Which type of sewage treatment is primarily focused on biological processes?

Secondary treatment is primarily focused on biological processes, which involve the use of microorganisms to break down organic matter in sewage. This stage of treatment typically follows primary treatment, where the larger solids are removed from the wastewater. During secondary treatment, bacteria and other microorganisms consume the organic pollutants, converting them into carbon dioxide, water, and additional biomass. This process not only helps to reduce the biochemical oxygen demand (BOD) of the sewage, making it less harmful when released into the environment, but also plays a crucial role in the overall goal of achieving effective wastewater treatment.

In contrast, physical treatment involves the removal of solids through physical means such as screening and sedimentation, while chemical treatment employs chemical reactions to remove pollutants. Tertiary treatment, on the other hand, is focused on further polishing the effluent to remove remaining contaminants and may involve advanced processes, such as filtration, disinfection, or nutrient removal. Thus, secondary treatment stands out specifically for its reliance on biological processes to achieve its objectives.