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Trends in Chemical Engineering   Volumes    Volume 12 
Removal of nitroimidazole antibiotics from water by adsorption/bioadsortion on activated carbon and advanced oxidation processes
J. Rivera-Utrilla, G. Prados-Joya, M. Sánchez-Polo, M. A. Ferro-García, J. J. López-Peñalver, M. I. Bautista-Toledo
Pages: 51 - 69
Number of pages: 19
Trends in Chemical Engineering
Volume 12 

Copyright © 2009 Research Trends. All rights reserved

The main objective of this study was to analyze the effectiveness of technologies based on the use of ozone, gamma irradiation and activated carbon for the removal of nitroimidazoles (metronidazole (MNZ), dimetridazole (DMZ), tinidazole (TNZ), ronidazole (RNZ)) from water, considering them as model compounds of pharmaceuticals. Results indicate that the adsorption of nitroimidazoles on activated carbon is largely determined by activated carbon chemical properties. Application of the Langmuir equation to the adsorption isotherms showed an elevated adsorption capacity (Xm = 1.04-2.04 mmol/g) for all contaminants studied. Nitroimidazoles are not degraded by microorganisms used in the biological stage of a wastewater treatment plant. However, the presence of microorganisms during nitroimidazole adsorption increased their adsorption/bioadsorption on the activated carbon, although it weakened interactions between the adsorbate and carbon surface. Ozone reaction kinetics showed that nitroimidazoles have a low reactivity, with kO3 values < 350 M-1s-1 regardless of the nitroimidazole and solution pH considered. However, nitroimidazoles have a high affinity for HO· radicals, with radical rate constant (kHO) values of around 1010 M-1s-1. The presence of activated carbon during nitroimidazole ozonation produces: i) an increase in the removal rate, ii) a reduction in the toxicity of oxidation by-products, and iii) a reduction in the concentration of dissolved organic matter. When using gamma irradiation to degradate nitroimidazoles, no differences in constant rates were detected for any nitroimidazole studied (0.0014 - 0.0017 Gy-1). The presence of t-BuOH (HO· radical scavenger) and thiourea (HO·, H· and e-aq scavenger) reduced the MNZ irradiation rate, indicating that degradation of this pollutant can take place via two pathways: oxidation by HO· radicals and reduction by e-aq and H·. MNZ gamma irradiation can achieve i) a decrease in the concentration of dissolved organic carbon, and ii) a reduction in the toxicity of the system with higher gamma absorbed dose.
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