jar test
DESCRIPTION
procedure of JAR TESTTRANSCRIPT
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Experiment 4
JAR TEST
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2Majority 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
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3Destabilization (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
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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.
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Flocculation
is the process in which the destabilised particles are bound together by hydrogen bonding of Van der Waals 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.
The dosage used in WT is 5-50 mg/L.
Effective pH for coagulation is 5.5-8.0.
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Example: Used alum as coagulation
agent
1Al2(SO4)314H2O + 6HCO-3 2Al(OH)3 3H2O(s) + 6CO2 +8H2O
+ 3SO-24
Al2(SO4)3.14H2O + 6HCO-3 2Al(OH)3(s) + 6CO2 + 3SO
-24 +
14H2O
The above reaction shifts the carbonate equilibrium and decreases
the pH
Alum sludge (alum floc,
aluminum hidroxide, dry
sludge) settle in the
flocculation tank
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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 Fe2+ as coagulant agent.
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Environmental Engineering Sem 2 2011/2012 8
PROCEDURE of COAGULATION and FLOCCULATION
Therefore, coagulation and flocculation designed to removeMicroorganisms and colloids that caused turbidity Toxic compounds that are sorbed to particles
JAR test (shown in Figure) 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.
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Procedure:
1. Prepare the wastewater sample
2. Measure temperature, pH and turbidity of
water sample
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..cont. PROCEDURE
3. 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.
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Students are allowed to choose:
JAR TEST 1: Set up with fixed coagulant dose at
varied pH (shown in Table 1 lab sheet)
JAR TEST 2: Set up the variation of coagulant dose
at a fixed pH=6 (shown in Table 2 in lab sheet)
..cont. PROCEDURE
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..cont. PROCEDURES
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.
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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
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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
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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
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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