Optimization of operational factors of a membrane bioreactor with gravity drain.

A new membrane bioreactor with gravity drain for municipal wastewater treatment was tested and its operational factors were investigated in this study. These factors include pressure head, MLSS, aeration intensity (an air flow rate per unit floor area) and temperature. Results of batch experiments showed that a critical pressure head of the MBR was 0.85-1.5 m-H2O. At a pressure head of 0.85 m-H2O, statistical analysis of batch experiments showed that aeration intensity significantly affected membrane flux, and the MLSS had no impact on membrane flux under a temperature of 22.0 +/- 1.0 degrees C. Results of the long-term continuous experiment showed that temperature significantly affected membrane flux. The impact of temperature on membrane flux in this case was about 4-10 times of that analyzed by using a classical cake layer model. During this experiment, the average removal efficiencies of COD, BOD5 and NH4+-N were over 85%, 97% and 94%, respectively.