How LCA can be Streamlined without losing information?

Life-cycle assessments (LCAs) of municipal solid waste management (MSWM) systems are time- and data-intensive. Reducing the data requirements for inventory and impact assessments will facilitate the wider use of LCAs during early system planning and design. Therefore, the objective of this study is to develop a systematic framework for streamlining LCAs by identifying the most critical impacts, life-cycle inventory emissions, and inputs based on their contributions to the total impacts and their effect on the rankings of 18 alternative MSWM scenarios. The scenarios are composed of six treatment processes: landfills, waste-to-energy combustion, single-stream recycling, mixed waste recycling, anaerobic digestion, and composting. The full LCA uses 1752 flows of resources and emissions, 10 impact categories, 3 normalization references, and 7 weighting schemes, and these were reduced using the streamlined LCA approach proposed in this study.

Human health cancer, ecotoxicity, eutrophication, and fossil fuel depletion contribute 75−83% to the total impacts across all scenarios, regardless of the choice of normalization and weighting schemes.

It was found that 3.3% (20 out of 650 distinct flows) of the inventory flows contribute ≥95% of the overall environmental impact. They are also relatively well established. Major contributors include waterborne heavy metals like chromium (VI) and zinc, phosphate and nitrate, as well as airborne emissions of biogenic methane, and benefits from storing biogenic CO2 resulting from landfills or anaerobic digestion followed by land application.

The results indicate that the streamlined LCA that uses only the 20 most critical flows provides consistent rankings across the 18 scenarios. Even the GHG-only system that only estimates GHG emissions and global warming impacts can agree on the top 3 scenarios with the full LCA. However, relying on GHG emissions altered the decisions in the 4th to 6th strategies. Instead, the GHG-only system preferred sending MSW to a landfill given carbon storage. Nevertheless, what decision makers care the most about are if the best strategies can be consistently selected rather the lower-ranked alternatives.

A streamlined LCA framework was developed and tested in MSWM systems. The results provide guidance on which impacts, flows, and inputs to prioritize during early strategy design, without loss of decision accuracy and consistency. A simpler LCA framework makes it easier for decision-makers and communities to develop a science-based understanding of the potential critical impacts of alternative MSWM strategies. The analysis found a substantial potential to reduce data requirements in impact assessments, inventory analysis, and inputs. The shorter list of impact categories, flows, and inputs enables the early incorporation of LCA into the MSWM strategy planning phase when an LCA can have the most influence on the project or system. The proposed streamlined LCA framework could also be applied to systems beyond MSWM and to regions beyond North America. The ranked strategies may vary with different regions that have a different electricity mix. The generalizability of the streamlining method in the other functional systems needs further exploration.

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