Microsoft Word - 3debree.docx CHEMICAL ENGINEERING TRANSACTIONS VOL. 54, 2016 A publication of The Italian Association of Chemical Engineering Online at www.aidic.it/cet Guest Editors: Selena Sironi, Laura Capelli Copyright © 2016, AIDIC Servizi S.r.l., ISBN 978-88-95608-45-7; ISSN 2283-9216 Performance of Field Based Activated Carbon Systems for Odour Control Ari Shammay*a,b, Eric C. Sivreta, Bei Wanga, Ian Evansonb, Richard M. Stuetza a School of Civil and Environmetal Engineering, University of New South Wales, Australia b MWH, Sydney, Australia a.shammay@unswalumni.com Community tolerance for odours from sewer infrastructure is lessening, providing pressure to wastewater utilities to target and treat odour emissions from sewer networks. Gas phase odour abatement systems within sewer networks typically target hydrogen sulfide (H2S) as an odorant and overall odour indicator. However other compounds can occur naturally, or be present from trade waste, that are either odorous themselves or may impact on the performance of odorant removal in odour abatement systems. Activated carbon (AC) systems adsorb most contaminants during their lifetime until most active sites are depleted. Samples from the inlet and outlet of 6 AC filters in Sydney and Melbourne (Australia) were taken monthly over 18 months and analysed for volatile sulfurous compounds (VSCs) using gas chromatography (GC) coupled with a sulfur chemiluminescence detection (SCD). H2S was measured by Jerome 631-X hydrogen sulfide analyser for each sample. Each sample returned approximately 14 VSCs. After screening the data for wet weather and cooler periods, 6 VSCs were studied further. This paper evaluates and compares the performance of 6 activated carbon filters for each compound identified and each appropriate grouping of compounds. H2S and methyl mercaptan were found to be removed well, yet dimethyl disulfide was found to have a negative removal more often than it had a positive removal. Dimethyl sulfide and dimethyl trisulfide also suffered from negative removals, yet not as often as dimethyl disulfide. Carbon disulfide was removed as often as it was released. 1. Introduction Community complaints for odours from sewer infrastructure is increasing, placing pressure on wastewater utilities to target and treat odour emissions from sewer networks (Mudliar et al., 2010). Gas phase odour abatement systems within sewer networks typically target hydrogen sulfide (H2S) as the key odorant and overall odour indicator (Perez et al., 2010). However, other compounds can occur naturally, or be present from trade waste that are either odorous themselves or may impact on the performance of odorant removal in odour abatement systems (Sivret et al., 2013, Wang et al., 2014). Sivret and Stuetz (2010) surveyed nine Australian water utilities to identify the use of different odour treatment gas phase technologies. They found that of the 204 odour abatement units the utilities identified, 76% of these were adsorption based systems with approximately half being activated carbon (AC) systems. Whilst other operational performance formulas of odour abatement systems exist, such as elimination capacity, removal efficiency is most commonly reported as per the formula below (Deshusses et al., 2001): ( ) = × 100 (%) (1) Samples are taken on the inlet and outlet in order to determine the above parameters. In general, H2S is sampled more frequently than other contaminants as a common surrogate for all odours and typically used to identify the adsorption capacity of isolated contaminants for AC systems. This is primarily due to its prevalence in wastewater systems, but also due to the ease in which it can be measured and logged. Other compounds often require more thorough sampling and analysis to obtain inlet and outlet information that can be time consuming and expensive (Wang et al., 2012, Wang et al., 2014). Where multiple contaminants are evaluated for AC systems, these are typically only for a small number of sample points, typically only on DOI: 10.3303/CET1654047 Please cite this article as: Shammay A., Sivret E., Wang B., Evanson I., Stuetz R., 2016, Performance of field based activated carbon systems for odour control, Chemical Engineering Transactions, 54, 277-282 DOI: 10.3303/CET1654047 277 startup to establish performance. This makes it difficult to evaluate the performance of AC systems throughout their useful life. The combined effect of multiple contaminants is poorly understood, particularly where the presence of one substance may cause another to desorb. The goal of this study was to identify expected removal efficiencies for different VSCs in activated carbon systems operating in the field. 2. Methodology Samples from 9 AC based odour control systems at sewer pumping in two of Australia’s major cities, Sydney and Melbourne, were collected over 18 months. Sample locations were from both the inlet and outlet of the units, allowing removal rates to be determined. Samples were analysed for volatile sulfur compounds (VSCs) using gas chromatography (GC) coupled with a sulfur chemiluminescence detection (SCD). Hydrogen sulfide was measured using a Jerome 631-X hydrogen sulfide analyser (Arizona Instruments, USA) (Wang et al., 2015, Sivret et al. 2014). Each sample returned approximately 6 VSCs. A list of compounds identified, their odour descriptor, odour threshold and common sources are presented in Table 1. Table 1: Volatile sulfur compounds found in sewers (adapted from Suffet et al. (2004)) Odorant Abbreviation Descriptor OTV (ppmv)A Common Sources Carbon disulfide CS2 Disagreeable, sweet 0.21 2 Dimethyl sulfide DMS Decayed cabbage 0.000033 3, 4, 5 Dimethyl disulfide DMDS Rotten cabbage 0.0022 3, 4, 6, 7, 8 Dimethyl trisulfide DM3S Sickening, putrid, foul, decaying, garlic, onion Unknown 3, 5 Hydrogen sulfide H2S Rotten eggs 0.00041 1 Methyl mercaptan MM Unknown 0.00007 3 A - OTV: Odour Threshold Value, Nagata (2003) 1 – Anaerobic respiration of sewage 2 – Solvent 3 – Bodily functions 4 – Bacteriological action 5 – Decomposition of plants and animals 6 – Polymer and/or petroleum manufacturing 7 – Pesticides 8 – Food and soil additives The magnitude of this field based dataset (in terms of volume of samples and the range of compounds identified for such a duration) allowed it to be filtered for known outside influences on activated carbon performance in order to produce a baseline of ‘normal’ operating conditions, whilst still maintaining sufficient data to provide meaningful results. The factors that were filtered out are listed below: • Wet weather – samples with cumulative rainfall for the previous 7 days greater than 50mm • Spikes – samples where inlet concentration of any contaminant greater than 3 times the standard deviation above the average • Non-‘warm’ period – average of maximum daily temperatures for each city were used. Data was averaged over the preceding 30 days. The ‘warm’ period was defined as the duration from where the 30 day preceding average increased above the 60th percentile temperature until when it decreased below the 60th percentile temperature. Figures 1 and 2 show these times for Sydney and Melbourne during the sampling times. The remaining data was evaluated for completeness. Sites where there was insufficient data to make a meaningful analysis (generally <5 data points) were removed. Six sites were deemed to have sufficient information to analyse further. Details of these sites are shown in Table 2. Each carbon was replaced close to the start of the sampling period. 278 Figure 1: Sydney meteorological data over sampling period Figure 2: Melbourne meteorological data over sampling period 279 Table 2: Site details Site Year installed City Carbon type Upstream chemical dosing Approximate contact time Design flow rate AC-3 2003 Sydney Potassium Iodide (KI) Impregnated Ferrous chloride 3.0 s 4.0 m3/s AC-5 2010 Sydney Caustic impregnated Ferrous chloride 3.0 s 4.0 m3/s AC-6 2003 Sydney Potassium Iodide (KI) Impregnated Ferrous chloride 3.5 s 3.0 m3/s AC-7 2003 Sydney Potassium Iodide (KI) Impregnated Ferrous chloride 4.4 s 3.0 m3/s AC-8 2009 Melbourne 75% activated alumina / 25% proprietary ‘high H2S’ activated carbon None 5.4 s 0.15 m3/s AC-9 2006 Melbourne Caustic impregnated / virgin carbon blend Note 1 None Unknown 0.39 m3/s Note 1 – Blend proportion and volume unknown 3. Results 3.1 Inlet concentration The inlet concentration for each VSC is provided in Table 3. AC-8 generally experienced lower concentration of VSCs than other sites. AC-3 and AC-5 generally experienced a greater concentration of VSCs than other sites. Table 3: Inlet concentration Carbon Disulfide Dimethyl Sulfide Dimethyl Disulfide Dimethyl Trisulfide Hydrogen Sulfide Methyl Mercaptan (μg/m3) (μg/m3) (μg/m3) (μg/m3) (mg/m3) (μg/m3) AC-3 15.8 (10.7 to 190.2) 136.4 (38.1 to 331.2) 10.9 (3.7 to 41.5) 13.2 (3.8 to 22.3) 3.83 (2.58 to 10.18) 873.7 (157.6 to 1464.8) AC-5 16.8 (14.9 to 23.8) 89.3 (61 to 124.2) 6.2 (2.7 to 68.4) 7.7 (2.9 to 71.7) 4.81 (1.16 to 19.52) 400.2 (66.3 to 1335.8) AC-6 10.4 (nd to 47.7) 90.6 (11.4 to 100.2) 9.9 (1.7 to 15.2) 7.4 (1.2 to 10.4) 2.02 (0.54 to 3.00) 423.1 (39.9 to 741) AC-7 10.0 (5.5 to 11.4) 83.9 (60.8 to 94.4) 5.0 (2 to 14.6) 6.4 (3.4 to 19.9) 1.06 (0.78 to 3.07) 222.2 (105.2 to 264.7) AC-8 2.0 (nd to 3.9) 6.7 (3.3 to 14.1) 2.2 (0.1 to 3.4) 0.3 (0.3 to 2.2) 0.04 (0.01 to 0.09) 24.5 (11.8 to 57.2) AC-9 4.6 (nd to 11.3) 25.7 (1.1 to 44.1) 16.6 (0.1 to 24.9) 25.4 (0.3 to 56.2) 0.77 (0.49 to 1.95) 35.5 (14.2 to 332.1) All 11.2 (nd to 190.2) 77.1 (1.1 to 331.2) 7.4 (0.1 to 68.4) 8.2 (0.3 to 87.3) 1.78 (0.01 to 19.52) 257.9 (0.3 to 1464.8) Values given as medians with range in brackets nd – not detected 3.2 Removal efficiency The overall removal for each VSC is shown in Figure 3 as box and whisker plots showing whiskers from the 5th to the 95th percentile. Boxes are shown between the 25th and 75th percentile. Figure 4 shows the removal efficiency for each site. Good removal was observed for hydrogen sulfide and methyl mercaptan across all AC systems. The exception being AC-8, which did not remove methyl mercaptan as well as the others, despite a higher contact time. This may be due to the inlet concentration of contaminants being lower than other sites, leading to a lower removal efficiency. This may also be due to the bulk of the media being activated alumina, rather than an activated carbon system. 280 C ar bo n di su lfi de D im et hy l s ul fid e D im et hy l d is ul fid e D im et hy l t ris ul fid e H yd ro ge n Su lfi de M et hy l m er ca pt an -30000 -20000 -10000 -100 -50 0 50 100 Figure 3: Overall removal efficiency R e m o v a l E ff ic ie n c y ( % ) AC-5 R e m o v a l E ff ic ie n c y ( % ) Carbon disulfide Dimethyl sulfide Dimethyl disulfide Dimethyl trisulfide Hydrogen Sulfide Methyl mercaptan Figure 4: Individual removal efficiency 281 Dimethyl sulfide groups (including dimethyl sulfide, dimethyl disulfide and dimethyl trisulfide) were not removed as well as hydrogen sulfide and/or methyl mercaptan with frequent zero or compound release occurring. Dimethyl disulfide generation may be caused by the conversion of methyl mercaptan to dimethyl disulfide on activated carbon molecules (Bashkova et al., 2002). The caustic impregnated carbon performed better than the potassium iodide impregnated carbon with respect to dimethyl sulfide, and had a smaller range of removal efficiencies. Carbon disulfide was found to have variable removal efficiencies from each unit as evidenced by the spread of the 25th to 75th percentile box. Caustic impregnated carbon provided a smaller range of removal efficiencies than the other types of carbon. The increased contact time in AC-7 and AC-8 showed little to no improvement in the removal efficiency of any of the VSCs identified. 3. Conclusions AC systems for odour removal in sewer networks have been designed to remove the major odorant, hydrogen sulfide (Perez et al., 2010). The AC units under investigation removed both hydrogen sulfide and methyl mercaptan well. However dimethyl sulfide groups, particularly dimethyl disulfide, had low removal rates and were regularly generated or desorbed. As the dimethyl sulfide groups tend to have very low odour thresholds, this could lead to residual odours occurring from AC unit discharges. It is recommended that AC units for odour removal of sewer gases should be designed and provided to remove all known significant odorants, and that the design should cater for generated byproducts from the adsorption process. Further research into the performance of AC units in cooler vs warmer periods, as well as the long-term performance of non-VSC compounds in installed systems is recommended. Acknowledgments This work is supported by the Australian Research Council Linkage Project (LP0882016) with industry support from Barwon Regional Water Corporation, Gold Coast Water, Hunter Water Corporation, Melbourne Water, South Australian Water Corporation, South East Water, Sydney Water Corporation, Veolia Water Australia, Water Corporation of Western Australia and WQRA, as well as CH2MHill Australia. Ari Shammay is supported by MWH. 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