Which of the following is a sign of effective wastewater treatment?

A low Biological Oxygen Demand (BOD) in effluent is indeed a sign of effective wastewater treatment. BOD measures the amount of oxygen that microorganisms will consume while decomposing organic matter in water. A lower BOD indicates that a treatment facility has effectively reduced the amount of organic pollutants in the wastewater before it is discharged into the environment. This is crucial in ensuring that the water released does not harm aquatic ecosystems and maintains water quality standards.

In contrast, high levels of contaminants in discharged water suggest inadequacies in the treatment process, while excess sludge accumulation in tanks signifies potential operational issues and inefficiencies in the system. Additionally, frequent odor complaints from the community can indicate that the treatment processes are not effectively managing odor-producing compounds, further signifying a poor level of treatment rather than effectiveness. Thus, low BOD is a key indicator of successful treatment performance in wastewater management.