In a sewage efficient treatment plan, during the tertiary treatment the decreased water is chlorinated with chlorine or perchlorate salts, ozonised or irradiate with UV to kill pathogens. Phenyl is not used for disinfection of drinking water. Phenyl is a strong deodorant and germicide for disinfecting surfaces, like floors and is extensively used for sanitation purpose.
Related Theory
Tertiary treatment is the final cleaning process that improves wastewater quality before it is reused, recycled or discharged to the environment. The treatment removes remaining inorganic compounds, and substances, such as the nitrogen and phosphorus. Bacteria, viruses and parasites, which are harmful to public health, are also removed at this stage. Alum is used to help remove additional phosphorus particles and group the remaining solids together for easy removal in the filters. Chlorine removes microorganisms in treated wastewater including bacteria, viruses and parasites such as Giardia and Cryptosporidium. The chlorinated water slowly winds its way along the discharge tank, giving it time to react. Any remaining chlorine is removed by adding sodium bisulphite just before it's discharged.
$Å$ Caution
$\rightarrow$ Chlorine and chloramine are the major disinfectants used in public water systems.