Environmental quality standards for brine discharge from desalination plants

When many desalination plants are operated closely together along coastal areas, the continuous brine discharges through marine outfall systems from these cluster plants can have a significant impact on the coastal marine environment. The potential impact can be minimized and regulated by treatment and recycling technologies, by limiting the concentration values of brine at the discharge point and also by imposing concentration values within a prescribed circular mixing zone in the coastal waters via the outfall design. The maximum concentration values for monitoring the coastal water quality standard are formulated using analytical solutions of the far-field mathematical model for single and two outfall discharges based on a flat seabed, developed to incorporate the effect of a tidally oscillating flow. The results for a single outfall model show that a smaller mixing zone is suitable only for a stronger ambient current condition at the discharge site. If a second outfall is allowed to discharge close to an existing outfall, the results show that the radius of the mixing zone should be increased to accommodate the compounded impacts.