EXPERIENCES OF CONSTRUCTED WETLANDS FOR THE TREATMENT OF NITROGEN IN LANDFILL LEACHATE / Erfarenheter av konstruerade våtmarker för behandling av kväve i lakvatten

This article reviews the worldwide experiences on possibilities of using constructed wetlands for landfill leachate treatment. On-site “high-tech” leachate treatment systems are often avoided due to large construction and operating costs. Two questions that are crucial for the success of constructed wetlands in future landfill leachate treatment are addressed—(i) does nitrification/denitrification occur and can it be managed, and (ii) can constructed wetlands be applied in the treatment of high ammonium content which appear in landfill leachate and meet high effluent standards. Many processes are involved in the nitrogen removal but most researchers argue that denitrification is the most important process. Unfortunately, very little evidence for that is presented in the literature. Available organic carbon is one of the limiting factors and there are discussions as to whether carbon additives other than those found in the wetland substrates should be used. Continuous leachate application is deleterious to the treatment process. Instead, a hydroperiodical system should be used, allowing a drying period when atmospheric oxygen can diffuse into the soil. Most of the constructed wetland types are generally effective in reducing ammonium-nitrogen down to effluent concentrations of about 10 mg/1. However effluent limits may be as low as 2 mg/1 when organisms in the receiving waters are sensitive. Guidelines for leachate treatment wetlands should be developed since the interest from the industry of this ecotechnology is growing.