Abstract
The study aimed to determine the effectiveness of docosahexaenoic acid (DHA) production by Schizochytrium sp. biomass fed with waste glycerol depending on the concentration of extracellular polymeric substances (EPS) in the culture medium and medium aeration effectiveness. The microalgae from the genus Schizochytrium sp. were proved to be capable of producing EPS composed of glucose, galactose, mannose, fucose, and xylose. The highest EPS concentration, reaching 8.73 ± 0.09 g/dm3, was determined at the stationary growth phase. A high EPS concentration caused culture medium viscosity to increase, contributing to diminished oxygen availability for cells, lower culture effectiveness, and reduced waste glycerol conversion to DHA. The Schizochytrium sp. culture variant found optimal in terms of the obtained technological effects and operating costs was performed at the volumetric oxygen mass transfer coefficient of kLa = 600 1/h, which enabled obtaining dry cell weight (DCW) of 147.89 ± 4.77 g/dm3, lipid concentration of 69.44 ± 0.76 g/dm3, and DHA concentration in the biomass reaching 29.44 ± 0.36 g/dm3. The effectiveness of waste glycerol consumption in this variant reached 3.76 ± 0.31 g/dm3·h and 3.16 ± 0.22 g/gDCW.
Highlights
Microalgae from the genus Schizochytrium sp. are known for producing valuable compounds, e.g., docosahexaenoic acid (DHA)—belonging to the Omega-3 family of fatty acids
A linear correlation was found between dry cell weight (DCW) of Schizochytrium sp. biomass, viscosity of the culture medium, and extracellular polymeric substances (EPS) concentration (Figure 2)
The Schizochytrium sp. population reached the stage of the stationary growth, which determined a ramped increase in EPS concentration to 7.25 ± 0.11 g/dm3, followed by its stabilization, and its final concentration of 8.73 ± 0.09 g/dm3 after 120 h of incubation (Figure 1)
Summary
Microalgae from the genus Schizochytrium sp. are known for producing valuable compounds, e.g., docosahexaenoic acid (DHA)—belonging to the Omega-3 family of fatty acids. Boost yield, and improve cost-effectiveness of DHA production by Schizochytrium sp., studies have analyzed multiple technological parameters having a significant impact on the final production results. These included: culture medium pH [4], temperature [5], turbine speed [6,7], nutrient concentration [8], oxygen concentration [9], initial inoculum concentration [10], and salinity [11]. Values of these basic parameters characterizing Schizochytrium sp. culture conditions determined under laboratory conditions are not always consistent with respective values obtained from large-scale installations [12,13]
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