Background One of the general objectives of the VI Environmental Action Programme is to improve environmental quality so that the level of anthropogenic pollutants does not represent a health risk to people. The programme aims to reduce wastes destined for complete phasing out by 20 percent by 2010, and by 50 percent by 2020 in comparison with the figures for the year 2000. In order to achieve these objectives, the programme seeks to follow an integrated approach with Community product integrated policy and Community strategy on chemical products. Disposal of animal sub-products produced in slaughterhouses generally follows two methods: transformation by grease extraction, and recycling into the animal feed chain. However, the impact of recent health and food safety crises means that recycling of dead animals must be reduced. Given the serious environmental and economic repercussions that this could entail, new methods have to be found to dispose of animal sub-products. Objectives The long term objective of the project was to improve the management of slaughterhouse wastes, by processing it in a Biogas plant. Biogas is used as renewable energy for the plant. In addition, the end-product of the waste processing can be used as a fertiliser. The specific objective was the establishment of a pilot plant to convert mainly slaughterhouse wastes into biogas. From this, reliable process data and experience would be obtained, serving as basis for a future upscaled biogas plant. Results The project has enabled the partners to study the process of anaerobic digestion of slaughterhouse waste. Lessons were learned about technical obstacles, meaning that technical difficulties will be avoided in the future industrial biogas plant planned in 2005. The results of the project can be summarised as follows: · Regarding pre-treatment: - The characteristic long fibres were difficult to cut at pilot plant scale, because the amounts to be processed were too small for existing industrial solutions and too big for laboratory solutions. - The input material therefore was partially introduced without shredding into the hygienisation tank. The hygienisation process "reduced" the input material in such a way that it could be processed through the macerator and introduced into the hydrolysis process. Nevertheless, this topic is still being looked at and probably another solution will be found. - Starting from the "reduction" (Aufschluß) effect achieved by the hygienisation unit the partners believe that their primary assumption that a sterilisation unit would even further degrade the input material and thus better facilitate the anaerobic digestion, was correct. · Regarding the anaerobic digestion process: - As expected, the anaerobic digestion process for these kind of residues was more complicated than in a conventional co-digestion plant and therefore must be more intensively monitored, - Biogas production seems to correspond or even exceed expected levels. § Specific gas production: 750-800 m3 biogas/kg volatile solids (oTS) § Methane contents: >70 percent § Degradation oTS: 65-75 percent - It was not possible to reach the target value for the organic load. - At the beginning, slurry with very low dry matter was used for developing the biological system. This led to an instable biology. In order to reach a stable operation at high levels of organic load, it was necessary to control the dry matter content in the digester in order to ensure a higher quantity of active biomass and reduce an overload. During this period, the NH3-N values stayed at reasonable levels. Yet, with the further increment of the organic load, it would be important to also control this parameter as it could lead to an inhibition of the bio system. - In order to reach a stable operation at high levels of organic load, a substrate mix of slaughterhouse waste rather than a monodigestion of only one of the components, is recommended. Notwithstanding the difficulties encountered and the delay, the observed tendencies and the lessons learned made the partners confident about the effective working of the planned industrial project. This project has been awarded the title of "Best of the Best" from a shortlist of 24 "Best" LIFE Environment projects in 2004-2005