Analytical Validation and Decision Functions of Microbial Fuel Cell Biosensors for Water Quality and Process Monitoring Beyond Electrical Correlation

Abstract

Microbial fuel cells (MFCs) have been widely investigated as low-power biosensors for environmental and process monitoring. However, their electrical response is not inherently specific to a target analyte, and similar changes in voltage or current may indicate changes in analyte concentration, process conditions, or overall microbial activity. This critical review evaluates MFC biosensors according to whether their signals can reliably support quantitative measurement, process monitoring, or early warning. Applications involving organic load and anaerobic processes, toxicity, dissolved oxygen (DO), and inorganic nitrogen are reviewed together with the main electrochemical operating modes. Signal generation and interpretation are governed by mass transport, microbial accessibility, extracellular electron transfer, electrode kinetics, reactor operation, and environmental conditions. Among current applications, MFC-based DO sensors show relatively strong potential for quantitative measurement and long-term environmental monitoring. Organic-load and volatile fatty acid sensors are better suited to locally calibrated process monitoring, while mixed-culture toxicity sensors primarily provide non-specific warning signals. Nitrate-reducing biocathodes offer further sensing opportunities but involve greater operational complexity. A major challenge remains the transferability of calibration across independently constructed devices, sample matrices, operating periods, and sites. Accordingly, this review proposes validation criteria and a pathway toward reliable autonomous field monitoring.