Small boreholes embedded in the sediment layers make big difference in performance of sediment microbial fuel cells: Bioelectricity generation and microbial community

The practical applications of sediment microbial fuel cells (SMFCs) are limited by their low power densities. In this work, a novel SMFC configuration with a cylindrical borehole embedded in the sediment layer is proposed with expectations of reducing internal resistance, enhancing mass transfer, and accordingly increasing power density. Two types of boreholes with same diameter of 10 cm, but different depths of 3 cm and 6 cm are constructed in SMFCs (SMFC-3 and SMFC-6). Results demonstrate that SMFC-3 produces the highest maximum power density (65.6 mW/m(2)), which is 25.5% and 65.6% higher than that in SMFC-6 (52.3 mW/m(2)) and the control SMFC (SMFC-C, 39.4 mW/m(2)), respectively. The improved power performance in SMFC-3 is mainly due to the greatly reduced internal resistance. Compared to SMFC-6, the higher power density in SMFC-3 is also due to the relatively low overlying water pH values, providing suitable pH condition for cathodic reactions. Microbial community analyses demonstrate that Alphaproteobacteria and Gammaproteobacteria are major contributors to the bioelectricity, and that electroactive species enriched on the top and bottom sides of anodes are significantly different. Generally, embedding a small borehole into the sediment layer is an easy-to-implement and costeffective strategy for improving the power performance of SMFCs. (c) 2021 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Superscript/Subscript Available

Automated summary

This study proposes a novel configuration for sediment microbial fuel cells (SMFCs) by embedding a cylindrical borehole in the sediment layer to reduce internal resistance, enhance mass transfer, and increase power density. Experimental results show that SMFC-3 with a borehole depth of 3 cm produces the highest maximum power density, which is 25.5% and 65.6% higher than that in SMFC-6 with a borehole depth of 6 cm and the control group SMFC-C, respectively. The improved power performance in SMFC-3 is mainly attributed to the greatly reduced internal resistance and suitable pH conditions for cathodic reactions.