Indole-3-Acetic Acid Action in Outdoor and Indoor Cultures of Spirulina in Open Raceway Reactors

A significant research gap exists in investigating large-scale microalgae cultures exposed to outdoor conditions, with the addition of phytohormones using non-sterile growth media. Implementing these conditions is crucial for verifying the industrial viability of this strategy. This study aimed to evaluate the effect of indole-3-acetic acid (IAA) supplementation on Spirulina sp. LEB 18 cultures conducted indoors and outdoors in raceway bioreactors. The outdoor experiments were performed under uncontrolled environmental conditions. The indoor cultures were maintained within a thermostat-controlled chamber at a consistent temperature and lighting intensity. The outdoor experiments supplemented with IAA achieved a biomass concentration of 5.43 g L−1 and productivity of 173.9 mg L−1 d−1. These values increased 122.5% and 130.9% in biomass concentration and productivity, respectively, compared to the indoor experiments with the same supplementation. Moreover, roughly half of the biomass generated from outdoor cultivation with IAA consisted of carbohydrates (45%). Compared to indoor cultivation, this approach reduced production costs for biomass (55%) and lowered production costs for carbohydrates, proteins, and lipids by 86%, 44%, and 50%, respectively. The successful application of phytohormones in microalgae cultures, particularly under larger scale, nonsterile, and outdoor conditions, represents a significant advancement toward industrial implementation.