Abstract:

The carbon-fixing methanogenic microbial electrosynthesis system uses a biofilm attached to the surface of its electrode as a catalyst, which can convert CO₂ into methane while treating wastewater, which has great application prospects. As one of the core components, the biocathode determines the performance of the system. Herein, we derived a Nernst-Monod equation applicable to biocathodes, and constructed a mathematical model of the electron and mass transfer within the biocathode. The effects of different biocathode potentials, biofilm conductivity, and biofilm porosity on transport characteristics of the biofilm are studied. The results showed that the current density within the biofilm increased, and the substrate concentration within the biofilm decreased towards the direction of electrode with the decreasing cathode potential when the potential > -0.5 V (vs SHE). On the other hand, the capability of biofilm consuming electrons was almost saturated when the cathode potential < -0.5 V(vs SHE). A low conductivity of the biofilm (<10^-3 S/m) could cause an obvious potential difference within the biofilm, reducing the substrate utilization rate and biocathode performance. When the biofilm porosity is controlled at 0.4, the microbial cathode can reach the optimal current density.

Key words: microbial electrosynthesis, carbon dioxide reduction, biofilm, mass transfer, kinetic modeling

摘要：

固碳产甲烷微生物电合成系统以附着其电极表面的生物膜为催化剂，可以在处理废水的同时将CO₂转化为甲烷，极具应用前景。微生物阴极是该系统的核心部件之一，其表面生物膜内的能质传输特性极大地影响系统性能。针对微生物阴极能质传输特性尚不明确的问题，推导了微生物阴极电极反应动力学方程（Nernst-Monod方程），构建了耦合生化/电化学反应的物质传输理论模型，研究了不同阴极电势、生物膜电导率以及孔隙率对阴极生物膜内电荷及物质传输的影响规律。研究结果表明当阴极电势高于-0.5 V (vs SHE)时，随阴极电势的降低生物膜内电流密度增大，底物浓度降低；但当阴极电势降低至-0.5 V(vs SHE)后，生物膜消耗电子还原底物的能力几乎达到饱和；低电导率（<10^-3 S/m）会导致生物膜内形成明显的电势差，使得底物利用速率降低，严重影响微生物阴极的性能；生物膜孔隙率控制在0.4时，微生物阴极可达到最佳电流密度。

关键词: 微生物电合成系统, 二氧化碳还原, 生物膜, 传质, 动力学模型