MFC-based biosensors for BOD monitoring: a structured review of recent advances and challenges

Rapid and reliable wastewater monitoring has become a global necessity as water pollution, urbanization, and industrial expansion continue to strain freshwater resources worldwide. Conventional biochemical oxygen demand (BOD) tests require five days, making them unsuitable for real-time decision-making in treatment plants. Microbial fuel cell (MFC)-based biosensors are increasingly explored as rapid, in situ alternatives to the BOD test, yet their sensitivity, response time, linear range, and robustness in real wastewater remain major challenges. This structured review synthesized peer-reviewed primary studies from 2020 to 2025, identified through structured searches of Scopus and Web of Science, using predefined eligibility criteria confined to MFC-based BOD sensing. Reported operating windows span low-level effluents (e.g., 5-100 mg L⁻1) to high-strength wastewaters (up to ~800 mg L⁻1), with limits of detection as low as ~3 mg L⁻1 depending on inoculum source; response times range from minutes in micro-MFCs to hours in bench-scale systems. Accuracy is strongly conditioned by the combined effects of temperature, pH, external resistance, cathode chemistry, inoculum/biofilm state, and substrate composition, which modulate electron-recovery efficiency relative to true BOD. Notably, several studies validate performance in municipal and industrial wastewater, while long-term operation (≥800 days) has been demonstrated under stable calibration in single-chamber formats. Collectively, this review clarifies the design-performance trade-offs and operational determinants of accuracy.