Environ. Sci. Technol. 1988, 22, 1182-1 186
Degradation and Dehalogenation of Polychlorobiphenyls and Halogenated Aromatic Molecules by Superoxide Ion and by Electrolytic Reduction Hiroshl Sugimoto, Shigenobu Matsumoto, and Donald T. Sawyer *
Department of Chemistry, Texas A&M University, College Station, Texas 77843 Polyhalogenated aromatic hydrocarbons (e.g., PCBs and hexachlorobenzene) are rapidly degraded by superoxide ion in dimethylformamide to carbonate and halide ions. The efficient destruction of such materials is accomplished via the in situ electrolytic reduction of dissolved oxygen to generate superoxide ion, which reacts with polyhalo aromatics by nucleophilic substitution. The reaction stoichiometries have been determined by cyclic voltammetric measurements, and the reactant/product profiles have been assayed by capillary gas chromatography and potentiometric titrations. For decachlorobiphenyl (Cl2CllO) the overall reaction is C12Cl10+ 2202’- 6H20 12 HOC(0)O- + 1OC1- + 702. Analogous complete destruction by superoxide ion occurs for PCB’s that contain three or more chlorine atoms per aromatic ring. Another means to the dehalogenation of halo aromatic hydrocarbons is their electrolytic reduction to the parent hydrocarbon in oxygen-free dimeth lformamide solutions (e.g., C12Cl10 10HzO + 20e- -2.6JGvssc$ C12Hlo + 1OC1- + 10-OH). Electrochemical studies confirm that all PCB’s can be dehalogenated via anaerobic electrolysis.
+
-
+
Polyhalogenated aromatic hydrocarbons (PCB’s, PBB’s, and hexachlorobenzene) represent a major environmental problem (1,2).These materials, which were extensively used as transformer oils and heat-exchanger fluids since 1929, are major components of the hazardous waste disposal problem of the EPA Superfund. The chemistry and toxicology of PCB’s, and of their impurities and partially oxygenated products (e.g., dioxins), have been extensively reviewed (3-5). Clearly the materials contain components that are animal carcinogens and can cause birth defects (6-8),and their continual release into the ecosystem has a deleterious effect on animal life [e.g., contamination of the blue fish in New York Harbor (9)]. Hexachlorobenzene, which is a byproduct of the poly(chloroethy1ene) solvent industry, is as environmentally persistent as PCB’s and is a human carcinogen (10, 11). Although storage and dispersal in landfills have been used for PCB’s in the past, their long environmental life has lead to the contamination of lakes, rivers, coastal estuaries, and groundwater. Currently, incineration is the most utilized technology for the destruction of halogenated aromatic hydrocarbons. The best systems are highly efficient in their conversion of PCB’s to HC1, C02, and H2O but appear to produce some dioxins (12). The major focus of a recent conference on PCB’s is the need for more effective technology for their destruction (13). In a recent report (14)we have described the facile and complete destruction of hexachlorobenzene by superoxide to give bicarbonate and chloride ions as the only ion (099%) (18). The PCB mixtures (Arochlor 1242,1262, and 1268) were obtained from Alltech, and decachlorobiphenyl was (Cl2CllO)from Supelco, and all were assayed by gas chromatography. Tetramethylammonium superoxide [(Me4N)02]was prepared by a solid-phase metathesis procedure from KO2 and (Me4N)OH.5H20(19,20). Methods. The reactivity of substrates with (Me4N)02 was determined via their addition to known excess amounts of 02’-(such that about 5 0 4 0 % of the 0;-was consumed) in dimethylformamide. Subsequent measurement of the unreacted 02‘-concentration by anodic voltammetry provided the stoichiometric ratios for the quantity of 02’-consumed per mole of substrate. The apparent rates of reaction for superoxide ion with the various substrates were determined from cyclic voltammetric peak-current measurements (21). The reaction products were characterized after stoichiometric amounts (10-20-mM concentrations) of substrate and superoxide ion were combined. Aliquots of the reaction mixture were analyzed for chloride ion by potentiometric titration with AgNO, and for base by an aqueous pH titration with HCl. The reaction mixture was directly analyzed by gas chromatography for organic components and residual substrate (22, 23).
Within DMF (0.1 M TEAP) solutions that contained substrate (10-15 mM) and O2 (1atm) a gold-plated electrode (area, -20 cm2)was controlled at -1.0 V vs SCE by During a potentiostat (BAS Model SP-2) to generate 02’-. the course of electrolysis, the solution was sampled and analyzed by capillary column gas chromatography. For the electroreductive dehalogenation experiments, a DMF (0.1 M TEAP) solution of substrates (10-20 mM) was electrolyzed at -2.5 V vs SCE at a gold-plated electrode (area, 20 cm2)under an argon atmosphere. During the
-
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0 1988 American Chemical Society
Table I. Reactions of Superoxide Ion with Polychloro Aromatics in Dimethylformamide
c1substrates (s)
Oi-/s 12.0
c6c1S
* 1.0 * *
released/ S 6.0 f 0.5
base released/ S 6.0 f 0.6
(1 A\
k1/ [SI, M-1 s-la 1X losb
22.0 f 4.0 10.0 & 1.0 12.0 f 2.0 2 X 10' C12C110 21.0 4.0 8.7 f 1.0 12.0 f 2.0 8 X 10' Arochlor 1268 (C12HCldav Arochlor 1262 19.0 4.0 6.8 i 1.0 12.0 f 2.0 3 X 10' (ClzH3C1d av Apparent pseudo-first-order rate constants, k (normalized to unit substrate concentration [SI),were determined from the ratio (iandic/iea~die) for the cyclic voltammogram of O2 in the.presence of excess substrate, ref 21. For C6Hcl5, 1,2,3,4-CsH2C14,1,2,4C6H3C13,CC4,and PhCC13, the respective values of kl/ [SI are 80, 2, 0.02, 1 X lo3, and 40 M-' 8,ref 14. *The values of k , / [ S ] for c&&in MeCN, Me2S0,and py solvents are 92,47, and 47 M-'s-', respectively.
A. Arochlor 1268
i' E,V vs SCE
Flgure 2. Cyclic voltammograms for dlssolved O2 (1 atm, 4.8 mM) In dimethylformamide (0.1 M tetraethylammonium perchlorate) at a glassy carbon electrode. The effect of 2 mM c&I, and 3 mM c&I, on the peak is illustrated by the dashed (---) and dash-dot ( - e - ) curves, respectively. Electrode area, 0.062 cm2; scan rate, 0.1 V s-'.
1," II
E. Arochlor 1268
+ 20 02 for 12 hours
matograms for Arochlor 1268 (a commercial PCB mixture of CI2Cll0,C12HC19,and CI2H2Cl8molecules) before exposure to 0;-and after 12 h in the presence of excess O;-. In accord with the kinetic data of Table I, the more heavily chlorinated isomers react first, and the initial step is rate-determining (21,24). The cyclic voltammograms for the reduction of O2to 02' in the absence and presence of c6c16 are illustrated in Figure 2. The enhancement in the cathodic peak current and the decrease in the peak current for the reverse scan that result from the presence of C&l6 indicate a facile multistep reaction between 02'-and c6c16. The destructive decay of the components of Arochlor 1268 that results from the electrolytic reduction of oxygen to 02'-in an air-saturated DMF solution is presented in Figure 3. This illustrates a system whereby heavily chlorinated PCB's can be degraded to inorganic ions in a continuous electrolytic reactor. Product assays of numerous related experiments confirm that the initial step is rate-limiting and that organic intermediates do not accumulate in the reactor. Electroreductive System. Figure 4 illustrates the electrolytic reduction of c&&, 1,2,3,4-C6H2C1,,Cl2CllO,and Arochlor 1268 in DMF at a glassy carbon electrode. Similar experiments for the other chloro derivatives of benzene and biphenyl confirm that each of the six peaks of Figure 4a is due to the successive reduction of the six chlorine atoms of c6c16. The decay and product profiles for the electrolytic reduction of C6C16are illustrated by Figure 5 and indicate that reduction produces the hydro derivative If the of the substrate molecule (e.g., C&C& from c&&). electrolysis of Figure 5 is controlled at -2.8 V vs SCE instead of -2.5 V, the final product is benzene rather than chlorobenzene (PhC1). Figure 6 illustrates the change in the composition of the Arochlor 1268 PCB mixture (average chlorine content, Environ. Sci. Technol., VoI. 22, No. 10, 1988
1183
Arochlor 1268 4 8mM O,(lafrn) Electrolysis at -1.oV vs SCE Au electrode in DMF
5
I
i 4 m cecie ~ in DMF, E i e ~ l r ~ lat~ -2 s i5V ~ YB SCE
Electrolysis time, hr
Flgure 3. Concentration profiles for the various PCB isomers of Arochlor 1268 during the course of an In sku electrolytic reductlon (-1.0 V vs SCE) of dlssolved O2 (1 atm, 4.8 mM) in DMF (0.1 M TEAP) at a gold-mesh electrode (-20 cm2). Sample concentration, 50 mg of Arochlor 1268 In 10 mL of DMF.
Electrolysis Time, h r
Flgure 5. Concentration profiles for the controlled potentlal (-2.5 V vs SCE) electrolysis of 14 mM C CI in DMF (0.1 M TEAP) at a goldmesh electrode (area, -20 cm2y. ?he relative amounts of products and reactants were determlnated by capillary gas chromatographic analysis of samples from the electrolysis solution. I
I
l A
Arochior 1268[50mg in lOml DMF(0 1M TEAP)]
B After Reductive Electrolysis at -2.5V vs SCE; 1hr
/ B 1,2,3,4 - CsHzCI.
I
--A-
1
~
~~
C
3hl
D.
5hr
D. Arochlor 1268
1OOpA
5
-1 0
-2 0
10
15
20
-3 0
GC R e t e n t i o n time, min
E,V vs SCE
Flgure 4. Cyclic voltammograms for chlorinated aromatic molecules In dlmethylformamide (0.1 M TEAP) at a glassy carbon electrode (area, 0.062 Cm2): (A) 1.1 mM CC , ;,I (B) 2.3 mM 1,2,3,4-C6H,Cl4; (C) 1.3 mM Cl2Cll0; (D) 1 mg/mL Arochlor 1268. Scan rate, 0.1 V s-’.
68% by weight) during the course of its controlled potential (-2.5 V vs SCE) reduction in dimethylformamide. The most heavily chlorinated derivatives of biphenyl are 1184
Eflvlron. Sci. Technol., Vol. 22, No. 10, 1988
Flgure 6. Gas chromatograms for Arochlor 1268 in DMF and for the product solution during the course of its electrolytic reduction at -2.5 V vs SCE with a 20-cm2 gold-mesh electrode. The peak with a retention time of 2 min is biphenyl, and that at 5 mln is chlorobiphenyl.
reduced first to the “lighter” members of the series; all are ultimately reduced to biphenyl. This experiment and that of Figure 5 demonstrate that halogenated aromatic hydrocarbon wastes (PCB’s, PBB’s, and halobenzenes) can
be completely dehalogenated to their parent hydrocarbons by electrolytic reduction in dimethylformamide. Such a system provides an efficient means for the safe transformation of these toxic materials into useful products.
by electrolytic reductions at a graphite or gold cathode with Me4NC1 as the supporting electrolyte. The data from Figures 4-6 indicate that the overall electrolysis reactions and c12Clloyield C&&Cland C12H10,respectively: for c&&
Discussion and Conclusions
The data of Table I confirm that the overall reaction stoichiometry for halogenated aromatic molecules is two 0;- ions per carbon-halogen and one per non-halogenated carbon: c6cI6
+
1202'-
-
+
3C206'-
+
6CI-
(1)
302
-
However, when 02'-is generated in situ by electrolytic reduction (at -1.0 V vs SCE) of dissolved O2 (0, + e02'-, Figure 2), the product O2of reaction 1is recycled and the overall electrolytic reaction becomes c6c16
-
+ 9 0 2 + 12e- 3c202-+ 6C1-
(2)
Likewise, for C6H2C1,and ClzCllothe respective superoxide and electrolytic stoichiometries are C6H2C14
+
100;-
-
2C20e2-
+
k
+
2HOC(0)0-
+
4HOC(0)0-
4'21-
+
02
02
(3)
C&&1
+
+
Cl2Cll0 10H20 20e-
-+
+ 5 c1- + 5-OH
(9)
-2.5 V
C12H10 1OC1- + 10-OH (10)
The anodic process involves the oxidation of the chloride ion that is produced in the cathode compartment: C1-
+ -OH
-
HOC1 + 2e-
(11)
Again the overall process is equivalent to an electrostimulated oxidation of water (eq 10 plus eq 11): ClzCllo lOH2O ClzHlo + lOHOCl (12)
+
with the anionic products produced at the cathode transfered via diffusion to the anode and oxidized to HOC1. Both systems provide the means to destroy and dehalogenate PCB's, PBB's, and related halogenated aromatic hydrocarbons. The superoxide-mediated process is effective for those substrates that contain three or more halo atoms per aromatic ring. For those halo aromatics that contain less than three halo atoms per ring, the electrolytic reduction process provides complete dehalogenation to give the parent hydrocarbon. Registry No. DMF, 68-12-2; Arochlor 1268, 11100-14-4;Ar1262,37324-23-5;c&&, 118-74-1;C&C&, 608-93-5;c12C110, 2051-24-3; 1,2,3,4-C6H&14, 634-66-2; O2'-, 11062-77-4. OChlOl'
These equations indicate the quantities of superoxide ion [from (Me,N)02 or KO2] required to destroy a halogenated aromatic hydrocarbon. The electrogeneration of 0;- from dissolved air represents a much more practical approach for an effective system to destroy PCB's and other halogenated aromatic hydrocarbons. A reasonable electrolytic reactor to process such wastes would involve graphite cathodes and anodes with Me4NC1as the supporting electrolyte in dimethylformamide and the cathode compartment saturated with air or pure O2 at 1atm. PCB's would be introduced into the cathode compartment and degraded by the reductive activation of dioxygen (eq 2,4,6). The anode reaction for this reactor involves the oxidation of the chloride ion produced in the cathode compartment: CI-
+
2HOC(0)0-
-
HOC1
+
C02
+
(7)
2e-
Clp
+
HOC(0)O-
Thus, the overall electrolysis reaction is the equivalent of an electrostimulated combustion (eq 2 plus eq 7)
with the anionic products produced at the cathode transferred via diffusion to the anode and oxidized t o C02 and C12. In the absence of dioxygen, halogenated aromatic hydrocarbons can be converted to their parent hydrocarbon
Literature Cited Waid, J. PCBs and The Environment; CRC Press: Boca Raton, FL, 1986; Col. 1-111. D'Itri, F. M.; Kamrin, M. A. PCBs: Human and Enuironmental Hazards; Ann Arbor Science Book Boston, 1983. Hutzinger, 0.;Safe, S.; Zitko, V. The Chemistry of PCBs; CRC Press: Cleveland, OH, 1974. Safe, S.; Bandiera, S.; Sawyer, T.; Robertson, L.; Safe, L.; Parkinson, R.; Thomas, P. E.; Ryan, D. E.; Reik, L. M.; Levin, W.; Denomme, M. A.; Fujita, T. EHP, Environ. Health Perspect. 1985,60,47-56. Safe, S. CRC Grit. Rev. Toxicol. 1984, 13, 319-396. Kimbrough, R. D. CRC Grit. Rev. Toxicol. 1974,2,445-498. Fishbein, L. Annu. Rev. Pharmacol. 1974, 14, 139-156. McConnell, E. E.; Moore, J. A. Ann. N.Y. Acad. Sci. 1979, 320, 138-150. Bryant, N. New York Times, Aug 9, 1987, p 21. Takazawa, R. S.; Strobel, H. W. Biochemistry 1986,25, 4804-4809. Cabral, J. R. P.; Shubik, P.; Mollner, T.; Raitano, F. Nature (London) 1977,269,510-511. Karasek, F. W.; Dickson, L. C. Science (Washington,D.C.) 1987,237, 754-756. "PCB Seminar", Oct 6-9, 1987, Hyatt Regency Hotel, Kansas City, MO; Electric Power Research Institute, Palo Alto, CA; 1987. Sugimoto, H.; Matsumoto, S.; Sawyer, D. T. J. Am. Chem. SOC.1987,109,8081-8082. Sawyer, D. T.; Roberts, J. L., Jr. U.S.Patent 4410402, Oct 18, 1983. Sawyer, D. T.; Caldenvood, T. S. U.S. Patent 4468297, Aug 28, 1984. Chin, D.-H.; Chiericato, G., Jr.; Sawyer, D. T. J. Am. Chem. SOC.1982, 104, 1296-1299. Rausch, M. D.; Tibbetts, F. E.; Gordon, H. B. J. Organometal. Chem. Rev. 1966, 1, 493. Sawyer, D. T.; Calderwood, T. S.; Yamaguchi, K.; Angelis, C. T. Inorg. Chem. 1983,22,2577-2583. Environ. Sci. Technol., Vol. 22, No. 10, 1988 1185
Environ. Sci. Technol. 1988, 22, 1186-1 190
Yamaguchi, K.; Calderwood, T. S.; Sawyer, D. T. Znorg. Chem. 1986,25, 1289-1290. Nicholson, R. S.; Shain, I. Anal. Chem. 1964,36,706-723. Mullin, M. D.; Pochini, C. M.; McCrindle, S.; Romkes, M.; Safe, S. H.; Safe, L. M. Environ. Sci. Technol. 1984, 18, 468-476. Ballschmiter, K.; Zell, M.; Fresenius' 2.Anal. Chem. 1980, 302, 20-31.
(24) Roberts, J. L., Jr.; Calderwood, T. S.; Sawyer, D. T. J. Am. Chem. SOC.1983, 105, 7691-7696. Received for review October 8, 1987. Accepted March 14,1988. This work was supported by the National Science Foundation under Grant CHE-8516247 and by the Welch Foundation under Grant A-1042.
Small Molecular Weight Organic Amino Nitrogen Compounds in Treated Municipal Waste Watert Frank E. Scully, Jr.," G. Dean Howell, Helen H. Penn, and Kathryn Marina
Department of Chemical Sciences, Old Dominion University, Norfolk, Virginia 23529-0126 J. Donald Johnson
Department of Environmental Sciences and Engineering, University of North Carolina, Chapel Hill, North Carolina 27599-7400
rn Concentrations of organic nitrogen compounds (total Kjeldahl nitrogen, total free amino acids, individual amino acids, and volatile amines) in primary and secondary effluents from municipal waste water treatment plants were measured and compared to concentrations of these compounds in primary and secondary effluents as reported by others. Primary treated municipal waste water effluents contained relatively low concentrations of dissolved free amino acids compared with those found in raw sewage as reported by others. A selective purge-and-trap method for the concentration of volatile amines was adapted to the analysis of waste water. Volatile organic amines, not previously reported in waste waters, were found in concentrations comparable to those of some of the amino acids. Secondary treatment generally reduces the concentrations of these amines below detection limits.
Introduction Typical nonnitrified municipal waste water effluents contain appreciable concentrations of ammonia (10-40 mg/L) ( I ) . When the water is disinfected by addition of chlorine, treatment plant operators rely on the rapid reaction of the ammonia with hypochlorous acid to produce monochloramine (NHzC1in eq l),the predominant disinfecting species in the effluent (1). In addition to amNHs HOC1 -* "$21 + HzO (1)
+
monia, waste waters contain a considerable number of organic amino nitrogen compounds which also react with chlorine but form nonbactericidal products (2-7). The organic N-chloramine products are particularly insidious because they respond to conventional chemical analysis for residual chlorine disinfectant concentration in the same way inorganic chloramines respond (8-10).Consequently, there has been concern that these methods (11)may be overestimating the disinfectant levels of treatment plant effluents (2-4). The compounds which compose the amino nitrogen fraction of waste water organics are poorly characterized. Jolley et al. (12)identified two nonvolatile amines, ten amino acids, and six purine or pyrimidine bases in HPLC concentrates of waste water effluents. Van Langenhove et al. (13) identified only two nitrogen-containingvolatiles, 'This paper was presented at the 193rd National Meeting of the American Chemical Society, Denver, CO, April 5-10, 1987. 1188 Environ. Sci. Technol., Vol. 22, No. 10, 1988
pyridine and trimethylamine, in an industrial waste water but suggested their presence was incidental. Several studies have identified most of the essential amino acids and quantitated them in raw sewage and in chlorinated raw sewage samples (14,15). As part of a program to evaluate the significance of amino nitrogen compounds in treated municipal waste waters, we have measured the concentrations of amino acids in unchlorinated primary and secondary effluents and identified and quantitated five volatile amines which appear to be natural components of municipal waste waters.
Materials and Methods General. All amines used as standards were of the highest purity available from Aldrich Chemical Co. and were used as received. Acid-washed Chromosorb W (60/80 mesh) was produced by Manville Products Corp. (Denver, CO) and obtained from Varian Associates. The copper chloride was reagent-grade obtained from Baker Chemical Co. Heptafluorobutyric anhydride (HFBA) was obtained from Pierce Chemical Co. (Rockford, IL). Chlorine-demand-free water (CDF water) (9) was used to prepare all solutions and to wash the XAD-2 and Dowex columns. Prepurified XAD-2 was obtained from Applied Science Laboratories (State College, PA) and further purified by Soxhlet extraction for 24 h each with methanol and methylene chloride. Before any waste water or standard solution was passed through the resin, it was washed successively with 300 mL of high-purity 2-propanol, 300 mL of high-purity methanol, with 300 mL of CDF water, and 300 mL of CDF water (adjusted to pH 2 with HC1. Dowex AG 50W-X8 cation-exchangeresin (100-200 mesh) in the hydrogen form was obtained from Bio-Rad Laboratories. Before any waste water or standard solution was passed through the resin, it was washed successively with 300 mL of 5050 methanol and 1 N HC1, 300 mL of 1 N HC1, 300 mL of CDF water, and 300 mL of CDF water adjusted to pH 2 with HC1. Equipment. A Hewlett-Packard Model 5890A gas chromatograph was operated in a purged splitless mode. A 0.32 mm i.d. X 30 m SPB-5 fused silica capillary GC column with a 0.25 pm film thickness (Supelco, Inc, Bellefonte, PA) was used. After a splitless injection for 0.50 min, purge was applied. After an initial temperature hold of 2 min at 50 "C, the column was temperature programmed at 10 "C/min to a final temperature of 150 OC and maintained at this temperature for 5 min. Chromatograms
0013-936X/88/0922-1186$01.50/0
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