Effect of ferric oxyhydroxide grain coatings on the transport of bacteriophage PRD1 and Cryptosporidium parvum oocysts in saturated porous media

To test the effect of geochemical heterogeneity on microorganism transport in saturated porous media, we measured the removal of two microorganisms, the bacteriophage PRD1 and oocysts of the protozoan parasite Cryptosporidium parvum, in flow-through columns of quartz sand coated by different amounts of a ferric oxyhydroxide. The experiments were conducted over ranges of ferric oxyhydroxide coating fraction of λ = 0−0.12 for PRD1 and from λ = 0−0.32 for the oocysts at pH 5.6−5.8 and 10^-4 M ionic strength. To determine the effect of pH on the transport of the oocysts, experiments were also conducted over a pH range of 5.7−10.0 at a coating fraction of λ = 0.04. Collision (attachment) efficiencies increased as the fraction of ferric oxyhydroxide coated quartz sand increased, from α = 0.0071 to 0.13 over λ = 0−0.12 for PRD1 and from α = 0.059 to 0.75 over λ = 0−0.32 for the oocysts. Increasing the pH from 5.7 to 10.0 resulted in a decrease in the oocyst collision efficiency as the pH exceeded the expected point of zero charge of the ferric oxyhydroxide coatings. The collision efficiencies correlated very well with the fraction of quartz sand coated by the ferric oxyhydroxide for PRD1 but not as well for the oocysts.