Note: Descriptions are shown in the official language in which they were submitted.
CA 02605358 2007-10-03
BIOFILTER MEDIA AND SYSTEMS AND METHODS OF USING SAME TO
REMOVE ODOUR CAUSING COMPOUNDS FROM WASTE GAS STREAMS
FIELD OF THE IIWENTION
[0001] The present invention relates to biofilter systems and the biofilter.
media employed in
such systems, as well as,.methods of using same to remove odour causing
compounds from
waste.gas streams.
BACKGROUND OF THE INVENTION
[0002] Biofiltration is a known air pollution control technique that has been
applied to control
odour and remove volatile organic compounds (VOC) from waste gas streams
generated by
wastewater treatment plants and chemical plants, as well as various rendering;
food processing,
flavour manufacturing and composting facilities.
100031 In a typical biofilter, a waste gas stream is urged to flow through a
moist, biologically
active, packed bed. The bed contains microorganisms that are immobilised on a
thin biofilm that
is formed on the surface of the packing material. The microorganisms serve as
the biocatalysts in
the contaminant degradation process. They transform the air contaminants into
biomass and
harniless products through their metabolic activities.
[0004] The process underlying the operation of a biofilter is a multi-step
process that involves.
phase transfer, adsorption and biodegradation. As a first step, contaminants
must be transferred
from the gaseous phase to the liquid phase since they cannot be degraded
directly while in the
gaseous phase. Once in the liquid phase, the contaminants are adsorbed to the
pacldng material
or biofilter media (as it is often referred to).. Therea$er, the contaminants
are biodegraded. within
the biofilm. The overall efficiency of the biofiltration process is determined
by the relative rates
of phase transfer, adsorption and the biological reactions.
[0005] Selecting the appropriate packing material or biofilter media is
critical to ensure proper
functioning of the biofilter. While the biofilter media serves multiples
purposes, its most
important function tends to be providing contact. between the gas-phase
contaminants and the
active microbial colonies immobilized on the biofilm. In considering the
suitability of a material
CA 02605358 2007-10-03
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for use as a biofilter media, the following factors are considered to be
desirable: the ability to
support bacterial growth, large surface area, structural integrity (i.e.
resistance to compaction),
high porosity, low chemical reactivity, pH buffering capacity, good adsorption
properties,
sufficient water retention capability and non-biodegradability.
[0006) Several different biofilter media have been used in the past. These
typically fall in one of
two categories: naturally bioactive or inert. However, in certain
applications, bioactive and inert
packing materials have been combined.
[0007] Bioactive packing materials typically include soil, peat, compost, bark
and manure. These
materials can retain water and generally contain enough nutrients to sustain
an initial microbial
population. These materials have been used in many applications because they
tend to be
abundantly available and are generally inexpensive. However, this type of
biofilter media has '
encountered various drawbacks in the field. Biofilters using these materials
tend to require large
filter beds on account of the low biodegradation rate and the significant bulk
density of the media
that tends to limit the filter bed height. Additionally, these media tend to
degrade over time. They
lose their water retaining characteristics and settling of the media due to
biomass growth tends to
occur. Eventually, biofilters using this type of media may experience a loss
of performance due
to a significant.gas phase pressure drop in the media and channelling of the
waste gas through
the filter bed.
[0008] Inert biofilter media are porous materials (either naturally occurring
or synthetic) that
usually require inoculation of microorganisms. Examples of inert biofilter
media that have, beeu
used in previous biofilter applications include activated carbon, gas-aerated
concrete, gravel, lava
rock, ceramics and polymeric foams. Some synthetic biofilter media have
yielded better
contaminant removal rates and generally performed better than bioactive
packing materials. This
is due in part to the fact that they tend to have a larger surface area and
have been able to achieve
a better distribution of gas flow through the media. However,. clogging,
compaction and
excessive gas-phase pressure drop due to extensive biomass growth still remain
a serious
problem for these types of biofilter media. These issues can severely impact
performance of the
biofilter causing a decline in the contaminant removal efficiency.
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[0009] An example of an engineered (synthetic) pacldng material is descnbed in
European
Patent No. 0 497 214 of Fattinger. The biofilter media of Fattinger has a
hydrophilic core coated
with a hydrophobic layer. The hydrophilic core is populated by microorganisms.
It is a granular
material made from a porous substance, such as gas-aerated concrete, swelling
clay or pumice,
.whereas the hydrophobic layer can be activated charcoal or adsorption resin.
A bonding agent
may also be used when applying the hydrophobic layer to the hydrophilic core.
Fattinger also
discloses that this biofilter, media may be used to purify exhaust air
containing toluene, xylene,
ethyl acetat.e and benzene. While this packing material tends to have better
structural and
biological properties than wood-based packing materials; it tends to suffer
from the'clogging
problem described above as well as the acid sohibility of gas-aerated
concrete. In addition, this
packing material tends to have a relatively high density resulting in
increased shipping costs
associated therewith:
[0010] A biofilter system using the packing material of Fattinger to remove
hydrogen sulfide
from waste gas streams was descnbed in United States Patent No. 6,358,729 of
Ferranti. The
patent describes a compact plant unit for the depuration of air polluted with
odorous substances,
such as hydrogen sulfide, mercaptans and dimethyl disulfide. The plant
includes a prescrubbing
section, a filtering bed and post-sciubbing section, all placed in sequence.
The filtering bed of
Ferranti preferably consists of particles of a filtering material made in
accordance with European
Patent No. 0 497 214 of Fattinger. Ferranti descri'bes that very high H2S
removal efficiencies
may be achieved using this compact plant unit. While the compact unit plant of
Ferranti was
found to be effective in removing hydrogen sulfide, its empty bed residence
time (EBRT) for the
H2S removal at high concentrations tended to be high.
[0011] The engineered biofilter media described in United States 'Patent
Publication No.
2005/0084949 of Shareefdeen et al. and currently made commercially available
by the assignee
of the present application, BIOREM Technologies Inc. of Guelph, Ontario under
the name
BIOSORBENSTm, has had greater success in removing hydrogen sulfide from waste
gas streams.
Shareefdeen et al. disclose a biofilter media that has a porous hydrophilic
nucleus and a
hydrophobic coating on the hydrophilic nucleus. The hydrophilic nucleus is
formed of
aggregates whose primary ingredients preferably include silica and alumina.
The hydrophobic
coating includes a metallic agent, microorganisms, nutrients, organic carbon,
an alkaline buffer,
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a bonding agent, an adsorptive agent, and a hydrophobic agent. The inclusion
of a metallic agent
(preferably iron) in the biofilter media of Shareefdeen et al. allows the
removal of sulfur by the.
formation of iron sulfide and also serves to enhance the conversion and
biological processing of
sulfur compounds in the contaminated air. The metallic agent acts as catalyst
to increase the rate
of biological oxidation and enhance the activity of the microorganisms. As a
result, the biofilter
media of Shareefdeen et al. has shown an improved ability to remove higher
concentrations of
hydrogen sulfide at lower -EBRTs and has achieved a higher H2S removal
efficiency than the
packing material of Fattinger. .
[0012] In light of the foregoing, it would be advantageous if a biofilter
system were capable of
achieving even higher removal rates of hydrogen sulfide at greater
concentrations with lower
EBRTs than conventional biofilter systems. Moreover, it would be desirable if
the biofilter
media used in such a system could be engineered to optimize its physical,
material and biological
properties for improved performance and versatility. -
SUMMARY OF THE IIWENTION
[0013] In accordance with a broad aspect of an embodiment of the present
invention, there is'
provided a biofilter media having a.plurality of expanded glass granules. Each
expanded glass
granule has a. coating thereon. The coating includes a bonding agent, an
adsorptive agent,
microorganisms and nutrients. In an additional feature, each expanded glass
granule measures
between 2mm and 40mm and preferably, between 8mm and 16mm. In a further
feature, the
bonding agent is cement. In still another feature, the adsorptive agent is
activated carbon.
[0014] Additionally, the microorganisms and nutrients are provided by at least
one of peat and
compost. In yet another feature, the microorganisms are provided by compost
and include at
least one of Pseudomonas pseudoalcaligenes, Pseudoxanthomonas and
Paenibaccilus lautus. In
a further feature, the microorganisms are provided from a source of inoculants
and include at
least one of Thiobacillus thioparus and Thiobacillus thiooxidans.
[0015] In an additional feature the nutrients include phosphorus, nitrogen and
potassium and
may further include zinc acetate.
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100161 In another feature, the coating on the expanded glass granule farther
includes an acid.
Optionally, the acid may be phosphoric acid.
100171. in another broad aspect of an embodiment of the present invention,
there is provided a
method for removing odour causing compounds from a waste gas stream. In
accordance with this '
method, a biofilter system having a biofilter media is provided. The biofilter
media includes a
plurality of expanded glass granules. Each expanded glass granule has a
coating thereon. The
coating includes a bonding agent, an adsorptive agent, microorganisms and
nutrients. The waste
gas stream is urged to flow through -the biofilter media of the biofilter
system. In an additional
feature, the odour causing compounds are selected from the group consisting
of: (a) hydrogen
sulfide;'(b) reduced sulfur compounds; and (c) volatile organic compounds. In
another feature,
the odour causing compounds are reduced sulfur compounds selected from the
group consisting
of: (a) methyl mercaptan; (b) dimethyl salfide; and (c) dimethyl disulfide.
[0018] In still another broad aspect of an embodiment of the present
invention, there is provided
a biofilter system. The biofilter system has a housing and an inlet provided
to the housing for
receiving contaminated air. An outlet is also provided to the housing for
exhausting cleaned air.
The biofilter system also includes a biofilter media situated between the
inlet and the outlet
through which the contaminated air flows. The biofilter media has a plurality
of expanded glass
granules. Each expanded glass granule has a coating thereon. The coating
includes a bonding
agent, an adsorptive agent, microorganisms and nutrients.
[0019] In an additional feature, the biofilter includes a water delivery
system for providing
moisture to the biofilter media. The moisture provided by the water delivery
system is in the
fornn of one of water and steam. The water delivery system includes a steam
generator for
supplying steam to the biofilter media and may also include irrigation
conduits to deliver the
water to the biofilter media. Nozzles are operatively connected to the
irrigation conduits for
spraying water onto the biofilter media. Also provided is a flow meter for
controlling the flow of
water through the irrigation conduits.
[0020] In another feature, the housing includes a drain line in fluid
communication with the
biofilter media for removing excess water therefrom.
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[0021] In still another feature, the biofilter system includes sensor means
operatively connected
to the biofilter media. The sensor means may include a temperature sensor for
measuring the
temperature of the biofilter media and a pressure sensor for measuring the
pressure at which the
contaminated air flows through the biofilter media. Optionally, the sensor
means includes a pH
monitoring probe. The pH rinonitoring probe is disposed in the drain line.
[0022] Tn a further feature, the biofilter system includes a control system
operatively connected
to the water delivery system and the sensor means. The control system is
operable to actuate the
water delivery system in response to input received from the sensor means.
Additionally, the
sensor means may include a temperature sensor for measuring the temperature of
the biofilter
media and a pressure sensor for measuring the pressure at which the
contaminated air flows
through the biofilter media. The control system may be operable to actuate the
water delivery
system to adjust the moisture being delivered to the biofilter in response to
input received from
the temperature sensor or the pressure sensor.
100231 In still another feature, the sensor means includes a pH monitoring
probe for measuring
the pH of the biofilter media. The control system is operable to adjust the pH
of the biofilter
media in response to input received from the pH monitoring probe.
10024] In yet another feature, the biofilter system includes a humidification
chamber disposed
within the housing'between the inlet and the biofilter media for moistening
the contaminated air
prior to entry of the contaminated air into the biofilter media. The
contaminated air is moistened
within the humidification chamber using one of: (a) a pneumatic spray; (b)
high-pressure water;
and (c) steam. Also provided is a steam generator operatively connected to the
humidification
chamber for delivery of steam thereto.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The embodiments of the present invention shall be more clearly
understood with
reference to the following detailed description of the embodiments of the
invention taken in
conjunction with the accompanying drawings, in which:
[0026] FIG. 1 is a simplified illustration of a biofilter system having a
biofilter media produced
in accordance with an embodiment of the present invention;
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[0027] FIG. 2 is a conceptual illustration of a granule of the biofilter media
shown in accordance.
with an embodiment of the present invention;
[0028] FIG. 3 is a graphical representation of the eliunination capacity vs.
the loading rate for a
biofilter system having the biofilter media provided in accordance with an
embodiment of the
present invention, treating hydrogen sulfide; and
[00291 FIG. 4 is a graphical representation showing the hydrogen sulfide
removal efficiency of a
biofilter system having the biofilter media provided in accordance with an
embodiment of the
present invention, plotted against the hydrogen sulfide concentration in the
waste gas stream and
specified empty bed residence times (EBRT).
DETAILED DESCRIPTION OF EMBODIMENTS OF THE IlWENTION
[0030] The description which follows, and the etnbodiments described therein
are provided by
way of illustration of an example, or examples of particular embodiments of
principles and
aspects of the present invention. These examples are provided for the purposes
of explanation
and not of limitation, of those principles of the invention: In the
description that follows, like
parts are marked throughout the specification and the drawings with the same
respective
reference numerals.
[0031] In the following specification, the terms "biofilter" or "biofilter
system" refer to a system .
that employs microorganisms to effect biodegradation of contaminants in a
waste gas stream.
The term "biofilter media" refers to the packing material used in the filter
beds of such systems.
Furthermore, the term "contaminants" or "air contaminants" refer to chemical
compounds
present in waste gas streams and includes, but is not limited to, sulfur-based
compounds, such as
hydrogen sulfide ("HZS"), organic sulfides, reduced sulfur compounds, for
instance, methyl
mercaptan, dimethyl sulfide and dimethyl disulfide, and volatile organic
compounds ("VOCs"),
such as aliphatic and aromatic compounds. Further, the terms "contaminated air
stream" or
"waste gas stream" refer to a flow of air/gas that contains contaminants.
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[0032] Biofilter System
[0033] Figure 1 shows a simplified illustration of a biofilter system 20
according to an
embodiment of the invention. The biofilter system 20 includes a housing 22
that encloses a
biofilter bed 24. The biofilter system 20 may be placed above or below ground
and may be
operated under positive or negative pressure with or without covers.
[0034] The biofilter bed 24 has a base 26 upon which rests a column 28 of
biofilter media 30. A
waste gas inlet 32 provides access to the housing 22 thereby allowing a
contaminated air stream
to enter the biofilter bed 24. Positioned adjacent to the waste gas inlet 32
is a humidification
chamber 34. The biofilter system 20 further includes, an outlet 36 to allow a
cleaned air stream to
exit the housing 22 following treatment in the biofilter bed 24.
[0035] A water supply system 40 is operatively connected to the housing 22 to
provide- the
required moisture (in the form of water and /or steam) to the. biofilter media
30. The water
supply system 40 includes a water inlet 42 for receiving water to be used for
either steam
generation or irrigation of the biofilter media 30. The water inlet 42 may
supply water to a steam
generator 44 through conduit 45. The steam generator 44 is operable to
generate steam (when
required) and supply it to the humidification chamber 34 via conduit 47 and
waste gas inlet 32.
Irrigation conduits 46 attached to the water inlet 42 are used to deliver
water into the housing 22.
The inrigation conduits 46 are fiirnished with spray nozzles 48 for spraying
water on the biofilter
media 30.
j00361 The water supply system 40 may also include a flow meter 50 disposed
downstream of
the water inlet 42 to control the amount of water that enters the biofilter
system 20 and more
specifically, the irrigation conduits 28. A drain line 52 disposed within the
housing 22 allows -for
the removal of excess water and any waste accumulated during the cleansing and
irrigation of the
biofilter media 30.
10037j In the present embodiment, the biofilter system 20 includes one or more
media
temperature sensors 56 (only one sensor shown) that measure the temperature of
the biofilter
media and one or more pressure sensors 58 (only one sensor shown) that measure
the pressure at
which the waste gas is flowing through the biofilter media 30. A biofilter
control system 60
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governs the operation of the biofilter system 20 and communicates with the
media temperature
sensor 56, the pressure sensor 58, and the water supply system 40. As will be
explained in '
greater detail below, the biofilter control system 60 may actuate the water
supply system 40 in
response to an input signal it receives from the temperature sensor 56. More
specifically, the.
control system 60 may adjust the temperatme of the biofilter media 30 by
selectively adding
steam to the contaminated air stream in the waste. gas inlet 32 or in the
humidification chamber
34; or by irrigating the biofilter media 30 with water:
[0038] The biofilter system 10 may also have a pH monitoring probe (not shown)
disposed in the
outlet 36 to monitor the operating environment of the biofilter media 14. A
more detailed.
description of the biofilter system 20 can be found in United States Patent
No. 5,869,323, the
content of which is hereby incorporated herein by reference.
[0039] Biofilter Media
[0040] Within the biofilter system 30, the biofilter media 30 is provided to
remove contaminants
from the contaminated, air stream received within the housing 22. Figure 2
conceptually
illustcates a granule, bead or pellet 70 of the biofilter media 30 according
to an embodiment of
the invention. Each granule 70 provides a surface area upon which may be
supported the biofilm
containing the microorganisms required to biodegrade the contaminants. Each
granule 70 is an
expanded glass granule 72 that has a hydrophobic coating 74 thereon.
[0041] The expanded glass granule 72 is stable, inorganic non-reactive, non-
flammable, non*
toxic, non-odorous, non-biodegradable and acid resistant. In addition, the
expanded glass granule
72 tends to be relatively hard and rigid which allows it to better resist
compaction from biomass
growth and avoid high-gas phase pressure drop that may adversely impact on
biofilter
performance. By virtue of its relatively high porosity, the expanded
glass'granule 72 tends 'to
exhibit excellent moisture retention properties and has a relatively low bulk
density. Te expanded
glass granule 72 is primarily composed of silica and alkali oxides (i.e.
predominantly sodium
oxide (Na20) and to a lesser extent, potassium oxide (K20)) with the remainder
being composed
of calcium oxide (CaO), 'alumina (A1203) and magnesium oxide (MgO). The
chemical
composition of the expanded glass granule of this embodiment is set out below:
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[004a]
Compound % (by weight)
Silica (SiOZ) 71
Sodium Oxide (Na20) ' 14
Potassium Oxide (K20) 1
Calcium Oxide (CaO) 9
Alumina (A1203) 3
Magnesium Oxide (Mg0) 2'
[0043] In this embodiment, the expanded glass granule 72 is a manufactured and
shaped granule
having a generally spherical shape. The expanded glass granule 72 may be sized
between 2mm
and 40mm. However, preferably it measures between 8mm and 16mm. The expanded
glass
granulate product made commercially available by Dennert Poraver GmbH of
Schlusselfeld,
Germany under the name PORAVER7M has been found to be suitable for use as the
expanded
glass granule 72. This product is manufactured from recycled glass and has
been used in the past as a component of building materials such as plasters,
mortars, adhesives and fillers. However, it
will be appreciated that other granulate products. exhibiting similar material
properties and
having different chemical compositions could also be employed to advantage.
[0044] The coating 74 includes a bonding agent for bonding the coating to the
expanded glass
granule 72, an adsorptive agent, microorganisms and nutrients. In the
preferred embodiment, the
bonding agent is an alkaline bonding agent such as, cement or other like
cementitious material.
Preferably, the bonding agent will have the following composition: tricalcium
silicate (- 50%),
dicalcium silicate (25%), tricalcium aluminate (10%), tetracalcium
aluminoferrite (10%), and
gypsum (5%). It will however be understood that the composition of the bonding
agent may be
adjusted to accommodate the chemical make-up of a particular waste gas stream.
For instance, in
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the case of higher sulfur loadings, a bonding agent with a lower level of
tricalcium aluminate
may be employed.
[0045]. The adsorptive agent may be one or more of activated carbon (a form of
inorganic
carbon), adsorption resin and clinoptilolite (natural or synthetic).
Preferably, some quantity of
activated carbon is used because it increases the adsorption of chemicals such
as reduced sulfides
and aliphatic and aromatic compounds. The.use of clirioptilolite may also be
desirable due to its
capacity for elevated cation exchange which tends. to make it adaptable to
different field
applications. In addition, clinoptilolite is provided with a large surface
area and can adsorb gases
including hydrogen sulfide, ammonia, mercaptans, formaldehyde, and VOC gases
from
contaminated air streams.
[0046] The microorganisms present in the coating may be aerobic mesophilic
bacteria or
thermophilic bacteria. In applications where mesophilic bacteria populate the
biofilter media 30,
the biofilter system 20 may be operated at temperatures in the range of 20 C
to 40 C. Where the
coating 74 includes thermophilic bacteria, an operating temperature of greater
than 45 C may be
maintained in the biofilthr bed 24. This can be achieved by supplying steam to
biofilter media 30,
for example.
[0047] The microorganisms can be supplied to the biofilter media 30, in
various ways. An
organic substrate such as peat or compost (which contain microorganisms)and
nutrient solution
may be added to the mixture of expanded glass granule 72 and coating 74 during
manufacturing
of the biofilter media 30. In applications where compost is added to the
mixture, it may not be
necessary to irioculate the biofilter media 30 since contaminants can be
biodegraded using the
natural microbial populations present in the compost. Such bacteria may
include Pseudomonas
pseudoalcaligenes, Pseudoxanthomonas and Paenibacillus lautus..These
microorganisms tend to
be effective in breaking down different sulfur compounds present in the waste
gas and have been
shown to achieve efficient contaminant removal without requiring the addition
of further
microorganisms by inoculation. It will however be appreciated that in certain
applications it may
be advantageous to supplement the naturally-occurring bacteria with additional
microorganisms
through inoculation of the biofilter media 30. This may be carried out to
generally improve the
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performance of the biofilter system or to specifically enhance degradation of
a particular
compound or group of compounds:
[0048] In other applications, the microorganisms may be provided by a single
strain or mixed
culture of inocula grown in a separate bioreactor. The source of inoculants
may be a standard
laboratory bacterial growth medium such as agar or broth. These microorganisms
could be added
to the coating 74'in liquid form either during manufacturing of the biofilter
media 30 or during
the operation of the biofilter system 20 (via the -water delivery system 40).
For instance, the
biofilter media 30 may be inoculated with the following bacteiia: Thiobacillus
thioparus,
begigiatoa, thiothrix genera, and T. feroxidants.
[00491 As will be appreciated by persons skilled in the art, a wide variety of
nutrients for the
microbial culture may be used. Such nutrients may include a source of organic
carbon and a
blend of nitrogen, phosphorus and potassium compounds, as well organic and
inorganic
compounds and other ingredients that may tend to support and promote bacterial
growth and
encourage degradation of certain contaminants. Examples 'of such. ingredients
include
magnesium, manganese; inorganic or, organic sulfur, calcium, iron, copper,
cobalt, zinc, boron
and molybdenum. In particular, the addition of zinc acetate to 'the biofilter
media 30 during
manufacture has.been found to improve the removal of reduced sulfur compounds,
in particular,
d:unethyl sulfide, from the contaminated air stream. By providing an
appropriate balance of
nutrients and by adjustment of nutrient concentration, it is possible to
achieve high levels of
growth of bacteria and thus accelerated rates of contaminant degradation.
[0050] Other additives may also be included to the coating 74, for example; to
adjust the pH of
the biofilter media 30 to the desired value. In certain applications, it may
be advantageous to add
an acid during the coating process: The acid may be an organic acid or an
inorganic acid.
However, preferably, the acid employed is phosphoric acid (H3PO4). It has been
found that
phosphoric acid tends to increase the porosity and the buffering properties of
the biofilter media
30. Moreover, the addition of phosphoric acid also tends to significantly
increase the surface
area and adsorption capacity of tlie biofilter media 30, allowing for better
retention and bonding
of the air contaminants. As an added benefit, the phosphorus from the
phosphoric acid may also
serve as a nutrient source to support microorganism growth. In other
applications where
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maintaining a neutral pH is desired, a neutralizing alkaline agent may be
added to the biofilter
media during the manufacture of same.
[00511 Advantageously, the expanded glass granule 72 with its coating 74 has a
relatively lower
weight and lower density than the coated hydrophilic nucleus of known
biofilter media. For
instance, whereas the bulk density of the coated expanded glass granule 72 is
0.29 kg/L on a dry
weight basis, the bulk density for the coated hydrophilic nucleus of the
biofilter media described
in United States Patent Application Publication No. 2005/0084949 and currently
made
cornmercially available by the assignee of the present application, BIOREM
Technologies Inc. of
Guelph, Ontario under the name BIOSORBENSTm, is 0.65 kg/L on a dry : weight
basis. It will
thus be appreciated that the biofilter media 30 of the present embodiment is
approximately 56%
lighter than the BIOSORBENSTm biofilter media. The relatively light-weight/low
density
characteristics of the biofilter media 30 tend to facilitate handling of the
biofilter media when
charging and discharging the biofilter media 30 in the biofilter bed 24 and
during maintenance
and servicing operations. In particular, the biofilter media 30 may be removed
from the biofilter
bed 24 to permit the excess biomass collected on the sarface of the biofilter
media to be washed
off thereby allowing recycling of the biofilter media.. In this'way, the
clogging problems typically
associated with conventional biofilter packing materials tend to be mitigated
in the biofilter
media 30.
[0052] In addition, freight costs associated with the biofilter media tend to
be lower than those
associated with the heavier conventional biofilter media thereby enhancing the
cost effectiveness
of the biofilter media 30.
[00531 Operation
[0054] The operation of the biofilter system 20 will now be described in
greater detail. The
biofilter system 20 is supplied with a waste gas stream from, for example, a
rendering plant. The
contaminated air enters the housing 22 through the waste gas inlet 24
typically under pressure,
either positive or negative, (preferably, approximately -12 to 12 inches of
water column), such
that it is urged to flow through the biofilter bed 26.
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[0055] As the waste gas stream flows through the biofilter media 30,
contaminants undergo
phase transfer from the gas phase to the liquid phase. In the biofilter system
of the present.
embodiment, the phase transfer of hydrogen sulfide tends to occur more rapidly
in the biofilter
media 30 than in conventional biofilter media. It is believed that the higher
rate of phase transfer
of hydrogen sulfide is due to its particiilar aifmity for the coated expanded
glass granule 72. This
increased affinity for the coated expanded glass granule 72 allows the
biofilter system 20 to
achieve higher removal efficiencies (elimination capacities) for hydrogen
sulfide than were
previously obtained with biofilter systems employing conventional biofilter
media. An example
of the elimination capacity for hydrogen sulfide at various concentrations is
shown in FIG. 3.
[0056] Once the contaminants have transitioned to the liquid phase, the
contaminants are
adsorbed onto the biofilm formed on the surface of the expanded glass granule
72 and then
degraded by the metabolic activities of the microorganisms. Carbon dioxide and
water are
produced as a result of the biological oxidation of VOCs. The sulfur-based
compounds may
break down into sulfites (S032), sulfates (SO42), sulfides (S2) or sulfur (S).
The water soluble
sulfur compounds can be easily flushed out of the biofilter bed 24 without the
use of chemicals
by washing out the biofilter media 30 with water, using irrigation at
intermittent intervals.
10057] The coarse granular configuration of. the expanded glass granule 72 as
well as. its
characteristic low density/light weight tends to permit easy washing of the
biofilter media to
remove not only the products of the contaminant degradation but also any
excessive biomass
which may have accumulated on the surface of the biofilter media 30. The
problems associated.
with high gas flow resistance and clogging encountered in known biofilter
media tend to be
minimized in the biofilter media 30. Accordingly, the biofilter media may be
*recycled,
regenerated and reused with relative ease thus tending to impart to it a
relatively.long service
life. . .
[0058] Advantageously, the residue water from the periodic flushing of the
biofilter media 30
can be discharged from the biofilter bed 24 through the drain line 52.
[0059] In this embodiment, the water content in the biofilter media 30 may be
adjusted by
humidifying the air stream prior to its entry into the biofilter bed 24 and/or
irrigating the surface
of the biofilter media 30. Humidification of the air stream may occur in the
humidification .
CA 02605358 2007-10-03
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chamber 34 using, for example, one of the following moisture delivery systems:
a pneumatic
spray, high-pressure water or steam (not shown). 'Fhe delivery of moisture to
the biofilter media
30 may be accomplished through the water supply system 40, more specifically,
via the irrigation
conduits 46 and the spray nozzles 48.
[0060] During operation of the biofilter system 20, the temperature sensor 56
detects the
temperature of the biofilter media 30 and transmits a signal to the control
system 60 which may
actuate the moisture delivery system or the water supply system 40 in response
to that signal to
cause water and/or steam to be delivered to the air stream or - dimctly to the
biofilter media. In
this way, the temperature of the biofilter media may be maintained in the
optimal range to best
promote the sustained growth and development of the microorganisms.
[0061] The delivery of moisture in the form of water or steani may be actuated
by the oontrol
system 60 in response to a signal received from the pressure sensor 58. For
instance, if the
pressure sensor 58 detects pressure at a particular point across the biofilter
media 30 which
exceeds the desired pressure range, this may be an indication that sulfur has
accumulated
excessively on the surfaice of the biofilter media 30 in that area thereby
impeding proper gas flow
through the media. In this case, the biofilter control system 60 may cause the
water supply
system 40 to irrigate the biofilter media 14 with water to wash away the
sulfur build-up.
[0062] The control system 40 may also be configured to monitor other
parameters in the biofilter
media 30 to ensure the optimal operating conditions are maintained within the
biofilter bed 24.
For instance, the biofilter system 20 can include a pH monitoring probe (not
shown) to
periodically measure the pH in the biofilter bed 24. If the pH value measured
falls outside of the
desired range, an appropriate chemical solution, such as a liquid buffer, may
be added through
the water supply system 40. Other sensors could also monitor the need for
further nutrients -
these could be delivered through the water supply system 40.
[0063] Unlike conventional biofilter systems, the biofilter system 20 tends to
have a shortened or
reduced acclimation period. The biofilter system 20 can begin removing H2S
within less than a
day and become fully operational within 48 hours of the start up operation.
This reduced
acclimation period is due to the fact that the expanded glass granule 72 tends
to exhibit improved
water retention properties and tends to present a larger and rougher surface
area than known
CA 02605358 2007-10-03
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biofilter media thereby tending. to enhance adhesion of the microorganisms
onto. the biofilter
media 30. The increased surface area and roughness in combination with the
improved water.
retention properties of the expanded glass granule tends to favour more rapid
initial microbial
colonization resulting in shortened biofilter start-up time. As a result of
the reduced start-up time,
it is possible to use a smaUer volume 'of biofilter media to treat a given
volume of contaminated
air.
[0064] With its light weightllow density characteristics, the biofilter media
30 allows for greater
flexi'bility in the design of biofilter systems, More specifically, the
biofilter media 30 can be used
to lighten the overall weight of a biofilter system thereby lessening the need
for more structural
support (i.e. larger and heavier foundations). In turn, this makes it possible
to install such
biofilter systems in a variety of locations, including on roof tops. In
addition, in biofilter systems
that employ the biofilter media 30, the height of the column in the biofilter
bed, may be increased
to permit greater bed depth. This may allow the installation footprint of the
biofilter system to be
reduced for even greater versatility. Additionally, inmased bed height may be
advantageous in
the case where one or more compounds are not degraded until after other
compounds have been
broken down to "very low concentrations. In such cases, spatial separation of
zones for the
biodegradation of different compounds as a function of height in a biofilter
bed tends to result.
[0065] The removal.kinetics of various contanminants using a biofilter system
having the biofilter
media 30 in accordance with an embodiment of the present invention have been
'examined
through performance data obtained in laboratory during initial pilot studies
The performance of
the biofilter media 30 was compared to that of BIOSORBENSTM, a known, high
performance
biofilter media currently made commercially available by the assignee of the
present application,
BIOREM Technologies Inc. of Guelph, Ontario..
100661 The findings obtained from the different studies are. described as
follows:.
- Using a biofilter system oonstructed and operated in accordance with the
principles of
the present invention, high H2S removal efficiency at high inlet
concentrations in low empty bed
residence times (EBRT) has been consistently obtained. More specifically, the
biofilter system
has achieved greater than 95% removal of 200 ppm of H2S in 10 to 30 seconds
EBRT. In a 30
seconds EBRT, the biofilter system successfully removed greater than 99% of
200 ppm -of H2S.
CA 02605358 2007-10-03
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The presence of reduced sulfur compounds in the waste gas stream did not.
appear .to affect the
removal efficiency of the hydrogen sulfide. In comparison, the high
performance biofilter media.
currently made commercially available by the assignee of the present
application, BIOREM
Technologies Inc. of Guelph, Ontario under the name BIOSORBENS~, is capable of
removing
only up to 90% of 150-200 ppm of H2S in a 30 'seconds EBRT.
- Performance data for the removal of H2S at concentrations of up to 100 ppm
with the
biofilter media provided in accordance with the principles of the present
embodiment (identified
as "LWE") and with the known BIOSORBENS7m media are compared in Table 1 below:
Table 1. Removal Efficiencies of H2S using the biofilter media provided in
accordance with the principles of the present invention and the known
BIOSORBENSm biofilter media
Removal efficiencies (%)
H2S concentration 30-second EBRT 20-second EBRT
(Ppm) LWE BIOSORBENS LWE BIOSORBENS
100 100 100 . 100
100 100 100 96
100 100 100 . 88
100 . 98 100 81
100 94 100 76
100 91 100 71
100 87 100 68
100 . 84 100 64
100 81 100 61
100 100 79 100 59
As will be appreciated, the biofilter media provided in accordance with the
principles of the
present invention exhibits improved removal efficiencies.
CA 02605358 2007-10-03
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In addition, it has been shown that the biofilter media provided in accordance
with the
principles of the present invention is capable of handling peak concentrations
of H2S of up to 400
ppm while the known BIOSORBENS77" is effective up to peak concentrations of
about 100 ppm.
100671 It was found that the removal of dimethyl sulfide could be
significantly improved by
adding a predetermined quantity of zinc acetate to the biofilter media during
the manufacture
thereof. More specifically, with the addition of zinc acetate, it was possible
to increase the rate of
removal of dimethyl sulfide to from 25% to 55% at 30 seconds EBRT.
10068J It will thus be appreciated that the physical, material and biological
characteristics of the
biofilter media 30 as described above enable the biofilter media to perform
better than- other,'
known biofilter media. Whereas some conventional biofilter media are able to
achieve
satisfactory removal rates for hydrogen sulfide by improving biodegradation of
the contaminants,
the biofilter media 30 is designed to encourage both phase transfer and
enhance biodegradation
of the contaminants. As a result, the biofilter media is able to remove
hydrogen sulfide and
reduced sulfur compounds from waste gas streams with superior efficiency.
[0069] Although the foregoing description and accompanying drawings relate to.
specific
preferred embodiments of the present invention as -presently contemplated by
the inventor(s), it
will be understood that various changes, modifications and adaptations, may be
made without
departing from the spirit of the invention.
