How does downstream processing influence the sustainability and techno-economics of polyhydroxyalkanoates production?
Isabel Thiele, Sebastian L. Riedel
Abstract
Polyhydroxyalkanoates (PHA) are viable alternatives to fossil-based plastics due to their biodegradability and bio-based nature as microbially synthesized polyesters. Although PHA-based products like packaging, cups, and drinking straws are already on the market, production capacity remains low. However, rapid growth is expected, potentially reaching 1 million tons annually by 2028, making a sustainable and economical production process essential. This review explores the environmental and economic viability of PHA manufacturing, emphasizing the crucial role of downstream processing (DSP) in the overall assessment. Various life cycle assessment (LCA) methodologies and techno-economic analyses have been employed to evaluate the environmental performance and cost-effectiveness of PHAs. Key challenges in PHA production include substrate costs, production yields, and DSP, accompanied by the need for reformed production grids, processing conditions, and recycling strategies to reduce reliance on petrochemical resources, while minimizing environmental impact and production costs. Strategies such as process integration, metabolic engineering, and the utilization of waste streams as carbon sources are discussed as potential solutions. The review highlights the significant environmental and economic impacts of DSP, which can constitute up to 70 % of total costs and environmental burden. Innovations in DSP, including green solvents and non-ionic surfactants, offer promising reductions in environmental impacts compared to traditional solvent extraction methods. Integrating PHA production with other waste valorization processes within biorefineries could substantially reduce environmental impacts, with case studies showing up to a 50 % reduction in greenhouse gas emissions and energy consumption. Techno-economic analyses indicate that scaling up PHA production and improving yields are critical for economic feasibility. The review concludes that while lab-scale studies provide valuable insights there is a pressing need for industrial-scale applications and specific case studies to refine and validate these processes, focusing on sustainable and integrated approaches.