Desalination 256 (2010) 43 47 Contents lists available at ScienceDirect Desalination journal homepage: www.elsevier.com/locate/desal Comparison of different advanced oxidation processes for treatment of antibiotic aqueous solution Emad S. Elmolla, Malay Chaudhuri Department of Civil Engineering, Universiti Teknologi PETRONAS, 31750 Tronoh, Perak, Malaysia article info abstract Article history: Received 25 November 2009 Received in revised form 11 February 2010 Accepted 11 February 2010 Available online 9 March 2010 Keywords: Amoxicillin Ampicillin Antibiotics Cloxacillin Comparison Photo- TiO 2 photocatalysis UV/ZnO process The study was undertaken to compare from technical and economic point of view the treatment of antibiotic aqueous solution containing amoxicillin, ampicillin, and cloxacillin by, photo-, TiO 2 photocatalytic and UV/ZnO processes. The best operating conditions for treatment of antibiotic aqueous solution containing 104, 105 and 103 mg/l of amoxicillin, ampicillin, and cloxacillin, respectively were: process COD/H 2 O 2 /Fe 2+ molar ratio 1:3:0.30 and ph 3; photo- process COD/H 2 O 2 /Fe 2+ molar ratio 1:1.5:0.075 and ph 3; UV/ TiO 2 /H 2 O 2 process TiO 2 1g/L,ambientpH 5andH 2 O 2 100 g/l; UV/ZnO process ZnO 0.5 g/l and ph 11. All studied processes were able to degrade the antibiotics and improve biodegradability (BOD 5 /COD ratio), except for UV/ZnO process which did not improve biodegradability. Photo- process exhibited higher rate constant (0.029 min 1 ) than that of process (0.0144 min 1 ) and this may be ascribed to photochemical regeneration of Fe 2+ ions by photoreduction of Fe 3+ ions and hence increasing hydroxyl radical production rate. Rate constants of UV/ZnO process (0.00056 min 1 ) and UV/TiO 2 /H 2 O 2 process (0.0005 min 1 ) were lower than that of and photo- processes. Photo- process appeared to be the most cost-effective compared to the other studied processes. 2010 Elsevier B.V. All rights reserved. 1. Introduction Among all the pharmaceutical drugs that cause contamination of the environment, antibiotics occupy an important place due to their high consumption rates in both veterinary and human medicine. Problem that may be created by the presence of antibiotics at low concentrations in the environment is the development of antibiotic resistant bacteria [1]. In recent years, the incidence of antibiotic resistant bacteria has increased and many people believe the increase is due to the use of antibiotics [2]. Furthermore, the presence of antibiotics in wastewater has increased in the past years and their abatement will be a challenge in the near future. Amoxicillin, ampicillin and cloxacillin are semisynthetic penicillin obtaining their antimicrobial properties from the presence of a beta-lactam ring. They are widely used in human and veterinary medicine. Amoxicillin and cloxacillin have been detected in wastewater [3,4]. Various treatment techniques can be applied to purify the effluent containing pharmaceutical compounds. The advanced oxidation processes (AOPs) appear more practical in comparison with other techniques (activated carbon adsorption, air stripping and reverse osmosis) because these techniques only transfer the pollutants from Corresponding author. Tel.: +60 14 9047313; fax: +60 5 365 6716. E-mail addresses: em_civil@yahoo.com, emadsoliman3@gmail.com (E.S. Elmolla). one phase to another without destroying them. Biological treatment is limited to wastewater which contains biodegradable substances and which are not toxic to the biological culture. Among different AOPs, and photo- processes are regarded as promising technology for the treatment of wastewater containing recalcitrant (non-biodegradable) organic compounds [5]. Oxidation with 's reagent is based on hydroxyl radicals (OH ) produced by catalytic decomposition of hydrogen peroxide in acidic solution. An alternative reaction mechanism in which ferryl ion (FeO 2+ ) acts as a key oxidant has been reported [6,7]. In the photo- process, additional reactions occur in the presence of UV light that produce hydroxyl radicals or increase the production rate of hydroxyl radicals [8], thus increasing the efficiency of the process. Increasing H 2 O 2 above the optimum concentration may cause negative effect to the process due to scavenging of OH by H 2 O 2 as in Reaction 1 [9]. This optimal H 2 O 2 concentration depends on the nature and concentration of the pollutants. The theoretically necessary H 2 O 2 concentration for complete mineralization of the organic pollutant can be calculated based on stoichiometric ratio (1 g/l COD=2.125 g/l H 2 O 2 ) [10]. OH þ H 2 O 2 H 2 O þ HO 2 Reaction1 TiO 2 photocatalysis has also emerged as a promising wastewater treatment technology. The main advantages of the process include lack of mass transfer limitations and operation at ambient conditions. The catalyst itself is inexpensive, commercially available, non-toxic and 0011-9164/$ see front matter 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.desal.2010.02.019
44 E.S. Elmolla, M. Chaudhuri / Desalination 256 (2010) 43 47 photochemically stable [11]. Daneshvar et al. [12] reported ZnO to be a suitable alternative to TiO 2 since its photodegradation mechanism is similar to that of TiO 2. ZnO can absorb a larger fraction of the solar spectrum than TiO 2, and hence ZnO photocatalyst is considered more suitable for photocatalytic degradation in presence of sunlight [13]. There have been studies on treatment of amoxicillin wastewater and penicillin formulation effluent by AOPs [14 16]. Degradation of amoxicillin by ozonation and photo- has been reported [17,18]. In our previous work, degradation of amoxicillin, ampicillin and cloxacillin antibiotics using [19], photo- [20], TiO 2 photocatalysis [21] and ZnO photocatalysis [22] have been reported. The present study was undertaken to compare from technical and economic point of view the treatment of antibiotic aqueous solution containing amoxicillin, ampicillin and cloxacillin by, photo-, TiO 2 photocatalytic (UV/TiO 2 and UV/TiO 2 /H 2 O 2 ) and ZnO photocatalytic (UV/ZnO) processes. 2. Materials and methods 2.1. Chemicals Hydrogen peroxide (30% w/w), ferrous sulphate (FeSO 4 7H 2 O) and Zinc oxide (ZnO) were purchased from R & M Marketing, Essex, U.K. TiO 2 powder (anatase, purity N99%) was purchased from Fluka. Analytical grade of amoxicillin (AMX) and ampicillin (AMP) were purchased from Sigma and cloxacillin (CLX) from Fluka to construct HPLC analytical curves for the determination and quantification of the antibiotics. AMX, AMP and CLX used to prepare antibiotic aqueous solution were obtained from a commercial source (Farmaniage Company). The commercial products were used as received without any further purification. Sodium hydroxide and sulfuric acid were purchased from HACH Company, USA. Potassium dihydrogen phosphate (KH 2 PO 4 ) was purchase from Fluka and acentonitrile HPLC grade was from Sigma. Fig. 1 shows the chemical structure and HPLC chromatograph of amoxicillin, ampicillin sodium and cloxacillin sodium. 2.2. Analytical methods Antibiotic concentration was determined by HPLC (Agilent 1100 Series) equipped with micro-vacuum degasser (Agilent 1100 Series), quaternary pumps, diode array and multiple wavelength detector (DAD) (Agilent 1100 Series), at wavelength 204 nm. The data was recorded by a chemistation software. The detection column was ZORBAX SB-C18 (4.6 mm x 150 mm, 5 µm). The column temperature was 60 C. Mobile phase was 55% buffer solution (0.025 M KH 2 PO 4 in ultra pure water) and 45% acentonitrile. Chemical oxygen demand (COD) was determined according to the Standard Methods [23]. When the sample contained H 2 O 2, to reduce interference in COD determination ph was increased to above 10 to decompose H 2 O 2 to oxygen and water [24]. The ph was measured by a ph meter (HACH Sension 4) with a ph electrode (HACH platinum series ph electrode model 51910, HACH Company, USA). Five-day biochemical oxygen demand (BOD 5 ) was measured according to the Fig. 1. Chemical structure and HPLC chromatograph of (a) amoxicillin, (b) ampicillin sodium and (c) cloxacillin sodium.
E.S. Elmolla, M. Chaudhuri / Desalination 256 (2010) 43 47 45 Standard Methods [23]. Dissolved oxygen (DO) was measured by a YSI 5000 dissolved oxygen meter. Bacterial seed for BOD 5 test was obtained from a municipal wastewater treatment plant. A TOC analyzer (Model 1010; O & I analytical) was used for determining dissolved organic carbon (DOC). 2.3. Antibiotic aqueous solution Antibiotic aqueous solution was prepared by dissolving specific amounts of amoxicillin (AMX), ampicillin (AMP) and cloxacillin (CLX) in distilled water. The aqueous solution characteristics were AMX, AMP and CLX concentration 104, 105 and 103 mg/l, respectively, initial COD 520 mg/l, BOD 5 /COD ratio 0 and DOC 145 mg/l. The antibiotic aqueous solution was prepared weekly and stored at 4 C. 2.4. Experimental procedure Batch, photo-, TiO 2 photocatalytic and UV/ZnO process experiments were conducted using a 600 ml Pyrex reactor with 500 ml of antibiotic aqueous solution. The processes were conducted at room temperature (22±2 C). The required amount of iron (FeSO 4 7H 2 O) for and photo- or TiO 2 and ZnO for TiO 2 photocatalytic and UV/ZnO processes was added to the aqueous solution and mixed by a magnetic stirrer to ensure complete homogeneity. The ph was adjusted to the required value using H 2 SO 4 or NaOH. Thereafter, necessary amount of H 2 O 2 for, photo- and UV/H 2 O 2 /TiO 2 processes was added to the mixture and this time was considered the beginning of the experiment. The mixture was subjected to UV irradiation in case of photo-, TiO 2 photocatalysis and ZnO photocatalysis. The source of UV light was an UV lamp (Spectroline; Model EA-160/FE; 230 V; 0.17 A; Spectronics Corporation, New York, USA) with nominal power of 6 W, emitting radiation at wave length 365 nm. For TiO 2 and ZnO photocatalysis, the mixure was kept in dark for 30 min for dark adsorption. The time at which the UV lamp was switched on was considered the beginning of the experiment for UV/TiO 2 and UV/ZnO processes. Samples were taken at pre-selected time intervals using a syringe and filtered through a 0.45 µm PTFE syringe filter for COD, BOD 5 and DOC measurement, and through a 0.20 µm PTFE syringe filter for determination of antibiotic concentration by HPLC. 3. Results and discussion 3.1. Antibiotic degradation, mineralization and biodegradability improvement Tables 1 and 2 show the effect of operating conditions such as oxidant and catalyst concentration, and ph on the treatment of antibiotic aqueous solution using, photo-, TiO 2 photocatalytic (UV/TiO 2 and UV/TiO 2 /H 2 O 2 ) and UV/ZnO processes. As shown in Tables 1 and 2, homogeneous advanced oxidation processes ( and photo-) are very effective in antibiotic degradation and mineralization, and biodegradability improvement compared to heterogonous advanced oxidation processes (TiO 2 photocatalysis and UV/ZnO). A comparison among the studied AOPs was conducted in terms of antibiotic degradation, mineralization, biodegradability (BOD 5 /COD ratio) improvement, kinetic constant and half-life (t 1/2 ) under their best operating conditions. The best operating conditions for degradation, mineralization and biodegradability improvement of amoxicillin, ampicillin and cloxacillin in aqueous solution were observed to be: process H 2 O 2 /COD molar ratio 3, H 2 O 2 /Fe 2+ molar ratio 10 (COD/H 2 O 2 /Fe 2+ molar ratio 1:3:0.30) and ph 3 [19]; photo- process H 2 O 2 /COD molar ratio 1.5, H 2 O 2 /Fe 2+ molar ratio 20 (COD/H 2 O 2 /Fe 2+ molar ratio 1:1.5:0.075) and ph 3 [20]; UV/TiO 2 /H 2 O 2 process TiO 2 concentration 1 g/l, ambient ph 5, H 2 O 2 concentration 100 g/l and reaction Table 1 Experimental conditions and results of and photo- processes. Process ph H 2 O 2 / H 2 O 2 / Time COD BOD 5 / DOC COD Fe 2+ (min) removal COD removal (MR) a (MR) a (%) (%) F01 3 1 50 50 21 0.04 11 F02 3 1.5 50 50 24 0.05 17 F03 3 2 50 50 47 0.20 25 F04 3 2.5 50 50 51 0.26 27 F05 3 3 50 50 55 0.30 32 F06 3 3.5 50 50 50 0.21 32 F07 3 3 2 50 72 0.20 39 F08 3 3 5 50 75 0.24 48 F09 3 3 10 50 79 0.35 52 F10 3 3 20 50 71 0.36 35 F11 3 3 50 50 55 0.30 32 F12 3 3 100 50 49 0.18 13 F13 3 3 150 50 39 0.11 14 F14 2 3 10 50 44 0.12 31 F15 2.5 3 10 50 52 0.18 42 F16 3 3 10 50 80 0.35 53 F17 3.5 3 10 50 76 0.25 48 F18 4 3 10 50 75 0.19 45 PF0l Photo- 3.5 1 50 50 66 0.18 41 PF02 3.5 1.5 50 50 72 0.23 46 PF03 3.5 2 50 50 61 0.16 40 PF04 3.5 2.5 50 50 46 0.11 41 PF05 3.5 1.5 10 50 76 0.34 47 PF06 3.5 1.5 20 50 75 0.34 46 PF07 3.5 1.5 50 50 72 0.23 46 PF08 3.5 1.5 100 50 54 0.14 36 PF09 3.5 1.5 150 50 48 0.12 34 PF10 2 1.5 20 50 42 0.13 33 PF11 2.5 1.5 20 50 71 0.28 40 PF12 3 1.5 20 50 81 0.39 58 PF13 3.5 1.5 20 50 75 0.34 46 PF14 4 1.5 20 50 73 0.27 46 Complete degradation of the antibiotics in 2 min. Irradiation or reaction time for the experiments was 50 min. a (MR) Molar ratio. time 30 min [21]; and UV/ZnO process ZnO concentration 0.5 g/l and ph 11 [22]. Table 3 shows a comparison among, photo-, TiO 2 photocatalysis (UV/TiO 2 and UV/TiO 2 /H 2 O 2 ) and UV/ZnO processes in terms of effluent characteristics under their best operating conditions. All studied AOPs were able to degrade and mineralize the antibiotics and improve the biodegradability (BOD 5 / COD ratio), except UV/ZnO which did not improve the biodegradability. Hence,, photo- and UV/TiO 2 /H 2 O 2 processes are suitable for treatment of simulated antibiotic wastewater. 3.2. Pseduo-first order kinetic constant and half-life time Kinetics for antibiotic oxidation by, photo- UV/TiO 2 / H 2 O 2 and UV/ZnO processes can be represented as a first-order rate equation as follows: ln DOC DOC 0 = k 0 t where, pseudo-first-order rate constant (k 0 ) can be obtained through a linear least-square fit of the DOC data. The half-life (t 1/2 ) is the time required to decrease the concentration of the reactant (DOC) to half the initial value. It was calculated according to the following equation: t 1=2 = 0:693 k 0 Value of the pseudo-first order kinetic constant was obtained by fitting the experimental data to a straight line (Fig. 2) and the results ð1þ ð2þ
46 E.S. Elmolla, M. Chaudhuri / Desalination 256 (2010) 43 47 Table 2 Experimental conditions and results of TiO 2 and ZnO photocatalysis. Process ph TiO 2 (g/l) H 2 O 2 (mg/l) ZnO (g/l) Antibiotic degradation, % BOD 5 / COD (AMX) (AMP) (CLX) COD removal (%) T01 UV/TiO 2 5 0.5 42 33 47 b0.05 6 3.4 T02 5 1.0 55 52 58 b0.05 9 6.3 T03 5 1.5 56 54 59 b0.05 10 6.0 T04 5 2.0 55 52 60 b0.05 10 5.3 T05 3 1.0 61 78 95 b0.05 12 4.0 T06 5 1.0 55 52 58 b0.05 9 6.3 T07 8 1.0 59 74 82 b0.05 10 4.5 T08 11 1.0 71 91 100 b0.05 11 5.0 T09 UV/TiO 2 /H 2 O 2 5 1.0 50 100 100 100 0.05 15 6.4 T10 5 1.0 100 100 100 100 0.10 26 14.0 T11 5 1.0 150 100 100 100 0.09 23 9.6 T12 5 1.0 200 100 100 100 0.07 16 6.9 T13 5 1.0 300 100 100 100 0.06 12 5.3 Z0l UV/ZnO 8 0.2 100 44 60 b0.05 18 5.2 Z02 8 0.4 100 52 69 b0.05 22 12.6 Z03 8 0.5 100 72 73 b0.05 33 15.6 Z04 8 1.0 100 71 70 b0.05 30 14.1 Z05 8 1.5 100 70 69 b0.05 25 11.9 Z06 8 2.0 100 69 68 b0.05 25 11.1 Z07 5 0.5 100 59 43 b0.05 25 11.1 Z08 8 0.5 100 72 71 b0.05 26 15.6 Z09 11 0.5 100 100 100 b0.05 28 16.3 Irradiation time for the experiments was 300 min. DOC removal (%) Table 3 Comparison among, photo-, UV/TiO 2 /H 2 O 2 and UV/ZnO processes in terms of effluent characteristics under their best operating conditions. Best operating conditions Effluent characteristics Parameter/ process Photo- UV/TiO 2 /H 2 O 2 UV/ZnO H 2 O 2 /COD (MR) 3.0/1.0 1.5/1.0 H 2 O 2 /Fe 2+ (MR) 10/1.0 20/1.0 COD/H 2 O 2 //Fe 2+ (MR) 1.0/3.0/0.30 1.0/1.5/0.075 TiO 2 (g/l)/h 2 O 2 (mg/l) 1/100 ZnO (g/l) 0.5 ph 3 3 5 11 Time (min) 50 50 300 300 Complete antibiotics 2 min 2 min 30 min 180 min degradation COD removal (%) 80 81 26 28 DOC removal (%) 53 58 14 16 BOD 5 /COD 0.35 0.39 0.1 b0.05 are summarized in Table 4. The values of half-life are also presented in Table 4. As can be observed, photo- showed the highest k 0 and it is 1.4, 28 and 25 times higher than that of, UV/TiO 2 /H 2 O 2 and UV/ZnO processes, respectively. Higher rate constant of the photo- process may be ascribed to photochemical regeneration of Fe 2+ ions by photoreduction of Fe 3+ ions and hence increased hydroxyl radical production rate. 3.3. Cost estimation Estimation of the treatment cost is an important aspect. The overall cost of the treatment process is represented by the sum of the capital, operating and maintenance cost. For a full-scale system, these costs strongly depend on the nature and the concentration of the pollutants, flow rate of the influent and configuration of the reactor [25]. In the literature, some efforts have been made to develop a procedure for estimation of the electrical consumptions for UV lamps [25,26]. One of these procedures is based on the electrical energy (EE) in kilowatt Table 4 Pseudo-first-order kinetic constants and half-life time for different AOPs under their best operating conditions. Process k 0 (min 1 ) t 1/2 (min) R 2 Fig. 2. Pseudo-first-order plot for antibiotic mineralization by different AOPs under their best operating conditions. 0.01 69.3 0.86 Photo- 0.014 49.5 0.97 UV/TiO 2 /H 2 O 2 0.0005 1386 0.99 UV/ZnO 0.00056 1238 0.99
E.S. Elmolla, M. Chaudhuri / Desalination 256 (2010) 43 47 47 Table 5 Price of reagents used. Reagent Unit Price $ H 2 O 2 (35%)[27] kg 0.35 FeSO 4 7H 2 O [27] kg 0.5 TiO 2 [27] kg 3 ZnO [28] kg 2.2 Table 6 Cost estimation for the studied AOPs. Chemical requirement (mg/l) Cost estimation ($/kg DOC) Total cost ($/kg DOC) hours (kwh) required to bring about the degradation of a unit mass (one kilogram, kg) of a pollutant and can be calculated using the following formula: p t 1000 EE = ð3þ V M 60 c i c f where, EE is the energy requirement per kilogram of organic pollutant as DOC, p is the lamp power (kw), V is the polluted water volume (L), t is the half-life (min) for achieving 50% mineralization of DOC, M is the molecular weight of the pollutant (g/mol), c i and c f are the initial and final concentration of the pollutant (mol/l), and the factor of 1000 converts g to kg [25]. Prices of electricity are highly dependent on the particular country and electricity price was taken $0.10 kwh as an average value [27]. The average price of reagents are shown in Table 5. An estimation of the operating cost per kg of DOC was calculated for the mineralization of 50% (half-life) of the initial DOC and shown in Table 6. Photo- process appeared to be the most cost-effective. However, the cost may reduce considerably when solar light is used [29 31]. 4. Conclusions Reagent Photo- UV/TiO 2 / H 2 O 2 UV/ZnO H 2 O 2 1657 828 100 FeSO 4 7H 2 O 1355 338 TiO 2 1000 ZnO 500 H 2 O 2 9 4 1 FeSO 4 7H 2 O 10 3 TiO 2 46 ZnO 17 UV 8 213 190 19 15 260 207 The study was undertaken to compare from technical and economic point of view the treatment of antibiotic aqueous solution containing amoxicillin, ampicillin and cloxacillin by, photo-, TiO 2 photocatalytic and UV/ZnO processes. The best operating conditions for treatment of antibiotic aqueous solution containing 104, 105 and 103 mg/l of amoxicillin, ampicillin and cloxacillin, respectively were: process COD/H 2 O 2 /Fe 2+ molar ratio 1:3:0.30 and ph 3; photo- process COD/H 2 O 2 /Fe 2+ molar ratio 1:1.5:0.075 and ph 3; UV/TiO 2 /H 2 O 2 process TiO 2 1 g/l, ambient ph 5 and H 2 O 2 100 g/l; UV/ZnO process ZnO 0.5 g/l and ph 11. All studied processes were able to degrade the antibiotics and improve biodegradability (BOD 5 /COD ratio), except UV/ZnO process which did not improve biodegradability. Photo- process exhibited the highest rate constant (0.029 min 1 ) followed by (0.0144 min 1 ), UV/ZnO process (0.00056 min 1 ) and UV/TiO 2 /H 2 O 2 process (0.0005 min 1 ). Photo- process appeared to be the most cost-effective compared to other studied processes. Acknowledgement The authors are thankful to the management and authorities of the Universiti Teknologi PETRONAS for providing facilities for this research. 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