How Does a Sewage Treatment Plant Work?

Wastewater treatment typically involves three stages. Primary treatment screens out large debris and lets solids settle in sedimentation tanks. Secondary treatment uses aerobic bacteria in aeration basins to break down dissolved organic matter — this stage removes roughly 85% of organic pollutants. Tertiary treatment may include sand filtration, nutrient removal, and disinfection with chlorine or ultraviolet light. A large plant can process hundreds of millions of litres per day, and the solid byproduct (biosolids) is often repurposed as agricultural fertiliser or used to generate biogas.