Résumé
Anaerobic digestion (AD) of sewage sludge is an already well-developed technology to convert waste to bioenergy and digestate. Despite its deployment, AD process still raises environmental, technical and economic issues and many researches have been done to improve the process yield, reduce environmental burdens from digestate application and allow a better distribution of energy. The integration of thermal processes with anaerobic digestion is explored to overcome some of the anaerobic digestion limitations. In this study, a cradle-to-grave life cycle assessment (LCA) is performed to compare a system integrating anaerobic digestion and pyrolysis (PY) with single anaerobic digestion, for the co-digestion of sewage sludge and quinoa residue. The results suggest that the environmental impacts of the two pathways are quite similar except for three impact categories: single anaerobic digestion is the best scenario in terms of global warming potential (−769 vs. -604 kg CO2 eq./t substrate), ozone depletion (−33.7 vs −2.11 mg CFC-11 eq./t substrate) and fossil resources use (−9900 vs −6900 MJ/t substrate). The multifunctional process could be a viable competitor to single anaerobic digestion by improving pyrolysis products upgrading. The application of liquid digestate to crop field revealed to have significant burdens to particulate matter, acidification and terrestrial eutrophication impact categories and must be carefully monitored in both pathways.