PROCEDURE
Procedure
Using the 1000 mL graduated cylinder, add 1000 mL (or 2000 mL if using the B-Ker2 2-liter square jar) of the raw water to be coagulated to each of the jar test beakers. Using the prepared alum (or other coagulant) stock solution dose each beaker with increasing amounts, using the following schedule as an example (Double the dosage when using B-Ker2 2-liter square jars). If necessary, add lime or soda ash stock solution to maintain correct alkalinity.


Jar
#
mL Alum
Stock
mL Lime\
Soda Ash
mg\L
Alum
mg\L Lime
Soda Ash
1
0.5
0
5.0
0
2
1.0
0
10.0
0
3
1.5
0
15.0
0
4
2.0
0.5
20.0
5.0
5
2.5
1.0
25.0
10.0
6
3.0
1.5
30.0
15.0

The above schedule is meant as an example. You should through trial and error establish your own sampling schedule that takes into account your own plant's operation and quality of the water at the intake. IMPORTANT: ALWAYS KEEP ACCURATE NOTES PERTAINING TO DOSING WHILE PERFORMING JAR TESTS.

Example: Your plant has a static mixer after the chemicals are injected, followed by 30 minutes in a flocculator, then 2 hours settling time before the filter.

After dosing each beaker, operate the stirrer at high rpm for approximately 1 minute. This simulates the static mixer. Then, slow to the rpm which matches the turbulence created in your flocculators and allow to stir for 30 minutes while observing the floc formation. At the end of the 30 minutes turn the stirrer off and allow to settle. Because there are 2 hours of settling time in this plant, at the end of 1 hour most of the settling will be complete.

A coagulant underfeed will cause the sample to appear cloudy, with little or no floc and almost no settling. A coagulant overfeed will form dense floc, however, it will appear fragile and fluffy; when the stirrer is turned off, it will not settle well. Floc formed by an overfeed is false floc which is very light and will carry to the filter. This is one of the most common treatment problems. A good floc will appear heavy and tight, not too dense, with spaces of bright, clear water between the particles and will begin to settle as soon as the stirrer is turned off.





INFORMATION

More Information
A tap installed in the raw water immediately after the chemicals are injected is indispensable. A sample taken from this tap can be placed on the stirrer to quickly determine the effectiveness of the dosage being used.

In order to add chemicals accurately, feeders must be calibrated.

If you are experiencing trouble when the raw water is clear and cold, and if your flocculators are adjustable, speed them up. This will improve the collision rate during cold water conditions.

A good formula to use for chemical application:

PPM x GPM / 2,000 = Ibs. per hour

PPM you determine by the jar test. GPM is the gpm at which your plant operates. 2,000 is a given number.

If you use alum as a coagulant you should test the finished water for aluminum content. This is a good indicator of how well the coagulation flocculation process is working. An elevated aluminum level could indicate alum overfeed.

Placing a black background behind the jar test will give you a better view of the floc process.

When purchasing jar test apparatus there are two very important features to look for: Adjustable stirring rate and an illuminated base. Without adjustable speeds you will be unable to simulate conditions in your plant. The light base provides a full and clear view of all the beakers simultaneously. Light bases using fluorescent bulbs will not change the temperature of the sample significantly.

 

The jar test is intended to simulate the coagulation flocculation process in your plant. Designing a jar test procedure to match conditions in your plant takes a little thought and practice on the operator's part. 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.
 

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