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.