Phosphate-ion Recovery from Wastewater with Polymer
Coated Zirconium Sulfate-surfactant Micelle Mesostructure
Niti Pitakteeratham
Candidate for the Degree of of Master of Engineering
Supervisor: Assoc. Prof. Hisashi Satoh
Division of Field Engineering for Environment
Introduction
Phosphorus (P) is an essential nutrient for living
organisms, which acts as a nutrient for growth, and it is
an essential material in many industries (Babatunde &
Zhao, 2010). The release of phosphate (PO43-) to
surface waters is of environmental concern, because it
enhances the growth of microorganisms in most
ecosystems, and therefore the cause of Eutrophication
resulting in deterioration of water quality (Chitrakar et
al., 2005). In addition, P resources are limited and there
have been some warning reports indicating that deposit
of high-grade P ores is likely to be depleted in the next
few decades due to excessive use. Thus, developing
processes for P recovery from wastewater is another
alternative choice for preventing P depletion and water
pollution.
The sorption reaction with solid adsorbents has been
largely used for the removal of undesired anions from
wastewaters and wastes (Koilraj & Kannan, 2009).
Zirconium Sulfate surfactant micelle mesostructure
(ZS) is an adsorbent which has used to treat arsenate
and selenite ions in wastewater (Takada et al., 2004).
Figure 1 shows structure of ZS, which has ability to
adsorb the elements in 5th column in periodic table.
Since arsenate and phosphorus are in the same column
in the periodic table, theoretically, the ZS powder must
also be able to apply to recover P. From this
hypothesis, the ability of ZS powder to adsorb PO43has been tested, and finally, whether PO43- can be
recovered from water samples with a very high
effectiveness will be investigated.
Figure 1: Structure of ZS
However, it was found the decomposition of the
ZS structure after desorption process, which led to the
non-reusable problem (Hanzawa et al., 2007).
Reduction in size was thought to be the problem of this
technology because this would lead to the reutilization
problem. To solve the problem, ZS powder has been
coated with polymer with the ZS/polymer ratio of 8 to
2 to stabilize its structure in order to prevent the
breakdown of the structure, and be reused repeatedly.
The objective of this study is to examine the adsorption
ability of polymer coated ZS (P-ZS) and to investigate
the applicability of P-ZS to recover PO43- from
wastewater.
Materials and Methods
ZS powder was prepared by following the procedure
reported in previous studies (Iwamoto et al., 2002).
Hexadecyl-trimethylammonium
bromide
(C16TMABr, template) was slowly added dropwise to 0.0485
g/L of Zr(SO4)24H2O solution. The mixture was
stirred overnight and then autoclaved at 110°C for 48
hours. After drying, it was ground into fine powder. ZS
powder was coated with polymer with the ratio of 8 to
2 by TEIJIN LITMITED Company
The experiments were carried in a batch test to
determine the adsorption capacity of P-ZS at various
PO43-concentrations. The experiments were conducted
at the pH range of 5-7 and room temperature (20-25°C)
for 2 hours. All the samples were analyzed by the
ascorbic method (Standard Methods for the
Examination of Water and Wastewater, 2005). For the
desorption test, the P-ZS adsorbing PO43- were treated
with sodium hydroxide (NaOH) to desorb PO43-. Before
using in the next batch, P-ZS weight was measured.
Since other anions are always present in wastewater,
the adsorption ability of typical 4 types of anions (i.e.,
carbonate (CO32-), acetate (CH3COO-), nitrate (NO-),
and chloride (Cl-)) was analyzed. The inhibition studies
were conducted by using 1 g of P-ZS in the solutions
including 10.5 mM of PO43-and one type of interfering
ion, respectively. Changes in the concentrations of both
ions were measured for 2 hours and the isotherm of
PO43- was compared with that of the pure PO43solution.
The continuous adsorption test was carried out by using
a transparent glass column of 3.5 cm diameter with 53
cm height with constant temperature at 25°C. 24.5 g
(corresponding 100 mL) of P-ZS was put into the
column. The solution of 30 mg PO43-/L was then fed
into the column with at a flow rate of 40 mL/h,
corresponding 2.5 h of retention time (the void
volume). Samples were collected at every one hour and
the PO43-concentrations were determined by using the
ascorbic method.
Results and Discussion
The adsorption process is explained by the ion
exchange of P-ZS (Wu & Iwamoto, 1998). For the
calculation in this study, the weight of polymer was
excluded, only the weight of ZS were considered.
Although at the beginning of the experiment the
amount of PO43- adsorbed in ZS was higher than P-ZS,
at the time 90 minutes, concentration of PO43- adsorbed
by ZS and P-ZS were tended to be equal (Figure 1).
The possible reason would be penetration of PO43through polymer might take several times to reach ZS
inside P-ZS.
90
80
70
60
For non-linear method, a trial and error procedure,
which is applicable to computer operation, was
developed to determine the isotherm parameters by
minimizing the respective coefficient of determination
between experimental data and isotherms using the
solver add-in with Microsoft's spreadsheet, Microsoft
Excel (Kumar, 2006). Figure 2 shows experimental
data and the predicted equilibrium curve using nonlinear method for the Langmuir-equilibrium isotherm.
50
40
30
20
10
ZS-50
ZS-100
P-ZS-50
P-ZS-100
0
0
50
100
150
Time (min)
Figure 2: ZS & P-ZS adsorption rate
In this study, isotherms were carried out to determine
the condition for maximum adsorption of PO43-onto PZS. The amounts of PO43- adsorbed by the P-ZS from
the solution at equilibrium (qe in mg/g) were computed
by equation (1)
qe =
(C 0 - C t ) V
M
(1)
Where C0 and Ct are the influent phosphate
concentration and the effluent concentration at time t,
respectively, V is the total volume of the aqueous
solution (mL) and M is the mass of the adsorbent (g).
Several isotherm models have been used to describe the
experimental isotherm data, and the two most
commonly used are Langmuir isotherm equation (2)
and Freundlich isotherm equation (3).
The isotherm curve for P-ZS was almost same as that
of ZS, indicating that polymer coating of ZS powder
did not affect the adsorption ability of ZS. At the low
sample concentration P-ZS absorbed almost 100% of
PO43-, but when the PO43- concentration of the sample
was higher, the adsorption efficiency tended to be
decreased (Jellali et al., 2010). Although the
concentration of PO43- varied in this experiment, the
amount of P-ZS used were 0.2 g at all batches, so the
saturation of the binding sites would be the reason to
explain this phenomenon.
400
Amount of phosphate adsorbed (mg/g)
Amount phosphate adsorbed (mg/g)
100
Langmuir isotherm can be linearized into at least four
different types. However the coefficient of
determination, r2, of all type calculated by linearized
Langmuir equation were varies, Table 1, so this mean
that the transformation of Langmuir equation into
linearized equations alters their error structure and may
also violate the error variance and normality
assumption of standard least squares methods (Ho,
2006).
350
300
250
200
150
ZS (exp)
P-ZS (exp)
ZS with Carbonate
P-ZS (cal)
ZS (cal)
100
50
0
0
1000
2000
3000
4000
5000
Phosphate concentration at equilibrium (mg/L)
qe =
qm bACe
1+ bACe
(2)
Where qe is equilibrium adsorbent-phase concentration
of adsorbate, (mg/g). qm is maximum adsorption
capacity (mg/g). bA is Langmuir adsorption constant of
adsorbate (L/mg).
qe = KCe1/n
(3)
Where KA is Freundlich
capacity factor,
(mg/g)(L/mg)1/n. 1/n is Freundlich adsorption intensity
parameter.
Figure 3: Adsorption isotherm curves for the powdered
ZS, P-ZS and P-ZS in coexistence of CO32Both adsorption data of ZS and P-ZS were better fit to
the non-linear method Langmuir model more than
Freundlich isotherm, with the maximum adsorption
capacity of 326 and 320 mg PO43-/g ZS in ZS and P-ZS
respectively, indicating that its follow Langmuir
theory. The good agreement of the Langmuir data
suggests that P-ZS has fixed numbers of accessible
sites, which were available on the surface, and had the
same energy. Moreover, adsorption is reversible
(Asano et al., 2007). The value of q m and b obtained
from Figure 2 are also shown in Table 1.
Table 1: Langmuir and Freundlich parameters for adsorption of PO43Equation
Parameter
linear ZS
nonlinear ZS
qm (mg/g-zs)
312.5
326.916
Langmuir
type 1
B (L/mg)
0.047
0.028
2
r
0.943
0.956
qm (mg/g-zs)
344.828
326.916
Langmuir
type 2
B (L/mg)
0.241
0.028
r2
0.956
0.956
qm (mg/g-zs)
233.030
326.917
Langmuir
type 3
B (L/mg)
0.112
0.028
r2
0.711
0.956
qm (mg/g-zs)
331.769
326.916
Langmuir
type 4
B (L/mg)
0.052
0.028
r2
0.939
0.956
30.953
27.445
Freundlich k ((mg/g)(mg/L)n)
n
3.083
3.083
2
r
0.917
0.924
160
Adsorption(mg-PO4/g-Ads)
Desorption(mg-PO4/g-Ads)
140
120
100
80
2
60
40
20
0
11
6 11
16
21
26
31
36
41
46
10
15
20
25
30
35
40
45
5
50
Number of Batch
Figure 4: P-ZS reusability data
However, the efficiencies of adsorption and desorption
of the P-ZS were still unstable so that desorption
amount sometimes exceeded the adsorption amount in
a batch test. The most probable reason would be
desorption of PO43-, which was adsorbed in P-ZS at the
previous adsorption process.
227.273
0.045
0.738
333.333
0.016
0.975
246.170
0.038
0.829
313.827
0.023
0.968
24.384
2.833
0.885
non-linear
P-ZS
320.703
0.016
0.978
320.704
0.016
0.978
320.704
0.016
0.978
320.704
0.016
0.978
20.744
2.833
0.897
5 shows the interference of other anions to the P-ZS.
CH3COO-, Cl-, and NO2- concentrations were almost
constant through the experiment which means that
these anions had no effect on the P-ZS adsorption
capacity. On the other hand, CO32- concentration
decreased gradually while the concentration of SO42increased sharply. It can be concluded that CO32- can be
adsorbed by P-ZS. By looking at the ZS mechanism,
PO43- was replaced with the SO42- in the ZS (Fig. 1) and
SO42- was then released out to the solution.
Concentration (mM)
Amount of Phosphate (mg/g p-ZS)
P-ZS was successfully used repeatedly in this
experiment for totally 50 times, and ability of
adsorption and desorption of P-ZS were shown in
figure 4. The maximum adsorption amount of PO43was 152 mg PO43-/g P-ZS and the highest desorption
amount of PO43- was 95 mg PO43-/g P-ZS.
linear P-ZS
Sulfate
Chloride
Carbonate
Acetate
Nitrate
1.5
1
0.5
0
0
30
60
90
120
Time(min)
Figure 5: Change in the interfering anion
concentrations over time in the batch experiment with
P-ZS.
After used for 50 times, the cumulative adsorption and
desorption amounts of PO43-were calculated. P-ZS
adsorbed almost 4000 mg PO43- and almost 3500 mg
PO43- were recovered in desorption process. The P-ZS
was able to be reused for more than 50 times but at the
37th batch the P-ZS started to be broken. However,
there was no significant effect on the adsorption and
desorption abilities.
Since P-ZS could adsorb CO32-, carbonate interference
to PO43- adsorption were also examined. Figure 2 has
clearly shown that the presences of carbonate in the
system have a huge effect on phosphate adsorption. At
equilibrium, ZS adsorbed 349 mgPO43-/g ZS, while
only 201 mgPO43-/g ZS could be adsorbed, which
contributed to 58% removal efficiency, if there was
carbonate in the system. From this result, carbonate
removal is necessary before applied the P-ZS in order
to reach its maximum efficiency.
Since there would be other anions rather than PO43- in
the reject waters (Takabatake et al., 2004), the other
anions competition experiment was conducted. Figure
Figure 6 shows breakthrough curve of PO43- in a
continuous mode operation using the column packed
with P-ZS. After water sample contain phosphate ion
100
98
96
94
92
90
88
86
84
82
80
5
Concentration (mg/L)
4.5
4
3.5
Concentration (mg/L)
3
2.5
Efficiency (%)
2
1.5
1
0.5
0
0
100
200
Removal Efficiency (%)
pass through the column packed with P-ZS (100ml,
24.5g), the concentration of phosphate in treated water
was reduced to its minimum value. Theoretically,
breakthrough is thought to be occurred at which the
effluent concentration reaches 5 percent of the influent
concentration [3].
300
Throughout Bed Volume (BV)
Figure 6: Continuous mode adsorption for phosphate
onto P-ZS
The influent solution containing 30 mg PO43-/L was fed
at the rate of 40 mL/h. Up to now, totally 40 liters of
the PO43- solution has been applied to the column (280
times of the volume of the P-ZS) and the PO43- removal
efficiency is still higher than 90%. Approximately 1200
mg PO43- has been adsorbed.
Conclusion
P-ZS was successfully used to recover phosphate ion
from the water with the reusable time for more than 50
times. From the non-linear Langmuir equation, the
maximum adsorption amount of ZS was 320 mg/g-ZS,
and 320.703 mg/g-ZS for P-ZS. If there was presence
of carbonate ion in the sample, the removal efficiency
dropped to 58% as compared with that without
carbonate ion. Therefore, this technology is one of the
applicable process to apply to wastewater treatment
plant to remove phosphorus efficiently, and be able to
reuse inform of phosphate solution.
Acknowledgement
This research was carries out with support from TEIJIN
LIMITED Company who supports to coat ZS with
polymer.
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