Wastewater is treated through several stages, often starting with preliminary treatment to remove large objects, followed by primary treatment to let solids settle. Secondary treatment uses biological processes to break down organic matter, and tertiary treatment removes nutrients like phosphates and nitrates. Finally, a disinfection stage kills harmful microorganisms before the water is discharged or reused.

Preliminary Treatment

Screens: Large bar screens remove large items like sticks, rags, and cans from the wastewater.

Grit chambers: Wastewater flows slowly, allowing heavier solids like sand and grit to settle at the bottom.

Primary Treatment

Sedimentation: The water flows into large tanks where smaller solid waste settles to the bottom as sludge, while lighter materials like grease and oil float to the top and are skimmed off.

Sludge treatment: The settled sludge is separated and sent to a digester for further processing.

Secondary Treatment

Biological processes: This stage uses naturally occurring microorganisms to break down organic matter that wasn't removed in primary treatment.

Aerobic or anaerobic methods: Bacteria consume the waste, converting it into less harmful substances.

Clarification: After the biological process, the water goes to another settling tank to separate the bacteria and remaining solids from the liquid.

Tertiary Treatment

Nutrient removal: This stage is used when the water will be discharged into the environment or reused and is designed to remove remaining pollutants like phosphates and nitrates.

Filtration: Advanced filters are used to remove any remaining small particles.

Disinfection

Kill pathogens: Chlorine, ultraviolet (UV) light, or other disinfectants are used to kill any remaining harmful bacteria and viruses.