Environ. Sci. Technol. 2000, 34, 4587-4592
Study of H2S Adsorption and Water Regeneration of Spent Coconut-Based Activated Carbon ANDREY BAGREEV,† HABIBUR RAHMAN, AND TERESA J. BANDOSZ* Department of Chemistry, The International Center for Environmental Resources and Development of The City College of New York, New York, New York 10031
A coconut shell-based activated carbon was studied as hydrogen sulfide adsorbent in four subsequent adsorption/ regeneration cycles. The regeneration of exhausted carbon was done using washing with cold and hot water with a defined ratio of water volume to the unit weight of carbon. The observed changes in the capacity were linked to such surface features of activated carbons as pH and porosity. The cold and hot water washing result in the similar capacity for H2S adsorption. After the first adsorption run the capacity of carbon for hydrogen sulfide adsorption significantly decreased (around 60%). The subsequent runs revealed more or less constant capacity with similar efficiency for the removal of sulfur species. The results indicate that after the first run the most active adsorption cites located in small pores are exhausted irreversibly. The sulfur adsorbed on those sites is strongly bound as elemental sulfur and sulfuric acid. Despite this, the carbon surface was found to have other adsorption/oxidation sites which can be regenerated using cold or hot water washing. Besides sulfuric acid being removed from the pore volume of activated carbon a significant percentage of elemental sulfur was also removed.
Introduction Activated carbons impregnated with caustics (KOH or NaOH) are widely used as hydrogen sulfide adsorbents at sewage treatment plants (1, 2). Oxidation of hydrogen sulfide in the presence of caustic results in the deposition of elemental sulfur. The carbon acts as an efficient adsorbent until the caustic compound is exhausted. Although the application of impregnated carbons for hydrogen sulfide odor removal is very effective, it is associated with a few significant disadvantages (3-5). They are as follows: (1) low temperature of self-ignition due to the exothermic reaction of caustics with CO2 present in the air, (2) limited capacity for physical sorption due to the filling of the pore system with the impregnate, (3) special precaution has to be used due to the presence of corrosive materials, and (4) costs of caustic impregnated materials are usually higher than as received unimpregnated carbons. These disadvantages directed the attention of the researchers to the evaluation of virgin, unimpregnated carbons as sorbents of hydrogen sulfide * Corresponding author phone: (212)650-6017; fax: (212)650-6107; e-mail:
[email protected]. † Permanent address: Institute for Sorption and Problems of Endoecology, Ukraine. 10.1021/es001150c CCC: $19.00 Published on Web 09/22/2000
2000 American Chemical Society
(6-12). They have high capacities for physical sorption, and they have been proven to work efficiently as odor adsorbents for several years in the North River Water Treatment Plant operated by the New York City Department of Environmental Protection (5, 12). Caustic impregnated carbons, when their capacity for odor removal is exhausted, are removed from vessels and new material is loaded. To minimize the costs, it would be advantageous if the carbon were regenerated in situ and used for multiple adsorption/regeneration cycles. Since in the case of caustic carbons the main product of hydrogen sulfide oxidation is sulfur located in small pores, it cannot be removed by inexpensive methods such as, for instance, washing with water. Regeneration is possible when the products of H2S oxidation are water soluble acids such as sulfuric acid. This acid is the main product of reaction on the surface of a catalytic carbon manufactured by Calgon Carbon, Centaur. According to the manufacturer’s specification, for the regeneration of Centaur to 80% of its capacity a minimum of 1046 L of water per kilogram of adsorbent (14) or 30 L/kg (15) are needed. As indicated the two sources (14, 15) differ significantly in the amount of water needed. Centaur, although very effective for hydrogen sulfide conversion to H2SO4, has relatively low capacity and its cost is high. As mentioned above, all of these, along with the disadvantages of application of caustic impregnated carbons, directed the attention of researchers toward as-received, unimpregnated carbons as hydrogen sulfide odor adsorbents at sewage treatment plants (10-15). It was shown that in the case of such carbons, besides elemental sulfur as the predominant product, around 30% of the sulfur is in the form of sulfuric acid (11). It was also demonstrated that a moderately low pH of the surface of unimpregnated carbons promotes the oxidation of hydrogen sulfide to sulfuric acid, whereas the only product at high pH is elemental sulfur in the form of ring (S8) or linear polymers (10, 11). A preliminary study of the possibility of regeneration of the surface of exhausted carbons showed that the majority of sulfur species can be removed by washing with hot water in a Soxhlet apparatus (16). This paper describes the performance of coconut shellbased carbon after four cycles of adsorption/regeneration. The changes in the capacity of the carbon are studied in relation to the changes in the quantitative deposition of sulfur species, their speciation, and location within the carbon microstructure. To choose the most economically feasible way of washing, hot and cold water were used. The number of washing cycles during regeneration was also modified to determine the amount of water needed to regenerate the sorption capacity of the carbon for hydrogen sulfide.
Experimental Section Materials. A S208c activated carbon, supplied by Waterlink Barnebey Sutcliffe, (irregular granules of about 5 × 1 mm) obtained from coconut shell was used for this study. Carbon of the same origin from the same supplier was used in a long-term test in the North River Water Treatment Plant (5). A subsample was washed in a Soxhlet apparatus to a constant pH of the leachate to remove the water-soluble impurities and then dried in an oven at 120 °C. The as received and washed samples are referred to as S and SW, respectively. The carbons were used in subsequent adsorption/ regeneration cycles. In the regeneration runs, the S sample was washed with cold water, whereas SW was regenerated in a Soxhlet apparatus with hot water. After each adsorption cycle the suffix “A” followed by the number of the cycle is VOL. 34, NO. 21, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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added. After regeneration the suffix “R” is added followed by the number consequent with the number of the adsorption run. For example, the carbon S-A1 is the exhausted sorbent after the first adsorption run. After regeneration (with cold water) the sample is designated as S-R1. Washing in a Soxhlet apparatus was done by placing 18 g of carbon in the extraction thimble. Five washing cycles were done with 200 mL of water for each cycle (total 55 L/kg). The cold water washing was done in a beaker in which 18 g of carbon was placed, mixed with 150 mL of cold water for 30 min, and then filtered. The water was changed 5 times (total 41.7 L/kg). The S-R2 sample was treated with 150 mL of 0.001 NaOH after the previous adsorption run and then washed using 5 washing cycles. The SW-R3 sample was washed using 198 L/kg and S-R3-167 L/kg. Methods. H2S Breakthrough Capacity. Moist air (relative humidity 80% at 25 °C) containing 0.3% (3000 ppm) H2S was passed through a column packed with granular carbon (length 370 mm, diameter 9 mm) at 0.5 L/min at room temperature. The column was widened at the top 60 mm to a diameter of 23 mm to minimize the wall effect. The H2S emission was monitored by an Interscan LD-17 H2S continuous monitor system (electrochemical detector) interfaced with a computer data acquisition program. The test was stopped at a breakthrough concentration of 500 ppm. The breakthrough capacity of the carbon was then calculated using the integrated area above the breakthrough curve (difference between inlet 3000 ppm and breakthrough concentration curves), the mass of carbon, and flow rate. The subsequent dynamic adsorption experiments were carried out with carbons after regeneration using both cold and hot water (S and SW). Boehm Titration. Although Boehm titration results were described previously for the carbon studied (12), new experiments were performed in order to check the susceptibility of carbon to air oxidation (the sample has been stored in the laboratory for almost 3 years). One gram of carbon sample was placed in 50 mL of the following 0.05 N solutions: sodium hydroxide, sodium carbonate, sodium bicarbonate, and hydrochloric acid. The vials were sealed and shaken for 24 h, then 5 mL of each filtrate was pipetted, and the excess of base or acid was titrated with HCl or NaOH. The numbers of acidic sites of various types were calculated under the assumption that NaOH neutralizes carboxyl, phenolic, and lactonic groups; Na2CO3 - carboxyl and lactonic; and NaHCO3 only carboxyl groups (17). The number of surface basic sites was calculated from the amount of hydrochloric acid that reacted with the carbon. pH of Carbon Surface. A sample of 0.4 g of dry carbon powder was added to 20 mL of water, and the suspension was stirred overnight to reach equilibrium. Then the sample was filtered, and the pH of the solution was measured. Thermal Analysis. Thermal analysis was carried out using a TA Instruments Thermal Analyzer. The instrument settings were as follows: heating rate 10 deg/min and either air or nitrogen atmosphere with 100 mL/min flow rate. Sorption of Nitrogen. Nitrogen isotherms were measured using an ASAP 2010 (Micromeritics) at -196 °C. Before the experiment the samples were heated at 100 °C and then outgassed at this temperature under a vacuum of 10-5 Torr to constant pressure. The isotherms were used to calculate the specific surface area, SN2, micropore volume, Vmic, and total pore volume, Vt. All of the above parameters were calculated using Density Functional Theory (DFT) (18, 19). In addition, the surface areas and pore volumes were calculated using the BET and Dubinin-Raduskevich methods (20). 4588
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FIGURE 1. H2S breakthrough curves for the SW and S carbons after subsequent adsorption/regeneration cycles.
TABLE 1. Breakthrough Capacities and pH Values of the Carbon Surfaces sample
H2S breakthrough capacity (mg/g)
pH
81
7.64 2.11
SW SW-A1 SW-R1 SW-A2 SW-R2 SW-A3 SW-R3 SW-A4 S S-A1 S-R1 S-A2 S-R2 S-A3 S-R3 S-A4
35 27 24 125 3.1 26 26
3.28 2.46 3.01 2.37 10.00 2.05 2.76 2.60 4.71 2.42 3.93 2.47
Results and Discussion The breakthrough curves for the carbons initially and after three regeneration cycles are collected in Figure 1. The X-coordinate axis represents the cumulative time for each sample after all adsorption cycles. The calculated H2S breakthrough capacities and pH values of the carbon surfaces are summarized in Table 1. Analysis of the data shows that there is a 50% difference in the capacity for the as received and washed carbons (A1 series). This is likely related to the differences in the pH values (10-12). The pH of the as received carbon is in the basic range (∼10), whereas after washing in a Soxhlet apparatus some basic species were removed and the pH decreased to almost neutral (∼7.6). As indicated elsewhere (10-12), high pH results in an increase of the adsorption capacity due to the enhanced dissociation of hydrogen sulfide within the adsorbed water film present on the carbon surface. After the first regeneration the capacities for the samples washed with cold and hot water do not differ significantly. Figure 2 shows the changes in pH for subsequent adsorption/regeneration runs for both the cold and the hot
FIGURE 2. Changes in pH after subsequent adsorption/regeneration runs.
FIGURE 4. DTG curves for chosen S series of samples.
FIGURE 3. DTG curves for chosen SW series of samples. water series. After the first adsorption cycle the pH decreases to around 2. Such a low value indicates the presence of sulfuric acid. After each regeneration the pH increases one unit (two units for the NaOH treated sample) and then decreases to pH 2 after the next adsorption run. It is well-known (1-12) that hydrogen sulfide on the surface of activated carbon (SAC) can be oxidized to elemental sulfur and/or sulfur dioxide according to the following reactions: SAC
H2S + 1/2O2 98 S° + H2O SAC
H2S + 3/2O2 98 SO2 + H2O
(1) (2)
Then during washing the following processes can occur:
SO2 + H2O + 1/2O2 f H2SO4 H2O
(3)
S° + O2 f SO2 + O2 98 H2SO4
(4)
SO2 + C f S + CO2
(5)
To evaluate the nature and amount of sulfur species, TA analysis was carried out in a nitrogen atmosphere (11, 12). The DTG curves for our samples after H2S adsorption and regeneration are presented in Figures 3 and 4. In the cases of exhausted samples (S-A series and SW-A series), two welldefined peaks are present. The first has its maximum at
240 °C, the second one, at around 450 °C. Following the assignment of peaks to the oxidized sulfur species described elsewhere (11, 12, 21-23), the first weight loss represents sulfur in the form of sulfur dioxide and the secondselemental sulfur. For the SW sample after first regeneration run, SWR1, the amount of adsorbed species decreased significantly (Figure 3). The biggest decrease in intensity is observed for the high-temperature peak, suggesting the capability of hot water to remove/oxidize elemental sulfur (eq 4). On the other hand, the amount of species desorbed as SO2 decreased only slightly suggesting strong bonds of sulfuric acid with the carbon surface (24, 25). After the second adsorption run the amount of species desorbed as SO2 increased, reaching the amount adsorbed in the first run. The amount of sulfur also increased, but the intensity of the peak representing this species is smaller than that obtained after the first run. These changes follow the trend in the adsorbed amount of hydrogen sulfide (Table 1). After regeneration of SW-A3 an interesting phenomena is noticed. Although the intensity of the peak representing SO2 decreased, as expected, the intensity of the peak assigned to elemental sulfur increased. The explanation of this unexpected behavior may be in fact that the SW-R3 sample, unlike the other samples, was regenerated after 1 month storage in the laboratory. It is likely that during this time adsorbed sulfuric acid migrated to more energetically favorable adsorption centers in small pores. This causes its removal from the surface to require more energy, which is reflected in a shift to higher temperatures of the weight loss associated with H2SO4 desorption. Such a phenomenon is not noticed for the cold water washed samples (Figure 4). All of these were analyzed promptly after the adsorption/ regeneration experiments. For the sample after first run a decrease in the intensity of the peak representing SO2 and a disappearance of the shoulder are noticed. On the other hand, the intensity of the peak associated with sulfur is unchanged. This is due to the inability of cold water to efficiently remove/oxidize elemental sulfur. After the third adsorption run the intensity of the first peak is the same as that observed after the first regeneration, suggesting low selectivity for SO2 formation. The intensity of the second peak also does not change significantly. These small changes in weight loss are associated with low capacity for adsorption (Table 1). Nevertheless, after regeneration (S-R3) a significant amount of SO2 was removed, and a decrease in the sulfur content was observed. The S-R3 sample was washed using VOL. 34, NO. 21, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 2. Sulfur Content and Efficiency of Regeneration efficiency of regeneration (%)
sulfur content (%) sample SW-A1 SW-R1 SW-A2 SW-R2 SW-A3 SW-R3 SW-A4 S-A1 S-R1 S-A2 S-R2 S-A3 S-R3 S-A4
S (Bth. cap.) 7.63 3.29 2.49 2.21 11.80 0.29 2.40 2.46
SO2 (TA)
Sel (TA)
St (TA)
Sef
SO2
5.21 5.63 8.24 7.63 3.30 2.12 3.77 36.7 5.16 3.57 6.15 5.56 2.07 1.26 2.30 37.3 3.12 3.28 4.84 3.28 1.59 8.42 9.22 3.00 11.06 12.56 9.92 7.89 6.28 10.23 11.08 3.43 2.66 4.38 56.5 4.67 1.65 4.23 5.06 4.11 7.09 9.15 5.95 2.10 5.68 6.73 48.9 3.45 7.52 9.25 7.69
Sel
St
62.3 54.2 40.6 39.1
57.6 57.2
19.9 26.4
four times more water than was used with the other samples. This results in more efficient regeneration, as indicated previously (16). The peak representing elemental sulfur is seen to be shifted to a higher temperature range than was observed previously by Adib et al. (16) on the same carbon. This is likely owing to changes in the carbon chemistry as a result of air oxidation. As was pointed out elsewhere (10, 12), surface chemistry is a very important factor governing the speciation of the oxidation products and the adsorption capacity of the carbon. After 3 years of storage in the laboratory, the carbon was slightly oxidized as reflected in an increased number of acidic groups determined using the Boehm titration. The analyses revealed that the quantity of acidic groups increased from 0.31 mmol/g to 0.70 mmol/g after the 3-year storage. The amounts of specific acids and basic groups are as follows: 0.12 mmol/g carboxylic acids, 0.55 mmol/g phenols, 0.03 mmol/g lactones, and 0.47 mmol/g basic groups. A significant increase is observed in the quantity of phenols, reported previously to be 0.12 mmol/g (12). It is likely that the “new” surface promotes the oxidation of sulfur to larger sulfur polymers than were observed for the “fresh” carbon sample. Therefore a higher temperature is needed for their removal from the surface. Surface oxidation of the stored samples also has its effect on the performance of carbons as H2S adsorbents. An increase in the number of surface acidic groups resulted in 20% lower breakthrough capacity than reported previously (∼110 mg/g of carbon) (12, 16). The percentages of sulfur species such as SO2 and S elemental (Sel), calculated from the weight loss between 130 and 330 °C and 330-530 °C, respectively, are collected in Table 2 along with an evaluated sulfur content from the breakthrough capacity, S (Bth. cap.), total sulfur content calculated from TA (St), and effective sulfur content (Sef) (the sum of the amount of sulfur evaluated from the breakthrough capacity and the amount of sulfur left after the previous regeneration run, Sefi ) SRi-1 + SAi). Generally good agreement between values of St and Sef is found. The small discrepancies can be due to the assumption that only two sulfur species are present (10, 11, 22). In the case of the cold water washed carbons the peaks are slightly broader, suggesting heterogeneity in the speciation of sulfur compounds deposited on the carbon surface. It is necessary to emphasize that the TA results obtained for the hot water washed sample after the third regeneration and fourth adsorption runs are exceptions from the other samples of the series. After washing, an increase in the sulfur content is revealed. As mentioned above, an increase in the content of sulfur after washing is apparently erroneous, and it likely due to changes in the adsorbed phase 4590
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FIGURE 5. Changes in the content of sulfur species after subsequent adsorption/regeneration cycles.
FIGURE 6. The selectivity for H2S oxidation during adsorption steps for the samples studied. and the rearrangement of sulfuric acid within the pore system. The acid likely moved into small pores and was strongly adsorbed there. If such a process occurred, the evaluated amount of elemental sulfur is overestimated due to the contribution of sulfuric acid oxygen (around 70%) to the weight loss represented by the peak assigned to sulfur. The efficiency of carbon regeneration was calculated from the TA data as the ratio of the difference in the content of species on the carbon surface after H2S adsorption and after regeneration to the content of species after the adsorption process. Obtained efficiencies for SO2, Sel, and total sulfur compounds, St, are collected in Table 2. Although the results do not differ significantly, total efficiencies are slightly higher for the hot water treatment. This is probably due to its ability to remove/oxidize more colloidal sulfur adsorbed on the carbon surface (eq 4). The changes in the content of sulfur species after subsequent adsorption/regeneration cycles are collected in Figure 5. Although the trends for cold and hot water washing are parallel, the relative content of elemental sulfur in the cold water washed carbon is higher than it is in the hot water washed material. Since SO2 is the most desired species (due to the feasibility of its removal from the surface (14, 15)) the selectivity for oxidation during the H2S adsorption steps was calculated as the ratio of the weight loss as SO2 (mmol/g) to the total weight loss due to the removal of SO2 and Sel(mmol/g). The results obtained are presented in Figure 6. They show that selectivity for oxidation on hot water washed samples is on the average slightly lower than that on the cold water washed counter-
FIGURE 7. Changes in the structural parameters after subsequent adsorption/desorption cycles
FIGURE 8. Pore size distribution for the chosen SW series of samples.
TABLE 3. Parameters of Porous Structure Calculated from Adsorption of Nitrogen sample SW SW-A1 SW-R1 SW-A2 SW-R2 SW-A3 SW-R3 S S-A1 S-R1 S-A2 S-R2 S-A3 S-R3 S-A4
SBET (m2/g)
Vmic(DR) (cm3/g)
Vt (cm3/g)
Vmic(DFT) (cm3/g)
SDFT (m2/g)
880 672 859 641 688 697 740 880 527 714
0.424 0.317 0.405 0.303 0.316 0.338 0.355 0.424 0.243 0.333
0.457 0.358 0.454 0.338 0.373 0.359 0.394 0.457 0.284 0.385
0.359 0.270 0.329 0.259 0.262 0.268 0.295 0.359 0.211 0.286
889 632 784 640 623 662 663 889 496 684
721 523 532 572
0.347 0.240 0.245 0.264
0.374 0.285 0.290 0.321
0.292 0.207 0.209 0.230
688 490 513 508
parts. A systematic decrease in the selectivity for the cold water washed sample may be the result of a significant deposition of elemental sulfur on active carbon sites responsible for the oxidation of H2S to SO2 which is not removed after washing (Figure 6). The low selectivity for oxidation of the SW-A4 sample can be the result of a bias in overestimating the elemental sulfur content discussed above. An increase in selectivity for SW-A2 compared to the sample after the first adsorption run can be a result of slight oxidation of the surface. As indicated elsewhere (10-12, 16) lower pH (being the result of the presence of surface oxides) leads to the larger contribution of SO2 to the oxidation products. The structural parameters calculated from nitrogen adsorption isotherms are given in Table 3. Analysis of the data in Table 3 indicates that after the first adsorption/ regeneration run the surface area was significantly renewed. Although the porosity did not reach its initial value, regeneration of porosity was significant, especially for the hot water washed sample, SW. With an increasing number of adsorption/regeneration cycles the surface area decreases as shown in Figure 7. A similar trend is followed by the porosity. Comparison of the changes in the pore volumes for the hot and cold water washed samples reflects the discussed above in the efficiency of removal of sulfur species. In the case of hot water washing, although the slight changes in the pore
FIGURE 9. Pore size distribution for the chosen S series of samples. volume for particular runs are noticed, the volume oscillates close to 0.3 cm3/g (Table 3, Figure 7). About 30% of the initial pore capacity of the carbon is inaccessible for nitrogen due to the deposition of sulfur species and their strong adsorption on the carbon surface. The almost constant value of the H2S breakthrough capacity for regenerated samples reported in Table 1 (between 30% and 40% of the initial capacity) suggests the relationship between volume of pores and capacity as was pointed out previously. For the sample after the last adsorption run a significant decrease is noticed. This may indicate the oxidation of the surface and destruction of the small pores due to 1 month storage of the exhausted sample with sulfuric acid adsorbed on the surface. In the case of the cold water washed sample, after the first regeneration the volume of micropores is more or less constant, and after the next regeneration (R2) it significantly decreases to around 50% of its initial value. This suggests that the deposition of sulfur occurs in micropores and cold water is less effective in the regeneration of their pore volume. A detailed view of the changes in the pore structure is presented in Figures 8 and 9 as pore size distributions (PSDs) VOL. 34, NO. 21, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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calculated using density functional theory (19, 20). However, in our calculations only nitrogen-carbon interactions were taken into account and the presence of sulfur was neglected; the effect of sulfur-nitrogen interactions on the resulting distributions is expected to be small and demonstrated only as a slight shift of the distributions on the X-axis. The data clearly show that mainly small pores are affected by sulfur deposition (Figures 8 and 9). Washing with both cold and hot water opens the active portion of pore space which can be used in the subsequent breakthrough capacity experiments. To study the effect of the amount of water and/or the number of washing cycles needed for regeneration of the carbons, the SW-R3 was washed with 4 times more water than in the other washing cycles (198 L/kg). The results described above do not show significant differences in the efficiency of regeneration, suggesting that a set of five washing cycles leads to the stable features of carbon surfaces. In the case of the cold water washed sample, S-A2, the H2S capacity after washing using 41.7 L/kg was very low, almost negligible. To check the neutralization effect the sample was treated with 0.001 M sodium hydroxide and then washed using five washing cycles (S-R2). After this treatment the capacity increased to the level measured for the hot water washed samples. In the next regeneration run, 20 washing cycles (167 L of water/kg) renewed the capacity to the previous level (S-R3). The results obtained show both the differences and similarities in the efficiency of regeneration using water of spent carbons previously used as hydrogen sulfide adsorbents. After the first adsorption run the significant capacity (around 60%) is lost irreversibly in the case of both series of samples. This is the result of the deposition of elemental sulfur in carbon micropores and strong adsorption of sulfuric acid leading to the low pH. Despite this, some capacity exists after the first runs, and this is maintained at a more or less constant level through the next three adsorption/regeneration cycles. Though the selectivities for oxidation are similar for both series, the efficiency of washing is slightly higher when hot water is used. This is due to its capability to remove/ oxidize some amount of elemental sulfur from the carbon pore system. Water used for regeneration can be neutralized with such neutralizing agents as lime, soda ash, and caustic soda and then released into ambient waters (with proper concentration) or treated along with main wastewater stream coming to water treatment plants (26).
Acknowledgments This study was supported by New York City Department of Environmental Protection.
Literature Cited (1) Turk, A.; Sakalis, E.; Rago, O.; Karamitsos, H. Ann. N. Y. Acad. Sci. 1992, 661, 221.
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(2) Turk, A.; Mahmood, K.; Mozaffari, J. Water Sci. Technol. 1993, 27, 121. (3) Bandosz, T. J.; Le, Q. Carbon 1998, 36, 39. (4) Bandosz, T. J. Carbon 1999, 37, 11. (5) Bandosz, T. J.; Bagreev, A.; Adib, F.; Turk, A. Environ. Sci. Technol. 2000, 34, 1069. (6) Kaliva, A. N.; Smith, J. W. Can. J. Chem. Eng. 1983, 61, 208. (7) Meeyoo, V.; Trimm, D. L.; Cant, N. W. J. Chem. Technol. Biotechnol. 1997, 68, 411 (8) Meeyoo, V.; Lee, J. H.; Trimm, D. L.; Cant, N. W. Catalysis Today 1998, 44, 67. (9) Dalai, A. K.; Majudar, A.; Tollefson, E. L. Environ. Sci. Technol. 1999, 33, 3, 2241. (10) Adib, F.; Bagreev, A.; Bandosz, T. J. J. Coll. Interface Sci. 1999, 214, 407. (11) Adib, F.; Bagreev, A.; Bandosz, T. J. J. Coll. Interface Sci. 1999, 216, 360. (12) Bandosz, T. J.; Bagreev, A.; Adib, F. Environ. Sci. Technol. 2000, 34, 686. (13) Bandosz, T. J.; Bagreev, A.; Adib, F.; Turk, A.; Murphy, T. NYWEA 71st Annual Meeting 1999. (14) Hayden, R. A. WIPO PCT WO9526230A1, 1995. (15) Carbon Regeneration Using Water: Centaur HSV. Calgon Carbon Corporation Manual. (16) Adib, F.; Bagreev, A.; Bandosz, T. J. Ind. Eng. Chem. Res. 2000, 39, 2439. (17) Boehm, H. P. In Adavances in Catalysis; Academic Press: New York, 1966; Vol. 1, p 179. (18) Lastoskie, C. M.; Gubbins, K. E.; Quirke, N. J. Phys. Chem. 1993, 97, 7, 4786. (19) Olivier , J. P.; Conklin, W. B. Presented at 7th International Conference on Surface and Colloid Science, Compiegne, France, 1991. (20) Dubinin, M. M. In Chemistry and Physics of Carbon; Walker, P. L. Jr., Ed.; Marcel Dekker: New York, 1966; Vol. 2, p 51. (21) Rodriguez-Mirasol, J.; Cordero, T.; Rodriguez, J. J. Extended Abstracts of 23rd Biennal Conference on Carbon; College Park, July 1997; p 376. (22) Chang, C. H. Carbon 1981, 19, 175. (23) Mochida, I.; Miyamoto, S.; Kuroda, K. Energy Fuels 1999, 13, 369. (24) Lisovskii, A.; Semit, R.; Aharoni, C. Carbon 1997, 35, 1639. (25) Lisovskii, A.; Shter, E.; Semit, R.; Aharoni, C. Carbon 1997, 35, 1645. (26) Holmes, G.; Singh, B. R.; Theodore, L. Handbook of Environmental Management and Technology; Wiley: New York 1993.
Received for review March 31, 2000. Revised manuscript received August 1, 2000. Accepted August 14, 2000. ES001150C
