Giardia and virus monitoring of sewage effluent in the state of Arizona

Virus and Giardia monitoring of wastewater used for irrigation has been initiated as a means for controlling the public's exposure to these pathogens. Treatment facilities must produce wastewater with no detectable Giardia cysts and one virus plaque forming unit (pfu) per 40 liters (L) for unrestricted reuse. For restricted reuse, 125 pfu/40 L is allowed. Methods based on filtration were used to monitor facilities at monthly, quarterly or biannual frequencies. Results after two years of monitoring are presented. All 11 treatment facilities produced water meeting the virus standard of 125 pfu/40 L. Only plants which used sand filtration and disinfection achieved consistent levels of virus below 1 pfu/40 L. Out of 70 samples, 74% contained no detectable viruses. Giardia was detected in 29 to 50% of the samples. Most plants would need to upgrade their treatment in order to meet standards for unrestricted irrigation.