A lagoon, also called a stabilization pond, can be an option for advanced pretreatment of wastewater or for final treatment and dispersal of wastewater. They are generally preceded by a septic tank that removes large solids. A lagoon is a large basin of wastewater that is undergoing a combination of chemical, physical, and biological treatment processes. These processes allow the wastewater to become more acceptable for discharge. Lagoons are categorized in four ways, depending upon the presence and their source of oxygen. The four categories are:
• Partial-mixed aerated
Partial-mixed aerated and anaerobic lagoons are typically used for industrial or agricultural uses, whereas aerobic and facultative lagoons are commonly used in onsite systems.
An aerobic lagoon is characterized by aerobic conditions throughout its entire depth. These lagoons are typically one to three feet in depth to allow sunlight to penetrate though out the entire water column. Facultative lagoons are comprised of two regions. The top surface region is aerobic, and the bottom subsurface zone is either anoxic or anaerobic.
Design of lagoons must conform to and abide by local and state laws which vary by location. A fence, buffer zone, and berms are the most common regulations. To improve efficiency, lagoons can be used in series or in parallel depending on system location, loading rate, size, climate and desired treatment level.