Disinfection is a necessary treatment for nearly all reclaimed and reuse wastewater project. The objective is the removal and the control of bacteria and virus growth. The disinfection process can have an excellent performance only with well-treated waters. Chemical disinfectants (chlorine, dioxide of chlorine, ozone, etc) as UV radiations, do not have actually a strong disinfection action when microorganisms are physically protected by suspended solids, except when elevated doses of additives are used that, however, increase the presence of noxious residual products. The most common type of disinfection is the chlorination with dosages of 5 to 20 mg/l, and with a maximum contact time of two hours. Since the chlorine can be harmful for the irrigated crops, the residual chlorine must be checked if wastewaters have to be reused for irrigation. The dechlorination can be carried on using chemical agents, such as the sulphur dioxide, or processes as carbon absorption. Another effective oxidant substance is the ozone, that also allows a reduction of the bad odours and an improvement of the organic constituent biodegradability. The ultraviolet (UV) disinfection has received an increasing attention over the last years as a valid alternative to the chemical disinfection processes. The effectiveness of UV disinfection depends essentially on the degree of the penetration of radiation through the superficial layer of the water around the lamp. For this reason, when a UV disinfection process is used, a filtration treatment is normally required.

Back