Fate of nitrogen along digestate post-processing : impact on agronomic value and environmental assessment
Résumé
Digestates are a key issue for the anaerobic digestion plants management. Indeed these residues from the digestion represent volumes comparable to the volumes of treated inputs and have to be properly valorized in order to ensure good environmental and economic performance of the whole biological treatment scheme. Digestates are generally used as soil improvers or organic fertilisers on cropped soils. Nevertheless the quality of the applied product is largely influenced by the type of organic resources treated in the digester and by the post-processing (liquid/solid separation, composting or drying of the solid fraction, membrane filtration of the liquid fraction, ammonia concentration, etc.). Moreover the way of post-processing and the quality of the final digestate product will influence the environmental impacts after their application. The proposed work aimed at characterizing the quality of different types of digestates and at studying the fate of nitrogen along post-processing and after spreading. Five digestion plants and the corresponding digestates were studied. Impact of postprocessing as liquid/solid separation, composting, drying and membrane filtration were characterized. Finally nitrogen fertilizing value of digestates and of the post-processed products was analysed along with the nitrogenous emissions after spreading.