CO₂ Bubbling to Improve Algal Growth, Nutrient Removal, and Membrane Performance in an Algal Membrane Bioreactor.

Algae generally prefer CO2 through passive gas diffusion to HCO-3 or CO2-3, as uptake of carbonate species relies on active transport. In this study, the effects of CO2 bubbling on algal growth, nutrient uptake, lipid accumulation, and membrane fouling control were investigated in an algal membrane bioreactor (A-MBR). Bubbling with 10% CO2 in the A-MBR system increased algal specific oxygen production rate by 43 ± 5% and algal productivity by 39 ± 1%, even though there was abundant dissolved inorganic carbon available in the secondary wastewater effluent (about 3.6 mM). Meanwhile, nitrogen removal capacity increased from originally 2.6 ± 0.4 g/m3•d to 3.6 ± 0.4 g/m3•d through continuous CO2 bubbling. Furthermore, membrane fouling was significantly reduced in the A-MBR system with CO2 addition, likely because of reduced mineral precipitation on the membrane at lower pHs.