Photocatalytic degradation of water taste and odour compounds in the presence of polyoxometalates and TiO2: Intermediates and degradation pathways

Article abstract of DOI:10.1016/j.jphotochem.2014.04.013

Geosmin (GSM) and 2-methylisoborneol (MIB) are produced by several species of cyanobacteria and actinomycetes. These compounds can taint water and fish causing undesirable taste and odours. Studies have shown that GSM/MIB are resistant in standard water treatments. Polyoxometalates (POM) are efficient photocatalysts in the degradation and mineralization of a great variety of organic pollutants, presenting similar behaviour with the widely published titanium dioxide (TiO₂). Photocatalytic degradation of GSM and MIB under UV-A light in the presence of a characteristic POM photocatalyst, SiW ₁₂O₄₀^4-, in aqueous solution has been studied and compared with the photodegradation by TiO₂ suspensions. GSM and MIB are effectively degraded in the presence of both photocatalysts. Addition of OH radical scavengers (KBr and tertiary butyl alcohol, TBA) retards the photodegradation rates of both compounds, suggesting that photodegradation mechanism takes place via OH radicals. Intermediates identified using GC-MS in the case of GSM and MIB, are mainly identical in the presence of both photocatalysts, also suggesting a common reaction mechanism. Possible photocatalytic degradation pathway for both GSM and MIB is proposed.

Full text of DOI:10.1016/j.jphotochem.2014.04.013

Journal of Photochemistry and Photobiology A: Chemistry 286 (2014) 1–9
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
Photocatalytic degradation of water taste and odour compounds in
the presence of polyoxometalates and TiO2: Intermediates and
degradation pathways
Theodora Fotioua, Theodoros M. Triantisa, Triantafyllos Kaloudisb,
Elias Papaconstantinoua, Anastasia Hiskiaa,∗
a Laboratory of Catalytic – Photocatalytic Processes (Solar Energy – Environment), Institute of Advanced Materials, Physicochemical Processes,
Nanotechnology & Microsystems, National Center for Scientific Research “Demokritos”, Athens 15310, Greece
b Quality Control Department, Athens Water Supply and Sewerage Company (EYDAP SA), Oropou 156, 11146 Galatsi, Athens, Greece
a r t i c l e i n f o
a b s t r a c t
Article history:
Geosmin (GSM) and 2-methylisoborneol (MIB) are produced by several species of cyanobacteria and acti-
nomycetes. These compounds can taint water and fish causing undesirable taste and odours. Studies have
shown that GSM/MIB are resistant in standard water treatments. Polyoxometalates (POM) are efficient
photocatalysts in the degradation and mineralization of a great variety of organic pollutants, presenting
similar behaviour with the widely published titanium dioxide (TiO2). Photocatalytic degradation of GSM
and MIB under UV-A light in the presence of a characteristic POM photocatalyst, SiW12O404−, in aque-
ous solution has been studied and compared with the photodegradation by TiO2 suspensions. GSM and
MIB are effectively degraded in the presence of both photocatalysts. Addition of •OH radical scavengers
(KBr and tertiary butyl alcohol, TBA) retards the photodegradation rates of both compounds, suggesting
that photodegradation mechanism takes place via •OH radicals. Intermediates identified using GC–MS
in the case of GSM and MIB, are mainly identical in the presence of both photocatalysts, also suggesting
a common reaction mechanism. Possible photocatalytic degradation pathway for both GSM and MIB is
proposed.
Received 9 December 2013
Received in revised form 15 April 2014
Accepted 17 April 2014
Available online 25 April 2014
Keywords:
Polyoxometalates
Titanium dioxide
Geosmin
2-Methylisoborneol
Photocatalysis pathway
© 2014 Elsevier B.V. All rights reserved.
1. Introduction
odour of GSM and MIB in water with odour concentrations reported
to be 9 and 4 pg mL−1, respectively [14,15].
Cyanobacteria cause many water-quality concerns, including
potential production of toxins and taste and odour compounds.
The most usually occurring taste and odour compounds produced
by cyanobacterial blooms as secondary metabolites, are geosmin
(GSM) and 2-methylisoborneol (MIB) [1]. They are often found in
surface waters such as lakes, rivers and eutrophic drinking water
reservoirs [2], indoor air [3], fish tissues [4,5] and foods [6–8]. GSM
is a bicyclic tertiary alcohol produced by certain species of Oscillato-
ria [9,10], Anabaena [11] and actinomycetes [12]. MIB is a terpenoid
also produced by the cyanobacterial species of Oscillatoria [9,10]
and Phormidium [13]. Actinomycetes have also been shown to pro-
duce MIB [12]. GSM has a distinct earthy-muddy flavour and aroma,
and is responsible for the earthy taste of beets and MIB gives a
musty taste and odour to water. The human nose can detect the
Communities whose water supply depends on surface water
periodically experience episodes of unpleasant tasting water. Upon
cellular death of above bacteria, GSM/MIB are released into the local
water supply, impacting greatly on the aesthetic quality and gen-
eral consumer acceptability of drinking water. For these reasons,
the removal of these compounds from water is very important
for its use and consumption. In cyanobacteria bloom events when
GSM and MIB are released, removal processes are required. Stud-
ies have shown that GSM and MIB are resistant in standard water
treatments such as coagulation, sedimentation and filtration, espe-
cially at very low concentrations [16]. Common disinfectants and
oxidants such as Cl2, ClO2 and KMnO4 are also shown to be inef-
fective in their removal [17,18]. Even aeration (air stripping), that
is generally effective for volatile compounds, is in this case not
the treatment of choice, due to the low Henry’s Law constant of
GSM/MIB [19].
Currently, powdered activated carbon (PAC) is the treatment
commonly used, with a number of studies reported for the removal
∗
Corresponding author. Tel.: +30 2106503643; fax: +30 2106511766.
E-mail address: hiskia@chem.demokritos.gr (A. Hiskia).
http://dx.doi.org/10.1016/j.jphotochem.2014.04.013
1010-6030/© 2014 Elsevier B.V. All rights reserved.

2
T. Fotiou et al. / Journal of Photochemistry and Photobiology A: Chemistry 286 (2014) 1–9
of organic pollutants such as seasonal tastes and odours in water.
Cook et al. [20] applied adsorption of GSM/MIB in four raw waters,
with GSM presenting better adsorption than MIB for all waters
studied, attributed to GSM’s lower molecular weight, solubility and
flatter structure. Bruce et al. [16] using several different types of
PAC studied GSM/MIB adsorption in natural water, with dissolved
organic carbon (DOC) competing for adsorption sites. With similar
results, Newcombe et al. [21,22] studied the simultaneous adsorp-
tion between MIB and natural organic matter (NOM). It was found
that the presence of NOM of similar size with MIB resulted more in
competition of adsorption sites. Granular activated carbon (GAC)
was also studied by several authors for GSM/MIB removal [23–25]
with efficiencies also influenced by NOM adsorption and reduced
after several times of operation.
The purpose of this work was to study and compare the pho-
tocatalytic degradation and mineralization of GSM and MIB in
water using a representative POM (SiW12O404−) and TiO2. The
comparative study of processes included also the identification of
intermediate products formed as well as the effect of hydroxyl rad-
ical scavengers. To the best of our knowledge (a) the photocatalytic
degradation of both GSM and MIB with POM and (b) the mineral-
ization and the complete degradation pathways in the presence of
POM or TiO2 is reported here for the first time.
2. Experimental
2.1. Chemicals and reagents
Biological activated carbon (BAC) was also used in several stud-
ies for GSM/MIB removal [26–29], presenting satisfactory results
with several parameters like temperature, media type etc. affect-
ing biofilter performance. Ho et al. [30] using a biologically active
sand filter, indicated that four different bacteria, i.e. Pseudomonas
sp., Alphaproteobacterium, Sphingomonas sp. and Acidobacteriaceae,
were responsible for the biodegradation of GSM/MIB.
GSM and MIB were purchased by Wako Pure Chemical Indus-
tries Ltd. GSM’s standard is a colourless slightly yellow, clear liquid
with min. 98.0% purity. MIB is white crystal solid with 99.8% purity.
Pottasium bromide was obtained from Fluka (Buchs,
Switzerland) and tertiary butyl alcohol (TBA) (≥99.0%) was
purchased from Sigma Aldrich (St. Louis, USA).
Silica tungstate (SiW12O404−) was obtained by Sigma Aldrich
and titanium dioxide commercial Degussa P25 TiO2 (Degussa AG,
Germany) was used.
In a recent review [31] on advanced oxidation processes (AOPs)
for the removal of taste and odour compounds from aqueous media,
processes such as ozone (O3), UV/O3 and UV/O3/H2O2 have been
used for the removal of GSM/MIB. O3 [32,33] was found to be inef-
fective, showing low removal rates. When UV illumination or H2O2
were used in combination with O3 higher removal efficiencies were
achieved [32,33]. Other AOP applied for GSM/MIB destruction were
ultrasonic [34] and UVC radiation [35]. Lawton et al. [36] reported
rapid degradation of both GSM/MIB with more than 99% removal
within 60 min of illumination in the presence of suspended TiO2.
Bellu et al. [37], using a pellet form of TiO2 completely removed
GSM within 25 min of treatment. In a later study using the same
material in a heavy water solvent, an isotopic effect was observed
upon GSM destruction. The results of the study showed the depend-
ence on the photocatalyst material used and also suggested that
the photocatalytic degradation took place on the catalysts sur-
face with •OH radicals generation being the rate determining step
[38]. In another study, TiO2 entrapped into EFAL (extra-framework-
aluminium)-removed Y-zeolites was applied for MIB degradation
presenting enhanced photocatalytic activity. This was due to mod-
ification of the surface states of TiO2 that leads to enhancement
of the photocalyst adsorption capability [39]. A preliminary study
was also performed by Pemu et al. [40] using TiO2 photocatalysis
of GSM in which few intermediate products were identified.
Polyoxometalates (POM) have previously been used for degra-
dation of several organic pollutants in water [41–45]. In almost
all cases final degradation products were CO2, H2O and inorganic
anions. POM are acid condensation products, mainly of molyb-
denum and tungsten [46–48], that upon excitation with near
visible and UV light become powerful oxidizing reagents capable
of destroying a great variety of organic compounds in aqueous
solutions through a hole–electron (h+ + e−) mechanism [49–51].
Hydroxyl radicals (•OH) generated by reaction of POM with H2O
seem to play a key role in the process [51]. Oxygen oxidizes
(regenerates) the catalyst and through reductive activation may
or may not participate further in the process, depending on the
substrate [52]. Due to their photocatalytic performance, POM can
be recognized as an AOP [42–44]. They have also been recog-
nized as building blocks for efficient photocatalysts by hybridizing
with photofunctional semiconductor nanostructures [53]. POM are
almost as effective as the widely published TiO2 [51], presenting
similar behaviour with the semi-contacting oxide [51]. •OH radicals
have been used to explain similarities of POM and TiO2, although
in some cases the nature of substrate and the mode of investigation
seem to play an important role in the process [54].
Extra pure oxygen and nitrogen were used for oxygenation and
evaporation of the solutions. Water was purified with a Millipore
Milli-Q Plus System.
2.2. Instrumentation
Irradiation in UV-A (315–400 nm) was performed with a labora-
tory constructed “illumination box” equipped with four F15W/T8
black light tubes (Sylvania GTE, USA). The maximum emission of
these tubes is around 365 nm, emitting 71.7 mW cm−2 at a distance
of 25 cm.
The GC–MS system used through was an Agilent 6890 Series
gas chromatograph equipped with an HP-5 MS capillary column
(30 m × 0.25 mm × 0.25 ␮m film thickness), interfaced to an Agilent
5973 mass selective detector.
Total organic carbon (TOC) measurements were carried out
using a Shimadzu TOC-5000A which was calibrated with potassium
hydrogen phthalate standards.
2.3. Photocatalysis experiments
In
a
typical experiment for GSM/MIB degradation, aque-
4−
ous solution (20 mL) containing the photocatalyst SiW12O40
(7 × 10−4 M, 200 mg L−1) or commercial available TiO2 Degussa P25
(200 mg L−1) was added to a cylindrical pyrex cell, oxygenated
for 20 min, spiked with GSM or MIB solution giving a total con-
centration of 1 mg L−1 and covered air tightly with a serum cap.
Photocatalysts loadings were selected according to previous stud-
ies for comparison reasons [43,54]. Illumination was performed
at ambient temperature in the photolysis apparatus. The solu-
tions were magnetically stirred throughout the experiment. In
experiments with •OH radical trapping reagents (scavengers) KBr
(10−2 M) and tertiary butyl alcohol (10−2 M) were used.
Analysis of the photolysed solutions was performed after filtra-
tion with Millex PVDF Durapore-GF 13 mm 0.22 ␮m, low protein
binding filters. Degradation experiments performed in triplicate
and the error bars on Figures represent the mean SD of the three
separate measurements. The initial rates of substrates degradation
were calculated from the slope of the curve obtained for the first
30% of the substrates destruction.

T. Fotiou et al. / Journal of Photochemistry and Photobiology A: Chemistry 286 (2014) 1–9
3
Fig. 1. Photocatalytic degradation of GSM (1 mg L−1) under UV-A (ꢀmax = 365 nm) irradiation with (a) SiW12O404−(7 × 10−4 M, 200 mg L−1) and (b) TiO2 (200 mg L−1) in the
presence and absence of scavengers. Conditions (ꢀ) Photolysis, (᭹) No scavenger, (ꢁ) KBr and (ꢂ) TBA.
2.4. Analytical determination
required longer time reaching complete degradation at 120 min.
Experiments were also performed in the absence of photocatalysts.
A destruction of ∼15% for GSM in UV-A was observed after 120 min
of illumination (Fig. 1), indicating photolytic cleavage. Pemu et al.
[40], in a study using TiO2 photocatalysis for degradation of GSM,
observed remarkable destruction in the absence of photocatalyst,
under experimental conditions used. This was attributed to the
energy of UV light emitted being of the same order of magnitude
The determination of GSM and MIB in the water samples
was performed by a headspace solid phase microextraction (HS-
SPME)/gas chromatography–mass spectrometry (GC–MS) method
[55]. Samples (2 mL) were placed in screw-capped, straight-sided
headspace vials with PTFE-lined silicone septa. Sodium chloride
(0.75 g) and a stirrer were added to the sealed vial and placed in
70 ◦C for 30 min. A GC temperature gradient program from 50 ◦C
(held for 1 min) to 250 ◦C (held for 6 min), using a temperature
ramp (12 ◦C min−1) under constant flow (1 mL min−1) was used.
Extraction of analytes by HS-SPME was achieved using a Supelco
fibre coated with Divinylbenzene/Carboxen/Polydimethylsiloxane
(DVB/CAR/PDMS), Stableflex, 50/30 ␮m. Detection was performed
in selected ion monitoring (SIM) mode at m/z: 112 (GSM) and
with those of bonds in GSM, causing cleavage of C O and C
bonds.
C
The photodegradation of oxygenated aqueous solution of MIB
with and without photocatalysts is presented in Fig. 2, in the
presence of (a) SiW12O404− and (b) TiO2. When photocatalysis per-
formed in the presence of TiO2, MIB was completely removed in the
first 25 min. In the case of SiW12O404−, the destruction of MIB was
complete after 100 min of illumination. Similar to GSM, photode-
composition of MIB also took place in the absence of photocatalysts
reaching ∼20% in 120 min of illumination.
95 (MIB), respectively. Method linear range was 0–500 ng L−1
.
Limit of Detection (LOD) at a signal to noise ratio greater than 3
(S/N > 3) was found to be 1 ppt for both compounds. For interme-
diates identification experiments, higher concentration was used
for GSM/MIB (20 mg L−1). Total volume (20 mL) was extracted in
dichloromethane and evaporated to 0.5 mL, using low nitrogen flow
at 35 ◦C.
Identification of intermediates was performed using the same
instrument apparatus. The temperature programme applied in
GC–MS was the same as above, in scan mode. Scanning was moni-
tored at a m/z range from 20 to 300 amu. The injection was carried
out splitless at 250 ◦C and the injection volume was 2.0 ␮l. The
electron energy was set at 70 eV, the ion source temperature was
maintained at 230 ◦C and the quadrapole temperature at 150 ◦C.
Data acquisition, processing and instrument control were per-
formed by the Agilent MSD Chem-Station software.
Results also showed that degradation of GSM was slightly slower
than MIB in the presence of both photocatalysts. This was also
observed by Lawton et al. using TiO2 photocatalysis [36]. In the
frame of this study, the observed rate constants of the photocat-
alytic degradation of the substrates were found to be 0.349 and
0.639 × 10−1 min−1 using POM, and 0.613 and 1.23 × 10−1 min−1
using TiO2, for GSM and MIB, respectively. Previous studies using
TiO2 gave similar results with the above. For GSM removal observed
rate constants were 0.633 × 10−1 min−1 [36], 0.27 × 10−1 min−1
[56], 0.90 × 10−1 min−1 [40] and 0.21–0.55 × 10−1 min−1 [57].
Also, for MIB removal using TiO2 observed rate constants were
1.979 × 10−1 min−1 [36] and 0.24 × 10−1 min−1 [58].
3.2. Photocatalytic degradation of GSM and MIB in the presence
of •OH radicals scavengers
3. Results and discussion
3.1. Photocatalytic degradation of GSM and MIB in the presence
of SiW12O40 and TiO2
Experiments were also performed in the presence of •OH radi-
cals scavengers, i.e. KBr and TBA.
4−
KBr and TBA are •OH radical trapping reagents (scavengers)
from which Br− is stronger [59,60]. Experiments with both photo-
catalysts (POM, TiO2), substrates (GSM, MIB) and scavengers were
conducted side by side, under exactly the same conditions. Results
are presented in Figs. 1 and 2, for GSM and MIB respectively.
In Table 1 the observed rate constants of the photodegradation
of the substrates and how these are modified in the presence of
•OH radical scavengers are given. Numbers in parentheses indi-
cate, percentage-wise, the effect of scavengers on the observed rate
constants. The observed rate constants of substrates degradation
Illumination of aqueous, oxygen saturated solutions of
GSM (1 mg L−1
) ) under UV-A irradiation
and MIB (1 mg L−1
(ꢀmax = 365 nm) in the presence of SiW12O404−(7 × 10−4 M,
200 mg L−1
)
or commercially available TiO2 Degussa P25
(200 mg L−1) results in the degradation of both substrates. In
Fig. 1, the disappearance of GSM at various illumination intervals
4−
in the presence of (a) SiW12O40 and (b) TiO2 is presented. Under
the experimental conditions used, GSM disappeared after 30 min of
illumination in the presence of TiO2, while in the presence of POM

4
T. Fotiou et al. / Journal of Photochemistry and Photobiology A: Chemistry 286 (2014) 1–9
Fig. 2. Photocatalytic degradation of MIB (1 mg L−1) under UV-A (ꢀmax = 365 nm) irradiation with (a) SiW12O404−(7 × 10−4 M, 200 mg L−1) and (b) TiO2 (200 mg L−1) in the
presence and absence of scavengers. Conditions (ꢀ) Photolysis, (᭹) No scavenger, (ꢁ) KBr and (ꢂ) TBA.
were calculated from the slope of the curve obtained for the first
30% of the substrates destruction upon illumination time.
Figs. 1 and 2 and Table 1, show that both scavengers retard the
photodegradation of GSM and MIB, in accordance with their ability
seen in Fig. 3, after 5 h of irradiation in the presence of TiO2 65%
and 80% of organic carbon has been recovered for GSM and MIB,
while their degradation has been almost completed in ∼30 and
4−
25 min, respectively (Figs. 1 and 2). In the case of SiW12O40 after
to scavenge •OH radicals. The second order rate constants (M−1 s−1
)
5 h of irradiation 50% and 65% mineralization of organic carbon was
observed for GSM and MIB, respectively (Fig. 3). The shorter time
needed for degradation than for mineralization is due to formation
of organic intermediates that also react with the photocatalysts.
Reduction of TOC is evidenced only after a small induction period
indicating also that the mineralization proceeds through several
intermediate steps. The incomplete removal of TOC (∼80–85%) can
be assigned to the formation of small partially oxidized molecules
that are mineralized slowly.
of the scavengers used with •OH radicals are: 1.1 × 1010 for Br− [59]
and 3.1 × 108 for TBA [60]. The retardation of the photodegradation
of GSM and MIB, in the presence of scavengers, denotes that •OH
radicals should be the main oxidant for both photocatalysts. It was
also appeared that both scavengers have the same influence on both
of the substrates. The similarity on mode of operation of the two
photocatalysts on GSM and MIB can be attributed on the similar
structure of the substrates. These results come in agreement with
previous study on atrazine, fenitrothion, chlorophenols and 2,4-
DCP [54], where it was stated that the photooxidizing mode of POM
and TiO2 (i.e. •OH radicals versus h+) is circumstantial depending
on the nature of the substrate and the mode of investigation.
3.4. Identification of intermediates and degradation pathway of
GSM
GSM is photodegraded slowly in the absence of catalysts (Fig. 1).
A small number of intermediates were produced three of which
were identified (Table S1, Fig. S1) by comparison using Wiley mass
spectra data base.
When illumination of GSM was performed in the presence of
POM, the formation of numerous intermediate products took place
(Scheme 1). In Table 2 all identified intermediates with match-
ing greater than 80% are presented with their chromatographic
3.3. Photocatalytic mineralization of GSM and MIB in the
presence of SiW12O40 and TiO2
4−
To the best of our knowledge, degradation process of GSM
and MIB has been studied only under limited time of illumina-
tion [36,37,40]. Even though mineralization of the total organic
carbon in the solution might not be necessary for the elimina-
tion of the undesirable taste and odour characteristics of GSM and
MIB in water, it can provide useful information on the mechanistic
aspects of the photocatalytic process of the two materials. Pro-
longed illumination of aqueous solutions of GSM and MIB leads to
the mineralization through the elimination of the organic carbon
in the solutions, in the presence of both photocatalysts. As can be
Table 1
Observed rate constants from the initial rates of photodegradation of GSM and
MIB in the presence of POM or TiO2 and scavengers, calculated from Figs. 1 and
2 respectively.
Scavenger catalyst
None
KBr
TBA
k × 10−3 min−1; % (kscavenger)/(knone
)
GSM
No catalyst
POM
TiO2
1.5
34.9 (100)
61.3 (100)
1.9 (5.6)
3.6 (5.9)
8.1 (23.1)
23.6 (38.4)
MIB
No catalyst
POM
TiO2
1.7
63.9 (100)
123(100)
Fig. 3. Photocatalytic mineralization of GSM (10 mg L−1) and MIB GSM (10 mg L−1
)
)
2.6 (4.2)
1.0 (0.8)
6.1 (9.6)
16.9 (15.3)
4−
under UV-A (ꢀmax = 365 nm) irradiation using SiW12O40 (7 × 10−4 M, 200 mg L−1
or TiO2 (200 mg L−1) catalyst.

T. Fotiou et al. / Journal of Photochemistry and Photobiology A: Chemistry 286 (2014) 1–9
5
4−
Scheme 1. Intermediates formed during photocatalytic degradation of GSM by SiW12O40 or TiO2.
Table 2
Intermediates identified during the photocatalytic degradation of GSM with their retention time (tR) and their spectral characteristics (M+, m/z), in Scheme 1.
4−
Name
Symbol
tR (min)
M+
m/z
SiW12O40
TiO2
GEOSMIN
10.89
13.28
12.44
13.34
12.11
12.61
7.48
11.83
12.86
11.41
12.44
11.82
12.86
12.55
5.27
12.20
11.37
6.37
7.73
7.48
11.96
7.98
11.26
182
182
178
182
126
150
126
128
182
140
154
140
182
170
112
126
138
140
152
138
126
144
136
112, 43, 55
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
8a-Hydroxy-4a-methyl-octahydro-naphthalen-2-one
4a-Methyl-4,4a,5,6,7,8-hexahydro-3H-naphthalen-2-one
8,8a-Dimethyl-decahydro-naphthalen-1-ol
2-Ethyl-cyclohexanone
IV
V
VI
VII
VIII
IX
X
XI
XII
XIII
XIV
XV
XVI
XVII
XVIII
XIX
XX
XXI
XXII
XXIII
XXIV
XXV
112, 55, 97, 82
121, 136, 93
112, 43, 55, 97, 126
98, 55, 126
150, 135, 79, 93
126, 56, 111, 43
97, 55
112, 55, 41
55, 97
136, 107, 121, 79
97, 55, 140, 41
112, 55, 41
112, 43, 94
68, 84, 112
126
107, 95, 67
82, 56, 69, 140
68, 96, 152
82, 138, 39, 54
55, 97, 126
60, 73, 41, 101
93, 79, 121, 108
7a-Methyl-1,4,5,6,7,7a-hexahydro-inden-2-one
2,4-Dimethyl-cyclopentane-1,3-dione
(1,2-Dimethyl-cyclopentyl)-methanol
1,8a-Dimethyl-decahydro-naphthalen-2-ol
1-(1-Methyl-cyclohexyl)-ethanone
5-Isopropenyl-2-methyl-cyclohexanol
1-Isopropyl-4-methyl-cyclohexane
3-(2,6,6-Trimethyl-cyclohex-2-enyl)-propenal
1-(2-Methoxy-cyclohexyl)-propan-2-one
Cyclohexanone
2,2-Dimethyl-cyclohexanone
3,5-Dimethyl-cyclohex-3-enecarbaldehyde
2,2,6-Trimethyl-cyclohexanone
5-Acetyl-3,3-dimethyl-cyclohexanone
3,5,5-Trimethyl-cyclohex-2-enone
2-Ethyl-hex-2-enal
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
√
Octanoic acid
2,4,5,6-Tetramethyl-hepta-1,3,6-triene

6
T. Fotiou et al. / Journal of Photochemistry and Photobiology A: Chemistry 286 (2014) 1–9
second main intermediate product VI could be formed by dehy-
dration of GSM and •OH addition followed ␲-bond rearrangement
(rgm) (Fig. S5) [61].
The presence of majority of oxygenated degradation products
suggests that the mechanism involved in most identified interme-
diates is indeed •OH oxidation, driven by electrophilic substitution
reactions. Subsequent bond cleavage at multiple sites produces
mainly cyclic ketones that upon further bond cleavage form open
chain saturated and unsaturated compounds, i.e. alkenes, alde-
hydes and acids.
A few studies concerning the identification of degradation prod-
ucts of GSM under various processes have been reported in the
literature. In 1999 Saito et al. [62] were the first to study a microbio-
logical degradation pathway for GSM. In total, three products were
identified; two of them were dehydration products of GSM and
the third resulted from dehydration followed by enolation. Another
study employing bacteria was performed by Eaton [63]. Two main
intermediates were identified, i.e. 2- and 7-ketogeosmin. Song et al.
[34] studied the ultrasonically induced degradation of GSM. Dehy-
drations, subsequent dehydrogenations and a ring opening reaction
were observed due to pyrolytic bond scissions taking place.
Prior to our work, Pemu et al. [58] studied GSM degra-
dation using photocatalysis with TiO2. Only a small number
of intermediates were identified (3,5-dimethylhex-1-ene, 2,4-
dimethylpentan-3-one, 2-methylethylpropanoate and 2-heptanal)
showing that GSM undergoes rapid ring opening producing
aliphatic saturated and unsaturated compounds, including some
alkanones and esters.
Fig. 4. Evolution and decay of main intermediate products (product IV: 8a-
hydroxy-4a-methyl-octahydro-naphthalen-2-one and product VI: 8,8a-dimethyl-
decahydro-naphthalen-1-ol), upon photocatalytic degradation of GSM (20 mg L−1),
using SiW12O40 (7 × 10−4 M, 200 mg L−1) under UV-A irradiation.
4−
retention time (tR) and their spectral characteristics (M + and m/z of
major ions). Identification of the species detected was performed on
the basis of comparison with Wiley mass spectra library, literature
data and EI fragmentation patterns. The majority of the identified
intermediates were cyclic ketones which upon ring opening lead to
formation of linear saturated and unsaturated products (Scheme 1).
The formation of all intermediates is followed by their decay during
the photocatalytic process, coming finally to total photodecompo-
sition to CO2.
The intermediates detected in this study were similar in the
4−
presence of SiW12O40
and TiO2 (Scheme 1). This is in good
agreement with previous studies where it has been demonstrated
that the photocatalytic performance of POM and TiO2 is similar in
terms of the overall mechanism of photodecomposition of organic
compounds, the intermediate species involved and the final pho-
todegradation products (i.e., CO2, H2O and inorganic anions) [51].
This also tends to suggest, despite the recent arguments that exist
[54], that the photodegradation mechanism in the case of GSM, by
both catalysts ought to take place mainly via a common reagent, i.e.
•OH radicals. On the contrary direct photolysis, that causes degra-
dation via direct absorption of light by GSM proceeds slowly via
different intermediates (Table S1, Fig. S1).
Identification of intermediates was also carried out upon photo-
catalysis in the presence of TiO2. As it can be noticed from the
chromatograms of the extracted photolysed solutions (Fig. S2) at
various illumination intervals, the chromatographic patterns were
mostly the same between POM and TiO2, supporting the fact that
the majority of intermediates reported in Table 3 are present during
the photocatalytic degradation using either of the two photocata-
lysts.
Product IV (8,8a-dimethyl-decahydro-naphthalen-1-ol) and
product VI (8,8a-dimethyl-decahydro-naphthalen-1-ol), due to
their high abundance could be considered as the main intermedi-
ates produced during the photocatalytic degradation of GSM under
UV-A irradiation in the presence of POM or TiO2. In Fig. 4, the for-
mation and decay of products IV and VI during the photocaralytic
procedure is presented, with a peak on their concentrations at ∼2 h
of irradiation. A possible mechanism followed for the formation of
product IV could be ␣-hydrogen abstraction from the tertiary car-
bon of GSM, ˇ-scission abstraction, followed by hydroxylation from
•OH radical attack and finally ketone formation (Fig. S4) [61]. The
3.5. Identification of intermediates and degradation pathway of
MIB
During photolysis of MIB in the absence of catalyst, a few
peaks were detected in the chromatogram of the photolysed solu-
tion indicating photolytic cleavage. One of them was identified as
1,2,7,7-tetramethyl-bicyclo[2.2.1]hept-2-ene (I) (Scheme 2), that is
Table 3
Intermediates identified during photolysis and the photocatalytic degradation of MIB with their spectral characteristics (M+, m/z), in Scheme 2.
4−
Name
Symbol
tR (min)
M+
m/z
SiW12O40
TiO2
2-Methylisoborneol
8.28
6.08
7.80
7.48
9.21
168
150
152
166
166
166
166
124
168
138
152
152
124
112
95, 108
1,2,7,7-Tetramethyl-bicyclo[2.2.1]hept-2-ene
1,7,7-Trimethyl-bicyclo[2.2.1]heptan-2-one (d-camphor)
1,6,7,7-Tetramethyl-bicyclo[2.2.1]hept-5-en-2-ol
1,7,7-Trimethyl-bicyclo[2.2.1]heptane-2,5-dione
1,7,7-Trimethyl-bicyclo[2.2.1]heptane-2,3-dione
1,7,7-Trimethyl-bicyclo[2.2.1]heptane-2,6-dione
3-Ethyl-2,5-dimethyl-furan
4-Methyl-3-pent-2-enyl-dihydro-furan-2-one
2,3,4,5-Tetramethyl-cyclopent-2-enone
(2,2,3-Trimethyl-cyclopent-3-enyl)-acetaldehyde
3,3,4-Trimethyl-cyclohex-1-enecarbaldehyde
2,6-Dimethyl-hepta-2,4-diene
I
II
107, 79, 93, 135
95, 81, 41, 55, 108
108, 93
166, 69, 109, 83, 123
95, 83, 69, 55
166, 41, 67, 97, 83
109, 124
99, 43
123, 95, 138, 67
108, 93, 67
√
√
√
√
√
√
√
√
√
√
√
√
√
III
IV
V
VI
VII
VIII
IX
X
√
√
√
√
√
√
√
9.64
9.73
10.85
10.74
8.77
11.34
9.03
XI
XII
XIII
95, 81, 123, 67
109, 124
69, 41, 55, 112
√
√
10.81
8.09
4-Methyl-hept-2-ene

T. Fotiou et al. / Journal of Photochemistry and Photobiology A: Chemistry 286 (2014) 1–9
7
4−
Scheme 2. Intermediates formed during photolysis and photocatalytic degradation of MIB by SiW12O40 or TiO2.
possibly formed by dehydration of MIB. Its retention time (tR) and
spectral characteristics are given in Table 3.
secondary alcohol, leading to the formation of ketone, starting from
product II. As far as concerning the other identified saturated and
unsaturated oxygen containing cyclic intermediates, mechanisms
involved are hydroxyl radical oxidation of compounds, driven by
electrophilic substitution. The majority of those are five-membered
rings revealing ring opening on MIB molecule. Linear aliphatic com-
pounds were identified during the later stages of photo-oxidation
similar to previous studies of Hiskia et al. [64].
A detailed study of the photodegradation of MIB (Scheme 2)
4−
with SiW12O40
revealed the formation and decay of several
products prior to the final decomposition to CO2. Many chromato-
graphic peaks appeared in the photolyzed solution in the presence
of SiW12O404− which were not present without photocatalyst. The
intermediates identified together with their retention times (tR)
and spectral characteristics are given in Table 3. They are compiled
as follows: alcohol-(III), ketone-(II) and diketone-(IV, V, VI) deriva-
tives of MIB, oxygen containing cyclic compounds (VII, VIII, IX, X,
XI) and open chain aliphatic compounds (XII, XIII).
Sumimoto [65] was the first to study MIB’s degradation pathway
using biodegradation by gravel sand filtration. Tanaka [66] using
biodegradation identified some of the products formed which were
camphor and two dehydration products, one of them also found in
current study (product I in Scheme 2). Song et al. [34] carried out
ultrasonically induced degradation of MIB and defined the pathway
due to pyrolytic transformations taking place. Qi et al. [58] and later
Li et al. [67] applying ozonation processes investigated the degra-
dation of MIB and proposed a pathway of ozonation of MIB. The
majority of the intermediates identified in those two studies were
identical. According to these studies, d-camphor was likely to be the
primary degradation product that it is further degraded into other
byproducts, including aldehydes. Qi et al. [58] also investigated the
effect of •OH using scavengers on the ozonation of MIB, with results
suggesting that the presence of •OH was the predominant oxidant.
The full agreement of our results with those of ozonation of MIB
[58,67] is a further evidence that the main oxidant is •OH in all
Similar photocatalytic experiments were also performed in the
presence of TiO2. The intermediates detected were identical with
4−
those found in the presence of SiW12O40
(Table 3, Fig. S3). We
propose here (Scheme 2) a possible photodegradation mechanism
for MIB, that applies to both POM and TiO2, which provides a rea-
sonable explanation for the similar intermediates formed in both
processes.
Product III (1,6,7,7-Tetramethyl-bicyclo[2.2.1]hept-5-en-2-ol)
is formed with hydroxylation of product I suggesting the presence
of •OH radicals. Product II (d-camphor) is proposed to be the pri-
mary intermediate produced during photocatalysis of MIB formed
with a ˇ-scission reaction mechanism on the methyl group of MIB
that generates a ketone. Products IV, V and VI are possibly formed
by hydrogen elimination followed by •OH addition and oxidation of
4−
cases, i.e. photocatalysis with SiW12O40 or TiO2 and ozonation.

8
T. Fotiou et al. / Journal of Photochemistry and Photobiology A: Chemistry 286 (2014) 1–9
3.6. Photocatalytic degradation mechanisms of GSM/MIB in the
presence of SiW12O40 and TiO2: a comparison study
removal of taste and odour compounds that taint water. Although
scaling up is necessary for application, the elucidation of degra-
dation pathways provides us with a better understanding of the
photocatalytic process. However, this initial study is promising pre-
senting a novel approach for water purification from compounds
resistant in standard water treatments.
4−
An objective of this study was the comparison of photodegrada-
tion mechanisms followed by POM and TiO2 in the cases of GSM and
MIB, via degradation, mineralization and identification of interme-
diate products, under UV-A irradiation.
Several examples, from both photocatalysts, have been reported
to demonstrate that their performance is similar in terms of the
overall mechanism of photodecomposition of organic compounds,
the intermediate species involved and the final photodegra-
dation products (i.e., CO2, H2O and inorganic anions) [51].
However, parallel experiments under similar conditions, using
various substrates (atrazine, fenitrothion, 4-chlorophenol and 2,4-
dichlorophenoxyacetic acid) and •OH radical scavengers, have
shown that the photooxidizing mode of POM and TiO2, i.e., •OH
radicals and/or holes (h+), depends on the nature of substrate and
the mode of investigation [54,68]. Atrazine showed that both POM
and TiO2 mainly operate through •OH radicals and with a lower
extent with h+, whereas fenitrothion suggested the almost exclu-
sive operation of both photocatalysts via •OH radicals. On the other
hand, differences between the two photocatalysts have been pro-
posed with 4-chlorophenol and 2,4-dichlorophenoxyacetic acid,
with POM operating via •OH radicals and TiO2 mainly via h+. Over-
all, the action of •OH radicals relative to h+ appears to be more
pronounced with POM than TiO2 [54]. An example against the
above mechanism for POM has been reported for the degradation
of dichlorobenzene in the presence of •OH radicals scavengers sug-
gesting that POM act via h+ rather than •OH mediated oxidations
[69]. As a conclusion, whether an •OH or h+ mediated mecha-
nism is followed depends on various parameters (e.g., the kind of
substrates, the substrate-photocatalyst interaction) and should be
considered on a case by case basis [68].
Acknowledgments
This research has been co-financed by the European Union
(European Social Fund–ESF) and Greek national funds through
the Operational Programme “Education and Lifelong Learning” of
the National Strategic Reference Framework (NSRF) – Research
Funding Programme: THALIS, investing in knowledge society
through the European Social Fund. The authors acknowledge COST
Actions ES 1105 “CYANOCOST – Cyanobacterial blooms and tox-
ins in water resources: Occurrence, impacts and management” and
CM1203 “PoCheMoN – Polyoxometalate Chemistry for Molecular
Nanoscience” for adding value to this study through networking
and knowledge sharing with European experts in the field. T. Tri-
antis and T. Fotiou are grateful to NCSR Demokritos, Institute of
Advanced Materials, Physicochemical processes, Nanotechnology
& Microsystems, for postdoctoral and PhD fellowships. Disclaimer:
The views expressed in this manuscript do not necessarily reflect
the views of EYDAP SA.
Appendix A. Supplementary data
Supplementary data associated with this article can be found,
in the online version, at http://dx.doi.org/10.1016/j.jphotochem.
2014.04.013.
In accordance with the results given in this study on degrada-
tion and mineralization (TOC measurements and identification of
formed intermediates) of GSM and MIB, it has been concluded that
the same photodegradation mechanism is followed when POM and
TiO2 are used as photocatalysts. The similarities of the interme-
diates identified (presence of the same oxidized derivatives) and
results from experiments with •OH radical scavengers, as well tend
to suggest that •OH is the common oxidant, as has been also men-
tioned for other organic compounds[43].
References
[1] G.A. Burlingame, R.M. Dann, G.L. Brock, A case study of geosmin in Philadel-
phia’s water, J. Am. Water Works Assoc. 78 (1986) 56–61.
[2] G.A. Codd, L.F. Morrison, J.S. Metcalf, Cyanobacterial toxins: risk management
for health protection, Toxicol. Appl. Pharmacol. 203 (2005) 264–272.
[3] P. Omür-Ozbek, J. Little, A.M. Dietrich, Ability of humans to smell geosmin 2-
MIB and nonadienal in indoor air when using contaminated drinking water,
Water Sci. Technol. 55 (2007) 249–256.
[4] Z.G. Papp, É. Kerepeczki, F. Pekár, D. Gál, Natural origins of off-flavours in fish
related to feeding habits, Water Sci. Technol. 55 (2007) 301–309.
[5] W.L. Steven, C.G. Casey, Analysis of 2-methylisoborneol and geosmin in catfish
by microwave distillation-solid-phase microextraction, J. Agric. Food Chem. 47
(1999) 164–169.
4. Conclusions
[6] G. Lu, J.K. Fellman, C.G. Edwards, D.S. Mattinson, J. Navazio, Quantitative deter-
mination of geosmin in red beets (Beta vulgaris L.) using headspace solid-phase
microextraction, J. Agric. Food Chem. 51 (2003) 1021–1025.
[7] H.H. Jelen, M. Majcher, R. Zawirska-Wojtasiak, M. Wiewiorowska, E. Wasowicz,
Determination of geosmin, 2-methylisoborneol, and a musty-earthy odor in
wheat grain by SPME-GC–MS, profiling volatiles, and sensory analysis, J. Agric.
Food Chem. 51 (2003) 7079–7085.
[8] S. Boutou, P. Chatonnet, Rapid headspace solid-phase microextraction/gas
chromatographic/mass spectrometric assay for the quantitative determination
of some of the main odorants causing off-flavours in wine, J. Chromatogr. A 1141
(2007) 1–9.
[9] P.E. Persson, Muddy odour: a problem associated with extreme eutrophication,
Hydrologia 86 (1982) 161–164.
[10] A. Matsumoto, Y. Tsuchiya, Earthy-musty odor-producing cyanophytes isolated
from five water areas in Tokyo, Water Sci. Technol. 20 (1988) 179–183.
[11] M. Yagi, U. Matsuo, K. Ashitani, T. Kita, T. Nakamura, Odor problems in Lake
Biwa, Water Sci. Technol. 15 (1983) 311–321.
[12] C. Klausen, M.H. Nicolaisen, B.W. Strobel, F. Warnecke, J.L. Nielsen, N.O.
Jorgensen, Abundance of actinobacteria and production of geosmin and 2-
methylisoborneol in Danish streams and fish ponds, FEMS Microbiol. Ecol. 52
(2005) 265–278.
[13] T. Negoro, M. Ando, N. Ichikawa, Blue-green algae in Lake Biwa which produce
earthy-musty odors, Water Sci. Technol. 20 (1988) 117–123.
[14] I.H. Suffet, A. Corado, D. Chou, M.J. McGuire, S. Butterworth, A.W.W.A. Taste and
odor survey, J. Am. Water Works Assoc. 88 (1996) 168–180.
This work focused on the removal of taste and odour compounds
(GSM/MIB) from water using photocatalysis with POM and TiO2.
Both photocatalysts found to be effective in degradation of target
analytes. Experiments were also performed in the presence of •OH
radicals scavengers showing retardation of the photodegradation
of GSM and MIB, which indicates that •OH radicals should be the
main oxidant for both photocatalysts. The photocatalytic degrada-
tion of GSM and MIB in the presence of both photocatalysts leads
to the formation of a plethora of intermediates prior to mineraliza-
tion. In the case of GSM the majority of the identified intermediates
were cyclic ketones which upon ring opening lead to formation
of linear saturated and unsaturated products. For MIB degrada-
tion identified intermediates are consisted by alcohol-, ketone- and
diketone-derivatives of MIB, oxygen containing cyclic compounds
and open chain aliphatic compounds. A complete degradation path-
way is proposed for target compounds during their photocatalytic
degradation with common intermediates identified, using either
POM or TiO2 with •OH radical attack to be mainly responsible for the
mechanism. These results suggest that photocatalysis using either
POM or TiO2 demonstrates significant potential for the complete
[15] D.M.C. Rashash, A.M. Dietrich, R.C. Hoehn, FPA of selected odorous compounds,
J. Am. Water Works Assoc. 89 (1997) 131–141.

T. Fotiou et al. / Journal of Photochemistry and Photobiology A: Chemistry 286 (2014) 1–9
9
[16] D. Bruce, P. Westerhoff, A. Brawley-Chesworth, Removal of 2-methylisoborneol
and geosmin in surface water treatment plants in Arizona, J. Water Supply Res.
Technol. Aqua. 51 (2002) 183–197.
[17] S. Lalezary, M. Pirbazari, M.J. McGuire, Oxidation of five earthy-musty taste and
odor compounds, J. Am. Water Works Assoc. 78 (1986) 62–69.
[18] W.H. Glaze, R. Schep, W. Chauncey, E.C. Ruth, J.J. Zarnoch, E.M. Aieta, C.H. Tate,
M.J. Mcguire, Evaluating oxidants for the removal of model taste and odor com-
pounds from a municipal water-supply, J. Am. Water Works Assoc. 82 (1990)
79–84.
from aqueous solutions by PW12O403−. The case of 2,4,6-trichlorophenol, Envi-
ron. Sci. Technol. 34 (2000) 2024–2028.
[43] P. Kormali, D. Dimoticali, D. Tsipi, A. Hiskia, E. Papaconstantinou, Photolytic
3−
and photocatalytic decomposition of fenitrothion by PW12O40 and TiO2: a
comparative study, Appl. Catal. B: Environ. 48 (2004) 175–183.
[44] A. Hiskia, M. Ecke, A. Troupis, A. Kokorakis, H. Hennig, E. Papaconstanti-
nou, Sonolytic, photolytic, and photocatalytic decomposition of atrazine
in the presence of polyoxometalates, Environ. Sci. Technol.
2358–2364.
3 (5) (2001)
[19] S. Lalezary, M. Pirbazari, M.J. McGuire, S.W. Krasner, Air stripping of taste and
odor compounds from water, J. Am. Water Works Assoc. 76 (1984) 83–87.
[20] D. Cook, G. Newcombe, P. Sztajnbok, The application of powdered activated
carbon fot MIB and geosmin removal: predicting PAC doses in four raw waters,
Water Res. 35 (2001) 1325–1333.
[21] G. Newcombe, J. Morrison, C. Hepplewhite, D.R.U. Knappe, Simultaneous
adsorption of MIB and NOM onto activated carbon: II. Competitive effects,
Carbon 40 (2002) 2147–2156.
[45] R.R. Ozer, J.L. Ferry, Photocatalytic oxidation of aqueous 1,2-dichlorobenzene
by polyoxometalates supported on the NaY zeolite, J. Phys. Chem. B 106 (2002)
4336–4342.
[46] M.T. Pope, Heteropoly and Isopoly Oxometalates, Springer-Verlag, Berlin, 1983.
[47] M.T. Pope, A. Müller (Eds.), Polyoxometalate chemistry: an old field with new
dimensions in several disciplines, Angew. Chem. Int. 30 (1991) 34–48.
[48] V.W. Day, W.G. Klemperer, Metal oxide chemistry in solution: the early transi-
tion metal polyoxoanions, Science 228 (1985) 533.
[22] G. Newcombe, J. Morrison, C. Hepplewhite, Simultaneous adsorption of MIB
and NOM onto activated carbon – I. Characterisation of the system and NOM
adsorption, Carbon 40 (2002) 2135–2146.
[23] Y. Kim, Y. Lee, C.S. Gee, E. Choi, Treatment of taste and odor causing substances
in drinking water, Water Sci. Technol. 35 (1997) 29–36.
[49] E. Papaconstantinou, Photochemistry of polyoxometallates of molybdenum
and tungsten and/or vanadium, Chem. Soc. Rev. 18 (1989) 1–31.
[50] A. Mylonas, E. Papaconstantinou, Photocatalytic degradation of chlorophenols
to CO2 and HCl with polyoxotungstates in aqueous solution, J. Mol. Catal. 92
(1994) 261–267.
[24] S. Ndiongue, W.B. Anderson, A. Tadwalkar, J. Rudnickas, M. Lin, P.M. Huck, Using
pilot-scale investigations to estimate the remaining geosmin and MIB removal
capacity of full-scale GAC-capped drinking water filters, Water Qual. Res. J.
Canada 41 (2006) 296–306.
[25] J. Ridal, B. Brownlee, G. McKenna, N. Levac, Removal of taste and odour com-
pounds by conventional granular activated carbon filtration, Water Qual. Res.
J. Canada 36 (2001) 43–54.
[26] S.L.N. Elhadi, P.M. Huck, R.M. Slawson, Factors affecting the removal of geosmin
and MIB in drinking water biofilters, J. Am. Water Works Assoc. 98 (2006)
108–119.
[51] A. Hiskia, A. Mylonas, E. Papaconstantinou, Comparison of the photoredox prop-
erties of polyoxometallates and semiconducting particles, Chem. Soc. Rev. 30
(2001) 62–69.
[52] A. Hiskia, E. Papaconstantinou, Photocatalytic oxidation of organic compounds
by polyoxometalates of molybdenum and tungsten. Catalyst regeneration by
dioxygen, Inorg. Chem. 31 (1992) 163–167.
[53] R. Sivakumar, J. Thomas, M. Yoon, Polyoxometalate-based molecular/nano
composites: advances in environmental remediation by photocatalysis and
biomimetic approaches to solar energy conversion, J. Photochem. Photobiol.
C: Photochem. Rev. 13 (2012) 277–298.
[27] S.L.N. Elhadi, P.M. Huck, R.M. Slawson, Removal of geosmin and 2-
methylisoborneol by biological filtration, Water Sci. Technol. 49 (2004)
273–280.
[54] P. Kormali, T. Triantis, D. Dimotikali, A. Hiskia, E. Papaconstantinou, On the pho-
tooxidative behavior of TiO2 and PW12O403−: OH radicals versus holes, Appl.
Catal. B: Environ. 68 (2006) 139–146.
[28] B. McDowall, D. Hoefel, G. Newcombe, C.P. Saint, L. Ho, Enhancing the biofil-
tration of geosmin by seeding sand filter columns with a consortium of
geosmin-degrading bacteria, Water Res. 43 (2009) 433–440.
[29] F. Persson, G. Heinicke, T. Hedberg, M. Hermansson, W. Uhl, Removal of geosmin
and MIB by biofiltration – an investigation discriminating between adsorption
and biodegradation, Environ. Technol. 28 (2007) 95–104.
[30] L. Ho, D. Hoefel, F. Bock, C.P. Saint, G. Newcombe, Biodegradation rates of 2-
methylisoborneol (MIB) and geosmin through sand filters and in bioreactors,
Chemosphere 66 (2007) 2210–2218.
[31] M. Antonopoulou, E. Evgenidou, D. Lambropoulou, I. Konstantinou, A review
on advanced oxidation processes for the removal of taste and odor compounds
from aqueous media, Water Res. 53 (2014) 215–234.
[32] C. Collivignarelli, S. Sorlini, AOPs with ozone and UV radiation in drinking water:
contaminants removal and effects on disinfection byproducts formation, Water
Sci. Technol. 49 (2004) 51–56.
[55] K. Saito, K. Okamura, H. Kataoka, Determination of musty odorants 2-
methylisoborneol and geosmin, in environmental water by headspace
solid-phase microextraction and gas chromatography–mass spectrometry, J.
Chromatogr. A 1186 (2008) 434–437.
[56] H. Tran, G.M. Evans, Y. Yan, A.V. Nguyen, Photocatalytic Removal of Taste and
Odour Compounds for Drinking Water Treatment, 2009, pp. 477–483.
[57] E.E. Bamuza-Pemu, E.M. Chirwa, Photocatalytic degradation of geosmin: reac-
tion pathway analysis, Water SA 38 (2012) 689–696.
[58] F. Qi, B. Xu, Z. Chen, J. Ma, D. Sun, L. Zhang, Efficiency and products investigations
on the ozonation of 2-methylisoborneol in drinking water, Water Environ. Res.
81 (2009) 2411–2419.
[59] D. Zehavi, J. Rabani, Pulse radiolysis of aqueous ferro-ferricyanide system.
−
1. Reactions of OH, HO2, and O2 radicals, J. Phys. Chem.
3703–3709.
7 (6) (1970)
[60] M. Anbar, P. Neta, A compilation of specific bimolecular rate constants for the
reactions of hydrated electrons, hydrogen atoms and hydroxyl radicals with
inorganic and organic compounds in aqueous solution, Int. J. Appl. Radiat. Iso-
tope 18 (1967) 493–523.
[33] A. Peter, U. Von Gunten, Oxidation kinetics of selected taste and odor com-
pounds during ozonation of drinking water, Environ. Sci. Technol. 41 (2007)
626–631.
[34] W. Song, K.E. O‘Shea, Ultrasonically induced degradation of 2-methylisoborneol
and geosmin, Water Res. 41 (2007) 2672–2678.
[61] M.A. Henderson, A surface science perspective on photocatalysis, Surf. Sci. Rep.
66 (2011) 185–297.
[35] K. Kutschera, H. Bornick, E. Worch, Photoinitiated oxidation of geosmin and 2-
methylisoborneol by irradiation with 254 nm and 185 nm UV light, Water Res.
43 (2009) 2224–2232.
[36] L. Lawton, P.K.J. Robertson, D. Bruce, The destruction of 2-methylisoborneol
and geosmin using titanium dioxide photocatalysis, Appl. Catal. B: Environ. 44
(2003) 9–13.
[37] E. Bellu, L.A. Lawton, P.K.J. Robertson, Photocatalytic destruction of geosmin
using novel pelleted titanium dioxide, J. Adv. Oxidation Technol. 11 (2008)
384–388.
[62] A. Saito, T. Tokuyama, A. Tanaka, T. Oritani, K. Fuchigami, Microbiological degra-
dation of (−)-geosmin, Water Res. 33 (1999) 3033–3036.
[63] R.W. Eaton, P. Sandusky, Biotransformations of (+/−)-geosmin by terpene-
degrading bacteria, Biodegradation 21 (2010) 71–79.
[64] A. Hiskia, E. Androulaki, A. Mylonas, S. Boyatzis, D. Dimoticali, C. Minero, E.
Pelizzetti, E. Papaconstantinou, Photocatalytic mineralization of chlorinated
organic pollutants in water by polyoxometallates. Determination of inter-
mediates and final degradation products, Res. Chem. Intermediat. 26 (2000)
235–251.
[38] P.K.J. Robertson, D.W. Bahnemann, L.A. Lawton, E. Bellu, A study of the kinetic
solvent isotope effect on the destruction of microcystin-LR and geosmin using
TiO2 photocatalysis, Appl. Catal. B: Environ. 108–109 (2011) 1–5.
[39] S.-J. Yoon, Y.H. Lee, W.-J. Cho, I.-O. Koh, M. Yoon, Synthesis of TiO2-
entrapped EFAL-removed Y-zeolites: novel photocatalyst for decomposition
of 2-methylisoborneol, Catal. Commun. 8 (2007) 1851–1856.
[40] E.E. Bamuza-Pemu, E.M.N. Chirwa, Photocatalytic degradation of geosmin:
intermediates and degradation pathway analysis, Chem. Eng. Trans. 24 (2011)
91.
[65] H. Sumimoto, Biodegradation of 2-methylisoborneol by gravel sand filtration,
Water Sci. Technol. 25 (1992) 191–198.
[66] A. Tanaka, T. Oritani, F. Uehara, A. Saiot, H. Kishita, Y. Niizeki, H. Yokota, K.
Fuchigami, Biodegradation of a musty odour component, 2-methylisoborneol,
Water Res. 30 (1996) 759–761.
[67] X. Li, Y. Huang, D. Wang, Efficiency and mechanism of degradation of 2-
methylisoborneol(2-MIB) by O3/H2O2 in water, in: 4th iCBBE, 2010.
[68] S. Kim, H. Park, W. Choi, Comparative study of homogeneous and heteroge-
3−
neous photocatalytic redox reactions: PW12O40 vs TiO2, J. Phys. Chem. B 108
[41] S. Antonaraki, T.M. Triantis, E. Papaconstantinou, A. Hiskia, Photocatalytic
degradation of lindane by polyoxometalates: intermediates and mechanistic
aspects, Catal. Today 151 (2010) 119–124.
[42] E. Androulaki, A. Hiskia, D. Dimotikali, C. Minero, P. Calza, E. Pelizzetti, E. Papa-
constantinou, Light induced elimination of mono- and polychlorinated phenols
(2004) 6402–6411.
[69] R.R. Ozer, J.L. Ferry, Kinetic probes of the mechanism of polyoxometalate-
mediated photocatalytic oxidation of chlorinated organics, J. Phys. Chem. B
104 (2000) 9444–9448.