Wastewater Disinfection Efficiency Using One- Step and Two-Step Chlorination

One-step chlorination (OSC) is a common method, generally implemented as the last step of wastewater treatment plants (WWTPs) and water treatment plants (WTPs). Improving disinfection efficiency is necessary to increase pathogen and organic matter removal. Two-step chlorination (TSC) has been studied as a new method of chlorination. This study aimed to compare OSC and TSC efficiency for coliform and organic matter removal. Chlorination was performed in a batch system and at laboratory scale using calcium hypochlorite. Samples were collected from WWTP effluent in an industrial estate located in Indonesia. The samples underwent the adsorption process beforehand. Chlorine dosage at 10-110 mg/L, at a 10-200-second time interval, and with a dosage ratio of 3:1-7:1 were evaluated. Results showed that the optimum dose for OSC is 80 mg/L. The optimum condition for TSC is a 50-second time interval and a 5:1 dosage ratio between the two steps. With the same total dose as in OSC, TSC improved efficiency for COD, BOD, and coliform removal up to 12%, 35%, and 0.39-log reduction, respectively (p < 0.05). Moreover, trihalomethane (THM) formation was reduced up to 13% by using the TSC method. However, an increasing ammonia concentration occurred because of the OSC and TSC processes (p < 0.05)