Application of microwave irradiation for the removal of polychlorinated biphenyls from siloxane transformer and hydrocarbon engine oils.

The removal of polychlorinated biphenyls (PCBs) both from siloxane transformer oil and hydrocarbon engine oil was investigated through the application of microwave (MW) irradiation and a reaction system based on polyethyleneglycol (PEG) and potassium hydroxide. The influence of the main reaction parameters (MW irradiation time, molecular weight of PEG, amount of added reactants and temperature) on the dechlorination behavior was studied. Promising performances were reached, allowing about 50% of dechlorination under the best experimental conditions, together time and energy saving compared to conventional heating systems. Moreover, an interesting dechlorination degree (up to 32%) was achieved for siloxane transformer oil when MW irradiation was employed as the unique driving force. To the best of our knowledge, this is the first time in which MW irradiation is tested as the single driving force for the dechlorination of these two types of PCB-contaminated oils.

Distribution of free radicals and intermediates during the photodegradation of polychlorinated biphenyls strongly affected by cosolvents and TiO2 catalyst.

Polychlorinated biphenyls (PCBs) pose potential ecological risk because of their high toxicity and carcinogenicity. Photodegradation, which is an important process for the removal of PCBs, is greatly influenced by the cosolvent and catalyst. Hence, it is important to explore their effects on the photodegradation behavior of PCBs. In this study, 2,4,4'-trichlorobiphenyl (PCB28) was selected as a model compound, and the effects of two typical cosolvents, namely acetone and ethanol, and TiO2 catalyst on the distributions of free radicals and intermediates were investigated. Interestingly, the TiO2 catalyst did not promote PCB28 photodegradation. Moreover, the free radical distribution was greatly influenced in the presence of the TiO2 catalyst, while was only slightly affected in its absence by the cosolvent kinds. The main photodegradation pathways are proposed on the basis of the distribution of detected intermediates, which were significantly regulated by both the cosolvent and TiO2 catalyst. The results provide novel insights into the photodegradation of PCBs and may have important implications for choosing cosolvent in desorbing soil PCBs and consequently enhancing PCBs degradation.

Application of microwave-irradiated manganese dioxide in the removal of polychlorinated biphenyls from soil contaminated by capacitor oil.

The removal of polychlorinated biphenyls (PCBs) from soil contaminated with capacitor oil, using microwave (MW)-irradiated manganese dioxide (MnO2), was examined under different conditions. The effects of different types of MnO2 added as oxidant, as well as the initial amount of water, MnO2, and sulphuric acid solution, were also investigated. The removal efficiencies for dichlorobiphenyls, trichlorobiphenyls, tetrachlorobiphenyls, pentachlorobiphenyls, hexachloro-biphenyls, heptachlorobiphenyls, and octachlorobiphenyls were approximately 95.9%, 82.5%, 52.0%, 71.6%, 62.5%, 28.6%, and 16.1%, respectively, by 800 W MW irradiation for 45 min with the assistance of 0.1 g delta-MnO2 and 0.2 mL water in 1.0 g severely PCB-contaminated soil (sigma PCB = 1560.82 mg/kg); meanwhile, the concentrations of Mn2+ ions detected were from 10.6 +/- 1.9 mg/kg at 0 min to 108.2 +/- 7.8 mg/kg after 45 min MW irradiation, indicating that MnO2 acted as not only a MW absorber but also an oxidizer. Removal efficiencies of PCBs from contaminated soil increased with increasing the amounts of water and MnO2 added. The type of MnO2 also affected the removal of PCBs, following an order of delta-MnO2 > alpha-MnO2 > beta-MnO2. The addition of low concentration of sulphuric acid (such as 1.0 mol/L) solution was favourable for the removal of low chloro-substituted PCBs, but the addition of more than 1.0 mol/L sulphuric acid reduced the removal of all PCBs. The pronounced removal of PCBs from contaminated soil in a short treatment time indicates that MW irradiation with the assistance of MnO2 is an efficient and promising technology for the remediation of PCB-contaminated soil.

Photosensitized degradation of 2,4',5-trichlorobiphenyl (PCB 31) by dissolved organic matter.

The presence of dissolved organic matter (DOM) in aquatic system has an important influence on the phototransformation of organic contaminants through the production of reactive substances, such as hydroxyl radicals (OH), singlet oxygen ((1)O(2)), and DOM triplet states ((3)DOM) under solar irradiation. Addition of 5mg/L of Humic acid sodium (HA), Suwannee River NOM (SRNOM) and Nordic Reservoir NOM (NRNOM) all accelerated the photodegradation of 2,4',5-trichlorobiphenyl (PCB 31) significantly, with a pseudo-first-order rate constant of 0.0933, 0.0651 and 0.0486 in the initial 12h, respectively. HA and SRNOM, the allochthonous DOM, showed higher reactivity in the photolysis of PCB 31. The maximum photodegradation rate was observed in 5mg/L of DOM solution. The roles of the reactive substances were studied by the inhibitory experiments, which suggested that OH and intra-DOM (1)O(2) were more important for the photolysis of PCB 31 than other reactive substances, accounting for 35.1% and 47.1% of the degradation, respectively. The main degradation products of PCB 31 detected by GC-MS were 4-chlorobenzoic acid, 2,5-dichlorobenzoic acid, hydroxy-2,5-dichlorobenzoic acid, 4-hydroxy-2',5'-dichlorobiphenyls and hydroxy-trichlorobiphenyls. The degradation pathways were accordingly proposed. Photosensitized degradation by DOM, especially the intra-DOM reactions, may be a very important mechanism for the transformation of PCBs and other hydrophobic organic contaminants in the environment.

Photocatalytic dechlorination of PCB 138 using leuco-methylene blue and visible light; reaction conditions and mechanisms.

A study of dechlorination of PCB 138, under visible light employing methylene blue (MB) and triethylamine (TEA) in acetonitrile/water has been conducted to investigate the details of the mechanism of dechlorination and to determine the efficiency of the process for this representative congener. Two other amines, N-methyldiethanolamine (MEDA) and (triethanolamine) TEOA also replaced TEA and two other solvents, methanol and ethanol replacing acetonitrile were examined for effects on reaction rates. The results show that PCB 138 can be dechlorinated efficiently in this photocatalytic reaction. Clarifying ambiguities in several previous reports, the reduced form of MB, leuco-methylene blue (LMB) was identified as responsible for the photoreaction with its excited state transferring an electron to PCBs; oxidized LMB (i.e. MB) is reduced back to LMB by the excess amine present. The reaction depends on a cycle driven by the amine as a sacrificial electron donor. MEDA proved to be the most efficient electron donor; apparently in consequence of the most favourable steady state concentration of LMB. Methanol and ethanol may be used to replace acetonitrile with little change in the efficiency of the reaction.

[Catalytic degradation of PCB77 by microwave-induced nano-particle metal oxides in diatomite].

The degradation of PCB77 in diatomite by microwave-induced catalytic oxidation was studied in a sealed vial, including four effects such as microwave (MV) radiating time, addition of different nano-particle metal oxides, concentration and type of acids and dosage of MnO2. The results indicated that PCB77 could be removed significantly by microwave-induced catalytic oxidation. Compared to control reactor (without MV radiation), the removal rate of PCB77 increased by twice after 1 min. In addition, the removal rate of PCB77 under MV radiation was gradually increased with time of radiation and then reached equilibrium after 10 min. The removal rates are about 50% and 20% by addition of H2SO4 and ultrapure water respectively. No significant removal was observed by addition of NaOH and without aqueous media. Moreover, catalytic degradation of PCB77 by microwave-induced nano-particle MnO2 had best removal rate was up to 90% after 1 min, in contrast with addition of nano-particle Fe2O3, CuO and Al2O3. The removal rate raised from 37.0% to 98.5% rapidly with the concentration of H2SO4 ranged from 1 mol/L to 8 mol/L, and H2SO4 mainly played a role of acidification but not oxidation. The addition of 0.01, 0.03 and 0.05 g MnO2 showed the similar result.

Radiation induced degradation of polychlorinated biphenyls (PCBs) pollutants in paint scrapings.

Polychlorinated biphenyls (PCBs) are synthetic organic chemicals which have been commercially used worldwide in many specialty applications. In paints, PCBs were used because of their unique properties such as thermal stability, flame-resistance and low volatility. However, due to their adverse effects on human health and environment, the use of PCBs has now been banned. PCBs are today considered widespread pollutants in the global system . PCBs sources still exist in various products and in waste streams such as oil, paints, rubbers etc. Various remedial technologies have been developed in the world to detoxify PCBs. In the present study, radiolysis has been investigated as a safe means to reduce or destroy PCBs. Under this study, detoxification of PCBs in paint scrapings by gamma radiation using Cobalt 60 source has been investigated. The experimental results demonstrate that the gamma radiations can be an alternative environment- friendly technology for destroying PCBs. Gamma radiations also have the potential of being a preferred tool in comparison to the most widely used incineration method for destroying PCBs. The method used was found highly effective and destruction efficiency was as high as 91%. The degradation efficiency of PCBs was dependent on absorbed radiation dose, the type of PCBs and also on the source of paint scrapings.

Photolysis of mono- through deca-chlorinated biphenyls by ultraviolet irradiation in n-hexane and quantitative structure-property relationship analysis.

The photolysis of 16 polychlorinated biphenyls (PCBs) (including mono- through deca-chlorinated) in n-hexane was investigated under ultraviolet irradiation using a 500-W high-pressure mercury lamp. Photolysis of PCBs follows pseudo-first-order reaction kinetics, with photolysis rate constants ranging between 0.0011 s(-1) for PCB-52 and 0.0574 s(-1) for PCB-118. The degradation rates of PCBs by high-pressure mercury lamp irradiation were remarkably independent with respect to the degree of chlorination. Furthermore, partial least squares (PLS) models were developed to provide insight into which aspect of the molecular structure influenced PCB photolysis rate constants. It was found that the photolysis rates of PCBs increased with an increase in the net charge on the carbon atom (qc), (E(LUMO)-E(HOMO))2, and the Y-axis dipole moment (mu(y)) values, or the decrease in the energy of the second highest occupied molecular orbital (E(HOMO-1)), energy of the lowest unoccupied molecular orbital (E(LUMO)), E(LUMO) + E(HOMO), E(LUMO)--E(HOMO), most positive atomic charge (q+), and the twist angle of the chlorine atom (TA) values.

QSPRs for the prediction of photodegradation half-life of PCBs in n-hexane.

By partial least squares (PLS) regression analysis, a quantitative structure-property relationship (QSPR) model was developed for photodegradation half-life (t1/2) of polychlorinated biphenyls (PCBs) in n-hexane solution under UV irradiation. Quantum chemical descriptors computed by PM3 Hamiltonian were used as predictor variables. The cross-validated value for the optimal QSPR model was 0.589, indicating good predictive capability for log t1/2 values of PCBs in n-hexane. The QSPR results show that standard heat of formation (DeltaHf), total energy (TE), and molecular weight (Mw) have dominant effect on t1/2 values of PCBs in n-hexane. Increasing DeltaHf and TE values or decreasing Mw values of the PCBs leads to decrease of log t1/2 values. In addition, increasing the largest negative atomic charge on a carbon atom and dipole moment of the PCBs leads to decrease of log t1/2 values.

Combined effect of microwave and activated carbon on the remediation of polychlorinated biphenyl-contaminated soil.

The application of microwave and activated carbon for the treatment of polychlorinated biphenyl (PCB) contaminated soil was explored in this study with a model compound of 2,4,5-trichlorobiphenyl (PCB29). PCB-contaminated soil was treated in a quartz reactor by microwave irradiation at 2450MHz with the addition of granular activated carbon (GAC). In this procedure, GAC acted as microwave absorbent for reaching high temperature and reductant for dechlorination. A sheltered type-K thermocouple was applied to record the temperature rising courses. It was shown that the addition of GAC could effectively promote the temperature rising courses. The determination of PCB residues in soil by gas chromatography (GC) revealed that rates of PCB removal were highly dependent on microwave power, soil moisture content, and the amount of GAC added. GC with mass spectrum (MS) detector and ion chromatography were employed for the analysis of degradation intermediates and chlorine ions, respectively. It was suggested that microwave irradiation with the assistance of activated carbon might be a potential technology for the remediation of PCB-contaminated soil.

Gamma radiation process for destruction of toxic polychlorinated biphenyls (Pcbs) in transformer oils.

Polychlorinated biphenyls (PCBs) are synthetic organic chemicals commercially used worldwide in many applications. PCBs were used in oils because of their excellent properties such as good thermal stability, flame resistance, dielectric constant, high break down voltage, high boiling point and low volatility. However, because of their adverse affects on environment and human health, the use of PCBs has been banned now. PCBs are today considered among the widespread pollutants in the global system. PCBs sources still exist in various industrial products and in waste streams such as capacitor oils, lubricating oils, transformer oils, hydraulic oils, paints, rubbers, cables, etc. Several such materials containing PCBs emanating from various sources need to be detoxified before their reuse or before going to landfill for final disposal. Various remedial technologies have been developed in the world to destroy toxic PCBs. The radiolysis has been investigated as an environment-friendly process for waste oil treatment contaminated with PCBs, which may be a better alternative to the globally most widely accepted incineration method. A study was undertaken to detoxify PCBs in transformer oil by gamma radiation using Cobalt 60 source. Analysis of PCBs in transformer oils before and after radiation was carried out by GC-MS instrument. The effect of radiation dose and destruction of PCBs in transformer oils are discussed in details in the present paper. The method used was found to be highly effective and destruction was as high as 79 %. Further, the transformer oil samples were also evaluated before and after radiation to check their quality. The properties of oils were not significantly altered by gamma radiation treatment as evident from the results given in the paper.

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.

Photo-induced binding of 2,2',4,4',5,5'-hexachlorobiphenyl to cultured human cells.

The polychlorinated biphenyl congener 2,2',4,4',5,5'-hexachlorobiphenyl can be photoactivated by brief high-intensity ultraviolet irradiation. Photoactivated intermediates are bound to neighboring biological macromolecules. Properties and stability of hexachlorobiphenyl photobinding were examined with bovine serum albumin, a protein known to strongly bind lipophilic compounds. Photobinding to cultured human Chang liver cells was a function of ligand and cell protein concentration as well as of irradiation time. Binding increased with incubation time, in support of the time course of uptake previously measured in the same system by alternative methods. Separation of cell proteins by gel electrophoresis showed that the distribution pattern of photobinding changed at different rates for different proteins. Photobinding to major cell lipid groups and to individual phospholipids likewise reflected uptake of the compound. Notably, photobinding to phosphatidyl choline was elevated relative to phosphatidyl ethanolamine. Thus, the presented method is suitable to follow up transport and intracellular equilibrium distribution of photoactivatable ligands. As a particular advantage, artefactual redistribution of persistent lipophilic compounds during cell fractionation can be avoided.