Biotechnology and Bioprocess Engineering 2009, 14: 248-255 DOI/10.1007/s12257-008-0177-2

Design of a Biofilter Packed with Crab Shell and Operation of the Biofilter Fed with Leaf Mold Solution as a Nutrient

Hyeouk Man Kwon and Sung Ho Yeom*

Department of Environmental and Applied Chemical Engineering, Kangnung National University, Gangneung 210-702, Korea

^Äëíê~Åí= After measuring toluene adsorption (15.7 mg-toluene/g-material), water holding capacity (18.5%), organic content (53.8%),

specific surface area (18.1 m2/g-material), and microbial attachment, crab shells were chosen as the main packing material

for a biofilter design. The crab shells, cheap and abundant in the Gangneung area, also have relatively rigid structure, low

density, and ability to neutralize acids generated during mineralization of toluene. Since towel scraps have water holding ca-

pacity as high as 301.2%, 10% of the total packing was supplemented with them to compensate for low water holding ca-

pacity of the crab shells. The biofilter fed with defined chemical medium under 0.8~1.3 mg/L of inlet toluene concentration

and 18 seconds of residence time showed satisfactory removal efficiency of over 97% and 72.8 g/h·m3 of removal capacity.

For the purpose of deceasing operation costs, leaf mold solution was tried as an alternative nutrient instead of a defined

chemical medium. The removal efficiency and removal capacity were 85% and 56.3 g/h·m3, respectively, using the same

inlet toluene concentration and residence time. This research shows the possibility of recycling crab shell waste as packing

material for biofilter. In addition, leaf mold was able to serve as an alternative nutrient, which remarkably decreased the op-

erating cost of the biofilter. © KSBB

hÉóïçêÇëW=íçäìÉåÉI=ÄáçÑáäíÉêI=Åê~Ä=ëÜÉääI=é~ÅâáåÖ=ã~íÉêá~äI=äÉ~Ñ=ãçäÇ=ëçäìíáçåI=åìíêáÉåí=

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Volatile aromatic compounds (VOCs) such as benzene,

toluene, and xylene (BTX) are major by-products of the petroleum and fine chemical industries and the most fre-quently used organic solvents [1,2]. However, their release into the environment is strictly controlled and they are clas-sified as priority environmental pollutants by the U.S. En-vironmental Protection Agency because they are suspected to be carcinogens and can produce offensive odors [3]. They frequently enter soil, sediments, and groundwater because of leakage from underground storage tanks, pipe-lines, accidental spills, improper practices, and leaching landfills [4]. In Korea, the discharge of toluene into the air is about 20% of the total amount of discharges and a re-moval system of the compound urgently needs to be devel-oped [5].

Biofiltration has been proven as an especially attractive technology for treatment of waste gases containing relatively G`çêêÉëéçåÇáåÖ=~ìíÜçê=

Tel: +82-33-640-2406 Fax: + 82-33-641-2410

e-mail: shyeom@kangnung.ac.kr

low concentration of VOCs, because of its simplicity, low cost, and non-generating hazardous residues [6]. Waste gases pass through the biofilter bed and mass transfer of pollutants from gas stream to biofilm formed on the packing material continuously occurs. The pollutants are then mineralized to carbon dioxide and water by the microbial populations in the biofilm. The performance of biofilter is mainly dependent on the packing materials [9]. An ideal packing medium should meet the following requirements [7-9]: (1) it is easy to main-tain in optimum conditions, such as high moisture content, sufficient nutrients, and suitable pH for microbial growth in the packing medium, (2) it should have large surface area and uniform pore distribution to gain high VOC mass-transfer efficiency from the gas phase to the packing media, (3) it should have low pressure drops to reduce energy con-sumption, (4) it should have minimum bed compaction and deterioration to avoid frequent replacement, and (5) it should be cheap and easy to obtain. The early biofilters are usually packed with natural sources such as soil [10], compost [11], peat [12], and wood chips [13]. The natural sources, how-ever, decay over time causing compaction, clogging, and short circuiting [14]. These problems require frequent re-placement of packing materials, which increases operation

Biotechnol. Bioprocess Eng. OQV

costs. As alternatives, inert packing materials such as syn-thetic polymers (polyurethane foam, polystyrene, etc.), acti-vated carbon, ceramic, and perlite are widely adopted as packing materials [6,15-17]. While the inert materials cause less clogging problems, they are usually expensive and re-quire large amounts of nutrient for the microorganism in a biofilter [15].

In this research, various cheap materials were tested as candidates for efficient packing materials for toluene degra-dation in a biofilter. In addition, a cheap nutrient source was explored to save operating costs. j^qbof^ip=̂ ka=jbqelap=

jáÅêççêÖ~åáëã= =

A microorganism capable of degrading toluene as a sole carbon and energy source was isolated from crude oil con-taminated soil and identified as Pseudomonas fluorescence [18]. The microorganism is also able to degrade benzene and phenol. m~ÅâáåÖ=j~íÉêá~äë=

Crab shells and scallop shells were collected from local restaurants in the city of Gangneung. Activated carbon and zeolite were purchased from a domestic supplier (DongY-ang Carbon, Korea). Leaf mold, earthworm castings, saw-dust, tire scraps, and rice straw were donated by local manufacturers. Soil and sand were scooped at the yard of Kangnung National University. The other miscellaneous materials (newspaper, used brick, chalk, wood stems, poly-styrene foam, pinecones, and pine needles) were collected around Gangneung. The materials were washed several times and autoclaved to ensure that no microorganisms existed on the materials. ^ëë~óë=

Cell concentration was measured using a UV/VIS spec-trophotometer (Jasco V-550, Japan) at 660 nm. Gaseous toluene concentration was determined with a GC (HP 5890II, USA) as follows. Next, 100 µL of toluene was withdrawn from sampling ports installed at the bottom, middle, and top of biofilter with a 2.5 mL gas-tight syringe (Hamilton, USA) and injected into the GC operating under the condition of 150°C for injector, 100°C for oven, and 250°C for detector. HP-5 column was installed in the GC and helium was used as a carrier gas. The surface of the crab shells was photo-graphed using a SEM (Hitachi S-4700, Japan) after the shells were pretreated as follows. Moisture in the crab shells were first removed by consecutive soakings in 30, 50, 70, and 90% ethanol for 5 minutes each and in absolute ethanol for 15 minutes. The shells was then stored at −70°C for 24 h followed by lyophilization for 24 h. The shells were finally coated with platinum and the surface of the crab shells was photographed.

`Ü~ê~ÅíÉêáò~íáçå=çÑ=m~ÅâáåÖ=j~íÉêá~äë= =

qçäìÉåÉ=̂ Çëçêéíáçå=Fifty milligrams of material was placed in a 120 mL se-

rum bottle and 3 mg of toluene was added to the bottle using a 25 µL micro-syringe (Hamilton, USA). The bottle was then closed tightly with a rubber septa and an aluminum cap. The bottle was incubated in a shaking incubator (Hanil combi-514R, Korea) operating at 30°C and 200 rpm for 12 h. The toluene concentration in the headspace of the bottle was de-termined and the amount of toluene adsorbed by the material was calculated. t~íÉê=eçäÇáåÖ=`~é~Åáíó=A material was dried in an oven (Jeio Tech OF-11E, Ko-

rea) at 105°C for 12 h to ensure complete dryness. After 10 g of dried material was soaked in water for 6 h, the material was placed in a clean bench at 25°C for 24 h. The water holding capacity (%) of the material was determined by di-viding the weight of wet material by that of dry material. jáÅêçÄá~ä=̂ íí~ÅÜãÉåí=Fifty milligrams of material was added to a 250 mL flask

containing 100 mL of basal mineral medium (2 g/L (NH4)2SO4, 0.3 g/L MgSO4·7H2O, and 0.1 g/L K2HPO4). The initial cell concentration was 1.0 g/L. The flask was placed in a shaking incubator operating 30°C and 200 rpm for 10 h. The concen-tration of free cell in the flask was measured and the amount of microorganism attached to the material was calculated. In the case of soil, leaf mold, earthworm castings, and crab shells, it was not easy to measure exact cell mass due to lots of minute colloidal particles with colors in the culture. Therefore, colony counting was alternatively used for the calculation of microbial attachment as follows. After 10 hours’ incubation of cell and a packing candidate, 100 µL of 10,000 times diluted culture was spread on a nutrient agar plate composed of 1 g/L sodium benzoate, 20 g/L agar, 0.2 g/L MgSO4·7H2O, 0.5 g/L NH4HCl, 0.1 g/L NaCl, and 1 g/L K2HPO4. Sodium benzoate, a good substrate to Pseu-domonas fluorescence, was used as a sole carbon source to prevent contamination. Culture solution without packing candidate was also prepared and assigned as a control. The plate was then placed in an incubator (Jeio Tech IB-15G, Korea) at 30°C for 24 h. The ratio of colony number of sam-ple to that of control was calculated and it was used to calcu-late microbial attachment. lêÖ~åáÅ=`çåíÉåí=After 10 g of material was completely dried at 105°C for 12

h, the material was put in a furnace (Lenton furnaces, Eng-land) at 600°C for 12 h. The organic content was calculated by subtracting the ash mass from dried material mass. ée=`Ü~åÖÉ=Äó=`ê~Ä=pÜÉääë=0.5, 1.0, 2.0, 3.0, or 5.0 g of crab shells were added to 100

mL of distilled water of which pH was 6.0. The pH change with time was measured using a pH meter (Orion 420A, USA).

ORM=

péÉÅáÑáÅ=pìêÑ~ÅÉ=̂ êÉ~ Specific surface area was measured using a surface ana-

lyzer (Micromeritics ASAP-2010, USA). Nitrogen gas was used as an adsorbed material. páòÉ=~åÇ=áíë=aáëíêáÄìíáçå=Raw material was crushed using a micro hammer mill

(Culatti AG MFC CZ 13, Switzerland) and sieved to get a sample with low size distribution. The sample was sus-pended in distilled water and their size and size distribution was determined with a particle size analyzer (Beckman Coulter LS230, USA). mêçíÉáå=`çåíÉåí=Thirty milligrams of crab shells were added to 10 mL of 6

N HCl and the protein in the crab shells were hydrolyzed at 110°C for 24 h. After HCl was completely evaporated by a rotary evaporator (BUCHI Rotavapor R-124, Switzerland), residue was dissolved in 10 mL of distilled water. Each amount of amino acid was analyzed using an amino acids analyzer (Hitachi L-8800, Japan) and protein content was calculated by summing up amino acid contents. ^äíÉêå~íáîÉ=kìíêáÉåí=mêÉé~ê~íáçå=Sixty milligram of leaf mold, crab shells, earthworm cast-

ings, or soil was added to 1 L of distilled water and the solu-tion was vigorously stirred for 5 h. After precipitating debris, the solution was decanted and used as a nutrient. mêÉJÅìäíìêÉ= =

The microorganism was pre-cultured to obtain enough cell mass for various experiments. The cells from agar plate stored at 4°C were inoculated into a 500 mL flask containing 250 mL of medium of which composition was 10.0 g/L glu-cose, 5.0 g/L yeast extract, 5.0 g/L (NH4)2SO4, 5.0 g/L KH2PO4, and 1.0 g/L MgSO4·7H2O. The flask was placed in a shaking incubator operating at 30°C and 200 rpm for 24 h. The cells were settled with a centrifuge (Hanil combi-514R, Korea) and supernatant solution was discarded. After the cells were resuspended in phosphate buffer solution (60 mM and pH 7.0), they were settled again by centrifuge. By re-peating the procedure three times, culture medium was re-moved and enough cells were prepared.

_áçÑáäíÉê=aÉëáÖå=~åÇ=léÉê~íáåÖ=`çåÇáíáçå=

A two-stage biofilter system was assembled as shown in Fig. 1. Each stage was made of a cylindrical acryl column 15 cm long and 6 cm in diameter. Sampling ports were installed at the bottom, middle, and top of the biofilter. Toluene gas was generated by purging air through a reservoir containing pure toluene. The toluene gas was mixed with air. Toluene concentration ranging from 0.8 to 1.3 mg/L was obtained by controlling flow rate of each stream with flow-meters (Dwyer, USA) and total flow rate of the synthetic toluene gas was fixed at 1.0 L/min. The resulting synthetic toluene gas was introduced through the bottom of the biofilter. The

cáÖK=NK Schematic diagram of biofilter.

biofilter and toluene reservoir were wrapped with a heating coil operating at 25°C. Drainage from the biofilter was col-lected and its pH was measured every 6 h. Nutrient solution of 70 mL was fed at the top of biofilter through a distributor every 8 h. Pressure drop along the biofilter was checked every 6 h using a differential pressure gauge (Konics Inc, Magnetic-2000, Korea).

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pÉäÉÅíáçå=çÑ=m~ÅâáåÖ=j~íÉêá~ä=

As stated above, packing material is the most important factor in biofilter design. The candidates for packing mate-rial were natural products or waste from around the city of Gangneung. For instance, crab shell waste was easily col-lected because the city is located at the seashore of East Sea in Korea and has many restaurants and crabmeat factories. Most crab shells are currently being dumped into landfills. In this study, toluene adsorption capacity, water holding capac-ity, microbial attachment, and organic content were consid-ered as the criteria for the selection. qçäìÉåÉ=̂ Çëçêéíáçå=

Inlet concentration of toluene can fluctuate with the sea-son, time of day, operation schedule, etc. Also, the inlet con-centration could abruptly increase due to accidents. In an emergency, packing material can act as a buffer to adsorb toluene and this alleviates the organic burden on the biofilter and inhibition on microorganism. Twenty-one materials were tested for their toluene adsorption as shown in Table 1. The results show that activated carbon, irrespective of size and origin, adsorbed approximately 56 mg of toluene per gram. Crab shells and tire scraps adsorbed 15.7 mg/g and 11.5 mg/g, respectively. The natural and agricultural prod-ucts such as rice straw, leaf mold, pinecones, and wood

Biotechnol. Bioprocess Eng. ORN

q~ÄäÉ=NK Toluene adsorption capacities of various packing materials

Material

Adsorption capacity

(mg-toluene/

g-material)

Material

Adsorption capacity

(mg-toluene/

g-material)

Activated carbon

powdera

56.9 Activated carbon

powderb

56.6

Activated carbon

granulec

56.3 Crab shell 15.7

Wasted tire

scrap

11.5 Zeolite 08.2

Earthworm

casting

06.6 Soil 05.7

Used briquette 04.3 Sawdust 04.2

Chalk 03.5 Styrofoam 03.2

Sand 02.7 Towel scrap 02.2

Pine needle 01.6 Scallop shell 01.1

Rice straw 00.2 Leaf mold 00.1

Wood 00.0 Newspaper 00.0

Pine cone 00.0

aFrom coconut,

bfrom sawdust,

cfrom coconut.

stems showed very low adsorption capacity. t~íÉê=eçäÇáåÖ=`~é~Åáíó=

Pollutants in air stream are to be dissolved in the wet layer of biofilm before being degraded by microorganisms. Also, water is essential for microbial survival and growth. Accord-ingly, it is crucial to prevent the biofilter bed from drying out. Humidification of the inlet pollutant is a frequently men-tioned method but it is not enough to ensure the filter bed from drying out. So, periodic sprays of water or medium are often employed [15]. In any case, the material having high water holding capacity is preferable for packing material. Water holding capacity was investigated as shown in Table 2. Towel scraps showed the highest water holding capacity of 301.2% followed by sawdust (245.5%), earthworm castings (31.7%), and activated carbons (30.5~31.7%). Crab shells exhibited 18.1% of water holding capacity and tire scraps only 1.3%. jáÅêçÄá~ä=̂ íí~ÅÜãÉåí=

If a microorganism attaches to a material easily, biofilm can be also readily formed on the material. Microbial at-tachment was investigated for 12 candidates as shown in Table 3. Coconut granular activated carbon showed the highest attachment (11.4 mg-cell/g-material) followed by sawdust activated carbon powder (10.5 mg/g), towel scraps (6.4 mg/g), zeolite (4.7 mg/g), and coconut powder activated carbon (3.9 mg/g). In the case of earthworm castings, soil, leaf mold, and crab shells, cell mass in culture solution was determined using a colony counting method as previously described. The results showed that free cell concentration increased after incubation, which was due to cell growth on

q~ÄäÉ=OK Water holding capacities of various packing materials

Material Water holding

capacity (%) Material

Water holding

capacity (%)

Towel scrap 301.2 Sawdust 245.4

Activated carbon

powdera

031.7 Earthworm casting 31.7

Activated carbon

granuleb

031.4 Activated carbon

powderc

30.5

Crab shell 018.1 Zeolite 5.4

Wasted tire scrap 001.3 Soil 0.9

Scallop shell 000.4 aFrom coconut,

bfrom coconut,

cfrom sawdust.

q~ÄäÉ=PK Microbial attachment to the various packing materials

Material

Microbial

attachment

(mg-cell/

g-material)

Material

Microbial

attachment

(mg-cell/

g-material)

Activated carbon

granulea

11.4 Activated carbon

powderb

10.5

Towel scrap 06.4 Zeolite 04.7

Activated carbon

powderc

03.9 Scallop shell 02.1

Wasted tire scrap 02.0 Sawdust 01.2

Earthworm castingd - Leaf moldd -

Soild - Crab shelld -

aFrom coconut,

bfrom sawdust,

cfrom coconut,

dnon-measurable.

their organic components (data not shown). Therefore, we could not measure microbial attachment onto the four mate-rials in this study. However, the phenomena gave the idea of using the materials as nutrient for biofilter, which will be discussed afterwards. péÉÅáÑáÅ=pìêÑ~ÅÉ=̂ êÉ~=

The higher specific surface area (SSA, m2/g) allows wider room for biofilm, which means easy contact of toluene with wet layer on biofilm. The SSA of candidate materials were measured or cited from a reference as shown in Table 4. The SSA of activated carbon was highest as 1,145 m2/g and those of zeolite and earthworm castings were also very high at 581.7 m2/g and 327.3 m2/g, respectively. The SSAs of tire scraps and crab shells were 87.6 m2/g and 18.1 m2/g, respec-tively. These differences are thought to have mainly arisen from the surface of micropores. The activated carbon and zeolite are known to have innumerable micropores of nano or angstrom size and this increases SSA tremendously. So, the micropores play a key role in adsorption of molecules [19]. However, a biofilter deals with low concentration of gaseous pollutants and the pollutants are continuously de-graded by the microorganism. Accordingly, packing material does not have to necessarily have SSA as high as activated carbon. For instance, a biofilter packed with monolith of

ORO=

q~ÄäÉ=QK Surface area of various packing materials

Material Surface area (m2/g) Remarks

Activated Carbon 1,145 literature [17]

Zeolite 0.581.7 measured

Earthworm casting 0.327.3 measured

Tire scrap 00.87.6 measured

Crab shell 00.18.1 measured

which SSA is less than 1.0 m2/g was successfully applied to the treatment of toluene [14]. cáå~ä=aÉÅáëáçå=çå=m~ÅâáåÖ=j~íÉêá~ä=

In the case of activated carbon, it shows relatively good toluene adsorption, water holding capacity, and microbial attachment. Activated carbon, however, has no organics and requires nutrients for biofilter operation. The binding be-tween activated carbon and toluene is thought to be strong and the removal of toluene may be mainly due to adsorption instead of biodegradation [19]. Therefore, it is necessary to replace or regenerate the activated carbon saturated with toluene, which increases operation costs. The activated car-bon can be a good choice to treat high concentration of tolu-ene. The leaf mold has as high as 72.5% of organics and this can serve as a nutrient for the microorganism in the biofilter. However, it may cause clogging as other organic packing materials do. The tire scraps show relatively high toluene adsorption (11.5 mg/g) but the water holding capacity and microbial attachment was relatively poor at 1.3% and 2.0 mg/g, respectively. Towel scraps have high water holding capacity and microbial attachment at 301.2% and 6.4 mg/g, respectively. However, since they are not rigid, they can cause a severe pressure drop problem. The towel scraps can be a supplementary packing material to prevent dryness in the biofilter. Crab shells shows relatively high toluene ad-sorption and organic content at 15.7 mg/g and 53.8%, re-spectively. And 12.0% of the crab shells were protein; in other words, 22.0% of organic material. So, crab shells can supply some nutrient for cell growth. In addition, the struc-ture of crab shells is rigid enough to support itself and may cause much less pressure drop. As the size of crab shells can be intentionally tailored for the biofilter, porosity is easily controlled. Crab shells were also found to act as a pH buffer to mitigate pH decrease during biofilter operation as shown in Fig. 2. The addition of 0.5~5 g of crab shells into 100 mL of distilled water increased the pH value from 6.5 to 9.5~10.5 and the crab shells are believed to prevent acidifi-cation of biofilter. The low water holding capacity of crab shells could be compensated by the addition of towel scraps. ^äíÉêå~íáîÉ=kìíêáÉåí=pçìêÅÉ=

Conventional packing materials such as compost and peat serve as a nutrient supply as well as a support for biofilm. Recently, most biofilters employing inorganic or composite

cáÖK=OK The pH increase by the addition of crab shell into the distilled

water. cáÖK=PK Cell growth on the organic packing material. �, distilled wa-

ter; �, earthworm casting; �, leaf mold; �, soil; �, crab

shell.

packing material require external nutrient supply, which in-creases operation costs [15]. In this study, organic natural products or wastes such as leaf mold, earthworm castings, crab shells, and soil were considered as nutrient sources in the biofilter. The possibility was tested by culturing the mi-croorganism in the medium containing one of the candidates. As shown in Fig. 3, cell concentration was gradually de-creased for the first 5 h, which was considered as an adapta-tion period. Thereafter, the cells grew steadily. The final concentration was highest as 224 mg/L for crab shells fol-lowed by leaf mold (186 mg/L) and earthworm castings (123 mg/L). Since leaf mold has the highest organic content (72.5%) and is very cheap (0.1 USD/Kg), it was finally se-lected as a candidate for nutrient supply. Just 1 Kg of leaf mold can serve as a nutrient for 8 days.

_áçÑáäíÉê=léÉê~íáçå=

The two two-stage biofilters were constructed and each

Biotechnol. Bioprocess Eng. ORP

cáÖK=QK Operation of biofilter fed with defined chemical medium. �,

influent toluene concentration; �, removal efficiency at first

stage; �, removal efficiency at second stage.

stage contained 15 cm of packing materials. Tire scraps with 1 cm height were placed at the bottom of each stage to sup-port the main packing material. The mixture of crab shells (90% of total volume) and towel scraps (10%) were cumu-lated on the tire scraps. The two materials were packed with 38% of porosity and residence time of toluene gas was 18 seconds. Before loading, the crab shells and towel scraps were incubated with Pseudomonas fluorescence for 5 h at 30°C and 200 rpm. Since toluene degradation by P. fluores-cence was most active around 25°C [18], each biofilter was wrapped with a heating coil at 25°C and placed in a hood at room temperature. Next, 70 mL of medium, defined or leaf mold solution was fed every 8 h. Drainage from the biofilter was collected for pH measurement. Pressure drop was also checked every 6 h as previously stated. _áçÑáäíÉê=léÉê~íáçå=cÉÇ=ïáíÜ=ÇÉÑáåÉÇ=`ÜÉãáÅ~ä=jÉÇáìã=

The defined medium was composed of 2 g/L (NH4)2SO4, 0.3 g/L MgSO4·7H2O, 0.1 g/L K2HPO4, and 100 µL/L trace element [1]. As shown in Fig. 4, biofilter was operated for 20 days with inlet toluene concentration of 0.8~1.3 mg/L and residence time of 18 seconds. Next, 50~70% of inlet toluene was removed at first stage and over 95% at second stage. The removal efficiency and removal capacity were summa-rized in Table 5. The removal capacity was defined as the

q~ÄäÉ=RK Comparison of removal efficiency and removal capacity of

the two biofilter operations

Defined chemical medium Leaf mold solution Medium

Stage

Removal

efficiency

(%)

Removal

Capacity

(g/h·m3)

Removal

efficiency

(%)

Removal

Rate

(g/h·m3)

First stage 60 90.0 45 67.5

Total 97 72.8 75 56.3

amount of removed toluene per cubic meter of packing ma-terial. The removal efficiencies at each stage were average values during operation. The removal capacity of the first stage was 90.0 g/h·m3 and the total removal capacity of the biofilter was 72.8 g/h·m3. There was a report that the re-moval capacity of toluene by a biofilter packed with compost was 82 g/h·m3 [20]. Another study showed that a biofilter packed with perlite exhibited 60 g/h·m3 of the removal ca-pacity of toluene [21]. So, it can be said that the removal capacity of toluene by the biofilter suggested in this study is adequate. The surface of crab shells before and after opera-tion was observed using the SEM. Biofilm was well formed on the surface of crab shells after 20 days’ operation as shown in Fig. 5. The Figure also indicated that a variety of morphologically different microorganisms coexisted in the biofilm. The pH of drainage was in the range of 5.9~6.7 and pressure drop was negligible during 20 days’ operation (data not shown). _áçÑáäíÉê=léÉê~íáçå=cÉÇ=ïáíÜ=iÉ~Ñ=jçäÇ=pçäìíáçå=

As described previously, organic component in packing ma-terial can supply nutrients to the microorganism in the biofilter. The natural products with high organic content such as com-post and peat are thereby often used as packing materials. However, they are easily decayed and compacted to increase pressure drop. Leaf mold had 72.5% of organic content and it was tried as a nutrient source. Except that leaf mold solution was used as a nutrient for the biofilter, the other operation condition was the same as the operation with defined chemical medium. The removal efficiency at the first stage was in the range of 45~60% and that at the second stage was 75~85%. The values were lower than the previous case by 10~20%. However, the result shows the possibility of using leaf mold solution as a nutrient for biofilter operation. And the removal efficiency could be hopefully enhanced by optimized medium preparation and elaborative feeding.

`lk`irpflk=

As an attempt to develop cheap and efficient packing ma-terial, various natural products, wastes, and conventional materials were tested on the basis of four criteria, which were toluene adsorption, water holding capacity, microbial attachment, and organic content. Crab shells, an abundant

ORQ=

^=

_=

cáÖK=RK SEM image of the surface of crab shell. (A) Before operation, (B) after operation.

cáÖK=SK Operation of biofilter fed with leaf mold solution. �, influent

toluene concentration; �, removal efficiency at first stage; �,

removal efficiency at second stage.

and cheap waste, showed relatively good properties except water holding capacity and has rigid structure as well. There-fore, towel scraps exhibiting the highest water holding ca-pacity were complementary packed with the crab shells. A defined chemical medium was periodically fed to the biofil-ter and the removal efficiency was over 95% under the op-eration condition of approximately 1 mg/L of inlet toluene concentration and 18 seconds of residence time. Leaf mold, having as high as 72.5% of organic content, was chosen as a nutrient source and its solution was fed to the biofilter in-stead of defined chemical medium. The biofilter showed around 80% of removal efficiency. This research showed two possibilities of recycling crab shells as packing material and leaf mold solution as a nutrient source. ^ÅâåçïäÉÇÖÉãÉåí This research was financially supported by grant No. RTI05-01-02 from the Regional Technology Innovation Program of the Ministry of Knowledge Economy (MKE), Korea. The authors are grateful for the support. Received August 6, 2008; accepted December 30, 2008 obcbobk`bp=

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