California Wastewater Treatment Operator Practice Exam 2025 - Free Wastewater Treatment Operator Practice Questions and Study Guide

The correct description of pre-chlorination is indeed the addition of chlorine to wastewater at the entrance to the plant. This practice serves multiple purposes: it helps control odors, reduces biochemical oxygen demand (BOD), facilitates the removal of grease, and assists in sedimentation processes. By introducing chlorine early on, the treatment plant can improve the overall efficiency of the treatment process, which ultimately leads to better water quality.

Other options describe different stages or processes involved in wastewater treatment. Using chlorine after primary treatment is characteristic of disinfection, which is a separate function from pre-chlorination. Removing chlorine before wastewater enters the plant is not a usual practice, as it is counterproductive to the benefits of pre-chlorination. Lastly, applying chlorine during the final polishing of effluent again refers to disinfection, which is not related to the pre-treatment phase. Each of these options highlights different stages of wastewater treatment, but only the addition of chlorine at the plant entrance aligns with the definition of pre-chlorination.