Evaporation reduces the liquid volume of wastewater, returning water vapor to the environment. Solids settle to bottom and form sludge.

There is an aerobic zone at the top of the wastewater layer where air movement introduces oxygen and aerobic microorganisms convert waste to:

1. carbon dioxide
2. ammonia
3. phosphates

Algae in the lagoon use these as a food source and give off oxygen.

There is an anaerobic zone near the bottom of the wastewater layer where anaerobic microorganisms break down waste producing:

1. hydrogen sulfide
2. ammonia
3. methane