Which two approaches are commonly used in wastewater secondary treatment?

The two approaches commonly used in wastewater secondary treatment are biological treatment and aerobic degradation. In secondary treatment, the primary goal is to reduce the organic matter and improve the quality of the effluent before it is discharged or further treated.

Biological treatment involves using microorganisms to consume organic pollutants in the wastewater. This process can take place in various systems, including activated sludge systems, trickling filters, and biofilm reactors. These microorganisms break down the organic materials, thereby reducing biochemical oxygen demand (BOD) and other pollutants.

Aerobic degradation is a key component of biological treatment, as it specifically refers to the breakdown of organic substances in the presence of oxygen. Aerobic processes typically result in the efficient conversion of organic matter into carbon dioxide, water, and biomass, making it essential for effectively treating wastewater.

The other approaches mentioned do not directly align with the secondary treatment processes. For example, grit removal and sedimentation are primarily associated with primary treatment, aiming to remove larger solids and settleable materials before biological treatment occurs. Similarly, filtration and chlorination typically occur in tertiary treatment, where the focus is on further polishing the effluent and disinfection after secondary treatment has been completed.