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Combined steam distillation and ECP treatment of river sediment contaminated by PCBs


Chemosphere 45 (2001) 1159±1165

www.elsevier.com/locate/chemosphere

Combined steam distillation and electrochemical peroxidation (ECP) treatment of river sediment contaminated by PCBs
Je?rey R. Chiarenzelli *, Ronald J. Scrudato, Michele L. Wunderlich, James J. Pagano
Environmental Research Center, Oswego, NY 13126, USA Accepted 10 November 2000

Abstract A combined treatment process utilizing steam distillation followed by electrochemical peroxidation (ECP) has been utilized to remove >90% of the polychlorinated biphenyls (PCBs) in St. Lawrence River sediment and destroy 95% of the PCBs recovered in the condensate. 2 l of condensate were collected by boiling 500 grams of sediment containing 4:3 mg PCBs. Most of the PCBs (82.3%) were recovered as a small volume (<1 ml) of yellow oil ?oating on the condensate and coating glassware surfaces. The aqueous phase PCBs ?182 lg=l? were destroyed (95%) by three sequential ECP treatments at 16.8°C and pH 5, utilizing 1 ml of H2 O2 (3%) and periodically reversed current (0.75±1.0 A @ 10 volts). Oxidation is primarily mediated by hydroxyl radicals produced by the reaction of hydrogen peroxide with electrochemically generated ferrous iron (Fenton's reagent). This work suggests steam extraction, in combination with advanced oxidation technologies, provides an e?ective treatment strategy for contaminated solids. ? 2001 Elsevier Science Ltd. All rights reserved.
Keywords: St. Lawrence river; Oxidation; Iron; Condensate; Fenton's reagent

1. Introduction While advanced oxidative technologies (AOTs) are widely utilized for the treatment of water and air contaminated by organic compounds, the development of these processes for solids has lagged behind (Pelizzetti et al., 1992; Zhang et al., 1993; Chiarenzelli et al., 1995a,b). In general, organically contaminated slurries are less amenable to AOT treatment because of higher contaminant concentrations, sequestering by solid particles, matrix e?ects including quenching of free radicals, mixing and/or reagent dispersion problems, greater

* Corresponding author. Present address: 5339 Brick Schoolhouse Road, North Rose, NY 13126, USA. Tel.: +1313-341-2891; fax: +1-315-341-5346. E-mail address: chiarenz@oswego.edu (J.R. Chiarenzelli).

catalyst fouling or erosion, and limited transparency (Chiarenzelli et al., 1995b). Hence innovative ways to desorb and treat contaminated solids (Chu, 1999), particularly in slurry form, are needed. The use of steam distillation, or boiling, to extract organic contaminants, particularly semi-volatile compounds, from solids is widely known and used (Veith and Kiwus, 1977; Cooke et al., 1979; Swackhammer and Anderson, 1986). Steam distillation allows the preferential recovery of organic contaminants and the simultaneous removal of inorganic minerals and salts. The increased purity, transparency, and temperature of the derived condensate signi?cantly improve the e?ciency of AOTs. The combination of steam distillation and AOTs therefore presents a viable option for the destruction of contaminants sorbed to solids. Fenton's reagent is a simple, but widely applied, oxidative technology which utilizes the reaction of H2 O2

0045-6535/01/$ - see front matter ? 2001 Elsevier Science Ltd. All rights reserved. PII: S 0 0 4 5 - 6 5 3 5 ( 0 0 ) 0 0 5 6 9 - 5

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with Fe2? (generally added as FeCl2 or FeSO4 ) to produce free radicals which are capable of oxidizing a broad range of organic contaminants (Walling, 1975; Masten and Davies, 1994). Because the addition of ferrous salts containing chlorine or sulfur to water is undesirable; electrochemistry provides an environmentally preferred method to introduce ferrous iron into solution. The electroreduction of ferric iron (Tzedakis et al., 1989) and oxygen (Sudoh et al., 1986) has been demonstrated and the products (respectively Fe2? and H2 O2 ) utilized to destroy benzene and phenolic compounds via Fenton's reagent. Recent studies have employed the electrogeneration of Fe2? in combination with H2 O2 to destroy a variety of aqueous phase organic compounds including pesticides, VOCs, BTEX, polychlorinated biphenyls (PCBs), chlorinated solvents, and organic dyes (Pratap and Lemley, 1994, 1998; Roe and Lemley, 1997). Electrochemical peroxidation (ECP) is a patented process (US Patent #6,045,707) that has been applied to degrade organic contaminants in various aqueous matrices (septic tank water, groundwater, slurries, pulp and paper waste) in previous studies (Chiarenzelli et al., 2000a). A byproduct of the process, colloidal iron hydroxide, is a voracious metal scavenger and has also been utilized to remove heavy metals from aqueous solutions (Pratap and Lemley, 1994) and thus may provide a potential solution for waters co-contaminated by organic compounds and metals. This study reports on the combined treatment of PCB-contaminated river sediment by steam extraction coupled with ECP. 2. Experimental procedures 2.1. Reagents and environmental samples All reagents utilized including hexane, sodium sulfate, sulfuric acid, tetrabutylammonium sulfate, and Florisil were reagent grade and checked for purity before use. Double-deionized water (DDI) was used throughout. Sediment consisting of ?ne-grained sand and mud, was obtained from a small cove along the St. Lawrence River adjacent to the General Motors Federal Superfund site located near Massena, New York (Chiarenzelli et al., 2000b) and contained 8:65 lg=g PCBs (wet weight). 2.2. PCB extraction and gas chromatography Water samples were extracted by three sequential liquid/liquid separations with hexane. Sediment was extracted by three sequential sonications with acetone, acetone/hexane (1:1), and hexane. Decachlorobiphenyl (DCB) was added to water and sediment samples before extraction as a surrogate standard. The extracts were

dried using sodium sulfate, oxidized with sulfuric acid and cleaned with tetrabutylammonium sulfate and 4% deactivated Florisil columns. The hexane extract was condensed and stored at 4°C until analyzed. Congener speci?c PCB analysis was performed on a HP5890 gas chromatograph using an electron capture detector and an Ultra DB-5 column (Pagano et al., 1995). All samples were analyzed in duplicate. 2.3. Steam extraction pretreatment A steam extraction pre-treatment step was utilized to remove PCBs from the sediment. A 500 g sample of sediment (Media A, Table 1) contaminated with 8:65 lg=g PCB was placed in a round bottom ?ask with 1 l of DDI water, boiled, and condensed in Nielsen± Kryger distillation unit (Veith and Kiwus, 1977). Double deionized water was incrementally added to the round bottom ?ask so that a total volume of 2 l of condensate was collected at a rate of  150 ml per hour. Condensate was collected in a separatory funnel and subsampled every 250 ml (Media C±J, Table 1) by draining the bottom 200 ml from the funnel to monitor aqueous phase PCBs. The remaining upper 50 ml was extracted separately to measure the PCB mass in small amounts of an oil phase (Media K±R, Table 1) observed ?oating on the water and coating the interior of the separatory funnel. Repeat hexane rinses were used to recover oil and small white crystals from the interior of the distillation apparatus (Media S, Table 1). After steam extraction, sediment subsamples were sonicated to measure the residual PCB concentration (Media B, Table 1). 2.4. ECP treatment 1 l of PCB contaminated condensate from the steam extraction pre-treatment step was added to a glass beaker and stirred for 30 min. Duplicate 25 ml control samples were then taken (Controls, Table 2) and the pH of the water adjusted to 5 with nitric acid. Nested steel pipe electrodes (2 and 1.5 in. diameters) were immersed into the beaker. Ten volts were applied and the current was allowed to vary during the experiment (0.75±1.0 A). The polarity of the electrodes was switched every 5 s. The initial pH, temperature, and amperage were measured. One milliliter of 3% H2 O2 solution was added corresponding to a solution concentration of 43 lg=ml. The concentration of H2 O2 (measured using EM-Quant test strips and a re?ectance meter, EM Science), temperature, pH, and amperage were monitored at 5 min intervals. By 10 min the H2 O2 concentration dropped below 1 mg/l and an additional ml of 3% H2 O2 was added and experimental parameters monitored. This was repeated twice. The cumulative treatment time was

J.R. Chiarenzelli et al. / Chemosphere 45 (2001) 1159±1165 Table 1 Data from the steam distillation experimenta Mediab A. Sediment (initial) B. Sediment (after) C. Condensate ± 0.25 l D. Condensate ± 0.50 l E. Condensate ± 0.75 l F. Condensate ± 1.00 l G. Condensate ± 1.25 l H. Condensate ± 1.50 l I. Condensate ± 1.75 l J. Condensate ± 2.00 l K. Oil ± 0.25 lc L. Oil ± 0.50 l M. Oil ± 0.75 l N. Oil ± 1.00 l O. Oil ± 1.25 l P. Oil ± 1.50 l Q. Oil ± 1.75 l R. Oil ± 2.00 l S. Glassware rinse T. Residual water
a b

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PCB mass (mg) 4.320 0.355 0.106 0.075 0.059 0.085 0.054 0.050 0.042 0.030 1.832 1.387 0.375 0.082 0.021 0.024 0.028 0.019 0.201 0.0001

PCB homologues (%) 6 Cl3 72.1 44.1 95.2 90.9 89.1 74.0 85.6 84.4 83.2 82.6 78.2 68.6 58.9 50.0 57.5 47.8 47.5 44.5 67.3 20.3 Cl4±6 23.0 42.6 4.7 8.9 10.5 24.6 13.7 14.7 15.5 15.9 21.3 30.2 38.5 46.1 37.1 45.5 45.0 45.7 29.4 47.6 P Cl7 4.9 13.3 0.1 0.2 0.4 1.4 0.7 0.9 1.2 1.5 0.5 1.1 2.6 3.9 5.4 6.7 7.5 9.3 3.3 32.1

Cl/Bi 3.13 3.80 2.01 2.20 2.23 2.68 2.34 2.44 2.46 2.44 2.71 2.94 3.14 3.43 3.10 3.46 3.44 3.64 3.18 5.09

Recovery of decachlorobiphenyl surrogate ranged from 77% to 105%. All values reported are the average of duplicate subsamples. c Exact volume of oil unknown; cumulative volume was less than 1 ml.

Table 2 Data from the electrochemical peroxidation experimenta Condensateb (1 l volume) Controls ECP treatment #1 (10 min) ECP treatment #2 (20 min) ECP treatment #3 (30 min)
a b

Conc. (lg=l) 181.5 26.7 14.5 9.0

C/C0 (%) 100 14.7 8.0 5.0

PCB homologues (%) 6 Cl3 88.8 75.2 59.0 47.9 Cl4±6 10.4 22.4 35.0 44.7 P Cl7 0.8 2.4 6.0 7.4

Cl/Bi 2.24 2.72 3.28 3.63

Recovery of decachlorobiphenyl surrogate ranged from 87% to 96%. All values reported are the average of duplicate samples.

30 min and duplicate 25 ml subsamples were taken at 10, 20, and 30 min (Table 2). 3. Results and discussion 3.1. Steam extraction Visual observation of the distillation experiment indicated that small amounts of clear yellow oil collected in the separatory funnel and white crystals on glassware surfaces. The oil ?oated on top of the water suggesting it was not pure phase PCBs; however, concentrations in discrete oil samples were as much as 12% PCBs by weight. Aqueous phase PCB concentrations of the condensate varied from 531 to 151 lg=l (Fig. 1) and gen-

erally decreased with each successive extraction. However, at a cumulative volume of 1 l, an increase in condensate PCB concentration was noted. The mass balance for the experiment was 111.7%. PCBs were recovered from the oil phase (78.1%), condensate (10.4%), glassware rinse (4.2%), and extracted sediment (7.4%). The PCB mass of the sediment was reduced by 91.8% from 4.32 to 0.36 mg (Media A and B, Table 1). At the end of the steam distillation extraction step,  500 ml of water containing 1.3 ng/ml PCBs (0.01%) remained in the round bottom ?ask containing the sediment (Media T, Table 1). Given the range of aqueous solubilities and vapor pressures for individual PCB congeners (Dunnivant et al., 1992; Ruelle et al., 1993), partitioning of PCBs was expected during the steam distillation extraction

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including from 4 to 6 chlorines (4.7 ! 15.9%) and seven or more chlorines ?0:1 ! 1:5%?. Similar trends are seen in the oil phase (Media K±R, Table 1). However, again at a cumulative volume of 1.0 l the trend is disrupted and a more chlorinated fraction of PCBs recovered. 3.2. Electrochemical peroxidation treatment The starting PCB concentration of the condensate was 181:5 lg=l. After 10 min of ECP treatment, the PCB concentration of condensate (determined from duplicate 25 ml subsamples) was reduced to 26:7 lg=l (Fig. 3, Table 2). After the third and ?nal treatment (30 min), the concentration was 9:0 lg=l, a reduction of 95% (Fig. 3, Table 2). During treatment, the pH of the solution varied from 3.2 to 5.5 and the peak in acidity corresponded to H2 O2 additions and the initiation of Fentons Reagent. The exothermic nature of the reaction caused an increase in temperature from 16.8°C to 22.3°C during the experiment. The current dropped after the initial treatment to 0.75 A, then slowly rose and remained relatively constant at 1.0 A afterwards. PCB congeners with greater chlorination were expected to be more resistant to free radical attack during ECP treatment of the aqueous phase condensate. An increase in the chlorine/biphenyl ratio of the condensate was observed (2.24±3.63) during treatment (Fig. 4), suggesting preferential destruction of lower chlorinated congeners. The congener-speci?c changes occurring during ECP treatment of the condensate are shown in Fig. 5. In general, the lower chlorinated congeners (left side of the diagram) show greater levels of disappearance than those with more chlorine did. Again a similar trend is shown in the homolog groupings; each successive treatment resulted in a residual fraction containing a greater proportion of higher chlorinated congeners (Table 2). Since hydroxylation is an important initial step in the PCB degradation pathways (Hong et al., 1998) lower chlorinated congeners may be more sus-

Fig. 1. Measured PCB concentrations in aqueous condensate by cumulative volume. Error bars show standard deviation.

step. The average chlorine/biphenyl (Cl/Bi) ratio of the aqueous condensate shows a general increase from 2.0 to 2.4 (17%) during the extraction (Fig. 2). At a cumulative volume of 1 l, a sharp increase in the ratio occurs coincidentally with the spike in concentration shown in Fig. 1. The reason for this increase in both concentration and Cl/Bi ratio is unknown. The Cl/Bi ratio of PCBs recovered from the extracted sediment by sonication increased by 18% over its initial value (3.1±3.8; Media A and B, Table 1). This suggests that lower chlorinated congeners were preferentially extracted during steam distillation. Analyzing the PCBs recovered by homologue groups also suggests that the lower chlorinated congeners were extracted ?rst and to a greater extent (Table 1). This is true for both the condensate and oil phase recovered. Congeners with three or less chlorines made up 95.2% of the initial 250 ml of condensate collected, but only 82.6% of the ?nal 250 ml. Consequentially large increases in proportion were measured in congener groups

Fig. 2. Chlorine per biphenyl (Cl/Bi) ratio of PCB fraction of aqueous condensate by cumulative volume.

Fig. 3. Measured PCB aqueous phase concentration during ECP treatment with time.

J.R. Chiarenzelli et al. / Chemosphere 45 (2001) 1159±1165

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Fig. 4. Chlorine per biphenyl (Cl/Bi) ratio of PCB fraction of aqueous condensate during ECP treatment.

ceptible to ECP destruction because of the greater number of sites available for hydroxylation. Alternatively, the lower solubility of more highly chlorinated congeners may inhibit interaction with oxidative species produced in the aqueous phase. In either case, the negative correlation between the extent of congener disappearance and chlorination may have important practical implications for PCB destruction by AOTs. 3.3. Degradation mechanism A variety of advanced oxidation technologies have been used to destroy aqueous phase PCBs. These include TiO2 photocatalysis (Carey et al., 1976), Fenton's Reagent (Sedlack and Andren, 1991), and UV/Fe3? =H2 O2 (Pignatello and Chapa, 1994). In each case the primary oxidant species is the hydroxyl radical which mediates the destruction of the PCB molecule and various inter-

mediates. A degradation sequence that involves early hydroxylation, followed by the formation of aldehydes, ketones, and acids, and results in the eventual production of CO2 and HCl has been identi?ed (Pignatello and Chapa, 1994; Hong et al., 1998). The ECP process utilizes sacri?cial steel electrodes and small amounts of current to electrogenerate Fe2? . Stoichiometric additions of H2 O2 are combined with the ferrous iron to e?ect Fenton's reagent. The hydroxyl radicals produced react with the PCBs resulting in the degradation sequence outlined above. While other mechanisms including reactions with solvated electrons (Patermarakis and Fountoukidis, 1990), zero valent iron (Rogers et al., 1999), and cathodic oxidation and anodic reduction (Chiarenzelli et al., 2000a), are possible, the relatively short reaction times observed favor Fenton's reagent as the dominant degradation mechanism. 3.4. Enhancements and process considerations One possible limitation of the application of the ECP process is the relatively low solubility of iron in near neutral aqueous solutions. Several ways to increase Fe2? concentrations in solution have been investigated. These include increasing the electrode mass/surface area, decreasing electrode spacing (and thereby increasing current at a given voltage), increasing retention time by utilizing ?ow through pipe reactors, periodically reversing the current to double the iron surface available for corrosion (Chiarenzelli et al., 2000a), and increasing solution conductivity with soluble salts (Pratap and Lemley, 1994, 1998; Roe and Lemley, 1997). Signi?cant advantages occur in oxidizing e?ciency when Fe2? and H2 O2 are added incrementally rather than in a single large dose (Roe and Lemley, 1997;

Fig. 5. Congener-speci?c changes in the concentration of aqueous phase PCBs after 10 min of ECP treatment. Note that the most abundant lower chlorinated congeners are nearly eliminated resulting in an overall destruction of 85% of the original PCB mass (Table 2). Congeners are listed by International Union of Pure and Applied Chemistry numbers and peaks without corresponding bars were not detected.

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J.R. Chiarenzelli et al. / Chemosphere 45 (2001) 1159±1165 Chiarenzelli, J., Scrudato, R., Wunderlich, M., Ra?erty, D., Roberts, R., Pagano, J., 1995b. Photodecomposition of PCBs absorbed on sediment and industrial waste: Implications for photocatalytic treatment of contaminated solids. Chemosphere 31, 3259±3272. Chu, W., 1999. Photodechlorination mechanism of DDT in a UV/surfactant system. Environ. Sci. Technol. 33, 421± 425. Cooke, M., Nickless, G., Povey, A., Roberts, D., 1979. Polychlorinated biphenyls, polychlorinated napthalenes and polynuclear aromatic hydrocarbons in Severn Estuary (UK) sediments. Sci. Total Environ. 13, 17±26. Dunnivant, F., Elzerman, A., Jurs, P., Hasan, M., 1992. Quantitative structure±property relationships for aqueous solubilities and Henry's Law constants of polychlorinated biphenyls. Environ. Sci. Technol. 26, 1567±1573. Hong, C-S., Wang, Y., Bush, B., 1998. Kinetics and products of the TiO2 photcatalytic degradation of 2-Chlorobiphenyl in water. Chemosphere 36, 1653±1667. Huang, I-W., Hong, C-S., Bush, B., 1996. Photocatalytic degradation of PCBs in TiO2 aqueous suspensions. Chemosphere 32, 1869±1881. Masten, S., Davies, S., 1994. Use of ozone and other strong oxidants for hazardous waste management. In: Nriagu, J., Simmons, M. (Eds.), Environmental Oxidants. Wiley, New York, pp. 517±547. Pagano, J., Scrudato, R., Roberts, R., Bemis, J., 1995. Reductive dechlorination of PCB-contaminated sediments in an anaerobic bioreactor system. Environ. Sci. Technol. 29, 2584±2589. Patermarakis, G., Fountoukidis, E., 1990. Disinfection of water by electrochemical treatment. Water Res. 24, 1491±1496. Pelizzetti, E., Minero, C., Carlin, V., Borgarello, E., 1992. Photocatalytic soil decontamination. Chemosphere 25, 343± 351. Pignatello, J., Chapa, G., 1994. Degradation of PCBs by ferric iron, hyrdogen peroxide and UV light. Environ. Toxicol. Chem. 13, 423±427. Pratap, K., Lemley, A., 1994. Electrochemical peroxide treatment of aqueous herbicide solutions. J. Agric. Food Chem. 42, 209±215. Pratap, K., Lemley, A., 1998. Fenton electrochemical treatment of aqueous Atrazine and Metolachlor. J. Agric. Food Chem. 46, 3285±3291. Roe, B., Lemley, A., 1997. Treatment of two insecticides in an electrochemical Fenton system. J. Environ. Sci. Health B 32, 261±281. Rogers, J., Jedral, W., Bunce, N., 1999. Electrochemical oxidation of chlorinated phenols. Environ. Sci. Technol. 33, 1453±1457. Ruelle, P., Buchman, M., Nam-Tran, H., Kesselring, U., 1993. Application of the mobile order theory to the prediction of aqueous solubility of chlorinated benzenes and biphenyls. Environ. Sci. Technol. 27, 266±270. Sedlack, D., Andren, A., 1991. Aqueous phase oxidation of polychlorinated biphenyls by hydroxyl radicals. Environ. Sci. Technol. 25, 1419±1427. Sudoh, M., Kodera, T., Sakai, K., Zhang, J-Q., Koide, K., 1986. Oxidative degradation of aqueous phenol e?uent with electrogenerated Fenton's reagent. J. Chem. Eng. Soc. Jpn. 19, 513±518.

Chiarenzelli et al., 2000a). Hydroxyl radicals can react with H2 O2 thus limiting their e?ciency in degrading target compounds. The speed of the observed reactions and monitoring of H2 O2 concentrations suggest a retention time of 5 min or less was su?cient to produce enough Fe2? to reduce H2 O2 concentrations to below 1 lg=ml. In spite of solubility limitations, signi?cant degradation was observed at a pH of 5, with sub-ppm Fe2? concentrations, and small (43 lg=ml) H2 O2 additions. The data presented suggest that at even relatively small (4:1) water to sediment ratios (2 l:500 g) signi?cant amounts (>90%) of PCBs can be extracted from aged sediment by steam distillation. Further,  82% of the PCBs extracted are carried in a small volume of ?oating oil which can be readily separated and recovered. ECP treatment of the condensate destroyed >95% of the aqueous phase PCBs. After extraction, the residual PCBs remaining in the sediment are relatively insoluble and unlikely to enter the aqueous phase. As previously reported (Pignatello and Chapa, 1994; Chiarenzelli et al., 1995a; Huang et al., 1996; Chiarenzelli et al., 2000a) lower chlorinated PCBs are both more easily extracted and destroyed than higher chlorinated congeners. The combination of extraction and AOT treatment of aqueous contaminants may present a viable solution to the treatment of sediments contaminated with recalcitrant organic compounds. Acknowledgements The authors gratefully acknowledge funding from the National Institute of Environmental Health Sciences Superfund Basic Research Program (grant P42 ESO4913) administered by the University at Albany Program. Drs. Ezio Pelizzetti and Chia-Swee Hong are thanked for critical review of the paper and A. Hutzinger for editorial handling. References
Carey, J., Lawrence, J., Tosine, H., 1976. Photodechlorination of PCBs in the presence of titanium dioxide in aqueous suspensions. Bull. Environ. Contam. Toxicol. 16, 697±701. Chiarenzelli, J., Falanga, L., Wunderlich, M., 2000a. Benchand pilot-scale applications of electrochemical peroxidation: A new remedial concept. Remediation 10, 3±17. Chiarenzelli, J., Bush, B., Casey, A., Barnard, B., Smith, R., O'Keefe, P., Gilligan, E., 2000b. Monthly monitoring of airborne polychlorinated biphenyls along the St. Lawrence River at Akwesasne. Can. J. Fisheries Aquatic Sci. 57, 86±94. Chiarenzelli, J., Scrudato, R., Ra?erty, D., Wunderlich, M., Roberts, R., Pagano, J., 1995a. Photocatalytic degradation of simulated pesticide rinsates in water and water ? soil matrices. Chemosphere 30, 173±185.

J.R. Chiarenzelli et al. / Chemosphere 45 (2001) 1159±1165 Swackhammer, D., Anderson, D., 1986. Estimation of the atmospheric and nonatmospheric contributions and losses of polychlorinated biphenyls for Lake Michigan on the basis of sediment records of remote lakes. Environ. Sci. Technol. 20, 879±883. Tzedakis, T., Savall, A., Clifton, M., 1989. The electrochemical regeneration of Fenton's reagent in the hydroxylation of aromatic substances: Batch and continuous processes. J. Appl. Electrochem. 19, 911±921.

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Veith, G., Kiwus, L., 1977. An exhaustive steam-distillation and solvent-extraction unit for pesticides and industrial chemicals. Bull. Environ. Contam. Toxicol. 17, 631±636. Walling, C., 1975. Fenton's reagent revisited. Accounts Chem. Res. 8, 125±131. Zhang, P-C., Scrudato, R., Pagano, J., Roberts, R., 1993. Photodecomposition of PCBs in aqueous systems using TiO2 as catalyst. Chemosphere, 26,1213±1223.


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