Bacterial response to formaldehyde in an MFC toxicity sensor

Microbial fuel cells (MFCs) have been extensively studied as toxicity sensors. MFCs have potential as toxicity sensors because when their anodes are exposed to toxic substances or the concentration of the target is changed, the voltage generated by certain microorganisms with active electrical activity attached to the anode changes. However, the underlying reasons behind this phenomenon have not been deeply explored. Therefore, the activity of anodic microorganisms during voltage drops in MFCs under formaldehyde (FA) stress was studied. The composition of the microbial community structure with similar active voltage drops under different concentrations of FA was investigated. The results showed that under exposure to high concentrations (169.20 mg/L) of FA, the voltage changes in MFCs could be divided into five stages. With prolonged exposure to FA, the ratio of live/dead bacteria decreased from 4.78 to 0.65. This result indicated that voltage drops may be caused by FA causing cell membrane rupture. Analysis of the microbial community structure under treatments including inoculation and three concentrations of FA revealed that Geobacter and other electrogenic bacteria were effectively enriched in the MFCs. Low-concentration and long-term exposure to FA had a greater impact on microbial communities than high-concentration and short-term exposure. Pseudomonas and Acidovorax were more significantly affected by FA than Flavobacterium and Geobacter. This study explains the reason for the voltage drop of MFCs after exposure to toxic substances from the perspective of the microorganisms.