From a grab sample at a wastewater treatment plant, which parameters must be tested and analyzed immediately?

The appropriate parameters to test and analyze immediately from a grab sample at a wastewater treatment plant include pH, chlorine residual, and dissolved oxygen.

Beginning with pH, it is crucial to measure this parameter as soon as possible because pH levels can fluctuate rapidly in wastewater due to changes in biological activity or chemical dosing. Maintaining the correct pH balance is essential for effective treatment processes and for the health of aquatic life.

Chlorine residual is another important immediate measurement because chlorine is often used as a disinfectant in wastewater treatment. The residual level can indicate whether sufficient chlorine is present to effectively disinfect the effluent before discharge. If not measured quickly, chlorine levels can dissipate and may not reflect the true disinfection effectiveness of the treatment process.

Dissolved oxygen levels must also be tested promptly since they are vital for the aerobic biological processes that help break down organic matter in wastewater. Rapid depletion of dissolved oxygen can jeopardize these processes and adversely affect wastewater treatment efficiency.

This combination of parameters not only provides insight into the current state of the wastewater but also informs operational decisions that need to be made quickly to ensure effective treatment. Other parameters offered in the choices may not require immediate testing as their changes are typically slower or less critical for immediate assessment.