Sustainable energy generation by bio fuel cell from septic ...€¦ · A prototype cell was fabricated and tested by polarization. It is found that the voltage gain is 0.59 V

Sustainable energy generation by bio fuel cell from septic

tank

Name of the college: Civil Engg. Dept., Nagarjuna College of Engineering and

Technology.

Students :

1. Yogashree G, 2. Vivek kumar, 3. Shalinee Singh, 4. Sanesh Regmi

Guide : Dr.K. Kumar, Dean R&D, NCET

Sustainable Energy from Bio Fuel cell 2016-17

Dept. of CIVIL ENGG, NCET, Bangalore Page 2

ABSTRACT

Non convention energy generation is one of the important social need .Our

country investing huge money on that for solar energy and wind energy. Lot of research is

in progress to utilize waste material. The sewage from the residential building generates

methane gas by microorganism in the sludge. So far the septic tanks are constructed in the

residential building for collection and draining of effluent from the residence. The

effluent collection at the septic tank is containing organic matter those are consumed by

micro-organism and are generating hydrogen ion and other gases in an anaerobic and

aerobic condition. It is proposed to utilize a septic tank into a power generation unit by

incorporating stack of bio fuel cell driven by micro-organism.

The bio fuel cell is designed by the concept of H+ ions in the anaerobic condition

reacting with oxygen in aerobic condition to form water through proton exchange

membrane. This process drives electron from anode to cathode is tapped. The generated

power is regulated and the constant power supply is obtained which is useful for

residential purpose. A prototype cell was fabricated and tested by polarization. It is found

that the voltage gain is 0.59 V. The power generation Design an electrolyte for anaerobic

and aerobic condition.



CONTENT PAGE NO

1. Introduction 1.1 The world energy situation 06

1.2 Alternatives to overcome energy crisis 07

1.3 Sewage Treatment and Septic Tank 07

1.4 Origins of Sewage 07

1.5 Septic Tank 08

1.6 Details of Microbes in Sewage Water and Septic Tank 08

1.7 Aerobic and Facultative Bacteria 09

1.8 Anaerobic Bacteria 09

1.9 Definition of bio fuel cell 10

2. Working of bio fuel cell 11

3. Literature Survey 14

4. Designing of Bio fuel cell 17

4.1 Micro-Organisms in an MFC 18

4.2 Design of Anode 18

4.2.1 Electrolyte 18 4.2.2 Carbon fiber as an electrode 18 4.2.3 Proton exchange membrane 19

4.3 Design of cathode 20

4.3.1 Electrolyte 20

4.3.2 Electrode 20

4.4 Modified Design 21

4.4.1 Electrolyte in anode 21

4.4.2 Proton exchange membrane 21

4.4.3 Electrolyte in cathode 22

4.4.4 Electrode 22

4.4.5 Stack of eight cells 22



4.4.6 Voltage Reading & current readings from cell design 23

5. Regulating and boosting

5.1 Features 24

5.2 Description 24

5.3 Pin diagram and functions 24

5.4 Principle of operation of IC ltc3108 25

5.5 Typical Applications 28

6. Advantages, disadvantages and applications

6.1 Advantages 30

6.2 Disadvantages 31

6.3 Applications 31

7. Future scope 33

8. Conclusion 34

9. References 35



CHAPTER 1

INTRODUCTION

1.1 The world energy situation

In the recent decades, the consumption of energy around the globe has been increased

exponentially. This excessive consumption of energy sources usage of non-renewable

energy sources i.e. Fossil fuels, nuclear sources etc. Fossil fuels account for over 90% of

the world’s total energy resources. The main sources of fossil fuel are; coal, 16%; natural

gas 29%; petroleum 36% and nuclear 9%. Renewable energy accounts for only 10% of

the total energy consumption [1].

Fig. 1.1 Pie chart of the world energy sources (2015)

At this consumption rate, soon it will lead to energy crisis also it will affect the nature.

For example, usage of fossil fuels negatively influences the nature owning to the emission

of CO2 which eventually leads to global warming and atmospheric pollution.

In the search for economic prosperity, too much emphasis has been placed on

conventional energy, mostly powered by fossil fuels that create serious environmental and

social costs. Local air pollution, regional acid deposition and global climate change are

only some of these costs which we all must pay, now or in the future, regardless of our

local address.



1.2 Alternatives to overcome energy crisis

The use of fossil fuels, especially oil and gas, in recent years has accelerated and this

triggers a global energy crisis. Renewable bio-energy is viewed as one of the ways to

alleviate the current global warming crisis [2].

Renewable energy technologies can provide clean, sustainable and ultimately affordable

supply of energy to the world while providing additional social and economic benefits.

Major efforts are devoted to developing alternative electricity production methods. New

electricity production from renewable resources without a net carbon dioxide emission is

much desired. One of the alternative energy sources that we can use the microbial fuel

cell or bio fuel cell.

1.3 Sewage Treatment and Septic Tank

Sewage treatment is the process of removing contaminants from wastewater, primarily

from household sewage. It includes physical, chemical, and biological processes to

remove these contaminants and produce environmentally safe treated wastewater (or

treated effluent). A by-product of sewage treatment is usually a semi-solid waste or

slurry, called sewage sludge that has to undergo further treatment before being suitable

for disposal or land application.

Sewage treatment may also be referred to as wastewater treatment, although the latter is a

broader term which can also be applied to purely industrial wastewater. For most cities,

the sewer system will also carry a proportion of industrial effluent to the sewage

treatment plant which has usually received pre-treatment at the factories themselves to

reduce the pollutant load. If the sewer system is a combined sewer then it will also carry

urban runoff (storm water) to the sewage treatment plant.

1.4 Origins of Sewage

Sewage is generated from the residential, institutional, commercial and industrial

establishments. It includes household waste liquid from toilets, baths and kitchen draining

into sewers. In many areas, sewage also includes liquid waste from industry and

commerce. The separation and draining of household waste into greywater and Black

water is becoming more common in the developed world, with treated greywater being

permitted to be used for watering plants or recycled for flushing toilets.

1.5 Septic Tank

A septic tank is a key component of a septic system, a small-scale sewage treatment

system common in areas that lack connection to main sewage pipes provided by local

governments or private corporations. Other components, generally controlled by local

governments, may include pumps, alarms, sand filters, and clarified liquid effluent



disposal methods such as a septic drain field, ponds, natural stone fiber filter plants or

peat moss beds.

The term "septic" refers to the anaerobic bacteria environment that develops in the

tank which decomposes or mineralizes the waste discharged into the tank. Septic tanks

can be coupled with other onsite wastewater treatment units such as bio filters or aerobic

systems involving artificially forced aeration.

1.6 Details of Microbes in Sewage Water and Septic Tank

Sewage is combination of solid and liquid waste from domestic and industries form of

waste. Water is the main constituent of sewage and approximately 0.5% inorganic and

organic solid matter is suspended in this water. Depending upon the input sources, sewage

is composed of carbon, nitrogen, phosphorous, sugars, fatty acids, proteins, fats, alcohols,

amino acids, pectin, cellulose, lignocelluloses, lignin, heavy metal residues and many

other complex forms. Looking at the chemical composition, it seems that sewage is an

ideal environment for growth microorganisms like protozoa, algae, fungi, yeasts,

bacteria and viruses. Bacteria from sewage are pathogenic, non-pathogenic,

saprophytes, autotrophic, heterotrophic, facultative, obligate, aerobic or anaerobic

forms. The millions of bacteria have been enumerated in per milliliter of diluted sewage

sample. The common sewage bacteria include species of coli forms, streptococci,

clostridia, lactobacilli, micrococci, Proteus and Pseudomonas. Most of these bacteria re

causative agents of fatal diseases like gastro, typhoid, cholera and food poisoning in

humans.

The query arises regarding the presence of multiple groups of bacteria in sewage. Why do

they grow in sewage and what are they for? The first most important reason is that

sewage has peculiar composition that favours and supports the growth of almost all types

of bacteria. The second important reason is that sewage bacteria carry out decomposition

of organic matter present in the sewage. Bacterial sewage degradation is very prolonged

but ecologically important process. The characteristic feature of sewage decomposition is

the shift in types of bacteria during time course of decomposition process. Let us use

these changes in bacterial flora from sewage.

1.7 Aerobic and Facultative Bacteria:

Coli forms like Escherichia and Enterobacter, micrococci, lactobacilli, pseudomonas,

facultative clostridia and streptococci) predominate during first course of sewage

decomposition. Diluted sewage provides aerobic conditions for the growth of these

aerobic and facultative aerobic bacteria. Such condition is obtained when sewage is

discharged into the water body like a river. Under these conditions, organic matter

containing protein, carbohydrates and fats is completely oxidized by aerobic bacteria.

Proteins are converted to amino acids and nitrates and carbohydrates and fats to carbon

dioxide and water during the process of bacterial oxidation. This results in stabilization of

sewage and changes in chemical composition. Since the oxygen present is consumed for



oxidation of organic matter, anaerobic conditions are introduced in sewage along with the

generation of high BOD (biological oxygen demand) and offensive odor.

1.8 Anaerobic Bacteria

The second course of sewage degradation is taken up by strictly anaerobic bacteria like

methanogens or methane producing bacteria (Methanobacterium, Methanococcus and

Methanogenium). As their name indicates, they produce methane from hydrogen and

carbon dioxide present in the sewage. Methanogens decrease load of organic solids by

degrading them into soluble substances and gases. Under anaerobic conditions, protein

and nitrogenous compounds are degraded to amino acids, nitrogen, ammonia, hydrogen

sulphide, carbon dioxide, methane, in dole, organic acids and alcohols; carbohydrates are

converted to carbon dioxide, alcohols, hydrogen, fatty and neutral acids and fats and fatty

acids are degraded into lower fatty acids, glycerol, carbon dioxide and hydrogen. The

typical gaseous mixture from sewage contains methane (biogas), nitrogen, hydrogen and

carbon dioxide. These gases have very high potential to be used for power generation in

industries. At this stage, the sewage is termed as digested sludge. Dewatered sewage

(after exposure to sunlight) can be used as soil conditioner or compost or for land filling.

The process of sewage degradation occurs naturally and also forms the basis of

functioning of artificial sewage treatment plants. Had not bacteria been actively present in

the sewage, water bodies on the Earth would have been turned into sewers by now.

1.9 Definition of Bio Fuel Cell

A biological fuel cell or microbial fuel cell (MFC) is a bio-electrochemical system that

drives a current by mimicking bacterial interactions found in nature. It converts chemical

energy directly to electrical energy by the catalytic reaction of micro-organisms.

A typical microbial fuel cell consists of anode and cathode compartments separated by a

cation (positively charged ion) specific membrane. In the anode compartment, fuel is

oxidized by microorganisms, generating electrons and protons. Electrons are transferred

to the cathode compartment through an external electric circuit, while protons are

transferred to the cathode compartment through the membrane. Electrons and protons are

consumed in the cathode compartment, combining with oxygen to form water.

The basic reactions which occur in MFCs are illustrated in the equations below:

Anode: H2 → 2H+ + 2e- Eo = 0 V (pH=0)

Cathode: O2 + 4H+ + 4e- → 2H2O Eo= 1.229 V (pH=0)



CHAPTER 2

WORKING OF BIO FUEL CELL

As shown in Fig. 2.1, the Microbial Fuel Cell is divided into two halves: aerobic and

anaerobic. The aerobic half has a positively charged electrode and is bubbled with

oxygen, much like a fish tank. The anaerobic half does not have oxygen, allowing a

negatively charged electrode to act as the electron receptor for the bacterial processes.

The chambers are separated by a semi-permeable membrane to keep oxygen out of the

anaerobic chamber while still allowing hydrogen ions (H+) pass through.

Fig. 2.1 Schematic of bio fuel cell

1. The bacteria on the anode decompose organic matter and free H+ ions and electrons.

2. The electrons flow from the bacteria to the anode, sometimes assisted by a mediator

molecule.

3. The electrons flow up from the anode, through a wire, and onto the cathode. While

flowing through the wire, an electrical current is generated that can be used to perform

work.

4. The H+ ions flow through the semi-permeable membrane to the cathode. This process

is driven by the electro-chemical gradient resulting from the high concentration of H+

ions near the anode.



5. The electrons from the cathode combine with dissolved oxygen and the H+ ions to

form pure H2O.

In the anaerobic chamber, a solution containing food for the bacteria is circulated.

This food consists of glucose or acetate, compounds commonly found in food waste

and sewage. The bacteria metabolize food by first breaking apart the food molecules

into hydrogen ions, carbon dioxide, and electrons. As shown in Fig. 3, bacteria use the

electrons to produce energy by way of the electron transport chain. The microbial fuel

cell disrupts the electron transport chain using a mediator molecule to shuttle electrons

to the anode. In many ways, a microbial fuel cell is an extension of the electron

transport chain where the final step of the process (the combination of oxygen,

electrons, and H+ to form water) is transferred outside of the bacterial cell from which

energy can be harvested.

Fig. 2.2Electron Transport Chain

1. The electron transport chain begins with NADH, a biological transport molecule,

releasing a high energy electron (e-) and a proton (H+).

2. The electron follows the red path through the proteins (large blobs) in the

mitochondrial membrane.

3. As the electron passes through each protein, it pumps hydrogen ions (H+) through the

membrane.



4. In a normal bacterial cell, the electron continues along the dotted red path where it

combines with oxygen to make water.

5. In a microbial fuel cell, the electron continues along the solid red path, where it is

picked up by a mediator molecule and taken to the anode.



CHAPTER 3

LITERATURE SURVEY

The earliest MFC concept was demonstrated by Potter in 1910 (Ieropoulos, 2005a).

Electrical energy was produced from living cultures of Escherichia Coli and

Saccharomyces by using platinum electrodes. This didn't generate much interest until

1980s when it was discovered that current density and the power output could be greatly

enhanced by the addition of electron mediators. Unless the species in the anodic chamber

are anodophiles, the microbes are incapable of transferring electrons directly to the anode.

The outer layers of most microbial species are composed of non-conductive lipid

membrane, peptididoglycans and lipopolysaccharides that hinder the direct electron

transfer to the anode. Electron mediators accelerate the transfer [3].

Mediators in an oxidized state can easily be reduced by capturing the electrons from

within the membrane. The mediators then move across the membrane and release the

electrons to the anode and become oxidized again in the bulk solution in the anodic

chamber. This cyclic process accelerates the electron transfer rate and thus increases the

power output. And how efficient the oxidized mediator gets reduced by the cells reducing

power is more important compared with other features. Although a mediator with the

lowest redox would in theory give the lowest anodic redox and thus maximize the redox

difference between anode and cathode (i.e. give biggest voltage difference) it would not

necessarily be the most efficient at pulling electrons away from the reduced intracellular

systems (NADH, NADPH or reduced cytochromes) within the microbes.

A mediator with a higher EO redox would give a higher overall power than a mediator

with the lowest redox. Typical synthetic exogenous mediators include dyes and metal

organics such as neutral red (NR), methylene blue (MB),) and Fe (III) EDTA

Unfortunately, the toxicity and instability of synthetic mediators limit their applications in

MFCs. Some microbes can use naturally occurring compounds including microbial

metabolites (Endogenous mediators) as mediators. Humic acids, anthraquinone, the

oxyanions of sulphur (sulphate and thiosulphate) all have the ability to transfer electrons

from inside the cell membrane to the anode [4].

A real breakthrough was made when some microbes were found to transfer electrons

directly to the anode [5].These microbes are operationally stable and yield a high



Columbic efficiency and are all electrochemically active and can form a bio film on the

anode surface and transfer electrons directly by conductance through the membrane anode

[5].When they are used, the anode acts as the final electron acceptor in the dissimilatory

respiratory chain of the microbes in the biofilm. Biofilm forming on a cathode surface

may also play an important role in electron transfer between the microbes and the

electrodes. Cathodes can serve as electron donors for Thiobacillusferrooxidans suspended

in a catholyte (Prasad et al., 2006) for an MFC system that contain microbes in both

anodic and cathodic chambers. G. metallireducensand G. Sulfurreducens or other

seawater biofilm may all act as final electron acceptors by grabbing the electrons from

cathode as electron donors. Since the cost of a mediator is eliminated, mediator-less

MFC’s are advantageous in wastewater treatment and power generation.

In fact, little development occurred on his primitive designs until the 1980s. M. J. Allen

and H.PeterBennetto from Kings College in London revolutionized the original microbial

fuel cell design. Spurred by their desire to provide cheap and reliable power to third world

countries, Allen and Bennetto combined advancements in the understanding of the

electron transport chain and significant advancements in technology to produce the basic

design that is still used in MFCs today. However, use of MFCs in third world countries is

still in the pilot stages because of the complexities of simplifying the design enough to

allow poor rural residents to build them. The advancements by the Kings College team

have shown the scientific community that the microbial fuel cell can be useful technology

and generate increased interest in its development.

As scientists all over the world began researching the microbial fuel cell, one major

question still remained: how do the electrons get from the electron transport chain to the

anode? While researching this problem in the 1990s, B-H. Kim, a researcher from the

Korean Institute of Science and Technology, discovered that certain species of bacteria

were electrochemically active and didn’t require the use of a mediator molecule to

transport electrons to the electrodes.

Thus, a new type of microbial fuel cell was born that eliminated the use of the expensive

and sometimes toxic mediators. Currently, researchers are working to optimize electrode

materials, types and combinations of bacteria, and electron transfer in microbial fuel cells.

Even though the idea of harnessing the energy produced by bacteria has been around for

almost 100 years, researchers have just begun to fully understand the MFC and how to



bring out its true potential. The microbial fuel cell has current and potential uses in

brewery and domestic wastewater treatment, desalination, hydrogen production, remote

sensing, pollution remediation, and as a remote power source. Many new applications are

beginning to be tested and may come into widespread use in the near future.



CHAPTER 4

DESIGNING OF BIO FUEL CELL

4.1 MICRO-ORGANISMS IN AN MFC

In its most basic form, a MFC is a device that uses microorganisms to generate an

electrical current through the oxidation of organic material. Microorganisms in the MFC

metabolize organic substrates and extracellularly transfer electrons to an electrode

surface. The oxidation of the organic material liberates both electrons and protons from

the oxidized substrate. Electrons are transferred to the anode and then to the cathode

through an electrical network. The protons migrate to the cathode and combine with the

electron and a catholyte, a chemical such as oxygen, which is reduced at the cathode

surface. As such, an electrical current is generated in a fashion similar to a chemical fuel

cell, but with microbes acting as a catalyst on the anode surface. Catalysts generally

increase the rate of a reaction without being changed by or receiving energy from the

reaction they catalyze. The microbes in a MFC are not true catalysts since they obtain

energy from the oxidation of the substrate to support their own growth and create an

energy loss. Microbes in a MFC may gain all the energy and carbon required for cellular

growth from the oxidation of the complex organic material and as such MFC technology

has been considered self-sustaining. As long as conditions remain favorable for current

production by the anode-associated microbes, a MFC has the potential to produce

electricity indefinitely [6]. A diverse range of microorganisms are found in association

with electrodes in MFC systems, especially when environmental inoculums are used to

seed the MFC. A general term for bacteria associated with a surface is a biofilm. It is

likely that not all of the organisms associated anode biofilm interact directly with the

anode but may interact indirectly through other members of the electrode community. For

example, Brevibacillus sp. PTH1 was found to be an abundant member of a MFC

community. Power production by Brevibacillus sp. PTH1 is low unless it is co cultured

with a Pseudomonas sp. or supernatant from a MFC run with the Pseudomonas sp. is

added. Pure cultures capable of producing current in a MFC include representatives of the

Firmicutes and Acidobacteria, four of the five classes of Proteobacteria as well as the

yeast strains Saccharomyces cerevisiae and Hansenula anomala [22]. These organisms

interact with an anode through a variety of direct and indirect processes producing current

to varying degrees.



4.2 DESIGN OF ANODE

4.2.1 ELECTROLYTE

Waste water is used as an electrolyte in the anode side. Water is mixed with the cow dung

in the ratio of 10:1.Cow dung host a wide variety of microorganisms varying in individual

properties. Exploitation of cow dung micro flora can contribute significantly in

sustainable agriculture and energy requirements. It is one of the Bioresources of this

world which is available on large scale and still not fully utilized. [7]

4.2.2 CARBON FIBER AS AN ELECTRODE

Carbon fiber’s or carbon fibers (alternatively CF, graphite fiber or graphite fiber) are

fibers about 5–10 micrometers in diameter and composed mostly of carbon atoms.

To produce a carbon fiber, the carbon atoms are bonded together in crystals that are more

or less aligned parallel to the long axis of the fiber as the crystal alignment gives the fiber

high strength-to-volume ratio (making it strong for its size). Several thousand carbon

fibers are bundled together to form a tow, which may be used by itself or woven into a

fabric.

The properties of carbon fibers, such as high stiffness, high tensile strength, low weight,

high chemical resistance, high temperature tolerance and low thermal expansion, make

them very popular in aerospace, civil engineering, military, and motorsports, along with

other competition sports. However, they are relatively expensive when compared with

similar fibers, such as glass fibers or plastic fibers. Carbon fibers are usually combined

with other materials to form a composite. When combined with a plastic resin and wound

or moulded it forms carbon-fiber-reinforced polymer (often referred to as carbon fiber)

which has a very high strength-to-weight ratio, and is extremely rigid although somewhat

brittle. However, carbon fibers are also composited with other materials, such as with

graphite to form carbon-carbon composites, which have a very high heat tolerance. [8-9]



Fig. 4.2 Schematic of Carbon Fiber

Fig. 4.2 Carbon Fiber Electrode

4.2.3 PROTON EXCHANGE MEMBRANE

A semi permeable membrane is used in between the anode and cathode which allows the

ions to pass through it. A semi-permeable membrane is a membrane that will allow some

atoms or molecules to pass but not others. A simple example is a screen door. [10] It

allows air molecules to pass through but not pests or anything larger than the holes in the

screen door. A semi permeable membrane is a type of biological or synthetic, polymeric

membrane that will allow certain molecules or ions to pass through it by diffusion—or

occasionally by more specialized processes of facilitated diffusion, passive transport or



active transport. The rate of passage depends on the pressure, concentration, and

temperature of the molecules or solutes on either side, as well as the permeability of the

membrane to each solute. Depending on the membrane and the solute, permeability may

depend on solute size, solubility, properties, or chemistry.

4.3 DESIGN OF CATHODE

4.3.1 ELECTROLYTE

Normal tap water and 0.1M of kcl is mixed in ratio of 1:5 and filled in the cathode

chamber. Potassium chloride (KCl) is a metal halide salt composed of potassium and

chloride. It is odorless and has a white or colorless vitreous crystal appearance. The solid

dissolves readily in water and its solutions have a salt-like taste.

4.3.2 ELECTRODE

Electrode used in the cathode side will be same as that in anode side. [8-9]

Fig. 4.3 Cell designed as per above specification

Sustainable Energy from Bio Fuel cell

Dept. of CIVIL ENGG, NCET, Bangalore

Fig. 4.4 Voltage Reading from cell design specified in section 4.3

As seen in graph above, voltage was increasing at slow rate as the days passed on. From

the above design, voltage

the current at this stage was few micro

application. So there was some modification made specifically at the cathode side to

increase the voltage as well as current value.

4.4 MODIFIED DESIGN

4.4.1 ELECTROLYTE

Yeast is added in the waste water.

cells that reproduce by budding, and capable of converting sugar into alcohol and carbon

dioxide. [11] Fermentation

glucose even though oxygen is not available. Fermentation occurs in yeast cells, and a

form of fermentation takes place in bacteria and in the muscle cells of animals

4.4.2 PROTON EXCHANGE MEMBRANE

Nafion membrane is used.

compartment of Proton Exchange Membrane fuel cells and water

thickness of this particular cation exchange membrane

separator and solid electrolyte in a variety of electrochemical cells that require the

membrane to selectively transport

chemically resistant and

movement of cations, however the membrane does not conduct anions or electrons.


, NCET, Bangalore

Voltage Reading from cell design specified in section 4.3


attains a maximum value of 0.54 V after almost 3 weeks also

the current at this stage was few micro-amps only which didn’t serve the purpose for any

there was some modification made specifically at the cathode side to

as well as current value.

MODIFIED DESIGN

ELECTROLYTE IN ANODE

Yeast is added in the waste water. Yeast is a microscopic fungus consisting of single oval


Fermentation is an anaerobic process in which energy can be released from


form of fermentation takes place in bacteria and in the muscle cells of animals

EXCHANGE MEMBRANE

used. Nafion Membrane is used to separate the anode and cathode

compartment of Proton Exchange Membrane fuel cells and water

thickness of this particular cation exchange membrane. The membrane performs as a


membrane to selectively transport captions across the cell junction. The polymer is

chemically resistant and durable [12].Pores in a Nafion membrane allow for the

however the membrane does not conduct anions or electrons.

2016-17

Page 19

Voltage Reading from cell design specified in section 4.3


attains a maximum value of 0.54 V after almost 3 weeks also

amps only which didn’t serve the purpose for any

there was some modification made specifically at the cathode side to

Yeast is a microscopic fungus consisting of single oval


is an anaerobic process in which energy can be released from


form of fermentation takes place in bacteria and in the muscle cells of animals.

Membrane is used to separate the anode and cathode

compartment of Proton Exchange Membrane fuel cells and water electrolyzes. The

The membrane performs as a


across the cell junction. The polymer is

embrane allow for the

however the membrane does not conduct anions or electrons.



Depending on the manufacturing process, the cation conductivity of a Nafion membrane

can be modified to meet a specified application requirement[13].Polymer electrolyte

membrane (PEM) fuel cells based on per fluorinated membranes have successfully been

operated in a temperature range of approximately 50–90 8C.Proton conductivity increases

exponentially with water activity in the membrane. Increasing the fuel cell temperature

raises the vapor pressure required to keep a given amount of water in the membrane,

thereby increasing the likelihood that water loss will occur and significantly reduce

proton conductivity. [14]

Pretreatment of the Nafion® membrane

• Slightly boiling (≈ 80°C) in 3 &percent; H2O2 for 1 hour.

• Slightly boiling (≈ 80°C) in deionized water for 2 hours.

• Slightly boiling (≈ 80°C) in 0.5M H2 SO4 the membrane needs to be rinsed between the

boiling steps and after the final boiling step. After the pretreatment the membrane needs

to be stored in deionized water all the time and must not dry.

4.4.3 ELECTROLYTE IN CATHODE

Potassium permanganate is used extensively in the water treatment industry. It is used as

a regeneration chemical to remove iron and hydrogen sulfide (rotten egg smell)

from well water via a "Manganese Greensand" Filter. "Pot-Perm" is also obtainable

at pool supply stores and is used additionally to treat waste water.

4.4.4 ELECTRODE

The literature collection advocates using copper as cathode so that the benefit of galvanic

effect may also be drawn. Then copper mesh electrode was introduced so that the surface

area can be increased. As the surface area increases the micro-organisms reactions will

increase which results in better power generation

4.4.5 STACK OF EIGHT CELLS:

The proto type cells are fabricated having capacity of 150ml in each compartment. Both

compartments are separated by “nafion-117” (membrane). Anaerobic condition was

created in anode side. Yeast was added in the anaerobic compartment. This mixture is

placed in a sealed chamber to create anaerobic condition thus forcing the micro-organism

to undertake anaerobic respiration. Eight numbers of such cells were fabricated and

connected by series. From those cells the desired voltage and current was obtained that

can boost and regulate easily



4.4.6 Voltage Reading & current readings from cell design specified in

section

SL.No Voltage Current

1.(1 cell) 0.567 V 0.6mA

2.(8 cells series connected)

5.03V 0.035 mA



CHAPTER 5

5 REGULATING AND BOOSTING

A boost converter (step-up converter) is a DC-to-DC power converter that steps up

voltage (while stepping down current) from its input (supply) to its output (load). Several

methods exist to achieve DC-DC voltage conversion. Each of these methods has its

specific benefits and disadvantages, depending on a number of operating conditions and

specifications. [20]

Utilizes a MOSFET switch to form a resonant step-up oscillator using an external step-up

transformer and a small coupling capacitor. For this we are going to use LTC 3108. [21-

22]

5.1 FEATURES

Operates from Inputs of 20mV

Complete Energy Harvesting Power

Management System

- Selectable VOUT of 2.35V, 3.3V, 4.1V or 5V

- LDO: 2.2V at 3mA

- Logic Controlled Output

- Reserve Energy Output

Power Good Indicator

Uses Compact Step-Up Transformers

5.2 DESCRIPTION

The LTCR3108 is a highly integrated DC/DC converter ideal for harvesting and

managing surplus energy from extremely low input voltage sources such as TEGs

(thermoelectric generators), thermopiles and small solar cells. The step-up topology

operates from input voltages as low as 20mV. Using a small step-up transformer, the

LTC3108 provides a complete power management solution for wireless sensing and data

acquisition. The 2.2V LDO powers an external microprocessor, while the main output is

programmed to one of four fixed voltages to power a wireless transmitter or sensors. A



second output can be enabled by the host. A storage capacitor provides power when the

input voltage source is unavailable. The LTC3108 is available in a small, thermally

enhanced 12-lead (3mm 4mm) DFN package and a 16

5.3 PIN DIAGRAM AND

VAUX (Pin 1/Pin 2): Output of the Internal Rectifier Circuit

VAUX with at least 1μF of capacitance

5.25V (typical)

.

VSTORE (Pin 2/Pin 3):

may be connected from this pin

voltage is lost. It will be charged up to the maximum

this pin should be left opener

.

VOUT (Pin 3/Pin 4): Main Output of the Converter.

to the voltage selected byVS1 and VS2 (see Table 1). Connect this pin to an

storage capacitor or to a rechargeable battery.

VOUT2 (Pin 4/Pin 5): Switched Output of the

load. This output is open until

through a 1.3Ω P-channel switch. If not used,

VOUT. The peak current in


, NCET, Bangalore



4mm) DFN package and a 16-lead SSOP package

AND FUNCTIONS

Fig.5.3 Pin diagram of IC LTC3108

Output of the Internal Rectifier Circuit and VCC

of capacitance. An active shunt regulator clamps VAUX to

VSTORE (Pin 2/Pin 3): Output for the Storage Capacitor or Battery. A large capacitor

this pin to GND for powering the system in the event the input

lost. It will be charged up to the maximum VAUX clamp voltag

opener tied to VAUX

Main Output of the Converter. The voltage at this pin is regulated

e voltage selected byVS1 and VS2 (see Table 1). Connect this pin to an

capacitor or to a rechargeable battery.

Switched Output of the Converter. Connect this pin to a switched

open until VOUT2_EN is driven high, then it is connected

channel switch. If not used, this pin should be left open or tied to

current in this output is limited to 0.3A typical.

2016-17

Page 23



lead SSOP package. [25]

and VCC for the IC. Bypass

. An active shunt regulator clamps VAUX to

Battery. A large capacitor

system in the event the input

voltage. If not used,

at this pin is regulated

e voltage selected byVS1 and VS2 (see Table 1). Connect this pin to an energy

this pin to a switched

driven high, then it is connected to VOUT

should be left open or tied to



VLDO (Pin 5/Pin 6): Output of the 2.2V LDO. Connect a2.2μF or larger ceramic

capacitor from this pin to GND. If not used, this pin should be tied to VAUX.

PGD (Pin 6/Pin 7): Power Good Output. When VOUT is within 7.5% of its programmed

value, PGD will be pulled up to VLDO through a 1MΩ resistor. If VOUT drops 9%below

its programmed value PGD will go low. This pin can sink up to 100μA.

VS2 (Pin 7/Pin 10): VOUT Select Pin 2. Connect this pin to ground or VAUX to

program the output voltage (see Table 1).

VOUT2_EN (Pin 9/Pin 12): Enable Input for VOUT2. VOUT2 will be enabled when

this pin is driven high. There is an internal 5M pull-down resistor on this pin. If not used,

this pin can be left open or grounded

.

C1 (Pin 10/Pin 13): Input to the Charge Pump and Rectifier Circuit. Connect a capacitor

from this pin to the secondary winding of the step-up transformer.

C2 (Pin 11/Pin 14): Input to the N-Channel Gate Drive Circuit. Connect a capacitor from

this pin to the secondary winding of the step-up transformer.

SW (Pin 12/Pin 15): Drain of the Internal N-Channel Switch. Connect this pin to the

primary winding of the transformer.

GND (Pins 1, 8, 9, 16) SSOP Only: Ground

GND (Exposed Pad Pin 13) DFN Only: Ground. The DFN exposed pad must be

soldered to the PCB ground plane. It serves as the ground connection, and as a means of

Conducting heat away from the die.



Table 5.3.1 Regulated voltage using Pins VS1 andVS2

5.4 PRINCIPLE OF OPERATION

Oscillator

The LTC3108 utilizes a MOSFET switch to form a resonant

external step-up transformer

voltages as low as 20mV high enough to provide multiple

powering other circuits. The

the transformer secondary winding and is typically in the

input voltages as low as

recommended. For higher input voltages, this ra

Fig.5.4


, NCET, Bangalore

Regulated voltage using Pins VS1 andVS2

PRINCIPLE OF OPERATIONOF IC LTC3108

The LTC3108 utilizes a MOSFET switch to form a resonant step-up oscillator using an

up transformer and a small coupling capacitor. This allows it to boost input

voltages as low as 20mV high enough to provide multiple regulated output voltages for

powering other circuits. The frequency of oscillation is determined by the inductance of

the transformer secondary winding and is typically in the range of 10 kHz to 100 kHz. For

voltages as low as 20mV, a primary-secondary turns ratio of about 1:100 is

recommended. For higher input voltages, this ratio can be lower.

Fig.5.4 Internal diagram of IC LTC3108

2016-17

Page 25

up oscillator using an

and a small coupling capacitor. This allows it to boost input

regulated output voltages for

on is determined by the inductance of

e of 10 kHz to 100 kHz. For

secondary turns ratio of about 1:100 is



Charge Pump and Rectifier

The AC voltage produced on the secondary winding of the transformer is boosted and

rectified using an external charge pump capacitor (from the secondary winding to pin C1)

and the rectifiers internal to the LTC3108. The rectifier circuit feeds current into the

VAUX pin, providing charge to the external VAUX capacitor and the other outputs.

VAUX

The active circuits within the LTC3108 are powered from VAUX, which should be

bypassed with a 1μF capacitor. Larger capacitor values are recommended when using

turns ratios of 1:50 or 1:20 (refer to the Typical Application examples). Once VAUX

exceeds 2.5V, the main VOUT is allowed to start charging. An internal shunt regulator

limits the maximum voltage on VAUX to 5.25V typical. It shunts to GND any excess

current into VAUX when there is no load on the converter or the input source is

generating more power than is required by the load.

Voltage Reference

The LTC3108 includes a precision, micro power reference, for accurate regulated output

voltages. This reference becomes active as soon as VAUX exceeds 2V.

Synchronous Rectifiers

Once VAUX exceeds 2V, synchronous rectifiers in parallel with each of the internal

diodes take over the job of rectifying the input voltage, improving efficiency.

Low Dropout Linear Regulator (LDO)

The LTC3108 includes a low current LDO to provide regulated 2.2V output for powering

low power processors or other low power ICs. The LDO is powered by the higher of

VAUX or VOUT. This enables it to become active as soon as VAUX has charged to

2.3V, while the VOUT storage capacitor is still charging. In the event of a step load on

the LDO output, current can come from the main VOUT capacitor if VAUX drops below

VOUT. The LDO requires a 2.2μF ceramic capacitor for stability. Larger capacitor values

can be used without limitation, but will increase the time it takes for all the outputs to

charge up. The LDO output is current limited to 4mA minimum.



VOUT

The main output voltage on VOUT is charged from the VAUX supply, and is user

programmed to one of four regulated voltages using the voltage select pins VS1 and VS2,

according to Table 2. Although the logic threshold voltage for VS1 and VS2 is 0.85V

typical, it is recommended that they be tied to ground or VAUX.

When the output voltage drops slightly below the regulated value, the charging current

will be enabled as long as VAUX is greater than 2.5V. Once VOUT has reached the

proper value, the charging current is turned off. The internal programmable resistor

divider sets VOUT, eliminating the need for very high value external resistors that are

susceptible to board leakage. In a typical application, a storage capacitor (typically a few

Hundred microfarads) is connected to VOUT. As soon as VAUX exceeds 2.5V, the

VOUT capacitor will be allowed to charge up to its regulated voltage. The current

available to charge the capacitor will depend on the input voltage and transformer turns

ratio, but is limited to about 4.5Matypical.

PGOOD

A power good comparator monitors the VOUT voltage. The PGD pin is an open-drain

output with a weak pull-up (1MΩ) to the LDO voltage. Once VOUT has charged to

within 7.5% of its regulated voltage, the PGD output will go high. If VOUT drops more

than 9% from its regulated voltage, PGD will go low. The PGD output is designed to

drive microprocessor or other chip I/O and is not intended to drive a higher current load

such as an LED. Pulling PGD up externally to a voltage greater than VLDO will cause a

small current to be sourced into VLDO. PGD can be pulled low in a wire-OR

configuration with other circuitry.

VOUT2

VOUT2 is an output that can be turned on and off by the host, using the VOUT2_EN pin.

When enabled, VOUT2 is connected to VOUT through a 1.3Ω P-channel MOSFET

switches. This output, controlled by a host processor, can be used to power external

circuits such as sensors and amplifiers that do not have a low power sleep or shutdown

capability. VOUT2 can be used to power these circuits only when they are needed.

Minimizing the amount of decoupling capacitance on VOUT2 will allow it to be switched

on and off faster, allowing shorter burst times and, therefore, smaller duty cycles in

pulsed applications such as a wireless sensor/transmitter. A small VOUT2 capacitor will



also minimize the energy that will be wasted in charging the capacitor every timeVOUT2

is enabled.VOUT2 has a soft-start time of about 5μs to limit capacitor charging current

and minimize glitching of the main output when VOUT2 is enabled. It also has a current

limiting circuit that limits the peak current to 0.3A typical. The VOUT2 enable input has

a typical threshold of 1V with 100mV of hysteresis, making it logic-compatible.

IfVOUT2_EN (which has an internal pull-down resistor) is low, VOUT2 will be off.

Driving VOUT2_EN high will turn on the VOUT2 output. Note that while VOUT2_EN

is high, the current limiting circuitry for VOUT2 draws an extra 8μA of quiescent current

from VOUT. This added current draw has a negligible effect on the application and

capacitor sizing, since the load on the VOUT2 output, when enabled, is likely to be orders

of magnitude higher than 8μA.

VSTORE

The VSTORE output can be used to charge a large storage capacitor or rechargeable

battery after VOUT has reached regulation. Once VOUT has reached regulation, the

VSTORE output will be allowed to charge up to the VAUX voltage. The storage element

on VSTORE can be used to power the system in the event that the input source is lost, or

is unable to provide the current demanded by the VOUT, VOUT2 and LDO outputs. If

VAUX drops below VSTORE, the LTC3108 will automatically draw current from the

storage element. Note that it may take a long time to charge a large capacitor, depending

on the input energy available and the loading on VOUT and VLDO. Since the maximum

current from VSTORE is limited to a few milliamps, it can safely be used to trickle-

charge NiCdor NiMH rechargeable batteries for energy storage when the input voltage is

lost. Note that the VSTORE capacitor cannot supply large pulse currents to VOUT. Any

pulse load on VOUT must be handled by the VOUT capacitor.

Short-Circuit Protection

All outputs of the LTC3108 are current limited to protect against short-circuits to ground.

5.5 TYPICAL APPLICATIONS

The LTC3108 is designed to gather energy from very low input voltage sources and

convert it to usable output voltages to power microprocessors, wireless transmitters and

analog sensors. Such applications typically require much more peak power, and at higher

voltages, than the input voltage source can produce. The LTC3108 is designed to



accumulate and manage energy over a long period of

for acquiring and transmitting data

such that the total output energy during the

power integrated over the accumulation time between bursts.


, NCET, Bangalore

and manage energy over a long period of time to enable short power bursts

transmitting data. The bursts must occur at a low enough

such that the total output energy during the burst does not exceed the average source

the accumulation time between bursts.

Fig 5.5 LTC3108 DESIGN

2016-17

Page 29

enable short power bursts

. The bursts must occur at a low enough duty cycle

eed the average source



CHAPTER 6

ADVANTAGES, DISADVANTAGES AND APPLICATIONS

6.1 ADVANTAGES

There are following advantages of the microbial cell

Energy Benefits

Direct electricity can be generated

Need no aeration

Low sludge yield

Adaptable to decentralized treatment

Operating Stability

Self regeneration of microorganisms

Good resistance to environmental stress

Amenable to real time monitoring and control

Economics

Energy recovery

Valuable product recovery

Low operation cost

Ease burden of subsequent treatment

Environmental impact

Water reclamation

Low carbon foot print

Less sludge disposal

MFCs as power sources have the advantage to be easily placed where the energy

is needed, like in remote locations.



6.2 DISADVANTAGES

Ohmic Losses. The Ohmic losses (or Ohmic polarization) in an MFC include

both the resistance to the flow of electrons through the electrodes and

interconnections, and the resistance to the flow of ions through the PEM (if

present) and the anodic and cathodic electrolytes. Ohmic losses can be reduced by

minimizing the electrode spacing, using a membrane with a low resistivity,

checking thoroughly all contacts, and (if practical) increasing solution

conductivity to the maximum tolerated by the bacteria.

Activation Losses. Activation energy needed for an oxidation/reduction reaction,

activation losses occur during the transfer of electrons from or to a compound

reacting at the electrode surface. Low activation losses can be achieved by

increasing the electrode surface area, improving electrode catalysis, increasing the

operating temperature, and through the establishment of an enriched bio film on

the electrode(s).

Use stacks of multiple small-scale MFCs, in series, parallel and series–

parallel configurations. Those configurations increase the total power output

compared to a single cell However, a connection in series of the fuel cells leads to

operating problems such as voltage reversal in one of the cell when the anode

potential shifts to positive values. This happens when a cell with limited

performances is operated at high currents or when a single MFC is connected to

an external load that is too demanding.

6.3 APPLICATIONS

1. Wastewater treatment

Micro-organisms can perform the dual duty of degrading effluents and generating power.

MFCs are presently under serious consideration as devices to produce electrical power in

the course of treatment of industrial, agricultural, and municipal wastewater.



2. Powering underwater monitoring devices

Data on the natural environment can be helpful in understanding and modelling

ecosystem responses, but sensors distributed in the natural environment require power for

operation. MFCs can be used to power such devices, particularly in river and deep-water

environments where it is difficult to routinely access the system to replace batteries.

3. Power supply to remote sensors

Replacing batteries of remote sensors on a regular basis can be costly, time consuming,

and impractical. A possible solution to this problem is to use self renewable power

supplies, such as MFCs, which can operate for a long time using local resources.

4. Biological Oxygen Demand (BOD) sensing

MFC technology can be used as a sensor for pollutant analysis and in situ process

monitoring and control.



7. FUTURE SCOPE

One of the first applications could be the development of pilot-scale reactors at industrial

locations where a high quality and reliable influent is available. Food processing

wastewaters and digester effluents are good candidates.

In the long term more dilute substrates, such as domestic sewage, could be treated with

MFCs, decreasing society’s need to invest substantial amounts of energy in their

treatment.

While full-scale, highly effective MFCs are not yet within our grasp, the technology holds

considerable promise, and major hurdles will undoubtedly be overcome by engineers and

scientists. The growing pressure on our environment, and the call for renewable energy

sources will further stimulate development of this technology, leading soon we hope to its

successful implementation.



8 .CONCLUSION

MFCs are a promising new technology for generation of electrical energy. This

technology involves using microorganisms to convert readily available substrates into

electricity through biological processes contained within the MFC reactor. The power

density produced judge performance, which is the most important aspect of the

technology.

Power density is affected by the kind of MFC reactor, bacterial culture, and the size of

electrode, the substrates, and the oxidants. Oxidation of the substrate, moving electrons to

the electrode, internal resistance, flow of proton, and reaction of the cathode are the

parameters governing MFC performance.

This technology is close to practical use but not there yet. Overcoming high resistance in

MFCs remains a major challenge. The development of less expensive materials for

enhancing MFC technology to produce highly sustainable efficient electrical energy is

another challenge. In the current state, MFCs can be used to power low power electrical

appliances especially in rural areas.



REFERENCES

[1] Data from International Energy Agency (IEA)

[2] Ministry of Energy, Economic Survey

[3] Potter, 1912, and Davis and Higson, 2007

[4] Park and Zeikus, 2000; Bennetto, 1990.

[5] Kimet al., 1999a, Chaudhuri and Lovley, 2003

[6] Electricity-producing bacterial communities in microbial fuel cells Bruce E. Logan

and John M. Regan Department of Civil and Environmental Engineering, Penn State

University, University Park, PA 16802, USA

[7]Current status of cow dung as a bio resource for sustainable development Kartikey

Kumar Gupta Email author, Kamal Rai Aneja and Deepanshu Rana Bioresources and

Bioprocessing20163:28 DOI: 10.1186/s40643-016-0105-9

[8] Carbon Fiber Mechanical Properties: Reconciling Models and Experiments Carlos A.

León y León and Xinzhang Zhou

[9] MECHANICAL PROPERTIES OF CARBON FIBER COMPOSITES FOR

ENVIRONMENTAL APPLICATIONS. Rodney Andrews and Eric GNlke, Chemical and

Materials Engineering Department, University of Kentucky, Geoff Kimber, Center for

Applied Energy Reswch, University of Kentucky, Lexington, KY 4051 1-8433

[10] A Brief Review of Reverse Osmosis Membrane Technology Michael E. Williams,

Ph.D., P.E

[11]Yeast and Fermentation. Dukes of Ale BJCP Preparation Course 2009 Jim Curry

[email protected] April 19, 2009

[12] DuPont™ Nafion® PFSA Membranes

[13] NR-211 and NR-212 CHARACTERIZATION OF NAFION PROTON

EXCHANGE MEMBRANE FILMS USING WIDE-ANGLE X-RAY DIFFRACTION

T.N. Blanton1 and R. Koestner2 1 International Centre for Diffraction Data, Newtown

Square, PA 19073, USA 2 General Motors Corporation, Pontiac, MI 48340,



[14] Mechanical Properties of Nafion and Titania/Nafion Composite Membranes for

Polymer Electrolyte Membrane Fuel Cells M. BARCLAY SATTERFIELD,1 PAUL W.

MAJSZTRIK,2 HITOSHI OTA,2 JAY B. BENZIGER,1 ANDREW B. BOCARSLY2 1

Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08544

2 Chemistry Department, Princeton University, Princeton, New Jersey 08544

[15] Logan IS... Exoelectrogenic bacteria that power microbial fuel cells. Nat Rev

Microbial 7: 375- 381 Article in Nature Reviews Microbiology · April 2009

[16] Microbial Fuel Cells: Methodology and Technology† BRUCE E. LOGAN,* , ‡

BERT HAMELERS, § RENEÄ ROZENDAL, § , | UWE SCHRO¨ DER, ⊥ J U¨ RG

KELLER, # STEFANO FREGUIA, # PETER AELTERMAN, @ WILLY

VERSTRAETE, @ AND KORNEEL RABAEY

[17] Microbial Fuel Cells: Methodology and Technology† BRUCE E. LOGAN,* , ‡

BERT HAMELERS, § RENEÄ ROZENDAL, § , | UWE SCHRO¨ DER, ⊥ J U¨ RG

KELLER, # STEFANO FREGUIA, # PETER AELTERMAN, @ WILLY

VERSTRAETE, @ AND KORNEEL RABAEY @

[18] Microbial Fuel Cells: A Source of Bioenergy Anand Parkash* Department of

Chemical Engineering, Mehran University of Engineering and Technology, Jamshoro,

Pakistan

[19] Microbial Fuel Cells: Electricity Generation from Organic Wastes by Microbes Kun

Guoa, Daniel J. Hassettb, and Tingyue Guc

[20] Working with Boost Converters Application Report SNVA731–June 2015

[21] LTC3108 - Ultralow Voltage Step-Up Converter and Power Manager

[22] bq25505 Ultra Low-Power Boost Charger with Battery Management and

Autonomous Power Multiplexer for Primary Battery in Energy Harvester Applications

[23] Microbiology: A Text-Book of Microorganisms, General and Applied by Charles

Edward Marshall Published 1911

[24] DC/DC Book of Knowledge Practical tips for the User by Steve Roberts, M.Sc.

B.SC Technical Director, RECOM First Edition © 2014 All rights RECOM Engineering

GmbH & Co KG, Austria



[25] Linear Technology LTC3108 Ultralow Voltage step up converter and power

management

Documents

Sustainable energy generation by bio fuel cell from septic ...€¦ · A prototype cell was fabricated and tested by polarization. It is found that the voltage gain is 0.59 V