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Effects of sludge retention time on the sludge characteristics and membrane fouling in membrane bioreactor. |
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Abstract The effect of sludge retention time (SRT) on the total extracellular polymeric substances (EPS), contents of tightly bound EPS (TB), loosely bound EPS (LB) and the ratios of protein and polysaccharide in TB and LB was investigated. The total EPS increased and the ratios of protein and polysaccharide in TB and LB changed with the extension of SRT. The above changes influenced the distribution of surface charge of bacteria, increased the proportion of hydrophilicity and hydrophobicity on the surface of bacteria, transformed the existence state change of bacteria from the instable (R type) to the stable (S type), decreased the Zeta potential and increased the values of sludge volume index (SVI). The correlation analysis for the main parameters of fouling resistance displayed that the correlation coefficient (rp) was -0.818 for Zeta potential, 0.853 for the content of suspended solids in supernatant and 0.832 for relative hydrophobicity, respectively. SRT of the membrane bioreactor (MBR) should be controlled below 120 times of the minimum generation-time of dominant bacteria considering the membrane fouling resistance and sludge characteristics.
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Received: 04 September 2008
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