The main pollutant in waste water discharged from a petroleum refinery is oil (both in free and emulsified form). Free oil is removed by_________________?
Correct answer: D. Gravity separator having oil skimming devices
- A. Biological oxygen pond
- B. Aerated lagoons
- C. Trickling filters
- D. Gravity separator having oil skimming devices
Explanation
Free oil floats because its density is lower than water, so it can be separated by gravity in an oil-water separator fitted with skimming devices. Biological ponds and trickling filters are used mainly for dissolved or biodegradable pollutants, not free oil.
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