Laboratory and pilot plant scale study on water dechlorination by medium pressure ultraviolet (UV) radiation

Ultra violet (UV) dechlorination was performed to eliminate residual chlorine as the byproducts of chlorination process. UV dechlorination utilizes photon energy generated by medium pressure (MP) UV lamp to produce powerful hydroxyls which in return break down chemical bond of the residual chlorine. This study was undertaken to investigate the removal of residual chlorine under a medium pressure UV radiation and evaluate the influence of UV fluence on chlorine removal efficiency based on both laboratory and plant scale experiments. In laboratory experiments, water samples were exposed to a UV collimated beam apparatus equipped with a medium pressure (MP) UV lamp over a specified exposure time. Chlorine concentrations were measured before and after UV exposure to calculate its chlorine removal efficiency. Results showed that chlorine residual decreased over time and the removal efficiency increased as the UV fluence increased. The maximum UV fluence applied in the laboratory experiments (513 mJ/cm(2)) resulted in less than 25% of total chlorine reduction. The field experiments were conducted at a waterworks in Singapore with total capacity of 22 1/s using an existing UV system. The plant scale studies supported laboratory findings with about 9% of chlorine removal efficiency. The chlorine decay rates (fluence-based first order constant) were also calculated.