שאלה | The main conventional wastewater treatment process is termed “activated sludge.” What is the source of this name?

The main conventional wastewater treatment process is termed “activated sludge.” What is the source of this name?

		The sludge is vigorously mixed and mechanically activated in the biological process.
		The sludge is chemically activated by oxidation so it can adsorb pollutants
		The secondary sludge is transferred back to the secondary reactor to increase biological activity.
		The digested primary sludge is centrifuged, and the resulting nutrient-rich stream can be reused as a fertilizer.