Science of the Total Environment 433 (2012) 296–301

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Removal of ibuprofen and its transformation products: Experimental andsimulation studies

N. Collado a, G. Buttiglieri b, L. Ferrando-Climent b, S. Rodriguez-Mozaz b, D. Barceló b,c,J. Comas a, I. Rodriguez-Roda a,b,⁎a LEQUiA, Laboratory of Chemical and Environmental Engineering, University of Girona, Campus Montilivi, Girona, 17071, Spainb ICRA, Catalan Institute for Water Research, Carrer Emili Grahit, 101, Parc Científic i Tecnològic de la Universitat de Girona, 17003 Girona, Spainc Dept. Environmental Chemistry, Institute of Environmental Assessment and Water Research (IDAEA), CSIC, c/Jordi Girona 18-26, E-08034 Barcelona, Spain

Abbreviations: ASM, activated sludge model; IBU,ibuprofen; IBU-1OH, 1-hydroxyl ibuprofen; IBU-2OH, 2carboxyl ibuprofen; Kbiol, biodegradation reaction rate ccient; PhACs, pharmaceutically active compounds; TP,total suspended solid; WWTP, wastewater treatment pl⁎ Corresponding author.

E-mail address: irodriguezroda@icra.cat (I. Rodrigue

0048-9697/$ – see front matter © 2012 Elsevier B.V. Alldoi:10.1016/j.scitotenv.2012.06.060

a b s t r a c t

a r t i c l e i n f o

Article history:Received 16 March 2012Received in revised form 8 June 2012Accepted 16 June 2012Available online 15 July 2012

Keywords:IbuprofenKineticsBiodegradationTransformation products

Pharmaceutically active compounds (PhACs) deserve attention because of their effect on ecosystems andhuman health, as well as their continuous introduction into the aquatic environment. Classification schemesare suggested to characterise their biological degradation, e.g., based on pseudo-first-order kinetics, but theseschemes can vary significantly, presumably due to pharmaceutical loads, sludge characteristics and experi-mental conditions. Degradation data for PhAC transformation products (TPs) are largely lacking.The present work focuses not only on the biodegradation of the pharmaceutical compound ibuprofen but alsoon its best-known TPs (i.e., carboxyl ibuprofen and both hydroxyl ibuprofen isomers). Ibuprofen is one of themost commonly consumed PhACs and can be found in different environmental compartments.The experiment performed consisted of a set of aerated batch tests with different suspended solid and ibu-profen concentrations to determine the influence of these parameters on the calculated biodegradation con-stant (Kbiol). Sampling of the liquid phase at different scheduled times was assessed, removal efficiencieswere calculated and pseudo-first-order kinetics were adjusted to obtain experimental Kbiol values for the par-ent compound and its TPs.The experimental data were successfully fitted to ASM-based models, with Kbiol values for the target com-pounds ranging from almost 1 to 17 L gSST−1 d−1, depending on the concentrations of the biomass and ibu-profen. This work provides innovative knowledge not only regarding the removal of TPs but also theformation kinetics of these TPs.

© 2012 Elsevier B.V. All rights reserved.

1. Introduction

Residues of pharmaceutically active compounds (PhACs) haveraised concern because of their continuous introduction into the aquaticenvironment (Barceló and Petrovic, 2007; Santos et al., 2009). PhACsare administered in large quantities to humans and animals and havebeen detected in all compartments of the aquatic environment(Castiglioni et al., 2006; Bartelt-Hunt et al., 2009). The real effect ofPhACs on ecosystems and human health, directly via drinking waterand/or indirectly via the food chain, has not been completely elucidated.Moreover, there is no legislation regarding the regulation of PhACs.However, the impact of PhACs, considering both acute and chronic ef-fects on non-target organisms, has been studied, with an emphasis on

ibuprofen; IBU-OH, hydroxyl-hydroxyl ibuprofen; IBU-CBX,onstant; KD, adsorption coeffi-transformation product; TSS,ant.

z-Roda).

rights reserved.

PhACs as a continuous threat to environmental stability (Santos et al.,2010; Schnell et al., 2009) and the need for a better understanding oftheir fate to facilitate their removal from the environment.

PhACs are primarily released through wastewater treatmentplant (WWTP) discharges (Heberer, 2002). WWTPs are not current-ly designed for complete removal of PhACs (Joss et al., 2008). Exten-sive WWTP sampling campaigns have been explored in severalcountries where various WWTP treatment technologies have beenapplied, and extensive information is available on PhAC influentand effluent concentrations with reported concentrations typicallyon the order of ng L−1 or low μg L−1 (Kolpin et al., 2002;Buttiglieri and Knepper, 2008; Carballa et al., 2008). Several studieshave demonstrated that some PhACs are efficiently removed withinWWTP facilities (e.g., ibuprofen, naproxen and ketoprofen), whileothers are more persistent (e.g., diclofenac and clofibric acid)(Quintana et al., 2005; Kosjek et al., 2007; Onesios et al., 2009;Tambosi et al., 2010). Within the WWTP, the PhAC may be removedfrom the liquid phase depending on its susceptibility to adsorptionor biodegradation (Ternes and Joss, 2006). Little information hasbeen reported on the presence of PhAC transformation products

297N. Collado et al. / Science of the Total Environment 433 (2012) 296–301

(TPs), the formation of these TPs or their removal because most ofthe available reports focus on the parent compound.

Modelling and simulation of the transport and removal of macro-pollutants (such as organic matter, nitrogen, phosphorus and suspendedsolids) in WWTPs can be considered a mature scientific discipline. Thestandard and most widely used models are deterministic, describingthe removal of organic matter and nutrients from activated sludge (AS)(Gernaey et al., 2004), or metabolic (van Loosdrecht and Heijnen,2002). Modelling and simulating micropollutants are currently a grow-ing area of interest and activity within urban water cycle modellingto support load estimation, predict environmental impact and find opti-mal organic removal technologies for micropollutants and PhACs inparticular.

The activated sludge models (ASMs) have been extended to in-clude the occurrence, transport and fate of micropollutants, withconsideration of parent compound formation, sorption and biodeg-radation processes, both aerobic and anoxic conditions and differentwastewater fractions (aqueous, solid, retransformable and seques-tered) to predict the capability of removing several micropollutantsfrom activated sludge systems (Plósz et al., 2010, 2011). Extensionsof the ASMs to micropollutants in different units of the urban watersystems (sewer systems, WWTP and receiving waters), includingphysical (sedimentation, resuspension and volatilisation), physico-chemical (sorption–desorption, hydrolysis and photolysis) and bio-logical (aerobic and anoxic biodegradation) processes have alsobeen documented (Benedetti et al., 2010).

For PhAC biodegradation processes in activated sludge,pseudo-first-order reaction kinetics and the use of biodegradation reac-tion rate constants (Kbiol) have been proposed (Joss et al., 2006). Dataare available for some pharmaceutical compounds under specificconditions and at specific concentrations. However, the Kbiol valuesreported in the literature differ significantly among authors. Some au-thors ascribe this variability of biodegradation rates to differences inthe initial pharmaceutical load (Abegglen et al., 2009), while othersalso highlight the importance of sludge composition (i.e., diversity ofbiomass, types of primary substrates, and so on) and experimental con-ditions (Tran et al., 2009). To the authors' knowledge, no modellingstudies have been published yet regarding the biodegradation of parentcompounds and their TPs.

Ibuprofen, a non-steroidal anti-inflammatory drug, has been se-lected for the study because of its worldwide use and presence. Theestimated annual consumption of ibuprofen in developed countriesis several hundred tonnes (Daughton and Ternes, 1999). The presenceof ibuprofen in raw wastewater (ranging broadly from low μg L−1 to373 μg L−1, with an average influent concentration of 37 μg L−1), itsremoval (95% or higher in secondary treatment; Smook et al., 2008)and transformation in WWTPs have been studied extensively(Onesios et al., 2009; Verlicchi et al., 2012). A large proportion ofthe active compound is excreted as the parent compound togetherwith its known human metabolites, hydroxyl ibuprofen (IBU-OH)and carboxyl ibuprofen (IBU-CBX) (Zwiener et al., 2002). However,the human metabolites of ibuprofen are identical to its TPs (Stumpfet al., 1999; Buser et al., 1999) i.e. generated from biotic/abiotic pro-cesses in the environment. Ibuprofen in the water environment hasbeen shown to affect on the reproduction in both vertebrates and in-vertebrates (Hayashi et al., 2008). Parental exposure to as low as0.1 μg L−1 ibuprofen can delay hatching of eggs of freshwater fish(Han et al., 2010). Acute and sub-chronic assays carried out atng L−1 ibuprofen concentrations demonstrated also genotoxic effectsfor fish (Ragugnetti et al., 2011).

The aimof thismanuscript is twofold. Thefirst objective is to presentan experimental study of the biodegradability of ibuprofen to deter-mine the influence of the initial concentration of the pharmaceuticaland biomass contents. The second objective is to fit the experimentaldata to ASM-based models with pseudo-first-order kinetics, relatingparent compound degradation to TP formation.

2. Materials and methods

2.1. Batch tests

A set of laboratory batch biodegradation studies with activatedsludge from a municipal WWTP has been performed to investigatethe biodegradation profiles of ibuprofen and the formation and re-moval of its major TPs.

The batch experiments consisted of a set of two-litre glass bottles,with permanent aeration and automatic continuous stirring. Experi-ments were performed at room temperature (20 °C±2 °C) andwith an oxygen content of approximately 7.5 mg O2 L−1. Dissolvedoxygen was not a limiting factor.

The sludge was taken from a conventional WWTP (Castell Platjad'Aro, NE Spain; 35,000 m3 d−1, 175,000 I.E.) with an observed influ-ent ibuprofen concentration of approximately 10 μg L−1 (Dolar et al.,in preparation).

Different suspended solid concentrations (ranging from 50 to1000 mgTSS L−1) and ibuprofen concentrations (from 10 to1000 μg L−1) were tested in a total of nine combinations. Accordingto the initial conditions, different scheduled times for sampling weredetermined to occur between 24 and 72 h (shorter intervals for higherTSS content). The sludge was sampled from the WWTP (averagesuspended solid concentration from 1 to 2 gTSS L−1), aerated for 2 hbefore use (to minimise the amount of rapidly degradable organicmatter still present) and diluted with tap water to the appropriateconcentration for each batch study.

2.2. Analysis of pharmaceuticals

Aqueous samples (10 mL) were filtered through 0.45 μm glass fibrefilters and kept in 20-mL glass vials with 1 mL of paraformaldehyde so-lution at 37% v/v to avoid any further degradation prior to analysis. All ofthe samples were well homogenised and frozen at −20 °C until theiranalysis. Ibuprofen and selected ibuprofen transformation products(carboxyl ibuprofen (IBU-CBX), 1-hydroxyl-ibuprofen (IBU-1OH) and2-hydroxyl-ibuprofen (IBU-2OH) (Fig. 1)) were analysed using a UPLCsystem (Waters Corp., Mildford, MA, USA) coupled to a triple quadru-pole–linear ion trap mass spectrometer (5500 QTRAP, Applied Bio-systems, Foster City, CA, USA) in negative ionisation mode.

2.3. Blanks, controls, reproducibility tests and interpretation of results

Several blank tests, with the same configuration as the batch testsdescribed in Section 2.1 but without ibuprofen, were performed inparallel, and no significant contamination was detected (ibuprofenconcentration was always less than 0.32 μg L−1).

Testswith ibuprofen (concentration ranging from10 to 1000 μg L−1)but without biomass (to check possible chemical or physical removal)confirmed that there was no abiotic removal in the system (b1%) thatwould decrease the ibuprofen concentration.

Experimental reproducibility, homogeneity and intrinsic variabilityof the final biodegradation rate values were assessed by performing atest with a set of six two-litre aerated glass bottles with the same con-tent (1 gTSS L−1 biomass and 10 μg L−1 ibuprofen). Almost completeremoval of ibuprofen (final concentrationb0.08 μg L−1) was observedin all of the tests, with a standard deviation of ±0.3 μg L−1 (samplesat 3, 5 and 24 h).

Removal efficiencieswere calculated and pseudo-first-order kineticswere adjusted with Matlab software. The experimental biodegradationrate constants (Kbiol; Joss et al., 2006)were obtained for the parent com-pound for each combination of the batch tests of paragraph 2.1 and,under specific conditions (100 mgTSS L−1 and 10 μgIBU L−1), for theaforementioned TPs.

Fig. 1. Structures of: (a) ibuprofen; (b) carboxyl ibuprofen (IBU-CBX); (c) 1-hydroxyl-ibuprofen (IBU-1OH); (d) 2-hydroxyl-ibuprofen (IBU-2OH).

298 N. Collado et al. / Science of the Total Environment 433 (2012) 296–301

3. Results

3.1. Biodegradation studies on ibuprofen

Aerobic batch tests were run at different initial ibuprofen and solidconcentrations. The removal efficiencies obtained are presented inFig. 2, illustrating variable degradation rates.

A final significant ibuprofen removal was achieved in most of thetested combinationswithin three days. The profiles shown in Fig. 2 dem-onstrate that the higher removal rates were obtained at higher concen-trations of biomass, with faster and more complete ibuprofen removal.In contrast, high loads of pharmaceutical compound with low biomassconcentration (50 mgTSS L−1) lead to a partial ibuprofen biodegrada-tion (b10%, 44% and 60% accounting for 10, 100 and 1000 μg L−1 ofibuprofen, respectively) and thus slower removal rates.

3.2. ASM-based model for ibuprofen

Due to the low Henry's law constant for ibuprofen (6,10E−06

atm m3 mol−1) volatilisation can be neglected as a potential removalpathway (Schwarzenbach et al., 2003). Photodegradation does notrepresent a relevant process for the fate of ibuprofen under the testedconditions (Tixier et al., 2003). These hypotheses were confirmed bycontrol tests without biomass (b1% decrease in the initial ibuprofenconcentration, Section 2.3).

Fig. 2. Ibuprofen removal normalised to the spiked concentration (C0) at the initial time.The continuous lines correspond to the lowest biomass concentration (50 mgTSS L−1);the discontinuous lines correspond to 100 mgTSS L−1, and the dotted and discontinuouslines correspond to 1000 mgTSS L−1.

Therefore, the most important degradation mechanisms for ibupro-fen are sorption into the sludge and biodegradation. The literature sug-gests that for most of the pharmaceutical compounds, removal inactivated sludge is typically described with pseudo-first-order or mixedsecond-order reaction kinetics (Joss et al., 2006; Schwarzenbach et al.,2003). The transformation of the total (soluble plus sorbed) concen-tration of micropollutant is proportional to the concentrations of bothsoluble micropollutant and suspended solids with a proportionalityrate constant Kbiol. If sorption equilibrium is assumed, the total concen-tration can be estimated as a function of the soluble concentration, asorption coefficient and the sludge concentration. Thus, the observed de-crease in ibuprofen concentration in solution can be expressed as

rbiol ¼dSIBUdt

¼ �Kbiol ;IBU � SIBU � XTSS

1þKD;IBU � XTSSL gSST�1d�1

� �

where SIBU is the soluble compound concentration [μg L−1], t is the time[d], Kbiol,IBU is the reaction rate constant [L gTSS−1 d−1], KD,IBU is the ad-sorption coefficient [L gTSS−1] and XTSS is the suspended solid concen-tration [gTSSL−1]. The latter parameter can be treated as constant forshort-term batch experiments.

Assuming a constant KD,IBU value of 0.007 L gTSS−1 from the liter-ature (Joss et al., 2006), the term KD,IBU XTSS is less than 0.1 for thebatch experiments described in this study (range 0.0035–0.07,depending on XTSS) and can thus be neglected (Urase and Kikuta,2005). The former equation can consequently be simplified as fol-lows:

rbiol ¼dSIBUdt

¼ �Kbiol ; IBU � SIBU � XTSS L gSST�1d�1� �

: ð1Þ

The experimental data at different biomass and ibuprofen concen-trations from the previous section were fitted to Eq. (1), and the ibu-profen biodegradation constants were calculated. Table 1 summarisesthe corresponding set of Kbiol values obtained and the pertinent R2

values (which were satisfactory (≥0.90), except for the batch test ata low biomass content (50 mgTSS L−1) and high ibuprofen concen-tration (1000 μg L−1)). A correspondence can be observed betweenthe highest Kbiol values (e.g., 1000 mgTSS L−1 with 10 μgIBUL−1)

Table 1Kbiol,IBU values with 95% confidence interval and R2 values in parentheses.

[gTSS L−1]

50 100 1000

[μgIBU L−1] 10 6.12 (0.97) 15.70 (0.95) 17.44 (0.99)100 3.97 (0.90) 6.92 (0.97) 8.57 (0.98)

1000 0.72 (0.47) 2.02 (0.98) 4.76 (0.99)

299N. Collado et al. / Science of the Total Environment 433 (2012) 296–301

and the more pronounced degradation profiles obtained (Fig. 2), indi-cating a high biodegradability. The degradation profiles were less pro-nounced for the lower reaction rate constants.

The Kbiol values obtained range from 0.72 to 17.44 L gTSS−1 d−1;these values correspond well with the classification proposed by Josset al. (2006), indicating a partial biodegradation (20–90%) for 0.1bK-biolb10 and substantial removal for Kbiol values higher than10 L gTSS−1d−1. Similar Kbiol values (9–35 L gTSS−1 d−1) wereobserved in activated sludge systems (3 μg L−1 ibuprofen and0.51 gTSS L−1), depending on the applied technology (Joss et al.,2006).

In contrast, lower values at higher biomass concentrations (3.8–6.2 gTSS L−1 at 1.33–3 L gTSS−1 d−1; Abegglen et al., 2009 and0.209 L gTSS−1 d−1 at 2.5 gTSS L−1; Urase and Kikuta, 2005) wereobtained for low (0.5–2 μgIBU L−1) and medium (100 μgIBU L−1)ibuprofen concentrations, respectively.

These values also depend on the sludge activity and operatingconditions. Our tests were only performed under aerobic conditions.Values obtained at concentrations (of ibuprofen or biomass) thatare different by one or more orders of magnitude may not be repre-sentative. Thus, the correlation between the different combinationsof ibuprofen concentration, biomass concentration and Kbiol valuesbecomes essential (Fig. 3). The higher the ibuprofen concentration,the lower the Kbiol value. A pattern of decreasing Kbiol values with adecrease in the biomass concentration was also observed.

3.3. Biodegradation studies on ibuprofen and ibuprofen TPs

The formation and removal of ibuprofen TPs were investigated toobtain valuable information regarding the parent compound metabolicdegradation pathways as well as the possible impact of the TPs on theenvironment. The batch test with a solid content of 100 mgTSS L−1

and 10 μg L−1 ibuprofen was also analysed for ibuprofen TPs within aperiod of 72 h. The resulting concentrations (μgL−1 and mM) arereported in Table 2 with the corresponding formation percentage ver-sus the initial concentration of the parent compound.

A significant removal of the three TPs, resulting in a final concentra-tion of less than 0.33 μg L−1, was observed; this finding correspondswith the literature from Buser et al. (1999), who found removals ofover 90%. According to Zwiener et al. (2002), TPs are expected tooccur as degradation products during sewage treatment at a level ac-counting for approximately 10% of the ibuprofen input. Based ourdata, however, this percentage reaches 32% over 24 h (comprising the

Ibuprofen [µg L-1]

Kbi

ol [L

gT

SS

-1d-1

]

TSS

[mgT

SS L

-1 ]

Fig. 3. Kbiol,IBU variability among the different combinations of TSS and ibuprofen con-centrations. The colour intensity of the graph changes according to the Kbiol value.

three TPs and IBU-2OH (the predominant TP)) but decreases to 3% atthe end of the test. Both ibuprofen and its TPs can be present in rawwastewater, modifying the ratio of ibuprofen to its transformationproducts and potentially explaining such differences.

The relatively low concentrations of IBU-1OH, IBU-2OHand IBU-CBXin this batch study, together with the rapid decrease in concentration,indicate that the TPs are easily degradable. IBU-2OH had the higher bio-degradability, while the other isomer (IBU-1OH) was not removedcompletely in 72 h. However, the final concentration of IBU-1OH wasrather low, and IBU-1OH was likely to be removed at longer times orhigher biomass contents. Quintana et al. (2005) found similar trends(easily biodegradable isomers that did not accumulate to higher con-centrations). IBU-OH was detected in raw, untreated wastewater butnot in biologically treated wastewater (Buser et al., 1999).

3.4. ASM-based model proposal for ibuprofen and ibuprofen TPs

A simplified ASM-model is proposed for the three TPs analysed(1-hydroxyl-ibuprofen, 2-hydroxyl-ibuprofen, and carboxyl ibupro-fen). The combined equations for each TP represent their formationaccording to ibuprofen removal and their further degradation. It is as-sumed that the metabolic pathways for the formation of the threeibuprofen TPs are completely independent.

The purpose of this study was to provide a Kbiol value not only forthe parent compound but also for each of its TPs, together with anindividualised yield factor to reflect the formation coefficient ofeach TP according to ibuprofen degradation. The defined formulasare Eq. (1), relating to the parent compound (ibuprofen) and the fol-lowing three equations for the three TPs considered in this study.

The following equation encompasses the formation and removalfor the TP 1-hydroxyl-ibuprofen:

dSIBU�1OH

dt¼ −Kbiol;IBU�1OH � SIBU�1OH � XTSS þ y1OH � KbiolIBU

� SIBU � XTSS ð2Þ

where Kbiol,IBU-1OH [L gSST−1 d−1] refers to the constant value of the1-hydroxyl-ibuprofen (IBU-1OH), SIBU-1OH [μg L−1] refers to the totalTP concentration in the liquid phase, and y1OH [gIBU-1OH gIBU–1] re-fers to the yield coefficient (calculated by the formation of the TP as afunction of ibuprofen degradation).

The following equations consider the other two TPs:

dSIBU�2OH

dt¼ −Kbiol;IBU�2OH � SIBU�1OH � XTSS þ y2OH � Kbiol; IBU

� SIBU � XTSS ð3Þ

dSIBU�CBX

dt¼ −Kbiol;IBU�CBX � SIBU�CBX � XTSS þ yCBX � Kbiol;IBU � SIBU

� XTSS ð4Þ

where the symbols, as presented for Eq. (2), pertain to 2-hydroxyl-ibuprofen and carboxy-ibuprofen for Eqs. (3) and (4), respectively.

The model was applied successfully, and the experimental data(TP formation and degradation included) were fitted satisfactorilyto the simulated curve, as shown in Fig. 4, leading to the determina-tion of Kbiol and the yield factors (Table 3). The values obtainedshow a higher TP formation for IBU-2OH, while the other two TPsmaintain lower concentrations.

No references regarding yield factors for TPs are available in theliterature so far because most of the research published on the topicinvestigates only their biodegradation (Quintana et al., 2005), nottheir formation coordinated with the parent compound removal. Asa preliminary result, we can affirm that the yield factors obtained il-lustrate a higher value for IBU-2OH, indicating the predominance ofthe formation of this compound compared to those of the other twocompounds. Regarding the Kbiol values, the increase in biodegradation

Table 2Concentrations of ibuprofen and its TPs, together with their formation percentage ratio according to the initial parent compound concentration (100 mgTSS L−1; 10 μg L−1

ibuprofen).

% TP/ibuprofen

t (h) IBU IBU-1OH IBU-2OH IBU-CBX IBU-1OH IBU-2OH IBU-CBX

μgL−1 mM μgL−1 mM μgL−1 mM μgL−1 mM % % %

0 10.89 5.29E−05 0.18 7.92E−07 0.00 0.00 0.00 0.00 1.50 0.00 0.001 8.89 4.32E−05 0.31 1.42E−06 1.04 4.66E−06 0.98 4.14E−06 2.68 8.82 7.8218 4.24 2.06E−05 0.21 9.57E−07 1.64 7.37E−06 1.21 5.14E−06 1.81 13.95 9.7224 3.61 1.75E−05 0.72 3.23E−06 2.29 1.03E−05 0.80 3.41E−06 6.11 19.49 6.4442 1.29 6.26E−06 0.43 1.93E−06 1.44 6.50E−06 0.59 2.51E−06 3.65 12.30 4.7548 0.81 3.93E−06 0.48 2.17E−06 0.93 4.19E−06 0.58 2.44E−06 4.10 7.93 4.6166 0.09 4.37E−07 0.34 1.52E−06 0.00 0.00 0.65 2.75E−06 2.87 0.00 5.2172 0.06 2.91E−07 0.33 1.47E−06 0.00 0.00 0.00 0.00 2.78 0.00 0.00

300 N. Collado et al. / Science of the Total Environment 433 (2012) 296–301

is in the following order: IBU-1OHb IBU-CBXb IBU-2OH. The most pre-sent yet most biodegradable TP was IBU-2OH, as shown by its higherKbiol value.

4. Conclusions

Ibuprofen removal was adjusted successfully to a pseudo-first-orderkinetic equation at different activated sludge and pharmaceutical com-pound concentrations under aerobic conditions, obtaining Kbiol valuesconsistent with the literature. Correlations of Kbiol values with thesetwo parameters were illustrated. The observed trend corresponds tohigher Kbiol values when the ibuprofen concentration decreases andwhen the biomass content increases.

Ibuprofen TP formation and removal were also monitored, and acomplete elimination of each TP was obtained, except for 1OH-IBU,which showed low residual concentrations at the end of the degrada-tion experiments. A major role for the formation of 2OH-IBU was ob-served, which also resulted in the consideration of 2OH-IBU as themost biodegradable transformation product (considering its Kbiol

value).

IBU

-1O

H

0

1

2

3 simulatedexperimental

IBU

02468

1012

simulatedexperimental

IBU

-2O

H

0

1

2

3 simulatedexperimental

0 10 20 30 40 50 60 70 80

IBU

-CB

X

0

1

2

3 simulatedexperimental

Time (h)

Fig. 4. Experimental and simulated data, in μg L−1, for ibuprofen and its TPs (test at100 mgTSS L−1, 10 μg L−1 ibuprofen).

Table 3Kbiol and yield values for the ibuprofen TPs (100 mgTSS L−1; 10 μg L−1 ibuprofen).

IBU IBU-1OH IBU-2OH IBU-CBX

Kbiol [L gSST−1 d−1] 15.7 6 12 9.6y [gTP gIBU−1] – 0.1 0.4 0.2

Amodel that separately encompasses both the formation and degra-dation of the threemajor ibuprofen TPs was suggested. A satisfactory fitwas obtained, and the yield factor and Kbiol values were calculated.

Acknowledgements

This study has been co-financed by the Spanish Ministry of Scienceand Innovation and the European Union through the European Re-gional Development Fund and national research projects (CTM2009-14742-C02-01, CDTI INNPRONTA ITACA project (IPT-2011102) andCTQ2010-21776-C02-02, DEGRAPHARMAC), as well as by the Cata-lan Agency for Administration of University and research grants(AGAUR, 2009 CTP 00034, MBRMed). Prof. Barceló acknowledgesKing Saud University for his visiting professorship.

References

Abegglen C, Joss A, McArdell CS, Fink G, Schlüsener MP, Ternes TA, et al. The fate of se-lected micropollutants in a single-house MBR. Water Res 2009;43:2036–46.

Barceló D, Petrovic M. Pharmaceuticals and personal care products (PPCPs) in the en-vironment. Anal Bioanal Chem 2007;387:1141–2.

Bartelt-Hunt SL, Snow DD, Damon T, Shockley J, Hoagland K. The occurrence of illicitand therapeutic pharmaceuticals in wastewater effluent and surface waters inNebraska. Environ Pollut 2009;157:786e–91e.

Benedetti L, De Baets B, Nopens I, Vanrolleghem PA. Multi-criteria analysis of wastewa-ter treatment plant design and control scenarios under uncertainty. Environ ModelSoftw 2010;25(5):616–21.

Buser HR, Poiger T, Müller MD. Occurrence and environmental behaviour of chiralpharmaceutical drug ibuprofen in surface waters and in wastewater. Environ SciTechnol 1999;33:2529–35.

Buttiglieri G, Knepper TP. Removal of emerging contaminants in wastewater treat-ment: conventional activated sludge treatment. In: Barceló D, Petrovic M, editors.Handbook of environmental chemistry. Volume 5: emerging contaminants fromindustrial and municipal wastewatersSpringer; 2008. p. 1-35.

Carballa M, Omil F, Lema JM. Comparison of predicted and measured concentrations ofselected pharmaceuticals, fragrances and hormones in Spanish sewage. Chemo-sphere 2008;72(8):1118–23.

Castiglioni S, Bagnati R, Fanelli R, Pomati F, Calamari D, Zuccato E. Removal of pharma-ceuticals in sewage treatment plants in Italy. Environ Sci Technol 2006;40:357e-363.

Daughton CG, Ternes TA. Pharmaceuticals and personal care products in the environ-ment: agent of subtable change? Environ Health Perspect 1999;107:907–38.

Dolar D, Gros M, Rodriguez-Mozaz S, Moreno J, Comas J, Rodriguez-Roda I, Barceló D.Removal mechanism of emerging contaminants from municipal wastewater withMBR-RO system. in preparation.

Gernaey KV, van Loosdrecht MCM, Henze M, Lind M, Jorgensen SB. Activated sludgewastewater treatment plant modelling and simulation: state of the art. EnvironModel Softw 2004;19(9):763–83.

Han S, Choi K, Kim J, Ji K, Kim S, Ahn B, et al. Endocrine disruption and consequences ofchronic exposure to ibuprofen in Japanese medaka (Oryzias latipes) and freshwatercladocerans Daphnia magna and Moina macrocopa. Aquat Toxicol 2010;98(3):256–64.

Hayashi Y, Heckmann LH, Callaghan A, Sibly RM. Reproduction recovery of the crusta-cean Daphnia magna after chronic exposure to ibuprofen. Ecotoxicology2008;17(4):246–51.

Heberer T. Tracking persistent pharmaceutical residues from municipal sewage todrinking water. J Hydrol 2002;266:175–89.

Joss A, Zabczynski S, Göbel A, Hoffmann B, Löffler D, McArdell CS, et al. Biological deg-radation of pharmaceuticals in municipal wastewater treatment: proposing a clas-sification scheme. Water Res 2006;40(8):1686–96.

301N. Collado et al. / Science of the Total Environment 433 (2012) 296–301

Joss A, Siegrist H, Ternes TA. Are we about to upgrade wastewater treatment for remov-ing organic micropollutants. Water Sci Technol 2008;57(2):251–5.

Kolpin DW, Furlong ET, Meyer MT, Thurman EM, Zaugg SD, Barber LB, et al. Pharma-ceuticals, hormones, and other organic wastewater contaminants in US streams,1999–2000: a national reconnaissance. Environ Sci Technol 2002;36:1202–11.

Kosjek T, Heath E, Kompare B. Removal of pharmaceutical residues in a pilot wastewa-ter treatment plant. Anal Bioanal Chem 2007;387:1379–87.

Onesios KM, Yu JT, Bouwer EJ. Biodegradation and removal of pharmaceutical and per-sonal care products in treatment systems: a review. Biodegradation 2009;20:441–66.

Plósz BG, Leknes H, Thomas KV. Impacts of competitive inhibition, parent compoundformation and partitioning behaviour on antibiotic micro-pollutants removal in ac-tivated sludge: measurements and modelling. Environ Sci Technol 2010;44(2):734–42.

Plósz BGy, De Clercq J, Nopens I, Benedetti L, Vanrolleghem PA. Shall we upgradeone-dimensional secondary settler models used in WWTP simulators? — an as-sessment of model structure uncertainty and its propagation. Water Sci Technol2011;63(8):1726–38.

Quintana B, Weiss S, Reemtsma T. Pathways and metabolites of microbial degradationof selected acidic pharmaceutical and their occurrence in municipal wastewatertreated by a membrane bioreactor. Water Res 2005;39:2654–64.

Ragugnetti M, Adams ML, Guimaraes ATB, Sponchiado G, de Vasconcelos EC, deOliveira CMR. Ibuprofen genotoxicity in aquatic environment: an experimentalmodel using Oreochromis niloticus. Water Air Soil Pollut 2011;218(1–4):361–4.

Santos JL, Aparicio I, Callejon M, Alonso E. Occurrence of pharmaceutically active com-pounds during 1-year period in wastewaters from four wastewater treatmentplants in Seville (Spain). J Hazard Mater 2009;164(2–3):1509–16.

Santos LHMLM, Araùjo AN, Fachini A, Pena A, Delerue-Matos C. Montenegro MCBSMecotoxicological aspects related to the presence of pharmaceuticals in the aquaticenvironment: review. J Hazard Mater 2010;175:45–95.

Schnell S, Bols NC, Barata C, Porte C. Single and combined toxicity of pharmaceuticalsand personal care products (PPCPs) on the rainbow trout liver cell line RTL-W1.Aquat Toxicol 2009;93:244e–52e.

Schwarzenbach RP, Gschwend PM, Imboden DM. Environmental organic chemistry.Hoboken, NJ: Wiley-Interscience; 2003.

Smook TM, Zho H, Zytner RG. Removal of ibuprofen from wastewater: comparing bio-degradation in conventional, membrane bioreactor, and biological nutrient remov-al treatment systems. Water Sci Technol 2008;57(1):1–8.

Stumpf M, Ternes TA, Wilken RD, Rodrigues SV, Baumann W. Polar drug residue insewage and natural waters in the state of Rio de Janeiro, Brazil. Sci Total Environ1999;225:135–41.

Tambosi JL, de Sena RF, Favier M, Gebhardt W, José HJ, Schröder HF, et al. Removal ofpharmaceutical compounds in membrane bioreactors (MBR) applying submergedmembranes. Desalination 2010;261(1–2):148–56.

Ternes TA, Joss A. Human pharmaceuticals, hormones and fragrances — the challengeof micropollutants in urban water management. London, UK: IWA Publishing;2006.

Tixier C, Singer HP, Oellers S, Müller SR. Occurrence and fate of carbamazepine, clofibricacid, diclofenac, ibuprofen, ketoprofen, and naproxen in surface waters. EnvironSci Technol 2003;37(6):1061–8.

Tran NH, Urase T, Kusakabe O. The characteristics of enriched nitrifier culture in thedegradation of selected pharmaceutically active compounds. J Hazard Mater2009;171(1–3):1051–7.

Urase T, Kikuta T. Separate estimation of adsorption and degradation of pharmaceuticalsubstances and estrogens in the activated sludge process. Water Res 2005;39(7):1289–300.

Van Loosdrecht MCM, Heijnen JJ. Modelling of activated sludge processes with struc-tured biomass. Water Sci Technol 2002;45(6):13–23.

Verlicchi P, Al Aukidy M, Zambello E. Occurrence of pharmaceutical compounds inraw wastewater: Removal, mass load and environmental risk after a secondarytreatment—a review. Sci Total Environ 2012. (http://dx.doi.org/10.1016/j.scitotenv.2012.04.028).

Zwiener C, Seeger G, Glauner T, Frimmel FH. Metabolites from the biodegradation ofpharmaceutical residues of ibuprofen in biofilm reactors and batch experiments.Anal Bioanal Chem 2002;372:569–75.