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VISVESVARAYA TECHNOLOGICAL UNIVERSITY

“Jnana Sangam”, Belgaum-590018

Student Project Programme- 39S_BE_0239

A Project report on

“OPTIMISATION OF FOOD-WASTE BASED BIOGAS DIGESTER

AND ITS IMPLEMENTATION IN RURAL AREAS”

Submitted to the Visvesvaraya Technological University, Belgaum.

In partial fulfilment for the award of the degree of

BACHELOR OF ENGINEERING IN CIVIL ENGINEERING

For the Academic year- 2015-2016

Submitted By

MR. BLESSON USN: 4SF12CV020

MR. NIRMITH ASHOK BANGERA USN: 4SF13CV027

MR. KOUSHIK M USN: 4SF13CV056

MR. ARTHIK RAI USN: 4SF13CV022

SPP coordinator Project Guides

Dr. Manjappa S. Dr. Prasanna Kumar. C Ms. Rashmishree K. N.

Director, Research and

Consultancy

Sahyadri College of Engineering

and Management

Associate Professor

Department of Electronic

and Communication

Engineering

Assistant Professor

Department of Civil

Engineering

Sahyadri College of Engineering and Management

Adyar, Mangalore-575007

SAHYADRI COLLEGE OF ENGINEERING AND MANAGEMENT

Adyar, Mangalore-575007

DEPARTMENT OF CIVIL ENGINEERING

CERTIFICATE

Certified that the project work entitled “OPTIMISATION OF FOODWASTE BASED

BIOGAS DIGESTER AND ITS IMPLEMENTATION IN RURAL AREAS” carried out

by MR. BLESSON S(4SF12CV020), MR. NIRMITH ASHOK

BANGERA(4SF13CV027), MR KOUSHIK M(4SF13CV056) and MR. ARTHIK

RAI(4SF13CV022) are bonafide students of Department of Civil Engineering,

Sahyadri College of Engineering and Management in partial fulfilment for the award of

Bachelor of Engineering in Civil Engineering of the Visvesvaraya Technological

University, Belgaum during the year 2015-2016. It is certified that all correction/suggestions

indicated for Internal Assessment have been incorporated in the Report deposited in the

department library. The project report has been approved as it satisfies the academic

requirements in respect of Project work prescribed for the said Degree.

Prof. Purushothama C T Dr. U M Bhushi

Head of the Dept. Principal

Dr. Prasanna Kumar. C Ms. Rashmishree. K.N

Project guide Project guide

OPTIMISATION OF BIOGAS PRODUCTION BY THREE STAGED DIGESTER

ACKNOWLEDGEMENT

The gratified feeling that we share at the completion of our project work is the

courtesy of those who were involved in our efforts to bring out a successful project

“OPTIMISATION OF FOODWASTE BASED BIOGAS DIGESTER AND

ITS IMPLEMENTATION IN RURAL AREAS”.

We salute our esteemed institution Sahyadri, Adyar which will shape us to

effective engineers of tomorrow. We express our deep sense of gratitude to

department of CIVIL Engineering, which is providing us a homely atmosphere to

develop our all-around skills.

We are grateful to Dr. U M Bhushi, Principal, SCEM, for having extended all

facilities to make this project a grand success.

Our sincere thanks to our respected SPP Coordinator Dr. S Manjappa, Director of

Research and Consultancy, SCEM for his valuable suggestions and providing all

facilities to carry out the project.

We are also grateful to Prof. Purushothama C T, Head of the department, Civil

engineering, and Prof. Umesh S, head of the department, M.Tech Civil, SCEM for

their constant support throughout the project.

We are grateful to Dr. Prasanna Kumar. C, Associate Professor, Department of

E&C Engineering and Ms. Rashmishree K. N., Department of Civil Engineering,

SCEM for their co-operation and guidance at each stage of the project.

Our sincere gratitude to Dr. Gautham P Jeppu, for his guidance and support

throughout the project. His encouragement and inspiration was guiding source

throughout the project work. We are also thankful to Dr. Savitha M, Ms. Sharadha,

(Department of Chemistry, SCEM), Mrs. Ranjini(Headmistress, Govt. School,

Nekkilady), Mrs. Sevrin(Asst. Teacher, Govt. School, Nekkilady) and Edison

Project Team for helping us throughout the project.

Finally we are ever grateful to our parents, teaching and non-

teaching staff members of civil engineering department and

friends for their encouragement, suggestions and help.


Sahyadri College of Engineering and Management Page 2

INDEX

Chapters Title Page No. 1. Introduction 3-5 2. Literature Review 6-8

3. Biogas 9-12 4. Design of Digester 13-16 5. Principles for the production of biogas 17-20 6. Tests, observation and results 21-23

7. Conclusion 24 8. Scope for future work 25 9. References 26-27



CHAPTER-1

INTRODUCTION

1.1 GENERAL

Due to scarcity of supply of petroleum and coal and its threats by emissions

has led to research throughout the world in different corners to get access to the

new sources of energy, like renewable energy resources. Solar energy, wind

energy, different thermal and hydro sources of energy, biogas etc. are all renewable

energy resources. But, biogas is distinct from other renewable energies because of

its characteristics of using, controlling and collecting organic wastes and at the

same time producing fertilizer and water for use in agricultural irrigation. Biogas

neither has any geographical limitations nor does it require any advanced

technology for producing energy. It is very simple to use and apply.

A biogas plant is an anaerobic digester that produces biogas from animal,

food waste or plant waste. Biogas can provide a clean, easily controlled source of

renewable energy from organic waste materials for a small labour input, replacing

firewood or fossil fuels (which are becoming more expensive as supply falls

behind demand). Biogas is generated when bacteria degrade biological material in

the absence of oxygen, in a process known as anaerobic digestion. Since biogas is

a mixture of methane (also known as marsh gas or natural gas, CH4) and carbon

dioxide it is a renewable fuel produced from waste treatment. Food waste is the

best feedstock for biogas production. It is 20times more efficient than conventional

methods of using cow dung and pig wastes.

Biogas does not require any new technology as it is a natural process. But the

optimisation of production can be made by availing proper environment

conditions. Environmental factors temperature, pH, alkalinity, agitation etc. greatly

affect the production of biogas. The mesophilic temperature favours the reaction.

Experiments are made on use of higher temperatures that is thermophilic

temperature for production of biogas and are found effective. Constant stirring

increases the rate of production as the bacteria gets exposed to large area for

decomposing. The pH plays an important role as it should be maintained moderate

for the survival of bacteria.



Considering all these factors a new technique digester designed to optimise

the biogas production. Three staged digester improves agitation process. The pH

was regulated and temperature was monitored to influence bacterial fermentation.

Three staged digester not only provides complete utilisation of food waste. But

also provides stirring effect.

1.2 AIM OF THE STUDY

The main objective of the project was to design a prototype and to study the

efficiency on using a three staged digester for production of biogas with food waste

and also to study the feasibility of implementation in rural areas as a community

reactor.

The project intended in comparing the production of normal digester with the

three staged digester. The aim was to develop a design of biogas digester for a

school in rural area, a community reactor to propose a disposal management

system for food waste.

1.3 OBJECTIVES

The objectives of our project are listed below-

To design two prototype biogas digesters and test them for biogas

production from food waste.

To study the production of biogas with normal digester and a three staged

digester.

To quantify the biogas produced with both normal and three staged digester

and thus obtaining the biogas yield at constant percentage of feedstock for

both prototypes.

To optimize the production of biogas using higher temperature with heat

exchanger.

To regulate the pH of slurry in the digester and thus promoting bacterial

activity.

To obtain the efficiency of using a three staged digester over normal

digester.

To survey a rural area and develop a design a biogas digester design by

considering yield and food waste produced.



1.4 METHODOLOGY

1. A normal biogas digester was designed and it was fed with constant

feedstock of 0.2% the size of the digester.

2. The gas produced was quantified daily and the conditions like pH and

temperature were regulated.

3. The yield per 100L size of the digester was calculated.

4. A new technique three-staged digester was designed and even that was fed

constantly with 0.2% the size of the digester.

5. The yield produced was quantified daily and yield for 100litre size of the

digester were calculated.

6. From the results the optimisation by using the three staged digester were

studied.

7. A survey was made on quantity of food waste produced in Nekkilady

village, near Uppinangady.

8. The quantity of LPG cylinders used and the waste produced in college were

studied.

9. Based on the results a digester was designed for the school which would

replace the use of LPG completely.

1.5 SOURCES OF INFORMATION

ARTI

GOOGLE

HANDBOOK OF BIOGAS UTILIZATION.

ENCYCLOPEDIA OF PHYSICAL SCIENCE AND TECHNOLOGY.

BIOGAS THESIS

JOURNALS

DOCUMENTS FROM OFFICE OF THE SCHOOL.



CHAPTER-2

LITERATURE REVIEW

2.1 INTRODUCTION

Food waste is a very good feedstock for biogas production. It is 20 times

more efficient than the conventional methods of using cow dung. Multi-stage

anaerobic digestion has the advantage of achieving superior performance compared

with single-stage conventional digestion. The multi-stage process is capable of a

higher volatile solids (VS) reduction with shorter residence times, production of

biogas of higher quality, and elimination of foaming. The purpose of stirring is to

distribute the nutrients in the biogas digester uniformly, to form a suspension of

liquid and solid parts, to avoid sedimentation of particles, to ensure uniform heat

distribution, to prevent foam formation and to enable gas lift from the fermentation

substrate at high dry matter (DM) contents.

2.2 ARTI

Appropriate Rural Technology of India, Pune (2003) has developed a

compact biogas reactor which uses waste food rather than any cow dung as

feedstock, to supply biogas for cooking. Dr. Anand Karve (ARTI) developed a

compact biogas system that uses starchy or sugary feedstock (waste grain flour,

spoilt grain, overripe or misshapen fruit, nonedible seeds, fruits and rhizomes,

green leaves, kitchen waste, leftover food, etc.). Just 2 kg of such feedstock

produces about 500 g of methane, and the reaction is completed with 24 hours. The

conventional biogas systems of cattle dung, sewerage, etc. use about 40 kg of

feedstock to produce the same quantity of methane and it requires about 40 days

for completing the reaction. Thus, from the point of view of conversion of

feedstock into methane, the system developed by Dr. Anand Karve is 20 times as

efficient as the conventional system, and from the point of view of reaction time, it

is 40 times as efficient. Thus, overall, the new system is 800 times as efficient as

the conventional biogas system.

2.3 SHALINI SINGH

Shalini Singh (2000) studied the increased biogas production using microbial

stimulants. They studied the effect of microbial stimulant aquasan and teresan on

biogas yield from cattle dung and combined residue of cattle dung and kitchen

waste respectively. The result shows that dual addition of aquasan to cattle dung on



day 1 and day 15 increased the gas production by 55% over unamended cattle dung

and addition of teresan to cattle dung kitchen waste (1:1) mixed residue 15%

increased gas production.

2.4 WASTEWATER INNOVATION- TDS-BIO-06-2015

Anaerobic digestion, a widely used biological process for treating wastewater

solids, refers to the process of converting organic matter into methane and carbon

dioxide through the help of anaerobic bacteria. There are three distinct steps during

anaerobic digestion, with each performed by a different group of microorganisms:

Hydrolysis,

Volatile acid fermentation

Methane formation.

Temperature and the amount of time the process is allowed to react define the

efficiency of each step. Multi-stage anaerobic digestion systems can be utilized for

all wastewater treatment systems, either new installations or retrofits. The only

requirement needed would be that the solids delivered to the system should be of

acceptable levels of concentration. For most wastewater solids and for all loading

rates, multi-stage anaerobic digestion has the advantage of achieving superior

performance compared with single-stage conventional digestion. The performance

increase is achieved even with smaller digester volumes because of the higher

loading rates that can be achieved with multi-stage digesters. The multi-stage

process is capable of a higher volatile solids (VS) reduction with shorter residence

times, production of biogas of higher quality, and elimination of foaming.

2.5 LISSENS

Lissens (2004) completed a study on a biogas operation to increase the total

biogas yield from 50% available biogas to 90% using several treatments including:

a mesophilic laboratory scale continuously stirred tank reactor, an up flow biofilm

reactor, a fiber liquefaction reactor releasing the bacteria Fibrobacter succinogenes

and a system that adds water during the process. These methods were sufficient in

bringing about large increases to the total yield. However, the study was under a

very controlled method, which leaves room for error when used under varying

conditions.

2.6 HANS–JOACHIM NAGELE, JANA SONDERMAN

A unique probe sampling system has been developed that allows probe

sampling from the top of the concrete roof into different parts and heights of the

digester. The samples were then analysed in the laboratory for natural fatty acids

concentrations. Three different agitation setups were chosen for evaluation at

continuous stirring and feeding procedures. The results showed that the analysis



approach for agitator optimization through direct measurement of the nutrients

distribution in the digester is promising. The type of the agitators and the agitation

regime showed significant differences on local concentrations of organic acids,

which are not correlated to the dry matter content. Simultaneous measurements on

electric energy consumption of the different agitator types verify that by using the

slow-moving incline agitator with large propeller diameters in favour of the fast-

moving submersible mixer with smaller propeller diameters, the savings potential

rises up to 70% by maintaining the mixing quality.

2.7 JANTSCH AND MATTIASSON

Jantsch and Mattiasson (2004) discuss how anaerobic digestion is a suitable

method for the treatment of wastewater and organic wastes, yielding biogas as a

useful by-product. However, due to instabilities in start-up and operation it is often

not considered. A common way of preventing instability problems and avoiding

acidification in anaerobic digesters is to keep the organic load of the digester far

below its maximum capacity. There are a large number of factors which affect

biogas production efficiency including: environmental conditions such as pH,

temperature, type and quality of substrate; mixing; high organic loading; formation

of high volatile fatty acids; and inadequate alkalinity.

2.8 TALEGHANI AND KIA

Taleghani and Kia, (2005) outlined the economic, and social benefits of

biogas production.

The economic benefits were as follows:

1. Treatment of solid waste without long-term follow-up cots usually due to soil

and water pollution.

2. Increased local distribution of fertilizer, chemical herbicides, and pesticide

demand. Generation of income through compost and energy sales

(biogas/electricity/heat) to the public grid.

3. Improved soil/agriculture productivity through long-term effects on soil

structure and fertility through compost use.

4. Reduction of landfill space and consequently land costs.

The social and health effects associated with biogas include:

1. Creation of employment in biogas sector.

2. Improvement of the general condition of farmers due to the local availability of

soil improving fertilizer.

3. Decreased smell and scavenger rodents and birds.



CHAPTER- 3

BIOGAS

3.1 COMPOSITION OF BIOGAS

BIOGAS is produced by bacteria through the bio-degradation of organic

material under anaerobic conditions. Natural generation of biogas is an important

part of bio-geochemical carbon cycle. It can be used both in rural and urban areas.

Table 3.1- Composition of biogas.

Component Concentration (by volume)

Methane (CH4) 55-60 %

Carbon dioxide (CO2) 35-40 %

Water (H2O) 2-7 %

Hydrogen sulphide (H2S) 20-20,000 ppm (2%)

Ammonia (NH3) 0-0.05 %

Nitrogen (N) 0-2 %

Oxygen (O2) 0-2 %

Hydrogen (H) 0-1 %

3.2 CHARACTERISTICS OF BIOGAS

Composition of biogas depends upon feed material also. Biogas is about 20%

lighter than air has an ignition temperature in range of 650 to 750 °C. Biogas is an

odorless & colorless gas that burns with blue flame similar to LP gas. Its calorific

value is 22 Mega Joules (MJ) /m3 and it usually burns with 60% efficiency in a

conventional biogas stove. Biogas digester systems provides a residue organic

waste, after its anaerobic digestion(AD) that has superior nutrient qualities over

normal organic fertilizer, as it is in the form of ammonia and can be used as

manure. Anaerobic biogas digesters also function as waste disposal systems,

particularly for human wastes, and can, therefore, prevent potential sources of

environmental contamination and the spread of pathogens and disease causing

bacteria. Biogas technology is particularly valuable in agricultural residual

treatment of animal excreta and kitchen refuse (residuals).



3.3 FACTORS AFFECTING YIELD AND PRODUCTION OF BIOGAS

Many factors affecting the fermentation process of organic substances under

anaerobic condition are,

The quantity and nature of organic matter

The temperature

Acidity and alkalinity (pH value) of substrate

The flow and dilution of material

Table 3.2 GENERAL FEATURES OF BIOGAS

Energy Content 6-6.5 kWh/ m3

Fuel Equivalent 0.6-0.65 l oil/ m3 biogas

Explosion Limits 6-12 % biogas in air

Ignition Temperature 650-750 °C

Critical Pressure 75-89 bar

Critical temperature -82.5 °C

Normal Density 1.2 kg/ m3

Smell Bad eggs

3.4 PROPERTIES OF BIOGAS

1. Change in volume as a function of temperature and pressure.

2. Change in calorific value as function of temperature, pressure and water vapor

content.

3. Change in water vapor as a function of temperature and pressure.

3.5 MECHANISM OF BIOGAS FERMENTATION

A) Group of biogas microbes: Fig-3.1

Biogas microbes

Non methane Methane

Fermentative bacteria Hydrogen producing acetogenic

bacteria



B) Group of microbes involved in 3 stages of biogas fermentation

1st stage: Fermentative bacteria:-

Saccharides amino acids Fatty acids

Fig. 3.2

2nd

stage: - Hydrogen producing acetogenic bacteria

Fig. 3.3

3rd

stage: - Methane producing bacteria

Fig. 3.4

3.6 BENEFITS OF BIOGAS TECHNOLOGY

Production of energy.

Transformation of organic wastes to very high quality fertilizer.

Improvement of hygienic conditions through reduction of pathogens.

Environmental advantages through protection of soil, water, air etc.

Micro-economic benefits by energy and fertilizer substitutes.

Macro-economic benefits through decentralizes energy generation and

environmental protection.

Cellulose decomposing

bacteria

Protein decomposing

bacteria

Fat decomposing

bacteria

Hydrolyze and Ferments organic substance

Volatile acid (H2 & CO2)

Decompose the substance

produced in 1st stage

Acetic bacteria

Convert the substance

produced in 1st & 2nd stage

CH4 & CO2



3.7 COMPARISON WITH THE CONVENTIONAL SYSTEMS

The current practice of using low calorie inputs like cattle dung, distillery

effluent, municipal solid waste, or sewerage, makes methane generation in

conventional biogas reactors highly inefficient. Through this compact system, it

has been demonstrated that by using feedstock having high calorific and nutritive

value to microbes, the efficiency of methane generation can be increased by

several orders of magnitude. Operating the system on this simple tenet also brings

in many more advantages over the conventional systems: As a result of the higher

efficiency, the size and cost of the new system are also lower. While the

conventional biogas system occupies about 4 cubic meters of space, the compact

ARTI biogas system is about as large as a domestic refrigerator. It is an extremely

user friendly system, because it requires daily only a couple of kg feedstock, and

the disposal of daily just 5 litres of effluent slurry.



CHAPTER- 4

DESIGN OF DIGESTER

4.1 SURVEY ON QUANTITY OF FOOD WASTE PRODUCED

Nekkilady, a village nearby Uppinangady, Puttur taluk, Dakshina Kannada

was selected for the study on implementation in rural areas. The study was based

on the area of interest near the Government school of Nekkilady. Nearly 50 houses

were surveyed for the quantity of food waste produced. At an average of

0.5kg/house of food waste is produced daily. One more survey was done on the

amount of food waste produced in the school. There is a production of about 3kg

of food waste per day. Around 2 LPG cylinders are used per month which accounts

to a daily usage 1L of LPG.



4.2 FABRICATION OF NORMAL DIGESTER

A prototype metal digester of 24L capacity was fabricated for the

quantification of biogas in single staged digester. It was metal fabricated digester

of dimensions 30cm diameter and height 34cm. the digester had an inlet pipe of

5cm diameter. Outlet pipe of size 4cm was used. The digester was a fixed dome

digester and rubber tubes were used for collection of gas. A gas outlet of 1.25cm

diameter was used.

The digester was initially fed with cow dung for start-up process and after one

week it started giving flammable gas. From seventh day after start-up it was fed

constantly with food waste at 0.2% the size of the digester that is 48g. The gas

produced was quantified daily by water displacement method.

Metal fabricated digester- Prototype of Normal Digester



4.3 FABRICATION OF THREE STAGED DIGESTER

A 30L metal fabricated digester with three stages was used as another

prototype. The digester had three compartments occupying same volume. The

digester was proposed in order to offer agitation by offering movement of slurry.

The compartments were separated by three metal sheets welded at the centre to a

metal pipe and at the periphery to the cylinder. The metal sheets had openings for

the flow of slurry the first chamber had the inlet fixed to it. Inlet was a 4cm

diameter metal pipe. The third chamber had the outlet for digested slurry of the

same size as inlet pipe. The openings in the chambers were provided such that after

the complete digestion period in first chamber it would flow to second chamber

and so on to the third chamber. The whole cylinder had cone shaped top for the

allowance of flow of gas to the gas outlet. The gas outlet was of 1.25cm diameter

size.

Chamber 2 Chamber 1

Chamber 3



4.4 COMPARISON BETWEEN NORMAL DIGESTER AND THREE

STAGED DIGESTER

The gas produced in both the digesters was quantified. After the 30th

day gas

production was stable. At this point the gas produced for 100L size of the digester

was calculated. The gas production varies with the size of the digester. So the

calculations were made for 100L size of the digester. The three staged digester

provides more time for decomposition and also provides stirring effect.



CHAPTER- 5

PRINCIPLES FOR THE PRODUCTION OF BIOGAS

5.1 PRODUCTION PROCESS

A typical biogas system consists of the following components:

I. Manure collection

II. Anaerobic digester

III. Effluent storage

IV. Gas handling

V. Gas use

Biogas is a renewable form of energy. Methanogens (methane producing

bacteria) are last link in a chain of microorganisms which degrade organic material

and returns product of decomposition to the environment.

Fig.5.1 Production Process



5.2 PRINCIPLES FOR THE PRODUCTION OF BIOGAS

Organic substances exist in wide variety from living beings to dead

organisms. Organic matters are composed of Carbon (C), combined with elements

such as Hydrogen (H), Oxygen (O), Nitrogen (N), and Sulphur (S) to form variety

of organic compounds such as carbohydrates, proteins & lipids. In nature MOs

(microorganisms), through digestion process breaks the complex carbon into

smaller substances.

There are 2 types of digestion process:

(1) Aerobic digestion

(2) Anaerobic digestion

5.3 AEROBIC DIGESTION

The digestion process occurring in presence of Oxygen is called Aerobic

digestion and produces mixtures of gases having carbon dioxide (CO2), one of the

main “greenhouse gasses” responsible for global warming. The digestion process

occurring without (absence) oxygen is called anaerobic digestion which generates

mixtures of gases. The gas produced which is mainly methane produces 5200-5800

KJ/m3 which when burned at normal room temperature and presents a viable

environmentally friendly energy source to replace fossil fuels (non-renewable).

5.4 ANAEROBIC DIGESTION

It is also referred to as Bio-Methanisation, is a natural process that takes place

in absence of air (oxygen). It involves biochemical decomposition of complex

organic material by various biochemical processes with release of energy rich

biogas and production of nutritious effluents.

Fig. 5.2 Anaerobic Digestion



5.5 BIOLOGICAL PROCESS

I. HYDROLYSIS

II. ACIDIFICATION

III. METHANOGENESIS

5.5.1 HYDROLYSIS:

In the first step the organic matter is acted upon externally by extracellular

enzymes, cellulose, amylase, protease & lipase, of microorganisms. Bacteria

decompose long chains of complex carbohydrates, proteins, & lipids into small

chains. For example, Polysaccharides are converted into monosaccharide. Proteins

are split into peptides and amino acids.

5.5.2 ACIDIFICATION:

Acid-producing bacteria, involved this step, convert the intermediates of

fermenting bacteria into acetic acid, hydrogen and carbon dioxide. These bacteria

are anaerobic and can grow under acidic conditions. To produce acetic acid, they

need oxygen and carbon. For this, they use dissolved O2 or bounded-oxygen.

Hereby, the acid-producing bacteria create anaerobic condition which is essential

for the methane producing microorganisms. Also, they reduce the compounds with

low molecular weights into alcohols, organic acids, amino acids, carbon dioxide,

hydrogen sulphide and traces of methane. From a chemical point, this process is

partially endergonic (i.e. only possible with energy input), since bacteria alone are

not capable of sustaining that type of reaction.

5.5.3 METHANOGENESIS: (Methane formation)

Methane-producing bacteria, which were involved in the third step,

decompose compounds having low molecular weight. They utilize hydrogen,

carbon dioxide and acetic acid to form methane and carbon dioxide. Under natural

conditions, CH4 producing microorganisms occur to the extent that anaerobic

conditions are provided, e.g. under water (for example in marine sediments), and in

marshes. They are basically anaerobic and very sensitive to environmental

changes, if any occurs. The methanogenic bacteria belong to the archaebacter

genus, i.e. to a group of bacteria with heterogeneous morphology and lot of

common biochemical and molecular-biological properties that distinguishes them

from other bacteria. The main difference lies in the makeup of the bacteria’s cell

walls.



5.6 SYMBIOSIS OF BACTERIA

Methane and acid-producing bacteria act in a symbiotically. Acid producing

bacteria create an atmosphere with ideal parameters for methane producing

bacteria (anaerobic conditions, compounds with a low molecular weight). On the

other hand, methane-producing microorganisms use the intermediates of the acid

producing bacteria. Without consuming them, toxic conditions for the acid-

producing microorganisms would develop. In real time fermentation processes the

metabolic actions of various bacteria acts in a design. No single bacteria are able to

produce fermentation products alone as it requires others too.



CHAPTER- 6

TESTS, OBSERVATIONS AND RESULTS

6.1 SURVEY AT RURAL AREA

The place selected for survey was 34th

Nekkilady, Uppinangady, Dakshina

Kannada. The region under consideration of Nekkilady was located. Based on the

documents from school office houses to be surveyed were taken into consideration

the school region covered 1126 houses.

PARTICULARS NUMBERS UNITS

Total number of students in school 77

Number of cylinders used 2 /month

0.067 /day

Waste produced in school 3 kg/day

Number of houses under school 1126

Number of houses surveyed 50

Waste produced in houses 0.5 kg/day

Total Quantity of food waste 25 kg

28 kg/day

The volume of digester required 14 m3

The digester produces sufficient gas for the complete replacement of LPG. In

addition to this extra gas is produced which can be used for other purposes. The

system can also be used to generate sufficient electricity to run the school. Design

calculations are given below.

6.2 COMPARISON BETWEEN NORMAL AND THREE STAGED

DIGESTER

GAS PRODUCED FOR 100L

DAYS GAS PRODUCED SIZE OF THE DIGESTER

NORMAL THREE STAGED

NORMAL THREE STAGED

1 0.425 0.860 1.771 2.867

2 0.575 1.160 2.396 3.867

3 0.865 1.750 3.604 5.833

4 1.000 2.000 4.167 6.667

5 1.150 2.300 4.792 7.667

6 1.250 2.500 5.208 8.333



7 1.300 2.550 5.417 8.500

8 1.450 2.800 6.042 9.333

9 2.200 3.800 9.167 12.667

10 3.000 5.800 12.500 19.333

11 3.800 7.700 15.833 25.667

12 4.675 9.300 19.479 31.000

13 4.800 9.700 20.000 32.333

14 5.000 10.200 20.833 34.000

15 5.600 11.200 23.333 37.333

16 5.700 11.500 23.750 38.333

17 5.850 11.750 24.375 39.167

18 6.000 12.050 25.000 40.167

19 7.000 14.000 29.167 46.667

20 7.500 15.100 31.250 50.333

21 8.100 16.300 33.750 54.333

22 8.800 17.650 36.667 58.833

23 8.900 17.800 37.083 59.333

24 9.000 18.200 37.500 60.667

25 9.100 18.300 37.917 61.000

26 9.500 19.100 39.583 63.667

27 10.000 20.200 41.667 67.333

6.3 REPRESENTATIVE GRAPH

FIG- 6.1- Graph showing the production of gas daily

0.000

5.000

10.000

15.000

20.000

25.000

0 5 10 15 20 25 30

Gas

pro

du

ced

in L

Days

GAS PRODUCTION

Normal Digester

Three stagedDigester



6.4 DESIGN OF BIOGAS DIGESTER FOR SCHOOL.

PARTICULARS UNITS

Volume of the digester required (28kg food waste) 14 m3

Total volume (assuming volume of partition walls) 15 m3

Depth of the digester 2.5 M

Inner diameter of the digester 2.7 M

3 M

Assuming 0.15m thick concrete cylinder Total volume 3.3 M

Gas collector dome volume 8.4 m3

As storage cylinders shall be used provide

Provide 30% size of the collector dome

2.52~

2.6

m3

Diameter shall be little less than the digester 2.4 M

Depth of collecting dome 1.72 M

6.5 COST ANALYSIS

Particulars Quantity Unit

Earthwork involved 23.95 m3

Cost involved in earthwork (Rs. 350/m3) 8382.5 Rs

Concrete volume 7.27 m3

Cost of concrete(Rs. 775/m3) 5634.25 Rs

Cost for metal dome 10000 Rs

Miscellaneous (collector system & piping) 30000 Rs

Total cost 54100 Rs

Savings per year (2*12*1000) 24000 Rs/year

Payback duration 2.3 Years

0.000

10.000

20.000

30.000

40.000

50.000

60.000

70.000

80.000

0 5 10 15 20 25 30

Gas

pro

du

ctio

n in

L f

or

10

0L

Dig

est

er

Days

Gas production for 100L size of Digester

Normal Digester

Three stagedDigester



CHAPTER- 7

CONCLUSION

• Biogas is a clean renewable source of energy and hence its substitution for

LPG will help in reducing greenhouse gas emissions.

• Food waste is a very good substitute for L P G because India is self-reliant in

food production and crude oil is imported.

• Three staged digester efficiently uses all the waste and produces more gas.

• The production can be increased by 25% if a conventional digester produces

42L of gas, three staged digester produces 67L gas.

• The three staged digester not only provides more time for digestion. But it also

provides stirring effect.

• The new technique digester developed is efficient than conventional reactors.

The effluent is completely digested and the gas production will be optimum.

• The gas produced is sufficient for the use in school for midday-meals. And

extra gas that is produced can be stored and supplied for nearby restaurants or

houses.

• A regular feeding of biogas reactor with proper amount will ensure consistent

release of biogas and ensures uninterrupted production of gas.

• Crushed and blended food improves the liberation of biogas as digestion

becomes easy.

• Underfeeding or overfeeding of reactor should be avoided. Underfeeding keeps

the reactor inefficient and overfeeding increases the pH value of food waste

and reduces the development of microbes.

• Payback period is small. Hence it can be adopted in all the rural places.



CHAPTER- 8

SCOPE FOR FUTURE WORK

The scarcity of petroleum and increased use of LPG have given rise for the

alternative fuel technology. And hence the scope of developing a biogas digester is

trending. With the Indian government keen on utilizing renewable resources for

energy production, it is likely that there will be a greater thrust and higher

incentives for concepts such as biogas production from waste. An increasing

awareness among the public regarding sustainable use of resources will only

enhance the production and use of biogas. It can hence be expected that biogas will

have a significant growth in India at all levels of usage (household, municipality

and industry) for both heat generation and electricity production.

It is also possible to earn carbon credits for biogas-based power or heat

generation in India. For instance, in Apr 2008, Andhyodaya, a non-government

agency working in the field of promoting water management and non-conventional

energy and social development distributed the first instalment of the biogas carbon

credit to farmers in the state of Kerala. Andhyodaya had helped construct 15,000

biogas reactors in the state and earned carbon credits. This trend is likely to grow

further.

In sum, India has significant potential for generating heat and electricity from

waste in the form of biogas. While only a portion of the potential has been tapped,

it is likely that more investments in this direction could accelerate exploitation of

this source in future.

The scope also lies in monitoring the factors thus developing a better digester

for effective working of biogas digester. The project can be developed into a better

system by ensuring the proper levels of temperature and pH. The production can be

increased by themophilic temperature. The use of kitchen steam and smoke can be

used to maintain the temperature in rural areas. The gas produced can be purified

in order to increase the calorific value.



CHAPTER- 9

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