Study On The Optimum Operation Of Membrane Bioreactor Treating Domestic Wastewater

In this paper, the domestic wastewater was treated using the membrane bioreactor. Experiments were carried out to investigate the operation efficiency, optimize the operation condition. The kinetics equation of substrate degradation and sludge growth were constructed. Economic and technical analysis of membrane bioreactor were investigated.The start up of the membrane bioreactor could be finished in 7 days, when the operating conditions were: the influent flux 8.5L/d, the HRT 3.4h,the influent COD 161.8-210.8 mg/L, the volume loading 0.15-0.20kgCOD/(m3·d),the influent temperature 18.2-20.0℃. When the operating conditions was the influent COD 219.3-393.1 mg/L, the influent flux were increased gradually from 8.5L/d to 61.5L/d, the volume loading was increased from 0.23kgCOD/(m3·d) to 2.97kgCOD/(m3·d), the average COD removal efficiency was 93.7%.The change of volume loading and sludge loading had not obvious effect on COD removal rates. The impact loading were come into being due to change of influent quality in the 40st and the 49st days, volume loading rose to 3.68kgCOD/(m3·d), 4.46kgCOD/(m3·d), COD removal efficiency were 98.9%, 97.5%. The operation effect of membrane bioreactor were not influenced. During the course of all operation, sludge appearance has been changed, that color was changed from black to dust color and finally changed to snuff color, moreover, MLSS increase from 2212mg/L to 8926mg/L, whereas the ratio of MLVSS/MLSS was decreased. In the phases of steadily operation, the rotifer that belongs to metazoa was found in course of observed the microbe phase of sludge mixed liquid by microscope. Thus it can be seen that the membrane bioreactor had many outstanding advantages, such as shorter start up period, higher organic contamination removal rates, quicker change of volume loading, more stability operation, stronger anti- impact loading capability, and operation status of the membrane bioreactor were estimated by the means that the microbe phase of sludge mixed liquid were observed by microscope.Based on the investigation of the membrane bioreactor treating the domesticwastewater, the kinetics equation of substrate degradation and sludge growth were constructed, the expressions were as follows:The investigation of the optimum operation indicated that the best operation parameters were MLSS 5500 mg/L, HRT 3.4h,optimum time for sludge drainage 15 days.Economic and technical analysis on membrane bioreactor process indicated that technical and economical feasibility of membrane bioreactor process to treat domestic wastewater for reuse has been approved, the gross investment of the project was 259,000 yuan, that was equal to the biochemistry and physical chemistry process, but the operation cost was power, and could save 0.09 yuan per stere.