ABSTRACT
Batch sorption and incubation experiments were carried out in the Soil Science Laboratory of Michael Okpara University of Agriculture, Umudike (MOUAU) to evaluate the effect of cow dung, poultry manure and cocoa pod on sorption of heavy metals; amendment and heavy metal effect on soil chemical properties. Batch sorption experiment was Completely Randomized Design (CRD) using two factors; (A) amendment with cow dung, poultry manure and cocoa pod as rates and (B) time with 15 minutes, 30 minutes and 60 minutes also as rates with three replications. Also, an incubation experiment was CRD consisting of twelve treatment combinations replicated three times. Soil samples used in the study were collected at the depth of 0-20 cm from arable land within MOUAU. All the amendments used were sourced locally. Batch study was conducted at room temperature using batch adsorption techniques. Heavy metals solution used for the batch study was prepared at the concentration of 100 mg/L. Whatman No.1 filter paper was used to filter heavy metal solution. Incubation experiment was also carried out at the same temperature for thirty days. The soils were amended with 1g of each amendment and contaminated with heavy metals at the rate equivalent to 60 mg/kg and wetted throughout the incubation period. Available metal was extracted using 50 ml of 0.05 ml EDTA solution at the end of incubation and analyzed for heavy metal concentration. Routine chemical analyses were carried out on the soils after incubation using standard laboratory procedures. The data obtained were subjected to analysis of variance (ANOVA) using Genstat edition 3 (GenStat, 2007) and the means separated using Fisher’s Least Significant Difference (LSD) at 5% level of probability. Batch study revealed no significant effect of contact time on sorption of metals while the amendments had significant effect with time amendment interaction being significant only on adsorption of copper. Highest Cu, Pb and Zn (2.34 mg/g, 2.41 mg/g and 2.39 mg/g) was adsorbed by cow dung, cocoa pod and cow dung at 60, 15 and 30 minutes of contact times respectively while the least; 1.84 mg/g, 0.87 mg/g and 1.99 mg/g were sorbed by poultry manure at 30, 15 and 30 minutes of contact times respectively in batch study. Isotherms of the three metals obtained in all the amendment had H shape. All the amendments had significant effect on extraction of the metals with the highest amount extracted from controls without amendments while the least Cu (30.33 mg/kg), Pb (36.17 mg/kg) and Zn (37.17 mg/kg) were extracted from poultry manure, cocoa pod and cow dung amended soils respectively. Also, the treatments had significant effect on soil chemical properties with the effect of organic amendments in combination with heavy metals being virtually higher than the sole effect of heavy metals in all the soils. Generally, all the amendments showed good potential in binding heavy metals in both soil and aqueous solution and improving soil chemical properties.
TABLE
OF CONTENTS
Title page i
Certification
ii
Declaration
iii
Dedication
iv
Acknowledgement
v
Table
of contents
vi
List
of tables
x
List
of figures
xi
Abstract
xii
CHAPTER
1:
INTRODUCTION 1
1.1
Background of the Study 1
1.2 Justification 4
1.3
Objectives of the Study
5
CHAPTER 2:
LITERATURE REVIEW 7
2.1
Sorption of Heavy Metals in
Soils
7
2.1.1 Adsorption
8
2.1.2 Surface
precipitation 10
2.1.3 Fixation 11
2.1.4 Adsorption isotherm 12
2.2 Sorption
Properties of Soils 19
2.3 Sources
of Heavy Metal Pollutants 20
2.4 Factors Affecting Heavy Metal Sorption
in Soils 21
2.5 Effect
of Heavy Metals on Soil Properties and Plant Growth 24
2.6 Effect of Organic Matter on Heavy Metal
Sorption 26
2.6.1 Effect of cocoa pod on heavy metal sorption 28
2.6.2 Effect of cow dung on heavy metal sorption 29
2.6.3 Effect of poultry manure on heavy metal
sorption 29
2 .7 Properties of Heavy Metal 30
2.7.1
Copper 31
2.7.2
Lead 31
2.7.3
Zinc 32
CHAPTER 3: MATERIALS AND METHODS 33
3.1
Description of the Studied Area 33
3.2
Soil Sample Collection and
Preparation 33
3.3 Preparation of Amendments 34
3.4 Batch Experiment 34
3.4.1 Experimental design 34
3.4.2
Preparation of heavy metal solutions 34
3.4.3 Experimental layout 37
3.4.4 Batch sorption 38
3.4.5 Isotherm models used 38
3.5 Incubation Experiment 40
3.5.1 Experimental design 40
3.5.2 Experimental procedures 40
2.5.3 EDTA solution 41
3.5.4 Extractable heavy metal determination
41
3.5.5 Experimental layout
41
3.6 Statistical Analysis 43
3.7 Laboratory Analysis 43
3.7.1 pH 43
3.7.2 Organic carbon 43
3.7.3 Total nitrogen 43
3.7.4 Available phosphorus 43
3.7.5 Exchangeable bases 44
3.7.6 Exchangeable acidity 44
3.7.7 Effective cation exchange capacity 44
3.8.8 Base saturation 44
3.8.9 Heavy metals 44
CHAPTER 4: RESULTS AND DISCUSION 45
4.1 Heavy
Metal Composition of the Amendments Used 45
4.2 Batch
Studies 47
4.2.1 Effect
of contact time and amendments and their interaction on
sorption of Cu, Pb, and Zn (100mg/L) 47
4.2.2 Adsorption isotherms 52
4.3
Incubation Studies 56
4.3.1
Extracted heavy metals after incubation 56
4.3.2 Effect of heavy metals and organic
amendments on soil
chemical
properties 58
4.3.2.1 pH 58
4.3.2.2 Available
phosphorus 61
4.3.2.3 Total nitrogen 63
4.3.2.4 Organic
carbon 64
4.3.2.5 Exchangeable bases 65
4.3.2.6 Exchangeable acidity 67
4.3.2.7 Effective
cation exchange capacity (ECEC) 68
4.3.2.8 Base
saturation (BS) 69
CHAPTER
5: CONCLUSION AND RECOMMENDATIONS 70
5.1 Conclusion 70
5.2 Recommendations 70
References
LIST OF TABLES
Page
3.1 Metal salts used in the study 36
3.2
Experimental layout of the batch studies 37
3.3 Layout of the incubation experiment 42
4.1 Copper, lead and Zinc composition of the
amendments used in the study 46
4.2 Effect of contact
time on sorption of Cu, Pb and Zn (mg/g) 48
4.3
Mean separation of the effect of amendment and contact time and their
interaction on sorption of Cu, Pb and
Zn (mg/g) 51
4.4
Langmuir and Freundlich Constants for adsorption of Cu, Pb and
Zn by cocoa pod, poultry manure and cow
dung 55
4.5
Extracted Cu,Pb and Zn (mg/kg) 57
4.6 Effect of
heavy metals and organic amendments on soil chemical
after 30
days of incubation 60
LIST
OF FIGURES
Page
4.1 Adsorption
isotherm for adsorption of Cu by Cd, Pm and Cp at different
time of
shaking 53
4.2 Adsorption
isotherm for adsorption of Cu by Cd, Pm and Cp at different
time of
shaking 53
4.3
Adsorption isotherm for adsorption of Zn by Cd, Pm and Cp at different
time of shaking 53
CHAPTER 1
INTRODUCTION
1.1 BACKGROUND OF THE
STUDY
Heavy metals are those elements in the
periodic table with properties such as atomic number higher than 20 and
densities greater than 6 g/cm3 except alkali metals and alkaline
earth metals (Sherene, 2010). The environmental challenges associated with
heavy metals are that they cannot be eliminated easily and most of them have
poisonous effects on plants and animals even at low concentration (Sherene,
2010). Furthermore, some heavy metals can bio- accumulate thereby posing
several health challenges to human when transferred to food chain. Soils,
whether found in urban or agricultural areas represent a major medium for sinking
of metals released into the environment from a wide variety of human activities
(Niragu, 1991).
Heavy
metals are toxins that frequently contaminate soils and bodies of water. In
very acid soil, they are generally toxic to plants because of their
availability at high concentration. Heavy metal ions are the highest harmful
inorganic contaminants existing in the environment and can be of natural
history or result from human activities (Siegel, 2002). They result from a
variety of industries such as mining, plating, dyeing, electrochemical, metal
processing and battery storage plus human activity (Kadirvelu,et al.,2001). Heavy metals are stable
elements and cannot be degraded or totally eradicated (Shi et al., 2009 and Vindoh et al., 2011) and may be found in soil,
earth water, ground water (Yaylali-Abanuz, 2011), sediments, plants (Dube, et al., 2001) and even in dust (Wei and
Yang, 2010). Accumulation of toxic metals in the environment occurs majorly as
a result of adsorption process and some of them are inimical even if their
concentration in the environment is very low and the harm they can cause rises as
their accumulation increases in the environment. Therefore, the study of adsorption
processes has become necessary to widen the understanding of the populace on
how heavy metal pollutants are transmitted from a liquid mobile phase to the solid
phase and their subsequent mobility in the environment (Bradl, 2004).
Anthropogenic
and natural sources release huge quantity of heavy metal pollutants to the
atmosphere which end up falling into surface water, on soil and plants, and upper
layers of soil receive the highest amount of these pollutants and the processes
occurring there and the materials present determine their further spreading and
environmental effect or consequence. This has made it relevant to observe the
changes in the level of concentrations and distribution of these chemical
substances in soil, to study the regularities and causes of their migration and
to forcast the changes in the state of soil layers and the resultant
consequence on the entire or larger environment (Priit et al., 2001). In some soil environment sorption is the predominant
means of heavy metal accumulation process and thus the largest proportion of
heavy metal pollutants in the soil environment resides in the solid phase of
the soil (Sherene, 2010). The bioavailability of a heavy metal critically
depends upon the chemical form in which the metal exists in the soil. Chemical
speciation of metals is the major means of classifying and quantitate the
various forms or phases in which the metals exist in the environment (Davidson et al., 1994), and it is fundamental for
better understanding metals behavior in soils. The physico-chemical properties
of the soil thus play significant roles in reducing the hazard caused by heavy
metals in the environment. The availability of heavy metals in soil is
regulated by interaction with solid phase (Sherene, 2010).
When
wastewater is discharged into soil, it seeps through the soil before it
progresses downward into groundwater, or it passes through surface soil to
lowland. Many studies have proven that heavy metals can be removed or taken up
by soils (Awan et al., 2003; Chaari et al., 2011; Veeresh et al., 2003; Abat et al., 2012; Tang et al., 2009,
Unuabonah, et al., 2009; and Jiang et al., 2010). Accordingly, soils are
natural materials that play a role in purifying waste water before the metals
seep into ground water or flow into other areas or bodies of water. The
solubility and availability of heavy metals is the major factor responsible for
their migration into the hydrosphere and biosphere (Francois et al., 2004) but the physical and chemical properties of any soil determine the
fate of its sorption and desorption characteristics and consequently, the
behavior of metals in such soils (During et
al., 2003). The state, transformations and fate of heavy metal pollutants
in the soil environment is complex. It is constantly changing and depending on
a myriad of factors. Sorbed metals can desorb into soil water, thus move into
plants or into different soil layers and subsequently ground water (Alumaa et al., 2001). According to Sherene
(2010), pH, ionic strength, soil texture, pore structure, temperature, residual
time, index cations and anions, amendments and additives, metal speciation,
competing ions, microbial metabolites, synthetic chelators, phenolic substances
and herbicides are the major factors influencing the mobility and adsorption of
heavy metals in soils. Soils have the ability to hold or render motionless
introduced chemicals like heavy metal ions. The solid state of soils composes
an average of 45% of soil bulk. It consists of mineral particles, organic
matter and organo-mineral particles. They all play a very significant role in providing
the soil ability to regulate the
mobility, hold, exchange, oxidize, reduce, catalyze and precipitate chemicals
and metal ions in particular (weber, 1991).
Batch experiments are effective methods of
assessing metal binding and desorption kinetics at the laboratory level
(Temminghoff et al., 1997), because
through them, broad means of possible field situation scenarios can be better
understood and simulated by modifying the factors which affect metal sorption.
Because of the sorption behavior of metals varies, such studies are very useful
in testing possible soil remediation or stabilization treatment specific to
individual metal. Batch studies take into account the initial metal
concentration, the weight of adsorptive material, the reaction time and
adsorptivity of other metals present in solution. Thus, it is efficient in
assessing the capacity of adsorptive materials, assessing the sorption of any
single metal, or the sorption of that same metal when in competition with other
metals (Morera et al., 2001 and
Voegelin et al., 2003).
The
major disadvantage of batch studies is lack of consistency or incompatibility when
in comparison with real field situations. When effluents containing heavy metal
contaminants are released into soil, sorption takes place as the water
progresses in its downward movement through the soil. This is not in line with
the batch method, but can be modeled with the help of the column method. Column
studies are preferred in determining the rate of dissolution of contaminants in
polluted soil. It is also mostly applied in evaluation or assessment of ground
water risk due to transportation of pollutants from contaminated soils
(Noppadol and Pongsakorn, 2014).
Sorption of metals, either from single (non-competitive), or multi-metal
(competitive) solutions is very important in determining metal stability within
the soil, metal uptake by plants and the capacity of amendments to immobilize
the contaminants (Markiewiez-patkowska et
al., 2005). It is therefore necessary to have full knowledge and understanding
of the metal binding properties of soils, come up with procedures or means for
metal speciation in soils and carefully select suitable models
for proper understanding of the fate of heavy metal pollutants in the soil
environment (Dube et al., 2001).
1.2 JUSTIFICATION
Soil
is a crucial element for all terrestrial ecosystems. It provides the nutrient
bearing medium for plant life and abundant plant growth requires soil
environment that is free of inhibitory factors. In small quantities, heavy
metals are essential to the efficient functioning of the plants. Although, in
excess of these small amounts, they become toxic to plants, contaminate the
aquatic environment and can adversely affect the organisms that feed on these
plants and aquatic resources. The capability of soil to adsorb metal ions from
aqueous solution has caught the interest of many scholars because it has
positive consequences in both agricultural issues like soil fertility and productivity
and environmental questions such as remediation and reclamation of polluted
land and waste deposition. Heavy metal pollution is becoming a common problem
due to rapid urbanization with concomitant proliferation of electroplating,
painting and dying, oil, steel and mechanic industries that release waste high
in heavy metal concentration into the environment. Soil organic matter, both
humic and non-humic can provide most of the interfaces needed for heavy metal
sorption in aqueous solution and soils which regulates their mobility. To avoid
acute concentrations of these metals in soil and the contamination of food
chain, there is need to find out ways of regulating/controlling their solution
concentrations by using appropriate organic materials as adsorbents in heavy
metal contaminated soils to enhance the productivity of such soils. Therefore,
evaluating the sorption effectiveness and capabilities of cocoa pod, cow dung
and poultry manure in heavy metal contaminated soils has become necessary as a
means of remediating their effects on the soil environment
1.3 OBJECTIVES OF THE STUDY
The major objective of this work is
to compare the sorption of copper, lead and zinc by selected soil amendments in
a Paleudult in Southeastern Nigeria.
The specific objectives of the work
are:
1. to
evaluate the effect of cow dung, poultry manure and cocoa pod on sorption of
copper, lead and zinc in solution.
2. to
evaluate the effect of soil amendments and heavy metals on soil properties.
- to
evaluate the effect of cow dung, poultry manure and cocoa pod on copper,
lead and zinc levels in soil.
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