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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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BIO GAS PLANTS
1.Agricultural BioGas Plants
1.1 Familyscale biogasplants
1.2 Farm scale biogas plants
1.3 Centralizedco - digestionplants
2. Industrial BioGas plants
3. Landfill Gasrecoveryplants
1. FixedDome type
3. Low cost polyethylene Tube digestors
ANAEROBIC DIGESTION PARAMETERS
ADVANTAGES OF BIO GAS TECHNOLOGIES
BENEFITS TO THE FARMERS
BENEFITS OF ANAEROBIC DIGESTION
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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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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.
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-
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.
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
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
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
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.
On the basis of the design as per conditions and liabilities, bio gas plants are further divided into
Floating drum type
Fixed dome type
Low cost polyethylene tube digestors
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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
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
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 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
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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
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
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
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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The process to produce bio gas in a bio gas plant includes:
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 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.
C6H12O6 → 3CO2 + 3CH4
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Fig no 9: All four stages of anaerobic digestion shown in simple flow chart
In 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.
Through hydrolysis the complex
organic molecules are broken down into simple sugars, amino acids, and fatty acids.
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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The 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.
The 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
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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.