Sustainable Utilization of CO2 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 CO2 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 CO2 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 CO2 source (V2). The highest CO2 reduction efficiency of 90.3 ± 3.2% was achieved in the case where waste gases from biogas combustion were the CO2 source (V1). In V2, the highest CO2 utilization efficiency was achieved (CO2UE = 46.7 ± 2.4%). Analyzing the biomass composition confirmed differences in total carbon content (TC) and polysaccharide fraction. The highest H2 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 H2 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 CO2 emissions with the production of renewable biohydrogen and thus contributes to climate protection and the promotion of circular economy concepts.