Review of energy balance in raceway ponds for microalgae cultivation: Re-thinking a traditional system is possible

The present work addresses energy consumption in raceway ponds (RWPs). This kind of systems are today the most utilized industrial plant for outdoor algae cultivation. The problem has been addressed combining theoretical correlations and experimental data. Head losses for conventional raceway ponds were evaluated, and the results were compared with data available in literature. Computational fluid dynamics was used to support the theoretical analysis. This study suggested possible improvements to the traditional RWP design: an Innovative Raceway Pond (IRP II) was therefore designed, built and operated in parallel with a reference pilot RWP in a test site. Several modifications to traditional RWP design were implemented in the IRP II: the paddle wheel was substituted by a propeller, the water head was reduced and baffle boards were installed in the curves. To validate the new design, head losses and therefore energy consumption in the different systems were evaluated, during cultivation experiments, with two microalgae strains. The theoretical and experimental study allowed a validated calculation, which showed the importance of concentrated head losses towards distributed ones. The analysis highlighted how these losses weight at different pond scales, suggesting possible improvements of the RWP energy performance – as achieved in the IRP II – through revised design for optimized mixing.