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Biofiltration for the Treatment of Complex Mixtures of VOCInfluence of the Packing Material

AIZPURU, A . , KHAMMAR, N . , MALHAUTIER*, L . , FANLO, J. L.

Laboratoire Gnie de l'Environnement Industriel * Corresponding authorEcole des Mines d'Als Phone: + 334 66 78 27 826 Avenue de Clavires Fax: + 334 66 78 27 0130319 Als Cdex, France E-mail: [email protected]

Summary

Currently air biofiltration is largely considered for the removal of Volatile Organic Compounds (VOC)from polluted airstreams. In order to select a suitable packing material for the treatment of VOCpolluted air and better understand the influence of the packing material properties upon the removalefficiency, a mixture of eleven VOC was treated in two down-flow biofilter units packed with eitherpeat or Granular Activated Carbon (GAC) and functioned under similar operating conditions for92 days. Using the peat biofilter under steady-state conditions achieved a removal efficiency of 90%

greater than the 80% achieved using the GAC filter. Moreover, in both cases, a stratification of theabatement along the column was observed but it differed according to the type of the packing materialused. For the peat biofilter, elimination of oxygenated compounds occurred in the first 50 cm of thecolumn, whereas aromatic and halogenated compounds were treated in the segments closer to theoutlet. In contrast, with GAC, the removal of oxygenated and aromatic compounds took place alongthe height of the column. For the removal of microorganisms fixed on peat and activated carbonparticles, the crushing with an ultra-turrax was the most efficient dispersing method, compared toagitation with a vortex and ultrasound. The counting of microorganisms using three culture media[Luria Bertoni (LB); Plate Count Agar (PCA); Tryptic Soy Agar, tenfold diluted (TSA 1/10)] demon-strated that the TSA 1/10 was likely most suitable for the recovery of the peat biofilter microflora(TSA 1/10: 5.6 109 CFU/gof dry peat, PCA: 1.5109 CFU/g of dry peat, LB: 0.3 109 CFU/g of drypeat) probably due to the dominance of oligotrophic bacteria, whereas for the activated carbon biofilterthere was no significant difference (PCA: 4.4 109; LB: 4.2 109; TSA 1/10: 4.5 109 CFU/g of dryactivated carbon) between these media suggesting that oligotrophic and zymogeneous bacteria arelikely in the same proportion.

The results illustrated that even the removal efficiency is associated with the pollutant properties; itwas assumed that the sorptive properties of GAC could modify the VOC degradation mechanisms andthen entail a real reduction of the removal efficiency.

Introduction

Air pollution is a growing problem; even factory emissions are tightly controlled.Attention is specifically focused on Volatile Organic Compounds (VOC) as these pollu

WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim, 2003 0138-4988/03/02-3-07-0211 $ 17.50+.50/0

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tants have significant effects on health and on the environment. Biological processeshave been used for the treatment of large volumes of air containing low concentrationsof pollutants and are found to be more economical and environmentally viable than longexisting air emission control [1, 2].Already commonly used for the control of odorant compounds [3], the application ofthis process has been recently extended to the control of volatile organic compounds(VOC) [46]. A screening of industrial VOC emissions reveals that, in most cases,effluents contain complex mixtures of VOC with different biodegradability and solu-bility [710].Generally, a biofilter is a column filled with a porous and humid packing materialinoculated with microorganisms able to degrade pollutants. The air pollutants are trans-ferred from the gas phase to the liquid phase and diffuse through the biofilm fixed on

the surface of the packing material. The pollutants are subsequently biodegraded in thebiofilm to water and CO2 and used as the essential carbon source for the microbialgrowth.Several authors have shown that the packing material properties have some effects uponthe removal efficiencies of biofilters [1115]. The materials used have more accuratelyincluded natural materials such as soil [11], compost [6, 16, 17], peat [12, 18, 19, 20]and synthetic materials including vermiculite [21, 22], granular activated carbon [23]and extruded diatomaceous earth pellets [24].The quantitative and qualitative characterisation of the biofilter microflora is essential inorder to better control the functioning of these bioreactors and, additionally, reveal ademand for the removal of the microorganisms from the solid particles of the packingmaterial. When considering an unknown microflora, as in the case of the biofilters, theremoval of the microorganisms must be as selective as possible. Hence, the removal of

microorganisms from the packing material represents an important step that could limitthe accuracy of studies. The characteristics (humic acids, surface functions, etc.) of ma-terials generally used for the biofiltration are similar to those reported for soil [25], andthis suggests that the dispersion of microorganisms from the packing material could bedifficult. In the literature, several physical and/or chemical dispersion methods havebeen proposed to remove the microorganisms from the soil particles [2629] and someof these methods have been used to remove the biofilter microflora from several pack-ing materials.Therefore, the aim of this work is to select a suitable packing material for the biofiltra-tion of air polluted with eleven VOC and to subsequently attain a better knowledge ofthe quantitative characterisation of the microbial community as well as of the influenceof the packing material upon the removal efficiency of a representative complex mixture

of VOC. Among the wide range of packing materials used, attention is specificallyfocused on peat and Granular Activated Carbon (GAC). OH and CHOI [30] showed that abiofilter packed with peat was more efficient to treat monoaromatic solvent vapoursthan bark chips, vermiculite and hydroball biofilters. Moreover, although characterisedby a low pH [31], peat has been widely used [32] mostly because of its high specificarea, void fraction and the ease in which its nutrient content can be assimilated [18, 20].A few workers applied GAC as a biofilter packing material to treat only gaseous VOCeffluents [33]. Moreover, modelling of biofiltration indicates that highly adsorptivemedia such as GAC could provide treatment advantages over moderately adsorptive

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media, such as compost or peat [34]. Therefore, a mixture of eleven VOC waseffectively treated in two down-flow biofilter units packed with either peat or activatedcarbon. The operating conditions were similar for both reactors and special attentionwas focused on the comparison of removal efficiencies as a function of the time and theheight of the column, on the one hand, and on the quantitative characterisation of themicrobial communities, on the other. Firstly, the packing material influence upon theremoval of microorganisms was studied by the use of three physical dispersionmethods. Then the counting of the culturable microflora containing colonised peat andGAC was performed applying three culture media.

Materials and Methods

VOC Mixture

A mixture of 11 VOC was prepared by using the following compounds: methanol, acetone, methylethyl ketone (MEK), methyl isobutyl ketone (MIBK), ethyl acetate, butyl acetate, toluene, ethylben-zene,p-xylene, 1.2 dichloroethane, dichloromethane (Carbo Erba Reagenti, 99%).

Pilot-Scale Units

The laboratory scale units consisted of two glass columns containing 4 kg of granular Irish peat(EUROPE ENVIRONMENT, France) or 6.5 kg of Granular Activated Carbon (GAC) (IG 90, CAR-BIO 12, France) (Fig.1). Each column had a diameter of 10 cm and a height of 1 m. Each wasequipped with five outlets at intervals of 20 cm. VOC levels were measured and samples for micro-biological analysis taken at these outlets. The characteristics of the packing materials are given inTab. 1. The advantages for using Irish peat were its interesting mechanical properties, and its highcapacity for holding water. Moreover, this packing was able to favour the biofilm growth.The column was supplied with air containing the VOC mixture in a concentration of 1.1 g/m3 air witha down-flow configuration. The concentration of each compound reached 0.1 g/m3 air. The VOCmixture was obtained by diluting and volatilising a VOC liquid mixture in atmospheric air. The VOCliquid mixture was made with an equivalent quantity of each compound. A syringe-pump (PRECIDORINFORS AG, Bottmingen, CH) delivered the desired flow rate. The volumetric flow was adjusted to0.8 m3/h,i.e., a gas velocity of 100 m/h (Empty-Bed Residence Time: 0.6 min). The volumetric loadapplied to the biofilters, considering the mixture of pollutants, was 110 g VOC s/m3 h (10 g/m3 h foreach compound) during 92 days.The peat was kept at constant humidity by a system that regularly sprayed it with a salt mineral nutri-ent solution HCMM2 [35], as modified by JUTEAUet al. [36] called HCMM3 (Tab. 2). According tothe packing material properties in terms of water holding capacity, 600 ml and 1800 ml of the nutrientsolution were introduced per day into the biofilters of peat and activated carbon, respectively.

The pressure drop was observed using a digital differential manometer (BIOBLOCK company,France).

Inoculum

Two hundred litres of activated sludge from an urban wastewater treatment plant were acclimatised fora period of two months with a volumetric gas flow of 1 l/min containing the VOC mixture. Before thestart-up, each column was inoculated over 24 h in closed-circulation with 4 l of the acclimated sludgeto ensure a homogeneous distribution of the selected microflora.

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Fig. 1. Diagram showing the pilot unit for VOC removal

Chemical Analysis

The concentrations of each compound were measured in the inlet and outlet gas streams of pilot unitsusing a gas chromatograph (Hewlett Packard 5890 II) equipped with a flame ionisation detector. A

30-meters HP-5 capillary column was used with a carrier gas (helium) flow rate of 2 ml/min. The ovenwas programmed as follows: 40 C for 5 minutes, then 10 C per minute until it reached 180 C. The

temperatures of the injector and detector were 150 C and 220 C, respectively. Separation of

compounds was conducted in 18 min.

Dispersion Methods of Microorganisms

The crushing was done with an ultra-turrax (continuous procedure, treatment duration of 2 min, 24,000

rpm), the agitation with a vortex (Heidolph Reax 2000, Germany) (continuous procedure, treatmentduration of 2 min, 2,400 rpm) and ultrasound (Branson sonifier bath, ENERGY) (energy outputs of

70 W, treatment duration of 60 min) in a sonifier bath were used to remove microorganisms fixed to

the surface of peat and GAC.

For both materials, three samples (E1, E2, E3) were collected at the same location of the biofilter and atthe same time. Each sample was divided into six sub-samples of 2 g (6 e1, 6 e2, 6 e3). Each desorption

method was used for the treatment of two of each of the sub-samples e1, e2, and e3placed in 20 ml ofphosphate buffer (PB). Enumeration of dispersed microorganisms in suspensions was carried out by

the plate counting technique on the solid Plate Count Agar (PCA) medium.

Culture Media

The counting of the microflora was performed using three solid culture media: Luria Bertoni (LB)

[Tryptone 10 g/l; Yeast extract 5 g/l; NaCl 5 g/l; Agar-agar 15 g/l], Tryptic Soy Agar tenfold diluted

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(TSA 1/10) [Peptone from casein 1.5 g/l; Peptone from soy meal 0.5 g/l; NaCl 0.5 g/l; Agar-agar15 g/l], Plate Count Agar (PCA) [Peptone from casein 5 g/l; Yeast extract 2.5 g/l;D (+)-Glucose 1 g/l;Agar-agar 14 g/l].The enumerations were performed with nine repetitions. Three samples (E1, E2, E3) were collected atthe same location of the biofilter and at the same time, for both peat and activated carbon. Each ofthese samples was divided into three sub-samples of 2 g (3 e1, 3 e2, 3 e3) that were all treated in 20 mlof PB by using the ultra-turrax over two minutes at 24,000 rpm. For each of the nine suspensions,100 l were plated in parallel on the three culture media. The number of Colony Forming Units (CFU)was then enumerated after 4 days of incubation at 28 C.

Tab. 1. Physical and chemical properties of peat and GAC____________________________________________________________________________________________________________________________________________________________________

Element [%] C H N O S

Peat 48.3 5.4 1.6 37.9 0.6

GAC 89 1 0.4 4 < 0.3___________________________________________________________________________________________________________________________________________________________________

Metals [mg/kg] P Fe Mn Zn Cu Pb Cr

Peat 200 1655 58 8 4 2 2GAC 336 452 39 150 41 33 6___________________________________________________________________________________________________________________________________________________________________

Organic matter [%]

Peat 95GAC ND_____________________________________________________________________________________________________________________________________________________________________

Silica [%]Peat 1GAC ND___________________________________________________________________________________________________________________________________________________________________

pH

Peat 4.6GAC 10___________________________________________________________________________________________________________________________________________________________________

dpsv [mm]

Peat 5.1GAC 2.8_____________________________________________________________________________________________________________________________________________________________________

Void degree(.)

Peat 0.66GAC 0.55

____________________________________________________________________________________________________________________________________________________________________

Surface functional groups Basic AcidicGI AcidicGII AcidicGIIIAcidicGIV

m2/g of peat 0 0.67 0.28 1.93 0.1m2/g of GAC 0.95 0 0 0.25 0.1_____________________________________________________________________________________________________________________________________________________________________

Acidic functional groupsGI, II, IIIandIV: carboxylic, lactone, phenol and carbonyl acidic groups, respectively.dpsv: SAUTER diameter of grains.ND: Not determined.


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Tab. 2. Mineral culture ingredients_____________________________________________________________________________________________________________________________________________

Ingredients Concentration [mM]_____________________________________________________________________________________________________________________________________________

KH2PO4 10Na2HPO4 10KNO3 5(NH4)2SO4 18MgSO4 7 H2O 0.1CaCl2 2 H2O 0.1Fe(NH4)2(SO4)2 6 H2O 9 103

H3BO3 46.2 103

MnSO4 H2O 9.11 103

CuSO4 0.016 103

ZnCl2 0.015 103CoCl2 6 H2O 0.017 103

Na2MoO4 2 H2O 0.01 103

_____________________________________________________________________________________________________________________________________________

Statistics

The results obtained were analysed statistically by analysis of variance. The significance of thedifferences between the means was established by theF-test at a p value of 0.05 by using theMicrosoft-Statview software. The variability of the data was expressed in terms of the relative standarddeviation (RSD).

Results and Discussion

Global Removal Efficiencies

Fig. 2 shows the removal of the VOC mixture for the load applied at 110 g VOC/m3 huntilt= 92 days for the biofilters packed with peat and GAC. The main difference isobserved at the beginning of the experiment. The removal efficiency of the GACbiofilter accounted for 100% while that of the peat biofilter only accounted for 48%.The high value of 100% was due to the sorption of initial compounds on the wet GAC,regardless of the inoculation of the filter with microorganisms as was shown byWEBSTER [37]. Then the peat biofilter removal efficiency increased due to the colonisa-

tion and activity of the microbial communities involved in VOC elimination. Theremoval efficiency reached 90% on the 50th day of the experiment. This removal effi-ciency was maintained for two months with a standard deviation of 3.5%. The GACbiofilter removal efficiency decreased from 100% to 80% after 92 days. Hence, the peatbiofilter achieved greater removal efficiency than the GAC filter. For the peat biofilter,the VOC removal increased simultaneously to the microbial growth and metabolismactivity. For the GAC biofilter, it could be assumed that the VOC removal efficiencydecreased in relation to the saturation of the adsorption sites. It is also probable that the


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adsorption capacity of GAC involved high pollutant concentrations and then preventedthe biomass colonisation and activity. Moreover, it could be assumed that the presenceof a biofilm and a biological oxidation process would diminish the quantity of pollut-ants adsorbed.

Fig. 2. VOC mixture removal reached for biofilters packed with peat or GAC as a func-tion of time

For the peat biofilter, the pressure drop measurement data during the study were highand estimated to 60 cm H2O/packing meter, while for the GAC biofilter, the measure-ments did not exceed 10 mm H2O/packing meter. In addition, the results demonstratedthat the GAC packing material has good hydrodynamic behaviour. For the peat biofilter,it is probable that the biofilm growth as a function of time could reduce the void degree[38] and, therefore, explain the high-pressure drop measurements.

Compound Abatement

The relevant results are presented in Tab. 3. At the beginning of the experiment, for theGAC biofilter, the efficiency of the eleven compounds is 100% while for the peatbiofilter, an efficiency of 100% is achieved only for esters, MIBK and MEK. Hence, theuse of GAC could be interesting in order to improve the elimination efficiency beforereaching the steady state and in order to reduce the variations in the pollutant concen-tration at the biofilter inlet.Nevertheless, for the GAC biofilter, according to the duration of the adaptation phase ofthe compounds, the steady state is reached 70 days after the start of the experiment


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while, for the peat biofilter, only 50 days are necessary to reach the steady state for allthe compounds. It was also demonstrated [33] that the use of GAC as a packing materialinvolves an increase in the duration of the adaptation phases. Moreover, the compoundremoval efficiency reached for each compound was ranged (Eq. 1).

Oxygenated compounds > ethylbenzene > toluene >p-xylene > DCM > DCE (1)

This range corroborates a biodegradability ranking of these compounds summarised inthe literature [8, 25] and is equivalent irrespective of the packing material used. Never-theless, at t= 90 days, the elimination efficiencies of the aromatic and chlorinated com-pounds achieved in the peat biofilter are higher than those obtained in the GAC filter.

Tab. 3. Comparison of compound removal efficiencies for peat and GAC biofilters____________________________________________________________________________________________________________________________________________________________________

PEAT GAC__________________________________________________________________ ______________________________________________________________________

Compound Abatement Adaptation Steady-state Abatement Adaptation Steady-state[1 day] phase abatement [1 day] phase abatement

[90 days] [90 days][%] [days] [%] [%] [days] [%]

_____________________________________________________________________________________________________________________________________________________________________

Methanol 30 14 100 100 0 100Acetone 80 0 100 100 0 100MEK 100 14 100 100 0 100MIBK 94 14 100 100 0 100Ethyl acetate 100 0 100 100 0 100Butyl acetate 100 0 100 100 0 100Ethylbenzene 10 25 89 100 70 82

Toluene 10 25 89 100 70 72p-Xylene 10 25 72 100 70 64DCM 0 46 65 100 50 27DCE 0 46 58 100 50 20_____________________________________________________________________________________________________________________________________________________________________

In general, the results illustrate that a combination of the adsorbent properties of GACwith the biological activity would not improve the elimination efficiency of the VOCmixture as it was also emphasised by several authors [3941] and studied for the case ofa VOC mixture.

Concentration Profiles at Different Biofilter Levels

The removal efficiencies reached for oxygenated, aromatic and halogenated compoundsversus the column height and the type of packing are presented in Figs. 3a, b and c. Theresults were achieved under steady state conditions and show that in both cases, astratification of the removal efficiency along the biofilter height was observed. Thestratification differed according to the packing material used. For the peat biofilter, theoxygenated compounds were eliminated on the first 50 cm of the column, whereas aro-matic and chlorinated compounds were treated in the segments closer to the outlet. Insuch a biofilter, the stratification seemed to be related to biodegradability, as the morerecalcitrant a compound was, the later its elimination occurred in the reactor.


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Fig.3a, b. Removal stratification of oxygenated compounds (a) and aromatic com-pounds (b) for an inlet load of 110g/m3 h for peat and GAC biofilters (t= 90 days) (p.t.o.)


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Fig.3 c. Removal stratification of chlorinated compounds (c) for an inlet load of110 g/m3 h for peat and GAC biofilters (t= 90 days)C0 inlet compound concentration; C compound concentration; h0 column height(0 m); h column height.

On the contrary, with GAC, the removal of the oxygenated and aromatic compoundstook place along the entire height of the column, demonstrating that another phenome-non was involved. Then, even if the removal efficiency is related to the pollutant prop-erties, such as solubility and biodegradability, the packing material properties play themost important role. According to the concentration profile results, the use of a highlyadsorptive packing material would favour the elimination of compounds having a highadsorptive affinity for the packing and a low solubility. This behaviour would beperformed by an increase in the residence time of these compounds in the reactor.Nevertheless, in the case of a VOC mixture, the removal efficiency of soluble andbiodegradable compounds would be reduced. Therefore, for the VOC mixture tested, itis assumed that the sorptive properties of GAC could modify the VOC degradation

mechanisms and then involve a real reduction of the removal efficiency.

Quantitative Enumeration of the Microflora

The quantitative microflora characterisation first requires the desorption of microorgan-isms from the packing material and then the counting of the microorganisms. Hence, thispaper studies the influence of the packing material upon the efficiency of the mechanicaldesorption procedure of the microorganisms and the counting of the microflora.


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Dispersion of the Microorganisms from the Packing Material

Fig. 4 presents the number of microorganisms obtained after crushing, agitation andsonication of peat and activated carbon suspensions. A significant difference (p = 0.05)between the crushing and the agitation or the sonication methods was observedirrespective of the packing material. The number of CFU per g of dry material obtainedafter the crushing is two or three times higher than that obtained after the agitation andsonication. In addition, the Relative Standard Deviation (RSD) for the crushing method(10%) was lower than that observed for ultrasound (20%) and agitation (30%). Hence,for the two packing materials compared, the crushing with an ultra-turrax is the mostefficient and reproducible method for the removal of microorganisms.Nevertheless, other workers [27, 28, 42] demonstrated that it is very difficult to define aunique standard method for the removal of fixed biomass, which varies with materialproperties, nature of binding and type of microorganisms fixed on the surface of thesematerials.

Fig. 4. Comparison between crushing, agitation and ultrasonication for the dispersion ofmicroorganisms from peat ( )) and GAC ( ) biofilters

Enumeration of the Microflora

Selectivity of agar media for the recovery of complex microbial flora is largely recog-nised [43, 44]. Three different agar solid media, rich (LB), semi-rich (PCA) and poor(TSA diluted tenfold) were used to enumerate the culturable microorganisms.Fig. 5a, b shows that the results achieved for peat or activated carbon were different.For activated carbon, the number of CFU obtained for three samples was notsignificantly different (p = 0.01) irrespective of the solid culture medium tested (PCA:4.4 109; LB: 4.2 109; TSA 1/10: 4.5 109 CFU/g of dry activated carbon, on aver-age for the three samples).


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Fig. 5. Comparison between TSA 1/10 , PCA and LB () solid media, for theculture of microorganisms from GAC (a) and peat (b) biofiltersTSA 1/10 Tryptic Soy Agar; PCA Plate Count Agar; LB Luria Bertoni.


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For peat, the number of CFU obtained on TSA 1/10 (5.6 109 CFU/g of dry peat, onaverage for three samples) was significantly (p = 0,01) higher than that reached on PCA(1.5 109 CFU/g of dry peat, on average for three samples) and on LB (0.3 109CFU/g of dry peat, on average for three samples). As the operating conditions and theinoculation of the packing are the same, the packing material type only seems to affectthe modality of the bacterial colonisation. Some authors showed that oligotrophicmicroorganisms grow preferentially on poor solid culture media and that zymogeneousmicroorganisms grow preferentially on rich solid culture media [43, 44]. Therefore, forthe biofilter packed with peat, most of the microorganisms could be oligotrophic while,for the biofilter packed with GAC, oligotrophic and zymogeneous microbial communi-ties could be in the same proportion. It is also probable that, for the biofilter packedwith GAC, the availability of the microorganisms for VOC is enhanced due to theaffinity of the compound to the packing.Moreover, it is noteworthy that a decrease of the pH of the percolate waters from 9.6 to6.2 was observed in the biofilter packed with activated carbon. Hence, the stabilisationof pH values towards neutrality corresponded to suitable conditions that also stronglyfavoured the microbial growth on GAC. In return, in the peat biofilter, it could beassumed that the acidic pH values and the low availability for substrate would inducethe selection and growth of adapted microorganisms populations. Nevertheless, only acharacterisation of microbial communities in the two biofilters would allow the confir-mation of this hypothesis.

Conclusion

The two down-flow biofilter units have been functioned for 92 days under similar

operating conditions. The most significant observations are as follows. At steady-state,the peat biofilter achieved a greater removal efficiency than that filled with GAC.Moreover, a stratification of the removal efficiency along the column is observed inboth cases but it differed according to the type of material used. For the removal ofmicroorganisms fixed on peat and activated carbon particles, the crushing with an ultra-turrax was the most efficient dispersing method, compared to agitation with a vortexand ultrasound. The microorganism counting using three culture media demonstratedthat a diluted medium (TSA 1/10) was probably the most suitable for the recovery of thepeat biofilter microflora due to the dominance of oligotrophic bacteria, whereas foractivated carbon biofilter there was no significant difference between these mediasuggesting that oligotrophic and zymogeneous bacteria were in the same proportion.The results indicated that even the removal efficiency is related to the pollutantproperties, it is assumed that the sorptive properties of GAC could modify the VOC

degradation mechanisms and then implicate a real reduction of the removal efficiency.Moreover, the knowledge of bacterial communities involved in biodegradation, and theinteractions between these communities is of great importance to improve control and toprevent dysfunctioning of these bioreactors.

Acknowledgements

The a u tho rs a re g ra tefu l t o F ranois GOURBIRE ( U .M .R . 555 7 Labo ra to ry of Mic robial Ecol-og y, Cla ude Be rna rd Univ e rs ity, L yon, F rance ) fo r t he s ta tis t ical analy s is . This w o rk wa s


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s u p p o rted b y the ADEME ( En vironmen t and Ene rg y Con trol Agenc y, F rance ) and b y E u ro pe-En vironmen t S.A .

Received 9 December 2002Received in revised form 5 May 2003Accepted 5 June 2003

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[37] WEBSTER, T.S.: Control of Air Emissions from Publicly Owned Treatment Works UsingBiological Filtration, Ph.D. Thesis, University of South California, Los Angeles, USA, 1996.[38] DELHOMENIE, M.C., BIBEAU, L . , GENDRON, J . , BRZEZINSKI, R . , HEITZ, M.: A study of clogging

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Book Review

WAITES, M. W., MORGAN, N. L., ROCKEY, J. S., HIGTON, G.

Industrial MicrobiologyAn Introduction

Oxford: Blackwell Science Ltd.288 pagesISBN 0-632-05307-0

In view of the advent of modern biotechnologies, the question What is biotechnology? has been

asked and discussed broadly during the last decades. One of the best answers to define those activitiesthat characterise the utilisation of micro-organisms for the production of enzymes and fermentationproducts is Industrial Microbiology; and this is the title of the present book. Thus, if you are inter-ested in obtaining a rather sound and at the same time comprehensive introduction to enzyme and fer-mentation technology, including the necessary basic knowledge of relevant micro-organisms, this textcould be a good choice.The book is organised in three parts: The first part Microbial Physiology provides an overview ofmicrobial cell structures, growth, nutrition and the relevant metabolism with pathways leading to themain industrial products. Growth kinetics in batch as well as in continuous operation are presented andthe respective derivations are described. A short section also discusses some features related to the


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