Temporal and space variation in the concentrations of pathogens is a key theme in the monitoring of drinking-water systems, resulting in underestimation of the infection risk in those monitoring programs based on punctual samples. Regarding this issue, the paper presents research carried out in pilot plant, aiming to verify the performance of the slow sand filtration, in a sudden increase in the Cryptosporidium oocysts concentration and in water turbidity. The pilot plant was operated in stationary conditions followed by the increase in the Cryptosporidium parvum oocysts concentration and, after 48h, with the same oocysts concentration, by the increase in the turbidity level. The tests revealed, for the oocysts, that, while in the stationary condition the effluent presented null concentrations medians, in the two transient conditions the effluent presented oocysts, however this difference did not accuse statistical significance. Despite the transient conditions, high average removal of Cryptosporidium sp oocysts (99,988-99,998%) was observed.
Cryptosporidium; slow sand filtration; peak load; turbidity; outbreak
