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Abstract: A new pathway was explored in order to gain insights into the role of biopolymers in sludge characteristics and membrane fouling. The biopolymers were discharged from a membrane bioreactor (MBR) using a unique design (called as dual-MBR in this study). The variations of soluble microbial products (SMP), extracellular polymeric substances (EPS), sludge surface charge, particle size and dewaterability were analyzed in the dual-MBR after the discharging of biopolymers from the system. It was found that carbohydrates in SMP, proteins in SMP and humics in SMP were decreased in the dual-MBR compared to the control-MBR. Gel filtration chromatography (GFC) analysis showed that the substances with macromolecular weight in SMP were reduced in the dual-MBR. Three-dimensional excitation–emission matrix (EEM) fluorescence spectra demonstrated that the aromatic protein-like substances in SMP were also lowered in the dual-MBR. The neutral hydrophilic (HPI-N) fraction in SMP, which was found to have larger molecular weight distribution and stronger fouling potential compared to the rest fractions, was significantly reduced in the dual-MBR. The exclusion of biopolymers from the dual-MBR also resulted in the decrease of the bound EPS and the reduction of proteins in bound EPS, which consequently caused the decrease of sludge surface charge, the increase of sludge flocs and the improvement of sludge dewaterability. The above changes induced by the exclusion of biopolymers can explain why the trans-membrane pressure in the dual-MBR exhibited a slower increase rate compared to the control-MBR. This study offered an evaluation of the contribution of biopolymers to sludge characteristics and membrane fouling through a different angle from previous publications. [Copyright &y& Elsevier]

Abstract: Traditionally, the chemical cleaning is unanimously considered to be an effective means to restore membrane permeability. However, the chemical solutions can also be responsible for changes in membrane properties and thus affect the life-span of membranes. The aim of this study was to gain a better understanding of the effect of sodium hypochlorite cleaning solutions on the changes of physiochemical characteristics of microfiltration (MF) flat sheet membranes made from polyvinylidene fluoride (PVDF). A pilot-scale MBR was operated for 63 d and frequent and high dose sodium hypochlorite cleaning was carried out. The properties of the original and cleaned membranes were compared by pure water flux evaluation, contact angle measurement, mechanical testing, and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra analysis. Effective removal of the foulant from the membrane surface resulted in more severe fouling. The pure water flux decayed faster with the extension of operation time and the membrane became more and more hydrophilic. The deterioration of ultimate tensile strength and the improvement of the ultimate elongation of membranes showed that membrane became more weak and flexible after hypochlorite cleaning. The results of ATR-FTIR indicated that the sodium hypochlorite cleaning had no vital damage to the chemical structure of PVDF membrane, but exerted impacts on its surface properties. [ABSTRACT FROM AUTHOR]

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]

Abstract: Membrane foulants were systematically characterized in an anaerobic membrane bioreactor (AnMBR), in which non-woven fabric was used as the membrane material. In this study, three-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy, gel filtration chromatography (GFC), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM) and energy-diffusive X-ray (EDX) analyzer were used to analyze the membrane foulants. The results indicated that the organic substances with fluorescence characteristics in the extracellular polymeric substances (EPS) extracted from the membrane foulants were identified as proteins and visible humic acid-like substances by EEM technology. The GFC analysis exhibited that the EPS had much broader distributions of molecular weight (MW) and a larger weight-average molecular weight (M w) compared with the influent wastewater and the effluent. Proteins and clay materials were also identified in the fouling layer by the FT-IR analysis. The examination by EDX demonstrated that Mg, Al, Ca, Si, and Fe were the major inorganic elements in the fouling cake. Furthermore, the results suggested that bridging between deposited biopolymers and inorganic compounds could enhance the compactness of fouling layer. During the operation of AnMBR, the protein-like and visible humic acid-like substances, which were main components of the organic matters with fluorescence characteristics in the influent, were partly removed. And the large MW organics (>4000Da) in the influent were partly metabolized into low MW organics by microorganisms combined with the separation function of the cake layer and the membrane pores. [Copyright &y& Elsevier]