ABSTRACT
C HLORINE is the most commonly used substance for disinfection (the selective destruction of disease-causing organisms) in the United States. (Note: Do not confuse disinfection with sterilization, which is the destruction of all organisms.) The addition of chlorine or chlorine compounds to water is called chlorination. Chlorination may have many uses within a wastewater treatment facility. Along with its most common use (disinfection of plant effluent), it is also used in odor control and in the control of filamentous organisms in the activated sludge process. Recent concerns with the effect of spills of elemental chlorine, Cl2, and with the effect of chlorination on plant effluent quality (production of disinfection by-products [DBPs], such as trihalomethanes) and the environment have prompted re-evaluation of its use as a disinfection agent for wastewater treatment. Many wastewater treatment plants have substituted hypochlorites (sodium or calcium hypochlorite) for elemental chlorine to reduce the risks associated with accidental releases and to get out from under complex regulatory compliance requirements. Despite these concerns, chlorination remains, at present, the single most important process for preventing the spread of waterborne disease and the most common means of disinfection in use.
