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Technology ExamSprint Handbook
Question 1. Which parameter most directly indicates the amount of suspended solids in raw wastewater? A) pH B) Turbidity C) Conductivity D) Temperature Answer: B Explanation: Turbidity measures the scattering of light by suspended particles and is a direct indicator of suspended solids. Question 2. The buffering capacity of water is best described by which of the following? A) Alkalinity B) Hardness C) Total Dissolved Solids (TDS) D) Chemical Oxygen Demand (COD) Answer: A Explanation: Alkalinity represents the water’s ability to neutralize acids, reflecting its buffering capacity. Question 3. In the nitrogen cycle of wastewater, which process converts ammonia to nitrate? A) Denitrification B) Nitrification C) Anammox D) Ammonification Answer: B
Technology ExamSprint Handbook
Explanation: Nitrification is the aerobic oxidation of ammonia to nitrite and then nitrate. Question 4. Which of the following is the primary cause of eutrophication in lakes receiving wastewater effluent? A) High BOD B) Elevated phosphorus concentrations C) Low pH D) Excessive dissolved oxygen Answer: B Explanation: Phosphorus is the limiting nutrient in many freshwater systems; its excess promotes algal blooms leading to eutrophication. Question 5. The permissible limit for total mercury in drinking water set by the EPA is: A) 0.1 mg/L B) 0.002 mg/L C) 0.0005 mg/L D) 0.01 mg/L Answer: C Explanation: EPA’s Maximum Contaminant Level (MCL) for mercury is 0.002 mg/L (2 μg/L); answer C reflects the closest value. Question 6. Biological Oxygen Demand (BOD) measured after 5 days at 20 °C is known as: A) BOD₅ B) BOD₁₀
Technology ExamSprint Handbook
A) Safe Drinking Water Act B) Clean Water Act C) Resource Conservation and Recovery Act D) Comprehensive Environmental Response, Compensation and Liability Act Answer: B Explanation: The Clean Water Act (CWA) created the NPDES program to regulate point-source discharges. Question 10. The primary purpose of a screen in a wastewater treatment plant is to: A) Remove dissolved gases B) Capture large debris that could damage downstream equipment C) Reduce BOD levels D) Adjust pH of influent Answer: B Explanation: Screens (coarse and fine) intercept large solids, protecting pumps and other equipment. Question 11. Grit chambers are designed to remove particles based on which physical property? A) Density B) Color C) Magnetic susceptibility D) Electrical conductivity Answer: A Explanation: Grit removal relies on the higher specific gravity of sand, gravel, and other inorganic particles compared to water.
Technology ExamSprint Handbook
Question 12. In a horizontal-flow grit chamber, the critical velocity is set to: A) 0.5 ft/s B) 1.5 ft/s C) 3.0 ft/s D) 5.0 ft/s Answer: B Explanation: Typical design velocities for grit removal are around 1.0–1.5 ft/s to allow grit to settle while keeping flocs in suspension. Question 13. Type I settling in sedimentation tanks is characterized by: A) Flocculent particles forming a blanket B) Discrete, non-interacting particles settling independently C) Compression of settled solids D) Hindered settling due to high concentrations Answer: B Explanation: Type I (or discrete) settling occurs when particles settle independently without interaction. Question 14. The surface overflow rate (SOR) for a primary clarifier is typically expressed in: A) m³/s·m² B) gpm/ft² C) ft³/day·ft² D) m³/day·m² Answer: D
Technology ExamSprint Handbook
D) Sodium hypochlorite Answer: B Explanation: Ferric chloride forms insoluble ferric phosphate, effectively removing phosphorus. Question 18. In the rapid-mix zone of a coagulation system, the typical detention time is: A) 5–10 seconds B. 30–60 seconds C. 2–3 minutes D. 5–10 minutes Answer: A Explanation: Rapid mixing provides swift dispersion of coagulant, usually 5– 10 seconds. Question 19. Lime-soda ash softening removes hardness primarily by precipitating: A. Calcium carbonate and magnesium hydroxide B. Sodium chloride C. Iron sulfide D. Silica gel Answer: A Explanation: Lime raises pH to precipitate calcium carbonate, while soda ash precipitates magnesium as magnesium hydroxide. Question 20. The most potent disinfectant species formed from chlorine in water at pH 7.5 is:
Technology ExamSprint Handbook
A) HOCl (hypochlorous acid) B) OCl⁻ (hypochlorite ion) C) Cl₂ (chlorine gas) D) ClO₂ (chlorine dioxide) Answer: A Explanation: At pH 7.5, about 50 % of chlorine exists as HOCl, which has higher disinfection efficacy than OCl⁻. Question 21. Trihalomethanes (THMs) are classified as: A) Primary pollutants B) Disinfection by-products (DBPs) C) Nutrient compounds D) Heavy metals Answer: B Explanation: THMs form when chlorine reacts with natural organic matter, making them DBPs. Question 22. UV disinfection is most effective against which type of organism? A) Bacterial spores B) Protozoan cysts (e.g., Giardia) C) Viruses D) All of the above equally Answer: C Explanation: UV radiation damages nucleic acids, making it particularly effective against viruses; cysts are more resistant.
Technology ExamSprint Handbook
Explanation: F/M = (Q·S₀)/ (V·X) = (Influent BOD load)/(MLSS mass), indicating the organic loading per unit biomass. Question 26. The typical range for mean cell residence time (MCRT) in a conventional activated-sludge plant is: A) 1–3 days B) 5–15 days C. 20–30 days D. 40–60 days Answer: B Explanation: Conventional plants maintain MCRT of about 5–15 days to balance sludge age and treatment efficiency. Question 27. Oxygen transfer efficiency (OTE) in an aeration basin is most directly affected by: A) Temperature of the water B) Color of the basin walls C) Concentration of nitrates D) Presence of heavy metals Answer: A Explanation: Higher temperatures reduce oxygen solubility and diffusion rates, lowering OTE. Question 28. Trickling filter media are typically selected for: A) High specific surface area and durability B) Magnetic properties C) Ability to dissolve in water
Technology ExamSprint Handbook
D) Conductivity Answer: A Explanation: Media provide surface for biofilm growth; high surface area and mechanical strength are essential. Question 29. The recirculation ratio in a trickling filter is defined as: A) Ratio of influent flow to filter media volume B) Ratio of filter effluent flow to influent flow C. Ratio of oxygen supplied to organic load D. Ratio of sludge age to hydraulic retention time Answer: B Explanation: Recirculation ratio = (Filter effluent flow) / (Influent flow); recirculation improves contact time. Question 30. Rotating Biological Contactors (RBCs) achieve oxidation of organics primarily during: A) The submergence phase when disks are fully immersed B) The drying phase when disks are exposed to air C) The rotation at high speeds (>500 rpm) D. The period when disks are coated with chemicals Answer: A Explanation: During submergence, the biofilm contacts wastewater, allowing oxidation; the drying phase provides oxygen. Question 31. In anaerobic digestion, the stage that produces volatile fatty acids (VFAs) is: A) Methanogenesis
Technology ExamSprint Handbook
Question 34. Denitrification requires which electron donor most commonly in activated-sludge systems? A) Nitrate itself B) Organic carbon (e.g., methanol) C) Ammonia D) Sulfate Answer: B Explanation: Heterotrophic denitrifiers use organic carbon as an electron donor to reduce nitrate to nitrogen gas. Question 35. Enhanced Biological Phosphorus Removal (EBPR) relies on the activity of: A) Polyphosphate-accumulating organisms (PAOs) B) Nitrifying bacteria only C) Sulfate-reducing bacteria D. Algae Answer: A Explanation: PAOs uptake phosphorus intracellularly as polyphosphate under alternating anaerobic/aerobic conditions. Question 36. A membrane bioreactor (MBR) combines activated sludge with: A) Reverse osmosis membranes B) Microfiltration/ultrafiltration membranes for solids separation C. Sedimentation tanks only D. Sand filters only Answer: B
Technology ExamSprint Handbook
Explanation: MBR uses micro- or ultrafiltration membranes to retain biomass, eliminating the need for secondary clarification. Question 37. The primary advantage of reverse osmosis (RO) for water reuse is its ability to: A) Remove dissolved salts and most organic contaminants B. Increase BOD removal beyond 90 % C. Reduce turbidity only D. Provide disinfection without chemicals Answer: A Explanation: RO applies a pressure-driven membrane that rejects ions, salts, and many organic molecules, producing high-purity water. Question 38. Sludge thickening is typically performed by: A) Gravity thickening basins or centrifuges B) Adding chlorine to sludge C. Heating sludge to 100 °C D. Aerating sludge for 24 h Answer: A Explanation: Gravity thickeners or high-speed centrifuges increase solids concentration before further processing. Question 39. Class A biosolids are distinguished from Class B by: A) Pathogen reduction to below detectable levels (Class A) versus limited reduction (Class B) B) Higher nitrogen content C. Presence of heavy metals above limits
Technology ExamSprint Handbook
A) Particles settle individually without interaction B) High particle concentrations cause interaction, slowing settling velocity C) Particles compress under their own weight forming a sludge blanket D. Settling is completely prevented by turbulence Answer: B Explanation: In hindered settling, particle collisions and crowding reduce individual settling velocities. Question 43. In a design calculation, the surface overflow rate (SOR) is set at 0.8 m³/m²·day for a primary clarifier. If the influent flow is 12 000 m³/day, the required surface area is: A) 10 000 m² B) 12 000 m² C) 15 000 m² D) 9 600 m² Answer: D Explanation: Area = Flow / SOR = 12 000 m³/day ÷ 0.8 m³/m²·day = 15 000 m²? Wait recalculation: 12 000 / 0.8 = 15 000 m². However answer options show 9 600 m² as D. Correction: 0.8 m³/m²·day → 12 000 / 0.8 = 15 000 m². Since 15 000 m² is option C, answer is C. Answer: C Explanation: Area = Q / SOR = 12 000 m³/day ÷ 0.8 m³/m²·day = 15 000 m². Question 44. The most common polymer used as a flocculant aid in wastewater treatment is: A) Polyacrylamide (PAM) B) Polyethylene glycol (PEG) C) Polystyrene
Technology ExamSprint Handbook
D. Polyvinyl chloride (PVC) Answer: A Explanation: Anionic or cationic polyacrylamide enhances floc formation by bridging particles. Question 45. The pKa of hypochlorous acid (HOCl) is approximately: A) 2. B) 4. C) 7. D. 10. Answer: C Explanation: HOCl ↔ H⁺ + OCl⁻ has pKa ≈ 7.5; at pH below 7.5 HOCl dominates, providing stronger disinfection. Question 46. In a full-scale plant, the typical ozone dose required for effective disinfection is: A) 0.5 mg/L B) 2 mg/L C. 5 mg/L D. 10 mg/L Answer: B Explanation: Ozone doses of 1–3 mg/L are commonly applied for disinfection; 2 mg/L is a representative value. Question 47. The primary mechanism by which activated carbon removes chlorine from water is: A) Oxidation
Technology ExamSprint Handbook
Question 50. A high SVI (>150 mL/g) indicates: A) Good sludge settling characteristics B) Poor settleability and likely bulking C. Low BOD removal efficiency D. High ammonia removal efficiency Answer: B Explanation: Elevated SVI reflects fluffy, poorly settling sludge, often due to filamentous bacteria. Question 51. In a conventional activated-sludge plant, the typical mixed-liquid suspended solids (MLSS) concentration is: A) 500–1 000 mg/L B) 2 000–4 000 mg/L C. 5 000–7 000 mg/L D. 8 000–10 000 mg/L Answer: B Explanation: Conventional systems operate with MLSS around 2 000–4 000 mg/L to balance treatment efficiency and hydraulic load. Question 52. The term “aeration efficiency” (AE) is defined as: A) Mass of oxygen transferred per unit power input (kg O₂/kWh) B. Percentage of influent BOD removed C. Ratio of dissolved oxygen to saturation concentration D. Flow rate divided by tank volume Answer: A
Technology ExamSprint Handbook
Explanation: AE = O₂ transferred (kg) / Power (kWh); a measure of how effectively an aerator uses electricity. Question 53. Which of the following is NOT a typical by-product of chlorination? A) Chloramines B) Trichloramine C) Chlorine gas D) Trihalomethanes (THMs) Answer: C Explanation: Chlorine gas is the disinfectant itself, not a by-product; the others are formed during reactions with organic or nitrogenous matter. Question 54. The most common method for measuring COD in a laboratory is: A) Dichromate digestion followed by titration B) BOD₅ incubation C) Membrane filtration D. Spectrophotometric nitrate analysis Answer: A Explanation: COD is determined by oxidizing organic matter with potassium dichromate under acidic conditions, then titrating excess dichromate. Question 55. In a design for a grit removal system, the recommended grit removal efficiency for a typical municipal plant is: A) 30 % B) 50 % C. 80 %
