Brine disposal from reverse osmosis desalination plants inOman 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 ofbrine (also known as concentrate or wastewater) is an integral part of the operation of 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 6 1.2 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 ofthe investigated desalination plants varies f?om 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-Scala&) 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.

The small-scale RO desalination plants in Oman use mostly lined evaporation ponds and unlined pits for the disposal ofbrine. Considering the high salt concentrations and the presence of other chemicals, it is imperative that safe methods of disposal be used for the protection of groundwater resources. Evaporation ponds (lined) and disposal pits did not show any noticeable increase in the concentration of various salts and EC levels. This is an indication that brine could be reaching the groundwater. In the UAE, the RO plants investigated dispose their brine in the sea. Due to technical, environmental, and economic constraints, it is unlikely that the brine reject from desalination plants can be used for any meaningful purposes in Oman and the UAE. As such, well designed and well constructed evaporation ponds under proper management will be the most appropriate disposal mechanism for inland desalination plants in Oman, while disposal to the sea will likely continue for foreseeable future in the UAE.