Guidance For Chemical Application Based On Lab Results
Chlorine
The application of chlorine to the finished water is driven by ability to meet disinfection standards.
Aluminum Sulfate (Alum) for Coagulation
Jar tests aid the operator in selecting the proper alum dosage. The optimum dosage is not fixed and will change as the raw water quality changes. It is desirable for the plant operator to run a jar test each day and even more frequently during rapidly changing raw water conditions.
To aid the plant operator in becoming familiar with the required alum dose, it is recommended that a record be maintained of the dosage applied versus the raw water turbidity, alkalinity, and pH.
Polymer Application
Both a liquid and dry polymers are available for application at the Glasgow WTP. The addition ofpolymer results in stronger flocs, reduced alum dosages, increased filter runlengths, and improved filter water quality. The use of these polymers introduces an addeddegree of flexibility for the plant operation by varying the dosage of alum, dry polymer, and liquid polymer.
Polymer dosages generally do not vary as widely as the alum. The recommended polymer dosage depends on the polymer used (nonionic or cationic). Polymer dosage should be determined by jar testing and filter operation. The laboratory is furnished with a 6 paddle jar tester. All operators should be trained in operation and provided with guideline of how to adjust the treatment components based on the results. Jar tests should be conducted frequently and during changing raw water quality conditions, daily jar testing is recommended. The dosage of alum and polymer should both be varied until the most effective and economical combination is found. A record of filter head loss and filter effluent turbidity should be kept. The correct polymer dose produces maximum head loss just slightly in advance of the turbidity filter breakthrough. Whereas, an excessive dose of polymer causes the maximum head loss to occur far in advance of breakthrough, and a low dose of polymer will not result in a maximum head loss before breakthrough occurs.
Caution should be observed in reducing plant polymer dosages, which may appear to be appropriate under improving water conditions, because there is some residual effect from the polymer within the filter bed and a time lag occurs before the full effect of the reduced dosage is realized. It is best to reduce the polymer dosage in small increments and observe the effects of three filter run cycles before further reducing the polymer dosage Conversely, there is little lag when the polymer dosage is increased. Increasing the polymer dosage can be accomplished more rapidly. Increasing dosage has many of the same effects as decreasing the size of filter media. Overfeeding, however, should be carefully avoided to prevent binding of the media.