Environ. Sci. Technol. 2008, 42, 3375–3380
Removal of Endocrine-Disrupting Chemicals during Ozonation of Municipal Sewage with Brominated Byproducts Control HEQING ZHANG,† HARUMI YAMADA,‡ AND H I R O S H I T S U N O * ,‡ Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, P. R. China, and Department of Urban & Environmental Engineering, Graduate School of Engineering, Kyoto University, Kyoto 6158540, Japan
Received October 28, 2007. Revised manuscript received January 8, 2008. Accepted January 15, 2008.
The decomposition of endocrine-disrupting chemicals (EDCs) including estrone (E1), 17β-estradiol (E2), estriol (E3), nonylphenol (NP), and bisphenol A (BPA) during ozonation of municipal sewage grabbed from the outlets of primary sedimentation tanks was studied through laboratory-scale experiments. A newly developed in vitro bioassay called nuclear receptor–ligand assay and GC-MS were both utilized to respectively determine the estrogenicity and individual EDCs in the wastewater samples. The original estrogenicity, expressed as the E2 equivalent concentration (EEQC), in the primary effluents was 315-1018 ng/ L. Results indicate that the EEQC can be reduced rapidly to below10ng/Lafterozonation.Theappearanceof0.1mg/Ldissolved ozone (DO3), which corresponds to a consumed ozone amount of 0.4 mg per initial TOC (total organic carbon) of wastewater samples, was an appropriate operational parameter to simultaneously achieve efficient EDC removal and control of BrO3- and total organic bromine (TOBr). The presence of suspended solids in the range of 38-67 mg/L exhibited no obvious impact on the removal of nonsorbed estrogenicity. A complete decomposition of E2, E3 and BPA was achieved once 0.1 mg/L DO3 appeared in the primary effluent. The oxidative decomposition of NP was relatively less efficient with a residual concentration of 100 ng/L. This work investigates the feasibility of EDC removal and brominated byproduct control during ozonation of original municipal sewage prior to biological treatment.
Introduction In recent years, many studies have reported the occurrence of considerable endocrine-disrupting chemicals (EDCs or estrogenic compounds) in natural water bodies. EDCs usually include steroid estrogens (e.g., estrone (E1), 17β-estradiol (E2), and estriol (E3)), synthetic estrogens (e.g., 17R-ethynyl estradiol (EE2)), and anthropogenic EDCs (e.g., nonylphenol (NP) and bisphenol A (BPA)) (1, 2). EDCs may pose a threat to aquatic organisms even at trace levels. It was reported that the lowest observed concentration of E2 with effect on Japanese medaka, in an early life stage study, was only 1-10 ng/L (3). * Corresponding author phone: (+81)-075-383-3352; fax: (+81)075-383-3351; e-mail:
[email protected]. † Chinese Academy of Sciences. ‡ Kyoto University. 10.1021/es702714e CCC: $40.75
Published on Web 03/22/2008
2008 American Chemical Society
The effluent discharged from sewage treatment plants (STPs) is the major source of estrogenic compounds existing in aquatic environments (4–6). Some EDCs present in the sewage may be transferred to the activated sludge in biological treatment tanks due to their hydrophobic nature (7, 8). It was reported that the EDC concentrations in the activated sludge were as high as 7.8-13 ng/gSS for the sum of E1 and E2 (9), 2517–3675 ng/gSS for 4NP, and 70-770 ng/gSS for BPA (10). In our previous work, it was found that the fractions of EDCs adsorbed on the solid phases of activated sludge were as high as 45-90%, and the EDCs, especially anthropogenic ones, preferred to accumulate in the activated sludge and circulate through biological treatment processes. To reduce the release of EDCs into aquatic environments or to remove them from wastewater intended for direct or indirect reuse, an advanced treatment process should be applied. In STPs, ozonation is usually appended to biological treatment for further purification of the sewage effluent. Some studies have been done on the behavior of micropollutants including EDCs, pharmaceuticals, and antibiotics during ozonation (11–14). However, EDCs adsorbed on the activated sludge in the biological treatment tanks can not be removed through the general ozone applied treatment processes. To remove EDCs from the sewage influent before their accumulation in activated sludge is becoming necessary if the farmland application of activated sludge is taken into consideration. Thus, preozonation of municipal sewage prior to biological treatment appears to suit this specific purpose. Nowadays, in some newly designed STPs, ozonation has been applied before conventional biological treatment in order to remove persistent substances such as dyestuff as well as to enhance biodegradability of water samples (15, 16). To our best knowledge, ozonation of sewage influents, especially the removal characteristics of micropollutants and the complex matrix effect of the sewage influents, has not yet been studied so far. The purpose of this study was to investigate the ozonation of primary effluents grabbed from three municipal STPs with the major objectives described as follows: (i) to study the reduction of total estrogenicity and individual EDCs during ozonation; (ii) to determine appropriate operational parameters for effective removal of EDCs and control of the formation of brominated byproduct including bromate ion (BrO3-) and total organic bromine (TOBr); and (iii) to examine the influence of suspended solid on EDCs removal.
Materials and Methods Target Compounds and Water Samples. In this work, E1, E2, and E3 were selected as representative steroid estrogens, and NP and BPA were selected as representative anthropogenic EDCs. EE2 was not examined because its concentration in the municipal sewage of Japan was generally below the detection limits of 0.5–1.2 ng/L (17–20). The primary effluents were sampled from three municipal STPs located in K City of Japan, denoted as STPs I, K, and T. The characteristics of the wastewater samples are shown in Table 1. It is seen that the anthropogenic EDCs exist in municipal sewage at concentrations higher than the natural estrogens. The concentration of Br- was 68–217 µg/L, which implies potential formation of brominated byproduct during ozonation. The original concentrations of BrO3- in all the primary effluents were below the detection limit of 0.085 µg/L. Ozonation System and Conditions. The semibatch system was utilized for ozonation experiments (see Figure S1-A, Supporting Information). Water samples were ozonated in VOL. 42, NO. 9, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Major Characteristics of the Tested Primary Effluents and Experimental Conditions for Ozonation of Primary Effluents major characteristics of primary effluents ozonation conditions
run
pre treatment
1 2 3 4 5 6 7 8
filtered filtered filtered nonfiltered filtered nonfiltered filtered nonfiltered
individual EDCs (ng/L)
inlet O3 concn water (mg/L) samplea 85 40 40 40 40 40 40 40
pH
SS TOC DOC UV254 SUVA (mg/L) (mg/L) (mg/L) (cm-1) (L/mg m)
Br(µg/L)
BrO3- (µg/L)
E3
NP
BPA
7.2
55
-b
28.7
0.367
1.30
217.0
NDc
-
-
-
-
-
I-2
7.9
67
48.6
31.2
0.292
0.94
129.0
ND
-
-
-
-
-
K
-
54
43.7
29.6
0.391
1.32
94.9
ND
ND 28 111 755
326
T
-
38
27.2
17.2
0.270
1.57
68.1
ND
ND 10 163 804
166
I-1, I-2: the primary effluent samples taken from STP I at two different times. (below the detection limit).
a cylindrical glass reactor (φ ) 80 mm, H ) 220 mm) with an effective volume of 1.1 L. The gaseous ozone generated from an ozone generator (PSA ozonizer, Sumitomo) was continuously bubbled into the reactor. In all experiments, the injected flow rate of ozone gas was maintained at 0.2 L/min (corresponding to 0.04 m3/m2 · min). The experimental conditions for ozonation of primary effluents were described in Table 1. Runs 1–2 and runs 3–8 were to examine the effects of injected ozone concentration and suspended solids (SS) concentration on the removal efficiency of EDCs, respectively. At each preselected time, the supply of ozone gas was stopped and the residual ozone gas in the reactor headspace was replaced with air using a glass syringe and collected into the 5% KI solution (see Figure S1-B, Supporting Information). After filtration, the water sample was analyzed for pH, UV254, estrogenicity, and the concentrations of dissolved organic carbon (DOC), Br-, BrO3-, and TOBr. For the direct ozonation of nonfiltered primary effluents, the concentrations of SS, total organic carbon (TOC), and estrogenicity in the SS phase were also measured. In runs 5–8, the individual EDCs including E1, E2, E3, NP, and BPA were quantified by GC-MS. Analytical Methods. Ultrapure water (UPW), produced with a UPW apparatus (Nanopure Diamond, Hansen), was used to prepare all aqueous solutions. The concentration of Br- was analyzed using an ion chromatograph (IC, DX-500, Dionex) equipped with a conductivity detector and an AS9HC column. Na2CO3 solution (9 mM) was used as the eluent solution. The concentration of BrO3- was determined with the IC equipped with a UV detector through postcolumn derivatization (U.S. EPA Method 317.0). The concentration of TOBr was measured with the following procedures: (i) adsorb halogenated organic compounds on two activated carbon columns using an adsorption equipment (TXA-03, Mitsubishi); (ii) decompose halogenated organic compounds into halogen ions, carbon dioxide, and water using an automatic sample combustion equipment (AQF-100, Mitsubishi); and (iii) detect halogen ions using the IC equipped with a conductivity detector. The concentration of dissolved ozone (DO3) was measured by the Indigo colorimetric method with a spectrophotometer (UV-1600, Shimadzu). Extraction of EDCs and Recovery Efficiencies. The water samples were separated by filtration with a 1 µm glass-fiber filter (GF/B, Whatman) into two parts as filtrate and SS. The filtrate part was acidified to pH 3 by 97% H2SO4 before solid phase extraction (SPE). The SS part was successively extracted with 20 mL of acetone and 20 mL of a mixed solution consisting of pure methanol and 1 M acetic acid (9:1 by volume) under ultrasonication for 15 min. The extracted solution was homogenized with UPW to 1 L, acidified to pH 3, and conducted with SPE. 9
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I-1
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E1
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b
-: not measured.
c
ND: not detected
FIGURE 1. Change of DO3, DOC, SUVA, EEQC, TOBr, and BrO3concentrations in primary effluents as a function of consumed O3/TOC0. SPE was conducted with Oasis HLB cartridges (Waters) to concentrate the target EDCs (see Figure S2, Supporting
FIGURE 2. Change of nonsorbed EEQC in filtered and nonfiltered primary effluents as a function of ozonation time and consumed O3/TOC0. Information). The recovery efficiencies of SPE for five target EDCs prepared as a mixture in UPW were determined to be within the range of 80–95%. In addition, fulvic acid with a concentration ranging from 20 to 200 mg/L exerted insignificant influence on the recoveries. To test the recovery efficiency of the NRL assay, 272 µg/L E2 was spiked into the primary effluent and 88 ( 18% (n ) 5) of E2 was successfully recovered. Bioassay. A nuclear receptor–ligand (NRL) assay was utilized to evaluate the estrogenicity of the wastewater. A gene-recombined human estrogen receptor (ERR) binding with a ligand (i.e., estrogenic compound) is activated by a coactivator to produce a yellow product. By measuring the optical absorbance of the yellow product at 405 nm, the estrogenicity of the wastewater sample can be determined. All the reagents used for this bioassay were purchased from MicroSystem Company, Japan (21). All measurements were done in duplicate. The applicability of the NRL assay to wastewater samples was substantiated in our previous work (22). E2 was selected as the standard EDC. It was first dissolved in DMSO to prepare a stock solution which was thereafter diluted to eight concentrations from 10-2 to 103 nM. The EC50 of E2 can be obtained from the sigmoid dose–response curve. Similarly, the SPE eluate of wastewater sample dissolved in DMSO was diluted into six concentrations in terms of its potential estrogenicity. The EC50 of the wastewater sample can also be obtained from the dose–response curve. The overall estrogenicity of wastewater sample was expressed as E2 equivalent concentration (denoted as EEQC), which was calculated by dividing the EC50 of the tested sample by the EC50 of E2. GC/MS Analytical Methods. The dried eluate post SPE was derivatized with 100 µL of pyridine and 200 µL of N,Obis(trimethylsilyl)-trifluoroacetamide (BSTFA) containing 1%
FIGURE 3. Change of nonsorbed individual EDC concentrations in filtered and nonfiltered primary effluents as a function of consumed O3/TOC0. trimethylchlorosilane (TMCS, Sigma) at 65 °C for 30 min, and thereafter cooled down to room temperature. The GC/ MS system (GC: 6890 Series; MS: 5973 Network, Agilent) used an HP-5MS capillary column (30 m × 0.25 mm × 0.25 µm) for organic separation and high-purity helium gas as carrier gas at a constant flow rate of 1.5 mL/min. The GC oven temperature was programmed as follows: equilibrate at an initial temperature of 100 °C for 1 min, successively increase to 200 °C (10 °C/min), 260 °C (15 °C/min), and 300 °C (3 °C/min), and maintain at 300 °C for 2 min. The inlet, MS transfer line, and ion source temperatures were set at 280, 280, and 250 °C, respectively. The quantification and confirmation ions used in SIM mode were as follows: 342, 218/257 (E1); 285, 326/416 (E2); 312, 387/415 (E3); 179, 292 (NP); 357, 372 (BPA).
Results and Discussion Changes of DO3, DOC, and SUVA. The change of DO3 concentrations as a function of consumed ozone during ozonation of primary effluents is shown in Figure 1A. The horizontal axis is indicated with consumed ozone per initial TOC (TOC0) of primary effluent. The consumed O3 was calculated according to the mass balance of ozone as follows: consumed O3 ) (CO3,gas,in)(QO3,gas,in)(T) - (MO3,out+head) (DO3)(V) (1) where CO3,gas,in (mg/L) is the concentration of ozone at the inlet, QO3,gas,in (L/min) is the gas flow rate, T (min) is the ozonation time, MO3,out+head (mg) is the total ozone mass in VOL. 42, NO. 9, 2008 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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FIGURE 4. Comparison of EEQC values measured by the NRL assay and calculated from the GC/MS results. both off-gas and headspace, and V (L) is the volume of water sample. In spite of different water samples and ozonation conditions, DO3 generally appeared at 0.1 mg/L or so when the consumed O3 per TOC0 exceeded 0.4 mg O3/mg C. The primary effluent consumed ozone rapidly during the initial stage of ozonation until the DO3 appeared at 0.1 mg/L. The change of DOC concentrations is shown in Figure 1B. The DOC values of the filtered water samples (runs 1, 2, 3, 5, 7) fluctuated a little during ozonation. The DOC values of nonfiltered water sample (runs 4, 6, 8) decreased in the initial stage and then increased quickly due to the dissolution of particulate organic carbon, resulting in 36%, 18%, and 16% increase of DOC values of the samples collected from STP I, K, and T, respectively. The reactivity of ozone with organic compounds has been shown to correlate with the specific ultraviolet absorbance per DOC (SUVA) (23, 24). The change of SUVA value along with the consumed ozone per TOC0 is shown in Figure 1C. In STP I, the average SUVA values of the primary and secondary effluents were 1.12 and 2.25 L/(mg m), respectively. This difference shows a lower reactivity of ozone with the primary effluent than the secondary effluent. It was reported that DO3 appears at 1.0 mg O3/mg C of consumed ozone during ozonation of the secondary effluent discharged from STP I (11). Therefore, the consumed ozone per TOC0 upon the appearance of DO3 decreased from 1.0 mg O3/mg C for the secondary effluent to 0.4 mg O3/mg C for the primary effluent. Estrogenicity Removal. The change of EEQCs in the filtrates of all the tested primary effluents as a function of consumed ozone is shown in Figure 1D. The initial EEQCs in the filtrate of the primary effluents were 315 and 816 ng/L in STP I (sampled at two different times), 1018 ng/L in STP K, and 823 ng/L in STP T. The estrogenicity decreased rapidly during the initial ozonation stage. For all the experimental runs, almost all the EEQCs were reduced to below 10 ng/L when the amount of consumed ozone per TOC0 reached 0.4 mg O3/mg C. Thus, the estrogenicity of the primary effluents can be reduced efficiently even in the presence of dissolved organic matters. It should be noted that the estrogenicity was reduced faster at the higher injected ozone concentration (85 mg/L, run 1) than the lower injected ozone concentration (40 mg/ 3378
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L, run 2) (see Figure S3, Supporting Information). However, the higher removal efficiency was achieved at 40 mg/L of injected ozone concentration from the viewpoint of consumed ozone per TOC0. More organic compounds were oxidized simultaneously with EDCs under the higher ozone concentration, and the utilization efficiency of ozone was shared by EDCs and coexisting reactants. Thus, an overdose of ozone may instead cause a decrease of EDCs removal efficiency. The reaction between ozone and EDCs can be assumed to be of second order as follows: d[EEQC] ) -k[EEQC][DO3] dt
(2)
During the initial stage of ozonation, the DO3 concentration ([DO3]) generally approached zero and could be assumed to be a constant. Thus, the average oxidation rate constant of EEQC was calculated to be 43400 (mg/L)-1 s-1 by fitting the experimental data. It was reported that the apparent rate constant of E2 with ozone in the pH range of 6–8 is 105-107 M-1 s-1 (25). Formation of Brominated Byproducts. Ozonation of municipal sewage containing Br- may result in the formation of harmful brominated byproduct, among which BrO3- and TOBr both have carcinogenic potential. In this study, 10 µg/L of BrO3- (the restricted concentration in the Drinking Water Quality Standards of Japan, U.S. EPA, and WHO) was basically set as an ideal objective level for all ozonated primary effluents. However, less than 100 µg/L of BrO3- is acceptable as dilution of treated wastewater by the receiving water body is generally achievable. Though there is no regulation for TOBr control up to date, TOBr is expected to be regulated in the coming future since they are more toxic than chlorinated species. The change of TOBr concentrations during ozonation is shown in Figure 1E. The initial concentrations of TOBr in the primary effluents were 37–53, 8, and 9 µg/L for STPs I, K, and T, respectively. TOBr was first decreased obviously in the initial stage of ozonation and then increased when the consumed ozone reached above 0.4 mg O3/mg C. As Figure 1F shows, BrO3- was not notably formed (less than 10 µg/L) during the initial stage in spite of different concentrations of Br- in the original primary effluents. From the behavior
of estrogenicity and BrO3-, it can be seen that the organic compounds in the primary effluent (including the estrogenic components) are more reactive than Br- toward ozone. Besides, a satisfactory mass balance of Br-, BrO3- , and TOBr was obtained at the initial stage of ozonation. It is thought that TOBr was initially decomposed to Br- with the obvious increase of Br- at the same time, and BrO3- was formed upon further ozonation. From the results mentioned above, the condition of 0.4 mg O3/mg C of consumed ozone, which corresponds to the appearance of 0.1 mg/L of DO3, can be proposed as an appropriate operational parameter for effective removal of EDCs without significant formation of harmful brominated byproduct from the primary effluent of municipal sewage by ozonation. Influence of SS on Estrogenicity Removal. The behavior of nonsorbed EEQC of the filtered and nonfiltered primary effluents during ozonation is shown in Figure 2. The horizontal axes represent both ozonation time and the consumed ozone per TOC0 of the wastewater sample. In runs 3 and 4, the EEQCs dissolved in the filtrate and adsorbed on the SS of the primary effluent from STP I were simultaneously measured. The nonsorbed EEQC in the filtrate phase was determined to be 315 ng/L, and the sorbed EEQC in the SS phase was 11 ng/L (equals to 164 ng/g SS). The fraction of EDCs adsorbed on the SS occupies only 3.4% of the total value. As Figure 2A shows, the sorbed EEQC in the SS phase decreased a little at the initial stage while kept constant in the successive ozonation. The initial decrease of the sorbed EEQC was mainly caused by the dissolution of SS upon ozonation. In general, the nonsorbed EEQCs in the filtered samples decreased slightly faster than those in the nonfiltered samples, as shown in Figure 2 with x axes captioned as ozonation time. The minor lag in the decrease of nonsorbed EEQC of the nonfiltered samples is due to the initial consumption of ozone by the coexisting SS. However, the influence of SS on the removal of nonsorbed EEQC became unobvious (in runs 5–8) or even inverse (in runs 3–4) if analyzed in terms of consumed ozone per TOC0. It is seen that the presence of SS, especially in the experimental range of 38–67 mg/L, had no obvious influence on the removal of nonsorbed estrogenicity in the primary effluents. Similar results with respect to the elimination of pharmaceuticals and estrogens during ozonation of secondary effluents in a pilot-scale study were reported (13). In this reference, the low efficiency of inactivation of microorganisms present in the floc implied that micropollutants sorbed on sludge particles were not oxidized efficiently. This agrees with the behavior of the sorbed EEQC in the nonfiltered samples during ozonation of the primary effluents (Figure 2A). Behavior of Individual EDCs. Figure 3 shows the behavior of individual EDCs during ozonation of primary effluents with or without the coexistence of SS. All the EDCs were reduced rapidly during the initial stage of ozonation. E2, E3, and BPA were all decomposed rapidly to less than 10 ng/L at 0.4 mg O3/mg C of consumed ozone. BPA and E3 were decomposed more rapidly than E2. The concentration of NP was decreased from 800 ng/L to about 100 ng/L during the initial stage and the residual NP concentration kept constant even with extended ozonation. Since the concentration of NP represents the sum of nine isomers with different side chains, some isomers may be resistant to ozone. The relative estrogenicity of E2, which was selected as the standard EDC, was set as 1.0. The relative estrogenicities of the tested individual EDCs were determined as 1.7, 1.0, 2.7, 0.007, and 0.018 for E1, E2, E3, NP, and BPA in the NRL assay, respectively. Thus, the EEQC of each tested compound can be calculated as the product of individual concentration (from GC/MS analysis) and its relative estrogenicity. The sum of
individual estrogenicities of five tested EDCs was compared with the total EEQC measured by the NRL assay, as shown in Figure 4. Results indicate that the calculated EEQC (from GC/MS analysis) showed a similar reduction trend as the measured EEQC (from NRL assay). However, the measured EEQC was always higher than the calculated EEQC. This is reasonable because only a limited number of EDCs were analyzed, while many unknown compounds in the municipal sewage may react positively with the ERR receptor in the NRL assay, thus contributing to the value of EEQC.
Acknowledgments The authors greatly appreciate the financial support from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. This study was partially supported by the Funds for Creative Research Groups of China (Grant 50621804). We are grateful to Dr. Zhimin Qiang for his valuable technical comments on this manuscript and modification of the English language.
Supporting Information Available Three figures are provided in the Supporting Information to present detailed information on the ozonation reaction system, EEQC removal at different injected ozone concentrations, and NRL assay. This material is available free of charge via the Internet at http://pubs.acs.org.
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ES702714E
