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Abstract: This paper examines the influence of activated sludge properties such as the mixed liquid of suspended solids (MLSS) concentration, sludge particle size distribution (PSD), extracellular polymeric substances (EPS), soluble microbial products (SMP), suspended solids in supernatant (SSs), dynamic viscosity (μ), relative hydrophobicity (RH), and zeta potential on membrane fouling. Activated sludge samples from different full-scale and lab-scale membrane bioreactor processes were used to study their impacts on membrane fouling. The influence of activated sludge properties on membrane permeation was identified with statistical methods. The results showed that MLSS concentration had an exponential relationship with membrane fouling resistance. The sludge particle size (r p =−0.730) was correlated inversely to the membrane fouling resistance significantly. The total EPS (r p =0.898) and protein (r p =0.810) had strong positive effect on membrane fouling resistance, but carbohydrate (r p =0.626) had a moderate correlation with membrane fouling resistance due to its low amounts. SMP (r p =0.757), SSs (r p =0.810), dynamic viscosity (r p =0.691), RH (r p =0.837), and zeta potential (r p =−0.881) also had significant influence on membrane permeability. However, protein (r p =0.936), SMP (r p =0.725), SSs (r p =0.783), dynamic viscosity (r p =0.633), RH (r p =0.877), and zeta potential (r p =−0.953) mainly resulted from the change of EPS concentration. These results confirm that MLSS concentration, PSD and EPS were the predominant factors affecting membrane fouling during membrane filtration of sludge suspension. The membrane fouling resistance can be predicted using a simple model based on MLSS concentration, PSD and EPS. [Copyright &y& Elsevier]

Abstract: A calefactive aerobic membrane bioreactor (MBR) equipped with a stainless steel membrane, 0.2 μm pore size, was used to treat simulated distillery wastewater of about 1000 mg·L−1 COD at 30–45°C (changed with a 5°C gradient). The activated sludge settleability, performance of the metallic MBR and membrane fouling were investigated in terms of short-term activities for about 10 days at each temperature. Sludge settleability became poorer with increasing temperature. The increase of sludge SVI with increasing temperature was probably mainly affected by increased EPS in the solution, thereby causing increased solution viscosity. With a HRT of 10–30 h and a VLR of 0.6–2.8 kgCOD·m−3·h−1, mean COD and TN removal efficiencies were 94.7% and 84.4%, respectively. Although SCOD and STN in supernatant increased with temperature, the permeate quality was steady, indicating that the metallic membrane had excellent retention for soluble organic compounds and suspended solids. Temperature had a significant effect on denitrification of the MBR. Low initial permeate flux was favorable to maintaining long-term stable flux. Without regard to its cost, a heat-durable metallic membrane was more suitable for wastewater treatment under higher temperature conditions than a polymer membrane. [Copyright &y& Elsevier]

Abstract: Membrane fouling is the major problem that hinders the practical application of membrane bioreactor (MBR) systems. Since the MBR system includes living microorganisms and their metabolites, the fouling mechanism is even more complex than that of conventional membrane separation processes. This paper provides an improved understanding of the influence of filamentous bacteria on membrane fouling in microfiltration of activated sludge wastewater. In order to make clear the membrane fouling mechanism of filamentous bacteria, the physicochemical characteristics of sludge flocs, including extracellular polymeric substance (EPS), zeta potential, relative hydrophobicity (RH) and floc morphology were systematically investigated. The results showed that the sludge flocs with negligible filamentous bacteria led to severe membrane pore blocking, and the sludge flocs with filamentous bacteria created the formation of a non-porous cake layer on the membrane surface. The excess growth of filamentous bacteria resulted in much more release of EPS, lower zeta potential, higher hydrophobicity of sludge flocs and more irregularly shaped flocs, which did great harm to membrane filtration. The sludge flocs with a small quantity of filamentous bacteria had a positive effect on membrane permeation. It is important to control filamentous bacteria concentration in the operation of MBRs. [Copyright &y& Elsevier]

Abstract: Cake layer formed on membrane surface presents a major challenge to membrane permeation, and it can be considered as a porous media. Determination of the cake layer permeability is critical for an accurate analysis and design of membrane filtration. A permeation model, based on fractal theory and Darcy''s law, for evaluating cake layer permeability in microfiltration of activated sludge wastewater was developed. The cake layer permeability was derived and found to be a function of the pore-area fractal dimension and microstructural parameters. The validity of the model was studied systematically in this paper. The permeation model was applied to study the effect of mixed liquid suspended solids (MLSS) concentration, particle size distribution (PSD) and extracelluler polymeric substance (EPS) on cake layer permeability in a submerged membrane bioreactor. Results showed that the permeation model was a useful tool to study the micromechanism of membrane fouling. There was a close correlation between MLSS concentration and cake layer permeability. There were a slight and a distinct decrease of the cake layer permeation as MLSS increased less and larger than 10,000mg/L, respectively. PSD and EPS are two significant factors affecting cake layer permeability in membrane bioreactor. Effect of activated sludge on cake layer permeability was mainly caused by EPS and small particles attached on membrane surface. [Copyright &y& Elsevier]

Abstract: A novel stainless steel membrane module with a 0.2 μm nominal pore diameter was applied in an aerated submerged membrane bioreactor to treat synthetic domestic sewage. The pore size of metal membrane was more homogeneous and of tighter distribution than that of organic membrane. The steady membrane flux was more than 17 Lm−2h−1. The mean COD removal efficiency achieved 97.0%. The mean NO− 3-N/TN ratio was 74.6% in effluent. There was a certain positive correlation between membrane fouling and extraceller polymeric substances of activated sludge solution. Membrane fouling could be effectively alleviated by the on-line backwash and intermittent running mode. In addition, membrane fouling could be eliminated almost entirely by off-line cleaning with 0.25% (wt) NaClO solution with pH 12. After off-line cleaning, membrane flux could be recovered by about 93.3%. These results implied that it was economical for using the stainless steel membrane in a membrane bioreactor for wastewater treatment. [Copyright &y& Elsevier]