What is the primary role of bacteria in an activated sludge treatment plant?

The primary role of bacteria in an activated sludge treatment plant is to perform most of the work involved in breaking down organic matter in wastewater. Activated sludge systems utilize microorganisms, particularly bacteria, to decompose organic pollutants. During the aeration process, these bacteria consume organic substances present in the wastewater, thus reducing the biological oxygen demand (BOD) and enabling the treatment of wastewater.

These microorganisms thrive in an aerated environment, where they multiply rapidly and form flocs, which help to aggregate and settle out the solids in the wastewater. This biological process not only purifies the water but also ensures that harmful pollutants are effectively removed from the effluent before it is released back into the environment.

While the other roles mentioned, like clarifying the wastewater, providing nutrients, and balancing chemical composition, are part of the overall process, they are secondary functions. The primary and most significant function remains the action performed by the bacteria to degrade organic material, making option B the most accurate choice.