Project Number # 1079
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Background and Relevance
Many conventional drinking water treatment plants use granular media filtration as a major barrier to Cryptosporidium entry into the potable water supply. Currently, turbidity is used as a performance target to grant Log10 treatment credits for Cryptosporidium. However, the actual performance of full-scale granular media filters for Cryptosporidium removal has not been directly measured and Log10 removal has been estimated based on studies using lab- and pilot-scale systems. It has also been suggested that oocysts can break through filters even when the turbidity is within guideline targets, with such events often associated with spikes in turbidity that are not sufficient to trigger an exceedance. Full-scale validation of water treatment plants for Cryptosporidium removal would provide more confidence in the performance of individual systems under local conditions, but suitable surrogates for Cryptosporidium are not available or have not been well validated.