Toward realistic LCAs of methanotrophic PHB: biological, operational, and environmental considerations

Abstract

Polyhydroxybutyrate (PHB) production by methanotrophs presents a compelling opportunity to couple greenhouse gas (GHG) mitigation with biodegradable plastic production. Despite this potential, only a limited number of life cycle assessment (LCA) studies have examined methanotrophic PHB systems, and many rely on assumptions that overlook fundamental biological and process-level constraints. In this critical review, we evaluate the key physiological traits of methanotrophs and the technical characteristics of CH₄-to-PHB bioprocesses that directly influence energy demand, material flows, and environmental impact. We assess whether existing LCAs adequately capture these factors, and identify systematic methodological omissions—including unrealistic assumptions of thermophilic strains, exclusion of energy for temperature control and gas pretreatment, and continued reliance on outdated data for high-performing strains such as Methylocystis sp. GB 25. These gaps collectively risk overestimating the environmental benefits of methanotrophic PHB. By integrating updated microbiological knowledge, future LCAs can more accurately represent the sustainability profile of gas-fermentation-based biopolymers. This review delineates the essential biological, operational, and methodological considerations needed to align LCA practice with the realities of methanotrophic PHB production and to support evidence-based development of sustainable bioplastic technologies.