Abstract
SUMMARY: Chlorella cultures were grown in a tubular loop reactor which facilitated both irradiation of the culture and gas mixing compared with a conventional stirred vessel with vortex aeration. Measurements of the inhibition of maximum specific growth rate (proportional to photosynthetic rate) in the tubular reactor showed that CO2 behaves as a typical inhibitory substrate at partial pressures (PCO2) up to 0.6 atm. The PCO2 for 50% reduction in maximum specific growth rate was 0.36 atm. At 0.6 atm there was a discontinuity in the inhibitory effect with a sharp increase in the inhibitory effect at higher PCO2 values. Cultures rapidly adjusted to step changes in the PCO2 up to 0.6 atm. At a PCO2 of 1 atm inhibition was complete but the inhibitory effect was readily reversed.