What occurs during the third part of chlorination?

During the third part of chlorination, the primary focus is on the breakdown and removal of chlorinated organic compounds, including chloramines that may have formed during the initial stages of chlorination. This phase is critical because chloramines, which are byproducts of the reaction between chlorine and organic nitrogen compounds in water, can lead to issues such as taste and odor problems, as well as reduced chlorine effectiveness.

In this stage, the water treatment process aims to effectively reduce these compounds to ensure safe drinking water is achieved. Through proper chlorine dosing and reaction time, the chloramines are oxidized and their concentrations decreased, thereby enhancing water quality.

The other options, while relevant to the overall chlorination process, do not describe the specific actions and objectives of this third stage. For instance, the formation of free residual chlorine is more about the outcomes of chlorine reacting with contaminants rather than the specific actions taken during the third part. Similarly, excess chlorine addition might be part of a preliminary phase to ensure a sufficient free chlorine level but is not the focus of the breakdown of chlorinated compounds. Lastly, filtration is a separate treatment step typically used for removing particulates and solids rather than addressing the chemical reactions involved in chlorination.