Ecologically friendly wastewater disinfection techniques

The toxicity of the by-products found in water disinfected by chlorination methods prompted the regulatory agencies to insist on the use of alternative, ecologically friendly methods. This paper presents new disinfection techniques developed in our laboratory, which use sunlight or artificial UV radiation to promote photochemical disinfection processes. The sunlight was either used as global irradiation or concentrated by mirrors via an intermediary photosensitizer dissolved in water. Under these conditions the sunlight produces oxidative species in water which kill the microorganisms and oxidize organic materials. The disinfection efficiency of these methods has been proven in two experimental pilot plants operating in a continuous process with outputs of 50 and 0.15 m3h−1, and retention times of 35 min and 3 s, respectively. The former process is economically competitive and is ready for practical use, especially in countries with high solar radiation flux densities. Data about a potential industrial application of concentrated solar radiation for detoxification of industrial wastewater polluted by a pesticide (bromacil) are presented. A new technique was used for UV (254 nm) water disinfection; it employs custom-designed elliptical UV reflectors which concentrate the radiation on a UV-transparent pipe through which the wastewater flows. The 5 m3h−1 laboratory installation provided efficient disinfection of wastewater with turbidities up to 20 NTU. For large UV water disinfection plants (> 100 m3h−1), a new design is proposed, which could replace the present gravitational systems.