Enhancement of waterborne pathogen removal by functionalized biochar with ε-polylysine ″dynamic arms″: Potential application in ultrafiltration system.

Widespread outbreaks of threatening infections caused by unknown pathogens and water transmission have spawned the development of adsorption methods for pathogen elimination. We proposed a biochar functionalization strategy involving ε-polylysine (PLL), a bio-macromolecular poly(amino acid)s with variable folding conformations, as a "pathogen gripper" on biochar. PLL was successfully bridged onto biochar via polydopamine (PDA) crosslinking. The extension of electropositive side chains within PLL enables the capture of both nanoscale viruses and micrometer-scale bacteria in water, achieving excellent removal performances. This functionalized biochar was tentatively incorporated into ultrafiltration (UF) system, to achieve effective and controllable adsorption and retention of pathogens, and to realize the transfer of pathogens from membrane surface/pore to biochar surface as well as flushing water. The biochar-amended UF systems presents complete retention (∼7 LRV) and hydraulic elution of pathogens into membrane flushing water. Improvements in removal of organics and anti-fouling capability were observed, indicating the broken trade-off in UF pathogen removal dependent on irreversible fouling. Chemical characterizations revealed adsorption mechanisms encompassing electrostatic/hydrophobic interactions, pore filling, electron transfer, chemical bonding and secondary structure transitions. Microscopic and mechanical analyses validated the mechanisms for rapid adsorption and pathogen lysis. Low-concentration alkaline solution for used biochar regeneration, facilitated the deprotonation and transformation of PLL side chain to folded structures (α-helix/ß-sheet). Biochar regeneration process also promoted the effective detachment/inactivation of pathogens and protection of functional groups on biochar, corroborated by physicochemical inspection and molecular dynamics simulation. The foldability of poly(amino acid)s acting like dynamic arms, significantly contributed to pathogen capture/desorption/inactivation and biochar regeneration. This study also inspires future investigation for performances of UF systems amended by poly(amino acid)s-functionalized biochar under diverse pressure, temperature, reactive oxygen species of feeds and chemical cleaning solutions, with far-reaching implications for public health, environmental applications of biochar, and UF process improvement.

Cobalt single-atom catalyst tailored ceramic membrane for selective removal of emerging organic contaminants.

Water reuse is an effective way to solve the issues of current wastewater increments and water resource scarcity. Ultrafiltration, a promising method for water reuse, has the characteristics of low energy consumption, easy operation, and high adaptability to coupling with other water treatment processes. However, emerging organic contaminants (EOCs) in municipal wastewater cannot be effectively intercepted by ultrafiltration, which poses significant challenges to the effluent quality and sustainability of ultrafiltration process. Here, we develop a cobalt single-atom catalyst-tailored ceramic membrane (Co1-NCNT-CM) in conjunction with an activated peroxymonosulfate (PMS) system, achieving excellent EOCs degradation and anti-fouling performance. An interfacial reaction mechanism effectively mitigates membrane fouling through a repulsive interaction with natural organic matter. The generation of singlet oxygen at the Co-N3-C active sites through a catalytic pathway (PMS→PMS∗→OH∗→O∗→OO∗→1O2) exhibits selective oxidation of phenols and sulfonamides, achieving >90% removal rates. Our findings elucidate a multi-layered functional architecture within the Co1-NCNT-CM/PMS system, responsible for its superior performance in organic decontamination and membrane maintenance during secondary effluent treatment. It highlights the power of integrating Co1-NCNT-CM/PMS systems in advanced wastewater treatment frameworks, specifically for targeted EOCs removal, heralding a new direction for sustainable water management.

Synergistic roles of oxidation and self-aggregation in efficient ultrafiltration membrane fouling alleviation using a flow-through Sb-SnO2 anode during wastewater reclamation.

The application of ultrafiltration (UF) in wastewater reclamation alleviates the demand for limited water supplies. However, the membrane fouling caused by the effluent organic matter (EfOM) becomes a major obstacle for UF application. In this study, a pre-oxidation strategy for UF using a Sb-SnO2 (ATO) anode in flow-through mode was proposed with the hopes to improve the performance of UF during wastewater reclamation. The results indicated that this flow-through ATO (FA) anode significantly outperformed a boron-doped diamond (BDD) anode in terms of EfOM degradation and membrane fouling control. It is noteworthy that apart from oxidation, the self-aggregation behavior of foulants was also involved in the mechanisms of membrane fouling mitigation. On the one hand, FA pre-oxidation relieved the burden of membrane fouling by decomposing the macromolecular EfOM into small molecular organic matter, and even mineralizing it. The effective destruction of unsaturated EfOM by FA pre-oxidation made a remarkable contribution to fouling mitigation due to the strong correlation between the total fouling index and UV254. On the other hand, the surface morphology of membrane and interface properties of foulants revealed the self-aggregation behavior of foulants. FA pre-oxidation made the foulants aggregate spontaneously and reduced the potential of forming a dense cake layer on the membrane surface, which was conductive for water permeation. Overall, FA pre-oxidation proved to be a feasible and chemical-free option for UF pretreatment to simultaneously produce high-quality reused water and alleviate membrane fouling during wastewater reclamation.

Replacing traditional pretreatment in one-step UF with natural short-distance riverbank filtration: Continuous contaminants removal and TMP increase relief.

Scientists have been focusing on applying more natural processes instead of industrial chemicals in drinking water treatment to achieve the purpose of carbon emissions reduction. In this study, we shortened the infiltration range of riverbank filtration, a natural water purification process, to form the short-distance riverbank filtration (sRBF) which retained its ability in water quality improvement and barely influenced the groundwater environment, and integrated it with ultrafiltration (UF) to form a one-step sRBF-UF system. This naturalness-artificiality combination could realize stable contaminants removal and trans-membrane pressure (TMP) increase relief for over 30 days without dosing chemicals. Generally, both sRBF and UF played the important role in river water purification, and the interaction between them made the one-step sRBF-UF superior in long-term operation. The sRBF could efficiently remove contaminants (90 % turbidity, 60 % total nitrogen, 30 % ammonia nitrogen, and 25 % total organic carbon) and reduce the membrane fouling potential of river water under its optimum operation conditions, i.e., a hydraulic retention time of 48 h, an operation temperature of 20 °C, and a synergistic filter material of aquifer and riverbank soil. Synergistic adsorption, interception, and microbial biodegradation were proved to be the mechanisms of contaminants and foulants removal for sRBF. The sequential UF also participated in the reduction of impurities and especially played a role in intercepting microbial metabolism products and possibly leaked microorganisms from sRBF, assuring the safety of product water. To date, the one-step sRBF-UF was a new attempt to combine a natural process with an artificial one, and realized a good and stable product quality in long-term operation without doing industrial chemicals, which made it a promised alternative for water purification for cities alongside the river.

Three-compartment membrane electrolyzer combining simultaneous desalination and oxidative degradation in treating nanofiltration concentrate.

The complex organic and inorganic solutes present in nanofiltration's purification by-product (NF concentrate, NFC) pose challenges to the water processing procedure. To address this, a three-compartment membrane electrolyzer was proposed that facilitates electro-driven ion migration for crystallization alongside synchronous anodic oxidation for organic degradation. With a hydraulic retention time (HRT) of 5 min and a current exceeding 50 mA, the system effectively separated over 25 % of inorganic salts and accomplished reclamation through crystallization in the concentration compartment. Simultaneously, it achieved oxidation of pollutants by more than 35 % based on the total nitrogen index and removed upwards of 15 % of organic carbon. Notably, the efficiency of pollutant removal correlated strongly with the intensity of the current. Furthermore, this study uncovered two issues encountered during the electrochemical process: membrane fouling and electrode fouling. During concentration, metal cations readily formed organic pollution by complexing with organic pollutants, while the crystallization of inorganics on the surface of anion exchange membranes emerged as a pivotal factor hindering current enhancement, similar to the formation of deposited salt in a solution. Long HRT can lead to electrode contamination and corrosion which subsequently affect current efficiency. Energy consumption verified the feasibility of the electrolyzer for NFC processing. Based on our findings, a current intensity of 100 mA (equivalent to a density of 8 mA/cm2) was deemed optimal, striking a balance between pollutant removal and various limiting factors associated with each pollutant. Consequently, this innovative advancement in membrane electrolyzers helps in overcoming limitations in synergistic desalination, ion recovery, and organic removal, establishing a fundamental component of the abbreviated flow process for future NFC treatment.

Simulated-sunlight enhances membrane aerated biofilm reactor performance in sulfamethoxazole removal and antibiotic resistance genes reduction.

Membrane aerated biofilm reactors (MABRs) can be used to treat domestic wastewater containing sulfamethoxazole (SMX) because of their favorable performance in the treatment of refractory pollutants. However, biologics are generally subjected to antibiotics stress, which induces the production of antibiotic resistance genes (ARGs). In this study, a simulated-sunlight assisted MABR (L-MABR) was used to promote SMX removal and reduce ARGs production. The SMX removal efficiency of the l-MABR system was 9.62 % superior to that of the MABR system (83.13 %). In contrast from MABR, in the l-MABR, only 28.75 % of SMX was removed through microbial activity because functional bacteria were inactivated through radiation by simulated sunlight. In addition, photolysis (64.61 %) dominated SMX removal, and the best performing indirect photolysis process was the excited state of effluent organic matters (3EfOMs*). Through photolysis, ultraviolet (UV) and reactive oxygen species (ROS) enriched the SMX removal route, resulting in the SMX removal pathway in the l-MABR no longer being limited by enzyme catalysis. More importantly, because of the inactivation of functional bacteria, whether in the effluent or biofilm, the copy number of ARGs in the l-MABR was 1-3 orders of magnitude lower than that in the MABR. Our study demonstrates the feasibility of utilizing simulated-sunlight to enhance the antibiotic removal efficiency while reducing ARG production, thus providing a novel idea for the removal of antibiotics from wastewater.

Nanofiltration Membranes with Salt-Responsive Ion Valves for Enhanced Separation Performance in Brackish Water Treatment: A Battle against the Limitation of Salt Concentration.

Utilizing brackish water resources has imposed a high requirement on the design and construction of nanofiltration membranes. To overcome the limitation of high salt concentration on the nanofiltration separation performance resulting from the weakened Donnan effect, a nanofiltration membrane with the effect of salt-responsive ion valves was developed by incorporating zwitterionic nanospheres into the polyamide layer (PA-ZNs). The interaction between the nanospheres and membranes at high salinity was revealed through a combination analysis from the perspectives of water transport model, positron annihilation spectroscopy, and solute rejection, contributing to the formation of the valve effect. The PA-ZNs membrane presented a breakthrough in overcoming the limitation of increased salt concentrations on nanofiltration separation performance, achieving a high selectivity of 105 for mono/multivalent anions. To reveal the role of the ion valve effect in ion transport through the membrane, the membrane conductance was determined at different salt concentrations, confirming channel-controlled transport at low salinity and ion valve-controlled transport at high salinity. Moreover, the main membrane separation mechanisms were systematically studied. The concept of salt-responsive ion valves may contribute to expanding the application of nanofiltration in brackish water treatment.

Employing Visible Light To Construct Photoinitiated Polymerized Nanofiltration Membranes for High Permeation and Environmental Micropollutant Removal.

Improving the nanofiltration (NF) performance of membrane-based treatment is conducive to promoting environmental water recycling and addressing water resource depletion. Combinations of light, electricity, and heat with traditional techniques of preparing membranes should optimize membrane performance. Interfacial polymerization and photopolymerization were integrated to construct a photopolymerized thin-film composite NF membrane with a ridged surface morphology. Under visible light initiation, 2-acrylamido-2-methyl-1-propanesulfonic acid was crosslinked with the polyamide network. The control effects of light on the membrane surface and physicochemical properties were revealed via infrared thermal images and response surface methodology. To present the diffusion motion of piperazine molecules, molecular dynamics simulations were implemented. Through density functional theory simulations, the crosslinking mechanism of the photoinduced NF network was identified and verified. The surface physicochemical characteristics and perm-selectivity performance were systematically illustrated. The photopolymerized membrane outperformed the pristine in permeability and selective separation competence; without degradation of solute repulsion, the water permeation was enhanced to 33.5 L m-2 h-1 bar-1, 6.6 times that of the initial membrane. In addition, the removal of organic contaminants and antifouling capacities were improved. This work represents a novel lead for applying sustainable resources in constructing high-performance membranes for environmental challenges.

Effect of a Permanganate-Bearing Reactive Oxidant on Flocs in Electrocoagulation: Transformations and Interfacial Interactions.

The electrocoagulation/ultrafiltration (ECUF) process is expected to address the issues of current wastewater increments and complex water reuse. However, the underlying mechanism associated with flocs remains unclear in the ECUF system, especially in the upgraded permanganate-bearing ECUF (PECUF) system. Herein, flocs and their formation, response to organic matter (OM), and interfacial features in the PECUF process were systematically explored. Results demonstrated that permanganate contributed to the rapid start-up of the coagulation process by forming MnO2 and blocking the ligand-metal charge transfer process between adsorbed Fe(II) and solid-phase Fe(III). The response of flocs to natural OM (NOM) exhibited obvious time- and particle size-dependent characteristics. Based on this, the optimal NOM adsorption window was found to be in the interval of 5-20 min, whereas the optimal NOM removal window was located at the 20-30 min interval. Furthermore, the extended Derjaguin-Landau-Verwey-Overbeek theory revealed the underlying principle of the PECUF module for optimizing UF performance. On the one hand, it reduced the inherent resistance of the cake layer by modifying the colloidal solution, which guaranteed a small drop (15%) in initial flux. On the other hand, it enhanced the repulsive force among suspended particles to achieve a long-term antifouling effect. This study may provide insights into the selection and performance control of on-demand assembly modules in decentralized water treatment systems.

Application of cellulose nanocrystals in water treatment membranes: A review.

Nanomaterials have brought great changes to human society, and development has gradually shifted the focus to environmentally friendly applications. Cellulose nanocrystals (CNCs) are new one-dimensional nanomaterials that exhibit environmental friendliness and ensure the biological safety of water environment. CNCs have excellent physical and chemical properties, such as simple preparation process, nanoscale size, high specific surface area, high mechanical strength, good biocompatibility, high hydrophilicity and antifouling ability. Because of these characteristics, CNCs are widely used in ultrafiltration membranes, nanofiltration membranes and reverse osmosis membranes to solve the problems hindering development of membrane technology, such as insufficient interception and separation efficiency, low mechanical strength and poor antifouling performance. This review summarizes recent developments and uses of CNCs in water treatment membranes and discusses the challenges and development prospects of CNCs materials from the perspectives of ecological safety and human health by comparing them with traditional one-dimensional nanomaterials.

Synergistic effects of prokaryotes and oxidants in rapid sand filters treatment of groundwater versus surface water: Purification efficacy, stability and associated mechanisms.

Effective elimination of manganese (Mn) and ammonium (NH4+-N) from drinking water is still challenging. Utilizing oxidants to improve the simultaneous removals of Mn and NH4+-N from rapid sand filter (RSF) systems has been extensively studied. However, the prokaryotes containing in the water geochemical properties greatly affected the RSF performance. In this study, groundwater and micro-polluted surface water were used to compare with/without potassium permanganate (KMnO4) assistant on the contaminants removals and system stability. Results showed that KMnO4 reduced the start-up period of RSF for treating groundwater and surface water to 20 and 41 days, respectively, with excellent Mn removal rates (>97%). The relative abundance of efficient ammonia-oxidizing bacteria (Nitrospira) in RSF treated groundwater without KMnO4 was higher than that in RSFs treated micro-polluted surface water or with KMnO4, resulting in a higher NH4+-N removal rate of the former (∼57%). Notably, KMnO4 and prokaryotes synergistically contributed to the amorphous structure, mixed phases (buserite, MnO2 and birnessite) and mixed-valence Mn system of active manganese oxides (MnOx), whose abundant oxygen vacancies and highly reactive Mn(III) favored the autocatalytic oxidation of Mn, while NH4+-N removal relied more on bacteria actions. Additionally, prokaryotes enriched the bacterial community diversity, leading to a more stable RSF system when facing hydraulic loading shock. This paper provided new insight into the synergistic effect of KMnO4 and prokaryotes on Mn and NH4+-N eliminations in RSFs and was helpful for practical applications.

Dual role of boron-doped diamond (BDD) anode in effluent organic matter degradation and ultrafiltration membrane fouling mitigation.

Ultrafiltration (UF) is effective in retaining macromolecules during tertiary treatment, but the membrane fouling caused by the effluent organic matter (EfOM) limits its application. This study employed electrochemical oxidation (EO) as a pretreatment method for UF in tertiary treatment to investigate the effects of anode materials on membrane fouling alleviation and EfOM degradation. Compared with the dimensionally stable (DSA) and platinum (Pt) anodes, EO with a boron-doped diamond (BDD) anode exhibited better performances for membrane fouling mitigation due to the higher hydroxyl radical production activity of the BDD anode. It was observed that the current density and electrolysis time were closely related to membrane fouling when using a BDD anode, where increasing the current density or electrolysis time led to a significant improvement of specific flux. The BDD-based pre-oxidation efficiently removed 64% DOC, 76% UV254, and 95% fluorescence organic matter in EfOM, among which the concentrations of DOC and UV254 were positively correlated with the total fouling index (TFI). Meanwhile, 70% SMX in the secondary effluent was removed by the BDD anode. Furthermore, the BDD anode also mitigated membrane fouling by decomposing high molecular weight organic matter into smaller fractions and enhancing the electrostatic repulsion between membrane and EfOM. Therefore, the BDD-based EO process is a promising pretreatment strategy for UF to alleviate membrane fouling and improve the permeate quality.

Nanofiltration Membranes with Octopus Arm-Sucker Surface Morphology: Filtration Performance and Mechanism Investigation.

Precisely tailoring the surface morphology characteristics of the active layers based on bionic inspirations can improve the performance of thin-film composite (TFC) membranes. The remarkable water adsorption and capture abilities of octopus tentacles inspired the construction of a novel TFC nanofiltration (NF) membrane with octopus arm-sucker morphology using carbon nanotubes (CNTs) and beta-cyclodextrin (ß-CD) during interfacial polymerization (IP). The surface morphology, chemical elements, water contact angle (WCA), interfacial free energy (ΔG), electronegativity, and pore size of the membranes were systematically investigated. The optimal membrane exhibited an enhanced water permeance of 22.6 L·m-2·h-1·bar-1, 180% better than that of the TFC-control membrane. In addition, the optimal membrane showed improved single salt rejections and monovalent/divalent ion selectivity and can break the trade-off effect. The antiscaling performance and stability of the membranes were further explored. The construction mechanism of the octopus arm-sucker structure was excavated, in which CNTs and ß-CD acted as arm skeletons and suckers, respectively. Furthermore, the customization of the membrane surface and performance was achieved through tuning the individual effects of the arm skeletons and suckers. This study highlights the noteworthy potential of the design and construction of the surface morphology of high-performance NF membranes for environmental application.

Evaluations of holey graphene oxide modified ultrafiltration membrane and the performance for water purification.

Membrane technology has been widely used in the fields of drinking water treatment with the advantages of pollutants separation. However, membrane fouling has become main obstacle in further application. Graphene oxide (GO) and its functionalized derivatives are considered to be ideal membrane modification materials of membrane fouling control. However, GO coated membranes were suffered from serious flux decline which raises challenges for GO modification. In this study, porous holey graphene oxide (HGO) was synthesized by hydrothermal etched GO to modify UF membranes. Water permeability of HGO membrane was more than twice that of GO membrane at the loading of 0.08 g/m2. At the optimal loading of 0.08 g/m2, the rejection rate of HGO coated membrane on natural organic matter (NOM) such as bovine serum albumin (BSA), sodium alginate (SA) and humic acid (HA) was increased from 55%, 29%, 58%-85%, 72%, 92%, and the contact angle was reduced from 71° to 35° with the HGO coating amount of 0.04 g/m2. Finally, the membrane fouling resistance distribution of each HGO membrane was analyzed given HA as model pollutant, and the effects of HGO on mitigating the organic fouling of Polyethersulfone (PES) membranes were discussed. The total fouling resistance decreased from 3.45 to 1.73 with HGO coating, the irreversible fouling decreased by 62.86%-95.83%. Standard blocking was dominated during filtration. It was also found that increasing the loading of HGO could delay the conversion of pore blocking to the cake layer. Overall, HGO coating has an application prospect for membrane fouling control.

Effects of oxidation on humic-acid-enhanced gypsum scaling in different nanofiltration phases: Performance, mechanisms and prediction by differential log-transformed absorbance spectroscopy.

The aim of this study was to evaluate the effects of oxidation on humic-acid-enhanced gypsum scaling in different nanofiltration phases, including the short-term membrane flux behaviors and the long-term ones. On the basic of correlation analysis between the changing physicochemical properties of feed solution and membrane fouling, the inner mechanisms were revealed from aspects of bulk crystallization (interaction between humic acid and inorganic ions) and surface crystallization (compositions and morphologies of surface crystallization). Furthermore, the reliability of applicating differential log-transformed absorbance spectroscopy for predicting membrane fouling was also systematically evaluated. There was an upward trend in short-term membrane fouling with increasing dosage of NaClO, while long-term membrane fouling decreased after an initial increase. During short-term filtration, the enhanced combination between inorganic ions and the humic acid with stronger density of carboxyl groups, which was generated more easily under stronger oxidation conditions, favored the earlier appearance of flux decline. During long-term filtration, the size of bulk crystallization depended on the total content of carboxyl groups in feed solution. Both of them increased firstly and then decreased with increasing oxidation. The terminal fouling layer resistance also shared a similar tendency with them, because the deposition of bulk crystallization on membranes and the formation of dense scaling layer were the direct reasons for the long-term membrane fouling. Furthermore, the differential log-transformed absorbance spectroscopy was proven to be an efficient approach to predict short-term membrane fouling, especially in the wavelength range of 260 to 280 nm. This research could not only provide guidance on alleviating oxidation-enhanced membrane fouling in nanofiltration but also propose an efficient way to predict the membrane fouling which was influenced by the interaction between organic matters and inorganic ions.

High-performance nanofiltration membranes with a sandwiched layer and a surface layer for desalination and environmental pollutant removal.

To overcome the permeability-selectivity limitation and improve the performance of desalination membranes, novel methods and design strategies are needed to prepare new types of thin film composite (TFC) nanofiltration (NF) membranes. In this work, a modified TFC membrane with a sandwiched layer and a surface layer was fabricated through a facile additional two-step approach. The microfiltration (MF) substrate and TFC surface were modified by a cellulose nanocrystal (CNC) sandwiched layer and a polydopamine (PDA) layer, respectively. Scanning electron microscopy (SEM) analysis indicated that the support modified by CNCs presented a more homogeneous surface than the control TFC. Cross-sectional SEM images showed that the underneath MF support, CNC interlayer, polyamide layer and PDA deposition layer were perfectly integrated. The surface charge was determined by an electrophoretic analyzer and revealed that the CNC interlayer increased the membrane electronegativity, while the PDA layer presented the opposite effect. Compared to the control TFC membrane, the solute permeability and rejection of the resultant CNC-TFC-PDA membrane were simultaneously increased, indicating a breakthrough in the trade-off limitation. The modified membranes exhibited a high removal rate for Congo red, Rose Bengal, sodium lignosulfonate and alkaline lignin, suggesting their excellent rejection performance for textile dyes and lignin derivatives. Fouling tests indicated that both the interlayer and surface layer exhibited positive effects on fouling alleviation. The effects of each functional layer were explored, and the main factors for performance improvement, including the modified hydrophilicity, surface charge, pore size and surface roughness, were discussed.

Application of heat-activated peroxydisulfate pre-oxidation for degrading contaminants and mitigating ultrafiltration membrane fouling in the natural surface water treatment.

Membrane fouling is posing a critical obstacle limiting the widespread application of ultrafiltration (UF). Among the numerous membrane foulants, natural organic matter (NOM) is one of the most problematic since it exists ubiquitously in natural waters and can cause severe membrane fouling. This study investigated the removal of NOM in surface water and the mitigation of membrane fouling using heat-activated peroxydisulfate (PDS) as a pretreatment for UF process. The results demonstrated that the NOM was efficiently removed, with ultraviolet absorbance (UV254) and dissolved organic carbon (DOC) decreasing by approximately 71% and 52%, respectively, at a PDS dose of 0.8 mM within 60 min (80 °C). The chromatograms of high performance size exclusion chromatography (HPSEC) indicated that some high molecular weight humic substances with a peak at approximately 10 kDa were oxidized to low molecular weight organic matters distributed in the range of < 100 Da during the pretreatment process. Moreover, three-dimensional fluorescence parallel factor analysis (PARAFAC) indicated that humic-like substances were much more easily degraded by heat-activated PDS pretreatment than protein-like substances. These results indicated that some unsaturated NOM fractions were first degraded and then mineralized to carbon dioxide during pretreatment. Meanwhile, the destroyed structure of humic substances might hinder its binding with high valence cations to reduce the possibility of high valence cations deposited on the membrane surface, thereby reducing membrane fouling. Therefore, membrane fouling could be significantly mitigated due to the shifts of NOM concentration and structure by heat-activated PDS pretreatment in the surface water treatment.

Toward enhancing the separation and antifouling performance of thin-film composite nanofiltration membranes: A novel carbonate-based preoccupation strategy.

High-performance nanofiltration (NF) membranes with simultaneously improved antifouling and separation performance are of great significance for environmental water purification. In this work, a high-performance thin-film composite (TFC) NF membrane (TFC-Ca) was constructed through in-situ incorporation of calcium bicarbonate during interfacial reaction. The surface morphology and chemical structure of the TFC-Ca membrane were systematically investigated by FTIR, XPS, AFM, and SEM. The results indicated that the surface characteristics of the pristine NF membrane were greatly changed by the incorporation of calcium bicarbonate. The TFC-Ca membrane exhibited improved hydrophilicity, narrowed pore size, declined negative charge, and increased surface area. Compared to the control membrane, the TFC-Ca membrane possessed a much greater water permeability and higher molecule rejections. For the TFC-Ca membrane, an optimized water permeance of 13.4 ± 0.3 L m-2 h-1 bar-1 with 99.9% Na2SO4 rejection was obtained. Impressively, the TFC-Ca membrane exhibited excellent antifouling performance during 5 cycles of humic acid fouling tests. A satisfactory flux recovery up to 90.0% was achieved after physical cleaning for the optimized membrane. Furthermore, the TFC-Ca membrane also presented superior performance stability when treated with strong acid and chelating agents for 7 days. Overall, this facile preoccupation strategy via in-situ incorporation of calcium bicarbonate allows the fabrication of high-performance TFC membranes with outstanding separation and antifouling properties.

The role of ferric coagulant on gypsum scaling and ion interception efficiency in nanofiltration at different pH values: Performance and mechanism.

Nanofiltration (NF) is extensively applied after coagulation, which is conducive to alleviate organic fouling on NF membranes and improve water purification performance. However, inorganic fouling, which remains the major obstacle to limit the wider application of NF, could be enhanced by even low dosage coagulant. Few researchers realize the existence of coagulant-enhanced scaling, much less control it. This study investigated the effects of pH values on ferric-coagulant-influenced membrane performance during the nanofiltration of brackish water. Both membrane flux behavior (initial membrane flux, normalized flux during filtration, scaling resistance and scaling composition) and ion interception (filtrate conductivity and ions removal) were considered. Solution properties (zeta potential and nanoparticle size) were measured, and coagulant speciation variation was stimulated by Visual MINTEQ software. Mechanisms of ferric-coagulant-influenced membrane performance were analyzed from two aspects on the basis of correlation analyses: interface interaction on membrane surface and salts crystallization process (bulk crystallization and surface crystallization). Results showed that both bulk crystallization in feed solution and surface crystallization on membrane surface were dramatically induced by coagulant. Coagulant-enhanced fouling layer resistance decreased after the initial increase when pH varied from 3.0 to 10.0. Fe(OH)3, a kind of active ingredients in ferric coagulant, was highly responsible for the enhanced scaling layer resistance. Coagulant was found improving ionic removal under acidic conditions despite the fact that it could worsen removal under alkaline conditions. This study is of valuable reference to figure out the mechanisms of coagulant-influenced membrane performance and find a feasible approach to avoid membrane deterioration in coagulant-influenced NF process.

Scaling behavior of iron in capacitive deionization (CDI) system.

This study investigated the fouling and scaling behaviors in a capacitive deionization (CDI) system in the presence of iron and natural organic matter (NOM). It was found that the salt adsorption capacity (SAC) significantly decreased when treating Fe-containing brackish water, with higher Fe concentrations leading to severer SAC reduction. Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis demonstrated that Fe2O3 appeared to be the predominant foulant attached on the electrode surface, which was difficult to be removed via backwashing, indicating the irreversible property of the foulant. Further characterizations (e.g., N2 sorption-desorption isotherms, electrochemical impedance spectroscopy and cyclic voltammetry) revealed that the CDI electrodes suffered from obvious deterioration such as specific surface area loss, resistance increase and capacitance decline with the occurrence of Fe scaling. While the presence of NOM alleviated the Fe scaling through NOM-Fe complexing effects, NOM itself was found to have negative impacts on CDI desalination performance due to their strong interactions with the carbon electrodes.