Environmental Engineering: Why Sewage Plants Farm Bacteria
How engineers measure, clean and protect water, air and land, from oxygen-hungry rivers to methane-making landfills.
Environmental Engineering · 50 questions
Try 3 questions
1. What does a water sample's BOD (biochemical oxygen demand) actually measure?
- Oxygen fish need to survive in the water
- Oxygen dissolved in the water right now
- Oxygen microbes use to break down organics
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Answer: Oxygen microbes use to break down organics
BOD is the oxygen consumed by microorganisms as they decompose organic matter, usually over five days.
2. Why are fish kills from low oxygen more common in rivers during hot summers?
- Fish swim faster and tire in warm water
- Sunlight destroys oxygen near the surface
- Warm water holds less dissolved oxygen
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Answer: Warm water holds less dissolved oxygen
Gas solubility falls as temperature rises, while microbes consume oxygen faster in warm water.
3. How much more hydrogen ion concentration does water at pH 5 have compared with water at pH 7?
- About twenty times as much
- Exactly twice as much
- A hundred times as much
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Answer: A hundred times as much
The pH scale is logarithmic, so each unit is a factor of ten: two units means 10 × 10 = 100.
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