Evaluating surrogates for Cryptosporidium removal in point‐of‐use systems

Abstract

Because of their small size, Cryptosporidium oocysts cannot be easily filtered from water. This study evaluated the use of surrogates for measuring the microbial treatment performance of two point‐of‐use devices incorporating filtration with electrostatic charge interaction mechanisms. Both systems were challenged with Cryptosporidium oocysts (4‐6 μm), Bacillus subtilis (B. subtilis) spores (~1.2 μm), polystyrene latex (PSL) beads (~ 3 μm), Escherichia coli, and MS2 bacteriophage. The target biological contaminants were more effectively removed than the PSL beads, and the smaller B. subtilis spores mimicked Cryptosporidium oocyst removal more closely than the ~ 3‐μm PSL beads. Thus, surface charge appears to be an important factor for microorganism attachment, and B. subtilis spores should be considered a more appropriate surrogate than PSL beads for evaluating Cryptosporidium movement through charged media. For noncharged devices, PSL beads may still be useful as a surrogate for Cryptosporidium.