Bio gas plant

SHARDA UNIVERSITYGREATER NOIDA

A BRIEF REPORT ON:

BIO GAS PLANTS

PRESENTED BY: PRESENTED TO:

Sumit Vikram Singh (120107234) Dr. Gaurav Saini

Tejash Agarwal (120107242 ) Assistant Professor

Syed Ali, Murtaza (120107239) Sharda University

Syed Aizaz Manzoor (120107238)

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CONTENTS:

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DESCRIPTION

INTRODUCTION

BIO GAS

COMPOSTION

BIO GAS PLANTS

CLASSIFICATION1.Agricultural Bio Gas Plants 1.1 Family scale bio gas plants 1.2 Farm scale bio gas plants 1.3 Centralized co - digestion plants2. Industrial Bio Gas plants3. Landfill Gas recovery plants

SUB CLASSIFICATION1. Fixed Dome type2. Floating drum type3. Low cost polyethylene Tube digestors4. Baloon plants

PROCESS

ANAEROBIC DIGESTION1. Hydrolysis2. Acidogenesis3. Acetogenesis4. Methanogenesis

ANAEROBIC DIGESTION PARAMETERS

ADVANTAGES OF BIO GAS TECHNOLOGIES

BENEFITS TO THE FARMERS

BENEFITS OF ANAEROBIC DIGESTION

CONCLUSION

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INTRODUCTION:

One of the main environmental problems of today’s society is the continuously increasing production

of organic wastes. In many countries, sustainable waste management as well as waste prevention and

reduction have become major political priorities, representing an important share of the common

efforts to reduce pollution and greenhouse gas emissions and to mitigate global climate changes.

Uncontrolled waste dumping is no longer acceptable today and even controlled landfill disposal and

incineration of organic wastes are not considered optimal practices.

Production of biogas through anaerobic digestion (AD) of animal manure and slurries as well as of a

wide range of digestible organic wastes, converts these substrates into renewable energy and offers a

natural fertiliser for agriculture sites. Anaerobic Digestion is a microbiological process of

decomposition of organic matter, in the absence of oxygen, common to many natural environments

and largely applied today to produce biogas in airproof reactor tanks, commonly named digesters. A

wide range of micro-organisms are involved in the anaerobic process which has two main end

products: biogas and digestate. Biogas is a combustible gas consisting of methane, carbon dioxide and

small amounts of other gases and trace elements. Digestate is the decomposed substrate, rich in

macro- and micro nutrients and therefore suitable to be used as plant fertiliser.

India is implementing one of the World’s largest programmes in renewable energy. The country ranks

second in biogas utilization. Biogas can be generated and supplied round the clock in contrast to solar

and wind, which are intermittent in nature. Biogas plants provide three-in-one solution of gaseous fuel

generation, organic manure production and wet biomass waste disposal/management.

Biogas is a product of bio-methanation process when fermentable organic materials such as cattle

dung, kitchens waste, poultry droppings, night soil wastes, agricultural wastes etc. are subjected to

anaerobic digestion in the presence of methanogenic bacteria. This process is better as the digested

slurry from biogas plants is available for its utilization as bio/organic manure in agriculture,

horticulture and pisciculture as a substitute/supplement to chemical fertilizers.

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BIO GAS:

Biogas typically refers to a mixture of gases produced in result of breakdown of organic matter by the

process of anaerobic fermentation. Biogas can be produced from raw materials such as agricultural

waste, manure, municipal waste, plant material, sewage, green waste or food waste. It is a renewable

energy source and in many cases exerts a very small carbon footprint. Biogas comprises of 60-65%

methane, 35-40% carbon dioxide, 0.5-1.0% hydrogen sulphide, rests of water vapors etc. Biogas is

non-toxic, color less and flammable gas. It has an ignition temperature of 650 - 7500C. Its density is

1.214kg/ m3 (assuming about 60% Methane and 40% CO2). Its calorific value is 20 MJ/m3 (or 4700

kcal.). It is almost 20% lighter than air. Biogas, like Liquefied Petroleum Gas (LPG) cannot be

converted into liquid state under normal temperature and pressure. It liquefies at a pressure of about

47.4 Kg/cm2 at a critical temperature of -82.10c. Removing carbon dioxide, Hydrogen Sulfide,

moisture and compressing it into cylinders makes it easily usable for transport applications & also for

stationary applications. Already CNG technology has become easily available and therefore, bio-

methane (purified biogas) which is nearly same as CNG, can be used for all applications for which

CNG are used. Purified biogas (bio-methane) has a high calorific value in comparison to raw biogas.

COMPOSITION:

Table no 1: Composition of bio gas.

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BIO GAS PLANTS:

A biogas plant is an anaerobic digester that produces biogas from animal wastes or energy crops.

Energy crops are cheap crops grown for the purpose of biofuels, rather than food. The history of

biogas plants goes back to ancient Persia and China. Biogas was used for heating bath water in

Assyria as long as 10th century B.C. .Well documented attempts to harness biogas dates from mid-

19th century in New-Zealand and India. It was observed that rotting vegetables produce flammable

gas. In 13th century the Chinese were using covered sewage tanks to generate power.

CLASSIFICATION:

Bio gas plants can be further divided on the basis of size, purpose and usage. We can classify them

into 3 types.

1. Agricultural Bio Gas Plants

i) Family scale bio gas plants

ii) Farm scale bio gas plants

iii) Centralized joint co-digestion plant

2. Industrial Bio Gas Plants

3. Landfill gas recovery plants

1. AGRICULTURAL BIO GAS PLANTS

The agricultural biogas plants are considered those plants which are processing feedstock of

agricultural origin. The most common feedstock types for this kind of plants are animal

manure and slurries, vegetable residues and vegetable by products, dedicated energy crops

(DEC), but also various residues from food and fishing industries etc

1.1 FAMILY SCALE BIO GAS PLANTS

In countries like Nepal, China or India operate millions of family scale biogas plants, utilising very

simple technologies. The AD feedstock used in these biogas plants originate from the household

and/or their small farming activity and the produced biogas is used for the family cooking and lighting

needs .The digesters are simple, cheap, robust, easy to operate and maintain, and can be constructed

with local produced materials. Usually, there are no control instruments and no process heating

(psychrophilic or mesophilic operation temperatures), as many of these digesters operate in warmer

climates and have long HRT.

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a) The Chinese type (Figure 4.1a) is an underground reactor of typically 6 to 8 m³. It is supplied

with household sewage, animal manure and organic household waste. The reactor is operated

in a semi-continuous mode, where new substrate is added once a day and a similar amount of

decanted mixed liquid is removed once a day. The reactor is not stirred, so the sedimentation

of suspended solids must be removed 2-3 times per year, occasion when a large portion of the

substrate is removed and a small part (about one fifth of the reactor content) is left as

inoculum.

b) The Indian type (Figure 4.1b) is similar to the Chinese type as it is a simple underground

reactor for domestic and small farming waste. The difference is that the effluent is collected at

the bottom of the reactor and a floating gas bell functions as a biogas reservoir.

c) Another small scale biogas plant is the displacement type, which consists of a horizontal

cylindrical reactor. The substrate is fed at one end and the digestate is collected at the

opposite end. The substrate moves through the reactor as a plug flow, and a fraction of the

outlet is re-circulated to dilute the new input and to provide inoculation.

Fig no 1: a) Chinese type b) Indian type

1.2 FARM SCALE BIO GAS PLANTS

A farm scale biogas plants is named the plant attached to only one farm, digesting the feedstock

produced on that farm. Many farm scale plants co-digest also small amounts of methane rich

substrates (e.g. oily wastes from fish industries or vegetable oil residues), aiming to increase the

biogas yield. It is also possible that a farm scale biogas plant receives and processes animal slurries

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from one or two neighboring farms (e.g. via pipelines, connecting those farms to the respective AD

unit). There are many types and concepts of farm scale biogas plants around the world. In Europe,

countries like Germany, Austria and Denmark are among the pioneers of farm scale biogas

production.

Fig no 2: Schematic representation of farm scale plant

1.3 CENTRALIZED JOINT CO-DIGESTION PLANT

Centralized co-digestion is a concept based on digesting animal manure and slurries, collected from

several farms, in a biogas plant centrally located in the manure collection area. The central location of

the biogas plant aims to reduce costs, time and manpower for the transport of biomass to and from the

biogas plant. Centralized AD plants co-digest animal manure with a variety of other suitable co-

substrates (e.g. digestible residues from agriculture, food- and fish industries, separately collected

organic household wastes, sewage sludge). The centralized co-digestion plants (also named joint co-

digestion plants) were developed and are largely applied in Denmark, but also in other regions of the

world, with intensive animal farming.

Fig no 3: Image of a joint co-digestion plant

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2. INDUSTRIAL BIO GAS PLANTS

Anaerobic processes are largely used for the treatment of industrial wastes and waste waters for more

than a century and AD is today a standard technology for the treatment of various industrial waste

waters from food-processing, agro-industries, and pharmaceutical industries. AD is also applied to

pre-treat organic loaded industrial waste waters, before final disposal. Due to recent improvements of

treatment technologies, diluted industrial waste waters can also be digested. Europe has a leading

position in the world regarding this application of AD. In recent years energy considerations and

environmental concerns have further increased the interest in direct anaerobic treatment of organic

industrial wastes and the management of organic solid wastes from industry is increasingly controlled

by environmental legislations. Industries using AD for wastewater treatment range from:

Food processes: e.g. vegetable canning, milk and cheese manufacture, slaughterhouses, potato

processing industry

Beverage industry: e.g. breweries, soft drinks, distilleries, coffee, fruit juices

Industrial products: e.g. paper and board, rubber, chemicals, starch, pharmaceuticals

3.LANDFILL GAS RECOVERY PLANTS:

Landfills can be considered as large anaerobic plants with the difference that the decomposition

process is discontinuous and depends on the age of the landfill site. Landfill gas has a composition

which is similar to biogas, but it can contain toxic gases, originating from decomposition of waste

materials on the site. Recovery of landfill gas is not only essential for environmental protection and

reduction of emissions of methane and other landfill gases (Figure 4.12), but it is also a cheap source

of energy, generating benefits through faster stabilisation of the landfill site and revenues from the gas

utilisation. Due to the remoteness of landfill sites, landfill gas is normally used for electricity

generation, but the full range of gas utilisation, from space heating to upgrading to vehicle fuel and

pipeline quality is possible as well.

SUB CLASSIFICATION

On the basis of the design as per conditions and liabilities, bio gas plants are further divided into

categories:

Floating drum type

Fixed dome type

Low cost polyethylene tube digestors

Balloon plants

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1. FIXED DOME TYPE

A fixed-dome plant consists of a digester with a fixed, non-movable gas holder, which sits on top of

the digester. When gas production starts, the slurry is displaced into the compensation tank. Gas

pressure increases with the volume of gas stored and the height difference between the slurry level in

the digester and the slurry level in the compensation tank. The costs of a fixed-dome biogas plant are

relatively low. It is simple as no moving parts exist. There are also no rusting steel parts and hence a

long life of the plant (20 years or more) can be expected. The plant is constructed underground,

protecting it from physical damage and saving space.

Fixed dome plants produce just as much gas as floating-drum plants, if they are gas-tight. However,

utilization of the gas is less effective as the gas pressure fluctuates substantially. Burners and other

simple appliances cannot be set in an optimal way. If the gas is required at constant pressure (e.g., for

engines), a gas pressure regulator or a floating gas-holder is necessary.

Gas Holder - The top part of a fixed-dome plant (the gas space) must be gas-tight. Concrete, masonry

and cement rendering are not gas-tight. The gas space must therefore be painted with a gas-tight

layer (e.g. 'Water-proofer', Latex or synthetic paints). A possibility to reduce the risk of cracking of

the gas-holder consists in the construction of a weak-ring in the masonry of the digester. This "ring" is

a flexible joint between the lower (water-proof) and the upper (gas-proof) part of the hemispherical

structure. It prevents cracks that develop due to the hydrostatic pressure in the lower parts to move

into the upper parts of the gas-holder.

Fig no 4: Fixed dome type bio gas plant structure

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Types of Fixed Dome Plants

Chinese fixed-dome plant is the archetype of all fixed dome plants. Several million have

been

constructed in China. The digester consists of a cylinder with round bottom and top.

Janata model was the first fixed-dome design in India, as a response to the Chinese fixed

dome plant. It is not constructed anymore. The mode of construction lead to cracks in the

gasholder -very few of these plant had been gas-tight.

Deenbandhu, the successor of the Janata plant in India, with improved design, was more

crackproof and consumed less building material than the Janata plant. with a hemisphere

digester

Advantages:

Low initial costs and long useful life-span; no moving or rusting parts involved; basic design is

compact, saves space and is well insulated; construction creates local employment.

Advantages are the relatively low construction costs, the absence of moving parts and rusting steel

parts. If well constructed, fixed dome plants have a long life span. The underground construction

saves space and protects the digester from temperature changes. The construction provides

opportunities for skilled local employment. Disadvantages: Masonry gas-holders require special

sealants and high technical skills for gas-tight construction; gas leaks occur quite frequently;

fluctuating gas pressure complicates gas utilization; amount of gas produced is not immediately

visible, plant operation not readily understandable; fixeddome plants need exact planning of levels;

excavation can be difficult and expensive in bedrock.

Disadvantages

Disadvantages are mainly the frequent problems with the gas-tightness of the brickwork gas holder (a

small crack in the upper brickwork can cause heavy losses of biogas). Fixed-dome plants are,

therefore, recommended only where construction can be supervised by experienced biogas

technicians. The gas pressure fluctuates substantially depending on the volume of the stored gas. Even

though the underground construction buffers temperature extremes, digester temperatures are

generally low.

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2. FLOATING DRUM TYPE

Floating-drum plants consist of an underground digester and a moving gas-holder. The gas-holder

floats either directly on the fermentation slurry or in a water jacket of its own. The gas is collected in

the gas drum, which rises or moves down, according to the amount of gas stored. The gas drum is

prevented from tilting by a guiding frame. If the drum floats in a water jacket, it cannot get stuck,

even in substrate with high solid content.

Drum - In the past, floating-drum plants were mainly built in India. A floating-drum plant consists of

a cylindrical or dome-shaped digester and a moving, floating gas-holder, or drum. The gas-holder

floats either directly in the fermenting slurry or in a separate water jacket. The drum in which the

biogas collects has an internal and/or external guide frame that provides stability and keeps the drum

upright. If biogas is produced, the drum moves up, if gas is consumed, the gas-holder sinks back.

Fig no 5: Floating drum type plant representation

Size - Floating-drum plants are used chiefly for digesting animal and human feces on a

continuousfeed mode of operation, i.e. with daily input. They are used most frequently by small- to

middle-sized farms (digester size: 5-15m3) or in institutions and larger agro-industrial estates

(digester size: 20- 100m3).

Material of Digester and Drum

The digester is usually made of brick, concrete or quarry-stone masonry with plaster. The gas drum

normally consists of 2.5 mm steel sheets for the sides and 2 mm sheets for the top. It has welded-in

braces which break up surface scum when the drum rotates. The drum must be protected against

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corrosion. Suitable coating products are oil paints, synthetic paints and bitumen paints. Correct

priming is important. There must be at least two preliminary coats and one topcoat. Coatings of used

oil are cheap.

Types of Floating Drum Plants:

KVIC model with a cylindrical digester, the oldest and most widespread floating

drum biogas plant from India.

Pragati model with a hemisphere digester

Ganesh model made of angular steel and plastic foil

Advantages: Advantages are the simple, easily understood operation - the volume of stored gas is

directly visible. The gas pressure is constant, determined by the weight of the gas holder. The

construction is relatively easy, construction mistakes do not lead to major problems in operation and

gas yield.

Disadvantages: Disadvantages are high material costs of the steel drum, the susceptibility of steel

parts to corrosion. Because of this, floating drum plants have a shorter life span than fixed-dome

plants and regular maintenance costs for the painting of the drum.

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3. LOW COST POLYETHYLENE TUBE DIGESTOR:

Digester - In the case of the Low-Cost Polyethylene Tube Digester model which is applied in Bolivia

(Peru, Ecuador, Colombia, Centro America and Mexico), the tubular polyethylene film (two coats of

300 microns) is bended at each end around a 6 inch PVC drainpipe and is wound with rubber strap of

recycled tire-tubes. With this system a hermetic isolated tank is obtained.

One of the 6" PVC drainpipes serves as inlet and the other one as the outlet of the slurry. In the tube

digester finally, a hydraulic level is set up by itself, so that as much quantity of added prime matter

(the mix of dung and water) as quantity of fertilizer leave by the outlet.

Because the tubular polyethylene is flexible, it is necessary to construct a "cradle" which will

accommodate the reaction tank, so that a trench is excavated.

Fig no 6: Low

cost, economical polyethylene tube digester.

Gas Holder and Gas Storage Reservoir - The capacity of the gasholder corresponds to 1/4 of the total

capacity of the reaction tube. To overcome the problem of low gas flow rates, two 200 microns

tubular polyethylene reservoirs are installed close to the kitchen, which gives a 1,3 m³ additional gas

storage.

4. BALOON PLANTS:

Baloon Plants - A balloon plant consists of a heat-sealed plastic or rubber bag (balloon), combining

digester and gas-holder. The gas is stored in the upper part of the balloon. The inlet and outlet are

attached directly to the skin of the balloon. Gas pressure can be increased by placing weights on the

balloon. If the gas pressure exceeds a limit that the balloon can withstand, it may damage the skin.

Therefore, safety valves are required. If higher gas pressures are needed, a gas pump is required.

Since the material has to be weather- and UV resistant, specially stabilized, reinforced plastic or

synthetic caoutchouc is given preference. Other materials which have been used successfully include

RMP (red mud plastic), Trevira and butyl. The useful life-span does usually not exceed 2-5 years.

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Fig no 7: Image of a low cost balloon type plant

Advantages: Standardized prefabrication at low cost, low construction sophistication, ease of

transportation, shallow installation suitable for use in areas with a high groundwater table; high

digester temperatures in warm climates; uncomplicated cleaning, emptying and maintenance; difficult

substrates like water hyacinths can be used.

Balloon biogas plants are recommended, if local repair is or can be made possible and the cost

advantage is substantial.

Disadvantages: Low gas pressure may require gas pumps; scum cannot be removed during operation;

the plastic balloon has a relatively short useful life-span and is susceptible to mechanical damage and

usually not available locally. In addition, local craftsmen are rarely in a position to repair a damaged

balloon. There is only little scope for the creation of local employment and, therefore, limited selfhelp

potential.

Variations: A variation of the balloon plant is the channel-type digester, which is usually covered

with plastic sheeting and a sunshade. Balloon plants can be recommended wherever the balloon skin

is not likely to be damaged and where the temperature is even and high.

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PROCESS:

The process to produce bio gas in a bio gas plant includes:

1. Transportation

2. Influent collection – Mixing - Pumping

3. Addition of water - Digestion

4. Retention time - Gas production – Gas cleansing

5. Generation of heat and power from bio gas

Fig no 8: Process of bio gas production in a plant.

ANAEROBIC DIGESTION:

Anaerobic digestion is a collection of processes by which microorganisms break

down biodegradable material in the absence of oxygen. The process is used for industrial or domestic

purposes to manage waste and/or to produce fuels. Much of thefermentation used industrially to

produce food and drink products, as well as home fermentation, uses anaerobic digestion.

Anaerobic digestion occurs naturally in some soils and in lake and oceanic basin sediments, where it

is usually referred to as "anaerobic activity".

The four stages of anaerobic digestion involves:

 Hydrolysis, acidogenesis, acetogenesis and methanogenesis. The overall process can be described

by the chemical reaction, where organic material such as glucose is biochemically digested into

carbon dioxide (CO2) and methane (CH4) by the anaerobic microorganisms.

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Fig no 9: All four stages of anaerobic digestion shown in simple flow chart

1. HYDROLYSISIn most cases, biomass is made up of large organic polymers. For the bacteria in anaerobic digesters

to access the energy potential of the material, these chains must first be broken down into their

smaller constituent parts. These constituent parts, or monomers, such as sugars, are readily available

to other bacteria. The process of breaking these chains and dissolving the smaller molecules into

solution is called hydrolysis. Therefore, hydrolysis of these high-molecular-weight polymeric

components is the necessary first step in anaerobic digestion. [18] Through hydrolysis the complex

organic molecules are broken down into simple sugars, amino acids, and fatty acids.

2.ACIDOGENESIS

The biological process of acidogenesis results in further breakdown of the remaining components by

acidogenic (fermentative) bacteria. Here, VFAs are created, along with ammonia, carbon dioxide,

and hydrogen sulfide, as well as other byproducts. The process of acidogenesis is similar to the

way milk sours.

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C6H12O6 → 3CO2 + 3CH4

3. ACETOGENESISThe third stage of anaerobic digestion is acetogenesis. Here, simple molecules created through the

acidogenesis phase are further digested by acetogens to produce largely acetic acid, as well as carbon

dioxide and hydrogen.

4. METHANOGENESISThe terminal stage of anaerobic digestion is the biological process of methanogenesis. Here,

methanogens use the intermediate products of the preceding stages and convert them into methane,

carbon dioxide, and water. These components make up the majority of the biogas emitted from the

system. Methanogenesis is sensitive to both high and low pHs and occurs between pH 6.5 and pH

8. The remaining, indigestible material the microbes cannot use and any dead bacterial remains

constitute the digestate.

ANAEROBIC DIGESTION PARAMETERS:

The efficiency of AD is influenced by some critical parameters, thus it is crucial that appropriate

conditions for anaerobic microorganisms are provided. The growth and activity of anaerobic

microorganisms is significantly influenced by conditions such as exclusion of oxygen, constant

temperature, pH-value, nutrient supply, stirring intensity as well as presence and amount of inhibitors

(e.g. ammonia). The methane bacteria are fastidious anaerobes, so that the presence of oxygen into the

digestion process must be strictly avoided.

ADVANTAGES OF BIO GAS TECHNOLOGIES:

1. Renewable energy source

2. Reduced greenhouse gas emissions and mitigation of global warming

3. Reduced dependency on imported fossil fuels.

4. Waste reduction

5. Increase in Employment opportunities

6. Flexible and efficient

7. Easy to produce and use

8. Requires less water inputs in generation.

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BENEFITS TO THE FARMERS:

1. Additional income for the farmers

2. Use of digestate as an excellent fertiliser

3. Closed nutrient and carbon cycle

4. Flexibility to use different feedstocks

5. Increase in hygienic conditions

BENEFITS OF ANAEROBIC DIGESTION:

Anaerobic digestion is particularly suited to organic material, and is commonly used for industrial

effluent, wastewater and sewage sludge treatment. Anaerobic digestion, a simple process, can greatly

reduce the amount of organic matter which might otherwise be destined to be dumped at sea,  dumped

in landfills, or burnt in incinerators.

Pressure from environmentally related legislation on solid waste disposal methods in developed

countries has increased the application of anaerobic digestion as a process for reducing waste volumes

and generating useful byproducts. It may either be used to process the source-separated fraction of

municipal waste or alternatively combined with mechanical sorting systems, to process residual mixed

municipal waste. These facilities are called mechanical biological treatment plants.

If the putrescible waste processed in anaerobic digesters were disposed of in a landfill, it would break

down naturally and often anaerobically. In this case, the gas will eventually escape into the

atmosphere. As methane is about 20 times more potent as a greenhouse gas than carbon dioxide, this

has significant negative environmental effects.

In countries that collect household waste, the use of local anaerobic digestion facilities can help to

reduce the amount of waste that requires transportation to centralized landfill sites or incineration

facilities. This reduced burden on transportation reduces carbon emissions from the collection

vehicles. If localized anaerobic digestion facilities are embedded within an electrical distribution

network, they can help reduce the electrical losses associated with transporting electricity over a

national grid.

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CONCLUSION:

Biogas technology offers a vast set of benefits. Except India and China, in other developing countries,

the proportion of functional plants is often 50% or less. There is an increasing demand for energy in

the near future. Alternatives have to be found to compensate these energy demands. Bio gas is a

green, efficient solution to all those requirements. It helps in producing green energy with minimal

investments and maintenance and also output’s green compost which can again serve as a green

alternative when compared to chemical fertilizers.

The design of bio gas plants have not developed drastically over time. Very minimal changes in the

design & construction have been seen over time. The process for cleansing of gas requires a lot of

energy and is also not 100% efficient. A lot of energy is also wasted in compressing the methane gas

as it requires higher pressure and lower temperatures to be compressed. New advancements in this

field are also keen points to be taken care of. Talking about anaerobic digestion, this simple yet so

efficient technique has helped humans deal with a vast set of problems. The anaerobic digestion

process helps us treat our sludge in the waste water treatment plant; it helps us produce bio gas, a

green source of energy. It also provides surplus benefits to the farmers.

What needs to be done is more investment of time, money and knowledge into these field so as to

harness them to their maximum potential.

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