Question

When a water is passed through filter beds of sand and gravel to remove smaller particles of dust is called
A. Oxygenation
B. Chlorination
C. Sedimentation
D. Filtration

Answer 1

Hint: Basically, oxygenation, chlorination, sedimentation and filtration are the processes involved in water treatment. The process in which the water flows through the designed filters that are made up of layers of gravel and sand to remove the smaller particles of the dust is called Filtration.

Complete Answer:
Wastewater or sewage water treatment is a process of purification of the water to make it suitable for drinking, industrial use etc. the wastewater contains impurities like pesticides, human feces, herbicide, oil, animal waste, nitrates, metals, phosphates and various bacteria and microbes that cause diseases. Water treatment involves physical process, biological process and chemical process.

1. Physical process
- Filtration: it is a process in which the water flows through the filter beds of sand and gravel, the suspended particles are filtered out.
- Sedimentation: here, the water is passed to a sedimentation tank where the solid particles settle down and the floatable impurities like oil, greece etc. are removed with the help of scraper and skimmer respectively. The impurity collected in the sedimentation tank is called sludge which is later sent to a sludge tank.

2. Biological process
- Oxygenation: this process is also called aeration. In this process the air is passed through the clarified water obtained after the physical process which helps the bacteria proliferate. It feeds on human waste and leaves soap, food waste and other materials in water. After several hours, the microbes settle down in the tank. Later the water is removed from the top.

3. Chemical process:
- Chlorination: the water obtained after the biological process is not fit for drinking. It has to be treated with chlorine to remove the leftover germs. In order to achieve this , bleaching powder is added. After chlorination, the water is fit for human consumption.

Therefore the correct answer is (D) filtration.

Note: In the filtration process,in the long run the filters get locked due to the waste and more of the filtered needs to be replaced which is expensive and the blockage of filtered results in improper purification. The sludge formed during the sedimentation process can be used to produce manure and gobar gas. The water obtained after the oxygenation process can be used for irrigation purposes.