Effect of aeration and anode material on the bioelectricity generation of floating microalgae biophotovoltaic device

Abstract

A biophotovoltaic (BPV) system is a developing renewable energy technology that promises carbon-free electricity generation from solar energy by utilizing photosynthetic exoelectrogenic microorganisms. However, further development of this novel technology is restricted by its relatively low power output. The problem could be solved by directly acquiring the bioelectricity from floating microalgae instead of forming thin biofilms on the anode surface. One technical concern is that previous studies emphasized the composition of anode materials and biofilm formation in the BPV devices, whereas there are limited studies regarding the bioelectricity generation of BPV devices with well-mixed microalgae cultivation medium. Therefore, the objectives of this research are to determine the effects of various anode materials on the bioelectricity generation of BPV devices in natural and aeration modes; and to determine the effects of aeration on bioelectricity generation in BPV devices with free surface and multiphase flow cultures. The methodology starts with voltage output measurement under gradually rising external load to form a polarization curve for each BPV device, with various anode materials of graphite, aluminium, indium tin oxide (ITO)-coated glass, and ITO-coated plastic in natural conditions and aeration mode. The result shows that graphite anode has poor absorption of electrons released by Spirulina (Arthrospira) platensis and aluminium anode dissolved into the culture medium and became an extra electron source. ITO-based BPV devices have comparable good performance among other electron materials. However, the devices experience significant power overshoot phenomena and have a low peak power output under natural conditions. In aeration mode, the peak power output of ITO-coated glass-based BPV devices increased to 0.659±0.009 mW/m2 as compared with 0.118±0.003 mW/m2 in natural conditions. In turbidity test, aeration prevented the formation of biofilms and sedimentation and produced a multiphase flow solution. In conclusion, aeration significantly alleviated the power overshoot phenomenon and enhanced the peak power output of ITO-coated glass-based and plastic-based BPV devices by 458.47% and 244.65%, respectively. The findings are expected to contribute to further understanding of the correlation of the selected parameters with regards to power generation of the BPV devices.