Which of the following is a common indicator of wastewater treatment efficiency?

Dissolved oxygen levels are a key indicator of wastewater treatment efficiency, particularly in biological treatment processes such as activated sludge systems. The presence of sufficient dissolved oxygen is crucial for the aerobic microorganisms that break down organic matter in the wastewater. When dissolved oxygen levels are optimized, these microorganisms can effectively decompose pollutants, leading to improved treatment outcomes and the reduction of biochemical oxygen demand (BOD).

High levels of BOD indicate that more organic matter is present in the wastewater, which necessitates greater oxygen consumption by bacteria. Monitoring and maintaining adequate dissolved oxygen levels not only enhance the efficiency of the treatment process but also help in ensuring that the effluent meets environmental regulations before being discharged into receiving waters.

In contrast, while pH levels, suspended solids concentration, and temperature variation also play roles in overall treatment performance, they do not specifically measure the biological treatment processes' efficiency as directly as dissolved oxygen levels do.