Comparative life cycle assessment of enhanced anaerobic digestion of agro-industrial waste for biogas production

Abstract

The enhancement of anaerobic digestion improves biogas production, but it has some environmental implications. The need to achieve a trade-off between the energy gains and environmental sustainability necessitated this research. In this study, a comparative assessment of the potential environmental impacts of biogas production from enhanced anaerobic digestion of agro-industrial wastes with different enhancement options, biogas utilization and digestate management was carried out. The anaerobic digestions (mono- or co-digestion) of okra and pig wastes were enhanced with polypyrrole magnetite nanocomposites (PPy/Fe3O4 NPs), nano zerovalent iron (nZVI), magnetite nanoparticles (Fe3O4 NPs) and alkaline pretreatment (NaOH). The impact categories were analyzed according to these adopted assessment processes: substrate production, substrate transportation and processing, feedstock enhancement (pretreatment, co-digestion and additive supplementation), biogas utilization, and digestate management. From the analyzed results of this assessment, it was revealed that among all other scenarios, the combined enhancement (co-digestion + PPy/Fe3O4NPs) option had the least global warming potential of 0.0053 kg CO2-eq/MJ. Based on the energy and environmental performances, the use of combined enhancement, followed by PPy/Fe3O4NPs only is recommended to minimize the adverse impacts of electricity generation from biogas on the environment. It is further recommended that techno-economic and life cycle cost analysis of the preferred scenario be conducted.