What biological process is commonly used in secondary treatment?

The biological process commonly used in secondary treatment is aerobic digestion. In secondary treatment, the primary goal is to further reduce the organic matter present in wastewater after primary treatment has removed larger solids and settled out the sludge. Aerobic digestion employs microorganisms that thrive in the presence of oxygen to break down organic pollutants.

In this process, aeration tanks introduce air to the wastewater, allowing aerobic bacteria to metabolize the organic compounds, effectively converting them into carbon dioxide, water, and biomass. This not only helps in reducing the biochemical oxygen demand (BOD) but also stabilizes the sludge created during primary treatment, making it easier to handle in subsequent processes.

In contrast, anaerobic digestion, while also a biological process, occurs without oxygen and is typically used in different contexts, such as energy recovery from waste or in sludge management rather than in the primary steps of secondary treatment. Filtration is a physical process used to remove solids from liquids but does not target the biodegradation of organic matter. Chemical precipitation involves adding chemicals to remove specific contaminants and does not rely on biological activity, making it less applicable in the context of secondary treatment, which is inherently biological in nature.