Photosynthetic Activity Measured In Situ in Microalgae Cultures Grown in Pilot-Scale Raceway Ponds

Area of Science:

• * Photosynthesis and photophysics in microalgae.
• * Aquatic botany and algal cultivation.
• * Environmental monitoring of biological systems.

Background:

• * Microalgae are cultivated in large-scale systems like raceway ponds (RWPs) for various applications.
• * Understanding in situ photosynthetic performance is key to optimizing RWP design and operation.
• * Factors like light availability, depth, and dissolved oxygen significantly influence microalgal growth.

Purpose of the Study:

• * To monitor the in situ photosynthesis performance of *Scenedesmus* sp. in a raceway pond.
• * To investigate the influence of culture depth on photosynthetic variables.
• * To correlate physicochemical parameters with microalgal photosynthetic activity.

Main Methods:

• * Cultivation of *Scenedesmus* sp. in a greenhouse raceway pond.
• * In situ monitoring of actual photochemical yield (Y(II)) using in vivo chlorophyll fluorescence.
• * Measurement of electron transport rate and photosynthetic oxygen production at various depths.
• * Recording of irradiance, temperature, and dissolved oxygen concentration.

Main Results:

• * The active photic layer in diluted cultures (0.6 g DW L⁻¹) was limited to approximately 1 cm.
• * Non-photochemical quenching mechanisms may not adequately protect cells moving to deeper, darker zones.
• * Cultures maintained high photochemical yield (Y(II) > 0.35) even at high dissolved oxygen levels (>200% saturation).

Conclusions:

• * Most of the microalgal culture in RWPs remains photosynthetically inactive due to limited light penetration.
• * Optimizing light distribution and managing cell concentration are critical for enhancing productivity in large-scale microalgae cultivation.
• * The study provides valuable data for refining growth strategies in raceway ponds.