New nitrogen circulation system technologies are being developed to detoxify and recycle harmful nitrogen compounds in exhaust gases and wastewater. In discussions of planetary boundaries, it has been noted that nitrogen pollutants are far beyond acceptable limits. Separation and concentration methods are important to produce ammonia resources from nitrogen compounds in wastewater. This paper introduces membrane and adsorption technologies for the preparation of ammonia resources.

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In the global framework of Sustainable Development Goals (SDGs), the Japanese government, like many other goverments of industrialized countries, declared its plan to go carbon neutral in real terms by 2050. This paper describes the application of quantum–beam–based technology to the R&Ds of ion–exchange membranes toward the 2050 carbon neutrality. The gamma–ray or electron–beam induced grafting offers a better way to prepare cation– and anion–exchange membranes (CEMs and AEMs). The approach using ion–track technology results in the preparation of “nano–structure controlled” CEMs and AEMs, which have perfect one–dimensional ion–conductive pathways parallel to their thickness direction. The hierarchical structures of the CEMs and AEMs, ranging from nanometers to micrometers, are revealed by small–angle scattering experiments using a cold or thermal neutron beam. I believe that quantum–beam technology can be developed as a powerful tool in the field of high–efficiency electrochemical energy devices and systems.

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A thermochemical water–splitting iodine–sulfur (IS) process enables us to provide the carbon–free hydrogen (H2) at high–efficiency levels using high–temperature heat sources, such as high–temperature gas–cooled reactors, solar heat, and more. Recently, Japan Atomic Energy Agency constructed the H2 production test facility made of the industrial– available corrosion–resistant components, and demonstrated the operations for 150 h at the rate of ca. 30 L/h. In addition, the cation exchange membranes (CEMs) for the HI mediated electro–electrodialysis (EED) were developed by a radiation graft polymerization method in order to improve the IS process efficiency. High proton (H+) conductivity and selectivity are required for the performance of CEMs to reduce the consumption energy for EED. The H+ conductivity of the radiation grafted CEMs was successfully improved by controlling the grafting amount, compared with that of the commercially–available membrane, Nafion®. Moreover, the H+ selectivity and water transport of the developed CEMs was improved by introducing divinylbenzene as the crosslinker. The crosslinkers suppress the permeation of water and I– ions except for H+ caused by the inhibition of the membrane swelling. Currently, the further improvement of the membrane performance is underway by using the ion–track grafting technique.

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In this review, the charged structure and the principle of ionic transport of charged mosaic (CM) membrane were introduced. Novel CMs prepared by the ion–track graft polymerization method with high performance were also introduced. Because the cation–exchange and anion–exchange domains of a CM membrane are alternately arranged and these charged domains are passed through the membrane, the membrane shows high electrolyte permselectivity. The CM membranes prepared by the ion–track graft polymerization method have high mechanical strength because the cation–exchange and anion–exchange domains are covalently bonded each other. Hence, the CM membrane will have high desalination performance at high applied pressures. For example, in a piezodialysis system consisting of the CM membrane and two NaCl solutions of 500 ppm, the concentration at the high–pressure side increased while that at the low–pressure side decreased, indicating that the CM membrane have potential application to desalination of salt solutions with low salt concentrations.

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Elucidation of the proton conductive mechanism is required for further improvement and/or development of a proton conductive membrane. Quasi elastic neutron scattering (QENS) is suited to reveal the water dynamics in the proton conductive membrane because the hydrogen has a huge incoherent neutron scattering cross section. In this paper, results of in–situ QENS measurements of a Nafion membrane under controlled water vapor pressure was introduced. The adsorbed water was categorized into two types; (1) strongly bound water, where a strong interaction occurred with the sulfonic group and the dynamics was frozen within the energy resolution and (2) weakly bound water which weakly interacted with the sulfonic group and showed one order of magnitude smaller diffusion coefficient. The relationship between the proton conductivity and the dynamics of weakly bound water was also discussed. The observed diffusion process of the weakly bound water could contribute to the proton conduction as a vehicle mechanism.

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Biofouling is a major cause of performance deterioration in membrane bioreactor (MBR) for wastewater treatment. In this article, a series of studies are introduced on the mechanisms of biofouling formation and its control by interference of microbial metabolisms. The key findings from those studies were that: (1) control of EPS quality is more important than EPS quantity in controlling MBR biofouling, (2) EPS quality depends on microbial metabolism rather than microbial community, and (3) control of growth conditions and interference with bioactive substances is effective for biofouling mitigation.

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Membrane bioreactor is promising wastewater treatment technology whereas remains major issue of biofilm formation on the membrane surface. Recently, various studies are focusing on microbial community of the biofilm and suggested that certain bacteria detected in the biofilm played an important role on biofilm formation (e.g., early colonization). This review summarized the biofilm forming bacteria which is divided into two types; pioneer bacteria and maturation bacteria existed in early and matured biofilm, respectively. Moreover, recent studies indicate that biological control represented by antisense method and bacteriophage are effective technologies to eliminate biofilm forming bacteria. This review also discussed applicability of these technologies from engineering point of view.

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In order to ensure sound operation of sewage facilities, sewage treatment plants sometimes requires not only repairing or retrofitting existing facilities but also meeting to increases of treatment capacity, as well as to stricter water quality regulations. To meet these demands, it is useful to upgrade existing wastewater treatment process by introducing Membrane Bioreactor (MBR) process with flat–sheet membrane. MBR is one of wastewater treatment processes that combines biological treatment process and membrane treatment process. Compared to the conventional activated sludge process, the MBR uses a membrane with microscopic pores for solid–liquid separation, enabling the collection of higher quality treated water. In addition, sedimentation tanks can be eliminated and the treatment capacity per reaction tank volume can be increased by maintaining a high activated sludge concentration in the biological reaction tank. Furthermore, the flat–sheet membrane can be operated at a higher activated sludge concentration than other membranes due to its structure, thus increasing treatment capacity. This report outlines the retrofit cases of three sewage treatment plants. 1) Nakahama Sewage Treatment Plant (Osaka, Japan) : In conjunction with the facility renovation, high–speed filtration and MBR were installed to reduce the pollution load during wet weather and achieve nitrogen and phosphorus removal. 2) Al Ansab Sewage Treatment Plant (Muscat, Oman) : To achieve increase of treatment capacity with minimal equipment modifications, the membrane equipment was replaced with a model with more filtration area. 3) Canton Water Reclamation Center (Canton, U.S.A.) : To comply with stricter phosphorus and nitrogen regulations for treated water in conjunction with facility renovation.

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Anaerobic biological treatment is a wastewater treatment technology that saves energy and waste sludge, and recovers energy. Its application is progressing, but conventional anaerobic treatment processes such as UASB and EGSB are difficult to apply to wastewater containing SS and oil and high COD wastewater of tens of thousands mg/L or more. Anaerobic MBR is a process that can be applied to these wastewaters without pretreatment or dilution, allowing wastewater treatment and biogas recovery. The features of the anaerobic MBR, application examples, and findings on membrane fouling, which is one of the issues for its widespread use, are described.

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