quality improvement of water resources by removal … · reverse osmosis (ro) process. reverse...

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International Journal of Civil Engineering and Technology (IJCIET)

Volume 8, Issue 12, December 2017, pp. 937–950, Article ID: IJCIET_08_12_102

Available online at http://http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=8&IType=12

ISSN Print: 0976-6308 and ISSN Online: 0976-6316

© IAEME Publication Scopus Indexed

QUALITY IMPROVEMENT OF WATER

RESOURCES BY REMOVAL OF MERCURY

AND LEAD CONTAMINANTS THROUGH

FORWARD OSMOSIS (FO) TECHNOLOGY

WITH VIBRATING MEMBRANE

Majid Meschi Nezami

Department of Energy, Institute of Science and High Technology and Environmental

Sciences, Graduate University of Advanced Technology, Kerman, Iran

Mohammad-Javad Khanjani

Department of Civil Engineering, Shahid Bahonar University of Kerman, Kerman, Iran

ABSTRACT

Nowadays, the forward osmosis (FO) has attracted a considerable attention due to

its numerous abilities in the field of seawater desalination and wastewater treatment,

fluid food processing and power production. This study is seeking to evaluate the

effects of various parameters before and after the membrane vibration on the function

of forward osmosis in mercury and lead desalination from water. In this study, a

laboratory pilot is prepared for these assessments, and thus the parameters, which

affect the removal of contaminants and membrane vibration, are evaluated. According

to the results of this study, the percentage of removed mercury and lead metals is

significantly increased, but the concentration of these elements is decreased in output

solution in the lack of membrane vibration by increasing the temperature. The more

the feed solution concentration has increasing trend, the more it shows the decreasing

trend in percentage of mercury and lead removal from the feed solution. The effective

osmotic pressure has a direct impact on the percentage of removed mercury and lead;

and the percentage of removal will be increased by enhancing the effective osmotic

pressure. The membrane vibration for 6000, 10000 and 14000 rpm of membrane

vibrating motor has a different impact on the removal of heavy metal at the first and

third stages respectively. The initial vibration always increases the percentage of

removal compared to the steady state. This process will be much faster in the second

vibration, and thus the percentage of removal will reach the highest level. The third

vibration shows a significant decrease on the percentage of removal which is different

depending on the rate of effective osmotic pressure. If the effective osmotic pressure is

high (about 18 atm), the percentage of removal will be significantly dropped and will

become less than before the vibration. If the effective osmotic pressure is measured

Majid Meschi Nezami and Mohammad-Javad Khanjani


within the average interval (about 8 atm), the percentage of removal will become

about more than the initial vibration or lack of vibration, and if the osmotic pressure

has the lowest value (about 4 atm), the third vibration has the percentage of removal

between the first and second vibration. According to the results, this rate will always

be lower than the second vibration. The results of this research indicate the

opportunity for adding the membrane vibration to a solution for fouling elimination

and increased percentage of as a novel method. According to the observed cases

about the osmotic pressure and percentage of removal in the third vibration, the

effective osmotic pressure can be considered as a parameter which affects the

selection of draw solution.

Keywords: Forward osmosis, quality improvement, Mercury, Lead, vibrating

membrane, removal efficiency, effective osmotic pressure

Cite this Article: Majid Meschi Nezami and Mohammad-Javad Khanjani, Quality

improvement of water resources by removal of mercury and lead contaminants

through forward osmosis (FO) technology with vibrating membrane, International

Journal of Civil Engineering and Technology, 8(12), 2017, pp. 937–950

http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=8&IType=12

1. INTRODUCTION

Water is one of the most abundant resources on the earth, but about 97% of available waters

are the salt water of seas and oceans. Only a small amount of fresh water is flowing in the

rivers and lakes and the rest of fresh water have permanent ice forms in the glaciers of the

North Pole. Therefore, the preparation of fresh water has become one of the most fundamental

human concerns. The desalination capacity has been significantly increased in the last decade

due to the increasing need for water and significant reduction in the cost of desalination

because of progressed membrane processes (El-Ghonemy, 2012).

Nowadays, most of the countries have investigated the effect of water resources and

desalination facilities on the growth and development of human societies, economic, cultural

and social systems. The adequate fresh water resources are the foundations and bases for

human societies in all dimensions from the daily life necessities to higher levels of economic

production. The absence of such resources provides the context for poverty and limits the

sustainable development options in different areas of the world. In fact, the weak governments

and economies around the world are often faced with serious water challenges, and are unable

to make effective use of innovative technologies or policies in the field of water production

and consumption (G.W.I, 2005; Mi and Elimelech, 2010).

In most of the applications such as the water purification and desalination, the membrane

process effectively compete with traditional technologies (VC, MED, MSF...). However, the

membrane process often has better efficiency in energy consumption and better product

quality and its implementation is easier than such technologies. Furthermore, the membrane

process can be simply increased and decreased in terms of size and can operate without any

change or reduction of goods at ambient temperature. The membrane separation is widely

used in many issues and aspects. A number of different processes should be used in order to

achieve an assumed separation. The separation objectives are generally as follows:

concentration, purification, analysis and intermediate reactions (Mulder, 1996).

In recent decades, the costs are stably and steadily declining for all desalination

technologies. In general, the heating systems with membrane systems bear higher costs. The

water production cost by thermal systems was about US$ 0.65 to 0.90 per cubic meter in 2005

(G.W.I, 2005). The use of membranes at the industrial large scales began by desalination and

Quality Improvement of Water Resources by Removal of Mercury and Lead Contaminants through

forward Osmosis (Fo) Technology with Vibrating Membrane


water treatment for industry in the early 1970s. From then on, the membranes have been

widely used as by technical and commercial methods. The forward osmosis process is one of

the new technologies which come to market for desalination.

2. FORWARD OSMOSIS (FO) PROCESS

Forward osmosis is a novel membrane process in the field of desalination and has a high

potential than the conventional membrane processes (Cath et al, 2006). This process can be

used in the field of desalination as a stand-alone process or as a preparatory phase before the

reverse osmosis (RO) process. Reverse osmosis operates based on the hydraulic pressure, but

the driving force of forward osmotic process is the osmotic pressure difference between the

feed and draw solution. High osmotic pressure of draw solution will create the water flow

from the feed solution to a semi-permeable membrane. Compared with the conventional

membrane processes such as the reverse osmosis, which operates based on the hydraulic

pressure, the forward osmosis process has numerous advantages. Low fouling and easy

cleaning, low operating cost, high water recovery and applications such as the desalination

and wastewater treatment are among the advantages of forward osmosis process (Amini et al,

2013).

The osmosis is the process of water transfer through membranes with selective

permeability from an area with higher chemical potential to an area with lower chemical

potential. Water is driven by the difference in solution concentration on both sides of the

membrane which allows the water passage, but most of the soluble molecules and ions are not

allowed. The osmotic pressure (π) refers to the pressure which its application in most of the

concentrated solutions prevents the water transfer through the membrane. Forward osmosis

(FO) utilizes the osmotic pressure difference (Δπ) in the membrane over the hydraulic

pressure difference (in reverse osmosis) as the driving force for transferring water through the

membrane. FO process concentrates the feed flow and dilutes the highly concentrated flow

(draw solution).

FO uses an osmosis phenomenon to transfer water from feed solution (high chemical

potential of water) to an draw solution (low chemical potential of water) through a semi-

permeable membrane. The driving force of this process is created by osmotic pressure

difference between the feed and draw solution. Osmotic pressure difference is the factor of

water seepage (passage) through a semi-permeable barrier, a low-concentration solution (high

chemical potential of water) to a solution with high concentration (low chemical potential of

water). The inherent energy of this natural process is known as a chemical potential or in

particular the water potential due to the difference in the concentrations of two solutions. The

driving force gradient resulting from the chemical potential difference of substances on two

sides of membrane overcomes the resistance force against the transfer from the membrane.

The FO has been recently taken into account as an alternative to other membrane

processes due to numerous advantages. The RO is compared with FO process in the use of

this process in water purification and desalination because both of them utilize the semi-

permeable membranes as a barrier to the passage of salt with the same performance.

Regardless of whether both processes have similar performance, FO has advantages over RO.

First, because the FO uses the osmotic pressure difference between the feed and draw

solutions as the driving force unlike the RO hydraulic pressure, the forward osmosis has a

lower energy consumption compared to the reverse osmosis. Secondly, because the feed

solution is not under the pressure in the FO process, it is expected that the fouling membrane

is minimal, so the forward osmosis membrane has a lower tendency towards fouling

compared with the reverse osmosis. (Cornelissen, 2008; Boo et al, 2010; Mi and Elimelech,

2010; Tang et al, 2010) It is also expected that the forward osmosis membrane has a longer



life than the current membranes of reverse osmosis, and thus it naturally reduces the costs of

chemical cleaning and membrane replacement, so that the FO benefits reduce the operating

costs in comparison with the RO in water treatment processes.

The osmotic pressure may be prevented by increasing the pressure (ΔP) in an area with

high concentration compared to the area with low concentration in order to reverse the water

movement; and this pressure should be at least equal to or greater than the osmotic pressure of

solution. The gradient or difference in osmotic pressure (Δπ) is a criterion and standard of

driving force of water transfer from solution with a low concentration through the membrane

to the solution with high concentration. Therefore, the determination of required driving force

for reverse osmosis process becomes possible by calculation of Δπ. The direction of water

flow through FO and RO is shown in Figure 1. The direction of water passage and driving

forces in all three processes were found by Lee et al in 1980. ΔP is zero in FO and much

water penetrates the other side of membrane, but water has low diffusion in RO due to the

hydraulic pressure towards the brine (Lee et al., 2010).

Figure 1 Solvent flow in FO and RO

2.1. Forward osmosis membrane

Before the development of membranes, which are specifically used for forward osmosis, the

reverse osmosis membranes were used in all studies on the forward and reverse osmosis from

the 1970s to 1980s. According to a similar result of all these studies, the water flow of FO and

PRO processes through the reverse osmosis membranes is generally low. Obviously, the basic

requirement of forward osmosis research includes the development of a new membrane with

high water flow and appropriate salt rejection. The osmosis phenomenon is seriously

dependent on separation of solutions on two sides of membrane and also the flow; and there is

only a kind of commercial flat sheet membrane of forward osmosis. This type of membrane

was first built by Company Hydration Technology (HTI) in the 1990s.

Figure 2 Forward osmosis membrane (Cornelissen et al, 2008)




Forward osmosis membranes have higher water flow due to the reduced ICP effects as the

result of reduced thickness of support layer. Based on the most of the results, most of the

researchers have found that the forward osmosis membrane needs the review, so that the

internal concentration polarization (ICP) is decreased resulting in maximum driving force of

draw solution, and thus numerous studies have been conducted on forward osmosis

membranes in recent years; and the membrane performance has been strengthened compared

with the HTI membrane.

Forward osmosis membrane for mechanical maintenance has a Polyester network (mesh)

located between two layers of Cellulose triacetate (CTA) substances. This network is unlike

the thick support layers in the reverse osmosis membrane. With a thickness of about 50

micrometers, this network reduces the effects of internal concentration polarization (ICP)

caused by the thick support layers of reverse osmosis membranes. This membrane is

introduced as the advanced generation of forward osmosis membranes in the HTI hydration

chambers (HTI, 2013).

Construction of forward osmosis membrane with proper function is one of the research

priorities on the forward osmosis. The performance of existing commercial membranes

(cellulose triacetate asymmetric membrane made by HTI Company) is generally limited by

low permeability and salt rejection. The thin-film composite membrane with high

performance is composed of a thin polyamide layer (salt rejection layer) and a porous sub-

layer (Mi and Elimelech, 2008). In general, the membranes with high separation power should

be as the flat sheets with hollow fiber configuration. The hollow fiber membranes have higher

potential than the flat sheet membranes due to the larger surface to volume ratio as well as the

self-support ability.

Since the sheet membranes made by the HTI is the only available forward osmosis

membrane in the commercial markets, the membrane module configuration will be in the

forms of frame and plate or spiral screw. Based on the literature on the commercialization of

forward osmosis membrane with hollow fiber for application in forward osmosis process, the

corresponding membrane module should also be consistent with this type of membrane

(Wang et al, 2010; Wang et al, 2009; Shi et al, 2010).

2.1.1. Membrane fouling

The average diameter of PBI membrane pores is modified in order to reach the dimension of

0.29 mm with Molecular weight cut-off (MWCO) of 354 Dalton (DA) in order to improve

the separation of electrolytes (usually the bivalent electrolytes such as Na2SO4 and MgCl2,

MgSO4) and solvents with low molecular weight. The surface modification of this membrane

is simply achievable by wetting (immersing) the membrane made in Poly-Xylene Di-hydrate

for a certain time. Based on the obtained results and depending on the degree of surface

modification, the removal efficiency is achievable over 95% for MgCl2 (1 molar feed

solution) compared to 75% for unmodified PBI membrane. However, due to the tighter pores

in the membrane, the water flow is reduced, and a third of water flow efficiency is not

modified compared with PBI membrane. Despite the fact that the electrolytic removal

efficiency is improved, there is a need for more work to reduce ICP. This study seeks to

introduce the membrane vibration as a way to reduce fouling and increase the percentage of

heavy metals; hence, we compare the vibration and non-vibration of membrane vibrator and

different numbers of vibration and parameters which affect the decreasing and increasing

percentage of heavy metal removal from the membrane.



2.2. Draw solution

The concentrated solution on the membrane leakage side is the driving force in the FO

process. The studies have considered different names for this solution including the draw

solution, osmotic agent, osmotic intermediate, stimuli solution, osmotic motor, sample

solution or the brine. When the draw solution is selected, the most important criterion is that

this material has higher osmotic pressure than the feed solution. In recent years, the selection

of draw solution has been on the basis of substances which are capable of creating high flow

and low diffusion in the reverse direction in the membranes. This is very important because

the inverse transmission of salt into the feed water effectively increases the operating costs of

system.

Hancock and Cath (2009) conducted a comprehensive study on the impact of operating

conditions on the feed and draw solutions of forward osmosis. This study indicates that the

polyvalent soluble substances have lower diffusion than the monovalent or unloaded soluble

substances. In a study by Achili et al. (2010) on electronic draw solutions, a protocol is

prepared for selection of suitable inorganic draw solution. 14 draw solutions are listed by

protocol, and seven suitable draw solutions are identified based on modeling and laboratory

tests. Different chemicals called the substances dissolved in draw solution are proposed and

tested. Batchelder proposed the use of sulfur dioxide solution as the draw solution in FO for

seawater desalination (Batchelder, 1965). Glew gave the idea of using a mixture of water and

gas (such as sulfur dioxide) or liquid (such as fatty alcohols) as the draw solution offered in

FO (Glew, 1965). He was also the first researcher who proposed the recovery of draw solution

combined with FO process. Frank used ammonium sulfate solution (Frank, 1972), Kravath

and Davis used glucose solution (Kravath and Davis, 1975), Stache applied the concentrated

fructose solution (Stache, 1989), and Kessler and moody used a mixture of glucose and

fructose (Kessler and moody, 1976) in the FO process for seawater desalination.

McGinnis provided the two-stage FO process by using the substance solubility at different

temperatures and also proposed KNO3 (potassium nitrate) and SO2 (sulfur dioxide) solutions

as the draw solutions in seawater desalination (McGinnis, 2002). According to the new FO

applications applied by McGinnis et al, the combination of ammonia and carbon dioxide

gases in certain proportions for heat removal of ammonium salts produces high concentrations

of draw solution. This method created the draw solution with osmotic pressure over 250 atm

for FO process and it allowed the unprecedented recovery of drinking water from

concentrated salty feed (Aaberg, 2003; Loeb, 2001).

3. RESEARCH METHOD

3.1. Forward osmosis membrane

In this research, the tests apply the forward osmosis membrane of cellulose triacetate (CTA)

made by HTI Company. This type of membrane is very unique compared with the other semi-

permeable membranes (RO membranes) and it is the best membrane in the field of forward

osmosis membrane process (Mccutcheon et al., 2006; Cath et al., 2006).

3.2. Feed and draw solution

All measured samples are sent to the laboratory for determining the percentage of removal,

and thus the final approval. Magnesium chloride (25 g/Lit), potassium chloride (15 g/Lit) and

ammonium bicarbonate (8 g/Lit) are used for draw solution. The osmotic pressure is

calculated for feed and draw solutions at temperatures of 14 and 24 degrees Celsius through

OLI software.




HgCl2 (Mercury (II) chloride) +deionized water is used in a test for removal of mercury.

The concentration of mercury in the feed solution is evaluated in three steps (0.5, 1 and 2

mg/Lit). Pb (No3)2 (Lead (II) nitrate) + deionized water is used to test the removal of lead.

The concentration of lead in the feed solution is evaluated in three steps (1, 2 and 4 mg/Lit).

3.3. The experimental pilot characteristics of forward osmosis and the operating

conditions

The pilot should be designed and built in a way that the experimental conditions are

consistent with operating conditions in order to achieve the accurate and reliable results.

Given the numerous restrictions in terms of preparation and use of membrane and draw

materials, this research is seeking to design and examine the target pilots by the best method.

The supporting plastic meshes are used on both sides to protect and maintain the test

conditions with and without vibration. Each of the feed and draw solutions are flowed in

distinct channels on both sides of membrane. The flow inside in the channels is retained

inside the path by the height adjustment conditions, the solenoid valve and flow meters in the

form of steady flow on both sides.

The reservoirs of feed and draw flows are constant at temperatures of 14 and 24°C; and an

automatic system is applied to retain the conditions for maintenance of osmotic pressure of

draw solution; and it retains this osmotic pressure at a constant level as soon as applying the

flow and osmotic pressure drop by injection of draw solution to a necessary extent to draw

solution reservoir. Figure 3 shows a schematic image of applied pilot in forward osmosis

system with the following components:

Draw solution reservoir containing Magnesium chloride (Mgcl2), potassium chloride

(Kcl), and ammonium bicarbonate (NH4HCO3)

Draw solution reservoir containing mercury II chloride and Lead(II) nitrate+ deionized

water

The Cellulose triacetate (CTA) membrane made by HTI company

Pneumatic vibrator of membrane with revolutions of 6000, 10000 and 14000 for each

stage of vibration 1, 2, 3

PH meter of HANNA pen model

Digital thermometer of Thermo-TA: 288KTJ

A&D laboratory scale model GH202 with precision of 0.00001 g

Control panel for controlling the solenoids and membrane vibration motor

The chemicals by Merck Company of Germany are utilized for FO tests.



Figure 3 Schematics of forward osmosis setup

3.4. Forward osmosis test procedure

All tests about forward osmosis are performed with at least two repeats verification. The

output concentration and subsequently the percentage of removal are applied for reflecting the

results of feed solution. The percentage of removal can be calculated according to the

following equation:

Magnesium chloride, potassium chloride and ammonium bicarbonate solutions are used

for mercury and lead removal test with concentrations of 25, 15 and 8 grams per liter and

concentration of mercury in the feed solution in three steps (0.5, 1 and 2 mg/Lit) and lead

concentration in the feed solution in three steps (1, 2 and 4 mg/Lit). The vibration test is done

for each revolution of vibration motor cycles with the same conditions. In some kinds of

fouling, the membrane is excluded in non-cleaned state for evaluation, and microscopic tests

and imaging.

3.5. Evaluation of flux mass transfer in forward osmosis

The membranes are tested in both directions of AL-FS (active membrane surface next to the

feed solution) and AL-DS (active membrane surface next to the draw solution). Water flux

leakage by changing the volume of draw solution is calculated as follows.

(1)

In equation (1), is the water flux leakage (in Litr/m2h); ΔV is the change of draw

solution volume (Litr); Δt is the time duration based on the hours (h); and is the

membrane cross section (m2). The diffusion of returned salt from the draw solution to the feed

solution is measured by changing the amount of salt in the feed solution.

(2)

In the equation (2), is the amount of returned salt diffusion; and are respectively

the final and initial volumes of feed solution (Litr), and finally and are the initial and

final concentrations of feed solution (mol/Litr).

4. RESEARCH RESULTS

4.1. Evaluation of draw solution effect on removal of contaminants at the lowest

and highest levels of input concentration

The type of draw solution at the lowest concentration of contaminants can be evaluated as an

effective parameter in selection of draw solutions type. For removal of mercury contaminant,

the Ammonium bicarbonate solution is put at the first rank among three vibrations before the

vibration. Magnesium chloride is put in the second rank and it has the removal percentage

higher than Potassium chloride from the pre-vibration to the second vibration. All three

solutions have the same removal percentage in the second vibration, but in the third vibration,

Potassium chloride has higher removal percentage in tests due to its declining procedure until

the third vibration. The lead contaminant removal is different from mercury. According to the

previous studies, the draw solution of Magnesium chloride has the highest efficiency before

the vibration and in the first and second vibration, but it has the severe decline in the third

vibration, and thus it is put in the lowest level of contaminant removal. Ammonium

bicarbonate is put in the second position at the stages without the vibration and during the first




and second vibration. In the third vibration, it is put in the first rank with a more gentle slope

of reduction than the other solutions at the third stage. Potassium chloride has the lowest

ability to remove the contaminants at three stages and before the vibration. The removal of

contaminant removal with very high slope in Magnesium chloride is due to its higher osmotic

pressure than the other solutions. The lower slope for reduced ability to remove the

contaminants can be understood according to the same reason. These results are presented in

Figure 4.

Figure 4 Evaluated impact of different types of draw solutions on the removal of mercury and lead at

the lowest concentration of contaminants and temperature of 14 °C

Unlike the lowest concentration of Mercury contaminant removal in Ammonium

bicarbonate, it is put in the last rank before the vibration and among 2 vibrations, but its

declining procedure has a gentle slope like the osmotic process; hence, the third vibration

reaches the highest removal rate. However, magnesium chloride has the highest percentage of

removal before to the second vibration, and it has the higher ability of reduction due to the

higher osmotic pressure. Potassium chloride is in the middle and has higher removal

percentage than Ammonium bicarbonate in high concentrations and without vibrations and

with vibrations with a few revolutions; and it is an appropriate draw solution. The removal of

Lead contaminant is totally different from Mercury. Ammonium bicarbonate has the highest

efficiency at all stages of test and it has a very limited decline in the third vibration, so that it

has the highest ability to remove the contaminants. Magnesium chloride is put in the second

rank in the state without vibration and with first and second vibration. In the third vibration, it

is put in the last rank in terms of slope for reduction of removal compared to the other

solutions. Potassium chloride is put in the lowest rank of ability to remove the contaminants

almost at three stages and also before the vibration.

The different performance of Ammonium bicarbonate in low and high concentrations and

also different contaminants can be evaluated according to the molecular structure and mass

transfer. The impact of draw solution type on the percentage of concentration removal is

evaluated in the lowest and highest concentrations of contaminants in input feed solution of

tests at the temperature of 24°C. The results do not indicate a significant change in the type of

draw solution. The growth and decline rates for the ability to remove the Lead and Mercury

contaminants in the highest concentrations are shown in Figure 6.



Figure 5 Graphs for study on the impact of different types of draw solution on the removal of mercury

and lead in the highest concentrations and temperature of 14°C

4.2. Assessment of solution temperatures in removal of contaminants

According to the diagrams above and since Magnesium chloride has the less unbalance in

behavior and higher stable output, it is considered as an appropriate draw solution for

temperature assessment. The tests are done for determining the temperature effects on the

ability to remove the contaminants in three different concentrations of contaminants in feed

solution and two temperatures of 14 and 24 °C in both solutions. The output diagrams are

shown in Figure 6.

According to the diagrams and output results, the removal of mercury contaminant is

clearly obvious. The significant difference indicates the higher ability to remove the

contaminants at higher temperatures. At 24°C, all three different concentrations removed the

contaminant at the level higher than the temperature of 14 °C. On the other hand, the removal

ability is reduced by increasing the concentration of contaminants in the feed solution. The

same process is seen in removal of Lead contaminant.

Figure 6 Graphs for study on the impact of temperature changes on the ability to remove mercury and

lead contaminants at temperatures of 14 and 24°C

4.3. Evaluated impact of contaminant concentrations in the feed solution

Like the temperature and type of solution, the concentration of input feed solution can be

considered as one of the main factors in determining the efficiency of method and percentage

of removal. The impact of Molarity in draw solutions on the removal ability can be assessed

according to the constant temperature at 14°C and the lowest instability in draw solution with




potassium chloride and magnesium chloride. In the field of removed mercury contaminant,

magnesium chloride has the highest ability to remove mercury in the concentration of 0.5

Mg/Lit, and then the removal ability is reduced to 1 Mg/Lit and 2 Mg/Lit due to the increased

concentration of mercury in the feed solution.

It should not be noted that Magnesium chloride has higher ability than potassium chloride

in removal of mercury as shown in the figure. However, the impact of changed input

contaminant concentration on the removal percentage is higher than the draw solution. The

draw solution of Potassium chloride in Mercury concentration of 0.5 Mg/Lit has higher ability

than Magnesium chloride with Mercury concentration of 1 Mg/Lit, and the same process is

seen in change of concentration. The changes in removal of lead contaminants follow the

same process. Figure 7 shows the diagrams for impact of feed solution contaminant

concentrations on the ability to remove mercury and lead.

Figure 7 Study on the impact of concentration change in feed solution on the ability to remove

mercury and lead contaminants at temperature of 14 °C

4.4. Relationship between the initial flux and concentration of draw solution

Previous studied on the forward osmosis process had led to limited achievements in water

flux in lower feed solution and also feed solution with low concentration (Ng et al., 2006).

This research performs the tests on the behavior of initial water flux in diversity of draw

solution and correspondingly the diversity of contaminant concentration in the feed solution.

The results are presented as follows. As shown, the diffusion of initial water flux is

considered as a function of osmotic pressure; and Magnesium chloride has the highest level of

initial flux due to the higher osmotic pressure in different concentrations. Accordingly,

Potassium chloride has the medium initial flux since the osmotic pressure of its draw solution

is at medium level; and Ammonium bicarbonate is put in the last rank among three solutions.

These procedures are exactly similar to what is predicted.

The impact of input contaminant concentration in the feed solution on the amount of

initial flux is another procedure in this field. According to the figures, the initial flux is

reduced by increasing the input contaminant concentration of feed solution. This reduction is

limited and very low, so that it will not lead to a significant difference in values according to

the type of draw solution. These procedures are observable in the same ratios for removal of

Lead contaminants from water. These procedures and values are shown in Figure 8.

This test is also done for the impact of contaminant concentration in input feed solution on

the initial flux at the temperature of 24°C, but it has not led to results different from 14°C.



Figure 8 Study on the impact of contaminant concentration and the type of draw solution on the initial

flux at the temperature of 14 °C

4.5. Relationship between the osmotic pressure, type of draw solution and

concentration of contaminant in the feed solution

The solution-diffusion model (Wijmans and Baker, 1995) has made predictions about the

reduction of osmotic pressure driving force and flow flux by considering the concentration of

feed and draw solution concentrations. According to the results of our test, Figure 9 shows the

differences in amount of flux for osmotic pressures, so that the higher feed solution

concentration will lead to the lower input flow flux at the longer time interval. However, the

osmotic pressure will not be changed by increasing the contaminant concentration, and thus

the osmotic pressure, which is a key parameter in driving force of membrane, is only

dependent on the type of draw solution and it remains constant in different concentrations of

input feed solution contaminant. Magnesium chloride with osmotic pressure of 17.84 atm and

Ammonium bicarbonate with 4.33 atm are put in the highest and lowest ranks of driving

force. On this basis, the osmotic pressure is dependent on the type of draw solution and

independent of feed solution contaminant concentration. The diagrams are shown in Figure 9.

Figure 9 Assessment of feed solution contaminant concentration on the osmotic pressure in removing

the mercury and lead contaminants

5. SUMMARY AND CONCLUSION

Forward osmosis technology development is one of the ways to reduce the operating costs of

desalination process and other processes. This technology is faced with challenges for its

development in spite of numerous benefits. Therefore, a lot of studies are now conducting on

this field around the world. Given the low cost of forward osmosis process and also the




minimum energy consumption compared with other desalination processes, the consumers of

underground salty and brackish water will be faced with bright future.

This research evaluates the impact of different parameters namely the temperature, type of

draw solution, feed solution contaminant concentration, and effective osmotic pressure on the

efficiency of mercury and lead contaminant removal. The increase in the temperature and

effective osmotic pressure directly increases the percentage of removal and efficiency of Lead

and Mercury contaminants from feed solution, but the increase in the contaminant

concentration of feed solution inversely reduces the efficiency of removal.

The membrane fouling phenomenon will reduce the membrane efficiency and removal

performance. This research tests and evaluates the efficiency of membrane vibration process

for removing fouling and increasing the efficiency of removal at three stages with revolutions

of 6000, 10000, and 14000 per minute under the same conditions for feed and draw solution

compared to the state without the vibration. According to the results, the efficiency and

removal percentage are increased in revolutions of 6000 and 10000, which represent the

vibration of first and second stages; and the decline of efficiency and increase in percentage of

contaminant in output solution are seen at the third stage with revolution of 14000, and this

reduction is different according to different amounts of osmotic pressure in draw solution, and

it can be analyzed and evaluated as an effective parameter in selecting the optimal draw

solution and feed solution concentration.

According to the challenges for water in our country, there is a need for development of

more comprehensive studies on the conservation of water resources and new and competing

technologies of desalination such as the forward osmosis.

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quality improvement of water resources by removal … · reverse osmosis (ro) process. reverse...

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