Filtration behaviors of Giardia and Cryptosporidium--ionic strength and pH effects.

The laboratory-scale filtration tests of Giardia cysts and Cryptosporidium oocysts in both 2 mm-phi glass beads and 2 mm-phi polystyrene beads filters were conducted to investigate their filtration behaviors. The protozoan parasites were used as target particles, while the chemical system altered by changing the electrolyte concentration and pH. The results significantly indicate that ionic strength have a positive effect on the removal efficiencies for Giardia cysts and Cryptosporidium oocysts. The removal efficiency of two filters for Giardia cysts slightly decreased from pH 2.4 to 8.7 and decreased significantly in pH as pH up to 8.7, while that for Cryptosporidium slightly rippled beyond pH 8.7, and with the decrease in pH up to pH 8.7. The experimental collision efficiencies from the interactions between colloids and the filter media were calculated with a semi-empirical approach of the single sphere model and clean-bed filtration theory. The results also indicated that experimental collision efficiencies for (oo)cysts corresponded to the (oo)cysts removal efficiencies in all trials, and oocysts exhibits higher collision efficiencies than cysts.