Civil Engineering PE Water and Wastewater Treatment Questions and Answers

Question 1

An operator at an activated sludge wastewater treatment plant observes persistent sludge bulking, characterized by a high Sludge Volume Index (SVI) and poor settling in the secondary clarifier.
Microscopic examination reveals a predominance of filamentous bacteria.
Which of the following operational conditions is the MOST likely cause of this type of bulking?

Accepted Answer

A consistently low Food-to-Microorganism (F/M) ratio

Answer

High dissolved oxygen (DO) concentration in the aeration basin

Answer

A short Mean Cell Residence Time (MCRT)

Answer

Excessive influent alkalinity

Question 2

In the process of water disinfection, what does the 'breakpoint' in the breakpoint chlorination curve represent?

Accepted Answer

The point at which the chlorine demand has been satisfied, and any further chlorine added results in a proportional increase in free available chlorine residual.

Answer

The point of maximum formation of combined chlorine residuals (chloramines).

Answer

The initial dose of chlorine required to overcome immediate demand from inorganic reductants like iron.

Answer

The optimal pH for chlorine disinfection, which is achieved by the addition of chlorine gas.

Question 3

A rectangular primary sedimentation basin at a water treatment plant is 100 ft long, 30 ft wide, and has a water depth of 12 ft. If the plant flow rate is 3.0 MGD (Million Gallons per Day), what is the surface overflow rate?

Accepted Answer

1,000 gpd/ft²

Answer

83,333 gal/day

Answer

1,250 gpd/ft²

Answer

83 gpd/ft²

Question 4

A wastewater treatment plant is being designed to achieve total nitrogen removal. Which of the following sets of conditions is essential for the biological process of denitrification?

Accepted Answer

An anoxic environment (DO < 0.2 mg/L) and an available carbon source

Answer

An aerobic environment (DO > 2.0 mg/L) and the presence of ammonia

Answer

A low pH (< 6.0) and a short solids retention time (SRT)

Answer

A high concentration of phosphorus and an aerobic environment

Question 5

A public water system is struggling with high levels of disinfection byproducts (DBPs), specifically trihalomethanes (THMs) and haloacetic acids (HAAs), exceeding regulatory limits. Which of the following strategies is generally considered a highly effective method for reducing the formation of these DBPs?

Accepted Answer

Switching the secondary disinfectant from free chlorine to chloramines for the distribution system.

Answer

Increasing the chlorine dose to ensure complete oxidation of organic precursors.

Answer

Lowering the water's pH prior to chlorination to increase the potency of hypochlorous acid.

Answer

Lengthening the chlorine contact time to allow for DBP degradation.

Question 6

What are the two primary objectives of utilizing anaerobic digestion for the stabilization of municipal wastewater sludge?

Accepted Answer

To reduce the mass of volatile solids and produce methane-rich biogas.

Answer

To increase the sludge volume and sterilize the material with high pressure.

Answer

To convert ammonia to nitrate and increase the dewaterability of the sludge.

Answer

To disinfect the sludge and precipitate heavy metals.