Jar test

Water Treatment - Jar Testing Procedure

Example - Jar tests can be used to evaluate the coagulation efficiency of a coagulant. The Phipps-Bird jar testing apparatus is recommended for use. It consists of six 1-Liter beakers or 2-Liter square jars and a gang mixer. A jar test is performed by first adding the same alum dose and varying the pH in each jar. The test can be repeated by holding the pH and varying the coagulant dose.

Water Treatment - Jar Testing Procedure

Water Treatment - Jar Testing Procedure

Water Treatment - Jar Testing Procedure

Example - In this example, two sets of jar tests were conducted on a raw water containing 15 NTU and an HCO3

- alkalinity of 50 mg/L expressed as CaCO3. Given the data below, find the optimal pH, coagulant dose, and the theoretical amount of alkalinity that would be consumed at the optimal dose.

Water Treatment - Jar Testing ProcedureJar Test 1

Test number 1 2 3 4 5 6

pH 5.0 5.5 6.0 6.5 7.0 7.5

Alum dose (mg/L) 10 10 10 10 10 10

Settled turbidity (NTU) 11 7 5.5 5.7 8 13

Jar Test 2

Test number 1 2 3 4 5 6

pH 6.0 6.0 6.0 6.0 6.0 6.0

Alum dose (mg/L) 5 7 10 12 15 20

Settled turbidity (NTU) 14 9.5 5 4.5 6 13

Solution: The above results are plotted in the following figures.

Water Treatment - Jar Testing Procedure

pH

Water Treatment - Jar Testing Procedure

Alum Dose, mg/L

Water Treatment - Jar Testing Procedure

Solution: Base on the plots of the data, the optimal pH was chosen as 6.25 and the optimal alum dosage was about 12.5 mg/L. The experiments may be repeated using a pH of 6.25 and varying the alum dose between 10 and 15 mg/L to pinpoint the optimal conditions.

The amount of alkalinity that will be consumed is found by using the stochiometric expressions which shows that one mole of alum consumes six moles of HCO3

- alkalinity.

Water Treatment - Jar Testing Procedure

Solution: The quantity of alkalinity that will be consumed is found by using the following stochiometric expression.

( ) ( )- =

2 4 2 3 4 2 23 3Al SO :14H O 6HCO 2Al OH 3SO 14H O 6CO+ ® ¯ + + +

Using the above equation, and a molecular weight of 594 for alum, the amount of alkalinity consumed is calculated as:

mgAlum 1mmoleAlum mmolesAlum12.5 0.021

L 594mgAlum L´ =

Water Treatment - Jar Testing Procedure

Solution:

3

3 3

3 3

33

Alkalinity6mmolesHCOmmolesAlum

Conc. 0.021L 1mmolesAlum

Consumed

1mmoleCaCO 100mgCaCO

2mmoleHCO 1mmolesCaCO

mgHCO6.3 asCaCO

L

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-

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