Biogas and Biomass

Biogas is a renewable energy source that is produced by the anaerobic digestion of organic
matter such as animal waste, food waste, and agricultural residues. During the digestion process,
microorganisms break down the organic matter and produce a gas that is primarily composed of
methane and carbon dioxide. Biogas can be used as a fuel for heating and electricity generation,
and the residue from the digestion process can be used as a fertilizer.

Biomass refers to any organic material that can be used as a fuel source, such as wood, crop
residues, and municipal solid waste. Biomass can be burned directly to generate heat or
converted into biofuels such as ethanol and biodiesel. Biomass is a renewable energy source, and
it can be used to reduce dependence on fossil fuels and reduce greenhouse gas emissions.
However, the production of biomass for energy purposes can have environmental and social
impacts, and careful management is required to ensure sustainability.

Difference between Biogas and Biomass

Let us study the difference between Biogas and Biomass below

S. Biomass Biogas
no
1. Smoke at the output is more Smoke emitted out is less
2. Destroyed and the dead matter is used as Organic matter is used as fuel and manure also can be
fuel used
3. It is available in a solid state It is available in gaseous state
4. It is made from biological material It is made from methane and carbon dioxide
5. The calorific value of the fuel is low The calorific value of biogas of the fuel is high

Need of Biogas and Biomass for Energy Production

Biofuels function best when carbon reduction is prioritized, Rather than fossil fuels, biofuels
may be assessed. By maximizing the carbon cycle on our planet, biofuels contribute to a
reduction in the carbon footprint of transportation and other industries. Each gallon of biofuel
that is used in place of a gallon of fossil fuel reduces greenhouse gas emissions. Hence fuels like
Biogas and Biomass are practiced.

What is Biogas?

Biogas is a renewable source of energy. It is a mixture of 55-65% methane, 30-40% carbon

dioxide, and the rest being the impurities (H, H, S, and some N,), which can be produced from
the decomposition of animals, and plant and human waste.

Moreover, the material from which the biogas is produced retains its value as a fertilizer and can
be returned to the soil. Biogas has been the material for its production, hitherto. It is not only the
excreta of the cattle but also the piggery waste as well as poultry dropping that are very
effectively used for biogas generation. A few other materials through which biogas can be
generated are algae. The biogas diagram is shown below.

Fig: Biomass plant

Biogas Power Plant

Biogas power plants take advantage of the natural decomposition process to generate electricity.
Because it is obtained from organic matter, as the gas is made of methane, and Carbon dioxide, It
is a clean but slow-burning gas and usually has a calorific value between 5000 to 5500 kcal/kg
(20935 to 23028 kJ/kg) or 38131 kJ/m³. It can be used directly in cooking, reducing the demand
for firewood.

And this gas is used as a source of fuel.

Construction of Biogas Plant

A biogas plant consists of an underground digester, which is a well-shaped tank constructed of

bricks, and its dome-shaped roof, which is made of cement and bricks. A type of airless sealed
tank is called a digester (or oxygen). The digester tank's dome serves as a gas storage tank or gas
holder for the biogas.

The top of the dome has a gas outlet with a valve. Both the sloping inflow chamber and the
rectangular exit chamber on the digester tank's right side are constructed of bricks.

The exit chamber is used to remove the used dung slurry after the biogas has been extracted,
whilst the intake chamber is used to introduce new dung slurry into the main digester tank.

While the outlet chamber is connected to the overflow tank, the inlet chamber is connected to a
mixing tank.
 Fig : Biogas plant diagram

Working of Biogas plant

To prepare the slurry, cow dung, and water are combined in the mixing tank in an equal ratio.

Through the entrance chamber, this mixture of dung and water is supplied into the digester tank.

The dome of the digester tank is left free for the collection of biogas, while the cylindrical level
of the tank is filled with dung slurry.

About 50 to 60 days pass until the new gas plant is operational (starts functioning) During this
time, anaerobic bacteria break down the cow dung while there is water present (but no oxygen),
gradually transforming the process into biogas. The dome begins to fill with this biogas.

The digester tank's slurry is under pressure as more and more biogas builds up in the dome,
which pushes the used slurry through the outflow chamber and into the overflow tank. The used
slurry is progressively evacuated from the overflow tank. The leftover spent dung slurry from the
biogas extraction process is high in nitrogen and phosphorus compounds and makes excellent
manure. More fresh dung slurry is routinely added to the digester tank after the gas plant is
operational, which results in continuous biogas production.

Through outlet S, the biogas that has accumulated in the digester tank's dome is removed and
sent through a system of pipes to residences in the community for use as cooking gas.

Biogas plants can also employ human excreta (human feces), in addition to the cow dung that we
currently use. Paper scrap, vegetable wastes, chicken droppings, and agricultural wastes can all
be utilized to create biogas.

Materials used for Biogas Generation

Feedstock materials: The following organic matter-rich feedstocks are found feasible for their
use as input materials for biogas production:

Animal wastes: Cattle dung, urine, goat and poultry droppings, slaughterhouse wastes, fish
wastes, fetus wastes, leather and wood wastes, sericulture wastes, elephant dung, piggery wastes,
etc.

Human wastes: Feces, urine, and other wastes emanating from human occupations.

Agricultural wastes: Aquatic and terrestrial weeds crop residue, stubbles of crops, sugarcane
trash, spoiled fodder, bagasse, tobacco wastes, oilcake fruit and vegetable processing wastes,
press mud, cotton and textile wastes, spent coffee and tea wastes.

Waste of aquatic origin: Marine plants, twigs, algae, water hyacinth, and water weeds.

Industrial wastes: Sugar factory, tannery, paper, etc.

The following three marine plants (waste of aquatic origin) are considered promising for biomass
production. Water hyacinth, Algae, and Ocean kelp.

Classification of Biogas plants

Biogas plants are mainly classified as

o Continuous and batch types (as per the process)

o The dome and the drum types
o Different variations in the drum type

Selection of Site for biogas plants

The following factors must be considered while selecting the site for a biogas plant

o Distance: The distance between the planet and the site of gas consumption, should be
less in order to achieve economy in the pumping of gas and minimizing gas leakage. For
a plant of capacity 2m^3 , the optimum distance is 10 m.
o Minimum Gradient: For conveying the gas a minimum gradient of 1% must be made
available for the line.
o Open Space : The sunlight should fall on the planet as a temperature between 15 C to 30
C is essential for gas generation at a good rate.
o Water table: The plant is normally constructed underground for ease of charging the
feed and unloading slurry requires less labor. In such cases, care should be taken to
prevent the seepage of water and the plant should not be constructed if the water table is
more than 10 ft. (3 m).
o Seasonal runoff: Proper care has to be taken to prevent the interference of runoff water
during the monsoon. Intercepting ditches or bunds may be constructed.
 o Distance from wells: The seepage of the fermented slurry may pollute the well water.
Hence a minimum of 15 m should be maintained from the wells.
o Space requirements: Sufficient space must be available for day-to-day operation and
maintenance. As a guideline 10 to 12 m² area is needed per m³ of the gas.
o Availability of water: Plenty of water must be available as the cowdung slurry with a
solid concentration of 7% to 9% is used.

Digester Design Considerations

Digestion tanks may be of any convenient shape and provided with a cover to retain the gas. The
cover may be a fixed one or floating. A number of factors are to be taken into account to arrive at
an optimum size for a biogas plant. These are

1. the volume of waste to be digested daily,

2. the type and amount of waste available for digestion consistently,
3. the period of digestion,
4. methods of stirring, the contents if any,
5. method of adding the raw waste and removing digested slurry,
6. efficiency of the collection of the raw waste,
7. the climate condition of the region,
8. the availability of other cellulosic fermentable waste in that area.
9. information about sub-soil condition and water table, and
10. type of cover.

Generally, no separate heating and stirring of the contents are provided for digesting entitle
waste (Gobar Gas digester), Stirring

Methods for maintaining Biogas Production are:

o Insulating the gas plant

o Composting
o Hot water circulation
o Use of Chemical
o Solar energy systems

Advantages and Disadvantages of Biogas

Till now we have studied the concepts related to biogas lets have an overview of its Advantages
and Disadvantages:

Advantages of Biogas plant

o Because it burns cleanly and doesn't pollute the air, biogas makes for an excellent
residential fuel.
o Having a high calorific value is biogas. In other words, biogas generates a lot of heat per
unit of mass.
 o Biogas burns entirely and leaves no trace behind (unlike wood, charcoal or coal). This
makes the fuel clean.
o Biogas has no storage issues because it is delivered through pipes straight from the gas
plant.
o Compared to most other fuels, biogas is less expensive.
o Lighting systems also use biogas. Engines are run on biogas as fuel.
o In many locations, biogas is used in place of diesel to power the water pumping systems
used for irrigation. Electricity is generated using biogas.

Disadvantages of Biogas

o Biogas cannot be used on a wide scale due to its low efficiency, which makes it
economically unviable. It has several contaminants that are challenging to control even
after subjecting it to numerous purifying processes.
o The container is severely corroded when biogas is compressed for use as fuel. Methane
interacts violently with oxygen to produce carbon dioxide when they come into contact.
As a result, methane is prone to explosions despite being very inflammable.

What is Biomass?

A renewable energy source that comes from living or recently living creatures is called biomass.
It is created by biological systems' metabolic processes (those of plants and animals) and/or by
the byproducts of those systems' breakdown or conversion. These materials' chemical and energy
worth is dependent on the bonds between carbon atoms and hydrogen atoms. Utilizing biomass
energy significantly minimizes our reliance on outside energy sources. It improves national
security and offers a wider variety of fuel. Biomass can be utilized as an energy source directly
by being burned to produce heat or indirectly by being transformed into different types of
biofuel.

Fig : Biomass energy diagram

Biomass power plants

The major source of renewable energy on Earth, biomass, is gaining popularity. The combustion
of plant or animal matter to produce energy and heat is known as biomass. As opposed to fossil
fuels, this method of energy generation has the main advantage of using an unlimited resource
because it is produced in an environmentally friendly manner.

Components of Biomass

o Equipment for managing and storing fuel.

o Pumps; Combustor/furnace
o Boiler;
o Fans.
o Steam engine.
o The generator
o The condenser.
o Refrigerating tower
o Controls for emissions and exhaust.
o System settings (automated).

Fig : Components of Biomass

Working of Biomass plant

A biomass plant is a construction that burns organic waste, to produce electricity or heat. Steam
is created during combustion, and this steam powers a turbine to provide energy. Because the
carbon dioxide generated during the burning process is balanced by the carbon absorbed during
the growth of the organic materials used as fuel, biomass plants are regarded as renewable
energy sources. Certain types of biomass feedstocks, nevertheless, raise questions regarding their
environmental impact and long-term viability.

Biomass Power Generation modes

Biomass energy can be converted to useful power i.e., Electricity using the following techniques
 o Combustion
o Gasification Combustion
o Mixed Burning
o Gasification Mixed burning Combustion

Biomass gasification

The word gasification implies converting a solid or liquid into a gaseous fuel without leaving any
solid carbonaceous residue.

Biomass Gasifier: It is an equipment which can gasify a variety of biomass such as wood waste,
agricultural waste like stalks, and roots of various crops, maize crops, etc. The gasifier is
essentially a chemical reactor where various complex physical and chemical processes take
place. Biomass gets dried, heated, pyrolyzed, partially oxidized, and reduced, as it flows through
it.

The gas produced in the gasifier is a clean burning fuel having a heating value of about 950-1200
kcal/m³. Hydrogen (18-20%), and carbon monoxide (18- 24%) are the main constituents of the
gas.

Methods of converting biomass into useful forms of energy can be broadly classified as:

o Biochemical and
o Thermochemical

Fig : Biomass gasification diagram

In some cases the gasifiers can be installed without any heat recovery system. In special cases,
the gasifier systems can have recovery in the form of hot water.

Energy conversion from Biomass

As biomass energy is a renewable source and not mostly used we can instead have some possible
conversions as follows.

Fig: Energy conversion from Biomass

Advantages and Disadvantages of Biomass

Till now we have studied the concepts related to biomass let's have an overview of biomass
energy advantages and disadvantages

Advantages of Biomass Energy

o Its a type of recycled fuel, and the left-out waste and emitted products can be used as
manure,
o The running cost of the plant is less, we can even be operated easily.
 o The power obtained from Biomass is Reliable and domestically produced, it is
economically competitive and sustainable.
o It minimizes the costs involved with waste disposal,
o It helps in providing opportunity in rural areas

Disadvantages of biomass

o It is comparatively inefficient when compared to fossil fuels

o The combustion of Biomass fuel requires a lot of space and creates smells.
o It may be harmful to the environment sometimes when the bacteria comes out
o High investment and maintenance cost

Biomass
Cow dung and agricultural waste have been used as fuel to cook food in
many villages since ancient times. However, it is not an effective source of
energy to use as a fuel since its efficiency is extremely poor, which means
that the energy generated by them is extremely low and generates a lot of
smoke while burning. This smoke is hazardous to both the environment and
the person preparing the meal. It is known that a large volume of farm waste
and cow manure is produced in an area. So, is there a method to turn them
into a form that we can use as a source of energy? The answer is Yes, we
can convert it to biogas by establishing a biogas plant.

What is Biomass?

The dead elements of plants and trees, as well as animal feces, are referred
to as biomass. Biomass is organic matter that is used as a fuel to generate
energy. Wood, agricultural waste (crop leftovers), and cow dung are all
examples of biomass.
Another way that solar energy presents itself is through biomass. This is
because all the plants and trees that generate biomass, such as wood, grew
using the sun’s energy.
Even animal wastes (such as cow manure) are produced by cattle that
developed by ingesting plant food produced with the aid of sunshine energy.
Because biomass fuels such as wood, agricultural waste, and cow dung are
all plant and animal products, they are referred to as such (or biofuels).
Biomass is a renewable energy source since it is derived from plants (or
animals) that can be reproduced indefinitely.

Different Ways of Extracting Energy from Biomass:

The various methods of biomass extraction can be broadly be classified as:

Solid fuel combustion: The simplest way of extracting energy from biomass
can be done directly by the combustion of solid matter. Many of the
developing countries especially in rural areas obtain most of their energy
needs by burning wood, animal dung, and other biomass. But burning can be
inefficient.
Gasification: Gasification can be defined as a process that exposes a solid
fuel to high temperatures and limited oxygen, in order to produce a gaseous
fuel. Gasification is the mixture of gases like carbon monoxide, carbon
dioxide, nitrogen, hydrogen, and methane. Gasification has many
advantages over burning solid fuel. One of the resultant gases, like methane,
can be treated similarly as natural gas and used for the same purposes.
Paralysis: Paralysis is an old technology that involves heating the biomass
to drive off the volatile matter, leaving behind the black residue known as
charcoal. It has double the energy density of its original material. The
charcoal will be half the weight of the original biomass, which contains the
same amount of energy that makes the fuel more transportable. The
charcoal also burns at a higher temperature than the original biomass,
making it more useful for the manufacturing processes.
Digestion: Biomass digestion works under the action of anaerobic bacteria,
these microorganisms live at the bottom of swamps or sometimes in other
places where there is no air, consuming dead organic matter to produce
among other things like methane and hydrogen. We can put these bacteria
to work for us, by feeding the organic matter such as human sewage or
animal dung into tanks called digesters and adding these bacteria, we can
collect the emitted gas that can be used as an energy source.
Fermentation: Compared to the above, fermentation isn’t a new idea.
Producing the fuel from biomass by the process of fermentation is just an
extension of this old process. And a wide range of plants or its material can
now be used, from sugar cane to wood fiber. For example, the waste from
the wheat mill has been used to produce ethanol by fermentation then it is
mixed with diesel to produce ‘dishelm’.
Anaerobic Digestion: Anaerobic Digestion can be defined as a biochemical
degradation process that converts the complex organic material, such as
animal manure, into methane and other byproducts. The anaerobic digester
device promotes the decomposition of manure into simple organics and
gaseous biogas products. The biogas can be formed by the activity of
anaerobic bacteria. And microbial growth, as well as biogas production, are
very slow at ambient temperatures. The biogas comprises about 60%
methane, 40% carbon dioxide, and 0.2 to 0.4% of hydrogen sulfide.
Biogas Plant
The biogas plant is a dome-shaped building. Organic material, such as
waste food waste, lipids, sludge, cow dung, and so on, is combined with
water and fed into the digester via the entrance depicted in the image. The
digester is a sealed room where organic matter is decomposed
anaerobically.
After a few days, the organic matter decomposes entirely, releasing gases
such as methane, carbon dioxide, hydrogen, and hydrogen sulfide. These
gases are then pulled through pipes from the storage tank above the
digester and sent to surrounding centers for usage via decentralization
pathways.
Construction of a Biogas Plant:
The biogas plant is a brick and cement structure having the following parts:
 Digester: The digester is a closed chamber that has no oxygen and
hence inside the chamber the digester anaerobic oxidation takes place.
 Gas Tank: After anaerobic oxidation in the digester the gases are
released into the gas tank.
 Mixing Tank: Cow dung and farm waste are mixed by adding some water
to the mixing tank.
Working of a Biogas Plant:
To extract biogases and manure from the biogas plant following steps takes
place as discussed below using multiple figures:
Step 1:
To make a biogas plant firstly, a hole is drilled into the soil and such a type of
arrangement will be formed.
Step 2:
Now some part of cow dung and farm waste is taken and three parts of water
mixed to this part. They are mixed very well in the mixing tank and the slurry
of the mixture fed into the mouth of the digester.
Step 3:
When the mixture of cow dung and water is known as slurry moves into the
digester, the microorganisms get an environment of non-oxygen so they start
decomposing the organic matter into simpler substances.
Step 4:
The decomposition process takes some days of time. After decomposition
gases like methane, carbon dioxide, hydrogen, and hydrogen sulfide on a
whole called Bio-gas are sent to the gas tank.
Step 5:
Biogas is highly rich in methane constituting around 75 % of biogas. As this
process continues after some days the slurry which gets left out after the
decomposition is very rich in nitrogen and phosphorous.
Step 6:
This slurry is taken out then it is supplied to the farm as “manure”.
It can that by setting up a biogas plant and feeding the cow dung and farm-
based to this plant we are getting a very good source of fuel i.ebiogas.
Additionally, we also get the source of manure which is very rich in nitrogen
and phosphorous.
Advantages of Biogas
 Since India has a very high rural population, the fuel will be easily
available.
 This fuel burns without the smoke.
 The slurry residue is used as manure on the farm.
 It is Environment friendly.
 Excellent fuel quality with reasonable heating efficiency.
 Many countries like India subsidized the biogas plants too.
Disadvantages of Biogas
 The fuel has less heating capacity compares to other resources.
 As biogas consists of carbon dioxide, methane, hydrogen, and hydrogen
sulfide, it can corrode the parts of the biogas plant.
 it can’t be constructed easily because cow dung is mostly available in
villages only.

Sample Problems

Problem 1: Why charcoal is better than fuel and wood?

Solution:
There are several reasons where we can say charcoal is better than
charcoal. They are:
 Charcoal has a very high calorific value than wood i.e the amount of heat
produced by charcoal is much higher than wood.
 Charcoal doesn’t produce smoke, whereas wood and fuel produce smoke
and cause pollution.
 Charcoal is much convenient to use than wood.
Problem 2: List two advantages and two disadvantages of using cow
dung?
Solution:
Advantages
 Cow dung gives clean fuel which is called Biogas.
 Used dung can be used as manure for the farms.
Disadvantages
 Cow dung produces a lot of smokes which can lead to pollution.
 Cow dung contains important elements like nitrogen and phosphorous,
which is getting wasted after burning them.
Problem 3: What are the ways to make biofuels?
Solution:
Ethanol and Biodiesel are two types of biofuels. By fermentation process
ethanol is produced on Biomass and used in producing biological crops.
Whereas Biodiesel is used in combination with gasoline for machines.
Problem 4: What are the inputs and outputs of the Biogas Plant?
Solution:
A biogas plant is used mainly to produce biogas which is a very pure form of
gas. Now let’s look into the inputs and outputs of the biogas plant:
Inputs: Cow dung and farm waste.
Outputs: Biogas and manure.
Problem 5: List some uses of Biogas?
Solution:
The uses of Biogas are listed below:
 Biogas is comparatively very cheaper than other common fuels.
 There is no storage problem of gas because it is directly supplied from
the plant through pipelines.
 In biogas, even the residue is very useful because it used as manure in
farms
 It is used for lighting and for generating electricity.
 At last, biogas burns without smoke. Hence, it doesn’t cause any air
pollution.
Problem 6: What are all the elements present in the produced biogas?
Solution:
After the process of anaerobic oxidation, the biogas is produced and taken
through pipes. The biogas majorly consists of methane element constituting
75% and thereafter carbon dioxide, hydrogen and hydrogen sulphide with
minimal contributions.