Two-stage Heterotrophic and Phototrophic Culture Technology for Microalgal Biofuel Production
Year: 2013
Type: dissertation
Abstract: Microalgae are attractive feedstocks for producing renewable biofuels.In this dissertation, I developed a two-stage heterotrophic and phototrophic microalgae culture system for biofuel production.Heterotrophic cultures could not only serve as seed for subsequent phototrophic growth, but also produ.cemicroalgal biomass and lipid separately by feeding with organic wastes.I demonstrated that the heterotrophically cultured microalga Chlorella sorokiniana was more efficient to be used as seed for subsequent phototrophic growth, due to the higher productivity and similar performance compared with its phototrophic counterpart.High inoculation of heterotrophically produced seeds was a potential tool for contamination control.High cell density heterotrophic cultivation of C. sorokiniana was achieved through two-stage fed-batch fermentation.With the optimized culture conditions, the algal biomass and lipid reached high concentrations of 103.8 g L -1 and 40.2 g L -1 .The lipid of C. sorokiniana contained a large amount of neutral lipids (92.9% of total lipids), triacylglycerols (82.8% of neutral lipids), and high contents of palmitic, oleic and linoleic acids, which were desirable feedstocks for biofuel production.v I evaluated the feasibility to culture C. sorokiniana for lipid production with cellulosic materials through a simultaneous saccharification and fermentation (SSF) process.The culture with substrate loading of 3% (w/v) and enzyme loading of 30 FPU/g cellulose was an appropriate combination for lipid production.Elevated temperature improved the SSF efficiency and the highest lipid concentration (2.98 g L -1 ), yield (99.2 mg g -1 ) and productivity (20.7 mg L -1 h -1 ) were achieved at 40°C.I studied D-xylose uptake and the related metabolism in C. sorokiniana.The sugar uptake kinetic analysis suggested that an inducible hexose symporter might be responsible for the transport of D-xylose.The maximum D-xylose transport rate was 3.8 nmol min -1 mg -1 cell with K m value of 6.8 mM.The enzymatic activities of NAD(P)Hlinked xylose reductase (XR) and NADP + -linked xylitol dehydrogenase (XDH) were detected in C. sorokiniana.Culturing C. sorokiniana under light improved D-xylose utilization due to additional NADPH from the light-dependent reaction of photosynthesis.The results presented in this study suggested that the two-stage heterotrophic and phototrophic process was a promising technology for microalgal biofuels production.vi
Author: Yubin Zheng
Language: English
Field: Energy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W2522341402