Presented at the 3rd Regional Conference on Chemical Engineering EDSA Sangri-la Hotel, Metro Manila, Philippines January 20 – 21, 2011
EFFECT OF ELECTRODE ASSEMBLY ON THE PERFORMANCE OF A COMPACT ELECTROCOAGULATION REACTOR SYSTEM APPLIED TO PHARMACEUTICAL RESIDUE IBUPROFEN Elaine G. Mission, Pag-asa D. Gaspillo, Lawrence P. Belo and Gladys Paz T. Cruz De La Salle University, Manila, Philippines Email :
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[email protected] Abstract: Electrocoagulation (EC) is an electrochemical treatment process that has been applied to a wide variety of wastewater. In this study, the influence of initial pH and applied voltage on the performance of the EC reactor system with varying electrode assembly on the treatment of pharmaceutical ibuprofen which is an emerging micropollutant was determined. Experiments were conducted in a pilot scale reactor using simulated wastewater with initial pH of 6 and 8, applied voltage of 10V and 21.4 V and electrode assembly Al-Al, Fe-Fe, Al-Fe and Fe-Al. It was found that the use of Fe-Fe at pH 6 and 21.4 V was the most preferable electrode assembly. Finally, the electrodes were characterized by scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) and the sludge produced during EC was characterized using x-ray diffraction (XRD) analysis. Key Words: Electrocoagulation, Ibuprofen, Electrode Assembly 1. INTRODUCTION Electrocoagulation (EC) is an electrochemical method that involves usage of soluble electrodes such as aluminum or iron. The soluble electrodes upon application of voltage can generate active cation species or “mediators” which can react with the target pollutant. Hydrogen also produced at the cathode help separate formed flocs. The use of electrochemical treatment in the removal of toxic organic pollutants is very interesting because of the use of electrons to facilitate treatment instead of chemical reagents or microorganisms (Carlesi Jara et al., 2007). Compared with biological treatments, EC involves lesser space requirements due to shorter residence time for treatment. Likewise, in contrast to chemical coagulation, EC minimizes addition of chemicals, hence sludge generation is reduced and the effluent is not enriched with anions (Asselin et al., 2008a). EC has been applied in the treatment of humic substances (Koparal et al., 2008); restaurant wastewater (Chen et al., 2000); olive oil mill wastewater (Inan et al., 2004); baker’s yeast wastewater (Kobya and Delipinar, 2008); landfill leachate (Ilhan et al., 2008); textile wastewater (Zongo et al., 2009); paper mill effluents (Ugurlu et al., 2008); and petroleum refinery wastewater (El-Naas et al., 2009) with varying degrees of success. This study aims to demonstrate the capability of EC in the treatment pharmaceutical ibuprofen (IBU) in simulated wastewater. IBU is a non-steroidal anti-inflammatory drug (NSAID) and is one of the most widely detected pharmaceutical and personal care product in wastewaters, 1
Presented at the 3rd Regional Conference on Chemical Engineering EDSA Sangri-la Hotel, Metro Manila, Philippines January 20 – 21, 2011
treated effluents and surface waters (Weigel et al., 2004). As an emerging micropollutant, IBU gained attention recently because it can pass through the conventional activated sludge process partly untreated and reach surface water and drinking water wells. Exposure of aquatic organisms to IBU residues was reported to impact their reproduction and survival patterns (Flippin et al., 2007). Relevant parameters that are important in the EC process, such as initial pH and applied voltage using Al-Al, Fe-Fe, Al-Fe and Fe-Al as electrode assemblies, were also considered in this study. 2. METHODOLOGY The aluminum (Al) and galvanized iron (Fe) electrodes used in the study measured 45.72 cm x 7.62 cm x 0.2cm. The electrodes were washed with of 0.1 M NaOH, 10% HNO3 acid solution and tap water then air-dried prior to each experiment. The IBU sodium sourced from Belman Laboratories (C13H17NaO2; Sigma-Aldrich CAS no. 31121-93-4, Batch no. 027K2111) was dissolved in distilled deionized water to form 100mg/Li solution. The simulated wastewater has an initial COD of 108 18 mg/L. Sodium sulphate (Na2SO4) was added as the supporting electrolyte at 0.035 M for Al-Al and Fe-Al experiments and 0.010 M Na2SO4 for Fe-Fe and Al-Fe assembly. Sulphuric acid (H2SO4) and sodium hydroxide (NaOH) were used for pH adjustment. The experiments were conducted in a pilot-scale EC unit fabricated by Livcor Technicon Inc. illustrated schematically in Figure 1. The EC reactor made of 1.2-cm thick acrylic material has a 40-liter capacity and holds four (4) completely submerged monopolar, parallel electrodes arranged horizontally. The gap between electrodes was fixed at 3 cm in between the anode-cathode pair and 6 cm in between the two pairs of electrodes. An in-line submersible pump (Sedra brand, Model KSP 2500) was used to continuously circulate the simulated wastewater at 130 mL per second. Floated sludge was removed manually at the end of the experiment using a plastic scraper. At the end of each run, the inside of the EC cell was thoroughly cleaned with 5% (v/v) HCl, rubbed with sponge for at least 15 minutes and washed with tap water to remove any adhered solid residues. LEGEND: 1 – Control Panel 2 – Acrylic tank 3 – Electrodes 4 – Recirculation pump 5 – Treated Effluent overflow
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Influent Effluent
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Figure 1: Schematic diagram of the Electrocoagulation setup 2
Presented at the 3rd Regional Conference on Chemical Engineering EDSA Sangri-la Hotel, Metro Manila, Philippines January 20 – 21, 2011
Experiments were conducted batch wise at ambient temperature for thirty (30) minutes. The effluent samples taken were allowed to settle for ninety (90) minutes and were filtered using ordinary filter paper prior to COD analysis to separate the supernatant from the sludge formed. pH was monitored using a digital pH stick while COD was determined by closed reflux titrimetric method according to the Standard Methods for Examination of Water and Wastewater. All the samples were analyzed in duplicate to ensure data reproducibility and an additional measurement was carried out when necessary. Residual IBU analysis was carried out by Jefcor Laboratories employing solid phase extraction followed by HPLC with UV absorbance detection following the methodology of Bechrackis et al., 2005. Peaks were identified in comparison with the retention time of molecular ibuprofen standard and concentrations were determined from peak areas in comparison to molecular ibuprofen standard. The surface of electrodes was characterized with a scanning electron microscope (SEM) and energy dispersive x-ray (EDX) while the sludge composition was determined using x-ray diffraction (XRD) analysis. 3. RESULTS AND DISCUSSION 3.1 Electrode Characterization The EDX characterization of the Al electrode indicated that it is 93% pure with traces of carbon and iron oxides while the Fe electrode was coated with zinc oxide with traces of carbon and aluminum oxide. The SEM analysis revealed that initially, the surface of Al and Fe electrodes is rough without cavities or dents. Both Al and Fe anodes developed pitting corrosion after 5 hours and 3 hours of usage, respectively. 3.1 Effect of Applied Voltage COD removal depends on the quantity of coagulant generated into the solution which is bound by time and applied potential (Zaroual et al., 2006). Figures 2 and 3 show the residual COD levels in the simulated wastewater during EC using the Al-Al, Fe-Fe, Al-Fe and Fe-Al assemblies at input voltages of 10V and 21.4 V. At 10V, the removal of COD was not very significant due to insufficient amount of formed metal hydroxides to coagulate the amount of pollutant present in the solution. Less bubbles were generated, thus, the opportunity for the pollutant-coagulant interaction decreases, resulting to ineffective pollutant removal. In contrast, lower residual COD values have been recorded for experiments at 21.4 V. This is because higher current density was achieved at higher input voltage which dosed more coagulants into the solution. More sludge was produced as well which improved removal of COD. At 21.4 V, more bubbles were produced which also helped improve mixing inside the tank and the collision of mobile ions, allowing interaction with the pollutant and coagulant. Average COD removal increased to about 22% for Fe-Fe, 18% for Al-Fe and 3.8% for Fe-Al after thirty minutes. At 10 V, the final temperature increases to around 29.4OC while at 21.4 V, the final temperature increases up to 33.6OC. The solution conductivity was found to be independent of the initial solution pH and applied voltage.
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Presented at the 3rd Regional Conference on Chemical Engineering EDSA Sangri-la Hotel, Metro Manila, Philippines January 20 – 21, 2011
Figure 2: Effect of Input Voltage of 10V on COD using different electrode assemblies
Figure 3: Effect of Input Voltage of 21.4V on COD using different electrode assemblies 3.2 Effect of Initial pH During EC process where pH control is not applied, the initial solution pH changes appreciably and then it is stabilized due to the buffering capacity of the various species present in the solution (Can and Bayramoglu, 2010). Contrary to this observation, for both acidic and basic solutions, the final pH came out to be higher than the initial condition. The increase in pH was attributed to the continuous generation and build up of OH- ions in the aqueous solution due to water reduction at the cathode vicinity. Solution pH is a significant factor in the solubility of electrodes, which affects the formation of coagulant species dosed into solution (El Naas et al., 2009) and also the hydrophobicity and solubility of IBU protonation of the functional group of IBU (Nghiem et al., 2005). Figures 4 and 5 show the solution COD measured at different electrode assemblies and initial pH of 6 4
Presented at the 3rd Regional Conference on Chemical Engineering EDSA Sangri-la Hotel, Metro Manila, Philippines January 20 – 21, 2011
and 8, respectively, for thirty minutes of operation. Lower residual COD values were obtained for acidic initial pH. Highly noticeable is the shift in pH to the basic region at the end of thirty minutes possibly due to continuous release of hydroxyl ions at the cathode. Only the positive complex has favored the destabilization of colloids, hence, changes towards more alkaline pH do not favor the colloid’s destabilization because of predominant negative charge Al(OH)4- or FeO2- which are soluble and are ineffective coagulants. At higher pH, the solubility and hydrophilicity of IBU is enhanced while coagulants being produced have weak positive charge (Mendez-Arriaga et al., 2008). This in turn will reduce the affinity between the coagulant and pollutant and decrease in COD removal. It can be deduced that final pH rather than initial pH is an important factor for COD removal involving acidic compounds (MorenoCasillas et al., 2007).
Figure 4: Effect of an Initial pH of 6 on COD using different electrode assemblies
Figure 5: Effect of an Initial pH of 8 on COD using different electrode assemblies
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Presented at the 3rd Regional Conference on Chemical Engineering EDSA Sangri-la Hotel, Metro Manila, Philippines January 20 – 21, 2011
3.3 Removal of Ibuprofen molecule from Simulated wastewater From among the electrode assemblies and operating conditions reported, it was observed that the use of Fe-Fe assembly at pH of 6 and voltage input of 21.4 V indicated better COD removal performance at 32%. The recovery for the residual IBU yielded 5.91 mg/L IBU. This translates to 50.53% IBU removal which may not necessarily represent true IBU removal due to formation of Fe-carboxylate complex which cannot be detected as molecular IBU and remained dissolved in the solution. 3.4 Sludge Characterization X-ray diffraction (XRD) analysis conducted on Fe-Fe sediment sludge reveals an amorphous or generally non-crystalline to poorly crystalline material which is indicated by the broad spectra illustrated in Figure 6. The general position of the broad spectra indicates clay-like material or poorly crystalline Fe-oxyhydroxides. In comparison with the results of Timmes et al., 2010, the peaks represent iron profile consisting of hematite and maghemite. Both Parga et al., 2005 and Gomes et al., 2007 also identified hematite and maghemite in their characterization of EC by-products. This finding indicates that the coagulants produced by locally-available electrodes are of comparable quality to high-purity custom-made electrodes.
Figure 6: XRD analysis for Fe-Fe sediment sludge
4. CONCLUSIONS This study assessed the effect of electrode assemblies in a pilot-scale electrocoagulation reactor as a possible treatment for the pharmaceutical pollutant ibuprofen in simulated wastewater. The initial pH of 6 was found favorable for EC because effective coagulant species are formed at this pH range. At an applied voltage of 21.4 V, more coagulants were generated, and more bubbles were produced for effective mixing which resulted to better pollutant removal. The use of Fe-Fe as anode–cathode assembly at pH of 6 and 21.4 V 6
Presented at the 3rd Regional Conference on Chemical Engineering EDSA Sangri-la Hotel, Metro Manila, Philippines January 20 – 21, 2011
yielded the highest COD removal within thirty (30) minutes operation. Both Al and Fe anodes developed pitting corrosion after 5 hours and 3 hours of usage, respectively. Several improvements as to the design of the reactor should be conducted to make the technology suitable as an alternative treatment process for pharmaceutical residues. A study to optimize the settings of EC and to determine extent of electrode life including passivation studies may be explored in the future. Identification of side reactions as well verification of the structure of Fe-carboxylate complex should also be conducted. ACKNOWLEDGEMENT The authors would like to thank DOST-GIA (PCIERD) for financially supporting the conduct of the study and DOST-SEI and DLSU-Manila. REFERENCES Asselin, M., Drogui, P., Benmoussa H. and Blais, J.F. (2008). Effectiveness of electrocoagulation process in removing organic compounds from slaughterhouse wastewater using monopolar and bipolar electrolytic cells. Chemosphere, Vol 72, 727-1733 Bechrackis, N. Lambropoulou, D., Selimi, P. and Albanis, T. (2005, September 1-3). High Performance Liquid Chromatographic determination of pharmaceutical compounds in wastewaters. Proceedings of the 9th International Conference on environmental Science and Technology. Rhodes Island, Greece Can, O.T. and Bayramoglu, M. (2010). The effect of process conditions on the treatment of benzoquinone solution by electrocoagulation. Journal of Hazardous Materials, Vol. 173, pp. 731–736 Carlesi Jara, C., Fino, D., Specchia, V., Saracco, G. and Spinelli, P. (2007). Electrochemical removal of antibiotics from wastewaters. Applied Catalysis B: Environmental, Vol 70, pp. 479–487 Chen, G., Chen, X. and Yue, P.L. (2000). Electrocoagulation and Electroflotation of Restaurant Wastewater. Journal of Environmental Engineering, pp. 858-863 El-Naas, M.H., Al-Zuhair, S., Al-Lobaney, A. and Makhlouf, S. (2009). Assessment of electrocoagulation for the treatment of petroleum refinery wastewater. Journal of Environmental Management, pp. 1–6 Flippin, J.L., Huggett, D. and Foran, C.M. (2007). Changes in the timing of reproduction following chronic exposure to ibuprofen in Japanese medaka, Oryzias latipes. Aquatic Toxicology, Vol. 81, pp. 73–78 Gomes, J. Daida, P., Kesmez, M. Weir, m & Moreno H. (2007). Arsenic removal by electrocoagulation using combined Al–Fe electrode system and characterization of products. Journal of Hazardous Materials, B139, pp. 220–231.
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Presented at the 3rd Regional Conference on Chemical Engineering EDSA Sangri-la Hotel, Metro Manila, Philippines January 20 – 21, 2011
Ilhan, F., Kurt, U., Apaydin, O. and Gonullu, M.T. (2008). Treatment of leachate by electrocoagulation using aluminium and iron electrodes. Journal of Hazardous Materials, Vol. 154, pp. 381-389 Inan, H., Dimoglo, A., Simsek, H. and Karpuzcu, M. (2004). Olive oil mill wastewater treatment by means of electro-coagulation. Separation and Purification Technology, Vol. 36, pp. 23–31 Kobya, M. and Delipinar S. (2008). Treatment of the baker’s yeast wastewater by electrocoagulation. Journal Hazardous Materials, Vol. 154, pp. 1133-1140 Koparal, A.S., Yildiz, Y.S., Keskinler, B. and Demircioglu, N. (2008). Effect of initial pH on the removal of humic substances from wastewater by electrocoagulation. Separation and Purification Technology, Vol. 59, pp. 175-182 Mendez- Arriaga, F.M., Torres-Palma, R.A., Petrier, C., Esplugas, S., Gimenez, J. and Pulgarin, C. (2008). Ultrasonic treatment of water contaminated with ibuprofen. Water Research, Vol. 42, pp. 4243- 4248 Nghiem, L.D., Schafer, A.I. and Elimelech, M. (2005). Pharmaceutical Retention Mechanisms by nanofiltration membranes. Envi. Sci. Technol., Vol. 39, No. 19, pp. 76987705 Parga, J. Cocke, D. Valenzuela, J.L., Gomes, J., Kesmez, M., Irwin, G., Moreno, H. et al. (2005). Arsenic removal via electrocoagulation from heavy metal contaminated groundwater in La Comarca Lagunera M´exico. Journal of Hazardous Materials B, Vol. 124, pp. 247–254 Timmes, T.C., Kim, H.C. & Dempsey, B.A. (2010). Electrocoagulation pretreatment of seawater prior to ultrafiltration: Pilot-scale applications for military water purification systems. Desalination, Vol. 250, pp. 6–13. Ugurlu, M., Gurses, A., Dogar, C. and Yalcin, M. (2008). The removal of lignin and phenol from paper mill effluents by electrocoagulation. Journal of Environmental Management, Vol. 87, pp. 420–428. Weigel, S., Berger, U., Jensen, E., Kallenborn, R., Thoresen, H. and Huhnerfuss, H. (2004). Determination of selected pharmaceuticals and caffeine in sewage and seawater from Tromsø/Norway with emphasis on ibuprofen and its metabolites. Chemosphere, Vol. 56, pp. 583–592 Zaroual, Z., Azzi, M., Saib, N. and Chainet, E. (2006). Contribution to the study of electrocoagulation mechanism in basic textile effluent. Journal of Hazardous Materials B, Vol. 13, pp. 73–78 Zongo, I., Maiga, A.H., Wéthé, J., Valentin, G., Leclerc, J.P., Paternotte, G. and Lapicque, F. (2009). Electrocoagulation for the treatment of textile wastewaters with Al or Fe electrodes: Compared variations of COD levels, turbidity and absorbance. Separation and Purification Technology, Vol. 66, pp. 159–166.
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