Water. Desalination + reuse
Issue link: https://fhpublishing.uberflip.com/i/749211
36 Far Site December 2016 Water. desalination + reuse Huntington Beach is 'precedent- setting' for California The screens on the wedgewire water intake system that Poseidon is proposing for its seawater RO desalination plant at Huntington Beach, California, will be 1mm wide in order to meet new regulations The challenges • Pacific Ocean salinity will corrode the screen's material and resistance to biofouling • Screens will be located 1,840 (560m) offshore at water depths of 35 (10m), making them difficult to clean The maTerial • Wedge wire screens are typically available in stainless steel, duplex, and super-duplex stainless steel, and copper nickel • Due to the salinity of the Pacific Ocean, the highest grade steel is preferred, however when overlaying the need for retarding biofouling growth on the screen, copper nickel is preferred When the California State Water Board adopted new regulations on seawater desalination plants in 2015, Poseidon, the developer of a proposed 50 million gallon a day (227,000 m3/d) capacity seawater RO plant in Huntington Beach, California, went back to the drawing board on its water intake technology. The regulations state that where feasible, plant develop- ers must use sub-surface water intake technology; that is, either wells or infiltration galleries. Poseidon's view, and that of the Independent Scientific Tech- nical Advisory Panel (ISTAP), which was convened by Posei- don and the California Coastal Commission from 2013 to 2015 to evaluate the feasibility of sub- surface water intake at Hunting- ton Beach, is that it's not feasible at the site. As well as infiltration galleries, ISTAP evaluated slant wells, horizontal wells, vertical wells, and tunnels. "It's not feasible to build one of these systems at Huntington Beach. It's a very high wave ac- tion environment, a very highly populated beach environment, and these type of intakes are not the norm. There was at one point a belief that they were an emerging technology, but in our experience and that of the industry around the world, they are the exception to the norm," says Scott Maloni, Poseidon vice president, project development. Where a sub-surface intake system is unfeasible, the regula- tions require plant developers to build a screened ocean intake, with slot widths of 1mm or less, and inflow velocity of water through the slots of less than half a foot (20cm) a second. The regulations are designed to mini- mise the intake and mortality of marine life. Poseidon's concept for water intake at Huntington Beach is just such a wedge wire screen intake (see picture, le—). However, there are two big chal- lenges to this approach at the Huntington Beach site. The first challenge is that the level of seawater salinity requires consideration of mate- rial corrosion resistance, and biofouling resistance; and the second is the distance offshore — the screens would be located 1,840— (560m) offshore at water depths of 35— (10m) — requiring consideration of methods for cleaning the screen faces. These