Removal of persistent organic pollutants from landfill leachates treated in three constructed wetland systems

The objective of the study was assessment of occurrence and removal of two groups of persistent organic pollutants: polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in landfill leachate (LL) treated in three constructed wetland systems (CWs) of different construction and flow regime. Two subsurface flow systems (SSF) were analyzed: one with horizontal flow and the second one consisting of two vertical flow beds followed by a horizontal flow bed. The third CW was a surface flow (SF) system, consisting of 10 ponds connected in series. The concentrations of 12 PAHs and 7 PCBs were measured in the samples of LL after subsequent treatment stages and in the sediment samples from the SF system as well as in the substrate samples from the SSF flow systems. It was confirmed that the major mechanism of PCB and PAH removal in CW systems was adsorption to the bottom sediments (in the SF system) or substrate of the beds (in the SSF systems) as well as adsorption to suspended solids, followed by sedimentation. The compounds characterized by higher octanol/water partition coefficient were more effectively retained in the sediments. Also removal of these substances occurred in the earlier stages of treatment.