The Influence Of Adding PAC And Fecl₃ To The Performance Of A/O-MBR

Membrance fouling control is a hot issue in the research of membrane bioreactor. In the experiment, coagulant is added to the mixed liquor of A/O-MBR for enhancing the membrane filterability and controlling membrane fouling in order to reduce membrane pollution. Firstly, different comparative experiments proceed by adding powdered activated carbon (PAC) and ferric chloride (FeCl₃). Secondly, after adding the coagulant the water quality of effluent and membrane fouling parameters are analyzed. Finally, the best concentration of each coagulant which adds into A/O-MBR is used and the system is operated under such condition for a long-term. The conclusions are following:These two kinds of coagulants have similar results on water treatment effect, concentration of EPS and status of membrane fouling. Coagulants have great impact on improving the characters of sludge mixture in the reactor, but the impact of the effluent is not so obviously. The change of transmembrane pressure (TMP) indicats that the right amount of coagulant can slow the growth of membrane differential pressure. After analyzing the composition and concentration of EPS, it is known that the contents of polysaccharide in EPS have relationship with the change of TMP obviously. The filterability of the sludge mixture can be improved by adding PAC or FeCl₃ respectively at the concentration of 2 g/L and 40 mg/L.Great changes of the quality of mixture have been detected when the system added the best concentration of coagulant operats for a long time. The results show that the concentration of CODcr,TP,NH₃-N and TN decrease evidently, but the effluent qualities don't change obviously.Adding coagulant can increase the sludge concentration, the effective is very obvious for FeCl₃. From the microscopic results we can see that the floc structure of the sludge by adding FeCl₃ is better than that of the reactor with no coagulant or adding PAC. It is also one of the reasons which slow the reactor's pollution by adding FeCl₃. The dehydrogenase activity does not change greatly in the reactor adds PAC, but the dehydrogenase activity increases in the reactor adds FeCl₃. Iron can improve the dehydrogenase activity, and it also can improve the microbial activity in the reactor and increase the degradation rate of the organic matter in the sewage water. Through the trend of TMP, it can reduce the rate of membrane fouling obviously by adding the coagulant of PAC or FeCl₃ obviously and improve the antidirty ability of the reactor. At the same time results show that the concentrates of EPS and polysaccharide have reduced significantly, these can enlarge the sludge particles and reduce the membrane fouling. After the experiment, membrane was cleaned. The membrane flux returns to 94.2% after hydraulic cleaning and 100% after chemical cleaning.