IT201600124094A1 - PROCESS AND APPARATUS FOR THE ELECTROCHEMISTRY OF WATER - Google Patents

Description

PROCESS AND EQUIPMENT FOR THE ELECTROCHEMICAL ACTIVATION OF WATER

SCOPE OF THE INVENTION

The invention refers to an apparatus for the treatment of drinking water, in order to restore and / or ensure its conditions of health and allow its use, also ensuring the healthiness of the relative hydraulic circuit and any directly connected equipment.

STATE OF THE ART

The contamination of the hydraulic circuits as well as the equipment connected to them is a real problem resulting from the fact that the water taken from the municipal water network, although suitable for human consumption, is certainly not sterile. The water network manager must in fact ensure the purification conditions of the water supplied (through appropriate treatment systems) but, by law, these conditions must be respected up to the point of use which, for normal domestic users, is represented by the valve interception between the operator's line and the start of the domestic water network.

The reliability of the water used is a particularly serious problem in the case, for example, of medical clinics and, in particular, of dental units, in which the working conditions are such as to allow contamination of the hydraulic circuit. In fact, the tools used (the so-called handpieces) provide for the use of water and / or compressed air lines to operate the tools themselves as well as to avoid overheating of the areas treated with them (for example the use of a cutter for the removal of a caries: during the operation, the abrasion generates heat which must be suitably eliminated).

The use of rotating means and / or compressed air causes the formation of aerosols, with consequences for the doctor and, indirectly, also for patients. The aerosol coming from the patient's mouth acts as a vehicle for the bacteria that the patient may unintentionally carry; furthermore, as a result of capillarity phenomena, the biological fluids coming from the oral cavity can rise through the hydraulic circuit of the handpiece and, in quiet conditions, determine the formation and proliferation of the so-called biofilm (consisting of bacterial cells, cellular debris and organic residues enclosed within a matrix of excreted polymeric compounds), which can promote further microbial growth but above all protect the microbial population from the disinfectant action of many preparations.

The growth of the biofilm inside the hydraulic circuit of the equipment (the so-called unit in the case of dental surgeries) is obviously facilitated by quiescent conditions and is preferably carried out during longer breaks (during the night and / or on weekends) . Subsequent use of the equipment can therefore lead to the involuntary dispersion of pathogens with the result of exposing the patient and the doctor himself to the risk of infections; in the case of the patient, the risk is increased by direct exposure to wounds or areas that are in any case sensitized.

In order to limit the aforementioned problems, as regards the dental field it is known the use of disinfectant agents added through discontinuous interventions (IT1310262B, EP1195145B1, EP1344499B1, US6177018B1, US2002 / 0127158A1), or the use of continuous treatments, based on for example on the use of ultraviolet lamps (IT1225005B, KR100904538B1), or on the use of heat (US6212333B1).

With regard to the use of UV radiation, they allow the temporary formation of radical species in the water and it is the latter that carry out the desired oxidant / disinfectant action. Unfortunately, the effect is not lasting and does not guarantee any residual action (radical species are very reactive but have an extremely short life); moreover, in order for the UV radiation to be effective, it is necessary to use very small tube sections, with obvious limitations in the flow rate of the fluid to be treated.

The approach suggested in US6212333B1, on the other hand, is based on the principle whereby pathogens are inactivated through a rise in temperature; however, the thermal shock is effective only if the temperature is raised above 60 ° C (sometimes it is necessary to reach 70-80 ° C) with possible repercussions and damage to the pipes, as well as entailing obvious energy costs.

Even discontinuous methods do not allow to solve the problem in a satisfactory way: the use of common disinfectant agents in fact involves making additions in significant quantities, in order to remove the pathogens in a short time, and to carry out a subsequent washing of the system to to remove the excess disinfectant and to bring the water back to the expected potable conditions. In order to ensure the maintenance or restoration of health conditions, it is necessary to repeat the disinfection process relatively frequently, with obvious repercussions on the operation of the instrumentation being treated.

A further approach, described in IT1367226B, involves an initial reverse osmosis treatment followed by an oxidation with chlorine dioxide (CI02). In this case, the disinfection intervention is carried out continuously but both the initial osmosis treatment and the subsequent addition of CI02 raise doubts about compliance with the envisaged drinking conditions for the treated water (current legislation provides that the drinkable has a hardness equal to at least 60 mg / l in calcium or equivalent cations; moreover, the synthesis of CI02, generally obtained by reaction between sodium chlorate and a strong acid - such as hydrochloric acid - can lead to the presence of chlorates or the unwanted formation of by-products such as chlorites, hypochlorite and chlorine).

From what has been said, it is clear that the problem of maintaining the appropriate health conditions of certain hydraulic circuits (those in the dental field in particular) has not yet been resolved.

It is a first objective of the present invention to obviate the limitations described above and of the known art by making available an invention which can be used continuously and whose effectiveness is based on the electrochemical activation of water and on the consequent disinfectant / sterilizing action of hypochlorous acid (HOCI ) electrogenerated.

It is a second objective of the present invention to provide an engineering solution that allows to synthesize hypochlorous acid through the electrolysis of slightly saline aqueous solutions and by means of an appropriate pH control.

A further objective of the present invention is to make available an engineering solution which minimizes the risks of formation of limestone deposits at the cathode of the electrochemical cell.

DESCRIPTION OF THE INVENTION

Unlike other chlorine-based oxidizing species (such as Cl2, hypochlorites, chlorine dioxide), hypochlorous acid is a sort of "reserve" of hydroxyl radicals: in higher organisms, it is synthesized by leukocytes (also called neutrophils) by reaction between the metabolically produced hydrogen peroxide and the physiologically present chloride anions.

The hypochlorites commonly used are the salts of hypochlorous acid: they are much more stable than HOCI and, in fact, have an oxidizing action about 80 times lower (Samuel D. Faust and Osman M. Aly, "Chemistry of water treatment" 2nd edition, Lewis Publishers / CRC, 1998).

By mimicking nature, hypochlorous acid can be generated through the electrochemical oxidation of solutions containing chlorides, as long as the pH is properly adjusted.

The concentration of chlorides in the water to be treated may be that initially present in drinking water (in which chlorine may have been introduced in the form of hypochlorite, molecular chlorine or chlorine dioxide, following the disinfection process) or, in the case if this concentration is insufficient, it can be increased up to 250 mg / l (limit for drinking water) by injecting small quantities of brine.

As mentioned above, hypochlorous acid is more reactive and effective than hypochlorite: without wishing to bind to any particular theory, it is reasonable to think that the electrically neutral molecule of the former is able to penetrate through the cell wall negatively charged by any microorganisms, thus exerting its oxidizing action within the microorganisms themselves.

In order to ensure the presence of the disinfectant agent, the pH of the aqueous medium must be appropriately maintained between 5.5 and 7.5: in this range, hypochlorous acid predominates, compared to its conjugated hypochlorite base.

There are commercial apparatuses for the electrochemical synthesis of disinfectant solutions based on active chlorine (ie a mixture of dissolved Cl2, HOCI and hypochlorite). In more complex devices, the pH control is obtained through a suitable dosage of the catholyte (solution, generally alkaline, coming out from the cathode compartment of an electrochemical cell with separate compartments) which is subsequently introduced into the anodic compartment (see, for example, what described in EP1969159B1).

In order to simplify the system, avoiding having to resort to an electrochemical cell with separate compartments (which requires the presence of a separation membrane between the compartments, with consequent construction complications) as well as having to properly dose the fluids entering and leaving the cell itself, the authors of the present invention have verified that an appropriate addition of carbon dioxide (C02) to the water to be treated allows to keep the pH of the electrolyzed solution within values close to neutrality. In this way, it is possible to maximize the synthesis of hypochlorous acid, and therefore the disinfectant power of the solution.

As a secondary effect, maintaining the pH at values close to neutrality also makes it possible to reduce the formation of any calcareous deposits at the cathode of the electrochemical cell, thus obviating the known problems connected with the treatment of unsoftened water.

The addition of C02 to minimize the formation of limestone deposits has been described in FR2725977B1, with reference to water treatment in cooling towers, while in JP61073893A it is suggested in the case of an electrochemical cell fed with sea water, in order to avoid the pH increase which would occur near the cathode (due to the hydrogen development reaction) and which would lead to the precipitation of slightly soluble and encrusting salts, such as magnesium hydroxide. Evidently, in none of the cases cited is the use of CO2 aimed at regulating the pH in order to maximize the production yield of a given electrolysis product.

The technical characteristics of the invention, according to the aforementioned purposes, can be clearly found in the content of the claims reported below, and the advantages thereof will be more evident in the following description, made with reference to the attached drawing, which represents a purely embodiment exemplary and not limiting.

In accordance with the attached figure, the apparatus 1 for the disinfectant treatment of drinking water, object of the present invention, comprising at least 2 blocks, namely:

(A) a system for adding carbon dioxide to the water to be treated, including at least a mixing tank (5) and a pump (4), and

(B) an electrochemical system for water treatment, comprising at least one electrochemical cell (7), a power supply (8) and a flow meter (9).

The apparatus can then be equipped with a third block (C), consisting of a system for adding chlorides to the water to be treated, including at least a storage tank for the brine (16) and a relative dosing pump (17).

Drinking water from the municipal water network (2) enters the apparatus (1) through a line equipped with a non-return valve (3) and feeds a mixing tank (5), the level of which is restored (if and when necessary, in order to guarantee constant pressures to the system and to prevent the flow of carbon dioxide from emptying the tank (5) from the water and therefore guaranteeing water flow) by a volumetric rotary vane pump (4) connected to a level meter (6), into which carbon dioxide is added. This gas is taken from a cylinder (11), connected to the aforementioned mixing tank (5) through a line which includes a pressure regulator (12) and a non-return valve (13).

The volumetric rotary vane pump (4) could alternatively be replaced by a volumetric piston pump (also called "piston"), diaphragm or diaphragm, or gear or lobe pump; in all cases, in order to ensure optimal and constant performance, it is important that the flow of water supplied is independent of the head. The choice of the rotary vane pump is justified by the fact that this device is self-priming (this feature is common for all volumetric pumps), and allows high performance (a pump suitable for the application described here is usually able to exercise up to 18 bar pressure, with flow rates up to 300 and more liters / hour) while working with a not particularly high number of revolutions (of the order of 1500_rpm per minute). The prevalence of this type of pump depends on the tightness of the blades and therefore on the precision of the machining and the degree of surface finish; these devices are well suited for pumping clean or in any case not very abrasive liquids, and are highly appreciated for their low level of noise and vibrations.

The expert in the field is aware that rotary volumetric pumps allow heads that are otherwise difficult to reach, for example, through the use of a centrifugal pump; being able to reach important heads guarantees the possibility of maintaining the correct water level in the mixing tank (5) regardless of the carbon dioxide pressure.

As an example, if it were necessary to work with very sparkling water, it would be necessary to use a high pressure of carbon dioxide but, at that point, a normal centrifugal pump would struggle to overcome the head and would therefore not be able to guarantee the desired level. of liquid in the mixing tank (5); similar problems could also arise as a result of malfunctioning of the carbon dioxide pressure regulator (12).

A further advantage, deriving from the use of a volumetric rotary vane pump, is the fact that this does not constitute an obstacle for the fluid being treated: if the pressure upstream of the pump is high enough (and the demand for water downstream of the apparatus object of the present invention is small), it is probable that the network pressure is sufficient to maintain the liquid level in the mixing tank (5), and that the intervention of the pump itself is therefore not required. On the other hand, any other type of rotary pump does not allow a similar result, and its intervention would always be necessary, regardless of the value of the network pressure.

The water added with carbon dioxide, coming out of the mixing tank (5), is sent to an electrochemical cell (7), where the oxidation of the chlorides present in the water takes place. By means of an appropriate dosage of carbon dioxide, the pH of the solution is adjusted in such a way that at the outlet from the electrochemical cell (7) it presents a value close to neutrality, and preferably between 6 and 7. In this way, it is possible maximizing the concentration of hypochlorous acid, to the detriment of hypochlorite (the active chlorine synthesized through the electrochemical oxidation process is in fact generally constituted by a mixture of hypochlorous acid and hypochlorite).

The electrochemical cell (7) comprises at least one anode and at least one cathode and, for the purposes of the present invention, does not provide for any separation between the electrode compartments; furthermore, this electrochemical cell is connected to a power supply (8) which can be activated through a suitable signal coming from a flow meter (9).

By way of example, the electrochemical cell (7) can have a cylindrical geometry, and therefore comprise an internal, central anode, consisting of a bar with a circular section, and an external cathode, tubular and coaxial to the first. Both electrodes can be made of titanium, with the anode which will also be characterized by the presence of a suitable catalytic coating on its surface.

In practice, the apparatus object of the present invention aims at the disinfection of the incoming mains water, through the conversion of the chlorides present in the water itself (physiologically present or as a result of the chlorination process carried out by the water network manager) into acid hypochlorous.

When the user requests water (through the opening of a tap, or through the use of any user connected to the water network located downstream of the machine), the flow meter (9) monitors the flow of water. outgoing water (10) by activating the power supply (8) in order to allow the electrochemical treatment of the water flowing through the electrochemical cell (7), this also allows to have a variable HOCI concentration according to the water flow rate out of the system.

In fact, for small flow rates (i.e. low water flow rates inside the electrochemical cell) the absolute quantity of HOCI produced will be greater than in the case of higher flow rates (higher flow speed, and therefore shorter residence time of the water inside the electrochemical cell).

It should be noted that, in any case, the concentration of HOCI remains small, in absolute terms, but in the case of low flow rates (for example between 0.2 and 1 liters / min), this concentration will be considerable, if considered in terms relative to the case of a high flow rate (by way of example, between 2 and 5 liters / min).

In the particular case of a dental unit, small flow rates may be required, for example, by the use of turbine handpieces: these devices require little water for their operation, but cause the production of an aerosol which can increase the risk of contamination between doctor and patient; in such conditions, it is evident that a greater antibacterial efficiency, although olfactively not perceptible, can be of help.

As already described above, the water that feeds the electrochemical cell (7) comes from the mixing tank (5), in which the mixing process with carbon dioxide takes place. Since the concentration of chlorides initially present in the mains water may not be sufficient to guarantee an appropriate concentration of disinfectant, the incoming water, coming from the municipal water mains (2), can be added with chlorides through a secondary circuit, consisting of a solenoid valve (14) connected to a level meter (15), which measures the level of the liquid present inside a brine storage tank (16). This tank is intended to contain a sodium chloride solution, preferably saturated, to feed a metering pump (17), also controlled by the flow meter (9); downstream of the metering pump (17) there is finally a non-return valve (18). In this way, when the flow meter (9) activates the operation of the apparatus object of the present invention, the metering pump (17) can carry out the foreseen addition of saline solution to the water of the water mains, which is preferably added upstream of the mixing tank (5), so as to ensure rapid mixing as well as homogenization of the two liquid flows in the tank itself.

The described invention allows to synthesize a disinfectant (hypochlorous acid), whose bactericidal activity is considerably higher than that of the hypochlorite usually used; this allows to obtain a more effective disinfectant action, while keeping the concentration of the disinfectant in the water low. With this solution it is therefore possible to restore and maintain a high degree of sterilization in the pipes of the water system placed directly downstream of this apparatus, while respecting the legal limits for drinking water.

The present invention will now be further illustrated by the following examples.

EXAMPLES

Example 1

The apparatus object of the present invention was equipped with a cylindrical geometry electrochemical cell, comprising a central titanium anode having a surface of 50 cm <2> and equipped with a catalytic coating containing Ir02 and Sn02 (mixture 1: 2, in moles) and a tubular titanium cathode having an internal surface equal to 88 cm <2>. The apparatus was fed with drinking water (having a chloride content equal to 27 mg / l) suitably added with carbon dioxide, in order to obtain a pH close to 6. The water request was then varied in exit from the apparatus, exploring values between 0.2 and 5 liters / min, and to measure the content of oxidizing substances present in the solution at the outlet. Powering the electrochemical cell with a constant voltage of 8 V, a current of about 0.46 A was recorded; the solution leaving the apparatus had a pH of 6.2 and a content of oxidizing substances (expressed as "free chlorine" and determined by colorimetric measurement - portable instrument Hanna Instruments HI96711) which varied according to the flow rate of the water, as reported in the following table 1.

Example 2

The apparatus described in example 1 was installed in a dental office, upstream of the unit. The water leaving the unit was sampled before installation and subjected to analysis at an accredited laboratory for the counting of colonies on agar at 22 and 36 ° C, according to the APAT CNR IRSA 7050 Man 29 2003 method. The water was carried out after one month (ie after about 60 hours of work in the dental clinic), a period during which the apparatus object of the present invention carried out its action on the water entering the unit. The results of the analyzes, expressed in terms of Colony Forming Units (CFU) per milliliter, are shown in the following table 2.

Example 3

The apparatus described in example 1 was installed in a dental office, upstream of the unit. The waste water from the unit was sampled before installation and subjected to analysis at an accredited laboratory for the counting of colonies on agar at 22 and 36 ° C, according to the APAT CNR IRSA 7050 Man 29 2003 method, as well as for total compliance , according to the APAT CNR IRSA 7010 Man 29 2003 method. A subsequent sampling of the waste water was carried out after one month, a period during which the apparatus object of the present invention carried out its action on the water entering the reunited.

The results of the analyzes are shown in the following table 3.

Claims (12)

CLAIMS 1. Apparatus for the disinfectant treatment of drinking water comprising at least 2 blocks, namely: (A) a system for adding carbon dioxide to the water to be treated, including at least a mixing tank (5) and a pump (4), and (B) an electrochemical system for water treatment, comprising at least one electrochemical cell (7), a power supply (8) and a flow meter (9), this apparatus being characterized by the fact that it can be used continuously and the whose effectiveness is based on the disinfectant / sterilizing action of hypochlorous acid (HOCI), obtained by electrochemical treatment of water containing chlorides. 2. Apparatus according to claim 1 characterized in that it comprises a third block (C), consisting of a system for adding chlorides to the water to be treated, comprising at least a storage tank for the brine (16) and a relative metering pump (17). 3. Apparatus according to claim 1 or claim 2 characterized by the fact that the concentration of the synthesized hypochlorous acid is maximized through an appropriate control of the pH of the electrolyzed solution, this control being carried out by means of the appropriate addition of carbon dioxide to the solution entering the cell electrochemistry. 4. Apparatus according to claim 2 characterized in that the concentration of chlorides in the water to be treated can be increased by the appropriate dosage of a solution containing sodium chloride. 5. Apparatus according to one of claims 1-4 and characterized in that the electrochemical cell (7) does not provide for separation between the electrode compartments. 6. Apparatus according to one of claims 1-5 and characterized in that the treated water has a pH close to neutrality. 7. Apparatus according to claim 6 characterized in that the pH of the treated water is between 6 and 7. 8. Apparatus according to one of claims 1-7 and characterized in that the level in the mixing tank (5) is ensured by a pump (4) managed by a level control (6). 9. Apparatus according to one of claims 1-8 and characterized in that the intervention of the electrochemical cell (7) for the production of hypochlorous acid is managed by a flow control (9). 10. Apparatus according to one of claims 1-9 and characterized by the fact that the flow of water sent to the mixing tank (5) is guaranteed by the use of a volumetric pump (4). 11. Apparatus according to claim 10 characterized in that the positive displacement pump (4) is a volumetric rotary vane pump. 12. Process for the treatment of drinking water, in order to guarantee its conditions of healthiness and maintaining its characteristics of potability, also ensuring the healthiness of the relative hydraulic circuit and of the directly connected equipment, characterized by the fact of using an apparatus _ according to any_ of the. previous claims.