Pilot-scale electrochemical disinfection of surface water: assessing disinfection by-product and free chlorine formation

Electrochemical disinfection of surface water using mixed metal oxide anodes was evaluated in a pilot-scale demonstration. Disinfection rates, chlorine generation, energy demand, and generation of disinfection by-products were monitored over the 190-day study. Particular attention was given to the generation of trihalomethanes (THMs) and haloacetic acids (HAAs) during the electrochemical treatment cycle. In addition, the potential for generation of THMs and HAAs during post-treatment storage of the water was assessed. The electrochemical treatment system resulted in a 2- to 3-log removal of total heterotrophic bacteria, with values below detection (<1 CFU/mL) often observed. Disinfection occurred with only very low levels of observed chlorine generation (<0.1 mg/L), suggesting that alternate disinfection mechanisms likely played a significant role in the observed removal of bacteria. THM and HAA concentrations after treatment were consistently well below regulatory levels. Results also showed that electrochemical treatment significantly reduced the formation of bromoform when the water received subsequent exposure to hypochlorite. Removal of naturally occurring bromide in the water by the electrochemical system may have been the cause (in part) for this observed mitigation of bromoform formation. The formation of calcium scale on the cathode surface over time was the primary operational challenge.