EXPERIMENT 2: JAR FLOC TEST

1.0 OBJECTIVE

i. To determine the optimum alum dose for suspended solids removal from

water using jar test.

ii. To determine the optimum pH suspended solid removal from water using the

jar test.

2.0 INTRODUCTION

The jar test is a method of measuring the effect of coagulation, flocculation, and

sedimentation on turbidity.  Although the procedure is not outlined in Standard

Methods, it is used in most water treatment plants to find the best coagulant dosages

under varying conditions.  

Coagulation/flocculation is the process of binding small particles in the water

together into larger, heavier clumps which settle out relatively quickly.  The larger

particles are known as floc.  Properly formed floc will settle out of water quickly in the

sedimentation basin, removing the majority of the water's turbidity. 

In many plants, changing water characteristics require the operator to adjust

coagulant dosages at intervals to achieve optimal coagulation.  Different dosages of

coagulants are tested using a jar test, which mimics the conditions found in the

treatment plant.  The first step of the jar test involves adding coagulant to the source

water and mixing the water rapidly (as it would be mixed in the flash mix chamber) to

completely dissolve the coagulant in the water.  Then the water is mixed more slowly

for a longer time period, mimicking the flocculation basin conditions and allowing the

forming floc particles to cluster together.  Finally, the mixer is stopped and the floc is

allowed to settle out, as it would in the sedimentation basin.

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The type of source water will have a large impact on how often jar tests are

performed.  Plants which treat groundwater may have very little turbidity to remove

are unlikely to be affected by weather-related changes in water conditions.   As a

result, groundwater plants may perform jar tests seldom, if at all, although they can

have problems with removing the more difficult small suspended particles typically

found in groundwater.  Surface water plants, in contrast, tend to treat water with a

high turbidity which is susceptible to sudden changes in water quality.  Operators at

these plants will perform jar tests frequently, especially after rains, to adjust the

coagulant dosage and deal with the changing source water turbidity.

3.0 MATERIAL AND APPARATUS

Reagent

Figure 3.1: Jar test equipment Figure 3.2: Beakers

– 6 places with stirring mechanism

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Figure 3.3 : PH Meter Figure 3.4: Pipette

Figure 3.5: Graduated Cylinder

Equipment / solution

Figure 3.6: Aluminium Sulphate Figure 3.7: Ferric

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Figure 3.8: Calcium carbonate Figure 3.9: waste water sample

Figure 3.10: H2SO4 Or NaOH

4.0 PROCEDURE

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Prior to the jar test procedure each 500ml sample must be corrected to the pH using

H2 H2SO4 or NaOH. In order to obtain the correct amount of acid or alkali for each

sample a separate titration must be carried out for each alum dose-pH combination.

Use 100ml water sample for your titration.

Test for optimum dose (pH constant)

1. Fill six 1 L beakers with 800ml the water sample.

Figure 1 : Beaker With 800ml

2. Prepare alum solution with the concentration 5.0g/L

3. Add to the beakers the amount of H2SO4 or NaOH that you yield final pH value

of 6.5

4. Add to the beakers alum solution corresponding to doses of 0(control) 1.5,

2.5,5,10 and 15ml.

5. Mix the sample at high speed (80rpm) for 1 minute.

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Figure 2 : Mixing The Sample

6. Reducing mixing speed to 30rpm and continue mixing for 15 minute.

7. Stop the stirrer and let the flocs settle for 20 minute.

Figure 3: Taking Sample Of Waste Water.

8. Determine supernatant turbidity using turbidity meter.

9. Plot turbidity vs alum dose.

5.0 RESULT

Optimum dose (pH constant)

Sample volume : 800 g/l (0.8 ɩ )

Alum concentration : 2.0 g/l

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Beaker Alum dose ,mLActual alum dose,

mg/LTurbidity (NTU)

1 0.0 0 54.4

2 1.5 3.0 52.1

3 2.5 5.0 43.4

4 5.0 10.0 22.8

5 10.0 20.0 11.2

6 15.0 30.0 4.64

CALCULATION

Example beaker 2

Alum concentration : 2.0 g/l

Sample volume : 800 ml / 1000 = 0.8 ɩ

Actual Alum Dose = Alum Dose (ml) × Alum concentration

1.5 × 2.0 = 3.0

6.0 PLOT TURBIDITY VS ALUM DOSE

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7.0 CONCLUSION

From this experiment we have learned to do the jar floc test successfully, and we

also knew how to handle the experiment materials and tools properly by using safety

precaution. We have determines the optimum alum dose for suspended solids

removal from water using jar test correctly and can determine the optimum pH

suspended solid removal from water using the jar test correctly. Hence the objective

of the experiment has been archived by our group

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8.0 DISCUSSION

From the experiment, we have obtained a result and the result has been interpreted

in graph. The graph shows that when the alum dose mixture 2.0 mL the turbidity

level is at the lowest and when the alum dose mixture at highest 15mL the turbidity

level is high. That means the 2.0 mL alum dose is the optimum volume for 800ml

(0.8 ɩ ) of water to remove suspended solids.

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