In wastewater treatment, the effluent from the activated sludge process is referred to as _____.

The effluent from the activated sludge process is indeed known as mixed liquor. During this process, microorganisms digest organic material in the wastewater, resulting in a mixture that contains both the microorganisms and the treated wastewater. This mixture, or mixed liquor, is subjected to further treatment to separate the solids (which can be removed for disposal or further processing) from the clarified liquid that can then be released as effluent or subjected to additional treatment stages.

Mixed liquor typically refers to the condition during aeration where both activated sludge and wastewater are combined, allowing for the biological treatment to occur effectively. Therefore, when discussing the effluent produced, it's appropriate to refer to it as mixed liquor, as it is the combination of the waste and the microbiological population actively working to treat it.

The other terms are related to different parts of the wastewater treatment process but do not accurately describe the effluent from the activated sludge process. Primary sludge refers to the solids removed during the primary treatment phase, biomass can refer generically to the biological material but does not specifically denote the treated effluent, and activated biosolids generally refer to the biomass that has been stabilized, which is a product of the activated sludge process but not the effluent itself.