Which of the following parameters are commonly measured in secondary effluent?

The correct choice focuses on parameters that are essential for evaluating the quality of secondary effluent in wastewater treatment processes. BOD, or Biochemical Oxygen Demand, measures the amount of organic matter present in the water that microorganisms will consume during decomposition, indicating the pollution level. TSS, or Total Suspended Solids, quantifies the solid particles suspended in water, which can interfere with light penetration and can be harmful to aquatic life if present in high concentrations. Fecal coliform levels are used as an indicator of pathogen presence, specifically from fecal sources, which is critical for assessing water safety for recreational use or as a potential source of drinking water.

These parameters are specifically focused on the effectiveness of the secondary treatment process, where biological treatment methods are employed to remove organic matter and suspended solids from the wastewater. Monitoring BOD, TSS, and fecal coliform is crucial for ensuring that the effluent meets regulatory standards before it is discharged into the environment or further treated.

In contrast, the other choices include parameters that may be relevant in different contexts but do not primarily reflect the effectiveness of secondary treatment for effluent quality assessment.