Which of the following treatment methods is most likely to occur before disinfection?

The treatment method that is most likely to occur before disinfection is secondary treatment. Secondary treatment in wastewater management typically follows primary treatment, which involves the removal of large solids and sediments. During secondary treatment, biological processes are employed to degrade organic matter and reduce the biochemical oxygen demand (BOD) of the wastewater. This step is crucial because it significantly improves water quality by reducing contaminants that could interfere with subsequent disinfection processes.

Once secondary treatment is complete, the wastewater is then ready for disinfection. Disinfection is intended to eliminate remaining pathogens and ensure the safety of the treated water before it is released into the environment or reused. Therefore, secondary treatment serves as a foundational step that prepares the water for effective disinfection.

In contrast, the other choices do not occur before disinfection in a typical treatment sequence. Coagulation is part of the primary treatment process, where chemicals are added to help aggregate and settle out suspended solids. Odor control is often an adjunct process that may occur at various stages, primarily during primary or secondary treatment. Filtration typically serves as a post-treatment step to remove remaining particulates before disinfection.