U.S. patent application number 11/650461 was filed with the patent office on 2007-05-17 for solution having biocidal activity.
This patent application is currently assigned to PuriCore Europe Limited. Invention is credited to Martin Bellamy, Alan Buckley, Phil Collins, Alexey Yurevich Popov.
Application Number | 20070108064 11/650461 |
Document ID | / |
Family ID | 26315822 |
Filed Date | 2007-05-17 |
United States Patent
Application |
20070108064 |
Kind Code |
A1 |
Buckley; Alan ; et
al. |
May 17, 2007 |
Solution having biocidal activity
Abstract
A method and apparatus for the electrochemical treatment of an
aqueous solution in an electrolytic cell is described. Output
solution having a predetermined level of available free chlorine is
produced by applying a substantially constant current across the
cell between an anode and a cathode while passing a substantially
constant throughput of chloride ions through the cell.
Inventors: |
Buckley; Alan;
(Buckinghamshire, GB) ; Popov; Alexey Yurevich;
(Moscow, RU) ; Bellamy; Martin; (Northamptonshire,
GB) ; Collins; Phil; (Buckinghamshire, GB) |
Correspondence
Address: |
KENYON & KENYON LLP
1500 K STREET N.W.
SUITE 700
WASHINGTON
DC
20005
US
|
Assignee: |
PuriCore Europe Limited
Stafford
GB
|
Family ID: |
26315822 |
Appl. No.: |
11/650461 |
Filed: |
January 8, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10663079 |
Sep 16, 2003 |
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11650461 |
Jan 8, 2007 |
|
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09633665 |
Aug 7, 2000 |
6632347 |
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10663079 |
Sep 16, 2003 |
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Current U.S.
Class: |
205/620 |
Current CPC
Class: |
C02F 2303/04 20130101;
C02F 2209/06 20130101; C02F 2001/46185 20130101; C02F 2001/46142
20130101; A61P 43/00 20180101; C02F 2201/46115 20130101; C02F
2103/22 20130101; C02F 2209/42 20130101; C02F 2209/008 20130101;
C02F 2001/425 20130101; C02F 2103/026 20130101; C02F 2201/4618
20130101; C02F 2209/04 20130101; C02F 1/4618 20130101; C02F 9/00
20130101; C02F 2201/46125 20130101; C02F 2201/46145 20130101; C02F
2209/05 20130101; C02F 1/46104 20130101; C02F 2303/20 20130101;
C02F 2001/46195 20130101; C02F 2201/46185 20130101; C02F 1/4674
20130101; C02F 2209/005 20130101 |
Class at
Publication: |
205/620 |
International
Class: |
C25C 1/02 20060101
C25C001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 24, 1999 |
GB |
9927808.7 |
Aug 6, 1999 |
GB |
9918458.2 |
Claims
1. A biocidal solution having a pH of from 5 to 7 and an available
free chlorine (AFC) concentration of about 3 parts per million
(ppm) to 300 ppm.
2. The biocidal solution of claim 1, wherein the AFC concentration
is approximately 100 to 250 ppm.
3. A method of disinfecting a medical instrument comprising
exposing the medical instrument to the biocidal solution of claim
2.
4. A method of treating a venous leg ulcer in a patient comprising
administering the biocidal solution of claim 1 to the leg
ulcer.
5. A method of disinfecting poultry or fish comprising exposing the
poultry or fish to the biocidal solution of claim 1.
6. A method of breaking down bacterial biofilm comprising exposing
the biofilm to the biocidal solution of claim 1.
7. A method of producing the biocidal solution of claim 1
comprising: providing an electrochemical cell comprising an anode
chamber having an anode and a cathode chamber having a cathode;
supplying a saline solution to the anode chamber and the cathode
chamber; applying a current across the cell between the anode and
the cathode; and obtaining the biocidal solution from the
electrochemical cell.
8. The method of claim 6, wherein obtaining the biocidal solution
comprises obtaining the solution from the anode chamber.
9. The method of claim 6, wherein applying a current comprises
applying a current of 8 amps when the surface area of the anode is
approximately 100 cm.sup.2.
10. The method of claim 6, wherein a larger proportion of the
saline solution is fed to the anode chamber than is fed to the
cathode chamber.
11. The method of claim 9, wherein 80% of the saline solution is
fed to the anode chamber and 20% of the saline solution is fed to
the cathode chamber.
12. The method of claim 6, further comprising applying a
substantially constant current across the cell between the cathode
and the anode and passing a substantially constant throughput of
chloride ions through the electrochemical cell.
13. The method of claim 6, wherein supplying a saline solution
comprises forming a saline solution by combining a diluent potable
tap water and a concentrated salt solution.
14. The method of claim 12, wherein forming a saline solution
comprises feeding the concentrated salt solution by pulsatile means
into a flow of the diluent water to produce the saline
solution.
15. The method of claim 13, wherein the concentrated salt solution
is pulsed into a continuous flow of the diluent water through a
plurality of apertures along the flow path to produce a uniformly
mixed saline solution.
16. The method of claim 6, wherein supplying a saline solution
comprises supplying a substantially constant concentration of a
saline solution to the anode chamber and the cathode chamber.
17. The method of claim 6, further comprising recirculating a
portion of the catholyte produced in the cathode chamber into the
anode chamber.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 10/663,079, filed on Sep. 16, 2003, which is a divisional of
U.S. application Ser. No. 09/633,665, filed Aug. 7, 2000, which
claims priority to GB Application No. 9918458.2, filed on Aug. 6,
1999 and GB Application No. 9927808.7, filed on Nov. 24, 1999, all
of which are incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] The present invention relates, among other aspects, to a
method of operating an electrochemical cell to produce a biocidal
solution and apparatus for producing a biocidal solution by way of
the electrolytic treatment of an aqueous chloride solution.
[0003] In hospitals it is important to provide appropriate levels
of sterility, particularly in operating theatres and other
situations where invasive treatments are performed. Surgical
instruments and other apparatus must be sterilised or disinfected,
depending on their application, before use in order to reduce the
risk of bacterial infection. One method of sterilisation is the
application of heat and pressure in an autoclave. However, this is
not suitable for some medical apparatus, such as heat-sensitive
endoscopes.
[0004] A typical method employed for reprocessing heat sensitive
instruments involves the use of chemical biocides, such as
glutaraldehyde. This can be unsatisfactory due to improper or
incomplete disinfection. Furthermore, exposure to glutaraldehyde
fumes can cause asthma and dermatitis in healthcare staff. Also,
glutaraldehyde is believed to have relatively low sporicidal
activity. Moreover, other disinfectants, such as chlorine dioxide
and peracetic acid may suffer from similar handling problems as
glutaraldehyde.
[0005] For some years, it has been known that electrochemical
activation of brine produces a super-oxidised water which is
suitable for many applications including general disinfection in
medical and veterinary applications and the sterilisation of
heat-sensitive endoscopes. There has been a recent interest in the
use of super-oxidised water as a disinfectant because of its rapid
and highly biocidal activity against a wide range of bacteria,
fungi, viruses and spores. Also, super-oxidised water is an
extremely effective sterilising cold non-toxic solution which is
free from highly toxic chemicals, thereby presenting reduced
handling risk.
[0006] GB 2253860 describes the electrochemical treatment of water
through an electrolytic cell. Co-axially arranged cylindrical and
rod electrodes provide anode and cathode (working and auxiliary)
flow chambers which are separated by a porous membrane made of a
ceramic based on zirconium oxide.
[0007] Water is fed from the bottom to the top of the device
through the working chamber. Simultaneously, water having a higher
mineral content flows through the auxiliary chamber to a
gas-separating chamber. An electric current is passed between the
cathode and anode through the water in both chambers and the porous
membrane separating the chambers. Water flowing through the
auxiliary chamber recirculates to the auxiliary chamber by
convection and by the shearing forces applied to the water through
the rise of bubbles of gas which are generated on the electrode in
the auxiliary chamber. The pressure in the working chamber is
higher than that in the auxiliary chamber, and gaseous electrolysis
products are vented from the gas-separating chamber by way of a
gas-relief valve. A change of working mode from cathodic to anodic
water treatment is achieved by changing polarity.
[0008] This electrolytic process acts on salts and minerals
dissolved in the water, such as metal chlorides, sulphates,
carbonates and hydrocarbonates. Where the working chamber includes
the cathode, the alkalinity of the water may be increased through
the generation of highly soluble metal hydroxides. Alternatively,
the electrolytic cell may be switched so that the working chamber
includes the anode, in which case the acidity of the water is
increased through the generation of a number of stable and unstable
acids.
[0009] A similar electrolytic cell is described in GB 2274113. This
cell includes two coaxial electrodes, separated by an
ultra-filtration diaphragm (porous membrane) based on zirconium
oxide, thereby defining a pair of coaxial chambers. A current
source is connected to the electrodes of a plurality of cells via a
switching unit to enable polarity alteration of the electrodes to
eliminate deposits on the cathode and to connect the cells
electrically either in series or parallel.
[0010] WO 98/13304 describes the use of such an electrolytic cell
in an apparatus to process a liquid, such as water. A liquid is
supplied to the cathode chamber only and part of the output from
the cathode (catholyte) is recycled to the input of the anode
chamber. This input serves as the total supply to the anode
chamber. In situations where not all of the solution output from
the cathode chamber is recycled to the input of the anode chamber,
a proportion of the output from the cathode chamber is drained to
waste, this proportion being measured by a flow meter. A
constant-voltage DC supply is applied between the anode and the
cathode, and the pH and redox potential of the treated solutions
are measured and maintained by controlling flow rates through the
cell.
[0011] A method and apparatus for producing a sterilising solution
is described in GB 2316090, the subject matter of which is
incorporated herein by reference, wherein a supply of softened
water is generated by passing water through an ion-exchange water
softener. A saturated salt solution, generated by mixing softened
water with salt, is passed through an electrolytic cell to produce
a sterilising solution, or used to regenerate the ion-exchange
resin in the water softener.
[0012] However, all of the systems described above have drawbacks
and difficulties. For example, the variable factors, such as the
degree of electrolysis in the electrolytic cells, the concentration
of dissolved salts and minerals and the flow rates, the
fluctuations in electricity supply, ambient temperature and the
variability of incoming water supplies present a barrier to
ensuring a consistent supply of sterilising or, more correctly,
biocidal solution. Thus in order to ensure delivery of a biocidal
solution, the electrochemical systems described all rely upon
expert intervention to calibrate the cells at the time of
installation and to re-calibrate whenever the chemistry of the
water supply changes to any significant degree.
[0013] As an illustration, the pH of the solution output from the
anode chamber (anolyte) may be regulated by adjusting the flow rate
of catholyte drained from the cathode chamber. This results in
changes to the anolyte flow rate and consequently in changes to the
electrochemistry taking place in the electrolytic cell.
[0014] Also, the performance of all the above cells and methods is
highly dependent on the alkalinity of the water and aqueous salt
solutions being treated. In Europe, for example, the alkalinity of
potable water can vary from very low (3-15 ppm CO.sub.3 as
CaCO.sub.3) to very high (470 ppm CO.sub.3) from one geographical
region to another. This means that a cell which is calibrated to
produce a biocidal solution of given composition in a first
geographical location may not produce the same biocidal solution in
a second location, making re-calibration necessary. This is a
time-consuming and laborious task.
[0015] Minimising variation is important to ensure a supply of
solution having the required properties, e.g. biocidal activity and
pH, especially when thorough sterilisation is required to maintain
the health of a population.
[0016] Furthermore, it is important to be able to control to a fine
degree the final composition of any biocidal solution produced,
since the solution must have a high enough concentration of, say,
available free chlorine (AFC) to be sufficiently biocidal, but not
so high as to corrode or otherwise damage any equipment which is
being sterilised. A still further disadvantage of the apparatus
described in the prior art is that they are prone to a high level
of wastage. Up to half of the initial supply of aqueous salt
solution may be discarded after being passed through the cathode
chamber. This is especially pertinent where resources such as water
are limited or costly.
[0017] In the Applicant's experience, none of the above systems is
suited to providing a wholly reliable or autonomous supply of
biocidal solution. As will be readily appreciated, a "sterilising"
solution which does not meet the required level of biocidal
efficacy carries a risk of allowing an instrument to spread
infection. Moreover, the end user will not be able to detect by
visual inspection alone whether the biocidal solution from any one
of these systems is within or outside specification.
SUMMARY OF THE INVENTION
[0018] Accordingly, the main object of the present invention is to
provide a system which delivers for use a biocidal solution only
when it has the desired properties, i.e. it is within
specification. In this way, the risk of mistakenly using a solution
which is not adequately biocidal can be substantially
eliminated.
[0019] There is also a need to provide a system which not only is
capable of producing a biocidal solution in specification but also
on demand. Moreover, there is a further need to provide a system
which is able to deliver a biocidal solution in specification, on
demand, at or close to where the solution is to be used. In
addition, there is a need to provide a system which can operate
irrespective of the parameters of the local source of input water.
Ultimately, the Applicant has set out to achieve a system which is
able to deliver biocidal solution in specification, on demand, on
site, anywhere.
[0020] To this end, and as a result of extensive trials and
experiments, the Applicant has devised a system which, by virtue of
various innovations, ensures that it will deliver biocidal
solutions which are within specification. As will become apparent,
the Applicant has also devised a system which is able to produce in
specification biocidal solution on demand, on site, anywhere.
[0021] From one aspect, the invention resides in a method of
operating an electrochemical cell to produce an output solution
having a predetermined level of available free chlorine, comprising
applying a substantially constant current across the cell between a
cathode and an anode and passing a substantially constant
throughput of chloride ions through the cell.
[0022] In this regard, the Applicant has surprisingly found that by
maintaining these two constants, the output solution will have a
predetermined level of available free chlorine irrespective of
other variables such as local water hardness, alkalinity, pressure
etc. In this way, reliance on expert intervention whenever the
water supply chemistry changes significantly may be substantially
reduced or even eliminated entirely.
[0023] Expressed in another way, the present invention resides in a
method of electrochemical treatment of an aqueous solution in an
electrolytic cell, wherein an output solution having a
predetermined level of available free chlorine is produced by
applying a substantially constant current across the cell between a
cathode and an anode while passing a substantially constant
throughput of chloride ions through the cell.
[0024] The level of available free chlorine will be set according
to the biocidal properties which are required to be imparted to the
output solution. The output solution will preferably be required to
act as a biocide against a wide range of bacteria, fungi, viruses
and spores. An available free chlorine content of about 3 ppm to
300 ppm will generally provide biocidal properties for most
envisaged applications. It will however be appreciated that
biocidal efficacy is also dependant on pH and therefore that an
appropriate balance must be achieved between pH and AFC in order to
provide the desired level of bio-compatibility and materials
compatibility. For example, the Applicant has found that a level of
available free chlorine of approximately 100-250 ppm at a pH of
between about 5 and 7 is particularly suitable for the application
of reprocessing heat sensitive medical instruments. Other
applications, such as its use in non-medical environments, for
example as in the processing of poultry and fish and general
agricultural and petrochemical uses, the breaking down of bacterial
biofilm and water treatment, may demand different levels of
available free chlorine.
[0025] As will be discussed hereinafter, the Applicant has found
that by using a particular cell and flow arrangement, it is
possible also to control the pH of the output solution. Where pH
control is required, it is preferable that the electrochemical cell
comprises two chambers separated by a separator, the first chamber
comprising an anode chamber and the second comprising a cathode
chamber.
[0026] It will be generally understood that the function of a
separator in the cell is to isolate the solution in one chamber
from the solution in the other chamber while allowing the migration
of selected ions between the chambers and the term "separator" as
used herein should be construed accordingly. Semi-permeable
diaphragms and ion-selective membranes are the most common forms of
known separators.
[0027] In an electrochemical reaction, it is known that the rate of
reaction is generally directly proportional to current within
certain limits of the current. Therefore, the current (and thus the
rate of oxidation of chloride to chlorine) and flow of chloride
through the cell may be set appropriately to produce an output
solution having the predetermined level of available free chlorine.
The desired current will depend not only on the type of cell being
used, for example, the material from which the electrodes are made
and the various rare metals used to provide active coatings on the
electrodes, but also the size of cell, for example, for a cell
having an anode surface area of approximately 100 cm.sup.2, an
applied current between cathode and anode of 8 Amps is particularly
suitable.
[0028] In general, the voltage will change as the resistance of the
electrolytic cell changes, for example, through deposition of scale
in the separator. Accordingly, if the voltage, but not the current,
is kept constant, the resistance in the cell will increase as the
cell is used. In accordance with Ohms Law, the current will drop
and therefore the concentration of available free chlorine in the
output solution will fall. This will result in an output solution
which may not have sufficient available free chlorine to enable it
to act as a biocide. Therefore, previous systems, such as that
described in WO 98/13304, which have relied on a constant voltage
across the cell are not always able to produce a predictable level
of available free chlorine. In other words, with constant voltage
systems, the biocidal properties of the output solution cannot be
guaranteed.
[0029] However, the Applicant has appreciated that under conditions
of constant current, the voltage across the electrolytic cell can
be monitored usefully to provide an indicator of other parameters,
such as the performance of the apparatus used to carry out the
method. For example, as described above, the voltage across the
cell will change as the separator becomes plugged with deposits.
Also, the voltage will alter as the active coating on the
electrodes decreases or a catastrophic event, such as rupture of
the separator, occurs in the cell. In this way, monitoring of the
voltage provides a means for predicting the longevity of the
cell.
[0030] In order to achieve a constant chloride ion throughput, it
is advantageous to control the flux of chloride ions into the cell.
For convenience, the chloride ions are supplied to the cell as a
saline solution. Therefore, the throughput of chloride ions through
the cell may be determined by controlling salinity and flow
rate.
[0031] While it is envisaged that the saline solution may be of
variable concentration and therefore the flow rate must also be
varied to provide a constant chloride feed into the cell, by
supplying the saline solution at a substantially constant
concentration, only relatively minor changes in flow rate need be
made to provide the constant chloride ion throughput.
[0032] Desirably, the substantially constant chloride ion
throughput is achieved by providing a substantially constant
salinity at a substantially constant flow rate. In this way, the
quality of the input, in terms of the desired concentration of
chloride ions supplied to the cell, is easier to predict and
control. A further advantage of aiming to provide a constant
salinity is that, should any significant changes in salinity be
detected, this may be correctly attributed to an error such as a
malfunction of the apparatus or loss of the saline supply. In these
circumstances, a failsafe mechanism which is preferably
incorporated in the system can operate to prevent output solution
which does not meet the desired level of biocidal efficacy, i.e. is
out of specification, from being dispensed.
[0033] Constant salinity may be achieved by a variety of means, for
example by dissolving a known quantity of salt in a known quantity
of water. However, this requires a level of skill as well as a
knowledge of local water parameters to ensure that the exact amount
of salt is added to produce the desired salinity. Accordingly, the
Applicant has devised a method of producing a desired salinity
which avoids these drawbacks.
[0034] In particular, and after much experimentation, the Applicant
has found that the chloride input to the cell can be more easily
regulated by producing a saline solution from a saturated salt
solution, or at least a concentrated salt solution, which is then
diluted to the required degree. Preferably, the concentrated salt
solution is obtained by adding an excess of salt to water, with
further water and/or salt being introduced as required.
[0035] More especially, by dispersing discrete volumes of
concentrated salt solution into a flow of diluent, the cell can be
fed with a substantially constant chloride concentration at a
constant rate. The Applicant has found that a saline solution
diluted to a concentration of less than 1% w/vol, more preferably
in the region of 0.3%, is particularly suitable. The preferred
concentration will however be determined according to a number of
factors specific to the electrolytic cell being used and the type
of output solution desired.
[0036] It is preferred if the concentrated salt solution is pulse
fed into a flow of diluent water, for example by means such as a
peristaltic pump. In this way, each pulse is directed to deliver a
known quantity of concentrated salt solution. Accordingly, as the
concentrated salt solution becomes more dilute, for example as the
supply of salt is depleted, the pulsing rate of the concentrated
salt solution into the water flow is increased.
[0037] The Applicant has found that benefits are achieved by
periodically allowing the concentrated salt solution to become
increasingly dilute. By such means, deposits of crystalline salt in
the apparatus in which the concentrated salt solution is prepared
are reduced.
[0038] After the concentrated salt solution has been dispersed in
the water, it is further preferred that the salinity is confirmed
before entry into the cell, for example, by measuring the
conductivity of the saline solution. Advantageously, this is
achieved by way of a conductivity probe.
[0039] If the conductivity does not fall within the desired range,
means for adjusting the salinity to return the conductivity to
within the desired range may be provided. This can be achieved by
increasing or decreasing the pulse rate to raise or lower the level
of concentrated salt solution being fed into the water flow.
Alternatively or in addition, means to adjust the flow rate of the
water to the cell may be provided. In this way, namely adjustment
of the pulses and/or the flow rate, fluctuations in the chloride
concentration reaching the cell may be substantially evened
out.
[0040] Simply pulse feeding discrete volumes of concentrated salt
solution into a flow of water diluent can result in a stream of
saline solution of variable chloride concentration. For example,
the saline concentration may have peaks and troughs along the
stream corresponding to the pulses of concentrated salt solution.
If the saline solution is not a substantially uniform mix, the
conductivity of the solution, if measured prior to entry into the
cell, may not be representative of the actual chloride ion content
of the saline solution as a whole. Accordingly, it is another
object of the invention to provide a means for achieving rapid and
effective mixing of the concentrated salt solution in the water
diluent.
[0041] To this end, the present invention also resides in a method
of mixing miscible liquids, comprising dispersing one liquid from a
pulsed source into another liquid supplied as a continuous stream,
wherein the pulsed liquid is discharged and dispersed in the
continuous stream through a plurality of apertures along the flow
path to produce a flow of uniformly mixed liquids.
[0042] By dispersing a pulsed liquid into another liquid flow
through a series of apertures, it is possible to minimise
fluctuations in concentration and produce a substantially
homogenous mixture.
[0043] Expressed in another way, the invention resides in a method
of combining at least two liquids, wherein a first liquid is
supplied as a continuous stream and a second liquid miscible with
the first liquid is supplied from a dispenser into which the second
liquid is pulsed and dispersed into the supply stream of the first
liquid through a plurality of apertures in the dispenser thereby to
produce a continuous homogeneous stream of first and second
liquids.
[0044] More particularly, the invention comprises a method of
combining at least two liquids, wherein a continuous stream of a
first liquid is caused to flow through a conduit and a second
liquid miscible with the first liquid is pulsed into a liquid
dispenser located in the conduit and dispersed into the flow of the
first liquid through a plurality of apertures provided in the
dispenser thereby to produce a continuous stream comprising a
homogeneous mixture of first and second liquids.
[0045] Preferably the dispenser is substantially elongate, for
example in the form of a length of tube having an external diameter
less than the internal diameter of the conduit, which itself may
comprise a tube, and has a closed end and an open, feed end. The
volume of second liquid which is pulsed into the first liquid will
be determined by the volume of the dispenser. Moreover, the length
and diameter of the dispenser may be selected to achieve
homogeneity of the mixed first and second liquids according to the
preferred pulsing rate and pulsed volume of the second liquid.
[0046] For maximum effect, the apertures are preferably arranged
substantially evenly both longitudinally and circumferentially of
the dispenser. Conveniently the apertures comprise perforations and
their size may be varied depending on the nature of the first and
second liquids involved, for example, in accordance with their
viscosities.
[0047] By means of the aforementioned mixing method, the Applicant
has found that it is able to deliver a fixed volume of concentrated
salt solution and simultaneously to disperse the said volume in
water to produce a continuous flow of uniformly mixed saline
solution. By such means, truly representative conductivity
measurements of the saline solution can be made prior to entering
the cell.
[0048] The final concentration of the mixed saline solution will be
determined by the volume of the dispenser, the pulsing rate of
concentrated salt solution into the dispenser and the flow rate of
the water diluent. For example, the Applicant has calculated that,
to produce a 0.3% saline solution from a concentrated salt solution
of about 12% w/vol, the dispenser should have a length in excess of
about 0.19 m. Ideally, the perforations in the dispenser have an
inner diameter of approximately 1 mm, and that about ten
perforations are sufficient for this application.
[0049] In a typical system practising the method of the invention,
the concentrated salt solution is preferably pulsed at a rate of
between about 1 to 5 liters per hour and the water diluent is
supplied at a rate of between about 150 to 250 liters per hour to
achieve the target chloride concentration from the dispenser.
[0050] As will be appreciated, the flow rate of the water diluent
will be largely determined by the pressure of the supply and may be
controlled by its back pressure. Alternatively, or in addition
thereto, the water pressure may be regulated by causing the water
to flow through one or more flow restrictors, for example, in the
form of one or more orifices, provided along the diluent flow path.
Ideally, the size of the or each orifice can be increased or
decreased to adjust the flow. In this way, the aperture size of the
or each orifice may be varied appropriately to regulate the pump
output to a constant flow.
[0051] Having now achieved the required salinity, for example by
the aforementioned mixing method, the actual flow of saline into
the cell is then preferably regulated by means of one or more flow
regulators before entry into the cell. Ideally, the saline supply
is split such that a portion is fed to the chamber including the
anode, and the remainder is fed to the chamber including the
cathode. Advantageously, the catholyte feed includes its own
regulator.
[0052] Preferably, a larger proportion of the saline solution is
fed to the anode chamber than is fed to the cathode chamber. The
Applicant has found that a ratio of at least 80% to 20% fed to the
anode and cathode chambers respectively is particularly suitable to
produce a biocidal solution from the anolyte. Moreover, in this
way, the amount of useful product is maximised whilst the amount of
waste is minimised. A particularly preferred feed ratio is 88%
saline solution to the anode to 12% to the cathode.
[0053] This parallel input to the two chambers of the cell
represents a further departure from the prior art which describes
the use of series inputs, first to the cathode chamber and then the
anode chamber. Such a dual parallel pass allows for even greater
control and regulation of the composition of the output solution,
thereby substantially ensuring that the final product has the
required biocidal properties.
[0054] As will be understood, the electrochemical process may be
achieved by a plurality of electrolytic cells connected in series
electrically, and in parallel hydraulically. Accordingly,
references herein to an electrolytic cell should be construed as
including a plurality of such cells.
[0055] In summary, by applying a constant current across the cell
and a constant throughput of chloride ions through the cell as
hereinbefore described, it is possible to produce an output
solution from the anode chamber which has sufficient available free
chlorine to impart biocidal properties to the solution.
[0056] Accordingly, the invention may alternatively be expressed as
a method of producing a biocidal solution whereby water and aqueous
salt solution are mixed to provide a saline solution of constant
concentration which is passed through an electrolytic cell at a
constant flow rate, and a constant current passed through the
saline solution in the cell to produce an output solution having a
desired level of available free chlorine.
[0057] As previously mentioned, the biocidal efficacy of the output
solution, and in particular the anolyte which provides the source
of available free chlorine, is strongly dependant on its pH. It is
therefore advantageous to tailor the final pH of the anolyte to
suit the desired end use. For example, and as described in the
Applicant's copending United Kingdom patent application no.
9919951.5, a pH of about 5 is suitable for use in treating venous
leg ulcers to reduce bacterial infection, while a pH of between 5
and 7 is more suitable for use in the disinfection and
sterilisation of heat-sensitive endoscopes. To avoid deterioration
of pH-sensitive material, a neutral pH of about 7 may be
appropriate. Accordingly, the method of the invention preferably
further includes adjusting the pH of the output solution which in
turn requires the pH of the anolyte to be monitored.
[0058] Altering the pH of the output solution may conveniently be
achieved by feeding at least part of the catholyte to the anolyte.
The catholyte may be fed to the anolyte either upstream or
downstream of the cell. Preferably, at least part of the catholyte
is recirculated into the anode chamber. The proportion of catholyte
which is fed to the anolyte depends on the final pH required and
may be determined by routine investigation. Accordingly, the method
of the invention preferably also includes regulating the proportion
of catholyte fed to the anolyte.
[0059] A further benefit achieved by recycling a proportion of the
catholyte is the reduction of the actual amount of catholyte which
goes to waste. This is especially desirable as the catholyte waste
contains sodium hydroxide. By means of catholyte recirculation, the
Applicant has achieved a reduction in waste to less than 10% of the
total liquid fed into the cell and even this level of waste can be
further substantially reduced. As will be appreciated, cutting the
amount of waste liquid to such levels provides a considerable
advantage where resources such as water are at a premium. Moreover,
by using a by-product of the process to control the pH, the
external supply of another process component which may otherwise be
required to control pH may be avoided.
[0060] Accordingly, and from yet another aspect of the present
invention, there is provided a method of electrochemically treating
a supply of saline solution in an electrolytic cell having an anode
chamber and a cathode chamber separated by a separator, the anode
and cathode chambers respectively being provided with an anode and
a cathode, and each chamber having input and output lines for the
solution being treated, wherein:
[0061] i) saline solution is supplied to the anode and cathode
chambers by way of their respective input lines, at least the
cathode chamber input line being provided with a flow regulator,
and output by way of their respective output lines;
[0062] ii) a substantially constant current is caused to flow
between the anode and the cathode; and
[0063] iii) a proportion of the solution output from the cathode
chamber is recirculated to an input or output line of the anode
chamber by way of a recirculation line.
[0064] This and other aspects of the invention are also disclosed
in the specification of United Kingdom patent application no.
9918458.2, the subject matter of which is incorporated herein by
reference.
[0065] It is believed that the output solution owes its biocidal
properties to the presence of available free chlorine in the form
of oxidising species including hypochlorous acid (HOCl) and sodium
hypochlorite (NaOCl.sup.-). Such reactive species have a finite
life and so, while the pH of the output solution will usually stay
constant over time, its biocidal efficacy will decrease with
age.
[0066] While the output solution will therefore have the desired
biocidal efficacy on production, there is a risk that it will fall
outside the required specification if stored for any period of time
rather than being used immediately. As a further safeguard
therefore, the method of the present invention further includes
disposing of the output solution after a period of time. In this
regard, the Applicant has found that the output solution generally
maintains a sufficient level of biocidal efficacy for a period of
more than twenty four hours. However, to be certain that the output
solution is sufficiently biocidal, the method includes disposing of
unused output solution if not used within about twenty four hours
of its production.
[0067] The Applicant has found that dilution of the output solution
produces a bacteria-free water which retains a measure of the
biocidal properties of the output solution. Such bacteria-free
water has a number of applications including the rinsing of
heat-sensitive medical instruments following disinfection or
sterilisation and the rinsing of glassware in sterile laboratory or
pharmaceutical manufacture applications. New standards are
continually being applied to such rinsing agents and the Applicant
considers that the properties of the output solution produced in
accordance with the present invention, when diluted, provide an
effective bacteria-free water (hereinafter referred to as
bacteria-free rinse water merely to distinguish it from the neat
output solution), which exceeds the required standards.
Advantageously, therefore, the method according to the invention
further includes the step of diluting the output solution to
produce a bacteria-free rinse water.
[0068] The Applicant believes that, to ensure the biocidal efficacy
of the bacteria-free rinse water, the output solution used to make
up the rinse water is preferably not more than about three hours
old. In accordance with various failsafe provisions in the
preferred method of the invention, any output solution which is
detected to fall outside the required specification is generally
discharged to waste regardless of its age. However, for the
purposes of bacteria-free rinse water, even "in specification"
output solution will not be used to generate bacteria-free rinse
water if it is more than the desired maximum age.
[0069] In order that only the most freshly produced output solution
is used to prepare bacteria-free rinse water, it is preferred that
output solution emerging from the cell is fed into an intermediate
holding location, for example in the form of a first holding means,
from which output solution can be drawn for preparation of
bacteria-free rinse water. Any output solution which is not used to
prepare bacteria-free rinse water is passed into a further holding
location, for example in the form of storage means.
[0070] For convenience, the output solution may be initially held
in the intermediate holding location and from where it is permitted
to overflow into the further holding location after a predetermined
volume of output solution has been produced. More conveniently, the
further holding location may be located beneath the intermediate
holding location such that output solution spills directly into it
from the intermediate holding location. Ideally, the intermediate
holding means comprises a weir tank from which output solution may
overflow into a storage tank. To save space and to reduce any risk
of external contamination, the weir tank is preferably housed
inside the storage tank.
[0071] The weir tank provides an ideal location at which to check
or confirm that the output solution has the desired parameters.
Thus, the weir tank is preferably provided with means to measure
redox potential and pH. If the measurement shows that the output
solution entering the weir tank falls outside the required
specification, the entire contents of the weir tank are preferably
diverted to waste thereby avoiding contamination of the second,
storage tank and its contents, and avoiding the risk of preparing
rinse water from a bad solution. In any event, it is desirable that
the contents of the storage tank are disposed of if it contains
output solution which has been held for more than about twenty four
hours. Furthermore, to ensure that bad output solution entering the
weir tank does not accidentally spill over into the storage tank,
it is desirable that the flow rate of output solution to waste is
faster than its flow rate, or rather its overflow rate, into the
storage tank.
[0072] The intermediate holding location is preferably open to the
atmosphere thereby to reduce the back pressure that may be exerted
on the cell and to which the cell is known to be sensitive. In this
regard, a weir tank again provides a particularly suitable
option.
[0073] It is preferable that the intermediate holding means such as
the weir tank is of sufficient capacity to meet a typical demand
for bacteria-free rinse water from output solution, whilst at the
same time minimising the volume which would be wasted should the
output solution fall out of specification. As will be understood,
the ideal capacity will depend on the desired output of the
machine.
[0074] A further advantage of using a tank, such as a weir tank, as
the intermediate holding means, is that it provides a known
capacity into which additional reagents may be added to the output
solution contained therein. For example, it is highly desirable to
add a corrosion inhibitor to the output solution to prevent
corrosion, not only of the apparatus used to generate and dispense
output solution, but also the items exposed to biocidal solution
during sterilisation and disinfection.
[0075] Accordingly, the method according to the invention
preferably further includes the step of adding a corrosion
inhibitor to the output solution. More preferably, the corrosion
inhibitor is added after the output solution has been confirmed to
have the desired parameters and prior to dispensing. In this way,
corrosion of any apparatus or equipment which is contacted by the
output solution is reduced or substantially eliminated.
[0076] It is however important that any corrosion inhibitor added
to the output solution does not significantly affect the biocidal
properties. Moreover, it is also important that the non-toxic,
non-hazardous properties of the biocidal solution are not
compromised. In this regard, a preferred corrosion inhibitor
comprises a combination of a polyphosphate with a molybdate, more
preferably a mixture of sodium hexametaphosphate and sodium
molybdate.
[0077] For convenience, it is desirable to be able to produce
output solution on demand, at or close to where the solution is to
be used, such as in a hospital. In this way, the need to transport
output solution, for example in bottles, to where the solution is
to be used may be avoided. In other words, the method of the
invention preferably allows for the output solution to be dispensed
directly for use.
[0078] While the output solution may be dispensed directly for use
from the cell if there is an immediate need for the solution, it is
also desirable to allow for output solution and, if produced,
bacteria-free rinse water to be stored until required. As will be
appreciated, the capacity of any such storage means will generally
be determined according to the required end use and level of
demand. Clearly, these storage means will generally have a greater
capacity than the intermediate holding means or weir tank. For
example, the Applicant has found that a storage capacity of about
90 liters is sufficient to supply a demand from several typical
washer-disinfecter machines which require filling in the shortest
possible time. Such washer-disinfecter machines are frequently used
for the sterilisation of medical instruments, such as endoscopes.
Furthermore, the volume of output solution produced will be
determined by the number of electrolytic cells utilised and
therefore the capacity of the storage means should ideally be
sufficient to cope with this volume. In this regard, it has been
found that eight cells connected hydraulically in parallel are
together capable of a production volume of approximately 200 liters
per hour.
[0079] A still further advantage is seen if the volume of output
solution and/or bacteria-free rinse water stored is sufficient to
facilitate the required dispersion of any additives, such as
corrosion inhibitor, to the solutions.
[0080] As a further safety mechanism, it is highly desirable for
the system producing the output solution to be self-monitoring. In
this way, should any parameters, such as process or materials
parameters, be detected to fall outside desired values, or any
rapid or unexpected changes be detected, the system can be alerted.
For example, measurements may indicate that more raw materials are
required or that there is a fault in the production process. By
incorporating self-monitoring in conjunction with an alert
mechanism, the risk of generating a volume of output solution which
is out of specification may be substantially reduced.
[0081] Advantageously, the system incorporates a self-alert
mechanism which is preferably adapted to trigger a self-correction
action and/or to notify a user of the system that there is a fault
or demand. However, auto-correction, where possible, is preferred
before an alarm is raised. For example, self-adjustment of flow
rates may be all that is required to cope with fluctuations in
local water pressure and alkalinity, whereas a disruption to the
supply of input water may not necessarily be susceptible to
auto-correction. As a yet further safety precaution or failsafe, it
is preferred that production of output solution be stopped should
self-correction not be possible or there be no response to an
alarm. In this way, the possibility of dispensing output solution
which fails to meet the desired parameters can be substantially
avoided.
[0082] From another aspect, it is desirable if the system allows a
user to interact with the production process, such as to obtain
information on the performance of the system. Such interaction
ideally allows the user to confirm that the production process is
functioning properly and, if not, provides the user with guidance
as to what action(s) can or should be taken to remedy any faults or
deficiencies. Of course, any system faults or deficiencies which
are not susceptible to auto-correction are likely to have been
brought to a user's attention already by way of an alarm. In
circumstances where faults or deficiencies are not easily remedied
by the user, or where an indication is provided that the system
will require servicing, the user may be prompted to call an
expert.
[0083] However, it is useful to permit a user to interact with the
system other than under alarm conditions, for instance to enable
the user to ascertain whether or not there is sufficient output
solution and/or bacteria-free rinse water to meet anticipated
demand, to advise the user to wait for sufficient output solution
to be generated, or to add salt and/or water. In addition, the user
may be provided with information as to cell performance and/or its
predicted lifespan thereby enabling the cell to be replaced at a
convenient time, rather than having to react to a cell failure.
[0084] It will be appreciated that the user interface may be
governed by computerised means, for example, with provision of
suitable firmware and software. Typically, the system may be
microprocessor controlled with the interface ideally provided
through a display, keypad and/or printer means to provide on-site
control.
[0085] While it is preferred that the process by which output
solution is produced is self-adjusting, in the event that a fault
cannot be rectified by self-adjustment, it is advantageous if
self-diagnostic means are provided to identify where possible the
nature of the fault. Accordingly, it is preferred that the system
of the invention further includes a service interface, through
which an engineer may gain access to diagnostic information prior
to taking remedial action. As with the user interface, the service
interface will also be governed by suitable software.
[0086] For flexibility and convenience, it is preferred that
service interface be accessed either on-site or remotely via a
modem or the Internet. An advantage of permitting remote access is
that an engineer may check the apparatus on a regular basis without
having to travel to the site of the apparatus. This is of
considerable benefit when the system has been installed in a far
location.
[0087] The service interface may also be adapted to provide a
history of the production process, for example how the production
process has functioned over a period of time and hence to ascertain
the remaining life expectancy of a particular component. Also the
consumption of output solution can be monitored periodically.
Different levels of access to the service interface may be
provided, for example access to the production process history may
be restricted to engineering personnel.
[0088] A further advantage is seen if a system engineer is provided
with means to alter operating parameters remotely where possible,
thus reducing the necessity for the engineer to attend the system
if the process requires only minor adjustment. Also, this enables
the engineer to monitor the system to keep it working smoothly.
Indeed, by facilitating remote access, it is possible for an
engineer to make adjustments to the system well before any alert
mechanism is triggered. In such a way, intervention by the user can
be kept to a minimum. Indeed, under typical conditions, a user may
be required only to feed the system with salt at appropriate
intervals, as any other controls or adjustments are made by the
system itself or remotely through the service interface.
[0089] If remote access is provided via the Internet, for example,
it is envisaged that such access may also include means by which
the system can alert an engineer of a problem, for example, by
e-mail, so that the apparatus may be attended to before a
potentially more serious fault occurs. It is also possible to alert
an engineer by fax, short message service (SMS) or other such
means. All of these service interface features can help to reduce
downtime of the apparatus and facilitate siting of apparatus in
diverse locations.
[0090] All of the aforementioned features contribute to providing a
system which delivers, for use, an output solution which has
sufficient available free chlorine to impart biocidal properties to
the solution. In other words, and by means of the various
self-checking and alert mechanisms, it will be appreciated that the
system is adapted to prevent output solution which is not within
specification from being dispensed.
[0091] From another aspect, the present invention resides in
apparatus for producing an output solution having a predetermined
level of available free chlorine comprising an electrolytic cell,
means for passing a saline solution having a substantially constant
chloride ion concentration through the cell, means for applying a
substantially constant current across the cell and means for
dispensing output solution from the cell.
[0092] As will be appreciated, by means of such apparatus, it is
possible to produce an output solution having biocidal properties
almost anywhere where there is a supply of process water, salt and
electricity.
[0093] Preferably, the apparatus is provided with water input means
including a supply tank for storing and dispensing process water.
Since pressure from a local water source may vary, such a supply
tank compensates for any fluctuations and thereby acts as a
hydraulic capacitor. Conveniently, the supply tank is of sufficient
capacity to cope with any such fluctuations. A further advantage of
storing process water is that the supply tank provides a `reserve`
supply of water to the process, should the local supply be
disrupted for any reason.
[0094] The means for generating saline solution having a
substantially constant chloride concentration preferably comprises
salt input means, water input means, means for dissolving salt in
water to produce a concentrated salt solution, means for mixing and
diluting the concentrated salt solution to a desired concentration
and means for feeding the resulting saline solution to the
electrolytic cell at a regulated rate.
[0095] It is preferred that the salt input means comprises a chute
which ideally holds a known quantity when filled to a predetermined
level and which transfers salt to a concentrated salt solution
make-up tank. For example, the Applicant has found that about 6 kg
of salt is convenient because this corresponds to an easily-handled
amount and, under typical operating conditions, provides an
adequate supply of salt to the apparatus for a period of, say, two
days.
[0096] Salt is generally dissolved in water from the input means to
produce a concentrated salt solution in the make-up tank. Following
an input of fresh salt, the solution may at least initially be a
saturated salt solution. A level detector may be provided in the
make-up tank to provide an indication when the salt level is
insufficient to produce a concentrated saturated solution. Such a
detector is preferably linked to an alert mechanism, such as a
visual or audible alarm, which is activated to advise a user that
more salt is required. Moreover, the apparatus is preferably
provided with a mechanism designed to halt production of output
solution if the alarm is not responded to within a specified time
period.
[0097] The concentrated salt solution is diluted with process water
to the desired concentration. As previously described, this is
preferably achieved by pulse feeding concentrated salt solution,
for example using a peristaltic pump, from the make-up tank into a
flow of process water supplied by the supply tank via a dispenser.
The dispenser may be provided with a series of apertures thereby
ensuring that the pulses of concentrated salt solution are
substantially evenly dispersed in the process water. By these
means, a saline solution of a desired concentration may be
produced.
[0098] Moreover, to confirm the concentration of chloride ions in
the resulting saline solution, a conductivity probe or any other
suitable measuring means is conveniently provided before the
solution enters the cell. If the chloride ion concentration as
measured does not fall within the desired range, the pumping rate
of the saturated salt solution and/or the process water may be
adjusted by feedback means from the conductivity probe.
Additionally, one or more flow regulators may be provided as a fine
tuning mechanism for the saline solution entering the cell.
[0099] Having confirmed the conductivity and regulated the flow
accordingly, the saline solution is fed into an electrolytic cell.
Electrolytic cells for producing biocidal solutions are of course
known and preferably comprise co-axial cylindrical and rod
electrodes separated by a separator, such as a semi-permeable or
ion-selective membrane. Usually the electrodes are made of
titanium, and the anode is provided with an active metal oxide
coating. Generally, the cylindrical electrode is connected to the
positive output of a current source, and the rod electrode is
connected to the negative output, but a reversal of this
arrangement is also known.
[0100] While such known cells may be used in the system according
to the present invention, the Applicant has developed a new cell
which is particularly suitable. From another aspect therefore, the
present invention comprises an electrolytic cell having an anode
chamber and a cathode chamber separated by a separator, the anode
and cathode chambers respectively being provided with an anode and
a cathode, each chamber having at least one input and output,
wherein the separator is in the form of a semi-permeable membrane
comprising an aluminium oxide based ceramic containing zirconium
oxide and yttrium oxide.
[0101] As will be understood, it is a desired function of the
separator that it be sufficiently permeable to permit an adequate
flow of solution between the two chambers to give an acceptable
electrical resistance while being sufficiently non-permeable to
prevent gross mixing of the anolyte and catholyte solutions. In
this regard, the Applicant has found that a ceramic comprising up
to 20% zirconium oxide and up to 2% yttrium oxide satisfies this
function. More desirably, the ceramic consists essentially of 80%
aluminium oxide, 18.5% zirconium oxide and 1.5% yttrium oxide. The
porosity of the ceramic is preferably within the range of 50-70%
and the pore size between 0.3-0.5 microns. Furthermore, the ceramic
preferably has a wall thickness of 0.3-1.0 mm.
[0102] A particularly suitable ceramic membrane composition and its
method of manufacture is disclosed in the specification of the
Applicant's own co-pending United Kingdom patent application no.
9914396.8, the contents of which are herein incorporated by
reference.
[0103] Alternative separation means may be provided by an
ion-selective membrane comprising a perfluorinated hydrocarbon
containing sulfonate ionic groups having channels which permit the
passage of cations only through the membrane, for example, the
membranes sold by DuPont under the trade mark Nafion.RTM.
[0104] As with the known cells referred to, the electrolytic cell
advantageously comprises co-axially arranged cylindrical and rod
electrodes, preferably with the cylindrical electrode forming the
anode and the rod electrode forming the cathode. Preferably, the
cathode has a uniform cross-section along its effective length.
[0105] Moreover, the anode is preferably formed from titanium, and
desirably includes an electrocatalytic (active) coating for the
oxidation of chloride ions, for example mixtures of any or all of
ruthenium oxide, iridium oxide, and titanium oxide.
[0106] The electrolytic cell may alternatively be of a filter-press
type design, with flat electrodes separated by an ion-selective
membrane, such as that previously referred to and sold under the
trade mark Nafion.RTM.. However, such a cell is less preferred than
the cylindrical and rod electrode type.
[0107] As previously described, the electrolytic cell preferably
includes separated anode and cathode chambers, and saline solution
is fed into both chambers simultaneously with a constant current
applied between the electrodes. Output solution is passed from the
anode chamber to dispensing means while the catholyte is either
directed to waste or a portion thereof recirculated into the anode
chamber.
[0108] The dispensing means preferably comprises one or more
storage tanks. However, in view of the desirability to use only the
output solution which has been produced within a preferred time
period, as described above, the Applicant has devised an
arrangement of storage tanks which allows for this. Accordingly,
the output solution is preferably fed into an intermediate holding
tank, such as a weir tank, before it is transferred to one or more
main storage tanks.
[0109] In order to confirm that output solution entering the
intermediate tank has the desired characteristics, quality control
means such as redox and pH probes maybe incorporated to provide
data on the output solution as it enters the tank. The intermediate
tank may be further provided with discharge means to divert output
solution, which does not fall within the specification, to waste.
Other means may also be provided to feed in-specification output
solution from the intermediate tank to a storage tank from which
the solution may be dispensed for use and/or dispensed to a yet
further storage tank where it may be diluted to produce
bacteria-free rinse water.
[0110] When charged to a predetermined level and having had its
redox potential and pH confirmed as falling within specification,
the weir tank allows output solution to overflow into the main
storage tank.
[0111] As will be appreciated, gases such as hydrogen and chlorine
are generated by the electrochemical reaction in the cell. Since
these gases are potentially dangerous and the chlorine itself
malodorous, it is highly desirable that these gases be removed from
the output solution before it is dispensed for use. Preferably, the
gases are vented from the output solution through one or more
filters. Ideally, a filter, such as a carbon filter, is located to
catch such gases from the output solution in the weir and/or other
storage tanks, such as the bacteria-free rinse water storage
tank.
[0112] For most applications, the apparatus as described is
preferably housed in a self-contained unit. However, it may
alternatively be provided in a modular format, for example so that
it may be constructed on site within the restrictions of the
available space. For ease of assembly and maintenance, and whether
a self-contained or modular format, connections between the
components of the apparatus are most conveniently provided in the
form of rigid pipes. The pipes may be connected to the components
and/or each other by means of universal joints or threaded
connections. Accordingly, when one or other of the components is
replaced or removed for maintenance, the need to use tools such as
spanners may be substantially avoided.
[0113] In assembling the individual components to form the
apparatus, the Applicant has done far more than simply arranging
the components in such a way as to accommodate them in a convenient
housing. In particular, the Applicant has expended much time and
effort to achieve an assembly which provides both practical and
technical benefits. For example, the Applicant has arranged the
components so that the various pumps are located at a low level
within the apparatus thereby not only lending stability to the
apparatus but also helping reduce vibration of the apparatus caused
by operation of the pumps. Similarly, location of the process water
supply tanks and the concentrated salt solution make-up tank at a
low level provides further stability. Low level location of the
saturated salt solution make-up tank is also particularly
convenient as it provides for feeding from the salt chute at a
comfortable height.
[0114] Furthermore, it has been found that by locating the
electrolytic cell at a level which is higher than the
aforementioned input tanks, back pressure on the cell is
substantially avoided. Moreover, since the electrolytic cell is at
a relatively high level, this makes it possible for output solution
to be transferred to one or more storage tanks also at a high
level. In this way, dispensing of the output solution from the or
each storage tank, either as neat biocidal solution or as
bacteria-free rinse water can be achieved by gravitational feed.
However, where it is required to dispense a large volume of
solution over a short period of time, for example, as required to
fill a washer-disinfecter machine, gravitational feed alone may not
be sufficient and so it is advantageous if the output lines also
include pumping means.
[0115] As will be appreciated, it is highly desirable for the
carbon filter to be located at a high level with respect to the
apparatus. In this way, it is possible to maximise the collection
of gases generated by the electrochemical reaction and to minimise
the risk of exposing personnel to those gases.
[0116] Means to detect any leakage of liquids from the apparatus
may also be included, such detection means advantageously being in
communication with the user and or service interface so that
remedial action may be promptly taken. Ideally, the user/service
interface will provide information as to the source of the leak.
Leak detection means may be conveniently located in a drip tray
positioned at the base of the apparatus.
[0117] In order that the system is not compromised through lack of
cleanliness in the apparatus, it is desirable that it be
self-cleaning, preferably by means of an automatic self-cleaning
cycle. In this respect, it is advantageous if the self-cleaning
cycle is designed to ensure that at least those parts of the
apparatus which may come in contact with output solution are
cleaned. Effectively, this means that various pipes, valves, pumps,
probes, connectors and storage tanks are required to be cleaned.
Since the apparatus is adapted to generate an output solution
having biocidal properties, this solution is ideal to carry out the
cleaning. In this way, the apparatus is also disinfected and
sterilised.
[0118] Accordingly, the method of the invention further includes an
automatic self-cleaning step whereby output solution is
periodically passed through substantially the entire apparatus. As
will be appreciated, because the system operates in such a way as
to prevent output solution which is not within specification from
being dispensed, only output solution which has the required
biocidal properties may be used in the cleaning step.
[0119] To ensure that all surfaces of the storage tanks are
contacted by the output solution during the cleaning process, it is
advantageous if the solution is introduced into each tanks by way
of a spray bar.
[0120] In addition, to minimise downtime of the system, it is
preferred that the operation of the self-cleaning cycle takes place
at a time when the solution is least likely to be demanded, for
example, at night.
[0121] It is a preferred object of the invention that the system
can operate irrespective of local conditions. Since the nature of
water supplies may vary enormously between locations, for example
its supply pressure and temperature, hardness, pH and microbial
count, it is desired to provide a system which can be adjusted to
perform irrespective of these parameters. Accordingly, it is
advantageous if the apparatus includes means to compensate for
parameters which fall outside the preferred operating range.
[0122] For example, variations in water supply pressure can be
compensated for by means of the process water supply tank. A high
microbial count can be reduced by suitable filtration before the
water is allowed to enter the supply tanks, this is especially
pertinent to use of apparatus in developing countries where the
water may be of poorer quality.
[0123] Variations in pH of the supply water may be compensated for
by adjusting the pH of the output solution to the required level by
recirculating a proportion of the catholyte from the cathode
chamber of the cell into the anode chamber. This pH adjustment
process and its advantages have been described above.
[0124] Water hardness may also affect the system, resulting in
deposition of magnesium and calcium ions not only in the supply
tanks, but more seriously, in the cell itself. Such deposition may
cause plugging of the separator which increases the cell resistance
and this in turn increases the wear on the cell. Life-expectancy
and cell efficiency are thereby reduced. Also, the use of
unsoftened water can make it more difficult to control the pH of
the anolyte. Accordingly, it is preferred to incorporate means for
substantially removing the hardness ions from the water supply or
at least reducing the amount of such ions before it passes into the
supply tanks. Such means maybe by way of a suitable water softener,
for example one containing a cation-exchange resin.
[0125] By virtue of the aforementioned features, the Applicant has
devised a new system for generating an extremely effective
non-toxic, biocidal solution which acts against a wide variety of
bacteria, fungi, viruses and spores and is suitable for many
applications including disinfection and cold sterilisation. In
addition, the system can be operated and maintained regardless of
location and requires only water, electricity and salt to be put
into effect. The system can be operated either continuously or in
response to demand and can be adjusted to produce a solution
tailored for a particular end use. Moreover, because of the various
failsafe means it incorporates, it is virtually impossible for an
end user to be provided with a biocidal solution of inadequate
efficacy.
[0126] In summary, the Applicant has invented a system which is not
only adapted always to deliver biocidal solution which falls within
the desired specification, but also to deliver such solution on
demand, on site, anywhere.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
[0127] The foregoing summary, as well as the following detailed
description of preferred embodiments of the invention, will be
better understood when read in conjunction with the appended
drawings. For the purpose of illustrating the invention, there is
shown in the drawings embodiments which are presently preferred. It
should be understood, however, that the invention is not limited to
the precise arrangements and instrumentalities shown. In the
drawings:
[0128] FIG. 1 shows an embodiment of the invention in schematic
outline;
[0129] FIG. 2 is a detailed flow diagram of the invention as
outlined in FIG. 1;
[0130] FIG. 3 illustrates a dispenser in accordance with another
aspect of the invention; and
[0131] FIG. 4 shows an electrolytic cell for use in the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0132] Referring first to FIG. 1, the schematic outline of the
invention is broken down into three main processing stages, namely
an inputs and pre-processing stage, a production stage and a
storage and dispensing stage. While referred to as stages, it will
of course be appreciated that the process of the invention may be
carried out continuously.
[0133] In the first (inputs and pre-processing) stage, there is an
input of potable water which, for the purpose of generating saline
solution for use in the electrolytic cell, is first passed through
a water softener zone where excessive magnesium and calcium ions
are removed. The softened water is then passed into a process water
buffer zone where it is held until required for use in the
production of brine. Potable water input is also passed directly to
the storage and dispensing stage for use in the preparation of
bacteria-free rinse water, but for this purpose there is no need
for the water to be softened prior to use.
[0134] The first stage also includes a salt (NaCl) input, usually
of vacuum dried crystalline salt which is commercially produced to
a consistent standard, to a brine generation zone where a
concentrated salt solution is made up from the salt and the
softened water obtained via the process water buffer zone.
[0135] A further input is provided for additional agents, such as a
corrosion inhibitor, used to condition output solution produced by
the process. The conditioner is passed to a conditioner storage
zone where it is held until required.
[0136] Turning to the second (production) stage, this comprises a
constant salinity subsystem in which a saline solution of
substantially constant concentration is produced by dilution of the
brine from the brine generation zone with softened water from the
process water buffer zone to the desired concentration. The
resulting saline solution is passed from the constant salinity
subsystem to one or more electrolytic cells, each including cathode
and anode chambers (not shown), and across which a substantially
constant electric current is applied. The applied electric current
is maintained constant via an energy control and monitoring
zone.
[0137] Catholyte and anolyte are produced from the cathode and
anode chambers respectively as a result of the electrochemical
treatment of the saline solution in the cells. Anolyte and a
portion of catholyte which is not recirculated to the anode chamber
are both dealt with in the third (storage and dispensing) stage. In
particular, catholyte which is not recirculated is directed to
waste and anolyte, otherwise referred to as output solution, is
passed to a buffer and quality subsystem. The output solution is
tested in the buffer and quality subsystem and, if it fails to meet
the quality standards, it is also directed to waste. If the output
solution falls within specification, a quantity of conditioner,
such as a corrosion inhibitor, is added to it in the buffer
subsystem and the output solution is then permitted to pass either
into an output solution storage zone from where it is subsequently
dispensed for use or into a rinse water subsystem.
[0138] Output solution directed to the rinse water subsystem is
diluted with potable water from the potable water input and is then
passed to a rinse water storage zone from where it is subsequently
dispensed.
[0139] Provision is also made for discharging output solution from
the output solution storage zone and rinse water from the rinse
water storage zone to waste.
[0140] Information on the various processing stages and the ability
to interact with the process is provided by means of a user
interface and a service interface. The service interface also
provides for remote access to the process, enabling an off-site
engineer to obtain information on and make adjustments to the
processing in each of the three stages.
[0141] There is also provided an autoclean subsystem to permit
cleaning of the system, either at regular intervals or whenever
convenient.
[0142] FIG. 2 is a flow diagram or "hydraulic map" showing in more
detail the invention already outlined in FIG. 1. Potable water is
passed through an external water softener containing a cation
exchange resin (not shown) thereby exchanging hardness ions of
calcium and magnesium onto the resin and releasing sodium ions into
the water.
[0143] Incoming softened process water is monitored by a sensor 10.
The sensor 10 ascertains whether the incoming water is at a
temperature within the range under which the process can reasonably
operate, namely between about 5 and 35.degree. C. Other parameters
such as the incoming water's pressure, softness, alkalinity, pH,
conductivity and microbial count can also be monitored by the
sensor 10 to establish that it falls within acceptable levels for
the process.
[0144] If the sensor 10 detects that the properties of the incoming
softened process water do not fall within acceptable limits
required by the specification, the water is diverted through a
waste discharge manifold (not shown) to a drain via valve 12. On
the other hand, if the incoming softened process water is in
specification, it is allowed to flow into internal process water
tank 14 through inlet valve 16 or is diverted via inlet valve 18 to
the concentrated salt make-up tank 20.
[0145] Buffer storage for the process water in the event of a
temporary interruption in the water supply is provided by the
process water tank 14 having a large enough volume. Moreover, the
tank 14 also has sufficient capacity in order to eliminate pressure
fluctuations in the fluid supply to the electrolytic cells.
[0146] The process water tank 14 includes a plurality of level
detectors for monitoring and controlling the process water level in
it. Level detector 22 is a safety device which is activated only
when the process water in the tank reaches a predetermined extra
high level to stop the charging of the tank with process water and
raise an alarm. Another level detector 24 is activated when the
level of liquid in the tank reaches a predetermined high level to
stop further inlet water from entering the tank 14 by closing a
valve 16. Water will begin to re-charge the tank 14 after a
predetermined time has elapsed below the high level. Level detector
26 is activated when the process water in the tank 14 reaches a low
level to prevent production of output solution. The tank 14 also
includes a valve 28 which allows liquid to be drained. Furthermore,
the tank 14 is designed to comply with local regulations, such as
the class A air break requirements as required in the United
Kingdom by Building Regulations Bylaw 11.
[0147] Concentrated salt solution is made-up and stored in a
concentrated salt solution make-up tank 20. To make up the
concentrated salt solution, vacuum dried crystalline salt
(BS998:1990) is added to the tank 20 via a salt chute 21 having a
capacity which is able not only to accommodate a typical salt input
of about 6 kg, but to tolerate an amount of overfilling sufficient
to keep the system supplied for approximately 1 to 2 days at a
normal operation level.
[0148] To monitor liquid levels within the concentrated salt
solution make-up tank 20, level detectors are also provided. Thus,
level detector 30 is a safety device which is activated by an extra
high level of liquid in the tank 20 and acts to close a valve 18 to
prevent overfilling of the tank 20 and to raise an alarm, but will
not halt production of output solution. A level detector 32 is
activated by a high level of liquid in the tank 20 to stop further
water filling the tank 20 by closing the valve 18. A level detector
34 is activated by a low level of liquid in the tank 20 and
operates to open the valve 18 to charge the tank 20 with softened
water. A low level detector 36 is activated by a very low level of
liquid in the tank 20 to halt production of output solution and to
raise an alarm.
[0149] Softened water is fed through the valve 18 and automatically
fills the tank 20 through a spray-bar 38 until the high level
switch 32 is activated. Salt in the tank 20 dissolves in the water
to produce a concentrated salt solution with the level of salt
reducing as more salt is dissolved.
[0150] A further level detector 40, this time for the salt, is
located towards the bottom of the tank 20. The salt level detector
40 is activated when the amount of salt in the tank 20 is depleted
such that it is approaching a level insufficient to produce a
concentrated salt solution. On activation, an alarm is raised which
alerts an operator that more salt is required. The request to add
salt is displayed on the user interface (FIG. 1) and replenishment
of the salt supply in the tank 20 may be carried out manually by an
operator or automatically through a control system. The user
interface is operative to display a suitable message when
sufficient salt has been added.
[0151] Finally, the tank 20 also includes a manual drain valve.
[0152] Concentrated salt solution from the salt make-up tank 20 is
diluted with process water from the process water tank 14 to
produce a saline solution of substantially constant chloride ion
concentration. In more detail, process water is continuously pumped
by process water pump 44 through a valve 46 towards an electrolytic
cell pack and concentrated salt solution is pulse fed into the flow
of process water via an adjustable speed peristaltic pump 48. The
pulses of concentrated salt solution are dispersed into the
substantially continuous stream of process water through a
perforated tube 50 thereby evening out the pulses to produce a flow
of saline solution of uniform concentration.
[0153] The flow rate of the resulting saline solution as it flows
towards the cell pack is monitored by a flow meter 52 and if
necessary is modulated by a flow regulator in the form of an
orifice plate 54. The flow rate is changed simply by changing the
size of the orifice in the plate. Different orifice plates may be
chosen to suit site conditions.
[0154] Prior to entering the cell pack, the concentration of
chloride ions in the saline solution is checked by means of a
conductivity sensor 56. If the conductivity measurement indicates
that the chloride ion concentration has fallen below the desired
level or has risen above it, the pulsing rate of the peristaltic
pump 48 is increased or decreased respectively to alter the amount
of chloride ions being dispersed into the process water through the
perforated tube 50 thereby compensating for the fall or rise in
chloride ion concentration. The size of the aperture in the orifice
plate 54 is also adjusted to regulate the flow of chloride ions
into the cell pack. Adjustment of the pulsing rate and the flow
rate together provide a fine tuning means to ensure that the cell
pack is supplied with a constant chloride ion throughput.
[0155] On the other hand, if the conductivity of the saline
solution as measured by the conductivity sensor 56 falls outside a
predetermined range such that it is not possible to adjust the
pulsing rate and/or flow rate to bring the conductivity within the
required range, and hence make it virtually impossible for the cell
pack to produce output solution having the desired level of
available free chlorine, an alarm is raised and the flow of saline
solution to the cells is ceased pending rectification of the
problem.
[0156] If the saline solution already provides or can be adjusted
to provide the requisite throughput of chloride ions, it is split
into two streams 58, 60 before being fed through the cell pack.
Typically the cell pack consists of eight electrochemical cells,
with two sets of four cells connected hydraulically in parallel.
For simplicity, only one cell is illustrated. However, the number
of cells in the cell pack is determined by the output volume
required from the particular system. Each cell has an anode chamber
62 and a cathode chamber 64 and the flow of saline solution is
split such that the greater portion is fed to the anode chamber 62
and the lesser portion is fed to the cathode chamber 64. In this
embodiment, approximately 90% of the saline solution is passed
through the anode chamber(s) with the remainder passed through the
cathode chamber(s). The flow rate of saline solution through the
cathode chamber is much lower than for the anode chamber and the
pressure in the cathode chamber is also lower.
[0157] As the saline solution flows through the electrolytic cells,
a fixed current of between 7-9 amps (typically 8 A) is applied to
each cell causing electrolysis of the saline solution thereby
generating available free chlorine in the resulting anolyte,
elsewhere generally referred to as the output solution. In order to
produce output solution at a relatively neutral pH, namely between
5 and 7, the pH of the output solution is at least partially
controlled by dosing a portion of the catholyte to the inlet stream
58 for the anode chambers 62. The catholyte is dosed to the inlet
stream 58 by an adjustable peristaltic pump 66 and the dosing rate
is increased or decreased to achieve the target pH. In this way,
the system is also adapted to cope with varying alkalinity of the
input potable water. The remaining catholyte which is not dosed
into the input stream 58 for the anode chambers 62 is directed to
waste, if necessary diluting it prior to disposal.
[0158] Since the flow rate of the saline solution into the cathode
chamber 64 also has an influence on the pH of the output solution,
a flow regulator 68 is provided to control the flow of saline
entering the chamber. The flow regulator 68 can be manually
adjusted if there is a variation in input water quality. Output
solution is fed from the outlet of the anode chambers 62 of the
cell pack into an intermediate weir tank 70.
[0159] The pH and redox potential of the output solution in the
weir tank 70 are measured by a pH meter 72 and a redox probe 74
respectively. If the pH and redox potential do not fall within the
desired parameters, a valve 76 is opened and the contents of the
weir tank 70 are drained to waste. The contents of the tank 70 are
drained to waste in any event if they have remained in the tank for
about three hours. The pH meter 72 is linked to pump 66 to adjust
the level of catholyte dosed to the anode chambers 62 thereby
enabling the pH of the output solution to be adjusted to bring the
output solution within the desired pH range. If the pH and redox
potential of the output solution are determined to fall within the
desired parameters, confirming that the output solution has the
necessary biocidal efficacy, the valve 76 is kept closed and the
output solution is allowed to fill the weir tank 70 until it
reaches a level where it floods over into a storage tank 78. The
weir tank 70 includes a level detector 80 for monitoring when the
level of output solution in the tank falls to a predetermined low
level. When the low level detector 80 is activated, the production
of sterile rinse water is stopped.
[0160] Provided the pH meter 72 and the redox probe 74 confirm that
the output solution has the desired parameters, a corrosion
inhibitor, such as a mixture of sodium hexametaphosphate and sodium
molybdate, is dosed as a solution from a storage container 82 into
the output solution in the weir tank 70 by a peristaltic pump 84. A
sensor 86 is mounted in the storage container to monitor low levels
of inhibitor and trigger an alert mechanism which alerts the system
that there is a need for inhibitor to be supplied to the storage
container 82.
[0161] In specification output solution spills from the weir tank
70 into the storage tank 78 where it remains until a demand for it
is received. For example, when it is required for a cycle of a
washer-disinfecter machine, the system receives a demand signal
from a washing machine interface control module triggering
operation of a dispensing pump 88. Typically, the dispensing pump
88 is rated so that it can supply output solution to three washing
machine vessels of 25 litre capacity in 180 seconds (1500 liters
per hour, 3 bar line pressure). The capacity of the storage tank 78
is therefore such that it too can fulfil the volume
requirement.
[0162] The storage tank 78 includes various level detectors for
monitoring liquid levels in the tank. A level detector 90 is
activated by an extra high level of output solution within the
tank, raising an alarm and stopping production. A level detector 92
is activated before the detector 90 as the volume of output
solution rises in the storage tank 78 and simply stops production.
As the output solution is dispensed and after a period of time
below the level of detector 92, production of output solution is
recommenced. A low level detector 94 is activated when the level of
the output solution falls to a low level, raising an alarm and
preventing further dispensing to the machine.
[0163] A pH probe 96 for monitoring the pH of the output solution
is provided within the storage tank 78 so that if the pH of the
output solution drops out of specification, it is routed to waste
by a valve 98 located on the outlet of the storage tank 78. In
addition, if the output solution has been stored for 24 hours, it
is similarly routed to waste. In this way, output solution which is
out of specification is never dispensed. In order to monitor the
flowrate and amount of output solution dispensed from the storage
tank 78, a flow meter 100 is linked to `no flow` and leak detection
routines within a user/service interface to alert the system, for
example, that the discharge valve 98 is closed during a requested
discharge, or that an unrequested discharge is occurring.
[0164] Since the output solution held in the weir tank 70 is never
more than three hours old, it is used to produce bacteria-free
rinse water. Fresh output solution is dosed at a predetermined rate
from the weir tank 70 to a rinse water storage tank 102 via a
peristaltic pump 104. Filtered potable water flows into the tank
102 through a valve 106 where it mixed with and dilutes the output
solution to a concentration of about 2%. If the local water supply
is of poor quality, a higher concentration of output solution in
the rinse water, for example a 5% solution, is preferred.
Accordingly, the dosing rate of pump 104 is determined by the
incoming potable water supply and is monitored by a flowmeter 108.
Both potable water and output solution are added to the rinse water
storage tank 102 simultaneously and a minimum standing time of two
minutes is always allowed before dispensing the resulting mix. This
ensures sufficient contact time for the output solution to diffuse
in and activate the potable water. Rinse water is stored in the
rinse water storage tank 102 until it is required by, for example,
an endoscope washing machine. A dispensing pump 110 is activated on
receipt of a demand signal from a washing machine interface control
module. As with the dispensing pump 88, the dispensing pump 110 is
similarly rated to meet the demand of filling three washing machine
vessels of 25 liters capacity in 180 seconds (1500 liters per hour,
3 bar line pressure) and the capacity of the rinse water storage
tank 102 is also dictated by this typical demand scenario.
[0165] The rinse water tank 102 is provided with a plurality of
level detectors to monitor levels of rinse water. A level detector
112 is activated when there is an extra high level of rinse water
the tank 102, alerting the system and stopping any further
production of rinse water. Another level detector 114 monitors high
rinse water level in the tank 102 and when activated stops rinse
water production. After a predetermined period of time has elapsed
and when the rinse water level has fallen, the high rinse water
level detector 114 is deactivated and the production of rinse water
is recommenced. When there is only a low level of rinse water in
the tank 102, a level detector 116 is activated raising an alarm
and preventing further rinse water from being dispensed.
[0166] The flowrate and total rinse water dispensed is monitored by
a flowmeter 118, which also is used in `no flow` and leak detection
routines linked to the user/service interface (FIG. 1). By
automatic monitoring of liquid levels in the weir tank 70, the
storage tank 78 and the rinse water tank 102, and by discharging
the output solution and rinse water periodically, the system is
able to self-adjust to allow it to meet demand at all times. Gases
generated by the electrolytic reaction in the cell pack, mainly
hydrogen and chlorine, are vented through a carbon filter located
above the weir tank 70 and rinse water tank 102 to reduce the
quantity of chlorine which escapes.
[0167] The system also includes a drip-tray provided with leak
detection means in communication with the user/service interface
(FIG. 1). The drip tray is a shallow vessel housing two level
detectors 120, 122, one being a low level detector and the other an
extra high level detector. The low level indicator 120 is activated
by any small leak within the machine and activates an alarm when
the liquid level rises above the detector, but does not halt the
production process in any way. However, the extra high level
detector 122 activates an alarm and halts the production and
dispensing of output solution. A manual valve 124 is provided at
the base of the drip tray to allow drainage of the tray.
[0168] To maintain the system properly, it is necessary to
sterilise the storage tanks and discharge lines on a regular,
typically daily, basis. Output solution having the desired biocidal
properties as confirmed by its measured parameters and age is
flushed through the filters, tanks and pipework to eliminate
bacterial growth in these areas. In particular, before the cleaning
cycle is commenced, the output solution tank 78 is replenished to a
high level as detected by the detector 92 ensuring that sufficient
output solution is available for the cycle, and the pH and redox
potential of the output water are confirmed as being within
specification by the pH probe 72 and the redox probe 74. The pH and
redox potential will change during the cleaning process and need
not be monitored once the cleaning process has commenced. On the
other hand, the rinse water tank 102 and the process water tank 14
are drained to low level prior to commencing the cleaning
cycle.
[0169] Output solution from the storage tank 76 is routed via a
valve 126 to fill the process water tank 14 via a spray bar 128.
The spray bar 128 causes the output solution to be sprayed onto the
tank walls throughout the filling process. Once process water tank
14 is full to the predetermined level, the output solution is
pumped by pump 44 through the cell pack into the weir tank 70. The
output solution is then drained to waste via the valve 76.
[0170] When the "cleaning" output solution reaches a low level in
the process water tank 14 as detected by the level detector 26, the
tank 14 is re-filled with output solution via the valve 126. Output
solution is then pumped by the pump 44 from the process water tank
14 and the valve 46 is opened to divert the output solution to the
rinse water tank 102 via a spray bar 130. When the rinse water tank
102 is filled, the tank is held full for about five minutes in
anticipation of a demand to flush the rinse water line. If no
signal is received, the rinse water tank 102 is allowed to drain
along with the process water tank 14 and the storage tank 76.
[0171] FIG. 3 shows a dispenser 200 for uniformly dispersing two
miscible liquids. The dispenser 200 is in the form of an elongate
tube 202 having an open first end 204 and a second end 206 closed
by an end cap 208. The tube 202 is provided with a row of
perforations 210 substantially along its length. In use in the
method of the invention, the open first end 204 of the dispenser
200 is fixed to the end of the feed line for the concentrated salt
solution which is pulse fed from the make up tank 20 (FIG. 2) by
the peristaltic pump 48. The dispenser 200 is located in and
aligned with the flow path of process water which is continuously
pumped from the process water tank 14 by the pump 44. As the pulses
of concentrated salt solution arrive in the dispenser 200, the
solution is forced out through the perforations 210 into the
process water flow. The resulting saline solution is of
substantially homogeneous concentration by virtue of the mixing
pattern achieved by the dispenser 200.
[0172] The dilution of the saturated salt solution is determined by
the length of the dispenser 200, or rather the length over which
the perforations are provided, the pulse rate of the saturated salt
solution and the velocity of the process water.
[0173] FIG. 4 shows an electrolytic cell 300 as used in the present
invention. The cell 300 comprises co-axial cylindrical and rod
electrodes 302, 304 respectively, separated by a semi-permeable
ceramic membrane 306 co-axially mounted between the electrodes thus
splitting the space between the electrodes to form two chambers
308, 310. The cylindrical electrode 302 forming the anode is
typically made from commercially pure titanium coated with an
electrocatalytic (active) coating suitable for the evolution of
chlorine from a chloride solution. The rod electrode 304 forming
the cathode is made from titanium and machined from an 8 mm stock
bar to a uniform cross-section over its effective length, which is
typically about 210 mm.+-0.5 mm. The semi-permeable ceramic
membrane 306 forming a separator and creating the anode and cathode
chambers 308 and 310 is composed of aluminium oxide (80%),
zirconium oxide (18.5%) and yttrium oxide (1.5%), and has a
porosity of about 50-70%, a pore size of 0.3 to 0.5 microns and a
wall thickness of 0.5 mm+0.3 mm/-0.1 mm. The ceramic of the
membrane 306 is more fully disclosed in the specification of patent
application number GB 9914396.8, the subject matter of which is
incorporated herein by reference.
[0174] The cell 300 is provided with entry passages 312, 314 to
permit the saline solution to enter the cell 300 and flow upwards
through the anode and cathode chambers 308 and 310 and is
discharged as anolyte and catholyte through exit passages 316, 318
respectively. The anolyte containing available free chlorine
constitutes the output solution.
[0175] As previously described, in order to provide a useful amount
of output solution within a reasonable period of time, a group of
cells are connected together to form a cell pack. For example, a
cell pack comprising eight cells connected together in parallel
hydraulically and in series electrically is capable of generating
about 200 liters/hour of output solution.
[0176] Although the invention has been particularly described, it
should be appreciated that the invention is not limited to the
particular embodiments described and illustrated, but includes all
modifications and variations falling within the scope of the
invention as defined in the appended claims. For example, means
other than the elongate, perforated dispenser described for mixing
the concentrated salt solution with process water to produce a
homogeneous saline solution may be used. Indeed, the concentrated
salt solution can be continuously fed into a stream of process
water rather than being pulse fed. In addition, while a weir tank
is described as being particularly suitable for providing
intermediate holding means for the output solution, other types of
holding means may be used, such as a more conventional tank having
appropriate outlet means for transferring its contents to the
output solution storage tank. The cell separator can be made of
ceramics other than the aluminium oxide, zirconium oxide and
yttrium oxide ceramic described and of any other suitable
semi-permeable or ion-selective material.
[0177] It will be appreciated by those skilled in the art that
changes could be made to the embodiments described above without
departing from the broad inventive concept thereof. It is
understood, therefore, that this invention is not limited to the
particular embodiments disclosed, but it is intended to cover
modifications within the spirit and scope of the present invention
as defined by the appended claims.
* * * * *