comparison between hybrid membrane bioreactor and activated sludge reactor on efficiency of treating municipal wastewater was made, and the factors affecting membrane fouling were studied. Then the following conclusions can be drawn:The study on membrane bioreactor (MBR) for municipal wastewater treatment indicates: in MBR filtrate, SS is very low, average turbidity is about 0.58NTU, average color is about 25.5 c.u.; average contaminant concentrations: COD=27.35mg/L, BOD₅=5mg/L, NH₃-N=0.65mg/L, TN=14.76mg/L, TP=2.69mg/L and the average removal rates are 94%, 98.53%, 98%, 61.78% and 77.7%, respectively; moreover, considering the retention ability of MF membrane, the filtrate quality can completely meet the secondary level of national integrated wastewater discharge standard.The experiment on the hybrid membrane bioreactor (HMBR) for municipal wastewater treatment was conducted in Xi'an Beishiqiao Wastewater Purification Center. The experiment indicates: under the condition of 45% carrier addition, the average concentration of HMBR system effluent is COD=31.32mg/L, NH₃-N=11.47mg/L, TN=29.32mg/L, TP=4.38mg/L and the average removal rate is 93.36%, 70.79%, 38.7% and 59.17%, respectively. The effect of removing NH₃-N, TN and TP is relatively better as well, but because of the short start-up time, membrane growth is not mature enough. As the operation time increases, the effect enhancesgreatly, which indicates obvious advantages. The study of impacts of operation conditions on membrane fouling indicates: the impact of aeration intensity on membrane fouling is comparatively low; membrane fouling rate increases along with the decrease of run/off time, which indicates that intermittent penetration mode can effectively decrease filtration resistance, retard membrane fouling; extending run/off time excessively dose not have an obvious effects on restraining the decrease of membrane flux; flux value has an obvious linear relation with the change of TMP.The preliminary study of impacts of adding coagulants on HMBR membrane fouling indicates that adding coagulant PAM can effectively reduce membrane fouling. The impacts of adding coagulants on membrane fouling control should be studied further in the future.