First desalination plant in Cyprus — product water aggresivity and corrosion control

Abstract

The first major desalination plant in Cyprus is the Dhekelia Desalination Plant, which utilises the reverse osmosis system. The Dhekelia Desalination Plant started its operation on 1st April 1997, with a capacity of 20,000m3/d, and by the 18th May 1998 its capacity increased to 40,000m3/d. The plant supplies potable water to the Famagusta, Larnaca and Nicosia Districts. During the summer of 1998 there was a change in the colour of the desalinated water 20–30 km far from the plant, where the water appeared to be yellowish-brown, especially in areas where the distribution systems consisted of metal/iron pipelines. The tests results of water samples from the affected areas (Famagusta Area, whose water supply was solely from the Dhekelia Desalination Plant), undertaken from the State General Laboratory and Khirokitia WDD's Laboratory, showed high iron content in the water and the Langelier index was found negative. In order to solve the problem, it was agreed to change the range of pH from 7.0–8.0 to 6.5–9.5. The pH of the desalinated water was then increased by readjusting lime and carbon dioxide dosages. Trials to increase calcium hardness and alkalinity more caused high turbidity in water (3–4NTU). By the increase of pH to values more than 8.5 the Langelier index increased to 0.0–0.5 and the iron content decreased. Later, from September 1999 for the further increase of the hardness of the desalinated water, magnesium sulphate is added at the post-treatment stage in addition to the lime and carbon dioxide. Additional tests have been carried out by installing mild steel corrosion-coupons to the desalinated water from the Dhekelia Desalination Plant as well as at the drinking water reservoirs of different communities in order to examine the corrosive tendency of desalinated water.