The landfill biocell as an ecofilter for recycling of bio-energy and nutrients from residual wastes

Abstract

Anaerobic fermentation in landfill reactorcells is a biological waste treatment technique where both energy and nutrients can be recovered. The landfill reactorcell ("biocell") serves as an ecological filter, where energy is extracted as biogas while nutrients are recovered through the leachates and can be used as fertilizer in e.g. energy forests, and thus brought back to an ecological cycling. At the same time anaerobic conditions result in an effective immobilization of heavy metals and other pollutants e.g. as insoluble metal sulphides, which are immobilized in the fermentation rest. The long-lived fraction, remaining after the fermentation process has declined, containing a high content of lignin, serves as a water-holding matrix, which helps to enforce a sustainable high moisture level, and thus sustainable anaerobic conditions with heavy metals retained on a longterm bases. Also non-degradable products, like plastics, help to shield off oxygen and maintain reliable anaerobic conditions. Landfilling of organic matter is a measure to counteract the increasing concentrations of CO2 in the atmosphere, resulting from different human activities. Landfilling at anaerobic conditions means that a small fraction of the organic matter is long-term accumulated in the landfill. Accordingly landfills have similar carbon accumulating effects as natural peatlands and lake or sea sediments. With low investment costs it is possible to convert traditional landfills to well controlled biological treatment facilities. Thus the technique can be performed both in large and small scale, avoiding energy demanding road transportation.