H.H. Al-Barwani

Modeling dispersion of brine waste discharges from a coastal desalination plant

Desalination of seawater leaves brine waste containing a high salt concentration to be disposed of into the environment. For coastal desalination plants, the most practical and least expensive brine disposal operation is to discharge it into the sea. Modeling studies on the effect of coastal water depth variations upon mixing and spreading of brine waste continuously being discharged into the sea are presented. Solutions are illustrated graphically, showing that the brine plumes are spreading downstream and heading towards the beach. For Oman in particular, the increase in salinity in coastal water will intensify the critical problems of seawater intrusion into coastal groundwater aquifers. However, this potential impact of brine disposal operations on coastal and marine environment can be alleviated by building longer sea outfalls.

A Computational Model Study of Brine Discharges from Seawater Desalination Plants at Barka, Oman

Oman is situated at the south-east of the Arabian Peninsula at the entrance to the Arabian Gulf, and its coastline stretches 1700 km along the Gulf of Oman in the north to the Arabian Sea in the south. Most of the population lives in the north-eastern coastal areas and in the capital area of Muscat. The climate of Oman is typically described as a tropical hyper-arid, with two distinct seasons: winter and summer. The winter period extends from late November to April, during which rains at irregular intervals occur. However, based on 27 years of rainfall data from 1977 (Kwarteng et al., 2009), the annual mean rainfall for the whole country is 117 mm. Hot weather with high humidity is experienced in the coastal areas during the summer months. The mean air temperature in northern Oman varies between 32 oC to 48 oC from May to September, and between 26 oC to 36 oC from October to April. The mean wind speeds range between 2 and 3.5 m/s, with high winds encountered during the summer months. Desalinated water has been used in Oman since 1976 when the Al-Ghubrah (co-location) power and seawater desalination plant using a thermal technology of multi-stage flash (MSF) was first commissioned in Muscat. To meet continuously growing water demand due to population growth and economic and social development and to reduce the reliance on groundwater resources, by 1999 the Al-Ghubrah plant had seven MSF desalination units installed. The first seawater desalination unit installed had a capacity of 22,750 m3/d, and the other six MSF units each have a capacity of 27,000 m3/d. Desalinated water usage in Oman is expected to increase further in the future, due to new industrial and tourismrelated developments. Desalination plants extract large volumes of seawater and discharge hot, hypersaline brine back into the marine environment. Therefore, the main concern of continuous brine discharges has been the potential impact upon the salinity of seawater (and possible thermal stress for discharges from MSF plants), and the resultant effects to marine communities around discharge outlets. Other occasional discharges from the plants include corrosion products, toxic antifoulants and antiscalants used in maintaining plant infrastructure (Roberts et al., 2010). As brine discharges are often denser and heavier than receiving marine waters, the brine streams tend to sink and spread further along the seabed than at the