Physiological and Biochemical Responses of Chlorella vulgaris to Real Cement Flue Gas Under Controlled Conditions

Photosynthetic microalgal growth is a promising tool for mitigation of gaseous effluent from the cement production, which is highly implicated in global warming and climate change. We investigated the effects of actual cement industry flue gas on the physiology of Chlorella vulgaris under laboratory-controlled conditions. We evaluated the growth, photosynthetic performance, intracellular metal content, total proteins, and carbohydrates of C. vulgaris under three gas input rates: 9, 36, and 54 L d⁻¹; compressed air (54 L d⁻¹) was used as control. The results showed no correlation between the flue gas input rates on total proteins and carbohydrates in the algal biomass, and no effects on growth rates. However, rapid light curves indicated that the light use efficiency (α) and the maximum relative electron transport rate (rETR_max) were stimulated when applying 9 and 36 L d⁻¹. Metal analysis revealed an accumulation of Cr, Zn, and Ni in the algal biomass exposed to flue gas (54 L d⁻¹) compared to the control. Thermogravimetry and differential thermal analysis showed that 70% of the cement kiln dust were composed by uncalcined limestone, which may have stimulated photosynthesis, as indicated by the rapid light curve parameters. In general, C. vulgaris can be considered a robust organism for cement flue gas bioremediation.