Environ. Sci. Technol. 1993, 27, 146-152
Gschwend, P. M.; Hites, R. A. Geochim. Cosmochim. Acta 1981,45, 2359-2367. Giger, W.; Schaffner, C. Anal. Chem. 1978, 50, 243-249. Jones, K. C.; Stratford, J. A.; Tidridge, P.; Waterhouse, K. S.; Johnston, A. E. Environ. Pollut. 1989, 56, 337-351. Jones, K. C.; Stratford, J. A.; Waterhouse, K. S.; Furlong, E. T.; Giger, W.; Hites, R. A.; Schaffner, C.; Johnston, A. E. Environ. Sci. Technol. 1989, 23, 95-101. Muller, G.; Grimmer, G.; Bohnke, H. Naturwissenschaften 1977,64, 427-431. Wakeham, S. G.; Schaffner, C.; Giger, W. Geochim. Cosmochim. Acta 1980,44, 403-413. Tan,Y. L.; Heit, M. Geochim. Cosmochim.Acta 1981,45, 2267-2279. Helfrich, J.; Armstrong, D. E. J. Great Lakes Res. 1986, 12, 192-199. Eadie, B. J. In Toxic Contaminants in the Great Lakes; Nriagu, J. O., Simmons, M. S., Eds.; John Wiley & Sons Publishers: New York, 1984; pp 195-211. Heit, M.; Tan, Y. L.; Miller, K. M. Water,Air, Soil Pollut. 1988, 37, 85-110. Smith, J. N.; Levy, E. M. Enuiron. Sci. Technol. 1990,24, 874-879. Sexton, K.; Liu, K. S.; Hayward, S. B.; Spengler, J. D. Atmos. Environ. 1985, 19, 1225-1236. Zhang, X.; Christensen, E. R.; Yan, L.-Y. Submitted for publication in J. Great Lakes Res. Hermanson, M.; Christensen, E. R. J . Great Lakes Res. 1991, 17, 33-50. Zhang, X. Ph.D. Dissertation, Dept. of Civil Engineering and Mechanics, University of Wisconsin-Milwaukee, 1991. Christensen, E. R.; Klein, R. J. Enuiron. Sci. Technol. 1991, 25, 1627-1637. Yan, L.-Y. M.S. Thesis, Dept. of Civil Engineering and Mechanics, University of Wisconsin-Milwaukee, 1991. McVeety, B. D.; Hites, R. A. Atmos. Environ. 1988, 22, 511-536. State Energy Data Report, Consumption Estimates
(27) (28) (29)
(30) (31) (32) (33)
(34) (35) (36) (37) (38) (39)
1960-1988; DOE/EIA-0214 (88); Energy Information Administration (EIA): Washington, DC, 1988a. Estimation of Wood Energy Consumption, 1949-1983; Energy Information Administration (EIA): Washington, DC, 1981,1983. Hottel, H. C.; Howard, J. B. New Energy Technology;MIT Press: Cambridge, MA, 1971. Hidy, G. M.; Henry, R. C.; Hansen, D. A.; Ganesan, K.; Collins, J. Analysis of Trends in Historical Acid Precursor Emissions and Their Airborne and PrecipitationProducts; ERT Document P-B538; Environmental Research and Technology, Inc., Westlake Village, CA, 1983. Minerals Yearbook; U.S. Department of the Interior: Washington, DC, 1950. Annual Review; DOE/EIA-0214(88); Energy Information Aministration (EIA): Washington, DC, 1988b. Ohta, K.; Handa, N.; Matsumoto, E. Geochim. Cosmochim. Acta 1983, 47, 1651-1654. Eadie, B. J.; Robbins, J. A.; Faust, W. R.; Landrum, P. F. In Organic Substances and Sediments in Water: Processes and Analytical; Baker, R., Ed.; Lewis Publishers: Ann Arbor, MI, 1991; Vol. 2, pp 171-189. Dasch, J. M. Enuiron. Sci. Technol. 1982, 16, 639-645. Goldberg, E. D.; Hodge, V. F.; Griffin, J. J.; Koide, M.; Edgington, D. N. Environ. Sci. Technol. 1981,15,466-471. Griffin, J. J.; Goldberg, E. D. Science 1979,206, 563-565. Furlong, E. T.; Cessar, L. R.; Hites, R. A. Geochim. Cosmochim. Acta 1987, 51, 2965-2975. Freeman, D. J.; Cattell, F. C. R. Environ. Sci. Technol.1990, 24, 1581-1585. Benner, B. A., Jr.; Gordon, G. E.; Wise, S. A. Enuiron. Sci. Technol. 1989,23, 1269-1278.
Received for review February 25, 1992. Revised manuscript received July 6,1992. Accepted September 24,1992. This work was sponsored by US.National Science Foundation Grants CES-8701184 and BCS-8921000.
Atmospheric Chemistry of Hydrofluorocarbon 134a. Fate of the Alkoxy Radical CF30 Jens Sehested
Section for Chemical Reactivity, Environmental Science and Technology Department, Riser National Laboratory, DK-4000 Roskiide, Denmark Timothy J. Wallington"
Research Staff, SRL-3083, Ford Motor Company, P.O. Box 2053, Dearborn, Michigan 48 121-2053
rn The atmospheric chemistry of the alkoxy radical CF30 produced in the photooxidation of hydrofluorocarbon (HFC) 134a has been investigated wing Fourier transform infrared spectroscopy. CFBOradicals are shown to react with methane and CF3CFH2to give CF30H. CF30H decomposes to give COFz and HF. The rate constant for the CF30H + reaction CF30 CF3CFHz (HFC-134a) CF CFH was determined to be kI9 = (1.1f 0.7) X cmd molecule-' s-' at 297 K. The implications of ow results for the atmospheric chemistry of CF30 radicals and HFC-134a are discussed.
+
-
Introduction Recognition of the adverse effect of chlorofluorocarbon (CFC) release into the atmosphere has led to an international effort to replace CFCs with environmentally acceptable alternatives (1-3). Hydrofluorocarbon 134a (1,1,1,2-tetrafluoroethane) is a viable substitute for CFC-12 148
Environ. Sci. Technol., Voi. 27, No. 1, 1993
in automotive air-conditioning systems. Prior to large-scale industrial use of HFC-l34a, the environmental consequences of i b release into the atmosphere should be considered. To define the environmental impact of HFC-134a release, the atmospheric photooxidation products of HFC-134a need to be determined. The main atmospheric loss mechanism for HFC-134a is reaction with the OH radical, reaction 1. Studies of the CF3CFH2 OH CF3CFH + HzO (1)
+
-
HFC-134a kinetics of this reaction ( 4 ) have shown that the atmospheric lifetime of HFC-134a is approximately 15 years. The alkyl radical formed in reaction 1 reacts rapidly (within 1p under tropospheric conditions) with molecular oxygen to give the peroxy radical CF3CFHO2(reaction 2). CF3CFH + 0 2 + M CF3CFHOz f M (2) Studies in our laboratories have shown that reaction with
0013-936X/93/0927-0146$04.00/0
-+
0 1992 American Chemical Society
Table I. Observed Product YieldsasbFollowing the Irradiation of HFC-134a/C12Mixtures in 700 Torr Air
expt
[HFC-134alo
[Cl~lo
tu"
(8)
A[HFC-l34a]
A[HC(O)F] 73.8 15 6.21 (69%)d 19.1 (64%) 5.41 (64%) 7.5 (87%)
100
207 194 95
300 60 300
nac na 9.0
4
100.3
1065
240
30
5
94.3
231 (FA
300
8.5
6e
95.6
101
300
8.6
1 2
1625 1452
3
A[CF3COF] 22.8
4.2 1.8 (20%) 6.9 (23%) 1.98 (23%) 0.6 (7%)
A[CF303CF3]
A[CF,O]
19.4 2.66 1.94 (22%) 6.78 (23%) 1.45 (17%) 2.4 (28%)
37.3 8.0 1.47 (16%) 3.7 (12%) 1.4 (l6?"0) 1.8
(21%)
Observed concentrations in units of milliTorr; no corrections of any kind applied to data. *Product analyses were performed after dark chemistry ceased. Not applicable. Values in parentheses are molar yields. e Experiment performed using 2.5 Torr O2in 700 Torr total pressure N2. a
NO is a significant atmospheric sink for CF3CFH02radicals and that the products of this reaction are CF3CFH0 radicals and NOz (5). CF3CFH02 + NO CF3CFHO + NO2 (3) CF3CFH0 radicals formed in reaction 3 either decompose to give CF3 radicals and HC(0)F or react with Oz to give CF3COF. In the atmosphere, approximately 70% of the CF3CFH0 radicals formed from the photooxidation of HFC-134a decompose, while 30% react with O2 (6). CF3CFHO + 02 CF3COF + HO2 (4) CFSCFHO CF3 + HC(0)F (5) CF, radicals formed in reaction 5 react with O2 to give CF302radicals, which in turn react rapidly with NO to form CF30 radicals (4, 7, 8): CF3 + 02 + M -* CF302+ M (6) (7) CF302 + NO CF30 + NO2 The atmospheric fate of CF30 radicals is uncertain. It is generally assumed that CF30 radicals are converted into COF2in the atmosphere (9),although the exact mechanism for this conversion is unclear. In a previous study of the simulated atmospheric chemistry of HFC-l34a, we observed the formation of COFzwhen reaction mixtures were left to age in the dark (6). However, we were unable to identify the mechanism by which this product was formed. As part of a collaborative research program between Ford and Rispr National Laboratory to determine the environmental impact of CFC replacements, we have revisited the mechanism by which COF2 is formed in the simulated atmospheric oxidation of HFC-134a. Results are reported herein.
-
-
-
Experimental Section The experimental setup used for the present work has been described previously (10) and is only briefly discussed here. The apparatus consists of a Mattson Instruments Inc. Sirius 100 FT-IR spectrometer interfaced to a 140-L, 2-m-long evacuable pyrex chamber. White-type multiple-reflection optics were mounted in the reaction chamber to provide a total path length of 28 m for the IR analysis beam. The spectrometer was operated at a resolution of 0.25 cm-l. Infrared spectra were derived from 128 coadded interferograms. Experiments were performed at 297 K and a total pressure of 700 Torr. CF3 radicals were generated by two different methods: chlorine- or fluorine-initiated oxidation of HFC-134a or photolysis of CF3NO. For the chlorine- or fluorine-initiated experiments, the following concentration ranges were used: HFC-l34a, 94-1625 mTorr; C12, 95-1065 mTorr, or F2,231 mTorr; 02,2.5-150 Torr, with Nz added
as appropriate to maintain a total pressure of 700 Torr. Chlorine or fluorine atoms were generated by the photolysis of the corresponding molecular halogen using the output of 24 UV fluorescent lamps (GTE F40BLB). ClZ/F2+ hu (A > 300 nm) 2C1/F (8)
-
For experiments using CF3N0, photolysis was achieved using visible light from 1 2 fluorescent lamps (GTE F40CW): CF3N0 + hu (A > 400 nm) CF3 + NO (9)
-
Initial concentrations used were as follows: CF3N0, 14-110 mTorr; CHI, 0-1300 mTorr. Products were quantified by fitting reference spectra of the pure compounds to the observed product spectra using integrated absorption features. Reference spectra were obtained by expanding known volumes of the reference material into the long-path-length cell. Systematic uncertainties associated with quantitative analyses using these reference spectra are estimated to be 50 km). Transport to such high altitudes is slow, so that photolysis is not expected to be a significant atmospheric fate of CF30H. By virtue of the strong O-H bond [109 kcal/mol(23)], the reaction of CF30H with OH radicals is expected to be slow. We can estimate the atmospheric lifetime of CF,OH with respect to OH attack by considering the atmospheric lifetime of CHI which is determined by OH attack. The C-H bond strength in methane is 104 kcal/mol, and each C-H bond is expected to be more reactive than the O-H bond in CF,OH. Since the atmospheric lifetime of methane is approximately 10 years, the lifetime of CF30H with respect to OH radical attack will probably be at least 40 years. In contrast to photolysis and reaction with OH, incorporation of CF30H into water is rapid (9). Following absorption into cloudwater or seawater, CF30H will decompose to give HF and CO, (9). Either decomposition (reaction 12) or rain-out will dominate removal of CF30H from the atmosphere. The exact removal mechanism is unimportant as the decomposition product from reaction 12, COF,, is removed by rain-out and decomposes in water to give CO, and HF (9). To conclude, it appears that reaction with hydrocarbons is an important atmospheric removal process for CF30 radicals. As shown here for HFC-134a and CHI, this reaction produces CF30H. Trifluoromethanol is expected to either directly or indirectly (via COF,) be incorporated into water droplets and decompose to COP and HF. Concentrations of HF in rainwater resulting from the release of HFCs will be low. For example, HFC-134a is a replacement for CFC-12. In 1986 the global production of CFC-12 was 4.0 X 10s kg. If HFC-134a replaces CFC-12 on an equal mass basis and all the HFC-134a is released without recovery, the emission to the atmosphere would be 4.0 X lo8 kg or 3.9 X lo9 mol/year. At steady state, assuming each F atom in HFC-134a is converted into HF, 1.6 X 1O1O mol of HF would be formed in the atmosphere annually. The annual global rainfall is 4.9 X l O I 7 L (26). Thus, rainwater might be expected to contain 3.3 X M (0.6 ppb) HF. This additional fluoride burden is not expected to have any direct effect on plant systems (9). For comparison, 1ppm fluoride level is currently added to drinking water in most U.S. cities.
-
Acknowledgments We thank Roscoe Carter and Steve Japar (both of Ford Motor Co.), Carl Howard (NOAA), Ole John Nielsen (Ris0 National Laboratory, Roskilde, Denmark), and Dave Rowley (Cambridge University, England) for helpful discussions. Literature Cited (1) F m a n , J. D.; Gardiner, B. G.;Shanklin, J. D. Nature 1985, 315, 207. (2) Solomon, S. Nature 1990,347,6291,and references therein. (3) World Meteorological Organization Global Ozone Research and Monitoring Project. Scientific Assessment of Stratospheric Ozone; Report No. 20; 1989; Vol. 1. (4) DeMore, W. B.; Sander, S. P.; Golden, D. M.; Molina, M. J.; Hampson, R. F.; Kurylo, M. J.; Howard, C. J.; RavishEnvlron. Scl. Technol., Voi. 27, No. 1, 1993
151
Environ. Sci. hchnol. 19Q3,27, 152-158
ankara, A. R. JPL Publ. 1990, No. 90-1. Wallington, T. J.; Nielsen, 0. J. Chem. Phys. Lett. 1991, 187, 33. Wallington, T. J.; Hurley, M. D.; Ball, J. C.; Kaiser, E. W. Environ. Sci. Technol. 1992, 26, 1318. Wallington, T. J.; Dagaut, P.; Kurylo, M. J. Chem. Rev. 1992, 92, 667. Lightfoot, P. D.; Cox, R. A.; Crowley, J. N.; Destriau, M.; Hayman, G. D.; Jenkin, M. E.; Moortgat, G. K.; Zabel, F. Atmos. Enuiron. 1992, 26, 1805. World Meteorological Organization Global Ozone Research and Monitoring Project. Scientific Assessment of Stratospheric Ozone; Report No. 20; 1989; Vol. 2. Wallington, T. J.; Gierczak, C. A.; Ball, J. C.; Japar, S. M. Int. J . Chem. Kinet. 1989,21, 1077. Morgan, H. W.; Staats, P. A.; Goldstein, J. H. J . Chem. Phys. 1956, 25, 337. Wallington, T. J.; Sehested, J.; Dearth, M. A.; Hurley, M. D. J . Photochem. Photobiol., A, in press. Francisco, J. S.; Zhao, Y. J . Chem. Phys. 1990, 93, 276. Wallington, T. J.; Hurley, M. D. Chem. Phys. Lett. 1992, 189, 437. Wallington, T. J.; Hurley, M. D.; Shi, J.; Maricq, M. M.; Sehested, J.; Nielsen, 0. J.; Ellermann, T. Znt. J . Chem. Kinet., submitted for publication.
Kloter, G.; Seppelt, K. J . Am. Chem. SOC.1979, 101, 347. Howard, C. J. Abstracts of Papers, 203rd National Meeting of the American Chemical Society, San Francisco, CA, April 1992; American Chemical Society: Washington, DC, 1992; PHYS 101. Tyndall,G. S.; Wallington, T. J.; Hurley, M. D.; Schneider, W. F. J . Phys. Chemy, in press. Patai, S. The Chemistry of finctionul Groups: Peroxides; John Wiley: New York, 1983, p 496. Hirschmann, R. P.; Fox, W. B.; Anderson, L. R. Spectrochim. Acta 1969, 25, 811. Braun, W.; Herron, J. T.; Kahaner, D. K. Znt. J . Chem. Kinet. 1988,20, 51. Niehen, 0. J.; Ellermann, T.; Sehested, J.; Bartkiewicz, E.; Wallington, T. J.; Hurley, M. D. Znt. J. Chem. Kinet. 1992, 24, 1009. Batt, L.; Walsh, R. Znt. J . Chem. Kinet. 1982, 14, 933. Maricq, M.; Szente, J. J . Phys. Chem., submitted for publication. Calvert, J. G.; Pitta, J. N., Jr. Photochemistry; John Wiley: New York, 1966. Erchel, E. World Water Balance; Elsevier: New York, 1975.
Received for review June 1I, 1992. Revised manuscript received September 10, 1992. Accepted September 21, 1992.
Sorption of Toxic Organic Compounds on Wastewater Solids: Mechanism and Modelingt Leplng Wang" and Rakesh Govlnd
Department of Chemical Engineering, University of Cincinnati, Cincinnati, Ohio 45221 Richard A, Dobbs Risk Reduction Engineering Laboratory, U S . Environmental Protection Agency, Cincinnati, Ohio 45268
It is proposed that sorption is a combination of two fundamentally different processes: adsorption and partitioning. A sorption model was developed for both single-component and multicomponent systems. The model was tested using single-component experimental isotherm data of eight toxic organic compounds. Partitioning dominates the sorption process for compounds with high sorbability or high octanol-water partition coefficient,KO,. Binary sorption data were compared with the present model. The proposed model fitted experimental data well. It was found that KO, could be used to assess the competition effect in a multicomponent system. The competition is negligible when KO,is larger than 1000. When KO,is smaller than 500, there is a significant competition effect. In very dilute solutions, the effect of the presence of a competing species can be ignored. W
Introduction The literature has provided ample evidence that many toxic organic compounds accumulate in sludges or wastewater solids at concentrations several orders of magnitude greater than influent concentrations (1-4). This accumulation phenomenon has been referred to as sorption because it differs from the adsorption process which has been extensively studied. Sorption of toxic organic compounds on wastewater solids is an important process in conventional biological wastewater treatment systems. The
* Current address: Ciba-Geigy Corp., McIntosh, AL 36553. 'This work was presented at the AIChE Annual Meeting in Loa Angeles, CA, Nov 1991. 152 Environ. Sci. Technol., Voi. 27, No. 1, 1993
extent of accumulation of toxic organic compounds by sorption onto wastewater solids not only affects the efficiency of the treatment system but also impacts the management of wastewater solids. However, the understanding of this process in wastewater treatment remains poor. Especially, there has been a lack of information in the literature on the mechanism of uptake of toxic organic Compounds by wastewater solids. Most published reports on sorption of toxic organic compounds on wastewater solids only correlate the experimental data using empirical equations such as the Freundlich equation. Few authors speculate on mechanism, and there appears to be no consensus regarding the mechanism of the uptake of toxic organic compounds. Little effort has been made to describe sorption based on the nature of wastewater solids. In fact, the concept of sorption on wastewater solids has not been clearly defined. Different terms, such as adsorption, partitioning, sorption, and biosorption, have been used in the literature to describe the uptake of toxic organic compounds by sludges. In the present study, the term sorption is used because neither adsorption nor partitioning represents the whole picture of the accumulation phenomenon. Since the objective of this work is to study the sorption on wastewater solids, it is for the convenience of discussion that volatilization and biodegradation are assumed to be absent in the process. Volatilization can be minimized by eliminating the head space in the sorption experiment (5, 6). Biodegradation can be controlled by pasteurization or cyanide treatment (7). In a previous paper (5),sorption of toxic organic compounds on wastewater solids and correlations with fun-
0013-936X/93/0927-0152$04.00/0
@ 1992 American Chemical Society
