Investigation of factors on a fungal biofilter to treat waste gas with ethyl mercaptan

Journal of Entironmental Sciences Vol 16. No 6. pp, 898-900, 2004Article n:I0010742(2004)06-89803CLC number: X512 Document code: AInvestigation of factors on a fungal biofilter to treat waste gas with ethymercaptanZHU Guo-ying, LIU Jun-xinResearch Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China. E-mail: jxliu@ mail rcees t cn andzhuguoyingl 163. com)Abstract: The biofilter is cost-effective for the waste gases treatment. The bacterial is the main microorganism in the conentionalbiofilters. However, it faces some problems on the elimination of hydrophobic compounds. In order to overcome these probens, thebiofilters with fungi were developed. The objective of this study is to investigate the factors affecting ethyl mercaptan( EM)-doadationsing a fungal biofilter. A laboratory experiment was set up. The effects of loading rate, empty bed residence times( EBRT) andy on EMdegradation were investigated. Over 95% removals of EM could be achieved, under the condition of the influent loadings belowi g/(mh). Removal efficiencies improved to 98% with EM loading decreased to 45 g/m h). For long EBRT of 58 s corresponding to abw rateof 0. 3 m/h. the EM removal efficiencies of over 98% were observed. However, when EBRt was decreased to 14 S, th emovalefficiencies fell under 80%. The ph range of 3-5 was feasible to fungiKeywords: off-gas treatment; odor; ethyl mercaptan; biofilter: fungiSchafer, 1995). EM can be produced from proteins degraion, theIntroductionpetroleum industry, waste and wastewater( Cha. 1999). Arding toOff-gases containing voc and odors may do great harm to characteristic of EM, fungi are more efficient than bacterias degradeenvironment and people's health. There are many methods for treating EM. Therefore, it is important that enriches EM-degrading igi in athem, such as physical methods, chemical methods and biologicalbiofilter and develops an EM-degrading biofilter with fungi, ich aremethods. Biological methods are widely applied in the process of off- stable at low phand low water activitygases purification for their low investment and operational costs. BiofilterThe purpose of this experiment is to investigate the sects ofis an economie and efficient biological technology for treating off-gases. loading rate, EBRT. and ph on the performance for treating in of-In the biofilter, the off-gases are foreed to rise through a packed bed gas to determine the optimal operating conditions of the bier withattached microorganisms. It is especially good for cases with a large fungivolume and a low concentration( Lim, 2001 ). Bacteria and fungi are twe1 Materials and methodsant microorganisms groups in the biofilter. Bacteria haveadvantage of rapid substrate uptake and growth, and they are dominant 1.1 Biofilter with fungia conventional biofilter, although fungi are also present( DevinnyEM treatment, a laboratory-scale biofilter was ad, The1999).However,the conventional biofilter, based on compost and experimental sel-up is presented in Fig. I. The volume of i biofilteracteria activity, faces some problems to eliminate hydrophobic was 4.8 L, with 0. 75 m of height. Air from a blower w bubbledcompounds. Because of the low solubility in water, the hydrophobic through an EM solution in a water-bathed Erlenmeyer fad o makempounds are poorly absorbed by the bacterial biofilms. Besides that. volatile EM. Concentrations of EM in the gas phase could b aried bythe biofilter operational stability is often hampered by acidification and adjusting the temperature of the water bath. The EM-rich a vas thendrying out of the filter bed( van Groenestijn, 2002)mixed with a main air stream, which then flowed through packingTo overcome these problems, a biofilter with fungi on inert packing material. The airflow rates were adjusted by mass flow conners, Themalerial has been developed. Fungi are more resistant to acid and dry gas entered the biofilter continuously from the top. Tr relevantconditions than bacteria, which is a helpful property when operating operating conditions used during the test period are collected Table Ifilters. Moreover. it is hypothesised that the aerial mycelia of fungi, During start-up the biofilter was operated with an EM inlet centrationwhich are in direct contact with the gas, can take up hydrophobic of 0.10 g/m and a gas flow rate of 0. 15 m/h, resulting inI specificacterial biofilm surfaces. In EM load rale of 3. 125principle the application of fungi in biofilters may offer two advantages:1) Stringent control of the water activity and/or pH in the filter bed isTable 1 Operating condition ranges of fungal biofilterless important, since fungi are generally tolerant to low water activityOperatin nngeand low pH. (2)Reduction of the water activity in the filter bed mayload Talesimprove the mass transfer of poorly water soluble waste gas compoundsGas now rateRelatively better growth of fungi at low pH compareEBRT14-邯erage bacterial species is a well known fact. A low pH is aprerequisite for fungal development in the biofilter, coinciding with a1.2中国煤化工high vOC elimination capacity( van Groenestijn, 2001)C N MH Gterials such as compst, peatMercaptans are important impurities distributed among petroleum and wehave been used as biofilter media. These rtia weproducts. They are toxic and produce odor. Ethyl mercaptan(EM)can found to have high removal capability due to high physica dsorptionause odor nuisance at a concentration as low as about 0.001 ppm capability and water holding capacity, but also to w sormeFoundation itemNational Natural Science Foundation of China( No, 50178066): Corresponding authorNo 6Investigation of factors on a fungal biofilter to treat waste gas with ethyl mercaptansteady state was over 20 g/(m. h), and the removal rates were over90%. After 150 d of operation, EC was 26 g/(m .h),and the removalof emthat the fungal biofilter has a high elimination capacity to EM. The EMremoval rates obtained in this study were significantly higher than that∴reported by other researchers using the bacteria biofilter( CWRTAICE。°0.10aIrEM Humidifier Mixing005c Inlet°gFig 1 Schematic diagram of the fungal biofilter for off- gas treatment with EMdisadvantages, such as the media decomposition and compactiTherefore some media that can hold andactive microbes, without degradation and distortion, were developedFig 2 Ethyl mercaptan inlet and outlet concentrations(Lim,2001)during the fungal biofilter operationIn order to overcome limitation of the conventional biofilter. a newbiofilter medium, polyurethane foam was developed. The polyurethane10015foam was served as solid supports for microbial attachment( Golla, 1994;910日experimental system of Fig. I, polyurethane foam cube with pore sizep0. 5 mm and weight 3. 6 mg/em was used. The specific surface area ofthe polyurethane foam cubes was 320m/m1.3 Nutriento Removal o Flow rategal biofilter to assure microbial activity, The compositionof nutrient solution is shown in Table 2. There is no carbonFig 3 Evolution of the removal efficiency and the flowTable 2 Nutrient medium provided to the fungal biofilte2. 2 Effect of loading rate on elimination capacityConstituentsConcentrationThe experimental results showed that maximum EM removalcapacity of the biofilters was highly influenced by the concentration(orloading rate)of EM in the gas. In order to detect the highest capacity ofthe fungal biofilter, the relationship between inlet concentration andelimination capacity of EM was investigated( Fig. 4)Fe(NO3)·9H201.4 Definitions and performance reporting100% removalThe performance of the experimental systems as eliminationcapacity( EC )or removal efficiency( RE )was expressed by Equation(1)and Equation (2). It is a function of the inlet and outlet gasconcentrations( C, u and CE. oa), the air flow rate( Q)and the packebed volume(V ). The elimination capacity represents the amount ofaded per unit volume of fungal biofilter and time: it isoften reported as a function of the pollutant loading( L)( Equation 3)k(")Q((m…h)(1)55Inlet loading rate, gEM/(m-n)REFig 4 EM elimination capacity of the fungal biofilter as a funetion of inletLsymbols2 Results and analysisremoval2.1 Experimental resultsHsolid line indicales 100中国煤化工roCNMHGsed with increased inletThe flow rate of off-gas. EM concentrations and removal efficiency loading, but an opposite trend was observed for the removal efficiencyare shown in Fig. 2 and Fig 3 respectively. The biofilter was operatedGreater than 95% removals could be achieved under inlet loadings belowith a low gas flow rate of 0. 15 m /h to culture the fungi for degrading 50 gEM/(m.h). Removal efficiencies improved to 98% with EMEM during start-up. The experimen was in steady state afterloading decreased to 45 g/(m h). For higher inlet load, the EMpu片芳数"mu: manon capacity or En removal is not complete and EC moves off the inlet loa,ECkZHU Guo-ying et al.aches the maximum value allowed to estimate the limits within which However, an opposite trend was observed for pH between 4 and 8. Thisthe biofilter functions. In this study, maximum elimination capacity indicated that the most EM degraded fungi in the biofilter preferreECm, )of EM is 62 gEM/(m.h). This reduction of removal weak acidic environment. In the ph range of 3-5, the removalfficiency of EM as a function of the load could be explained by the efficienc ie of EM was over 90%limitations of the microbial metabolisms( Aizpuru, 2001: Cook. 19993 ConclusionsMcNevin, 2000). When loading rate or inlet concentrationspreponderate over the maximum elimination capacity of the biofilter, theThe remoral efficiency of EM in off-gas and some effect factorsremoval efficiency decreaseshave been investigated using a bench-scale biofilter with fungi. The2.3 Effect of EBRT on removal efficiencyexperiment carry on over one year, and the results are as followsIn order to study the influence of airflow rate on the EM removalThe fungal biofilter can remove efficiently EM from off-gathe Em concetmaintained at 0.40 g/ elimination capacity of EM in steady state was over 26 g/(m.h),andmand the airflow rate was changed to change EBRT. Fig.5 shows the the removal rates were over 99%6impact of EBRT on the average removal efficiency of EM in the biofilterThe loading rate, EBRT and pH value have prominent effect on theis to be noted that the removal efficieney inereased with EBRT. Thus, elimination capacity of the fungal biofilter. In this study, the maximumfor long EBrT of 58 s corresponding to a flow rate of 0.3 m/h, the EM elimination capacity of EM is 62 gEM/(m.h). however. correspondingremoval efficiencies of over 98% were observed. A long EBRT was removal efficiency is under 90%. If the loading rate of EM decreased tofavorable for the em degradation because the contact time between the 45 g/(mh), its removal efficiencies improved to 98%. In order tomicroorganisms and EM was increased( Delhomenie. 2002). However, obtain a high removal efficiency of EM, about I min of EBRT and 3-5when EBRT was decreased to 14 s, the removal efficiencies of EM fell to of ph value are feasibleunder 80%. The reason of this result was that contacting time betweenthe hypha and the EM was too short and microorganisms had insufficient Referencestime to perform the required degradation on the available amount of EMAizpuru A. Malhautier L, Roux J C ef al., 2001. Biofiltration of a mixture ofvolatile organiAssociation,51(12):1662-1670Center for Waste Reduction Technologies uf the American Institute of Chemical900Engineers( CWRTAICE). 1999. Biofiltration: project report, scale-up and[RIha J M. Cha WS. Lee J H, 1999. Removal of organo-sulphur odour compoundby Thiobacillus novellusBiochemistry, 34(6-7): 659-665Cook L L, Gostomski PA. Apel WA, 1999, Biofiltration uf asphalt75EBRT.s[J. Environmental Progress, 18(3):178-187Cox HH J, Houtman J H M. Doddema H J et al., 1993. Enrichment of fungi5 Influence of the EBrT on the removal efficiency ofand degradation of styrene in biofilters[J Biotechnology Letters. 15(7)737—742Devinny JS, Deshusses M A, Webster T s, 1999, Biofiltration for air pollution2. 4 The effect of pH valuecontrol. Boea Raton[ M].FL USA: CRC Press LLCThe pH value in the biofilter depending on the contaminant being Delbomenie M C. Bibeau L, Bredin n et al.2002.Biofiltration of airtreated and the characteristics of the microbial ecosystem. The optimalonpost-basedbed[ J]. Advances in Environmental Research, 6(3):239-254pH of the bacteria biofilter is in the 7-8 range. Changes of the pHGolla P S, Reddy M P, Simins M K et al., 1994. Three years of full-scaleocess operation at Moundsville WWTP[J],Watercontaining organics lead to H, SO, buildup. Process failure is the mostx,310:15dramatic result of acidic biofilters dominated by bacteria. Fungi growHe PJ, Liming S, Zhiwen Y ef al., 2001. Removal of hydrogen sulfide andmethyl mercaptan by a packed tower with immobilized micro-organism beadsrelatively better at low pH compared with the average bacterial speciesJ]. Wat Sci Tech. 44(9): 327-333lidman J A. Brenner R C. Shah H J, 1988. Pilot-plant evaluation of porousThe ph values of the nutrient feed and leachate were measured. itbiomass supports[J]. Journal of Environmental Engineering, 114(5):was found that the difference between the two pH values were within 0. I Kondo m. Hozu S. Inamori Y, 1992. Simultaneous removal of BOD and nitrogenpH units, which indicated that the ph of the environment within thefungal biofilter could he controlled by adjusting the pH of the nutrientfeed. Fig. 6 shows the removal efficiencies of EM as a function of pH of Lim J S, Park S J. Kou J K et al., 200I. Evaluation of porous ceramie ashe nutrient feed. It was seen that Em removal efficiencies increased asmicrobial carrier of biofilter to remove toluene vapor[[ JJ.Environmethe ph of the nutrient feed increased in the pH range of 2Technology, 22: 47-56Lu C, Lin M R, Chu C, 2002. Effects of pH, moisture, and flow pattern ontriekle-bed air biofilter performance for BTEX removal[ J 1. Advances inEnvironmental Research. 6: 99-106McNevin D, Barford J, 2000. Biofiltration as an odour abatement strategy[J]ng intIrnal.5:231-242.Schafer中国煤化工control in wastewater treatmentASCE. manuals and reportsCNMHGKen w I n van, Braakman NJR. 2001. Biofiltersbased on the action of fungi J]. Water Sci&Tech, 44(9):227-232pH valuevan Groenestijn JW, Liu J X. 2002. Removal of alpha-pinene from gases usingbiofilters containing fungi[ J], Atmospheric Environment, 36: 5501-550Fig. 6 The relationship between the pH value and EMReceived for review December 13, 2003. Accepted May 8. 2004)