Class 7 Science Waste Water Management Exam Notes

Covers following topics:

This Class 7 Science exam notes page on Waste Water Management covers the meaning of waste and sewage, the sources of waste water, the three stages of a sewage treatment plant, the uses of treated water, ways to reduce sewage generation, and the diseases caused by contaminated water.

WASTE

Any material which cannot be used in the form in which it is produced is called waste. According to their physical state, wastes can be classified into three categories: solid waste, liquid waste and gaseous waste.

The impurities present in waste water are called contaminants. This waste water is called sewage.

SOURCES OF WASTE WATER

Domestic Waste Water:
It includes all kinds of wastes such as human excreta, food waste, soaps, detergents, oil, animal excreta and urine.

Agricultural Waste Water:
Waste water generated from farms and agricultural fields contains harmful pesticides, weedicides and animal wastes.

Industrial Waste Water:
Waste water generated from various industries contains harmful chemicals. The discharge of industrial waste water is called industrial effluent.

Petroleum Oil:
The leakage of petroleum oil into the sea during drilling and shipping pollutes sea water. An oil spill is caused by the release of oil into rivers and oceans, knowingly or unknowingly.

Mining:
Waste water is also generated as a result of mining activities.

Construction Activity:
A lot of waste water is generated during the various stages of building houses, homes, malls and multiplexes.

SEWAGE TREATMENT PLANT

Waste water is treated in three processes before it is discharged into water reservoirs:
1. Primary treatment
2. Secondary treatment
3. Tertiary treatment

Primary Treatment (First Stage):
The waste water is passed through rotating screens to remove large objects. It is then passed through a grit and sand tank to remove small stones and pebbles. The solid wastes, such as faeces, settle down at the bottom of the tank and are removed with the help of a scraper. This is called sludge. The sludge can be used for the production of biogas, which can be used as fuel, or for producing electricity. Light materials float on top and are known as scum. The scum is removed with the help of a skimmer.

Secondary Treatment (Second Stage):
The treatment at this stage involves pumping air into the clarified water to help aerobic bacteria grow. The bacteria decompose the suspended waste. The decomposed organic material settles down at the bottom of the tank as activated sludge. It is passed through sand drying beds to separate the solid material from it. This solid waste can be used as manure.

Tertiary Treatment (Third Stage):
The treated water now undergoes chemical treatment. The water is disinfected with chemicals such as chlorine, or it may be exposed to ultraviolet rays to kill disease-causing organisms. It can also be treated with ozone gas. The water is then discharged into the distribution system.

The schematic diagram of a waste water treatment plant is shown below.

Table: Stages of a waste water treatment plant

USES OF TREATED WATER

The treated water obtained from the sewage treatment plant is used for irrigating fields and lawns, and for aquaculture. In Kolkata, the treated water is used for fisheries and for growing crops and vegetables. The treated water is finally released into streams and rivers.

HOW WE CAN REDUCE SEWAGE GENERATION

1. Leakage in sewer lines should be checked and repaired regularly.
2. Use flushes with a low capacity to reduce the volume of flushed water.
3. Waste water from basins, sinks and washing machines can be used again for watering plants or wiping floors.
4. Never pour household products such as cooking oil, fat, butter or plastic down the drain. These materials can block the pipes, and sewage may start overflowing in your home or in public places.
5. Never throw paints, solvents, insecticides, automobile oils or medicines down the drain, as they may kill the microbes that help to purify water.
6. Used tea leaves, solid food remains, sanitary towels and toys should not be thrown into the waste water pipe, because these materials may choke the drains.
7. Ask civic authorities to cover the open drains of your area.
8. Plant eucalyptus trees all along sewage ponds, as these plants absorb surplus water rapidly.

WASTE WATER AND DISEASES

Drinking waste and contaminated water causes many human diseases in India. People consuming contaminated water may suffer from diseases such as gastroenteritis, dysentery, typhoid, cholera, meningitis and hepatitis.

→ SEWAGE TREATMENT PLANT

There are three processes which are involved in treating waste water before it is discharged into the water reservoirs. These processes are :

→ USES OF TREATED WATER