Front. Environ. Sci. Eng. 2014, 8(6): 888–894 DOI 10.1007/s11783-014-0735-0
RESEARCH ARTICLE
Occurrence and fate of antibiotics in advanced wastewater treatment facilities and receiving rivers in Beijing, China Xinwei LI1,2, Hanchang SHI (✉)1, Kuixiao LI2, Liang ZHANG2, Yiping GAN2 1 School of Environment, Tsinghua University, Beijing 100084, China 2 Beijing Drainage Group Co. Ltd., Beijing 100044, China
© Higher Education Press and Springer-Verlag Berlin Heidelberg 2014
Abstract The occurrence and removal of 13 antibiotics were investigated in five wastewater treatment plants (WWTPs) with advanced wastewater treatment processes in Beijing, China. Most of the target antibiotics were detected in the secondary and tertiary effluents, with the concentrations of 4.8–1106.0 and 0.3–505.0 ng$L–1. Fluoroquinolone antibiotics showed relatively high concentrations in all samples (782–1814 ng$L–1). Different tertiary treatment processes showed discrepant antibiotics removal performances. Ozonation process was found more effective in removing target antibiotics compared to the coagulation-flocculation-sedimentation process and sand filtration process. Investigation of the target antibiotics in three typical urban rivers in Beijing was carried out to understand antibiotics occurrence in surface water environment. Eight antibiotics were detected in the studied rivers, with highest concentration of antibiotics in the river which was mainly replenished by reclaimed water. This study showed the necessity of employing more effective advanced treatment facilities to further reduce the discharge amount of antibiotics. Keywords antibiotics, advanced treatment, urban river, reclaimed water
1
Introduction
Antibiotics have been widely used for humans and animals in the last decades. However, antibiotics are usually only partially metabolized, and excreted unchanged or as conjugates into the environment. The antibiotics have been frequently detected in wastewater [1–3], surface water [4] and even sources of drinking water [5], which Received December 30, 2013; accepted May 10, 2014 E-mail:
[email protected]
may select bacterial resistance and engender toxicity to aquatic organisms. Wastewater treatment plants (WWTPs) are regarded as one of the important sources of antibiotics residues in the aquatic environment, because the elimination of antibiotics seemed to be inefficient in most WWTPs which only included traditional primary and secondary treatment processes [6–8]. With increasing use of reclaimed water in Beijing, China, different advanced treatment facilities have been installed following the secondary treatment processes in many WWTPs in recent years. Among 680 million m3 reclaimed water was produced in Beijing in 2010, of which 210 million m3 was discharged into urban rivers and lakes. Various advanced treatment technologies, such as membrane filtration, ozonation, chlorination, ultraviolet (UV) disinfection, have been evaluated from the perspective of antibiotic removal [9–12]. Among these processes, ozonation was found to be effective to remove antibiotics in fullscale municipal WWTPs [13,14]. Studies on antibiotics in full-scale WWTPs in China have mainly focused on the occurrence and elimination during secondary biologic treatment processes [7,15,16]. However, the assessment of the antibiotic removal efficiency in different advanced wastewater treatment processes in Beijing, the capital of China with over 20 million inhabitants and great consumption of antibiotics, has seldom been reported. Moreover, limited information is available for the occurrence of antibiotics in receiving rivers of reclaimed water in Beijing. The objective of this study was to investigate the occurrence and levels of antibiotics in the secondary and tertiary effluents from WWTPs and three typical receiving rivers (a canal as drinking water source, a central important natural river and a river replenished by reclaimed water) in Beijing. Based on the investigation, fates of antibiotics during different advanced treatment processes and after discharge will be better understood. This work will provide scientific support for the selection of technologies in
Xinwei LI et al. antibiotics in advanced wastewater treatment facilities and receiving rivers
WWTPs and surface water management concerning use of reclaimed water.
2
Materials and methods
2.1
Materials
Thirteen antibiotics representing 5 different groups (tetracycline, sulfonamide, macrolide, fluoroquinolone, and trimethoprim) that have been frequently reported in WWTPs and aquatic systems were chosen as the target antibiotics (Table 1). All the standards were analytical grade, with Ofloxacin (OFL, 98.6%), Tetracycline (TC, 98%), Oxytetracycline (OTC, 98%), chlortetracycline (CTC, 97%), Doxycycline (DXC, 98%), Roxithromycin (ROX, 90%), Sulfapyridine (SPD, 99%), Sulfadiazine (SDZ, 99%), Sulfamethoxazole (SMX, 98%), Sulfadimidine (SDMD, 99%), and Trimethoprim (TMP, 99%) purchased from Sigma–Aldrich (Steinheim,Germany), Norfloxacin (NOR, 98.5%) purchased from Dr. Ehrenstorfen (Augsburg, Germany), and Acetyl Spiramycin (ASPI, 98.5%) purchased from Toronto Research Chemical (Toronto, Canada), respectively. Isotopically labeled compounds, used as internal standards, were 13C6-sulfamethazine (13C6-SMA) obtained from Cambridge Isotope Laboratories (Tewksbury, USA), and demeclocycline (DMC) from Sigma–Aldrich. 2.2
Sampling and sites
Wastewater samples were collected with 24h composite samples taken 8 times every 3h. River water samples were collected using grab sampling. The sampling campaign was carried out in April 2009, when no rain event was
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registered either during the previous week or on the sampling days. All glassware used in the present study was heated at 450°C for 2 h, rinsed with 2.5 mL of saturated methanolic ethylenediaminetetraacetic acid solution, and air-dried prior to analysis. Water samples were collected in 4L brown bottles that were rinsed with water samples three times. The sampling sites surveyed in this study are presented in Fig. 1. These WWTPs located in different drainage areas (referred as A, B, C, D, E) employ similar conventional treatment processes, primary treatment to remove particles coupled with secondary biologic treatment to remove organics, nitrogen and phosphorous, followed by different advanced treatment processes. In particular, to understand the fate of antibiotics in different advanced treatment processes, water samples were collected at the inlet (secondary effluent of WWTP) and the outlet of each WWTP. Table 2 shows the main advanced treatment processes and operation parameters in WWTPs. Samples from three typical urban rivers (the South Moat, the Jingmi Canal and the Tongzi River) were collected to determine the antibiotic pollution level. As shown in Fig. 1, these rivers flow in the north-west (Jingmi Canal), the central (Tongzi River), and the south (South Moat) parts of Beijing City. These rivers were selected for study due to their importance of public water safety. The Jingmi Canal is an important drinking water source for Beijing. Tongzi River, the moat of the Forbidden City, is connected with the lakes in Zhongnanhai and Beihai Park. The South Moat has been mainly replenished by reclaimed water (secondary effluent from WWTP E followed by coagulationflocculation-sedimentation, sand filtration and chlorination) since 2006. All samples were collected in pre-washed amber glass bottles and refrigerated immediately. The sample extraction was performed within two weeks.
Table 1 Characteristics of selected target antibiotics class Fluoroquinolones (QNs)
target antibiotics
acronym
MW
CAS number
molecular formula
Ofloxacin
OFL
361
82419-36-1
C18H20FN3O4
Norfloxacin
NOR
319
70458-96-7
C16H18FN3O3
Sulfapyridine
SPD
249
144-83-2
C11H11N3O2S
Sulfadiazine
SDZ
250
68-35-9
C10H10N4O2S
Sulfamethoxazole
SMX
253
723-46-6
C10H11N3O3S
Sulfadimidine
SDMD
278
57-68-1
C12H14N4O2S
Trimethoprime (TMP)
Trimethoprime
TMPs
290
738-70-5
C14H18N4O3
Macrolides (MLs)
Roxithromycin
ROX
837
80214-83-1
C41H76N2O15
Acetyl Spiramycin
ASPM
885
–
C45H76N2O15
Sulfonamides (SAs)
Tetracyclines (TCs)
Tetracycline
TC
444
60-54-8
C22H24N2O8
Oxytetracycline
OTC
460
79-57-2
C22H24N2O9
Chlortetracycline
CTC
479
57-62-5
C22H23ClN2O8
Doxycycline
DXC
444
564-25-0
C22H24N2O8
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Front. Environ. Sci. Eng. 2014, 8(6): 888–894
Table 2 Information of the investigated advanced treatment processes of WWTPs treatment process
capacity/(t$d–1)
operational dosage
A
Inf (*)-UF-O3 -NaClO- Eff (*)
80000
O3: 3.5 mg$L–1 NaClO: 5–8 mg$L–1
B
Inf (*) -O3 -NaClO-CFS- SF- UV- Eff (*)
60000
O3: 3.5 mg$L–1 NaClO: 5–8 mg$L–1 UV: 800 J$m–2
WWTP
C
Inf (*) -NaClO-CFS- SF- UV- O3- Eff (*)
40000
O3: 2 mg$L–1 NaClO: 5–8 mg$L–11 UV: 800 J$m–2
D
Inf (*)- CFS- SF- ClO2 - Eff (*)
3000
ClO2: 5.6 mg$L–1
E
Inf (*)- CFS- SF- Eff (*)
10000
–
Notes: “*” represents for sampling sites; Inf: influent of the advanced treatment (secondary effluent); Eff: effluent (final outlet); SF: sand filtration; UF: ultra filtration; O3: ozonation; UV: ultraviolet disinfection; CFS: coagulation-flocculation and sedimentation
Fig. 1 Locations and sampling sites of the five WWTPs and three rivers in Beijing. A, B, C, D and E represent the locations of five WWTPs. △ represent the sampling sites in three urban rivers
2.3
Sample extraction and analysis
The samples were extracted using solid phase extraction (SPE) (500 mg, 6 mL, Waters Corp., USA). Before the extraction, all water samples were filtered with 1.2 μm glass fiber filters (Whatman, UK). The samples (1000 mL) were spiked with 0.5 g of disodium ethylenediamine tetra acetic acid dihydrate (Na2EDTA-2H2O) and 50 μL of internal standards solution (250 ng$mL–1). The SPE cartridges were preconditioned with dichloromethane, methanol and water, and then the samples were loaded
onto the cartridge. Next, the cartridges were washed with water and dried for 30 min with nitrogen gas. The dried cartridges were eluted with methanol. The extracts were concentrated to 1 mL. The final extracts were analyzed by Ultra-high-performance liquid chromatography/tandem mass spectrometry (UPLC/MS-MS, Waters Corp., USA). A Waters ACQUITYTM 1100 UPLC system coupled with a Micromass®-Quattro Premier XE mass spectrometer (Waters Corp., USA) was used with a Waters ACQUITY UPLC BEH C18 column (Waters Corp., 1.7 μm, 2.1 100 mm, USA) in a 40°C column oven to
Xinwei LI et al. antibiotics in advanced wastewater treatment facilities and receiving rivers
separate analytes using a binary gradient (USEPA, 2007). Analytes were detected using a multiple reaction monitoring (MRM) mode.
3
Results and discussion
3.1 Occurrence of antibiotics in secondary effluent of WWTPs
Figure 2 shows the concentrations of antibiotics in the secondary effluent samples collected from five municipal WWTPs. The total concentration in the secondary effluents ranged from 1722.2 to 3013.1 ng$L–1. The overwhelming majority of selected antibiotics had a relatively high frequency of detection (9 out of 13) in all the five WWTP effluents, except for SDMD, ASPI, CTC, and DXC.
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fluoroquinolones in China, especially in Beijing. The sulfonamides (SMX, SPD, and SDZ) and their synergist (TMP) also showed high concentrations in the secondary effluents, which were much higher than those detected in other areas [15,21,22]. For example, TMP was 4 times higher in the effluent samples (90.8–391.6 ng$L–1) than that in Australia and Korea [23]. As for SMX, the concentration (146.7–383.1 ng$L–1) was close to Li’s result in a WWTP in Beijing [17] and higher than that detected in South-west Korea [23]. However, the concentrations of SMX and TMP were slightly lower than those in WWTPs in USA [22,24]. Hence, the distribution pattern of antibiotics detected in municipal WWTP secondary effluents in this study was different from those of other regions in China and other countries. The high antibiotic levels in the WWTP effluents in Beijing were probably because of relatively large consumption of antibiotics in such a metropolis with more than 20 million dwellers. The results also indicated that the antibiotics might be only partially eliminated by the traditional biologic treatment. Therefore, it would pose an environmental risk to discharge wastewater after secondary treatment into rivers or lakes. Thus the advanced treatment processes following the secondary treatment is imperative to guarantee water environment safety. 3.2 Removal of antibiotics in advanced wastewater treatment processes
Fig. 2 Concentrations of target antibiotics in the secondary effluents of 5 municipal WWTPs in Beijing
Among the target compounds, fluoroquinolone antibiotics in the samples from WWTPs showed remarkably high concentrations: OFL (438–1106 ng$L–1) and NOR (277–708 ng$L–1), which showed similar levels compared to other studies in Beijing, China [7,17]. However, the concentrations of fluoroquinolone antibiotics were much higher than those detected in other regions of China, such as Hangzhou (429 ng$L–1 of OFL, 96 ng$L–1 of NOR) [18] and Dalian (211 ng$L–1 of OFL, 205 ng$L–1 of NOR) [16], and even approximately 10 times higher than those detected in Guangzhou (418 ng$L–1 of OFL, 4419 ng $L–1 of NOR) [15] and Hong Kong (about 50 ng$L–1 of OFL, 35 ng$L–1 of NOR) [8]. Compared with Sweden, Finland and Australia, the levels of OFL and NOR in Beijing were more than 15 times or even higher [6,19,20]. In USA and Spain, the levels of fluoroquinolone antibiotics were approximately half of the levels in this study [21,22]. This result might reflect the relatively high use of
Considering the higher concentration of antibiotics in secondary effluents in Beijing mentioned above, as well as the use of reclaimed water in replenishment of Beijing’s rivers, advanced treatment processes are necessary to further remove these risk compounds. The removal efficiencies of the selected antibiotics showed some differences among the advanced treatment units of five WWTPs in this study (Fig. 3). The highest removal efficiency of overall antibiotics was found in WWTP B (91.1%), followed by WWTP A (81.9%), WWTP C (67.7%) and WWTP D (62.5%), and the lowest one occurred in WWTP E (11.3%). Moreover, WWTP B also showed relatively high removal efficiency (82.6% to 99.0%) of most target antibiotics, however, the lowest removal efficiency of each antibiotic ( < 24.9%) occurred in WWTP E without exception. Especially, tetracycline antibiotics (TC and OTC) showed remarkably high removal efficiency (93.1% to 99.6%) in WWTPs A, B and C similar to their fate reported by Huber [9], indicating that ozonation is an efficient way to remove tetracyclines from wastewater before reuse. The result demonstrated that the type of the treatment process and dosage of chemical oxidants are key factors influencing removal rates. In our study, the advanced treatment units of WWTPs A, B and C all included an ozonation process (Table 2). Although the dosing position of chemical oxidants were different, the advanced treat-
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Front. Environ. Sci. Eng. 2014, 8(6): 888–894
Fig. 3 Total concentrations of major antibiotic groups in the reclaimed wastewater (a) and removal efficiencies during advanced treatment (b)
ment processes were generally the same between WWTPs B and C, while WWTP A had an ultrafiltration process substituted for coagulation-flocculation-sedimentation and sand filtration, and it didn’t had UV for disinfection. The removal efficiencies in these three WWTPs (A, B and C) were higher than those in WWTPs D and E (without dosing ozone). Ozone is a strong oxidant (E0 = 2.07 V) capable of acting with antibiotics directly or indirectly [9,25]. Hence, it is considerably more efficient for pharmaceutical control than ClO2 and chlorine because it exhibited higher rate constants and reacted with a larger number of pharmaceuticals [10]. Numerous literatures reported effective degradation of ozonation for a wide variety of compounds including most of antibiotics [9,13,26,27], which could support the result of this study. However, it should be noted that WWTP C had lower total removal efficiency than those of WWTPs A and B despite they all used ozone. The possible reason was that the dosage of ozone in WWTP C (2 mg$L–1) was much lower than those in WWTPs A and B (both 3.5 mg$L–1), leading to inadequate reactions. Only coagulation and sandfiltration processes were used as advanced treatment at WWTP E, which showed the lowest antibiotic removal efficiency. This result was in agreement with earlier studies suggesting that coagulationflocculation-sedimentation and sand filtration processes could contribute little to the removal of antibiotics [20,28]. WWTP D using ClO2 disinfection also showed higher
removal efficiency of antibiotics than WWTP E using sand filtration. Macrolides, sulfonamides and tetracyclines were removed by 75.0% – 99.6% in WWTP D, which were closed to the removal efficiencies in WWTPs using ozonation, indicating that ClO2 is an efficient disinfectant for the removal of antibiotics from municipal wastewater. Some previous reports found that ClO2 was slightly more powerful than chlorine for the oxidation of pharmaceuticals, although it was less efficient than ozonation, moreover, macrolides, sulfonamides and tetracyclines were readily oxidized by ClO2 [10,12]. However, the removal efficiency of TMP was low (13.7%) in WWTP D, which was found to be related to its chemical structure [29]. Compared to WWTP B, WWTP A had no coagulation or sandfiltration processes, which could contribute about 10% removal of antibiotics mentioned above [30]. Moreover, UF membrane maybe has little elimination contribution to the target antibiotics because of its pore size [17]. Consequently, the removal of the antibiotics in advanced treatment processes of WWTP A is probably mainly due to the ozonation and NaClO addition. The removal of antibiotics in WWTP B and C were not improved in this study, which was consistent with the previous report. UV radiation units at normal disinfection dosages did not effectively reduce the antibiotic concentrations both in drinking water treatment plants and WWTPs [8,20,31,32]. 3.3
Occurrence of antibiotics in the urban rivers of Beijing
Eight compounds were detected out of 13 target antibiotics in the rivers, with the concentrations ranging from 0.6 to 26 ng$L–1. As shown in Fig. 4, fluoroquinolones (OFL and NOR) was the most dominant among the antibiotics analyzed in the rivers, which was similar to the results observed in secondary and tertiary effluents. Besides, SMX, SDZ, TMP and OTC showed relatively high concentrations in most of surveyed rivers as well. However, the concentrations of most antibiotics in the rivers of this study were much lower than those found in the Pearl River of South China (66 to 460 ng$L–1 in low water season) [33], possibly due to the fact that the Pearl River was the sole receiving water for treated and untreated wastewater from Guangzhou, but these three rivers in our study consist of two natural surface water (the Jingmi Canal and the Tongzi River) and a river receiving reclaimed water after advanced treatment (the South Moat), without industry or agriculture discharge. The highest total concentration of antibiotics (87.5 ng $L–1) occurred in the South Moat, which was mainly supplied by reclaimed water. However, the concentration in the South Moat was much lower than those of final effluents from WWTPs in this study. The probable explanations are the dilution of a small amount of surface
Xinwei LI et al. antibiotics in advanced wastewater treatment facilities and receiving rivers
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References
Fig. 4 Concentrations of target antibiotics in three urban rivers
water and rains, and sorption of the suspended solids and sediments according to previous studies [34,35].The lowest antibiotic concentration was found in the downstream of Jingmi Canal, a drinking water source. Since Tongzi River connects Zhongnanhai and Beihai Park with relatively good water quality and had no wastewater discharging in, it showed low antibiotic concentrations similar to those of the downstream of Jingmi Canal. In general, the typical classes of antibiotics were detected in the three studied rivers more or less, with the highest frequency and greatest abundance in the South Moat supplied with reclaimed water. Great attention should be paid to the risk of antibiotics to the aquatic environment in Beijing, especially through reclaimed water. Advanced treatment processes, particularly ozonation, are vital for WWTPs to efficiently remove antibiotics.
4
Conclusions
Nine out of 13 antibiotics were detected in both secondary and tertiary effluents at five WWTPs in Beijing, China. The concentrations of most antibiotics in the secondary effluent were higher than those reported in the other regions in China and other countries. The removal efficiencies of the advanced treatment varied with different processes and properties of compounds. Better removal was achieved by ozonation and ClO2 with adequate dosage than by coagulation, flocculation, clarification and sand filtration. The typical antibiotics were detected in three urban rivers, especially in a river supplied by reclaimed water, which demonstrated the necessity of employing more effective advanced treatment facilities to further reduce the discharge amount of antibiotics. Acknowledgements This study was supported by the Environmental Public Welfare Scientific Research (No. 201209053).
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