What is sewage and what are its main components?

Sewage is the wastewater from domestic, commercial, and industrial sources carried in sewers. Main components include: water (99.9%), suspended solids, dissolved organic matter, nutrients (nitrogen and phosphorus), pathogens (bacteria, viruses, parasites), and various chemicals. Domestic sewage contains human waste, kitchen waste, and wash water. Understanding sewage composition is essential for designing treatment systems.