What type of treatment process is known as secondary treatment?

Secondary treatment is primarily defined as a biological treatment process used in wastewater treatment facilities. This stage aims to remove dissolved and suspended organic matter that remains after primary treatment, where solids are primarily settled out. In secondary treatment, biological organisms, typically bacteria, are employed to break down organic pollutants present in the wastewater. Common methods of secondary treatment include activated sludge processes and trickling filters, both of which rely on microbial activity to decompose organic materials and convert them into biomass.

This process is critical in reducing biochemical oxygen demand (BOD) and ensuring that the effluent released into receiving waters is significantly cleaner and less harmful to aquatic ecosystems. While other treatment types, such as physical or chemical processes, can also play a role in wastewater treatment, secondary treatment is distinctly characterized by its biological mechanisms, making it an essential step in achieving effective wastewater purification.