Photocatalytic degradation of Metronidazole with illuminated TiO2 nanoparticles
© Farzadkia et al.; licensee BioMed Central. 2015
Received: 15 September 2014
Accepted: 15 April 2015
Published: 21 April 2015
Metronidazole (MNZ) is a brand of nitroimidazole antibiotic, which is generally used in clinical applications and extensively used for the treatment of infectious diseases caused by anaerobic bacteria and protozoans. The aim of this investigation was to degrade MNZ with illuminated TiO2 nanoparticles at different catalyst dosage, contact time, pH, initial MNZ concentration and lamp intensity. Maximum removal of MNZ was observed at near neutral pH. Removal efficiency was decreased by increasing dosage and initial MNZ concentration. The reaction rate constant (k obs ) was decreased from 0.0513 to 0.0072 min−1 and the value of electrical energy per order (EEo) was increased from 93.57 to 666.67 (kWh/m3) with increasing initial MNZ concentration from 40 to 120 mg/L, respectively. The biodegradability estimated from the BOD5/COD ratio was increased from 0 to 0.098. The photocatalyst demonstrated proper photocatalytic activity even after five successive cycles. Finally, UV/TiO2 is identified as a promising technique for the removal of antibiotic with high efficiency in a relatively short reaction time.
Recently, several different types of emerging contaminants in water systems are known as new environmental hazards those need to be treated with suitable methods . As various pharmaceutical compounds have been used since the 1950s due to rapid population growth and development of medical science, several pharmaceutical compounds have been found in surface water, ground water and effluents from wastewater treatment plants. Metronidazole (2-methyl-5-nitroimidazole-1-ethanol) has been widely used to treat infections caused by anaerobic bacteria, bacteroides and protozoa [2-4]. Residual concentrations of metronidazole (MNZ) in surface waters and wastewater are 1 ~ 10 ng/L [5,6]. As MNZ is non-biodegradable and highly soluble in water, it can be accumulated in the aquatic environment [7,8]. Elimination of MNZ from water system is an important issue considering its toxicity, potential mutagenicity and carcinogenity [7,8]. In order to remove MNZ, many techniques such as adsorption [9,10], reduction with nanoscale zero-valent iron particles , biological methods [12,13], ozonation technology , photolysis , Fenton and photo-Fenton processes , heterogeneous photocatalysis [15,17,18] and electro-Fenton process with a Ce/SnO2–Sb coated titanium anode  have been applied.
Adsorption is widely used method for the treatment of wastewater containing toxic organic compounds. However, it just transfer contaminants from water to a solid phase without any degradation [9,10,19,20]. Biological method is also known as one of the suggested techniques. However this method generally requires long periods for treatment [12,21]. Oxidation is a promising process but sometimes it is regarded as a limited process due to the formation of intermediates with higher toxicity than the parent compound [5,8,22]. Therefore near complete mineralization of MNZ is the most relevant option. For this purpose, advanced oxidation process (AOP) is regarded as a promising option to treat wastewater containing MNZ due to a complete mineralization of parent material as well as lack of selectivity [7,23]. Generally AOPs involve generation of hydroxyl radicals through UV/photocatalyst, UV/H2O2 and UV/O3 processes [24-26]. Among these methods, photocatalytic reaction using TiO2/UV can treat non-biodegradable organic compounds to biodegradable species [23,24,27]. Considering characteristics of the AOP, it can be used as pre- or post-treatment process in wastewater treatment because of its installation easiness in conventional wastewater treatment facilities [23,24,27].
Therefore, in the present work, P-25 TiO2 was selected as a catalyst in the photocatalytic removal of MNZ. Effects of several operational parameters including pH, TiO2 dosage and MNZ concentration on photocatalytic degradation of MNZ were investigated. Kinetic parameters for the photocatalytic degradation were obtained by application of the Langmuir–Hinshelwood (L–H) model. Finally, electrical energy per order (EEo) was obtained to evaluate cost-efficiency of the processes used in this research.
Material and methods
Experimental procedure and analysis
All experiments were repeated three times and the average values with error percents were reported.
Results and discussion
Effect of TiO2 dosage
Biodegradability of MNZ was evaluated in this work. To measure the biodegradability, BOD5 and COD values were measured before and after UV irradiation and the ratio of BOD5/COD was used as a biodegradability indicator. After 3 h reaction time, removal efficiency of COD was above 97.6% at all catalyst dosages and the ratio of BOD5/COD increased from 0 to 0.098 as the dosage increased from 0.5 to 3 g/L. This result indicates that MNZ can be changed to more biodegradable products.
Effect of pH
Effect of initial MNZ concentration
Kinetic study and electrical energy determination
Pseudo-first order kinetic parameters and E Eo values for the photocatalytic degradation of MNZ at different initial MNZ concentrations (catalyst dose = 0.5 g/L and pH =7)
E Eo (kWh/m 3 )
1/k obs (min)
k obs (1/min)
[MNZ] 0 (mg/L)
The E Eo values for the removal of MNZ ([MNZ] 0 = 80 mg/L, catalyst dose = 0.5 g/L and pH =7)
E Eo (kWh/m 3 )
UV 8 W-alone
UV 8 W/TiO2
UV 125 W/TiO2
Comparison of different MNZ removal processes and reusability test
Based on the above experiments and analysis, mechanism of the photocatalysis could be proposed as following:
Comparison of photocatalytic degradation of MNZ
Catalyst dosage (g/L)
[MNZ ] 0 (mg/L)
Removal efficiency (%)
k obs (min −1 )
From the application of TiO2 for the photocatalytic degradation of MNZ in aqueous solutions, a maximum removal of MNZ was observed at neutral pH. Removal efficiency was decreased by increasing TiO2 dosage and initial MNZ concentration. Electrical energy per order was increased and reaction rate constant was decreased with increasing initial MNZ concentration. Photocatalytic activity was maintained even after five consecutive runs. Finally, UV/TiO2 is identified as a promising technique for the removal of MNZ with high efficiency in a relatively short reaction time.
The authors thank the Iran and Zahedan Universities of Medical Sciences, Iran for all of the support provided. Also, authors would like to thank Mr. Bonyani for the HPLC analysis in the laboratory of nutrition department.
- Cheng W, Yang M, Xie Y, Liang B, Fang Z, Tsang EP. Enhancement of mineralization of metronidazole by the electro-Fenton process with a Ce/SnO2–Sb coated titanium anode. Chem Eng J. 2013;220:214–20.View ArticleGoogle Scholar
- Chatzitakis A, Berberidou C, Paspaltsis I, Kyriakou G, Sklaviadis T, Poulios I. Photocatalytic degradation and drug activity reduction of chloramphenicol. Water Res. 2008;42:386–94.View ArticleGoogle Scholar
- Dong S, Li Y, Sun J, Yu C, Li Y, Sun J. Facile synthesis of novel ZnO/RGO hybrid nanocomposites with enhanced catalytic performance for visible-light-driven photodegradation of metronidazole. MCP. 2014;145:357–65.Google Scholar
- Farzadkia M, Esrafili A, Baghapour MA, Shahamat YD, Okhovat N. Degradation of metronidazole in aqueous solution by nano-ZnO/UV photocatalytic process. Desalin Water Treat. 2013;52:4947–52.View ArticleGoogle Scholar
- Dantas RF, Rossiter O, Teixeira AKR, Simões AS, da Silva VL. Direct UV photolysis of propranolol and metronidazole in aqueous solution. Chem Eng J. 2010;158:143–7.View ArticleGoogle Scholar
- Vulliet E, Cren-Olivé C. Screening of pharmaceuticals and hormones at the regional scale, in surface and groundwaters intended to human consumption. Environ Pollut. 2011;159:2929–34.View ArticleGoogle Scholar
- Zhenhu X, Zaixu C, Jianming L. Comparison of metronidazole degradation by different advanced oxidation processes in low concentration aqueous solutions. Chin J Environ Eng. 2009;3:465–9.Google Scholar
- Johnson MB, Mehrvar M. Aqueous metronidazole degradation by UV/H2O2 process in single-and multi-lamp tubular photoreactors: kinetics and reactor design. Ind Eng Chem Res. 2008;47:6525–37.View ArticleGoogle Scholar
- Méndez-Díaz J, Prados-Joya G, Rivera-Utrilla J, Leyva-Ramos R, Sánchez-Polo M, Ferro-García MA, et al. Kinetic study of the adsorption of nitroimidazole antibiotics on activated carbons in aqueous phase. JCIS. 2010;345:481–90.Google Scholar
- Rivera-Utrilla J, Prados-Joya G, Sánchez-Polo M, Ferro-García M, Bautista-Toledo I. Removal of nitroimidazole antibiotics from aqueous solution by adsorption/bioadsorption on activated carbon. J Hazard Mater. 2009;170:298–305.View ArticleGoogle Scholar
- Fang Z, Chen J, Qiu X, Qiu X, Cheng W, Zhu L. Effective removal of antibiotic metronidazole from water by nanoscale zero-valent iron particles. Desalination. 2011;268:60–7.View ArticleGoogle Scholar
- Ingerslev F, Halling-Sørensen B. Biodegradability of metronidazole, olaquindox, and tylosin and formation of tylosin degradation products in aerobic soil–manure slurries. Ecotoxicol Environ Saf. 2001;48:311–20.View ArticleGoogle Scholar
- Ingerslev F, Toräng L, Loke M-L, Halling-Sørensen B, Nyholm N. Primary biodegradation of veterinary antibiotics in aerobic and anaerobic surface water simulation systems. Chemosphere. 2001;44:865–72.View ArticleGoogle Scholar
- Sánchez-Polo M, Rivera-Utrilla J, Prados-Joya G, Ferro-García M, Bautista-Toledo I. Removal of pharmaceutical compounds, nitroimidazoles, from waters by using the ozone/carbon system. Water Res. 2008;42:4163–71.View ArticleGoogle Scholar
- Prados-Joya G, Sánchez-Polo M, Rivera-Utrilla J, Ferro-Garcia M. Photodegradation of the antibiotics nitroimidazoles in aqueous solution by ultraviolet radiation. Water Res. 2011;45:393–403.View ArticleGoogle Scholar
- Shemer H, Kunukcu YK, Linden KG. Degradation of the pharmaceutical metronidazole via UV, Fenton and photo-Fenton processes. Chemosphere. 2006;63:269–76.View ArticleGoogle Scholar
- Gao J, Liu B, Wang J, Jin X, Jiang R, Liu L, et al. Spectroscopic investigation on assisted sonocatalytic damage of bovine serum albumin (BSA) by metronidazole (MTZ) under ultrasonic irradiation combined with nano-sized ZnO. Spectrochim Acta A Mol Biomol Spectrosc. 2010;77:895–901.View ArticleGoogle Scholar
- Wang H, Zhang G, Gao Y. Photocatalytic degradation of metronidazole in aqueous solution by niobate K6Nb10.8O30. Wuhan Univ J Nat Sci. 2010;15:345–9.View ArticleGoogle Scholar
- Ahmed MJ, Theydan SK. Microporous activated carbon from Siris seed pods by microwave-induced KOH activation for metronidazole adsorption. J Anal Appl Pyrolysis. 2013;99:101–9.View ArticleGoogle Scholar
- Çalışkan E, Göktürk S. Adsorption characteristics of sulfamethoxazole and metronidazole on activated carbon. SS&T. 2010;45:244–55.Google Scholar
- Saidi I, Soutrel I, Floner D, Fourcade F, Bellakhal N, Amrane A, et al. Indirect electroreduction as pretreatment to enhance biodegradability of metronidazole. J Hazard Mater. 2014;278:172–9.View ArticleGoogle Scholar
- Jimmy C. In situ synthesis of Zn2GeO4 hollow spheres and their enhanced photocatalytic activity for the degradation of antibiotic metronidazole. DTr. 2013;42:5092–9.Google Scholar
- Palominos RA, Mondaca MA, Giraldo A, Peñuela G, Pérez-Moya M, Mansilla HD. Photocatalytic oxidation of the antibiotic tetracycline on TiO2 and ZnO suspensions. Catal Today. 2009;144:100–5.View ArticleGoogle Scholar
- Elmolla ES, Chaudhuri M. Photocatalytic degradation of amoxicillin, ampicillin and cloxacillin antibiotics in aqueous solution using UV/TiO2 and UV/H2O2/TiO2 photocatalysis. Desalination. 2010;252:46–52.View ArticleGoogle Scholar
- Giraldo AL, Penuela GA, Torres-Palma RA, Pino NJ, Palominos RA, Mansilla HD. Degradation of the antibiotic oxolinic acid by photocatalysis with TiO2 in suspension. Water Res. 2010;44:5158–67.View ArticleGoogle Scholar
- Farrokhi M, Yang J-K, Lee S-M, Shirzad-Siboni M. Effect of organic matter on cyanide removal by illuminated titanium dioxide or zinc oxide nanoparticles. J Environ Health Sci Eng. 2013;11:23.View ArticleGoogle Scholar
- Dimitrakopoulou D, Rethemiotaki I, Frontistis Z, Xekoukoulotakis NP, Venieri D, Mantzavinos D. Degradation, mineralization and antibiotic inactivation of amoxicillin by UV-A/TiO2 photocatalysis. J Environ Manage. 2012;98:168–74.View ArticleGoogle Scholar
- Federation WE, Association APH. Standard methods for the examination of water and wastewater. Washington, DC, USA: American Public Health Association (APHA); 2005.Google Scholar
- Wang J, Wang Z, Jin X, Guo Y, Gao J, Li K, et al. Catalytic damage of bovine serum albumin by metronidazole under ultrasonic irradiation in the presence of nano-sized TiO2 powder. Rus J Physic Chem A. 2012;86:867–74.View ArticleGoogle Scholar
- Daneshvar N, Salari D, Khataee AR. Photocatalytic degradation of azo dye acid red 14 in water: investigation of the effect of operational parameters. J Photochem Photobiol A Chem. 2003;157:111–6.View ArticleGoogle Scholar
- Daneshvar N, Salari D, Khataee AR. Photocatalytic degradation of azo dye acid red 14 in water on ZnO as an alternative catalyst to TiO2. J Photochem Photobiol A Chem. 2004;162:317–22.View ArticleGoogle Scholar
- Homem V, Santos L. Degradation and removal methods of antibiotics from aqueous matrices - A review. J Environ Manage. 2011;92:2304–47.View ArticleGoogle Scholar
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