CBSE Class 7 Science Waste Management Assignment

Waste

Waste refers to any discarded material which no longer remains useful. According to the Environment
Protection Act, 1990, waste is any substance which constitutes a scrap material, or an effluent or an
unwanted surplus which arises out of the application of any process. There are three types of wastes—solid, liquid and gaseous wastes.

Solid Wastes: It include garbage, food leftovers, decaying fruits and vegetables, cans, bottles and ashes.

Liquid Wastes: It refers to sewage discharged from houses, hospitals, restaurants, offices and factories.
Oil spill is also a liquid waste.

Gaseous Wastes: It includes fuel exhausts containing carbon dioxide, carbon monoxide, sulphur dioxide etc. Smog is an example of gaseous waste.

Wastes can also be classified into toxic and non-toxic wastes. Differences between them are

Sources of Wastes
Wastes are classified into the following categories depending on their source of origin:

Domestic Wastes
Wastes generated as a result of domestic activities are known as domestic wastes. It includes polythene bags, toilet sewage, batteries, expired medicines and scrap metals.

Industrial Wastes
Wastes emanating from various large and small-scale industries are known as industrial wastes. Industrial wastes can be categorised into the following groups depending on the nature of industry:

Mining: Wastes generated during mining activities are known as mining wastes. Many chemicals and
liquids get discharged leading to the deterioration of land and water resources.

Cement Industry: These industries discharge fine dust particles which can cause serious health hazards.

Oil Refineries: These industries cause serious environment problems. They generate wastes such as
organic sulphur compounds, hydrocarbons and organic acids.

Construction Sites: The wastes include bricks, plastics, pipes, roofing and insulating materials.

Paper Industry: The effluents of the industry include sulphur dioxide and chlorine which can endanger
the lives of aquatic organisms.

Textile Industry: Its wastes include effluents resulting from boiling and processing of fibres.

Chemical Industries: These industries include manufacturing industries and fertiliser and pesticide
industries.

Metal industries: These industries produce wastes containing copper, lead, acids, chromium and zinc
which can affect the life of aquatic animals.

Agricultural Wastes
The following table shows the nature of agricultural wastes:

Municipal Wastes
Waste generated in a municipality or a local area is known as municipal waste. It is discharged by shops,
offices, banks, hospitals and schools. It can be divided into the following categories:

Sewage: It is a liquid waste which is discharged from kitchens, bathrooms, lavatories, laundries and
laboratories. It includes mineral and organic matter, wastewater and human excreta. As municipal sewage contains large quantities of nitrogen and organic matter, it can affect the ecosystem if it is not treated.

Degradable and Non-Degradable Wastes

Biodegradable wastes can be further classified into simple biodegradable wastes and complex biodegradable wastes. While biodegradable wastes can be easily broken down by natural processes
(Examples: Leaves, vegetable peels), non-biodegradable wastes cannot be easily decomposed
(Examples: Leather shoes, tin cans).

Biomedical Wastes
Wastes which are generated during medical treatment, diagnoses and immunisation of humans and animals are known as biomedical wastes. It also includes wastes generated during research and experiments conducted in laboratories. These wastes include needles, syringes, tissues, parts of the body, chemicals used during pathological tests and polythene bags.

Nuclear Waste
Radioactive wastes which are generated from nuclear reactors, nuclear power plants, trident submarines and X-ray machines are known as nuclear wastes. They are the most hazardous of all as they emit radiation which can cause several diseases, cancer and genetic disorders.
Medical X-rays constitute about 18% of artificial radiations used in radiotherapy for diagnostic purposes.

Need for Management of Wastes
It is important to dispose wastes safely and scientifically. This is because wastes can result in the spread of many diseases.

Waste on Lands
There are dangers of spreading many diseases when wastes get accumulated on land and water bodies.
The following table shows the lists of common diseases spread by various insects and organisms

Wastes in Water
Industrialisation and urbanisation pollute water in the following ways:
• Sewage has pathogenic agents. A pathogen is a microorganism which can cause disease.
• Effluents discharged by water include metal salts and complex organic chemicals.
• Fertilisers and pesticides can pollute water resources.
• Radioactive substances can affect reproductive organs in humans and can cause several diseases, cancer and genetic disorders

Greenhouse Effect and Global Warming
The Earth receives sunrays which keep it warm. The Earth does not absorb all the heat but emits a part of the heat back into space. This helps in maintaining uniform temperature on the surface of the Earth.
A greenhouse is a building made of glass in which plants are grown. The building made of glass absorbs the heat of the Sun but does not allow it to go out. This increases the temperature inside the glass building. Similarly, many greenhouse gases present in the atmosphere (such as carbon dioxide) absorb
the Sun’s energy and do not reflect it into space, leading to the increase in the temperature of the Earth. Four gases are mainly responsible for creating the greenhouse effect on the Earth. These gases are carbon dioxide, methane, nitrogen oxide and chlorofluorocarbons (CFCs). Many human activities such as burning of fossil fuels and deforestation have resulted in global warming.

Effects of Global Warming
• The temperature of the Earth is likely to increase by 2°C to 5°C in the next hundred years.
• This increase in temperature will result in the melting of snow in the polar regions of the Earth. This will result in the rise of the sea level leading to the submergence of coastal lands.
• Increase in temperature will result in changes in climatic conditions all over the world by influencing the wind and rain patterns.
• Rise in temperature will result in an increased rate of transpiration which will lead to the depletion of the groundwater table.

Depletion of the Ozone Layer
The ozone layer lies in the stratosphere. It absorbs the ultraviolet rays of the Sun and protects the Earth from its harmful effects.
The ozone layer has been depleting because of the emission of nitrogen oxide and CFCs. Supersonic jets release nitrogen gas which depletes the ozone layer. CFCs are used in many countries today. During the use of materials such as paints, foam and thermal insulating materials, CFCs escape into the
atmosphere and harm the ozone layer.
A hole in the ozone layer has been discovered over Antarctica. Without the ozone layer, exposure to sunrays can cause diseases such as skin cancer and cataract in humans. Ultraviolet rays can cause genetic disorders. It also disturbs the ecological balance in the marine ecosystem.

Acid Rain
Pollutants present in the air such as sulphuric acid and nitrogen oxides (released by burning of fossil fuels and industrial emissions) combine with the droplets of water in the air and come down as rain; this is known as acid rain.

Effects of acid rain are
• Affects the human nervous system by causing neurological diseases
• Affects the lives of aquatic animals
• Leads to the corrosion of buildings, monuments and bridges
• Increases acidity of soil, leading to reduced fertility

Soil Pollution
Acid rain can cause soil pollution. Soil pollution leads to reduction in mineralisation and decomposition. It also reduces soil fertility and soil aeration. Further, it is important to check the accumulation of wastes and reduce soil pollution.

Waste Management
It is thus required to effectively manage wastes. One of the easiest ways of managing wastes is following the 3-R system—reduction, reuse and recycle. We should reduce the use of resources by not overusing and overexploiting them. Materials should also be used several times to conserve resources. Materials such as glass and paper should be recycled to make new materials. This helps in protecting our environment.

• Kinetic Theory of Gases
1. All matter is made up of molecules.
2. All molecules of a substance are identical.
3. Molecules of different matter differ in composition, shape and size.
4. Molecules are continuously in motion.
5. Intermolecular forces depend on the distance between the molecules and the type of molecules.
6. Motion of molecules is affected by change in temperature – higher the temperature, more they move.

• Intermolecular Force – The attractive force between the molecules
• Arrangement of molecules in Solids
1. Molecules are tightly packed
2. Intermolecular forces are very strong
3. Molecules can only vibrate; no movement is allowed
4. Thus, solids have fixed shape and volume, and cannot be compressed
5. On heating, molecules vibrate more; the distance between the molecules increases slightly

• Arrangement of molecules in Liquids
1. Molecules are slightly further apart than in solids.
2. Intermolecular forces are also less strong.
3. Molecules can move from their positions in liquids.
4. Thus, liquids flow and take the shape of the container.
5. Liquids do not have definite shape, but they do have definite volume.
6. On heating, molecules vibrate and move faster; it only expands slightly
7. Liquids can only be compressed a little.

• Arrangement of molecules in Gases
1. Molecules are far apart; hardly any interaction between them
2. Intermolecular forces are negligible.
3. Molecules are free to move around.
4. It has no definite shape or volume.
5. A gas can easily be compressed.

• Change of state
• A change of state occurs because heat energy breaks the force of attraction between particles. Kinetic energy of the particle increases.

• Melting point
• The temperature at which a solid melts into a liquid at normal atmospheric pressure.
• At melting point, the temperature does not change until all solid converts into liquid.

• Latent heat
• The heat required to break the force of attraction between the particles at transition temperature. This heat becomes confined within the material and is called the latent heat.
• Amount of heat required to change 1 kg of material to change its state at normal atmospheric pressure at transition temperature is called the latent heat for that transition.

• Sublimation
• Solid ⇔ gas [directly]
• Example: Ammonium chloride

• Effect of change of pressure
• If pressure is applied,
• Melting point → decreases
• Boiling point → increases

• Dry Ice – Solid CO₂ [directly converts to gas]

• Laws of Chemical Combination

• Law of conservation of mass
Mass can neither be created nor destroyed in a chemical reaction. It means that the sum of the masses of the reactants and the products remains the same during a reaction.

Q.1.Fill in the blanksa-

Sea water is unfit for _______ purpose.

b- Discharge of waste water from industries is called__________.

c- Disinfection is the _________stage of water treatment.

d- Secondary treatment is also known as___________treatment.

e- Waste water discharged from our homes is called__________.

f- ____________is a non biodegradable waste.

Q.2.Write true or false for the following statementsa-

Domestic sewage is free from microorganisms. ( )

b-Chlorination kills harmful bacteria in water. ( )

c-The solubility of gases increases with falling temperature. ( )

d-Sewage water should flow in closed drains.( )

e-Sewage water contains solid as well as biological waste.( )

f-Waste is an important environmental and public health issue of global concern.( )

g-Diarrhoea is a disease caused by polluted air.( )

h-Industrial waste contaminate the water.( )

Q.3.Choose the correct answer:

a- Sewage pollutes

i- soil ii-air iii-sea iv-water

b- Improper sewage disposal does not cause

i-Cholera ii-Jaundice iii-Heart Attack iv-Typhoid

c- The solid waste separated from domestic sewage is called

i-Slurry ii-Humus iii-Sludge iv-Manure

d- Biodegradable wastes

i-accumulate in nature ii-enter in food chain

iii-are dangerous iv-decompose in nature

e- Disinfection of water is done by

i-Chlorine ii-Ozone iii-UV radiation iv-All of these

Q.4.Match the following:

i-Malaria                                             a-Non-biodegradable waste

ii-Potable water                                   b-Excessive algae growth

iii-Incineration                                     c-Biodegradable waste

iv-Secondary treatment                      d-Landfill

v-Plastic                                              e-Open drains

vi-Vegetable matter                            f-Bio-accumulation

vii-Eutrophication                               g-Water suitable for drinking

viii-Automobiles                                 h-Burning at high temperature

ix-Modes of waste disposal                i-Gaseous waste

x-DDT accumulated in food chain      j-Biological treatment

Q.5.Answer the following questions:

a-What happens when there is leakage in sewer pipes?

b-Mention some of the most common water born diseases?

c-What are the different ways of solid waste disposal?

d-Distinguish between Biodegradable and Non-biodegradable wastes?

e-What problem can arise due to improper drainage?

f-Define: i-sewage ii-Landfill iii-Leaching

g-What is sludge? How is it obtained? How can it be used?