Which wastewater treatment method is typically used for disinfection following the secondary treatment stage?

Chlorination is commonly used for disinfection following the secondary treatment stage of wastewater treatment. After biological treatment processes, which effectively reduce the concentration of organic matter and nutrients, disinfection is essential to eliminate pathogens that may remain in the effluent. Chlorine, when applied at appropriate concentrations and contact times, is highly effective against a wide range of bacteria, viruses, and protozoa, thus significantly improving the safety of the treated water before it is discharged into the environment or reused.

The other methods listed, such as mechanical filtration, activated carbon treatment, and settling tanks, serve different purposes in the treatment process. Mechanical filtration is primarily designed to remove suspended solids, whereas activated carbon treatment is effective for removing organic contaminants and improving taste and odor, but not specifically targeted at pathogen reduction. Settling tanks are used to allow sedimentation of solids and are part of the primary treatment process. While these methods have their roles in the overall wastewater treatment hierarchy, chlorination stands out specifically for its disinfection capability post-secondary treatment.