Development of an innovative MFC-biosensor for real-time monitoring of anaerobic digestion for biogas production: Controlled substrate feeding strategy

A microbial fuel cell (MFC) based biosensor was designed to monitor volatile fatty acids (VFAs) in anaerobic digestion (AD) to control substrate feeding. The VFAs concentrations 7–40.83 mM showed a linear relationship with biosensor voltage (18–67 mV) indicating that voltage < 18 mV was due to low organic matter. Likewise, VFAs concentration lower than 7.87 mM resulted in decreased biogas production rate (BPR) and required substrate feeding. In a continuous food waste AD, the biosensor guided feeding produced 558 mL/g VS with the highest biomethane (62.17%), comparing with 344 and 387 mL/g VS produced by conventional 3- and 7-days intervals feeding, respectively. The microbial community was also more stable under the new strategy, where Prevotella and Methanosarcina were ~6-fold and 1.5-fold higher than conventional groups. The developed portable biosensor (~$200) worked effectively during outdoor monitoring of a domestic biogas plant. The VFAs based MFC biosensors can enhance the biogas yield with minimum substrate feeding while maintaining a suitable microbial community.