Hydrodynamic stress and lethal events in sparged microalgae cultures

The effect of high superficial gas velocities in continuous and batch cultures of the strains Dunaliella tertiolecta, Chlamydomonas reinhardtii wild-type and cell wall-lacking mutant was studied in bubble columns. No cell damage was found for D. tertiolecta and C. reinhardtii (wild-type) up to superficial gas velocities of 0.076 and 0.085 m s(-1), respectively, suggesting that high superficial gas velocities alone cannot be responsible for cell death and, consequently, bubble bursting cannot be the sole cause for cell injury. A death rate of 0.46 +/- 0.08 h(-1) was found for C. reinhardtii (cell wall-lacking mutant) at a superficial gas velocity of 0.076 m s(-1), and increased to 1.01 +/- 0.29 h(-1) on increasing superficial gas velocity to 0.085 m s(-1). Shear sensitivity is thus strain-dependent and to some extent the cell wall plays a role in the protection against hydrodynamic shear. When studying the effect of bubble formation at the sparger in batch cultures of D. tertiolecta by varying the number of nozzles, a death rate of 0.047 +/- 0.016 h(-1) was obtained at high gas entrance velocities. D. tertiolecta was cultivated in a pilot-plant reactor under different superficial gas velocities of up to 0.026 m s(-1), with relatively low gas entrance velocities and no cell damage was observed. There is some indication that the main parameter causing cell death and damage was the gas entrance velocity at the sparger. (C) 2003 Wiley Periodicals, Inc.