An API separator is commonly used as a first-stage oil removal unit in wastewater treatment. Which option best matches this description?

• A. Primary Clarifier
• B. First-Stage Oil Removal Unit
• C. Secondary Clarifier
• D. Aeration Basin

Answer: (B)

The concept being tested is recognizing that an API separator is designed specifically to remove free oil from oily wastewater as a first-stage step, using gravity separation. Oil, being less dense than water, floats to the surface where it can be skimmed off, while the bulk of the water continues on to subsequent treatment. This early oil removal protects downstream equipment and reduces hydrocarbon load for the rest of the treatment train. The other options describe units whose primary roles are different: a primary clarifier focuses on settling solids, a secondary clarifier handles solids after biological treatment, and an aeration basin provides oxygen for microbial degradation. So the best fit is the First-Stage Oil Removal Unit.