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Cryptosporidium surrogate removal in pilot-scale rapid sand filters comprising anthracite, pumice or engineered ceramic granular media, and its correlation with turbidity.

Abstract

Removal of Cryptosporidium protozoa by granular media filtration is a critical step in conventional multi-barrier drinking-water treatment, and turbidity is commonly used to monitor system performance. We assessed the efficiencies of 3 different filter media at removing a Cryptosporidium parvum surrogate comprising glycoprotein-coated 4.5 μm polystyrene microspheres, and evaluated the responses of turbidity levels to surrogate concentrations. Field trials were performed using pilot-scale rapid sand filters comprising anthracite, pumice or engineered ceramic sand, while simulating a typical water treatment plant's operational conditions. Data from 44 trials indicated that the surrogate's log10 reduction values (LRVs) based on the peak concentrations were >3 in 100%, 70% and 41% of the trials with the ceramic sand, pumice sand and anthracite filters, respectively. The LRVs achieved in the ceramic sand filter trials (4.44 ± 0.38) were significantly greater than those in the pumice sand (3.21 ± 0.30) and anthracite (3.01 ± 0.70) filter trials (P < 0.00001).

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