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BIO301 Chemostat Group Report
Generation of Electricity by Mediatorless Microbial Fuel Cell using
Bacteria Source from Activated Sludge
Lester Fong, Tony Ho, Ankit Broker, David Hii, Yousif Hanna, Jeremy Hartley &
James Atem.
Abstract
Microbial fuel cells generate electricity by harnessing the electron transport chain of
bacteria under controlled conditions, the basic design of most microbial fuel cells
consists of an anaerobic anode chamber containing feed source and inoculated with a
mixed microbial culture and an anode chamber which contains an oxidizing agent
such as dissolved oxygen of ferricyanide. The power output of a microbial fuel cell
was measured in terms of a polarisation curve, which shows the relationship between
current and voltage over a range of resistances. The polarisation curves were
performed for two different methods. Firstly, when the MFC were in batch culture the
maximum voltage obtained for the first set of results was 0.272V and the second set
of results revealed 0.278V indicating bacteria had increased in health. The columbic
efficiency in the batch was recorded at 0.665%, which revealed the bacteria were
extremely weak. The first power cure recorded was at 0.0035 mW at a current of
0.0372 mA which was rather low. Furthermore the second power curve showed a
maximal power output of 0.0089 mW at a current of 0.063 mA revealing the bacteria
were healthier as the maximal power was higher and at a lower resistance compared
to the previous one. Resistance kept decreasing when the power was at its maximum.
Finally when the MFC were introduced in a continuous culture (chemostat), the
maximum voltage obtained from both sets of chemostat curves was 0.556V, which
showed an increase in the voltage when compared to the batch culture (0.278V &
0.272V).
1
Introduction
Microbial fuel cells (MFC’s) generate electricity by harnessing the electron transport
chain of bacteria under controlled conditions (Mohan et al., 2007). They have
potential to generate electricity from a wide variety of organic wastes while oxidising
the wastes to less harmful forms (Moon et al., 2006, Ieropoulos et al., 2005, Liu et al.,
2004). Research into developing efficient MFC’s remains a very current field, with
both engineering and biological challenges yet to be met (Moon et al., 2006, Mohan et
al., 2007).
The basic design of most microbial fuel cells consists of an anaerobic anode chamber
containing a feed source and inoculated with a mixed microbial culture, and an anode
chamber which contains an oxidizing agent such as dissolved oxygen of ferricyanide
(Mohan et al., 2007). Being deprived of a direct electron acceptor for respiration, the
bacteria in the anode chamber donate electrons to the anode, which are then
transferred via a conductor to the cathode, where reduction occurs (Ieropoulos et al.,
2005). Charge balance is maintained by migration of H+ across a proton exchange
membrane (Mohan et al., 2007).
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Figure 1: Schematic representation of a mediatorless MFC operating in batch
mode using acetate as an electron donor and ferricyanide as an electron
acceptor.
MFC’s may be broadly classified into two categories depending on the means of
electron transfer between the bacteria and the anode. Mediated fuel cells contain an
artificial mediator in the anode chamber (Liu et al., 2004). Bacteria transfer electrons
to the mediator in solution, which is then regenerated at the anode (Ieropoulos et al.,
2005, Liu et al., 2004). This mechanism of electron transfer has several disadvantages
relating to the cost and toxicity of artificial mediators (Ieropoulos et al., 2005, Mohan
et al., 2007, Liu et al., 2004). A second category of MFC’s does not contain an
artificial mediator, but relies on natural electron transfer processes of the bacteria.
While these processes are as yet poorly understood, they are thought to include direct
electron transfer by membrane bound enzymes as well as synthesesis of natural
mediators (Ieropoulos et al., 2005, Stams et al., 2006, Liu et al., 2004).
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Because not all substrate is completely oxidised, with some mass necessarily being
used for biosynthesis, then not all high energy electrons supplied in the substrate are
transferred to the cathode and available to do work. The percentage of electrons which
are transferred is expressed in terms of columbic efficiency, which is essentially a
percentage ratio of the number of electrons supplied against the number of electrons
transferred. This parameter is a useful measure of the overall efficiency of the MFC
(Liu et al., 2004, Min and Logan, 2004, Williams, 1966).
The power output of a MFC is also a useful quantity to measure. This is measured in
terms of a polarisation curve, which shows the relationship between current and
voltage over a range of resistances(Mohan et al., 2007, Larminie and Dicks, 2003). By
the relationships V=IR and P=IV, where V is voltage, I is current, R is resistance, and
P is power, then observations of current, voltage and resistance can be manipulated to
give information about power output (Atkins and de Paula, 2006, Serway and Faughn,
2003).
The aim of this experiment shall be to create a MFC which is capable of degrading
wastewater to produce electricity, and to investigate it’s performance under both batch
and continuous flow conditions.
Materials and Methods
Microbial Fuel cell setup
The fuel cell consisted of two chambers (each 500 mL), an anode chamber and a
cathode chamber, which were separated by a proton exchange membrane between
solutions, and a conductor between the electrodes. The anode consisted of a carbon
sponge connected to a platinum wire, while the cathode was composed of platinum
foil.(Figure 9).The anode chamber was inoculated with activated sludge and kept
under anaerobic conditions, while the cathode chamber was filled with 500mL
Potassium Ferricyanide and kept under aerobic conditions. (Figure 10).Both chambers
were stirred magnetically and maintained in a water bath at 30oC. The circuit between
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electrodes was closed to allow electron transfer. (Figure 2). The solution in the
cathode chamber was changed when the fading colour of the solution indicated near
complete reduction of the Ferricyanide.
Operation
Batch mode:
Synthetic wastewater was prepared with acetate as a carbon source and electron
donor. At this stage of the experiment the acetate was kept as a separate solution to
limit microbial contamination. The acetate solution was prepared to a concentration of
1.00 M , and the composition of the other component of the synthetic wastewater is
given below):
1L Synthetic wastewater consists 20mL of sodium acetate 1.0M, 1.25mL trace
elements, 480mg NaHCO3, 95.5mg NH4Cl, 10.5 K2HPO4, 5.25 KH2PO4, 63.1
CaCl2.2H20, and 19.2 MgSO4.7H20 (Ghangrekar and Shinde, 2006).
Chemostat mode:
Synthetic was supplied to the anode chamber at a rate of 50 mL per day via a
peristaltic pump running on a timer cycle of 288 minutes off, 1 minute on. The
substrate reservoir contained a single part AWW including diluted acetate component.
It was kept in an insulated icebox to reduce microbial activity, and stirred
magnetically and intermittently on a timer cycle of 0.5 minutes every 70 minutes to
increase homogeneity but minimise aeration. (Figure 11).
Monitoring of voltage
Voltmeter was used to measure the potential against 1000ohm and the values were
recorded down periodically.
Polarization curves
Polarisation curves were used as a means of determining the capacity of the bacterial
culture. A substrate saturated culture was used, and voltage was measured at a series
of stepwise increasing resistances until no voltage was measurable between the
electrodes. Using the relationship V=IR, then current was thus calculated at each point
of the curve, allowing power to also be calculated by the relationship P=IV
5
Methods for obtaining polarization curve
The resistor was disconnected and the potential was allowed to build up to a point
where no further increment of voltage can be observed. This was followed by
observation of voltage increment using voltmeter until it reaches the maximum
potential point. Then, the resistor was connected and ensured that the connection is a
close circuit system as illustrated below:
Figure 2: Closed circuit system of microbial fuel cell
The potential values were recorded while varying the resistance from the highest to
the lowest resistance at time intervals of 5 minutes. (Note: The voltage values must be
taken only when the pseudo-steady-state conditions have been established).Graphs of
cell cottage (V) versus current (mA) and Power (mW) versus current (mA) were
plotted by referring to the recorder values.
Methods for obtaining Columbic efficiency in batch culture
The resistor was connected to the anode and cathode chambers to establish a closed
circuit system (As illustrated in figure 4). After that, the potential was measured using
a voltmeter. the microbial fuel cell was left to run overnight for the voltage reading of
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the potential to reach stabilization. Then, 1mL sodium acetate 1.0M was added to the
anode chamber using Terumu needle (0.65 x 32mm) with syringe. After addition, the
voltage reading from the voltage meter was recorded at an interval of 2 hours (Take
note of the highest possible voltage reading before the curve start to drop – refer
results) and eventually stabilize.
Stirring speed
When
Speed
During batch culture
220rpm
1st polarization curve (batch mode)
360rpm
2nd polarization curve (batch mode)
360rpm
3rd polarization curve (chemostat)
200rpm
4rd polarization curve (chemostat)
200rpm
Temperature
The temperature of the water in aquarium was maintained at around 30°C (this is to
ensure suitable temperature for the bacteria to grow in the anode chamber). The ice in
the Esky Box was changed 2 times per day (this prevents contamination due to growth
of other microorganisms)
pH
pH of the anode chamber was maintained at around pH6.5 – pH7.0.
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Results
Initially, results were taken when the MFC was in a batch culture.
Figure 3: Batch polarization curves.
From such calculations, a variety of curves were produced. The polarisation curves
produced showed the effects of voltage on the current (Fig 3). Such a graph shows the
lowering of the potential of an electrode from equilibrium, which is caused by the
passing of an electric current. On the other hand, a power curve illustrates the highest
amount of power that the bacteria could produce, showing that the higher the
maximum power, the ‘stronger’ the bacteria were. The other main reason for a power
curve is that, not only does it show that maximum potential output of the MFC but
also at what resistant.
For the first polarisation curve, the higher the current, the greater the drop was in the
voltage (maximal velocity of 0.2724V) (Fig 3). Although it was not really visible
from the graph (refer to table 1), at the beginning (peak voltage), there was a slight
increase and then decrease in voltage. This area is where activation losses are
dominant (voltage area between 0.2725V and 0.2704V). Furthermore, ohmic losses
were dominant when the voltage was between 0.2704V and 0.2664V. When there was
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a rapid, linear decrease in the voltage, at higher currents (between 0.2664V and about
0.0103V), concentration loss (mass transport effect) was overriding.
The second polarisation curve was produced according to results that were taken three
days after the initial set of results (Fig 3). As seen in the previous results, the higher
the current, the greater the drop was in the voltage (Fig 3; Table 2). A higher maximal
voltage was achieved, which was 0.278V compared to 0.2724V. Activation losses did
not really dominate at all in this polarisation curve. If there was any domination, it
would have been between a voltage of 0.278V and 0.270V. Ohmic losses were
dominant when the voltage was between 0.270V and 0.2438V. When there was a
linear decrease in voltage, concentration loss (mass transport effect) was dominant at
a voltage between 0.2438V and 0.0055V. To compare with the first polarisation
curve, the second one slightly shifted to the right, showing higher voltages at higher
currents (0.097mA (0.0145V) compared to the first curve, which had a current of
0.097mA and a voltage of 0.0032V).
Figure 4: Batch power curves.
The first power curve showed that the power of the bacteria had a maximal output
potential of 0.0035mW, which was rather low (closed circuit only, as open circuit
showed no power) (Fig 4). This power was achieved at a current of 0.03728mA. At
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maximal power, also, the resistance was 2500 ohms. The maximal volumetric power
equals power (W) divided by metres cubed (volume (L) of anode) (Table 1). This
occurs at the maximal output potential and in this part of the experiment, it equalled
1.39x10-5 W/m3, which was also a very low number. The reason for the drop in
power, after it maximises, is due to an increase in ohmic loss and electrode over
potentials (short circuit situation).
The maximal power output achieved for the second power curve was higher than the
previous curve (a slight shift to the right) (Fig 4). The second power curve showed a
maximal power output of 0.0089mW at a current of 0.063mA. At the maximal power,
the resistance was 2200 ohms, showing that the bacteria had become slightly more
‘healthier’, as the maximal power was higher and at a lower resistance (compared to
the previous power results). The maximal volumetric power was 3.54x10-5 W/m3,
which was also higher than the previous result of 1.39x10-5 W/m3, emphasising vast
bacterial improvement.
In batch mode, the columbic efficiency curve was plotted with current (mA) versus
time (h). It represents the total amount of time required for the bacteria in the MFC to
completely metabolise 1mL of 1M acetate. Calculated values for the graph can be
seen in Table 5 of the appendix.
10
Added 1mL
Acetate (1M)
Figure 5: Current as a function of time (determines coulombic efficiency)
This part of the experiment was carried out three days after the second set of batch
results were achieved. The resistance used was the one that gave maximal output
potential in the latest set of results (2200 ohms) (Fig 4).
It is known that, current = coulomb per time, while the area under the curve and above
the baseline = (Coulomb / Time) x Time = Coulomb. From Table 5, the area under the
curve and above the baseline was calculated to be 5.1 Coulombs using integration.
Calculating Columbic Efficiency %:
On addition of 1mL of 1M acetate
Number of moles of acetate added = 1/1000 x 1 = 0.001 moles of acetate
Number of moles of electrons available in 0.001 moles of acetate = 0.001 x 8 = 0.008
moles of eSince 1 moles of electrons = 96485 Coulombs, 0.008 moles of electrons = 96485 x
0.008 = 771.88 Coulombs. Hence, in theory, 0.001 moles of acetate should have
771.88 Coulombs.
Columbic efficiency =
___________Coulombs calculated from the curve x 100__________
Theoretical amount of Coulombs in added amount of acetate
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= 5.1 / 771.88 x 100 = 0.665% (which is an extremely low efficiency)
At a resistance of 2200 ohms, the voltage stabilised at 61.5mV (0.028mA), showing
that since the resistance is stable, an increase in voltage will cause an increase in
current (I=V/R) (Fig 5). Once the 1mL of acetate was added, a slow increase in
voltage occurred over about 7.2 hours, maxing out at 73mV (0.033mA). Once all the
acetate was metabolised, the voltage decreased over 13.8 hours, going back to the
baseline voltage of 61.5mV. The current baseline that was constructed over about 21
hours was used to find the area of the graph, which further assisted in calculating the
coulombic efficiency.
Figure 6: Correlation of acetate oxidation rate and current (Second batch
results).
The current shows the electron flow rate occurring in the MFC, which also equals the
current in coulombs per second (C/s). As known, one mole of electrons (e-) equals
96485 C / mole e- (Faradays constant), therefore, to get the current in moles of e-/sec
it would be (C/s) divided by 96485. To get the moles of acetate per hour it would be
moles e- per second divided by 8 (acetate yields eight electrons (requires two moles of
oxygen)) x3600 (assuming all electrons are used to make electricity). To get the
acetate oxidation rate (moles of acetate/L/h), it would be moles of acetate per hour
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divided by the volume of the anolyte (0.5L). This answer should equal to the current
(linear correlation), however, it was off by a factor of about 111 in this experiment
(Fig 6). The reason for this is due to the extremely low coulombic efficiency (0.665%)
(decrease coulombic efficiency, decreases oxidation rate), as at low coulombic
efficiencies, the chances of an accurate finding of the acetate oxidation rate decreases
severely.
The following day was when the MFC was when the culture was put in a continuous
culture (chemostat). 50mL of acetate (1M) was pumped into the anode vessel
everyday (vessel total volume = 500mL). Further on, the dilution rate is equal to the
flow rate (L/h) divided by the volume (L). Therefore, the dilution rate equals
(0.05/24)/0.5, which equals 0.0042 h-1, and the average treatment time, also known as
the hydraulic retention time (HRT) equals 1/0.0042 h (240 h or 10 days).
Figure 7: Chemostat polarisation curves.
These results were taken five days after the chemostat was put into place (Fig 7; Table
3). As usual, an increase in current caused an eventual decrease in voltage. In the first
chemostat polarization curve, there was quite a high increase in the voltage compared
13
to the batch culture (0.453V compared to 0.278V and 0.2724V) (Fig 7; Fig 1).
Activation losses dominated at a voltage between 0.453V and 0.452V (may not have
even occurred), while ohmic losses surged at a voltage between 0.452V and 0.412V.
The linear drop in voltage (concentration loss) was evident when the voltage was
between 0.412V and 0.0335V. Once again, if this polarisation curve was added to the
other two, there would be a larger shift to the right and the graph would be starting at
a higher point, showing that the voltage stayed higher at a higher current for a longer
time, in comparison to the others.
The second set of chemostat results were obtained the following day. A voltage of
0.556V occurred in the final set of results and this was the healthiest stage of the
bacteria in this experiment (previous voltage of 0.453V) (Fig 7). Activation loss was
not really evident but ohmic losses occurred at voltages between 0.557V and 0.535V,
while concentration loss dominated at a voltage between 0.535V and 0.215V. Overall,
it was clear to see that the highest voltages, over various currents, occurred in the last
set of results that were conducted in this experiment.
Figure 8: Chemostat power curves.
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A new maximal output potential was achieved, being about 13 times higher than the
previous maximum one (0.115mW compared to 0.0089mW) (Fig 8; Fig 4). This
occurred at a current of 0.45mA and at a resistance of 560 ohms, which was almost
2000 less ohms than the final batch culture results. This, once again, showed that the
bacteria were a lot stronger compared to the previous tests. The maximal volumetric
power was 3.54x10-5 W/m3, which was also higher than the previous maximum result
of 1.39x10-5 W/m3.
The highest maximal output achieved in this experiment occurred at the final readings
of the chemostat (0.48mW, compared to the previous maximum of 0.115mW) (Fig 8).
The corresponding current was 1.5mA. The resistance decreased even more, settling
at 220 ohms, emphasising that the bacteria just kept getting better. 0.002 W/m3 was
the maximal volumetric power, also, being higher than the previous power (3.54x10-5
W/m3).
Summing up, over time, it was clear to see that the bacteria improved their ability to
make electricity. The maximum voltage increased over the four set of results (from
0.272V to 0.556V) and the voltages stayed higher over lower resistances. The
resistance at which the power was maximal kept decreasing (2500 ohms to 220
ohms), also showing the improvement of bacteria over time (days/weeks). On top of
this, a continuous improvement in the maximal volumetric power (1.39E-05 W/m3 to
0.0019 W/m3) and maximal power (0.003474 mW to 0.477164 mW) was evident, too.
However, at a batch coulombic efficiency of only 0.665%, this shows that the
bacteria, in the batch culture, were extremely weak.
Discussion
In this experiment, the behavioural characteristics of microbial fuel cell was
investigated and observed. From the results, it confirmed the hypothesis that bacteria
can be forced to act like a battery under certain conditions. The results evidently
showed that the bacteria were getting better or more capable of charging up the
15
electric potential in the microbial chamber. This can be observed from Figure 3 and 7,
showing a two fold increase in voltage readings from 0.272 V (first batch results) to
0.556 V (second chemostat results) at 1M ohms resistance.
Other than voltage, the MFC also recorded better readings in key performance
parameters, such as maximum power output at corresponding resistances. This is
apparent from Figure 4 and 8 where the maximum power output increased from
0.0035 mW at 2500 ohms (first batch results) to 0.48 mW at 220 ohms (second
chemostat results). The increase in maximum power output and voltage at decreasing
resistance confirmed that the bacteria were improving in health; resulting in an
increase in the amount of bacteria which can transfer electrons to the carbon anode.
During the course of this experiment, the MFC ran in two feeding modes which were
fed-batch and chemostat batch. However, the chemostat mode of this experiment is
technically more of a semi-continuous batch mode. The reason for the phrase ‘semicontinuous’ was because the inflow and outflow of the bacteria anode chamber,
though having the characteristics of a chemostat, was only semi-continuous as it had
an inflow of 10 mL substrate 4 hours 48 minutes interval. A true chemostat has a
continuous inflow and outflow. In the semi-continuous batch mode, the bacteria may
be experiencing starvation during the 4 hours 48 minutes interval. This semicontinuous feeding schedule may affect the bacteria physiologically. The reason for
the long interval is due to the limitations introduced by the pumping system which
allows the slowest pumping rate of 10 mL per minute. The reason why 50 mL of 0.02
M of acetate was fed to the bacteria per day during the semi-continuous mode, was
due to the fact that during the experiment for the coulombic efficiency in batch mode,
the bacteria took more than 20 hours to fully metabolise 1 mL of 1 M acetate.
The coulombic efficiency (CE) for this MFC in batch mode was 0.665 %. This is
significantly lower than the usual CE published in literatures which range from 6080% [2]. From Figure 6, acetate oxidation rate was out by a factor of 111. This is
because, the lower the CE, the more inaccurate will the acetate oxidation rate be. The
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low CE may be due to the fact that 1 mL of 1 M acetate was used in getting the feed
spike curve. This caused the long hours needed for the acetate added to be fully
metabolised, which may result in inaccuracies. A aliquot of 30 uL of 1 M acetate
should produce a more accurate result. The coulombic efficiency for the semicontinuous mode was not done as it was impossible to determine the amount of
acetate present in the anode chamber at any one time without doing gas
chromatography. However, the results also clearly showed that the MFC in semicontinuous batch mode was significantly more capable than the MFC in batch mode
as its power output and maximum potential build up were both almost twice of that in
batch mode. However, no further concrete conclusions can be made from this
comparison as the biomass in both modes were not collected and measured. Further
investigation is recommended in determining the amount of biomass present in semicontinuous batch and batch mode as it is expected that the amount of biomass in semicontinuous batch will be significantly more than those in batch mode.
Further experiments should be conduced to find out whether the increase of potential
was caused by the increase in amount of bacteria or simply the bacteria were
becoming more efficient in donating electrons to the anode.
Hence, it is recommended for further experiments, the weight of the carbon sponge to
be weighed first before starting the experiment to allow the biomass to be measured.
The effect of temperature on the electric potential produced by the bacteria is worth
further investigations, as the increase in temperature to 30°C increases the electric
potential significantly. Changing different substances at the cathode chamber may
also produce different results worth investigating.
17
References
Atkins, P. & De Paula, J. (2006) Atkins' Physical Chemistry, Oxford University Press.
Gangrekar M.M & Shinde V.B (2006) Performance of membrane-less microbial fuel
cell treating wastewater and effect of electrode distance and area on electricity
production. Bioresource Technology, 97, 543-550.
Ieropoulos, I., Greenman, J., Melhuish, C. & Hart, J. (2005) Comparative study of
three types of microbial fuel cell. Enzyme and Microbial technology, 37, 238-245.
Larminie, J. & Dicks, A. (2003) Fuel Cell Systems Explained, West Sussex, John
Wiley and Sons LTD.
Liu, H., Ramanarayanan, R. & Logan, B. (2004) Production of electricity during
wastewater treatment using a single chamber microbial fuel cell. Environmental
Science and Technology, 38, 2281-2285.
Min, B. & Logan, B. (2004) Continuous electricity generation from domestic
wastewater and organic substrates in a flat plate microbial fuel cell. Environmental
Science and Technology, 38, 5809-5814.
Mohan, S., Raghavulu, S., Srikanth, S. & Sarma, P. (2007) Bioelectricity production
by mediatorless microbial fuel cell under acidophillic condition using wastewater as a
substrate: Influence of substrate loading rate. Current Science, 92, 1720-1726.
Moon, H., Chang, I. S. & Kim, B. H. (2006) Continuous electricity production from
artificial wastewater using a mediator-less microbial fuel cell. Bioresource
Technology, 97, 621-627.
Serway, R. & Faughn, J. (2003) College Physics, Melbourne, Thompson Brooks\Cole.
Stams, A., De Bok, F., Plugge, C., Van eekert, M., Dolfing, J. & Schraa, G. (2006)
Exocellular electron transfer in anaerobic microbial communities. Environmental
Microbiology, 8, 371-382.
Williams, K. (Ed.) (1966) An Introduction to Fuel Cells, London, Elsevier Publishing.
18
Recommendations (Overview)
Intrepid biotechnologists, congratulations on choosing the bioelectricity project. Here
are a few of points to help you on your journey.
1 – The anode chamber is the brown sludgy one. The cathode chamber is the one that
looks like cordial. Someone who marks your work will probably ask you that
sometime, so try and remember it. If you can’t remember it, then leap forward keenly
as if you are bursting with the answer, and Ralf will tell you to shutup and pick on
someone else.
2 – The anode is not really anaerobic because the oxygen is bad for electricity
production, it is because it stinks like real sewerage even though it is fake (at least
they told me it was)
3 – The cathode solution is not very nice. I don’t think there is even any real cordial in
there. Maybe the cyanide bit is a hint.
4 – Ralf likes pumps, so put one in there early on, even if it is just for looks. That way
you will still get to do nothing for the first two weeks, but no-one will bug you about
progress. It doesn’t hurt to keep him happy, and not many people are so easily
amused.
5 – Don’t worry so much about polarisation curves. I think it will give someone a
headache to mark anyway. Just put a pump on it and play around with lots of different
things, I would suggest dilution rate and different oxidising agents in the cathode
chamber. Measure the current which you achieve at steady state. It is quicker too.
If anyone actually figures out what a polarisation curve is, can you please email me?
6 – Kayu is the most helpful, knowledgeable and genuinely kind demonstrator you
will ever come across. Pay attention to this guru. Even though he is quiet he is
packing the most powerful MFC in the world today in that lab of his. He will probably
rule the world one day by solving the energy crisis with a car that runs on sewerage
with the added bonus of not having to stop for toilet breaks on long trips.
19
Recommendations (In detail)
1. It is best to place the MFC into a tank of 30°C as early as possible. This is the
optimum temperature for the bacteria to live in.
2. Ensure the water level in the incubation tank is at the correct height level at all
times.
3. The setup should be done in such a way so that the wire connecting to the two
electrodes are not being disturbed too much. ie. Use crocodile clip wires in
between the electrodes and the resistor & voltmeter.
4. Current should be calculated using Ohm’s law instead of reading off the
voltmeter.
5. The MFC equipments are all very expensive. Handle with care.
6. It is recommended to go straight into chemostat mode and conduct
experiments in that mode instead of using precious time doing a batch mode.
7. A pump which can pump very small amounts of substrate for very short
intervals of time should be secured as early as possible for the experiment.
8. Stirring rate is recommended to be at around 200 rpm. Too high a stirring rate
may dislodge the electricity producing bacteria from the anode.
9. The total concentration of acetate in the anode chamber at any one time is
recommended to be not more than 0.1 mM to 0.5 mM.
10. After running the MFC for 3 to 5 days, the blackish sludge can be poured
away carefully and slowly and replace the anode chamber with synthetic
wastewater. Ensure that the carbon sponge anode is not disturbed too much
during the transition as the electric producing bacteria should be adhering
themselves to it. Initial voltage may be lowered drastically but will increase
dramatically soon after.
11. pH should be monitored frequently to ensure that the pH does not rise or fall
too much.
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12. If carbon source was added into the synthetic wastewater, proper measures
should be taken to prevent or delay its contamination with bacteria in the
surroundings.
13. Ensure that the circuit is not opened for too long as the bacteria may die off
due to lack of means to transfer electrons.
14. If any stirring is to be introduced in any thing, ensure that it is as air tight as
possible to reduce oxygen dissolving into the system. The system is to be keep
as anaerobic as possible for maximum electricity production.
15. Ferricyanide should be changed in the cathode when it turns turbid or loses
colour. Alternatively, peroxide can be added to reoxidise it.
16. If a pump is added, a compromise in the air-tightness of the system may occur.
This is because an opening need to be introduce so that an inflow and outflow
can occur. Without the opening, the pressure in the vacuum will prevent the
pump from doing its job. Measures can be taken to both reduce the oxygen
dissolution as well as contamination.
17. Prior knowledge on MFC and electrochemistry is preferable to do this
experiment. The first week should be used to familiarise these concepts from
literature.
18. Using a polarisation and power curve is the best way to illustrate that the
bacteria culture in the anode chamber is getting enriched as the experiment
proceeds. Similarly, columbic efficiency should improve over time.
19. When producing the polarisation/power curves, there is no need to wait for the
voltage to completely stabilise. It could take half a day to a day to stabilise. As
soon as the increase in voltage, during the charging up, is significantly slow
(about 0.1 mV every 10 to 15 minutes) it is good enough to be considered as
stabilised. Proceed with the experiment from there.
20. Then doing the columbic efficiency curve, 30 uL of 1 M acetate solution is
more than enough to produce the “feed spike”. Adding more than that will
result in long hours of waiting time for all the added acetate to be fully
metabolised.
21
21. As this experiment is very new and you will probably be the second group to
be doing this, MAKE SURE you know exactly what your experiment is going
to achieve and how are you going to carry it out latest by 3rd week. This is
probably loads of things you can find out about MFCs but be realistic and
choose those that interest you most and discuss with your supervisors.
22. You will probably hear a lot of recommendations on what you can do with
your experiment. Listen to those BUT choose only those that you think you
are able to carry out. Time, equipment, complexity of the tasks should be some
of your considering factors.
23. During the first week, have a serious meeting and layout house rules. Identify
those members who are most likely not going to have much contribution and
lay down the terms and conditions. This is essential and should be done as
soon as possible.
In summary, this project is relatively easy, and will probably be a lot easier for you
than for us. It will better if any group doing this project has a bit of Chemistry and
Physics background, don’t panic, just the basic stuff. You can get very technical on
this one, but I would suggest playing around with more things and collecting simpler
information, maybe columbic efficiency and current output at steady state. I think we
made a valuable contribution to science too. We probably generated enough power to
run a single LED to read by for 2 seconds. It is amazing what you can read in two
seconds. Other methods of power generation from sewerage might also be worth
investigating. Like putting it on your garden, growing potatoes, feeding them to rats,
and making the rats generate power on a treadmill. Try and put a pump in there
though to keep Ralf happy (BLESS HIM).
Good luck!
22
Acknowledgement
We
would
like
to
thank
our
lecturer, Dr Ralf, for his valuable
guidance
and
advices
for
our
project.
We would like to thank our Mentor,
Kayu Cheng who assisted us in
configuring and the setting up of
Microbial Fuel Cell.
23
Appendix
Materials and equipment
1L Sodium acetate 1.0M for batch culture
1L Sodium acetate 0.02M for chemostat
1L activated sludge
2 electronic timers (LT48W)
2 magnetic stirrer bars
2000mL synthetic waste added with 2.mL of trace elements
3 Terumu needles (0.65 x 32mm) with syringes
70% ethanol spray
Aquarium (500mL)
Bandages (for insulation purpose)
Cotton wool (for insulation purpose)
Crocodile clips wire
Distilled water
Electronic speed adjustable pump (Chemap AG)
Esky box
Hot plate stirrer
MaCartney bottles
Oxygen probe (Hanna instrument HI9145)
Pen knife
pH meter
Pipette tips
24
Pipette (P200)
Potassium Ferricyanide ~ 50mM at pH7 + 100mL Phosphate biffer ~ 100mM
PVC fasteners
Trace element (1.25mL/L)
Voltmeter
Rubber pipes (approximately 1.5 meters for whole experiment)
Resistor
Scissor
1L Synthetic wastewater consists 20mL of sodium acetate 1.0M, 1.25mL trace
elements, 480mg NaHCO3, 95.5mg NH4Cl, 10.5mg K2HPO4, 5.25mg KH2PO4,
63.1mg CaCl2.2H20 and 19.2mg MgSO4.7H2O.
25
A set of MFC which consists of the following:
Figure 9: Batch culture set up
26
Figure 10: Chemostat set up
27
Figure 11: In detail of chemostat set up
28
Table 1: First set of results taken to form a power and polarisation curve.
Resistance Voltage Voltage
(Ohms)
(V)
(mV)
Current
(mA)
Power
(mW)
1000000
560000
330000
220000
100000
68000
47000
33000
4700
2500
1150
1000
660
550
330
150
56
33
5
0.000272
0.000486
0.000826
0.001238
0.00272
0.003976
0.005719
0.008073
0.025638
0.03728
0.053739
0.055
0.058485
0.06
0.066061
0.068667
0.096429
0.09697
0.098
7.4E-05
0.000133
0.000225
0.000337
0.00074
0.001075
0.001537
0.002151
0.003089
0.003474
0.003321
0.003025
0.002258
0.00198
0.00144
0.000707
0.000521
0.00031
4.8E-05
0.272
0.2724
0.2725
0.2724
0.272
0.2704
0.2688
0.2664
0.1205
0.0932
0.0618
0.055
0.0386
0.033
0.0218
0.0103
0.0054
0.0032
0.00049
272
272.4
272.5
272.4
272
270.4
268.8
266.4
120.5
93.2
61.8
55
38.6
33
21.8
10.3
5.4
3.2
0.49
Volumetric
Power
(W/m3)
2.96E-07
5.3E-07
9E-07
1.35E-06
2.96E-06
4.3E-06
6.15E-06
8.6E-06
1.24E-05
1.39E-05
1.33E-05
1.21E-05
9.03E-06
7.92E-06
5.76E-06
2.83E-06
2.08E-06
1.24E-06
1.92E-07
Table 2: Second set of results taken to form a power and polarisation curve
Resistance Voltage Voltage Current
(Ohms)
(V)
(mV)
(mA)
Power
(mW)
1000000
560000
330000
220000
100000
68000
47000
33000
22000
15000
10000
6800
4700
2200
1500
7.73E-05
0.000137
0.000233
0.000349
0.000762
0.001104
0.001574
0.002214
0.003108
0.004315
0.005944
0.007564
0.008725
0.008858
0.00769
0.278
0.277
0.277
0.277
0.276
0.274
0.272
0.2703
0.2615
0.2544
0.2438
0.2268
0.2025
0.1396
0.1074
278
277
277
277
276
274
272
270.3
261.5
254.4
243.8
226.8
202.5
139.6
107.4
0.000278
0.000495
0.000839
0.001259
0.00276
0.004029
0.005787
0.008191
0.011886
0.01696
0.02438
0.033353
0.043085
0.063455
0.0716
29
Volumetric
Power
(W/m3)
3.09E-07
5.48E-07
9.3E-07
1.4E-06
3.05E-06
4.42E-06
6.3E-06
8.86E-06
1.24E-05
1.73E-05
2.38E-05
3.03E-05
3.49E-05
3.54E-05
3.08E-05
1000
820
330
150
56
33
10
5
0.0796
0.0682
0.0308
0.0145
0.0055
0.0034
0.0011
0.00006
79.6
68.2
30.8
14.5
5.5
3.4
1.1
0.6
0.0796
0.083171
0.093333
0.096667
0.098214
0.10303
0.11
0.12
0.006336
0.005672
0.002875
0.001402
0.00055
0.00035
0.000121
0.000072
2.53E-05
2.27E-05
1.15E-05
5.61E-06
2.16E-06
1.4E-06
4.84E-07
2.88E-07
Table 3: First set of chemostat results taken to form a power and polarisation curve
Resistance Voltage Voltage Current
(Ohms)
(V)
(mV)
(mA)
Power
(mW)
1000000
560000
330000
150000
82000
47000
10000
4700
1000
560
220
100
47
22
5
0.000205
0.000366
0.000622
0.001368
0.002492
0.004366
0.019097
0.036116
0.094864
0.115207
0.084073
0.040196
0.023878
0.011636
0.002738
0.453
0.453
0.453
0.453
0.452
0.453
0.437
0.412
0.308
0.254
0.136
0.0634
0.0335
0.016
0.0037
453
453
453
453
452
453
437
412
308
254
136
63.4
33.5
16
3.7
0.000453
0.000809
0.001373
0.00302
0.005512
0.009638
0.0437
0.08766
0.308
0.453571
0.618182
0.634
0.712766
0.727273
0.74
Volumetric
Power
(W/m3)
8.21E-07
1.47E-06
2.49E-06
5.47E-06
9.97E-06
1.75E-05
7.64E-05
0.000144
0.000379
0.000461
0.000336
0.000161
9.55E-05
4.65E-05
1.1E-05
Table 4: Second set of chemostat results taken to form a power and polarisation curve
Resistance Voltage Voltage Current
(Ohms)
(V)
(mV)
(mA)
Power
(mW)
1000000
560000
330000
150000
82000
47000
10000
0.000309
0.000552
0.000937
0.002061
0.003784
0.006601
0.03003
0.556
0.556
0.556
0.556
0.557
0.557
0.548
556
556
556
556
557
557
548
0.000556
0.000993
0.001685
0.003707
0.006793
0.011851
0.0548
30
Volumetric
Power
(W/m3)
1.23654E-06
2.20811E-06
3.7471E-06
8.24363E-06
1.51341E-05
2.64042E-05
0.000120122
4700
1000
560
220
100
47
22
5
0.535
0.473
0.428
0.324
0.215
0.105
0.052
0.012
535
473
428
324
215
105
52
12
0.11383
0.473
0.764286
1.472727
2.15
2.234043
2.363636
2.4
0.060899
0.223729
0.327114
0.477164
0.46225
0.234574
0.122909
0.0288
31
0.000243596
0.000894916
0.001308457
0.001908655
0.001849
0.000938298
0.000491636
0.0001152
Table 5: Calculations for Columbic Efficiency.
Time
sec
Normalized Curr
Mean Curr
with baseline curr
in intrv.
Coulomb
mC/s
mC
C
interv.
voltage
Resistance
Current
sec
mV
Ohm
mA
mC/s
mC/s
61.5
999
0.06156
0.06156
0.0000
0
3600
3600
61.5
1000
0.0615
0.0615
-0.0001
0.062
222
0.222
4500
900
61.8
1000
0.0618
0.0618
0.0002
0.062
55
0.055
4920
420
62.1
1000
0.0621
0.0621
0.0005
0.062
26
0.026
5520
600
62.3
1000
0.0623
0.0623
0.0007
0.062
37
0.037
6120
600
62.6
1000
0.0626
0.0626
0.0010
0.062
37
0.037
6720
600
62.8
1000
0.0628
0.0628
0.0012
0.063
38
0.038
7320
600
63
1000
0.063
0.063
0.0014
0.063
38
0.038
7920
600
63.2
1000
0.0632
0.0632
0.0016
0.063
38
0.038
8520
600
63.4
1000
0.0634
0.0634
0.0018
0.063
38
0.038
9120
600
63.5
1000
0.0635
0.0635
0.0019
0.063
38
0.038
9720
600
63.6
1000
0.0636
0.0636
0.0020
0.064
38
0.038
12720
3000
65.3
1000
0.0653
0.0653
0.0037
0.064
193
0.193
32
13320
600
65.7
1000
0.0657
0.0657
0.0041
0.066
39
0.039
16320
3000
68.1
1000
0.0681
0.0681
0.0065
0.067
201
0.201
16920
600
68.4
1000
0.0684
0.0684
0.0068
0.068
41
0.041
17520
600
68.9
1000
0.0689
0.0689
0.0073
0.069
41
0.041
18120
600
69.4
1000
0.0694
0.0694
0.0078
0.069
41
0.041
18720
600
69.7
1000
0.0697
0.0697
0.0081
0.070
42
0.042
20520
1800
71
1000
0.071
0.071
0.0094
0.070
127
0.127
24120
3600
72.6
1000
0.0726
0.0726
0.0110
0.072
258
0.258
24720
600
72.65
1000
0.07265
0.07265
0.0111
0.073
44
0.044
25920
1200
73
1000
0.073
0.073
0.0114
0.073
87
0.087
26520
600
73
1000
0.073
0.073
0.0114
0.073
44
0.044
27120
600
72.9
1000
0.0729
0.0729
0.0113
0.073
44
0.044
27720
600
72.8
1000
0.0728
0.0728
0.0112
0.073
44
0.044
28320
600
72.7
1000
0.0727
0.0727
0.0111
0.073
44
0.044
28920
600
72.6
1000
0.0726
0.0726
0.0110
0.073
44
0.044
29520
600
72.5
1000
0.0725
0.0725
0.0109
0.073
44
0.044
30120
600
72.4
1000
0.0724
0.0724
0.0108
0.072
43
0.043
33
30720
600
72.3
1000
0.0723
0.0723
0.0107
0.072
43
0.043
31320
600
72.2
1000
0.0722
0.0722
0.0106
0.072
43
0.043
31920
600
72.1
1000
0.0721
0.0721
0.0105
0.072
43
0.043
32520
600
72
1000
0.072
0.072
0.0104
0.072
43
0.043
33120
600
71.8
1000
0.0718
0.0718
0.0102
0.072
43
0.043
33720
600
71.7
1000
0.0717
0.0717
0.0101
0.072
43
0.043
34320
600
71.5
1000
0.0715
0.0715
0.0099
0.072
43
0.043
34920
600
71.4
1000
0.0714
0.0714
0.0098
0.071
43
0.043
35520
600
71.2
1000
0.0712
0.0712
0.0096
0.071
43
0.043
36120
600
70.3
1000
0.0703
0.0703
0.0087
0.071
42
0.042
36720
600
70
1000
0.07
0.07
0.0084
0.070
42
0.042
37320
600
69.6
1000
0.0696
0.0696
0.0080
0.070
42
0.042
60120
22800
65
1000
0.065
0.065
0.0034
0.067
1534
1.534
72120
12000
62.1
1000
0.0621
0.0621
0.0005
0.064
763
0.763
72720
600
62
1000
0.062
0.062
0.0004
0.062
37
0.037
73320
600
61.8
1000
0.0618
0.0618
0.0002
0.062
37
0.037
73920
600
61.7
1000
0.0617
0.0617
0.0001
0.062
37
0.037
34
74520
600
61.5
1000
0.0615
0.0615
-0.0001
0.062
37
0.037
75120
600
61.4
1000
0.0614
0.0614
-0.0002
0.061
37
0.037
75720
600
61.3
1000
0.0613
0.0613
-0.0003
0.061
37
0.037
76320
600
61.3
1000
0.0613
0.0613
-0.0003
0.061
37
0.037
76920
600
61.3
1000
0.0613
0.0613
-0.0003
0.061
37
0.037
Sum of C
5.1
35
36