Answer: Option D. -> Pass chlorine through it
:
D
He should pass chlorine or ozone gas through it before supplying it to different parts of the city as they are disinfecting agents. They kill the bacteria and germs present in the water and make it fit for consumption.

Answer: Option B. -> (i) - b, (ii) - a, (iii) - c
:
B
Sewage is a complex mixture containing suspended solids, organic and inorganic impurities, nutrients and disease causing bacteria and other microbes.
It contains organic impurities such as human faeces and animal wastes, inorganic impurities such as metals, nitrates and disease causing bacteria such as vibrio cholerae which causes cholera.

Answer: Option B. -> Sedimentation
:
B
Wastewater is a complex mixture of lather, oil, organic and inorganic impurities. It needs to be purified before it is discharged into the water bodies. The whole process is called wastewater treatment.
Sedimentation is the process in which the heavy dirt particles and sand is allowed to settle at the bottom of the tank under the influence of gravity.
Screening is the first step in wastewater treatment. In this wastewater is passed through screens and bars to remove large objects like plastic bag, sticks, and cans.
In aeration, air is pumped into the water to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soaps and other unwanted matter still remaining in water.

Answer: Option A. -> sludge
:
A
The sludge is a semiliquid waste, which is obtained from the processing of municipal sewage. After drying, the sludge is used as manure.
Sewage is a complex mixture containing suspended solids, organic and inorganic impurities.
Sewerage is like a transport system that carries sewage from the households and industries to the treatment plant.

Answer: Option C. -> Biogas and sludge
:
C
When wastewater is allowed to settle in a large tank, solids like mud, faeces settle at the bottom of the tank. This is called sludge. It is transferred to a separate tankwhere it is decomposed by anaerobic bacteria. Biogas is produced during this process. Dried sludge can be used as a manure.

:
Explanation: 2 Marks
Air is pumped into the clarified water to help aerobicbacteria grow. Bacteria consume human waste, food waste, soaps and other unwanted matter still remaining in the clarified water. After some time, the suspended microbes settle at the bottom of the tank as activated sludge. The pure water is then removed from the top.

:
a) 2 Marks
b) 3 Marks
a) Water pollutionrefers to the mixing of contaminants orpollutantsinto thewaterbodies (sea, lakes, rivers, oceans, groundwater, etc) through direct or indirect discharges which causes environmental degradation and affects whole biosphere.
Sources of water pollution are:domestic waste and sewage, hot water released fromcooling power plants.
b)Sewage is a mixture of wastewater coming out of homes and other places.
Sewers are pipes which carry sewage.
Sewerage is a network of sewage carrying pipes.

Answer: Option A. -> True
:
A
Untreated human excreta is a health hazard because this results in poor sanitation. A very large fraction of people defecate in the open, on railway tracks or directly into water. It causes water and soil pollution. This can lead to a lot of water borne diseases such as typhoid and cholera.

Answer: Option B. -> Eucalyptus tree
:
B
Eucalyptus trees are suggested to be grown near sewage ponds as eucalyptus trees absorb all surplus waste water rapidly and release pure water vapour into the atmosphere.

Answer: Option C. -> To remove the large objects
:
C
In a wastewater treatment plant, the wastewater is passed through bar screens. Large objects like plastics, rags, cans, etc are filtered in this process. This process is also known as screening.
Screening is the first stage of a wastewater treatment process.