AbstractIn a CO2‐limited algal culture, grown in a tubular loop photobioreactor, the maximum rate of CO2absorption increased about 1.5‐fold when the culture pH value was increased from 6.5 to 7.5 with a fixed initial PCO2. The mean volumetric CO2transfer coefficient (KLa) increased about 1.8‐fold. The bicarbonate ion concentration would be increased 10‐fold by the pH increase. The effect of pH on the absorption rate is attributed to changes in either the CO2diffusivity, the gas bubble size, or the CO2reaction kinetics at the gas/liquid b