| dc.description.abstract | Chlorella strains as compared to terrestrial oil crops such as palm, jatropha, soybean and rapeseed having higher oil content and shorter generation time have been considered as the promising candidates for alternative biodiesel.
Mixed culture of Chlorella sp. and Saccharomyces cerevisiae was proposed as a novel strategy for enhancing CO2 biofixation rate and oil formation as compared with the traditional monoculture of microalgae.
A symbiotic relationship was observed between S. cerevisiae and Chlorella sp., resulting in the improvements of cellular biomass and oil accumulation reached 128.1 % and 165.2 %, respectively. Influence of light intensity ranging from 1000 to 8000 lux on the cell growth and product formation of the mixed culture was significant but different; the optimal light intensity for cell growth was at 5000 lux, but the highest specific product yield was at 8000 lux. The CO2 biofixation rate of a mixed culture reached 64.76 mg L-1 h-1, which was 195 % improvement as compared to that of the monoculture of Chlorella sp. aerated with air. The biodiesel from the mixed culture would show low degree of unsaturation (71.74), resulting in better quality in terms of oxidative stability and ignition delay time property as compared to those from the monoculture.
Since the influence of light quality on oil formation of microalgae in either monoculture or mixed culture in literature was either inconsistent or ambiguous, a light-emitting diode (LED) photo-bioreactor with different light sources and intensities was used in this study to propose a cost-effective lipid production process. The oil accumulation in a mixed culture of Chlorella sp. and Saccharomyces cerevisiae was higher than that of the monoculture in spite of different light sources used. Results of the influence of light quality on the mixed culture indicated that the optimal light wavelength and intensity for biomass formation was red LED light at 1000 lux, whereas the optimum for oil formation was blue LED light at 1000 lux. A novel two-stage LED photo-bioreactor was thus proposed and the highest Pmax and productivity in this section were obtained as 261 mg L−1 and 8.16 mg L−1 h−1, respectively. The improvements of the productivity of the two-stage light control fermentation process over the cultures of blue LED light and red LED light under 1000 lux were 96% and 10%, respectively. A novel two-stage LED photo-bioreactor of a mixed culture was proposed to optimize microalgal oil production and successfully demonstrated in this study.
Compared with the modified Walne’s medium, the fish waste hydrolysate (FWH) medium had more efficiency in biodiesel production. The highest product concentration and productivity in this section were obtained as 1154 mg L−1 and 20.61 mg L−1 h−1, respectively. The improvement of product concentration and productivity of FWH medium condition were 222 % and 176 %, respectively, as compared with Walne’s medium condition. Considering its low-cost, FWH medium could be a potential nutrient and a substitute for commercial complex medium, with an environmental solution in addition.
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