250+ TOP MCQs on Characteristics of Wastewater – 2 and Answers

Waste Water Engineering Questions and Answers for Freshers on “Characteristics of Wastewater – 2”.

1. Turbidity in water is caused by which of these following?
a) Total dissolved solids
b) Suspended solids
c) Ions
d) Heavy metals
Answer: b
Clarification: Suspended solids majorly contribute to the turbidity present in water. This is defined as an expression of optical property that causes light to be scattered and absorbed with no change in the flux level. This is measured in NTU.

2. What is the relationship between turbidity and TSS For a settled secondary effluent?
a) TSS = (2.3) x Turbidity
b) TSS = (2.0) x Turbidity
c) TSS = (2.5) x Turbidity
d) TSS = (1.3) x Turbidity
Answer: a
Clarification: TSS = (2.3) x Turbidity. This relationship holds good for a settled secondary effluent. In case of effluent from a granular filter bed TSS = (1.3 to 1.6) x Turbidity.

3. Which characteristic of water does Calcium contribute to?
a) Hardness
b) Suspended solids
c) pH
d) Colour
Answer: a
Clarification: Hardness is caused by the salts of Calcium and magnesium. The sulphate salts contribute to permanent hardness whereas the carbonate and bicarbonate salts contribute to temporary hardness. The hardness is measured in mg/L.

4. Sodium ions contribute to which characteristic of the water?
a) pH
b) Total Dissolved Solids
c) Colour
d) Suspended solids
Answer: b
Clarification: Sodium ions contribute to Total Dissolved Solids. This is removed by the ion exchange method. In sea water the Sodium chloride is > 25000ppm.

5. What is the role of chlorine in water treatment?
a) To remove hardness
b) To remove ions
c) Coagulant agent
d) To remove bacteria
Answer: d
Clarification: Chlorine is used to remove bacteria from the water. The free chlorine in water should not exceed 2 mg/L. In surface water, the chloride level is around 10 mg/L.

6. Which heavy metal is found in cooling water treatment?
a) Zinc
b) Arsenic
c) Lead
d) Copper
Answer: a
Clarification: Zinc is the heavy metal found in cooling water. Other heavy metals such as arsenic are found in the waste from the pesticide industry. Zinc is also found in wastes dissolved from galvanized pipes.

7. How is hardness represented?
a) Hardness = 2 ( Ca²⁺) +2( Mg²⁺)
b) Hardness = Ca ²⁺ + 2 (Mg ²⁺)
c) Hardness = 3(Ca ²⁺) + Mg ²⁺
d) Hardness = 3(Ca ²⁺) +2( Mg²⁺)
Answer: a
Clarification: Hardness is 2 (Ca ²⁺) +2( Mg ²⁺). Hardness is contributed by the Magnesium and Calcium salts. It is of two types; permanent and temporary hardness.

8. What is the level of Calcium carbonate for a moderately hard water?
a) Hardness >150 ppm
b) Hardness= 50 ppm
c) Hardness is in between 50-100 ppm
d) Hardness <50 ppm
Answer: c
Clarification: Hardness is in between 50-100 ppm in the case of moderately hard water. In the case of soft water it is less than 50 ppm. In the case of hard water, it is in between 100-150 ppm. In case of very hard water it is greater than 150 ppm.

9. How is TDS and conductivity related?
a) TDS = 0.5 conductivity
b) Conductivity= 0.5 TDS
c) TDS=3 Conductivity
d) TDS=Conductivity
Answer: a
Clarification: TDS = 0.5 Conductivity. This relationship holds good at low TDS. At high TDS values, TDS = 0.9 (slope of line) × electrical conductivity.

10. Colour is contributed to which of the following?
a) Natural organic matter
b) Inorganic compounds
c) Total dissolved solids
d) Suspended solids
Answer: a
Clarification: Natural organic compound contributes to the colour of the water. This is secreted by the metabolic activity of algae, protozoa etc. This imparts a yellowish colour to the water.

11. What will be the Total Organic Carbon (TOC) of coloured water?
a) 100-200ppm
b) 100ppm
c) 200ppm
d) 200-300 ppm
Answer: a
Clarification: The TOC of coloured water would be in the range of 100-200 ppm. The TOC of groundwater is 0.2-2 ppm. The TOC of surface water is 1-20 ppm.

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