Which is the proper detention time for disinfecting a water storage tank mixed with hypochlorite such that the free chlorine is 10 mg/L after proper detention time is complete?

The proper detention time for disinfecting a water storage tank with hypochlorite, ensuring that the free chlorine concentration achieves 10 mg/L after the necessary period, is typically a longer duration, such as 24 hours. The reason for this extended detention time is rooted in the chemistry of disinfection, which requires sufficient contact time for the chlorine to effectively eliminate pathogens and ensure water quality.

The effectiveness of chlorine as a disinfectant depends not only on its concentration but also on the time it remains in contact with the water. Different factors can influence this, including water temperature, pH, and the presence of other organic materials. A longer detention time allows for a more thorough reaction, ensuring that the hypochlorite can effectively neutralize potential contaminants within the tank.

Choosing 24 hours ensures that there is adequate time for the chlorine to work effectively, allowing for any residual effects and maximizing the disinfection process. This aligns with best practices in water treatment, where achieving a specific residual chlorine level is critical to ensuring the safety and quality of the water supply.