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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: Four flat-sheet membrane modules, which were operated under four different filtration modes but with the same treatment capacity, were used to treat synthetic wastewater in a submerged membrane bioreactor (MBR). Particle size distribution (PSD), gel filtration chromatography (GFC), capillary suction time (CST), and three-dimensional excitation–emission matrix (EEM) fluorescence spectroscopy were used to characterize membrane fouling properties. The high instantaneous flux induced faster fouling rate and continuous filtration mode was the most applicable filtration mode in this study. The average particle size of all foulants was smaller than that of bulk sludge; and the higher the instantaneous flux was adopted, the larger the average particle size of foulants would be. Only macromolecule substances were detected in all the foulants. The macromolecule substances in the influent were degraded by microorganism and retained by membrane, and small molecular substances could pass through membrane pores to enter the effluent. The membrane foulants had poorer dewaterability compared to the mixed liquor confirmed by CST measurement. Although there were several peaks associated with protein-like fluorophores, fulvic acid-like substances and humic acid-like organics in soluble microbial products (SMP) and extracellular polymeric substances (EPS) sample, it was found that the dominant fluorescence substances in membrane foulants were protein-like substances. [ABSTRACT FROM AUTHOR]

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]