What effect does chlorine have in Area 4 of the breakpoint chlorination curve?

In Area 4 of the breakpoint chlorination curve, a significant chlorine residual is produced. At this stage, enough chlorine has been added to effectively oxidize not only the ammonia but also to reach the point where free available chlorine stabilizes. This means the chlorine concentration has surpassed the breakpoint, and the system has transitioned from consuming chlorine to creating a stable residual, which is critical for maintaining disinfection in the treated wastewater.

This residual is essential for ensuring continued protection against pathogens as the water moves through distribution systems or treatment facilities. It acts as a safety measure, helping to keep the water safe from potential recontamination as it flows through pipes or storage. Thus, the correct choice reflects the importance of maintaining a chlorine residual to sustain disinfection efficacy in wastewater treatment processes.