Certified in Public Health (CPH) Practice Exam

Municipal sewage is typically processed to remove organic material before disposing of the treated water. What treatment method is generally used in large cities?

1. Biological treatment in an aerated activated sludge system

2. Chemical treatment by coagulation and flocculation

3. Filtering through sand beds

4. Super-chlorination to destroy organic materials

The correct answer is: Biological treatment in an aerated activated sludge system

The use of biological treatment in an aerated activated sludge system is the prevailing method employed in large cities for processing municipal sewage. This method is favored because it effectively utilizes microorganisms to break down organic materials present in the wastewater. In an aerated activated sludge system, the wastewater is aerated, which promotes the growth of bacteria and other microorganisms that metabolize the organic matter, resulting in a significant reduction of pollutants. Aeration also helps in preventing the formation of anaerobic conditions, which can lead to odors and the production of harmful gases. After the biological treatment stage, the treated water typically undergoes further processes to remove any remaining solids and pathogens before being released or reused. This comprehensive approach makes the aerated activated sludge method particularly suitable for the large volumes of wastewater generated in urban environments, ensuring that the effluent meets environmental standards for discharge. Other treatment methods, while beneficial in their own right, do not offer the same level of efficiency or effectiveness in a large urban context. For instance, chemical treatment methods like coagulation and flocculation are often used for specific issues such as removing particulates but are not sufficient alone for the extensive organic load typical of municipal sewage. Similarly, sand bed filtering and super-chlorination serve distinct roles within wastewater treatment