Gas‐Sparged bioreactors for CO₂ fixation by Dunaliella tertiolecta

Abstract

Two kinds of bioreactors, a bubble-column and an air-lift bioreactor, have been designed. The influence of operating conditions such as medium composition, light intensity, carbon dioxide concentration in the flushing gas, culture temperature, and gas flow rate, on photosynthesis of Dunaliella tertiolecta were studied using a chemometrics approach. The bubble-column bioreactor system was shown to be advantageous over the air-life because of a weaker intensity of hydrodynamic stress derived from gas bubble dispersion and culture broth mixing. Optimal conditions for carbon dioxide fixation or maximal growth rate were determined. The effect of hydrodynamic shear forces on the algal wall produced by gas bubbling was identified as one of the most significant factors for algal growth.

Influence of Organic Carbon Sources on Growth and Lipid Content of Marine Green Alga Dunaliella tertiolecta

“…This result is somewhat different from other studies in that the optimal condition for maximum growth rate of D. tertiolecta was under 6% CO 2 or 10% CO 2 [17,32]. Since the growth rate may depend on species chosen, gas supply rate and other multiple factors, it is difficult to generalize optimal CO 2 levels.…”

Effects of agitation on the microalgae Phaeodactylum tricornutum and Porphyridium cruentum

“…Algae such as Dunaliella are extremely fragile [18,19], but many other species will tolerate high levels of turbulence and sparging with gas. For example, the microalga Ochromonas malhamensis (8-20 lm average diameter cells) has withstood an impeller tip speed of up to 1.4 m s -1 with low-level sparging.…”

“…Damage to microalgae and cyanobacteria under processing conditions can be a real problem [6,[13][14][15][18][19][20], but susceptibility to damage is dependent on the species. Algae such as Dunaliella are extremely fragile [18,19], but many other species will tolerate high levels of turbulence and sparging with gas.…”

“…Supplementing the culture with carboxymethyl cellulose or agar improved cell survival. In one study with D. tertiolecta, culture in a bubble column was quite successful, but when the bubble column was converted to an airlift device by inserting a vertical baffle, the productivity declined [19]. Under conditions that were earlier identified as optimal, no growth was observed in the airlift reactor, whereas good growth occurred in the bubble column.…”

Growth aspects of the marine microalga Nannochloropsis gaditana

“…Bubbling also promotes the stirring of the culture, which affects both the mass transfer of nutrients through the cell membrane and the light distribution, by the light/dark cycles inside the reactor. On the other hand, the sensitivity of different species to shear forces produced by gas bubbling is a main factor that affect algal growth [21] and must be taken into account. Cell fragility is even referred as a key problem in microalgae biomass production in photobioreactors [15].…”