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Faculty of Engineering

School of Chemical and Environmental Engineering

H83CEL- Chemical Engineering Laboratory

Flocculation

Supervisor:

Dr. Chong Mei Fong

Prepared by:

Adnaan Abbas Malak

UNIMKL-012117

Group Members:

Jack Maxwell

Low minh ge

Ong sze yinh

Khiarul Aamir

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Table of Contents 1. SUMMARY ............................................................................................................................................. 3

2. SAFETY ASSESMENT .............................................................................................................................. 4

3. INTRODUCTION ..................................................................................................................................... 6

4. AIMS AND OBJECTIVES ...................................................................................................................... 7

5. LITERATURE REVIEW ......................................................................................................................... 8

5.1 Principles of flocculation and coagulation: ....................................................................................... 8

....................................................................................................................... Error! Bookmark not defined.

5.2 Factors affecting Coagulation and flocculation: ............................................................................. 10

Comments: the data obtained from the literature uses waste water of different contents, with

experiment repeated more than ................................................................................................................ 13

5.3 Use of PACl as effective coagulant: ................................................................................................. 13

6. EXPERIMENTAL PLANNING & DEVELOPMENT ................................................................................ 18

7. METHODS ........................................................................................................................................ 20

7.1 MATERIALS & APPRATUS REQUIRED: ............................................................................................. 20

7.2 PREPARATION OF RAW WATER: ..................................................................................................... 21

7.3 Preparation of 1 M Ca (OH) 2 Solution: ........................................................................................... 21

7.4 Preparation of 0.15 M Polyaluminium Chloride: ............................................................................ 22

7.5 Experimental Procedures ................................................................................................................ 23

7.5.1 Set 1: Variation of PAC dosage .................................................................................................... 23

7.5.2 Set 2: Variation of pH (optimum dosage of PAC) ........................................................................ 23

7.5.3 Set 3: Variation of settling time .................................................................................................. 24

7.5.4 Set 4: Variation of stirring speed ................................................................................................ 24

7.6 TESTING METHODS: ........................................................................................................................ 25

8. RESULTS & DISCUSSION: ..................................................................................................................... 28

9. ERRORS AND UNCERTANITIES: ........................................................................................................... 37

10. Conclusion, recommendation and future works ............................................................................ 39

11. REFERENCES .................................................................................................................................... 40

12. APPENDIX: ....................................................................................................................................... 44

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1. SUMMARY

This Lab report is compiled to carry out the study of the efficient removal of

turbidity, color, aluminum, and TSS from river water by varying coagulant dosage,

pH , settling time and stirring speed of the flocculator. An optimum dosage of

0.1mL of PACl was selected with optimum pH 7.12 , settling time as 1.5 hrs and

optimum stirring speed of 250 RPM. Lovibond flocculator along with HACH

spectrophotometer and colorimeter were used in the experiment. A literature

review was also conducted to compare the experimental results with that of

literature. Experimental results obtained for pH and coagulant dosage don’t

agree with the literature study. Also the results obtained for stirring speed and

settling time agrees with the theory stated in literature review and further details

are discussed in section 8 and 9 of the report. Finally errors and uncertainties

experienced during the experiment were discussed; along with recommendation

and future works so that to improve our results the next time when this

experiment is performed.

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2. SAFETY ASSESMENT

Hazard and Operability Study Report

Project Title HAZOP FOR JAR TEST

Line of Study Flocculator and experimental procedure

Study Team

Process

Parameter

Guideword

Deviation

Likelihood Ranking (Low=1- High =5)

Possible Causes

Consequences

Action required

Safeguard

Recommendatio-n

Impeller

Speed

High High Speed 4 Malfunction of controller

Scratches in beaker Breakage of beaker Overflow of liquid Breakage of impeller

Turn off and re-calibrate controller

Check calibration every few months

Write calibrati-on procedu-re

Low Low Speed 3 Malfunction of controller

Insufficient mixing

Turn off and re-calibrate controller

Check calibration every few months

Write calibrat-ion procedu-re

Sample level

High High level 3 Raw water container opening too large

Overflow of fluid Corrosive materials spill Beaker becomes too heavy to move Liquid on floor causing slipping

Clean surfaces Use chemical for cleaning if solution is acidic

Use a funnel More people controlling the tilt of the container Wear PPE at all times

Use of smaller raw water Containe-rs Smaller opening on containe-r

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Lime preparation heat

High High temperature

4 Too much solid added

Breakage of beaker due to rapid temperature change Injury due to burning

Set vessel down and leave to cool Use emergency shower if skin contact is made

Wear PPE Do not hold beaker Measure amount of reagent required before addition

Use alternative material Use thicker reaction vessel

Lime liquid level

High High level 4 Too much liquid added

Overflow of hazardous material Spillage causing corrosion Slipping due to wet surfaces

Clean spillage Use chemicals to neutralize Use emergency shower if skin contact is made

Wear PPE Monitor filling Use a funnel

Prepare over a sink Larger vessel opening Aim to fill vessel to lower height

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3. INTRODUCTION

Water is a major essential to sustain life. Hence, a satisfactory constant supply of

adequate, safe and accessible must be available to everyone. It is very essential to

improving access to safe drinking-water as it can result in tangible benefits to

health and social welfare. Every effort should be made to achieve a drinking-

water quality as safe as possible. The raw water is collected from Sungai Sering

Ulu Kelang. The composition of the water is shown in Table 4 under section 8 of

the report. in addition to the contents mentioned in table 4, waste water also

contains NOM (Natural organic material) which is derived from decaying organic

matter and dead organisms and can impart color, taste and odour to the water (Yi

Geng, 2005).

The important aspect of water and wastewater treatment process is the

coagulation and flocculation process which is widely used due to its simplicity and

cost effectiveness. This process is carried out because surface water generally

contains a wide variety of colloidal particles that may impart turbidity and color to

the water (Benefield et al., 1982). These particles are very small to be settled by

gravity or to be filtered through common filtration media. In addition, colloidal

suspension is quite stable in surface water due to its electrical surface charge (Yi

Geng, 2005) for this reason coagulants are used to destabilize the colloidal

particles and carry out the separation. The principles of coagulation and

flocculation are discussed in detail in section 5. The purpose of the experiment is

efficient removal of turbidity, aluminum, color and TSS (Total Suspended solids)

by changing the parameters which are pH, coagulant dosage, settling time and

stirring speed of lovibond flocculator. The lovibond flocculator consists of 6

impellers or spindles which are cleaned before and after every experiment. The

coagulant used is PACl (polyaluminium chloride) and the equipment used to

perform turbidity, color, aluminum and TSS test are HACH spectrophotometer

and a colorimeter.

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4. AIMS AND OBJECTIVES

The objective of the experiment is to investigate the removal efficiency of total

suspended solid, color intensity, turbidity and aluminum content by varying the

following parameters in the production of drinking water:

Coagulant dosage

pH value

settling time

stirring speed

The target of the experiment is to fulfill the standard of drinking water as below:

Total suspended solid : 90 mg/l

Color intensity :15 TCU; where 1 TCU=1 PtCo

Turbidity : 5 NTU ; where 1 NTU = 1 FAU

Aluminum content : 0.2mg/l

pH level : 6.5-9.0

The following data for Color, Turbidity, Aluminum content and pH level is taken

from (Ministry of Health Malaysia, 2010). The value for TSS (Total Suspended

Solid) is taken from using Utah’s standard (US EPA office of water, 2003).

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5. LITERATURE REVIEW The purpose of the literature review is to present an overview of the concept and

principle of coagulation and flocculation processes. Certain important factors

affecting coagulation and flocculation are discussed in detailed in this section.

Also a detailed study on PACl used as a coagulant in water treatment is also

discussed here.

5.1 Principles of flocculation and coagulation:

Coagulation is the “electrochemical process of aggregating small particles into

larger particles or flocs that settle rapidly due to increased weight. In this process

coagulants are added to turbid water in order to destabilize particles and reduce

the repulsion forces. Destabilization increases the tendency of particles to

coalesce, resulting in heavier agglomerated particles. The heavier particle then

settles out of solution. Whereas flocculation refers to the process by this

destabilized particles actually conglomerate into larger aggregates so that they

can be separated from the waste water.

In simple terms flocculation is a physical process of prompting particle contacts to

enhance aggregation for destabilized particles. This physical process of collisions

between destabilized particles, in flocculation units are achieved by three

separate mechanisms (Weber, 1972):

Brownian diffusion or perikinetic flocculation due to the continuous

bombardment by surrounding water molecules

Fluid shear or orthokinetic flocculation due to velocity differences or

gradients in either laminar or turbulent fluid fields

Differential sedimentation due to gravities of particles, as faster settling

particles overtake and collide with slower settling particles.

This mechanism of flocculation depends on the size of the particles present in

suspension. Perikinetic flocculation or fluid share dominates the latter when

particles are approximately of 1um and it promotes further aggregation by stirring

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and settling (Benefield et al., 1982). Further details on stirring speed (fluid share)

and sedimentation is discussed later in the report.

One of the common theories for coagulation used is charge neutralization where

the flocculant and the adsorption site are of opposite sites which leads to

neutralization. In most cases, hydrophobic colloidal particles in waste water are

negatively charged and thus inorganic flocculants and cationic poly-electrolytes

are preferable. The flocculation could occur simply as a result of reduced

charged at surface and hence a decreased electrical force between colloidal

particles, which allows the formation of van der wall forces between colloidal and

fine suspended materials to form microfloc (Chong, john robinson and chai siah

lee).

A jar test is carried out which is a common laboratory coagulation test. Before

treatment can begin a coagulant must be first selected. The selection of coagulant

is further discussed in detail in this section. Use of lime is also encouraged in

some of the jar test to maintain the pH at approximately 7.0. If the waste water is

acidic the lime addition which is Ca (OH) 2 leads towards neutralization of acid

before colloid removal can take place. A bench-scale jar test is used containing a

series of standard beakers and a stirrer for mixing. The purpose of a jar test is to

determine optimal pH, coagulant dosage, stirring speed and settling time.

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Figure 1: Picture of Levibond flocculator

5.2 Factors affecting Coagulation and flocculation:

Alkalinity/pH: Alkalinity is the acid neutralizing capacity of water, and is a general

indication of water’s buffering capacity (D.J.Pernitsky, 2003). The salts used for

coagulation form certain ions in solution that are responsible for coagulation

process. But however the ions produced depend upon the pH of the water

sample. pH that is too low may not allow the coagulation process to proceed

while high pH can cause coagulated particles to disperse (ROSEMOUNT Analytical,

2009) .

Hatfield found the optimum pH range for color removal to be 6.1 to 6.3, but it

worth to be noted that the value for maximum floc formations depends upon the

anion present in the solution, such as SO42-, Cl-, etc. (Hatfield, W.D., J Am 6

Water Works Assoc, 11, 554 (1924)).

In another document the functionality of coagulation has been found to reduce

after a pH in the region 7-9 (Greville, 1997; Uyak and Toroz 2007; Al Mubaddal et

al. 2009, Dwyer et al., 2009).

From (G.Seyrig and W.Shan , 2007) we can see on those graphs that the pH which

allows the best either color and turbidity removal is around 6.5. At this pH the

color removal is more than 76% when the turbidity removal is around 73%.

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However according to Malaysian standards the pH for a drinking water should be

in the range of 6.5-9.0.

Coagulant Dosage: There is a range of optimum dosages for a coagulant at which

maximum settling and removal of suspended particles is most efficiently and

effectively achieved. Below this range will destabilize the particles. Above this

range the coagulant serves as a chemical coating of the colloids which in turn re-

stabilizes the particles (KIM LUU, 2000) .In water treatment practice the required

coagulant dose generally falls within the range 2-8 mg·L-1 as metal ion. In

wastewater treatment practice coagulant concentrations up to 40 mg·L-1 (as

metal ion) have been used (Casey 1997). So the coagulant dose really depends on

the required treatment extent and the purpose of treatment.

From (G.Seyrig and W.Shan , 2007) The decreasing of the river water color seems

to be the more efficient (with a bit less than 80% removal) with a higher alum

concentration ranging between 120 and 200 mg/L.

Though different literature states different optimum dosage value but optimal

coagulant dosage is highly related to source of raw water used. Therefore it has to

be determined experimentally by reducing turbidity, color, aluminum content and

TSS.

Stirring speed and settling time: Once the flocks are made then it all comes to

the factors effecting sedimentation. One of the factors involved is the degree of

agitation of the suspension. Gentle stirring may lead to accelerated settling if the

suspension behaves as non-Newtonian fluid in which the apparent viscosity is a

function of the rate of shear. The change in viscosity can probably be attributed to

the re-orientation of the particles (Coulson and Richardson, Vol 3). Mixing or

stirring disperses precipitating agents, coagulant and coagulant aids throughout

the wastewater to ensure rapid reaction and settling of precipitates possible. The

extent to which mixing or stirring can be done depends on number of factors like:

amount of energy supplied, mixing residence time and turbulence effect which in

turn depends on size and shape of mixing tanks. There are two types of mixing

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rapid or flash. The main objective is to mix one substance completely into

another. ( Aquacultural engineering, 2002)

Also stated in (Aquacultural engineering,2002) that the lower mixing speed may

improve the removal of turbidity at low concentrations due to reduced shearing

of the floc during initial formation. Also at high stirring speeds velocity gradients

tend to be high which in turn promotes particle contacts for aggregation (Yi Heng,

2005).

For settling time after the coagulation process is done then it depends upon the

sedimentation rate of the particles and also the velocity gradients existing in the

fluid which can affect the velocity of settling particles. If the process is at steady

state particles will settle quickly and there will be only minor changes for

prolonged settling time (Coulson and Richardson).

Turbidity: It is caused by suspended colloidal particles, such as slit, clay

microscopic organisms, soluble colored organic compounds, finely divided organic

or inorganic matter (Benefield et al, 1982). Higher turbidity water containing

higher amount of particles generally requires higher dosages of coagulant. It is

one of the most commonly used parameters for the testing of drinking water

quality. As the number of particles increase a higher intensity of light is scattered

and a higher turbidity value is obtained. The European standards do not appear

to address turbidity, however, the World Health Organization, establishes that the

turbidity of drinking water should not be more than 5 NTU, and should ideally be

below 1 NTU (LENNTECH, 1998-2015). Malaysian drinking water standards state a

maximum value of 5 NTU.

Color: It can be caused by any suspended particle in waste water. But according

to (Beneield, 1982) it is caused by colloidal forms of iron and manganese or more

commonly by NOM. According to (A.S.Greville, 1997) The choice of chemicals

must be one that will create a water in which the color will be least stable (usually

at a pH between 5.5 and 7.0), the alkalinity will be preserved for turbidity

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precipitation, and the finished water will be neither corrosive or scaling.

According to Malaysia standards the maximum allowable limit for drinking water

is 15 TCU.

Comments: Based on the literature review both turbidity and pH don’t fall in the

range if Malaysia water drinking standards are ignored. This can be due to the

fact that optimum dosage, pH varies widely depending on the wastewater used.

One limitation of our experiment is that detailed analysis of wastewater

contents is not carried out, for which it makes it difficult to compare my results

with the literature.

5.3 Use of PACl as effective coagulant:

1) This literature has been taken form “I water wiki”. The commonly used

metal coagulants are aluminium and iron based. The aluminium coagulants

include: include aluminum sulfate, aluminum chloride and sodium aluminate.

The iron coagulants include ferric sulfate, ferrous sulfate, ferric chloride and

ferric chloride sulfate. Themain advantage of using these coagulants is because

of their ability to form multi-charged polynuclear complexes with enhanced

adsorption characteristics. There have been great improvements in

development of pre-hydrolyzed inorganic coagulants. These include aluminum

chlorohydrate, polyaluminum chloride, polyaluminum sulfate chloride,

polyaluminum silicate chloride and forms of polyaluminum chloride with

organic polymers. These polymers can work efficiently over a wide range of pH

and raw water temperatures. They are less sensitive to low water

temperatures; lower dosages are required to achieve water treatment goals;

less chemical residuals are produced; and lower chloride or sulfate residuals

are produced, resulting in lower final water TDS. They also produce lower

metal residuals.

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2) Based on another paper written by (Peter Gebbie, 2001) carries out a study

based on PACL coagulants for water treatment. Two main aluminum based

coagulants are widely used Alum and PACL. Alum (aluminum sulfate is

commonly used but has a number of disadvantages :

limited coagulation pH range: 5.5 to 6.5,

¨ supplemental addition of alkalinity to the raw water is often required to

achieve the optimum coagulation pH, particularly for soft, coloured surface

waters that are common in Australia,

¨ residual aluminum levels in the treated water can often exceed

acceptable limits, and

¨ Alum floc produced is particularly fragile. This is especially important if a

coagulant is required to maximize color removal in a microfiltration-based

water treatment process.

Alum reacts in water to produce aluminum hydroxide and as a by-product

sulphuric acid is also formed. The metal hydroxide precipitates out of

solution and entraps neutralized charged dirt particles (turbidity), as well as

coagulating soluble color and organics by adsorption. The sulphuric acid

produced reacts with alkalinity in the raw water to produce carbon dioxide,

thus depressing the pH.

Polyaluminium coagulants have a general formula (Aln (OH) mCl (3n-m)) x

and have a polymeric structure, which is totally soluble in water.

Characteristics like polymerized chain, molecular weight and number of

ionic charges is determined by the degree of polymerization. However in on

application bases there is little difference between the performance of ACH

and PACl in water treatment applications, even though ACH is more

hydrated. Following are the advantages of Polyaluminium coagulants:

Have higher basicity due to the ratio of hydroxyl to aluminum ions in the

hydrated complex

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They are effective over a broader pH range compared to alum and they

work satisfactorily between range of 5.0-8.0

Another important advantage of using polyaluminium coagulants in water

treatment processes is the reduced concentration of sulphate added to the

treated water.

low levels of residual aluminum in the treated water can be achieved,

typically 0.01-0.05 mg/L,

¨ PACl and ACH work extremely well at low raw water temperatures. Flocs

formed from alum at low temperatures settle very slowly, whereas flocs

formed from polyaluminium coagulants tend to settle equally well at low

and at normal water temperatures,

¨ less sludge is produced compared to alum at an equivalent dose, lower

doses are required to give equivalent results to alum. For example, a dose

of 12 mg/L

PACl (as 100%) was required for treatment of a coloured, low turbidity

water (Otway region, Victoria) compared to similar performance obtained

when using an alum dose of 55 mg/L, and

¨ the increase in chloride in the treated water is much lower than the

sulphate increase from alum, resulting in lower overall increases in the TDS

of the treated water.

Following are the examples illustrated from the paper which shows the

results of using PACL and alum as coagulants by different water treatment

companies

DAYLESFORD

Table 1: Raw water analysis, Wombat Reservoir at Daylesford

ION (mg/L) CaCO3

CALCIUM 1.8 4.5

MAGNESIUM 2.3 9.5

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A

jar test is carried out to determine the treatability of raw water supplies at this

company. Following are the results obtained:

Table 2: treated water quality Predicted Using WaterQual, Wombat Reservoir

COAGULANT LSI CCPP TDS SO4 (AS ION)

ALUM -2.2 -8.2 94 21.0

PACl -2.2 -7.9 67 1.5

TIDAL RIVER

The raw water supplied at Tidal River is derived from a small weir and off

take. The volume of the weir and areas relatively small and therefore substantial

changes to the raw water can occur during rainfall. Initially liquid alum and casting

soda were used in the treatment regime. The water was found difficult to be

treated and in an attempt to improve plant performance, PACL was used.

Table 3: Predicted performance of ALUM vs. PACl at Tidal River (at 15oC)

COAGULANT DOSE (mg/L)

ALKALI AND DOSE (mg/L)

Pre Post

pH CCPP LSI $/ML

ALUM (as 100%)

50 NaOH 18.0

0 6.6 -28.7 -3.1 174

PACl as (100%)

17.5 5.0 0 6.8 -21.1 -2.8 150

SODIUM 9.0 19.6

POTASSIUM 0.7 0.9

ALKALINITY 19.0 16.3

CHLORIDE 11.7 16.5

SULPHATE 1.5 1.6

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Both PACL and ACH provide significant advantage over alum including:

Reduced chemical cost

lower residual aluminum levels in the treated water,

improved treated water quality including lower TDS and sulphate levels

and possibly higher CCPP values, and

Lower sludge production.

Comments : As for the consideration of the use of coagulant is considered;

satisfactory results are obtained from the experiment which are shown in Table

5 – Table 8. If carefully observed that values obtained for Color, TSS, turbidity

and aluminum is all below the range for a standard drinking water which to a

large extent agrees with the literature and also the range of pH for which is used

varies roughly from 6.9-9.02 after PACl addition which agrees with ( Peter

Gabbie, 2001) where it is specified from 6.0-8.0 and for our experiment it only

crosses 8 in SET 2 for reasons mentioned above. However from our experiment

it cannot be stated that it is better than ALUM or any other coagulants because

comparison wasn’t made for which it can be a part for future works.

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6. EXPERIMENTAL PLANNING & DEVELOPMENT

A Gantt chart is used to display the activities for experimental planning carried

out during the spring semester. A Gantt chart is a type of bar chart, displaying

project activities as bars measured against a horizontal time scale.

Table 4: experiment schedule from the start till the end

1 Preparation stage Sat 17/1/15 Wed 4/3/15

1.1 Literature research Sat 17/1/15 Sat 24/1/15

1.2 Decide on objective and parameters to test

on Mon 26/1/15 Wed 28/1/15

1.3 Draft of experimental procedure

Thu 29/1/15 Tue 3/2/15

1.4 Prepare Risk Assessment

Mon 2/2/15 Fri 6/2/15

2 Get HIRACH approval Mon 9/2/15 Wed 4/3/15

2.1 Prepare experimental proposal

Tue 10/2/15 Tue 17/2/15

2.2 Get proposal approved by dr. Chong

Wed 18/2/15 Sun 1/3/15

2.3

Collect Water Sample Wed 25/2/15 Thu 26/2/15

2.4 Collect Chemicals and apparatus

Mon 2/3/15 Wed 4/3/15

3 Experimental stage Wed 4/3/15 Thu 19/3/15

3.1 Carry out Experiment Set 1

Wed 4/3/15 Fri 6/3/15

3.2 Carry out Experiment Set 2

Mon 9/3/15 Wed 11/3/15

3.3 Carry out Experiment Set 3

Thu 12/3/15 Mon 16/3/15

3.4 Carry out Experiment Set 4

Tue 17/3/15 Thu 19/3/15

4 Report Writing Stage Fri 3/4/15 Mon 20/4/15

4.1 Analyse Results Fri 3/4/15 Tue 7/4/15

4.2 Write on discussion Thu 9/4/15 Mon 13/4/15

4.3 Write on uncertainty and error

Tue 14/4/15 Fri 17/4/15

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Based on the above activity schedule a Gantt chart was drawn which is shown

below.

Figure 2 : Gantt chart

4.4 Write on conclusion Thu 9/4/15 Wed 15/4/15

4.5 Compiling Report Thu 16/4/15 Fri 17/4/15

4.6 Report Submitted Mon 20/4/15 Mon 20/4/15

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7. METHODS

7.1 MATERIALS & APPRATUS REQUIRED:

40 L of raw water

1.5 L beakers

Coagulant dosage

pH value

150 mL beakers

Electronic weigh balance

Spatula

Glass rod

200 mL volumetric flask

250 mL volumetric flask

Funnel

Stopper

Stop watch

pH meter

syringe

HACH spectrophotometer

Sample cells

Double- manometer pump

Conical flask

Filter papers

Flocculator

Deionized water

Ascorbic acid powder

AluVer 3 (Aluminum reagent powder)

Bleaching 3 reagent powder

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7.2 PREPARATION OF RAW WATER:

1. 40 L of raw water will be collected by the security guard from Sungai Sering Ulu Kelang.

2. The raw water will be enclosed tightly in a large plastic container to prevent leakage.

3. The raw water will be shaken and mix thoroughly before the experiment to ensure a homogeneous mixture is obtained.

4. The raw water will be poured into a bucket before transferring into beakers to reduce spillage due to the choking effect from the big plastic container.

5. Clean 1.5 L beakers labeled ‘control’ and 1 to 5 will be filled with 1 L of raw water each.

7.3 Preparation of 1 M Ca (OH) 2 Solution:

1. Gloves and goggles should be worn when preparing dilute Ca (OH) 2 solution with water because the reaction is highly exothermic.

2. A clean and dry 100 mL beaker will be placed on an electronic weigh balance and set the reading to zero.

3. Use a dry spatula to transfer 18.53 g of Ca (OH) 2 solid into the beaker.

4. Distilled water will be added into the beaker and stirred with a glass rod to fully dissolve the Ca (OH) 2 solid.

5. The solution will be left to cool down for 15 minutes as dissolving Ca (OH) 2 in water is exothermic.

6. The solution will be poured slowly into a 250 mL volumetric flask using a funnel to avoid spillage.

7. Rinse the beaker and glass rod thoroughly with distilled water and pour the rinsing water into the volumetric flask.

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8. Distilled water will be added into the volumetric flask carefully until the bottom of the meniscus is level with the horizontal line on the neck of the flask.

9. The flask will be stoppered and by holding the stopper into the neck of the flask, carefully turn the flask upside down multiple times to ensure thorough mixing of the solution.

10. The volumetric flask will be labeled as ‘1M Ca (OH) 2 solution’.

7.4 Preparation of 0.15 M Polyaluminium Chloride:

1. A clean and dry 200 mL beaker will be prepared and placed on an electronic weigh balance and set the reading to zero.

2. Use a dry spatula to transfer 6.54 g of Polyaluminium Chloride (PAC) powder into the beaker.

3. Distilled water will be added into the beaker and stirred with a glass rod to fully dissolve the PAC powder.

4. The solution will be poured slowly into a 250 mL volumetric flask using a funnel to avoid spillage.

5. Rinse the beaker and glass rod thoroughly with distilled water and pour the rinsing water into the volumetric flask.

6. Distilled water will be added into the volumetric flask carefully until the bottom of the meniscus is level with the horizontal line on the neck of the flask.

7. The flask will be stoppered and by holding the stopper into the neck of the flask, carefully turn the flask upside down multiple times to ensure thorough mixing of the solution.

8. The volumetric flask will be labeled as ‘0.15 M PAC solution’.

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7.5 Experimental Procedures

7.5.1 Set 1: Variation of PAC dosage

1. Place the samples prepared under the stirrers of Lovibond Flocculator.

2. Lower down the stirrer manually and make sure the stirring blade do not contact with wall of the beaker.

3. Set the speed of stirring at 150 rpm and start stirring. Add the PAC stock solution to beakers labeled 1 to 5 with dosage 0.1, 0.2, 0.3, 0.4 and 0.5mL respectively. No PAC is added to the “control” beaker.

4. Start the stopwatch right after PAC is added to all beakers.

5. Use pH meter to measure the pH in each beakers and record the values.

6. Reduce the stirring speed of the stirring blade to 100rpm after 5 minutes.

7. Stop the stirrer after 15 minutes of stirring and allow the samples to settle for 15 minutes.

8. Use a syringe to collect about a 750mL supernatant from each beaker (the beaker can be tilted and try to avoid getting solids into the needle).

9. Carry out experiment to test for its turbidity, color, total suspended solid and aluminum content. Record all the readings.

10. Choose the sample with least turbidity and its corresponding coagulant dosage as the optimal coagulant dosage.

11. Plot graph of coagulant dosage vs. color, turbidity, aluminum and TSS

7.5.2 Set 2: Variation of pH (optimum dosage of PAC)

1. Repeat the experiment of Set 1 from steps 1 to 9.

2. Increase the pH of the samples in beakers 1 to 5 to pH 7.36, 8.1, 8.5, 9.04 and 9.02 respectively by adding calcium hydroxide.

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3. Instead of adding the PAC dosage differently in each beaker in step 4, add the optimum dosage of PAC found in experiment Set 1 to beakers 1 to 5.

4. Measure and record the pH of the samples after adding PAC.

5. Based on the results of the parameters tested, choose the optimum pH for the sample.

6. Plot graph of pH vs. color, turbidity, aluminum and TSS

7.5.3 Set 3: Variation of settling time

1. Repeat the experiment of Set 1 from steps 1 to 9.

2. Adjust the pH of the samples in beakers 1 to 5 to the optimum pH found in Set 2.

3. Instead of adding the PAC dosage differently in each beaker in step 4, add the optimum dosage of PAC found in experiment Set 1 to beakers 1 to 5.

4. Instead of allowing all the samples to settle for 15 minutes in step 7, change the settling time of beakers 1 to 5 to 0.5, 1, 1.5, 2.0 and 2.5 hrs. respectively.

5. Record all the experimental results obtained.

6. Plot graph of settling time vs. color, turbidity, aluminum and TSS

7.5.4 Set 4: Variation of stirring speed

1. Adjust the pH for each beaker up to 7 before adding 0.1mL of PACl

2. Start the stop watch and set the desired stirring speed time for 35 min

3. Put the beakers one by one with varying speeds of 150, 200, 250, 300 RPM; not all at once. 35 min for each desired speed.

25 | P a g e

4. Then let the particles in beaker settle down for 1.5 hrs after every 35 min of mixing

5. Observe the behavior of solids in samples and records all the experimental results obtained.

6. Plot graph of stirring speed vs. color, turbidity, Aluminum and TSS

7.6 TESTING METHODS:

Color 1. Stored program: 120 2. Preparing blank

-Prepare 100mL deionized water -Pour the 50mL into filter paper -Turn on vacuum and throw the deionized water away -Pour the remaining deionized water into filter paper -Turn on vacuum -Blank is prepared (10mL)

3. Preparing sample -Prepare 50mL of sample -Pour into filter paper -Sample is prepared (10mL)

4. Line of cell faces right

Aluminum 1. Stored program: 10 2. Fill the centrifuge tube (50mL) with sample

-Put ascorbic acid and invert it to dissolve the powder -Add aluminum reagent powder and keep inverting it for 1 min

3. Preparing blank -Pour 10mL into the cell -Add bleaching powder

26 | P a g e

-Shake vigorously -Leave it for 15 minutes

4. Preparing sample -Pour 10mL into the cell

Turbidity

1. Stored program: 95 2. Prepare 1 blank of deionized water and 1 sample with 10mL each.

Total Suspended Solid (TSS)

1. Stored program: 630 2. Prepare 1 blank of deionized water and 1 sample with 10mL each

Figure 3: HACH spectrophotometer used for color and aluminum test

27 | P a g e

Figure 4: HACH Colorimeter used for TSS and turbidity test

28 | P a g e

8. RESULTS & DISCUSSION:

Table 5: Data obtained for a blank solution

TSS 24 mg/L

Turbidity 34 FAU

Color 190 PtCo

Al 0.017 mg/L

The values obtained for the blank as shown in table… are way above the required

values of standard drinking water which was expected as this water was not

treated.

SET 1:

Table 6: data obtained for set 1

PAC (ml) pH before adding PAC TSS (mg/L) Turbidity (FAU) Al (mg/L) Color(PtCo)

0.1 7 0 0 0.026 4

0.2 6.9 2 1 0.028 12

0.3 6.9 1 1 0.03 11

0.4 6.9 1 1 0.035 8

0.5 6.9 1 1 0.051 14

From graph 1 the trend observed for the aluminum is that the concentration is

increasing with increase in dosage. The coagulant added is an aluminum based

coagulant which leads to an increase in the aluminum content. It can also be

noted from the graph that TSS increases until it reaches a maximum point and

then starts decreasing gradually and then remains constant. The sudden rise of

TSS initially suggest that coagulant added is not enough to carry out the charge

29 | P a g e

neutralization process, due to which the coagulant added also becomes the part

of suspended solids. Further increase in coagulant dosage aids in the coagulation

process and brings the TSS down. 0.1 mL of PACl dosage which is equivalent to

2.6mg is selected as optimum dosage.

Graph 1: Effect of varying PACl dosage on TSS and Aluminum

Graph 2: Effect of varying PACl dosage on Color and Turbidity

0

0.01

0.02

0.03

0.04

0.05

0.06

0

0.5

1

1.5

2

2.5

0 0.2 0.4 0.6A

lum

iniu

m

(mg/

L)

Tota

l Su

spe

nd

ed

So

lids

(mg/

L)

PACl Dosage (mL)

TSS

Aluminium

0

0.2

0.4

0.6

0.8

1

1.2

0

2

4

6

8

10

12

14

16

0 0.1 0.2 0.3 0.4 0.5 0.6

Turb

idit

y (F

AU

)

Co

lou

r (P

tCo

)

PAC Dosage (mL)

Colour

Turbidity

30 | P a g e

From Graph 2 the trend observed for color is unusual. It increases up to a

maximum point then decreases to a minimum point and shoots up again. The

color factor can be due to present of NOM (Natural organic material) that has not

settled since the color is caused by the dissolved species. On the other hand,

turbidity can be also another factor which increases the color of water which is in

turn caused by the particles in suspension, which may differ in size form colloidal

to aid dispersion and they reduce the clarity of water (Reynolds and Richards ,

1996) ( G.Seyrig and W.Shan , 2007 ). It is also observed that as PACl dosage

increases turbidity linearly increases then reaches a steady state value. One of

the trends observed from (A.F.Ashery, K.Radwan and M.L. Gar Al-Alm Rashed;

2010) is that the trend for tubudity decreases exponentially and becomes

constant with increase in alum dosage. The trend observed from our results

definitely does not match the one observed from the literature and this can be

due to the presence of suspended solids in the supernatant.

SET 2:

Table 7: Data obtained for set 2

PACl (ml)

pH before adding PAC l pH after adding PAC l TSS (mg/L) Turbidity (FAU) Al (mg/L) Color (PtCo)

0.1 7.36 7.18 0 0 0.02 0

0.1 8.1 7.91 1 1 0.026 2

0.1 8.5 8.27 1 1 0.044 9

0.1 9.04 8.85 1 1 0.018 3

0.1 9.44 9.02 1 1 0.036 5

31 | P a g e

Graph 3: Effect of varying pH on TSS and Al

Graph 4: Effect of varying pH on Turbidity and Color

From graph 3 it is observed that TSS linearly increases with pH and then reaches a

constant. For aluminum the graph shows a zig-zag trend which basically means it

doesn’t have any trend. A similar trend for turbidity is observed in graph 4 which

is similar to that of TSS in graph 3. Also a similar trend is observed for color in

graph 4 which is in turn similar to that of aluminum in graph3. The similarity

observed for TSS and turbidity is because measurement of turbidity is done by the

diffusion of scattered light which is caused by undissolved particles. This degree of

diffusion depends on: type of particles, size of particles, concentration (number of

particles), type and shape of particles, etc. (John Daly ,2007). The similar trend of

0

0.01

0.02

0.03

0.04

0.05

0

0.2

0.4

0.6

0.8

1

1.2

7 7.5 8 8.5 9 9.5 10

Alu

min

ium

(m

g/L)

Tota

l Su

spe

nd

ed

So

lids

(mg/

L)

pH before adding PAC

TSS

Aluminium

0

0.2

0.4

0.6

0.8

1

1.2

0

1

2

3

4

5

6

7

8

9

10

7 7.5 8 8.5 9 9.5 10

Turb

idit

y (F

AU

)

Co

lou

r (P

tCo

)

pH before adding PAC

Colour

Turbidity

32 | P a g e

TSS and turbidity pretty much says for itself that turbidity is affected by TSS and

TSS is in turn affected by pH which affects the coagulation process as stated in

literature review. Similarly color is also caused by dissolved organic matter e.g.

(humic and fulvic acids ). From this explanation it is quite obvious that zig zag

trend of aluminum affects the color change and also if observed the zig zag

pattern or trend shows that the value is different at every pH and is changing

which can be because with different pHs the color is different, is that the color-

producing substances in water behave inconsistently. pH adjustment may cause a

change in the ionization of the color molecule with corresponding effects on bond

lengths and configurations and thus light absorption (Gregoire Seyrig, Wenqian

Shan, 2007). Also if compared to the literature review the pH at which maximum

removal of turbidity occurs is usually between 6-6.5 and for our experiment the

pH variation itself starts from 7.0. But the drinking water standards in Malaysia

allow the pH level to be in a range of 6.5-9.0. So selecting pH 7.0 is the right

choice.

SET 3:

Table 8: Data obtained for set 3

PACl (ml) Settling Time (Hr) pH before adding PACl pH after adding PACl TSS (mg/L)

Turbidity (mg/L)

0.1 0.5 7.12 6.87 2 2

0.1 1 7.22 7.09 2 1

0.1 1.5 7.12 7.02 0 0

0.1 2 7.12 7.09 2 4

0.1 2.5 7.1 7.09 1 2

Aluminum (mg/L) Color (mg/L)

0.028 14

,0.021 9

0.028 5

0.026 4

0.025 2

33 | P a g e

Graph 5: Effect of settling time on TSS and Al

Graph 6: Effect of settling time on Color and turbidity

From graph 5 it is observed that with settling time both aluminum and TSS show a

similar trend. 1.5 hrs is selected as the optimum settling time for our experiment.

Aluminum content is maximum but TSS is minimum at that value. As shown in

table 1 that raw water already contains 0.017mg/L of aluminum in it. Adding PACl

just adds the amount of Al content already present to a higher value which then

gives a maximum value at 1.5 hrs. But as settling time is an increased aluminum

content decrease due to coagulation process leading to formation of flocks which

0

0.005

0.01

0.015

0.02

0.025

0.03

0

0.5

1

1.5

2

2.5

0 0.5 1 1.5 2 2.5 3

Alu

min

ium

(m

g/L)

Tota

l Su

spe

nd

ed

So

lids

(mg/

L)

Settling Time (Hours)

TSS

Aluminium

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0

2

4

6

8

10

12

14

16

0 0.5 1 1.5 2 2.5 3

Turb

idit

y (F

AU

)

Co

lou

r (P

tCo

)

Settling Time (Hours)

Colour

Turbidity

34 | P a g e

settles down with time. But now after 1.5 hrs both content of TSS and turbidity

(in graph 6) increases; whereas color decreases with time. Such inconsistency in

TSS and turbidity can be because the flocs might fall apart a period of time. The

mechanism of PAC coagulation is charge neutralization. Flocs from this are often

loosely packed and fragile (Lee et al., 2014).

SET 4:

Table 9: Data obtained from set 4

PACl (ml) Settling Time (Hr) Stirring Speed pH before adding PACl pH after adding PACl TSS (mg/L)

0.1 1.5 150 7.36 7.15 0

0.1 1.5 200 7.33 7.1 1

0.1 1.5 250 7.31 7.08 0

0.1 1.5 300 7.3 7.15 1

Turbidity (FAU) Al (mg/L) Color (Pt/Co)

1 0.009 8

1 0.023 4

0 0.013 6

1 0.023 14

35 | P a g e

Graph 7: Effect of impeller speed on TSS and Al

Graph 8: effect of impeller speed on Color and Turbidity

From graph 7 it is observed that both aluminum and TSS follow the same trend

where TSS and aluminum content is maximum at RPM of 250 and it is minimum at

RPM of 250. A similar trend is followed by turbidity where it is minimum at 250

RPM but color shows a different trend than the rest of the graphs. The color

content increases with increase in RPM and it is minimum at 200 RPM. But there

is a similarity between all the 4 graphs which is that the slope for all the graphs

0

0.005

0.01

0.015

0.02

0.025

0

0.2

0.4

0.6

0.8

1

1.2

140 190 240 290 340

Alu

min

ium

(m

g/L)

Tota

l Su

spe

nd

ed

So

lids

(mg/

L)

Impeller Speed (RPM)

TSS

Aluminium

0

0.2

0.4

0.6

0.8

1

1.2

0

2

4

6

8

10

12

14

16

140 190 240 290 340

Turb

idit

y (F

AU

)

Co

lou

r (P

tCo

)

Impeller Speed (RPM)

Colour

Turbidity

36 | P a g e

increases after 250 RPM whereas for color it increases after 200 RPM. The rise in

the trend TSS and aluminum suggest that there was inappropriate mixing. Even

though there is only a slight variation of turbidity and TSS. These results varied

because of the fact that the device measured in only whole numbers. The trend of

the increasing slope after a certain speed for all the graph suggest that the

increased in impeller speeds have caused shearing stress (as stated in the

literature) on the molecule causing re-stabilization of colloids which remains in

suspension then. Another consideration which can be made is the presence of

turbulent eddies which would have dissipated a considerable amount of energy,

leading to break up of the flocs. As discussed in literature review that high

velocity gradients results in greater aggregation but as it is observed from graph 8

that after a impeller speed of let’s say 200 RPM the trend increases for color again

which tells us that speed below or above an optimal RPM would cause a decrease

in flocculation effectiveness due to the kinetic energy and potential energy of the

particles hitting so hard that they break up the floc. 250 RPM is selected as

optimal stirring speed for the process which comparatively than the other three

speeds has lower values for all the 4 dependent variables.

37 | P a g e

9. ERRORS AND UNCERTANITIES: One of the important factors which were not considered was temperature. There

are some unusual trends observed in turbidity for which reasons are specified in

the discussion part but temperature plays an important role as well; which was

not considered in our experiment. Slight reduction in color removal was detected

at lower temperatures by some researchers; other researchers found that the

temperature had no impact on the reduction of color (Braul et al., 2001; Knocke

et al, 1986; Hansen and Cleasby 1990). But turbidity is sensitive to temperature

which also affects the particle counts during coagulation (Braul et al, 2001). This

might be the reason for the fluctuation in our results. Also its effect on the

kinetics of hydrolysis reaction, particle flocculation, and coagulant dosage is

ignored.

As it seen in graph 4 in Result and Discussion section both color and aluminum (in

graph 3) shows peaks and a trough at pH 8.5 and 9. This trend is explained in

discussion section but another error which might affect the results is the over

dosage of PACl in the process. No experiment was carried out with a dosage of

less than 2.6mg/L to know the changes. This argument can also be supported by

the fact that throughout the experiment for set 2, set 3 and set 4 pH values were

taken before and after addition of PACl (shown in Table 3, 4 and 5) with negligible

change observed which suggest that the pH didn’t affect coagulant process so it

might be because of over dosage that affected the results.

Values of turbidity, TSS, Al and color obtained might not be true because the

supernatant which was collected from the experiment for set 3 and 4 were not

immediately tested. The samples were left for 3-4 days uncovered without any

paraffin sheets or any other sort of cover. This might result in settling of particles

when it is not required or might be a change in chemical composition of

supernatant. Some uncertainties observed during the experiment like; the

38 | P a g e

formation of a visible scum on the surface of the water. This might have shoot up

the values for turbidity and TSS.

Also an error later in the experimental procedure is realized after the experiment

was done. That is set 4 should have been carried out before set 3 . As written in

experimental procedure in section 7 of the report that 35 min were allotted to

each stirring speed and then additional 1.5 hrs was then allotted for each stirring

speed. Due to which the flocks would eventually have settle, along with number

of suspended colloids (Greville, 1997). This also means that with sufficient settling

time, the removal efficiency by stirring speed is difficult to investigate.

Final source of error is the accumulation of human error and random error.

Parallax error might have been when taking supernatant by pipette; even the

pipette used is not accurate as well. Scratches in sample cell, inaccurate readings

of volume, and inappropriate mixing of solutions for testing are some of the

random errors which might have resulted in strange results.

39 | P a g e

10. Conclusion, recommendation and future works

To conclude the report the values observed for all the sets were mostly within the

specified range for drinking water which also means that turbidity, color,

aluminums and TSS were efficiently removed which was the main aim of the

experiment. If compared to the literature review for set 1 it didn’t follow the

trend for turbidity or color which is stated as in literature. For set 2 the pH values

varied and the optimal pH selected was again not within the range as specified in

the literature. For settling time and stirring speed as such literature data or values

were not discussed but the theory predicted in literature was somewhat

applicable to our situation.

To mitigate the errors and to undo the mistakes occurred following are the

recommendations and future work which should be taken into account:

Temperature should be investigated in the experiment with proper

literature studied

More than one coagulants should be used in the experiment to investigate

the effective of each individual for water treatment

A range of stock solutions should be prepared and results should be carried

out accordingly to get proper trends and results

Additional jar test with different natural raw water should be conducted to

verify the observation in this study.

Water turbidity and settled coagulation flocs were tested and analyzed in

this study. Further study should be extended to suspended flocs to find a

direct relationship between water turbidity and suspended flocs

Test for BOD (biological oxygen demand), DOC (dissolved organic carbon)

and other minerals should be carried out to further purify water.

40 | P a g e

11. REFERENCES

Yi Geng (2005). Application of Flocs Analysis for Coagulation

Optimization at the split lake water treatment plant

at:http://www.collectionscanada.gc.ca/obj/s4/f2/dsk3/MW

U/TC-MWU-189.pdf. [Accessed 16 April 2015].

Safaa.N.hassan (2011). The effect of settlement time on

reducing coagulant doasage in water treatment plants.

Avalilable at

http://www.jes.sohag.edu.eg/VOL.%20VII/4.pdf. [Accessed

20 April 2015]

Emerson Process Management. (2009). Coagulation and

Flocculation. Available:

http://www.neilstoolbox.com/bibliography-

creator/reference-website.htm. [Accessed 15th April

2015.].

Dr.Adil Al –Hemiri and Tahseen Hameed Al-Taey. (2008).

The Effect of Temperature and pH on the Removal /

Recovery of ZN++ from Solution by Chemical Coagulation.

Iraqi Journal of Chemical and Petroleum Engineering. 9 (-),

1-6.

HEM TRADE. (2014). Color Removal in Pulp and Paper

Effluent Using Inorganic Coagulants. Available:

http://www.generalchemical.com/assets/pdf/Color_Remov

al_in_Pulp_and_Paper_Effluent.pdf. [Accessed 19th April

2015.].

KIM LUU (2000). STUDY OF COAGULATION AND SETTLING

PROCESSES FOR IMPLEMENTATION IN NEPAL.

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MASSACHUSETTS at

http://web.mit.edu/watsan/Docs/Student%20Theses/Nepa

l/Luu2000.pdf. [Acessed 15 April 2015]

S.D.Freese, K. Hodgson and D.J. Noziac (2004). FACTORS

AFFECTING COAGULATION WITH POLYELECTROLYTES: ARE

THESE QUANTIFIABLE. Cape Town. Document

Transformation Technologies at

http://www.ewisa.co.za/literature/files/031.pdf. [Accessed

18th April 2015].

J. R. Backhurst, J. H. Harker and J. F. Richardson. (2005).

Sedimentation. In: J. F. Richardson and J. H. Harker Coulson

and Richardson's Chemical Engineering Volume 2- Particle

Technology and Separation Processes (5th edition). 5th ed.

Oxford: Butterworth-Heinemann. 237-267.

IWA WATER WIKI. (-). Coagulation and Flocculation in

Water and Wastewater Treatment. Available:

http://www.iwawaterwiki.org/xwiki/bin/view/Articles/Coag

ulationandFlocculationinWaterandWastewaterTreatment.

[Accessed 18th April 2015].

D.J.Pernitsky (2003). COAGULATION 101.Calgary at

https://awwoa.ab.ca/pdfs/Coagulation%20101.pdf.

[Accessed 18th April 2015].

James M. Ebelinga, , , Philip L. Sibrellb, Sarah R. Ogdena,

Steven T. Summerfelta. (2003). Evaluation of chemical

coagulation–flocculation aids for the removal of suspended

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solids and phosphorus from intensive recirculating

aquaculture effluent discharge. Aquacultural Engineering.

29 (1-2), 23-42.

John Daly. (2007). What is Turbidity?. Available:

http://www.isanorcal.org/download/tech2007_presentatio

ns/turbidity.pdf. [Accessed 17th April 2015].

Minisry of Health Malaysia. (-). Drinking Water Quality

Standard. Available: http://kmam.moh.gov.my/public-

user/drinking-water-quality-standard.html. [Accessed 20th

April 2015].

U.S. EPA Science Advisory Board Consultation. (2003).

DEVELOPING WATER QUALITY CRITERIA FOR SUSPENDED

AND BEDDED SEDIMENTS (SABS). ,20.

Peter Gebbie. (2001). USING POLYALUMINIUM

COAGULANTS IN WATER TREATMENT. 64th Annual Water

Industry Engineers and Operators’ Conference. 40-47.

Ahamed Fadel Ashery, Kamal Radwan, and Mohamed I. Gar

Al-Alm Rashed. (2010). The effect of pH control on turbidity

and NOM removal in conventional water

treatment. Fifteenth International Water Technology

Conference, IWTC. 1-14.

Anthony S. Greville.. (1997). How to Select a Chemical

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Grégoire Seyrig , Wenqian Shan. (2007). COAGULATION

AND FLOCCULATION: COLOR REMOVAL. 1-14.

Chai SiahLee, JohnRobinson, MeiFongChong. (2014). A reviewonapplicationofflocculantsin wastewatertreatment. ProcessSafetyandEnvironmentalProtection. 1-20.

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44 | P a g e

12. APPENDIX:

Preparation of 1M Ca(OH)2 solution:

Molar weight of Ca(OH)2 = 74.1 g/mol

Concentration of Ca(OH)2 needed = 1 M

Volume of Ca(OH)2 solution needed = 250mL = 0.25 L

Number of mole of Ca(OH)2 = (0.25 L) x (1 mol/L) = 0.25 mol

Weight of Ca(OH)2 needed = (74.1 g/mol) x (0.25 mol) = 18.53 g

Preparation of 0.15M Polyaluminium Chloride:

Molar weight of PAC = 174.45 g/mol

Concentration of PAC needed = 0.15 M

Volume of PAC solution needed = 250ml = 0.25 L

Number of mole of PAC = (0.25 L) x (0.15 mol/L) = 0.0375 mol

Weight of PAC needed = (174.45 g/mol) x (0.0375 mol) = 6.54 g

Wt% of PAC solution = 6.54g / 250g = 2.6%

45 | P a g e