Wisconsin DNR Wastewater Operator Certification Practice Test

What is the purpose of grit removal in a municipal wastewater treatment plant?

To remove inorganic dense solids (sand and grit) early to protect pumps, avoid abrasion, and prevent wear or clogging in downstream equipment. To remove dissolved organic matter to lower BOD in the effluent. To capture suspended solids that are readily biodegradable in the aeration tank. To sterilize the wastewater before discharge.

Correct Answer:

To remove inorganic dense solids (sand and grit) early to protect pumps, avoid abrasion, and prevent wear or clogging in downstream equipment.

Explanation:

Grit removal targets heavy, inorganic solids that would threaten equipment if left in the flow. Sand, gravel, and similar grit are dense enough to settle quickly and cause abrasion and wear on pumps, valves, and piping, and they can clog downstream channels. By pulling these solids out early—before biological treatment and pumps—the plant protects equipment, reduces maintenance, and helps keep downstream processes running smoothly. The other options describe goals that grit removal doesn’t directly address: reducing dissolved organic matter to lower BOD happens in biological treatment; capturing readily biodegradable suspended solids happens in the aeration basin; and disinfection is a separate, downstream step.

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