Removal of water hardness causing constituents using alkali

International Journal of Environmental Monitoring and Analysis
2015; 3(1): 7-16
Published online January 13, 2015 (http://www.sciencepublishinggroup.com/j/ijema)
doi: 10.11648/j.ijema.20150301.12
ISSN: 2328-7659 (Print); ISSN: 2328-7667 (Online)
Removal of water hardness causing constituents using
alkali modified sugarcane bagasse and coffee husk at
Jigjiga city, Ethiopia: A comparative study
Adhena Ayaliew Werkneh1, *, Angaw Kelemework Abay1, Anbisa Muleta Senbeta2
1
2
Department of Chemistry, College of Natural Science, Jigjiga University, PO. Box: 1020, Jigjiga, Ethiopia
Department of Food Science and Nutrition, College of Dryland Agriculture, Jigjiga University, PO. Box: 1020, Jigjiga, Ethiopia
Email address:
adhena1988@gmail.com (A. A. Werkneh)
To cite this article:
Adhena Ayaliew Werkneh, Angaw Kelemework Abay, Anbisa Muleta Senbeta. Removal of Water Hardness Causing Constituents Using
Alkali Modified Sugarcane Bagasse and Coffee Husk at Jigjiga City, Ethiopia: A Comparative Study. International Journal of Environmental
Monitoring and Analysis. Vol. 3, No. 1, 2015, pp. 7-16. doi: 10.11648/j.ijema.20150301.12
Abstract: Alkaline modified sugarcane bagasse and coffee husk were used for the adsorption of water hardness causing
constituents (Ca+2 and Mg+2). The water hardness sample was collected using polyethylene bottle from Jigjiga city drinking
water supply, Ethiopia. The adsorbents were characterized using FTIR and BET surface area techniques. The concentration of
the constituents were determined using AAS Spectroscopy. It was found that, using the ABC and ACHC as an adsorbent, the
maximum sorption capacity obtained for Ca and Mg hardness adsorption are 46.8 and 37.35, and 52.9 and 41.23 mg g-1 for
ACHC and ABC respectively. Activated carbon filtration also depends on various parameters such as pH, contact time,
adsorbent dose, temperature and initial Ca and Mg ion concentrations. The maximum recovery of the adsorbed calcium and
magnesium was achieved in less than 200 minutes leading to 78% and 73% respectively. After treating synthetic water solution
simulating an actual water stream with the alkali-modified bagasse and coffee husk, total hardness of the treated sample meets
the required standard for drinking water, below 60 mg/L of CaCO3. Therefore, ABC is more suitable for the removal of
hardness ions than ACHC from drinking water; and are considered as effective low cost adsorbents.
Keywords: Water Hardness, Activated Carbon, Bagasse, Coffee Husk
1. Introduction
Quality of water is one of the most important natural
resources of the world. It plays a vital role in the
development of communities; hence a reliable supply of
water is essential. It needs to be maintained all the time for
human and industrial use. As for human consumption,
quantity and quality of drinking water have been recognized
as increasingly critical issues. Addressing the deterioration of
water quality in developing countries, where an estimated
one billion people lack access to potable quality water, is a
primary motivating factor for many community development
efforts and is a key component of the Millennium
Development Goals [1]. The provision of safe water to the
people is an urgent development priority of any country in
the world [1], [2].
Most of the water resources should be treated for
purification before consumption. In some countries,
groundwater is the main safe drinking water resource [1]. In
some cases, the resource does not satisfy to the desirable
levels regarding their chemical properties, such as hardness,
nitrate contamination, heavy metals, soluble iron, etc. [2].
Among them, water hardness can appear problematic in some
cases; it can also be considered as an important aesthetic
parameter. However, because public acceptance of hardness
differs remarkably according to local conditions, a maximum
acceptable level has not been defined. In general, water
supplies with total hardness higher than 200 mg/L can be
tolerated by consumers but are considered as poor resources;
while values higher than 500 mg/L are not acceptable for
most of the domestic consumptions [3], [4].
Recently, various methods including electro deionization
process, electro membrane processes, capacitive deionization,
membrane and fluidized pellet reactor, ion exchange process
and adsorption have been studied for the removal of a wide
variety of ionic and molecular species from various water
8
Adhena Ayaliew Werkneh et al.: Removal of Water Hardness Causing Constituents Using Alkali Modified Sugarcane Bagasse and
Coffee Husk at Jigjiga City, Ethiopia: A Comparative Study
streams, including those responsible for hardness (e.g. Ca+2
and Mg+2 cations). Amongst the developed processes,
adsorption has been widely studied for the uptake of various
ionic and molecular species from water [6]-[8].
In an effort to reduce the proportion of people without
sustainable access to safe drinking water, there is a need to
optimize the production of activated carbon from locally
available wastes and apply it for water treatment in diverse
communities. This has led to the development of alternative
low-cost technologies such as activated sugar cane bagasse
for the treatment of drinking water in the developing world.
Research has also been focused on the indigenous production
of water treatment chemicals using locally available raw
materials [1]. Carbon adsorption offers significant advantages
including low cost, availability, profitability, ease of
operation and efficiency in comparison with conventional
methods especially from economically and environmentally
points of view [4],[5].
In countries with poor economic base, the high cost of
importing the water treatment chemicals prevents
consistently good drinking water quality being achieved in
many cases. The activated carbon has been widely used
worldwide as an effective filtration or adsorption material for
removing chemical contaminants from drinking water. In
most developing countries, the activated carbon is imported
at high cost, limiting the quantities of safe drinking water
available to the people. The high cost of importing the
activated carbon puts a significant burden on the water
treatment budget since foreign currency is scarce [6],[7]. The
main aim of the study was to apply activated carbon prepared
from coffee husk and bagasse wastes in drinking water
treatment and assess the efficiency of the carbons in the
purification of hardness of water as a function of operating
parameters [3].
2. Materials and Methods
2.1. Description of the Study Area
Jigjiga is a city in eastern Ethiopia and the capital of the
Somali Region of the country. The city is located in the
Jigjiga Zone approximately 80 km (50 mi) east of Harar and
60 km (37 mi) west of the border with Somalia. The city has
an elevation of 1,609 meters above sea level and are found
with coordinates of 9°21′N42°48′E. The climate of Jigjiga is
a subtropical highland climate (Köppen climate
classification), with the influence of mountain climate, with
hot and dry summers and cold winters. The temperature
range of the city was between 25 and 29 oc. As of 2008,
Jigjiga has about 34.1% of the total population has access to
drinking water from underground water
Figure 1.1. Map of the study area.
International Journal of Environmental Monitoring and Analysis 2015; 3(1): 7-16
9
Figure 1.2. Shows (A) Raw sugarcane bagasse, (B) Alkali activated carbon, (C) Raw Coffee Husk.
2.2. Chemicals and Solutions
Apparatus and instruments: pH meter (MP 220,
METTLER
TOLEDO),
FTIR
spectrometer,
AAS
spectrophotometer (BUCK SCIENTIFIC MODEL VGP210,
USA), Rotary Shaker (VRN - 480, GEMMY Orbit Shaker,
Taiwan), Balance (OHAUS, E11140, Switzerland),
Desiccators, Electrical mill (IKA-WERKE, M20 GMBH &
CO.KG, GERMANY), Filter Paper (Whatman 542, 90 mm
diameter), Sieve no of different size (IMPAOT, UK),
Deionizer, hot air Oven (OV150CGENL ABWIDNES,
England).
2.2.1. Reagents and Chemicals
Analytical grade CaCl2 and MgSO4. 7H2O purchased from
Avishkar LAB TECH CHEMICALS, LOT which were used
as a model compound to stimulate the total hard water,
Sulphuric acid (H2SO4) purchased from Reagent chemical
service limited Company, Runcorn Cheshire used to activate
bagasse and coffee husk, Sodium hydroxide (NaOH) from
Avishkar LAB TECH CHEMICALS, LOT used to adjust the
pH, HCl from Reagent chemical service limited Company,
Runcorn Cheshire used for titration, Sodium Chloride (NaCl)
purchazed from TITAN BIOTECH LIMITED, BHIWADI
which was used for titration in Sear’s surface area analysis.
All experiments were conducted according to the standard
methods for the examination of water and wastewater [21].
2.2.2. Sampling and Sample Collections
Tap ground water samples were collected in clean 1000 ml
plastic bottles. The containers were first washed with deionized water, and then several times with the sample water
before collection in order to avoid any contamination. The
samples were then carried in ice-packed coolers to the
laboratory for analysis within 24 hours.
2.3. Collection and Preparation of Adsorbent
Raw Sugarcane Bagasse and coffee husk were collected
from Wonji sugar factory and coffee refinery S. C in Ethiopia,
which are collected as a waste. The samples were soaked for
24 hours and washed with distilled water before use in order
to remove any impurities. Raw sugar cane bagasse sample
was boiled for 30 min to remove remain soluble sugars. They
were kept in drying oven maintained at 105 oC for a period of
24 hours. The dried materials were grounded with electrical
grinder to get the desired particle size of 500 µm. Then, they
were treated with concentrated sodium hydroxide, 2 M
NaOH for 24 hours at room temperature with the ratio of 1:1
(base to carbon ratio) then stirred for 30 min and left for
overnight. The purposes of treating carbon using 2 M NaOH
were to create a suitable environment for its ring opening
which increase the number of adsorption sites. Finally, the
treated carbons were washed with distilled water to remove
excess bases and any other soluble substances before the
sample were dried in Furnace and adjusted its pH to about
6.5. These materials are referred as activated Sugarcane
bagasse and coffee husk. All experiments were conducted
according to the standard methods for the examination of
water and wastewater.
2.4. Batch Filtration Experiments
All experiments were conducted in batch mode in 250 mL
conical flasks. Several operating parameters including pH (210), temperature (10-50 oC), adsorbent mass (2-10 g/L),
initial calcium and magnesium concentrations (40-120 mg/L)
and contact time (40-120 minutes) were investigated.
Optimized adsorption times for modified adsorbents were
first examined by varying the contact time at room
temperature, pH= 6.0 and for an adsorbent mass of 2 g per
liter of solution. For this purpose, 2 g of adsorbent were
added to 1 L of solution in a conical flask containing Ca+2 or
Mg+2 cations at a concentration in the range of 40 to 120
mg/L. The mixture was then shaken at 200 rpm.
The removal efficiency (%R) and sorption capacity (Qe)
was determined as follows (Eq. 1 and 2):
R(%)=[(Ci-Ce)/Ci ]×100
(1)
Qe (mg/g) = [(Ci-Ce)/m]V
(2)
Where, Co and Cf are the initial and final concentration of
metal in solution (mg l-1), V is the volume of solution (l) and
m is the mass of sorbent (g).
After investigation of the effect of the contact time and the
initial ion concentration, the effects of pH and adsorbent
mass were examined. The effect of temperature was then
investigated in the optimal conditions for pH, adsorbent mass
and contact time, for three initial concentrations of Ca+2 or
Mg+2 cations (60, 120 and 180 mg/L). All the experiments
had performed in duplicate and the mean values were
10
Adhena Ayaliew Werkneh et al.: Removal of Water Hardness Causing Constituents Using Alkali Modified Sugarcane Bagasse and
Coffee Husk at Jigjiga City, Ethiopia: A Comparative Study
reported.
Analysis of the Adsorbate Solution:
Spectrophotometric measurements were carried out using
Atomic Absorption spectrophotometer using calcium and
magnesium hollow-cathode lamp at respective wavelengths
and an air/acetylene flame with strict adherence to standard
calibration guidelines.
Characterization of Adsorbents: In order to understand
the mechanism of the sorption, large quantities of work was
done to investigate the influence of the sorption process
using different kinds of techniques. Fourier Transform
Infrared (FTIR) Spectroscopy analysis was conducted at
Ethiopia Pharmaceutical Factory, Addis Ababa, Ethiopia
which is used to asses functional groups of the adsorbents.
Determination of BET surface area: The specific surface
areas of the adsorbents were determined using the Sear’s
method (1956). For this 1.5 g of modified adsorbents were
acidified with 0.1 M HCl to pH value of 3-3.5. The volume
in the beaker was made to 150 ml with distilled water after
addition of 10.0 g of NaCl. Titration was then carried out
with 0.1 M of NaOH to pH value of 4.0 and then to pH value
of 9.0. The volume V (ml), required to raise the pH from 4.0
to 9.0 was noted and the specific surface area was computed
from the following equation [20].
S(m2/g) =32V-25
(3)
Determination of the zero point charge: The zero point
charge was determined using 0.01 M solution of NaCl as an
electrolyte and by adding 0.1 M solutions of HCl. For this
purpose, the pH of eight beakers containing 50 mL of
electrolyte was set to the desirable values in the range of 2 to
12. Then 2 gram of adsorbent was added into each beaker
and shaken for 48 hours. After completion of the reaction, the
adsorbent was filtered and the final pH of each beaker was
measured. By plotting the initial pH versus the pH after 48
hours of agitation, the zero point charges of the adsorbents
were determined, which were found to be 6.5 for modified
bagasse and coffee husk.
2.5. Regeneration of the Spent Adsorbents
Regeneration tests for saturated modified adsorbents were
carried out by adding 2 g/L of spent adsorbent in 2 M
solution of NaOH. For adsorbent saturation, 2 g/L of
adsorbent were let in contact with 250 mL solution
containing 100 mg/L calcium or magnesium and stirred at
200 rpm until equilibrium time was reached (120 minutes).
The spent of the adsorbents were filtered, washed and dried
at 55 oC for 24 h. The dried spent adsorbents were let in
contact of 2 N NaOH for 2 hours; then filtered, washed
several times with deionized water and dried at 55 0C for 24
h. The regenerated adsorbents were then tested for the
adsorption of calcium and magnesium and the regeneration
percentage were calculated based on the comparison of the
removal efficiencies of fresh and regenerated adsorbents.
3. Result and Discussion
3.1. Adsorbent Characteristics
The various physical and chemical characteristics of the
AC for both coffee husk and bagasse are represented in table
3.1.
Table 3.1. Physico-Chemical properties.
Parameters
pHzpc
BET (m2/g)
Mesh size
ABC
7.58
546.6
500µm
ACHC
103
410
500µm
The modified adsorbents were characterized by means of
instrumental techniques called Transform Infrared
spectroscopy (FTIR) and BET surface area.
The specific surface area of the adsorbents was measured
using the BET technique. It showed a significantly higher
specific surface area for the ABC and CHC, 546.60 and 410
m2/g respectively. The remarkable improvement of the
surface area can most likely be attributed to the removal of
components occupying the pores of the AC resulting in more
accessible pores and consequently larger surface area.
3.1.1. Infrared Spectral Analysis
The adsorption of Ca and Mg ions on bagasse and coffee
husk were also affected by other interactions between
functional groups of Ca and Mg and bagasse, coffee husk in
addition to electrostatic interaction. FTIR analyses were
conducted in order to identify possible locations for these
interactions. The result is presented in figure 3.1 (a and b). As
it can be seen, the FTIR spectra of Ca and Mg ions, bagasse
and coffee husk and after adsorption are discussed below.
3.1.2. FTIR Spectra of Bagasse
FTIR spectra of bagasse has a broad band centered
between 3154.63 cm-1 and 3334.98 cm-1 ( hydrogen bonded
OH), the band at 2853.73 to 2954.03 cm-1( –CH2 and –CH3
asymmetric and symmetric stretching), the peak at 1774.54
cm-1 (associated with C-O carbonyl), the peaks at 1590.34
cm-1 and 1462.07 cm-1 (associated with the aromatic ring of
lignin) and the large peak at 1022 to 1249.89 cm-1 (associated
with the C-O bond bending of cellulose). FTIR spectra of
SBC show peaks at 3568.37 cm-1. This could be due to (N-H
stretching), 1590.34 cm-1(N=N stretching), 1462.07 cm-1
(aromatic C-C stretching), and 1377.20 cm-1 (S-O bending).
International Journal of Environmental Monitoring and Analysis 2015; 3(1): 7-16
Figure 3.1. (a) FTIR spectral analysis of AC from Sugar cane bagasse.
Figure 3.1. (b) FTIR spectral analysis of AC from coffee husk.
11
Adhena Ayaliew Werkneh et al.: Removal of Water Hardness Causing Constituents Using Alkali Modified Sugarcane Bagasse and
Coffee Husk at Jigjiga City, Ethiopia: A Comparative Study
3.1.3. FTIR Spectral Analysis of Coffee Husk
The FTIR spectral analysis shows that several functional
groups are available on the surface of coffee husk for binding
hardness causing agents hardness causing divalent ions. The
result was shown in fig 3.2 (b), Wavelengths corresponding
to their respective functional groups. Therefore, the
wavelengths appeared in the graph i.e. 3431, 2925, 1726,
1652 and 1450 indicates the applicability of –OH, -CH, C=O,
C=C, -COO respectively. The FTIR spectra obtained for the
activated coffee husk samples are shown in Fig. 1. The broad
band at about 3400 cm−1 included many vibration modes
mainly attributed to -OH groups with a minor contribution of
-NH functional groups. The presence of methyl and
methylene groups is confirmed by the two sharp peaks at
2925 cm−1 and 2855 cm−1 attributed to asymmetric and
symmetric stretching of C- H bonds in aliphatic chains.
The peaks located at 1737 and 1633 cm-1 are
characteristics of carbonyl group stretching from cellulose
and ketones. The presence of -OH group, along with carbonyl
group, confirms the presence of carboxylic acid groups in the
biosorbent. The peaks at 1508 cm-1 are associated with the
stretching in aromatic rings. The peaks observed at 1071 and
1024 cm-1 are due to C-H and C-O bonds. The -OH, -NH,
carbonyl and carboxylic groups are important sorption sites.
3.2. pH Point of Zero Charge
The point of zero charge of the adsorbent ABC and ACHC
were assessed from the graph of final pH versus initial pH for
0.5 g of the adsorbents. The results are presented in figure 3.2
(a and b). As shown from the graphs, the values of pHpzc of
an adsorbent are determined from the points where the initial
pH equals the final pH. The pHpzc values are 7.50 and 8.103
for ABC and ACHC respectively. As presented in the graphs
it seems that, the adsorbents were negatively charged at pH
greater than the pHpzc and below pHpzc there was a charge
reversal.
12
10
4
2
2
4
6
8
10
12
In itia l p H
F ig . p H z e ro p o in t c h a rg e (p H z p c ) fo r A C H C
Figure 3.2. (b) pH point zero charge (pHpzc) for ACHC.
It has been reported by earlier researchers that, the pHpzc
of an adsorbent increases with increase in basic groups on the
surface of the adsorbents [19]. This is due to that, the
adsorbents have basic surfaces since the pHpzc values is
greater than 7.
From the results, it can be concluded that alkali
modification of the adsorbent gave a negative (basic) surface
charge for the adsorbent. The relationship between pHpzc
and adsorption capacity is that cations adsorption on any
adsorbent will be expected to increase at pH value higher
than the pHpzc while anions adsorption will be favorable at
pH values lower than the pHpzc [21].
3.3. Batch Activated Carbon Filtration
In the present study, alkali treated bagasse and coffee husk
are used as an adsorbent for water hardness causing
constituents from aqueous solutions and polluted water.
Based on the results obtained, the effects of these parameters
are discussed in the subsequent sections.
98
A C fr o m b a g a s s e
A C fr o m c o ffe e h u s k
97
12
96
95
% of Softening
10
Final pH
8
6
In it ia l p H
F in a l p H
14
In itia l p H
F in a l p H
14
Final pH
12
8
6
94
93
92
91
4
90
2
89
20
2
4
6
8
10
12
40
60
80
100
120
140
160
In itia l C a io n c o n c e n tr a tio n (m g /l)
In it ia l p H
Figure 3.2. (a) pH point zero charge (pHpzc) for ABC.
Figure 3.3. Effect of initial Ca hardness concentrations on softening
efficiency (2 g adsorbent, pH 6.5, room temperature, agitation speed 200
rpm.
International Journal of Environmental Monitoring and Analysis 2015; 3(1): 7-16
Effect of the contact time and initial hardness agent
concentration: The effects of the initial calcium and
magnesium concentrations and the contact time on the
softening efficiency of ABC and ACHC are illustrated in
figure 3.3. As it can be seen, adsorption efficiency was
improved by increasing the contact time and decreased by
increasing the initial ions concentration.
94
A C fro m b a g a s s e
A C fr o m c o f fe e h u s k
93
% of Softening
92
91
90
13
The optimum time observed for removal of 96.1% and
93.4 % of Ca and Mg hardness were 120 min. There was no
appreciable increase in percentage removal of total hardness
after these optimum times. As shown in Figure 3.4(b) and 3.5,
the adsorption process took place in two stages. The first
stage was rapid. This may be due to that, at the start large
number of vacant surface site may be available for adsorption
process. The second stage represented a slower progressive
adsorption. The reason is that, the remaining vacant surface
sites may be exhausted due to repulsive forces between the
solute molecules of solid and bulk phase [24],[26]. With the
progressive occupation of these sites, the process becomes
slower in the second stage. Moreover the initially deposited
metal ions penetrate to the interior of the sorbent through
intra-particle diffusion which was slower process. This was
similar with the observations of other studies [21], [24,].
89
A C fr o m b a g a s s e
A C fr o m c o ffe e h u s k
90
88
80
40
60
80
100
120
140
160
In itia l M g io n c o n c e n tr a tio n (m g /l)
Figure 3.4. (a) Effect of initial Mg ion concentrations on softening efficiency
(2 g adsorbent, pH 6.5, room temperature, agitation speed 200 rpm.
Accordingly, for an initial metal concentration of 120
mg/L, 97% and 94.1% of calcium and 90.8% and 93.3% of
magnesium were adsorbed by ABC and ACHC respectively,
showing for both adsorbents a higher affinity for calcium
over magnesium. Furthermore, alkali modification of both
adsorbents improved the adsorption capacity toward both
tested cations.
The effect of contact time on Ca and Mg ions was
investigated by varying the contact time (30-150 min), while
other parameters were kept constant. The result is presented
in figure 3.4 and 3.5. As it can be seen in the figure, softening
efficiency increased with an increasing in contact time before
equilibrium is reached and after equilibrium removal
efficiency would be constant.
A C fr o m b a g a s s e
A C fr o m c o ffe e h u s k
100
90
% of Softening
80
70
60
50
40
30
20
40
60
80
100
120
140
160
C o n ta c t t im e (m in u te )
Figure 3.4. (b) Effect of contact time on softening efficiency of calcium
hardness (2 g/L adsorbent, pH 6.5, room temperature, agitation speed 200
rpm and at 120 mg/l initial concentration
% of Softening
20
70
60
50
40
20
40
60
80
100
120
140
160
C o n ta c t tim e (m in u te )
Figure 3.5. Effect contact time on softening efficiency of magnesium
hardness (2 g/L adsorbent, pH 6.5, room temperature, agitation speed 200
rpm, 120 mg/l.
Surface adsorption and ion exchange can be considered as
the driving forces of ion removal. While bonding of metal
ions to the surface can be considered as the main mechanism
responsible for metal uptake by natural pumice, in addition to
surface adsorption, ion exchange can also be involved in the
case of the alkali-modified pumice leading to a remarkable
enhancement of the adsorption capacity [19]. Furthermore,
alkali modification can contribute to the removal of
impurities, which can unblock some pores improving
accessibility to the active adsorption and ion exchange sites
of the modified sample. Removal efficiency also showed an
increase with the initial metal concentration, which can be
attributed to an increase of the concentration gradient
increasing the driving force [24].
Effect of the pH and the adsorbent mass: The pH of the
solution should be considered as an important factor affecting
metal adsorption process due to its impact on the degree of
ionization of metal specie and the surface charge of the
adsorbent. The effect of pH of the reaction mixture on the
adsorption efficiency at various adsorbent doses was
examined in order to optimize the adsorbent dosage and the
pH. According to the results summarized in fig 3.6 and 3.7,
the highest adsorption capacity towards Ca+2 and Mg+2 ions
Adhena Ayaliew Werkneh et al.: Removal of Water Hardness Causing Constituents Using Alkali Modified Sugarcane Bagasse and
Coffee Husk at Jigjiga City, Ethiopia: A Comparative Study
was achieved at pH = 6.5 for ABC and ACHC and for all
tested dosages. This optimal pH was in accordance with the
zero point charge values (6.50 and 8.310 for ABC and ACHC
respectively).
A C fr o m b a g a s s e
A C fr o m c o ffe e h u s k
100
90
The removals of water hardness causing constituents by
ABC and ACHC at different dose (0.5 - 2.5 g) for the
constant Ca and Mg concentration of 120 mg/l are
investigated. Results are presented in figure 3.8 and 3.9. The
percentage removal of Ca and Mg increases from 37.0 to
96.2% with an increase in the activated bagasse and coffee
husk carbon amount from 0.5 to 2.5 g respectively. This is
due to the increasing of the adsorption sites available for
adsorption.
% of Softening
A C fr o m b a g a s s e
A C fr o m c o ffe e h u s k
100
80
90
70
80
60
50
2
4
6
8
10
pH
Figure 3.6. Effect of pH on softening of calcium hardness (contact time 120
min, ions concentration 120 mg/L, room temperature, 200 rpm agitation).
% of S oftening
14
70
60
50
40
30
100
0 .5
2 .0
2 .5
Figure 3.9. Effect of adsorbent dose on softening of magnesium hardness
(contact time 120 min, ions concentration 120 mg/L, room temperature, 200
rpm agitation).
80
% of Softening
1 .5
A d s o r b e n t d o s e (g )
90
70
60
50
A C fr o b a g a s s e
A C fr o m c o ff e e h u s k
40
2
4
6
8
10
pH
Figure 3.7. Effect of pH on softening of magnesium hardness (contact time
120 min, ions concentration 120 mg/L, room temperature, 200 rpm
agitation).
A C fr o m b a g a s s e
A C fr o m c o ffe e h u s k
100
90
80
% of Softening
1 .0
70
60
50
40
30
20
0 .5
1 .0
1 .5
2 .0
2 .5
A d s o r b e n t d o s e (g )
Figure 3.8. Effect of adsorbents dose on softening of calcium hardness
(contact time 120 min, ions concentration 120 mg/L, room temperature, 200
rpm agitation).
As it shows in fig 3.6 and 3.7 of the pH, 79 and 96% of
calcium and 51 and 93% of magnesium were removed by 2
g/L of the ABC and ACHC adsorbents, respectively. The
lower removal efficiencies observed in acidic medium (i.e.
pH in the range 2-5) can be attributed to the protonation of
adsorbent functional groups or competition of H+ with metal
ions to bind and occupy the active sites of the adsorbents. On
the other hand, in alkaline environment (i.e. pH in the range
7-10), the formation of metal hydroxide can be considered as
the main reason for decreasing metal uptake. Similar results
were reported [26]. The highest removal capacity at pH=7.5,
namely close to the zero point charges of both adsorbents,
confirms that the studied adsorbents can be considered as
promising low cost adsorbents suitable for the softening of
hardness ions from drinking water.
The linear increase of the adsorption capacity for
increasing adsorbent dosage indicated the accessibility of a
larger number of sorption sites at higher dosage to adsorb
calcium and magnesium ions. Contrarily, in the removal of
calcium using raw and modified sugar cane bagasse,
adsorption capacity remained constant above 100 mg
adsorbent.
Effect of the temperature: The temperature effect in the
range of 10 oC to 60 oC was studied and thermodynamic
parameters were calculated. As shown in Fig 3.10, while the
effect of temperature on magnesium adsorption seemed to be
negligible, a low maximum for the adsorption of calcium was
absorbed at 20 oc.
International Journal of Environmental Monitoring and Analysis 2015; 3(1): 7-16
under 8 cycles of adsorption and desorption (n) are presented
in fig 3.12 and 3.13. As the n increased, the percentage of Ca
and Mg recovered and adsorbent regeneration and also Ca
and Mg removal, until 4 of these cycles slightly decreased
and after that, until 8, sharply decreased. It is shown that
ABC and ACHC can be reused for softening/regeneration
processes; but after that, it loses its softening/regeneration
ability and its performance drops down.
94
93
% of Softening
15
92
A C fro m b a g a s s e
A C fro m c o ffe e h u s k
91
90
S o fte n in g e ffic ie n c y ( % )
% re c o v e ry
100
88
10
20
30
40
50
o
T e m p e ra tu re (K )
Figure 3.10. Effect of temperature on softening of Calcium hardness
(contact time 120 min, ions concentration 120 mg/L, 2 g adsorbents, 200
rpm agitation).
8 9 .0
8 8 .8
% Softening efficiency/% recovery
89
90
80
70
60
50
40
30
8 8 .6
1
2
3
4
5
6
7
8
9
n
8 8 .2
Figure 3.12. Successive softening/regeneration efficiency of Ca hardness.
8 8 .0
8 7 .8
S o fte n in g e ffic ie n c y ( % )
% re c o v e ry
100
8 7 .6
8 7 .4
90
8 7 .2
80
8 7 .0
10
20
30
40
50
o
T e m p e r a tu r e ( K )
Figure 3.11. Effect of temperature on softening of magnesium hardness.
3.4. Regeneration of the Saturated Adsorbents
Regeneration experiments were conducted to study the
reusability of the spent adsorbents, which is a very important
parameter in terms of economic feasibility of the developed
process. Regeneration using sulphuric acid solution was
carried out on the spent bagasse and coffee husk samples. As
it were shown in the figure below, maximum recovery of the
adsorbed calcium and magnesium was achieved in less than
200 minutes leading to 78 and 73% desorption of the
adsorbed calcium and magnesium at 97 and 93% of the
adsorbed calcium and magnesium from ABC and ACHC
respectively. Furthermore, maximum cation desorption for
saturated carbon were observed after 300 min of regeneration,
while only 200 min of regeneration was needed to achieve
maximum cation desorption of the saturated modified
adsorbent. It should be noticed that even if the modified
sugar cane bagasse showed higher sorption capacity for
calcium and magnesium rather than modified coffee husk, its
regeneration potential was lower than that of the activated
carbon from bagasse.
Generally, Ca and Mg recovery and adsorbent regeneration
% Softening/% recovery
% of Softening
0
A C fr o m b a g a s s e
A C fr o m c o ffe e h u s k
8 8 .4
70
60
50
40
30
0
1
2
3
4
5
6
7
8
9
n
Figure 3.13. successive softening/regeneration efficiency of Mg hardness.
4. Conclusion
Softening of hard water by removing Ca2+ and Mg2+
cations was studied using alkali-modified sugar cane bagasse
and coffee husk as adsorbents. Increasing the mass of
adsorbent, the contact time and decreasing the initial ions
concentration leads to an increase of cations removal. The
studied adsorbents showed a higher selectivity for calcium
adsorption if compared to magnesium in ABC than ACHC.
Both adsorbents are efficient to adsorb water hardness
causing constituents; but, ABC is more critical than ACHC.
After treating synthetic water solution simulating an actual
water stream with the alkali modified activated bagasse and
activated coffee husk, total hardness of the treated sample
met the required standard for drinking water.
16
Adhena Ayaliew Werkneh et al.: Removal of Water Hardness Causing Constituents Using Alkali Modified Sugarcane Bagasse and
Coffee Husk at Jigjiga City, Ethiopia: A Comparative Study
Acknowledgement
This paper was sponsored by Jigjiga University under
Research and Community Service Directorate as part of the
2014 funded proposal. I am grateful to Haramaya University
and Ethiopian pharmaceutical factory for their cooperation in
AAS and FTIR analysis and characterization respectively.
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