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Bioremediation of Waters Contaminated with Heavy Metals Using Moringa oleifera Seeds as Biosorbent

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Chapter 10
Bioremediation of Waters Contaminated with Heavy
Metals Using Moringa oleifera Seeds as Biosorbent
Cleide S. T. Araújo, Dayene C. Carvalho,
Helen C. Rezende, Ione L. S. Almeida,
Luciana M. Coelho, Nívia M. M. Coelho,
Thiago L. Marques and Vanessa N. Alves
Additional information is available at the end of the chapter
http://dx.doi.org/10.5772/56157
1. Introduction
Water is not only a resource, it is a life source. It is well established that water is important for
life. Water is useful for several purposes including agricultural, industrial, household,
recreational and environmental activities. Despite its extensive use, in most parts of the world
water is a scarce resource. Ninety percent of the water on earth is seawater in the oceans, only
three percent is fresh water and just over two thirds of this is frozen in glaciers and polar ice
caps. The remaining unfrozen freshwater is found mainly as groundwater, with only a small
fraction present above ground or in the air. Thus, almost all of the fresh water that is available
for human use is either contained in soils and rocks below the surface, called groundwater, or
in rivers and lakes.
The contamination of soil and water resources with environmentally harmful chemicals
represents a problem of great concern not only in relation to the biota in the receiving envi‐
ronment, but also to humans. The continuing growth in industrialization and urbanization has
led to the natural environment being exposed to ever increasing levels of toxic elements, such
as heavy metals. Approximately 10% of the wastes produced by developed countries contain
heavy metals. Figure 1 gives some indication of the amounts of metal-containing waste
produced in developed countries. Much of the discharge of metals to the environment comes
from mining, followed by agriculture activities.
© 2013 Araújo et al.; licensee InTech. This is an open access article distributed under the terms of the Creative
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distribution, and reproduction in any medium, provided the original work is properly cited.
Mining
Agricuture
Wastewater
Industry
Urban
Figure 1. Waste containing heavy metals produced in developed countries [1].
Many different definitions have been proposed for heavy metals, some based on density, some
on atomic number or atomic weight, and others on chemical properties or toxicity, which are
not necessarily appropriate. For example, cobalt, iron, copper, manganese, molybdenium,
vanadium, strontium and zinc are required to perform vital functions in the body and therefore
cannot be considered as compounds with high toxicity or ecotoxic properties. Regarding the
meaning of the term “heavy metal” it was found that there can be misinterpretation due to the
contradictory definitions and lack of a coherent scientific basis [2].
In conventional usage “heavy” implies high density and “metal” refers to the pure element or
an alloy of metallic elements. According to Duffus [2], a new classification should reflect our
understanding of the chemical basis of toxicity and allow toxic effects to be predicted. Various
publications have used the term “heavy metals” related to chemical hazards and this definition
will also be used herein. Among the classes of contaminants, heavy metals deserve greater
concern because of their high toxicity, accumulation and retention in the human body.
Moreover, heavy metals do not degrade to harmless end products [3, 4]. It is well established
that the presence of heavy metals in the environment, even in moderate concentrations, is
responsible for producing a variety of illnesses of the central nervous system (manganese,
mercury, lead, arsenic), the kidneys or liver (mercury, lead, cadmium, copper) and skin, bones,
or teeth (nickel, cadmium, copper, chromium) [5].
Due to its properties, water is particularly vulnerable to contamination with heavy metals.
Table 1 shows the maximum limits for some metals in drinking water, according to the US
Environmental Protection Agency (US EPA) [6]. The US EPA requires that lead, cadmium and
total chromium levels in drinking water do not to exceed 0.015, 0.005 and 0.1 mg L
-1
, respec‐
tively. Corresponding values for other metals are presented in Table 1.
Within this context, and considering that heavy metals do not decay and are toxic even at low
concentrations, it is necessary to remove them from various types of water samples. Of the
conventional treatments used for the removal of metals from liquid waste, chemical precipi‐
tation and ion exchange are the predominant methods. However, they have some limitations
since they are uneconomical and do not completely remove metal ions, and thus new removal
processes are required [7-9]. Table 2 illustrates in more detail the advantages and limitations
of the traditional methods applied to treat effluents.
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226
Process Disadvantages Advantages
Precipitation and filtration For high concentrations
Separation difficult
Not very effective
Produces sludge
Simple
Low cost
Biological oxidation and reduction When biological systems are used the
conversion rate is slow and susceptible
to adverse weather conditions
Low cost
Chemical oxidation and reduction Requires chemicals
Applied to high concentrations
Expensive
Mineralization
Enables metal recovery
Reverse osmosis High pressures
Expensive
Pure effluent (for recycling)
Ion exchange Responsive to the presence of particles
Resins of high cost
Effective
Enables metal recovery
Adsorption Not effective for some metals Conventional sorbents (coal)
Evaporation Requires an energy source
Expensive
Produces sludge
Pure effluent obtained
Table 2. Traditional process used in wastewater treatment: advantages and disadvantages [10].
Element US EPA Limit (mg L
-1
)
Antimony 0.006
Arsenic 0.010
Beryllium 0.004
Chromium (total) 0.1
Cadmium 0.005
Cupper 1.3
Lead 0.015
Mercury 0.002
Selenium 0.05
Silver 0.1
Table 1. Maximum acceptable concentrations of metals in drinking water according to the US EPA [6].
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For these reasons, alternative technologies that are practical, efficient and cost effective for low
metal concentrations are being investigated. Biosorption in the removal of toxic heavy metals
is especially suited as a 'nonpolluted ' wastewater treatment step because it can produce close
to drinking water quality from initial metal concentrations of 1-100 mg L
-1
, providing final
concentrations of < 0.01-0.1 mg L
-1
[11]. Biosorption has been defined as the ability of certain
biomolecules or types of biomass to bind and concentrate selected ions or other molecules from
aqueous solutions. It should to be distinguished from bioaccumulation which is based on
active metabolic transport; biosorption by dead biomass is a passive process based mainly on
the affinity between the biosorbent and the sorbate [12]. The biosorption of heavy metals by
non-living biomass of plant origin is an innovative and alternative technology for the removal
of these pollutants from aqueous solution and offers several advantages such as low-cost
biosorbents, high efficiency, minimization of chemical and/or biological sludge, and regener‐
ation of the biosorbent [13].
Recently, natural adsorbents have been proposed for removing metal ions due to their good
adsorption capacity. Technologies based on the use of such materials offer a good alternative
to conventional technologies for metal recovery. In this context, Moringa oleifera represents an
alternative material for this purpose [14-16].
2. Moringa oleifera
Moringa oleifera is the best known species of the Moringaceae family. Moringaceae is a family of
plants belonging to the order Brassicales. It is represented by fourteen species and a single genus
(Moringa), being considered an angiosperm plant. It is a shrub or small tree which is fast
growing, reaching 12 meters in height. It has an open crown and usually a single trunk (Figure
2). It grows mainly in the semi-arid tropics and subtropics. Since its preferred habitat is dry
sandy soil, it tolerates poor soils, such as those in coastal areas [17].
Native to northern India, it currently grows in many regions including Africa, Arabia,
Southeast Asia, the Pacific and Caribbean Islands and South America [3, 16, 19]. It is cultivated
for its food, medicinal and culinary value and its leaves, fruits and roots are the parts used. It
is commonly known as the ‘horseradish’ tree arising from the taste of a condiment prepared
from the roots or ‘drumstick’ tree due to the shape of the pods. Figures 3 and 4 show the pods
and seeds of this tree. M. oleifera has a host of other country-specific vernacular names, an
indication of the significance of the tree around the world [16, 20-23].
Research has focused on the use of M. oleifera seeds and fruits in water purification and the
treatment of turbid water is the best-known application. The seeds of various species contain
cationic polyelectrolytes which have proved to be effective in the treatment of water, as a
substitute for aluminum sulfate. Interest in the study of natural coagulants for water clarifi‐
cation is not new. The coagulant is obtained from a byproduct of oil extraction and the residue
can be used as a fertilizer or processed for animal fodder. Compared to the commonly used
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228
Figure 2. Tree of Moringa oleifera species [18].
Figure 3. Pods of Moringa oleifera [18].
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coagulant chemicals, Moringa oleifera has a number of advantages including low cost, biode‐
gradable sludge production and lower sludge volume, and also it does not affect the pH of the
water. Apart from turbidity removal, M. oleifera seeds also possess antimicrobial properties
[24, 25], although the mechanism by which seeds act upon microorganisms is not yet fully
understood.
Tissues of M. oleifera from a wide variety of sources have been analyzed for glucosinolates and
phenolics (flavonoids, anthocyanins, proanthocyanidins, and cinnamates). M. oleifera seeds
reportedly contain 4-(α-L-rhamnopyranosyloxy)-benzylglucosinolate in high concentrations.
Roots of M. oleifera have high concentrations of both 4-(α-L-rhamnopyranosyloxy)-benzylglu‐
cosinolate and benzyl glucosinolate. Leaves contain 4-(α-L-rhamnopyranosyloxy)-benzylglu‐
cosinolate and three monoacetyl isomers of this glucosinolate and only 4-(α-L-
rhamnopyranosyloxy)-benzylglucosinolate has been detected in M. oleifera bark tissue [26].
Every glucosinolate contains a central carbon atom which is bonded to the thioglucose group
(forming a sulfated ketoxime) via a sulfur atom and to a sulfate group via a nitrogen atom.
These functional groups containing sulfur and nitrogen are good metal sequesters from
aqueous solution. The leaves of M. oleifera reportedly contain quercetin-3-O-glucoside and
quercetin-3-O-(6‘ ‘-malonyl-glucoside), and lower amounts of kaempferol-3-O-glucoside and
kaempferol-3-O-(6‘ ‘-malonyl-glucoside), along with 3-caffeoylquinic acid and 5-caffeoylquin‐
ic acid. Neither proanthocyanidins nor anthocyanins have been detected in any of the tissues
[26]. Although M. oleifera seeds have been most widely applied as a coagulant agent, many
studies have been performed in order to explore other potential applications of this material,
especially in the removal of metals from aqueous systems.
Figure 4. Seeds of Moringa oleifera [18].
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230
3. Biosorption of metals using Moringa oleifera
Since Moringa oleifera seeds have the ability to retain metals, it is necessary to define and to
understand the functional groups responsible for the adsorption phenomenon. Biosorption by
dead biomass or by some molecules and/or their active groups is a passive process based
mainly on the affinity between the biosorbent and the sorbate. In this case, the metal is
sequestered by chemical sites naturally present in the biomass. The diagram in Figure 5
illustrates the main steps in this process. In most cases, the biosorption process is rapid and
takes place under normal temperature and pressure. After the process of phase separation a
biomass “charged” with metal ions and an effluent free of contamination are obtained. Two
paths can be followed to deal with the “contaminated” biomass, the one of greatest interest
being biosorbent regeneration and metal recovery. This process is the most attractive because
biomass can be used for the removal of other metal species from other contaminated effluents.
The other option is the destruction of the biomass, which offers no possibility of reuse.
Solution containing
metal ions
Biomass
Biosorption
Solid liquid
separation
Metal
Metal containing
biomass
Decontaminated
effluent
Nondestructive
regeneration
Destruction of the
biomass
Regenerated
biomass
Metal
Figure 5. Main steps in biosorption process [27].
The mechanisms associated with heavy metal biosorption by biomass are still not clear;
however, it is important to note that this process is not based on a single mechanism. Since
metals may be present in the aquatic environment in dissolved or particulate forms, they can
be dissolved as free hydrated ions or as complex ions chelated with inorganic ligands, such as
hydroxide, chloride or carbonate, or they may be complexed with organic ligands such as
amines, humic or fulvic acids and proteins. Metal sequestration occurs through complex
mechanisms, including ion-exchange and complexation, and it is quite possible that at least
some of these mechanisms act simultaneously to varying degrees depending on the biomass,
the metal ion and the solution environment.
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In reference [28] indicated that ion-exchange is an important concept in biosorption, because
it explains many of the observations made during heavy metal uptake experiments. In this
context, the term ion-exchange does not explicitly identify the mechanism of heavy metal
binding to biomass, and electrostatic or London–van der Waals forces should be considered
as the precise mechanism of chemical binding, i.e., ionic and covalent bonds. Figure 6 provides
a schematic representation of an ion-exchange mechanism for a biosorbent material where
“Me” represents a metal with valence +2.
Figure 6. Schematic diagram of an ion exchange mechanism [29].
The seeds of Moringa oleifera and its parts can be classified as lignocellulosic adsorbents,
consisting mainly of cellulose, hemicellulose and lignin. These functional groups are com‐
prised of macromolecules that have the ability to absorb metal ions through ion exchange or
complexation [30] phenomena which occur on the surface of the material through the inter‐
action of the metal with the functional groups present. In order to understand the adsorption
process it is also important to characterize the biomass material. Several techniques can be
used to define the functional groups responsible for the adsorption phenomenon.
Infrared spectroscopy is an important technique in the qualitative analysis of organic com‐
pounds, widely used in the areas of natural products, organic synthesis and transformations.
It is applied as a tool to elucidate the functional groups which may be present in substances
[31], particularly with respect to the availability of the main groups involved in adsorption
phenomena.
Figure 7 shows FT-IR spectra for Moringa oleifera seeds which verify the presence of many
functional groups, indicating the complex nature of this material. The bandwidth centered at
3420 cm
-1
may be attributed to the stretching of OH bonds present in proteins, fatty acids,
carbohydrates and lignin units [32]. Due to the high content of protein present in the seed there
is also a contribution in this region from N-H stretching of the amide bond. The peaks present
at 2923 cm
-1
and 2852 cm
-1
, respectively, correspond to asymmetric and symmetric stretching
of the C-H bond of the CH
2
group. Due to the high intensity of these bands it is possible to assign
them to the predominantly lipid component of the seed, which is present in a high proportion
similar to that of protein [33]. In the region of 1800-1500 cm
-1
a number of overlapping bands
are observed and between 1750 and 1630 cm
-1
this can be attributed to C=O stretching. Due to
the heterogeneous nature of the seed, the carbonyl group may be bonded to different neighbor‐
hoods as part of the fatty acids of the lipid portion or amides of the protein portion. The carbonyl
Applied Bioremediation - Active and Passive Approaches
232
component that appears due to the presence of lipids can be seen at 1740 and 1715 cm
-1
, as can
be observed in the infrared spectra as small peaks, and the shoulders forming part of the main
band that appears at 1658 cm
-1
are attributed to the carbonyl amides present in the protein
portion. The peak observed at 1587 cm
-1
may be attributed to stretching connecting CN and also
the deformation of the N-H bond present in the proteins of seeds [34, 35].
Figure 7. FT-IR spectrum of Moringa oleifera seeds. The arrows indicate the maximum signal obtained [36].
Among the various techniques for material characterization, the X-ray diffraction (XRD)
technique is recommended for the evaluation of the presence of crystalline phases present in
natural materials. In general, we can classify materials as amorphous, semicrystalline or
crystalline. Figure 8 shows the XRD patterns for M. oleifera seeds. The XRD pattern for crushed
seeds, due to the high amount of oils and proteins present in the composition of the material
which represent around 69% of the total mass [36], shows unresolved signals (predominantly
amorphous). For this reason intact seeds are analyzed, constituting a complex matrix com‐
prised of a wide variation of substances including proteins, lipid structures and, to a lesser extent,
carbohydrates. It was possible to separate a broad peak at around equals 10º. The presence of
this peak is probably associated with the diffraction of the protein constituent surrounded by
other components which have a more amorphous pattern [37]. The amorphous nature of the
biosorbent suggests that the metal ion could more easily penetrate the biosorbent surface.
Thermogravimetric (TG) analysis was used to characterize the decomposition stages and
thermal stability determined through the mass loss of a substance subjected to a constant
heating rate for a specified time. The mass loss curve for a sample of Moringa oleifera seeds can
be observed in Figure 9, showing a typical profile that indicates several stages of the decom‐
position process. This thermogravimetric curve verifies the sample heterogeneity, since the
intermediates formed are a mixture of several components. The mass loss curve can be divided
into three stages: i) the first step occurs from 30°C to 128°C where a mass loss in the order of
8%, associated with water desorption, was observed. The amount of water loss from seeds
determined by this technique is similar to the value of 8.9% found in [38]; ii) in the second step
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32% of mass loss was observed in the temperature range of 128–268°C. This stage occurs due
to the decomposition of organic matter, probably the protein component, present in seeds; and
iii) the third step occurs from 268°C to 541°C with decomposition of the greater part of the seed
components, which probably includes fatty acids, for example, oleic acid has a boiling point
of 360°C. At 950°C a total residue of around 14.6% was observed, due to the ash content and
probably inorganic oxides.
Figure 8. X–ray diffractogram for Moringa oleifera seeds [36].
Figure 9. Thermogravimetric curve for Moringa oleifera seeds [36].
The morphological characteristics of the crushed seeds obtained using a scanning electron
microscopy (SEM) can be seen in Figure 10. The results reveal that the material exhibits a
relatively porous matrix with heterogeneous pore distribution. This feature is attributed to the
fact that the whole seed comprises a wide variety of biomass components. The presence of
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234
some deformations on the surface of the plant tissue can be observed, containing available
sites, from which it is possible to infer that the adsorbent provides favorable conditions for the
adsorption of metal species in the interstices [35].
(a)
(b)
Figure 10. Scanning electron micrographs of Moringa oleifera. In the order of (a) 10 µm and (b) 50 µm [36].
4. Influence of parameters in biosorption process
Many variables can influence metal biosorption and experimental parameters such as tem‐
perature, stirring time, pH, particle size of the biomass, ionic strength and competition between
metal ions can have a significant effect on metal binding to biomass. The biomass mass also
influences the adsorption process because as the adsorbent dose increases the number of
adsorbent particles also increases and there is greater availability of sites for adsorption. Some
of the most important factors affecting metal binding are discussed below. In general, adsorp‐
tion experiments are carried out in batch mode.
The pH is one of the most important parameters affecting any adsorption process. This
dependence is closely related to the acid-base properties of various functional groups on the
adsorbent surfaces [39]. The literature shows that a heterogeneous aqueous mixture of M.
oleifera seeds contains various functional groups, mainly amino and acids groups. These groups
have the ability to interact with metal ions, depending on the pH. An increase in metal
adsorption with increasing pH values can be explained on the basis of competition between
the proton and metal ions for the same functional groups, and a decrease in the positive surface
charge, which results in a higher electrostatic attraction between the biosorbent surface and
the metal [40]. Low pH conditions allow hydrogen and hydronium ions to compete with metal
binding sites on the biomass, leading to poor uptake. Biosorbent materials primarily contain
weak acidic and basic functional groups. It follows from the theory of acid–base equilibrium
that, in the pH range of 2.5–5, the binding of heavy metal cations is determined primarily by
the dissociation state of the weak acidic groups. Carboxyl groups (–COOH) are important
groups for metal uptake by biological materials. At higher solution pH, the solubility of a metal
complex decreases sufficiently for its precipitation, leading to a reduced sorption capacity.
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Therefore, it is recommendable to study biosorption at pH values where precipitation does
not occur. Biomasses are materials with an amphoteric character; thus, depending on the pH
of the solution, their surfaces can be positively or negatively charged. At pH values greater
than the point of zero discharge (pH
pzc
), the biomass surface becomes negatively charged,
favoring the adsorption of cationic species. However, adsorption of anionic species will be
favored at pH < pH
pzc
. The pH
pzc
of the M. oleifera seeds is between 6.0 and 7.0 [41], indicating
that the surface of the biosorbent presents acid characteristics. Figure 11 illustrates the surface
charge or the point of zero net proton charge of Moringa oleifera seeds. The surface charge of
the seeds is positive at pH < PZC, is neutral at pH = PZC and is negative at pH > PZC. The
variation in pH caused by protonation and deprotonation of the adsorbent reflects the presence
of functional groups. Table 3 shows the use of components of the M oleifera in the pH range of
2.5 to 8.0.
0 2 4 6 8 10 12
0
2
4
6
8
10
12
final pH
initial pH
Figure 11. Point of zero net proton charge of Moringa oleifera seeds.
It has been noted that the temperature can influence the sorption process. Simple physical
sorption processes are generally exothermic, i.e., the equilibrium constant decreases with
increasing temperature. According to data reported in the literature (Table 3), the binding of
the metal to different parts of the M. oleifera plant can be observed when the temperature is
raised from 22 to 50 °C.
The contact time (or stirring time) is another important parameter that influences the efficiency
of the adsorption process. As can be seen in Table 3, a period of 5 min was chosen for the nickel
sorption process and good results were obtained; however, longer times (240 min) are required
when using activated carbon.
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236
Moringa oleifera is capable of directly sorbing metal ionic species from aqueous solutions. An
interesting characteristic assigned to these biosorbents is the high abrasive content and the
relative chemical resistance, allowing them to be subjected to different chemical treatments to
increase their affinity and/or specificity for metal ions. Results previously published show the
potential use of untreated seeds, although biosorbent materials are generally derived from
plant biomass through different kinds of simple procedures. They may be chemically pre‐
treated for better performance and/or suitability for process applications. However, good
results have been obtained when the seeds were treated with NaOH. This treatment can
remove organic and inorganic matter from the sorbent surface. Chemical treatments are
commonly performed employing alkaline solutions or with phosphoric and citric acids [42].
Recently, however, efforts have been made to remove and subsequently also recover metals.
Metal-saturated biosorbent materials can be easily regenerated applying a simple (e.g. acidic)
wash which then contains a very high concentration of released metals in a small volume,
making the solution quite amenable to metal recovery.
Moringa Oleifera
Modifying agent(s) Heavy metal Temperature
(°C)
pH Contact time
(min)
Ref.
Seeds Petroleum ether Cd (II)
Cu (II)
Co (II)
Ni (II)
Pb (II)
22 3.5 – 8.0 60 [4]
Leaves NaOH and Citric acid Cd (II)
Cu(II)
Ni(II)
40 5.0 50 [32]
Bark Original state Ni(II) 50 6.0 60 [35]
Wood Activated carbon Cu(II)
Ni(II)
Zn(II)
30 6.0 240 [31]
Leaves NaOH and Citric acid Pb(II) 40 5.0 50 [34]
Bark Original state Pb(II) 25 5.0 30 [19]
Pod Original state
NaOH,
H
2
SO
4
CTAB
HCl
Ca(OH)
2
Triton X-100
H
3
PO
4
Al(OH)
3
Zn(II) 30 7.0 50 [16]
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Moringa Oleifera Modifying agent(s) Heavy metal Temperature
(°C)
pH Contact time
(min)
Ref.
SDS
Shelled seeds Original state Cd(II)
Cr(III)
Ni(II)
- 6.5
6.5
7.5
40 [15]
Shells Original state As (III)
As (V)
- 7.5
2.5
60 [43]
Husk and pods Unmodified
CTAB
H
3
PO
4
H
2
SO
4
HCl
Pb(II) 30 5.8 120 [3]
Shelled seeds Original state Cd(II) - 6.5 40 [14]
Seeds Original state Ag(I) 25 6.5 20 [36]
Seeds NaOH Ni(II) 25 4.0-6.0 5 [44]
CTAB: Cetyl trimethylammonium bromide, SDS: Sodium dodecyl sulfate
Table 3. Study parameters for the removal of metal ions using Moringa oleifera.
5. Adsorption models
An important physicochemical aspect in terms of the evaluation of sorption processes is the
sorption equilibrium. Adsorption isotherms are a basic requirement in understanding how the
adsorbate is distributed between the liquid and solid phases when the adsorption process
reaches the equilibrium state [45, 46]. Over the years a wide variety of isotherm models have
been introduced. The most commonly used isotherm models include Langmuir [47], Freund‐
lich [48], Dubinin-Radushkevich [49] and Temkin [50].
It can be observed that in most of the cases the Langmuir adsorption model has been success‐
fully used to predict metal adsorption processes. The Langmuir isotherm model assumes
monolayer adsorption onto an adsorbent surface containing a finite number of identical sites
and without interaction between adsorbed molecules. The Langmuir isotherm model assumes
that: each site can accommodate only one molecule or atom; the surface is energetically
homogenous; there is no interaction between neighboring adsorbed molecules or atoms; and
there are no phase transitions [51]. The Langmuir equation is expressed as follows:
q
e
=
q
m
K
L
C
e
1 + K
L
C
e
(1)
Applied Bioremediation - Active and Passive Approaches238
where q
e
is the amount of metal adsorbed at equilibrium (mg g
-1
), C
e
is the concentration of
metal in solution at equilibrium (mg L
-1
), and q
m
(mg g
-1
) and K
L
(L mg
-1
) are the Langmuir
constants related to the adsorption capacity (amount of adsorbate needed to form a complete
monolayer) and adsorption energy, respectively. The constants q
m
and K
L
can be calculated
from the intercepts and the slopes of the linear plots of C
e
/q
e
versus C
e
.
The Freundlich model describes adsorption onto an energetically heterogeneous surface not
limited by the monolayer capacity [48]. It can be presented in the following form:
q
e
= K
f
C
e
n
(2)
where q
e
is the amount of metal adsorbed at equilibrium (mg g
-1
), C
e
is the concentration of
metal in solution at equilibrium (mg L
-1
), and K
f
(mg g
-1
)(L mg)
(1/n)
and n (g L
-1
) are the Freund‐
lich constants related to the multilayer adsorption capacity and adsorption intensity, respec‐
tively. According to the theory, n values between 1 and 10 represent favorable adsorption
conditions [52]. Values of K
f
and n can be calculated from the slope and intercept of the plot of
Log q
e
versus Log C
e
. Experimental adsorption results with high coefficient correlation (R
2
)
values obtained for Freundlich isotherms have been reported as shown in Table 4.
The Dubinin-Radushkevich model has been used to distinguish between physical and
chemical adsorption [53]. The Dubinin-Radushkevich is more general than the Langmuir
model because it does not assume a homogenous surface or constant sorption. The Dubinin-
Radushkevich equation is given by:
q
e
=q
m
e
(
-β
2
)
(3)
where, q
m
(mg g
-1
) is the theoretical sorption capacity (mol g
-1
), ε is the Polanyi potential which
is related to the equilibrium concentration and the constant β gives the mean energy of sorption,
E (KJ mol
-1
). The constants q
m
and β are obtained from the intercept and slope of ln q
e
versus
ε
2
, respectively. If the magnitude of E is between 8 and 16 KJ mol
-1
the adsorption process
proceeds by ion-exchange or chemisorptions, while for values of E < 8 KJ mol
-1
the adsorption
process is of a physical nature [54]. In [31] reported that the sorption energy (E) values obtained
with the Dubinin-Radushkevich model showed that the interaction between metal ions and
the adsorbent proceeded principally by physical adsorption.
The Temkin isotherm model is based on the assumption that the heat of adsorption of all the
molecules in the layer decreases linearly with coverage due to adsorbent-adsorbate interac‐
tions, and the adsorption is characterized by a uniform distribution of binding energies, up to
a maximum binding energy [50]. The model is represented by the following equation:
q
e
= B ln
(
AC
e
)
(4)
Bioremediation of Waters Contaminated with Heavy Metals Using Moringa oleifera Seeds as Biosorbent
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239
where A (L g
-1
) and B (J mg
-1
) are Temkin isotherm constants relating to adsorption potential
and heat of adsorption, respectively. A plot of q
e
versus ln C
e
gives the values of Temkin
constants A and B. In the adsorption of copper, nickel and zinc onto activated carbon produced
from Moringa oleifera wood [31] the Temkin isotherm showed a higher correlation coefficient,
which may be due to the linear dependence of the heat of adsorption on low or medium
coverage. The repulsive force probably occurs between the different adsorbate species or for
intrinsic surface heterogeneity may be associated with the linearity.
Table 4 details some of the results for the biosorption studies using Moringa oleifera which have
been reported in the literature from 2006 onwards. From this table it is clear that Moringa
oleifera shows versatility, removing a variety metals under favorable conditions and is among
the most promising metal biosorbents.
Comparing the Langmuir and Freundlich models, M. oleifera seeds demonstrated a good
removal capacity for Co(II), Cu(II), Pb(II), Cd(II) and Ag(I), as compared to reports related to
other parts of the plant (Table 3). The variations in the removal percentage for metal ions can
be explained by the different ionic radii of chemical species. In general, for the single metal
solutions, ions with larger ionic radii are preferentially adsorbed. Among the metals tested,
Pb(II) has the largest ionic radius and hence shows the highest adsorption percentage, whereas
Co(II) presents the lowest level of adsorption [55].
Kinetics models are important in evaluating the basic qualities of an adsorbent as well as the
time required for the removal of particular metals, the effectiveness of the adsorbent and the
identification of the types of mechanisms involved in an adsorption system [56-58]. In order
to investigate the mechanism of biosorption and its potential rate-controlling steps, which
include the mass transfer and chemical reaction processes, kinetics models are exploited to test
experimental data obtained in kinetics studies. These usually show an initial period of rapid
metal adsorption with a subsequent decreased until reaching equilibrium of the system. This
occurs due to the rapid adsorption of metallic ions by the surface of the adsorbent followed
by a step of slow diffusion of ions from the surface film to the adsorption sites in the micropores
which are less accessible [59].
In practice, the kinetic studies are carried out in batch experiments, typically varying the
adsorbate concentration, the adsorbent mass, the agitation time and the temperature, as well
as the type of adsorbent and adsorbate. Subsequently, the data are processed and used in the
linear regression to determine the kinetics model which provides the best fit. However, for the
validity of the order of the adsorption process two criteria should be evaluated, the first based
on the regression coefficient (R
2
) and the second on the calculated q
e
values, which must
approach the experimental q
e
[60]. The main models used to evaluate the kinetics model profile
are pseudo-first-order and pseudo-second order. However, other models are also are applied,
such as Bangham's model and the Weber and Morris sorption kinetic model.
Applied Bioremediation - Active and Passive Approaches
240
Heavy metal Langmuir model Freundlich model Ref.
qm
(mg g
-1
)
KL
(L mg
-1
)
R
2
Kf
(mg g
-1
) (L mg
)(1/n)
n
(g L
-1
)
R
2
Cd (II)
Cu(II)
Ni(II)
171.37
167.90
163.88
0.037 0.029 0.023 > 0.99
> 0.99
> 0.99
- - - [32]
Ni(II) 30. 38 0.31 0.9994 - - - [35]
Cu(II)
Zn(II)
Ni(II)
11.534
17.668
19.084
0.2166
0.1430
0.6165
0.9979
0.9528
0.9973
3.8563
3.7708
-
2.9214
2.2528
-
0.9976
0.9996
-
[31]
Pb(II) 209.54 0.038 > 0.99 - - - [34]
Ni(II) 29.6 - 0.9913 - - - [44]
Ag(II) 23.13 0.1586 0.9935 - - - [36]
Zn(II) 52.08 0.150 0.9994 50.35 - 0.9953 [16]
Cd(II)
Cr(III)
Ni(II)
1.06
1.01
0.94
0.51
0.40
0.34
0.94
0.96
0.96
- - - [15]
As (III)
As (V)
1.59
2.16
0.04
0.09
0.96
0.98
- - - [43]
Pb(II) - - 0.9981 - - - [3]
Pb (II) - - - 8.6 2.8 0.9981 [19]
Cd(II) - - - 3.04 1.37 - [14]
Table 4. Langmuir and Freundlich isotherm parameters for Moringa oleifera.
The pseudo-first order equation, also known as the Lagergren equation, is expressed as follows
[16, 61]:
log
(
q
e
- q
t
)
=log q
e
-
k
1
2.303
t
(5)
where q
t
and q
e
(mg g
−1
) are the amount of metal ions adsorbed per unit weight of the adsorbent
at time t and equilibrium, respectively; and k
1
(min
−1
) is the pseudo-first order rate constant of
the sorption process and t (min) is the mixing time [60]. Table 5 presents the data of calculated
q
e
, pseudo-first order rate (k
1
) and correlation coefficient (R
2
). This kinetics model is based on
the assumption that the adsorption rate is proportional to the number of free sites available,
occurring exclusively onto one site per ion [34, 62].
In most studies discrepancies occurred between the value of q
e
calculated by the pseudo-first
order model and the experimental q
e
, as shown in Table 5, highlighting the inability of this
Bioremediation of Waters Contaminated with Heavy Metals Using Moringa oleifera Seeds as Biosorbent
http://dx.doi.org/10.5772/56157
241
model to describe the kinetics of the metal ion adsorption processes. In general, calculated q
e
values are smaller than the experimental q
e
, which may occur because of a time lag, probably
due to the presence of the boundary layer or external resistance at the beginning of the sorption
process [63]. Considering the papers detailed in Table 5, only in [43] and [14] used only the
pseudo-first order kinetics model to examine the data obtained, even though in the latter case
the correlation values obtained were relatively low. In [43] noted no change in the adsorption
rate constant when varying the concentrations of As(III) and As(V) and therefore this model
could describe the adsorption process. In [14] used this model to compare the adsorption rate
constants of ternary metal ions and single metal ions and noted that these constants were lower
for ternary metal ions. Their explanation for this was that metal ions compete for vacant sites
and uptake by binding sites within the shortest possible time.
The pseudo-second-order kinetics model is also based on the assumption that the sorption rate
is controlled by a chemical sorption mechanism involving electron sharing or electron transfer
between the adsorbent and adsorbate [64]. It can be expressed as:
t
q
t
=
1
k
2
q
e
2
+
t
q
e
(6)
where q
t
and q
e
(mg g
−1
) are the amount of metal ions adsorbed per unit weight of the adsorbent
at time t and equilibrium, respectively; and k
2
(g mg
-1
min
−1
) is the pseudo-second order rate
constant of the sorption process and t (min) is the mixing time.
Table 5 presents the data of calculated q
e
, pseudo-second order rate (k
2
) and correlation
coefficient (R
2
). For most of the pseudo-second order kinetics models the calculated q
e
values
approach the experimental q
e
values and the correlation coefficients are close to 1, indicating
a good ability of this model to describe the kinetics of the metal ion adsorption process. This
observation indicates that the rate-limiting steps in the biosorption of metallic ions are
chemisorption involving valence forces through the sharing or exchange of electrons between
the sorbent and the sorbate, complexation, coordination and/or chelation, in which mass
transfer in the solution was not involved.
Considering that neither the pseudo-first-order nor the pseudo-second-order model can
identify the diffusion mechanism, other kinetic models are needed to study this process, such
as Bangham's model and the Weber and Morris sorption kinetics model [65]. The latter model
is also known as the intra-particle diffusion model, this process in many cases being the rate-
limiting step, which can be determined through the following equation:
q
t
=k
id
t
1
2
+ c
id
(7)
where q
t
(mg g
−1
) is the amount of metal ions adsorbed per unit weight of the adsorbent at time
t, c
id
(mg g
−1
) is a constant of Weber and Morris, and k
id
(mg g
−1
min
−1/2
) is the intra-particle
diffusion rate constant and t (min) is the mixing time [66]. The value of the intercept gives an
idea of the thickness of the boundary layer, i.e., the larger the intercept the greater the boundary
Applied Bioremediation - Active and Passive Approaches
242
layer effect will be. When there is a complete fit of the model the value of c
id
should be zero,
and the deviation of this constant is due to differences in the mass transfer rate during the
initial and final stages of adsorption. This is indicative that there is some degree of boundary
layer control and shows that the intra-particle diffusion is not the only rate-limiting step, and
thus several processes operating simultaneously may control the adsorption [34].
According to this model, if the plot of q
t
versus t
1/2
gives a straight line, then the sorption process
is controlled by intra-particle diffusion, while if the data exhibit multi-linear plots then two or
more steps influence the adsorption process [67]. In two studies performed in [32, 19], multi-
linear plots were observed with three distinct steps involved in the biosorption, the initial
region of the curve relative relating to the adsorption on the external surface. The second region
corresponds to the gradual uptake, where the intra-particle diffusion is the rate-limiting step.
The final plateau region indicates the equilibrium uptake.
In reference [3] compared different types of carbon through the k
id
values and observed that
the effect of intra-particle diffusion may be significantly increased by chemically modifying
the adsorbents. Although none of the data collected in the studies detailed in Table 5 were
well-described by the kinetics model proposed by Weber and Moris, the intraparticle diffusion
may not be the only rate-limiting step in these studies.
Bangham's model evaluates whether pore diffusion is the only rate-controlling step in the
adsorption process [65] and can be represented by the following equation:
log log
(
c
o
c
o
- q
t
m
)
=log
(
k
o
m
2.303 V
)
+ σlog t
(8)
where q
t
(mg g
−1
) is the amount of metal ions adsorbed per unit weight of the adsorbent at time
t; c
o
(mg L
-1
) is the initial metal ion concentration in liquid phase; m (g L
‒1
) is adsorbent
concentration at time t (min); V (L) solution volume, t (min) is the mixing time and k
o
(L g
-1
)
and σ (σ < 1) are constants of Bangham's model. Of the studies published, only in [3] used
Bangham’s kinetic model to compare the rate constants for the adsorption of Pb(II) onto
different types of functionalized carbon prepared from the seed husks and pods of M.
oleifera and thereby assess the efficiency of the functionalization of this material.
The temperature is reportedly an important parameter for the adsorption of metal ions. An
increase or decrease in temperature can cause a change in the amount of metal removed or
adsorbed by the adsorbent. A change in temperature causes a change in the thermodynamic
parameters of free energy (∆G°), enthalpy (∆H°) and entropy (∆S°). These parameters are
important to understand the adsorption mechanism [68]. For a given temperature, a phenom‐
enon is considered to be spontaneous if the ∆G° has a negative value. Moreover, if ∆H° is
positive the process is endothermic and if it is negative the process is exothermic [69]. Negative
values of ∆S° show a decreased randomness or increased order at the metal-biomass interface.
The positive value showed a change in the biomass structure during the sorption process,
causing an increase in the disorder of the system [68]. The parameters ∆G° (kJ mol
-1
), ∆H° (kJ
mol
-1
) and ∆S° (J mol
-1
K
-1
) can be evaluated from the following equations [70].
Bioremediation of Waters Contaminated with Heavy Metals Using Moringa oleifera Seeds as Biosorbent
http://dx.doi.org/10.5772/56157
243
G ° = - RT ln K
c
(9)
ln K
c
= -
H °
RT
+
S °
R
(10)
where R(8.314J mol
-1
K
-1
) is the gas constant, T(K) the absolute temperature and K
c
(mL g
-1
) the
standard thermodynamic equilibrium constant defined by q
e
/C
e
. ∆H° and ∆S° can be deter‐
mined from the slope and the intercept of the linear plot of Ln K
c
versus 1/T.
The studies performed on Moringa oleifera using chemically-modified leaves for the adsorption
of Pb(II) [34], bark for Ni(II) [35] and leaves for Cd(II), Cu(II) and Ni(II) [32] showed the
endothermic nature and spontaneity of the adsorption process. The positive values of ∆S°
suggest an increase in randomness at the solid/liquid interface with some structural changes
in the sorbate.
6. Final considerations
Although the biosorption of heavy metals from aqueous solutions is a relatively new process
that has proven very promising in the removal of contaminants from aqueous effluents,
offering significant advantages like the low-cost, availability, profitability, easy of operation
and efficiency. Other technologies have also been very attractive ensuring an appropriate
process to treat industrial waste effluents [71-77]. However, biosorption is becoming a
potential alternative to the existing technologies for the removal and/or recovery of toxic metals
from wastewater. The major advantages of biosorption technology are its effectiveness in
reducing the concentration of heavy metal ions to very low levels and the use of inexpensive
biosorbent materials.
7. Conclusions
The studies described herein indicate that Moringa oleifera seeds are an alternative sorbent for
metal ion removal from contaminated waters. This can be found in most papers which report
60 to 90% removal of metals (Cd(II), Cu(II), Ni(II), Pb(II), As(III), As(V), Cr(III) and Zn(II)). In
these cases, not only the seeds were used, but also leaves, bark and pods showing the great
versatility of this plant. The results show that even with the high heterogeneity of the matrix
confirmed through characterization techniques there is a great potential for the application of
these seeds in effluent treatment without component separation, which makes the process
economically and technically attractive.
Biosorption is the most economical and eco-friendly method for the removal of heavy metals
from domestic as well as industrial wastewater and it is particularly important to promote the
development of biosorption for industrial processes. Notable advantages are: (a) low cost of
Applied Bioremediation - Active and Passive Approaches
244
Metal
c
o
(mg L
−1
)
qe, exp
(mg g
−1
)
Pseudo-first-order Pseudo-second-order Ref.
qe
(mg g
-1
)
k1 (min
−1
)
R
2
qe (mg g
-1
)
k2 (g mg
-1
min
-1
)
h
0
(mg g
−1
min
−1
)
R
2
Zn (II)
50
a
50
b
50
c
45.00
45.76
42.80
-
-
-
-
-
-
-
-
-
46.94
47.16
43.47
4.51 10-4
2.85 10-4
2.04 10-5
-
-
-
0.997
0.999
0.997
[16]
Pb(II)
30
d
30
e
30
f
30
g
30
h
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
24.57
27.70
28.49
29.08
29.46
0.0085
0.0052
0.0060
0.0062
0.0087
5.131
3.989
4.868
5.243
7.550
0.999
0.998
0.998
0.999
0.999
[3]
As (III)
As (V)
25
50
25
50
-
-
-
-
-
-
-
-
0.047
0.049
0.063
0.065
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
[43]
Cd(II)
Cr(III) Ni(II)
25
25
25
1.06
1.01
0.94
-
-
-
0.51
0.40
0.34
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
[14]
Pb(II)
10
25
40
12.7343
19.8988
23.9233
-
-
-
-
-
-
-
-
-
13.26
20.64
25.01
15.35
10.08
9.3
0.20
0.21
0.23
0.9974
0.997
0.9995
[34]
Pb(II)
10.4
30.1
50.4
8.7
10.2
12.5
-
-
-
-
-
-
-
-
-
8.8
10.3
12.53
27.8
18.2
12.6
2.5
1.9
1.6
0.9999
0.9999
0.9998
[19]
Ni(II)
10
25
50
9.7
6.74
3.27
-
-
-
-
-
-
-
-
-
10.29
7.14
3.43
1.91
2.70
12.74
2.03
1.38
1.05
0.9971
0.9964
0.996
[35]
Cu(II)
Zn(II)
Ni(II)
30
30
30
8.3406
13.2537
9.5847
-
-
-
-
-
-
-
-
-
8.3264
13.2450
9.6154
0.0848
0.2457
0.0957
-
-
-
0.9998
1
0.9999
[31]
Cd (II)
Cu(II)
Ni(II)
10
25
40
10
25
40
10
25
40
13.54
13.80
20.86
11.92
13.55
16.01
10.24
12.49
14.07
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
10.99
10.50
15.24
11.03
12.45
12.86
10.24
12.49
14.07
1.39
1.46
1.22
3.4
1.66
1.56
1.51
1.31
1.52
2.73
3.09
5.61
5.58
3.37
4.31
1.70
2.29
3.27
0.9951
0.9969
0.9981
0.9992
0.9958
0.9977
0.9951
0.9952
0.9967
[32]
Table 5. Kinetics parameters for metal biosorption using Moringa oleifera.
Bioremediation of Waters Contaminated with Heavy Metals Using Moringa oleifera Seeds as Biosorbent
http://dx.doi.org/10.5772/56157
245
the biosorbent, (b) high efficiency for metal removal at low concentration, (c) potential for
biosorbent regeneration and metal valorization, (d) high sorption and desorption rates, (e)
limited generation of secondary residues, and (f) relatively environmentally-friendly life cycle
of the material (easy to eliminate compared to conventional resins, for example).
However, after the metal removal from aqueous solutions by the biomass, the recovery of the
metal is an important issue. This can be achieved through a metal desorption process, aimed
at weakening the metal-biomass linkage. Thus, studies to evaluate the reversibility of the
adsorption reactions involved in the biosorption of heavy metals are of great importance. The
problems associated with the disposal of exhausted adsorbent can be solved either by its
activation or incineration or its disposal after proper treatment. For biosorption and desorption
processes, another important aspect is the biosorbent reuse in successive biosorption-desorp‐
tion cycles, the viability of which is determined by the cost-benefit relationship between the
loss in biosorption capacity during the desorption steps and the operational yield in the metal
recovery. Thus, further studies need to focus on the development of new clean environmen‐
tally-acceptable technologies.
Acknowledgements
The authors are grateful for financial support from the government agencies Conselho
Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Fundação de Amparo à
Pesquisa do Estado de Minas Gerais (FAPEMIG), Fundação de Amparo à Pesquisa do Estado
de Goiás (FAPEG) and Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
(CAPES).
Nomenclature
A
Temkin isotherm constant relating to adsorption potential, (L g
-1
)
B Temkin isotherm constant relating to heat of adsorption, (J mg
-1
)
β mean energy of sorption, E (KJ mol
-1
)
c
o
initial metal ion concentration in liquid phase, (mg L
-1
)
C
e
concentration of metal in solution at equilibrium, (mg L
-1
)
c
id
constant of the Weber and Morris model, (mg g
−1
)
CAPES Coordination of Improvement of Higher Education Personnel
CNPq National Council for Scientific and Technological Development
ε Polanyi potential which is related to the equilibrium concentration
FAPEMIG Research Foundation of the State of Minas Gerais
FAPEG Research Foundation of the State of Goiás
Applied Bioremediation - Active and Passive Approaches246
FT-IR Fourier transform infrared
∆G° free energy, (kJ mol
-1
)
∆H° enthalpy, (kJ mol
-1
)
K
c
standard thermodynamic equilibrium constant defined by q
e
/C
e
, (mL g
-1
)
K
L
Langmuir constant related to adsorption energy, (L mg
-1
)
K
f
Freundlich constant related to the multilayer adsorption capacity
k
1
pseudo-first order rate constant of the sorption process, (min
−1
)
k
2
pseudo-second order rate constant of the sorption process, (g mg
-1
min
−1
)
k
id
intra-particle diffusion rate constant, (mg g
−1
min
−1/2
)
k
o
constant of the Bangham's model, (L g
-1
)
σ constant of the Bangham's model
m adsorbent concentration at time t (min), (g L
‒1
)
n Freundlich constant related to the multilayer adsorption intensity
q
e
amount of metal adsorbed per unit weight of the adsorbent at equilibrium, (mg g
-1
)
q
m
Langmuir constant related to the adsorption capacity, (mg g
-1
)
q
t
amount of metal ions adsorbed per unit weight of the adsorbent at time t, (mg g
−1
)
R gas constant, (8.314J mol
-1
K
-1
)
R
2
coefficient correlation
∆S° entropy, (J mol
-1
K
-1
)
SEM scanning electron microscopy
t mixing time, (min)
T absolute temperature, (K)
TG thermogravimetric
US EPA United States Environmental Protection Agency
V solution volume, (L)
XRD X-ray diffraction
Author details
Cleide S. T. Araújo
1
, Dayene C. Carvalho
2
, Helen C. Rezende
2
, Ione L. S. Almeida
2
,
Luciana M. Coelho
3
, Nívia M. M. Coelho
2*
, Thiago L. Marques
2
and Vanessa N. Alves
2
*Address all correspondence to: nmmcoelho@ufu.br
1 State University of Goiás, Anápolis, GO, Brazil
2 Institute of Chemistry, Federal University of Uberlândia, Uberlândia, MG, Brazil
3 Department of Chemistry, Federal University of Goiás, Catalão, GO, Brazil
Bioremediation of Waters Contaminated with Heavy Metals Using Moringa oleifera Seeds as Biosorbent
http://dx.doi.org/10.5772/56157
247
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Bioremediation of Waters Contaminated with Heavy Metals Using Moringa oleifera Seeds as Biosorbent
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... It was found that contact time, biosorbent dosage, and biosorbent pretreatment concentration had statistically significant effect (p values < 0.05) on arsenate removal. A maximum percentage removal of 99.9% was achieved in the human body with substantial health challenges (Araujo et al., 2013). In addition, they are highly resistant to natural deterioration which makes them even more harmful (Balali-Mood et al., 2021;Mitra et al., 2022;Nadeem et al., 2006;Obuseng et al., 2012). ...
... oleifera). The brunt of its application is in the use of the seed and its extract as coagulation agents in water purification (Araujo et al., 2013). In recent years, its capability for heavy metal removal has become an emerging application. ...
... The bands between 1800 and1600 cm −1 are strongly linked with the C = O stretching of carboxylic acids. These units are major components of lipids or amino acids in proteins that characterizes the Moringa seeds (Araujo et al., 2013). More so, the band at 1426 cm −1 can be directly linked to the O-H bending of alcohol, while the band at 1254 cm −1 is associated with the C-N stretching of amine group, which is likely present due to the protein-rich content of the Moringa seed. ...
Article
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The arousal of environmental concerns due to spike in environmental degradation has necessitated proper waste management and disposal. Arsenic, a potentially toxic element in cassava wastewater, requires treatment prior to the wastewater disposal to minimize environmental pollution and associated health implications. The present study thus addressed the treatment of As⁵⁺ heavy metal in cassava wastewater using an efficient biosorbent from chemically pretreated unshelled Moringa oleifera seeds. The effect of various factors influencing the biosorption process for arsenate removal was studied including pH, contact time, biosorbent dosage, and biosorbent pretreatment concentration. The results of Fourier transform infrared spectroscopy clearly suggested that additional functional groups attributed to esters were formed in the pretreated biosorbent, which is responsible for improvement in biosorption. It was found that contact time, biosorbent dosage, and biosorbent pretreatment concentration had statistically significant effect (p values < 0.05) on arsenate removal. A maximum percentage removal of 99.9% was achieved in the synthetic solution at pH 4.0, contact time of 30 min, and dosage of 2 g for biosorbent pretreated with 1 M of chemical solution. Furthermore, through isotherm and kinetics studies, it was discovered that the biosorption process for untreated biosorbent is by ion exchange, while that for treated biosorbents indicated a multifarious adsorption mechanism. Moreover, the biosorption process was exothermic and spontaneous. Also, it is noted that the sorption capability of the biosorbent increases with pretreatment concentration. A statistical model has been developed with prediction R² of 0.898, which incorporates the effect of treatment concentration on the percentage removal of As⁵⁺ from cassava wastewater.
... The seeds of M. oleifera are classified as lignocellulose adsorbents which consist of cellulose, hemicellulose, and lignin. These have functional groups which can absorb metal ions through ion-exchange or complexation process (Araujo et al. 2013). ...
... The spectra showed a broad band at 3,897 cm À1 assigned to the stretching vibration of hydroxyl groups (O-H) on the surface of the MOSB. The presence of the high content of protein in MOSB gives it a high content of N-H stretching of amide groups (Araujo et al. 2013). The peaks at 2,924 and 2,854.8 ...
... The peaks at 2,924 and 2,854.8 cm À1 are the symmetrical and asymmetrical stretching of -CH 3 and -CH 2 groups, respectively, present in fatty acids (Araujo et al. 2013). The peaks at 1,745.2 and 1,659 cm À1 are assigned to the C¼O bond stretching of ketone. ...
Article
Full-text available
This study demonstrated that Moringa oleifera seed biomass (MOSB) has the potential to be used as a natural alternative in the removal of lead (Pd), cadmium (Cd), and copper (Cu) from water which was justified by the level of toxicity, environmental unfriendliness, and costly nature of chemical coagulants presently used. The Fourier Transform Infrared (FTIR) analysis was used to identify the MOSB and functional groups present in the adsorption of metal ions. The maximum removal at pH 5, room temperature, and 0.8 g dosage was 90, 81.77, and 70% for Pb(II), Cd(II), and Cu(II), respectively. The order of biosorption preference was Pb(II)>Cd(II)>Cu(II) in single sorption and is in a consistent correlation between physiochemical properties of metal ions and selective biosorption of MOSB functional groups. The adsorption data fitted better to the Langmuir than the Freundlich models as the sorption capacities (qm) of MOSB for Pb(II), Cd(II), and Cu(II) were 6.19, 5.03, and 3.64 mg/g, respectively. The separation factor (RL) was within the range of 0–1 which showed that the Pb(II), Cd(II), and Cu(II) adsorption processes were favourable for M. oleifera adsorbent. The results showed that MOSB is an effective adsorbent in the removal of the studied heavy metals from contaminated water. In all these water-purifying properties of the moringa seed biomass, no deliberate attempt has been made to study the use of a ternary system of very toxic metals like Pb, Cd, and Cu knowing the anti-bacterial properties of the metal system. Similarly, the reproducibility, low cost, and no requirement of a power source make this an efficient process for obtaining potable water even in homes in rural settings.
... This is because the conventional process of water treatment may not only be expensive but usually environmentally unfriendly (Adhiambo et al., 2015). Araujo et al., (2013) agreed that the presence of heavy metals such as Lead (Pb) in the environment (even in moderate concentrations) can produce variety of diseases of the central nervous system hypophosphatemia, cardiovascular diseases, liver damage, cancer, sensory disturbances, and kidney impairment. ...
... It is an angiosperm plant that is represented by fourteen species and a single genus Moringa. It is a shrub or small tree that grows up to the height of 12 meters (Araujo et al., 2013). It is usually a single trunk with an open crown trunk. ...
... The seeds of M. oleifera are classified as lignocellulose adsorbents which consist of cellulose, hemicellulose and lignin. These have functional groups which can absorb metal ions through ion-exchange or complexation process (Araujo et al., 2013). ...
Article
Full-text available
This study was based on the evaluation of the efficiency and applicability of Moringa oleifera seed biomass (MOSB) as adsorbent in the removal of Lead (Pb) in water. The study was justified by the toxic nature of the study metal as the current conventional processes of heavy metals' removal are not environmentally friendly and chemical coagulant very exorbitant. Fourier transform Infrared (FTIR) analysis was used to characterise the Moringa oleifera seeds biomass functional groups that may be present in the adsorption of metal ions. The observed components were the carboxylic acid and amine functional groups (-COOH and-NH). The effects of contact time, adsorbent dosage, metal ion concentration and pH were studied. Pb (II) ion had a maximum adsorption capacity of 90% at pH 5, room temperature, and 0.8 g dose of Moringa oleifera seeds biomass. The adsorption data fit better with the Langmuir than Freundlich isotherm models. From the Langmuir model, the sorption capacity (qm) of MOSB for Pb (II) ion was 6.19 mg/g. The results showed that Moringa oleifera seed biomass is an effective adsorbent in the removal of the studied heavy metal in water.
... Bioaccumulation of heavy metals in human bodies is very detrimental because they are toxic and cause multiple damages to organs (Tchounwou et al., 2012). Araujo et al. (2013) supported the outcome of the study of Tchounwou et al. (2012) availability of heavy metals like copper even at controlled amounts can lead to organ illnesses such as kidney or liver, skin, bones and teeth. Copper is one of the toxic metals hence said to be a heavy metal according to Koller and Saleh (2018), and its presence in water poses a potential threat to public health. ...
... It is an angiosperm plant that is represented by fourteen species and a single genus Moringa. It is a shrub or small tree that grows up to the height of 12 meters (Araujo et al., 2013). It is usually a single trunk with an open crown trunk and grows mainly in the steppe climates and subtropics zone. ...
... The seeds of Moringa oleifera are classified as lignocellulose adsorbents which consist of cellulose, hemicellulose and lignin. These have functional groups which can absorb metal ions through ion-exchange or complexation process (Araujo et al., 2013). The spectra showed a broad band at 3897 cm −1 assigned to the stretching vibration of hydroxyl groups (O-H) on the surface of the Moringa oleifera seeds biomass. ...
Article
Full-text available
study was based on the evaluation of the potential effectiveness of Moringa oleifera seeds biomass as a biosorbent in the removal of copper (Cu) in water which was justified by the level of toxicity, environmental unfriendliness and costly nature of chemical coagulants presently used. Fourier transform infrared (FTIR) analysis was used to identify the Moringa oleifera seeds biomass functional groups present in the adsorption of metal ions and found to be the carboxylic acid and amine functional groups (-COOH and -NH). The effects of contact time, adsorbent dosage, metal ion concentration and pH were studied. The maximum adsorption capacity at pH 5, room temperature and 0.8 g dosage was 70% for Cu(II). The adsorption data fitted better to the Langmuir than the Freundlich models as the sorption capacity (qm) of Moringa oleifera seeds biomass for Cu(II) was 3.64 mg/g. The separation factor (RL) was within the range of 0 and 1 which showed that the Cu(II) biosorption processes were favourable for Moringa oleifera biosorbent. The results showed that Moringa oleifera seed biomass is an effective adsorbent in the removal of the studied heavy metals in water. The effective pH for the Cu(II) removal was 5.0 as equilibrium was achieved practically in 35 min. The quantitative analysis of defatted Moringa oleifera should be studied in order to have a fair mixing ratio between Moringa oleifera seeds biomass and the adsorbate. There is also the ardent need to work on environmentally friendly disposal of adsorbent after saturation of adsorbent by analyte to avoid secondary pollution.
... As shown in Fig. 3, all the XRD patterns are continuous, which furnish the fact that all the samples are primarily amorphous. Pure MO seed membrane shows two amorphous peaks at 2θ = 5.63° and 21.73° which agree with reports of prior studies [35,36]. The presence of these peaks may possibly be due to the diffraction of proteins in MO seed surrounded by more amorphous components [36]. ...
... Pure MO seed membrane shows two amorphous peaks at 2θ = 5.63° and 21.73° which agree with reports of prior studies [35,36]. The presence of these peaks may possibly be due to the diffraction of proteins in MO seed surrounded by more amorphous components [36]. The [37]. ...
Article
Full-text available
Novel, eco-friendly, and cost-effective biomaterial membranes based on Moringa oleifera (MO) seed as a host medium are fabricated by solution casting technique. Tannic acid (TA) is employed as a stability enhancer, and the addition of NH4SCN increases the proton conduction of the membranes. The particle size of the prepared MO seed powder is obtained by SEM analysis. The amorphous properties of the prepared biomaterial membrane are examined by XRD analysis. The change in vibrational patterns of biomaterial membranes with salts is studied using FTIR analysis. The glass transition temperatures of the prepared biomaterial membranes are measured by DSC measurement. As measured by the AC impedance technique, the biomaterial membrane 1 gm MO seed, 250 mg TA, and 0.8 mol.wt% NH4SCN displays the highest ionic conductivity as 1.83 × 10⁻² S/cm at room temperature. By employing the highest ion-conducting biomaterial membrane in the primary proton battery and proton-exchange membrane fuel cell (PEMFC), open circuit voltage and cell potential were 1.68 V and 531 mV observed respectively. It showed the high potential of MO seed-based biomaterial membrane in primary proton battery and PEMFC.
... Moringa oleifera Lam. is native to the north of India and grows well in tropical regions. It has been extensively studied because it is rich in amino acids, antioxidants, phytohormones, and minerals (Araújo et al. 2013). The content of compounds in Moringa extract depends on extraction techniques. ...
... In addition, Chuang et al. (2007) discovered that leaves of M. oleifera contain essential oils which have anti-fungal activities against dermatophytes. Apart from its medicinal benefits, Moringa extract has been shown to remove heavy metals and contaminants in water by a significant amount (Araújo et al. 2013). This is possibly due to some components, such as thiol-containing proteins present in the extracts that interact with heavy metals, resulting in ion adsorption and charge neutralization. ...
Article
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The contamination of paddy fields and rice grains by cadmium (Cd) adversely affects human health. Thus, many approaches have been proposed to reduce the accumulation of Cd in rice. Here, we investigate the potential of aqueous Moringa oleifera leaf extract (AMOLE) in decreasing uptake and toxicity of Cd in a popular Thai jasmine rice variety, Khao Dawk Mali 105 (KDML105). Plants were grown in Petri dishes, a hydroponic system, and a pot system under different concentrations of Cd, in the presence and absence of AMOLE. In Petri dishes, Cd reduced the percentage of germination by 79%, but the treatment with 0.5 mg mL⁻¹ AMOLE significantly increased the germination percentage. Moreover, AMOLE significantly decreased Cd accumulation in rice seedlings by 97%. In the hydroponics system, 0.5 mg mL⁻¹ AMOLE decreased Cd content in shoots by 48%. Although no significant physiological changes in response to Cd treatments were observed in the pot system, a large amount of Cd was accumulated in rice roots. The AMOLE treatments significantly reduced Cd accumulation in rice shoots and decreased Cd content in milled grain by half compared to those without AMOLE treatment. We conclude that AMOLE reduced Cd toxicity, enhanced seedling growth, and reduced Cd accumulation in rice grains.
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