PCB Decomposition Research Articles

環境汚染物質 PCB の処理技術(話題を探る)

環境汚染物質 PCB の処理技術(話題を探る)

Laser decontamination and decomposition of PCB-containing paint

Decontamination of concrete surfaces contaminated with paint containing polychlorinated biphenyls is an elaborate and complex task that must be performed within the scope of nuclear power plant dismantling as well as conventional pollutant cleanup in buildings. The state of the art is mechanical decontamination, which generates dust as well as secondary waste and is both dangerous and physically demanding. Moreover, the ablated PCB-containing paint has to be treated in a separate process step.Laser technology offers a multitude of possibilities for contactless surface treatment with no restoring forces and a high potential for automation.An advanced experimental setup was developed for performing standard laser decontamination investigations on PCB-painted concrete surfaces. As tested with epoxy paints, a high-power diode laser with a laser power of 10kW in continuous wave (CW) mode was implemented and resulted in decontamination of the concrete surfaces as well as significant PCB decomposition.The experimental results showed PCB removal of 96.8% from the concrete surface and PCB decomposition of 88.8% in the laser decontamination process. Significant PCDD/F formation was thereby avoided. A surface ablation rate of approx. 7.2m2/h was realized.

Influence of activated-carbon-supported transition metals on the decomposition of polychlorobiphenyls. Part I: Catalytic decomposition and kinetic analysis

In this study, the synergism between activated carbon (AC) as a catalyst support and transition metals (TMs) is used to destroy low concentrations of PCBs. AC-supported TM catalysts were prepared according to two different methods: impregnation and ion exchange. Thermal reactions between 2,2′,4,4′,5,5’-hexachlorobiphenyl (PCB-153) and catalysts generated using AC-supported Ni or Cu ion exchange were conducted under a N2 atmosphere and resulted in a decomposition efficiency > 99.0%. Decomposition efficiency of PCB-153, the residual PCB-153 distribution, and the fingerprint characteristics of the decomposition products are investigated. Important findings include: (i) establishing a ranking of TM reactivities with respect to PCB decomposition of: Ni > Cu > Zn > Fe, (ii) PCB degradation reactions proceed via adsorption, reaction, and desorption, (iii) for ion-exchange-type catalysts, the activation energy order was IRNi-C < IRCu-C < IRZn-C < IRFe-C, which matches the order of the catalytic effects of the catalyst.

The Effect of Solvent, Hydrogen Peroxide and Dioxide Titanium on Degradation of PCBs, Using Microwave Radiation in Order to Reduce Occupational Exposure

Abstract Polychlorinated biphenyls (PCBs) are one group of persistent organic pollutants (POPs) that are of international concern because of global distribution, persistence, and toxicity. Removal of these compounds from the environment remains a very difficult challenge because the compounds are highly hydrophobic and have very low solubility in water. A 900 W domestic microwave oven, pyrex vessel reactor, pyrex tube connector and condensing system were used in this experiment. Radiation was discontinuous and ray powers were 540, 720 and 900 W. The PCBS were analyzed by GC-ECD. The application of microwave radiation and H2O2/TiO2 agents for the degradation of polychlorinated biphenyl contaminated oil was explored in this study. PCB – contaminated oil was treated in a pyrex reactor by microwave irradiation at 2450 MHz with the addition of H2O2/TiO2. A novel grain TiO2 (GT01) was used. The determination of PCB residues in oil by gas chromatography (GC) revealed that rates of PCB decomposition were highly dependent on microwave power, exposure time, ratio to solvent with transformer oil in 3:1, the optimal amount of GT01 (0.2 g) and 0.116 mol of H2O2 were used in the study. It was suggested that microwave irradiation with the assistance of H2O2/TiO2 might be a potential technology for the degradation of PCB – contaminated oil. The experiments show that MW irradiation, H2O2 oxidant and TiO2 catalyst lead to a degradation efficiency of PCBs only in the presence of ethanol. The results showed that the addition of ethanol significantly enhanced degradation efficiency of PCBs.

PCB decomposition and formation in thermal treatment plant equipment

In this study we investigated both the decomposition and unintentional formation of polychlorinated biphenyl congeners during combustion experiments of refuse-derived fuel (RDF) and automobile shredder residue (ASR) at several stages in thermal treatment plant equipment composed of a primary combustion chamber, a secondary combustion chamber, and other equipments for flue gas treatment. In both experiments, the unintentional formation of PCB occurred in the primary combustion chamber at the same time as the decomposition of PCB in input samples. By combusting RDF, non-ortho-PCB predominantly formed, whereas ortho-PCB and symmetric chlorinated biphenyls (e.g., #52/69, #87/108, and #151) tended to be decomposed. ASR formed the higher chlorinated biphenyls more than RDF. These by-products from ASR had no structural relation with ortho-chlorine. Lower chlorinated biphenyls appeared as predominant homologues at the final exit site, while all congeners from lower to higher chlorinated PCB were unintentionally formed as by-products in the primary combustion chamber. This result showed that the flue gas treatment equipments effectively removed higher chlorinated PCB. Input marker congeners of RDF were #11, #39, and #68, while those for ASR were #11, #101, #110/120, and #118. Otherwise, combustion marker congeners of RDF were #13/12, #35, #77, and #126, while those for ASR were #170, #194, #206, and #209. While the concentration of PCB increased significantly in the primary combustion chamber, the value of toxicity equivalency quantity for dioxin-like PCB decreased in the secondary combustion chamber and the flue gas treatment equipments.

On-fibre photodegradation studies of polychlorinated biphenyls using SPME–GC–MS–MS: a new approach

The known advantages of solid-phase microextraction as a simple, one-step, rapid and solvent free extraction technique are exploited to study the photodegradation kinetics of polychlorinated biphenyls “on-fibre”. The obtained results show the possibilities of this new approach not only to monitor the photolysis pathways of such compounds but to determine the photoproducts produced at different irradiation times and/or wavelengths. Photoproducts of PCB decomposition were less chlorinated biphenyls, among them some coplanar congeners have been found, which is important from a toxicological point of view.

Peroxidative degradation of selected PCB: a mechanistic study

The enzyme-induced decomposition and biodegradation of PCB were investigated. 2,5-Dichlorobiphenyl (PCB 9) and 2,2 ′,5,5 ′-tetrachlorobiphenyl (PCB 52) were used as example compounds to study efficiency and mechanism of the degradation processes. It was found that the application of horseradish peroxidase (HRP) together with defined amounts of hydrogen peroxide removed 90% of the initial concentration of PCB 9 and 55% of the initial concentration of PCB 52 from an aqueous solution after a reaction period of 220 min. Dechlorination was observed as the initial step. Although the metabolites identified were mainly chlorinated hydroxybiphenyls, benzoic acids and non-substituted 1,1 ′-biphenyl, some higher chlorinated biphenyl isomers also appeared. The biodegradation of PCB 9 using the white rot fungus Trametes multicolor took about four weeks and reduction was about 80% of the initial concentration. The metabolites produced (dichlorobenzenes, chlorophenols and alkylated benzenes) were not quite the same as those observed upon incubation with HRP.

Method To Simultaneously Improve PCB Radiolysis Rates in Transformer Oil and To Close the Chlorine Mass Balance

The addition of alkaline 2-propanol to isooctane and transformer oil solutions of PCBs was found to increase the rate of PCB dechlorination by γ-radiolysis. Simultaneously, it facilitates the closure of the chlorine mass balance. The chlorine liberated from PCBs irradiated in alkaline 2-propanol-spiked solutions precipitated as an inorganic salt in a stoichiometric amount. This was demonstrated for an individual PCB congener (PCB 155) in isooctane and for Aroclor 1260 in transformer oil. Radiolysis rates are reported in terms of dose constants, d (kGy-1), the exponential rate constant for PCB decomposition with respect to absorbed dose. These are the highest decomposition rates yet reported for the radiolytic treatment of PCB-contaminated transformer oil.

Degradation pathways of PCBs upon UV irradiation in hexane

The photodegradations of eight individual PCB congeners ( 5, 31, 52, 77, 87, 126, 138, 169 ) in hexane have been investigated employing a mercury lamp. All degradation reactions of the above mentioned PCB congeners are of the pseudo first order. The principal products of PCB decomposition are the less chlorinated biphenyls. and no PCB-solvent adducts are found. Symmetrical and coplanar PCB congeners show lower photoreactivities. The reactivities of the chlorine atoms at various positions of PCB rings are generally in the order: ortho > meta > para. Photodechlorinations occur mainly on the more substituted rings. when the numbers of chlorine atoms on the two phenyl rings are unequal. During photodegradation, some coplanar PCB congeners are formed, which make the TEQ of solutions to decrease slowly or even to increase.

Decomposition of PCB's and other polychlorinated aromatics in soil using microwave energy

Conditions are described whereby hexachlorobenzene, pentachlorophenol, 2,2′,5,5′-tetrachlorobiphenyl, and 2,2′,4,4′,5,5′-hexachlorobiphenyl are decomposed in soil using microwave energy. The most efficient decompositions are achieved in the presence of Cu 2O or Al powder and 10N NaOH. Minute amounts of mixtures of decomposition products are extractable from the soil following remediation, but the vast majority of the decomposition products are not, and are probably either mineralized or very tightly bound to the soil. The higher the chlorine content of the biphenyl, the less efficient the decomposition. A modified ceramic alumina bomb is described which allows the bomb walls to remain much cooler than the one used earlier.

PCB radiolysis in Isooctane in the presence of ozone

In a single set of experiments we have investigated the effect of ozone on the radiation chemistry of PCB 155 in isooctane. The results suggest that PCB decomposition in this oil-like alkane solution is inhibited by ozone, probably due to the ozone-electron capture reaction. Hydroxyl radicals generated by ozone-electron capture apparently do not play role in PCB decomposition in this matrix.

γ-Ray Destruction of PCBs in Isooctane and Transformer Oil

The radiolytic degradation of PCBs in air-equilibrated isooctane and transformer oil was investigated. Significant degradation was observed in both solvents studied at moderate absorbed dose. Scavenging studies implicate the electron as the major reactive species responsible for decomposition. This is consistent with what has been observed in neutral 2-propanol; however, surprising differences between the radiolytic behavior of PCBs in polar 2-propanol and nonpolar isooctane are observed. PCB degradation was found to be enhanced in isooctane relative to neutral 2-propanol. Chlorine number and substitution pattern have been found to influence degradation efficiency but to a lesser extent in isooctane than in 2-propanol. Deviations in PCB degradation behavior between isooctane and 2-propanol are interpreted in terms of differences in electron behavior between the two solvents. The products of PCB decomposition appear to be less chlorinated PCBs and PCB−solvent adducts.

Gamma-ray-induced degradation of PCBs in neutral isopropanol using spent reactor fuel

In this study we report new results concerning the γ-radiolysis of the PCB octachlorobiphenyl. The radiolytic decomposition rate of octachlorobiphenyl (8CB) in neutral isopropanol was studied as a function of dose using spent nuclear fuel as a γ-ray source. The G-values measured were small (approx. 0.01 μmol J −1), however the easy access to very high γ-ray doses and dose rates has allowed for the investigation of a process not constrained to deaerated, alkaline conditions. The G-value was suppressed by the addition of a solvated electron and solvent radical scavenger, but not by the addition of hydrogen atom and hydroxyl radical scavengers, suggesting that in neutral alcoholic solvent the solvated electron and possibly solvent radicals are the primary species responsible for PCB decomposition.

Decomposition of PCB's in the radio-frequency glow discharge plasmas of oxygen, hydrogen, and water vapor

A study was made on the decomposition of PCB's in a radio-frequency glow discharge plasma. PCB's were completely decomposed in plasmas of a few Torr of oxygen, hydrogen, and water vapor. Gaseous products from PCB's in an oxygen plasma were carbon monoxide, carbon dioxide, water, hydrogen chloride, chlorine, and chlorine dioxide. Hazardous compounds such as phosgene and vinyl chloride were not detected by gc–ms analysis. The total quantity of oxygen flowed past the sample was only about three times the stoichiometric oxygen required for the perfect oxidation of PCB's. In a hydrogen plasma, PCB's gave ethane and isobutane as major gaseous products and several higher hydrocarbons as minor products. Almost all of the chlorine in PCB's was converted to hydrogen chloride. Major products from PCB's in a water vapor plasma were carbon dioxide, carbon monoxide, and hydrogen chloride. No other products were detected. The mechanisms for reactions occurring in plasmas are discussed. The importance of the wall effect for the formation of solid products is discussed.

DECOMPOSITION OF PCB′s IN A HYDROGEN GLOW DISCHARGE PLASMA

Abstract A study was made on the decomposition of PCB’s in a radio-frequency glow discharge plasma of hydrogen. PCB’s were completely decomposed in a plasma of hydrogen at 1 Torr. Major gaseous products were ethane, isgbutane, and several higher hydrocarbons were recognized as minor products. Almost all of chlorine in PCB’s was converted to hydrogen chloride.

DECOMPOSITION OF POLYCHLORINATED BIPHENYLS (PCB’s) IN A RADIO-FREQUENCY GLOW DISCHARGE PLASMA

Abstract A study was made on the decomposition of PCB’s in a radio-frequency glow discharge plasma. When PCB’s were decomposed in a plasma of oxygen at a few Torr, they were completely decomposed to gaseous products: carbon monoxide, carbon dioxide, water, hydrogen chloride, chlorine, and chlorine dioxide. Hazardous compounds such as phosgene and vinyl chloride were not detected by a GC-MS analysis.