Question 1

Which of the following contaminants in wastewater is most directly responsible for causing eutrophication in natural water bodies?

Accepted Answer

Nutrients

Question 2

A primary goal of pretreatment in municipal wastewater treatment is to:

Accepted Answer

Remove materials that can cause operational problems in downstream processes

Question 3

Given a grit chamber with a horizontal velocity of $$0.25\ \mathrm{m\cdot s$$^{-1}$$}$$, a width of $$0.56\ \mathrm{m}$$, and a length of $$13.5\ \mathrm{m}$$, will a grit particle with a radius of $$0.04\ \mathrm{mm}$$ and a specific gravity of $$2.65 be $$collected if the settling velocity is $$0.039\ \mathrm{m/s}$$? Assume the depth is sufficient for settling.

Accepted Answer

Yes, because the particle will settle before reaching the end of the chamber

Question 4

Which equation correctly describes the settling velocity $$v_s of a $$spherical particle in laminar flow in a grit chamber?

Accepted Answer

$$v_s = \frac{g(p_p - p_w)d_p^2$}{18\mu}$$

Question 5

A primary sedimentation tank has a flow rate of $$0.150\ \mathrm{m^3$/s}$$, a length of $$40.0\ \mathrm{m}$$, a width of $$10.0\ \mathrm{m}$$, and a liquid depth of $$2.0\ \mathrm{m}. $$What is the detention time in seconds?

Accepted Answer

$$5333\ \mathrm{s}$$

Question 6

Which process in municipal wastewater treatment is designed to remove approximately 85% of BOD and solids?

Accepted Answer

Secondary treatment

Question 7

Industrial wastewaters must be pretreated before discharge to municipal systems primarily to:

Accepted Answer

Remove materials not treatable by municipal systems

Question 8

Which of the following is NOT a typical contaminant found in untreated domestic wastewater?

Accepted Answer

Radioactive isotopes

Question 9

Calculate the cross-sectional area $$A_k of a $$grit chamber if the flowrate $$Q is$$ $$10,000\ \mathrm{m^3$/d}$$ and the velocity $$v is$$ $$0.3\ \mathrm{m/s}. $$Use $$1\ \mathrm{d} = 86,400\ \mathrm{s}.$$

Accepted Answer

$$A_k = 0.39\ \mathrm{m^2$}$$

Question 10

Which of the following best describes the purpose of bar racks and grinders in wastewater treatment?

Accepted Answer

To remove and grind larger objects

Question 11

If the width $$W of a $$grit chamber is calculated as $$W = \sqrt{A_k/1.5}$$ and $$A_k = 0.39\ \mathrm{m^2$}$$, what is the width?

Accepted Answer

$$0.51\ \mathrm{m}$$

Question 12

Which of the following is a correct statement about the relationship between primary, secondary, and tertiary treatment in municipal wastewater systems?

Accepted Answer

Secondary treatment follows primary treatment and removes more BOD and solids

Question 13

A primary sedimentation tank has a surface area of $$400\ \mathrm{m^2$}$$ and a flow rate of $$0.150\ \mathrm{m^3$/s}. $$What is the overflow rate $$v_o in$$ $$\mathrm{m^3$\cdot m$$^{-2}$$\cdot d$$^{-1}$$}$$? (Use $$1\ \mathrm{d} = 86,400\ \mathrm{s})$$

Accepted Answer

$$32\ \mathrm{m^3$\cdot m$$^{-2}$$\cdot d$$^{-1}$$}$$

Question 14

Which of the following is a plausible consequence of failing to remove grit in a wastewater treatment plant?

Accepted Answer

Abrasion and damage to pumps and mechanical devices

Question 15

If the depth $$D of a $$grit chamber is $$1.5$$ times the width $$W$$, and $$W = 0.51\ \mathrm{m}$$, what is the depth?

Accepted Answer

$$0.76\ \mathrm{m}$$

Question 16

Which of the following is the correct formula for calculating the detention time $$t_d$$ required for a particle to fall the entire tank depth $$D at $$settling velocity $$v_s$$?

Accepted Answer

$$t_d = \frac{D}{v_s}$$

Question 17

Which of the following is a typical BOD value (as $$\mathrm{O_2$}) $$for strong municipal waste?

Accepted Answer

$$300\ \mathrm{mg/L}$$

Question 18

Which of the following statements about sludge in wastewater treatment is correct?

Accepted Answer

Sludge must be treated and disposed of to prevent environmental harm

Wastewater Treatment: Principles, Contaminants, and Primary Treatment Processes

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