Mixed liquor is a combination of which three components?

Mixed liquor is a crucial component in the wastewater treatment process, particularly in activated sludge systems. It is defined as a mixture that consists of activated sludge (which is the biomass microorganisms), primary effluent (the liquid portion that has been partially treated during the primary treatment stage), and return sludge (which is the excess activated sludge that is returned to the aeration tank from the clarifier).

This combination is essential for the biological treatment of wastewater. The activated sludge contains microorganisms that help in the breakdown of organic matter present in the primary effluent. By including primary effluent in the mixed liquor, the organic load is introduced for treatment. Additionally, returning the sludge ensures that enough biomass is present to effectively treat the incoming wastewater, enhancing the overall efficiency of the treatment process.

The other choices focus solely on one of the components, excluding the integral relationship among all three. By including only primary effluent, activated sludge, or return sludge separately, they do not represent the complete picture of mixed liquor, which relies on the synergy of all components to efficiently treat the wastewater.