Microbial Fuel Cell-based

Biosensors for Biochemical

Oxygen Demand and Toxicity

Martin Spurr

m.w.spurr@newcastle.ac.uk

• 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)