What is secondary treatment in the context of wastewater treatment?

Secondary treatment refers specifically to the biological processes employed after primary treatment to further reduce the solid waste and organic matter in wastewater. During primary treatment, physical processes such as sedimentation remove larger solids, but many dissolved organic substances remain in the effluent.

In secondary treatment, microorganisms are utilized to biologically digest these remaining organic materials, effectively reducing the biochemical oxygen demand (BOD) and suspended solids. This process may take place in various systems, such as activated sludge or trickling filters, where the conditions are optimized for microbial growth and activity.

This treatment is crucial for enhancing the quality of the effluent before it proceeds to further treatment steps or is discharged into the environment, thereby playing a vital role in ensuring the effluent meets regulatory standards for environmental protection.