Effect of Polyphosphate on Removal of Endocrine-Disrupting Chemicals of Nonylphenol and Bisphenol-A by Activated Carbons

Transcription

1 Water Qual. Res. J. Canada, 2005 Volume 40, No. 4, Copyright 2005, CAWQ Effect of Polyphosphate on Removal of Endocrine-Disrupting Chemicals of Nonylphenol and Bisphenol-A by Activated Carbons Keun J. Choi, 1 Sang G. Kim, 1 Chang W. Kim 2 and Seung H. Kim 3 * 1 Water Quality Institute, Busan City Waterworks, Korea 2 Department of Environmental Engineering, Busan National University, Korea 3 Department of Civil and Environmental Engineering, Kyungnam University, Korea This study examined the effect of polyphosphate on removal of endocrine-disrupting chemicals (EDCs) such as nonylphenol and bisphenol-a by activated carbons. It was found that polyphosphate aided in the removal of nonylphenol and bisphenol- A. Polyphosphate reacted with nonylphenol, likely through dipole-dipole interaction, which then improved the nonylphenol removal. Calcium interfered with this reaction by causing competition. It was found that polyphosphate could accumulate on carbon while treating a river. The accumulated polyphosphate then aided nonylphenol removal. The extent of accumulation was dependent on the type of carbon. The accumulation occurred more extensively with the wood-based used carbon than with the coal-based used carbon due to the surface charge of the carbon. The negatively charged wood-based carbon attracted the positively charged calcium-polyphosphate complex more strongly than the uncharged coal-based carbon. The polyphosphate-coated activated carbon was also effective in nonylphenol removal. The effect was different depending on the type of carbon. Polyphosphate readily attached onto the wood-based carbon due to its high affinity for polyphosphate. The attached polyphosphate then improved the nonylphenol removal. However, the coating failed to attach polyphosphate onto the coal-based carbon. The nonylphenol removal performance of the coal-based carbon remained unchanged after the polyphosphate coating. Key words: endocrine-disrupting chemicals, nonylphenol, bisphenol-a, polyphosphate, activated carbon Introduction Nonylphenol is an endocrine-disrupting chemical (EDC) commonly found in water bodies (Rudel et al. 1998; Roefer et al. 2000; Yamamoto et al. 2000). It is generally used as detergents, emulsifiers, and wetting and dispersing agents. After being used in households and industry, it is eventually discharged into wastewater treatment plants (Roefer et al. 2000). Fortunately, nonylphenol is prone to wastewater treatment. According to Nasu et al. (2001), nonylphenol and bisphenol-a were very effectively removed (>99%) during wastewater treatment. Since nonylphenol is commonly found in water bodies, it is also important in drinking water treatment. Nonetheless, very few studies are available to assess the fate during water treatment. Kim et al. (2002) evaluated the treatability of nonylphenol and bisphenol-a during drinking water treatment. According to their study, granular activated carbon (GAC) adsorption was effective in removing EDCs at an empty bed contact time of 15 min. Adsorption of these chemicals could be affected by many parameters, including base material of activated carbon. The adsorption capacity could be different depending upon * Corresponding author; shkim@kyungnam.ac.kr the base material (e.g., coal, coconut or wood). peration time also affects the adsorption capacity. The adsorption capacity gradually decreases with time in normal operation, as adsorption sites are filled up. This suggests that the used carbon is a less effective adsorbent than the virgin carbon. However, it was found during preliminary experiments that the wood-based used carbon was superior to its corresponding virgin carbon in nonylphenol removal (Choi et al. 2004). Subsequent chemical analysis revealed exceptionally high polyphosphate content in the wood-based used carbon (Table 3). It was therefore suspected that polyphosphate might be related to the improved removal capacity of the woodbased used carbon. This study examines the effect of polyphosphate on removal of EDCs (nonylphenol and bisphenol-a). Whether polyphosphate helps improve the removal capacity of the activated carbon for nonylphenol and bisphenol-a was evaluated. Materials and Methods Materials Nonylphenol or bisphenol-a (product of Dr. Ehrenstorfer, GmbH) was dissolved in methanol and then diluted with distilled water to make the working solution 484

2 Effect of Polyphosphate on Removal of EDCs mg L -1. A predetermined amount of this solution was then added into the treated water from a nearby water treatment plant to make the raw water. This water treatment plant has treated the river water (Nakdong river) using conventional processes of coagulation, sedimentation and filtration combined with advanced processes of ozonation and GAC adsorption. The treated water had turbidity and DC (dissolved organic carbon) levels in the range of 0.04 to 0.08 NTU and 0.6 to 0.8 mg L -1, respectively. The raw water for this study was prepared from the above treated water to represent the real water conditions more closely. The Nakdong river was not used directly for the preparation due to the possible interferences from its suspended solids. The final concentrations of nonylphenol and bisphenol-a in the raw water were in the range of 472 to 1187 µg L -1. The polyphosphate solution was prepared by dissolving the anticorrosion chemical (P 2 5 content of 70%) in nitric acid and diluting with distilled water at the concentration of 1000 mg L -1. Activated carbon with different base materials was used in this study, i.e., wood-based carbon (WB) and coal-based carbon (CB). Picabiol products were used for WB, while Calgon products (F400) were used for CB. Table 1 shows characteristics of the carbons used in this study. WB-0 and WB-3.1 are the wood-based virgin and used carbons (3.1 years old). Similarly, CB-0 and CB-5.9 are the coal-based virgin and used carbons (5.9 years old). The used carbons were taken from the nearby water treatment plants. These plants have also treated the Nakdong river. Methods Polyphosphate was either added directly into the raw water or coated onto the adsorbent (e.g., anthracite coal or activated carbon). A jar test was used to add polyphosphate into the raw water. The volume of the raw water was 2 L. Predetermined amounts of the polyphosphate solution were added into the raw water while it was stirred for 0.5 to 3.5 h. The final polyphosphate concentration used in this study was in the range of 0.5 to 9.6 mg L -1. The polyphosphate coating was conducted by soaking adsorbent of anthracite coal or activated carbon into a high concentration of polyphosphate solution (1000 mg L -1 ). It was then dried at 105ºC for 24 h. The coated media was crushed into 200-mesh size before use. After the addition of polyphosphate, the supernatant was filtered through filter paper with 1.2-µm pore size. The filtrate was then analyzed for its concentration of nonylphenol or bisphenol-a. Each experiment was conducted 2 to 6 times. The concentrations of nonylphenol and bisphenol-a were analyzed by FIA (flow injection analysis) using Agilent LC/MSD. Table 2 shows the analytical conditions used in this study. For a quick analysis, pretreatment was not done. Calibrations were conducted with pure water as well as raw water. Their ratio was used to adjust the difference in sample matrix (Morizane et al. 2003). The quantitation limits were 15 µg L -1 (nonylphenol) and 5 µg L -1 (bisphenol-a). The standard deviation of five replicates at the quantitation limits was ±5%. The ash contents of the activated carbons were analyzed using a Philips PW2400 x-ray spectrometer. Results and Discussion Micropores (<2 nm) and macropores (>50 nm) are well developed in the wood-based virgin carbon (Choi et al. 2004). This led to the large pore volume for the woodbased carbon. According to Table 1, WB-0 had a larger pore volume and specific area than CB-0. The specific area and pore volume reduced with operation as contaminants were adsorbed. The extent of the reduction was dependent on carbon type. The wood-based carbon experienced greater reduction. Table 1 shows that WB-3.1 had smaller specific area and pore volume than CB-5.9 despite the shorter operation period. The ash characteristics were also different depending on the carbon type, as shown in Table 3. The coal-based carbon (CB) had a higher content of Al 2 3 or Si 2 than the wood-based carbon (WB), while WB had a higher content of P 2 5 than CB due to chemical activation. The amount of ash increased and the characteristics of the ash changed with operation. Al 2 3 and Ca increased the most. Interestingly, the increase of P 2 5 was substantial for the wood-based carbon. The P 2 5 content of WB-3.1 (2.410 g) was more than 15 times greater compared to that of CB-5.9 (0.152 g), due to the phosphate contained in the Nakdong river. According to regular analysis, this river maintained a total phosphorus concentration of 0.02 to 0.1 mg L -1 (Yu 1998). The phosphate in the river TABLE 1. Physical characteristics of the activated carbons used in this study Activated carbon WB-0 WB-3.1 CB-0 CB-5.9 Material Wood Wood Coal Coal Bed volume used 0 89, ,000 peration year Specific area, m 2 g Pore volume, cm 3 g

3 486 Choi et al. TABLE 2. Analytical conditions of LC/MSD used in the measurement of the EDCs Endocrine-disrupting chemical Nonylphenol Bisphenol-A Mode APCI, negative APCI, negative Fragment voltage, V Mobile phase ACN:50 mm ACN:50 mm CH 3CNH 4 = 45:55 CH 3CNH 4 = 45:55 Flow, ml min Extract ion 219 (M-1) 227 (M-1) could accumulate at the activated carbon during operation. The extent of accumulation was different depending on carbon type. The wood-based carbon accumulated more polyphosphate than coal-based carbon. Addition of Polyphosphate TABLE 3. Ash characteristics of the activated carbons used in this study Specific content a g(activated carbon, g) -1 WB-0 WB-3.1 CB-0 CB-5.9 Si Al Fe Mn Ca Mg K Na P Ti Sum a Specific content: g of content/g of activated carbon. Figure 1 shows results of the direct addition of polyphosphate at two different doses (4.8 and 9.6 mg L -1 as P 2 5). Polyphosphate was directly added into the raw water, of which the nonylphenol concentration was 1187 µg L -1. According to Fig. 1, the direct addition of polyphosphate brought in the nonylphenol removal, although the removal extent was minimal. Sixteen percent removal was obtained at 4.8 mg L -1 of P 2 5, while the removal efficiency became 9% at 9.6 mg L -1 of P 2 5. These results led to a hypothesis that there was a chemical reaction between polyphosphate and nonylphenol, but that the reaction product was too small to be separated by filtration. That is why the addition of polyphosphate caused the nonylphenol removal, but the removal extent was not a function of the polyphosphate dosage. The separation efficacy determined the removal extent. Since the reaction product was smaller than the pore size of the filter paper (1.2 µm), the removal efficiency was poor. In order to improve the separation efficiency, the adsorbent was added. Two different adsorbents (anthracite coal and activated carbon) were used. These differ in their adsorption capacities. Anthracite coal is a poor adsorbent, while activated carbon is a good adsorbent. Addition of anthracite coal together with polyphosphate improved removal efficiency. This result suggests that the reaction product was adsorbed onto the anthracite coal after nonylphenol reacted with polyphosphate. However, the removal efficiency of nonylphenol was still low (34%) because anthracite coal was not an effective adsorbent. Figure 2 shows the effect of polyphosphate dosage on the nonylphenol removal when anthracite coal was added as an adsorbent. The dosage of anthracite coal was fixed at 3 mg L -1 because most water treatment plants added powdered activated carbon at this dosage. The nonylphenol concentration was 452 µg L -1. This figure clearly shows that the nonylphenol removal improved as the polyphosphate dosage was increased. There was no removal of nonylphenol without polyphosphate. The nonylphenol removal was noted only after addition of polyphosphate. This result suggests that nonylphenol could not be adsorbed onto anthracite coal, but that the reaction product of nonylphenol with polyphosphate was adsorbable. Accordingly, this confirmed that a reaction occurred between nonylphenol and polyphosphate. The more polyphosphate that was added, the more the reaction product was. The nonylphenol removal improved 4.8 ppm 9.6 ppm 9.6 ppm w/anthracite Fig. 1. Nonylphenol removal using polyphosphate with and without anthracite coal.

4 Effect of Polyphosphate on Removal of EDCs Polyphosphate dosage, mg/l Fig. 2. Nonylphenol removal as a function of polyphosphate dosage with anthracite coal as adsorbent. with increasing polyphosphate dosage. The polyphosphate addition at 1 mg L -1 resulted in approximately 21% removal of nonylphenol. Although results are not shown here, this removal efficiency was consistent under different experimental conditions. Figure 3 compares the nonylphenol removals by different adsorbents (the virgin and used wood-based activated carbon as well as anthracite coal). The dosages of these adsorbents and polyphosphate were 4.8 mg L -1. The nonylphenol concentration in the raw water was µg L -1. The raw water was agitated for 60 min. This figure shows that the activated carbons removed nonylphenol more effectively than anthracite coal. The removal efficiency of nonylphenol was 41% for anthracite coal, but the use of the activated carbon improved the removal efficiency more than two times. Interestingly, the used carbon removed nonylphenol more effectively than the virgin carbon. It was originally assumed that the virgin carbon would remove nonylphenol more effectively than the used carbon because the adsorption capacity decreased with operation. According to Table 1, WB-0 had a specific area of 1610 m 2 g -1, and a pore volume of 1.12 cm 3 g -1, while WB-3.1 had a specific area of 295 m 2 g -1 and a pore volume of cm 3 g -1. These values indicate that the adsorption capacity of the used carbon (WB-3.1) significantly deteriorated. However, the experimental result was different from the assumption. The used carbon maintained the removal capacity of nonylphenol despite the deteriorated adsorption properties. This could be caused by polyphosphate. The polyphosphate content of the activated carbon increased with operation, as mentioned earlier. It increased from g to g after 3.1 years of use (Table 3). It seemed that there was a reaction between polyphosphate in solid-phase activated carbon and nonylphenol in the solution. The wood-based used carbon removed nonylphenol more effectively than its corresponding virgin carbon because nonylphenol-bonding polyphosphate was available more at the used carbon. Polyphosphate also explains why the difference between the nonylphenol removal in the presence and absence of polyphosphate by the used carbon (WB-3.1) was insignificant. Since the used carbon already contained enough polyphosphate, further addition of polyphosphate could not make any difference in the removal performance of nonylphenol. Effects of contact time were then examined. While the contact time was varied from 0.5 to 3.5 h, the nonylphenol removal were compared under different conditions (Fig. 4). This figure shows that the nonylphenol removal was not affected by contact time. There was practically no difference in the nonylphenol removal once the contact time of more than 0.5 h was provided. All experiments were therefore conducted at the contact time of 0.5 h. Polyphosphate-Coated Activated Carbon Table 4 shows nonylphenol removal by the polyphosphatecoated activated carbons at two doses (1 and 2 mg L -1 ). The coated carbon was added into the raw water, of which the nonylphenol concentration was µg L -1. Four different carbons (CB-0/5.9, WB-0/3.1) were used in this experiment. WB-3.1 w/polyphosphate WB-0 w/polyphosphate WB-3.1 w/o polyphosphate Anthracite w/polyphosphate Fig. 3. Comparison of nonylphenol removal by different adsorbents. Fig. 4. An effect of contact time on nonylphenol removal.

5 488 Choi et al. TABLE 4. Comparison of nonylphenol removal by various activated carbons with and without polyphosphate coating Activated carbon Nonylphenol removal, % Dosage, Without With Type mg L -1 coating a coating b CB CB WB WB a Without polyphosphate coating. b With polyphosphate coating. These carbons were different depending on the base material and operation year. As expected, the nonylphenol removal improved with increasing carbon dosage. The wood-based carbon (WB) removed nonylphenol more effectively than the coal-based carbon (CB), due to the larger pore volume and the higher polyphosphate content. WB-0 had larger pore volume and higher polyphosphate content than CB-0 (Tables 1, 3). The larger pore volume could result in more adsorption of nonylphenol. The higher polyphosphate content might also contribute to the better removal of nonylphenol. As the adsorption capacity of the used carbon deteriorated, the polyphosphate content became important in the nonylphenol removal. The wood-based used carbon (WB-3.1) was able to maintain the removal capacity of nonylphenol, while the coal-based used carbon (CB-5.9) lost the capacity completely. This could be explained by the polyphosphate content of these carbons. The reduced pore volume would deteriorate the adsorption capacity of nonylphenol, while the increased polyphosphate content would improve the removal capacity of nonylphenol through the bonding. After the used carbon lost its adsorption capacity, the accumulated polyphosphate at the carbon drove the nonylphenol removal. Table 1 shows that the pore volumes and specific areas of the used carbons were smaller than those of the virgin carbons. Accordingly, the coal-based used carbon (CB-5.9) lost its nonylphenol removal capacity completely. However, the wood-based used carbon (WB-3.1) maintained the removal capacity due to the high content of polyphosphate. The high content of polyphosphate compensated the reduced adsorption properties. Reaction between nonylphenol and polyphosphate. Since the reaction between nonylphenol and polyphosphate was noted during the study, further experiments were conducted. It was hypothesized that nonylphenol would react with polyphosphate through dipole-dipole interaction. A positive charge was concentrated at the phosphorus atom in polyphosphate, while a negative charge was concentrated at the oxygen atom in nonylphenol. These two compounds were then attracted to each other through dipole-dipole interaction. Since polyphosphate is a strong ligand, it could form a complex (probably with calcium) in the water. The complex formation would then deter the reaction between nonylphenol and polyphosphate. The nonylphenol solution was prepared by adding 1.1 mg L -1 of nonylphenol into distilled water. Activated carbon of 2 mg L -1 was then added into the nonylphenol solution with and without polyphosphate and calcium ions. Polyphosphate was added at 2.8 mg L -1. Calcium chloride (CaCl 2 H 20) was added to the distilled water when effects from the calcium ion were examined. The calcium concentration was adjusted to 54 mg L -1, which is the typical value of the Nakdong river. Table 5 summarizes the results. The coal-based and wood-based carbons showed similar removal of nonylphenol without calcium and polyphosphate. Both carbons removed about 50% of nonylphenol. Their removal performances differed upon addition of polyphosphate. The coal-based carbon (CB-0) removed 65% of nonylphenol, while the wood-based carbon (WB-0) removed 72% of nonylphenol. This result clearly indicates that the addition of polyphosphate improved the removal performance of nonylphenol by activated carbon. The affinity for polyphosphate seemed different with each carbon type. The wood-based carbon showed a higher affinity for polyphosphate than the coal-based carbon. Unlike polyphosphate, calcium deteriorated the removal performance. The removal performance of CB-0 reduced to 60% and that of WB-0 reduced to 70% with calcium and polyphosphate. TABLE 5. Comparison of nonylphenol removal under various conditions Carbon type Distilled water alone a With polyphosphate b With polyphosphate and calcium ion c CB-0 51% 65% 60% WB-0 52% 72% 70% a 2 mg L -1 activated carbon was added into the distilled water containing 1.1 mg L -1 of nonylphenol. b 2 mg L -1 activated carbon was added into the distilled water containing 1.1 mg L -1 of nonylphenol and 2.8 mg L -1 of polyphosphate. c 2 mg L -1 activated carbon was added into the distilled water containing 1.1 mg L -1 of nonylphenol and 2.8 mg L -1 of polyphosphate and 54 mg L -1 of calcium.

6 Effect of Polyphosphate on Removal of EDCs 489 These results suggest that polyphosphate reacted with nonylphenol as well as calcium. Nonylphenol reacted with polyphosphate probably through dipoledipole interaction. The resulting reaction product was more adsorbable to activated carbon than nonylphenol, which contributed to the improved nonylphenol removal. Calcium interfered with the above reaction. Positively charged calcium ions formed a complex with negatively charged polyphosphate. Polyphosphate would be completely consumed by nonylphenol without calcium; however, there would be competition between nonylphenol and calcium ions for polyphosphate when calcium was present. Subsequently, the removal performance of nonylphenol by the activated carbon deteriorated. Since the complex between polyphosphate and calcium was positively charged, it would preferably adsorb onto the negatively charged activated carbon. That is why the polyphosphate accumulation was different depending on the carbon type. According to Mick et al. (1999), the wood-based carbon (WB) is negatively charged at neutral ph, while the coal-based carbon (CB) shows almost no charge. The negatively charged carbon evidently attracted the positively charged complex more than the carbon with no charge. Subsequently, the wood-based used carbon showed a high content of polyphosphate, while the coal-based used carbon showed a low content (Table 3). The nonylphenol removal performance of the wood-based used carbon remained intact due to high polyphosphate content. The affinity for polyphosphate was important for the polyphosphate coating. Polyphosphate easily attached to the wood-based carbon due to its high affinity for polyphosphate, but it was not easily attached to the coal-based carbon. When the polyphosphate coating was attempted on the coal-based carbon, a white gelatinous material was seen at the carbon surface. Figure 6 compares the activated carbon before and after coating. These microscopic pictures show that the surface of the WB-3.1 WB WB dosage, mg/l Fig. 5. Comparison of bisphenol-a removal by virgin and used carbons. wood-based carbon became different after the coating. However, such a change was not observed for the coalbased carbon due to the poor coating. The poor coating of polyphosphate resulted in poor removal of nonylphenol. The high affinity of the wood-based carbon for polyphosphate conspicuously aided the nonylphenol removal. According to Table 4, the polyphosphate coating improved the nonylphenol removal of the woodbased carbon. However, such improvement was not noticed for the coal-based carbon. The nonylphenol removal performance of the coal-based carbon remained unchanged after the polyphosphate coating. Removal of Bisphenol-A In order to examine that an effect of polyphosphate was limited to nonylphenol removal, the removal performances of bisphenol-a by the wood-based carbons were examined (Fig. 5). These carbons were added into the raw water, of which the bisphenol-a concentration was 540 µg L -1. According to Fig. 5, the used carbon was more effective in bisphenol-a removal than the virgin carbon. This was in line with the results of the nonylphenol removal. This result suggests that an effect of polyphosphate also existed for the bisphenol-a removal. Polyphosphate could attract bisphenol-a, which led to the better removal performance of bisphenol-a by the used carbon. Conclusions This study found that polyphosphate aided in the removal of nonylphenol and bisphenol-a. Polyphosphate reacted with nonylphenol likely through dipole-dipole interaction, which then improved the nonylphenol removal. Calcium interfered with this reaction by causing competition. Nonylphenol competed against calcium for polyphosphate, which subsequently deteriorated the nonylphenol removal performance of the activated carbon. It was found that polyphosphate could accumulate at the activated carbon during the normal operation of treating river water. The accumulated polyphosphate at the carbon then aided in nonylphenol removal. The accumulated polyphosphate enabled the wood-based used carbon to maintain its removal capacity of nonylphenol, comparable to the capacity of the virgin carbon. The extent of the accumulation differed depending on the carbon type. The accumulation occurred more extensively at the wood-based used carbon than at the coal-based used carbon due to the surface charge of the carbon. Polyphosphate formed a complex with calcium in water. The positively charged complex was then attracted more strongly to the negatively charged wood-based carbon than to the coal-based carbon without a charge. The polyphosphate-coated activated carbon was also effective in nonylphenol removal. The effect differed depending on the carbon type. Polyphosphate attached

7 490 Choi et al. readily onto the wood-based carbon during the coating due to its high affinity for polyphosphate. The attached polyphosphate then improved the nonylphenol removal. However, the coating failed to attach polyphosphate onto the coal-based carbon. White gelatinous material formed at the carbon surface, and subsequently, the nonylphenol removal performance of the coal-based carbon remained unchanged after polyphosphate coating. References Choi KJ, Kim SG, Kim CW, Kim SH Effects of activated carbon types and service life on removal of endocrine disrupting chemicals: amitrol, nonylphenol, and bisphenol-a. Chemosphere 58(11): Kim SG, Choi KJ, h KJ Fate of endocrine disruptor in water treatment processes. In The proceedings of IWA World Congress, Melbourne Convention Center. CD-Rom. Mick B, Gayle N, Rob H Adsorption of NM onto activated carbon: effect of surface charge, ionic strength, and pore volume distribution. J. Colloid Interface Sci. 210: Morizane K, Hara I, Shiode S Removal effect by Cl 2 & 3 and determination by LC/MSD in YDGWA using acrylamide. J. Japan. Water Works Assoc. 72:2 11. Nasu M, Goto M, Kato H, shima Y, Tanaka H Study on endocrine disrupting chemicals in wastewater treatment plants. Water Sci. Technol. 43(2): Roefer P, Snyder S, Zegers RE, Rexing DJ, Fronk JL Endocrine-disrupting chemicals in a source water. J. Am. Water Works Assoc. 92(8): Rudel RA, Melly SJ, Geno PW, Sun G, Brody JG Identification of alkylphenols and other estrogenic phenolic compounds in wastewater, septage, and groundwater on Cape Cod, Massachusetts. Environ. Sci. Tech. 32(7): Yamamoto T, Yasuhara A, Shiraishi H, Nakasugi Bisphenol A in hazardous waste landfill leachates. Chemosphere 42(4): Yu MH The characteristics of water quality to water system in Nakdong river. In The report of water quality research 4. Institute of Busan, Korea. Fig. 6. Comparison of the activated carbons before and after the polyphosphate coating. Received: June 9, 2004; accepted: June 8, 2005.