An experimental study of ATCC (American Type Culture Collection) 8739 Escherichia coli bacteria inactivation in water by means of pulsed dielectric barrier discharge (PDBD) atmospheric pressure plasmas is presented. Plasma is generated by an adjustable power source capable of supplying high voltage 25 kV pulses, ∼30 μs long and at a 500 Hz frequency. The process was conducted in a ∼152 cm 3 cylindrical stainless steel coaxial reactor, endowed with a straight central electrode and a gas inlet. The bacterial concentration in water was varied from 10 3 up to 10 8 E. coli cells per millilitre.The inactivation was achieved without gas flow in the order of 82% at 10 8 colony-forming units per millilitre (CFU mL -1 ) concentrations in 600 s. In addition, oxygen was added to the gas supply in order to increase the ozone content in the process, raising the inactivation percentage to the order of 90% in the same treatment time. In order to reach a higher efficiency however, oxygen injection modulation is applied, leading to inactivation percentages above 99.99%. These results are similarly valid for lower bacterial concentrations.
In this work, phenol oxidation in aqueous solution promoted by the effect of the oxidizing agents H2O2, O3 and UV radiation and their synergy in four different advanced oxidation processes (O3, O3/UV, H2O2/O3 and O3/H2O2/UV) were assayed. Studies were performed with a closed-loop hydraulic circuit set up with a relatively high volume of solution (500 cm 3) during 90 min of treatment time. Parameters such as concentration for oxidizing species, pH, presence of UV irradiation were evaluated. The resulting degradation efficiencies were evaluated using GC-MS. The agents here used were selected considering their ease of handling and low toxicity, generation of deposited matter or sludge, so a filtration treatment for the analysis of the samples was not required. In all cases, it was observed that with increasing treatment time better degradation efficiencies were obtained. The best results were obtained with the combination of O3/H2O2/UV where up to 95% degradation was attained at pH 9, which is due to active species generated in the process, e.g., O3 and OH , on the contaminant. SPE was performed for determining the presence of several by-products, mainly: catechol, resorcinol and hydroquinone, which were identified.
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