Efficiency in removing pollutants by constructed wetland purification systems in Poland

The aim of this study was to compare the efficiency between Phragmites communis, Salix viminalis, and Populus canadensis in removing the heavy metals Al, Ba, Mn, Ni, Sr, V, Zn, Cd, Cu, and Pb and the eutrophying macroelements phosphate, nitrate, nitrite, ammonia, chloride, sulfate, Ca, Mg, K, and Fe from sewage in subsurface flow constructed wetlands in Poland. The effectiveness of the sewage treatment system was higher in summer compared to winter for the removal of (1) all heavy metals, phosphate (P) and mineral nitrogen (N) for all of species, (2) sulfates (S) for Phragmites and Salix, (3) iron (Fe) for Salix, and (4) chloride (Cl) for Salix and Populus. Analysis of variance indicated that there was no significant difference between the purifications systems in phytoremediation of Mn; so all species were equally effective (99%, prob. level 0.001). The Salix wetland system was most effective in purification of water and removal of macroelements (24-82% in summer, 10-80% in winter with Fe 97%), Cd (58-71%), V (100%), and Zn (84-92%). The Phragmites system was most effective in purification and removal of Al (81-97%), Ba (70-95%), Pb (64-81%), and Sr (24-51%), while in the case of Cu (49-60%) and Ni (55-67%) the Populus wetland system proved most effective. The outflowing water of the wetlands contained elements in amounts exceeding the admissible levels as established for unpolluted water both in winter and summer. Therefore the effectiveness of the observed phytoremediation systems in this study was not sufficient alone to remove these elements and can be considered as a supplemental tool in purification of sewage.