Human: What is the difference between a septic system and a sewage system? Assistant: 
The main difference between a septic system and a sewage system is that a septic system uses biological processes to treat wastewater, while a sewage system relies on mechanical or chemical processes to remove pollutants from wastewater. A septic tank is used in a septic system, which contains bacteria that break down organic matter into water and carbon dioxide. This process produces methane gas, which can be released into the atmosphere. In contrast, a sewage treatment plant uses physical and chemical processes such as sedimentation, oxidation, and chlorination to remove pollutants from wastewater.