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Keywords:

  • tetracyclines;
  • advanced oxidation/reduction process (AORP);
  • antibiotics;
  • radiolysis;
  • toxicity

Abstract

Background

This study analyzes the efficacy of a gamma radiation advanced oxidation/reduction process (AORP) to treat waters contaminated with the antibiotics tetracycline (TC), chlortetracycline (CTC), and oxytetracycline (OTC).

Results

Study results indicate that: (1) radiolysis of the three TCs fits a pseudo-first-order kinetic model in which the radiation-chemical yield decreases with higher absorbed dose; (2) the value of the dose constant depended on the dose rate, which ranged from 3.83 to 1.66 Gy min–1, and depended to a small extent on the medium pH between pH values of 2.0 and 10.0, since aqueous electrons and hydroxyl radicals both act in TC degradation; (3) the effectiveness of the process was slightly increased at low concentrations of H2O2; (4) the presence of Cl, inline image, inline image, inline image and humic acid influenced TCs degradation, which was higher at low concentrations of Cl, inline image and HA and markedly decreased at low concentrations of of inline image and inline image; (5) the dose constant is lower in natural waters; (6) TOC values for ultrapure water, surface water, groundwater and wastewater showed that it is not possible to obtain complete TC mineralization at the absorbed doses; (7) the toxicity of byproducts formed during the radiolytic process was lower.

Conclusions

Gamma radiation, an oxidation/reduction procedure, is an effective treatment for removing TC, CTC and OTC from aqueous solutions. TC degradation takes place by both oxidation and reduction pathways, with a predominance of the latter, as demonstrated by the markedly reduced dose constant in the presence of aqueous electron scavengers.