Which process follows primary treatment and further separates materials from water?

The correct process that follows primary treatment and further separates materials from water is secondary treatment. During primary treatment, physical processes are utilized to remove solids and settleable organic matter from wastewater. However, this process primarily focuses on the removal of larger solids and does not effectively eliminate dissolved or suspended organic matter.

Secondary treatment is designed to biologically degrade the organic matter that remains after primary treatment. This involves processes such as activated sludge systems, trickling filters, or biological nutrient removal systems, which harness microorganisms to metabolize organic pollutants. These biological processes significantly reduce the biochemical oxygen demand (BOD) and improve water quality by utilizing natural processes to break down contaminants.

By employing biological methods, secondary treatment enhances the separation of materials from the water, clarifying the effluent further. This step is crucial for preparing the water for subsequent tertiary treatment or for discharge into the environment, ensuring compliance with regulatory standards.

In contrast, preliminary treatment refers to processes like screening or grit removal that occur before primary treatment and focuses on larger debris and sand removal. Final treatment and tertiary treatment are terms that may refer to further purification and advanced treatment processes that occur after secondary treatment, primarily targeting specific constituents and achieving higher quality effluent.