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Microbial Fuel Cell-based
Biosensors for Biochemical
Oxygen Demand and Toxicity
Martin Spurr
• Introduction
Background to Oxygen Demand and BOD
• PhD Project
Introduction to MFCs
Multi-staged MFC Sensor Setup
Results
• Conclusions
• Future Work
• Acknowledgements
Outline
Oxygen Demand
Total BOD, COD, ThOD for
completely biodegradable
substrates
COD, ThOD for non-completely
biodegradable substrates
Total CBOD
BOD5 / CBOD5
Delzer, G.C., McKenzie, S.W. (2003) ‘Five-Day Biochemical Oxygen Demand’, in
USGS Techniques of Water-Resources Investigations, Book 9, United States
Geological Survey, pp. 1–21.
Image: http://www.hydrotox.de/en/services/
laboratory- services/biological-degradation/ready-
biological-degradation/closed-bottle-test.html
• BOD5 test (change in DO over 5-day incubation).
Time consuming (5 days) Inaccurate
No online measurements Labour intensive
• Respirometric, photometric and mediated-electrochemical BOD sensors.
Online process control Expensive transducers
Instability issues Frequent maintenance req.
• MFC-based BOD sensors (electrical current ∝ BOD)
Stability (> 5 years) Relatively maintenance free
Suitable for online process control/monitoring
Low operating costs
Biochemical Oxygen Demand
Image: http://www.progensci.co.uk/page581/Laboratory-Equipment/Environmental-Equipment
• Anode saturation at high
substrate concentrations.
• Current affected by other
variables (pH, temperature,
conductivity).
Requires correction or modelling
• Toxicants/inhibitors may
be misinterpreted as BOD
concentration decrease.
Current inhibition enables toxicity
sensing
MFC-based BOD Sensors Limitations
M T W T F S S
PhD Project
• Development of a novel MFC BOD sensor to
improve dynamic range/response time
Using single-pass, continuous-flow, multi-staged MFC
system
Effluent analysis performed by hydraulically
connected MFCs in series
Each MFC biofilm adapted for high – low substrate
concentration
• Effect of toxic inhibition by 4-nitrophenol.
Microbial Fuel Cell (MFC)
e- e-
External Resistance
Anaerobic Chamber
(contains substrate)
Aerobic Chamber
(oxygen reduction)
H+
Anode (biofilm)
Cathode (chemical)
O2
Ion Exchange
Membrane Substrate + H2O
CO2 + H+ + e-
O2 + 4H+ + 4e-
2H2O
Single Chamber Microbial Fuel Cell (SCMFC)
e- e-
External Resistance
Anaerobic Chamber
(contains substrate)
H+
Anode (biofilm)
Air Cathode (chemical)
O2
Ion
Exchange
Membrane
Substrate + H2O
CO2 + H+ + e-
O2 + 4H+ + 4e-
2H2O
• Multi-staged 10 ml MFCs: Hydraulically connected in series
Electrically connected as individual cells
Each cell feeds off effluent of previous cell
• Setup: Anode: Carbon cloth
Cathode: Carbon paper coated with 0.5 mg/cm2 Pt (GDE)
Membrane: Fumapem F-930 cation exchange membrane
• Operated for 2 years (757 days) Same anode carbon cloth material/biofilm for entire operating
period
Multi-staged Microbial Fuel Cells
Single-Pass Flow System Setup
Row
1
Row
2
Row
3
BOD Calibration
Row 1 Row 2 Row 3
% 𝐴𝑛𝑜𝑑𝑒
𝑠𝑎𝑡𝑢𝑟𝑎𝑡𝑖𝑜𝑛= 𝐼/𝐼𝑚𝑎𝑥
Fitted Calibration Curves
Error bars ±1SD from triplicate cells Error bars ±1SD from triplicate cells
• Hill equation: V = Vmax[S]
n
(K0.5)n
+[S]n
V = Reaction rate; Vmax = Maximum reaction rate; [S] = Substrate
concentration; K0.5 = Half-maximal concentration constant; n = Hill coefficient
Reduces to Michaelis-Menten equation at n=1
1.25 ml/min 0.50 ml/min
Effect of Flow Rate
Combined BOD & Toxicity Sensing
Response to Low BOD event
Row 1 Row 2 Row 3
Array (sum) % 𝐴𝑛𝑜𝑑𝑒
𝑠𝑎𝑡𝑢𝑟𝑎𝑡𝑖𝑜𝑛= 𝐼/𝐼𝑚𝑎𝑥
Row 1 Row 2 Row 3
Array (sum)
Response to 4-NP
% 𝐴𝑛𝑜𝑑𝑒
𝑠𝑎𝑡𝑢𝑟𝑎𝑡𝑖𝑜𝑛= 𝐼/𝐼𝑚𝑎𝑥
BOD increase vs BOD decrease vs Toxicity
Sensor Calibration
(BOD increase)
BOD decrease
Toxicant presence With changes in BOD:
• Cell 1 first to saturate, last to starve
• Cell 3 last to saturate, first to starve
• Mirrors sensor calibration curve
With toxicity presence:
• All cells inhibited
• Cell 1 last to recover (strongest dose)
% 𝐴𝑛𝑜𝑑𝑒
𝑠𝑎𝑡𝑢𝑟𝑎𝑡𝑖𝑜𝑛= 𝐼/𝐼𝑚𝑎𝑥
MFC-based BOD Sensors in the Literature
Dual Chamber MFC
Continuous-mode
Single Chamber MFC
MFC cell optimisation
“Submersible” MFC
• MFC sensors with
greater dynamic range and accuracy (750 mg/l ± 10%)
than BOD5 test (8 mg/l ± 15%)
within a smaller incubation time (5 – 10 hrs vs 5 days).
• Multi-staged MFCs can significantly increase
dynamic range of the BOD sensing system.
• Multi-staged MFCs allow explicit differentiation
between a BOD decrease and toxic inhibition.
Conclusions
• ‘The management and use of Biofilms’-Jan 2016
Working with University of South Wales and WH
Partnership to develop sensor from lab proof-of-
concept to prototype suitable for on-site operation.
Future Work
Acknowledgements
Supervisors: Ian Head, Eileen Yu, Keith Scott & Tom Curtis
Funding: SUPERGEN Biological Fuel Cells (EPSRC)