Process development for biomass and lipid production from a local chlorella isolate using a miniature parallel raceway pond reactor.
Year: 2020
Type: dissertation
Abstract: The consumption of fossil fuels such as coal and oil are unsustainable and has proved to be detrimental to the environment.There was a need to explore alternative sources of energy.Microalgal biomass and lipids have the potential to produce a variety of high value products; such as biofuels, bioactive medicinal products and food additives and these microorganisms have attracted worldwide interest.Microalgal biodiesel was an excellent substitute to liquid fossil fuels due to its cost effectiveness, renewability and environmental benefits.Although biodiesel production from microalgal feedstock was a feasible source of bioenergy, its commercialization was still curbed by a number of techno-economical challenges.Bioprocess modelling and optimization at upstream and downstream stages was necessary to enhance product yields and improve viability of the technoeconomic output.In this study, the Response Surface Methodology (RSM) was used to model and optimize their biomass and lipid productivity of Chlorella sp.based on the input parameters; nitrogen concentration, iron concentration and phosphorus concentration within the ranges of 0.50 -2.00 g L -1 , 3.00 -9.00 mg L -1 , and 0.00 -40.00 mg L -1 , respectively.The experiments were carried out in a novel miniature raceway pond photobioreactor.This reactor comprised of 15 units of 1.5L raceway ponds enclosed in a transparent plexiglass case with dimensions of 820 × 970 × 190 mm.This structure allowed for parallelization raceway pond experiments.Experimental data were used to develop polynomial models.Analysis of variance (ANOVA) carried out on the developed models gave coefficient of determination values of 0.99 and 0.98 for biomass and lipid productivity, respectively.Nitrogen was found to be the most important input factor to biomass productivity whereas iron was most influential to lipid productivity.Optimized process yielded biomass and lipid productivities of 114.5 mg L -1 d -1 and 38.23 mg L -1 d -1 , respectively.The use of a parallel miniature raceway pond photobioreactor enabled high throughput experimentation for microalgae process development with the geometrical configuration of large-scale raceway ponds vi The kinetic studies of Chlorella sp growth showed a maximum specific growth rate (µmax) of 0.01 g L -1 h -1 and a cell concentration (Xmax) of 1.78 g L -1 .The logistic model fitted well to the experimental data (R 2 value of 0.98).These kinetics data provide insights into Chlorella bioprocess scale up as well as the biological characteristics of a microorganism involved in a bioprocess.Knowledge of such characteristics will inevitably enhance the feasibility of a bioprocess.An additional challenge in microalgae bioprocessing was the harvesting of microalgae biomass.In this study, the potential of using magnetic iron oxides for harvesting Chlorella sp. was investigated.The response surface methodology was used to optimize the recovery efficiency of crude (uncoated), tri-sodium citrate (TSC) and chitosan coated magnetic iron oxides.The operational parameters consisted of nanoparticles to microalgae culture exposure time, magnet retention time, pH and nanoparticles concentration.Experimental data were used to fit polynomial models using RSM.Analysis of variance gave coefficients of determination (R 2 ) values of >0.7 for crude, TSC and chitosan nanoparticles.Findings showed that tri-sodium citrate coated magnetic nanoparticles had the highest recovery efficiency of 95% compared to crude and chitosan (efficiencies of 85% and 87%, respectively).Additionally, the exposure time of the algae culture to the nanoparticle's solution was found to be a significant factor for the recovery efficiency of crude nanoparticles, whereas magnet retention time had a higher positive influence on the recovery efficiency of TSC nanoparticles.The concentration of nanoparticles positively affected the recovery efficiency of chitosan coated nanoparticles.This was evident from the polynomial model equations illustrating individual and interactive effects of the input parameters on the output.Sensitivity studies on the recovery efficiency as a function of changes on process inputs revealed that for crude nanoparticles, the concentration of nanoparticles has a non-linear relationship with the recovery efficiency.Magnet retention time displayed a linear relationship for all nanoparticles types where an increase in this factor resulted in a proportional increase in the recovery efficiency.Increasing the exposure time of the algae culture to nanoparticles as well as pH increased recovery efficiency of chitosan coated nanoparticles whereas the opposite effect was observed for crude and TSC nanoparticles.vii These findings demonstrated that Chlorella sp. was an attractive biodiesel feedstock.Modelling of biomass and lipid productivity revealed that optimal productivities of both biomass and lipid could be obtained using an appropriate mixture ratio of nitrogen and iron.The kinetic model provided crucial information on the growth of Chlorella sp for bioprocess development and scale up.The use of a novel miniature raceway pond photobioreactor provided a throughput experimentation using a geometrically similar environment for large scale microalgae production using raceway reactor.This ensured that reliable process data were generated for subsequent scale up.For downstream processing, tri-sodium citrate coated nanoparticles displaying the highest recovery efficiency.Sensitivity studies revealed shorter exposure time to algal culture and a lower pH resulted in a higher recovery efficiency from TSC coated nanoparticles.Findings from this study provided insight for upstream and downstream microalgae process development using the local isolate of Chlorella sp.
Author: Gumbi, Zanenhlanhla Gugulethu.
Language: English
Field: Energy
Domain: Physical Sciences
Open Access status: green
Funder: National Research Foundation
OpenAlex ID: W3096688478