A smart and precise mixing strategy for efficient and cost-effective microalgae production in open ponds

Microalgae biotechnology is a great candidate for carbon neutralization, wastewater treatment and the sustainable production of biofuels and food. Efficient and cost-effective microalgae production depends on highly coordinating the resources used for algal growth. However, dynamic natural disturbances such as culture temperature and sunlight can lead to the poor coordination and waste of resources. Open ponds are the most commonly used commercial microalgal production systems, and enhanced mixing can significantly increase their productivity, but mixing energy can be seriously wasted due to dynamic disturbances, presenting a hindrance to further reducing production costs. Herein, a smart and precise mixing strategy was developed for open ponds in which a paddle wheel's stirring speed for an open pond was smartly and precisely controlled in real time based on dynamic variations in light intensity and culture temperature. The proposed technology achieved the same biomass productivity of Spirulina platensis (8.37 g m^-2 day^-1) as a control with a constant high mixing rate under dynamic disturbances while reducing mixing energy inputs by approximately 30 % compared to the control. This study provides a promising method to address serious resource waste and poor coordination due to dynamic natural disturbances, holding great potential for efficient and cost-effective microalgae production.