Advanced Control for Photoautotrophic Growth and CO2-Utilization Efficiency Using a Membrane Carbonation Photobioreactor (MCPBR)

A membrane carbonation (MC) module uses bubbleless gas-transfer membranes to supply inorganic carbon (C-i) for photoautotrophic cyanobacterial growth in a photobioreactor (PBR); this creates the novel MCPBR system, which allows precise control of the CO2-delivery rate and minimal loss of CO2 to the atmosphere. Experiments controlled the supply rate of C-i to the main PBR by regulating the recirculation rate (Q(R)) between the module of MC chamber and the main PBR The experiments evaluated how Q(R) controls the CO2 mast; transport in MC chamber and how it connects with the biomass production rate, C-i concentration, pH in the PBR, and CO2-utilization efficiency. The biomass production rate and C-i concentration increased in response to the C-i supply rate (controlled by Q(R)), but not in linear proportion. The biomass production rate increased less than C-i due to increased light limitation. Except for the highest Q(R), when the higher C-i concentration caused the pH to decrease, CO2 loss to gas ventilation was negligible. The results demonstrate that this MCPBR offers independent control over the growth of photoautotrophic biomass, pH control, and minimal loss of CO2 to the atmosphere.