Ions play different roles in virus removal caused by different NOMs in UF process: Removal efficiency and mechanism analysis.

In this study, we investigated the effect of different compositions of aquatic natural organic matter (NOM) and ions on virus removal by ultrafiltration (UF). MS2 bacteriophage was used as a surrogate. Humic acid (HA) improved the MS2 removal rate from 1.95 ± 0.09 LRV to 2.40 ± 0.03 LRV at the HA dosage of 9 mg/L through the combined mechanisms of size exclusion, electrostatic repulsion and hydrophobicity. MS2 removal rate further increased to 3.10 ± 0.05 LRV by 10 mmol/L Na+ dosage and 3.19 ± 0.12 LRV by Ca2+ 1 mmol/L in the HA-containing UF system. Size exclusion turned into the dominant virus removal mechanism according to the results of the fouling model fitting and the weakening of electrostatic repulsion and hydrophobicity. The complexation of Ca2+ also played a role in MS2 removal based on the analysis of interaction force. MS2 removal rate by bovine serum albumin (BSA) was poor, which was 2.07 ± 0.06 LRV at the BSA dosage of 9 mg/L. Hydrophobicity was greatly reduced and the dominant virus removal mechanisms were size exclusion and electrostatic repulsion. 10 mmol/L Na+ in the presence of BSA deteriorated MS2 removal rate to 2.02 ± 0.07 LRV by the weakening of electrostatic repulsion, hydrophobicity and size exclusion. Electrostatic repulsion severely decreased by 1 mmol/L Ca2+ and the enhanced adsorption barrier represented competitive adsorption of Ca2+ by BSA and MS2 contributed for MS2 removal further decline (1.99 ± 0.05 LRV). Complex components in water will have different effects on virus removal due to their properties and interactions. This study can provide references for selecting more efficient water treatment methods according to the different compositions of raw water in actual water treatment applications during the UF process. Moreover, the retention of virus by UF can be predicted based on our study results.

Oxidation and coagulation/adsorption dual effects of ferrate (VI) pretreatment on organics removal and membrane fouling alleviation in UF process during secondary effluent treatment.

Ultrafiltration (UF) has been widely used in water and advanced sewage treatment. Unfortunately, membrane fouling is still the main obstacle to further improvement in the system. Fe (III) salt, a type of traditional coagulant, is often applied to mitigate UF membrane fouling. However, low molecule organic weight cannot be effectively removed, thus the water quality after single coagulation treatment does not effectively meet the standard of subsequent water reuse during secondary effluent treatment. Recently, it has been found that potassium ferrate (Fe (VI)) has multiple functions of oxidation, sterilization and coagulation, with other studies proving its good performance in organics removal and membrane fouling mitigation. However, the respective contributions of oxidation and coagulation/adsorption have not yet been fully understood. The oxidation and coagulation/adsorption effects of Fe (VI) during membrane fouling mitigation were investigated here. The oxidation effect of Fe (VI) was the main reason for organics with the MW of 8-20 kDa removal, and its coagulation/adsorption mainly accounted for the smaller amounts of molecular organics removed. The oxidation of Fe (VI) was the main method for overcoming membrane fouling in the initial filtration; it largely alleviated the standard blockage. The formation of a cake layer transformed the main membrane fouling alleviation mechanism from oxidation to coagulation/adsorption and further removed smaller amounts of molecule organics with the increase of filtration cycles and Fe (VI) dosages. The main fouling mechanism altered from standard blocking and cake filtration to only cake filtration after Fe (VI) treatment. Overall, the mechanism of the oxidation and coagulation/adsorption of Fe (VI) were differentiated, and would provide a reference for future Fe (VI) pretreatment in UF membrane fouling control during water and wastewater treatments.

Effects of the metabolic uncoupler TCS on residual sludge treatment: Analyses of the microbial community and sludge dewaterability potential.

Residual sludge is a by-product with a large volume and complex composition from wastewater treatment plants. It is significant to reduce sludge volume to decrease the negative effects of sludge on environmental pollution and needless land use. We investigated the effects of uncoupler 3, 3', 4', 5-tetrachlorosalicylanilide (TCS) on the properties of sludge. After adding 0.12 g TCS/g VSS with 24 h mixing, the sludge concentration and total ATP content decreased by 51.1% and 60.8%, respectively. At the same time, the microbial community also changed significantly, leading to the decrease of richness and diversity. Additionally, the secretion of extracellular polymeric substances (EPS) reduced approximately 43% under the addition of 0.12 g/g VSS compared with the control. The decrement of EPS may be explained by the decreased relative abundance of functional bacteria (i.e. Chloroflexi reduced about 60% and Nitrospirota reduced about 31%). Notably, the addition of TCS before coagulation conditioning (FeCl3) promoted the adhesion of sludge flocs according to the theory of Extended Derjaguin Landau Verwey Overbee (XDLVO), leading to the increased hydrophobicity of the residual sludge. Therefore, energy uncoupling has the potential of improving sludge dewaterability.

Coupling sodium percarbonate (SPC) oxidation and coagulation for membrane fouling mitigation in algae-laden water treatment.

To alleviate algal fouling in membrane water treatment processes, conventional technologies such as coagulation with poly aluminum chloride (PACl) has been widely adopted by many drinking water treatment plants. However, coagulation alone exhibited relatively weak removal effect for algal pollutants, and the coagulant residues due to the excess dosage also raised concerns. Thus, a novel process of coupling sodium percarbonate (SPC) oxidation and PACl coagulation was proposed, integrated with membrane filtration for algae-laden water treatment. The dosages of PACl and SPC were optimized, and the SPC dosing strategies were systematically compared. The changes in the characteristics of algal pollutants were investigated, and the results revealed that the resistance of algal foulants to aggregation was decreased, and the particle size of algal foulants became larger. With the synergism of coagulation and oxidation, the degradation of fluorescent organics was strengthened, and macromolecular biopolymers were decomposed into low molecular weight organics. The fouling control efficiency was further explored, and the results indicated that both irreversible and reversible fouling were effectively controlled, among which PACl/SPC (simultaneous treatment) performed best with the irreversible fouling reduced by 90.5%, while the efficiency of SPC-PACl (SPC followed by PACl) was relatively lower (57.3%). The fouling mechanism was altered by slowing the formation of cake filtration, and the reduction of algal cells played a more important role for the fouling alleviation. The interface properties of contaminated membranes (i.e., functional groups, images, and micromorphology) were characterized, and the efficiency of the proposed strategy was further verified. The proposed strategy exhibits great application values for improving membrane performance during algae-laden water treatment.

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.

Ferrous-activated sodium percarbonate pre-oxidation for membrane fouling control during ultrafiltration of algae-laden water.

Membrane technology has been shown to be promising for the treatment of algae-laden water, but membrane fouling is still an obstacle influencing the purification efficiency and effluent quality. To mitigate ultrafiltration membrane fouling during Microcystis aeruginosa-laden water treatment, a strategy of sodium percarbonate pre-oxidation activated with ferrous ion (Fe2+/SPC) was put forward in this study. Due to the synergistic effect of Fe2+ and SPC, this process was significantly more efficient with the terminal specific flux increased from 0.097 to 0.397, and the reversible fouling resistance reduced by approximately 80%. It was also found that subsequent sedimentation followed by Fe2+/SPC could further improve the fouling control efficiency. The model fitting results indicated that Fe2+/SPC pre-oxidation delayed the transition from standard blocking to cake filtration. Extracellular organic matter and algal cells were extracted from algal foulants to explore the contribution of each component, and the fouling control efficiencies were systematically studied. The characteristics of the algal foulants were determined with fluorescence excitation-emission matrix spectrum, and the results suggested that macromolecular proteinaceous substances were more efficiently removed by Fe2+/SPC, in comparison with humic-like matters. The alleviation of membrane fouling was also verified by the characterization methods of scanning electron microscopy and attenuated total reflection-Fourier infrared spectroscopy. Overall, the proposed strategy of Fe2+/SPC has an application prospect for membrane fouling control in algal-laden water treatment.

Improving ultrafiltration membrane performance with pre-deposited carbon nanotubes/nanofibers layers for drinking water treatment.

To efficiently improve the performance of ultrafiltration (UF) membrane for drinking water treatment, carbon nanotubes (CNTs) and carbon nanofibers (CNFs) were utilized as pre-deposited coating layers on membrane surface. A comparative study between these two carbon nanomaterials for enhancing pollutants removal and mitigating membrane fouling induced by natural organic matter (NOM) was carried out. The surface morphologies were characterized by scanning electron microscopy, and the results indicated that the CNTs coating layer was more dense and homogeneous with a smaller pore size than that of CNFs. The removal and antifouling performance of CNTs/CNFs coated membranes were investigated with typical NOM, i.e., humic acid, bovine serum albumin, sodium alginate, as well as natural surface water. The results showed that the presence of coating layers was very effective to improve the rejection rate of NOM, among which CNTs exhibited significant better performance than CNFs. The fouling control performance was influenced by the NOM fraction and coating mass (6-50 g/m2). Generally, CNTs coating layer was more efficient in alleviating both reversible and irreversible membrane fouling, while CNFs exhibited limited effect on irreversible fouling control. Both pre-adsorption and size exclusion contributed to the rejection of membrane foulants, thus reducing the organics directly contacted with the underlying membrane. In natural surface water treatment, the pre-deposited coating layers significantly delayed the transition of fouling mechanisms from pore blocking to cake filtration. The experimental results were expected to illustrate the feasibility of pre-deposited CNTs/CNFs layers for enhancing membrane performance during drinking water treatment.

Effect of peroxymonosulfate oxidation activated by powdered activated carbon for mitigating ultrafiltration membrane fouling caused by different natural organic matter fractions.

Powdered activated carbon (PAC) adsorption has been widely applied prior to ultrafiltration membrane for potable water production. However, the impact of PAC adsorption on membrane fouling was still controversial. To solve this problem, combined PAC and peroxymonosulfate (PMS) pretreatment was proposed in this study. The application of PAC/PMS for mitigating membrane fouling by natural organic matter (NOM) has been evaluated, and compared with PMS oxidation or PAC adsorption alone. The influence of NOM fractions on the control efficiency was also investigated using humic acid (HA), bovine serum albumin (BSA), sodium alginate (SA), and their mixture (HA-BSA-SA). The performance was examined through normalized flux decline, fouling resistances analysis, scanning electron microscopy, and model fits. The results indicated that PAC and PMS exhibited a remarkable synergistic effect in the reduction of NOM, with the DOC reduction rates of 53.6%, 24.3%, 27.1% and 31.4% for HA, BSA, SA and HA-BSA-SA, respectively. PAC adsorption exhibited limited influence on mitigating membrane fouling, and the co-existence of PAC and HA even exacerbated fouling due to the synergistic fouling effect between them. By contrast, PAC/PMS pretreatment efficiently reduced both reversible and irreversible fouling resistances. The control efficiency was closely associated with the NOM fractions in the feed water, and followed the order of SA > HA-BSA-SA > BSA > HA. The fouling mitigation by PAC/PMS was attributed to both PAC adsorption and oxidation with SO4- and OH. The experimental results are expected to provide a feasible strategy of PAC/PMS for fouling mitigation, and simultaneously solve the problem faced by PAC adsorption.

Fabrication of Tween-20 coated PVDF membranes for wastewater treatment: optimization of preparation parameters, removal and membrane fouling control performance.

In the present study, polyoxyethylene (20) sorbitan monolaurate (Tween-20) was employed as a surface coating agent for hydrophilic modification of poly(vinylidene fluoride) microfiltration membranes. The optimized parameters for membrane preparation (i.e., coating temperature, coating concentration, coating time and drying time) were systematically investigated. Contact angle and transmembrane pressure were employed to evaluate the efficiency of the modified membranes, and the optimized parameters were proposed. The removal of chemical oxygen demand (COD) and suspended solids (SS), as well as fouling control performance, was further evaluated. The results showed that the optimized parameters were 40 °C, 4.5 mmol L-1, 45 min and 45 min for coating temperature, coating concentration, coating time and drying time, respectively. Under these conditions, a hydration layer on the surface was formed, resulting in a more hydrophilic membrane surface. During domestic wastewater treatment in membrane bioreactor (MBR), the Tween-20 modified membrane exhibited better performance with rejection efficiencies of 94.56% and 97.53% for COD and SS, respectively. Tween-20 coating could mitigate the increase of transmembrane pressure and reduce the concentration of proteins accumulated on the membrane surface, which was effective for membrane fouling control. Simultaneously, the operation time of MBR was extended from 25 to 46 days. Furthermore, the stability of Tween-20 coated PVDF membrane was also verified. The results indicated that surface coating with Tween-20 is efficient and easy to be carried out, showing a great potential for application in MBR during wastewater treatment.