U.S. patent application number 11/917361 was filed with the patent office on 2008-12-25 for use of an anode for elimination or reduction of microbial impurities in liquids..
Invention is credited to Martin Ebro, David Napper.
Application Number | 20080314760 11/917361 |
Document ID | / |
Family ID | 35094126 |
Filed Date | 2008-12-25 |
United States Patent
Application |
20080314760 |
Kind Code |
A1 |
Napper; David ; et
al. |
December 25, 2008 |
Use of an Anode For Elimination or Reduction of Microbial
Impurities in Liquids.
Abstract
The present invention relates to the use of an anode suitable
for use in inter alia a reactor for elimination or reduction of
microbial impurities from liquids, such as inter alia waste water
and water intended for human or animal consumption. The anode
comprises an expanded metal plate, preferably titanium, covered
with a non-corrosive metal layer, preferably a platinum layer. The
surface of the anode is endowed with dents, which enhances the
electrochemical effect between the anode and the corresponding
cathode and thereby enhances the microbial effect and at the same
time reduces the energy required to obtain an efficient kill of the
microorganisms,
Inventors: |
Napper; David; (Aabenraa,
DK) ; Ebro; Martin; (Frederiksberg, DK) |
Correspondence
Address: |
BUDDE, SCHOU & OSTENFELD, A/S
VESTER SOEGADE 10, 5TH FLOOR
COPENHAGEN
DK-1601
DK
|
Family ID: |
35094126 |
Appl. No.: |
11/917361 |
Filed: |
July 5, 2006 |
PCT Filed: |
July 5, 2006 |
PCT NO: |
PCT/IB06/01858 |
371 Date: |
April 11, 2008 |
Current U.S.
Class: |
205/660 |
Current CPC
Class: |
C02F 1/46109 20130101;
C02F 1/4674 20130101; C02F 2303/04 20130101; C02F 2001/46133
20130101; C02F 2001/46138 20130101 |
Class at
Publication: |
205/660 |
International
Class: |
C25F 3/00 20060101
C25F003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 5, 2005 |
EP |
05254213.1 |
Claims
1. Use of an anode comprising a plate of expandable base-material
subjected to: degreasing acidic washing glass-blowing plating with
anti-corrosive material in a process for elimination or reduction
of microbial impurities in liquids.
2. Use of an anode according to claim 1 wherein the expandable
base-material is resistant to corrosion and at which platinum or
similar metals can attach
3. Use of an anode according to claim 1 wherein platinum or similar
metals can attach to the expandable base-material.
4. Use of an anode according to claim 1 wherein the expandable
base-material is titanium or similar metals.
5. Use of an anode according to claim 1 wherein the anode is
characterised in comprising indentations or dents, the diameter of
said indentations or dents being between 10-40 .mu.m.
6. Use of an anode according to claim 5 wherein the number of
indentations or dents per square millimetre of the plate is between
50-500.
7. Use of an anode according to claim 1 wherein said acidic washing
is carried out with nitric acid
8. Use of an anode according to claim 1 wherein said glass-blowing
is applied using glass particles or glass beads of 75-150 .mu.m in
diameter.
9. Use of an anode according to claim 1 wherein the plating layer
comprises pure platinum with a thickness 1.5.+-.0.3 .mu.m.
10. Use of an anode according to a claim 1 wherein the anode has a
cylindrical geometrical shape.
11. Use of an anode according to claim 1 wherein multiple the
plates are arranged in a sandwich-like or similar fashion.
12. Use of an anode according to claim 1 wherein the distance
between the plates are 0.5-2.0 mm.
13. Use of an anode according to claim 1 wherein said liquid is
water, including waste water from, for example, sewage plants,
electroplating operations, food processing plants, fabric dye
facilities, and the like.
14. Use of an anode according to any of claim 1 wherein said liquid
is subjected to a filtrating pre-treatment.
15. Use of an anode according to claim 1 wherein said liquid is
oil-water emulsions.
16. Use of an anode according to claim 1 wherein said anode is
applied as offshore treatment of said liquid.
17. Use of an anode according to claim 1 wherein said liquid is
intended for drinking water or other purposes in which water of
drinking water quality is required.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the technical field of
electrochemical elimination or reduction of microbial impurities of
liquids. The liquids treated may inter alia include waste water and
water intended for human consumption.
BACKGROUND OF THE INVENTION
[0002] Conventional methods of elimination or reduction of
microbial impurities in liquids, such as waste water and water
intended for human and animal consumption, typically included use
of chemicals, biochemical treatment, sedimentation, distillation,
filtration, electrochemical devices or the like.
[0003] Electrochemical devices comprise one or more anodes and
cathodes that typically are arranged in order to allow liquids to
pass therebetween. Moreover, various types of structural and
compositional surfaces of the electrodes are possible in order to
generate a variety of different reactions in the liquid that passes
between the two electrodes. At the anode, halides may be oxidised
to their corresponding halogen, most commonly chlorine, via
dimerisation of halogen radicals and water may be oxidised to
dioxygen and protons. At the cathode dioxygen may be reduced to
hydrogen peroxide, and water to hydrogen and hydroxyl ions.
Chlorine, chlorine radicals, hydrogen peroxide and ozone may all
have a biocidal effect on the bacteria content in the treated
liquid.
[0004] There are several problems associated with the use and
generation of chlorine in water treatment, particularly due to its
potential negative effects on the environmental as well as the
legal limits of the chlorine level present in water intended for
human and animal consumption. Examples of undesirable environmental
effects of the use of chlorine are that it reacts with nitrogenous
compounds resulting in chloramines, which are poor biocides with
unpleasant odours. Furthermore, chlorine is reactive with other
organic materials and may result in environmentally harmful,
carcinogenic and/or teratogenic compounds such as chloroform or
chloroalkanes as well as reacting with naturally occurring phenolic
compounds to form chlorinated compounds. In waste water treatment,
chlorination must be followed by process of laborious and
potentially noxious dechlorination using sulphur dioxide or an
equivalent chemical thereof in order to comply with discharge
chlorine levels.
[0005] However, in recent years the use of chlorine has been
increasingly discouraged and limited. For example, the German
drinking water directive (based on EU Council Directive 98/83/EC of
November 1998 on the quality of water intended for human
consumption) limits the presence of chlorine in drinking water to
0.5 mg/l. Additionally, in large parts of the food industry high
concentrations of chlorine in water that come in direct contact
with food products are also prohibited. Usually water of "drinking
quality" is considered acceptable in that context and is generally
the quality of water specified for use in many processes in e.g.
food factories.
[0006] In order to provide the desired reduction in water in the
number of bacteria capable of creating colonies, including
pathogenic bacteria, it is often necessary to use concentrations of
chlorine that are markedly higher than the allowable limit in
drinking water. In the European Hygienic Engineering and Design
Group guidelines "Shafe and Hygienic Water Treatment in Food
Factories" it is stated that levels of chlorine up to 1000 ppm can
be required to control bacteria, i.e. maintaining the number of
bacteria below the colony forming level. This obviously complicates
even further the utilization of chlorine in water cleansing
systems.
[0007] Another major problem with electrochemical cleansing of e.g.
waste water and water intended for human and animal consumption,
has been the economically unfavourable energy requirements of the
cleansing systems. In recent years considerable efforts to reduce
the energy costs of said systems, e.g. via optimisation of the
electrodes utilized, has been made.
[0008] Prior art describing similar systems for purification of
liquid includes.
[0009] U.S. Pat. No. 4,316,787 discloses an anode comprising a
laminated body of a platinum group metal foil bonded to a niobium
or tantalum layer, which in turn is bonded to a titanium substrate.
The anode is operable at a voltage above 20 volts and a watt
density above 100 watts per square inch surface. Hence, this anode
consists of three metals whereas the anode of the present invention
only consists of two metals, preferably titanium and platinum, and
furthermore is operable at lower voltages at 10-15 volts.
[0010] US2003/0164308 discloses a method and an apparatus to obtain
drinking water from waste water, based on the use of an
electrolytic cell forming a part of a dynamic flow system which
operates at a relatively low voltage (20-200 volts, 1-6 amperes)
and at very high flow rates. The anode is in contrast to the anode
according to the present invention--formed from iron, stainless
steel, carbon or copper.
[0011] U.S. Pat. No. 4,290,873 discloses an electrode mesh
comprised of titanium or tantalum as the base-material and covered
with platinum. The platinum may be mechanically clad to the
titanium or tantalum substrate, or the platinum may be plated
electrolytically onto the substrate. The shape and surface of the
anode together with the thickness of the titanium layer of one
hundred microinches (2.54 .mu.m) is different from the anode
according to the present invention.
[0012] U.S. Pat. No. 3,616,355 discloses an anode, which comprises
a laminated body of a platinum metal foil on a substrate or backing
of a metal such as titanium, tantalum or niobium. The bonding of
said materials is being effected by a highly localised pressure and
thermoelectric heat. In contrast to this, the anode of the present
invention consists of expanded metal and is also endowed with dents
in the platinum surface.
[0013] DE19625254 discloses an anode of expanded titanium covered
with a layer of platinum. The anode is characterised by the way the
two layers are attached, which is different from the anode of the
present invention. Furthermore, the anode is not endowed with dents
on the surface.
[0014] DE2223240 discloses an anode comprising titanium and
platinum. However, this anode is not made from expanded metal and
is also not endowed with dents on the surface. Furthermore, the
anode is made with the purpose of applying nitration during
electrolysis.
[0015] DE3823760 discloses an anode comprising an expanded metal
titanium plate covered with platinum. However, the thickness of the
platinum layer is more than three times thicker and thus more
expensive than the anode of the present invention. Furthermore, the
anode is not endowed with dents in the platinum surface.
SUMMARY OF THE INVENTION
[0016] The present invention relates to a novel use of an
anode--which comprises a plate of expanded base-material,
preferably titanium, endowed at the surface with dents having a
diameter of preferably 10-40 .mu.m in an amount of preferably
50-500 dents per square millimetre--In a method for elimination or
reduction of microbial impurities in liquids. The structure of the
anode is best defined by the process at which it is produced. The
process involves subjecting the anode plate--in succession--to
degreasing, acid washing, preferably with nitric acid (HNO.sub.3),
glass-blowing and electrolysis in order to cover the anode plate
with a layer of pure platinum. The structure of the anode obtained
by this particular sequence of process-steps has surprisingly shown
to produce a considerably higher biocidal effect in relation to the
energy required to operate the system i.e. the current and voltage
required, compared to the anodes known in the art.
DESCRIPTION OF THE INVENTION
[0017] The present invention relates to the use of a specifically
prepared anode in a method of electrochemical elimination or
reduction of microbial impurities of liquids, such as waste water
and water intended for human consumption. The elimination or
reduction of microbial impurities via the anode according to the
present invention is based on the biocidal effect, which is
achieved from the produced chloride-based and oxygen-based
compounds. The anode comprises a plate of an expanded
base-material, preferably consisting of titanium, covered by an
anti-corrosive material, preferably platinum. The surface of the
anode is endowed with dents, which enhances the electrochemical
effect between the anode and its corresponding cathode and thereby
enhances the biocidal effect of the microorganisms while--at the
same time--reducing the energy required to obtain an efficient
biocidal effect.
[0018] More specifically, the utilisation of extendable
base-material with well defined dents provides a natural turbulence
when the liquid passes through its surface, which consequently
enhances the formation of biocidal chlorine as the individual water
molecules has to be in close proximity of the surface of the anode
in order to perform the required chemical reactions. Furthermore,
the well-defined dents result in changed flow-conditions and/or
larger surface areas, which further enhances the formation of
biocidal chlorine. As the chemical reactions takes place at the
close proximity of the surface of the anode a large surface area as
well as increased waterflow, i.e. via turbulence or the like, over
the anode inevitably increases the resulting biocidal effect.
[0019] Furthermore, the present invention relates to a novel use of
an specifically prepared anode suitable for a method of elimination
or reduction of microbial impurities in liquids, such as waste
water and water intended for human or animal consumption, while--at
the same time--maintaining drinking water quality and avoiding
excess use of chemicals. Maintenance of drinking water quality is
defined herein, as the presence of chlorine in drinking water is
limited to 0.5 mg/l or below (in accordance with the German
drinking water directive based on EU Council Directive 98/83/EC of
November 1998 on the quality of water intended for human
consumption). The water resulting from the disinfection process can
be used directly for human consumption or used in a variety of
industrial processes in which such a high quality is required.
Advantages Over Prior Art
[0020] The anode according to the present invention provides a
comparatively high biocidal effect in relation to the
energy-requirements of the system. At the same time the chlorine
content produced by the system is below the levels allowed or in
accepted International drinking water directives, e.g. the above
mentioned German drinking water directive. This improved
functionality is provided by the unique structure of the anode
according to the present invention, which is best defined by the
specific process of which it is produced, i.e. by degreasing, acid
washing, preferably with nitric acid (HNO.sub.3), glass-blowing and
electrolysis in order to cover the anode plate with a layer of pure
platinum.
[0021] The extent of the applicability of the invention appears
from the following description. It should, however, be understood
that the detailed description and the specific examples are merely
included to illustrate the preferred embodiments and that various
alterations and modifications within the scope of protection will
be obvious to persons skilled in the art on the basis of the
detailed description.
Applications of the Anode of the Present Invention
[0022] In preferred embodiments the anode of the present invention
is applicable to waste water streams such as waste water from, for
example, sewage plants, electroplating operations, food processing
plants, fabric dye facilities, and the like. The present invention
is also useful for treating water streams for producing purified
drinking water. The present invention is particularly applicable to
oil-water emulsions. The terms waste stream or liquid stream, as
used herein, refers to such waste water streams and other liquid
streams, including some non-aqueous liquid streams.
[0023] In a further embodiment the anode according to the present
invention can also be used in systems for on-site treatment of
inter alia domestic-type waste, such as ships, trains, aircrafts
and off-shore drilling platforms. At such locations, the waste
typically flows through a biological or fermentation unit on board,
and then into a holding tank. When the effluent in the holding tank
reaches a certain level, it is pumped through a sterilising unit
where the effluent is sterilised, usually with sodium or calcium
hypochlorite. The effluent is then pumped overboard. Such treatment
is usually costly and requires the use of large and heavy, space
consuming equipment.
[0024] In an even further preferred embodiment the anode of the
present invention is applicable to water supply plants including
plants for treatment of ground water, surface water, desalted
water, rainwater and drinking water from devices such as drinking
water automat machines.
[0025] In an even further preferred embodiment the anode of the
present invention is applicable to water utilized in the
manufacturing of soap and cosmetics.
[0026] In an even further preferred embodiment the anode of the
present invention is applicable to water utilized in the production
of plastic.
[0027] In an even further preferred embodiment the anode of the
present invention is applicable to water utilized in the food
industry, including water utilized in the preparation of spices,
fish/shellfish, chicken/poultry, pork/beef, margarine,
confectionery, dairy products, beer/mineral water, vegetables,
candy/chewing gum, animal feed and In water used in cold or
refrigerated storage facilities.
[0028] In an even further preferred embodiment the anode of the
present invention is applicable to water from district heating
station, bath water, domestic hot water plant such as jacuzzis and
pools, hospitals and old people's home.
[0029] In an even further preferred embodiment the anode of the
present invention is applicable to water from printing houses,
retail trade, fountain basins, metal industry, paint and lacquer
industry, households, gardening, such as water from liquid manure,
and biotech industry, such as water from the fermentation and
pharmaceutical industry.
[0030] The anode is suitable for water treatment using various
apparatus for instance such apparatuses as described in U.S. Pat.
No. 6,309,519, EP0997437 and U.S. Pat. No. 6,652,733.
DETAILED DESCRIPTION OF THE INVENTION
[0031] The biocidal effect shown by an anode according to the
present invention depends on the magnitude of the flow over the
anode--or through the reactor equipped with said anode--as well as
the density of the current on the anodes. Therefore, if the water
is led slowly through the reactor and/or a high current density is
applied, a higher biocidal effect is obtained. Hence, it is a
matter of optimisation to find the suitable flow rate and current
density in a given application in order to achieve a satisfying
biocidal effect as well as maintaining a high capacity. Therefore
the number of reactors, the flow and the current density must be
corrected according to the given conditions.
Preparation of the Anode According to the Present Invention
[0032] In order to provide the specific structure of the anode
plate according to the present invention, the plate is--in the
following order--subjected to: [0033] degreasing [0034] treatment
with suitable acid, preferably nitric acid (HNO.sub.3) or oxalic
acid (H.sub.2C.sub.2O.sub.4) (acidic washing) [0035] glass-blowing,
preferably with glass-particles or--beads of preferably 75-150
.mu.m in diameter [0036] platinum plating (e.g. via conventional
electrolysis)
[0037] The dents produced at the surface of the anode have
diameters of 10-40 .mu.m and are present in an amount of 50-500
dents per square millimetre.
The Electrochemical Mechanisms of the Anode According to the
Present Invention
[0038] At the anode according to the present invention, hydroxide
ions (OH.sup.-) naturally contained in the water donates electrons
to the cathode and are thus converted to oxygen gas. This gas is
subsequently eliminated from the water. Hence, the concentration of
hydrogen tons (H.sup.+) in the water increases rendering the water
acidic. Also at the anode chloride ions (Cl.sup.-) contained in the
water donate electrons to the cathode and become chlorine gas
(Cl.sub.2). The chlorine gas dissolves in the acidic water and is
converted to hypochlorous acid (HOCl).
[0039] The cathode donates--at the close proximity of the
cathode--electrons to the hydrogen ions (I) contained in the water
to become hydrogen gas, which subsequently is eliminated from the
water. Also at the cathode, sodium ions (Na.sup.+) as well as
hydroxide ions (OH.sup.-)--if present in the water--are bonded and
sodium hydroxide is formed.
[0040] The bacteria are killed--i.e. the bioddal effect--by
chemically derived oxidation occurring when the water is
electrolysed. The anode according to the present invention produces
both chlorine-based and oxygen-based oxidants, which are formed
according to the following reactions:
2Cl.sup.-.fwdarw.Cl.sub.2+2e.sup.-
Cl.sub.2+H.sub.2O.fwdarw.HOCl+HCl
HOCl+H.sub.2O.fwdarw.OCl.sup.-+H.sup.+
2H.sub.2O+2e.sup.-.fwdarw.H.sub.2+2OH.sup.-
2H.sub.2O.fwdarw.2H.sub.2+O.sub.2
O.sub.2.fwdarw.O.sup.-
H.sub.2O+O.fwdarw.H.sub.2O.sub.2
[0041] Of these, dichlorine (Cl.sub.2), hypochlorous acid (HOCl),
ozone (O.sub.3), hydrochloric acid (HCl), hydrogen peroxide
(H.sub.2O.sub.2), oxychloride (OCl.sup.-) and hydroxide (OH.sup.-)
have proved to be hazardous to microorganisms.
EXAMPLES
Example 1
Killing Efficiency and Time of Treatment
[0042] An example of the present invention will now be described
with reference to the accompanying drawing, in which:
[0043] FIG. 1 is a schematic perspective diagram of an example
water treatment device according to the present invention.
[0044] Referring to FIG. 1, a water treatment device according to
an example of the present invention comprises anodes 1 with an
expandable base-material and cathodes 2, which are held in
non-conducting structures (not shown) to maintain a constant
distance between the electrodes. The electrodes are connected to a
DC power supply. The electrodes 1 and 2 are inserted into the water
to be treated.
[0045] A reactor being 12 cm wide, 7 cm high and 40 cm long (=3,360
cm.sup.3=3.36 liter) comprising numerous of the anodes as described
in example 2 as well as cathodes of stainless steel was used to
disinfect 500 litre of water per hour at 10-15 Volts. Prior to
treatment, the microorganisms contained in the water corresponded
to 10,000 CFU/ml. After the flow through the reactor, the content
of microorganisms was reduced to 1 CFU/ml and contained a chloride
concentration of less than 0.5 mg/l chlorine. The process is
continues and the time for the water to pass through the reactor
was approximately 7 seconds, i.e. a "pass through time" of 3.36
liter/7 seconds, i.e. 0.48 liter/second.
Example 2
Method for Preparing an Anode
[0046] An anode of 10.times.33 cm having a thickness of 1.5 mm was
made of a plate of expanded metal titanium with the following
characteristics:
[0047] Standard: DIN Standard 791 Type F
[0048] Mesh Dimensions 6.times.3.times.1.0.times.1.0 mm
(mesh-length .times. mesh-with .times. rib-with .times.
rib-thickness)
[0049] Material: Titanium Gr. 1: Type 3.7025 DIN 17860
[0050] The plate was degreased and treated with oxalic acid. It was
then glassblown with glass particles having sizes of 75-150 .mu.m.
By use of electrolysis the plate was covered with pure platinum by
a conventional process. The thickness of the resulting platinum
layer was 1.5.+-.0.3 .mu.m. The dents at the surface of the anode
had diameters of 10-40 .mu.m and was present in an amount of 50-500
dents per square millimetre.
Example 3
Comparative Study of the Chlorine Production Versus Different
Methods of Producing the Anode
[0051] In order to evaluate possible effects on the chlorine
production as a consequence of different methods of producing the
anode, the following three anode plates were tested under the same
electrical conditions, i.e. at current intensities between 11-11.8V
and at a voltage of 10A.
TABLE-US-00001 Chlorine liberated in close vicinity of Anode plate
produced by (in following order) the anode (mg/l) Acidic washing
with nitric acid .fwdarw. Glass blowing 0.136 Glass blowing
.fwdarw. Acidic washing with oxalic acid 0.060 Acidic washing with
oxalic acid .fwdarw. Glass blowing 0.082
[0052] As can be seen the specific sequence of acidic washing
followed by glass blowing was superior in relation to the
liberation/formation of chlorine compared to the sequence of glass
blowing followed by acidic washing, Secondly, the use of nitric
acid (HNO.sub.3) in the acidic washing appeared to be superior over
oxalic acid in the relation to the subsequent liberation/formation
of chlorine.
[0053] It also appeared that the concentrations of liberated
chlorine was well below the acceptable 0.5 mg/l limit according to
the previously mentioned drinking water directive.
[0054] As part of the biocidal effect of the anode is a direct
consequence of chlorine-based compositions naturally occurring in
the surrounding water, application of sodium chloride (NaCl.sup.-)
might be beneficial. For example if the chlorine content in the
liquid of a certain application is very low or non-existing, the
kill-effect will also be lowered due to the reduced production of
the chlorine compositions. In such a situation, it may optionally
be necessary to apply NaCl.sup.-.
* * * * *