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Journal of the U.S. SJWP

For the Future, From the Future

Copyright 2008 Water Environment Federation. All rights reserved.

72

Low-Cost, Single-Chambered Microbial Fuel Cells for

Harvesting Energy and Cleansing Wastewater

Ashutosh Patra

Portland, Oregon

[email protected]

______________________________________________________________________________________ABSTRACT

An attractive solution to the pressing issues of energy production and wastewater treatment is the use

of microbial fuel cells (MFCs). The goal of this project was to build low-cost, single-chambered MFCs that

harvest electricity and produce reclaimed water from wastewater. MFCs were constructed from cheap

alternatives to traditionally used, expensive Nafion membranes made by DuPont and platinum cathodes.

Alternatives used were household containers Gore-Tex and agar for membranes and metal screens for

cathodes. Several simple MFC construction methods and designs suitable for developing countries were

evaluated. A novel electrode-membrane-cathode assembly was shown to produce at least 4.33 times the

amount of energy per dollar than the typical current laboratory MFC. The small initial prototype MFC

produced about 0.087 mA/cm2 of anode area at a potential of 0.59 V. The experiments investigated methods

for reducing resistive losses, constructing single-chambered systems, and preparing economical membranes

with good oxygen isolation properties.

KEYWORDS: low-cost, microbial fuel cell, anaerobic, wastewater treatment, electricity, alternative energy

doi: 10.2175/ SJWP (2008)1:72

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1. INTRODUCTION

A. Problems of Energy Production and Wastewater Management

Because the worlds known oil and gas reserves are not infinite, it is necessary to evaluate alternative

and renewable energy sources such as wind, solar, and hydropower. Microbial fuel cells (MFCs) provide a

method of adding wastewater to the list of renewable energy sources. MFCs are attractive for wastewater

treatment, because they could allow for harvesting energy from wastewater for producing electricity. The

anaerobic microbes required for MFCs are commonly found in wastewater (Lui et al., 2004; Min and Logan,

2004), so influent wastewater could act as both a substrate and a source of microorganisms. Logan (2005)

estimates that electricity accounts for roughly 25% of the total operating costs of a wastewater treatment

plant. The wastewater from 100,000 people amounts to1.64*107 Liters/year from which MFCs could, at a

maximum, produce 2.3 MW/year (Logan, 2005).

In addition, a problem local to Oregon is that large quantities of anaerobic bacteria can kill fish in

local streams. This is because the anaerobic bacteria consume food and use up oxygen, which fish need to

survive [10]. The Oregon Department of Environmental Quality currently tests water to ensure there are not

high quantities of both anaerobic and aerobic bacteria in effluent wastewater that is dumped into streams that

contain local fish populations. Treating wastewater with MFCs could remove anaerobic microbes because

they attach themselves to the carbon anode so that electricity production occurs.

B. Background Information on MFCs

MFCs produce electric current from the

microbial oxidation of organic matter. An MFC

consists of an anode compartment separated from a

cathode compartment by a membrane that is permeable

to ions but not to microorganisms and organic matter

(the internal circuit). The external circuit is a wire

connecting the anode and the cathode. In the anode

compartment microorganisms oxidize the organic matter in

wastewater and transfer the electrons to the anode. The

hydrogen ions produced by the oxidation half reaction pass

Figure 1. The basic reaction and conductionprocess inan MFC. Depicts how the cell reactsand the resulting products.Note: All figures arecited in bibliography.

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was $12.00/m2. The Kiwi-Mesh allowed air to flow through it so that good contact was obtained between the

two reactants in the reduction half reaction (the O2 in the air and the H+

in the liquid).

Anode: Most conventional MFC anodes use carbon cloth: the MFC used in this experiment utilized carbon

cloth that cost $620/m2.

Membrane: Most MFCs have Nafion membranes that cost $2500/m2. Agar ($165/m2) and Gore-Tex

($82.5/m2) were evaluated as membrane materials.

Solution Containing Organic Matter: A wastewater solution was created with 2.5 grams of glucose, 0.5

grams of lactose, 0.5 grams of fructose, and 0.5 grams of maltose all mixed in 500ml of influent wastewater.

Bacteria: Many labs use specific electro-active microorganisms, such as Geobacterspp. andRhodoferax

ferrireducens. Because obtaining and maintaining cultures of such microorganisms was costly, the mixed cultures

of microorganisms present in Portland influent wastewater were used. Wastewater bacteria have several advantages

over isolated strains. Aside from being available at close to no cost, wastewater contains a diverse microbial

population that should be more resilient to changes than a pure culture of a single bacterium.

Materials: PVC pipe (2 diameter, 3 long), galvanized Kiwi-Mesh, agar, Gore-Tex, carbon cloth.

B. Construction and Designs

Five single-chamber MFC designs were tested initially as follows: (Later I built 4 more designs only one of

which is described as design 6). Six caps were constructed from the lids of

discarded peanut butter jars. A 5 mm hole was drilled into the middle of

each cap then an alligator clip with a 22 cm wire on its end was inserted

through the hole. A 4.4 x 6.6 cm carbon cloth anode was fastened to the

end of the alligator clip. The hole was then sealed with plumbers putty to

prevent air from entering once the cap had been attached to the chamber.

Agar membranes were prepared by cooling a solution made by

adding 23.5 g agar to 1 L of boiling water.Figure 4. Agar Preparation

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C. Design Descriptions

Design

Number

Materials

Used

Description Membrane

Type

1 2

PVC pipe, 100cm2 of Kiwi-Mesh,agar, Epoxy glue,29 cm

2carbon

cloth

The PVC pipe was placed on top of the Kiwi-Mesh. Liquidagar was poured into the pipe and allowed to solidify 30min. Epoxy glue was used to bond the PVC pipe to theKiwi-Mesh. This allowed for contact between the agarmembrane and the metal cathode. When agar formed overthe Kiwi-Mesh it was scraped off so that the metal couldproperly contact the air.

Agar

2 2 PVC pipe, 100cm2 of Kiwi-Mesh,agar, Epoxy glue,

29 cm

2

of carboncloth

Same as Design 1 but with an extra layer of liquid agar toprevent water from leaking out of the membrane.

Agar

3 2 PVC pipe, 100cm2 of Kiwi-Mesh,agar, Epoxy glue,29 cm2 of carboncloth

Same as Design 2 but plumbers putty was used connect thechamber to cathode.

Agar

4 2 PVC pipe, 10cm2 of Kiwi-Mesh,agar, Epoxy glue,

pencils, 29 cm2

ofcarbon cloth

The PVC pipe was placed on the Kiwi-Mesh. Liquid agarwas poured into the pipe. A second agar layer was appliedto the membrane to seal the chamber. Excess agar scraped

from the middle. The remaining excess agar was allowed tostay connected to the Kiwi-Mesh to bond them togetherCarbon filaments were created by removing graphite frompencils and pulverizing it into a powder which was thenlayered across the membrane and the cathode.

Agar

5 2 PVC pipe, 10cm2 of Kiwi-Mesh,Gore-Tex, rubberbands, 29 cm

2of

carbon cloth

Gore-Tex was stretched out over one side of a 2 PVC pipethen attached to it with rubber bands to make a watertightseal.

Gore-Tex

6 2 PVC pipe, 100

cm2 of Kiwi-

Mesh, Agar, Epoxy

Glue, 9 cm2 of

carbon cloth

Same as Design 4 except that a 9 cm2 piece of carbon cloth

was bonded to the agar membrane while it was half molten.

Agar

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D. Testing of Designs

All MFCs were tested in the same environment at 30 oC.

The MFCs were filled with the solution. Caps were fastened to each

MFC and one alligator clip was attached to each Kiwi-Mesh

cathode.

Resistors were attached to each MFC so that power could be

determined. A multi-meter was connected to each MFC and the

initial voltage and current readings were taken. For MFC Design 4,

the Vernier equipment was connected to the MFC and the voltage

and the current were recorded in graphical form by a computer

except for trials 1, 2, and 3 whose currents were recorded at start

and finish.

3. RESULTS

Data was collected from the MFCs after two weeks of bacterial growth. Designs 1 and 2 seemed to

show aberrant data because their initial voltages matched their final voltages. This suggests that there was nobacterial growth. Also a starting initial voltage should not be present because it takes some time for the

anaerobic microbes to build up on the cathode and the microbes respiration creates the voltage and current.

Design 5 seemed flawed because it started with very high voltage, which should not occur if the voltage was

caused by microbes. The voltages also did not increase once again suggesting no bacterial growth. Design 3

Figure 7. Sample layout of MFCsconnected to the Vernierequipment

Figure 6. Photo of Trial 4

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on the other hand had a high starting current that decreased over time. This also suggests no bacterial growth.

In Design 1 water leaked out of the MFC and the anode chamber became aerobic; MFC did not

develop either a potential or a current.

Design 2 had some water leakage and its

initial potential and current were high, possibly

because of the chemical reactions between metal

and water inside the chamber. They were not

caused by microbial activity because the initial and

final potentials and currents were the same.

Design 3 showed some microbe buildup on

the anode but the potential increased significantly

while the current decreased. These observations

suggest that the results were probably caused by a

reaction between metal and water rather than microbes.

Design 4 performed well. A thin biofilm

developed on the anode that could be seen when the

MFC was disassembled. The increase in potential

and current from their low initial values suggested

that these increases were due to microbial growth

rather than faulty wiring or spurious electrochemical

reactions.

Design 5 produced very little current,

possibly because electrochemical reactions between

the cell solution and the Kiwi-Mesh cathode caused

the development of a false potential. This was

indicated by the presence of an initial potential. The

increase in potential between 56 h and 73 h

Design

Number

Potential

(V)

Final

Potential

(V)

Initial

Current

(mA)

Final

Current

(mA)

1 0.0 0.0 0.0 0.00

2 0.55 0.55 0.20 0.21

3 0.46 5.0 1.6 0.03

4 0.06 0.40 0.01 0.96

5 5.4 0.20 0.01 0.01

6 0.44 0.59 0.01 0.78

Figure 8. Voltage change over time for Design 4

(Truncated to first week of observation)

Table 1. Data from Design Testing

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suggested that some bacterial growth may have occurred during

this period but then died off for unknown reasons.

Design 6, which had the anode directly bonded to the

membrane, produced the best results. A current and potential of

0.78 mA and 0.59 V respectively were generated by a 9 cm2

anode. This design worked the best likely because the direct

contact between the anode and membrane helped to reduce the

internal resistance.

The power outputs of the successful cell designs

(Designs 4 and 6) were compared to that of a conventional design.

Power was calculated from Ohms Law as follows:

P = I*V

Where P = power in milliwatts, mW

I = current in milliamps, mA

And V = potential in millivolts, mV.

A power to cost ratio (PCR) metric was used to compare the low-cost MFCs to more costly MFCs thatproduce higher amounts of power. Since the preliminary results reported above indicated that power was a

function of the electrode surface area, the term PCR electrode surface was used for this comparison as

follows:

For Design 6, Voltage = 0.59 V

Current = 0.78 mA

Electrode surface area = 9 cm2

Therefore, P = 0.59 * 0.78 = 0.46 mW

Assuming power output is proportional to anode surface area, then:

P/m2 = 0.46 mW * 10,000 cm2 / 9.0 cm2 = 510 mW/m2 Cost = $1205.56/m2

Final power to cost ratio = 510mW/$1205.56 = 0.42 mW/$

Figure 9. Voltage-Time plots for Design (red) and Design 7 (blue)

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Table 2 and 2.1 present estimates of the approximate power per m2 of anode for current MFCs

based on figures obtained from Liu [2]. The cost figures used for making these estimates include only the

major material costs for the anode, cathode, and membrane.

Table 2: Component Costs for Baseline MFC

Component Units Value

Carbon cloth $/ 100 cm2 6.5

Carbon electrode w/ Pt $/ 100 cm2

217

Nafion membrane $/ 100 cm2 31.7

MFC $ / m2 of anode 25,500

Table 2.1. Power Estimates of Baseline MFCs

Table 3. Material SourceMaterial Source of Price Information

Carbon Cloth E-Tek, ((B-1 Carbon Cloth at 33 cm x 33 cm)

Carbon electrodewith Pt

E-Tek, (Carbon Cloth Electrode, standard 0.5mg/cm2

TM loading using10% Pt on Vulcan XC-72, with standard ionomer application at 100 cm2)

NafionMembrane

www.fuelcell.com

Gore-Tex Jo-Ann Fabrics

Carbon Clothwithout catalyst

E-Tek, ((B-1 Carbon Cloth at 33 cm x 33 cm)

Baseline Design

Powerper m2anode*(mW)

MFCcost perm2 anode

Power/cost

(mW/$)

2500 $25,500 0.098

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Table 4. Performance and Cost Data for the Low-Cost MFCs

Design

Number

InitialVoltage

(V)

InitialCurrent

(mA)

FinalVoltage

(V)

FinalCurrent

(mA)

AnodeArea

(cm2 )

Cost ofAnode,

Cathode

andMembrane($)

Cost ofOther

Material($)

Power

(mW/m2

)

Anode,Cathode

and

Membranecost ($/m2)

Powerto Cost

Ratio(PCR)

FactorImprove-

ment

OverBaseline

4 0.06 0.01 0.40 0.96 29 2.39 1.25 130 820 0.16 1.7

6 0.44 0.01 0.59 0.78 9.0 1.09 1.25 510 1200 0.42 4.3

4. DISCUSSION

The experimental MFCs confirmed the presence of anaerobic electro-active microbes in Portland,

OR, influent wastewater. The experiments demonstrated the ability to construct low-cost, effective MFCs.

For example, Design 6 was 4.3 times as cost efficient ($/mW) as the typical MFC. Using an MFC such as

Design 6 for providing electricity for a city of 100,000 people where electricity costs 9.8 c/KW would save

approximately $300,000 a year (Extrapolated from Logan, 2005 estimates).

In addition the use of MFCs for electricity generation can accrue benefits in terms of reduced CO 2

emissions and wastewater treatment. MFCs are a largely untapped source of energy. Their application could be

useful in the following areas:

1. MFCs could replace current costly secondary wastewater treatment procedures while producing

electrical power that could be used both in the wastewater treatment plant and the local community.

2. MFCs constructed from cheap materials may have applications in developing countries both for the

treatment of wastewater and the efficient generation of electricity.

3. MFCs can be up to 90% efficient in power production compared to 50% for typical fossil fuel

power plants. Furthermore MFCs that treat wastewater would not generate any more CO2 than typical

biological wastewater treatment processes. Thus their substitution for fossil fuel power plants would

result in a net reduction of CO2 emissions.

To date there has been little work on finding cheap, locally available materials for constructingefficient MFCs. Most research is directed towards increasing energy production rather than lowering the

cost. Most MFCs employ expensive materials such as Nafion for membranes and platinum for cathodes.

Traditionally MFC efficiency is expressed in terms of energy/unit MFC. This research showed that

electricity production was a function of electrode area, and the electrode and membrane sizes are major

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determinants of MFC. This finding led to the development of the Power to Cost Ratio (PCR) - a new tool for

assessing MFC efficiency.

1. Additional MFC designs and component materials, e.g., graphite rocks for anodes, etc.

Experiments along these lines are being conducted.

2. The ability to scale MFC designs is important should be developed. To this end, a model electricity

production by MFCs in a large-scale wastewater treatment plant is being developed. This model

includes such variables as membrane size, substrate type, and anode size.

3. The quality of the effluent produced by MFCs should be determined. Processes for producing

reclaimed water from MFC effluent should be identified and evaluated.

4. The environmental impacts of using MFCs for electricity should be determined.

5. Process models for MFCs should be developed that will allow prediction of optimum MFC

configuration for different feedstocks.

6. The possibility of developing an efficient membrane-less MFC should be evaluated.

7. The ability to use MFCs for other treatment processes (e.g. heavy metals removal) should be

determined.

5. CONCLUSIONS

This research showed that:

1. MFC efficiency can be evaluated with the novel parameter of Power to cost Ratio (PCR).

2. A typical municipal wastewater contains microorganisms that can function to tret wastewater and

produce electricity in a MFC.

3. Functioning MFCs can be constructed from inexpensive, readily available components.

4. The technique of bonding the anode directly to the membrane achieves the important objective of

reducing the internal resistance and increasing the power output of the MFC. This technique led to an

MFC design that had approximately 4 times the (estimated) PCR efficiency of existing MFC designs.

6. ACKNOWLEDGEMENTS

A. Credits

I would like to thank Mr. K. Aldrich for the donation of influent wastewater and other chemicals; Mrs.

RaeAnn Haynes for risk assessment of the wastewater; Dr. Hong Liu for the donation of carbon cloth and for

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showing me her lab at OSU; Mr. Soule and Dr. Sheu for acting as my sponsoring teachers, and finally, my family

for driving me everywhere I needed to go, and for their love and constant encouragement.

B. Author

I was born in Austin, TX, to Priyadarsan and Anu Patra. Currently I am a junior at the Sunset High

School in Portland, OR. I like to keep myself busy with a variety of activities. I enjoy debate, tennis, music,

developmental work for the less fortunate, international travel, and the academic areas of math and science. Of

particular interest to me is the use of science to better the world around us, especially for sustainable

development.

My interest in developmental work grew at an early age, thanks to my father. He started a nonprofit

organization called Sustainable Economic and Educational Development Society (SEEDS) while in college. The

organization focuses on helping people generate sustainable sources of income and empower the underprivileged

in a number of ways. In the summer of ninth grade I traveled to remote areas of India with my dad to look at

ongoing developmental projects. I realized that there was a major lack of sanitation and safe drinking water in

developing countries, which prompted me to do further research.

I hope to study environmental engineering as well as socially-responsible business. That way I can

address both the technological and the social aspects of issues affecting us all. I hope to test the ideas in the field

by working with such organizations as SEEDS or Engineers Without Borders.

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7. REFERENCES

A. Picture Citations

1. E. A. Zielke, Design of a Single-Chamber Microbial Fuel Cell. None. 2005.12

2. H. Liu, B.E. Logan. Production of Electricity during Wastewater Treatment Using a Single-Chamber

Microbial Fuel Cell. Environmental Science Technology. 2004.38, 2281-2295

3. Oregon State University, Microbial Fuel Cell Lab of Dr. Hong Liu. *Picture taken by author.

Note: All figures/pictures not created, taken, or owned by author are cited below.

B. References

1. H. Liu, B.E. Logan. Production of Electricity during Wastewater Treatment Using a Single Chamber

Microbial Fuel Cell. Environmental Science and Technology. 2004. 2281-2295.

2. H. Liu, B. Logan, Electricity Generation Using an Air-Cathode Single Chamber Microbial Fuel Cellin the presence and Absence of a proton Exchange Membrane. Environmental Science and

Technology. 2004. 4040-4046.

3. R. M. Allen, H. P. Bennetto. Microbial fuel-cells-electricity production from carbohydrates.Applied Biochemistry and Biotechnology. 1993 39/40, 27-40.

4. E. A. Zielke, Design of a single Chamber Microbial Fuel Cell, None. 2005.5. Venkata Mohan, S. Veer Raghavulu, S. Srikanth, and P.N. Sarma. Bioelectricity production by

mediatorless microbial fuel cell (MFC) under acidophilic condition using wastewater as substrate:

influence of substrate loading rate.Current Science. 2007. 92(12): 1720-1726.

6. B.E. Logan, J.M. Regan. Feature Article: Microbial fuel cells-challenges and applications.Environmental Science Technology.2006.40(17):5172-5180.

7. T. H. Pham, J. K. Jang, H. Moon, I. S. Chang, and B. H. Kim.Improved performance of a microbialfuel cell using a membrane-electrode assembly. J. Microbiol. Biotechnol. 2005. 438-441.

8. B.H. Kim, I. S. Chang, and G. M. Gadd. Challenges in microbial fuel cell development andoperation.Applied Biochemistry and Biotechnology. 2007. 76, 485-494

9. B.E. Logan. Simultaneous wastewater treatment and biological electricity generation. WaterScience and Technology. 2005. 52(1-2):31

10.RaeAnn Haynes, Inorganic Section Manager, ODEQ Laboratory

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8. Bibliography

1. F. Davis, S. Higson. Biofuel cellsRecent advances and applications. Biosensors andBioelectronics. 2007.

2. SD Minteer, BY Liaw, and MJ. Cooney. Enzymebased biofuel cells. Current Opinion inBiotechnology. 2007. 18:228-234.

3. N. Canter, "Developing and using microbial fuel cells". Tribology & Lubrication Technology. Jul2005. FindArticles.com on 21 May, 2008.

4. S. Oh, B.E. Logan. Proton exchange membrane and electrode surface areas as factors that affectpower generation in microbial fuel cells. Applied Microbiology and Biotechnology. 2006.

70(2):162-169.

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