A soil microbial fuel cell-based biosensor for dissolved oxygen monitoring in water

Abstract Water pollution can cause serious depletion of dissolved oxygen (DO) in water systems with serious environmental and economic consequences. Online and continuous monitoring of DO can help prevent or minimise the risks associated with low DO values in water. Current DO sensors are, however, expensive and not suitable for continuous and autonomous in-field operation. In this study, we propose a novel and affordable Ceramic Soil Microbial Fuel Cell (CSMFC) for in situ, continuous and autonomous monitoring of DO in water. The system consists of a submersible ceramic vessel containing a soil-based anodic chamber, while the cathode, wrapped around the vessel, is used as the DO probe. The sensor signal, in terms of output voltage, correlates with the DO in water up to a saturating value of 4.5 ± 1.2 mg L−1, at a maximum voltage output of 321 ± 29 mV (20 C, pH=7, 1.65 mS cm−1) with a sensitivity in the linear range of 53.3 ± 22.6 mV L mg−1. A factorial Design of Experiments (DoE) on pH, conductivity, DO and temperature shows that the sensor voltage response is mainly affected by temperature and DO, as well as by their mutual interaction. The resulting model was used to assess the DO in water samples, showing an error as low as 0.05 mg L−1. The calibration model is normalised by the output voltage baseline, thus accounting for any variability in performance, within the same device during long-term performance and from one device to another, which is a challenge in microbial-based systems. As such, this work not only reports an innovative microbial fuel cell-based DO sensor, but also demonstrates the necessity of a DoE to effectively calibrate the sensor.