Date of this Version
Li, M. 2015. Adding value to lignocellulosic biorefinery: efficient process development of lignocellulosic biomass conversion into polyhydroxybutyrate. in: Biological Systems Engineering, Vol. Ph.D. dissertation, University of Nebraska-Lincoln. Lincoln, Nebraska, pp. 172.
Polyhydroxybutyrate (PHB) is bacteria synthesized polymer that has comparable mechanical properties as petroleum-based plastics and high biocompatibility. Current commercial PHB production process is not cost effective. Raw materials make up about 50% of the production cost. Lignocellulosic biomass are cheap, abundant feedstocks that can be converted into PHB to add profit and sustainability to lignocellulosic biorefinery. Lignocellulosic biorefinery upstream process produces polymeric sugar rich stream and lignin-enriched stream. Polymeric sugars are then hydrolyzed into a sugar stream with glucose, xyloseand arabinose mainly present. To the best of the author’s knowledge, limited studies have been done on sugar mixture conversion into PHB. For lignin, previous research achieved a PHB production ranging from 0.13 to 1 g/L, which is too low to be economical. The primary objectives of this research were twofold: (1) process development of polymeric sugars conversion into PHB, with a focus on sugar mixture conversion into PHB by Burkholderia sacchari DSM 17165, and (2) process development of lignin into PHB by Cupriavidus necator DSM 545, with a focus on enhancing PHB production using various types of supplements. For sugar mixture conversion into PHB, first, shake flask (250 mL) scale statistical experimental design and modeling were performed to optimize sugar mixture ratio and process variables for maximal PHB production; second, bioreactor scale (3L) fed-batch cultivation was conducted to produce PHB from simulated corn fiber sugar mixture. The highest PHB production reached 67 g/L for 4:2:1 (glucose:xylose:arabinose) mixture at 41 h corresponding to an accumulation of 77% of cell dry weight. Corresponding sugar conversion efficiency and productivity were 0.33 g PHB/g sugar consumed and 1.6 g/L/h, respectively, which are comparable to or higher than most previous studies. For lignin conversion into PHB, first, shake scale (250 mL) study achieved 10-fold increase (0.2 to 2.1 g/L) in PHB production by optimizing supplement formulations with Plackett-Burman and central composite designs. Second, fed-batch cultivation at bioreactor scale (1.7 L) were conducted to enhance PHB production to 4.5 g/L. This is the highest PHB production from lignin that the author has been aware of in the literature.
Advisor: Mark R. Wilkins