WO2010142655A1

WO2010142655A1 - System for purification of microbiologically contaminated water through the use of ozono

Info

Publication number: WO2010142655A1
Application number: PCT/EP2010/057953
Authority: WO
Inventors: Paolo Broglio; Sergio Bui; Gianteresio Iacometti
Original assignee: S.T.I.A. S.R.L. Sviluppo Tecnologie Innovative Per L'ambiente Unipersonale
Priority date: 2009-06-08
Filing date: 2010-06-08
Publication date: 2010-12-16
Also published as: ITMI20091001A1

Abstract

There is disclosed a system (100) for purification of microbiologically contaminated water comprising an ozone producing generator (6), a reactor (2) for contact of the water with ozone, Venturi effect ejectors (5) having the water contained in the reactor (2) as driving fluid and in fluid communication with the ozone producing generator (6), a pump (4) to supply said ejectors (5) through recirculation of the water contained in said contact reactor (2), in which the ejectors (5) are inside the contact reactor (2) and immersed in the water contained in said reactor (2).

Description

SYSTEM FOR PURIFICATION OF MICROBIOLOGICALLY CONTAMINATED WATER THROUGH THE USE OF OZONE

DESCRIPTION

The present invention refers to a system for purifying water contaminated by bacteria, viruses, protozoa, spores or other micro-organisms, through the use of ozone.

Ozone (O₃) is a known oxidizing agent able to inactivate bacteria, viruses and protozoa present in water through lysis of the cell wall, outer coatings and cell enzymes. It is also capable of transforming many non biodegradable substances into biodegradable forms.

Ozone is produced from dried air thanks to the action of an electrical discharge which leads to rupture of the oxygen molecule and thus to the formation of mono-atomic oxygen. The atoms of oxygen thus released are strongly reactive and some can recombine to form the ozone molecule, whilst others bind to re-form the oxygen molecule (O₂), according to the following reactions.

O₂ + e D 20 + e

O + 2O₂ D O₃ + O₂ O + O₃ D 2O₂

The bactericidal activity of ozone is high and for some micro-organisms is also manifested when it is dissolved in a few micrograms, for example 0.1 mg/1.

In simple systems for purifying water of the prior art, ozone is generally bubbled by blowing it into a tank containing the mass of water to be treated without any mixers. The concentration of dissolved ozone is generally less than 0.6 mg/1 since it is determined by physical factors (Henry's law). In fact at 25⁰C and at atmospheric pressure, the solubility of ozone in water ranges from 0.3 to 0.6 mg/1.

Since the effective concentrations of ozone for all types of bacterial load are not always known, in systems of the prior art a second pass of the water to be treated in the ozonizing system tends to be performed so as to increase the contact time between the water and the ozone and increase the content of ozone dissolved in the mass of water in order to ensure complete removal of all the bacteria. In fact, with ozone concentrations between 2 and 5 mg/1 there is the certainty that all types of micro-organisms are inactivated. However, this prolongs treatment times and increases running costs and the volumes of water to be handled.

In order to avoid the above drawback, it would be necessary to increase the concentration of oxygen dissolved in the mass of water to be treated: but today this is made impracticable for various reasons.

Ozone has a high reactivity and a very short half-life so that its concentration in water (at a constant temperature) tends to decrease quickly. In practice, 5 minutes after contact with water, ozone (at 25⁰C and at atmospheric pressure) stabilises in water.

In fact it is because of the high reactivity of ozone and its short average life that it is very difficult or even impossible to store and transport it. For these reasons it is necessary to produce ozone in situ for immediate use.

To compensate in part for the above mentioned drawbacks, an attempt has been made to improve mixing of water and ozone by increasing as far as possible the concentration of the bubbles of ozone dispersed in the water, reducing the diameter of these bubbles in order to speed up the transfer of ozone into the water and maximize its solubility. However, to date these parameters have already been maximized in the mixers used in this type of process. In any case even in the case of an optimal mixer, the concentration of ozone dissolved in the water contained in the tanks after blowing in ranges from 0.3 to 0.6 mg/1.

Ozonizing systems with improved efficiency and efficacy provide for the reactor containing the water requiring treatment to be kept below the ozone pressure, and for said water to be cooled and/or for its pH to be modified in order to maximize the amount of ozone dissolved. However, these arrangements are costly from the point of view of consumption both of electrical power and of reagents, to which must be added the cost of drying the air for the ozonizer, thus making these ozone water purification systems economically disadvantageous.

Other purification systems involve the use of chlorine and its derivatives, for example hypochlorite salt, but chlorination can hold drawbacks such as the formation of toxic chlorinated compounds if in contact with particular substances. Object of the present invention is to eliminate the drawbacks of the prior art, by providing a system capable of reducing contact times (hydraulic retention times) and moving smaller volumes of water.

Another object of the present invention is that of providing such a system that is also practical, reliable and at the same time simple to produce.

Yet another object is that of providing such a system capable of providing limited energy costs and that allows a good efficiency of liquid-gas mixing and bacteriological efficacy without having to work under ozone pressure, cool said water and/or modify its pH and dry the air suitable for ozone generation.

These objects are achieved according to the invention with the characteristics listed in appended independent claim 1.

Advantageous embodiments of the invention are apparent from the dependent claims. The system according to the invention for purifying bacteriological Iy contaminated water by means of ozone comprises

- means for producing gaseous ozone, for example an ozone generator (ozonizer), able to use undried air;

- means for placing the contaminated water in contact with ozone, optionally operating under pressure, for example, a closed cylindrical contact reactor

- means for liquid-gas (water-ozone) mixing, for example a Venturi effect injection mixer (ejector), contained inside said contact reactor and suitably positioned to create high turbulence in the water contained in said reactor,

- means for supplying a liquid to said mixing means by recirculation of the liquid contained in the contact reactor, for example a high pressure pump.

The above defined water contained in the contact reactor can be either contaminated water not containing ozone or any water-ozone mixture, for example partially contaminated water containing dissolved ozone etc. or purified water.

The above defined system preferably also involves the presence of means for filtering any solids optionally present in the water to be treated, placed upstream of the contact reactor, for example a particulate filter suitable for filtering suspended solids measuring less than 1 micron and trapping suspended solids measuring more than 1 micron up to 1 mm. Furthermore, the system preferably provides means for collecting and storing the treated water placed downstream of said contact reactor, for example a water collection/acclimatization tank as well as means for drawing the polluted water from any source and feeding it to the contact reactor, for example a submerged or immersion pump.

In particular, the system of the present invention provides for the bacteriological Iy contaminated (i.e. polluted) water to pass, generally in amounts (flow rates) between 100 and 9000 litres/h, in at least one special injection mixer (also defined as an ejector), placed inside a contact reactor.

The injection mixer, preferably represented by nozzle ejectors, is placed in the lower part of said reactor and is thus completely submerged by liquid. The ejector is fed by a high pressure pump and uses the polluted water sent by said pump as driving fluid. Said ejector is further connected by piping to an ozone generator. In said ejector the water is nebulized and its drops mix intimately with the ozone sucked from the generator through the Venturi effect that is generated in said ejector on passage of the water. At least two ejectors as above described are preferably used, more preferably spaced apart from each other along the vertical axis of said contact reactor. This allows a high-turbulence spiral movement to be created in the column of water between the two ejectors which is to the advantage of the efficiency of mixing and/or gas-liquid transfer.

Therefore, thanks to the fact that "Venturi effect" ejectors show a high liquid-gas mixing efficiency and to the high-turbulence spiral movement between the two ejectors, the present system allows a good transfer of gas (ozone) into the liquid to be achieved.

The water-ozone mixture that recirculates inside the contact reactor has a far greater amount of dissolved ozone compared with the solutions in which ozone is normally blown, temperatures being equal, when the contact reactor operates substantially with a slight overpressure, preferably less than 10 psi. In said system a concentration of dissolved ozone in the mass of water to be treated of 3-5 mg/1 can be reached compared with the 1.5-2 mg/1 of the other known ozone systems.

Further characteristics of the invention will be made clearer by the detailed description that follows, referring to a purely exemplifying and therefore non limiting embodiment thereof, illustrated in the appended drawings, in which: Figure 1 illustrates diagrammatically the system including piping and the direction of the water flow (by arrows);

Figure 2 illustrates diagrammatically a water/ozone contact reactor containing two ejectors inside it.

With reference to the above figures, a system according to a first embodiment of the invention, indicated as a whole in Figure 1 with reference numeral 100, is described.

A submerged pump 1, provided with an extendable pipe, draws the desired amount of polluted water to be treated from a collecting tank 8, preferably having a depth of at least 1.5 m, in order to send it to a reactor 2 without particular handling and therefore without danger for any operators. Before reaching the reactor 2, the polluted water drawn by the pump 1 passes through a filter 3, placed upstream of the reactor 2, which serves to eliminate any solids suspended in the polluted water.

Inside the reactor 2, near its lower portion, there are positioned two ejectors 5 (Fig. 2) set spaced apart. These ejectors 5 are connected to the outlet of a high-pressure centrifugal pump 4 which draws from the bottom of said reactor 2 the water contained therein. In this manner the pump 4 recirculates the water in a zone of reactor 2 comprised between the ejectors 5 and the bottom of the reactor.

The ejectors 5 are also in fluid communication with the ozone producing reactor since they are connected to the gaseous ozone outlet pipe of the ozone generator 6 by means of two pipes 11 (Figure 2) which fit onto the pipes of the ejectors 5.

During the recirculating operation the liquid is made to pass at high pressure through two ejectors 5, creating a vacuum through the Venturi effect in the pipes 11 connected to the ozone generator 6: this vacuum causes a certain amount of ozone produced by the generator 6 to be sucked up. When the sucked ozone enters the ejectors 5 it mixes intimately with the polluted water passing in the ejectors 5. The amount of ozone sucked in depends upon the size of the pipe 11 delivering the ozone to the ejector 5 and the vacuum created by the passage of polluted water in each ejector 5.

After purification the treated water is discharged from the reactor 2 to an atmospheric pure water tank 7: this discharge can takes place automatically after checking the bacterial load or after a known period of time previously identified as effective for sterilization.

Sterilization is taken to mean the absence of micro-organisms of any kind in a litre of water.

The collecting tank 8 can also be any source of polluted water such as a well, a water basin, a river, etc.

The filter 3 can be any type of pressure filter able to trap suspended solids measuring between 2 and 50 microns, for example a filter with plastic or quartz sand filtering elements.

The recirculating pump 4 is a advantageously a centrifugal pump, preferably operating at eight atmospheres (8 atm) and having a pump body made of AISI 316 steel.

The reactor 2 is a closed tank that can optionally operate under pressure, preferable with an overpressure ranging from 1 to 4 psi. In this manner the dissolved ozone can reach decidedly higher concentrations in solution than those measured at the outlet from the mouth of the ejector at ambient temperature and pressure (1.2-2.4 mg/1 compared with 0.4-0.6 mg/1). In this case the reactor 2 is further provided with a safety valve calibrated at a preset overpressure, preferably 10 psi, and mounted on the pipe 10 at the top of the reactor 2 (Figure 2). Discharge of the water takes place automatically, after having reached sterilization of the water, through the piping 9 (Figure 2) on which is mounted an automatic valve not shown in the figures.

It is also possible to provide fluxing of the reactor 2 with gaseous nitrogen in order to keep the environment sterile and at the same time keep the overpressure in said reactor constant.

The reactor 2 can operates under overpressure (greater than atmospheric pressure) thanks to recirculation of the water of the pump 4, the presence of a suitably calibrated safety valve on said reactor 2, partial vaporization of the ozone dissolved in water and the possible fluxing performed with gaseous nitrogen (not shown in the figure).

The reactor 2 can advantageously be made of steel or PVC. The contact reactor 2 can sterilize water both continuously and in batch mode. When operating in batch mode, the reactor 2 is filled only once and ozone is injected for a set time by recirculating the liquid with the pump 4 and the ejectors 5 or for a sufficient time to destroy completely the bacterial load. Once the sterility of the water contained in the 5 reactor 2 has been verified, the liquid is discharged into the purified water collecting tank 7.

If the reduction time necessary for sterilization/sanitization of the water is known, the reactor 2 can be fed continuously with a constant flow rate, while fixing the contact time !0 suitable for destroying the microbial load present. These contact times can vary from a few seconds to half an hour. In this continuous operating mode the sanitized water is accumulated progressively in the tank 7 ready to be distributed.

The purified water collecting tank is a closed tank and can advantageously be made of IS PVC.

The ejectors 5 are placed inside the reactor so that the incoming flow of water mixed with ozone inside the reactor 2 and leaving from each ejector is tangential to the horizontal section of the reactor 2. In this manner vortices are created in a similar way to 20 what happens in cyclones: this makes it possible to have a high turbulence inside the liquid and thus a high mixing degree of ozone with the water to be treated.

The ejector 5 used is preferably that described in patent application MI2006A00058 wholly incorporated herein as reference. Said ejector 5 is able to nebulise ozone in water 25 with very high efficiency and thus to "dissolve" ozone in water in the most efficient way possible.

Said preferred ejector 5 comprises a substantially cylindrical body which has a first axial connector for coupling with a nozzle for dispensing liquid under pressure, a second radial

30 connector for coupling with a gas dispensing duct (for connection to the pipe 11 of Figure 1), and an axial channel comprising four cylindrical chambers of different diameters. The opening in the head of the nozzle is in the first chamber of the axial channel and the radial connector has a channel communicating with the first chamber, so that the liquid can be injected through the nozzle and the gas can be sucked, through a

35 Venturi effect, through the radial channel, thus causing mixing of the gas with the liquid inside the chambers of the axial channel of the body. Two pairs of radial holes which open into the third and fourth chambers, respectively, are formed in the body. The axis of the first pair of radial holes is orthogonal to the axis of the second pair of radial holes.

The first mixing takes place in the first chamber. The liquid and gas mixture passing from the first chamber to the second chamber, which has a smaller diameter that that of the first chamber, is compressed so as to obtain the maximum mixing. Thus the liquid- gas mixture passing from the second chamber to the third chamber increases its speed, since the second chamber has a smaller diameter, and the liquid from the outside enters into the third chamber, which has a greater diameter than that of the second, through the radial holes with the consequent formation of micro-bubbles loaded with gas. Similarly, the liquid-gas mixture in the micro-bubbles expands on passing from the third chamber to the fourth chamber and part of the liquid exits through the other radial holes of the fourth chamber, with the consequent formation of micro-vortices in the fourth chamber, which cause a further subdivision of the gas-loaded micro-bubbles, immediately before exit.

It should be noted that each ejector is immersed in the liquid, therefore entry and exit of the liquid from said ejector, through the radial holes, contributes to an increase in the turbulence of the liquid in the third and fourth chamber. This increase in turbulence contributes to the formation of micro-bubbles, fragmentation thereof and further mixing thereof with the liquid injected. At the same time the micro -vortices produced in the fourth chamber prevent bubbling of the ozonized micro-bubbles towards the outside, through said radial holes. In fact such bubbling of the micro-bubbles towards the outside would lead to a loss of ozone which would be dispersed, exiting through the free surface of the liquid. The geometry of the four chambers is designed so as to maximize mixing. As a result, micro-bubbles of gas with an extremely small diameter, less than 1 micron, are obtained at the outlet of the ejector and are dispersed in the liquid.

The ejector thus defined preferably has the following characteristics:

- a substantially cylindrical body that extends from a proximal end to a distal end, with a total length of about 200 mm;

- an internal threaded connector is provided at the proximal end of the body for coupling with an injection nozzle having an external thread; - the injection nozzle ends in a frustoconical head provided with a liquid discharge aperture with an external diameter of about 3 mm; - the first chamber has a diameter of about 23 mm and extends for a length of about 40 mm. When the injection nozzle is coupled, the aperture in the head of the nozzle is situated at the centre of the first chamber;

- the radial channel communicating with the first chamber has a diameter of 15 mm, the axis of the radial channel passes substantially through the centre of the first chamber, and said channel has an external thread for coupling with a delivery duct for the gas which must be mixed with the liquid;

- the second chamber has a diameter of 14 mm which extends for a length of 29 mm, the third chamber has a diameter of 19 mm and extends for a length of 49 mm, the fourth chamber has a diameter of 23 mm and extends for a length of 40 mm;

- the axis of the first pair of radial holes is situated at a distance of 70 mm from the liquid outlet end and the axis of the second pair of radial holes is situated at a distance of 19 mm from the liquid outlet end;

- the flow rate of the liquid mixed with the gas by the mixing device 1 is about 150 litres/min and the flow of gas sucked through the radial duct is about 16 Htres/min.

Any ozone generator can be used as the ozone generator 6. The one described in patent application MI2006A000859, wholly incorporated herein as reference, is preferably used because it has very low power consumption and heat losses, and is able to use undried air.

Said preferred ozone generator is made up of a plurality of tubular reactors, each of which comprises a pair of electrodes (one internal and one external) connected to electrical power supply means to generate between them a difference in potential suitable to set off a crown discharge. The electrodes are disposed coaxially inside a tubular container closed at the ends by two perforated covers (caps) and suitable to be passed through by a flow of gas containing oxygen through which said crown discharge passes for conversion of the oxygen to ozone.

The tubular ozone generator further comprises a tubular element of dielectric material (glass, pyroceram, borosilicate, etc.) located between said two electrodes, in direct contact with the external electrode and spaced apart from the internal one, so as to define a gap for the passage of said gaseous flow containing oxygen. The dielectric element serves to distribute the electrical discharge evenly in the gap in which the gas containing oxygen passes and thus avoid the formation of electrical arcs, with a consequent uncontrolled increase in the electrical current of discharge which would cause an increase in the electrical power necessary for ozone production, as well as damage to the ozone generator. On each cover there are further formed a plurality of air passage channels which put the outside into communication with the cylindrical space formed between the internal electrode and the dielectric tube.

In one embodiment of the above defined tubular reactor relating to a preferred ozone generator, said reactor advantageously presents the following characteristics:

- the internal electrode consists of a cylindrical metal tube, hollow on the inside, having an external diameter between 14 and 17 mm and a thickness of 1.0-2.0 mm, and is made of a conducting metal resistant to the action both of ozone and of the high electrical voltages in play, for example AISI 316 stainless steel, and its outer surface is subjected to a mechanical mirror lapping treatment:

- the radial distance between the outer surface of the inner electrode and the inner surface of the dielectric tube is between 2 and 4 mm;

- the tube of dielectric material has an inside diameter between 20 and 22 mm, thickness between 1.8 and 2.2 mm and an outside diameter between 23.6 and 26.4 mm;

- the external electrode is located on the outer surface of the tube of dielectric material and is in the form of a sheet of metal having a thickness between 0.1 mm and 0.4 mm;

- the external electrode, the dielectric tube and the internal electrode are made of insulating material, such as PVC (polyvinyl chloride) and the latter has a slightly larger diameter than the outside diameter of the external electrode so that the external electrode is packed between the dielectric tube and the containing tube;

- the inner diameter of the containing tube is slightly greater than the outer diameter of the external electrode so that the outer electrode is packed between the dielectric tube and the containing tube; - the outer containing tube and the dielectric tube have the same length of between 300 and 340 mm whereas the internal electrode has a length between 290 and 310 mm;

- the internal electrode and the external electrode are connected to respective special electrical cables having such a dielectric stiffness as to withstand high voltages: said cables can be tungsten cables with silicone insulator for example; - the covers are sealed to the PVC containing cylinder by means of a circumferential outer line of bonding carried out by heat sealing or ultrasound sealing and are further provided with O-ring flanges so as to block the dielectric tube in position inside the containing tube;

- the electrical cables are connected to a high-voltage electric power supply able to deliver a maximum voltage of about 10-12 kV with alternating current of about 5-10 mA and the electric power supply can be an electrical transformer able to transform the mains power (220/230 Vac) into high-voltage power (10-12 kVac);

- the operating temperature of the ozone generator is kept below -330 K (57°C), thanks to the large internal surface of the dielectric tube which defines the gap for passage of the gas.

The above described geometry of the tubular reactor contained in the ozone generator allows the contact time of the air or oxygen flow with the electric discharge inside said tubular reactor to be regulated as desired.

The possibility of maintaining low working temperatures in the tubular reactor makes it possible further to increase the efficiency of ozone production, in that the rate of reconversion of the ozone into oxygen is considerably lowered. In fact, at slightly higher temperatures (-350 K) this reconversion rate is such as to reduce the efficiency of the normal generators on the market by about 40%.

Maintenance of temperatures that are not high (<330 K) is ensured both by the high efficiency of ozone generation in the above described tubular reactor (only about 8% of the energy related to the electronic impacts with the molecules of input gas is converted into heat) and by the incoming air flow itself, which is preferably cooled before entering the generator in order further to increase the efficiency of said generator. Thanks to this high efficiency it is possible to obtain ozone from air with a mean concentration between 2.7 and 5.8 g/m³ of ozone for each tubular reactor depending upon the incoming air flow rate. This amount is achievable without the use of a dryer for the incoming air. If oxygen cylinders are used, it is possible to obtain amounts of ozone up to 12 g/m³ per ozone generating device.

The generator for producing ozone advantageously comprises a configuration with eight tubular ozone generating reactors as described above, to produce 35 g/h of ozone from air with a consumption of about 110 W (the consumption of a light-bulb): this value is about 20 times less than the consumption of systems of the prior art for producing the same amount of ozone.

In another preferred embodiment the generator 6 comprises three reactors as defined above to produce 30 g/h of ozone from air with a consumption of about 100 W.

Given the low energy consumption of said ozone generator 6 it can also advantageously be supplied with photovoltaic means.

Once the ozone flow leaving the generator 6 has been regulated, the concentration of ozone in the water (polluted or treated) can be determined, for example by the "Standard Methods 4500-03 B Indigo Colorimetric". This determination can even be performed after each pre-set contact time to check the concentration of ozone in the sterilized water leaving the reactor 2. The above method is based on the principle that in acid solution indigo is rapidly decolorized by ozone: the decrease in absorbance based on spectrophotometric reading at the wavelength of 600 nm, is directly proportional to the increase in ozone concentration.

The above described items of equipment are connected to each other by means of pipes having suitable shut-off and control valves known to a person skilled in the art. These pipes, valves etc. can be made of PVC or stainless steel.

The system 100 of the present invention further comprises electronic instrumentation and the related control system able to regulate the amount of ozone in the water and control the flow rate of the water entering the reactor 2 and leaving said reactor 2 and the tank 7. The system 100 according to the present invention can advantageously have a cooling system capable of maintaining the temperature of the water ejected and recirculated into the reactor 2 below 1O⁰C. In this case there will be a further improvement in the solubility of the ozone with a consequent further reduction in contact times and the possibility of treating greater amounts of water in the course of the day.

The system 100 of the present invention shows a series of advantages. In fact it ensures the utmost operating flexibility, not encountered in any apparatus or set of apparatus currently in operation. In practice the temperature, pressure, fineness and quantity of bubbles can be regulated according to the desired results. Furthermore the system 100 allows more ozone to be introduced into the contact reactor 2: the bacterial load being equal, the increase in the concentration of dissolved ozone with respect to simple bubbling systems of the prior art allows the hydraulic retention time to be halved, also leaving room for considerable reductions in the volume of the apparatus, with great savings in space, materials and money.

Furthermore, the presence of a closed collecting/acclimatization tank for the treated water having a residual amount of ozone still dissolved allows the water to be kept substantially sterile for significant times, thus further improving the quality of the product deriving from the process developed in the system in its entirety, thanks to the fact that the residual dissolved ozone remains in the treated water for 20-30 minutes after said treatment. This highly ozonized water can be used in the first 20-30 minutes, to medicate or wash wounds and to sterilize implements, for example medical equipment, before being used as drinking water.

Therefore, the use of "Venturi effect" ejectors as described above, in combination with a contact reactor operating under pressure containing said nebulizing ejectors, makes it possible to obtain a high concentration of dissolved ozone and thus a greater efficacy of purification with respect to the known systems which entail bubbling of ozone inside an atmospheric tank, the bacterial load being equal. The greater efficiency also makes it possible to reduce the volumes of polluted water to be handled.

The applicant has found that the above described system makes it possible to disinfect effectively water polluted by different microbial species, for example contaminating micro-organisms (X. brevis, P.acidilactici e S. cerevisiae), fecal contaminants(£. aerogenes, E. coif), pathogens (S. aureus) and environmental contaminants (L. innocua), in particular Saccharomyces cerevisiae, Escherichia coli, Lactobacillus brevis, Pediococcus acidilactici, Listeria innocua.

Equally good results have been obtained with fungal spores such as A.acidoterrestris, B. subtilis, even if these require the use of higher ozone doses and longer contact times than with the above described micro-organisms.

The purification system with ozone 100 of the present invention further presents the following advantages compared with systems using chlorine or other chemical reagents:

- low running costs: energy is required only to produce ozone (use takes place at low temperatures), water consumption is reduced, as are the costs for treatment of the waste water;

- absence of toxic residues: by rapidly decomposing into oxygen, ozone in fact does not leave unwanted residues and is therefore advantageous both from the point of view of the safety of food (rinsing of the product is not necessary) and for the quality of the wastewater; - low electrical conductivity of the affluents thanks to the fact that ozone lowers the concentration of salts in solution; - reduction in the development of unpleasant odours because of the better oxygenation of the wastewater due to the conversion of ozone which improves the efficacy of the biological processes necessary for disposal;

- no storage of hazardous chemical substances since the ozone is produced in situ.

The above described system 100 can be installed inside a shed or in a container or micro- container with movable supports.

Numerous variations and modifications of detail within the reach of a person skilled in the art can be made to the present invention without thereby departing from the scope of the invention as set forth in the appended claims.

Claims

1. A system (100) for purification of microbiologically contaminated water comprising - a ozonizer (6) able to use undried air,

- a reactor (2) for contacting the water with ozone optionally operating under pressure of nitrogen,

- at least two nebulizing "Venturi effect" ejectors (5) using the water contained in said reactor (2) as driving fluid and in fluid communication with the ozonizer (6), - a pump (4) for feeding said at least one ejector (5) by recycling the water contained in said reactor (2), wherein said at least two ejectors (5) are inside said reactor (2) and are submerged by the water contained in said reactor (2), said ejectors being spaced apart from each other along the vertical axis of said reactor (2) as to create a high-turbulence spiral movement in the column of water between the two ejectors.

2. System according to claim 1 further comprising at least a particulate filter (3) placed upstream of said contacting reactor (2), a tank (7) for storage of the treated water placed downstream of said contacting reactor (2), a submerged pump (1) for charging the water to be purified in the reactor (2) and the relevant connecting piping.

3. System according to claim 1 or 2 wherein the contacting reactor (2) is cylindrical.

4. System according to any one of the preceding claims wherein the reactor (2) operates under an overpressure less than 10 psi, preferably under an overpressure ranging from 1 to 4 psi.

5. System according to any one of the preceding claims wherein said ejectors (5) are placed inside said reactor (2), such that the flow of the mixture water-ozone leaving from each ejector (5) entering said reactor (2) is tangential to the horizontal section of said reactor (2).

6. System according to any one of the preceding claims wherein each ejector (5) has a substantially cylindrical body having a first axial connection for coupling with a nozzle suitable for dispensing pressurized liquid and a second radial connection for coupling with a duct suitable for dispensing gas, and having an axial channel comprising four cylindrical chambers of different diameters, the third and fourth chambers being each equipped with a pair of radial holes and the axis of the first pair of radial holes being orthogonal to the axis of the second pair of radial holes.

7. System according to any one of the preceding claims wherein the ozonizer (6) comprises at least a generating ozone reactor formed by a pair of electrodes placed coaxially within a tubular container, which is closed at the ends by two perforated caps and is adapted to be passed through by a gaseous flow containing oxygen, and by a tubular dielectric element, preferably made of glass, pyroceram, borosilicate, located between said two electrodes in direct contact with the external electrode and spaced apart from the internal one so as to define a gap for the passage of said gaseous flow containing oxygen.

8. System according to any one of the preceding claims further comprising a refrigeration unit suitable to cool the temperature of the air entering the ozone generator (6).

9. System according to any one of the preceding claims constructed in form of a container or micro-container with movable supporting means.

10. A reactor (2) for contacting water-ozone for use in a system for purification of microbiologically contaminated water according to any one of the preceding claims.