Cryptosporidium was the cause of 65 of the reported waterborne disease outbreaks in swimming pools between 1993 and 2002, and Cryptosporidium continues to pose a significant threat to public health in these venues. Cryptosporidium is very resistant to chlorine disinfection (surviving several days to a week under typical free chlorine and pH levels found in swimming pools) because it is protected by thick-walled outer shell, called an oocyst wall. This leaves filtration to serve as the primary means of safeguarding public health against cryptosporidiosis. This research work was focused on sand filtration as barrier to Crypotosporidium in swimming pools. In addition to straight sand filtration, multiple doses and types of chemical polymers (or clarifiers) were used in an innovative approach to optimize Cryptosporidium removal from swimming pool water and to better understand the removal of Cryptosporidium oocysts via commonly-used sand filters.
In Phase I, the electrostatic surface charge (or zeta potential) of oocysts was measured under a range of water conditions, coagulant types, and coagulant dosages applicable to swimming pool systems to identify optimum coagulant dosages for subsequent experiments. In Phase II, both uncoagulated and a variety of batch coagulated water samples were filtered through sand filters under simulated swimming pool conditions, and the oocyst removals were calculated after the first and successive passes through the bench-scale filter. Phase III involved determining oocyst removals under uncoagulated and optimally coagulated conditions (based on Phase II results) in a 1:25 scale mode
