Landfill Bioreactor Cells as Ecofilters for Extraction of Bio-energy and Nutrients from Solid Wastes

This paper describes a modified, ecologically based waste treatment technique, where municipal solid waste is anaerobically treated in landfill reactorcells in a way that both bio-energy and nutrients can be recovered. The controlled landfill reactorcell ('bioreactor-cell') serves as an anaerobic filter, where energy is extracted as biogas while nutrients are recovered through the leachates. The leachates can be used as fertilizer in e.g. energy forests within the controlled landfill area, and thus nutrients can be brought back into an ecocycle. At the same time anaerobic conditions result in an effective immobilization of heavy metals and other pollutants, e.g. through complexation to organic matter or as insoluble metal sulphides, which are immobilized in the fermentation residue. The long-lived organic fraction, remaining after the fermentation process has declined, containing a high content of lignine, serves as a water-holding matrix. Thus it helps to enforce a sustainable high moisture level, resulting in sustainable anaerobic conditions with heavy metals retained on a long-term basis. Also non-degradable products, like plastics, help to shield off oxygen and maintain reliable anaerobic conditions. Landfilling of organic matter under anaerobic conditions is a measure to counteract increasing concentrations of CO₂ in the atmosphere, resulting from human activities. A small fraction of the organic matter is long-term accumulated in the landfill, and the processes can be compared to those of natural wetlands.