Water reuse for landscape irrigation requires the production of high quality virus-free effluents to minimize risk for human health. In order to establish the relevance of MS2 phages as an appropriate biodosimeter for UV design, a pilot plant study has been carried out with different types of wastewater effluents. The two pilot systems tested (low-pressure high output and medium-pressure UV units) were able to achieve 4 and 5 log MS2 reduction in tertiary filtered effluent at high calculated UV doses of 170 _ 10 and 300 mJ/cm2, respectively. UV disinfection was extremely efficient for MS2 inactivation in high quality effluents after reverse osmosis: detention times as low as one second and UV dose of 40 mJ/cm2 were sufficient to reach 5 log inactivation of MS2. UV irradiation also produced rapid inactivation of human pathogens such as poliovirus type 1 and indigenous enteroviruses at UV doses up to 3 times lower that those for MS2 disinfection. It was concluded that accurate UV unit design for a given type of wastewater could be ensured by pilot tests using laboratory-propagated MS2 as biodosimeter and collimated-beam tests as the calibration-check.

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