CONSTRUCTION 4

1. 1
TITLE: JAR TEST
1.0 INTRODUCTION
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.
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.

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2.0 OBJECTIVE:
1. To conduct jar test.
2. To show the effectiveness of chemical treatment in a water treatment facility.
3. To evaluate coagulation efficiency.
4. To determine the most effective dosage of the recommended coagulants and
flocculants.
5. To selects the best chemical or best dosage to feed on the basis of clarifies of effluent
and minimum cost of chemicals.
6. To gain a ’hands on’ understanding of the treatment process for removing suspended
solids from water.
3.0 THEORY:
Raw water or wastewater must be treated to remove turbidity, color and bacteria.
Colloidal particles are in the size range between dissolved substance and suspended
particles. The particles are too small to be removed by sedimentation or by normal
filtration processes. Colloidal particles exhibit the Tyndall effect; that is, when light
passes through liquid containing colloidal particles, the light is reflected by the particles.
The degree to which colloidal suspension reflects light at 90º angle to the entrance beam
is measured by turbidity. The unit of measure is a Turbidity Unit (TU) or Nephlometric
Turbidity Unit (NTU). It is determined by reference to a chemical mixture that produces a
reproducible refraction of light. Turbidities in excess of 5 TU are easily detectable in a
glass of water and are usually objectionable for aesthetic reasons. For a given particle
size, the higher the turbidity, the higher the concentration of colloidal particles.
Color is a useful term that is used to describe a solution state. But it is difficult to
distinguish ‘dissolved color’ and ‘colloidal color’. Some color is caused by colloidal iron
or manganese complexes. Although, the most common cause of color is from complex
organic compounds that originate from the decomposition of organic matter. Most color
seems to be between 3.5 and 10μm, which is colloidal. Color is measured by the ability of

3. 3
the solution to absorb light. Color particles can be removed by the methods discussed for
dissolved or colloidal, depending upon the state of the color.
Finely dispersed solid (colloids) suspended in wastewater are stabilized by
negative electric charges on their surfaces, causing them to repel each other. Since this
prevents these charged particles from colliding to form larger masses, called flocs, they
do not settle. To assists in the removal of colloidal particles form suspension, chemical
coagulations and flocculation are required. These processes, usually done in sequence,
are a combination of physical and chemical procedures. Chemicals are mixed with
wastewater to promote the aggregation of the suspended solids into particles large enough
to settle or be removed. Coagulation is the destabilization of colloids by neutralizing the
forces that keep them apart. Cationic coagulants provide positive electric charges to
reduce the negative charge of the colloids. As a result, the particles collide to form larger
particles (floc). Rapid mixing is required to disperse the coagulant throughout the liquid.
The coagulants overdose can cause a complete charge reversal and destabilize the colloid
complex.
A coagulant is the substance (chemical) that is added to the water to accomplish
coagulation. There are three key properties of a coagulant;
1. Trivalent cation: As indicated in the last section, the colloids most commonly
found in natural waters are negatively charged; hence a cation is required to neutralize the
charge. A trivalent cation is the most efficient cation.
2. Nontoxic: This requirement is obvious for the production of safe water.
3. Insoluble in the neutral pH range. The coagulant that is added must precipitate
out of solution so that high concentrations of the ion are not left in the water. Such
precipitation greatly assists the colloid removal process.
The two most commonly used coagulants are aluminum (Al3+
) and ferric iron
(Fe3+
). Both meet above three requirements. Aluminum can be purchased as either dry or
liquid alum [Al2(SO4)3·14H2O]. Commercial alum has an average molecular weight of
594. When alum added to a water containing alkalinity, the following reaction occurs;

4. 4
Al2(SO4)3·14H2O + 6HCO-
3 ↔ 2Al(OH)3(s) + 6CO2 + 14H2O + 3SO4
2-
The above reaction shifts the carbonate equilibrium and decreases the pH. When
sufficient alkalinity is not present to neutralize the sulfuric acid production, the pH may
be greatly reduced;
Al2(SO4)3·14H2O ↔ 2Al(OH)3(s) + 3H2SO4 + 8H2O
If the second reaction occurs, lime or sodium carbonate may be added to neutralize the
acid. The optimal pH range for alum is approximately 5.5 to 6.5 with coagulation
possible between pH 5to pH 8 under some conditions.
In flocculation process, the flocculating agent is added by slow and gentle mixing
to allow for contact between the small flocs and to agglomerate them into larger particles.
The newly formed agglomerated particles are quite fragile and can be broken apart by
shear forces during mixing. Increasing the dosage will increase the tendency of the floc to
float and not settle. Once suspended particles are flocculated into larger particles, they
can usually be removed from the liquid by sedimentation, provided that a sufficient
density difference exists between the suspended matter and liquid. When a filtering
process is used, the addition of a flocculants may not be required since the particles
formed by the coagulation reaction may be of sufficient size to allow removal. The
flocculation reaction not only increases the size of the floc particles to settle them faster,
but also affects the physicals nature of the floc, making these particles less gelatinous and
thereby easier to dewater.

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4.0 EQUIPMENT AND MATERIAL
1. Jar test apparatus with six rotating paddles
2. Six (6) beaker
3. Thermometer

6. 6
4. Time / Stopwatch
5. pH meter
6. Turbidity meter
7. pipette

7. 7
5.0 REAGENT
1. Coagulant e.g. aluminum sulfate (alum), polyaluminum chloride (PAC), ferrous
sulfate, ferric chloride, etc.
2. Coagulant aid e.g. pH adjusters (lime or sulfuric acid), activated silica, polyelectrlye
(e.g. synthetic polymer such as acrylamide), clays (e.g. bentonite, montmorillonite,
etc.)
3. Liquid sample
6.0 PROCEDURES
1. The waste water from the treatment plant was prepared. The sodium was use to
stability the PH of the waste water to the neutral.
2. The temperature, pH, color, alkalinity and turbidity of the synthetic water sample
were measured.
3. 600ml was filled each of the prepared synthetic water suspension into six different
beakers (Plexiglas beakers)
4. The prescribed dose of coagulant was added to each jar by using a pipette. One jar has
no coagulant since a control sample was required.
5. If a coagulant aid is required, it is added to each jar (except for control sample) during
the last 15 seconds of the rapid mix stage.
6. Start stirring rapidly (60 to 80 rpm) for 3 minute (Rapid mix stage).
7. After the rapid mix stage, reduce the speed to 30 rpm for 20 minutes.
8. Floc formation were record ed by referring to the chart of particle sizes in final 10
minutes.
9. After the stirring period was over, stop the stirrer and the flocs was allowed to settle
for about 5 minutes as in scheme (iv)
10. 500mL of settle water was separate out into another beaker.
11. The temperature, pH, color, alkalinity and turbidity of the clarified water were
determined.
12. A graph of turbidity versus coagulant dose (mg/L) was plotted. The most effective
dose of coagulant (or with the present of coagulant aid) that gives the least turbid

8. 8
results also determined.
13. The qualitative characteristics of floc as bad, moderate, good and very good were
recorded. 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.
14. The following graph: color versus coagulant dose, pH versus coagulant dose,
temperature versus coagulant dose, etc. were plotted. These graphs will assist students
in the interpretation of the coagulation-flocculation process.

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7.0 RESULT AND DATA ANALYSIS
Floc sizes for:
Very fine is 0.30mm to 0.75mm
Fine is 0.50mm to 0.75mm
Moderate fine is 1.00mm to 1.50mm.
From the graphs we could conclude;
The most effective coagulant dose is 10 mg/L, and 20 mg/L
The most effective pH is 5.35
The expected temperature was 22.90 at optimum coagulant dose.
JAR NO. 1 2 3 4 5 6
Initial pH 6.42 6.42 6.42 6.42 6.42 6.42
Initial Temperature (o
C) 26.5 26.5 26.5 26.5 26.5 26.5
Coagulant dose (mg/L) 10 20 30 40 50 control
Agigate (minutes) 23 23 23 23 23 23
Fast (rpm) 70 70 70 70 70 70
Slow (rpm) 30 30 30 30 30 30
Settling Depth (mm) 10 8 4 3 2 2
Final pH 5.35 4.06 3.60 3.25 3.22 -
Final Temperature (o
C) 23.1 23.1 22.9 22.9 22.9 -
Final Turbidity (NTU) 7 5 4 17 32 108
Floc Formation fine
Very
fine moderate Coarse
Very
coarse
Moderately
fine
Time of floc formation = 5 minutes

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8.0 DISCUSSION
We had successfully done this experiment because the objective of this
experiment, to conduct various experiments on chemical coagulation and flocculation and
to determine the optimum dose combination of coagulant aid (when used) which will
produce the highest removal of turbid water sample has achieved.
Jar tests have been used to evaluate the effectiveness of various coagulants and
flocculants under a variety of operating conditions for water treatment. . This procedure
allows individual polymers to be compared on such criteria as floc formation, settling
characteristics, and clarity. Generally, the best performing products provide fast floc
formation, rapid settling rate, and clear supernatant. This test should be performed on-
site, since large amounts of water may be required for testing.
Turbidity is essentially a measure of the cloudiness of the water which indicates
the presence of colloidal particles. The particles should be making sure removed from
the water before for the publics use. However these colloids are suspended in solution
and can be removed by sedimentation or filtration. Very simply, the particles in the
colloid range are too small to settle in a reasonable time period, and too small to be
trapped in the pores of a filter. For colloids to remain stable they must remain small. Most
colloids are stable because they posses a negative charge that repel other colloidal
particles before they collide with one another. The colloids are continually involved in
Brownian movement, which is merely random movement. Charges on colloids are
measured by placing Dc electrodes in a colloidal dispersion. The particles migrate to the
pole of opposite charge at a rate proportional to the potential gradient. Generally, the
larger the surface charge, the more stable the suspension.
Based on this experiment, the first jar is serving as a control and no coagulant was
added. The coagulant doses increased in the containers from no 1to no 6. For this water,
as the dose of coagulant increased the residual turbidity improved. It is important to note
that the optimum coagulant dose is the dose which meets the specified turbidity required
on the regulatory permit. The addition of excess coagulant may reduce turbidity beyond

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what is required but also could lead to the production of more sludge which would
require disposal.
The most effective dose of coagulant we get from the Graph turbidity versus
coagulant after the experiment is 20 mg/L. The most effective pH is 5.36.
Jar tests are used in these procedures to provide information on the most effective
flocculants, optimum dosage, optimum feed concentration, effects of dosage on removal
efficiencies, effects of concentration of influent suspension on removal efficiencies,
effects of mixing conditions, and effects of settling time.
The general approach used in these procedures is as follows:
a) Prepare stock suspension of sediment.
b) Test a small number (six) of polymers that have performed well on similar
dredged material which has 2-grams-per-litre suspensions and is a typical concentration
for effluent from a well-designed containment area for freshwater sediments containing
clays. If good removals are obtained at low dosages (10 milligrams per liter or less), then
select the most cost-effective polymer. If good removals are not obtained, examine the
polymer under improved mixing and settling conditions and test the performance of other
flocculants
c) The effects of settling time on the removal of suspended solids and turbidity
from a suspension of average concentration should be exanimate using the selected
dosage and likely mixing conditions.
d)The effects of the range of possible mixing conditions on the required dosage of
flocculants for a typical suspension should be exanimate.

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9.0 CONCLUSION
As conclusion, this experiment is successfully been done and it is because the
objective of this experiment which to conduct various experiments on chemical
coagulation and flocculation and to determine the optimum dose combination of
coagulant aid (when used) which will produce the highest removal of turbid water sample
has achieved.
Jar testing is an experimental method where optimal conditions are determined
empirically rather than theoretically. Jar test are meant to mimic the conditions and
processes that take place in the clarification portion of water and wastewater treatment
plants. The values that are obtained through the experiment are correlated and adjusted in
order to account for the actual treatment system. After the experiment, Graph turbidity
versus coagulant dose are plot, from the graph we get the most effective dose of
coagulant is 60mg/L
Base on the data, we conclude that although the turbidity is generally declines as
the amount of the alum which added into the water but there is a point where more alum
should not be added. This is because alum will make the water more acidic. Therefore, to
overcome these problems, buffer should be added with same amount of alum at the same
time the alum is added.
After this experiment, we realize that a successful Jar Test is very reliant upon the
proper preparation of the polymers being tested. Dilution technique ("make down") is
especially critical, since it involves compactly coiled large molecules in emulsions, prior
to activation. The polymer must be uncoiled to provide maximum contact with the
colloidal particles to be flocculated. If the following procedures are not followed, the Jar
Test results will be very unreliable. As conclusion, after we analyzed the data, we have
decided that the optimum dosage of alum for this experiment is 10 mg/L. we reach this
conclusion base on the fact that the turbidity minimum at 7 NTU.

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10.0 QUESTIONS
Two sets of experimental data obtained from a jar test on water samples with initial
turbidity of 15NTU and HCO3 alkalinity of 50mg/L CaCO3
Jar No 1 2 3 4 5 6
Ph 5.0 5.5 6.0 6.5 7.0 7.5
Coagulant
dose
(mg/L)
10 10 10 10 10 10
Turbidity
(NTU)
11 7 5.5 5.7 8 13
JAR TEST 1
Jar No 1 2 3 4 5 6
pH 6.0 6.0 6.0 6.0 6.0 6.0
Coagulant
dose
(mg/L)
5 7 10 12 15 20
Turbidity
(NTU)
14 9.5 5 4.5 6 13
JAR TEST 2
10.1 Plot a graph of turbidity versus pH and turbidity versus coagulant dose (mg/L).
10.2 State the optimum pH value and optimum alum dose of the coagulation process of
the raw water.
The optimum pH was chosen as 6.25 and the optimal alum dose was about 12.5mg/L
(based on graph 7.1)

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10.3 What is the usage of Jag test?
The purpose of Jar Testing is to predetermine the amount of chemicals requird
to treat and precipitate as sludge the contaminants in a given volume of wastewater.
The phrase "Jar Testing" is commonly used in the waste treatment industry. It is used
in reference to a method that will determine treatability of a solution or establish a
sequence of steps required to achieve treatability. Jar Testing is used as a tool to
determine why proper treatment is not being achieved.
10.4 How to reduce dosage of alum in treatment plant?
Since the two important factors in coagulant addition are pH and dose.
Therefore to reduce the dosage of alum we can add coagulant aids such as pH
adjusters (lime or sulfuric acid), activated silica, clay (bentonite montmorilionite)and
polymers . The addition of activated silica and clays is especially useful for treating
highly colored, low turbidity waters as it add weight to the floc .
10.5 Name and explain briefly three types of alkalis that are suitable for pH control.
Lime Ca(OH)2 ,soda ash (NA2CO3), Sodium Bicarbonate, Sodium Hydroxide
Magnesium Hydroxide, Calcium Bicarbonate and others .The alum reacts rapidly
with compounds in the water that contain carbonates, bicarbonates and hydroxides to
produce a jelly-like substance that absorbs impurities. At the same time, alum, with a
positive charge, neutralizes the negative charge common to natural particles,
which draws them together. Small particles microfloc are formed. The following
equation shows the reaction of alum with alkalinity:
Al2(SO4)3
.
14H2O +3Ca(HCO3)2 2Al(OH)3 +3CaSO4 +6CO2 +14H2O
Aluminum Sulfate
Calcium
Bicarbonate
Aluminum
Hydroxide
Calcium
Sulfate
Carbon
Dioxide
Water
10.6 What are the advantages of using coagulant aids?
To accelerate settling, minimum the usage of chemical in treatment and adjustd
the pH of the water into the optimal range for coagulation.

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10.7 What are the effects of alum dosage in treatment criteria?
Alum will have the effect of lowering pH so careful monitoring is necessary when
applying alum. Alum contains aluminum, which is toxic to fish in acid water,
therefore overdose of alum can give negative effect to the environment. Alum use
results in sludge of precipitated particles that should either be vacuumed out or
removed via a bottom drain .
10.8 Name five differences between alum and ferric coagulants.
a. Ph- The optimum pH range for alum is generally about 5 to 8. The optimum pH
range for ferric chloride is 4 to 12.
b. Dosage - Ferric dosage is typically about half of the dosage required for alum.
c. Chemical Reaction- Ferric coagulant reacts in water with hydroxide alkalinity to
form various hydrolysis products that incorporate Fe(OH)3. These compounds
possess high cationic charge which allows them to neutralize the electrostatic
charges found on colloidal compounds and also to bind to negatively charged
particles, including the ferric hydroxide itself. This ability to bind to itself is the
mechanism for the formation of floc aggregates and the basis for ferric chloride’s
flocculation abilities.
FeCI3 + 3 HCO3 = Fe (OH) 3 + 3CO2 + 3CI-
In the case of alum coagulants, these reactions can be represented as follows:
Al2(SO4)3 + 3 Ca(HCO3)2 = 2 Al(OH)3 + 3 CaSO4 + 6 CO2
Al2(SO4)3 + 3 Ca(OH)2 = 2 Al(OH)3 + 3 CaSO4
Al2(SO4)3 + 3 Na2CO3 + 3 H2O = 2 Al(OH)3 + 3 Na2SO4 + 3 CO2
The alum reacts rapidly with compounds in the water that contain carbonates,
bicarbonates and hydroxides to produce a jelly-like substance that absorbs
impurities. At the same time, alum, with a positive charge, neutralizes the negative

16. 16
charge common to natural particles, which draws them together. Small particles
microfloc are formed.
d. Ferric coagulant can be purchased either in sulfate salt (Fe2(SO4)3.xH2O) or chloride
salt (FeCl3.xH2O) where as alum only in sulfate salt Al2(SO4)3.
e. Liquid alum is sold approximately 48.8 percent alum (8.3%Al2O3) and 51.2 percent
water.if it is sold as a more concentrated solution, there can be probles with
crystallization of the alum during shipment and strorage. While ferric coagulant is
available in various dry and liquid forms.

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11.0 APPENDIX AND REFERENCE

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References:
G. J. Schroepfer, M. L. Robins, and R. H. Susag, (1964)“Research Program on the
Mississippi River in the Vicinty of Minneapolis and St. Paul,” Advances in Water
Pollution Research, vol. 1
L.Davis , I.Cornwell. Introduction to Environmental Engineering. Third Edition.
Lab sheet: Enviromental Engineering, Test: JAR Test
Website: 4th
Feb 2006 (date retrieved)
http://www.waterspecialists.biz/html
http://www.phippsbird.com/
http://home.alltel.net/mikeric/PretreatMaint/
Hammer, MarkJ. (2001)”Water and Waste water Technology Frouth Edition” New
Terzey: Prentice Hall
Master, Gelbert M (1998) “Introduction to Environmental Engineering and Science”
Black, J.G. (1996). Microbiology. Principles and Applications. Third Edition. Prentice
Hall. Upper Saddle River, New Jersey.
Tortora, G.J., Funke, B.R., Case, C.L. (1995). Microbiology. An Introduction. Fifth
Edition. The Benjamin/Cummings Publishing, Co., Inc., Redwood City, CA.
H. A. Thomas,(1998) “Graphical Determination of B. O. D. Curve Constants, “Water
and Sewage Works”, McGraw Hill Companies Inc.