Water. Desalination + reuse
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Technology overview MIDES is using a microbial fuel cell in which an electrical current is generated by specific bacteria called geobacter. This electrical current is used to power the desalination of high saline water flowing between two ion exchange membranes. The new configuration is called a microbial desalination cell (MDC). The MDC will lower the salinity of the seawater to brackish water level, which will then be completely desalinated by reverse osmosis (RO) with far lower energy consumption. In the MIDES system, the accompanying treatment of wastewater is carried out in a bioreactor. Acetate that is produced in the bioreactor provides nutrients for the geobacter. The bioreactor combined with the MDC greatly reduces the need for an external energy source. This innovative process could make it possible for RO to work using less than 0.5 KwH/m3 of water. The MIDES project is developing testing and demonstration sites in Spain, Tunisia, and Chile. The MIDES project is a consortium of 10 organisations funded by the European Union. The targets of the MIDES programme are: • Lower energy consumption in desalination; • wastewater treatment; • fewer chemicals involved; • less waste; • high recovery; and • positive social impact with new water resources. 28 FAR SITE June 2017 Water. desalination + reuse Project to demonstrate low energy technology The MIDES project kicked off in April 2016, with the aim that by the end of four years the tech- nology will have demonstrated a dramatic reduction in energy consumption for desalination. Demo sites are to be installed in Chile, Spain, and Tunisia, with the one at FCC Aqualia's site in Denia, Spain, the first to start in 2018. "They need to run for one consecutive year as a minimum. The project involves innovation in the cathodes and anodes that are part of the mi- crobial desalination cell (MDC), and the ion exchange mem- branes that are being devel- oped by FujiFilm," says Sergio Salinas, senior lecturer in water supply engineering at IHE DelŽ Institute for Water Education. The programme includes lifecycle analysis and environ- mental impact assessments of the MDC, "so that by the end of the project we have not only demonstrated the consumption on energy, but also we can show that MDCs are a real option that are suitable for implementa- tion in different countries in the world," Salinas says. The MDC is a prototype developed at IMDEA research centre in Madrid, Spain, which is now being scaled up for a full demonstration. The team in Denia is currently in the early stages of building out the demo plant. Other pilot scale mem- brane-based pre-treatment is already under evaluation there. The demo site will be treat- ing brackish surface water and brackish groundwater depend- ing on the time of year, and aims to produce 250 l/d of desali- nated water by the end of 2018. "This is a brand new technology so we still have some techni- cal challenges to overcome," says Victor Monsalvo, head of eco-efficiency, innovation and technology department, FCC Aqualia. "In the MDC, the main challenge is to move from batch operation to continuous op- eration. The problem is that we have to control several reactions in one system." The MDC has three cham- bers: the first takes a feed of wastewater, using microbes to remove organic matter and to produce electricity for desali- nation; the second is a saline water chamber, where the focus is to increase the production per square metre of membrane; and the third is a cathodic chamber, "because in the first chamber we have an oxidation reaction, so we need a contra reaction to make the process stable," explains Monsalvo. "We are ana- lysing two options with the third chamber. The first is to have Microbial desalination technology is not new, however past attempts to develop it have been plagued by problems including membrane fouling and an inability to scale it up to a practical size, among other challenges. 0.5 kWh per cube of desalinated water