Enhanced removal of Cryptosporidium parvum oocysts and Cryptosporidium-sized microspheres from recreational water through filtration

Cryptosporidium species are the cause of cryptosporidiosis, which has symptoms such as watery diarrhea, dehydration, fever, nausea, body fatigue, and abdominal cramps. Infants, the elderly, and people with severely compromised immune systems are more susceptible and could die from cryptosporidiosis. Numerous waterborne outbreaks of cryptosporidiosis have been linked to swimming pools in United Kingdom, United States, Australia, and Canada. The concerns of public health and increasing demands for recreational opportunities have pushed the need for enhanced removals of Cryptosporidium from swimming pools to emergent. Unfortunately, relatively little information is available on Cryptosporidium removal from pilot-scale or full-scale swimming pools or spas. Water quality was evaluated for thirty five national swimming pools at first to evaluate the chemical constituents of the swimming pools. Based on these data, three representative swimming pool waters were developed using cluster analysis, which were applied in subsequent experiments. Based on this survey, an average pool would have a pH of 7.5 with 1.5 mg/L of free chlorine, and the alkalinity and hardness would be 94 mg/L and 238 mg/L as CaCO3, respectively. The average turbidity would be 0.33 NTU, and the DOC concentration would be 5 mg/L. Zeta potentials of Cryptosporidium oocyst-sized microspheres in three pool waters were titrated with six coagulants to determine dose-response relationships. Overdosing of organic polymer coagulants (i.e., coagulants A, B, and F) was shown to be possible. No significant differences were observed for any of the coagulants' performance in the three water formulations test. High-rate sand filtration (which refers to a filtration rate up to 37 m/h with coagulant addition before sand filtration) was evaluated in this study. A series of experiments were conducted to develop a novel operational procedure for high-rate sand filtration and provide field-relevant results. Results indicated that the highest removals occurred when coagulant was fed continuously by a coagulant pump. Extended/excessive dosing coagulant A (the only coagulant used in this part of the study) led to coagulant A build up in the system and reduced microsphere removal efficiency. Three alternative treatment techniques were evaluated for ability to enhance Cryptosporidium-sized microsphere removals from a 5,500 L pilot-scale pool, including feeding coagulants prior to sand filter, adding a layer of perlite on top of the sand filter's media without coagulation, and diatomaceous earth (DE) filtration. High-rate sand filtration without coagulation (control experiment) removed 20% - 63% of microspheres. Up to 99% Cryptosporidium-sized microsphere removal was achieved through high-rate sand filtration with coagulants A, B, D, and F at 37 m/h. Coagulant C was a chitosan-based product that removed less than 80% of microspheres under the studied conditions. Coagulant E (polyaluminum chloride) removed more than 90% of microspheres at 30 m/h. Adding perlite on the top of a sand filter increased the Cryptosporidium oocysts-sized microsphere removals to 79%, 99%, 99.7%, and 99.8% with 0.24 kg·perlite/m2, 0.37 kg·perlite/m2, 0.49 kg·perlite/m2 and 0.61 kg·perlite/m2, respectively. At least 0.7 kg·bull;DE/m 2 was required to achieve approximately 99% of Cryptosporidium-sized microspheres by DE filtration. Cryptosporidium parvum and Cryptosporidium -sized microsphere removals from full-scale swimming pools were evaluated. Coagulants B, D, E, and F were individually fed into swimming pools both with remediation dose and maintenance dose. Approximately 90% of Cryptosporidium parvum and microspheres were removed by filtration with coagulant B (1.56 mg/L), coagulant D (305g/m2), and coagulant F (1.56 mg/L) under remediation conditions. Eighty two percent of Cryptosporidium and 97% of microspheres were removed with coagulant E (0.1 mg·Al/L) under remediation conditions. Under maintenance dosing conditions: up to 93% of Cryptosporidium and 77% of microsphere were removed by coagulant B; as high as 99% of Cryptosporidium and 98% of microsphere were removed with coagulant D; 98% of Cryptosporidium and 93% of microsphere were removed with coagulant E; up to 85% of Cryptosporidium and 82% of microsphere were removed with coagulant F. Organic polymer coagulants accumulated in the swimming pool water (as measured for coagulant A concentration under the study conditions) and led to poor filter performance over time. Additionally, Cryptosporidium parvum removals by perlite/sand filter was 88%, and microspheres removal was 99.8% (0.5 kg·perlite/m2). DE filtration provided above 99.8% removals both for Cryptosporidium parvum and microspheres. Cartridge filters only achieved 22% removal of microspheres from a full-scale spa. To summarize, Cryptosporidium and microspheres could be effectively removed on a continuing basis by DE filtration, perlite/sand filtration, and high-rate sand filtration with continuously feeding of coagulant D or E. Performance of coagulant D and E tended to decrease with increased filter pressure, which could warrant additional research. Coagulant A, B, and F achieved up to 99% removal at the recommended dosage, but Cryptosporidium and microsphere removals decreased to less than 90% (typically within 48 hours) as the polymer coagulants accumulated in the pool.

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