With reference to unit operations used in wastewater treatment, the role of a skimmer is to:

The correct option is A.

Explanation

Wastewater treatment involves a series of physical, chemical, and biological unit operations designed to remove contaminants. A skimmer is a mechanical device utilized during the primary treatment phase to separate non-miscible substances from the liquid phase based on density differences.

• Statement A is Correct: Skimmers are specifically designed to remove materials that have a lower specific gravity than water, such as oil, grease, fats, and floating debris. These substances rise to the surface of the primary sedimentation tank or grease trap, where the skimmer collect and removes them to prevent interference with subsequent biological treatment processes.
• Statement B is Incorrect: The removal of suspended grit and sand is achieved through a Grit Chamber or Detritus Tank, where flow velocity is reduced to allow heavy inorganic solids to settle by gravity.
• Statement C is Incorrect: Chemical sterilization or disinfection is a tertiary treatment process typically involving the addition of chlorine, ozone, or exposure to UV radiation to eliminate pathogenic microorganisms.
• Statement D is Incorrect: Odor neutralization is managed through aeration (physical) or the addition of oxidizing agents like hydrogen peroxide or activated carbon adsorption (chemical/physical).

Key Takeaway: A skimmer is a physical unit operation used in primary wastewater treatment to remove floatable impurities (oil and grease) based on the principle of buoyancy.