Integration of CO2 capture and microalgae cultivation: demonstration assessment of outdoor Scenedesmus acutus cultivation using gaseous ammonia as a nitrogen source

Abstract

Background: Towards the goal of integrating CO2 capture using aqueous ammonia with its utilization for algae cultivation, Scenedesmus acutus (UTEX B72) was grown in 1100 L open raceway ponds using CO2 and NH3 supplied from gas cylinders. CO2/NH3 mole ratios of 7 and 10 were employed, the gas mixture acting as a surrogate for the output from a CO2 scrubbing system using aqueous ammonia. Results: Compared to Scenedesmus acutus grown in open ponds using gaseous CO2 and NaNO3 as the N-source, the ponds supplied with gaseous CO2 and NH3 displayed higher productivity at both CO2/NH3 ratios, with the higher ratio providing the best growth. Depending on the culturing conditions and CO2/NH3 ratio, CO2 utilization ranged up to 15.8% and NH3 utilization to 23.0%. These rather low values reflect the fact the high CO2/NH3 feed rate used, resulting in a substantial release of NH3 from the ORPs (~45%). Conclusions: These findings demonstrate the suitability of gaseous NH3 as a N-source for microalgae cultivation, while highlighting the need for a control strategy that closely balances the CO2/NH3 supply with the algae growth rate. The produced algae biomass possessed a high protein and low ash content, rendering it particularly suitable for use as a bioplastic feedstock. © 2025 Society of Chemical Industry (SCI).