Anaerobic digestion of sewage sludge: overview of the French situation

Following the French environmental national debate, called 'Grenelle de l'Environnement' and according to the Kyoto Protocol, France looks at increasing its production of renewable energies, among them biogas production from organic wastes and more specifically from sewage sludge. A quick survey of official data shows that in 2009, sludge biogas only represented 0.93% of the total renewable electricity production, far from the situation in the neighbourhood countries. To understand this situation, this article aims at inventorying sludge anaerobic digestion process, in Europe then more precisely in France. The different technologies used to perform anaerobic digestion process have been investigated, including the type of waste, pre-treatments, digester specificities, mixing and heating systems. In France, a survey has been realised to determine the situation for wastewater treatments plants bigger than 30,000 equivalent inhabitants. Mesophilic digestion in a constantly mixed reactor is mainly used. Moreover, some plants have given specific details about the cost of the process or its efficiency. These results are discussed.