Some conservative pollutants (trace elements) contained in biosolids may cause significant environmental impacts when applied in soils, even if present at low concentrations. In order to enable a better understanding of the transport mechanisms into soil, two sets of tracer assays were performed in a saturated soil column at flow velocities from 0.26 to 0.65 m h-1 for three section lengths. The response curves obtained were analyzed based on their moments and the magnitude of longitudinal dispersion was estimated by curve-fitting an analytical solution of the Advection-Dispersion-Reaction equation.
The results showed a considerable amount of longitudinal dispersion through the maximum media length, which seemed to be related to the presence of stagnated areas approaching its behaviour to plug flow. In the column section close to the entry the flow regime was characterized by a completely mixed flow pattern with a large extent of dispersion, which seemed to be related to the presence of dead zones and hydraulic short-circuiting. The analytical solution of the advection-dispersion-reaction equation, developed for a semi-infinite system, explained well the tracer results for the overall column length. From a statistical point of view, it was also concluded that the variation in magnitude of dispersion seems to be independent of the flow velocity applied.
Conservative pollutant transport, dispersion, least-square optimization, moment analysis.
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