Decomposition of persistent pharmaceuticals in wastewater by ionizing radiation

Radiation Physics and Chemistry 81 (2012) 1508–1512

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Decomposition of persistent pharmaceuticals in wastewater by ionizing radiation Atsushi Kimura a,n, Misako Osawa b, Mitsumasa Taguchi a a b

Japan Atomic Energy Agency, 1233 Watanuki-machi, Takasaki-shi, Gunma 370-1292, Japan Gunma Prefectural Sewerage Management General Office, 1846-1 Kaminote, Tamamura-machi, Sawa-gun, Gunma 370-1127, Japan

a r t i c l e i n f o

a b s t r a c t

Article history: Received 24 August 2011 Accepted 15 November 2011 Available online 2 December 2011

Pharmaceuticals in wastewater were treated by the combined method of activated sludge and ionizing radiation in laboratory scale. Oseltamivir, aspirin, and ibuprofen at 5 mmol dm  3 in wastewater were decomposed by the activated sludge at reaction time for 4 h. Carbamazepine, ketoprofen, mefenamic acid, clofibric acid, and diclofenac were not biodegraded completely, but were eliminated by g-ray irradiation at 2 kGy. The rate constants of the reactions of these pharmaceuticals with hydroxyl radicals were estimated by the competition reaction method to be 4.0–10  109 mol  1 dm3 s  1. Decompositions of the pharmaceuticals in wastewater by ionizing radiation were simulated by use of the rate constants and the amount of total organic carbon as parameters. Simulation curves of concentrations of these pharmaceuticals as a function of dose described the experimental data, and the required dose for the elimination of them in wastewater by ionizing radiation can be estimated by this simulation. & 2011 Elsevier Ltd. All rights reserved.

Keywords: Pharmaceuticals 60 Co g-rays Activated sludge Total organic carbon Wastewater

1. Introduction Many kinds of water pollutants in the environmental water have been widely spread worldwide. The pollutants such as halogenated organic compounds, endocrine disruptors, and heavy metals are persistent, high toxic, and low biodegradability (Aoki et al., 1992; Colborn et al., 1996; Ohtake et al., 2003). Some pharmaceuticals are hazardous on humans and aquatic animals because of their chronic and reproduction toxicities (Fent et al., 2006). The environmental movement and risk evaluation of these pharmaceuticals and personal care products are studied recently. The concentrations of the pharmaceuticals in the water environment increased gradually because of the population growth and the diversification of advanced medical worldwide (Cooper et al., 2008; Cunningham et al., 2009; Fent et al., 2006; Oaks et al., 2004). However, it is difficult to manage the environment risk of the pharmaceuticals having great benefits for human life. The direct removal methods such as activated sludge system and Advanced Oxidation Processes (AOPs) are considered to be suitable for the treatment of the pharmaceuticals in the water environment. Some anti-inflammatory medications, anticonvulsant drugs, antiviral drugs, antilipemic agents, and so on were detected at the downstream of water treatment plants, and could not be decomposed by the combination method of the

n

Corresponding author. E-mail address: [email protected] (A. Kimura).

0969-806X/$ - see front matter & 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.radphyschem.2011.11.032

physical–chemical treatment with the activated sludge system completely (Alonso et al., 2010; Fent et al., 2006; Go´mez et al., 2007). The development of new treatment method is required to minimize the risk. Ionizing radiation method, one of the AOPs, succeeded to decompose effectively persistent organic pollutants such as dioxin, polychlorobiphenyls, endocrine disrupting chemicals (EDCs), and so on (Dajka et al., 2003; Getoff, 2002; Chaychian et al., 2002; Kimura et al., 2004; Wasiewicz et al., 2006; Wojna´rovits et al., 2005). Trace amount of EDCs, which give hazardous effect to aquatic animals at 1 ng dm  3, were difficult to be treated by existing water treatment methods. However, g-ray irradiation method detoxified EDCs and its irradiation products in wastewater at the dose of 200 Gy, and the economic cost of the treatment plant using electron beam was estimated to be 17 yen m  3. (Kimura et al., 2004; Kimura et al., 2006; Kimura et al., 2007). Moreover, the ionizing radiation method was already tried on an industrial stage of the water treatment, and the plant using the electron beam combined with the biodegradation process is operated at the papermill factory and the dye industrial complex (Han et al., 2002; Shin et al., 2002). The electron beam irradiation promotes the decrease in the amount of total organic carbon (TOC), biological oxygen demand (BOD), and chemical oxygen demand (COD) of wastewater and results in a realization of an efficient process. The persistent pharmaceuticals also could be decomposed by AOPs, and some papers have been reported on the treatment of the some pharmaceuticals and antibiotics in pure water (Kim et al., 2009; Szabo´ et al., 2011). However, decomposition of pharmaceuticals by

A. Kimura et al. / Radiation Physics and Chemistry 81 (2012) 1508–1512

ionizing radiation was difficult to carry out in the real influent sewage water because of the large number of contaminants. The purpose of this work is to treat the pharmaceuticals in combination of the activated sludge and ionizing radiation. Decomposition of the pharmaceuticals in wastewater was first carried out by the activated sludge system in order to decompose biodegradable pharmaceuticals and reduce the TOC value in wastewater. Persistent pharmaceuticals, which were not decomposed by the activated sludge system, were treated by g-ray, and their decomposition efficiencies depended on the amount of TOC in wastewater.

2. Experimental 2.1. Sample preparation and irradiation Aspirin: acetylsalicylic acid (99.5%, Wako), ibuprofen: (S)-(þ)4-isobutyl-a-–methyl-phenylactic acid (99%, Aldrich), carbamazepine: 5 H-dibenzo[b,f]azepine-5-carboxamide (99%, Aldrich), mefenamic acid: 2-(2,3-dimethylphenyl)aminobenzoic acid (99%, Wako), ketoprofen: (RS)-2-(3-benzoylphenyl)propanoic acid (99%, Aldrich), oseltamivir: ethyl (3R,4R,5S)-5-amino-4-acetamido-3-(pentan-3-yloxy)cyclohex-1-ene-1-carboxylate (TYUGAI PHARMACEUTICALS CO.), clofibric acid: 2-(4-chlorophenyl)-2methyl-propionic acid (97%, Aldrich), and diclofenac: 2-[(2,6dichlorophenyl)amino]benzeneacetic acid sodium salt (Aldrich) were selected as experimental samples because they were reported to be consumed in large amount and detected in the water environment used without purification (Fent et al., 2006). Molecular structures of these pharmaceuticals were shown in Fig. 1. Each pharmaceutical was dissolved at 5 mmol dm  3 concentration in real wastewater of pH 7.45. The amount of TOC was about 50 mgC dm  3. The water was collected at an aeration tank of a water treatment facility, Gunma Prefectural Central Wastewater Treatment Plant. The pH and TOC values were measured by a pH meter (MP220, METER TOLEDO) and a TOC analyzer (VWP-T, Shimadzu). Activated sludge was supplied by the wastewater treatment plant and was studied by a microscopy. Vorticella and Epistylis, which exist in the biota under aerobic sludge condition, were detected in the supplied sludge. This sludge was acclimated by adding 1 g dm  3 of glucose (98.0%, Wako) and/or granulated sugar (NISSIN) of 0.5 dm3 day  1 for 2 days. The acclimated sludge

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solution of 5.0  10  2 dm3 was mixed with equal amount of the pharmaceutical solution of 10 mmol dm  3, and stirred at 100 rpm from 8 to 24 h with aeration at 0.1 dm3 min  1. Biologicaly treated samples were filtered by a filter paper (150 mm+, Whatman), and concentrations of the pharmaceuticals in these filtrates were measured by HPLC (Agilent, 1100 series) with a reverse phase column (Shodex, RS pak DE-613). Ultra-pure water (TOC: 4 ppb, electric resistance: 18.2 MO cm) was supplied from Milli-pore Milli-Q system to be used as an eluent of HPLC. The pharmaceuticals, which remained at 80% of the initial concentration after biodegradation for 8 h, were decomposed by g-ray irradiation. The irradiation was carried out at 298 K using 60Co g-ray sources at JAEA, Takasaki, at dose range of 50 to 20000 Gy (Gy¼J kg  1). The pharmaceutical solutions before and after g-ray irradiations were analyzed by HPLC. Phenol (Wako Pure Chemical Industries, Ltd., 499.0%) was used without further purification as a reference material to evaluate the rate constant of the reaction of the pharmaceuticals with hydroxyl radicals. Pharmaceuticals and phenol at 5 mmol dm  3 were dissolved in pure water, and g-ray irradiation of the mixed solution was carried out at the dose range of 1 to 40 Gy.

3. Results and discussion 3.1. Decompositions of pharmaceuticals in wastewater by activated sludge The pharmaceuticals in wastewater were decomposed by the activated sludge system as shown in Fig. 2. Concentrations of oseltamivir and aspirin readily decreased and eliminated at 2 h, and decomposition of ibprofen was obtained almost 100% for 4 h. On the other hand, carbamazepine, ketoprofen, mefenamic acid, clofibric acid, and diclofenac were not decomposed completely for 8 h, which is the average reaction time of the aeration tank in the real wastewater treatment plant. Decompositions of organic compounds by the activated sludge system have been previously conducted. Vaishnav et al. (1987) determined biodegradations of 17 alcohols and 11 ketones using the BOD technique. BarriosMartinez et al. (2006) discussed biodegradation mechanism and efficiency of phenol in wastewater. These biodegradation results indicate that decomposition efficiency of organic compounds by activated sludge treatment decreases in the order of

Aromatic pharmaceuticals O

HOOC COOH

COOH OCOCH

Aspirin

N

N

COOH

O

Ibprofen

Carbamazepine

Mefenamic acid

Ketoprofen

Chlorinated pharmaceuticals

Aliphatic pharmaceuticals

Cl O HO N

O

O

COOH

NH Cl

Cl

COOH

O

Oseltamivir

Clofibric acid Fig. 1. Chemical structures of pharmaceuticals.

Diclofenac

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A. Kimura et al. / Radiation Physics and Chemistry 81 (2012) 1508–1512

electron acceptor and an alkoxy group as a strong electron donor, while the phenyl rings of diclofenac have also two chlorine substituents and two electron donating groups. The electron densities of the phenyl rings of clofibric acid and diclofenac may be similar, and the decomposition curves by g-ray irradiation were almost the same.

Concentration (µmol dm - 3 )

5

4

Mefenamic acid Ketoprofen Carbamazepine Diclofenac Clofibric acid Ibprofen Oseltamivir Aspirin

3

2

1

3.3. Kinetics and simulation of decomposition of pharmaceuticals in real wastewater by ionizing radiation

0 0

2

4 6 Reaction time (h)

8

Fig. 2. Biodegradation of pharmaceuticals in wastewater by activated sludge system.

Concentration (µmol dm -3)

5 Mefenamic acid Ketoprofen Carbamazepine Clofibric acid Diclofenac

4

3

kPharm

Pharmaceuticalsþ OH ! products kPhenol

Phenolþ OH ! products

2

1

0 0

1000

Carbamazepine, ketoprofen, mefenamic acid, clofibric acid, and diclofenac have phenyl rings, which would be attacked by the radiation generated hydroxyl radical. The hydroxyl radicals attack phenol with the rate constant at 6.6  109 mol  1 dm3 s  1, and more than 94% of phenol molecules were degraded to produce OH substituted compounds (Elliot et al., 1990; Field et al., 1982). In the presence of dissolved O2, hydrated electrons and hydrogen atoms are converted into superoxide radical anions immediately (Elliot, et al., 1990), which are very less reactive compared with hydroxyl radicals. Phenol can be regarded as a standard to estimate the relative rate constant of pharmaceuticals with reactious hydroxyl radicals (OH).

2000



saturated-aliphatics, unsaturated-aliphatics, aromatics, and chlorinated compounds. These persistent pharmaceuticals are considered to be decomposed by further water treatment methods such as ionizing radiation. 3.2. Decompositions of pharmaceuticals in wastewater by ionizing radiation Decompositions of the persistent pharmaceuticals at 5 mmol dm  3 in wastewater were investigated by the g-ray irradiation as shown in Fig. 3. Concentrations of carbamazepine decreased exponentially as function of dose up to 1 kGy and were less than 0.05 mg dm  3, which is the threshold concentration of chronic toxicity of pharmaceuticals (Fent et al., 2006), while mefenamic acid and ketoprofen were decomposed at 2 kGy. Radiation generated hydroxyl radical, which is generally the main reactive species for radiolysis of organic compounds in water, has a strong electrophilicity, and preferentially attacks the high electron density places such as phenyl ring. Thereby carbamazepine, which has azepine group as an electron donor, was easy to be attacked by hydroxyl radicals. Decomposition yields of ketoprofen and mefenamic acid, which have electron accepting groups such as carbonyl and carboxyl, were lower than that of carbamazepine. Concentrations of clofibric acid and diclofenac also decreased as a function of dose, and were eliminated at 1 kGy. A phenyl ring of clofibric acid was substituted by a chlorine group as a weak

ð2Þ

kPharm and kPhenol are the reaction rate constants of the hydroxyl radicals with the pharmaceuticals and phenol, respectively. The percentage of the hydroxyl radicals reacting with the pharmaceuticals among the total hydroxyl radicals should be related to the rate constants with solutes at the same concentration of the pharmaceutical and phenol. When the dose rate (DR) is constant, the decomposition yield of the pharmaceuticals can be expressed by the rate constant and the concentration of the hydroxyl radicals (Kimura et al., 2007):

Dose (Gy) Fig. 3. Decomposition of pharmaceuticals in wastewater by ionizing radiation.

ð1Þ

d½Pharmaceutical 1 d½Pharmaceutical ¼ dD DR dt 1 k ¼ ½Pharmaceutical½OH DR Pharm

ð3Þ

where D and t are dose and irradiation time, respectively. When the initial concentrations of both solutes are the same, the decomposition ratio of the pharmaceuticals to phenol is the ratio of the rate constants under the same dose rate irradiation:  d½Pharmaceutical d½Phenol   ¼ kPharm =kPhenol ð4Þ dD dD Amines and chlorinated aromatic compounds, however, would react with not only hydroxyl radicals but also hydrated electrons rapidly (Getoff and Solar, 1988; Johnson et al., 2002). The initial concentrations of the pharmaceuticals and phenol, therefore, were set at 5 mmol dm  3, which was lower than the dissolved O2 concentration in air-saturated water (about 250 mmol dm  3). The reaction of hydrated electrons with O2 is faster than that with the chlorinated pharmaceuticals (clofibric acid and diclofenac) in this condition, and the rate constants with the hydroxyl radicals could be determined by the competition reaction method. Fig. 4 shows the decomposition of carbamazepine and phenol under mixed condition by g-ray irradiation. The ratio of the decomposition yield of carbamazepine to that of phenol was determined to be 1.47 from the slope of the fitted lines for initial decomposition curves. The rate constant of the reaction of carbamazepine with the hydroxyl radicals (kPharm) was estimated at 9.7  109 mol  1 dm3 s  1. The rate constant of reaction of pharmaceuticals with the hydroxyl radicals are listed in Table 1. These rate constants were used as parameters

A. Kimura et al. / Radiation Physics and Chemistry 81 (2012) 1508–1512

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5

5

Carbamazepine -3

Concentration (µmol dm-3)

Concentration (µmol dm-3)

Organic carbon at 300 mg C dm

4

Phenol

-3

4

Organic carbon at 50 mg C dm

3

2

1

Carbamazepine

3

0

2

4 6 Dose (Gy)

8

0

10

0

Table 1 Rate constant of the reaction of pharmaceutical with hydroxyl radical in water estimated by competition reaction method. Rate constant (mol  1 dm3 s  1)

Carbamazepine Ketoprofen Mefenamic acid Clofibric acid Diclofenac Phenoln

9.7  109 5.6  109 4.0  109 1.0  1010 9.0  109 6.6  109

n

4000

5000

Fig. 5. Simulation curves for decomposition of carbamazepine in wastewater having organic carbons at 50 and 300 mg C dm  3 by ionizing radiation.

4. Conclusion

Elliot et al., 1990.

GOH kPharm 1001:6  1019 NA kOC

3000

in Fig. 5. Thereby the activated sludge system would be reduced the amount of TOC in wastewater, and was considered to support the treatment of persistent pharmaceuticals by the ionizing radiation. Simulated decomposition curves of the pharmaceuticals strongly depend on [OC], and the required dose for the treatment of the pharmaceuticals could be calculated by use of this simulation and the measurement value of TOC in the wastewater.

for the simulation of the decompositions of the pharmaceuticals in wastewater by ionizing radiation. Decomposition efficiency of the pharmaceuticals by the hydroxyl radicals would be interfered by the organic carbons (OC) in the wastewater, and were represented as follows:   A D ½Pharmaceutical ¼ ½Pharmaceutical0 exp  ½OC _A ¼

2000

Dose (Gy)

Fig. 4. Decomposition of pharmaceuticals and phenol in mixed aqueous solution by ionizing radiation.

Chemicals

1000

ð5Þ

where D, GOH, NA, [OC], and kOC are the absorbed dose of the wastewater, G-value of hydroxyl radical and Avogadro’s number, the concentration of total organic carbons, and the rate constant of OC with the hydroxyl radicals, respectively. GOH is selected to be 2.7 molecules 100  1 eV  1 (Buxton, 1987), and [OC] were set at 50 mg C dm  3 near to the average value of real wastewater samples in this experiment. The rate constants of many organic compounds with the hydroxyl radicals are reported to be about 106–1010 mol  1 dm3 s  1 (Buxton et al., 1988), and kOC in the simulation was assumed to be 1  108 mol  1 dm3 s  1. Decreases in the concentrations of the pharmaceuticals in the wastewaters were simulated by use of the Eq. (5) and the obtained rate constants of the pharmaceuticals (Table 1). Simulation curves for the decomposition of carbamazepine in wastewater were shown in Fig. 5, and the curves for the amount of TOC at 50 mg C dm  3 fit well with the plot of the decreased concentration of carbamazepine. Required dose for the treatment of carbamazepine in wastewater before biodegradation at the amount of TOC of 300 mg C dm  3, which was similar to reported TOC values of some industrial influents (Cao and Meharvar, 2010; Rajkumar and Palanivelu, 2004; Thomas et al., 1999), was calculated by the simulation to be 5000 Gy as shown by dashed line

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