An accidental spill of toxic substances. The pollution caused by long established industries. The impact of pesticides used in agriculture.
The reasons may be different, but the problem is the same. That is, water pollution of rivers, streams, lakes and aquifers. And once water has been polluted, it is difficult to clean it, because the contamination does not depend solely on the polluting agents but also on other factors, included the way water moves underground.
A theoretical research study on how to generate vorticity within a porous medium opens the way to more efficient actions to tackle the problem. The results of the study have been presented in an article, “Impact of the spatial structure of the hydraulic conductivity field on vorticity in three-dimensional flows”, that has been recently published in the science journal “Proceedings of the Royal Society A”.
The main author of the study is Mariaines Di Dato, from the doctoral school in Civil, Environmental and Mechanical Engineering of the University of Trento and currently visiting fellow at the University of Southern California in the framework of the school’s international mobility scheme.
Alberto Bellin, full professor of Marine and hydraulic constructions and Hydrology at the Department of Civil, Environmental and Mechanical Engineering - DICAM of the University of Trento, co-authored the paper.
The other contributing authors are Aldo Fiori (University of Roma III), Gabriele Chiogna (Technical University of Munich) and Felipe P.J. de Barros (University of Southern California).
“Our research work - explains Alberto Bellin - shows that kinematical features, and vorticity in particular, influence the shape of solute clouds and their fate, and this might make it possible to clean contaminated aquifers. In fact, facilitating the mixing of reactants with the pollutants present in water increases the efficacy of water treatments. Motion and vorticity depend on the morphology of the aquifer, but they can also be induced, for instance using pumping devices.
“Water - says Bellin - moves very slowly because it is constrained in extremely narrow spaces in the pores of the soil; this makes it very difficult for potential reactants, introduced through wells, to mix with contaminants, therefore their efficacy is limited. However, vorticity induced by the uneven morphology of the pores or by external “forcing factors” may facilitate the mixing, making the process more successful”.
“We can picture this process as a washing machine that uses rotation to wash our clothes. Or as the vortexes that Leonardo observed in rivers and drew, with the difference that they have never been theorized before and, least of all, have never been observed in aquifers. Think of the whirlpool we create with a spoon to dissolve some sugar in a glass of water: the rotational motion speeds up the dissolution of sugar”.