| The effects of pH, alum dose, and natural organic matter (NOM) on the removal of Cryptosporidium parvum oocysts by coagulation and sedimentation were evaluated with jar test experiments using synthetic water. The changes in zeta potential during coagulation and sedimentation were also studied. Several different combinations of pH, NOM concentration, and alum dose were tested. For each experimental combination, Cryptosporidium parvum oocyst removal and dissolved organic carbon (DOC) removal were measured.; Oocyst removals higher than 0.5 log were observed in the pH 5 to 8 range, and at 30 mg/L to 100 mg/L alum doses. When initial DOC concentration increased, oocyst removal was more efficient. Oocyst removals higher than 0.5 log and DOC removals higher than 20%, occurred at alum dose and pH conditions where aluminum hydroxide precipitate was expected to be formed.; Cryptosporidium parvum oocyst removal in synthetic water was compared with removal in natural lake water, during pilot-scale experiments with Lake Mendota water. The comparisons suggested that the presence of turbidity or the presence of a coagulant aid might improve oocyst removal. The possible use of turbidity or NOM as surrogates for Cryptosporidium parvum removal was evaluated during the pilot scale experiments. The removal of oocysts was not highly correlated with the removal of turbidity or the removal of NOM, but the pilot data suggested that low turbidity or NOM removal would increase the risk for low oocyst removal.; The same matrix of pH, alum dose, and NOM content that was used to study the removals, was used to study the zeta potential of Cryptosporidium parvum oocysts and associated particles. When no alum was added, the zeta potential of live Cryptosporidium parvum oocysts was slightly negative and did not vary with pH. Increasing NOM concentration changed zeta potential in almost all cases. The data suggested that the entrapment in an aluminum hydroxide precipitate was the most important factor for oocyst removal. |
