[Abstract] This study was carried out in response to odour problems around a bitumen mixing and storage plant. The general objective of this study was to determine the potential of biofiltration for the treatment of air containing bitumen vapours. Two pilot-scale biofilters, a single-stage system and a two-stage system, were operated using a synthetic gas for a period of 106 days. Results demonstrated that a period of about 50 days was necessary to reach a steady state. The two biofilters performed very well in regards to H2S, while VOC treatment was much less efficient. Maximum elimination capacities of 25 g·m-3·h-1 for H2S and 5.3 g·m-3·h-1 for VOCs were obtained with the two-stage system. It was possible to establish certain operating conditions necessary for proper operation and to determine that a two-stage system is more efficient for the simultaneous treatment of H2S and VOCs

Buelna, Gerardo

Fanlo, Jean-Louis

Girard, Matthieu

Lessard, Paul

Turgeon, Nicolas

Repositorio da Universidade da Coruña

587Biofiltration of bitumenvapours – Operational aspectsMATTHIEU GIRARD1, JEAN-LOUIS FANLO2, NICOLAS TURGEON3, GERARDO BUELNA3AND PAUL LESSARD11 Civil Engineering Department, Pavillon Pouliot, University Laval, Québec, Qc., Canada,G1K 7P42 École des Mines d’Alès, 6 Avenue de Clavières, 30319 ALES Cedex, France3 Industrial Research Center of Québec, 333 Franquet street, Québec, Qc., Canada, G1P 4C7587ABSTRACTThis study was carried out in response to odour problems around a bitumen mixing and storageplant. The general objective of this study was to determine the potential of biofiltration for thetreatment of air containing bitumen vapours. Two pilot-scale biofilters, a single-stage system and atwo-stage system, were operated using a synthetic gas for a period of 106 days. Results demonstratedthat a period of about 50 days was necessary to reach a steady state. The two biofilters performedvery well in regards to H2S, while VOC treatment was much less efficient. Maximum eliminationcapacities of 25 g·m-3·h-1 for H2S and 5.3 g·m-3·h-1 for VOCs were obtained with the two-stagesystem. It was possible to establish certain operating conditions necessary for proper operation andto determine that a two-stage system is more efficient for the simultaneous treatment of H2S andVOCs.1 INTRODUCTIONThe deterioration of air quality, whether it is in terms of health risks or odour issues,has caused an increase in public awareness towards air pollution.  Furthermore, sincethe beginning of the 20th century, emissions of atmospheric pollutants in North Americahave been in continual increase (Delhoménie and Heitz, 2005).  This type of pollutionis caused by a number of different components which are released by a variety ofindustries.  Because of their effects on human health and their prevalence in industrialemissions, two types of pollutants are particularly interesting, VOCs and odours.588VOCs are organic compounds which have a vapour pressure above 10 Pa at20°C according to European regulations (Fanlo, 2006).  Due to the vague aspect ofthis definition, these components have a wide range of effects on human health andthe environment. VOCs can cause nausea, headaches, irritation of the nervous andrespiratory systems and even certain cancers (Delhoménie and Heitz, 2005). Theyalso contribute to the production of tropospheric ozone which is an importantcomponent of smog (Thérrien, 2005).Odours can be defined as the result of interpretation by the brain of an interactionbetween a volatile compound and the olfactory senses (Fanlo, 2006). The measurement ofodours is therefore difficult since there is no way to know beforehand whether a specificcompound is odorous or not. Odours can be described by their quality, hedonic tone andintensity and are often composed of sulphur, nitrogen or organic compounds (Brandy,1997). Reduced sulphur compounds, such as hydrogen sulphide (H2S), are reported toby highly odorous molecules. Symptoms can vary from simple discomfort, allergies ornausea to loss of concentration and depression (Météoglobe Canada Inc., 1993).Traditionally, the emission of air pollutants has been managed by physico-chemical treatment methods. However, biological treatment technologies are rapidlygaining in popularity because of their low investment and operating costs as well asthe simplicity of their operation (Michel, 1997). There are three types of bioreactors,the biofilter, the bioscrubber and the biotrickling filter, which are distinguished by themobility of the biomass and the liquid phase (Devinny et al., 1999). Biofiltration isthe oldest and most widespread biotechnology for the treatment of air pollutants (Jorioand Heitz, 1999). There are two distinct steps in the biofiltration process: transfer ofthe pollutants to the aqueous phase or the filter media and their degradation by themicroorganisms (Malhautier et al., 2005). There are many parameters to considerwhen designing and operating a biofilter, such as filter media, air flow, pollutants,moisture content, pressure loss, microorganisms, temperature and pH. Biofiltrationhas been used to treat a great deal of different components, several authors havecompiled some of the industrial and laboratory applications of this technology (Easteret al., 2005; Iranpour et al., 2005; Mulligan, 2002; Kennes and Thalasso, 1998).In recent years, the industrial sector of storage and use of bitumen has been inthe spotlight concerning its gaseous emissions. Bitumen is a residue of the distillationof petroleum which is used in many industries, as in asphalt production for example.When the bitumen is stored, it must be kept hot, around 170°C, to maintain its fluidity.This causes an important production of bitumen vapours, which can then disturb agreat deal of people. If solid bitumen contains mainly heavy hydrocarbons, its vapouris composed of much lighter compounds, such as VOCs and odourous substances ofwhich H2S is the most important (Cook et al., 1999).Biofiltration of single substances or of compounds from the same chemicalfamily (sulphur compounds, VOCs, etc.) is well documented but few studies haveM. GIRARD, J. L. FANLO, N. TURGEON, G. BUELNA AND P. LESSARD589examined the simultaneous treatment of pollutants from different families as is thecase of bitumen vapours. Koe and Liang (2005) studied two biofilter configurationsfor the co-treatment of toluene and H2S. They found that H2S significantly decreasedthe pH of the filter bed without pH control and that a two-stage biofilter was moreefficient to treat H2S and toluene. Closer to bitumen vapours, Cook et al. (1999)published a paper on the biofiltration of emissions from a polymer-modified asphaltplant.  The objective of their study was the removal of H2S since it was considered asthe main contributor to the odour problem. This was achieved very well except duringpeaks of H2S which reached 30 000 ppmv. However, VOC removal was negligible.The general objective of this study was to determine the potential of biofiltrationfor the treatment of air containing bitumen vapours. Two biofilters configurationswere studied: a single-stage system and a two-stage system. A secondary objectivewas to determine the operating parameters necessary for proper operation.2 MATERIALS AND METHODS2.1 BITUMEN VAPOUR ANALYSISConsidering the technical difficulties of reproducing bitumen vapours in alaboratory setting, it was decided to create a synthetic gas representative of thesevapours to test the pilot-scale biofilters.  A portion of solid bitumen was first heated to170°C and then samples of vapour were drawn directly from the headspace above thebitumen. Analysis of the vapours was done first with a GC-MS (gas chromatographwith a mass spectrometer detector) for a general approach and then with a GC-PFPD(gas chromatograph with a pulsed flame photometric detector) for sulphur compounds.It was possible to identify over a hundred compounds, ranging from light to heavyhydrocarbons (C-2 to C-24) with several sulphur compounds. Subsequently, thisanalysis was used to select specific compounds to incorporate in the synthetic gas.The final composition of the gas is given in table 1.Table 1.Composition of the synthetic gas.Component Concentration(mg·m3)Hexane 73.5Decane 73.5Toluene 12.5p-Xylene 12.5Thiophene 3H2S 150BIOFILTRATION OF BITUMEN VAPOURS-OPERATIONAL ASPECTS5902.2 EXPERIMENTAL SETUPThe experimental setup used for this study is represented by the schematic inFigure 1.Figure 1. Schematic of the biofilters.The biofilters are 25 cm in diameter and were packed with 1 m of an organicfilter media made up of wood chips and peat moss. Biofilter 1 was composed only ofcolumn 1 and biofilter 2 was composed of columns 2A and 2B. The gas flow rate wasconstant at 4.9 m3·h-1, corresponding to a gas velocity of 100 m·h-1 and empty bedresidence times of 36 and 72 seconds for biofilter 1 and 2 respectively. H2S wasintroduced with a bottle of liquefied gas while the blend of the five VOCs was injectedusing a micropump. A nutrient solution was periodically sprayed on the surface of thebiofilters to maintain proper humidity and to ensure bacterial growth. Sampling portswere located at the inlet, the outlet and at 5 equidistant intervals over the height ofeach biofilter. The two biofilters were operated for a period of 106 days according tothe schedule in table 2:M. GIRARD, J. L. FANLO, N. TURGEON, G. BUELNA AND P. LESSARD591Table 2.Operation schedule.Phase Description Duration (d)I Start-up 50II H2S starvation period 23III pH control 29IV Removal of hexane 42.3 ANALYTICAL METHODSH2S concentrations were measured with a gas chromatograph (GC) equippedwith a photo-ionisation detector (PID) from HNU Systems with an oven temperatureof 80°C, a temperature of 200°C for the injector and the detector and an analysis timeof 2 minutes. Total VOC concentrations were determined with a Graphite 700 flameionisation detector (FID) from Cozma which was calibrated with methane at 100 mg·m-3before every series of measurements. Individual VOC concentrations were evaluatedwith an HP-5890 Series II GC-FID equipped with a 30m×0.53mm HP-1 column.Oven temperature was held at 80°C and analysis time was 6 minutes.  Samples wereinjected automatically with the sampling pump on each of three systems.3 RESULTS AND DISCUSSION3.1 H2S ELIMINATIONA graph of the H2S concentration versus time is presented in Figure 2.Figure 2. H2S concentration versus time.BIOFILTRATION OF BITUMEN VAPOURS-OPERATIONAL ASPECTS592Immediately after start-up, the biofilters offered a certain treatment, system 1reduced the H2S concentration to about 130 mg·m-3 while system 2 reached 45 mg·m-3.Two weeks later, H2S was removed below the detection limit by biofilter 2. The rapiddrop for biofilter 1 around day 20 was due to an increase in liquid flow to rectify theinadequate moisture level in this biofilter. After 40 days of operation, both biofiltersremoved all of the H2S that was introduced. Even the starvation period (phase II)between days 50 and 64 had no effect on performance. During the first 70 days ofoperation, lixiviate pH slowly decreased and reached values around 1 due to sulphuricacid production from the biodegradation of H2S. To counteract this acidification andmaintain a neutral pH, sodium bicarbonate was added in the nutrient solution duringphase III. This adjustment of the pH had no obvious effect on H2S removal. Using theintermediate sampling ports, it was possible to determine that only 80 cm of biofilter1 and 60 cm of biofilter were necessary to remove all the H2S. This corresponds toelimination capacities of 18.8 g·m-3·h-1 and 25 g·m-3·h-1.3.2 VOC TREATMENTResults for total VOC concentration in this section are given in methaneequivalents since the FID was calibrated using this gas. A graph of total VOCconcentrations versus time is given in Figure 3.Figure 3. Total VOC concentration versus time.From Figure 3, it can be seen that there is no biodegradation for the first 25days, then biofilter 2 starts removing the VOCs and their concentration falls to astable value of 75 mg·m-3 on day 50. It is this stabilization that was used to define thestart-up time of the biofilters. During this first phase, biofilter 1 only begins to treatM. GIRARD, J. L. FANLO, N. TURGEON, G. BUELNA AND P. LESSARD593VOCs, removing about 10 mg·m-3. There is an interesting connection to be madebetween the complete removal of H2S and the start of VOC treatment by biofilter 2.This could just be a coincidence, but it could also be caused by the acidifying effect ofH2S (Koe and Liang, 2005).  However, it could also be the standard time required bythe microorganisms to adapt to the specific VOCs in the synthetic gas.During phase II, H2S starvation had a negligible effect on biofilter 2, but asignificant improvement of VOC removal for biofilter 1 was observed. Adjustment ofthe pH in phase III didn’t seem to have any effect on VOC elimination. Maximumremoval efficiencies of 20% and 60% were obtained with biofilter 1 and 2 respectively,corresponding to elimination capacities of 3.5 g·m-3·h-1 and 5.25 g·m-3·h-1.3.3 HEXANE REMOVALTo explain the mediocre results concerning total VOC removal, individual VOCconcentrations were examined.  Figure 4 shows the average removal efficiency fordays 53 to 67 for the five individual VOCs and the total VOC.Figure 4. Individual VOC Removal Efficiencies for Days 53 to 67.From the data shown in Figure 4, it is possible to establish an order ofbiodegradability: alkanes > aromatics > thiophene. However, hexane does not fit inthis classification since it was barely treated by the biofilters. It was also this compoundthat greatly limited overall VOC elimination. According to Maier et al. (2000), mediumsize alkanes (n-alkanes ranging from C-10 to C-18) are more biodegradable than smallerand larger molecules of the same family. The low solubility of long alkanes reducestheir bioavailability while it is a toxicity problem with short alkanes. This could explainwhy hexane was not removed by the biofilters whereas decane was almost entirelytreated.BIOFILTRATION OF BITUMEN VAPOURS-OPERATIONAL ASPECTS594Knowing this, it is possible to recalculate removal efficiencies while consideringonly the four VOCs other than hexane. Maximum values of 41% and 98% were obtainedfor biofilters 1 and 2 using this method. It was also decided to remove hexane fromthe synthetic gas while maintaining the same total VOC load in phase IV. This changecaused a rapid decrease in total VOC concentrations for both biofilters as can be seenin Figure 3. Unfortunately, due to technical difficulties, it was not possible to pursuethe experiments further to observe complete VOC removal. Nevertheless, it waspossible to obtain elimination capacities of 6.5 g·m-3·h-1 and 8.6 g·m-3·h-1 for biofilters1 and 2.4 CONCLUSIONSThis study was carried out in response to odour problems around a bitumen mixingand storage plant. The potential of biofiltration for the treatment of a synthetic gasrepresentative of bitumen vapours was shown. Of the two configurations tested, thetwo-stage system proved to be more efficient for the simultaneous removal of H2Sand VOCs. Adequate filter bed moisture content and pH were essential operatingparameters for proper performance. Maximum elimination capacities of 25 g·m-3·h-1for H2S and 8.6 g·m-3·h-1 for VOCs were obtained with the two-stage biofilter.5 ACKNOWLEDGEMENTSThis project was funded by the Laboratoire du Génie de l’Environnement Industriel(LGEI) at the École des Mines d’Alès (EMA) in France and by the Industrial ResearchCenter of Québec (CRIQ). Matthieu Girard was supported financially by a Master’sgrant from the Natural Sciences and Engineering Research Council of Canada(NSERC).REFERENCESBrandy, J. (1997) Hydrodynamique et transfert gaz-liquide dans un bioréacteur. Application autransfert d’émissions gazeuses par lavage biologique. Thesis from the Université de Pau etdes pays de l’Adour, France.Cook, L.L., Gostomski, P.A. and Appel, W.A. (1999) Biofiltration of asphalt emissions: Full-scaleoperation treating off-gases from polymer-modified asphalt production. Environ. Prog. 18(3):178-187.M. GIRARD, J. L. FANLO, N. TURGEON, G. BUELNA AND P. LESSARD595Delhoménie, M-C. and Heitz, M. (2005) Biofiltration of air: a review. Critical Reviews Biotechnol.25(1-2): 53-72.Devinny, J.S., Deshusses, M.A. and Webster, T.S. (1999) Biofiltration for air pollution control.CRC Press LLC, United States. 109 p.Easter, C., Quigley, C., Burrowesa P., Witherspoon, J. and Apgar, D. (2005) Odor and air emissionscontrol using biotechnology for both collection and wastewater treatment systems. Chem.Engin. J. 113: 93-104Fanlo, J.-L. (2006) Odeurs et Composés Organiques Volatiles-Contexte général, Problématique etProcédés de traitement, Course Notes, École des Mines d’Alès, FranceIranpour R., Cox H.H.J., Deshusses, M.A. and Schroeder, E.D. (2005) Literature review of airpollution control biofilters and biotrickling filters for odor and volatile organic compoundremoval. Environ. Prog. 24(3): 254-267.Jorio, H. and Heitz, M. (1999) Traitement de l’air par biofiltration, Canadian Journal of CivilEngin. 26: 402-424.Kennes, C. and Thalasso, F. (1998) Waste gas biotreatment technology. J. Chem. Technol. Biotechnol.72(4): 303-319.Koe, L.C.C. and Liang, J. (2005) Comparison of two-stage and single-stage biofiltration for H2Sand toluene co-treatment. Proceedings of the International Congress Biotechniques for AirPollution Control, La Coruña, Spain, October 5-7 2005, pp. 95-102.Maier, R.M., Pepper I.L. and Gerba, C.P. (2000) Environmental Microbiology, Academic Press,United States, pages 380, 381 and 385.Malhautier, L., Khammer, N., Bayle, S. and Fanlo, J-L. (2005) Biofiltration of volatile organiccompounds. Appl. Microbiol. Biotechnol. 68(1): 16-22.Météoglobe Canada Inc. (1993) Applicabilité de méthodes de mesure d’odeurs au voisinage deslieux de production, d’entreposage et l’épandage du purin de porc : rapport final, Québec:Ministère de l’Environnement, 193 pages, QEN/AE93-8/6Michel, M-C. (1997) Traitement de l’hydrogène sulfuré par biolavage, Master’s Dissertation. LavalUniversity, Québec.Mulligan, C.N. (2002) Environmental Biotechnology – Technologies for Air, Water, Soil, and Wastes,ABS Consulting, United States, pages 39-76.Thérrien, M. (2005) Les composés organiques volatils (COV) dans l’air ambiant au Québec, Bilan1989-1999, Québec, Ministère du Développement durable, de l’Environnement et des Parcs,Direction du suivi de l’état de l’environnement, ISBN 2-550-46063-4, Envirodoq n° ENV/2005/0283, 24 pages.BIOFILTRATION OF BITUMEN VAPOURS-OPERATIONAL ASPECTS

Biofiltration of bitumen vapours - Operational aspects

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Biofiltration of bitumen vapours - Operational aspects

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