Catalytic steam reforming of chlorocarbons: trichloroethane, trichloroethylene and perchloroethylene

The effective destruction of trichloroethane, trichloroethylene and perchloroethylene by steam reforming with a commercial nickel catalyst has been demonstrated. Conversion levels of up to 0.99999 were attained in both laboratory and semi-pilot experiments, with the products consisting of HCl, H₂ and carbon oxides. Care had to be exercised in maintaining these high conversion levels to prevent parallel pyrolysis reactions that resulted in carbonaceous deposits and catalyst deactivation. The importance of these pyrolysis reactions appears to follow established incinerability patterns and is more pronounced for alkanes than alkenes.

By using relatively large amounts of catalyst in the large semi-pilot reactor, it was possible to maintain high conversions for up to 50 h without appreciable carbon deposition in the bed. However, the activity of the catalyst for the water gas shift reaction declined progressively with process time. This deactivation effect was reversed by treatment with steam over prolonged periods, leading to the speculation that shift activity is poisoned by exposure to HCl in the product.

This process offers an attractive alternative to conventional technologies (thermal incineration and catalytic combustion) for the destruction of chlorocarbons used as industrial solvents or found in waste streams, and applicable process conditions are given.     

Enhancement of Nitrate Reduction in Fe0-Packed Columns by Selected Cations

Tests were conducted in Fe0-packed columns to investigate the effects of adding selected cations on nitrate removal by Fe0. Due to a rapid passivation of Fe0, only negligible nitrate was reduced in the columns without adding the selected cation. However, adding certain selected cations (Fe2+, Fe3+, or Al3+) in feed solution can significantly enhance nitrate reduction. Extending hydraulic retention time (HRT) increased nitrate removal by the columns, but the increase was not linearly proportional to HRT. Decreases in columns’ hydraulic conductivity (K) were monitored in an 8?month operating period. A modest decrease in K was recorded in the upper and the middle section of the media bed, whereas a significant decrease in K occurred in the inlet section. X-ray diffraction analyses indicate that magnetite (Fe3O4) was the dominant species of the iron corrosion products in the entire height of the column media under anoxic and other test conditions. In the inlet section, however, lepidocrocite and goethite were also identified. Cementation was found to occur only in the inlet section, suggesting that lepidocrocite and goethite, rather than magnetite, might be responsible for the cementation and thereby cause the hydraulic clogging. The magnetite coating would not necessarily cause clogging of the media.     

Modeling the Removal of Arsenic by Iron Oxide Coated Sand

An arsenic filtration experiment using iron oxide coated sand was modeled using the USGS geochemical program PHREEQC. Despite some uncertainty regarding the initial conditions of the groundwater and the simplicity of the model, it replicated the experimental results within 10%. The original experiment filtered 165 bed volumes to concentrations less than 0.01 mg/L As and approximately 210 bed volumes to 0.05 mg/L As. The model filtered 168 bed volumes to 0.01 mg/L As and 228 bed volumes to 0.05 mg/L.     

Modeling Elution Histories of Copper and Lead from Contaminated Soil Treated by Poly(amidoamine) Dendrimers

A dynamic “two-site” model was formulated and tested for simulating the elution histories of copper (Cu2+) and lead (Pb2+) from a contaminated soil treated by poly(amidoamine) dendrimers. In the model, the metal sorption sites of the soil were divided into two compartments: one with a fast desorption rate and the other with a slow desorption rate. The model was tested for simulating and predicting Cu2+ and Pb2+ elution histories obtained from column experiments. Compared to the classical “one-site” model and the modified “gamma distribution” model, the “two-site” model not only provides much improved power for simulating the observed metal elution data, but also can more accurately predict the metal elution histories under various experimental conditions including initial metal concentration in soil, dendrimer concentration, and pH.     

Oxidation of Toluene in Waste Gas Streams Using Mesoporous Ti-Hexagonal Mesoporous Silica

Various mesoporous catalysts with titanium loadings between 0.5 and 4 Ti wt.?% and surface areas between 600 and 1,600 m2/g were synthesized using the molecular designed dispersion technique. These catalysts were tested using toluene oxidation in a fixed bed reactor at temperatures between 300 and 550°C. The reaction products were found to be CO2 and CO with selectivity towards CO2 above 80% for all catalysts. The catalytic activity of the catalysts increases with titanium loading. The total conversion at 550°C was not affected by the textural porosity, but increased textural porosity did significantly reduce the ignition temperature by up to 50°C. The Thiele modulus was calculated to be much less than one for all these materials indicating that the reaction rate is not diffusion limited.     

Simplified Model for the Class-I Settling Tanks Design

The purpose of this paper is to simplify the original one-dimensional mathematical model that is used to simulate the performance of nonuniform particle sizes in Class-I settling tanks. This paper shows that the modified model is both efficient and economical. The model is capable of providing such information as removal efficiency, particle size distributions in sludge and effluent suspension, and the thickness of bottom sludge. If the desired removal efficiency is provided, a simple equation from the simplified model can be used to calculate the length of the tank. Moreover, the model is quite straightforward and does not require a computer program to obtain results. It deals with only one parameter, the sediment coefficient α, which shows great advantages. Here α is taken as 1.2 for the Class-I settling tanks, however calibration is still recommended. Effluent information, which is important for further treatment units, can be calculated directly from the simplified model. The simplified model is qualitatively reasonable in comparison with other models.     

Simultaneous Removal of Naphthalene and Sulfur Dioxide using Surfactant

Anionic surfactant was added during absorption to investigate the solubility of vapor phase naphthalene and SO2 in water. Anionic surfactant employed was sodium dodecyl sulfate. Lower than critical micelle concentration (CMC), the apparent solubility and absorption rates of SO2 or naphthalene with or without SO2 were practically identical to those of pure water. However, higher than CMC, equilibrium SO2 or naphthalene apparent solubility increased linearly in proportion to the surfactant concentrations. The solubilization effect of micelles resulted in the increase. Because the micelle solubilization effect was greater than that of the decrease of the mass transfer coefficient, the gas absorption rate increased. When surfactant concentration was 0.1 M, the enrichment factor (EF) value of naphthalene with SO2 was 4.54, which was only half of its value without SO2. When surfactant concentration was 0.2 M, the SO2 EF values increased to 2.24. These empirical findings confirm that to increase the removal efficiency of simultaneous absorption of hydrophobic organic compounds and SO2 via a spray or packed tower, an anionic surfactant can be employed.     

Evaluation of Electrokinetic Removal of Heavy Metals from Tailing Soils

Electrokinetic remediation was studied for the removal of toxic heavy metals from tailing soils. The study emphasized the dependency of removal efficiencies upon their speciations, as demonstrated by the different extraction methods used, which included sequential extraction, total digestion, and 0.1 N HCl extraction. The tailing soils examined showed different physicochemical characteristics, such as initial pH, particle size distribution, and major mineral constituents, and they contained high concentrations of target metal contaminants in various forms. The electrokinetic removal efficiencies of heavy metals were significantly influenced by their partitioning prior to treatment, and the pHs of the tailing soils. The mobile and weakly bound fractions of heavy metals, such as the exchangeable fraction, were easily removed by electrokinetic treatment (more than 90% removal efficiency), but immobile and strongly bound fractions, such as the organically bound species and residual fractions, were not significantly removed (less than 20% removal efficiencies).     

Visibility Improvements with Overplow Deflectors during High-Speed Snowplowing

Windtunnel and field experiments are presented to quantify visibility improvements with deflectors that were placed over the top of snowplow blades and were designed to reduce airborne debris. Windtunnel measurements provide the influence of overplow deflectors on the distribution of debris around the truck. Road tests on airport taxiways and highways show that the visible area of the plow truck increases by about 50% for following traffic and that snow debris, which blows over the top of the plow, is eliminated with trap angles less than 50°.     

Electrochemical Pretreatment of Wastewater from Color Photograph Processing Unit

Wastewater emanating from color photograph processing units is usually in small quantities (5–20 L per day) and contains high concentrations of recalcitrant organic compounds. Disposal of such highly recalcitrant wastewater into a public sewer may result in an inhibiting effect on biological treatment system of a sewage treatment plant and thus these persistent organics can escape to receiving water bodies. A continuous full-scale treatment unit for such a small quantity of wastewater is not a viable option, economically and technically. In this study, a small batch type of an electrochemical reactor has been utilized to investigate the feasibility of electrochemical treatment of wastewater from a color photograph processing unit. The treatability studies were conducted using cast iron electrode. It was found that the cast iron electrode was efficient in removing both chemical oxygen demand and biochemical oxygen demand to the levels that meet the standards for discharge to surface water and public sewer. The energy consumption to meet the standards for sewer disposal was less compared to that of surface water disposal. The electrochemical reactor was found to be cost effective in both installation and operation for meeting the sewer disposal standards. It was concluded that the wastewater could be partially treated (pretreatment) electrochemically to meet the standard for sewer disposal rather than that of surface water disposal.