Lipid accumulation and profiling in microalgae Chlorolobion sp. (BIOTECH 4031) and Chlorella sp. (BIOTECH 4026) during nitrogen starvation for biodiesel production

Abstract

Lipid-accumulating microalgae are an emerging feedstock for production of liquid biofuel because of their high biomass and lipid productivity. The potential of the green microalgae, Chlorolobion sp. (BIOTECH 4031) and Chlorella sp. (BIOTECH 4026), for biodiesel production was evaluated by analyzing the effect of nitrogen starvation (0.375–1.500 g L−1 NaNO3) on growth response, oil yield, and fatty acid methyl ester (FAME) profiles of the two algal strains. Maximum biomass yields for Chlorolobion sp. and Chlorella sp. were obtained after 20 days of cultivation using the control medium (1.5 g L−1 NaNO3) with 0.873 g L−1 and 0.757 g L−1, respectively. An increasing trend in the total lipid yield was observed under a nitrogen-starved culture condition (0.375 g L−1 NaNO3). When the amount of nitrate was limited, the mean oil contents of Chlorolobion sp. and Chlorella sp. were 31.61 and 28.77% with lipid productivity of 227.84 and 151.14 mg L−1 day−1, respectively. Nitrogen starvation caused an increase in the lipid yield and a decrease in biomass production of the two microalgae. The FAME profile of the obtained algal biodiesel shows a high concentration of saturated fatty acid (SAFA) and monounsaturated fatty acid (MUFA) methyl esters which are desirable for biodiesel production. The fuel properties of biodiesel from the two microalgae were predicted based on the molecular properties of fatty acid methyl esters using empirical equations showing that the biodiesel properties of the two microalgae satisfied the set specifications of biodiesel standards EN 14214 (European) and ASTM D6751 (American). The quality properties of biodiesel obtained for Chlorolobion sp. were low density (0.89 g cm−3), low kinematic viscosity (2.79 mm2 s−1), cetane number (65.17), and oxidation stability (8.93 h). On the other hand, Chlorella sp. has low density (0.88 g cm−3), low kinematic viscosity (2.78 mm2 s−1), good cetane number (68.79), and oxidation stability (10.44 h). Hence, Chlorolobion sp. (BIOTECH 4031) and Chlorella sp. (BIOTECH 4026) have potential as raw material for production of biodiesel with superior fuel quality.