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International Journal of Environmental
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Pharmaceutical wastewater
degradation: effective and economical
treatment using waste-metallic iron
shavings
Yolanda Seguraa, Fernando Martíneza & Juan Antonio Meleroa
a Department of Chemical and Environmental Technology, Rey
Juan Carlos University, Madrid 28933, Spain
Published online: 29 Apr 2014.
To cite this article: Yolanda Segura, Fernando Martínez & Juan Antonio Melero (2014)
Pharmaceutical wastewater degradation: effective and economical treatment using waste-
metallic iron shavings, International Journal of Environmental Studies, 71:2, 200-208, DOI:
10.1080/00207233.2014.903128
To link to this article: http://dx.doi.org/10.1080/00207233.2014.903128
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Pharmaceutical wastewater degradation: effective
and economical treatment using waste-metallic
iron shavings
YOLANDA SEGURA*, FERNANDO MARTÍNEZ AND JUAN ANTONIO MELERO
Department of Chemical and Environmental Technology, Rey Juan Carlos University,
Madrid 28933, Spain
Industrial wastewater generated by a drug manufacturing plant located in Spain was degraded by
Fenton oxidation processes, which employ waste-metallic iron shavings as heterogeneous zero-
valent iron (ZVI) catalyst and hydrogen peroxide. The effluent comprises a complex mixture of
organic substances which are very refractory to common conventional treatments and it is charac-
terized by a low BOD/COD ratio. The stirring speed or the particle size has been found to be the
determining factors, greatly influencing the degradation of the organic pollutants present in the
wastewater. The influence of the initial hydrogen peroxide concentration has also been evaluated.
The optimal conditions for degradation led to total organic carbon (TOC) reductions of up to 60%.
The remarkable results of TOC mineralization could also be attributed to the physico-chemical
modification of the ZVI during the oxidizing process. This study shows that the ZVI/H
2
O
2
system
can be considered as an easy, economic and effective alternative solution as a pre-treatment step
before biological treatments.
Keywords: Wastewater; Fenton process; ZVI; Iron shavings
Introduction
During the last century, a huge amount of industrial wastewater was discharged into rivers,
lakes and coastal areas. This has caused serious pollution problems in the water environ-
ment with negative consequences for ecosystems and human life. Because each industrial
sector produces its own particular combination of pollutants, their treatment must be
designed specifically. Pharmaceutical waste is one of the most complex and toxic industrial
wastes [1]. The pharmaceutical industry generates a number of waste streams with differ-
ent characteristics and volumes. The active substances and their metabolites reach the sew-
age treatment plants and sometimes directly enter the environment. Accordingly, an
evaluation of the pharmaceutical concentration and the risk assessment is useful to evaluate
the level of risk to the aquatic environment in the area [2].
Biological processes are commonly used for the domestic and industrial wastewater
treatment. It is relatively simple and efficient to mineralize organic constituents in indus-
trial discharges. But, the treatment of some industrial wastewaters by conventional biologi-
cal process is difficult due to the presence of refractory and toxic organic substances.
Various pre-treatment technologies for enhancing biodegradability or refractory compounds
*Corresponding author. Email: yolanda.segura@urjc.es
© 2014 Taylor & Francis
International Journal of Environmental Studies, 2014
Vol. 71, No. 2, 200–208, http://dx.doi.org/10.1080/00207233.2014.903128
Downloaded by [University Rey Juan Carlosi], [Yolanda Segura Urraca] at 02:34 21 May 2014
have been reported, including advanced oxidation processes (AOPs) such as photocatalytic
pre-treatment, ozonation and Fenton oxidation [3,4]. AOPs have been found to be success-
ful for the abatement of refractory and/or toxic organic pollutants in water and wastewater,
being mostly used in combination with conventional biological and chemical methods [5].
Most AOPs are cost-intensive operations and the time of treatment is a limiting factor in
the overall cost. Fenton oxidation processes are considered as a viable alternative for the
removal of a great variety of organic pollutants [6]. Nevertheless, this process operates at
the optimum pH 3. The use of excess quantities of ferrous ions is the major disadvantage
with the conventional Fenton process. Therefore, lately alternatives such as the heteroge-
neous zero-valent iron (ZVI) particles have been successfully applied [7,8].
ZVI has been used for the degradation of different model pollutants [9] through the acti-
vation of dioxygen for the generation of hydrogen peroxide (equation 1), which will be
decomposed to hydroxyl radicals by the ferrous ions dissolved.
Fe0þO2þ2Hþ!Fe2þþH2O2(1)
This Fenton-like ZVI process has also been successfully applied on the treatment of sev-
eral wastewaters such as olive mill effluents [10], pharmaceutical wastewaters (PWWs)
[11] and landfill leachates [12].
This works investigates the efficiency of the ZVI/H
2
O
2
system for the removal of
mixed-complex organic compounds contained in the wastewater produced by a pharmaceu-
tical business located in Madrid, before discharge to the receiving environment or sewer
system. The aim of this work was to obtain a cost-effective technique by using moderate
loadings of hydrogen peroxide and ZVI, employing inexpensive metallic iron shavings as
a heterogeneous catalyst which can be easily removed from the treated effluent by mag-
netic separation. In order to study diffusion problems from use of the iron shavings, we
studied the effect of various reaction parameters such as the mixing velocity or the particle
size.
Materials and methods
Iron metal powder (Sigma-Aldrich, 97% pure) and hydrogen peroxide (Scharlab, 30% pure)
were used as purchased. The iron shavings were wastes collected from a metallurgical
processing plant.
In a typical experimental setup, a cylindrical glass vessel was filled with 0.5 L of the
PWW. The PWW was previously diluted 1/50 until initial total organic carbon (TOC) of
ca. 100 mg L
−1
. Thereafter, appropriate amounts of hydrogen peroxide and ZVI (commer-
cial powder or iron shavings) were added in the presence of aeration with a flow rate of 5
L min
−1
. The temperature was controlled at 22 ± 2 °C during the reaction. The iron metal
was suspended in the aqueous solution and gently mixed using a magnetic stirrer while
adjusting the pH to ca. 3 with H
2
SO
4
. Iron shavings were separated by using shape-selec-
tive sieves with mesh ranging from 2 mm to 300 μm. The amount of initial hydrogen per-
oxide is equivalent to the stoichiometric amount, half or twice (coded as 100, 50 or 200%,
respectively) for the complete mineralization of the organic compounds contained in the
PWW to CO
2
and H
2
O (equation 2)
CþH2O2!CO2þH2O (2)
Pharmaceutical wastewater degradation 201
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Samples were taken throughout reaction time (0, 10, 20, 40, 60 and 120 min) and filtered
through 0.22 μm nylon membranes prior to analysis. TOC content of the samples was
determined using a combustion/non-dispersive infrared gas analyser model TOC-V
(Shimadzu). Hydrogen peroxide concentration was measured by iodometric titration and
the iron content in the filtered solution after reaction was measured by ICP-AES analysis
using a Varian Vista AX spectrometer. The pH of the solution was measured using a
Metrohm pH meter.
Characterization of the pharmaceuticals wastewater and blank reactions
The drug manufacturing plant located in Madrid (Spain) is dedicated to producing different
active drugs for hypertension, heart diseases, osteoporosis and anti-depressive compounds.
The major operations in these plants generally include chemical reactions in vessels, sol-
vent extraction, crystallization, filtration and drying. The wastewaters generated in the syn-
thesis of those organic compounds (active ingredients or intermediate products) contain a
wide array of various chemical components prevailing at relatively high concentration. The
wastewater produced inhibits biological systems.
Various types of waste streams are generated by this plant depending upon the manufac-
turing process. All mixed streams were firstly treated to remove volatile solvents. The
resultant effluent was collected for study. Table 1shows the physico-chemical characteris-
tics of the wastewater. As above mentioned, the effluent contains a high organic load, con-
sidered non-biodegradable as the BOD
5
/COD ratio is 0.18.
The efficiency of the ZVI/H
2
O
2
system was evaluated by comparing several blank
experiments: (i) aeration/stirring in the presence of ZVI without H
2
O
2
, in order to evaluate
the oxidizing power of the ZVI system; (ii) aeration/stirring in the presence of H
2
O
2
with-
out ZVI, in order to determine the oxidizing potential of the hydrogen peroxide in a non-
catalytic system; and (iii) aeration/stirring with neither ZVI nor hydrogen peroxide, in
order to evaluate the stripping process (figures not shown).
All blanks showed very low TOC removals, obtaining TOC degradations after 2 h of
less than 10% for all the blank reactions. The absence of H
2
O
2
and ZVI revealed an insig-
nificant reduction of the overall TOC content. The pH was kept uncontrolled during all the
experiments. Values of pH did not change throughout time; values obtained ranged
between 2.8 and 3 during the two hours of the blank experiments.
Application of iron shavings
The metallic shavings, generated as wastes from a metallurgical firm, were used and com-
pared to the commercial powder ZVI. The use of those wastes makes the Fenton-like ZVI
Table 1. Physico-chemical characteristics of the PWW generated by a pharmaceutical industry.
pH 6.50 ± 0.5
BOD
5
,mgL
−1
2700 ± 150
COD, mg L
−1
15,000 ± 100
Conductivity, μScm
−2
70 ± 10
TOC, mg L
−1
4550 ± 100
Turbidity, NTU 267 ± 1
BOD
5
/COD 0.18
Suspended solids, mg L
−1
522 ± 100
202 Y. Segura et al.
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system very attractive from the economic and environmental points of view. Therefore, we
studied the degradation efficiency of both types of metallic iron for the treatment of diluted
PWW 0.1 g/L TOC, using 2.4 g/L of ZVI and 200% H
2
O
2
of the stoichiometric amount
for the total mineralization of the organic compounds to CO
2
and H
2
O.
Figure 1shows TOC and H
2
O
2
conversions obtained for the commercial ZVI powder
and for the waste-metallic iron shavings. The iron shavings reached TOC conversions of
9, 15, 20 and 40%, after 20, 40, 60 and 120 min of reaction, respectively. Compared to the
results observed for the commercial ZVI powder, using the same experimental conditions,
(20, 32, 40 and 55% over 20, 40, 60 and 120 min, respectively) lower TOC degradations
was obtained. The particle sizes of the iron shavings are bigger than those of the powder
catalyst. Further, the slightly lower degradation obtained in the case of the iron shavings
was probably due to the diffusion problems of the iron shavings as we used a mix of dif-
ferent particle sizes (ranging from 5 mm to 200 μm).
The pH values were kept acidic throughout the reaction in both cases. A lower H
2
O
2
consumption for the iron shavings with final H
2
O
2
conversions of 65% was also observed;
unlike the almost total oxidant conversion obtained after 120 min (90%) when using ZVI
powder.
Even if the TOC degradation obtained is slightly higher when using commercial iron
powder (due to the smaller particle size) in order to obtain a more cost-effective technol-
ogy, the optimization of the different parameters of the Fenton-like process can be carried
out using the metallic waste of iron shavings as a heterogeneous catalyst.
Influence of the stirring velocity
The influence of the mixing velocity during the Fenton reaction using iron shavings was
evaluated using two identical vessels containing the PWW in the presence of ZVI and
H
2
O
2
, under the same experimental conditions (200% H
2
O
2
and 2.4 g/L). Two types of
agitation velocities (500 and 1000 rpm) were tested using magnetic stirrers. The results
20 40 60 80 1 120
0
20
40
60
80
100
X (%)
Time (min)
commercial ZVI powder
ZVI shavings
100
0
20
40
60
80
100
XH2O2 (%)
TOC
Figure 1. The effect of the ZVI source in terms of TOC (columns) and hydrogen peroxide (lines) conversions.
Initial experimental conditions: TOC
0
0.1 g L
−1
, acidic pH (3), ZVI (2.4 g L
−1
), H
2
O
2
(200%), stirring velocity
(500 rpm) and 5 L min
−1
air flow.
Pharmaceutical wastewater degradation 203
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showed (figure 2) a remarkable influence when the mixing stirring velocity increases. The
effect of increasing the mixing agitation velocity was especially significant during the first
period (up to one hour) of the reaction obtaining TOC conversions after 40 and 60 min of
30–35% instead of 18–20% conversions for the 500 and 1000 rpm, respectively. A moder-
ate difference, however, was observed after 2 h of reaction, obtaining 39 and 43% of TOC
removal for the 500 and 1000 rpm, respectively. This proves that the flow velocity and tur-
bulence significantly increased the TOC mineralization in the treatment of the PWW.
Influence of the particle size of the iron shavings
Experiments were carried out using mixed shavings with different particle sizes ranging
from 5 mm to 200 μm. In order to evaluate the influence of the particle size on the TOC
degradation, the iron shavings were sieved, obtaining different particle lengths (350, 700
and 2000 μm). Figure 3shows the effects of the particle size of the iron shavings on the
hydrogen peroxide conversion and on the removal of the organic compounds present in
the PWW. It is evident that the TOC degradation depends on the iron particle size, with
higher catalytic activity being obtained in terms of TOC as the particle size decreases.
TOC conversions of 35, 46 and 55% after 2 h of reaction were obtained for the particle
sizes of 2000, 700 and 350 μm, respectively.
Shavings with smaller particle sizes (350 μm) were the most active (obtaining 16, 28
and 55% after 40, 60 and 120 min, respectively), whereas the biggest sizes led to lower
degradations (4, 16, 27% compared to 4, 9, 15% respectively, after 20, 40 and 60 h of
reaction).
It is well known that the activity can be improved by using nano-sized F0
eparticles com-
pared to bigger sizes and different physical structures of F0
e. The use of bigger particle
sizes imposes mass transport limitations and clearly inhibits the Fenton degradation. Values
of pH kept acidic throughout the reaction time, as the hydrogen peroxide is still present
after 2 h.
20 40 60 80 100 120
0
20
40
60
80
100
XTOC (%)
Time (min)
500rpm
1000rpm
0
20
40
60
80
100
XH2O2 (%)
Figure 2. The effect of the mixing velocity on the TOC (columns) and hydrogen peroxide (lines) conversions.
Initial experimental conditions: TOC
0
0.1 g L
−1
, acidic pH (3), ZVI (2.4 g L
−1
), H
2
O
2
(200%) and 5 L min
−1
air
flow.
204 Y. Segura et al.
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Influence of the concentration of the oxidant
The effectiveness of the Fenton-like ZVI treatment depends on the formation of oxidizing
species such as hydroxyl radicals, which are produced by the decomposition of the hydro-
gen peroxide. We studied the influence of different H
2
O
2
amounts (stoichiometric amount,
half or twice, codified as 100, 50 and 200%, respectively) for the treatment of PWW 0.1
g/L TOC using 2.4 g/L of ZVI and initial pH of 3. Figure 4shows the results of the TOC
and hydrogen peroxide conversions using different oxidant concentrations for the treatment
of PWW. The increase of the hydrogen peroxide concentration evidenced a clear enhance-
ment of performance when using 50 and 100%. But, when an excess of 200% was used
0 20 40 60 80 100 120
0
20
40
60
80
100
X (%)
Time (min)
350 µ m
700 µ m
2 mm
0
20
40
60
80
100
XH2O2
(%)
TOC
Figure 3. The effect of the shavings particle size (350, 700 and 2000 μm) in terms of TOC (columns)
and hydrogen peroxide (lines) conversions. Initial experimental conditions: TOC
0
0.1 g L
−1
, acidic pH (3), ZVI
(2.4 g L
−1
), (200%) H
2
O
2,
stirring velocity (1000 rpm) and 5 L min
−1
air flow.
0 20 40 60 80 100 120
0
20
40
60
80
100
XTOC(%)
Time (min)
200%
100%
50%
0
20
40
60
80
100
XH2O2
(%)
Figure 4. The effect of the hydrogen peroxide concentration (50, 100 and 200% of the stoichiometric amount)
in terms of TOC (columns) and hydrogen peroxide (lines) conversions. Initial experimental conditions: TOC0 0.1
gL
−1
, acidic pH (3), ZVI (2.4 g L
−1
), stirring velocity (1000 rpm), particle size (350 μm) and 5 L min
−1
air flow.
Pharmaceutical wastewater degradation 205
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the degradation decreased. We obtained TOC conversions of 45, 62 and 53 when using
50, 100 and 200% respectively of the stoichiometric amount.
It is well known that when one of the Fenton reactants (Fe or H
2
O
2
) is overdosed it can
react with the hydroxyl radicals inhibiting the organic degradation. An excess of oxidant
induces the radical scavenging reaction (equation 3). Such inhibition was observed using
2.4 g/L of ZVI and an excess of the hydrogen peroxide (200%).
H2O2þHO!HO
2þH2O (3)
Regarding the hydrogen peroxide conversions, a reasonable decrease was observed; the
oxidant concentration decreased keeping the ZVI concentration constant (2.4 g/L). Total
oxidant consumptions were achieved after 120 min of treatment when 50 and 100% of
H
2
O
2
were used. When an excess of 200% was used, conversions of 90% were obtained
after 2 h of reaction. The pH values kept acid (2.9–3.1) throughout the reaction, except in
the case of 50 and 100%. In those cases, the pH went up to 4.5 after 2 h of reaction,
which occurred when the hydrogen peroxide depleted.
In order to use less oxidant making the process as economic as possible, the stoichiome-
tric amount of the hydrogen peroxide is used in the rest of the experiments.
Effectiveness of fresh and reused iron shavings
Accompanying the ZVI corrosion during the process, iron oxides are built up on the metal-
lic surface. Formation of iron corrosion layers starts with dissolved O
2
oxidation of metal-
lic iron. Figure 5shows TOC and hydrogen peroxide conversions of experiments
performed using fresh and reused materials after two or three times, for the treatment of
0.1 g/L PWW using ZVI concentrations of 2.4 g/L and the stoichiometric amount of H
2
O
2
(100%), with the highest mixing velocity (1000 rpm) and smallest particle size (350 μm).
Results revealed a rapid initial degradation of the fresh iron shaving material in terms of
TOC mineralization, compared to degradation obtained when the catalyst was twice or
020406080100120
0
20
40
60
80
100
XTOC(%)
Time (min)
1st use
2nd use
3rd use
0
20
40
60
80
100
XH2O2
(%)
Figure 5. The effect of reusing iron shavings (1, 2 or 3 times) in terms of TOC (columns) and hydrogen perox-
ide (lines) conversions. Initial experimental conditions: TOC
0
0.1 g L
−1
, acidic pH (3), ZVI (2.4 gL
−1
), H
2
O
2
(100%), stirring velocity (1000 rpm), particle size (350 μm) and 5 L min
−1
air flow.
206 Y. Segura et al.
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three times reused. But, the TOC removal after two hours was only slight superior than in
the case of the reused material, with 63% compared to 58 and 59% of TOC mineralization
after 2 h for the 2nd and 3rd use, respectively.
Although chemical composition of the iron shavings obtained after reaction was not
identified in this study, the shavings were likely a mixture of different iron oxides/oxy-
hydroxides. These iron oxides likely play a vital role in improvement of the water quality.
The formation of iron oxides on the metallic ZVI surface has been reported in literature as
another mechanism that could generate hydroxyl radicals due to the formation of galvanic
cells between ZVI and the iron oxides formed on the metallic surface [9]. But, with
increasing thickness of the layer of iron corrosion products, diffusion of dissolved O
2
to
the metallic iron surface becomes more difficult [13]. On fresh surfaces, the adsorption
ability and reactivity of the ZVI might be high.
These promising results suggest that the metallic shavings, despite initial rapid oxidation
of the particle surface and slower initial activity in terms of TOC degradation after use,
have sufficient residual oxidizing power to enable them to be reused a few more times or
to even to be included in a continuous longer treatment process.
Conclusions
This study shows that ZVI/H
2
O
2
can be considered as an effective alternative solution for
the removal of many organic pollutants present in a wastewater generated by a drug manu-
facturing plant located in Madrid. Iron shavings, wastes from a metallurgical business, are
a promising, low-cost material which can be employed as a heterogeneous Fenton-like
catalyst. TOC reductions of up to 60% were obtained after 2 h reaction, being an easy,
economic and effective pre-treatment step.
This degree of organic mineralization was reached by using moderate loadings of ZVI
shavings and hydrogen peroxide. The shavings can be easily removed magnetically after
the treatments. The consumption of hydrogen peroxide was total at the end of the reaction,
when the stoichiometric amount of oxidant was used, which was the optimal amount within
the studied dose range. The researchers have also assessed the effect of the stirring velocity
during the process on the TOC degradation, as well as the particle size of the shavings
employed. These parameters both influenced remarkably the overall TOC removal. Higher
mixing velocities as well as the use of smaller particle sizes of iron shavings were found to
be more effective. Moreover, the waste-metallic iron shavings were reused three times and
even if a slower kinetic was shown through time of reaction, the TOC conversion was up to
60% in all cases with a total consumption of the oxidant after two hours.
Acknowledgements
We gratefully acknowledge financial support from the Regional Government of Madrid
provided through project REMTAVARES and the European Social Fund.
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