Assessment Of Optimum Performance Of Membrane Bioreactor Applied To Municipal Wastewater Treatment

Membrane Bioreactor (MBR) is a new type of biological reactor that wastewater biological treatment technology and membrane separation technology have been combined together. MBR has the advantages of good effluent quality, easy to operate, reduced sludge production rate, small footprint and so on. The application range and scope of MBR are becoming greater and greater. However, our study is still in primary stage, in which the basic data of membrane module made in China applied to MBR is absent. Due to the experimental conditions, the results obtained were considerably different from real production. Membrane fouling and high cost is main factors that prevent MBR from applied further. In this paper, the operation parameter optimization was attempted and the long-term operation performance parameter system of membrane module was further consummated to give gist to technical design.Through collecting the daily operation data from startup from May 2006 to March 2007 the experimental operation procedure was summarized, the main pollutants removal effects of MBR treating municipal wastewater were analyzed, and the removal mechanism was also discussed. The pollutants removal efficiencies were shown as below. The influent COD (chemical oxygen demand)was221-139mg/L and the average was 169mg/L. The effluent COD average was 32.1mg/L and the average removal efficiency was 80.0%. The removal efficiencies of BOD(biochemical oxygen demand), LAS(Linear Alklybezene Sulfonates), NH3-N and so on were above 95%. The effluent turbidity was 0.20-0.16NTU and the average was 0.18NTU. The removal mechanism mostly lies on biochemical action, followed by physiochemical action of membrane. According to the analysis of orthogonal experiment,the effect of the effluent reached the optimal operating conditions.According to the analysis of orthogonal experiment, membrane fouling was accelerated with the increase of MLSS (Mixed Liquid Suspended Solid). Proper increase of suction time would not influence membrane fouling significantly, and under adequate pause time, the proper increase of suction time would raise effluent quantity to add operation benefit. Aeration increased MLSS circulation velocity, prevented pollutants from depositing on the membrane surface and contributed to the pollutants separation from membrane surface. Whereas, when aeration was further enhanced, the effect became not obvious. Furthermore, over-intense aeration would decrease mixed liquid granular diameter, influence membrane filtration, and then increase the ascend velocity of membrane suction pressure. Considering synthetically effluent quantity and long-term operation stability, the optimum operation conditions were determined as follow. MLSS concentration was 3500-5000, on/off ratio was 13:2, and air/water ratio was 30-35:1.