While the use of chlorine has long been considered as the disinfectant of choice for majority of the treatment systems because of its reliability, the same may not be a feasible alternative for all combined sewer overflows (CSO). This unsuitability as a disinfectant is based on several factors such as: (i) intermittent occurrence of CSO events and high variability of flow rate; (ii) high concentration of suspended solids; (iii) varied temperature and bacterial composition; (iv) prohibition imposed on residual disinfectants from chlorine disinfection on receiving bodies; and (v) location of outfalls, which are often in remote areas and may require an automated disinfection system.
The development of alternative disinfectants was spurred by the increased health and safety concerns arising from the use of chlorine disinfection to treat CSOs. Alternatives have been developed and continuously evaluated in disinfecting wastewater being discharged to various receiving bodies of water. These alternative disinfection methods include chlorine dioxide, ozonation, ultraviolet (UV) radiation, peracetic acid, and Electron Beam Irradiation (E-Beam).