Answer: Option A. -> Sewerage
:
A
Sewerage is like a transportation system that carries sewage from the point of production i.e. households, industries, hospitals, to the point of disposal i.e. wastewater treatment plant.
These systems have manholes located at fixed frequency. It is necessary to have a sewerage system without which we may be exposed to various air-borne diseases.
 

Answer: Option B. -> False
:
B

Sewage is a complex mixture which contains various organic and inorganic impurities. They need to be removed before they are discharged into water bodies. If they are directly discharged into the water bodies it will harm the aquatic life as well as the human population.

Answer: Option D. -> It is used to disinfect water and absorb ultraviolet rays
:
D

Ozone is used to disinfect water and it also absorbs ultraviolet rays. Other uses of ozone are as follows:

1. Kills bacteria effectively.

2. Oxidises substances such as iron and sulphur so that they can be filtered out of the solution.

3. There are no nasty odours or residues produced from the treatment.

4. Ozone converts back into oxygen quickly and leaves no trace once it has been used.

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 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 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 tank where it is decomposed by anaerobic bacteria. Biogas is produced during this process. Dried sludge can be used as a manure.
 

Answer: Option A. -> nitrogen
:
A

Sewage contains harmful nutrients such as phosphorus and nitrogen. 
Too much nitrogen and phosphorus in water causes algae to grow faster. Significant increase in algae will lead to decrease in oxygen which is required by other aquatic animals.
Hence, excess of nutrients in sewage is harmful.

Answer: Option A. -> It is used to disinfect water.
:
A and B
Ozone has various usage. It is used to disinfect water. Germs and bacteria present in water get degrade when ozone is passed through water. Ozone also removes the foul smell from wastewater.
The ozone layer present in the atmosphere protects us from harmful ultraviolet rays by absorbing them. 

Answer: Option B. -> Septic tanks
:
B

Septic tanks are suitable for places, such as hospitals, isolated buildings or a cluster of 4-5 houses, where there is no sewerage system. A septic tank is a tank, that is typically underground, in which sewage is collected and allowed to decompose through bacterial activity before draining by means of a leaching field.