Question 12.4: TYPICAL JAR TEST PROCEDURES FOR CHEMICAL FEED DOSAGE DETERMI...
TYPICAL JAR TEST PROCEDURES FOR CHEMICAL FEED DOSAGE DETERMINATION
This section introduces an example of jar test procedure. There are numerous techniques that can be used to run jar tests and many are site specific. Normally site-specific jar test procedures should be developed to best correlate jar test results to individual water or wastewater treatment plant performance. It is important to note that a jar test procedure for a conventional water treatment plant (involving chemical feeding, rapid mixing, flocculation sedimentation, filtration, etc.) is different from that for a lime-soda ash softening plant (involving chemical feeding rapid mixing, flocculation, sedimentation, softening, recarbonation, etc.) Besides, a jar test procedure for a sedimentation-filtration plant is different from that for a flotation-filtration plant. In this example, recomend a common jar test procedure for the conventional WTP. Explain how to modify a standard jar test for (a) simulating an intended lime-soda ash softening process; (b) simulating a dissolved air flotation process; (c) simulating a test and odor removed process.
The following is a recommended jar test procedure for simulating a conventional WTP:
1. Prepare dry chemical’s stock solutions in accordance with the methods introduced in Example 12.2.
2. Prepare liquid chemical’s stock solutions in accordance with the methods introduced in Examples 12.1 and 12.3.
3. Set up jar test apparatus and arrange glassware.
4. Fill all jars to the 2-L mark with plant raw water.
5. Measure the appropriate amount of chemicals into syringes and place syringes nest to jars.
6. Rapid mix
A. Turn mixer to maximum speed.
B. Dose alum and cationic polymer coagulant in all jars simultaneously and stir 30 seconds. Place chemicals as close to the impeller tip as possible.
C. After 30 seconds of mixing, reduce mixer speed to 35 rpm.
7. Flocculation
A. Maintain mixer speed at 35 rpm and mix for 20 minutes.
B. Observe formation of floc particles in each jar.
C. Note: Set mixer speeds and mix times to approximate actual plant conditions.
8. Setting
A. Turn off the mixer and let jars set 20 minutes or set to actual plant condition such as actual settling time.
B. Take samples of 30 to 40 mL from the sample tap located 10 cm from the top of jar.
C. Sample all jars “simultaneously” and place sample into small beakers.
D. Measure the turbidity or other target water quality parameters of each sample.
9. Recording results
A. Record test results on the attached lab sheet.
B. Jar with lowest turbidity or other target water quality parameters indicates best coagulant dose.
Notes:
a. For simulation of a lime-soda ash softening process, the required lime, soda ash and CO_{2} gas, etc. must be fed to the jars, and there may be multiple settling periods.
b. For simulation of a dissolved air flotation process involving chemical feeding, rapid mixing, flocculation, DAF clarification, etc., the standard jar tests may also be used for determining approximate chemical dosages, order of chemical dosing, detention time, velocity gradient G, etc. because the chemistry of coagulation-sedimentation is very similar to that of coagulation-DAF although the coagulant dosage, mixing detention time, and flocculation detention time of DAF are slightly lower. For detailed bench-scale coagulation-DAF testing, the readers are referred to the literature (Shammas et al., 2010).
c. For taste and odor control, aeration step, powdered activated carbon addition, ozonation step, or potassium permanganate addition, etc. can be incorporated into the standard jar tests. Learning how to modify the jar test procedures for simulation of various physicochemical treatment processes is very important.