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Emission of odorous volatile organic compounds from a municipal manure treatment plant and their removal using a biotrickling filter a
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Jian-Jun Li , Yan-Di Wu , Yan-Li Zhang , Pei-Yuan Zeng , Xiang Tu , Mei-Ying Xu & Guo-Ping Sun
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Guangdong Institute of Microbiology, Guangdong Provincial Key Laboratory of Microbial Culture Collection and Application, State Key Laboratory of Applied Microbiology Southern China, Guangzhou 510070, People's Republic of China b
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Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, People's Republic of China Accepted author version posted online: 10 Oct 2014.Published online: 31 Oct 2014.
To cite this article: Jian-Jun Li, Yan-Di Wu, Yan-Li Zhang, Pei-Yuan Zeng, Xiang Tu, Mei-Ying Xu & Guo-Ping Sun (2015) Emission of odorous volatile organic compounds from a municipal manure treatment plant and their removal using a biotrickling filter, Environmental Technology, 36:8, 1050-1056, DOI: 10.1080/09593330.2014.974679 To link to this article: http://dx.doi.org/10.1080/09593330.2014.974679
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Environmental Technology, 2015 Vol. 36, No. 8, 1050–1056, http://dx.doi.org/10.1080/09593330.2014.974679
Emission of odorous volatile organic compounds from a municipal manure treatment plant and their removal using a biotrickling filter Jian-Jun Lia , Yan-Di Wua , Yan-Li Zhangb , Pei-Yuan Zenga , Xiang Tua , Mei-Ying Xua and Guo-Ping Suna∗ a Guangdong
Institute of Microbiology, Guangdong Provincial Key Laboratory of Microbial Culture Collection and Application, State Key Laboratory of Applied Microbiology Southern China, Guangzhou 510070, People’s Republic of China; b Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, People’s Republic of China
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(Received 14 April 2014; final version received 2 October 2014 ) Odorous volatile organic compounds (VOCs) from municipal manure treatment facilities are considered as a major nuisance issue for operators and nearby residents. In this study, up to 71 odorous VOCs were detected by gas chromatography–mass spectrometry at the manure treatment plant. These compounds can be classified into five different categories, including alkanes, olefins, aromatics, volatile organosulphur compounds and terpenes. Toluene, dimethyl disulphide, dimethyl sulphide, xylene and ethylbenzene were the five most abundant pollutants. A pilot-scale biotrickling filter (BTF) was employed to treat the complex odorous gases. Correlation analysis showed that the removal efficiency (RE) of the BTF was related with the molecular weight and chemical structure of contaminants. Higher than 85% of REs could be reached for aromatic, terpenes and most alkanes compounds after 180 days of operation. Comparatively, most olefins and partial alkanes compounds with a molecular weight lower than 70 were not removed easily. The REs of these compounds ranged from 0% to 94%, and the average removal efficiency (RE) was only about 33.3%. Keywords: odorous; manure; volatile organic compounds (VOCs); biotrickling filter; complex gases
Introduction Environmental and sanitary problems arising from the treatment facilities of municipal manure have been considered as one of the most sensitive issues in many populated cities. Large volumes of odorous gases containing volatile organic compounds (VOCs) are released into the atmosphere during the treatment process of municipal manure, and results in air contamination in the vicinity of the municipal manure treatment plant. Therefore, qualitative and quantitative analyses of odorous VOCs are necessary for environmental regulation purposes, and for developing and evaluating mitigation strategies. Some researchers have focused on the emission characteristics of odorous VOCs that are mainly generated from livestock manure. Phenols, indoles, skatoles, alcohols, reduced organic sulphide and volatile fatty acids have been reported as the most common odorous VOCs associated with livestock manure.[1–3] However, limited works have been conducted to analyse the odorous emission of the municipal manure treatment plant. Many odorous VOCs are characterized by extremely low olfactory threshold concentration, and have negative effects on human health and welfare.[4,5] For this reason, strict environmental regulations have come into force, and various control methods for VOCs removal from waste air stream have been developed over the past decades,
*Corresponding author. Email: [email protected] © 2014 Taylor & Francis
including absorption, adsorption, catalytic oxidation, condensation and biofiltration.[6] Of those, biofiltration is by far the most commonly implemented technology for odour abatement due to its relatively low investment and operating costs, high efficiency, safe operating conditions and the absence of generation of hazardous by-products.[7,8] Up to now, most studies have been conducted in laboratory with synthetic waste gas stream that only contained single or several contaminants.[6,9–11] However, odorous emissions from the manure treatment process are generally complex mixtures of contaminants with low concentrations. It was reported that 311 volatile compounds were detected from faeces of adults.[12] Results of degradation studies on VOC mixtures showed that the removal of one component may be affected by other components in the mixture.[13–15] So far only limited experimental tests have been done regarding the evaluation of the overall performance of the biofiltration system treating complex waste gases. Tymczyna et al. evaluated the effectiveness of air biofiltration in rendering plant, the average VOCs removal efficiency (RE) reached more than 88%.[16] The abatement of odorous gases emitted from sludge-handling activities was evaluated in a compost-based biofilter. Eight compounds including reduced sulphur compounds and VOCs were identified. REs higher than 99% were recorded for limonene, ketones and benzene, while toluene and
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Environmental Technology dimethyl trisulphide REs exceeded 80% at an empty bed retention time (EBRT) of 60 s.[17] Biofiltration of waste gases mainly relies on the versatile microorganisms, which usually attach to the surface of the support medium, and immobilize to form a thin socalled biofilm. When synthetic inert material was used as a support medium, particular microbes must be inoculated to establish a stable microbial ecosystem with degrading capacity of the corresponding pollutants. Xue et al. studied the removal of mixed VOCs produced from compositing using a biotrickling filter (BTF), and found that the RE of total VOC (TVOC) notably increased from 26.1% to 81.5% after inoculation of VOC-degrading microbes.[18] This study was conducted to identify and quantify chemical composition of the odorous VOCs emission produced during the municipal manure pre-treatment process. Furthermore, a pilot-scale BTF was installed in the manure treatment plant. The abatement performance of the BTF to remove the odorous VOCs from the complex waste gases was evaluated.
Materials and methods Site characterization This study was performed in the municipal manure treatment plant of Guangzhou, Guangdong, China, which is located nearby a municipal wastewater treatment plant.
Figure 1. Schematic diagram of the BTF for odorous VOCs removal.
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Municipal manure that are daily collected from septic tanks and public toilets throughout Guangzhou urban area is transported using special vehicles to a closed house within the municipal treatment plant, in which these collected manure are firstly poured into a feed port. Solid particles within manure are removed through a fine grid and a sand pool, and then the liquid is subsequently transported to the municipal sewage treatment plant.
BTF set-up A pilot-scale BTF with an inside diameter of 90 cm and a height of 210 cm was installed next to the closed house, and operated under ambient temperature. The schematic diagram of the BTF is shown in Figure 1. The BTF was filled with bamboo charcoal to a depth of about 80 cm. This packing material featured particle sizes of 0.8–2.4 cm, porosity of 54.5% and bulk density of 0.21 g cm−3 . A perforated sieve plate was placed at the bottom of the filter bed to support the packing materials. The effective packed volume of the filter bed was 0.5 m3 . Waste gases collected from the closed house were extracted by a blower at a flow rate of 169 m3 h−1 (corresponding to an EBRT of 11 s), and supplied into the BTF through the bottom. Two sampling ports were set on top and bottom of the BTF for the measurement of VOCs’ concentrations of the outlet and inlet gas stream, respectively.
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Three aromatic compounds oxidizing consortiums that were originally enriched from petroleum-contaminated soil were maintained in three desiccators with an inorganic salt medium. Toluene, xylene and styrene were added, respectively, into the desiccators as sole carbon sources for microbial growth, and were supplemented once a week. Five weeks later, the three consortiums with same optical density and equal amounts were mixed. Totally, 30 L of the mixed microbial culture was used as inoculums of the BTF. The buffered nutrient solution was continuously circulated by a stainless steel pump from a 40 L of a hold tank through a solenoid valve. The nutrient solution was uniformly sprayed as a fine mist onto the top of the packing bed through a spray nozzle. The base nutrient solution contained 5 g KH2 PO4 ·12H2 O L−1 , 1.4 g Na2 HPO4 L−1 , 0.1 g MgSO4 ·7H2 O L−1 , 0.03 g CaCl2 ·2H2 O L−1 , 0.06 g FeSO4 ·7H2 O L−1 and 5 g NH4 Cl L−1 . The pH of the recycling solution was manually adjusted at about 7.2 by the periodical addition of NaOH solution. The nutrient solution was completely renewed every week to avoid possible inhabitation caused by metabolites.
Gas sampling and chromatograph/mass spectrometry analysis For the analysis of emission characterization of odorous VOCs during the manure treatment process, samples were collected at three different sites of the closed house: the feed port, the fine grid and the sand pool. For evaluating the performance of the BTF in treating odorous VOCscontaining waste gases, samples were taken from the inlet and outlet gas stream at day 30 and day 180 of the experimental periods. A detailed description of the air samples collection and analysis can be found elsewhere.[19,20] Briefly, all samples were collected using 2.7-L stainless steel canisters (Entech Instruments Inc., CA, USA) in duplicate and transported directly to the laboratory. The canisters were cleaned and pre-evacuated prior to sampling. The VOCs’ samples were analysed with a Model 7100 Preconcentrator (Entech Instruments Inc., CA, USA) coupled with an Agilent 5973N gas chromatography– mass selective detector/flame ionization detector (GC– MSD/FID, Agilent Technologies, USA). The air was first separated by a HP-1 capillary column (60 m × 0.32
mm × 1.0 μm, Agilent Technologies, USA) with helium as the carrier gas, and then split into two ways: one was to a PLOT-Q column (30 m × 0.32 mm × 2.0 μm, Agilent Technologies, USA) followed by FID detection; another was to a 65 cm × 0.10 mm ID stainless steel line followed by MSD detection. The GC oven temperature was programmed to be initially at − 50°C, holding for 3 min, increasing to 10°C at 15°C min−1 , then to 120°C at 5°C min−1 , and then to 250°C at 10°C min−1 and holding for 10 min. The MSD was operated in a selected ion monitoring mode and the ionization method was electron impacting (70 eV). C2 –C3 and C4 –C11 VOC compounds were identified and quantified by FID and MSD, respectively.
Results Identification and determination of the concentrations of odorous VOCs from the municipal manure treatment process Seventy-one odorous VOCs were detected and identified in the existing municipal manure pre-treatment building house. As given in Table 1, these compounds can be classified into five different categories, including alkanes, olefin, aromatics, volatile organosulphur compounds (VOSCs) and terpenes. TVOC concentration detected at the feed port, fine grid and sand pool were 1147.8, 1086.1 and 578.3 μg m−3 , respectively. Aromatics compounds, alkanes compounds and VOSCs were three main kinds of VOCs at the three different sites in the municipal manure pre-treatment house. Aromatic compounds at the feed port, fine grid and sand pool represented 49.9%, 50.5% and 54.4% of TVOCs, respectively. Toluene was the most abundant aromatic species detected in the manure pre-treatment house, followed by xylene and ethylbenzene. Average concentrations of toluene at above sites were 282.5 ± 126.7, 401.4 ± 163.8 and 213.6 ± 11.1 μg m−3 , respectively. The percentage value of alkenes at sand pool was 33.5%, which was higher than 23.7% at the feed port and 18.5% at the fine grid. Totally 29 alkane species were identified at all three sites, most of which belonged C5 to C8 compounds. Dimethyl disulphide (DMDS) and dimethyl sulphide (DMS) were two main reduced organosulphur compounds which accounted for more than 90% of VOSCs. Both olefins and terpenes
Table 1. Average concentrations of five kinds of odorous VOCs (μg m−3 ) at three manure treating sites. Sites Alkanes Olefines Aromatic VOSCs Terpenes Total
Feed port 272.28 15.84 572.19 220.94 66.51 1147.76
± ± ± ± ± ±
191.18 7.38 378.53 263.60 87.62 928.31
Fine grid 201.11 13.47 548.15 317.06 6.35 1086.14
± ± ± ± ± ±
26.17 0.90 221.53 236.02 1.82 486.44
Sand pool 193.72 15.92 314.54 49.87 4.22 578.28
± ± ± ± ± ±
21.02 1.21 15.39 13.21 0.83 51.66
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Environmental Technology Table 2. Average concentrations and percentages of the most abundant odorous volatile compounds at three sites of the municipal manure treatment plant. Average concentration(μg m−3 )
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Compounds Toluene DMDS DMS m/p-Xylene Ethylbenzene n-Decane n-Unecane 1,2,4-Trimethylbenzene Propane m-Ethyltoluene n-Butane o-Xylene d-Limonene Isobutane n-Nonane Isopentane n-Pentane 1,3,5-Trimethylbenzene 1,2,3-Trimethylbenzene α-Pinene 3-Methylhexane n-Heptane 2-Methylhexane Methylcyclohexane Cyclohexane
Average percentage (%)
Feed port
Fine grid
Sand pool
Feed port
Fine grid
Sand pool
282.5 143.2 72.5 62.0 48.2 52.9 52.3 37.4 20.2 28.3 18.8 25.2 40.6 18.1 29.6 13.9 11.0 19.7 17.1 16.8 4.7 4.1 3.8 2.8 1.8
401.4 213.0 101.4 57.7 37.9 2.5 3.7 5.0 21.5 4.1 20.5 23.5 0.9 14.1 1.7 12.9 12.1 1.4 1.8 2.6 9.3 22.2 9.0 12.1 14.3
213.6 37.8 11.4 37.9 23.7 1.3 1.9 4.1 21.0 2.4 21.1 14.4 0.7 14.8 0.9 14.7 11.4 1.2 1.3 2.2 8.6 21.0 8.3 12.5 13.7
30.0 8.6 5.8 5.6 4.3 3.7 3.5 2.9 2.5 2.4 2.4 2.3 2.3 2.0 2.0 1.8 1.4 1.4 1.3 1.2 0.5 0.4 0.4 0.3 0.2
37.3 19.4 9.2 5.4 3.5 0.2 0.3 0.5 2.0 0.4 1.9 2.2 0.1 1.3 0.2 1.2 1.1 0.1 0.2 0.2 0.9 2.0 0.8 1.1 1.3
37.0 6.5 1.9 6.6 4.1 0.2 0.3 0.7 3.6 0.4 3.7 2.5 0.1 2.6 0.2 2.6 2.0 0.2 0.2 0.4 1.5 3.6 1.4 2.2 2.3
were present in small quantities, and the highest percentage of 5.8% of terpenes was found at the feed port. Table 2 lists the average concentrations and the percentages of the top 25 odorous VOCs that were identified in the municipal manure pre-treatment house. Toluene, DMDS, DMS, xylene and ethylbenzene were the five most abundant pollutants, hence could be considered as a marker of odorous VOCs.
The abatement performance of the BTF in treating the complex odorous VOCs from the municipal manure treatment process The performance of a BTF treating the odorous gases generated from the municipal manure pre-treatment house was evaluated within about six months. TVOCs’ concentrations of influent gases of the BTF on day 30 and day 180 were 445.9 and 302.1 μg m−3 , respectively, which were lower than that detected at the above three sites of the manure pre-treatment house. With respect to individual chemical species, toluene, ethylbenzene and xylene were three most abundant compounds. The percentages of DMDS and DMS were only 3.5% and 1.4% on day 30, and both were lower than 1.0% on day 180. These changes can be attributed to the relatively shorter atmospheric lifetime of reduced sulphur compounds than the other detected compounds.
After inoculation, the BTF was operated continuously at EBRT of 11 s throughout this experiment. RE of the BTF for each compound ranged from 0% to nearly 100%. Correlation analysis revealed that there were strong correlation between RE and molecular weight of compounds. The correlation coefficients between molecular weight and RE of the BTF obtained on day 30 and day 180 were 0.6551 and 0.8197 (P < 0.01), respectively. It can be found from Figure 2 that REs of the most compounds with a higher
Figure 2. Correlation analysis between REs and molecular weight of VOCs detected in this study.
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Figure 3. Correlation analysis between REs and chemical categories of VOCs detected in this study.
molecular weight than 100 were very high ( > 85%). This chemical family included almost all of aromatic compounds, and more than half of alkanes. Only the REs of one kind of aromatic compound (p-diethylbenzene), and four kinds of alkane compounds (2,3,4-trimethylpentane, n-decane, n-uoecane and n-dodecane) within this chemical family were lower than 85% (60–83%) on day 30, but all finally increased to higher than 85% on day 180. Comparatively, most olefins and partial alkane compounds with a molecular weight lower than 70 were not removed easily. The REs of these compounds ranged from 0% to 94%, and the average RE was only about 33.3%. Although the correlation between REs on day 30 and chemical structure was relatively weak (0.2515, P < 0.05), it still could be found from Figure 3 that the BTF showed different removal performances for different chemical categories. Terpenes, including α-pinene and βpinene, were nearly completely removed by the BTF on day 30, but the REs decreased to about 90% on day 180. Terpenes were at trace level concentrations (lower than 2.0 μg m−3 ), such a low concentration may not support the development of corresponding microbes in the BTF. Average RE for aromatic compounds reached 93% on day 30, and to 92% on day 180, respectively. The REs on day 30 for most olefins were lower than 40%, and close to 0% on day 180. The REs of alkanes ranged from 0% to 98% on day 180, as mentioned above, their REs closely correlated with the molecular weight. About 23% of DMDS and 83% of DMS could be removed by the BTF on day 30, but the REs on day 180 for these two compounds were closer to 0%. Discussion Odour and VOCs’ emissions have been an important issue at the manure treatment plant. It has been considered that odorous compounds mainly are caused by the microbial degradation of organic matter present in manure.[3,21] Hence, volatile metabolites such as alcohols, ketones, fatty
acids, indoles as well as reduced sulphide compounds were in general the odour-causing substances of manure. However, the issue of which substances do most significantly contribute to odour of manure has been controversially discussed in previous reports. Parker et al. reported that three compounds (4-methylphenol, skatole and 4-ethlphenol) accounted for 93% of the summed odour activity value during swine manure land application.[22] Sato et al. reported that about 90% of the malodour-causing substances of human manure were volatile fatty acids; hydrogen sulphide and ammonia were other two odour substances with higher proportions.[23] Kuroda et al. found that ammonia and sulphur compounds were the main elements of the malodour from swine faeces.[1] Five categories of chemical substances were detected in this study; among them, aromatics, alkanes and VOSCs were three major class odorous VOCs at the municipal manure treatment plant. It has been well documented that benzene, toluene, ethylbenzene and isomers of xylene were predominant traffic-related VOCs.[6,24] Many alkanes and olefins also were emitted from engine combustion or the gasoline evaporation process.[25–27] The municipal manure treatment plant receives most of the manure that are collected throughout Guangzhou urban area. Dozens of vehicles are employed daily to transport manure from urban area to the treatment site, and the engines of vehicles still keep running during the manure unloading at the feed port. Therefore, vehicle exhaust may be considered as a major source of aromatics, alkanes and olefins, and indeed accounted for more than half of odorous VOCs of the municipal manure treatment facilities. The VOCs’ emission from vehicle exhaust should not be ignored because long-term exposure can be a health risk.[28] Fatty acid, indole and skatole, which in general were identified as the important malodorous components from manure, were not detected in this study. The method we used was mainly suitable for the volatile organic species, while for the detection of fatty acid, indole and skatole, the air samples need to be treated differently from those VOC species, that is, collecting organic acids in ambient air needs adsorption, absorption by alkaline matters or solid-phase microextraction technique.[29] In this study, aromatic compounds were the components that could be best efficiently removed from waste air stream even on day 30. This can be mainly attributed to the inoculation of the pre-acclimating microbial consortium, with which the BTF could easily adapt to the aromatic compounds within a shorter time. Comparatively, although the REs of olefins and alkanes increased a little on 180 day, but the overall performance of the BTF on removing these compounds was still poorer than that on aromatic compounds, indicating that sufficient microbes with degrading activities on olefins and alkanes may not successfully develop within the BTF. Therefore, in order to efficiently remove all components simultaneously from a gas mixture with various compounds, suitable microbial
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Environmental Technology consortium is commonly required. Some authors have also reported that when multiple species of microorganisms were inoculated, the removal capacity could be enhanced through the synergistic effect of microorganisms.[30,31] A field experiment from Lin et al. demonstrated that a granular-activated carbon BTF inoculated with five different microbes achieved high REs for all substances of the gas mixture, and no interspecific inhibition or competition within different microflora was observed.[32] However, the kind of microbial strains that should be inoculated depends on the target contaminant species and their per cent within the off-gas treated. Hence, the qualitative and quantitative analysis is a prerequisite for the design of the bioreactor and preparation of inoculums. Despite the fact that the waste gases treated by the BTF actually included dozens of compounds with different chemical properties, it was difficult to analyse substrate interactions among VOCs in mixture due to limited data and too many species being involved. Pollutant mass transfer from gas to liquid phase was recognized as one important process influencing the performance of the bioreactor, which is related to not only the properties of packing materials, but also the characteristics of pollutant, and running parameters such as the contaminants’ solubility and diffusivity in the liquid phase, gas velocity and so on.[33,34] Most reported studies on biofiltration are often carried out at concentrations much higher than those typically found in real situations. When inlet loading rate reached a certain value, which could have resulted from either increase in inlet concentration or decrease in EBRT, microbial activities became the ratelimiting step.[35] Comparatively, in our particular case, the TVOCs inlet concentrations of the BTF were found less than 500 μg m−3 , which were much lower than that reported in the literature. Mass transfer rates, therefore, may be another factor limiting the removal of some VOCs’ species. For example, the REs of VOSCs significantly decreased nearly to zero on day 180. As shown in Table 3, the inlet concentrations of DMDS and DMS changed from 17.2 and 6.0 μg m−3 to 2.2 and 0.02 μg m−3 , respectively. Hence, the decrease in REs for both compounds may be caused mainly by mass transfer rates rather than biological activities because such low inlet concentrations could not
Table 3. Inlet concentrations and REs of volatile organic sulphide compounds. Time (d)
Compounds
30
DMS DMDS CS2 DMS DMDS CS2
180
Inlet concentration (μg m−3 )
REs (%)
6.29 17.23 0.64 0.02 2.21 0.96
83.4 22.5 0.0 1.5 0.0 0.0
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in general inhibit the microbial activities. Similar results have been obtained in a full-scale biofilter treating odorous emissions from a composting plant.[36] Conclusion This study confirmed the complex composition of odorous emissions from a municipal manure treatment plant. Five categories of chemical substances were detected, including alkanes, olefins, aromatics, VOSCs and terpenes. Toluene, DMDS, DMS, xylene and ethylbenzene were the five most abundant pollutants. Under real operating conditions, the research presented here demonstrates that the removal of the complex VOCs using bamboo charcoal-based BTF is possible. The REs were related with the molecular weight and chemical structure of contaminants. Pre-acclimating microbial consortium could enhance the removal capabilities of the bioreactor on the corresponding pollutants. Aromatic compounds were the components that could be best efficiently removed from waste air stream. At very low inlet concentrations, the mass transfer rate was one important factor influencing the RE. Acknowledgements This work was supported by the Science and Technology project of Guangzhou, China (no. 2011J4200074), Science and Technology project of Guangdong province, china (no. 2012B091000160) and the Natural Science Foundation of China (no. 31270169).
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Environmental Technology Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tent20
Emission of odorous volatile organic compounds from a municipal manure treatment plant and their removal using a biotrickling filter a
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Jian-Jun Li , Yan-Di Wu , Yan-Li Zhang , Pei-Yuan Zeng , Xiang Tu , Mei-Ying Xu & Guo-Ping Sun
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Guangdong Institute of Microbiology, Guangdong Provincial Key Laboratory of Microbial Culture Collection and Application, State Key Laboratory of Applied Microbiology Southern China, Guangzhou 510070, People's Republic of China b
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Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, People's Republic of China Accepted author version posted online: 10 Oct 2014.Published online: 31 Oct 2014.
To cite this article: Jian-Jun Li, Yan-Di Wu, Yan-Li Zhang, Pei-Yuan Zeng, Xiang Tu, Mei-Ying Xu & Guo-Ping Sun (2015) Emission of odorous volatile organic compounds from a municipal manure treatment plant and their removal using a biotrickling filter, Environmental Technology, 36:8, 1050-1056, DOI: 10.1080/09593330.2014.974679 To link to this article: http://dx.doi.org/10.1080/09593330.2014.974679
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Environmental Technology, 2015 Vol. 36, No. 8, 1050–1056, http://dx.doi.org/10.1080/09593330.2014.974679
Emission of odorous volatile organic compounds from a municipal manure treatment plant and their removal using a biotrickling filter Jian-Jun Lia , Yan-Di Wua , Yan-Li Zhangb , Pei-Yuan Zenga , Xiang Tua , Mei-Ying Xua and Guo-Ping Suna∗ a Guangdong
Institute of Microbiology, Guangdong Provincial Key Laboratory of Microbial Culture Collection and Application, State Key Laboratory of Applied Microbiology Southern China, Guangzhou 510070, People’s Republic of China; b Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, People’s Republic of China
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(Received 14 April 2014; final version received 2 October 2014 ) Odorous volatile organic compounds (VOCs) from municipal manure treatment facilities are considered as a major nuisance issue for operators and nearby residents. In this study, up to 71 odorous VOCs were detected by gas chromatography–mass spectrometry at the manure treatment plant. These compounds can be classified into five different categories, including alkanes, olefins, aromatics, volatile organosulphur compounds and terpenes. Toluene, dimethyl disulphide, dimethyl sulphide, xylene and ethylbenzene were the five most abundant pollutants. A pilot-scale biotrickling filter (BTF) was employed to treat the complex odorous gases. Correlation analysis showed that the removal efficiency (RE) of the BTF was related with the molecular weight and chemical structure of contaminants. Higher than 85% of REs could be reached for aromatic, terpenes and most alkanes compounds after 180 days of operation. Comparatively, most olefins and partial alkanes compounds with a molecular weight lower than 70 were not removed easily. The REs of these compounds ranged from 0% to 94%, and the average removal efficiency (RE) was only about 33.3%. Keywords: odorous; manure; volatile organic compounds (VOCs); biotrickling filter; complex gases
Introduction Environmental and sanitary problems arising from the treatment facilities of municipal manure have been considered as one of the most sensitive issues in many populated cities. Large volumes of odorous gases containing volatile organic compounds (VOCs) are released into the atmosphere during the treatment process of municipal manure, and results in air contamination in the vicinity of the municipal manure treatment plant. Therefore, qualitative and quantitative analyses of odorous VOCs are necessary for environmental regulation purposes, and for developing and evaluating mitigation strategies. Some researchers have focused on the emission characteristics of odorous VOCs that are mainly generated from livestock manure. Phenols, indoles, skatoles, alcohols, reduced organic sulphide and volatile fatty acids have been reported as the most common odorous VOCs associated with livestock manure.[1–3] However, limited works have been conducted to analyse the odorous emission of the municipal manure treatment plant. Many odorous VOCs are characterized by extremely low olfactory threshold concentration, and have negative effects on human health and welfare.[4,5] For this reason, strict environmental regulations have come into force, and various control methods for VOCs removal from waste air stream have been developed over the past decades,
*Corresponding author. Email: [email protected] © 2014 Taylor & Francis
including absorption, adsorption, catalytic oxidation, condensation and biofiltration.[6] Of those, biofiltration is by far the most commonly implemented technology for odour abatement due to its relatively low investment and operating costs, high efficiency, safe operating conditions and the absence of generation of hazardous by-products.[7,8] Up to now, most studies have been conducted in laboratory with synthetic waste gas stream that only contained single or several contaminants.[6,9–11] However, odorous emissions from the manure treatment process are generally complex mixtures of contaminants with low concentrations. It was reported that 311 volatile compounds were detected from faeces of adults.[12] Results of degradation studies on VOC mixtures showed that the removal of one component may be affected by other components in the mixture.[13–15] So far only limited experimental tests have been done regarding the evaluation of the overall performance of the biofiltration system treating complex waste gases. Tymczyna et al. evaluated the effectiveness of air biofiltration in rendering plant, the average VOCs removal efficiency (RE) reached more than 88%.[16] The abatement of odorous gases emitted from sludge-handling activities was evaluated in a compost-based biofilter. Eight compounds including reduced sulphur compounds and VOCs were identified. REs higher than 99% were recorded for limonene, ketones and benzene, while toluene and
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Environmental Technology dimethyl trisulphide REs exceeded 80% at an empty bed retention time (EBRT) of 60 s.[17] Biofiltration of waste gases mainly relies on the versatile microorganisms, which usually attach to the surface of the support medium, and immobilize to form a thin socalled biofilm. When synthetic inert material was used as a support medium, particular microbes must be inoculated to establish a stable microbial ecosystem with degrading capacity of the corresponding pollutants. Xue et al. studied the removal of mixed VOCs produced from compositing using a biotrickling filter (BTF), and found that the RE of total VOC (TVOC) notably increased from 26.1% to 81.5% after inoculation of VOC-degrading microbes.[18] This study was conducted to identify and quantify chemical composition of the odorous VOCs emission produced during the municipal manure pre-treatment process. Furthermore, a pilot-scale BTF was installed in the manure treatment plant. The abatement performance of the BTF to remove the odorous VOCs from the complex waste gases was evaluated.
Materials and methods Site characterization This study was performed in the municipal manure treatment plant of Guangzhou, Guangdong, China, which is located nearby a municipal wastewater treatment plant.
Figure 1. Schematic diagram of the BTF for odorous VOCs removal.
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Municipal manure that are daily collected from septic tanks and public toilets throughout Guangzhou urban area is transported using special vehicles to a closed house within the municipal treatment plant, in which these collected manure are firstly poured into a feed port. Solid particles within manure are removed through a fine grid and a sand pool, and then the liquid is subsequently transported to the municipal sewage treatment plant.
BTF set-up A pilot-scale BTF with an inside diameter of 90 cm and a height of 210 cm was installed next to the closed house, and operated under ambient temperature. The schematic diagram of the BTF is shown in Figure 1. The BTF was filled with bamboo charcoal to a depth of about 80 cm. This packing material featured particle sizes of 0.8–2.4 cm, porosity of 54.5% and bulk density of 0.21 g cm−3 . A perforated sieve plate was placed at the bottom of the filter bed to support the packing materials. The effective packed volume of the filter bed was 0.5 m3 . Waste gases collected from the closed house were extracted by a blower at a flow rate of 169 m3 h−1 (corresponding to an EBRT of 11 s), and supplied into the BTF through the bottom. Two sampling ports were set on top and bottom of the BTF for the measurement of VOCs’ concentrations of the outlet and inlet gas stream, respectively.
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Three aromatic compounds oxidizing consortiums that were originally enriched from petroleum-contaminated soil were maintained in three desiccators with an inorganic salt medium. Toluene, xylene and styrene were added, respectively, into the desiccators as sole carbon sources for microbial growth, and were supplemented once a week. Five weeks later, the three consortiums with same optical density and equal amounts were mixed. Totally, 30 L of the mixed microbial culture was used as inoculums of the BTF. The buffered nutrient solution was continuously circulated by a stainless steel pump from a 40 L of a hold tank through a solenoid valve. The nutrient solution was uniformly sprayed as a fine mist onto the top of the packing bed through a spray nozzle. The base nutrient solution contained 5 g KH2 PO4 ·12H2 O L−1 , 1.4 g Na2 HPO4 L−1 , 0.1 g MgSO4 ·7H2 O L−1 , 0.03 g CaCl2 ·2H2 O L−1 , 0.06 g FeSO4 ·7H2 O L−1 and 5 g NH4 Cl L−1 . The pH of the recycling solution was manually adjusted at about 7.2 by the periodical addition of NaOH solution. The nutrient solution was completely renewed every week to avoid possible inhabitation caused by metabolites.
Gas sampling and chromatograph/mass spectrometry analysis For the analysis of emission characterization of odorous VOCs during the manure treatment process, samples were collected at three different sites of the closed house: the feed port, the fine grid and the sand pool. For evaluating the performance of the BTF in treating odorous VOCscontaining waste gases, samples were taken from the inlet and outlet gas stream at day 30 and day 180 of the experimental periods. A detailed description of the air samples collection and analysis can be found elsewhere.[19,20] Briefly, all samples were collected using 2.7-L stainless steel canisters (Entech Instruments Inc., CA, USA) in duplicate and transported directly to the laboratory. The canisters were cleaned and pre-evacuated prior to sampling. The VOCs’ samples were analysed with a Model 7100 Preconcentrator (Entech Instruments Inc., CA, USA) coupled with an Agilent 5973N gas chromatography– mass selective detector/flame ionization detector (GC– MSD/FID, Agilent Technologies, USA). The air was first separated by a HP-1 capillary column (60 m × 0.32
mm × 1.0 μm, Agilent Technologies, USA) with helium as the carrier gas, and then split into two ways: one was to a PLOT-Q column (30 m × 0.32 mm × 2.0 μm, Agilent Technologies, USA) followed by FID detection; another was to a 65 cm × 0.10 mm ID stainless steel line followed by MSD detection. The GC oven temperature was programmed to be initially at − 50°C, holding for 3 min, increasing to 10°C at 15°C min−1 , then to 120°C at 5°C min−1 , and then to 250°C at 10°C min−1 and holding for 10 min. The MSD was operated in a selected ion monitoring mode and the ionization method was electron impacting (70 eV). C2 –C3 and C4 –C11 VOC compounds were identified and quantified by FID and MSD, respectively.
Results Identification and determination of the concentrations of odorous VOCs from the municipal manure treatment process Seventy-one odorous VOCs were detected and identified in the existing municipal manure pre-treatment building house. As given in Table 1, these compounds can be classified into five different categories, including alkanes, olefin, aromatics, volatile organosulphur compounds (VOSCs) and terpenes. TVOC concentration detected at the feed port, fine grid and sand pool were 1147.8, 1086.1 and 578.3 μg m−3 , respectively. Aromatics compounds, alkanes compounds and VOSCs were three main kinds of VOCs at the three different sites in the municipal manure pre-treatment house. Aromatic compounds at the feed port, fine grid and sand pool represented 49.9%, 50.5% and 54.4% of TVOCs, respectively. Toluene was the most abundant aromatic species detected in the manure pre-treatment house, followed by xylene and ethylbenzene. Average concentrations of toluene at above sites were 282.5 ± 126.7, 401.4 ± 163.8 and 213.6 ± 11.1 μg m−3 , respectively. The percentage value of alkenes at sand pool was 33.5%, which was higher than 23.7% at the feed port and 18.5% at the fine grid. Totally 29 alkane species were identified at all three sites, most of which belonged C5 to C8 compounds. Dimethyl disulphide (DMDS) and dimethyl sulphide (DMS) were two main reduced organosulphur compounds which accounted for more than 90% of VOSCs. Both olefins and terpenes
Table 1. Average concentrations of five kinds of odorous VOCs (μg m−3 ) at three manure treating sites. Sites Alkanes Olefines Aromatic VOSCs Terpenes Total
Feed port 272.28 15.84 572.19 220.94 66.51 1147.76
± ± ± ± ± ±
191.18 7.38 378.53 263.60 87.62 928.31
Fine grid 201.11 13.47 548.15 317.06 6.35 1086.14
± ± ± ± ± ±
26.17 0.90 221.53 236.02 1.82 486.44
Sand pool 193.72 15.92 314.54 49.87 4.22 578.28
± ± ± ± ± ±
21.02 1.21 15.39 13.21 0.83 51.66
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Environmental Technology Table 2. Average concentrations and percentages of the most abundant odorous volatile compounds at three sites of the municipal manure treatment plant. Average concentration(μg m−3 )
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Compounds Toluene DMDS DMS m/p-Xylene Ethylbenzene n-Decane n-Unecane 1,2,4-Trimethylbenzene Propane m-Ethyltoluene n-Butane o-Xylene d-Limonene Isobutane n-Nonane Isopentane n-Pentane 1,3,5-Trimethylbenzene 1,2,3-Trimethylbenzene α-Pinene 3-Methylhexane n-Heptane 2-Methylhexane Methylcyclohexane Cyclohexane
Average percentage (%)
Feed port
Fine grid
Sand pool
Feed port
Fine grid
Sand pool
282.5 143.2 72.5 62.0 48.2 52.9 52.3 37.4 20.2 28.3 18.8 25.2 40.6 18.1 29.6 13.9 11.0 19.7 17.1 16.8 4.7 4.1 3.8 2.8 1.8
401.4 213.0 101.4 57.7 37.9 2.5 3.7 5.0 21.5 4.1 20.5 23.5 0.9 14.1 1.7 12.9 12.1 1.4 1.8 2.6 9.3 22.2 9.0 12.1 14.3
213.6 37.8 11.4 37.9 23.7 1.3 1.9 4.1 21.0 2.4 21.1 14.4 0.7 14.8 0.9 14.7 11.4 1.2 1.3 2.2 8.6 21.0 8.3 12.5 13.7
30.0 8.6 5.8 5.6 4.3 3.7 3.5 2.9 2.5 2.4 2.4 2.3 2.3 2.0 2.0 1.8 1.4 1.4 1.3 1.2 0.5 0.4 0.4 0.3 0.2
37.3 19.4 9.2 5.4 3.5 0.2 0.3 0.5 2.0 0.4 1.9 2.2 0.1 1.3 0.2 1.2 1.1 0.1 0.2 0.2 0.9 2.0 0.8 1.1 1.3
37.0 6.5 1.9 6.6 4.1 0.2 0.3 0.7 3.6 0.4 3.7 2.5 0.1 2.6 0.2 2.6 2.0 0.2 0.2 0.4 1.5 3.6 1.4 2.2 2.3
were present in small quantities, and the highest percentage of 5.8% of terpenes was found at the feed port. Table 2 lists the average concentrations and the percentages of the top 25 odorous VOCs that were identified in the municipal manure pre-treatment house. Toluene, DMDS, DMS, xylene and ethylbenzene were the five most abundant pollutants, hence could be considered as a marker of odorous VOCs.
The abatement performance of the BTF in treating the complex odorous VOCs from the municipal manure treatment process The performance of a BTF treating the odorous gases generated from the municipal manure pre-treatment house was evaluated within about six months. TVOCs’ concentrations of influent gases of the BTF on day 30 and day 180 were 445.9 and 302.1 μg m−3 , respectively, which were lower than that detected at the above three sites of the manure pre-treatment house. With respect to individual chemical species, toluene, ethylbenzene and xylene were three most abundant compounds. The percentages of DMDS and DMS were only 3.5% and 1.4% on day 30, and both were lower than 1.0% on day 180. These changes can be attributed to the relatively shorter atmospheric lifetime of reduced sulphur compounds than the other detected compounds.
After inoculation, the BTF was operated continuously at EBRT of 11 s throughout this experiment. RE of the BTF for each compound ranged from 0% to nearly 100%. Correlation analysis revealed that there were strong correlation between RE and molecular weight of compounds. The correlation coefficients between molecular weight and RE of the BTF obtained on day 30 and day 180 were 0.6551 and 0.8197 (P < 0.01), respectively. It can be found from Figure 2 that REs of the most compounds with a higher
Figure 2. Correlation analysis between REs and molecular weight of VOCs detected in this study.
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Figure 3. Correlation analysis between REs and chemical categories of VOCs detected in this study.
molecular weight than 100 were very high ( > 85%). This chemical family included almost all of aromatic compounds, and more than half of alkanes. Only the REs of one kind of aromatic compound (p-diethylbenzene), and four kinds of alkane compounds (2,3,4-trimethylpentane, n-decane, n-uoecane and n-dodecane) within this chemical family were lower than 85% (60–83%) on day 30, but all finally increased to higher than 85% on day 180. Comparatively, most olefins and partial alkane compounds with a molecular weight lower than 70 were not removed easily. The REs of these compounds ranged from 0% to 94%, and the average RE was only about 33.3%. Although the correlation between REs on day 30 and chemical structure was relatively weak (0.2515, P < 0.05), it still could be found from Figure 3 that the BTF showed different removal performances for different chemical categories. Terpenes, including α-pinene and βpinene, were nearly completely removed by the BTF on day 30, but the REs decreased to about 90% on day 180. Terpenes were at trace level concentrations (lower than 2.0 μg m−3 ), such a low concentration may not support the development of corresponding microbes in the BTF. Average RE for aromatic compounds reached 93% on day 30, and to 92% on day 180, respectively. The REs on day 30 for most olefins were lower than 40%, and close to 0% on day 180. The REs of alkanes ranged from 0% to 98% on day 180, as mentioned above, their REs closely correlated with the molecular weight. About 23% of DMDS and 83% of DMS could be removed by the BTF on day 30, but the REs on day 180 for these two compounds were closer to 0%. Discussion Odour and VOCs’ emissions have been an important issue at the manure treatment plant. It has been considered that odorous compounds mainly are caused by the microbial degradation of organic matter present in manure.[3,21] Hence, volatile metabolites such as alcohols, ketones, fatty
acids, indoles as well as reduced sulphide compounds were in general the odour-causing substances of manure. However, the issue of which substances do most significantly contribute to odour of manure has been controversially discussed in previous reports. Parker et al. reported that three compounds (4-methylphenol, skatole and 4-ethlphenol) accounted for 93% of the summed odour activity value during swine manure land application.[22] Sato et al. reported that about 90% of the malodour-causing substances of human manure were volatile fatty acids; hydrogen sulphide and ammonia were other two odour substances with higher proportions.[23] Kuroda et al. found that ammonia and sulphur compounds were the main elements of the malodour from swine faeces.[1] Five categories of chemical substances were detected in this study; among them, aromatics, alkanes and VOSCs were three major class odorous VOCs at the municipal manure treatment plant. It has been well documented that benzene, toluene, ethylbenzene and isomers of xylene were predominant traffic-related VOCs.[6,24] Many alkanes and olefins also were emitted from engine combustion or the gasoline evaporation process.[25–27] The municipal manure treatment plant receives most of the manure that are collected throughout Guangzhou urban area. Dozens of vehicles are employed daily to transport manure from urban area to the treatment site, and the engines of vehicles still keep running during the manure unloading at the feed port. Therefore, vehicle exhaust may be considered as a major source of aromatics, alkanes and olefins, and indeed accounted for more than half of odorous VOCs of the municipal manure treatment facilities. The VOCs’ emission from vehicle exhaust should not be ignored because long-term exposure can be a health risk.[28] Fatty acid, indole and skatole, which in general were identified as the important malodorous components from manure, were not detected in this study. The method we used was mainly suitable for the volatile organic species, while for the detection of fatty acid, indole and skatole, the air samples need to be treated differently from those VOC species, that is, collecting organic acids in ambient air needs adsorption, absorption by alkaline matters or solid-phase microextraction technique.[29] In this study, aromatic compounds were the components that could be best efficiently removed from waste air stream even on day 30. This can be mainly attributed to the inoculation of the pre-acclimating microbial consortium, with which the BTF could easily adapt to the aromatic compounds within a shorter time. Comparatively, although the REs of olefins and alkanes increased a little on 180 day, but the overall performance of the BTF on removing these compounds was still poorer than that on aromatic compounds, indicating that sufficient microbes with degrading activities on olefins and alkanes may not successfully develop within the BTF. Therefore, in order to efficiently remove all components simultaneously from a gas mixture with various compounds, suitable microbial
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Environmental Technology consortium is commonly required. Some authors have also reported that when multiple species of microorganisms were inoculated, the removal capacity could be enhanced through the synergistic effect of microorganisms.[30,31] A field experiment from Lin et al. demonstrated that a granular-activated carbon BTF inoculated with five different microbes achieved high REs for all substances of the gas mixture, and no interspecific inhibition or competition within different microflora was observed.[32] However, the kind of microbial strains that should be inoculated depends on the target contaminant species and their per cent within the off-gas treated. Hence, the qualitative and quantitative analysis is a prerequisite for the design of the bioreactor and preparation of inoculums. Despite the fact that the waste gases treated by the BTF actually included dozens of compounds with different chemical properties, it was difficult to analyse substrate interactions among VOCs in mixture due to limited data and too many species being involved. Pollutant mass transfer from gas to liquid phase was recognized as one important process influencing the performance of the bioreactor, which is related to not only the properties of packing materials, but also the characteristics of pollutant, and running parameters such as the contaminants’ solubility and diffusivity in the liquid phase, gas velocity and so on.[33,34] Most reported studies on biofiltration are often carried out at concentrations much higher than those typically found in real situations. When inlet loading rate reached a certain value, which could have resulted from either increase in inlet concentration or decrease in EBRT, microbial activities became the ratelimiting step.[35] Comparatively, in our particular case, the TVOCs inlet concentrations of the BTF were found less than 500 μg m−3 , which were much lower than that reported in the literature. Mass transfer rates, therefore, may be another factor limiting the removal of some VOCs’ species. For example, the REs of VOSCs significantly decreased nearly to zero on day 180. As shown in Table 3, the inlet concentrations of DMDS and DMS changed from 17.2 and 6.0 μg m−3 to 2.2 and 0.02 μg m−3 , respectively. Hence, the decrease in REs for both compounds may be caused mainly by mass transfer rates rather than biological activities because such low inlet concentrations could not
Table 3. Inlet concentrations and REs of volatile organic sulphide compounds. Time (d)
Compounds
30
DMS DMDS CS2 DMS DMDS CS2
180
Inlet concentration (μg m−3 )
REs (%)
6.29 17.23 0.64 0.02 2.21 0.96
83.4 22.5 0.0 1.5 0.0 0.0
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in general inhibit the microbial activities. Similar results have been obtained in a full-scale biofilter treating odorous emissions from a composting plant.[36] Conclusion This study confirmed the complex composition of odorous emissions from a municipal manure treatment plant. Five categories of chemical substances were detected, including alkanes, olefins, aromatics, VOSCs and terpenes. Toluene, DMDS, DMS, xylene and ethylbenzene were the five most abundant pollutants. Under real operating conditions, the research presented here demonstrates that the removal of the complex VOCs using bamboo charcoal-based BTF is possible. The REs were related with the molecular weight and chemical structure of contaminants. Pre-acclimating microbial consortium could enhance the removal capabilities of the bioreactor on the corresponding pollutants. Aromatic compounds were the components that could be best efficiently removed from waste air stream. At very low inlet concentrations, the mass transfer rate was one important factor influencing the RE. Acknowledgements This work was supported by the Science and Technology project of Guangzhou, China (no. 2011J4200074), Science and Technology project of Guangdong province, china (no. 2012B091000160) and the Natural Science Foundation of China (no. 31270169).
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