Role of reactive manganese and oxygen species in the KMnO4/Na2SO3 process for purification of algal-rich water and membrane fouling alleviation.

Ultrafiltration (UF) is a highly efficient technique for algal-rich water purification, but it is heavily contaminated due to the complex water characteristics. To solve this problem, potassium permanganate (KMnO4) oxidation enhanced with sodium sulfite (Na2SO3) was proposed as a pretreatment means. The results showed that the end-normalized flux was elevated from 0.10 to 0.91, and the reversible fouling resistance was reduced by 99.95%. The membrane fouling mechanism also changed obviously, without the generation of cake filtration. Regarding the properties of algal-rich water, the zeta potential was decreased from -29.50 to -5.87 mV after KMnO4/Na2SO3 pretreatment, suggesting that the electrostatic repulsion was significantly reduced. Meanwhile, the fluorescent components in algal-rich water were significantly eliminated, and the removal of dissolved organic carbon was increased to 67.46%. In the KMnO4/Na2SO3 process, reactive manganese species (i.e., Mn(V), Mn(III) and MnO2) and reactive oxygen species (i.e., SO4•- and •OH) played major roles in purifying algal-rich water. Specifically, SO4•-, •OH, Mn(V) and Mn(III) could effectively oxidize algal pollutants. Simultaneously, the in-situ adsorption and coagulation of MnO2 could accelerate the formation of flocs by decreasing the electrostatic repulsion between cells, and protect the algal cells from being excessive oxidized. Overall, the KMnO4/Na2SO3 process showed significant potential for membrane fouling alleviation in purifying algal-rich water.

Enhancing microfiltration membrane performance by sodium percarbonate-based oxidation for hydraulic fracturing wastewater treatment.

Low pressure membrane takes a great role in hydraulic fracturing wastewater (HFW), while membrane fouling is a critical issue for the stable operation of microfiltration (MF). This study focused on fouling mitigation by sodium percarbonate (SPC) oxidation, activated by ultraviolet (UV) and ferrous ion (Fe(II)). The higher the concentration of oxidizer, the better the anti-fouling performance of MF membrane. Unlike severe MF fouling without oxidation (17.26 L/(m2·h)), UV/SPC and Fe(II)/SPC under optimized dosage improved the final flux to 740 and 1553 L/(m2·h), respectively, and the latter generated Fe(III) which acted as a coagulant. Fe(II)/SPC oxidation enabled a shift in fouling mechanism from complete blocking to cake filtration, while UV/SPC oxidation changed it to standard blockage. UV/SPC oxidation was stronger than Fe(II)/SPC oxidation in removing UV254 and fluorescent organics for higher oxidizing capacity, but the opposite was noted for DOC removal. The deposited foulants on membrane surface after oxidation decreased by at least 88% compared to untreated HFW. Correlation analysis showed that UV254, DOC and organic fraction were key parameters responsible for membrane fouling (correlation coefficient＞0.80), oxidizing capacity and turbidity after oxidation were also important parameters. These results provide new insights for fouling control during the HFW treatment.

Investigation of membrane fouling and mechanism induced by extracellular organic matter during long-term exposure to pharmaceuticals and personal care products.

This study investigated ultrafiltration membrane fouling by extracellular organic matter (EOM) and the mechanism operating during long-term exposure to pharmaceuticals and personal care products. The results indicated that carbamazepine and diclofenac in algal-laden water altered the filtration flux and membrane fouling by EOM. Exposure to low-concentration carbamazepine (0.25 µg/L) improved the filtration flux and the total (Rtot) and reversible fouling resistance (Rc), whereas the filtration flux and Rtot and Rc were reduced when EOM was used during long-term exposure to high carbamazepine concentrations (>1 µg/L). Both Rtot and Rc were increased when algae were exposed to 0.25 µg/L diclofenac, whereas the filtration flux and Rtot and Rc were alleviated when algae were exposed to >1 µg/L diclofenac. Moreover, carbamazepine and diclofenac (0.25 µg/L - 1000 µg/L) in water enhanced the irreversible fouling resistance (Rb) when ultrafiltration was used to treat algal-laden waters. The mechanism indicated that membrane fouling induced by standard blocking was transformed to complete blocking when EOM was exposed to high levels of carbamazepine (>0.25 µg/L) in the initial filtration process, whereas cake layer formation played an important role during the later filtration process; with low carbamazepine levels (0.25 µg/L), standard blocking of EOM was dominant during the entire filtration process. The membrane fouling mechanism also changed when algal-laden waters were exposed to diclofenac, the membrane fouling was transformed from complete blocking to standard blocking when DFC was present in the initial filtration process, whereas cake layer formation exerted an important role during the late filtration process. This research provides important information on the long-term risks caused by pharmaceutical and personal care products and potential threats to membrane treatment.

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.

Ultrathin Thin-Film Composite Polyamide Membranes Constructed on Hydrophilic Poly(vinyl alcohol) Decorated Support Toward Enhanced Nanofiltration Performance.

Traditional polyamide-based interfacial polymerized nanofiltration (NF) membranes exhibit upper bound features between water permeance and salt selectivity. Breaking the limits of the permeability and rejections of these composite NF membranes are highly desirable for water desalination. Herein, a high-performance NF membrane (TFC-P) was fabricated via interfacial polymerization on the poly(vinyl alcohol) (PVA) interlayered poly(ether sulfone) (PES) ultrafiltration support. Owing to the large surface area, great hydrophilicity, and high porosity of the PES-PVA support, a highly cross-linked polyamide separating layer was formed with a thickness of 9.6 nm, which was almost 90% thinner than that of the control membrane (TFC-C). In addition, the TFC-P possessed lower ζ-potential, smaller pore size, and greater surface area compared to that of the TFC-C, achieving an ultrahigh water permeance of 31.4 L m-2 h-1 bar-1 and a 99.4% Na2SO4 rejection. Importantly, the PVA interlayer strategy was further applied to a pilot NF production line and the fabricated membranes presented stable water flux and salt rejections as comparable to the lab-scaled membranes. The outstanding properties of the PVA-interlayered NF membranes highlight the feasibility of the fabrication method for practical applications, which provides a new avenue to develop robust polyamide-based NF desalination membranes for environmental water treatment.

Hybrid UF/NF process treating secondary effluent of wastewater treatment plants for potable water reuse: Adsorption vs. coagulation for removal improvements and membrane fouling alleviation.

Coagulation and adsorption are gradually adopted as pre-treatments to produce reclaimed potable water. However, previous researches on membrane fouling mechanisms were currently insufficient to minimize dual membrane fouling. This study aimed at investigating the effects of pre-coagulation and pre-adsorption on the removal performance and membrane fouling alleviation of dual membrane UF/NF process in treating secondary effluent from a wastewater treatment plant. The results indicated that both types of pretreatments conferred positive effects on organic membrane fouling removal of the UF process whereas diverse effects on NF process. Pre-coagulation could enhance the removal of nitrogen and phosphorus to contribute towards producing microbiologically-stable water. On the other hand, introduction of Al3+ reduced the removal efficiency of UF/NF systems on heavy metals. From the perspective of UF membrane fouling, two pretreatments employed could increase the flux of UF, but simultaneously aggravating irreversible membrane fouling. Hermia and Tansel models revealed an unstable cake filtration was caused by pre-coagulation and pre-adsorption. Both the models consistently demonstrated the rapid formation of cake filtration onto UF membrane surface. Interestingly, the powdered activated carbon (PAC) adsorption could significantly reduce cake layer fouling onto the surface of NF membrane, while pre-coagulation aggravated the NF fouling. These results are essential to developing robust, cost-effective and energy-efficient strategies based on membranes to produce reclaimed potable water.

Roles of ERα during mouse trophectoderm lineage differentiation: revealed by antagonist and agonist of ERα.

During mouse early embryogenesis, blastomeres increase in number by the morula stage. Among them, the outer cells are polarized and differentiated into trophectoderm (TE), while the inner cells remain unpolarized and give rise to inner cell mass (ICM). TE provides an important liquid environment for ICM development. In spite of extensive research, the molecular mechanisms underlying TE formation are still obscure. In order to investigate the roles of estrogen receptor α (ERα) in this course, mouse 8-cell embryos were collected and cultured in media containing ERα specific antagonist MPP and/or agonist PPT. The results indicated that MPP treatment inhibits blastocyst formation in a dose-dependent manner, while PPT, at proper concentration, promotes the cavitation ratio of mouse embryos. Immunofluorescence staining results showed that MPP significantly decreased the nuclear expression of CDX2 in morula, but no significant changes of OCT4 were observed. Moreover, after MPP treatment, the expression levels of the genes related to TE specification, Tead4, Gata3 and Cdx2, were significantly reduced. Overall, these results indicated that ERα might affect mouse embryo cavitation by regulating TE lineage differentiation.

Promoted production of Fe(IV)/Fe(V) intermediates in the calcium peroxide/ferrate(VI) process for low-damage removal of algal contaminants and membrane fouling control.

Ultrafiltration (UF) is widely employed for harmful algae rejection, whereas severe membrane fouling hampers its long-term operation. Herein, calcium peroxide (CaO2) and ferrate (Fe(VI)) were innovatively coupled for low-damage removal of algal contaminants and fouling control in the UF process. As a result, the terminal J/J0 increased from 0.13 to 0.66, with Rr and Rir respectively decreased by 96.74 % and 48.47 %. The cake layer filtration was significantly postponed, and pore blocking was reduced. The ζ-potential of algal foulants was weakened from -34.4 mV to -18.7 mV, and algal cells of 86.15 % were removed with flocs of 300 µm generated. The cell integrity was better remained in comparison to the Fe(VI) treatment, and Fe(IV)/Fe(V) was verified to be the dominant reactive species. The membrane fouling alleviation mechanisms could be attributed to the reduction of the fouling loads and the changes in the interfacial free energies. A membrane fouling prediction model was built based on a long short-term memory deep learning network, which predicted that the filtration volume at J/J0= 0.2 increased from 288 to 1400 mL. The results provide a new routine for controlling algal membrane fouling from the perspective of promoting the generation of Fe(IV)/Fe(V) intermediates.

Ferrate(VI)-based oxidation for ultrafiltration membrane fouling mitigation in shale gas produced water pretreatment: Role of high-valent iron intermediates and hydroxyl radicals.

Ultrafiltration (UF) is increasingly used in the pretreatment of shale gas produced water (SGPW), whereas severe membrane fouling hampers its actual operation. In this work, ferrate(VI)-based oxidation was proposed for membrane fouling alleviation in SGPW pretreatment, and the activation strategies of calcium peroxide (CaO2) and ultraviolet (UV) were selected for comparison. The findings indicated that UV/Fe(VI) was more effective in removing fluorescent components, and the concentration of dissolved organic carbon was reduced by 24.1 %. With pretreatments of CaO2/Fe(VI) and UV/Fe(VI), the terminal specific membrane flux was elevated from 0.196 to 0.385 and 0.512, and the total fouling resistance diminished by 52.7 % and 76.2 %, respectively. Interfacial free energy analysis indicated that the repulsive interactions between pollutants and membrane were notably enhanced by Fe(VI)-based oxidation, thereby delaying the deposition of cake layers on the membrane surface. Quenching and probe experiments revealed that high-valent iron intermediates (Fe(IV)/Fe(V)) played significant roles in both CaO2/Fe(VI) and UV/Fe(VI) processes. Besides, hydroxyl radicals (•OH) were also important reactive species in the UV/Fe(VI) treatment, and the synergistic effect of Fe(IV)/Fe(V) and •OH showed a positive influence on SGPW fouling mitigation. In general, these findings establish a theoretical underpinning for the application of Fe(VI)-based oxidation for UF membrane fouling mitigation in SGPW pretreatment.

Mechanistic insight into single-atom Fe loaded catalytic membrane with peracetic acid and visible light activation.

Advanced oxidation is an effective method for removing hard-to-degrade organic pollutants from water. In this paper, a novel structure of a single atom Fe anchored g-C3N4 (FeCN) membrane was proposed to remove pollutants from water by coupling membrane technology with photocatalytic and peroxyacetic acid oxidation. The presence of zero-dimensional Fe atoms in FeCN membranes allows for the removal of acetaminophen (APAP) in mobile membrane filtration systems without compromising permeation performance by simultaneously possessing visible photocatalytic capability and peroxyacetic acid (PAA) activation. Existence of inter-membrane domain-limiting conditions led to 100 % degradation of APAP within 10.5 ms, which is 5 orders of magnitude faster than conventional catalytic systems. Notably, photo-generated electrons/holes generated by light and HClO generated by Cl- promote the conversion of Fe(V) and the removal of pollutants during the catalytic process. The spatial separation ability of the membrane catalytic layer surface mitigates the catalyst's passivation by macromolecular organics. Furthermore, surface photocatalysis of the membrane and interlayer catalysis generated by PAA mitigate the surface and interlayer pollutants of the membrane, respectively. This study explores a novel approach for the development of highly efficient atom-catalyzed membrane systems with multiple purposes.

Activation of peroxymonosulfate with biochar-supported CuO (CuO@BC) for natural organic matter removal and membrane fouling control.

To achieve excellent activation efficiency of peroxymonosulfate (PMS), this work prepared a biochar-supported CuO (CuO@BC) catalyst, and the CuO@BC/PMS system was proposed to remove the organic matter in natural surface water and reduce the fouling of ultrafiltration membrane. The successful synthesis of CuO@BC was demonstrated through characterization of its microscopic morphology and chemical composition by various techniques. The prepared heterogeneous catalyst showed a strong catalytic effect on PMS, which significantly removed natural organic matter through the production of active substances (•OH, SO4•-, O2•- and 1O2) from water. With respective degradation rates of 39.4% and 59.4%, the concentrations of DOC and UV254 dropped to 1.702 mg/L and 0.026 cm-1, respectively. Additionally, the CuO@BC/PMS oxidation displayed potent oxidation capabilities for contaminants and fluorescent organics with various molecular weights. The system effectively decreased the amount of organic matter that caused reversible and irreversible fouling of polyethersulfone membranes in natural water by 85.8% and 56.3%, respectively. The main fouling mechanisms changed as well, with standard and complete blocking dominating the entire filtration process. The results demonstrated the capacity of the CuO@BC/PMS system to remove contaminants in natural water and mitigate membrane fouling.

Proteotoxic stress disrupts epithelial integrity by inducing MTOR sequestration and autophagy overactivation.

Macroautophagy/autophagy, an evolutionarily conserved degradation system, serves to clear intracellular components through the lysosomal pathway. Mounting evidence has revealed cytoprotective roles of autophagy; however, the intracellular causes of overactivated autophagy, which has cytotoxic effects, remain elusive. Here we show that sustained proteotoxic stress induced by loss of the RING and Kelch repeat-containing protein C53A5.6/RIKE-1 induces sequestration of LET-363/MTOR complex and overactivation of autophagy, and consequently impairs epithelial integrity in C. elegans. In C53A5.6/RIKE-1-deficient animals, blocking autophagosome formation effectively prevents excessive endosomal degradation, mitigates mislocalization of intestinal membrane components and restores intestinal lumen morphology. However, autophagy inhibition does not affect LET-363/MTOR aggregation in animals with compromised C53A5.6/RIKE-1 function. Improving proteostasis capacity by reducing DAF-2 insulin/IGF1 signaling markedly relieves the aggregation of LET-363/MTOR and alleviates autophagy overactivation, which in turn reverses derailed endosomal trafficking and rescues epithelial morphogenesis defects in C53A5.6/RIKE-1-deficient animals. Hence, our studies reveal that C53A5.6/RIKE-1-mediated proteostasis is critical for maintaining the basal level of autophagy and epithelial integrity.Abbreviations: ACT-5: actin 5; ACTB: actin beta; ALs: autolysosomes; APs: autophagosomes; AJM-1: apical junction molecule; ATG: autophagy related; C. elegans: Caenorhabditis elegans; CPL-1: cathepsin L family; DAF: abnormal dauer formation; DLG-1: Drosophila discs large homolog; ERM-1: ezrin/radixin/moesin; EPG: ectopic P granule; GFP: freen fluorescent protein; HLH-30: helix loop helix; HSP: heat shock protein; LAAT-1: lysosome associated amino acid transporter; LET: lethal; LGG-1: LC3, GABARAP and GATE-16 family; LMP-1: LAMP (lysosome-associated membrane protein) homolog; MTOR: mechanistic target of rapamycin kinase; NUC-1: abnormal nuclease; PEPT-1/OPT-2: Peptide transporter family; PGP-1: P-glycoprotein related; RAB: RAB family; RIKE-1: RING and Kelch repeat-containing protein; SLCF-1: solute carrier family; SQST-1: sequestosome related; SPTL-1: serine palmitoyl transferase family.

Effect of ferrous-activated calcium peroxide oxidation on forward osmosis treatment of algae-laden water: Membrane fouling mitigation and mechanism.

Forward osmosis (FO) is a high-efficiency and low-energy consumption way for algae-laden water treatment, whereas membrane fouling is still an unavoidable problem in its practical application. In this work, a strategy of ferrous-activated calcium peroxide (Fe(II)/CaO2) was proposed to control FO membrane fouling in the purification of algae-laden water. With the treatment of Fe(II)/CaO2, the aggregation of algal contaminants was promoted, the cell viability and integrity were well preserved, and the fluorescent organics were efficiently removed. With respect to the fouling of FO membrane, the flux decline was generally alleviated, and the flux recovery was promoted to varying degrees under different process conditions. It could be revealed through the extended Derjaguin-Landau-Verwey-Overbeek theory that the adhesion of contaminants and membrane surfaces was reduced by Fe(II)/CaO2 treatment. The interface morphologies and functional groups of membrane verified that Fe(II)/CaO2 could mitigate the fouling by reducing the amount of algal contaminants adhering to the FO membrane. The co-coagulation of in-situ Fe(III) together with Ca(OH)2, as well as the oxidation of •OH were the main mechanisms for fouling mitigation. In sum, the Fe(II)/CaO2 process could effectively improve the efficiency of FO for algae-laden water treatment, and has broad application prospects.

Mutual activation between ferrate and calcium sulfite for surface water pre-treatment and ultrafiltration membrane fouling control.

In this work, ferrate (Fe(VI)) and calcium sulfite (CaSO3) were combined to treat surface water for improving ultrafiltration (UF) performance. During the pre-treatment process, the Fe(VI) and CaSO3 activated each other and a variety of active species (Fe(V), Fe(IV), OH, SO4-, 1O2, etc.) were generated. All of the five fluorescent components were effectively eliminated to different extents. With Fe(VI)/CaSO3 = 0.05/0.15 mM, the dissolved organic carbon and UV254 reduced by 44.33 % and 50.56 %, respectively. After UF, these values were further decreased with the removal rate of 50.27 % and 70.79 %. In the UF stage, the terminal J/J0 increased to 0.42 from 0.17, with the reversible and irreversible fouling decreased by 67.08 % and 79.45 % at most. The membrane pore blocking was significantly mitigated, as well as the foulants deposition on membrane surfaces was decreased to some extent. The complete blocking was altered to standard blocking and intermediate blocking, the volume when entering cake filtration was also delayed slightly. The extended Derjaguin-Landau-Verwey-Overbeek theory was employed to judge the interface fouling behavior, and the results indicated that the foulants became more hydrophilic, as well as the adhesion trend between foulants and membrane surface was weakened. Overall, these results provide a theoretical foundation for the practical application of the combined Fe(VI)/CaSO3-UF process in surface water purification.

Insights into olation reaction-driven coagulation and adsorption: A pathway for exploiting the surface properties of biochar.

In this study, characterization of biochar for the efficient removal of cadmium was investigated. Biochar has a specific distribution of functional groups on its surface and has a natural electronegativity. Using carbonate as an olation reagent, the biochar coagulates with the olation reaction products. The maximum removal capacity reached 430.4 mg/g at pH = 4 (Langmuir Fit). Carbonate hydrolyzed on the surface of biochar, Cd2+ in solution undergoes olation with OH- and forms specially structured nanochains that are positively charged on the surface. The biochar with electronegativity on the surface coagulates with the cadmium hydroxide nanochains, and the cadmium-containing colloid formed by electrostatic attraction settles rapidly and removed. The biochar's re-flocculation performance was consistent, and the loadings could be changed to effectively remove cadmium while keeping the pH neutral at equilibrium.

Calcium sulfite oxidation activated by ferrous iron integrated with membrane filtration for removal of typical algal contaminants.

Oxidation treatment of algae-laden water may cause cells rupture and emission of intracellular organics, thus restricting its further popularization. As a moderate oxidant, calcium sulfite could be slowly released in the liquid phase, thus exhibiting a potential to maintain the cells integrity. To this end, calcium sulfite oxidation activated by ferrous iron was proposed integrated with ultrafiltration (UF) for removal of Microcystis aeruginosa, Chlorella vulgaris and Scenedesmus quadricauda. The organic pollutants were significantly eliminated, and the repulsion between algal cells was obviously weakened. Through fluorescent components extraction and molecular weights distribution analyses, the degradation of fluorescent substances and the generation of micromolecular organics were verified. Moreover, the algal cells were dramatically agglomerated and formed larger flocs under the premise of maintaining high cell integrity. The terminal normalized flux was ascended from 0.048-0.072 to 0.711-0.956, and the fouling resistances were extraordinarily decreased. Due to the distinctive spiny structure and minimal electrostatic repulsion, Scenedesmus quadricauda was easier to form flocs, and its fouling was more readily mitigated. The fouling mechanism was remarkably altered through postponing the formation of cake filtration. The membrane interface characteristics including microstructures and functional groups firmly proved the fouling control efficiency. The reactive oxygen species (i.e., SO4•- and 1O2) generated through the principal reactions and Fe-Ca composite flocs played dominant roles in alleviating membrane fouling. Overall, the proposed pretreatment exhibits a brilliant application potential for enhancing UF in algal removal.

Enhanced hydroxyl radical generation for micropollutant degradation in the In2O3/Vis-LED process through the addition of periodate.

Periodate (PI) as an oxidant has been extensively studied for organic foulants removal in advanced oxidation processes. Here PI was introduced into In2O3/Vis-LED process to enhance the formation of ·OH for promoting the degradation of organic foulants. Results showed that the addition of PI would significantly promote the removal of sulfamethoxazole (SMX) in the In2O3/Vis-LED process (from 9.26% to 100%), and ·OH was proved to be the dominant species in the system. Besides, the process exhibited non-selectivity in the removal of different organic foulants. Comparatively, various oxidants (e.g., peroxymonosulfate, peroxydisulfate, and hydrogen peroxide) did not markedly promote the removal of SMX in the In2O3/Vis-LED process. Electrochemical analyses demonstrated that PI could effectively receive photoelectrons, thus inhibiting the recombination of photogenerated electron-hole (e-/h+) pairs. The holes then oxidized the adsorbed H2O to generate ·OH, and the PI converted to iodate at the same time. Additionally, the removal rate of SMX reduced from 100% to 17.2% as Vis-LED wavelengths increased from 440 to 560 nm, because of the low energy of photons produced at longer wavelengths. Notably, the species of PI do not affect its ability to accept electrons, resulting in the degradation efficiency of SMX irrespective of pH (4.0-10.0). The coexistence of inorganic cations and anions (such as Cl-, CO32-/HCO3-, SO42-, Ca2+, and Mg2+) also had an insignificant effect on SMX degradation. Furthermore, the process also showed excellent degradation potential in real water. The proposed strategy provides a new insight for visible light-catalyzed activation of PI and guidance to explore green catalytic processes for high-efficiency removal of various organic foulants.

Overlooked flocs in electrocoagulation-based ultrafiltration systems: A new understanding of the structural interfacial properties.

An integrated ferrate-induced electrocoagulation-ultrafiltration (FECUF) process is proposed to cope with the growing demand for water treatment. Although flocs formed during the electrocoagulation (EC) process are useful for contaminant reduction and mitigation of membrane fouling, few studies have been focused on their structures and properties. Herein, we investigated the formation and structural transformations of flocs and their responses to organic matter, as well as the relationships between their interfacial properties and membrane fouling mitigation. It was found that ferrate contributed to the fast formation of flocs during the ferrate-induced electrocoagulation (FEC) process, which accelerated the FECUF process. Physicochemical analyses indicated that the flocs formed in the FEC process were mainly composed of Fe(III)-(hydr)oxides with abundant hydroxyl groups and poor crystallinity, which allowed complexation with NOM. Therefore, the mobilities of the NOM and the soluble coagulant ions were reduced. The responses of flocs to NOM suggested that the period of 0-20 min resulted in the most efficient NOM removal. In addition, two patterns revealed the relationships between the interfacial properties of the small colloidal particles (SCPs) and the membrane filtration performance: i) the decline in the initial flux was closely related to the composition (gel-type substances or metal-(hydr)oxides) of the SCPs and ii) the steady-state flux was influenced by the energy barrier between the SCPs. However, when the SCPs had the same composition, the interfacial properties influenced both the initial flux and the steady-state flux. This study provides an alternative FECUF process for intensive upgrades of centralized water treatment systems.

Secondary pollution of microplastic hetero-aggregates after chlorination: Released contaminants rarely re-adsorbed by the second-formed hetero-aggregates.

In urban waters, microplastics (MPs) usually form hetero-aggregates through adsorption of organics and microbes. However, the effects of hetero-aggregates on water quality are rarely reported. In this study we found that the hetero-aggregates, which accumulated contaminants, were like a "time bomb". Chlorination was able to trigger the "time bomb" through destruction of hetero-aggregates, lysis of microbial cells and elevation of the concentration of low-molecular-mass organics. Thereupon previously adhered organics desorbed from MPs, intracellular metabolites were released from lysed cells, and re-formation of hetero-aggregates was limited. This process rapidly increased the concentration of organics but prevented the re-adsorption of organics, which leads to secondary pollution. Thus, to alleviate the risks of secondary pollution caused by hetero-aggregates, the choice of oxidant species and dose should be optimized based on the characteristics of existent hetero-aggregates when purifying urban waters containing MPs.

Improving ultrafiltration of algae-laden water with chitosan quaternary ammonium salt enhanced by sodium percarbonate.

Ultrafiltration (UF) is extensively used for algae removal because of its ability to retain algal cells with high efficiency, but it still faces the problem of membrane fouling and low retention capacity of dissolved organics. Hence, a strategy of coagulation with chitosan quaternary ammonium salt (HTCC) enhanced by sodium percarbonate (SPC) pre-oxidation was proposed to improve the UF performance. The fouling resistances were calculated by a resistance-in-series model based on Darcy's formula, and the membrane fouling mechanism was evaluated using a pore plugging-cake filtration model. The effect of SPC-HTCC treatment on the properties of algal foulants was explored, and the result showed that the water quality was improved with the maximum removal rates of 78.8 %, 52.4 % and 79.5 % for algal cells, dissolved organic carbon and turbidity, respectively. The SPC could achieve a mild oxidation effect that degraded the electronegative organics attached to algal cells without destroying the cell integrity, making the algal pollutants easier to agglomerate through subsequent HTCC coagulation by forming larger flocs. In terms of membrane filtration, the terminal normalized flux was increased from 0.25 to 0.71, with the reversible and irreversible resistances reduced by 90.8 % and 40.2 %, individually. The synergistic treatment reduced the accumulation of algal cells and algae-derived organics on the membrane surface as inferred from the interface fouling characteristics. The interfacial free energy analysis showed that the synergistic treatment reduced the adhesion of contaminants to the membrane surface, as well as the attraction among pollutants. Overall, the proposed process has high application prospects for algae-laden water purification.