AU2013366297B2

AU2013366297B2 - Method for electrochemically disinfecting water

Info

Publication number: AU2013366297B2
Application number: AU2013366297A
Authority: AU
Inventors: Didier Ginestet; Jean-Marie Morales; Stephane Morales
Original assignee: Soc Europeenne De Traitement Des Eaux
Current assignee: EUROPEENNE DE TRAITEMENT DES EAUX Ste
Priority date: 2012-12-21
Filing date: 2013-12-20
Publication date: 2018-05-10
Anticipated expiration: 2033-12-20
Also published as: CN104936906B; FR3000053A1; BR112015014921B1; AU2013366297A1; FR3000053B1; JP2016508066A; HK1209408A1; CN104936906A; EP2935127A1; EP2935127B1; BR112015014921A2; WO2014096575A1

Abstract

The invention relates to a method for electrochemically disinfecting water by passing this water through at least one cell contained in a housing provided with means for conveying and removing the water. The method according to the invention is characterized in that it consists: a) in using an electrolytic cell which comprises an anode and a cathode, both in plate form, and mutually parallel, the opposing catalytic faces of which have identical surface areas and form a symmetrical inter-electrodes space with no preferential path or short circuit; b) in creating, between said plates, along the entire length of the passage of the water to be treated, a turbulent flow that has the effect of alternately and successively casting any microorganisms contained in the dissolved substances against the anode and against the cathode so that they experience the deactivating effect caused by the strong variations in pH that there are between the electrodes and the additional bactericidal effect upon contact with the O

Description

The invention relates to a method for electrochemically disinfecting water by passing this water through at least one cell contained in a housing provided with means for conveying and removing the water. The method according to the invention is characterized in that it consists: a) in using an electrolytic cell which comprises an anode and a cathode, both in plate form, and mu tually parallel, the opposing catalytic faces of which have identical surface areas and form a symmetrical inter-electrodes space with no preferential path or short circuit; b) in creating, between said plates, along the entire length of the passage of the water to be trea ted, a turbulent flow that has the effect of alternately and successively casting any microorganisms contained in the dissolved sub stances against the anode and against the cathode so that they experience the deactivating effect caused by the strong variations in pH that there are between the electrodes and the additional bactericidal effect upon contact with the O 2 and OH radicals formed at the surface of the electrodes.

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L'invention conceme un precede de desinfection electrochimique des eaux par le passage de celles-ci dans au moms une cellule contenue dans un boltier pourvu de moyens d'amenee et d'evacuation des eaux. Le precede selon l'invention se caracterise en ce qu'il consiste : a) a utiliser une cellule electrolytique qui comporte, une anode et une cathode en forme de plaques, paralleles entre elles, dont les faces catalytiques en regard ont des superficies identiques et foment un espace inter-electrodes symetrique sans trajet preferentiel et court-circuit; b) a creer, entre lesdites plaques, tout au long du passage des eaux a traiter, un regime turbulent ayant pour effet de projeter, de maniere alternative et successive, sur l'anode et sur la cathode, les micro-organismes contenus dans les matieres dissoutes afin de leur faire subir l'effet desactivant provoque par les fortes variations de pH existant entre les elec trades ainsi que l'effet bactericide complementaire au contact des radicaux O2 et OH formes a la surface des electrodes.

METHOD FOR THE ELECTROCHEMICAL DISINFECTION OF WATER

DESCRIPTION

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method for electrochemically disinfecting water, without the addition of any chemical product, by passing this water through at least one electrolytic cell contained in a casing provided with means for conveying and removing the water and by exploiting the direct virucide, bactericide and bacteriostatic effect linked to the oxidation actions in the anode and the reduction action in the cathode, as well as the supplementary indirect bactericide effect and the residual bacteriostatic effect linked to the action of the oxidants generated by the electrolysis of water.

DESCRIPTION OF THE TECHNICAL BACKGROUND

The patent EP1597202 by the same applicant describes a method:

- which consists of making the water to be continuously treated pass through an electroperoxidation module using catalytic electrodes so it undergoes an electrochemical treatment;

- using, on the one hand, the direct effect linked to the oxidation actions in the anode and the reduction action in the cathode on the solved organic materials (virucide, bactericide and bacteriostatic effects) and on the other hand, the indirect effect linked to the action of the oxidants generated by the water electrolysis (supplementary bactericide effect and residual bacteriostatic effect);

-which enables, by prolonged contact with the electrochemically generated oxidants, an additional reduction of bacteria and water protection during the transportation and storage thereof to the point of use, the action being prolonged at the outlet of the electrolyzer (residual disinfection capacity).

The oxidants generated from the dissolved oxygen (cathodic reduction) and water (anodic oxidation), posses an appreciable residual effect and induce oxidation products at harmless rates, contrary to the most used oxidants, such as chlorine.

The device for implementing said method includes an anode and a cathode, both plate-shaped and parallel to one another, the opposing catalytic faces of which are symmetrical and have identical surface areas in order to enable the inversion of polarity in optimum conditions (the current density being identical on both electrodes) with the effect of preventing premature degradation relative to each other due to the decarbonation, which is not identical, and side reactions, which are more Important on the smaller electrode (higher current density).

The operating conditions applied to said device were as follows:

- implementation of a continuous laminar flow regime between the two opposing electrodes in order to limit turbulence that promote the adhesion of lime deposits (encrusting) on or between the electrodes, which have the effect of producing premature aging thereof;

- feeding the opposing anodes and cathodes, by means of a direct and/or pulsed electric current, in order to compensate for variations in the current density from one end to the other of each electrode.

During qualification tests under real conditions, it was found that certain bacteria were less or even hardly affected by the passage between the electrodes.

Among these the Pseudomonas aeruginosa and Clostridium perfringens bacteria are worth mentioning.

The performance of the bacterial treatment has therefore proved to be inefficient in laminar regime mainly for the aforementioned bacteria.

In fact, in laminar regime, the sheet of water that passes right through the cell from one end to the other, equidistant from the anode and the cathode, undergoes only the effect linked to the current passing between the electrodes (via electron transfer between anions and/or cations and electrodes).

SUMMARY OF THE INVENTION

It is with the aim of increasing the efficiency of the bactericidal treatment mainly for Pseudomonas aeruginosa and Clostridium perfringens bacteria that the applicant has developed the claimed method, which also uses an electrochemical cell including an anode and cathode, both plate-shaped, parallel to one another, the opposing catalytic faces of which have identical surface areas and form a symmetrical inter-electrodes space with no preferential path or short circuit.

Using the result of his research as starting point and based on the fact that the potential of hydrogen (pH), reflecting the acidity of the water, is very low (lower than 1) in the vicinity of the anode (where the oxygenation takes place) and on the contrary very high (higher than 14) in the vicinity of the cathode (where the reduction takes place), the applicant has implemented a specific turbulent hydraulic regime between the opposing electrodes in order to:

- apply, alternatively and successively, on the microorganisms existing in the water, along their entire passage within the cell, strong pH variations with the aim of deactivating them;

- place, alternatively and successively, said microorganisms in very close contact with the radicals O₂ and OH formed on the surface of the electrodes with the aim of improving direct and indirect effects.

In addition, the electric field between the electrodes being of the order of ten volts, at the level of bacterial membranes is sufficient to induce a dielectric breakdown.

The operation of the cell in such turbulent regime, constitutes a real advancement in the performance of the system, thus allowing for tests on more evolved organisms such as protozoa (for example, amoeba), fungi and yeasts.

In order to optimize the treatment performance, namely the disinfection treatment, the applicant has found that the introduction, in the downstream flow, of metal parts, namely made of copper, in contact with water, had the effect of accelerating, by the formation of powerful radical compounds with a short life span, decomposition rates of oxidizing compounds generated by the water system (formation of powerful radical compounds with a short life span).

As for the scaling of the electrodes and the water circuit, it has been limited by controlling the scaling capacity of the water upstream from the cell using at least one of the following technologies:

- the selective retention of calcium and magnesium cations on the cation exchange resin;

- the sequestration of calcium ions by contact with polyphosphates in the form of crystals or in liquid form;

- the inhibition of the encrusting capacity of limestone (calcium carbonate) by the action of a magnetic, inductive or equivalent scale inhibitor.

PRESENTATION OF THE FIGURES

The characteristics and advantages of the invention will appear more clearly on reading the following detailed description of at least a preferred embodiment thereof, given by way of non-limiting example and the accompanying drawing (Fig. 1), which is a schematic outline showing the path of microorganisms between the electrodes and the chemical reactions in the vicinity thereof.

DETAILED DESCRIPTION OF THE INVENTION

The invention relates to a method for the electrochemical disinfection of water by passing said water through at least one electrolytic cell contained in a casing provided with means for conveying and removing said water and by exploiting the direct virucide, bactericide and bacteriostatic effect linked to the oxidation actions in the anode and the reduction action in the cathode, as well as the supplementary indirect bactericide effect and the residual bacteriostatic effect linked to the action of the oxidants generated by the electrolysis of water.

The method according to the invention is substantially characterized in that it consists:

a) of using an electrolytic cell that includes one anode and one cathode, both plate-shaped and parallel to one another, the opposing catalytic faces of which have identical surface areas and form a symmetrical inter-electrode space with no preferential path or short circuit;

b) of creating, between said plates, by means of a device located upstream or downstream thereof, along the entire length of the passage of the water to be treated, a turbulent regime that has the effect of alternately and successively casting, the microorganisms contained in the dissolved substances against the anode and against the cathode so that they experience the deactivating effect caused by the strong variations in pH that are present between the electrodes, as well as the additional bactericidal effect upon contact with the O₂ and OH radicals formed on the surface of the electrodes.

Figure 1 exhibits:

- the anode A (pH < 1) and the cathode C (pH > 14)

- the path followed by the microorganisms M between said two electrodes;

- the chemical reaction at the anode: 2 H₂O = 4 H⁺ + 3e + O₂'

- the chemical reaction at the cathode: 2 H₂O = 2 OH' + H₂

The method according to the invention, further consists, in order to optimize the treatment's performance, particularly regarding disinfection, of placing, in the downstream flow, metal parts, namely made of copper, in contact with the water, so as to accelerate, by the formation of powerful radical compounds with a short life span, the decomposition rates of oxidizing compounds generated by the water system.

In addition, it further consists, in order to inhibit the scaling of the electrodes and the water circuit, of applying, upstream thereof, a technology chosen from among:

- the sequestration of calcium ions by contact with polyphosphates in the form of crystals or in the liquid form;

- the inhibition of the encrusting capacity of calcium carbonate by the action of a magnetic or inductive scale inhibitor.

In addition, it further consists, in order to clean the electrodes, of applying thereto:

- either an ultrasonic field;

- or a high-frequency field that generates resonance phenomena.

The device for implementing said method includes flow disturbers such as for example:

- at the inlet of the cells, a turbulence generator provided with a series of deflectors mounted in opposite directions and supported by a cylindrical ring, which fits over the inlet nozzle of the electrolytic cell;

- on the leading edges of the plates, in order to increase the turbulence regime between the plates, U-shaped interlocking profiles.

The role of a disinfection system is to maintain sufficient concentrations of oxidizing disinfectants in the water flowing through the internal distribution network so that the bacteria, which are suspended in the water (coming from the existing city's cold water system, backwaters or biofilms), are destroyed or deactivated before they reach the drawing points. The assurance of using a quality water, consistent with its use implies therefore checking on site and over time, for the presence of a sufficient concentration at the water drawing points, the target values measured as chlorine equivalent being comprised between 0.5 and 1 mg/l.

The implemented electrolysis principle enables producing oxidizing disinfectants based on the oxygen contained in the water.

An internal study has shown that the persistence of the oxidants generated by the method according to the invention tended to a logarithmic evolution of the persistence as a function of the initial concentration of oxidizing agents. For example, the life span is approximately 24 hours for an initial concentration of 0.5 mg/l and increases to 30 hours for 1 mg/l. It is 15 days for 2.5 mg/l and more than one month (31 days) for 10 mg/l.

The electrolytic cell is generally associated with a flow meter (of the paddle type, with pulse generator, or other) and an electronic panel, which manages the control of the electric current sent to the cell as a function of the flow volume passing by and the settings adopted by the operator.

According to two operating variants of the invention, several cells may be hydraulically mounted:

- either in series to cumulate the disinfectant effects thereof;

- or in parallel to cumulate the flow rates thereof.

The cells may be, in both cases, enclosed in a common casing provided with conveying and removing means that are also common to said cells assembly.

The cells may be hydraulically mounted in series or in parallel, but not necessarily electrically, each cell can be fed separately.

According to various operating variants of the invention, an electrochemical treatment module may be:

a) submerged in a treatment or sedimentation tank;

b) placed on the loop of a treatment or sedimentation tank;

c) coupled with a filtering system, especially of the granular type, or with membranes, and/or to other electro-chemical treatment module.

The cell or cells may be supplied with direct and/or pulsed current.

The electrode polarity reversal is programmed according to a well determined percentage of the elevation of the voltage as a function of the characteristics of the water to be treated and/or according to a well-determined timing depending on the water quality.

The space between the two electrodes is generally comprised between 2 and 6 mm depending on the conductivity of the water used.

The electrodes have thickness generally comprised between 1 mm and several millimeters.

The electrochemical treatment modules may include, 2, 4, 6 or more electrodes.

The direct and/or pulsed electric current that is used has a value generally comprised between 1 and 10 A per dm².

The optimal water pressure in the cell is 3 bar.

When the cells are mounted forming a loop on a vat, they produce a volume of water at a higher concentration of total oxidants, for example to protect the treated water against any recontamination caused by germs and/or organic matter in the storage and distribution system and that up to the points of use. This water can then be injected into the water to be treated, as in this application only the indirect effect is used.

This implementation can be used to disinfect equipment for example surgical instruments, by immersion in the vat described above.

The system can also be used as tertiary wastewater treatment or as a main or secondary treatment of water intended for recreational or therapeutic uses (thermal waters, thalassotherapy...).

For the applications mentioned above, as well as for water disinfection, cooling towers or other air treatment system, the implementation may be different in the case where the sets of electrodes are bare (not contained in a cell).

The liquid mass can then be brought into contact with the oxidants generated by convective motions (convection phenomenon). This type of implementation can be adopted for example, in buffer tanks and water cisterns.

Several sets of electrodes can be implemented in the same vat.

The electrode sets may also be implemented integrated inside or outside the pipes and submerged in the water to be treated (for example for pools in the water recycling system).

The water treated with the device, regardless of the implementation type, can eventually be used for medical applications (therapies).

When this technique is combined with a granular filtration system, a technical synergy occurs since microfiltration stops completely parasites and bacteria, but not viruses while the device contributes to the destruction of virus.

In addition, the device brings about a residual disinfection capacity to the water that neither microfiltration nor ultra-violet irradiation can supply.

Finally, the device contributes to the degradation of dissolved organic matter, while the microfiltration only stops the suspended matter (particles larger than 0.1 microns, or 0.01 microns in the case of ultrafiltration).

Of course, the skilled person will be capable of performing the invention as described and depicted by applying and adapting known means without being it necessary to describe or represent them.

The skilled person may also envisage other variants without departing from the scope of the invention as determined by the terms of the claims.

Claims

1. A method for the electrochemical disinfection of water by passing this water through at least one electrolytic cell contained in a casing provided with means for conveying and removing the water and by exploiting the direct virucide, bactericide and bacteriostatic effect linked to the oxidation actions in the anode and the reduction action in the cathode, as well as the supplementary indirect bactericide effect and the residual bacteriostatic effect linked to the action of the oxidants generated by the electrolysis of water;

characterized in that it consists:

a) of using an electrolytic cell, which has an anode and a cathode, both plate-shaped and parallel to one another, the opposing catalytic faces of which have identical surface areas and form a symmetrical inter-electrode space with no preferential path or short circuit;

b) of creating, between said plates, along the entire length of the passage of the water to be treated, a turbulent regime that has the effect of alternately and successively casting, the microorganisms contained in the dissolved substances against the anode and against the cathode so that they experience the deactivating effect caused by the strong variations in pH that are present between the electrodes, as well as the additional bactericidal effect upon contact with the O₂ and OH radicals formed on the surface of the electrodes.

2. The method according to claim 1, characterized in that it consists, in order to optimize the treatment's performance, particularly regarding disinfection, of placing, in the downstream flow, metal parts, namely made of copper, in contact with the water, so as to accelerate, by the formation of powerful radical compounds with a short life span, the decomposition rates of oxidizing compounds generated by the water system.

3. The method according to claim 1, characterized in that it consists, in order to inhibit the scaling of the electrodes and the water circuit, of applying, upstream thereof, a technology chosen from among:

- the sequestration of calcium ions by contact with polyphosphates;

5 4. The method according to claim 1, characterized in that it consists, in order to clean the electrodes, of applying an ultrasonic field thereto.

5. The method according to claim 1, characterized in that it consists, in order to clean the electrodes, of applying a high-frequency field thereto that

10 generates resonance phenomena.

1/1

FIG.1