A new method for the online determination of mass transfer and oxygen production rates in microalgae raceway reactors

Abstract

In this study, a novel methodology for the real-time determination of mass transfer coefficient and oxygen production rates in large-scale raceway reactors for microalgae cultivation was developed. An innovative approach based on dissolved oxygen (DO) measurements and controlled air pulse injections provided accurate and real-time insights into the photosynthetic performance of microalgae cultures and the efficiency of gas exchange mechanisms within the reactor. Experiments were performed in 80 m² raceway reactors under continuous operation. A set of controlled aeration pulses at different flow rates (125, 250, 375, and 500 L/min) is applied throughout the day, enabling the evaluation of oxygen production under varying light intensities. The method is designed to operate without disrupting culture stability and ensures continuous monitoring of mass transfer dynamics in raceway reactors. The optimal conditions for the utilization of the proposed methodology are defined, and the robustness and accuracy of results are validated. Results demonstrate that oxygen production rates directly correlate with solar radiation, following a linear trend that serves as a proxy for biomass productivity. The study confirms that the sump section plays a crucial role in oxygen desorption, with mass transfer coefficients reaching up to 200 h⁻¹ at maximal superficial gas velocities below 0.02 m/s, then operating in a homogeneous aeration regime. This research provides a powerful tool for optimizing large-scale microalgae production systems, enabling real-time performance monitoring and dynamic process control to enhance biomass productivity.