Q: A rapid-mixing basin has a flow rate $Q = 7570\ m^3/d$ and a detention time $t_o = 5\ s$. What is the required volume $V$ of the basin? (1 day = 86400 s)

$V = (5\ s) \times (7570\ m^3/d) \times \left(\frac{1\ d}{86400\ s}\right) = 0.438\ m^3$

Question 1

Which of the following best describes the difference between palatable and potable water?

Accepted Answer

Palatable water is esthetically pleasing and does not pose a health threat, while potable water is safe to drink but may not be esthetically pleasing.

Question 2

Which regulation sets the maximum contaminant levels (MCLs) for drinking water in the United States?

Accepted Answer

Safe Drinking Water Act (SDWA)

Question 3

A water treatment plant uses alum as a coagulant. What is the primary chemical reaction that occurs when sufficient alkalinity is present?

Accepted Answer

$2Al^{3+} + 6HCO_3^- \rightarrow 2Al(OH)_3(s) + 6CO_2$

Question 4

Which of the following is a typical characteristic of groundwater compared to surface water?

Accepted Answer

Constant composition and high hardness

Question 5

What is the main goal of coagulation and flocculation in water treatment?

Accepted Answer

To alter the surface charge of particles so they can adhere and settle by gravity

Question 6

A rapid-mixing basin has a flow rate $Q = 7570\ m^3/d$ and a detention time $t_o = 5\ s$. What is the required volume $V$ of the basin? (1 day = 86400 s)

Accepted Answer

$V = (5\ s) 	imes (7570\ m^3/d) 	imes \left(\frac{1\ d}{86400\ s}ight) = 0.438\ m^3$

Question 7

Which of the following is NOT a typical coagulant used in water treatment?

Accepted Answer

Sodium chloride ($NaCl$)

Question 8

What is the purpose of backwashing in rapid sand filtration?

Accepted Answer

To remove trapped particles by reversing the flow of water

Question 9

Which of the following best describes the categories used to assess drinking-water quality?

Accepted Answer

Physical, chemical, microbiological, and radioactivity

Question 10

A water treatment plant has a flow rate of $0.044\ m^3/s$ and uses dual media filters with each filter bed measuring $3\ m 	imes 2\ m$. If the design loading rate is $150\ m^3/(day \cdot m^2)$, how many filter beds are needed?

Accepted Answer

6

Question 11

Which of the following statements about surface water treatment is correct?

Accepted Answer

Filtration is used to remove particles too small to be removed by sedimentation.

Question 12

What is the formula for the velocity gradient $G$ in a rapid mixing basin?

Accepted Answer

$G = \sqrt{\frac{P}{\mu V}}$

Question 13

Which of the following is a reason why trivalent cations are preferred as coagulants?

Accepted Answer

They are more effective at neutralizing the negative charge on colloids.

Question 14

What is the main difference between single media and multimedia filters in water treatment?

Accepted Answer

Single media filters use only sand, while multimedia filters use layers such as anthracite coal, sand, and garnet.

Question 15

A sedimentation basin has a flow rate $Q$ and a surface area $A_s$. What is the formula for the overflow rate $V_o$?

Accepted Answer

$V_o = \frac{Q}{A_s}$

Question 16

Which of the following is a typical detention time for water in a sedimentation basin?

Accepted Answer

At least 4 hours

Question 17

Why is hydrofluosilicic acid often added to water prior to distribution?

Accepted Answer

To improve dental health by providing fluoride

Question 18

Which of the following is a common misconception about the purpose of flocculation?

Accepted Answer

It is used to rapidly mix chemicals and water for immediate reaction.

Question 19

Which of the following is a physical parameter used to describe drinking-water quality?

Accepted Answer

Turbidity

Chapter 10: Water Treatment – Principles and Processes

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