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Diffusion dialysis (DD) for acid recovery is significantly restricted by the poor acid dialysis coefficient (UH+) of anion exchange membranes (AEMs). To overcome such problem, porous AEMs with extremely high free space volume have been fabricated herein based on porous membrane substrate, drawing inspiration from the dissolution‐diffusion concept. Specifically, chloromethylated polyethersulfone (CMPES) has been used as the starting material to create the porous substrate via non‐solvent phase inversion, then in‐situ crosslinked and quaternized using ethylenediamine (EDA) and N‐methylimidazole (NMI), respectively. In this study, the degrees of modification of EDA and NMI are controlled to adjust the microstructure and DD performance of the produced porous AEMs. The ideal AEM's UH+and acid/salt separation factor (S) are 4.3 and 2.6 times greater, respectively, than those of the commercial DF‐120 membrane at the same condition. Additionally, it shows strong organic solvent resistance and thermal stability, and therefore demonstrate the potential for widespread use.

Sustainable textile wastewater treatment strongly demands an indispensable paradigm shift from removal of contaminants to effective recovery of resources. In this work, a hybrid tight ultrafiltration (TUF) and bipolar-membrane electrodialysis (BMED) process was explored to recover resources (i.e., dye extraction, acid/base conversion, and pure water regeneration) from highly saline textile wastewater. Using a TUF membrane with 5000 Da molecular weight cutoff (MWCO) can obtain a sufficient rejection (>99.6%) of both reactive and direct dyes, due to the dye aggregation. Additionally, the considerably large pore size of the TUF membrane endowed the process with free transport of NaCl and Na2SO4(i.e., >99.42%), exhibiting promise as an alternative means of separation of dyes and Na2SO4. Additionally, an integrated TUF-based diafiltration was designed to separate the model dye (i.e., reactive blue 194) and Na2SO4. Particularly, reactive blue 194 was remarkably concentrated from 997.9 to 7952.8 mg·L–1by the TUF membrane with 99.5% dye recovery and 99.95% desalination efficiency after 8.0 diavolumes. Furthermore, a trace amount (i.e., 2.7 mg·L–1) of reactive blue 194 was observed in Na2SO4-containing TUF permeate, enabling a subsequent BMED operation. With the implementation of BMED, the Na2SO4-containing TUF permeate was sufficiently desalinated for acid/base conversion and pure water regeneration with no obvious fouling on the ion exchange membranes. These results demonstrate a potential applicability of the hybrid TUF/BMED process for sustainable management of textile wastewater, providing a strategy for practical applications in treatment of other high-salinity wastewaters.

Surface modification with advanced nanomaterials (i.e., 2D nanosheets) can be used to strategically tailor membrane properties, providing improved solute permselectivity to targeted molecules. In particular, 2D graphite-like carbon nitride (g-C3N4) nanosheets are a promising alternative for membrane modification, due to their exceptional physicochemical properties and facile synthesis. Herein, high-flux nanofiltration (NF) membranes were designed using bio-inspired co-deposition of hydrophilic g-C3N4nanosheets with a polydopamine (PDA)/polyethylenimine (PEI) layer onto porous ultrafiltration (UF) substrates. The g-C3N4nanosheets created additional nanochannels in the PDA/PEI layer to facilitate water molecule transport, resulting in high permeability (28.4 ± 1.2 L m−2h−1bar−1). Particularly, the bio-inspired layer structure was tailored from the UF to the NF (592 Da) scale by incorporating g-C3N4nanosheets, thereby breaking through the permeability–selectivity trade-off effect. The tailored NF membrane enabled ultrahigh retention of three reactive dyes (610–630 Da, >99.3%) and low salt rejection (2.9% for NaCl; 7.6% for Na2SO4), significantly promoting the fractionation of dyes and salts for dye desalination. Additionally, the hydrophilic g-C3N4nanosheets with oxygen plasma treatment further enhanced the wettability of the membrane surfaces, resulting in a superior antifouling performance. This study indicates the promise of g-C3N4nanosheets to engineer high-flux NF membranes with desirable fractionation performance for sustainable treatment of highly saline wastewater.

Use of tight ultrafiltration (UF) membranes has created a new pathway in fractionation of dye/salt mixtures from textile wastewater for sustainable resource recovery. Unexpectedly, a consistently high rejection for the dyes with smaller sizes related to the pore sizes of tight UF membranes is yielded. The potential mechanism involved in this puzzle remains unclear. In this study, seven tailored UF membranes with molecular weight cut-offs (MWCOs) from 6050 to 17530 Da were applied to separate dye/salt mixtures. These UF membranes allowed a complete transfer for NaCl and Na2SO4, due to large pore sizes. Additionally, these UF membranes had acceptably high rejections for direct and reactive dyes, due to the aggregation of dyes as clusters for enhanced sizes and low diffusivity. Specifically, the membrane with an MWCO of 7310 Da showed a complete rejection for reactive blue 2 and direct dyes. An integrated UF-diafiltration process was subsequently designed for fractionation of reactive blue 2/Na2SO4mixture, achieving 99.84% desalination efficiency and 97.47% dye recovery. Furthermore, reactive blue 2 can be concentrated from 2.01 to 31.80 g·L–1. These results indicate that UF membranes even with porous structures are promising for effective fractionation of dyes and salts in sustainable textile wastewater treatment.

Graphene-based nanocomposites have a vast potential for wide-ranging antibacterial applications due to the inherently strong biocidal activity and versatile compatibility of such nanocomposites. Therefore, graphene-based functional nanomaterials can introduce enhanced antibiofouling and antimicrobial properties to polymeric membrane surfaces. In this study, reduced graphene oxide–copper (rGOC) nanocomposites were synthesized as newly robust biocides via in situ reduction. Inspired by the emerging method of bridging ultrafiltration membrane surface cavities, loose nanofiltration (NF) membranes were designed using a rapid (2 h) bioinspired strategy in which rGOC nanocomposites were firmly codeposited with polydopamine (PDA) onto an ultrafiltration support. A series of analyses (SEM, EDS, XRD, XPS, TEM, and AFM) confirmed the successful synthesis of the rGO–Cu nanocomposites. The secure loading of rGOC composites onto the membrane surfaces was also confirmed by SEM and AFM images. Water contact angle results display a high surface hydrophilicity of the modified membranes. The PDA-rGOC functionalization layer facilitated a high water permeability (22.8 L m–2h–1bar–1). The PDA-rGOC modification additionally furnished the membrane with superior separation properties advantageous for various NF applications such as dye purification or desalination, as ultrahigh (99.4% for 0.5 g L–1reactive blue 2) dye retention and high salt permeation (7.4% for 1.0 g L–1Na2SO4, 2.5% for 1.0 g L–1NaCl) was achieved by the PDA-rGOC-modified membranes. Furthermore, after 3 h of contact with Escherichia coli(E. coli) bacteria, the rGOC-functionalized membranes exhibited a strong antibacterial performance with a 97.9% reduction in the number of live E. coli. This study highlights the use of rGOC composites for devising loose NF membranes with strong antibacterial and separation performance.

Metal–organic frameworks (MOFs) are studied for the design of advanced nanocomposite membranes, primarily due to their ultrahigh surface area, regular and highly tunable pore structures, and favorable polymer affinity. However, the development of engineered MOF-based membranes for water treatment lags behind. Here, thin-film nanocomposite (TFN) membranes containing poly(sodium 4-styrenesulfonate) (PSS) modified ZIF-8 (mZIF) in a polyamide (PA) layer were constructed via a facile interfacial polymerization (IP) method. The modified hydrophilic mZIF nanoparticles were evenly dispersed into an aqueous solution comprising piperazine (PIP) monomers, followed by polymerizing with trimesoyl chloride (TMC) to form a composite PA film. FT-IR spectroscopy and XPS analyses confirm the presence of mZIF nanoparticles on the top layer of the membranes. SEM and AFM images evince a retiform morphology of the TFN-mZIF membrane surface, which is intimately linked to the hydrophilicity and adsorption capacity of mZIF nanoparticles. Furthermore, the effect of different ZIF-8 loadings on the overall membrane performance was studied. Introducing the hydrophilizing mZIF nanoparticles not only furnishes the PA layer with a better surface hydrophilicity and more negative charge but also more than doubles the original water permeability, while maintaining a high retention of Na2SO4. The ultrahigh retentions of reactive dyes (e.g., reactive black 5 and reactive blue 2, >99.0%) for mZIF-functionalized PA membranes ensure their superior nanofiltration performance. This facile, cost-effective strategy will provide a useful guideline to integrate with other modified hydrophilic MOFs to design nanofiltration for water treatment.

This study selects two types of modified zeolites used as the ion exchanger to treat the groundwater for removing Fe2+and Mn2+, the column experiments of modified zeolites are conducted, the performance of ion exchange and regeneration of modified zeolites are investigated, and the operation parameters and regeneration conditions are established. The results illustrate that the modified zeolites have excellent performance on removal of Fe2+and Mn2+, the effluent of modified zeolites contains 8 × 10–3mg/l Fe2+and no content of Mn2+. The flow rate and initial concentration of Fe2+and Mn2+affect the effective cation exchange capacity of modified zeolites. The flow rate has no obvious impact on the performance of modified zeolite for removing Fe2+and effects sharply the performance of modified zeolite for removing Mn2+, the flow rate is 30 m/h for modified zeolite for removing Fe2+and 20 m/h for modified zeolite for removing Mn2+. And solution concentration influences the effective capacity of both of the modified zeolites. The cation exchange capacity of zeolite regeneration by sodium chloride (NaCl) is twice times than hydrochloric acid (HCl) for removing Fe2+and NaCl is also regeneration agent for zeolite for removing Mn2+. The dosage of NaCl solution for regeneration of zeolite to remove Fe2+is 0.92 l/(mol/l) and the ratio of dosage of NaCl and the effective capacity is 17.1, the dosage of NaCl solution for regeneration of zeolite to remove Mn2+is 0.92 l/(mol/l) and the ratio of dosage of NaCl and the effective capacity is 19.9, respectively.

This study selects two types of modified zeolites used as the ion exchanger to treat the groundwater for removing Fe2+and Mn2+, the column experiments of modified zeolites are conducted, the performance of ion exchange and regeneration of modified zeolites are investigated, and the operation parameters and regeneration conditions are established. The results illustrate that the modified zeolites have excellent performance on removal of Fe2+and Mn2+, the effluent of modified zeolites contains 8 × 10–3mg/l Fe2+and no content of Mn2+. The flow rate and initial concentration of Fe2+and Mn2+affect the effective cation exchange capacity of modified zeolites. The flow rate has no obvious impact on the performance of modified zeolite for removing Fe2+and effects sharply the performance of modified zeolite for removing Mn2+, the flow rate is 30 m/h for modified zeolite for removing Fe2+and 20 m/h for modified zeolite for removing Mn2+. And solution concentration influences the effective capacity of both of the modified zeolites. The cation exchange capacity of zeolite regeneration by sodium chloride (NaCl) is twice times than hydrochloric acid (HCl) for removing Fe2+and NaCl is also regeneration agent for zeolite for removing Mn2+. The dosage of NaCl solution for regeneration of zeolite to remove Fe2+is 0.92 l/(mol/l) and the ratio of dosage of NaCl and the effective capacity is 17.1, the dosage of NaCl solution for regeneration of zeolite to remove Mn2+is 0.92 l/(mol/l) and the ratio of dosage of NaCl and the effective capacity is 19.9, respectively.

In order to get the best performance of ultrafi ltration (UF) process in the pilot test, this paper chooses the appropriate coagulant for coagulation process used as the pretreatment of UF process, investigates the key infl uence factor of coagulant dosage, membrane fouling and permeability, and proposes a method to optimize the operation parameters of UF process. In this study, UF module is fed with three different types of raw water to verify the adaptability of UF membrane. The results indicate that polymer ferric sulfate (PFS) is the appropriate coagulant for low temperature seawater due to its economical efficiency and good coagulation performance, and the content of the silica in the raw water is the key infl uence factor of coagulant dosage. During the UF process, the UF membrane module (SXL-225 FSFC) could offer the permeate of stable quality characterizations, which meets the feeding requirement of RO. But the key influence factor of the membrane fouling is not the temperature but the components of feed water, especially the content of silica and other colloids.

In order to get the best performance of ultrafi ltration (UF) process in the pilot test, this paper chooses the appropriate coagulant for coagulation process used as the pretreatment of UF process, investigates the key infl uence factor of coagulant dosage, membrane fouling and permeability, and proposes a method to optimize the operation parameters of UF process. In this study, UF module is fed with three different types of raw water to verify the adaptability of UF membrane. The results indicate that polymer ferric sulfate (PFS) is the appropriate coagulant for low temperature seawater due to its economical efficiency and good coagulation performance, and the content of the silica in the raw water is the key infl uence factor of coagulant dosage. During the UF process, the UF membrane module (SXL-225 FSFC) could offer the permeate of stable quality characterizations, which meets the feeding requirement of RO. But the key influence factor of the membrane fouling is not the temperature but the components of feed water, especially the content of silica and other colloids.

Predicting the permeate flux is critical for evaluating and optimizing the performance of the forward osmosis (FO) process. However, the solution diffusion models have poor applicability in accessing the FO process. Recently, the data-driven eXtreme Gradient Boosting (XGBoost) algorithm has been proven to be effective in processing structure data in engineering problems and has not been utilized to assess the FO process. Herein, a combination of the XGBoost model with a genetic algorithm (GA) was first proposed to predict the permeate flux, highlighting its superiority in the FO process through comparison of the support vector regression (SVR) model, the artificial neural network (ANN), and the multiple linear regression (MLR). Moreover, the performance of these models was optimized by tuning hyperparameters with a genetic algorithm (GA) and compared via Taylor Diagram. Among these machine learning (ML) models, the GA-based XGBoost model is superior to the other three models in terms of mean square error (MSE, 2.7326) and coefficient of determination (R2, 0.9721) on the test data, and its prediction power was compared to that of the solution diffusion (SD) model in the literature. Finally, further insight into the feature importance that affects the permeate flux in the FO process was examined by utilizing the SHapley Additive exPlanations (SHAP) to estimate the contribution value of various variables. The results demonstrated that the XGBoost model could predict the permeate flux in the FO system with high accuracy and good generalization ability for the given data set and even on the unseen data. Furthermore, the findings of the SHAP method show that the osmotic pressure difference, the osmotic pressure difference of draw solution and FS solution, the crossflow velocity of the feed solution and draw solution, and the water permeability coefficient have a significant impact on water flux.

Compared with super/hydrophobic membranes, omniphobic membranes have superior anti-wetting and anti-fouling properties and thus can achieve better separation performance by membrane distillation for sustainable desalination and water treatment.