Ultrasound-Assisted Extracellular Polymeric Substance Removal from the Diatom Navicula sp.: A Route to Functional Polysaccharides and More Efficient Algal Biorefineries

Abstract

Extracellular polymeric substances (EPS) from microalgae have potential as functional polysaccharides for various food and industrial applications. This study investigates the use of ultrasonication to remove EPS from the diatom Navicula, first as a potentially useful byproduct of lipid and protein production and second in terms of the effect of EPS removal on downstream processing, including slurry rheology, dewatering, and lipid extraction. Ultrasound (20 kHz) was effective at removing EPS; however, cell rupture also resulted, particularly at high yields involving the removal of bound EPS. Increasing the power intensity/density did not affect the cell rupture at a given EPS yield but halved the energy requirement. Importantly, EPS removal improved the rheology and dewaterability of the cell suspensions, by interrupting intercellular connections and reducing the overall hydrodynamic volume of the cells. For a 5 wt. % cell slurry, EPS removal by sonication for 30 s reduced the shear-dependent viscosity by about 10-fold, and increased the solid concentrations following centrifugation by >sevenfold. Subsequent biphasic lipid extraction was also accelerated by the removal of EPS as a barrier between the cells and the solvent. The decreased viscosity, increased concentration, and improved extraction kinetics should enable greatly intensified downstream processing.

Flue gas waste heat affects algal liquid temperature for microalgal production in column photobioreactors

“…During the initial 12 h of cultivation, the different temperature conditions did not cause significant differences in growth rates; however, after 12 h, the differences gradually increased. The highest growth rates were consistently observed at 35°C and 37.5°C, with the highest biomass concentration (1.464 g/L) measured at 48 h. Afterwards, because of the rapid algal growth rate and higher temperature, the concentration of extracellular polymers increased, causing a higher liquid viscosity 32,33 . As a result, the phenomenon of clumping and walling occurred in the vent tube and above the algal liquid, leading to a decrease in the biomass concentration of the algal liquid.…”

“…The highest growth rates were consistently observed at 35°C and 37.5°C, with the highest biomass concentration (1.464 g/L) measured at 48 h. Afterwards, because of the rapid algal growth rate and higher temperature, the concentration of extracellular polymers increased, causing a higher liquid viscosity. 32,33 As a result, the phenomenon of clumping and walling occurred in the vent tube and above the algal liquid, leading to a decrease in the biomass concentration of the algal liquid. Conversely, wall flocculation was less severe at 30°C and 40°C, where the growth rate was slightly slower, while at 25°C and 42°C, flocculation was almost nonexistent and the biomass concentration in the algal liquid continued to increase after 48 h. At low temperatures, the metabolic processes and enzyme activity of algal cells are constrained, resulting in a sluggish growth rate of microalgae.…”