21, 83-90
Environ. Sci. Technol.
Challis, B. C.; Kyrtopoulos, S. A. J . Chem. SOC.,Perkin Trans. 1, 1979, 299-304. Saltzman, B. E. Anal. Chem. 1954,26, 1949-1954. Lijinsky, W.; Keefer, L.; Loo, J. Tetrahedron 1970, 26,
Spengler, J. D.; Ryan, P. B.; Yanagisawa, Y.; Wallace, L. A. Abstract of Papers; 190th National Meeting of the American Chemical Society,Chicago, IL; American Chemical Society: Washington, DC, 1985; ENVR 60. Challis, B. C.; Kyrtopoulos, S. A. Br. J. Cancer 1977,35,
5137-5140.
Emmons, W. D. J. Am. Chem. SOC.1954, 76,3470-3473. White, E. H.; Feldman, W. R. J. Am. Chem. SOC.1957, 79,
693-696.
Mirvish, S. S.; Bulay, 0.; Runge, R. G.; Patil, K. J . Natl. Cancer Inst. 1980,40,1435-1439. Iqbal, Z. M.; Dahl, K.; Epstein, S. S. Science (Washington, D.C.) 1980,207, 1465-1477. Van Stee, E. W.; Sloane, R. A.; Simmons, J. E.; Brunnemann, K. D. J. Natl. Cancer Inst. 1983, 70, 375-379. Mirvish, S. S.; Sams, J. P.; Issenberg, P. In N-Nitroso Compounds; ACS Symposium Series 174; American Chemical Society: Washington, DC, 1981; pp 181-191. Norkus, E. P.; Boyle, S.; Kuenzig, W.; Mergens; W. J. Carcinogenesis 1984, 5, 549-554.
5832-5833.
Challis, B. C.; Shuker, D. E. G.; Fine, D. H.; Goff, E. U.; Hoffman, G. A. ZARC Sci. Publ. 1982, No. 41, 11-20. Douglass,M. L.; Kabakoff, B. L.; Anderson, G. A,; Cheng, M. C. J. SOC.Cosmet. Chem. 1978,29, 581-606. Received for review February 18,1986. Accepted August 4,1986. This study was supported by Grant BC-443 from the American Cancer Society.
Activated Alumina Adsorption of Dissolved Organic Compounds before and after Ozonation Abraham S. C. Chen" and Vernon L. Snoeyink Department of Civil Engineering, University of Illinois, Urbana, Illlnois 61801
Frangois Fiessinger Laboratoire Central, Lyonnalse des Eaux, Le Pecq, France
Adsorption of natural organic matter on activated alumina was improved when it was preoxidized with ozone, but the effect was small when doses typical of those applied in drinking water were used. Adsorption capacity increased as pH decreased and ozone dose increased, but adsorption on activated carbon decreased as ozone dose increased. The lower molecular weight fraction both before and after ozonation was not well adsorbed on activated alumina.
Introduction Ozone has been used for drinking water treatment in Europe for many years. It disinfects water and effectively removes taste, odor, and color from water supplies (I). It also reacts with dissolved organic compounds, such as humic substances, to produce more polar compounds (2, 3),which are less adsorbable on granular activated carbon (GAC) (4). Microbial activity in the GAC contactor, however, often improves the dissolved organic carbon (DOC) removal from ozonated water, indicating that some of the compounds produced are also more biodegradable (5). Ozonation of water before coagulation has increased the removal of color, particles, organic compounds, and trihalomethane (THM) precursors by coagulation with aluminum salts (6-8). The increased removal of THM precursors suggests that polar compounds produced by ozonation can be more easily removed by aluminum coagulants. Kuhn and co-workers (4) supported this concept with the results of their study which compared the adsorption of compounds from ozonated and nonozonated activated sludge effluent. After ozonation they found a decrease in adsorption of DOC on activated carbon but an increase in adsorption on the more polar activated alumina.
* Address correspondence to this author at his present address: Alcoa Technical Center, Alcoa Center, PA 15069. 0013-936X/87/0921-0083$01.50/0
Activated alumina, usually y-A1203,is produced by heat treatment of hydrated alumina or aluminum hydroxide at approximately 450 "C. The resulting transition-phase alumina has a relatively high total pore volume (0.3-0.5 cm3/g) and surface area (200-400 m2/g). In the presence of water, activated alumina surfaces are covered with amphoteric hydroxyl groups (9) that exhibit a distribution of acidities ranging from very basic to partially acidic. These functional groups, together with the unsaturated lattice sites that are present (IO), make the activated alumina surface heterogeneous and complex. The heterogeneity of the activated alumina surface has been demonstrated in many studies in which single-solute and bisolute model compounds, such as surfactants, were adsorbed on to different aluminas (e.g., y-, 77-, 6-, and aA1,0,) in aqueous solutions (11-13). The adsorption isotherms of most of these compounds are nonlinear and have the shape illustrated in Figure 1 (12,13). At low equilibrium concentration (CJ, adsorption of organic anions increases linearly with increasing aqueous concentration (region I). In region 11, adsorption increases more rapidly with increasing C,,probably due to lateral interactions of adsorbed molecules (12)and the formation of hemimicelles by two-dimensional condensation on the most energetic sites (12, 13). A t still higher concentrations (region 111), fewer high-energy sites are available, causing the increase in adsorption to occur more slowly with increasing C,. Above the critical micelle concentration (CMC),adsorption is independent of C,. Most investigations of the applications of activated alumina in drinking water treatment have concerned the removal of various inorganic substances, such as fluoride, arsenic, and phosphate (14-18, and organic matter (9,11, 18,19). To our knowledge, no studies have been done on the effect of preozonation of humic substances on adsorption by activated alumina. In this paper we report the effects of ozonation on adsorption by several commercial activated aluminas in comparison with activated carbon. The effect of ozonation on molecular-size distribution was
0 1986 American Chemical Soclety
Envlron. Sci. Technol., Vol. 21, No. 1, 1987
83
Table I. Typical Properties"of Selected Activated Aluminas and Activated Carbons
activated alumina B
A commercial name F-1 raw material alumina scale from bauxite typical analysis 92 Y-Alz03 Na20, % 0.6 SiOz loss on ignition, % particle form size, mm BET surface area, m2/g total pore vol, cm3/g manufacturer a
Compalox AN/V aluminum hydroxides from bauxite
activated carbon C GFSC
D
E
F-400 bituminous coal
NORIT ROW
4-8
6
7
91 0.4-0.6 0.01-0.03 0.01-0.02 8
granular
granular
extruded
granular
extruded
1.4-2.4 250
0.5-1 180-100
0.8-1.2' 200
0.25-0.42 1000-1200
1,oa
0.4
0.35
1.07
1.1
0.04-0.06 0.09-0.12
Alcoa, Pittsburgh, Martinswerk, Bergheim, Rh6ne-Poulenc, Calgon, Pittsburgh, Norit N.V., PA West Germany Aubervilliers, France PA Amersfoort, Holland
From manufacturers' literature.
* Cylindrical diameter of the extruded granule. M , 5000 (22), were also used in some of the tests. Test
CMC PLATEAU ADSORPTION REGION
I
log Ce Flgure 1. A conceptual isotherm for single-solute and/or blsolute adsorption [after Scamehorn et al. (72)].
also determined. These data provide the basis for determining whether further research is warranted on incorporation of activated alumina into drinking water treatment processes. Materials and Methods
Activated Aluminas and Activated Carbons. Several commercially available activated aluminas (AAs) and activated carbons (ACs) were selected (see Table I). In all experiments the AAs were acclimated in glass columns to a solution containing hardness (2 mM Ca2+and 1.6 mM Mg2+) and alkalinity (3.6-6.0 mequiv/L). Complete hardness and alkalinity saturation at these concentrations occurred at 60-120 bed volumes (BV) at a flow rate of 4-12 BV/h. The AAs were then retrieved from the glass columns, dried at 105 OC overnight, and sealed in glass jars for further use. The activated carbons were prepared by sieving to the desired sue fraction, washing to remove fines, and drying at 175 " C for at least 1 week. GWFA Solution. A groundwater fulvic acid (GWFA) was extracted from the groundwater of a local well, purified, freeze-dried, and characterized by infrared spectrophotometry as described by Liao (20). It was selected for the majority of the tests because it has a strong tendency to form THMs when chlorinated (21) and its molecular size is most representative of the humic substances usually found in surface waters, Other humic substances with unique molecular weight characteristics, such as a soil humic acid (SHA) with 56.4% > M , 50000 and 11.3% < 84
Envlron. Scl. Technol., Vol. 21, No. 1, 1987
solutions of GWFA were prepared by adding stock solution of GWFA to water containing hardness and alkalinity at concentrations similar to those used for acclimation of the AA. A constant solution pH was used for the tests. Ozonation of GWFA. The pH 7.0 GWFA solution was ozonated in a 14-L batch-type ozone contractor (see Figure 2). A Welsbach T-408 laboratory ozonator (Welsbach Corp., Philadelphia, PA) was used to generate the 0,-O2 mixture. The ozone concentration in the gas phase was determined iodometrically (23). The pH of the solution generally increased 1order of magnitude during ozonation; pH was adjusted to 5.5, 7.0, or 8.5 after O3 residual was stripped from the solution with a high-purity N2 gas. Apparent ozone dose (AOD) was used to quantify the degree of ozonation and is defined as AOD (mg of 03/mg of DOC) = (03,iQt- 03,J/CV where 03,i is O3gas concentration before contacting water (mg of 03/L), Q is the O3 gas flow rate (L/min), t is the is the total O3mass that escaped ozonation time (min), from the contactor (mg), C is the DOC mass before ozonation (mg), and V is the solution volume (L). Thus, the AOD defined here includes the ozone that self-destructed after it was introduced into the contactor but does not include ozone that escaped the contactor. The concentrations of the GWFA before and after ozonation were quantified by DOC measurements on a Dohrmann DC-80 TOC analyzer (Xertex Corp., Santa Clara, CA). Before ozonation, UV absorbance at 260 nm (Acta 111, Beckman Instruments, Fullerton, CA) correlated well with DOC and could also be used in place of the DOC measurement. Isotherm Study. The adsorption isotherm tests consisted of mixing a solution containing a known concentration of GWFA with a series of accurately weighed doses of granular activated alumina or pulverized activated carbon in sample bottles. The bottles were placed in a rotary shaker at room temperature (-22 "C), and constant pH of all test solutions was maintained by daily adjustment until no further change took place. Kinetic tests showed that the decrease in GWFA concentration from the 6th to the 21st day was less than 5 1 0 % for granular AA. Therefore, the AA isotherm tests were run for 6 days. The time to reach equilibrium with activated carbon was taken as 5 days if it was pulverized
Vent
4
Vent
+
Stop -COCk Power
80-92V
Sample Tap
Stop -COC k BATCH OZONE CONTACTOR
-I
WE L SBACH T - 4 0 8 Ozonotor
-
I L 03-Op/rnin
Flgure 2. Experimental setup of the batch-type ozone contactor.
(24,25). Comparison of AA isotherms from sterilized and nonsterilized bottles showed no measureable difference, in agreement with our previous studies with AC (24),so we assumed biological activity was not important. The solutions were filtered through 0.45-pm Ultipor NG6Nylon 66 membranes (Pall Trinity Micro Corp., Cortland, NY), centrifuged at 8000 rpm for 20 min to remove any fines that may have penetrated the filter paper, and analyzed. Molecular-Size Distribution Analysis. An analytical column of Sephadex G-25 gel (fine grade, Pharmacia, Sweden) was used to estimate the molecular-size distribution of dissolved organic compounds in water. The gel was boiled to degas, swelled, and packed into a 1.9 cm i.d., 1m long glass column. The eluent (a 0.01 M phosphate buffer solution at pH 7.0) was delivered by gravity at 130-140 mL/h to the top of the column where a 10-mL aliquot of an aqueous fulvic acid concentrate was applied. [Fulvic acid concentrates were prepared by passing water samples through a weak acid cation-exchange resin in the sodium form (Duolite C-20, Diamond Shamrock, Redwood City, CA) and subsequently concentrating 15-fold at 40 OC with a vacuum rotary evaporator.] Samples of each 10-mL fraction from the Sephadex column were collected with an automatic fraction collector (SMI, Emeryville, CA). The column was calibrated with blue dextran dye to determine the exclusion limit (fraction 22, MI 5000), glucose to determine the completely permeated fraction (fraction 41, MI 120), and other compounds including vitamin B12and other dextran compounds. Mass balances showed that more than 90-95% of the ozonated and nonozonated humic substance injected to the column was recovered and thus that irreversible adsorption on the gel was qot a major problem. A slight tailing after the completely permeated fraction was often observed, but the TOC accounting for the tailing was no more than 5-8% of the total TOC applied. Results and Discussion
Adsorption Isotherm before Ozonation. The adsorbability of GWFA on activated alumina and activated
I
1
I
I 0 2 0 3 A 4 5 1 6 A GWFA
I
I
AA-C pH55 AA-C pH 7.0 AA-C pH 8.5 AC-D p H 5 . 5 AC-D pH 7.0 AC-D pH85 8.73 mg/L (DOC)
I l 1 1 1 l I
I
I
I I I I I I I
I
I
I I I I L
Ce (rng/L)
Flgure 3. Adsorption isotherms of nonozonated groundwater fulvic acid for activated carbons and activated alumina.
carbon was examined with a series of isotherm tests. Typical adsorption isotherms are presented in Figure 3. AC has a better adsorptive capacity than AA. For example, the capacity of AC-D ranges from 25 (at pH 8.5) to 45 mg/g (at pH 5.5) at an equilibrium concentration of 1 mg/L. The capacities of all AAs, however, are lower, ranging from 11 (AA-C at pH 5.5) to 3.5 mg/g (AA-A at pH 7.0, data not shown in Figure 3) at 3 mg/L equilibrium concentration. Among the three AAs, AA-C adsorbs slightly better than AA-B, and AA-B in turn adsorbs slightly better than AA-A. All AAs adsorb only small amounts of GWFA at pH 8.5 and thus do not appear to be useful at this pH. Environ. Sci. Technol., Vol. 21, No. 1, 1987
85
I t is not surprising that AAs do not adsorb as much as ACs because A A s do not have as much surface area. Also, not all of the AA pores and surface area are accessible to GWFA. Examination of the AA granules at the end of the isotherm tests revealed a dark perifery, indicating adsorption, and a white core. Nonadsorption in the AA core is probably due to slow diffusion of the GWFA molecules and/or to the inaccessibility of the small pores. For example, more than 70% of the porosity in AA-A exists in pores less than 70 A (26);these probably are too small for molecules larger than M, 1000 (24). Most of the GWFA molecules are larger than M, 1000 as data in this paper show. Large molecules may have plugged some of the micropores, thus hindering adsorption of other molecules. (In fact, pulverization of the A A s increases their adsorptive capacities up to 80% or more.) This hypothesis needs to be verified by fractionating the GWFA before adsorption or by using AAs with different pore sizes. Both AC and AA adsorb better as solution pH decreases. The increase in AA adsorption capacity with decreasing pH has been reported by several researchers (9,18,27,28). A plausible explanation for this effect is that anionic humates are adsorbed at positively charged sites, and as pH decreases, AA becomes progressively more positively charged (15). The pH-capacity relationship coincides with the measurements of [ potential and zero point of charge (ZPC) of many activated aluminas (191,as well as with the equilibrium constants for surface hydroxyls on one AA as determined by Kummert and Stumm (9): A10H2+-eAlOH AlOH
A10-
+ H+
+ H+
pKal = 7.4 pKa, = 10.0
Environ. Sci. Technol., Vol. 21,
No. 1 , 1987
uv 0 0 b
5 10 40
DOC 0
8 4
GWFA 4 8 7 m g / L (DOC1
Ozone Contact T i m e (minutes)
Figure 4. Change of DOC concentration and UV absorbance with ozone gas concentration and ozonation time. I
I
1.
(1) (2)
The nonlinearity of the AA isotherms can be attributed to the heterogeneity of the adsorbate and possibly to the nature of the AA surface. A large amount of nonadsorbable material was present as shown by equilibrium experiments using very high AA dosages. At pH 6.5, for example, 1 5 3 0 % DOC remained unadsorbed as the AA dose was increased from about 1.5 to 40 g/L. The presence of nonadsorbable material causes the isotherm slope to approach infinity as the AA surface concentration decreases at low equilibrium concentration. The very steep slope at high equilibrium concentration is consistent with the presence of a small amount of strongly adsorbing material. Sharp increases in slope as equilibrium concentration increases at high equilibrium concentration have also been observed for adsorption of heterogeneous mixtures of organics on AC (29),although the slope increase usually is not as great as is shown in Figure 3 for adsorption on AA. Isotherm slope may also be affected by lateral interaction of adsorbed molecules, as has been shown by others for adsorption of surfactants and other molecules on AA (11-13). However, the GWFA-AA system is too complex to show conclusively that this mechanism was important. Ozonation of GWFA. Hardness and alkalinity were added to the GWFA solution (see Materials and Methods) to simulate a natural water. The addition of alkalinity is important when the solution is to be ozonated because bicarbonate is a radical scavenger (30,31)that can affect the ozonation reaction by slowing the rate of ozone decomposition. However, Reckhow and Singer (32)reported that the reaction of ozone with humic substances is still M HC03-. very fast in the presence of The GWFA solution was ozonated in the batch ozone contactor under different conditions. Figure 4 shows the change in DOC and UV absorbance as a function of ozonation time for several ozone gas concentrations. As ex86
03 Gas Conc (mg 0311 Gas1
Non - Ozonated I 2 3 4 0 5 0
t
F
01
AC-D ACD AC.0 AC-E AC.E
Ozonoted
pH55 pH7.0 pH 8 5 pH 5.5 pH 7.0
6 A 7 A 8 A 9
10 I1 m
AC-D AGD AC.D AGE AC.E AC.E
pH5.5 pH7.0 pH8.5 pH 5 5 ~H7.0 pH 8.5
AOD 3.1 mg/mg GWFA (W/O 03) 8.73 m g / L (DOC1 GWFA ( W O 3 ) 7.31 m g / L (DOC1 I
I
l / l i 1 I l
I
I
1
I I I I I I
i
I
I
I I l l
Ce (mg/L)
Figure 5. Adsorption isotherms of nonozonated and ozonated (AOD 3.1 mg/mg) groundwater fulvic acid for two activated carbons.
pected, UV absorbance (at 260 nm) of the GWFA was significantly reduced by ozonation even under very mild ozonation conditions. This implies that ozonation can easily alter the molecular structure of the GWFA from aromatic and unsaturated constituents to UV-insensitive, saturated intermediates (33-35). Ozonation did not significantly reduce DOC concentration, especially under mild ozonation conditions, as also has been observed by others (32). Adsorption Isotherms after Ozonation. The adsorption isotherms of GWFA on AC-D and AC-E at an AOD of 3.1 mg of 03/mg of DOC are presented in Figure 5. The GWFA isotherms for AC-D (taken from Figure 3) and AC-E before ozonation are presented for comparison. The adsorptive capacities of both ACs are significantly reduced when the fulvic acid is ozonated, consistent with the poor adsorbability of ozonation products. The ozonation products may also be more biodegradable. Since the adsorption test solutions in this study were not sterilized, biological activity in the ozonated solutions might have taken place, but if so, its effect would have been to
Table 11. Activated Alumina Adsorption Capacities for Groundwater Fulvic Acid before and after Ozonatione 4er mg/g
ozone dose, mg/mg
AA-A pH 7.0
C,, mg/L
pH 5.5
0
1.0
b
3.0 5.0
4.5
b 3.5
b b
5.5
4.4
2.7
3.1
1.0
3.3 6.2 26.0
b
b
4.2
2.2 3.9
3.0 5.0
10.5
pH 8.5
pH 5.5
AA-B pH 7.0
pH 8.5
3.6
b
b
6.4
4.5 5.8
2.6 4.0
b
b
7.6 6.0 8.8 26.0
5.2 8.1
2.6 10.2
pH 5.5
AA-C pH 7.0
7.0
b
11.0 14.0
5.4 7.8
8.2 12.5
b
27.0
6.6 10.5
pH 8.5 b 2.5
3.7
b
3.8 6.8
DOC values before and after ozonation were 8.73 and 7.31 mg/L, respectively. * N o qe available. AC-D Ce = I mg/L AOD (mg/mg DOC)
50 -
0
1.0-
> 3.3
------- GWHA (S.6mg/L x15) (9.25mg/Lx15) --- GWFA SHA (8.12 mg/L x 15)
0
Eluent QOl
PO4 at P H 7.0
(3
Fraction
No.
PH
Figure 0. Effects of pH and apparent ozone dose on activated carbon adsorption.
decrease the difference between the isotherms for nonozonated and ozonated GWFA. The effect of AOD on AC-D adsorption was further determined at a low and a very high AOD. Figure 6 compares the surface loadings (4,) of GWFA at C, = 1 mg/L before and after ozonation at an AOD of 0.32,3.1, and >25 mg of 03/mg of DOC. Ozonation at 0.32 mg/mg causes a decrease in adsorption capacity of 17-50% in the pH range from 5.5 to 8.5. This dosage is in the lower range of those that are common in drinking water treatment. The effect of 3.1 mg/mg AOD was to decrease the capacity from 55 to 99% Over the same pH range* However, OZonation at an AOD that is much in excess of that used for drinking water treatment, 25 mg/mg, did not further reduce the carbon capacity. Table I1 compares the AA capacities for GWFA before and after ozonation at an AOD of 3.1 mg of 03/mg of DOC. The data presented are surface loadings (q,) vs. corresponding equilibrium concentration (C,)obtained from the isotherm plots. All AA types adsorb the ozonated GWFA better than the nonozonated GWFA at all pH values. The adsorptive capacities improve by 14-90%. The increase in capacity by ozonation is probably due to the increase in molecular polarity and, possibly, in the amount of strongly adsorbing material. A decrease in molecular size may also enhance adsorption by AA since the reduced-size molecules might diffuse more easily into the micropores. AA isotherms were also determined before and after ozonation at AODs of 0.32 and 25 mg of O,/mg of DOC. In contrast to the results for AC, ozonation at 0.32 mg/mg
20 -
L’ 5 2 03
Figure 7. Sephadex chromatograms of a groundwater fulvic acid, a groundwater humic acid, and a soil humic acid,
(a dosage in the lower range of those commonly used in drinking water treatment) does not have any effect on AA adsorption. Further, an AOD of 25 mg/mg resulted in only a very slight additional improvement in removal when compared with that by the AOD of 3.1 mg/mg. Molecular-Size Distribution Analysis. The molecular weight of adsorbates has been reported to have a strong effect on adsorption by AA (9,18,36). It is therefore interesting to examine this effect both before and after ozonation of the adsorbate. Figure 7 illustrates the apparent molecular-size distribution of the GWFA. The distributions of a groundwater humic acid (GWHA) and a soil humic acid (SHA) are shown for comparison. The Sephadex chromatograms show both DOC and UV as a function of the number of sample fractions (fn). When the phosphate buffer solution was used as the eluent, the totally excluded fraction (M, >5000 based on blue dextran Environ. Sci. Technol., Vol. 21, No. 1, 1987
87
0.8-
.- ___ -.. - --.-.0.6 O'L
GWFA (8.6mgIL x15) I.0g AA C/L a t pH 5.5 I.0g AA B/L at pH 8.5 I.0g AA A I L at pH 8.5
AOD (mg 03/mg GWFA) - 0 --______
0.6 -
Eluent 001 M P O 4 at pH 70
0
8
---
12 23
31 5.1 GWFA (W/O 03) 9OBmg/Lx15 Eluent 001 M P O 4 at pH 7.0
0.4-
c
>
3
15L
Figure 8. Sephadex chromatograms of nonozonated groundwater fulvlc acid after activated alumina adsorption.
dye) and the totally permeated fraction ( M , e120 based on glucose) occurred at fn 22 and fn 41, respectively. As shown in the figure, the molecular weight of the GWFA is predominantly less than 5000, which is comparable to that found in other surface waters (18). This is one reason it was used as a model for natural dissolved organic compounds in the adsorption study. Figure 8 shows the Sephadex chromatograms of the nonozonated GWFA remaining in solution after equilibration with 1.0 g/L of each of the three AAs at pH 5.5 or 8.5. The GWFA chromatogram is reproduced from Figure 7 for comparison. On the basis of the area between the chromatograms before and after adsorption, 34.0% and 45.6% of DOC are removed by AA-A and AA-B, respectively, a t pH 8.5, and 85.6% by AA-C at pH 5.5. The percent removal, however, is much greater for the higher molecular weight fractions (between fns 22 and 31), Le., 46.9%, 61.4%, and 93.1%, respectively, for AA-A at pH 8.5, AA-B at pH 8.5, and AA-C a t pH 5.5. These results indicate an increase in affinity for the AA surface as the molecular weight of the GWFA increases. Similar results were obtained by Davis and Gloor (18), who reported that compounds of M , 1000-3000 adsorbed best from a lake water in Switzerland (the molecular weight of the dissolved organic carbon in this lake was less than 3000). The change of molecular-size distribution for GWFA by ozonation was examined at AODs of 1.2, 2.3, 3.1, and 5.1 mg of O,/mg of DOC; the Sephadex chromatograms together with that of the nonozonated GWFA are shown in Figure 9. When the AOD was 1.2 mg/mg, ozone attacked primarily the smaller molecular weight fractions (from fn 25), as shown by the UV absorbance, without leading to any apparent DOC reduction. As the AOD increased, however, the size distribution of DOC remaining in water gradually shifted from larger molecular weight fractions toward intermediate and smaller ones (see peak between fns 33 and 37). Further, the shift in molecular weight increases with increasing AOD. Using similar techniques, 88
Envlron. Sci. Technol., Voi. 21, No. 1, 1987
Figure 9. Sephadex chromatograms of groundwater fulvic acid ozonated at different apparent ozone doses.
Gloor and co-workers (37) observed a similar shift in molecular weight as a result of ozonation; the amount of organic carbon with MI >1500 was reduced, and a new peak at M , 500 emerged. A similar molecular weight shift, from M I>lo00 before ozonation to MI 1%. This method should be used for on-site analysis of hazardous waste samples to identify major constituents of organic chemical mixtures in conjunction with compatibility testing and/or GC/MS analyses.
Introduction During hazardous waste cleanup activities, a need exists to identify the major components of the waste mixtures. This information is useful in selecting worker and community protection programs, correctly determining which compounds can be bulked together, and helping identify appropriate disposal techniques ( I ) . The two most common methods used to identify/classify hazardous wastes found in drums, tanks, and ponds are compatibility testing and gas chromatography/mass spectroscopy (GC/MS). Compatibility testing is a group of basic qualitative methods that separates the waste into disposable categories. Because they can easily be performed on-site, the major advantages of compatibility testing procedures are their speed and relative low cost. The major disadvantage of compatibility testing is that the method separates unknown wastes into general categories (i.e., halogenated organic, acid, base, sulfide) but does not identify specific compounds ( 1 ) . Also, compatibility testing screening procedures yield extremely limited results for mixtures of organic compounds. The most recent EPA-suggested 90
Environ. Sci. Technol., Vol. 21, No. 1, 1987
method (2) for screening hazardous wastes for organic compounds involves a GC equipped with a flame ionization detector, using standards to identify possible compounds by comparing retention times. This method is semiqualitative a t best. GC/MS offers the ability to identify many volatile and semivolatile organic hazardous substances; however, recent findings ( 2 , 3 )have documented major compound classes in hazardous waste that are not detected by this method. In addition to chromatographic problems, other disadvantages of GC/MS as a waste screening tool on remedial action sites include high cost and time constraints ( I ) . Although GC/MS has been performed on-site (4,samples are usually sent off-site to a laboratory when GC/MS analyses is required. This adds additional time and cost associated with preservation, shipping, and tracking the chain of custody of samples. The emergence of Fourier-transform infrared (FT-IR) spectrometry has provided a method of sufficient sensitivity and rapidity for environmental analysis, especially as a method for the identification of major components of hazardous waste (5-10). FT-IR meets many of the requirements of a real-time screening technique for organic hazardous waste samples ( 1 ) . Once the identity of the components of a complex mixture are known (11-14), FT-IR techniques can also be used to analyze the mixture quantitatively (15). Preliminary reports of its use in identifying components of hazardous waste samples suggest a promising role for this technique in the analysis of environmental samples (5-10). Interpretation techniques that can identify the components of a mixture have been reported (16-22). An advantage of these techniques is the availability of search algorithms for the identification of pure compounds or commercial products. Most of these techniques employ forward-search algorithms where the unknown spectrum is compared to each member of the spectral database (11-14). These methods are successful for pure compounds, but they tend to fail when the compound is heavily contaminated by a second compound. In this paper, we will demonstrate the use of two FT-IR methods to quickly identify major components of organic waste samples. The first method is forward searching the
0013-936X/87/0921-0090$01.50/0
0 1986 American Chemical Society
