Removal of Cryptosporidium and Giardia through Conventional Water Treatment and Direct Filtration

Pilotand full-scale evaluations of Giardia and Cryptosporidium cyst removals through direct filtration and conventional water treatment were conducted by the Utah Department of Environmental Quality. Cysts were seeded continuously in a step dose at a 0.5 gpm pilot plant, and in a spike at a 900 gpm full-scale plant; both plants were operated under conventional treatment and direct filtration regime. The results of 20 pilot-scale cyst seeding trials and 8 full-scale trials indicated that source water quality (turbidity and algal content), as well as treatment effectiveness in removing turbidity, controlled the removal of seeded Giardia and Cryptosporidium. Changes in source water quality influenced removal rates more than the mode of treatment. Higher removal rates were consistently observed for Giardia cysts (3.3-log) than for Cryptosporidium oocysts (3.0-log). A high correlation was found between cyst removal rates and removal of the respective size particles; poorer correlation existed between cysts and turbidity removal, while no significant correlation was established between the removals of cysts and heterotrophic bacteria. To assure that the best available detection method was used in enumeration of the cysts in raw and treated water, two versions of the immunofluorescence staining method were evaluated for their efficiencies in detecting Giardia cysts and Cryptosporidium oocysts seeded at known concentrations in water: (1) the ASTM method for detection of Giardia cysts and Cryptosporidium oocysts in low-turbidity water and (2) a modified Sauch’s procedure employing sampling by 2.0 μm membrane filters, Percoll/Percoll step gradient flotation, and immunofluorescence staining on 2.0 μm porosity polycarbonate membrane filters. The second method was selected, since it was characterized by higher recovery rates in all three types of waters tested: raw surface water, partially treated water from a flocculation basin, and filtered water. Cyst and oocyst recovery efficiencies decreased with increasing water turbidity regardless of the method used. Recoveries of seeded Giardia cysts exceeded those of Cryptosporidium oocysts in all types of water sampled. This Project Summary was developed by EPA’s National Risk Management Research Laboratory, Cincinnati, OH, to announce key findings of the research project that is fully documented in a separate report of the same title (see Project Report ordering information at the back).