Removal of ammoniacal nitrogen from landfill leachate by irrigation onto vegetated treatment planes

Leachate is a contaminated liquor resulting from the disposal of solid and liquid wastes at landfill sites that must be treated before discharge. Vegetated leachate treatment planes have been used at landfill sites in the UK but have received little scientific attention. This paper describes studies of model leachate treatment planes with a focus on the removal of ammoniacal nitrogen (NH 3-N). Small-scale and field-scale experimental treatment planes were constructed, filled with clay loam soil and vegetated with grass ( Agrostis stolonifera). Landfill leachate was applied at hydraulic loading rates ranging from 17–217 l/m 2/d. An exponential relationship was used to characterise the pattern of NH 3-N removal. No relationship was observed between the hydraulic loading rate and the NH 3-N removal rate constants ( R 2=0.0039). The daily specific NH 3-N mass removal rate was found to be linearly related to the NH 3-N concentration at the start of that day of treatment ( R 2=0.35). Possible causes of variation in the rate of NH 3-N removal between experiments are discussed. A simple inorganic nitrogen balance indicated that the mass of NH 3-N and NO 2-N removed was not accounted for by NO 3-N production. Explanations for this apparent nitrogen deficit are discussed.