Experiences with the conventional pretreatment system in the seawater reverse osmosis plant at Kalpakkam

A 1800 m³/day Seawater Reverse Osmosis (SWRO) plant was commissioned in October 2002 at Kalpakkam, India, as part of the Nuclear Desalination Demonstration Project (NDDP). The conventional pretreatment scheme was adopted consisting of a lamella clarifier, pressurised sand filter, activated carbon filter and cartridge filter. The dosing of pretreatment chemicals, ferrous sulphate and polyelectrolytes was done at optimum levels to keep the Silt Density Index (SDI) value between 3 and 4. Experimental trials indicated that the dosing of chemicals may not be necessary below a particular turbidity level. Similarly, the dosing of proprietary antiscalant chemicals instead of sodium hexametaphosphate to control the sulphate scaling did not affect the process performance. Rather it helped the operation, as the antiscalant is in liquid form and the addition of hydrochloric acid could be eliminated. The overall cost per unit water production was also reduced.