Study on Influencing Factors of Methane Production Efficiency of Microbial Electrolytic Cell with CO2 as Carbon Source

Reducing CO₂ to produce methane through microbial electrolytic cell (MEC) is one of the important methods of CO₂ resource utilization. In view of the problem of low methanogenesis rate and weak CO₂ conversion rate in the reduction process, the flow field environment of the cathode chamber is changed by changing the upper gas circulation rate and the lower liquid circulation rate of the cathode chamber to explore the impact on the reactor startup and operation and products. The results showed that under certain conditions, the CO₂ consumption and methane production rate could be increased by changing the upper gas recirculation rate alone, but the increase effect was not obvious, but the by-product hydrogen production decreased significantly. Changing the lower liquid circulation rate alone can effectively promote the growth of biofilm, and change the properties of biofilm at the later stage of the experiment, with the peak current density increased by 16%; The methanogenic rate decreased from the peak value of 0.561 to 0.3 mmol/d, and the CO₂ consumption did not change significantly, which indicated that CO₂ was converted into other organic substances instead of methane. The data after coupling the upper gas circulation rate with the lower liquid circulation rate is similar to that of only changing the lower liquid circulation rate, but changing the upper gas circulation rate can alleviate the decline of methane production rate caused by the change of biofilm properties, which not only improves the current density, but also increases the methane production rate by 0.05 mmol/d in the stable period. This study can provide theoretical and technical support for the industrial application scenario of flow field regulation intervention of microbial electrolytic cell methanogenesis.