Question

primary municipal wastewater treatment... operates to allow suspended solids to settle out of solution. uses microorganisms to remove organic matter. slows water movement significantly. requires the water to be aerated.

Explanation:

Primary municipal wastewater treatment mainly involves physical - based processes like sedimentation to remove suspended solids. Using microorganisms, aeration, and significantly slowing water movement are more characteristic of secondary or other advanced treatment steps.

Answer:

Operates to allow suspended solids to settle out of solution.