Degradation of the endocrine disrupting chemicals (EDCs) carbamazepine, clofibric acid, and iopromide by corona discharge over water

Abstract

Common wastewater treatment plants often do not eliminate endocrine disrupting chemicals (EDCs). Aqueous solutions of three EDCs were treated with an enhanced corona discharge technology. The three EDCs were clofibric acid, a blood lipid regulator, carbamazepine, an antiepileptic drug, and iopromide, a contrast media. To simulate real conditions, EDC solutions containing landfill leachate were also used. In our setup, two barrier electrodes provided an atmospheric pressure corona discharge over a thin water film, in which the counter-electrode was submerged. Clofibric acid, carbamazepine, and iopromide were effectively removed from a single solution. After a treatment of 15 min, there were no traces of iopromide estrogen activity either as a single substance or as degradation products when using an E-Screen Assay. Continuous treatment was compared with pulsed treatment using carbamazepine solutions mixed with pretreated landfill leachate. Best degradation results were achieved with a 500 W continuous duty cycle treatment. Counter-electrodes from materials such as boron doped diamond (BDD), titanium iridium oxide, and iron were investigated for their influences on the process effectivity. Significant improvements were achieved by using an enclosed reactor, BDD electrodes, and circulating only a fresh air or argon/air mixture as cooling gas through the barrier electrodes.

Introduction

Certain pharmaceuticals or chemicals, which are harmful in very low concentrations, can pass easily through sewage treatment plants. These chemicals can later be detected in surface waters, groundwater, and drinking water (Ternes, 1998, Ternes et al., 2001). An important group of such harmful compounds are endocrine disrupting chemicals (EDCs). Additional wastewater treatment methods such as ozonation and advanced oxidation processes (AOP) could be applicable for the elimination of these substances (Zwiener and Frimmel, 2000, Ternes et al., 2003, Esplugas et al., 2007). Ozonation was shown to remove pharmaceuticals and musk fragrances (antibiotics, beta blockers, antiphlogistics, lipid regulator metabolites, and carbamazepine) from sewage treatment plant effluents. They were degraded to over 90% with 15 mg L⁻¹ O₃, while other compounds, like iodinated contrast media, were not successfully degraded (Ternes et al., 2003). Zwiener and Frimmel (2000) described the degradation of the EDC clofibric acid (2 μg L⁻¹) in river water to about 98%, using a combination of ozone (5 mg L⁻¹) with hydrogen peroxide (1.8 mg L⁻¹). Some EDCs like carbamazepine, however, are not degraded successfully by AOP, or in conventional sewage water treatment plants (Doll and Frimmel, 2005, Joss et al., 2005).

Other investigated AOPs include photo catalytic treatment with TiO₂ (Doll and Frimmel, 2005) or H₂O₂ (Andreozzi et al., 2003, Vogna et al., 2004). More than 90% of the initial carbamazepine concentration of 4.2 mg L⁻¹ was degraded after 9 min by using 100 mg L⁻¹ TiO₂ and a 1000 W xenon short arc lamp at pH 6.5 (Doll and Frimmel, 2005). Degradation of lake water was impaired by the presence of natural organic matter and by deactivation of the catalyst surface by adsorption (Doll and Frimmel, 2005). Degradation of 2.0 × 10⁻² mM of carbamazepine treated with UV/H₂O₂ (254 nm, 170 mg L⁻¹ H₂O₂) at pH 5 was complete after 4 min (Andreozzi et al., 2003). Humic substances decreased the degradation of carbamazepine. With both treatment methods, acridine, an azareene with mutagenic and carcinogenic activity, was observed as a degradation product. Treatment with UV/H₂O₂ and TiO₂ requires large exposure times compared to ozonation (Esplugas et al., 2007). In some ozonation and photo catalysis treatments, the estrogenic activity of EDCs like 17β-estradiol and 17α-ethinylestradiol was not completely removed (Esplugas et al., 2007). Photo catalysis can be impaired by suspended solids and colors due to light scattering and absorption (Ikehata et al., 2006). The aforementioned experiments were conducted with Milli-Q water, river, lake, ground-, and drinking water.

Electric discharges with various electrode configurations for water treatment were also investigated (Locke et al., 2006). The wet type non-thermal plasma reactor consists of a high voltage electrode placed in the gaseous phase over the water surface or in the liquid phase and grounded either in the liquid phase or on the liquid surface. In non-thermal plasma, electrons can reach temperatures of 10 000–100 000 K (Petitpas et al., 2007, with various electrode configurations) while molecules remain at ambient temperature. The major products of electrical discharge in gaseous phase over liquid surface are O₃, OH radicals and H₂O₂, whereas the amount of OH radicals is promoted by increased humidity (Hayashi et al., 2000). In the liquid phase the dominant discharge products are OH radicals and H₂O₂ (Sun et al., 1998).

Hayashi et al. (2000) investigated the degradation of phenol in aqueous solutions. They applied a pulsed corona discharge in a closed glass vessel at a frequency of 10 Hz using various atmospheres over the liquid phase. Significant degradation results were achieved under an oxygen atmosphere. Sun et al., 1999, Sun et al., 2000, who degraded phenol by corona discharge in liquid phase, discovered, that besides the production of radicals through collision of electrons with molecules, the generated ultraviolet radiation degrades the H₂O₂ formed during the discharge, to OH radicals. Manolache et al. (2004) degraded aromatic compounds and dyes with the help of radicals formed by corona discharge in the liquid phase or in the liquid phase with gas bubbles. Njatawidjaja et al. (2005) also degraded aromatic compounds and dyes using electrostatic atomization and corona discharge in gaseous phase when liquid droplets were injected.

Other investigated chemicals include various organic dyes, carbon tetrachloride, perchloroethylene, pentachlorophenol, phenols, chlorophenols, benzoic acid, and aniline (Locke et al., 2006). However, it is our understanding, that the degradation of endocrine disruptive pharmaceuticals with corona discharge has not yet been studied.

If the degradation processes are able to degrade the target pollutants, the degradation products could be more toxic or more endocrine active than the initial pollutant (Vogna et al., 2004). Effective degradation of the target compounds and elimination of possible impacts of the degradation products are important factors for the preservation of clean freshwater supplies.

The aim of our study was to develop an advanced corona discharge technology integrating catalysis by testing different catalytic materials under various atmospheres using pulsed and continuous corona discharge. We analyzed ultra pure water and landfill leachate containing solutions of the blood lipid regulator clofibric acid, the antiepileptic drug carbamazepine, and the contrast media iopromide. These pertinacious pharmaceuticals are endocrine active and found in the effluents of sewage treatment plants, surface waters, groundwater, and drinking water (Ternes, 1998, Ternes et al., 2001). The results were verified by HPLC. The endocrine activity of the degradation products was tested by an E-Screen Assay.