GB2409464A

GB2409464A - Process and apparatus for the preparation of a liquid biocidal medium

Info

Publication number: GB2409464A
Application number: GB0330084A
Authority: GB
Inventors: James Daly
Original assignee: Individual
Current assignee: Individual
Priority date: 2003-12-24
Filing date: 2003-12-24
Publication date: 2005-06-29
Also published as: GB0330084D0

Abstract

A feed liquid is passed through an electrolyser that has at least two electrodes, one of which is an anode and one of which is a cathode, where the cathode and anode are located in separate chambers, and an electric current applied to said electrodes. The liquid medium is created at and collected from the anode chamber. Alternatively, at least part of the feed liquid is caused to flow from the anode chamber to the cathode chamber and the liquid medium can be collected from the cathode chamber (figure 2). A further liquid medium can be produced by mixing the products of the cathode and anode chambers. The liquid media can retain biocidal activity for up to two years.

Description

LIQUID MEDIUM, ITS USE AND METHODS FOR ITS PRODUCTION The present

invention relates to methods for production of liquid media which have long lasting broad spectrum biocidal properties, to the liquid media and to their use as biocidal liquids.

Electro-chemical cells and processes using them have been around for about 100 years and many types of cells exist. This technology was developed in the 1930's by Austrians and Germans and further work to develop a harmless sporicidal solution for treating components of satellites prior to launch was carried out in Russia as part of its space programme.

lo There is a need for powerful cold sterilization products which are eco and human friendly but which have effective long lasting, biocidal properties with good storage characteristics.

A number of patents exist which cover similar technology and liquids but none of these produce liquid media which have long shelf lives and which can be stored in suitable Is containers rather than being produced onsite and on demand.

For example WO98/13304 describes a process in which the flow configuration is such that the liquid being electrolysed flows from a cathode chamber at least partly to an anode. The process described and liquids produced are different to those of the present inventions and produce liquids with poorer storage stabilities and poorer performance as biocides.

According to the present invention there is provided a process for the preparation of a liquid medium with biocidal properties in which a feed liquid is passed through an electrolyser that has at least two electrodes, one of which is an anode and one of which is a cathode each in its own chamber, applying an electric current to the electrodes characterized in that the feed liquid is caused to flow into the anode chamber and the liquid medium is created at and collected from the anode chamber or that at least a part of the feed liquid is caused to flow from the anode chamber to the cathode chamber and the liquid medium is collected from the cathode chamber.

According to a further feature of the present invention there is provided an apparatus for preparation of a liquid medium by the process with biocidal properties in which a feed liquid is passed through an electrolyser that has at least two electrodes, one of which is an anode and one of which is a cathode each in its own chamber, applying an electric current to the electrodes characterized in that the feed liquid is caused to flow into the anode chamber and the liquid medium is created at and collected from the anode chamber or that at least a part of the feed liquid is caused to flow from the anode chamber to the cathode chamber and the liquid medium is collected from the cathode chamber.

The liquid medium produced is a safe, non-toxic, fast-acting, environmentally friendly, broad spectrum biocide effective on a wide range of micro organisms including bacteria, fungi, yeasts, moulds, bacterial spores and viruses and which may be used at room temperature in sterilization, disinfection, and big-film removal applications. The biocidal properties of liquid media produced by the present process compare favourably with the lo performance of materials already used as biocides such as glutaraldehyde, peracetic acid and chlorine dioxide but do not have the disadvantages associated with these materials such as handling and disposal problems.

The feed liquid used in the process is water or comprises water and an alkali metal halide, preferably sodium chloride or potassium chloride.

The electrolyser comprises at least one anode and at least one cathode each in its own chamber. The chambers are separated by a membrane which may be fabricated from any suitable material which will allow ions to pass through it. The membranes are preferably selected from a rigid ceramic or a flexible polymeric material. Preferred ceramic membranes include metal oxides more preferably aluminium oxide. The ceramic membranes are preferably from 1 to 5 and more preferably from 1 to 2 mm thick.

Preferred polymeric materials include fluoropolymers, more preferably polytetrafluoroethylene (PTFE) and perfluorinated polymers that contain small proportions of sulphonic or carboxylic ionic functional groups, especially NAFION perfluorinated polymers (NAFION is a trade mark of DuPont Corporation) such as NAFION 810. The flexible polymeric membrane material is preferably from 25 to 500 microns thick.

The electrolyser may be of any suitable shape such as a cylinder, disc or flat plate.

Where the electrolyser is cylindrical the electrodes are preferably cylindrical tubes with one electrode having a larger internal and external diameter than the other, the smaller electrode arranged to be placed, essentially coaxially, within the inner bore of the larger electrode with a suitable membrane, which is also a cylindrical tube, placed between the electrodes. The spaces between the cylindrical electrodes and the membrane form the electrode chambers.

Where the electrolyser is a flat plate assembly it preferably comprises at least a membrane to separate the electrode chambers, at least one anode and at least one cathode each electrode being within or forming part of an electrode chamber. The flat plate electrolyser may further comprise spacers which can be used in various thicknesses to s vary the volume of the electrode chambers.

Optionally flow baffles may be formed within the electrode chamber of any of the above electrolysers for creating a turbulent flow pattern.

The electrolysers may be used singly, or used in combinations with flows of feed liquid passing into the electrolysers either in series or in parallel.

0 The electrodes used in the above electrolysers may be made of any suitable material which is capable of conducting a current applied to the electrodes. The electrode materials include metals or alloys, particularly those which are resistant to oxidation or corrosion or those which have coatings which are resistant to oxidation or corrosion.

Preferred electrode materials include those with a titanium substrate which are coated with metals, metal oxides or alloys which are resistant to oxidation or corrosion, preferred coatings include Noble metal or metal oxide coatings particularly nickel, palladium and platinum. It is preferred that the titanium substrate is of high purity.

The electrolysers have a useful lifetime typically of up to five years. They have the advantage that they are recyclable for recovery of the metal from the electrodes.

The liquid media produced by the present process have properties which are dependent on a number of factors such as the pipe-work configuration, power absorbed, electrode coating material and physical size, shape and spacing of the electrodes. The membrane material is also an important feature since it affects to mobility of ions passing between the electrodes.

2s The process is operated by applying a DC current across the electrodes, preferably a full wave rectified DC current. A steady current is applied to the electrodes, this current may be adjusted based on the saline content of the liquid feed.

The process is preferably operated at temperatures below 55 C which gives a good cell lifetime. Preferred temperatures are from 25 C to 45 C, more preferably from 30 C to 40 C, and especially from 34 C to 39 C.

The conductivity of the feed liquid is preferably from 0.3 to 13 mS A current from 2 to 50 amps flows through the electrolyser, preferably at least 20 amps and more preferably at least 30 amps flows through a low voltage electrolyser. For a high voltage electrolyser a current of at least 50 amps preferably flows through the electrolyser. The power consumed per unit size of electrode has a bearing on the properties of the product. High volts may need low amps and visa versa, the number of watts absorbed is important and this is preferably in the range 40 to 1800 watts depending on electrode design.

The liquid media produced by the present process can maintain their positive redox potential and their biocidal properties for up to 2 years.

The present process uses untreated towns water as part of the liquid feed to the electrolyser and this does not require any pre-treatment to remove hard salts, this is an lo advantage over other available electrolysers where a pre-treatment is needed.

The present process uses a stock brine solution typically containing up to 70%w/v sodium chloride.

The stock brine solution is diluted with towns water, to give the liquid feed, before feeding the liquid feed to the electrolyser. The dilution of the stock brine solution may be conveniently achieved by mixing in a mixing column which may optionally be packed with an inert support, such as plastics rings to promote good mixing of the stock brine solution and the towns water. The liquid feed preferably comprises up to 26%w/v sodium chloride, more preferably up to 20%w/v sodium chloride.

The process may optionally include a means of pre-treating the feed liquid to prevent any hard salts from caking or scaling within the pipework feeding the feed liquid into the electrolyser. A preferred means of pre-treating the feed liquid is via a low band frequency radio wave transmitter which is placed on the feed line to the electrolyser and/or between electrolysers positioned in series. This prevents/minimises salt caking and deposition within the feed lines and on the electrode surfaces. The transmitter works on the principle of induction through the feed line walls via aerials which are wound around the feed lines in both clockwise and anticlockwise directions. The frequencies that the transmitter operates at can be from 50 to 500 hertz, preferably dwelling from X? to 500 hertz.

Where at least a part of the feed liquid is caused to flow from the anode chamber to the so cathode chamber the flow may be regulated by a flow control means, such as a valve.

In a further feature of the present process an in-line heater may advantageously be included to warm the feed liquid before it enters the electrolyser. The performance of the electrolyser is improved if the feed liquid temperature is from 30 C to 60 C,

- - - -

preferably from 30 C to 40 C. Where the feed liquid is warmed the ions in the feed liquid have greater mobility and passage across the membrane is promoted. The salt levels in the liquid feed can be lowered with no detriment to the current drawn through the electrolyser, less energy is consumed and lower salt residues are obtained in the liquid s medium.

The liquid medium produced by the process may optionally undergo one or more post- treatments.

One post-treatment disengages gases such as hydrogen, oxygen, ozone and chlorine which are produced in the process. This post-treatment may be conveniently achieved lo by passing the liquid medium through a column, typically made of glass or plastics material which is packed with an inert support, such as plastics rings.

A further post-treatment removes hydrogen from the liquid medium; this post-treatment has advantages where hydrogen cannot be vented to atmosphere. The liquid medium is contacted with a charged metallic catalyst, preferably a catalytic wire, typically a Is platinum wire. This is conveniently carried out in a column through which the liquid medium is passed. The column may further contain an activated or absorbent material such as charcoal.

A further post-treatment incorporates a surfactant dose device via which a surfactant, preferably a non-ionic low foaming surfactant, can be added to the liquid medium, no preferably to the liquid medium produced at the anode. The surfactant is preferably dosed at a ratio of from 500 to 1000, preferably from 700 to 1000 parts of liquid medium to 1 part of surfactant. A liquid medium which further comprises a surfactant has the advantage that it's long lasting broad spectrum biocidal properties, particularly its sporicidal properties, are effective in the presence of organic materials such as fats, oils as and greases.

The electrolysers used in the present process are generally low maintenance but where deposits and surface contamination build up for example on the electrode surface these may be removed easily by reversing the polarity of the electrolyser.

The electrolysers further comprise an outer body. The outer body, particularly for so electrolysers of the flat plate design are constructed using an outer body of a corrosion resistant material, typically a plastics material such as Perspex (Perspex is a trade mark of Lucite International UK Limited) which has the advantage of being transparent and allows the electrode surfaces to be inspected without disassembling the electrolyser. The components of the electrolysers are bonded together with proprietary resins and/or polymer sealants which has the advantage that no complex gaskets are required and the electrolysers can be assembled relatively easily and without problems arising from leaks.

Where multiple electrolysers are used in combination these are generally supported and s held together generally with stainless steel nuts and bolts, these do not contribute significantly to the mechanical sealing characteristics of the electrolyser.

Where the feed liquid is passed through the anode chamber of the electrolyser and the liquid medium is created at and collected from the anode this liquid medium is hereinafter referred to as acid anolyte (AA).

lo Where the feed liquid is brine and this is passed through the anode chamber of the electrolyser and at least a part of the feed liquid is caused to flow from the anode chamber to the cathode chamber and the liquid medium is collected from the cathode chamber this liquid medium is hereinafter referred to as anolyte neutral catholyte (ANK or ANC used as abbreviations herein to describe the same liquid media).

ANK is particularly suitable as a disinfectant for endoscope reprocessing, and for use in disinfecting wipes and sprays.

The AA liquid medium is acidic, with a pH typically in the range from pH 2.3 to 6.4 This has a total chlorine content of up to 1200ppm, typically from 700 pm to 1000 pm, and a log 6 sporicidal kill in less than 1 minute.

The ANK liquid medium is essentially pH neutral, with a pH typically in the range from pH 7.5 to 9.0, with a redox potential of +680 to +790mV, and a total active chlorine content typically from 200 ppm to 700 ppm.

A blend (ANB) liquid medium is generated by blending AA with neutral anolyte ANK giving a formulation of high redox and neutral pH. The ANB liquid medium is 2s essentially pH neutral, with a pH typically in the range from pH 6.5 to 7.5. This has a total chlorine content typically from 200 ppm to 800 ppm, and a log 6 sporicidal kill in about 10 minutes.

In the liquid medium from the anode chamber the products include hypochloric acid in a complex with oxygen compounds of active chlorine (hypochlorite ions, hypochloric acid, chlorine monoxide), and the basic gases produced during electrolysis (chlorine, oxygen and ozone).

In the liquid medium from the cathode chamber the products include peroxides, elementary hydrogen and hydroxides of alkaline metals.

In a further feature of the present invention the process is characterized in that the feed liquid is caused to flow into the anode chamber of a first electrolyser and the liquid medium is created at the anode chamber of the first electrolyser is caused to flow into the anode chamber of a second electrolyser and collected from the anode of the second s electrolyser In a further feature of the present invention the process is characterized in that the feed liquid is caused to flow into the anode chamber of a first electrolyser and at least part of the feed liquid is caused to flow from the anode chamber to the cathode chamber the liquid medium is created at the anode chamber of the first electrolyser is caused to flow lo into the anode chamber of a second electrolyser and collected from the anode of the second electrolyser.

A process and apparatus in accordance with the invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a diagrammatic cross-section through an electrolyser suitable for use in the process showing flow path into and out of the anode and cathode chambers; Figure 2 is a diagrammatic cross- section through an electrolyser suitable for use in the process showing flow path from anode chamber to cathode chamber; Figure 3 is a schematic showing electrolyser components; Figure 4 is a side part exploded view of an electrolyser; Figure 5 is a schematic showing fluid flow through the electrolyser of Figure 4; and Figure 6 is a schematic flow diagram showing an electrolyser system.

With reference to Figures 1 and 2 the cross-sectional diagrams show examples of the flow path into and out of the electrolysers. In Figure 1 the liquid feed is caused to enter separately the anode (+) chamber and the cathode (-) chamber of the electrolyser, application of an electric current to the electrodes produces two different liquid media, one is AA and the other is referred to as caustic catholyte (CC). In Figure 2 the liquid medium exiting the anode chamber is further processed by feeding it into the cathode chamber whilst maintaining the current applied to the electrodes. This produces a liquid medium referred to as ANK.

Figure 3 illustrates the components of an electrolyser. Module A shows a front and side view of one example of an electrode chamber component of an electrolyser, in this case for a flat plate electrolyser, suitable for use in the present process and shows an arrangement of flow baffles which help to mix the feed liquid, the spacer gasket which may be varied in depth to make the cell volume smaller or larger as required, and an example of fittings which may be used to connect the liquid feed and liquid medium outlet to suitable pipework These fittings are supplied by John Guest International Limited (John Guest is a trade mark of John Guest International Limited). Module B is a side view of one example of an electrode chamber component showing long reach fitting for supporting multi chamber electrolysers. Modules C, D, E, F and G illustrate spacer, electrode and membrane components of the electrolyser and sub-assemblies of the electrolyser. The modular design of the electrolyser means that many different arrangements of electrode, spacer, flow baffles and membranes can be easily assembled lo including electrolysers with multiple anode and cathode chambers.

The modular design is illustrated in Figure 4 which shows a side part exploded view of an electrolyser comprising one central module D and two each of modules B and G. Figure 5 shows a fluid flow through the electrolyser of Figure 4 where the feed liquid is a brine solution and this is fed firstly into the anode chamber and then into the cathode chamber. The liquid medium produced is ANK.

Figure 6 shows an example of an electrolyser system and a typical flow through such a system. The process of the present invention may be operated as illustrated by and with reference to Figure 6 as follows: A water supply, such as towns water, is fed via an optional pre-heater (a) which is typically controlled at from 30 to 40 C through feed lines around which is wound aerials of a low band frequency radio wave transmitter (b). The water is optionally passed through a hard salt deioniser (c). The towns water supply feeds both the mixer column (d) and the brine tank. The towns water supply to the mixer column (d) is used to dilute the brine solution feed. The towns water supply to the brine tank is used to prepare the brine solution, typically from sodium chloride and towns water. The towns water feed line has a T-connector to direct the towns water feed to the mixer column and to the brine tank. A first valve, in a first feed line after the T-connector, in the towns water feed line controls the flow of towns water to the mixer column (d); a second valve, in a second feed line after the T-connector, in the towns water feed line controls the flow of towns water to the brine tank. Regulation of these valves controls the flow of towns water to the mixer column and to the brine tank. A second T-connector is situated after the valve between the towns water supply (a) and the mixer column (d). A feed line from the brine tank, via this second T-connector, provides a supply of brine, via a third valve to the mixer column (d). Regulation of the first and third valves allows the concentration of brine fed to and exiting from the mixer column (d) to be controlled. It will be appreciated that closing the third valve will isolate the brine feed to the mixer column (d) and result in only towns water being fed into the mixer column (d). It will also be appreciated that the first, second and third valves may be automated and controlled in response to a suitable signal from the electrolyser system. For example, the second valve may be controlled by a level detector in the brine tank, the valve closing when a particular pre-set level is reached. The first and third valves may be controlled by a a suitable means such as a conductivity detector situated before or after the mixer column lo (d) which adjusts the relative flows of towns water to obtain a pre-set range of conductivity. Further the first and third valves may be controlled by a redox meter or pH meter measuring the redox or pH value of the liquid medium exiting the electrolyser(s) (E). In this example the feed liquid exiting the mixer column (d) is caused to flow into the anode chamber of the first electrolyser (E) and from the anode chamber to the cathode chamber of the first electrolyser (E). The liquid exiting the cathode chamber of the first electrolyser (E) is caused to flow into the anode chamber of the second electrolyser (E) and from the anode chamber to the cathode chamber of the second electrolyser (E).

The liquid medium exiting the electrolyser (E), or if more than one electrolyser the last electrolyser is caused to flow into a gas entrainment column (i) where gases such as hydrogen, oxygen, ozone and chlorine which are produced in the process are disengaged.

The gas entrainment column, is typically made of glass or plastics material which is packed with an inert support, such as plastics rings.

A non-foaming non-ionic surfactant held in a surfactant tank (h) may be fed into the liquid medium exiting the electrolyser (E) either before or after the gas entrainment column (i) (shown before in Figure 6). The surfactant may be fed into the liquid medium via a T-connector and using a suitable pump, such as a peristaltic pump, to transfer the surfactant. The liquid medium exiting the gas entrainment column is ready for use as a broad spectrum biocide in sterilization, disinfection, and big-film removal applications and the like.

It will be appreciated that any number of electrolysers may be operated in series or in parallel as part of the electrolyser system. It will be further appreciated that the pipework connecting the electrolysers may be arranged in different ways to provide liquid media with different characteristics.

In a second example the liquid medium exiting the anode chamber is collected via an outlet from the anode chamber (not shown in Figure 6).

In a third example part of the liquid medium exiting the anode chamber is collected and part is fed into the cathode chamber via a T-connector and outlet (not shown in Figure 6).

In a fourth example the feed liquid exiting the mixer column (d) is fed via a manifold device into electrolysers connected in parallel.

The liquid media produced by the present process may comprises additional components such as surfactants and fragrances.

The liquid media produced by the present process which additionally contain a surfactant preferably contain a surfactant such as a Synperonic (Synperonic is a trade mark of ICI Chemicals & Polymers Limited) preferably Synperonic 850. As an example a 0.1% of a 30% Synperonic 850 solution may be added to the liquid media.

The liquid media produced by the present process have been evaluated for their effectiveness and storage stability. The ARK liquid medium is a neutral anolyte which has a long shelf life as determined by its sporicidal activity. This was assessed against Bacillus subtilis var niger under clean conditions, without organic contamination, and under 'dirty' conditions in which horse serum was present. Contact times of 30 seconds, 1, 2, 5, 10 or 15 minutes from contacting the B. subtilis with the liquid medium under test were used and the ability of the liquid medium to obtain a kill rate (log reduction) of log 6 or more over a given contact time under clean conditions (no horse serum) and dirty conditions (1% horse serum) was assessed.

General Method for assessing sporicidal activity Fresh cultures of B. subtilis spore solutions (obtained from Don Whitely Scientific, Shipley, West Yorkshire, England) were used and kept in a refrigerator until needed.

Immediately before use the B. subtilis were placed in a pre-heated incubator set at 70 C for 30 minutes and allowed to cool to room temperature for 30 minutes. 1.7ml of liquid medium was used and to it 0. 2ml of sterile water was added for tests under clean conditions, and 0. 2ml of horse serum (obtained from Oxoid Limited, Basingstoke Hampshire, RG24 8PW, England) was added for tests under dirty conditions. lml of spore solution was added to either the clean or the dirty test solutions and samples taken at time intervals. The samples were added to a neutralization broth (containing nutrient broth Oxoid no2 (from Oxoid Limited), lecithin, tween 80, 1% sodium thiosulphate) which deactivated the liquid medium, after 5 minutes a portion of the neutralization broth was removed and added to MRD [max recovery diluent] (which contains Peptone and sodium chloride from Oxoid Limited). After mixing thoroughly samples of the MRD mixture and the neutralization broth were plated out on to Tryptone Soya agar (TSA) plate and incubated for 18 hours at 37 C. The plates were examined after 18, 24 and 48 hours and the spores counted. Controls were prepared by substituting the liquid medium with MRD. The control and test plates were compared and the log reduction in spores 0 calculated.

The results obtained (for SUPROX Blend) are summarised in Table 1: Time since liquid Sporicidal Sporicidal medium produced activity activity minutes, 5 minutes clean 1% horse conditions serum dirty conditions

_

days >log 6 Log6 reduction reduction weeks >log 6 Log 6 reduction reduction 9 weeks >log 6 Log 2.19.

reduction reduction 12 weeks >log 6 Log 0.5 reduction reduction Further testing of this liquid medium gave the following: After 4 months for a 5 minute contact time a log 4 reduction was obtained under dirty conditions with 0.8% horse serum.

Up to 6 months for a 30 minute contact time a log 6 reduction was obtained under dirty conditions with 1.0% horse serum.

By comparison use of an industry standard sterilizer, glutaraldehyde, takes 2 hours to achieve a log 6 reduction in spores where 1.0% horse serum is present.

- s - The results obtained for ANK for sporicidal activity and bactericidal activity using European standard EN1276 for Chemical disinfectants and antiseptics against S. aureus and P. aerugznosa is summarised in Table 2: Time since S. aureus and P. B. subiilis B. subtilis liquid medium aeruginosa Dirty Dirty conditions Clean conditions produced conditions 0.3% 1.0% horse serum, 5 1.0% horse serum, horse serum, 5 minutes 5 minutes minutes 2 months pass Pass 8 months Dass Dass 12 months pass 18 months Log 6 reduction in mins A pass indicates that a greater than log reduction in spores o - a greater than log 5 reduction in bacteria was obtained in 5 minutes.

European standard EN1276 test procedures was used to evaluate the performance of the liquid medium against other microorganisms. Under clean conditions in the presence of 0.3g/1 bovine albumin with a 5 minute contact time a greater than log 5 reduction was obtained for E. colt, S.typhimurium, K pneumonias and C. albicans. Under dirty lo conditions, in the presence of 3.0g/1 bovine albumin with a 5 minute contact time a greater than log 5 reduction was obtained for E colt, S. typhimurium, and K pneumonias and a greater than log 4 reduction for C. albicans.

Claims

Claims 1. A process for the preparation of a liquid medium with biocidal

properties in which a feed liquid is passed through an electrolyser that has at least two electrodes, one of which is an anode and one of which is a cathode each in its own chamber, applying an electric current to the electrodes characterized in that the feed liquid is caused to flow into the anode chamber and the liquid medium is created at and collected from the anode chamber or that at least a part of the feed liquid is caused to flow from the anode chamber to the cathode chamber and the liquid medium is collected from the cathode chamber
2. A process according to claim 1 which is characterized in that the feed liquid is caused to flow into the anode chamber and at least a part of the feed liquid is caused to flow from the anode chamber to the cathode chamber and the liquid medium is collected from the cathode chamber.
3. A process according to claim 1 which is characterized in that the feed liquid is caused to flow into the anode chamber and the liquid medium is created at and collected from the anode chamber.
4. An apparatus for preparation of a liquid medium with biocidal properties in which a feed liquid is passed through an electrolyser that has at least two electrodes, one of which is an anode and one of which is a cathode each in its own chamber, applying an electric current to the electrodes characterized in that the feed liquid is caused to flow into the anode chamber and the liquid medium is created at and collected from the anode chamber or that at least a part of the feed liquid is caused to flow from the anode chamber to the cathode chamber and the liquid medium is collected from the cathode chamber.
5. An apparatus according to claim 4 which is characterized in that the feed liquid is caused to flow into the anode chamber and the liquid medium is created at and collected from the anode.
6. An apparatus according to claim 4 which is characterised in that the feed liquid is caused to flow into the anode chamber and at least a part of the feed liquid is caused to flow from the anode chamber to the cathode chamber and the liquid medium is collected from the cathode chamber.
7. A liquid medium produced by the process of claims 2 and 3.
8. A liquid medium produced using the apparatus of claims S and 6.

lo
9. A liquid medium produced by blending the liquid medium obtained by the process of claim 2 with the liquid medium obtained by the process of claim 3.
10. Use of a liquid medium of any one of claims 7, 8 and 9 as a broad spectrum biocide.
11. Use according to claim 10 in which the liquid medium is used as a biocide to treat micro organisms selected from bacteria, fungi, yeasts, moulds, bacterial spores and viruses
12. Use according to claim 10 in which the liquid medium is used in sterilization, disinfection, and big-film removal applications.