<human>: I've always wondered: What is the difference between a septic tank and a sewage treatment plant?
<bot>: The main difference between a septic tank and a sewage treatment plant is that a septic tank is designed to treat and store wastewater from a single residence or small building, while a sewage treatment plant is typically larger in size and designed to treat wastewater from multiple buildings. A septic tank is usually made of concrete or fiberglass and has an outlet pipe connected to a leach field, which is a shallow layer of soil that absorbs and treats the wastewater before it enters the ground water. In contrast, a sewage treatment plant uses a variety of methods to remove contaminants from the wastewater before it is discharged into a river or lake.