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Widespread applications of membrane technology call for the development of antifouling membranes, and preparation of mixed matrix membranes (MMMs) by mixing nanoparticles (NPs) into polymeric membrane matrix has attracted much attention. In this work, polyvinylidene fluoride (PVDF) MMMs were prepared by two TiO 2 sols with different NPs size (one from hydrolysis and condensation with an average size of 5 nm, and the other from dispersion of TiO 2 nanoparticles with a particle size of 21 nm), and comparison of their antifouling behaviours was conducted. Compared to the pristine PVDF membrane (N0) and membrane (N1) modified by TiO 2 sol from dispersion of TiO 2 NPs, the surface pore size, porosity and permeability of modified membrane (N2) by TiO 2 sol from hydrolysis and condensation were slightly decreased, while the hydrophilicity and the absolute value of Zeta potential were obviously improved. Moreover, the N2 membrane showed a higher surface energy barrier, smaller frequency shift in quartz crystal microbalance with dissipation monitoring, and higher relative flux than N1, indicating a better antifouling performance. The abundant hydroxyl groups and the increased Ti and O elements on the membrane surface accounted for the enhanced hydrophilicity and antifouling ability. Scanning electron microscope (SEM) images clearly show that TiO 2 particles were uniformly distributed for N2; however, the severe agglomeration and sedimentation were observed for N1. Multiple light scattering spectroscopy (MLiSSP) analysis showed that N2 casting solution had a higher stability as revealed by the negligible backscattering change, decreased demixing thickness and low turbiscan stability index (TSI) value. The different stability of casting solutions might result in the different NPs’ behaviours during membrane formation process, accounting for the discrepancy in the physicochemical properties and antifouling ability between N1 and N2 membranes. [ABSTRACT FROM AUTHOR]

Biofouling is one of the major obstacles to the widespread application of membrane technology in water and wastewater treatment, and use of anti-biofouling membrane materials is an effective approach to suppress biofouling. In this study, anti-biofouling polyvinylidene fluoride (PVDF) membranes were prepared by blending quaternary ammonium compound (QAC). Effects of QAC dosages on the physicochemical properties and anti-biofouling behaviours of the modified membranes were systematically investigated. The results showed that QAC was successfully present on the membrane surfaces, as revealed by X-ray photoelectron spectroscopy, Zeta potential and contact angle analyses. Anti-fouling tests using individual organic model foulants showed that the modified membranes had higher membrane fouling rate against organic matters, which is consistent with the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory. In contrast, the modified membranes demonstrated evident anti-bacterial behaviours when individual model bacteria were used, which cannot be evaluated by this theory. Interestingly, the modified membrane showed a clear anti-fouling activity in a membrane bioreactor (the sludge mixture contained both organic foulant and microorganisms), suggesting its concurrent efficiency in controlling fouling induced by both organic matters and bacteria. This might be attributed to the contact-killing effects of QAC and the dual interactions between bacteria and organic foulants in the mixed liquor of membrane bioreactor. The study offers an effective way to enhance membrane anti-biofouling ability through the addition of antibacterial agent QAC. [ABSTRACT FROM AUTHOR]

Metagenomic sequencing was used to investigate the microbial structures, functional potentials, and biofouling-related genes in a membrane bioreactor (MBR). The results showed that the microbial community in the MBR was highly diverse. Notably, function analysis of the dominant genera indicated that common genes from different phylotypes were identified for important functional potentials with the observation of variation of abundances of genes in a certain taxon (e.g., Dechloromonas). Despite maintaining similar metabolic functional potentials with a parallel full-scale conventional activated sludge (CAS) system due to treating the identical wastewater, the MBR had more abundant nitrification-related bacteria and coding genes of ammonia monooxygenase, which could well explain its excellent ammonia removal in the low-temperature period. Furthermore, according to quantification of the genes involved in exopolysaccharide and extracellular polymeric substance (EPS) protein metabolism, the MBR did not show a much different potential in producing EPS compared to the CAS system, and bacteria from the membrane biofilm had lower abundances of genes associated with EPS biosynthesis and transport compared to the activated sludge in the MBR. [ABSTRACT FROM AUTHOR]

Titanium dioxide (TiO 2 ) nanoparticles/polyethylene glycol (PEG) mixture was used to modify polyvinylidene fluoride (PVDF) membranes aiming to improve their antifouling ability. The use of PEG could improve the dispersion of nanoparticles thanks to steric hindrance effects. Test results showed that compared to the original PVDF membrane, the modified membranes had higher hydrophilicity and lower negative Zeta potential, facilitating membrane fouling control. The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) analysis indicated that the addition of TiO 2 nanoparticles improved their electron donor monopolarity, i.e., enhanced electron-donating ability. The interaction energy barrier between soluble microbial products (SMP) and membrane surfaces was also improved, indicating that anti-fouling ability of the modified membrane was elevated. The optimal dosage of nano-TiO 2 was found to be 0.15%, and further increase of dosage resulted in the aggregation of nanoparticles which consequently impaired the modification efficiency. Quartz crystal microbalance with dissipation (QCM-D) monitoring and SMP filtration tests confirmed the antifouling ability of the modified membrane. [ABSTRACT FROM AUTHOR]

Abstract: In membrane bioreactors (MBRs), soluble microbial products (SMPs) are a key factor in membrane fouling. In this study, the production, characteristics, and fouling potential of SMPs in the presence of zinc oxide (ZnO) nanoparticles (NPs) were investigated in order to clarify the impact of environmental nanoparticle pollutants (ENPs) on SMP behavior in MBRs. Batch tests showed that the SMP production was elevated as both NP concentration and exposure time increased. It was also found that the increase of SMPs was mainly due to the enhanced production of biomass-associated products (BAPs). Further examination of bound extracellular polymeric substances (EPS) demonstrated that the release of intracellular polymeric substances (IPS) occurred, which subsequently caused the production of BAPs in the presence of NPs. Chemical analysis and Fourier transform infrared (FTIR) spectroscopy confirmed the increased production of polysaccharides and proteins of SMPs while no significant changes were observed in EPS concentration and composition. Quartz crystal microbalance with dissipation monitoring (QCM-D) analysis indicated that the increase of adsorption abilities was attributed to the elevation of SMP concentration in presence of ZnO NPs rather than the change of fluidity. Filtration tests showed that membrane fouling worsened with elevated SMP and NP concentrations. Scanning electron microscopy (SEM) demonstrated that a slime gel layer with NPs scattered within was formed on membrane surfaces in high NP concentrations. Energy dispersive X-ray (EDX) microanalysis and X-ray mapping (XRM) indicated that more NPs were present during membrane surface fouling when ZnO concentrations were increased. The escalation of membrane fouling may not only be due to elevated SMP concentration under the presence of ZnO NPs, but also be due to the complex interactions with SMPs and subsequent NP aggregation in organic matters to form a dense fouling layer on membrane surfaces. [Copyright &y& Elsevier]

Abstract: Ultrasonication has been widely used for bound extracellular polymeric substance (EPS) extraction. However, the used ultrasonic power density is quite different in literature, which makes their results non-comparable. In this study, the effects of different ultrasonic power densities on extracting bound EPS were assessed via analyzing carbohydrates, proteins, humic acids and DNA. Experimental results proved that ultrasonication power density had a significant effect on loosely bound EPS (LB-EPS) extraction, and an appropriate power density termed critical power density was found to be 35W/10mL according to the variations of DNA which represented the intactness or damage of cell membrane. Nevertheless, carbohydrates, proteins and humic acids did not change obviously in tightly bound EPS (TB-EPS) until a very high power density was applied. The critical power density was determined as 65W/10mL for TB-EPS extraction. The results indicated that a critical power density should be used in order to extract maximal EPS but not to damage cell membrane intactness. [Copyright &y& Elsevier]

Abstract: For understanding of the microbial community structure and composition under different aeration intensities, 454 high-throughput pyrosequencing was applied to analyze the 16S rRNA gene of bacteria in two submerged membrane bioreactors (MBRs) under low (RL) and high aeration (RH) conditions. In total, 7818 (RL) and 9353 (RH) high-quality reads were obtained, and 1230 (RL) and 924 (RH) operational taxonomic units (OTUs) were generated at 3% cutoff level, respectively. 454 pyrosequencing could also reveal the minority bacteria that were hardly detected by the conventional molecular methods. Although the core populations were shared with highly functional organization (>80%), clear differences between the samples in the two MBRs were revealed by richness–diversity indicators and Venn analyses. Notably, microbial diversity was decreased under high aeration condition, and the evolution of the populations was observed mainly in the shared OTUs. Moreover, specific comparison down to the class and genus level showed that the relative abundances of β-Proteobacteria and γ-Proteobacteria in the RH community were respectively decreased by 41.5% and 66.6%, consistent with the observed membrane fouling mitigation during the reactor operation. It was also found that Nitrospira and Nitrosomonas, being nitrite oxidizing bacteria (NOB) and ammonium oxidizing bacteria (AOB), were the dominant phylogenetic groups at the genus level of both reactors, and that the high ratio of NOB to AOB populations well supported the complete ammonium oxidation performance in the two reactors. Although some populations of NOB and AOB decreased with the increase of aeration intensity, the functional stability of the nitrification process was less affected, probably due to the low influent substrate concentration and the high level of functional organization. [Copyright &y& Elsevier]

Membrane fouling is one of the major obstacles for wide applications of MBRs. Over the past decade, the behaviors of colloidal and soluble substances have attracted much attention, and intensive efforts have been dedicated to the clarification of their role in membrane fouling. However, to date, the conclusions are often different and even controversial. The review is attempted to clarify their interrelations and to eliminate some confusions by reviewing the recent literature. The similarities and differences of those potential foulants are analyzed through comparing definitions, extraction methods, fouling indicators, and fouling behaviors. The implications of future research directions are also discussed in this paper. [ABSTRACT FROM PUBLISHER]

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: Two distinct fouling layers, i.e., a gel layer and a sludge cake layer were observed in two MBRs operated under same constant fluxes but different aeration rates. The formation mechanisms and properties of the two fouling layers were systematically analyzed. It was found that the gel layer had lower porosity and higher specific resistance (α c ) compared to the sludge cake layer. The mean particle size of the gel layer was smaller than that of the sludge cake layer. Soluble microbial products (SMP) were found to be the major soluble organic materials in both fouling layers. Mg, Ca and Al were the major inorganic elements in solid state of the foulants, and the monovalent elements such as Na and K were mainly detectable in the soluble component of the foulants. SMP and tightly bound extracellular polymeric substances (EPS) of both fouling layers featured macromolecular characters. The molecular weight (MW) of gel foulants was larger than that of cake foulants. The loosely bound EPS and the fouling layers had very similar MW distribution profiles. Only the peaks associated with protein-like fluorophores were detectable in gel foulants, while besides the protein-like materials the humic acid-like substances were present in sludge cake foulants. [Copyright &y& Elsevier]

Abstract: Filtration performances and fouling behaviours of polyacrylonitrile (PAN) and polyvinylidene fluoride (PVDF) membranes were studied in a pilot-scale membrane bioreactor. Results showed that removable fouling was dominant for both membranes while irremovable fouling of the PVDF membrane was severer than that of the PAN membrane. The PAN membrane could reject more soluble microbial products (SMP) than the PVDF membrane due to different pore sizes. The PVDF membrane rejected more carbohydrates and fewer proteins than the PAN membrane. The mean particle size of surface foulants on the PAN membrane was smaller than that on the PVDF membrane. Gel filtration chromatography analysis indicated that the surface foulants of the PVDF membrane were comprised of larger molecular weight molecules than those of the PAN membrane. Three-dimensional excitation–emission matrix fluorescence spectroscopy analysis showed that soluble microbial by-product-like substances were the key factor causing membrane fouling of the two membranes. Hydrophobic humic-like substances played a more important role in forming irremovable fouling of the PAN membrane whereas protein-like substances were the main contributor to the irremovable fouling of the PVDF membrane. Hydrophobic fraction had the largest fouling propensity for the PAN membrane, while neutral hydrophilic fraction demonstrated the strongest fouling potential for the PVDF membrane. [Copyright &y& Elsevier]

Abstract: Two submerged anoxic/oxic membrane bioreactors (MBRs) were operated in parallel under same conditions but different aeration intensities. The Aeolosoma hemprichi and Tubificidae proliferated in the MBR operated under high aeration intensity but were never observed in the MBR with low aeration intensity. Sludge yield coefficient, sludge physicochemical characteristics and filtration performance in the two MBRs were systematically investigated. Results showed that the presence of aquatic worms decreased the total phosphorus removal efficiency while it had no impacts on chemical oxygen demand and nitrogen removal. High aeration intensity could decrease the floc size and increase dispersed bacteria population, thus providing more feed for the worms. The worm growth led to a reduction of the sludge production, an increase of soluble microbial products, an improvement of sludge settleability and a deterioration of sludge dewaterability. The excess growth of worms resulted in a higher membrane fouling rate in the MBR. [Copyright &y& Elsevier]

Abstract: Membrane foulants including external foulants and internal foulants were systematically characterized in a full-scale membrane bioreactor (MBR) for supermarket wastewater treatment 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 characterize the membrane foulants. The results indicated that the organic substances with fluorescence characteristics in both external and internal foulants were identified as protein-like substances and soluble microbial by-product-like materials by EEM technology. The GFC analysis exhibited that the external foulants had much broader distributions of molecular weight (MW) than the effluent and the internal foulants. Analyses of MW distributions suggest that the external and internal foulants were formed due to distinct fouling mechanisms. Besides proteins and polysaccharides, the oil substances were identified on the fouled membranes by the FT-IR analysis. SEM and EDX analyses indicated that the foulants covering the membrane surfaces comprised not only organic substances but also inorganic elements including Mg, Ca, Na, Al, K, and Si. [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: Two membrane bioreactors (MBRs) with different operation conditions were employed to investigate the role of dissolved organic matter (DOM) in membrane fouling. DOM characteristics and their correlations with membrane fouling in the MBR systems were studied by using three-dimensional excitation-emission matrix (EEM) fluorescence technology, gel filtration chromatography (GFC) analysis, and column chromatographic method for DOM fractionation, etc. The three-dimensional EEM fluorescence spectroscopy analysis indicated that the fluorescence intensity of protein-like peaks in DOM samples collected from the MBR zones showed positive correlations with membrane fouling. The fluorescence spectra of membrane foulants also exhibited two protein-like peaks, confirming that proteins played an important role in membrane fouling. The DOM samples collected from MBR zones were fractionated into four components, i.e., hydrophobic (HPO), transphilic (TPI), charged hydrophilic (HPI-C) and neutral hydrophilic fractions (HPI-N). It was found that HPI-N was the most abundant fraction in all the samples, accounting for 42.0–48.9% of the total DOM. Test results also showed that HPI-N had the highest fouling potential, which could be attributed to the high molecular weight (MW) distribution and the high membrane rejection rate of macromolecules. [Copyright &y& Elsevier]

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]

Membrane bioreactor (MBR) has been deemed to be a promising technology for wastewater treatment and reclamation; however, the MBR filtration performance inevitably decreases with filtration time attributed to the deposition of soluble and particulate materials onto and into the membrane under the interactions between activated sludge components and the membrane. Cake layer formation on membrane surfaces has been a major challenge in the operation of MBRs under supra-critical flux operation, and/or caused by uneven distribution of aeration intensities, etc.; however, it was argued that a thin cake layer might improve filtration operation by some researchers. This paper provides a critical review on the formation mechanisms, properties, the role of sludge cake in membrane filtration, and the corresponding strategies of controlling cake fouling in MBRs. Drawbacks and benefits of the formation of sludge cake were also discussed in order to better understand the characteristics and role of sludge cake formation in MBRs. [ABSTRACT FROM AUTHOR]

A pilot-scale submerged membrane bioreactor (MBR) for real municipal wastewater treatment was operated for over one year in order to investigate extracellular polymeric substances (EPS) properties and their role in membrane fouling. The components and properties of bound EPS were examined by the evaluation of mean oxidation state (MOS) of organic carbons, Fourier transform infrared (FT-IR) spectroscopy, three-dimensional excitation¿emission matrix (EEM) fluorescence spectroscopy, and gel filtration chromatography (GFC), etc. Test results showed that MOS of organic carbons in the bound EPS was ranging from ¿0.14 to ¿0.51, and major components could be assessed as proteins and carbohydrates. FT-IR analysis confirmed the presence of proteins and carbohydrates in the bound EPS. The organic substances with fluorescence characteristics in the bound EPS were identified as proteins, visible humic acid-like substances and fulvic acid-like substances by EEM technology. GFC analysis demonstrated that EPS had part of higher MW molecules and a broader MW distribution than the influent wastewater. It was also found that a high shear stress imposed on mixed liquor could result in the release of EPS, which would in turn influence membrane fouling in MBRs. Bound EPS solution was observed to have a stronger potential of fouling than mixed liquor. During long-term operation of the MBR, bound EPS demonstrated positive correlations with membrane fouling while temperature was verified as a negative factor affecting EPS concentration. Compared to tightly bound EPS (TB-EPS), loosely bound EPS (LB-EPS) showed more significant correlations with membrane fouling. This critical investigation would contribute towards a better understanding of the behavior, composition and fouling potential of EPS in MBR operation. [Copyright &y& Elsevier]

Three-dimensional excitation–emission matrix (EEM) fluorescence spectroscopy was employed to characterize dissolved organic matter (DOM) in a submerged membrane bioreactor (MBR). Three fluorescence peaks could be identified from the EEM fluorescence spectra of the DOM samples in the MBR. Two peaks were associated with the protein-like fluorophores, and the third was related to the visible humic acid-like fluorophores. Only two main peaks were observed in the EEM fluorescence spectra of the extracellular polymeric substance (EPS) samples, which were due to the fluorescence of protein-like and humic acid-like matters, respectively. However, the EEM fluorescence spectra of membrane foulants were observed to have three peaks. It was also found that the dominant fluorescence substances in membrane foulants were protein-like substances, which might be due to the retention of proteins in the DOM and/or EPS in the MBR by the fine pores of the membrane. Quantitative analysis of the fluorescence spectra including peak locations, fluorescence intensity, and different peak intensity ratios and the fluorescence regional integration (FRI) analysis were also carried out in order to better understand the similarities and differences among the EEM spectra of the DOM, EPS, and membrane foulant samples and to further provide an insight into membrane fouling caused by the fluorescence substances in the DOM in submerged MBRs. [Copyright &y& Elsevier]

Abstract: Membrane foulants and gel layer formed on membrane surfaces were systematically characterized in a submerged membrane bioreactor (MBR) under sub-critical flux operation. The evaluation of mean oxidation state (MOS) of organic carbons and Fourier transform infrared (FT-IR) spectroscopy demonstrated that membrane foulants in gel layer were comprised of not only extracellular polymeric substances (EPS) (proteins, polysaccharides, etc.) but also other kinds of organic substances. It was also found that fine particles in mixed liquor had a strong deposit tendency on the membrane surfaces, and membrane foulants had much smaller size than mixed liquor in the MBR by particle size distribution (PSD) analysis. Gel filtration chromatography (GFC) analysis showed that membrane foulants and soluble microbial products (SMP) had much broader distributions of molecular weight (MW) and a larger weight-average molecular weight (M w) compared with the influent wastewater and the membrane effluent. Scanning electron microscopy (SEM) and energy-diffusive X-ray (EDX) analysis indicated that membrane surfaces were covered with compact gel layer which was formed by organic substances and inorganic elements such as Mg, Al, Fe, Ca, Si, etc. The organic foulants coupled the inorganic precipitation enhanced the formation of gel layer and thus caused membrane fouling in the MBR. [Copyright &y& Elsevier]

Abstract: Critical flux is an important concept in membrane bioreactor (MBR) process for wastewater treatment, and the study on it could enhance the understanding of MBR process and facilitate its application. In this study, the effects of various factors, such as sludge concentration, aeration intensity, soluble chemical oxygen demand (SCOD) of the mixed liquors, and measurement parameters including initial flux, step length and step height, and membrane properties including membrane materials and membrane history, on critical flux were critically investigated. Test results showed that the critical flux decreased with the increase of sludge concentration and it could be enhanced by improving aeration intensity. SCOD, which was used to indicate sludge characteristics, was found to have a negative effect on critical flux. It was also observed that the increase of step length or step height would lower the critical flux; however, the variations of initial fluxes did not clearly affect critical flux. In addition, membrane materials also had significant influences on critical flux, and membrane M3 had a higher critical flux value, which was more suitable for the application to the submerged MBR compared to M1 and M2 membranes. Membrane history was found to have negative impacts on membrane critical flux, and the critical flux decreased as the membrane operation prolonged. [Copyright &y& Elsevier]

Abstract: Rheological and physiological characteristics of sludge in a submerged membrane bioreactor (MBR) were studied in order to classify their effects on filtration properties and membrane fouling. Viscosity, mixed liquor suspended solids (MLSS), extracellular polymer substances (EPS), soluble chemical oxygen demand (SCOD), dewaterability in terms of capillary suction time (CST), proteins and carbohydrates in the mixed liquor and their correlations with membrane fouling were investigated during a long-term performance. Statistical analysis was employed to specify the influence of temperature, viscosity, MLSS, EPS, CST, SCOD, proteins and carbohydrates in the mixed liquor on membrane fouling. It was found that high MLSS concentration with a high apparent viscosity not only changed rheological characteristics of the mixed liquor, but also affected oxygen transfer coefficient in the submerged MBR. Among all these variables, viscosity, MLSS, EPS, CST, SCOD, carbohydrates and proteins in the mixed liquor were found to have positive correlations with membrane fouling. CST had the greatest impact on membrane fouling, followed by SCOD, carbohydrates, EPS, proteins, apparent viscosity and MLSS, respectively. Test results demonstrated that temperature had negative correlations with membrane fouling rate. [Copyright &y& Elsevier]

Abstract: The effect of sludge characteristics on membrane fouling in a pilot-scale submerged membrane bioreactor (MBR) during long-term performance was investigated. Viscosity, mixed liquor suspended solids (MLSS), extracellular polymer substances (EPS), soluble chemical oxygen demand (SCOD), dewaterability in terms of capillary suction time (CST), proteins and carbohydrates in the mixed liquor and their correlations with membrane fouling were studied. Among these variables, CST, SCOD, EPS and carbohydrate were found to have significant influence on membrane fouling by statistical analysis method. CST was then chosen as an indicator parameter and its relationship with critical flux (J c) was established. The concept of proper operational flux (J p) was introduced and further determined through parallel experiments. The difference between critical flux and proper operational flux in submerged MBRs was analyzed and discussed. Test results in this study show that the proper operational flux is only 56% of the critical flux value. [Copyright &y& Elsevier]

In this study, the different graphene derivatives, graphene oxide (GO), carboxylic acid‐modified graphene (G‐COOH), and amine‐modified graphene (G‐NH2), were used to prepare polyvinylidene fluoride (PVDF) composite membranes. The membrane modification performance was evaluated using the extended Derjaguin–Landau–Verwey–Overbeek theory and quartz crystal microbalance dissipation monitoring. The results show that the addition of low‐dose GO and G‐NH2 can improve membrane surface porosity and permeability. The hydrophilicity and electron donor monopolarity of PVDF/GO composite membranes were enhanced by adding more than 0.024 wt% GO, thus improving its antifouling ability. In addition, the enhancement of hydrophilicity, free energy of cohesion, and antifouling ability of composite membrane modified with G‐COOH and G‐NH2 was more significant compared with that of GO with the same dosage, which implies the important role of functional group in additives. This study provides new insights for the blending modification of PVDF membranes by systematically comparing the addition of graphene derivatives with different functional groups. Practitioner points: The comprehensive comparison of membrane modification with different graphene derivatives was investigated.The enhancement of hydrophilicity and antifouling ability of membranes modified with G‐COOH and G‐NH2 was more significant than that of GO.The free energy of cohesion of nanocomposite membrane was affected by the functional group of additives.G‐NH2 composite membrane had the best comprehensive performance with great hydrophilicity, permeability, and antifouling performance. [ABSTRACT FROM AUTHOR]

Membrane fouling is one of the major obstacles that hinder the widespread applications of anerobic membrane bioreactors (AnMBRs) for wastewater treatment. Due to the intrinsic complexity of membrane fouling, identifying critical fouling factors and predicting fouling behavior are of great significance in membrane fouling control. Herein, artificial intelligence (AI) algorithms and their modeling framework were developed to predict membrane fouling behaviors in AnMBRs. Operating parameters, biomass properties, and membrane characteristics were considered as input variables for membrane fouling prediction. The results of hyper-parameter optimization showed that the optimal architecture of artificial neural network (ANN) model for membrane fouling prediction was "14-9-6-1" while the best hyper-parameters of random forest (RF) model were n_trees = 1200 and n_features = 14. After hyper-parameter adjusting, RF had more robustness of predictive capabilities (R 2=0.906, mean squared error (MSE) = 0.061) for membrane fouling than the ANN model (R 2=0.800, MSE = 0.118). More importantly, the feature importance and Shapley additive explanations analysis indicated SMPp/SMPc (0.281) > EPSp/EPSc (0.110) > organic loading rate (0.106), which were the most critical factors affecting membrane fouling. Partial dependence plot analysis further verified the marginal and interaction effects of various input features on membrane fouling. The revealed partial dependence relationships of critical variables can provide theoretical reference for optimization of practical operation. Overall, this study established a novel AI-based approach for predicting membrane fouling and comprehensively understanding the complicated effects of various influencing factors on membrane fouling while overcoming the "black-box" nature of conventional models. [Display omitted] • AI-based algorithms accurately predicts and interprets membrane fouling in AnMBRs. • RF model (R 2=0.906) demonstrates better prediction capabilities than ANN model. • Interpretable analysis shows that SMPp/SMPc is the most critical fouling factor. • PDP analysis reveals the partial dependence relationships of contributing factors. [ABSTRACT FROM AUTHOR]

Quaternary ammonium compounds (QACs) are emerging contaminants with the extensive applications in a variety of fields. However, little is known about their potential impacts on activated sludge and performance of biological wastewater treatment processes. In this work, the effects of benzalkonium chloride (BAC, a kind of QACs) on acute and chronic responses of microorganisms and on MBR performance were systematically investigated. The results showed that a low concentration (0.5–2.0 mg BAC/g SS) caused no significant effects on activated sludge property. In contrast, an elevated concentration of BAC led to severer inhibition on activated sludge and key enzyme activity (e.g., dehydrogenase activity) in both short-term and long-term exposure, thus deteriorating the pollutant removal efficiency. Compared with the control MBR (R1) and the reactor with 0.5 mg/L BAC (R2), the removal efficiency of ammonia in R3 with 5.0 mg/L BAC at identical hydraulic retention time (4.3 h) and sludge retention time (30 d) was decreased, i.e., ammonium removal efficiency in R1∼R3 was 95.4 ± 6.1, 93.4 ± 8.1 and 89.3 ± 17.6%, respectively. Moreover, MBR tests showed that membrane fouling was aggravated in the presence of high-concentration BAC. Long-term exposure to BAC reduced microbial community diversity and enriched the BAC-resistant microbes. For instance, the abundance of Pseudomonas genus in R3 was increased from 0.02% to 14.9% with the increase of operation time. Microbial community structure was changed to resist the environmental stress induced by BAC during long-term exposure, thus decreasing the inhibition effects. [ABSTRACT FROM AUTHOR]

Anaerobic osmotic membrane bioreactor (AnOMBR) has gained increasing interests in wastewater treatment owing to its simultaneous recovery of biogas and water. However, the forward osmosis (FO) membrane fouling was severe during a long-term operation of AnOMBRs. Here, we aim to recover the permeability of fouled FO membranes by chemical cleaning. Specifically speaking, an optimal chemical cleaning procedure was searched for fouled thin film composite polyamide FO (TFC-FO) membranes in a novel microfiltration (MF) assisted AnOMBR (AnMF-OMBR). The results indicated that citric acid, disodium ethylenediaminetetraacetate (EDTA-2Na), hydrochloric acid (HCl), sodium dodecyl sulfate (SDS) and sodium hydroxide (NaOH) had a low cleaning efficiency of less than 15%, while hydrogen peroxide (H 2 O 2 ) could effectively remove foulants from the TFC-FO membrane surface (almost 100%) through oxidizing the functional group of the organic foulants and disintegrating the colloids and microbe flocs into fine particles. Nevertheless, the damage of H 2 O 2 to the TFC-FO membrane was observed when a high cleaning concentration and a long duration were applied. In this case, the optimal cleaning conditions including cleaning concentration and time for fouled TFC-FO membranes were selected through confocal laser scanning microscope (CLSM) and scanning electron microscopy (SEM) images and the flux recovery rate. The results suggested that the optimal cleaning procedure for fouled TFC-FO membranes was use of 0.5% H 2 O 2 at 25 °C for 6 h, and after that, the cleaned TFC-FO membrane had the same performance as a virgin one including water flux and rejection for organic matters and phosphorus during the operation of AnMF-OMBR. [ABSTRACT FROM AUTHOR]

In this study, a chemically enhanced backflush (CEB) cleaning method using NaOH solution was proposed for fouling mitigation in anaerobic membrane bioreactors (AnMBRs). Ex-situ cleaning tests revealed that NaOH dosages ranging from 0.05 to 1.30 mmol/L had positive impacts on anaerobic biomass, while higher dosages (>1.30 mmol/L) showed inhibition and/or toxic impacts. In-situ cleaning tests showed that anaerobic biomass could tolerate much higher NaOH concentrations due to the alkali consumption by anaerobic process and/or the buffering role of mixed liquor. More importantly, 10–20 mmol-NaOH/L could significantly reduce membrane fouling rates (4–5.5 times over the AnMBR with deionized water backflush) and slightly improve methanogenic activities. COD removal efficiencies were over 87% and peaked at 20 mmol-NaOH/L. However, extremely high NaOH concentration had adverse effects on filtration and treatment performance. Economic analysis indicated that 12 mmol/L of NaOH was the cost-efficient and optimal fouling-control dosage for the CEB cleaning. [ABSTRACT FROM AUTHOR]

Influences of fractal dimension ( D f ) of membrane surface on interfacial interactions related to membrane fouling in a membrane bioreactor were investigated based on thermodynamic methods. It was found that membrane surface had significant fractal features, and its fractal dimension could be characterized by the power spectrum method. The modified Weierstrass-Mandelbrot (WM) function was found to be effective to model the fractal membrane surface, and higher D f corresponded to higher number of fine asperities in the modeled surface. Moreover, the modeled surface roughness exponentially decreased with D f . Interaction calculations according to a novel method showed that the interactions for fractal membrane surface were elongated and weakened as compared with smooth membrane surface. It was interestingly found that the absolute value of total interaction monotonically decreased with D f of membrane surface. As D f is a measure of substance stiffness, this result indicates that softer surface is more susceptible to adhesion by sludge foulant. The results offered new insights into membrane fouling mechanisms and alleviation. [ABSTRACT FROM AUTHOR]

Membrane technology has emerged as a crucial method for obtaining clean water from unconventional sources in the face of water scarcity. It finds wide applications in wastewater treatment, advanced treatment, and desalination of seawater and brackish water. However, membrane fouling poses a huge challenge that limits the development of membrane-based water treatment technologies. Characterizing the dynamics of membrane fouling is crucial for understanding its development, mechanisms, and effective mitigation. Instrumental techniques that enable in situ or real-time characterization of the dynamics of membrane fouling provide insights into the temporal and spatial evolution of fouling, which play a crucial role in understanding the fouling mechanism and the formulation of membrane control strategies. This review consolidates existing knowledge about the principal advanced instrumental analysis technologies employed to characterize the dynamics of membrane fouling, in terms of membrane structure, morphology, and intermolecular forces. Working principles, applications, and limitations of each technique are discussed, enabling researchers to select appropriate methods for their specific studies. Furthermore, prospects for the future development of dynamic characterization techniques for membrane fouling are discussed, underscoring the need for continued research and innovation in this field to overcome the challenges posed by membrane fouling. [Display omitted] • Principal technologies for characterizing dynamics of membrane fouling are reviewed. • The technologies are classified into three categories based on their functionalities. • Their principles, applications, and limitations in fouling analysis are discussed. • Their characteristics and applicability in different fouling stages are summarized. • Future perspectives on the incorporation of new technologies are proposed. [ABSTRACT FROM AUTHOR]

Abstract: The modification of poly(vinylidene fluoride)/polyethersulfone (PVDF/PES) blend membranes was carried out by adding polyvinyl alcohol (PVA) to improve their antifouling ability. The physicochemical characteristics of the membranes in terms of porosity, contact angle, pure water flux, critical flux and fouling rate were systematically analyzed. The extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory was used to assess the antifouling ability of the modified membranes, and the membrane׳s long-term performance was also evaluated in a pilot-scale submerged anoxic/oxic membrane bioreactor for wastewater treatment. The results showed that the hydrophilicity and permeability of PVDF/PES blend membrane were efficiently improved by adding 0.3% PVA. The increase of critical flux and the decrease of fouling rate for the modified membrane were also observed in batch filtration experiments. XDLVO analysis indicated that the addition of PVA significantly improved the cohesion free energy of the membranes. The energy barrier between soluble microbial products and membrane surfaces was increased, which therefore reduced the adsorption of membrane foulants. The long-term filtration process also demonstrated that the antifouling ability of PVDF/PES membrane modified by 0.3% PVA was significantly enhanced. The study offers an effective way to enhance membrane antifouling ability of PVDF/PES membrane through the addition of PVA additives. [Copyright &y& Elsevier]

Chemical cleaning was investigated for a membrane bioreactor (MBR) treating restaurant wastewater. Test results showed that membrane foulants were comprised of inorganic and organic substances. Sparingly soluble salts containing Mg, Al, Ca, and Fe were the major components of the inorganic foulants, and protein was likely to be the organic foulant with high hydrophobicity. It was also found that the chemical cleaning could modify the contact angle of the membranes, and the membranes became more hydrophobic than the virgin membrane after chemical cleaning. 2% sulfuric acid, 3% sodium hydroxide, and 4% sodium hypochlorite with 66.0%, 59.0%, and 56.3% flux recovery efficiency showed better performance than others. [ABSTRACT FROM AUTHOR]

Abstract: Membrane foulants were extracted at different operation time in simultaneous sludge thickening and digestion reactors using flat-sheet membranes. Temporal variations of foulants were analyzed by three-dimensional excitation–emission matrix (EEM) fluorescence spectroscopy, gel filtration chromatography (GFC), particle size distribution (PSD) and attenuated total reflection–Fourier transform infrared (ATR–FTIR) spectroscopy. Results showed that during the first 4days fouling was mainly assigned to internal membrane foulants (IMFs), and afterwards external membrane foulants (EMFs) increased dramatically. EEM analysis showed that both IMFs and EMFs changed during the operation. Cluster analysis demonstrated that the characteristics of IMFs were relatively similar; however, both quantity and properties of EMFs were changed. GFC analysis showed that EMFs contained more molecules with large molecular weight compared to IMFs. PSD analysis illuminated that particle size of EMFs gradually increased and was larger than that of IMFs. ATR–FTIR analysis indicated that the foulants on membranes consisted of polysaccharides and proteins. [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: The feasibility of using flat-sheet membrane for simultaneous thickening and digestion of activated sludge (MSTD) was studied in this paper, and the membrane fouling mechanisms of this process under high and changing mixed liquor suspended solids (MLSSs) were investigated. About 30g/L concentrated sludge and 45% mixed liquor volatile suspended solids (MLVSSs) destruction efficiency were achieved at the end of each period of sludge treatment. Test results showed that viscosity, capillary suction time (CST), soluble microbial products (SMPs) and chemical oxygen demand concentrations of colloids (CODc) had significant influences on membrane fouling among various sludge variables. CST was then chosen as an indicated parameter, and the empirical relationship between CST and membrane permeability was established. It was also found that the filtration cake and the irreversible foulants consisted of large numbers of carbohydrate and protein, and membrane fouling of membrane modules was not homogeneous. [Copyright &y& Elsevier]

Membrane cleaning is crucial to maintain the permeability and selectivity of membranes. Physical cleaning can mitigate membrane fouling, lower the frequency of chemical cleaning, thus prolong membrane lifetime, and reduce operational costs. Backpulsing is a promising physical cleaning method, which can effectively mitigate external and non-adhesive fouling and has been used in many industrial fields. However, a comprehensive understanding of backpulsing and the optimization of this technology is still lacking. This paper critically reviews the development of backpulsing technique in microfiltration (MF) and ultrafiltration (UF) processes. Firstly, the fundamentals of backpulsing are addressed. Secondly, applications of backpulsing are summarized according to the applied fields. Results of pilot- and commercial-scale operations are presented. Moreover, factors influencing backpulsing efficiency are illustrated, including feed properties, membrane properties and operating parameters. Furthermore, mathematical models of backpulsing are overviewed. The models not only predict membrane productivity, but also provide a perspective to evaluate the performance of backpulsing in fouling mitigation. Finally, the existing challenges and future outlook are discussed. [ABSTRACT FROM AUTHOR]

The aim of this study was to investigate membrane fouling performance of anaerobic side-stream reactor (ASSR) coupled membrane reactors (MBR), and effects of representative enhancement strategy, namely packing carriers and low-strength ultrasonication, on sludge properties and membrane fouling by four pilot-scale MBRs. Compared to anoxic/oxic MBR (AO-MBR) for control, ASSR coupled AO-MBR (ASSR-MBR), ASSR-MBR with ASSR packed with carriers (AP-MBR) and AP-MBR with part of sludge ultrasonicated before fed into ASSR (AUP-MBR) reduced sludge production by 8.4%, 17.5% and 32.9% with efficient pollutants removal. ASSR-MBR showed more severe membrane fouling because inserting ASSR disintegrated sludge floc structure, increased the secretion of extracellular polymeric substances (EPS) and deteriorated viscoelastic property of sludge. Packing carriers in ASSR alleviated membrane fouling of ASSR-MBR by inhibiting EPS-secreting bacteria (Flavobacteriia, γ-Proteobacteria, δ-Proteobacteria and norank_Saccharibacteria), enlarging particle size and improving dewaterability. AUP-MBR showed the most severe membrane fouling and obvious cake layer fouling because ultrasonication disintegrated sludge to small particles, increased adherence property of EPS, and deteriorated dewaterability and viscoelastic property of sludge. MiSeq sequencing revealed Proteobacteria and Bacteroidetes were responsible for membrane fouling at the phylum level, and norank_Neisseriaceae , Arcobacter , norank_Parcubacteria and Mycobacterium were dominant genera easily attached on membrane surface. Image 1 • Membrane fouling (MF) of anaerobic side-stream reactor (ASSR) - MBR was studied. • ASSR-MBR deteriorated MF, dewaterability and flowability due to sludge reduction. • Carriers in ASSR alleviated MF by inhibiting EPS secretion and enlarging particles. • Ultrasonication caused severe MF due to flocs disintegration and high EPS adhesivity. • MiSeq sequencing revealed dominant bacteria easily attached on membrane surface. [ABSTRACT FROM AUTHOR]

Forward osmosis (FO) has gained increasing interests in wastewater treatment and reclamation. However, membrane fouling has become one major obstacle hindering FO application. A novel mitigation approach for FO membrane fouling via in situ extracting Ca2+ binding with the organic foulants using the gradient diffusion thin-films (DGT) was proposed in this study. The DGT could effectively adsorb the Ca2+ binding with the sodium alginate via the chelation of the Chelex functional groups, and its adsorption amount of Ca2+ correspondingly increased as a function of the Ca2+ concentration in the feed solution. Owing to the extraction of Ca2+ from the fouling layer by the DGT, the FO membrane fouling was effectively mitigated evident by significant enhancement of water flux, and at the same time, foulants became easily removed by physical cleaning. The alleviation of FO membrane fouling by the DGT could be attributed to the fact that the structure of the fouling layer became more porous and looser after in situ removing Ca2+ from the alginate-Ca2+ gel networks. The feasibility of fouling control strategy via in situ removing Ca2+ binding with the foulants in the fouling layer was demonstrated, which provides new insights into fouling control mechanisms during FO treating wastewater. Image 1 •DGT can effectively adsorb Ca2+ binding with organic foulants on the FO membrane. •DGT adsorption amount increased as a function of Ca2+ concentration in the feed. •Fouling layer became more porous and looser after in situ removing Ca2+ by DGT. •FO membrane flux significantly increased after removing Ca2+ from fouling layer. •Foulants became easily removed by physical cleaning after in situ removing Ca2+. [ABSTRACT FROM AUTHOR]

Abstract Membrane fouling remains as a critical issue limiting the widespread applications of membrane-based technologies for water and wastewater treatment. In this work, an electrochemical ceramic membrane reactor (ECMR), in which ceramic membrane with built-in Ti mesh acted as cathode/filter and Ti/SnO 2 -Sb-Ce as anodes, was developed for mitigating membrane fouling during wastewater treatment. Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) of Ti/SnO 2 -Sb-Ce electrode demonstrated favorable electrochemical properties. Filtration tests with influent wastewater containing 50 mg/L sodium alginate (SA) showed that TMP increase rate for the ECMR was decreased by 23.9–72.7% compared to the control, dependent on the exertion modes of electric field in this reactor. It was found that all the oxidants contributed to the enhanced antifouling performance of the ECMR due to in-situ membrane cleaning effects while the hydrogen peroxide and active chlorine (Cl T) played a more important role compared to superoxide anions and hydroxyl radicals. SA was oxidized to a smaller size after reacting with reactive oxygen species (ROS) and Cl T , benefiting the mitigation of membrane fouling in ECMR. Graphical abstract fx1 Highlights • An electrochemical ceramic membrane reactor was developed for mitigating fouling. • TMP increase rate for the system was decreased by 23.9~72.7% compared to control. • H 2 O 2 and active chlorine played a more important role compared to O 2 •- and HO•. • The exertion modes of electric field in this reactor is an important factor. [ABSTRACT FROM AUTHOR]

Membrane fouling remains the most challenging issue in membrane bioreactors (MBRs); however, fouling mechanisms are as yet incompletely understood. In this study, 20 membranes with different characteristics and the mixed liquors derived from MBRs treating sewage wastewater (SAS), restaurant wastewater (RAS), and landfill leachate (LAS) were adopted to study membrane fouling mechanisms. Statistical analyses were conducted to explore the correlations between different membrane properties, and results found that characteristics of membranes were not independent of each other but mutually influential. However, the trend of fouling propensity within each membrane was dependent on the filtering medium. Membranes with smaller pore sizes and strong hydrophobicity showed a slower fouling rate when filtering LAS, whereas an opposite fouling trend was evident for SAS. Furthermore, dissolved organic matter (DOM) derived from MBRs treating SAS (SASDOM) showed the highest permeability followed by DOM derived from MBRs treating RAS (RASDOM), whereas DOM derived from MBRs treating LAS (LASDOM) exhibited the worst permeability due to its strong hydrophobicity. Finally, fouling propensities of hydrophobic and hydrophilic fractions isolated from SASDOM were predicted using extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, and the hydrophobic fraction and charged hydrophilic fraction with the lowest and highest free energy of cohesion, respectively, showed the fastest and slowest fouling propensity, respectively. Results indicate that membrane fouling potential was affected by the interactions between membranes and filtering mediums, rather than the specific properties of individual membranes. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mechanisms and effectiveness of electrochemical and NaClO cleaning was investigated. • Electrochemical oxidation can convert BSA into foams and flocs by electrocoagulation. • Indirect electrochemical oxidation by OH· and O 2 ·- could degrade foulants. • Combination of electric field and NaClO showed great membrane cleaning efficiency. • Applying electric field before adding NaClO could efficiently inhibit the generation of HBPs. Membrane fouling can be effectively alleviated by using conductive membrane and external electric field in membrane bioreactor. However, the transformation and removal mechanism of foulants during the electrochemical process needs to be further explored. The present work investigated the degradation mechanisms and cleaning efficiency of organic foulants by electric field and sodium hypochlorite (NaClO) on the composite conductive microfiltration membranes. The results show that the electrochemical oxidation obtained a great degradation efficiency of bovine serum albumin (BSA) at current densities of 40 and 80 A/m2, which was equivalent to that of high-dose NaClO (160 mg/L). However, the degradation efficiency of sodium alginate (SA) was much lower than that of BSA under the same cleaning strategy, due to its strong antioxidant activity. It was also found that NaClO oxidation can decompose BSA macromolecules into small molecules instead of mineralization, while electrochemical oxidation can convert dissolved BSA into foams and flocs by electrocoagulation, thus reducing the BSA concentration in the solution. During the electrochemical cleaning, indirect electrochemical oxidation through the formation of strong oxidants played an important role in the degradation of BSA and SA, and the role of OH· was more significant than that of O 2 ·-. The combination of electric fields and NaClO showed great membrane cleaning efficiency. Moreover, the combination of electrochemical cleaning could not only prevent a large number of precursors from being converted to halogenated by-products, but also shorten the chlorination time and reduce the chlorine concentration, which can alleviate the secondary pollution of cleaning solution. [ABSTRACT FROM AUTHOR]

• Membrane fouling in a ZLD system was investigated for multiple NF & RO steps. • A correlation between water quality and membrane fouling behavior was unraveled. • The membrane fouling behaviors varied along the flow direction in the ZLD system. • The 2nd pass RO process was subject to severe aluminum-silica scaling. • The aromatic substances and TPHs were universally present on various membranes. The challenge of water scarcity drives zero liquid discharge (ZLD) treatment to maximize reuse of industrial wastewater. Deciphering the characteristics and mechanisms of membrane fouling in the membrane-based ZLD system is crucial for the development of effective fouling control strategies. However, current studies only focused on the membrane fouling of single step, lacking in-depth understanding on the ZLD systems using multiple membrane processes. Herein, membrane fouling characteristics and mechanisms in a full-scale ZLD system for cold-rolling wastewater brine treatment were investigated via a comprehensive analysis on multiple nanofiltration (NF) and reverse osmosis (RO) membrane processes. The membrane fouling behaviors showed distinct characteristics along the wastewater flow direction in the ZLD system. Increasing amounts of foulants were deposited on the membrane surfaces with the sequence of the 1st pass RO, 1st stage NF, and 2nd stage NF processes. The organic fouling and silica scaling were more intensive in the 1st stage NF and 2nd stage NF for treating the brine of the 1st pass RO, as the foulants were rejected and concentrated by previous membrane processes. Severe inorganic fouling, containing amorphous SiO 2 , Al 2 O 3 , and Al 2 SiO 5 , occurred on the membrane surface of the 2nd pass RO membrane, due to the recirculated high-concentration silica, high water recovery, and concentration polarization. For the 3rd pass RO process, both the amounts of organic and inorganic foulants decreased dramatically, due to the low foulant concentration in its influent. This work provides a comprehensive understanding of membrane fouling in a membrane-based ZLD system, facilitating the development of membrane fouling control strategies for multiple membrane processes. [Display omitted] [ABSTRACT FROM AUTHOR]

• The advantages of external field-assisted forward osmosis are emphasized. • The alleviating mechanisms of ICP and membrane fouling in external field-assisted forward osmosis are outlined. • The development of forward osmosis technology with external field assistance is discussed. • New research perspective is provided for the development of forward osmosis technology. Forward osmosis (FO) is an emerging permeation-driven membrane technology that manifests advantages of low energy consumption, low operating pressure, and uncomplicated engineering compared to conventional membrane processes. The key issues that need to be addressed in FO are membrane fouling, concentration polarization (CP) and reverse solute diffusion (RSD). They can lead to problems about loss of draw solutes and reduced membrane lifetime, which not only affect the water treatment effectiveness of FO membranes, but also increase the economic cost. Current research has focused on FO membrane preparation and modification strategies, as well as on the selection of draw solutions. Unfortunately, these intrinsic solutions had limited success in unraveling these phenomena. In this paper, we provide a brief review of the current state of research on existing external field-assisted FO systems (including electric-, pressure-, magnetic-, ultrasonic-, light- and flow-assisted FO system), analyze their mitigation mechanisms for the above key problems, and explore potential research directions to aid in the further development of FO systems. This review aims to reveal the feasibility of the development of external field-assisted FO technology to achieve a more economical and efficient FO treatment process. [Display omitted] [ABSTRACT FROM AUTHOR]

• Recent advances in artificial intelligence for predicting fouling are presented. • Working principles of AI technologies for membrane fouling prediction are discussed. • Comparisons of the inputs, outputs, and accuracy of AI approaches are conducted. • Future research efforts are highlighted for AI technologies in predicting membrane fouling. Membrane fouling is one of major obstacles in the application of membrane technologies. Accurately predicting or simulating membrane fouling behaviours is of great significance to elucidate the fouling mechanisms and develop effective measures to control fouling. Although mechanistic/mathematical models have been widely used for predicting membrane fouling, they still suffer from low accuracy and poor sensitivity. To overcome the limitations of conventional mathematical models, artificial intelligence (AI)-based techniques have been proposed as powerful approaches to predict membrane filtration performance and fouling behaviour. This work aims to present a state-of-the-art review on the advances in AI algorithms (e.g., artificial neural networks, fuzzy logic, genetic programming, support vector machines and search algorithms) for prediction of membrane fouling. The working principles of different AI techniques and their applications for prediction of membrane fouling in different membrane-based processes are discussed in detail. Furthermore, comparisons of the inputs, outputs, and accuracy of different AI approaches for membrane fouling prediction have been conducted based on the literature database. Future research efforts are further highlighted for AI-based techniques aiming for a more accurate prediction of membrane fouling and the optimization of the operation in membrane-based processes. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Nature breaks new ground in the design of antifouling membranes. • The review summarizes the recent progress of nature-inspired antifouling membranes. • Fundamentals, strategies and applications of antifouling membranes are reviewed. • Challenges and perspectives for nature-inspired antifouling membranes are provided. Membrane separation technologies have been widely used for water purification. However, membrane fouling, which arises from unwanted deposition and adhesion of foulants, significantly hinders the applications of membrane technology. In recent years, inspirations that come through materials, processes and designs of nature open a new avenue for the development of antifouling membranes. The review aims to summarize the recent progress in nature-inspired antifouling membranes. The fundamentals of membrane fouling are first discussed based on the classical theories and recent advances in available literature. Subsequently, antifouling surfaces inspired from nature, involving superwetting surfaces, antimicrobial approaches and bio-synthesis strategies, are systematically summarized and antifouling membrane fabrications based on these strategies are critically reviewed. The challenges and perspectives are also discussed to facilitate the future research and development of nature-inspired antifouling membranes. This review provides comprehensive understanding and practical guidance on the construction of nature-inspired antifouling membranes for water purification. [ABSTRACT FROM AUTHOR]