Control of Silt Density Index of Osmosis Membranes Through Chlorine Injection and Its Effect on Cartridge Filter Replacement Period

Various suspended organic and inorganic contaminants including biological deposits, different types of algae and barnacles and causative factors of water turbidity result in irreparable damages to pretreatment systems and membranes in reverse osmosis systems. In this study, the effect of injection of disinfectant materials such as calcium hypochlorite on the reduction of silt density index (SDI) value at the inlet of reverse osmosis system has been investigated. In this research, correlations between fundamental parameters in pretreatment system such as turbidity, chlorine injection, residual chlorine content and SDI values were thoroughly analyzed and evaluated at one of the desalination plants located in Persian Gulf. The results indicated that there is a close link between the amount of chlorine injection and SDI inlet value. By adjusting the nephelometric turbidity unit values in specific ranges of 35 - 55, 55 - 80 and 80 - 150 and oxidation reduction potential in the ranges of 280 - 680, 315 - 680 and 420 - 680 mV, favorable SDI value of inlet water was obtained. SDI control via chlorine injection increased the lifetime of cartridge filters at reverse osmosis input units and reduced the operation costs significantly.