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Abstract: A pilot-scale submerged membrane bioreactor (MBR) for the treatment of real municipal wastewater was operated in this study under various sludge retention time (SRT) in order to verify the correlations of fluorescent dissolved organic matter (DOM) with membrane fouling. The fluorescent DOM determined by three-dimensional excitation–emission matrix (EEM) fluorescence spectroscopy and the trans-membrane pressure (TMP) under different SRT operation were investigated, and the correlations between them were analyzed. The results showed that the variations of fluorescent DOM (Peaks B and C) in the sludge supernatants correlated well with the variations of EEM spectra signal of bound extracellular polymeric substances (EPS) even though they were different in nature, i.e., the bound EPS were found to be more non-biodegradable than DOM. The fluorescent intensity (FI) variations of Peaks A and B in the EEM spectra of DOM were closely related to the TMP increase rate (membrane fouling) in the MBR, suggesting that they might be used to monitor the DOM variations and to indicate MBR performance. Through the EEM spectra analysis, it was confirmed in this work that the DOM in the sludge supernatants was not only originated from the bound EPS but also from the influent wastewater. [Copyright &y& Elsevier]

Abstract: Two identical submerged membrane bioreactors (MBRs) for synthetic wastewater treatment were operated in parallel under different dissolved oxygen (DO) levels for over 3 months in this study. The digital biological microscopy, particle size distribution (PSD) analysis, gel filtration chromatography (GFC), three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy, and column chromatographic method, etc. were used to identify the difference between bulking sludge (BS) caused by filamentous bacteria (low DO operation, about 0.4mg/L) and normal sludge (NS) (high DO operation, about 4.0mg/L) and to obtain a comprehensive insight into the behaviours of filamentous bacteria in MBRs. Test results showed that the MBR with bulking sludge (BS-MBR) exhibited a better filtration performance and a reduced membrane fouling compared to the MBR with normal sludge (NS-MBR). It was found that the mitigation of membrane fouling by the abundant filamentous bacteria in the BS-MBR could be attributed to the larger PSD, lower hydrophobic contents in SMP, and the retention effects of a special fouling layer induced by filamentous bacteria. [Copyright &y& Elsevier]