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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]

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]