Sustainable Utilization of CO 2 from Exhaust Gases for the Autotrophic Cultivation of the Biohydrogen-Producing Microalga Tetraselmis subcordiformis

The aim of the study was to evaluate the feasibility of using exhaust gases as a CO 2 source in the cultivation of Tetraselmis subcordiformis microalgae for biomass and hydrogen production. It was shown that the growth rate of T. subcordiformis biomass and its biochemical composition depended on the CO 2 source. The highest growth rate of 286 ± 15 mgVS/L-d and a final biomass concentration of 2710 ± 180 mgVS/L were achieved in the variant where exhaust gases from a coal and biomass supplementary combustion plant were the CO 2 source (V2). The highest CO 2 reduction efficiency of 90.3 ± 3.2% was achieved in the case where waste gases from biogas combustion were the CO 2 source (V1). In V2, the highest CO 2 utilization efficiency was achieved (CO 2 UE = 46.7 ± 2.4%). Analyzing the biomass composition confirmed differences in total carbon content (TC) and polysaccharide fraction. The highest H 2 production efficiency and rate, which were 70.9 ± 2.7 mL/gVS and 2.27 ± 0.08 mL/gVS·h, respectively, were obtained in V2. The results obtained indicate the possibility of integrating fuel combustion processes with the cultivation of T. subcordiformis and photobiological H 2 production, which is a promising solution in the context of climate neutrality and the implementation of circular economy postulates. This approach demonstrates a sustainable strategy for linking industrial CO 2 emissions with the production of renewable biohydrogen and thus contributes to climate protection and the promotion of circular economy concepts.