Phytoremediation efficiency: assessment of removal processes and hydraulic performance in constructed wetlands

Constructed wetlands are now widely recognised as effective treatment facilities for controlling pollution, restoring stream values within urban areas, for their recreational and aesthetic qualities, and for conserving flora and fauna. The aim of the study was to examine two important functions of wetland systems: removal efficiency and hydraulic performance. The first research line was carried out to examine the pollutant removal efficiency and plant nutrient and metal translocation of a pilot constructed wetland in Fusina, Venice (Italy) receiving Naviglio Brenta river freshwater. The second investigation was performed in 18 pilot wetlands in Halmstad (Sweden) in order to assess the influence of different vegetation in the hydraulic conditions. From this study, the effluent quality in the pilot wetland in Venice showed a significant improvement during the period of monitoring and the plants nutrient and metal contents, particularly in roots, were correlated with sediment concentrations. Hydraulic efficiency in the pilot wetlands in Sweden studied by tracer test application was influenced by vegetation type and density, with higher performance in the wetlands planted with mixed vegetation. The two aspects analysed in this research are strictly connected because a principal controlling factor of contaminants removal in wetlands is water movement patterns; based on that, wetland design may play an important role for nutrient and metal retention, as well as for enhancing biodiversity and recreational values in constructed wetland systems.