Background Decomposing organic waste in landfills generates large quantities of methane, a greenhouse gas that contributes significantly to the global problem of climate change. Conventional technology for extracting methane for use as an energy resource is seldom cost-efficient and generally captures only 40-60% of the gas produced. The adoption of the EU landfill directive has led to improvements in waste management practices, along with a reduction in the amount of organic waste produced. Nevertheless, Europe’s existing landfills continue to generate vast quantities of methane, and improved methods are needed for reducing greenhouse gas emissions from landfills. Objectives The project’s objective was to demonstrate an innovative technology for reducing methane emissions from landfills by up to 90%. This would have been achieved by building a “bio-cover” with “windows” on a landfill, to increase the biological oxidation of methane and consequently reduce greenhouse gas emissions. The approach was expected to be cheaper and more effective than current methods. The technology was to be transferred to at least four further sites in Europe, as well as two outside the EU, so as to prove its applicability under different climatic conditions. Results The BIOCOVER project did not reach its planned objective, as the reduction of methane emissions due to its bio-cover technology was significantly lower than anticipated. Methane emissions were reduced by some 30% instead of the expected 90%, due to complex reasons related to the methane gas and flux formation in the landfill structure, and also to the technical structure of the landfill enabling some uncontrolled leaks. However, the project created a range of knowledge and experience that will enable avoidance of the weaker parts of the bio-cover approach in the future. The project produced a bio-cover improvement report. Ongoing monitoring and data collection from landfills covered by different bio-cover methods will add to this knowledge. It is likely that certain project components, such as the monitoring of the methane movements (especially for ‘hot spots’) and the developed characteristics of the bio-cover material, can be utilised in future landfill management. The project trialled the bio-cover approach at the Fakse landfill site, located in the Southeastern part of Sealand (Denmark) and operated by BIOCOVER consortium member I/S Fasan. The project started with a landfill characterisation, a baseline study of methane emissions, and the testing of improvement strategies (e.g. the testing of 7 covering compost materials). After establishing a full-scale demonstration bio-cover system, the project evaluated its operating efficiency (e.g. methane oxidation efficiency) and economic viability. The project identified particular ‘hot spots’ of methane gas emissions and sealed those with impermeable clay. The BIOCOVER project was the first of its kind to demonstrate the use of a bio-cover system for mitigating methane emissions from a landfill by improving the existing soil cover. The full-scale bio-cover extended over 5 000 m2, and incorporated ‘windows’ and monitoring equipment. In many cases landfills have been temporary covered over large areas with soil layers having relatively low gas permeability, but this can be costly and impractical to remove. Thus implementing a bio-cover system incorporating the presence of the temporary cover makes this a much more cost-effective approach. Establishing permeable regions – the so-called windows – in the temporary cover, using materials with higher permeability to enhance gas transport into the window area that has a high methane oxidation potential to oxidize the methane into carbon dioxide, has the potential to significantly lower greenhouse gas emissions. The project was also the first to demonstrate a documentation procedure and to disseminate the procedure through the production of guidelines to the technology. As proposed, the bio-cover solution could supplement traditional gas collection technologies at landfills, increasing gas collection efficiency and reducing greenhouse gas emissions. If successful, this change in existing management practice could be implemented at a low cost. In addition, bio-cover systems could reduce emissions of nuisance odorous compounds.