Giardia in Wastewater-Effect of Treatment

Giardiasis is one of the most commonly identified waterborne intestinal diseases in the U. S. A person infected with Giardia lamblia may shed on the order of$10^{8}$cysts/day, which may be collected in wastewater. The objective of this research was to study the removal of Giardia cysts by selected unit processes during wastewater treatment at three wastewater treatment plants in the U. S. Background data were obtained during a nationwide study of cyst concentrations in raw and treated wastewaters. These data suggest seasonal and geographic differences in Giardia cyst concentrations in raw wastewater. More intensive sampling indicated that cysts are removed with varying effectiveness during primary clarification and almost completely removed in the biological treatment processes. However, a direct comparison of cyst removal efficiencies showed that cyst concentrations in the trickling filter effluent were higher than in the activated sludge process effluent. These data also suggest that cysts are concentrated in the mixed liquor suspended solids and, thus, in the sludges.