What does the stabilization process add to treated water?

The stabilization process primarily adds nutrients to treated water to promote biological activity and improve the water's overall quality. Nutrients, such as nitrogen and phosphorus, can enhance the growth of beneficial microorganisms that help in further treatment processes, making the water safer for release into the environment or for reuse. This process helps in forming a stable ecosystem that can break down remaining organic matter and absorb excess nutrients, which is important for maintaining water quality.

The other options, while relevant in different contexts, do not directly relate to the stabilization process. Filtration agents are typically used in the physical removal of particles rather than in stabilization, chlorination is a method used for disinfection rather than stabilization, and metal ions are commonly involved in coagulation and flocculation processes rather than stabilization directly.