IB Chemistry Extended Essay

Aluminium sulphate coagulation should make seawater purification a viable source of fresh water for Qatar

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Pratyaksha Sinha 004881-0036

Aluminium sulphate coagulation should

make seawater purification a viable

source of fresh water for Qatar

Chemistry Extended Essay

Word Count: 3865 words

Abstract Word Count: 254 words

Research Question: How effective is flocculation of metal ions using the coagulant aluminium

sulphate (Al2(SO4)3.16H2O) for the treatment of seawater?

International School of London, Qatar

Candidate Number: 004881-0036

Candidate Name: Pratyaksha Sinha


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Abstract

I am exploring treatment of seawater by coagulation, using the question: How efficient

is flocculation of ions using the coagulant aluminium sulphate (Al2(SO4)3.16H2O) for the

treatment of seawater? To carry out this investigation, I compared the efficiency, in terms of

the comparative result of the highest percent yield, using aluminium sulphate as a coagulant for

three different types of water and then evaluated its practicality as a coagulant for large-scale

water treatment.

A coagulant was dissolved in the water to neutralize the ions carried by the colloidal

particles suspended in the water and precipitate them. But for effective coagulation, there

were many variables to keep in mind such as concentration of coagulant and the type of

coagulant. To determine these controls, a preliminary experiment was conducted where the

trial and error method was used to determine the masses of coagulant and coagulant aid that

were to be used. It was found that ≈ 7.930 × 10−2𝑀 Al2(SO4)3.16H2O was the only

concentration of the coagulant which coagulated the floc.

The main experiment compared the mass of salt in a solution and the mass of salt

coagulated by aluminium sulphate. The result for the NaCl solution was used as the reference

point as the solution was made purely of salt and no organic substances. Three types of water

were coagulated: grey water, seawater and NaCl solution. The percent yield for all the three

were 76.1%±0.10%, 90.3%±0.08% and 95.5%±0.10% respectively. Hence this result concluded

that aluminium sulphate is an effective coagulant for the flocculation process in the treatment

of seawater.


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Contents

Section Title Page

Abstract 2

1 Introduction 4

2 Background Information 6

2.1 Colloidal Chemistry 6

2.2 Coagulation 8

2.3 Aluminium Sulphate 9

3 Investigation 11

3.1 Aim 11

3.2 Hypothesis 11

3.3 Coagulation Process 11

3.4 Method 12

4 Data Analysis 15

4.1 Experiment 1 15

4.2 Experiment 2 16

5 Conclusion & Evaluation 18

6 Discussion 20

Bibliography 24

Appendix A – Jar Test 25

Appendix B – Raw Data & Calculations 26

Appendix C – Apparatus & Chemicals List 30


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Research Question

How effective is flocculation of metal ions using the coagulant aluminium sulphate

(Al2(SO4)3.16H2O) for the treatment of seawater?

1. Introduction

Dr. Adel Sharif of the Qatar Environment and Energy Research Institute mentioned in his

speech at Qatar Foundation Annual Research Forum that overconsumption of water remains a

key problem for the country as it develops. One of his visions is to use seawater and reuse

water as a source of domestic supply in an economic and ecological way. But for both of these

ideas, an efficient method to harvest these waters needs to be found.

Whilst researching into this topic, I found that an important process in water treatment

is flocculation which makes use of coagulating chemicals to extract unnecessary metal ions and

other microbes from water. A common coagulant used for this process is potassium aluminium

sulphate for the minor flocculation of water which is later sent for further treatment. A cheaper

coagulant which could work in the same way is hydrated aluminium sulphate. On further

research, I defined a clear question: Can aluminium sulphate efficiently coagulate colloids

present in seawater? For this investigation, I decided to equate efficiency to percent yield. In

literature, I could not find reference to the actual efficiency of aluminium sulphate in any type

of water, so I decided to conduct an experiment comparing the efficiency of the coagulant in

different types of water; grey water, standard saline solution and seawater.


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My investigation is specifically focused on the quantity of colloids coagulated from the

different sources of water. Grey water was obtained from the household draining system,

which contains high concentrations of organic materials from the waste filtered from everyday

uses. This should result in lower masses of salt measured than in seawater and sodium chloride

solution as coagulants do not coagulate all organic materials. The seawater was collected from

Al Wakra beach. As for the sodium chloride solution, the yield of the coagulation of this water

should be the highest as the solution itself is only distilled water and a weighed mass of salt.

Prior to the experiment, the mass of the various compounds used as the coagulant and

coagulant aid, a compound which increases the rate of coagulation, had to be quantified. Due

to the paucity of data available, I conducted an experiment to determine the approximate

concentration of aqueous aluminium sulphate required to flocculate ions from water. For this, I

used a constant concentration of NaCl solution (≈0.8557M NaCl, which is ≈ 5.000𝑔 𝑁𝑎𝐶𝑙 in

100ml of water) and varied the strength of aqueous Al2(SO4)3. Ca(OH)2, which was used as pro-

coagulant and its quantity required to aid the coagulation process the best was determined in

another experiment but it is not presented in the body of this research. These experiments

were conducted to determine the conditions under which the coagulation would work at its

peak efficiency. As this was the most important aspect, a larger number of trials were

conducted to provide a more accurate result. Although these were not relevant to my original

research focus, they helped me understand more about the hydrated aluminium sulphate as a

coagulant and the process of coagulation and flocculation.


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2. Background Information

2.1 Colloidal Chemistry

Colloidal chemistry is closely associated with various parts of water purification as the

processes of coagulation, flocculation and filtration involve colloidal phenomena. Colloids,

which are non-crystalline substances consisting of molecules of one substance dispersed

through a second substance, carry positive or negative charge. These charges are important as

they are present in all liquid mediums.

Frictional electrification potentially explains the dispersal of colloidal particles in a

medium as friction between each them result in charge. The dissociation of surface molecules is

another cause that leads to electric charge on colloidal particles, for example:

Figure 1: Dissociation of surface molecules (Oakley, H.B.)

In this example, the cation (Na+) passes in the solvent while the anion (C15H31 COO-) has a

tendency to form negative charges aggregated by itself due to weak attractive forces present in

the long hydrocarbon chains.

Another explanation is the presence of acidic or alkaline groups in the solution. As an

example, protein molecules give rise to either positive or negative charges depending on the

pH, the H+ concentration, of the medium.


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Figure 2: Proteins create negative or positive charges (Oakley, H.B.)

They form a positively charged particle in low pH mediums and a negatively charged

particle in high pH mediums as illustrated above.

When more than one ions are present in a medium, the selective accumulation of ions

common to the colloidal particles takes place, resulting in the formation of positively charged or

negatively charged particles. This is called ‘creation of charges due to the selective adsorption

of molecules’.

Figure 3: Positively charged silver chloride (Oakley, H.B.)

This plays an important role during the flocculation as this phenomena aids complete

flocculation of the ions. As the experiment will test three different types of water, it is


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important to keep in mind the type and number of these colloidal ions will be different for

every trial.

2.2 Coagulation

Sols, which are fluid suspensions of colloidal solids in a liquid, are stable after

precipitation due to the presence of electric charges on the particles. Due to electric repulsion,

the particles do not come close to one another and hence do not aggregate. The removal of

charge or attraction due to another charge by any means will lead to the aggregation of

particles and hence cause immediate precipitation. This process of precipitation is known as

coagulation or flocculation. Chemical precipitation is considered to be one of the most effective

methods of removing colloids due to the coagulating effect of the precipitate formed as shown

above. (Stein, Milton F.)

Coagulation, as a phenomenon, can be cause by different methods. A simple and basic

method is heating or cooling which can be seen when the albumin in a boiled egg gets

coagulated. In other cases, as different colloids have opposing charges, when these are mixed,

they neutralise themselves and this results in the precipitation of both the sols simultaneously.

When large quantities of electrolytes are added to the solution, the electrolyte

oppositely charged to the ions in the water neutralize each other due to which they aggregate

and coagulated. This process will be used in the following investigation.


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2.3 Aluminum Sulphate

Figure 4: 16-Hydrated Aluminium Sulphate

(Pubchem)

Aluminium sulphate reacts with the hydroxide and carbonates of the alkali and alkaline

earth metals according to the already well-known equations (Stein, Milton F):

𝐴𝑙2(𝑆𝑂4)3(𝑎𝑞)+ 3𝐶𝑎(𝑂𝐻)2(𝑎𝑞)

→ 𝐴𝑙2(𝑂𝐻)6(𝑠)+ 3𝐶𝑎𝑆𝑂4(𝑠)

𝐴𝑙2(𝑆𝑂4)3(𝑎𝑞)+ 3𝑁𝑎2𝐶𝑂3(𝑎𝑞)

+ 2𝐻2𝑂(𝑙) → 𝐴𝑙2(𝑂𝐻)2(𝐶𝑂3)2(𝑠)+ 3𝑁𝑎2𝑆𝑂4(𝑠)

+ 𝐻2𝐶𝑂3(𝑠)

𝐴𝑙2(𝑆𝑂4)3(𝑎𝑞)+ 3𝐶𝑎(𝐶𝑂)3(𝑎𝑞)

+ 𝐻2𝐶𝑂3(𝑎𝑞)+ 2𝐻2𝑂(𝑙)

→ 𝐴𝑙2(𝑂𝐻)2(𝐶𝑂3)2(𝑠)+ 3𝐶𝑎𝑆𝑂4(𝑠)

+ 4𝐻2𝐶𝑂3(𝑠)

These reactions are relevant in this investigation as the salts mentioned above are

commonly present in the different kinds of water and the first equation refers to the coagulant

and coagulant aid used in the experiment.

Aluminium sulphate (as

anhydrous dialuminium;trisulphate

Al2(SO4)3) is a clear salt.

Hexadecahydrated aluminium

sulphate, which is a while crystalline

salt, is used in the experiment. Among

its uses, it’s most common use is for

wastewater treatment and seawater

treatment as both absorbents and

adsorbents.


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When aluminium sulphate is added to solutions of sodium carbonate, hydroxide,

calcium hydroxide or calcium bicarbonate of equivalent strength in distilled water, the reaction

is very slow. As mentioned by Milton F Stein in his notes on colloidal chemistry, “With a

temperature of 20°C, and with 10 grains per gallon of aluminium sulphate, coagulation

becomes visible in one hour, and the reaction completes itself in two hours.” (Stein, Milton F.)

But the coagulation process is more efficient in terms of the end yield in turbid water; this is

why during coagulation for this experiment, the turbidity of the water has been increased as

much as possible by using a magnetic stirrer.


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3. Investigation

3.1 Aim

Referring to the research question, the main focus of this essay is to calculate the

efficiency of the compound aluminium sulphate as a coagulant in three different types of water

(grey water, seawater and a prepared≈ 0.8557𝑀 𝑁𝑎𝐶𝑙 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛) and evaluate its potential as

a seawater treatment coagulant.

3.2 Hypothesis

The investigation looks at coagulation in three different types of water: grey water,

seawater and NaCl solution. Based on pilot testing, the highest yield would be of the NaCl

solution, the second for the seawater and the lowest wastewater. This is due to limited or

abundant presence of salt in the water for the given coagulant dose.

3.3 Coagulation Process

Ideally, the coagulation process is done using the jar test method as to be able to keep

in control all the necessary variables. The jar testing apparatus consists of six paddles which stir

the contents of six 1 liter containers. Different settings can be set for each of the paddles using

the rpm gauge at the top-center of the device. Through this, comparisons can be made over the

range of the six containers. (Christophersen, Dave)

During coagulation-flocculation, there are many variables which have to be taken into

account such as the type of coagulant use which varies in yield based on molecular structure,


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coagulant dose, the pH of the water, the type of additional chemical dosages apart from the

primary coagulant, the sequence of chemical addition, the intensity and duration of mixing

during the process, the type of rapid mix and stirring device and the floc retention time.

If all the variables are carefully controlled, a simple experiment in stoichiometry and

calculating the limiting reagent should provide a reliable model to investigate the efficiency of

aluminium sulphate as a viable coagulant.

3.4 Method

The aim of the first experiment was to find the exact mass of aluminium sulphate required,

under the conditions of the working space, to coagulate the salt from solutions. The controlled

variables were the concentration of the NaCl solution, the volume of main medium, and the

concentration of Ca(OH)2, the coagulant aid. The pressure, temperature, and pH were not

controlled but the latter two were recorded.

To make the NaCl solution, I added 5.000g of NaCl salt to 100ml of unionised water which

made 0.8557M liquid NaCl.

5.000𝑔 𝑁𝑎𝐶𝑙 (1 𝑚𝑜𝑙 𝑁𝑎𝐶𝑙

58.43𝑔 𝑁𝑎𝐶𝑙) = 0.08857𝑚𝑜𝑙 𝑁𝑎𝐶𝑙

(0.08857𝑚𝑜𝑙 𝑁𝑎𝐶𝑙

100𝑚𝑙) ×

1000𝑚𝑙

1 𝐿= 0.8557

𝑚𝑜𝑙

𝐿 𝑁𝑎𝐶𝑙 = 0.8557𝑀 𝑁𝑎𝐶𝑙 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛

To make the Ca(OH)2 solution: Add 0.200g of Ca(OH)2 salt to 10ml of unionised water which

made a 2.699 × 10−2𝑀 𝐶𝑎(𝑂𝐻)2 𝑠𝑜𝑙𝑢𝑡𝑖𝑜𝑛. To make the hydrated Al2(SO4)3 solutions: Add a


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range of 0.500g, 1.000g, 1.500g, 2.000g of Al2(SO4)3∙ 16𝐻2𝑂 salt to a 20ml solution which

creates the range of 3.966 × 10−2𝑀 𝐴𝑙2(𝑆𝑂4)3 ∙ 16𝐻2𝑂 , 7.930 × 10−2𝑀 𝐴𝑙2(𝑆𝑂4)3 ∙

16𝐻2𝑂 , 11.89 × 10−2𝑀 𝐴𝑙2(𝑆𝑂4)3 ∙ 16𝐻2𝑂 𝑎𝑛𝑑 23.79 × 10−2𝑀 𝐴𝑙2(𝑆𝑂4)3 ∙

16𝐻2𝑂 solutions respectively.

To carry out the coagulation, fill a beaker with 100ml of the ≈ 0.8557𝑀 NaCL solution to be

the primary medium and place the beaker on a magnetic stirrer stand. Measure the pH of the

solution using a pH paper. Add 10ml of the 2.699 × 10−2𝑀 𝐶𝑎(𝑂𝐻)2 solution to the same

beaker. Place the magnetic stirrer in the solution and mix at 50% of its capacity for a minute.

Measure the pH again. Then add a 100ml of 3.966 × 10−2𝑀 of Al2(SO4)3 solution to the primary

medium. Cover this beaker and switch on the magnetic stirrer to 100% of it’s capacity for 30

minutes. After this rapid mix stage, let the solution rest for 60 minutes. Remove the magnetic

stirrer from the solution. Check the pH of this solution using pH paper. Repeat the procedure 8

times for the same concentration. Repeat the steps by changing the concentration of the

Al2(SO4)3∙ 16𝐻2𝑂 solution to 7.930 × 10−2𝑀, 11.89 × 10−2𝑀 𝑎𝑛𝑑 23.79 × 10−2𝑀.

The mass of the floc was quantified by measuring the weight of the filter paper before and

after the floc was placed on it. Only after making sure that the filter papers has dried and only

contains the floc on it, measure the weight of the floc+fliter paper. Assure that the filtered

water does not show any signs of floc floating in the cylinder, then measure the volume of

distilled water.

Mass of floc = (Mass of floc + filter paper) − Mass of filter paper


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The pH of the distilled water was also measured for further analysis.

The same procedure of the above stated experiment was used for the main experiment

in which the independent variable was the three different types of water. Repeat the procedure

8 times for the same concentration.

For coagulation of wastewater and sea water, there was an adjustment in the first step; the

wastewater was filtered to remove physical impurities. For reference purposes, 100ml of

wastewater was previous heated (with five trials) and 4.620g(±0.001g) of salt was extracted.

This experiment has been conducted assuming that the salt is evenly spread in the water.

100ml of seawater was previous heated (with five trials) and 5.139g(±0.001g) of salt was

extracted. This experiment has been conducted assuming that the salt is evenly spread in the

water.


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4. Data Analysis

4. 1: Experiment 1 : Obtaining the mass of (Al2SO4)3 to be used

Table 1: Obtaining the mass of (Al2SO4)3 to be used

Trial Set Weight of Al2(SO4)3.16H2O (g) ± 0.001g

Weight of NaCl (g) ± 0.001g

Weight of Ca(OH)2 (g) ± 0.001g

Resultant floc

Weight of floc + filter paper (g) ± 0.001g

Weight of filter paper (g) ± 0.001g

1 0.510 6.053 0.212 No floc

2 1.080 5.084 0.213 Floc formed

5.766 0.369

3 1.524 5.082 0.211 Floc was feathery in nature and dissolved when attempts were made to measure it

4 2.064 5.114 0.210 Some of the floc passed through the filter paper and tinted filtered water white and yellow (for the trials with resultant the yellow tint)

Analysis and Result

The relevance of this experiment is to identify the right concentration of aluminium

sulphate required for the coagulation of 100ml water. As shown in the table, trial 2 was

successful as floc, which could be measured, was formed. The rest of the trials were

unsuccessful and hence have minimal relevance to the rest of the investigation.


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4.2: Experiment 2: Checking the efficiency of (Al2SO4)3 as a coagulant

Table 2: Average percent yield of the three types of water

Trials No Weight of floc –

weight of

Al2(SO4)3.16H2O

added (g) ±0.003g

Original weight

of salt (g) ±

0.001g

Difference in

weight of the

salt (g) ±

0.004g

Per cent yield

(%)

Grey Water Average 3.517 Expected

average:

4.620g(±0.001g)

0.961 79.1%

Seawater Average 4.639 Expected

average:

5.139g(±0.001g)

0.770 90.3%

NaCl

Solution

Average 4.851 5.080 0.227 95.5%

Table A.4: Comparison of averages of mass of salt

Grey Water SeawaterNaCl

solution

Expected Average (g) 4.62 5.139 5.08

Actual Average (g) 3.517 4.639 4.851

00.20.40.60.8

11.21.41.61.8

22.22.42.62.8

33.23.43.63.8

44.24.44.64.8

55.25.4

We

igh

t o

f sa

lt (

g)

Different types of water

Graph 1: Mass of Coagulated Salt

Expected Average (g)

Actual Average (g)


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As summarised in the graph and table above, the experiment showed different degrees of

success in the different types of water. For grey water, the yield was the lowest, being

76.1%±0.10% and the highest being for the NaCl solution being 95.5%±0.10%. The seawater

had a 90.3%±0.08% yield, which is a fairly significant result, considering the variable nature of

the experiment, as discussed below. The NaCl solution will be used as a standard as the solution

was made of only salt without any possible interference from organic matter.


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5. Evaluation

The results of the experiment support my hypothesis that the coagulant Al2(SO4)3∙

16𝐻2𝑂 would be most effective on the NaCl solution, less so on the seawater and least on the

grey water. The error in all the measurements were 0.08% and 0.10% in the processed data.

The pH paper used to determine the acidity or alkalinity of the solution had a large error of

±1pH which could have been decreased by the titration of the solution. As the main aim of this

experiment was to compare the percent yield, the following errors did not affect my conclusion

as the three types of water were all subjected to the same conditions. If a more accurate result

were to be needed, the jar test method outlined in the appendix could be undertaken.

The methodology of the experiment itself resulted in multiple inaccuracies and errors.

For one, it was difficult to determine exactly when the flocculation was complete. There was no

predetermined end point so it was assumed that it should be complete over a time period of 60

minutes (Stein, Milton F). Another experiment could be conducted to find the exact length of

time the solutions would take to wholly coagulate.

Another major drawback of the experiment was the nature of the experiment itself.

There were various variables to take into account as mentioned under section 3.3. Not all of

these factors could be measured due to the limitations posed by available apparatus. Whether

different concentrations of calcium hydroxide would have been more effective or better

coagulant aids could have been used was not evaluated in this methodology but should be

considered for further evaluation. Similarly, although prior testing was conducted to find the


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most efficient mass of all the chemicals required, only certain values were tested. It is possible

that there is another value, which could result in higher yield and accuracy.

A variable which I attempted to take into consideration was the pH of the solution. Both

the coagulant aid and the coagulant have alkaline and acidic effects on the solution

respectively. Although it is known that aluminium sulphate works best under alkaline conditions

(Stein, Milton F), the exact pH of the solution could not be controlled. However, it has been

reported in the Appendix to be used as justification of the data.

As the stirrer was not an ideal rapid mixer but a magnetic stirrer, the turbidity of the

entire solution could have been affected and so would have the effectiveness of the

coagulation. The apparatus for stirring and rapid mixing does not provide us a quantitative

value to designate to the speed of mixing, so the rate used by the magnetic stirrer could have

varied. As mentioned in section 3.3, the ideal set up would have been the jar test method but,

due to lack of the apparatus, it was not used.

One problem with the wastewater was the water source. The grey water used in

the experiment was obtained from different local households. The wastewater did not

coagulate as efficiently as the other two solutions; this could have been due to influence of the

organic compounds in the water. As the specific compounds were not identified, the exact

influence cannot be determined. Also, as the average quantity of salts present in the water was

found to be slightly lower than the quantity tested for optimum coagulant, the dose may have

been higher or lower than the optimum dose required for the specific type and volume of

water.


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6. Discussion

The aim of the experiment was to determine the efficiency of aluminium sulphate as a

coagulant for three different types of water. A potential practical application of the results

could be the coagulation of sols present in seawater, rendering it suitable for domestic use.

According to the results of the experiment, aluminium sulphate was successful in coagulating

the metal ions, such as chloride, sodium, magnesium, strontium, silicate, iodide and others,

which are commonly present in the seawater (W. Johnson, Martin). This is an effect method of

coagulation as it was not only the ions that were successfully flocculated, but also microbes and

other small particles (LeChevallier, Mark W.) However, due to the increasing rate of pollution of

seawater it is difficult to determine all of its specific components.

Whilst testing the efficiency of aluminium sulphate as a coagulant in wastewater, the

results were not as successful. They demonstrated an average percent yield of only

76.1%±0.10% as opposed to the 90.3%±0.08% yield of coagulation of seawater and

95.5%±0.10% yield of the NaCl solution. This implies that it is possible for the coagulation to be

less effective in certain types of water with different constituents. The different components of

seawater can vary with the origin of the water and therefore depending on this process without

previous testing would be unwise. But for the seawater present in Qatar this result is suitable as

the abundant seawater can be practically used as a public water source.

Another major factor that affects yield of coagulation is the pH of the water. Different

coagulants work better in different levels of pH. The optimum pH of the final distilled solution

required is 7 as it should be pure water. As aluminium sulphate works better in alkaline


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solutions, a coagulant aid was added to increase the pH and add more ions to aid the

flocculation. Taking into consideration the fact that the original pH of the water varies as well,

for different pHs, different masses of coagulant aids and other pH adjusting substances would

be needed. This would be a difficult task to carry out frequently on a large scale such as for

public water supply. Attempts to average out the pH could prove to be slightly useful.

The steady but very gradual decrease in pH of the world’s oceans due to the increase of

dissolved carbonate ions would affect this calculation. This could also be a positive effect, as

some of the pH levels would not need a coagulant aid as the pH of the water itself would be the

optimum pH level for the coagulant.

A drawback of coagulation of seawater is the colour of the water. Seawater usually has a

clear yellow or brownish tint, which cannot be removed by passing it through filter paper. The

colour of the water is enhanced in turbid state, which is predominantly seen during the later

stages of the rapid mixing process. Water generally acquires colour through contact with

decaying vegetation in swamps, as a result of underwater life. When aluminium sulphate is

added to these, a coloured precipitate is formed but, depending on the cause of the colour,

there is a possibility that aluminium sulphate may not be as efficient. Although coloured water

would be a disadvantage, if the cause of the colour is an alkaline agent, coagulant aid would not

be needed. This again depends on the possibility of being able to measure the quantities of

these constituents in the water. Also, as this precipitation of ions is only one of the methods

involved in the long process of water treatment which includes reverse osmosis, this weakness

can be easily overcome.


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One of the most important factors to consider is the cost. The cost of the whole process

is extremely relevant as the public need to be able to afford the water supply. As outlined in

‘The Manufacture Of Sulphate Of Alumina At The Colombus Water Softening And Purification

Works’ by Charles P. Hoover, in the manufacturing of aluminium sulphate, the important

features are bauxite and sulphuric acid; including the costs of setting up the plant, an overall

estimate would be $10,493.50. This is for the production of 1000 tonnes of 17% alum solution.

According to him, a minimum of $12,000 original investment and a minimum annual

expenditure of $6,000 would be needed. For a higher concentration and for further

development, more costs would be incurred.

Although the majority of the costs are spent in one-time investments in the plant, more

costs would be incurred for repair and maintenance of the plant, along with the high costs of

constantly obtaining the bauxite and sulphuric acid, which are the reagents which make

aluminium sulphate. These costs only include the manufacture of alum but further expense

would be required for building and usage of the actual water treatment plant. However, this

method can be very useful for the public, as a large supply of drinkable water can be easily

delivered to them with just these costs.

Another aspect to keep in mind is that although the majority of the salt coagulated, in

most of the trials some ions remained suspended in the water. This could raise ethical issues

concerning the health of the people who consume this water, considering the possibility that

ingesting these ions could affect their heath.


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If this idea were to be implemented on a larger scale, more research should be

conducted. Further exploration should include; testing for other coagulants which could be

more effective for the coagulation of seawater; testing of other coagulant aids and its different

concentrations which could result in a higher percent yield for seawater; and perhaps testing

whether there is a different concentration of aluminium sulphate which was not tested in this

experiment and could be more suited for the coagulation. The two major variables which were

hard to control and manipulate were the pH and the colour of the solutions. It is possible that a

different level of pH would create a better environment for the coagulation. Dilution of the

water for a lower colour could be effective but this could also increase the costs due to greater

use of coagulant aids and coagulants for the larger quantity of water. If all the variables are

carefully controlled, a simple experiment in stoichiometry and calculating the limiting reagent

should provide a reliable model to investigate the efficiency of aluminium sulphate as a viable

coagulant for the large scale.

In conclusion, the process of coagulation of seawater can be a useful method for

tapping the large seawater resource as public use for the residents of Qatar. The method itself

can be improved and, with further exploration, it can be developed into a working model.


Page | 24


Bibliography

1. Hoover, Charles P. "THE MANUFACTURE OF SULPHATE OF ALUMINA AT THE COLUMBUS WATER

SOFTENING AND PURIFICATION WORKS [with DISCUSSION]." Journal (American Water Works

Association) 2.4 (1915): 693-702. JSTOR. Web. 18 Dec. 2015.

2. Johnson, Martin W., and Fleming H. Richard. "Biological Chemistry and Physics of Sea Water."

Nature 123.3106 (1929): 709-10. Web. 20 Jan. 2016.

3. Lechevallier, Mark W. "Water Treatment and Pathogen Control: Process Efficiency in Achieving

Safe Drinking-water." Water Intelligence Online Wio 12 (2013): n. pag. Web. 18 Dec. 2015.

4. Mohlman, F. W. "COLLOID CHEMISTRY AND ITS RELATION TO TANK TREATMENT OF SEWAGE."

Journal (American Water Works Association) 9.2 (1922): 311-18. JSTOR. Web. 16 Dec. 2015.

5. National Center for Biotechnology Information. PubChem Compound Database;

CID=23065692, https://pubchem.ncbi.nlm.nih.gov/compound/23065692 (accessed Jan.

20, 2016).

6. Oakley, H. B. "The Origin of the Charge on Colloidal Particles." The Origin of the Charge on

Colloidal Particles (1925): 902-16. - The Journal of Physical Chemistry (ACS Publications). Web. 20

Jan. 2016. <http://pubs.acs.org/doi/abs/10.1021/j150265a005>.

7. Pirnie, Malcolm. "APPLICATION OF COLLOID CHEMISTRY TO STUDY OF FILTER EFFLUENTS."

Journal (American Water Works Association) 9.2 (1922): 247-73. JSTOR. Web. 18 Dec. 2015.

8. Stein, Milton F. "SOME NOTES ON COLLOIDAL CHEMISTRY AND WATER PURIFICATION." Journal

(American Water Works Association) 8.6 (1921): 571-82. JSTOR. Web. 18 Dec. 2015.


Page | 25


Appendix A: Jar Test

Jar Test

Ideal aluminum sulphate coagulation follows the following basic steps:1

1. Fill the jar testing apparatus containers with sample water. One container will be used

as a control while the other containers can be adjusted depending on the variable

constant.

Different variables could be the pH of the jars, variations in coagulant doses,

variations in coagulant aid doses, etc.

2. Add the coagulant to each container and stir at approximately 100 rpm for 1 minute.

The rapid mix stage helps to disperse the coagulant throughout each container.

3. Turn off the mixers and allow the containers to settle for 30 to 45 minutes. Then

measure the final turbidity in each container.

4. Reduce the stirring speed to 25 to 35 rpm and continue mixing for 15 to 20 minutes.

This slower mixing speed helps promote floc formation by enhancing particle collisions

which lead to larger floc.

1 Hawley's Condensed Chemical Dictionary (2007): n. pag. The National Environmental Services Centre. Web.


Page | 26


Appendix B: Raw Data

Experiment 1 : Obtaining the correct mass of (Al2SO4)3 to be used

Trial

s

No. of

Repeat

s

Weight of

Al2(SO4)3.16

H2O (g) ±

0.001g

Weight

of NaCl

(g) ±

0.001g

Weight of

Ca(OH)2

(g) ±

0.001g

Resultant

floc

Weight

of floc

+ filter

paper

(g) ±

0.001g

Weight

of filter

paper

(g) ±

0.001g

1 1 0.515 5.017 0.210 No floc2

2 0.521 5.081 0.221

3 0.504 5.048 0.207

4 0.512 5.089 0.218

5 0.508 5.011 0.202

6 0.509 5.029 0.212

7 0.511 5.143 0.215

8 0.502 5.007 0.209

Average 0.510 6.053 0.212

2 9 1.027 5.160 0.200 Floc

formed

5.733 0.373

10 1.121 4.989 0.211 5.621 0.339

11 1.111 5.107 0.218 5.898 0.367

12 1.038 5.003 0.221 5.601 0.366

13 1.056 5.090 0.206 5.884 0.382

14 1.076 5.011 0.219 5.911 0.374

15 1.114 5.102 0.220 5.798 0.381

16 1.098 5.211 0.211 5.689 0.369

Average 1.080 5.084 0.213 5.766 0.369

3 17 1.531 5.110 0.210 Feathery floc- unable to

measure accurately as a

minimal mass of it dissolved

in the water while filtering

18 1.510 5.013 0.200

19 1.493 5.065 0.219

20 1.523 5.041 0.205

21 1.564 5.094 0.214

22 1.521 5.090 0.219

23 1.503 5.147 0.213

24 1.548 5.093 0.204

2 Floc did not form even after longer detention time periods (2 hours)


Page | 27


Average 1.524 5.082 0.211

4 25 2.137 5.156 0.217 Flaky floc

with

yellow tint

Some of the floc

passed through

the filter paper

and tinted

filtered water

white and yellow

(for the three

trials with

resultant the

yellow tint)

26 2.007 5.076 0.210

27 1.999 5.084 0.199

28 2.101 5.163 0.203 Flaky floc

29 2.118 5.123 0.221

30 2.046 5.010 0.215

31 2.099 5.114 0.203 Flaky floc

with

yellow tint

32 2.003 5.187 0.214 Flaky floc

Average 2.064 5.114 0.210

Table 4.1: Quantitative data and qualitative data of the first experiment

Experiment 2: Checking the efficiency of (Al2SO4)3 as a coagulant

Trials No

.

Weight of

Al2(SO4)3.16H2O

(g) ± 0.001g

Weight

of

NaCl

salt (g)

±

0.001g

Weight

of

Ca(OH)2

(g) ±

0.001g

Weight

of Filter

Paper

(g)

±0.001g

Weight

of

floc+filter

paper

(g) ±

0.001g

Total

mass

of

distilled

water

(ml) ±

1ml

1*

(grey

water)

1 1.072 N/A 0.203 0.367 5.098 125

2 1.102 0.212 0.366 4.989 119

3 1.221 0.211 0.382 4.880 129

4 1.033 0.206 0.364 5.176 123

5 1.098 0.200 0.379 4.878 126

Average 1.105 N/A 0.212 0.371 5.004 124

2

(seawater

)

1 1.034 N/A 0.202 0.370 5.889 115

2 1.003 0.203 0.380 6.270 112

3 1.165 0.205 0.369 5.699 112

4 1.210 0.210 0.373 6.424 115

5 1.087 0.213 0.339 5.745 114

Average 1.099 N/A 0.214 0.366 5.785 114

3

(NaCl

Solution)

1 1.156 5.093 0.207 0.375 5.384 113

2 1.128 5.143 0.209 0.368 6.598 112

3 1.054 4.997 0.201 0.389 6.198 115


Page | 28


4 1.128 5.160 0.211 0.378 5.989 114

5 1.007 5.009 0.213 0.367 6.437 112

Average 1.095 5.080 0.208 0.375 5.661 113

Table A.1: Quantitative data from the second experiment

Trials No. First pH

(ph)

±1pH

pH Before

(ph)

±1pH

pH

During(ph)

±1pH

pH After

(ph) ±1pH

1*

(grey water)

1 6 7 7 6

2 6 8 7 7

3 7 8 7 6

4 5 8 6 7

5 6 8 7 7

2

(seawater)

1 7 8 7 7

2 8 8 7 8

3 8 9 7 8

4 7 9 7 8

5 7 8 7 8

3

(NaCl

Solution)

1 6 8 7 7

2 7 9 7 8

3 7 8 7 7

4 7 9 7 7

5 7 9 7 8

Table A.2: Measured pH of the solutions

Trials No Weight of

floc+ filter

paper (g) ±

0.001g

Weight of

Filter Paper

(g) ± 0.001g

Weight of

floc (g)

±0.002g

Weight of floc-

weight of

Al2(SO4)3.16H2O

added (g)

±0.003g

1*

(grey

water)

1 5.098 0.367 4.731 3.659

2 4.989 0.366 4.623 3.521

3 4.880 0.382 4.498 3.227

4 5.176 0.364 4.812 3.779

5 4.878 0.379 4.499 3.401

2 1 5.889 0.370 5.519 4.485


Page | 29


(seawater) 2 6.270 0.380 5.890 4.887

3 6.199 0.369 5.830 4.665

4 6.424 0.373 6.051 4.841

5 5.745 0.339 5.406 4.319

3

(NaCl

Solution)

1 6.384 0.375 6.009 4.853

2 6.598 0.368 6.230 5.102

3 6.198 0.389 5.809 4.755

4 5.989 0.378 5.611 4.483

5 6.437 0.367 6.070 5.063

Table A.3: Weight of floc and possible salts

Trials No Weight of floc –

weight of

Al2(SO4)3.16H2O

added (g)

±0.003g

Original weight

of salt (g) ±

0.001g

Difference

in weight of

the salt (g)

± 0.004g

Per cent

yield (%)

1*

(grey

water)

1 3.659 Expected

average:

4.620g(±0.001g)

0.961 79.2%

2 3.521 1.099 76.21%

3 3.227 1.393 69.84%

4 3.779 0.841 81.8%

5 3.401 1.219 73.61%

Average 3.517 1.103 76.12%

2

(seawater)

1 4.485 Expected

average:

5.139g(±0.001g)

0.654 87.2%

2 4.887 0.252 95.1%

3 4.665 0.474 90.8%

4 4.841 0.298 94.2%

5 4.319 0.820 84.0%

Average 4.639 0.770 90.27%

3

(NaCl

Solution)

1 4.853 5.093 0.240 95.3%

2 5.102 5.143 0.041 99.2%

3 4.755 4.997 0.242 95.2%

4 4.483 5.160 0.667 86.9%

5 5.063 5.009 -0.054 101%

Average 4.851 5.080 0.227 95.49%

Table A.4: Comparison of mass of salt


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Appendix C: Apparatus and Chemicals List

Chemicals

1. Al2(SO4)3∙ 16𝐻2𝑂

2. Ca(OH)2

3. NaCl

4. Distilled water

Apparatus

1. 1 heating/magnetic stand

2. 1 magnetic stirrer

3. 3 1000cm3 ±0.01cm3 beaker

4. 4 100cm3 ±0.01cm3 beaker

5. 2 50cm3 ±0.02cm3 measuring cylinder

6. 4 100cm3 ±0.1cm3 measuring cylinder

7. 3 250cm3 ±0.01cm3 beakers

8. 1 scale

9. 1 spatula

10. Johnson’s litmus paper

11. Filter paper

12. 1 thermometer

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