Indirect membrane-based bubbling as an alternative technique to increase the carbonation of microalgal media

•The indirect membrane-based bubbling resulted in carbonation efficiency up to 82%.•The indirect membrane-based bubbling prevented cell collection in the membrane.•The indirect membrane-based bubbling increased CO2 uptake by microalgae.•Optimum ratio of gas to liquid flow rate is less than 2:1.

This work discusses an indirect membrane-based bubbling technique and operating conditions for using membranes for high carbonation efficiency and microalgae productivity. The technique resulted in 82% carbonation efficiency compared to 42% and 29% using a direct membrane-based bubbling and direct bubbling without using a membrane, respectively. The indirect membrane-based bubbling resulted in microalgae productivity that was approximately 10% higher than the typically accepted technique, prevented cell collection from fouling the membrane, and increased microalgae capacity to capture and use CO2 for photosynthesis. This technique has significance not only for CO2 mitigation progress but also for the biomass production of microalgae. This technique also decreases the amount of CO2 that escapes into the bioreactor headspace and atmosphere during carbonation.