Correlation Of Extracellular Polymeric Substances And Properties Of Activated Sludge In Membrane Bioreactor

Membrane bioreactor (MBR) technology is a highly efficient combination of membrane separation with activated sludge process. Due to the complete cutoff of activated sludge, consequently increasing microbial concentration and decreasing surplus sludge, MBR becomes a relatively closed system to microorganisms. In the meantime, extracellular polymeric substances (EPS) generated going with that course also are cutoff and accumulated in MBR, which heavily affect sludge properties and the filtration of mixed liquid. In order to probe the correlation between EPS and sludge properties from different aspects and know its kenetic changes as well as the possibility of sludge granulation in MBR system, the following contents are investigated.(1) The influence of EPS accumulated in MBR during treating synthetic municipal wastewater on sludge properties was investigated. The results showed that EPS turned into accumulation period at 35 d of operation after experiencing a low vale. Accordingly, the specific substrate degraded rate of sludge and its SVI had changes. The increases in total content of system EPS and the ratio of proteins to polysaccharides improved both sludge activity and its settling ability. From another point of view, it was proved by more EPS existing in sludge, but not in supernatant, during EPS accumulation period.(2) Larger quantity of discharged sludge (295 g in this study) would result in bound EPS concentration presented a hump-shaped profile. The main reason was related to the F/M ratio. Larger quantity of discharged sludge had advantaged influence on the sludge properties. It can keep the SVI steady in the favorable range and affect the hydrophobicity of sludge indirectly through EPS. Larger quantity of discharged sludge did not have direct influence on the membrane fouling. Whereas, from the aspect of EPS attached to the membrane, it induced severe membrane fouling.(3) Simulating SBR technics completely in MBR, the sequential function was changed into intermission function. Through the compare between the two functions, the results showed that the intermission function had positive effect on settleability and hydrophobicity of sludge. This function reduced the accumulation of EPS, and this feast-amine pattern could hasten microorganism excreting and decomposing EPS periodically, accelerating growth balance of microorganism and aerobic biogranulation.(4) A dead-end filtration test was conducted, and the fouling characteristics on PVDF membrane of EPS were evaluated in this study. The EPS concentration had significant influence on relative flux. The relative flux was in the tendency to the attenuation along with filtration time, as with EPS concentration increased. The relative flux decreased more quickly at higher pressure, and cake resistance increased at high pressure.