Impact Of Flocculants On Physical And Chemical Propertied Of The Activated Sludge In MBR

MBR(membrane bioreactor) is an efficient water treatment technology, with the advantages of highly remove efficiency, stable water quality, easily management and low area. However, the increased operating costs and inconvenience due to the membrane fouling , is the key issue of restricting the wide application of MBR. The key of MBR technology is the methods of delaying membrane fouling, fast recovery method of flux, according to the causes of membrane fouling. In order to reduce the pollution load of the membrane fouling rate, flocculant can artificially improve quality of the activated sludge, remove suspended particles, organic and inorganic colloids, inorganic salts in the solution. However, the current research lack comparative studies of different types of flocculants on membrane fouling, but also lack investigations of activated sludge flocculation from the physical and chemical properties. In order to explore what kind of coagulant is more applicable on membrane fouling mitigation, and how is the mechanism of flocculation. Impact of three types of flocculants(FeCl3, PAC, Chitosan) on physical and chemical properties of activated sludge in MBR was tested.The results showed that sludge dewatering performance was highly improved, specific resistance of sludge could be reduced by 80%, when the PAC dosage is 300mg/L. The dewatering performance of Chitosan and FeCl3 on activated sludge is smaller than the PAC. The specific resistance of sludge is stable when the dose of the Chitosan is 100mg/L. The specific resistance of sludge is between Chitosan and the PAC when the dosage of FeCl3 was 100mg/L, and it has a gradually increasing tread with the increase of the dosage. Therefore, the dosage of the Chitosan and FeCl3 is 100mg/L. The results also revealed that three kinds of flocculants had significant effects on the properties of activated sludge, PAC is the most suitable coagulant to avoid membrane blocking.When PAC was using, specific resistance of sludge could be reduced by 80%, the average diameter of sludge floc increased by 53%, supernatant TOC concentration decreased by 63%, and EPS increased slowly, which illustrated that PAC had a significant impact on the physical and chemical properties of the activated sludge, the use of PAC in MBR could be help for reducing the membrane fouling. Membrane cleaning showed that water cleaning is an effective cleaning method, but soak in the chemicals does not work, in the 1-4 times of membrane cleaning. The recovery rate of the membrane flux is above 80%, with increasing the concentration of NaClO to 0.02%, the concentration of H2SO4 to 0.5%, and extending the time of incubation to 1h. Therefore, the result of cleaning is good, which can get a better control of membrane fouling, when the combining methods of water flushing and chemical cleaning are applied.