Disinfection efficiency of secondary effluents with ultraviolet light in a Mediterranean area

This paper deals with the study of physicochemical and microbiological parameters affecting disinfection efficiency of secondary effluents in a municipal wastewater treatment plant, for irrigation purposes. There appears to be an important increase on turbidity values as chlorine values increases, due to the conversion of particulate organic carbon into dissolved organic carbon. The nitrification-denitrificacion processes appeared to be sensitive to changes in pH, with a minimum nitrate value in the wastewater when pH ranged between 7.018.00. With a similar behaviour, the phosphate removal was conditioned by pH, showing the highest efficiency in the same pH range. Both anions probed to be strongly correlated. Total coliforms were more UV light resistant than faecal coliforms, after an exposure of 10 min, corresponding to an UV dose of 73 mJ/cm. The experimental results for both groups of microorganisms followed first order reaction kinetics, with a gradual flattening at higher UV doses. A total elimination of both indicators would be achieved with doses over 95 mJ/cm. A previous step on the treated wastewater would improve its quality before the disinfection process.