Inactivation of E. coli and helminth eggs in aerobic and anaerobic effluents using UV radiation

This paper evaluates the performance of a simplified bench-scale UV-photoreactor used to inactivate Escherichia coli and eggs of Ascaris lumbricoides. The photoreactor consisted of a tubular unit constructed with PVC tube, 100 mm diameter and 45 cm total height, with a low-pressure mercury lamp adapted in the centre of the tube. The reactor was tested to disinfect the effluents from a trickling filter and from an UASB reactor, both fed with domestic sewage. The results showed an excellent performance of the photoreactor, with very high E. coli inactivation efficiencies being observed for the aerobic effluent (in the range of 4 to 5 log-units, for doses varying from 50.7 to 13.6 mW.s.cm⁻²) and also for the effluent from the UASB reactor (usually above 4 log-units, for doses of 20.3 and 13.6 mW.s.cm⁻²). In relation to the inactivation of helminth eggs, it was observed that UV radiation significantly affected the development of eggs of Ascaris lumbricoides, with the better results being obtained for radiation times of 40 and 60 seconds (doses of 13.6 and 20.3 mW.s.cm⁻², respectively), when approximately 65% of the eggs remained in the stage of single cell and only 9 to 10% were able to fully develop to the stage of motile larva.