Environ. Sci. Technol. 1983, 17, 628-631
thank Ronald Dressman, U.S. EPA, Cincinnati, OH, for performing the total organic halogen measurements. Registry No. CHCl,, 67-66-3; trichloroacetic acid, 76-03-9; dichloroacetic acid, 79-43-6; dichlorosuccinic acid, 42342-97-2. Literature Cited (1) Symons, J. M.; Bellar, T. A.; Carswell, J. K.; De Marco, J.; Kropp, K. L.; Robeck, G. G.; Seeger, D. R.; Slocum, C. J.; Smith, B. L.; Stevens, A. A. J.-Am. Water Works Assoc. 1975, 67, 634-647. (2) “Report on Carcinogenesis Bioassay of Chloroform”; National Cancer Institute: Washington, DC, 1976. (3) National Interim Primary Drinking Water Regulations. Fed. Regist. 1979,44, 68624-68707. (4) Cotruvo, J. Environ. Sci. Technol. 1981, 15, 268. (5) Rook, J. J. Water Treat. Exam. 1974, 23, 234-243. (6) Stevens, A. A.; Slocum, C. J.; Seeger,D. R.; Robeck, G. G. J.-Am. Water Works Assoc. 1976,68, 615. (7) Babcock, D. B.; Singer, P. C. J.-Am. Water Works Assoc. 1979, 71, 149. (8) Morris, J. C.; Baum, B. In “Water Chlorination: Envi-
ronmental Impact and Health Effects”;Jolley, R. L., et al., Eds.; Ann Arbor Science: Ann Arbor, MI, 1978; Vol. 2, pp 29-48.
(9) Christman, R. F.;Johnson, J. D.; Pfaender, F. K.; Norwood,
D. L.; Webb, M. R.; Has, J. R.; Bobenrieth, M. J. In “Water Chlorination: Environmental Impact and Health Effects”; Jolley, R. L., et al., Eds.; Ann Arbor Science: Ann Arbor, MI, 1980; Vol. 3, Chapter 7. (10) Johnson, J. D.; Christman, R. F.; Norwood, D. L.; Millington, D. s. Environ. Health Perspect. 1982, 46, 63-71. (11) Norwood, D. L.; Johnson, J. D.; Christman, R. F.; Millington, D. S. In “Water Chlorination: Environmental Impact and Health Effects”; Jolley, R. L., et al., Eds.; Ann Arbor Science: Ann Arbor, MI, 1983; Vol. 4, Chapter 13.
(12) Quimby, B. D.; Delaney, M. F.; Uden, P. C.; Barnes, R. M. Anal. Chem. 1980,52,259-263. (13) Miller, J. W.; Uden, P. C. Environ. Sei. Technol. 1983, 17, 150-157. (14) Christman, R. F.; Liao, W. T.; Millington, D. S.; Johnson, J. D. In “Advances in the Identification and Analysis of (15) (16) (17) (18) (19) (20)
Organic Pollutants in Water”;Keith, L. H., Ed.; Ann Arbor Science: Ann Arbor, MI, 1981; Vol. 2, Chapter 49. Liao, W. T.; Christman, R. F.; Johnson, J. D.; Millington, D. S.; Hass, J. R. Environ. Sei. Technol. 1982,16,403-410. Bellar, T. A.; Lichtenberg, J. J. J.-Am. Water Works ASSOC. 1974,66, 739-744. Liao, W. T. Ph.D. Dissertation, University of North Carolina, 1981. “Total Organic Halide. Interim Method 450.1”;Environmental Monitoring and Support Laboratory, U.S.Environmental Protection Agency: Cincinnati, OH, 1980. Rook, J. J. In “Water Chlorination: Environmental Impact and Health Effects”; Jolley, R. L., et al., Eds.; Ann Arbor Science: Ann Arbor, MI, 1980; Vol. 3, Chapter 8. Miller, J. W.; Uden, P. C.; Barnes, R. M. Anal. Chem. 1982,
54, 485-488. (21) Havlicek, S. C.; Reuter, J. H.; Ingols, R. S.; Ghosal, M.;
Lupton, J. D.; Stratton, L. W.; Rolls, J. W. ”Identification of major and minor Classes of Natural Organic Substances Found in Drinking Water”. Final progress report submitted to the U.S.Environmental Protection Agency, 1980. Received for review January 21,1983. Accepted May 23,1983. Although the research described in this article has been funded wholely or in part by the US.Environmental Protection Agency through Cooperative Agreement CR806679 to the University of North Carolina, it has not been subjected to Agency review and therefore does not necessarily reflect the views of the Agency, and no offical endorsement should be inferred.
Degradation of Chloroform by Photoasslsted Heterogeneous Catalysis in Dilute Aqueous Suspensions of Titanlum Dioxide Ann Lorette Prudent and David F.
oil is"^
Department of Chemical Engineering, Princeton University, Princeton, New Jersey 08544
The complete mineralization of trichloromethane (chloroform) to inorganic products is demonstrated with heterogeneous photoassisted catalysis by using near-UVilluminated TiOz aqueous slurries. Introduction Chloroform was studied because it is the major haloform produced from organic matter during the disinfection of municipal waters by chlorination (1-3) and because it is a suspected carcinogen ( 4 ) . Disappearance of polychlorinated biphyenyl (5) and of p-dichlorobenzene (6) from aqueous solutions of UV-illuminated T i 0 2 slurries has been reported; in neither case was a chlorine mass balance or product identification established. In this paper, we report the complete degradation of chloroform (CHC1,) to hydrogen chloride ion and carbon dioxide by dilute aqueous suspensions (0.1 wt %) of a heterogeneous Present address: Mobil Research and Development Laboratory, Pennington, Princeton, NJ 08540. t Present address: Chemical Engineering Department, University of California, Davis, CA 95616. 628
Environ. Scl. Technol., Vol. 17. No. 10, 1983
photoassisted catalyst, titanium dioxide. Experimental Procedures The reactions were carried out in a batch reactor (Figure 1) constructed of glass and Teflon (7). A 0.1 w t % aqueous slurry of titanium dioxide was recirculated with a polypropylene/ceramic pump. The catalyst was Fisher certified grade TiOz (Lot no. 745547) with a surface area of 7 m2/g, as determined from B.E.T. nitrogen adsorption (8). The catalyst loading and illumination intensity were held constant at 0.1 wt % TiOz and 6.6 X einstein/min, respectively. The illumination wavelength range of the “black light” fluorescent bulbs (GE BLB-15W) was predominantly 320-440 nm, with virtually no emission below 300 nm or above 500 nm. Freshly boiled distilled deionized water was stripped with helium in the reactors to diminish COz and O2before the catalyst and chloroform were added. Chloroform was Baker analyzed reagent grade, supplied with -0.6 wt % ethanol as stabilizer (weight percent was estimated by gas chromatography (GC) analysis, assuming detector response factor for ethanol and methanol is equal). Ita solubility in water at 20-25 “C and 1atm total pressure is 8.2 X lo3 mg/L, about 8200 ppm (9). In 150 ppm aqueous CHC13 solution, only trace ethanol, CHC13, and
0013-936X183/0917-0628$01.50/0
0 1983 American Chemical Society
Flgure 1. Recirculating, differential conversion photoreactor. (A) Quartz annular photoreactor; (B) black llghts parallel to reactor axis (7 GE BLB (15 W each)); (C) thermocouple: (D) Pyrex sampling vessel; (E) centrifugal recirculation pump; (F) Teflon tublng; (G) sampling port with Teflon-faced septum; (H) chloride ion electrode; (I) reference electrode; (J) millivoltmeter. 300
1 1 1 1 1
TIME ( m i n ) Flgure 3. Photocatalyzed degradation of chloroform (run B1, Initial [Cl-] < 2 ppm; lnitlal [CHCI,] = 104 ppm). Regions I, 11, and 111 as in Flgure 2. Chloroform (A),chloride (O),and methanol (W).
Table 1. Chloroform Conversion to Chloride initial fraction chlorine Of in concn Of CHCl, CHC1, chloride run CHCl,, conconobsd, ppm verted verted ppm no. A1 A2 B1 B2 0
60
120
180
T I M E (rnin)
Flgure 2. Photocatalyzed degradation of chloroform (run A l , initial [Cl-] < 2 ppm; initial [CHCI,] = 122 ppm). Regions: I, illumination, no Ti02 catalyst; 11, Ti02 catalyst, no lllumlnation; 111, illumination and Ti02 catalyst present slmuitaneously. Chloroform (A)and chloride (0).
an unidentified contaminant eluting a t -7 min (120 OC isothermal operation, 15 cm3/min He carrier gas) appeared as new peaks in the GC trace compared to analyses of distilled water and laboratory air (7). A small peak appeared during reaction, as noted by GC-FID; it was identified by retention time comparison (0.53 min) with a known sample such as methanol, and the identification was confirmed in the final reaction mixture of run A by purge and trap analysis with gas chromatography-mass spectrometry (GC-MS). (The liquid sample was purged with an inert gas and the resultant effluent passed through a Tenax/silica gel column. The trapped organics were then desorbed into the GC-MS by heating the trap.) The maximum methanol concentration was about 3.5 ppm. Chloride ion was determined by in situ specific chloride electrode analysis (HNU Systems) and by silver nitrate titrations (9, IO),and carbon dioxide by barium carbonate precipitation. Chloroform does not absorb near-UV light as shown by its 100% transmission between 300 and 500 nm (7).
Results In the presence of both TiOz slurries and near-UV illumination, CHCl, was rapidly dehalogenated (region 111, Figures 2 and 3), while in the presence of either illumination (region I) or TiOz (region 11) alone, no CHCl, dis-
122 112 104 135
0.931 0.445 0.774 0.874
101 45 72 105
104 46 72 109
chlorinea recovery, %
103.0 102.2 100.0 103.8 av: 102.3
Chlorine recovery :(chlorine contained in converted CHCI, X 100)/chloride observed in solution.
appearance or chloride production was observed. For the CHC13reactions with catalyst and illumination, complete dechlorination of converted chloroform was evident from the chlorine mass balances (Table I). The 3-5% uncertainty in chloride recovery was within the experimental error of the chloroform determinations. Carbon dioxide product was confirmed by precipitate formation in the barium hydroxide trap. The only organic product noted by GC-FID or GC-MS in either the liquid or vapor phases of the reactor was methanol, which appeared and disappeared during illumination with TiOz. The lower detection limit for methanol was estimated as -0.05 ppm by assuming that the calibration curve was linear between 0 and 100 ppm. This estimate provides a lower bound of a t least 99% on the ultimate conversion of organic carbon to carbon dioxide. The total chlorine mass balances, the production of barium carbonate precipitate, and the disappearance of the trace methanol product observed show the complete degradation of chloroform to C02 and C1- a t 34-44 "C in illumination aqueous suspensions of titanium dioxide. Initial reaction rates for both chloroform degradation and chloride production were first order, as shown by the initial straight line behavior of the semilog plots (Figures 2 and 3); this apparent order changed with reaction extent. Trace methanol was detected by GC-FID in Figure 3 but was observed only by GC-MS (at -100 ppb) for Figure 2. The reaction could be continued by adding chloroform (to 120 ppm) to the final reaction mixture of Figure 3, after overnight shutdown (lamps off, continuous recirculation). Environ. Scl. Technol., Vol. 17, No. 10, 1983 629
Table 11. Initial Conditions and Rates of Chloroform Degradation app specific rate/ first-order photon absorbed,c rate specific rate,a turnover no.,* Mmol.cm-2. constan t , initial concn, ppm umol. molecules. min-'.(pmol k C H Cl?, run no. CHCI, c1 temp, "C cm-z.min" site-' 'sof photon)-' min' A1 122
