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Early breakthrough of colloids and bacteriophage MS2 in a water-saturated sand column

Chrysikopoulos Constantinos, Arturo A. Keller , Sanya Sirivithayapakorn

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Summary

We conducted column-scale experiments to observe the effect of transport velocityand colloid size on early breakthrough of free moving colloids, to relate previousobservations at the pore scale to a larger scale. The colloids used in these experimentswere bacteriophage MS2 (0.025 mm), and 0.05- and 3-mm spherical polystyrene beads, andwere compared with a conservative nonsorbing tracer (KCl). The results show that earlybreakthrough of colloids increases with colloid size and water velocity, compared with thetracer. These results are in line with our previous observations at the pore scale thatindicated that larger colloids are restricted by the size exclusion effect from sampling allpaths, and therefore they tend to disperse less and move in the faster streamlines, if theyare not filtered out. The measured macroscopic dispersion coefficient decreases withcolloid size due to the preferential flow paths, as observed at the pore scale. Dispersivity,typically considered only a property of the medium, is in this case also a function ofcolloid size, in particular at low Peclet numbers due to the size exclusion effect. Otherparameters for colloid transport, such as collector efficiency and colloid filtration rates,were also estimated from the experimental breakthrough curve using a numerical fittingroutine. In general, we found that the estimated filtration parameters follow the clean bedfiltration model, although with a lower filtration efficiency overall.

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