Which of the following is a stage in wastewater treatment?

All of the above

The correct answer is option 4. All of the above.

The three steps of wastewater treatment are filtration, aeration, and chlorination. The first step in treating wastewater is filtering. Solid contaminants including sand, gravel, human waste, and floating debris are completely removed from the water during filtering. The second stage of wastewater treatment is aeration. The air is blasted on the solid pollutants that settle in the sedimentation tank during aeration (sludge). Chlorination completes the wastewater treatment process. Chlorine is added to wastewater during chlorination to eradicate any bacteria that may be present.