A two-year monitoring program of microbiological and physical–chemical parameters at 2 waste water treatment plants (WWTPs) in Mallorca (Spain) was performed in order to (1) evaluate the efficiency of lagooning and UV radiation as tertiary treatment processes; (2) determine the characteristics of wastewater effluent for its potential agricultural reuse; and (3) establish correlations between bacteriological and virological parameters. The presence of currently established bacterial indicators (total coliforms, faecal coliforms, Escherichia coli, enterococci, and spores of sulphite-reducing clostridia), virological (enteroviruses, somatic coliphages, F-specific coliphages, and phages infecting Bacteroides fragilis and Bacteroides thetaiotaomicron), and helminth eggs were tested during this study. Bacterial and viral indicators were removed at least with one log reduction in the lagooning system, and to a lesser extent with UV-radiation treatment. The lagooning system was less efficient in removing phages and viruses than were bacterial indicators, with the exception of F-specific phages. Phages of B. fragilis and B. thetaiotaomicron were less removed than all of the other microbiological parameters. In the UV-radiation treatment, however, the faecal coliforms proved the most sensitive, while clostridial spores, somatic coliphages, Bacteroides phages, and enteric viruses were the more resistant. Helminth eggs were not detected in any samples from effluents of either the secondary or tertiary treatments.

Indicator levels in both treatments met the established regulations of both local and national authorities for the disposal or reuse of wastewater in irrigation for non-human crop. We demonstrate that somatic coliphages are effective indicators of enteric viruses in both of the WWTPs studied.

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