Brine disposal from reverse osmosis desalination plants in Oman and the United Arab Emirates

Reverse osmosis (RO) desalination plants are used for supplying potable water to small communities in inland areas of Oman as well as small to large communities in the United Arab Emirates (UAE). Most of these desalination plants use brackish groundwater as feedwater. The production of brine (also known as concentrate of wastewater) is an integral part of the operation od desalination plants. Ten small-scale desalination plants in the interior parts of Oman and eight RO plants in the coastal areas of the UAE were investigated with regard to their brine disposal methods. The capacity of the Omani plants varied from 50 m³/d to a maximum of 1000 m³/d. The salinity level of wastewater varied from 9.8 to 61.2 dS/m (1 dS/m = 640 mg/L). Various disposal methods were observed. These included lined evaporation ponds, ocean/beach disposal, and unlined small bores. The depth to the water table in the areas of the investigated desalination plants varies from 40 to 80m, while the average distance between feedwater intake and disposal areas was approximately 200 m. In the UAE, the capacities of the investigated plants varied between 950 to 15,000 m³/d. All the UAE plants dispose of their brine in the sea, although some of the plants dispose of their brine in nearby creeks that are linked to the sea. The chemical characteristics of the brine, feedwater, product water, and water from evaporation ponds (or bores) were determined. The presence of other chemicals including iron, copper, zinc, and cleaning agents (such as hydrochloric acid, sodium hexametaphosphate, and anti-scalants) is likely to pollute the groundwater, if the brine were to reach the underlying aquifers. Under certain conditions, brine from the desalination plants can have useful applications. Potentials for such applications are addressed in this paper.