Answer: Option C. -> ${22}^{nd}$ March      
:
C

World water day is celebrated on ${22}^{nd}$ March every year to create awareness about water conservation and its significance.

Answer: Option B. -> Phosphates
:
B

Organic impurities generated from organic material such as food, garden, etc, in sewage include animal waste, urine, oil, vegetable and fruit waste, faeces and herbicides. Inorganic impurities (all impurities excluding organic) include phosphates, nitrates and metals.

Answer: Option B. -> False
:
B
Vermi-processing toilet is a type of toilet in which human excreta is treated by earthworms. The human excreta is converted into vermi-cakes which are rich in nutrients and can be used as manure for soil. They benefit the soil as they do not contain any harmful chemicals which present in pesticides.
Also, they consume less amount of water than normal household toilets. 
 

Answer: Option A. -> Poor sanitation and contaminated drinking water is the cause for a large number of diseases.
:
A

There is a direct relationship between sanitation and diseases. Poor sanitation and contaminated drinking water are the cause of a large number of diseases. Under poor sanitation, people may resort to defecating in the open, near fields or directly in the water. It causes water and soil pollution. The surface and groundwater, both get polluted and becomes the most common carriers of water-borne diseases.

Answer: Option A. -> Septic tanks
:
A, B, and C

In order to improve sanitation, low cost onsite sewage disposal systems are being encouraged. Following are the alternate arrangements for sewage disposal:

1. Septic tanks

2. Chemical toilets

3. Composting pits
Manholes are part of a sewer system. Manholes are strategically placed in a fixed frequency in a sewer system.

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.

Answer: Option C. -> To remove the large objects
:

A setup that treats or purifies wastewater is waste-water treatment plant. Treatment of wastewater involves physical, chemical, and biological processes, which remove physical, chemical and biological matter that contaminates water.

Answer: Option C. -> To remove the large objects
:

Sewerage: 1 Mark
Inorganic impurities: 0.5 Mark each
Sewerage is like a transport system(consisting of pipes) that carries the sewage from the point of being produced to the point of disposal, i.e. wastewater treatment plant.
Various kinds of inorganic impurities present in wastewater are:
i) Nitrates
ii) Phosphates
iii) Metals
iv) Sulphates

Answer: Option C. -> To remove the large objects
:
Steps: 0.5 Mark each
Steps involved in getting clarified water from wastewater are:
1. Wastewater is passed through bar screens. Large objects like rags, sticks, cans, plastic packets, napkins are removed.
2. Water then goes to a grit and sand removal tank. The speed of the incoming wastewater is decreased to allow sand, grit and pebbles to settle down.
3. The water is then allowed to settle in a large tank which is sloped towards the middle. Solids like faeces settle at the bottom and are removed with a scraper. This is the sludge. A skimmer removes the floatable solids like oil and grease. Water so cleared is called clarified water. 
4. Air is pumped into the clarified water to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soaps and other unwanted matter still remaining in clarified water. Chemicals like chlorine is added to disinfect the clarified water, before releasing it into distribution systems.

Answer: Option C. -> To remove the large objects
:

Advantages: 0.5 Mark each
The various advantages of vermi-processing toilets are given below:
i) low water usage.
ii) safe for processing human wastes.
iii) Operation of the toilet is very simple and hygienic.
iv) Human excreta is completely converted into vermi-cakes, a resource much needed for the soil.