United States Patent
`
`[19]
`
`Eibl
`
`[54}
`
`APPARATUS FOR DESTROYING
`MICROORGANISMS IN AN AQUEOUS
`LIQUID BY ELECTROLYTIC OXIDATION
`
`'
`
`[75]
`
`Inventor: Volker Eibl, Munich, Germany
`
`[73]
`
`Assignee:
`
`Sachs Systemtechnik GmbH,
`Schweinfurt am Main, Germany
`
`[21]
`
`[22]
`
`[30]
`
`[51]
`[52]
`[53]
`
`[56]
`
`Appl. No.: 608,245
`
`Filed:
`
`Aug. 27, 1975
`
`Foreign Application Priority Data
`Sept. 5, 1974
`Germany ............................. 2442474
`
`Int. C1.2 ................................................ C023 1/82
`US. Cl. ..................................... 204/268; 204/269
`Field of Search ............... 204/149, 152, 255, 275,
`204/272, 268, 269
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`820,113
`883,170
`1,440,091
`
`5/1906 Hinkson ............................... 204/268
`204/268
`3/1908 Christy.
`12/1922
`Long .....
`7/1925
`Casale .............................. 204/272X
`
`204/272 1,547,362
`
`[11]
`
`[45]
`
`4,062,754
`
`Dec. 13, 1977
`
`1,925,322
`3,402, l 17
`3,779,889
`3,835,020
`
`9/1933 Hills ................................. 204/269X
`
`9/1968
`Evans ......
`. 204/268
`
`Loftfield .
`12/1973
`204/268
`9/1974 Galneder .............................. 204/268
`
`FOREIGN PATENT DOCUMENTS
`
`430,477
`433,576
`
`6/1935 United Kingdom.
`8/1935 United Kingdom.
`
`Primary Examiner—Arthur C. Prescott
`Attorney, Agent, or Firm—Hans Berman
`
`[57]
`
`ABSTRACT
`
`The disinfecting effect of electric current passing be-
`tween a contaminated aqueous liquid and an anode
`immersed in the liquid is enhanced by providing bipolar
`electrodes between the directly energized anode and
`cathode so that the flow channels for the liquid between
`the electrode faces are limited to a width Of 3 mm or
`
`less, the auxiliary electrodes being insulated from each
`other and from the directly energized electrodes and
`disposed in such a manner that the potential difference
`between each pair of adjacent electrodes is equal.
`
`10 Claims, 3 Drawing Figures
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`—-—..——.———-——
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`.uar-_"‘-‘“-----““_-“-‘-—“-‘-‘v,.
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`—_—_——
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`20
`
`—
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`Tennant Company
`Exhibit 1044
`
`Tennant Company
`Exhibit 1044
`
`

`

`US. Patent
`
`Dec. 13, 1977
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`Sheet 1 of 2
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`4,062,754
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`U.S. Patent
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`IDec'. 13, 1977
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`Sheet 2 of 2
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`4,062,754
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`1
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`4,062,754
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`2
`embodiments when considered in connection with the
`
`APPARATUS FOR DESTROYING
`MICROORGANISMS IN AN AQUEOUS LIQUID
`BY ELECTROLYTIC OXIDATION
`This invention relates to the destruction of microor-
`
`ganisms in aqueous liquids, and particularly to appara-
`tus for destroying microorganisms in an aqueous liquid
`by electrolytic oxidation.
`It is known to pass a contaminated aqueous liquid
`through an electrolytic cell while a voltage is applied to
`electrodes in the cell, and to destroy microorganisms in
`the liquid by exposure to the anolyte.
`It has been proposed in the German Pat. application
`No. 2,337,355, published without examination, to purify
`water of heavy metal ions, cyanides, sludge, coloring
`matter, organic ions and compounds in an electrolytic
`cell packed with spherical auxiliary electrodes which
`are insulated from each other and from the directly
`energized electrodes. It has now been found that the
`spherical auxiliary electrodes, because of their tight
`packing, shield each other so that the potential distribu-
`tion among the auxiliary electrodes is uneven, and the
`oxidizing effect on the contaminants is limited. This is
`tolerable when contaminants of the afore-described
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`types are to be reduced to an acceptable level, but not
`sufficient if the contaminants are viable microorganisms
`which multiply again unless practically completely
`destroyed by the treatment. The known process thus is
`not practical in the removal of microorganisms from
`drinking water.
`It is the primary object of this invention to provide
`electrolytic apparatus which permits effective destruc-
`tion of microorganisms in drinking water and like aque-
`ous liquids.
`A complementary object is the provision of such .
`apparatus which is of small bulk even when suitable for
`treating aqueous liquids at a high rate.
`It has been found that these objects can be achieved
`in an apparatus in which a row of electrodes is mounted
`in a cavity of a vessel in spaced, electrically insulated
`relationship. The row includes two terminal main elec-
`trodes and a plurality of auxiliary electrodes interposed
`between the main electrodes. Each main electrode has a
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`30
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`35
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`face spacedly opposite the corresponding face of the
`other main electrode, and each auxiliary electrode has
`two faces substantially parallel to the faces of the two
`main electrodes. The faces of each pair of adjacent
`electrodes in the row define therebetween a channel for
`flow of liquid parallel to the defining faces.
`The main electrodes may be connected conductively
`to respective terminals of a source of electric power for
`thereby establishing a voltage between the main elec-
`trodes. An inlet and an outlet are provided on the vessel
`for passing therebetween respective portions of a
`stream of liquid through the channels. Each of the
`stream portions provides the sole path of electric cur-
`rent between the pair of electrodes defining the asso-
`ciated channel. The spacing of the electrodes in each
`pair is such that the potential differences between the
`electrodes of each pair of adjacent electrodes in the row
`are equal when a voltage is established between the
`main electrodes and the stream of aqueous liquid is
`passed through the several channels.
`Other features, additional objects, and many of the
`attendant advantages of this invention will readily be
`appreciated as the same becomes better understood
`from the following detailed description of preferred
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`appended drawing in which:
`FIG. 1 shows electrolytic apparatus of the invention
`in elevational section;
`FIG. 2 illustrates the apparatus of FIG. 1 in section
`on the line II — II in FIG. 1; and
`FIG. 3 shows another apparatus of the invention in
`elevational section.
`
`Referring now to the drawing in detail, and initially
`to FIG. 1, there is shown a cylindrical vessel 1 of insu-
`lating plastic. An inlet nipple 2 is mounted on the lower-
`most portion of one circular end wall of the vessel 1,
`and an outlet nipple 3 is provided at the highest point of
`the other circular vessel wall. Electrodes 4, 5, of stain-
`less steel sheet stock (Type A181 316) are adhesively
`fastened to the inner faces of the two end walls, and
`eight auxiliary electrodes 6 of the same material are
`evenly spaced between the electrodes 4, 5 by somewhat
`resilient, cylindrical spacers 7 of polyurethane foam, the
`spacers being loaded in compression to clamp the elec-
`trodes 6 in the illustrated position in which their major
`faces are parallel to each other and to the exposed faces
`of the main electrodes 4, 5. The latter are connected by
`respective leads to the positive and negative terminals
`of a rectifier indicated by + and —- signs.
`As seen in FIG. 2, the several, plate-shaped elec-
`trodes 4, 5, 6 have identical configurations of a segment
`of a circle bounded by two parallel chords 8 equidistant
`from the center of the circle. The chords are aligned in
`the direction of the vessel axis to define a collecting
`duct 9 communicating with the outlet 3 and a distribut-
`ing duct 10 communicating with the inlet 2. The arcuate
`edges of the electrodes are sealed to the cylindrical
`vessel wall. A pump 20 feeds the liquid to be purified to
`the inlet 2 at a constant rate, and the stream of liquid is
`distributed by the duct 10 among the several transverse
`channels between respective faces of adjacent elec-
`trodes 4, 5, 6. The portions of the stream emerge from
`the channels into the collecting duct 9, and the liquid is
`discharged from the outlet 3. The spacers 7 are of so
`much smaller diameter than the electrodes as not signifi-
`cantly to affect the liquid flow through the channels.
`When the rectifier applies a voltage between the
`anode 4 and the cathode 5, the auxiliary electrodes 6
`become bi-polar, their faces directed toward the anode
`4 becoming cathodic, and the faces directed toward the
`cathode 5 becoming anodic. Because of the uniform
`spacing of the identical electrodes 4, 5, 6 which bound
`each of the several channels between the ducts 9, 10, the
`potential differences between the electrodes of each
`pair bounding a channel are equal.
`The number of auxiliary electrodes 6 in the illustrated
`apparatus may be varied to suit specific condition, but is
`preferably not smaller than three. The following Exam-
`ples illustrate the operation of apparatus of the general
`type shown in FIGS. 1 and 2.
`EXAMPLE 1
`
`The electrolytic cell employed had two main elec-
`trodes and 55 auxiliary electrodes, and each electrode
`face had an area of 95 (ml. The total anodic surface area
`engaged by the flowing liquid thus was 5,320 cm2. The
`channels between adjacent electrode faces had a uni-
`form width of 2 mm. The vessel 1 had an outer diameter
`of 133 mm.
`The cell was used for disinfecting drinking water
`contaminated with 2.8 X 106 cells of E. coli per milli-
`liter, and having a specific resistivity of 2,200 ohms.cm.
`
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`4,062,754
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`4
`gaged by the liquid flowing through the apparatus. The
`following, empirically developed relationship has been
`found to hold:
`
`F=K><v
`
`5
`
`3
`The voltage across the main electrodes was set to pro-
`duce an anode current density of 5 mA/cmz. The con-
`taminated liquid was pumped through the cell at such a
`rate that the average dwell time in the channels between
`the electrodes was 31 seconds. No viable microorgan-
`isms could be detected in the purified water discharged
`from the outlet 3.
`
`EXAMPLE 2
`
`In an apparatus having only seven auxiliary elec- 10
`trodes and a correspondingly shorter vessel, but not
`otherwise significantly different from that employed in
`Example 1, drinking water contaminated with 1.9 X
`105 E. coli per ml was treated between the electrodes
`having a combined anode area of 760 cm2 for an average 15
`dwell time of 15 seconds at an anode current density of
`1.5 mA/cmz, the electrode faces being spaced 2.0 mm
`apart. No viable germs could be detected in the treated
`water.
`
`For best current efficiency, the anode current density 20
`should not exceed 8 mA/cmz, and other parameters
`should be selected to maintain a potential difference of
`at least 1.5 volt between electrodes bounding a flow
`channel therebetween.
`The disinfecting effect of the oxidizing compounds 25
`formed at the anodes is not materially affected by the
`hydrogen simultaneously generated at
`the cathodic
`electrode surfaces. Any undesirable effects that nascent
`hydrogen may have are readily avoided by covering the
`cathodic electrode faces with a porous non-conductive 30
`material which impedes migration toward the cathode
`face.
`While continuous direct current was supplied to the
`electrodes in the Examples described above, pulsed or
`intermittent direct current, as furnished by a half-wave 35
`rectifier,
`is equally effective. The cells of the type
`shown in FIGS. 1 and 2 are of simple design, make
`effective use of the current supplied, and may be modi-
`fied readily for adaptation to available sources of elec-
`tric power. When the electrodes are replaced by others 40
`of equal number, but greater area, the resistance of the
`cell is decreased, and an effective current can be pro-
`duced by a smaller applied voltage. Increasing the num-
`ber of electrodes at unchanged individual surface area
`increases the electrical resistance of the cell and thus 45
`adapts the cell to a power source of higher voltage
`under otherwise identical conditions.
`Other parameters being comparable, the largest possi-
`ble number of auxiliary electrodes is desirable. The
`multiplicity of flow channels permits treatment of the 50
`aqueous liquid at a high rate, yet the narrowness of
`individual channels, preferably 3 mm or less, causes
`each contaminating microorganism to move past an
`anode at a distance small enough for interaction with
`the somewhat labile anodic products of electrolysis 55
`other than molecular oxygen.
`To operate at the elevated voltage necessitated by a
`large number of auxiliary electrodes is generally advan-
`tageous because of the lower energy losses in bus bars
`and other conductors. To use fewer than three auxiliary 60
`electrodes has been found to reduce the germicidal
`effect of the treatment.
`
`The capacity of apparatus of the invention for suc-
`cessfully treating contaminated aqueous liquids, of
`which drinking water is merely a characteristic exam- 65
`ple, has been found to be related to the total available
`anode area which in turn is one half of the combined
`‘ surface area of the main and auxiliary electrodes en-
`
`In this equation, F is the numerical value (in cm?) of the
`combined area of the anodic electrode surfaces in the
`cell, v is the numerical value (in cm3/sec.) of the rate of
`liquid flow through all channels between the electrodes,
`and K is a factor whose numerical value is between 30
`and 160 and which remains unchanged for a chosen
`applied cell voltage,
`thus permitting adjustment of
`anode area for different flow rates controlled, for exam-
`ple, by varying the rotary speed of the pump 20 without
`loss of cell effectiveness, or vice versa.
`The apparatus shown in FIGS. 1 and, 2 combines
`desirable hydrodynamic and electrical properties, but is
`capable of many modifications without significant
`change in function or loss of effectiveness. One such
`modification is shown by way of example in FIG. 3.
`The modified apparatus has a cathode 11 which is a
`cylindrical rod of austenitic stainless steel, a tubular
`anode 12, and three auxiliary electrodes 13 which are
`cylindrical, stainless steel
`tubes of varying diameter
`coaxial with each other and with the main electrodes
`11, 12.- The five electrodes radially define four, coaxial,
`annular flow channels which connect two insulating
`headers 14, 15. The headers, jointly with the tubular
`anode 12, constitute the outer walls of the cell casing or
`vessel, and the cathode rod 11 and auxiliary electrodes
`13 are secured to the headers by insulating fasteners 16.
`The liquid to be purified is admitted to the header 14 by
`an inlet 17 from a non-illustrated pump, and the treated
`liquid is discharged from the header 15 through an
`outlet 18.
`Because the electrode faces are arcuate about a com-
`mon axis at different radii of curvature, their surface
`areas differ, and the required equal potential difference
`between radially adjacent electrodes is maintained by
`varying the radial width of the flow channels between
`adjacent electrodes, the channel partly bounded by the
`anode 12 being widest, and that adjacent the cathode
`rod 11 being narrowest, as is generally indicated in FIG.
`3 which, however, is not drawn to scale.
`The apparatus described above with reference to
`FIG. 3 is functionally closely analogous to the embodi-
`ment of the invention illustrated in FIGS. 1 and 2. It
`operates in the same manner not requiring separate
`description, and is affected by the same operating vari-
`ables in substantially the same manner.
`It should be understood, of course, that the foregoing
`disclosure relates only to preferred embodiments of the
`invention, and that it is intended to cover all changes
`and modifications of the examples of the invention
`herein chosen for the purpose of the disclosure which
`do not constitute departures from the spirit and scope of
`the invention set forth in the appended claims.
`What is claimed is:
`
`1. Apparatus for destroying microorganisms in an
`aqueous liquid comprising:
`a. a vessel bounding a cavity;
`b. a row of electrodes mounted in said cavity in
`spaced, electrically insulated relationship and in-
`cluding two terminal, main electrodes and at least
`one auxiliary electrode interposed between said
`main electrodes,
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`4,062,754
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`6
`the faces defining the same being no greater than
`3 millimeters;
`c. conductive means for connecting said main elec-
`trodes to respective terminals of a source of elec-
`tric power and for thereby establishing a voltage
`between said main electrodes;
`(1. inlet means and outlet means on said vessel for
`simultaneously passing therebetween respective
`portions of a stream of aqueous liquid through said
`channels, each of said portions providing the sole
`path of electric current between the pair of elec-
`trodes defining the associated channel.
`4. Apparatus as set forth in claim 3, wherein said row
`includes at least three of said auxiliary electrodes.
`5. Apparatus as set forth in claim 3, further compris-
`ing means defining a distributing duct and a collecting
`duct, said distributing duet communicating with said
`inlet means and with a first portion of each of said chan-
`nels, and said collecting duct communicating with said
`outlet means and a second portion of each of said chan-
`nels, the first and second portions of each channel being
`spaced in the direction of said flow of liquid.
`6. Apparatus as set forth in claim 5, wherein said
`direction is vertical.
`
`7. Apparatus as set forth in claim 3, further compris-
`ing spacers between the faces of each pair of adjacent
`electrodes, the spacers having a constant cross section
`along the entire distance between the faces and the
`peripheral surface of the spacers extending perpendicu-
`larly to the electrode faces.
`8. Apparatus as set forth in claim 7, wherein the spac-
`ers are cylindrical and the axes of the cylindrical spacers
`extend perpendicularly to the electrode faces.
`9. Apparatus as set forth in claim 3, further compris-
`ing a spacer in each of said channels interposed between
`the faces of the pairs of electrodes defining said chan-
`nels respectively, the cross section of each spacer paral-
`lel to said faces being uniform and smaller than the area
`of said faces over the entire distance of said faces, the
`faces of each of said pairs projecting in all directions
`beyond the interposed spacer.
`10. Apparatus as set forth in claim 3, wherein said at
`least one auxiliary electrode is plate-shaped, and said
`two faces of said at least one electrode are substantially
`planar.
`
`5
`1. each main electrode having a face spacedly op-
`posite the corresponding face of the other main
`electrode,
`2. said at least one auxiliary electrode having two
`faces substantially parallel
`to said respective
`faces of said main electrodes, said two faces
`being arcuate about a common axis of curvature,
`theaxes of curvature of the faces of said at least
`one auxiliary electrode substantially coinciding,
`3. respective faces of each pair of adjacent elec-
`trodes in said row defining therebetween a chan-
`nel for flow of liquid parallel to the defining
`faces;
`c. conductive means for connecting said main elec-
`trodes to respective terminals of a source of elec-
`tric power and for thereby establishing a voltage
`between said main electrodes;
`d. inlet means and outlet means on said vessel for
`simultaneously passing therebetween respective
`portions of a stream of aqueous liquid through said
`channels, each of said portions providing the sole
`path of electric current between the pair of elec-
`trodes defming the associated channel.
`2. Apparatus as set forth in claim 1, wherein said row
`includes a plurality of said auxiliary electrodes, said
`auxiliary electrodes being tubular andcoaxial.
`3. Apparatus for destroying miroorganisms in an
`aqueous liquid Comprising:
`a. a vessel bounding a cavity;
`b. a row of electrodes mounted in said cavity in
`spaced, electrically insulated relationship and in-
`cluding two terminal, main electrodes and at least
`one auxiliary electrode interposed between said
`main electrodes,
`1. each main electrode having a face spacedly op-
`posite the corresponding face of the other main
`electrode,
`2. said at least one auxiliary electrode having two
`faces substantially parallel
`to said respective
`faces of said main electrodes,
`3. respective faces of each pair of adjacent elec-
`trodes in said row defining therebetween a chan-
`nel for flow of liquid parallel to the defining
`faces, the width of each of said channels between
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