U.S. patent application number 12/895197 was filed with the patent office on 2011-04-07 for method and apparatus for the electrochemical treatment of liquids using frequent polarity reversal.
Invention is credited to Dennis E. Bahr, Ajit K. Chowdhury, Brian R. Hale, Karl W. Marschke, Myron F. Miller, James A. Tretheway, Jeremy J. Vogel.
Application Number | 20110079520 12/895197 |
Document ID | / |
Family ID | 43416654 |
Filed Date | 2011-04-07 |
United States Patent
Application |
20110079520 |
Kind Code |
A1 |
Tretheway; James A. ; et
al. |
April 7, 2011 |
Method and Apparatus for the Electrochemical Treatment of Liquids
Using Frequent Polarity Reversal
Abstract
An electrolytic method and apparatus for treating liquids using
a flow cell with widely spaced electrodes and polarity reversing
power designed to prevent electrode fouling and provide for long
continuous liquid treatment running times.
Inventors: |
Tretheway; James A.;
(Madison, WI) ; Hale; Brian R.; (Lake Mills,
WI) ; Chowdhury; Ajit K.; (Madison, WI) ;
Vogel; Jeremy J.; (Fort Atkinson, WI) ; Bahr; Dennis
E.; (Madison, WI) ; Miller; Myron F.;
(Sacramento, CA) ; Marschke; Karl W.; (Madison,
WI) |
Family ID: |
43416654 |
Appl. No.: |
12/895197 |
Filed: |
September 30, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61248077 |
Oct 2, 2009 |
|
|
|
Current U.S.
Class: |
205/744 ;
204/229.6 |
Current CPC
Class: |
C02F 2301/043 20130101;
C02F 2209/04 20130101; C02F 2103/32 20130101; Y02E 60/366 20130101;
C02F 1/46104 20130101; A61L 2/035 20130101; C02F 2103/42 20130101;
C02F 2001/46142 20130101; C02F 1/4674 20130101; C02F 2209/29
20130101; A23L 3/325 20130101; C02F 2103/343 20130101; C02F 2103/22
20130101; C02F 2201/4611 20130101; C02F 2201/4613 20130101; C02F
2209/06 20130101; C02F 2101/305 20130101; Y02E 60/36 20130101; C02F
2201/003 20130101; C02F 1/4672 20130101; C02F 2201/46115 20130101;
C02F 2301/046 20130101; C02F 2303/04 20130101 |
Class at
Publication: |
205/744 ;
204/229.6 |
International
Class: |
C02F 1/461 20060101
C02F001/461; C25B 15/00 20060101 C25B015/00 |
Claims
1. A liquid treatment system comprising: a treatment cell receiving
a liquid to be treated at a rate of at least 5 gallons per minute;
at least a first and a second electrode positioned within the
treatment cell and having a separation of no less than 5 mm
permitting the liquid with suspended solids or an organic load to
pass therebetween wherein at least one of the electrodes has a
surface selected from the group consisting of metals, metal oxides
and doped diamond; a polarity reversing power supply connected
across the at least two electrodes, the power supply providing an
alternating positive and negative electrical power; and a power
supply controller communicating with the polarity reversing power
supply to provide a polarity reversal of the electrical power to
the at least two electrodes during a cycle period having a length
of at least 10 seconds and no more than 60 minutes.
2. The liquid treatment system of claim 1 wherein the electrodes
are opposed substantially planar conductive plates.
3. The liquid treatment system of claim 1 wherein the at least two
electrodes are a substantially concentric tube and center
electrode.
4. The liquid treatment system of claim 1 wherein the at least two
electrodes have a surface containing at least one platinum group
metal consisting of platinum, palladium, rhodium, iridium, osmium,
and ruthenium.
5. The liquid treatment system of claim 1 wherein one of the at
least two electrodes has a different surface material composition
than the other of the at least two electrodes.
6. The liquid treatment system of claim 1 wherein the cycle period
provides different durations of negative and positive electrical
power.
7. The liquid treatment system of claim 1 wherein the cycle period
provides substantially equal durations of negative and positive
power.
8. The liquid treatment system of claim 1 wherein the liquid being
treated has a chemical oxygen demand of at least 200 mg/l.
9. The liquid treatment system of claim 1 wherein a flow splitting
means delivers a side stream of a circulating liquid to the
treatment cell, which side stream after treatment is then blended
back into the circulating liquid after treatment.
10. A method of treating a liquid with suspended solids or organic
load comprising the steps of: passing the liquid through a
treatment cell containing at least a first and second electrode
positioned within the treatment cell and having a separation of no
less than 5 mm, wherein one or more of the electrodes has surfaces
selected from the group consisting of metals, metal oxides and
doped diamond; wherein said liquid flows through the treatment cell
at a rate of at least 5 gallons per minute; applying power to the
electrodes the power having an alternating negative and positive
polarity during a cycle period having a length of at least 10
seconds and no more than 60 minutes.
11. The liquid treatment method of claim 10 wherein the at least
first and second electrode have surfaces containing at least one
platinum group metal consisting of platinum, palladium, rhodium,
iridium, osmium, and ruthenium.
12. The liquid treatment method of claim 10 wherein at least one
electrode has a different surface material composition than at
least one other electrode.
13. The liquid treatment method of claim 10 wherein the cycle
period provides different durations of negative and positive
electrical power.
14. The liquid treatment method of claim 10 wherein the cycle
period provides substantially equal durations of negative and
positive power.
15. The liquid treatment method of claim 10 wherein the liquid
being treated has a chemical oxygen demand of at least 200
mg/l.
16. The liquid treatment method of claim 10 wherein a side stream
of a circulating liquid is treated and blended back into the
circulating liquid.
17. The liquid treatment method of claim 10 wherein a portion of
the treated liquid is circulated back into the liquid treatment
system inlet.
18. The liquid treatment method of claim 10 wherein the treatment
is disinfection of the liquid stream.
19. The liquid treatment method of claim 10 wherein the treatment
is disinfection of materials selected from the group consisting of:
food processing liquids, processed meat and poultry chiller brine
or water, raw poultry processing chiller water, and fruit and
vegetable processing flume water.
20. The liquid treatment method of claim 10 wherein the treatment
oxidizes organic and inorganic contaminants of the liquid stream
being treated.
21. The liquid treatment method of claim 20 wherein the treatment
is a destruction of pharmaceutical and personal care product
residuals.
22. The liquid treatment method of claim 10 including the step of
monitoring a bacteria in the liquid and wherein a disinfection
efficacy of bacteria in the liquid is used as a proxy for the
efficacy of oxidation of trace residual chemicals.
23. The liquid treatment method of claim 22 including the steps of
dosing the liquid with a known concentration of bacteria and
testing results of killing of the bacteria to estimate the efficacy
of oxidation of trace residual chemicals.
24. The liquid treatment method of claim 10 wherein the treatment
is a generation of hydrogen and oxygen and separated by an external
means.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application 61/248,077 filed Oct. 2, 2009 hereby incorporated by
reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to an apparatus for treating
liquids to disinfect and oxidize contaminants and in particular to
a method and apparatus of this type using frequent polarity
reversal of the power applied to the electrodes.
[0003] Liquids, including water and solvent based ones, are capable
of being treated by many different methods known the in art.
Biological methods can disinfect and oxidize, but require long
treatment times, a large equipment footprint and other
complications. Such methods are commonly used to treat municipal
wastewater but have had limited application in liquid treatment at
the industrial scale.
[0004] The treatment of liquid streams through the addition of
disinfecting chemicals such as chlorine or bromine is also
well-known. The class of chlorine disinfectants includes chlorine
gas, hypochlorous acid, sodium hypochlorite, and chlorine dioxide.
These chemicals typically are purchased in bulk, with attendant
cost, storage and dosing issues. Chlorine gas has significant
safety and security issues associated with it.
[0005] Chlorine is often used because of its low cost. But in some
applications, for example in chiller water, cold brine and flume
water used in poultry, meat and vegetable processing, the addition
of these chemicals may be disfavored because of concerns about the
generation of off-taste in the product and chemical byproducts that
may adversely affect product quality, plant personnel or the
environment. Chlorine's efficacy is also dramatically affected by
pH levels, oftentimes requiring additional pH adjustment that adds
to cost and operating complications. As another disadvantage,
chlorine dosage requirements in some applications can be very high
due to high organic loads and pathogen levels. High dosages of
these chemicals make the process difficult to control to maintain
reliable disinfection without generating excessive unwanted
chlorinated byproducts, such as trichloramines. They also make it
difficult to maintain residual chlorine levels within the levels
that may be permitted by the United States Department of
Agriculture (USDA) or other application-specific regulations.
[0006] Other chemicals such as hydrogen peroxide and peracetic acid
are used as disinfectants but typically have high cost and other
issues associated with them.
[0007] High temperature pasteurization can be used for disinfection
but requires high energy use and post-treatment cooling.
Ultraviolet light is sometimes used for water and wastewater final
effluent disinfection. A significant drawback to ultraviolet
systems is their inability to work in turbid liquids with suspended
solids or color.
[0008] It also is known that electrical methods can be used to
disinfect liquids. Electroporation is a high voltage, low current
process that disinfects by penetrating the cell walls of pathogens
and either destroying or inactivating them. Electroporation has
many laboratory scale uses, including for the insertion of genes in
cells, but has not scaled up well to industrial use due to the high
voltages used and other reasons.
[0009] Research has also been done on disinfection at various
alternating current frequencies, including those in the low
kilohertz to microwave range. However, it has been shown that the
primary method of disinfection at these frequencies comes through
the heating of liquid to low pasteurization temperatures, an energy
inefficient process.
[0010] Direct current electrolytic processes have also been
demonstrated to disinfect contaminants in liquids. In electrolysis,
comparatively low voltage, high current electrical power is passed
through the liquid, breaking bonds in chemical compounds and
causing destructive changes to biological cells. Depending on the
application, this can be a more energy efficient method.
[0011] Electrolytic systems called hypochlorite generators have
been used commercially for indirect disinfection of liquids.
Electrodes are immersed in a relatively pure salt water solution
and direct current is applied to generate hypochlorite. The
hypochlorite-enhanced solution is then injected into the liquid
stream to be treated. Such systems typically use different anode
and cathode materials. They have the same issues with pH control as
with the direct addition of hypochlorite.
[0012] Another electrolytic method uses an ion exchange membrane in
a salt solution between direct current electrodes to create
separate acidic anolyte and alkaline catholyte solutions with
purported electrochemically activated properties. Sometimes these
two liquids are used separately for cleaning, or sometimes may be
combined and marketed under rather fanciful names implying health
and longevity effects.
[0013] Another electrolytic process is used to directly treat
swimming pool water to which salt is added. Since swimming pool
liquid is less controlled regarding contaminants, the polarity is
reversed on the electrodes, typically every few hours, to reduce
electrode fouling caused by the electrochemical deposition of
materials onto the electrodes.
[0014] These electrolytic systems use plate or expanded metal
electrodes that typically are spaced 0.5-2 mm apart. Any polarity
reversal is done only very infrequently, typically 2-6 hours
between reversals. The anodes typically use one or more metal
oxides from the platinum group metals as a coating over a valve
metal such as titanium. It has generally been observed that
polarity reversing power is highly destructive to these coatings
with various mechanisms of failure being described including
hydrogen embrittlement when the electrode is operated as a
cathode.
[0015] Lab scale research has been done with electrolytic systems,
typically with static treatment cells or very low volume flow
cells, to demonstrate disinfection and also the oxidation of trace
levels of contaminants such as endocrine disruptors in water and
wastewater. This research generally has been done with liquids
containing low chemical oxygen demand (COD) and biological oxygen
demand (BOD) loads, an unrealistic situation for many industrial
liquid treatment applications. Some of this research has used
conventional metals like 300 series stainless steel for their
electrodes. These test results are not relevant to industrial
applications where the liquid flowing through a treatment cell may
have significant COD and BOD loads, with these loads being
continuously replaced by a new influx of organic and inorganic
contaminants. In addition, these tests typically have not analyzed
the treated solution for an increase in dissolved heavy metal ions.
Under such electrolytic treatment, these heavy metal concentrations
can quickly rise to levels above those permitted by the EPA, USDA,
FDA or other relevant regulatory agency.
SUMMARY OF THE INVENTION
[0016] The present invention provides direct, high flow rate,
electrical treatment of liquids with significant organic loads and
suspended solids, including but not limited to poultry chiller
water and processed meats chiller brine. While the inventors do not
wish to be bound by a particular theory, it is believed that such
direct treatment may provide significant advantages in exposing the
water to short-lived chemical species. The possibility of such
direct treatment required a determination that treatment
effectivity could be maintained for relatively large electrode gaps
(5 mm or larger) and without debilitating electrodes fouling, both
empirically confirmed by the present inventors.
[0017] Specifically then, the present invention provides a liquid
treatment system with a first and second electrode having a
comparatively large separation between them that permits the
passage of a significantly large volume of liquid that may contain
small solids. A polarity reversing power supply is connected across
the first and second electrodes, the power supply switching the
polarity of the voltage at a period determined empirically for each
liquid being treated within a specified range.
[0018] The inventors have determined that there is an optimum
narrow frequency range around 0.03 Hz for high performance duplex
stainless steel electrodes above or below which a substantial
reduction of treatment performance occurs for a particular liquid
stream. This equates to a polarity reversal approximately every 17
seconds. In addition, the disinfection falls off rapidly when the
period between polarity reversals is less than 5 seconds (0.1 Hz)
or greater than 50 seconds (0.01 Hz).
[0019] In addition, the inventors have determined that for
catalytic platinum group metal electrodes, the detrimental effects
of frequent polarity reversal on electrode life can be balanced
against the need to change polarities to prevent electrode fouling
and that the optimal time between polarity reversals is
approximately between 10 seconds and 60 minutes, depending on the
composition of the liquid stream.
[0020] It is thus a feature of at least one embodiment of the
invention to maximize treatment efficacy while balancing electrode
lifetimes by performing a polarity reversal in the range of
approximately 10 seconds to 60 minutes.
[0021] Laboratory research results with electrochemical treatment
of liquids has heretofor been difficult or impossible to scale up
to commercially useful liquid treatment due to the need to separate
out any solids plus organic or inorganic load that could physically
plug the electrodes with their narrow spacing or otherwise cause
fouling. Separation processes are capital intensive, require
regular cleaning and maintenance, and are not warranted or
desirable in many applications.
[0022] It is thus a feature of at least one embodiment of the
invention to space the electrodes greater than 5 mm apart.
[0023] In electrochemistry things that work at the lab scale with
closely spaced electrodes, low flow rates, and very short running
times typically cannot be duplicated even at low commercial flow
rates treating liquids with varying composition and with a
necessarily wider gap between the electrodes to provide the
required higher flow rates, acceptable pressure drops and to permit
passage of small solids. The inventors have successfully treated
very challenging liquid streams at flow rates up to 650 gallons per
minute.
[0024] It is thus a feature of at least one embodiment of this
invention to treat flow rates of five gallons per minute and
higher.
[0025] The inventors have also found that electrolysis degrades
many metals and their oxides when used for electrolysis. Very high
levels of metal ions, such as chromium, nickel, iron, and tin are
found in liquids that have been treated with electrode materials
containing them. This prevents conventional electrolysis with such
electrodes from being used in applications where metal toxicity is
a concern. They remain quite appropriate for various other
treatment applications, such as electrowinning and
electro-flocculation. The inventors have also found that catalytic
electrodes, for example those from the platinum group metals and
metal oxides, do not dissolve into the liquid under polarity
reversing electrolysis to any measurable extent.
[0026] It is thus a feature of at least one embodiment of the
invention to use catalytic electrode surfaces including those from
the platinum group metals and metal oxides, and from the doped
diamond category.
[0027] It is known in the art that various catalytic metals and
metal oxides in liquids containing water and salt generate
differing proportions of reactive oxygen species and/or chlorine
species that may be useful for liquid treatment, such as
disinfection and oxidation. For example, under electrolysis,
ruthenium oxide is known to generate a high proportion of chlorine
species and fewer reactive oxygen species when used as an anode.
Boron doped diamond is known to produce a much higher ratio of
reactive oxygen species when used as an anode.
[0028] It is thus a feature of at least one embodiment of the
invention to provide electrode pairs of opposite polarity with
surfaces of different metals or metal oxides. Polarity reversal can
be controlled to provide different times between polarity reversal
for each specific electrode surface, enabling the control system to
tailor the reactive species being generated to meet the needs of a
particular liquid stream being treated.
[0029] Lab scale testing has typically been done on liquids where
such contaminants that affect process performance, like organic
loads and bacteria levels are not replaced during the test cycle,
further contributing to the inability to extrapolate test results
to commercial reality.
[0030] It is thus a feature of at least one embodiment of this
invention to treat liquids that have a chemical oxygen demand of
200 mg/l or higher with a continuing influx of organic and
inorganic loads.
[0031] In many commercial applications, for example the
disinfection of processed meats chilling brine, a fluid is
continuously recirculated at high flow rates for another purpose,
such as cooling a product and rechilling the liquid to maintain its
desired temperature. The inventors have shown that in many cases a
proportionally smaller liquid flow is all that is required to
maintain the desired level of treatment in the liquid, reducing the
size of the electrolytic treatment cell, associated piping and
other components.
[0032] It is thus a feature of at least one embodiment of this
invention to treat a side stream or smaller volume of a main
flow.
[0033] In certain commercial applications the liquid stream is
directly discharged and is not recycled for another reason. In such
situations the desired treatment level may be difficult to achieve
at reasonable equipment cost in a single pass. The inventors have
determined that recycling a portion of the treated liquid back to
the treatment cell can have a synergistic effect on process
efficacy.
[0034] It is thus a feature of at least one embodiment of this
invention to directly treat a liquid stream on a one-pass basis,
but to recycle a portion of this liquid back through the treatment
cell to obtain the overall treatment efficacy desired.
[0035] Methods for disinfecting example food processing liquid
streams are disclosed.
[0036] It is thus a feature of at least one embodiment of this
invention to disinfect food processing liquids.
[0037] A method for oxidizing and destroying trace pharmaceuticals
and personal care products is disclosed.
[0038] It is thus a feature of at least one embodiment of this
invention to provide a method to remove pharmaceutical and personal
care product (PPCP) residuals from a liquid stream.
[0039] In addition, the inventors have found that disinfection
efficacy, a low cost, easily measured value, serves as a robust
surrogate for the efficacy of removal of trace pharmaceuticals and
personal care product residuals.
[0040] It is thus a feature of at least one embodiment of this
invention to use the results from tests for disinfection efficacy
as a practical means to estimate the efficacy of PPCP residual
oxidation.
[0041] In addition, the inventors have determined that for liquid
streams without significant bacterial load, a safe, food grade
bacteria like Lactobacillus Acidophilus, used to make yogurt, can
be added to the liquid to provide this surrogate disinfection
measure.
[0042] It is thus a feature of at least one embodiment of this
invention to add bacteria to a liquid stream and use the results of
tests for disinfection efficacy of this bacteria as a practical
means to estimate the efficacy of PPCP residual oxidation.
[0043] This electrochemical process produces oxygen at the anode
and hydrogen at the cathode. With the polarity reversal of this
process, each electrode in a pair alternates between generating
hydrogen and oxygen.
[0044] It is thus a feature of at least one embodiment of this
invention to generate hydrogen and oxygen both as a mixed species
and as separate elements, the latter achieved by an external
separation means such as a selective membrane.
[0045] These particular objects and advantages may apply to only
some embodiments falling within the claims and thus do not define
the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0046] FIG. 1 is a perspective view of a liquid treatment system in
one embodiment of the present invention showing a main housing
holding opposed planar electrodes between liquid inlets and
outlets, a power distribution module, and a control unit;
[0047] FIG. 2 is a detailed block diagram of the components of FIG.
1 showing the electrodes as flat plates;
[0048] FIGS. 3a and 3b are graphs of disinfection versus frequency
showing a preferred range of operation of the present invention for
stainless steel and catalytic electrodes;
[0049] FIG. 4 is a simplified representation of a method to
disinfect processed meat and processed poultry products immediately
after a cooking cycle to rapidly cool them for further processing,
packaging or storage;
[0050] FIG. 5 is a simplified representation of a method to
disinfect raw poultry chiller water to rapidly cool the birds for
further processing, packaging or storage;
[0051] FIG. 6 is a simplified representation of a method to
disinfect water used to wash and chill vegetables and fruits, such
as cut leafy greens, to help ensure the safety of the product and
permit extended reuse of the water;
[0052] FIG. 7 is a graph of performance achieved with the method of
the patent for removing trace pharmaceuticals from wastewater
showing the strong correlation of trace pharmaceutical destruction
with bacterial disinfection performance on this same liquid;
[0053] FIG. 8 is a graph of performance achieved with the method of
the patent for removing trace personal care product residuals from
wastewater showing the strong correlation of trace personal care
product destruction with bacterial disinfection performance on this
same liquid; and
[0054] FIG. 9 is a simplified representation of an alternate
electrode arrangement using a rod and cylinder configuration;
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0055] Referring now to FIGS. 1 and 2, a liquid treatment system 10
per the present invention may include a treatment unit 12 providing
a liquid inlet 14 and outlet 16 to conduct liquid across internal
electrodes 28. The electrodes 28 are contained in an insulating
housing 18 supported on frame 20. A power distribution module 22
provides electrical connections 24 to the internally contained
electrodes 28 for power received from a control unit 26. The
control unit 26 has a touchscreen user interface 27 for the display
and entry of data including critical operation parameters.
[0056] Referring now to FIG. 2, the treatment unit 12 includes two
or more generally planar and parallel electrodes 28 held in a
channel 36 between the inlet 14 and the outlet 16. The electrodes
28 are separated along an axis 30 generally perpendicular to the
flow of liquid by gaps 32 to receive the influent liquid 34
therethrough. The separation of the electrodes 28 will be greater
than 5 mm to permit the passage of influent liquid 34 without undue
risk of clogging.
[0057] One or more chemical sensors 40 may be positioned in sensor
fitting 38 downstream from the electrodes 28 and channel 36 to
measure chemical properties of the liquid and/or a flow sensor 42
may be positioned in the influent liquid 34 or effluent liquid 35
to measure the flow across the electrodes 28. The chemical sensors
40 may include those measuring pH, oxidation-reduction potential,
chlorine level, free chlorine level, or total chlorine level.
[0058] The amount of flow through the channel 36 may be controlled
by an electrically driven pump 44 and/or valve 46 alone or in
combination.
[0059] The electrodes 28 are electrically isolated from each other
as held by the housing 18 but may be joined by the connections 24
from power distribution module 22 so that some or all of the
electrodes 28 are electrically connected to electrical conductors
48a and 48b. In some configurations alternating electrodes may be
connected to opposite power polarities, in others some electrodes
may not be directly connected to the power supply but instead
become electrically activated by the ionic currents in the liquids
being treated, resulting in each side of such intermediate
electrodes having opposite polarities.
[0060] Conductors 48a and 48b are connected to a switching unit 50
contained in the control unit 26 that may alternate the electrical
polarity of alternate electrodes 28. The switch is depicted
logically as a double pole, triple throw electrical switch and will
be typically implemented by solid-state electronics controllable by
control line 51. One pole connects to a positive voltage line 52
from a voltage controllable DC power supply 58 and the other pole
connects to a negative voltage line 53 from the voltage
controllable DC power supply 58. The voltage controllable DC power
supply 58 receives power from electrical mains 62.
[0061] The throws of the switching unit 50 are controllable so that
one conductor 48a or 48b may be connected to a given voltage
(positive or negative) while the other conductor 48a or 48b is
connected to the opposite voltage.
[0062] The positive voltage line 52 may connect to a current sensor
54 and voltage sensing point 56, both of which are connected to
inputs of a controller 60, the latter being a special-purpose
computer, for example, a programmable logic controller executing a
stored program to control of the process as will be described. A
similar current sensor 54 and voltage sensing point 56 (not shown)
may be provided on negative voltage line 53. Sensors 54 and 56 may
also be built into the power supply 58. The programmable controller
60 also receives signals from the chemical sensors 40 and flow
sensor 42 and may provide control signals to the pump 44 and valve
46. In addition, the controller 60 communicates with the
touchscreen 27 or alternative user input device which may be a
keyboard or other means known in the art.
[0063] The controller 60 includes a processor 70 and a control
program 72, the latter contained in the memory 81 communicating
with the processor 70 as is generally understood in the art. In
operation, the program 72 will read various parameters of the
process including the electrode current from current sensors 54,
the electrode voltage from voltage sensing points 56, user entered
parameters through touchscreen 27, chemical environment sensing
from the chemical sensors 40, and/or the flow rate from the flow
sensor 42, and will provide output signals on control line 51
controlling the switching unit 50 and the power supply 58. In
addition, output signals controlling the pump 44 and valve 46 and
providing information on the touchscreen 27 may be provided.
[0064] Pump 44 or the valve 46 may be used as the flow controller,
Pump 44 may be a variable speed pump and valve 46 may be a
continuously adjustable valve.
[0065] Referring now to FIG. 3a, the present inventors have
determined that the quality of disinfection 82 of the liquid (for
example, measured by log kills of test bacteria) peaks when the
period between polarity reversals is approximately 17 seconds (0.03
Hz) in duration for high performance duplex stainless steel
electrodes 28. In addition, the disinfection falls off rapidly when
the period between polarity reversals is less than 5 seconds (0.01
Hz) or greater than 50 seconds (0.1 Hz). This measurement was
produced on a laboratory scale in a 12 mL cell volume with
electrodes spaced 1 cm apart, and a flow rate of 750 mL/min in
replicated experiments.
[0066] Referring now to FIG. 3b, for platinum-group catalytic
electrodes 28 the performance peak appears to be occur the closer
the electrodes approach direct current. This measurement does not
consider the counteracting issues of electrode fouling due to
organic and inorganic loads, which occur the closer the electrodes
are run to pure unswitched direct current. In commercial scale
operations with organic and inorganic loads of 200 mg/l and more of
measured chemical oxygen demand, the inventors have shown that
disinfection performance degrades and electrode fouling occurs when
the time between current reversals exceeds 60 minutes and at even
shorter current reversal periods for very high organic and
inorganic loads.
[0067] Referring now to FIG. 4, the diagram illustrates one
configuration of a system to disinfect cold food processing
liquids. Housing 400 contains liquid outlets or spray nozzles 414
through which a cooling liquid 404, normally salt brine or water,
flows to impinge on food products (not shown) to cool them down
from a higher temperature to a lower one for further processing or
storage. A main flow stream 406 is drawn from the sump 402 at the
bottom of this chamber and provides a source of cooling liquid 404
which may flow through a pump 408 and a strainer 410 to filter out
larger particles and a heat exchanger 412 which chills the liquid
prior to discharge through the liquid outlets 414.
[0068] A side stream 416 is taken from the sump 402 through a pump
418 and strainer 420 to the electrolytic cell 422 where treatment
occurs and is then discharged back to the sump 402. Alternatively,
this flow may be a side stream of the main flow stream 406 taken
after strainer 410 eliminating the need for a second pump 418 and
strainer 420 but removing the capability of operating these two
liquid circuits independently. Makeup liquid 424 is added as
required to keep the sump full.
[0069] Referring now to FIG. 5, the diagram illustrates one
configuration of a system to chill solid food products with a
liquid, normally water, that is disinfected by the invention
disclosed herein. A water tank 500 containing water 502 a conveying
means 504 for moving products from one end to the other receives
food products 506, such as recently slaughtered and eviscerated
poultry which are then conveyed through the water 502. Chilled
product is removed by unloading means 508. Makeup water 510
replaces water lost due to carry-off on the product and additional
flow may be provided to freshen the water, which then overflows to
drain 512.
[0070] Temperature rises in the water 502 due to the heat removed
from the food product. A pump 514 connected with the water tank 500
propels a stream of water 516 into a rechiller 518 which removes
heat from the water stream exits back into the chiller tank 500.
Flow control valve 520 redirects some or all of the water stream
522 through the electrode cell 524 where electrolytic disinfection
takes place. The side stream 526 exits the electrode cell 524 and
is recombined with the main rechiller water stream 516 to go
through the rechiller 518 and back to the water tank 500.
[0071] Referring now to FIG. 6, this block diagram represents a
flume water system designed to wash food products such as
vegetables and fruits. Product to be treated 600 enters the flume
602 where washing and conveying water 604 moves the product under
the shower header 608 where shower water 606 is distributed. Washed
product exits the flume 610 and enters a strainer 612, oftentimes a
shaking one, and the drained product 614 is transported for further
processing or packaging.
[0072] The drain water enters a fine strainer 616 where smaller
solids and impurities are removed via outlet 618. A pump 620
propels the drained water through a flow control valve 622 a
rechiller 624 and then back into the flume 602 or shower header
608.
[0073] Flow control valve 622 redirects some or all of the strainer
water 626 through the electrode cell 628 for disinfection with the
discharge water 630 being blended back into the main flow.
[0074] Referring now to FIG. 7, this graph shows the percentage
removal 700 of a pharmaceutical, the estrogen
17-alpha-ethinylestradiol, using the disclosed electrochemical
treatment process with the treatment fluid being final wastewater
effluent with pharmaceutical and personal care product residuals at
their normal levels for such liquids. The graph compares this with
disinfection efficacy 702 achieved during each test number, with
these tests being conducted at varying power levels and treatment
times. The tests show the high pharmaceutical removal efficacy of
the process even when operated to achieve relatively low
disinfection levels. There is a strong correlation between
contaminant destruction 700 and disinfection efficacy 702.
[0075] Referring now to FIG. 8, this graph shows the percentage
removal 800 of a personal care product residual, the antibiotic
triclosan, using the disclosed electrochemical treatment process
with the treatment fluid being final wastewater effluent with
pharmaceutical and personal care product residuals at their normal
levels for such liquids. The graph compares this with disinfection
efficacy 802 achieved during each test number, with these tests
being conducted at varying power levels and treatment times. The
tests show the high pharmaceutical removal efficacy of the process
even when operated to achieve relatively low disinfection levels.
There is a strong correlation between contaminant destruction 800
and disinfection efficacy 802.
[0076] Referring now to FIGS. 7 and 8, the present inventors have
discovered that for the electrochemical method of this patent, that
disinfection efficacy, a low cost, easily measured value, serves as
a robust surrogate for the efficacy of removal of trace
pharmaceuticals and personal care product residuals. In addition,
the inventors have determined that for liquid streams without
significant bacterial load, a safe, food grade bacteria like
Lactobacillus Acidophilus, used to make yoghurt, can be added to
the liquid to provide this surrogate disinfection measure. This is
an inexpensive alternative to the expensive, time-consuming,
analysis required to measure trace pharmaceuticals and personal
care product oxidation performance.
[0077] Referring now to FIG. 9, in an alternate configuration
electrode 28a may be a conductive tube or rod surrounded by a
concentric conductive tube electrode 28b wherein an annular space
is created for passage of the liquid being treated 34 and 35.
[0078] The present invention has been described in terms of the
preferred embodiment, and it is recognized that equivalents,
alternatives, and modifications, aside from those expressly stated,
are possible and within the scope of the appending claims.
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