Which one of the following is a step in waste water treatment ?

All of these

The correct answer is Option (4) – All of these

Aeration, Filtration, and Chlorination all of these are steps in wastewater treatment.

Aeration is the process by which air circulates, mixes, or dissolves a liquid or substance.

Filtration is the process in which solid particles in a liquid or gaseous fluid are removed using a filter medium that allows the fluid to pass through but retains the solid particles.

Chlorination is the process of adding chlorine to drinking water to kill parasites, bacteria, and viruses.