AWWA PATH50784

Bench scale filtration experiments with two different silica sand media (geometric mean diameter of 0.51 mm and 1.41 mm respectively) were conducted to investigate the effect of filtration velocity (1.5 m/h, 5 m/h, 10 m/h) on the removal of Cryptosporidium parvum under clean bed conditions. Kaolin clay and 5.1 um polystyrene latex particles (PSL) were also selected to compare the transport characteristics in the removal process. Experimental results show no clear removal effect with changes in filtration velocity for Cryptosporidium parvum in contrast with results for the other selected particles where a clear increase in removal efficiency was observed as filtration velocity decreased. Although similarities in size and density are noticeable between Cryptosporidium parvum and PSL particles, previous settling experiments show differences in settling velocities among them suggesting the influence of unique removal mechanisms for this organism. A theoretical approach is used to help in the interpretation of the experimental results; single collector efficiency calculations are presented along with clean bed filter coefficients and preliminary collision coefficients for Cryptosporidium parvum and the other selected particles. Includes 32 references, tables, figures.