Effects of small-scale turbulence on microalgae

Abstract

Turbulence flows are characterized by their viscous dissipation rates ɛ and the kinematic viscosity of the fluid ν, but the effects of turbulence on organisms such as microalgae smaller than the Kolmogorov inertial-viscous length scale LK ≡ (ν3/e)/14 depend on the stress τ ≡ µγ, where µ = ϱν is the dynamic viscosity, ρ is the density, and the rate-of-strain γ ≡ (e/ν)/12. While various workers have shown qualitatively that turbulence affects several microalgal physiological processes, these effects have not been quantified in terms of e, τ or γ. Various microalgal groups seem to have different sensitivities to inhibition by turbulence. The relative sensitivities aregreen algae 0.18 cm2s−3, τ > 0.04 dynes cm−2 (0.002 N M−2 or Pa), γ > 4.4 rad s−1, cell numbers and chlorophyll fluorescence declined, and cells lost their longitudinal flagella and the ability to swim forward. At lower e, τ and γ values growth rates and cell morphology were the same as in unsheared control cultures. High turbulence may affect other algae, such asSpirulina, which are commonly mass cultured.