Kinetic and mass balance analysis of constructed wetlands treating landfill leachate.

Experiments were conducted to investigate the feasibility of applying constructed wetlands to treat a sanitary landfill leachate containing high nitrogen (TN) and bacterial contents. Two-pilot scale subsurface-flow constructed wetland (SFCW) units located at the Asian Institute of Technology, Thailand, campus, were fed with a synthetic wastewater and landfill leachate collected from a nearby sanitary landfill. Under the tropical conditions (temperature of about 30 degrees C), the SFCW units operating at the hydraulic retention time(HRT) of 8 days yielded the best treatment efficiencies with BOD, removal of 91%, TN removal of 96%, total and fecal coliforms (TC and FC) removal of more than 99% and cadmium removal of 99.7%. The treatment performance was found to follow first-order reaction rate, in which the k20 values of BOD5, COD, TN, TC, FC and Cd were 0.201, 0.121, 0.247, 0.346, 0.354 and 0.690 d(-1), respectively. Mass balance analysis, based on TN contents of the plant biomass and dissolved oxygen (DO) and oxidation- reduction potential (ORP) values, suggested that 88% of the input TN were uptaken by the plant biomass; 8% removed by nitrification-denitrification reactions and adsorption on the wetland media, while the remaining 4% were discharged with the effluent.