Enhanced Chlorination Strategy to Tackle the Challenge of Stringent THM Limits: A Journey from Bench Scale Testing to Full Scale Demonstration

City of Vacaville Easterly WWTP is currently facing an unintended consequence resulting from an upgrade in the treatment process from BOD removal to Biological Nutrient Removal (BNR), which has led to the significant generation of THMs without the presence of ammonia. The WWTP is on a time schedule order (TSO) to meet more stringent THM limits in its final effluent set forth by CRWQCB. To address the challenge, a study was conducted to explore alternative methods of chlorination that could effectively and reliably reduce THMs while also ensuring Total coliform compliance. The study included both bench scale dose-response tests and a fullscale demonstration. Through the bench scale testing, various chlorination methods were examined, ultimately identifying that "step dosing" effectively reduced THM levels. The subsequent field demonstration validated the feasibility and reliability of "step dosing" as an alternative approach for minimizing THM concentrations and maintaining Total coliform compliance in full-scale operations.