This work has been carried out to evaluate the environmental impact through a Life Cycle Assessment (LCA) of a collective biogas plant incorporating pig slurry, cattle manure and waste from food processing industry. This collective biogas plant is actually a project located in an intensive farming and agro-industry area close to Rennes (France). Water from surface resources (river) located within this area is used to supply the towns located around for tap water. However, the excess of nitrogen locally applied on agricultural soils led to an increase of nitrate concentration in the water of the area and consequently, the water plant was recently closed. A collective manure management including biogas plant and post-treatment of digestate is seen as a possible solution to reduce the local pollution (mainly nitrate) through export of nitrogen. In this context, the aim of this study was to provide scientific elements on such solutions and to take into account the global environmental impact. So, a LCA has been realised to compare different scenarios of manure management according to an environmental point of view. Three scenarios of manure management are evaluated including a reference scenario representing the common practice and two other scenarios with collective biogas plant. The difference between the scenarios with collective biogas plant concerns the post-treatment of digestate: the post-treatment is composting in one scenario while it is evaporation process with concentration of digestate in the second one. These three scenarios make it possible to focus (1) on the impact of transport which was precisely modelled for each scenario using Geographic Information System (GIS), (2) on uses of energy from biogas and (3) on treatment techniques and agronomical management of the digestate. In order to compare these three scenarios, a functional unit describes scenarios functions related to the practices of the area. The boundaries of this study begin to the storage until the export and application of digestate. The scenarios were modelled thanks to GaBi 4 software.The CML 2001 method was used to calculate environmental impacts. The scenario with biogas plant and evaporation seems to be the least impacting even if the differences between the two scenarios with biogas plant are small. Results analysis only focuses on three impacts categories: acidification potential, eutrophication potential and global warming potential. These three impact categories are judged relevant to provide answers to nitrogen excess, manure management and transportation importance. These results are examined through foreground and background boundaries and through generated and avoided impacts. For climate change, at the foreground, biogas plant by itself does not contribute to the reduction of greenhouse gases but the manure management plays a major role, through the reduction of storage time in farm. The LCA results clearly show, especially for global warming, the interest of the utilization of biogas thanks to energetic recovery through electricity and heat in terms of avoided impacts to the background. For the impact of acidification, the evaporation and concentration scenario presents the lowest impact mainly due to the reduction of ammonia emissions during land spreading (because of the acidification of the digestate during post-treatment). On the contrary, the composting scenario does not present a decrease of the impact compared to the reference because the decrease of ammonia emissions during storage are compensated by an increase of ammonia emissions during composting and land spreading. For eutrophication, we do not find a global trend. The scenario with evaporation shows a lowest eutrophication impact within the local area resulting from the nitrogen export but firstly the reduction of the impact is low in comparison with the quantity exported due to the increase of ammonia emissions and secondly it is just a potential impact transfer to another place. To identify potential impact transfers especially for local impact like eutrophication, it would seem wise to more precisely locate nitrogen releases. This study provides interesting results but also highlights several limitations as regards the assumptions and results. Certain assumptions are questionable especially the allocation rules for mineral fertilizer and the modelling of nitrate leaching. The complexity of a rural area, the plurality of stakeholders and the waste diversity show that the implantation of a collective biogas plant should result from a consultation process. Such a project must combine interest of each stakeholder and take into account features of area and environmental issues. The realization of LCA may bring some elements to the collective debate and insert environmental considerations in decision making support.