Center forAgriculturalMolecularBiology

ANEWJERSEYCOMMISSION ONSCIENCEANDTECHNOLOGYCENTER

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Bioscrubbing of Gaseous Emissions

Published by

Interdisciplinary Bioremediation Working Group

Cook College, Rutgers The State University of New Jersey

Time

9:00 a.m.

9:15 a.m.

9:45 a.m.

lo:15 a.m.

lo:30 a.m.

11:15 a.m.

11:45 a.m.

12:15 p.m.

1:30 p.m.

PROGRAM

BIOSCRUBBING OF GASEOUS EMISSIONS

Wednesday, November 18, 19928:30 a.m. - 2:30 p.m.

A Mini-Symposium Sponsored by NJDEPE and

the AgBiotech Center of Rutgers University

Introductory Remarks

Biofiltration of Industrial Solventsand Solvent Mixtures

Principles of Packed-bed BiofilterModelling and Design

Break

Biological Waste Gas Purification inEurope

Biological Vapor-phase Treatment:Practical Operating Regimes

Cornposting Facility Odor ControlUsing Biofilters

Lunch break

Discussion

AuthorsISneaker underlined)

Richard Bartha, Rutgers University, NewBrunswick, NJ

Young-Sook Oh, Richard Bartha, RutgersUniversity, New Brunswick, NJ

Basil Baltzis, Zarook Shareefdeen, New JerseyInstitute of Technology, Newark, NJ

R.M.M. Diks, S.P.P. Ottengraf, TechnischeUniversiteit Eindhoven, The Netherlands

Paul Togna, Envirogen, Lawrenceville, NJ

Frederick C. Miller, Sylvan Foods,Worthington, PA

Richard Bartha, Moderator

Marine & Coastal Sciences Building, Room 102BDudley Road and College Farm Road, Cook College

Rutgers University, New Brunswick, NJ 08903

INTRODUCTORY REMARKS

Richard Bartha, Rutgers University

I wish to welcome all participants to our Mini-Symposium and I am gratified by theunexpectedly high turnout of over 80 persons. This certainly indicates the timeliness of ourSymposium topic. I wish to thank the speakers who agreed to contribute, and I especiallywelcome Dr. Ottengraf and his associate Dr. Diks from the Netherlands. Dr. Ottengraf isregarded as the foremost expert in the biological treatment of air emissions, and his participationlends our Mini-Symposium international stature. I wish to thank the New Jersey Departmentof Environmental Protection and Energy for its financial support of this event and Dr. LauraMeagher and the Agbiotech Institute for all the planning and organizational details.

To comply with the Clean Air Act and its 1990 Amendments without losing competitiveedge constitutes a severe challenge to many U.S. manufacturers. They will need all availabletools to meet this challenge. The biological treatment of volatile organic compound (VOC)emissions is one of the possible air pollution abatement options that, until very recently, hasbeen relatively unknown and certainly underutilized in the USA. In contrast, the biologicaltreatment of air emissions has extensive scientific literature and widespread practical use inEurope. In part to create more awareness for the biological treatment option, and in part toextend biotreatment to various xenobiotic solvents and solvent mixtures, with the sponsorshipof the Hazardous Substances Management Research Center (NJIT, Newark) my laboratory atRutgers University cooperated with Dr. B. Baltzis at NJIT to perform experimental andmodeling work in this area. This program was initiated in 1989 and we will report here ourprogress in this area which was novel to our two laboratories. Dr. Diks and Dr. Ottengraf willreport on the much more extensive utilization of VOC biotreatment in Europe. Dr. P. Tognafrom Envirogen will report on the recent construction and operational experience with a pilot-scale biofilter unit. Dr. F.C. Miller from Sylvan Foods will tell about operational experienceswith a classic industrial biofilter for odor control. We will end our Mini-Symposium with abrief discussion period that will formulate some recommendations designed to promote anawareness and an increased use of the biotreatment option for gaseous emissions. I am lookingforward to a very informative and enjoyable session!

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Microbial Scrubbing of BTX Solvent Mixturesand Chlorinated Solvents from Air.

YOUNG-SOOK OH AND RICHARD BARTHA

Depcirtment of Biochemistry and Microbiology, Cook College,Rutgers University, New Brunswick, New Jersey 08903-0231

Microbial enrichments immobilized on perlite/peat-packed columns removed vapors ofseveral industrial solvents from air. The same technique was applied now to scrub commonsolvent mixtures such as benzeneltoluene/p-xylene (BTX) and chlorinated solvents such aschlorobenzene (CB)Io -dichlorobenzene ( D C B ) a n d nitrobenzene(NB). Solvent vaporconcentrations in metered air flow were measured by GC prior to and after passage throughthe column. In long-term experiments, liquid medium was recirculated and replenished asneeded. At air flow rates of 36.7 m3m-2h-1, BTX was removed at up to 16 g rnq3 packing h-l.The column half close to the inlet removed preferential ly toluene and benzene with verylittle xylene degradation. Xylene was removed predominantly in the distant half of thecolumn. CB and DCB scrubbing led to a rapid pH drop and column inactivation, but withrecirculation of l iquid through a neutralizing unit, sustained CB and DCB scrubbing wasachieved at rates up to 300 g me3 packing h-t. NB was removed at 67 gmm3h-‘. The columnsdid not lose their act iv i ty when solvent loading was interrupted for several days andscrubbing resumed as soon as solvent vapor was reintroduced.

The clean Air Act Amendments of 1990 greatly expandthe EPA rule-making authority over toxic or hazardous airpollutants. The law lists 189 chemicals and the toxicchemical regulations have specifically targeted theemissions of organic and halogenated organic compounds.All industries which emit volatile organic compounds willbe subject to new federal and state permits. Among variousemission control measures such as chemical, physical, andbiological treatments, biological systems, known asbiofiltration or bioscrubbing, appear to be the most cost-effective and environmentally sound. Currently,biofiltrations are employed primarily in Europe, however,research on and commercial use of biofilters have been lessextensive in the USA. In response to these problems, weinitiated research on the “Microbial Scrubbing of VOCEmissions”. Initially, bioscrubbing of nonhalogenatedsingle solvents such as methanol, butanol, acetonitrile, andhexane was performed and by mathematical analysis of thedata a model was developed that describes the removal of asingle solvent. As the next step, solvent mixtures,chlorinated solvents, and nitroaromatic solvents weresubjected to bioscrubbing.

MATERIALS AND METHODS

Isolations of solvent-util izing microorganisms.Microorganisms were enriched under selected solvent

vapors from sludge with pre-exposure history to varioussolvents. Individual microbes were isolated on plates ofmineral agar and consortia were established in a liquidmineral medium.Quantitative tests for solvent uti l izations.

Quantitative tests for solvent utilization were conducted inclosed flasks. Flasks received a liquid mineral medium,isolated microbes, and 20 to 350 ppm(w/v ratio) solvent.Single solvents(B, T, X, CB, DCB, and NB) and solventmixtures(BT, BX, TX, BTX, CB-DCB) were tried in flasktests. The solvent disappearance from the headspace of theflask was monitored by GC. At the same time, increase inbiomass was measured by protein determination(Bradford,1976) and chloride released as the result of CB and DCBdegradation was quantified as described by Bergmann andSanik(1957).Apparatus for scrubbing of solvent vapor.

Figure 1 shows the apparatus used for the measurement ofmicrobial solvent vapor scrubbing.

WATER FLOW N R F L O W

TREATMENTCOLUMN

Fig. 1. Flow-through apparatus for measurement ofmicrobial solvent vapor scrubbing. A glass column waspacked with porous support material, 60% perlite and 40%peat moss (v/v ratio). Air samples were taken for GCanalysis by gas-tight syringe prior to, after and at threelevels within the column. For long-term experiments, acontinuous water recycling system and a pH control unitwere added. Removal rates were calculated as g solventremoved per m3 filter bed per hour.

RESULTS

Quantitative tests of solvent utilization.Removal of BTX. Fig. 2 and Fig. 3 show benzene

and xylene removal by a single strain which was identifiedas Pseudmwnas putida and selected as the most effectivestrain in the removal of BTX among the isolated strains.

o! , 1 I I I0 20 40 60 80 loo

Time (min)

Fig. 2. Removal of p-xylene vapor from the headspace offlasks in the presence of benzene. gXylene was removedonly in the presence of benzene or toluene and no biomassformation resulted from xylene degradation. p-Xylenemetabdiim was blocked at dimethylcatechol stage and theaccumnlating intermediate was polymerized.

0 .a.,.‘$.0 20 40 60 00 loll

Time (min)

Fig. 3. Removal of benzene vapor from the headspace oflasks. Benzene concentration was fixed at 8 ppm(w/v) anttoluene was added in the range of 0 to 173 ppm. Similaexperiments were performed with toluene. Both benzencand toluene appeared to be removed by the same enzymesystems and competitive inhibition between the substratewas apparent.

Removal of chlorobenzene. All flask experimentfor the removal of chlorobenzene were conducted witlmicrobial consortia enriched on chlorobenzene.

Time(h)

Fig. 4. Removal of CB vapor from the headspace of ffasks.Concentration of CB used was 110 ppm. Chloride releaseand biomass formation were measured along with CBremoval, and 30% of the CB added was converted tobiomass. Similar experiments were performed with DCB.

Bioscrubbing of solvents.Biuscrubbing of BTX. Bioscrubbing of BTX mixture

was conducted with a consortium enriched on BIX.

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Layer 2

TI

Layers of the column

Fig. 5. Bioscrubbing of BTX mixture. The columnconsisted of four layers; layer l(closest to the inflowingair), layer 2, layer 3, layer 4(closest to the out flow). Theflow rate was 36.7 m3m-2h-1 and individual concentrationsof benzene, toluene, and p-xylene were 0.16.0.23, and 0.18g m-3, respectively. The graph shows % removal ofindividual solvents by each column layer. Total removalrate of BTX mixture was 19 g m-3h-1.

Bioscrubbing of chlorobenzene.

0 2 4 6 8 1 0 1 2 1 4 1 6 1 8

Time (day)

Fig. 6. Bioscrubbing of chlorobenzene. The flow rate was1.22 msnr2h-l and CB vapor concentration in the inflowingair was 0.75 gmm3. The column without inoculum wassaturated with CB vapor after 2 days. The column withoutpH adjustment started to loose its activity after 5 days dueto the pH drop by chloride accumulation. The column witha pH adjustment maintained its activity for several weeksand removal rate was 5.1 gm-3h-1.

Table 1. Maximal removal rates of industrial solvents inbioscrubbing experiments. Air flow rates (0.5-37 m3m2h-*)and solvent vapor concentrations (0.560 gm-3) were variedindependently and the steady-state solvent vapor removalrates were measured.

SolventsRemoval rate

(g/m3 packing/h)

MethanolButanolAcetonitrileHexane

TolueneBTXChlorobenzeneDichlorobenzeneNitrobenzene

112.865.321.747.674.768.115.9

159.6174.267.0

DISCUSSION

Bioscrubbmg of BTX and chlorobenzenes were performedand removal rates in the range of 5-174 g m-3h-1 wereobtained. In contrast to the bioscrubbing of a singlesolvent, bioscrubbing of solvent mixtures requires a lot ofbasic experiments to understand the interactions of allcomponents in the mixture. Removal of benzene andtoluene was competitive but removal of p-xylene was bycometabolism. Although there are microorganisms whichcan utilize p-xylene as a sole carbon and energy source,cometabolic utilization of pxylene was also noted by others(Alvarez & Vogel, 199 1). The presence of p-xylene did notretard the degradation of benzene or toluene. The kinetic dataobtained from the flask tests are being analyzed further inorder to determine specific affinity constants for eachsolvent. These, when used in mathematical models, help inpredicting scrubbing performance for a wide range of solventmixtures.

No substrate interactions were noted in case of CB/DCBmixtures which were removed at surprisingly high rates.The efficient bioscrubbing of the explosives-related andhighly toxic nitrobenzene is also very encouraging.

pH control was found to be very critical in case ofchlorobenzenes. This was first accomplished by CaC03,but an automated pH control unit, as used by Diks andOttengraf (1991) proved to much more efficient and trouble-free, necessitating only the periodic removal of accumulatedsalt(NaC1). Nitrobenzene scrubbing necessitated no pH

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control since the nitro group was reduced and volatilized asNH+

CONCLUSIONS

1. Pseudomonas putidu strain 01 was isolated from aconsortium enriched on BTX mixture. This strain appearedto use the same enzyme system for degradation of benzeneand toluene, and competitive inhibition between thesubstrates was apparent

2. P. putida strain 01 did not use p-xylene for carbon andenergy and required benzene or toluene as a primarysubstrate.

3 . Bioscrubbmg of BTX mixture was performed on a packedglass column (5 cm x 150 cm) with the immobilizedconsortium, and the BTX removal rate was 16 gms3h-l.

4. With continuous water recycling and pH control,bioscrubbing of a chlorobenzene and o-dichlorobenzenemixture was accomplished at high rates.

5. An appropriately conditioned consortium removedrelatively recalcitrant and toxic nitrobenzene vapors from air.This may offer a bioven ting alternative for explosives-relatedvolatiles.

REFERENCES

1. Alvarez, P.J.J. and T.M. Vogel. 1991. Substrateinteractions of benzene, toluene, and paru-xylene duringmicrobial degradation by pure cultures and mixed cultureaquifer slurries. Appl. Environ. Microbial. 57:2981-2985.

2. Bergmann, J.G. and J. Sanik, Jr. 1957. Determination oftrace amounts of chlorine in naphtha. Anal. Chem. 29:241-243.

3. Bradford, M.M. 1976. A rapid and sensitive method forthe quantitation of microgram quantities of protein utilizingthe principle of protein-dye binding. Biochem. 72:248-254.

4. Diks, R.M.M. and S.P.P. Ottengraf. 1991. Utilizationstudies of a simplified model for the removal ofdichloromethane from waste gases using a biologicaltrickling filter. Bioproc. Engineer. 6:93-99.

PRINCIPLES OF PACKED-BED BIOFILTER MODELING AND DESIGN

B. C. Baltzis and 2. ShareefdeenDepartment of Chemical Engineering, Chemistry

and Environmental ScienceNew Jersey Institute of Technology

Newark, New Jersey 07102

ABSTRACT

Biotilters can be efficiently used in cleaning airstreams from volatile organic compounds (VOC) emitted fromvarious manufacturing operations. Optimal design and operation of a biotilter unit requires knowledge of the reactronkinetics as well as of the characteristics of mass transport of the various compounds involved in the biotiltrationprocess, namely pollutants and osygen. When this knowledge IS translated into a mathematical model of the process.simulation studies can be used, along with experiments, to study all possible types of behavior of a biotilter. Anexperimentally validated model can be used for predictive and scale-up calculations.

This study demonstrates the importance of oxygen transfer and of kinetics of biodegradation of single pollutantsand mixtures. It is shown that for mised VOCs. competrtive interactions at the kinetic level intluence the removalrates

INTRODUCTION

Use of soil beds is a common practice for odorcontrol. I t is the pioneering work of ProfessorOttengraf at Eindhoven University of Technology inthe Netherlands which has shown that biofilters can beused for treating vapors of industrial solvents. Asreviewed by Leson and Winer [l] biofiltration is a verypromising technology which needs furtherdevelopment.

The work presented here has been done incollaboration with Dr. Bartha’s laboraton, at RutgersUniversity and the reader should read it in conjunctionwith the extended abstract by Y.-S. Oh and R. Barthapublished in the same volume. Methanol was chosenas the model compound in order to study biofiltrationof single pollutants and extensive details of this study,have been already published 121. For mixtures, thekinetics of benzene and toluene and their competitiveinteractions have been studied with a pure strain and aconsortium of microorganisms [3]. All kinetic modelspresented here have been experimentally derived. Thebiofilter model for methanol has been validated withcolumn experiments. We also prcscnt somesimulation studies for biofiltration of benzene/toluenemixtures: column data for such and more complexmixtures (BTX and BTEX) are currently beingcollected and will be used for validating a moregeneral biofilter model.

Our modeling approach involves determination ofkinetics and csplicit consideration of mass transferproblems associated with the pollutants as well as withoxygen which is an essential chemical for thebiodegradation process.

MATHEMATICAL MODEL

Basic Principles and Assumptions

We assume steady state operation of a biolilter. Themodeling is based on mass balances which are writtenfor the gas phase. as the airstream moves along thebiofilter column. and for the biolayer at each particularpoint along the biolilter bed. The column is assumedto be packed with porous solid support material andthere is no continuous flow of water along the column.The latter would require consideration of mass transferfrom the air to the water phase and then to thebiolayer. For this reason. the model is valid for whatcould be called a classical bioftlter where moisture isprovided by saturating the airstream before it entersthe bed: it is not valid for bioscrubbers wherecontinuous recirculation of a water stream isemployed. The concentration of each chemicalcompound in the gas phase is assumed to bc inequilibrium with the concentration of the samecompound in the biolayer at the air/biolayer interface.The concept of the model is shown schematically inFigure I and is the one lirst mtroduccd by Ottcngraf

‘.i/

s.J

X-B 0 6 6

Figure 1 : Schematic representation of the biofiltermodel at a particular location h along the column.Any chemical j (pollutant/oxygen), with aconcentration cj in the gas phase, has aconcentration sj in the biofilm at the air/biolayerinterface. Concentrations cj and sj are related via athermodynamic distribution coefficient. Aschemical j diffuses and reacts in the biolayer itsconcentration drops and may go to zero (depletion)at position 6 or 6*. It is assumed that no biofilmgrows in the pores of the solid sulrlrort.

and van den Oever 14). In the biolayer. theconcen t ra t ion o f the chemica l d rops since thecompound diffuses and reacts in the biofilm. For themodel. the actual biofilm thickness 8” is not asimportant as 6 which indicates the position in thebiolayer where the concentration of a pollutant or ofoxygen drops to zero. and thus reaction cannot proceedfurther: 6 is the effective biolayer thickness andchanges from one position to another along thecolumn.

Model Equations for Biofiltration of Methanol

In the biolayer at a position h along the column.

D d”s, X,

“T=YMpM

D d’s0 X,

Odx’=cM

with boundary conditions

(1)

(2)

CM coat s = 0. s, = __: So = -mM m0

0)

at x=6. -=--dSM dso _ 0

dx dx(4)

tn rne gas pnase.

u (3

(6)

with boundary conditions.

at h = 0, c, = c,,: co = co, (7)

where. D is the diffusion coefficient. s is theconcentration in the biolayer. Y is the yield coefficient.Xv is the biofilm density. m is the thermodynamicdistribution coefftcient. c is the concentration in thegas phase . ug is the superticial velocity of theairstream. A, is the contact area between gas phaseand biolayer per unit volume of reactor. s denotes theposition in the biolilm. and h denotes the positionalong the bioliltcr bed. Subscripts M and 0 refer tomethanol and osygen. respectivcl\,. The specific rateof methanol biodegradation. pi,, is given b! theexpression

63O+s,, + Sk!20,000 1

(0.26+s,,)

The units of concentration are g/m3 and of pi,,. I/hr

Model Equations for Biofiltration ofBenzene/Toluene Mixtures

In the biolayer at a position h along the column.

D d ’ sI3 -xi.- - -13 dx: y, cl,?

D.. d2% x\5F= y, cLi

D d’s, X,: X”Oz=Y,,,,p” +y,,,p.‘-

(8)

(9)

(10)

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with boundary conditions.

at s = 0. s, CB CT C O= -: ST XI -* so = -7mB mT

at s = 6. ds, d% dso = 0-=----=-dx dx dx

m0

(11)

(12)

In the gas phase.

dc

” d hdSBL=A,D, -[ 1dx x=0

%uP dh = A,D, 2[ 1\=u

dc

ug d hds0A=A,D, -[ 1dx s=o

with boundary conditions

(13)

(14)

(13

at h = 0. c, = cn,: c, = c,,: co = co, (16)

The meaning of the symbols is the same as that givenearlier. Subscripts B. T. and 0 refer to benzene.toluene. and oxygen. respectively. Subscript i refers tothe conditions at the inlet of the column. The specificrates of benzene and toluene depletion with apseudomomd strain (in l/hr) have been found to be(when concentration is expressed in g/m3).

o.44s,sopB = (3.36+s, +8.4~.,)(0.26+s,) (I’)

P-i =I.j6s,s,

!

Sf15.07+s, +--

44.43+ 0.35s, (0.26+s,,)

(18)

Numerical Techniques

The purpose of modeling the bioiiltration process isto be able to predict the performance of a unit given its

dimensions and the load of pollutants (i.e.. inletconcentrations and volumetric flowrates of theairstream). One also wants to use the model forcalculating the removal rate. and percent removal. aswell as for studying the effect of design parameterssuch as the residence time. For the case of methanolvapor removal one needs to simultaneously solveequations (l)-(7). while for benzene/toluene misturesequations (8)-(16) need to be simultaneously solved.The numerical code uses the method of orthogonal orspline collocation for solving the equations in thebiolayer and then a Runge-Kutta integrator for solvingthe equations in the gas phase. Solutton o f t h eequations starts at the biofiltcr entrance conditions andproceeds with small steps along the column till theesit position is reached. Details regarding the modelparameter values used in solving the equations can befound elsewhere [ 21.

DISCUSSION

The model has been esperimentally~ validated for thecase of methanol. Figures 2 and 3a show esperimentaldata from small columns (60cm high. km diameter)along with model predictions. The curves represent

0.8 _

0.6 _

o., _

11.2 _

1L

0.0 0.2 0 .a 0.6 0 . X 1

z

Figure 2 : Methanol concentration profile in theair along the biofilter. Esperimental data andmodel prediction (curve). Conditions for theexperiment: inlet methanol concentration 6.56g/m3; air velocity 6.12 m/h; volume of packing 932cm3. Symbols 2 and z denote dimensionlessmethanol concentration and height, respectively; Cis the actual concentration divided by its value atthe inlet (6.56 g/m3) ; z is the actual position dividedby the total height of the column (6Ocm).

actual predictions and are not a fit to the data As canbe seen the agreement between csperiments and theoryis excellent. Figure 3b shows a concentration protilc-

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in the biolayer at a particular position in the biofilter.The importance of this graph is that it shows thatoxygen gets depleted very fast and before anyconsiderable change occurs in methanol concentrationin the biolayer. This finding suggests that the processis limited by oxygen transfer and kinetics of methanolbiodegradation. This is always true when methanolconcentration is high and explains the almost linearconcentration profiles in the gas phase along the

000 0 .* O..l 0.6 0.8 I

z

S*

(b)

0.8'

0.6.

0.4 -

O.l-

0 0.2 ,,..I 0.6 0.8 1

8

Figure 3 : Methanol concentration profile (topgraph) in the air along the biofilter when the inletmethanol concentration is 2.67 g/m3 ; air velocit!9.48 m/h; volume of packing 932 cm3. Symbols asin Figure 2. Complete methanol removal isachieved. Data agree perfectly with modelpredictions (curve). For the same esperiment, atthe middle point of the column, concentrationprofiles in the biolayer are predicted to be as shownin the lower graph. Curve 1 for methanol andcurve 2 for osygen. Oxygen is depleted muchfaster. Symbol 8 stands for the actual position inthe biofilm divided by the effective biolayerthickness; s* is the actual concentration ofmethanol/oxygen divided by the correspondingvalue at s = 0, i.e. at the airlhiolayer interface.

biofilter shown in Figure 2 and for the most part ofFigure 3a. For the case of Figure 3a. toward the exit

of the column oxygen transfer stops being rate limitingand this esplains the tail of the curie. Thus lindlngsuggests that in some cases one can enrich theairstream with oxygen to avoid oxygen transferlimitation and thus achieve higher removal rates in abiofilter of given dimensions.

Figure 4 shows percent removal versus residencetime. The agreement between data and modelpredictions (curve) is again very good. This suggeststhat the model can be used in determining theresidence time (or column size) required for achievingthe percent removal which will lead to an exitairstream complying with cn\,ironmcntal regulations.

nercent removal (%j

loo-

SO-

60..

01 I1 Ls 1 15 3 3 . 5 4

residence time (min.)

Figure 4 : Percent methanol removal as a functionof the residence time when the inlet methanolconcentration is about 6.5 g/m3. Experiments wereperformed with Us values between 6.12 and 12.75m/h. The volume of packing was 932 cm3 for datashown as 0 and 706 cm3 for data shown as A. Thecurve indicates model predictions.

For the case of bcnzcnc/tolucnc misturcs. it is wonhnoticing form espressions (17) and (18) that thepresence of toluene reduces the rate of benzcncremoval. and the same effect is cshibited on theremoval of toluene due to benzene presence.Nonetheless. comparing coefficients S.-i and 0.35 inthe two espressions. one can see that the effect oftoluene on benzene removal is much more severe.

Figure 5 shows computer simulations with thebenzene/toluene misture biofiltration model. Figure5a shows concentration profiles in the gas phase. Onecan see that under the conditions used for thesimulation. although the toluene concentration dropsfaster than that of benzene in the column. the samefinal concentrations are achieved at the esit. Figure 5bshows concentration profiles in the biolayer at aparticular position along a biofilter column. In thiscase the pollutants get depleted in the biolayer while

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the oxygen presence is high thus. there is no oqgentransfer limitation (compare Figures 3b and 5b).

0 0 . 2 0.4 0.6 0 . 8 1

Z

S*

0 0 2 0.4 0.6 0.8 1

8

Figure 5 : Model simulations for a benzene/toluenemixture. Curves 1, 2, and 3, are for oxygen,benzene, and toluene respectively. Assumedconditions: each pollutant is present in the inlet airat a level of 0.5 g/m3 ; air velocity 6.42 m/h; volumeof packing 932 cm3. Profiles in the gas phase (top)and in the biolayer at the middle point of thecolumn (bottom). Symbols have the same meaningas in Figure 3. A comparison of Figures 3 and 5(bottom parts) indicates that oxygen transfer islimiting methanol removal but not the removal ofbenzene/toluene, under the specific conditions ofthe experiment/simulation.

CONCLUSIONS

l Oxygen transfer may be ver)? important in somecases. hence it needs to be always considered inderiving models for biofilters

l As expected. biodegradation kinetics have a stronginfluence on the performance of biofilters. Theimportant finding of this study is that pollutantscan interact at the kinetic level and for this reason.

in dealing with misturcs one cannot simpl! add thekinetic expressions of individual pollutants toespress the overall degradation rate.

l A steady state model for biofiltration of single andmixed pollutants has been derived and numericallysolved. The model has been experimentallyvalidated for the case of single pollutants. Columnesperiments with mixtures are underway.

l In most cases biofilters are expected to operateunder transient rather than steady state conditionsdue to fluctuations in the composition of theairstream which needs to be treated. The modelsneed to be estended to describe the transient statebehavior of biofilter columns.

This work was supporred through gm17~

BlC.WZ8from the Hazardous SubstanceManagement Research Center

REFERENCES

1. G. Leson and A. M. Wincr. “Biofiltration: Aninnovative Air Pollution Control Technology forVOC Emissions.” J. .3ir Manage. .4ssoc. 41:1045-1054 (1991).

2. Z. Shareefdeen. B. C. BaltLis. Y.-S. Oh. and R.Bartha. “Biofitration of Methanol Vapor.”Biotechnol. Bioeng. 41: 5 12-524 (1993).

3. Y.-S. Oh. R. Bartha. Z. Shareefdeen. and B. C.Baltzis. “Interactions Between Benzene. Toluene.and p-Xylene (BTX) during theirBiodegradation.” preprint (1993).

4 . S. P. P. Ottengraf and A. H. C. van den Oever.“Kinetics of Organic Compound Removal fromWaste Gases with a Biological Filter.” Biorechnol.Bioeng. 25: 3089-3 102 (1983).

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BIOLOGICAL WASTE GAS PURIFICATION

IN EUROPE

R.M. DIKS’ and S.P.P. OTTENGRAF’p2

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1) Department of Chemical Engineering, Eindhoven Universityof Technology, Eindhoven, The Netherlands

2) Department of Chemical Technology, University ofAmsterdam, Amsterdam, The Netherlands

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The use of biofilters in Europe has an extensive track record and, in many situations,is considered the preferred alternative for waste gas purification. As compared to physicaland chemical alternatives of waste gas purification, biofilters offer safe operation atrelatively low cost. Experience to date is much more limited with trickling air biofilters andair bioscrubbers, but these systems are very promising for certain applications wherebiofilters do not offer sufficient process control. This is particularly true for the removalof haloorganics and other compounds that cause strong pH shifts during theirbiodegradation. A good example is the removal of dichloromethane vapors by a tricklingair biofilter colonized by Hvnhomicrobium 6521. Some engineering aspects of this systemand operational experience in .using this trickling air biofilter are presented.

In most industrially developed countries, emissions of potentially harmful volatilepollutants into the atmosphere are subject to increasingly stringent government regulation.This situation has increased the demand for reliable, inexpensive and simple techniquesto control volatile emissions. Consequently, during the last few decades interest inbiological processes for waste treatment has increased greatly. Reports on the use oflarge-scale biofilters date back to the early 1950s when soil bed filters were mostlyapplied to purify odorous waste gases from municipal sewage treatment plants. Eversince, a substantial volume of microbiological as well as process engineering research hasbeen carried out on the development of biological systems for the removal of volatileorganic and inorganic compounds. Although at the outset biofiltration was mainlyapplied for odor abatement, it has nowadays become an important alternative to thephysical and chemical methods of waste gas purification, as the application of biofiltersgenerally appears to be quite reliable and effective at relatively low cost.

Some general considerations concerning biological waste gas treatment.

The performance of a continuously operating bioreactor is the ultimate result ofcomplex interactions between microbiological and physical phenomena, often denoted asthe macro-kinetics of the process. The physical phenomena include the mass transfer

between gas- and liquid phase, the mass transfer to the mobile phases etc. Some of themicrobial phenomena, often denoted as the micro-kinetics, are e.g. the reaction rate ofthe degradation, the substrate or product inhibition and diauxic phenomena. The micro-kinetics of the degradation process are generally investigated and modelled for purecultures of suspended microorganisms. However, in bioreactor systems forenvironmental purposes, mainly heterogenous mixed cultures of microorganisms are usedrather than monocultures. This limits the usefulness of the conventional micro-kineticsfor bioreactor design purposes. Also, in many bioreactor systems, the degradation takesplace within fixed biofilms, which means that additional mass transfer phenomena (i.e.mass transfer to the biofilm and internal diffusion) need to be taken in account.

The degradability of a compound often reflects its origin: biogenic compounds areeasily biodegraded, while anthropogenic (i.e. man-made) compounds sometimes possessunnatural structures (xenobiotics) that render their biodegradation difficult (recalcitrantcompounds). However, in recent years much progress has been made in isolating,selecting or constructing strains or mixed cultures of microorganisms (mainly bacteria),which can degrade some recalcitrant compounds at rates that appear suitable forbiological waste gas treatment. This is illustrated by Table 1 which lists the growth ratesof some bacteria on xenobiotic chlorinated hydrocarbons isolated from activated sludgeor contaminated soils.

Table 1. The aerobic degradation of some xenobiotic chlorinated hydrocarbons by purecultures of microorganisms.

I

-I

From the data in Table 1, the surprising conclusion emerges that microbial growthrates on some xenobiotic compounds are within the same order of magnitude asencountered in the degradation of many biogenic substrates.

The degradation of substrates and the subsequent growth of microorganisms isgenerally described by the Monod equation. The value of the Monod-constant K, fororganic substrates generally amounts to l-10 g/m3, while for oxygen it is about 0.1 g/m3(Cooney, 1981). However, the concentrations of substrate and oxygen in the liquidphase of bioreactor systems often exceeds the value of &. Therefore, the degradationprocess can be described as having zero order kinetics.

Apart from substrate availability, microbial growth rates also depend uponenvironmental conditions such as temperature, pH and inorganic nutrients. Fig. 1 showsthe influence of the temperature on the maximum growth rate of Hyphomicrobium GJ21growing on dichloromethane (Diks, 1992). An optimum around 30 “C can be observed,whereas at higher temperatures the growth rate decreases rapidly. Within thetemperature range of practical interest (15°C - 25°C) this influence can be described byan activation energy of 76 W/mol, according to the Arrhenius equation. In general,temperature influence on the growth rate of many mesophylic bacteria is similar to theone shown in Fig. 1. Most microorganisms are able to grow over a pH range of about4 pH units, but the growth rate generally has a pH optimum around 6.5 - 7.5. Above8.5 and below 5, the growth rates may become very low.

200 2 9 0 3 0 0 310 320

TEMPERATURE [K]

Fig. 1: The influence of the temperature on themaximum growth rate of Hyphomicrobium GJ21. Forthe range of 15°C to 25°C an activation energy of 76kJ/mol was calculated.

In contrast to conventional suspension cultures, biological air purification systems areoften based on fixed film degradation processes. The microorganisms are immobilized insidethe pores or on the surface of a carrier material. A spontaneous formation of aggregates may

also occur. The immobilization of microorganisms has the advantage that biomassconcentrations, hence the volumetric reaction rates, can be considerably increased. However,the kinetics of immobilized cells may substantially differ from that of freely suspended cells.

The most important feature of a biofilm is the existence of concentration gradients ofsubstrates and products. These gradients result from the internal mass transport by diffusion andthe substrate depletion by reaction (De Beer, 1990). The reaction rate therefore may varythroughout the biofilm and also serious diffusion limitations may occur. This may result instarvation and decay of cells in deeper parts of the biofilm, eventually resulting in detachment.

ADDITIONAL

FILTER MATERIAL

Fig. 2: Schematic illustration of a biofilter packed witha mixture of compost and additives.

Types of biological waste gas purification systems.

Three groups of biological waste gas purification systems are known, which can bedistinguished by the behavior of the liquid phase and of the microorganisms, as shown in Table2 .

Table 2: Distinctions between different biological waste gas purifications y s t e m s .

Microbiota

Dispersed

Immobilized

Aqueous PhaseMobile Stationary

Bioscrubber - - -

Trickling Filter B i o f i l t e r

-I

I-I

Biofilters. As compared to other biological purification systems, biofilters are the simplestdevices. In a biofilter (Fig. 2) the waste gas is forced to pass through a simple packed bed ofmaterials, in which a suitable microbial population develops spontaneously, or after inoculationby specific microbial strains. It is generally assumed, that the particles of the packing materialare surrounded by a wet biolayer.

The volatile compounds and oxygen present in the waste gas are transferred from the gasphase into this biofilm, where the microbial degradation takes place. The packing materialnormally consists of small particles (d < 10 mm), hence usually large specific surface areas andhigh rates of mass transfer are characteristic for biofilters.

Characteristic for the soil and compost filters in the early 1950s were high pressuredrops. To reduce energy consumption, the height of such filter beds were restricted to 0.5 -1.0 m in thickness while the initial gas loads applied amounted to 5 - 10 m3/m2/h. Fairly longresidence times, up to several minutes, were needed to achieve high removal efficiency. Incurrent biofilters, various additives succeeded in decreasing pressure drop, increased the rate ofair flow and reduced typical contact time to 10 - 30 sec.

Microorganisms used in biofilters are generally mesophilic, and biofilter temperaturesneed to be maintained in the 15 - 40 “C range. Water will evaporate from the filter bed, andthis process will be enhanced by the heat generated by the microbial substrate degradation.Therefore, it is desirable to pre-humidify the gas stream. As a 100% saturation is rarelyachieved, periodic additions of liquid water may be necessary to prevent drying.

Trickling: air biofilters. In the biological purification of waste gases problems may arise if acidmetabolites are produced during the biological degradation (Diks and Ottengraf, 1991). Thisprocess may take place to such an extent that the pH buffering capacity of the filter material iseffective for only short periods of time. Low pH may inhibit biofiltration (Fig. 3).

3 L4 5 6 7 6 9 10

PH

Fig. 3: The relative activity of Hyphomicrobium GJ21from a trickling filter versus the pH in the liquid phase.

In such cases, the presence of a flowing liquid phase is required in the system for the continuousneutralization of the acids produced, as well as for the removal of neutralization products fromthe system. This situation is encountered in the degradation of halogenated hydrocarbons,ammonia, hydrogen sulfide etc. The problems of acidification and neutralization can easily besolved by the application of a biological trickling filter (Fig. 4).TATER

RRClRCULATlON

1y NaOE SOLUTION

Fig.4: Schematic drawing of a trickling air biofilter.

In this system a water phase is continuously recirculated over a packed bed of a carriermaterial, on which the biofilm is immobilized. The contaminants in the waste gas are absorbedin the liquid phase and transferred to the biolayer. Simultaneously, the acids produced areremoved from the filter bed, while the pH value of the liquid is controlled by adding an alkalinesolution (e.g. NaOH). As the neutralization product (NaCl) also inhibits the biological activity,as shown in Fig. 5, it is necessary to keep diluting the liquid phase and to keep the NaClconcentration below inhibiting levels ( < 200 n&l).

o.00’0 200 4 0 0 600 Boo too0 1200

CONCNRRATIOW N&I [d]

Fig. 5: The influence of the NaCl concentration on thedegradation rate of dichloromethane by HyphomicrobiumGJ21.

The rate of liquid recirculation is critical in trickling biofilters and needs to be increasedproportionally to the reaction rates in order to prevent pH drop within the biofilter.

Bioscrubbers. As indicated in Table 2, the common aspect of trickling filters and bioscrubbersis the mobility of the liquid phase. However, in a biotrickling filter the biomass is immobilizedon a carrier material, while in a bioscrubber (Fig. 6) the biomass is freely suspended in theliquid phase. A bioscrubber normally consists of a scrubber section, in which the mass transferbetween the gas- and liquid phase takes place. This section may be a packed bed, similar to atrickling filter, or a chamber with water spray only.

Gas effluent

Fig. 6: Schematic drawing of a bioscrubber.

Regeneration of the liquid phase takes place in a stirred tank by the suspendedmicroorganisms. An additional oxygen supply in this compartment may be necessary, if theconcentration of the substrates is so high, that the liquid itself does not contain enough oxygenfor a complete degradation.

After the regeneration, the water is returned to the scrubber section. In order to increasethe efficiency, biomass is also often recirculated to the scrubber compartment, where the masstransfer rate is increased by the simultaneous biological reaction. In a bioscrubber a superficialgas flow rate of 0.5 - 1 m/s is normally applied. Degrees of conversion of over 90% can bereached in a bioscrubber for compounds with a relatively low value of the Henry-coefficient ( <ca. .50 (pa m3/mol}). At much higher values of the Henry-coefficient, the required liquid flowrate, hence the energy consumption for liquid recirculation becomes too high (Shippert, 1989).This problem can be solved, at least in part, by allowing the biological degradation to take placealso in the scrubber section, either by suspended biomass, or by immobilized biomass as donein a trickling filter.

Also another solution for this problem has recently been presented. This concerns theaddition of a high boiling organic solvent to the liquid phase. For a successful operation, theorganic solvent must have a very low water solvability, a very low Henry-coefficient of thecompound to be absorbed and a high boiling point, thus a low partial pressure at operatingconditions. Besides, it must neither be toxic for the microorganisms nor biodegradable.Organic fluids applied for this purpose mostly are silicone fluids or phtalates. A high masstransfer rate can be realized in the scrubber compartment by the high absorption capacity of thesolvent. In this way both the reactor and the energy consumption can be reduced. The substrateconcentration in the organic phase may be 100 to 1000 times higher than those in the aqueousphase. Thus in the regeneration compartment the compounds, which have been absorbed in theorganic phase, are transferred to the aqueous phase where the microbial degradation takes place.Due to the buffering capacity of the organic phase, high substrate concentrations in the aqueousphase, hence toxic effects, can be avoided (Shippert, 1989). For bioscrubbers a smaIl numberof full scale applications are known, hence their comparison with trickling filters is still quitedifficult.

In conclusion, biofilters have a respectable track record in waste gas treatment in Europe.Trickling air biofilters and air scrubbers offer technical advantages for certain applications andtheir potential for practical application is likely to be realized in the near future.

REFERENCES

Beer D. de, Ph.D. Thesis Univ. of Amsterdam, Amsterdam The Netherlands (1990)

Bont J. de et al., Appl. Environ. Microbial. 52 (1986) 677-680.

Brunner W. et al., Appl. Environ. Microb. 40 (1980) 950-958.

Cooney L., in Biotechnology, Rehm H. Reed G. eds. VCH-Verlaggesellschaft Weinheim vol1, chap. 2 (1981)

Diks R.M.M., Ottengraf S.P.P., part I-II Bioproc. Eng. 3 (1991), 390-399.

Diks R.M.M., Thesis Eindhoven University of Technology, Eindhoven, The Netherlands (1992)

Hartmans S. et al., Biotechnol. L.&t. (1985) 383-388.

Hartmans, S. et al., J. Gen. Microbial. 132 (1986) 1139-1142.

Janssen D. et al., Appl. Environ. Microb. 163 (1985) 635-639.

Oldenhuis, R. et al., Appl. Microbial. Biotechnol. 30 (1989) 211-217.

Reineke W. et al., Appl. Envirdn. Microbial. 47 (1984) 395-402.

Schippert E., VDI-Berichte 735 (1989) 77-88, 161-177.

Scholtz R. et al., J. Bacterial. 170 (1988) 5698-5704.

Schraa G. et al., Appl. Environ. Microbial. 52 (1986) 1374-1381.

Wijngaard v.d. A. et al., J. Gen. Microb. 135 (1989) 2199-2208.

Mini-Symposium on Bioscrubbing of Gaseous Emissions

Presented before the Center for Agricultural Molecular Biology

Rutgers, The State University of New Jersey

Cook College, November 18,1992

Biological Vapor-Phase TreatmentUsing Biofilter and Biotrickling

Filter Reactors - Practical Operating Regimes

A. Paul Togna and Manjari Singh

ENVIROGEN, Inc.

Princeton Research Center

4100 Quakerbridge Road

Lawrenceville, New Jersey 08648

(609) 936-9300

ABSTRACT

The biological treatment of volatile organic compounds (VOCs) and air toxics has received

increased attention in recent years. Biotreatment of air-borne contaminants offers an inexpensive

alternative to conventional air treatment technologies such as carbon adsorption and incineration. Most

biological air treatment technologies commercially available are fixed-film systems that rely on growth of a

biofilm layer on an inert organic support such as compost or peat (biofilters), or an inorganic support such

as ceramic or plastic (biotrickling filters). If designed properly, these systems combine the advantages of

high biomass concentration with high specific surface area for mass transfer.

At economically viable vapor residence times (1 to 1.5 minutes), biofilters can be used for treating

vapor streams containing up to approximately 1500 ug/L of readily biodegradable compounds.

Biotrickling filters may offer greater performance than biofilters at high contaminant loadings, possibly due

to higher internal biomass concentrations. Both systems are best suited for treating vapor streams

containing one or two major compounds. If designed properly, biofilters are especially well suited for

treating streams that vary in concentration from minute to minute.

INTRODUCTION

The biologrcal treatment of VOCs and air toxics has received increased attention in recent years.

Biotreatment of air-borne contaminants offers an inexpensive alternative to conventional air treatment

technologies such as carbon adsorption, wet scrubbing, and incineration.

Vapor-phase problems can be roughly separated based on contaminant concentration, stream

composition, and vapor flow rate. The bioreactor configuration best suited for one particular application

may not be suitable for others.For example, low flow rate vapor streams are most efficiently treated

biologically within a bubble column, stirred tank, or airlift loop configuration, where the vapor stream of

interest is bubbled into a vessel containing a suspended culture of microorganisms. Alternative bioreactor

designs which have much lower pressure drops must be used at higher air flow rates (typically greater than

5000 scfm) to compete favorably with conventional technologies. Most of these high flow rate biological

air treatment designs which are commercially available are fixed-film systems that rely on the growth of a

biofilm layer on an inert organic support such as compost or peat (biofilters), or an inorganic solid support

such as ceramic or plastic (biotrickling filters). If designed properly, these systems combine the

advantages of high biomass concentration, high specific surface area for mass transfer, and low operating

cost.

FIXED-FILM BIOTREATMENT SYSTEMS

-I-I

-a-a

Figure 1 is a schematic of a biofiltration system. Biofiltration is a process that utilizes

microorganisms immobilized in the form of a biofilm layer on an adsorptive filter substrate such as compost,

peat, or soil. As a contaminated vapor stream passes through the filter bed, pollutants are transferred from

the vapor to the biolayer, and are oxidixed.

The simplest form of biofiltration system is the soil bed, where a horizontal network of perforated

pipe is placed about two or three feet below the ground (1,2). Vapor contaminants are pumped through

the piping, flow upward through the soil pores, and are oxidized by microorganisms present within the soil.

More sophisticated enclosed units allow for the control of temperature, bed moisture content, and pH to

optimize degradation efficiency.

Biofiltration has been used for many years for odor control (H2S and related sulfur compounds,

esters, etc.) at rendering plants and slaughter houses in Germany, the Netherlands, the United Kingdom,

Japan, and to a limited extent in the United States. The use of biofilters to degrade more complex volatile

emissions from chemical plants has occurred only within the last few years. Biofilters and soill beds have

been shown to be effective for treating aromatics such as styrene and toluene (3,4), aliphatics such as

propane and isobutane (5), and more easily degraded compounds such as esters and alcohols (4,6).

A second type of fixed-film biological system used to treat VOCs is the biotrickling filter (see

Figure 2) (7). Biotrickling filters are similar to biofilters, but contain conventional scrubber packing material

instead of compost or peat, and operate with a recirculated liquid flowing over the packing. Only the

recirculating liquid is initially inoculated with microorganisms, but a biofilm layer establishes itself on the

packing shortly after start-up.

The pH of the recirculating liquid within biotrickling filters is easily monitored and controlled by the

automatic addition of acid or base. The pH within biofilters is controlled only by the addition of a solid

buffering agent to the packing material at the beginning of operation. Once this buffering capacity is

exhausted, the filter bed is removed and replaced with fresh material. For the biodegradation of

halogenated contaminants, biofilter bed replacement can be quite frequent. Therefore, biotrickling filters

are more effective than biofilters for the treatment of readily biodegradable halogenated contaminants

such as methylene chloride.

PERFORMANCE CHARACTERISTICS OF FIXED-FILM SYSTEMS

Operating Regimes

Biofilters. Figure 3 shows bench-scale biofilter performance results for the treatment of air

contaminated with styrene at a nominal bed residence time (bed volume/vapor flow rate) of 1 minute. For

the packing used, the maximum volumetric performance (also called elimination capacity) was

approximately 70 g/m3 packingehr. At styrene loading rates of less than 70 g/m3 packingahr, greater than

95% degradation was achieved.Figure 4 shows analogous results for the treatment of air contaminated

with ethanol, a contaminant which is degraded three times faster in dilute liquid culture than styrene. The

maximum volumetric performance of the biofilter bed for ethanol degradation was approximately 175 g/m3

packingehr. At ethanol loading rates of less than 100 g/m3 packingahr, greater than 95% degradation was

achieved.

A number of simple mathematical models have been developed to help explain and predict

biofilter performance as a function of residence time and inlet contaminant concentration. Elimination

rates have been approximated by zero-order kinetics (4), first-order kinetics (8,9), and saturation kinetics

(5). The data from Figures 3 and 4 were fit to a simple fixed-film, zero-order kinetics model for biofilters

developed by Van Lith et al (10). This model applies rigorously only in the high contaminant concentration

range, but is sufficient for illustrative purposes. The theoretical biofilter performance curves shown in

Figure 5 suggest that at economically viable residence times (1 to 1.5 minutes), biofilters can be used for

treatment of vapor streams containing up to approximately 1500 pg/L of ethanol or styrene. However, the

bench-scale experiments described above were conducted under ideal, steady-state conditions. In real

applications, fluctuating contaminant loads and the presence of multiple contaminants can have a dramatic

effect on biofilter performance.

Biotricklina Filters. Biotrickling filters, possibly due to higher internal biomass concentrations,

may offer greater performance than biofilters at high contaminant loadings. At a 0.5 minute vapor

residence time, the maximum concentration of styrene that can be degraded with 90% efficiency using

biotrickling filters is two times higher than can be degraded using biofilters (11). Likewise, the maximum

concentration of benzene that can be degraded with 90% efficiency using biotrickling filters is three times

higher than can be degraded using biofilters (data not shown).

Treatment of Mixed Waste Streams

Many industrial discharges are composed of complex mixtures of chemical compounds. The

treatment of these waste streams is frequently more difficult than the treatment of waste streams

containing a single component. The pollution control industry therefore places a premium on

technologies able to handle complex mixtures of compounds as well as fluctuations in concentration.

For example, biofilters have been suggested as a possible alternative to incineration and carbon

adsorption for treatment of vapors extracted from soils contaminated with petroleum hydrocarbons. This

possibility was tested at the bench scale by passing benzene, toluene, ethylbenzene, xylenes (BTEX),

and gasoline vapors through biofilter columns inoculated with BTEX, gasoline, and aliphatics (isopentane,

-a-a-a

pentane, and octane) degraders. Figures 6 and 7 show that the BTEX compounds were degraded with

high efficiency (75%) within these columns while the lighter aliphatic components of gasoline (gas

chromatograph peaks before benzene) were not degraded. Comparable results were obtained using

biotrickling filters. These results suggest that the simultaneous removal of BTEX and light-end aliphatics

from petroleum hydrocarbon vapors using biofilters may require two or more optimized biofilters or

biotrickling filters in series. Any complex mixture of contaminants with widely different chemical, physical,

and biodegradative properties such as petroleum hydrocarbon vapors may require such a sequential and

optimized treatment train.

Treatment of Fluctuating Inlet Concentrations

Figure 8 shows the typical average hourly performance of ENVIROGEN’s field-pilot biofilter

system (30 fts of packing) treating a slip stream of styrene-contaminated air discharged from a spray booth

operation. The concentration of organics in the spray booth effluent stream varied from as high as 1000

ppmv methane equivalents (550 ug/L styrene) to as low as 100 ppmv methane equivalents (55 ug/L

styrene) as the spray booth guns were turned on and off repeatedly. These extreme swings in

concentration occurred some 20 to 40 times over a typical one hour period. As shown in Figure 8, these

minute to minute fluctuations in influent styrene concentration had a negligable effect on system effluent

quality.For this application, the biofilter packing was designed to have a high adsorptive capacity for

styrene so that movement of styrene through the biofilter bed could be controlled primarily by adsorption

onto the packing (8). Movement of high concentrations of styrene through the bed was therefore

retarded by the packing, increasing the time available for biodegradation.

CONCLUSIONS

Biofilters and biotrickling filters offer an alternative to conventional air treatment technologies for

the treatment of waste streams containing low concentrations of volatile or semi-volatile organics.

Biofiltration has been used for many years for odor control (H2S and related sulfur compounds, esters,

etc.) at rendering plants and slaughter houses in Germany, the Netherlands, the United Kingdom, Japan,

and to a limited extent in the United States. The use of biofilters to degrade more complex VOC

emissions from chemical plants has occurred only within the last few years.

Biotrickling filters have not been used as often as biofilters for the control of VOCs, possibly

because they are considered more difficult to operate than biofilters. Biotrickling filters have been

considered only for those applications where biofilters would not be appropriate, such as for treatment of

halogenated contaminants, where continuous pH monitoring and control are critical.

At economically viable residence times (1 to 1.5 minutes), biofilters can be used for treating vapor

streams containing up to approximately 1500 ug/L of readily biodegradable compounds. Biotrickling

filters may offer greater performance than biofilters at high contaminant loadings, possibly due to higher

internal biomass concentrations.Both systems are best suited for treating vapor streams containing one

or two major compounds. If designed properly, biofilters are especially well suited for treating streams that

vary in contaminant concentration from minute to minute due to the adsorptive characteristics of the

engineered packing.

LITERATURE CITED

1 .

2.

3.

4.

5.

6.

7.

8.

9.

10.

11.

Bohn, H. and R. Bohn, Chem. Eng., Aoril25. 1988,73.

Bohn, H., Chem. Eng. Prog., 88, (4) 48 (1992).

Ottengraf, S.P.P., J.J.P. Meesters, A.H.C. van den Oever, and HR. Rozema, Bioprocess Eng.,

1, 61 (1986).

Ottengraf, S.P.P. and A.H.C. van den Oever, Biotechnol. Bioeng., 25, 3089 (1983).

Kampbell, D.H., J.T. Wilson, H.W. Read, and T.T. Stockdale, JAPCA, 37, (10) 1236 (1987).

Hodge, D.S., V.F. Medina, Y. Wang, and J.S. Devinny, “Biofiltration: Application for VOC

Emission Control,” in Proceedinas of the 47th Annual Purdue Industrial Waste Conference, West

Lafayette, Indiana, May 11-13, 1992.

Hartmans, S. and J. Tramper, Bioprocess Eng., 6,83 (1991).

Devinny, J.S., V.F. Medina, and D.S. Hodge, “Bench Testing of Fuel Vapor Treatment by

Biofiltration,” in Proceedinas of the 1991 National Research & DeveloDment Conference on the

Control of Hazardous Materials, Hazardous Materials Control Research Institute, Anaheim,

California, February 20-22, 1991.

Hodge, D.S., V.F. Medina, R.L. Islander, and J.S. Devinny, Environ. Technol., 2, 655 (1991).

Van Lith, C., S.L. David, and R. Marsh, Trans IChemE, 68. Part B, Mav 1990, 127.

Togna, A.P. and B.R. Folsom, Removal of Stvene from Air Usina Bench-Scale Biofilter and

Biotricklina Filter Reactors, Paper No. 92-l 16.04, 85th Annual Air & Waste Management

Association Meeting & Exhibition, Kansas City, Missouri, June 21-26, 1992.

3Idd

dd

I

1

1

1

I

1

1

1

1

1

1

1

1

Clean Air

Humidifier Biofilter

Figure 1. Biofilter schematic.

Clean Air

Liquid Recirculation

Liquid Media FeedBiotrickling Filter

Figure 2. Biotrickling filter schematic.

Waste

0 50 100 150Styrene Load (g/msahr)

200

Figure 3. Biofilter performance for styrene removal at a vapor residence time of 1 .O min.Volumetric performance (grams styrene degraded per m3 packing per hr) is plottedas a function of styrene load (grams styrene fed per m3 packing per hr). Pointscannot fall above the 100% degradation line.

/

100% Degradation Line

0

0 200 400 600 800

Ethanol Load (g/m3*hr)

Figure 4. Biofilter performance for ethanol removal at a vapor residence time of 1 .O min.Volumetric performance (grams styrene degraded per m3 packing per hr) is plottedas a function of ethanol load (grams styrene fed per m3 packing per hr). Pointscannot fall above the 100% degradation line.

2-

0 : I I0 1000 2000 3000 4000

pg/L Contaminant

Figure 5.Theoretical biofiolter performance curves for styrene and ethanol. Thedata from figures 3 and 4 were fit to a simple fixed-film, zero-order kineticsmodel for biofilters.

’ BTEX Load’ BTEX EC

20 30Days

Figure 6. Biofilter performance on BTEWgasoline-contaminated air. BTEX load andelimination capacity (EC) are plotted as a function of time for a vaporresidence time of 1 .O min.

c 150s 0

E22100’2‘CI 0

E O Aliphatics Load

%0 l Aliphatics EC

4 50-O 0 0

3 0 8‘Z 0 OS 8.E 0 0 0 0.E

000o”-oocoz ()-. l $-�*:� *

0 IO 20 30 40 50Days

Figure 7. Biofilter performance on BTEXIgasoline-contaminated air. Aliphatics loadand elimination capacity (EC) are plotted as a function of time for a vaporresidence time of 1 .O min.

600 lWednesday, 12/9/92

120 scfm, Upflow

m

Hrs After Start of Operations-35th Day

Figure 8. Typical average hourly performance of ENVIROGEN’s field-pilot biofiltersystem (30 fts of packing) treating a slip stream of styrene-contaminated airdischarged from a spray booth operation.Concentrations are in units of ppmvmethane equivalents @g/L styrene = ppmv methane equivalents x 0.54).

.

I1IIIIIIIIIIIIIIIII

Compostin? Facilitv Odor Control

Using Biofilters

Frederick C. Miller, Sylvan foodsWorthington, PA

A written version of this presentation is not available.

.

DISCUSSION

Moderator: Richard Bartha, Rutgers University

Following the formal presentations, ideas and comments were solicited from theparticipants how to create an increased awareness of the biotreatment option for VOC emissionsand how to promote the practical use of this option. Comments received were put on theblackboard and, with some editing, are summarized below. The recommendations areunderlined and are followed by brief interpretive statements.

1)

2)

3)

4)

5)

6)

Publicize the biotreatment ontion for VOCs. There is an insufficient awareness of thistreatment option in the USA, and most of the relevant scientific literature is not in theEnglish language. Needed are both scientific and popular publications to spreadinformation about this treatment option.

Define the economic niche for air emission biotreatment more nreciselv. There is ageneral perception that biotreatment is economically advantageous at low VOCconcentrations, while condensation or incineration are economically viable at high VOCconcentrations. However, the relevant concentrations to be treated and the economicsof the alternative treatments at such concentrations need to be defined more closely.

ExDlore further the anplication range of biological air emission treatment. Control ofodors from sewage, cornposting and food industry by biotreatment is well established.Applicability to xenobiotic solvents is promising, especially when selected microbialinocula are used. Applicability to non-substrate type of volatile xenobiotics in thepresence of added maintenance substrates needs further exploration.

Develon models and scaleun factors to speed the transition from the laboratorv tocommercial-scale facilities. Mathematical and computer modeling, verified by laboratorydata, will speed the transition to, and lower the cost of commercial scale facilities.

Increase the lifetime and reliabilitv of biofiltration/bioscrubbing installations throughbetter maintenance techniaues. Like catalysts, biofilters do not last forever, but theirproper management can greatly increase their lifetime, lower their costs and prevent theiraccidental performance loss.

Consider biotreatment as a notential comnonent of an integrated air treatment svstem.Biotreatment may not be suitable for every kind of air emission generated by amanufacturer. Nevertheless, it still may be the most economic alternative for theremoval of certain pollutants from the air stream. Non-biological components maycomplete the treatment process.

7 ) Establish rational and realistic nermitting nrocesses for biotreatment. Rigidity or mistrustby regulators could greatly obstruct the utilization of biotreatment. Performancestandards should be rational. Emissions not to be exceeded at any time make sense incase of toxic or noxious compounds. On the other hand, with compounds that have onlylong-range effects (e.g. on the ozone layer) regulatory emphasis should be on the totalpercentage of pollutant removed over extended time periods.

8) Continue to address safetv concerns about emission of bacteria or funrral snores frombiotreatment units. To date, there is no evidence for any harmful emission ofmicroorganisms from biological air treatment units. Nevertheless, because of publicconcern, continued research on this topic is warranted to reassure the public and theregulatory agencies about the safety of this treatment option.

IIIIIIIIIIIII

Interdisciplinary Bioremediation

Working Group

Spiros AgathosChemical and Biochemical EngineeringCollege of EngineeringRutgers, The State University of NewJerseyPiscataway, NJ 08855908/932-3865FAX: 908/932-5313

Laura MeagherAgBiotech CenterCook College, NJAESRutgers, The State University of NewJerseyP.O. Box 231New Brunswick, NJ 08903-02319081932-6571FAX: 9081932-6535

Richard BarthaBiochemistry and MicrobiologyCook College, NJAESRutgers, The State University of NewJerseyP-0. Box 231New Brunswick, NJ 08903-0231908/932-9739FAX: 908/932-5870

Joe RoblesOffice of Continuing ProfessionalEducationCook College, NJAESRutgers, The State University of NewJerseyP-0. Box 231New Brunswick, NJ 08903-0231908/932-9271FAX: 9081932-8726

Burt EnsleyEnvirogen, Inc.4100 Quaker Bridge RoadPrinceton Research CenterLawrenceville, NJ 08648609/936-9301FAX: 609/936-9221

Peter StromEnvironmental SciencesCook College, NJAESRutgers, The State University of NewJerseyP-0. Box 231New Brunswick, NJ 08903-0231908/932-8078FAX: 908/932-8644

Douglass Eveleigh Paul TomasekBiochemistry and Microbiology Food ScienceCook College, NJAES Cook College, NJAESRutgers, The State University of New Rutgers, The State University of NewJersey JerseyP-0. Box 231 P-0. Box 231New Brunswick, NJ 08903-0231 New Brunswick, NJ 08903-0231908/932-9829 9081932-9663FAX: 908/932-5870 FAX: 9081932-6776

Allen LaskinLaskin/Lawrence AssociatesR.D. 2 Box 392TSomerset, NJ 088739081873-8741FAX: 9081873-8741

Gerben ZylstraAgBiotech CenterCook College, NJAESRutgers, The State University of NewJerseyP.O. Box 231New Brunswick, NJ 08903-0231908/932-1044FAX: 9081932-6535

THE STATE UNIVERSITY OF NEW JERSEY

RUTGERSCenter for Agricultural Molecular Biology (AgBiotech)

Rutgers, The State University of New JerseyCook College, P.O. Box 231

New Brunswick, NJ 09083-0231908/932-8165