Conversion of Pine Sawdust into Polyhydroxyalkanoate Bioplastics

This study investigated the potential of producing polyhydroxyalkanotes (PHAs) from pine sawdust through chemical and microbial conversions. The woody biomass was treated in an acidic solution to form levulinic acid (LA) and other hydrolysates that were used by Cupriavidus necator for microbial growth and PHA synthesis. To overcome microbial inhibition by the hydrolysates, we systematically investigated the role of different potential inhibitors in defined media and tested the effects of different detoxification treatments on microbial activity. In defined media, we measured the inhibitive concentration levels of organic acids, phenolic compounds, furanics, and nickel, a representative heavy metal ion that leached out from the equipment material under biomass hydrolysis conditions. Results from model compounds in defined media suggest that C. necator is able to tolerate furanics (10 mM) and phenolics (2.5 mM). Microbial growth and PHA synthesis were completely inhibited by an untreated hydrolysate solution but recovered to different extents after treatments. In addition to the organic inhibitors, nickel could inhibit microbial activity at a concentration as low as 0.25 mM, much higher than the concentration (3.6 mM) in a real hydrolysate solution. This work demonstrates an effective strategy for sustainable production of PHA from pine biomass.