Water and Wastewater Treatment Flashcards
7 cards from real Civil Engineering PE practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Water and Wastewater Treatment flashcards as text
Nitrification in biological wastewater treatment converts ammonia (NH₄⁺) to nitrate (NO₃⁻). Which bacteria perform the second step, converting nitrite (NO₂⁻) to nitrate?
Answer: Nitrobacter
Nitrobacter (and related genera) oxidize nitrite to nitrate in the second step of nitrification, requiring a long SRT due to slow growth.
What is the primary purpose of a grit chamber at the headworks of a wastewater treatment plant?
Answer: Remove heavy inorganic particles to protect downstream equipment
Grit chambers remove sand, gravel, and heavy inorganic solids to prevent abrasion and clogging of pumps, pipes, and downstream treatment units.
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?
Answer: 1.0-log
Total required inactivation = 3-log; UV provides 2-log; therefore chlorination must provide 3 − 2 = 1-log inactivation.
In anaerobic digestion of biosolids, what is the primary end product that is captured for energy recovery?
Answer: Methane (biogas)
Anaerobic digestion produces biogas composed predominantly of methane (~65%) and CO₂ (~35%), which can be captured and used for energy.
The Langelier Saturation Index (LSI) is used in water distribution systems to assess:
Answer: The tendency of water to precipitate or dissolve calcium carbonate
LSI = pH − pHs; a positive LSI indicates scale-forming water, a negative LSI indicates corrosive water, and zero indicates equilibrium with CaCO₃.
A wastewater treatment plant achieves 90% BOD removal. If influent BOD = 250 mg/L, what is the effluent BOD?
Answer: 25 mg/L
Effluent BOD = influent × (1 − removal efficiency) = 250 × (1 − 0.90) = 250 × 0.10 = 25 mg/L.
Which membrane process is capable of removing dissolved salts and is commonly used for desalination or advanced water treatment?
Answer: Nanofiltration (NF) and Reverse Osmosis (RO)
NF and RO membranes have pore sizes small enough (< 1 nm) to reject dissolved ions and salts via solution-diffusion transport.