What is a common reason to use prechlorination at a wastewater treatment facility?

• A. Inhibit growth of odor-producing bacteria
• B. Begin sterilization process
• C. Decrease TSS load
• D. Promote settling of inorganic materials

Answer: (A)

Prechlorination is used to suppress odors by inhibiting odor-producing bacteria early in the treatment process. Introducing chlorine oxidizes reduced sulfur compounds like hydrogen sulfide and other odorous organics produced in anaerobic parts of the system, reducing the formation of rotten-egg smells and helping protect downstream equipment from odor-related corrosion. This is different from disinfection aimed at killing pathogens later in the process, and it doesn’t meaningfully reduce total suspended solids or promote settling of inorganic materials, which rely on physical separation and coagulation rather than chlorine. So the common reason is to keep odor-producing bacteria in check.