Civil Engineering PE Water and Wastewater Treatment 3

Question 1

A wastewater treatment plant has a BOD₅ of 200 mg/L and a flow of 2 MGD. What is the BOD load entering the plant in lb/day?

Accepted Answer

3,338 lb/day

Answer

400 lb/day

Answer

1,000 lb/day

Answer

2,000 lb/day

Question 2

Which type of lagoon uses algae to supply oxygen to heterotrophic bacteria for BOD removal?

Accepted Answer

Facultative lagoon

Answer

Anaerobic lagoon

Answer

Aerated lagoon

Answer

Polishing lagoon

Question 3

In a water softening process using lime-soda ash, what does the addition of soda ash (Na₂CO₃) primarily remove?

Accepted Answer

Non-carbonate (permanent) hardness caused by calcium sulfate or chloride

Answer

Carbonate hardness caused by Ca²⁺ and Mg²⁺

Answer

Iron and manganese

Answer

Total dissolved solids

Question 4

What is the mean cell residence time (MCRT or SRT) if the aeration basin volume is 500,000 gallons, MLSS = 2,500 mg/L, daily sludge wasting = 5,000 lb/day, and effluent TSS is negligible?

Accepted Answer

~2.1 days

Answer

~4.2 days

Answer

~6.3 days

Answer

~8.4 days

Question 5

Ultraviolet (UV) disinfection of wastewater is most effective at which UV wavelength range?

Accepted Answer

254 nm (germicidal UV-C)

Answer

200–230 nm

Answer

300–320 nm (UV-B)

Answer

365–400 nm (UV-A)

Question 6

In a trickling filter, the hydraulic application rate (HAR) is typically expressed in units of:

Accepted Answer

million gallons per day per acre

Answer

lb BOD/1,000 ft³/day

Answer

gallons per minute per square foot

Answer

gpm/ft² of cross-section

Question 7

Which parameter is used to measure the oxygen-depleting strength of industrial wastewater when biological methods are not applicable?

Accepted Answer

Chemical oxygen demand (COD)

Answer

Total suspended solids (TSS)

Answer

Biochemical oxygen demand (BOD₅)

Answer

Total organic carbon (TOC)