FAME properties, bio-oil productivity and carbon yield coefficient of Chlorella sorokiniana grown with low and high initial nitrogen concentrations

Abstract

In this work the effect of the initial nitrogen concentration on the fatty acid methyl ester (FAME) properties namely the saponification number (SN), the iodine value (IV), the cetane number (CN) and the higher heating value (HHV) of bio-oil produced by Chlorella sorokiniana was examined. Also, the lipid and protein content of the biomass of C. sorokiniana and the biomass yield were measured. Anaerobic digestate and glycerol were used to formulate the culture media. The initial concentration of atomic nitrogen varied in the four cultivations and it was equal to 108.2 mg/l, 300 mg/l, 800 mg/l and 2000 mg/l while the initial concentration of carbon was held constant and equal to 13.99 ± 0.1 g/l. As the initial nitrogen concentration was increased, the lipid content decreased while the protein content and the biomass yield increased. Fatty acids (FA) from C10:0 to C26:1 were produced, however, the fatty acids that were found in the highest percentage were C16:0, C16:1, C18:1 and C18: 2. With respect to saturation, monosaturated FA were predominant in all treatments constituting from 55.9% to 59.4% of the total FA, while significant percentages of saturated FA were produced ranging from 24.5% to about 31.1%. With respect to the chain length, medium chain FA predominate constituting from 59.5% to 81.3% of the total FA. The four measured FAME properties, with the exception of the cetane number (CN) for the No = 2000 mg, were within acceptable limits. It was shown that when the nitrogen concentration in the medium increases, while the carbon concentration remains constant, the biomass carbon yield coefficient increases substantially.