Which of the following describes the appearance of healthy activated sludge?

The appearance of healthy activated sludge is characterized by a brown color and a moderate amount of crisp, white foam. This indicates that the micro-organisms present in the sludge are active and functioning well, which is essential for the biological treatment process in wastewater facilities.

Brown coloration suggests that the biomass is predominantly composed of healthy microorganisms, which have a natural brown pigment due to the presence of organic materials being processed during treatment. The crisp, white foam indicates that the sludge has a good balance of solids and is actively removing waste materials from the water, aiding in the aeration process.

In contrast, other options suggest unhealthy or undesirable conditions in the activated sludge. For example, thick, greasy, dark tan foam would indicate a problematic condition, possibly related to excessive fats or oils, which can lead to foaming issues and interfere with treatment efficiency. Clear liquid with clear foam may indicate a lack of biomass or poor microbial activity while gray liquid with no foam could suggest an absence of active microorganisms altogether, making it ineffective for wastewater treatment.