Will Chlorine Disinfection Be Banned Because of THMs in Highly Treated Reuse Waters

In many States, the concentrations of Trihalomethanes (THMs) in disinfected wastewater effluents entering reuse systems and receiving waters are required to be reduced to very low levels. Plants using chlorine for basic disinfection have varying levels of THMs based on their dosage, contact time, concentrations, and residual requirements. Most regulators are particularly interested in the effluent concentration of dichlorobromomethane and dibromochloromethane, which are two of the THM compounds often regulated in the NPDES permit. If the EPA or State lower the current THM concentration levels for these two disinfection byproducts, then disinfection using chlorine may not be feasible for wastewater effluents depending on the discharge point.This paper addresses the investigation of the formation and control of THMs in the treated wastewater effluent, and presents case histories from several treatment plants in Florida. In particular, the work addressed the chemistry of formation and etiology of THMs in the wastewater effluent of five Florida Wastewater Treatment Plants using chlorine based disinfection, including summaries of the historical plant data and plant processes related to THM formation, and a summary of cost evaluations of alternative disinfection and THM control methods.