What percentage of sewage is usually removed by BOD treatment?

The correct percentage of sewage typically removed by Biochemical Oxygen Demand (BOD) treatment is usually around 65 percent, making this the most appropriate choice. BOD is a measure of the amount of organic material in water, and the treatment processes designed to reduce BOD are effective at breaking down this organic matter, thereby improving water quality.

BOD treatment is an essential part of sewage treatment processes, including both primary and secondary treatment stages, where microorganisms are used to decompose organic pollutants. This process effectively decreases the organic load in sewage, significantly reducing its environmental impact before it is discharged into water bodies.

While lower percentages like 25% or 35% may occur in very minimal or poorly designed treatment scenarios, or for specific types of wastewater that are less organic in nature, stating 50% does not capture the efficiency of modern treatment processes that aim for higher removal rates. Thus, emphasizing that BOD treatment typically achieves around 65% removal illustrates the capability of these systems to mitigate pollution effectively. This understanding is crucial for environmental health specialists in assessing and designing wastewater treatment systems.