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Application of moving bed biofilm reactor in the removal of pharmaceutical compounds (diclofenac and ibuprofen)
Journal of Environmental Chemical Engineering 6 (2018) 5530–5535
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Application of moving bed biofilm reactor in the removal of pharmaceutical compounds (diclofenac and ibuprofen)
T
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Maryam Fatehifar, Seyed Mehdi Borghei , Ali Ekhlasi nia Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, Iran
A R T I C LE I N FO
A B S T R A C T
Keywords: Pharmaceutical Ibuprofen Diclofenac Biodegradation MBBR Wastewater
Pharmaceutical waste has attracted significant attention in the past two decades due to the current high consumption of pharmaceuticals together with the development of reliable detection technologies. In order to acquire better understanding on pharmaceuticals removal in biological processes, the treatment of synthetic wastewater containing diclofenac (DFN) and ibuprofen (IBU), two of the most commonly prescribed medicines worldwide, was studied using a moving bed biofilm reactor (MBBR). An 8.5-L aerobic MBBR with Kaldnes packing filling ratio of 40% was designed. The controlled parameters were pH within neutral range, temperature of 37 °C, mixed liquor suspended solids (MLSS) of 2100 mg/L, and attached growth equal to 1300 mg/L. Tests were conducted for four different initial pharmaceuticals concentrations: 2, 4, 7 and 10 mg/L, two hydraulic retention times (HRT): 5 and 10 h and two chemical oxygen demands (COD): 500 and 1000 mg/L. Results demonstrated that generally, DFN had higher removal percentage than IBU in the MBBR. At HRT = 10 h, DFN removal was between 30.83 and 66.01%, while it was 11.33 and 37.33% for IBU. At HRT = 5 h, DFN and IBU removal were respectively between 31.10–65.33 and 0–35.10%. It can be concluded that HRT = 5 h is the optimal time for DFN, while 10 h HRT promises noticeably better IBU removal. Furthermore, results revealed that DFN is better removed in the lower COD, while IBU showed better removal in the higher COD. Finally, the study on their toxicity reveals that pharmaceuticals exert slightly negative effect on COD removal.
1. Introduction Occurrence of pharmaceuticals in wastewater and treated water has significantly increased in the last decades. Two important facts has contributed to this issue and made it a growing concern: first, the improvement of quantification technologies have provided researchers with the ability to measure the concentrations in the range of ng/L to μg/L [1]; second, their consumption has rapidly increased worldwide [2]. Micropollutants, pollutants with concentration of ng/L to μg/L, have been repeatedly found in the environment, mainly in water supplies; thus, a lot of attention has been paid to them [3–5]. Pharmaceutically-active compounds (PhACs), a certain category of micropollutants, also included in “emerging new contaminants” category are found in rivers and ground water since conventional treatment plants are not specifically designed to eliminate them. In fact, the low concentration and relatively high polarity of these pollutants have made them difficult to eliminate [6]. Therefore, some will remain in the effluent and pollute the surface water. Taking the accumulative effect of micropollutants into account, their concentration is increasing and soon, concentrations much higher than previously reported will be
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detected in our environment. Two highly prescribed PhACs are diclofenac and ibuprofen, both non-steroidal anti-inflammatory drugs (NSAIDs) with analgesic and antipyretic properties [7,8]. Characteristics of these two PhACs are presented in Table 1. Many researchers have focused on the consumption of these PhACs worldwide. In 2012, Fierce Pharma reported that DFN was the 12th bestselling generic molecule globally [11]. Zhang et al. (2008) estimated that 940 ton DFN was consumed annually around the world, excluding veterinary consumption [12]. In 2005, IBU ranked 17th on the list of the most prescribed drugs in the United States [13]. These compounds either enter in original form or are discharged via excretion in urine and feces into wastewater [14]. Many authors have reported that DFN and IBU are not completely removed in sewage treatment plants [15,16]. Studies, mainly in Europe, have documented that DFN is found in raw wastewater with a medium concentration of 0.7 μg/L and a maximum concentration of 11 μg/L. IBU has been detected in raw wastewater with average values of 37 μg/L and maximum value of up to 100 μg/L [17]. PhACs, even in low concentration (ng/L to μg/L), may have
Corresponding author. E-mail address: [email protected] (S.M. Borghei).
https://doi.org/10.1016/j.jece.2018.08.029 Received 7 April 2018; Received in revised form 7 August 2018; Accepted 11 August 2018 Available online 17 August 2018 2213-3437/ © 2018 Elsevier Ltd. All rights reserved.
Journal of Environmental Chemical Engineering 6 (2018) 5530–5535
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Table 1 Characteristics of pharmaceuticals. Diclofenac-Na (DFN)
Ibuprofen (IBU)
2-[(2,6-Dichlorophenyl)- aminolbenzeneacetic acid-Na 15307-79-6 296.16 g/mol 5000 mg/L Moderately low (6-39%)
a-Methyl-4-(2-methylpropyl)- benzeneacetic acid 15687-27-1 206.28 g/mol 21 mg/L Low (less than 5%)
Structure [4]
CAS name [9] CAS numbera Molar mass [9] Water solubility [6] Human excretion [10] a
Obtained from CAS database list.
2. Materials and methods
negative impact on human health and the environment [18]. A great number of toxicity studies have been conducted to determine the toxicity of DFN in aquatic animals and organisms. Potential adverse effect of DFN on aquatic organisms was confirmed byCleuvers (2004) using Daphnia and algae in a ecotoxicity study [19]. Lawrence et al. (2007) reported that DFN is a major risk, even at the predicted environmental concentrations [20]. DFN at concentration of 50 μg/L inflicted heavy damage on gill, liver and kidney of brown trout fish [21]. Ecotoxicity studies on IBU revealed that it has negative effect on aquatic life. For example, IBU at the concentration of 1000 ng/L inhibited the growth of freshwater microalga, S. rubescens [22]. In another study, Geiger et al. (2016) claimed that 1 mg/L of IBU inhibited the growth of algal cells and reduced the chlorophyll content of Chlorella vulgaris [23]. These reports all suggests that elimination of DFN and IBU should be taken into serious consideration, and thus, more studies are required to address the problems the environment is encountering. Furthermore, it is of utmost importance to make every endeavor to control and eliminate the abovementioned pollutants from the environment. MBBR is a biological treatment technology which was first introduced in 1988 in Norway [24]. The main purpose of MBBR development is to simultaneously benefit from attached and suspended growth. In this type of reactor, neutral carriers are added to the reactor to let the biomass attach and grow [25]. As a result, this technology has numerous advantages, including high quality of the effluent, small footprint, high loading rate, high treatment efficiency and low overall cost. The MBBR has been successfully devised in many treatment plants since then and implemented in more than 400 treatment plants around the world [25,26]. Another aspect of the biological treatment of pharmaceutical wastewater that has gained attention in the past decade is the mechanism of degradation. The type of microorganisms favoring a certain PhAC, the pathway of its removal, metabolites, and co-substrates are all vital questions that have yet to be addressed to construct a thorough understanding of the biodegradation mechanism. Even though there are number of researches in this area, the answer to these questions are still vague because numerous research studies are required to cover a variety of PhACs and microorganisms. Moreover, findings and reports are not always consistent with each other. For instance, Kosjek et al. [27] reported seven metabolites for DFN, while Langenhoff et al. [4] detected eight metabolites. In case of IBU, Ferrando-Climent et al. [28] detected three main metabolites, while Langenhoff et al. [4] found no metabolite and concluded that complete mineralization had occurred and all IBU had been transformed to CO2 and H2O. The aim of this research was to study the removal of DFN and IBU in a Moving Bed Biofilm Reactor (MBBR). For this purpose, first, the effect of initial concentration of PhACs on their removal was studied. Then, optimized HRT and the initial COD of the wastewater was investigated discussed. The last analysis was assessment of the toxicity effect of PhACs on reactor’s COD removal.
2.1. Materials and reagent DFN sodium and IBU, both 98% pure, were purchased from Raha Pharmaceuticals, Isfahan, Iran (a well reputed pharmaceutical producer). All other chemicals including sugar, KH2PO4, urea, NaOH, H2SO4 98%, HgSO4 (extra pure), Ag2SO4, ethanol, acetonitrile (HPLC grade) and acetic acid (glacial) were obtained from Merk, Germany. Glass microfiber filters (GF/A 125 mm, ∅, Cat No. 1820–125) were obtained from Whatman (Maid- stone, UK).
2.2. Instrumentation Instruments used in the present study includes: pH meter (metrohm, Swiss), oven (MAMMER W 270), scale (AND-HR 200), vacuum pump (Edwards High Vacuum), COD reactor (HACH DRB 200), spectrophotometer (HACH, DR5000), HPLC (MACHEREY-NAGEL, nucleodur, C18 column) followed by UV–vis detector and DO meter (WTW-YSI55).
2.3. Characteristics of MBBR A cubic Plexiglas with a total volume of 12 L (L = 20 cm, W = 20 cm, H = 30 cm) and effective volume of 8.5 L was employed. Forty percent of the reactor’s effective volume was filled with carriers (Kaldnes type) with an internal diameter of 21 mm, an internal length of 41 mm, a density of 96 g/cm3 and a specific biofilm surface area of 480 m2/m3. Two 20 cm air stones were installed at the end of the reactor to ensure the dissolved air concentration of 2 mg/L and completely mixed regime in the reactor. The outlet valve diameter of reactor was carefully selected in order to prevent the escape of carriers. A sedimentation tank with a volume of 2.5 L was placed at the outlet of the reactor for effluent clarification and sludge separation, and if necessary, sludge return to the reactor.
2.4. Setup The first step was to create an environment that allowed the growth of biofilm on carriers. Seeding of the reactor was performed by addition of an active sludge from a nearby domestic sewage treatment plant (Ekbatan Treatment Plant, Tehran). Approximately, 8 L of sludge (MLSS ∼6050 mg/L, COD = 450 mg/L) was added to the reactor. First, the reactor was operated in batch mode for 7 days. Synthetic reactor feed was injected once every 8 h with a COD of 500 mg/L, and then gradually increased to 1000 mg/L within 7 days. In order to make the MLSS to remain high, the settled sludge at the bottom of the sedimentation tank was returned to the reactor on daily basis. 5531
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Table 2 Characteristics of synthetic wastewater. Chemical
Amount (mg/L)
DFN IBU COD Urea KH2PO4
2.000 2.000 500.00 53.625 21.935
2.000 2.000 1000.00 107.250 43.870
4.000 4.000 500.00 53.625 21.935
4.000 4.000 1000.00 107.250 43.870
7.000 7.000 500.00 53.625 21.935
7.000 7.000 1000.00 107.250 43.870
10.000 10.000 500.00 53.625 21.935
10.000 10.000 1000.00 107.250 43.870
Fig. 1. Effect of pharmaceuticals initial concentration on their removal, HRT = 5 h.
2.5. Wastewater characteristics
3. Results and discussion
Synthetic wastewater with four different initial concentrations of PhACs, and two different chemical oxygen demands (COD) of 500 and 1000 mg/L were harnessed. The influent flow rate was controlled to have two retention times: 5 and 10 h. Hence, it is worth mentioning that the loading rates were 6.25–25 gCOD/(m2.day). In order to adapt the biomass population, the input wastewater was initially prepared by mixing sugar, urea and K2HPO4(COD:N:P = 100:5:1) [29]. After 7 days of feeding without drugs and when a thin biofilm has formed on the surface of carriers (Kaldnes media), the drugs were added to the wastewater. First, drug concentration was 0.1 μg/L, then gradually increased to 2 mg/L. Table 2 presents the characteristics of the synthetic wastewater.
To date, information on the treatment of pharmaceuticals is limited; thus, it necessitates more research in this area. This research focused on the biological treatment of pharmaceuticals in an aerobic reactor. Effects of various parameters on efficiency of the MBBR are discussed as following. 3.1. Effect of pharmaceuticals concentration In this section, the effect of pharmaceuticals initial concentrations on their removal percentage was studied. It has been reported that initial concentration of the pollutant may have considerable effect on removal rate [10,30]. In order to compare the degree of removal, 4 different concentrations (2, 4, 7, 10 mg/L) were selected to feed the reactor, then the final concentrations were quantified using the HPLC tests. The flow to the reactor was changed to have different HRTs. Both compounds were biologically degraded to some extent in the presence of microorganisms. Figs. 1 and 2 show that IBU had lower degradation than DFN in all the runs. It can be ascribed to differences in their removal mechanism.
2.6. Sample preparation In all the experiments, 50 mL of sample taken from the reactor were filtered using Whatman-45 μm, transferred into a clean falcon, then stored in a fridge at 4 °C. The required tests were conducted within 24 h. 2.5 mL and 100 μL of samples were utilized for COD and high performance liquid chromatography (HPLC) tests, respectively.
3.1.1. DFN removal rate Removal percentages of DFN for different initial concentrations at HRT = 5 and 10 h are shown in Figs. 1 and 2. As shown in the figures, in all the tests, higher concentrations of DFN resulted in higher removal percentages. DFN which has been repeatedly referred to as recalcitrant or difficult to biodegrade [11,31], was removed up to 65.3%. When DFN concentration was 2 mg/L, at COD = 500 mg/L and HRT = 10 h, the elimination of DFN was 32.5% and it reached 66% at the concentration of 10 mg/L. This may be due to the fact that increase in the concentration of DFN makes access of microorganisms to its molecules easier and, as a result, its consumption in the reaction increases. These results are consistent with those of Lonappan et al.’s [11] review paper stating that 30–70% of DFN, on average, could biodegrade by existing biological methods.
2.7. Pharmaceutical analysis (HPLC-UV spectroscopy) HPLC-UV spectroscopy was used for quantifying pharmaceuticals in the effluent of the treatment plant. The HPLC was equipped with S 7131 reagent organizer, S 2100 solvent delivery system, S 2500 sample injector, EC 250/4.6 Nucleodur 100-5 C18ec, S 4011 column thermo controller and S 3210 UV/Vis detector. The concentrations used were higher than the limit of quantifications (LOQs) reported by Stafiej et al. [2]. The mobile phase was acetic acid solution with concentration of 6.9 mmol/L adjusted to pH 6.0 (by NaOH) and 35% v/v acetonitrile with the flow rate of 1 mL/min. Acetonitrile was selected as phase A and acetonitrile/6.9 mmol/L acetic acid at pH 6.0 (30:70%, v/v) as phase B. 20 μL of the sample was injected into the HPLC and UV detection wavelength was 230 nm as suggested by Stafiej et al [2]. DFN and IBU peaked at 4.7 and 6.3 min, respectively.
3.1.2. IBU removal rate When IBU concentration was 2 mg/L, at COD = 1000 mg/L and 5532
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Fig. 2. Effect of pharmaceuticals initial concentration on their removal, HRT = 10 h.
HRT = 10 h (equal to the loading rate of 12.25 gCOD/(m2.day)), its elimination was 14.33%, and then it reached 37.33% at concentration of 10 mg/L. Similar to DFN, increase in the concentration of IBU in the range of 2–10 mg/L resulted in better access of microorganisms to the IBU; hence, better IBU removal was achieved. Lower removal percentage of contaminants in lower concentrations have also been reported by other authors [32]. 3.2. Effect of retention time Fig. 4. DFN removal at two different HRTs, (COD = 1000 mg/L).
Two different HRTs (5 and 10 h) were selected to assess the effect of retention time on DFN and IBU removal. A proper HRT for sufficient removal of each pharmaceutical was studied. 3.2.1. DFN removal rate In this study, at two HRTs (5 and 10 h) in all the tests, percentage of removal was almost the same. DFN was considerably removed by microorganisms in the first 5 h and had no significant removal in the next 5 h as shown in Figs. 3 and 4. Therefore, it can be concluded that optimum HRT for DFN is 5 h. This result is consistent with that of Tang et al. [33] stating that half-life of DFN is 2.1 h. 3.2.2. IBU removal rate On the contrary, IBU did not exhibit much transformation when HRT was 5 h. Comparing IBU removal rate at two different HRTs in Figs. 5 and 6 reveals that 10 h retention time resulted in significantly higher removal percentage. It indicates that half-life of IBU is higher than that of DFN and inevitably, it requires more time to react. Fair biodegradability of IBU was previously reported by Yu et al. [34], with 77% IBU biodegradation in 4 days using immobilized cell process.
Fig. 5. IBU removal at two different HRTs, (COD = 500 mg/L).
3.3. Effect of initial COD As mentioned in Section 2.5, sugar was added to the feed as carbon source to obtain the required COD and ensure microbial growth. Sugar is a preferred, easy to digest feed for microorganisms. Different concentrations of COD may cause different reaction rates and pathways of
Fig. 6. IBU removal at two different HRTs, (COD = 1000 mg/L).
microbial reactions. In this section, effects of COD on DFN and IBU removals were studied. It was observed that different initial CODs resulted in different DFN and IBU removal rates.
3.3.1. DFN removal rate DFN is degraded in biological reactions and transformed to less poisonous products [35]. It is shown in Figs. 7 and 8 that in all the runs, DFN removal rate was higher when COD was 500 mg/L as compared to its counterpart when feed COD was 1000 mg/L. This can be explained by the DFN mechanism of removal. Since DFN is biologically degraded
Fig. 3. DFN removal at two different HRTs, (COD = 500 mg/L). 5533
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Fig. 7. Effect of COD on DFN removal, HRT = 5 h. Fig. 10. Effect of COD on IBU removal, HRT = 10 h.
Fig. 8. Effect of COD on DFN removal, HRT = 10 h. Fig. 11. Effect of pharmaceuticals on COD removal, initial COD = 500 mg/L.
[4], as long as sugar is present in the reactor, microorganisms prefer to use sugar as organic feed and not DFN; after a decrease in the sugar concentration, consumption of DFN increased. Hence, higher COD resulted in lower DFN removal. This was observed in all the tests for both HRTs.
several researches [32,37]. In a reactor, even if the aim is to remove micropollutants, COD removal of the reactor should be checked to be sure of the wastewater treatment quality. Hence, in this study, COD removal was also investigated in the presence of DFN and IBU. The results are shown in Figs. 11 and 12. An initial outcome of this study depicted that difference between COD removal in HRTs = 5 and 10 h was not significant, indicating microorganisms removed most of the COD during the first 5 h and did not engage in any noticeable activity in the next 5 h. The highest variation recorded was in the test with COD = 500 mg/L and HRT = 10 h (equal to loading rate of 6.25 g COD/(m2.day)). Increase in the pharmaceuticals (DFN & IBU) concentration up to 10 mg/L decreased the removal rate from 91.8 to 85.7%. It can be concluded that even concentrations much higher than environmentally relevant concentrations, do not have major negative effects on COD removal in the MBBR.
3.3.2. IBU removal rate Degradation of IBU in biological reactor was reported by Langenhoff et al. [4]. As shown in Fig. 1, when COD was maintained at 500 mg/L, 5 h retention time was not sufficient at all, and in some cases, no reduction was achieved. Considering Figs. 9 and 10, IBU was removed better at higher initial COD (1000 mg/L) concentrations. This is related to the pathways of removal, which yet has certain vague aspects to researchers and further research is needed to gain a vivid grasp of such behavior. One hypothesis is that COD acts as a co-substrate in the digestion mechanism of IBU. So, higher concentration of COD would help the microorganisms to consume the IBU. Meanwhile, this observation could possibly be attributed to higher microbial concentration in the reactor at higher inlet COD concentration.
4. Conclusion Moving bed biofilm reactor (MBBR), known to be an efficient, reliable and economical technology for removing organic nutrients from wastewater, was used for treatment of wastewater containing two common PhACs namely DFN and IBU. The main findings are:
3.4. COD removal of the reactor Chemical Oxygen Demand (COD) is the most important and known characteristic of wastewater [36], since it represents it’s organic content. Thus when investigating wastewater strength and pollution effect, the first factor to be taken into consideration is COD. The MBBR technology is capable of removing COD up to and above 95%, according to
• The MBBR showed considerably higher removal of DFN than IBU in •
Fig. 9. Effect of COD on IBU removal, HRT = 5 h.
all the tests, that is, removals of DFN and IBU were 31–66 and 0–37.33%, respectively, Higher concentrations of PhACs up to 10 mg/L led to higher removal rates,
Fig. 12. Effect of pharmaceuticals on COD removal, initial COD = 1000 mg/L. 5534
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• The optimum HRT for DFN removal was 5 h, while IBU required at least 10 h to reach considerable biodegradation. • Elimination of DFN in the lower COD was more conspicuous than in • •
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the higher COD, that is 32.5–66% of DFN removal for the lower COD and 30.8–59.7% of DFN removal at higher COD, which is attributed to its biological degradation pathway. The MBBR assured a better performance in the higher COD for IBU removal. IBU removal was 14.32–37.4 at higher COD value and 11.33–35.10% at lower COD value, which is attributed to its biodegradation, Both PhACs had slight negative effect on COD removals of the MBBR.
The presented research demonstrates vividly, that more study on the removal pathway of PhACs is necessary, to control their intrusion in environment and contamination of water supplies. Acknowledgement This research was carried out at Biochemical and Bio-environmental Research center (BBRC) of Sharif University of Technology. Appendix A. Supplementary data Supplementary material related to this article can be found, in the online version, at doi:https://doi.org/10.1016/j.jece.2018.08.029. References [1] J. Martín, W. Buchberger, E. Alonso, M. Himmelsbach, I. Aparicio, Comparison of different extraction methods for the determination of statin drugs in wastewater and river water by HPLC/Q-TOF-MS, Talanta 85 (2011) 607–615, https://doi.org/ 10.1016/j.talanta.2011.04.017. [2] A. Stafiej, K. Pyrzynska, F. Regan, Determination of anti-inflammatory drugs and estrogens in water by HPLC with UV detection, J. Sep. Sci. 30 (2007) 985–991, https://doi.org/10.1002/jssc.200600433. [3] C. Miège, J.M. Choubert, L. Ribeiro, M. Eusèbe, M. Coquery, Fate of pharmaceuticals and personal care products in wastewater treatment plants - conception of a database and first results, Environ. Pollut. 157 (2009) 1721–1726, https://doi.org/ 10.1016/j.envpol.2008.11.045. [4] A. Langenhoff, N. Inderfurth, T. Veuskens, G. Schraa, M. Blokland, K. KujawaRoeleveld, H. Rijnaarts, Microbial removal of the pharmaceutical compounds ibuprofen and diclofenac from wastewater, Biomed Res. Int. 2013 (2013), https://doi. org/10.1155/2013/325806. [5] A. Joss, S. Zabczynski, A. Göbel, B. Hoffmann, D. Löffler, C.S. McArdell, T.A. Ternes, A. Thomsen, H. Siegrist, Biological degradation of pharmaceuticals in municipal wastewater treatment: proposing a classification scheme, Water Res. 40 (2006) 1686–1696, https://doi.org/10.1016/j.watres.2006.02.014. [6] B.N. Bhadra, I. Ahmed, S. Kim, S.H. Jhung, Adsorptive removal of ibuprofen and diclofenac from water using metal-organic framework-derived porous carbon, Chem. Eng. J. 314 (2017) 50–58, https://doi.org/10.1016/j.cej.2016.12.127. [7] G.-G. Ying, R.S. Kookana, D.W. Kolpin, Occurrence and removal of pharmaceutically active compounds in sewage treatment plants with different technologies, J. Environ. Monit. 11 (2009) 1498, https://doi.org/10.1039/b904548a. [8] R.W. Murdoch, A.G. Hay, Genetic and chemical characterization of ibuprofen degradation by Sphingomonas Ibu-2, Microbiology (United Kingdom). 159 (2013) 621–632, https://doi.org/10.1099/mic.0.062273-0. [9] C.G. Daughton, T.A. Ternes, Pharmaceuticals and personal care products in the environment: agents of subtle change? Environ. Toxicol. 107 (1999) 907–938, https://doi.org/10.1021/bk-2001-0791. [10] Y. Luo, W. Guo, H.H. Ngo, L.D. Nghiem, F.I. Hai, J. Zhang, S. Liang, X.C. Wang, A review on the occurrence of micropollutants in the aquatic environment and their fate and removal during wastewater treatment, Sci. Total Environ. 473–474 (2014) 619–641, https://doi.org/10.1016/j.scitotenv.2013.12.065. [11] L. Lonappan, S. Kaur Brar, R. Kumar Das, M. Verma, R.Y. Surampalli, Diclofenac and its transformation products : Environmental occurrence and toxicity - a review, Environ. Int. 96 (2016) 127–138, https://doi.org/10.1016/j.envint.2016.09.014. [12] Y. Zhang, S.U. Geißen, C. Gal, Carbamazepine and diclofenac: removal in wastewater treatment plants and occurrence in water bodies, Chemosphere 73 (2008) 1151–1161, https://doi.org/10.1016/j.chemosphere.2008.07.086. [13] S.M. Richards, S.E. Cole, A toxicity and hazard assessment of fourteen pharmaceuticals to Xenopus laevis larvae, Ecotoxicology 15 (2006) 647–656, https://doi. org/10.1007/s10646-006-0102-4. [14] J. Margot, C. Kienle, A. Magnet, M. Weil, L. Rossi, L.F. de Alencastro, C. Abegglen, D. Thonney, N. Chèvre, M. Schärer, D.A. Barry, Treatment of micropollutants in municipal wastewater: Ozone or powdered activated carbon? Sci. Total Environ. 461–462 (2013) 480–498, https://doi.org/10.1016/j.scitotenv.2013.05.034.
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Application of moving bed biofilm reactor in the removal of pharmaceutical compounds (diclofenac and ibuprofen)
T
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Maryam Fatehifar, Seyed Mehdi Borghei , Ali Ekhlasi nia Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, Iran
A R T I C LE I N FO
A B S T R A C T
Keywords: Pharmaceutical Ibuprofen Diclofenac Biodegradation MBBR Wastewater
Pharmaceutical waste has attracted significant attention in the past two decades due to the current high consumption of pharmaceuticals together with the development of reliable detection technologies. In order to acquire better understanding on pharmaceuticals removal in biological processes, the treatment of synthetic wastewater containing diclofenac (DFN) and ibuprofen (IBU), two of the most commonly prescribed medicines worldwide, was studied using a moving bed biofilm reactor (MBBR). An 8.5-L aerobic MBBR with Kaldnes packing filling ratio of 40% was designed. The controlled parameters were pH within neutral range, temperature of 37 °C, mixed liquor suspended solids (MLSS) of 2100 mg/L, and attached growth equal to 1300 mg/L. Tests were conducted for four different initial pharmaceuticals concentrations: 2, 4, 7 and 10 mg/L, two hydraulic retention times (HRT): 5 and 10 h and two chemical oxygen demands (COD): 500 and 1000 mg/L. Results demonstrated that generally, DFN had higher removal percentage than IBU in the MBBR. At HRT = 10 h, DFN removal was between 30.83 and 66.01%, while it was 11.33 and 37.33% for IBU. At HRT = 5 h, DFN and IBU removal were respectively between 31.10–65.33 and 0–35.10%. It can be concluded that HRT = 5 h is the optimal time for DFN, while 10 h HRT promises noticeably better IBU removal. Furthermore, results revealed that DFN is better removed in the lower COD, while IBU showed better removal in the higher COD. Finally, the study on their toxicity reveals that pharmaceuticals exert slightly negative effect on COD removal.
1. Introduction Occurrence of pharmaceuticals in wastewater and treated water has significantly increased in the last decades. Two important facts has contributed to this issue and made it a growing concern: first, the improvement of quantification technologies have provided researchers with the ability to measure the concentrations in the range of ng/L to μg/L [1]; second, their consumption has rapidly increased worldwide [2]. Micropollutants, pollutants with concentration of ng/L to μg/L, have been repeatedly found in the environment, mainly in water supplies; thus, a lot of attention has been paid to them [3–5]. Pharmaceutically-active compounds (PhACs), a certain category of micropollutants, also included in “emerging new contaminants” category are found in rivers and ground water since conventional treatment plants are not specifically designed to eliminate them. In fact, the low concentration and relatively high polarity of these pollutants have made them difficult to eliminate [6]. Therefore, some will remain in the effluent and pollute the surface water. Taking the accumulative effect of micropollutants into account, their concentration is increasing and soon, concentrations much higher than previously reported will be
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detected in our environment. Two highly prescribed PhACs are diclofenac and ibuprofen, both non-steroidal anti-inflammatory drugs (NSAIDs) with analgesic and antipyretic properties [7,8]. Characteristics of these two PhACs are presented in Table 1. Many researchers have focused on the consumption of these PhACs worldwide. In 2012, Fierce Pharma reported that DFN was the 12th bestselling generic molecule globally [11]. Zhang et al. (2008) estimated that 940 ton DFN was consumed annually around the world, excluding veterinary consumption [12]. In 2005, IBU ranked 17th on the list of the most prescribed drugs in the United States [13]. These compounds either enter in original form or are discharged via excretion in urine and feces into wastewater [14]. Many authors have reported that DFN and IBU are not completely removed in sewage treatment plants [15,16]. Studies, mainly in Europe, have documented that DFN is found in raw wastewater with a medium concentration of 0.7 μg/L and a maximum concentration of 11 μg/L. IBU has been detected in raw wastewater with average values of 37 μg/L and maximum value of up to 100 μg/L [17]. PhACs, even in low concentration (ng/L to μg/L), may have
Corresponding author. E-mail address: [email protected] (S.M. Borghei).
https://doi.org/10.1016/j.jece.2018.08.029 Received 7 April 2018; Received in revised form 7 August 2018; Accepted 11 August 2018 Available online 17 August 2018 2213-3437/ © 2018 Elsevier Ltd. All rights reserved.
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Table 1 Characteristics of pharmaceuticals. Diclofenac-Na (DFN)
Ibuprofen (IBU)
2-[(2,6-Dichlorophenyl)- aminolbenzeneacetic acid-Na 15307-79-6 296.16 g/mol 5000 mg/L Moderately low (6-39%)
a-Methyl-4-(2-methylpropyl)- benzeneacetic acid 15687-27-1 206.28 g/mol 21 mg/L Low (less than 5%)
Structure [4]
CAS name [9] CAS numbera Molar mass [9] Water solubility [6] Human excretion [10] a
Obtained from CAS database list.
2. Materials and methods
negative impact on human health and the environment [18]. A great number of toxicity studies have been conducted to determine the toxicity of DFN in aquatic animals and organisms. Potential adverse effect of DFN on aquatic organisms was confirmed byCleuvers (2004) using Daphnia and algae in a ecotoxicity study [19]. Lawrence et al. (2007) reported that DFN is a major risk, even at the predicted environmental concentrations [20]. DFN at concentration of 50 μg/L inflicted heavy damage on gill, liver and kidney of brown trout fish [21]. Ecotoxicity studies on IBU revealed that it has negative effect on aquatic life. For example, IBU at the concentration of 1000 ng/L inhibited the growth of freshwater microalga, S. rubescens [22]. In another study, Geiger et al. (2016) claimed that 1 mg/L of IBU inhibited the growth of algal cells and reduced the chlorophyll content of Chlorella vulgaris [23]. These reports all suggests that elimination of DFN and IBU should be taken into serious consideration, and thus, more studies are required to address the problems the environment is encountering. Furthermore, it is of utmost importance to make every endeavor to control and eliminate the abovementioned pollutants from the environment. MBBR is a biological treatment technology which was first introduced in 1988 in Norway [24]. The main purpose of MBBR development is to simultaneously benefit from attached and suspended growth. In this type of reactor, neutral carriers are added to the reactor to let the biomass attach and grow [25]. As a result, this technology has numerous advantages, including high quality of the effluent, small footprint, high loading rate, high treatment efficiency and low overall cost. The MBBR has been successfully devised in many treatment plants since then and implemented in more than 400 treatment plants around the world [25,26]. Another aspect of the biological treatment of pharmaceutical wastewater that has gained attention in the past decade is the mechanism of degradation. The type of microorganisms favoring a certain PhAC, the pathway of its removal, metabolites, and co-substrates are all vital questions that have yet to be addressed to construct a thorough understanding of the biodegradation mechanism. Even though there are number of researches in this area, the answer to these questions are still vague because numerous research studies are required to cover a variety of PhACs and microorganisms. Moreover, findings and reports are not always consistent with each other. For instance, Kosjek et al. [27] reported seven metabolites for DFN, while Langenhoff et al. [4] detected eight metabolites. In case of IBU, Ferrando-Climent et al. [28] detected three main metabolites, while Langenhoff et al. [4] found no metabolite and concluded that complete mineralization had occurred and all IBU had been transformed to CO2 and H2O. The aim of this research was to study the removal of DFN and IBU in a Moving Bed Biofilm Reactor (MBBR). For this purpose, first, the effect of initial concentration of PhACs on their removal was studied. Then, optimized HRT and the initial COD of the wastewater was investigated discussed. The last analysis was assessment of the toxicity effect of PhACs on reactor’s COD removal.
2.1. Materials and reagent DFN sodium and IBU, both 98% pure, were purchased from Raha Pharmaceuticals, Isfahan, Iran (a well reputed pharmaceutical producer). All other chemicals including sugar, KH2PO4, urea, NaOH, H2SO4 98%, HgSO4 (extra pure), Ag2SO4, ethanol, acetonitrile (HPLC grade) and acetic acid (glacial) were obtained from Merk, Germany. Glass microfiber filters (GF/A 125 mm, ∅, Cat No. 1820–125) were obtained from Whatman (Maid- stone, UK).
2.2. Instrumentation Instruments used in the present study includes: pH meter (metrohm, Swiss), oven (MAMMER W 270), scale (AND-HR 200), vacuum pump (Edwards High Vacuum), COD reactor (HACH DRB 200), spectrophotometer (HACH, DR5000), HPLC (MACHEREY-NAGEL, nucleodur, C18 column) followed by UV–vis detector and DO meter (WTW-YSI55).
2.3. Characteristics of MBBR A cubic Plexiglas with a total volume of 12 L (L = 20 cm, W = 20 cm, H = 30 cm) and effective volume of 8.5 L was employed. Forty percent of the reactor’s effective volume was filled with carriers (Kaldnes type) with an internal diameter of 21 mm, an internal length of 41 mm, a density of 96 g/cm3 and a specific biofilm surface area of 480 m2/m3. Two 20 cm air stones were installed at the end of the reactor to ensure the dissolved air concentration of 2 mg/L and completely mixed regime in the reactor. The outlet valve diameter of reactor was carefully selected in order to prevent the escape of carriers. A sedimentation tank with a volume of 2.5 L was placed at the outlet of the reactor for effluent clarification and sludge separation, and if necessary, sludge return to the reactor.
2.4. Setup The first step was to create an environment that allowed the growth of biofilm on carriers. Seeding of the reactor was performed by addition of an active sludge from a nearby domestic sewage treatment plant (Ekbatan Treatment Plant, Tehran). Approximately, 8 L of sludge (MLSS ∼6050 mg/L, COD = 450 mg/L) was added to the reactor. First, the reactor was operated in batch mode for 7 days. Synthetic reactor feed was injected once every 8 h with a COD of 500 mg/L, and then gradually increased to 1000 mg/L within 7 days. In order to make the MLSS to remain high, the settled sludge at the bottom of the sedimentation tank was returned to the reactor on daily basis. 5531
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Table 2 Characteristics of synthetic wastewater. Chemical
Amount (mg/L)
DFN IBU COD Urea KH2PO4
2.000 2.000 500.00 53.625 21.935
2.000 2.000 1000.00 107.250 43.870
4.000 4.000 500.00 53.625 21.935
4.000 4.000 1000.00 107.250 43.870
7.000 7.000 500.00 53.625 21.935
7.000 7.000 1000.00 107.250 43.870
10.000 10.000 500.00 53.625 21.935
10.000 10.000 1000.00 107.250 43.870
Fig. 1. Effect of pharmaceuticals initial concentration on their removal, HRT = 5 h.
2.5. Wastewater characteristics
3. Results and discussion
Synthetic wastewater with four different initial concentrations of PhACs, and two different chemical oxygen demands (COD) of 500 and 1000 mg/L were harnessed. The influent flow rate was controlled to have two retention times: 5 and 10 h. Hence, it is worth mentioning that the loading rates were 6.25–25 gCOD/(m2.day). In order to adapt the biomass population, the input wastewater was initially prepared by mixing sugar, urea and K2HPO4(COD:N:P = 100:5:1) [29]. After 7 days of feeding without drugs and when a thin biofilm has formed on the surface of carriers (Kaldnes media), the drugs were added to the wastewater. First, drug concentration was 0.1 μg/L, then gradually increased to 2 mg/L. Table 2 presents the characteristics of the synthetic wastewater.
To date, information on the treatment of pharmaceuticals is limited; thus, it necessitates more research in this area. This research focused on the biological treatment of pharmaceuticals in an aerobic reactor. Effects of various parameters on efficiency of the MBBR are discussed as following. 3.1. Effect of pharmaceuticals concentration In this section, the effect of pharmaceuticals initial concentrations on their removal percentage was studied. It has been reported that initial concentration of the pollutant may have considerable effect on removal rate [10,30]. In order to compare the degree of removal, 4 different concentrations (2, 4, 7, 10 mg/L) were selected to feed the reactor, then the final concentrations were quantified using the HPLC tests. The flow to the reactor was changed to have different HRTs. Both compounds were biologically degraded to some extent in the presence of microorganisms. Figs. 1 and 2 show that IBU had lower degradation than DFN in all the runs. It can be ascribed to differences in their removal mechanism.
2.6. Sample preparation In all the experiments, 50 mL of sample taken from the reactor were filtered using Whatman-45 μm, transferred into a clean falcon, then stored in a fridge at 4 °C. The required tests were conducted within 24 h. 2.5 mL and 100 μL of samples were utilized for COD and high performance liquid chromatography (HPLC) tests, respectively.
3.1.1. DFN removal rate Removal percentages of DFN for different initial concentrations at HRT = 5 and 10 h are shown in Figs. 1 and 2. As shown in the figures, in all the tests, higher concentrations of DFN resulted in higher removal percentages. DFN which has been repeatedly referred to as recalcitrant or difficult to biodegrade [11,31], was removed up to 65.3%. When DFN concentration was 2 mg/L, at COD = 500 mg/L and HRT = 10 h, the elimination of DFN was 32.5% and it reached 66% at the concentration of 10 mg/L. This may be due to the fact that increase in the concentration of DFN makes access of microorganisms to its molecules easier and, as a result, its consumption in the reaction increases. These results are consistent with those of Lonappan et al.’s [11] review paper stating that 30–70% of DFN, on average, could biodegrade by existing biological methods.
2.7. Pharmaceutical analysis (HPLC-UV spectroscopy) HPLC-UV spectroscopy was used for quantifying pharmaceuticals in the effluent of the treatment plant. The HPLC was equipped with S 7131 reagent organizer, S 2100 solvent delivery system, S 2500 sample injector, EC 250/4.6 Nucleodur 100-5 C18ec, S 4011 column thermo controller and S 3210 UV/Vis detector. The concentrations used were higher than the limit of quantifications (LOQs) reported by Stafiej et al. [2]. The mobile phase was acetic acid solution with concentration of 6.9 mmol/L adjusted to pH 6.0 (by NaOH) and 35% v/v acetonitrile with the flow rate of 1 mL/min. Acetonitrile was selected as phase A and acetonitrile/6.9 mmol/L acetic acid at pH 6.0 (30:70%, v/v) as phase B. 20 μL of the sample was injected into the HPLC and UV detection wavelength was 230 nm as suggested by Stafiej et al [2]. DFN and IBU peaked at 4.7 and 6.3 min, respectively.
3.1.2. IBU removal rate When IBU concentration was 2 mg/L, at COD = 1000 mg/L and 5532
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Fig. 2. Effect of pharmaceuticals initial concentration on their removal, HRT = 10 h.
HRT = 10 h (equal to the loading rate of 12.25 gCOD/(m2.day)), its elimination was 14.33%, and then it reached 37.33% at concentration of 10 mg/L. Similar to DFN, increase in the concentration of IBU in the range of 2–10 mg/L resulted in better access of microorganisms to the IBU; hence, better IBU removal was achieved. Lower removal percentage of contaminants in lower concentrations have also been reported by other authors [32]. 3.2. Effect of retention time Fig. 4. DFN removal at two different HRTs, (COD = 1000 mg/L).
Two different HRTs (5 and 10 h) were selected to assess the effect of retention time on DFN and IBU removal. A proper HRT for sufficient removal of each pharmaceutical was studied. 3.2.1. DFN removal rate In this study, at two HRTs (5 and 10 h) in all the tests, percentage of removal was almost the same. DFN was considerably removed by microorganisms in the first 5 h and had no significant removal in the next 5 h as shown in Figs. 3 and 4. Therefore, it can be concluded that optimum HRT for DFN is 5 h. This result is consistent with that of Tang et al. [33] stating that half-life of DFN is 2.1 h. 3.2.2. IBU removal rate On the contrary, IBU did not exhibit much transformation when HRT was 5 h. Comparing IBU removal rate at two different HRTs in Figs. 5 and 6 reveals that 10 h retention time resulted in significantly higher removal percentage. It indicates that half-life of IBU is higher than that of DFN and inevitably, it requires more time to react. Fair biodegradability of IBU was previously reported by Yu et al. [34], with 77% IBU biodegradation in 4 days using immobilized cell process.
Fig. 5. IBU removal at two different HRTs, (COD = 500 mg/L).
3.3. Effect of initial COD As mentioned in Section 2.5, sugar was added to the feed as carbon source to obtain the required COD and ensure microbial growth. Sugar is a preferred, easy to digest feed for microorganisms. Different concentrations of COD may cause different reaction rates and pathways of
Fig. 6. IBU removal at two different HRTs, (COD = 1000 mg/L).
microbial reactions. In this section, effects of COD on DFN and IBU removals were studied. It was observed that different initial CODs resulted in different DFN and IBU removal rates.
3.3.1. DFN removal rate DFN is degraded in biological reactions and transformed to less poisonous products [35]. It is shown in Figs. 7 and 8 that in all the runs, DFN removal rate was higher when COD was 500 mg/L as compared to its counterpart when feed COD was 1000 mg/L. This can be explained by the DFN mechanism of removal. Since DFN is biologically degraded
Fig. 3. DFN removal at two different HRTs, (COD = 500 mg/L). 5533
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Fig. 7. Effect of COD on DFN removal, HRT = 5 h. Fig. 10. Effect of COD on IBU removal, HRT = 10 h.
Fig. 8. Effect of COD on DFN removal, HRT = 10 h. Fig. 11. Effect of pharmaceuticals on COD removal, initial COD = 500 mg/L.
[4], as long as sugar is present in the reactor, microorganisms prefer to use sugar as organic feed and not DFN; after a decrease in the sugar concentration, consumption of DFN increased. Hence, higher COD resulted in lower DFN removal. This was observed in all the tests for both HRTs.
several researches [32,37]. In a reactor, even if the aim is to remove micropollutants, COD removal of the reactor should be checked to be sure of the wastewater treatment quality. Hence, in this study, COD removal was also investigated in the presence of DFN and IBU. The results are shown in Figs. 11 and 12. An initial outcome of this study depicted that difference between COD removal in HRTs = 5 and 10 h was not significant, indicating microorganisms removed most of the COD during the first 5 h and did not engage in any noticeable activity in the next 5 h. The highest variation recorded was in the test with COD = 500 mg/L and HRT = 10 h (equal to loading rate of 6.25 g COD/(m2.day)). Increase in the pharmaceuticals (DFN & IBU) concentration up to 10 mg/L decreased the removal rate from 91.8 to 85.7%. It can be concluded that even concentrations much higher than environmentally relevant concentrations, do not have major negative effects on COD removal in the MBBR.
3.3.2. IBU removal rate Degradation of IBU in biological reactor was reported by Langenhoff et al. [4]. As shown in Fig. 1, when COD was maintained at 500 mg/L, 5 h retention time was not sufficient at all, and in some cases, no reduction was achieved. Considering Figs. 9 and 10, IBU was removed better at higher initial COD (1000 mg/L) concentrations. This is related to the pathways of removal, which yet has certain vague aspects to researchers and further research is needed to gain a vivid grasp of such behavior. One hypothesis is that COD acts as a co-substrate in the digestion mechanism of IBU. So, higher concentration of COD would help the microorganisms to consume the IBU. Meanwhile, this observation could possibly be attributed to higher microbial concentration in the reactor at higher inlet COD concentration.
4. Conclusion Moving bed biofilm reactor (MBBR), known to be an efficient, reliable and economical technology for removing organic nutrients from wastewater, was used for treatment of wastewater containing two common PhACs namely DFN and IBU. The main findings are:
3.4. COD removal of the reactor Chemical Oxygen Demand (COD) is the most important and known characteristic of wastewater [36], since it represents it’s organic content. Thus when investigating wastewater strength and pollution effect, the first factor to be taken into consideration is COD. The MBBR technology is capable of removing COD up to and above 95%, according to
• The MBBR showed considerably higher removal of DFN than IBU in •
Fig. 9. Effect of COD on IBU removal, HRT = 5 h.
all the tests, that is, removals of DFN and IBU were 31–66 and 0–37.33%, respectively, Higher concentrations of PhACs up to 10 mg/L led to higher removal rates,
Fig. 12. Effect of pharmaceuticals on COD removal, initial COD = 1000 mg/L. 5534
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• The optimum HRT for DFN removal was 5 h, while IBU required at least 10 h to reach considerable biodegradation. • Elimination of DFN in the lower COD was more conspicuous than in • •
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the higher COD, that is 32.5–66% of DFN removal for the lower COD and 30.8–59.7% of DFN removal at higher COD, which is attributed to its biological degradation pathway. The MBBR assured a better performance in the higher COD for IBU removal. IBU removal was 14.32–37.4 at higher COD value and 11.33–35.10% at lower COD value, which is attributed to its biodegradation, Both PhACs had slight negative effect on COD removals of the MBBR.
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