Résumé
In many European countries, biogas production through anaerobic digestion (AD) is a very fastgrowing market in the agricultural sector. AD converts biologically organic matrix into biogas anddigestate, the latter corresponding to the anaerobically not degraded fraction. Until yet, digestate ismostly used as soil improver or fertilizer at farm scale, but its increasing amount causes problemsrelative to its transport cost, greenhouse gases emissions during its storage and its used is regulate bythe European Nitrate Directive.In this study, we investigated two energetically valorization routes (i.e. biofuels, pyrolysis) tomaximize the energy recovery from the initial feedstock and reduce the digestate amount.In the first experiment, digestate that contains still a high amount of sugars especially cellulose wasinvestigated for soluble sugars production for further biofuels used (i.e. bioethanol, biohydrogen…).For this purpose, digestate was mechanically treated (i.e. centrifugal milling, 0.12 mm) and furthersubmitted to enzymatic hydrolysis. Energy requirement of mechanical pretreatment and enzymatichydrolysis yields were compared between the anaerobic digestate and the original feedstock. First,energy requirement for mechanical pretreatment was less important for digestate (1.3 kWh.kg-1) thanoriginal feedstocks (3.3 kWh.kg-1). AD has a positive effect on the physicochemical structures of theoriginal feedstocks and consequently leads to a reduction of the energy requirement. Then, theenzymatic hydrolysis yield of digestate (63%) was increased compared to raw feedstock (54%). Theseresults suggests that digestate from AD process could represent a suitable residues for sugar release inthe optic of biofuels production.In the second experiment, a new concept of coupling AD with digestate post-pyrolysis wasinvestigated. Pyrolysis of digestate at 500°C results to 8.8 wt. %, 58.4 wt. % and 32.8 wt. % of syngas,oil and pyrochar, respectively. Like methane produced from AD process, syngas and bio-oil can befurther converted into heat and electricity through a combined Heat and Power system. By couplinganaerobic digestion with pyrolysis process the electricity producted raised from 9896 KWhel day-1 to14066 KWhel day-1 corresponding to an increase of 42% compared to AD process alone. On the otherhand, pyrochar can be used as soil amendment in order to preserve the fragile soil quality, a practicewhich is in line with the principles of ecology and sustainable agriculture.