Influence of humidity and of the electric and magnetic microwave radiation fields on the remediation of TCE-contaminated natural sandy soils.

The influence of moisture content (15% w/w) on the remediation (vaporization) of trichloroethylene (TCE) present in natural sands, chosen as a TCE-polluted model system for soils, was investigated with regard to applied microwave power levels, the depth of the sand sample, and the dielectric factors. The heating process occurring in the sand samples arises through the microwave conduction loss heating and dielectric loss heating mechanisms. The characteristic relevance of the electric and magnetic microwave radiation fields to the heating mechanisms was also examined. Heating by the magnetic microwave radiation field was considerable when magnetite was added to the dry and wet sand samples as the microwave absorber. Optimal microwave conditions are reported for a single-mode microwave applicator. Near-quantitative elimination of the TCE contaminant was achieved for sandy soils within a very short time.

A study on radiation technological degradation of organic chloride wastewater--exemplified by TCE and PCE.

This paper describes the potential of using gamma radiation technology to degrade trichloroethylene (TCE) and perchloroethylene (PCE) wastewater. The experimental method is divided into two parts: (1) using the gamma-ray to irradiate the TCE and PCE solution, the dose-rate is 10Gy/minute, the irradiation dosage is 0-2.5kGy and (2) self-making the UV irradiation system, the tube specification is 254nm and 6W, and turning on 8 tubes at the same time to make the irradiation. The efficiency of degradation ratio for gamma-ray is better than UV in the range of 0.1-250ppm; for example, as for the concentration of 0.1ppm, when TCE is degraded to D(90) and T(90), the gamma-ray only needed 46.7Gy and took about 4.67 minutes, but UV needed to take about 28.1 minutes. The dose-concentration equations of TCE and PCE are: TCE: y=44.58+8.832x, R(2)=0.999; and PCE: y=81.33+12.81x, R(2)=0.997. We verified that the radiation technology is able to effectively degrade the organic chlorine wastewater without yielding the secondary pollution, and the TCE and PCE that degraded by using gamma-ray will be reached US-EPA and Taiwan Effluent Standard (5ppb).

Degradation of gas-phase trichloroethylene over thin-film TiO2 photocatalyst in multi-modules reactor.

The present paper examined the photocatalytic degradation (PCD) of gas-phase trichloroethylene (TCE) over thin-film TiO2. A large-scale treatment of TCE was carried out using scale-up continuous flow photo-reactor in which nine reactors were arranged in parallel and series. The parallel or serial arrangement is a significant factor to determine the special arrangement of whole reactor module as well as to compact the multi-modules in a continuous flow reactor. The conversion of TCE according to the space time was nearly same for parallel and serial connection of the reactors.

Trichloroethylene degradation by photocatalysis in annular flow and annulus fluidized bed photoreactors.

The effects of trichloroethylene (TCE) gas flow rate, relative humidity, TiO(2) film thickness, and UV light intensity on photodegradation of TCE have been determined in an annular flow type photoreactor. Phosgene and dichloroacetyl chloride formation could be controlled as a function of TCE gas flow rate and photodegradation of TCE decreased with increasing relative humidity. The optimum thickness of TiO(2) film was found to be approximately 5 mum and the photocatalytic reaction rate of TCE increased with square root of UV light intensity. In addition, the effects of the initial TCE concentration, phase holdup ratio of gas and solid phases (epsilon(g)/epsilon(s)), CuO loading on the photodegradation of TCE have been determined in an annulus fluidized bed photoreactor. The TCE photodegradation decreased with increasing the initial TCE concentration. The optimum conditions of the phase holdup ratio (epsilon(g)/epsilon(s)) and CuO wt.% for the maximum photodegradation of TCE was found to be 2.1 and 1.1 wt.%, respectively. Therefore, an annulus fluidized bed photoreactor is an effective tool for TCE degradation over TiO(2)/silica gel with efficient utilization of photon energy.

Trichloroethylene radicals generated by ionizing radiation. An EPR/spin trapping study.

Trichloroethylene (TCE) was exposed in the presence of the spin trap N-tert-butyl-alpha-phenyl nitrone (PBN, 0.1 M) to ionizing radiation from two different sources in an attempt to determine the origin of the spin-trapped radicals generating the EPR spectra in precision cut liver slices. TCE samples were irradiated with 18 MeV electrons to a total dose of 1000 Gy in a linear accelerator (LINAC) or exposed to 60Co gamma-rays to total doses of 100 Gy and 1000 Gy. The results show that three PBN adducts were generated during the LINAC radiations. Two of these spin adducts correspond to the addition of carbon-centered radicals to PBN, and the third adduct is consistent with a decomposition product of PBN. The predominant carbon-entered radical yields a PBN adduct that is more stable, persists for over 24 h and has identical hyperfine coupling constants (aN = 1.61 mT, aH beta = 0.325 mT) to the PBN adduct obtained when precision-cut liver slices were exposed to TCE. Gamma radiation (100 Gy) of TCE yields PBN adducts with lower primary nitrogen hyperfine coupling constants (aN = 1.45 mT and aN = 1.54 mT). The results (gamma-radiation) suggest that the carbon-centered radical is formed on a single TCE carbon that is different than the predominant radical formed during LINAC radiations. This difference is confirmed by experiments using 13C-TCE. The results further suggest that, during gamma-radiation of TCE, the radicals are formed by dechlorination at the TCE carbon containing two chlorine atoms. The results obtained during LINAC radiations suggest that the predominant radical is formed by dechlorination at the TCE carbon containing a single chlorine and a single proton. In addition, it is possible that this radical is the initial TCE radical formed during exposure of liver slices to TCE.

Radiation-induced decomposition of small amounts of trichloroethylene in drinking water.

Solutions of 10 ppm trichloroethylene in air-saturated drinking waters are decomposed by gamma radiation with initial G-values, G0, around 3-5 molecules per 100 eV. At lower concentrations, the G0-values decrease with decreasing trichloroethylene concentration and with increasing amounts of inorganic (especially HCO3- and NO3-) and organic solutes. From the results, a semi-empirical formula is derived which allows an estimation of G0-values for the trichloroethylene decomposition in drinking waters of given composition.

Radiation-induced degradation of trichloroethylene and tetrachloroethylene in drinking water.

The gamma-radiation degradation of trace amounts (70-440 ppb) of trichloroethylene and tetrachloroethylene in drinking water has been investigated. The doses necessary to reduce the pollutant concentration to 1 ppb are in the order of 1 kGy.