Geobacter-dominated biofilms used as amperometric BOD sensors

•New type of BOD sensor using a Geobacter-dominated biofilm selected with ethanol.•Ethanol selection resulted in electro-active biofilm with a broad metabolism.•The 1mL biosensor detected BOD contents from 174mg/L to 1200mg/L in 17.5h.•Biosensor showed accuracy and reproducibility for BOD evaluation of wastewater/milk The biochemical oxygen demand (BOD) of a given water sample is typically measured using a conventional BOD5 assay, which requires 5 days of incubation at 20°C of the sample with mixed communities of bacteria. The study presents a new type of BOD sensor using a Geobacter-dominated biofilm selected with ethanol as the sole carbon source. Ethanol selected for biofilms with a broader substrate usage than those selected with acetate, making them better for BOD biosensing applications. The biosensor was operated at room temperature with a voltage input of −0.08V vs SHE (−0.36V vs Ag/AgCl) and calibrated using several dilutions of synthetic wastewater with known BOD concentrations ranging from 174mg/L to 1200mg/L. The charge transferred by the biofilm over a reaction time of 17.5h was linearly correlated (R2=0.96) with BOD. Once calibrated, the biosensor was used to measure the BOD of cow’s milk with a reproducibility of 94% and an error of only 7.4% compared to BOD5 values. In contrast to the 5 days incubation currently required by standard BOD methods our novel biosensor offers a rapid monitoring alternative for assessments of the BOD of dairy effluent.