Course: BFM 203 Water Treatment and Control

Lecture

(5/5)

Disinfection Effectiveness

Several critical factors affect disinfection, including the following:

- Effectiveness of upstream treatment processes
- Effectiveness of mixing at injection point
- Temperature (higher is better)
- Dosage and type of disinfectant
- pH (lower is better)
- Contact time
- Chlorine residual

Effectiveness of upstream treatment processes means reducing turbidity in the finished water to the lowest level possible. pH at neutral or slightly below is best for chlorination while water that is greater than 8.5 requires more more chlorine for effective disinfection. Cold water can more than double the contact time for effective disinfection. jar testing can help determine the best type of disinfectant and the most effective dose.

Types of Chlorination

Pre-chlorination may increase the formation of THM's when organic precursors are present and T/O when phenolic compounds exist, but benefits include control of algae and slime growth, control of mud ball formation, reduction of T/O, increased chlorine contact time, and increased safety factor in disinfection of heavily contaminated waters

Post-chlorination refers to the application of chlorine after water has been treated but before it enters the distribution system.

Rechlorination is the practice of adding chlorine in the distribution system. This technique is used when the distribution system is long and complex. Rechlorination may occur in storage tanks, booster stations, or at specifically engineered re-chlorination stations. A comprehensive chlorine residual analysis program and/or continuous monitoring may be required when re-chlorination systems are in use.