Effect of pH, Temperature, and CO 2 Concentration on Growth and Lipid Accumulation of Nannochloropsis sp. MASCC 11
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Effect of pH, Temperature, and CO2 Concentration on Growth and Lipid Accumulation of Nannochloropsis sp. MASCC 11 PENG Xiaoling, MENG Fanping*, WANG Yuejie, YI Xiaoyan, and CUI Hongwu Key Laboratory of Marine Environmental Science and Ecology, Ministry of Education, Ocean University of China, Qingdao 266100, China (Received August 3, 2019; revised March 2, 2020; accepted May 1, 2020) © Ocean University of China, Science Press and Springer-Verlag GmbH Germany 2020 Abstract This study determined growth and lipid accumulation in Nannochloropsis sp. MASCC 11 cultivated at different pH, temperatures, and CO2 concentrations in 10-day period. The suitability for biodiesel production was also evaluated based on the fatty acid profiles of microalgae lipid. Nannochloropsis sp. MASCC 11 showed an excellent tolerance to acidic pH (as low as 4.0), high temperatures (at least 40℃), and high CO2 concentrations (5%15%), which are major stressed conditions in flue gas. The highest algal biomass was acquired at pH of 9.0 (0.44 g L–1), a temperature of 35℃ (0.63 g L–1), and a CO2 concentration of 5% (2.27 g L–1). Maximum lipid production was obtained at pH of 6.0 (108.2 mg L–1), a temperature of 35℃ (134.6 mg L–1), and a CO2 concentration of 5% (782.7 mg L–1). Synthesis of polyunsaturated fatty acids (PUFAs) in biomass was stimulated under high CO2 concentrations, remaining above 80% of total fatty acids, mainly composed of C16:3, C18:2, and C18:3. This led to the algae-based biodiesel having a lower oxidation stability, better cold flow properties, and other parameters such as its kinematic viscosity, cetane number, and specific gravity complied with ASTM or EN 14214 biodiesel specifications. Therefore, the improvement of oxidative stability needs to be considered before Nannochloropsis sp. MASCC 11 lipid can be used for biodiesel production, even if this species can grow well under stressful conditions. Key words
Nannochloropsis sp. MASCC 11; tolerance; high CO2; biodiesel
1 Introduction In recent decades, energy crisis and global warming induced by CO2 emissions are worldwide environmental problems (Kan et al., 2019). Biodiesel is a compatible alternative to fossil fuel, which is biodegradable, renewable, and clean-burning (Mwangi et al., 2015). Microalgae are among the most promising feedstock for biodiesel production (Chisti, 2007). They can assimilate and convert CO2 from flue gas into biomass containing high amounts of lipids for subsequent biodiesel production (Parupudi et al., 2016); however, several challenges need to be overcome before microalgae can be successfully used for CO2 biofixation and biodiesel production. A typical power plant flue contains 5%15% CO2 (Vuppaladadiyam et al., 2018), accompanied by toxic associated gases such as SO2 (300 to 500 ppm), as well as high temperatures (more than 150℃) (Yoshihara et al., 1996; Kao et al., 2014). A continuous ventilation of flue gas will result in the decrease of pH in the liquid medium, which has an inhibitory effect on autotrophic algal growth (Ronda et al., 2014). T
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