Sewage is a common term used for all wastewater produced from a household, commonly called domestic wastewater comprises water produced from toilets, sinks, baths/showers, washing machines, laundry and kitchens. This wastewater contains suspended and dissolved organic solids that have to be treated before letting into the environment or before reuse and recycling. The various characteristics that have to be analysed for treatment and discharge are

· Biochemical oxygen demand (BOD)

· Chemical oxygen demand (COD)

· Ammonia (NH4)

· Nitrogen (N)

· Phosphate (PO4)

· Oil, fat, grease

· Suspended solids (SS)

· Total organic content (TOC)

· Alkalinity

· pH

·Temperature

The composition of this waste in disposed water varies based on usage on an hourly, daily and seasonal basis influenced by habits, diets, living styles and cultural patterns. Physically sewage contains suspended particles, colour, odour contributed by faeces, food, toilet paper, oil, soap, salt, chemicals, coffee, tea, solids, sand, grit, etc.  The chemical composition of this wastewater in dissolved and suspended form contains, carbohydrates, lipids, fat, protein or CHNOPS. There are other inorganic chemicals such as nitrogen, ammonia, chlorides, sulphides and phosphates. Biologically there are various microorganisms such as including bacteria, fungi, protozoa, algae and some invertebrates.

In terms of analytical parameters sewage can be classified as,