Boosting of energy efficiency and by-product quality of anaerobic digestion of Kitchen Waste: Hybridization with pyrolysis using Zero-Waste strategy

In this study, anaerobic digestion (AD) and integrated process of anaerobic digestion, followed by pyrolysis (PY), have been studied for the generation of energy and chemicals from kitchen waste (KW). A 2.5 L anaerobic digestor has been run on semi-batch mode. The solid part of the digestate stream of AD has been pyrolyzed in a 200 mL semi-batch pyrolyzer. The cumulative biogas generation of 275.76 mL/kgVS and a biodegradability index of 64.39 % have been obtained. The yields of pyro-products of digestate have been compared with those obtained with original KW. The yields of char and oil pyrolysis of digestate are higher than those obtained from the original feedstock. The quality of pyro-char from digestate has superior quality than that obtained from original wastes with respect to surface area and micropore volume. Pyro-oil and gas from digestate have higher heating values compared to those obtained directly from KW pyrolysis. The results of FTIR and GC/MS analyses indicate that pyro-oil obtained from KW and its digestate can serve as a source of liquid fuel and chemicals. The maximum energy return of 9.11 MJ/kg can be achieved from the integrated process, and the value is 30 % higher than that from the stand-alone anaerobic digestion process. The values of energy return on energy investment of stand-alone and integrated processes are 0.38 and 0.49, respectively. The study reveals that the zero-waste strategy is validated for the generation of fuels and chemicals from KW through the AD-PY hybridization.