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Membrane distillation (MD) is a promising thermally-driven desalination process for various applications in food, pharmaceutical, textile, and chemical industries. However, membrane fouling and wetting are still major challenges, which limit the stability of MD membranes over long-term use. From 2005, researchers have developed many strategies to enhance membrane fouling resistance by simultaneously engaging reactions, but these works have not been systematically reviewed and categorized. Therefore, this review aims to identify research gaps and provide an overview of the state-of-the-art reactive MD processes, which are categorized broadly based on two configurations: 1 – " hybrid" involving coupling MD with an oxidation or biological process as a pre-treatment step and 2 – " integrated" involving immobilizing reactive materials on the membrane. The reactive MD processes were sub-classified into five categories based on reaction technology then analysed in terms of working mechanisms, advantages, limitations, and their application potentials. It shows that minimizing fouling in both hybrid and integrated processes can be attributed to the interaction of the organics/degraded by-products with the membrane surface/immobilized reactive layer, and the capability of the pollutants to be oxidized. In addition, depending on the types of the coupled process, oxidation can be accompanied by other mechanisms, such as electrostatic repulsion and electro flotation which is the most promising mechanism. Overall, despite the current developments in hybrid and integrated MD processes, many challenges exist including flux decline in the case of the complex feed solutions, a trade-off between oxidation and other accompanied mechanisms (e., electrostatic repulsion), and the possibility of membrane alteration. Future opportunities can be explored in terms of dedicated fouling studies, energy efficiency, removing/converting waste streams to valuable by-products, durability of the process equipment against oxidation, and targeting unique applications such as the treatment of concentrated organic waste streams. [Display omitted] • Reactive MD categorized into "hybrid" and "integrated" configurations. • Oxidation processes are a major focus in reactive MD. • Challenges include membrane fouling and material degradation. • Reactive MD demonstrates highly efficient treatment simultaneous with desalination. • Future studies should focus on fouling, reaction efficiency and targeted applications. [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]