Hybrid Nanofiltration Research Articles

PH-Responsive graphene oxide/poly (methacrylic acid) hybrid nanofiltration membrane performance for water treatment

Graphene oxide (GO) membranes have been proposed for water treatment. GO can be used to prepare membranes that remove organic molecules, such as model dyes from contaminated wastewater. In practical applications, wastewater is often acidic or alkaline. The physico-chemical properties of GO are only weakly affected by pH, and this can lead to poor membrane performance for the removal of positively charged model compounds. In this work, we used pH-responsive poly (methacrylic acid) (PMAA) to prepare GO-PMAA materials through chemical crosslinking. GO-PMAA materials with different compositions were used to prepare membranes via physical intercalation. The membranes were tested for removal of five different dyes of different sizes and valency (including those that are positively charged, negatively charged, and neutral at neutral pH). We identify a membrane composition that works well for the removal of negatively charged methyl orange and Evans blue under acidic conditions (with 73.1% and 99.7% rejection, respectively) with improved water permeance compared to membranes prepared with GO alone. In addition, we evaluated the long-term stability of the nanofiltration membrane. After continuous operation for 20 h, the rejection rate of MnB by 5p-nGOM was about 85.37%, and the water permeance relatively stable, while the rejection rate of MnB by nGOM was about 26.59%, and the water permeance changed greatly. These findings indicate that GO membranes modified with pH-responsive polymers can achieve superior performance with respect to separation, water permeance, long-term operation, and pressure resistance, compared to GO membranes.

Hybrid ceramic nanofiltration membranes prepared by impregnation and solid-state grafting of organo-phosphonic acids

Grafting of oligomers into the mesopores of ceramic membranes (e.g. γ-alumina) represents an attractive strategy for deploying durable, resistant, and efficient hybrid membranes for the industrial treatment of wastewater containing organic solvents and divers solutes. In general, to control the membrane/solute/solvent interactions, homogeneous surface modification and high grafting yields are required. However, reaching this goal is rather challenging with the current grafting approaches where the active diffusion of the oligomers to the membrane pore surface may be hampered. To mitigate such diffusion limitation, we present here a novel synthesis method consisting of an infiltration of concentrated PEG organophosphonic acid oligomer solution in ceramic ultrafiltration membranes before initiating the solid-state grafting reaction to form a PEG-brush-grafted nanofiltration ceramic membrane. The infiltration step was found to be decisive for the formation of weak bonds between the oligomer linking functions and the ceramic membrane ensuring the final synthesis of robust PEG-based membranes by a grafting reaction. The influence of the solvent polarity (water vs. cyclohexane) on the conformation of the grafted PEG brush inside the γ-alumina mesopores was observed as a key parameter in the analysis of the pore size and permeability results. In addition to this, it was studied here for the first time by molecular dynamic simulations. The as-prepared PEG-brush/ceramic membranes were found very efficient in the separation of small organic dyes such as Rhodamine B (479 g mol−1) up to 85%. As a result, the present synthesis method represents a sustainable and simple alternative way for the preparation of hybrid nanofiltration membranes with controlled surface properties and attractive separation performance. Moreover, the vacuum impregnation and solid-state grafting approach requires a minimal amount of functional oligomers and solvent (0.5 mmol for 2–3 mL of solvent) and can be applied to other porous materials used in separation technologies.

Improvement of membrane-forming ability and separation performance of hydroxylated BN membrane by GO via π-π interaction

Two-dimensional hydroxylated boron nitride (OH-BN) nanosheets were prepared using a new approach of ball milling and monoethanolamine (MEA) assisted sonication. OH-BN/graphene oxide (GO) hybrid nanofiltration membranes were developed for the improvement of the membrane-forming ability of OH-BN nanosheets by π-π interaction between GO and OH-BN nanosheets. The membrane-forming ability of OH-BN nanosheets were improved significantly after the introduction of GO nanosheets, and typical layered structure and enhanced separation performances were achieved for OH-BN/GO hybrid membrane with 40 wt% of GO (OH-BN40GO). OH-BN40GO membrane with a thickness of 500 nm possessed a favorable water permeance of 162.3 L/m2·h·bar and a pleasant rejection rate of 97.7 % for Methyl Blue (MB). Moreover, OH-BN40GO hybrid membrane exhibited an excellent anti-swelling ability in aqueous solution, and kept almost unchanged after soaking in water for 3 months. The flux recovery ratio of OH-BN40GO membrane reached to 85.8 % after BSA contamination and NaClO solution rinse, revealing a suitable anti-fouling property of OH-BN40GO membrane.

The effect of green sorption media pretreatment on nanofiltration during water treatment for long- and short-chain per- and polyfluoroalkyl substances (PFAS) removal

Short-chain per- and polyfluoroalkyl substances (PFAS) have higher mobility than long-chain PFAS. This study investigated the application potential of two specialty adsorbents as pretreatment media for nanofiltration (NF) to enhance the removal of both short- and long-chain PFAS from water matrices. In this hybrid process, two specialty adsorbents, known as green sorption media (GSM), were prepared using recycled and natural materials for cost-effective, scalable, and sustainable water pretreatment. These two GSM are named the clay-perlite and sand (CPS) sorption media and zero-valent iron and perlite-based green environmental media (ZIPGEM). Such pretreatment led to significant removal of long-chain PFAS (up to 100 %) in addition to natural organic matter (NOM) and Ca2+ from the source water (canal water); however, for the short-chain PFAS (Perfluorobutanoic acid and Perfluorobutanesulfonic acid), the removal rate only rose to approximately 25 %. Such a contrasting removal rate is attributable to the source water concentration of PFAS and the hydrophobic and electrostatic interactions of the compounds within the treatment media. Yet the CPS–NF and ZIPGEM–NF hybrid processes exhibited significantly higher removal of perfluorooctanesulfonic acid (long-chain PFAS; approximately 16 % higher) when compared to the control (i.e., NF only). Because the pretreatment media removed higher percentages of long-chain PFAS, NOM, and Ca2+ from the water, the performance of the subsequent NF declined due to less calcium bridging involving NOM and PFAS and less micelle/complex formation by the compounds in bulk water. However, the integration of GSM with NF significantly improved (up to approximately 25 % higher) PFAS removal efficiency via the hybrid functionality. This signifies the membrane plays a complementary role in enhancing the overall removal efficiency of PFAS. In addition to contributing to PFAS removal from the source water, GSM pretreatment can help reduce NF membrane fouling/scaling by removing NOM and cations.

Fabrication of polyamide/zwitterion functionalized mesoporous silica nanofiltration membrane with highly enhanced antifouling performance

BackgroundThe nanofiltration membrane plays an important role in wastewater treatment and desalination. Fabricating the hydrophilic separation layer is a good way to construct nanofiltration membranes with both high water flux and antifouling performance. MethodsThe chemical and physical structure of the membrane surface are optimized simultaneously to enhance its performance. Three kinds of zwitterions bearing different positively and negatively charged units are grated onto mesoporous silica (MS), then the functionalized MS nanoparticles are introduced into polyamide separation layer on porous polyethersulfone substrate to construct hybrid nanofiltration membranes. The influence of zwitterion functionalized MS on the structure and comprehensive performance of hybrid membranes is thoroughly investigated by experimental and computational means. Significant findingsThe existence of zwitterion functionalized MS overcomes the tradeoff effect between water flux and salt rejection. The hybrid membrane shows a high water flux of 334.0 L m − 2h − 1 MPa−1 and a superior flux recovery ratio of 94.1% against bovine serum albumin. The corrected zero-point binding energies of three kinds of zwitterions with water molecules are computed for the first time, the carboxybetaine methacrylate shows the highest energy of 36.99 kJ mol−1, explaining why the as-prepared hybrid membranes possess outstanding antifouling performance.

Reactive membranes for groundwater remediation of chlorinated aliphatic hydrocarbons: Competitive dechlorination and cost aspects

A nanocomposite membrane incorporating reactive Pd-Fe nanoparticles (NPs) was developed to remediate chlorinated aliphatic hydrocarbons (CAHs) from groundwater. Other than recapturing the produced Fen+ for in-situ regeneration, the functionalized polyanions prevented NPs agglomeration and resulting in a spherical Fe0 core (55 nm, O/Fe = 0.05) and an oxidized shell (4 nm, O/Fe = 1.38). The reactive membranes degraded 92% of target CAHs with a residence time of 1.7 s. After long-term treatment and regeneration, reusability was confirmed through recovered reactivity, recurrence of Fe0 in X-ray photoelectron spectroscopy, and >96% remaining of Fe and Pd. The total cost (adjusted present value for 20 years) was estimated to be 13.9% lower than the granular activated carbon system, following an EPA work breakdown structure-based cost model. However, non-target CAHs from groundwater can compete for active sites, leading to decreased surface-area normalized dechlorination rate (ksa) by 28.2–79.9%. A hybrid nanofiltration (NF)/reactive membrane was proposed to selectively intercept larger competitors, leading to 54% increased dechlorination efficiency and 1.3 to 1.9-fold enlarged ksa. Overall, the practical viability of the developed reactive membranes was demonstrated by the stability, reusability, and cost advantages, while the optional NF strategy could alleviate competitive degradation towards complex water chemistry.

Intelligent process optimisation based on cutting-edge emotional learning for performance evaluation of NF/RO of seawater desalination plant

As decision-makers, researchers encounter highly dynamic, complex problems requiring suitable nature-based and industrial quantitative tools for performance analyses, syntheses, and modelling. This study employed a new-generation emotional artificial neural network (EANN) and other stand-alone approaches to model the performance of hybrid nanofiltration (NF) and reverse osmosis (RO) desalination plants in terms of permeate recovery (PR) (%) and permeate flow rate (PFR) (m3/h). With the obtained experimental data, augmented Dickey-Fuller (ADF) and Philip Perron tests, evaluated using the Akaike information criterion and Schwarz information criterion, were employed to assess stability and stationarity. Nonlinear input-variable feature selection based on mutual information and neuro-sensitivity analysis (NSA) was conducted on several input variables before modelling. The EANN was compared with stand-alone predictive models: backpropagation neural network and classical stepwise regression. Predictive simulations were evaluated using the Nash–Sutcliffe model efficiency coefficient (NSE), correlation coefficient (CC), mean absolute error (MAE), determination coefficient (DC), root mean square error (RMSE), and two-dimensional Taylor graphical visualisation. For PR, in the calibration phase, the NSE and MAE (%) were 27–99 % and 0.0064–0.1410, respectively. For PFR, NSE and MAE (m3/h) were 50–99 % and 0.0064–0.1410, respectively. The bibliography review indicated the popularity of artificial intelligence (AI) applications in desalination. Results revealed that this new-generation EANN demonstrated superior accuracy over all models; accordingly, it can serve as a reliable tool for evaluating the performance of NF/RO hybrid seawater desalination plants.

Hybrid nanofiltration membranes prepared by a simultaneous synthesis method for precise molecular separation

Incorporation of nanofillers is an option to break through the trade-off of nanofiltration membranes. In the present work, a simultaneous synthesis method, ZIF and selective layer formed in one step, was proposed to prepare hybrid nanofiltration membrane. Co2+ ions pre-assembled on hydrolyzed polyacrylonitrile (PANH) support provided nucleation sites for ZIF-67 formation. The growth of ZIF-67 and the formation of polyethyleneimine (PEI) selective layer on the support completed in one step through co-depositing of a solution of PEI and Hmim (2-methylimidazole). The feasibility of the simultaneous synthesis method was verified by using different supports, PEIs, and the precursor concentrations. All results show that ZIF-67 incorporation improved the water permenace, without significant compromising of membrane rejection. At an optimized condition, the obtained hybrid composite membrane showed high permeance of 35 L/(m2*h*bar) and rejection of 93% toward PEG 200. The permeance increased by about 150%–200% compared with the membrane without ZIF-67. Meanwile, the rejections of salts of the hybrid membrane were very low, exhibiting outstanding organic selectivity.

Hybrid NF and UF membranes tailored using quaternized polydopamine for enhanced removal of salts and organic pollutants from water

In this work, a quaternized polydopamine (QSiPD) nanohybrid was synthesized via condensation reaction between the silicon hydroxyl moieties of the hydrolyzed QSiP and hydroxyl moieties of polydopamine (PDA) and applied for the first time as a single additive to Poly(ether sulfone) (PES) ultrafiltration (UF) and loose nanofiltration (NF) membranes made via non-solvent induced phase separation (NIPS). QSiPD was added at a maximum loading of 8 and 20 wt% in UF and NF membranes, respectively. The nanohybrid material and membranes were thoroughly characterized. The hydrophilicity, surface charge, and pore structures of the hybrid membranes were progressively tuned with the increase of the QSiPD loading. The UF membrane water permeability of the membrane with 2 wt% QSiPD was as high as ~559 L m−2 h−1 bar−1. The hybrid UF membranes also exhibited superior antifouling activity with a BSA rejection rate of ~99 % uncompromised by the high membrane flux. The hybrid NF membranes showed significant rejection (45–67 %) of several monovalent (NaCl) and divalent (CaCl2, MgSO4, Na2SO4) salt solutions and an outstanding rejection of Congo red dye (>99.9 %). Furthermore, both hybrid UF and NF membranes showed a strong antibacterial activity against E. coli.

Molecularly microporous polyarylate-polyamide nanofiltration membrane patched by tris(2-aminoethyl)amine for ionic sieving

Macrocyclic molecules with intramolecular cavities have shown great potential in membrane science. However, the nanofiltration (NF) membranes fabricated by macrocyclic monomers often suffer from inferior ionic rejection due to the commonly formed intermolecular defects among these large molecules. Herein, a patching strategy was employed to fabricate polyarylate-polyamide hybrid NF membrane through interfacial polymerization (IP) by introducing tris(2-aminoethyl)amine (TAEA) with low concentration into Noria solution as the aqueous phase. The polyamide patch could repair the defects of polyarylate film formed by Noria with trimesoyl chloride and endow it with irregularly reticulate morphology. Specially, the Na2SO4 rejection of hybrid NF membrane fabricated with a TAEA doping concentration of 0.03 wt% was improved from 28.1 % to 96.8 %, while it maintained high permeance up to 15.3 L·m−2·h−1·bar−1. In order to compare the intrinsic permeability of fabricated polyarylate-polyamide membrane with other state-of-the-art NF membranes reported recently, the separation layer thickness was normalized. Benefitting from the inner cavity of Noria, its permeability was calculated to be 2.85 L·m−2·h−1·bar−1·μm, which was among the most permeable NF membranes. Additionally, the hybrid NF membrane exhibited excellent anti-compression ability and long-term stability. This patching method as a simple and effective strategy would further promote the application of various macrocyclic molecules in membrane science.

A hybrid nanofiltration and reverse osmosis process for urine treatment: Effect on urea recovery and purity

Human urine can be treated and concentrated using reverse osmosis (RO), but this process also concentrates pharmaceuticals and undesirable salts along with valuable nutrients such as urea. The final fertilizer product, therefore, has limited use on salt-sensitive crops or edible crops as the effects of pharmaceuticals remain a concern.Tight and loose nanofiltration (NF) pre-treatment was investigated as a method to recover urea in the permeate (which could then be further concentrated using RO), whilst pharmaceuticals and undesirable salts would be removed in the brine. Both NF options removed pharmaceuticals (NF90 – 99%, NF270 – 70%). Using a loose NF membrane, 78% of the urea was recovered in the permeate (80% water removal), however, the salt removal was poor (44%), and the urea purity only increased from 37 to 56%. Tight NF membranes provided better rejection of salts and organics (96% and 90% removed respectively). The urea purity in the permeate (75% water removal) from the tight NF process was 89%, however, the urea recovered was lower (48%). The tight NF permeate was then further concentrated with RO. At an overall water removal of 80%, 32.7% of the urea could be recovered with a purity of 85%. A decision tree was also developed to determine the optimum treatment process based on the desired final product. This decision tree could be used to determine the economic feasibility of each treatment process based on the final product choice and product value.

New Hybrid Nanofiltration Membranes with Enhanced Flux and Separation Performances Based on Polyphenylene Ether-Ether-Sulfone/Polyacrylonitrile/SBA-15.

This study presents the preparation of hybrid nanofiltration membranes based on poly(1,4-phenylene ether ether sulfone), polyacrylonitrile, poly(vinyl pyrrolidone), and SBA-15 mesoporous silica. Laser treatment of polymeric solutions to enhance the hydrophilicity and performance of membranes was investigated. The membranes’ structure was characterized using scanning electron (SEM) and atomic force (AFM) microscopy and contact angle measurements. The addition of PAN in the casting solution produced significant changes in the membrane structure, from finger-like porous structures to sponge-like porous structures. Increased PAN concentration in the membrane composition enhanced the hydrophilicity of the membrane surface, which also accounted for the improvement in the antifouling capabilities. The permeation of apple pomace extract and the content of polyphenols and flavonoids were used to evaluate the efficacy of the hybrid membranes created. The results showed that the hybrid nanofiltration membranes based on PPEES/PAN/PVP/SBA-15: 15/5/1/1 and 17/3/1/1 exposed to laser for 5 min present a higher rejection coefficient to total polyphenols (78.6 ± 0.7% and 97.8 ± 0.9%, respectively) and flavonoids (28.7 ± 0.2% and 50.3 ± 0.4%, respectively) and are substantially better than a commercial membrane with MWCO 1000 Da or PPEES-PVP-based membrane.

Hybrid nanofiltration thin film hollow fiber membranes with adsorptive supports containing bentonite and LDH nanoclays for boron removal

This study focused on removal of boron from water via hybrid nanofiltration (NF) thin film composite (TFC) hollow fiber (HF) membranes. To do so, nanocomposite polyvinyl chloride (PVC) HF membranes containing bentonite and layered double hydroxide (LDH) nanoparticles as natural and synthetic adsorbents were fabricated as the adsorptive support layers with high efficiency in boron removal. The phase inversion behavior of dope solutions and mechanical strength of the adsorptive nanocomposite PVC HF membranes were investigated and the results showed that LDH interacts better with PVC polymeric chains than bentonite. It was found that LDH with smaller pores and better adsorption capability in comparison with bentonite results in more hydrophilic membranes with better performance. On the other hand, bentonite tends to become agglomerated at above 1.5 wt%. Moreover, the fabricated membranes containing LDH have lower MWCO and more uniform pore size distribution which make them better options as support for the TFC layer formation to fabricate NF TFC membranes. The selective TFC layer was then fabricated via interfacial polymerization of m-phenylenediamine (MPD) and 1,3,5- benzenetricarbonyl trichloride (TMC) on the outer layer of the nanocomposite PVC HF membranes. Boron removal, and recovery and reusability of the fabricated NF TFC membranes were investigated by Na₂CO₃ solution. It was found that the NF TFC membranes containing LDH with boron removal of more than 83.6% and water flux of 16.1 L/m2.h at 4 bar operational pressure exhibit better performance than the NF TFC membranes containing bentonite.

Life Cycle Assessment of Hybrid Nanofiltration Desalination Plants in the Persian Gulf.

Although emerging desalination technologies such as hybrid technologies are required to tackle water scarcity, the impacts of their application on the environment, resources, and human health, as prominent pillars of sustainability, should be evaluated in parallel. In the present study, the environmental footprint of five desalination plants, including multi-stage flash (MSF), hybrid reverse osmosis (RO)–MSF, hybrid nanofiltration (NF)–MSF, RO, and hybrid NF–RO, in the Persian Gulf region, have been analyzed using life cycle assessment (LCA) as an effective tool for policy making and opting sustainable technologies. The comparison was based on the impacts on climate change, ozone depletion, fossil depletion, human toxicity, and marine eutrophication. The LCA results revealed the superiority of the hybrid NF–RO plant in having the lowest environmental impact, although the RO process produces more desalinated water at the same feed and input flow rates. The hybrid NF–RO system achieves 1.74 kg CO2 equivalent, 1.24 × 10−7 kg CFC-11 equivalent, 1.28 × 10−4 kg nitrogenous compounds, 0.16 kg 1,4-DB equivalent, and 0.56 kg oil equivalent in the mentioned impact indicators, which are 7.9 to 22.2% lower than the single-pass RO case. Furthermore, the sensitivity analysis showed the reliability of the results, which helps to provide an insight into the life cycle impacts of the desalination plants.

A field study of desalination of high-salinity surface brackish water via an RO-NF hybrid system

In this work, a pilot-scale membrane desalination demonstration system for producing drinking water from surface brackish water with a total dissolved solids (TDS) of ≤ 10 g/L was designed and constructed. The production capacity and water recovery were at least 1 m3/h and 50%, respectively. Brackish water was pretreated with microflocculation – precision filtration – ultrafiltration, and the quality of the produced water met the feed water requirements of nanofiltration (NF)/reverse osmosis (RO). The performances of various design configurations, including single NF, single RO, and NF-RO hybrid systems, were evaluated and compared in terms of water recovery and product water TDS. The hybrid RO-NF systems were found to be more effective than either NF or RO alone, and the 4RO-4NF design configuration was most favorable. At a TDS of 10 g/L in the feed, the processing capacity and product water TDS of the 4RO-4NF hybrid system was able to meet the design specs at a feed flow rate of 2 m3/h and an operating pressure of 1.5 MPa. Its long-term stability was examined as well, and it was demonstrated that the desalination performance of the system was mainly affected by seasonal temperature changes and rainfall. The total process cost was estimated to be $1.56/m3, which is considered economically suitable for remote areas where safe drinking water cannot be provided centrally.

Desalinated brackish water with improved mineral composition using monovalent-selective nanofiltration followed by reverse osmosis

Typical product water from desalination plants is depleted of salts and important minerals that are essential for its final consumption as well as its conveyance in the distribution system. In this study, we propose a hybrid nanofiltration (NF)-reverse osmosis (RO) filtration scheme that can produce desalinated brackish water with improved mineral composition. Here, the monovalent-divalent ion selectivity of NF membranes is used in a preliminary step to remove and “store” divalent minerals in the NF retentate stream, which are later dosed back to the mineral-free RO permeate to replenish the product water. We combine experimental data from pilot-scale NF with RO simulation to demonstrate the feasibility and economic viability of the proposed treatment scheme. In particular, we show the potential to operate the hybrid filtration scheme at high recovery ratios (>85%) and minimum saturation indices of potential scaling solids. A cost assessment further supports the applicability of the proposed treatment scheme, estimating the total capital and operating cost at $0.24/m3 product, which is on par with existing brackish-water desalination costs.

Pilot-scale field demonstration of a hybrid nanofiltration and UV-sulfite treatment train for groundwater contaminated by per- and polyfluoroalkyl substances (PFASs)

Previous laboratory scale studies indicate nanofiltration (NF) and UV-sulfite photochemical treatments as promising technologies for the removal and destruction, respectively, of per- and polyfluoroalkyl substances (PFASs) from contaminated water. This study reports on a field demonstration of a pilot-scale hybrid NF and UV-sulfite treatment train for the remediation of 12 PFASs detected in groundwater impacted by aqueous film-forming foam (AFFF) at a U.S. Department of Defense installation. For most of the detected PFASs, NF rejection was consistently ≥ 95% over a 30-day field trial when operating at 90% total permeate recovery. Rejection of short-chain perfluorosulfonic acids (PFSAs) by NF decreased when recoveries increased from 90 to 97%; tests with a reverse osmosis (RO) membrane showed ≥ 99% rejection of all PFASs regardless of increasing recovery. UV treatment of the NF reject following 90% permeate recovery resulted in variable destruction of individual PFASs, with rates also being dependent on pH and the identity and concentration of UV photosensitizer. Rates of perfluorocarboxylic acid (PFCA) degradation were greater than those measured for PFSAs and perfluoroalkyl acid (PFAA) precursors and were independent of perfluoroalkyl chain length. In contrast, rates of PFSA degradation increased with increasing chain length. Consistent levels of PFAS degradation by UV-sulfite were observed during a 30-day demonstration experiment in NF reject water amended with 10 mM sulfite and adjusted to pH 11.2. Collectively, > 75% of the detected PFAS mass in the NF reject was destroyed after 4 h of UV treatment, increasing to > 90% after 8 h of treatment. An analysis of electrical energy inputs for the hybrid NF/UV-sulfite treatment train showed energy per order magnitude (EE/O) requirements ranging from ≤ 13.1 kWh/m3 for PFCAs and 14.1 kWh/m3 for PFOS to values > 100 kWh/m3 for more recalcitrant short-chain PFSA analogues. The UV reactor and water-cooling system were the major contributors to overall energy requirements and represent the greatest opportunities for improving efficiency of the technology.

Poly(vinyl alcohol)/polydopamine hybrid nanofiltration membrane fabricated through aqueous electrospraying with excellent antifouling and chlorine resistance

Nanofiltration membrane with excellent antifouling and chlorine resistance properties fabricated through green and sustainable strategy was one of recent research hotspots. In this study, poly(vinyl alcohol)/polydopamine hybrid nanofiltration membrane was fabricated through aqueous electrospraying. Crosslinked poly(vinyl alcohol) favors the hydrophilic and antifouling surfaces and the incorporated polydopamine significantly enhanced membrane permeance due to its greater spatial structure. Meanwhile, hydrogen bond between poly(vinyl alcohol) and polydopamine facilitated the compatibility. The fabricated C-M2 membrane exhibited excellent antifouling property with low total flux decline ratio (FDR = 6.1%) and high flux recovery ratio (FRR = 98.9%), which was superior to commercial NF270 membrane (FDR = 10.7%, FRR = 96.6%). More significantly, C-M2 membrane showed excellent chlorine resistance property due to the absence of chlorine sensitive acyl carbonyl structure that commonly encountered in polyamide based membrane (e.g., NF270 and NF90). In general, an aqueous electrospray strategy was proposed for fabricating nanofiltration membrane with enhanced antifouling and chlorine resistance.

Reclaimed water application to vegetation restoration in mining area: Determination of water quality standards and optimization of moderate treatment technology

Water shortage severely restricts vegetation restoration of mining area in the northwest China. Moderate treatment of reclaimed water is essential for improving the local ecological environment. In this study, relevant water quality standards issued by the states and research results were comprehensively considered to propose a reclaimed water quality standard suitable for vegetation restoration of mining area. The available domestic sewage and mine water was moderately treated by hybrid biological reactor system and nanofiltration membrane system, respectively. The effluent quality meet the requirement of reclaimed water quality standards in this study. This study provides theoretical support for vegetation restoration of mining area.

A comparative study of membrane filtration, electrocoagulation, chemical coagulation and their hybrid processes for greywater treatment

The aim of the present work was to treat greywater using standalone and hybrid processes and to reuse the treated water for irrigation and toilet flushing. Microfiltration (MF), ultrafiltration (UF) and nanofiltration (NF) membrane processes, electrocoagulation (EC) with Al and Fe electrodes, and chemical coagulation (CC) with alum, polyaluminium chloride (PAC), ferric chloride, and ferric sulphate were performed as standalone processes. In the standalone membrane processes, the Desal 5DL NF membrane showed the lowest flux decline caused by fouling and almost the highest removal efficiency. The Fe electrode showed the best performance with a low operating cost (0.067 $/m3) and disposal cost of sludge (0.019 $/m3) at optimum conditions (pH: 7.5; current density: 5 A/m2) in the standalone EC process. Among the standalone coagulation processes, the lowest operating cost (0.06 $/m3) and high removal efficiencies of chemical oxygen demand (COD), UV254, DFZ436, and turbidity were achieved with PAC at a pH of 7.5 and coagulant dosage of 100 mg/L. The water treated with standalone processes did not meet the standards for toilet flushing water and Class A for irrigation water. Therefore, the hybrid processes using the Desal 5 DL NF membrane‒BW 30 reverse osmosis (RO) membrane, Fe electrode‒Desal 5DL NF membrane, and PAC coagulant‒Desal 5DL NF membrane were performed to improve water quality. All the hybrid processes provided high‒quality water for toilet flushing purposes. The quality of the water treated with hybrid processes was determined as Class A. In addition, Class II for drip irrigation was achieved using the Fe electrode‒NF and PAC coagulant‒NF hybrid processes. However, water treated using the two‒step membrane process was not suitable for irrigation.