Jar Testing 3

Using Jar Test Results to Determine System Dosages

After you determine the optimum ppm dosage from the jar tests, you will have to calculate your pounds/hr or pounds/day dosage in the water flow to be treated.

Water flow: GPM 60 = GPH or GPM 1,440 = GPD

GPH 8.34 = lbs. of water/hr or  GPD 8.34 = lbs. of water/day

Remember that ppm (or parts/million parts) is the same as pounds/million pounds. As an example, if you want to treat a 1,000 GPM of water flow at 5 ppm, then:

Jar test dosage equation

Note that in the second equation above that 1,440 8.34 ≈ 12,000.

 Pounds of product/day = flow rate ppm product dosage:

Jar test dosage equation

If the specific gravity of the polymer is 1.12 this means it is 1.12 times the weight of water, which is 8.34 pounds/gallon. Therefore, this hypothetical polymer weighs:

Jar test dosage equation

And

And

Jar test dosage equation

Since 1.0 U.S. gallon = 3.785 liters, then 0.27 gals/hr 3785 = 1,022 mLs/hr

But all of the above is based on neat polymer and since you are going to dilute the polymer before addition to the system you will have to take the solution concentration into consideration.

Example

You have made up a polymer solution in a day tank at 0.5 percent. This means that the polymer has been diluted 200. Your application rate of the diluted polymer must be 200 times the gallon or mL figure given above in order to have the application rate in neat polymer, as previously calculated.

Therefore,

Program Considerations

The following should be considered after you have completed the jar testing protocol and have determined the optimum program:

  • What is your proposed program remembering that coagulants need thorough, rapid mixing followed by slow mixing and that the flocculants require some rapid mixing for adequate dispersion in the water followed by longer periods of quiescence?
  • How much and where will the coagulant be applied to the system? Will the coagulant be inorganic, organic, or a combination?
  • If flocculant is required, what is the proposed dosage and where will it be applied? (Always following coagulant.)
  • What pumps, tanks, and mixing equipment will be necessary?
  • How will you measure the success of the program?
  • How will you determine whether or not the plant operators are using your prescribed dosage?

Summary

The jar test is intended to simulate the coagulation and flocculation process in your plant. Consequently, designing a jar test procedure to match conditions in your plant takes a little thought and practice. However, when you have developed the proper routine and then properly applied the results, you will be producing the best water possible at the lowest cost.

This completes the discussion on jar testing procedures.