Page 178 - Science Class 07

light. In this way, pathogens are totally used to remove the rest pathogens. It includes
removed. Some chemical methods are also chlorina on.

1. What is sewer system?
2. How liquid wastes are disposed off in small ci es?

3. Why eutrophica on is harmful?
4. What is the importance of sewage treatment?

5. How pathogens are removed from sewage water?

Wastes : Useless or discarded materials
Industrialisation : Rapid growth in number of industries
Urbanisation : Rapid growth in number of towns or cities or their expansion

Consumerism : A trend of creating more and more consumers
Population explosion : Unexpected growth in population

Biodegradable wastes : Wastes which can be decomposed by micro-organisms
Non-biodegradable wastes : Wastes which cannot be decomposed by micro-organisms
Sewage : Liquid or semi-liquid wastes produced from households
Treatment of wastes : Methods used to convert harmful and toxic wastes into
harmless and non-toxic materials

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i Waste management means dealing with wastes properly and efficiently to reduce their
impact on the environment.
I Wastes are generated everywhere in the household, in the offices, in the hospitals, in the
industries, in schools, etc.

i Industrial wastes include metal scraps, chemicals, effluent and other solid wastes.
I Wastes are of two types— biodegradable wastes and non-biodegradable wastes.
i Remain of plants and animals, paper, cotton, rope, etc. are biodegradable wastes.

i Polythene bags are very harmful non-biodegradable wastes.
i Gaseous wastes includes smokes, harmful gases, ash, metal particles, etc.
I Sewage contains a lot of pollutants and other harmful materials which generally lead to the
pollution of water bodies as well as groundwater.

i Treatment of the sewage is completed in three phases— primary treatment, secondary
treatment and tertiary treatment.

178 Science-7