Experiment 4

JAR TEST

2

Majority of ions in surface water consist of negatively charged particle/colloids which are stable in nature ( stable = existing in ionized form) .

They repel other colloidal particles before they collide with one another. The colloids are continually involved in Brownian movement.

COAGULATION AND FLOCCULATION

3

Destabilization (Coagulation) Particles Flocculation

Al(OH)3 (s) @ Fe(OH)3 (s)

Settle down at the bottom of the flocculation tank

Al 3+ / Fe3+

Al 3+ / Fe3+

COAGULATION AND FLOCCULATION

Coagulation Coagulation – process utilizes what is known as a chemical

coagulant is mixed thoroughly with the water and various species of the positively charged particles (such as Al3+, Fe3+)adsorb to the negatively charged colloids such as colour, clay, turbidity and other particles through the processes of charge neutralisation to produce microfloc.

Once the charge is neutralized, the small suspended particles are capable of sticking together microflocs.

The water surrounding the newly formed microflocs should be clear. If it is not, all the particles' charges have not been neutralized, and coagulation has not been carried to completion. More coagulant may need to be added.

Flocculation

is the process in which the destabilised particles are bound together by hydrogen bonding of Van der Waal’s forces to form larger particle flocs.

High molecular weight polymers, (i.e coagulant aids) added during this step to help bridge, bind, and strengthen the floc, add weight, and increase settling rate

Example: Used alum as coagulation agent

1Al2(SO4)3•14H2O + 6HCO3-↔2Al(OH) 3• 3H2O(s) + 6CO2 +8H2O + 3SO42-

The above reaction shifts the carbonate equilibrium and decreases the pH

Alum sludge , settle in the flocculation tank

Coagulant agents: Trivalent cations considered as good

coagulant as follows:

Cations such as Fe3+ and Al3+ has a higher molecular weight, so its easy to settle .

it removes turbidity effectively even a small dose was used.

In FKAAS laboratory, frequently we used Al3+ or Fe+ as coagulant agent.

Environmental Engineering Sem 2 2011/2012 8

PROCEDURE of COAGULATION and FLOCCULATION

Therefore, coagulation and flocculation designed to remove•Microorganisms and colloids that caused turbidity •Toxic compounds that are sorbed to particles•NOM (precursor of DBPs)

JAR test is a laboratory works to illustrate the coagulation and flocculation concepts associated to nature water. From this experiment the optimal pH, coagulant dose ,and coagulant aid could be determined.

Procedure:

1. Prepare the wastewater sample 2. Measure temperature, pH and turbidity of

water sample

..cont. PROCEDURE3. Add 1 - 5 ml of coagulant (alum/ferrous sulfate) by using a

measuring pipette into beaker 1,2,3,4 and 5 while in beaker 6, no alum was added as it acts as a control sample.

JAR TEST: Set up the variation of coagulant dose at selected pH (shown in Table 1 lab sheet)

..cont. PROCEDURE

..cont. PROCEDURE

4. Measure the pH and turbidity of each beaker by using pH and turbidity meter.

5. Start stirring rapidly (60 to 80 rpm) for 3 minutes.

6. Reduce the speed (30 rpm) for about 20 minutes.

7. Observe the flocculation process and record the floc formation in final 10 minutes by referring to the chart of particle sizes provided as in lab sheet.

7. After the stirring period is over, stop the stirrer and allow the flocs to settle for about 5 minutes.

8. Separate out 500 mL of settled water into another beaker.

9. Determine the temperature, pH and turbidity of the clarified water.

..cont. PROCEDURE

Please record the qualitative characteristics of flocs as bad, moderate, good and very good.

Cloudy samples indicate bad coagulation while good coagulation refers to rapid floc formation resulting in clear water formation on the upper portion of the beaker.

..cont. PROCEDURE

Figure: The scale for measures of floc particle sizes. It gives the qualitative characteristics of flocs.

Very fine

Very fine / fine

Fine

Moderately fine

Moderate

Coarse

Very Coarse

Analysis:

Example of results:

Plot the graph:Example of graph: From the graph, the optimal alum dosage was

estimated to be 12.5 mg/L