Aquatic environment

Mechanism of calcium mitigating membrane fouling in submerged membranebioreactors

ZHANG Hanmin , XIA Jie , YANG Yang , WANG Zixing , YANG Fenglin


Received September 18, 2008,Revised December 29, 2008, Accepted , Available online

Volume 21,2009,Pages 1066-1073

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Two parallel membrane bioreactors (MBRs) were operated under di erent calcium dosages (168.5, 27 mg/L) to gain a better understanding of the mechanism of retarding membrane fouling by adding calcium. The results showed that the particle size of sludge flocs increased and the particle size distribution tended to be narrow at the optimum dosage (168.5 mg/L). Calcium was e ective in decreasing loosely bound extracellular polymeric substances (LB-EPS) in microbial flocs and soluble microbial products (SMP) in the supernatant at the dosage of 168.5 mg/L by strengthening the neutralization and bridging of EPS with flocs. Furthermore, the amount of CODS and CODC decreased in both the mixed liquor and the fouling cake layer on the membrane surface. In order to compare the filtration characteristics of cake layers from the MBRs with the two calcium dosages, the specific cake resistance and the compressibility coe cient were measured. The specific cake resistance from the MBR with optimum dosage (168.5 mg/L) was distinctly lower than that with low dosage (27 mg/L). The compressibility coe cient of the cake layers under two dosages were respectively attained as 0.65, 0.91. Scanning electron microscopy (SEM) and three-dimensional confocal scanning laser microscope analysis (CLSM) images were utilized to observe the gel layer directly.

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