WasteWater Operator Certification - Grade 1 Practice Test

The mixture of primary effluent and returned activated sludge is known as mixed liquor. This term refers specifically to the combined liquid containing both the waste material from primary treatment (primary effluent) and the bacteria-rich sludge that has been returned from the secondary treatment process (returned activated sludge).

Mixed liquor is critical in biological treatment processes such as activated sludge systems, as it allows for the necessary biological reactions to occur. In these systems, microorganisms within the mixed liquor consume organic matter present in the wastewater, facilitating its treatment.

Wasted activated sludge refers to the portion of sludge that is removed from the system, often during routine operations to maintain the proper concentration of microorganisms. Secondary sludge is another term that may relate to the clarified sludge produced after biological treatment but does not specifically describe the mix of primary effluent and returned sludge. The term activated essence does not have standard usage in wastewater treatment terminology. Thus, mixed liquor is the precise term used to describe the combination of the primary effluent and the returned activated sludge.