BIOSCRUBBING IS DRAMATICALLY IMPROVED
WHEN INTEGRATED WITH OTHER
TECHNOLOGIES
Robert Richardson Ph.D.
Pacific Rim Design & Development Inc
PO Box 146 Shingletown, CA 96088
ABSTRACT
Bioscrubbers/ Biofilters (Bioscrubbers) are dramatically improved when they are
effectively combined with other proven abatement methodologies. This paper describes
the successful combination of three abatement technologies. This new integrated system
successfully demonstrated real improvements in areas of where bioscrubbers are
inherently lacking: bed clogging, overall bed volume and sensitivity to rate of change for
inlet gas temperature.
This new integrated technology was developed and pilot tested to meet EPA compliance
requirements for the engineered wood industry. This integrated process is exceptional
because it effectively removes volatile organic compounds from an air stream with high
particulate loading, varying gas temperature and inconsistent target compound
concentrations. The triple integrated process (TIP) has the potential to be a best available
control technology for a variety of applications that require the removal of water soluble
organic and/or sulfide compound in process air with high particulate loading.
The TIP has definite performance and operating cost advantages over
biofiltration/bioscrubbing technology thermal oxidation and regenerative thermal
oxidation.
1
INTRODUCTION
Bioscrubbers are inherently GREEN – they naturally digest target compounds rather than
chemically oxidize or incinerate them and that is a very important reason to improve on
the technology. Bioscrubbers certainly have room for improvement, they occupy
substantial volume, are easily clogged by air streams that contain particulate matter and
are upset by deviations in inlet air temperature, moisture and target compound speciation.
This paper describes an abatement process that integrates three technologies in an
innovative way that effectively improves the previously mentioned bioscrubber
shortcomings. Furthermore this integrated technology cost competitive to purchase and
reduces operating costs too.
The integrated technology described in this paper was developed and proven during pilot
testing to meet the EPA MACT standard, Subpart DDDD of Part 63 (Treatment of
process gas from the engineered wood industry fabrication plants). Although this
combination of processes is relatively untried – each of the individual components have
demonstrated proficiency for many years. When combined, each process derives
operational benefits from the others and in the end the combination of processes is
synergistic because abatement results for the integrated system are greater than any of the
processes could accomplish individually. Furthermore the unique patented process
design saves operational costs because it utilizes gravity and other physical forces to
minimize the need for electrical power. Process details are described in the body of the
paper.
THE THREE PROCESS COMPONENTS

Scrubbing with fine mist that is laden with compounds that enhance target
compound solubility and particulate agglomeration.

Aerobic digestion – convert airstream particulate into an asset rather than a
problem by utilizing it as a substrate for colony growth. This process also
2
provides the long residence time necessary for destruction of some organic
compounds and treats bioscrubber leachate.

Bioscrubbing – a process step that effectively abates volatile organic and sulfide
compounds in the process air stream that were not removed during the mist
scrubbing (because of Henry’s Law solubility limits).
These three processes work collaboratively. Although the gas flows is only directly
affiliated with two of the three processes, first traveling through the mist and then
through the bioscrubber before exiting clean, the aerobic digester is integrally linked to
the functionality of both processes. A detailed process flow description and drawing
identifying the process components, follows a description of each of the three
components of this new and proven combination of abatement technologies.
One of the surprises revealed in pilot testing and confirmed with mathematical modeling
was the removal efficiency of methanol and formaldehyde in the initial mist scrubbing
phase of this overall process. Test results demonstrated that over 70 percent of the
formaldehyde and methanol is removed from the air in the first few seconds of treatment.
In addition to this removal efficiency, the innovative physical orientation of the misting
stage allows it to contribute even more to the overall scrubbing process. This first stage of
treatment accomplishes the following:

This initial mist treatment absorbs soluble organic and sulfide compounds in the
process gas stream, transferring them to the aerobic digester, thereby lessening the
amount of treatment work done in the bioscrubber. This dramatically reduces the
bioscrubber bed volume by several hundred percent (exact size depends upon
process steam characteristics) and that allows the complete TIP process to fit in
on a footprint that is typically less than one third the size of a comparable
bioscrubber.

Carefully selected biodegradable surfactants and or other compounds added to the
mist treatment enhance solubility of partially soluble target compounds in the
process gas stream. The mist scrubber orientation allows the saturated mist to
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coalesce and fall directly into the aerobic digester where a required long residence
time is available to biologically consume the more complex organic compounds.

Removes particulate from the air stream. The mist and particulate agglomerate
and fall by gravity into the aerobic digester below.

Regulates temperature and humidity.
Mist scrubbing in the 10 micron diameter range has advantages over other technologies
that can remove particulate from wet air that also contains odorous or toxic compounds.
Deluge washing with coarse droplets, electrostatic precipitation and venturi scrubbers
will work but when the cost of operation and removal efficiency for the particulate
abatement and targeted odor or toxic compound remediation is compared, the fine mist is
typically the best choice.
The bioscrubber in this integrated process utilizes counter current flow. The air enters
from the bottom of the bed and the nutrient rich liquid is dripped from the top. This
configuration enhances target compound removal efficiency because the cleaner air is
exposed to moisture with progressively greater nutrient concentration as it moves upward
through the bed. This configuration also reduces the tendency for bed clogging by
partially overcoming the natural tendency for biofilm growth to be the greatest near the
process air steam inlet to the bioscrubber.
The unique airflow and component configuration in this integrated process allows the
majority of the airborne particulate to be removed from the air stream prior to the
bioscrubber treatment. However we found that despite the effectiveness of the mist
process particulate removal, there was still a propensity for the bioscrubber bed to clog if
porous rock (or equal) was used as the media (even with vigorous periodic rinsing of the
media bed). This potential problem was averted by selecting a bioscrubber packing media
that had a high surface area to volume and an ability to easily slough off excess biological
and particulate buildup. In this integrated process, the biofilm thickness is regulated by
periodically increasing the recirculated water flow over the bioscrubber packing bed. This
rinse liquid with entrained solids is dripped into the aerobic digester where organic
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material is digested, allowing the nutrients to be reutilized by the system. The process
control equipment on a full scale system would utilize packing differential pressure to
regulate the duration and volume of the vigorous periodic rinse cycles.
The aerobic digester which is strategically located at the bottom of the reaction vessel
serves many purposes. These include the following:

Provide the long residence time required to digest more complex organic
compounds. This feature allows the TIP to address the buildup of naturally
occurring semi-volatile organic compounds before they build up forming a “tar”
in the reaction vessel, which must be removed by a maintenance crew
mechanically.

Treats the bioscrubber leachate, returning the nutrients to be re-utilized thereby
minimizing the need for bioscrubber nutrient augmentation.

Provides a heat sink to minimize thermal shock from deviations in process
airstream temperature. In applications where the process airstream needs to be
heated or cooled to reach an optimum biological temperature range, it is easier
and less expensive to regulate the process temperature by adjusting the aerobic
sump temperature than attempting to make the same adjustment in temperature to
the process gas stream (due to the thermal characteristics of liquids and gases).

Makes the particulate in the process airstream an asset rather than a problem by
utilizing it as a free-floating substrate for biological growth. This enhances the
effectiveness of the aerobic digester thereby minimizing the volume required for
this phase of the overall process.
5
DRAWINGS
SO
K
M
AIR
P
J
L
TO ST
E
X
H
KEY
A
B
C
D
E
F
G
H
I
DESCRIPTION
Duct routes dirty air from process to Triple Integrated Process for removal of toxic or
odorous compounds.
Water with optional biodegradable surfactants (increase solubility of organic
compounds)
Mist nozzles (fine mist)
Dirty air mixes with fine mist – coalescing particulates and dissolving soluble
compounds.
Coalesced droplets (particulate) fall into aerobic digester below.
Air laden with mist turns 180 degrees and moves up through bioscrubber above.
Bioscrubber packing bed – proprietary packing allows washing of excess biomass into
aerobic digester below.
Coarse nozzles to wet bioscrubber bed
Blower – pulls air through triple integrated process scrubber.
6
J
K
L
M
N
O
P
Q
R
Liquid recirculation pump.
Automated backwash filter.
Belt press or similar dewatering device.
Venturi - adds air to liquid (supplies oxygen to aerobic digester).
Aerated liquid to the aerobic digester.
Large diameter jets – minimize clogging
Clumped particulate matter acts as media – supporting biological growth.
Optional biodegradable surfactant
Chemical metering pump for surfactant.
PROCESS FLOW DESCRIPTION
The following description is graphically displayed in the drawing above. The letters in
parenthesis in the descriptions identify components depicted on the drawing.
The contaminated exhaust air steam is treated in the following sequence in the triple
integrated process. Initially the air interacts with the fine mist (C) at the top of the central
reaction chamber (D). The mist and the contaminated air thoroughly mix as they move
concurrently downward through the central reaction chamber (D). The mixing transfers
the water soluble target organic and sulfide compounds from the gas phase into the liquid
phase. The residence time is process specific.
The gas stream then makes a 180 degree turn and moves upward carrying the remainder
of the entrained organic compounds through a synthetic bioscrubber media (G) bed while
gravity pulls the larger agglomerated droplets out of the air steam, dumping them into the
aerobic digester sump below (E). The bioscrubber media contains biological organism
that digest organic compounds and is wet with recirculated water that is sprayed (H) over
the top of the packing material. The VOC / sulfide laden air interacts with the wet surface
of the bioscrubber media, and transfers most of the remainder of the VOC’s and sulfides
into this biologically rich slime layer where they are consumed. The overall system
removal efficiency for methanol and formaldehyde is typically in excess of 99%
7
The liquid in this digester is continuously recirculated (J) through a backwash filter (K) to
remove excess particulate and through ventures’ (M) that transfer oxygen into the water
for continued aerobic digestion.
The bioscrubber media (G) utilized in this process is engineered to prevent the
accumulation of thick biomass. We have chosen a polypropylene packing with a
geometry that facilitates a natural sloughing off of the excessive biomass. The high open
area of this structured packing also insures this discarded biomass will wash through the
packing into the aerobic sump (R) where it is biologically decomposed. Lantec’s HD QPAC has 132 square feet of surface area per cubic foot of packing with a void fraction of
87.8% and ideally meets this requirement. An ancillary benefit of using polypropylene
packing is its weight. The Lantec packing seen to the right is dramatically lighter than
ceramic or soil media and therefore
requires less structural support.
Furthermore the high void fraction
insures the differential pressure
necessary to move the air through
the bed is lower than that required in
biological beds made from ceramic
or soil media.
This photo to the right shows the
biofilm on the packing. Note how
the thermophilic bacterial film is
thin and how the packing surface is
not clogged. Some of the cells are
covered with water, but they are not clogged with biofilm.
The treated air is pulled through the triple integrated reaction vessel by blowers (I). The
blowers are on the discharge side of the vessel to insure the entire process is under a
slight vacuum, thereby insuring any contaminated air is unable to leak out of the process
stream.
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TEST DATA AND PROCESS CALCULATIONS
TABLE #1 - TEMPERATURES AND FLOWS DURING PILOT TESTING
DATE
SCRUBBER TEMPERATURES
SUMP
SUMP
SCRUBBER LIQUID FLOW
(°F)
DO
pH
(gpm)
(mg/L)
T1
T2
T3
T4
T5
Fi
Fii
Fiii
Fiv
9-11-07
93.1
109.2
102.3
99.5
81.8
5.45
7.4
0.3
0.4
1.0
30
14-11-07
91.5
89.1
77.6
75.6
76.8
6.33
7.91
0
0.5
4.8
15
15-12-07
121.3
120.6
117.4
116.3
117.0
3.47
7.48
16-12-07
115.8
114.1
113.4
112.4
123.4
3.20
7.40
0
0.8
2.0
27.0
16-12-07
112.7
111.5
110.9
110.3
118.0
3.39
7.25
17-12-07
113.4
115.0
114.9
114.2
129.4
6.30
0
0.9
1.8
28
1912-07
114.1
113.6
111.8
111.3
115.7
3.21
7.92
0
1.0
2.0
28
20-12-07
111.5
109.4
102.1
99.4
99.5
4.67
8.16
0
1.0
2.0
20
SYMBOL
T1
T2
T3
T4
DEFINITION
Horizontal duct prior to water spray
Horizontal duct after water spray
Center duct fine mist spray
Air space above sump
SYMBOL
Fi
Fii
Fiii
Fiv
DEFINITION
Horizontal duct nozzle
Center duct fine mist
Spray above bioscrubber
Recirculated through heat
exchanger & spray above sump
9
TABLE #2 - PERFORMANCE TESTING RESULTS SUMMARY
DATE
SCRUB
AIR
FLOW
(SCFM)
MeOH
IN
(ppm)
MeOH
OUT
(ppm)
%
REM.
HCHO
IN
(ppm)
(Note D)
HCHO
Above
Sump
(ppm)
(Note E)
HCHO
OUT
(ppm)
%
REM.
SUMP
MeOH
(µg)
SUMP
HCHO
(µg)
NOTE
4,934
1,690
A, D
9-11-07
480
18.82
8.01
57.4
52.03
0.38
99.3
14-11- 07
14-11- 07
14-11- 07
14-11- 07
92
350
690
910
34.01
35.04
34.60
35.74
0.35
0.51
2.32
7.03
99.0
99.0
95.5
80.3
12.64
15.66
13.85
11.28
0.14
0.09
0.225
1.02
99.1
99.4
98.4
91.0
B, D
B, D
B, D
B, D
16-12-07
530
24.05
0.11
99.6
C, D
HCHO
OUT
(ppm)
%
REM.
0.42
1.79
0.86
0.64
93.9
91.6
96.5
99.1
DATE
SCRUB
AIR
FLOW
(SCFM)
16-12- 07
17-12-07
19-12- 07
19-12- 07
MeOH
IN
(ppm)
530
920
530
530
MeOH
OUT
(ppm)
%
REM.
HCHO
IN
(ppm)
(Note D)
HCHO
Above
Sump
(ppm)
(Note E)
6.91
21.13
24.33
68.95
SUMP
MeOH
(µg)
SUMP
HCHO
(µg)
NOTE
C, E
C, D
C, D
C, D
NOTES IDENTIFIED ON TABLE #2
LETTER
A
COMMENT
The high concentrations of methanol and formaldehyde in the sump are an indication of ineffective aerobic
digestion. The low methanol removal efficiency is a direct result of the high concentration in the sump.
B
The sampling was performed the morning after the plant had an unexpected day long shutdown. The
aerobic colony in the sump had not yet acclimated.
C
Analytical equipment was only available for formaldehyde testing.
D
Inlet sample taken in the duct just after leaving the cyclone. Exhaust sample taken from the exhaust stack
after the fan.
E
Inlet sample taken from the space between the aerobic digester liquid sump and the bottom of the bioscrubber. Exhaust sample taken from the exhaust stack after the fan.
TABLE #3 - HENRY’S LAW CONSTANTS USED IN THIS MODEL
COMPOUND
Formaldehyde in water
CONSTANT
log10 H  8.062  2943 / T
10
Methanol in water
log10 H  6.391  2047 / T
α - Pinene in water
log10 H  9.875  1792 / T
TABLE #4 - ASSUMPTIONS USED IN THIS MODELING
1
2
Site is very close to sea level – therefore one atmosphere is used for ambient pressure.
Water recirculated from the sump through fine mist nozzle contained no formaldehyde.
1. DETERMINING THE FORMALDEHYDE REMOVAL BY THE MIST AND
BIO-SCRUBBER TREATMENT STAGES.
Table #1 reports inlet concentrations for the two process comparison tests on 16
December. One sample measures the concentration difference across the entire system
and the other the difference across the bio-scrubber alone.
The removal by the mist stage is:
24.05  6.91
(100)  71%
24.05
The two tests were not conducted concurrently, so the result is subject to some error
caused by deviations in the process conditions. In any event, these tests do show that the
preponderance of the formaldehyde removal is occurring in the mist scrubbing process.
This is remarkable, since the mist scrubbing stage uses little water, and co-current contact
is inherently less efficient than counter-current contact. Is it really possible to absorb so
much of the formaldehyde using so little water? We can compare this result to the
theoretical maximum possible efficiency based on the known vapor-liquid equilibrium
for formaldehyde in air and water.
2. MODELING OF THE MAXIMUM POSSIBLE REMOVAL EFFICIENCY
FROM THE MIST SCRUBBING PROCESS USING HENRY’S LAW
The Henry’s Law constant is the ratio of the partial pressure of formaldehyde in air to the
concentration of formaldehyde in water when the air and water have come to equilibrium:
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H HCHO 
pHCHO
x *HCHO
The calculation will use the mean temperature at the fine mist spray on Dec. 16.
At 112.1°F (44.5°C, 317.5 K)
So
log10 H HCHO  8.062 
2943
317.7
H HCHO  101.202  0.063atm  mol / mol
The study will compare the scrubber inlet formaldehyde concentration (24.05 ppm) with
the formaldehyde concentration after the mist scrubbing process (6.9 ppm). Because the
treatment process is occurring at atmospheric pressure near sea level, then the partial
pressure of formaldehyde vapor in the air at the end of the mist scrubbing stage was 6.9 x
10-6 atm.
The mole fraction of dissolved formaldehyde in the mist droplets could at most be:
xHCHO * 
pHCHO
6.9 x106 atm

 1.10 x104 molHCHO / molH 20
H HCHO 0.063atm  mol / mol
One mole of water weighs 18 g/mol = 18 ml = 0.018 L of water. Substituting this value
for water into the equation we can solve for the concentration.
1.10 x104 molHCHO / molH 20
 6.11x103 molHCHO / L
0.018L / molH 2O
One mole of formaldehyde weights 30.03 g = 30,030 mg. Substituting this value for
formaldehyde into the equation we have:
 6.11x10
3
molHCHO / L   30,030mg / molHCHO   183.5mg / L  183.5 ppm
The mist nozzles sprayed 1.0 gpm of water; this is equal to 3.8 L/min.
If the amount of dissolved formaldehyde in the sprayed water was negligible, the
maximum amount of formaldehyde this volume of water could remove from the gas
stream is;
 3.8L / min   6.11x103 molHCHO / L   2.32 X 102 molHCHO / min
The number of moles of air in the 560 acfm (530 scfm) pilot scrubber air flow at the time
of testing was:
12
530scf / min
 454mol / # mol   622mol / min
387 scf / # mol
The untreated inlet air had 24.05 ppm of formaldehyde. To reduce this to 6.9 ppmv, the
mist scrubbing stage would have to remove formaldehyde at a rate of
 622 mol   24.05  6.9 molHCHO 
 1.07  102 molHCHO / min



6
10 mol
 min  

This is less than the theoretical maximum removal rate of 2.32×10-2 molHCHO/min, so the
measured removal efficiency is consistent with the known volatility of formaldehyde
over its dilute solutions in water.
CONCLUSION FOR CALCULATIONS:
The fine mist scrubbing process alone is theoretically capable of removing
2.32x10-2 molHCHO/min. This exceeds the measured formaldehyde removal rate of
1.44x10-2 molHCHO/min. Therefore the mist section of this scrubber system is certainly
capable of removing 71% of the formaldehyde that is currently being scrubbed in both
the mist and bio-scrubber.
FINAL CONCLUSION FOR PAPER
The triple integrated process technology provides benefits not available in any other
abatement technology, it is less expensive to operate and has a comparable capital cost.
This is the Best Available Control Technology for a wide variety of applications.
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