Microbial fuel cell biodetector for in-situ monitoring of clogging in vertical flow treatment wetlands

Monitoring clogging in treatment wetlands (TW) remains challenging, as existing methods are typically non-continuous, invasive, or impractical for long-term operation. Microbial fuel cells (MFCs) have been proposed as non-invasive biosensors for clogging detection in horizontal flow treatment wetlands, exploiting natural redox gradients. However, their applicability to French vertical flow treatment wetlands (VFTW), which operate predominantly under unsaturated aerobic conditions, is unknown. This proof-of-concept study evaluates whether oxygen limitation induced by clogging in a vertical-flow (VF) filter can be indirectly detected via changes in MFC electrical output. Two air-cathode MFCs, hydraulically coupled to filtration columns, were operated in parallel, under laboratory scale. The tested-MFC received raw wastewater with a high suspended solids load to induce progressive clogging and oxygen limitation, while the control-MFC operated without imposed clogging. Over 14 days, oxygen saturation in the air-cathode chamber decreased from 100% to 0%, coinciding with a decline in current output from 0.36 to 0.14 mA. In contrast, the control MFC maintained a stable current of 0.36 mA. These results demonstrate a clear qualitative sensitivity of MFC electrical output to oxygen depletion associated with clogging under controlled VF conditions. These initial findings highlight the potential of MFCs as non-invasive, early warning biodetector for clogging in VFTW by targeting oxygen limitation as an indicator.