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Ferrate (VI) is a unique and “green” chemical that can be utilized for oxidation, disinfection and coagulation simultaneously in a single unit without producing by-product. Herein, for the first time, we reported the integrated process of ferrate (VI) pretreatment coupled with ceramic membrane reactor for mitigating membrane fouling in natural reclaimed water treatment. Membrane fouling was effectively mitigated by ferrate pretreatment with the maximum trans-membrane pressure (TMP) reduction of 81.8% achieved at ferrate dosage of 0.15 mM. Moreover, the fouling mechanism changed from intermediate-standard blocking to cake-intermediate blocking with ferrate pretreatment and the contribution of cake layer fouling was significantly diminished with increase of ferrate dosage (≤ 0.15 mM). Statistical analysis including redundancy analysis and clustering correlation analysis showed that chemical oxygen demand (COD), dissolved organic carbon (DOC) and polysaccharide were the most important positive factors to R t with their correlation coefficients above 0.92 while SS and turbidity were the most important negative factors to R t with their correlation coefficients below − 0.87. Long-term filtration experiments also confirmed the membrane fouling control performance by ferrate with the significant extension of the onset of membrane fouling. [ABSTRACT FROM AUTHOR]

The integrated process of ozonation coupled with ceramic membrane filtration has been actively utilized to alleviate membrane fouling in water/wastewater treatment, however, the effect of ozonation on protein-based ceramic membrane fouling is still contradictory. Herein, for the first time, we reported the severe protein-based ceramic membrane fouling at high ozone dosage in the integrated process of ozonation coupled with ceramic membrane filtration and the related fouling mechanism was systematically explored. Ozonation at low dosage slightly mitigated membrane fouling, whereas severe membrane fouling occurred at high ozone dosage (10 mg/L for pre-ozonation; 4 and 10 mg/L for in-situ ozonation). At high ozone dosage, the trans-membrane pressure (TMP) remarkably increased (> 40 kPa) within 90 min and both hydraulically reversible and irreversible fouling contributed to the total membrane fouling resistance. Electro kinetic potential and particle size of the bovine serum albumin (BSA) solution were not the key factors affecting the aggravated membrane fouling at high ozone dosage. The remarkably deteriorated membrane fouling at high ozone dosage can be accounted for the formation of BSA crosslinks ascribed to the oligomerization and agglomeration of BSA and the intermolecular disulfide bridge formation with the crosslinks progressively accumulating on the membrane surface and in the membrane pores during filtration. The modeling results confirmed that the BSA-based membrane fouling mechanism was changed from cake-intermediate to cake-standard with ozonation at high ozone dosage. Meanwhile, the cake layer and/or gel layer played a more important role for the aggravated membrane fouling at high ozone dosage even though the contribution of pore blocking was also significant. [ABSTRACT FROM AUTHOR]

Four pathways for cleaning of iron oxide-fouled membranes, namely i) proton (acid)-assisted, ii) ligand-promoted (citric acid), iii) reductive (ascorbic acid), and iv) ligand-promoted reductive (ascorbic acid-citric acid-mediated) were examined and their effectiveness were compared in this study. The cleaning effectiveness under oxic conditions followed the order: proton-assisted < ligand-promoted < reductive < ligand-promoted reductive. Iron oxide dissolution rate initially increased with increase of citrate concentration in the ascorbic acid-citric acid solutions but declined at higher citrate concentrations indicating that an intermediate citrate concentration was required for optimal cleaning. The mechanism of ligand-promoted reductive dissolution mediated by ascorbate and citrate was investigated through studies of dissolution behaviour under both oxic and anoxic conditions with citrate shown to have a mitigating effect on the consumption of oxygen, apparently by reducing the iron catalyzed oxidation of ascorbate. Kinetic modelling showed that the dynamics of dissolution could be reasonably well simulated with the inclusion of a surface > Fe(III)-citrate-Fe(II) ternary complex which facilitates the detachment of surface Fe(II). Use of dual reagents (ascorbic acid and citric acid) under oxic conditions is recommended for the cleaning of iron-fouled membranes in view of the extreme cleaning effectiveness though it is critical that cleaning conditions be carefully optimised. [ABSTRACT FROM AUTHOR]

Pre-ozonation or in-situ ozonation coupled with membrane filtration has been actively utilized for membrane fouling control in water treatment, however, the comparative analysis of these two ozonation processes on membrane fouling control has not been reported so far. In this study, the comparative effect of pre-ozonation and in-situ ozonation on mitigation of ceramic UF (ultrafiltration) membrane fouling caused by alginate was systematically investigated through characterization of TMP, fouling resistance, MW distribution, dissolved ozone concentration, the formation of hydroxyl radical and modeling. Results showed that both pre-ozonation and in-situ ozonation were effective in alleviating the cake layer fouling. Ozonation efficiently broke down the high molecular weight (MW) fractions (>150 kDa and 80–150 kDa) of alginate into the low MW fractions (6–80 kDa; 0.4–6 kDa and 0.1–0.4 kDa), reducing the membrane interception of alginate. Pre-ozonation achieved better fouling mitigation performance compared with in-situ ozonation at low ozone dosages of 2 and 4 mg/L. However, in-situ ozonation had better fouling control performance at high ozone dosage of 10 mg/L with the normalized TMP (ΔTMP) maintaining below 0.2 kPa after 60 min filtration. Besides, in-situ ozonation was more effective in hydraulically irreversible fouling control than pre-ozonation regardless of ozone dosage. Integration of in-situ ozonation and ceramic membrane filtration catalyzed ozone decomposition with the increased generation of hydroxyl radical, which further strengthened the oxidation of the accumulated foulants on the membrane surface and within the membrane pores and thus effectively alleviated the reversible and irreversible fouling. [ABSTRACT FROM AUTHOR]

The effect of mixed liquor properties changed by ozonation especially with high dosages on membrane fouling is very complex and remains unclear. In this study, the effect of mixed liquor properties changed by ozonation especially with high dosages on ceramic ultrafiltration (UF) membrane fouling in wastewater treatment and the corresponding mechanism were systematically studied by characterization of the mixed liquor properties, hydraulic performance, the fouling layers and modeling at different ozone dosages (0, 2, 5, 10 mg/L). The membrane filterability of the mixed liquor after pre-ozonation (⩽5 mg/L) was enhanced and the corresponding membrane fouling was mitigated. After pre-ozonation, activated sludge had the better settleability and larger floc size. Meanwhile, there was a remarkable reduction of dissolved organic carbon (DOC), soluble microbial products (SMP) and extractable extra-cellular polymeric substances (EPS) after pre-ozonation and the removed organics were mainly belonged to the high molecular weight (MW) (1–10 kDa) and very high MW (10–200 kDa) substances. Intermediate blocking was the main membrane fouling during the mixed liquor filtration process and the best fouling mitigation performance was achieved for the sample with an intermediate ozone dosage of 5 mg/L (1.7 mg-ozone/g-mixed liquor suspended solids (MLSS)). Meanwhile, the water quality of permeate was even better after pre-ozonation (⩽5 mg/L) with the lower DOC and total nitrogen (TN) concentrations. Severe cell lysis occurred with the significant increase of the released organics in the mixed liquor and the activated sludge had smaller floc size and worse settleability when the pre-ozonation dosage was above 10 mg/L, which in turn resulted in the deteriorated membrane fouling control performance. [ABSTRACT FROM AUTHOR]

The ascorbic acid (Asc)-mediated cleaning of iron-fouled membranes from submerged membrane bioreactors (MBRs) dosed with iron salts for facilitation of phosphorus removal is investigated here with the cleaning process, involving the reductive dissolution of iron oxides on the membrane surface and within membrane pores, conducted under both oxic and anoxic conditions and in the presence of 1,10-phenanthroline, a strong Fe(II)-binding ligand. A significant reduction in cleaning effectiveness was observed when oxygen was present with kinetic modelling of key processes operating in this system indicating that the reduced effectiveness could be attributed to the Fe(III)-catalysed oxidation of ascorbate with Fe(III) being replenished by the relatively rapid heterogeneous oxidation of Fe(II). While either removal of oxygen or addition of Fe(II)-binding agents such as phenanthroline are effective in preventing the Fe(III)-catalysed oxidation of ascorbate, cleaning of iron oxide-fouled membranes under oxic conditions with frequent replenishment of freshly prepared Asc is recommended as a reasonable balance between cleaning effectiveness and cost. [ABSTRACT FROM AUTHOR]

The effect of continuously dosing membrane bioreactors (MBRs) with ferric chloride (Fe(III)) and ferrous sulphate (Fe(II)) on phosphorus (P) removal and membrane fouling is investigated here. Influent phosphorus concentrations of 10 mg/L were consistently reduced to effluent concentrations of less than 0.02 mg/L and 0.03–0.04 mg/L when an Fe(III)/P molar ratio of 4.0 and Fe/P molar ratio (for both Fe(II) and Fe(III)) of 2.0 were used, respectively. In comparison, effluent concentrations did not decrease below 1.35 mg/L in a control reactor to which iron was not added. The concentrations of supernatant organic compounds, particularly polysaccharides, were reduced significantly by iron addition. The sub-critical fouling time ( t crit ) after which fouling becomes much more severe was substantially shorter with Fe(III) dosing (672 h) than with Fe(II) dosing (1200–1260 h) at Fe/P molar ratios of 2.0 while the control reactor (no iron dosing) exhibited a t crit of 960 h. Not surprisingly, membrane fouling was substantially more severe at Fe/P ratios of 4. Fe(II) doses yielding Fe/P molar ratios of 2 or less with dosing to the aerobic chamber were found to be optimal in terms of P removal and fouling mitigation performance. In long term operation, however, the use of iron for maintaining appropriately low effluent P concentrations results in more severe irreversible fouling necessitating the application of an effective membrane cleaning regime. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ceramic membrane (CM) market is growing with many full-scale applications. • CM is superior to polymeric membrane–high stability & flux, long life, low fouling. • Physicochemical processes (e.g., ozonation) are effective for fouling control. • Catalytic (nano) CMs can enhance antifouling, and pollutant removal capability. • Cost analysis of CMs, fouling control & cleaning should be evaluated at full-scale. Application of ceramic membrane technology in water and wastewater is rapidly growing. Inherent advantages of ceramic membrane including chemical/thermal stability, low fouling propensity and long lifespan make ceramic membrane technology attractive, and the ceramic membrane market is expected to achieve a compound annual growth rate of 12%. Ceramic membranes could be integrated with advanced oxidation processes such as in-situ ozonation that cannot be applied in the case of polymeric membrane due to their potential degradation during long-term exposure. In addition, the hybrid-ceramic membrane processes such as ceramic membrane bioreactor are superior to polymeric counterparts due to higher flux, higher pollutant removal, lower fouling rate and higher cleaning efficiency. Although ceramic membrane has high capital cost, life-cycle costs of ceramic and polymeric plants are comparable. Notably, full-scale ceramic membrane water/wastewater treatment plants have been installed in many countries such as Japan, USA, Singapore and United Kingdom. Given the attractiveness of this technology, performance of ceramic membrane is critically reviewed with a focus on their applications in water and wastewater treatment under mild conditions. In addition, fouling mechanisms and control strategies are elucidated and are compared with polymeric membranes. Importantly, for the first time, the status of full-scale applications and market prospects of ceramic membranes are critically analysed to show their future potential. Lastly, future research directions such as development of cost-effective ceramic membranes, understanding the biofouling evolution and economic evaluation of physicochemical processes for fouling control are proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electrochemically activated peroxymonosulfate (PMS) pretreatment was applied. • PMS pretreatment effectively removed dissolved organic carbon. • Electrochemical activation of PMS generated •OH directly. • Membrane fouling of membrane distillation was greatly mitigated by PMS pretreatment. • The one-time dosing mode of PMS was better for membrane fouling control. Membrane distillation (MD) provides a potential method to supply large volumes of good quality potable water from surface water resources, avoiding the risk of long-term water shortages. However, the high abundance of dissolved natural organic matter (DOM) in surface water induces severe membrane fouling, which reduces productivity and increases energy consumption. Therefore, for the first time, electrochemically activated peroxymonosulfate (PMS) treatment was applied prior to the direct contact (DC)-MD process with the aim of reducing the deposition of organics and inorganics on the membrane and reducing membrane fouling. Results showed that supplying PMS continuously at a rate of 0.10 mM/min, eliminated 30.4% of dissolved organic carbon (DOC). Furthermore, fluorescence parallel factor (PARAFAC) analysis showed that >60% of two fluorescent substances were removed after 60 min of the electrochemically activated PMS pretreatment at a current density of 5 mA/cm2. Electrochemical activation of PMS generated •OH directly, facilitating the removal and degradation of DOM. In terms of the DCMD performance, almost no normalized flux decline was observed for the DCMS process after 0.01 mM/min pre-oxidation, while 44.8% flux decay occurred in the standalone DCMD treating raw surface water. Compared with continuous dosing, the use of a one-time dosing mode achieved a better outcome, as more small organic molecules generated in continuous dosing mode are not conducive to membrane fouling control. Therefore, electrochemically activated PMS could be an effective tool to mitigate membrane fouling in MD processes, although the characteristics of membrane and feed should be considered. [ABSTRACT FROM AUTHOR]

Abstract The comparison of long-term ceramic membrane bioreactors (MBRs) without and with in-situ ozonation was investigated in this study in terms of membrane fouling, activated sludge, effluent quality and microbial community in wastewater treatment. The optimal dosage of in-situ ozonation for long-term MBR operation was firstly determined as 5 mg/L (0.66 mg-ozone/g-mixed liquor suspended solid (MLSS)) with the optimal filterability of mixed liquor. During the long-term filtration experiment, MBR-ozone with in-situ ozonation demonstrated its significantly alleviated ceramic membrane fouling performance compared with MBR-control without in-situ ozonation as a result of the enhanced filterability of mixed liquor and organic foulants removal from membrane surface by in-situ ozonation oxidation. Furthermore, ozonation was beneficial to phosphorus removal and the total phosphorus (TP) concentration in effluent of MBR-control (0.82 ± 0.63 mg/L) was >2-fold higher than that of MBR-ozone (0.29 ± 0.41 mg/L). The improved phosphorus removal performance by ozonation was due to the increased abundance of phosphate accumulating bacteria of Candidatus Accumulibacter in activated sludge. However, ozonation was detrimental to nitrogen removal mainly as a result of the inhibition of denitrification with the decreased relative abundance of denitrification genus of Dechloromonas in activated sludge. Overall, ceramic MBR with in-situ ozonation had not only significantly alleviated membrane fouling but also remarkably improved phosphorus removal performance. Graphical abstract Unlabelled Image Highlights • Long-term ceramic MBRs without and with in-situ ozonation were compared. • The optimal filterability of mixed liquor was achieved at ozone dosage of 5 mg/L. • In-situ ozonation significantly alleviated ceramic membrane fouling. • Ozonation was beneficial to phosphorus removal but detrimental to nitrogen removal. • Microbial community of activated sludge was significantly changed by ozonation. [ABSTRACT FROM AUTHOR]

[Display omitted] • Photothermally-activated PMS pre-treatment was applied for MD fouling alleviation. • NOM in the surface water can be effectively removed after PMS pre-treatment. • Stable permeance (PMS (2 mM)) vs 50 % reduction (control) of flux were obtained. • •OH and SO 4 •− radicals generated by PMS contributed to the NOM removal. • The MD membrane properties could be kept conserved by the PMS pre-treatment step. Membrane distillation (MD) has demonstrated its efficacy for seawater desalination, which prompted researchers to investigate its performance for the treatment of surface water containing natural organic matter (NOM). However, membrane fouling remains a significant technological constraint in the acceptability and implementation of MD modules. Herein, for the first time, a photothermally-activated PMS pre-treatment process is coupled to a direct contact (DC)-MD module for effective membrane fouling control. Photothermally-activated PMS (2 mM) pre-treatment achieved 69 % of UV 254 removal and 30.9 % of dissolved organic carbon removal and allowed stable operation of the DCMD without any reduction in water permeance vs 50 % reduction obtained without the pretreatment step. The analysis of NOM fractions after pre-treatment using Parallel Factor Analysis and molecular weight distribution indicated changes in NOM composition, which facilitated membrane fouling control. The photothermally-activated PMS pre-treatment seems to alleviate membrane fouling by limiting the foulant-membrane interaction, which was observed to result in the formation of the fouling layer containing aromatic proteins, microbial byproducts-like substances, and inorganic (e.g., calcium) foulants. Finally, characterization of the used MD membranes revealed that the MD membrane properties could be kept unchanged by the photothermally-activated PMS pre-treatment step, thereby making the integrated DCMD system sustainable and attractive for widespread applications. [ABSTRACT FROM AUTHOR]

Integration of an electrochemical process with membrane bioreactor (MBR) has attracted considerable attention in the last decade for simultaneous improvement in pollutant removal and hydraulic performance of MBR. Electrochemical MBR (eMBR) with sacrificial anodes has been observed to achieve enhanced phosphorus (up to 40%) and micropollutant removal (5–60%). This is because direct anodic oxidation, indirect oxidation by reactive oxygen species and electrocoagulation can supplement the biological process. The application of an electric field can substantially reduce membrane fouling by 10% to 95% in the eMBR as compared to the conventional MBR. Sacrificial electrodes (e.g., iron or aluminium) have been reported to be more suitable for fouling mitigation than non-sacrificial electrodes (e.g., titanium). However, during prolonged operation, metal ions released from sacrificial electrodes can adversely affect microbial activity and could accumulate in activated sludge. Depending on the current density and electrode material (sacrificial or non- sacrificial), anodic oxidation, electrocoagulation, electrophoresis and/or electroosmosis mechanisms are responsible for suppressing membrane fouling propensity. This paper critically reviews the current status of the electrochemical MBR technology and presents a concise summary of eMBR configurations and electrode materials. Comparative removal of bulk organics, nutrients and micropollutants in the eMBR and conventional MBR is discussed, and performance governing factors are elucidated. Impacts of operating conditions such as current density on mixed liquor properties (e.g., floc size and zeta potential) and microbial activity are elucidated. The extent of membrane fouling mitigation along with associated mechanisms as well as energy consumption is explained and critically analysed. Future research directions are suggested to fast track the scalability of eMBR, which include but are not limited to electrode lifetime, development of self-cleaning conductive membranes, optimisation of operating parameters, removal of emerging micropollutants, accumulation of toxic metals in activated sludge, and degradation by-products and ecotoxicity. Unlabelled Image • Electrochemical membrane bioreactor (eMBR) is an emerging alternative of MBR • eMBR can achieve enhanced pollutant removal and membrane performance • Electric current affects sludge properties, microbial activity and diversity • Electrode lifetime and toxic metals accumulation in sludge are the major drawbacks [ABSTRACT FROM AUTHOR]

Membrane fouling is an obstacle impeding the wide applications of ceramic membranes and organics are responsible for most of the membrane fouling issues in wastewater treatment. In this study, Fenton cleaning strategy was firstly proposed to clean ceramic membrane fouling in wastewater treatment. Fe2+ efficiently catalyzed fouling cleaning with H 2 O 2 (1.5%) to recover the filterability of ceramic membrane. The maximum ∆ TMP recovery (over 99%) was achieved at an optimal Fe2+ dosage of 124 mg/L after 6 hr of immersion cleaning. The total residual membrane fouling resistance decreased gradually from this optimum value as the Fe2+ dosage increased above 124 mg/L. The residual hydraulically reversible fouling resistance accounted for most of the membrane fouling and was basically removed (≤ 3.0 × 109 m−1) when Fe2+ dosages higher than 124 mg/L were used. The foulants responsible for the formation of a residual hydraulically reversible fouling layer (DOC (dissolved organic carbon), proteins, polysaccharides, EEM (fluorescence excitation-emission matrix spectra), SS (suspended solids), and VSS (volatile suspended solids)) were gradually removed as the Fe2+ dosage increased. These residual organic foulants were degraded from biopolymers (10–200 kDa) to low molecular weight substances (0.1–1 kDa), and the particle size of these residual foulants decreased significantly as a result. The strong oxidation power of hydrogen peroxide/hydroxy radicals towards organic foulants was enhanced by Fe2+. Fe2+ played a significant role in the removal of hydraulically reversible fouling and irreversible fouling from the ceramic membrane. However, Fe2+ (≥ 124 mg/L) increased the likelihood of forming secondary iron-organics aggregates. Unlabelled Image [ABSTRACT FROM AUTHOR]

Highlights • Iron pretreatment significantly mitigates ceramic membrane fouling. • Ferrate pretreatment achieves the best membrane fouling control performance. • Ferrate greatly improves the water quality of reclaimed water. • Biopolymers with the MW of 20–2000 kDa are mainly removed. • Ferrate has dual functions of chemical oxidation and coagulation. Abstract Coagulation-membrane filtration hybrid process has been widely applied in water treatment to improve water quality and alleviate membrane fouling. Herein, we systematically investigated the comparable effect of ferrate, ferrous and ferric pretreatment on fouling alleviation of ceramic membrane in reclaimed water treatment. Our results showed that the pretreatment of ferric, ferrous and ferrate remarkably alleviated membrane fouling with the fouling alleviation performance following the order: ferrate > ferrous > ferric > control. The t crit (subcritical fouling time) after which the fouling rate (dTMP/dt) became much more severe was remarkably extended from 0 (control) to 432 (ferric), 576 (ferrous) and 888 h (ferrate), respectively. Meanwhile, hydraulically reversible fouling resistance had the greatest contribution (58.3%) to the overall fouling resistance in the control case, however, hydraulically irreversible membrane fouling caused by inorganics (R ir-citrate) became more severe in long-term operation with the contribution of R ir-citrate to the total fouling resistance of 40.7%, 46.3% and 50.3% in the cases with ferric, ferrous and ferrate pretreatment, respectively. Moreover, the redundancy analysis results showed that the alleviated membrane fouling was principally owing to the sharp reduction of organic matters and the significant increase of particle size and particle concentration in influent. Compared with ferric and ferrous, ferrate had the best fouling alleviation performance, which was mainly due to its dual functions of chemical oxidation (including OH, Fe(V) and Fe(IV)) and coagulation (ferric oxyhydroxides). [ABSTRACT FROM AUTHOR]

Abstract Ferrous dosing is used to reduce phosphorus concentration and alleviate polymeric membrane fouling in membrane bioreactor (MBR). However, limited studies have been conducted to investigate the impacts of ferrous dosing on ceramic membrane fouling, nutrient removal efficiency and microbial community. Accordingly, the aim of this study was to investigate the effect of intermittent ferrous dosing with Fe/P molar ratios of 2 and 1 (with a dosing frequency of every two days) on the overall nutrient removal, functional microbial changes and membrane fouling in ceramic membrane bioreactors (CMBR) in treatment of wastewater. TP concentration of 10 mg/L in influent decreased to 1.94 ± 0.62 mg/L (control), 0.38 ± 0.22 mg/L (Fe/P = 1) and 0.31 ± 0.18 mg/L (Fe/P = 2) in the effluent, respectively. Meanwhile, the effluent total nitrogen (TN) concentrations with Fe/P = 1 treatment (6.80 ± 2.02 mg/L) and Fe/P = 2 treatment (5.12 ± 2.28 mg/L) were lower than that of the control (7.72 ± 2.36 mg/L). Compared to Fe/P = 1, the TN removal performance was better for Fe/P = 2 mainly due to the increased abundance of denitrifying bacteria (Zoogloea and Acinetobacter). In addition, excess iron dose might have toxic effects on bacterial physiology, however the Fe concentrations that cause cell damage vary for different bacteria. The relative abundance of Zoogloea (aerobic denitrifying bacteria) continuously increased with ferrous addition (Fe/P = 2), while other bacteria including Dechloromonas , Hyphomicrobium and Thauera (anoxic denitrifying bacteria), Nitrospira (nitrifying bacteria) and Candidatus Accumulibacter (phosphorus accumulating organism) decreased sharply. Furthermore, membrane fouling was effectively moderated by ferrous dosing and Fe/P = 1 treatment showed improved membrane fouling mitigation than Fe/P = 2. Overall, intermittent ferrous addition in CMBR with Fe/P molar ratio of 1 was beneficial to the removal of nutrients (TP, TN and organics), enhanced succession of microbial community and membrane fouling mitigation. Graphical abstract Unlabelled Image Highlights • Ferrous dosing (Fe/P = 1) is beneficial to phosphorus and nitrogen removal. • Microbial community of activated sludge is significantly changed by ferrous dosing. • Excess iron dose has toxic effects on bacterial physiology. • The optimal fouling control performance is achieved at Fe/P molar ratio of 1. [ABSTRACT FROM AUTHOR]

[Display omitted] • Dopamine-functionalized PTFE (DA@PTFE) membranes were fabricated. • Membrane distillation (MD) performance of DA@PTFE membranes was investigated. • Secondary effluent from a WWTP was selected for MD to produce reclaimed water. • The DA-9@PTFE membrane demonstrated the best MD performance. • The water quality of MD permeate was significantly improved. Using secondary effluent from municipal wastewater treatment plants by membrane distillation (MD) to produce reclaimed water is an effective strategy for solving the growing global water shortage problems, however, membrane fouling caused by natural organic matter in the secondary effluent tends to reduce the water production rate of MD systems or destabilize these systems. Herein, the well-known dopamine (DA) surface functionalization method was applied and for the first time, DA-functionalized PTFE membranes (DA@PTFE) were fabricated to address the membrane fouling issue by treating secondary effluent enriched with effluent organic matter (EfOM) via direct contact membrane distillation (DCMD). The results showed that dopamine deposition formed a thin hydrophilic layer on the membrane surface, which inhibited the adhesion of contaminants and slowed down membrane fouling. The DA-9@PTFE membrane (with the C/F ratio of 1.25) demonstrated the best MD performance, with an increased flow rate of 13.8 % and much less membrane fouling compared with the pristine PTFE membrane (26.2 % vs. 56.8 % flux decay after three cycles). Meanwhile, using the DA@PTFE membranes in MD operation led to high water quality permeate, exhibiting a conductivity rejection rate above 99.6 % and a dissolved organic carbon retention rate above 90 %. This study demonstrates the good stability, wettability, and anti-pollution performance of DA@PTFE membranes in a DCMD system for real application in reclaimed water treatment. [ABSTRACT FROM AUTHOR]

The operational issues of low-pressure ultrafiltration (UF) membrane are associated with its long-term membrane fouling caused by organic and inorganic matters, especially in treating shale gas wastewater (SGW) with complex water compositions. Herein, the effect of ferrate (Fe(VI)) pretreatment on UF membrane fouling and water quality in treating SGW was systematically investigated. Fe(VI) pretreatment significantly mitigated membrane fouling and slightly improved the effluent quality. The hydraulically irreversible fouling index and the total fouling index decreased by 69%–87% and 58%–84%, respectively. The mechanism of membrane fouling mitigation was comprehensively analyzed by the classical pore blocking model, correlation analysis between membrane fouling index and water quality, and the extended Derjaguin-Landau-Verwey-Overbeek theory. The synergistic mechanisms of membrane fouling mitigation were as follows: (i) Macromolecular organic matters (high molecular weight humics and biopolymers) which would block the membrane pores were oxidized into low fractions organics and removed by Fe(VI); (ii) Fe(VI) pretreatment improved interaction free energy of cohesion of foulants-foulants making foulants more hydrophilic and stable, and increased interaction free energy of adhesion of membrane-foulants making it more difficult for foulants to deposit on the membrane surface. Fe(VI) pretreatment had huge potential in alleviating membrane fouling in treating SGW and other complex wastewater. [Display omitted] • Fe(VI) is combined with UF to treat shale gas wastewater for the first time. • Fe(VI) notably decreases TFI and HIFI by 58%–84% and 69%–87%, respectively. • Biopolymers and high MW humics are the main foulants causing membrane fouling. • XDLVO theory confirms fouling mechanism by analyzing adhesion/cohesion energies. [ABSTRACT FROM AUTHOR]

Membrane distillation (MD) has attracted significant attention in recent years; however, MD membrane fouling is still a big issue. For the first time, this study explored the performance of a standalone direct contact membrane distillation (DCMD) and an integrated peroxymonosulfate (PMS)/DCMD for the treatment of surface water mainly containing algogenic organic matter (AOM) to elucidate pollutant removal as well as fouling propensity and mitigation. The results indicated that the overall conductivity and dissolved organic carbon (DOC) removals by the standalone DCMD and PMS/DCMD were comparable (98–99.8%). However, permeate flux of the standalone DCMD reduced by 62% due to severe membrane fouling. After pre-treatment at 60 °C, flux reduction of 27–40% and no flux decline were observed at PMS concentrations of 1–5 mM and 10–15 mM, respectively. The optimum PMS concentration of 10 mM was also demonstrated to be effective for membrane fouling mitigation at 40 and 50 °C. Characterisation of AOM indicated the presence of protein-like and high MW (≥10 kDa) compounds, which were readily degraded by the reactive species (OH and 1O 2) generated by heat-activated PMS. Characterisation of fouled MD membrane confirmed that fouling was mainly caused by protein-like compounds, consequently affecting permeate flux and membrane properties. [Display omitted] • DCMD achieved effective removal of algogenic organic matter (AOM). • PMS pre-treatment showed concentration-dependent organics removal (10–60%). • OH and 1O 2 reactive species produced by PMS degraded protein-like compounds. • Severe fouling caused by AOM was alleviated (27–100%) by PMS at 40–60 °C. • Developed PMS/DCMD process could be made sustainable using solar or waste heat. [ABSTRACT FROM AUTHOR]

Inorganic salts (e.g., FeCl 3 and FeSO 4) are typically added to membrane bioreactor (MBR) for achieving improved total phosphorus (TP) removal and hydraulic performance. However, at the iron dose (e.g., Fe to P molar ratio of 1–4) required for effective TP removal, severe irreversible membrane fouling could become a significant concern. In this context, intermittent in-situ ozonation was provided for the first time directly in the membrane tank of Fe(II)-dosed membrane bioreactor, and its effect on membrane fouling mitigation was assessed and elucidated. The basic effluent quality remained unaffected, indicating that in-situ ozonation had no detrimental effects. In addition, concentration of foulants and the relative abundance of biofilm-forming microbes were comparable in both the Fe-MBR and Fe/O 3 -MBR. Importantly, as compared to the Fe-MBR, a 33% reduction in membrane fouling was achieved in the Fe/O 3 -MBR. The enhanced filterability of mixed liquor and the scrubbing of the membrane surface by ozone with the direct/indirect oxidation of the deposited foulants contributed to membrane fouling mitigation in the Fe/O 3 -MBR. Meanwhile, trans -membrane pressure profiles of MBRs followed cake-intermediate fouling mechanism. This study demonstrates that provision of intermittent in-situ ozonation is a simple and attractive approach to extend the operation of iron-dosed MBR. [Display omitted] • Performance of in-situ ozonation combined with Fe-MBR (Fe/O 3 -MBR) was elucidated. • Abundance of biofilm-forming bacteria was comparable in both Fe- and Fe/O 3 -MBR. • Ozonation improved mixed liquor properties and delayed the onset of severe fouling. • Increased floc size and membrane scrubbing by ozone contributed to fouling control. • Cake-intermediate fouling was the fouling mechanism in both Fe- and Fe/O 3 -MBR. [ABSTRACT FROM AUTHOR]

• Long-term performance of MBRs with and without in-situ ozonation was investigated • in-situ ozonation achieved improved (up to 26%) micropollutant removal • in-situ ozonation increased microbial diversity and favoured the growth of PAOs • Denitrifying taxa reduced in Oz-MBR, but effluent quality remained unaffected • Cake-complete model was effective to explain the fouling mechanisms in Oz-MBR In this study, impacts of in-situ ozonation applied directly in the membrane tank of a ceramic MBR (Oz-MBR) were assessed to elucidate its implications on micropollutant removal, microbial taxa and membrane fouling. The basic effluent quality (i.e. , bulk organics and nutrients) of the MBR without and with in-situ ozonation was comparable. Importantly, pollutant-specific (10-26%) improvement in micropollutant removal was achieved by the Oz-MBR, which could be attributed to the increase in the abundance of microbial taxa responsible for the removal of structurally complex pollutants and/or ozone-assisted oxidation. In-situ ozonation affected the abundance of denitrifying bacteria and functional genes but total nitrogen removal by the Oz-MBR was comparable to that achieved by the control (C)-MBR. Improved mixed liquor properties, and the reduced accumulation of foulants on the membrane surface resulted in membrane fouling alleviation (53%) in the Oz-MBR. In addition, fouling models evaluated for the first time in the case of Oz-MBR indicated that the cake-complete model was suitable to explain membrane fouling mechanism. This comprehensive study demonstrates the performance of MBR coupled with in-situ ozonation, and the obtained results would serve as a useful reference for its implementation at pilot- and/or full-scale. [ABSTRACT FROM AUTHOR]

Owing to the lack of comprehensive studies on the impacts of a high concentration of powdered activated carbon (PAC) in a ceramic membrane bioreactor (MBR), its performance (at 20 g/L) in terms of mixed liquor properties, hydraulic performance and fouling mechanism was elucidated in this study. In addition to the increase in floc size by 29%, zeta potential of the mixed liquor in PAC-MBR increased (from −19 ± 2 mV to −11 ± 2 mV), which was due to the sorption of soluble microbial products on PAC. Importantly, even at a high dose of 20 g/L, membrane fouling was reduced by 33% in PAC-MBR and was attributed to the membrane scouring by PAC and reduced SMP and EPS concentration in the mixed liquor. The viability of the four single and five combined fouling models was assessed to explain the membrane fouling mechanisms in ceramic MBRs for the first time. The intermediate-standard and cake-intermediate models well explained the fouling mechanism in the 'control' and PAC-MBR, respectively, and the intermediate fouling was the major component of the combined models. This study clarifies that MBR could be operated at a high PAC concentration without compromising the effluent quality, mixed liquor properties and membrane hydraulic performance. Image 1 • PAC addition (20 g/L) in MBR improved mixed liquor properties and mitigated fouling. • Average fouling rate reduced from 1.67 kPa/d (in Control) to 1.17 kPa/d in PAC-MBR. • Fouling retardation was due to membrane scouring and EPS/SMP adsorption on PAC. • Cake-intermediate fouling was the main fouling mechanism in PAC-MBR. [ABSTRACT FROM AUTHOR]