The correct answer is option (A) partial-mix aerated lagoon.
Partial mix lagoons are used to treat municipal, agricultural and industrial wastewater. In these lagoons, the aeration is provided by either mechanical surface aerators or submerged diffused aeration system. The submerged systems include the perforated tubing or piping with a variety of diffusers attached to it. Mechanical aeration provides dissolved oxygen needed for the aerobic organisms in the lagoon for the conversion and oxidation of organic material in the wastewater. The depth of the lagoon is up to 20 feet.