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Environmental Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tent20
Removal of endocrine disrupting compounds in a labscale anaerobic/aerobic sequencing batch reactor unit a
a
ab
M. Muz , S. Ak , O.T. Komesli
a
& C.F. Gokcay
a
Department of Environmental Engineering, Middle East Technical University, Ankara 06531, Turkey b
Department of Environmental Engineering, Ataturk University, Erzurum 25250, Turkey Published online: 27 Nov 2013.
To cite this article: M. Muz, S. Ak, O.T. Komesli & C.F. Gokcay (2014) Removal of endocrine disrupting compounds in a lab-scale anaerobic/aerobic sequencing batch reactor unit, Environmental Technology, 35:9, 1055-1063, DOI: 10.1080/09593330.2013.861020 To link to this article: http://dx.doi.org/10.1080/09593330.2013.861020
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Environmental Technology, 2014 Vol. 35, No. 9, 1055–1063, http://dx.doi.org/10.1080/09593330.2013.861020
Removal of endocrine disrupting compounds in a lab-scale anaerobic/aerobic sequencing batch reactor unit M. Muza∗ , S. Aka , O.T. Komeslia,b and C.F. Gokcaya a Department
of Environmental Engineering, Middle East Technical University, Ankara 06531, Turkey; b Department of Environmental Engineering, Ataturk University, Erzurum 25250, Turkey
Downloaded by [University of Western Ontario] at 07:44 11 November 2014
(Received 13 May 2013; accepted 24 October 2013 ) The fate and removal of six selected endocrine disrupting compounds in a lab-scale anaerobic/aerobic (A/O) sequencing batch reactor (SBR), operating at 5 days, solids retention time (SRT) were investigated. A carbamazepine (CBZ), acetaminophen (ATP), diltiazem (DTZ), butyl benzyl phthalate (BBP), estrone and progesterone mix was spiked as model endocrine disrupting compounds (EDC) into domestic wastewater obtained from a nearby sewage treatment plant. The influent, effluent and sludge samples from the SBR unit were analysed by using an LC/MS/MS instrument equipped with electrospray ionization. More than 80% removal was observed for all the EDCs tested. It was found that biodegradation is the most important mechanism for BBP, ATP and progesterone. Biodegradation constants were calculated according to the simplified Monod model for these compounds. The DTZ seemed to have lower rate of biodegradation. The CBZ appeared totally resistant to biodegradation. However, it presented a high rate of sorption onto the sludge and was thereby treated. This contradicts with the literature studies. Keywords: sequencing batch reactor; SBR; endocrine disrupting compounds; EDC; A/O process; LC (ESI)/MS/MS; biodegradation
1. Introduction Endocrine disrupting compounds have been a significant issue for the last decades as their adverse effects on wildlife and humans have been demonstrated.[1] Studies have shown that the main source of these compounds in surface waters is the discharges of wastewater treatment plants; for these are not designed to treat micropollutants effectively.[2–5] Hospitals and infirmaries are the most important contributors of endocrine disrupting compounds (EDC) into sewage. Another important contribution to the environment is by the sewage sludge. The non-polar and hydrophobic natures (log Kow > 4) of many of these chemicals make them easily adsorb onto the solid particles.[6] Particular attention should therefore be given to those with low biodegradability since their cycling in the environment is through the use of sludge in agriculture or disposal into non-sanitary landfills. Inappropriately disposed sludge may contaminate groundwater and increase the pollution load on surface waters by way of run-offs.[7,8] Therefore, a better understanding is needed on the fate of these compounds in treatment systems in order to develop and implement appropriate strategies for their elimination in both effluents and sludge. Conventional activated sludge is deemed not efficient in removing micropollutants from effluents, hence advanced treatment techniques, such as ultrafiltration and ∗ Corresponding
nanofiltration membranes,[9,10] pulverized and granular activated carbon addition [11–13] and advanced oxidation methods, such as chlorination and ozonation [14–17], have been studied in order to improve their treatability. The biological nutrient removing systems seem promising to achieve better removals compared to the conventional activated sludge according to Li et al. [18] and Pholchan et al. [19] Among others, sequencing batch reactors (SBRs) are a strong option for improved micropollutant removal due to their ability to perform anaerobic/anoxic/oxic conditions in a single tank and for their capability of enduring shock loads.[12] Their dynamic operating conditions favour micro-organisms that are able to develop specific metabolic pathways that are required for the degradation of biorefractory compounds.[20] Zhou et al. [21] achieved more than 95% removal of typical endocrine disrupting compounds, namely 17-β estradiol, estriol, bisphenol A and 4-octylphenol, in an aerobic SBR with an solids retention time (SRT) of 10 days and observed relationship between SRT, removal efficiency, hydrophobicity and biodegradability of these compounds and concluded that the critical SRT for the removal of total estrogenicity was 5 days with a 90% removal of 17 β estradiol equivalent quantity. In another study by Kong et al.,[22] selected phthalate esters were removed completely in an anaerobic/aerobic process (A/O). In nitrogen removing systems, long sludge
author. Email: [email protected], [email protected]
© 2013 Taylor & Francis
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retention times allegedly enable growth of slowly growing micro-organisms which results in a more diverse microbial community which improves EDCs removal.[23] However, phosphorus only removing systems with an SRT less than 5 days, hence efficiency of phosphate accumulating organisms (PAOs) has not yet been clarified. One of the most popular recalcitrant compounds that cannot be removed with conventional treatment systems is carbamazepine (CBZ). Reif et al. [24] reported that a pilot aerobic membrane (MBR) unit fed with synthetic wastewater, spiked with 20 ppb CBZ and with 11 other micropollutants failed to substantially remove this compound from the influent. The CBZ removal was merely 9% due to its recalcitrant nature and appeared at high concentration in the permeate. Similarly, Serrano et al. [21] operated three parallel lab-scale activated sludge reactors fed with synthetic sewage. One reactor was simulating a conventional activated sludge and second being dosed with FeCl3 to precipitate phosphates. The third unit was supplemented with granular activated carbon (GAC) to maintain 0.1–1 g/L GAC concentration in the aeration tank. It was observed that up to 43% removal of CBZ was possible in GAC added reactor. By contrast, no significant removals were obtained in the other two reactors (< 12%). In another study by Serrano et al.,[25] using a membrane SBR pilot unit, CBZ and several other EDC compounds were fed to the reactor for over 100 days. The unit was operated in anoxic and oxic phases and received synthetic wastewater spiked with several pharmaceutical micropollutants, including CBZ. No significant removal of CBZ could be recorded without the addition of powdered activated carbon, PAC. However, CBZ removal increased by up to 85% when PAC was added into the aeration tank. Therefore, in an attempt to demonstrate effect of PAOs on EDCs removal, an anaerobic/aerobic lab-scale SBR has been studied with an SRT of 5 days considering the finding that the critical SRT for total estrogenicity removal was observed as 5 days. A short SRT prevents nitrification but enhances phosphorus removal in anaerobic/aerobic (A/O) systems.[26] The aim was to understand the fate of six selected endocrine disrupting compounds, namely, ATP, diltiazem (DTZ), CBZ, butyl benzyl phthalate (BBP), estrone and progesterone, in this system and the role of sorption and biodegradation on their removals. The compounds were selected based on their high frequency of occurrence in sludge and wastewater samples.
2. Materials and methods 2.1. Sequencing batch reactor A lab-scale SBR was operated with an SRT of ∼ 5 days, to enhance phosphorus removal by PAOs by employing anaerobic/aerobic conditions and to prevent nitrogen removal by keeping the SRT short. Total volume of the reactor was 5 L with a working volume of 4 L.
The reactor was inoculated with sludge obtained from Middle East Technical University-Vacuum Rotating Membrane WWTP (METU-VRM) operating at SRT of ∼ 10 days. Domestic wastewater collected from dormitories and the academic village at METU is being treated in this plant. The plant is comprised of two tanks placed in series. The first tank receives sewage influent where it is treated aerobically under diffused aeration. The second tank (VRM tank) houses the rotating membrane module where a cross flow over the membranes is maintained by coarse aeration. The D.O concentration in the first tank was around 2 mg/l for most of the time while it was zero in the VRM tank. A recirculation, 1Q, from the VRM tank to the aeration tank was maintained to balance the biomass concentration in both tanks. Although no P-removal was initially planned during the design of the plant, yet 50–60% P-removal was generally observed during operation, which was associated with the anaerobic conditions prevailing in the VRM tank. The molar Ca2 + and Mg2+ ion concentrations and the pH of the wastewater suggest that P-removal cannot wholly be attributed to chemical precipitation; thereby suggesting removal by PAO organisms. The feed of the lab unit was taken from the influent of the same plant after a fine screen. Inflow to the reactor was 5.1 L d−1 ; the hydraulic retention time (HRT) was calculated as 19 h; as was the HRT in the VRM plant. The system included three peristaltic pumps for the feed (influent), discharge (effluent) and sludge withdrawals, respectively; an aeration pump and an electronic timer unit. The inflow and outflow (consequently the HRT) were set according to the operation capabilities of the peristaltic pumps. One operating cycle of the system was 12 h, which included 1 hour of anaerobic and 7 h of aerobic period. The duration of aerobic period was kept long to facilitate longer contact time for the dissolved components with the activated sludge. The anaerobic phase was set as 1 h to fall within the recommended 1–2 h contact period for the P-treating plants. Feeding and withdrawal (effluent) from the system were without mixing or aeration and took 45 min each. The mixed liquor suspended solids (MLSS) concentration in the aeration tank was 2.2–2.5 g L−1 .The sludge withdrawal was performed automatically by a sludge withdrawal pump at the last half hour of each aerobic stage, under mixing since it was difficult to withdraw settled sludge due to clogging problems. The fill volume of the reactor was 36–40%. Effluent MLSS was consistently below 20 mg L−1 and around 4.5 L of effluent and 0.7 L of waste sludge were being discharged from the system daily to keep SRT stable at 5 days. The MLSS measurements were carried out daily, according to the Standard Method 2540B. Following the set-up of the reactor, soluble chemical oxygen demand (COD), Total Phosphorus and OrthoPhosphate in influent and effluent samples were measured routinely. The soluble COD was measured by using high range (150–1500 mg/L COD) or low range (15–150 mg/L COD) Hach Lange kits according to HACH 8000 (US EPA
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approved) method. Total-P (TP) and Ortho-P (OP) analyses were conducted by using LCK350 Hach kits (unit: PO4 –P). Analysis of nitrogen compounds was not carried out systematically since the short SRT employed in the reactor would not warrant an efficient nitrification. The dissolved oxygen concentration in the aerobic phase was between 2.2 mg/L and 2.5 mg/L and was below 1 mg/L in the anaerobic phase. The pH of the system was steady around 7.
2.3.
2.2. Mass balance studies The system was operated for 10 days (two SRT) to reach steady state (6 February 2013–16 February 2013). Onset of steady-state conditions was confirmed by the stable readings of effluent COD values, calculated stable COD removal percentages and steady effluent MLSS concentrations on three consecutive samples obtained at 12 h apart. Upon reaching steady-state, a 100 ppb mixture of selected analytes, prepared in methanol, was spiked into the feed and the reactor was operated for 7 days with this feed before sampling. At the end of seventh day (24 February 2013), feed, sludge and effluent samples were collected and were extracted by SPE method and analysed by using LC/MS/MS instrument, according to Sönmez et al. [27] and Muz et al.,[28] respectively. Same analyses were also performed on the next day (25 February 2013) as duplicate. As biodegradation and adsorption are the two important mechanisms in the removal of micropollutants from wastewaters, a mass balance has been constructed to demonstrate the governing mechanism(s) by using the determined analyte concentrations in the feed, sludge and effluents, as given in Equation (2). The biological degradation was expressed by a simplified first-order equation developed from the Monod model in Equation (1); by neglecting, concentration (S) term in the denominator as S 4) is biologically degradable in wastewater treatment facilities. Similarly, according to Lindemann, [31] over 90% progesterone (log Kow 3.87) degradation could be achieved in surface waters and the addition of activated sludge to water samples increased the biodegradation rate. Complete removal of ATP (log Kow < 1) by biodegradation was reported by Schröder et al. [32] The CBZ degradation rate was literally zero, as expected. Estrone removals are highly variable in AS systems (10–98%), but mainly by biodegradation.[33,34] In our case, estrone did not show a high degradation rate as BBP or progesterone but adsorption had seemingly important contribution in its removal. This observation was also consistent with those of Mes et al.,[35] where they showed that biodegradation is the most efficient way of removing selected estrogenic compounds but sorption has also a significant role. The situation is nearly the same for DTZ, where biodegradation seems as the most important removal mechanism for this compound; yet its rate is slow. In a study by Kasprzyk-Hordem et al.,[36] more than 80% DTZ removal by biodegradation was achieved in AS process. The high EDC biodegradation rates obtained in partially anaerobic P-removing systems might have been due to their possible role as soluble carbon feed to PAOs. In their energy metabolism, the PAO organisms normally rely on fatty acids to produce poly hydroxy alkanoic acid (PHA) inclusions with concomitant P release. The PHAs later undergo oxidation when conditions are aerobic.[33] In this case, EDCs might have been fermented into simple acids during anaerobiosis and any residuals might have been aerobically digested. In the absence of relevant information in the literature, this speculation deserves further investigation. The CBZ shows an interesting situation. It is reported that CBZ is resistant to biodegradation in sewage treatment facilities. This too was the case in our study. However, the studies so far conducted mostly show that its tendency to adsorb onto the sludge is low due to its low distribution coefficient between water and sludge (K = 1.2 L kg−1 ss ).[27] Some studies conducted with full-scale plants show that CBZ tends to stay in the aqueous phase.[28,29] This was not the case in our study where almost 86% removal was achieved simply by sorption onto the sludge. This effect may be attributed to the anaerobic phase of the SBR unit
employed, and/or to the fact that, contrary to the previous researches with synthetic sewage, true domestic wastewater was being used as feed in our system. Xue et al. [37] showed that the refractory compounds were adsorbed onto the sludge much more rapidly in the anaerobic phase than in other units. They also pointed out that sorption capabilities mainly depend on the soil/sludge content. It has been observed that the strength of sorption of CBZ depends highly on the organic content of the solid phase.[38,39] Study by Drillia et al. [40] showed that the adsorption of CBZ was not only dependent on the organic content but also on other matrix properties, and it is higher in anaerobic sludge. The CBZ has better sorption potential in the protonated form due to particular ionic interactions.[41,42] This could not be tested in this study since the pH was neutral in our reactor. Radjenovic et al. [43] also estimated a relatively high solid–water distribution coefficient (Kd ) value for CBZ in primary sludge, but did not discuss this matter in any detail. Considering the findings presented this far regarding the target compounds, it is implicit that in the elimination of EDCs and other micropollutants, adsorption by sludge is an important mechanism, if not the only mechanism in some cases, during treatment of wastewaters. Therefore, contamination of sludge by micropollutants becomes an issue to be addressed for the environmental safety. 4. Conclusion The fate and removal of six selected endocrine disrupting compounds, EDCs, have been investigated in an anaerobic/aerobic lab-scale SBR unit. It was found that more than 80% removal of all the target compounds could be achieved at an SRT of 5 days without the contribution of the nitrifying micro-organisms. For most of the compounds studied it was observed that biodegradation is the most important removal mechanism, except for CBZ, which showed a different removal trend by highly accumulating onto the sludge. This finding somewhat contradicts with those in the literature, where lab-scale results using synthetic wastewater did not report any significant CBZ removals. This effect may be attributed to the existence of an anaerobic stage in our SBR system or to the particular sludge matrix obtained during feeding with true wastewater. Results also indicate that the disposal of excess sludge necessitates appropriate treatment before discharge, as it can be a source of further contamination at that state.
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[18] Li YM, Zeng QL, Yang SJ. Removal and fate of estrogens in an anaerobic-anoxic-oxic activated sludge system. Water Sci Technol. 2011;63:51–56. [19] Pholchan P, Jones M, Donnelly T, Sallis PJ. Fate of estrogens during the biological treatment of synthetic wastewater in a nitrite-accumulating sequencing batch reactor. Environ Sci Technol. 2008;42:6141–6147. [20] Tomei M, Annesini M. 4- Nitrophenol biodegradation in a sequencing batch reactor operating with aerobic-anoxic cycles. Environ Sci Technol. 2005;39:5059–5065. [21] Zhou Y, Huang X, Zhou H, Chen J, Xue W. Removal of typical endocrine disrupting chemicals by membrane bioreactor: in comparison with sequencing batch reactor. Water Sci Technol. 2011;64:2096–2102. [22] Kong X, Li D, Cao L, Zhang X, Zhao Y, Lv Y, Zhang J. Evaluation of municipal sewage treatment systems for pollutant removal efficiency by measuring levels of micropollutants. Chemosphere. 2008;72:59–66. [23] Koh YKK, Chiu TY, Boobis A, Cartmell E, Scrimshaw MD, Lester JN. Treatment and removal strategies for estrogens from wastewater. Environ Technol. 2008;29:245–267. [24] Reif R, Suárez S, Omil F, Lema JM. Fate of pharmaceuticals and cosmetic ingredients during the operation of a MBR treating sewage. Desalination. 2008;221:511–517. [25] Serrano D, Lema JM, Omil F. Influence of the employment of adsorption and coprecipitation agents for the removal of PPCPs in conventional activated sludge (CAS) systems. Water Sci Techol. 2010;62:728–735. [26] Metcalf L, Eddy H, Tchobanoglous G. Wastewater engineering : treatment, disposal, and reuse. New York: McGrawHill; 2004. [27] Sönmez MS, Muz M, Komesli OT, Bakirdere S, Gökcay CF. Determination of selected endocrine disrupter compounds at trace levels in sewage sludge samples. Clean. 2012;40:980– 985. [28] Muz M, Sönmez MS, Komesli OT, Bakı rdere S, Gökçay CF. Determination of selected natural hormones and endocrine disrupting compounds in domestic wastewater treatment plants by liquid chromatography electrospray ionization tandem mass spectrometry after solid phase extraction. Analyst. 2012;137:884–889. [29] Gros M, Petrovic M, Ginebreda A, Barcelo D. Removal of pharmaceuticals during wastewater treatment and environmental risk assessment using hazard indexes. Environ Int. 2010;36:15–26. [30] Roslev P, Vorkamp K, Aarup J, Frederiksen K, Nielsen PH. Degradation of phthalate esters in an activated sludge wastewater treatment plant. Water Res. 2007;41:969–976. [31] Lindemann K. Biodegradation of progesterone in surface water [PhD diss.]. Berlin: Frei Universität; 2006. [32] Schröder HF, Tambosi JL, Sena RF, Moreira RF, Jose HJ. The removal and degradation of pharmaceutical compounds during membrane bioreactor treatment. Water Sci Technol. 2012;65:833–839. [33] Thayanukul P, Zang K, Janhom T, Kurisu F, Kasuga I, Furumai H. Concentration-dependent response of estronedegrading bacterial community in activated sludge analyzed by microautoradiography-fluorescence in situ hybridization. Water Res. 2010;44:4878–4887. [34] Kanda R, Churchley J. Removal of endocrine disrupting compounds during conventional wastewater treatment. Environ Technol. 2008;29:315–323. [35] Mes T, Zeeman G, Lettinga G. Occurrence and fate of estrone, 17b-estradiol and 17a-ethynylestradiol in STPs for domestic wastewater. Rev Environ Sci Biotechnol. 2005;4:275–311.
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[36] Kasprzyk-Hordern B, Dinsdale RM, Guwy AJ. Illicit drugs and pharmaceuticals in the environment - Forensic applications of environmental data, Part 2: Pharmaceuticals as chemical markers of faecal water contamination. Environ Pollut. 2009;157:1778–1786. [37] Xue W, Wu C, Xiao K, Huang X, Zhou H, Tsuno H, Tanaka H. Elimination and fate of selected microorganic pollutants in a full-scale anaerobic/anoxic/aerobic process combined with membrane bioreactor for municipal wastewater reclamation. Water Res. 2010;44:5999– 6010. [38] Ifelebuegu AO. The fate and behavior of selected endocrine disrupting chemicals in full scale wastewater and sludge treatment unit processes. Int J Environ Sci Technol. 2011;8:245–254. [39] Stamatelatou K, Frouda C, Fountoulakis M, Drillia P, Kornaros M, Lyberatos G. Pharmaceuticals and health care
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Environmental Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tent20
Removal of endocrine disrupting compounds in a labscale anaerobic/aerobic sequencing batch reactor unit a
a
ab
M. Muz , S. Ak , O.T. Komesli
a
& C.F. Gokcay
a
Department of Environmental Engineering, Middle East Technical University, Ankara 06531, Turkey b
Department of Environmental Engineering, Ataturk University, Erzurum 25250, Turkey Published online: 27 Nov 2013.
To cite this article: M. Muz, S. Ak, O.T. Komesli & C.F. Gokcay (2014) Removal of endocrine disrupting compounds in a lab-scale anaerobic/aerobic sequencing batch reactor unit, Environmental Technology, 35:9, 1055-1063, DOI: 10.1080/09593330.2013.861020 To link to this article: http://dx.doi.org/10.1080/09593330.2013.861020
PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions
Environmental Technology, 2014 Vol. 35, No. 9, 1055–1063, http://dx.doi.org/10.1080/09593330.2013.861020
Removal of endocrine disrupting compounds in a lab-scale anaerobic/aerobic sequencing batch reactor unit M. Muza∗ , S. Aka , O.T. Komeslia,b and C.F. Gokcaya a Department
of Environmental Engineering, Middle East Technical University, Ankara 06531, Turkey; b Department of Environmental Engineering, Ataturk University, Erzurum 25250, Turkey
Downloaded by [University of Western Ontario] at 07:44 11 November 2014
(Received 13 May 2013; accepted 24 October 2013 ) The fate and removal of six selected endocrine disrupting compounds in a lab-scale anaerobic/aerobic (A/O) sequencing batch reactor (SBR), operating at 5 days, solids retention time (SRT) were investigated. A carbamazepine (CBZ), acetaminophen (ATP), diltiazem (DTZ), butyl benzyl phthalate (BBP), estrone and progesterone mix was spiked as model endocrine disrupting compounds (EDC) into domestic wastewater obtained from a nearby sewage treatment plant. The influent, effluent and sludge samples from the SBR unit were analysed by using an LC/MS/MS instrument equipped with electrospray ionization. More than 80% removal was observed for all the EDCs tested. It was found that biodegradation is the most important mechanism for BBP, ATP and progesterone. Biodegradation constants were calculated according to the simplified Monod model for these compounds. The DTZ seemed to have lower rate of biodegradation. The CBZ appeared totally resistant to biodegradation. However, it presented a high rate of sorption onto the sludge and was thereby treated. This contradicts with the literature studies. Keywords: sequencing batch reactor; SBR; endocrine disrupting compounds; EDC; A/O process; LC (ESI)/MS/MS; biodegradation
1. Introduction Endocrine disrupting compounds have been a significant issue for the last decades as their adverse effects on wildlife and humans have been demonstrated.[1] Studies have shown that the main source of these compounds in surface waters is the discharges of wastewater treatment plants; for these are not designed to treat micropollutants effectively.[2–5] Hospitals and infirmaries are the most important contributors of endocrine disrupting compounds (EDC) into sewage. Another important contribution to the environment is by the sewage sludge. The non-polar and hydrophobic natures (log Kow > 4) of many of these chemicals make them easily adsorb onto the solid particles.[6] Particular attention should therefore be given to those with low biodegradability since their cycling in the environment is through the use of sludge in agriculture or disposal into non-sanitary landfills. Inappropriately disposed sludge may contaminate groundwater and increase the pollution load on surface waters by way of run-offs.[7,8] Therefore, a better understanding is needed on the fate of these compounds in treatment systems in order to develop and implement appropriate strategies for their elimination in both effluents and sludge. Conventional activated sludge is deemed not efficient in removing micropollutants from effluents, hence advanced treatment techniques, such as ultrafiltration and ∗ Corresponding
nanofiltration membranes,[9,10] pulverized and granular activated carbon addition [11–13] and advanced oxidation methods, such as chlorination and ozonation [14–17], have been studied in order to improve their treatability. The biological nutrient removing systems seem promising to achieve better removals compared to the conventional activated sludge according to Li et al. [18] and Pholchan et al. [19] Among others, sequencing batch reactors (SBRs) are a strong option for improved micropollutant removal due to their ability to perform anaerobic/anoxic/oxic conditions in a single tank and for their capability of enduring shock loads.[12] Their dynamic operating conditions favour micro-organisms that are able to develop specific metabolic pathways that are required for the degradation of biorefractory compounds.[20] Zhou et al. [21] achieved more than 95% removal of typical endocrine disrupting compounds, namely 17-β estradiol, estriol, bisphenol A and 4-octylphenol, in an aerobic SBR with an solids retention time (SRT) of 10 days and observed relationship between SRT, removal efficiency, hydrophobicity and biodegradability of these compounds and concluded that the critical SRT for the removal of total estrogenicity was 5 days with a 90% removal of 17 β estradiol equivalent quantity. In another study by Kong et al.,[22] selected phthalate esters were removed completely in an anaerobic/aerobic process (A/O). In nitrogen removing systems, long sludge
author. Email: [email protected], [email protected]
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retention times allegedly enable growth of slowly growing micro-organisms which results in a more diverse microbial community which improves EDCs removal.[23] However, phosphorus only removing systems with an SRT less than 5 days, hence efficiency of phosphate accumulating organisms (PAOs) has not yet been clarified. One of the most popular recalcitrant compounds that cannot be removed with conventional treatment systems is carbamazepine (CBZ). Reif et al. [24] reported that a pilot aerobic membrane (MBR) unit fed with synthetic wastewater, spiked with 20 ppb CBZ and with 11 other micropollutants failed to substantially remove this compound from the influent. The CBZ removal was merely 9% due to its recalcitrant nature and appeared at high concentration in the permeate. Similarly, Serrano et al. [21] operated three parallel lab-scale activated sludge reactors fed with synthetic sewage. One reactor was simulating a conventional activated sludge and second being dosed with FeCl3 to precipitate phosphates. The third unit was supplemented with granular activated carbon (GAC) to maintain 0.1–1 g/L GAC concentration in the aeration tank. It was observed that up to 43% removal of CBZ was possible in GAC added reactor. By contrast, no significant removals were obtained in the other two reactors (< 12%). In another study by Serrano et al.,[25] using a membrane SBR pilot unit, CBZ and several other EDC compounds were fed to the reactor for over 100 days. The unit was operated in anoxic and oxic phases and received synthetic wastewater spiked with several pharmaceutical micropollutants, including CBZ. No significant removal of CBZ could be recorded without the addition of powdered activated carbon, PAC. However, CBZ removal increased by up to 85% when PAC was added into the aeration tank. Therefore, in an attempt to demonstrate effect of PAOs on EDCs removal, an anaerobic/aerobic lab-scale SBR has been studied with an SRT of 5 days considering the finding that the critical SRT for total estrogenicity removal was observed as 5 days. A short SRT prevents nitrification but enhances phosphorus removal in anaerobic/aerobic (A/O) systems.[26] The aim was to understand the fate of six selected endocrine disrupting compounds, namely, ATP, diltiazem (DTZ), CBZ, butyl benzyl phthalate (BBP), estrone and progesterone, in this system and the role of sorption and biodegradation on their removals. The compounds were selected based on their high frequency of occurrence in sludge and wastewater samples.
2. Materials and methods 2.1. Sequencing batch reactor A lab-scale SBR was operated with an SRT of ∼ 5 days, to enhance phosphorus removal by PAOs by employing anaerobic/aerobic conditions and to prevent nitrogen removal by keeping the SRT short. Total volume of the reactor was 5 L with a working volume of 4 L.
The reactor was inoculated with sludge obtained from Middle East Technical University-Vacuum Rotating Membrane WWTP (METU-VRM) operating at SRT of ∼ 10 days. Domestic wastewater collected from dormitories and the academic village at METU is being treated in this plant. The plant is comprised of two tanks placed in series. The first tank receives sewage influent where it is treated aerobically under diffused aeration. The second tank (VRM tank) houses the rotating membrane module where a cross flow over the membranes is maintained by coarse aeration. The D.O concentration in the first tank was around 2 mg/l for most of the time while it was zero in the VRM tank. A recirculation, 1Q, from the VRM tank to the aeration tank was maintained to balance the biomass concentration in both tanks. Although no P-removal was initially planned during the design of the plant, yet 50–60% P-removal was generally observed during operation, which was associated with the anaerobic conditions prevailing in the VRM tank. The molar Ca2 + and Mg2+ ion concentrations and the pH of the wastewater suggest that P-removal cannot wholly be attributed to chemical precipitation; thereby suggesting removal by PAO organisms. The feed of the lab unit was taken from the influent of the same plant after a fine screen. Inflow to the reactor was 5.1 L d−1 ; the hydraulic retention time (HRT) was calculated as 19 h; as was the HRT in the VRM plant. The system included three peristaltic pumps for the feed (influent), discharge (effluent) and sludge withdrawals, respectively; an aeration pump and an electronic timer unit. The inflow and outflow (consequently the HRT) were set according to the operation capabilities of the peristaltic pumps. One operating cycle of the system was 12 h, which included 1 hour of anaerobic and 7 h of aerobic period. The duration of aerobic period was kept long to facilitate longer contact time for the dissolved components with the activated sludge. The anaerobic phase was set as 1 h to fall within the recommended 1–2 h contact period for the P-treating plants. Feeding and withdrawal (effluent) from the system were without mixing or aeration and took 45 min each. The mixed liquor suspended solids (MLSS) concentration in the aeration tank was 2.2–2.5 g L−1 .The sludge withdrawal was performed automatically by a sludge withdrawal pump at the last half hour of each aerobic stage, under mixing since it was difficult to withdraw settled sludge due to clogging problems. The fill volume of the reactor was 36–40%. Effluent MLSS was consistently below 20 mg L−1 and around 4.5 L of effluent and 0.7 L of waste sludge were being discharged from the system daily to keep SRT stable at 5 days. The MLSS measurements were carried out daily, according to the Standard Method 2540B. Following the set-up of the reactor, soluble chemical oxygen demand (COD), Total Phosphorus and OrthoPhosphate in influent and effluent samples were measured routinely. The soluble COD was measured by using high range (150–1500 mg/L COD) or low range (15–150 mg/L COD) Hach Lange kits according to HACH 8000 (US EPA
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approved) method. Total-P (TP) and Ortho-P (OP) analyses were conducted by using LCK350 Hach kits (unit: PO4 –P). Analysis of nitrogen compounds was not carried out systematically since the short SRT employed in the reactor would not warrant an efficient nitrification. The dissolved oxygen concentration in the aerobic phase was between 2.2 mg/L and 2.5 mg/L and was below 1 mg/L in the anaerobic phase. The pH of the system was steady around 7.
2.3.
2.2. Mass balance studies The system was operated for 10 days (two SRT) to reach steady state (6 February 2013–16 February 2013). Onset of steady-state conditions was confirmed by the stable readings of effluent COD values, calculated stable COD removal percentages and steady effluent MLSS concentrations on three consecutive samples obtained at 12 h apart. Upon reaching steady-state, a 100 ppb mixture of selected analytes, prepared in methanol, was spiked into the feed and the reactor was operated for 7 days with this feed before sampling. At the end of seventh day (24 February 2013), feed, sludge and effluent samples were collected and were extracted by SPE method and analysed by using LC/MS/MS instrument, according to Sönmez et al. [27] and Muz et al.,[28] respectively. Same analyses were also performed on the next day (25 February 2013) as duplicate. As biodegradation and adsorption are the two important mechanisms in the removal of micropollutants from wastewaters, a mass balance has been constructed to demonstrate the governing mechanism(s) by using the determined analyte concentrations in the feed, sludge and effluents, as given in Equation (2). The biological degradation was expressed by a simplified first-order equation developed from the Monod model in Equation (1); by neglecting, concentration (S) term in the denominator as S 4) is biologically degradable in wastewater treatment facilities. Similarly, according to Lindemann, [31] over 90% progesterone (log Kow 3.87) degradation could be achieved in surface waters and the addition of activated sludge to water samples increased the biodegradation rate. Complete removal of ATP (log Kow < 1) by biodegradation was reported by Schröder et al. [32] The CBZ degradation rate was literally zero, as expected. Estrone removals are highly variable in AS systems (10–98%), but mainly by biodegradation.[33,34] In our case, estrone did not show a high degradation rate as BBP or progesterone but adsorption had seemingly important contribution in its removal. This observation was also consistent with those of Mes et al.,[35] where they showed that biodegradation is the most efficient way of removing selected estrogenic compounds but sorption has also a significant role. The situation is nearly the same for DTZ, where biodegradation seems as the most important removal mechanism for this compound; yet its rate is slow. In a study by Kasprzyk-Hordem et al.,[36] more than 80% DTZ removal by biodegradation was achieved in AS process. The high EDC biodegradation rates obtained in partially anaerobic P-removing systems might have been due to their possible role as soluble carbon feed to PAOs. In their energy metabolism, the PAO organisms normally rely on fatty acids to produce poly hydroxy alkanoic acid (PHA) inclusions with concomitant P release. The PHAs later undergo oxidation when conditions are aerobic.[33] In this case, EDCs might have been fermented into simple acids during anaerobiosis and any residuals might have been aerobically digested. In the absence of relevant information in the literature, this speculation deserves further investigation. The CBZ shows an interesting situation. It is reported that CBZ is resistant to biodegradation in sewage treatment facilities. This too was the case in our study. However, the studies so far conducted mostly show that its tendency to adsorb onto the sludge is low due to its low distribution coefficient between water and sludge (K = 1.2 L kg−1 ss ).[27] Some studies conducted with full-scale plants show that CBZ tends to stay in the aqueous phase.[28,29] This was not the case in our study where almost 86% removal was achieved simply by sorption onto the sludge. This effect may be attributed to the anaerobic phase of the SBR unit
employed, and/or to the fact that, contrary to the previous researches with synthetic sewage, true domestic wastewater was being used as feed in our system. Xue et al. [37] showed that the refractory compounds were adsorbed onto the sludge much more rapidly in the anaerobic phase than in other units. They also pointed out that sorption capabilities mainly depend on the soil/sludge content. It has been observed that the strength of sorption of CBZ depends highly on the organic content of the solid phase.[38,39] Study by Drillia et al. [40] showed that the adsorption of CBZ was not only dependent on the organic content but also on other matrix properties, and it is higher in anaerobic sludge. The CBZ has better sorption potential in the protonated form due to particular ionic interactions.[41,42] This could not be tested in this study since the pH was neutral in our reactor. Radjenovic et al. [43] also estimated a relatively high solid–water distribution coefficient (Kd ) value for CBZ in primary sludge, but did not discuss this matter in any detail. Considering the findings presented this far regarding the target compounds, it is implicit that in the elimination of EDCs and other micropollutants, adsorption by sludge is an important mechanism, if not the only mechanism in some cases, during treatment of wastewaters. Therefore, contamination of sludge by micropollutants becomes an issue to be addressed for the environmental safety. 4. Conclusion The fate and removal of six selected endocrine disrupting compounds, EDCs, have been investigated in an anaerobic/aerobic lab-scale SBR unit. It was found that more than 80% removal of all the target compounds could be achieved at an SRT of 5 days without the contribution of the nitrifying micro-organisms. For most of the compounds studied it was observed that biodegradation is the most important removal mechanism, except for CBZ, which showed a different removal trend by highly accumulating onto the sludge. This finding somewhat contradicts with those in the literature, where lab-scale results using synthetic wastewater did not report any significant CBZ removals. This effect may be attributed to the existence of an anaerobic stage in our SBR system or to the particular sludge matrix obtained during feeding with true wastewater. Results also indicate that the disposal of excess sludge necessitates appropriate treatment before discharge, as it can be a source of further contamination at that state.
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