What is a common indicator of water quality in sewage treatment plants?

Biochemical oxygen demand (BOD) is a crucial indicator of water quality in sewage treatment plants because it measures the amount of oxygen that microorganisms will consume while decomposing organic matter in water. This measurement reflects the level of organic pollution present in wastewater; higher BOD levels indicate greater amounts of organic material, which can lead to oxygen depletion in receiving waters if not properly treated. Monitoring BOD allows treatment plants to assess the effectiveness of their treatment processes and the potential environmental impact of the effluent they discharge.

While pH level, temperature, and chlorine concentration are also significant parameters in water quality monitoring, they serve different purposes. The pH level indicates the acidity or alkalinity of the water, temperature can affect the rate of biochemical reactions, and chlorine concentration is relevant for assessing disinfection effectiveness. However, BOD is specifically focused on measuring organic pollution and the capacity of water to support aerobic life, making it the most relevant indicator among the choices for assessing overall water quality in sewage treatment.