Journal of The Electrochemical Society, 161 (14) H867-H873 (2014) H867 0013-4651/2014/161(14)/H867/7/$31.00 © The Electrochemical Society Degradation of Dipyrone by Electrogenerated H2O2 Combined with Fe2+ Using a Modified Gas Diffusion Electrode Willyam R. P. Barros,a Michelle P. Borges,a Juliana R. Steter,a,∗ Juliane C. Forti,b Robson S. Rocha,a and Marcos R. V. Lanzaa,z aInstituto de Quı́mica de São Carlos, Universidade de São Paulo, São Carlos, 13566-590 São Paulo, Brazil bUNESP, Campus Experimental de Tupã, Tupã, 17602-496 São Paulo, Brazil The aim of the present study was to investigate the electrochemical degradation of dipyrone in a single compartment electrochemical cell equipped with a gas diffusion electrode (GDE) modified with cobalt (II) phthalocyanine. Degradations were performed under conditions of anodic oxidation (GDE pressurized with N2) and under conditions promoting the electrogeneration of H2O2 (GDE pressurized with O2) both in the absence and presence of 1 mmol FeSO4.7H2O (electro-Fenton conditions). The efficiency of the electro-Fenton process was satisfactory at all studied potentials, and achieved a maximum reduction of 67% in electrolyte absorbance at 262 nm after 90 min electrolysis at −0.7 V (vs. Ag/AgCl). The reduction in dipyrone concentration attained 95% after 90 min of reaction with electrogenerated H2O2 in the absence or presence of Fe2+ ions at all potentials except −0.5 V (vs. Ag/AgCl). The removal of total organic carbon (TOC) was most efficient under electro-Fenton conditions with a decrease of 54.4% in organic load attained at -0.9 V (vs. Ag/AgCl) and energy consumption (EC) of 270 kWh per kg of TOC removed. © 2014 The Electrochemical Society. [DOI: 10.1149/2.0091414jes] All rights reserved. Manuscript submitted July 21, 2014; revised manuscript received September 9, 2014. Published September 23, 2014. The increase in levels of human and veterinary drugs and metabo- lites detected in urban sewage represents an issue of growing concern. Pollution of surface and ground water by pharmaceutical products can occur via a number of mechanisms including incorrect disposal of expired drugs, metabolic excretion of medications, or the discharge of effluent from the cleaning and decontamination of machinery and equipment involved in drug production.1–8 Although the effects of drugs on the organisms to which they are administered have been widely studied, the undesirable consequences of the presence of these molecules and their corresponding metabolites in the environment re- main poorly understood.9–11 It is, therefore, essential to minimize the pollution of the environment by such compounds. The pharmaceuticals most commonly encountered as contami- nants in wastewater systems are non-steroidal anti-inflammatories, such as acetylsalicylic acid, diclofenac and dipyrone (DIP), since these medications are consumed in the largest quantities by the gen- eral population.6,11 Dipyrone (syn. metamizole), for example, is used widely as an analgesic and antipyretic in various countries in Eu- rope, Africa and South America, although it has been banned in North America and some European countries because of its potential collat- eral effects.2,12–16 In view of the reported increase in the level of pharmaceutical pollution, it is clearly of paramount importance to develop method- ologies that could prevent contact between these biologically active compounds and the environment. Unfortunately, the techniques cur- rently employed in the treatment of public sewage are not able to remove completely these types of compounds from aqueous medium. A number of alternative methods are available for the removal of drugs from wastewaters,17 but straightforward approaches such as incinera- tion generally involve high operating costs, while the more complex biological strategies depend on the continued survival of a microbial colony without genetic alteration. Given these serious limitations, advanced oxidation processes (AOPs) would appear to offer an im- portant alternative for the removal of pharmaceutical contaminants.18 Such processes depend on the in situ production of the metastable hy- droxyl radical (•OH), the high oxidizing potential of which promotes the non-selective oxidation of a wide range of organic compounds in an aqueous matrix.19–21 The reactive radicals may be formed from a primary oxidant such as oxygen, ozone or hydrogen peroxide (H2O2), generally in the presence of UV light or a catalyst.22–27 However, oxi- dation processes involving H2O2 are limited by the relatively low rate of formation of •OH, which implies decreased treatment efficiency. In the Fenton reaction, Fe2+ ions are employed as catalyst in order ∗Electrochemical Society Student Member. zE-mail: marcoslanza@iqsc.usp.br to increase •OH production and, thereby, improve the efficiency of degradation of organic compounds.22 The use of the Fenton reagent is described in the literature for the treatment of organic compounds in wastewater, but the traditional process suffers from two specific difficulties.22,23 Firstly, the reaction must be performed in acidic medium in order to prevent precipitation of the catalyst, and secondly H2O2 is a powerful oxidizing agent, the transport and storage of which can be dangerous under certain conditions. However, application of the gas diffusion electrode (GDE) allows the production of high levels (hundreds of mg per liter) of H2O2 directly in the acidic reaction medium, thereby eliminating the need for transport, storage and manipulation of the primary oxidant.24–28 In this system, H2O2 is electrogenerated in an O2-pressurized GDE by an oxygen reduction reaction (ORR) involving a two-electron transfer (equation 1) which, in acidic medium, may be accompanied by a number of parallel reactions (equations 2 to 5).29–34 O2 + 2H+ + 2e− + H2O2 [1] O2 + 4H+ + 4e− + 2H2O [2] H2O2 + 2H+ + 2e− → 2H2O [3] H2O2 + 2H+ + 2e− + O2 [4] 2H+ + 2e− → H2 [5] In this context, the use of GDE for the in situ generation of H2O2 in the electro-Fenton (e-Fenton) process appears to be a viable possibility for the oxidation of organic compounds, and reports are available concerning the degradation of ranitidine and sodium diclofenac by this route.35,36 The aim of the present study was to evaluate the e-Fenton degradation of DIP in acidic medium with H2O2 electrogenerated in situ in an electrochemical cell comprising a GDE modified with 5.0% cobalt (II) phthalocyanine (CoPc). Experimental Configuration and components of the electrochemical cell.— Ex- periments were carried out in a cylindrical single compartment elec- trochemical cell (total capacity 450 mL) constructed of polypropylene. The working electrode was a modified GDE prepared by the hot press- ing method using a catalytic mass composed of Printex 6L carbon (De- gussa Brazil) with 5.0% of CoPc (97% dye content; Sigma-Aldrich, ) unless CC License in place (see abstract).  ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 186.217.236.117Downloaded on 2015-02-25 to IP http://dx.doi.org/10.1149/2.0091414jes mailto:marcoslanza@iqsc.usp.br http://ecsdl.org/site/terms_use H868 Journal of The Electrochemical Society, 161 (14) H867-H873 (2014) St Louis, MO, USA; cat. # 307696) and a 60% PTFE dispersion (DuPont Teflon PTFE DISP 30) as hydrophobic binder. The prepara- tion of the catalytic mass and the construction of the modified GDE fol- lowed published procedures.11,35,36 The counter electrode comprised a 30.0 mm diameter screen fabricated from platinum wire (99.95% pure; wire diameter 0.25 mm; space between wires 4.0 mm), and an Ag/AgCl electrode served as the reference electrode. Electrochemical conditions.— Electrochemical reactions were performed with an aqueous electrolyte (400 mL) containing DIP (50 mg L−1), H2SO4 (0.1 mol L−1) and K2SO4 (0.1 mol L−). In experi- ments involving the anodic oxidation of DIP, the GDE was pressurized with N2 (0.2 bar) and a constant potential in the range −0.5 V≤ E ≤ −0.9 V (vs. Ag/AgCl) was applied for 90 min with the electrolyte maintained at 20◦C. The degradation of DIP by H2O2 electrogenerated in situ was investigated under similar conditions but with the GDE pressurized with O2 (0.2 bar), whereas in the e-Fenton experiments, the electrolyte was supplemented with 1 mmol FeSO4.7H2O. Electrogeneration of H2O2.— The amount of H2O2 electrogener- ated as a function of time during electrolysis was determined using the peroxymolybdate complex method. Briefly, a sample (0.5 mL) of electrolyte was added to 4.0 mL of solution containing 2.4 × 10−3 mol L−1 (NH4)6Mo7O24 and the absorbance at 350 nm of the yellow solution so-formed was measured using an Agilent Varian Cary 50 spectrometer. Electrochemical degradation of DIP.— For each series of experi- ments, samples of electrolyte were collected at appropriate time inter- vals and the UV-Vis spectra recorded in the range 200–800 nm using an Agilent Varian Cary 50 spectrometer. The degradation of DIP was monitored in terms of the change in absorbance of the electrolyte at 262 nm. The quantitative evaluation of DIP at each time interval was car- ried out by high performance liquid chromatography (HPLC) using a Shimadzu model LC-20AT chromatograph equipped with a SPD-20A UV detector and a Phenomenex Luna C18 column (250 × 4.6 mm i.d.; 5 μm). The mobile phase comprised a 30:70 (v/v) mixture of methanol and phosphate buffer (pH 7), elution was isocratic at a flow rate of 1.0 mL min−1, and the UV detector was set at 262 nm. The quan- tification of DIP was performed with the aid of a calibration curve constructed using analytical grade reference standard drug. Total or- ganic carbon (TOC) in electrolyte samples was determined using a Shimadzu model TOC-VCPN analyzer. Results and Discussion Electrogeneration of H2O2.— In an earlier investigation concern- ing the electrogeneration of H2O2 at GDEs modified with different amounts of CoPc,37 we demonstrated that the addition of 5.0% of modifier produced the highest concentrations of H2O2. On this basis, the present study of the electrodegradation of DIP in acidic medium was carried out using a single compartment electrochemical cell com- prising a GDE modified with 5.0% of CoPc as the working electrode. A plot of H2O2 concentration vs applied potential obtained using this system (Figure 1) revealed that the maximum concentration of H2O2 (331 mg L−1) was produced after 90 min of electrolysis at a constant potential of −0.7 V (vs. Ag/AgCl).37 However, the amount of H2O2 used in a degradation process should be proportional to the quantity of organic matter present, since excess of oxidant in the reaction medium may promote the sequestration of •OH.22,35,36 In consideration of this limitation, it was important to evaluate the best potential for the degradation of DIP associated with the largest amount of electrogenerated H2O2, thus experiments were performed at five different potentials, namely −0.5 V (corresponding to a final concentration of 136 mg L−1 H2O2), −0.6 V (202 mg L−1 H2O2), −0.7 V (331 mg L−1 H2O2), −0.8 V (112 mg L−1 H2O2) and −0.9 V (147 mg L−1 H2O2).37 -0.9 -0.8 -0.7 -0.6 -0.5 50 100 150 200 250 300 350 C H 2O 2 / m g L -1 E (vs. Ag/AgCl) / V 331 mg L -1 Figure 1. Final concentration of electrogenerated H2O2 (CH2O2) as a function of the potential applied to a GDE modified with 5.0% CoPc and pressurized with O2 (0.2 bar). The supporting electrolyte comprised an aqueous solution of H2SO4 (0.1 mol L−1) and K2SO4 (0.1 mol L−1). (Adapted from Barros et al.).37 Electrochemical degradation of DIP.— Since the degradation ex- periments were performed in a single compartment electrochemical cell, all species present in the electrolyte were in contact with both electrodes, thus allowing reduction reactions to occur at the cathode and oxidation reactions at the anode. Three series of experiments were performed at each potential studied in which: (i) the GDE was pres- surized with N2 in order to evaluate the degradation of DIP by anodic oxidation in the absence of H2O2; (ii) the GDE was pressurized with O2 such that the degradation of DIP was through oxidation by H2O2 together with anodic oxidation; and (iii) the experiments were con- ducted under the same conditions as series (ii) but with 1 mmol of FeSO4.7H2O added to the electrolyte such that DIP degradation was through H2O2/•OH oxidation together with anodic oxidation. Figure 2 shows the decrease in absorbance of DIP at 262 nm dur- ing electrodegradation experiments under the three different reaction conditions and at five different applied potentials. When the GDE was pressurized with N2, the reductions in absorbance at 262 nm were ex- tremely small under all applied potentials, and attained a maximum of only ≈ 4.0% after 90 min of electrolysis. In contrast, the reductions in absorbance achieved in experiments involving the generation of H2O2 in the absence or presence of FeSO4.7H2O were associated with the participation of •OH in the oxidation of organic matter present and were, therefore, much greater than those obtained with anodic degra- dation. The greatest decreases in absorbance occurred in experiments involving the generation of H2O2 in the presence of Fe2+, i.e. the e-Fenton process, where a reduction of 67% in absorbance at 262 nm was attained at −0.7 V (vs. Ag/AgCl) after 90 min of electrolysis. The results obtained in the experiments involving electrogener- ation of H2O2 in the presence of FeSO4.7H2O are consistent with published reports.38,39 According to Batista and Nogueira,40 degra- dation by the Fenton process is more efficient than degradation by H2O2 alone because the Fe2+ ions catalyze the formation of •OH from H2O2 present in solution. The results shown in Figure 2 verify that the changes in absorbance of the electrolyte followed the profile of electrogenerated H2O2, and that increasing the applied potential from −0.5 to −0.7 V (vs. Ag/AgCl) promoted an increase in the gen- eration of H2O2 and a reduction in total absorbance of the electrolyte. However, at more negative potentials, the decrease in absorbance was diminished, thereby confirming the dependency of the degradation of DIP on the electrogeneration of H2O2. The observation of a significant decrease in the absorbance of the aqueous electrolyte during electrolysis may be indicative of the degradation of DIP but did not provide conclusive evidence that the concentration of organic matter had also been reduced. Quantitative ) unless CC License in place (see abstract).  ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 186.217.236.117Downloaded on 2015-02-25 to IP http://ecsdl.org/site/terms_use Journal of The Electrochemical Society, 161 (14) H867-H873 (2014) H869 0 30 60 90 0.2 0.4 0.6 0.8 1.0 A bs t / A bs o Time / min (A) 0 30 60 90 0.2 0.4 0.6 0.8 1.0 A bs t / A bs o (B) Time / min 0 30 60 90 0.2 0.4 0.6 0.8 1.0 A bs t / A bs o (C) Time / min 0 30 60 90 0.2 0.4 0.6 0.8 1.0 A bs t / A bs o (D) Time / min 0 30 60 90 0.2 0.4 0.6 0.8 1.0 A bs t / A bs o (E) Time / min Figure 2. Decrease in normalized absorbance (Abst/Abs0) at 262 nm of an aqueous solution of DIP as a function of time of electrolysis performed at applied potentials of (A) −0.5 V, (B) −0.6 V, (C) −0.7 V, (D) −0.8 V and (E) −0.9 V under three different experimental conditions, namely anodic oxidation (. . . +. . . ), electrogenerated H2O2 (–•–) and e-Fenton (–◦–). HPLC analysis of DIP during electrolysis (Figure 3) revealed that the decrease in concentration of analyte was minimal under conditions of anodic oxidation, i.e. in the absence of H2O2 (GDE pressurized with N2), with only 5.0% of DIP being degraded after 90 min at a potential −0.9 V (vs. Ag/AgCl). Such low levels of drug removal are also associated with small current densities under experimental conditions that promote degradation by the electrochemical process alone.17 In contrast, experiments involving the generation of H2O2 in the absence or presence of FeSO4.7H2O achieved reductions of 96% in the concentration of DIP at an applied potential −0.9 V (vs. Ag/AgCl). While both of these procedures were able to remove the analyte almost completely, the rate of degradation was greater under e-Fenton conditions. Thus, at the optimal applied potential for the electrogeneration of H2O2 (−0.7 V vs. Ag/AgCl), 88% of DIP was removed in 40 min by the e-Fenton process compared with 66% of DIP removed in the same time when Fe2+ was absent. At more negative ) unless CC License in place (see abstract).  ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 186.217.236.117Downloaded on 2015-02-25 to IP http://ecsdl.org/site/terms_use H870 Journal of The Electrochemical Society, 161 (14) H867-H873 (2014) 0 30 60 90 0.0 0.2 0.4 0.6 0.8 1.0 (A) Time / min C [D IP t/ D IP 0] 0 30 60 90 0.0 0.2 0.4 0.6 0.8 1.0 C [D IP t/ D IP 0] (B) Time / min 0 30 60 90 0.0 0.2 0.4 0.6 0.8 1.0 C [D IP t/ D IP 0] (C) Time / min 0 30 60 90 0.0 0.2 0.4 0.6 0.8 1.0 C [D IP t/ D IP 0] (D) Time / min 0 30 60 90 0.0 0.2 0.4 0.6 0.8 1.0 C [D IP t/ D IP 0] (E) Time / min Figure 3. Decay in normalized concentration (as determined by HPLC) of an aqueous solution of DIP [C(DIPt/DIP0)] as a function of time of electrolysis performed at applied potentials of (A) −0.5 V, (B) −0.6 V, (C) −0.7 V, (D) −0.8 V and (E) −0.9 V under three different experimental conditions, namely anodic oxidation (. . . +. . . ),electrogenerated H2O2 (–•–) and e-Fenton (–◦–). potentials, the removal of DIP was less efficient showing that the degradation process was associated directly with H2O2 generation. The profiles of plots of concentration of DIP with respect to time obtained under all experimental conditions indicated that the reaction followed first-order kinetics.22,35,36 The rate constant (kapp) for the degradation of DIP was determined from the slope of the function ln[DIP] (mg L−1) vs. time (min) for each experiment, and the values are displayed in Figure 4. Under conditions of anodic oxidation, i.e. in the absence of H2O2, the kapp at −0.9 V (vs. Ag/AgCl) was 4.0 × 10−4 min−1, with the lower values established at less negative potentials being associated with smaller current densities. Degradation experiments conducted in the presence of H2O2 showed much higher values for kapp, attaining a maximum of 4.0 × 10−2 min−1 under e- Fenton conditions at −0.7 V (vs. Ag/AgCl). It is noteworthy, however, that in the e-Fenton process, the values of kapp were reduced at the most negative potentials, decreasing to 3.6 × 10−2 min−1 at −0.9 V ) unless CC License in place (see abstract).  ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 186.217.236.117Downloaded on 2015-02-25 to IP http://ecsdl.org/site/terms_use Journal of The Electrochemical Society, 161 (14) H867-H873 (2014) H871 0.00 0.01 0.02 0.03 0.04 0.0000 0.0001 0.0002 0.0003 0.0004 0.0005 k ap p / m in -1 (D) (C) (E) (B) (A) (D)(C) (E) (B) (A) oxidation e-Fenton H 2 O 2 Anodic k ap p / m in -1 (D) (C) (E) (B) (A) Figure 4. Values of the apparent rate constant (kapp) obtained from a plot of ln[DIP] (mg L−1) vs. time (min) (determined by HPLC) for the electrodegra- dation of DIP performed at applied potentials of (A) −0.5 V, (B) −0.6 V, (C) −0.7 V, (D) −0.8 V and (E) −0.9 V under three different experimental conditions, namely anodic oxidation, electrogenerated H2O2 and e-Fenton. (vs. Ag/AgCl). The mechanism of degradation associated with the e-Fenton process is described in equations 6 and 7 in which a DIP molecule reacts with •OH formed by decomposition of H2O2 in the presence of Fe2+ ions to yield degradation products. However, in the e-Fenton process other reactions may occur such as those shown in equations 8–10 involving the formation of •OHads, the recombination of •OH to produce H2O2 and the generation of hydroperoxyl radicals (•O2H). In addition, the •O2H radical can oxidize Fe2+ (equation 11) promoting a deficiency in the production of •OH.20,41 Fe2+ + H2O2 → Fe3+ +• OH +− OH k1 = 63.0 L mol −1 s−1 [6] •OH + DIP → degradation products [7] H2O →• OHads + H+ + e− [8] 2•OH → H2O2 [9] H2O2 +• OH →• O2H + H2O [10] Fe2+ +• O2H → Fe3+ +− O2H [11] The observed reduction in kapp values under e-Fenton conditions at more negative potentials is, therefore, associated with the decrease in generation of H2O2 at such potentials (Figure 1), resulting in a decline in the formation of •OH and a lower degradation rate, as shown in Figure 4. Although the results presented in Figures 3 and 4 demonstrate removal of DIP from the electrolyte, they do not provide proof of reduction in the amount of organic matter present. The level of TOC in samples was monitored directly, and the results are shown in Figure 5. Under conditions of anodic degradation, the removal of organic matter was small, reaching only 2.7% after 90 min at an applied potential of −0.9 V (vs. Ag/AgCl). Reduction of TOC was much greater in degradation experiments involving the electrogeneration of H2O2 in the absence of FeSO4.7H2O, with 13.8% of organic matter removed at the end of electrolysis at −0.9 V (vs. Ag/AgCl). However, the highest 0 10 20 30 40 50 60 0.0 0.5 1.0 1.5 2.0 2.5 3.0 T O C r em ov al / % (D) (C) (E) (B) (A) T O C r em ov al / % (D)(C) (E)(B) (A) oxidation e-Fenton H 2 O 2 Anodic (D)(C) (E) (B) (A) Figure 5. TOC removal (%) after 90 min of electrolysis of an aqueous solution of DIP performed at applied potentials of (A) −0.5 V, (B) −0.6 V, (C) −0.7 V, (D) −0.8 V and (E) −0.9 V under three different experimental conditions, namely anodic oxidation, electrogenerated H2O2 and e-Fenton. levels of TOC removal were observed with the e-Fenton process, under which conditions a maximum decrease of 54.4% in organic load was recorded at the end of electrolysis at −0.9 V (vs. Ag/AgCl). The profiles of DIP decay, established by UV/Vis (Figure 2), HPLC (Figure 3) and TOC (Figure 5) analyses, revealed large differences between degradative processes carried out with and without H2O2, whereby the presence of H2O2 promoted a greater removal of analyte and other organic matter at all potentials studied. This difference in behavior may be attributed to the type of catalysis involved. Degra- dation in the absence of H2O2 is a heterogeneous anodic catalysis in which reactions occur on the surface of the anode. Under such condi- tions, DIP molecules present in solution have to reach the surface of the anode and, therefore, the reaction is controlled by the mechanisms of mass transport. In contrast, in degradative processes carried out in the presence of H2O2 (with or without FeSO4.7H2O), catalysis occurs in a homogeneous phase in which •OH radicals (derived from H2O2 electrogenerated in the GDE) promote the degradation of DIP. Since both •OH and DIP are present in solution, reaction occurs without the limitation of mass transport and higher removal values are achieved. The evaluation of energy consumption (EC; kWh kg−1) during the process of electrochemical degradation is of fundamental importance because the technique is based on electron flow. In the present study, the amount of energy required to remove 1 kg of DIP was evaluated according to equation 12: EC = i.Ecel .t �T OC.1000 [12] where i is the current (A), Ecel is the cell potential (V), and �TOC is the mass of TOC removed (kg) in time t (min). Figure 6 shows the values of EC determined after 90 min of electrolysis under the three degradation conditions studied. Anodic oxidation, which produced the smallest reductions in TOC, was associated with the highest values of EC, attaining 1750 kWh kg−1 at an applied potential of −0.9 V (vs. Ag/AgCl). Compared with anodic degradation, reactions involving the electrogeneration of H2O2 in the absence of FeSO4.7H2O exhib- ited lower EC values, attaining a maximum of 532 kWh kg−1 at an applied potential of −0.9 V (vs. Ag/AgCl). According to equation 12, the decrease in EC values obtained in these experiments in compari- son with those involving anodic oxidation is related directly to TOC removal and not to the values of potential and current, since the latter showed little variation [3.7 ± 0.1 A and 7.8 ± 0.1 V, respectively, ) unless CC License in place (see abstract).  ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 186.217.236.117Downloaded on 2015-02-25 to IP http://ecsdl.org/site/terms_use H872 Journal of The Electrochemical Society, 161 (14) H867-H873 (2014) 0 250 500 750 1000 1250 1500 1750 E C / kW h kg -1 (D) (C) (E) (B) (A) oxidation e-Fenton H 2 O 2 Anodic (D)(C) (E) (B) (A) (D) (C) (E) (B) (A) Figure 6. Energy consumption (EC) for the removal of 1 kg of TOC evaluated after 90 min of electrolysis of an aqueous solution of DIP performed at applied potentials of (A) −0.5 V, (B) −0.6 V, (C) −0.7 V, (D) −0.8 V and (E) −0.9 V under three different experimental conditions, namely anodic oxidation, electrogenerated H2O2 and e-Fenton. at −0.9 V (vs. Ag/AgCl)] in the series of experiments performed at different potentials. The lowest levels of energy consumed for the degradation of DIP were obtained under e-Fenton conditions, with an EC value of 270 kWh kg−1 being recorded at an applied potential of −0.9 V (vs. Ag/AgCl) and values of 3.6 ± 0.1 A and 7.9 ± 0.1 V for current and cell potential, respectively. Consideration of these findings revealed that the e-Fenton process promoted a reduction in energy involved in the degradation of DIP of approximately 547% in comparison with anodic degradation and of 97% compared with H2O2 degradation in the absence of Fe2+ ions. Although the e-Fenton process produced a decrease in TOC of 54% after 90 min of reaction at −0.9 V (vs. Ag/AgCl), the overall process did not comply with Brazilian legislation for the disposal of treated wastewater, which demands 80% removal of organic matter prior to discharge into class III water bodies.42 In order to determine the conditions required for the complete removal of TOC, the degradation of DIP under e-Fenton conditions was monitored over a period of 8 h. For this experiment, an applied potential of −0.7 V (vs. Ag/AgCl) was chosen based on the higher amount of electrogenerated H2O2 in 90 min as compared with the other potentials studied. As shown in Figure 7, 99% of the original TOC was removed after 8 h of reaction, 0 1 2 3 4 5 6 7 8 0 20 40 60 80 100 T O C re m ov al / % Time / h 88% Figure 7. TOC removal (%) after 8 h of electrolysis of an aqueous solution of DIP performed at an applied potential of −0.7 V (vs. Ag/AgCl) under e-Fenton conditions. The electrolyte contained DIP (50 mg L−1), H2SO4 (0.1 mol L−1) and K2SO4 (0.1 mol L−1). while the 80% reduction in organic load required by Brazilian law was achieved in less than 3 h. These findings verify that the e-Fenton process with H2O2 generated in a GDE modified with 5.0% CoPc is efficient in eliminating DIP from aqueous solution to the level required by Brazilian legislation. Conclusions The electrogeneration of H2O2 in acidic medium using a single compartment electrochemical cell equipped with a GDE modified with 5.0% CoPc and pressurized with O2 was most effective when a potential of −0.7 V (vs. Ag/AgCl) was applied. Under these condi- tions, 95% of DIP and 13.8% of TOC could be removed in 90 min. The process was more efficient when H2O2 was electrogenerated in the presence of FeSO4.7H2O and, at an applied potential of −0.9 V (vs. Ag/AgCl), 96% of DIP was degraded (kapp = 4.0 × 10−2 min−1) and 54.4% of TOC removed (EC 270 kWh kg−1). In an extended experiment conducted under e-Fenton conditions, a reduction of 88% in organic matter was achieved within 3 h of electrolysis, a level of removal that was well within the 80% limit required by Brazilian leg- islation, while after 8 h of reaction the reduction in TOC attained 99%. In contrast, conditions that promoted anodic oxidation were ineffec- tive in the removal of DIP and organic matter, being limited by low current density and mass transport of DIP to the electrode surface. It is concluded that e-Fenton conditions are the most appropriate for DIP degradation, although process parameters must be selected in order to comply with local legislation relating to the removal of organic load from drug-contaminated waters. Acknowledgments The authors acknowledge the financial support of Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) (grants 2007/04759-0, 2011/08588-1, 2011/06681-4, 2011/01694-0 and 2009/15357-6), Conselho Nacional de Desenvolvimento Cientı́fico e Tecnológico (CNPq) and Coordenação de Aperfeiçoamento de Pes- soal de Nı́vel Superior (CAPES). References 1. A. T. Wuersch, L. F. De Alencastro, D. Grandjean, and J. Tarradellas, Water Res., 39, 1761 (2005). 2. K. Fent, A. A. Weston, and D. Caminada, Aquatic Toxicol., 76, 122 (2006). 3. A. Joss, S. Zabczynski, A. Gobel, B. Hoffmann, D. Loffler, C. S. McArdell, T. A. Ternes, A. Thomsen, and H. Siegrist, Water Res., 40, 1686 (2006). 4. M. Carballa, F. Omil, T. Ternes, and J. M. Lema, Water Res., 41, 2139 (2007). 5. B. Kasprzyk-Hordern, R. M. Dinsdale, and A. J. Guwy, Water Res., 42, 3498 (2008). 6. M. J. M. Bueno, M. D. Hernando, S. Herrera, M. J. Gómez, A. R. F. Alba, I. Bustamante, and E. G. Calvo, Int. J. Environ. Anal. 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