Notice of Retraction Study on Characteristics of Sludge Mixed Liquor and Microbial Population Succession in Membrane Bioreactor without Sludge Purge

This work reported the characteristics of sludge mixed liquor and microbial community succession in a membrane bioreactor (MBR) operated at a hydraulic retention time (HRT) of 6 h and without sludge purge. It showed that extracellular polymeric substances (EPS) were positively correlated with median diameter of sludge and with specific resistance of sludge; the correlation coefficients were 0.8457 and 0.6890 respectively; Zeta potential and the ratio of protein to polysaccharides in EPS were negatively correlated with a correlation coefficient of 0.8364; SVI value and Zeta potential were negatively correlated with a correlation coefficient of 0.9431. A cultivation-independent approach (polymerase chain reaction-temperature gradient gel electrophoresis, PCR-TGGE) was used to analyze the changes in the structure of the bacterial communities in the sludge. Unweighted pair-group method with arithmetic means (UPGMA) cluster analysis of TGGE profiles demonstrated significant differences in community structure related to run time. The operation period can be divided into three stages: inoculation period, acclimation period and stable period. The content of EPS first increased, then decreased and finally stablized with run time. The turning point of the concentration of EPS and the dividing point of the three periods inosculate with each other.