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[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]

[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]

[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]