Microalgae growth in ultra-thin steady-state continuous photobioreactors: assessing self-shading effects

Abstract

To disclose the net effect of light on microalgal growth in photobioreactors, self-shading and mixing-induced light–dark cycles must be minimized and discerned from the transient phenomena of acclimation. In this work, we performed experiments of continuous microalgal cultivation in small-scale photobioreactors with different thicknesses (from 2 to 35 mm): working at a steady state allowed us to describe the effect of light after acclimation, while the geometry of the reactor was adjusted to find the threshold light path that can discriminate different phenomena. Experiments showed an increased inhibition under smaller culture light paths, suggesting a strong shading effect at thicknesses higher than 8 mm where mixing-induced light–dark cycles may occur. A Haldane-like model was applied and kinetic parameters retrieved, showing possible issues in the scalability of experimental results at different light paths if mixing-induced light–dark cycles are not considered. To further highlight the influence of mixing cycles, we proposed an analogy between small-scale operations with continuous light and PBR operations with pulsed light, with the computation of characteristic parameters from pulsed-light microalgae growth mathematical modeling.

Geranyl Diphosphate Synthase (CrtE) Inhibition Using Alendronate Enhances Isoprene Production in Recombinant Synechococcus elongatus UTEX 2973: A Step towards Isoprene Biorefinery

“…Techno-economic analyses of most of cyanobacteria-based biorefineries face challenges in regard to meeting economic feasibility and efficient bio-valorization due to expensive downstream processes, high input cost investment, and the production of limited products [12]. Furthermore, the self-shading in standard photobioreactor systems is one of the significant challenges to achieving high cell density [52]. To overcome this, the thickness of photobioreactors has to be curtailed.…”

“…To overcome this, the thickness of photobioreactors has to be curtailed. In one such study, Saccardo and colleagues made photobioreactors with thicknesses from 2 to 35 mm and observed strong self-shading at thicknesses above 8 mm [52]. Rapid growth rate and high amounts of cyanobacterial biomass accumulation are necessary to achieve the target volumetric productivity.…”