Which of these methods are not performed in sewage treatment plants?

Humification is not a process that is carried out inside wastewater treatment plants. Humification is a natural process that occurs in soil, where organic matter is broken down by microorganisms over a long period of time, forming humus, which is a dark, organic-rich substance that improves soil quality.

In wastewater treatment plants, the processes that are typically used to treat wastewater include physical, chemical, and biological processes, such as sedimentation, filtration, and decomposition.

Sedimentation is used to remove suspended solids and heavy particles from wastewater by allowing them to settle to the bottom of a tank or basin. Filtration is used to remove smaller particles and contaminants by passing the wastewater through filters or membranes. Decomposition is a biological process that is used to break down organic matter in wastewater using bacteria and other microorganisms.

Therefore, humification is not carried out inside wastewater treatment plants because it is a natural process that occurs in soil and is not necessary for the treatment of wastewater.