Sensitivity enhancement for microbial fuel cell type oil sensor by regulation of anode area, external resistance and substrate concentration

Abstract

To promote application of the microbial fuel cell (MFC)-based oil sensor in monitoring oil leak risks of oil pipelines and to overcome the influence of signal fluctuation, the sensor sensitivity needs to be enhanced. Simple and viable start-up measures such as regulating anode area, external resistance and substrate concentration were implemented to investigate their influence on the sensitivity. Results show that enlarging anode area and lessening external resistance will significantly promote the sensitivity (change of current signal per oil amount). Increasing anode area from 3.1 to 9.6 cm2 resulted in a 711 % increase in the initial sensitivity and a 358 % increase in the average sensitivity. Decreasing external resistance from 1300 to 400 Ω led to a 797 % increase in the initial sensitivity and a 378 % increase in the average sensitivity. While controlling substrate concentration from 155.7 to 500.7 mg-COD/L had a much smaller impact on the sensitivity. Manipulating substrate concentration over an augmented range (41.2–500.7 mg-COD/L) showed that insufficient substrate (< 80 mg-COD/L) induced a drastic current drop. A theoretical sensitivity formula was derived from a data fitting model based on charge conservation. The formula reveals that a sensitivity factor relating to the ratio of ORR and oxygen transfer is key to enhancing sensitivity, which was verified to have a strong positive correlation with current by data analysis and EIS. In general, this study shows that measures to elevate current will significantly enhance sensitivity besides keeping substrate concentration at a high level is a prerequisite for maintaining it.