Microbial Fuel Cell-Based Biological Oxygen Demand Sensors for Monitoring Wastewater: State-of-the-Art and Practical Applications

Environmental pollution has been a continuous threat to sustainable development and global well-being. It has become a significant concern worldwide to combat the ecological crisis using low-cost innovative technologies. Biological oxygen demand (BOD) is a key indicator to comprehend the quality of water to guarantee environmental safety and human health; however, none of the present technologies are capable of online monitoring of the water at the source. Microbial fuel cells (MFC) are a promising technology for simultaneous power generation and wastewater treatment. MFCs have also been shown in fascinating applications to measure and detect the toxic pollutants present in wastewater. These are the bioreactors where exoelectrogenic microorganisms catalyze the conversion of the inherent chemical energy stored in organic compounds to electrical energy. Sensors employ energy conversion to measure BOD, which is considered an international index for the detection of organic material load present in wastewater. The MFC-based BOD sensors have gone through a wide range of advancement from mediator to mediator-less, double chamber to single-chamber, and large size to miniature. There have been detailed studies to improve the accuracy and reproducibility of the sensors for commercial applications. Additionally, multistage MFC-based BOD biosensors and miniature MFC–BOD sensors have also been ubiquitous in recent years. A considerable amount of work has been carried out to improve the performance of these devices by fabricating the proton exchange membranes and altering catalysts at the cathode. However, there remains a dearth for the fabrication of the devices in aspects like suitable microbes, proton exchange membranes, and cheaper catalysts for cathodes for effective real-time monitoring of wastewater. In this review, an extensive study has been carried out on various MFC-based BOD sensors. The efficiency and drawbacks associated with the different MFC-based BOD sensors have been critically evaluated, and future perspectives for their development have been investigated. The breadth of work compiled in this review will accelerate further research in MFC-based BOD biosensors. It will be of great importance to broad ranges of scientific research and industry.