FATE OF SULFUR ODORANTS IN ODOUR COLLECTION

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1 FATE OF SULFUR ODORANTS IN ODOUR COLLECTION Gavin Parcsi 1 *, Julie le Gouézigou 2, Eric C. Sivret, Xinguang Wang 1, Richard M. Stuetz 1 1. UNSW Water Research Centre, UNSW, Sydney, NSW, Génie Energétique & Environnement, INSA, Lyon, France * g.parcsi@unsw.edu.au ABSTRACT Odorous emissions from intensive livestock operations, waste management and wastewater treatment facilities are becoming an increasing concern to facility managers with decreasing buffer distances and increasing community awareness. Regulations relating to odour emissions are governed by numerical determination by dilution olfactomtry, however despite standardisation of olfactometry methodologies, little work has been done investigating the transformation of volatile species within a sample between source and result. Highly volatile sulfur species (e.g. mercaptans) can contribute significantly to the malodorous character of an emission. The chemical speciation of an emission can often yield misleading results pertaining to the chemical species present at the source owing to transformation of chemicals within a sample during transport, storage and analysis. This paper outline areas of potential chemical transformation and work taken to understand the stability of selected volatile sulfur species. INTRODUCTION The emission of an odour from any facility can cause nuisance to a local receptor, whilst receptors may have differing sensitivities to different odorants. In Australia a normal receptor is someone who has a sensitivity of between 20 and 80ppm n- butanol as outlined in the standard for odour determination by dilution olfactometry (AS/NZS 4323 Part 3: 2001). Different emissions sources will have different chemical compositions, and have a different odour character. The use of dilution olfactometry to give an odour a numerical value aids in legislation and regulation, however the chemical composition gives more value in designing and implementing effective mitigation and abatement stratergies. Volatile organic compounds (VOCs) are often considered the main contributor to odorous emissions and methodologies (often based around US EPA TO series) exist to accurately quantify these species. However, the emission of volatile sulfur species, in particular from facilities where biological processes (Kadota and Ishida 1972; Rajagopal and Daniels 1986) are present, can be a major contributor to odour emissions (Headley 1987). Volatile organo-sulfur compunds (VOSCs) often found in emissions from intensive livestock (O'Neill and Phillips 1992; Trabue, Scoggin et al. 2008), waste management (Kim, Jeon et al. 2006) and wastewater treatment (Defoer, De Bo et al. 2002; Ras, Borrull et al. 2008) facilities include thiols (mercaptans) and mono- and poly- thioethers (sulfides, disulfides and trisulfides). The volatility of the thiols lend them to dimerisation (via a thiyl radical (RS ) intermediate) to dithioethers (disulfides). Speculation as to the exact mechanism still continues (Jee and Tao 2006) (Cardey, Foley et al. 2007; Witt 2008), in addition experimental evidence supports the dimerisation of thiols to disulfides. The oxidation of disulfides is also possible, with disulfide monoxides, disulfide dioxides and disulfide tetraoxides and also sulfuonic acid (RSO3H) have been isolated. The reduction of disulfides is also a reaction pathway that can be pursued by a chemical mixture. Therefore the results of chemical speciation of sulfur containing emissions should be issued with a caveat relating to the presence of one compound in the VOSC suite may indicate the presence of related VOSCs at the source. Maintaining the sample integrity through the collection stage is the principle concern, that is to ensure that the sample collected reflects accurately the composition of the matrix from which it has been sampled. The methodologies that are used for VOC collection (in particular sorbent tubes and SPME fibres) have been adapted for capture and analysis of VOSCs (Przyjazny 1985; Murray 2001; Nielsen and Jonsson 2002; Lestremau, Andersson et al. 2004; Ras, Borrull et al. 2009). The use of canisters (Trabue, Scoggin et al. 2008) or odour bags (Kim, Choi et al. 2006) for sampling offers a better method of capturing the whole sample, however caution should be paramount when addressing the introduction of the sample to the instrument to avoid sample degradation. Post collection, the samples must be transported and possibly stored prior to chemical or odour e v a l u a t i o n. T h e d e c a y, d e g r a d a t i o n o r transformation of the sample may result in

2 fallacious results. Exposure of the sample to light, and/or temperature fluctuations could result in chemical transformation and lead to erroneous conclusions. The aim of these experiments is to improve our understanding of the fate and transformation of volatile organo-sulfur compounds during storage under controlled conditions. EXPERIMENTAL METHOD Sample Preparation Neat standards were purchased of ethyl mercaptan, dimethyl disulfide, diethyl disulfide and a 5ppm (v:v) standard of methyl mercaptan and ethyl mercaptan in methanol (Sigma-Aldrich, Australia). The neat standards were made up in 5ppm (v:v) in methanol for injection into different odour bags. Each standard was made fresh for each series of experiments and disposed of after 24hrs to ensure reliability. For the laboratory scale experiments, the standards were injected into odour bags of 1 or 10 L volume. The bags were made of Tedlar (polyvinyl fluoride), Nalophan (poly(ethylene terephtalate)) or Mylar (polyethylene terephthalate). These materials are commonly used to collect odour samples from field locations for assessment by dilution olfactometry. Each standard was injected into quartz wool with a stream of high purity (moisture and hydrocarbon free) air passing though into a odour bag. The gas phase samples were then sealed prior to injection into the analytical instrumentation. The primary standards (ethyl mercaptan, dimethyl disulpide and diethyl disulfide) were each injected (5 ul) into 1 L sample bags to accurately determine the retention times. To observe the transformation of the thiols 100 ul of the methyl mercaptan and ethyl mercaptan standard was injected into a 10 L bag. The larger sample size enabled the same sample to be observed throughout a time sequence of 100hrs. Sample Storage Following sample preparation the samples were maintained at room temperature (22±2ºC) and exposed to constant low intensity ambient fluorescent lighting. The sample bags were each attached to an individual sampling port for the duration of the observation to limit sample losses. Sample Analysis Pre-Concentration Prior to injection of the sample into the gas chromatograph the samples were pre-concentrated utilising a whole air sampling device (Markes Int l. AirServer - Unity). The AirServer was configured to collect a 100 ml sample from the bulk matrix to analyse. The Unity was equiped with a specific sorbent trap (U-T6SUL, Markes Int l. UK) targeted towards sulfur and highly labile species. To maintain sample integrity the flow path of the AirServer was held at 50ºC and Unity was held at 120ºC. Through experimental experience the importance of addressing the potential sources of sample degradation have been elucidated, for example the use of some sorbents do not favour the accurate representation of the compounds within some matrices. Separation The chromatographic separation was performed using a Agilent 7890 GC (Agilent Technologies, Australia). The samples matrices were separated on a intermediate polarity (6% polymethylsiloxane) column (DB-VXR, 30 m 0.25 mm 1.40 µm, J&W Scientific, Agilent Technologies, Australia). The carrier gas was ultra high purity helium (BOC Gases, Australia) pressure controlled to maintain a constant flow of 1.8 ml.min -1. The oven temperature was programmed as follows: 50 Detection The chemicals within the sample matrices were detected using a Sulfur Chemiluminescence Detector (355 SCD, Agilent Technologies, Australia) operated to the manufacturers specifications. The use the SCD allowed for significantly lower levels of detection than could be afforded by a mass selective detector. EXPERIMENTAL RESULTS Preliminary experiments and results from prior studies indicated the mercaptans (thiols) would dimerise under moderate conditions to form disulfides and possibly further oxidise to disulfide monoxides, disulfide dioxides and disulfide tetraoxides. The experiments undertaken indicated that there was a loss of total sulfur due to permeation through the bag material and also transformation of chemical species as time progressed. Figures 1~3 illustrate the typical chromatogram from an injection of the ethyl mercaptan and methyl mercaptan mixture; Figure 1 is representative of a sample taken at approximately T0hrs, Figure 2 represents a sample at approximately T24hrs and Figure 3 represents a sample taken at approximately T48hrs. These figures may appear identical, however subtle variations reflect the dynamic interactions between the sulfur species present in these sample. Quantitation of the results reflected a change in the ratios of the chemical species present and also a reduction in the total amount of sulfur compounds within a sample matrix.

3 The principle reaction that was observed throughout the experiments was the dimerisation of the thiols to disulfides, that is methyl mercaptan to dimethyl disulfide and ethyl mercaptan to diethyl disulfide, and the co-formation of the asymmetric disulfide; ethyl methyl disulfide. This reaction had been observed under preliminary investigation utilising a mass spectrometer to identify the key chemical components. MeSH + EtSH Table 1 lists the key sulfur species that were investigated during this study. Table 1 Retention times of target sulfur species RI (min) Chemical 2.20 ethyl mercaptan (EtSH) 5.36 dimethyl disulfide (DMDS) 6.71 methyl mercaptan (MeSH) 7.03 ethyl methyl disulfide (EMDS) 7.90 diethyl disulfide (DEDS) There is speculation that the other peaks present in the spectra are from further oxides of the symmetric disulfides (dimethyl- and diethyl-), however the low relative abundances of these peaks reflect the low concentration. Further work will seek to elucidate the actual identity of the other peaks. The different bag materials yielded different storage characteristics, under the controlled conditions. Illustrated in Figures 4~9 are the respective amounts of the different sulfur species that were the main focus of this experiment. Table 2 outlines the percentage loss in the total mass of sulfur recovered from each of the bag materials after approximately 24 and 48 hrs. Table 2 - Percentage Loss of Total Sulfur Material 24 hrs 48 hrs Tedlar 0% 12% Nalophan 1% 10% Mylar 5% 19% The loss of total sulfur observed during the experiment is illustrated in Figure 4. For the first 24 hrs the sample maintains moderate integrity for the Nalophan and Tedlar material. The recovery from the Mylar proved to be more unreliable. As the time continued beyond 24 hrs there was an observed and significant (>10%) loss from all three of the bag materials. Investigation of the individual matrix component quantities revealed there was variability during the time sequence. Whilst there was a notable decrease in the overall amount of sulfur in the successive samples, there was also a variation in the percentage composition of the matrix elements. The transformation of chemicals within an odour sample will potentially change the character of the odour. Observing the variation in the composition of the odour matrix will improve the understanding of the interactions of the chemicals. Ethyl mercaptan showed the highest rate of transformation, dimerising to diethyl disulfide. Figure 5 illustrates the decrease in the mount of ethyl mercaptan within the samples, whilst Figure 6 illustrates to increase in the amount of diethyl disulfide. Table 3 outlines the variation in the percentage composition of ethyl mercaptan within the samples. Table 3 Percentage Composition of Ethyl Mercaptan. Material 0 hrs 24 hrs 48 hrs Tedlar 27% 24% 22% Nalophan 21% 18% 16.5% Mylar 25% 21% 18% The transformation of the assymetric disulfide ethyl methyl disulfide first incresased in abundance during the first 24 hrs and then decreased in abundance during the remainder of the time sequence. This sporadic transformation is illustrated in Figure 9. Table 4 outlines the variation in the percentage composition of ethyl methyl disulfide throughout the experiments. Table 4 Percentage Composition of Ethyl Methyl Disulfide. Material 0 hrs 24 hrs 48 hrs Tedlar 5% 9% 7.5% Nalophan 5% 9% 7% Mylar 6% 10.5% 9% The experimental results yielded a moderate stability of methyl mercaptan and dimethyl disulfide, as illustrated by Figure 7 and Figure 8. Observed to maintain stable concentrations throughout the entire experiment, further work is currently being performed to elucidate the rationale behind the unusual results from the laboratory scale experiments. FURTHER WORK

4 These experiments were conducted under controlled conditions, with temperature and lighting maintained consistent throughout the experimental process. This reflects idealise sampling conditions, and it is accepted that fluctuations in temperature may result in accelerated sample transformation, this is the focus of current ongoing work. The samples that were used for this study were also highly idealised, being pure compounds in dry high purity air, a realistic sample would constitute a multitude of different chemical species including VOCs, and other volatile and non-volatile species that will potentially interact within the sample post collection. Investigating potential interactions within sample matrices is also a component of current studies. CONCLUSION The results of this preliminary laboratory scale investigation show that there is a definite and measurable transformation of volatile organo-sulfur compounds during storage in polymer odour bags. Tedlar and Nalophan were observed to maintain the highest sample integrity during the first 24 hrs, however all three materials showed significant losses beyond 24 hrs, highlighting the importance of rapid assessment of a sample after collection. The numerical determination of an odour concentration is a result of the chemical composition of the sample, if the chemical composition of a sample transforms between source and analysis there is the potential for erroneous results to be generated. Understanding the potential pathways of reaction of volatile compounds and in particular volatile organo-sulfur compounds will aid in addressing concerns over the determination of odour concentrations, and assist in accurately determining the odour concentration at the source. ACKNOWLEDGMENT The experiments were funded as part of Australian Research Council Linkage Project LP with industry support from Barwon Regional Water Corporation, Gold Coast Water, Hunter Water Corporation, Melbourne Water Corporation, South Australia Water, South East Water Limited, Sydney Water Corporation, United Water International, Water Quality Research Australia, and Water Corporation Western Australia. REFERENCES Cardey, B., S. Foley, et al. (2007). "Mechanism of Thiol Oxidation by the Superoxide Radical." The Journal of Physical Chemistry A 111(50): Defoer, N., I. De Bo, et al. (2002). "Gas chromatography-mass spectrometry as a tool for estimating odour concentrations of biofilter effluents at aerobic composting and rendering plants." Journal of Chromatography A 970(1-2): Headley, J. V. (1987). "GC/MS identification of organosulfur compounds in environmental samples." Biological Mass Spectrometry 14(6): Jee, J. and F.-M. Tao (2006). "Reaction Mechanisms and Kinetics for the Oxidations of Dimethyl Sulfide, Dimethyl Disulfide, and Methyl Mercaptan by the Nitrate Radical." 110(24): Kadota, H. and Y. Ishida (1972). "Production of Volatile Sulfur Compounds by Microorganisms." Annual Review of Microbiology 26(1): Kim, K.-H., G.-H. Choi, et al. (2006). "The effects of sampling materials selection in the collection of reduced sulfur compounds in air." Talanta 68(5): Kim, K.-H., E.-C. Jeon, et al. (2006). "The emission characteristics and the related malodor intensities of gaseous reduced sulfur compounds (RSC) in a large industrial complex." Atmospheric Environment 40(24): Lestremau, F., F. A. T. Andersson, et al. (2004). "Investigation of Artefact Formation During Analysis of Volatile Sulfur Compounds Using Solid Phase Microextraction (SPME)." Chromatographia 59(9): Murray, R. A. (2001). "Limitations to the Use of Solid-Phase Microextraction for Quantitation of Mixtures of Volatile Organic Sulfur Compounds." Analytical Chemistry 73(7): Nielsen, A. T. and S. Jonsson (2002). "Quantification of volatile sulfur compounds in complex gaseous matrices by solid-phase microextraction." Journal of Chromatography A 963 (1-2): O'Neill, D. H. and V. R. Phillips (1992). "A review of the control of odour nuisance from livestock buildings: Part 3, properties of the odorous substances which have been identified in livestock wastes or in the air around them." Journal of Agricultural Engineering Research 53: Przyjazny, A. (1985). "Preconcentration of volatile organosulfur compounds from the atmosphere on selected porous polymers." Journal of Chromatography A 333: Rajagopal, B. S. and L. Daniels (1986). "Investigation of mercaptans, organic sulfides, and inorganic sulfur compounds as sulfur sources for the growth of methanogenic bacteria." Current Microbiology 14(3): Ras, M. R., F. Borrull, et al. (2008). "Determination of volatile organic sulfur compounds in the air at sewage management areas by thermal desorption and gas chromatography-mass spectrometry." Talanta 74(4): Ras, M. R., F. Borrull, et al. (2009). "Sampling and preconcentration techniques for determination of volatile organic compounds in air samples." TrAC Trends in Analytical Chemistry 28(3): Trabue, S., K. Scoggin, et al. (2008). "Field sampling method for quantifying volatile sulfur compounds from animal feeding operations." Atmospheric Environment 42(14): Witt, D. (2008). "Recent Developments in Disulfide Bond Formation." 2008(16):

5 Figure 1: Chromatogram obtained from a Mylar bag at T 0hrs Figure 2: Chromatogram obtained from a Mylar bag at T 24hrs Figure 3: Chromatogram obtained from a Mylar bag at T 48hrs

6 Figure 4: Loss of total sulfur from the different sample bags through 5 days. Figure 5: Loss of Ethyl Mercaptan from the different sample bags through 5 days.

7 Figure 6: Increase of Diethyl Disulfide from the different sample bags through 5 days. Figure 7: Variation of Methyl Mercaptan from the different sample bags through 5 days.

8 Figure 8: Variation of Dimethyl Disulfide from the different sample bags through 5 days. Figure 9: Variation in Ethyl Methyl Disulfide from the different sample bags through 5 days.

Sampling and Analysis Methodology Concerns for Volatile Organo-Sulfur Compounds (VOSCs)

Sampling and Analysis Methodology Concerns for Volatile Organo-Sulfur Compounds (VOSCs) Paper 614 Eric C. Sivret, Gavin Parcsi, and Richard M. Stuetz UNSW Water Research Centre, The University of New South