Prospective LCA to provide environmental guidance for developing waste-to-PHA biorefineries

Abstract

Polyhydroxyalkanoates (PHA) production from waste streams using mixed microbial cultures (MMC) can unlock the potential of PHA to substitute oil-based plastics. However, these processes are still at low technology readiness level (4–6). Demonstrating a better environmental performance would boost their deployment at industrial scale. Hence, including environmental guidance during their development, when there are still opportunities for major alterations, is essential. To the best of our knowledge, this work elucidates for the first time how waste-to-PHA biorefineries could develop in the future by combining prospective LCA with scenario methodology and where the attention of stakeholders should be focused. Four future scenarios were derived considering both surrounding (e.g., scale, environmental or bioeconomy policies) and technological parameters (e.g., acidification yield, PHA content in biomass or recovery yield). Those scenarios derived under ambitious environmental and bioeconomy policies shop up to 50% lower environmental impacts than those under business-as-usual policies. These differences are caused by the different background processes’ environmental burdens (e.g., electricity mix with low renewable energies share) and the higher consumption of chemicals and utilities. However, the environmental impacts caused by lower yields can be partially mitigated by valorizing the intermediate waste streams into biogas. Sensitivity analysis results pointed out recovery yield and PHA content as the parameters that influence most the environmental performance, being responsible for up to 60% of variance in environmental performance. These parameters determine the chemicals and utilities consumption in PHA downstream processing, which is confirmed as the main environmental hotspot. This work goes beyond previous LCA studies on PHA production and quantifies the influence of different parameters on the environmental performance.