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.

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

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

DEDICATION

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

for this project.

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.

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 70oC) 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 70oC. 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.

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

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

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

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

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

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).

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).

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.

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

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

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.

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.

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.

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.

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.

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

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,

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

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.

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.

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

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.

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.

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).

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

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).

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.

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

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

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

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.

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.

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.

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.

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.

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).

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.

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

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.

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.

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 (HAsO42−). 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

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.

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).

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.

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

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

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 300c 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, 300C and at optimum pH for each metal. Similarly, effects

of electrode distance (3cm, 4cm, 5cm, 6cm) and temperature (300C,400C, 500C, 600C,

700C) 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, 300C, 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.

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.

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.

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.

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.

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

Rem

oval

Eff

icie

ncy

(%

)

Potential of Hydrogen [pH]

Effect on

Copper

Effect on

Nickel

Effect on

Chromium

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.

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94

96

98

100

102

0 0.05 0.1 0.15 0.2

Rem

oval

Eff

icie

ncy

(%

)

Current Density (A/cm²)

Effect on

Copper

Effect on

Nickel

Effect on

Chromium

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).

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 70oC. 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

Rem

oval

Eff

icie

ncy

(%

)

Inter-Electrode Distance (cm)

Effect on

Copper

Effect on

Nickel

Effect on

Chromium

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

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90

92

94

96

98

100

102

0 10 20 30 40 50 60 70 80

Rem

oval

Eff

icie

ncy

(%

)

Temperature of Solution (°C)

Effect on

Copper

Effect on

Nickel

Effect on

Chromium

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.

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92

94

96

98

100

102

0 5 10 15 20 25 30 35

Rem

oval

Eff

icie

ncy

(%

)

Charging Time (Minutes).

Effect on

Copper

Effect on

Nickel

Effect on

Chromium

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.

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

Rem

oval

Eff

icie

ncy

(%

)

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

Rem

oval

Eff

icie

ncy

(%

)

Charging Time (Minutes)

Effect on 50mg/L

Effect on 100mg/L

Effect on 150mg/L

Effect on 250mg/L

Effect on 500mg/L

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

Rem

oval

Eff

icie

ncy

(%

)

Charging Time (Minutes)

Effect on 50mg/L

Effect on 100mg/L

Effect on 150mg/L

Effect on 250mg/L

Effect on 500mg/L

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

En

ergy C

on

sum

pti

on

/Cost

of

Tre

atm

ent

Charging Time (Hour)

Energy

Consumption

(KWh/L)

Cost of

Treatment

(₦/L)

CHAPTER FIVE

CONCLUSIONS AND RECOMMENDATIONS

5.1 Conclusions

In this study, the removal of heavy metals from simulated wastewater by

electrocoagulation technique using iron electrodes was investigated; also the effects of

the different process parameters such as charging time, initial pH, current density,

electrode distance, temperature and initial metal ion concentration on the removal

efficiency of heavy metal from the simulated wastewater were studied.

The main conclusions from this work are:

The electrocoagulation process was successful in removing the heavy metals

from the wastewater by determining the heavy metal removal efficiency, this

heavy metal removal efficiency was found to be dependent on the charge time,

initial PH, current density, temperature, electrode distance and initial metal ion

concentration.

The results showed that the current density, charge time, initial PH and initial

metal ion concentration were directly proportional to the heavy metal removal

efficiency while electrode distance was inversely proportional to the heavy metal

removal efficiency.

The energy consumption of the process increased with increase in charge time

and current density.

The results have demonstrated that the electrocoagulation technique using iron

electrodes is an effective method in the treatment of simulated heavy metal

wastewater by reducing the concentration/level of heavy metal hence reducing

treatment cost for industries if adopted.

5.2 Recommendations

This work has demonstrated the effectiveness of the electrocoagulation technique using

iron electrodes in the treatment of simulated heavy metal wastewater, however the

potentials of this study has not been thoroughly exhausted by this work. The following

recommendation should be considered for further studies.

Investigate the effectiveness of aluminium-aluminium electrodes and iron-

aluminium electrodes for wastewater treatment by electrocoagulation.

The effect of other operating variables such as stirring speed, electrode type and

conductivity affecting the removal efficiency of the electrocoagulation process

should be investigated.

Another important area in this study that should be covered is the kinetics and

thermodynamics of the process as well as the adsorption isotherms should be

incorporated.

5.3 Contribution to Knowledge

The present research work established the simplicity and supports the effectiveness of

using electrocoagulation process for water and wastewater treatment.

Also the effects of inter-electrode distance and solution temperature, as an operating

variable affecting the removal efficiency of the electrocoagulation process were studied

owing to the fact that they have not been discussed extensively previously.

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APPENDIX A

SIMULATED WASTEWATER PREPARATION

The stock solution of the wastewater was prepared by measuring and dissolving

appropriate mass of the heavy metal salt in a liter of water. The mass of each salt to be

measured depends on the mass proportion of the heavy metal ion in the salt. For

example to prepare 500mg/l of cobalt, the following relation was used to calculate the

mass of cobalt salt to dissolve in a liter of water (Chemiasoft, 2014)

500mg

L Of Cu2+×

1g Cu2+

1000mg Cu2+×

159.609g CuSO₄

63.546g Cu2+ × 1L = 1.256g of CuSO₄ i

Where the molecular weight of CuSO₄ = 159.609g/mol and atomic mass of copper =

63.546 a.m.u

To get the solution to other concentrations other than that of the stock solution, the

following relation was used:

C1V1= C2V2 ii

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).

Using these method other values for the metals were calculated and tabulated as shown

in table A(i) below

Table A(i): Stock solution preparation

Species Molecular weight

of species (g/mol)

Amount to be

dissolved(g)

Molecular weight

of metal

CuSO4 159.61 1.256 63.546

NiSO4.6H2O 262.79 2.23 58.69

Cr(SO4) 148.03 1.42 51.996

REMOVAL EFFICIENCY CALCULATIONS FOR THE METALS; Copper

(Cu2+), Nickel (Ni2+), and Chromium (Cr3+).

Removal efficiency = 𝐢𝐧𝐢𝐭𝐢𝐚𝐥 𝐜𝐨𝐧𝐜𝐞𝐧𝐭𝐫𝐚𝐭𝐢𝐨𝐧−𝐫𝐞𝐬𝐢𝐝𝐮𝐚𝐥 𝐜𝐨𝐧𝐜𝐞𝐧𝐭𝐫𝐚𝐭𝐢𝐨𝐧

𝐢𝐧𝐢𝐭𝐢𝐚𝐥 𝐜𝐨𝐧𝐜𝐞𝐧𝐭𝐫𝐚𝐭𝐢𝐨𝐧× 100% iii.

Mathematically it is given as = 𝐂𝐢−𝐂𝐫

𝐂𝐢× 𝟏𝟎𝟎% iv.

Effect of Initial pH on the Removal Efficiency

Using an initial pH of 2 for Copper, having initial concentration of 500mg/L and a

residual concentration of 274.97mg/L

Removal efficiency = 𝑪𝒊−𝒄𝒓

𝒄𝒊× 100 =

500−274.97

500× 100% = 45.01%

Using equation (iv) and pH values of 2, 4, 6, 8 and 10 at 500mg/L initial concentration,

other values of removal efficiency for Copper, Nickel, and Chromium were calculated

and tabulated as shown in table A(ii) below.

Table A(ii): effect of initial pH on removal efficiency.

Effect of Current Density on the Removal Efficiency

Current density = 𝒄𝒖𝒓𝒓𝒆𝒏𝒕

𝒔𝒖𝒓𝒇𝒂𝒄𝒆 𝒂𝒓𝒆𝒂 𝒐𝒇𝒊𝒓𝒐𝒏 𝒆𝒍𝒆𝒄𝒕𝒓𝒐𝒅𝒆 v.

Where the Iron electrode surface area is given by 𝝅 × 𝒅 × 𝒍 vi.

Initial

pH

Copper, Cu2+ Nickel, Ni2+ Chromium, Cr3+

Residual

concentration

(mg/L)

Removal

efficiency

(%)

Residual

concentration

(mg/L)

Removal

efficiency

(%)

Residual

concentration

(mg/L)

Removal

efficiency

(%)

2 274.97 45.01 406.69 18.66 222.13 55.57

4 167.50 66.50 239.24 52.15 169.91 66.02

6 129.33 74.31 242.11 51.58 10.32 97.94

8 0.96 99.81 83.36 83.33 9.73 98.05

10 37.38 92.52 9.54 98.09

Where d is the diameter of the electrode = 0.5cm, l is iron electrode length = 8.54cm

Thus iron electrode surface area = 𝝿×0.5×8.54 = 13.416cm²

Thus, current density for 1amp = 𝟏

𝟏𝟑.𝟒𝟏𝟔 = 0.0745A/cm2

Using equation (iv), the removal efficiency is given as = 500−1.988

500× 100 = 99.60%

Using other calculated values of current density, the removal efficiency was found and

Tabulated for Copper, Nickel, and Chromium as shown in table A(iii) below.

Table A(iii): effect of current density on removal efficiency.

Effect of Electrode Distance on the Removal Efficiency

Considering the electrode distance of 3.0cm for Copper, using equation (iv),

Removal efficiency = 500−0.872

500× 100 = 99.83%

Considering different electrode distances of 3, 4, 5 and 6cm for Copper, Nickel, and

Chromium, their respective removal efficiencies are shown in table A(iv).

Current

density

(A/cm²)

Copper, Cu2+ Nickel, Ni2+ Chromium, Cr3+

Residual

concentration

(mg/L)

Removal

efficiency

(%)

Residual

concentration

(mg/L)

Removal

efficiency

(%)

Residual

concentration

(mg/L)

Removal

efficiency

(%)

0.075 1.988 99.60 59.535 88.07 11.225 97.76

0.112 1.802 99.64 42.134 91.57 11.065 97.79

0.149 1.616 99.68 24.732 95.05 10.906 97.82

0.186 1.519 99.70 17.640 96.47 10.746 97.85

Table A(iv): Effect of electrode distance on removal efficiency.

Effect of Solution Temperature on Removal Efficiency

Using an initial solution temperature of 30°C the removal efficiency was calculated for

Copper using equation (iv), as

Removal efficiency = 500−2.145

500× 100 = 99.57%

Different values of temperatures 30, 40, 50, 60 and 70°C were tested for Copper, Nickel,

and Chromium. While their respective removal efficiencies were determined and

tabulated as shown below.

Table A(v): Effect of solution temperature on removal efficiency.

Effect of Charging Time on the Removal Efficiency

Using equation (iv) and varied minutes charging time, considering a 500mg/L initial

concentration, the removal efficiencies for Copper, Nickel, and Chromium were

calculated for the electrolysis times of 5, 10, 15, 20 and 30 minutes, and the results

tabulated as shown in the Table A(vi) below.

Table A(vi): Effect of charging time on removal efficiency.

Charging

Time

(Minutes)

Copper, Cu2+ Nickel, Ni2+ Chromium, Cr3+

Residual

concentration

(mg/L)

Removal

efficiency

(%)

Residual

concentration

(mg/L)

Removal

efficiency

(%)

Residual

concentration

(mg/L)

Removal

efficiency

(%)

5.00 2.857 99.42 57.370 88.53 11.192 97.76

10.00 2.620 99.48 45.255 90.95 10.806 97.84

15.00 2.308 99.54 40.991 91.80 10.645 97.87

20.00 2.093 99.58 39.172 92.17 10.584 97.88

30.00 1.849 99.63 28.146 94.37 10.414 97.92

Concentration – Time Composite data for the Heavy Metals.

Using equation (iv) and varied minutes charging time, considering also the different

concentrations from 50 to 500mg/L, the removal efficiencies for Copper, Nickel, and

Chromium were calculated for the electrolysis times of 5, 10, 15, 20 and 30 minutes,

and the results tabulated as shown in the Tables A(vii), A(viii), and A(ix) below.

Table A(vii): Concentration-time composite data for Copper

Initial

Metal

Ion

Concent

ration

(mg/L)

5 Minutes 10 Minutes 15 Minutes 20 Minutes 30 Minutes

Residual

Concent

ration

(mg/L)

Remo

val

Effici

ency

(%)

Residual

Concent

ration

(mg/L)

Remo

val

Effici

ency

(%)

Residual

Concent

ration

(mg/L)

Remo

val

Effici

ency

(%)

Residual

Concent

ration

(mg/L)

Remo

val

Effici

ency

(%)

Residual

Concent

ration

(mg/L)

Remo

val

Effici

ency

(%)

50

4.245

91.51

3.185

92.37

2.510

94.98

1.885

96.23

0.430

99.14

100

11.38

88.62

10.86

89.14

7.81

92.19

4.16

95.84

2.83

97.17

150

19.605

86.93

18.495

87.67

15.45

89.70

9.435

93.71

4.74

96.84

250

34.85

86.06

32.725

80.91

29.750

88.10

18.475

92.61

9.40

96.24

500

76.85

84.63

70.40

85.92

62.30

87.54

44.10

91.18

24.85

95.03

Table A(viii): Concentration-time composite data for Nickel

Initial

Metal

Ion

Concent

ration

(mg/L)

5 Minutes 10 Minutes 15 Minutes 20 Minutes 30 Minutes

Residual

Concent

ration

(mg/L)

Remo

val

Effici

ency

(%)

Residual

Concent

ration

(mg/L)

Remo

val

Effici

ency

(%)

Residual

Concent

ration

(mg/L)

Remo

val

Effici

ency

(%)

Residual

Concent

ration

(mg/L)

Remo

val

Effici

ency

(%)

Residual

Concent

ration

(mg/L)

Remo

val

Effici

ency

(%)

50

7.995

84.01

6.07

87.86

5.045

89.91

3.40

93.20

1.19

97.62

100

18.35

81.65

16.61

83.39

12.86

87.14

10.46

89.54

3.11

96.89

150

29.88

80.08

26.145

82.57

20.55

86.30

17.16

88.56

7.965

94.69

250

54.575

78.17

50.05

79.98

39.30

84.28

31.35

87.46

22.10

91.19

500

122.35

75.53

105.25

78.95

85.90

82.82

64.95

87.01

50.65

89.87

Table A(ix): Concentration-time composite data for Chromium

ENERGY CONSUMPTION

Below is the study of power consumed during the course of the batch experiments run.

Relation: 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.

Substituting v = 0.5L; I = 2; V = 220 volts.

Therefore Cenergy = 220 х 2 х t

1000 х 0.5 = 0.88t

The amount to be spent per litre of water treated was calculated using PHCN 2014

Power tariff of 16.97₦/Kwh. See tabulated data below for the energy consumption and

amount spent for treatment of wastewater for the different charging times used.

Table A(x) Energy consumption and Cost of treatment.

Charging Time Energy

Consumption

(KWh/L)

Cost of Treatment

(₦/L)

Minutes

Hour

5.00 0.083 0.073 1.245

10.00 0.167 0.147 2.489

15.00 0.250 0.220 3.733

20.00 0.333 0.293 4.978

30.00 0.500 0.440 7.467

APPENDIX B

LABORATORY PHOTOGRAPHS

The Electrocoagulation Reactor Setup, showing a treatment in progress.

Treated Samples undergoing sedimentation (settling) for 30 minutes.

Electronic Weighing Balance. Handheld Thermometer.

Hot Plate Magnetic Stirrer Handheld pH Meter

The Atomic Absorption Spectrometer (AAS) Machine.

The Source Lamp for different metals, to enable absorption of wavelengths.