Secondary sewage treatment is basically which type of treatment process ?

Biological process.

Secondary sewage treatment primarily involves a biological process.

In secondary sewage treatment, biological methods are utilized to further treat wastewater following the initial removal of solids and debris in the primary treatment stage. This stage aims to remove dissolved and suspended biological matter that remains in the wastewater.

Biological treatment methods often involve the use of microorganisms, such as bacteria and other biological agents, to break down organic substances present in the sewage. These microorganisms consume and metabolize the organic matter, reducing the pollutant load in the wastewater. Processes like activated sludge, trickling filters, and various types of biological reactors are commonly employed in secondary sewage treatment to facilitate the breakdown of organic pollutants through biological activity.