feasibility of producing sodium hypochlorite for water ... · nowadays. desalination has become...
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1
Feasibility of Producing Sodium Hypochlorite for
Water Disinfection Purpose Using Seawater
Desalination Brine
لمعالجة المياه هيبوكلورايت الصوديوم النتاجدراسة جدوى مياه البحرلتحلية ال لمحلول الملحي الناتج عن عمليةا باستخدام
By:
Mohammed Rezeq Rashad Al Dalou
Supervised by:
Dr. Fahid Rabah
Associate Prof. Water & Environmental
Engineering
A thesis submitted in partial fulfilment of the requirements for the degree of
Master of Civil Engineering-Infrastructure
October/2017
زةــغب ةــالميــــــة اإلســـــــــامعـالج
البحث العلمي والدراسات العليا عمادة
الهنـــــدســـــــــــــــــــــة ة ــــــــليـــك
هندسة مدنية –ماجستير بنية تحتية
The Islamic Universityof Gaza
Deanship of Research and Postgraduate
Faculty of Engineering
Master of Infrastructure-Civil Engineering
2
إقــــــــــــــرار 1
أنا الموقع أدناه مقدم الرسالة التي تحمل العنوان:
دراسة جدوى النتاج الصوديوم هيبوكلورايت لمعالجة المياه باستخدام المحلول الملحي الناتج عن عملية التحلية لمياه البحر
Feasibility of Producing Sodium Hypochlorite
for Water Disinfection Purpose Using Seawater
Desalination Brine
إليه أقر بأن ما اشتملت عليه هذه الرسالة إنما هو نتاج جهدي الخاص، باستثناء ما تمت اإلشارة
حيثما ورد، وأن هذه الرسالة ككل أو أي جزء منها لم يقدم من قبل اآلخرين لنيل درجة أو لقب
علمي أو بحثي لدى أي مؤسسة تعليمية أو بحثية أخرى. وأن حقوق النشر محفوظة للجامعة
غزة. –اإلسالمية
Declaration
I hereby certify that this submission is the result of my own work,
except where otherwise acknowledged, and that this thesis (or any part
of it) has not been submitted for a higher degree or quantification to any
other university or institution. All copyrights are reserves to IUG.
:Student's name ق رشاد صالح الدلومحمد رز اسم الطالب:
:Signature محمد رزق رشاد صالح الدلو التوقيع:
:Date 2017أكتوبر التاريخ:
I
Abstract
Scarcity of water has become one of the largest challenges to human beings
nowadays. Desalination has become widely use to provide safe and clean water in
many countries. Brine disposal or management is a major environmental challenge to
most communities. This research investigated a method for brine treatment by using
technology of on-site generation of sodium hypochlorite and thus reducing the
quantity of the disposed brine to the sea. The batch experiment investigated the
characteristics of producing sodium hypochlorite for disinfection purposes, thus
seven main factors were investigated in brine samples: electrolysis time, current
intensity, surface area ratio, type of rods, distance between rods, stability of sodium
hypochlorite, and stability of electrode rod. The best condition for generation sodium
hypochlorite was found by using graphite electrodes, with diameter 1.3cm, the space
between the electrodes was 1cm, and the electrolysis time was 120Min, at voltage
12V and at current density of 176.5mA.cm-2
with 25oC ambient temperature. The
best effective concentration value of sodium hypochlorite at the previous conditions
was 2.17% of brine concentration. The research is also studying the fesability of
using on-site generation of sodium hypochlorite among other chlorination options
that are commercial bulk hypochlorite with (12%-15%) concentration and bubbling
chlorine gas into dilute sodium hydroxide which generate sodium hypochlorite with
concentration (3%-6%). The research studied four aspects affecting on the choosing
of the best chlorination procces that are the environmental, health and safety aspects,
the economical aspects, the political aspects and the operational aspects. The
research concludes that using sodium hypochlorite generated on site was the most
cost-effectiveness option among other options and it recommends running it instead
of the commercial bulk hypochlorite which is used in Gaza Strip nowadays.
Key words: On-site generation, Sodium hypochlorite, Brine, Electrolysis, seawater
Gaza Strip.
II
الملخص
أصبحت ندرة المياه أحد أكبر التحديات التي يواجهها البشر في الوقت الحاضر. وقد أصبحت تحلية المياه
التخلص من المياه ويمثل والنظيفة في العديد من البلدان. تستخدم على نطاق واسع لتوفير المياه اآلمنة
وتهدف هذه الدراسة لمعالجة المحلول حديا بيئيا كبيرا لمعظم المحطات.المالحة الناتجة من تحلية المياه ت
ذلك بتحقيق فائدة مزدوجة من انتاج هيبوكلوريت الصوديوم في الموقع ألغراض التطهير والتقليل من و الملحي
إنتاج هيبوكلوريت الصوديوم خصائصالتجربة درستوقد .الذي يتم ضخه إلى البحر المحلول الملحي كمية
سبعة عوامل رئيسية في عينات محلول ملحي: زمن التحليل الكهربائي، شدة ، حيث تم دراسة ألغراض التعقيم
ر التيار، المساحة السطحية، نوع األقطاب، المسافة بين األقطاب، استقرار هيبوكلوريت الصوديوم، استقرا
فيتأفضل قيمة لتركيز الهيبوكلوريت الصوديوم باستخدام أقطاب الجراكانت األقطاب من التأكل و االهتراء.
ند شدة تيار فولت وع12دقيقة، و جهد 120سم بين األقطاب، عند زمن 2سم، بمسافة 1.3 قطر ذات
هيبوكلوريت قيمة تركيزحيث كانت درجة مئوية. 25درجة حرارة محيطة ب و ، 2ملم أمبير/سم176.5
استخدام كما يدرس البحث قابلية ملحي.المحلول ال٪ من تركيز 2.1الصوديوم في الظروف السابقة
األخرى التي هي هيبوكلوريت من بين خيارات الكلور في الموقع إنتاج هيبوكلوريت الصوديوم تكنولوجيا
غاز الكلور إلى هيدروكسيد الصوديوم المخفف ضخ كذلك٪( و 15-٪ 12تركيز ) ذي الصوديوم التجاري
أربعة جوانب تؤثر على اختيار ٪(. وقد درس البحث 6-٪ 3الذي يولد هيبوكلوريت الصوديوم مع تركيز )
ب أفضل أنواع المعالجة بالكلورة وهي الجوانب البيئية، والصحة والسالمة، والجوانب االقتصادية، والجوان
ويخلص البحث إلى أن استخدام هيبوكلوريت الصوديوم المتولد في الموقع كان السياسية، والجوانب التشغيلية.
تشغيله بدال من هيبوكلوريت لفة من بين الخيارات األخرى، وتوصي بالخيار األكثر فعالية من حيث التك
التجاري الذي يستخدم في قطاع غزة في الوقت الحاضر. صوديومال
III
Dedication
This research is dedicated to:
My father and my mother…
My brothers and sisters…
My family for their encouragements …
All my friends and colleagues…
IV
Acknowledgment
Thanks to Allah the compassionate the merciful for giving me patience and strength
to accomplish this research.
I would like to express my deep gratitude to my supervisor (Dr. Fahid Rabah) for his
encouragement, continuous support, fruitful assistance and vision which inspired me
in accomplishing this research.
My appreciation is also extended to the IUG for giving me the opportunity to carry
out this study.
Furthermore, great thanks are also to my colleagues and lecturers in
the Engineering Faculty and the Civil Engineering Department in particular for their
continual encouragement and support.
Thanks go to Mr. Aladdin Ajubb and Ahmed Jendia from environmental and earth
science department for providing me all the necessary information that was helpful in
accomplishing this work.
My appreciation also is going to the MEDRC for giving me the opportunity to carry
out this study and to support me financially.
Finally, my most appreciations are to my parents, brothers and sisters for their full
support, encouragement and patience that give me the power all life.
V
Table of Contents
ABSTRACT ............................................................................................................................. I
II ...................................................................................................................................... الملخص
DEDICATION ...................................................................................................................... III
ACKNOWLEDGMENT ..................................................................................................... IV
TABLE OF CONTENTS ...................................................................................................... V
LIST OF TABLES ............................................................................................................... IX
LIST OF FIGURES .............................................................................................................. X
LIST OF ABBREVIATIONS.............................................................................................. XI
CHAPTER 1 INTRODUCTION .......................................................................................... 1
BACKGROUND ............................................................................................................. 1 1.1
STATEMENT OF PROBLEM ........................................................................................... 2 1.2
OBJECTIVES ................................................................................................................. 3 1.3
THESIS STRUCTURE ..................................................................................................... 4 1.4
2 CHAPTER 2 LITERATURE REVIEW ......................................................................... 5
2.1 INTRODUCTION ............................................................................................................ 5
2.2 DESALINATION IN GAZA STRIP .................................................................................... 6
2.3 DEFINITION OF BRINE .................................................................................................. 7
2.4 CHARACTERISTICS OF BRINE ...................................................................................... 9
Temperature and Salinity .................................................................................. 10 2.4.1
Biocides ............................................................................................................. 10 2.4.2
Heavy metal ....................................................................................................... 11 2.4.3
Antiscalants ....................................................................................................... 11 2.4.4
Coagulants (RO plants) ..................................................................................... 11 2.4.5
Antifoaming agents (thermal plants) ................................................................. 12 2.4.6
Cleaning chemicals ........................................................................................... 12 2.4.7
2.5 BRINE MANAGEMENT ............................................................................................... 13
2.5.1 Deep Injection Wells .......................................................................................... 13
2.5.2 Irrigation Systems .............................................................................................. 14
2.5.3 Evaporation Ponds ............................................................................................ 15
2.5.4 Salt Recovery/Harvesting Systems (or Salt Harvesting) ................................... 17
VI
2.5.5 Direct Discharge of the Brine at the Coastline ................................................. 18
2.5.6 Discharging the Brines by a Long Pipe Far into the Sea .................................. 18
2.5.7 Direct discharge of Brine through the Outlet of the Power Station’s Cooling
Water……………………………………………………………………………………… ...... ..20
2.5.8 Direct Discharge to sewage system ................................................................... 21
2.5.9 Direct Discharge to wastewater treatment plant outfall. .................................. 21
2.6 ON-SITE SODIUM HYPOCHLORITE .............................................................................. 22
2.6.1 Sodium hypochlorite .......................................................................................... 22
2.6.2 What is on-site sodium hypochlorite? ............................................................... 22
2.6.3 The characteristic and significance of the sodium hypochlorite ....................... 24
2.7 BASIC OPERATING THEORY ....................................................................................... 27
2.8 THEORETICAL CONSIDERATIONS .............................................................................. 27
2.9 THE IMPACTS OF ON-SITE HYPOCHLORITE GENERATION ......................................... 30
2.10 LITERATURE REVIEW ON ONSITE-GENERATION OF SODIUM HYPOCHLORITE ............ 31
2.10.1 Examples for using on-site sodium hypochlorite ............................................... 34
2.10.2 Factors effects on sodium hypochlorite generating ........................................... 36
2.11 KEY COMPONENTS OF AN ON-SITE GENERATION OF SODIUM HYPOCHLORITE SYSTEM ........... 39
A- System Control Panel ........................................................................................ 39
B- Power Supply / Rectifier .................................................................................... 39
C- Electrolyze Cell ................................................................................................. 39
E- Water Softener ................................................................................................... 39
F- Brine Tank (Salt Saturator) ............................................................................... 39
G- Brine Pump ........................................................................................................ 40
H- Sodium Hypochlorite Storage Tank ................................................................... 40
3 CHAPTER 3 MATERIALS AND METHODS ............................................................ 41
3.1 INTRODUCTION .......................................................................................................... 41
3.2 MATERIALS AND CHEMICALS ................................................................................... 41
APPARATUS AND GLASSES ........................................................................................ 41 3.3
EXPERIMENTAL PROGRAM ........................................................................................ 42 3.4
3.4.1 Experimental set up ........................................................................................... 43
3.4.2 Hardness removal .............................................................................................. 45
ANALYTICAL METHODS ............................................................................................. 46 3.5
Colourmetric Method ........................................................................................ 46 3.5.1
Iodometric method ............................................................................................. 49 3.5.2
3.5.3 Samples Collection ............................................................................................ 50
VII
3.6 CALCULATIONS ......................................................................................................... 55
4 CHAPTER 4 RESULTS AND DISCUSSION .............................................................. 56
INTRODUCTION .......................................................................................................... 56 4.1
CHARACTERISTICS OF SEAWATER, PRODUCT AND BRINE OF AL-BASSA SEAWATER 4.2
DESALINATION PLANT…………………………………………………………… ............ 56
RELATIONSHIP BETWEEN RUNNING TIME AND EFFECTIVE CONCENTRATION OF 4.3
NAOCL…………………………………………………………….. ................................. 57
RELATIONSHIP BETWEEN CURRENT DENSITY AND PROCESS EFFICIENCY ................. 60 4.4
RELATIONSHIP BETWEEN SURFACE AREA RATIO, CURRENT DENSITY AND PROCESS 4.5
EFFICIENCY……………………………………………………………… ......................... 64
EFFECTS OF ELECTRODE MATERIAL .......................................................................... 65 4.6
EFFECTS OF INTER-ELECTRODE SPACING ................................................................. 67 4.7
EFFECTS OF TEMPERATURE ....................................................................................... 68 4.8
STABILITY OF SODIUM HYPOCHLORITE ..................................................................... 68 4.9
OTHER FACTORS RELATIONS ..................................................................................... 69 4.10
TOTAL DISSOLVED SOLID EFFECTS ........................................................................... 71 4.11
POWER CONSUMPTION ............................................................................................... 72 4.12
FEASIBILITY OF PRODUCING SODIUM HYPOCHLORITE FROM SEAWATER BRINE ....... 56 4.13
Scenario 1 .......................................................................................................... 56 4.13.1
Scenario 2 .......................................................................................................... 56 4.13.2
Scenario 3 .......................................................................................................... 56 4.13.3
THE ENVIRONMENTAL, SAFETY AND HEALTH ANALYSIS.......................................... 57 4.14
Scenario 1 .......................................................................................................... 57 4.14.1
Scenario 2 .......................................................................................................... 57 4.14.2
Scenario 3 .......................................................................................................... 58 4.14.3
THE POLITICAL ANALYSIS ......................................................................................... 58 4.15
Scenario 1 .......................................................................................................... 58 4.15.1
Scenario 2 .......................................................................................................... 59 4.15.2
Scenario 3 .......................................................................................................... 59 4.15.3
THE PROCESS OPERATION ANALYSIS ......................................................................... 60 4.16
Scenario 1 .......................................................................................................... 60 4.16.1
Scenario 2 .......................................................................................................... 60 4.16.2
Scenario 3 .......................................................................................................... 61 4.16.3
THE ECONOMICAL ANALYSIS .................................................................................... 61 4.17
Scenario 1 .......................................................................................................... 61 4.17.1
VIII
Scenario 2 .......................................................................................................... 62 4.17.2
Scenario 3 .......................................................................................................... 62 4.17.3
COMPARING THE RESULTS ......................................................................................... 62 4.18
CHAPTER 5 CONCLUSIONS AND RECOMMENDATIONS ..................................... 82
CONCLUSIONS ........................................................................................................... 82 5.1
RECOMMENDATIONS ................................................................................................. 83 5.2
REFERENCES ..................................................................................................................... 84
APPENDIX 1: RELATION BETWEEN CURRENT DENSITY AND PRODUCTION
OF NAOCL. .......................................................................................................................... 88
APPENDIX 2: RELATION BETWEEN SURFACE AREA RATIO AND
PRODUCTION OF NAOCL. ........................................................................................... 108
APPENDIX 3: STABILITY OF NAOCL. ....................................................................... 109
IX
List of Tables Table (2.1): Sureface Water Disposal Problems and Mitigation ............................... 20
Table (3.1): Relation between current density (A) and time (min) for graphite rod
under certain conditions. ............................................................................................ 51
Table (3.2): Relation between current density (A) and time (min) for aluminium rod
under certain conditions. ............................................................................................ 52
Table (3.3): Relation between current density (A) and time (min) for copper rod
under certain conditions. ............................................................................................ 53
Table (3.4): Relation between current density (A) and time (min) for stainless steel
rod under certain conditions ...................................................................................... 54
Table (4.1): characteristics of water into and out of Al-Bassa desalination plant ..... 56
Table (4.2): Stability of rods material during operation ............................................ 67
Table (4.3): The reduction of the concentration of sodium hypochlorite .................. 69
Table (4.4): Optimum conditions for production of hypochlorite ............................. 70
Table (4.5): Result of sodium hypochlorite ............................................................... 72
Table (4.6): Comparison between the three chlorination options. ............................. 63
X
List of Figures Figure (2.1): Breakpoint chlorination curve. ............................................................. 25
Figure (2.2): Typical system configuration. .............................................................. 40
Figure (3.1): Schematic diagram of production of sodium hypochlorite process ..... 44
Figure (3.2): Photographic pictures for the electrocoagulation system ..................... 45
Figure (3.3): Free Chlorine Absorptivity at 20 C ...................................................... 47
Figure (3.4): Stock solution curve ............................................................................. 48
Figure (4.1): Relation between electrolysis time and effective concentration of
NaOCl using graphite electrodes ............................................................................... 57
Figure (4.2): Relation between time of electrolysis and effective concentration of
NaOCl using aluminium electrodes. .......................................................................... 58
Figure (4.3): Relation between electrolysis time and effective concentration of
NaOCl using cooper electrodes. ................................................................................ 59
Figure (4.4): Relation between electrolysis time and effective concentration of
NaOCl using stainless steel electrodes. ..................................................................... 60
Figure (4.5): Relation between current density and NaOCl effective concentration
using graphite electrode at 120min. ........................................................................... 61
Figure (4.6): Relation between current density and NaOCl effective concentration
using Aluminum electrode at 60min. ......................................................................... 62
Figure (4.7): Relation between current density and NaOCl effective concentration
using Copper electrode at 30min. .............................................................................. 63
Figure (4.8): The deformation of Copper Electrode shape by increasing current
density. ....................................................................................................................... 63
Figure (4.9): Relation between current density and NaOCl effective concentration
using Stainless steal electrode at 30min. ................................................................... 64
Figure (4.10): Relation between surface area ratio and concentration of NaOCl ...... 65
Figure (4.11): The effect of different electrode material on the production of sodium
hypochlorite ............................................................................................................... 66
Figure (4.12): Relation between hypochlorite concentration and inter electrode
spacing. ...................................................................................................................... 67
Figure (4.13): Effect of Temperature on NaOCl generation. .................................... 68
Figure (4.14): Relation between TDS concentration and time (min). ....................... 71
Figure (4.15): Relation between temperature and time (min). .................................. 71
XI
List of Abbreviations
APHA American Public Health Association
AWWA American Water Works Association
AWWARF American Water Works Association Research Foundation's
Ceff Effective Concentration
CMWU Coastal Municipalities Water Utility
FRC Free Residual Chlorine
IS Indian Stadard
OSGs On-site Generation
MCM Million Cubic Meters
NaOCl Hypochlorite Sodium
NRC Norwegian Refugee Council
MSF Multi-stage flash
PCBS Palestinian Central Bureau of Statistics
PWA Palestinian Water Authority
PWS Public Water Systems
RMP Risk Management Plan
RO Reverse Osmosis
TDS Total Dissolved Solids
U.S. EPA U.S. Environmental Protection Agency
WEF Water Environment Federation
WHO World Health Organization
WWTP WasteWater Treatment Plant
Chapter 1
Introduction
1
Chapter 1
Introduction
Background 1.1
Scarcity of water has become one of the largest challenges to human beings
nowadays. Providing clean drinking fresh water is a high priority confrontation in
many countries e.g. Middle East and North of Africa. In the last 20 years, an
evolution has gradually accelerated in the field of construction of seawater
desalination plants to meet the shortfall in the water supply among countries, many
of the RO and thermal desalination plants have been established to overcome the
problems of paucity of water to people around the world (Bohissi & Mogheir, 2015).
In Gaza Strip, Water for domestic use is suffering from a severe shortage and it will
continue in the coming years especially with a steady population growth of 3.4%
(PCBS, 2016) in a highly populated area and a high polluted ground water in the
aquifer. The sharp shortage of water resources and the increasing water demand lead
the authorities to construct a number of seawater desalination plants to fulfill the
needs of Civilians in Gaza strip.
Seawater desalination is a method that separates saline water into a stream of pure
water with low concentration of salts called "Fresh Water" and another stream of
concentrated salt solution called "Brine".
Brine is salty water, it accounts about 60% from the of residual water from
desalination plants (Alazaiza & Mogheir, 2013), usually brine has a high
concentration of salts (TDS), and sometimes a high concentration of toxic and
chemical metals which come from the various chemical treatments that aim to
control formation of mineral scale and biological growth, the constituents of brine
can significantly affect the marine environment and can destroy the aquatic life in the
seawater.
Three main seawater desalination plants are working or expected to be working
during the next years, the biggest among them is the Gaza central desalination plant,
which will produce 110Mm3/year in 2035, the produced brine will be pumped to
seawater, this huge amount of brine is a challenge to the marine life in Gaza strip
2
which is already suffering from deteriorations and sewage pumping (Bohissi &
Mogheir, 2015).
Brine management and disposal is considered one of the major challenges that faces
the seawater desalination technology in Gaza strip, the least expensive and the most
used method is to pumping the brine to the sea water, this method considered as a
non-environmental and hazardous method, and need prior treatment technologies.
Generation of sodium hypochlorite is one of the methods which are used to treat the
brine before disposing to the beach, this method is focusing in two different
directions, the first is to treat the brine and thus alleviate the damages caused by
pronation the brine into sea water, the second is to provide a substance which is
considered as a basis to sterilize water, and thus get out from the treatment process
with a significant important material in the market
This research will study the feasibility of using brine for producing Sodium
Hypochlorite (NaOCl) which is a strong disinfectant required to disinfect water or to
prevent algae formation and bio fouling in all the Desalination plants in Gaza Strip.
Statement of Problem 1.2
The disposal or management of desalination brine is an environmental challenge to
most communities. It is not only costly but also it affects the surrounding
envieronment. The rejected brine from the desalination has a high salinity rate and it
contains variable concentrations of different chemicals used on desalination process
such as anti-scale additives and inorganic salts that can affect negatively on soil,
groundwater and seas. The presence of these different chemicals can change the
salinity, alkalinity and the temperature averages of the seawater in case of pumping
the brine to seawater, and it also has the ability to cause a real unfavorable change to
marine environment. This raises the imperious need for significant dilution and
treatment for brine before it being pumped into the sea.
As we stated above Gaza central seawater desalination plant will produce a huge
amount of brine 24,400 m³/h. In addition to some other desalination plants will be
established or gotten improvement. The intended destination for the disposal of the
3
brine is the sea, and if this happen, there will be a real danger for the marine life and
environment (Tayef, Al-Najjar, Mogheir, & Seif, 2016).
Pumped brine into the sea sinks to the seabed and threatens the marine environment
beneath the sea level or it may concentrate along the shore of sea, and thus it will
affect the productivity of fisher’s resources (Purnama, Al-Barwani, & Al-Lawatia,
2003). This will affect the Palestinian life in Gaza strip since beaches and coastal
areas are considered the basic entertainment milestones for residents and the main
destination for fishing as well. Hence, it is important to handle brine generated by the
desalination process effectively and carefully. Basicly, the suggested experimental
process will aim to handle with brine in the technology of on-site generation of
sodium hypochlorite and thus reducing the quantities of the brine pumped to the sea.
Therefore, the process will aim to enhance protection for the environment besides
generating a disinfictant which is used in the desalination plant itslef. This research is
supposed to be done using the brine produced by the AlBassa Desalination Plant.
Objectives 1.3
The main goal of this research is to study the feasibility of producing Sodium
Hypochlorite for water disinfection purposes using seawater desalination brine and to
contribute in minimizing the brine quantities disposed into the sea. This goal will be
achieved through the following research objectives:
Study the characteristics of producing sodium hypochlorite by using seawater
brine; this includes the effects of seven parameters on the production of
NaOCL.
Optimizing the best conditions for producing sodium hypochlorite on site by
using brine.
Asses the feasibility of the system by conducting environmental healthy and
safety, economical, political, and operational analysis.
4
Thesis structure 1.4
The basic structure of the thesis is organized in five chapters, as follows:
Chapter One: Introduction
It includes a general background about water situation and brine status
follows by statement of the problem, objectives, methodology used in order
to achieve the objectives and thesis outline.
Chapter Two: Literature Reviews
It summarizes the literature reviews along with background information
related to seawater treatment, sodium hypochlorite production, effecting
factors on electrolysis, feasibility study and observations from the past.
Chapter Three: Materials and methods
Experimental methods, Materials and analytical methods used to determine
the concentration of sodium hypochlorite concentration, as well as the
materials are also discussed.
Chapter Four: Results and Discussions
It provides the test results and discussion.
Chapter Five: Conclusion and Recommendations
It provides a brief summary of the research findings as a conclusion followed
by future recommendations for the best practices.
Chapter 2
Literature Review
5
2 Chapter 2
Literature review
2.1 Introduction
Gaza strip is a very small area about 365 km2
(approximately 45 Km in length and 7
to 12 Km in width) located at the eastern coastal of the Mediterranean, it surrounded
by Sinai Desert in the south, the Naqab Desert in the east and the Mediterranean Sea
in the west. The population of Gaza strip is 1.85M with a growth rate of 3.2%
annually, in this regard, the population density of Gaza Strip is considered the
highest in the world (PCBS, 2016).
Gaza Strip where it is located in a region which is considered an arid to semiarid; the
rainfall begins in October until April. The annual precipitation in Gaza strip is
ranging between 230 mm in the south to 410 mm in the north while the average rate
for the annual precipitation is 327 mm/year (PWA, 2013).
Sand dunes are covering the entire coastline along Gaza strip. It rises over the sea
level by 20 to 40 m. The soil in the Gaza Strip is consisting of a clay-like material at
most. The Pleistocene granular aquifer of Gaza Strip is an extension of the
Mediterranean seashore coastal aquifer. Gaza strip begins from Beit-hanoun and
Beit-Lahia in the North and end in Rafah city in the South, and from the beach from
west to almost 10 km inland to the east. Different layers of dune sandstone, silt clays
and loams are composing a high porosity and permeable aquifer for Gaza strip,
which begins at shore and extends out to about 5 km to the west of Gaza strip,
applying a separation for the aquifer into major upper and deep sub aquifers (Aish,
2010). The aquifer of Gaza Strip within the distance of (1-3 km) from the coastline is
consisting of four sub-aquifers, and then the aquifer unifies together to form one
aquifer. The thickness of Gaza strip aquifer is ranging between 100 to 180 m, with
150 m average thickness in the East. This shallow coastal aquifer considered as the
original source of water for the domestic and agricultural uses in Gaza Strip (Alagha
& Mortaja, 2005).
6
Gaza strip suffers from a big water problem in terms of water quantity and water
quality. It lies under high conditions of blockade for land, air, and sea decreed by
Israel, this blockade limits the people on Gaza from utilizing or importing alternative
water resources. Having a high population and a polluted groundwater aquifer, in
addition to the Israeli control of Palestinian water resources, the weak storm water
collection systems and low long term rainfall average rate, this lead to create a big
gap between high demand and limited resources of water.
People in Gaza strip depend on groundwater as the main and regular source for the
domestic, agricultural, industrial, and drinking water supplies. The groundwater
quality in Gaza Strip has got a change in both vertical and horizontal directions.
Groundwater salinity (TDS: 2200 mg/l and above) is increased over time due to
seawater intrusion and mobilization of deep contaminated water resulting from
groundwater abstraction. According to the PWA, the salinity of the aquifer
groundwater is too high, and around 60% of the total underground water have a
salinity degrees which don’t meet WHO standards. In addition PWA declared that
the contamination reaches 95% of Gaza’s water supply with high levels of either
nitrate (NO3) or chloride (Cl), and puts Gaza people's lives at risk (PWA, 2014). As
a result People in Gaza Strip have started to install RO domestic units to solve the
problem the high salinity and high rates of unaccepted clorine and nitrate.
2.2 Desalination in Gaza strip
Desalination of brackish and seawater have been used by the Palestinian Water
Authority (PWA) to face water deficit and scarcity in reasonable technology and
thus, providing sustainable and safe water to people in Gaza (Sheikh, Ahmed, &
Hamdan, 2003). Nowadays, 90% or more of the residents of the Gaza Strip are
essentially depending on desalination to obtain fresh and safe drinking water.
Desalination facilities have become existed in different sizes from large seawater
plants located in different places on Gaza Strip and serve thousands of people to
home-based small brackish desalination units which supply residents with water for
small scale. The responsibility of the desalinated water distribution system lies with
7
governmental, non-governmental, Municipalities, local community forums and even
individuals.
The first RO plant in the Gaza Strip was built in 1991 in Deir Al Balah town to
desalinate brackish water and has a capacity of 45 m3/h with a recovery of 75%, then
between 1997-1998 two RO plants were constructed in Khan Younis, each had a
capacity of 50 m3/h using brackish water wells. Another two desalination plants were
built in north and middle area of Gaza strip, with a capacity of 5000 m3/d and 2400
m3/d respectively and both are fed by water from beach wells (Bohissi & Mogheir,
2015).
According to (Bohissi & Mogheir, 2015), recently, Seven public desalination plants
are distributed all around Gaza strip. The responsibility of operation lies over the
Coastal Municipal Water Utilities (CMWU), who is the water service provider in
Gaza Strip. Large numbers of people living on the middle and the south of Gaza strip
are served by these plants. There is only one sea water desalination plants which is
located in Deir Albalah city, the rest of the desalination plants are using brackish
water. Some of them have been working since 12 years, where 3 plants have been
established 4 to 5 years ago.
Currently, there are 154 private and public desalination plants distributed around all
Gaza Strip, only 48 of them are licensed by the designated authorities. The public
desalination plants have a significant performance with continuous calibration and
monitoring when it compared with small private plants due to the combined effects
of inadequate disinfection at the desalination plants, the improper handling during
distribution, and poor user storage habits (PWA & WASH partner, 2016).
2.3 Definition of Brine
Desalination process produces two current flows of water. One is called the product
water, which is desalinated water. The other line is called the brine water which
contains the salts expelled out of desalination process (Bine is also called
concentrate, reject water).
The degree of salinity for the brine is varying depending on the type of desalting
plant. Brine concentrations in the RO for Sea Water Desalination Plants are
8
approximately double or close to be double that of the natural (up to 65,000–85,000
mg/L). In other hands, the brine concentrations on the thermal MSF seawater
desalination plants are estimated to be about (50,000 mg/L). The difference returns to
the desalting process where the MSF plant effluents are mixed with cooling water
which leads to reduce the concentrations of brine on large size (Lattemann &
Höpner, 2008). In essence, Most of thermal desalination plants are used in
cogeneration with power generation, so the brine of thermal plants are plended with
cooling water discharged from the power plants. The temperature of this brine may
also increase as the effluent of discharged brine is higher in temperature than it in the
intake point. Temperature might reach +5◦C to 15◦C above ambient (Lattemann &
Höpner, 2008; Abdul-Wahab & Al-Weshahi, 2009).
Brine discharged from desalination plants has a high salinity and includes substances
and chemicals used on the backwash which containing corrosion salts, scale and
antifouling chemicals, and also pre-treatment chemicals which typically includes the
treatment against foaming, scaling, biofouling and corrosion in thermal plants, and
against scal deposits, biofouling and suspended solids in RO membrane plants. The
disposal or handling of the rejected concentrate from these sources is considered
major economic and environmental concerns, especially in regions that depend on
desalination for potable water (El-Naas, 2011).
The best handling or management of concentrate is depending on different factors
such as the location, access to the oceans and sensitive aquifers, the toxic materials
concentrations. Depending of the conditions, the best handling or disposing of
concentrate can be be directly discharge to the sea, mixing before discharge with
other waste flow, discharge into a wastewater treatment plant, pumped into lined
lagoons and allow to evaporate. Disposing of brine is considered one of the most
challenging concerns for the desalination technology. Salt harvesting and recovery of
a special type of minerals from brine are vital solutions and in some times, it may be
economically reasonable, as it reduces the costs of brine disposal (WHO, Public
Health and the Environment - Desalination for Safe Water Supply, 2007).
Two completely different processes can be used for the brine disposal. The best
process between them can be identified by the location of the plant. The two
classifications are brine disposal in inland areas and in coastal areas. The importance
9
of proper brine disposal management sometimes affects site selection for the whole
facility. Desalination of brackish water at inland locations should take into
considerations the equipment and energy required to drive the process effectively, as
well as the apporpariate management and/or disposal of the brine which is
environmentally accepted, lies under the regulations and standards and cost-effective
before setting up the facility (Swift, Lu, & Becerra, 2002). While in seawater
desalination plants, two brine discharge options can be applied, through a water
channel and a pipeline.
2.4 Characteristics of Brine
In RO desalination plants, the feed water is pressured into permeable membranes,
which refuse over 99.5% of suspended contaminants and dissolved salts in the feed
water. It produces brine with dissolved and suspended constituents that increase its
concentration by 2 to 7-fold. Different chemicals are used frequently to the system,
these chemicals depend on the characteristics of feed water in order to prevent
membrane fouling and membrane element feed channels by scales, gel-like deposits
of coagulated colloidal particles, and biofilms. In additions, regular cleaning and
flushing of the membrane can cause different in the composition of the brine
discharged. So, many chemicals can be existed on the brine concentrates forminga
complex mixtures solution (Bohissi & Mogheir, 2015).
Many kinds of chemicals are used in pre- and post-treatment process for a
desalination plant. These contain: aluminium chloride (AlCl3) or Ferric chloride
(FeCl3), that are used as flocculants to remove suspended solids existed on water; for
chlorination, Sodium hypochlorite (NaOCl) is used to protect the desalination
facilities from growing bacteria; Where to inhibit scale formation on the pipes and on
the membranes, Sodium hexa meta phosphate (NaPO3) and other kinds of anti-scale
additives are used; and to adjust the pH of the seawater, sulfuric acid (H2SO4) or
hydrochloric acid (HCl) or other acids can be applied (Bohissi & Mogheir, 2015).
Many undesireable effects on the aquatic environment can happen particularly with
discharging high concentrated brine coincide with sensitive ecosystems. The physical
and chemical properties of the brine, and the characteristics of the receiving
10
environment (hydrographical and biological) are two important factors that affect on
the aquatic life when brine discharged to sea. The effects get higher when the
receiving body is enclosed and shallow where the marine life is abundant more than
when the sites of discharge have exposed open locations with high energy of waves
that can assist in dilution and dispersion of brine discharged (Lattemann & Höpner,
2008). The characteristics of brine are different based on the desalination techniques
used; thermal or RO technologies. In Gaza strip most of the plants are RO
desalination plants.
Temperature and Salinity 2.4.1
The aquatic life can be deteriorated with the constant discharging of high saline and
high temperature level of bine, this can cuase a huge negative impact on the marine
life and can make a full change in the composition of the marine environment.
Without using a process of difussing, the saline brine will cause a column or cloud of
saline water and will sink to the sea floor as it is denser than seawater especially
when the coastal waters are shallow. These clouds or columns of brine will affect on
the benthic communities due to high salinity and temperature levels (Lattemann &
Höpner, 2008).
Biocides 2.4.2
Chlorine is added to the intake water in most desalination plants in order to decrease
the biofouling, which cause to form hypochlorite and mainly hypobromite in
seawater. 200–500 mg/L is the FRC levels (the sum of combined and free available
chlorine residuals) for brine, which is almost 10–25% of the dosing concentration.
Depending on toxicological data from a wide spectrum of marine species, the U.S.
EPA suggests a short-term criterion of 13μg/L and a long-term water quality criterion
for chlorine in seawater of 7.5 μg/L (EPA, 2004). EU conducted an environmental
risk evaluation for hypochlorite which determined a PNEC (predicted no effect
concentration) for saltwater species of 0.04 μg/L free available chlorine (European
Union, 2007). Environmental concentrations up to 100 μg/L and discharge levels of
200–500 μg/L therefore represent a serious danger to marine life.
11
Heavy metal 2.4.3
Brine contamination with copper resulted from corrosion could make a bugbear of
thermal plant brine. Generally the brine discharged from RO process contains effects
of chromium, nickel, iron and molybdenum. As a result of fact that non-metal
equipment and stainless steels dominate in reverse osmosis desalination plants, the
contamination with metals become in low levels. It is expected that concentrations of
copper in brine solutions is ranging between 15–100 μg/L. In spite of the copper
presence on brine, the environment may not to be affected negatively.
The U.S. EPA recommends that the maximum concentration of copper to be 4.8μg/L
in seawater for the brief exposure and 3.1 μg/L in case of long-term exposure (EPA,
2004). Copper as most other metals which are transported and accumulated in
sediments can cause a significant concern of point discharges, which can cause to
increase the sediment concentrations in these sites. Benthic organisms can absorbe
the minerals in sediment, which often form the basis of the marine food chain
(Lattemann & Höpner, 2008).
Antiscalants 2.4.4
In both RO and thermal plant, antiscalants are provided to the water to prevent scale
formation. The concept of this process is belonging to the polymeric substances
associated with different structures of chemicals, espeically phosphonates and
policarbonic acids (e.g. polymaleic acid). To prevent scale formation at small scales,
Polyphosphates and sulfuric acid are also utilized. The impact on the marine life due
to the toxicity of antiscalants is considered very low. Eutrophication problems was
shown closed to the outlets of desalination plants in the Gulf due to polyphosphates
using, as these substances can be simply hydrolysed to form orthophosphate, a major
food component of primary producers (Lattemann & Höpner, 2008).
Coagulants (RO plants) 2.4.5
Coagulant aids (such as high molecular organics like polyacrylamide) and coagulants
(such as ferric-III-chloride) are added to the source of water to coagulate and media
12
filter the existed suspended material. The media filters are washed from time to time,
and the backwash water that contains the suspended materials and coagulants is
normally pumped without treatment to the closed ocean. The potential toxicity of
chemicals is very low. But the continuous discharge can make an intense coloration
of brine in case of using ferric salts (“red brines”), this can lead to decrease light
penetration and increase turbidity or lead the benthic organisms to be buried in the
discharge site. (Lattemann & Höpner, 2008).
Antifoaming agents (thermal plants) 2.4.6
To reduce foaming in thermal plants, antifoaming agents like polyethylene and
polypropylene glycol can be added to the feed water. Polyglycols are not toxic, but
may be rather persistent in the environment due to a poor biodegradability
(Lattemann & Höpner, 2008).
Cleaning chemicals 2.4.7
The type of fouling affects on the cleaning procedure. In RO plants, silt deposits and
biofilms from membranes are normally removed by alkaline solutions (pH 11–12),
while the metal oxides or scales are dissolved by acidic solutions (pH 2–3). These
solutions usually include additional chemicals to make the cleaning process better,
such as detergents (e.g. dodecylbenzene sulfonate, dodecylsulfate) or oxidants (e.g.
sodium hypochlorite, sodium perborate). After cleaning or prior to storage,
membranes are often purified. For this purpose, either oxidizing biocides (such as
hydrogen peroxide and chlorine) or non-oxidizing biocides (such as glutaraldehyde,
formaldehyde or isothiazole) can be applied. Normally, Alkaline scales from heat
exchanger surfaces are removed by washing the distillation plants with warm acidic
seawater, since they may contain corrosion inhibitors (e.g. benzotriazole derivate).
The cleaning solutions, especially their additives, may be toxic to aquatic life in case
of it discharged to surface water without any treatment (Lattemann & Höpner, 2008).
13
As the existence of these different chemicals with variable concentrations, reject
brine discharged to the sea can change the alkalinity, salinity and the temperature
averages of the seawater and can make changes in the marine environment.
2.5 Brine Management
Numerous disposal options for brine have been installed in the last decades since
desalination plants have got widely expansion as a result of the increasing of the
need for drinking water with high growth of population.
Brine management has lately become a big challenge to the utilities worldwide, this
belongs to many factors such as increasing the number and size of desalination plants
especially in semi-arid regions which put the disposal options under high limitations;
the increased discharge regulations that also limit the disposal options (Mickley,
2006). The planners and designers of the best kind of the disposal systems must
consider on their account important factors which affect on their decision of
choosing the best brine management method. These factors include the quantity and
quality of the brine, the location of the desalination plant, the environmental impact
and the environmental regulations. Public acceptance, capital and operating costs and
the ability for future plant expansion are also important factors to be considered
(Younos, 2005).
2.5.1 Deep Injection Wells
In deep injection method, the brine is injected to the deepest to reach the unusable
groundwater aquifers under with depth between 330 to 2,600m. Despite the area
aquifer is too big and can accept large amount of brine, this method can’t be
applicable. So that, for the construction of a new injection well, the selection of the
site is too important, this relies on the geological and hydrogeological conditions of
the area. Areas with high risks of earthquakes or regions with mineral resources or
areas where people depend mainly on ground water aquifer for the domestic and
agricultural supply should be kept away from injection wells (Ahmed, Shayya, Hoey,
Mahendran, Morris, & A1-Handaly, 2000). So to avoid this, a complete detailed
assessment must be carried out before the drilling of any injection well to define the
best location and the required depth for the injection well construction. Moreover, it
14
is necessary to conduct “brine conditioning” and filtration before injection (Glater &
Cohen, 2003).
The injection of industrial and municipal wastes and liquid hazardous wastes into
deep wells is a significant disposal practice for wastes all around the world (Saripalli,
Sharma, & Bryant, 2000).
Recently, the deep-well injection has been chosen as an important way for disposing
brine. It is considered the most environmentally friendly way of getting rid of brine
even though it needs many considerations during the designation and
implementation. Despite the several factors which affect on the performance and
reliability of this method, it is successfully used around the world such as in South
Florida (Skehan & Kwiatkowski, 2000). It also considered as the most cost effective
method in comparison with other practiced land disposal methods (Skehan &
Kwiatkowski, 2000; Glater & Cohen, 2003). However, its cost-effectiveness, it has a
significant constrain which is presence of total suspended solid in the brine which
will be injected deep in the aquifer, this forces to make continuous measurements of
the TSS to be assure from the steady performance of the well (Glater & Cohen,
2003).
According to (Abdul-Wahab & Al-Weshahi, 2009), the deep well injection is a
feasible method for disposing brine. It is cost effective disposal option. The
disadvantages of this technology can be mentioned as: (1) site well selection; (2)
costs of brine conditioning to meet the standards; (3) Potential corrosion and
subsequent leakage in the well casing; (4) Earthquakes activity that can lead to
damage well and cause contamination to ground water; and (5) Well half-life
uncertainty, that can only be estimated by mathematical simulation techniques.
2.5.2 Irrigation Systems
Brine has been shown to be a good choice for irrigations by operating dilution or/and
changing some of the irrigation practices. This was extremely shown with
horticultural crops such as olives, almonds, and pistachios (Agriculture, Fisheries, &
Forestry, 2002). The challenges faces this system are the disadvantages associated
with the impact on the existing vegetation, and the potential increasing the of aquifer
15
salinity besides increasing the salinity of underlying soil. It also requires large area of
farm lands with crops which would not be damaged by high salinity of water
(Balasubramanian, 2013). So that, the salt concentrations and the chemical existed on
the brine should be clearly studied before using on the irrigation system to avoid
harming the corps or increasing the contamination on soil and groundwater.
These concentration levels should go with vegetation tolerance and underlying
groundwater salinity (Mickley M. , 1995). If the brine is not meeting the quality
standards required for soil and crops, a treatment process should take a place to
reduce the undesirable concentrations which may be very expensive (Ahmed,
Shayya, Hoey, Mahendran, Morris, & A1-Handaly, 2000). Livestock also can be
affected with this technology of treatment as the brine may carry toxic substances
and chemicals used on the backwash and cleaning activities.
Several creiterias should take consideration when using brine for irrigation systems
includes site selection, pre-treatment process, hydraulic loading rates, requirements
of the land, vegetation selection and surface runoff control (Ahmed, Shayya, Hoey,
Mahendran, Morris, & A1-Handaly, 2000).
2.5.3 Evaporation Ponds
In this method, the brine is pumped to collective ponds and allowed to be evaporated
to dryness for final disposal.
Evaporation ponds are generally more effective in arid and semiarid climates which
have steady and relatively rapid evaporation rates, since they rely on solar energy to
evaporate water from the brine stream, which are ultimately landfilled. Ahmed, et al.,
(2000) had studied the related literature to the evaporation ponds and suggested the
best design for the evaporation ponds. Two main important factors were found to be
the main parameters for designing ponds which are surface area and pond depth.
According to (Ahmed, Shayya, Hoey, Mahendran, Morris, & A1-Handaly, 2000) the
pond open surface area (A) and minimum pond depth (d) can be estimated from
16
𝐴 =𝑉𝑓1
𝐸𝑎𝑣𝑒 (1)
𝑑 = 𝐸𝑎𝑣𝑒 𝑓2 (2)
Where 𝑉is volume of reject water,
𝐸𝑎𝑣𝑒 is evaporation rate,
𝑓1 is an empirical safety factor to allow for lowers than average evaporation rate,
And 𝑓2 is an empirical factor that accounts for the length of the winter season.
From the equations, it is obvious that there is a directional relation between the area
needed and the volume of brine and an inversely relation between area needed and
the evaporation rate. (Glater & Cohen, 2003).
Pondleakage is the main environmental concern with using evaporation pond as a
disposal for brine, which may lead to subsequent pollution in the aquifer. In the
evaporation bonds, the current installations should be lined with polyethylene or
other various polymeric materials to save aquifer and avoid leakage and seepage of
contaminants and pollutants into the nearby groundwater. Evaporative ponds are
proposed for a desalination project in the Salton Sea Area (California Water
Desalination Task Force, 2003).
Evaporation mainly used in arid and semi-arid regions where land is available.
However, according to a survey by Mickley et al. (1993), until 1993 there was 6% of
the installations on USA using evaporation ponds as a method for treating brine.
After this 1993, the rate became 2% only and the utilities changed to other types of
brine management.
This may be due to the large quantities of land required, and because only small
number of desalination plants have been installed in inland locations away from
surface water (Gilron, Folkman, Savliev, Waisman, & Kedem, 2003) (Mickley,
Hamilton, Gallegos, & Truesdall, 1993)
The need of large amount of land associated to the large amount of brine discharged
by plants makes evaporation ponds are not considered sustainable solution (Poulson,
2010). As a solution, additional treatment can be applied for brine before discharging
to the evaporation ponds. This treatment depends on the chemicals and biological
characteristics of brine (GHD, 2003).
17
Salts recovery and harvesting systems are applications for evaporation bonds
2.5.4 Salt Recovery/Harvesting Systems (or Salt Harvesting)
In this method, the brine solutions are pumped into large basins and allow water to
evaporate, and then the salt precipitates in the basins’ bed. This method is very useful
especially when all the salt production on Australia, which is ranked sixth in the
world in salt production, comes from the solar evaporation of sea water, and saline
lake waters where the salt is harvested from the dry lakes bed after the evaporation of
water. Many different useful uses for the harvested salts including commercial salt
sales, road base additives, and dust suppressants, stock feed, medical and chemical
uses (Lyday, 1998).
To perfrom the harvesting of salts, many processes can be operated on concentrated
brine such as mechanical evaporation, Vertical Tube Falling Film Brine
Concentrator, Brine Crystallizer and evaporation ponds (Balasubramanian, 2013).
One of the disadvantages of using salt harvesting systems is the associated capital
cost related to the construction of appropriate evaporation ponds. Other
disadvantages of this method of brine handling can include cost of operation and
maintenance, costs of labour and tools needed for the harvesting, cleaning and
packaging are also needed (Agriculture, Fisheries, & Forestry, 2002).
In general, the smal scale harvesting operation for slats are not profitable, thus it is
recommended to be used by medium to large scale. Sometimes to produce a special
mineral, adjustment for mechanical process or chemical compositions of water in the
evaboration basins must be required. (Agriculture, Fisheries, & Forestry, 2002;
California Water Desalination Task Force, 2003). The harvesting systems of brine
still in the development stages, but previous attempts have indicated that recovery of
marketable by-products is economically difficult and Salt pond are very sensitive and
should not allowed to completely dry out, otherwise the liner system will be
damaged (California Water Desalination Task Force, 2003; GHD, 2003).
18
2.5.5 Direct Discharge of the Brine at the Coastline
Although brine solution contains substances, which have arisen in the sea, its high
rate of concentration and the possibility of existing additional chemicals raised by the
pre-treatment process can extremely harm the marine environment around the outlet
discharge point (Einav, Hamssi, & Periy, 2002). A plume or column of high salinity
seawater will be formed by the brine discharging. This plume will be seen over
hundreds of meters distances from the outlet depending on brine volume, sea’s wave,
salinity of sea, and other marine conditions (Einav, 2007). Most of the plants in the
Middle East are using this type of discharge (California Water Desalination Task
Force, 2003).
Direct discharging of brine to the coastline is not recommended regardless any
conditions such as small pants or insensitive coastlines, where sometimes the
economic considerations force utilities to do it.
The discharge of brine directly on the shore may increase salinity of water along the
coastline and thus increase the intensity of saltwater intrusion impact instead of
limiting (Purnama, Al-Barwani, & Al-Lawatia, 2003). Generally, Seas, which have
high sensitivity, must be away from this method. It is not recommended also to use
this method with large desalination plants which pumps large amount of brine
frequently. Moreover, it is not recommended for areas with high environmental
populations (Einav, Hamssi, & Periy, 2002).
2.5.6 Discharging the Brines by a Long Pipe Far into the Sea
The brine, which will be continuously pumped into the sea, will form a column of
high saline sea water, proportional to the quantity, concentration and the status of the
receiving sea (e.g. depths and currents). This column may sink, float or settle to see
floor depending on the density of the brine compared to seawater. The effects of the
brine on the sea may extend over hundreds of meters. The type of dispersion and
natural dilution for the brine depend on several factors such as location of the
discharge tube, the waves, tides, water depth, sea currents, and bathymetry. These
factors can explain the nature and the shape of the mixing of the brine with the sea on
the outfall disposal point. (Mickley M. , 2000).
19
This continuous and cumulative source of pollution to the sea will cause a negative
change to the marine life on the sea around the column's vicinity. Thus, the design of
the outfall should contain multiport diffusers to relieve brine concentration rapidly to
avoid and decrease the sea floor columns. Moreover, the location of the outfall
should be accurately chosen, it is very important to set up the brine discharge points
away from the shore and rocky areas that are rich in living organisms as well as away
from recreation, touring and fishing areas where the residents participate in activities
(Einav, Hamssi, & Periy, 2002).
Brine concentration can be alleviated by effectively blending, diffusers, or by using
mixing zones where the brine can be mixed with cooling water, hot water, feed water
or any other low TDS effluent before disposing to the surface. Mixing zones are
defined as quantitative limits within the receiving water bodies where the law
permits the characteristics of the surface water to exceed water quality standards due
to a source of disposal. Diffusers are jets that dilute the concentration in the outlet of
the disposal point to maximizing the mixing rate. (Younos, 2005).
If the mixing zones have low salinity than the brine pumped, and the tidal (mixing)
zones have a limited capacity to transport and dissipate the coming brine, then
diffusers are used and in the case of large desalination plants ocean outfall with
diffusers are extended beyond the tidal zone (Masnoon & Glucina, 2011). The design
of the outfall and diffuser should take into consideration the hydrodynamic
modelling when they decide the length, size and configuration. all must meet the
specific conditions on the discharge location (WHO, 2007).
The number of the diffusers and the spacing between them are the mainly factors
affect on the diffusing process. The dispersion efficiency can be improved by the
using of special type diffusers like red valve diffusers. These diffusers enhance the
brine pressure in the outlet of the discharge tubes thus maximize the dilution process.
Using the diffusers with a direction angel of 30–90o to the seafloor is another method
to improve the diffusing process. In this method, the brine is pushed towards the sea
surface (Einav, Hamssi, & Periy, 2002). The vicinity of the discharged brine will be
the main causer of impact on the marine organisms, and will be related to salt
concentration. This will most likely affect benthic organisms living in bottom of the
sea (Einav, Hamssi, & Periy, 2002).
20
Table (2.1) shows the major concerns associated with surface water disposal and the
methods of best mitigation in order to face those concerns.
Table (2.1): Surface Water Disposal Problems and Mitigation (Mahi, 2001)
Environmental Concern Process Mitigation Method
From raw water ..
Contaminants present in raw
water
Brackish-RO Limit degree of concentration,
blending, mixing zones, post-
treatment.
Imbalance in essential ions
(come groundwater)
Brackish-RO Diffusers, blending, mixing zones
Low dissolved oxygen, high
H2S2 etc. (some groundwater)
Brackish-RO Aerate, degasify, or otherwise treat
prior to discharge
From pre-treatment..
Toxicity of additives All Use non-toxic assistive
Low pH (due to acid addition) RO Raise pH prior to discharge
From the concentrate salinity ..
Different salinity than receiving
water
RO more than
thermal
Diffusers, blending, mixing zones,
ZLD
2.5.7 Direct discharge of Brine through the Outlet of the Power Station’s
Cooling Water
This option proposes to use hot water that discharged from the power plant to dilute
the concentrated brine solutions. The high dilution rate can be achieved by this
method is considered the main environmental advantage. Another advantage is the
low specific weight of hot water which will partly compensate for the high specific
weight of saline solution, reducing its tendency to sink to the bottom (Einav, Hamssi,
& Periy, 2002). This means that the desalination plant should be located near the
coastal power station. The brine will be blended with the cooling water of the power
plant inside the downstream line before discharging into the open ocean (California
Water Desalination Task Force, 2003). This is used very widely for thermal
desalination plants as hybrid facilities common when water and energy production
are combined.
21
2.5.8 Direct Discharge to sewage system
Discharging brine into waste water collection system is one of the options for brine
disposal; this way is applicable only for very small desalination plants to into large-
capacity wastewater treatment facilities (WHO, Public Health and the Environment -
Desalination for Safe Water Supply, 2007). Adding brine to wastewater prior to
treatment would completely alter the treatment process and potentially lead to
untreated water. It also can expose the facilities of the collection system to high
deteriorations in with the high volume of brine and large scale of chemicals and
additives which are pumped with concentrate. Important factors to be considered in
brine disposal into a sewage system include the volume and composition of the brine
solution with respect to the treatment capacity and the size of the wastewater
treatment plant, the transport operations and the potential impacts of high TDS flow
the wastewater treatment plant equipment (Younos, 2004).
2.5.9 Direct Discharge to wastewater treatment plant outfall.
Numerous of desalination plants around the world discharge brine through the
outfalls of the existing wastewater treatment plant (WWTP), To add the discharged
brine to treated wastewater is considered more economical and effective than to
pumping it to sewage collection system. The brine, therefore, will be mixed with
treated effluent from a wastewater treatment plant and pumped through the outfall of
the treatment plant. It is not feasible to treat the brine in the wastewater treatment
plant, blending with the wastewater effluent is more feasible and goal achieving.
This considered as a dual dilution process of wastewater and brine discharge, when
high salinity is blended with low salinity wastewater, this will result in reduction the
density of the concentrate. Also the higher levels of metals, organics and pathogens
present in wastewater discharge will be diluted with brine; the wastewater
reclamation plant operated by West Basin Municipal Water District in El Segundo is
a good example of this type of treatment (California Water Desalination Task Force,
2003).
22
Important factors should be studied when a utility decides to discharge brine to a
WWTP outfall includes; the wastewater outfall availability and cost, and the capacity
and the potential for whole effluent toxicity that may result from ion imbalance of
the blended discharge (Mickley M. , 2006) This method can be applied only if there a
wastewater treatment plant is existed near to a desalination plant and have an extra
outfall discharge capacity (WHO, 2007).
2.6 On-site sodium hypochlorite
2.6.1 Sodium hypochlorite
Sodium hypochlorite (NaOCl) is a yellow green liquid with a faint chlorine-like
odor. It is widely used for surface purification, disinfection of water, tissue
bleaching, and removing odor (Chlorine Chemistry Council, 2016; K.Asokan &
K.Subramanian, 2009). The term "hypochlorite" refers to the hypochlorosic acid salts
(HOCL). Since acid is very unstable, most users prefer to deal with more stable
hypochlorite solutions instead.
Household bleach is commonly used to refer a sodium hypochlorite solution
(NaOCl). This can be prepared by chlorine reaction with strong alkali, such as
caustic soda, or alkaline earth hydroxide. In stronger concentrations, NaOCl is used
for bleaching paper, textiles and pulp. Different uses for the NaOCl in different
applications include using it as an intermediate chemical for the manufacture of
organic chemicals, in large size for water disinfection, in medicine and fungicides as
well. It also used commercially as pool disinfectants and germicide.
Water must be disinfected and purified before drinking to prevent diseases.
Commonly chlorine is method used on many water utilities in the world. In essence,
three main types of chlorine can be used for disinfection, Sodium hypochlorite,
calcium hypochlorite and chlorine gas.
2.6.2 What is on-site sodium hypochlorite?
On-site generation of sodium hypochlorite is an important technique based on
scientific principles which has been practiced for decades. It uses sodium chloride
23
(NaCl) dissolved on water and apply electricity current with low DC voltage to
produce sodium hypochlorite and other oxidant species. The on-site generated
chlorine has different uses in the commercial and industrial world, such as
disinfection of swimming pools and cooling towers and etc. The biggest application
of OSGs technology is municipal drinking water purifying. The benefits of using
OSGs have been transformed into several water municipalities to replace traditional
chlorine delivery systems such as chlorine gas, sodium hypochlorite concentrate, and
bulk calcium hypochlorite for using of OSG systems (Parkson, 2016; Boal, 2009).
The on-site generated sodium hypochlorite produced by passing a sodium chloride
solution through electrolytic cells with applying electricity current. The potential
benefits of the technology turned many communities move to use OSGs for disinfect
water systems, these benefits include high-quality disinfection, greener processes and
significant economic savings. Despite its cost, OSGs has low risk level and provide
safety for operators as the concentration of the produced hypochlorite is between
(0.5-0.8%) which lies below the threshold for hazardous classification (1%), This
low concentrate provides more stability for the hypochlorite and less scaling of
injection lines and fittings coming from its low pH. (Morganti, 2002).
In the USA, the on-site generation of sodium hypochlorite has been operated for
water disinfection purposes since the early 1970s. Nowadays, several applications
are currently using Sodium Hypochlorite Generation units to definitely generate a
safe, stable and economical disinfectant for water. Sodium Hypochlorite Water
Solution provides a strong biocide and sterilizer in many applications and provides
effective protection of equipment against the growth of total and partial organic
waste (Ainsworth & Hampton, 1997).
The on-site and off-site Sodium Hypochlorite generator units are generally operated
for many purposes such as:
Off shore platforms.
Small and large desalination plants.
The cooling plants.
Petrochemical complex for associated water facilities.
Sea water outlets.
Power stations.
Generally, where a large mass of water needs to be cleared before final use.
24
2.6.3 The characteristic and significance of the sodium hypochlorite
Sodium hypochlorite (NaOCl) is the active ingredient in commercial bleach. It is
often available in markets as a solution with concentrations of 6%, 12% and 15%. Its
relatively short shelf life is dependent on different agents such as; sunlight,
temperature, vibration, and the concentration. Increasing of these factors will affect
negatively on the shelf life of the hypochlorite. It also should be stored under a
certain condition to maintain its strength and stability. An opaque container in a cool
room with trying not to shake it during transportation, all these are considered
significant steps for an ideal dealing with hypochlorite. Solutions with higher
concentration have the tendency to degrade faster than the others with lower
concentration. But solutions with lower concentration need more space in the room
to store it. Also, if a solution with 12% concentration rate compared to a 6%
concentrated solution, the change in the stronger solution will be more apparent than
it's in the lower concentration solution, but as it breaks down the reaction slows
down too. When the 12% reaches the 6% level, it breaks down like the one that
started at 6% did on day one (Morganti, 2002; Omega Man Journal, 2012).
Sodium hypochlorite is considered a good disinfectant due to its high strength as an
oxidizing agent. Sodium hypochlorite is considered one of the options for
disinfection purposes beside other disinfectants options, it has a high corrosive
nature, and a tendency to decays over time during storage. Chlorine removes
electrons from the outer shell of living organisms, destabilizing the structure until
that organism is dead. Free chlorine is the disinfectant used in most of municipal
water treatment facilities, it can be produced by adding sodium hypochlorite
(NaOCl) to water, this will form hypochlorite (OCl- ion), it is called also free
chlorine (Omega Man Journal, 2012; Boal, 2009).
In the beginning, the addition of sodium hypochlorite to the water will cause to start
the reactions in the water, where the added quantity will disappear because of the
substances in the water which will reduce the chlorine to reach nothing. Secondly,
the chlorine will react with any organic matter present in the water to produce
chlororganics as well as it will be associated with the ammonia compounds which are
existed primarily in the water and will form chloramines. Some substances arising
from interactions with organic matter are toxic substances, so it is always necessary
25
to eliminate as much organic material as possible before starting chlorination.
Therefore, it is important to filter and settle the water before chlorination begins. Non
organic compounds in the water will just use up chlorine and protect some bacteria
from the chlorine. Adding chlorine will cause a partially destruction for the
chloramines and chlororganics, since some will always remain. When chlorine level
reaches the required amount, this means that the disinfection has occurred and any
increasing of the dosage of chlorine after this point will remain as disinfection
residual. This residual is very important when the hypochlorite will be stored for any
length of time. The Figure (2.1) below is illustrating the breakpoint chlorination
curve which is the official name for the process described above (Omega Man
Journal, 2012).
Figure (2.1): Breakpoint chlorination curve.
When water by large amounts needs to be stored for long time, it might be feasible to
go for other disinfectant than free chlorine residual. Monochloramine can be
formatted by adding ammonia (NH4) solution to the chlorinated water with ratio of
(1:4) ammonia to free chlorine. The shelf life for monochloramine is considered
much longer with no negative side effects known. In the other hands, it is a weak
disinfectant, and preferable to be used for the secondary disinfection (Omega Man
Journal, 2012).
26
Sodium hypochlorite can be prepared chemically by bubbling chlorine gas into dilute
sodium hydroxide at room temperature; it also can be produced on-site by the direct
electrolytic oxidation of sodium chloride (NaCl).
The purpose of using hypochlorite produced on-site was for the anodic oxidation of
dye molecules and phenols in the wastewater (C.H. Yang, 2000; Walsh, 1990).
Several characteristics are known for using NaOCl as a disinfectant such as the safe
handling, simplicity of dosing, decreasing transportation, the low decomposition rate,
and no residual effluent. Sodium hypochlorite with the concentration of (5%) is used
as bleach for removing stains from clothes (K.Asokan & K.Subramanian, 2009).
Acetic acid and other wear organic acids are capable to neutralize the NaOH and
volatilize the chlorine in post treatment from the residual hypochlorite. Most of
bacteria and viruses will be killed or controlled by adding 1 to 5 dilution of
household bleach. This bleach is also used in hospitals to clean surfaces. In other
ways, sodium hypochlorite is one of the main disinfectants for drinking water; one
litter of sodium hypochlorite can disinfect 4000 litters of water. It is also used for
disinfection in swimming pools and also used for destroying cyanide wastes. One of
the most important advantages for NaOCl is that microorganisms don't show any
resistance to it. The high concentration of NaOCl is considered hazardous materials,
so that most the bleach solutions which sold have the concentrations between 3 - 5%
of electro synthesis of NaOCl. Sodium Hypochlorite is well known now and
commonly used for many plants, where some of them are producing their
hypochlorite by means of undivided electrolytic cells by direct electrolysis of weak
brine or seawater. The choosing of cell should consider the production capacity
needed. The strength of sodium hypochlorite is gradually decreases after
manufacturing. (K.Asokan & K.Subramanian, 2009).
The major concern in using sodium hypochlorite as disinfectant is the degradation.
The concentration of hypochlorous acid and hypochlorite ion in water solution
decreases over time in a definite process depending on the temperature, light, pH,
concentration of initial available chlorine and organic matter and metal ions
presence. (Hoffman, Death, & Coats, 1981; Gordon, Adam, & Bubnis, 1997). To
increase sodium hypochlorite stability in the solution, the process of storage should
provide the following: maintain pH between 11.5 to 13, and the concentration of
27
NaOCl should be low, maintain temperature around 303 K, conserve the solutions
away from graphite particles and metallic ions and provide impermeable containers
to light (K.Asokan & K.Subramanian, 2009).
The electrolyser systems in the process of on-site generation of sodium hypochlorite
use the solved crystallized salts for the electrolysis. The design of the electrolysis cell
made to afford low brine flow rate with small spacing between electrodes to produce
low concentrated sodium hypochlorite near to 1%. On-site generation of NaOCl is a
feasible and safer alternative to the chlorination approach. It is considered one of the
viable options, since it can be produced with the quantity and quality of disinfectant
required on the time needed. The capital cost of the technology and the cost and
existence of energy are the main disadvantages of these systems. Electrodes
replacement also is a big disadvantage since it usually manufactured by expensive
materials such as titanium coated with iridium, ruthenium, titanium or platinum
oxides, assembled in proprietary units with an average lifetime of 5-8 years (White,
1999). In contrast, the advantages of the system are its simplicity, and its cost of
maintenance and operation which is considered modest.
2.7 Basic operating theory
Salt, water and electricity are the three factors needed for the electrolysis process. It
is considered a simple process. It starts by passing brine though the electrolytic cells
which contains an anode and cathode and connecting them to a low voltage DC
current to produce sodium hypochlorite by a process of chemical reactions. The
products then stored into tanks and used as a disinfectant for the chlorination process
in the desalination plants. The system operates automatically once the hypochlorite
reaches the low-level set point, and work to fill the tanks for another round (Pristine
Water, 2012).
2.8 Theoretical Considerations
The electrolysis of brine begins by running an electric current between two surfaces
facing each other, representing a cathode and an anode and having the brine between
them. This process called electrolysis. The electric current forces some of sodium
chloride existed in the brine to be divided into ions to produce chlorine on the anodic
28
surface and caustic soda and some hydrogen gas on the cathode surface. Chlorine
and caustic soda then instanteously mixed together and react to produce sodium
hypochlorite. The amount of sodium chloride electrolyzed is directly proportional to
the current density. Electrolytic conduction happens when ions move between poles
in the solution. This occur when the positive ion (Na+) moves to Cathode and the
negative ion (Cl−) moves to Anode to make electricity close circuit. At the anode,
oxidation happens and forces the positive ion to release its electron while at the
cathode; reduction occurs and allows the negative ion to receive an electron (Abdul-
Wahab & Al-Weshahi, 2009).
In general, the electrolysis process for brine is following the chemical reactions
which are listed below:
At first, at the anode an oxidation for the chloride ions occurred:
2Cl− → 2Cl2 + 2e
−.
Then, a rapid hydrolysis process occurs for the chlorine which is generated by the
oxidation process:
Cl2 + H2O → HOCl + HCl.
In the other hand, a reduction for sodium ion happens at the cathodic surface:
Na+ + e
− → Na.
Then, a rapid reaction of sodium, which is generated by the reduction reaction, with
water:
Na+ + H2O → ½ H2 + NaOH.
A reaction happens between the acids (HCl and HOCl) which are produced at the
anode reaction with the base (NaOH) which has been produced at the cathode
reaction:
HCl + NaOH → NaCl + H2O and,
HOCl + NaOH → NaOCl + H2O.
The net reaction of electrolysis is:
NaCl + H2O → e− → NaOCL + H2
29
Advantages related to the generation NaOCl using seawater brine
The On-site sodium hypochlorite generator on site has many advantages such as:
It is a simple process, requires brine and electricity only (Pristine Water,
2012).
The substance used in the electro chlorination process is salt which is
considered a non-toxic material (Abdul-Wahab & Al-Weshahi, 2009).
It is safe, where hypochlorite can be generated once needed and with the
quantity required and thus, avoiding risks of storing and handling hazardous
materials.
Cost-effective method to generate chlorine in comparison with other
conventional Chlorination methods (Abdul-Wahab & Al-Weshahi, 2009).
The degradation of the concentration of sodium hypochlorite generated on-
site is lower than other commercial high concentrated hypochlorite, so that,
the dosage does not need to be frequently modified according to the strength
of the hypo solution (Casson & James W. Bess, 2006).
Compatible with drinking water regulations, providing more safety
requirements to chlorine-gas-based systems.
It has a long service life when compared with other electrolysis cells such as
the membrane cell electrolysis.
It is safer for the Environment once compared to 12.5% sodium hypochlorite,
since it reduces the carbon emission to 1/3rd
by using water and salts (Boal,
2009).
It is helpful to protect the equipment from the micro organic fouling growth.
It also helping by controlling the growth of algae and crustaceans.
Disadvantages related to the generation NaOCl using seawater brine
The possibility for hydrogen explosions. So that, the design of the electrolytic
cell and storage tank should be well studied and provided with vents to
prevent the accumulation of hydrogen (Boal, 2009).
A sufficient electricity experience is required from the operators.
The initial capital cost is higher than it is in commercial hypochlorite.
30
It needs electricity to operate where the Gaza strip has lack of electricity
supply.
Expensive electrode replacement after end of life which is between 5 to 8
years (Morganti, 2002).
2.9 The impacts of On-Site Hypochlorite Generation
Considering the safety, economic and environmental concerns, the on-site generation
of sodium hypochlorite presents the most reasonable and effective choice. The
following reasons are considered environmental factors affected by OSGs of
hypochlorite:
Assist on the reducing of the environmental effects of the brine on the
surrounding environment (Abdul-Wahab & Al-Weshahi, 2009).
Take the negativity of the waste brine and positively using brine into
generates a useful product.
Generate a safe disinfection material where the only chemical to be used and
stored in bulk is salt.
The process is clean and it happens in an isolated system where there is no
dripping, leaks, mixture of or exposure to chemicals or fumes. Hydrogen,
which generated by product, can be safely vented into the atmosphere or it
can be diluted below 4 mol% to prevent any flammability concerns (Parkson,
2016).
The generated hypochlorite has a low concentration (0.8% concentration) and
it is classified as a non-hazardous chemical while the commercial
hypochlorite has 12% or 15% rate which is considered very high to the
standards since hypochlorite with concentration above 1%is classified as a
hazardous chemical (Abdul-Wahab & Al-Weshahi, 2009).
Generation happens upon needs, so no bulk storage needed (a unique safety
feature).
It is a safer for workers and operators where there is no touch with toxic and
high concentrated chemical materials.
31
2.10 Literature review on onsite-generation of sodium hypochlorite
Rengarajan, et al. (1996), studied the effect of current density, temperature and the
concentration of sodium chloride in the efficiency of producing sodium hypochlorite,
beside the ratio of sodium hypochlorite and chloride and the energy consumption.
Experiments also were carried out to study the effect of temperature in the range of
303 to 333K for the production of sodium hypochlorite. The results of the
experiments indicated that the maximum current efficiency for the production of
sodium hypochlorite is achieved at current density of 5-10 A.dm2, 313K, between 5-
10 A.dm2
and keeping the NaCl concentration between 40-50 gm l-1
. The current
efficiency for the formation of NaCl decreased with duration. (Rengarajan, Sozhan,
& Narasimham, 1996)
Morganti, (2002), carried out several tests in Nepal to estimate and study the
performance of the production process and the quality of the sodium hypochlorite
solution produced for household water disinfection. The technical and organizational
factors which aim to a successful commissioning of a sodium hypochlorite
generation program were identified. The sodium hypochlorite solution with 0.56%
concentration generated by production process displayed that with a proper
production and suitable storage conditions were maintained, the average decay rate
will be of 230 mg/L (0.023%) per month over the first three and half months. A
higher decay rate (0.10% per month) can happened with accidental contamination
with iron, by use of an iron spigot, subsequently replaced by a plastic spigot. Hence,
it is necessary to protect the solution from iron contamination this will result into
maintain sufficient shelf life to the solution. In addition, to obtain more stability, the
alkalinization of the solution is recommended.
He also declared that “tap water chlorine demand in Kathmandu was found to be
about 0.5 mg/L and thus a sodium hypochlorite dose of three drops per litter (about
1.5 mL/L) proved adequate to provide a free residual chlorine level above 0.2 mg/L.
However, further investigation of the actual chlorine demand in different seasons and
in different areas of the country is suggested”. (Morganti, 2002)
32
Hooper, (2005) discussed the technical advances that have been made in the
equipment used for generating 0.8% Sodium Hypochlorite on-site (at the point of
use) and the benefits & limitations associated with this technology. Among other
disinfection choices which are chlorine gas, commercial grade 12.5%, calcium
hypochlorite tablets and on-site generation of sodium hypochlorite, he concluded that
generating Sodium Hypochlorite on-site is a viable, cost effective and safe
alternative to 12.5% Commercial Grade Sodium Hypochlorite and Chorine Tablets.
It is more expensive per kg than Chlorine Gas, however if safety issues are taken into
account, it can still be a viable alternative (Hooper, 2005).
Abdul-Wahab and Al-Weshahi, (2009) studied the problems associated with brine or
wastewater generated from desalination production process. They have been
shedding light on the business opportunities associated with brine wastes by using
the brine for on-site generation of sodium hypochlorite. The results of the
experiments were producing Sodium hypochlorite which examined by HACH tables.
Hydrogen was also generated at the anode and was examined by spark. Sodium
chloride was accumulated at the cathode electrode and brine salts (carbonates and
hydroxides) were deposited at the bottom. They also indicated that the amount of
hypochlorite generated depends on the time of the reaction and the DC voltage
supplied (Abdul-Wahab & Al-Weshahi, 2009).
Asokan and Subramanian (2009) designed a tank electrolyser for in-site generation
of sodium hypochlorite. Experiments were conducted to fix, the optimum current
density, electrolyte flow rate, operating cell temperature and hold up or volume
current concentration. As results it has been shown that as current density is
increased, hypochlorite production also increases but cell temperature also increases
with increase in current density. Above a temperature 308 K, sodium hypochlorite
tends to chemically decompose to sodium chlorate.
3NaClO → NaClO3 + 2 NaCl
The concentration of NaOCl increases up to 50 mA.cm-2
, but at higher current
densities the concentration decreases due to increase in temperature. For the flow
rate, it was obviously shown that the flow rate is inversely related to the NaOCl
33
concentration and directly related to the current efficiency. Increase in flow rate
decreases the rate of decomposition reaction but at the same time decreases the
NaOCl concentration. The optimum flow rate is 3.6 L h-1
, at which the maximum
concentration of the hypochlorite is obtained at a reasonable current efficiency. By
studying the optimum operating temperature, they indicated that the increase of
temperature decreases NaOCl concentration and current efficiency of the reaction.
Where the electrolyser has to be maintained at the ambient temperature at which a
maximum NaOCl concentration of about 8 g. L-1 is produced (K.Asokan &
K.Subramanian, 2009).
Nasser Abu Ghalwa et al. (2012), studied the generation of sodium hypochlorite
(NaOCl). As results they indicated that NaCl is the most effective conductive
electrolyte for the generation of NaOCl. The optimum current density obtained at the
maximum hypochlorite concentration is 1 A⋅cm−2
. The electrolyser has to be
maintained at ambient temperature (10°C) at which the maximum NaOCl
concentration is maximum. The effect of temperature on the production of NaOCl
was showing that an increase of electrolysis duration up to 90 and 60 min leads to the
increase in hypochlorite generation for Pb/PbO2 and C/PbO2 electrodes, respectively.
In addition, the studying of the effect of NaCl concentration showed that the
concentration of 20 g/L NaCl is considered as the optimum concentration (Abu
Ghalwa, Tamos, ElAskalni, & ElAgha, 2012).
Chakrabarti, et al., (2012), have studied the on-site Electrochemical Production of
Sodium Hypochlorite Disinfectant for a Power Plant Utilizing Seawater. They
studied the effects of different type of electrodes, current density, surface area ratio
between anode to cathode and the spacing between the anode and cathode. The
results showed that titanium electrode coated with DSA demonstrated excellent
stability as compared to other tested electrode materials and production of NaOCl
reached to an optimum value of about 6315 mg/l; current density of 72.4 mA/cm2
was found to be a promising value for an efficient production of NaOCl; An anode to
cathode surface area ratio of unity was found to be the most advantageous value for
an efficient production of NaOCl and reduced operating cost. Inter-electrode spacing
was found to be an important parameter with respect to the process economy. An
34
inter-electrode spacing of 7 cm was found to be a better value giving the highest
production of NaOCl (Chakrabarti, et al., 2012).
2.10.1 Examples for using on-site sodium hypochlorite
City Utilities (CU) in Missouri is a municipally-owned utility serving Springfield and
surrounding areas of the community. In 1980, Blackman Water Treatment Plant
(BWTP) has been established for serving the residents of Springfield city, Missouri.
BWTP have been used chlorine gas for water disinfection since establishing. CU had
been looking to alternatives disinfection options as a result of increasing regulatory
requirements and increased local population. Keeping the chlorine gas and
maintaining it in a new building with a scrubber unit was an option in addition to
other options such as switching to bulk 12.5% sodium hypochlorite solution and
using OSGs of NaOCL were all options under CU studying. High investigation for
the best disinfection option was conducted included into considerations the safety of
community and plant personnel, the risks associated with gas chlorine, and the
potential future limits on gas chlorine were factors affecting the choice for the best
disinfection option for the city of Springfield. After careful large investigations and
studies, City Utilities decided to choose on-site generation of sodium hypochlorite as
it is the best option for the residents of Springfield and surrounding communities. By
this method of disinfection, they addressed the concerns of transporting chlorine gas
though their growing community, and it would be more cost-effective than bulk
delivery and no RMP would be required.
In April 2013, three systems have been started up by CU, each rated at 1,500 pounds
per day of free available chlorine. The water quality of CU has remained excellent
after running the new systems; in addition, a new unexpected benefit was discovered
by the CU which is increasing the pH in their finished water. CU feeds soda ash for
pH adjustment to comply with lead and copper rule requirements. Since the
switching to the on-site generation of sodium hypochlorite from gas chlorine, they
noticed that the amount of soda feed has been ducted since replacing acidic gas
chlorine with the slightly base low strength hypo. In the end, they were satisfied by
their decision of using OSGs of sodium hypochlorite as a disinfection option, this
35
resulted in a safer, more cost-effective treatment method for the city of Springfield,
Missouri, and the surrounding communities (PSI On-Site Disinfection, 2014).
The California water utility wanted to move away from the dangers of gas
chlorination to consider new disinfection methods such as bulk hypochlorite delivery
and on-site generation of sodium hypochlorite. The increasing of regulation and
scrutiny, the safety of operators, the aging of gas system, and a good-neighbour ethic
were the motivation factor to begin an investigation for the best disinfection choice
instead of chlorine gas. Richard MacLean, the Chief Operator, set up a methodical
process of evaluating the best method for disinfection between bulk-delivered
hypochlorite and on-site hypochlorite generation.
The main difference between liquid “bulk” hypochlorite and on-site-generated
hypochlorite is the concentration, with bulk supplied as a 12.5 % concentration of
sodium hypochlorite and on-site systems generating a roughly 0.8 % concentration of
sodium hypochlorite. The dangers of handling and transporting of a high
concentrated bulk hypochlorite make the bulk hypochlorite method to be
cumbersome and worrisome. Beside to that, the complains raised by the bulk
operators about the splash concerns, and the need to choose a plant’s location away
from a resident neighbourhood are also disadvantages for the bulk of concentrated
hypochlorite.
According to MacLean, the more highly concentrated version of hypochlorite is
unstable and degrades particularly in warm weather above 75°F. This forces the
operators to make continuous tests for the concentration of hypochlorite and to
frequently adjust the metering equipment to meet the required levels. In the Vacaville
area, bulk hypochlorite is widely available at reasonably costs. The lowest initial
capital cost for the bulk hypochlorite was a good advantage where a bulk system
consists essentially of storage tanks and metering pumps which significantly less
complex than an on-site generation system.
In the other hand, operation a complex on-site generation of sodium hypochlorite
was unknown. The operational and maintenance staffing was going to be similar for
either system, but the need for maintenance for the on-site generation system
possibly requires personnel with more electrical experience. Many researches and
36
studies had been done with field visits to some working units for generating sodium
hypochlorite. In the final analysis, upon on the experience gained by operating bulk
hypochlorite and in-site generation of hypochlorite systems led the city to choose on-
site generation of hypochlorite as the safer method and more cost-effective choice for
its wells and water plant (Seidel, 2014).
2.10.2 Factors effects on sodium hypochlorite generating
1- pH value.
Researchers (K.Asokan & K.Subramanian, 2009) studied the effects of pH,
and indicated that the stability of the solution becomes higher when the pH
solution is between 11.5 and 13. Abu Ghalwa et al. (2012) studied the effect
of pH on the production of sodium hypochlorite. They indicated that the rate
of NaOCl generation increases as the pH value increases up to 12 for both
Pb/PbO2 and C/PbO2 electrodes (Abu Ghalwa, et al., 2012).
2- Temperature value.
The relation between temperature and production of sodium hypochlorite has
been studied by (Casson & James W. Bess, 2006). They indicated that low
temperature is a challenge for on-site generation of sodium hypochlorite.
They also reported that when water temperature drop under 40oF (5
oC), it can
cause a reduction on the performance of on-site generation systems. These
systems in general are affected with water temperature less than 15oC. Thus,
when water temperatures go down 15oC, a form of heat exchanger should
installed at the outlet of the cell to increase water temperatures.
Similarly, (Boal, 2009) stated that to avoid damaging of the electrolytic cell,
water entering the electrolytic cell should have a temperature between 40 to
80 degrees Fahrenheit, unless the temperature of water entering to the on-site
generation electrolytic have a degree between this range, a heater or chiller
unit should be added to the overall system to maintain the temperature in the
range. (Sconce, 1962) also stated if the temperature reaches 85oF (30
oC), the
37
rate of decomposition can affect negatively to deplete the chlorine available
on the solution. High concentration of chlorine, which is a strong oxidant, can
be hazardous and need an extra degree of precaution.
3- Light
(Boal, 2009), investigated the exposure of sodium hypochlorite storage tanks
to the sunlight. He stated that the exposure of NaOCl to sunlight may cause
hypochlorite loss through other chemical degradation pathways. According
to (Casson & James W. Bess, 2006), hypochlorite exposure to the excessive
sunlight causes rapid degradation of the product due to the increasing
temperature on the storage tanks and to direct exposure to ultraviolet
radiation. This indicates that sodium hypochlorite stability is inversely
proportional to exposure light.
4- Electrode Material.
The electrode material is a key factor in the efficiency of generating sodium
hypochlorite. Many researchers have studied the relationship between the
type of electrode and the amount of sodium hypochlorite produced.
The proper selection of an electrode material leads to a real success of the
electrochemical technology. Selection of electrode material will extremely
affect on the formation and purity of the generation of sodium hypochlorite,
so that; the electrode material should have an efficient electro catalytic
activity and selectivity. Stability of electrode material under open circuit
conditions and its availability at a reasonable cost are also important factors
to be studied before selection of the electrode material. Usually a compromise
between activity, selectivity and cost should be done for the selection of the
material. In general, a material with high stability and low electro catalytic
properties is more interesting than a material with low chemical stability and
high electro catalyst. (K.Asokan & K.Subramanian, 2009).
38
5- Sodium hydroxide (NaCl) initial concentration.
Sodium chloride (NaCl) is the essential salt in water, often found in nature in
crystalline form. Researchers (Rengarajan, Sozhan, & Narasimham, 1996)
reported that sodium chloride was the best electrolyte for the production of
sodium hypochlorite in many researches. They concluded that the best
concentration of NaCl for the generation NaOCL was recorded to be 40-50
gpl, the associated current efficiency was high (56.3-59%), with energy
consumption corresponding to (4.8KWh kg-1
). Higher concentration of NaCl
can lead to the formation of Chlorate. Low concentration leads to minimize
the current efficiency due to water discharge leading to O2 evolution and the
chlorate formation was 7.6 times higher than expected.
6- Current density.
(Rengarajan, Sozhan, & Narasimham, 1996) studied the influence of the
current density on the current efficiency for the production of sodium
hypochlorite. The result was at current density rage of 5 -10 A.dm-2
maximum current efficiency 56-57% was achieved. At higher current
densities the current efficiency was decreased since the increase of current
density tends to increase the formation of chlorate or oxygen evolution.
(K.Asokan & K.Subramanian, 2009) indicted the current density has a
significant effect on the production of sodium hypochlorite due to the need of
sufficient current density to generate sodium hypochlorite. In general, in the
electro-chemical reactions, the chemical change is based on quantity of
current passed, as per faraday’s first law of electrolysis. In Industry, current
passed is usually reported in terms of current density which denotes the
current passed per unit electrode. They concluded that when current density
increases, the hypochlorite production also increases. And thus temperature
of the cell also increases. When temperatures increase beyond 308 K, sodium
hypochlorite tends to chemically decompose to sodium chlorate.
3NaClO → NaClO3 + 2 NaCl
39
(M. A. Aziz, Ali, & Islam, 2010) studied the power consumption and current
efficiency for the production of sodium hypochlorite, they concluded that the
maximum current efficiency obtained was 91.06% at current density of
625Am-2
at 22oC using dichromate to the electrolyte.
2.11 Key components of an on-site generation of sodium hypochlorite
system
A- System Control Panel
1 Mimic Panel of all components
2 Electrolyze Cell status
3 System Start / Stop & Reset
4 Brine Pump Status
5 Brine Flow Rate
6 Brine Tank usage to date
7 Water Softener status
8 Product Tank level
9 Metering Pump status
10 Chlorine Residual
11 Process Alarms
B- Power Supply / Rectifier
It is used to convert VAC to low voltage DC to power Electrolyser Cell(s)
C- Electrolyze Cell
UV stabilized PVC body containing Anode and Cathode
E- Water Softener
Ion Exchange type Water Softener that removes Scaling Calcium and Magnesium
Salts with non-scaling Sodium Salts preventing fouling of the cells. Provides water
supply to Brine Tank.
F- Brine Tank (Salt Saturator)
A tank which contains the brine generated from the desalination process. This
Saturated Brine Solution will be pumped to the Electrolyser Cells.
40
G- Brine Pump
It is used to pump the Saturated Brine Solution to the Electrolyser Cells.
H- Sodium Hypochlorite Storage Tank
A storage tank for storing the bulk 0.8% Sodium Hypochlorite, the tank includes
Hydrogen Vent and Ultrasonic Level Switch.
Figure (2.2) shows the configuration of the on-site generation system for producing
sodium hypochlorite.
Figure (2.2): Typical system configuration.
Chapter 3
Materials and Methods
41
3 Chapter 3
Materials and methods
Introduction 3.1
This chapter will discuss the materials, equipment, and the analysis procedures which
have been used on the experimental work which was performed in a batch mode to
produce sodium hypochlorite from brine water.
The concept of this experiment is to produce Sodium hypochlorite measured from
seawater brine, using different operating treatment conditions. Experimental work
was conducted at the laboratories of the Environmental and Land Science
Department of Islamic University in Gaza (IUG).
Materials and Chemicals 3.2
The following materials and chemicals were used in the electrolysis process to
generate sodium hypochlorite from seawater brine.
Brine samples from Al-Bassa desalination plant.
Sodium Hydroxide purity equal to 98.0% wt, produced by: HiMedia
Laboratories Pvt. Ltd., India).
Hydrochloric acid (HCl), with concentration 37% volume.
Sodium hypochlorite 3% concentration as stock solution.
Distilled water.
Acetic Acid, conc. (glacial).
Potassium iodide, Klm crystals.
Sodium thiosulphate.
Starch indicator.
Apparatus and glasses 3.3
The following apparatus and glasses were used in the experiments.
Magnetic stirrer.
Digital balance.
42
Flasks 1000 ml, Conical flask 500ml, cylinders 100 ml and 250ml, plastic sample
bottles 100 ml.
Burette and Burette stand.
Porcelain tile.
Pipette with elongated tips.
Wash bottle.
Digital pH meter made by AQWA company.
Spectrophotometer CT-2200.
Electrodes which are: two 0.3 cm copper wire, two 0.8 cm and two 1.3 cm graphite
rods, two 2x15cm stainless steel plates, two 1.3 aluminum rods;
DC supply system (Gwinstek GPS-3303);
Experimental program 3.4
The experimental study used the following factors to study the efficiency of
production of sodium hypochlorite under following conditions:
1. Type of rods (Graphite, Copper, Aluminum, Stainless steel) factor.
2. Changing distance between rods.
3. Changing current density (mA/cm2).
4. Changing contact time (min).
Previous conditions, we take six samples for each condition to measure effect for each of
them and describe relation between these conditions and efficiency of production of sodium
hypochlorite. The operating conditions for each test run are summarized in Table (3.1).
43
Table (3.1): Test runs plan summery for operating parameters.
Test
run
#
Test
run
description
Electrode
Material Current intensity Voltage
Distance
between rod
Effective
surface
area
1 Electrolysis
time
Graphite,
Copper,
Aluminum,
Stainless
steel
0 to 300mA.cm-1 12V 4cm Different
2 Current
intensity
Graphite,
Copper,
Aluminum,
Stainless
steel
0 to 300mA.cm-1 12V 4cm different
3 Type of rods Graphite,
Copper,
Aluminum,
Stainless
steel
Optimum for each
electrode
12V 4cm Different
for type
of
electrode
4 Surface area
ratio
Graphite 176.5mA.cm-1 12V 4cm (33.9,
2.26)
cm2
5
Distance
between rods.
Graphite 176.5mA.cm-1 12V (0.5,1,2,4,6)cm 33.9
6 Stability of
sodium
hypochlorite
Graphite 176.5mA.cm-1 12V 2cm 33.9
7 Stability of
electrode rod
Graphite,
Copper,
Aluminum,
Stainless
steel
176.5mA.cm-1 12V 4cm Different
for type
of
electrode
Experimental set up 3.4.1
Figure (3.1) shows the electrolysis process of brine which generates sodium
hypochlorite, hydrogen and other deposit.
44
Figure (3.1): Schematic diagram of production of sodium hypochlorite process
As shown in the schematic sketch Figure (3.1) the cylindrical shaped reactor consists
of two electrodes each having the same dimension for the same type of electrode.
The electrodes were immersed in the brine and connected to a DC power supply
(Gwinstek GPS-3303) to transform AC to DC. For each experimental run, a constant
electrode spacing of 4 cm was maintained.
In each batch experiment 1,000 ml of seawater brine was utilized under room
temperature between (25±3 °C). Each experimental run continued for at least 3
hours. At each stage the reactions were occurring and recorded at both the anode and
the cathode electrodes.
The operating electrolysis was carried out under the following condition: current
density, 0.1-6 A; pH 10-13; potential voltage, 3-12 V; temperature, 25° to 26°C, and
the brine TDS is about 65,000 ppm. The time of electrolysis ranged from 0 to 210
min. The distance between the two electrodes (anode and cathode) varies from 0.5 to
6 cm, and the ratio of surface area between cathodes is 1:2.5.
45
Seawater brine samples were collected from the cell every 30 min and transported to
the laboratory for NaOCl concentration. The laboratory tests were carried out in
Laboratory of environment and land science in the Islamic university of Gaza.
Figure (3.2): Photographic pictures for the electrocoagulation system
Hardness removal 3.4.2
Removal of Hardness aims to remove Scaling Calcium and Magnesium Salts with
non-scaling Sodium Salts preventing fouling of the cells and sedimentation of salts in
the flasks. There are number of methods to remove the hardness present in brine
water. One of those methods is being followed; the brine water gets converted to soft
water by adding washing soda (Sodium Hydroxide) to remove hardness from water.
For each litter of seawater brine an amount of 14g of sodium hydroxide were added
to remove hardness from brine water where the pH raised up to 12 or 13.
46
Analytical methods 3.5
The concentration of sodium hypochlorite was determined by two ways; CT-2200
Spectrophotometer and iodometric titration. The samples were collected each 30
minutes and transported to the Laboratory to determinate the NaOCl concentration.
The spectrophotometer was turned on and warmed up for 20 minutes before the start
of measuring for any sample. The cuvette was also cleaned with a detergent-saturated
cotton-tipped stick each time before using.
The analytical measurements performed in this study were conducted according to
- IS 3025 (Part 26): Method of Sampling and Test.
- The Standard Methods for the Examination of Water and Wastewater (APHA,
2005).
- Dichloropropanone Lab of the UMass College of engineering.
Colourmetric Method 3.5.1
In the colourmetric method, sodium hypochlorite has been investigated using
Spectrophotometer CT-2200 device.
Reagents and Standards 3.5.1.1
According to the Dichloropropanone Lab of the UMass College of engineering,
Hypochlorite can be read at maximum wavelength 292nm. It is also the same reading
used by (Abu ghalwa et al., 2015) to measure the wavelength absorption at 292nm in
Al-Azhar University in Gaza. No reagents have been used for the determination of
Sodium hypochlorite (NaOCl) using CT-2600 Spectrophotometer.
47
Figure (3.3): Free Chlorine Absorptivity at 20 C
Procedure 3.5.1.2
Stock solution preparation
1) A stock solution was taken from pure sodium hypochlorite with concentration 3%,
and then it had used to prepare a solution with concentration 0.1% in 100 ml and
blank sample.
2) The solution was diluted serially with concentration 0.05%, 0.025% and 0.0125%.
3) The spectrophotometer was turned and adjusted wavelength to 292 nm.
4) Spectrophotometer had read blank sample and give the machine zero reading.
5) Read the wavelength of the prepared stock solution samples with concentration of
(0.0025%, 0.005%, 0.01%, 0.02%) respectively and prepare a stock solution trend
line
6) A relation was drawn between concentration of stock solutions and
spectrophotometer readings by using M.S. Excel.
7) Use the equation to conclude the concentration of other samples.
8) To have correct readings, the value of R2 of the drawing was maintained to be about
95% or above.
48
Figure (3.4): Stock solution curve
Reading for Brine Samples. 3.5.1.3
a- Turn on the spectrophotometer, and adjust the wavelength reading to 292nm.
b- Read the blank sample and give the machine zero reading.
c- Read the wavelength of samples which delivered to the device each 30 minutes
and record the results by using the best dilution for each sample.
d- Use the stock solution equation and dilution times to conclude the concentration
of each sample.
e- Draw the curve of each sample.
y = 22.339x R² = 0.9969
0
0.5
1
1.5
2
2.5
0 0.02 0.04 0.06 0.08 0.1 0.12
Series1
49
Iodometric method 3.5.2
This method is more precise than colorimetric method, where residual concentration
exceeds 1 mg/L, but for lower concentration it is not so accurate. This method is
according to (IS 3025 (Part 26): Method of Sampling and Test) in accordance with
The Standard Methods for the Examination of Water and Wastewater (APHA, 2005).
Preparation of reagents 3.5.2.1
Weigh approximately 2.482 g of sodium thiosulphate, transfer to the beaker and
dissolve it in boiled distilled water. Transfer it to standard flask and make it up to
1000ml.
Testing of samples 3.5.2.2
1. Rinse the burette with sodium thiosulphate and then fill the burette with sodium
thiosulphate.
2. Fix the burette to the stand.
3. Take 200 mL of a given sample in a conical flask.
4. Add 5 mL Acetic acid. To acidify the sample. It is used to reduce the pH
between 3 and 4 in the conical flask.
5. Add about 1 g Potassium Iodide (KI) measured using the spatula and dissolve it
by thoroughly mixing it with stirring rod.
6. Perform the titration quickly, since iodine liberate faster.
7. Titrate the solution with standard Na2S2O3 solution until the yellow color of
liberated Iodine is almost faded out. (Pale yellow color).
8. Add 1 mL of starch solution and continue the titration until the blue color
disappears.
9. In many cases residual chlorine is very low and starch needs to be added before
starting up the titration.
10. Note down the burette reading (to know the volume of sodium thiosulphate
added).
11. The reading is 10.6 mL.
50
3.5.3 Samples Collection
Samples were collected using sterilized 100 ml plastic bottles from each experiment.
There are four experiments, each experiment includes six samples.
Each experiment represents one of previous conditions, to model results of each
experiment (mathematical model) that describes concentration of sodium
hypochlorite under previous condition. The sterilize bottles were numbered and
labelled. Attention was also paid during sampling to avoid mixing effluents as this
could lead to a change in the percentage of sodium hypochlorite.
The samples bottles were then immediately brought to the lab for analysis in term of
sodium hypochlorite concentrations and pH. For sodium hypochlorite analysis, the
samples were separated in 100 ml bottles. The characteristics and the conditions of
operations for the four types of electrode material at different current densities are
described in Table (1, 2, 3&4) below.
51
Table (3.1): The characteristics and conditions associated with producing NaOCl under certain conditions using graphite electrode.
Voltage
(v)= 12
length of
Rode (cm)=
15
rode
weight
initial (g)
=
62.3 Volume of
brine (ml) 1000
current
(A)= 0.5
surface area
(cm2)=
29.39
rode
weight
final (g) =
61.5 wet length of
rod (cm)
7.5
Rod
Dia.
(cm)=
1.2
current
density
(mA.cm-2
)
17.01 First Iteration
Distance
between
rode cm
4
Iteratio
n No. Time(min)
Rod
Dia.m
m
TDS
initial
(mg/L)
TDS final
(mg/L)
pH
initial
pH
Final
temperature
initial
temperature
final
1 30 12 81280 81280 12.6 12.6 27 27.3
2 60 12 81280 81280 12.6 12.6 27 27.3
3 90 12 81280 81280 12.6 12.6 27 27.3
4 120 12 81280 81280 12.6 12.6 27 27.3
5 150 12 81280 81408 12.6 12.7 27 27.6
6 180 12 81280 81344 12.6 12.6 27 27.7
52
Table (3.2): The characteristics and conditions associated with producing NaOCl under certain conditions using Aluminium electrode.
voltage(v)= 12
length of Rode (cm)= 15
rode weight initial
(g) = 32.58
Volume of brine
(ml) 1000
current
(A)= 1
surface area (cm2)=
80.54 rode weight final
(g) =30.58
wet length of rod
(cm) 9.5
internal
dia cm 1.1
Rod
Dia.(cm)= 1.6
current density
(mA.cm-2
) 12.416 First Iteration
distance between
rode cm 4
Iteration
No. Time(min)
Rod
Dia.mm
TDS
initial(mg/L)
TDS final
(mg/L)
pH
initial
pH
Final
temperatu
re initial
temperat
ure final
1 30 16 60928 60288 12 12 16.7 17.1
2 60 16 60928 59840 12 12 16.7 17
3 90 16 60928 60416 12 12.1 16.7 17.4
4 120 16 60928 60608 12 12.1 16.7 17.6
5 150 16 60928 60992 12 12.1 16.7 17.5
6 180 16 60928 59904 12 12.2 16.7 17.9
7 210 16 60928 61312 12 12.2 16.7 18.1
53
Table (3.3): The characteristics and conditions associated with producing NaOCl under certain conditions using Copper electrode.
Voltage
(v)= 12
length of Rode
(cm)=
15 rode weight
initial (g) = 8.119
Volume of
brine (ml) 1000
current
(A)= 0.7
surface area
(cm2)=
7.4575 rode weight final
(g) = 6.995 wet length of rod (cm)
9.5
Rod
Dia.(cm)= 0.25
current density
(mA.cm-2
)
93.86 First Iteration
distance cm 4
Iteration
No. Time(min)
TDS
initial(mg/L)
TDS final
(mg/L) pH initial pH Final
temperature
initial
temperature
final
1 30 68672 732160 12.9 12.8 16.8 20.4
2 60 68672 73920 12.9 12.9 16.8 21
3 90 68672 7564.8 12.9 12.8 16.8 21.9
4 120
68672 75840 12.9 12.9 16.8 21.2
5 150 68672 76224 12.9 12.8 16.8 22.4
6 180 68672 76352 12.9 12.8 16.8 23.1
7 210 68672 76462 12.9 12.8 16.8 24.3
54
Table (3.4): The characteristics and conditions associated with producing NaOCl under certain conditions using Stainless steel electrode.
Voltage
(v)= 12
length of Rode (cm)= 15
rode weight
initial (g) = 18.84
Volume of brine
(ml) 1000
Current to time
study
current
(A)= 1
surface area (cm2)=
38 rode weight
final (g) = 16.65 wet length of rod (cm)
9.5
Rod
width
(cm)=
2
current density
(mA.cm-2
)
26.316 First Iteration
distance
cm 4
Iteration
No.
Time
(min)
TDS
initial
(mg/L)
TDS
final
(mg/L)
pH
Initial
pH
Final
temperature
initial C
temperature
final C
1 30 60672 61888 11.9 12 16.7 17.9
2 60 60672 61504 11.9 12.1 16.7 18.7
3 90 60672 61440 11.9 12.1 16.7 19.5
4 120 60672 60480 11.9 12.2 16.7 20.3
5 150 60672 64576 11.9 12.1 16.7 20.8
6 180 60672 59840 11.9 12.2 16.7 21.1
7 210 60672 67840 11.9 12.2 16.7 21.5
55
3.6 Calculations
Based on the experiment measurements, some items were calculated. The following
formulas are used for calculating the items:
Dilution equation:
Ci × Vi = Cf × Vf
Where,
Ci : Initial concentration of solution,
Vi : Initial volume of solution,
Cf : Final concentration of solution,
Vf : Final volume of solution,
Residual chlorine by titration method
Residual chlorine (mg/L) =
volume of sodium thiosulphate×𝑛𝑜𝑟𝑚𝑎𝑙𝑖𝑡𝑦×𝑒𝑞𝑢𝑖𝑣𝑎𝑙𝑒𝑛𝑡 𝑤𝑒𝑖𝑔ℎ𝑡 𝑜𝑓 𝑐ℎ𝑙𝑜𝑟𝑖𝑛𝑒×1000
𝑉𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑠𝑎𝑚𝑝𝑙𝑒
Power consumption
Power consumption = IEt/1000×3600 kW⋅h
Where,
I is the applied current, A;
E is the voltage of the electrolytic cell;
t is the electrolytic time, s.
Chapter 4
Results and Discussion
56
4 CHAPTER 4
Results and Discussion
Introduction 4.1
This chapter discusses the experimental observations, phenomenas and results.
Generation of sodium hypochlorite using seawater brine was determined by studying
many factors that affects the production process of sodium hypochlorite. These
factors are electrode material, current density, surface area ratio, inter-electrode
spacing, and temperature.
Characteristics of seawater, product and brine of Al-Bassa seawater 4.2
desalination plant
The characteristics of seawater, product and brine for Al-Bassa seawater desalination
plant have been studied in the laboratory of CMWU. The results of the analysis are
recorded in table (4.1).
Table (4.1): characteristics of water into and out of Al-Bassa seawater desalination
plant in Deir Albalah
No. Tests Seawater Product Brine
1. pH 7.78 6.9 7.53
2. EC (µS) 59800 180 95000
3. TDS (mg/L) 43050 70 68800
4. Chloride (mg/L) 22657.94 60 37562.00
5. Hardness (mg/L) 8590.00 30 19800
6. Calcium (mg/L) 400 2 700
7. Magnesium (mg/L) 1843.42 6.07 2926
8. Alkalinity (mg/L) 146 3.8 216
9. Nitrate (mg/L) 4.7 0 5.4
10. Sulfates (mg/L) 3650 1 5850
11. Sodium (mg/L) 12126.9 28 18929.27
12. Potassium (mg/L) 488.10 1.80 625
13. Boron (mg/L) 4.2 0.7 7.1
14. Quantity (m3/hr) 30 15 15
57
Relationship between running time and effective concentration of 4.3
NaOCl
The current time of process affects the production of NaOCl. In this study the effect
of current time on the production of Sodium hypochlorite using four electrodes
materials; graphite, aluminium, stainless steel, and copper was examined. The
current duration was different from 0 to 210mins. It was observed that increasing the
duration time has a direct relation with the production of NaOCl until a definite
point, and then the increase of time will have no effects on the process efficiency as
it reaches to a steady state condition. These relations are shown in the figures below.
In Figure (4.1) the effects of the current time on the effective concentration (Ceff) of
sodium hypochlorite was investigated using graphite electrodes with diameter 1.3 cm
and the space between the electrodes was 4cm, at voltage 12V and at different
current densities. The Figure (4.1) shows at a current density equal to 176.5mA.cm-2
,
the (Ceff) of NaOCl was increasing by increasing the time duration until around
120min. then the increasing of time duration will have no effects on the effective
concentration of sodium hypochlorite. This can be attributed to the efficiency of the
current density which can generate a maximum rate of sodium hypochlorite using the
selected graphite electrode, so that, any increasing of time, will have no touchable
effects on the (Ceff) of NaOCl. As a result of graphite electrodes, the time 120mins
was the best duration time for generation of NaOCl at different current density. The
highest rate of production of NaOCl was recorded as 1.9% under these conditions.
Figure (4.1): Relation between electrolysis time and effective concentration of
NaOCl using graphite electrodes
0
0.5
1
1.5
2
2.5
0 50 100 150 200 250Effe
ctiv
e c
on
cen
trat
ion
of
NaO
Cl (
%)
Time (min)
17 mA.cm-2
29.5 mA.cm-2
59 mA.cm-2
73.5 mA.cm-2
102.9 mA.cm-2
102.9 mA.cm-2
176.5 mA.cm-2
294.5 mA.cm-2
58
Figure (4.2) shows the rate of production of sodium hypochlorite using aluminium
electrodes versus electrolysis time. Figure (4.2) shows that for the different current
densities, the increasing time of electrolysis will lead to increasing the effective
concentration of sodium hypochlorite until a time of 60mins, and then increasing the
electrolysis time will not affect the effective concentration of NaOCl. This fact
returns to the efficiency of current density under the electrolysis conditions using
4cm space between two aluminium electrodes.
The highest rate of production of NaOCl using aluminium electrode was recorded as
0.156% after 60 minutes using a current density 74.4mA.cm-1
. Increasing the time of
electrolysis after 60 minutes will have insignificant impact on the generation of
sodium hypochlorite.
Figure (4.2): Relation between time of electrolysis and effective concentration of
NaOCl using aluminium electrodes.
The same is shown in the Figure (4.3), increasing the electrolysis time under the
different current densities lead to increasing the Ceff of NaOCl.
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
0 50 100 150 200 250Effe
ctiv
e c
on
cen
trat
ion
of
NaO
Cl (
%)
Time (min)
12.5 mA.cm-2
37.5 mA.cm-2
62 mA.cm-2
74.4 mA.cm-2
99.2mA.cm-2
59
Figure (4.3): Relation between electrolysis time and effective concentration of
NaOCl using cooper electrodes.
Where at current density of 170mA.cm-2
increasing the time of electrolysis will
increase the effective concentration of sodium hypochlorite until 30 minutes, then
any increasing of the time will not lead to increase the Ceff of NaOCl. From the
Figure (4.3), it was shown that almost all the current densities have one optimum
electrolysis time which is 30mins. These phenomena attributed to the material
conductivity which has a high limit under special conditions of electrolysis process.
With stainless steel electrodes, the results were almost the same, the increasing of
electrolysis time will increase Ceff of NaOCl. This is clear at 26.5mA.cm-2
current
density, where increasing the time of electrolysis will increase the Ceff until a time of
210 mins, then any increasing of the time will not increase the Ceff of NaOCl.
0
0.1
0.2
0.3
0.4
0.5
0.6
0 50 100 150 200Effe
ctiv
e c
on
cen
trat
ion
of
NaO
Cl (
%)
Time (min)
26.8 mA.cm-2
67 mA.cm-2
93 mA.cm-2
134 mA.cm-2
170 mA.cm-2
60
Figure (4.4): Relation between electrolysis time and effective concentration of
NaOCl using stainless steel electrodes.
As a result, the four electrode materials under the same conditions of electrolysis
showed that the time of electrolysis is directly proportional to the concentration of
Ceff of NaOCl until a definite time which is different for each electrode, and then any
increasing of the time will not have an effect on the concentration of sodium
hypochlorite as Ceff of NaOCl reaches to a steady state value.
Relationship between current density and process efficiency 4.4
The efficiency of the production of NaOCL is very dependent on the appropriate
current density. In this study the effect of current density on the production of NaOCl
using graphite, aluminium, stainless steel and copper electrodes was studied. The
current density was varied between 12.4 to 294.5mA/cm2 in four experiments for
each electrode. Temporal variation of NaOCl production at different current densities
is shown in Figures down.
In Figure (4.5) by using graphite electrodes, it was observed that the concentration of
NaOCl have a direct relation with increasing current density up to 176.5mA.cm-2
. A
further increase in the current density will effect negatively in the concentration of
NaOCl of the process as shown in Figure (4.5). By using a current density of 176.5
mA.cm-2
, the production of NaOCl reached a rate of 1.9%. The decrease in the
production of sodium hypochlorite is due to the fact that each material connected to
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
0 50 100 150 200 250 300
Effe
ctiv
e c
on
cen
trat
ion
of
NaO
Cl (
%)
Time (min)
26.5 mA.cm-2
65.7 mA.cm-2
92.1 mA.cm-2
157.89 mA.cm-2
61
the current has a value that is considered the optimum current density for connecting
current. By increasing current density over this magnitude, the electrode material
begins to corrode and dissolve. In addition to the increasing of temperature, which
led to lower the NaOCl production rate and NaOCl tended to chemically decompose
to sodium chlorate.
In general, current density is proportionally directed to the production cost, thus, it
mandatory to use the optimum value for the current density to achieve the effective
production of NaOCl and maintain cost as minimum. From this research, the best
current density was found to be 176.5 mA.cm-2
, which is the most suitable for an
effective generation of NaOCl.
Figure (4.5): Relation between current density and NaOCl effective concentration
using graphite electrode at 120min.
Figure (4.6) shows the rate of production of sodium hypochlorite using aluminium
electrodes by electrolysis process. The highest rate of production of NaOCl using
aluminium electrode was recorded 0.156% using a current density 74.4mA.cm-2
.
Increasing beyond this magnitude of the current density of the electrolyzing cell will
cause in decreasing of the concentration of sodium hypochlorite generated in the
process due to the increasing the temperature of the electrolysis cell. This is noticed
when the current density increased from 12.5 mA.cm-1
to 99.2 mA.cm-2
.
0
0.5
1
1.5
2
2.5
17 29.5 59 73.5 88.5 102.9 176.5 294.5
Effe
ctiv
e c
on
cen
trat
ion
of
NaO
Cl (
%)
Current density mA/cm2
62
Figure (4.6): Relation between current density and NaOCl effective concentration
using Aluminium electrode at 60min.
The same relation was shown in copper electrodes in Figure (4.7), the efficiency of
producing sodium hypochlorite was increasing with increasing current density until it
became 134 mA.cm-2
. The increasing of current density beyond will cause to
decrease the rate of production of sodium hypochlorite due to the conductivity
optimum magnitude for cooper and the increasing of temperature and it will also
affect adversely on the shape of the electrode as shown in Figure (4.8). The rate of
consumption of the copper electrodes indicates that it will be costly as an electrode
material. The highest effective production for copper electrode was 0.54 % which is
low in comparison with graphite electrodes.
0
0.02
0.04
0.06
0.08
0.1
0.12
0.14
0.16
0.18
12.5 37.5 62 74.4 99.2
Eff
ecti
ve
con
cen
tra
tio
n o
f N
aO
Cl
(%)
Current mA/cm2
63
Figure (4.7): Relation between current density and NaOCl effective concentration
using Copper electrode at 30min.
Figure (4.8): The deformation of Copper Electrode shape by increasing current
density.
The rate of production of sodium hypochlorite using Stainless steel electrodes is
shown in Figure (4.9). It describes the relation between current density and the
effective concentration of sodium hypochlorite. it is clear with current density
reaches 26.5 mA.cm-2
, the rate of NaOCl concentration increase to an optimum value
by using stainless steel electrodes, increasing more of current density has negative
0
0.1
0.2
0.3
0.4
0.5
0.6
26.8 67 93 134 170
Eff
ecti
ve
con
cen
tra
tio
n o
f N
aO
Cl
(%)
Current Density mA/cm2
64
effects on generation of sodium hypochlorite, this returns to the effect of current on
the stainless steel plate which exposes it to corrosion and losing its weight, thus
decreasing surface area of electrodes.
Figure (4.9): Relation between current density and NaOCl effective concentration
using Stainless steel electrode at 30min.
Relationship between surface area ratio, current density and process 4.5
efficiency
The surface area of the electrodes was examined in Figure (4.10). Two couples of
graphite electrodes have been selected with different diameters, namely, 1.3 cm and
0.8 cm each has a surface area of 33.9 cm2 and 3.2 cm
2. Both of the electrodes have
generated NaOCl but with different concentration. The figure shows that as the
surface area of the electrode increased, the generation of sodium hypochlorite
increases. This presents the proportional relationship between the surface area of the
electrode and the total amount of sodium hypochlorite.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
14.5mA.cm-2
26.5mA.cm-2
65.7mA.cm-2
92.1mA.cm-2
157.89mA.cm-2E
ffec
tiv
e co
nce
ntr
ati
on
of
Na
OC
l (%
)
Current Density mA/cm2
65
Figure (4.10): Relation between surface area ratio and concentration of NaOCl
Effects of Electrode material 4.6
Graphite, copper, stainless steel and aluminium were studied as candidate materials
for selection investigation of the best electrode material. The production of sodium
hypochlorite associated with using different type of electrode material is discussed in
in Figure (4.11). Figure (4.11) shows that at times greater than 150 min the sodium
hypochlorite production was insignificant for both aluminium and copper. That
returns to the fact that both metals are characteristiced with their good conductivity,
they are both easily available and frequently used in the electrolytic industry. The
relatively low efficiency of the production of NaOCl for aluminium and copper
concludes that they are not feasible to be used as electrode materials (0.149 % and
0.5 % respectively). Stainless steel electrode showed more efficiently than copper
and aluminium but it was not selected due to insufficient production of NaOCl in this
study (1.46 %). Similar results are also reported in the literature. Production of
NaOCl reached about 1.9 % using the graphite electrodes. In addition, the stability of
aluminium and graphite electrodes showed better performance than other tested
electrodes during experimental runs. Graphite showed better results than other
electrodes in the research that maybe return to the garphite is an inert component.
0
0.5
1
1.5
2
2.5
0 50 100 150 200 250 300
Effe
ctiv
e c
on
cen
trat
ion
of
NaO
Cl (
%)
Time (Mins)
Surface area ratio and Concentration of NaOCl
Dia=1.3cm
Dia=0.8cm
66
Figure (4.11): The effect of different electrode material on the production of sodium
hypochlorite
By using the difference between the initial and final mass of electrodes, the
electrodes stability and Consumption rate were measured, it was seen that the
consumption of the electrode is directly proportional to the economics of the process
since the electrodes should be changed after their life-time is reached. Table (4.2)
shows the results of mass consumption for the electrode materials which are
consumed during 180 min running time. Results revealed that the consumption of the
stainless steel electrode is the highest. This related to the shape of the stainless steel
electrode which was a plate while other electrodes were cylindrical rods. However,
copper lost half of its total weight which is considered also a high consumption and
this shows that copper can react fast in the process and lose its weight fast. Graphite
and aluminium showed more stability than other electrodes that makes them
preferable as electrodes based on noble metals, which were known for their superior
resistivity to corrosion and oxidation.
0
0.5
1
1.5
2
2.5
0 50 100 150 200 250 300
Effe
ctiv
e c
on
cen
trat
ion
of
NaO
Cl (
%)
Time (min)
Electrode material and Concentration of NaOCl
Graphite Rod Aluminum Rod Copper weir Satinless steel
Distance=4cm
67
Table (4.2): Stability of rods material during operation
Electrode Material Mass Consumed (g) Rate of Mass
Consuming
Graphite 0.7 2.1875%
Aluminum 0.1 0.25%
Copper 3.4 28.3%
stainless steel 9.467 11.61%
Effects of Inter-Electrode spacing 4.7
The production of sodium hypochlorite was investigated in the seawater brine up to
210 minutes, the inter-electrode distance was fixed at certain values (0.5, 1, 2,4 and 6
cm) while two electrodes with 1.3cm diameter were sank in the brine solution as
anode and cathode with the optimum current density 176.5 mA/cm2 for 210 minutes.
Figure (4.12) below illustrates the different production of NaOCl with time for the
different spacing. It was clear that at 1 cm distance the production of NaOCl reaches
the highest rate of 2.17% and was more significant. Similar to literature the increase
in the electrode spacing made reduction in the total effective concentration of NaOCl
due to water resistance to current, which decrease current density between electrodes.
Figure (4.12): Relation between hypochlorite concentration and inter electrode
spacing.
The Figure (4.12) also shows that the increasing of the time of the experiment will
have no significant effect on the effective concentration of sodium hypochlorite after
0
0.5
1
1.5
2
2.5
0 50 100 150 200 250
Effe
ctiv
e c
on
cen
trat
ion
of
NaO
Cl
(%)
Time (min)
Inter-Electode spacing
2 cm
4 cm
6 cm
1 cm
0.5 cm
68
120min. This indicated that the best time for generation sodium hypochlorite with
graphite electrodes is 120 minutes.
Effects of Temperature 4.8
Hypochlorite generation relies mainly on temperature as one of the important factors
affecting the electrolysis process. It is noticed that the increase of temperature will
result in decreasing the concentration of NaOCl and thus, the efficiency of the
reaction. NaOCl gave more concentration with Low temperature. The chemical
decomposition rate of the hypochlorite was increased by the increasing of
temperature as mentioned already. The increasing of temperature also increases the
solution temperature which allows Cl2 gas to generate and evaporate which leads to
decrease the concentration of NaOCl. The electrolysis process has to be performed at
the ambient temperature at which a maximum NaOCl concentration can be generated
at 25C◦. Figure (4.13) shows the relation between temperature and NaOCl
concentration.
Figure (4.13): Effect of Temperature on NaOCl generation.
Stability of sodium hypochlorite 4.9
The hypochlorite is a relatively stable product, even though the degradation occurs,
mainly as a result of; chlorine volatilization (accelerated during forced air venting),
0
0.5
1
1.5
2
2.5
25 30 35 40 45 50
Hy
po
chlo
rite
gen
era
tio
n (
%)
Temperature C
Effect of Temperature on NaOCl generation
NaOCl prodution
69
hypochlorite decomposes into O2 and NaCl in case those contaminations reach the
tank, and the chemical reactions that form chlorate (very slow relative to commercial
hypochlorite because of relatively small hypochlorite concentration).
The stability of the sodium hypochlorite was investigated using the samples of the
optimum generation of NaOCl, six samples having a size of 100 millilitres where
kept for seven days in closed bottles, where three of them were kept in normal daily
light and the other three were stored in a dark place. The six bottles were tested every
day for seven days. Table (4.3) down shows the results of the reduction of the
concentration of the sodium hypochlorite
Table (4.3): The reduction of the concentration of sodium hypochlorite
25 C -
light
25 C –
Dark
0 day 0 0
1 day 0.8 0.2
2 days 4.7 0.9
3 day 7.2 1.4
4 days 12.6 2
5 days 18 2.7
6 days 19.2 3.3
7 days 22.55 4.6
Other factors relations 4.10
Table (4.4) shows the results of experiment for the best electrocoagulation process
for producing sodium hypochlorite using seawater brine. The table shows the
difference on the graphite rod weight during the run time of the process. The
differences on TDS, pH value and temperatures on each iteration were also recorded.
70
Table (4.4): Optimum conditions for production of hypochlorite
Optimum conditions for production of hypochlorite
voltage
(v)= 12
length of
Rode (cm)= 15
rode weight
initial (g) = 61.6
Volume of
brine (ml) 1000
current
(A)= 6
surface area
(cm2)= 33.892
rode weight
final (g) = 60.9
wet length
of rod (cm) 9
Rod
Dia.(c
m)= 1.3
current
intensity
(mA.cm-1) 176.56
Iteratio
n No.
Time
(min)
TDS
initial(mg/L)
TDS
final pH initial
pH
Fina
l
temperature
initial
tempe
rature
final
1 30 69120 77284 12.6 12.6 15.6 23
2 60 77284 81408 12.6 12.8 23 31
3 90 81408 84672 12.8 12.7 31 45
4 120 84672 87744 12.7 12.9 45 52
5 150 87744 87488 12.9 12.7 52 60
6 180 87488 89465 12.7 12.8 60 65
7 210 89465 89335 12.8 12.8 65 73
8 240 89335 89434 12.8 12.7 73 79
The TDS relation with electrolysis process was studied for each experiment, it has
been noticed that the TDS concentration increased with the increasing of the time of
the electrolysis process. This belongs to the composition of the hypochlorite on the
solution. Figure (4.14) shows the relation between TDS and the electrolysis process
for the production of NaOCl for the graphite electrodes, under 176.56mA/cm2
current density, 12V voltage, 4cm inter electrode distance; effective surface area is
33.89 and pH 12.6. It has been noticed that the temperature of the solution increased
with increasing time of the electrolysis process as shown in Figure (4.15).
71
Figure (4.14): Relation between TDS concentration and time (min).
Figure (4.15): Relation between temperature and time (min).
Total Dissolved solid effects 4.11
The presence of dissolved solids in water may affect its taste. The palatability of
drinking water has been rated by panels of tasters in relation to its TDS level as
follows: excellent, less than 300 mg/litre; good, between 300 and 600 mg/litre; fair,
between 600 and 900 mg/litre; poor, between 900 and 1200 mg/litre; and
65000
70000
75000
80000
85000
90000
0 50 100 150 200
TDS
(mg/
L)
Time (min)
TDS (mg/L)with Time(min)
0
10
20
30
40
50
60
70
80
30 60 90 120 150 180 210 240
tem
pe
ratu
re (
C )
Time (min)
Temperature
Temperature
72
unacceptable, greater than 1200 mg/litre. Water with extremely low concentrations
of TDS may also be unacceptable because of its flat, insipid taste (WHO, Guidelines
for drinking-water quality, 1996).
The sodium hypochlorite (with TDS 89465) will be added to the desalinated water to
be in the accepted levels to the WHO, the rate of sodium hypochlorite in the drinking
water should be in the rage of 0.5 ppm. This amount is considered too low value. An
amount of 50milliliters is added to each 10000 Litter using 12% sodium
hypochlorite. To study the total dissolved solid a tank of 1000 litter was filled with
desalinated water, and 25 millilitres added to sodium hypochlorite with the
concentration of 2% to achieve the standards of chlorine in drinking water. The
experiment was used to examine the effect of the TDS related to the NaOCl to the
water. The results are shown down
Table (4.5): Result of sodium hypochlorite
TDS initial TDS final
70.056 mg/l 72.281
Table (4.5) shows that the effect of sodium hypochlorite on the production of
drinking water is too low and the water still valid the drinking and under the
standards of drinking water.
Power consumption 4.12
The electrical energy consumed for NaOCl using graphite electrodes was calculated
by the following equation:
Electrical energy consumed = IEt/1000×3600 kW⋅h,
where I is the applied current, A; E the voltage of the electrolytic cell; and t the
electrolytic time in seconds.
The best Electrical energy consumed = 6*12*2/1000=0.144 kW⋅h
The cost of generating one litter of NaOCl =0 .144*0.15= 0.0216USD
The cost associate with 1000 litter is = 1000*0.0216=21.6 USD
Where the cost of 1m3 of commercial NaOCl equal to 125 USD, Hence the OSGs of
sodium hypochlorite shows more cost-effectiveness than the commercial
Hypochlorite
56
Feasibility of producing Sodium hypochlorite from seawater brine 4.13
The aim of this study is to investigate the using of Sodium hypochlorite generated on
site instead of the other types of sodium hypochlorite that are used on Gaza strip to
disinfect water. This part will study three possible scenarios to provide Sodium
hypochlorite in order to investigate the best scenario for providing sodium
hypochlorite to be used for water disinfection. The study will focus on the economic,
political, Health, safety and environmental aspects of using the three scenarios of
sodium hypochlorite. The three scenarios were supposed to be used inside Al Bassa
seawater desalination plant. This plant operates with 30 m3/h of seawater where
approximately half of them is discharged as brine. The hourly need of sodium
hypochlorite for the plant to generate 15 m3
of desalinated water is around 4 litters.
Scenario 1 4.13.1
The first scenario is to keep using commercial sodium hypochlorite with
concentration (12% - 15%) for the disinfection process inside Al Bassa seawater
desalination plant. This will keep the system the way it is going. No new change
should happen.
Scenario 2 4.13.2
The second scenario is to use chlorine produced by bubbling gas chlorine in Caustic
soda. This scenario needs modification on the system of the plant to be used for
generating NaOCl on the site.
Scenario 3 4.13.3
The third scenario is to use sodium hypochlorite generated on site. This option also
needs modification on the system of the plant for establishing these small parts to be
used on the system process for disinfection.
57
The environmental, safety and Health analysis 4.14
In the environmental, safety and health analysis, the effects related to the three
scenarios on the environment and health is discussed on this part of the research.
Scenario 1 4.14.1
Using commercial (12% - 15%) hypochlorite is considered a hazardous process as its
concentration increased beyond the critical limit. The dangers of handling and
transporting of a high concentrated bulk hypochlorite make the bulk hypochlorite
method to be cumbersome and worrisome. Have the tank truckloads that transport
the bulk hypochlorite drive on the streets of the city can lead to a dangerous
undesirable disaster. Hypochlorite also should be stored under a certain condition to
maintain its strength and stability. The high concentration of the bulk hypochlorite
can increase the possibility of arising toxic substances from the interactions with
organic matter, thus it is obligation to eliminate as much organic material as possible
before starting chlorination. In other way, handling with commercial bulk sodium
hypochlorite with its high rate of concentration exposes the operators to be under
safety risks. A small leak in the hypochlorite feed lines can expose the life of
operators to danger. Leakage on the feed lines also would result in the evaporation of
the water and release chlorine gas, which is toxic gas, and affects the skin, eyes, nose
and mucous membranes. Besides the intense or continued exposure with bulk
hypochlorite can result in temporary incapacitation or residual injury. Operators
always claim about the splash concerns which always at least make burned holes on
their clothes during work.
Scenario 2 4.14.2
Handling with chlorine gas requires very careful process as it is considered very
dangerous gas. The transportation and conserving of chlorine gas is very critical and
need very a certain protection steps. Any leakage on chlorine gas can affect the skin,
58
eyes, nose and mucous membranes and can expose the life of human beings to risk.
Chlorination process by gas requires keeping the chlorine gas and maintaining it in a
new building with a scrubber unit. Volatility and leaking of chlorine gas can destroy
surrounding life because it is toxic gas. Thus the regulation increased worldwide to a
drift the gas plants away from residential areas which it cannot be happen with
AlBassa SWDP. The same problem can be associated with transportation chlorine
gas through city streets which affect negatively on the neighbourhood ethics. The
operators who are working with such systems always suffer from health problems
associated with their daily dealing with chlorine gas. This kind of chlorination is not
existed on Gaza strip since it is not desirable by the agencies that are operating the
desalination, water and wastewater plants.
Scenario 3 4.14.3
Using sodium hypochlorite generated on-site is becoming acceptable worldwide
since it is safer than the other types of chlorination options. The (0.5%-0.8%)
concentration is considered nonhazardous rates, and this shows low risk level and
provides safety for operators. The process is clean and it happens in an isolated
system where there is no dripping, leaks, mixture of or exposure to chemicals or
fumes. Hydrogen, which generated by product, can be safely vented into the
atmosphere or it can be diluted below 4 mol% to prevent any flammability concern.
By this way, AlBassa SWDP can minimize the quantities of brine discharged to the
seawater and turn it into a good disinfectant. Thus it will help to minimize the effects
of brine on the sea.
The Political analysis 4.15
Scenario 1 4.15.1
The problems associated with the first option are mainly related to the presence of
the substance in the Gaza Strip, where the Gaza strip depends mainly on the purchase
of hypochlorite from outside the Gaza Strip. It has been reported that many of times,
59
the sector has been completely cut off from the outside world, and therefore there has
been a severe shortage of hypochlorite in the Gaza Strip suck like on the 2008 and
2012 conflicts. The Egyptian crossing has been also closed for the importing of
chemicals and goods since long time, so mainly the Gaza Strip relies on the Israeli
side for importing the Sodium hypochlorite. On the other hand, the Israeli side
always restricts the import of chemicals into the Gaza Strip which resulted many
time to completely closure of many water facilities in Gaza strip. This challenge is
always facing the disinfection process on Gaza strip continuously.
Scenario 2 4.15.2
The Chorine Gas is not existed on the Gaza Strip. Hence the same problem
associated with the importing of such gas is still existed. The Israeli side always put
restrictions on the importing of such gases especially chlorine gas which can enter on
the military weapons. The extremely constrains on gas make this choice to can be
more difficult than the bulk hypochlorite itself.
Scenario 3 4.15.3
The process is too simple which depends on water and salt, so the political concerns
can be overridden. The mainly political concern related to sodium hypochlorite
generated on time is the existing of power to run the system. But through the
investigation process, it is shown that the process does not need a high voltage
power. And the system can be running for some hours and it can produce sufficient
hypochlorite to be used for (1-2) days on the Al Bassa SWDP. This way will also
minimize the coordination to get disinfection since by the two previous scenarios,
full continuous coordination is needed monthly to get disinfectant but by OSGs, this
coordination will happen once or twice yearly to import electrodes.
60
The process operation analysis 4.16
Scenario 1 4.16.1
Hypochlorite Solutions with higher concentration have the tendency to degrade
faster. Thus the commercial hypochlorite has relatively a short shelf life. This life is
dependent on different agents such as; sunlight, temperature, vibration, and the
concentration. Maintaining pH between 11.5 to 13 is important to decrease the rate of
degradation. However, this high pH rates and high chlorine concentration can lead
the equipment to be deteriorated by the corrosion. This can result in exploit any
weakened area in the tanks or pipes and may cause leaks on the hypochlorite
solution. Another problem associated with high pH is calcium carbonate scale
formation which can affect highly the performance of pipes and valves of the system.
Storing hypochlorite for someday under its high rate of decomposition force the
operators to make continuous tests for the concentration of hypochlorite and to
frequently adjust the metering equipment to meet the required levels. The storage
tanks need to be maintained in a quiet place, away from overcrowded populations,
and made by a strong material which can endure the high corrosively of chlorine and
can defend the scaling of hypochlorite.
Scenario 2 4.16.2
Hypochlorite solutions generated by chlorine have many of operation considerations.
The chlorine gas storage is not recommended to be on site, so it needs to be away
from the desalination site, thus a transportation will be needed with its high problems
and challenges described before. Any gas leakage can lead to a huge disaster to the
operators and surrounded neighborhood. The chlorine gas needs to be handled on a
very careful process. And the amount of soda feed needed is more than it is on other
types of scenarios. The need of continuous monitoring and the fears associated with
gas are more increasing on this scenario than other types of chlorination. The system
needs to have sufficient employees with sufficient knowledge to work under
complicated process such as generating NaOCl by Chlorine gas.
61
Scenario 3 4.16.3
The generation process of sodium hypochlorite is clean and simple. It happens in an
isolated system where there is no dripping, leaks, mixture of or exposure to
chemicals or fumes. It is safer for operators where there is no touch with toxic or
high concentrated chemicals. It also provides hypochlorite which is more suitable
and friendly with fittings, pipes and valves. The major advantage of this chlorination
process is that hypochlorite can be produced on time with the quantity and quality
required, therefor no need for special bulk storage. The generated hypochlorite has a
low concentration which shows more stability with time. Hydrogen, which generated
by product, can be safely vented into the atmosphere or it can be diluted below 4
mol% to prevent any flammability concerns.
The economical analysis 4.17
The economical analysis between the three scenarios is discussed under this part of
the research.
Scenario 1 4.17.1
The lowest initial capital cost for the bulk hypochlorite is a good advantage where a
bulk system consists essentially of storage tanks and metering pumps which
significantly less complex than an on-site generation system or chlorine system. The
operation cost is modest. No need for training for the operators as they are familiar
with it. The scaling and corrosivity make the maintenance of the system and its pipes
and fittings are costly. The transportation of NaOCl from the borders to the site of
the plant is also costly and need special types of trucks. The cost of electricity is low
for this scenario as it is not relying on electricity and it is advantage on the current
situation of Gaza strip. Special containers are needed for storing sodium hypochlorite
which is costly. The degradation is considered also another costly concern where the
purchase payment was for bulk hypochlorite (12%-15%) and with time the
62
concentration goes below this rate so the dosage of NaOCl which will be added for
the disinfection process will increase than it is with high concentration.
Scenario 2 4.17.2
This system of bubbling chlorine gas into dilute sodium hydroxide at room
temperature is new and need a big initial capital cost for establishing the system
which is considered disadvantage for the system. Special type of containers and
trucks are needed to maintain and transport gas carefully which is also costly.
The operation cost is low as the systems mainly work in automatic and no many
operators are needed. But a special training on the system and safety is obligation to
any operators. The cost of electricity is modest for this scenario as it is relying on
electricity on the bubbling of gas. The containers for hypochlorite should be bigger
than its on scenario 1 as the low concentration requires bigger containers. The aging
of the gas system which goes faster than other types of chlorination is also a concern
which results on continuously renewing the system and replacing of different parts.
Scenario 3 4.17.3
The capital cost of the technology and the cost and existence of energy are the main
concerns related to OSGs of hypochlorite. Besides the regular electrodes replacement
after its life which is also considered as costly. On the other hands, the simplicity of
the system let the cost of maintenance and operation to be modest. It does not need
special containers and the costs of transportation are not existed on this part. The
aging of the system is not fast. While the low concentration of generated sodium
hypochlorite makes the system to consume the power as minimum.
Comparing the results 4.18
Comparing the results related to the different analysis discussed before is expressed on the
Table (4.6) below:
63
Table (4.6): Comparison between the three chlorination options.
Concern Scenario 1 Scenario 2 Scenario 3
Corrosion and
leakage
High risk of leakage
at fittings and
corrosion may occur
on the weak points.
Moderate Risk No risk associated
Scaling Scaling often
happens once
contact occurs with
hard water
Moderate Risk of
scaling due to the
amount of wash soda
added.
No risk associated
Product
degradation
Shorter shelf life Small degradation
rate.
The smallest
degradation rate.
Chlorine gas
production
Risk if pH is reduced No risk associated No risk associated
Storage FRP or HDPE FRP or HDPE FRP or HDPE
Product Dangerous products Dangerous products Not dangerous
products
pH rates High pH rate which
can affect on the
system badly
High pH rate which
can affect on the
system badly
Acceptable pH
Continuous tests for
the concentration
Needs continuous
testing and metering
for pump
Need tests less than
the first scenario
No need required
Potential of arising
toxic material
High High Low
Safety of operators It is high dangerous.
Operators always
claim from the
handling of it.
It is high dangerous. Provide safety for
operators.
Neighborhood
ethics
High risk for
neighbors
High risk for
neighbors
Maintain the
neighborhood
ethics and protect
them from danger.
64
Concern Scenario 1 Scenario 2 Scenario 3
Environmental
friendly
- - Can help on
decreasing the brine
discharged to sea
Israeli restrictions Very affected Very affected Moderate affected
Coordination for
importing
It needs continuous
coordination to get
hypochlorite
It needs continuous
coordination to get
chlorine gas
It minimizes the
coordination to be
once or two yearly.
Initial cost low High Moderate
Operation costs Moderate Moderate Moderate
Maintenance costs High High High
Transportation costs High High No costs required
Operators training No need Training should be
happened to
operators to get
knowledge how to
run the system
Training should be
happened to
operators to get
knowledge how to
run the system
Aging of system Moderate High Moderate
Power consumption low Moderate High
Chapter 5
Conclusions and
Recommendations
82
Chapter 5
Conclusions and Recommendations
Conclusions 5.1
The objective of this research was to study the feasibility of producing sodium
hypochlorite for water disinfection using seawater brine. Effects of different
parameters on the process efficiency were studied such as; Electrolysis time, Current
density, Surface area ratio, Type of rods, Distance between rods, Stability of sodium
hypochlorite, Stability of electrode rod.
As a result of this research project, the following points can be concluded:
1. It is technically possible to use seawater brine into the on-site generation of
sodium hypochlorite with concentrate 0.8% to be used as water disinfectant,
since it was generated in the research by a concentrate of 2.1%.
2. Four types of electrodes materials were used in producing NaOCl, the Sodium
hypochlorite produced using graphite, aluminum, copper and stainless steel
were 2.1%, 0.15%, 0.52%, and 1.5%, respectively. Thus, it was concluded that
graphite electrode was the best material in under the experimental conditions of
this research.
3. The best condition for generation sodium hypochlorite was found by using
graphite electrodes, with diameter 1.3cm, the space between the electrodes was
1cm, and the electrolysis time was 120min, at voltage 12V and at current
density of 176.5mA.cm-2
with 25oC ambient temperature. The best effective
concentration value of sodium hypochlorite at the previous conditions was
2.17% of brine concentration.
4. For conserving the electrodes, the current density should not increase beyond
the conductivity allowable magnitude for the electrode material, the most
stable electrode was aluminum with maximum magnitude 74.4mA/cm2 and
worst in stability was stainless steel with magnitude 26.54mA/cm2. Where the
magnitude for graphite was 176.5mA/cm2.
83
5. Comparing the different analysis aspects, taking the safety considerations, the
environmental, healthy, economic and political issues. It was clear the sodium
hypochlorite generated on-site was the best cost-effectiveness scenario that
maintains sufficient safety and health concerns and overcomes the political and
operational challenges.
Recommendations 5.2
1. Future studies should focus on using continuous flow experiments mode in
generation of Sodium hypochlorite.
2. It is recommended to use electrolysis cell manufactured by worldwide
companies, it could give better and more sustainable results for NaOCl
generation in comparison to batch mode experiments.
3. Through the work of laboratory tests, it was noticed the safety of using and
handling of NaOCl solution in comparison to market sodium hypochlorite,
and the feasibility of using brine in producing sodium hypochlorite is high,
therefore it is recommended to giving this issue a priority by researchers.
4. It is more feasible to increase the surface area of the electrodes, since it will
generate more sodium hypochlorite and will be also more economic in using
electrical current.
References
84
References
Abdul-Wahab, S., & Al-Weshahi, M. (2009). Brine Management: Substituting
Chlorine with On-Site Produced Sodium Hypochlorite for Environmentally
Improved Desalination Processes. Water Resour Manage, 23, 2437–2454.
Abu Ghalwa, N., Tamos, H., ElAskalni, M., & ElAgha, A. R. (2012). Generation of
sodium hypochlorite (NaOCl) from sodium chloride solution using C/PbO2
and Pb/PbO2 electrodes. International Journal of Minerals, Metallurgy and
Materials, 19, 651.
Agriculture, Fisheries, & Forestry. (2002). Economic and technical assessment of
desalination technologies in Australia: with particular reference to national
action plan priority regions. Agriculture, Fisheries and Forestry, Australia.
Ahmed, M., Shayya, W. H., Hoey, D., Mahendran, A., Morris, R., & A1-Handaly,
J. (2000). Use of evaporation ponds for brine disposal in desalination plants.
Desalination, 130, 155-168.
Ainsworth, L., & Hampton, J. (1997). A safe option for disinfection: On-site
sodium hypochlorite generation. Water Engineering & Management,
144(12), 25-27.
Aish, A. (2010). Water quality evaluation of small scale desalination plants in the
Gaza Strip, Palestine. Desalination and Water Treatment.
Alagha, M., & Mortaja, R. (2005). Desalination in the Gaza Strip: drinking water
supply and environmental impact. Desalination, 173, 157–171.
Alazaiza, M. Y., & Mogheir, Y. K. (2013). Development of Safety Plan for
Desalinated Water Use in Gaza Strip. Gaza.
Baalousha, H. (2006). Desalination status in the Gaza Strip and its environmental
impact. Desalination, 196, 1–12.
Balasubramanian, P. (2013). A brief review on best available technologies for reject
water (brine) management in industries. International Journal of
Environmental Science, 3.
Boal, A. K. (2009). On-Site Generation of Disinfectants. Tech Brief, 9(1), 1-4.
Bohissi, N. A., & Mogheir, Y. (2015). Optimal Management of Brine from
Seawater Desalination Plants in Gaza Strip: Deir AL Balah STLV Plant as
Case Study. Journal of Environmental Protection, 6, 599-608.
C.H. Yang, C. L. (2000). Hypochlorite generation on Ru–Pt binary oxide for
treatment of dye wastewater. J. Appl. Electrochem, 30, 1043.
California Water Desalination Task Force, .. (2003). Issue paper on concentrate
management associated with desalination facilities. California: Office of
Water Use Effeciency.
Casson, L. W., & James W. Bess, J. (2006). On-Site Sodium Hypochlorite
Generation. Water Environment Foundation, 6335-6352.
Chakrabarti, M. H., Hasan, D. B., Islam, M. S., Saleem, M., Yussof, R.,
Hajimolana, S. A., et al. (2012). On site Electrochemical Production of
Sodium Hypochlorite Disinfectant for a Power Plant utilizing Seawater.
International Journal of Electrochemical Science, 7, 3929 - 3938.
Chlorine Chemistry Council. (2016). Drinking water chlorination. A review of
disinfection practices and issues. Washington: Chlorine Chemistry Council.
85
Einav, R. (2007). Environmental Aspects of Concentrate Disposal. Retrieved from
AWE international: http://www.aweimagazine.com/article/environmental-
aspects-of-concentrate-disposal-423
Einav, R., Hamssi, K., & Periy, D. (2002). The footprint of the desalination
processes on the environment. Desalination, 152, 141-154.
El-Naas, M. H. (2011). Reject Brine Management. In M. Schorr (Ed.),
Desalination,Trends and Technologies (pp. 237-252).
EPA, U. S. (2004). National Recommended Water Quality Criteria. Environmental
Protection Agency.
European Union. (2007). Risk Assessment Report for Sodium Hypochlorite. Rome,
Italy.
GHD. (2003). Desalination in Queensland. Department of Natural Resources and
Mines, Final Report, July.
Gilron, J., Folkman, Y., Savliev, R., Waisman, M., & Kedem, O. (2003). WAIV—
wind aided intensified evaporation for reduction of desalination brine
volume. Desalination, 158, 205–214.
Glater, J., & Cohen, Y. (2003). Brine disposal from land based membrane
desalination plants: a critical assessment. Prepared for the Metropolitan
Water District of Southern California.
Gordon, G., Adam, L., & Bubnis, B. (1997). Predicting liquid bleach
decomposition. Journal AWWA, 89(4), 142-149.
Hoffman, P., Death, J., & Coats, D. (1981). “The stability of sodium hypochlorite
solutions”. In C. Collins, & al, Disinfectants, their use and evaluation of
effectiveness (pp. 77-83). London: Academic Press.
Hooper, J. (2005). On-Site generation of Sodium Hypoclorite basic operating
pricniples and design considerations. Annual Water Industry Engineers and
Operators Conference, (pp. 59-66).
K.Asokan, & K.Subramanian. (2009, October). Design of a Tank Electrolyser for
In-situ Generation of NaClO. Proceedings of the World Congress on
Engineering and Computer Science, 1, 20-22.
Lattemann, S., & Höpner, T. (2008). Environmental impact and impact assessment
of seawater desalination. Desalination, 220, 1-15.
Lienhard, J. H., Antar, M. A., Bilton, A., Blanco, J., & Zaragoza, G. (2012). Solar
Desalination. In Annual Review of Heat Transfer (pp. 277-347). Begell
House, Inc.
Mahi, P. (2001). Developing Environmentally Acceptable Desalination Projects.
Desalination, 138, 167-172.
Masnoon, S., & Glucina, K. (2011). Desalination: Brine and Residual
Management. Global water Research coalition.
Mickley, M. (1995). Environmental considerations for the disposal of desalination
concentrate. Proceedings of IDA world congress on desalination and water
science, 7, 351-363.
Mickley, M. (2000). Major Ion Toxicity in Membrane Concentrates. AWWA
Research Foundation Project.
Mickley, M. (2006). “Membrane Concentrate Disposal: Practices and
Regulation”. U.S. Department of Interior Bureau of Reclamation. Denver,
Colorado: Desalination and Water Purification Research and Development
Program.
86
Mickley, M., Hamilton, R., Gallegos, L., & Truesdall, J. (1993). Membrane
Concentrate Disposal. AwwaRF and AWWA.
Morganti, L. (2002). Sodium Hypochlorite Generation for Household Water
Disinfection: a Case Study in Nepal.
Omega Man Journal. (2012). Disinfection With Sodium Hypochlorite. Retrieved
from Omega Man Journal:
https://omegamanjournal.wordpress.com/2012/03/23/disinfection-with-
sodium-hypochlorite/
Parkson. (2016). On-Site Generation of Disinfectants.
PCBS, P. C. (2016). Palestine in Figures 2015. Ramallah – Palestine.
Poulson, T. K. (2010). Central Arizona Salinity Study, Strategic Alternatives for
Brine Management in the Valley of the Sun. Arizona.
Pristine Water. (2012). Electrolysis. Retrieved from Pristine Water:
http://www.pristinewater.in/electrolysis.html
PSI On-Site Disinfection. (2014). Case study springfield Missori. Retrieved from
PSI on-site disinfection: http://www.4psi.net/case-study-springfield-mo.php
Purnama, A., Al-Barwani, H., & Al-Lawatia, M. (2003). Modeling dispersion of
brine waste discharges from a coastal desalination plant. Desalination, 155,
41-47.
PWA, P. W. (2013). Status Report of Water Resourses in the Occupied State of
Palestine-2012. West Bank and Gaza.
PWA, P. W. (2014). No drinking water, Not enough energy, and threatend future.
Gaza: Palestinian Water Authority.
PWA, P. W., & WASH partner, .. (2016). Desalinated Water Chain in the Gaza
Strip ‘From Source to Mouth'. Gaza: NRC.
Rengarajan, V., Sozhan, G., & Narasimham, K. C. (1996). Influence factors in the
electrolytic production of sodium hypochlorite. bulletin of electrochemistry,
12, 327-328.
Saripalli, K., Sharma, M., & Bryant, S. (2000). Modeling injection well
performance during deep-well injection of liquid wastes. Elsevier, 41–55.
Sconce, J. (1962). Chlorine, its manufacture, properties and uses. New York:
Reinhold Publishing Corporation.
Seidel, A. (2014). Disinfectant Strategies. claifronia: american water works
association.
Sheikh, R. E., Ahmed, M., & Hamdan, S. (2003). Strategy of water desalination in
the Gaza Strip. Desalination, 156, 39-42.
Skehan, S., & Kwiatkowski, P. J. (2000). Concentrate Disposal Via Injection
wells—permitting and design considerations. Florida Water Resources , 19-
21.
Swift, A. H., Lu, H., & Becerra, H. (2002). Zero Discharge Waste Brine
Management for Desalination Plants. University of Texas at El Paso, U.S.
Department of the Interior. Texas: University of Texas.
Tayef, M., Al-Najjar, H., Mogheir, Y., & Seif, A. (2016). Numerical modeling of
brine disposal from Gaza central seawater desalination plant. Arabian
Journal of Geosciences, 9.
Walsh, D. P. (1990). Industrial Electrochemistry. London: Chapman and Hall Ltd.
White, G. C. (1999). The handbook of chlorination and alternative disinfectants.
New York: Black & Veatch Corporation.
87
WHO, W. H. (1996). Guidelines for drinking-water quality. Health criteria and
other supporting information, 2.
WHO, W. H. (2007). Public Health and the Environment - Desalination for Safe
Water Supply. Geneva.
Younos, T. (2004). "The Feasibility of Using Desalination to Supplement Drinking
Water Supplies in Eastern Virginia" VWRRC Special Report SR25-2004,.
Blacksburg, Virginia.: Virginia Water Resources Research.
Younos, T. (2005). Environmental Issues of Desalination. Journal of
Contempopary Water Resarch & Education(132), 11-18.
Appendices
88
Appendix 1: Relation between current density and production of NaOCl.
Sodium Hypochlorite concentration table using Graphite
voltage(v)= 12
length of Rode
(cm)= 15
rode weight initial
(g) = 32.1
Volume of brine
(ml) 1000 Current to time
current
(A)= 0.5 surface area (cm2)= 29.3904
rode weight final
(g) = 32
wet length of rod
(cm) 7.5
Rod
Dia.(cm)= 1.3
current intensity
(mA.cm-2) 17.012 First Iteration
Iteration
No.
Time(mi
n) Dia. Rod(mm)
Δ Rod
Dia. TDS initial(mg/L)
TDS
final pH initial
pH
Final
temperat
ure
initial
temperat
ure final
1
30
81280 81280 12.6 12.6 27 27.3
2
60
81280 81280 12.6 12.6 27 27.3
3
90
81280 81280 12.6 12.6 27 27.3
4
120
81280 81280 12.6 12.6 27 27.3
5
150
81280 81408 12.6 12.7 27 27.6
6
180
81280 81344 12.6 12.6 27 27.7
89
Sodium Hypochlorite concentration table using Graphite
voltage(v)= 12
length of Rode
(cm)= 15
rode weight
initial (g) = 32.2
Volume of
brine (ml) 1000 Current to time
current (A)= 1
surface area
(cm2)= 33.9827
rode weight
final (g) = 32
wet length
of rod (cm) 8
Rod Dia.(cm)= 1.3
current intensity
(mA.cm-2) 29.427 Second Iteration
Iteration
No.
Time(m
in)
NaOCl(
mg/l) Dia. Rod(mm)
Δ Rod
Dia.
TDS
initial(mg/L) TDS final pH initial pH Final
temperat
ure
initial
temperat
ure final
1 30 13 81280 82560 12.7 12.7 26.1 27.1
2 60 13 81280 83200 12.7 12.7 26.1 27.7
3 90 13 81280 83840 12.7 12.6 26.1 28.3
4 120 13 81280 84544 12.7 12.6 26.1 28.4
5 150 13 81280 85120 12.7 12.5 26.1 29.2
6 180 13 81280 85184 12.7 12.6 26.1 29.5
90
Sodium Hypochlorite concentration table using Graphite
Voltage
(v)= 12
length of Rode
(cm)= 15
rode weight
initial (g) = 32.1
Volume of
brine (ml) 1000 Current to Time
current (A)= 2
surface area
(cm2)= 33.9827
rode weight final
(g) =
31.9
wet length
of rod (cm) 8
Rod Dia.(cm)= 1.3
current
intensity
(mA.cm-2) 58.854 Third Iteration
Iteration
No. Time(min) Dia. Rod(mm)
Δ Rod
Dia.
TDS
initial(mg/L) TDS final pH initial pH Final
temperat
ure
initial
temperat
ure final
1
30
13 81280 84800 12.8 12.7 26 28.4
2
60
13 81280 87360 12.8 12.7 26 29.6
3
90
13 81280 89600 12.8 12.6 26 31
4
120
13 81280 90304 12.8 12.6 26 32
5
150
13 81280 92224 12.8 12.6 26 33.1
6
180
13 81280 92992 12.8 12.5 26 34
91
Sodium Hypochlorite concentration table using Graphite
voltage(v)= 12
length of Rode
(cm)= 15
rode weight
initial (g) = 32.2
Volume of
brine (ml) 1000 Current to Time
current (A)= 2.5
surface area
(cm2)= 33.9827
rode weight
final (g) = 31.9
wet length of
rod (cm) 8
Rod Dia.(cm)= 1.3
current intensity
(mA.cm-2) 73.567 First Iteration
Iteration
No. Time(min) Dia. Rod(mm)
Δ Rod
Dia.
TDS
initial(mg/L
)
TDS final pH initial pH
Final
tempera
ture
initial
tempera
ture
final
1
30
13
73280 75712 12.3 12.2 26 28.3
2
60
13
73280 79360 12.3 12.2 26 31.3
3
90
13
73280 84032 12.3 12.1 26 33.6
4
120
13
73280 87744 12.3 12 26 36.1
5
150
13
73280 87680 12.3 11.9 26 37.7
6
180
13
73280 87593 12.3 11.9 26 37.1
92
Sodium Hypochlorite concentration table using Graphite
voltage(v)= 12
length of Rode
(cm)= 15
rode weight
initial (g) = 33.1
Volume of
brine (ml) 1000 Current to Time
current (A)= 3
surface area
(cm2)= 33.9827
rode weight
final (g) = 32.6
wet length of
rod (cm) 8
Rod Dia.(cm)= 1.3
current intensity
(mA.cm-2) 88.28 Second Iteration
Iteration
No.
Time(
min)
NaOCl(
mg/l) Dia. Rod(mm)
Δ Rod
Dia.
TDS
initial(mg/L
)
TDS final pH initial pH
Final
tempera
ture
initial
temperat
ure final
1 30
13
73280 77824 12.3 12.2 26 29.1
2 60
13
73280 81408 12.3 12.2 26 32.2
3 90
13
73280 84672 12.3 12 26 35
4 120
13
73280 87744 12.3 11.9 26 37.1
5 150
13
73280 87488 12.3 11.9 26 38.5
6 180
13
73280 8746 12.3 11.9 26 38.6
93
Sodium Hypochlorite concentration table using Graphite
voltage(v)= 12
length of Rode
(cm)= 15
rode weight
initial (g) = 32.1
Volume of
brine (ml) 1000 Current to Time
current (A)= 3.5
surface area
(cm2)= 33.9827
rode weight
final (g) = 31.7
wet length
of rod (cm) 8
Rod Dia.(cm)= 1.3
current
intensity
(mA.cm-2) 102.99 Third Iteration
Iteration
No. Time(min) Dia. Rod(mm)
Δ Rod
Dia.
TDS
initial(mg/L
)
TDS final pH initial pH Final temperature
initial
temperat
ure final
1 30
13
73280 77824 12.3 12.2 26 29.3
2 60
13
73280 81408 12.3 12.2 26 33.2
3 90
13
73280 84672 12.3 12.1 26 35.6
4 120
13
73280 87744 12.3 12.3 26 38.1
5 150
13
73280 87488 12.3 11.9 26 40.5
6 180
13
73280 87466 12.3 11.9 26 43.6
94
Sodium Hypochlorite concentration table using Graphite
voltage(v)= 12
length of
Rode (cm)= 15
rode weight
initial (g) = 32.6
Volume of
brine (ml) 1000 Current to Time
current (A)= 6
surface area
(cm2)= 33.9827
rode weight
final (g) = 31.5
wet length of
rod (cm) 8
Rod Dia.(cm)= 1.3
current
intensity
(mA.cm-2) 176.56 Third Iteration
Iteration
No. Time(min)
Rod weight
(g)
Δ Rod weight
(g)
TDS
initial(mg/L
)
TDS final pH initial pH
Final
tempera
ture
initial
tempera
ture
final
1 30 32.6 32.65 73280 77824 12.3 26 22
2 60 32.65 32.52 73280 81408 12.3 26 30
3 90 32.52 32.36 73280 84672 12.3 26 41
4 120 32.36 32.22 73280 87744 12.3 26 48
5 150 32.22 32.16 73280 87488 12.3 26 56
6 180 32.16 32.3 73280 87466 12.3 26 60
7 210 32.3 31.9 73280 87824 12.3 26 65
8 240 31.9 31.5 73280 87408 12.3 26 69
95
Sodium Hypochlorite concentration table using Graphite
voltage(v)= 12
length of Rode
(cm)= 15
rode weight
initial (g) = 32.6
Volume of
brine (ml) 1000 Current to Time
current (A)= 9
surface area
(cm2)= 36.0237
rode weight
final (g) = 31.3
wet length of
rod (cm) 8.5
Rod Dia.(cm)= 1.3
current intensity
(mA.cm-2) 249.84 Third Iteration
Iteration
No. Time(min)
TDS
initial(mg/L
)
TDS final pH initial pH
Final
tempera
ture
initial
temperat
ure final
1 30 69120 107520 12.1 12.1 26 43.1
2 60 69120 128000 12.1 11.6 26 56
3 90 69120 128000 12.1 11.5 26 63.5
4 120 69120 128000 12.1 11.3 26 70.2
5 150 69120 128000 12.1 11.1 26 76.8
6 180 69120 128000 12.1 11 26 79.3
96
Sodium Hypochlorite concentration table using Aluminium rode
voltage(v
)= 12
length of Rode
(cm)= 15
rode weight
initial (g) =
40.
1
Volume of
brine (ml) 1000 Current to Time
current
(A)= 1
surface area
(cm2)= 80.541
rode weight
final (g) =
41
.1
wet length of
rod (cm) 9.5 internal dia cm 1.1
Rod
Dia.(cm)
= 1.6
current intensity
(mA.cm-2) 12.416 First Iteration
distance
between rode
cm 4
Iteration
No.
Time(
min)
NaOCl(
mg/l) Dia. Rod(mm)
Δ Rod
Dia.
TDS
initial(mg/L)
TDS
final pH initial
pH
Final
temperature
initial
temper
ature
final
1 30 16 60928 60288 12 12 16.7 17.1
2 60 16 60928 59840 12 12 16.7 17
3 90 16 60928 60416 12 12.1 16.7 17.4
4 120 16 60928 60608 12 12.1 16.7 17.6
5 150 16 60928 60992 12 12.1 16.7 17.5
6 180 16 60928 59904 12 12.2 16.7 17.9
7 210 16 60928 61312 12 12.2 16.7 18.1
97
Sodium Hypochlorite concentration table using aluminium rode
voltage(v
)= 12
length of Rode
(cm)= 15
rode weight
initial (g) =
40.
1
Volume of
brine (ml) 1000 Current to Time
current
(A)= 3
surface area
(cm2)= 80.541
rode weight
final (g) =
41.
1
wet length of
rod (cm) 9.5 internal dia cm 1.1
Rod
Dia.(cm)
= 1.6
current intensity
(mA.cm-2) 37.248
1 First Iteration
distance
between rode cm 4
Iteration
No.
Time(
min)
NaOCl(
mg/l) Dia. Rod(mm)
Δ Rod
Dia.
TDS
initial(mg/L)
TDS
final pH initial
pH
Final
temperature
initial
temper
ature
final
1 30 63424 63424 12.9 12.7 16.8 17
2 60 63424 63424 12.9 12.7 16.8 17.1
3 90 63424 64000 12.9 12.6 16.8 17.5
4 120 63424 64768 12.9 12.6 16.8 17.5
5 150 63424 62208 12.9 12.5 16.8 17.5
6 180 63424 63360 12.9 12.6 16.8 17.6
7 210 63424 12.9 16.8
98
Sodium Hypochlorite concentration table using aluminium rode
voltage(v
)= 12
length of Rode
(cm)= 15
rode weight
initial (g) = 40.1
Volume of
brine (ml) 1000 Current to Time
current
(A)= 5
surface area
(cm2)= 80.541
rode weight
final (g) = 40.1
wet length of
rod (cm) 9.5 internal dia cm 1.1
Rod
Dia.(cm)
= 1.6
current intensity
(mA.cm-2) 62.080
2 First Iteration
distance
between rode
cm 4
Iteration
No.
Time(
min)
NaOCl(
mg/l) Dia. Rod(mm)
Δ Rod
Dia.
TDS
initial(mg/L) TDS final pH initial pH Final
temperature
initial
tempera
ture
final
1 30 16 66880 65216 12.8 12.7 17.2 17.3
2 60 16 66880 64960 12.8 12.7 17.2 17.5
3 90 16 66880 65152 12.8 12.6 17.2 17.9
4 120 16 66880 64768 12.8 12.6 17.2 18.3
5 150 16 66880 66304 12.8 12.7 17.2 18.4
6 180 16 66880 65472 12.8 12.5 17.2 18.4
7 210 16 66880 65536 12.8 12.5 17.2 18.4
99
Sodium Hypochlorite concentration table using aluminium rode
voltage(v
)= 12
length of Rode
(cm)= 15
rode weight
initial (g) =
40.
1
Volume of
brine (ml) 1000 Current to Time
current
(A)= 6
surface area
(cm2)= 80.541
rode weight final
(g) = 40
wet length of
rod (cm) 9.5 internal dia cm 1.1
Rod
Dia.(cm)
= 1.6
current intensity
(mA.cm-2) 74.4962 First Iteration
distance between
rode cm 4
Iteration
No.
Time(
min) Rod weight (g)
Δ Rod
weight
(g)
TDS
initial(mg/L
)
TDS final pH initial pH
Final
temperature
initial
temper
ature
final
1
30
40.1 40.1 64960 64960 12.6 12.6 16.7 16.7
2
60
40.1 40.09 64960 64640 12.6 12.6 16.7 16.7
3
90
40.09 40.08 64960 64320 12.6 12.6 16.7 17.1
4
120
40.08 40.05 64960 64320 12.6 12.5 16.7 17.2
5
150
40.05 40.02 64960 64320 12.6 12.5 16.7 17.4
6
180
40.02 40 64960 66240 12.6 12.4 16.7 17.5
7
210
40 39.99 64960 64960 12.6 12.4 16.7 17.5
100
Sodium Hypochlorite concentration table using copper rode
voltage(v)= 12
length of
Rode (cm)= 15
rode weight
initial (g) =
8.00
6
Volume of brine
(ml) 1000 Current to Time
current (A)= .2
surface area
(cm2)= 7.4575
rode weight
final (g) =
7.41
2
wet length of rod
(cm) 9.5
Rod Dia.(cm)= 0.25
current
intensity
(mA.cm-2) 26.819 First Iteration
distance
cm 4
Iteration
No. Time(min) Dia. Rod(mm)
Δ Rod
Dia.
TDS
initial(mg/L) TDS final pH initial
pH
Final
temperat
ure
initial
temperat
ure final
1
30
68672 67328 12.9 12.9 16.8 17
2
60
68672 67456 12.9 12.9 16.8 17.1
3
90
68672 68224 12.9 12.8 16.8 17.2
4
120
68672 68800 12.9 12.9 16.8 17.2
5
150
68672 68032 12.9 12.8 16.8 17.3
6
180
68672 67968 12.9 12.9 16.8 17.4
7
210
68672 67838 12.9 16.8
101
Sodium Hypochlorite concentration table using copper rode
voltage(v)
= 12
length of Rode
(cm)= 15
rode weight
initial (g) = 8.006
Volume of
brine (ml) 1000 Current to Time
current
(A)= 0.5
surface area
(cm2)= 7.4575
rode weight
final (g) = 7.328
wet length of
rod (cm) 9.5
Rod
Dia.(cm)= 0.25
current intensity
(mA.cm-2) 67.047 First Iteration
distance
cm 4
Iteration
No.
Time(
min)
NaOCl(
mg/l) Dia. Rod(mm)
Δ Rod
Dia.
TDS
initial(mg/L)
TDS
final pH initial
pH
Final
tempera
ture
initial
tempera
ture
final
1 30 68672 68800 12.9 13 16.8 17.3
2 60 68672 69568 12.9 13 16.8 18
3 90 68672 70848 12.9 12.9 16.8 18.5
4 120 68672 71680 12.9 12.9 16.8 18.2
5 150 68672
11227
2 12.9 12.8 16.8 20
6 180 68672
11377
3 12.9 12.9 16.8 20.2
7 210 68672 12.9 16.8
102
Sodium Hypochlorite concentration table using copper rode
voltage(v)= 12
length of Rode
(cm)= 15
rode weight
initial (g) = 8.119
Volume of brine
(ml) 1000 Current to Time
current (A)= 0.7
surface area
(cm2)= 7.4575
rode weight
final (g) = 6.995
wet length of
rod (cm) 9.5
Rod Dia.(cm)= 0.25
current intensity
(mA.cm-2) 93.865 First Iteration
distance
cm 4
Iteration
No. Time(min) Dia. Rod(mm)
Δ Rod
Dia.
TDS
initial(mg/L)
TDS
final pH initial
pH
Final
temperat
ure
initial
temperat
ure final
1
30
68672 732160 12.9 12.8 16.8 20.4
2
60
68672 73920 12.9 12.9 16.8 21
3
90
68672 7564.8 12.9 12.8 16.8 21.9
4
120
68672 75840 12.9 12.9 16.8 21.2
5
150
68672 76224 12.9 12.8 16.8 22.4
6
180
68672 76352 12.9 12.8 16.8 23.1
7
210
68672 12.9 16.8
103
Sodium Hypochlorite concentration table using copper rode
voltage(v)= 12
length of Rode
(cm)= 15
rode weight
initial (g) = 7.97
Volume of
brine (ml) 1000 Current to Time
current (A)= 1
surface area
(cm2)= 7.4575
rode weight
final (g) = 4.57
wet length of
rod (cm) 9.5
Rod Dia.(cm)= .25
current intensity
(mA.cm-2) 134.09 First Iteration
distance cm 4
Iteration
No.
Time(
min)
NaOCl(
mg/l) Rod weight (g)
Δ Rod
weight
(g)
TDS
initial(mg/L
)
TDS final pH initial pH Final
tempera
ture
initial
tempera
ture
final
1 30 7.97 7.56 60672 63232 11.9 12.1 16.7 18.5
2 60 7.56 7.03 60672 65536 11.9 12.1 16.7 20
3 90 7.03 6.76 60672 67072 11.9 12.2 16.7 21.7
4 120 6.76 6.23 60672 19200 11.9 12.2 16.7 22.1
5 150 6.23 5.97 60672 69440 11.9 12.1 16.7 22.6
6 180 5.97 5.07 60672 68800 11.9 12.2 16.7 23
7 210 5.07 4.57 60672 69312 11.9 12.2 16.7 23.1
104
Sodium Hypochlorite concentration table using stainless steel rode
voltage(v)= 12
length of Rode
(cm)= 15
rode weight
initial (g) =
18.84
3
Volume of brine
(ml) 1000 Current to Time
current (A)= 1
surface area
(cm2)= 38
rode weight
final (g) =
16.65
5
wet length of rod
(cm) 9.5
Rod width cm 2
current intensity
(mA.cm-2) 26.316 First Iteration
distance
cm 4
Iteration
No. Time(min)
Rod weight
(g)
Δ Rod weight
(g)
TDS
initial(mg/L) TDS final pH initial
pH
Final
temperat
ure
initial
temperat
ure final
1
30
18.843 18.698 60672 61888
11.9 12 16.7 17.9
2
60
18.698 18.368 60672 61504
11.9 12.1 16.7 18.7
3
90
18.368 17.963 60672 61440
11.9 12.1 16.7 19.5
4
120
17.963 17.536 60672 60480
11.9 12.2 16.7 20.3
5
150
17.536 17.298 60672 64576
11.9 12.1 16.7 20.8
6
180
17.298 16.986 60672 59840
11.9 12.2 16.7 21.1
7
210
16.986 16.655 60672 67840
11.9 12.2 16.7 21.5
105
Sodium Hypochlorite concentration table using stainless steel rode
voltage(v)= 12
length of Rode
(cm)= 15
rode weight
initial (g) = 16.655
Volume of
brine (ml) 1000 Current to Time
current
(A)= 2.5
surface area
(cm2)= 38
rode weight
final (g) = 11.303
wet length of
rod (cm) 9.5
Rod width
cm 2
current intensity
(mA.cm-2) 65.789 First Iteration
distance
cm 4
Iteration
No.
Time
(min
)
NaOCl(
mg/l) Dia. Rod(mm)
Δ Rod
Dia.
TDS
initial(mg/L)
TDS
final pH initial
pH
Final
tempera
ture
initial
tempera
ture
final
1 30 67520 67392 12.8 12.7 17.4 20.2
2 60 67520 72384 12.8 12.6 17.4 22.5
3 90 67520 74880 12.8 12.6 17.4 23.6
4 120 67520 83264 12.8 12.6 17.4 24.3
5 150 67520 81920 12.8 12.5 17.4 27.4
6 180 67520 83840 12.8 12.5 17.4 28.5
7 210 67520 83840 12.8 12.5 17.4 28.6
106
Sodium Hypochlorite concentration table using stainless steel rode
voltage(v
)= 12
length of Rode
(cm)= 15
rode weight
initial (g) = 18.847
Volume of
brine (ml) 1000 Current to Time
current
(A)= 3.5
surface area
(cm2)= 38
rode weight
final (g) = 9.38
wet length of
rod (cm) 9.5
Rod
width cm 2
current intensity
(mA.cm-2) 92.105 First Iteration
distance
cm 4
Iteration
No.
Time(
min)
NaOCl(
mg/l) Dia. Rod(mm)
Δ Rod
Dia.
TDS
initial(mg/L)
TDS
final pH initial
pH
Final
tempera
ture
initial
tempera
ture
final
1 30 74688 74688 12.8 12.8 20 22.2
2 60 74688 82048 12.8 12.7 20 26.1
3 90 74688 90036 12.8 12.7 20 29.8
4 120 74688
10752
0 12.8 12.5 20 36.5
5 150 74688
11584
0 12.8 12.5 20 38
6 180 74688
12224
0 12.8 12.5 20 41
7 210 74688
11737
6 12.8 12.5 20 38.3
107
Sodium Hypochlorite concentration table using stainless steel rode
voltage(v
)= 12
length of Rode
(cm)= 15
rode weight
initial (g) = 18.847
Volume of
brine (ml) 1000 Current to Time
current
(A)= 6
surface area
(cm2)= 38
rode weight
final (g) = 9.38
wet length of
rod (cm) 9.5
Rod
width cm 2
current intensity
(mA.cm-2) 157.89 First Iteration
distance
cm 4
Iteration
No.
Time(
min)
NaOCl(
mg/l) Dia. Rod(mm)
Δ Rod
Dia.
TDS
initial(mg/L)
TDS
final pH initial
pH
Final
tempera
ture
initial
tempera
ture
final
1 30 80128 96000 12.7 12.5 16.7 32.2
2 60 80128
11328
0 12.7 12.5 16.7 41
3 90 80128
12544
0 12.7 12.2 16.7 46
4 120 80128
13523
2 12.7 12 16.7 51
5 150 80128
14726
4 12.7 12.1 16.7 50.1
6 180 80128
15974
4 12.7 12 16.7 52.1
7 210 80128
17356
8 12.7 11.9 16.7 55.5
108
Appendix 2: Relation between surface area ratio and production of NaOCl.
Sodium Hypochlorite concentration table
voltage(v)
= 12
length of Rode
(cm)= 15
rode weight
initial (g) = 61.6
Volume of
brine (ml) 1000 Surface area ratio
and time
current
(A)= 0.4
surface area
(cm2)= 2.26582
rode weight
final (g) =
wet length of
rod (cm) 9
Rod
Dia.(cm)
= 0.08
current intensity
(mA.cm-2) 176.54 Third Iteration
Iteration
No.
Time(
min)
NaOCl(
mg/l) Dia. Rod(mm)
Δ Rod
Dia.
TDS
initial(m
g/L)
TDS final pH initial pH
Final
temperatu
re initial
temperatu
re final
1 30 69120 69952 12.6 12.6 15.6 16.5
2 60 69120 70208 12.6 12.8 15.6 16.7
3 90 69120 70528 12.6 12.7 15.6 17.1
4 120 69120 69888 12.6 12.9 15.6 17.2
5 150 69120 71040 12.6 12.6 15.6 17.5
6 180 69120 71360 12.6 12.8 15.6 17.7
109
Appendix 3: Stability of NaOCl.
First
sample
Second
sample
Third
sample
25 C -
light
First
sample
Second
sample
Third
sample
25 C –
Dark
0 day 2.1 2.1 2.1 0 2.1 2.1 2.1 0
1 day 2.0833 2.0832 2.0830 0.008 2.0955 2.095 2.096 0.002
2 days 2.0016 2.0013 2.0010 0.047 2.083 2.08 2.0811 0.009
3 day 1.9488 1.9487 1.9488 .072 2.0706 2.0705 2.0707 0.014
4 days 1.8360 1.8350 1.8354 0.126 2.076 2.058 2.04 0.02
5 days 1.723 1.721 1.723 0.18 2.0433 2.042 2.0446 0.027
6 days 1.699 1.696 1.690 0.192 2.0314 2.03 2.0307 0.033
7 days 1.628 1.626 1.630 0.225 2.0068 2 2.0034 0.046