Question

Which of the following could be a substance found in waste water that floats on the top and is removed in the Primary Treatment of water?

• A. Oil and grease
• B. Human faeces
• C. Hair
• D. Plastic

Answer 1

The correct option is A Oil and grease

• Primary treatment removes material that will either float or readily settle out by gravity. It includes the physical processes of screening, comminution, grit removal, and sedimentation.
  
• Human faeces, hair and plastic settle down at bottom while Oil and grease are immiscible in water and are found floating on top.

So, the correct option is 'Oil and grease'.