Objective Question & Answer

Wastewater treatment units are strategically sequenced so that each unit operation targets a specific size and

category of impurity based on its settling property or chemical nature.

grit chamber is a preliminary treatment unit designed to reduce the flow velocity of sewage just enough to allow heavy,

coarse inorganic solids like sand, silt, and gravel to settle out by gravity without letting organic particles settle.

Following this, the wastewater moves into the primary sedimentation tank, where the velocity is dropped even further

over a few hours to facilitate the gravitational settling of fine suspended organic impurities (or "impurifiers").

Conversely, a detritus tank is structurally designed to remove much finer inorganic silt and sand than a standard grit

chamber, not bulk organic matter. For floating materials like oils, grease, and fats, a specialized skimming tank is

utilized rather than an aeration tank, which is instead reserved for biological oxidation of dissolved organic matter in an

activated sludge plant. Because only the firstand third pairs accurately describe the intended target impurities of those

specific units, they form the correct combination.