Geobacter-dominated biofilms used as amperometric BOD sensors

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 −0.08 V vs SHE (−0.36 V vs Ag/AgCl) and calibrated using several dilutions of synthetic wastewater with known BOD concentrations ranging from 174 mg/L to 1200 mg/L. The charge transferred by the biofilm over a reaction time of 17.5 h 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.