Investigation of a landfill leachate treatment plant in southern Sweden

Sammanfattning: Dissolved ammonia is often referred to as one of the major contaminants in landfill leachates. Discharge concentration limits for municipal wastewater treatment plants in Sweden have been tightened in order to meet higher water quality standards. Because of REVAQ, a certification system tailored to ensure better sludge quality, wastewater treatment plants may decide whether to accept leachate from landfills or not. Usually leachate contains potentially harmful compounds and environmental pollutants such as man-made organics, heavy metals, and ammonia. Therefore there is a growing interest in investigating actual capacities of landfills to treat leachate on-site rather than off-site, especially with regard to ammonia which is a potential inhibitor of nitrification. Since the 1980s, lagooning represents among biological treatment methods a versatile, long-term, and low-cost solution for removing organics and ammonia despite yearly climate fluctuations and leachate volume variations. This thesis focuses on the understanding of nitrogen transforming and removal processes that might occur in Hedeskoga, a landfill site provided with a series of basins and a spray irrigation area meant to treat leachate within the facility. A simple water budget and a nitrogen mass balance gave important information on the pathways followed by nitrogen: nitrification and denitrification are the main nitrogen removal processes occurring during summer in the ponds´ system in Hedeskoga; retention times longer than 30 days and temperatures lower than 5°C enhance the possibility for ammonia nitrogen to be removed by sedimentation during winter rather than by active nitrification. Further biological assays could be made in the future to elucidate just as important nitrogen removal pathways within the ponds.