Oxidation reduction potential as a measure of disinfection effectiveness for chlorination of wastewater

Chlorine is commonly added as a disinfectant to potable water before distribution and to wastewater before discharge. The chlorine residual is usually monitored to verify proper disinfectant dose and to ensure adequate pathogen kill before wastewater discharge. Measuring chlorine residual usually requires time-intensive techniques, whereas the measurement of oxidation-reduction potential (ORP) is a possible alternative method with real-time results. Experiments were conducted in which inactivation of total coliform, E. coli, and enterococci was measured with chlorine dose, and ORP was evaluated as a predictor of kill of these organisms. Raising ORP through chlorination was effective at disinfection, yet disinfection effectiveness was found to be not well predicted with ORP measurements.