The influence of plants on nitrogen removal from landfill leachate in discontinuous batch shallow constructed wetland with recirculating subsurface horizontal flow

Three discontinuous batch shallow constructed wetland systems with recirculating subsurface horizontal flow with reed, willow, and without plants were used to assess the removal of nitrogen from landfill leachate in relation to hydraulic retention time and climatic conditions. In all systems redox potential in the beds increased asymptotically from negative anoxic conditions to +67 (reed bed), −2 (willow bed), and +17 mV (control bed), reaching a plateau in two wk. During the first 24 h after feeding the beds all forms of nitrogen decreased significantly. It has been shown that plants release O2 and Norg which was then hydrolyzed to ammonia. Plant-available radiation significantly (p < 0.05) increased the release of Norg and removal of ammonia after the 9th day of the experiment. Low, and relatively constant concentrations of nitrite and nitrate indicated that denitrification had taken place in the beds