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A new class of thin film nanocomposite (TFN) hollow fiber (HF) membrane of polydopamine (PDA) modified HKUST-1 (mHKUST-1) incorporated in polyamide (PA) matrix supported by polyethersulfone (PES) substrate was constructed via interfacial polymerization method for brackish water desalination in low-pressure reverse osmosis (RO) process. The PDA modification facilitated the HKUST-1 even dispersion, thus resulting in better compatibility between the inorganic nanofillers and the organic matrix. The impact of HKUST-1 loadings on the overall performances of the resultant HKUST-1@PA/PES membranes was investigated. Introducing the mHKUST-1 nanofillers not only enhanced surface hydrophilicity and negative surface charges for the selective layer, which improved membrane's fouling resistance to humic acid (HA), but also led to nearly doubled water permeance when comparing with the pristine PA membrane (increasing from 3.51 to 6.94 Lm−2h-1bar−1), without obvious salt rejection deterioration (~98.2% at 2 bar and 97.4% rejections at 4 bar for 500/2000 ppm NaCl solutions, respectively). The integrity of the HKUST-1@PA/PES membrane was examined and verified after 30-days operation. Overall, the results achieved in this work demonstrate promising potential of the metal organic framework (MOF)-based TFN membranes used for desalination in low-pressure RO process. To sum up, this work has exhibited a facile method to incorporate the metal organic framework (MOF) into the PA layer, and the resultant MOF-based TFN membrane indicates its great potential for desalination in low-pressure RO process. • A thin film nanocomposite hollow fiber membrane was constructed via interfacial polymerization. • Polydopamine (PDA) modified HKUST-1 was incorporated in polyamide matrix supported by polyethersulfone substrate. • The PDA modification facilitated the HKUST-1 even dispersion in PA matrix, without the formation of defects. • A water permeability of 6.94 Lm−2h-1bar−1 and 97.4% rejections at 4 bar for 2000 ppm NaCl solution were achieved. • The long-term stability test verified the good integrity of the HKUST-1@PA/PES membranes after 30-days operation. [ABSTRACT FROM AUTHOR]

The emerging technology of pressure retarded osmosis (PRO) has been intensely studied over the past decades due to its potential in harvesting salinity gradient energy, but membrane fouling can deteriorate the PRO performance. To mitigate membrane fouling, the outer surface of the inner-selective thin-film composite (TFC) polyetherimide (PEI) hollow fiber membrane was modified by depositing poly-(allylamine hydrochloride) (PAH) and poly acrylic acid (PAA) polyelectrolytes. The results show that the outer surface of the modified membrane had less pores exposed and was more negatively charged, which was beneficial for preventing the entrance and adsorption of the negatively charged foulants into the membrane substrate. It was further proved that the modified membrane was effective in reducing PRO fouling by organic macromolecules such as alginate and bovine serum albumin, while maintaining the mechanical properties and intrinsic separation properties well. Interestingly, after 200 ppm alginate was introduced to the feed water, the power density of the modified membrane could be maintained constant at 16.2 W·m − 2 at 15 bar while that of the non-modified membrane reduced around 17% at the end of a 300-min testing period. The results suggest that the polyelectrolytes deposition is a feasible strategy for adding anti-fouling property to PRO membranes. [ABSTRACT FROM AUTHOR]

Aquaporins are water channel proteins with high permeability and solute rejection, making them ideal components for the preparation of desalination biomimetic membranes. In one strategy, E. coli aquaporin Z (AqpZ) proteoliposomes are immobilized in a polyamide layer formed by interfacial polymerization at the inner surface of hollow fibers. However, once polymerization occurs, the system is almost a black box where it is difficult to disentangle the relative contribution to performance of (i) water permeation through AqpZ channels and (ii) the possible modification of the properties or structure of the polymer layer by the mere presence of protein and lipid. Indeed, the fate of protein and lipid once the polymer is formed, and how much of it is actually used, is under debate. Also, the performance of these modules has been reported to be stable over several months. This is intriguing because of the expected degradation of functional AqpZ and lipid with time. Herein, we used lipid and AqpZ, both fluorescently labeled, to unequivocally localize both components only at the inner surface of the hollow fibers. To characterize module performance, we tested about 30 half-inch modules containing five hollow fibers each. Those reconstituted with wild type AqpZ produced higher permeability (∼8.5 ± 0.9 LMH/bar) than those reconstituted with AqpZ mutant (R189A) (∼5.6 ± 1.7 LMH/bar) or lipid-only liposomes (3.7 ± 1.1 LMH/bar). However, while these differences are significant, they are smaller than expected from the comparison of relative permeabilities of membranes incorporating wild-type AqpZ, R189A mutant and only-lipid. In addition, we show that in a five-month long experiment, performance of two of these modules showed only minor deterioration, if any, which is not consistent with the observed rapid degradation of proteoliposomes at room temperature. Overall, these data obtained in this set-up suggests that although both AqpZ and lipid are localized at the inner of the hollow fibers, they mainly behave as additives that modify the properties of the robust polyamide layer. A small contribution of AqpZ channel activity to module performance is possible, but to be significant it would require full coverage and a higher protein density in the proteoliposomes, which at present cannot be achieved in the current protocol. [Display omitted] • Thirty half-inch modules (5 hollow fibers each) were tested. • Fluorescent lipid and AqpZ are only found co-localized with the IP layer. • Modules perform better with wild type AqpZ than with R189A inactive mutant. • Module performance does not directly correlate with proteoliposome permeability. • Long-term module performance is inconsistent with degradation of proteoliposomes. [ABSTRACT FROM AUTHOR]

The ultra-permeable membranes (UPMs) are expected to reduce the specific energy consumption (SEC) of desalination, but the potential of UPMs in hollow fiber configuration has not been well quantified. Herein, we analyse the SEC and footprints of UPM modules in three feed salinities: seawater reverse osmosis (SWRO), brackish water RO (BWRO) and low-pressure RO (LPRO). Through the modelling the fluid dynamics and mass transport of RO systems, we find that a tripling in spiral-wound SWRO membrane permeability (based on the current value of 1 L m−2 h−1 bar−1; LMH/bar) could result in 16% decrease in SEC. Contrastingly, the quadrupling of hollow fiber SWRO membrane permeability (based on the current value of 0.25 LMH/bar) could reduce the SEC by 23%. According to our analysis, hollow fiber and spiral-wound SWRO membranes with permeabilities up to 1 LMH/bar and 3 LMH/bar, respectively, can reduce the SEC of seawater desalination. On the other hand, membranes with permeabilities up to 9 LMH/bar and 12 LMH/bar can lead to SEC savings in BWRO and LPRO desalination, respectively. This study provides a general guidance to RO membrane researchers on the permeability upper-limit of which UPMs could bring about SEC and footprint savings at a system level. [Display omitted] • Energy savings achievable by high permeability RO membranes were quantified. • Modelling was performed by simulating fluid dynamics in various RO configurations. • Hollow fiber SWRO membranes (up to 1 LMH/bar) could reduce energy consumption. • Spiral-wound SWRO membranes (up to 3 LMH/bar) could reduce energy consumption. • High permeability RO membranes could bring about greater benefits in BWRO/LPRO. [ABSTRACT FROM AUTHOR]