Water. desalination + reuse

RESEARCH | 38 | Desalination & Water Reuse | November-December 2014 demand of seawater desalination. As shown in figure 1, a pressure exchanger stage is added to the conventional PRO set up so that the hydraulic pressure produced can be transferred from the PRO to the inlet seawater with high efficiency. The system has considerably higher energy efficiency than other SWRO-PRO applications, where lower efficiency turbines are used to produce electricity with attendant losses. GS works together with Toray Chemical Korea (TCK), and several Korean research institutes as partners under the GMVP umbrella. These partners are working on each component of the GMVP-PRO system. TCK, as the membrane developer, has a goal to produce eight-inch, spiral wound PRO membrane modules with a power density of around 10 W/m 2 . The Korea Institute of Construction Technology has conducted a study to develop an efficient pretreatment process that will reduce fouling of PRO membranes. And the Korea Institute of Science and Technology has carried out research to develop an efficient hydro- turbine. Aside from domestic partners, GS works closely with US company Energy Recovery as a key technology provider, GS Inima, which it acquired in 2011. SCAlE up The scaling-up plan of the GMVP-PRO is to build two PRO pilot plants with respective outputs of 20 m 3 /d and 200 m 3 /d based on the flow capacity of draw solution. The 20 m 3 /d pilot plant is already built and the larger demonstration plant is currently being designed. Its construction will be complete before the end of 2015. The pilot plant has two purposes. First, it will test membrane modules. Second, it will establish design values for the demonstration plant that will evaluate the performance and integrity of the GMVP- PRO system. Various configurations and sizes of PRO modules will be tested for their performance at this plant. Although TCK, the membrane partner, develops and produces the spiral wound modules, a separate test rig to examine hollow fibre modules will also be provided at this plant. Pairs of modules will be also tested in series. Of six sessions at a recent international symposium (see box, PRO in the frame), two sessions – covering research and development and membrane and application – were allocated exclusively to PRO. In the summary session covering the feasibility, commercialization, and future research and development directions for PRO, participants were generally optimistic about PRO's future. They shared the view that PRO can be comparable to other renewable energy processes if it is applied with the osmotic pressure differences encountered with SWRO brine and wastewater. But the prevailing view was that PRO might not compete with lower osmotic pressures – as found in the use of seawater. On the question of business potential of PRO, there was again shared optimism. Indeed the prevailing view was that the technology, based on SWRO brine, could be commercially viable even right now. But the commercial prospects of PRO based on seawater in the short term were seen as less strong. It was generally accepted that a few more years would be needed before PRO with seawater becomes economically feasible. Statkraft's former partner in its osmotic power pilot, IDE Technologies, said that it would continue to work on PRO. Fouling problems in PRO was seen as an area in particular need of further research. The performance of PRO can be degraded very quickly once the membranes are fouled so scientific and engineering communities agree that they need to build up more knowledge on fouling in PRO as well as FO operation. Research to mitigate the pRO in the frame In September this year GMVP organized the 1st International Symposium on Innovative Desalination Technologies (ISIDT), together with King Abdullah University of Science and Technology, in Seoul, Republic of Korea. The symposium looked at innovative aspects of MD, PRO, FO, and hybrids of these three technologies. presenters are listed here. Research and development session Masaru Kurihara, Toray Industries Sarper Sarp, Qatar Foundation Avi Efraty, Desaltech/Osmotech) Membranes and applications Professor Joon Ha Kim, Gwangju Institute of Science and Technology Yonggeun Park, GS E&C Professor Neal Chung, National University of Singapore, Boris Liberman and Udi Tirosh, IDE Technologies The parallel Integrated Network for Energy from Salinity Gradient Power meeting Edvard Sivertsen and Willy Thelin, Foundation for Scientific and Industrial Research. References 1. PE Pattle, Production of electric power by mixing freshwater and salt water in the hydroelectric pile, Nature 174 (1954) 660. 2. S Loeb, Large-scale power production by pressure-retarded osmosis, using river water and sea water passing through spiral modules, Desalination 143 (2002) 115-122. PRO's susceptibility to fouling was deemed essential to take it into commercial viability. In this context, participants at the ISIDT symposium generally agreed that "another Statkraft" was needed to lead a PRO study to expedite its commercialization. While participants were positive about PRO's future, the overriding view was that more research was necessary in key components of PRO. For example, PRO- exclusive membrane and modules were seen as an important element for development. Currently, the development of PRO membrane module is in its early stages, and there is much room for improvement. The development of membranes optimized for use in PRO could make the technology significantly more competitive. COnCluSiOn Although two major players in Statkraft and Mega-ton have disappearred from PRO research and development, there is still an affirmative view for PRO's future among the industry. PRO has great potential as a means to reduce the energy consumption and environmental impact of seawater desalination using RO. However, scaling- up and piloting are essential next steps towards its commercialization. And greater knowledge in: membrane and modules, fouling, systems, and operations is needed. To bridge the gap between research and practical implementation, a research programme aimed at scaling-up and piloting is essential. In this context, GMVP is focused on the construction and operation of a demonstration plant, which will help the desalination community to build up its understanding of PRO and support this promising technology. l Acknowledgement The authors would like to express their thanks to Kyung-Mi Chung (GS), Yong-Jun Choi (GMVP), Sangho Lee (Kookmin University) for their help in preparation of this article. Thanks also go to all participants at ISIDT for their active and frank discussion.

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