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Schematic diagram of two stages of membrane fouling. [Display omitted] • Desalination performance of PV membrane to industrial reverse osmosis concentrate is first reported. • The produced water meets the discharge standard. • Chemical softening pretreatment is necessary to mitigate fouling. • Membrane flux is recovered 98% after chemical washing. Pervaporation (PV), as a cost-efficient concentrating process, has been studied for Zero Liquid Discharge (ZLD) of desalination. Although high water flux and excellent salt rejection have been reported for many PV membranes. The desalination performance, fouling behavior, and cleaning protocol for treating real reverse osmosis concentrate (ROC) generated from industrial plants have never been studied. Meanwhile, understanding the fouling behavior and cleaning method in the treating process is crucial for the development of suitable PV desalination membranes. In this study, we used a lab-made PV membrane to treat industrial ROC with a high chemical oxygen demand (COD) value and high salt concentrations. The results showed that conductivity and COD of the produced water were below 20 μs/cm and 70 mg/L, respectively, which fulfilled the discharge standard. However, the membrane fouling problem was not trivial. To address the fouling issue, a chemical softening method was adopted to remove the calcium salts of the ROC, and a membrane cleaning method was developed to regenerate the water flux. As a result, a long-term water flux of 31.27 kg/m2·h with a flux recovery rate of 98% were realized. This highlights the potential of PV desalination technology for ROC reclamation. [ABSTRACT FROM AUTHOR]

Pervaporation (PV) is a low-energy membrane separation technology widely studied for desalination, water treatment and solvent recovery where heat is applied to vaporize the feed solution and a vacuum is applied at the permeate side to drive the separation of miscible mixtures. The heart of this technology – polyvinyl alcohol (PVA) that is commonly used as the separation layer of polymer membranes is often fabricated over long cross-linking durations, high temperatures or toxic cross-linkers to prevent it from being dissolved in water. Here we overcome these intrinsic material limitations with a photo-crosslinkable polymer, poly(vinyl alcohol)-stilbazol quaternized (PVA-SBQ), commonly deployed in the printing industry, as the dense selective layer of a thin-film composite PV membrane. The separation performances of the resultant PVA-SBQ/nanofiber thin-film composite membranes were optimized as a function of photo-crosslinking conditions where ultra high water fluxes of 122.6 ± 10.8 kg·m−2·h−1 were achieved while desalinating 3.5 wt% NaCl from water at 75 °C and a permeate pressure of 100 Pa. This high PV desalination performance was also maintained during brine (containing 10 and 20 wt% of NaCl) treatment. [Display omitted] • A fast and green preparation method of PV composite desalination membrane was developped. • Nanocellulose was used as a transition layer for pore size control. • The composite membrane show ultra-high water flux of 122.6 ± 10.8 kg·m−2·h−1 with salt rejection>99.9%. • This membrane was suitable for desalinating brine solutions (containing 10 and 20 wt% of NaCl). [ABSTRACT FROM AUTHOR]

Chlorine resistance mechanism diagram of SMA-g-PVA/FS layer. [Display omitted] • 1, 2-diols of PVA were removed to improve chlorine resistance. • Crystallinity of PVA was decreased by grafting reaction. • Grafted PVA was crosslinked by crosslinker compound to increase both chlorine resistance and hydrophilicity. • PV membranes exhibit high desalination property and superior chlorine resistance. Pervaporation (PV) desalination membranes have good anti-fouling properties due to its hydrophilic dense surface structure. However, organic fouling is inevitable in long-term operation. Sodium hypochlorite (NaClO) is commonly used for cleaning organic pollutant, but it may damage polymeric membrane. Thus, designing membrane material with good chlorine resistance is crucial for expanding its lifespan. In this study, polyvinyl alcohol (PVA) was selected to prepare PV membrane in concern of its hydrophilicity and good film forming property. Its chlorine resistance was improved by removing the more active 1,2-diols of PVA by reacting with sodium periodate, grafting with poly (styrene-co-maleic anhydride) to decrease its crystallinity, and crosslinking using a fluorocarbon surfactant (FS). The resulting PV membrane exhibited the highest reported chlorine resistance of 768000 ppm·h among PV and RO membranes with a high-water flux of 44.5 ± 1.5 kg/m2·h and salt rejection of 99.93%. A long-term fouling and cleaning cycle experiment was carried out using 10000 ppm humic acid to mimic organic foulants. The flux was recovered 100% after the NaClO cleaning. Hence, the chlorine-resistant PV membrane had the ability for sustainable desalination application. [ABSTRACT FROM AUTHOR]

Pervaporation membranes have exhibited great potential for desalinating brine solutions. However, the flux recovery after membrane washing and the membrane's resistance to chemical cleaning reagents were barely studied. Our group has reported excellent desalination properties of PVA based pervaporation membranes. Nevertheless, the membranes were damaged during chemical cleaning due to the poor chlorine resistance of PVA. In this study, the more active 1, 2-diol units of PVA were removed by sodium periodate treatment. And then, the modified PVA was crosslinked by FS-3100, a fluorocarbon based crosslinker, to improve its hydrostability and chlorine resistance. The FS-3100 crosslinked composite (PVA-FS/PVDF) showed a water flux of 34 ± 1 kg m−2 h−1 with a NaCl rejection of 99.93% when desalinated a 35000 ppm NaCl solution at 70 °C. Salt rejections were maintained after soaking in 2000 ppm NaClO, acid (pH = 2), and alkali (pH = 12) solutions for 168, 180, and 180 h, respectively. A long term desalination experiment was carried out using Tween 20 and HA as foulants. The water fluxes could be recovered to 100% after chemical washing without losing salt rejections, indicating an excellent long term operation stability of the FS-3100 crosslinked PV membranes. PVA with superior chemical resistance is obtained by crosslinked with fluorocarbon containing chemical. Image 1 • 1, 2-diols of PVA were removed to improve chlorine resistance. • The PVA was further crosslinked by FS-3100. • The crosslined PVA membrane had superior tolerance to acid, alkali, and chlorine. • Membrane flux could be recovered 100% after chemical washing. [ABSTRACT FROM AUTHOR]