GIARDIA AND CRYPTOSPORIDIUM REMOVALS by clarification and filtration under challenge conditions

This research examined removals of Giardia and Cryptosporidium by clarification (either dissolved‐air flotation [DAF] or plate sedimentation) and by dual‐media filtration following clarification. Studies were conducted for challenge conditions of cysts and oocysts (i.e., high influent concentrations) and for process design detention times and hydraulic loadings. To evaluate the effect of water temperature on performance, sets of experiments were performed for winter and spring seasons. DAF clarification performed better than plate sedimentation and consistently resulted in lower turbidity levels and particle counts. Overall log removals of Giardia and Cryptosporidium by clarification and filtration were about the same for DAF versus plate sedimentation. Although DAF is not recognized under the Surface Water Treatment Rule or the Interim Enhanced Surface Water Treatment Rule, the authors argue that based on these findings, DAF plants should receive Giardia and Cryptosporidium removal credits at least equal to those received by sedimentation plants.