1. What is sewage? Explain why it is harmful to discharge untreated sewage into rivers or seas?

Ans. Sewage is wastewater released by homes, industries, hospitals, offices and other users.

Sewage is harmful to discharge untreated into rivers or seas because sewage is a complex mixture of suspended solids, organic and inorganic impurities, nutrients, saprotrophic and disease causing bacteria and other microbes.

2. Why should oils and fats be not released in the drain? Explain.

Ans. Oils and fats should not be thrown down the drain. They get harden and block the pipes. In an open drain the fats clog the soil pores reducing its effectiveness in filtering water.

3. Describe the steps involved in getting clarified water from wastewater.

Ans. 

Step 1: When wastewater passes through bar screens. Large objects like rags, sticks, cans, plastic packet are removed.

Step 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

Step 3: The water is then allowed to settle in a large tank which is sloped towards the middle solid like faeces, that settle at the bottom and are removed with scraper.

Step 4: Air is pumped into step 3 to clarify water and to help aerobic bacteria to grow. Bacteria consume human waste, food waste, soap and other unwanted matter that still remains in clarified water.

After several hours, the suspended microbes settle at the bottom of the tank as activated sludge. The water is then removed from the top.

4. What is sludge? Explain how it is treated?

Ans. Solids like faeces settle at the bottom of tank and are removed with a scarper is called sludge. The sludge is transferred to a separate tank where it is decomposed by the anaerobic bacteria. The biogas produced in the process can be used as fuel or can be used to produce electricity.

5. Untreated human excreta is a health hazard. Explain.

Ans. Human excreta may cause water pollution and soil pollution. Both the surface water and ground water get polluted. Ground water is a source of water for wells, tubewells, springs and many rivers. Thus it becomes the most common route for water borne diseases. They include cholera, typhoid, polio, meningitis, hepatitis and dysentery.

6. Name two chemicals used to disinfect water.

Ans. 1. Chlorine 2. Ozone.

7. Explain the function of bar screens in a wastewater treatment plant.

Ans. When wastewater passes through the bar screens, large objects like rags, sticks, cans, plastic packets, napkins are removed under the filtration process.

8. Explain the relationship between sanitation and disease.

Ans. Poor sanitation and contaminated drinking water is the cause of a large number of diseases.

9. Outline your role as an active citizen in relation to sanitation.

Ans. Waste generation is a natural part of human activity. But we can limit the type of waste and quantity of waste produced. Open drains are common in our localities causing unhygienic and unsanitary conditions. As an active citizen we can approach the municipality or the gram panchayat, to insist that the open drains must be covered. If the sewage of any particular house makes the neighbourhood dirty, we should request them to be more considerate about others' health.

10. Study the following statements about ozone:

(a) It is essential for breathing of living organisms.

(b) It is used to disinfect water.

(c) It absorbs ultraviolet rays.

(d) Its proportion in air is about 3%.

Which of these statements are correct?

(i) (a), (b) and (c)

(ii) (b) and (c)

(iii) (a) and (d)

(iv) All four

Ans. (ii) b and c