Description
Abstract
This research study addresses a problem of water pollution caused by heavy and toxic
metals Cd, Cr, Cu and Pb. The work proposes the use of the technique of
phytoremediation using Phragmites australis (PA) plants that have the capacity to
absorb and to accumulate such metals in their roots and leaves. The metal uptake and
their location of accumulation in the PA plants were determined using flame atomic
absorption spectroscopy (FAAS) and transmission electron microscopy (TEM)
respectively. Leachates from contaminated plant biomass were mixed with silver
nitrate to assess the manufacture of metal nanoparticles as an added value step in the
process from remediation to biomass disposal. Silver nanoparticles were readily
manufactured by the leachates without, with the exception of copper, any
incorporation of the pollutant metal. The presence of copper in the manufactured silver
nanoparticles may be of some commercial use.
The results obtained show that PA plants will accumulate toxic metals when in
hydroponic culture and that the majority of the accumulated metals are sequestered in
the roots and do not enter the aerial parts of the plants in significant amounts. Silver
nanoparticles were manufactured from the biomass using a low energy route with no
additional chemicals, apart from silver nitrate thus reducing the environmental load
that would otherwise be present if a chemical means of nanoparticle production was
used.
Table of contents
Title 1
Abstract 2
Table of contents 3
Acknowledgement 8
List of figures 9
List of tables 13
Declaration 14
Publications from this work 15
Glossary 16
1 Introduction 17
1.1 Context of the work 17
1.2 Research overview 19
1.2.1 Pollution by heavy metals 19
1.2.2 Reed plants characteristics 29
1.2.3 Pollution removal methods 30
1.2.4 Laboratory methods 32
1.2.5 Nanoparticles manufacturing 33
1.3 Topic selection 34
1.4 Empirical proposition 34
1.5 Aim and objectives 36
1.6 Significance of the study 37
1.7 Work structure 37
2 Literature review 38
2.1 Introduction 38
2.2 The research trends in heavy metals pollution and removal 38
2.3 Sources and behaviour of toxic heavy metals 39
2.4 Water pollution and prevalent treatment methods 51
2.4.1 Water quality constituents 51
2.4.2 The scale of water pollution 54
2.4.3 Sources and effects of water pollution 56
2.4.4 Types of toxicity 59
2.4.5 Factors influencing toxicity 60
2.5 Heavy metals pollution control approaches and comparison 61
2.5.1 Chemical precipitation 62
2.5.2 Coagulation – flocculation 62
2.5.3 Flotation 63
2.5.4 Aeration 63
2.5.5 Membrane filtration 64
2.5.6 Ion exchange 64
2.5.7 Electrochemical treatment 65
2.5.8 Use of micro-organisms 65
2.5.9 Modelling microbial bio sorption 66
2.5.10 Use of plants 67
2.6 Metal absorption by plants: ‘Phytoremediation’ process 68
2.7 Use of reed plants in pollution control 70
2.8 Accumulation of heavy metals in plants 77
2.9 Metal extraction from plants: ‘Phytoextraction’ process 79
2.10 Nanoparticles (NPs) formation by metal adsorption 80
2.10.1 Biological manufacturing methods 81
2.10.1.1 Unintentionally produced NPs 81
2.10.1.2 Engineered inorganic NPs 82
2.10.2 NPs characteristics 83
2.11 Biomass utilization or disposal 84
2.12 Application of reed plants for commercial use 85
2.13 Conclusion 87
3 Materials and technique 88
3.1 Introduction 88
3.2 Research theme 88
3.3 Key components of this research study 89
3.4 Apparatus and their application 93
3.4.1 Propagator 93
3.4.2 Greenhouse 94
3.4.3 Hydroponic 95
3.4.4 Microwave digestion 97
3.4.5 Atomic absorption spectrometry (AAS) 99
3.4.6 Transmission electron microscopy (TEM) 104
3.4.7 UV/Vis spectroscopy 107
3.4.8 Zetasizer 108
3.5 Plants and chemicals 109
3.5.1 Phragmites Australis 109
3.5.2 Nutrient Solutions 112
3.5.3 Heavy metals solution 113
3.6 Summary 114
4 Laboratory methods and tests 115
4.1 Introduction 115
4.2 Sampling 115
4.3 Seedling production 117
4.3.1 Seed germination 118
4.3.2 Growing on 119
4.4 Metal concentration selection 119
4.5 Hydroponic cultivation 121
4.6 Preparation of plants for atomic absorption spectroscopy 123
4.6.1 Drying and grinding 123
4.6.2 Microwave digestion of plants 124
4.7 Flame atomic absorption 124
4.8 Location of sites of metal deposition 125
4.8.1 Introduction 125
4.8.2 Preparation of Phosphate buffer 126
4.8.3 Preparation of fixatives 126
4.8.4 Preparation of resin 126
4.8.5 Protocol of sample preparation 127
4.9 Transmission electron microscopy 127
4.10 Manufacture of metallic silver nanoparticles 128
4.11 Further application and disposal of biomass 130
4.12 Data reporting and analysis 132
4.13 Summary 132
5 Results of the laboratory tests 133
5.1 Introduction 133
5.2 FAAS results for metal uptake 133
5.2.1 Introduction 133
5.2.2 Experimental Results 134
5.2.3 Discussion 143
5.3 TEM images of nanoparticles and size data 144
5.4 Possible incorporation of metals into nanoparticles 162
5.5 TEM results for metal location in plants 178
5.6 Results from UV/Vis for nanoparticle synwork 196
5.7 Comparison of metals extracts between PA plants and Zea mays 200
5.8 Effect of hydrogen ion concentration (pH) on the rate of
Production of nanoparticles 202
5.9 Summary 204
6 Discussion of the findings 205
6.1 Introduction 205
6.2 Phytoremediation of metals using reed plants 205
6.3 Metal absorption, uptake or extraction by reed plants 207
6.4 Location of accumulated metals in reed plants 212
6.5 Use of reed plants 213
6.6 Nanoparticle manufacturing from biomass 216
6.7 Validity of the research findings 218
6.8 Summary 221
7 Conclusion 222
7.1 Research summary 222
7.2 Implications to theory and practice 224
7.3 Contributions of this research 225
7.4 Limitations 226
7.5 Recommendations 227
7.6 Future scope of research 228
References 230
Appendix A – Zetasizer results for metal nanoparticles 249
Acknowledgements
All praise to Allah, lord of creations, the most merciful and compassionate who blessed me
with prospective ability to attain my task in this research work.
I want to thank and express my gratitude to my supervisors Dr. Alan Reynolds and Dr.
A J Chaudhari. Without their support and guidance, this journey of PhD study would
not have been completed.
I am highly thankful to my wife Nouf Al Nassar and my children Nawaf, Najla and
Yara for sacrificing their time and enjoyment for my studies. I would also like to
acknowledge the support from other researchers and colleagues in UK and Saudi
Arabia for extending their valuable suggestions to prepare me.
I dedicate this work to my late mother Najla and my father Abdul Aziz who has taught
me values and excellence which has enabled me to reach at this point of scholarship in
the life.
List of figures
Chapter 1
1.1 Empirical Research Plan
Chapter 3
36
3.1 Propagator 93
3.2 Author with hydroponic containing 30 PA plants in the green house 94
3.3 Working of a hydroponic culture system 96
3.4 Schematic diagram of single beam FAAS 100
3.5 Specimen beam interactions 105
3.6 UV/Vis spectroscopy 107
3.7 PA plants in seedling and mature stages
Chapter 4
110
4.1 Propagator 117
4.2 PA plants in growth stage in greenhouse 118
4.3 PA plants trials with single metal concentrations 120
4.4 Hydroponic cultivation in the greenhouse 122
4.5 Biomass utilization or safe disposal process
Chapter 5
Fig 5.2.1 AA results for leafs exposed to cadmium in single or multiple metal
130
Combinations
Fig 5.2.2 AA results for roots exposed to cadmium in single or multiple metal
133
combinations. 134
Fig 5.2.3 AA results for cadmium concentration in the leachate
Fig 5.2.4 AA results for leafs exposed to chromium in single or multiple metal
135
combinations
Fig 5.2.5 AA results for roots exposed to chromium in single or multiple metal
136
combinations. 136
Fig 5.2.6 AA results for chromium concentration in the leachate Fig 5.2.7
AA results for leafs exposed to lead in single or multiple metal
137
combinations
Fig 5.2.8 AA results for roots exposed to lead in single or multiple metal
138
combinations. 138
Fig 5.2.9 AA results for lead concentration in the leachate
Fig 5.2.10 AA results for leafs exposed to copper in single or multiple metal
139
combination
Fig 5.2.11 AA results for roots exposed to copper in single or multiple metal
140
combinations. 140
Fig 5.2.12 AA results for copper concentration in the leachate 141
5.3.1. a,b,c&d TEM images of nanoparticles for copper leaf and root 143
5.3.2. a,b,c&d TEM images of nanoparticles for chromium leaf and root 144
5.3.3. a,b,c&d TEM images of nanoparticles for cadmium leaf and root 145
5.3.4. a,b,c&d TEM images of nanoparticles for lead leaf and root 146
5.3.5. a,b,c&d TEM images of nanoparticles for Cu-Cr leaf and root 147
5.3.6. a,b,c&d TEM images of nanoparticles for Cu- Cd leaf and root 148
5.3.7. a,b,c&d TEM images of nanoparticles for Cu-Pb leaf and root 149
5.3.8. a,b,c&d TEM images of nanoparticles for Cr-Cd leaf anmd root 150
5.3.9. a,b,c&d TEM images of nanoparticles for Cr-Pb leaf and root 151
5.3.10. a,b,c&d TEM images of nanoparticles for Cd-Pb leaf and root 152
5.3.11. a,b,c&d TEM images of nanoparticles for Cu-Cr-Cd leaf and root 153
5.3.12. a,b,c&d TEM images of nanoparticles for Cu-Cr-Pb leaf and root 154
5.3.13. a,b,c&d TEM images of nanoparticles for Cu-Cd-Pb leaf and root 155
5.3.14. a,b,c&d TEM images of nanoparticles for Cr-Cd-Pb leaf and root 156
5.3.15. a,b,c&d TEM images of nanoparticles for Cu-Cd-Cr-Pb leaf and root 157
5.4.1.a X-ray spectrum from silver nanoparticles produced from leaf extract
containing copper 162
5.4.1.b X-ray spectrum from silver nanoparticles produced from root extract
containing copper 162
5.4.2.a X-ray spectrum from silver nanoparticles produced from leaf extract
containing chromium 163
5.4.2.b X-ray spectrum from silver nanoparticles produced from root extract
containing chromium 163
5.4.3.a X-ray spectrum from silver nanoparticles produced from leaf extract
containing cadmium 164
5.4.3.b X-ray spectrum from silver nanoparticles produced from root extract
containing cadmium 164
5.4.4.a X-ray spectrum from silver nanoparticles produced from leaf extract
containing lead 165
5.4.4.b X-ray spectrum from silver nanoparticles produced from root extract
containing lead 165
5.4.5.a X-ray spectrum from silver nanoparticles produced from leaf extract
containing copper and chromium 166
5.4.5.b X-ray spectrum from silver nanoparticles produced from root extract
containing copper and chromium 166
5.4.6.a X-ray spectrum from silver nanoparticles produced from leaf extract
containing copper and cadmium 167
5.4.6.b X-ray spectrum from silver nanoparticles produced from root extract
containing copper and cadmium 167
5.4.7.a X-ray spectrum from silver nanoparticles produced from leaf extract
containing copper and lead 168
5.4.7.b X-ray spectrum from silver nanoparticles produced from root extract
containing copper and lead 168
5.4.8.a X-ray spectrum from silver nanoparticles produced from leaf extract
containing chromium and cadmium 169
5.4.8.b X-ray spectrum from silver nanoparticles produced from root extract
containing chromium and cadmium 169
5.4.9.a X-ray spectrum from silver nanoparticles produced from leaf extract
containing chromium and lead 170
5.4.9.b X-ray spectrum from silver nanoparticles produced from root extract
containing chromium and lead 170
5.4.10.a X-ray spectrum from silver nanoparticles produced from leaf extract
containing cadmium and lead 171
5.4.10.b X-ray spectrum from silver nanoparticles produced from root extract
containing cadmium and lead 171
5.4.11.a X-ray spectrum from silver nanoparticles produced from leaf extract
containing copper, chromium and cadmium 172
5.4.11.b X-ray spectrum from silver nanoparticles produced from root extract
containing copper, chromium and cadmium 172
5.4.12.a X-ray spectrum from silver nanoparticles produced from leaf extract
containing copper, chromium and lead 173
5.4.12.b X-ray spectrum from silver nanoparticles produced from root extract
containing copper, chromium and lead 173
5.4.13.a X-ray spectrum from silver nanoparticles produced from leaf extract
containing copper, cadmium and lead 174
5.4.13.b X-ray spectrum from silver nanoparticles produced from root extract
containing copper, cadmium and lead 174
5.4.14.a X-ray spectrum from silver nanoparticles produced from leaf extract
containing chromium, cadmium and lead 175
5.4.14.b X-ray spectrum from silver nanoparticles produced from root extract
containing chromium, cadmium and lead 175
5.4.15.a X-ray spectrum from silver nanoparticles produced from leaf extract
containing all metals 176
5.4.15.b X-ray spectrum from silver nanoparticles produced from root extract
containing all metals 176
Fig 5.5.1 Cr leaf semi-thin section 178
Chart 5.5.1 X-ray spectrum from Cr Leaf section 178
Fig 5.5.2 Pb leaf semi-thin section 179
Chart 5.5.2 X-ray spectrum from Pb Leaf section 179
Fig 5.5.3 Cu Root semi-thin section 180
Chart 5.5.3 X-ray spectrum from Cu Root section 180
Fig 5.5.4 Cr Root semi-thin section 181
Chart 5.5.4 X-ray spectrum from Cr Root section 181
Fig 5.5.5 Cd Root semi-thin section 182
Chart 5.5.5 X-ray spectrum from Cd Root section 182
Fig 5.5.6 Pb Root semi-thin section 183
Chart 5.5.6 X-ray spectrum from Pb Root section 183 Fig 5.5.7 Cu-Cr Root
semi-thin section 184
Chart 5.5.7 X-ray spectrum from Cu-Cr Root section 184
Fig 5.5.8 Cu-Cd Root semi-thin section 185
Chart 5.5.8 X-ray spectrum from Cu-Cd Root section 185
Fig 5.5.9 Cu-Pb Root semi-thin section 186
Chart 5.5.9 X-ray spectrum from Cu-Pb Root section 186
Fig 5.5.10 Cr-Cd Root semi-thin section 187
Chart 5.5.10 X-ray spectrum from Cr-Cd Root section 187
Fig 5.5.11 Cr-Pb Root semi-thin section 188
Chart 5.5.11 X-ray spectrum from Cr-Pb Root section 188
Fig 5.5.12 Cd-Pb Root semi-thin section 189
Chart 5.5.12 X-ray spectrum from Cd-Pb Root section 189
Fig 5.5.13 Cu-Cr-Cd Root semi-thin section 190
Chart 5.5.13 X-ray spectrum from Cu-Cr-Cd Root section 190
Fig 5.5.14 Cu-Cd-Pb Root semi-thin section 191
Chart 5.5.14 X-ray spectrum from Cu-Cd-Pb Root section 191
Fig 5.5.15 Cr-Cd-Pb Root semi-thin section 192
Chart 5.5.15 X-ray spectrum from Cr-Cd-Pb Root section 192
Fig 5.5.16 Cu-Cd-Cr-Pb Root semi-thin section 193
Chart 5.5.16 X-ray spectrum from Cu-Cd-Cr-Pb Root section 193
Fig 5.5.17 All Metals Root semi-thin section 194
Chart 5.5.17 X-ray spectrum from ALL Metals Root section 194
5.6.1: Absorbance of control containing AgNO 3 solution 195
5.6.2: Absorbance due to Cd 196
5.6.3: Absorbance due to Copper 196
5.6.4: Absorbance due to Cr 196
5.6.5: Absorbance due to Pb 196
5.6.6: Absorbance due to Cu-Pb 197
5.6.7: Absorbance due to Cd-Pb 197
5.6.8: Absorbance due to Cr-Cd 197
5.6.9: Absorbance due to Cr-Pb 197
5.6.10: Absorbance due to Cu-Cd 197
5.6.11: Absorbance due to Cu-Cr 197
5.6.12: Absorbance due to Cu-Cd-Cr 198 5.6.13: Absorbance due to Cu-Cr-Pb
198 5.6.14: Absorbance due to Cu-Cd-Pb 198
5.6.15: Absorbance due to Cd-Cr-Pb 198
5.6.16: Absorbance due to Cu-Cd-Cr-Pb 199
5.7.1 Comparison of nanoparticle production of PA v ZM at neutral pH. 200
5.8.1 Graph of rate of nanoparticle production. 201
5.8.2 Comparison of the rate of nanoparticle production
between PA and ZM plants. 202
List of tables
Chapter 1
1.1 WHO standards for fresh water 24
Chapter 2
2.1 Periodic table 42
2.2 Classification of metals 43
2.3 Heavy metals concentration 44
2.4 Examples of American and European heavy metal sites with
commercial application of Phytoremediation 85
Chapter 3
3.1 Currently practised mechanisms of Phytoremediation 90
3.2 FAAS detection limits 101
3.3 Standard atomic absorption conditions 102
3.4 Hoagland solution consists of plant nutrients 112
Chapter 4
4.1 Sampling combinations of metals 116
4.2 Heavy metals concentrations applied 119
4.3 Components of the nutrient solution 121
4.4 Dilution factors and FAAS linear range 124
Chapter 5
5.3.1, 2, 3& 4b Comparison of particle size analysis of leaves with single metal 158
5.3.1, 2, 3& 4d Comparison of particle size analysis of roots with single metal 158
5.3.5, 6,7,8,9&10b Comparison of particle size analysis of leaves with two metals 159
5.3.5, 6,7,8,9&10d Comparison of particle size analysis of roots with two metals 159
5.3.11,12,13&14b Comparison of particle size analysis of leaves with three metals 160
5.3.11,12,13&14d Comparison of particle size analysis of roots with three metals 160
Chapter 6
6.1 Reed plants capacity for metal phytoremediation 209
6.2 Nanoparticles manufactured from extracted metals 216 6.3 Validity of the
methodology applied 218
6.4 Validity of the findings 219
Declaration
The work described in this work has not been previously submitted for a degree in this or
any other university, and unless stated otherwise it is the author’s own work.
Introduction
Environmental science provides the scope of studying various components of chemical
processes related to water, soil and plants. This branch of science when interlinked
with engineering applications, produce useful techniques and processes that can lead
researchers to new manufacturing and control techniques for example, pollution
control systems or nanoparticle applications. This research is divided into segments of
heavy metal pollution, reed plant characteristics, pollution removal methods,
laboratory methods and nanoparticle manufacture.
Pollution from human made sources creates the conditions wherein metal presence is
elevated to toxic levels in natural water resources. The major causes of water pollution
include sewage, waste water, industrial waste, marine dumping, radioactive waste, oil
pollution, underground storage leakages, atmospheric deposition and global warming.
Now, water pollution has become a major problem globally and a leading cause of
diseases worldwide with approximately 14000 people daily losing life because of
water pollution (Pink, 2006; West, 2006). Both developing and industrialized countries
are struggling to solve water pollution problems. Adding to this problem, industrial
and technological developments have been using this important and natural source and
made it a recipient of toxic, solid and liquid wastes from its variety of usages, instead
of preserving it. For example, national water quality report of USA states that 27.9%
of assessed rivers and stream (miles), 42.9% of assessed lake, reservoirs and ponds
(acres) and 37.2% of bays and estuarines (square miles) are classified as polluted
(EPA,USA 2012). The preservation of aquatic resources for ecosystem and human
health and wellbeing is a paramount concern worldwide and it has become evident that
approaches to managing aquatic resources should be undertaken within the context of
ecosystem dynamics in order that their exploitation for human utility remains
sustainable (Nakamura et al, 2006). Exposure to toxic metals can cause serious health
problems. For example, lead can be present in the tap water as a result of dissolution
from lead pipes in the plumbing system, use of ceramic ware and food cans, dust or
fume of paints, or from smelter processing of metal scrap, old batteries or cable
sheathing. These are just few sources of lead contamination. There are other toxic
metals apart from lead such as Cadmium, Mercury, Chromium and Arsenic which can
cause severe health hazards when organisms are exposed to such metals.
The specific contaminants leading to pollution in water include a range of chemicals,
pathogens, physical and sensory changes like high temperature and discolouration.
Chemical contaminants may include organic and inorganic substances. Major research
performed by Kamlbell et al (1996), MacDonald et al (1999), Boopathy (2000),
Schreiber and Bahr (2002), McGuire et al (2005), Farhadian et al (2006) and Andreoni
and Gianfreda (2007) in the field of soil contamination and bio-remediation of
contaminated soil and water includes main points as listed below.
Pollutant sources and concentration levels
Chemistry and toxicity of contamination
Solubility, transportation, adsorption, dispersion and volatility of pollutant
compounds
Detection, determination and monitoring of groundwater
Chemistry and mechanics of soil at contaminated site
Hydrogeology and hydrology of contaminated site
Limitations of environmental standards for water and soil
Environment conditions, nutrient sources and presence of electron acceptors
The term heavy metal refers for all the metals having density over 6. However, the
official term toxic metal is more valid for the group of metals such as Cd, Cu, Cr, Pb,
Hg and As. This is because some of them are essential within limits for human,
animals, plants and other living organisms but in excess they prove to be toxic. The
chronic exposure or quantity beyond permissible level makes them toxic for humans
and other organisms. It is also valid for metals such as Zinc and Iron which are
essential metals in humans. The term heavy metal has become interchangeable with
toxic metal because usually toxic metals such as Cu, Cr, Cd and Pb all can be
classified as heavy metal because of their density is in excess of 6g/cm 3 . For example,
Cu – 8.93, Cr – 7.14, Cd – 8.65 and Pb has density of 11.34 g/cm 3 (Duffus, 2002).
Also, these metals in their metallic state (valence 0) are not generally toxic unless they
are fine enough to be breathed in or ingested. It is normally their various compounds
that are toxic (Blaylock et al, 2000).
The toxic metals group (Cu, Cr, Cd, and Pb) is one of the major pollutants which
contain elements with an atomic density greater than 6g/cm 3 . These elements’
concentration in soil water varies from 1000 parts per million (ppm) to a few parts per
billion (ppb) except Manganese (Mn). This Mn element is found in soil from 20 to
10,000 ppm. Soils described as metalliferous may have higher levels of certain
elements. Beyond a certain level and environmental condition, these heavy metals in
soil can cause pollution to living organisms and make the soil unusable for farming.
Operations such as mining, energy production and agricultural activities using higher
quantities of fertilizers have increased the concentration of these metallic elements in
the soil causing hazardous pollution problems (Woolhouse et al, 1981; Alloway,
1995). This can lead to accumulation by living organisms (Sager, 1992) and levels of
Cr, Cu and Zn reaching to toxic effects levels (Sager and Stoeppler, 1992; Ensley,
2000). The increased use of fertilizers contributes to the amount of metals in soils and
water tables. The use of manure in developed countries has a higher rate of pollution
through fertilizers; for instance, Copper is used to promote growth in animals
especially pigs.
Eutrophication is the enrichment of surface waters with plant nutrients. It occurs
naturally but normally it is a process of change from one trophic state to a higher
trophic state by the addition or accumulation of nutrient(s). Agriculture is a major
factor in Eutrophication of surface waters. Eutrophication is generally an increase in
nitrogen and phosphorous causing accelerated plant growth, especially algae. The
presence of toxic metals is secondary and is mainly from industrial sources.
Phosphorous and Nitrogen are mainly from fertilisers. When fertilizers are used
extensively for higher yield all over the globe, they make the ground water table
enriched with heavy metals from these fertilizers (Ongley, 1996). Therefore,
fertilization of surface waters, both as a result of direct discharges of manure and as a
consequence of nitrate, phosphate and potassium being leached from the soil causes
contamination of the groundwater by toxic metals. High concentrations of these
substances lead to acidification of water and pose a greater threat to the health of
humans and animals. To a certain extent, these heavy metals keep accumulating in the
soil as well and are extracted by crops which we consume for food. For example,
acidification occurs as a result of ammonia emission (volatilization) from livestock
accommodation, manure storage facilities and manure being spread on the land
(Ongley, 1996). Therefore, controlled use of minerals and organic fertilizers along
with sludge management is necessary to prevent water pollution though surface run
offs and leaching of toxic metals to ground water tables. This can even lead to
damaging DNA properties (Wang and Lin, 1995). The following table 1.1 shows the
admissible and permissible level of these toxic metals in the fresh water. These
standards are prepared and recommended by World Health Organisation.
From different sources of pollution, heavy metals are accumulated as high
concentrations in water, soil sediments and plants. This poses a challenging problem to
the world of science and human kind. Prevailing technologies to remove
contamination from these type of polluted soil sites are isolation, mechanical
separation, pyro-metallurgical separation, or chemical treatment these are efficient but
expensive, labour intensive and soil disturbing (Mulligan et al, 2001).
More recently, the use of plants in metal extraction (phytoremediation) has been
investigated as a potential alternative in the removal of heavy metal excess from soil
and water (Chaney et al, 1997; Glass, 2000). This can be further categorised based on
the contaminant or the mechanisms involved. Based on the contaminant, it can be
degraded, extracted, contained or a combination of these; and as for mechanisms,
phytoremediation can be classified as extraction, plant tissue concentrations,
contaminant degradation, volatilization, immobilization at root level, and finally,
erosion level and infiltration control. Extraction processes when used in water based
culture are called Rhizofiltration which is a maturing technology (Dushenkov et al,
1995; EPA, 2000). This can also be called phytofiltration which is based on
hydroponically grown plants that have shown to be efficient in heavy metal removal
from water. Plants such as Eichhornia crassipes (Mart) have shown potential to store
6000 ppm of Cd and Pb in the whole plant and more than 8000 ppm of Cu when
grown with 5 ppm of these heavy metals (Sela et al, 1989, 1990). Another plant, the
Water Fern (Azolla filiculoides Lam.) can extract and absorb elements like Cd, Cu, Ni
and Zn. On individual exposure to these elements, Azolla filiculoides can uptake
10,000, 9000, 9000 and 6500 ppm of Cd, Cu, Ni and Zn respectively (Stratford et al,
1984). Aquatic plants such as Nelum bonucifera Gaertn and Nymphaea alba L. have
been tested for their Cr uptake capacity. For example in experiments, these plants have
shown accumulation of Cr to a level of 3000 mg Cr per kilogram of tissue. Cr is very
toxic for most plants (Vajpayee et al, 2000).
As an example, Chromium (Cr) oxidation state has a range from (-II) to (+VI) with the
most common oxidation states being (0), (III) or (VI); and Cr (III) trivalent is the most
stable state. Naturally Cr is found present in complex cubic isomorphic minerals called
Spinel. Cr can be melted with other metals to manufacture alloys or plating, for
example chromium steel. In water, Cr concentrations are limited because of the low
solubility of its oxides. Major chromium contamination is through waste water but no
food or animal feed plants have been found with high chromium concentrations (Wang
et al, 2009).
Hence, it can be inferred from the above discussion that water pollution can be resolved
by using aquatic plants. In this scenario, governments, scientists and researchers face
major problems: how to purify the polluted water and how to reduce pollution and keep
it under control. The central theme of this research project is embedded in solving these
two problems. Finding out the water purification method by means of empirical
investigation using Phragmites australis (common reed plant) is the solution to this
increasing problem. A permanent solution may be obtained by knowing what causes this
pollution and using plants or other technology to prevent it.
Phragmites australis (PA) plant also known as common reed is a perennial plant
which is widely used and has received considerable attention for remediating soils and
water polluted by multi-metals due to its ability of thriving in various range of adverse
conditions with rapid growth and high yields. Furthermore, reed plants can grow well
in soils contaminated by Cd, Ni, As or wastewater contaminated with As. Previous
long-term field experiments exhibited that giant reed is useful for eco-remediating soil
contaminated by As, Cd, Pb and Zn (Papazogloua et al, 2005; Miao et al, 2012).
Government regulators, researchers and the public’s concerns regarding ecological
threats such as global warming and resource availability have increased leading to
intensive research in new technologies such as removal of toxic metals using new
economical plants based on existing and emerging remediation technologies (Sarma,
2011). Danh et al (2009) and Wang et al (2009) add that existing conventional
methods of soil and water pollutant removal, such as chemical physical and
microbiological methods are costly for installation and operation. Also, the pollution
problem is multiplied for industrialised, densely populated and developing countries
due to increasing industries and population adding large amounts of toxic and
hazardous waste into their environments (Zhuang et al, 2007; Wenzel, 2009; Bonanno
and Giudice, 2010; Sarma, 2011). This has led to the evolution of plants based
phytoremediation techniques and use of easily available reed plants for pollution
removal.
The additional issue is removal of nutrients done by leaching, crop harvesting and
water clogging. As a consequence of this, nutrient levels are increased in drainage
canals. The aquatic grass is not useful in its primary role as an extra to but it can
extract significant amounts of toxic and non-toxic pollutant materials (Wenzel, 2009;
Lu et al, 2010). Phytoremediation is a process which uses plants for containment,
degradation or extraction of Xenobiotics from water or soil substrates and it creates the
opportunity of being used as an economic and non-destructive method to remove
pollution from soils or water. This is confirmed by many researchers from laboratory
experiments of plant tissues analyses performed on the leaves, stem and root samples
for chlorophyll and mineral content (Raskin et al, 1997; and Shamsuddin, 2010).
Phytoremediation is the use of plants to remove, contain and render harmless
environmental contaminants. This refers to all those biological, chemical or physical
processes that can make use of plants to aid cleaning of contaminated substances. Two
basic principles applied in this technique are phytoextraction (harvesting) and
phytostabilization (root fixing) (Dushnekov et al, 1997; Raskin et al, 1997; Wang et al,
2009). Rhizofiltration is one category of phytoremediation technology which uses
plant roots to absorb, concentrate, and precipitate metals from wastewater which may
include leachates from soil. Rhizofiltration makes use of terrestrial plants and not the
aquatic plants because terrestrial plants have characteristics such as longer and fibrous
roots covered with root hairs that have extremely large surface areas. The absorption
of metals does not involve biological processes in the rhizofiltration (Salt, 1995;
Kumar, 1995; Wang et al, 2009). In this study, phytoremediation is applied using the
aquatic plant commonly known as reed plant.
The (Reed plants) aquatic plant characteristics of being able to extract and to
accumulate metallic pollutants and also to keep growing at the same time is the basis
of this empirical investigation (Zurayk et al, 2001; Bonanno and Giudice, 2010). These
aquatic plants have two important characteristics of high metal absorption capacity and
still be at the same time inactive in the water, which makes them major pollutant
removers (Sawidis et al, 1995). Using these important findings, a process developed as
Phytoremediation to extract xenobiotics from water and soil is an economic and non-
invasive technique. Once polluting metals are absorbed from water using the above
mentioned aquatic plants, the next issue of concern is the disposal of these plants
containing the accumulated metals. Extracted heavy metals may be useful in the
manufacture of metallic nanoparticles for industries (Tilman, 1996). So far, there has
been little development in this line of research for author’s country Saudi Arabia or
elseware using grasses. Hence, this sequential procedure forms the basis of this
experimental research. This work is centred on the basis of this concept of using plant
technology for pollution control and removal. Present technologies such as filtration,
absorption, chemical precipitation and ion-exchange are costly. However, this
proposed study of using reeds is more promising as compared to other methods. There
are few empirical studies found in the literature wherein PA plants are exposed to
multiple toxic metals such as Cd, Cr, Cu and Pb as rteported in this study (Horsfall and
Abia, 2003). Study would reveal novel findings about accumulation of each metal and
behaviour of PA plants subjected to different toxic metals simultaneously.
The most common reed plant species, ‘Phragmites australis’ (PA plants) can grow in
natural or artificial conditions. It is found in North America, Europe, Middle East,
Africa and Australia. It is generally found in low level coastal plains or river flood
area but these plants also exist above sea level. PA plants can grow in height up to 3.5
metres and have ability to pass oxygen through its stems to roots. Roots can grow even
in moist or water logged soil conditions.
The first ever use of PA plants is in the form of reed beds for water and sewage treatment
which is the improved version of original contribution made by Prof.
Kilkuth of Germany in 1970s. These reed beds utilize the plant’s characteristics that it
can transfer oxygen to roots and rhizomes which in turn increases the production of
enzymes and that attracts bacteria to breakdown the pollution levels in the water or
effluents. This method was first used in the UK in 1985
(www.constructedwetland.co.uk, 2009). Demirezen and Aksoy (2006) found that
Phragmites australis is useful to measure concentration of heavy metals such as Iron
and Manganese and PA plants can be used as biological indications in the
determination of environmental pressures. Hence, literature and current industrial
applications suggest that Phragmites australis can be used in this study based on their
characteristics as compared to other grass or plant species such as P.pectinatus or
G.densa.
Many metals are essential to life and living organisms' eco-systems. Low or excessive
levels of metals can cause adverse effects on the health and the environment. The
major toxic metals can be divided into two groups: 1. Lead, Arsenic, Cadmium,
Mercury; and 2. Nickel, Zinc, Copper and Chromium. The first group Pb, As, Cd and
Hg are non-essential (not required for normal growth) and the second group Ni, Zn,
Cu and Cd are essential (necessarily required for normal growth) to plant and animals.
These metals’ easy transportation from one environment to another increases the
complexity in controlling their measurement, accumulation level, removal or
reduction. These metals can cause simultaneously air, water and soil pollution which
has drawn much attention from researchers (Wang et al, 2009).
Heavy metals are considered as one of the biggest sources of environmental pollution
due to their severe damage to human health and serious impacts on overall ecosystems
(Roman-Silva et al, 2003). The sources of these toxic metals arise from industrial
activities and inappropriate handling of effluents treatment processes. This requires
understanding of each production method and each effluent treatment technique in
addition to pollution removal methods. The sources of such toxic metal pollution are
acid mine drainage, metal finishing and surface treatment operations. Leather tanning
processes, ferrous metal industries, coal-fired power generation, paint, pigments,
plastic and food beverages also contribute a lot.
Industrial processes usually involve hazardous and pollution prone activities such as
effluent from metal or uranium mines that carry sulphide, pyrite and pyrhotite which
are converted into sulphate in ground water streams. Uranium mining produces a large
amount of radioactive material; electroplating during metal finishing generating toxic
compounds of Cr, Cd, Ni, Cu, Fe, Zn and Sn for example organic pollutant EDTA,
chromium tanning during leather tanning operations generate waste water with high
proteins and sulfides containing dyes and sulfonated oils (Naja and Volesky, 2009).
The above mentioned pollutants are conventionally removed using various methods
such as chemical precipitation, coagulation–flocculation, flotation, aeration, membrane
filtration, ion exchange and electrochemical treatment (Philippis and Micheletti,
2009). Metal finishing industries mainly make use of sedimentation, electrolysis, ion
exchange, evaporation, reverse osmosis and ultra-filtration (Vymazal et al., 2007;
Shammas and Wang, 2009). Prevailing treatment methods for heavy metal pollution
control are adsorption, sludge activation, phytoextraction, ion exchange, electro-
kinetic and electro-osmosis processes (Ho and El-khaiary, 2009).
However, these methods are proving costly and resource consuming which have given
way to new technologies such as phytoremediation using plants, grass and trees. The
various new technologies that are used in the removal of these heavy metals from soil
and water are containment (immobilization), stabilization, vitrification, soil washing,
soil flushing, pyrometallurgy, electro-kinetics and phytoremediation (Shammas, 2009).
The aquatic macrophyte – Phragmites australis (PA) is one of the most common
plants living in wet eco systems and is found all over the world. This plant can
withstand extreme environmental conditions including toxic contaminants such as
heavy or toxic metals (Quan et al, 2007). PA plants are widely deployed to construct
wetlands to treat industrial waste waters containing metals (Bonanno and Giudice,
2010). The detailed analyses of these new methods are presented later in the work in
literature review section.
1.5 Aim and objectives
The main aims of this research study are to assess the capability of Phragmites
australias a ‘phytoremediator’ to remove (or to decrease) metal pollution in water and
to find a useful function for the biomass generated. In this process the author would
fulfil the objectives mentioned below.
a. Heavy metals absorptions and analysis techniques
b. Nanoparticles formation and their further industrial use
c. Biomass formation from reed plants, their use and disposal methods
1.6 Significance of the study
The purpose of this research is to benefit Saudi Arabia in its efforts to contain and
reduce metal pollution and this will also benefit other countries with similar climates
and pollution problems and the findings may also be applied to wider geographical
areas. This research when finished with proven results can have further commercial
applications and international implications, potentially leading to research publications
and patents and surely, can benefit the environment around all of us in a time to come.
1.7 Work structure
The work is divided into seven sections, each described as one chapter and follows in a
logical manner. First chapter comprises of back ground and overview information with
precise problem definition and contribution of the research to the academia and
industry. Second chapter reviews relevant academic literature and critically analyse it
to find the solution from this secondary data. Third chapter introduces the proposed
empirical research in detail. Fourth chapter provides complete outline of how each
laboratory test is set up and how testing is carried out including all instruments and
apparatuse deployed. Fifth and sixth chapter discuss the results, findings and their
detailed analysis. Seventh and final chapter discusses implications for theory and
practice and concludes with research limitations, further scope of research and
contribution made to the body of the knowledge and industry. Appendices include
experiment data, observations, graphs and photos along with publications made during
the research study.