Occurrence of enteroviruses and Giardia cysts in sewage sludge before and after anaerobic digestion

Abstract

The disposal of anaerobically digested sewage sludge onto farmland in Pima county has created the need to evaluate the potential public health impact of pathogens which are indigenous to sewage and may be present in sludge. The occurrence of enteroviruses and Giardia cysts in sewage sludge before and after anaerobic digestion was monitored for a period of 14 months. This study showed that significant concentrations of enteroviruses and Giardia cysts are present in anaerobically digested sewage sludge being applied to farmland in Pima County. The concentration of Giardia cysts ranged from 1.33 x 103 to 8.6 x 104 per liter of raw sludge and 2.0 x 103 to 2.8 x 104 per liter of treated sludge. The concentration of enteroviruses in sludge ranged from 1.74 x 102 to 1.28 x 104 per liter before anaerobic digestion and from <2 to 5.63 x 10 2 per liter after treatment. The percentage of virus removal after anaerobic sludge digestion varied from 73% to >99.95%. Methods to study the fate of enteroviruses in the sludge-soil matrix were also evaluated. An increase in the ratio of eluant to solids seemed to enhance virus recoveries from sludge:soil mixtures.