JAR TESTING

Tina Lafleur

1. Using a 1,000 mL graduated cylinder, add 1,000 mL of raw water to be coagulated to each of the jar test beakers.
2. Using a prepared coagulant stock solution (Alum), dose each beaker with increasing amounts of solution.
   
   Here's an example for dosing the beakers:
   
   

   Jar #	mL Alum Stock Added	mg\L Alum Dosage
   1	0.5	5.0
   2	1.0	10.0
   3	1.5	15.0
   4	2.0	20.0
   5	2.5	25.0
   6	3.0	30.0

   
   
   There can be anywhere from 4 to 6 beakers for this test, the above chart should be modified to reflect the correct amount of beakers and reflect the dosages required for a specific plant.
   
   Here's a picture of what a jar testing apparatus might look like.
   
   
   
   
3. After dosing each beaker, it is time to turn on the stirrers. This part of the procedure should reflect the actual conditions of the specific plant.
   For example, let's say the plant has a static mixer following chemical addition, followed by 35 minutes in a flocculator, then 1.5 hours of settling time before the filters. The jar test would be performed as follows:
   Operate the stirrers at a high RPM for 1 minute to simulate the static mixer. Then reduce the speed of the stirrers to match the conditions in the flocculator and allow them to operate for 35 minutes. Observe the floc formation periodically during the 35 minutes. At the end of the 35 minutes turn off the stirrers and allow settling. Most of the settling will be complete after 1 hour.
   
   
4. Next, look at the beakers and determine which one has the best results (if any). An underfeed will cause the sample to look cloudy with little or no floc and almost no settling. An overfeed will cause a dense fluffy floc to occur and will not settle well. The beaker with an appropriate dosage of coagulant will have floc that has settled to the bottom and the water above it will be clear.
   If none of the beakers appear to have good results then the procedure should be run again using different dosages until the correct dosage is determined.