| A stainless steel membrane bioreactor (MBR) with 0.2μm pore size was utilized to treat synthetic domestic wastewater at 25℃ and distillery wastewater at shifted temperature, respectively. During temperature shift, the temperature began with 30℃, then ascended with a 5℃ or a 10℃ gradient, and reached 80℃ at last. Removal performance of the MBR, main factors influencing membrane penetrability and methods to clean metallic membrane were investigated under mesophilic and thermophilic conditions. The feasibility for using stainless steel membrane in wastewater treatment was evaluated.For domestic wastewater treatment, metallic MBR had a high removal capacity. Temperature had an evident influence on chemical oxygen demand (COD) removal. Microbial lysis released soluble microbial products (SMP) and extracellular polymeric substances (EPS) into mixed liquids, hence increased effluent soluble COD (SCOD). However, effluent quality was comparatively stable, showing that the stainless steel membrane had an excellent retain capacity to suspended solids, colloid and soluble macromolecular compounds.Due to the existence of aerobic and anoxic circumstances, the conventional MBR could remove more than 30% TN through nitrification and denitrification. The inner cycling MBR did favor to the two kinds of circumstances, the upflow aerobic circumstance (nitrification) and the downflow anoxic circumstance (denitrification), enhancing the TN removal efficiency to about 50%. The component analysis of filter cake on membrane surface showed that metallic membrane played a very important role in TN removal by retaining macromolecular soluble and colloid compounds. TN removal capacity of MBR was more influenced by temperature than COD removal. Comparison of TN in supernatant and effluent showed that biological nitrogen removal was dominant under lower temperature (30℃), biological nitrogen removal was equivalent with membrane retain removal at 35℃, and membrane retain removal was dominant under thermophilic conditions (40-70℃).Decreased sludge specific oxygen uptake rate (SOUR) with temperature showed that metabolism of microbes was inhibited and substrate removal rate of activated sludge decreased. Also the sludge yield decreased with increased temperature, indicating that thermophilic MBR was favorable to sludge reducing. Diversity of microbial communitydecreased in thermophilic condition than mesophilic condition.There were close relations between properties of sludge and membrane fouling. Weaker sludge settleability, increased concentrations of EPS, suspended solids and free bacterias in sludge mixed liquids, smaller floe particle and bigger viscosity of mixed liquids at higher temperature caused more serious membrane fouling. Although there was no common change with sludge hydrophobicity, it was consistent with membrane fouling resistance, indicating that higher sludge hydrophobicity enhanced membrane fouling.Filter cake fouling was the main part of membrane fouling. The contribution of gel layer increased at higher temperature for higher concentration of polymeric substances (mainly EPS) in supernatant at higher temperature. And the contribution of suspended solids decreased.Properties of sludge were related to each other and their influence on membrane. The experiment results implied the importance of EPS and sludge particle size distribution, especially EPS. In thermophilic conditions with shifted temperature, constituents content in sludge liquids comparatively varied, causing greater influence on membrane fouling than in normal temperature.Inner cycling MBR could alleviate membrane fouling, induce higher membrane permeate flux and favor to energy saving. Membrane cleaning on line could greatly alleviate membrane fouling and lengthen membrane service time. There were much more cleaning agents for stainless steel than polymer membrane.In general, the wastewater treatment experiment results of the MBR with stainless steel membrane indicated that stainless steel membrane was more adaptive than organic membrane under critical conditions, such as high temperature and rigider need for effluent quality. Thermophilic MBR was favorable to reduce cost and energy of specific wastewater treatment and sludge reduction. There was a potential for thermophilic MBR to treat high temperature and high strength wastewater. However, membrane fouling was more severe and pollutants removal capability decreased in thermophilic conditions. Many factors need to be considered to determine proper operating conditions for practical application. The results of the paper suggested that temperature below 50°C was appropriate for thermophilic MBR running, considering both pollutant removal and membrane fouling.
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