酸性冲击对微生物电解产氢阳极菌群影响及功能基因变化解析

微生物电解产氢工艺是借助能够直接与电极传递电子的功能菌在阳极降解有机质并将产生的电子在阴极与质子结合回收氢气能源的新技术.采用市政废水在固定外加电压相同条件下直接启动15个反应器,以葡萄糖为碳源驯化获得电极功能菌群,稳定运行1个月获得反应器稳定产氢和伴随产甲烷效能.初始稳定时采用pH为7的磷酸盐缓冲液可以获得稳定的产气量,平行反应器表现出不同的氢气和甲烷产量.最高产氢反应器的氢气转化率为32.2%,氢气产率为(3.9±0.6)mol·mol-1(以每mol葡萄糖产生的H2量(mol)计,下同);相同条件下最低产氢效率反应器的甲烷转化率则可达到48.4%.通过48 h阳极生物膜的酸性冲击试验对阳极菌群功能恢复效果进行分析,发现消除冲击10~15 d反应器的电子传递效率得到恢复,但功能菌群多样性增加,氢气与甲烷比例发生变化.最高产氢反应器氢气产率降低1.8 mol·mol-1,而甲烷增量为0.4 mol·mol-1(以每mol葡萄糖产生的CH4量(mol)计,下同).通过关键功能基因分析发现,初始产氢效能高的反应器功能菌群中电子传递功能菌优势较大;阳极功能菌群受到短暂酸性冲击后,基于细胞色素C基因的相关菌群能够较快恢复,其电子传递能力恢复更快;与碳源降解和产甲烷相关基因群落受酸性冲击后变化较为显著,甲烷增量与氢气减少量基本符合反应计量关系.

Impact of low pH shock on anodic community structure and functional gene change in microbial electrolysis cells(MECs)

Microbial electrolysis cells (MECs) has been recently developed as a new technology for hydrogen production. The organics are degraded by exoelectrogens in anode biofilm and transport electrons directly to anode, while hydrogen is produced by combining electrons and protons on the surface of Pt-catalyzing cathode under a small external voltage between anode and cathode. Municipal waste water was used as the same inoculum to enrich functional communities in 15 single chamber MEC reactors. Various gas production (hydrogen and methane) was maintained over 1 month using glucose as the sole carbon source in phosphate buffer solution (50 mmol·L^-1, pH=7.0). The highest hydrogen production rate was up to (3.9±0.6) mol H₂/mol glucose with conversion rate of 32.2% for high-H₂ generation MECs. The highest methane conversion rate was 48.4% in low-H₂ generation MECs. A 48 h low pH shock was put into anode biofilm and MEC performances were recovered to their functions in 10~15 d. The microbial diversities increased and gas production rates were changed after low pH shock. Hydrogen yield was reduced by 1.8 mol H₂/mol glucose in high- H₂ generation MECs, while the methane yield increased by 0.4 mol CH₄/mol glucose. Based on Geochip analysis, cytochrome C genes were mostly enriched in high-H₂ yield MECs. Thus functional genes were still recovered dominantly after low pH shock and it supported the recovery of electron transport. The carbon degradation genes were substantially changed among anodic communities in most MECs. The functional genes of labile carbon degradation and methane production were significantly changed after microbial community recovery. The carbon degradation gene structure was more significantly changed in high-H₂ yield MECs than high-methane yield MECs. The methane increase and hydrogen decrease matched well with their stoichiometric relationship.