Online Response Performance and Optimization of Sediment Microbial Fuel Cell-Based Sensors to pH

Abstract

Sediment microbial fuel cells (SMFCs) offer a promising approach for in situ and online pH monitoring, and enhancing their sensitivity is critical for promoting practical application. In this study, the sensors with different anode areas (4, 18, and 81 cm²) and external resistance (50, 1 k, 20 kΩ, and open-circuit) were constructed in flooded soil. Buffer solutions with pH values ranging from 2.2 to 11.8 were added to the surface of the cathode to simulate acidic and alkaline contaminations. Results showed that the addition of acidic buffer solutions triggered voltage peaks whereas alkaline solutions caused voltage drops. The highest sensitivity was observed with a 20 kΩ resistor and a larger anode area than 4 cm². The two-way ANOVA confirmed that the factors of the anode area and external resistance were significant (p < 0.001) for the sensitivity. The repeated contaminations did not alter pH value of soil where the anode was buried, and electrogenic bacteria were enriched on the anode after the operation of the SMFC sensors. As external resistance increases, the relative abundance of exoelectrogenic bacteria-associated genera (EB-genera) to total bacteria progressively decreased. Clostridium, Thermincola, Anaeromyxobacter, Acinetobacter, and Desulfitobacterium were the most abundant EB-genera on the anode.