Water. desalination + reuse

RESEARCH November-December 2014 | Desalination & Water Reuse | 37 | profitable in the Norwegian energy market if the power density of the membrane was 4-6 W/m 2 . On this basis, 2,000 m 2 of membrane were installed at the prototype to give an electricity production capacity of 10 kW. But the actual power density they obtained during operation, at 3 W/m 2 , fell short of Statkraft's target. The Mega-ton project claimed that its system produced 13 W/m 2 using 7% SWRO brines, which was substantially higher than the Statkraft result in terms of power density even when taking into account the greater osmotic pressure difference. Both plants have now been taken out of operation. Statkraft announced its decision to terminate the PRO project in 2013, saying that it was not possible to justify osmotic power in Europe. Japan's government-founded, four-year Mega-ton project ended this year. So, the momentum of large-scale PRO has, currently, been lost. REvivAl Large-scale PRO has, however, recently been revived in a research programme named Global MVP (GMVP). The MVP title is drawn from its three main strands: membrane distillation (MD), valuable resource recovery (VRR), and PRO. Like Mega-ton, GMVP is a government-funded research and development project. In this instance Korea's Ministry of Land, Infrastructure and Transportation and the Korea Agency for Infrastructure Technology Advancement are providing the financial support. GMVP is looking to go beyond the RO process. About 140 researchers are studying MD, VRR and PRO applications, as well as hybrids of these technologies, all under the GMVP umbrella. The programme has a budget of some US$ 35 million over the five years to 2018. It is focused on scaling- up and piloting rather than on laboratory experiments. Plants of various sizes will be installed and operated including a 1,000 m 3 /d SWRO pilot plant, a 400 m 3 /d MD pilot plant, and a 200 m 3 /d PRO pilot plant. The vision of GMVP is to make seawater desalination plants more energy efficient and environmentally friendly. It endeavours to develop technologies that transform waste into resources. SWRO brines currently discharged into the ocean are creating environmental concern because the discharge volumes are growing as seawater desalination plants gets bigger. GMVP regards SWRO brines as resources and attempts to recover as much value from them by applying MD, PRO, and VRR. Through hybridization of RO and MD technologies, GMVP is attempting to reduce the volume of RO brines by 30% while increasing fresh water production by 30%. The novel desalination system being developed by GMVP is based on the recovery of osmotic energy using a hybrid of RO and PRO technologies. It also enables the recovery of lithium and strontium from RO or MD brines, as well as the production of construction materials. Examples include paving blocks made from RO by-products, such as backwash effluent and membrane cleaning solutions. Editor's note PROs and cons The US$ 43 million government- funded Mega-ton project completed its planned four-year term this year. It closed with claims that it had achieved its aims of demonstrating a low-cost, low environmental impact desalination system. The heart of the plant is PRO using SWRO concentrate as the draw solution and treated wastewater feed. It forms an integrated 1 million m 3 /d SWRO plant and 100,000 m 3 /d wastewater reclamation plant. As a result of the research, Japan hopes to increase its activities in the Middle East and North Africa, China and other regions that are expected to increase their development of water supply and wastewater reclamation projects. The Norwegian project concluded at the end of 2013 with a very different outlook than the Japanese one with Statkraft declaring that PRO was not competitive in the European power market and "will not be sufficiently developed to become competitive within the foreseeable future," as it abruptly ended its funding of the project. Statkraft said commercially viable PRO needed membranes to generate 5 W/m 2 and cost the same as standard RO membranes. While there are experimental membranes capable of 10W/m 2 there are no cheap PRO membranes available today. Figure 1. Flow diagram of SWRO PRO. GMvP And PRO Environmental engineering company GS Engineering and Construction (GS) is responsible for the GMVP-PRO research and development theme in GMVP. Through the GMVP-PRO hybrid application, GS is looking to achieve low- cost seawater desalination. The pairing of wastewater and SWRO brine was chosen for its high osmotic pressure drop, and consequent high potential for energy recovery. Having a greater pressure drop than the Statkraft system, which drew its energy from a seawater and river water combination, the GMVP approach promises better economic feasibility. GMVP-PRO focuses on pressure recovery itself instead of energy production from it. The hydraulic pressure from PRO is used to lower the pressure

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