Enhanced heavy metal removal by wetland vegetations and its significance for vegetation-activated sludge process configuration

Under the present investigation, removal capacities and influential factors of four heavy metals (HMs) (Cu, Pb, Cr, and Ni) by three wetland vegetations, i.e. Canna indica, Dracaena sanderiana, Cyperus alternifolius, were conducted to assess their feasibility and reliability to collocate into an ecological vegetation-activated sludge process (V-ASP) for HMs contained wastewater treatment. The maximum specific Cu, Pb, Cr, and Ni removal rate of D. sanderiana, C. indica, C. indica, and C. alternifolius was 17.6, 6.39, 19.09, and 7.05 mg/kg WW-d, respectively. Co-existence of organic and nitrogenous pollutants and their content fluctuation affected significantly on Cu, Pb, and Ni removal efficiency, and moderately on Cr removal. A weak alkaline (7.5–8.0) in bulk favored Cu and Pb removal, while a weak acidic (~6.5) was beneficial to Ni elimination. Vegetation roots had a much higher HMs concentration than their stems and leaves, and continuous HMs accumulation within vegetation decreased its photosynthesis rates, and made various morphological changes, although which would be recovered under proper conditions. Evidences of stable HMs removal by proper vegetation collocation give direct guideline for V-ASP configuration, which have profound significance for its practical application.