MICROBIAL AND PLANT MICROBIAL FUEL CELLS - THE EMERGING GREEN TECHNOLOGIES

Presented by

Deepti Bansod,Tulika Srivastava,K.Sudhakar

Energy Centre,

Maulana Azad National Insitute of Technology,Bhopal,M.PICAER 2013,IIT Bombay

INTRODUCTION :MICROBIAL FUEL CELL

A microbial fuel cell is a device that converts chemical energy to electrical energy by the catalytic reaction of microorganisms.

A microbial fuel cell (MFC) or biological fuel cell is a bio-electrochemical system that drives a current by using bacteria and mimicking bacterial interactions found in nature.

Microbial Fuel Cell (MFC) technology generates either electricity or hydrogen from bacterial growth in carbon-containing solutions, including sources of low or negative economic value such as wastewater.

The operating principles of a microbial fuel cell. Electrons can flow to the anode via chemical mediators or directly.

Electrons produced by the bacteria from these substrates are transferred to the anode (negative terminal) and flow to the cathode (positive terminal) linked by a conductive material containing a resistor, or operated under a load .

By convention, a positive current flows from the positive to the negative terminal, a direction opposite to that of electron flow.

Electrons can be transferred to the anode by electron mediators or shuttles , by direct membrane associated electron transfer , or by so-called nanowires produced by the bacteria, or perhaps by other as yet undiscovered means.

In most MFCs the electrons that reach the cathode combine with protons that diffuse from the anode through a separator and oxygen provided from air; the resulting product is water.

The potential difference between the anode and the cathode, together with flow of electrons, results in the generation of electrical power.

Unfortunately, this reaction is not kinetically catalyzed. In order to obtain sufficient oxygen reduction reaction rate a precious metal-catalyst such as platinum to the cathode.

EXPERIMENTAL METHODOLOGY An MFC apparatus was employed that consisted of a

20 Litre cylindrical plastic container of dimension 30 cm height and 28 cm diameter.

A rectangular solid graphite of (28 cm x 10cm x 15 cm) was used as anode and buried inside the mud.

A rectangular zinc cathode plate of (14 cm x 4 cm) was placed on the top surface of the bucket filled with water.

All the electrodes were clean and used as received; they were conducted out with copper wire.

Fig. Schematic representation, Photograph of the MFC and electrodes

MEASUREMENTS •Copper wire leads contacting the anode and cathode surfaces were connected with various resistances ranging from 10 Ω to 500 Ω resistor. •A digital multimeter (RISH multi 15S) was used to measure voltage produced by the MFCs at intervals of one hour .•Voltage (v) and current (mA) was measured across the external resistor connected between the anode and cathode.• Current density and power density were calculated by dividing I and P by the anode surface area. •Power (P) was calculated according to P = V * I (mW).•Power density (p) was calculated according to p= P/A. The anode area was used to calculate current density and power density. Power density (p) was calculated according to p= P/A (mW/m2).•Current density(i) was calculated as i = I/A(mA /m2) where A (cm2) is the projected surface area of the anode.

EXPERIMENTAL RESULTS The output voltage was monitored for the whole day. The power

output and voltage of MFC increased gradually because of the

biological activity of microorganism. The voltage reached from the initial value of 0.56V to 0.88 V

during the 1st day. The steady state voltage of cell was maintained at 0.88V over the complete cycle.

When the cell reached to the stable condition, polarization curve was obtained by changing the external resistance. The maximum current density of MFC was 50.69 mA/m2 for the steady phase.

The polarization curve as a function of current density and power density measured at variable resistances (10Ω-500Ω). Current generation in different resistors was observed once the MFC attained the maximum voltage

CONTD… Current and power density showed decreasing trend with

increasing in resistance and is consistent with the reported literature, which indicated a typical fuel cell behaviour.

At higher resistance used (500Ω), relatively less power density of 27.08 mW/m2 was observed.

Relatively less drop and constant voltage was observed at various resistances studied. Maximum power peak in this period was equal to 1.92 mw.

TIME Voltage(V)

10.00AM 0.56

10.30AM 0.57

11.00AM 0.58

11.30AM 0.59

12.00PM 0.59

12.30PM 0.60

1.00PM 0.65

1.30PM 0.68

2.00PM 0.69

2.30PM 0.78

3.00PM 0.85

3.30PM 0.88

4.00PM 0.88

4.30PM 0.88

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0.570.580000000000001

0.5900000000000010.590000000000001

0.6000000000000010.650000000000007

0.6800000000000010.690000000000002

0.78

0.8500000000000010.8800000000000010.8800000000000010.880000000000001

Voltage(V)

ADVANTAGES OF MFC The unswerving conversion of substrate energy to

electricity enables high conversion efficiency. MFCs operate efficiently at optimum and even at low,

temperatures distinguish them from all present bio-energy processes.

MFC have become popular as it has the capacity to produce energy in the form of electricity or hydrogen from renewable sources like industrial or household waste.

It uses organic squander stuff as fuels and easily available microbes as catalysts.

Since microbial fuel cells can be setup at remote locations where water resources exist, they are a convenient power source for remote environmental sensors.

LIMITATIONS MFC technology is still elementary and there are several areas for

development. Traditional MFC show low columbic efficiencies due to

ineffective electron transfer linking the microbial cells, and the anode.

This ineffectiveness consequence in partial oxidation of the fuel and unsought digestion of some of the fuel carbon in to biomass.

However the problem with MFCs is that their power generation (the rate of electron abstraction) is still very low.

PLANT MFC

INTRODUCTION• The PMFC is a technology that uses electrochemically active

bacteria as a catalyst to oxidize organic and inorganic matter to generate current.

• The microbial fuel cell consists of an anode compartment where the electrons are released by electrochemically active bacteria and transferred to the electrode.

• Plant-Microbial Fuel Cell generates electricity from the natural interaction between plant roots and soil bacteria.

• Microbes living in the plant soil create ions by digesting excess glucose from the plants

The plant microbial fuel cell operates on the principle that microbes are able to an-aerobically break down & release electrons from the small molecular mass carbohydrates that are exuded from the roots of plants as a result of photosynthesis.

During photosynthesis, the carbon dioxide fixed in the leaves is converted to small molecular weight carbohydrates and are sent to the plant roots where they are lost as root exudates.

In microbial decomposition, protons, electrons and carbon dioxide are released.

The carbon dioxide release to the atmosphere The protons and electrons are used for the production of

electricity as in the microbial fuel cell.

The plant-MFC is based on two proven processes

i. Rhizo-deposition of organic compounds by living plants

ii. electricity generation from organic compounds in the microbial fuel cell.

The principal idea is that plant rhizodeposits will be utilized as substrates by the bacteria to generate electricity in the microbial fuel cell.

The basic working of PMFC:

(i) photosynthesis

(ii) transport of organic matter to the anode compartment

(iii) anodic oxidation of organic matter by electrochemically active bacteria

(iv) cathode reduction of oxygen Anode and Cathode compartment , mostly separated by a membrane -

separate the oxidation and reduction process.

METHODOLOGY Plant Microbial Fuel Cell Aglaonema hybrids, was obtained from

Energy Centre, M.A.N.I.T, Bhopal. constructed plant microbial fuel cells - based on an anode

compartment consisting of Terracotta flower pot with height of 35 cm and diameter of 18 cm.

Anode compartment - a graphite anode felt on the bottom (length=15, breadth=5.15cm width=0.5cm)

zinc cathode (4x4 cm and 3mm thick)t is suspended in the water column.

Naturally occurring micro-organisms were already present on the roots of the plants at the time of placement into the plant-MFC. The plant-MFC therefore contains a whole range of micro-organisms, which was confirmed by microscopic analyses of samples.

Fig. Schematic representation, Photograph of the PMFC and electrodes

MEASUREMENTS Copper wire leads contacting the anode and cathode surfaces were connected with various resistances ranging from 10 Ω to 500 Ω resistor. A digital multimeter (RISH multi 15S) was used to measure voltage produced by the MFCs at intervals of one hour .Voltage (v) and current (mA) was measured across the external resistor connected between the anode and cathode. Current density and power density were calculated by dividing I and P by the anode surface area. Power (P) was calculated according to P = V * I (mW).Power density (p) was calculated according to p= P/A. The anode area was used to calculate current density and power density. Power density (p) was calculated according to p= P/A (mW/m2).Current density(i) was calculated as i = I/A(mA /m2) where A (cm2) is the projected surface area of the anode

TIME VOLTAGE

1.00PM 0.68

1.10PM 0.69

1.20PM 0.70

1.30PM 0.78

1.40PM 0.89

1.50PM 0.91

2.00PM 0.95

2.10PM 0.96

2.20PM 0.97

2.30PM 0.98

2.40PM 0.99

2.50PM 0.99

3.00PM 1.00

3.10PM 1.01

3.20PM 1.01

1.00PM

1.10PM

1.20PM

1.30PM

1.40PM

1.50PM

2.00PM

2.10PM

2.20PM

2.30PM

2.40PM

2.50PM

3.00PM

3.10PM

3.20PM

0

0.2

0.4

0.6

0.8

1

1.2

0.680000000000002

1.01

Time

Vol

tage

(V)

RESULTS AND DISCUSSION

The power output and voltage of PMFC increased gradually because of the biological activity of microorganisms.

The voltage reached from the initial value of 0.68V to 1.01 V during the 1st day. The steady state voltage of cell was maintained at 1.01V over the complete cycle.

Though the steady state potential of 1.01V is very much lower, but it was maintained for longer time period.

Even though theoretical power output is estimated at 3.2 W/m2 geometric planting area , power output obtained from this study ranged only from 263 mW/m2 to 118 mW/m2 with plants as sole organic matter source.

COMPARISON OF MFC & PMFC

9:00 AM 10:00 AM

11:00 AM

12:00 PM

1:00 PM 2:00 PM 3:00 PM 4:00 PM 5:00 PM0

0.2

0.4

0.6

0.8

1

1.2

MFC VOLTAGE

P MFC VOLTAGE

Time

Vol

tage

ADVANTAGES OF PMFC Environmental advantages such as no transport of harvested

biomass, preservation of nutrients in the ecosystem, use of a renewable energy source, no combustion or extra greenhouse gas emissions during production.

Green Power Generation Low temperature power generation Renewable and Sustainable Energy Source It can solve industrial energy concerns Energy production is mostly in-situ PMFC could be used to power small gadgets like LED lights,

laptops and cell phones.

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