The circular value of polyhydroxyalkanoate (PHA) bioplastic production from sludge at a large-scale wastewater treatment plant

This paper presents the circular performance of polyhydroxyalkanoate (PHA) bioplastic production to operate in parallel with an anaerobic digestion system for a municipal wastewater treatment plant sludge in Ireland. The circularity assessment quantified that 98.1 % of process inflows were derived from circular sources, 83.0 % of system outflows were recirculated to the biological cycle, and 44.2 % of energy requirements was derived from circular sources. A complementary Life Cycle Assessment (LCA) presented a net benefit for ecosystem quality (EQ), human health (HH) and natural resources (NR) as endpoint indicators. Currently, anaerobic digestion has a greater benefit across all impact categories than PHA production; however, a greener 2030 electricity grid mix leads to PHA production providing greater EQ and HH benefits. An optimised system between PHA production and anaerobic digestion in 2030 was estimated at a 3:1 ratio, outlining the future scope to realise this potential through full-scale demonstration of a coupled system. • Circularity assessment and life cycle assessment (LCA) to evaluate PHA production from sludge • PHA scores highly on circular metrics such as process inflows, outflows and energy. • LCA presents net-benefit for ecosystem quality, human health and natural resources. • Optimal 3:1 ratio split for sludge between PHA production and anaerobic digestion in 2030 • Diversifying the use of sludge to produce bioplastics can replace fossil-derived plastics