Disinfection by-product formation from chloramination of clarified water after prechlorination and preozonation

The formation of disinfection by-products (DBPs) was evaluated from a chloraminated water after coagulation with and without prechlorination or preozonation. Prechlorination enhanced formation of trihalomethane (THM), 1,1,1-trichloro-2-propanone (1,1,1-TCP) and total organic chlorine (TOCl) and the concentrations of most DBPs increased with increasing chlorine dosages. Preozonation reduced dichloroacetonitrile (DCAN) and TOCl formation but increasing ozone (O₃) dosages did not necessarily reduce the formation of THM, 1,1-dichloro-2-propanone (1,1-DCP) and total organic bromine (TOBr). Increasing coagulant doses reduced the formation of most DBPs and TOCl. However, the formation of TOBr cannot be readily controlled by coagulation in most cases except the case involving prechlorination.