Why do we prefer to call secondary wastewater treatment as biological treatment?

(N/A) Secondary wastewater treatment is referred to as biological treatment because it primarily relies on the activity of living organisms,such as aerobic and anaerobic bacteria and fungi,to decompose and mineralize the organic matter present in the sewage. These microorganisms consume the organic waste as their food source,thereby significantly reducing the Biological Oxygen Demand $(BOD)$ of the effluent.