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BACKGROUND Membrane fouling is still a big problem to be solved. In order to reduce membrane fouling and improve the efficiency of phenol degradation, a Pd/carbon conductive membrane, used as both a filter membrane and a cathode, was prepared by electrodeposition of Pd on a carbon membrane and then employed to develop an electro-microbial membrane system ( EMMS). RESULTS The degradation rate of phenol was higher than that in a microbial membrane system ( MMS) and in an electrocatalytic membrane system ( EMS). The phenol degradation followed zero-order kinetics in the three systems. The degradation efficiencies of phenol and COD were 99.6% and 95.4%, respectively, at 10 h in the EMMS. The mean membrane flux in the EMMS was 2.64 times that in the MMS and 1.25 times that in the EMS. The reasons for the excellent anti-fouling of Pd/carbon membrane were: (1) the membrane had repulsion potential for the pollutant because it carried negative charges; (2) H2 bubbles generated on the membrane surface possibly induced gas and liquid microflows to detach and even blow-out the foulants; and (3) the membrane was scoured by shear stress resulting from aeration. CONCLUSIONS A carbon/Pd conductive membrane as cathode has great potential for membrane fouling mitigation in EMMS. © 2016 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Magnetic anion exchange (MIEX) has been increasingly concerned owing to its excellent performance for the removal of dissolved organic carbon in the treatment of drinking water. In this study, the ability of ultrafiltration (UF) membrane fouling control was analyzed by different combination processes of MIEX-UF. A single cycle and multi-cycle operations were conducted, and the separated and integrated processes of MIEX-UF were compared. Membrane filtration resistance, removal of organics, and morphologies of the membrane surface were analyzed. The results of the short-term operation did not show any obvious improvement in the membrane fouling control in the separated process (compared to UF alone); however, a marked improvement was obtained in the integrated process. The membrane filtration resistance analysis showed that the cake resistance (Rc) and pore blocking resistance (Rp) in the integrated process were only 52 and 24% of the values in the separated process. The multi-cycle operation demonstrated that the cumulative rate of hydraulically irreversible fouling was 0.0021 in the integrated process and was much lower than that in the separated process (0.0182). The mechanistic analysis shows that in the integrated process, a dynamic layer was formed on the membrane surface by the deposited MIEX beads, which markedly decreased the accumulation of the membrane foulants on the membrane surface and in the membrane pores. [ABSTRACT FROM PUBLISHER]

Abstract: According to effluent water quality character- ristics of membrane bioreactor (MBR) in the municipal sewage treatment plant, major foulants which causing fouling of nanofiltration membrane elements in subsequent nanofiltration system were analyzed. And based on finding out the major foulants, a suitable cleaning method was determined in this paper. In this paper, determining the fouling level of nanofiltration membrane fouled with the effluent of membrane bioreactor (MBR) based on the change of pressure about nanofiltration system. In order to investigate the fouling reasons and cleaning methods of nanofiltration membrane, SEM and EDX were applied to analyze the membrane fouling layer. The experimental results showed that, the pressure of nanofiltration system was increased 30% after 90 days running. And the result of SEM-EDX about membrane showed that, the major foulants of membrane include organic substances and silicon dioxide. And there may be some inorganic substances, which contained magnesium (Mg) and calcium (Ca). Thought cleaning experiments with HCl, NaOH, STPP (Sodium tripolyphosphate, Na5P3O10) +Na-DDBS (sodium dodecyl benzene sulfonate, C6H5(CH2)12SO3Na)about fouled membrane, it was further showed that the foulants of membrane include organic substances, silicon dioxide and some inorganic substances which contained magnesium(Mg) and calcium(Ca). [Copyright &y& Elsevier]

Highlights • The effects of membrane backwashing on hollow fiber length are simulated directly in MBR. • Laser bijection sensors are imported to verify the simulation results. • The different membrane resistance distribution play important role in backwashing effectiveness. Abstract In this study the effect of different fouling stages of hollow fiber membranes on effective backwashing length in MBR has been investigated. Computational fluid dynamics (CFD) is imported to simulate backwashing process. A multi-physics coupling model for free porous media flow, convective mass transfer and diluted species transport was established. The laser bijection sensors (LBS) were imported to monitor the backwashing solution position inside fiber lumen. Simulation results indicated that membrane fouling degree could change the velocity of backwash solution inside fiber lumen and make a further effect on effective backwash length. The signal variations of LBS are in accordance with the simulation results. The backwashing process can only play an active role when the filtration pressure is below the critical TMP. It can be concluded that backwash duration in industrial applications need to be set based on changes in TMP. [ABSTRACT FROM AUTHOR]

In this work, a filtration cell for synchronized UV–vis spectroscopic and electrochemical impedance investigation of the membrane fouling process has been designed. The setup achieves in situ monitoring of the interfacial region during filtration by fiber-optic UV–vis spectroscopy and electrochemical impedance spectroscopy. The influence of ionic strength on protein fouling of membrane was investigated in detail. Results indicate that the flux decline rate decreased slightly when the ionic strengths increased from 0 to 10 and 100 mM during initial filtration stage, however, membrane fouling at higher ionic strengths became more serious at longer fouling duration. This was mainly due to the generation of concentration polarization (CP) and electroosmotic back flow (EOBF) for longer duration, which caused elevated concentration of salt ions near the membrane surface and additional filtration resistance, and accompanied by salting-out dehydration of protein on membrane surface. This is the process that occurs in protein fouling during long-term run, the hydration forces experience from enhancement to disappearance. This study not only expends our knowledge of the effect of ionic strength on protein fouling behavior but also provides a method for the in situ and real time characterization of membrane-solution interface and filtration performance. [ABSTRACT FROM AUTHOR]

Natural organic matter (NOM) plays a key role in membrane fouling, especially in irreversible fouling. Different PVDF membrane aging degrees lead to variations in the chemical/physical properties of membrane which further affect membrane permeability and fouling behavior. In the present work, the interaction energy between foulants and membranes with different ageing degrees was assessed by the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory, using bovine albumin serum (BSA), sodium alginate (SA) and humic acids (HA) as model foulants. Fluorescence labeling and confocal laser scanning microscopy (CLSM) was applied to characterize the distribution rule of binary foulants formed on membrane surfaces. The calculation of CLSM images via COMSTAT could quantify each foulant distribution in the fouling layer, which provides insights on combined fouling mechanisms. Results showed that membrane ageing modifies NOM fouling behaviors in according to the degree of ageing. Furthermore, filtration of the SA/BSA mixtures showed that BSA was first absorbed on the membrane surface in a competitive environment, which then plays a bridge role in promoting the SA to form a denser cake layer on the membrane. That is to say, different ageing degrees mainly affected the attachment of BSA to the membrane surface with regard to mixture of organics. [ABSTRACT FROM AUTHOR]

Sodium hypochlorite (NaClO) is a common chemical cleaning agent in water treatment due to its effective removal of irreversible pollutants that cannot be removed by physical cleaning. In this research, PVDF ultrafiltration (UF) membranes were exposed to NaClO for 120–960 h, and then the structural/surface characteristics of the control and exposed membranes were compared. Results showed that different exposure doses lead to variations in PVDF membrane structural/surface characteristics according to different mechanisms and further influence the permeability and fouling behaviors of PVDF membranes during ultrafiltration (UF) processes. Reversible fouling was the most common fouling behavior of membranes and exposure to NaClO resulted in higher degree of irreversible fouling. The irreversible flux decline of the membranes could not only caused by physically irremovable fouling but also irreversible compaction of the membranes due to the formation of macro-voids in the membrane skin layer. The changes in membrane mechanical properties caused a sharp increase in the inherent membrane resistance (R m ) which was generally considered as a constant. ‘Dynamic resistance mechanism’ could be proposed based on the impact of different NaClO exposure doses on the total membrane resistance (R t ), which is the sum of the changes in R m and the variation of fouling resistance (R f ) resulted from the changes in surface characteristics of the membranes. According to this concept, the filtration operating conditions and cleaning processes could be optimized in water treatment. [ABSTRACT FROM AUTHOR]

A newly synthesized magnetic hydrogel was applied to physical cleaning of low pressure microfiltration (hollow fiber) membranes. MC(50%)-90-3 h was chosen from several kinds of high-intensity magnetic hydrogels for its superior performance. According to the properties of the hydrogels, membrane filtration and cleaning tests was conducted under a orthogonal experiment with different factors and levels. An optimal combination of factors and levels was got as particle size of 5 mm, aeration intensity of 1 L/min and volume percent of 10%. The comparison of traditional aeration cleaning, backwashing and the hydrogels cleaning showed the superiority of the hydrogels with the TMP recovery of 93.07%. The results of shear stress detection showed that the outlet of membrane module received the lowest shear stress in corresponding with the most serious fouling. Therefore, a new cleaning method containing enhanced cleaning in position was created to make the intensive cleaning to the position with severe fouling. The recovery of TMP reached up to 96.62% after cleaning of the new method which indicated that reversible fouling can almost be removed completely. This good cleaning effect was hoped to provide support for further membrane physical cleaning. [ABSTRACT FROM AUTHOR]

This study used the ultraviolet-visible (UV–vis), synchronous fluorescence, and excitation-emission matrix (EEM) spectroscopy coupled with zeta potential and particle size to explore the dissolved organic matter (DOM) solutions properties with the addition of two kinds of coagulants, including aluminum chloride and ferric chloride, in humic solutions and surface water. The results of zeta potential and particle size showed the size of aggregates became larger with the addition of coagulant. The binding sequence of coagulant to DOM was followed from aromatic amino acids to fulvic-like and humic-likes fractions. The results of the unified membrane fouling index (UMFI) were showed negatively correlated with the concentrations of coagulant due to the cake layers formed by aggregates being looser and more permeable. Among all the 12 spectral parameters, slope radio (S R) and specific fluorescence intensities (SFI) had the most significant correlation to UMFI. The multi-spectral fusion for predicting UMFI was established via multiple linear regressions and the backpropagation neural network (BPNN) by using the parameters with both S R and SFI with good accuracy and robustness. Sensitivity analyses results showed that SFI was more sensitive than S R in solutions with high protein-like substances, while S R was more sensitive than SFI with high humic-like substances. [Display omitted] • The binding sequence was followed from aromatic amino to fulvic and humic fraction. • Multi-spectral fusion models for predicting UMFI were established via MLR and BPNN. • SFI was more sensitive with high protein substances, while S R with high humic acid. • BPNN was suitable for predict UMFI and had good robustness and adaptability. [ABSTRACT FROM AUTHOR]

Abstract In ultrafiltration (UF) applications, the antifouling modification of semi-crystalline poly (vinylidene fluoride) (PVDF) membrane aroused extensive attention. However, efforts have paid less attention to the roles of PVDF polymorphs in fouling alleviation. In this study, we report a new strategy to tailor the polymorphs and pore structure of the PVDF membranes, simultaneously, via incorporating the in-situ blending of Pluronic F127 (F127) with a sodium chloride (NaCl) coagulation bath (CB). The NaCl CBs were utilized to create ion-dipole interactions between Na+ and PVDF molecule chains, and to promote the formation of polar β-PVDF phase during phase inversion process. When cooperated with the NaCl CBs, due to the intensified copolymer-polymer interactions, blending amphipathic F127 was demonstrated more effective in manipulating the membrane morphology compared with blending hydrophilic additives. The prepared membrane possessed a highly porous surface with narrowed size distribution, resulting in a great enhancement for both the permeability and selectivity. Furthermore, isopropanol (IPA) post-treatment was purposely performed to wash out the F127 embedded in the membrane matrix. The dominating β-PVDF phase almost doubled the surface energy of the pure PVDF membrane compared with the α-PVDF phase, especially in electron donor functionality, which endowed the membrane enhanced fouling resistance for natural organic matter. As the fouling resistance introduced by polymer itself is more attractive than by exotic additives due to the better stability, we anticipate this new strategy will have numerous potential applications in the future. Graphical abstract Image 1 Highlights • Ion-dipole interactions induced the formation of polar β-PVDF phase. • Copolymer-polymer interactions played important role in tailoring pore structure. • Dominant β-PVDF phase enhanced membrane electron donor ability and wettability. • Membrane's permeability, selectivity and fouling resistance were simultaneously improved. [ABSTRACT FROM AUTHOR]

This paper presents a study on the impact of sodium hypochlorite (NaClO) on the performance and fouling behavior of polysulfone (PSF) membranes. The performance of aged PSF membranes was studied under different transmembrane pressures (TMPs), and three critical TMPs including the pressure corresponding to critical flux (P C ), the pressure corresponding to critical filtration efficiency (P V ), and the pressure corresponding to the greatest retention ability (P R ) were innovatively proposed. In terms of an aged membrane, the filtration efficiency (η v ) and retention ability (R) were decreased, while, the enhanced sieving capacity (η s ) were experimentally proved. These are strongly related to modified surface properties and enlarged pore diameters of aged PSF membranes. The fitting results of Hermia’s model and critical flux analysis mutually verified that the formation of cake layer fouling on an aged PSF membrane surface was delayed. However, the specific fouling results indicated the aged membrane suffered a more severe pore block fouling. Moreover, the target plot also implied that the critical parameters (P C , P V and P R ) can serve as indicators of the evolution of membrane performance and fouling behaviors. [ABSTRACT FROM AUTHOR]

[Display omitted] • The particles scale was regulated by in-situ Fe(VI) oxidation-hydroxide coagulation. • Meso-particle in range of 20–100 nm was positive related to irreversible fouling. • The meso-particle had more stable and tight structure than micro-particle. • The interfacial interaction between membrane and multi-scopic particles were revealed. This study applied a ferrate in-situ oxidation-coagulation ultrafiltration integrated system in drinking water treatment, illustrating the influence of meso-particles on membrane fouling behavior by oxidation-coagulation regulating. Under neutral conditions, the meso-particles between 20 and 100 nm were the mainly components at initial oxidation phase. Subsequently small molecules gathered to meso-particles of 200–500 nm under the flocculation, and 40 % of micro-particles aggregates were detected finally. According to the statistical correlation between multiscale particles and membrane flux and resistance, wherein meso-particle especially in range of 20–100 nm principally contributed to the irreversible fouling while the correlation coefficients above 0.9, and reversible fouling related to the synergy of meso- and micro-particles. Additionally, the fouling behavior of meso-particles on the membrane surface and the structural evolution of the fouling layer were illustrated based on the interfacial interaction, UV–vis reflectance spectroscopy and molecular dynamics simulation. The changes in hydrophilicity and charge of the meso-particle (20–100 nm) increased the attractive interaction with the membrane, causing severe membrane fouling. As flocculation progressed, the polynuclear Fe-hydroxide interacted with HA molecular fragments, and aggregated to meso-particles in range of 200–500 nm, which had smaller molecular gap and more tight structure than micro-particle (500–1000 nm), due to the HA molecular fragments were more strongly bound on the polynuclear Fe-hydroxide compared to iron hydroxide cluster. The stable and compact structure induced the meso-particles deposited on membrane surface and hardly be physically cleaned. The investigation of meso-particle on membrane fouling was provided new insight into the membrane separation process. [ABSTRACT FROM AUTHOR]

Membrane fouling (especially biofouling) as a critical issue during membrane reactor (MBR) operation has attracted much attention in recent years. Although previous review papers have presented different aspects of MBR’s fouling when treating various wastewaters, the information related to biofouling in MBRs has only simply or partially reviewed. This work attempts to give a more comprehensive and elaborate explanation of biofilm formation, biofouling factors and control approaches by addressing current achievements. This also suggests to a better way in controlling biofouling by developing new integrated MBR systems, novel flocculants and biomass carriers. [ABSTRACT FROM AUTHOR]

The practical applications of water treatment techniques based on hydrophobic aeration membrane are limited due to membrane pores blocking. Various studies have revealed that both biofilm and microbial secretion can exacerbate membrane fouling. Recently, we constructed a membrane-aerated biofilm reactor (MABR) system for treating micro-polluted surface water in order to identify the primary cause for oxygen transfer rate (OTR) decline. It was found that microbial secretion had a more prominent negative effect than that caused by biofilm, as manifested by the fact the effect of microbial secretion (66.49%) was greater than the resistance of biofilm (38.83%). Fouling decreased the total pore volume of all membrane. The peak location of adsorption capacity was more likely to occur at smaller pore sizes with longer running time. Notably, continuous fluorescence distribution between the separating layer and pores like finger in MABR system exhibited an increasing trend with the operation time, indicating a gradual increase of microbial viability. Core protein structure was revealed by different bond peaks (0–90 d). Specifically, for different organic components of EPS, the hydrophilic HIS was the main content, while the mass transfer resistance caused by the gel increased, which reduced the contact angle and increased the bubble point pressure. Therefore, effects of EPS content and composition should be considered during the application of water treatment techniques based on MABR. [Display omitted] • Microbial secretion caused faster pore blocking than biofilm. • Fouling caused adsorption peak shifted to smaller pore sizes. • Chemical compositions of the biofouling were detected in XPS spectra. • Composition of EPS could be responsible for OTR decline. [ABSTRACT FROM AUTHOR]

The understanding of fouling behaviors and mechanism is critical for membrane fouling that is a bottleneck for the sustainable application of membrane technology. Therefore, it is essential to develop new analytical tools that can in situ characterize membrane fouling processes during filtration. In this work, we demonstrate a capability of high-resolution large-scale in situ visualization that can rapidly differentiate foulants and their temporal-spatial-distributions on/in/over the membrane matrix during filtration process based on multi-color light sheet fluorescence imaging platform. The rapid-evolving fouling process of different foulants were directly monitored and analyzed during the ultrafiltration of bovine serum albumin (BSA), dextran and their mixture solutions. Inner adsorption was found to play a more critical role for dextran-induced fouling on polymeric membranes compared with BSA-induced fouling. During the ultrafiltration of BSA/dextran mixture solutions, BSA was directly observed as the major contributor to the decrease of permeate flux, which could be employed as a complementary evidence for the interfacial free energy calculations during membrane fouling and vice versa. This work provides new insights into combined membrane fouling process and offers a highly-sensitive, non-invasive characterization tool for a wide range of explorations in membrane-based processes and interfacial processes. [Display omitted] In situ large-scale characterization of combined membrane fouling behaviors Strong relations between flux decline rate and foulant distributions in/on membrane Direct observation of key foulant in combined fouling process Facilitation of exploring interfacial processes (dynamic and thermodynamic) [ABSTRACT FROM AUTHOR]

Abstract: A new experimental method was proposed to obtain local fluxes along the membrane fibers of double-end and dead-end submerged hollow fiber membrane modules (SHFMMs) and to investigate the impact of average operating flux, fiber length and filtration modes (dead-end and double-end filtration) on local flux distribution. The relationship between the local flux and fouling behavior was monitored through the development of local fouling during filtration of 5g/L yeast suspension using the non-invasive ultrasonic technique. The experimental results showed that the local flux distribution in the double-end SHFMM was more uniform than that in the dead-end SHFMM at the same operating conditions. Furthermore, the local flux obtained near the upper suction end of the double-end SHFMM was higher than that near the lower suction end. The difference value between the maximum and minimum local fluxes decreased with the decrease of fiber length and average operating flux in the double-end SHFMM. In addition, the ultrasonic measurements revealed that the behavior of fouling deposition on the membrane surface was consistent with the local flux distribution, which led to the self-adjustment and redistribution of local flux during the operation. [Copyright &y& Elsevier]

[Display omitted] • The novel surface conductive membrane as cathode mitigated membrane fouling. • A unimodal pattern of SFR led to flocs on the surface of membrane to gel layer. • Basophilic methanogens and metabolic activity were influenced by electricity. • High specific surface area and biocompatibility contributed to form MEC system. This study investigated the possibility of using a novel type of surface conductive hollow fiber membrane during the Anaerobic membrane bioreactor process (AnMBR). In particular, the membrane fouling control mechanisms of Surface electric field AnMBR (S-AnEMBR) were evaluated through comparing with the operation of Conventional AnMBR (AnMBR) and Electric field AnMBR (AnEMBR). Results showed that S-AnEMBR had longer running time, stronger anti-fouling capability, and more stable Total organic carbon (TOC) removal efficiency. And S-AnEMBR could extend the running time of the rapid fouling phase (Stage 2). Electrochemical analysis and microbial community analysis showed that enhanced electron transfer in S-AnEMBR accelerated the decomposition of organic matter and further improved acidification efficiency from 83.75% to 234.78%, indicating the methane concentration ranged between 24.56 mmol/L and 36.99 mmol/L. Cake layer compression was reduced because significant changes were observed in increased particle size and more negative Zeta potential. In addition, basophilic methanogens (48%) were enriched at cathode, which improved electrochemical activity of carbon electrode biocathode and promoted anaerobic digestion. Therefore, it was found that S-AnEMBR was more conducive to controlling the properties and structure of the gel layer, and further achieving the resistance towards protein and polysaccharide adhesion in membrane. This work demonstrated that the surface conductive hollow fiber membrane possessed good anti-fouling ability in AnMBR, and provided an alternative membrane material for AnMBR application. [ABSTRACT FROM AUTHOR]

Abstract: Ultrasonic time-domain reflectometry (UTDR) was extensively employed to visualize and analyze quantitatively the effect of aeration rate, operating flux and fiber length on sub-critical flux fouling profiles in a double-end submerged hollow fiber membrane (SHFM) module. Five 10MHz transducers were externally mounted in contact with the outside surface of the double-end SHFM module. A single polyethersulfone hollow fiber membrane was used to filter 5g/L yeast suspension. Results showed that the double-end SHFM module has better filtration performance by comparison with one-end SHFM module. The acoustic measurements revealed that the membrane near the upper suction end of the double-end SHFM module was more easily suffered from fouling than that near the lower suction end under sub-critical flux operation. Furthermore, the progress of foulant deposition gradually migrated from both ends to middle and reached the plateau finally. Moreover, a low operating flux was more effective to reduce membrane fouling. And a short double-end SHFM module was more easily subjected to membrane fouling than a long one at the same operating conditions. [Copyright &y& Elsevier]

Abstract: This study described the extension of ultrasonic time-domain reflectometry (UTDR) for monitoring the fouling profile in a submerged hollow fiber membrane module under different operation conditions including aeration rate, fiber length and operational flux. Five 10MHz ultrasonic transducers employed were mounted along the tubular test module with a single hollow fiber membrane evenly. A polyethersulfone hollow fiber membrane with inside and outside diameter of 1.0 and 1.6mm was employed to treat 5g/L yeast suspension. The experimental results showed that the fouling could not be completely prevented under the operation of the sub-critical flux, and still deposited at the upper part of the submerged hollow fiber membrane. The progress of foulant deposition onto the membrane surface gradually migrated from top to bottom and reached the plateau finally. Further, the increase of aeration and curtailing fiber length could only slow down fouling and reduce deposition rate to some extent, but could not fully avoid the membrane fouling. Moreover, UTDR technique was successfully employed to measure the relationship between the operational flux and particle deposition on the membrane surface so as to obtain threshold flux, under which could obviously alleviate membrane fouling. [Copyright &y& Elsevier]

Model suspensions are important substances for characterizing fouling processes to study the mechanism of membrane fouling, thus, choosing a suitable standard suspension is critical for researches on membrane fouling processes. The pretreatment methods of model suspensions have long been neglected, which can alter the physical and chemical properties and affect fouling results. This study compared four different pretreatment methods (centrifuging and drying, magnetic stirring, ultrasonic processing, and dissolving in buffer solution) and found effects on size distribution, dispersion stability, pH variation over time, and fouling properties. Among the characterization of model suspensions, different pretreatment methods led to various changes in physical and chemical properties in this study. Membrane filtration experiments showed that these four pretreatments changed the rate of membrane fouling. The results of the analysis of filtration flux for suspensions indicated that for ultrasonic processing of all suspensions and magnetic stirring of kaolin suspensions, pore blocking was the main mechanism, while cake formation was dominant for the others. Therefore, special attention should be placed on different pretreatment methods and selecting appropriate model foulants. Finally, some guidance on selecting appropriate model foulants was given in the study. [Display omitted] • The effects of four different pretreatment methods were compared. • Properties that model suspensions need to be equipped were put forward. • The fouling mechanism of suspension after ultrasonic was pore blocking. • Zeta potential and turbidity were used to characterize sedimentation. [ABSTRACT FROM AUTHOR]

• MIEX and UF were combined to treat biologically contaminated water. • The fouling behaviors in the integrated and separated processes were compared. • The integrated process worked better to alleviate membrane fouling. • The difference was mainly due to the MIEX layer formed in the integrated case. • The impact of EPS on the fouling process was also discussed. In this work, three different processes including ultrafiltration (UF), separated magnetic ion exchange resin (MIEX)-UF and integrated MIEX/UF were employed to investigate the introduction of MIEX on biological membrane fouling control in synthetic bacteria solutions. Independent UF was firstly performed using extracellular polymeric substances (EPS)- free live bacteria, live bacteria, or dead bacteria as feed, and the operation time when TMP reached 35 kPa was 105, 75 or 55 min respectively. The most severe fouling with dead bacteria was attributed to EPS and some endocellular components which favored the adhesion of bacteria on membrane surface. The introduction of MIEX helped to alleviate membrane fouling, and the alleviation effect for EPS-free live bacteria feed was the least significant. It was inferred that the organic substances could be firstly adsorbed by the anion-exchange resin and then promote the adhesion of bacteria. This was supported by direct adsorption tests with MIEX where the removal efficiencies followed the order of dead bacteria > live bacteria > EPS-free live bacteria. The integrated process worked better than the separated one in both single cycle and multi cycle filtration tests, and this was mainly attributed to the dynamic resin layer, which worked in several manners, including acting as a physical barrier, enhancing adsorption/adhesion of foulants and suppressing reproduction of the bacteria. Regeneration of MIEX was also conducted with aqueous NaCl or NaHCO 3. The removal efficiency was much more stable in the latter case, which could still reach 33% after five cycles (~83% of the initial capacity). [ABSTRACT FROM AUTHOR]

• In situ large-scale 3D visualization of membrane fouling by LSFM. • An inner concentrated DEX layer was observed in hydrophilic membrane. • Foulant distribution and penetration shown correlations with membrane fouling. Membrane fouling restricts the wide applications of membrane technology and therefore, it is essential to develop novel analytical techniques to characterize membrane fouling and to further understand the mechanism behind it. In this work, we demonstrate a capability of high-resolution large-scale 3D visualization and quantification of the foulants on/in membranes during fouling process based on light sheet fluorescence microscopy as a noninvasive reproducible optical approach. The adsorption processes of dextran (DEX) on/in two polyvinylidene fluoride membranes with similar pore structure but distinct surface hydrophilicity were clearly observed. For a hydrophilic polyvinylidene fluoride (PVDF) membrane, the diffusion and adsorption of the DEX in membrane matrix were much slower compared to that for a hydrophobic membrane. A concentrated foulant layer was observed in the superficial potion of the hydrophilic membrane matrix while the foulants were observed quickly penetrating across the overall hydrophobic PVDF membrane during a short adsorption process. Both the inner concentrated fouling layer (in membrane superficial portion) and the foulant penetration (in membrane asymmetric structure) presented correlations with membrane fouling irreversibility, which could elucidate the microscopic events of hydrophilic membrane in resisting fouling. In addition, the imaging results could be correlated with the XDLVO analysis, suggesting how the membrane-foulant and foulant-foulant interfacial interactions resulted in a time-dependent membrane fouling process. This work provides a fast, highly-sensitive and noninvasive imaging platform for in situ characterization of membrane fouling evolution and should be useful for a wide range of membrane-based process explorations. Image, graphical abstract [ABSTRACT FROM AUTHOR]