Influence of Ventilation Modes on Carbon Dioxide Fixation of Chlorella vulgaris in a Flat-Plate Photobioreactor

Abstract

Microalgae have the ability to mitigate CO2 emission with a high productivity, thereby having the potential for applications in reducing CO2 with high concentration. To date the effect of different ventilation modes in photobioreactor on the high level CO2 fixing capacity was still unclear. To explore an efficient, convenient and cheap aerating method for high concentration CO2, an inner parallel flat-plate photobioreactor configuration (IPFP) was designed and the effect of inner-mixing ventilation and intermittent ventilation modes on the CO2 fixation rate (CFR) in a laboratory-scale IPFP was determined. Chlorella vulgaris, a promising freshwater green algal strain with high CO2 fixation rate under CO2 concentration lower than 5% (v/v) but cannot survive under 15% CO2, was used to perform the experiments. Results showed that both of the novel ventilation modes can effectively enhance microalgal performance on growth and carbon biofixation rates when 15% CO2 was directly provided. The CFR of Chlorella vulgaris in this photobioreactor ranged 1.30 to 1.78 g CO2L-1d-1. The pH value of cultural medium was also determined. Results showed that the distribution of pH values was uniform in the IPFP cross section during the inner-mixing ventilation mode, which indicating a good mixing characteristic of the fluid in the IPFP. In the intermittent ventilation mode, the pH values demonstrated periodical variation with the maximum value of 8.2 and the minimum value of 6.5. Aerating 15% CO2 for 12 minutes and air for 48 min in one hour (12 min 15% CO2/48 min air) provided a longer period in pH<7.0 than that of aerating 15% CO2 for 6 minutes and air for 54 min in one hour (6 min 15% CO2/54 min air), and thus, was more beneficial to the CFR. IPFP with an inner-mixing ventilation mode effectively enhances the performance of C. vulgaris on microalgal growth and CO2 biofixation, indicating that this PBR has the potential for use in the field of carbon reduction.