Application of pH-ORP titration to dynamically control the chlorination and dechlorination for wastewater reclamation

Abstract

An automatic pH–ORP (oxidation–reduction potential) titration device was developed and applied to dynamically control the wastewater chlorination and dechlorination doses in this study. In the pH–ORP titration and back-titration process, the monitoring peaks and valleys on the pH and ORP profiles could indicate the influent concentrations of chlorine-consumed materials (mainly ammonia nitrogen for chlorination) and residual chlorines (for dechlorination). The required chlorination dose can be optimized by multiplying the identified ammonia concentration to the optimal Cl/N ratio (chlorine to ammonia nitrogen weight ratio). The required dechlorination dose was also found to be correlated to the residual chlorine concentration with linear relationship. Therefore, an innovative and dynamic feed-forward dose control strategy was proposed. Finally, a series of continuous wastewater chlorination and dechlorination experiments were conducted to evaluate this proposed control strategy. Two control factors, CF C and CF D , were also used to regulate the doses to meet the water qualities for different wastewater reclamation proposes. The experimental result has shown that both chlorination and dechlorination doses were effectively controlled, and appropriate disinfection efficiencies and remaining chlorine residuals in effluent were achieved.