Sewage Treatment Process – AP Enviro Science

Clean Water Act

The CWA establishes the basic structure for regulating discharges of pollutants into the waters of the United States, mandating secondary treatment for all municipal sewage.

Primary (Physical)

Removes large debris, grit, and 50-60% of suspended solids through mechanical screening and gravity settling.

Secondary (Biological)

Uses aerobic bacteria to break down 85-90% of organic matter (BOD). Requires massive aeration to keep bacteria alive.

Tertiary (Chemical)

Advanced treatment removes N, P, and remaining pathogens before discharge. Disinfection is the final step.

Tags

APESSewageBODCWA

Treatment Timeline

Advance through the stages of municipal wastewater treatment.

P Raw Sewage Inlet

Wastewater arrives full of debris, organic matter (feces/food), and chemicals.

1 Physical Screening

Bar screens physically catch large trash. Grit chambers slow water down so sand and coffee grounds sink.

1 Primary Clarification

Still physical: Heavy organic solids sink to form primary sludge. Oil/grease floats and is skimmed off.

2 Aeration (Biological)

Massive oxygen injection keeps aerobic bacteria alive to consume dissolved organic matter (reducing BOD).

2 Secondary Clarification

Bacteria clump together and sink as 'activated sludge'. Some is returned to the aeration basin.

3 Disinfection

Treated water is hit with Chlorine, UV Light, or Ozone before release into rivers.