U.S. patent application number 14/997527 was filed with the patent office on 2016-05-12 for method and apparatus for use of reacted hydrogen peroxide compounds in industrial process waters.
The applicant listed for this patent is Steen Research, LLC. Invention is credited to Michael J. Stoltz, Stephen R. Temple.
Application Number | 20160129392 14/997527 |
Document ID | / |
Family ID | 46325545 |
Filed Date | 2016-05-12 |
United States Patent
Application |
20160129392 |
Kind Code |
A1 |
Temple; Stephen R. ; et
al. |
May 12, 2016 |
Method and Apparatus for Use of Reacted Hydrogen Peroxide Compounds
in Industrial Process Waters
Abstract
Methods and apparatuses are described for contacting an
oxidizing solution such as an aqueous hydrogen peroxide composition
of hydrogen peroxide and at least one additive that catalyzes the
decomposition of the hydrogen peroxide into hydroxyl radicals with
an atmospheric effluent containing odorous and/or noxious
components. These components are absorbed by the aqueous hydrogen
peroxide composition to produce an atmospheric effluent having
reduced amounts of the odorous and/or noxious components. Various
methods are described for adding the hydrogen peroxide and the
decomposition additive.
Inventors: |
Temple; Stephen R.; (Santa
Cruz, CA) ; Stoltz; Michael J.; (Duncansville,
PA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Steen Research, LLC |
West Linn |
OR |
US |
|
|
Family ID: |
46325545 |
Appl. No.: |
14/997527 |
Filed: |
January 16, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13797882 |
Mar 12, 2013 |
9265854 |
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14997527 |
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12890268 |
Sep 24, 2010 |
8409512 |
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13797882 |
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12478603 |
Jun 4, 2009 |
7815879 |
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12890268 |
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11442554 |
May 26, 2006 |
7550123 |
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12478603 |
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10704238 |
Nov 7, 2003 |
7112309 |
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11442554 |
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09797859 |
Mar 2, 2001 |
6645450 |
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10704238 |
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60186694 |
Mar 3, 2000 |
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Current U.S.
Class: |
422/4 |
Current CPC
Class: |
A61L 9/00 20130101; B01D
53/18 20130101; B01D 53/38 20130101; B01D 2251/104 20130101; B01D
2251/106 20130101; Y10S 423/05 20130101; A61L 9/145 20130101; B01D
53/44 20130101; B01D 53/1493 20130101; B01D 2251/10 20130101; A61L
2209/22 20130101; B01D 2257/708 20130101; B01D 53/1487 20130101;
B01D 53/86 20130101 |
International
Class: |
B01D 53/44 20060101
B01D053/44; A61L 9/00 20060101 A61L009/00 |
Claims
1. A method for removing an odorous or noxious component from a gas
stream, comprising: contacting a gas stream comprising at least one
odorous or noxious component with a liquid stream comprising an
oxidant.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 13/797,882 filed Mar. 12, 2013, which is a continuation of U.S.
application Ser. No. 12/890,268 filed Sep. 9, 2010, now U.S. Pat.
No. 8,409,512, which is a continuation of U.S. application Ser. No.
12/478,603 filed Jun. 4, 2009, now U.S. Pat. No. 7,815,879, which
is a continuation of U.S. application Ser. No. 11/442,554 filed May
26, 2006, now U.S. Pat. No. 7,550,123, which is a
continuation-in-part application of U.S. application Ser. No.
10/704,238 filed Nov. 7, 2003, now U.S. Pat. No. 7,112,309, which
is a divisional of U.S. application Ser. No. 09/797,859 filed on
Mar. 2, 2001, now U.S. Pat. No. 6,645,450, which claims the benefit
of U.S. Provisional Patent Application No. 60/186,694, filed Mar.
3, 2000, all of which are incorporated by reference herein in their
entireties.
BACKGROUND
[0002] 1. Background of the Invention
[0003] This invention relates to the use of hydrogen peroxide
reacted with strong reducing agents or stronger oxidizing agents to
produce hydroxyl radicals. More specifically, the invention relates
to utilizing in-situ generation of hydroxyl radicals to effectively
oxidize odor and/or noxious compounds found in the food processing
industry, such as poultry, beef, or fish processing, as well as
rendering of meat, fish, or fowl by-products. This invention also
relates to the use of hydroxyl radicals in the reduction of
volatile organic compounds in aqueous gas scrubbers.
[0004] 2. Description of Related Art
[0005] In the processing of poultry, beef, and fish, the large
volume of organic material processed, as well as secondary
processing (rendering), can generate large quantities of odiferous
gases including organic sulfides, thiols, amines, alcohols,
inorganic sulfides, ammonia, and simple carboxylic acids. These
compounds are usually the result of biological action on the
organic materials being processed. The odors produced are offensive
and can travel significant distances to surrounding real estate. In
other industries, such as chemical processing, paint production,
wastewater treatment, etc., noxious compounds, such as volatile
organic compounds (VOCs), are produced and are subject to
environmental air quality regulations.
[0006] These gases are usually captured by a water media in air
scrubber systems. In an air scrubber system, typically, air from
the processing step is evacuated into a tower where water, broken
into droplets either by contact with mixed media or distribution
channels, absorbs the odiferous and noxious gas compounds. This
water is recirculated and discharged typically to wastewater
treatment systems. U.S. Pat. No. 6,015,536 to Lokkesmoe et al.,
provides a detailed description of the available air scrubbing
systems on the market and is hereby incorporated by reference
herein.
[0007] It can readily be seen that the scrubbing water media will
quickly saturate with the offensive gases and lose its absorbing
potential. At this point, the water has an intense disagreeable
odor. Additives are commonly injected into the scrubbing water
stream to reduce the odor content of the aqueous scrubbing media.
The water is either dumped to the wastewater treatment facility or
a portion is withdrawn to the wastewater facility and fresh makeup
water is added to account for the difference.
[0008] It can also be seen that as the water saturates with gases,
particularly nitrogen-bearing gases (ammonia), the pH of the water
will rise proportionally. This marked increase in pH reduces the
solubility of the gases causing them to flash to the atmosphere.
This results in a decrease in the efficiency of the gas transfer to
the water media.
[0009] Numerous attempts have been made to reduce the odor
components in the air scrubbing system. Some technologies attempt
to reduce the odor by injecting a maskant, which is a stronger,
more pleasing odor compound. These maskants are extremely
expensive, and the duration of the effectiveness is very short.
These compounds do nothing to the actual structure of the odor
molecule.
[0010] Maskants are also "fogged" or injected into spray orifices
under high pressure to create a small droplet mist effect. These
misted materials are directed into the atmosphere around the odor
causing process. The misted materials either mask the odor or
combine with the odor-causing molecule in the atmosphere to
temporarily lower the offensive odor. These compounds, which are
usually essential oils, are then blown with the prevailing winds.
These materials are limited by extreme cost and do nothing to
actually affect the odor-causing molecule.
[0011] U.S. Pat. Nos. 4,443,342 and 4,595,577, to Stas et al.,
describe a treatment method using hydrogen peroxide and copper
sulfate as the catalyst for treatment of wastewater and gases
containing organic sulfur compounds in a pH range below 6.5. It is
well known to those of skill in the art that the efficiency of
hydrogen peroxide as an oxidizer is increased in the pH range of 3
to 6.5. Stas et al. also describe using hydrogen peroxide in acidic
aqueous media with 1 to 5 ppm of ferric sulfate as a catalyst when
comparing the efficacy of the use of copper. This catalyst choice,
in the amount used, only increases the efficiency of the hydrogen
peroxide and does not effectively reduce the hydrogen peroxide to
free radicals in the quantities that would be needed to oxidize
odor components to soluble compounds to enable their removal.
[0012] Hydrogen peroxide by itself has only moderate success in air
scrubbing systems. It reacts very slowly and is limited in the
number of organic molecules it can oxidize. Some odor reduction can
be achieved using hydrogen peroxide, but it is usually via
microbiological control or an increase in oxygen content of the
aqueous scrubbing media.
[0013] Halogen donors such as chlorine dioxide, chlorine gas,
sodium hypochlorite, and hypobromous acids have had limited success
in the art. The low electronegativity of these halogens (1.0 to 1.7
volts) limits their ability to oxidize odor constituents down to
simple soluble compounds. Therefore their odor removal efficiency
is low compared to the quantity needed. The use of halogen donors
is falling under environmental scrutiny due to the formation of
haloamines as well as trihalomethanes. Use of these halogens in
aqueous streams eventually contributes to trihalomethanes and
haloamines in surface waters.
[0014] U.S. Pat. No. 6,015,536, to Lokkesmoe et al, describes the
use of peroxyacid compounds at a pH of 3 to 6 for odor reduction in
air scrubbers. Peroxyacid, namely peracetic acid, is used as an
oxidizer of odor causing molecules, and a reduction of odors from 5
to 50% is described. However, the large doses of peracetic acid
needed preclude higher odor removal rates due to cost as well as
the contribution of a pungent odor from the acetic and peracetic
acids. The peracid compounds also lack sufficient electronegative
potential to break up odor causing compounds to the degree needed
for greater than 50% removal rates.
[0015] Ozone has been used with limited success in aqueous gas
scrubbers. Ozone has an inherent high capital expenditure cost and
is difficult to utilize the ozone gas in aqueous media. It is
difficult to force enough gas into contact with the aqueous media
to effectively oxidize odor compounds into simple soluble
reduced-odor compounds. Ozone is also characterized by large
electric utility costs associated with corona discharge type ozone
production units.
[0016] Inorganic percompounds, such as percarbonates, persulfates,
perborates, and permangenates, have demonstrated odor control
potential. These compounds, however, are notoriously slow to
liberate oxygen in cold water at elevated pH.
[0017] There exists a need in the art for a treatment process that
has a high enough electronegative potential to reduce substantially
all odor and/or noxious compounds to simple, soluble,
reduced-odor/noxious, or odor/noxious-free compounds. This
treatment process would offer even greater advance in the art if
the process could also eliminate or greatly reduce the high cost of
treating the scrubber water effluent in the wastewater treatment
process.
SUMMARY OF THE INVENTION
[0018] In general, the present invention relates to chemical
compositions and systems, including processes and equipment for
removing odor and/or noxious components from an atmospheric
effluent. In one embodiment, the chemical composition includes an
oxidizer capable of oxidizing the odor and/or noxious components.
In another embodiment, the chemical composition includes an aqueous
hydrogen peroxide composition of hydrogen peroxide and an additive
that catalyzes the decomposition of hydrogen peroxide into hydroxyl
radicals. When contacted with the atmospheric effluent, the
oxidizer or aqueous hydrogen peroxide composition oxidizes the odor
and/or noxious components to produce an atmospheric effluent having
reduced amounts of the odor component and/or noxious component and,
in some embodiments, a non-odor offensive, environmentally
acceptable by-product.
[0019] A method is described for removing at least one of an odor
component and a noxious component from an atmospheric effluent. In
one embodiment, the atmospheric effluent is contacted with a
solution comprising an oxidizer. In another embodiment, the
atmospheric effluent is contacted with an aqueous hydrogen peroxide
composition including hydrogen peroxide and at least one additive
that catalyzes the decomposition of the hydrogen peroxide to
produce hydroxyl free radicals. The odorous and/or noxious
component in the atmospheric effluent is absorbed by the oxidizer
solution or the aqueous hydrogen peroxide composition and oxidized.
In another embodiment, the method further comprises contacting the
gas and liquid in a counter-current fashion. In another embodiment,
the oxidizer solution or the aqueous hydrogen peroxide composition
can be collected after contacting the gas in a tank and recycled
via a recycle stream to again contact the gas. In this embodiment,
additional oxidizer or additional hydrogen peroxide and
decomposition additive may be added to the recycle stream as
required or based upon measurement of a given solution parameter
that is used to indicated whether additional oxidizer or additional
hydrogen peroxide or decomposition additive is required. In some
embodiments, the measurement of the solution parameter may be done
continuously, periodically, or manually. In some embodiments, the
addition of the oxidizer or other additives may be done
automatically using a flow control valve based upon the measured
value of the solution parameter to provide a more precise addition
rate of these components and better control of the solution
composition compared to a simple on/off valve.
[0020] In some embodiments, the decomposition additive comprises a
metal-based compound, such as a ferrous or ferric salt, such as
ferrous sulfate or ferric sulfate. In other embodiments, the
decomposition additive comprises ozone, which may be added
concurrently with the hydrogen peroxide to the liquid stream to
improve contacting between the ozone gas and the hydrogen peroxide
in the liquid stream.
[0021] In one embodiment, the method for removing an odorous or
noxious component from a gas stream comprises adding hydrogen
peroxide, a hydrogen peroxide decomposition additive, and a
chelating agent to a liquid stream; contacting a gas stream
comprising at least one odorous or noxious component with the
liquid stream; and absorbing at least a portion of said odorous or
noxious component in the gas stream into the liquid stream. The
chelating agent is added to increase the solubility of the hydrogen
peroxide decomposition additive. In some embodiments, the chelating
agent allows the pH of the liquid stream to be controlled at a
higher value than the liquid stream would otherwise have under
similar operating conditions without the chelating agent. This may
improve removal of certain odorous or noxious components. In some
embodiments, the decomposition additive comprises a ferrous salt,
such as ferrous sulfate, and the chelating agent comprises
aminopolycarboxylates, such as nitrilotriacetic acid and
hydroxyethyliminodiacetic acid; N-heteroxcyclic carboxylates, such
as picolinic acid; polyhydroxy aromatics, such as gallic acid; or
other compounds, such as rhodizonic acid, tetrahydroxy-1,4-quinone,
and hexaketocyclohexane.
[0022] In some embodiments the pH of chemical composition or the
liquid stream may be controlled at a select pH by adding acid or
base directly to the liquid stream or to a tank that collects the
liquid stream after contacting the gas. In other embodiments, the
acid or base may be mixed with the decomposition additive before
addition to the chemical composition or the liquid stream or the
tank that collects the liquid stream after contacting the gas.
[0023] Other advantages of the present invention will become
apparent from the following detailed description taken in
conjunction with the accompanying drawings that illustrate, by way
of example, the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 shows a diagram of one embodiment of a process for
removing an odor and/or noxious component from an atmospheric
effluent;
[0025] FIG. 1A shows a diagram of another control system for the
system of FIG. 1;
[0026] FIG. 1B shows a diagram for a system for adding additive(s)
and acid or base for pH control to one or more gas/liquid
contactors or scrubbers;
[0027] FIG. 1C shows a diagram for a system for adding an oxidizer
to one or more gas/liquid contactors or scrubbers; and
[0028] FIG. 2 shows the system of FIG. 1 within a wastewater
effluent system of a processing plant illustrating the
pre-treatment properties of the present invention on the waste
treatment facility according to one embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0029] The present invention will now be more fully described with
reference to the accompanying drawings. To facilitate explanation,
the invention will be described primarily in the context of a
particular embodiment, namely, a wet scrubber system comprising a
packed column. While the invention will be described in conjunction
with this particular embodiment, it should be understood that the
invention can be applied to a wide variety of applications, and it
is intended to cover alternatives, modifications, and equivalents
as may be included within the spirit and scope of the invention as
defined by the appended claims. Accordingly, the following
description is exemplary in that several embodiments are described
(e.g., by use of the terms "preferably" or "for example"), but this
description should not be viewed as limiting or as setting forth
the only embodiments of the invention, as the invention encompasses
other embodiments not specifically recited in this description.
Further, the use of the term "invention" throughout this
description is used broadly and is not intended to mean that any
particular portion of the description is the only manner in which
the invention may be made or used.
[0030] In general, the present invention uses a liquid stream or
chemical composition comprising an oxidizer to oxidize absorbed
odor and/or noxious components from an atmospheric gas stream. In
some embodiments, additives may also be added to the liquid stream,
including, for example, acid or base to control the pH of the
liquid stream, additives to enhance the effectiveness of the
oxidizer (e.g., when using hydrogen peroxide as the oxidizer the
additive may be a hydrogen peroxide decomposition additive that
catalyzes the decomposition of hydrogen peroxide to hydroxyl free
radicals, chelating agents that, for example, increase the
solubility of the hydrogen peroxide decomposition additive, wetting
agents, and dispersants). It should be appreciated that any
chemical added to the liquid stream may be referred to as an
additive.
[0031] In one embodiment, the liquid stream comprises an aqueous
hydrogen peroxide composition of hydrogen peroxide and at least one
additive that serves to catalyze the rapid decomposition of the
hydrogen peroxide into hydroxyl radicals. When contacted with an
atmospheric effluent containing odor and/or noxious components, the
hydroxyl radicals formed oxidize the odor and noxious components to
a non-odor offensive, environmentally acceptable by-product. The
by-product in combination with the aqueous hydrogen peroxide
composition form a liquid effluent that provides charge
neutralizing and adsorption species that, in addition, aid in
treatment of wastewater effluents.
[0032] As can be seen in Table 1 below, the hydroxyl radical is
known in the art as the second most electronegative species, second
only to fluorine, and is significantly higher in oxidation
potential than other compounds known in the art. The highly
electronegative hydroxyl radical is, therefore, capable of a much
greater decomposition of odor-causing molecules than any
composition known in the art. Accordingly, it is not necessarily
the intent of the invention to utilize the oxidation potential of
the hydrogen peroxide but rather to utilize the hydroxyl radical
produced from the decomposition of the hydrogen peroxide. It will
be appreciated that in the decomposition of hydrogen peroxide some
diatomic oxygen may also be produced, which also has an oxidation
potential; however, the present invention is directed at utilizing
the hydroxyl radical generated from the hydrogen peroxide
decomposition. Accordingly, in one embodiment of the invention, at
least a portion of the hydrogen peroxide in a solution used to
contact atmospheric effluent containing odor and/or noxious
components is decomposed to produce hydroxyl radical, which, in
turn, oxidizes the odor and/or noxious components. In another
embodiment, although not necessary, it is desirable to drive the
hydrogen peroxide decomposition reaction to produce predominantly
hydroxyl radicals to act in the oxidation of the odor and/or
noxious components in the atmospheric effluent. It should be
appreciated that neither all of the hydrogen peroxide needs to be
decomposed to hydroxyl radicals nor does the decomposition need to
result in only the production of hydroxyl radicals. In some
embodiments, it is sufficient that a portion of the hydrogen
peroxide decomposes to produce at least some quantity of hydroxyl
radicals.
TABLE-US-00001 TABLE 1 Oxidation Potential Oxidizer (Volts)
fluorine 3.0 hydroxyl radical 2.8 ozone 2.1 hydrogen peroxide 1.8
potassium permanganate 1.7 hypobromous acid 1.6 chlorine dioxide
1.5 chlorine 1.4
[0033] FIG. 1 shows a diagram of one embodiment of a process for
removing an odor and/or noxious component from an atmospheric
effluent. In this embodiment, a wet scrubber system is used to
contact an atmospheric or gaseous effluent comprising an odorous or
noxious component with an aqueous hydrogen peroxide composition
comprising hydrogen peroxide and at least one additive that
catalyzes the decomposition of the hydrogen peroxide to hydroxyl
radicals. According to this embodiment, an atmospheric effluent 102
enters a packed scrubber 106 through an atmospheric effluent intake
104. The atmospheric effluent 102 may be from a food processing
process, rendering process, or other industrial process that
produces an atmospheric or gaseous effluent having odoriferous
and/or noxious components. In this embodiment, the wet scrubber
comprises a packed column 108. The atmospheric effluent 102 enters
the packed column 108 where it is contacted with an aqueous
hydrogen peroxide composition 110 supplied by dispenser(s) 112. The
aqueous hydrogen peroxide composition 110 comprises hydrogen
peroxide and at least one additive that catalyzes the decomposition
of at least a portion of the hydrogen peroxide to hydroxyl
radicals. In one embodiment, the aqueous hydrogen peroxide
composition leaving dispenser(s) 112 has a relatively high
concentration of hydroxyl radicals compared to a hydrogen peroxide
solution without such an additive. In another embodiment, the
additive catalyzes the decomposition to produce predominantly
hydroxyl free radicals.
[0034] In the packed column 108, the atmospheric effluent 102 and
the aqueous hydrogen peroxide composition 110 comprising hydroxyl
free radicals contact each other, and the hydroxyl radicals oxidize
the odorous and/or noxious components in the atmospheric effluent
102 to produce a substantially non-odor-offensive,
environmentally-acceptable by-product that exits the packed column
108 with the aqueous hydrogen peroxide composition 110 as a liquid
effluent 114. Dependent on the oxidation of the odor and/or noxious
component, the liquid effluent 114 may contain by-product that is
soluble in the aqueous hydrogen peroxide composition 110 or that
may adsorb onto semi-colloidal particles formed in the aqueous
hydrogen peroxide composition 110. The concentration of odorous
and/or noxious components is reduced in the atmospheric effluent
102, which exits the packed column 108 as a gaseous exhaust
effluent 116 by way of a vent 118.
[0035] The liquid effluent 114 exits the packed column 108 and is
collected in a reservoir 120 for discharge to a wastewater
facility. In some embodiments, the reservoir is integral to the
scrubber or packed column 108, in which case, the reservoir 120 may
also be vented. In some embodiments, the liquid effluent 114 may be
collected and the entire reservoir 120 dumped into a waste
treatment pathway or waste treatment facility. In other
embodiments, the reservoir 120 may be equipped with an overflow
system so that a portion of the liquid effluent 114 is continually
or periodically overflowed into a waste treatment pathway for
delivery to a waste treatment facility. In the latter case, the
reservoir 120 may also have an add-back line to allow introduction
of makeup water into the reservoir 120 so that a constant effluent
level is maintained in the reservoir 120.
[0036] A recycle line or sidestream 121 in fluid communication with
the reservoir 120 and the dispenser(s) 112 is used to transfer
liquid effluent 114 from the reservoir back to the top of the
packed column 108 by using a pump 122 within the recycle line 121.
The fluid in this recycle line or sidestream 121 may be referred to
as a recycle stream or fluid. Those of skill in the art will
appreciate that a wide variety of pumps may be used. The pump
should be chosen to provide sufficient power to move fluid at the
mass flow rate required by the particular scrubber. It should also
resist chemical attach by the liquid effluent and any additives
present in the liquid effluent. For certain applications, it may be
desirable to use specific types of pumps. For example, as described
below, when using the pump to introduce ozone or other gaseous
catalysts, a pump capable of introducing a gas into a liquid stream
could be used, such as a regenerative turbine pump.
[0037] It will be appreciated that at the start of the process the
contents of the reservoir 120 may be essentially makeup water until
the process has completed several cycles in which the aqueous
hydrogen peroxide composition 110 has been contacted with the
atmospheric effluent 102. Aqueous hydrogen peroxide and any
additives are added to the liquid effluent 114 in the recycle line
or sidestream 121 to form the aqueous hydrogen peroxide composition
110, which is then delivered to the atmospheric effluent 102 in the
packed column 108 via dispenser(s) 112.
[0038] The hydrogen peroxide in the aqueous hydrogen peroxide
composition is delivered from a source container 124 into the
recycle line or sidestream 121 via an inlet valve 126, which is
positioned upstream of the pump 122. The concentration of hydrogen
peroxide in the source container 124 should be chosen to allow safe
handling given the equipment in use and to provide sufficient
concentration for the needs of the scrubber. Although the
concentration of hydrogen peroxide in the source container 124 may
be selected within a wide range, specific embodiments will range
between about 35% to 50% by weight in an aqueous solution as these
ranges are currently industrially available and legally
transportable. In a preferred embodiment, the concentration is
about 50% by weight in aqueous solution.
[0039] At least one decomposition additive in the aqueous hydrogen
peroxide composition is delivered from a source container 128 into
the recycle line or sidestream 121 via an inlet valve 130, which is
positioned downstream of the pump 122. Upon the addition of the
additive on the downstream side of the pump 122, the decomposition
of at least a portion of the hydrogen peroxide to hydroxyl radicals
is catalyzed. In another embodiment, the decomposition produces
predominantly hydroxyl radicals. As noted above, it is not
necessary that all of the hydrogen peroxide decompose to hydroxyl
radicals or that the decomposition itself only produce hydroxyl
radicals. Depending upon the amount of hydroxyl radicals produced,
which can be determined based upon the removal efficiency of the
odorous and/or noxious components from the gas stream, the rate and
amount of additive delivered to the system can be adjusted.
Addition of the additive on the backstream or downstream side of
the pump 122 is preferred over arrangements on the vacuum side as
it reduces wear on the pump 122 from the decomposition product of
hydrogen peroxide, e.g., the hydroxyl radicals. However, it should
be appreciated that the additive may be added upstream of the pump
122 using a similar inlet valve. The aqueous hydrogen peroxide
composition comprising the hydroxyl radicals is then delivered to
the packing column 108 via dispensers 112 to contact the
atmospheric effluent 102.
[0040] In some embodiments, the aqueous hydrogen peroxide
composition may include additional additives, including additives
that catalyze the decomposition of hydrogen peroxide, wetting
agents, and/or chelating agents (discussed further below). Addition
of these additives would be made similar to the addition of the
additive for catalyzing the decomposition of the hydrogen peroxide
discussed above. Thus, there may be separate source containers and
inlet valves to enable the regulated delivery of these additional
additives in aqueous form to the recycle or sidestream 121.
Preferably, these additional additives are added on the downstream
side of the pump 122; however, these additives could be added at
other locations, including, for example, anywhere along the recycle
line or sidestream 121 or directly to the reservoir 120.
Additionally, some or all of the other additives, wetting agents,
and/or chelating agents may be mixed together and delivered from a
single source container. Alternatively, any one or more of these
additives may be provided together with one or more other source
materials. For example, the hydrogen peroxide in its source
container 124 may contain any one or more chemically compatible
(e.g., resistant to oxidation) additives such as certain chelating
agents and/or wetting agents. Of course, the additives may also be
provided with the decomposition additive from its source container
128 and/or from the source container 140 for the acid or base
(discussed further below).
[0041] It will be appreciated that the inlet valves discussed in
FIG. 1 are regulated so that the aqueous hydrogen peroxide
composition in the recycle line or sidestream 121 has a desired
composition. Regulation of the inlet valves may be by any means,
such as a controller or formulator system, such that the individual
components are delivered into the recycle or sidestream 121 in the
desired amounts to form the aqueous hydrogen peroxide composition.
Further, this system for feeding these components may stand-alone
or be incorporated as part of a larger control system, particularly
in the case where the system includes more than one scrubber. It
will be appreciated that other embodiments may be utilized in which
the components of the aqueous hydrogen peroxide composition are
added at different locations within the system, including different
locations along the recycle or sidestream 121 or directly to the
reservoir 120.
[0042] One of skill in the art will appreciate that the actual
composition of the aqueous hydrogen peroxide composition in the
recycle line or sidestream 121 and, specifically, the concentration
of hydrogen peroxide, the additive, and hydroxyl free radicals
therein, is determined based upon the composition of the gas stream
entering the scrubber and the specific gaseous components to be
removed, as well as the scrubber operating conditions. At a given
set of scrubber operating conditions (such as the gas flow rate and
concentration of odorous and/or noxious components and the liquid
flow rate through the scrubber), the addition rate of either or
both of the hydrogen peroxide and the additive may be adjusted to
provide the necessary production of hydroxyl free radicals to
achieve the desired removal rate of odorous and/or noxious
components. Of course, the concentration of the hydrogen peroxide
and the additive in their respective source containers may be
adjusted to achieve the desired rate of addition of each to the
system in balance with overall water balance considerations.
[0043] The system and process of the embodiment of FIG. 1 may also
include a pH control loop to measure the pH of the liquid effluent
114/aqueous hydrogen peroxide composition 110 in the recycle line
or sidestream 121 and, in response, to regulate the addition of an
acid or base into the recycle line or sidestream 121 to maintain
the pH of that stream within a preferred pH range. In such an
embodiment, an inlet valve 132 permits the withdrawal of a portion
of the aqueous stream in the recycle line or sidestream 121. This
stream contacts a pH probe 134 and passes back to the packed
scrubber 106 or the reservoir 120. The pH probe 134 measures the pH
of this stream and communicates the measured pH to a pH controller
138. The pH controller 138 then regulates, as needed, the addition
of an acid or base from an acid or base source container 140 into
the recycle line or sidestream 121 via an inlet valve 142. In one
embodiment, the inlet valve 142 is located upstream of the inlet
valve 126. In another embodiment, the acid or base is added to the
stream withdrawn from the recycle line or sidestream 121 that
contacts the pH probe (not shown). In this case, the acid or base
would be added downstream of the pH probe before this stream is
returned to the reservoir 120. In another embodiment, the acid or
base can be added directly to the reservoir 120 (not shown).
[0044] Through the addition of acid or base using the pH control
loop, the pH of the liquid effluent 114/aqueous hydrogen peroxide
composition 110 in the recycle line or sidestream 121 is maintained
at a level that maximizes the decomposition of the hydrogen
peroxide by the additive(s) that catalyze such decomposition. This,
in turn, allows the removal of the odor and/or noxious component
from an atmospheric effluent to be optimized. One of skill in the
art will appreciate that the optimal pH to be used will be
dependent upon the particular gaseous component to be removed and
oxidized and its properties and concentration in the atmospheric
effluent, as well as the composition of the aqueous hydrogen
peroxide composition and operating conditions of the scrubber. For
example, in removing hydrogen sulfide, its solubility is pH
dependent and increases with increasing pH above about pH 5 to
about pH 9.5. Accordingly, this solubility property needs to be
taken into account in selecting an operating pH. Additionally, the
solubility of the decomposition additive, particularly a
metal-based additive (discussed below), relative to the pH of the
aqueous hydrogen peroxide composition needs to be taken into
account. Typically, metal-based additives are less soluble at
higher pH, so that the pH may need to be controlled at a lower
level to maintain an adequate concentration of such an additive in
solution and available to catalyze the decomposition of the
hydrogen peroxide.
[0045] As described above, at least one additive is added to form,
in conjunction with the added hydrogen peroxide, the aqueous
hydrogen peroxide composition. This additive is used to catalyze
the decomposition of hydrogen peroxide to hydroxyl free radicals.
Generally, the catalyst source is chosen relative to the gas stream
being treated and the specific gaseous components to be removed so
as to generate an aqueous hydrogen peroxide composition having
optimal concentrations of hydroxyl free radicals. The catalyst
source is also selected with a view toward safety and
effectiveness. Obviously, the concentration of the catalyst used
will vary depending upon the particular catalyst chosen for the
task. Typically, the catalyst will be delivered using an aqueous
solution, although for some catalyses, such as ozone and certain of
the group VII elements (discussed further below), a direct gaseous
addition will be necessary.
[0046] In one embodiment, the additive used is ferrous sulfate. The
use of ferrous sulfate in sufficient quantities to catalyze the
decomposition of the hydrogen peroxide into hydroxyl radicals is
well known to those of skill in the art as "Fenton's Reagent".
However, the use of the highly electronegative hydroxyl radicals
has not been explored in air scrubbers, such as those utilized in
food processing and in other process industries that produce
atmospheric effluents, such as rendering, containing odor and/or
noxious components, for example, volatile organic compounds
(VOCs).
[0047] In aqueous media, ferrous iron decomposes hydrogen peroxide
in the following manner:
Fe.sup.2++H.sub.2O.sub.2.fwdarw.Fe.sup.3++OH.sup.-+OH*
As earlier described, the hydroxyl radical formed oxidizes the odor
producing components and/or noxious components via electron
transfer.
[0048] It should be appreciated that the solubility limit of the
catalyst presents an upper bound on concentration of the catalyst
in the source container. In the case of ferrous sulfate, the
concentration may be selected within a wide range with specific
embodiments within the range between about 20% to about 38% by
weight in aqueous solution. In a preferred embodiment the
concentration of ferrous sulfate is about 38% by weight in aqueous
solution. In this embodiment, the aqueous hydrogen peroxide
composition may be added as a 50% by weight hydrogen peroxide
solution in its source container.
[0049] The ratio by weight of the hydrogen peroxide solution to the
ferrous sulfate, based on a 50% by weight hydrogen peroxide
solution and a 38% by weight ferrous sulfate solution should be
within the range between about 1:1 to about 100:1, with a preferred
ratio within the range between about 2:1 to about 50:1, and with a
most preferred ratio within the range between about 5:1 to about
15:1. The higher the ferrous sulfate ratio the more the
decomposition reaction is driven to producing hydroxyl free
radicals. The ratio can be as high as one part 50% by weight
hydrogen peroxide solution to ten parts 38% ferrous sulfate
solution, but an extreme amount of heat is generated. While this
amount of heat may be acceptable in some settings, it may not be
desirable in others.
[0050] It should be appreciated that the use of highly
electronegative hydroxyl radicals is capable of a much greater
decomposition of odor-causing molecules than any composition known
in the art. Further, the use of some of the decomposition
additives, particularly, ferrous sulfate, not only reduces the
hydrogen peroxide into the hydroxyl radicals but also introduces a
semi-colloidal substrate into the aqueous media that is capable of
effectively adsorbing odor-causing and/or noxious compounds.
[0051] As noted above, in some embodiments, additional additives
may be added to the aqueous hydrogen peroxide composition, their
choice depending on the particular system in which they will be
used, cost, environmental concerns, and organic loading of the
effluent being treated. These additional additives may include
additional catalysts or other additives and may be added alone or
in combination, such as wetting agents, dispersant polymers, and
chelating agents.
[0052] Additives that act as catalysts, other than ferrous sulfate,
may be used alone or in combination with ferrous sulfate. In one
embodiment, the catalytic additive may be any element chosen from
elements in groups 3B, 4B, 5B, 6B, 7B, 8B, 1B, and 2B of the
Periodic Table of Elements and may include combinations thereof. It
will be readily apparent to one of normal skill in the art that the
additive(s) selected from these elements would be chosen based upon
cost, speed of reaction and environmental impact. Among these
elements, iron and its conjugates are the cheapest, most readily
available, and are of lowest environmental impact.
[0053] More preferred are the "d" block transition elements,
characterized by the "d" electrons in their valence shell, and
combinations thereof. For example, the additive may be cobalt. In
one embodiment, the aqueous hydrogen peroxide composition may be
formed using an amount of cobalt within the range between about
0.5% wt/wt % to about 1% wt/wt % of the total aqueous hydrogen
peroxide composition. Or, the amount of cobalt may be between about
0.5% wt/wt % to about 1% wt/wt % of a solution comprised of cobalt
and a 50% by weight hydrogen peroxide solution. In another
embodiment, the additive may be any element selected from elements
in Group 7A of the Periodic Table of Elements and combinations
thereof, for example, fluorine.
[0054] In one embodiment, the decomposition additive may be ozone.
Using ozone as the additive to catalyze the decomposition of the
hydrogen peroxide provides numerous advantages. In particular,
using ozone allows for operation at higher pH because the ozone is
not as solubility limited at higher pH compared to the
decomposition additives that comprise metals. As discussed below,
the solubility of a metal-based decomposition additive typically
decreases at higher pH, but a chelating agent may be used to
enhance its solubility. The use of ozone, however, may displace the
need to use a chelating agent in combination with a metal-based
decomposition, thereby allowing operation at higher pHs. As noted
above, operation at higher pH provides the aqueous hydrogen
peroxide composition with a greater capacity to absorb acidic
odorous and noxious components in the gas stream to be treated,
thereby increasing the removal efficiency of the process.
Accordingly, when using ozone, because solubility of a metal-based
catalytic additive is not an issue, the pH of the aqueous hydrogen
peroxide composition may be increased. The particular pH used in
operation can be determined as discussed above and is based upon
factors such as the type and concentration of the odorous and/or
noxious components in the gas stream and the operating conditions
of the scrubber. Generally, it should be appreciated that virtually
any pH above, for example, 5.0, may be used.
[0055] When using ozone very poor gas transfer to liquid media has
been observed in the art. As part of the present invention, use of
a regenerative turbine pump, for example, a Burks regenerative
turbine pump manufactured by Burks Manufacturing, can be used as
the pump for the recycle line or sidestream to provide sufficient
to excellent mixing of the ozone with the liquid stream in the
recycle line or sidestream. Referring back to FIG. 1, such a
regenerative turbine pump can be used as the pump 122 in the
recycle or sidestream 121. In this case, the hydrogen peroxide is
added as shown in FIG. 1 upstream of or on the vacuum side of the
regenerative turbine pump 121. An ozone/air mixture is then added
to an inlet port pre-built on the vacuum side of the regenerative
turbine pump 121. The resulting liquid discharged from the
regenerative turbine pump 121 provides a well mixed stream. In
particular, pressurizing the discharge side of the pump to a
minimum of 100 psi by using a pinch valve (not shown) gives
excellent gas transfer of the ozone to the liquid media in the
recycle line or sidestream. In this instance, rather than the ozone
being delivered through the inlet valve 130 used for other liquid
phase additives, the ozone would instead be connected to the inlet
port pre-built on the vacuum side of the regenerative turbine pump
122 and regulated through the pinch valve. It will be appreciated
that this pinch valve may also be controlled using the same control
system or formulator system that regulates the other inlet valves
of FIG. 1. It should be appreciated that in some embodiments, the
ozone may be added either upstream or downstream of the circulation
pump or in any other manner to maximize the transfer of the ozone
into the liquid phase and the decomposition of the hydrogen
peroxide.
[0056] More particularly, as the liquid effluent 114, enriched with
hydrogen peroxide (due to the addition of hydrogen peroxide from
the hydrogen peroxide source container 124), enters the vacuum side
of the regenerative turbine pump 122, the air/ozone mixture is
introduced through a pre-machined air port. Intense shear is
developed inside the regenerative turbine pump 122 that breaks the
ozone/air mixture into microbubbles entrained in the liquid
solution. The discharge from the regenerative turbine pump 122 is
pressurized to a minimum of 100 psi through a pinch valve assembly,
ensuring solubilization of the ozone into the liquid effluent 114
enriched with hydrogen peroxide. This allows for the efficient
decomposition of the hydrogen peroxide by the ozone into hydroxyl
radicals.
[0057] In another embodiment, a nonionic wetting agent may be added
to the scrubber or to the aqueous hydrogen peroxide composition to
enhance its activity by allowing further penetration of the
oxidizing agent into crevices of bacterial forms of odor and/or
noxious components. While the exact mechanism is not known, it is
believed that certain nonionic surfactants, i.e., wetting agents,
assist in the degradation of bacterial cell walls allowing the
aqueous hydrogen peroxide composition to more readily kill the
bacteria in the medium.
[0058] Preferred wetting agents are octylphenols, ethylene oxide
block copolymers, propylene oxide block copolymers, and
combinations thereof. The determining factors for wetting agent
choice is organic loading of the effluent, i.e., the level of
proteins or starches in the effluent, cleanliness of the system
being treated, i.e., the amount of deposits and slime on the
surfaces of the scrubber tank and packing, as well as need for
defoaming capabilities.
[0059] In one embodiment, the wetting agent, as 100% active
material, is present in an amount up to about 10% by weight of the
aqueous hydrogen peroxide composition (in the scrubber or as
additives to a scrubber sidestream), with a preferred embodiment
being an amount up to about 5% by weight of the aqueous hydrogen
peroxide composition, and in a most preferred embodiment an amount
up to about 1% by weight of the aqueous hydrogen peroxide
composition.
[0060] In another embodiment, a low molecular weight dispersant
polymer may be added to the scrubber or to the aqueous hydrogen
peroxide composition in order to prevent iron and other particle
agglomeration in the aqueous media as well as to prevent iron and
organic deposition in lower liquid flow areas. In one embodiment,
the average molecular weight of these low molecular weight
dispersants is within the range between about 1,000 to about
22,000, with a preferred average molecular weight within the range
between about 1,000 to about 9,000. These low molecular weight
dispersants may be, but are not limited to, homopolymers of acrylic
acid, methacrylic acid, acrylamide, copolymers and terpolymers
acrylates, methacrylates, acrylamide, AMPS (2-acrylamido-2-methyl
propane sulfonic acid), and combinations thereof. For example, a
dispersant resistant to oxidation may be desirable in situations
where sulfur-based compounds that are formed as a result of
operation at higher pHs and interaction with a metal-based
decomposition additive in which insoluble agglomerations, such as
zinc sulfate, are formed.
[0061] The low molecular weight dispersant polymer is added on a
weight percent basis (i.e., wt/wt % on the total composition weight
of the aqueous hydrogen peroxide composition in the scrubber or as
additives to a scrubber sidestream). A preferred percentage of the
low molecular weight dispersant, in the aqueous hydrogen peroxide
composition, is within the range between about 0.5% active wt/wt %
to about 10% active wt/wt % of the total aqueous hydrogen peroxide
composition. A more preferred percentage is within the range
between about 0.5% active wt/wt % to about 5% active wt/wt % of the
total aqueous hydrogen peroxide composition, and a most preferred
percentage is within the range between about 0.5% active wt/wt % to
about 2% active wt/wt % of the total aqueous hydrogen peroxide
composition.
[0062] In another embodiment, a chelating agent may be added to the
aqueous hydrogen peroxide composition. As earlier discussed, a
semi-collodial metal complex may form during the oxidation process,
and in some instances, the development of this colloidal metal
complex is undesirable. A chelating agent may be added to prevent
the formation of metal hydroxides or other insoluble metal
complexes. In one embodiment, the chelating agents may be organic
acids such as gluconic acids, glycolic acids, lactic acids, and
combinations thereof. It will be appreciated that a large number of
chelating agents may also be used and their selection readily
apparent to those of skill in the art; however, the chelating agent
should not be of such potent chelating ability as to prevent the
availability of the metal complex for decomposition purposes.
[0063] A chelating agent may also be added to enhance the
solubility of the decomposition additive or catalysts. This may, in
some embodiments, allows for operation at higher pH. As noted
above, higher pH increases removal of the odorous and/or noxious
components in the gas compared to lower pH operation. It should be
appreciated, however, that a chelating agent may be used to enhance
the solubility of the decomposition additive in some embodiments
where increasing the pH may not be necessary.
[0064] Generally, chelating agents can be selected based upon the
particular decomposition additive being used. For example,
chelating agents known in the art may be used to increase the
solubility of metal-based decomposition additives, such as ferrous
ion and other metal complexes. In addition, ferric (Fe.sup.3+) ion
may be used as the decomposition additive to decompose hydrogen
peroxide to produce hydroxyl radicals, and chelating agents may be
added to increase the solubility of the ferric ion, thereby
increasing the production of hydroxyl free radicals and allowing
for operation at a higher pH. Chemical Treatment of Pesticide
Wastes--Evaluation of Fe(III) Chelates for Catalytic Hydrogen
Peroxide Oxidation of 2,4-D at Circumneutral pH, Sun et al., J.
Agric. Food Chem, 1992, 40, 322-327, which is incorporated by
reference herein, describes several chelating agents that may be
used to solubilize ferric ion. Such chelating agents that showed
"high" catalytic activity and that may be used in the present
invention include: aminopolycarboxylates, such as nitrilotriacetic
acid and hydroxyethyliminodiacetic acid; N-heteroxcyclic
carboxylates, such as picolinic acid; polyhydroxy aromatics, such
as gallic acid; and other compounds, such as rhodizonic acid,
tetrahydroxy-1,4-quinone, and hexaketocyclohexane. These chelating
agents may be used separately. However, it may be possible to use
mixtures of these chelating agents as well.
[0065] It should be appreciated that the chelating agent and the
decomposition additive, such as ferrous ion or ferric ion (which
may be added, for example, as ferric sulfate) may be mixed before
use to allow for chelation. For example, referring to FIG. 1, the
chelating agent and the ferric ion may be chelated prior to placing
such a mixture in the additive source container 128. In this case,
the selection of the decomposition additive and chelating agent can
be based upon the specific application or particular gaseous
components to be removed and the desired operating pH. By mixing
the decomposition additive and the chelating agent prior to use,
this mixture is essentially "tailor-made" and is ready for
immediate use in the particular application at issue. In fact, this
mixture can be prepared remote from the facility where it will be
used and shipped to that facility for immediate use.
[0066] Alternatively, the decomposition additive and the chelating
agent may be added separately to the additive source container 128,
thereby allowing for in-situ chelation in the source container 128.
In this case, consideration must be given to the rate at which this
solution is added through the valve 130 to the system to provide
sufficient time for chelation to occur. One of skill in the art
will appreciate the conditions necessary to chelate, including use
of the proper pH, which may be, for example, pH 6. Alternatively
still, the chelating agent may be added through the use of a
separate source container (not shown) in a manner similar to that
of the additive source container 128. Further, the use of a
separate source container for the chelating agent may be used to
dispense the chelating agent into the recycle line or sidestream
either upstream or downstream of the pump 122; however, it is
preferable to dispense the chelating agent into the recycle line or
sidestream as closely as possible to the point where the additive
is added to the recycle line or sidestream.
[0067] As noted above, use of a chelating agent to increase the
solubility of the decomposition additive (for example metal-based
additives and, in particular, ferrous or ferric ions) allows for
operation at a higher pH in the aqueous hydrogen peroxide
composition that is fed to the scrubber. Operation at higher pH
increases the capacity of the aqueous hydrogen peroxide composition
to absorb additional acidic gases, thereby increasing the removal
efficiency of the process. It should be appreciated that the
specific pH used will be dependent upon the particular gaseous
components to be removed from the gas stream and, correspondingly,
may include a wide range of pHs. In some embodiments, it may be
desirable to not change the operating pH significantly or at all
upon the addition of a chelating agent.
[0068] The present invention has been described above primarily
with reference to removal of odor and/or noxious components from an
atmospheric effluent in which the oxidized odor and/or noxious
components are oxidized during contact with an aqueous hydrogen
peroxide composition to produce a substantially non-odor offensive,
environmentally acceptable by-product that is solubilized in or
adsorbed into the aqueous hydrogen peroxide composition to form a
liquid effluent. It should be appreciated, however, that various
oxidizers or solutions containing oxidizers may be used. For
example, oxidizing compounds such as chlorine gas, sodium
hypochlorite, hypobromous acid, chlorine dioxide, hydrogen
peroxide, peroxy acids, ozone, and permanganate may be used.
[0069] In addition, the present invention has been described above
in the context of one embodiment: the use of a wet scrubber system
using a single packed column with a single integrated reservoir. It
should be appreciated that other gas/liquid contactors may be used
in the wet scrubber system. For example, spray towers, Venture
spray condensers, or a combination of spray towers and packed
columns may be used. Further, counter-current scrubbers, where the
direction of the gas flow is opposite the direction of the liquid
flow; co-current scrubbers, where the direction of the gas flow is
in the same direction as the liquid flow; and cross-flow scrubbers,
where the direction of the gas flow is at an angle to the direction
of the liquid flow; may be used. In addition, it should be
appreciated that more than one reservoir may be used for a single
scrubber or, alternatively, one reservoir may be used for more than
one scrubber. Further, it should be appreciated that the reservoir
does not necessarily need to be integral to the gas/liquid
contactor and may be a separate tank, provided that appropriate gas
seals are in place.
[0070] It should be appreciated that more than one gas/liquid
contactor may be used in a single system. Such gas/liquid
contactors may be of the same or various types and may be
configured to operate in series or in parallel. Each gas/liquid
contactor could also have its own reservoir or multiple gas/liquid
contactors may share the same reservoir. In using more than one
gas/liquid contactor with one or more reservoirs, it is possible to
utilize one set of source containers for hydrogen peroxide,
additives, and any acid or base required for pH control.
[0071] FIG. 1A illustrates another control system for the system of
FIG. 1. As noted above, the addition of the hydrogen peroxide and
the decomposition additive, as well as other additives, is
regulated to provide the desired composition in the liquid solution
in the scrubber. Similar to the pH control loop discussed above,
FIG. 1A shows a probe 135 that is designed to measure a given
solution parameter or measurable parameter that can be used to
control the addition rate of the hydrogen peroxide or the additives
or both. For example, the probe 135 may measure the
oxidation-reduction potential of the solution or a particular
chemical species, such as a given additive, a species that is
indicative of the concentration of the additive, the concentration
of gaseous species absorbed by the scrubber, or a combination of
these. This probe 135 may be placed in a sidestream similar to the
one described above in connection with the pH probe 134. A
controller 139 may be used to receive the output from the probe 135
and in response automatically control the addition rate via the
pumps that add the hydrogen peroxide from its source container 124
or the additive from its source container 128. In one embodiment,
the hydrogen peroxide addition rate may be set at a given, constant
value, and the probe 135 and controller 139 would be used to
control the addition rate of the decomposition additive (as shown
by the solid line between the controller 139 and the source
container 128 for the additive). Alternatively, the rate of
addition of the decomposition additive may be set at a given,
constant value, and the probe 135 and controller 139 would be used
to control the addition rate of the hydrogen peroxide (as shown by
the dashed line between the controller 139 and the source container
124 for the hydrogen peroxide). It should be appreciated, that
separate control loops may be used for the hydrogen peroxide and
the additive, respectively, depending upon the type of probe used
and the solution parameter that is being measured. It should also
be appreciated that a pH control loop may be used in combination
with the control loop shown in FIG. 1A.
[0072] FIG. 1B shows a diagram for a system for adding additive(s),
such as the decomposition additive and other additives described
above, and acid or base for pH control to one or more gas/liquid
contactors or scrubbers. As noted above, a system may include more
than one scrubber/reservoir combination. In the system shown in
FIG. 1B, each source container for each additive and for acid or
base (e.g., a ferrous sulfate source container 150 and a source
container for acid or base for pH control 152) is fluidly connected
to a single feed tank 154. The feed tank 154 may have a level
controller 155 that is used to control the addition rate of the
additive(s), the acid or base, the make-up water, or a combination
of these to the feed tank 154. Of course, the concentration of the
additive(s) and acid or base in their respective source containers
150, 152 will need to be accounted for in determining their
addition rate to the feed tank 154 or visa versa. It should be
appreciated that while FIG. 1B is shown for use in adding additives
and acid or base to multiple scrubbers, the use of a single tank
154 for mixing additives and acid or base may be used for systems
having only one scrubber/reservoir as well.
[0073] The feed tank 154, accordingly, comprises a solution 156 of
the various additives fed to it and any desired acid or base for pH
control of the recirculating solution for each scrubber. Depending
upon the additive or combination of additives used, the chemical
effect of the addition of acid or base to the feed tank 154 on any
such additives needs to be considered to ensure that the desired
chemical effect of the additives would not be adversely altered
before its addition to the scrubbers.
[0074] The feed tank 154 is fluidly connected to a distribution
pump 158 that is fluidly connected to each scrubber's recycle line
or sidestream (not shown) via a flow control valve 159 at the
desired location along each recycle line or sidestream. One desired
location for distributing the solution 156 from the feed tank 154
to each recycle line or sidestream may be downstream of each
scrubber's recycle line or sidestream pump, as shown, for example,
by the relative location of the additive addition via the valve 130
to the pump 122 in FIG. 1. It should be appreciated, however, that
the point of addition to each scrubber may vary from scrubber to
scrubber and may include points other than the recycle line or
other or additional points along the recycle line. In other words,
the solution 156 may be added to different locations along each
scrubber's recycle line or at different points for each scrubber,
such as each scrubber's reservoir.
[0075] The flow control valve 159 may be any flow control valve,
including a valve having precise control over the flow rate that
passes through it, such as an analog valve, or, alternatively, an
on/off valve. In either case, the flow control valve 159 may be
controlled based upon a certain solution parameter measured, either
on a continuous, semi-continuous or periodic, or manual basis, in
each scrubber's recycle line or in each scrubber's reservoir. The
solution parameter measured may be the concentration of any
chemical species or solution specific measurement that provides
information that can be used to determine whether to add additional
additive(s). The solution parameter may include such parameters as
pH, oxidation reduction potential, the concentration of the
decomposition additive or a particular chemical species indicative
of the concentration of the additive, the concentration of gaseous
species absorbed by the scrubber, or a combination of these as
further described below. In some embodiments, the measurement of
the solution parameter is done automatically either on a
continuous, semi-continuous or periodic basis, and the results of
such measurement are used to automatically control the flow control
valve 159. Of course, the required feed rate of the solution 156 in
the feed tank 154 to each scrubber will be based upon each
particular application, including, for example, the particular
noxious components to be removed, the amount of gas being treated,
and the operating conditions of each scrubber (e.g., the
recirculation rate of the aqueous hydrogen peroxide composition
through the scrubber) and the concentration of the various
components in the solution 156 in the feed tank 154.
[0076] In operation, the addition rate of the solution 156 from the
feed tank 154 to each recycle line or sidestream of each scrubber
may be controlled in various manners. In some embodiments, the
addition of this solution 156 is controlled by the pH control loop
on each recycle line as described above in connection with FIG. 1.
In this case, a separate pH controller would be used for each
scrubber and would control a respective flow control valve 159 to
determine the flow rate of solution 156 from the feed tank 154 to
that scrubber's recycle line. In other embodiments, different
solution parameters could be monitored and used to control the
addition rate of the solution 156 from the feed tank 154 by the
flow control valve 159. As noted above, oxidation reduction
potential, the concentration of the decomposition additive or a
particular chemical species indicative of the concentration of the
additive, the concentration of gaseous species absorbed by the
scrubber, or a combination of these could be monitored and used to
control the addition rate of the solution 156.
[0077] As described above, depending upon the specific application,
the concentrations of the additive(s) and the acid or base in the
solution 156 can be adjusted so that the appropriate amount of each
is fed to each scrubber. In addition, the relative concentrations
in the solution 154 in the feed tank 156 may need to be adjusted
for each specific application so that the appropriate amount of
each additive and acid or base can be fed to each scrubber. This
can be accomplished by adjusted the concentration of the additives
and the acid or base in their respective source containers 150,
152. Further, these concentrations must be adjusted to be
consistent with each scrubber's and the overall system water
balance.
[0078] It should be appreciated that using a flow control valve 159
allows for more precise control of the flow rate to each scrubber,
as opposed to a simple on/off valve, in combination with monitoring
either pH or another solution parameter provides for better control
of the solution chemistry and removal of the noxious and odorous
components. Particularly by monitoring the pH or another solution
parameter in the recycle stream, as shown in FIGS. 1 and 1A, the
composition of the solution that is contacting the gas stream is
more well known than, for example, monitoring the solution in the
reservoir. Further, by adding the additive and/or acid or base
directly to the recycle stream based upon the results of monitoring
of the solution in the recycle stream allows the recycle stream
chemistry to be properly controlled or adjusted just prior to
entering the scrubber. This allows for more optimal control of the
removal of the noxious and odorous components.
[0079] Optionally, any make-up water required for each reservoir
may also be added to the feed tank 154. In this case, the dilution
effect of any water added to the feed tank 154 must be taken into
account so that the desired amount of each additives and acid or
base are ultimately added to each recycle line. In addition, the
water make-up needs of each reservoir, to the extent that they are
different, must be taken into account. In other words, a water
balance must be achieved for the overall system, which will also
impact the amount of water in the feed tank 154, as discussed
above. Alternatively, make-up water may be added directly to each
scrubber's reservoir.
[0080] In the system as shown in FIG. 1B and as described above,
the hydrogen peroxide can be added from separate source containers
directly to the recycle line or sidestream of each scrubber, or a
single source container can be used with a distribution system to
each recycle line or sidestream of each scrubber. Preferably, the
hydrogen peroxide would be added upstream of each scrubber's
recycle or sidestream pump, such as shown by the relative location
of the additive addition via the valve 126 to the pump 122 in FIG.
1. In all cases, a control valve would be used to monitor and
regulate the flow of hydrogen peroxide for each scrubber. The
control of such a control valve could be based upon the removal
efficiency of each scrubber or it could be based upon the relative
addition rate of the decomposition additive to the recycle line of
each scrubber.
[0081] As an alternative to FIG. 1B, each source container of
additive or acid or base may be separately connected to a separate
corresponding main header line that is fluidly connected to each
recycle line or sidestream of each scrubber at the desired location
along the recycle line or sidestream (not shown). In other words,
the source container for each additive would be separately
connected to each scrubber via its own main header line. As
described above, one desired location for the addition of additives
that catalyze the decomposition of hydrogen peroxide to each
scrubber may be downstream of each scrubber's recycle line or
sidestream pump, as shown, for example, by the relative location of
the additive addition via the valve 130 to the pump 122 in FIG. 1.
It should be appreciated, however, that the desired location for
the addition of other additives may vary according to the
particular additive used. For example, as described above, in using
ozone as the catalyst, an air/ozone mixture may be added directly
to a regenerative turbine pump in the recycle line or sidestream of
each scrubber. Alternatively, a regenerative turbine pump may be
used to pump hydrogen peroxide from its source container to a main
header line that is fluidly connected to each scrubber, wherein an
air/ozone mixture is added to that regenerative turbine pump rather
than to each pump in each recycle line or sidestream.
[0082] Desired locations for the addition of acid or base for pH
control in this alternative embodiment include upstream of each
scrubber's recycle or sidestream pump, such as shown by the
relative location of the additive addition via the valve 126 to the
pump 122 in FIG. 1 and in some embodiments upstream of the addition
point for the hydrogen peroxide also as shown in FIG. 1. In this
alternative, the hydrogen peroxide may be added, for example, in
the same manner as described above in connection with FIG. 1B.
[0083] Generally, it should be appreciated that the addition of the
various components comprising the aqueous hydrogen peroxide
composition may be added at various locations throughout the
scrubber system and are not limited to those described in the above
embodiments. For example, the hydrogen peroxide and other additives
may be added at other locations in the recycle line or sidestream
or directly to the reservoir or tank, although some of these
locations are more desirable than others, as discussed in the
embodiments above.
[0084] FIG. 1C shows a diagram for a system for adding an oxidizer
to one or more gas/liquid contactors or scrubbers. A feed tank 180
is used to hold the oxidizer, which may include hydrogen peroxide
or another oxidizer such as chlorine gas, sodium hypochlorite,
hypobromous acid, chlorine dioxide, hydrogen peroxide, peroxy
acids, ozone, and permanganate. The feed tank 180 may also have a
level controller 182 that functions to provide an alert when the
tank level is low and additional hydrogen peroxide and/or water is
required. It should be appreciated that certain additives may also
be added to the feed tank 180 provided they are chemically
compatible with an oxidizer, such as hydrogen peroxide, so that
their chemical activity is not lost prior to being added to the
scrubber. It should also be appreciated that the system of FIG. 1C
can be used in conjunction with the system of FIG. 1B and further
in conjunction with a pH control loop.
[0085] The feed tank 180 is fluidly connected to a distribution
pump 184 that is fluidly connected to each scrubber's recycle line
or sidestream (not shown) via a flow control valve 186 at the
desired location along each recycle line or sidestream. One desired
location for distributing the oxidizer from the feed tank 180 to
each recycle line or sidestream may be upstream of each scrubber's
recycle line or sidestream pump, as shown, for example, by the
relative location of the additive addition via the valve 126 to the
pump 122 in FIG. 1. It should be appreciated, however, that the
point of addition to each scrubber may vary from scrubber to
scrubber and may include points other than the recycle line or
other or additional points along the recycle line. In other words,
the oxidizer may be added to different locations along each
scrubber's recycle line or at different points for each scrubber,
such as each scrubber's reservoir.
[0086] In operation, the addition rate of the oxidizer from the
feed tank 180 to each recycle line or sidestream of each scrubber
may be controlled in various manners. In some embodiments, the
addition of the oxidizer is simply set a given feed rate for each
scrubber using the flow control valve 186. In other embodiments,
different solution parameters could be monitored and used to
control the addition rate of the oxidizer from the feed tank 180 by
the flow control valve 186. As noted above, oxidation reduction
potential, the concentration of the decomposition additive or a
particular chemical species indicative of the concentration of the
additive, the concentration of gaseous species absorbed by the
scrubber, or a combination of these could be monitored and used to
control the addition rate of the oxidizer from the feed tank 180.
Of course, the concentration of the oxidizer will need to be
accounted for in determining its addition rate to each scrubber or
visa versa.
[0087] It should be appreciated that using a flow control valve 186
allows for more precise control of the flow rate to each scrubber,
as opposed to a simple on/off valve. Particularly, by monitoring a
given solution parameter in the recycle stream, as shown in FIGS. 1
and 1A, the composition of the solution that is contacting the gas
stream is better known than, for example, monitoring the solution
in the reservoir. Further, by adding the oxidizer directly to the
recycle stream based upon the results of monitoring of the solution
in the recycle stream allows the recycle stream chemistry to be
properly controlled or adjusted just prior to entering the
scrubber. This allows for more optimal control of the removal of
the noxious and odorous components. However, it should be
appreciated that in one embodiment it is desirable to simply set
the addition rate of the oxidizer to a given, constant value and to
adjust the addition rate of any additives (e.g., a decomposition
additive in the case of using hydrogen peroxide as the oxidizer)
accordingly.
[0088] Optionally, any make-up water required for each reservoir
may also be added to the feed tank 180 (not shown). In this case,
the dilution effect of any water added to the feed tank 180 must be
taken into account so that the desired amount of each additives and
acid or base are ultimately added to each recycle line. In
addition, the water make-up needs of each reservoir, to the extent
that they are different, must be taken into account. In other
words, a water balance must be achieved for the overall system,
which will also impact the amount of water in the feed tank 180, as
discussed above. Alternatively, make-up water may be added directly
to each scrubber's reservoir.
[0089] As mentioned above, the liquid effluent produced by the
present invention also offers advantages to influent to the
wastewater treatment process. For example, when using ferrous
sulfate as the additive to catalyze the decomposition of the
hydrogen peroxide, the gas/water scrubber water, e.g., the liquid
effluent, can be evacuated to a wastewater treatment facility, for
example, by dumping the entire liquid content of the reservoir or
by continuous overflow of from the reservoir or recycle line or
sidestream, and this stream will have been effectively "pretreated"
by cationic ferric hydroxide complexes that offer effective
colloidal charge neutralization as well as the ability to adsorb
wastewater constituents into its floc matrix. The addition of a
charge neutralizing/adsorption species is always an added cost at
the wastewater treatment plant. By use of the present invention
that cost is eliminated or greatly reduced.
[0090] FIG. 2 shows the system of FIG. 1 within a wastewater
effluent system of a processing plant illustrating the
pre-treatment properties of the present invention on the waste
treatment facility according to one embodiment of the present
invention. In FIG. 2, liquid effluent is discharged from the system
100 earlier described with reference to FIG. 1, for example,
through a wastewater pathway 202. As earlier described, the liquid
effluent may be discharged by dumping the reservoir or by continual
overflow of the liquid effluent from the reservoir. The wastewater
pathway 202 may merge with other wastewater pathways 204 exiting
from other process areas 206 in the processing plant, for example,
wash and rinse waters, chicken feather processing waters, rendering
cooker waters, etc. These wastewater pathways 202, 204 eventually
converge into one or more wastewater pathways 208 that discharge
into one or more large reservoirs in a wastewater treatment
facility 210.
[0091] When the liquid effluent enters the reservoir at the
wastewater treatment facility 210, the liquid effluent is
effectively "pre-treated". The liquid effluent contains metal
hydroxide complexes, for example, cationic ferric hydroxide
complexes, that offer effective colloidal charge neutralization, as
well as provide for adsorption of wastewater constituents into its
floc matrix. While some of the complexes are utilized by the
components of the liquid effluent, a residual amount of these
complexes are also available to the other wastewater effluent in
the reservoir of the wastewater treatment facility. As wastewater
treatment facilities typically purchase additives to accomplish
these results, the addition of these charge neutralizing and
adsorption species eliminates or greatly reduces any costs incurred
by the waste treatment facility.
[0092] The present invention has been described above with
reference to removal of odor and/or noxious components from an
atmospheric effluent in which the oxidized odor and/or noxious
components are oxidized during contact with an aqueous hydrogen
peroxide composition to produce a substantially non-odor offensive,
environmentally acceptable by-product that is solubilized in or
adsorbed onto the aqueous hydrogen peroxide composition to form a
liquid effluent, and the advantages of such a system provided to
wastewater treatment processes. The present invention also has
application in other areas of processing plants as an effective
biocide, especially in areas related to aqueous food transport
flumes.
[0093] Food primary and secondary processing involves the handling
of large amounts of organic materials. As a result of the amount of
organics being processed, biological activity is inevitable. In
fruit and vegetable processing, large amounts of water are used to
wash and transport food through the various processing steps.
Because of the buildup of organic matter, the transport and wash
waters are very prone to biological growth, as well as accumulation
of toxic organic materials such as herbicides and pesticides. A
need exists to provide microbial control of these waters without
imparting further toxic products to the aqueous food contact
streams. Also needed is an economical method for eliminating or
reducing the buildup of toxic herbicides and pesticides in the food
transport system.
[0094] Attempts in the art have been made utilizing oxidizing
compounds such as chlorine gas, sodium hypochlorite, hypobromous
acid, chlorine dioxide, hydrogen peroxide, peroxy acids, ozone, and
permanganate. While some are effective in limiting microbial
growth, either toxic by-products, cost, or inefficiencies are
limiting factors.
[0095] Particularly, the use of chlorine and chlorine dioxide,
while effective antimicrobial agents, has come under environmental
scrutiny due to the toxic by-products it produces. When contacted
with amines, toxic chloramines are formed, as well as
trihalomethane compounds, which are now prevalent in most ground
waters in the United States. Chlorine-based technologies also use
large quantities of these materials, as they are rapidly consumed
by the high organic loading of the aqueous media before they can
impart antimicrobial properties. Hypobromous acid produced by the
decomposition of sodium bromide by chlorine has been used with some
success, but it too is affected by high organic loading and the
chlorine substrates, which, while reduced, still impart the same
toxicities as hypochlorous acid.
[0096] Hydrogen peroxide has been used with limited success.
Hydrogen peroxide is a slow reacting compound with known
antimicrobial properties. The reaction rates are too slow for
effective, cost advantageous microbial control. Peroxy acids such
as peracetic acid have proven to be effective antimicrobial
compounds in aqueous systems. Peracids are usually manufactured by
the combination of hydrogen peroxide, acetic acid, and inorganic
acid catalyst, and various wetting and sequestering agents.
Peracetic acid is normally provided in 5 to 15% peracetic acid
concentrations. These peracid compounds contain large amounts of
the manufacturing precursors, such as hydrogen peroxide, and acetic
acid. These peroxy acid materials have a strong pungent odor and
residual acetic acids are toxic by ingestion or exposure at 10 ppm
in misted form. Peroxy acids are also limited in use by the high
costs that are associated with it. Ozone has found limited use in
aqueous food transport and processing streams. Ozone is an
effective biocide and its high electronegativity is capable of
breaking down selected organic compounds. Ozone is associated with
extremely high capital investments cost, and the efficiency is
limited by poor transfer coefficients from the generated ozone gas
phase to the liquid media being treated.
[0097] Use of the present invention, however, in which an aqueous
hydrogen peroxide composition of hydrogen peroxide decomposed by
ozone is contacted with the transport waters, results in an
effective biocide. This allows sterilization of food transport
waters with no toxic by-products. Further, in food transport
flumes, regulation of the ozone can also break down accumulated
pesticide and herbicide compounds from fruit and vegetable washing
into simple non-toxic carboxylic acids. Accordingly, this
technology offers significant cost and efficiency advantages over
current technologies.
EXAMPLES
[0098] The following examples describe specific aspects of the
present invention to illustrate the invention and aid those of
skill in the art in understanding and practicing the invention. The
examples should not be construed as limiting the present invention
in any manner.
Example #1
[0099] A 1000 ml sample of chicken feather processing scrubber
water having a pH of 5.5 due to sulfuric acid addition in the
scrubber reservoir was evaluated. The sample had an intense odor
after treatment with chlorine dioxide. The sample was treated
concurrently with 300 ppm of hydrogen peroxide (50% solution) and
100 ppm ferrous sulfate (38% solution). The reaction was
instantaneous, and there was no detectable odor, other than a
slight chlorine smell.
Example #2
[0100] A 1000 ml sample from a rendering cooker was adjusted to pH
5.5 with sulfuric acid. The sample had a very intense odor. The
sample was treated concurrently with 300 ppm of hydrogen peroxide
(50% solution) and 100 ppm ferrous sulfate (38% solution). The
reaction was instantaneous, and the odor was eliminated within 15
seconds. The sample was then undisturbed for 48 hours, and there
was no re-occurrence of any odor.
Example #3
[0101] A five gallon sample from a rendering cooker was adjusted to
pH 5.5. The sample was recirculated at 10 gpm through a Burks
regenerative turbine pump throttled by pinch valve assembly to 100
psi. Hydrogen peroxide was introduced into the suction line at 300
ppm. Ozone as a 6% gas stream generated by a corona discharge type
ozonater on dried air was added into the air inlet for the Burks
pump (suction side). The ozone dose was 10 ppm as ozone. The sample
was recirculated for 2 minutes, and odors were completely
neutralized. The sample was then un-aearated and undisturbed for 48
hours, and there was no re-occurrence of any odor.
Example #4
[0102] A trial was performed at a mixed proteins rendering plant
that used chlorine dioxide in a scrubber to reduce VOC emissions by
88%. In this system, the pH was reduced to pH 5.5 with sulfuric
acid. 300 ppm of hydrogen peroxide (50% solution) and 100 ppm
ferrous sulfate (38% solution) were added concurrently. As a
result, VOC emissions were reduced by 96%.
[0103] In the above examples, odor reduction was measured using the
sense of smell and VOC emission measurements using standard
emission detectors. It will be appreciated that various other
devices and measurement techniques may also be used that conform to
standard practices as may be required for a particular processing
industry.
Example #5
[0104] A pilot plant test using hydrogen peroxide decomposed by
ozone was conducted to evaluate microbiological control. The test
or run was performed using 100 gallons and a Pennsylvania apple
wash/transport flume with the following characteristics: BOD=900
ppm, COD=2100 ppm, and a significant amount of large organic
matter. The material was recirculated for 36 hours and the
following data was collected: bio count via dip slide=109, filtered
BOD (0.45 micron)=685 ppm, filtered COD (0.45 micron)=1725 ppm.
[0105] 300 ppm hydrogen peroxide (50% solution) was added, and
ozone was added at 10 ppm into a regenerative turbine pump used to
recirculate solution. When the addition of hydrogen peroxide and
ozone was completed the addition was stopped. The following bio
count in colonies was observed: @ t=4 min bio count=102, @ t=10 min
bio count=none detected, @ t=8 hours bio count=none detected, @
t=12 hours bio count=10, and @ t=18 hours bio count=102. Additional
data included: filtered BOD=210 ppm and filtered COD=720 ppm.
[0106] As can be seen by this test, microbial control was excellent
with good sustained kill of biopopulation. The lowering of the COD
showed decomposition of organic material in the sample water.
Analysis for toxicity indicated a sharp drop.
[0107] Although the foregoing invention has been described in some
detail to facilitate understanding, it will be apparent that
certain changes and modifications may be practiced within the scope
of the appended claims. Accordingly, the described embodiment is to
be considered as illustrative and not restrictive, and the
invention is not to be limited to the details given herein, but may
be modified within the scope and equivalents of the appended
claims.
* * * * *