PhD Oral Defence: Sustainable polyhydroxybutyrate production in integrated forest biorefineries
PhD Oral Defence of Karolin Dietrich, Bioresource Engineering
Biopolymers can provide environmentally friendly alternatives to the use of fossil fuel derived polymers. Among the most promising, yet expensive biopolymers are the microbiologically produced polyhydroxyalkanoates (PHAs), since they are compostable and also biodegrade in the marine environment. To produce PHAs sustainably, this work explores the feasibility of integrating the most well-known PHA, polyhydroxybutyrate (PHB), into forest biorefineries using the bacterium Paraburkholderia sacchari. The first forest biorefinery scheme was based on the hydrolysis of softwood hemicellulose as a feedstock for PHB production. The softwood hemicellulose sugars mannose and galactose were tested as carbon sources for P. sacchari for the first time and showed maximum specific growth rates of 97% and 60% relative to glucose, respectively. However, the presence of inhibitory compounds (acetate, 5‑hydroxymethylfurfural, furfural and phenols) inhibited all bacterial growth. The second biorefinery scheme studied was based on a pilot plant process developed by FPInnovations using hardwood biomass. In high-cell density bioreactor fermentations, the wood hydrolysate afforded one of the highest PHB concentrations to date from lignocellulosic biomass. Similar to literature values of PHB, the number average molecular mass was 246.4 kDa with a PDI of 3.29. These results make PHB from hardwood hydrolysate, as co‑product with H‑lignin, a sustainable production scheme for industrial PHB production.