Using Filamentous Bacteria And Membrane Sepration Technology To Treating Domestic Wastewater

Activated sludge process is effetive and promising wastewater treating technology. However, no matter which improved activated sludge process, sludge bulking is one of the main problems hard to be solved .Now, thanks to the development of membrane separation technology, sludge bulking problem has been satisfactorily resolvedThe purpose of this study is to investigate the removal reaction of the reactor for the COD and NH3-N and other pollutants, to investigate the process and characters of sludge bulking, as well as the impact of membrane fouling under different conditions when the membrane bioreactor occurs sludge bulking. Based on the experimental results, looking for the optimized operating conditions in the different circumstances of sludge bulking.The submerged membrane - bioreactor of this study is the long rectangular plexiglass container and using a perforated pipe to aeration at the bottom of the reactor, which is equipped with hollow fiber membrane module above. Through aeration, one hand the activated sludge mixture in the membrane - bioreactor can maintain certain circulation speed in order to reduce the deposition of the activated sludge on the surface of the membrane,on the other hand,it can supply the needed oxygen in the process of microbial decomposition of organic sewage . Raw water enters into the reactor from the top of the reactor and is extracted through membrane filtration by the suction after treated adequately.The main conclusions are shown as follows:1.Activated sludge occurs sludge bulking easily under low load . In this experiment, when the load reachs 0.05 kgCOD / kgMLSS·d, sludge bulking happen.2.When the sludge load is higher (this experiment is 0.40 kgCOD / kgMLSS·d) and N,P is an extreme shortage , sludge bulking can happen. In the testing process, the function of membrane separation employs the interception of nitrifying bacteria that grows slowly in the large number, so that the membrane bioreactor has high removal rate for NH₃-N.3.When the sludge load is higher (this experiment is 0.40 kgCOD / kgMLSS·d) and the DO concentration is lower, DO often becomes the restriction factor for the growth of bacteria micelles and filamentous bacteria multiply, forming low-DO expansion.4.Low pH is an important reason that caused sludge bulking.Generally,when the pH of the reactor is 6.5 to 8.0, the sludge has good settlemen performance.when the pH is below 6.0, filamentous bacteria will be turned into advantaged genus. In this experiment when the pH reduce to 4.0, sludge bulking occurred.5.Filamentous bacteria proliferation is the root cause that induces sludge bulking. Under the conditions of the low load, nutrient imbalances, low DO, and low PH, filamentous bacteria has advantages in the competition with the micelle, activated sludge process will provide for the filamentous bacteria favourable environment in any of these conditions so that filamentous bacteria proliferates arising sludge bulking.6. Along with the occurrence of sludge bulking,massive filamentous bacteria grow, extending its interwoven filaments and creating the flocculationa that has network structure. In the process of sludge sedimentation, the flocculationa play a filtering role for the rising water,adsorbing and intercepting small particles and bacteria in the sewage, therefore, in the testing process, the supernatant liquid is clarified, filamentous bacteria has efficient removal rate for pollutants. After sludge bulking, system COD removal rate still maintains a relatively high level, on the one hand because of the biodegrading role of filamentous bacteria, on the other hand because of the solid-liquid separation role of the membrane. So the membrane has a role of polluting substances interception ,to a certain extent the membrane maintains the stability of the system and reduces the suspended solids concentration, improves effluent quality. 7.With the extension of operation, H shows increasing trend, needing for greater pressure to meet flux requirements. Under normal circumstances, in the start-up phase membrane fouling is slowly, in the stable operational phase membrane fouling is faster. This is because of that in the stable operational phase a large number of filamentous bacteria grow, the result indirectly reflects the degree of membrane fouling during the sludge bulking and shows that filamentous bacteriathat have greater influence for membrane fouling,which is caused by large surface and the physiological and biochemical characteristic that secreting mucus of filamentous bacteria.