1. REMOVAL OF COPPER, NICKEL, AND CHROMIUM
FROM SIMULATED WASTEWATER USING
ELECTROCOAGULATION TECHNIQUE
BY
OKECHUKWU PASCAL CHISOM
[NAU/2011214087]
A RESEARCH WORK SUBMITTED TO
THE DEPARTMENT OF CHEMICAL ENGINEERING,
FACULTY OF ENGINEERING.
IN PARTIAL FULFILMENT OF THE
REQUIREMENTS FOR THE AWARD OF
BACHELORS DEGREE IN CHEMICAL
ENGINEERING, NNAMDI AZIKIWE UNIVERSITY,
AWKA, ANAMBRA STATE.
SUPERVISOR: ENGR. (DR.) J.T. NWABANNE
SEPTEMBER, 2016.

2. CERTIFICATION
This is to certify that the thesis entitled “Removal of copper, nickel and
chromium from simulated wastewater using electrocoagulation technique” being
submitted by Okechukwu Pascal Chisom, for the award of Bachelor degree in
Engineering (Chemical Engineering) is a record of research carried out by me
under the supervision of Engr. Dr. J.T. Nwabanne. The work incorporated in this
research has not been submitted elsewhere earlier in part or in full, for the award
of any degree or diploma of this or any other institution.
Okechukwu Pascal Chisom Date

3. APPROVAL PAGE
We hereby approve this research work presented by Okechukwu Pascal Chisom
with registration number: 2011214087
Engr. Dr. J.T. Nwabanne Date
Supervisor
Engr. Dr. J.T. Nwabanne Date
Head of Department
Prof. D.O. Onwu Date
External Examiner
Engr. Prof. C.C. Ihueze Date
Dean, Faculty of Engineering

4. DEDICATION
I dedicate this work to God Almighty, for everything. And for being the reason
for this project.

5. ACKNOWLEDGEMENTS
My heartfelt gratitude goes to God almighty for being the beginning and the end
of all knowledge. Then to my parents, Mr Boniface Okechukwu Ofor and Mrs
Ngozi T. Ofor for their immense contribution towards everything in my life since
I was born.
My sincere appreciation goes to my unique supervisor and Head of Department;
Chemical Engineering, Engr. (Dr.) J.T. Nwabanne who remained to me a father,
friend, and great teacher, for the love, priceless advice, sense of direction, and
support(s) he provided me through my final year. I really cannot thank him
enough.
My candid gratitude also goes to Engr. Chinedu Umembammalu, our able
Laboratory Chief Technologist, who set things right for and provided helpful
directions during my experimental work. I equally thank all the lecturers in the
Chemical Engineering department, especially Prof. P. K. Igbokwe, Engr. J.A.
Okeke, Engr. V.I. Ugonabo.
I am thankful as well to the technologist in PRODA research facility, Enugu. A
good friend, Engr. Idogwu, who helped me in my sample analysis. And to ASUU
for not embarking upon any strike till the completion of this work.
I am grateful to all my coursemates and friends in school, for being in my Life,
and making it worthwhile. Then, I specially acknowledge all wonderful People
who take it upon themselves to shape their destiny as they see fit.

6. ABSTRACT
Due to their occurrence in water and most wastewater; above allowable limits, heavy
metals such as nickel and chromium causes serious problems to both human and animal
health, as well as the environment. The pollution of the environment by these heavy
metals have led to grave issues such as blood level poisoning, kidney and brain damage,
inhibited growth, etc. thus, this work was carried out to investigate the efficacy of
electrocoagulation in removing copper, nickel, and chromium from simulated waste
water by varying the process parameters. In this study, laboratory scale experiments
were conducted using iron electrodes while the working parameters such as pH, current
density, initial ion concentration, charging time, inter-electrode distance and
temperature were varied with the aim of establishing the optimal removal state.
Variables of: pH (2, 4, 6, 8, 10 and 12), charging time (5, 10, 15, 20 and 30min),
electrode distance (3, 4, 5 and 6cm), current (1.0, 1.5, 2.0 and 2.5A) and temperature
(30, 40, 50, 60 and 70o
C) were studied to observe their effect on the removal efficiency.
The results obtained showed that the optimum pH was within the range of 6.5 – 10 with
removal efficiency of 99% for copper, 92% for nickel, and 98% for chromium. The
charging time was found to increase exponentially with optimal removal occurring
within the first 15mins. The optimal inter-electrode distance was generally found to be
3cm with removal efficiency of 99%, 95% and 97% for copper, nickel, and chromium
respectively. The treatment temperature was found to increase with removal efficiency
and optimum removal occurred at the highest temperature of 70o
C. The results also
showed that removal efficiency increases with current density, while the highest current
2.5A produced the quickest removal rate, with a 99% removal for copper, 96% removal
for nickel and 97% removal for chromium occurring just after 10mins. The results
further revealed that removal efficiency increased with a decline in initial metal ion
concentration. It can thus be concluded that the electrocoagulation technique is an
effective treatment process for the removal of copper, nickel, and chromium from waste
water.

7. TABLE OF CONTENTS
Title page i
Certification ii
Approval page iii
Dedication iv
Acknowledgement v
Abstract vi
Table of contents vii
List of tables x
List of figures xi
CHAPTER ONE: INTRODUCTION
1.1 Background of the study 1
1.2 Problem statement 5
1.3 Aim and objectives of the study 6
1.4 Significance of the study 7
1.5 Scope of the study 8
CHAPTER TWO: LITERATURE REVIEW
2.1 General aspects of wastewater treatment 9
2.1.1 Biological treatment technique 10
2.1.2 Chemical treatment technique 11
2.1.3 Electrocoagulation treatment technique 13
2.2 Electrocoagulation technology 13
2.2.1 Definitions 13

8. 2.2.2 History of electrocoagulation 15
2.2.3 Theory of electrocoagulation 16
2.2.4 Mechanism of electrocoagulation 22
2.2.4.1 Electrocoagulation using iron electrodes 23
2.2.4.2 Electrocoagulation using aluminium electrodes 24
2.2.5 Description of the technology 25
2.2.6 Practical considerations of electrocoagulation 28
2.2.6.1 Constructions of electrocoagulation systems 28
2.2.7 Advantages and disadvantages of electrocoagulation 29
2.2.7.1 Advantages of electrocoagulation 29
2.2.7.2 Disadvantages of electrocoagulation 31
2.3 Comparison between chemical coagulation and electrocoagulation 31
2.4 Review of previous works on electrocoagulation 33
2.4.1 Heavy metal wastewater 33
2.5 Problems encountered 37
CHAPTER THREE: MATERIALS AND METHODS
3.1 Introduction 39
3.2 Apparatus and materials 39
3.2.1 Apparatus 39
3.2.2 Materials/reagents 40
3.3 Experimental procedure 40
3.3.1 Simulated wastewater preparation 40
3.3.2 Electrocoagulation set-up 41
3.4 Analysis of samples 42
3.4.1 Atomic absorption spectrometer 43
3.4.1.1 Calibration 44

9. CHAPTER FOUR: RESULTS AND DISCUSSION
4.1 Batch electrocoagulation studies 45
4.1.1 Effect of pH on the removal efficiency 45
4.1.2 Effect of current density on the removal on removal efficiency 47
4.1.3 Effect of inter-electrode distance on removal efficiency 49
4.1.4 Effect of solution temperature on removal efficiency 50
4.1.5 Effect of charging time on removal efficiency 52
4.1.6 Effect of initial metal ion concentration on removal efficiency 53
4.2 Energy consumption 56
CHAPTER FIVE: CONCLUSIONS AND RECOMMENDATIONS
5.1 Conclusions 57
5.2 Recommendations 57
5.3 Contribution to knowledge 58
REFERENCES 59
APPENDIX A 64
APPENDIX B 73

10. LIST OF TABLES
Table 2.1: Comparison between electrocoagulation and chemical coagulation 32
Table 3.1: Electrocoagulation process parameters for the treatment of the simulated
wastewater using iron electrodes 45
Table A(i): Stock solution preparation 64
Table A(ii): Effect of initial pH on removal efficiency 65
Table A(iii): Effect of current density on removal efficiency 66
Table A(iv): Effect of electrode distance on removal efficiency 67
Table A(v): Effect of solution temperature on removal efficiency 67
Table A(vi): Effect of charging time on removal efficiency 68
Table A(vii): Concentration-time composite data for Copper 69
Table A(viii): Concentration-time composite data for Nickel 70
Table A(ix): Concentration-time composite data for Chromium 71

11. LIST OF FIGURES
Figure 2.0 The electrocoagulation process. Source: Halliburton. 14
Figure 2.1 Conceptual framework for electrocoagulation as a synthetic technology 16
Figure 2.2 Schematic diagram of a two-electrode electrocoagulation cell 19
Figure 2.3 Dimeric and Polymeric structures of Al3+
hydroxo complexes 25
Figure 2.4 Bench-scale EC reactor with monopolar electrodes in parallel 26
Figure 2.5 Bench-scale EC reactor with monopolar electrodes in series 26
Figure 2.6 Bench scale EC reactor bipolar electrodes in parallel connection 27
Figure 2.7 Connection and electrode polarity in bipolar and monopolar EC system 28
Figure 3.0 Calibration curve for the metal concentration inspected 44
Figure 4.1 Effect of pH on removal efficiency of the heavy metals 47
Figure 4.2 Effect of current density on removal efficiency of the heavy metals 48
Figure 4.3 Effect of electrode distance on removal efficiency of the heavy metal 50
Figure 4.4 Effect of solution temperature on removal efficiency of the heavy metals 51
Figure 4.5 Effect of charging time on removal efficiency of the heavy metals 52
Figure 4.6 Effect of initial metal ion concentration on removal efficiency of copper 54
Figure 4.7 Effect of initial metal ion concentration on removal efficiency of nickel 54
Figure 4.8 Effect of initial ion concentration on removal efficiency of chromium 55
Figure 4.9 Energy consumption 56

12. CHAPTER ONE
INTRODUCTION
1.1 BACKGROUND OF THE STUDY
Water is very necessary to life on earth because all organisms contain it; some live in
it; and most drink it. Plants and animals require water that is moderately pure, and they
cannot survive if their water is loaded with toxic chemicals or harmful microorganisms.
Water Pollution can be any of contamination of streams, lakes, underground water,
bays, or oceans by substances harmful to living things. This becomes very easy because
of the capacity of water to dissolve numerous substances in large amounts. And the
sources of contamination are quite many, and can be categorized under broad groups
including: petroleum products, pesticides and herbicides, heavy metals, hazardous
wastes, excess organic matter, sediment, infectious organisms, and even thermal
pollution. If severe, water pollution can kill large numbers of fish, birds, and other
animals, in some cases killing all members of a species in an affected area, where people
who ingest polluted water can become ill, and, with prolonged exposure, may develop
cancers or bear children with birth defects (John Hart; Microsoft® Encarta®, 2009).
Wastewater refers to water that has been used. It originates mainly from domestic,
industrial, groundwater, and meteorological sources, and these forms of wastewater are
commonly referred to as domestic sewage, industrial waste, infiltration, and storm-
water drainage, respectively. For instance, domestic sewage results from people's day-
to-day activities, such as bathing, body elimination, food preparation, and recreation,
averaging about 227 litres (about 60 gallons) per person daily. Where, the quantity and
character of industrial wastewater is highly varied, depending on the type of industry,
the management of its water usage, and the degree of treatment the wastewater receives
before it is discharged. A steel mill, for example, might discharge anywhere from 5700
to 151,000 litres (about 1500 to 40,000 gallons) per ton of steel manufactured. Less
water is needed if recycling is practiced. A typical metropolitan area discharges a
volume of wastewater equal to about 60 to 80 percent of its total daily water
requirements, the rest being used for washing cars and watering lawns, and for
manufacturing processes such as food canning and bottling (Karadi, et al., 2009).

13. Wastewater, specifically referring to all kinds of polluted water generated by human
activities is now, not only a main cause of irreversible damage to the environment but
a contributor to the depletion of our fresh water reserves, posing a major threat to the
upcoming generations. We carry out a lot of activities involving the use of large
amounts of water, ranging from domestic and agricultural processes, to industrial
activities. These are often carried out at the expense of plenty fresh water which is
exhausted as a wastewater, and needs to be treated properly to reduce or eradicate the
pollutants and achieve he purity level for its reuse (Ali et al., 2012).
Heavy metals are defined as metallic elements that have a relatively high density
compared to water (Fergusson, et al., 1990). While the Encarta dictionaries defined
them as metals having high relative densities, usually of 5.0 or higher. These
heavy metals such as copper, lead, mercury, and selenium, get into water from many
sources, including industries, automobile exhaust, mines, and even natural soil. Like
pesticides, heavy metals become more concentrated as animals feed on plants and are
consumed in turn by other animals. When they reach high levels in the body, heavy
metals can be immediately poisonous, or can result in long-term health problems similar
to those caused by pesticides and herbicides.
The generation of wastewater containing heavy metals is ever on the increase, due to
the growing population of various industries employing processes that produce these
contaminants as waste. Industries that carry out activities such as paint and pigment
production, battery production, fertilizers and herbicides production, metals processing,
etc. produce a vast amount of heavy metals wastewater on a daily basis. This wastewater
is usually treated by techniques including biological processes for nitrification,
denitrification, and phosphorous removal and physico-chemical treatment processes for
filtration, air stripping, ion-exchange, chemical precipitation, oxidation, carbon
adsorption, ultrafiltration, reverse osmosis, electrodialysis, volatilization and gas
stripping. The common physico-chemical processes such as coagulation and
flocculation require addition of chemicals. Electrochemical technologies which include
electrocoagulation, electrofloatation, and electrodecantation do not require chemical
additions (Mollah et al., 2001).

14. Presently, the techniques for the removal of heavy metals, such as chromium, cobalt,
copper, lead, and nickel, from industrial wastewater include chemical coagulation,
precipitation, ion exchange, adsorption, advanced oxidation, electrodialysis and
filtration (Abdel-Ghani et al., 2009; Malakootian et al., 2009), but these techniques have
inherent limitations of selective separation, poor removal efficiency, production of low
quality sludge and the problems of high investment cost and equipment operation (Choi
and Kim, 2005). The unreliable results offered by these classical techniques and the
need for eco-friendliness as a desired feature of water treatment technology have led to
increasing global interest in electrocoagulation (EC) as a research subject (REF). so
that, while the biological and chemical treatment of wastewater are usually associated
with the production of greenhouse gases and activated sludge, along with some other
limitations regarding required area and removal of residual chemicals respectively (Ali
et al., 2012), electrocoagulation on the other hand is an extremely effective technique;
since it has the capability to overcome the disadvantages of the conventional treatment
techniques.
In recent times, from the past few decades, various literary works in the environmental
science field have indeed shown a growing interest towards the treatment of different
types of wastewater by electrocoagulation (EC).
Electrocoagulation (EC) is an emerging technology that combines the functions and
advantages of conventional coagulation, electro-flotation, and electrochemistry in water
and wastewater treatment (REF). Electrocoagulation can be defined as the process of
destabilizing suspended, emulsified, or dissolved contaminants in an aqueous medium
by introducing an electric current into the medium (Emamjomeh and Sivakumar, 2009;
Top et al., 2011). It is considered to be potentially an effective tool in the treatment of
various wastewaters and has shown to be highly efficient in the removal of heavy metals
from aqueous medium (Bazrafshan et al., 2014). It is an electrochemical technique for
treating polluted water using electricity instead of expensive chemical reagents. The
chemistry behind the EC process in water is such that the positively charged ions are
attracted to the negatively charged hydroxides ions producing ionic hydroxides with a
strong tendency to attract suspended particles leading to coagulation.

15. The use of electricity to treat water was first proposed in 1889 in England as
documented by (Chen et al, 2007). The application of electrolysis in mineral
beneficiation was patented by Elinore in 1904. Electrocoagulation (EC) with aluminium
and iron electrodes was patented in the united states in 1909. The electrocoagulation of
drinking water was first applied on a large scale in the United states in I946 (Tamer,
2013). At that time because of the relatively large capital investment and the expensive
electricity supply, electrochemical water or wastewater technologies did not find wide
application worldwide. However, in the United States and former USSR extensive
research during the following half century has accumulated abundant amount of
information (Tamer, 2013). With the ever increasing standard of drinking water supply
and the stringent environmental regulations regarding the wastewater discharge,
electrochemical technologies have regained their importance worldwide during the past
two decades and processes such as electrochemical metal recovery electrocoagulation
(EC, electrofloatation (EF) and electrooxidation (EO) can be regarded nowadays as
established technologies (Butler et al., 2011).
Electrocoagulation is a complex process, with many synergistic mechanisms operating
to remove water pollutants (metals, anions, organic compounds, etc.) (Zaleschi et al.,
2012). This technology is a treatment process which applies electrical current to treat
and flocculate contaminants without having to add coagulants. The process involves the
simultaneous removal of heavy metal ions, solids in suspension, organic emulsions and
many others water pollutants, using electric energy and sacrificial metallic plates
(electrodes) instead of expensive chemical reagents. In the process, the “sacrificial”
anode corrodes and discharges in the solution active precursor coagulant (usually iron
or aluminium cations) (Zaleschi et al., 2012) that form polymeric metal hydroxide
species in solution used in dosing polluted water. After the polymeric metal hydroxide
species neutralize negatively charged particles, the particles bind together to form
aggregates of flocs, resulting in pollutant removal by adsorption of soluble organic
compounds and trapping of colloidal particles. Finally, these flocs are removed easily
from aqueous medium by sedimentation or flotation. Additionally, electrolytic gas

16. bubbles (mainly hydrogen) which induce electro-flotation are generated (Holt et al.,
2002; Behbahani et al., 2011). As a result of their dissolution, the anodes disappear
during the treatment, reaching a time when it is necessary to replace the anodes. In the
electrocoagulation process it is important to use soluble anodes made of aluminium,
iron or other material, and cathodes made of the same material, or steel (Zaleschi et al.,
2012).
Several studies have investigated the use of EC to improve the quality of industrial
wastewater (Niam et al., 2010). The process has been employed successfully to
decontaminate waste streams of toxic cations and anions, as well as heavy metals,
foodstuff, oil wastes, textile and dyes fluorine, polymeric wastes, organic matter from
landfill leachate, suspended particles, chemical and mechanical polishing wastes,
aqueous suspension of ultrafine particles, nitrates, phenolic waste, arsenic, and
refractory organic pollutants including lignin (Charturvedi, 2013). Also and
importantly, electrocoagulation is applicable for the treatment of drinking water.
Generally, the EC process has been positively documented to treat the wastewater from
commercial laundry services, textile manufacturing, metal plating, fish and meat
processing, mining operations, municipal sewage system plants, and palm oil industrial
effluent (Ali et al., 2012).
Electrocoagulation (EC) consists of number of benefits which include: environmental
compatibility, ease of operation, amenability to automation, cost effectiveness, energy
efficiency, and high sedimentation velocity, reduced amount of sludge, safety, and
versatility (Rajeshwar et al). These are all in addition to it removing pollutants, and
producing hydrogen gas simultaneously as revenue to compensate the operational cost.
1.2 PROBLEM STATEMENT
Often, wastewaters from most industries are rich in heavy metals. This is because these
heavy metals find intense application in industrial processes in the form of construction

17. materials, salts, pigments, etc. due to their toxicity, the discharge of wastewater
containing heavy metals in concentrations high above the acceptable standards pose a
significant threat to human health, water bodies and aquatic life, and the environment
at large.
Heavy metals, such as Copper, Lead, Mercury, and Selenium, get into water from many
sources, including industries, automobile exhaust, mines, and even natural soil. Like
pesticides, heavy metals become more concentrated as animals feed on plants and are
consumed in turn by other animals. When they reach high levels in the body, heavy
metals can be immediately poisonous, or can result in long-term health problems similar
to those caused by pesticides and herbicides. For example, Cadmium in fertilizer
derived from sewage sludge can be absorbed by crops. If these crops are eaten by
humans in sufficient amounts, the metal can cause diarrhoea and, over time, liver and
kidney damage. Lead can get into water from lead pipes and solder in older water
systems; children exposed to lead in water can suffer mental retardation. And according
to the United States EPA classification, Copper could be toxic in high concentrations.
Conventional water treatment techniques are basically burdened with a number of
drawbacks in the removal of heavy metals from wastewater. Thus, it becomes the
purpose of this work to attempt to investigate the effectiveness of electrocoagulation in
the removal of heavy metals in wastewater and solutions in general.
1.3 AIM AND OBJECTIVES
The aim of this research is to remove heavy metals from simulated wastewater using
the electrocoagulation technique, through batch experiments. The objectives of the
work thus include the following:
 To study the effects of electrocoagulation parameters: initial PH, initial
concentration, electrolysis time, current density, temperature, and electrode distance
on the removal efficiency.

18.  To determine the power consumption during electrocoagulation process using the
treatment time and current density.
 To study the kinetics of electrocoagulation reaction by experimental verification.
 To establish conditions for optimal removal for various metals.
 To evaluate the effectiveness of electrocoagulation in the removal of heavy metals
from wastewater.
1.4 SIGNIFICANCE OF THE STUDY
As the demand for quality drinking water is increasing globally and environmental
regulations regarding wastewater discharge are becoming increasingly stringent (REF),
it has become necessary to develop more effective treatment methods for water
purification and/or enhance the operation of current methods.
In the realm of resource sustainability/conservation, it is advised that water should be
recycled endlessly in the manufacturing cycle by treatment to meet its reutilization
quality. Reutilization of water in the manufacturing cycle also has been identified as an
effective means of monitoring environmental pollution and electrocoagulation provides
an effective and viable means of achieving this end.
From the environmental perspective, the discharge of wastewater into the natural
environment has been implicated as a major cause of environmental pollution (REF).
As the need for sustainability of the environment increases globally, electrocoagulation
represent an effective tool towards meeting this need.
As the awareness on the challenges of global warming increases globally in a world that
has been ravaged by the menace of climate change, there is need to transcend to an eco-
friendly water treatment technology, which is a standout feature of electrocoagulation
that makes it inevitable within the water treatment circle.
The electrocoagulation process also can serve as a field of learning to students,
researchers and industries.

19. 1.5 SCOPE OF THE STUDY
For the purpose of accomplishing the objectives outlined previously, this work would
cover a detailed information on the electrocoagulation technology and process, while
previous works on the electrocoagulation method of treating wastewaters would be
reviewed.
The work would proceed to investigate the effects of the various process variables
including; electrode distance, initial and varied pH, electrolysis time, varied initial
concentration, current, and water temperature on the efficient removal of the pollutants
that characterize the wastewater. The energy consumption during the course of each
experimental run will be determined.

20. CHAPTER TWO
LITERATURE REVIEW
2.1 GENERAL ASPECTS OF WASTEWATER TREATMENT
The materials in waters and wastewaters stem from land erosion, the mineral
dissolution, the vegetation decay, and domestic and industrial waste discharges. Such
materials may contain suspended and/or dissolved organic and/or inorganic materials,
and various biological forms such as bacteria, algae, and viruses (Bratby, 2006).
It is thus undeniable that one of the major challenges facing mankind today is to provide
clean water to a vast majority of the population around the world. The need for clean
water is particularly critical in Third-World Countries. Rivers, canals, estuaries and
other water-bodies are being constantly polluted due to indiscriminate discharge of
industrial effluents as well as other anthropogenic activities and natural processes. In
the latter, unknown geochemical processes have contaminated ground water with
arsenic in many countries. Highly developed countries, such as the US, are also
experiencing a critical need for wastewater cleaning because of an ever-increasing
population, urbanization and climatic changes. The reuse of wastewater has become an
absolute necessity. There is, therefore, an urgent need to develop innovative, more
effective and inexpensive techniques for treatment of wastewater. A wide range of
wastewater treatment techniques are known which includes biological processes for
nitrification, denitrification and phosphorous removal; as well as a range of physico-
chemical processes that require chemical additions. The commonly used physico-
chemical treatment processes are filtration, air stripping, ion-exchange, chemical
precipitation, chemical oxidation, carbon adsorption, ultrafiltration, reverse osmosis,
electrodialysis, volatilization and gas stripping. A host of very promising techniques
based on electrochemical technology are being developed and existing ones improved
that do not require chemical additions. These include electrocoagulation,
electrofloatation, electrodecantation, and others. Even though one of these,
electrocoagulation, has reached profitable commercialization, it has received very little
scientific attention. This process has the potential to extensively eliminate the
disadvantages of the classical treatment techniques.

21. Moreover, the mechanisms of EC are yet to be clearly understood and there has been
very little consideration of the factors that influence the effective removal of ionic
species, particularly metal ions, from wastewater by this technique.
2.1.1 Biological Treatment Technique
Biological treatment involves the use of microorganisms to remove dissolved nutrients
from a discharge (Henry et al., 2006). Organic and nitrogenous compounds in the
discharge can serve as nutrients for rapid microbial growth under aerobic, anaerobic, or
facultative conditions.
The three conditions above differ in the way they use oxygen. Aerobic microorganisms
require oxygen for their metabolism. Whereas, anaerobic microorganisms grow in the
absence of oxygen: the facultative microorganism can proliferate either in the absence
or presence of oxygen, although using different metabolic processes. Most of the
microorganisms present in wastewater treatment use the organic content of the
wastewater as a source of energy to grow, and are thus classified as heterotrophs from
a nutritional point of view.
Biological treatment systems can convert approximately one-third of the colloidal and
dissolved organic matter into stable end products and convert the remaining two-thirds
into microbial cells that can be removed through gravity separation. The organic load
present is incorporated in part as biomass by the microbial populations, and almost all
the rest is liberated gas. Carbon dioxide (CO2) is produced in aerobic treatments,
whereas anaerobic treatments produce both carbon dioxide and methane (CH4).
Biological treatment systems are most effective when operating continuously; every
hour in each day and 365 days/year. Systems that are not operated continuously have
reduced efficiency because of changes in nutrient loads to the microbial biomass. The
biological treatment systems also generate a consolidated waste stream consisting of
excess microbial biomass, which must be properly disposed.

22. 2.1.2 Chemical Treatment Technique
These are processes that require chemical additions. The commonly used chemical
treatment processes are air stripping, ion-exchange, chemical precipitation, chemical
oxidation, carbon adsorption, ultrafiltration, reverse osmosis, electrodialysis and
chemical coagulation. In chemical coagulation, the process involves the removal of
colloids and is commonly used for water purification and wastewater treatment.
Coagulation is the most widespread and practical method of removing colloidal solids
from wastewater. This is a process of destabilizing colloids, aggregating them, and
joining them together for ease of sedimentation. It entails the formation of chemical
flocs that adsorb, entrap, or otherwise bring together suspended matter, more
particularly suspended matter that is so finely divided as to be colloidal. The chemicals
used are: aluminium sulphate, Al2(SO4)3.18H2O; ferrous sulphate, FeSO4.7H2O
(copperas); ferric sulphate, Fe2(SO4)3; ferric chloride, FeCl3. Aluminium sulphate is
commonly used for coagulation. The use of chemical coagulants, able to act as either
negatively or positively charged ions, has highly improved the effectiveness of removal
of colloids by coagulation (Nemerow and Agardy, 1998).
The coagulation mechanisms, depending on the physical and chemical properties of the
solution, pollutant and coagulant, include charge neutralization, double layer
compression, bridging and sweep (Holt et al., 2002). The process of coagulation
separation consists of four steps. The initial step is simple: the chemical is added to
wastewater. This is followed by the second step, where the solution is mixed rapidly in
order to make certain that the chemicals are evenly and homogeneously distributed
throughout the wastewater. In the third step, the solution is mixed again, but this time
in a slow fashion, to encourage the formation of insoluble solid precipitates, the process
known as "coagulation". The final step is the removal of the coagulated particles by
way of filtration or decantation (Yılmaz et al., 2007).
Natural coagulation is another area to be looked at. It is desirable to have a progressive
replacement of these chemical coagulants with alternative coagulants and flocculants
preferably from natural and renewable sources. Biopolymers would be of great interest
since they’re are natural low-cost products, characterized by their environmentally

23. friendly behaviour. And presumed to be safe for humans’ health. Even though, scientific
community is researching new natural coagulant sources as Nirmali seeds (Strychnos
potatorum), tannins cactus and specially Moringa oleifera (Deepa et al., 2013). The
history of the use of natural coagulants is long. Natural organic polymers have been
used for more than 2000 years in India. Africa and China as effective coagulants and
coagulant aids at high water turbidities. They may be manufactured from plants seeds.
Leaves and roots (Deepa et al, 2013). These natural organic polymers are interesting
because comparative to the use of synthetic organic polymers containing acrylamide
monomers, no human health danger and the cost of these natural coagulants would be
less expensive over to the conventional chemicals like since it is locally available most
rural communities. Natural coagulants have bright future and are concerned by many
researchers because of their abundant source, low price, environment friendly,
multifunction and biodegradable nature in water purification.
Mineral treatment processes generally produce wastewaters including suspended and
colloidal particles, such as clay particles. Dewatering of waste clay mineral tailings is
an important part of mining and mineral processing activities worldwide. For instance,
clay tailings which arise from hydrometallurgical processing of mineral ores are always
seen but cause problems in waste treatment and disposal (McFarlane et al., 2006).
Dewatering of the clay tailings is commonly achieved through flocculated, gravity-
assisted thickening processes (Mpofu et al., 2005). Most colloidal particles are stable
and remain in suspension, and thus lead to pollution in water into which they are
discharged or degrade re-circulation water in processing plants (Rubio et al., 2002). The
mutual repulsion among colloidal particles owing to the same sign of their surface
charges is the main reason for the stability of the system. It is difficult to remove
colloidal particles in gravitational sedimentation ponds or devices without any size
enlargement treatment. Size enlargement treatment may involve destabilization of
particles or collision of particles to form aggregates. Destabilization means either a rise
in ionic strength of the medium or a neutralization of the surface charge of particles by
the addition of chemicals called coagulants or flocculants. These chemicals promote
different processes involved in the charge destabilization as they increase ionic strength,

24. and adsorb on the surface of colloidal particle compensating its former electrical charge,
and they can promote the formation of precipitates.
Electrocoagulation (EC) has thus been suggested as an advanced alternative to chemical
coagulation in pollutant removal from raw waters and wastewaters. Wastewaters
usually contain suspended solids and dispersed particles that do not sediment easily,
mainly colloids. The colloidal systems are stable when they have the same charges on
their surface, which cause repulsion between them (Zaleschi et al., 2012). Due to this
fact, colloids do not aggregate to each other and therefore do not form bigger particles
that can be able to precipitate by themselves (Riera – Torres et al., 2010). It is observed
that the quality indicators present significant removal efficiency, making this
technology suitable for treatment of wastewater especially after conventional treatment
(Zaleschi et al., 2012).
2.1.3 Electrocoagulation Treatment Technique
Electrocoagulation is an efficient treatment process for various type of wastes such as
soluble oils, liquids from food, textile industries, cellulose and effluents from the paper
industry (Ghanim et al., 2013). According to Can et al., (2006) EC has been proposed
in recent years as an effective method to treat various wastewaters such landfill
leachate, effluent from restaurants, saline wastewater, tar sand and oil shale wastewater,
textile wastewater, Laundry wastewater, urban wastewater, tannery wastewater, nitrate
and arsenic bearing wastewater, and chemical-mechanical polishing wastewater.
2.2 Electrocoagulation Technology
2.2.1 Definition(s)
BakerCorp™, a United States based technological company that supplies
Electrocoagulation and other water treatment facilities defined Electrocoagulation as
an electro-chemical process that simultaneously removes heavy metals, suspended
solids, emulsified organics and many other contaminants from water using electricity
instead of expensive chemical reagents, using electricity and sacrificial plates to

25. combine with contaminants in a waste stream, producing insoluble oxides and
hydroxides - Floc - that are easily separated from the clear water.
While an infographic from Brian Mikelson, Halliburton explained the basic principles
of the electrocoagulation process.
Figure 2.0 The electrocoagulation process. Source: Halliburton.
According to shivayogimath et.al (2013), Electrocoagulation (EC) is a process in which
the anode material undergoes oxidation with the formation of various monomeric and
polymeric metallic hydrolysed species. These metal hydroxides remove organics from
wastewater by sweep coagulation and/or by aggregating with the colloidal particles
present in the wastewater to form bigger size flocs which ultimately are removed by
settling.
Electrocoagulation technique is a technology for water and wastewater treatment which
uses an electrochemical cell, where a DC voltage is applied to the electrodes that are
corroded to generate a coagulant in which the electrolyte are usually water effluents.
This process has proven very effective in removing contaminants from water and is
characterized by reduced sludge production, no requirements for chemical use and ease
of operation.

26. 2.2.2 History of Electrocoagulation Technology
Electrocoagulation was a long history been employed to remove a wide range of
pollutants. Vik et.al (1889) was the first to propose electrocoagulation in London where
a sewage treatment plant was built and electrochemical treatment had been used via
mixing the domestic wastewater with saline water.
At the turn of the nineteenth century, the electrocoagulation system was seen as a
promising technology. In 1906, A.E Dietrich was the first to patent the principle of
electrocoagulation which was used to treat bilge water from ships. In the United States,
a patent for the purification of wastewater using an electrocoagulation treatment using
sacrificial aluminium and iron electrodes was awarded by J.T Harris, since then a wide
range of water and wastewater applications followed under a variety of conditions. In
the following decade, the process was used for purifying drinking water and was first
applied in the United States in 1946.
Treatment of wastewater by electrocoagulation has been practiced for most of the
twentieth century with limited success and popularity. More investigations in 1946 and
1956 showed that electrocoagulation technology was not developed for other industrial
purposes because of the low level environmental awareness and insufficient financial
incentives were probably reasons for abandoning the technology.
However, since 1970 the concept became popular in North America, electrocoagulation
has been used primarily to treat wastewater from pulp and paper industries, mining and
metal processing industries. In the last decade, this technology has been increasingly
used in South America and Europe for treatment of industrial wastewater containing
metals. In the 1980’s
there was an array of the study on electrocoagulation technology
by Russian scientists on the treatment of wastewater. Further studies have showed the
possibility of treating natural water in small systems by two-stage filtration under the
influence of aluminium ions which produced electrolytic dissolution.

27. 2.2.3 Theory of Electrocoagulation
The foundation under which the electrocoagulation process is based may be
conveniently classified according to the contribution of three basic sciences namely:
Electrochemistry, coagulation, Floatation. The inter-relationship between these three is
shown in figure 2.1 below
Figure 2.1 Conceptual frame work for electrocoagulation as a synthetic technology
(Chaturvedi, 2013).
2.2.3.1 Electrochemistry
This deals with a branch of chemistry concerned with the interaction of electrical and
chemical effects. Electrocoagulation technologies are based on the concept of
electrochemical cells known as ‘electrolytic cells’. In an electro coagulator, electrolysis
is based on applying an electric current through the solution to be treated by electrodes.
The anode is a sacrificial metal (usually aluminium or iron) that withdraws electrons

28. from the electrode which releases aluminium or iron ions to the bulk solution and
precipitation of Al(OH)3 or Fe(OH)3 at the electrocoagulator.
When the electrodes are immersed into a solution to allow a direct current to flow
through the solution, a chemical change occurs at the electrodes. The fundamentals of
the chemical change depend on the type of electrodes, the potential difference or
electromotive force and the type of wastewater. The material used at the anode
determines the type of coagulant released into the solution depending on the type of
electrodes. Different electrode materials that could be used for this process includes:
Aluminium, iron, stainless steel and platinum which have been reported by other
researchers.
To pass current to each electrode and release the coagulant, a potential difference and a
current flow is required. The potential difference can be assumed from the
electrochemical half-cell reactions occurring at each electrode, which differ depending
on the PH and species present in the solution. A half-cell is an electrochemical reaction
from an electrode containing an oxidized and reduced species. For example, the
electrolytic dissolution of Al anode in water produces Al3+
SPECIES.
AL(S) AL3+
+ 3e-
(2.0)
2.2.3.2 Coagulation
Coagulation and flocculation are both used for treating pollutants in water treatment
processes. Coagulation simply means a process used to cause the destabilization and
initial coalescing of colloidal particles whereas flocculation is an aggregation of smaller
particles into larger particles. In order to overcome the stability of particles in treated
water a coagulant can be added either with chemical (as shown above) or electricity.
The coagulants released by the passage of electric current causes the aggregate in the
particles to form into larger heavier mass known as flocs, which can be more easily
removed by settling and filtration.

29. Precipitation pathways describe the interaction of the pollutant with the metal hydroxide
precipitates. These metal hydroxides are known as ‘sweep flocs ‘. When the coagulants
precipitates, it can react with particles of pollutants binding them to the precipitate. Also
by the continuous addition of more coagulants to a solution , the attracting force
between the primary charges and other trivalent FE3+
or AL3+
ions increase causing the
double layer to minimize when the Van der Waals forces exceed the forces of repulsion.
The coagulant dose is a function of the chemistry of the treatment water, particularly
the PH, alkalinity, hardness, ionic strength and temperature (Binnie et al., 2002).
2.2.3.3 Floatation
The process works by the attaching fine bubbles to the particles concerned. Since the
overall density of the bubble particle complex is significantly less than the liquid, it
rises to the surface where the floated material (scum) is skimmed off.
There are main methods of floatation namely: Air floatation, Dissolved air floatation
and Electrofloatation. The main difference between electrofloatation and more
conventional floatation methods is the method of producing bubbles. The basis of
electrolytic or electrofloatation is the generation of hydrogen bubbles in dilute
aqueous solution by passing direct current between two electrodes (Chen et al., 2002).
In electrofloatation smaller bubbles are generated, it has been reported that an
electrolyzed gas bubble is about 20µm (Emamjumeh, 2006).
The effectiveness of the floatation process for removing pollutants depends on the
type of electrodes, current effects on the mixing within the reactor, possible contacts
between individual pollutants particles, coagulant and bubbles. Thus, the pollutant
removal rate by floatation is expected to increase accordingly when the current in the
electrocoagulator increased.

30. 2.2.3.4 How the process works
The electrocoagulation process operates on the base of the principle that the cations
produced electrolytically from iron and/or aluminium anodes as shown in figure 2.2 is
responsible for the increasing of the coagulation of contaminants from an aqueous
medium.
Electrophoretic motion tends to concentrate negatively charged particles in the region
of the anode and positively charged particles in the region of the cathode (Chaturvedi,
2013). The consumable metal anodes are used to continuously produce polyvalent metal
cations in the region of the anode. These cations neutralize the negative charge of the
particles moved towards the anodes by production of polyvalent cations from the
oxidation of the sacrificial anodes (Fe or Al) and the electrolysis gases like hydrogen
evolved at the anode and oxygen evolved at the cathode (Chaturvedi, 2013).
Figure 2.2 Schematic diagram of a two-electrode EC cell (Essadki, 2012).

31. It is generally accepted that the electrocoagulation process involves three successive
stages:
a) Formation of coagulants by electrolytic oxidation of the “sacrificial anode”.
b) Destabilization of the contaminants, particulate suspension and breaking of
emulsions.
c) Aggregation of the destabilized phases to form flocs.
Where the pollutants can be in the form of (Essadki, 2012):
 Large particles easy to separate them from water by settling.
 Colloids.
 Dissolved mineral salt and organic molecules.
It is possible to use the decantation as a technique to eliminate the maximum amount of
particles. This remark is especially valid for colloids. Thus, colloids are organic or
mineral particles in which the size is between some nanometres and approximately 1µ
responsible for colour and turbidity (Essadki, 2012).
The destabilization mechanism of the contaminants, particulate suspension and
breaking of emulsions has been described in broad steps and may be summarized as
follows (Tamer, 2013):
 Migration to an oppositely charged electrode (electrophoresis) and aggregation
due to charge neutralization.
 The cations or hydroxyl ions (OH-
) forms precipitate with the pollutant.
 The metallic cations interacts with OH-
to form a hydroxide, which has high
adsorption properties thus bonding to the pollutant (bridge coagulation).
 The hydroxides form larger lattice-like structures and sweeps through the water
(sweep coagulation).
 Oxidation of pollutants to less toxic species.
 Removal by electrofloatation or sedimentation and adhesion to bubbles.
Due to electrophoretic action negative ions which are produced from the cathode moves
towards the anode and the combination of the metal cations with these negative particles

32. turns into the coagulation. At the anode small bubble of oxygen and at the cathode small
bubble s of hydrogen are generated which are responsible for electrolysis of water thus
water becomes electrolyzed as the process is carried out continuously. The flocculated
particles are attracted by these bubbles and these flocculated particles float due to the
natural buoyancy towards the surface.
The quantity of electricity passed through is actually responsible for dissolution and
deposition of metal ions at the electrodes. A relationship between current density
(A/cm2
) and the quantity of the metals (M) dissolved (g of M/cm2
) is determined using
faraday’s law:
W =
𝒊×𝒕×𝑴
𝒏×𝑭
(2.1)
Where W = the amount of dissolution of electrode (g of M/cm2
)
i = current density (A/cm2
)
t = time in seconds
M = Relative molar mass of the electrode
n = no. of electrons in oxidation/reduction reaction
F = Faraday’s constant, 96500C/mol.
Electrocoagulation operating conditions are mostly dependent on the chemistry of the
aqueous medium, mainly conductivity and PH. Also other important characteristics are
particle size, type of electrodes, retention time between plate, plate spacing and
chemical constituent concentrations. The mainly operating principal is that the cations
produced electrolytic from iron and/or aluminium anodes enhance the coagulation of
contaminants from an aqueous medium. Generally, oxidation of organic matter by
electrochemical treatment can be classified as direct oxidation at the surface of the
anode and indirect oxidation from the anode surface which are influenced by the anode
material (Chaturvedi, 2013).

33. 2.2.4 Mechanism of Electrocoagulation
The mechanisms of electrocoagulation for water and wastewater treatment are very
complex. It is generally believed that there are three other possible mechanisms
involved besides electrocoagulation, which are electrofloatation, electrochemical
oxidation and adsorption (Kobya, et al., 2011). The main electrochemical reactions at
the electrodes during electrocoagulation process (Katal and Pahlavanzadeh, 2011):
At the cathode, H2 gas is liberated:
3H2O(I) + 3e-
(3/2)H2(g) + 3OH-
(aq) (2.2)
The metal cathode (M) may be chemically attacked by OH-
especially at high PH values:
2M(s) + 6H2O(l) + OH-
(aq) 2M(OH4)-
(aq) (2.3)
At the anode, sacrificial metal (M), Al or Fe, is dissolved:
M(S) M3+
+ 3e-
(2.4)
In the case of Fe electrode, the anodic reactions also occur:
Fe(s) Fe2+
+ 2e-
(2.5)
In conclusion the formation of metal hydroxide flocs proceeds according to a set of
complex mechanisms which may be simplified as:
M3+
Monomeric species Polymeric species Amorphous M(OH3)
In the case of Al electrode; monomeric species such as Al(OH)2+
, Al(OH)2+
2,
Al2(OH)4+
2, Al(OH)4-
and polymeric species such as Al6(OH)3+
15, Al7(OH)4+
17,
Al8(OH)4+
20, Al1304(OH)7+
24, Al13(OH)5+
34 are formed during the EC process.
In the case of Fe(OH)2+
, Fe2(OH)24+
, Fe(OH)4-
, Fe(H2O)2+
, Fe(H2O)5OH2+
,
Fe(H2O)4(OH)2+
, Fe(H2O)8(OH)24+
, Fe2(H2O)6(OH)42+
are produced. Formation rates of
these different species depend on PH of the medium and types of ions present and play
an important role in the EC process.

34. 2.2.4.1 Electrocoagulation using iron (Fe) electrodes:
By using an iron anode with the Fe(OH)n formation where n=2 or 3 is released at the
anode. Simplified oxidation and reduction mechanisms at the anode and
cathode of the iron electrodes as represented as follows (Parga et al., 2009):
Mechanism 1(a) (basic wastewater)
Anode:
Fe(s) Fe2+
(aq) + 2e-
(2.6)
Fe2+
(aq) + 2OH-
(aq) Fe(OH)2(S) (2.7)
Cathode:
2H2O(l) + 2e-
H2(g) + 2OH-
(aq) (2.8)
Overall:
Fe(s) + 2H2O(l) Fe(OH)2(S) + H2(g) (2.9)
Mechanism 1(b) (acidic wastewater):
Anode:
4Fe(s) 4Fe2+
(aq) +8e-
(2.10)
4Fe2+
(aq) + 10H2O(l) + O2(g) 4Fe(OH)3(S) + 8H+
(aq) (2.11)
Cathode:
8H+
(aq) + 8e-
4H2(g) (2.12)
Overall:
4Fe(S) + 10H2O(l) + O2(g) 4Fe(OH)3(S) + 4H2(g) (2.13)
According to Larue et al., (2003), the generation of iron hydroxides Fe(OH)n is followed
by an electrophoretic concentration of colloids (usually negatively charged) in the
region close to the anode. The produced ferrous ions hydrolyse to form monomeric
hydroxide ions and polymeric hydroxide complexes that depend on the pH of the

35. solution. The polymeric hydroxides, which are highly charged cations, destabilize the
negatively charged colloidal particles allowing their aggregation and formation of flocs.
Mechanism 2 (acidic and basic wastewater):
Fe(s) +6H2O(l) Fe(H2O)4(OH)2(S) +H2(g) (2.14)
Fe(s) +6H2O Fe(H2O)3(OH)3(S) +1.5H2(g) (2.15)
In the appropriate conditions, iron (II) and iron (III) hydroxides combine in the
following proportion to generate Green Rust, GR (Parga et al., 2009):
x Fe(OH)3(aq) + (6-x) Fe(OH)2(aq) x Fe(OH)3 .(6-x)Fe(OH)2(S) (2.16)
Electrocoagulation can be considered as an accelerated corrosion process. GR is
recognized as an important intermediate phase in corrosion of FeO. GR’s are layered
Fe(II)-Fe(III) hydroxides having a pyroaurite-type structure consisting of alternating
positively charged hydroxide layers and hydrated anion layers.
2.2.4.2 Electrocoagulation using aluminium (Al) electrodes:
It is well known that in electrocoagulation process the main reactions occurring at the
aluminium electrodes during electrolysis are (Mouedhen et al., 2008):
Anode
Al(s) Al3+
(aq) +3e-
(2.17)
Cathode
2H2O(l) + 2e-
H2(g) +2OH-
(2.18)
When the anode potential is sufficiently high, secondary reactions may occur especially
oxygen evolution:
2H2O(l) O2(g) + 4H+
+4e-
(2.19)
Aluminium ions (A13) produced by electrolytic of the anode equation 2.17

36. immediately undergo Spontaneous hydrolysis reactions which generate species
according to the following sequence (omitting coordinated water molecules for
convenience):
Al3+
(aq) + H2O(l) Al(OH)2+
(aq) + H+
(2.20)
Al(OH)2+
(aq) + H2O(l) Al(OH)2+
(aq) + H+
(2.21)
Al(OH)2+
(aq) + H2O(l) Al(OH)3 + H+
(2.22)
These cationic monomeric species (Al3+
, Al(OH)2+
) is produced at low pH, which at
appropriate pH values are transformed initially into Al(OH)3 and finally polymerized to
Aln(OH)3n. for example, the structures of dimeric and polymeric Al3+
hydroxo
complexes are shown below:
Figure 2.3 Dimeric and Polymeric structures of Al3+
hydroxo complexes (Mollah et al.,
2001)
2.2.5 Description of the Technology
The electrocoagulation reactor is basically an electrolytic cell with an anode and a
cathode. Oxidation will cause the anode material to undergo electrochemical corrosion,
whereas the cathode will be subjected to passivation, when the cell is connected to an
external power sour. But since electrodes with large surface area for a workable rate of
metal dissolution, the afore-mentioned arrangement is generally not suitable for the
treatment of pollutant liquid medium. This requirement was satisfied by use of
monopolar electrodes either in parallel or series connections. Figure 2.4 shows a simple
arrangement in which a pair of anodes and cathodes is connected in parallel mode,
forming an electrocoagulation cell. In this set-up, a resistance box is necessary to

37. regulate the current density, as well as requiring a multimeter to read the current values.
The conductive metal plates are commonly known as ‘sacrificial electrodes’. The
sacrificial electrodes may be made up of the same or of different materials as anode.
Figure 2.4 Bench-scale electrocoagulation reactor with monopolar electrodes in parallel
connection.
An arrangement of an electro coagulation cell with monopolar electrodes in series is
shown in Figure 2.5. As depicted in the figure, the ‘sacrificial electrodes’ while having
internal connection within each other, do not have any inter-connections with the outer
electrodes.
Figure 2.5 Bench scale electrocoagulation reactor with monopolar electrodes in series.

38. Since cells that are connected in a series mode have higher resistance, a higher potential
is necessary for a given current flow, although the same current would, however, flow
through the electrodes. On the other hand, cells connected in a parallel mode have their
electric current divided between all the electrodes in relation to the individual resistance
of the cell. The use of bipolar electrodes in a parallel connected cell is also possible. In
such case as shown in Figure 2C, two parallel electrodes that are connected to the
electric power source are situated on either side of the sacrificial electrode, with no
electrical connection to the sacrificial electrode. This way, conducting maintenance
during use becomes easier in comparison due to the simple set-up. If an electric current
is passed through the electrodes, the neutral sides of the connected plate will be
transformed to charged sides, which have opposite charged compared to the parallel
side beside it. In this setup, the sacrificial electrodes are referred to as bipolar electrodes
(Mollah et al., 2004). Thus, during electrolysis, the positive side undergoes an anodic
reaction, whereas a cathodic reaction takes place on the negative side.
Figure 2.6 Bench scale electro coagulation reactor bipolar electrodes in parallel
connection.

39. 2.2.6 Practical Considerations of Electrocoagulation
2.2.6.1 Constructions of electrocoagulation systems
EC systems are typically constructed of plate electrodes and water flows through the
space between the electrodes (Chen et al., 2004). There are several methods how
electrodes can be arranged in the EC system. Flow between the electrodes can follow a
vertical or horizontal direction. Electrodes can be monopolar or bipolar. In the
monopolar systems (Fig. 2.7A) all anodes are connected to each other and similarly all
cathodes are also connected to each other. In the bipolar systems (Fig. 2.7B) the
outermost electrodes are connected to a power source and current passes through the
other electrodes, thus polarizing them. In the bipolar systems the side of the electrode
facing the anode is negatively polarized and vice versa on the other side facing the
cathode.
Figure 2.7 Connection and electrode polarity in a (A) Bipolar and (B) Monopolar EC
System.

40. The pollutant removal efficiencies and operating costs of monopolar and bipolar
configurations have been compared in several studies (Golder et al.,2007; Bagramoglu
et al.,2007) 2007. Slaughterhouse wastewaters have been treated with mild steel and
aluminium electrodes arranged in bipolar or monopolar configurations (Bagramoglu et
al., 2007) The best performance was obtained using mild steel electrodes in bipolar
configuration. Economic calculations were made based on the results but electrode
consumption was calculated according to Faraday’s law which gives false results,
especially when aluminium electrodes are used (Golder et al., 2007) studied Cr3+
removal with EC by mild steel electrodes. Current efficiency for the dissolving of the
mild steel electrodes was lower when electrodes were in bipolar configuration (64.5%)
than when they were in monopolar configuration (91.7%). This is probably due to the
higher electrode potential of the electrodes in bipolar arrangement and competing
reactions taking place on the electrodes. A complete removal of Cr3+
was obtained when
electrodes were in the bipolar arrangement. However, treatment cost was lower with a
monopolar arrangement when the treatment was continued to the discharge limit.
Similar results were reported when EC was used for the removal of fluoride from
drinking water.
2.2.7 Advantages and Disadvantages of Electrocoagulation
The advantages of the electrocoagulation technique in treating wastewater are
discussed below. As well as some disadvantages it has.
2.2.7.1 Advantages of Electrocoagulation
Elecrocoagulation is alternative wastewater treatments that dissolves metal anode using
elctricity and provide active cations required for coagulation without increasing the
salinity of the water.The process has the capability to remove a large number of
pollutants under a variety of conditions.
Below are the advantages of electrocoagulation as outlined by (Mollah et al 2001):
 The process requires simple equipment and is easy to operate with sufficient
operational latitudes to handle most problems encountered on running.

41.  Wastewater treated by elctrocoagulation gives palatable,clear,colorless,and
odorless.
 Sludge formed by elctrocoagulation tends to be readily settleable and easy to
dewater,because it is composed mainly of metallic oxides/hydroxides.Above all
it is a low sludge producing techniques.
 Flocs formed by this process are similar to the chemical flocs,except that these
flocs tends to be much larger ,contain less bound water,is acid resistant and more
stable and therefore can be separated easily by filtration.
 This process has the advantage of removing the smallest colloidal
particle,because the applied electric field sets them in motion,thereby facilitating
the coagulation.
 The electrolytic process are controlled by electricity with no moving parts ,hence
require less maintenance.
 The EC process avoids uses of chemicals, and so there is no problem of
neutralizing excess chemicals and no possibility of secondary pollution caused
by chemical substances added at high concentration as when chemical
coagulation of wastewater is used.
 EC produces effluent with less total dissolved solids (TDS) content as compared
with chemical treatments. If this water is reused, the low TDS level contributes
to a lower water recovery cost.
 The gas bubbles produced during electrolysis can carry the pollutant to the top
of the solution where it can be more easily concentrated, collected and removed.
 The EC technique can be conveniently used in rural areas where electricity is not
available, since a solar panel attached to the unit may be sufficient to carry out
the process.

42. 2.2.7.2 Disadvantages of Electrocoagulation
Mollah et al., 2001 listed the disadvantages of using electrocoagulation as follows
 The sacrificial electrodes are dissolved into the wastewater stream as a result of
oxidation,and need to be regularly checked.
 An impermeable oxide film may be formed on the cathode leading to loss of
efficiency of the electrocoagulator.
 The use of electricity may be costly in some places.
 High conductivity of the wastewater suspension is required.
 Gelatinous hydroxide may tend to solubilize in some cases.
2.3 COMPARISON BETWEEN CHEMICAL COAGULATION AND
ELECTROCOAGULATION
Chemical coagulation and electrocoagulation have the same principle in which charged
particle in colloidal suspension are neutralised by mutual collision with metallic
hydroxide ions and are agglomerated ,followed by sedimentaton or flotation.These
technologies can be considered competing technologies and therefore the comparisons
of treatment eficiencies are important.
As previously mentioned, reliable comparisons are difficult to conduct due to the
dynamic nature of the process. Change of pH during the process and its effect on
aluminium species formed has been studied by various authors. The formation of
monomeric and polymeric aluminium hydroxides were compared when aluminium was
added as AIC13 or by electrocoagulation. According to results, there are no significant
differences in the speciation of aluminium obtained by these two methods. The
difference between electrocoagulation and chemical coagulation is mainly in the way
of which aluminium or iron ions are delivered (Avsar et al., 2007).
The comparison between electrocoagulation and chemical coagulation is reported in
Table 2.1 (Liu, et al., 2010).

43. Table 2.1 Comparison between Electrocoagulation and Chemical Coagulation (Liu, et
al., 2010).
Electrocoagulation Chemical Coagulation
The pH neutralization effect is made
effective in a much wider range (4-9).
The final pH always needs to be
modulated because the hydrolysis of the
metal salt will lead to a pH decrease. The
chemical coagulation is highly sensitive
to pH change and effective coagulation is
achieved at pH 6-7.
Flocs formed by EC are much larger than
flocs formed by chemical coagulation.
Chemical coagulation flocs are smaller
than EC flocs.
The EC process can be followed by
sedimentation or flotation.
The chemical coagulation process is
always followed by sedimentation and
filtration.
The gas bubbles produced during
electrolysis can help carry the pollutant to
the top of the solution.
There is no bubble generation.
EC is a low sludge production technique. High sludge production technique.
The EC process treats water with low
temperature and low turbidity.
The chemical coagulation has difficulty
in achieving a satisfying result in case of
low temperature and turbidity.
The EC process is a simple equipment and
easy to be operate.
High operating problems.

44. 2.4 REVIEW OF PREVIOUS WORKS ON ELECTROCOAGULATION
The electrocoagulation technique has been employed successfully to decontaminate
waste streams of toxic cations and anions, as well as heavy metals of all sorts.
2.4.1 Heavy Metal Wastewater
The central focus of study/research performed by Nouri et al (2010) was to investigate
the removal of zinc and copper from aqueous solution using electrocoagulation. In this
study, simulated waste water prepared from analytical grade chemicals was used with
potassium chloride as the supporting electrolyte. The experiment was performed in a
bipolar batch reactor with aluminium electrodes connected in parallel at optimum
distance of 1.5cm. The influence of several parameters such as initial pH (3 – 10),
applied voltage (20, 30, 40V) and initial concentration (5, 50, 500mg/L) on removal
efficiency was investigated. The result obtained at the selected condition (pH = 7,
reaction time = 60min, and voltage = 40V) indicated that the removal efficiency for
various concentrations of zinc and copper was constant. The result showed a removal
efficiency of 99.8 per cent for zinc and 99.57 per cent for copper.
Again, the energy consumption for the removal of one gram of zinc and copper at
electrical potential of 40V, initial concentration of zinc and copper (5mg/L) and pH
values of 3, 7, and 10 was 20.74, 19.98, and 26.16KWh and 31.15, 35.06, and
34.94KWh respectively. Also consumed energy for the removal of one gram of zinc
and copper at electrical potential of 40V, initial concentration of 50mg/L and pH values
of 3, 7, and 10 was 1.67, 2.32, and 1.82KWh and 2.24, 2.28, and 2.24KWh respectively.
In addition, with initial concentration increased to 500mg/L, under the same condition
of pH and voltage, the energy consumed for the removal of zinc and copper was 0.07,
0.095, and 0.16KWh and 0.07, 0.29, and 0.22KWh respectively.
In a separate study by Riyad et al (2008), electrocoagulation applied in the treatment
of simulated solutions containing Zn2+,
Cu2+
, Ni2+
, Cr3+
, Cd 2+
and Co2+
has been
investigated. A continuous flow electrocoagulation device containing twelve

45. electrolytic cells was used. The device consists of a ladder series of electrolytic cells
containing (carbon steel) anodes and stainless-steel cathodes. The electrodes were
connected in parallel with a maximum concentric gap of 2mm. The electrolytic cell
assembly was operated with flow rates up to 1.9m3
/hr.
Results obtained with simulated wastewater revealed the following:
The most effective removal capacities of studied metals could be achieved when the pH
was kept at 7 with removal efficiency as high as 99% for zinc, copper, chromium and
nickel and seem not to be affected as long as the pH is kept between the range of 7 –
12. Removal efficiency for cadmium and cobalt reached a maximum of 83% and 80%
respectively at optimum pH of 7 but a slight decrease was observed at pH above 7.
Charge loading was found to be the only variable that affected the removal efficiency
significantly. Again the study observed an increase of charge loading for all metal ions,
when current density was varied in the range 0.27 - 1.35mA/cm2
. The amount of iron
delivered per unit of pollutant removed is not affected by the initial concentration. Riyad
reported that the removal efficiencies of all studied ions increased with charge loading
(Qe). The removal rate was observed to decrease upon increasing initial concentration.
The result indicated that longer electrolysis times are necessary for chromium, cadmium
and cobalt removal. Lower efficient removal of chromium compared to zinc, copper
and nickel and the less efficient removal of cadmium and cobalt was also reported.
Result show that iron is very effective as sacrificial electrode material for heavy metals
removal efficiency and cost points.
The central focus of study performed by Umran et al, (2015) was to investigate the
effectiveness of Electrocoagulation in the removal of heavy metals from waste water.
In this study, removal of cadmium (Cd), copper (Cu) and nickel (Ni) from a simulated
wastewater by electrocoagulation (EC) method using batch cylindrical iron reactor was
investigated. The influences of various operational parameters such as initial pH (3, 5,
7), current density (30, 40, 50 mA/cm2
) and initial heavy metal concentration (10, 20,
30ppm) on removal efficiency were investigated. It was observed from the results that
removal efficiencies were significantly affected by the applied current density and pH.

46. The experimental results indicated that after 90mins electrocoagulation, the highest Cd,
Ni, Cu removal of 99.78%, 99.98%, 98.90% were achieved at the current density of 30
mA/cm2
and pH of 7 using supporting electrolyte (0.05 M Na2SO4) respectively. The
highest removal of Cd was obtained at pH 7. The initial Cd concentration of 20ppm was
reduced to the 0.16 ppm with the removal efficiency of 99.2% after 90minutes EC. It
was observed that pH has no significant effect on the removal efficiencies for the
electrocoagulation of Cu and Ni. The removal efficiencies at pH 7 for the Cu and Ni
were 98.3% and 99.8%, respectively. Similar result was obtained at pH 7 by Khosa et
al., for the removal of heavy metals.
Simulated lead solution
The present study performed by Vasudevan et al., provides an electrocoagulation
process for the removal of lead from water using magnesium and galvanized iron as
anode and cathode, respectively. The various operating parameters such as the effect of
initial pH, current density, electrode configuration, inter-electrode distance, co-existing
ions and temperature on the removal efficiency of lead were studied. The results showed
that the maximum removal efficiency of 99.3 % at a pH of 7.0 was achieved at a current
density 0.8 A/dm2 with an energy consumption of 0.72kWh/m3
.
Ashraf et al, studied the removal of Mn2+
ions from synthetic wastewater by
electrocoagulation process. In this study, using aluminium electrodes, the effect of
influential parameters such as initial PH, applied current density, electrolysis time,
solution conductivity and initial metal concentration on the performance of EC process
has been investigated. It was found that the optimum initial pH to remove Mn2+ ions
was 7.0. Also, the results indicated that increasing the current density and electrolysis
time has a positive effect on the Mn2+ removal efficiency. The removal of Mn2+ ions
was not influenced by the solution conductivity but the electrical energy consumption
decreased with an increase in the solution conductivity. In addition, the results of our
study revealed that Mn2+ removal rate decreased with increasing the initial
concentration of the contaminant.

47. Omar et al., investigated arsenic removal from groundwater by electrocoagulation
(EC) using aluminium as the sacrificial anode in a pre-pilot-scale continuous filter press
reactor. The groundwater was collected at a depth of 320m in the Bajío region in central
Mexico (arsenic50 μg/L, carbonates 40mg/L, hardness 80 mg/L, pH 7.5 and
conductivity 150 μS/cm). The influence of current density, mean linear flow and
hypochlorite addition on the As removal efficiency was analyzed. Poor removal of total
arsenic (60 %) in the absence of hypochlorite is due to a mixture of arsenite (HAsO2(aq)
and H3AsO3(aq)) and arsenate (HAsO4
2−
). Arsenic removal is more efficient when
arsenite is oxidized to arsenate by addition of hypochlorite at a concentration typically
used for disinfection (1mg/L). Arsenate removal by EC might involve adsorption on
aluminium hydroxides generated in the process. Complete arsenate removal by EC was
satisfactory at a current density of 5mA/cm2
and mean linear flow of 0.91cm/s, with
electrolytic energy consumption of 3.9kWhm3.
Pravin .D, study on arsenite and arsenate removal from wastewater by
Electrocoagulation using iron electrodes in a laboratory scale 2L volume reactor and 16
L volume bucket filter were investigated. In a EC process hydrous ferric oxide (HFO)
generates and oxidized As(III) to As(V) due to Fe2+
ions and adsorbs arsenic and forms
precipitate and then settle down and separated by filtration using double layer cotton
cloth with current 0.20 amp to 0.30 amp. Experiments were carried out with initial
arsenic concentration of 1 mg/L and 2 mg/L with varying current flow of 0.20 amp to
0.30 amp. In field trials bucket filter having fine sand at bottom with 16L volume run
continuously for 6 to 8 hrs. The effluent samples were analysed and residual arsenic
was found below 50μg/L and 10μg/L which is the drinking water standards in India and
Bangladesh. Experimental results depicts that arsenic levels below 50μg/L could be
achieved, which is the drinking water standard in India and Bangladesh. EC process
requires less electrical energy consumption as 0.50 kWh/m3.
Xuhui et al, in his study presents enhanced reduction of soluble contaminants in a
modified electrocoagulation process that is capable of treating a mixture of aqueous
contaminants. By incorporating an iron foam cathode, the process can remove aqueous

48. trichloroethylene (TCE) by 99.1% and nitrate ions by 98.2%, which represents 58.1 and
20 percent higher than the removal rates achieved by iron plate cathode, respectively.
pH and ORP measurements indicate the development of a reducing electrolyte
condition due to the ferrous generation from an iron anode, which facilitates the
reduction of soluble contaminants because the competition from O2 reduction is
eliminated in the system. Both iron foam and vitreous carbon foam electrodes are
compatible with polarity reversal, without any deterioration in the efficiency of electro-
reduction of TCE and nitrate. The modified iron electrolysis process demonstrates
versatility for the treatment of mixtures of contaminants, including a binary mixture of
TCE and dichromate, a mixture of selenate and nitrate and a mixture of phosphate and
nitrate. The ferrous species generated from the iron anode can reduce and (or) co-
precipitate certain aqueous contaminants such as dichromate, selenate and phosphate,
while the cathodic process can directly reduce contaminants like TCE and nitrate.
Compared with the conventional electrocoagulation system that consists of two planar
electrodes, the proposed process is not only more effective, but also suitable for the
development of integrated and versatile process for the treatment of contaminated
wastewater or groundwater.
2.5 PROBLEMS ENCOUNTERED
In conclusion without doubt the provision of an adequate water supply suitable for a
diversity of uses by the world’s growing population is one of the 21st century’s more
pressing challenges. Even in the developed countries, the use of large scale continuous
throughput waste treatment plant is not a complete solution. Electrocoagulation has
successfully treated a wide range of polluted wastewater. According to Chaturvedi (201
3) the full potential of the technique as a waste water treatment is not yet to be fully
realized due to the following deficiencies in a number of following key areas:
 It is still an empirically optimized process that requires more fundamental
knowledge for engineering design.
 No dominant reactor design exists, adequate scale-up parameters have not been
defined, and material of construction are varied.

49.  No widely applicable mechanistically based approach to the mathematical
modelling of electrocoagulation reactors.
 Failure to fully appreciate that the performance of an electrocoagulation reactor
is largely determined by the interaction that occur between the three foundation-
technologies of electrochemistry, coagulation and flotation.
 No generic solution to the problem of electrode passivation.
After all electrocoagulation has been used successfully to treat a wide range of polluted
Wastewaters. Nevertheless this technology has an excellent future because of numerous
advantages and the nature of the changing strategic water needs in the world
(Chaturvedi 2013).

50. CHAPTER THREE
MATERIALS AND METHODS
3.1 INTRODUCTION
In this chapter, the materials, equipment and analytical procedures are described. The
experimental work was performed in a batch mode to determine the removal efficiency
in terms of the final ion concentration of the wastewater after treatment. The concept of
this model is to reduce the metallic concentration and determine the final pH of the
wastewater using different operating treatment conditions. All analytical measurements
performed in this study were conducted according to the standard method for the
examination of water and wastewater (APHA, 2005).
The experimental work was conducted at the laboratory of the chemical Engineering
Department of Nnamdi Azikiwe University in Awka, Anambra state, Nigeria and
samples were analysed at PRODA research institute in Enugu state.
3.2 APPARATUS AND MATERIALS
3.2.1 APPARATUS
The following apparatus were used in the experiments.
 A laboratory model DC power supply apparatus (HUPE model LLN003C) was
used to maintain constant DC current.
 Iron electrodes.
 Magnetic stirrer.
 Stop watch
 Hot plate/stirrer
 PH meter (PH/ORP/ISE Graphic LCD PH Bench top meter, HANNA
instruments).
 Ammeter.

51.  Glass ware: some glass wares were used in this work such as 500ml beakers,
volumetric flasks and others.
 PH adjustment [HCl (1 mol/L) and NaOH (1 mol/L)].
 Sand paper.
 Syringe.
 Electronic weighing balance.
 Meter rule.
 Electrocoagulation cell.
 Filter paper.
 Atomic Absorption Spectrometer (AAS) Machine.
3.2.2 MATERIALS and REAGENTS
The materials used in the experiment were as follows:
 Deionized water
 Sodium chlorite salt (supporting electrolyte)
 Salts of the heavy metals:
o NiSO4.6H2O
o CuSO4
o Cr(SO4)
 Aqueous sodium hydroxide (1M)
 Aqueous Hydrochloric acid (1M)
 Acetone
 Buffer solutions
3.3 EXPERIMENTAL PROCEDURE
3.3.1 SIMULATED WASTEWATER PREPARATION
The stock solution of the wastewater was prepared by measuring and dissolving
appropriate mass of the heavy metal salt in a little water. The mass of each salt to be
measured depends on the mass proportion of the heavy metal ion in the salt. For

52. example, to prepare 500mg/l of copper, the following relation was used to calculate the
mass of copper salt to dissolve in a litre of water (Chemiasoft, 2014).
𝟓𝟎𝟎𝐦𝐠
𝐋
Of Cu2+
×
𝟏𝐠 𝐂𝐮𝟐+
𝟏𝟎𝟎𝟎𝐦𝐠 𝐂𝐮𝟐+
×
𝟏𝟓𝟗.𝟔𝟎𝟗𝐠 𝐂𝐮𝐒𝐎₄
𝟔𝟑.𝟓𝟒𝟔𝐠 𝐂𝐮𝟐+
× 1L = 1.256g of CuSO₄
Where the molecular weight of CuSO₄ = 159.609g/mol and atomic mass of copper =
63.546 a.m.u
Hence it could be said that 1.256g of CuSO₄ should be dissolved in a litre of water to
give 500mg/l of Cu2+
ions
To get the solution to other concentrations other than that of the stock solution, the
following relation was used:
C1V1= C2V2
Where C1=concentration of the stock solution (mg/l)
C2= new concentration of the solution (mg/l)
V1= volume of the stock solution to be taken (ml)
V2= Final volume of the solution (ml).
3.3.2 ELECTROCOAGULATION SET-UP
The Electrocoagulation unit is made of Perspex sheet with dimensions of 36 cm × 15
cm × 23 cm with an in-built current regulator. The electrodes used in the
electrocoagulation process were iron electrodes of size 13 cm × 0.5cm with immersion
depth of 8.4 cm , the number of electrodes used were two (anode & cathode) and a
distance of 3.5 cm maintained between them with a direct current power supply.
The electrocoagulation cell has a working volume of 500ml, the current dosage could
be regulated at a given level. The currents were regulated at 1A, 1.5A, 2A and 2.5A
with a constant voltage of 220v. Before each experiment, the pH of the wastewater was
adjusted with HCl or NaOH solution within a range of 2-12. Also, 1ml of aqueous NaCl
was added to the volume as a supporting electrolyte to introduce charge to the
wastewater. All runs were performed with a magnetic stirrer immersed into each beaker
which was placed on a hot plate stirrer to agitate the electrolyte with constant charge

53. time of 10mins and settling time of 30mins. After the elapsed settling time of 30mins
samples were withdrawn from a depth of 2cm using a syringe and were taken to PRODA
to analyse the heavy metal ion final concentration.
Before each run, the electrodes were cleaned thoroughly to remove any surface grease
or solid residues. Initial runs were conducted at 10mins charging time, 2A current
density and 300
c to determine the effect of PH on heavy metal ion removal efficiency,
pH was varied thus 2, 4, 6, 8, 10, and 12. The optimum pH was determined for each
metal. Subsequently, current densities were varied (1A, 1.5A, 2.0A and 2.5A) with
charging time of 10mins, 2A, 300
C and at optimum pH for each metal. Similarly, effects
of electrode distance (3cm, 4cm, 5cm, 6cm) and temperature (300
C,400
C, 500
C, 600
C,
700
C) on removal efficiency were separately studied by conducting batch experiments
at various inter-electrode distances and temperatures at a 2A constant current density,
10mins charging time, 30mins settling time. Afterwards initial heavy metal ion
concentration (50mg/l, 100mg/l, 150mg/l, 200mg/l and 250mg/l) was varied against
charging time (5mins, 10mins, 15mins, 20mins and 30mins) to study the effects of
initial heavy metal ion concentration and charging time 2A, 300
C, 30mins settling time
and optimum pH for each metal. The variables whose effects were studied and their
various values are presented in table 3.1. The removal efficiency was calculated using
the equation below.
Removal efficiency (%) =
𝐢𝐧𝐢𝐭𝐢𝐚𝐥 𝐦𝐞𝐭𝐚𝐥 𝐜𝐨𝐧𝐜𝐞𝐧𝐭𝐫𝐚𝐭𝐢𝐨𝐧−𝐫𝐞𝐬𝐢𝐝𝐮𝐚𝐥 𝐦𝐞𝐭𝐚𝐥 𝐜𝐨𝐧𝐜𝐞𝐧𝐭𝐫𝐚𝐭𝐢𝐨𝐧
𝐢𝐧𝐢𝐭𝐢𝐚𝐥 𝐦𝐞𝐭𝐚𝐥 𝐜𝐨𝐧𝐜𝐞𝐧𝐭𝐫𝐚𝐭𝐢𝐨𝐧
× 100
3.4 ANALYSIS OF SAMPLES
After each batch experiment run, and the set up settled for 30 minutes, the samples were
carefully withdrawn into little samples bottles and labelled accordingly to specify each
metal and parameter run. The samples would be analysed using an AAS machine.

54. 3.4.1 ATOMIC ABSORPTION SPECTROMETER
The AAS machine was used to analyse the samples of the batch experiments of treated
wastewater. This was to determine the residual concentration of metal ions remaining
in the treated water. The machine in general is comprised of the main machine, a
compressed air tank, and a gas (acetylene) tank. See figure 3 in the Appendix A of this
work.
The working principle of the AAS is based on the sample being aspirated into the
flame generated by the supply of compressed air and acetylene, and atomised when the
AAS’s light beam is directed through the flame into the monochromator, and onto the
detector that measures the amount of light absorbed by the atomised element in the
flame. Since metals have their own characteristic absorption wavelength, a source lamp
composed of that element is used, making the method relatively free from special or
radiational interferences. The amount of energy of the characteristic wavelength
absorbed in the flame is proportional to the concentration of the element in the sample
(APHA, 1995).
For example with lead, a lamp containing lead emits light from excited lead atoms that
produce the right mix of wavelengths to be absorbed by any lead atoms from the sample.
In AAS, the sample is atomized – i.e. converted into ground state free atoms in the vapor
state and a beam of electromagnetic radiation emitted from excited lead atoms is passed
through the vaporized sample. Some of the radiation is absorbed by the lead atoms in
the sample. The greater the number of atoms there is in the vapour, the more radiation
is absorbed. The amount of light absorbed is proportional to the number of lead atoms.
A calibration curve is constructed by running several samples of known lead
concentration under the same conditions as the unknown. The amount the standard
absorbs is compared with the calibration curve and this enables the calculation of the
lead concentration in the unknown sample. Consequently an atomic absorption
spectrometer needs the following three components: a light source; a sample cell to
produce gaseous atoms; and a means of measuring the specific light absorbed.

55. 3.4.1.1 CALIBRATION
A calibration curve is used to determine the unknown concentration of an element– eg
lead– in a solution. The instrument is calibrated using several solutions of known
concentrations. A calibration curve is produced which is continually rescaled as more
concentrated solutions are used– the more concentrated solutions absorb more radiation
up to ascertain absorbance. The calibration curve shows the concentration against the
amount of radiation absorbed (Fig. 3.0)
The sample solution is fed into the instrument and the unknown concentration of the
element, such as lead, is then displayed on the calibration curve.
Figure 3.0 Calibration curve for the metal concentration inspected.

56. Table 3.1 Electrocoagulation process parameters for the treatment of the
simulated wastewater using Iron electrodes.
Variables X1 X2 X3 X4 X5 X6
pH 2 4 6 8 10 12
Inter-electrode distance (cm) 3 4 5 6
Current (amperes) 1.0 1.5 2.0 2.5
Temperature (ºC) 30 40 50 60 70
Charging Time (minutes) 5 10 15 20 30
Initial metal ion
concentration (mg/L)
50 100 150 250 500
The Energy consumption was calculated using the relation below,
Cenergy =
𝐕𝐈𝐭
𝟏𝟎𝟎𝟎𝐯
[Kilowatt-hour per litre (KWh/L)]
Where,
Cenergy - Specific electrical energy consumption (KWh/L)
V – Applied voltage (V);
I – Current flow (A);
t – Time (hour).
Energy consumption was studied at different charging times using 500ml of wastewater
at current of 2 ampere and an applied voltage of 220 volts.

57. CHAPTER FOUR
RESULTS AND DISCUSSION
Having carried out the batch electrocoagulation experiments while considering the
various variables involved in the work, the results obtained would be fully discussed in
this chapter, with some references to previous works on similar variables studied.
4.1 BATCH ELECTROCOAGULATION STUDIES
4.1.1 Effect of pH
It has been established that the initial pH (Chen et al., 2000 and Do et al., 1994) is an
important factor and has a considerable influence on the performance of
electrocoagulation process. Generally, the pH of the medium changes during the
process, as observed by other investigator (Vic et al., 1984).this change depends on the
type of electrode and on initial pH.
To evaluate the pH effect, a series of experiments were performed, using solutions
containing each of the three heavy metals (copper, chromium, nickel) of 50 mg/l each
with initial pH varying in the range (2-12). The solutions of these metals were adjusted
to the desired pH for each experiment using sodium hydroxide or hydrochloric acid.
As illustrated in Figure (4.1), the removal efficiency of copper, Chromium and nickel,
reached value as high as 99%, when pH is between (6.5 - 10) and as long as this is kept
in the range between 6.8 and 10 the heavy metal removal efficiency is not affected i.e.
it increases. In contrast a slightly decrease of the removal efficiency of chromium is
observed, when the initial pH is increased above 7.
The removal efficiency of copper and nickel reaches a maximum of about 99% and 92%
respectively when initial pH is 8 and 10 as it seems from the same figure. However as
the same as chromium, when the initial pH is increased above 8 and 10, a slightly
decrease of the removal efficiency of copper and nickel is observed.

58. Figure 4.1 Effect of pH on the Removal Efficiency of the Heavy Metals.
4.1.2 Effect of Current Density
The current density not only determines the coagulant dosage rate, but also the bubble
production rate and size (Kobia et al., 2003 and Holt et al., 2002).Thus, this parameter
should have a significant impact on pollutants removal efficiencies. A large current
means a small electrocoagulation unit. However, when too large current is used, there
is a high chance of wasting electrical energy in heating up water.
Figures (4.2) show the effect of current density on removal efficiency of the studied
metal ions for typical electrocoagulation runs, where the initial pH was fixed at their
respective optimum level. The removal rate of all studied metal ions increased upon
increasing current density. The highest current (0.18634A/cm2
) produced the quickest
removal. In addition, it was demonstrated that bubbles density increases with increasing
current density (Holt et al., 2002), resulting in more efficient and faster removal.
Moreover, it was previously shown (Khosla et al., 1991) that the bubble size decreases
with increasing current density, which is beneficial to the separation process.
Indeed, the amounts of iron and hydroxide ions generated at a given time, within the
electrocoagulation cell are related to the current flow, using Faraday's law:
m = I t M / z F (1)
0
20
40
60
80
100
120
0 2 4 6 8 10 12 14
RemovalEfficiency(%)
Potential of Hydrogen [pH]
Effect on
Copper
Effect on
Nickel
Effect on
Chromium

59. where I is the current intensity, t is the time, M is the molecular weight of iron or
hydroxide ion (g/mol), z is the number of electrons transferred in the reaction and F is
the Faraday's constant (96486 C/mol).
As the current decreased, the time needed to achieve similar removal efficiencies
increased. This expected behavior is explained by the fact that the treatment efficiency
was mainly affected by charge loading (Q = I * t), as reported by Chen et al. (2000). As
the time progresses, the amount of oxidized iron and the required charge loading
increase. However, these parameters should be kept at low level to achieve a low-cost
treatment.
Figure 4.2 Effect of current density on the Removal Efficiency of the heavy metals.
86
88
90
92
94
96
98
100
102
0 0.05 0.1 0.15 0.2
RemovalEfficiency(%)
Current Density (A/cm²)
Effect on
Copper
Effect on
Nickel
Effect on
Chromium

60. 4.1.3 Effect of Inter-electrode Distance
Inter-electrode spacing is a vital parameter in the reactor design for the removal of
pollutant from effluent. The inter-electrode spacing and effective surface area of
electrodes are important variable when an operational costs optimization of a reactor is
needed (Bukhari et al., 2008). To decrease the energy consumption (at constant current
density) in the treatment of effluent with a relatively high conductivity, larger spacing
should be used between electrodes. For effluent with low conductivity, energy
consumption can be minimized by decreasing the spacing between the electrodes (Vik
et al., 1984). The inter electrode distance plays a significant role in the EC as the
electrostatic field depends on the distance between the anode and the cathode. The
maximum pollutant removal efficiency is obtained by maintaining an optimum distance
between the electrodes. At the minimum inter electrode distance; the pollutant removal
efficiency is low. This is due to the fact that the generated metal hydroxides which act
as the flocs and remove the pollutant by sedimentation get degraded by collision with
each other due to high electrostatic attraction (Aoudj et al., 2015). The pollutant removal
efficiency increases with an increase in the inter electrode distance from the minimum
till the optimum distance between the electrodes. This is due to the fact that by further
increasing the distance between the electrodes, there is a decrease in the electrostatic
effects resulting in a slower movement of the generated ions. It provides more time for
the generated metal hydroxide to agglomerate to form the flocs resulting in an increase
in the removal efficiency of the pollutant in the solution. On further increasing the
electrode distance more than the optimum electrode distance, there is a reduction in the
pollutant removal efficiency. This is due to the fact that the travel time of the ions
increases with an increase in the distance between the electrodes. This leads to a
decrease in the electrostatic attraction resulting in the less formation of flocs needed to
coagulate the pollutant (Aoudj et al., 2015). The pollutant removal efficiency is low at
the minimum inter electrode distance. From the figure 6 above the optimum inter
electrode distance is (3).

61. Figure 4.3 Effect of inter-electrode distance on the Removal Efficiency of the heavy
metals.
4.1.4 Effect of Solution Temperature
Temperature is one of the most important factors that can influence heavy metal
removal by Electrocoagulation (Chen, 2004 and Koren/Syversen, 1995). To determine
the optimum initial temperature for the removal of (copper, nickel and chromium)
through the electrocoagulation process using two iron electrodes, various EC tests were
conducted for the different initial temperatures of 30, 40, 50, 60 and 70o
C. The results
obtained during testing the EC for different values of initial temperature are reported in
Table 6e.
Fig. 4.4 illustrates the importance of the initial temperature in the removal efficiency of
copper, nickel and chromium from wastewater. It was found that with increase in
temperature and reduction of charging time the removal efficiency was significantly
improved, but no difference was made in terms of cost and energy consumption. In
effect, due to the increase in the temperature, the mass transfer increased and the
84
86
88
90
92
94
96
98
100
102
0 1 2 3 4 5 6 7
RemovalEfficiency(%)
Inter-Electrode Distance (cm)
Effect on
Copper
Effect on
Nickel
Effect on
Chromium

62. kinetics of particle collision improved. Furthermore, dissolution of the anode was
improved and the amount of the hydroxide that was formed and necessary for the
adsorption of copper, nickel and chromium was greater at elevated temperature allowed
a production of larger hydrogen bubbles, which increased the speed of floatation and
reduced the adhesion of suspended particles (Koren and Syversen, 1995). This is why
the EC process needed to start with a high temperature rather than heating the reaction.
This allowed the removal efficiency to be improved. We found that the yield was
significantly improved with increasing the initial temperature of the solution, which
resulted in a reduction in the electrolysis time.
Figure 4.4 Effect of Solution Temperature on the Removal Efficiency of the heavy
metals.
86
88
90
92
94
96
98
100
102
0 10 20 30 40 50 60 70 80
RemovalEfficiency(%)
Temperature of Solution (°C)
Effect on
Copper
Effect on
Nickel
Effect on
Chromium

63. 4.1.5 Effect of Charging Time
Charging time is another parameter that directly affects removal efficiency in the sense
that as charging time increases removal efficiency also increases. The effect of charging
time were studied by carrying out electrocoagulation process at various
charging/electrolysis time ranging from 5 - 30 minutes. The pollutant removal
efficiency is also a function of the electrolysis/charging time. The pollutant removal
efficiency increases with an increase in the electrolysis/charging time. For a fixed
current density, the number of generated metal hydroxide increases with an increase in
the electrolysis time. For an electrolysis time beyond the optimum electrolysis time, the
pollutant removal efficiency does not increase as sufficient numbers of flocs are
available for the removal of the pollutant [45]. Effect of different electrolysis time on
removal efficiency of EC process is shown in Table 6f and from figure 4.5, we observed
that the highest removal efficiency was obtained at 30mins.
Figure 4.5 Effect of charging time on the removal efficiency of the heavy metals.
86
88
90
92
94
96
98
100
102
0 5 10 15 20 25 30 35
RemovalEfficiency(%)
Charging Time (Minutes).
Effect on
Copper
Effect on
Nickel
Effect on
Chromium

64. 4.1.6 Effect of Initial Metal Ion Concentration
In order to examine the effect of metal ion concentration on the removal rate, several
solutions containing increased concentrations (50 - 500mg/l) of all three heavy metals
were prepared and treated .the residual concentrations of ions were measured at
different times. Figure (4.6, 4.7, and 4.8) show the change in the removal rate of copper,
chromium and Nickel with initial concentration respectively. They all showed the same
trends. As expected, it appears that the removal rate has increased upon increasing initial
concentration. This induced a significant increase of charge loading required to reach
residual metal concentrations below the levels admissible for effluents discharge into
the sewage system (2 mg/l) for copper, chromium and nickel.
It can be observed that charge loading undergo an increase with initial concentration.
This result proves that the amount of iron delivered per unit of pollutant removed is not
affected by the initial concentration. In addition, the charge loading required to remove
chromium to the admissible level, is higher than that required of copper and nickel. This
confirmed lower efficient removal of chromium compared to copper and nickel.
To demonstrate the effect of initial metallic pollutants concentration and the time
required for their quantitative removal, a set of experiments were conducted with three
different aliquot solutions containing same concentrations of 50, 100, 150, 250 and
500mg/L of each metal ion respectively. The mixed solutions were treated at a constant
current density of 0.149072A/cm2
and different times of electrolysis ranging from 5-
10mins. Fig. 9, 10 and 11 shows the variation of the initial concentrations of nickel,
copper and chromium with time. The corresponding concentrations of Cr needed 30
minutes to be quantitatively removed. According to Fig. 9, 10 and 11, no direct
correlation exists between metal ion concentration and removal efficiency. Certainly,
for higher concentrations longer time for removal is needed, but higher initial
concentrations were reduced significantly in relatively less time than lower
concentrations. The electrocoagulation process is more effective at the beginning when
the concentration is higher than at the end of the operation when the concentration is
low.

65. Initial metal concentration effect was examined separately for Cr and Ni using two Fe
electrodes for each solution with a constant current of 2A.
Fig. 4.6 Effect of initial metal ion concentration on removal efficiency for copper
Fig. 4.7 Effect of initial metal ion concentration on removal efficiency for Nickel
82
84
86
88
90
92
94
96
98
100
0 5 10 15 20 25 30 35
RemovalEfficiency(%)
Charging Time (mins)
Effect on 50mg/L
Effect on 100mg/L
Effect on 150mg/L
Effect on 250mg/L
Effect on 500mg/L
0
20
40
60
80
100
120
0 5 10 15 20 25 30 35
RemovalEfficiency(%)
Charging Time (Minutes)
Effect on 50mg/L
Effect on 100mg/L
Effect on 150mg/L
Effect on 250mg/L
Effect on 500mg/L

66. Fig. 4.8 Effect of initial metal ion concentration on removal efficiency for
Chromium.
70
75
80
85
90
95
100
0 5 10 15 20 25 30 35
RemovalEfficiency(%)
Charging Time (Minutes)
Effect on 50mg/L
Effect on 100mg/L
Effect on 150mg/L
Effect on 250mg/L
Effect on 500mg/L

67. 4.2 Energy Consumption
The electric power consumption of the process was calculated per L of the wastewater
solution for the varied charging times used in the treatment. From the figure 4.9
below, it is clear that an increase in current will increase power consumption. This
increase in power consumption is as a result of the increased polarization on the two
electrodes by increasing the current supplied (El-Shazly and Danous 2013).
Fig. 4.9 Energy Consumption of the EC treatment with respect to time.
0
1
2
3
4
5
6
7
8
0 0.1 0.2 0.3 0.4 0.5 0.6
EnergyConsumption/CostofTreatment
Charging Time (Hour)
Energy
Consumption
(KWh/L)
Cost of
Treatment
(₦/L)