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EVALUATING SURROGATES FOR CRYPTOSPORIDIUM REMOVAL IN POINT-OF-USE SYSTEMS
Citation:
MUHAMMAD, N., R. SINHA, E. KRISHNAN, H. PIAO, C. L. PATTERSON, J. COTRUVO, S. L. CUMBERLAND, V. P. NERO, AND C. DELANDRA. EVALUATING SURROGATES FOR CRYPTOSPORIDIUM REMOVAL IN POINT-OF-USE SYSTEMS. JOURNAL OF THE AMERICAN WATER WORKS ASSOCIATION. American Water Works Association, Denver, CO, 100(12):98-107, (2008).
Impact/Purpose:
To inform the public.
Description:
Cryptosporidium oocysts are resistant to chlorination and are particularly difficult to remove from drinking water by filtration due to their small size (4 µm to 6 µm). Filters with nominal pore sizes of 1 µm are recommended to assure effective removals. Properly designed and operated Point-of-Use (POU) treatment systems have numerous applications for providing a final barrier from contamination of drinking water in the home especially for water that is not provided from a public water supply that meets drinking water standards. This paper summarizes the results of studies that were conducted at the U.S. Environmental Protection Agency (EPA) Test and Evaluation (T&E) Facility in Cincinnati, Ohio to examine surrogates for measuring the performance of POU units. Two different POU systems utilizing electrostatic charge interaction mechanisms in some respect were used to examine the removal of several microbial contaminants in drinking water. The units were challenged with high doses of several microorganisms including Cryptosporidium oocysts, B. subtilis spores (~1.2 µm) and ~ 3 µm polystyrene latex (PSL) beads as surrogates for Cryptosporidium removal, E. coli and MS2 bacteriophage (as a surrogate for viruses). The results demonstrated that both POU systems were much more effective in removing the target biological contaminants than the PSL beads. The studies showed that the smaller B. subtilis spores more closely mimicked Cryptosporidium oocyst removal than did ~3 µm PSL microspheres (beads). The gap of removal efficiencies between microspheres versus Cryptosporidium and B. subtilis was so great that it calls into question protocols that use microspheres for testing Cryptosporidium removal by filtration when charged interactions between media and microorganism are a removal mechanism in addition to physical filtration. The implication is that surface charge is a more important factor than size exclusion for filtration effectiveness, if positively charged surfaces are available for negatively charged particulate (microorganism) attachment. This also supports studies by other researchers comparing B. subtilis spores and Cryptosporidium oocysts in lime-softened public water supplies, and provides impetus for greater use of B. subtilis spores as a simple and inexpensive test surrogate for coagulation/filtration removal of Cryptosporidium oocysts in public water systems. Based upon the above one could postulate similar potential value of B. subtilis spores vs. PSL beads as surrogates for Cryptosporidium migration in charged ground media such as karstic limestone.
