The research task of the “Mega–ton Water System” was to build core water–treatment technologies, using Japanese initiative, with the low cost, low environmental impact and energy reduction demanded by the 21st century.With contribution to the resolving of global water problems as its core concept, “1,000,000 m3/day scale seawater desalination”, as research with a view to release around 2020, and “100,000 m3/day scale sewage treatment system”,as basic research for the core technologies of the future, were positioned as the final deliverables and output, and of these, for the seawater desalination system, we aimed to develop a practical system with top–level global competitiveness (price, performance, reliability).In order to carry out this development, we worked on a total of eight research subthemes for elemental technologies and system technologies, with the societal needs of energy reduction, low environmental impact and low cost as challenges. With a view to get the latest trends in relevant research areas and societal needs, we have been actively participating in international symposia held in Europe, America, China, the Middle East and Asia.With regard to research in the eight subthemes, in addition to holding periodic subtheme leader meetings in order to gauge their progress, by holding SSD (Senior Scientific Director) rounds for individual themes and engaging in cooperative working between subthemes for related themes, we confirmed and reviewed the direction for the research as a whole. In addition to these research activities, we have been engaged in bibliographic surveys and analyses, exchanged information with international experts gaining a review of the direction of the research, as well as an evaluation.With regard to the dissemination of information, we have also been making active use of academic conference presentations and lecture requests and news reports.In the final year, from the viewpoint of international business, we held an international symposium as a place for disseminating strategic information on the results of research, inviting a group of foreign lecturers from a wide variety of fields of industry, government and academia.The main challenge of development goal is the construction of mega–ton–scale system for seawater desalination for half the current cost. Accordingly, we developed the world’s first low–pressure, multi–stage, high yield RO system, using a low–pressure seawater desalination membrane, and, as a result of incorporating into it the elemental technologies gained from research in subthemes, such as highly–efficient pressure energy recovery, low–cost and highly durable plastic piping, pretreatment without the use of chemicals and intelligent mega-ton plant, and system technologies, we have gained confidence in our ability to succeed in achieving our goal of “Halving conventional equipment costs and desalination costs with mega–ton scale”. As a result of aiming for a paradigm shift to an“energy generation sewage treatment system”from the conventional“ energy-intensive sewage treatment system”as research to pursue future core technologies in regards to sewage treatment systems, it become possible to obtain technical prospects that allow significant benefits to be obtained,such as energy generation, reclaimed water utilization and valuable materials recovery.

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Three types of membrane and module were studied as core technologies in Mega–ton Water System project for realizing mega–scaled seawater desalination plant which is capable of producing 1,000,000 m3 of freshwater per day.Firstly, research for highly efficient spiral reverse osmosis (RO) element focusing on membrane design and element structure was executed. Low pressure polyamide RO membrane was obtained based on structure analyses of the membrane by means of microscopic method and pore size measurement. Regarding to element structure, the numerical simulation method for the whole area of a membrane leaf was developed by using the flow and mass trans-fer characteristics for modeling the spacer–filled channel. Secondly, world’s largest–size hollow fiber type RO element (16 inch diameter)was developed for the first time in the history of hollow fiber membrane business. The prototype element which has more than 4 times higher flow rate than the conventional size element was successfully produced. This element configuration was optimally designed by using simulation model developed to analyze the axial distribution of flow in RO module in consideration for membrane flux. Thirdly, highly efficient UF membrane and module for pretreatment of RO process were studied. Chemical structure of the membrane material was modified to reduce membrane fouling, and pore structure of the membrane was optimized by controlling spinning condition of hollow fiber membrane. The flux of the modified hollow fiber UF membrane has almost doubled compared to that of the conventional UF membranes. Furthermore, the actual large membrane module (12 inch diameter) with the modified membrane was successfully produced.

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For the reduction of energy consumption at a mega–ton scale SWRO plant, pressure–retarded osmosis (PRO)system is proposed in the Mega–ton Water Project. The PRO system recovers power from salinity gradient between the concentrated brine from the SWRO plant and fresh water from regional waste water treatment facility. PRO performance of cellulose triacetate hollow–fiber membrane modules was examined in a prototype PRO plant and the test operation was carried out for more than one year.We have reached the maximum output power density, 13.3 W/m2, using 10–inch module at our prototype PRO plant in Fukuoka and 17.1W/m2 in the laboratory–scale experimental using 5–inch module between tap water and concentrated brine (Ca.7%). These results indicate that a commercial PRO plant could be available in very near future.

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An energy recovery device has an important role in reducing specific energy consumption in seawater reverse osmosis desalination process. A next–generation isobaric energy recovery device (ERD) has been developed under the Mega–ton Water System Project. The device achieved 2% higher energy recovery effectiveness and low volumetric mixing without over–flush compared to the conventional ERD. The design concept and its characteristic feature of the next–generation ERD is presented together with the results of experimental validation and numerical computations.

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A new RO system for the large–scaled SWRO plant has been developed in the project named “Mega–ton Water System”with the private–public cooperation in Japan. The characteristics of the newly developed RO system to increase the recovery rate are to use the short vessel that contain 2~4 elements for the first stage, and to use relative-ly long vessel for the second stage after inter booster pump in order to reduce the pressure and the flux of the lead element. The new RO system used by the new low pressure SWRO elements studied by this project is capable of the high recovery rate (under 65%)and allows the scale of the intake and the pretreatment equipment to reduce com-pared to a conventional system. Considering also to the new isobaric Energy Recovery Device (ERD)that has been developed in this project, the energy consumption was estimated and compared the results with that of a conventional system. It is suggested that the reduction of energy consumption is to be about 20% compared with a conventional system.

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The influence of addition of sodium hypochlorite and sodium bisulfite to reverse osmosis (RO) process was examined quantitatively by parallel tests of several pilot-scale UF+RO units. The differential pressure of RO elements and modified Biofilm Formation Rate (mBFR) clearly showed that the addition of these chemicals could be the trigger of the biofouling. In addition, chemical free pretreatment processes of RO are now being established according to the levels of the seawater quality measured by the rapid and easy biofouling risk assessment method which was newly devised.

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Although RO membrane system has been widely used, it often faces serious problems caused by the developments of biofilm on the membrane that lowers the efficiency. The biofilm is a complex mixture of organic polymers, microbial cells and sometimes larger organisms. In order to properly maintain and operate RO system, the understanding of biofilm is prerequisite. In this review, basic characteristics of microorganisms and experimental observations on the biofilm formation processes with special emphasis on microbial community structures are described and dis-cussed.

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The development of MBR based sewage treatment system “MBR+ system”proposed in this work aims at a para-digm shift of existing waste water treatment system with considerable energy consumption toward an energy and resource productive system. The system consists of three modules: Ultra compact MBR with inclined tubes (itMBR), hybrid membrane system (HMS), and hydrothermal gasification (HTG). Each module is specialized in its function and inter–related each other to constitute the system: biomass production and carbonaceous treatment (itMBR), nutrient recovery and concentration (HMS)and conversion of biomass to energy (HTG). In this paper, the fundamental concept of each module will be highlighted accompanied with demonstrative data, such as long–term operation of pilot–itMBR. Perspectives of energy and cost balances of the system will also be introduced.

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To improve the CO2 permeability of facilitated transport membranes, we investigated the effect of ionic liquid additives into the membrane. In this study, glycine was used as a CO2 carrier and polyvinyl alcohol as a gel matrix to contain the CO2 carrier and additives. To investigate the effect of the water vapor absorbability of the gel membrane on the CO2 permeability, ionic liquids with various degrees of hydrophilicity were examined as additives. When the highly hydrophilic ionic liquids were added to the membrane, a large amount of water was absorbed in the membrane under humid conditions. With the aid of water, glycine dissolved in a fully water stained gel membrane could react with CO2 under humid conditions and elevated temperatures from 110 to 130℃. Because of the high liquidity of the ionic liquid within a wide temperature range, the formed CO2 complex could easily diffuse into the membrane from the feed side to the permeate side. Thus, CO2 permeability and CO2/N2 selectivity were highly improved; e.g.,at 110℃, the CO2 permeance was increased from 3.6×10–6 to 6.4×10–5 mol/(m2skPa) and CO2/N2 selectivity from 17.3 to 192 (–). Moreover, the non–volatility and thermal stability of an ionic liquid enabled improved CO2 permeation for extended periods under elevated temperature conditions. Therefore, the addition of ionic liquid was useful to enhance the gas permeation properties whilst maintaining high stability.

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Filter systems for seawater, river or lake water have big problems of filter clogging. These problems were mainly caused by fibrous particle’s twisting to the filter media and/or adhesive particle’s sticking to filter media. And back-washing difficulty of cylindrical filter element accelerates filter clogging. To overcome these problems, filter system using filter elements furnished back washable scraping head through slit with brush was employed. Using this filter system, filter clogging problem was improved and high speed filtering has realized.

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