Use of evaporation ponds for brine disposal in desalination plants

Desalination plants are being used increasingly in inland areas of many countries for supplying water for domestic purposes. If these areas are too far away from the sea, the opportunity to dispose the reject brine (also known as concentrate, reject water, or wastewater) in the ocean no longer exists, given that ocean disposal is the common practice for plants located in coastal areas. Evaporation ponds are especially suitable to dispose of reject brine from inland desalination plants in add and semi-arid areas due to the abundance of solar energy. In irrigation projects facing a soil salinity problem due to a shallow saline groundwater table, evaporation ponds are also in use. Saline water tables are lowered by pumping or tile draining and the drainage water is stored in evaporation ponds. While evaporation ponds have long been used for salt production in many parts of the world, the disposal of concentrate from desalination plants in inland areas using evaporation ponds is of much significance both economically and environmentally. Guidelines are needed for the design, construction, maintenance, and operation of evaporation ponds for reject brine disposal in an economical and environmentally-sensitive manner. This paper provides a critical review of concentrate disposal technology using evaporation ponds. Relevant topics are also covered including chemistry of brine, brine disposal methods, use of evaporation ponds in agriculture, determination of evaporation rate, and evaporation enhancement methods.

The subject of concentrate disposal technology using evaporation ponds was critically reviewed. The topics covered, among others, include brine disposal methods, use of evaporation ponds in agriculture, evaporation pond design considerations, surface disposal of brine and pollutant movement through the soil, and evaporation rate determination and enhancement methods. It was evident that there are economic and environmental imperatives for proper disposal of reject brine from inland desalination plants using evaporation ponds. The latter can be successfully used as a disposal method especially in countries with dry and warm weather, high evaporation rates, and availability of land at low cost. Typically, arid and semi-arid areas are environments where evaporation ponds can be successfully used for disposal of reject brine from inland desalination plants. The last 20 years have seen rapid growth in the number of desalination plants for producing drinking water in many parts of the world. Unfortunately, the environmental implications associated with the discharge of concentrate from desalination plants have not received adequate considerations by concerned authorities. The likelihood of causing environmental problems from desalination plants in inland areas is much greater as concentrates are mostly disposed of on land. Improperly designed and managed disposal systems have the potential of contaminating groundwater resources. While RO plants in inland areas produce concentrate of high salinity, such plants are not usually associated with the presence of residual chlorine, heavy metals, and the problem of thermal pollution. In addition, the salinity of concentrate from RO plants in inland areas is much lower than that of seawater plants. The cost of disposal of reject brine from inland desalination plants can be quite substantial. However, there is an urgent need to find cheaper but environmentally-friendlymethods of disposal. This will ensure that good-quality drinking water can be supplied to areas of water shortages where desalination remains the only viable option. Evaporation ponds, when properly designed and managed, can be a viable means for disposal of brine from desalination plants, especially in inland areas. Evaporation ponds have also long been used for salt production in many parts of the world. In irrigation projects facing soil salinity problem due to a shallow saline groundwater table, evaporation ponds have been widely in use. Water tables are lowered by pumping or tile-draining and the drainage water is stored in evaporation ponds. Evaporation ponds are usually the least costly means of brine disposal in areas with high evaporation rates and low land costs. However, seepage from poorly constructed evaporation ponds can contaminate underlying aquifers. Contamination of feed water sources is also likely if the reject brine is improperly disposed, on the surface close to inland desalina-tion plants.