APSC Assistant Engineer - Environmental Engineering Questions
1. A wastewater treatment plant treats 5000 m³/day of sewage with a BOD of 200 mg/L. If the treatment removes 90% of the BOD, what is the BOD of the effluent in mg/L?
b. 20 mg/L
Description: BOD removal reduces the initial concentration by 90%, so 10% remains. Calculation: 200 × (1 - 0.9) = 20 mg/L. This reflects efficient secondary treatment typical in wastewater plants.
Description: BOD removal reduces the initial concentration by 90%, so 10% remains. Calculation: 200 × (1 - 0.9) = 20 mg/L. This reflects efficient secondary treatment typical in wastewater plants.
2. Which of the following statements is true about the activated sludge process?
c. It uses aeration to promote microbial growth
Description: The activated sludge process is a biological treatment where aeration supplies oxygen to aerobic microbes, which degrade organic matter. It’s not physical, anaerobic, or for heavy metals.
Description: The activated sludge process is a biological treatment where aeration supplies oxygen to aerobic microbes, which degrade organic matter. It’s not physical, anaerobic, or for heavy metals.
3. A water sample has a hardness of 200 mg/L as CaCO₃. If 1 mg/L of CaCO₃ is equivalent to 0.4 mg/L of Ca²⁺, what is the calcium concentration in mg/L?
b. 80 mg/L
Description: Hardness as CaCO₃ is converted to Ca²⁺ using the given factor. Calculation: 200 × 0.4 = 80 mg/L. This measures calcium’s contribution to water hardness.
Description: Hardness as CaCO₃ is converted to Ca²⁺ using the given factor. Calculation: 200 × 0.4 = 80 mg/L. This measures calcium’s contribution to water hardness.
4. Which statement is correct regarding eutrophication?
b. It leads to oxygen depletion due to algal blooms
Description: Eutrophication occurs when excess nutrients (e.g., nitrogen, phosphorus) cause algal blooms, which die and decompose, consuming oxygen. It’s human-influenced and affects freshwater and marine systems.
Description: Eutrophication occurs when excess nutrients (e.g., nitrogen, phosphorus) cause algal blooms, which die and decompose, consuming oxygen. It’s human-influenced and affects freshwater and marine systems.
5. A clarifier has a surface area of 100 m² and treats a flow of 12000 m³/day. What is the surface overflow rate in m³/m²/day?
b. 120
Description: Surface overflow rate is flow rate divided by surface area. Calculation: 12000 ÷ 100 = 120 m³/m²/day. This parameter ensures efficient settling in clarifiers.
Description: Surface overflow rate is flow rate divided by surface area. Calculation: 12000 ÷ 100 = 120 m³/m²/day. This parameter ensures efficient settling in clarifiers.
6. Which of the following statements about acid rain is true?
b. It results from sulfur dioxide and nitrogen oxides
Description: Acid rain forms when SO₂ and NOx react with water vapor to produce acids, lowering precipitation pH. It affects urban and rural areas, harming aquatic ecosystems.
Description: Acid rain forms when SO₂ and NOx react with water vapor to produce acids, lowering precipitation pH. It affects urban and rural areas, harming aquatic ecosystems.
7. If a water treatment plant uses 0.5 mg/L of chlorine for disinfection and treats 10,000 m³/day, how much chlorine is used daily in kg?
b. 5 kg
Description: Chlorine usage is calculated as dose times volume, converted to kg. Calculation: 0.5 × 10,000 × 10⁻³ = 5 kg. This ensures adequate disinfection.
Description: Chlorine usage is calculated as dose times volume, converted to kg. Calculation: 0.5 × 10,000 × 10⁻³ = 5 kg. This ensures adequate disinfection.
8. Which statement is true about photochemical smog?
b. It is caused by reactions involving ozone and VOCs
Description: Photochemical smog forms when sunlight triggers reactions between NOx and VOCs (from vehicles), producing ozone. It’s common in summer, not winter, and unrelated to CO₂.
Description: Photochemical smog forms when sunlight triggers reactions between NOx and VOCs (from vehicles), producing ozone. It’s common in summer, not winter, and unrelated to CO₂.
9. A wastewater sample has a COD of 400 mg/L. If 80% of the COD is removed during treatment, what is the COD of the effluent in mg/L?
b. 80 mg/L
Description: COD removal leaves 20% of the initial value. Calculation: 400 × (1 - 0.8) = 80 mg/L. This indicates effective chemical oxygen demand reduction.
Description: COD removal leaves 20% of the initial value. Calculation: 400 × (1 - 0.8) = 80 mg/L. This indicates effective chemical oxygen demand reduction.
10. Which of the following statements about groundwater contamination is correct?
b. It can result from leachate from landfills
Description: Landfill leachate, containing pollutants, can seep into groundwater, causing contamination. Agricultural runoff and industrial activities also contribute, not just coastal areas or volcanoes.
Description: Landfill leachate, containing pollutants, can seep into groundwater, causing contamination. Agricultural runoff and industrial activities also contribute, not just coastal areas or volcanoes.
11. An air pollution control device removes 95% of particulate matter from a gas stream with an initial concentration of 1000 µg/m³. What is the final concentration in µg/m³?
b. 50 µg/m³
Description: A 95% removal leaves 5% of particulates. Calculation: 1000 × (1 - 0.95) = 50 µg/m³. This shows high efficiency in air pollution control.
Description: A 95% removal leaves 5% of particulates. Calculation: 1000 × (1 - 0.95) = 50 µg/m³. This shows high efficiency in air pollution control.
12. Which statement is true about the ozone layer?
b. It protects Earth from ultraviolet radiation
Description: The ozone layer, in the stratosphere, absorbs harmful UV rays, protecting life. It’s not in the troposphere, not formed by CO₂, and is environmentally critical.
Description: The ozone layer, in the stratosphere, absorbs harmful UV rays, protecting life. It’s not in the troposphere, not formed by CO₂, and is environmentally critical.
13. A sedimentation tank has a volume of 2000 m³ and a flow rate of 8000 m³/day. What is the detention time in hours?
b. 6 hours
Description: Detention time is volume divided by flow rate, converted to hours. Calculation: (2000 ÷ 8000) × 24 = 6 hours. This ensures adequate settling time.
Description: Detention time is volume divided by flow rate, converted to hours. Calculation: (2000 ÷ 8000) × 24 = 6 hours. This ensures adequate settling time.
14. Which of the following is true about biodegradable waste?
b. It can be broken down naturally by microbes
Description: Biodegradable waste, like food scraps, is decomposed by microorganisms into simpler substances. It’s not inherently toxic and comes from domestic and natural sources, not just industry.
Description: Biodegradable waste, like food scraps, is decomposed by microorganisms into simpler substances. It’s not inherently toxic and comes from domestic and natural sources, not just industry.
15. A water sample requires 10 mg/L of alum (Al₂(SO₄)₃) for coagulation. If the flow rate is 5000 m³/day, how much alum is needed daily in kg?
b. 50 kg
Description: Alum requirement is dose times volume, converted to kg. Calculation: 10 × 5000 × 10⁻³ = 50 kg. This supports effective coagulation in water treatment.
Description: Alum requirement is dose times volume, converted to kg. Calculation: 10 × 5000 × 10⁻³ = 50 kg. This supports effective coagulation in water treatment.
16. Which statement is correct about non-point source pollution?
b. It includes agricultural runoff
Description: Non-point source pollution, like runoff from farms, is diffuse and hard to control, unlike point sources (e.g., pipes). It significantly impacts water bodies with nutrients and pesticides.
Description: Non-point source pollution, like runoff from farms, is diffuse and hard to control, unlike point sources (e.g., pipes). It significantly impacts water bodies with nutrients and pesticides.
17. A trickling filter treats 2000 m³/day of wastewater with a BOD of 150 mg/L. If the effluent BOD is 30 mg/L, what is the BOD removal efficiency?
b. 80%
Description: Removal efficiency is the percentage of BOD reduced. Calculation: [(150 - 30) ÷ 150] × 100 = 80%. This indicates effective biological treatment.
Description: Removal efficiency is the percentage of BOD reduced. Calculation: [(150 - 30) ÷ 150] × 100 = 80%. This indicates effective biological treatment.
18. Which of the following statements about desalination is true?
b. It removes salt from seawater
Description: Desalination, via processes like reverse osmosis, extracts salt to produce freshwater. It’s not biological, doesn’t remove solids directly, and reduces hardness.
Description: Desalination, via processes like reverse osmosis, extracts salt to produce freshwater. It’s not biological, doesn’t remove solids directly, and reduces hardness.
19. A landfill produces 100 m³/day of leachate with a COD of 500 mg/L. If treatment removes 60% of the COD, what is the COD of the treated leachate in mg/L?
b. 200 mg/L
Description: COD after 60% removal is 40% of the initial value. Calculation: 500 × (1 - 0.6) = 200 mg/L. This reduces the pollution load from leachate.
Description: COD after 60% removal is 40% of the initial value. Calculation: 500 × (1 - 0.6) = 200 mg/L. This reduces the pollution load from leachate.
20. Which statement is true about the role of wetlands?
b. They naturally purify water
Description: Wetlands filter pollutants and nutrients, improving water quality naturally. They reduce erosion, are found in diverse ecosystems, and don’t cause air pollution.
Description: Wetlands filter pollutants and nutrients, improving water quality naturally. They reduce erosion, are found in diverse ecosystems, and don’t cause air pollution.
21. What is the primary purpose of aeration in water treatment?
b. To increase dissolved oxygen
Description: Aeration adds oxygen to water, supporting aerobic microbes in degrading organic matter. It doesn’t remove solids, adjust pH, or target metals directly.
Description: Aeration adds oxygen to water, supporting aerobic microbes in degrading organic matter. It doesn’t remove solids, adjust pH, or target metals directly.
22. Which gas is primarily responsible for the greenhouse effect?
c. Carbon dioxide
Description: CO₂ traps heat in the atmosphere, driving the greenhouse effect. Nitrogen, oxygen, and argon don’t significantly contribute to this phenomenon.
Description: CO₂ traps heat in the atmosphere, driving the greenhouse effect. Nitrogen, oxygen, and argon don’t significantly contribute to this phenomenon.
23. The BOD test measures:
b. Oxygen required to decompose organic matter
Description: BOD quantifies oxygen needed by microbes to break down organic material, indicating pollution levels. It’s unrelated to solids, acidity, or metals.
Description: BOD quantifies oxygen needed by microbes to break down organic material, indicating pollution levels. It’s unrelated to solids, acidity, or metals.
24. What is the typical pH range for drinking water as per WHO standards?
b. 6.5–8.5
Description: WHO recommends a pH of 6.5–8.5 for drinking water to ensure safety and palatability. Extreme pH values can affect taste and pipe corrosion.
Description: WHO recommends a pH of 6.5–8.5 for drinking water to ensure safety and palatability. Extreme pH values can affect taste and pipe corrosion.
25. Which process is used to remove hardness from water?
c. Ion exchange
Description: Ion exchange swaps calcium and magnesium ions for sodium, reducing hardness. Filtration, coagulation, and distillation serve other purposes.
Description: Ion exchange swaps calcium and magnesium ions for sodium, reducing hardness. Filtration, coagulation, and distillation serve other purposes.
26. The primary source of air pollution in urban areas is:
b. Vehicle emissions
Description: Vehicles emit NOx, CO, and particulates, dominating urban air pollution. Volcanic eruptions and fires are less frequent, and runoff affects water, not air.
Description: Vehicles emit NOx, CO, and particulates, dominating urban air pollution. Volcanic eruptions and fires are less frequent, and runoff affects water, not air.
27. Which of the following is a secondary air pollutant?
c. Ozone
Description: Ozone forms from reactions of NOx and VOCs in sunlight, making it secondary. CO, SO₂, and particulates are emitted directly, hence primary.
Description: Ozone forms from reactions of NOx and VOCs in sunlight, making it secondary. CO, SO₂, and particulates are emitted directly, hence primary.
28. Which device is used to measure particulate matter in air?
b. High-volume sampler
Description: High-volume samplers collect particulates on filters for analysis. Spectrophotometers measure light absorption, chromatographs analyze gases, and barometers measure pressure.
Description: High-volume samplers collect particulates on filters for analysis. Spectrophotometers measure light absorption, chromatographs analyze gases, and barometers measure pressure.
29. The permissible limit of turbidity in drinking water is:
a. 5 NTU
Description: Turbidity below 5 NTU ensures drinking water clarity and safety, per WHO standards. Higher values indicate potential contamination.
Description: Turbidity below 5 NTU ensures drinking water clarity and safety, per WHO standards. Higher values indicate potential contamination.
30. Which chemical is commonly used for disinfection in water treatment?
b. Chlorine
Description: Chlorine kills pathogens effectively, making it the standard disinfectant. Sodium chloride is salt, calcium carbonate adjusts pH, and permanganate is less common.
Description: Chlorine kills pathogens effectively, making it the standard disinfectant. Sodium chloride is salt, calcium carbonate adjusts pH, and permanganate is less common.
31. The COD test is used to measure:
b. Chemical oxygen demand
Description: COD measures oxygen needed to chemically oxidize organic and inorganic matter, indicating pollution. It’s distinct from BOD, solids, or pH tests.
Description: COD measures oxygen needed to chemically oxidize organic and inorganic matter, indicating pollution. It’s distinct from BOD, solids, or pH tests.
32. The primary function of a grit chamber is to remove:
b. Sand and gravel
Description: Grit chambers settle heavy inorganic particles like sand to protect equipment. Organic matter, dissolved solids, and microbes are removed elsewhere.
Description: Grit chambers settle heavy inorganic particles like sand to protect equipment. Organic matter, dissolved solids, and microbes are removed elsewhere.
33. Which layer of the atmosphere contains the ozone layer?
b. Stratosphere
Description: The ozone layer resides in the stratosphere, absorbing UV radiation. Other layers lack significant ozone concentrations.
Description: The ozone layer resides in the stratosphere, absorbing UV radiation. Other layers lack significant ozone concentrations.
34. The permissible limit of fluoride in drinking water is:
b. 1.5 mg/L
Description: Fluoride up to 1.5 mg/L is safe per WHO, preventing dental issues without toxicity. Higher levels cause fluorosis.
Description: Fluoride up to 1.5 mg/L is safe per WHO, preventing dental issues without toxicity. Higher levels cause fluorosis.
35. Which of the following is a renewable source of energy?
c. Solar energy
Description: Solar energy is renewable, harnessing sunlight continuously. Coal, natural gas, and nuclear rely on finite or complex resources.
Description: Solar energy is renewable, harnessing sunlight continuously. Coal, natural gas, and nuclear rely on finite or complex resources.
36. Which pollutant is most responsible for smog formation?
b. Nitrogen oxides
Description: NOx, with VOCs, forms photochemical smog via sunlight-driven reactions. CO₂, SO₂, and ammonia play lesser roles in smog.
Description: NOx, with VOCs, forms photochemical smog via sunlight-driven reactions. CO₂, SO₂, and ammonia play lesser roles in smog.
37. The primary purpose of a clarifier in wastewater treatment is to:
b. Remove settleable solids
Description: Clarifiers allow solids to settle out of wastewater, improving clarity. Other processes handle gases, pH, and disinfection.
Description: Clarifiers allow solids to settle out of wastewater, improving clarity. Other processes handle gases, pH, and disinfection.
38. Which of the following is a greenhouse gas?
c. Methane
Description: Methane traps heat, contributing to global warming. Nitrogen, oxygen, and argon don’t act as greenhouse gases.
Description: Methane traps heat, contributing to global warming. Nitrogen, oxygen, and argon don’t act as greenhouse gases.
39. The process of coagulation in water treatment involves:
b. Adding chemicals to form flocs
Description: Coagulation uses chemicals like alum to clump particles into flocs for removal. It’s not for pH, oxygen, or hardness adjustment.
Description: Coagulation uses chemicals like alum to clump particles into flocs for removal. It’s not for pH, oxygen, or hardness adjustment.
40. The permissible limit of arsenic in drinking water is:
a. 0.01 mg/L
Description: Arsenic above 0.01 mg/L is toxic, per WHO standards, requiring strict control to prevent health risks like cancer.
Description: Arsenic above 0.01 mg/L is toxic, per WHO standards, requiring strict control to prevent health risks like cancer.
41. Which of the following is a biological treatment process?
b. Activated sludge process
Description: Activated sludge uses microbes to degrade organic matter biologically. Filtration, coagulation, and distillation are physical or chemical processes.
Description: Activated sludge uses microbes to degrade organic matter biologically. Filtration, coagulation, and distillation are physical or chemical processes.
42. The main purpose of a septic tank is to:
b. Treat domestic sewage
Description: Septic tanks settle and digest domestic sewage anaerobically. Disinfection, metal removal, and hardness adjustment occur in other systems.
Description: Septic tanks settle and digest domestic sewage anaerobically. Disinfection, metal removal, and hardness adjustment occur in other systems.
43. Which of the following is a measure of water hardness?
c. Calcium carbonate concentration
Description: Hardness is quantified as CaCO₃ equivalent, reflecting calcium and magnesium levels. pH, turbidity, and BOD measure other properties.
Description: Hardness is quantified as CaCO₃ equivalent, reflecting calcium and magnesium levels. pH, turbidity, and BOD measure other properties.
44. The primary source of thermal pollution is:
b. Industrial cooling water
Description: Industries discharge warm water, raising water body temperatures. Runoff, emissions, and leachate cause chemical or solid pollution, not heat.
Description: Industries discharge warm water, raising water body temperatures. Runoff, emissions, and leachate cause chemical or solid pollution, not heat.
45. The permissible limit of nitrate in drinking water is:
b. 45 mg/L
Description: Nitrate up to 45 mg/L is safe per WHO, preventing health issues like methemoglobinemia. Higher levels indicate contamination.
Description: Nitrate up to 45 mg/L is safe per WHO, preventing health issues like methemoglobinemia. Higher levels indicate contamination.
46. The main purpose of an electrostatic precipitator is to:
b. Remove particulate matter
Description: Electrostatic precipitators trap particulates using electric charges. They don’t address odors, gases, or noise.
Description: Electrostatic precipitators trap particulates using electric charges. They don’t address odors, gases, or noise.
47. Which of the following is a characteristic of hazardous waste?
b. Toxicity
Description: Hazardous waste is toxic, corrosive, reactive, or ignitable, posing environmental risks. Biodegradability and solubility aren’t defining traits.
Description: Hazardous waste is toxic, corrosive, reactive, or ignitable, posing environmental risks. Biodegradability and solubility aren’t defining traits.
48. The main purpose of a skimming tank is to remove:
b. Oil and grease
Description: Skimming tanks float off oil and grease from wastewater surfaces. Other pollutants require different treatment methods.
Description: Skimming tanks float off oil and grease from wastewater surfaces. Other pollutants require different treatment methods.
49. Which of the following is a primary treatment process in wastewater treatment?
b. Sedimentation
Description: Sedimentation, a primary treatment, removes settleable solids physically. Activated sludge, disinfection, and nitrification are secondary or tertiary.
Description: Sedimentation, a primary treatment, removes settleable solids physically. Activated sludge, disinfection, and nitrification are secondary or tertiary.
50. The main purpose of an oxidation pond is to:
b. Treat wastewater using natural processes
Description: Oxidation ponds use sunlight, algae, and microbes to degrade organic matter naturally. They don’t target metals, hardness, or pH specifically.
Description: Oxidation ponds use sunlight, algae, and microbes to degrade organic matter naturally. They don’t target metals, hardness, or pH specifically.