Advances in the scale-up of microalgae production systems

Abstract of the oral presentation made at the 1st International Conference on Novel Photorefineries for Resource Recovery 2024, Valladolid, Spain.

The most relevant advances in the scale-up of microalgae production systems, especially those based on the use of raceway reactors, are reviewed. They include (i) the knowledge of the biological systems, (ii) the improvement of the design and operation of reactors, (iii) the enhancement of harvesting/processing technologies, and (iv) the implementation of advanced control systems including artificial intelligence-based tools. Concerning the biological systems, the models recently developed provide a complete overview of phenomena taking place, including the influence of culture conditions, the presence of different microorganisms, and the role of parasites (Sánchez Zurano et al., 2021). These models allow to determine the most efficient strategies to optimize their performance as a function of these variables, including the prevention of crashes. Concerning design, the use of computational fluid dynamics allows building units up to 1 ha, while minimizing energy consumption below 5 W/m³, and improving the light utilization efficiency by 25%(Inostroza et al., 2023). In the case of temperature, new heat exchangers designed allow to envisage the opportunity for controlling this variable including in large-scale facilities(Rodríguez-Miranda et al., 2021). The optimization of mass transfer capacity allows for the prevention excess of dissolved oxygen concentrations at the same time optimizing the use of CO₂ for pH control, and allowing the direct capture of CO₂ from the air(Barceló-Villalobos et al., 2022). The use of membranes is a major advance for harvesting/processing. Non-pressure membranes allow to pre-concentrate of the cultures at minimum cost/energy consumption while obtaining cell-free supernatants to be recirculated or for safe disposal, while low-pressure membranes allow to fractionate of the compounds of microalgae biomass without using solvents to achieve sustainable processes with zero emissions (Bilad et al., 2014). However, the most revolutionary improvement is the use of advanced control systems that allow for optimisation of the performance of the cultures/systems as a function of target function and environmental conditions. Low-level control strategies allow for the optimization of resources such as energy, nutrients, water, CO₂, etc(Pawłowski et al., 2018). High-level control strategies based on artificial intelligence are capable of adjusting the operation conditions to optimise the performance of the overall system(Munoz et al., 2022). All these advances have been already demonstrated with examples of those applications being provided.