May 17, 2018
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.
This project conducted a literature review to identify potential Cryptosporidium surrogates and use a small pilot-scale treatment plant consisting of coagulation, flocculation, sedimentation and granular medium filtration system to evaluate the removal of the surrogates in comparison with Cryptosporidium. In parallel, this project also evaluated process measures such as turbidity or particle removal to determine if any are suitable indicators of on-going removal of Cryptosporidium. This work identified suitable surrogates for future full-scale validation experiments (a Phase II project). Furthermore, this project also identified the challenges and knowledge gaps which need to be addressed in order to conduct any Phase II full-scale validation project.
The report is now available for WaterRA members to download from the 1079 project page.
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