Experiment 4 coagulation

CIVL 375 Experiment 4
REMOVAL OF COLLOIDAL PARTICLES BY COAGULATION
Introduction
Coagulation is the destabilisation and initial aggregation of colloidal and finely divided
suspended matter (colloidal particles) by addition of floc-forming chemical such as
aluminium sulphate (alum) or one of the iron coagulants. The flocculation process is the
agglomeration of collected and finely divided suspended matter after coagulation by
gently stirring through either mechanical or hydraulic means. Optimum removal of
colloidal particles from water and wastewater depends on, among other factors, the type
of coagulant used, the dose, and the pH.
Objective
To determine the optimum coagulant dosage for removal of colloidal particles from the
provided sample.
Equipment and Reagents
(a) Equipment and glassware
Jar test apparatus.
pH meter.
Turbidimeter.
Six 1-L beakers.
Five 100-ml beakers
Pipettes
(b) Reagents
A coagulant (either aluminium sulphate (Al 2(SO4)3.16H2O or ferric chloride
FeCl3) at a concentration of 1%. Every 1 ml of this coagulant solution gives a
concentration of 10 mg/L when added to 1 liter of sample.

Schematic of the Jar Test Apparatus
Procedure
1. Transfer 1 liter of the sample to each 1-L beaker and place on stirrer base. Immerse
paddles to a fixed depth below liquid surface in the beakers.
2. Set paddles to rotate at 100 RPM.

3. Add a given volume of the coagulant solution to each of the five 100-ml beakers as
directed by the engineer (commonly 1, 2, 5, 10, and 20 ml with one beaker is left
without addition of coagulant)


4. Add the coagulant dose in the 100-ml beakers to five of the 1-L beakers while the
paddles are rotating. Make sure that there is no significant time difference between
the additions of coagulant to different beakers.
5. Use the sixth 1-L beaker as a blank (i.e don’t add a coagulant to this beaker).
6. Stir for approximately 1 minute at 100 RPM, then reduce the speed of stirring to 30
RPM for additional 20 minutes. Rapid mixing allows distributing the coagulant
uniformly within the solution while slow mixing allows flocculation of the particles.
7. Stop stirring, lift the paddles from the solution, and allow sample to stand for about 30
minutes.
8. Sample the supernatant of each beaker without shaking or stirring the settled portion.
9. Measure the pH, alkalinity and suspended solids of the withdrawn sample from each
beaker.
10. A table similar to the one shown below should be filled
Beaker

Coagulant dose
ml

Coagulant dose
mg/l

0

0

1
2
3
4
5
6 blank

pH

Alkalinity

Suspended solids
mg/l

Requirements:
1. Fill out the provided experiment data sheet and carry out the required calculations.
2. If you are requested to submit a report of this experiment then your report should
contain (a) an introduction that ends with the objective (b) methodology including
sample identification (c) results and discussion (d) conclusion (e) references and (f) an
appendix that contains the filled data sheet.


CIVL375: Experiment 4 Data Sheet
REMOVAL OF COLLOIDAL PARTICLES BY COAGULATION
Name

ID

Experimental Conditions
Experiment date

Sample identification
Coagulant used
Coagulant solution concentration, %
Sample suspended concentration, mg/l
Sample alkalinity, mg/l as CaCO3
Rapid mixing time, seconds
Slow mixing time, minutes
Settling time, minutes
Jar Test Results
Jar No. Coagulant dose
(ml of
coagulant
solution)

Coagulant
dose (mg/l)

pH

Suspended solids
(mg/l)

Required Calculations
1. Plot pH versus coagulant dose (mg/l).
2. Plot suspended solids versus coagulant dose (mg/l).
3. Plot alkalinity versus coagulant dose (mg/l).
4. What is the optimum dose?

Alkalinity
(mg/l as

CaCO3)