Influence of desalination effluents on marine ecosystems

Abstract

Water, re-entering a marine ecosystem after transit through a desalination plant, may be altered in three major ways. One, its thermal energy may be increased; two, its chemical make up may be altered; and three, its microbial biota may be modified. The effect of thermal enrichment on natural marine ecosystems varies with the change in temperature, the duration of that temperature change, and its geographical extent. If the desalination plant is sited in such a manner so as to allow rapid dissipation of the thermal input, the effect of the temperature change will be minimized. Signs of thermal effect on marine ecosystems could be manifested by changes in community structure (types of organisms), as well as the changes in features of individual species. The most obvious chemical changes in desalination effluents may include increase in salinity, a decrease in dissolved oxygen, an increase in dissolved organics, and an increase in pretreatment chemicals. As with thermal input, the effect of these chemical changes in the effluent on natural ecosystem will depend upon the rate of entrance and dispersion. As the rate of dispersion is increased, the effect of chemical changes on ecosystems is correspondingly decreased. Desalination plants, due to their design, provide surface areas for rapid microbial proliferation. Depending upon the sequence of chemical pretreatment, it is possible that these viable microbes will enter the ecosystem and supplement the existing biota, if conditions permit their continued growth. The environmental impact in several types of desalination plants (distillation and reverse osmosis) on natural marine ecosystems will be discussed. The problems imposed on the environment by these desalination plants will be presented and similarities to problems encountered in other types of condenser-heat exchanger systems (Power plants and ocean thermal energy converters) will be analyzed.