Reduction of Infectious Cryptosporidium and Microbial Indicators in Wastewater Effluents by Disinfection with UV Irradiation or Chlorine

When properly treated, domestic wastewater should be considered a potential reliable water source in arid and semi-arid regions of the world for none-potable purposes. In Israel and other countries around the world, the main biological standards for water reuse are based on fecal coliform (FC) and turbidity. Furthermore, in secondary treatment, the Israeli standard for water reuse and for unrestricted irrigation comprises additional steps such as filtration and chlorination. The present study was conducted to compare the reduction efficiency of live Cryptosporidium oocysts in wastewater effluents by filtration and disinfection by either UV irradiation or chlorination. Cryptosporidium oocysts infectivity reduction was compared to those of the conventional microbial indicators (FC). The study was conducted in two full-scale wastewater treatment plants. The average concentration of FC and Cryptosporidium in secondary effluent was 2.8 × 10 cfu/100ml and 5.7 oocysts/10L, respectively. Infectious Cryptosporidium oocysts were detected in 2 out of 7 secondary effluent samples (28.5%). Infectious Cryptosporidium oocysts were not detectable in UV disinfected tertiary effluent. Conversely, 3 out of 7 (42.8%) tertiary effluent samples disinfected with chlorine were positive for infectious Cryptosporidium oocysts. The results of this study revealed that the application of a multi barrier treatment, including UV irradiation, for the reduction of Cryptosporidium oocysts and microbial indicators could improve tertiary effluent safety for unrestricted irrigation and other reuse purposes.