Septic Tank Bacteria

Sewage
Sewage typically contains 95% to 99% water.

Impurities in sewage

Micro organisms
Often includes disease causing organisms (pathogens), including bacteria, viruses, protozoa and parasitic worms. Usually measured by the presence of E.coli (a common type of bacteria found in the intestines).
100 mL of sewage contains around 10 million E. coli bacteria.

Phosphorus compounds
These are present in human wastes (feces) and in detergents. Typical levels are 15 to 20 mg per liter of sewage.

Nitrogen compounds
These are mostly present as ammonia or urea. Typical levels are up to 100 mg per litre of sewage.

Suspended solids
Includes inert material such as sand and organic solids such as food scraps. Typical levels in sewage are 400 mg per litre.

Organic matter
Usually measured by BOD (Biological Oxygen Demand) or COD (Chemical Oxygen Demand).
This can include feces, fats and oils. Typical BOD levels in sewage approximately 400 mg per liter.
Additionally, sewage will contain rags, plastics, sanitary products and other large solids.
Trace amounts of other compounds, including heavy metals and various organic compounds (e.g. pesticides, herbicides, and weedicides) will also be present, even in purely domestic sewage and in higher levels if incorrectly treated trade wastes have entered the sewerage system.
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