Heavy metals in Phragmites australis and Phalaris arundinacea biomass in constructed wetlands for wastewater treatment: a comparative study

Jan Vymazal1, Tereza Břdezinová1
1 Czech University of Life Sciences Prague, Faculty of Environmental Sciences, Department of Applied Ecology, Kamýcká 29, 165 21 Praha 6, Czech Republic

O 8.5 in Trace element and metal biogeochemistry

14.07.2014, 15:15-15:35, H20

Common reed (Phragmites australis)  and Reed canarygrass (Phalaris arundinacea) are frequently used in constructed wetlands for wastewater treatment in the Czech Republic. Most constructed wetlands in the Czech Republic have been designed with horizontal subsurface flow and majority of these systems treat domestic or municipal wastewater from small settlements.  Heavy metals are usually not the target parameters in municipal sewage and therefore the information on the heavy metals in the constructed wetland vegetation is limited. The objectives of this study was to evaluate and compare concentrations of heavy metals (Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn) in Phragmites and Phalaris growing  in two constructed wetlands during the period 2002 – 2013. In both constructed wetlands, Phalaris and Phragmites are planted together and the vegetation was sampled in 2002, 2004, 2006, 2007 and 2013. In each constructed wetland both plants were sampled in four replicates from a quadrant 0.25 m2 during the peak biomass. The stems were cut at the ground level, divided into stem, leaves and flowers, dried at 60°C to a constant weight and ground. The belowground biomass from the same quadrants was thoroughly washed by pressure water, divided into roots and rhizomes and handled the same way as aboveground biomass. The homogenized samples were mineralized using pressure microwave apparatus in a mixture of H2O2 and HNO3 under high temperature and pressure and analysed using ICP MS. The results revealed that in the aboveground biomass, higher concentrations were measured in Phalaris for Cr, Cu, Fe, Ni and Pb. On the other hand concentrations of Cd, Mn and Zn were higher in Phragmites.  In the belowground biomass, concentrations of all metals but Cu were higher in Phalaris. Standing stocks for all monitored metals in aboveground biomass were higher in Phalaris with the exception of Mn and Zn. In belowground biomass, all standing stocks were higher in Phalaris than in Phragmites. In Phragmites, the belowground/aboveground standing stock ratios varied between 0.46 (Mn) to 10.2 (Fe). In Phalaris, the ratios varied between 0.75 (Ni) and 8.1 (Fe). In general, the results indicated that more heavy metals was accumulated in Phalaris biomass however, the difference was mostly statistically significant. Therefore, both plants should be regarded equally efficient in heavy metal accumulation from the wastewater.

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last modified 2014-06-20