Potential for direct interspecies electron transfer in an electric-anaerobic system to increase methane production from sludge digestion.

Zhiqiang Zhao,Liying Wang,Xie Quan,Yaobin Zhang

doi:10.1038/srep11094

Abstract

Direct interspecies electron transfer (DIET) between Geobacter species and Methanosaeta species is an alternative to interspecies hydrogen transfer (IHT) in anaerobic digester, which however has not been established in anaerobic sludge digestion as well as in bioelectrochemical systems yet. In this study, it was found that over 50% of methane production of an electric-anaerobic sludge digester was resulted from unknown pathway. Pyrosequencing analysis revealed that Geobacter species were significantly enriched with electrodes. Fluorescence in situ hybridization (FISH) further confirmed that the dominant Geobacter species enriched belonged to Geobacter metallireducens. Together with Methanosaeta species prevailing in the microbial communities, the direct electron exchange between Geobacter species and Methanosaeta species might be an important reason for the “unknown” increase of methane production. Conductivity of the sludge in this electric-anaerobic digester was about 30% higher than that of the sludge in a control digester without electrodes. This study not only revealed for the first time that DIET might be the important mechanism on the methanogenesis of bioelectrochemical system, but also provided a new method to enhance DIET by means of bioelectric enrichment of Geobacter species.

Highlights

Metabolism, resulting in the accumulative short-chain fatty acids (SCFAs), which further inhibits the activity of H2-consuming methanogens to exacerbate the digester function
There was no significant difference of accumulative methane production between R2 and R3 during the 51 days experiments (P > 0 .05), which implied that the electrode materials themselves nearly had no effect on the methane production
These results indicated that the bioelectrochemical system had a significant contribution to the methane production

Summary

Introduction

Metabolism, resulting in the accumulative short-chain fatty acids (SCFAs), which further inhibits the activity of H2-consuming methanogens to exacerbate the digester function. For some important methanogenic environments, such as anaerobic digestion of municipal sludge or of saccharides, the relative abundance of Geobacter species detected are low[18,19,20]. It meant that DIET from Geobacter species to Methanosaet a species for methane production was weak in these anaerobic system. It was reported that Geobacter species usually adapt to grow with Fe (III) oxides[21,22,23] or electrodes[24,25] as electron acceptors This discovery revealed the reason why Geobacter species could be detected in most bioelectrochemical systems with over 30–40% of 16S rRNA gene sequences recovered in the anodic microbial communities[26,27,28].

Methods

Results

Conclusion