No re-calibration required? Stability of a bioelectrochemical sensor for biodegradable organic matter over 800 days

Abstract

Microbial Fuel Cells (MFCs) operated as biosensors could potentially enable truly low-cost, real-time monitoring of organic loading in wastewaters. The current generated by MFCs has been correlated with conventional measures of organic load such as Biochemical Oxygen Demand (BOD), but much remains to be established in terms of the reliability and applicability of such sensors. In this study, batch-mode and multi-stage, flow-mode MFCs were operated for over 800 days and regularly re-calibrated with synthetic wastewater containing glucose and glutamic acid (GGA). BOD 5 calibration curves were obtained by normalising the current measured as a percentage of maximum current. There was little drift between recalibrations and non-linear Hill models of the combined dataset had R 2 of 88–95%, exhibiting a stable response over time and across devices. Nonetheless, factors which do affect calibration were also assessed. Increasing external resistance (from 43.5 to 5100 Ω) above the internal resistance determined by polarisation curve decreased the calibration upper limit from 240 to 30 mg/l O 2 BOD 5 . Furthermore, more fermentable carbon sources increased the detection range, as tested with samples of real wastewater and synthetic media containing GGA, glucose-only and glutamic acid-only. Biofilm acclimatisation therefore did not account for differences between aerobic oxygen demand determinations and anaerobic MFC responses; these are likely attributable to competitive processes such as fermentation. This further highlights the potential for MFCs as real-time sensors for organic load monitoring and process control in addition to BOD-compliant measurement systems.

Layered Design of a Highly Repeatable Electroactive Biofilm for a Standardized Biochemical Oxygen Demand Sensor

“…In comparison, DEABs stably measured the BOD of real domestic wastewater within 20 h. With an optimized sensor design, the measuring time was reported to be further decreased to 5 min . The sensors achieved stability in BOD measurement in a real wastewater treatment plant by repeated calibration over long-term operation . DEABs were also demonstrated to be feasible for measuring the BOD of supernatant in anaerobic digestion.…”

Microbial Biofilms: Features of Formation and Potential for Use in Bioelectrochemical Devices

“…Thus, the biosensor can determine BOD concentrations ranging from those typical of municipal wastewaters up to those found in certain industrial wastewaters. Using a periodic and multi-stage flow mode, the authors managed to achieve biosensor operation for more than 800 days [ 152 ].…”

Microbial Fuel Cell-Based Organic Matter Sensors: Principles, Structures and Applications

“…The calibration range is also notably influenced by the external resistance (R e ). A com-parison between R e = 43.2 Ω and 305 Ω reveals a 60 mg/L decrease in the linear calibration range [ 90 ], which ranges from 15 to 180 mg/L BOD. Subsequently, at elevated R e values (953 Ω and 5100 Ω), the calibration range is further constrained to 15–150 mg/L and 15–30 mg/L, respectively.…”