闭合回路电子流强化硝酸盐异化还原为铵性能及功能菌群分析

Performance and functional bacterial community analysis for highly efficient nitrate dissimilatory reduction to ammonium induced by electron flow with closed circuit

硝酸盐异化还原为铵(DNRA)是氮循环中的一个重要过程,DNRA能够将硝酸盐还原为铵,是将活性氮保留在自然生态系统中的重要路径.然而,DNRA的效率仍然较低,其内在反应机理仍然不清楚.本研究采用自主搭建的电强化-DNRA(E-DNRA)连续流式反应器,利用闭合回路电子流构建单个细菌周围强还原环境,以提高细菌周围局部微环境的电子供体比例,进而提高DNRA效率.据此,进一步深入探究了电子流强化DNRA过程的内在反应机理及DNRA功能菌的群落特征.结果表明,电阻为50Ω,水力停留时间为20 h,电极面积为847 cm^(2)时可以有效提高硝酸盐异化还原为铵(DNRA)的活性,反应器中c(NH_(4)^(+))/c(NO_(3)^(-))最高可达79.1%.胞外聚合物(EPS)、电子传递系统活性(ESTA)及NADH分析表明,电子流促进了电极生物膜上各菌属的生物的活性.宏基因分析结果表明,反应器内Thauera、Azonexus、Cupriavidus、Pseudomonas为主要功能菌属.以nrf A基因编码的细胞色素c型亚硝酸盐还原酶在电子流的作用下由0.18%升高至32.84%,促进了细胞周质内DNRA过程的发生;以nir B基因编码的NADH依赖型亚硝酸盐还原酶在电子流的作用下由6.05%升高至12.71%,强化了细胞质内DNRA过程的发生.研究结果将为开发强化的DNRA技术提供新策略.

Nitrate allotropic reduction to ammonium(DNRA)is an important process in the nitrogen cycle,and DNRA is capable of reducing nitrate to ammonium and is an important pathway for retaining reactive nitrogen in natural ecosystems.However,the efficiency of DNRA is still low and its intrinsic reaction mechanism remains unclear.In this study,an electro-enhanced-DNRA(E-DNRA)continuous flow reactor was built in-house to construct a strong reducing environment around individual bacteria using closed-loop electron flow in order to increase the proportion of electron donors in the local microenvironment around the bacteria and thus improve the DNRA efficiency.Accordingly,the intrinsic reaction mechanism of the electron flow-enhanced DNRA process and the community characteristics of DNRA functional bacteria were further investigated in depth.The results showed that the activity of nitrate isomerization reduction to ammonium(DNRA)could be effectively enhanced at a resistance of 50Ω,a hydraulic residence time of 20 h,and an electrode area of 847 cm2,and the c(NH_(4)^(+))/c(NO_(3)^(-))in the reactor was up to 79.1%.Extracellular polymer(EPS),electron transfer system activity(ESTA),and NADH analysis showed that electron flow promoted the activity of organisms of each genus on the electrode biofilm.Macrogenic analysis showed that Thauera,Azonexus,Cupriavidus,and Pseudomonas were the main functional genera in the reactor.The cytochrome c-type nitrite reductase encoded by nrfA gene increased from 0.18%to 32.84%in response to electron flow,which promoted the occurrence of DNRA process in the periplasm;the NADH-dependent nitrite reductase encoded by nirB gene increased from 6.05%to 12.71%in response to electron flow,which enhanced the occurrence of DNRA process in the cytoplasm.The results of the study will provide new strategies for the development of enhanced DNRA technology.