Transcript Optimizing the Microbial Fuel Cell as an Alternative Fossil Fuel Source

INTERNATIONAL
STUDENT SCIENCE
July 2012
CONFERENCE 2-8
Hong Kong
Optimizing the Microbial Fuel
Cell as an Alternative Fossil
Fuel Source
Philip Ong, Alex Cheah, Daniel Chew
Anglo-Chinese School (Independent),
Singapore
Introduction – The Microbial Fuel Cell
•A bio-electrochemical system that uses bacteria to
produce electricity
•Converts chemical energy to electrical energy by
catalytic reaction of microorganisms
•Used to generate electricity for storage
Our Aims
• Curbing carbon emissions by offering a cheap,
efficient method of obtaining energy
• To conserve fossil fuels and oil
• To reduce the emissions of environmentallyunfriendly substances into the earth
Our Set-Up
• Our experiment involved the use of a soil-based
Microbial Fuel Cell (MFC) through the construction
of a Winogradsky Column.
• Variables:
• [Independent]: Salinity as controlled by the amount of
NaCl per set-up
• [Dependent]: Current (in miliamperes)
• [Controlled]: Temperature, Location, Container Size &
Shape, Type of electrode, Amount of soil.
Materials and Apparatus
• Materials:
• 1. Clay soil used: 50% clay [Al 2Si2O5(OH)4] 50% soil [SiO2]
• (400g per set-up)
• 2. Sulfur
• (50g per set-up)
• 3. Water
• 4. Newspaper Shreds
• (10g per set-up)
•
•
•
•
•
•
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5. NaCl
Apparatus:
1. 2 Graphite Electrodes per set-up (as the anode and cathodes)
2. 2 Crocodile Clips
3. Multimeter
4. Stopwatch
5. Plastic containers
Conversions
Added amount of salt / g
0
5
10
15
20
Added salt concentration / ppm
0
2320
4630
6928
9217
Trend of current output against time
1.4
1.2
Current, I/mA
1
0
0.8
2320
0.6
4630
6928
0.4
9217
0.2
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
Day
Last day results
1.6
1.4
Curent, I/mA
1.2
1
0.8
0.6
0.4
0.2
0
0
2000
4000
6000
8000
Added Molar Concentration of NaCl/ppm
10000
Analysis
• Increase ionic strength  Decrease resistance
• I = 1.6 x 10-5 x Specific Conductance (in µmho/cm)
• I = ½ Σ zi2 mi
• Provide nutrients
• Tonicity: Too much salt causes crenation
• Lower oxygen levels
Limitations
• Carbon surfaces not pure
• Denitrification of nitrogen containing functionalities
• Pt electrodes might oxidize separate substrates
• Electroactive chemicals naturally present
• Contaminants easily absorbed
Conclusion
• Optimal range: 4000ppm-7000ppm
• Good current output
• Renewable energy source
• Easily accessible
Further Research
• Different genera involved
• Optimal soil for involvement in MFC
• Using other substitutes for soil eg. Wastewater
• Research into MFCs as a method of reducing toxicity
of soil
• Use of Sulfate Reducing Bacteria
• Polysulfides to sulfur
• Electrochemically active bacteria
References
• Newton. Oxygen Levels in Salt and Fresh Water.
http://www.newton.dep.anl.gov/askasci/chem03/chem03339.htm
• U.S. Geological Survey. Saline water. http://ga.water.usgs.gov/edu/saline.html
• CaCt. Chemical Reactivity: A Study Guide.
http://www.science.uwaterloo.ca/~cchieh/cact/applychem/reactivity.html
• University of Massachusetts: College of Engineering. Chapter XVIII: Electrochemical
methods.
http://www.ecs.umass.edu/cee/reckhow/courses/572/572bk18/572BK18.html
• Glass Properties. Definitions: Resistance, Specific resistance (resistivity),
Conductance, Specific conductance (conductivity).
http://glassproperties.com/resistivity/Conductivity_Resistivity.pdf
• Xi Wang et al., Impact of salinity on cathode catalyst performance in microbial fuel
cells (MFCs). International Journal of Hydrogen Energy [online] 2011, 36, 1390013906 http://www.engr.psu.edu/ce/enve/logan/publications/2011-Wang-etalIJHE.pdf
• Korneel Rabaey et al., Microbial Fuel Cells for Sulfide Removal. Environ. Sci.
Technol. [online] 2006, 40, 5218-5224
http://www.microbialfuelcell.org/Publications/LabMET/Rabaey%20Environ%20Sci%2
0Techn%2040%205218-5224%20Sulfide%20removal.pdf