Environ. Sci. Technol. 2009, 43, 4858–4863
Using Ultraviolet Absorbance and Color To Assess Pharmaceutical Oxidation during Ozonation of Wastewater ERIC C. WERT,* FERNANDO L. ROSARIO-ORTIZ, AND SHANE A. SNYDER Southern Nevada Water Authority (SNWA), P.O. Box 99955, Las Vegas, Nevada 89193-9955
Received December 11, 2008. Revised manuscript received April 22, 2009. Accepted April 28, 2009.
The reduction of ultraviolet (UV) absorbance at 254 nm (UV254) and true color were identified as appropriate surrogates to assess the oxidation of six pharmaceuticals (i.e., carbamazepine,meprobamate,dilantin,primidone,atenolol,andiopromide) during ozonation of wastewater. Three tertiary-treated wastewaters were evaluated during oxidation with ozone (O3) and O3 coupled with hydrogen peroxide (O3/H2O2). The correlation between pharmaceutical oxidation and removal of UV254 was dependent upon the reactivity of each specific compound toward ozone, as measured by the second-order rate constant (k′′O3). Oxidation of compounds with k′′O3 > 103 M-1 s-1 correlated well (R2 > 0.73) with UV254 reduction between 0-50%. Oxidation of compounds with apparent k′′O3 < 10 M-1 s-1 resulted primarily from hydroxyl radicals and correlated well (R2 > 0.80) with the UV254 reduction of 15-65%. The removal of true color also correlated well (R2 > 0.85) with the oxidation of pharmaceuticals during the ozonation of two wastewaters. These correlations demonstrate that UV254 reduction and true color removal may be used as surrogates to evaluate pharmaceutical oxidation in the presence or absence of dissolved ozone residual during advanced wastewater treatment with O3 or O3/H2O2. The use of online UV254 measurements would allow wastewater utilities to optimize the ozone dose required to meet their specific treatment objectives.
Introduction The detection of various pharmaceuticals and endocrine disrupting compounds (EDCs) in drinking water supplies has elevated public interest in removing these contaminants from the environment. Because of advances in modern analytical technology, many of these compounds can be detected at low levels (ng/L), and widespread occurrence is still being evaluated in drinking water (1). At this time, little information exists regarding the human health impacts of these substances. However, trace concentrations of steroids and other EDCs from wastewater outfalls have been linked to reproductive disruption in fish (2, 3). As more information is gathered regarding the environmental impacts, wastewater treatment alternatives are needed to remove these contaminants prior to discharge into the environment. * Corresponding author phone: + 1-702-567-2306; fax: + 1-702567-2085; e-mail:
[email protected]. 4858
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 43, NO. 13, 2009
Ozonation has been demonstrated as an effective treatment technology for the oxidative removal of many trace organic contaminants from wastewater (4-7). Contaminant oxidation occurs through reactions with ozone (O3), hydroxyl radicals (•OH), or both. The importance of each pathway can be determined from the chemical reactivity between a specific contaminant and O3 or •OH, as measured by the secondorder reaction rate constants (k′′O3 and k′′OH). Published values for k′′O3 are in the range of 105 M-1 s-1, whereas values for k′′OH are typically >108 M-1 s-1 (8). Water quality plays an important role in determining the degree of contaminant oxidation during ozonation (7, 9). Rapid O3 consumption, commonly referred to as O3 demand, typically occurs within the first 30 s of ozonation due to reactions initiated by organic [i.e., effluent organic matter (EfOM)] and inorganic (i.e., nitrite) water quality constituents (10). Greater O3 dosages are required to overcome these initial demands and result in enhanced contaminant oxidation. Integrating the dissolved O3 residual concentration (C) over the contact time (T) provides a measure of O3 exposure (∫O3dt), commonly referred to O3 CT (11). Ozone CT is used to assess disinfection during drinking water applications and can also be used to evaluate contaminant oxidation (7). However, the use of O3 CT as a surrogate to evaluate pharmaceutical oxidation is limited during wastewater treatment. Significant removal of pharmaceuticals can occur during the O3 demand phase when CT cannot be measured due to the absence of measurable dissolved O3 residual ( 103 M-1 s-1) was oxidized below the MRL of 25 ng/L. The difference in removal rates can be explained by the differences in k′′O3 (103-105 M-1 s-1). As the reactivity with O3 increases for each compound, greater pharmaceutical oxidation was observed when UV254 reduction was between 0-30%. These results agree with pCBA degradation results shown in Figure 3, where limited •OH exposure was observed (as quantified by a change in pCBA) when the change in UV254 was 15%, which corresponded well with the pCBA results in Figure 3. From this information, meprobamate, dilantin, and primidone appear to have a similar reactivity as that of pCBA and could be used as •OH indicator compounds. Iopromide was shown to be slowreacting with O3 (k′′O3 < 10 M-1 s-1) and fast-reacting with • OH (k′′OH > 109 M-1 s-1) in Table 2. Although detected in only one wastewater, the removal of iopromide (R2 ) 0.95, n ) 8) also showed excellent linear correlation with the percent reduction of UV254 (Figure S1 of the Supporting Information). Oxidation of these four compounds occurred when the UV254 reduction was between 15-65%. Meprobamate results also illustrate that the correlation between contaminant oxidation and UV254 can be applied for compounds that are not aromatic. At O3 dosages approximately equal to the IOD, UV254 reductions of 29%, 33%, and 42% were observed in LVNV, RMCO, and PCFL, respectively. When operating within these ranges of UV254 reduction, compounds with k′′O3 > 105 M-1 s-1 can be oxidized to below the MRL, while compounds with k′′O3 < 10 M-1 s-1 may be up to 55% oxidized. The results obtained from this study agree with those obtained by Buffle •
FIGURE 5. Linear correlation between the percent removal of UV254 with contaminants apparently slow-reacting with O3 (k′′O3 < 10 M-1 s-1) and fast-reacting with •OH (k′′OH > 109 M-1 s-1) during O3 and O3/H2O2 experiments: (a) meprobamate, (b) dilantin, and (c) primidone. et al. (23). Within the IOD phase of ozonation, Buffle et al. showed organic contaminants with k′′O3 > 104 M-1 s-1 were >95% oxidized, while compounds with k′′O3 < 104 M-1 s-1 were 20-50% oxidized. Therefore, UV254 reduction would be an acceptable surrogate to assess the O3 oxidation of these compounds because significant compound degradation occurred in the absence of measurable O3 CT. Correlation between True Color Removal and Pharmaceutical Oxidation. Excellent correlation was observed between the removal of true color and the transferred O3 dose in PCFL (R2 ) 0.95) and RMCO (R2 ) 0.98) (Figure 6). Good correlations were also observed between the removal of true color and oxidation of pharmaceuticals in PCFL and RMCO (Figure 7). The oxidation of carbamazepine correlated linearly (R2 ) 0.91, n ) 9) with the removal of true color over the range of 0-65% (Figure 7). Carbamazepine was shown in Table 2 to be fast-reacting with O3 and •OH. The oxidation of meprobamate (R2 ) 0.98, n ) 10) showed excellent correlation with the removal of true color when removal was >40% (Figure 7). Dilantin (R2 ) 0.94, n ) 12) and primidone (R2 ) 0.85, n ) 11) showed similar strong correlations (Figures S2 and S3 of the Supporting Information). These compounds are apparently slow-reacting with O3 and fast-reacting with • OH. The results indicate that true color could be applied as a surrogate to assess the removal of the compounds investigated. Practical Implications. In this manuscript, we have taken three established concepts (i.e., UV254 reduction, color removal, and kinetic information) and combined them into novel methods to evaluate pharmaceutical oxidation during the ozonation of wastewater. Strong correlations observed in Figures 4, 5, and 7 illustrate that UV254 and/or color removal VOL. 43, NO. 13, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
4861
FIGURE 6. Removal of true color during pilot-scale O3 experiments. True color removal was measured upon the completion of first-order O3 decay (t < 10 min). establish the relationship between UV254 reduction and pharmaceutical oxidation due to different EfOM compositions and different wastewater treatment processes.
Acknowledgments The authors thank the WateReuse Foundation (Project 06012) for providing financial support. The authors also thank the following staff members within the SNWA Water Quality Research and Development team: Julia Lew for her assistance during the O3 testing and Rebecca Trenholm, Douglas Mawhinney, and Brett Vanderford for the analysis of pharmaceuticals and pCBA.
Supporting Information Available Correlations for other pharmaceuticals studied. This information is available free of charge via the Internet at http:// pubs.acs.org.
Literature Cited
FIGURE 7. Correlation between true color removed during ozonation and removal of select pharmaceuticals: (a) carbamazepine and (b) meprobamate. If a compound was removed to below the minimum reporting limit (MRL), these data points were not included in the regression line. can be applied as surrogates to assess the oxidation of pharmaceuticals reacting with O3 and/or •OH. Therefore, online UV254 instrumentation could be applied for process control purposes at wastewater or water reuse utilities using ozonation. Measurement of UV254 before and after ozonation would provide a real-time evaluation of pharmaceutical oxidation. Online measurements may also account for source water variations as the correlations are normalized based on the change in UV254. Furthermore, the decreases in UV254 may be measured without exceeding the IOD. This method provides an alternative to the conventional O3 CT approach, which may not be practical during wastewater applications with greater TOC concentrations and corresponding IOD. Wastewater treatment objectives may be met with or without establishing a measurable dissolved O3 residual. For example, a UV254 reduction from ozonation can make subsequent disinfection with UV photolysis more efficient by increasing the UV transmittance. Additional studies are needed to further validate the use of UV254 as a surrogate for a broader set of compounds in different water matrices (i.e., primary-treated wastewater, secondary-treated wastewater, and drinking water). Site specific evaluations are also recommended to 4862
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 43, NO. 13, 2009
(1) Benotti, M. J.; Trenholm, R. A.; Vanderford, B. J.; Holady, J. C.; Stanford, B. D.; Snyder, S. A. Pharmaceuticals and endocrine disrupting compounds in U.S. drinking water. Environ. Sci. Technol. 2009, 43, 597–603. (2) Jobling, S.; Nolan, M.; Tyler, C. R.; Brightly, G.; Sumpter, J. P. Widespread sexual disruption in wild fish. Environ. Sci. Technol. 1998, 32, 2498–2506. (3) Vajda, A. M.; Barber, L. B.; Gray, J. L.; Lopez, E. M.; Woodling, J. D.; Norris, D. O. Reproductive disruption in fish downstream from an estrogenic wastwater effluent. Environ. Sci. Technol. 2008, 42, 3407–3414. (4) Huber, M. M.; Gobel, A.; Joss, A.; Hermann, N.; Loffler, D.; Mcardell, C. S.; Ried, A.; Siegrist, H.; Ternes, T. A.; von Gunten, U. Oxidation of pharmaceuticals during ozonation of municipal wastewater effluents: A pilot study. Environ. Sci. Technol. 2005, 39, 4290–4299. (5) Snyder, S. A.; Wert, E. C.; Rexing, D. J.; Zegers, R. E.; Drury, D. D. Ozone oxidation of endocrine disruptors and pharmaceuticals in surface water and wastewater. Ozone: Sci. Eng. 2006, 28, 445– 460. (6) Huber, M. M.; Canonica, S.; Park, G.-Y.; von Gunten, U. Oxidation of pharmaceuticals during ozonation and advanced oxidation processes. Environ. Sci. Technol. 2003, 37, 1016–1024. (7) Wert, E. C.; Rosario-Ortiz, F. L.; Snyder, S. A. Effect of ozone exposure on the oxidation of trace organic contaminants in wastewater. Water Res. 2009, 43, 1005–1014. (8) Buxton, G. V.; Greenstock, C. L.; Helman, W. P.; Ross, A. B. Critical review of rate constants for reactions of hydrated electrons, hydrogen atoms, and hydroxyl radicals (•OH/•O-) in aqueous solutions. J. Phys. Chem. Ref. Data 1988, 17, 513–886. (9) Rosario-Ortiz, F. L.; Mezyk, S. P.; Doud, D. F. R.; Snyder, S. A. Quantitative correlation of absolute hydroxyl radical rate constants with non-isolated effluent organic matter bulk properties in water. Environ. Sci. Technol. 2008, 42, 5924–5930. (10) von Gunten, U. Ozonation of drinking water: Part I. Oxidation kinetics and product formation. Water Res. 2003, 37, 1443–1467.
(11) Rakness, K. L.; Najm, I.; Elovitz, M.; Rexing, D.; Via, S. Cryptosporidium log inactivation with ozone using effluent CT10, geometric mean CT10, extended integrated CT10, and extended CSTR calculations. Ozone: Sci. Eng. 2005, 27, 335– 350. (12) Pi, Y.; Schumacher, J.; Jekel, M. Decomposition of aqueous ozone in the presence of aromatic organic solutes. Water Res. 2005, 39, 83–88. (13) Westerhoff, P.; Aiken, G.; Amy, G.; Debroux, J. Relationships between the structure of natural organic matter and its reactivity towards molecular ozone and hydroxyl radicals. Water Res. 1999, 33, 2265–2276. (14) Takahashi, N.; Nakai, T. Ozonolysis of humic acid and its effect on decoloration and biodegradability. Ozone: Sci. Eng. 1995, 17, 511–525. (15) Clesceri, L. S., Greenberg, A. E., Eaton, A. D., Eds. Standard Methods for the Examination of Water and Wastewater, 20th ed.; American Public Health Association, American Water Works Association, Water Environment Federation: Washington, DC, 1998. (16) Bader, H.; Hoigne, J. Determination of ozone in water by the indigo method: A submitted standard method. Ozone: Sci. Eng. 1982, 4, 169–176. (17) Yao, C. C. D.; Haag, W. R. Rate constants for direct reactions of ozone with several drinking water contaminants. Water Res. 1991, 25, 761–773.
(18) Neta, P.; Hule, R. E.; Ross, A. B. Rate constants for reactions of inorganic radicals in aqueous solution. J. Phys. Chem. Ref. Data 1987, 17, 1027–1284. (19) Wert, E. C.; Rosario-Ortiz, F. L.; Drury, D. D.; Snyder, S. A. Formation of oxidation byproducts from ozonation of wastewater. Water Res. 2007, 41, 1481–1490. (20) Hongve, D.; Akesson, G. Spectrophotometric determination of water color in hazen units. Water Res. 1996, 30, 2771–2775. (21) Vanderford, B. J.; Pearson, R. A.; Rexing, D. J.; Snyder, S. A. Analysis of endocrine disruptors, pharmaceuticals, and personal care products in water using liquid chromatography/tandem mass spectrometry. Anal. Chem. 2003, 75, 6265–6274. (22) Vanderford, B. J.; Rosario-Ortiz, F. L.; Snyder, S. A. Analysis of p-chlorobenzoic acid in water by liquid chromatography/ tandem mass spectrometry. J. Chromatogr., A 2007, 1164, 219– 223. (23) Buffle, M.-O.; Schumacher, J.; Salhi, E.; Jekel, M.; von Gunten, U. Measurement of the initial phase of ozone decomposition in water and wastewater by means of a continuous quenchflow system: Application to disinfection and pharmaceutical oxidation. Water Res. 2006, 40, 1884–1894. (24) Benner, J.; Salhi, E.; Ternes, T.; von Gunten, U. Ozonation of reverse osmosis concentrate: Kinetics and efficiency of beta blocker oxidation. Water Res. 2008, 42, 3003–3012.
ES803524A
VOL. 43, NO. 13, 2009 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
4863
