Biopolymers and Bioplastics

Biography

Biography: Jian Yu

Abstract

Poly(3-hydroxybutyrate) or PHB is an eco-friendly thermoplastic synthesized by some microbial species from renewable carbohydrates. A conventional production route of PHB therefore includes two stages: (1) agricultural farming to produce carbohydrates (CH2O) from CO2, water and sunlight via natural photosynthesis (CO2 + H2O  CH2O + O2), and (2) microbial conversion of the organic carbonaceous substrates into PHB. The green plastic can now be produced directly from CO2, water and sunlight via an artificial photosynthesis system, consisting of a photovoltaic panel, a water electrolysis cell, and a dark fermenter. The intermittent solar radiation is captured and converted into electricity that immediately splits water into H2 and O2 for direct use and/or storage. CO2 is fixed continuously in dark conditions by a Knallgas bacterium that grows on CO2, H2 and O2. A laboratory facility was demonstrated including: a solar panel with 17% efficiency of sunlight to electricity, a membrane water electrolyzer with 84% efficiency of electricity to H2, and a bioreactor in which microbial cells fixed CO2 by using H2 and O2 with an efficiency of 20-50%, depending on gas composition. The overall energy efficiency therefore ranged from 2.9 to 7.1, or an average efficiency of 5% from solar energy to biomass (CH2O), which is much higher than the efficiency of conventional photosynthesis of plants (<1%) and microalgae (2-3%). About 50% of cell mass formed from CO2 was PHB. The microbial residues, after PHB recovery, can be reused in dark fermentation as a nutrient source. The mass transfer of gas molecules to microbial cells in bioreactor was the rate-limiting step and characterized with a volumetric mass transfer coefficient (kLa). The productivity of PHB in a conventional bioreactor with a moderate kLa was improved by 57% in a novel bioreactor. More importantly, the PHB yield per amount of H2 fed is increased by 475%.