What concentration of chlorine is required for slug disinfection of water mains?

The required concentration of chlorine for slug disinfection of water mains is typically around 300 mg/l. This concentration is effective for rapidly disinfecting newly constructed, repaired, or flushed water mains. It ensures that any pathogens present in the system are effectively inactivated. The higher concentration is necessary because chlorine dissipates quickly in water and must be present at sufficient levels to maintain disinfection throughout the entire water main, especially in larger diameter pipes or systems with heavy biofilm.

In practical applications, this concentration provides a balance between effective microbial destruction and the potential for chemical residuals to be remaining in the water system post-disinfection. Lower concentrations, like 50 mg/l or 150 mg/l, may not achieve the desired efficacy for disinfection, while concentrations above 300 mg/l, such as 450 mg/l, may result in excessive chlorine residual and could lead to taste and odor issues or harmful byproducts. The use of 300 mg/l is thus a widely accepted standard that addresses safety, effectiveness, and practicality in water treatment operations.