Research Note: Measurement of Ozone via an Indirect Gas Chromatography Method

Gas chromatography was used to measure the ozone concentration in oxygen produced by an ozone generator. In this indirect method, the ozone reacts with the coating of the capillary column and produces carbon dioxide, which is then detected. The primary methods of calibration for this technique were based on a wet-chemistry process and absorption of ultraviolet light. This finding also is important if the primary reason for using gas chromatography is detection of carbon dioxide, as artificially high readings of carbon dioxide would be measured in the presence of ozone. The method was tested for ozone concentrations of 3–70?mg/L but the method should also be applicable to higher concentrations.     

Destruction of Ozone Off–Gas by Thermal Catalytic Method

In the operation ofozone treatment plants, one will have to deal with ozone inthe off–gas exhaust air. In higher concentrations in the exhuast air, ozone has the unpleasant property of being detrimental to plant, animal and man.

The normal ozone concentration inambient air should not be more than 1/10of the MAK–value. Insmall treatment plants inEurope the small amount of ozone off–gas can be diluted with atmospheric airso that itis permitted to be discharged into the outside air. For larper plants there isthe choice between a thermal and catalytic ozone destruction, or a process that combines both. In the Lengg Waterworks the exhaust air of the reaction chamber was passed through a thermal destruction systen. From the granular activated carbon (GAC) filters theair was passed into the atmosphere untreated. It was ascertained that during GAC back–washing 1200 PPtl ozone were in the exhaust air. This ozone concentration was much too high.     

Effective Ozone Generation in Oxygen Using a Mesh Electrode in an Ozonizer with Variable Linear Velocity

Results of studies on ozone synthesis under discharges proceeding in a metal mesh-ceramic dielectric system have been presented. The experiments were carried out in the reactor with unique reaction space geometry, in which the reacting gas flew with consequently increasing linear velocity. The high voltage electrode was made of a metal mesh, which caused intensification of the gas mixing in the reaction space. Using a simple reactor with one-side cooling of the reaction space, high ozone maximum concentrations (100 g/Nm³) and energy efficiencies (180–200 g/kWh) were obtained at 25 °C.     

Development and Evaluation of Gas Diffusion Layer Using Paraffin Wax Carbon for Proton Exchange Membrane Fuel Cells

A gas diffusion layer (GDL) with carbon prepared from paraffin wax was developed for the first time to impart hydrophobicity and porosity for fuel cell application. It is also intended to reduce the non‐functional binder content in the microporous layer and to achieve optimum performance. The topography of the GDL was examined using 3D digital microscope. Membrane electrodes assemblies (MEAs) fabricated with GDLs of paraffin wax carbon (PWC) based microporous layer were evaluated in proton exchange membrane fuel cell between 50 and 100% RH conditions using H₂ and O₂ at ambient pressure. The fuel cell performance of the GDLs fabricated with Pureblack carbon was also evaluated under identical operating conditions for comparison. It was observed that the MEA with GDLs containing PWC showed excellent fuel cell performance at all RH conditions at 80 °C both with H₂/O₂.     

Evaluating Magnetic Ion Exchange Resin (MIEX)® Pretreatment to Increase Ozone Disinfection and Reduce Bromate Formation

Magnetic ion exchange resin, known by its commercial name (MIEX®) provides one pretreatment alternative that could maximize ozonation disinfection while decreasing bromate formation in bromide-containing waters. During a 5-week pilot study, the MIEX® process removed up to 30 % of the dissolved organic carbon (DOC) and reduced ultraviolet absorbance at 254 nm (UV 254) by up to 60%. When MIEX® pretreated water was ozonated, ozone decay rates were reduced, increasing the CT achieved by 40% to 65%. The increased disinfection capability reduced the transferred ozone dosages required for Cryptosporidium inactivation by 15% to 25% and bromate formation by 35%.     

Development of a Practical Method for Using Ozone Gas as a Virus Decontaminating Agent

Our objective was to develop a practical method of utilizing the known anti-viral properties of ozone in a mobile apparatus that could be used to decontaminate rooms in health care facilities, hotels and other buildings. Maximum anti-viral efficacy required a short period of high humidity (>90% relative humidity) after the attainment of peak ozone gas concentration (20–25 ppm). All 12 viruses tested, on different hard and porous surfaces, and in the presence of biological fluids, could be inactivated by at least 3 log_10, in the laboratory and in simulated field trials. The ozone was subsequently removed by a built-in catalytic converter.     

Intensification of Rate of Diffusion Controlled Reactions in a Parallel Plate Electrochemical Reactor Stirred by a Curtain of Electrochemically Generated Gas Bubbles

Rates of mass transfer were measured at a vertical plate stirred by a rising curtain of oxygen bubbles generated electrochemically at an upstream plate by measuring the limiting current of the cathodic reduction of K₃Fe(CN)₆ in alkaline solution. The rate of mass transfer was found to increase over the natural convection value by a factor ranging from 2.4 to 25 compared to the previously reported range of 2–5 in the case of copper deposition from acidified solutions. The high tendency of oxygen bubbles to coalesce in alkaline solutions is believed to be responsible for the high rates of mass transfer in alkaline solutions. The rate of mass transfer at a plate stirred by a curtain of oxygen bubbles was found to decrease with increasing plate height and electrolyte concentration. Curtains of H₂ bubbles were found to be less effective in enhancing the rate of mass transfer compared to that of oxygen. Practical application of the results in designing a modified parallel plate electrochemical reactor stirred by a counterelectrode gas curtain was highlighted. The suggested design has the potential of saving part or all of the mechanical stirring energy as well as floor space since it extends vertically.     

Raman Spectroscopic Mapping of the Carbon and PTFE Distribution in Gas Diffusion Layers

Raman microspectroscopy was used to gather spatially resolved chemical information on the carbon and poly(tetrafluoroethylene) (PTFE) distribution of fuel cell gas diffusion layers (GDL). GDLs with varying PTFE content were imaged over areas of 1,000 μm × 1,000 μm and it was found that the distribution of concentrated PTFE regions on the surface of the GDLs and morphology of the carbon fibre paper was readily observed. Spectroscopic measurements with point‐by‐point resolutions varying between 10 and 500 μm were performed on samples having 1.8–44 wt.% PTFE before and after the PTFE was sintered. The average PTFE signal detected on the surface of the GDLs increased monotonically for both unsintered and sintered GDLs with increasing bulk PTFE loading. The unsintered GDLs had higher PTFE signals on their surface compared to sintered GDLs and showed more concentrated PTFE regions in the mapping experiments.     

Application of Response Surface Methodology for Coffee Effluent Treatment by Ozone and Combined Ozone/UV

This paper reports a study using ozone (O₃) and combined ozone/ultraviolet (O₃/UV) processes for color removal and caffeine degradation from synthetic coffee wastewater using a second-order response surface methodology (RSM) with a three-level central composite face-centered (CCF) design. The effects of O₃ concentration, initial pH, and reaction time were examined for both processes. The reaction time and pH were statistically significant for caffeine degradation and color removal. In the ozonation process, higher caffeine degradation and color removal were observed in alkaline pH, indicating that ozone attacks indirectly, consequently generating hydroxyl radicals. Regarding the ozone/UV process, it was observed that lower caffeine degradation and color removal occurred at neutral pH, indicating an adverse effect due to lower ozone dissolution and consequently the production of a smaller amount of free hydroxyl radicals. The achieved results showed that the techniques were efficient for color removal (85% and 99%, respectively) and caffeine degradation (88% and 98%, respectively).     

Selection and Design Considerations of Diffusers,Piping Systems,and Basin Configurations Producing Optimum Performance for the Ozone Treatment of Drinking Water

The performance of ozone diffusion systems is determined by the conversion of the engineered treatment theory to the hardware needed to accomplish the task. The correct design, selection, and fabrication of the ceramic gas piping systems which interface with the overall treatment scheme configuration achieves this end. Design details such as selection of proper stainless steel, ceramic, gasket materials, diffuser type, diffuser anchoring systems, and fabrication techniques assure the optimum performance of the treatment system.     

A Study of the Physical and Chemical Processes Active in Ozone Generation by Carbon Dioxide Fed Corona Discharges

Ozone generation in both positive and negative corona discharges DC corona, both operated in glow regime, feed by dry CO₂ has been studied. Higher ozone concentrations were observed in negative corona discharges. Ozone formation was found to be strongly dependent upon both the flow rate of the gas and on the radius of the outer electrode. The physical characteristics of the discharge were monitored through measurement of the discharge current. Small increases in the gas flow rate were observed to cause a significant increase in the discharge current of a negative corona discharge but little/no effect was observed in positive corona.     

Preparation,ex situ and in situ Characterization of Gas Diffusion Media Containing and Non‐Containing Carboxymethylcellulose for PEM Fuel Cells

In this paper the effect of the addition of carboxymethylcellulose (CMC) to microporous layers (MPLs) formulation is reported and the rheological, morphological and electrical properties of the so‐obtained MPLs are assessed. Two different PTFE/carbon black ratios are considered, with and without CMC in the ink formulation. CMC addition results in a better homogeneity and stability of the inks. Moreover, the presence of CMC leads to a better shear thinning behaviour and to a general increase in viscosity that makes these slurries more appropriate for coating deposition via doctor blade technique. The presence of CMC in MPL formulation also affects the electrochemical performances in terms of I–V curves and impedance spectra. CMC‐containing MPLs show the best performances in terms of generated power at high temperature (80 °C) and low cathodic relative humidity (RH 60 %). Ohmic resistances too, in presence of CMC, are lower than those exhibited by CMC‐free MPLs.     

Investigation of Ozone Loss Rate Influenced by the Surface Material of a Discharge Chamber

Decay characteristics of ozone concentration in oxygen in a chamber with three types of wall material (stainless steel, copper, and aluminum) are measured using the 254 nm photoabsorption method. Effective lifetimes of ozone are estimated from decay curves of ozone concentration. These values depend on the wall material: They are largest for stainless steel and smallest for aluminum. The relationship between effective lifetime and gas pressure is investigated precisely to determine three values. The equivalent diffusion coefficient of ozone in oxygen and the reflection coefficient of ozone at the wall correspond to the loss rate of ozone at the wall. The collisional loss (quenching) rate coefficient of ozone in oxygen is also determined.     

Pyruvic Acid Removal from Water by the Simultaneous Action of Ozone and Activated Carbon

Activated carbon (AC) has been used to catalyze the ozonation of pyruvic acid in water. Pyruvic acid conversions were found to be 9 and 37% after 90 min of single ozonation and single adsorption with 40 gL^?1 AC, respectively, while 82% was reached at the same conditions during the AC catalytic ozonation. Also, for similar conditions, mineralization reached values of 67% in the AC catalytic ozonation against hardly 5% in the non-catalytic experiment. The process likely develops through both adsorption of ozone and pyruvic acid on the AC surface and generation of hydroxyl radicals that eventually is the responsible oxidizing species. Rate constants for both non-catalytic ozonation and AC-Ozone catalytic surface reaction, at 20°C and pH 7.5, were found to be 0.025 min^?1 and 87.9 Lg^?1s^?1, respectively. For AC concentrations higher than 2.5 gL^?1 gas-liquid mass transfer of ozone constituted the limiting step. At lower concentrations, internal diffusion plus surface reaction controlled the process rate.     

Decomposition of 2-Chlorophenol in Aqueous Solutions by Ozone and UV/Ozone Processes in the Presence of t-Butanol

The decomposition of 2-chlorophenol in aqueous solutions by ozone and UV/ozone process was studied with the presence of t-butanol. The addition of t-butanol decreased the surface tension of aqueous solutions and subsequently increased the gas-liquid contact area. The presence of t-butanol did not affect the steady-state dissolved ozone concentration in aqueous solution; however, the ozone transfer rate between gas-liquid interface was noticeably enhanced and the time required to reach the steady state was reduced. The presence of t-butanol was found to promote the decomposition of 2-chlorophenol for both ozone and UV/ozone processes. Nonetheless, the presence of excessive dosages of t-butanol might decrease the reaction rates for experiments conducted in alkaline solutions probably because t-butanol also served as the scavenger for hydroxyl free radicals.     

CO Tolerance of Commercial Pt and PtRu Gas Diffusion Electrodes in Polymer Electrolyte Fuel Cells

The CO tolerance of commercial Pt and PtRu anode electrodes from different suppliers (E‐Tek and Tanaka) has been examined in polymer electrolyte fuel cells (PEFC) using AC‐impedance spectroscopy along steady‐state current‐voltage curves. A simple mathematical model has been derived in order to extract important kinetic parameters for CO poisoning on different anode electrodes. The Tanaka PtRu (40:60) electrode demonstrated the best CO tolerance under the selected operating conditions. Inductive behavior in the low frequency region of the impedance spectra for the E‐Tek Pt and PtRu electrode proved to be characteristic for CO poisoning. However, the impedance spectra of the Tanaka PtRu electrode did not show any inductive behavior and its CO surface coverage, extracted by fitting the experimental data to the model, was lower than the surface CO coverage of the E‐Tek electrodes.     

Oxidation by UV and Ozone of Organic Contaminants Dissolved in Deionized and Raw Mains Water

Organic contaminants dissolved in deionized pretreated and raw mains water were reacted with ultraviolet light and ozone. Ozone first was used for partial oxidation followed by ozone combined with ultraviolet radiation to produce total oxidation. The reduction of TOC level and direct oxidation of halogenated compounds were measured throughout the treatment process. The rate of TOC reduction was compared for ozone injected upstream and inside the reactor.     

Polyamide/Polystyrene Blend Compatibilisation by Montmorillonite Nanoclay and its Effect on Macroporosity of Gas Diffusion Layers for Proton Exchange Membrane Fuel Cells

This work deals with a new route to modify polymer blend morphology in order to improve the porosity of gas diffusion layers (GDLs) for proton exchange membrane fuel cells (PEMFCs). First, electrically conductive polymer‐based blends were carefully formulated using a twin‐screw extrusion process. Blend electrical conductivity was ensured by the addition of high specific surface area carbon black and synthetic graphite flakes. Final GDL porosity, in particular its macroporosity, was generated by melt blending polyamide 11 (PA11) matrix with polystyrene (PS) followed by PS extraction with tetrahydrofuran (THF) solvent at room temperature. In order to improve GDL porosity by the optimisation of PS dispersion in the PA11 matrix, PA11/PS blends were compatibilised by the addition of 2 wt.‐% of clay. It was observed that both macroporosity and pore size distribution were beneficially modified after blend compatibilisation. Final GDL conductivity of about 1.25 S cm^–1, a porosity of 53% and a specific pore surface area of 75 m² g^–1 were achieved.     

Removal Characteristics of Organic Pollutants in Sewage Treatment by a Pre-Coagulation,Ozonation and Ozone/Hydrogen Peroxide Process

The applicability of a sequential process of ozonation and ozone/hydrogen peroxide process for the removal of soluble organic compounds from a pre-coagulated municipal sewage was examined. 6–25% of initial T-COD_Cr was removed at the early stage of ozonation before the ratio of consumed ozone to removed T-COD_Cr dramatically increased. Until dissolved ozone was detected, 0.3 mgO₃/mgTOC₀ (Initial TOC) of ozone was consumed. When an ozone/hydrogen peroxide process was applied, additional COD_Cr was removed. And we elucidated that two following findings are important for the better performance of ozone/hydrogen peroxide process; those are to remove readily reactive organic compounds with ozone before the application of ozone/hydrogen peroxide process and to avoid the excess addition of hydrogen peroxide. Based on these two findings, we proposed a sequential process of ozonation and multi-stage ozone/hydrogen peroxide process and the appropriate addition of hydrogen peroxide. T-COD_Cr, TOC and ATU-BOD₅ were reduced to less than 7 mg/L, 6 mgC/L and 5 mg/L, respectively after total treatment time of 79 min. Furthermore, we discussed the transformation of organic compounds and the removal of organic compounds. The removal amount of COD_Cr and UV₂₅₄ had good linear relationship until the removal amounts of COD_Cr and UV₂₅₄ were 30 mg/L and 0.11 cm^?1, respectively. Therefore UV₂₅₄ would be useful for an indicator for COD_Cr removal at the beginning of the treatment. The accumulation of carboxylic acids (formic acid, acetic acid and oxalic acid) was observed. The ratio of carbon concentration of carboxylic acids to TOC remaining was getting higher and reached around 0.5 finally. Removal of TOC was observed with the accumulation of carboxylic acids. When unknown organic compounds (organic compounds except for carboxylic acids) were oxidized, 70% was apparently removed as carbon dioxide and 30% was accumulated as carboxylic acids. A portion of biodegradable organic compounds to whole organic compounds was enhanced as shown by the increase ratio of BOD/COD_Cr.     

Electrochemical behavior of glassy carbon electrodes modified by multi-walled carbon nanotube/surfactant films in a buffer solution and an ionic liquid

The electrochemical behavior of glassy carbon (GC) electrodes coated with multi-walled carbon nanotube (MWCNT)/surfactant films was studied in an ionic liquid and a phosphate buffer solution (pH = 6.86), using cyclic voltammetry. The dispersion of MWCNTs in different media was investigated by scanning and transmission electron microscopy. Cast films of MWCNT/zwitterionic dodecyldimethylamine oxide on a GC electrode show a typical redox couple in phosphate buffer solution, which is better than that of MWCNT/anionic sodium dodecyl sulfate and cationic alkyltrimethylammonium bromide. However in the ionic liquid, 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF₆]), the GC electrode modified by MWCNT/cationic surfactant films shows a well-defined irreversible reduction of MWCNTs. The cyclic voltammograms clearly show that the surfactant hydrophilic group plays an important role in the electrochemical behavior of the MWCNTs. The electrolytes also have an important effect. In an ionic liquid, the strong binding of the ionic liquid cations with the MWCNTs may change the structure of the modified films and lead to changes of electrochemical behavior.