Development and optimization of the BDD-electrochemical oxidation of the antibiotic trimethoprim in aqueous solution Teresa González a , Joaquín R. Domínguez a, ⁎, Patricia Palo a , Jesús Sánchez-Martín a , Eduardo M. Cuerda-Correa b a Department of Chemical Engineering and Physical Chemistry, Area of Chemical Engineering, Faculty of Sciences, University of Extremadura, Avda. de Elvas, s/n, E-06006 Badajoz, Spain b Department of Organic and Inorganic Chemistry, Faculty of Sciences, University of Extremadura, Avda. de Elvas, s/n, E-06071 Badajoz, Spain abstract article info Article history: Received 16 September 2010 Received in revised form 2 June 2011 Accepted 3 July 2011 Available online 3 September 2011 Keywords: Electrochemical advanced oxidation processes Electro-oxidation Anodic oxidation Boron-doped diamond electrodes Pharmaceuticals Trimethoprim The occurrence of antibiotics in the aquatic environment has led to an increasing concern about the potential environmental risks and the maintenance and spread of antibacterial resistance among microorganisms. Electrochemical oxidation processes are promising technologies to treat low contents of toxic and biorefractory pollutants in water. Anodic oxidation of Trimethoprim, the most frequently detected antibiotic in surface waters, was carried out using boron-doped diamond electrodes at galvanostatic mode. A statistical design of experiments has been used to study the influence of the different operating variables: pH (in the range 3–11), current intensity (from 0 to 320 mA cm -2 ), supporting electrolyte concentration Na 2 SO 4 in the range 0–0.5 mol L -1 , and solution flow rate between 1.25 and 10.80 cm 3 min -1 . Response Surface Methodology technique was used to optimize Trimethoprim degradation. Current intensity resulted to be the main variable influencing Trimethoprim degradation, followed by salt concentration and pH. ANOVA test reported significance for five of the fourteen involved variables. An optimum Trimethoprim degradation of 100% was found at pH 3, under a flow rate equal to 1.25 cm 3 min -1 , and with a current density equal to 207 mA cm -2 , using a supporting electrolyte concentration equal to 0.49 mol L -1 . © 2011 Elsevier B.V. All rights reserved. 1. Introduction Considering the wide variety and different applications of antibiotics and the ever increasing tendency to use them, it is no surprise that these drugs are among the most ubiquitous environ- mental contaminants [1,2]. The occurrence of antibiotics in the aquatic environment has led to an increasing concern about the potential environmental risks as well as about the maintenance and spread of antibacterial resistance among microorganisms. Develop- ment of antibiotic resistance of bacteria was demonstrated in surface and groundwater affected by the sewage treatment plant effluent [3]. Whether antibiotics transported in the environment from human and livestock sources lead to increased antibiotic resistant bacteria or have deleterious effects on water quality is an important but largely unresolved issue. The use of antibiotics may also accelerate the development of antibiotic resistance genes and bacteria, which shade health risks to humans and animals [4]. The main source of antibiotics in the environment is the excretion of incompletely metabolized drugs by humans and animals. Other sources may include the disposal of unused antibiotics and waste from pharmaceutical manufacturing processes [5]. Residential care facilities and hospitals are known contributors of antibiotics to municipal wastewater [6]. Other contributors to surface and groundwater are effluent from wastewater treatment plants [6] and industrial facilities (including pharmaceutical plants), and surface run-off from concentrated animal feeding operations [1]. Recently, scientists have raised concerns about pharmaceutical residues detected in surface waters and wastewaters and their potential to cause adverse effects in humans and aquatic species [7,8]. Wastewater typically contains a number of medications and antibiotics that people have either used or discarded. Many of these chemical compounds remain biologically active and some of them, especially antibiotics, stimulate the development of antibiotic resistant bacteria. Recent studies have confirmed the presence of low levels of pharmaceuticals in estuaries, rivers, streams, and ground water as well as in sediments [9,10]. The ecological effects of these contaminants in coastal waters are largely unknown. However, there is growing evidence that some of these chemicals may have negative effects on reproduction in aquatic species. Trimethoprim (TMP) [2,4-diamino-5-(3′,4′,5′-trimethoxybenzyl- pyrimidine)] (molecular formula C 14 H 18 N 4 O 3 , molecular weight 290.32, CAS Number 738-70-5, pKa = 7.2) is a very good antifolate drug. It selectively inhibits the bacterial form of the dihydrofolate reductase enzyme [11,12]. TMP is among the most important synthetic antibiotics used worldwide in human and veterinary Desalination 280 (2011) 197–202 ⁎ Corresponding author. Tel.: + 34 924289300x86888; fax: + 34 924289385. E-mail address: jrdoming@unex.es (J.R. Domínguez). 0011-9164/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2011.07.012 Contents lists available at ScienceDirect Desalination journal homepage: www.elsevier.com/locate/desal