V. Janda

Generation of ozone by pulsed corona discharge over water surface in hybrid gas–liquid electrical discharge reactor

Ozone formation by a pulse positive corona discharge generated in the gas phase between a planar high voltage electrode made from reticulated vitreous carbon and a water surface with an immersed ground stainless steel plate electrode was investigated under various operating conditions. The effects of gas flow rate (0.5–3 litre min−1), discharge gap spacing (2.5–10 mm), applied input power (2–45 W) and gas composition (oxygen containing argon or nitrogen) on ozone production were determined. Ozone concentration increased with increasing power input and with increasing discharge gap. The production of ozone was significantly affected by the presence of water vapour formed through vaporization of water at the gas–liquid interface by the action of the gas phase discharge. The highest energy efficiency for ozone production was obtained using high voltage pulses of approximately 150 ns duration in Ar/O2 mixtures with the maximum efficiency (energy yield) of 23 g kW h−1 for 40% argon content.

Supercritical fluid extraction in environmental analysis

Abstract Supercritical fluid extraction (SFE), usually with carbon dioxide and often with a modifier, is a rapid, selective and convenient method for sample clean-up in environmental analysis. Three inter-related factors influence analyte recovery in SFE: solubility in the fluid, diffusion through the matrix and adsorption in the matrix. SFE may be coupled on-line to various analytical methods: gas, liquid and supercritical fluid chromatography. A wide range applications of SFE from environmental samples is described: hydrocarbons, chlorobenzenes and chlorobiphenyls, dioxins and chlorinated pesticides, herbicides and ionic surfactants. Organic compounds may be concentrated from air and water and extracted from adsorbents by SFE. Direct SFE from water is also possible.

Recovery of phenols from water by continuous steam distillation-extraction

Continuous steam distillation—continuous liquid—liquid extraction was used for the isolation of phenols from water and the extract was analysed by capillary gas chromatography. The recovery for a concentration range about 0.1–30 mg 1−1 approaches 100% using acidification and strong salting of the water sample and a distillation—extraction time of 1.5 h. The detection limit of the method using splitless injection and glass capillary columns is approximately 10 μg 1−1 of each phenol tested.

Direct supercritical fluid extraction of water-based matrices

Abstract A short review on direct supercritical fluid extraction (SFE) of organic compounds from aqueous samples is presented. The SFE methodology of water samples is conceptually different from that of solid matrices, and a relatively small number of papers on this subject has been published. As the most promising appears continual SFE of water samples with pure CO2.

The catalytic role of tungsten electrode material in the plasmachemical activity of a pulsed corona discharge in water

The effects of tungsten material used as a high-voltage needle electrode on the production of hydrogen peroxide and the degradation of dimethylsulfoxide (DMSO) caused by a pulsed corona discharge in water were investigated. A reactor of needle?plate electrode geometry was used. The erosion of the tungsten electrodes by the discharge was evaluated. The yields of H2O2 production and the decomposition of DMSO by the discharge, which were obtained using the tungsten electrodes, were compared with those determined for titanium electrodes. The electrode erosion increased significantly with an increase in the solution conductivity. A large fraction (50?70%) of the eroded tungsten electrode material was released into the solution in dissolved form as tungstate ions. A correlation between the amount of eroded tungsten material released into the solution and the chemical effects induced by the discharge was determined. Lower yields of H2O2 and a higher degradation of DMSO by the discharge were obtained using the tungsten electrodes than were determined using titanium electrodes. Tungstate ions were shown to play a dominant role in the decomposition of H2O2, which was produced by the discharge using a tungsten electrode. The higher degradation of DMSO that was determined for tungsten was attributed to the tungstate-catalyzed oxidation of DMSO by H2O2, in addition to the oxidation of DMSO by OH radicals. Such a mechanism was supported by the detection of degradation by-products of DMSO (methanesulfonate, sulfate and dimethyl sulfone). The catalytic role of tungstate ions in the plasmachemical activity of the discharge generated using a tungsten electrode was also demonstrated on a pH-dependent decomposition of H2O2 and DMSO.

Design of packed aeration towers to strip volatile organic contaminants from water

The reliability of a design procedure for packed strippers of volatile organic contaminants (VOC) removal from water is tested. The required mass transfer coefficients for VOC are recalculated from oxygen mass transfer coefficients which are available in literature for various types of packings. The data for polypropylene Pall rings and Super Torus saddles are summarized in this paper for hydrophilized and nonhydrophilized versions of the packings. The reliability is tested by comparison of removal efficiency calculated by the procedure with that observed experimentally for stripping tetrachloroethylene, trichloroethylene, trichloromethane, chlorobenzene, bromobenzene and benzene from water in pilot plant column packed with hydrophilized or nonhydrophilized PP Pall rings 25 mm. Differences between experimental and calculated values did not exceed 10%. Differences between experimental and calculated values reported in previous literature are discussed and possible reason for this discrepancy is given. Due to better wettability of hydrophilized packing, the mass transfer coefficients for this type of packing were higher by 65% compared with the nonhydrophilized ones.

Determination of inorganic oxyhalides in drinking water by on-line coupled capillary isotachophoresis— capillary zone electrophoresis

Some oxyhalides can be found in drinking waters as inorganic disinfection byproducts. An on-line coupled capillary isotachophoresis—capillary zone electrophoresis (CITP-CZE) method was developed for the analysis of chlorate, chlorite and bromate in water. The optimized CITP-CZE electrolyte system consisted of the following: 10 mM—HCl+20 mM—β-Alanine (leading electrolyte), 5 mM—succinic acid (terminating electrolyte), and 10 mM—succinic acid +5 mM—β-Alanine +0.1% HPMC (carrier electrolyte). A clear separation of oxyhalides from other components of drinking water was achieved within 25 min. Method characteristics, i.e., linearity (0–200 ng/mL), accuracy (88–110%), intra-assay (3–5%), quantification limit (5–15 ng/mL), and detection limit (2–5 ng/mL), were determined. Minimum labor requirements, sufficient sensitivity and low running cost are important attributes of this method. It was found that the developed method is useful for the routine analysis of oxyhalides in water.

Effect of amino acids on the composition and properties of extruded mixtures of wheat flour and glucose.

Wheat flour was extruded at 100-120 degrees C with 5% D-glucose or mixtures of 5% D-glucose and 0.5% or 2.0% of L-alanine, L-leucine, L-lysine, L-threonine or L-cysteine. The extent of browning was only moderate, and yellow and red pigments were produced. The odour intensity increased with the addition of either glucose or a mixture of glucose and amino acids; the odour was not significantly intensive according to sensory acceptancy analysis. The odour profile was influenced by the structure of amino acid present in the extruded material. The addition of D-glucose increased the production of furan derivatives, and in lesser degree, of pyrazines in the extruded product. The pyrazine content increased with the addition of amino acids, except cysteine which enhanced the production of sulphur compounds instead of pyrazines. The composition of the pyrazine fraction varied depending on the amino acid added. Pretreatment of D-glucose with an amino acid in aqueous solution affected the composition of volatiles, but it did not significantly enhance the pyrazine production.

Supercritical fluid extraction and chromatography of aromatic amines

Supercritical fluid extraction (SFE) was used for the isolation of antioxidant aromatic amines from tyre rubber. The efficiency of SFE was comparable with that of Soxhlet microextraction. Aromatic amines were also extracted from different matrices (inert silanized material, sand and humic soil) with supercritical carbon dioxide. It was found that the extraction efficiency depends on the nature of the matrix. Whereas the recovery of amines from the inert material approached 100%, that from acidic matrices was poor and some amines were not recovered.

Removal of chlorinated solvents from carbonate-buffered water by zero-valent iron

The performance of a ground level reactive cell, filled with Fe0, designed for the treatment of water contaminated by chlorinated solvents, having a total input concentration of approximately 2 mg 1−1 of the principal contaminants trichloroethene and perchloroethene, was tested at the Milovice site in the Czech Republic. A residence time of 1.62 days in the box was sufficient to reduce concentrations to a fraction less than 0.015 of the initial concentration. However, incomplete degradation of cis-1,2-DCE was observed. Reactions approximated first-order kinetics. The principal changes of concentrations of inorganic dissolved species in the reactive cell occurred for Ca2+, HCO3−, NO3− (decreased) and for Fe (initially increased, then decreased). Changes for Ca2+ and HCO3− were caused by the precipitation of secondary carbonate mineral phases such as aragonite and siderite with the minor presence of green rust-CO3. Concentration changes were gradual, along the complete length of the cell with a maximum at the inlet zone. The observations were attributed to minor increases of pH and slow kinetics of precipitation in the carbonate-buffered system. The average porosity loss was estimated to be approximately 2.7 % of the initial porosity per year, suggesting the long-term function of the permeable reactive barrier.