From PET waste to biomaterials: life cycle analysis of PHB synthesis and enriched biomass strategies for PET upcycling

Plastic pollution is a complex global challenge that demands both creative solutions and thorough environmental evaluation. This study evaluates the environmental impacts of two novel approaches for producing poly(3-hydroxybutyrate) (PHB) and polyhydroxyalkanoate (PHA)-enriched biomass, respectively, utilising terephthalic acid recovered from waste PET through reactive extrusion depolymerisation. Life cycle assessment revealed that for PHB production, the highest environmental impacts are associated with the use of sodium hypochlorite and the high energy consumed during processing, resulting in significant effects on climate change, freshwater eutrophication, and photochemical ozone formation. On the other hand, the production of PHA-enriched biomass, which omits the PHA extraction step, derives that its main impacts from the electrical energy consumption, primarily affecting climate change and fossil resource use. When compared to conventional PET mechanical recycling, both processes exhibit lower impacts on climate change and fossil resource depletion footprints, but they still present greater burdens in terms of photochemical ozone formation and freshwater eutrophication. According to the results, improving sustainability will require higher fermentation yields, the adoption of renewable energy, greener extraction methods, and effective wastewater treatment. The findings suggest that innovative PET repurposing routes can reduce reliance on fossil resources and lower CO₂ emissions but also highlight the need for further process improvements to reduce harm to freshwater ecosystems and air quality. Overall, this work adds to the conversation around sustainable plastics and emphasises the trade-offs involved in biopolymer production.