EVALUATION OF ENHANCED MIXING AND ORP CONTROL FOR WASTEWATER DISINFECTION

A wastewater disinfection system utilizing oxidation-reduction potential (ORP) control and enhanced mixing sodium hypochlorite chemical feed was evaluated. The principal objective of the testing was to reduce effluent total residual chlorine (TRC) concentrations while not compromising compliance with effluent fecal coliform concentrations. The system was evaluated by comparison of effluent fecal coliform concentrations, effluent TRC, and sodium hypochlorite consumption during pilot system control with those values measured during primary system control. In addition, diurnal fluctuations of selected constituents (ammonia, TRC, and free residual chlorine) were analyzed to correlate with overall disinfection efficiency. The testing was performed at two facilities for three months each. Both facilities currently employ a primary disinfection system utilizing effluent TRC feedback control and flow trimming to adjust sodium hypochlorite chemical feed. Based on these investigations, ORP control appears to be highly sensitive to ammonia concentrations, to the detriment of reducing effluent TRC.