Docstoc

20320130406024

Document Sample
20320130406024 Powered By Docstoc
					 INTERNATIONAL JOURNAL OF ADVANCED and Technology (IJARET), ISSN 0976 –
International Journal of Advanced Research in Engineering RESEARCH IN ENGINEERING
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME
                               AND TECHNOLOGY (IJARET)

ISSN 0976 - 6480 (Print)
ISSN 0976 - 6499 (Online)
Volume 4, Issue 7, November - December 2013, pp. 198-206
                                                                          IJARET
© IAEME: www.iaeme.com/ijaret.asp
Journal Impact Factor (2013): 5.8376 (Calculated by GISI)                 ©IAEME
www.jifactor.com




   EFFECT OF COD ON OCV, POWER PRODUCTION AND COULOMBIC
    EFFICIENCY OF SINGLE-CHAMBERED MICROBIAL FUEL CELLS

                 T. Opoku-Donkor,      R. Y. Tamakloe,      R. K. Nkum,    K. Singh
          Department of Physics, Kwame Nkrumah University of Science and Technology,
                                  Kumasi, Ghana (West Africa)



ABSTRACT

       An attempt has been made to find the effect of Chemical Oxygen Demand (COD) on the
Open Circuit Voltage (OCV), Power production and Coulombic efficiency of single – chambered
Microbial Fuel Cells (MFCs). Three different MFCs of similar design have been fabricated using
carbon paper doped with platinum as cathode and graphite as anode separated by Proton Exchange
Membrane (PEM).It has been found that the Open Circuit Voltage (OCV), power production and
Coulombic efficiency obtained are in direct proportion with COD level.

Keywords: MFC = Microbial Fuel Cell; SC-MFC = Single Chambered MFC;
          Ecell = Total Cell Potential; OCV = Open Circuit Voltage
          GGBL = Guinness Ghana Brewery Limited

INTRODUCTION

       Power generation from MFCs using anaerobic microbes is a novel technology with great
potential for alternative energy generation and environmental pollution reduction. Microbial fuel cell
is a system that drives a current to generate electricity using bacteria found in nature. Organic
substances are degraded by micro-organisms through anaerobic metabolism liberating electrons and
protons in a biochemical cell using anode and cathode separated by proton exchange membrane
(PEM). For example, nutrient such as glucose is broken down into carbon dioxide, hydrogen ions
and electrons.

                            C12H22O11 + 13H2O -> 12CO2 + 48H+ +48e-



                                                 198
International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME

        The current is generated through the flow of electrons via a complete electric circuit. In 1910,
Potter had proposed the idea of production of EMF during fermentation of organic compounds by
yeast. However the first known patent of MFC was in 1967. Since then, different researchers worked
on the development of MFCs with different setups. For example, dual chambered cell with a proton
exchange membrane or single chambered cell with anode and cathode separated by cotton cloth,
were successful [1].
        There are two main components of the fuel cell; cathode and anode compartments along with
a cation specific membrane. In the anode compartment, microorganism oxidizes substrates which
generate electrons and protons. Electrons are then transferred to the cathode compartment via an
external electric circuit. Protons are transferred to the cathode compartment through the cation
specific membrane. Consumption of electrons and protons in the cathode compartment with oxygen
results in formation of water. As stated by Logan et al [2] virtually any biodegradable organic matter
can be used in an MFC, including volatile acids, carbohydrates, proteins, alcohols, and even
relatively recalcitrant materials like cellulose.
        A large amount of beer brewery wastewater is produced from cooling (eg. saccharification
cooling, fermentation) and washing units in brewery industry and often causes several environmental
problems. The wastewater is non-toxic, but has high Biological Oxygen Demand (BOD) compared
with other industrial wastewater. Generally, biological methods used for the beer brewery
wastewater treatment are reported to perform well in COD removal [3]. Domestic wastewater is also
reported in electricity generation in several MFC configurations (Liu et al. 2004; Liu & Logan 2004;
Min & Logan 2004) [4]. Beer brewery wastewater might be good source for electricity generation in
MFCs due to its nature of high carbohydrate and low ammonium-nitrogen concentration.
        In this study, we have successfully verified the potential of brewery wastewater (Malta
Guinness - brewed from barley, hops, and water) to be used as fuel to generate electricity in a single-
chamber MFCs. All the experiments have been performed at temperature between 25 oC and 26 oC.
The scope of this study comprises two aspects: (i) to examine the possibility of direct power
generation from brewery wastewater; (ii) to investigate effect of different loading of COD on OCV
and Coulombic efficiency (CE). Besides, the main purpose of the study was also to validate
workability of a novel MFC design in terms of current generation and cheap materials, hence
showing current generation could be increased with multiple anodes sharing a common cathode and
also providing possibility for serial connectivity for increasing voltage output.

COULOMBIC AND ENERGY EFFICIENCY OF MFC

        The generation of power is a main goal of MFC operation, but there is a need to extract as
much of the electrons stored in the biomass as possible as current, and to recover as much energy as
possible from the system. The recovery of electrons is defined as the fraction (or percent) of
electrons recovered as current versus that in the starting organic matter and referred as Coulombic
efficiency(CE) [5].

       CE = Coulombs recovered/Total coulombs in the substrate

        The energy eficiency of an MFC is based on energy recovered in the system compared to the
energy content of the starting material. The energy efficiency, ηMFC, is the ratio of power produced
by the cell over a time interval ‘t’ divided by the heat of combustion of the organic substrate, or

          ηMFC = ∫ EMFC I dt / H ns

where H is the heat of combustion n (J mol-1) and n, is the amount (mol) of substrate added.

                                                  199
International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME

POWER PRODUCTION BY MFC

From the graph, we read off a peak power in mW/cm2. Converting this to just power production from
the system as given below

                         P = PAN AAN
Where PAN is the peak power in mW/cm2 and AAN is the area of PEM.

EXPERIMENTAL PROCEDURES

Preparation of PEM: Nafion 117 of area 12.6 cm2 was taken through the normal cleaning process
[distilled water → 3% hydrogen peroxide → dilute sulfuric acid → distilled water ].

Fabrication of MFCs: Figures 1 – 6 show the necessary steps for the fabrication of MFCs.
   - 2 Perspex slabs were cut, shaped and dilled for each cell (Fig 1).
   - Carbon paper doped with platinum was cut and shaped (Fig 2).
   - PEM (Nafion 117 – Fig 3)
   - Cupper conductor was cut and shaped (Fig 4).
   - Graphite electrode (Fig 5)
   - A plastic container of 2 liters capacity served as the anodic chamber (Fig 6). The anode
      chamber contains the wastewater and the graphite electrode. The carbon paper tightens onto
      the PEM served as the cathode.

Types of Wastewater for MFCs: Following three types of wastewater of different COD and pH
from GGBL (Kumasi, Ghana) were used as Fuel for these cells. The characteristics of the wastewater
are listed in Table 1:

                                        Table 1
                 Wastewater              COD[mg/L]                     pH
                  Influent                 3790.0                     11.18
                 Anaerobic                 748.0                      6.80
                  Balance                  4330.0                     6.01




                      Fig 1: Perspex slabs                        Fig 2: Carbon paper


                                               200
International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME




             Fig 3: Nafion 117                             Fig 4: Cupper plate and wire




                                    Fig 5: Graphite electrode




      Fig 6: a) Block diagram of finished cell                  Fig 6: b) Finished cell




                                                 201
International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME




   Fig 7: Operational Cells setup with Campbell Scientific Ltd Datalogger CR10X, Logger to PC
  adapter, USB to RS232 Cable and 12 V Battery to power the logger. The Datalogger stores data
  every minute. We programmed the logger using Shortcut (CS PC200W 4.1 Datalogger Support
                                        Software –CR10X)


Operation
       The cells were kept at 25 oC (+- 0.5 oC). The anode was immersed in the wastewater such that
the cupper conductor did not touch the water in order to avoid corrosion. The anode chamber was
sealed to maintain anaerobic system throughout the experiment. OCV readings were taken for 35
days with the CR10X datalogger which stores the differential voltage every one minute. A
multimeter (Peak Tech 2010DMM) was used in the reading of the load voltage and the current
through a resistance box ranging from 0 to 10,000 ohms.

RESULTS AND DISCUSSION

       The experiment was operational for 35 days. A constant increment of OCV was observed
from day one of the operation of MFCs until it got to their peak values of OCV. These values were
maintained for about 10 days. The graph of OCV against time is shown in Fig 8. Also their pH and
COD values at the end experiment are given in Table 2. The experiments were performed with the
wastewater as collected in order to check the viability of the cells without adding inoculants and
other chemicals.

                                             Table 2
         Wastewater        Starting COD      Ending COD         Starting pH     Ending pH
          Influent            3790.0               133             11.18           8.3
         Anaerobic             748.0               59                6.8           8.9
          Balance             4330.0               267              6.01           8.6




                                               202
International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME




 Fig 8: Open circuit voltage (OCV) as a function of time as measured (stored every munite) by the
       Datalogger. The lines shown are actual measured throughout the experimental period


        The red line indicated that the Balance produced very high voltage for a long period and thus
maintains that for the period compare to Anaerobic and Influent substrates. This may be attributed to
the high value of COD.
        The effect of external load on the voltage is shown in Fig 9. This characteristic curves show
wide variation in the three substrates indicating the dominance of Balance type of wastewater. As
expected, the power generation was observed to be highest when the COD was higher and the pH
skews towards acidity. Using the potential drop as function of load we calculated the current density
in mA/cm2 and the power. The polarization curve is shown in Fig 10.
        According to Logan [5] the determination of power produced varied depending on the
relative sizes of the anode, cathode and PEM. We therefore, chose to normalize the current density
by the PEM surface area. To obtain a polarization curve we used a series of different resistances
from 0 to 10,000 on the circuit, measuring the voltage at each resistance, as shown in Fig. 9 and
10.

INTERNAL RESISTANCE

        According to Logan [5] the maximum power occurs when the internal and external
resistances are equal. From the graph shown in Fig. 11 the peak occurred at (8.04, 31.01) and this
corresponds to an external resistance of 3,000 . Consequently the internal resistance for Balance is
equal to 3,000      in the anode system (6 cm separation between anode and PEM). The peak for
Influent occurred at 8,000 and that for Anaerobic occurred at 10,000 . The high values of the
internal resistances may be due to the fact that the conductivities of the substrates were not tempered
with.


                                                 203
International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME




Fig 9: This depicts the potential dropped verses load (external resistance). We obtained a data set as
                            a function of resistance for the three systems




                          Fig 10: Polarization Curves for the Three Cells




                                                 204
International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME




                                 Fig 11: Power Density Curves

Power Production by MFC
       From Fig. 11 we read off a peak power of 31.01 mW/cm2. Converting this to power
production from the system we obtain

      P = 31.01 (mW/cm2) x (12.6 cm2) = 30 x 10-4 W

Coulombic Efficiency (CE)
        The recovery of electrons is referred to as Coulombic efficiency, defined as the fraction
(or percent) of electrons recovered as current versus that in the starting organic matter [6].




That is




Where tb = Total cycle (s)
      I = Current (A)
      F = Faraday’s constant (C/mole)
      VAn = volume of liquid in the anode compartment (L)
      ∆COD = Change in COD (g/L)
      CE = 11.3 %

Partition Surface Area of PEM per Volume = 0.7 m2/m3

                                              205
International Journal of Advanced Research in Engineering and Technology (IJARET), ISSN 0976 –
6480(Print), ISSN 0976 – 6499(Online) Volume 4, Issue 7, November – December (2013), © IAEME

CONCLUSION

       It has been found that the Balance wastewater produced power most significantly than the
other two. It has been observed that the current generation of the cells increased for a higher COD
and lower pH. Characterization curves for Influent and Anaerobic wastewaters are insignificant
compared to that of Balance wastewater. The removal of COD of observed to be highest for the cell
which produces higher current. The COD for Balance dropped from 4386 to 267mg/L for the 36
days of running.

Summary of other Generated Parameters

       Substrate    Max. OCV       Max Current           Power       Current        Internal
                      (mV)           (mA)               Density      Density       Resistance
                                                       (mW/cm2)     (mA/cm2)          ( )
   Balance              782            0.330              246          8.04            3k
   Influent             345            0.021              37.9         0.34            8k
   Anaerobic             66            0.003              10.7        0.028           10 k


ACKNOWLEDGEMENTS

       Authors would like to thank Dr. Young-Gi Yoo of Korea Institute of Energy Research for
providing Carbon paper doped with platinum. We would also like to thank the Head of Physics
Department, KNUST and Guinness Ghana Brewery Limited for necessary facilities for this work.

REFERENCES

 [1]    Banik et al, 2012 Greener Journal of Biological Sciences ISSN: 2276-7762 Vol. 2 (2),
        pp. 013-019, October 2012.
 [2]    Logan, B.E. 2008, Microbial Fuel Cells pp. 6.
 [3]    X. Wang; Y. J. Feng, H. Lee 2008, Electricity production from beer brewery wastewater
        using single chamber microbial fuel cell – Water Science & Technology – WST, 57.7, 1117.
 [4]    Liu, H., Cheng S. and Logan, B.E. 2005b, Production of Electricity from acetate or butyrate
        in a single chamber microbial fuel cell, Environ. Sci. Techno, 39(2), 658 -662.
 [5]    Logan, B.E. 2008, Microbial Fuel Cells, pp 46 – 48.
 [6]    Chonde Sonal G, Mishra A. S. and Raut P.D., “Bioelectricity Production from Wastewater
        using Microbial Fuel Cell (MFC)”, International Journal of Advanced Research in
        Engineering & Technology (IJARET), Volume 4, Issue 6, 2013, pp. 62 - 69, ISSN Print:
        0976-6480, ISSN Online: 0976-6499.




                                                 206

				
DOCUMENT INFO
Shared By:
Categories:
Tags:
Stats:
views:0
posted:12/31/2013
language:Unknown
pages:9