Challenges and Issues of Life Cycle Assessment of Anaerobic Digestion of Organic Waste

Life Cycle Assessment (LCA) is a widely used tool to measure the environmental sustainability of products or processes. Integrating LCA into the assessment of waste diversion strategies recognizes that current waste diversion strategies are insufficient to stem the global impacts of waste effectively. The increased pressure to divert organic and inorganic materials to reduce landfills impacts and promotes the circular economy. Historically, waste diversion efforts in municipalities and industries focused on higher-profile inorganic wastes, such as plastics and other recyclables. However, organic waste is increasingly identified as a key waste fraction that must be effectively managed and regulated. This research surveys published LCAs from 2019 to 2023 focusing on the anaerobic digestion (AD) of organic waste. Notable conclusions include the lack of studies comparing AD with the latest treatment options such as co-gasification; the insufficient attention to the LCAs on biogas upgrading methods; and the monetization of LCA results using carbon credits. In addition, more than 50% of reviewed LCA studies concluded the results with a sensitivity analysis, which was not a common practice before 2019 in LCA studies on anaerobic digestion. This signifies the increasing need to understand uncertainty in the circumstances governing applying AD to wastes. Finally, neglecting the combined effect of several parameters in the sensitivity analysis might have reduced the accuracy of the sensitivity analyses in the reviewed LCAs. Overall, LCAs conducted on AD-related applications vary widely in terms of scope and consistency, implying that the outcomes may not be as applicable as intended. The identified challenges, issues, and other findings related to this research are expected to help standardize LCA procedures as applied to AD to promote greater comparability.