The study on coupled CO₂ fixation and power generation in microalgae-microbial fuel cells embedded with oxygen-consuming biofilms

Owing to the virtues of high efficiency, green and sustainability, the microalgae photobioreactor (PBR) is coupled with microbial fuel cell (MFC) to achieve CO₂ fixation and electricity/bioenergy collection. In this paper, a novel self-breathing oxygen-consuming carbon felt (SOC) is firstly proposed. It is subsequently integrated into the PBR-MFC to optimize O₂ concentration distribution and separate microalgae/bacteria. The results show that the solution environment (pH, dissolved oxygen and internal resistance) of the PBR-MFC coupling system are significantly regulated by SOC. After the introduction of SOC, the solution environment tends to be neutral (the value of pH on the day 7 increases from 6.88 to 7.0), and the dissolved oxygen concentration of electrolyte in cathode is increased by 6.1 %. The dissolved oxygen concentration in anode, system's ohmic resistance and charge transfer resistance are dramatically decreased by 64.6 %, 59.2 % and 19.0 %, respectively. After embedding a 1 cm-thick SOC in PBR-MFC, the maximum CO₂ fixation efficiency and power density of this system reaches 26.7 % and 474 mW·m⁻², improving by 21.9 % and 36.1 % compared to PBR-MFC, respectively. The integration of SOC into the PBR-MFC is credited with the improvement of system performance. The optimization of protons transport and the regulation of oxygen distribution are the two key aspects of its favorable benefits. This strategy of integrating SOC into PBR-MFC system will provide a new sight on high-efficiency energy conversion technologies for CO₂ fixation and electricity/bioenergy collection.