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Chennai Seawater Desalination Plant (SWDP), with a production capacity of 100 MLD with a maximum extended capacity in future of up to 120 MLD, is located at Minjur (Chennai, India) and is being developed under a 25-year DBOOT contract. It will supply drinking water to the city of Chennai which currently experiences poor water quality, water shortages and restrictions. The Chennai SWDP is situated in close proximity to a river creek, an important port and an overpopulated urban area, resulting in a difficult to treat raw water source subject to very high suspended solids values, and a high level of pollutants. The different pilot plant treatment processes (gravity settling, flotation, gravity filtration and pressure filtration) can be connected in series or in parallel. Therefore, this paper describes the pilot plant studies performed to determine the feasibility, efficiency and best operation mode of the pre-treatment process designed for Chennai SWDP at the time of the publication as well as the main conclusions inferred from those studies. By applying the results of these studies to the full-scale design, the performance of the RO membranes will be kept optimal while reducing production and maintenance costs. It can be concluded that this pilot study has been important in developing the Chennai SWDP design, and provided valuable information for the plant start up and its operation later on.

With a production capacity of 100,000 m 3 /d, Qingdao seawater desalination plant (SWDP) will be located in the eastern part of China (Shandong Province) and it is being developed under a 25-year DBOO contract in order to supply drinking water to this city. The Qingdao SWDP is situated near to a seawater lagoon shared with other already existing factory and the raw water is withdrawn to it from the shallow waters of the bay by means of a submerged pipe when the tide is high. Therefore, the raw water has a high suspended solids values and a high level of pollutants. The desalination technology selected has been reverse osmosis (RO) with a previous and specific pretreatment which has been designed to get optimal seawater previously to RO membranes. This pre-treatment consists on: self-cleaning travelling screen, dissolved air flotation (DAF), 100 mm filtration, ultrafiltration (UF). Nowadays, to determine the feasibility and efficiency of the process, it is performing some experimental tests by means of different pilot studies. Therefore, this paper shows the engineering design of a high efficiency SWDP that will significantly increase the water resources of the region.