250+ TOP MCQs on Chemical Reactions Associated with Water Treatment and Answers

Waste Water Engineering Multiple Choice Questions on “Chemical Reactions Associated with Water Treatment”.

1. The chemical composition of wastewater naturally reflects the origin from which it came.
a) True
b) False
Answer: a
Clarification: Wastewater is the liquid end-product, or by-product, of municipal, agricultural, and industrial activity. As such, the chemical composition of wastewater naturally reflects the origin from which it came.

2. The world’s available fresh water supply is about _______ percent of that total water supply.
a) 10
b) 4
c) 3
d) 7
Answer: c
Clarification: The world’s available fresh water supply is about 3 percent of that total water supply. Only 20 percent of this amount is available for use in drinking water supplies. The remainder of the world water is salt water, which is costly to desalinate for drinking water purposes.

3. Which of the following related to the aerobic organic matter is true?
a) Essential nutrients for growth
b) Development of sludge deposits
c) Growth of undesirable aquatic life
d) Development of septic conditions
Answer: d
Clarification: Both nitrogen and phosphorus are essential nutrients for growth. These nutrients can lead to the growth of undesirable aquatic life. Their biological stabilization can lead to the depletion of natural oxygen resources and to the development of septic conditions.

4. ______ tend to resist conventional methods of wastewater treatment.
a) Suspended solids
b) Nutrients
c) Refractory organics
d) Priority pollutants
Answer: c
Clarification: Refractory organics tend to resist conventional methods of wastewater treatment. Typical examples include surfactants, phenols, and agricultural pesticides.

5. The quality of the fish habitat begins to increase when the dissolved oxygen concentration drops below 4 or 5 mg L-1.
a) True
b) False
Answer: b
Clarification: The quality of the fish habitat begins to decrease when the dissolved oxygen concentration drops below 4 or 5 mg L-1. Even if the receiving stream is at saturation, which is unlikely, that leaves only 3 or 4 mg L-1 of oxygen to be used for assimilation of the wastewater discharge.

6. Organic matter + nutrients + O₂ → CO₂ + H₂O + _______
a) Biomass
b) O₂
c) Nutrients
d) Organic matter
Answer: a
Clarification: This is the general form of the equation for decomposition of organic matter during the BOD test. It should be noted that oxygen is consumed in the reaction and biomass is the catalyst for the reaction.

7. 2NH₃ +3O₂ -> 2NO₂^– + ___ + 2H₂O.
a) O₂
b) 2H⁺
c) H⁺
d) 2O₂
Answer: b
Clarification: This equation represents the first step of nitrification. Ammonia combines with oxygen to give nitrite and water in the presence of nitrosomonas bacteria. Two hydrogen free radicles are produced.

8. Which among these is the alternative BOD test for determining the oxygen consuming potential of a wastewater sample?
a) ThOD
b) COD
c) BOD
d) TOC
Answer: b
Clarification: An alternative to the BOD test for determining the oxygen consuming potential of a wastewater sample is the chemical oxygen demand (COD) test. As the name implies, the carbonaceous oxygen demand is oxidized chemically in the COD test.

9. What does SWOT stand for?
a) Solid Waste Operation and Treatment
b) Storm Water Operation and Treatment
c) Supercritical Water Oxidation
d) Storm and Wastewater Operation and Treatment
Answer: c
Clarification: Supercritical water oxidation (SCWO) is an intensive version of the WAO process. SCWO has become a rapidly developing innovative waste treatment technology for the oxidation of organic wastes and hazardous materials in water.

10. What is the combination of using a photocatalyst and UV or visible light for the treatment of wastewater and gaseous pollutants is called?
a) Photocatalysis
b) Super critical water oxidation
c) Advanced oxidation process
d) Wet air oxidation
Answer: a
Clarification: Photocatalysis is the combination of using a photocatalyst and UV or visible light for the treatment of wastewaters and gaseous pollutants. When illuminating a photocatalyst using UV or visible light, various organic compounds can be oxidized and mineralized at the photocatalyst surface or oxidized in solution ambient and atmospheric condition.

11. What is stoichiometry?
a) A quantitative relationship between reactants and products
b) Defines a qualitative value of the reactants and products
c) Defines the quantity of reactants and products upon reaching equilibrium
d) It defines quantity of only reactants
Answer: a
Clarification: Stoichiometry is a quantitative relationship between reactants and products. This is arrived only after balancing a chemical equation. This is required to calculate the rate of a reaction.

12. What is the rate of a chemical reaction not dependent on?
a) Stoichiometry
b) Surface area of reactants
c) Temperature
d) Pressure
Answer: d
Clarification: The rate of a reaction is independent of the pressure. Stoichiometry is the basis on which the rate of a reaction is defined. Greater the surface area of the reactants, greater is the rate of a reaction.

13. How is iconic strength related to total dissolved solids?
a) I= (2.5 x 10^-5)TDS
b) I = (2.5 × 10⁵) TDS
c) I= 2.5 TDS
d) I = 2.5 x10 TDS
Answer: a
Clarification: I = (2.5×10^-5) TDS .This correlation was defined by Stumm and Morgan in 1996. The ionic strength can be found if the TDS is known. TDS is measured in mg/L.

14. In solutions as ionic concentration increases a non-ideal condition arises. To account for this non-ideal condition due to the ion-ion interaction what is the effective concentration term called as?
a) Activity
b) Dielectric constant
c) Ionic coefficient
d) Ionic strength
Answer: a
Clarification: Activity is the effective concentration term used to account for the non-ideal conditions encountered due to ion-ion interaction. Activity is defined at 1 atm pressure and 298.15 K temperature. It is measured in mol/L (M).

15. In dilute solutions which are normally encountered in water treatment what is the value of the activity of coefficient assumed?
a) 0.5
b) 0.75
c) 1.0
d) >1
Answer: c
Clarification: In dilute solutions usually encountered in water treatment the activity of coefficient assumed is 1. For electrolytes the activity coefficient is assumed <1 and for non-electrolytes >1.

16. What will be the activity coefficient of a solution consisting of monovalent ions?
a) Equal to 1
b) >1
c) Close to 1
d) <0
Answer: c
Clarification: The activity coefficient of a solution consisting of monovalent ions would be close to 1. For water supplies usually, the ionic strength is <5millimole/L. The Davies Equation is used to calculate the activity for concentrated solutions <0.1 M.

17. In case of Moving Bed Bioreactor and Activated Sludge process which is the factor that limits the rate of the reaction?
a) temperature
b) pressure
c) pH
d) ionic composition
Answer: a
Clarification: Temperature limits the rate of reaction in case of both Moving bed bioreactor and Activated Sludge Process. As temperature increases the rate of the reaction increases. But beyond a value of the temperature the rate decreases, as the enzymes present in the bacteria get deactivated.

18. What is the value of activity coefficients for monovalent and divalent ions for a potable water at an ionic strength of 0.01 M?
a) 0.9 and 0.66 respectively.
b) 0.9 in both the cases
c) 0.66 and 0.9 respectively.
d) 0.66 in both the cases
Answer: a
Clarification: The value of the activity coefficient for the monovalent ion is 0.9. The value of the activity coefficient for the divalent ion is 0.66. The activity coefficients for neutral species is negligible.

19. In water treatment which factor which has a major control over reaction selectivity and product distribution?
a) pH
b) temperature
c) pressure
d) ionic concentration
Answer: a
Clarification: The pH has a major control over reaction stability and product distribution. The pH determines whether the reactant species are catalyst or ionic. Control of the pH will result in an acceleration of desired pathways.

20. The degradation of BOD is classified as what type of reaction?
a) First Order Reaction
b) Zero Order Reaction
c) Second Order Reaction
d) Third Order Reaction
Answer: a
Clarification: The degradation of Biological Oxygen Demand is classified as First Order Reaction. r_L =− k_LL. This is the equation that depicts the degradation of BOD. Here r_L represents the rate of reaction, k_L represents coefficient of rate of degradation of BOD and L represents the BOD concentration.