A Practical Approach to Meet Total Residual Chlorine Minimization Requirement at CSO Basins – Using Onsite TSS Measurement as a Guidance to Adjust NaOCl Dosage

As part of the optimization efforts to meet Total Residual Chlorine (TRC) Minimization Program for CSOs, Detroit Water and Sewerage Department initiated a study to assist CSO operators in dosing NaOCl accurately during the storm events. The objectives of the study were to identify critical factors affecting disinfection performance at the CSO facilities, to identify the relation between onsite chlorine demand and onsite TSS, to develop a model/relationship between NaOCl injection rates with onsite TSS measurements, and to verify the above model during the storm events in the field. The study showed that this approach could be used as guidance in meeting the fecal coliform limits while minimizing TRC, reducing chemical overdosing. TSS, more specifically VSS was proven to be a successful surrogate to predict chlorine demand in the influent flow to CSO basins in real time for the purpose of pacing chemical feed rates to achieve optimal disinfection performance.