Currently, technologies for recovering ammonia from wastewater and sewage at low cost and with minimal environmental impact have not yet been fully developed; therefore, ammonia contributes to global warming through both its synthesis and treatment. To improve the nitrogen cycle and realize an ammonia–based society, it is essential to develop new technologies for the efficient recovery of low–concentration ammonia from wastewater. In this review, we introduce membrane–based ammonia recovery processes utilizing various membrane technologies and discuss the future prospects for the development of ammonia recovery technologies.

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Japan, as an island nation with limited land area, has scarce natural resources and energy sources, making the establishment of a sustainable society an important challenge. Membrane technologies are expected to contribute significantly to the realization of the sustainable society because they enable material separation with low energy consumption and a compact footprint. Among various membrane technologies, ion exchange membranes (IEMs) possess unique characteristics that are not available in reverse osmosis (RO) membranes, such as high ion selectivity and the simultaneous production of acids and alkalis, owing to their charged structures. This article introduces several ion exchange membrane–based processes, including electrodialysis using ion–selective membranes, a desalination process based on charged mosaic membranes that operates on a principle different from that of RO membranes, acid and alkali co–production using bipolar membranes, and salinity-gradient energy conversion using IEMs.

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Wastewater recycling in semiconductor fabrication plants has become increasingly important to meet the growing demand for semiconductors under constrained water resources. The chemical mechanical polishing (CMP) process for wafer planarization generates a large volume of wastewater containing fine slurry particles, creating a strong need for cost–effective wastewater recycling technologies. To address this challenge, continuous filtration tests of oxide CMP wastewater were conducted using an outside–in, dead–end hollow fiber membrane module applicable to high–suspended solids (SS) wastewater. Stable filtration of CMP wastewater was achieved at a maximum water recovery rate of 95.5%, and the backwash wastewater from the membrane filtration system was successfully concentrated to approximately 42000 mg/L. Based on the pilot test results, it was estimated that, compared with a conventional system, the proposed system could reduce the operation cost by approximately 69%.

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Pharmaceutical purification processes are among the most energy–intensive operations in the chemical industry and involve substantial consumption of organic solvents. In recent years, organic solvent nanofiltration (OSN) membranes have attracted significant attention because of their potential to enhance these processes in terms of continuous operation, improved efficiency, and scalability. This paper introduces the development of OSN membranes within the Toyobo Group, outlines their efforts toward applications in the purification of medium–sized pharmaceutical molecules, and discusses future perspectives.

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Membrane separation has attracted considerable attention as an environmentally friendly technology. However, many membranes are prepared from fossil–based plastics, and the application of bioplastics has been investigated to further reduce environmental impact. This review focuses on bioplastics, including poly(lactic acid) (PLA), poly (hydroxyalkanoate) (PHA), and poly(ethylene furanoate) (PEF). Their characteristics and applications to membranes for liquid separation are summarized, and their potential and challenges are discussed. PLA and PHA are bio–based and biodegradable materials, and many studies have reported their applications mainly to microfiltration and ultrafiltration membranes. Although challenges such as high cost and limited studies on scalability remain, new materials such as PEF and advances in control of membrane properties are expected to further expand the potential of bioplastic–based membranes.

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Upcycling of food residues is attracting attention as an approach to a circular society in the food industry. Okara, a by–product of tofu and soymilk production, is a promising feedstock for microbial fermentation processes because it contains abundant protein, but its direct use is hindered by high viscosity caused by insoluble solids. In this article, we present our work on okara valorization using membrane processes, with triacylglycerol (TAG) production by the oleaginous yeast Lipomyces starkeyi as a model case. Direct addition of okara enabled TAG production, but the yield was lower than that of conventional medium. Enzymatic extraction and removal of insoluble solids reduced viscosity and improved TAG production. Further application of membrane concentration enhanced productivity, and nanofiltration (NF) resulted in the highest TAG yield, reaching 20.0 g/L with a 5–fold concentrate. These results demonstrate that membrane processes are effective for converting okara into a valuable fermentation resource for circular bioprocesses.

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Efficient concentration of lithium–containing solutions is essential in direct lithium extraction (DLE) and lithium–ion battery recycling processes. Conventional reverse osmosis (RO) suffers from an inherent concentration limit imposed by osmotic pressure, while thermal evaporation requires large energy input due to phase change. Osmotically assisted reverse osmosis (OARO) has attracted attention as a membrane–based concentration process capable of achieving high concentration without phase change, enabling concentration beyond the practical limits of RO. In principle, OARO does not impose an intrinsic upper limit on achievable concentration and allows stepwise concentration without phase change. Concentration tests using lithium chloride (LiCl) and lithium sulfate (Li2SO4) solutions demonstrated stable performance under both short–term and long–term operation, even at high osmotic pressures. Initial membrane compaction was observed, followed by stable continuous operation. Furthermore, a commercial application for concentrating black mass–derived Li2SO4 solution is introduced. Operational data show stable concentration from approximately 2 ～ 3 g/L to 14 ～ 17 g/L over extended periods. These results indicate that BC membrane–based OARO is a practical and energy–efficient concentration technology for DLE and recycling processes.

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