Sewage is the wastewater released by residences, businesses and industries in a community. It is 99.94 percent water, with only 0.06 percent of the wastewater dissolved and suspended solid material. The cloudiness of sewage is caused by suspended particles which in untreated sewage ranges from 100 to 350 mgl. A measure of the strength of the wastewater is biochemical oxygen demand, or BOD5. The BOD5 measures the amount of oxygen microorganisms require in five days to break down sewage. Untreated sewage has a BOD5 ranging from 100 mgl to 300 mgl. Pathogens or diseasecausing organisms are present in sewage. Coliform bacteria are used as an indicator of diseasecausing organisms. Sewage also contains nutrients such as ammonia and phosphorus, minerals, and metals. Ammonia can range from 12 to 50 mgl and phosphorus can range from 6 to 20 mgl in untreated sewage.

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