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Membrane-based technologies are increasingly used for water and wastewater treatment; however, biofouling, the adhesion of microorganisms to the membrane and subsequent formation of biofilm, remains a major obstacle in real applications. In this study, we report a novel method to fabricate a highly antibiofouling membrane by grafting quaternary ammonium compounds (QAC) onto a silica-decorated membrane via alkoxysilane polycondensation reaction. A controlled architecture was created by initially coating polydopamine (PDA)/polyethylenimine (PEI) layer, followed by in situ synthesizing a hydrophilic silica nanoparticle layer through silification reaction and then immobilizing QAC on the silica-decorated membrane to form an antibacterial surface. Although the QAC modified membrane exhibited comparable surface roughness, hydrophilicity and water permeability with the pristine membrane, the former displayed clear antibacterial effects against both Gram-positive and Gram-negative bacteria compared to the pristine membrane, i.e., ~93% and ~92% inhibition of S. aureus and E. coli , respectively. The excellent biofouling resistance imparted by the QAC layer was further confirmed by filtration experiment, showing lower water flux decline compared to the control. In addition, QAC-modified membranes exhibited high stability during repeated chemical cleaning cycles. This grafting protocol for QAC provides a new dimension to modify a wide range of water and wastewater treatment membranes for mitigating biofouling. [ABSTRACT FROM AUTHOR]

Widespread applications of membrane technology call for the development of antibiofouling membranes. For the in-situ membrane surface modification, the antibiofouling efficacy is always hindered by the inefficient presence of antimicrobial agents on membrane surface since they are blended with the polymers and distributed into the bulk membrane matrix. In this study, a compatible carbon carrier was adopted to assemble the quaternary ammonium compound (QAC@Carbon) for enhancing its surface segregation of polyvinylidene fluoride (PVDF) microfiltration membranes and simultaneously controlling QAC release, thereby improving the efficiency in mitigating biofouling. The results indicated that carbon carrier was capable of driving surface segregation of QAC without deteriorating the physicochemical properties of membranes. The QAC concentration on surface of the membrane modified by QAC@Carbon (MCQ) was 2.5-fold of membrane blended with QAC alone (MQ). Meanwhile, carbon carrier was capable of improving QAC stability in membrane matrix to ensure a lasting antibiofouling efficacy for engineering applications. Batch tests clearly exhibited that both MCQ and MQ had antibiofouling efficiency, while MCQ membrane under cross-flow filtration demonstrated better antibiofouling behaviors compared to MQ. This is mainly attributed to the reduced accumulation of microbial biomass and improved membrane physicochemical properties (higher permeability and porosity) compared to MQ. These findings highlight the potential of introducing QAC@Carbon into polymeric membranes as an effective strategy for fabricating antibiofouling 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]

An ideal separator is essential for efficient power production from air-cathode single-chamber microbial fuel cells (MFCs). In this study, we use different kinds of membranes as separators, including Nafion 117 proton exchange membrane, polyethersulfone and poly(vinylidene fluoride) microfiltration membranes. Temporal variations of cathode performance are monitored during the experiment. Results show that MFCs with microfiltration membranes present higher power output but deterioration is still observed after about 600-h operation. With the utilization of appropriate separators (e.g., polyethersulfone membrane), biofouling, cation fouling and chemical scale fouling of the cathodes are alleviated while reaction fouling seems inevitable. Moreover, it is found that Coulombic efficiency (CE) and energy efficiency (EE) are also related to the cathode performance. Despite relatively high oxygen diffusivity (1.49 × 10 −5 cm 2 s −1 ), CE and EE of the MFC with 0.1 μm pore-size polyethersulfone membrane can reach 92.8% and 13.7%, respectively, when its average power density registers 403.5 mW m −2 . This phenomenon might be attributed to the finding that the overall substrate consumption rate due to oxygen reduction and respiration is almost constant in the air-cathode MFCs. Oxygen leakage into the electrolyte can be inhibited due to the efficient oxygen reduction reaction on the surface of the cathode. [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]

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: Polyvinylidene fluoride (PVDF)-based microfiltration membranes applied in membrane bioreactor for wastewater treatment were prepared by immersion-precipitation method. The effects of different solvent compositions such as N-N dimethylformamide (DMF), N-N dimethylacetylamide (DMAC), triethyl phosphate (TEP), dimethyl sulphoxide (DMSO) and the mixed solvents on physicochemical characteristics of the final membranes were studied. The membrane permeability and fouling performance were assessed via pure water flux and critical flux experiments, respectively. Experimental results proved that the formation of the top-layer of the PVDF membranes prepared from different solvents was controlled by the equilibrium thermodynamics, whereas the sub-layer of those membranes was dominated by the diffusion rate of solvent-nonsolvent. Furthermore, the mixture of reagents facilitated the formation of porous top-layer and the finger-like pore except for DMF and TEP. There was no significant correlation found between the solvent compositions and the hydrophilicity of the membranes. However, the membranes prepared with DMSO as the solvent or part of the solvents exhibited more negative charge and greater permeability than the membranes without DMSO in the casting solution, and these properties were supposed to improve the critical flux value and mitigate the membrane fouling potential. [Copyright &y& Elsevier]

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: An anaerobic dynamic membrane bioreactor (AnDMBR) treating municipal wastewater with a high flux of 65L/(m2 h) was operated for 11 months. Organic and inorganic membrane foulants and bulk sludge characteristics were investigated using particle size distribution analyzer, three-dimensional excitation–emission matrix fluorescence spectroscopy and X-ray fluorescence analysis. The fouling layers exhibited a double-layered structure, i.e., a loosely bound outer layer and a tightly bound internal layer. Besides that, there were foulants in membrane chambers due to the imperfect interception effect of solid particles by the dynamic membranes. Compared with the bulk sludge, membrane foulants in the internal layer and in the membrane chamber were found to have more fine particles. The Dacron mesh with large pore size could not achieve a good rejection of soluble macromolecules, which led to low soluble microbial products and extracellular polymeric substances contents in the membrane fouling layers but high contents in the foulants in membrane chambers. Microorganism activity and abundance analyses showed that the membrane foulants had some different communities and lower activities compared with the bulk sludge, which was attributed to the suppressed mass transfer in the foulants. [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]

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]

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]

Osmotically driven membrane processes (ODMPs) have gained renewed interests in recent years as an emerging separation/desalination process. However, fouling, specifically biofouling, is still an inevitable and crucial issue for long-term application of FO processes. Due to the limited studies on biofouling in ODMPs, the formation and control of biofouling are still not fully understood. This brief review focuses on the insights into the analysis techniques, formation mechanisms, and uniqueness of biofouling in FO processes. Furthermore, the control strategies of biofouling on FO membranes are highlighted and future perspectives are presented. [ABSTRACT FROM AUTHOR]

Sodium hypochlorite (NaOCl) is a widely used cleaning reagent for membrane separation processes to recover membrane permeability; however, the competitive interactions of different chlorine species with fouling layers have not been adequately elucidated. In this work, we investigated the pH-dependent diffusion of the active chlorine species and reactions involved in the consequent dissociation and/or destruction of the fouling layers. The hypochlorite conductivity and dynamic diffusion tests showed that an increase in pH facilitated the uneven and fast diffusion of active chlorine via relaxing the matrix structure of the fouling layer. Under the synergetic effects of oxidation, hydrolysis and hydraulic shearing, the enhanced diffusion resulted in an uneven but massive removal of the foulants rather than a layer-by-layer dissociation, leading to a higher membrane cleaning efficiency. Sodium dodecyl sulfate (SDS), an anionic surfactant, was added into the cleaning solution to further validate the diffusion-dependent cleaning mechanisms. With a faster diffusion process aided by SDS, the cleaning efficiency was significantly improved. These findings provide new insight into the chemical cleaning mechanisms, which are of great importance to the optimisation of cleaning efficiency for various membrane-based processes. [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]

During the long-term operation of NF membranes, the occurrence of combined gypsum-organic fouling is a significant challenge. While numerous studies have focused on enhancing the fouling resistance of NF through various methods (e.g., antiscalants, pretreatment), there has been limited exploration into the correlation between its structural looseness and fouling resistance. Herein, we conducted an experimental study to evaluate the correlation by employing three NF membranes with different looseness degrees: a custom-developed loosely structured NF membrane (CLNF), the moderately loose NF270, and the tightly structured NF90. Our findings indicated that NF membranes with loose polyamide structure exhibited superior fouling resistance to gypsum scaling and combined gypsum-organic fouling, induced by model organic matters like bovine serum albumin (BSA), humic acid (HA), and sodium alginate (SA). After applying SA-coating to calibrate the surface properties of the membranes to exclude the influence of surface roughness, hydrophilicity, and functional groups, our study attributed the difference in fouling resistance to variations in ionic selectivity stemming from membrane looseness. Specifically, the primary advantage of looser polyamide NF membranes lies in enhanced Ca2+ permeation, which not only reduces the "egg-box" effect and surface foulant accumulation but also diminishes cake-enhanced concentration polarization, effectively mitigating gypsum-organic fouling. In real water testing scenarios, the enhanced fouling resistance of loose NF membranes was further affirmed. This research underscored the unexpected benefit of loose NF membranes in terms of fouling resistance, providing a novel insight for future application. [Display omitted] • Polyamide layers of CLNF, NF270, and NF90 possessed different degrees of looseness. • Looser structure enhanced resistance to gypsum scaling and gypsum-organic fouling. • The looser NF membrane still mitigated fouling after calibrating surface properties. • Improved Ca2+ permeation and reduced polarization effect resulted in fouling mitigation. • Enhanced fouling resistance of loose NF membranes was confirmed in real conditions. [ABSTRACT FROM AUTHOR]

• A pilot-scale UF-RO system was constructed for treating real microelectronic wastewater. • The UF-RO system showed removal rate of > 99.5 % for tetramethylammonium hydroxide. • Inorganic, organic, and biofouling were identified on the RO membrane surface. • The 2nd stage experienced the most pronounced organic fouling in the RO system. • High concentration of toxic contaminants might inhibit development of biofouling. The microelectronic industry faces the significant challenge of managing vast volumes of wastewater containing toxic and harmful pollutants. While the Ultrafiltration-Reverse Osmosis (UF-RO) system has gained recognition as a potential solution for the reclamation and reuse of such wastewater, there is a lack of comprehensive understanding on its performance and membrane fouling conditions in the context of actual microelectronic wastewater. In this study, we continuously monitored the performance of a pilot-scale UF-RO system treating microelectronic wastewater. The RO membrane was subject to autopsy characterization at the end of its operation. The UF pretreatment performance remained consistent, with the UF-RO system showcasing high removal efficiency (>99.5 %) for tetramethylammonium hydroxide (TMAH), the primary pollutant in the microelectronic wastewater. Inorganic, organic, and biofouling were identified on the membrane surface, with the biofouling as the predominant form. A microbial community analysis showed that Proteobacteria and Bacteroidetes were the dominant bacteria on the membrane surface at the phylum level, while Alicycliphilus , Chryseobacterium , and Flavobacterium were predominant at the genus level. Fouling characteristics and degrees varied across the four stages, with the fouling in the 2nd stage being the most severe. Interestingly, an increased concentration of TMAH in the influent of the 4th stage seemed to inhibit the development of biofouling to some extent. This study offers valuable insights into the practical performance of the pilot-scale UF-RO technology when treating microelectronic wastewater and lays the groundwork for developing strategies to address membrane fouling concerns within the microelectronics industry. [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]

Oil fouling is the crucial issue for the separation of oil-in-water emulsion by membrane technology. The latest research found that the membrane fouling rate was opposite to the widely used theoretical prediction by Derjaguin-Landau-Verwey-Overbeek (DLVO) or extended DLVO (XDLVO) theory. To interpret the contradiction, the molecular dynamics was adopted to explore the molecular behavior of oil and emulsifier (Tween 80) at membrane interface with the assistance of DLVO/XDLVO theory and membrane fouling models. The decreased flux attenuation and fitting of fouling models proved that the existence of Tween 80 effectively alleviated membrane fouling. Conversely, DLVO/XDLVO theory predicted that the membrane fouling should be exacerbated with the increase of Tween 80 concentration in O/W emulsion. This contradiction originated from the different interaction energy between oil/Tween 80 molecules and polyether sulfone (PES) membrane. The favorable free energy of Tween 80 was resulted from the sulfuryl groups in PES and hydrogen bonds (O-H...O) formation further strengthened the interaction. Therefore, Tween 80 could preferentially adsorb on membrane surface and form an isolation layer by demulsification and steric hindrance and resist the aggregation of oil, which effectively alleviated membrane fouling. This study provided a new insight in the interpretation of interaction in O/W emulsion. [Display omitted] • Tween 80 enhanced the stability, homogeneity, stable flux of O/W emulsions. • Interaction energy of Tween-PES was at least 2 times higher than that of oil-PES. • Tween 80 shows favorable free energy and forms O-H...O bonds with sulfuryl groups. • MD interprets the contradiction between DLVO/XDLVO theory and fouling propensity. [ABSTRACT FROM AUTHOR]

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]

Environmental and economic concerns necessitate the recycle of end-of-life (EOL) reverse osmosis (RO) membranes. Controlled downcycling of EOL RO membrane to nanofiltration (NF)-like or ultrafiltration (UF)-like membrane through regulating sodium hypochlorite (NaClO) exposure doses has been developed in recent years. However, the impact of foulants on the chlorination-based membrane downcycling is often overlooked. An alkaline-NaClO treatment strategy was employed to downcycle Si-Al complex-fouled EOL RO membrane. Alkaline cleaning not only partially removed Si-Al complex foulants via dissolution, but also converted Al 2 O 3 ·SiO 2 to Al-O-Si amorphous oxides. Subsequent NaClO treatment gradually deconstructed the Si-Al complex fouling layer by dissolving Al contained in Al-O-Si amorphous oxides and degraded the polyamide (PA) layer with extended exposure time, resulting in membrane with loose NF-like characteristic. Moreover, the conversion of Al-contained component with alkaline pre-treatment prevented Al3+-catalyzed degradation of PA layer and ensure controlled downcycling. For the downcycling to UF-like membrane, complete removal of PA layer with sufficient chlorine oxidation was essential while alkaline pre-treatment process was optional. Both downcycled loose NF-like and UF-like membranes exhibited satisfactory filtration and antifouling performance. Our study presents an effective and robust protocol for controllable downcycling of EOL RO membrane with alkaline pre-treatment based on their fouling characteristic. [Display omitted] • Alkaline-NaClO treatment was used to downcycle Si-Al complex fouled RO membrane. • Pre-treatment prevents PA layer from Al-catalyzed oxidation by converting the foulants. • Alkaline pre-treatment is essential to controlled downcycle of loose NF-like membrane. • Sufficient chlorine exposure is more important for downcycle of UF-like membrane. • Downcycle strategy should be designed based on fouling characteristic of EoL membrane. [ABSTRACT FROM AUTHOR]

The recycling of end-of-life water purification membranes is of great significance for environmental sustainability. However, only techniques for downcycling end-of-life high-pressure membranes are available. Here, we propose to upcycle fouled microfiltration membranes for fabricating new high-pressure polyamide (PA) thin-film composite membranes via interfacial polymerization (IP). A cross-linked, defect-free, and ultrathin PA active layer was formed on biopolymer-fouled substrates. In contrast to the decreased pure water permeance of substrates caused by biopolymer fouling, the upcycled membranes show excellent water permeance (∼30 L m−2 h−1 bar−1) and Na2SO4 rejection (∼95%) in nanofiltration tests for water purification. The biopolymer foulants regulate the IP process and the formation of the PA layer. Furthermore, the foulants between the PA layer and substrate can create additional channels for water transport. The PA layer formation could also be achieved on real fouled microfiltration substrates. This proof-of-concept study paves the way for upcycling fouled/end-of-life low-pressure membranes to fabricate new high-pressure membranes for water purification, forming a closed eco-loop of membrane recycling. [ABSTRACT FROM AUTHOR]

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]

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]

• 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]

There are two types of popular forward osmosis (FO) membrane materials applied for researches on FO process, cellulose triacetate (CTA) and thin film composite (TFC) polyamide. However, performance and fouling mechanisms of commercial TFC FO membrane in osmotic membrane bioreactors (OMBRs) are still unknown. In current study, its biofouling behaviors in OMBRs were investigated and further compared to the CTA FO membrane. The results indicated that β- d -glucopyranose polysaccharides and microorganisms accounted for approximately 77% of total biovolume on the CTA FO membrane while β- d -glucopyranose polysaccharides (biovolume ratio of 81.1%) were the only dominant biofoulants on the TFC FO membrane. The analyses on the biofouling structure implied that a tighter biofouling layer with a larger biovolume was formed on the CTA FO membrane. The differences in biofouling behaviors including biofoulants composition and biofouling structure between CTA and TFC FO membranes were attributed to different membrane surface properties. [ABSTRACT FROM AUTHOR]

This study aims at comparatively evaluating anaerobic and aerobic MBRs for the treatment of azo-dye containing synthetic wastewater. Also, the filtration performances of AnMBR and AeMBR were compared under similar operating conditions. In both MBRs, high COD removal efficiencies were observed. Although almost complete color removal was observed in AnMBR, only partial (30–50%) color removal was achieved in AeMBR. AnMBR was successfully operated up to 9 L/(m 2 h) (LMH) and no chemical cleaning was required at 4.5 LMH for around 50 days. AeMBR was operated successfully up to 20 LMH. The filtration resistance of AnMBR was generally higher compared to AeMBR although reversible fouling rates were comparable. In both MBRs, offline chemical cleaning with NaOCl and sulfuric acid almost completely removed irreversible fouling and the resistances of chemically cleaned membranes were close to those of new membranes. [ABSTRACT FROM AUTHOR]

• Fouling deteriorated pollutant degradation in electrochemical filtration system. • Biofouling suppressed the effluent toxicity of electrochemical filtration system. • Live microorganisms played important roles in the degradation of intermediates. • Synergetic effects of electro-oxidation and biodegradation reduced effluent toxicity. Electrochemical filtration system (EFS) has received broad interest due to its high efficiency for organic contaminants removal. However, the porous nature of electrodes and flow-through operation mode make it susceptible to potential fouling. In this work, we systematically investigated the impacts of biofouling on sulfanilic acid (SA) removal and effluent toxicity in an EFS. Results showed that the degradation efficiency of SA slightly deteriorated from 92.3% to 81.1% at 4.0 V due to the electrode fouling. Surprisingly, after the occurrence of fouling, the toxicity (in terms of luminescent bacteria inhibition) of the EFS effluent decreased from 72.3% to 40.2%, and cytotoxicity assay exhibited similar tendency. Scanning electron microscopy and confocal laser scanning microscopy analyses revealed that biofouling occurred on the porous cathode, and live microorganisms were the dominant contributors, which are expected to play an important role in toxicity suppression. The relative abundance of Flavobacterium genus, related to the degradation of p -nitrophenol (an aromatic intermediate product of SA), increased on the membrane cathode after fouling. The analysis of degradation pathway confirmed the synergetic effects of electrochemical oxidation and biodegradation in removal of SA and its intermediate products in a bio-fouled EFS, accounting for the decrease of the effluent toxicity. Results of our study, for the first time, highlight the critical role of biofouling in detoxication using EFS for the treatment of contaminated water. [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]

A novel vermiculite nanoparticles (Verm NPs) modified poly(vinylidene fluoride) (PVDF) ultrafiltration membrane was firstly fabricated via surface coating at pH 7.2–7.3. The dense but porous modified surface formed by controlling the self-polymerization rate of dopamine at relatively weak alkalinity provided both high water flux and rejection rate of BSA, which broke the trade-off between permeability and rejection rate. The contact angle of optimal modified membrane decreased from 69.6° to 45.0°, showing the effectively enhancement of hydrophilicity. By filtrating two kinds of real oil-in-water emulsions, the stable flux of modified membrane was approximately 2 times higher than that of pristine membrane for both low and high concentration oil-in-water emulsions. In addition, the Verm-PVDF membrane also showed a higher removal efficiency of oil and total organic carbon. According to membrane fouling model analysis, the fouling behavior including adsorption, deposition, blockage of membrane pores and formation of cake layer had obviously alleviated after Verm modification for the two kinds of oil-in-water emulsions due to the formation of water layer by isomorphism substitution and surface hydroxylation of Verm NPs. Assessed by extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, Verm-PVDF membrane exhibited a higher energy barrier and an extremely strong repulsive force for foulants to overcome in low and high concentration emulsions during fouling. Overall, the improved antifouling ability and separation performance of modified membrane indicated that the inartificial Verm NPs was a robust material for pH-control membrane modification with potential application value in oil/water separation. [Display omitted] ● Verm NPs coated PVDF membranes were fabricated via surface modification by pH control. ● The dense but porous Verm-PVDF membrane formed to obtain both high permeability and rejection rate. ● Verm-PVDF membrane exhibited great foulant removal efficiency and antifouling performance for compressor cleaning fluids. ● All the fouling behaviors alleviated after modification due to the isomorphism substitution and surface hydroxylation of Verm NPs. ● Verm-PVDF membrane showed a higher energy barrier and an extremely strong repulsive interaction assessed by XDLVO theory. [ABSTRACT FROM AUTHOR]

The effective treatment of oily saline wastewater has posed a challenge for membrane distillation (MD) technology due to the severe oil fouling. To address this dilemma, a Janus membrane was successfully developed in this study by incorporating tannic acid (TA)/ferric chloride (FeCl 3) complex and polyvinylidene fluoride (PVDF) onto the polytetrafluoroethylene (PTFE) membrane surface via the nonsolvent-induced phase separation (NIPS) method. The characterization results demonstrated that the TA-Fe3+ complex was compatible with the PVDF, and the composite surface layer was firmly attached on the PTFE substrate. Furthermore, the Janus membrane showed a high hydrophilicity and strong underwater superoleophobicity (oil contact angle, 154.80 ± 1.07°), with had an excellent vapor flux (28.30 ± 1.18 Lm−2 h−1) compared with the membrane without the embedding of TA-Fe3+ complex (18.16 ± 1.45 Lm−2 h−1). According to theoretical arithmetic of mass transfer, the evaporation interface of the Janus membrane had transferred during the MD process, contributing to promoting the mass transfer performance and fouling resistance. When treating oily saline emulsion, the Janus membrane exhibited a good desalination and anti-oil fouling stability compared to the control membranes. This study suggests that the fabricated lipophobic Janus MD membrane has great potential in the treatment of oily saline wastewater. [Display omitted] • Underwater superoleophobic dual-layer Janus membrane was fabricated. • TA-Fe3+ complex was used as an additive to enhance the hydrophilicity of matrix. • The Janus membrane has a long-term stable distillate flux for oily saline emulsion treatment. • The mass-heat transfer efficiency was assessed by establishing mathematic model. • The Janus membrane has a low mass transfer resistance. [ABSTRACT FROM AUTHOR]

Biofouling remains to be one of major obstacles in membrane bioreactors (MBRs), calling for the development of antibiofouling membranes. Silver nanoparticles (AgNPs), being a kind of broad spectrum bactericidal agent, have been widely used for modifying membrane; however, uncontrollable release of AgNPs and thus a short lifetime of modified membranes are thorny issues for the AgNPs-modified membranes. In this study, silica nanopollens were used as AgNPs nanocarriers for membrane modification (ASNP-M), which could improve silver delivery efficacy, avoid agglomeration and control Ag+ release towards bacteria. At a silver loading of 107.7 ± 10.9 μg Ag/cm2, ASNP-M effectively inhibited growth of Escherichia coli and Staphylococcus aureus , with an Ag+ release rate of 0.5 μg/(cm2 d). Long-term MBR tests showed that ASNP-M exhibited a significantly reduced transmembrane pressure increase rate of 0.88 ± 0.34 kPa/d which was much lower than that of two control membranes, i.e., pristine membrane (M0) (2.32 ± 0.86 kPa/d) and Ag@silica nanospheres (without spikes) modified membrane (ASNS-M) (2.25 ± 1.28 kPa/d). No significant adverse influences on the pollutant removal were also observed in the reactor. Foulants analysis revealed that biofilm of ASNP-M was thinner and comprised of mainly dead cells, and only organic matter with strong adhesion properties was allowed to attach onto the membrane surface. Bacterial community analysis suggested that the incorporation of Ag@silica nanopollens inhibited colonization of bacteria which are capable of causing membrane biofouling (e.g., Proteobacteria and Actinobacteria). These findings highlight the potential of the antibiofouling membrane to be used in MBRs for wastewater treatment and reclamation. Image 1 • Silica nanopollens (SNP) were used as AgNPs nanocarriers for membrane modification. • Ag@SNP improved Ag delivery efficacy, avoided agglomeration and control Ag+ release. • Long-term MBR tests showed lasting antibiofouling property of the modified membrane. • The modified membrane had thin fouling layer that was comprised of mainly dead cells. [ABSTRACT FROM AUTHOR]

• Anaerobic side-stream reactor (ASSR) coupled MBR was proposed for sludge reduction. • Effect of filling fractions of carriers in ASSR on membrane fouling (MF) was studied. • 25 % carriers alleviated MF by promoting hydrolysis and reducing sludge viscoelastic. • 50 % carriers improved MF little due to the increase of shear forces to biofilm. • MiSeq revealed biomarkers related to severe MF easily attached on membrane surface. An anoxic/oxic membrane bioreactors (AO-MBR) and three identical anaerobic side-stream reactor coupled with anoxic/oxic membrane bioreactors (ASSR-MBR) were constructed and operated in parallel to investigate the appropriate filling fraction of carriers packed in ASSR, influences on pollutants removal, sludge reduction, membrane fouling and microbial community of ASSR-MBR. Inserting ASSR achieved efficient COD removal and nitrification, and packing carriers in ASSR obtained the highest sludge reduction efficiency of 50.5 % at filling fraction of 25 %. Compared to AO-MBR, inserting ASSR without carriers induced the release of viscous components in extracellular polymeric substances (EPS) and the formation of calcium carbonate-related bacteria on membrane surface, and thus deteriorated membrane fouling. Packing carriers with 25 % filling fraction promoted the hydrolysis of soluble microbial products and EPS, whilst reduced the viscoelasticity of sludge flocs. Higher filling fraction of 50 % increased the shear forces to the biofilm and biomarkers related to membrane fouling, and thus showed little improvement to alleviate membrane fouling. MiSeq sequencing revealed that although it enriched in the bulk sludge of conventional ASSR-MBR and the coupled reactor with filling fraction of 50 %, the floc-forming, hydrolytic and fermentative bacteria were more inclined to attach on the membrane surface and alleviate fouling process. [ABSTRACT FROM AUTHOR]

Membrane biofouling is one of major issues impeding the applications of polyvinylidene fluoride (PVDF) membrane for water and wastewater treatment. In this work, quaternary ammonium compounds loaded on silica nanopollens (QAC@SNP) were developed to modify polyvinylidene fluoride (PVDF) membrane for mitigating biofouling. The modified membrane (M-Si-Q) by QAC@SNP demonstrated efficient antibacterial efficiency against E. coli (inhibition rate ~98.2%) and S. aureus (inhibition rate ~99.9%) compared to the control (M0), respectively. The inhibition rate of M-Si-Q was also higher than the membrane blended with silica nanopollens (M-Si) (~86.1% of E. coli and ~70.9% of S. aureus , respectively), suggesting the synergetic effects of SNP and QAC for biofouling mitigation. Batch filtration tests showed that M-Si-Q could effectively alleviate the decline of membrane permeate flux compared to the control. Confocal laser scanning microscope analysis of membrane samples after fouling showed that almost all of cells on the M-Si-Q membrane were dead cells, while abundant live cells were observed for the M-Si and M0. Moreover, the M-Si-Q membrane had less quantity of proteins on the surface, demonstrating that M-Si-Q had excellent antibiofouling ability. The above findings indicated a strong potential of using QAC@SNP to fabricate antibiofouling membranes for water and wastewater treatment. • QAC@silica nanopollens (SNP) were used to modify polyvinylidene fluoride membrane. • The modified membrane had efficient antibacterial efficiency against model bacteria. • Synergetic effects of SNP and QAC for biofouling mitigation were observed. • QAC@SNP had a strong potential to be used to fabricate antibiofouling membranes. [ABSTRACT FROM AUTHOR]

Applications of membrane technologies for water and wastewater treatment call for antibiofouling membranes. Inspired by nature's spiky topological features of pollen grains, we developed silver-decorated biomimetic silica nanopollens (SNPs) to modify a polyvinylidene fluoride microfiltration membrane. The modified membrane demonstrated compelling antibiofouling performance compared to the pristine membrane, which was attributed to the synergetic effects of SNPs and loaded silver nanoparticles. The surface spikes of SNPs could act as multiple 'entry claws' to bind to the cell membrane upon contact, inducing physical deformation and metabolic disturbance of cells. More importantly, the SNPs could serve as a delivery vector for silver ions that were released from silver nanoparticles loaded in SNPs, further leading to cell damage due to the generation of reactive oxygen species and respiratory inhibition. These synergetic effects of SNPs and loaded silver nanoparticles imparted the modified membrane with potent antibiofouling behavior both in batch and continuous flow tests using model bacteria, Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive), respectively. Our strategy provides a novel pathway using biomimetic materials to fabricate antibiofouling membranes for water and wastewater treatment. Image 1 • Silver-decorated silica nanopollens (SNPs) were used to modify PVDF membrane. • The modified membrane demonstrated compelling antibiofouling performance. • The antibiofouling behaviors were related to the synergetic effects of SNPs and Ag. • Physical penetration of SNP and released Ag ions caused damage of bacterial cells. [ABSTRACT FROM AUTHOR]

Membrane fouling is the bottleneck limiting the wide application of membrane processes. Herein, we adopted an electroactive polyether sulfone (PES) membrane capable of mitigating fouling by various negatively charged foulants. To evaluate anti-fouling performance and the underlying mechanism of this electroactive PES membrane, three types of model foulants were selected rationally (e.g., bovine serum albumin (BSA) and sodium alginate (SA) as non-migratory foulants, yeast as a proliferative foulant and emulsified oil as a spreadable foulant). Water flux and total organic carbon (TOC) removal efficiency in the filtering process of various foulants were tested under an electric field. Results suggest that under electrochemical assistance, the electroactive PES membrane has an enhanced anti-fouling efficacy. Furthermore, a low electrical field was also effective in mitigating the membrane fouling caused by a mixture of various foulants (containing BSA, SA, yeast and emulsified oil). This result can be attributed to the presence of electrostatic repulsion, which keeps foulants away from the membrane surface. Thereby it hinders the formation of a cake layer and mitigates membrane pore blocking. This work implies that an electrochemical control might provide a promising way to mitigate membrane fouling. [ABSTRACT FROM AUTHOR]