| The shortage of water resources in China is serious problems that have been limiting the development of industry and agriculture. Wastewater reclamation is an important solution of water conservation and sewage treatment. MBR Tech. uses a membrane separation unit to replace a secondary clarifier of an activated sludge process. It is a combination of membrane separation technology and the tradition activated sludge process. It has been widely used in wastewater treatment and reclamation for its innovated efficiency. MBR uses microfiltration membranes to keep the activated sludge in the tank. This leads to an effective separation of bacteria and treated water, a high microbial concentration in the reactor and less sludge production. However,membrane fouling causes declining permeate flux and increasing operation costs which limits the wide application of MBR. The objectives of this study are to investigate the sludge characteristics and their influence on membrane filtration in submerged membrane bioreactor(MBR)at various gas-water ratio. Three lab-scale submerged MBRs with hollow fiber microfiltration membranes are performed under a constant permeate flux of 2 L/h and gas-water ratio of 20:1,40:1,80:1,respectively. In order to evaluate the contribution of the sludge to the membrane fouling,the sludge is performed at dead-end filtration and cross flow filtration, respectively. Experimental results show that the sludge filtration characteristics are degraded in the MBR as increasing of gas-water ratio. The total amount of extracellular polymeric substances(EPS)is an important key to membrane fouling, it has a good correlativity to sludge settleability. High-concentration EPS is accumulated in the aeration tank, which causes non-filamentous bulking. Non-filamentous bulking affected filtration characteristics of the mixed liquor. When the non-filamentous bulking happened, the filtration resistance was significantly increased. The amount of EPS attached on the membrane changed with the suspended EPS concentration in tank. Both the amount of EPS in MBR and the filtration resistance will be decreased during periodic sludge discharge. The quantitative relationship between the amount of EPS attached on the membrane and filtration resistance is R=7×105×Pv3.3385, and suspended EPS concentration in tank and filtration resistance is R=3.1525×1013×Pu-2.201×1012. Most of soluble microbial products(SMP) having generated in microbial endogenous growth can be accumulated in the bioreactor. SMP has a good correlativity to filtration resistance. Quantitative relationship between SMP and filtration resistance is R=1.76×1012(TOC)0.1914 . The test on resistance distribution shows the SMP is the main source of gelatinoids filtration resistance.
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