Comparison based on environmental effects of nitrogen management techniques in a manure digestate case study.

Due to climate issues and favourable energy market, biogas is spreading as a manure management technique. Digestate is rich in nutrient and has to be handled in order to respect the 'nitrate directive' that limits nitrogen field application in areas defined as vulnerable. In this study, we compared different nitrogen management scenarios: a non-treatment option, a biological short-cut nitrification, a complete autotrophic process (anammox) and ammonia stripping from membrane filtration concentrate. The environmental effect comparison was obtained with 'Cross media effects analysis' and life cycle assessment (LCA). The results were different in some aspects, especially the impacts on eutrophication. According to cross media, the best process is DENO 2, while LCA shows similar impacts for all techniques and the best solution would be the no-treatment option. The main reason to adopt a digestate treatment technique is the lack of area for a correct disposal. If LCA eutrophication results are multiplied with the hectares necessary for each technology, a result similar to that of cross media is obtained.