What is the typical method used for secondary treatment?

The typical method used for secondary treatment is biological treatment methods, such as activated sludge or trickling filters. Secondary treatment is focused on removing dissolved and suspended organic matter that remains after primary treatment. This process utilizes microorganisms to break down organic pollutants in the wastewater.

Activated sludge is a popular biological treatment process where air is pumped through wastewater to encourage the growth of beneficial microbes. These microorganisms consume organic matter, which is then settled out in a secondary clarifier. Similarly, trickling filters allow wastewater to flow over a bed of media colonized by microorganisms, which also metabolize organic contaminants. Both methods effectively reduce the biological oxygen demand (BOD) of the wastewater, making it cleaner.

The other methods listed, such as chemical precipitation, filtration, sedimentation, and reverse osmosis, are generally associated with either primary treatment or tertiary treatment processes rather than secondary treatment. Therefore, the emphasis on biological treatment inherently defines the characteristic approach of secondary treatment.