Combined sewer overflows (CSO) generally discharge raw sewage, watershed runoff and its pollutants and scoured materials accumulated in the collection systems. These discharges contain pollutants (e.g., suspended solids, pathogenic microorganisms, viruses, cysts, chemical, and floatable debris), which, when discharged into receiving water bodies, may cause adverse impacts.
CSO disinfection is achieved through the reduction of solids and the oxidation and/or radiation of pathogens. Common chemical oxidizing agents include chlorine, bromine, and hydrogen peroxide or their compounds. Other alternative disinfectants include ultraviolet radiation and ozonation.
Chlorine is applied to a CSO either in gaseous form or as an ionized solid. It is important to note that the prevailing disinfection mechanism will depend on factors such as microorganism in question, wastewater characteristics, and chlorine compound used.