Influence of different reactor types on Nannochloropsis oculata microalgae culture for lipids and fatty acid production

Abstract

Greenhouse gases emitted into the atmosphere by burning of fossil fuels cause global warming. One option is obtaining biodiesel. Nannochloropsis oculata was cultured under different light intensities and reactors at 25°C for 21 days with f/2 medium to assess their effects on cell density, lipid, and fatty acids (FAs). N. oculata improved cell density on fed‐batch glass tubular reactor (7 L) at 200 μmol E m−2 s−1, yielding 3.5 × 108 cells ml−1, followed by fed‐batch Erlenmeyer flask (1 L) at 650 μmol E m−2 s−1 with 1.7 × 108 cells ml−1. The highest total lipid contents (% g lipid × g dry biomass−1) were 44.4 ± 0.8% for the reactor (1 L) at 650 μmol E m−2 s−1 and 35.2 ± 0.2% for the tubular reactor (7 L) at 200 μmol E m−2 s−1, until twice as high compared with the control culture (Erlenmeyer flask 1 L, 80 μmol E m−2 s−1) with 21.2 ± 1%. Comparing the total lipid content at 200 μmol E m−2 s−1, tubular reactor (7 L) and reactor 1 L achieved 35.2 ± 0.2% and 28.3 ± 1%, respectively, indicating the effect of shape reactor. The FAs were affected by high light intensity, decreasing SFAs to 2.5%, and increased monounsaturated fatty acids + polyunsaturated fatty acids to 2.5%. PUFAs (20:5n‐3) and (20:4n‐3) were affected by reactor shape, decreasing by half in the tubular reactor. In the best culture, fed‐batch tubular reactor (7 L) at 200 μmol E m−2 s−1 contains major FAs (16:0; 38.06 ± 0.16%), (16:1n‐7; 30.74 ± 0.58%), and (18:1n‐9; 17.15 ± 0.91%).

LASSO Regression with Multiple Imputations for the Selection of Key Variables Affecting the Fatty Acid Profile of Nannochloropsis oculata

“…In other cases, the cell density was provided as a function of time along with the final biomass concentration [ 6 ] or with information regarding the biomass productivity, which could be used to estimate the final biomass concentration [ 45 , 66 ]. In those cases, the initial biomass concentration was estimated using the cell count and the assumption that the average single cell weight was 10 pg for the lower limit and equal to the final biomass weight/cell count for the upper limit [ 67 ].…”

“…The FA composition of N. oculata can be affected by various factors, including temperature, light intensity, pH, and the type of reactor used for cultivation [ 1 , 5 , 6 ]. Temperature plays a significant role in the FA composition of N. oculata , with total lipid content increasing with temperature, while polyunsaturated fatty acid (PUFA) levels decrease and saturated fatty acid (SFA) levels increase [ 5 ].…”

“…Su et al reported that irradiance of 500 μmol photons m −2 s −1 resulted in the highest total lipid productivity [ 8 ]. In another study, Martínez-Macias et al found that saturating light intensity reduced the levels of SFAs and increased the combined levels of monounsaturated fatty acids (MUFAs) and PUFAs, although the variation was marginal [ 6 ]. Additionally, the type of reactor used for cultivation had a great impact on the FA profile, as demonstrated by the same authors, who observed a decrease in PUFAs (20:5n-3) and (20:4n-3) when using a tubular reactor instead of an Erlenmeyer flask [ 6 ].…”