Environmental Challenges
Conventional desalination is energy intensive—up to three-quarters of the cost of desalinated water is electricity. Energy consumption continues to be a challenge for the sector particularly when generation is from non-sustainable sources such as coal. A moderate-sized reverse osmosis plant supplying municipal water to approximately 1.5 million people may produce 125,000 cubic metres (or 32 million gallons) per day and consume about 24 megawatts of electricity. Global Water Intelligence, analysts of the international water industry state, "the greatest challenge for the desalination industry is to increase the energy efficiency of the process faster than the price of generating electricity from fossil fuels." With mounting concerns over carbon impacts and increasing energy prices, delivering electricity consumption savings is a top priority.
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In addition to fresh water, all desalination methods produce a concentrated brine output. This waste stream is typically discharged into the ocean and consists of everything that was removed from the feed water, including chemicals that may have been added during pre-treatment. The brine discharge may increase the salinity of surrounding water, impacting marine life. Environmentalists have been known to call the area of brine outflow the "dead zone." Brine can be diluted with other available process water such as power plant cooling water. It is also possible to evaporate the brine and harvest solid salt; however, this is typically not economic unless the output from the desalination is already highly concentrated. Most desalination technologies, except electrodialysis, are unable to produce a sufficiently concentrated brine to allow salt harvesting.
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