AWWA WQTC65937

The objective of this powerpoint presentation was to evaluate the dependence of Cryptosporidium oocyst and Giardia cyst removal on the influent concentration of oocysts and cysts. The sampling approach included: Grab Sampling (10 L samples, concentrated to 200 mL with CSCC); continuous sampling (CSCC hooked up directly to filter effluent for 30 hour run time); and, CSCC concentrated 288 L of filter effluent to 200 mL. The analytical approach at Wisconsin State Laboratory of Hygiene (WSLH) included: centrifugation; fluorescent antibody staining; flow cytometry used to separate microbes from other particles in sample; and, separated microbes placed on slide and counted by microscopy. The analytical approach at Marshfield Clinic Research Foundation (MCRF) included: membrane filtration; fluorescent antibody staining; and, counting under a microscope. Potential implications include: water utilities using conventional surface water treatment may not be achieving the level of oocyst and cyst removal that they think they are achieving; when detected, typical counts in U.S. source waters are on the order of 100 microbes/L or less; and, extrapolation of Lake Mendota results to this level suggests removal may only be 0.5 log to 1.0 log, rather than 2.5 log to 3.0 log. Includes table.