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