Life cycle sustainability assessment of kerbside glass recycling: Separate vs. mixed bin collection and its reuse in asphalt and glass container production

Abstract

This paper pilots a Life Cycle Sustainability Assessment (LCSA) to scrutinize the sustainability performance of kerbside waste glass recycling alternatives in a local municipality, where three major innovations are underlined. First, the study utilizes the LCSA method to evaluate the sustainability impact of street collection methods on waste glass recycling, which examines both open-loop and closed-loop recycling processes. Second, the study overcomes a common difficulty in sustainability assessment, where environmental and economic impacts are more accessible to quantify, but social impact often lacks a clear functional unit for assessment. This research addressed this gap, ensuring a holistic evaluation. Third, the study introduces an innovative way to visualize the findings from the LCSA. This visualization technique makes the results easily understandable to all stakeholders, enhancing the comprehensibility of multifaceted data. Two street collection methods (separate and mixed bin collection) are combined with two production methods (asphalt and glass container) to form four kerbside waste glass recycling scenarios. It also employs two functional units, weights of annually collected glass waste and 1 ton of produced asphalt or glass container, to demonstrate the LCSA-generated results under different perspectives. Evaluating the annual waste glass collection in the mixed bins implies better environmental, economic, and social outcomes than separate bins. In 1 ton of products, asphalt production is more sustainable environmentally and economically than glass container production. Separate bins enhance glass container production's environmental and economic sustainability by greater than 80%, but they have a minimal 5–6% improvement on asphalt production. A similar trend in social sustainability is indicated for asphalt and glass container production. However, a significant decline in social sustainability is observed when transitioning to separate bins from mixed bins methods. Sensitivity and uncertainty analyses show that a 50% increase in transportation distance results in minor impacts: CO2 emissions increase by 7% for separate bin-asphalt and 4% for mixed bin-asphalt, and by 0.8% for separate bin-glass container and 0.7% for mixed bin-glass container. Equipment costs also increase slightly: 3.6% for separate bin-asphalt, 4.7% for mixed bin-asphalt, 3.4% for separate bin-glass containers, and 1% for mixed bin-glass containers. These results underscore the robustness of the LCSA findings.