Role of collector alternating charged patches on transport of cryptosporidium parvum oocysts in a patchwise charged heterogeneous micromodel

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% Fe₂O₃ patches. The experimental values of average removal efficiencies (η) of the Fe₂O₃ 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 Fe₂O₃ patches on the heterogeneous collectors were significantly less (p < 0.05, t test) than those obtained for collectors coated entirely with Fe ₂O₃. However, η calculated for Fe₂O 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 Fe₂O₃. The dependence of η for Fe ₂O₃ patches on the DLVO energy barrier indicated the importance of periodic favorable and unfavorable electrostatic interactions between colloids and collectors with alternating Fe₂O₃ 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.