ENVIRONMENTAL IMPACTS OF SEAWATER DISTILLATION AND REVERSE-OSMOSIS PROCESSES

The paper presents and compares the marine and atmospheric discharges of typical large MSF and RO plants. Distillation plants require an inl et seawater flow around 8 to 10 times the fresh water production rate, for, cooling and feed make-up. The discharge is raised in salinity an d in temperature, due to heat rejection from the process. A seawater R O plant generally requires a lower feedwater flow rate of around 2.5 t o 3 times the production. Salinity of the discharge is correspondingly greater than in distillation, but temperature rise is small. Chemical discharges are compared for the different processes. A comparison is made of atmospheric emissions from generating the power to drive RO pr ocess pumps and the emissions resulting from generation of steam and a uxiliary power for distillation (in dual purpose desalination/power pl ants). The factors affecting site selection and requirements for seawa ter intakes and outfalls are briefly discussed, with examples. The lan d area needed for a desalination plant is compared with the catchment and reservoir areas needed for a typical surface water collection sche me to illustrate the much lower impact of desalination on land resourc es. Factors such as noise and aesthetics are also briefly discussed.