Nitrogen mass balance and microbial analysis of constructed wetlands treating municipal landfill leachate

Experiments were conducted to investigate the feasibility of applying constructed wetlands to treat a sanitary landfill leachate containing high nitrogen and bacterial contents. Under a tropical condition (temperature of about 30 °C), the constructed wetland units operating at the hydraulic retention time of 8 d yielded the best treatment efficiencies with BOD5, TN and fecal coliforms removal of 91%, 96% and more than 99%, respectively. Cadmium removal in the SFCW bed was 99.7%. Mass balance analysis, based on total nitrogen contents of the plant biomass and dissolved oxygen and oxidation–reduction potential values, suggested that 88% of the input total nitrogen were uptaken by the plant biomass. Fluorescence in situ hybridization results revealed the predominance of bacteria, including heterotrophic and autotrophic, responsible for BOD5 removal. Nitrifying bacteria was not present in the constructed wetland beds.