Human: What are the most popular types of septic systems? Assistant: 
The most popular types of septic systems include conventional septic tanks, aerobic treatment units (ATUs), and biodigesters. Conventional septic tanks are made up of a tank that holds wastewater and a leach field or drain field where the wastewater is released into the soil. ATUs are similar to conventional septic tanks but use air instead of water for the biological treatment process. Biodigesters are essentially anaerobic digesters that break down waste in an oxygen-free environment.