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

Area of Science:

• Biotechnology
• Photobioreactor Engineering
• Microalgal Cultivation

Background:

• Accurate assessment of light's effect on microalgal growth requires minimizing self-shading and distinguishing mixing-induced light-dark cycles from acclimation.
• Photobioreactor design significantly influences light availability and distribution within the culture.

Purpose of the Study:

• To determine the net effect of light on microalgal growth by isolating it from self-shading and mixing phenomena.
• To identify the critical light path threshold for differentiating various light-related effects in microalgal cultures.
• To evaluate the impact of mixing-induced light-dark cycles on experimental results and scalability.

Main Methods:

• Continuous microalgal cultivation experiments in small-scale photobioreactors with varying thicknesses (2–35 mm).
• Steady-state operation to analyze post-acclimation light effects.
• Geometric adjustments to identify phenomena-discriminating light paths.
• Application of a Haldane-like model to retrieve kinetic parameters.

Main Results:

• Increased light inhibition observed with smaller culture light paths.
• Significant shading effects identified at thicknesses exceeding 8 mm.
• Potential for mixing-induced light-dark cycles at higher thicknesses.
• Haldane-like model indicated potential scalability issues if mixing effects are ignored.

Conclusions:

• Microalgal growth is significantly affected by light path length and mixing dynamics in photobioreactors.
• Self-shading becomes pronounced beyond an 8 mm light path.
• Accurate modeling and scalability assessments necessitate consideration of mixing-induced light-dark cycles, analogous to pulsed-light conditions.