Gravity-based separators primarily remove free oil by exploiting which property difference?

• A. Color
• B. Density
• C. Temperature
• D. Viscosity

Answer: (B)

Gravity-based separators rely on density differences between immiscible liquids to separate them under gravity. Free oil typically has a lower density than water, so when the wastewater flows through the separator, the oil floats to the surface and forms a distinct layer that can be skimmed off or removed. This separation is driven by buoyancy: the oil’s density is less than that of water, so gravity causes the water to stay lower while the lighter oil rises. Color isn’t what drives the separation, and while temperature and viscosity can influence how quickly droplets coalesce and separate, they aren’t the fundamental mechanism.