AWWA WQTC69368

Bench-scale experiments were conducted to evaluate the reaction kinetics between chlorine and hydrogen peroxide in effluent from the ultraviolet (UV)/H₂O₂ advanced oxidative process (AOP) at the Valley County (Valley County) Water District SA1 Arrow Lante treatment plant in Baldwin Park, California. A relatively new potassium titanium oxalate method was used for hydrogen peroxide analysis in the bench experiments. Results from the experiments revealed that the reaction between chlorine and hydrogen peroxide is complete within approximately three minutes in UV effluent from Valley County. The experiments were designed to test the hypothesis that Valley County's difficulty in maintaining a target chlorine residual in the distribution system is at least partially due to continued reaction of chlorine with residual hydrogen peroxide downstream of the finished water chlorine monitoring point. Based on Valley County's chlorine addition and monitoring configuration (i.e., chlorine analysis approximately 20 seconds after chlorine addition), the chlorine-hydrogen peroxide reaction is not complete in water sampled by the online chlorine monitor, explaining the additional drop in chlorine concentration in the distribution system. Valley County is in the process of moving their chlorine injection point further upstream of their online chlorine monitor to allow adequate reaction time with H₂O₂ prior to Cl analysis, ultimately aiding in process control. Includes 3 references, tables, figures.