Civil Engineering PE Water and Wastewater Treatment 4

Question 1

Nitrification in biological wastewater treatment converts ammonia (NH₄⁺) to nitrate (NO₃⁻). Which bacteria perform the second step, converting nitrite (NO₂⁻) to nitrate?

Accepted Answer

Nitrobacter

Answer

Nitrobacter (and related genera) oxidize nitrite to nitrate in the second step of nitrification, requiring a long SRT due to slow growth.

Question 2

What is the primary purpose of a grit chamber at the headworks of a wastewater treatment plant?

Accepted Answer

Remove heavy inorganic particles to protect downstream equipment

Answer

Grit chambers remove sand, gravel, and heavy inorganic solids to prevent abrasion and clogging of pumps, pipes, and downstream treatment units.

Question 3

A water utility must achieve 3-log (99.9%) Giardia inactivation. If UV provides 2-log inactivation, how much additional log inactivation must chlorination provide?

Accepted Answer

1.0-log

Answer

Total required inactivation = 3-log; UV provides 2-log; therefore chlorination must provide 3 − 2 = 1-log inactivation.

Question 4

In anaerobic digestion of biosolids, what is the primary end product that is captured for energy recovery?

Accepted Answer

Methane (biogas)

Answer

Anaerobic digestion produces biogas composed predominantly of methane (~65%) and CO₂ (~35%), which can be captured and used for energy.

Question 5

The Langelier Saturation Index (LSI) is used in water distribution systems to assess:

Accepted Answer

The tendency of water to precipitate or dissolve calcium carbonate

Answer

LSI = pH − pHs; a positive LSI indicates scale-forming water, a negative LSI indicates corrosive water, and zero indicates equilibrium with CaCO₃.

Civil Engineering PE Practice Test

Civil Engineering PE Practice Test

Civil Engineering PE Water and Wastewater Treatment 4