Variations Of The Active Characteristics Of Sludge During The Operation Of An Aerobic Membrane Bioreactor And Their Effects On Membrane Fouling

With the increasing sewage water in Chinese urban area,the conventional activated sludge process find it difficult to meet the requirements of the increasingly strict discharge standards. With this in mind, the developing of new technology of wastewater treatment and improvement of traditional process is the future of the wastewater treatment industry. As a highly effective wastewater treatment process, membrane bioreactor (MBR) has been study intensively in the last few decades. Solid liquid separation is conduct with the remaining effect of the membrane module instead of the secondary sedimentation tank in conventional activated sludge process. Compared with the conventional activated sludge process, membrane bioreactor is famous for its small footprint, high quality of effluent and independence of hydraulic residence time and sludge retention time. Still, membrane fouling is the main limit fact that prevents membrane bioreactor for wider application. Studies on membrane fouling have lasted for decades. Mechanism of membrane fouling has not yet been fully understood. Solution to solve membrane fouling still to be drew. By far, a lot of researches have been conducted on how to retard the membrane fouling. The outcomes are so far so good, together they greatly prolong the lifetime of the membrane modules.The first series ofworkinvestigated the variations of the active characteristics of sludge during the operation period of an aeration membrane bioreactor, as well as their effects on the fouling of membrane module. Through discharging the excess sludge, the concentration of the mixed liquor was maintained at around4000g/L for75days, during which the characteristics of sludge were carefully tested every day to reflect its variation. Results indicated the dehydrogenase activity increased as the prolonging of operation time.The increased activity of dehydrogenase had two effects on the operation of the bioreactor, one was the enhancing of the microorganisms to remove pollutants,while the other effect wasthe increasement ofextracellular polymeric substance (EPS), which led to a deteriorative effect on the membrane fouling. As the operation of the bioreactor, the sludge yield coefficient increased first, and then it decreased to a certain degree with obvious decreasing in particle size and increasing in the amount of EPS, which also enhanced the quality of the effluent. At the same time, protozoon and metazoan were observed in the whole bioreactor at the later operational phase but relatively rare at the initial phase. On the basis of analyzing to the membrane fouling, the results showed that the fouling rate of the membrane module increased during the later operational period, which was attributed to the deposition of fine sludge particles and EPS led by the decreasing particle size of the sludge and the increasing amount of EPS. The second series focus on an internal circulation MBR treating synthetic wastewater. With100day operation, the MLSS grew from4000mg/L to more than14000mg/L. In one reactor combining aerobic circumstance and anaerobic circumstance was fulfilled.TMP jump only occurred in low flux operation. This phenomenon can be attributed to the different structure property of the formed cake layer under different applied suction force.