将沼气提纯后用作生物天然气替代部分化石燃料是助力“双碳目标”实现的有效手段。然而厌氧发酵产生的沼气中CH4含量仅为50%~70%，CO2含量达30%~50%，不满足作为生物天然气的标准。微生物电解池（Microbial electrolysis cell, MEC）是新兴的微生物电催化技术，可将沼气中的CO2还原为CH4。但是，MEC生物阴极启动速率慢、电子接受能力差，导致反应器连续运行难、产CH4速率低，限制了MEC在沼气脱碳提纯中的应用。基于此，本研究开发了一种生物阴极启动技术，构建了可提高生物阴极电子接受能力和产CH4速率的碳基阴极，为推动MEC技术在沼气脱碳提纯中的应用提供理论和技术支撑。研究发现，无电场条件下在碳基材料表面形成的微生物膜具有良好的电子接受能力，并基于此开发了一种产CH4生物阴极启动新技术：将碳基材料置于以嗜氢型和可进行直接电子传递的产甲烷菌为主的厌氧反应器中12 d以上，可成功启动具有良好电子接受能力和产CH4性能的生物阴极。该方法启动的生物阴极的产CH4能力约为1.35 L·m-2·d-1，电子接受能力比传统在有电场条件下启动的生物阴极提高了2倍。通过探究碳基阴极表面羧基和内部石墨化结构对产CH4性能的影响，明确了碳基阴极的构建策略为：控制表面羧基含量为13.32%以上，并调控石墨化程度满足给定公式。基于此构建的生物阴极在相对低电压（0.56 V）下，可将CH4产量至少提高2倍，在相对高电压（0.76 V）下，可至少提高25%。研究发现在碳基阴极表面负载适量羧基可促进阴极析氢反应，提高Methanobacterium的相对丰度，从而促进H2介导的电子传递产CH4过程；也可以提高Methanosaeta的相对丰度和基因omcB、omcF、omcZ的拷贝数，促进胞外聚合物中蛋白质的表达，从而促进直接电子传递产CH4过程。研究发现调整碳基阴极的石墨化结构可以优化阴极的电场强度，进而提高Methanosaeta的相对丰度和胞外聚合物的电子接受能力，促进以Methanosaeta为主要功能微生物的生物阴极的直接电子传递产CH4过程。将开发的启动技术和构建的生物阴极应用于实际沼气处理，研究发现当沼气处理量为17.3~21.3 L·m-2·d-1时，处理后沼气中CH4含量可达96%以上，达到GB/T 41328-2022《生物天然气》一类标准。生物阳极通过降解沼液回收能量为阴极沼气脱碳提纯提供质子和电子。基于此构建了沼液、沼气协同处理工艺，为协同推进减污降碳和“双碳目标”的实现提供技术支撑。

Refining biogas and using it as biogas-based natural gas to replace some fossil fuels is an effective mean to achieve the “double carbon” goal. However, the methane content in biogas produced by anaerobic fermentation is only 50%~70%, and the carbon dioxide content is as high as 30%~50%, which does not meet the requirements of bio-based natural gas standards. Microbial electrolysis cell (MEC) has emerged as a new microbial electrocatalytic technology that can reduce CO2 in biogas to CH4. However, slow startup rate and poor electron accepting capacity of MEC biocathode limit the continuous operation and CH4 production rate of reactors, thereby limiting the application of MEC in biogas decarbonization purification. To address these issues, this study developed a startup method of biocathode and constructed a carbon-based cathode that can enhance electron accepting capacity and CH4 production rate of biocathode, providing theoretical and technical support for promoting the application of MEC technology in biogas decarbonization purification.This study found that the biofilm formed on the surface of the carbon-based material without electric field showed good electron accepting capacity. And based on this new discovery, a new startup method of biocathode was developed. The biocathode with good electron accepting capacity and methanogenic ability was successfully started by placing the carbon-based material into the anaerobic reactor dominated by hydrogenotrophic methaogens and methaogens with direct electron tansfer ability for more than 12 days. The CH4 yield of the started biocathode was about 1.35 L·m-2·d-1. The electron accepting capacity of the biocathode started by this method was more than twice that of the traditional startup methods, which were started under the condition of electric field.By investigating the effects of surface carboxyl groups and graphitic structure of the carbon-based cathodes on the CH4 production efficiency, the regulating strategy of the carbon-based cathode was defined as follows: the surface carboxyl groups should be controlled above 13.32%, and the degree of graphitization should meet the given formula. The biocathode constructed based on this strategy can increase CH4 production by at least 2 times at relatively low voltage (0.56 V) and at least 25% at relatively high voltage (0.76 V). It was found that loading moderate carboxyl groups could enhance the H2 evolution and increase the relative abundance of Methanobacterium, thus promoting the H2-mediated electron transfer process for CH4 production. Loading moderate carboxyl groups could also increase the relative abundance of Methanosaeta, promote the expression of genes of omcB, omcF, and omcZ and the expression of protein in extracellular polymeric substances, thus promoting the direct electron transfer process for CH4 production. It was found that the electric filed intensity could be optimized by adjusting the graphitic structure of carbon-based cathode, thereby increasing the relative abundance of Methanosaeta and the electron accepting capacity of extracellular polymeric substances. And this could promote the CH4 production by enhancing the electron transfer process of the biocathode with Methanosaeta as the main founctional microorganism.The developed startup method and constructed biocathode were applied to actual biogas treatment. It was found that when the biogas treatment volume was 17.3~21.3 L·m-2·d-1, the CH4 contents in treated biogas could reach more than 96%, which meets the Class I standard of GB/T 41328-2022 “Biogas-based natural gas”. The bioanode recovered energy by degrading biogas slurry to provide protons and electrons for the biogas decarbonization purification. Based on these, the simultaneous treatment process of biogas slurry and biogas has been established, which provided technical support for collaborative promotion of pollution reduction and carbon reduction and the achievement of the “double carbon” goal.