Which of the following is not done during the process of treatment of waste water?

The correct option is Inorganic impurities such as nitrates and phosphates are removed by chlorination.

Step-by-step Explanation:

1. Wastewater Treatment Steps:
During the wastewater treatment process, physical, chemical, and biological processes are used to remove contaminants:

• Sand and Grit Removal: Wastewater is passed through a grit and sand removal tank where the speed of incoming wastewater is decreased to allow sand, grit, and pebbles to settle down.
• Sedimentation & Skimming: Solids like feces settle at the bottom and are removed with a scraper (sludge), while floating materials like grease and oil are removed using a skimmer.
• Disinfection (Chlorination): Chlorination is a chemical process used to kill harmful micro-organisms, pathogens, and bacteria in water before it is released into the distribution network or natural water bodies.

2. Why the chosen option is correct (Not done during treatment):
Chlorination is used specifically for disinfection (killing germs), not for removing dissolved inorganic chemical impurities such as nitrates and phosphates. Dissolved nutrients like nitrates and phosphates require specialized advanced or tertiary chemical/biological treatments for removal, not standard chlorination.