Experimental Study of Ozone Generation by Negative Corona Discharge in Mixtures of N2 and O2

Ozone generation by negative DC corona discharge in N₂-O₂ mixtures has been experimentally investigated using a coaxial wire-cylinder corona reactor operating at room temperature and atmospheric pressure. The experiments have been carried out under different gas flows (15 cm³ min^?1 to 200 cm³ min^?1) and gas compositions (5% to 90% of O₂), and the effect of these parameters on the corona current, the ozone density and the efficiency of the ozone generator have been analyzed. The global rate coefficients for ozone formation and destruction have also been evaluated, and their values compared with those reported by other authors. The maximum efficiency for ozone production was found in gas mixtures with oxygen content about 70–80%.     

The Effect of Relative Humidity on Ozone Production by Corona Discharge in Oxygen or Air – A Numerical Simulation – Part I : Oxygen

The simulation of the temporal evolution of the various neutral gaseous species studied (O, O₃, H, OH, HO₂, H₂O₂) use corona effects. The physical conditions of the discharge were used. The reactions take place in dry or humid oxygen, after the dissociation of O₂ and H₂O by an electronic pulse. When water vapor is present, there is a probability of production of H₂O₂ in oxygen. Temperature and humidity have cumulative effects. With multiple pulses, the O₃ maximal concentration is obtained for a limited number of pulses.     

The Effect of Relative Humidity on Ozone Production by Corona Discharge in Oxygen or Air – A Numerical Simulation – Part II : Air

The simulation of the temporal evolution of the various neutral gaseous species studied (O, O₃, H, OH, HO₂, H₂O₂, N, NO, NO₂, NO₃, N₂O, N₂O₅, HNO₂, and HNO₃) use corona effects. The physical conditions of the discharge were used. The reactions take place in dry or humid air, after the dissociation of O₂, N₂, and H₂O by an electronic pulse. When water vapor is present, there is a probability of production of H₂O₂, HNO₂, and HNO₃ in air. Temperature and humidity have cumulative effects. With multiple pulses, the O₃ maximal concentration is obtained for a limited number of pulses.     

Effect of Silica Packing on Ozone Synthesis from Oxygen-Nitrogen Mixtures

The effect of silica packing in an ozone generator fed with oxygen-nitrogen mixtures has been studied. The measurements were carried out in an ozone generator with a double-sided cooled discharge gap, in which silica packing has been placed. In the presence of the packing considerably higher ozone concentrations were achieved than in the ozone generator without packing. An especially clear effect of silica packing was observed in air-fed conditions. It has been found that the increase in the concentration of the obtained ozone coincides with the increase of N₂O in the post-reaction gas.     

The Efficacy of Ozone/BAC Treatment on Non-Steroidal Anti-Inflammatory Drug Removal from Drinking Water and Surface Water

Three non-steroidal anti-inflammatory drugs (NSAIDs)—ketoprofen, naproxen and piroxicam—in both deionized (DI) water and surface lake water (SW) (Tallahassee, FL), were exposed to varying ozone treatment regimes or H₂O₂/O₃ advanced oxidation on the laboratory bench. Recently used biofilm-supporting granular activated carbon (BAC) was sampled from a municipal drinking water treatment facility (Tampa, FL, USA), and employed to determine the bio-availability of chemical intermediates formed in ozonated water. Advanced chemical analysis was used to identify oxidation by-products formed and combined with a bioanalytical tool to assess non-specific toxicity (Microtox assay). All 3 target pharmaceuticals were efficiently removed by different processes, with a lower NSAIDs removal yield observed in lake water compared to DI water experiments. The removal yields of ketoprofen, naproxen, and piroxicam improved with increasing ozone dose, H₂O₂/O₃ ratio and empty bed contact time (EBCT) with BAC. Ozonation with BAC filtration had a positive impact by reducing the initial ozone dose required to achieve > 90% removal of all 3 pharmaceuticals (when an initial ozone dose < 1 mg L^-1 was combined with EBCT < 15 min). The toxicity evolution of the treated samples was monitored by Microtox bioassay. Ozone doses higher than 2 mg L^-1 for 2 min contact time were optimal to reach the lower water samples toxicity with NSAIDs removal yields ranging from 95.5 to 99.0% in DI water and from 77 to 90% in SW. Also, higher ozone doses were not shown to remove the residual toxicity. In contrast, the BAC filtration hardly decreases the sample toxicity when an EBCT of 15 min was chosen despite a NSAIDs removal yield equal or higher than 90% in SW.     

The Effect of Ozonation and Filtration on AOC (Assimilable Organic Carbon) Value of Water from Eutrophic Lake

The effects of applying ozone into the source water of Cheng-Ching Lake Water Works (CCLWW) on the analysis of AOC (assimilable organic carbon) were compared in the laboratory and pilot-scale tests. CCLWW takes its raw water from an eutrophic lake. A pilot plant, established in CCLWW in southern Taiwan, was performed to improve the quality of water obtained by the former treatment processes. The direct application of ozone to the source water of CCLWW is called the pre-O₃ process. The post-O₃ process involves the treatment of effluent with ozone through a sand filter, following other treatments, including pre-O₃, coagulation and sedimentation. In a laboratory test, a 0.45 μm membrane filter was used to replace the facility of filtration for a sand filter. AOC_Total comprises AOC_P17 and AOC_NOX, which were determined using the P. fluorescens strain P17 and the Spirillum species strain NOX, respectively. During over 2 years' sampling in eutrophic lake, it revealed that AOC_P17 contributed substantially to AOC_Total. However, the filtrate from the source water obtained by filtering through a 0.45 μm membrane filter had an AOC_Total much lower than that of the source water, especially for the considerable decrease of AOC_P17. Also, the AOC value in source water is increased with algae number but not with NPDOC (non-purgeable dissolved organic carbon). This result indicated that algae numbers existing in the eutrophic lake might affect the analysis of AOC. Following the pre-O₃ process at the pilot-scale plant, the AOC_P17 was markedly lower than that of the source water, and AOC_NOX was slightly higher than that of the source water. However, when post-O₃ was added to the effluent from a sand filter at the pilot-scale plant, AOC_NOX exceeded that before post-O₃, while AOCP17 differed slightly from that before post-O₃. Apparently, this difference may be due to the algae number existing in the water samples. These results were verified by applying ozone to the source water, and to filtrate obtained by filtering through a 0.45 μm membrane filter in a lab-scale test, respectively.