Submersible mixers can be completely immersed in water. They are used to treat wastewater before it enters another body or is reused. A wastewater treatment system performs several activities: preliminary treatment, primary treatment, secondary treatment, tertiary treatment, and sludge treatment. During preliminary treatment, screens are used to remove large, solid inorganic materials such as paper and plastic. During primary treatment, the wastewater passes through a sedimentation tank to remove smaller, solid organic materials using a gravity settling process. During the secondary treatment stage, an activated sludge process uses submersible mixers to break down any dissolved or suspended organic solids. This is followed by the tertiary treatment stage in which disinfectants, usually chlorine, are mixed into the water to eliminate harmful microbes. Finally, during the sludge treatment stage, the collected sludge is processed for reuse.

Submersible mixers use a wastewater pump during the secondary stage of the wastewater treatment process. During this stage, the wastewater pump or process water pump is used to aerate the liquid and prevent sludge sedimentation. Several different types of wastewater pumps are used. A suspended pump has a motor mounted on the top of the treatment pool that is supported by a shaft that connects the motor to the pump. A submersible pump submerges the motor, the pump housing, and the impeller in the treatment basin. Proper mixing (or aeration) of the wastewater is essential during this stage to properly treat the wastewater pollutants. A centrifugal pump has an impeller to force the liquid into motion using a centrifugal force to generate velocity. A propeller pump, or axial flow pump, has a vertical shaft for bottom suction and a propeller mounted near the bottom of the shaft. Propeller pumps are completely submerged (and can be clogged by large solids or trash) and therefore should only be used in clear water applications. Important wastewater pump specifications for submersible mixers include maximum discharge flow, maximum discharge pressure, inlet size, discharge size, and horsepower.

Submersible mixers are used to continually mix wastewater so that biological treatment can occur and dissolve any suspended organic solids using naturally occurring micro-organisms. Like other wastewater treatment equipment, they are used in a variety of industrial, commercial, military, and municipal treatment processing environments. Submersible mixers are convenient to install, are often energy efficient solutions, and provide energy consumption savings. The U.S. Clean Water Act regulates the protection of water and is enforced by the Environmental Protection Agency and corresponding state agencies.