Influence of recirculation in a lab-scale vertical flow constructed wetland on the treatment efficiency of landfill leachate.

Landfill leachate taken from a landfill situated in the north-western region of Bulgaria has been treated in a laboratory scale vertical flow constructed wetland (VF-CW) at different flow rates (40, 60 and 82 ml min(-1)) and recirculation ratios (time of water running through wetland to time of quiet water - 1:1; 1:2; 1:3). Young Phragmites australis was planted on the top layer of the reactor. The low flow rate (40 ml min(-1)) and recirculation ratio of 1:3 allowed removal efficiencies of 96% for COD (in 8 days), 92% for BOD(5) (in 3 days), 100% for ammonia (in 5 days) and 100% for total phosphorus (in 2 days).