Which chemical is commonly used in both water purification and sewage treatment for long-term disinfection?

Chlorine is commonly used in both water purification and sewage treatment due to its effective disinfectant properties. When chlorine is introduced into water systems, it reacts with organic materials and pathogens, effectively killing bacteria, viruses, and protozoa, which are essential considerations for ensuring safe drinking water and treating wastewater. Chlorine has a long-lasting residual effect, meaning that it continues to disinfect even after it has been added, making it ideal for long-term disinfection processes in various water treatment applications.

Ozone, while also a powerful disinfectant, is less commonly used for long-term disinfection due to its instability; it decomposes quickly and requires generation on-site. Hydrogen peroxide is typically used for specific types of wastewater treatment but does not have the same broad application or residual effect as chlorine. Ultraviolet light is effective for disinfection but does not provide any residual protection, meaning it cannot maintain disinfection in stored water. Thus, chlorine is the most suitable choice for long-term disinfection in water purification and sewage treatment processes.