Perspective on desalination discharges and coastal environments of the Arabian Peninsula.

Two opposing views are held about the effects of desalination plants on coastal environments. One view is that brine discharged from desalination plants has minimal impact on the coastal environment. The other opinion claims that discharges from desalination plants pose a potential environmental hazard to coastal environments and particularly to those of the Arabian Gulf. The present study was carried out to determine whether negative environmental impacts could be detected in coastal waters of the Gulf and Red Sea near discharges from desalination plants in Saudi Arabia. Phytoplankton abundance, concentrations of chlorophyll a, nutrients, total suspended solids, trace metals, chlorination by-products, bacterial growth, and toxicity of effluents were assessed. Results indicate the brine discharges were not toxic to fish or brine shrimp. Mitigation of impacts from elevated temperature, salinity and chemicals in dual purpose plants is partly achieved by pre-dilution of brine reject stream with cooling water. Alternative pretreatment methods, chlorination and waste treatment are considered. There is accumulation of corrosion metals in sediments at the discharge site of a plant on the Gulf coast. However, their concentrations were within regulatory limits.

Evaluating suitability of source water for a proposed SWRO plant location.

SWRO membranes are characterized by their ability to reject particles of larger than 0.001 µm diameter and approximately 200 molecular weight. This indicates the selectiveness of the SWRO membranes and the relative ease by which they can be clogged or fouled. For this reason, membrane filtration needs the cleanest possible feed water. Without extensive feed water purification, the reverse osmosis (RO) technology of simple filtration under pressure could be fraught with problems. The quality of source water determines the pretreatment regimen and consequently success or failure of a SWRO plant. The present study evaluated the suitability of source water for a proposed SWRO plant on the Gulf coast of Saudi Arabia. Various physico-chemical and biological parameters were assessed: temperature, pH, salinity, conductivity, total dissolved solids (TDS), silt density index (SDI), turbidity, total suspended solids (TSS), total hardness, total alkalinity, total organic carbon (TOC), dissolved carbohydrates and proteins, dissolved oxygen (DO), biochemical oxygen demand (BOD), chlorophyll-a, bacterial count, major ions, and trace metals. With the exception of total suspended solids, chemical and physicochemical variables measured in this study had concentrations typical of the Arabian Gulf water and seawater in general. Average TSS values were slightly higher than those reported for Gulf coastal waters, and more importantly they were highly variable. This variability may result in episodes of filtration problems for the SWRO plant. The plant should seek deeper sea water a distance from shore as the location of its intake. The study allowed recommendations for treatment options to assure more successful operation of the plant.