7th Class Science Wastewater Story Treatment of Wastewater

Treatment of Wastewater

Category : 7th Class

*     Treatment of Wastewater


Disposal of waste water in water bodies pollutes the water bodies. To cope up with this pollution of water bodies, treatment or cleaning of waste water is done. However, due to increasing population, the more and more sewage is generated and therefore, the cleaning process is not adequately able to handle all the generated waste water.




*         Treatment of Municipal Waste Water

Sewage is carried from sewers to a sewage treatment plant. In the sewage treatment plant, strainers separate large solids such as leaves, rags, plastic, etc.


Then the sewage is passed to settlement tank to settle down the suspended solids to the bottom. The solids settled at the bottom of the settlement tank are called primary sludge. The sludge is used for producing compost and biogas. After this the sewage undergoes secondary treatment. In this, organic matters break down by the action of bacteria. This is done in open tanks called aeration tanks. Aerobic bacteria that needs oxygen act on the sewage in the aeration tanks. Air is blown into these tanks to speed up the process.

Sometimes the organic matters in the sewage break down by anaerobic bacteria in closed tanks. The solids get settled at the bottom of tank by the action of bacteria and are called biological or secondary sludge. The sewage can further undergo tertiary treatment before being discharged into water bodies. In this, the sewage passes through sand filters, man-made ponds containing reeds and other organisms that clean out dissolve chemicals.




*         Wetlands

An Alternative and cheaper method of sewage treatment is wetland. In this treatment of sewage bacteria, worms and protozoans act on organic matter. Wetlands also have grasses and reeds that filter pollutants.





       In the sewage treatment plant, which one of the following separate large solids such as leaves, rags, plastic, etc?

(a) Aeration tank

(b) Strainers

(c) Sedimentation tank,

(d) All of these

(e) none of these


Answer: (b)



        In which one of the following tanks aerobic bacteria breaks down organic waste present in sewage?

(a) Grit and sand removal tank

(b) First sedimentation tank

(c) Second sedimentation tank

(d) Aeration tank

(e) none of these


Answer: (d)




Used water is called wastewater.

Municipal wastewater comes from homes, offices, etc. and is carried by sewers or sewage pipes.

The rain water is also a source of wastewater.

Sewage is the liquid waste which contains water dissolved and suspended solid, organic and inorganic impurities.

The solid part of sewage is called sludge.

The sludge is used for producing compost and biogas..

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