Investigating the Fate of Geosmin on Microalgal Cells: A Comprehensive Study on Adsorption and Desorption Processes

ABSTRACT Microalgal biomass has emerged as a valuable resource in recirculating aquaculture systems (RAS), due to its natural capacity to recover nutrients. In addition, microalgae are potential source of fish‐feed in the aquaculture industry. However, its application in RAS needs careful consideration, as microalgae can interact with geosmin, a common off‐flavor compound found in RAS, which may taint fish quality and makes it unsaleable for the market. In this study, we investigate the potential interaction between geosmin and different microalgal strains, Nannochloropsis oculata and a consortium of Tetraselmis suecica and Phaeodactylum tricornutum , including both living and dead biomasses. Experimental studies with dead biomass revealed that N. oculata and the microalgal consortium can uptake geosmin with an efficiency of 53 ± 0.48% and 25 ± 1.63% over 24 h, respectively. Similarly, with living biomass, uptake efficiencies were 54 ± 0.68% and 42 ± 4.14%, respectively. Based on the higher uptake efficiency, N. oculata was selected for further investigation. Different non‐linear isotherm models (Langmuir, Freundlich, and Henry's Law), kinetic models (pseudo‐first order model, pseudo second‐order model, and Elovich model), and desorption study were used to understand potential sorption mechanisms and assess risks associated with geosmin accumulation in microalgal biomass. Geosmin adsorption by dead N. oculata was best described by Henry's isotherm law and the pseudo‐second order kinetic model, while adsorption on living biomass aligned best with Langmuir isotherm model and the pseudo‐second order kinetic model. Geosmin is released higher from living biomass (79 ± 3.18%) than dead biomass (47 ± 1.74%) when desorbed in water, suggesting harvested microalgae may contain geosmin. While microalgal water treatment combined with biomass utilization for fish feed fits very well within the circular economy, more research is needed to ensure the safe use of microalgal biomass.