International Journal of Geosciences, 2013, 4, 24-29
http://dx.doi.org/10.4236/ijg.2013.45B005 Published Online September 2013 (http://www.scirp.org/journal/ijg)
Geosmin Sorpt ion on Cycl od ex trin Pol yme rs
Redel Gutierre z1,2, Niwooti Whangchai1, Nakao Nomura3
1Faculty of Fisheries Technology and Aquatic Resources, Maejo University, Sansai, Chiang Mai, Thailand
2College of Arts and Sciences, Central Luzon State University, Science City of Munoz, Nueva Ecija, Philippines
3Graduate School of Life and Environmental Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibarak, Japan
Received June 2013
ABSTRACT
Geosmin is one of the major causative compounds of earthy-musty odor and taste (off-flavor) in drink ing water (lakes)
and in farmed fish. In this study, the sorption of cyclodextrin polymers (CDPs) towards geosmin in aqueous solution
was investigated. Sorption kinetics, the effect of solution pH and contact time on the sorption capability of α-, β- and
γ-cyclodextrin polymers was discussed. Results disclosed that the sorption of geosmin by the CDPs followed the Ho
and McKay kinetic mechanism with the liquid film diffusion as the rate -determining step. Both β-CDP and γ-CDP ex-
hibit high removal efficiencies of 93.4% and 96%, respectively, within 240 minutes at 25˚C and pH 7, whilst α-CDP
was not effective, removing only 40% geosmin, at an initial concentration of 5 µg·L−1 and 5 g·L−1 of CDP dose. The
cyclodextrin polymers can adapt to a wide range of pH from 3.0 to 11.0 for geosmin adsorption with pH 7.0 as optimum.
Results indicate that these sorbents demonstrate significant potential in reducing the concentration of geosmin in water
that presents taint problems in both drinking water and f ish.
Keywords: Geosmin; Cyclodextrin Polymers; Water; Sorption Kinetics
1. Introduction
Off-flavor comprises one of the biggest problems in the
drinki ng wa ter industry and aqua cultu re . Geosmin (trans-
1, 10-dimethyl-trans-9-decalol) is a naturally occurring
germacranoid sesquiterpene, produced by several species
of cyanobacteria (i.e. Anabaena, Oscillatoria and Phor-
modium) and actinobacteria (especially Streptomyces)
that impart an earthy-musty odor to water and fish when
present at extremely low concentrations [1]. It is one of
the most common taste- and odor-causing compounds
found in drinking water supplies and in freshwater aqu a-
culture ponds.
The use of conventional treatment techniques such as
flocculation, sedimentation and filtratio n, for the removal
of geosmin from water are not effective [2]. Furthermore,
electrochemical, biochemical or photochemical degrada-
tion are effective processes but expensive. Adsorption is
a much better process, in terms of efficiency and econo-
my, than other physical techniques mentioned above. It is
one of two treatment methods that have been successful-
ly employed by water treatment plants to remove geos-
min, the other bei n g oxidati on by ozone .
Suitable adsorbents for water purification are conti-
nuously being developed and tested, and cyclodextrin
polymers (CDPs) are one of these materials. Several va-
riants of insoluble CDPs were intensively investigated
and were found to be very effective in the removal of
organic pollutants and heavy metals in water [3,4]. It is
well known that cyclodextrins polymers (α-, β- and
γ-cyclodextrins) form inclusion complexes with mole-
cules having a suitable size and shape. Other than surface
adsorption, the removal of organic pollutants from water
with CDPs occurs primarily via the formation of these
inclusion complexes [3]. In this paper, we report on the
application of CDPs (α, β and γ forms) in the removal of
geosmin from aqueous solutions.
2. Materials and Methods
2.1. Materials
Synthesized α-, β- and γ-CDPs were provided by Kankyo
Kougaku Co., Japan and were used without further puri-
fication. Geosmin standard solution (2,000 mg·L−1 in
methanol) was obtained from Sigma-Aldrich Chemicals
Co., USA. Working standard solutions for calibration
and spiking were prepared from standard stock solution
(100 mg·L−1) using Milli-Q water. Solid phase microex-
traction (SPME) fiber (50/30 µm) coated with divinyl-
benzene/carboxen/polymethylsiloxane (DVB/CAR/PDMS)
was purchased from Supelco Co. (Bellefonte, PA, USA).
All chemical reagents, including methanol and sodium
chloride crystals, used in this study were of analytical
grade (Labscan Asia Co. Ltd., Thailand).

R. GUTIERREZ ET AL.
25
2.2. Extraction and Analytical Methods
Residual geosmin in the spiked water samples was ex-
tracted using headspace SPME. A 50/30 µm DVB/CAR/
PDMS SPME fiber was extended into the headspace of
samples (10 mL aqueous solution) placed in a clear
20-mL straight-sided vial. Sodium chloride (1.9 g) and a
polytetrafluoroethylene (PTFE)-coated stirring bar were
added and the vial was sealed with an aluminum crimp
cap fitted with PTFE-faced silicone septum. Extraction
time was 15 minutes and extraction temperature was
maintained at 65˚C with vigorous agitation. Geosmin
concentration was quantitatively analyzed by gas chro-
matography-mass spectrometry (GC/MS) using a HP
6890 Network gas chromatograph equipped with a 5973
mass selective detector (Agilent Technologies, USA) by
desorbing the fiber in the injection port under a splitless
mode at 230˚C for 5 m inutes.
Specific surface area and pore size distributions were
determined by N2 gas adsorption using a Brunau-
er-Emme tt -Teller (BET) specific surface analyzer (Au-
tosorb-1-MP Quantachrome, USA). Morphological im-
ages of CDPs were acquired by SEM (JSM-5410LV,
JEOL, Japan).
2.3. Sorption Studies and Kinetics
Spiked standard geosmin solution (initial concentration:
5 ug/L) was prepared and pH-adjusted to 3, 7 and 11
using 1 M NaOH and 1 M HCl solutions. One-hundred
milliliters of spiked geosmin standard solution was
placed in a 250-mL conical flask, 500 mg each of dry
cyclodextrin polymer (α-, β- and γ-CDP) was added and
the flask securely covered. Three replicates were pre-
pared for each pH level. A blank (without CDP addition)
was included with each isotherm experiment to evaluate
sorbate losses by mechanisms other than sorption. Sorp-
tion batch experiment was conducted in a thermostat
horizontal shaker (WB14/SV1422, Memmert, Germany)
set at 25˚C with an agitation of 100 rpm. Samples were
collected at various contact times (0, 15, 60, 120 and 360
min) and filtered through a 0.45 µm membrane filter
(Advantech, Japan). Residual geosmin was quantified
using HS-SPME and GC-MS. The data obtained were
used to calculate the sorption capacity of the CDPs by:
0
()
e
e
VC C
qm
−
=
(1)
where, qe is the amount of geosmin adsorbed at equili-
brium (mol·L−1); C0 is the initial concentration of geos-
min solution (mg·L−1); Ce is the geosmin aqueous con-
centration at equilibrium (mg·L−1); V is the volume of
geosmin solution used (L); and m is the mass of the sor-
bent used ( g ).
3. Results and Discussion
3.1. Effect of Contact Time
The influence of contact time on the sorption of cyclo-
dextrin polymers toward geosmin is shown in Figure 1.
The sorption amount increased evidently with the in-
crease of contact time initially after the first 15 min.
Thereafter, the rate of geosmin sorption on the 3 CDPs
was found to be slow until the equilibrium was reached
and remained constant. Pseudo-equilibrium is achieved
after approximately 240 min with maximum geosmin
removals of 40%, 93.4% and 96% by the α-CDP, β-CDP
and γ-CDP, respectively. The results reveal that rapid
surface attachment (physical sorption) of geosmin onto
the polymers played a major role at the initial stage,
which consequently led to a fast initial geosmin removal
from the water especially for β-CDP and γ-CDP. With
time, the active sites on the polymers surfaces gradually
decrease and the sorption process becomes slow. Diffu-
sion of geosmin into the polymer network (via meso-
pores and micropores) possibly took place at this stage
causing the particles of CD Ps to slowly swell in the so lu-
tion, until the equilibrium was reached [5].
3.2. Effect of pH
The results presented in Figures 2(a) to 2(c) indicate that
sorption capacities of the CDPs slightly depend on solu-
tion pH. The sorption capacity varies slightly among the
3 pH values, which means that the CDPs can adapt to a
wide range of pH for geosmin sorption from water. The
values of the sorption capacity for geosmin on CDPs in
pH 7 are slightly higher than the other two pH solutions
and therefore, considered the optimal pH. The slight in-
crease at pH = 7 could be due to some of CDP may get
hydrolyzed, dissociated and reverted back to water-so-
luble cyclodextrin (CD), which in turn the geosmin mo-
lecule formed inclusion complex with CD, increasing the
sorption effect. Due to this reason the sorption capacity is
higher in p H = 7 [6].
Figure 1. Effect of contact time on the sorption of geosmin
(conditions: sorbent: 0.5 g; geosmin initial concentration: 5
µg·L−1; volume: 100 mL; temperature: 25˚C; pH = 7).

R. GUTIERREZ ET AL.
26
3.3. Sorption Kinetics
The model equation used for fitting geosmin adsorption
data was the Ho and McKay Model:
2
2
1
te e
tt
qq kq
= +
(2)
where, qt and qe are the amount of geosmin adsorbed at
time t and at equilibrium (mg·g−1), respectively; k2 is the
rate constant (g·mg−1·mi n−1). The values of k2 and expe-
rimental qe,expt were calculated from the intercept and
slope of the linear plots of t/qt against t (Figure 1(d)).
Table 1 shows the calculated qe,calc from Equation 1, the
results of kinetic fittings and the parameters associated
with Ho and McKay model as well as the regression
coefficients. Noteworthy are the high regression coeffi-
cients obtained from the plots and the high agreement
between the calculated qe,calc and the experimental qe,expt
values. This suggests the high applicability of the Ho and
McKay model in describing the sorption process. Ho and
McKay model follows the pseudo-second order mechan-
ism, confirming that sorption of geosmin on CDP was
complex, probably initially dominated by surface sorp-
tion (physical adsorption, hydrogen bonding) and the-
reafter, diffusion into the polymer network, chemisorp-
tions via the formation of an inclusion complex due to
the presence of the CD sites [7,8].
3.4. Rate Limiting Step in Sorption Process
To further interpret the sorption process, the moving
boundary model [9-11] was used to discriminate the rela-
tive importance of adsorption steps involved to play in
the pseudo-second order kinetic model. If the adsorption
process was controlled by liquid film diffusion, in-
tra-particle diffusion or chemical interaction, the rate
constant can be expressed by Equation (3), (4) and (5),
respectively.
ln(1 )kF=−−
(3)
23
13(1 )2(1)kFF=−− +−
(4)
13
1 1(1)kF=−−
(5)
where F is the adsorption fraction (qt/qe), and k is the
Table 1. Ho and McKay sorption kinetic parameters of
CDPs for geosmin (conditions: sorbent: 0.5 g; geosmin ini-
tial concentration: 5 µg·L−1; volume: 100 mL; temperature:
25˚C; pH = 7).
Sorbent
q
e,calc
(10−4)
(mg·g −1)
q
e,expt
(10−4)
(mg·g −1)
k
2
(g·mg−1·min−1) R2
α-CDP 4.0 4.1 2997.7 0.9869
β-CDP 9.3 9.5 162.3 0.9993
γ-CDP 9.6 9.7 492.5 0.9999
(a)
(b)
(c)
Figure 2. Effect of pH on sorption of geosmin on α-CDP (a),
β-CDP (b) and γ-CDP (c).
Figure 3. Ho and McKay plots for sorption of geosmin on
CDPs (D) (conditions: sorbent: 0.5 g; geosmin initial con-
centration: 5 µg·L−1; volume: 100 mL; temperature: 25˚C;
pH = 7).
0
20
40
60
80
100
0100 200 300 400
% Removal
Contact tim e, min
pH3
pH7
pH11
0
20
40
60
80
100
0100 200300 400
% Removal
Contact tim e, min
pH3
pH7
pH11
0E+00
2E+05
4E+05
6E+05
8E+05
1E+06
0100 200 300 400
Tim e /A mount adsorbe d
at t, t/q
t
, (min g mg
-1
)
Time, t(min)
α-CDP
β-CDP
γ-CDP

R. GUTIERREZ ET AL.
27
sorption rate constant. By plotting a linear relation ship of
k versus contact time t (min ) (Figure 4), the regression
coefficients (R2) for the three sorption steps were ob-
tained, of which the one with the highest R2 value was
assumed to be the rate controlling step [11]. Result
shows that the sorption of geosmin on the CDPs exhi-
bited the highest regression coefficients for Equ atio n (3)
(Table 2), indicating that liquid film diffusion was the
rate controlling step. Similar findings were reported by
Li et al. [5] who found that film diffusion, and neither
particle diffusion nor chemical interaction, was the rate
limiting step in the sorption process of CDPs for 2,4-
dichlorophenol. Noteworthy, geosmin has comparable
hydrophobicity with 2,4-dichlorophenol, having an oc-
tanol-water partition coefficient (log Kow) of 3.57 as
compared to the latter’s 3.06.
3.5. Sorption Capacity and Characteri st ics of
CDPs
The different extents of geosmin sorption among the 3
CDPs may be attributed to BET specific surface area,
pore size distribution and the inclusion effect between
the sorbent and the sorbate. However, previous studies
on CDPs [12,13] showed that BET specific surface area
does not play an important role in the sorption process,
which is in agreement with the BET result. BET surface
area and total pore volume of γ-CDP are larger than
α-CDP and β-CDP, so the sorption capacity of geosmin
on γ-CDP is higher than that of α-CDP and β-CDP.
However, α-CDP had the lowest sorption capacity among
the CDPs despite its higher surface area and total pore
volume than β-CDP (Table 3). Total pore volumes of the
CDPs are quite low which ranged from 0.0108 to 0.0139
cm3·g−1. SEM micrographs of the CDPs (Figure 5) show
their spherical morphologies with a rather smooth surface
and low porosity. The pore size distributions (Figure 6)
show that the observed pore sizes mostly varied between
1.5 and 10 nm. Pore sizes of 2 - 50 nm are classified as
mesopores, whilst pore sizes of less than 2 nm are mi-
cropores. The results also indicated that a large percen-
tage of the pores in γ-CDP (60%) were under 2 nm,
which are a favorite adsorption size for geosmin (and
2-methyisoborneol) according to previous reports [14].
The sized-matched structure of geosmin relative to these
pores could have contributed to γ-CDP’s high sorption
capacity. The sorption mechanisms of CDP are believed
Figure 4. Plots of Equations (1), (2) and (3) for geosmin sorption on CDPs.
Table 2. Regression coefficient (R2) fitted by moving boundary model for geosmin sorption on CDPs.
Sorbent Equat ion (3) (liquid film diffusion) Equati on (4) (intra-particle diffusion) E quation (5) (chemical interaction)
α-CDP 0.8879 0.7793 0.7242
β-CDP 0.9128 0.9096 0.8338
γ-CDP 0.8516 0.7873 0.7259
0
1
2
3
4
5
6
7
050100 150 200
Sorption Rate Constant, k
Time, t(min)
Eq. 3γ
Eq. 4γ
Eq. 5γ
Eq. 3β
Eq. 4β
Eq. 5β
Eq. 3α
Eq. 4α
Eq. 5α

R. GUTIERREZ ET AL.
28
Table 3. BET specific surface area and pore properties of CDPs.
Sorbent BET Surface Area, S (m2·g−1) BET C-constant Total pore volume, Vp (c m3·g−1) Average pore radius (Å)
α-CDP 3.07 14.09 0.0118 77.08
β-CDP 1.82 50.60 0.0108 121.70
γ-CDP 5.37 4.36 0.0139 51.94
Figure 5. SEM images of α-CDP (A) β-CDP (B) and γ-CDP (C).
Figure 6. SEM images of α-CDP (A) β-CDP (B) and γ-CDP
(C).
to involve physical sorption on surface and network, hy-
drogen bonding and inclusion complexation [15]. It is
possible that the inclusion effect was strongest in γ-CDP
and weakest in α-CD which is dependent on the molar
content of CD units in the CDPs.
4. Conclusion
The result of this study indicates that β-CDP and γ-CDP
are effective sorbents for the removal of the taste and
odor compound, geosmin, from water. The optimum pa-
rameters for equilibrium study at a 0.5 g sorbent dose are
time of contact 240 min and pH 7. Sorption kinetics of
geosmin by the CDPs followed the Ho and McKay mod-
el (pseudo-second order) and the rate limiting step in the
process of sorption was film diffusion. The high good-
ness of fitting for the pseudo-second order model could
be ascribed to the nature of cyclodextrin-based polymers
with multiple adsorption sites, which are responsible for
different adsorption steps. The differences in sorption of
geosmin by the CDPs could be attributed to the size-
match structure of geosmin relative to the polymers’
pores. Future work is required to evaluate the perfor-
mance of the CDPs’ in different types of natural waters
to further address the challenges facing the water and
aquaculture industries.
5. Acknowledgements
The authors thank the Kankyo Kougaku Co., Japan for
supplying the polymer materials. Support from the Fa-
culty of Fisheries Technology and Aquatic Resources,
and Institute of Product and Quality Standards in Maejo
University, Thailand and the Graduate School of Life and
Environmental Science, University of Tsukuba, Japan for
the laboratory instruments and research facilities are
greatfully appreciated.
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