California Wastewater Treatment Operator Practice Exam

How does an activated sludge system remove waste from wastewater?

1. Chemical treatment

2. Mechanical filtration

3. Biological treatment

4. Physical sedimentation

The correct answer is: Biological treatment

An activated sludge system primarily removes waste from wastewater through biological treatment. This method utilizes microorganisms, particularly bacteria, to break down organic matter present in the wastewater. In the system, wastewater is aerated in a reactor, allowing these microorganisms to thrive and consume the organic pollutants. As the bacteria assimilate the waste, they reproduce and form flocs, which are clusters of microorganisms that can settle out when the wastewater is later allowed to stand. The effectiveness of this biological treatment process is enhanced by creating conditions that promote the growth of microbial populations, thereby efficiently reducing the concentration of harmful substances in the wastewater. This process is integral to the activated sludge system's ability to produce treated effluent that meets regulatory standards for discharges. Other methods, such as chemical treatment or mechanical filtration, may also play a role in wastewater treatment but are not the primary means by which an activated sludge system achieves waste removal. Chemical treatment would involve the use of chemicals to neutralize or precipitate contaminants, while mechanical filtration focuses on physically removing solids through screens or filters, neither of which reflect the biological mechanism integral to the activated sludge process.