Microorganisms are used during which stage of the purification of the sewage water?

1. Primary treatment

2. Secondary treatment

3. None of the above

4. Both (1) and (2)

BOD of waste water is estimated by measuring the amount of:

(1) total inorganic matter

(2) biodegradable organic matter

(3) oxygen evolution

(4) oxygen consumption.

The primary treatment of waste water involved the removal of:

(1) dissolved impurities

(2) stable substances

(3) toxic substances

(4) harmful bacteria.

High value of BOD (Biochemical Oxygen Demand) indicates that

1. Water is pure

2. water is highly polluted

3. water is less polluted

4. Consumption of organic matter in the water is higher by the microbes

Which of the following in sewage treatment removes suspended solids?

(1) Tertiary treatment

(2) Secondary treatment

(3) Primary treatment

(4) Sludge treatment

What gases are produced in anaerobic sludge digesters?

1. Methane and CO₂ only

2. Methane, Hydrogen sulphide and CO₂

3. Methane, hydrogen sulphide and O₂

4. Hydrogen sulphide and CO₂

Secondary sewage treatment is mainly a

1. mechanical process

2. chemical process

3. biological process
4. physical process

Select the correct statement from the following

1. Biogas is produced by the activity of aerobic bacteria on animal waste

2. Methanobacterium is an aerobic bacterium found in rumen of cattle.

3. Biogas, commonly called gobar gas, is pure methane

4. Activated sludge-sediment in settlement tanks of sewage treatment plant is a right source of aerobic bacteria

The domestic sewage in large cities

1. has a high BOD as it contains both aerobic and bacteria

2. is processed by aerobic and then anaerobic bacteria in the secondary treatment in Sewage Treatment plants (STPs)

3. when treated in STPs does not really require the aeration step as the sewage contains adequate oxygen

4. has very high amounts of suspended solids and dissolved salts

The primary treatment of sewage involves:

1. Digestion

2. Decomposition

3. Sedimentation and filtration

4. None of these