Life Cycle Environmental Impacts of Bioenergy Recovered from Wastewater Treatment Facilities

Wastewater has emerged as a potential bioenergy resource. Previous research has largely focused on assessing individual bioenergy supply pathways and products, limiting system boundaries to recovery processes, or considering only a limited range of environmental impacts. This study evaluated the life cycle environmental impacts of three forms of bioenergy products (i.e., bioelectricity, bioheat, and biohydrogen) recovered through 27 pathways from sewage sludges at wastewater treatment facilities and benchmarked them against their conventional energy counterparts across 311 pathways. The results indicate that bioelectricity and bioheat have substantial lower global warming and fossil resource scarcity impacts than conventional energy commodities. All bioenergy products involve trade-offs in specific environmental categories, such as toxicity, eutrophication, and mineral resource depletion. This study further compared the environmental impacts of both intermediate and final forms of bioenergy products─bioelectricity, bioheat, biomethane, and biohydrogen. Bioelectricity had the highest impacts per unit energy due to exergy-based allocation, while bioheat had the lowest. With similar environmental impacts and no end-use greenhouse gas emissions, biohydrogen could be preferable to biomethane. Accounting for the multifunctional nature of anaerobic digestion, beyond bioenergy production, can further improve the environmental performance of most bioenergy pathways.