"DEVICE FOR THE INTRODUCTION OP GASEOUS FLUIDS IN A

LIQUID MEANS"

The present invention relates to devices for the introduction of gaseous fluids in liquids, and, in particular, it finds application in the waste water and drainage treatment field, as well as in conditioning plants or for water oxygenation and refrigeration. DESCRIPTION OF THE PRIOR ART

Modern industrialization involves a continuous exploitation at an intensive level of environmental resources and raw materials, but it has to be able to return to the ecosystem what has not been used or what cannot be used anymore, in a form that is as much compatible with the environment itself as possible .

The environmental protection issue has recently become particularly a topical one, due to a higher sensitization of the population. The disposal of wastes and pollution abatement, for example, have by now become objectives the achievement of which the society has imposed upon itself, and also the rules have become much more stringent and restrictive in this regard.

The protection of the water supplies requires that the waste water is treated, before being discharged into watercourses, rivers, or the sea.

In this regard, the large cities, as well as the large industrial settlements, have to provide themselves with suitable depuration plants. Typically, such plants are extended on a large area that is often at the city outskirts, and comprise a series of tanks, each of which having specific functions .

In fact, on the whole, the treatment of the waste water or discharge water comprises more steps in sequence-, in order to separate the polluting substances, which are concentrated in the form of muds, from an effluent having such characteristics as to be able to be reintroduced both in the soil and in water basins without compromising the ecosystem. For example, as a totally general rule, a primary treatment step can be recognized, which mainly comprises processes of a physical nature, such as screening, crushing, or primary settling. Next, the secondary treatment follows, comprising the aerobic bacterial oxidation, also referred to as aeration, and optionally the secondary settling. The tertiary treatment, instead, provides for more advanced steps, aimed at reducing the nitrogen and phosphorous content. Furthermore, the treatment with activated carbon allows removing by adsorption the possible dissolved solids. Subsequently, the bacterial load abatement is possible thanks to disinfection treatments, for example, by means of chlorinating agents, or ozone, or weak organic acids.

The water depuration process allows reintroducing in the environment, for example, through the discharge into a river or directly into the sea, water that is no more polluted, thereby preserving the typical flora and fauna of the ecosystem.

As stated before, the protection environmental rules impose obligations not only to the community, such as in the case of the conditioning plants for the sewerage water treatment, therefore of civil origin, but also to the firms and private industries, which are required to meet to the costs necessary to the waste water disposal, which costs are often considerable, given the large dimensions and volumes of water that have to be treated and that may range from a few tens to thousands mVday.

The traditional conditioning plants comprise one or more waste water or drainage water treatment tanks, within which a stirring system can be placed, to the aim of keeping the liquid under stirring, thereby promoting the treatment processes. One or more air distribution systems are placed in the tanks in which the process of biologic oxidation takes place. Such systems are generally composed of a gaseous fluid source, connected to a compressor conveying air under pressure through a tubing system to one or more membrane diffusers, placed in series after one another, such that a same tube can supply more diffusers. Such diffusers can be anchored to the suppling tube through a clamp saddle, which is located at the opening in the tube wall and matching with the gaseous fluid inlet hole into the diffuser. Such a diffuser is, in turn, composed of a base, usually circular-shaped and in an air- and liquid- impermeable material, coated by an upper membrane that is secured at the edges to said base and having micro-holes. The gaseous fluid entering from the opening, then diffuses in the gap between the impermeable base and the upper membrane, and exits in the form of bubbles, having dimensions of 1-3 millimetres, through the upper membrane holes. However, such plants have a number of drawbacks. For instance, the upper membrane can withstand only pressures not exceeding 0.8 atmospheres, since it could tear at higher pressures.

Since the membrane is made from a limitedly elastic and quite delicate material, it shall be considered that high operative pressures cause the dilatation of the membrane pores, thereby originating bubbles having larger dimensions.

Since the exchange between gaseous fluid and liquid means is directly proportional to the contact surface, it follows that an increase of the bubbles dimensions causes a reduction of the exchange surface .

Furthermore, the breaking of one of the diffusers necessarily involves the interruption of the process. In fact, an uncontrolled and excessive gaseous fluid leakage from the damaged diffuser would occur, with consequent decrease of the pressure downstream such diffuser. In addition to this, the repair thereof would necessarily require the complete emptying of the tank, which therefore would remain non-operative. All of this causes a considerable lengthening of the times required for the waste water depuration, as well as an increase of the costs. Also . in the case where the cleaning of the upper membrane is required, for example, in order to remove debris which could obstruct the pores thereof, it would be necessary to remove the entire diffuser, the cleaning in countercurrent not being possible, since it would be hindered by the lower membrane.

Therefore, besides the implementation and repair cost, also the cost for the routine maintenance thereof, such as repair and cleaning, has not to be underestimated. Exactly in order to make the waste water depuration or treatment plants more economically accessible, the development of innovative systems, which are easier, less bulky and less expensive to be managed, and which are at the same time highly efficient is continuous. Therefore, the object of the present invention is to provide a device for diffusing a gaseous fluid into a liquid means, such as to completely overcome the drawbacks mentioned with reference to the prior art. These and other objects are achieved by a diffuser according to claim 1 and dependant claims 2 to 18, said diffuser being further able to be used in the implementation of waste water treatment plants, as from claims 19 and 20.

A method is also described, for the repair of a diffuser of the invention, according to claim 21. In order to better understand the invention and appreciate the advantages thereof, some exemplary, non-limiting embodiments thereof will be described herein below, with reference to the annexed Figures, in which:

Fig. 1 is a schematic view of a diffuser according to the invention; Figs. 2A and 2B represent front sections of the diffuser of the invention according to the section plane II'' in accordance with two aspects of the invention described herein below; Fig. 3 is a cross-section of the diffuser of the invention according to the section plane IH''' .

With reference to the Figures, a diffuser according to the invention is generally indicated with the reference 1; Fig ^' . 4 represents a schematic view of a further embodiment of the diffuser according to the invention; while

Fig. 5 represents a sectional view according to the plane II'' of a detail of the diffuser according to a further embodiment of the present invention. The diffuser 1 comprises gaseous fluid conveying means, indicated with the reference 6 in Fig. 1, and means for diffusing the gaseous fluid in a liquid means which are either connected or connectable to the conveyor means, wherein said diffusion means comprise a panel of porous material 2, said diffuser 1 being suitable to diffuse the gaseous fluid in the liquid means by means of its own porosity and an opening 4.

According to the present invention, by gaseous fluid is meant a gas or a mixture of gases, such as air, which has to be diffused into a liquid means. For example, nitrogen or, preferably, oxygen can be diffused. Said "gaseous fluid" can be stored in special containers, defined as "gaseous fluid source", indicated in Fig. 1 with the reference 7. In particular, said panel of porous material 1 is advantageously made from a porous resin. More particularly, said resin is advantageously highly porous, preferably having a density of about 0.9-1 g/cm ³ , and still more preferably it has pores with a diameter from about 6 to 30 microns through which the gaseous fluid exits.

Such material, therefore, advantageously allows a homogeneous diffusion of the gaseous fluid towards the liquid means, especially through bubbles of dimensions comparable to those of the pores of the resin and, therefore, very fine.

Consequently, the contact surface at the gas-liquid interface that is generated between the gaseous fluid and the liquid means in which the panel 2 is immersed is very high, and it is furthermore higher than the contact surface that there .is in the presence of bubbles characterized by higher dimensions, as occurs, for example, in the devices according to the prior art. Since the contact surface between the gaseous fluid and the liquid means is very large, the depuration activity performed by the fluid is more intense, thereby allowing shortening the times required for the liquid means treatment. Preferably, the resin material in which the panel 2 is made has a glass transition (tg=glass transition) ^• temperature of about 115 ⁰ C and a mechanical compressive strength of 30 N/mm ² . Furthermore, advantageously, it has a tensile strength of 10 N/mm ² . Consequently, such material is capable of withstand service pressures higher than the membrane diffusers known in the field, which, as stated before, generally do not exceed 1.5 atmospheres. In fact, the diffuser 1 of the invention, also thanks to the material from which the panel 2 is made, can operate up to internal pressures exceeding 5 atmospheres. ^' '

The mechanical strength and tensile resistance properties ensure, besides a higher general strength of the diffuser, a constant size of the micropores upon time; therefore, the performances of the panel 2 are reproducible upon time.

In addition, such resin or resin material is •preferably chemically resistant to acids, alkalis,- hypochlorites, civil, agricultural, industrial wastewater, and to seawater.

Consequently, the diffusers 1 will be able to be advantageously used for the depuration of water containing corrosive substances or compounds that can generally damage the known membrane diffusers. For the purposes of the present invention, said panel in porous material 2 can be made in different shapes, for example, it can be cubic-, parallelepiped-shaped, or it can be cylinder-shaped, or toroidal, or tube- shaped, the thickness of which can be of about 1-4 cm, or mixed solutions thereof.

By way of example, the panel 2 can be implemented by using a resin having the following percentage weight composition:

50-100 microns polymethylmethacrylate beads:

55.0%

- water: 24.0% methylmethacrylate: 11.645% - styrene: 3.90%

2-hydroxyethylmethacrylate: 1.8%

- benzoyl peroxide-added beads 1.5% trimethyloylpropane triacrylate: 1.0%

- ethoxylated surfactant: 0.9% - ethylene glycol - propylene glycol adipate: 0.16%

- N,N-dimethyl-p-toluidine: 0.08% antifoam agent: 0.015%

The above-indicated components are readily commercially available to those of ordinary skill in the art..

Furthermore, he/she will be able to vary the composition of the resin indicated above by using similar products, or by varying the percentages stated, so as to obtain a resin having however the above-indicated properties .

In a preferred aspect of the invention, the panel 2 of the diffuser 1 of the present invention has a sealing (not shown in the Figures) along the entire outer perimeter of the panel 2 and throughout the height of the panel itself. Such sealing has the effect of preventing the gaseous fluid from exiting the panel 2 side walls, which will thus diffuse in the liquid means only through the upper face 11.

Said sealing can be of a chemical type, for example, obtained by the application of impermeable materials, adhesives, resins, or it can be implemented through a rubber gasket, for example, of the "O-Ring" type, surrounding the edge of the entire panel 2. The same support plate (5') of the support structure (5), for example, can form an edge facing upwardly, thereby surrounding the panel 2 side walls. There are provided conveyor means β in order to convey the gaseous fluid coming from a source 7 to the panel 2 of the diffuser 1. Such source 7 can be represented by a cylinder in which the gaseous fluid is contained, for instance, under pressure, or it can be represented by the surrounding environment, from which the fluid is taken and preferably conveyed to the panel 2 under pressure, thanks to a compressor

(indicated with the reference 8 in Fig. 1) . Said conveyor means are preferably movable, i.e., they are not anchored to any fixed support, nor, for example, to the tank bottom, and can include one or more tubes in flexible material, departing from the source and entering the panel 2 in the proximity of one or more corresponding openings 4 made in the panel 2 itself. Preferably, said one or more openings 4 is/are obtained on the lower surface 12 of the panel itself, in a central or non-central position. Furthermore, the means for diffusing the gaseous fluid in the liquid means comprise a distribution circuit 3 realized within said panel 2, comprising one or more ducts and/or grooves extending in a substantially longitudinal direction (not shown in Fig. 1) , fluidically-connected to each other and/or to said opening 4.

In this manner, the gaseous fluid coining from the source 7 arrives to the opening 4, for example, through a conveyor means 6 represented by a connection tube, and homogeneously diffuses within the panel through said distribution circuit 3 represented by ducts and/or grooves.

In this manner, the emission of the microbubbles can take place from the entire upper surface 11 of the panel 2.

Advantageously, the thus-obtained diffusion of the gaseous fluid in the liquid means is more homogeneous when compared to the common membrane diffusers. Said conveying ducts and/or grooves can have a shape and cross-section that are different according to the needs; for example, they can be of a circular, or oval or squared or rectangular cross-section.

Furthermore, they can be parallel to one another, or they can intersect, thereby originating a grid or can radially depart from the opening 4, or they can be free recesses.

Alternatively, there are possible mixed embodiments with respect to what above described. In particular, Figures 2A and 2B represent two aspects of the invention, wherein the ducts and/or grooves of the conveying circuit have a closed cross- section, i.e., they have a duct surface having an annular cross-section, being entirely realized in the panel thickness (Fig. 2A), or they have an open cross-section, being obtained in the panel 2 lower surface 12 (Fig. 2B) ; in this manner, since said lower surface 12 of the panel 2 resting on the support plate 5, the total duct surface results to be partially defined by said support plate 5. Advantageously and surprisingly, the panel comprising the ducts and/or grooves of the thus-implemented distribution circuit 3 allows the transportation of the gaseous fluid with negligible load losses, even when the gaseous fluid inlet pressure, i.e., detected at the opening 4, is very high, such as of about 8-10 bars . Fig. 2 shows a cross-section of an exemplary embodiment of the distribution circuit 3 comprising ducts and/or grooves within a panel 2 of the invention, in which the ducts and/or grooves, in particular, form a grid. The implementation of the above-described ducts and/or grooves within the panel 2 of the diffuser 1 can take place during the preparation of the resin itself, for example, during the polymerization step or during the casting step of the resin into the mould, by introducing some bodies having suitable dimensions and shape equal to those of the ducts and/or grooves that are desired to be obtained. Once the panel has been formed, these bodies are removed, thereby leaving the ducts and/or grooves within the resin material.

Alternatively, the above-described ducts and/or grooves can be realized with suitable means, such as drill tips or mills having suitable dimensions and shapes.

Instead, the opening 4 will be able to be obtained in the preparation step of the panel 2. by suitably shaping the matrix or obtaining the suitable mouth with a mill. As regards, instead, the connection between the gaseous fluid source 7 and said opening 4, this can be advantageously implemented with readily commercially available standard fittings, such as, for example, conventional plastic tubes. The diffuser of the invention 1 can further comprise a support structure 5 suitable to support the panel 2 and to allow the positioning thereof.

Said support structure 5 can comprise a support plate 5' , and one or more support elements 10 for said plate. In particular, said support plate can be anchored to the panel 2 by means of screws or hooks through the interposition of a gasket, for example, of the "O-Ring" type, or it can bonded thereto by means of two-component, epoxy, or single-component adhesives (for example, the Loctite® product can be used) . Alternatively, there may be provided that the panel 2 and the support plate 5' are kept together by a suitably structured frame, for example, in metal. In an aspect ^' of the invention, the support plate 5' comprises one or more openings (not shown in Fig. 1) at the opening/s 4 obtained in the panel 2 to allow the passage of the conveyor means 6. Thanks to said support structure 5, the diffuser remains spaced from the bottom of the depuration tank in which it is located, for example, it can be spaced by about 4-5 cm, thereby reducing the "dead space", i.e., that portion of liquid means wherein no gaseous fluid is directly introduced and that, therefore, stagnates on the bottom of the tank itself. In addition, said support structure 5 can comprise hooking means 9 to move the support structure and, therefore, the panel itself.

Said hooking means 9 can be rings placed, for example, at the corners of the support structure 5 allowing to easily place and move the diffuser of the invention also without the aid of machineries. In accordance with a further embodiment, which is illustrated by way of example in Fig. 4, the panel 2 comprises a recess which forms a distribution chamber 13 that is intended to be placed in fluidic communication with the conveyor means 6 and having one or more outlet openings which the ducts and/or grooves of the distribution circuit 3 are connected to, or, alternatively, in direct communication with the porosity of the panel 2. In accordance with an embodiment of the present invention, such distribution chamber 13 has a substantially parallelepiped- or curved arch- (in cross-section) shape.

In accordance with such embodiment, such distribution chamber 13 is defined, on one side, by the above- mentioned recess formed in the panel 2 lower surface 12, and, on the other side, by the support plate 5' in which the opening 4 is formed.

This configuration facilitates the production and manufacturing of the panel 2 by moulding or casting, thanks to the open cross-section thereof. Consequently, the gaseous fluid coming from the source 7 will diffuse from the opening 4 into said distribution chamber 13 and from said distribution chamber 13 into the liquid means, through the porosity of the panel 2.

It has been surprisingly seen that this configuration, wherein the panel (2) of the diffuser (1) has a hemispheric shape or, more generally, a dome shape, is capable of providing a particularly advantageous performance.

In fact, the conducted tests have shown that, in such manner, it is possible to diffuse an amount of gaseous fluid that is much higher compared to the panels of conventional diffusers.

Consequently, a lower number of hours will be sufficient to obtain the same results that can be achieved in longer times with the conventional plants, thus reducing also the operative costs. In addition to that, the panel 2 according to this embodiment has shown to be capable of being able to operate at much higher pressures compared to the traditional panels and also compared to those having a cube-, parallelepiped-, or tubular shape, without being subjected to breaks.

Consequently, the panel will be able to be employed for a higher number of hours without being damaged, thereby allowing reducing the costs and times for the maintenance and repairing.

In a preferred aspect, the distribution chamber 13 has a tapered shape towards the opposite side of the plate.

This particular embodiment enhances the panel 2 structural strength and allows an easy withdrawal of the semi-finished product from the mould. In an aspect of the invention, the diffuser described can be used in the implementation of depuration plants. In order to prepare a plant of the type described by the present invention, the operator can connect the panel opening (s) 4 through the above-described conveyor means 6 to the gaseous fluid source 7. Next, the operator themselves can place one or more or tne diffusers 1 of the invention within the tank. Advantageously, the operation of placing the panels can occur also when the filling of the tank is already underway, or even also when the tank is already full.

On the contrary, when the step of the depurationprocess has been completed, or when a damage to one of the diffusers occurs, the latter will be able to be individually removed from the tank without emptying this one.

The skilled person in the art will be able to appreciate the extreme flexibility of use of the diffusers described in the present invention. In particular, said diffusers are very lightweight and easy to handle, so as to be able to be moved also by only one technician or operator.

Furthermore, the high porosity of the resin material from which the panel 2 is made, together with the high mechanical strength thereof, makes it possible to operate at service pressures that are high and that exceed those allowed by the known systems. In this manner, while keeping the used diffusion surface constant, the diffusers of the invention allow the introduction of an amount of gaseous fluid in the liquid means that is 4 ^" to 5 folds that dispensed by a conventional plant, such as, for example, a plant comprising membrane diffusers, in an equal time interval and at equal operative pressures. Furthermore, it shall be apparent to the skilled person in the art that the panel 2 of the diffuser 1 of the present invention involves lower maintenance costs . For example, for the cleaning of the panels, it will be sufficient to inject a suitable cleaning solution into the panel, i.e., injecting a basic or acidic aqueous solution in the same direction of the gaseous fluid diffusion, which operation can be carried out at the exterior of the tank simply by extracting the panel .

Furthermore, in the case of chipping or breaking or cracking of the panel ^* , this one will be able to be repaired by means of simple in situ micro-injections of resin material, in particular, of the same resin material from which the panel 2 is made. Advantageously, such repairing does not compromise in any manner the performances of the diffuser itself, which are thereby completely restored. The above described diffusers 1 of the invention can be used for the realization of plants useful in many fields, thanks to the high performances and the various advantages above listed. For example, they can be used for the oxygenation of active muds or landfill site percolates, to oxygenate lubricant- refrigerant liquid in the mechanical field or civil drainages . The possibility of being able to insert or remove panels from any positions, make them an absolutely indispensable tool -in all those situations wherein temporary interventions have to be performed, such as, for example, ponds, expanses of water, watercourses, which are polluted due to unforeseeable events, thus ensuring an intervention efficiency that had been impossible to date, providing for the possibility of establishing emergency response units, A further and very important application is in the field of fish-farming, where the need to maintain a sufficient water oxygenation is a factor of crucial importance. The high oxygen transfer ability ensured by the plant of the invention makes it an irreplaceable technical aid, also in those open sea sites where the conventional plant has no reason of being present, thus allowing, whenever necessary, the integration of air with pure oxygen, ensuring a very high yield due to the microbubbles action. The possibility of anchoring the panels to bearing structures, positioning them at the bottom of the retaining net of the sea fish-farming sites, with extremely rapid times and easy modes contributes to an optimization of the fish-farm yields. In a further aspect, the diffusers of the present invention can be employed for the refrigeration of process waters.

In fact, the current systems provide, for the thermal exchange, the distribution of the liquid on very large surfaces in order to maximize the air-liquid contact surface, which, however, involves machines and structures of notable dimensions, whose efficiency tends to quickly decrease upon time and the maintenance of which is complex and expensive. The diffusers of the present invention allow to multiply the contact surface thanks to the production of millions of microbubbles, in reduced surface units, vastly improving the exchange quality, at the same time offering the possibility to carry out an extremely efficient and rapid maintenance, as well as at definitely lower costs compared to the traditional plants .

Furthermore, it is possible to foreseen, at the exit of the refrigeration air flow, a condenser for the recovery of evaporated water and recovered heat.

The shapes of the panels for the uses indicated will be able to be easily determined by the technician in the field, based on the volumes and positions in which they shall be inserted. In a further aspect, the diffusers 1 described in the present invention can be used for the realization of plants in the hydromassage sector, and can find application in swimming pools .

In a still further aspect, the diffuser according to the present invention will be able to be advantageously used in tanks for enzymatic treatment, for example, for the denitrification of waste water and process water.

In fact, the diffuser of the present invention allows diffusing a gaseous fluid in the liquid means in a constant and homogeneous manner.

In a further aspect, there can be foreseen the use of the device of the present invention for the nitration of liquid and, therefore, for the implementation of filtration.

Therefore, in such an embodiment, the liquid to be filtered, which is coming from a source, passes through conveyor means and suitable means, such as, for instance, the above mentioned distribution circuit, to the panel 2, which passes therethrough thanks to its porosity. In this manner, the collected liquid exiting the panel 2 is free from the corpuscular material initially comprised in the liquid to be filtered, which remains entrapped within the panel 2 itself. To the above described embodiments of the diffuser 1 of the invention, thee skilled person in the art, in order to meet contingent specific needs, will be able to make a number of additions, modifications or replacements of elements with the functionally equivalent ones, without however departing from the scope of the annexed claims. Each of the characteristics described as belonging to a particular embodiment can be implemented independently of the other described embodiments .