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., Tthe 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 cathode 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 with 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
couloumbic efficiency in the batch was recorded at 0.665%, which revealed the
bacteria were extremely weak. The first power curve 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 was operated introduced in as 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). It is a bit inconsistent first evaluating the fuel cell
by power output (mW) and then switch to volts. If volts are used the resistance needs
to be specified otherwise it does not mean much.
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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
(unclear) , 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
cathode chamber which contains an oxidizing agent such as dissolved oxygen of
ferricyanide (Mohan et al., 2007). The use of cut and paste for sentences is not a
good idea, in particular if the same mistake (refer to abstract) is made (confusing
anode with cathode). 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 (of what?) 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 (it has still not been
explained what this means) 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). (good, to have it explained
now) 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 couloumbic efficiency, which is essentially a
percentage ratio of the number of electrons supplied as the organic substrate 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).
(Good)
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.
(The intro is pretty good, finishing by introducing the aim. Could attempt to refer to
the fact that this is supposed to be a chemostat project).
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
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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 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.
(It would be good to see a schematic drawing)
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 wastewater 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. (It is strange to run a chemostat essentially as a sequencing batch system, 288 min off is almost 5 hours. It would be better to use seconds instead of minutes) 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). (Explanations are nice)
Monitoring of voltage
A Voltmeter was used to measure the potential against 1000ohm and the values were recorded down periodically.
Polarization curves
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Polarisation curves were used as a means of determining the capacity of the bacterial culture. (Would be nice to have some further explanations why polaristion curves are needed.) 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 (OK, but…. Show units to allow next years students an easier start)
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 (explain what it is and why it is necessary)
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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 (it was not the Spanish conquerer Columbus but the French Coulomb) efficiency in batch culture
The resistor was connected to between the anode and cathode chambers to establish a closed circuit system (As illustrated in figure 4 (Figure missing?) ). After that, the potential was measured using a voltmeter. Tthe microbial fuel cell was left to run overnight for the voltage reading of 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 (You need to refer to the figure that shows this) 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
Each result is being first introduced, then explained and interpreted. This needs at
least one paragraph. Also before a figure is shown, the text needs to refer to it (as in
the journal papers that you have been reading) 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
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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 resistance. (You start talking about power curve. The reader would now
expect that you show the curve)t.
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
a rapid, linear decrease in the voltage, at higher currents (between 0.2664V and about
0.0103V), concentration loss (mass transport effect) was overriding. (I am missing
some more simple observations such as: there was increased voltage or current after
acetate addition, indicating that acetate caused some electricity flow.)
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. (Unclear to me) If there was any
domination (??) , it would have been between a voltage of 0.278V and 0.270V.
Ohmic losses (explain what that is) were dominant when the voltage was between
0.270V and 0.2438V. When there was a linear decrease in voltage (linear as a
function of time or current or resitor?) , concentration loss (mass transport effect (??
What specifically is meant? Write more simply and more clearly) 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). (Overall there is too much writing on the two polarisation
curves without actually saying what they prove in terms of improvement of the MFC.)
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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
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,
(good to see you use volumetric power, now you just need to compare to literature
values) which was also higher than the previous result of 1.39x10-5 W/m3,
emphasising vast bacterial improvement.
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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.
Figure 5: Current as a function of time (determines coulombic efficiency) (It
would be more useful to jut give the final acetate concentration)
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. (Good to see this explanation, it
shows good understanding an is really useful) From Table 5, the area under the curve
and above the baseline was calculated to be 5.1 Coulombs using integration. Table 5
is a good example to show how the calculation works. It looks OK to me.
Calculating Columbic Efficiency %:
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Added 1mL Acetate (1M)
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 e- (OK)
Since 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. - (OK)
Columbic efficiency =
___________Coulombs calculated from the curve x 100__________
Theoretical amount of Coulombs in added amount of acetate
= 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. (Describing the fig.)
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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 (wow, you got the spelling right this time, It would have just
required a bit more thorough spell checking) 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 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 above chapter repeats to some extent
what was calculated earlier. Keep it concise )
Any speculations as to what has happened to the acetate?
The following day was when the MFC was when the culture was put in a continuous
culture (chemostat). (unclear sentence) 50mL of acetate (1M) was pumped into the
anode vessel every day (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).
(OK)
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Figure 7: Chemostat polarisation curves. (nice graphs (colours and fonts))
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
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. (The
experimental plan is not obvious 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
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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.
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
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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.
Results section could have been more structured by using sub-chapters.
Also the results section focuses just on
You did not mention how you judged that acetate was degraded.
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
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
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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. (True) The reason for the phrase
‘semi-continuous’ 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 semi-
continuous 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 60-
80% [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
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 semi-
continuous 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 semi-
continuous 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
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comparison as the biomass in both modes were not collected and measured. Further
investigation is recommended in determining the amount of biomass present in semi-
continuous batch and batch mode as it is expected that the amount of biomass in semi-
continuous 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.
Overall, clearly written apart from some sections as indicated.
The only results you have shown and discussed is polarisation curves.
The feeding rate of the chemostat was not adjusted to the rate of current.
With this quality of writing and understanding the project would have been
excellent had it started earlier (allowing the buildup of biomass with
coulombic efficiencies higher than 20%.
Comparison of own reslts with literature or other authors missing.
Marks: 7/10 because of the reasonably good writing and good
understanding. More versatile experiments, more comparision with the
literature and better explanations of terms findings could have given more.
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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.
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Williams, K. (Ed.) (1966) An Introduction to Fuel Cells, London, Elsevier Publishing.
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 agree!) 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?
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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.
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.
21
11. pH should be monitored frequently to ensure that the pH does not rise or fall
too much.
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.
22
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. 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.
Quite some useful hints here. Well done.
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).
23
Good luck!
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.
24
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
25
MaCartney bottles
Oxygen probe (Hanna instrument HI9145)
Pen knife
pH meter
Pipette tips
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.
26
A set of MFC which consists of the following:
Figure 9: Batch culture set up
27
Figure 10: Chemostat set up
28
Figure 11: In detail of chemostat set up
29
Table 1: First set of results taken to form a power and polarisation curve.
Resistance (Ohms)
Voltage (V)
Voltage (mV)
Current (mA)
Power (mW)
Volumetric Power (W/m3)
1000000 0.272 272 0.000272 7.4E-05 2.96E-07560000 0.2724 272.4 0.000486 0.000133 5.3E-07330000 0.2725 272.5 0.000826 0.000225 9E-07220000 0.2724 272.4 0.001238 0.000337 1.35E-06100000 0.272 272 0.00272 0.00074 2.96E-0668000 0.2704 270.4 0.003976 0.001075 4.3E-0647000 0.2688 268.8 0.005719 0.001537 6.15E-0633000 0.2664 266.4 0.008073 0.002151 8.6E-064700 0.1205 120.5 0.025638 0.003089 1.24E-052500 0.0932 93.2 0.03728 0.003474 1.39E-051150 0.0618 61.8 0.053739 0.003321 1.33E-051000 0.055 55 0.055 0.003025 1.21E-05660 0.0386 38.6 0.058485 0.002258 9.03E-06550 0.033 33 0.06 0.00198 7.92E-06330 0.0218 21.8 0.066061 0.00144 5.76E-06150 0.0103 10.3 0.068667 0.000707 2.83E-0656 0.0054 5.4 0.096429 0.000521 2.08E-0633 0.0032 3.2 0.09697 0.00031 1.24E-065 0.00049 0.49 0.098 4.8E-05 1.92E-07
Table 2: Second set of results taken to form a power and polarisation curve
Resistance (Ohms)
Voltage (V)
Voltage (mV)
Current (mA)
Power (mW)
Volumetric Power (W/m3)
1000000 0.278 278 0.000278 7.73E-05 3.09E-07560000 0.277 277 0.000495 0.000137 5.48E-07330000 0.277 277 0.000839 0.000233 9.3E-07220000 0.277 277 0.001259 0.000349 1.4E-06100000 0.276 276 0.00276 0.000762 3.05E-0668000 0.274 274 0.004029 0.001104 4.42E-0647000 0.272 272 0.005787 0.001574 6.3E-0633000 0.2703 270.3 0.008191 0.002214 8.86E-0622000 0.2615 261.5 0.011886 0.003108 1.24E-0515000 0.2544 254.4 0.01696 0.004315 1.73E-0510000 0.2438 243.8 0.02438 0.005944 2.38E-056800 0.2268 226.8 0.033353 0.007564 3.03E-054700 0.2025 202.5 0.043085 0.008725 3.49E-052200 0.1396 139.6 0.063455 0.008858 3.54E-051500 0.1074 107.4 0.0716 0.00769 3.08E-051000 0.0796 79.6 0.0796 0.006336 2.53E-05
30
820 0.0682 68.2 0.083171 0.005672 2.27E-05330 0.0308 30.8 0.093333 0.002875 1.15E-05150 0.0145 14.5 0.096667 0.001402 5.61E-0656 0.0055 5.5 0.098214 0.00055 2.16E-0633 0.0034 3.4 0.10303 0.00035 1.4E-0610 0.0011 1.1 0.11 0.000121 4.84E-075 0.00006 0.6 0.12 0.000072 2.88E-07
Table 3: First set of chemostat results taken to form a power and polarisation curve
Resistance (Ohms)
Voltage (V)
Voltage (mV)
Current (mA)
Power (mW)
Volumetric Power (W/m3)
1000000 0.453 453 0.000453 0.000205 8.21E-07560000 0.453 453 0.000809 0.000366 1.47E-06330000 0.453 453 0.001373 0.000622 2.49E-06150000 0.453 453 0.00302 0.001368 5.47E-0682000 0.452 452 0.005512 0.002492 9.97E-0647000 0.453 453 0.009638 0.004366 1.75E-0510000 0.437 437 0.0437 0.019097 7.64E-054700 0.412 412 0.08766 0.036116 0.0001441000 0.308 308 0.308 0.094864 0.000379560 0.254 254 0.453571 0.115207 0.000461220 0.136 136 0.618182 0.084073 0.000336100 0.0634 63.4 0.634 0.040196 0.00016147 0.0335 33.5 0.712766 0.023878 9.55E-0522 0.016 16 0.727273 0.011636 4.65E-055 0.0037 3.7 0.74 0.002738 1.1E-05
Table 4: Second set of chemostat results taken to form a power and polarisation curve
Resistance (Ohms)
Voltage (V)
Voltage (mV)
Current (mA)
Power (mW)
Volumetric Power (W/m3)
1000000 0.556 556 0.000556 0.000309 1.23654E-06560000 0.556 556 0.000993 0.000552 2.20811E-06330000 0.556 556 0.001685 0.000937 3.7471E-06150000 0.556 556 0.003707 0.002061 8.24363E-0682000 0.557 557 0.006793 0.003784 1.51341E-0547000 0.557 557 0.011851 0.006601 2.64042E-0510000 0.548 548 0.0548 0.03003 0.0001201224700 0.535 535 0.11383 0.060899 0.0002435961000 0.473 473 0.473 0.223729 0.000894916560 0.428 428 0.764286 0.327114 0.001308457
31
220 0.324 324 1.472727 0.477164 0.001908655100 0.215 215 2.15 0.46225 0.00184947 0.105 105 2.234043 0.234574 0.00093829822 0.052 52 2.363636 0.122909 0.0004916365 0.012 12 2.4 0.0288 0.0001152
32
Table 5: Calculations for Columbic Efficiency.
Time Normalized Curr Mean Curr
interv. voltage Resistance Current with baseline curr in intrv. Coulomb
sec sec mV Ohm mA mC/s mC/s mC/s mC C
0 61.5 999 0.06156 0.06156 0.0000
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
33
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
34
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
35
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
36
37