Georgia Septic Installer Practice Test

How many parts per million of free oxygen does raw sewage typically contain?

1. 1-2 parts per million

2. 3-5 parts per million

3. 10-15 parts per million

4. 20-25 parts per million

The correct answer is: 3-5 parts per million

Raw sewage typically contains around 3-5 parts per million of free oxygen. This concentration reflects the oxygen content that is present in untreated sewage, which is critical for the biological processes involved in wastewater treatment. In sewage treatment systems, the microorganisms responsible for breaking down organic matter require oxygen to thrive and effectively decompose waste. The 3-5 parts per million range indicates a low oxygen content, which is characteristic of raw sewage due to its high organic load and the decomposition processes occurring before treatment. Understanding the oxygen levels in sewage is essential for septic system installers and wastewater treatment professionals, as it informs the design and operation of systems intended to promote effective microbial activity and breakdown of pollutants.