Role of Collector Alternating Charged Patches on Transport of Cryptosporidium parvum Oocysts in a Patchwise Charged Heterogeneous Micromodel

Abstract

The role of collector surface charge heterogeneity on transport of Cryptosporidium parvum oocyst and carboxylate microsphere in 2-dimensional micromodels was studied. The cylindrical silica collectors within the micromodels were coated with 0, 10, 20, 50, and 100% Fe(2)O(3) patches. The experimental values of average removal efficiencies (η) of the Fe(2)O(3) patches and on the entire collectors were determined. In the presence of significant (>3500 kT) Derjaguin-Landau-Verwey-Overbeek (DLVO) energy barrier between the microspheres and the silica collectors at pH 5.8 and 8.1, η determined for Fe(2)O(3) patches on the heterogeneous collectors were significantly less (p < 0.05, t test) than those obtained for collectors coated entirely with Fe(2)O(3). However, η calculated for Fe(2)O(3) patches for microspheres at pH 4.4 and for oocysts at pH 5.8 and 8.1, where the DLVO energy barrier was relatively small (ca. 200-360 kT), were significantly greater (p < 0.05, t test) than those for the collectors coated entirely with Fe(2)O(3). The dependence of η for Fe(2)O(3) patches on the DLVO energy barrier indicated the importance of periodic favorable and unfavorable electrostatic interactions between colloids and collectors with alternating Fe(2)O(3) and silica patches. Differences between experimentally determined overall η for charged heterogeneous collectors and those predicted by a patchwise geochemical heterogeneous model were observed. These differences can be explained by the model's lack of consideration for the spatial distribution of charge heterogeneity on the collector surface.