Floating treatment wetlands (FTW) at microcosm scale for the removal of Cr(III) and Cr(VI)

DI LUCA, G.A.; MUFARREGE, M.M.; MONTAÑEZ, F.; HADAD, H.R.; MAINE, M.A.; NOCETTI, E.; CAMPAGNOLI, M.A.

Viena

Simposio; 9th International Symposium on Wetland Pollutant Dynamics and Control, WETPOL 2021; 2021

University of Natural Resources and Life Sciences (BOKU)

The aim of this work was to evaluate the removal of Cr(III) and Cr(VI) by Floating Treatment Wetlands (FTW) at microcosm scale. Wetlands were planted with Typha domingensis. The metal distribution in the system water-plants-bottom sediment was also studied. The FTW were designed and constructed in such a way that the roots and rhizomes remain submerged in the water while the aerial parts emerge. The treatments were 5 and 10ppm of Cr(III) and 5 and 10ppm of C(VI). Controls without FTW and without Cr addition were installed. T. domingensis plants, sediment and water were collected from an unpolluted pond from the Paraná River floodplain near Santa Fe City, Argentina. Plastic reactors (70 L) were installed outdoors under a semi-transparent plastic roof. All reactors contained 4 Kg of sediment. In the reactors, this sediment mass generates a layer of 3-4 cm depth. The experiment lasted 45 days and it was performed in triplicate. Conductivity, pH, dissolved oxygen (DO), Cr(VI) an total Cr were measured periodically in water in all treatments. Sediment and plants were sampled at the beginning and the end of the experiment. Plants were separated into roots, rhizomes and leaves. In the sediment, pH, Eh and organic loss on ignition (%OM) were measured in all treatments. Total Cr concentrations in plant tissues and sediment were determined. Besides, Cr fractionations in sediments were performed.Both Cr species were efficiently removed from water in all treatments (> 80%). The highest removals were obtained in the FTW treatments, suggesting that T. domingensis is directly involved in metal removal. Cr(III) removal was faster than Cr(VI) removal, probably due Cr(III) can be taken up by plant roots without energy cost , sorbed by the root cell walls or precipitated in the bottom sediment. Cr concentration in sediments increased in all treatments, being significantly higher in Controls without FTW. Cr was mainly accumulated in the fraction bound to organic matter in all treatments. In general, Cr bound to Fe-Mn oxides was higher in Cr(III) treatments than in Cr(VI), the opposite situation was observed for the exchangeable fraction. At the end of the experiment, Cr concentration in tissues of T. domingensis were significantly higher than the obtained at the beginning of the experiment. In all treatments, roots showed the highest Cr concentration, while the lowest concentration was measured in leaves. Since this macrophyte did not translocate the metal to the aerial parts, its pruning in winter will not affect the removal capacity of the system. In addition, the presence of FTW minimized algal formation, which would allow the biota further develop in aquatic systems. The obtained results demonstrated the ability of FTW planted with T. domingensis to remove Cr(III) and Cr(VI) from water. The use of FTW planted with T. domingensis is a promising tool to remediate water bodies contaminated with Cr.