Chemical impacts from seawater desalination plants - a case study of the northern Red Sea

Seawater desalination facilities range from heavy coastal industry to small local plants, with the majority being either thermal multi-stage flash (MSF) or membrane-based reverse osmosis (RO) plants. Irrespective of the process, pretreatment chemicals are added to the intake water to improve plant performance. Furthermore, corrosion cannot be entirely prevented and heavy metals add to the chemical load of the brines, which are discharged to the marine environment. For impact assessment, information about chemical loads as well as the sensitivity of the impacted ecosystem is required. Loads of selected chemicals were estimated for 21 plant locations in the Red Sea including the Gulf of Aqaba and Gulf of Suez. Locations were identified from the 2000 IDA Worldwide Desalting Plants Inventory Report and localized on GIS data maps from the World Conservation Monitoring Center (WCMC). Their combined capacity exceeds 1.5 million ml/d, with approximately 1.2 million ml/d from MSF and 0.38 million m(3)/d from RO plants. Based on these figures, the daily chemical discharge amounts to 2,708 kg chlorine, 36 kg copper and 9,478 kg antiscalants, when effluent concentrations of 0.25 ppm, 0.015 ppm and 2 ppm are assumed, respectively. The sensitivity of the Red Sea and the Gulf of Aqaba to chemical loads is discussed and comparisons to the Arabian Gulf and the Mediterranean Sea are drawn.