Cradle-to-gate life cycle assessment for a cradle-to-cradle cycle: biogas-to-bioplastic (and back).

At present, most synthetic organic materials are produced from fossil carbon feedstock that is regenerated over time scales of millions of years. Biobased alternatives can be rapidly renewed in cradle-to-cradle cycles (1-10 years). Such materials extend landfill life and decrease undesirable impacts due to material persistence. This work develops a LCA for synthesis of polyhydroxybutyrate (PHB) from methane with subsequent biodegradation of PHB back to biogas (40-70% methane, 30-60% carbon dioxide). The parameters for this cradle-to-cradle cycle for PHB production are developed and used as the basis for a cradle-to-gate LCA. PHB production from biogas methane is shown to be preferable to its production from cultivated feedstock due to the energy and land required for the feedstock cultivation and fermentation. For the PHB-methane cycle, the major challenges are PHB recovery and demands for energy. Some or all of the energy requirements can be satisfied using renewable energy, such as a portion of the collected biogas methane. Oxidation of 18-26% of the methane in a biogas stream can meet the energy demands for aeration and agitation, and recovery of PHB synthesized from the remaining 74-82%. Effective coupling of waste-to-energy technologies could thus conceivably enable PHB production without imported carbon and energy.