What is the correct sequence of steps in a Publicly Owned Treatment Works (POTW)?

The correct sequence of steps in a Publicly Owned Treatment Works (POTW) follows the logical and structured approach to treating wastewater effectively. The process starts with preliminary treatment, which involves the removal of large debris and grit that could damage equipment or hinder subsequent treatment stages. Following this, primary treatment occurs, where the majority of suspended solids and some biological material are removed through sedimentation.

Secondary treatment then takes place, typically involving biological processes to break down organic matter remaining after primary treatment. This stage is crucial for achieving considerable reduction of pollutants. Tertiary treatment, also referred to as advanced treatment, is the final step that targets remaining contaminants, including nutrients like nitrogen and phosphorus, and may also include filtration and disinfection processes.

Chlorination may be involved for disinfection purposes, ensuring pathogens are effectively eliminated before the wastewater is returned to the environment or reused. Dechlorination may follow to remove any chlorine residual, safeguarding aquatic life in receiving waters.

This comprehensive understanding of the treatment sequence aligns with standard wastewater management practices, reinforcing why this particular order is essential for effective, regulatory-compliant treatment of sewage in POTWs.