Ammonium and nitrate removal from Belle Isle landfill leachate in constructed wetland cells (Phragmites australis, Typha latifolia, Scirpus validus)

A bench-scale subsurface flow wetland for treating Belle Isle Landfill leachate was designed, built, and operated in the ESF Research and Development Greenhouse. The wetland system utilizes a synthetic soil product consisting of yardwaste compost and municipal solid waste incinerator bottom ash. The system, consisting of seven subsurface flow cells vegetated with Phragmites australis, Typha latifolia, and Scirpus validus, was effective for eight months in reducing high levels of ammonium and nitrate-nitrogen, the key constituents of the landfill leachate. Greater than 90% of nitrate and ammonium-nitrogen was removed during the growing season and less than 60% of the inorganic nitrogen in the influent was removed during the nongrowing season. Such use of constructed wetlands reduces the amount of incinerator ash entering solid waste landfills while potentially attenuating excessive nutrient loads to surface and groundwater. A 5:1 ash/compost substrate could minimize the overall cost of constructed wetland treatment systems.; Results indicate that nitrogen removal is temperature dependent, may require a long hydraulic residence time, and appears to be limited in unvegetated systems. The high ammonium-nitrogen removal efficiency reported in this research shown by the vegetated cells is attributed to the ability of these plants to translocate O{dollar}sb2{dollar} from the shoots to the roots. A mass balance study infers that the sequential microbial processes of nitrification and denitrification provided the highest removal of inorganic nitrogen.