Effect of cement industry flue gas simulation on the physiology and photosynthetic performance of Chlorella sorokiniana

Cement plants account for significant emissions of CO2 and other pollutants into the atmosphere. As a means for its mitigation, we tested the effect of a cement industry-based flue gas simulation (FGS - 18% CO2, 9% O-2, 300 ppm NO2, 140 ppm SO2) on the green alga, Chlorella sorokiniana. Culture pH, cell density, cell viability and productivity, specific growth rates, photosynthetic performance, and biochemical composition were monitored. The treatments consisted of different FGS volumes (0.1, 0.3, 0.8, 1.5, 6, and 48 L day(-1) ) that were applied in a series of laboratory-scale semi-continuous batch cultures under controlled conditions. Controls were exposed to 18% CO2 enriched air. Cell density showed that C. sorokiniana was able to grow in all treatments, but compared to the controls, low pH (similar to 5.0) caused by 48 L FGS day(-1) led to 27% decrease in specific growth rate. Increasing FGS exposure decreased maximum and operational quantum yields obtained by pulse amplitude modulated fluorometry, while photochemical quenching remained constant (similar to 0.93). The a and rETR(max), parameters calculated from rapid light curves decreased with increasing FGS exposure. Total proteins and carbohydrates (per cell basis) increased after 6 and 48 L FGS day(-1), which can be advantageous for biotechnological applications, but cell productivity (cells L-1 day(-1)) decreased. Despite the effects in physiology, C. sorokiniana could withstand a pH range of 6.0-5.0 imposed by 48 L FGS day(-1). Overall, C. somkiniana can be considered a robust species in flue gas bioremediation.