Evaluation of Water Melon Peels as Economic Adsorbents for Removal of High Levels of Iron
from Different Water Sources
Hassouna MEM1*, Marzouk MA2, Elbably MA3 and El Maghrabi AH1
1Department of Chemistry, Beni-Suef University, Egypt
2Department of Botany & Microbiology, Beni-Suef University, Egypt
3Department of Hygiene, Management & Zoonoses, Beni-Suef University, Egypt
Submission: November 19, 2018; Published: March 08, 2019
*Corresponding author: Hassouna MEM, Department of Chemistry, Faculty of Science, Beni-Suef University, Egypt
How to cite this article: Hassouna MEM, Marzouk MA, Elbably MA, El Maghrabi AH. Evaluation of Water Melon Peels as Economic Adsorbents for
Removal of High Levels of Iron from Different Water Sources. Int J Environ Sci Nat Res. 2019; 17(4): 555970. DOI:10.19080/IJESNR.2019.17.555970
Optimum conditions for the adsorption of iron onto crude and modified (with lactic acid and tri sodium citrate) water melons peels (WMP) from aqueous solution are investigated as inexpensive and eco-friendly available adsorbents. Water samples are gathered from different sources (surface, tap and ground). The three WMP forms are characterized by FT-IR and SEM. Adsorption variables such as: adsorbent dose, stirring time and pH have been optimized. The removal efficiency of the unmodified WMP reaches its maximum uptake in the pH range 4-6, the other modified WMP powders in the range 5-7. The removal process is slow in the first 10min. then it is gradually increased till equilibrium after 20min in case of unmodified WMP, the two modified forms reach equilibrium after 15min. Kinetic studies indicated that adsorption follows the Langmuir and Freundlich adsorption isotherms. Desorption processes assured the possibility to regenerate and reuse the adsorbents..
Keywords: Heavy metals; Fe; Water melon peels; Economic sorbent; Water sources; Adsorption
Heavy metals have become a question of global concern considering their hard consequences which requires ongoing evaluation and revision of water resource policy at all standard international levels down to individual aquifers and wells [1,2]. Their main sources include wastewater discharged from health facilities , other industries, metal plating and alloy manufacturing [4,5]. The technological advancement in electronic industry is posing a new environmental challenge in the form of electronic waste, the electronic devices after their disposal into the soil are not processed properly which result in the accumulation of the toxic metals in the soil . Heavy metals present in the wastewater are persistent and non-degradable in nature . Presence of these metals in waste stream and ground water is one of the most environmental concerns since these metal ions are toxic to various life forms especially if their concentration is more than the accepted limit [8,9]. For the elimination of dissolved heavy metal ions, literature  is full of techniques that have been performed such as solvent extraction, ion exchange, membrane process, electro dialysis, precipitation, phytoextraction, ultra-filtration, reverse osmosis and adsorption. These methods, generally, are of
high cost with troubles such as incomplete metal removal, high reagent consumption, energy requirements and generation of toxic sludge or other waste products that need further disposal or treatment . Iron is commonly found in rocks and soil. Under suitable conditions, iron will leach into water resources. Iron concentration greater than 0.3mg/L causes water staining that negatively affects plumbing fixtures dishware and clothes and produce a yellow to reddish color in water appearance. These levels may also change the taste and odor of drinking water. This led many investigators to search for inexpensive substitutes such as zeolites, silica gel, chitosan, clay materials and agricultural wastes [12,13]. The adsorption technique remains the more favorable method because of its high capacity and low cost. During the past few years, several research articles were published reporting the successful use of different kinds of agricultural wastes for the removal of metal ions from aqueous solutions [14-17]. Such as Acacia leucocephala bark powder , Moringa oleifera bark (MOB) , cork waste biomass [20,21] rice straw , sugarcane bagasse waste [23,24], garden grass (GG) , castor leaf powder , green bean husk (GBH) , ficus carcia leaves , Avenafatua biomass . Fruit peels have been extensively used [30-34] for the same purpose including banana (Musa paradisiaca), lemon (Citrus
limonum) and orange (Citrus sinensis) peels . The present
study has been carried out to investigate the possibility of the use
of peels of water melons (Citrullus vulgaris) (WMP) powder as an
effective and efficient agricultural solid waste byproduct for the
removal of iron ions from aqueous solutions.
a) Standard Iron (II) solution (1000 ppm) Fe (II) stock solution
was prepared by dissolving 0.7016g of ammonium ferrous
sulphate (NH4)2SO4. FeSO4.6H2O, (Aldrich, USA) in DDW containing
5mL conc. H2SO4 and accurately dilute to volume in
100mL volumetric flask.
b) 1, 10 Phenanthroline (0.2%) Phenanthroline hydrochloride
or hydrate (phen), in 100mL volumetric flask 0.2gm
of phenanthroline are dissolved in doubly distilled water
(DDW) and diluted to the mark with 0.1M HCl.
c) Tri sodium citrate (10 %) solution in 100mL volumetric flask,
10g of tri sodium citrate are dissolved in doubly distilled water
(DDW) and dilute to the mark.
d) Hydroxylamine hydrochloride (10 %): 10g of hydroxylamine-
HCl are dissolved in DDW and diluted to 100mL.
Water melon peels (WMP) are collected from the agricultural
Egyptian fields. The white part of peels is cut, washed, air dried
and then are finely powdered in a mixer till being near the nano
size. The final product is applied as the crude peels powder for
the removal of iron from water samples according to the proposed
Lactic Acid Modified (WMP) powder
100g of the crude (WMP) powder are refluxed with 500mL
of 0.5M lactic acid solution over a boiling water bath for 6h. The
produced precipitate is separated, repeatedly washed with DDW
till free from acid then dried in an oven at 60oC for two hrs. After
cooling in a desiccator to room temperature, it is finely grinded
Tri sodium citrate Modified WMP powder
100g of the crude (WMP) are, similarly, refluxed with 500mL
of 0.5M tri sodium citrate solution over a boiling water bath for
6h. The produced precipitate is, similarly, separated, washed,
dried and grinded.
UV/Vis. Spectrophotometer (Shimadzu UV/Vis. Perkin Elemer
Lambada 3B Spectrophotometer using 1cm Quartz cell is
applied to determine the concentration of the residual iron ions
in the effluents after the application of the adsorption processes);
Flame Atomic Absorption Spectrophotometer AA 240FS,
Agilent Technologies, applied for the rapid and confirmation determination
of the concentration of iron ions; pH meter (The pH
measurements are carried by using the microprocessor pH meter
BT 500 BOECO, Germany, which is calibrated versus two standard
buffer solutions at pH4 & 9 and Mechanical Shaker (with up to
200rpm with speed control was used). The morphologies of the
prepared samples and composites are examined using Scanning
Electron Microscopy (SEM), FTIR spectroscopy Fourier transform
infrared spectra of crude and chemically modified (WMP) powder
forms are recorded with a Shimadzu FTIR spectrometer (resolution
4cm−1), equipped with highly sensitive pyroelectric detector
(DLATGS). The IR shows the structure morphology, nature of surface
hydroxyl groups, and adsorbed H2O.
The remaining iron in the solution is determined spectrophotometrically
after reduction to the Fe (II). In a 25mL volumetric
flask, add 0.5mL of the 10% hydroxylamine solution, 2mL 10%
tri sodium citrate solution and 5mL of the standard Fe (II) solution.
The pH is adjusted in the range 3-4. Add 2.5mL of 0.2% 1, 10
phenanthroline solution, dilute to the mark with DDW and mix
thoroughly. After 5min the absorbance of the solution is measured
at 512nm against a blank.
FAA spectrometric method: Flame Atomic Absorption Spectrophotometer
is used for the rapid and confirmation determination
of the residual concentrations of iron ions after carrying out
both the adsorption or the desorption procedures after making
appropriate dilutions. The solution is directly measured at λmax
equals 372.0nm with detection limit of 50μg/L using a mixture of
Acetylene - Nitrous Oxide flame.
To investigate the effect of pH on the uptake % (adsorption)
of iron from aqueous media by the crude (WMP) powder, aliquots
of 25 mL containing 20 ppm of the metal ion are transferred to a
group of 100 mL conical flasks each containing 0.1 g of the crude
adsorbent. Adjust the pH for each flask in the order ranging from
2-10, respectively by using 0.1M NaOH and HCl solutions and stir
for 1hr. Centrifuge the contents of each flask and determine the
remaining iron content in the supernatant solution. The sorption
percentage of the metal ion by the WMP powder is calculated by
Where Ci and Cf are the initial and final concentrations of metal
ion respectively. Biosorption capacity q (mg/g) is calculated by
Where Ci and Cf are the initial and final concentrations of
iron (ppm), Wt is the dose of sorbents (g) and V is the volume of
solution (mL). The optimum pH is adjusted to be in the range 4-7.
When the same procedure is parallel repeated using the sodium
citrate and lactic acid modified powders, the optimum pH is in the
range 5-6 in both cases.
Effect of temperature
The effect of temperature on the removal of iron ions by the
three modified (WMP) powdered forms are studied at different
temperatures between 30 and 70°C.
Aliquots of 25mL solution containing 20ppm iron are transferred
to a group of 100mL conical flasks. Adjust the pH for each
flask to the optimum value. Varying amounts of the crude (WLP)
powder in the range 50-350mg are added to each flask, respectively.
The mixtures are stirred for 1h. The remaining iron content
in supernatant soln. separated by centrifugation is determined
spectrophotometrically. The procedure is repeated with the other
two (WLP) modified powders.
A set of 100mL conical flasks, each of which is uploaded with
0.2g of the three (WMP) powder forms and aliquots of 25mL solution
containing 20ppm of iron at the optimum pH and the shaking
time is varied for different intervals of time (10-80min) for each
flask in its turn, respectively.
Metal ion concentration range
Applying the optimum conditions of the weight of (WMP)
powder, pH and stirring time in a group of flasks. Aliquots of
25mL solution containing varying concentrations of iron ions in
the range 10-100ppm are added to each flask, respectively. The
same procedure is applied, and the remaining iron content is determined
from which the uptake percent is calculated.
Optimum sample volume
Different volumes of iron sample in the range from 10-100mL
Bio sorbent production may be an added value to the agrowastes
and eventually reduces the agro-wastes management
problems over the world. Agro-materials usually have their composition
of lignin and cellulose as major constituents and may also
include other polar functional groups of lignin, which include alcohols,
aldehydes, ketones, carboxylic, phenolic and ether groups.
These groups can bind to some extent heavy metals by donation
of an electron pair from these groups to form complexes with the
metal ions in solution . During the past few years, several
research articles were published reporting the successful use of
different kinds of agricultural wastes in the removal of metal ions
from aqueous solutions. The use of plant’s peels is reported in literature
e.g., Ni (II) and Cd (II) removal from aqueous solution on
modified plantain peels , biosorption of cadmium and nickel
by grapefruit peels , biosorption of heavy metals present on
polluted water by using different waste fruit cortex, banana (Musa
paradisiaca), lemon (Citrus limonum) and orange (Citrus sinensis)
peel , biosorption of aquatic cadmium (II) on unmodified rice
straw , biosorption on peanut shell , equilibrium and kinetics
of biosorption of cadmium(II) , copper(II) ions by wheat
straw  and iron by green clover leaves . Watermelon’s
botanical name, Citrullus vulgaris, comes from the diminutive
form of citrus, referring to the color and shape of the fruit, and
vulgaris meaning common or ordinary fruit . Our thinking
was forwarded towards trying (WMP) fine powder as a low cost
adsorbent for the treatment of a real local problem viz., the existence
of iron (and manganese) in the ground water of some wells
at El-Wasta, a town which lies 35 Km to the north of Beni-Suef
The pH is directly related to the competition ability of hydrogen
ions with metal ions to active sites on the bio sorbent surface.
The results indicated low sorption efficiency at low pH values
(pH=2-3), this was attributed to the high concentration and high
mobility of H+, which are preferentially adsorbed instead of metal
ions. The removal efficiency of the sorbent is increased by increasing
the pH value until reaches its maximum uptake in the range
4-6 by the unmodified (WMP). The sodium citrate and lactic acid
modified (WMP) powders showed maximum adsorption at the pH
range 5-7. Heavy metal biosorption on the specific and nonspecific
bio sorbents is pH dependent; other researchers found that
an increase in adsorption is a result of increasing the pH of the
solution (Figure 1, Table 1).
Effect of temperature
Maximum adsorption recovery is obtained at 30 °C for the
three adsorbent forms. The uptake percentage decreased with the
increase in temperature suggesting that the adsorption process is
exothermic . As observed in (Figure 2, Table 2), tri sodium citrate
modified form gave better adsorption performance than the
crude and lactic acid forms. These results also proved that during
the adsorption process, no permanent chemical bonds are formed
Equilibrium time is one of the important parameters for selecting
a wastewater treatment system . The results show that
removal is slow in the first 10 min, then the adsorption % is gradually
increased till equilibrium is reached after 20 min for the unmodified
powder. While both the tri sodium citrate and the lactic
acid modified forms attained equilibrium after 15 min. The rate of
biosorption seems to pass through two steps, the first one is very
rapid surface biosorption, while the second is slow intracellular
diffusion (Figure 3, Table 3).
For a specific metal initial concentration, increasing the adsorbent
dose provides greater surface area and availability of
more active sites, thus leading to the enhancement of metal ion
uptake till reach equilibrium . For the unmodified powder, a
dose of 0.3 g sorbent can achieve an uptake of 90.5% of iron at
optimum pH conditions. While for the tri sodium citrate modified
form, a dose of 0.2 g achieved better uptake % of iron of 95.5%.
Correspondingly, 0.2 g of the lactic acid modified one achieved an
intermediate iron removal % of 92. (Figure 4, Table 4).
The initial metal ion concentration does a substantial force
to overcome all mass transfer resistances of the metal ions between
aqueous and solid phase . At lower concentrations the
adsorption sites utilize the available metal ion more rapidly in
comparison to higher concentrations where the metal ions need
to diffuse to the sorbent surface by intra particle diffusion. The
maximum metal uptake was 90.5 % in the case of the unmodified
(WMP) powder, 92.5% for lactic acid modified one and 95.5% in
the case of tri sodium citrate form at metal ion concentration of 20
ppm, (Figure 5, Table 5).
At optimum conditions the volume of 25 mL achieved the best
adsorption percentage with all tested (WMP) powders. It is clear
from the Table 6, it is clear that iron removal percentage decreases
with the increase of the volume.
The composition and topography of the studied adsorbents
have been characterized by FT-IR and SEM.
Infra-red spectroscopy: Figure 9 & 10 adepicts the FT-IR
spectrum of the unmodified (WMP) powder form. The broad band
in the region around 3425cm−1 is specific to the surface hydroxyl
groups of bonded carboxylic acid. The O–H stretching vibrations
occurred within a broad range of frequencies indicating the
presence of free hydroxyl groups and bonded O–H bands of
carboxylic acid, the -OH carbonyl and carboxylic groups have
been reported as very important sorption sites for metal ions.
The asymmetric C–H stretching of surface methyl groups usually
present on the lignin structure is observed at 2900cm−1. The
characteristic peaks because of the C-O group in carboxylic and
alcoholic groups are present at 1053cm−1 . The ionization of
both the carboxylic acid and hydroxyl functional groups present in
the structure of the adsorbent can be achieved by deprotonation
that allowing it to interact with metals more easily and therefore
provides the major biosorption sites for the removal of iron ions
from solutions . A broadening peak at around 1650cm−1 due to
carbonyl group peak is observed. This indicates the involvement
of both the hydroxyl and carbonyl groups in the adsorption of
iron. Figure 7 the presence of COO− of the carboxylate can be
attributed to the peak positions at 1452.30cm−1 and 1400.22cm−1.
Alkyl chains around are observed at 2920-2850cm−1. The peaks in
range 1000-1200cm−1 symbolize C-C and C-O stretching.
The Morphologies of the prepared adsorbents
This study revealed the micro porous structure of the adsorbent.
The SEM micrographs of (WMP) are as shown in Figures
9-11. The micrographs showed that the bio sorbent has a smoothening and irregular surface (Figure 9). A significant
change in the bio sorbent surface is observed after the modification
(Figure 11&12). A rough effect is perceived in (Figure 12) It
is observed as providing a large area for ion–surface interaction.
Different surface shapes of the bio sorbent may be due to its modification
with lactic acid and tri sodium citrate.
Selectivity of the adsorbent
Adsorption studies applying the three adsorbents under investigation,
proved that they are nonselective towards different
heavy metals that may be present in wastewaters as pollutants.
However, the non-selectivity of such types of adsorbents is frequent
in the literature; their tolerance is attributed to being low
cost and available. Current work in our laboratory is devoted for
the development and applications of selective and low-cost adsorbent.
Adsorption isotherm studies
For solid–liquid adsorption system, the adsorption behavior
can well be described as adsorption isotherm model, the adsorption
isotherm meaning the distribution of adsorbate molecules
among the solid phase and the liquid phase at equilibrium. Equilibrium
is said to be reached when the concentration of adsorbate
in bulk solution is in dynamic balance with that on the liquid adsorbate
interface. It is significant to study the adsorption behavior
in order to describe adsorption process using appropriate adsorption
Langmuir adsorption isotherm
The Langmuir isotherm model assumes a surface with homogeneous
binding sites, equivalent sorption energies, and no interaction
between the sorbet species . The equilibrium adsorption
data for the concentrations of iron ions is fitted into the linear
form of Langmuir’s isotherm equation, to determine the distribution
of iron ions between the adsorbent and solution according to
Where Ce is the concentration of the iron ions in solution (mg
L−1), Qe is the equilibrium concentration of iron ions on (WMP)
adsorbent (mg g−1), Qm and KL are Langmuir constants related to
sorption capacity and the rate of adsorption respectively. Maximum
adsorption capacity (Qm) is the monolayer capacity of the
adsorbent (mg g−1) and KL is the Langmuir adsorption constant.
A plot of Ce/Qe against Ce over the entire concentration range is
a straight line with a slope of 1/Qm and the intercept of 1/Qm KL.
The correlation coefficient (R2) values reported are very close to
1 indicating that the adsorption follows the Langmuir adsorption
isotherm. The quality of Langmuir isotherm can be determined
by the magnitude of a dimensionless constant RL known as the
separation factor expressed in equation (4):
where Co is the initial concentration of the iron ions in mg L−1
and KL is the Langmuir constant described earlier. The adsorption
process is favorable within the range 0 1, becomes linear when RL = 1, and the process is irreversible
when RL = 0. The value of RL for crude WMP is 0.0475 and
for forms modified with tri sodium citrate and lactic acid equal to
0.0408 and 0.0460 respectively; hence the adsorption process is
favorable (Figure 13, Table 7).
Freundlich adsorption isotherm
The Freundlich isotherm model applies to adsorption on heterogeneous
surfaces with the interaction between adsorbed molecules,
and the application of the Freundlich equation also suggests
that sorption energy exponentially decreases on completion
of the sorption centers of an adsorbent . The linear form of the
Freundlich adsorption Model equation (5):
Where Qe is the amount of iron ions adsorbed at equilibrium
per gram of the adsorbent (mg g−1), Ce is the equilibrium concentration
of the iron ions in the solution (mg L−1), and Kf and n are
the Freundlich adsorption model constants related to the adsorption
capacity and adsorption intensity respectively. Loge Qe is plotted
against loge Ce and a straight line obtained gave the intercept
of log Kf and the slope of 1/n. The numerical value of 1/n reported
is less than1, (Figure 13, Table 7).
Analysis of real samples
Water samples are collected from tap water, Bahr Youssef
water, ground water and Ibrahemia (stream)water; samples are
subjected to the adsorption procedure as explained previously
and the residual iron is analyzed by two methods of finish viz.,
colorimetry and AAS (Table 8).
Reusability of the adsorbent is tested by regenerating the
spent adsorbent following a modified literature procedure .
The adsorbed iron ions onto the three WMP surfaces are treated
with 25 mL 0.1M HCl and stirred for 1h. The amount of iron ions
remained in the solution after filtration or centrifugation is measured
using the mentioned spectrophotometric and/ the FAAS
methods and the percentage desorption (Rb) was calculated relatively
to the equation (6):
Where Ct is the experimental concentration in the solution at
time t (ppm), Ca is the adsorbed concentration of sorbate onto the
In strong acidic media at pH range (1.2-1.9) the three forms
of the WMP powder showed high desorption percentages, on increasing
the pH values desorption percentage decreases (Figure
11, Table 9).
The desorption percentages are gradually increased till equilibrium
is reached after 25 min in case of the crude WMP powder,
while the powders modified with lactic acid and tri sodium citrate
show equilibrium after 30min. A desorption value of 87% has
been recorded for the unmodified WMP powder, 92.5% for the tri
sodium citrate modified form and 89% for lactic acid one (Figure
14, Table 9).
Water melon peels powder (WMP) and its modified forms
proved to be potential bio sorbents for the removal of iron and
other co present heavy metals from aqueous solutions, being
available low-cost material. The proposed adsorbents were applied
on real water samples. The adsorption process is best described
by the Langmuir and Freundlich isotherm models. Results
of desorption investigations also, assured the possibility to regenerate
and reuse the bio sorbents once again.