When should chlorine be added in a treatment system relative to other processes?

Chlorine is typically added in a treatment system immediately after aeration for several reasons. Aeration is a process where water is exposed to air, which helps to remove unwanted gases, such as volatile organic compounds and hydrogen sulfide, and improve the water quality by oxidizing certain contaminants.

Adding chlorine immediately after aeration allows for effective disinfection while still having the benefits of the aeration process. The oxidizing conditions help to enhance the effectiveness of chlorine by ensuring that any remaining contaminants that may not have been completely aerated are readily available for chlorine's disinfecting action. This timing also ensures that chlorine can react with pathogens and other harmful microorganisms present in the water before it moves onto subsequent treatment steps, such as filtration, where water quality can improve further.

Putting chlorine into the system before filtration allows any remaining particles and microorganisms to be removed efficiently by the filter media, making it a critical step in ensuring the effectiveness of the disinfection process. In contrast, adding chlorine after disinfection or before storage would not align with the typical processes to ensure maximum pathogen removal and disinfection effectiveness prior to water reaching consumers.