What is the minimum chlorine residual required during a 24-hour disinfection procedure?

In water distribution and treatment, maintaining an adequate chlorine residual is crucial for effective disinfection. The correct answer indicates a minimum chlorine residual of 25 mg/L during a 24-hour disinfection procedure. This concentration ensures that enough chlorine is present to effectively kill pathogenic organisms and provide a robust barrier against potential contamination.

Chlorine is a powerful disinfectant, and its efficacy is highly dependent on concentration and contact time. The specified 25 mg/L level is established based on standards meant to provide a strong assurance of disinfection, especially when considering various water quality conditions and the presence of organic materials that can react with chlorine.

Using a residual below this level, such as 10 mg/L or 5 mg/L, may not be sufficient to maintain effective disinfection over the designated time period, particularly in environments with higher levels of microbial load or turbidity. Thus, ensuring a chlorine residual of at least 25 mg/L helps achieve the desired health and safety standards in drinking water treatment.