Experimental and simulation-based reactor-scale strategies for engineering high mixotrophic synthesis, carbon sequestration and inter-trophic synergy in algal photobioreactors.

This experimental and simulation study employs radial sparging - along with other reactor-scale parameters, such as illumination intensity and carbon (CO2 and acetate) and nitrogen loading - to enhance carbon sequestration and inter-trophic synergy in mixotrophic cultivation of Chlorella sorokiniana in bubble-column photobioreactors. Radial mixing produces (3-5 times) higher flashlight frequencies, which enhance the synergy between phototrophy and heterotrophy and increase CO2 sequestration by 23-72 % at 0.04-6 % CO2 loading and 10,500-14,000 lx light. Lipid amounts obtained at 10,500, 12,000 and 14,000 lx peak at 3 %, 4 % and 6 % CO2 to 1.61, 1.03, and 0.90 g/L, respectively, with corresponding inorganic carbon concentrations of 1.85, 1.40, and 1.49 g/L. A tetrad of reactor-scale engineering strategies - super-optimal CO2 (6 %) and illumination (14,000 lx) with 12-hour light-dark circadian cycle, radial mixing and nitrogen limitation - in industrial-scale outdoor algal photobioreactors could sequester 23 % more CO2 from flue-gases, with simultaneous bioremediation of acetate-rich wastewater.