Matrix effect in the hydroxyl radical induced degradation of ß-lactam and tetracycline type antibiotics

Due to the spread of antibiotic resistant bacteria, elimination of antibiotics from purified wastewater is a highly important task. Purified wastewater contains large variety of organic/inorganic compounds that strongly influence the efficiency of advanced oxidation processes (AOP). In this work, we investigate the radiation-induced degradation of selected antibiotic contaminants (oxacillin and cloxacillin from the beta-lactams; tetracycline and chlortetracycline from the tetracyclines) in four matrices: pure water, tap water, synthetic wastewater and purified wastewater received from a wastewater treatment plant. Changes in technically important parameters, such as COD, TOC, BOD, OUR, acute toxicity and antibacterial activity, were investigated at 0.1 mmol dm(-3) (40-48 mg dm(-3)) antibiotic concentration. None of the four antibiotics were biodegradable in any of the four matrices, however, after irradiation with relatively low doses the obtained products were biodegradable. Oxacillin and cloxacillin were not toxic in Vibrio fischeri test, while tetracycline and chlortetracycline showed toxicity that was strongly reduced by the irradiation treatment. Both COD and TOC decreased after irradiation, their ratio shifted towards TOC indicating an increase in the average oxidation state (AOS). The increase in AOS was lower in purified wastewater matrices: this matrix may contain various small, highly oxidized molecules in high concentration, which degrade very slowly in AOP. The antibacterial activity in most of matrices was greatly reduced or completely disappeared at around 2-4 kGy. However, in purified wastewater matrices some antibiotic activity remained even at 4 kGy. Here the degradation of antibiotic is slow (small delta COD/dose value) because a large fraction of the reactive radicals is scavenged presumably by small, highly oxidized molecules in the solution. Although the water radiolysis product H2O2 affected some of the bioassays, this phenomenon was absent in purified wastewater. The purified wastewater after ionizing radiation treatment can be safely released into the receiving lakes or rivers

Azo dye degradation by high-energy irradiation: kinetics and mechanism of destruction

The kinetics and mechanism of dye destruction is discussed on the example of Apollofix Red (AR-28) and Reactive Black 5 (RB-5) radiolysis in dilute aqueous solution. The dose dependence of colour disappearance is linear when the reactive intermediate reacts with the colour bearing part of the molecule causing destruction of the conjugation here with nearly 100% efficiency. In this case, spectrophotometry can be used to follow-up dye decomposition. Such a linear dependence was observed when hydrated electrons or hydrogen atoms reacted with the dye. However, in the case of hydroxyl radical reactions some coloured products form with absorption spectra very similar to those of the starting dye molecules. For that reason, spectrophotometric measurements give false results about the concentration of intact dye molecules. Analysis made by the HPLC (high-pressure liquid chromatography) method reveals logarithmic time dependence in agreement with a theoretical model developed