Human: I've always wondered: What is the difference between a septic tank and a sewage treatment plant? Assistant: 
A septic tank is a small, underground chamber that contains bacteria that break down the waste in your home's sewer system. The bacteria in the septic tank digest the waste, which helps to reduce the amount of harmful pollutants in the water. Sewage treatment plants are larger facilities that use a combination of physical, chemical, and biological processes to remove pollutants from wastewater.