Which of the following is an indication of successful sewage treatment?

The indication of successful sewage treatment is represented by a low chemical oxygen demand (COD). Chemical oxygen demand measures the amount of oxygen that is required to chemically oxidize organic matter in water. A lower COD indicates that there is less organic pollution present in the treated water, meaning that the treatment process has effectively removed a significant portion of pollutants.

In successful sewage treatment, the objective is to reduce the levels of harmful substances, including organic materials that consume oxygen in aquatic environments. As a result, a low COD reflects a cleaner effluent that is less likely to deplete oxygen levels in receiving water bodies, thus supporting aquatic life and maintaining ecosystem health.

Other factors, like high coliform counts, high nutrient levels, and the presence of sludge, suggest that the sewage treatment process may not be functioning effectively, as these conditions often lead to pollution and potential harm to the environment. Therefore, a low COD is a positive sign of effective sewage treatment.