Every year around 3.4 million people die from water-related diseases, mainly amoebiasis and diarrhoea caused by bacteria. The assessment of the efficiency of a UV light disinfection process in the inactivation of indicators, pathogen bacteria and amphizoic amoebae in a secondary treated effluent was carried out. Wastewater was irradiated with different doses of UV light using a collimated-beam reactor. Dose-response results showed that a UV dose of 15 mW·s/cm2 was enough to inactivate FC to the limit established in Mexican legislation (<1,000 MPN/100 ml) for irrigation reuse, as well as reaching a 2 log inactivation for faecal streptococci. Also, the final concentration reached for Salmonella typhi was <103 MPN, which is the minimal concentration for a disease response in humans. The isolation from the secondary effluent and the pathogenicity determination of Acanthamoeba were carried out. Amoebae were concentrated to higher concentrations than those of the effluent for irradiation tests. Radiation tests showed that amoebae required higher doses than bacteria for their total inactivation (60 mW·s/cm2 for a 2 log reduction). Results showed that UV light is an alternative to inactivate high contents of bacteria and amoebae trophozoites, although higher doses were needed for the high concentrations of amoebae used.

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