What is the primary purpose of secondary treatment in wastewater processing?

The primary purpose of secondary treatment in wastewater processing is to biologically reduce biochemical oxygen demand (BOD). This stage follows primary treatment, where larger solids and debris are removed. During secondary treatment, microorganisms play a crucial role as they consume organic matter in the wastewater, which effectively lowers the BOD levels. This reduction is essential because high BOD in effluent can deplete oxygen in receiving waters and harm aquatic life.

Secondary treatment typically involves processes such as activated sludge systems or trickling filters, where bacteria and other microorganisms thrive, breaking down organic pollutants effectively. The goal is to enhance the quality of water being discharged into the environment or to further treatment processes, ensuring that it meets regulatory and health standards.

While other steps in the wastewater treatment process address different aspects, such as removing large debris or preparing water for drinking, the core function of secondary treatment centers on biological processes aimed specifically at reducing BOD levels.