Remineralization of Reverse Osmosis (RO)-desalted water for a Moroccan desalination plant: optimization and cost evaluation of the lime saturator post

Desalted waters produced by desalination plants cannot be directly used as they are unpalatable, corrosive and unhealthy. In order to solve the problem, a post-treatment process is always required.From the launching of the Laâyoune desalination plant, the post-treatment process was based on caustic soda for the remineralization of the produced water. Consequently, two problems were encountered during the plant operation: both the aggressivity and the corrosivity of the produced water cause the gradual damage of the water transport canalizations. To reduce these negative impacts, the caustic soda was substituted by the lime, using a saturator.The newly adopted process was described. The optimisation of the functioning conditions of the saturator by the lime was carried out. Since the replacement operation, no abnormal corrosivity or negative impact have been observed. The produced water presents a satisfactory quality with an excellent reproducibility, according to the Moroccan guidelines of drinking water.The investment cost of the remineralization step by the saturator for the Laâyoune desalination plant having a capacity of 13,000 m3/d was estimated to be 74,042 € and the calculated operating cost to 0.065€/m3.