Microbial Fuel Cells

And You!

What are MFCs?

o MFCs are bioelectrical devices that harness the natural metabolisms of microbes to produce electrical power directly from organic material

MFC Basics

Oxygen Poor

Oxygen Rich

Key Players

Mr. Clean(aka Shewanella)

The Iron-Breather(aka Geobacter)

1um1um

Key Players

o Direct Transfer

o Electron Shuttling

o Nanowires

Electron Transfer Mechanisms:

Mr. Clean(aka Shewanella)

The Iron-Breather(aka Geobacter)

1um1um

Key Players

o Direct Transfer

o Electron Shuttling

o Nanowires

Electron Transfer Mechanisms:

Mr. Clean(aka Shewanella)

The Iron-Breather(aka Geobacter)

1um1um

Respiration

cell

OC

CO2 SO4--

H2S

Redox Gradients

Max potential ~1.2 V (= potential difference between NADH and O2)

If terminal e- acceptor has lower potential than O2: Bacteria gain less ATP per

mole organic carbon oxidized Remaining energy is

available to be used in MFC

Anaerobic Microbial Food Chain

H2 + CO 2

H2 + CO 2

Acetate

AcetateAcetate

Acids, Alcohols

CH4 + CO 2

H2 + CO 2

H2 + CO 2

Acetate

AcetateAcetate

Acids, Alcohols

CH4

Macromolecules MonomersFermenting BacteriaFermen ting Bacteria

MethanogensMethanogens Methanogens

Acetogens AcetogensFermen ters Acetogen s Fermen ters Acetogen s

Southern We tlands Northern We tlandsWa rming

Fig. 1. Simplified model of anaerobic processes in northern (right) and southern wetlands. Acetate is not a precursor of CH4 andaccumulates in the north. The disruption of terminal activities in the north leads to a unique microbial consortium at virtually all

levels including bacteria in the food chain well above the methanogens. Climate warming causes the northern system to convert toone similar to the south where CH4 is derived also from acetate leading to a marked increase in CH4 emissions and a change inbacterial population composition.

Applications

Soil-based MFCs

The MudWatt

+Food

The MudWatt

MudWatt Steps

1) Make Fuel2) MudWatt Construction3) Monitor4) Submit Data

MudWatt Steps

Put ~3 cups of soil in bowl (Optional) Add mystery ingredient Hint: if your mystery ingredient is liquid, add just enough to

make the soil “cookie dough” consistency

Add water until “cookie dough” consistency

Record your ingredients (and volume fraction of secret ingredient if one was used)

1) Make Fuel

MudWatt Steps

Attach electrodes to dome lid (through donut disk)

Attach ruler sticker to the side of vessel Put mud in vessel up to 1cm. Pat smooth Place in Anode (make sure there are no air

bubbles)

Put in more soil up to 4 cm Place in Cathode Let rest for 2min Decant liquid if needed (Cathode cannot be

submerged)

2) Construct MudWatt

MudWatt Steps

3) Monitor (Perform this technique every week)

Nob #1= Blinker Nob #2 = 100Nob #3 = 500Nob #4 = 1000Nob #5 = 5000Nob #6 = 10,000

S1) Switch the electronics panel to Open Circuit mode by turning all switches off.

S2) After 30 minutes, check the voltage across the two leads using any voltmeter (black to “-“, and red to “+”). Record the voltage and the resistance. (the resistance is infinite under “Open Circuit” mode)

S3) Repeat S2 for the 5 different resistances provided on the electronics panel. Turn only one Nob on at a time.

The resistance for each Nob is outlined as follows (in Ohms):

MudWatt Steps

Enter the data you’ve collected at www.keegotech.com/community/datashare

4) Submit Data

Thank You! With the data collected and submitted by you and your fellow Keegoites, we hope to uncover trends and peculiar behaviors of microbial fuel cell technology. In this way, we aim to catalyze the development of this technology in the hope that someday MFCs will be a viable option in providing affordable and reliable energy for those who would benefit greatly from it. Developed by the public, for the public. All hail the Keegoites!