LANDFILL LEACHATE NUTRIENT RECOVERY BY WILLOW SHORT ROTATION COPPICE III. SOIL WATER QUALITY

Abstract

Summary The treatment of landfill leachate with Short Rotation Coppice (SRC) is reliant on both the plant and soil of the system (GODLEY et al., 2004a and b). In summer there is virtually no drainage of water from the soil and moisture losses are almost exclusively from evapotranspiration. This means that there is the potential for contaminants in applied leachate to become concentrated in the soil. During winter, plant dormancy and rainfall infiltration means that water losses from drainage of the soil will be maximised and soil microbes will play the major role in treatment. Therefore in winter contaminants accumulated during summer leachate applications may be removed from the soil by drainage. Low soil temperatures and water-saturated soils in winter may reduce the rate of aerobic microbial activity. Consequently leachate applications in winter need to consider contaminant losses from drainage and reduced microbial activity in order to avoid increasing the concentration of contaminants in soil pore water further. In particular the concentrations of nitrogen compounds and chloride in landfill leachate have the potential to encourage leaching of these components. This paper describes an investigation of the soil pore water quality following irrigation with landfill leachate at the Hatfield willow SRC trial (GODLEYE et al, 2004a and b). Over the duration of the trial, the water input to leachate irrigated plots was dominated by rainwater (89% of the total water input). This diluted the dissolved leachate components discharged from the plantation to considerably lower levels than found in the leachate. The nitrate emissions from drainage water were low and did not impact nitrate concentrations in an on-site ditch and would have had little impact on effluents discharged from the site at the site boundary. Chloride and nitrate-nitrogen concentrations were higher in 2001/2002 than the 2 proceeding years in response higher loading levels.