Which factor is not listed as an 'other factor' affecting activated sludge?

• A. Salinity
• B. pH
• C. Temperature
• D. Dissolved Oxygen

Answer: (A)

Understanding factors that influence activated sludge shows why salinity isn’t typically included in the “other factors” list. pH, temperature, and dissolved oxygen directly affect how well the aerobic microorganisms perform, which in turn drives COD and BOD removal, floc formation, and overall reactor performance. pH affects enzyme activity and nutrient availability; temperature changes alter metabolic rates and reaction speeds; dissolved oxygen provides the essential electron acceptor for aerobic metabolism and helps keep flocs stable.

Salinity can influence microbial activity, especially in high-salt or marine environments, but in standard municipal wastewater treatment, salinity is not commonly treated as a separate factor to monitor alongside pH, temperature, and DO. That’s why salinity is the one not listed in the typical group of “other factors.”