Environmental issues in seawater reverse osmosis desalination: Intakes and outfalls

Seawater reverse osmosis (SWRO) desalination has some environmental impacts associated with the construction and operation of intake systems and the disposal of concentrate. The primary impact of conventional open-ocean intake systems is the impingement and entrainment of marine organisms. These impacts can be minimized by locating the intake in a geographic position where oceanic productivity is low. Velocity-cap intakes tend to reduce impacts by minimizing the number of fish entrained and some new traveling screens can allow the survival of some marine organisms. Mitigation, such as environmental restoration of habitat or restocking, can provide an acceptable solution to impacts where they are significant. Subsurface intake systems avoid impingement and entrainment impacts, but can cause other, less important impacts (e.g., visual, beach access). Concentrate disposal can locally impact benthic communities, if poorly diluted discharge is allowed to flow across the marine bottom. Impacts to benthic communities from concentrate discharges can be minimized by using properly-designed diffuser systems, designed and located based current and flow modeling. The experiences of SWRO desalination to date indicate that environmental impacts can be satisfactorily minimized with proper design based on a reasonably complete environmental impact analysis prior to facility siting and design.