Abstract
The treatment of landfill leachate in constructed wetland systems is a common practice in Europe. However, very few studies were made to evaluate their performance over a long period of time. A free surface constructed wetland system consisting of sediment traps followed by 10 ponds connected with overflows was built at Atleverket near Örebro, Sweden in 2001. It receives pre-treated leachate from the municipal landfill. As part of the wetland monitoring programme a large data set on the surface concentrations of 15 metals and 2 metalloids has been collected from different sampling sites within the wetland during the operation period. In this study, the data from inlet and outlet of the wetland were compiled and analysed. The aim of this paper is therefore to estimate the removal efficiency of metals and metalloids using data on concentrations and flow and investigate the effect of wetland age on removal pattern. The elements with the highest removal efficiency were Al, As, Ba, Ca, Cr, Cu, Fe, Mn, Pb, V and Zn ranging from 95% for Pb to 65 % for Ca. The elements with the lowest reduction were B, Co K, Mg, Ni and S ranging from Co 56 % to 40 % for S. It was found that the removal efficiency was not related to inlet concentrations of the elements as the elements with high and low inlet concentrations were found in both groups. Analysis of reduction pattern also revealed that the group with higher removal efficiency showed fairly constant outlet concentrations during the study period, while the elements with lower removal efficiency demonstrated variable outlet concentrations. No statistical difference in removal due to age of the wetland was found. The study results showed that the wetland system has high removal efficiency of metals and metalloids and the removal pattern is not affected by age of the wetland. The influence on reduction due to leachate characteristics, wetland design and retention time will be discussed.
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