醇的使用花生壳为介质的有机生物滤池生物过滤

This article appeared in a journal published by Elsevier.The attached copy is furnished to the author for internal non-commercial research and education use,including for instruction at the authors institutionand sharing with colleagues.Other uses,including reproduction and distribution,or selling or licensing copies,or posting to personal,institutional or third partywebsites are prohibited.In most cases authors are permitted to post their version of thearticle(e.g.in Word or Tex form)to their personal website orinstitutional repository.Authors requiring further informationregarding Elsevier’s archiving and manuscript policies areencouraged to visit:/copyrightBiofiltration of methanol in an organic biofilter using peanut shells as mediumE.M.Ramirez-Lopez a ,J.Corona-Hernandez a ,F.J.Avelar-Gonzalez b ,F.Omil c ,F.Thalasso a,*aDepartment of Biotechnology and Bioengineering,CINVESTAV,Av.IPN 2508,E-07000Mexico City,MexicobDepartment of Pharmacology and Physiology,University of Aguascalientes,Av.Universidad 940,20100Aguascalientes,Mexico cInstitute of Technology,University of Santiago de Compostela,E-15706Galicia,Spaina r t i c l e i n f o Article history:Received 25October 2006Received in revised form 6October 2008Accepted 11October 2008Available online 22August 2009Keywords:Gas treatmentBiofiltration carrierAgricultural byproducts Methanol degradationa b s t r a c tBiofiltration consists of a filter-bed of organic matter serving both as carrier for the active biomass and as nutrient supply,through which the polluted gas passes.The selection of a suitable medium material is of major importance to ensure optimum biofilter efficiency.Peanut shells are an agricultural byproduct locally available in large quantities at a low price in most tropical and sub-tropical countries.A previous study showed that peanut shells are physically and chemically suitable for biofiltration.This paper pre-sents the results obtained during a six month biofiltration experiment using peanut shells as medium and methanol as air pollutant.It is shown that peanut shells are potentially suitable as biofiltration medium,since degradation rates of up to 30kg MeOH/m 3d with an empty bed residence time of 19s was obtained.The biofilter showed a good resistance to shock load and no operational problems were observed.Ó2009Elsevier Ltd.All rights reserved.1.IntroductionDifferent cleaning technologies of gaseous effluents have been developed.Among these technologies,biological methods are increasingly applied for the treatment of air polluted by a wide variety of pollutants.Biofiltration is certainly the most commonly used biological gas treatment technology.Biofiltration involves naturally occurring microorganisms immobilized in the form of a biofilm on a porous medium such as peat,soil,compost,synthetic substances or their combination.The medium provides to the microorganisms a hospitable environment in terms of oxygen,temperature,moisture,nutrients and pH.As the polluted air stream passes through the filter-bed,pollutants are transferred from the vapour phase to the biofilm developing on the packing particles.Given enough residence time,the microorganisms metabolise the pollutants to their primary components (such as carbon dioxide and water in the case of carbonaceous pollutants)plus additional biomass and innocuous metabolic products (Ott-engraf,1987;Wani et al.,1997).The absorption and/or adsorption capacity of the filter media is thus continuously renewed by the biological oxidation of the sorbed pollutants (Wani et al.,1997;Kennes and Thalasso,1998;Devinny et al.,1999;Pineda et al.,2004).Undoubtedly,biofiltration provides an economic,efficient,simple and versatile treatment method for a wide variety of both organic and inorganic pollutants,including numerous compounds classified as hazardous,odorous and/or toxic.The selection of the medium material is of major importance to ensure biofilter efficiency.A large number of materials have been used (Kennes and Thalasso,1998).Bohn et al.(1996)has listed 13important physical,chemical and biological characteristics for good biofilter media.Additionally,as biofiltration is a low cost technology and because large amounts of medium material are usually needed,low cost materials locally available are preferred.A previous study showed that peanut shells are potentially an interesting biofiltration medium (Ramírez-López et al.,2003).Pea-nut shells are locally available in large quantities at low price in most tropical and sub-tropical countries and have interesting physical and chemical characteristics:large specific surface area,neutral pH,large water holding capacity,nutrients for microbial growth and limited pressure drops when packed into a biofilter.In this context,peanut shells were selected as biofiltration medium material to study the treatment of a gaseous stream polluted with methanol.Methanol is an industrial solvent largely used in inks,resins,adhesives and dyes production,listed as one of the major Air Pollutants included in the EPA list of hazardous air pollutants.This paper presents the main results obtained during a contin-uous six months biofiltration experiment.The study included the stability of the medium and the biofilter response to short-term shock loads.2.MethodsPeanut shells were obtained from a peanuts oil factory located in the Chiapas State (México).The peanut shells were used as wasted without any previous treatment or inoculation.Peanut0960-8524/$-see front matter Ó2009Elsevier Ltd.All rights reserved.doi:10.1016/j.biortech.2008.10.064*Corresponding author.Tel.:+525557473320;fax:+525557473313.E-mail address:thalasso@cinvestav.mx (F.Thalasso).Bioresource Technology 101(2010)87–91Contents lists available at ScienceDirectBioresource Technologyj o u r n a l ho m e p a g e :w w w.e l s e v i er.com/locate/biortechshells were previously physically and chemically characterized (Table1;Ramírez-López et al.,2003).A stainless steel lab-scale reactor was built(diameter0.25m; height0.86m)with42L of total volume and an operating volume of20L.Air and water/nutrient solution were fed jointly on the top of the reactor using an atomising Venturi type nozzle.The atomis-ing nozzle was the type156.330.30.16from Lechler(Fellbach,Ger-many).This atomiser was previously characterized(Thalasso et al., 1993).The gasflow rate was obtained from a compressed air dis-tribution system and controlled by a valve and aflowmeter(Gil-mon,Barrington,USA).The airflow rate was maintained between1.95and3.90m3/h(98–195m3/m3h)and this stream was polluted with methanol as a model gaseous pollutant.Metha-nol was injected into the compressed air distribution line,through a vaporisation tank using a peristaltic pump(Masterflex pump C/L 6–60rpm;Cole Parmer,Mexico).Methanol concentrations were regulated in order to reach volumetric loading rates from2to 55kg MeOH/m3d.The liquid supply was maintained at approxi-mately0.07–0.13L/d(3.5–6.5L/m3d).Methanol degradation rates were determined from the inlet methanol gas concentration and the outlet gas and liquid concentrations.Prior to the biofiltration experiment and in order to distinguish the biological degradation from the abiotic sorption of methanol, wet peanut shells(41%moisture content)were sterilised at 120°C for30min and placed into the biofilter.The reactor was fed with a specific gas and waterflow rate of100and 3.5Â10À3m3/m3h,respectively.The methanol loading rate was main-tained at2.25kg/m3d.Influent and effluent gas samples were fre-quently analysed.Except during thefirst period of the biofiltration experiment (day0to day30),the liquidflow injected to the biofilter contained buffer and nutrients solution in order to promote a higher biolog-ical activity.The nutrient solution contained(in mg/L):KH2PO4 5120;Na2HPO4Á2H2O2720;(NH4)2SO4876;MgSO4Á7H2O400; EDTA20;FeSO4Á7H2O10;MnCl2Á4H2O 2.4;CoCl2Á6H2O0.9; ZnSO4Á7H2O0.5;CuSO4Á5H2O0.4;CaCl2Á2H2O2.0;Na2MoO4Á2H2O 0.4;Inositol4.0;pyridoxine chloride2.0;thiamine chloride2.0; pH7.0.The water/nutrient solution was injected continuously using a Masterflex pump(model755-05,Masterflex pump C/L Sys-tem;Cole Parmer,México).The experiment was run at ambient temperature.Effluent gas temperature and humidity were fre-quently measured using a thermohygrometer controller(Taylor 5368,Taylor,Mexico).Pressure drops through the column were continuously measured using a water column manometer.pH of the influent and effluent liquid solution were measured using a pH meter(Consort C835,Consort,Belgium).Methanol concentration of the influent and effluent gas phase as well as the liquid effluent was determined by gas chromatogra-phy using a Perkin–Elmer GC chromatograph equipped with a2m Porapak Q column and a FID detector.From time to time,samples of peanut shells were taken for analysis.Apart of visual observation,the moisture content of the medium was measured according to the2.166method(AOAC, 2002)and the water holding capacity(WHC)was measured according to2.181b method(AOAC,2002).At the beginning and the end of the experiment,total nitrogen and total phosphorus content of the peanuts shell were measured according to Jackson’s methods(Jackson,1976).Total potassium was also measured by atomic absorption after ashing the sample at550°C(AOAC, 2002).Total aerobic microorganisms were counted using the plate count technique(Benson,1985).At the beginning and at the end of the biofiltration experiment a drying test of the peanut shells was carried out using a drying com-puterised tower at Celaya Institute of Technology(Celaya,Mexico). Prior to the drying test,the peanut shells were washed three times with tap water in an ultrasonic bath(150T,VWR,USA)for5min and then saturated with water for48h.Peanut shells were then put on a tray(0.18by0.27m and0.015m height)and introduced into the drying tower.An airflow of2m3/h at90°C was main-tained through the peanut samples up to constant weight(4–8h).The influent and effluent air temperature and humidity as well as the sample weight and temperature were continuously monitored.From the results obtained,the drying velocity versus the moisture content was plotted.3.Results and discussionThe biofilter wasfirst loaded with sterilized peanut shells to evaluate the abiotic methanol absorption.At the onset of this experiment,the effluent methanol concentration was close to zero. Twenty-four hours later,the influent and effluent concentrations were close enough to consider that the sorption equilibrium was reached.Considering the complete sorption curve(data not shown),the sorption capacity of thefilter-bed was estimated to about0.5kg MeOH/m3of medium,this value being obviously pro-portional to the influent methanol concentration.After the abiotic methanol sorption experiment,the reactor was filled with fresh,peanut shells(47%moisture content)and the bio-filtration experiment was started.During thefirst period(Table2), water was injected instead of nutrient solution and the gasflow rate and the volumetric loading rate were maintained at100m3/ m3h and2.76kg MeOH/m3d,respectively.As presented in Fig.1, the apparent degradation rate started close to the loading rate, due to the sorption mechanisms,and rapidly decreased to an elim-ination efficiency of45%.After few days,methanol removal effi-ciency increased and remained around80%.At day30,assuming that the removal efficiency was limited by nutrients,the liquid feeding was changed from water to nutrient solution.During the following42days of operation,the removal efficiency increased and reached90%(Fig.1).From day72to104 the inlet methanol concentration was increased to0.66g/m3,while the airflow rate was increased to191m3/m3h,maintaining the loading rate at3kg MeOH/m3d.This caused a continuous increase in the removal efficiency,up to values close to100%(Fig.1).At day 104,the loading rate was duplicated to6kg/m3d.This increase had a direct negative impact on the elimination efficiency,decreas-ing for few days to around85%.Progressively,the degradation rate returned to higher values and stabilised at around95%.At day135, the loading rate was increased to15kg/m3d and the degradation rate increased in the same proportion.Nevertheless,after a few days the elimination efficiency started to decrease.Up to the end of the experiment,the loading rate was increased three times to reach a maximum value of45kg/m3d.During this period,the deg-radation rate increased proportionally to the loading rate applied up to30kg/m3d.Nevertheless,during the same period of time,Table1Physico-chemical characteristics of peanut shells.Water holding capacity(kg/kg dry weight) 2.8±0.03Specific surface area(m2/m3)268±6Dry density0.223±0.022Dry bulk density0.052±0.01Void fraction(%)74.02±0.5Number of particle per m3220Â103pH 6.8±0.04Ash(%dry weight) 3.5±0.21Organic matter(%dry weight)95.7±0.72Total nitrogen(%dry weight) 2.3±0.1Total potassium(%dry weight)0.31±0.01Total phosphorus(%dry weight)0.025±0.001Total aerobic microorganisms(UFC/g)1Â10888 E.M.Ramirez-Lopez et al./Bioresource Technology101(2010)87–91the removal efficiency decreased progressively from90%to60%. During the complete experiment,the cumulative methanol degra-dation reached1400kg MeOH/m3of medium.The volumetric removal rates obtained during the biofiltration experiment indicate the suitability of using peanut shells as a bio-filter medium.The best average removal efficiencies(96%)were obtained with a volumetric loading rate of3kg/m3d and a removal efficiencies of92%were observed with loading rates of6kg/m3d. Table3shows that these values are comparable to those obtained by Shareefdeen et al.(1993),Lee et al.(1996)and by Arulneyam and Swaminathan(2003),using wood wastes,peat based and com-post-polystyrene biofiltration media,respectively.The methanol removal efficiencies observed during thefirst135days of the experiment satisfied gas emissions criteria of most important reg-ulatory agencies.Indeed,the effluent gas methanol concentration was below the time weighted average(TWA)threshold limits established by the American,Australian and European Health Agencies(260mg/m3,OSHA,1998;AIHA,1998;NPI,2008and 270mg/m3,CEC,1988).By increasing the loading rates,maximum methanol degrada-tion rates of about30kg/m3d were obtained during a few days period.Nevertheless,these removal rates were obtained at the ex-pense of an important efficiency decline,namely from100%to60–65%.During the experiment,pressure drops across the biofilter in-creased as a result of biomass growth,as commonly observed in biofilters(Ottengraf,1986;Morgan-Sagastume et al.,2001).While at the beginning of the experiment the pressure drops were about 50Pa/m,by the end of the experiment the pressure drops were about200Pa/m(Fig.2).These pressure drops were within com-monly reported values(Kennes and Thalasso,1998).The relative humidity of the influent gas was steadily around20%.The humid-ity of the effluent gas was not constant.At the beginning of the experiment the effluent gas humidity changed cyclically from 80%to values close to100%.These oscillations progressively de-creased and from the day150onwards,the relative humidity of the effluent gas remained constantly over98%(Fig.2).This obser-vation was not clearly understood but the growth of a biofilm on the medium,the increase of the HWC and of the drying velocityTable2Operational conditions.Periods(d)0–3030–7272–104104–135135–156156–163163–170170–178 Gasflow rate(m3/m3h)10196191187191198191189 Empty bed residence time(s)3736191919181919 Inlet methanol concentration(g/m3) 1.18 1.160.66 1.35 3.69 4.897.9710.64 Specific loading rate(kg/m3d) 2.88 2.67 3.02 6.0516.8723.1836.5048.18 Specific degradation rate(kg/m3d) 2.35 2.35 2.89 5.5914.3217.3323.6434.53 Elimination efficiency(%)8086969284726169 Outlet gas concentration(g/m3)0.1370.1720.0170.0680.3700.686 1.810 1.949Table3Methanol biodegradation reported for different biofilter media.Medium Inlet(g/m3)Eliminationefficiency(%)Removal rates(kg/m3d)Reference1 6.33– 2.71Shareefdeen et al.(1993)2 6.33– 1.25Shareefdeen et al.(1993)3 6.33– 1.74Shareefdeen et al.(1993)4 6.33– 2.10Shareefdeen et al.(1993)5 6.33– 1.80Shareefdeen et al.(1993)60.785–1000.50Lee et al.(1996)7-95 1.68Johnson andDeshusses(1997)8 1.395–98 3.5Mohseni and Allen(2000)9 2.07Arulneyam andSwaminathan(2003)100.3100 3.22Chetpattananondhet al.(2005)110.6696 3.02This study11 1.3592 5.59This study1.Peat/perlite.2.Polyurethane foam/peat.3.Polyurethane foam/perlite/vermiculite.4.Polyurethane foam/peat/perlite.5.Polyurethane foam/peat/vermiculite.6.Wood waste/perlite.post/wood chips.8.Wood chips/compost/perlite.post/polystyrene.10.Palm shells.11.Peanutshells.E.M.Ramirez-Lopez et al./Bioresource Technology101(2010)87–9189of the medium(described below)could be somehow involved, increasing water availability.The biofilter was operated at the ambient temperature.During the experiment,the average effluent gas temperature was21°C while the average daily maximum and minimum were25and 15°C,respectively.The maximum effluent gas temperature ob-served was43°C while the minimum observed value was11°C. The average daily temperature variation was over10°C(maximum 22°C,minimum2°C).These temperature variations were mainly due to the extreme climate of Mexico City,a high altitude city lo-cated at2200m over sea level.No apparent effect of temperature was observed on the pollutant removal efficiencies.The pH of the liquid effluent also changed significantly during the experi-ment.While the influent pH was7.0,for an unknown reason,at the beginning of the experiment,the effluent pH was over8.5 and decreased slowly to reach afinal constant value of6.5±0.2 after day60.Microbial growth was clearly observed in the form of biofilm covering the external part of the peanut shells(Fig.3).Due to the concavity of the peanut shells,part of the medium surface was iso-lated from the liquidflow.On this area a clear fungus growth was observed instead of a wet biofilm.Before the biofiltration experi-ment,bacterial density was1Â108CFU/g of dry peanut shells. At the end of the biofiltration experiment,the total bacteria count gave a result of3Â1011CFU/g of dry peanut shells.Excluding microbial development,the visual observation did not provide any clear evidence of structural nor physical modifica-tion of the peanut shells.Nevertheless,a closer characterization pointed out several changes.On thefirst hand,the WHC of peanut shells increased from74%at the beginning of the experiment to 81%at the end of the experiment.This could be explained by the presence of a hydrophilic biofilm developing on the medium.Be-fore the experiment,total nitrogen,potassium and phosphorus content of peanut shells were2.30%,0.31%and0.025%dry weight, respectively.At the end of the experiment,these values were re-duced to0.65%,0.14%,and0.008%dry weight,showing a clear con-sumption or washing-out of these elements(decreases of72%,55%, and68%,respectively).Moreover,as presented on Fig.4,the drying test carried out showed that used peanut shells permitted a higher drying velocity.Wani et al.(1997)previously reported that behav-iour in a compost biofilter.This higher drying velocity indicates an increased drying vulnerability of the biofilter.At the end of the biofiltration experiment,the loading rate was reduced to3kg/m3d for24h and a fast increase of the loading rate was then applied in order to evaluate the resistance of the biofilter to a shock load.In less than20h,the loading rate was increased from3to57kg/m3d.As presented on Fig.5,the elimination effi-ciency was increasing with the loading rate increase.The biofilter showed a good resistance to shock loads,probably by combination of abiotic and biological mechanisms,which is of major interest for potential full-scale applications where influent pollutant concen-trations are usually unstable.The lower methanol removal effi-ciency observed at the beginning of the short-term experiment can be explained as a result of a desorption mechanism.The reduc-tion of the applied volumetric rate from48(end of previous oper-ation)to3kg/m3d,caused a shift in the adsorption equilibrium to lower values,which implies that a certain amount of the methanol originally adsorbed into the packing material was desorbed into the airstream,thus leading to lower observed removal rates asob-Fig.3.Scanning microscope picture of the peanuts shell before the biofiltration experiment(A)and at the end of the experiment(B).90 E.M.Ramirez-Lopez et al./Bioresource Technology101(2010)87–91served by Baltzis and Androutsopoulou(1994).Afterwards,the high removal rates observed at the end of this experiment can be also attributed to a combination of abiotic and biotic phenomena. The increase of the methanol loading rate caused changes in the sorption equilibrium in the packing material,which resulted in higher apparent methanol removal rates.Since organic biofilter materials provide most of the nutrient supply to the microorganisms involved in biofiltration processes, a natural decay of medium materials is generally observed.In full-scale biofilters,the medium material must be replaced after 3–5years of continuous operation(Kennes and Thalasso,1998). One of the major aspects to be discussed is therefore the long-term behaviour of peanut shells as biofilter medium.Firstly,during the 180days of experiment,no operational problems such as clogging, activity inhibition or bulking have been observed.Secondly,no sig-nificant change of the peanut shells structure was visually ob-served.Nevertheless,a clear increase of the drying velocity (Fig.4)and of the WHC was observed,that indicates a modification of the medium structure.Thirdly,during the same period of time, the cumulative mass of methanol degraded reached1400kg/m3, which is equivalent to the treatment of air polluted by1g/m3of methanol with an average gasflow rate of100m3/m3h(average of polluted air treated in commercial biofilters)during20months. Thus,the long-term operation of peanut shells biofilter can be con-sidered as feasible.Nevertheless,a clear decay of the nitrogen, phosphorous and potassium content of the peanut shells was ob-served,additional long-term experiments should be preferably performed before deciding on the use of peanut shells as biofilter media.4.ConclusionsPeanut shells are locally available in large quantities at low price in most tropical and sub-tropical countries and can be suc-cessfully used as a biofiltration medium.During a continuous oper-ation of6months,treating a methanol polluted airstream in a lab-scale biofilter,peanut shells were able to induce active biomass growth and methanol removal rates of up to30kg/m3d.In parallel to the degradation rates,the major results obtained were:(i)the absence of operation problems such as clogging,bulking or process inhibition,(ii)a cumulative methanol degradation of1400kg/m3, and(iii)a good resistance to shock loads.In addition,a clear decay of the nitrogen,phosphorus and potassium content of the peanut shells was observed.These results confirm the potential of peanut shells as a biofilter medium but point out the need for a long-term experiment and/or other pollutants before deciding on the use of peanut shells as biofilter material.AcknowledgementsThe authors wish to thank Prof.R.Auria from the IRD,France and Prof.S.Revah from the National Autonomous Metropolitan University of Mexico for they active scientific and technical ad-vises,J.Ballinas from the Tuxtla Gutierrez Technological Institute for providing the peanut shells used in this study and Dr.E.Escam-illa from the Celaya Technological Institute for the drying experiments.ReferencesAmerican Industrial Hygiene Association(AIHA),1998.The AIHA1998Emergency Response Planning Guidelines and Workplace Environmental Exposure Level Guides Handbook.Association of Official Agricultural Chemists(AOAC),2002.Methods of Analysis of the Association of Official Analytical Chemists,13th ed.George Banta Company Inc.,Menasha,Wisconsin,USA.Arulneyam,D.,Swaminathan,T.,2003.Biodegradation of methanol vapour in a biofilter.J.Environ.Sci.–China15(5),691–696.Baltzis,B.C.,Androutsopoulou,H.,1994.A study on the response of biofilters to shock-loading.In:87th Annual Meeting and Exhibition.Air and Waste Management Assoc.,Cincinnati,OH(A905).Benson,H.J.,1985.Microbiological Applications:A Laboratory Manual in General Microbiology.Brown,Dubuque,Iowa.Bohn,H.L.,1996.Biofilter media.In:89th Annual Meeting and Exhibition.Air and Waste Management Assoc.,Nashville,Tennessee(96-WP87A.0).CEC,1988.Solvents in common use.In:Health Risks to mission of the European Communities,Cambridge,Royal Society of Chemistry,EUR1155. Chetpattananondh,P.,Nitipavachon,Y.,Bunyacan, C.,2005.Biofiltration of air contaminated with methanol and toluene.Songklanakarin J.Sci.Technol.27(3), 761–773.Devinny,J.S.,Deshusses,M.A.,Webster,T.S.,1999.Biofiltration for Air Pollution Control.CRC-Lewis Publishers,Boca Raton,FL,USA.Jackson,M.L.,1976.Análisis químico de suelos,Tercera edición.Omega,Barcelona, Spain,pp.300–303.Johnson,C.T.,Deshusses,M.A.,1997.Quantitative structure-activity relationships for VOC degradation in biofilters.In:Proceedings of the Fourth In situ On-site Bioremediation Symposium.Columbus,Ohio.Kennes,C.,Thalasso,F.,1998.Waste gas biotreatment technology.J.Chem.Technol.Biotechnol.72,303–319.Lee, B.D.,Appel,W.A.,Walton,M.R.,Cook,L.L.,1996.Treatment of methanol contaminated air stream using biofiltration.In:89th Annual Meeting and Exhibition.Air and Waste Management Assoc.,Nashville,Tennessee(96-RP87C.0).Mohseni,M.,Allen, D.G.,2000.Biofiltration of mixtures of hydropilic and hydrophobic volatile organic compounds.Chem.Eng.Sci.55,1545–1558. Morgan-Sagastume,F.,Sleep,B.E.,Allen,G.,2001.Effects of biomass growth on gas pressure drop in biofilters.J.Environ.Eng.127(5),388–396.National Pollutant Inventory(NPI),2008.Department of the Environment and Water Resource,Australian Government.Available form:<http://www.npi.gov.au/epg/npi/contextual_info/glossary.htm>.Occupational Safety and Helath Administration(OSHA),1998.Occupational Safety and Health Standards,Toxic and Hazardous Substances.Code of Federal Regulations29CFR1910.100.Ottengraf,S.P.P.,1986.Exhaust gas purification.In:Rehm,H.J.,Reed,G.(Eds.), Biotechnology.VCH Verlagsgesellschaft,Weinheim,Germany,pp.425–452 (Chapter12).Ottengraf,S.P.P.,1987.Biological system for waste gas elimination.TIBTECH5,132–136.Pineda,R.,Alba,J.,Thalasso,F.,Ponce-Noyola,T.,2004.Microbial characterization of organic carrier colonization during a model biofiltration experiment.Lett.Appl.Microbiol.38(6),522–526.Ramírez-López,E.,Corona-Hernández,J.,Dendooven,L.,Rangel,P.,Thalasso,F., 2003.Charaterization offive agricultural;by-products as potential biofilter carriers.Biores.Technol.88,259–263.Shareefdeen,Z.,Baltzis,B.C.,Oh,Y.-S.,Bartha,R.,1993.Biofiltration of methanol vapor.Biotechnol.Bioeng.41(5),512–524.Thalasso,F.,Ancia,R.,Willocx,B.,L’Hermite,P.,Naveau,H.,Nyns,E.-J.,1993.The ‘‘Mist-foam”concept:a concept for biological treatment of gaseous organic compounds.In:Vigneron,S.,Hermia,J.,Chaouki,J.(Eds.),Characterisation and Control of Odours and VOC in the Process Industries.Elsevier,Amsterdam,The Netherlands,pp.419–429.Wani,A.H.,Branion,R.M.R.,Lau,A.K.,1997.Biofiltration:a promising and cost-effective control technology for odours,VOC’s and air toxic.J.Environ.Sol.Health A32,2027–2055.E.M.Ramirez-Lopez et al./Bioresource Technology101(2010)87–9191。