What is one purpose of secondary treatment in wastewater management?

One purpose of secondary treatment in wastewater management is to remove remaining organic matter after primary treatment. During primary treatment, larger solids and some organic material are removed through physical processes such as sedimentation and screening. However, some dissolved and suspended organic compounds remain in the effluent, which can contribute to overall pollution and negatively affect the receiving water bodies.

Secondary treatment employs biological processes, such as activated sludge or trickling filters, where microorganisms break down the remaining organic material. This process significantly reduces biochemical oxygen demand (BOD) and total suspended solids (TSS) in the effluent, leading to cleaner water that can be safely discharged into the environment or further treated. This reduction in organic matter is crucial for protecting aquatic life and achieving regulatory compliance for water quality standards.

The other options, while they relate to wastewater treatment, do not accurately describe the main objective of secondary treatment. For instance, cooling down the wastewater, chemically neutralizing toxins, or adding nutrients back to the water might be tasks performed in different treatment stages or processes, but they do not directly pertain to the primary goal of secondary treatment, which is focused on organic matter removal.