Development of High-Flux and Robust Reinforced Aliphatic Polyketone Thin-Film Composite Membranes for Osmotic Power Generation: Role of Reinforcing Materials

Recent advances in innovative osmotic membranes for resource enrichment and energy production in wastewater treatment

Wastewater is a valuable resource that we can no longer afford to overlook. By recovering the nutrients and metals it contains and generating renewable energy, we can not only meet the rising demands for natural resources but also create a more sustainable and resilient future. Forward osmosis (FO) membranes are one of the most intriguing resource recovery process technologies because of their high organic retention, economical energy usage, and straightforward operation. However, the widespread adoption of FO membranes on a full-scale basis is hindered by several issues with previous membrane products. These include limited selectivity to different types of ions, insufficient water flux, and high susceptibility to membrane fouling during extended periods of operation. Hence, it is essential to either invent new FO membranes or modify the existing ones. The objective of this work is to provide a comprehensive and organized review of up-to-date advancements in the development of innovative osmotic membrane (IOM) materials for resource recovery (RR) and energy production (EP). The paper covers several aspects, including the limitations of current osmotic membrane technologies, a review of new membranes specifically designed for effective RR/EP, their applications in various industrial fields, integrated IOM systems, recent improvements in IOM fabrication processes using artificial intelligence, and a discussion of the challenges and prospects of the potential research. In general, recently developed IOMs have proven to be highly efficient in recovering organics (>99 %), nutrients (>86 %), and precious metals (>90 %). These new membranes have also demonstrated an ability to effectively harvest osmotic energy (with power output ranging from 6 to 38 W/m2) by applied pressure in the range of 8 to 30 bar. These findings suggest that IOMs is promised for efficient resource recovery and renewable energy production.

Fluidics for energy harvesting: from nano to milli scales

A large amount of untapped energy sources surrounds us. In this review, we summarize recent works of water-based energy harvesting systems with operation scales ranging from miniature systems to large scale attempts. We focus particularly on the triboelectric energy, which is produced when a liquid and a solid come into contact, and on the osmotic energy, which is released when salt water and fresh water are mixed. For both techniques we display the state of the art understanding (including electrical charge separation, electro-osmotic currents and induced currents) and the developed devices. A critical discussion of present works confirms the significant progress of these water-based energy harvesting systems in all scales. However, further efforts in efficiency and performance amelioration are expected for these technologies to accelerate the industrialization and commercialization procedure.

Development and Industrial-Scale Fabrication of Next-Generation Low-Energy Membranes for Desalination

Spiral-wound modules have been the most common configuration of packing flat-sheet membranes since the early development of polyamide (PA) membranes for water treatment applications. Conventional spiral-wound modules (SWMs) for desalination applications typically consist of several leaf sets, with each leaf set comprising feed spacers, membranes, and a permeate carrier (PC) wrapped around a permeate-collecting tube. The membrane area that can be packed into a given module diameter is limited by the overall leaf set thickness, restricting module productivity for a given membrane permeability. We describe here a novel industrial-scale method for successfully coating the polysulfone (PSf) ultrafiltration (UF) support layer directly onto a permeate carrier, instead of conventional non-woven fabric, as a precursor to the polyamide TFC coating, resulting in twofold benefits: (a) drastically simplifying the membrane fabrication process by eliminating the use of non-woven fabric and (b) increasing the throughput of each membrane module by facilitating the packing of a larger membrane area in a standard module housing. By combining the permeate carrier and membrane into a single sheet, the need for the non-woven support layer was eliminated, leading to a significantly reduced leaf set thickness, enabling a much larger membrane area to be packed in a given volume, leading to lower energy consumption per cubic meter of produced water. Molecular-weight cutoff (MWCO) values in the range of 36–96 kDa were found to be dependent on PC thickness and material. Nevertheless, the reinforced membranes were successfully fabricated with a ~9% reduction in membrane leaf thickness compared to a conventional membrane. Preliminary trials of coating a thin-film composite PA layer resulted in defect-free reverse osmosis (RO) membranes with a salt rejection of 94% and a flux of 40 L m⁻² h⁻¹ when tested against a 2000 mg/L NaCl feed solution at an operating pressure of 15 bar. Results from the testing of the 1812 and 2514 elements validated the novel concept and paved the way for further improvements towards full-scale RO membranes with the potential to be the next low-energy workhorse of the water industry.