EPA/600/A-94/055
Development of Aerobic Biofilter
Design Criteria for Treating VOCs
George A. So rial
Francis L Smith
Paul J. Smith
Makram T. Suldan
PratJm Biswas
University of Cincinnati
Cincinnati, Ohio
Richard C. Brenner
U.S. Environmental Protection Agency
Cincinnati, Ohio
Air & Waste Management
association
For Presentation at the
86th Annual Meeting & Exhibition
Denver, Colorado
June 13-18, 1993
Simci 1907
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93-TP-52A.04
INTRODUCTION
With the enactment of the 1990 amendments of the Clean Air Act, the control of
volatile organic compounds (VOCs) in contaminated air streams has become an important
issue.1 The concept of using biological processes for controlling undesirable compounds in
different kind of wastes has increasingly been applied. With respect to the purification of
polluted air, biofiltration is a potential cost effective process for treatment of large gas flows
contaminated with low concentrations of biodegradable VOCs, especially in comparison to the
conventional VOC control technologies such as incineration and carbon adsorption.' The low
operating cost is due to the use of microbial oxidation, which is achieved at low operating
temperatures, rather than thermal or chemical oxidation. Essentially, biofiltration operates at
ambient temperatures, and is a self regenerating, enzymatic catalytic process. It consists of
contacting a contaminated air stream with a moist film of microbes attached to a stationary
synthetic or natural support material. VOCs are oxidized to simple end products such as HjO
and CO,. More recently, biofiltration as a hazardous VOC control technology has been the
subject of extensive research, and the design criteria have been identified.''4
In bench scale research, the use of trickle bed biofilters has become popular. This type
of biofilter allows for more uniform surface area and gas distribution, resulting in better
pressure drop control, as well as more consistent operation due to better nutrient and pH
control. Such biofilters consist of a filter containing microbes supported on an inert material,
with nutrients applied at the top at a minimal liquid flow rate. Effluent recycle is typical, both
for pH control as well as microbe reseeding, and an effluent purge removes excess salts and
biomass. Kirchner el alP investigated the effect of contaminant solubility by examining the
treatment of acetone, propionaldehyde, naphthalene, and toluene in a trickle bed biofilter. Diks
and Ottengraf1 found that a recirculating trickle bed biofilter using saddle packings was
effective in treating methylene chloride. They directly correlated the amount of sodium
hydroxide added to the recycle stream for pH control to the elimination capacity. Cocurrent
flow air and recycle liquid flow avoided stripping of VOCs at the exit of the filter although the
difference appeared to be minimal. Hartmans and Tramper' investigated the treatment of
methylene chloride in a trickle bed biofilter and concluded that recirculated biofilters were
superior to compost beds for treatment of halogenated compounds because pH and salt were
more easily controlled. Utgikar et al.10 proposed the use of activated carbon packed trickle
biofilters for treatment of landfill leachate offgasses for adsorbing the substrate, that is not
consumed by the microbes, on the support media.
This paper reports preliminary results of studies performed utilizing trickle bed
biofilters with monolithic channelized microbial support for the treatment of VOCs typical of
landfill leachate stripping. For the initial studies, toluene has been used for the purpose of
characterizing the trickle biofilter apparatus, to be followed with ethylbenzene, chlorobenzene,
trichloroethylene, and methylene chloride. The objectives of the experiment are to investigate
2
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93-TP-52A.04
the use of such biofilters, both cocurrent and countercurrent, for treating these compounds with
high removal efficiency at inlet concentrations which are high, relative to most biofilter
research to date. The further research objective is to reduce to practice biofiltration for the
treatment of such VOC containing air streams.
MATERIALS AND METHODS
Experimental Apparatus
The experimental apparatus consists of two independent, parallel, trickle biofilters
designated as biofilter "A" and biofilter "B". Each biofilter is made of 304 stainless steel, and
has a square cross-section with internal dimension of 5.75" and consists of the following
sections from top to bottom:
1) a 4" module for nutrient and buffer addition, and for air inlet (or outlet);
2) a 12" module for housing the nutrient and buffer distribution apparatus;
3) four 12" modules containing the biofilter biological attachment media; the media used
is Coming Celcor® channelized media (a magnesium aluminosilicate material) having
7.75 channels per cm3.
4) a 4" module for waste water outlet, and air inlet (or outlet).
In order to minimize condensation and to maintain a constant temperature, the biofilters are
insulated and temperature controlled with external cooling coils.
The air supply to the biofilters is purified with complete removal of water, oil, C02,
VOCs, and particulates, especially microbes. After purification, the air to each biofilter is split
off, humidified, externally heated to assist vaporizing the injected toluene into the air stream
via a syringe pump, and finally fed to the biofilters. The air is mass flow controlled. A
schematic of the experimental apparatus is shown in Figure 1.
Each biofilter is equipped with separate systems for feeding 20 L/day of a nutrient
solution containing all necessary macro-, micro-nutrients and buffers. The compositions of the
mixed nutrient solutions (consisting of trace salt, salts and vitamin solutions) are presented in
Tables I, II and III. The daily recipe consists of 9.0 mL stock salt solution, 2.3 mL vitamin
solution, 4 mL of 0.01M FeClj solution, and 5 mL of nutrient spike solution (2M NH4CI,
0.5M NaH2P04). One molar sodium bicarbonate was used as a buffer (45 mL). Since
observing that most of the ammonia in the feed is converted to nitrate, the nitrification inhibitor
TCMP (2-chloro-6-(trichloromethyl)pyridine) is added to the nutrient formulation. Each
biofilter is also equipped with effluent recirculation in order to provide even distribution of the
biomass throughout the attachment media. Biofilter "A" is operated in a cocurrent mode, top
to bottom, with the air flov., nutrient, and effluent recycle flows directed downwards. Biofilter
"B" is operated in a countercurrent mode, with the air flow directed upwards and the nutrient
3
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93-TP-52A.04
and effluent recycle flows directed downwards.
Materials
Reagent grade Toluene (99.9%, Fisher Scientific Co., Inc., Fair Lawn, NJ) was used as
the target VOC contaminant in this study.
The seed for the biofilters was an activated sludge acclimated to the target VOCs:
toluene, ethylbenzene, chlorobenzene, irichloroethylene, and methylenechloride. A synthetic
solution containing 2% by volume of each VOC in toluene was fed daily, batchwise, to a
stirred, aerated reactor. The growth of the biomass was monitored indirectly by observing the
volume of 10M NaOH required for daily pH adjustment.
Analytical Methods
Concentrations of toluene were measured by chromatographic separation on a 30-m
megabore column (DB 624, J&W Scientific, Folsom, CA) using a gas chromatograph (GC)
(HP 5890, Series II, Hewlett-Packard, Palo Alto, CA) equipped with a liquid sample
concentrator (LSC 2000, Tekmax, Cincinnati, OH), and a photoionization detector (P1D)
(Model 4430 , 01 Corp., College Station, TX). The liquid sample concentrator was
programmed according to USEPA Method 601, a Tenax trap was used with helium (He) purge
flow of 40 mL/min. The GC oven temperature was programmed from 40 to 120 °C at 5
degrees/min with a 4-min hold at 40 °C and a 6-min hold at 120 °C. The carrier gas (He) flow
rate was set at 8 mL/min and the PID detector was used with He make-up gas at a flow-rate of
20 mL/min, sweep gas flow (H2) at 100 mL/min and base temperature of 250 °C.
Gas phase samples, for VOC analysis, were taken with gas tight syringes through low
bleed and high puncture tolerance silicone GC septa (replaced every week) installed in the
sampling ports at the gas inlet and outlet from the biofilters. Samples from the liquid phase,
for VOC analysis, were taken out in a similar way from the liquid outlet from the biofilters.
Both gas and liquid phase samples were introduced to the GC through the liquid sample
concentrator accessory. The gaseous phase VOC analysis was conducted by introducing 5 mL
of purged distilled deionized water into the purge vessel of the liquid sample concentrator prior
to the injection of the gas sample.
Liquid phase samples were also analyzed for nitrate and ammonia concentrations by
using the electrode method of analysis according to Standard Methods" 4500-D, and 4500-F,
respectively. Samples were filtered through 0.45 nm nylon filters (Micron Separation, Inc,
Westboro, MA) prior to analysis.
The pH determinations were conducted by using Fisher Accumet pH meter, Model 50
(Fisher Scientific Co., Inc., Fair Lawn, NJ). The pH meter was calibrated before use by using
buffers (pH of 3.0 and 7.0) supplied by the manufacturer.
4
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93-TP-52A.04
RESULTS AND DISCUSSION
Startup of each biofilter was with 50 ppmv toluene at a 12 minute residence time, and a
nutrient solution feed 20 L/day. Each biofilter was maintained at a constant temperature of
14±2 °C and 7.7+0.2 pH range.
Biofilter "A": The mass flow of toluene was increased steadily up to 400 ppmv at a
residence time of 12 minutes. On day 85 it was noticed that most of the ammonia in the
nutrient solution went to nitrate formation instead of biosynthesis. A nitrate inhibitor was then
added to the nutrient solution in order to minimize the nitrate production, in both the feed tank
and the biofilter. The maximum percent removal of toluene that could be obtained at 400
ppmv was only S0%. In order to improve the performance, the effluent was recycled to
provide even distribution of the biomass throughout the suppon media. On day 127, the
recycle was started and the percent removal increased to about 90%. The mass flow of toluene
was then increased to 500 ppmv at 12 minutes residence time. When the percent removal of
toluene was stable at 99%, a residence time cycle test was performed, with the residence time
being varied from 12 to 1 minutes and then back to 12 minutes. This was done while holding
constant the total mass of toluene fed per day. Figure 2 shows the performance of the biofilter
with respect to toluene removal. Note that during the second leg of the residence lime cycle
test, when the VOC concentration was being increased with each step, more time was required
for the biofilter to achieve the same performance as on the first leg. Figure 2 also shows that
the influent concentrations obtained from the GC analysis are in good agreement with the
theoretical concentrations obtained from the flow rate of the syringe pump, used for injecting
toluene to the biofilter system, and the air flow rate. Figure 3, showing the performance of the
biofilter with respect to ammonia utilization, shows the amount of ammonia going to synthesis.
This amount is indicated by the difference between influent ammonia and effluent ammonia
plus nitrate formed. Figure 4 shows the performance of the biofilter during the residence time
cycle test. From Figure 4 it is seen that the toluene removal stabilized at better than 96% up
to 4 minutes residence time. At 2 minutes residence time the removal efficiency dropped to
about 90% and the performance further dropped to 65% at 1 minute residence time. At 1
minute residence time the pressure drop was about 1 inch of water.
Biofilter "B": The mass flow of toluene was increased steadily up to 200 ppmv at a
residence time of 12 minutes. The performance was very poor compared to biofilter "A". The
removal of toluene did not exceed 70%, and after day 87 the performance in fact started to
drop. On day 90 the nitrate inhibitor was added to the nutrient feed. On day 113 the removal
of toluene dropped to about 57%, and at this point it was decided to introduce effluent recycle
to the biofilter. On day 114 the recycle was started, and by day 122 the removal of toluene
was 85%. At this point the mass flow of toluene was increased steadily until it reached 500
ppmv at a residence time of 12 minutes. The biofilter was maintained at these conditions until
5
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93-TP-52A.04
a stable effluent was obtained. At this point a residence time cycle test was started, conducted
in a manner similar to biofilter "A". Figure 5 shows the performance of biofilter "B" with
respect to toluene removal. Note that during the second leg of the cycle test, when the VOC
concentration was being increased with each step, more time was required for the biofilter to
achieve the same performance as on the first leg. This behavior also was noticed previously
with biofilter "A". Figure 5 also shows that the influent concentrations obtained from the GC
analysis are in good agreement with the theoretical concentrations obtained from the flow rate
of the syringe pump, used for injecting toluene to the biofilter system, and the air flow rate.
Figure 6, showing the performance of the biofilter with respect to ammonia utilization, shows
the amount of ammonia going to synthesis. This amount is indicated by the difference between
influent ammonia and effluent ammonia plus nitrate formed. Figure 7 shows the performance
of the biofilter during the residence time cycle test. From Figure 7 it is seen that toluene
removal during the cycle test stabilized between 87 and 89% up to 6 minutes residence time,
then 72% at 4 minutes, 45% at 2 minutes, and 30% at 1 minute. At a 1 minute residence time
the pressure drop was about 1.75 inches of water.
CONCLUSIONS AND FUTURE WORK
The removal efficiency for each residence time was similar, for both increasing and
decreasing residence times. However, it appears that when reducing the residence time, which
causes an increase in the VOC concentration at constant mass loading, more time is required by
the biofilter to achieve maximum efficiency. Effluent recycle was necessary to achieve
maximum efficiency.
Biofilter "A", which was operated cocurrently, showed the highest VOC removal
efficiency. The efficiencies ranged from 99% to 65% for residence times of 12 and 1 minute,
respectively. On the other hand biofilter "B", which was operated counter-currently, showed
efficiencies less than 90%. The efficiencies ranged from 90% to 30% for residence times of 12
and 1 minute, respectively. The lower toluene removal efficiencies correlate with the
substantially lower ammonia utilization, indicating a lower rate of cell synthesis in Biofilter
"B".
The pressure drop for both biofilters were quite low, with a maximum of 1 and 1.75
inches of water for biofilters "A" and "B", respectively. This low pressure drop, even for the
countercurrent mode, is very promising as it indicates that the major operating cost for this
biofilter design, blower motor power, will be lower than for most typical biofilter designs.
Continuing work will include investigating the effect of the recycle flow rate on the
performance of each biofilter. Investigation will also be made of increasing the mass loading to
500 ppmv at lower residence times. Xenobiotic VOCs will be tested for degradation after
6
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93-TP-52A.04
Initial characterization is complete.
REFERENCES
1. Lee, B. "Highlights of the Clean Air Act Amendments of 1990," J.Air Waste
Manage. Assoc. 41(1): 16 (1991).
2. Ottengraf, S.P.P "Exhaust Gas Purification," in Biotechnology, Vol. 8, Rehn.H.J.;
Reed, G. Eds., VCH Verlagsgesellschaft, Weinham, 1986.
3. Hodge, D.S.; Median, V.F.; Islander,R.L.; Devinney, J.S. "Treatment of
Hydrocarbon Fuel Vapors in Biofilters," Environmental Technology 12:655 (1991).
4. Leson, G., TabatabaJ, F., Winer, A.M. "Control of Hazardous and Toxic Air
Emissions by Biofiltration," Presented at the 85th Annual Meeting and Exhibition of the Air
and Waste Management Association, Kansas City, Missouri, June 21-26, 1992.
5. Van Langenhove, J.; Lootens, A.; Schamp, N. "Inhibitory Effects of SOj on
Biofiltration of Aldehydes," Water, Air, & Soil Pollution 47:81 (1989).
6. Van Lith, C.; David, S.L.; Marsh, R. "Design Criteria for Biofilters," Trans. Inst.
Chem. Eng. 68B:127 (1990).
7. Kirchner, K.; Schlachter, U.; Rehm, H.J. "Biological Purification of Exhaust Air
Using Fixed Bacteria] Monocultures," Appl. Microbiol. Biotechnol. 31:629 (1989).
8. Diks, R.M.M.; Ottengrapf, S.P.P. "Verification Studies of a Simplified Model for
the Removal of Dichloromethane from Waste Gases Using a Biological Trickling Filter (Parts I
and II)," Bioprocess Eng. 6:131 (1991).
9. Hartmans, S.; Tramper, J. "Dichloromethane Removal from Waste Gases with a
Trickle Bed Bioreactor," Bioprocess Eng. 6:83 (1991).
10. Utgikar, U.; Shan, Y.; Govind, R. "Biodegradation of Volatile Organic
Compounds in Aerobic and Anaerobic Biofilters," in Remedial Action, Treatment, and Disposal
of Hazardous Waste, Proceedings of the 17th Annual Hazardous Waste Research Symposium,
Cincinnati, Ohio, 1991.
11. Standard Methods for the Examination of Water and Wastewater, 18th Edition,
American Public Health Association, Washington, D.C. (1992).
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93-TP-52A.04
Table I. Stock trace salt solution.
Component
Concentration, g/L
(NH4)jMo70;4.4H20
2.08
Na2B4G,. IOHjO
1.15
MnCl,.4H,0
4.74
CoC1j.6H20
2.86
ZnC12
3.27
CuC1j.2H20
2.05
Table 11. Stock salt solution.
Component
Concentration
g rL
Trace salt solution
33.1 mL/L
MgClj.6H20
8.13
NaHjP04.Hj0
8.28
KH7P04.Hj0
13.6
nh4ci
49.2
(NH4),S04
5.28
CaClj.2HjO
4.44
8
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Table ITT. Stock vitamin solution.
Component
Concentration,
g/L
p-Aminobenzoic Acid
0.01
Biotin
0.0039
Cya^ocobalamin (B12)
0.0002
Folic Acid
0.0039
Nicotinic Acid
0.01
Pantothenic Acid
0.01
Pyriodoxine Hydrochloride
0.02
Riboflavin
0.01
Thiamin Hydrochloride
0.01
Thioctic Acid
0.01
NOTE TO EDITORS
Uoder the new federal copyright law,
publication rights to this paper are
retained by the authors).
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To SyiUm B
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Figure 3. Biofilter "A" Performance w.r.t. Ammonia Consumption.
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During a Residence Time Cycle.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completir.^
1. REPORT NO. 2.
EPA/600/A-94/055
3. RECIPIENT'S ACCESSION NO.
4. TITLE AND SUBTITLE
DEVELOPMENT OF AEROBIC BIOFILTER DESIGN
CRITERIA FOR TREATING VOCS
5. REPORT DATE
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
G.A. Sorial', F.L. Smith1, P.J. Smith1,
M.T. Suidan1. P. Biswas1, and R.C. Brenner2
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
1 University of Cincinnati Cincinnati,OH 45221-0071
2 U.S. EPA/RREL, Cincinnati, OH 45268
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
Cooperative Agreement
CR-821029
12. SPONSORING AGENCY NAME AND ADDRESS
Risk Reduction Engineering Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati. Ohio. 45268
13. TYPE OF REPORT AND PERIOD COVERED
PpnrppHinqc 1QQf-]QQ^
14. SPONSORING"AG'ENCY CODE
EPA/600/14
Tweeting & Exhibition of Air & Waste Management Association, Denver, Co
6/13-18/93 p.2-16
Pro.iect Officer: Richard C. Brenner, 513/569-7657
16. ABSTRACT
This paper reports preliminary results on the use of trickle bed
biofilters with monolithic ceramic channelized microbial support structures
for the treatment of VOCs typical of landfill._l.eachate it_rip.pjng. Toluene was
used for the purpose of characterizing the trickle bed biofilter apparatus.
The objectives of the experiment were to investigate the performance of such
biofilters, with both cocurrent and countercurrent gas VOC and liquid
nutrient/buffer flows, at inlet toluene concentrations that are high, relative
to most biofilter research to date.^^fSture research objective is to reduce
to practice biofiltration for the treatment of air streams containing mixtures
of VOCs, such as ethyl benzene, chlorobenzene, trichloroethylene, and methylene
chloride in addition to toluene.
KEY WORDS AND DOCUMENT ANALYSIS
a. descriptors
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATi Field/Group
Air pollution, Toluene
Volatile organic
compounds, Trickle
bed biofilter,
Ceramic Monolithic
channelized media
18. distribution statement
RELEASE TO PUBLIC
19. SECURITY CLASS (Tins Report)
UNCLASSIFIED
21. NO- OF PAGES
15
20. SECURITY Class (This pagt-;
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (R«V. 4-77) previous edition is obsolete
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