Removal of dexamethasone from aqueous solution and hospital wastewater by electrocoagulation

Abstract

This study is concerned with the removal of the anti-inflammatory dexamethasone from aqueous solution and hospital wastewater by electrocoagulation. The variation of the toxicity during the electrocoagulation was also studied through experiments that were designed and optimized by means of response surface methodology. The coagulation efficiency was evaluated by measuring the dexamethasone concentration by high performance liquid chromatography coupled to a diode array detector. In addition, variation was evaluated through a Vibrio fischeri test. The results showed an increase in the removal of dexamethasone (up to 38.1%) with a rise of the current applied and a decrease of the inter-electrode distance, in aqueous solutions. The application to hospital effluent showed similar results for the removal of dexamethasone. The main effect of the electrocoagulation was that it removed colloids and reduced the organic load of the hospital wastewater. Regarding the current applied, the calculated energy efficiency was 100%. Without pH adjustment of the aqueous solution or hospital wastewater, the residual aluminum concentration always remained lower than 10mgL(-1), and, with adjustment (to pH6.5), lower than 0.30mgL(-1), at the final stage. No toxicity variation was observed during the electrocoagulation process in aqueous solution, either in the presence or absence of dexamethasone.

Full text

Removal of dexamethasone from aqueous solution and hospital wastewater
by electrocoagulation
Daniel R. Arsand
a
, Klaus Kümmerer
b
, Ayrton F. Martins
a,
⁎
a
Chemistry Department, Federal University of Santa Maria, RS, Brazil
b
Institute for Environmental Chemistry, Leuphana University Lüneburg, Germany
HIGHLIGHTS
►Removal of DEX and organic load from aqueous solution and hospital wastewater by EC
►Evaluation of the toxicity during the removal of DEX by EC
►Suggestion of the EC process as a pretreatment for subsequent processes
abstractarticle info
Article history:
Received 25 August 2012
Received in revised form 23 October 2012
Accepted 30 October 2012
Available online 30 November 2012
Keywords:
Electrocoagulation
Dexamethasone
Hospital effluent
Vibrio fischeri test
Residual aluminum
This study is concerned with the removal of the anti-inflammatory dexamethasone from aqueous solution
and hospital wastewater by electrocoagulation. The variation of the toxicity during the electrocoagulation
was also studied through experiments that were designed and optimized by means of response surface
methodology. The coagulation efficiency was evaluated by measuring the dexamethasone concentration
by high performance liquid chromatography coupled to a diode array detector. In addition, variation was
evaluated through a Vibrio fischeri test. The results showed an increase in the removal of dexamethasone
(up to 38.1%) with a rise of the current applied and a decrease of the inter-electrode distance, in aqueous
solutions. The application to hospital effluent showed similar results for the removal of dexamethasone.
The main effect of the electrocoagulation was that it removed colloids and reduced the organic load of
the hospital wastewater. Regarding the current applied, the calculated energy efficiency was 100%. Without
pH adjustment of the aqueous solution or hospital wastewater, the residual aluminum concentration al-
ways remained lower than 10 mg L
−1
, and, with adjustment (to pH 6.5), lower than 0.30 mg L
−1
,atthe
final stage. No toxicity variation was observed during the electrocoagulation process in aqueous solution,
either in the presence or absence of dexamethasone.
© 2012 Elsevier B.V. All rights reserved.
1. Introduction
In the last two decades, there has been evidence worldwide attribut-
able to the discharge of wastewater containing pharmaceutical residues
(Daughton, 2008; Halling-Sørensen et al., 1998; Santos et al., 2010). A
number of studies have pointed to the presence of endocrinedisruptors
in effluents discharged in streams, e.g. as a cause of sexual disturbance
in fish (Kümmerer, 2008; Woodling et al., 2006,) and mutagenicity for
living organisms (Bagatini et al., 2009).
After administration and excretion, the pharmaceuticals can reach
the sewage system and, then superficial waters. Investigations have
shown that conventional municipal sewage treatment plants are not al-
ways effective in dealing with effluents containing pharmaceuticals
(Cha et al., 2006; Jelic et al., 2011; Schuster et al., 2008; Sim et al.,
2010; Sui et al., 2010). Moreover, active substances, such as ciprofloxa-
cin, have been found in hospital effluents after local treatment (Brenner
et al., 2011; Martins et al., 2008a, 2011; Vasconcelos et al., 2009).
Several processes for treating wastewater containing pharmaceuticals
have been studied including the following: an improvement of conven-
tional processes employing anaerobic reactors (Chelliapan et al., 2011)
and membrane bioreactors (Wen et al., 2004), and an evaluation of ad-
vanced oxidation processes, as well as combinations of these techniques
(Arslon-Alaton and Dogruel, 2004; Arslan-Alaton et al., 2004; Andreozzi
et al., 2005; Borràs et al., 2011; Martins et al., 2009; Sui et al., 2010;
Vasconcelos et al., 2009). Other processes, such as electrocoagulation
Science of the Total Environment 443 (2013) 351–357
Abbreviations: CC, chemical coagulation; DEX, dexamethasone; EC, electrocoagulation;
GC, glucocorticoid; HUSM, University HospitaloftheFederalUniversityofSantaMaria;
HPLC–DAD, high performance liquid chromatography coupled to diode array detector;
RSM, response surface methodology.
⁎Corresponding author at: Departamento de Química, Universidade Federal de
Santa Maria, Campus Camobi, CEP 97105-900 Santa Maria, RS—Brasil. Tel.: +55
55 3220 8664; fax: +55 55 3220 8031.
E-mail addresses: danielarsand@pelotas.ifsul.edu.br (D.R. Arsand),
klaus.kuemmerer@leuphana.de (K. Kümmerer), martins@quimica.ufsm.br,
ayrton@pq.cnpq.br (A.F. Martins).
0048-9697/$ –see front matter © 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.scitotenv.2012.10.100
Contents lists available at SciVerse ScienceDirect
Science of the Total Environment
journal homepage: www.elsevier.com/locate/scitotenv

(EC) have been investigated for the treatment of hospital effluent
(Gürses et al., 2002; Ryan et al., 2008; Tir and Moulai-Mostefa, 2008).
A study comparing EC and chemical coagulation (CC) showed that the
CC needs 20 times more mass of reagent to treat the same volume of
wastewater, to achieve the same degree of efficiency (Ryan et al., 2008).
Chen et al. (2002) has carried out extensive study about the EC reactions.
There are a number of advantages in EC such as low-cost, easy
handling, and high efficiency in the removal of organic matter. On
the other hand, the sludge generation rate, the use of sacrificial elec-
trodes, and electrical energy consumption can be cited as drawbacks
(Mollah et al., 2001).
Anti-inflammatories constitute an important pharmaceutical class
and include glucocorticoids (GC) that are widely used in human and vet-
erinary medicine, but carry the risk of side effects (Reid, 2000; Schäcke
et al., 2002). The most potent GC cortisone derivate used in hospitals
and clinics is dexamethasone (DEX) and relatively high levels of DEX
have been detected in sewage effluent (Herrero et al., 2012). Fig. 1
shows the main structure of DEX.
This study forms part of a major project which is attempting to
deal with the problem of pharmaceuticals in the environment and
the main objective here is to investigate the features of EC and its ef-
fectiveness in the removal of DEX from water solution and hospital
wastewater. Experiment design and response surface methodology
(RSM) were employed to optimize the EC operational conditions for
DEX removal. In addition, the chemical oxygen demand (COD) and re-
sidual aluminum concentration were evaluated and the variation of
the toxicity was monitored throughout the evaluation, with the aid of
the Vibrio fischeri test. An analysis of the advantages of the V. fischeri
test was undertaken by Parvez et al. (2006).
As far as we are aware, this is the first study of how electrocoagulation
can be a means of removing dexamethasone from hospital wastewater.
2. Material and methods
2.1. Reagents
The DEX base (Sigma-Aldrich, Munich, Germany) standard solu-
tions were prepared shortly before the experiments. NaCl 99.5%
(Sigma-Aldrich, Munich, Germany) was used as electrolyte. Aceto-
nitrile HPLC grade (JT Baker, Mexico City, Mexico) and analytical
grade sodium formate (Sigma-Aldrich, Munich, Germany) were
used to prepare the mobile phase. All the solutions were prepared
with chemicals of at least analytical grade, by using ultrapure water
(Millipore, Molsheim, France).
2.2. Sampling of hospital wastewater
The studied wastewater samples were collected end-of-pipe from
the University Hospital (HUSM) of the Federal University of Santa
Maria after leaving the sewage treatment system. A composite sample
was formed by collecting samples, every 2 h, from 8:00 to 16:00 h.
The wastewater samples were collected, kept in the dark, at 4–8°C
and, at end of the day, filtered (cellulose filter, 7 μm) and submitted
to the EC experiments. The physico-chemical characteristics of the
HUSM effluent are shown in Table 1 (different samples, different
analysts).
2.3. Aliquot collection for the analytical measurements
Samples were taken in 0, 5, 15, 30 and 45 min of the EC experiments
conducted. The standard solutions and the hospital wastewater samples
treated, were passed through cellulose filter (7 μm), and afterwards,
through PTFE Millipore filter (0.45 μm),andthen,storedat4–8°C,in
the dark, until the analytical measurement.
2.4. Analytical methods
The residual aluminum was measured by means of a 1-02
Nanocolor test (Macherey-Nagel, Düren, Germany) and UV–vis
Shimadzu Multispec-1501 spectrophotometer (Schimadzu GmbH,
Duisburg, Germany).
A WTW LF 196 microprocessor conductivity meter was employed
for measuring conductivity and temperature; pH and dissolved oxygen
(DO) were measured by using WTW pH/Oxi 340i equipment (WTW
GmbH, Weilheim, Germany).
The DEX concentration was determined with the aid of a Shimadzu
high performance liquid chromatography coupled to a diode array de-
tector, and equipped with a LC-20AT pump (Shimadzu, Duisburg,
Germany). The mobile phase used was acetonitrile:formate buffer
[33:67] (0.0209 mol L
−1
sodium formate, pH 3.6); the column employed
was a Nucleodur CC 70/3 C18 ec equipped with a pre-column containing
thesamematerial;theflow rate was set to 0.5 mL min
−1
and the injec-
tion volume to 50 μL; the measurement was at 254 nm. The retention
time of DEX was 3.5 min under these conditions. The deconvolution
method based on UV absorbance (Martins et al., 2008b) was used to esti-
mate the organic load of the hospital wastewater.
2.5. Electrocoagulation
The electrocoagulation was carried out by using commercial alumi-
num electrodes (61 cm
2
effective area) immersed vertically and, in par-
allel, monopole configuration. NaCl was added as the electrolyte; an EC
Apparatus Corporation EC570 (Milford, MA, USA) power supply and a
VC-840 digital multimeter (Volcraft, Meggen, Switzerland) were used.
The experimental conditions were defined by factorial design.
A glass reactor (d
e
=105 mm) was used for the treatment of 1 L of
sample. The optimization step was performed using standard solution
of 100 μgL
−1
DEX, which is also used for the fortification of the hos-
pital wastewater samples. For the measurement of the initial conduc-
tivity, (3.3 mS cm
−1
), 2.0 g L
−1
NaCl as electrolyte was added to the
samples of wastewater, which had been previously filtered through a
cellulose filter (7 μm). All the experiments were performed at room
temperature (20–25 °C). The EC experiments were conducted under
Fig. 1. Dexamethasone structures.
352 D.R. Arsand et al. / Science of the Total Environment 443 (2013) 351–357

gentle magnetic stirring (120–150 rpm) and the system used can be
seen in Fig. 2.
2.6. Design of the experiments
Optimization of the experiments was conducted by employing an
experimental design. The fixed parameters were: applied current
(100–500 mA); inter-electrode distance (6–30 mm); electrolyte
concentration (NaCl, 250–1250 mg L
−1
) and 5 levels of significance
(−2, −1, 0, +1 and +2). The matrix that is formed comprises a
group of 17 experiments: 8 factorial, 3 central and 6 axial. These ex-
periments were performed at random to ensure the reliability of the
results. The parameter used to evaluate the efficiency of the process
was the lowering of the DEX concentration.
2.7. The efficiency of the procedure
The efficiency of the EC was calculated by means of Eq. (1) in opti-
mized conditions. The electrode mass loss during the process was mea-
sured by means of material balance in a time interval of 0–45 min.
φ¼ΔΜexp
ΔΜtheor
100 ð1Þ
where φis the current efficiency (%), ΔM
exp
is the experimental mass
variation and ΔM
theor
is the theoretical mass variation of the electrodes
during the EC experiments. The theoretical mass loss can be calculated
according to Eq. (2).
ΔΜtheor ¼ItM
zF ð2Þ
where I is the current (A), t is the time (s), M is the molar mass of the
predominant element of the electrode, z is the number of electrons in-
volved in the oxidation of the electrode (3 e
−
) and F is the Faraday con-
stant (C mol
−1
). Eq. (3) was used to evaluate the cost of the process,
where EE is the electric energy consumption (kWh), I is the current ap-
plied (A), U is the tension (V), and t, the time of treatment (h).
EEtheor ¼IUt
1000 ð3Þ
2.8. Toxicity test
The toxicity variation was monitored by using the V. fischeri test in ac-
cordance with ISO 11348-1 (1998), under optimized conditions; four
groups of experiments were carried out in aqueous solution: 1) without
DEX (blank), to evaluate the toxicity of the residual aluminum; 2) to
measure the toxicity of the DEX solution without EC treatment; 3) sub-
mitting DEX solution to EC with an inter-electrode distance of 6 mm,
or 4) with an inter-electrode distance of 30 mm. The different times of
exposure in the V. fischeri test were assumed to be those for acute and
chronic toxicity: 30 min and 24 h, respectively (Blaschke et al., 2010).
3. Results and discussion
3.1. Removal of dexamethasone —Pareto chart
The Pareto chart from the factorial design of experiments indicates
that the current is the most important variable for DEX removal, followed
by the electrolyte concentration (with 0.05 reliability; mean square pure
error8.40).BothvariableshaveahighimpactonEC,buttheappliedcur-
rent is dominant. The regression coefficient (R
2
) was 0.943 and the ad-
justed R-square (R
2adj
) was 0.870 for the DEX removal.
3.2. Surface response curves for removal of dexamethasone by
electrocoagulation
Astronginfluence of the applied current was observed in the removal
of DEX from aqueous solutions: the DEX removal increased along with
the current, even when there were greater electrode distances. As well
as the no significant effect of the inter-electrode distance, a compensa-
tion effect was detected: when the electrolyte concentration decreased,
a reduction of the inter-electrode distance restored the level of conduc-
tivity. The best results for DEX removal (up to 38%) were obtained in
two situations: by a small inter-electrode distance combined with low
electrolyte concentration, and by high electrolyte concentration com-
bined with a large inter-electrode distance. The results can be seen in
Fig. 3.
These were expected results because EC depends on the anode
reaction–aluminum oxidation (Dalvand et al., 2011; Gürses et al.,
2002). However, account should be taken of the mass transfer and
polarization close to the electrodes, and the occurrence of concomi-
tants, that may change the optimum conditions for the removal of a
specificsubstance(Gómez and Callao, 2008).
Table 1
Physico-chemical characteristics of the HUSM effluent.
Parameter Value
Chloride (mg L
−1
) 132.0
BOD
5
(mg O
2
L
−1
) 303.7
COD (mg O
2
L
−1
) 420.0
Phosphate (mg L
−1
) 7.5
Nitrate (μgL
−1
) 680.0
Ammoniacal nitrogen (mg L
−1
) 52.0
Total nitrogen (mg L
−1
) 59.1
pH 7
Potassium (mg L
−1
) 21.9
Sodium (mg L
−1
) 150.5
Total suspended solids (mg L
−1
) 57.0
Total solids (mg L
−1
) 484.0
Sulfate (mg L
−1
) 4.0
Temperature (°C) 22.0
Fig. 2. EC assembly used for the treatment of the aqueous solutions and hospital
wastewater samples containing DEX, where: (a) oxymeter and (a′) oxymeter elec-
trode; (b) conductivity meter and (b′) conductivity electrode; (c) 1 L glass reactor
and magnetic stirrer; (d) aluminum electrodes; (e) power supply and (f) multimeter.
353D.R. Arsand et al. / Science of the Total Environment 443 (2013) 351–357

3.3. Dissolved oxygen (DO) variation during the electrocoagulation
experiments
The DO variation was measured during the EC: an exponential de-
cline rate was observed when the applied current was increased. A
lower variation was observed when there was a higher electrolyte
concentration and a greater inter-electrode distance. This phenome-
non can be attributed to the lower gas solubility in a saline solution
and to the warming effect close to the electrodes, as well as to the for-
mation of gas during the process. When the inter-electrode distance
is greater, the electric current is deprived of power; as a result, the
electrolysis of water increases, and this leads to a higher rate of H
2
gas formation and, thus, a reduction of DO.
The higher the current applied, the higher the DO variation, the final
DO value reached 0.5 mg L
−1
O
2
. After EC, the DO of an aqueous medi-
um is not high enough for a subsequent aerobic biological treatment, or
for any other direct use where a higher DO concentration is required,
e.g., for fish farming (Becker et al., 2009; Kempton et al., 2002).
Nilsson et al. (2007) found that fish could not tolerate DO levels
below 0.78 mg L
−1
. In these cases, an oxygenation step will be
needed. Moreover, EC can be regarded as a useful pre-treatment
stage for anaerobic processes, where an absence of oxygen is need-
ed, e.g. by Anammox (Yang et al., 2010). The same can be said for
photocatalytic mechanisms where a transparent solution is highly
desirable.
3.4. Loss of mass of the electrodes
During the EC, aluminum electrodes are decomposed by the electro-
chemical oxidation. The real metal loss was determined by weighing
the electrodes before and after each experiment and carried out under
optimized conditions. The correlation coefficient for the mass loss of
aluminum and the current applied was 0.998 by p-levelb0.0001,
which suggests that the electrical energy applied was almost entirely
used for the electrode oxidation in the EC process. This is a matter of in-
terest with regard to the economic balance, as no significant waste of
energy occurred in an undesired heating process. Essadki et al. (2008)
recommend conducting the experiments by applying a current density
lower than 30 mA cm
−2
in order to avoid unnecessary aluminum oxi-
dation and thus achieve more economical results.
3.5. Physical–chemical parameters
The results of all the EC experiments showed that there was no
significant temperature increase (+1.8 ±0.94 °C) and the pH varia-
tion was only +2.0±0.15 units. This behavior can be attributed to
the high conductivity and the low electrical current applied: the elec-
trolysis of water was not enough to modify the pH significantly and
the variation of the conductivity was only + 8.0 ± 2.8 μScm
−1
. The
experiments using 400 and 500 mA showed a temperature variation
of +3 °C, and when 100 mA was applied, only +0.3 °C. Similar re-
sults were obtained for the pH variation.
Aluminum ion is a byproduct in the EC process when Al-electrodes
are used. The residual aluminum was7.0± 1.5 mg L
−1
without pH cor-
rection, below the general threshold limit for aluminum concentration
in wastewater.
3.6. Optimized conditions
The experiments were carried out under optimized conditions,
and a higher current (1000 mA) and higher electrolyte concentra-
tion (2000 mg L
−1
) were applied. These higher values were employed
by inter-electrode distance 6 and 30 mm, because the distance was clas-
sified as no significant by the Pareto chart for the experimental design.
Fig. 3. Surface response curves for dexamethasone removal by electrocoagulation: (a) inter-electrode distance and the applied current; (b) applied current and the electrolyte con-
centration; and (c) electrode distance and the electrolyte concentration as variables —mean square pure error 8.40.
354 D.R. Arsand et al. / Science of the Total Environment 443 (2013) 351–357

Fig. 4 shows the DEX variation during the experiments: the DEX removal
was similar when both inter-electrode distances were used, after 45 min
of treatment.
The variables of the EC process were monitored during the exper-
iments (at 0, 5, 15, 30 and 45 min) with the exception of the temper-
ature and the pH. It is well known, that slight temperature variations
do not constitute a problem for the EC processes. As pH adjustment
was used to control the residual aluminum, pH variations were not
taken into account. The residual aluminum concentration was 4.0 ±
1.40 mg L
−1
without pH adjustment (actual pH 8.5) and 0.25±
0.03 mg L
−1
with pH adjustment (to pH 6.5). The DEX concentration
was 68.2 ± 1.5% by pH 8.5 and 67.2± 2.9% by pH 6.5. These results
show that the pH adjustment to 6.5 does not influence the DEX re-
moval; however, it is a very efficient means of reducing the residual
aluminum. This pH range (6.5–8.5) is very important for the practical
application of EC. Emamjomeh and Sivakumar (2006) also found that
the pH interval 6–8 was the best pH work zone for the removal of
fluoride from waters by means of the EC process.
The profile of the DO decay curve during the EC process is almost
the same, regardless of the inter-electrode distance (see Fig. 5).
3.7. Process efficiency and energy consumption
The absolute value of the process efficiency (φ) of the experiments
carried out under optimized conditions was calculated as 117.9% and
113.7%, by using 6 and 30 mm inter-electrode distances, respectively.
The values higher than 100% can be attributed to the addition of the
electrochemical to the chemical oxidation process of the electrodes.
Moreover, this high process efficiency remains in accordance with what
is shown in Section 2.8. The electric tension of the system was 20 V in
both cases and the cost of the EC treatment under these conditions was
15 kWh m
−3
. The total aluminum consumption was 405.4 g m
−3
and 412.5 g m
−3
using 6 and 30 mm inter-electrode distance, respec-
tively, with no perceptible conductivity variations, during the 45 min
of treatment.
The cost of the process depends on energy consumption: Asselin
et al. (2008), e.g. studied the EC process under optimal conditions
and the cost of treatment reached 0.46 US$ m
−3
wastewater.
3.8. Hospital wastewater treatment by electrocoagulation
Fortified hospital wastewater with DEX (100 μgL
−1
) was treated by
EC under optimized conditions. The DEX removal showed similar char-
acteristics to the effects of the aqueous solution treatment. However,
the removal of DEX only starts after 15 min of treatment (Fig. 6). This
behavior can be attributed to the competition between DEX and other
concomitants in the wastewater.
The absorbance profile was monitored (see Fig. 7) during the process:
the absorbance decays in accordance with the removal of colloids and
reduction of the organic load of the hospital wastewater. In general,
organic molecules absorb ultraviolet light as a result of double bonds
and aromatic groups; thus, UV absorbance measurements can provide
a quick means of estimating the level of the organic carbon content
(Martins et al., 2008b). At the end of the EC process, the treated hospital
wastewater was almost clarified but the DEX concentration only par-
tially removed.
Most of the colloidal particles in wastewater have a negative charge,
depending on the related Zeta Potential (Harif et al., 2012). In EC, the
hydrolyzed species destabilize the suspended particles and react to
the dissolved organic material, and are thus able to determine the floc
growth kinetics. The particles can be effectively destabilized by neutral-
ization of the surface charge, which leads to precipitation. In general, or-
ganic molecules are large and contain many functional groups, such as
DEX, which means that different destabilization mechanisms can
occur (Harif et al., 2012). As the DEX base shows low hydrosolubility,
its removal mechanism can be attributed to repression of the double
layer and entrapment of colloidal particles by a sweeping floc.
As mentioned in Section 3.3, EC may be used as a pre-treatment
for advanced oxidation processes, as well as in anaerobic degradation
treatments. Since it can achieve a high rate of removal for the inter-
fering organic substances, EC may also be employed in cleaning up
the sample solutions before the analytical determinations.
Fig. 4. DEX concentration variation during the EC treatment in optimized conditions
using inter-electrode distances 6 mm (♦) and 30 mm (■).
Fig. 5. DO variation during the experiments using 6 (♦) and 30 mm (■) inter-electrode
distances.
Fig. 6. Hospital effluent treatment containing 100 μgL
−1
DEX in optimized conditions.
355D.R. Arsand et al. / Science of the Total Environment 443 (2013) 351–357

3.9. Variation of toxicity during the electrocoagulation process
The toxicity variation during the DEX removal by the EC process
was evaluated by carrying out experiments using pH adjustment
(pH 6.5), and obtaining a maximum residual aluminum concentra-
tion of 0.30 mg L
−1
. Acute and chronic toxicity were evaluated in a
blank sample (without DEX spike); in a standard solution of DEX
without EC treatment (100 μgL
−1
); in the standard DEX solution
after 45 min treatment using 6 mm inter-electrode distance; and in
the DEX standard solution after 45 min treatment using 30 mm
inter-electrode distance. The results obtained from tests usingV. fischeri
assay, demonstrate that the residual aluminum concentrations in the
final solutions from the EC process are not toxic. The experiments
with DEX aqueous solutions, whether submitted to electrocoagulation
or not, showed similar average values for acute and chronic toxicity.
However, in view of possible undetectable problems arising from the
DEX response to the V. fischeri test, the application of another toxicity
test is recommended. In this particular case, the toxicity test may lead
to a false response because allegedly, the V. fischeri bacterium has no
glicocorticoid receptor.
4. Conclusions
This study shows that the process of removing DEX increased
when higher EC current and electrolyte concentration were applied
to aqueous solutions of DEX. The EC process under optimized condi-
tions only showed a DEX removal rate of up to ~38%. Apart from
the different curve profiles of the decay, almost the same result was
achieved after 45 min of EC treatment of the hospital wastewater.
There was a significant removal of colloidal material and reduction
of the organic load by the EC treatment of the hospital wastewater in
the first 15 min of the process; however, most of the DEX remained in
solution. This means that most of the analyte that occurred was not
adsorbed on the organic matter.
The final DO concentration, which was close to 0.5 mg L
−1
O
2,
suggests that the EC process as a pretreatment for subsequent pro-
cesses, where reduced DO is needed.
The residual aluminum concentration in all the experiments
was lower than 10.0 mg L
−1
without pH adjustment, and below
0.30 mg L
−1
by adjustment to pH 6.5. Given the environmental
concerns related to free aluminum ions, an adjustment of the pH
by the EC treatment is advisable.
When the values of acute and chronic toxicity that were measured
by V. fischeri tests, both before and after the EC treatment of aqueous
solutions of DEX were compared, no noticeable toxicity variation was
found, even when by the process was carried out with or without
DEX, i.e., no toxic byproducts were formed.
Finally, it is hoped that this study can make a significant contribu-
tion to knowledge of the environmental occurrence of DEX, since as
far we know, no similar work dealing with this subject can be found
in the literature.
Acknowledgments
The authors are grateful to Capes Foundation (Brazilian Ministry
of Education) and the German Academic Exchange Service (DAAD),
for providing grants for this study, and to the Brazilian National Coun-
cil for Scientific and Technological Development (CNPq), for its finan-
cial support.
The authors have declared no conflict of interests.
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://
dx.doi.org/10.1016/j.scitotenv.2012.10.100.
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