Thermal Decontamination Research Articles

Investigation of Heat Exchange Processes during Thermal Decontamination of Industrial Sewage Water in Foam Generating Reactors

Investigation of Heat Exchange Processes during Thermal Decontamination of Industrial Sewage Water in Foam Generating Reactors

A laboratory pilot study of thermal decontamination of soils polluted by PCBs. Comparison with thermogravimetric analysis

Real soils contaminated with a mixture of polychlorinated biphenyls were thermally decontaminated in a laboratory scale thermal desorption apparatus, under different operating conditions including two operating pressures ( P=0.01 and 0.1 MPa), different sample masses (80–320 g), carrier gas flow rates (0–30–280 Nl h −1) and two initial contamination levels. A standard European soil artificially contaminated with 4-chlorobiphenyl was decontaminated using a thermogravimetric analyser (TGA). The same parametric study as cited earlier was performed. With both techniques, the extent of decontamination was studied as a function of temperature during the heating programs (2–3 °C min −1 for the thermal desorption apparatus; 5 °C min −1 for TGA). Only a few differences were noticed between the two techniques. The decontamination starts when the melting temperature of the contaminant is reached (30 °C) and is complete before 350 °C. Thermogravimetric analysis which does not necessitate any chemical analysis appears to be a very attractive technique to investigate the feasibility of a decontamination and to quickly determine the best operating conditions.

A pilot study of three methods for the reduction of bacterial contamination of dental unit water systems in routine use

AbstractThree different methods for minimizing the bacterial contamination of the water system in a SIRONA C2 type dental unit were investigated sequentially. Without any decontamination method, water from the hand piece, air-water-jet and mouthwash were continuously contaminated by 103 to 105 colony forming units (cfu) of aerobic mesophilic bacteria per milliliter.A reduction to below 100cfu/ml was achieved by continuous adding of a chemical microbicide based on hydrogen peroxide and silver ions. However, this was only possible after rinsing the system thoroughly for at least two minutes after interruptions of the treatment. Long-lasting low counts of below 100/ml were obtained by means of an in-line bacteria filter, in connection with the provision of a thermo-chemical or thermal decontamination of the water pipes and hand pieces after the filter.The electrolyte release of chlorine from the dental unit tap water by anodic oxidation without addition of any chemical disinfectant also resulted in continuously low colony numbers of the water. In this case, regular decontamination of the end parts of the pipes and hand pieces was not necessary.

COMPARING ATTACHMENT, HEAT TOLERANCE AND ALKALI RESISTANCE OF PATHOGENIC AND NONPATHOGENIC BACTERIAL CULTURES ON ORANGE SURFACES

Trials were conducted to compare surrogate organisms (PSO) to human pathogens (Salmonella spp. and Escherichia coli O157:H7) on the surface of orange fruit. Among the six evaluated PSO, E. coli ATCC 8739 and E. coli ATCC 35218 showed a significantly lower attachment (SR) on fruit in comparison to Salmonella spp. In thermal tolerance studies, the D70C values of the evaluated PSO were either no different from or greater than those of the pathogens. However, the D80C ofE. coli ATCC 25922 was significantly lower than that of the E. coli O157:H7. In general, E. coli ATCC 11229 exhibited a higher level of alkali sensitivity than both pathogens; whereas Lactobacillus plantarum ATCC 14917 and, to a lesser extent, Lactobacillus fermentum ATCC 538 showed a significantly greater tolerance to the alkali treatments. The results suggest that nonpathogenic cultures ofE. coli ATCC 11229, L. fermentum ATCC 538, and L. plantarum ATCC 14917 may be utilized in fresh fruit research as surrogates for pathogens to evaluate the efficacy of thermal decontamination. In addition, E. coli ATCC 25922, L. fermentum ATCC 538, and L. plantarum ATCC 14917 cultures may be used to represent pertinent pathogens for validating fruit decontamination by alkaline cleaners.

Thermodynamic driving forces for PAH isomerization and growth during thermal treatment of polluted soils

For a limiting case of thermodynamic equilibrium, the importance of two classes of thermal chemical reactions that modify the structure and bioactivity of polycyclic aromatic hydrocarbons (PAH) was assessed computationally. These reactions are molecular weight (MW) growth by acetylene addition, and intramolecular rearrangement (isomerization). Temperatures (300–1100°C), and the chemical environment (C 2H 2/H 2 molar ratios) were selected for relevancy to thermal treatment of PAH-contaminated soils under oxygen-free conditions. Molecular mechanics methods [MM3(92)] were used to compute thermochemical properties for calculation of equilibrium constants, i.e., heats of formation, standard entropies, and heat capacities for 30 PAH with empirical formulae C 14H 10, C 16H 10, C 18H 10, C 18H 12, C 20H 10, and C 20H 12. Included were 11 PAH containing only six-membered rings and 19 PAH containing both five- and six-membered rings. For each of these PAH the calculations predict that with increasing temperature, isomerization increases the “complexity” of the PAH mixture, i.e., the relative abundance of each PAH isomer in the mixture other than the most stable isomer, increases. Isomerization also partially transforms non-mutagens to mutagens, e.g., pyrene and benzo[ e]pyrene to fluoranthene and benzo[ a]pyrene, respectively, and partially converts cyclopenta[ c, d]pyrene (CPEP) and chrysene, both human cell mutagens, to one and three additional human cell mutagens, respectively. Acetylene addition transforms the non-mutagens phenanthrene and pyrene to the mutagens triphenylene and CPEP, respectively. Some of the predicted PAH have been observed elsewhere among the products of aromatics pyrolysis. This study elucidates PAH reactivity for comparison with measurements, and identifies PAH reactions to be monitored and avoided in soil thermal decontamination and other waste remediation processes.

Thermogravimetric study of thermal decontamination of soils polluted by hexachlorobenzene, 4-chlorobiphenyl, naphthalene, or n-decane

To determine decontamination behavior as affected by temperature, shallow beds of a clay-rich, a calcerous, and a sedimentary soil, artificially polluted with hexachlorobenzene, 4-chlorobiphenyl, naphthalene, or n-decane, were separately heated at 5°C min −1 in a thermogravimetric analyzer. Temperatures for deep cleaning of the calcerous and the sedimentary soil increased with increasing boiling point (bp) of the aromatic contaminants, but removal efficiencies still approached 100% well below the bp. Decontamination rates were therefore modelled according to a pollutant evaporation–diffusion transport model. For the calcerous and sedimentary soils, this model reasonably correlated removal of roughly the first 2/3 of the naphthalene, but gave only fair predictions for hexachlorobenzene and 4-chlorobiphenyl. It was necessary to heat the clay soil above the aromatics bp to achieve high decontamination efficiencies. Weight loss data imply that for temperatures from near ambient to as much as 150°C, interactions of each aromatic with the clay soil, or its decomposition products, result in lower net volatilization of the contaminated vs. neat clay. A similar effect was observed in heating calcerous soil polluted with hexachlorobenzene from near ambient to about 140°C. Decontamination mechanisms remain to be established, although the higher temperatures needed to remove aromatics from the clay may reflect a more prominent role for surface desorption than evaporation. This would be consistent with our estimates that the clay can accommodate all of the initial pollutant loadings within a single surface monolayer, whereas the calcerous and sedimentary soils cannot.

Microwave-Enhanced Thermal Decontamination of Soil

Results of bench-scale and pilot-scale investigations on the remediation of contaminated sand and soil using microwave energy are presented. Microwave radiation penetrates the soil and heats water and contaminants. Developing vapors are withdrawn from the soil. The experiments suggest that microwave heating is an effective soil remediation technology. The process is rapid as compared to other methods, and its efficiency depends on the dielectric and physicochemical properties of the soil and the contaminant. It allows for the removal of volatile and semivolatile components, and it is especially effective in the case of polar compounds. In the presence of soil moisture, the removal of both polar and nonpolar compounds can be described quantitatively in terms of steam distillation. The remediation proceeds at a temperature not exceeding 100 °C. It is of particular importance in the case of soil rich in organic matter, where too high a temperature could result in carbonization of humic substances. The remediation of trichloroethylene-contaminated sand in a pilot-scale microwave heating system simulating the in-situ process is also reported. The profiles of temperature and contaminant concentration in the remediation zone are presented. The pilot-scale investigations indicate a possibility of the use of microwave heating as an in-situ remediation technique. The use of inexpensive low-power generators for the supply of power to individual antennas may help to reduce costs and allow for an unconstrained design of the array of antennas in the ground.

Hydrogen radical cleaning and low energy electron stimulated desorption of surface contaminants for MBE regrowth of GaAs

Modulation doped two-dimensional electron gas (2DEG) samples have been used to characterise the quality of epitaxial growth achieved within 400Åof a hydrogen radical (H*) cleaned GaAs regrowth interface. For planar ex-vacuo exposed substrates, regrowth of a high quality InGaAs/GaAs pseudomorphic 2DEG has been achieved at only 125Åfrom the cleaned interface. For patterned substrates, a GaAs/AlGaAs modulation doped 2DEG with a 1.5 K, dark mobility of 1 × 106cm2 V−1 s−1 at a carrier concentration of 8 × 1011cm−2 has been regrown at a separation of 375 Å after H* cleaning at 500°C. These results highlight the improved growth morphology which occurs following H* cleaning of the regrowth interface in comparison to that achieved using standard thermal decontamination. Static SIMS analysis shows that low energy electron irradiation at an energy of 100 eV may also be used as an alternative non-destructive method for contaminant reduction at an air exposed GaAs(100) surface.

Eradicating Legionella From Hospital Water

<h3>To the Editor.</h3> —The report by the Centers for Disease Control and Prevention (CDC) on transmission of nosocomial legionnaires disease¹documents failure to eradicate<i>Legionella</i>organisms from the water distribution systems of 2 hospitals despite the use of hyperchlorination, thermal disinfection, and/ or metal ionization. The efficacy of these decontamination methods can be compromised by a variety of factors. The duration of thermal decontamination (160°F/71°C at the tap) used in hospital Y was only 5 minutes. The original report on the use of this method specified a 30-minute flush at the tap.²Thus, failure to maintain the elevated temperature for a sufficient period undoubtedly contributed to this failure to eradicate<i>Legionella</i>. In fact, when one California hospital applied thermal eradication with a flush time of 5 minutes, as recommended by the CDC, distal site colonization by<i>Legionella</i>organisms was unaffected. When the process was repeated using a 30-minute flush

Hydrogen radical surface cleaning of GaAs for MBE regrowth

Modulation-doped GaAs AlGaAs two-dimensional electron gas (2DEG) structures have been regrown on air-exposed GaAs buffer layers, at varying proximity to the regrowth interface. The degradation in 2DEG quality with decreasing separation from a hydrogen radical (H∗) cleaned regrowth interface was found to be much reduced in comparison to that for a thermally cleaned interface. H∗ cleaning has allowed for the growth of a 2DEG lying only 50 nm from the regrowth interface with a mobility, after illumination, of 5.3 × 10 5 cm 2 V − 1 s − 1 at a carrier concentration of 4.2 × 10 11 cm − 2 . SIMS characterisation has been used to measure significant reductions in contamination at the regrowth interface at cleaning temperatures of 500°C. Cathodoluminescence data, measured for a 5 nm quantum well lying 30 nm from the regrowth interface, further indicate the improved growth morphology achieved following H∗ cleaning, in comparison to that achieved by thermal decontamination.

Surface decontamination of patterned GaAs substrates for molecular beam epitaxy regrowth using a hydrogen radical source

To investigate the efficiency of hydrogen radical surface cleaning of patterned GaAs substrates, resonant tunneling devices have been fabricated in which the regrowth interface lies between the collector and the double barrier structure. Secondary-ion-mass spectroscopy data collected at the patterned substrate/regrown layer interface show a significant reduction of contaminant species after radical cleaning at ∼450 °C for 2 h. The current–voltage characteristics of the resonant tunneling device further indicate a significant improvement in the quality of the regrowth interface in comparison to that achieved by standard thermal decontamination.

Evaporation Phenomena during Thermal Decontamination of Soils

Effects of thermal treatment conditions on removal of a low volatility aromatic contaminant from soil are quantified. Shallow beds (10 mg) of a clay soil pretreated with 8 ± 0.4 wt % pyrene were heated in a thermogravimetric analysis at 5, 25, or 50 °C/min or isothermally. Effects of temperature, time, initial soil mass, initial contaminant mass, heating rate, and flow rate of carrier gas (helium at standard conditions) were studied, as were weight loss of uncontaminated soil and evaporation rates of pure pyrene. Extensive pyrene removal from foil (85−90%) was found between 200 (at 5 °C/min) and 300 °C (at 50 °C/min). Soil decontamination was modeled as pyrene transport without chemical reaction, i.e., (1) evaporation from a liquid sheath encasing each soil particle; (2) diffusion through the soil pile; and (3) diffusion to the ambient through a concentration boundary layer between the soil pile and the top of the thermobalance crucible. Evaporation is important in removing most, i.e., 70% or more, of the...

Glove Permeation by Propylene Glycol Monomethyl Ether Acetate — A Photoresist Solvent Used in Semiconductor Device Processing

Abstract Propylene glycol monomethyl ether acetate (PGMEA) has been introduced as a replacement solvent for ethylene glycol ethers and ether acetates in photoresist formulations used in semiconductor processing. While PGMEA does not exhibit the adverse reproductive health effects found with the structurally related ethylene glycol derivatives, it is nevertheless readily absorbed through the skin, and proper protection against dermal absorption is warranted. This article describes the results of permeation tests of several glove materials commonly used in semiconductor fabrication facilities when challenged with PGMEA. Glove permeation was tested at 25 and 37°C according to the ASTM F739-85 permeation test method. The effects of repeated exposure and postexposure thermal decontamination on permeation resistance were also examined for one type of glove. Of the gloves tested, those composed of butyl rubber afforded the highest level of protection against PGMEA, with no breakthrough being observed after more ...

Electrochemical monitoring of the thermal reordering of platinum single-crystal surfaces after metallographic polishing from the early stage to the equilibrium surfaces

In this paper the voltammetry of hydrogen adsorption-desorption on platinum is presented as an alternative standard laboratory method to monitor a complex surface reorganization process such as that occurring during the thermal reordering of the thick perturbed layer resulting from the polishing of oriented platinum samples. By using an electrochemically perturbed Pt (111) surface as a test surface sensitive to atomic reorganization, a thermal decontamination procedure has been developed which allows the cleaning of a disordered platinum surface with minimum change in its initial crystalline structure. This decontamination procedure has been applied successfully to newly polished Pt (111), (100), (110) and (775) surfaces. After decontamination, no preferential site distribution relative to their crystalline direction is detected as resulting from polishing. The modification of the clean perturbed surface during annealing to its final equilibrium state is described, giving evidence for the disappearance of the surface defects. The significant diminution of the mean total electric charge during the reordering process is related to the elimination of the microroughness present on the newly polished surfaces. The effect of a cooling atmosphere, either air or a H 2-Ar stream, after the flame-cleaning procedure was also studied with the well-ordered samples. Major differences for the two types of cooling were observed for Pt (100), giving rise to two types of voltammograms, while for Pt (111) no difference was detected. The differences are interpreted in terms of surfaces with different degrees of two-dimensional long-range order. On the other hand, it is demonstrated that the rearrangement of randomly distributed (110) sites in steps with long-range order along the step rows makes the corresponding hydrogen adsorption state narrower.

Decontamination of chemical protective clothing.

This study explored decontamination procedures for removing some organic solvents from protective clothing. The permeation experiments were performed on new and decontaminated specimens in seven polymer/chemical pairs. The decontamination methods investigated were thermal decontamination and air drying at room temperatures followed by detergent washing. Breakthrough time and steady-state permeation rate were determined by two different methods for new and decontaminated materials. The results showed that unless the contamination is limited to the outside surface of an elastomer (a material found in most barrier fabrics used in chemical protective clothing) or the chemical has a very large diffusion coefficient in the material, aeration and washing with detergent may not be an effective decontamination procedure for the type of solvent studied. On the other hand, thermal decontamination was shown to be effective in removing the contaminant from the matrix of the elastomers, and the decontaminated materials had permeation parameters similar to the new materials.

Study on Sorption of Tritium on Various Material Surfaces and Its Application to Decontamination of Tritium-Sorbing Materials

Behavior of sorption of tritium on surfaces of stainless steel, aluminum and borosilicate glass has been studied using gaseous tritium with high specific activity and the newly obtained knowledge has been applied to chemical and thermal decontamination of tritium-sorbing materials. The behavior depends on a character of surface of each material. The total amount of sorbed-tritium is evaluated as a function of time of exposure to gaseous tritium. The depth-profile of sorbed-tritium is obtained by chemical etching method. From these results, practical samples of stainless steel were decontaminated. The vacuum-bakeout for 21, hours at 773 K and dissolution by dilute (5%) HCl for 2 hours enable us to obtain the decontamination factor of 200.

Thermal treatment of gaseous discharges from degreasing furnaces

An analysis of the discharges from furnaces in the Zaporozh'e Hardware Plant (ZHP) and Artem Voroshilovgrad Enameling Plant (VEP) has shown that the discharges from these two plants differ considerably in composition owing to differences in the burnoff technology and systems used to remove the discharges. Thermal treatment of model mixtures of gases and real discharges (in the VEP) was investigated in an experimental unit. These studies defined the following optimal conditions for decontamination: temperature 950/sup 0/C, residence time in reaction zone 2.5 sec. The statistical mean composition of the VEP degreasing furnace discharge after thermal decontamination under these conditions is shown.

Design and evaluation of a system for thermal decontamination of process air.

AbstractAerobiology studies at the Naval Biological Laboratory require use of a vacuum system to provide safe disposal of air contaminated with pathogenic, microorganisms. A system for thermal decontamination of this process air has been installed and tested. The system uses a natural gas burner to heat approximately 550 cfm of air to temperatures exceeding 750°F. Tests showed a reduction in number of acrosolized viable hardy spores (Bacillus subtilis var. niger) of more than 8 logs at design flow rates. The kill rate (D values) measured in this system is somewhat higher than those reported by other workers. The annual owning and operating cost of the system is approximately $9000.

Thermal decontamination of aqueous waste from Anid (Nylon 66) production

Thermal decontamination of aqueous waste from Anid (Nylon 66) production