WO2017013566A1

WO2017013566A1 - Continuous self-regenerating filter

Info

Publication number: WO2017013566A1
Application number: PCT/IB2016/054258
Authority: WO
Inventors: Antonino Schillaci; Giovanni SCHILLACI
Original assignee: Remediation S.R.L.
Priority date: 2015-07-17
Filing date: 2016-07-18
Publication date: 2017-01-26
Also published as: ITUB20152260A1

Abstract

A filtering apparatus for liquids, based upon the structure and technology of ascending-flow deep filters of the continuous-backwash type, equipped with means for continuous self-regeneration of the filter bed, whether this be constituted by active material or inert material, of the type comprising a vertical cylindrical tank (1) having the bottom part that narrows in the form of an upturned truncated cone (3a) or that narrows by means of a crowned end plate, where the liquid to be filtered, referred to as "influent", is fed through an inlet (4) and evenly distributed over the filter bed from the bottom of the unit through a distributor (5) in which the liquid flows upwards traversing the filter bed (8) and is discharged from the filtering apparatus through an outlet overflow (9) for the effluent, regulated by an overflow, which determines the static level (10) of liquid present in the filter; where the granular particles that constitute the filter bed and the possible solids trapped therein are drawn downwards and then sent towards the top of the filter by a purposely provided lifting device referred to as "airlift" (11) present in the proximity of the bottom of the tank (1) and positioned at the centre of the filter; where the granular particles drawn downwards and lifted by the airlift free the trapped suspended solids; and where the granular particles at a high sedimentation rate are left to fall back onto the filter bed (8), thus reconstituting it, whereas the particles with a low sedimentation rate, i.e., the suspended solids that have been freed, are discharged into a purposely provided conduit (26); thus obtaining a backflow filtering: the influent, rich in suspended solids and/or dissolved substances, in its ascending motion encounters in the first filtering steps the granular filtering medium that, with descending motion, prepares to undergo the cleaning steps so that a large part of the pollutant charge is immediately removed from the filter bed, said filtering apparatus being characterized in that to apply regeneration of the filter bed in the filter itself, provided at the intake mouth of the airlift device (11) is a purposely designed washing and contacting chamber (22), referred to as "contacting reactor", and in that provided at the other end of the airlift device is a separation and finishing section (15 and 18), referred to as separator reactor.

Description

CONTINUOUS SELF-REGENERATING FILTER

~k ~k ~k ~k ~k

The invention basically relates to application of regeneration of granular media in ascending-flow deep filters of the continuous-backwash type and to removal of the pollutants present in a liquid.

By "regeneration of the granular media" is meant advanced removal of particles that are trapped in the filter bed or of contaminating substances that were dissolved in the filtered fluid and that are fixed on the solid phase, so as to preserve as long as possible, thanks to continuous backwash, the filtering properties of the bed.

To obtain the foregoing it is required to adopt constructional stratagems that enable, by means of a more energetic washing, a better cleaning of the filter bed from the trapped particles, and, by means of conventional or advanced oxidation techniques, removal and oxidation of the substances adsorbed or chemically bonded to the filter bed.

PRIOR ART

Deep ascending-flow filter with continuous backwash of the filter bed Removal of suspended solids or abatement of substances dissolved in water can be carried out with a granular filtering medium inserted in a deep ascending-flow filter of the continuous-backwash type.

REMOVAL OF THE S USPENDED SOL I DS

The liquid to be treated is fed from the bottom of the unit, conveyed by a series of ascending-flow pipes and evenly distributed over the bed of sand through the holes of a distribution system. The liquid flows upwards traversing the bed of sand, which, instead, moves downwards drawn by the washing system. The liquid that has been filtered is collected by means of an outlet overflow and then discharged from the filter. Simultaneously, the particles of sand, together with the solids trapped therein, flow downwards conveyed by the intake duct of a pipe of the airlift type positioned at the centre of the filter. Introduction of small amounts of air in the bottom part of the ascending-flow pipe entails an action of return upwards of the sand, of the solids, and of the water, thus giving rise to a mixed fluid with a density lower than that of water. The impurities are removed from the granular particles as a result of an action of abrasion during the turbulent ascending motion. Once the top of the airlift has been reached, the suspension containing the impurities overflows in the central discharge section. The sand is moreover subject to a further cleaning action in its descending movement through the washing compartment . By positioning the weir for the effluent that has been filtered above the weir of the washing compartment, it is possible to generate an ascending flow of water that has been filtered, which traverses the washing system itself, whereas the sand traverses it with descending motion. In its motion upwards the liquid entrains the impurities, which have a lower sedimentation rate than that of the sand. The clean sand is redistributed over the filter bed, thus making it possible to obtain a continuous flow of filtrate and continuous washing of the filter bed.

Washing of the surfaces from the particles that constitute the filter bed occurs thanks to the shear stresses that are generated in the turbulent ascending motion up the airlift pipe. Use of the current of air used for supplying the ascending flow enables production of an action of abrasion that is more energetic than in the case where the particles traverse the same stretch only conveyed by the water. Consequently, in this way, a substantial saving of effluent used for washing is obtained .

REMOVAL OF DISSOLVED SUBSTANCES

In the case of removal of dissolved substances, for the filter bed active carbons are used instead of sand to exploit their adsorbent capacity. Adoption of active carbons entails minor modifications to the apparatus described above (to prevent fluidization of the granules of active carbon on account of the lower specific density as compared to sand) and different settings for the washing operations. In fact, the influent that requires filtering with the active carbons usually has low concentrations of suspended solids and low turbidity, and consequently the washing cycles may be intermittent in so far as the risk of clogging of the filter is low. By so doing there is a saving of washing water and energy.

The filters charged with active material transfer the pollutant substances to another phase (solid phase), thus creating an accumulation that leads to exhaustion of the filtering capacity. Once saturation of the active material has been reached, it is indispensable to stop filtering in order to replace the charge of the filter.

Advanced chemical-oxidation processes

Advanced chemical-oxidation processes generally envisage generation and use of free hydroxyl radicals (^"OH) as strong oxidizing agents for the destruction of compounds that cannot be oxidized by conventional oxidants such as oxygen, ozone, or chlorine. The oxidizing power of hydroxyl radicals is amongst the highest and these reacts with the dissolved species, triggering a series of oxidation reactions that can lead to their complete mineralization (complete degradation) . Hydroxyl radicals are able to oxidize almost all the substances present at the reduced state, without any particular restrictions.

At the current state of the art, a number of technologies are available for producing the ·0Η radicals in aqueous phase, the most interesting ones for this purpose being, for example: • O3 with high pH

• 0₃ + UV

• 0₃ + H₂0₂

• 0₃ + UV + H₂0₂

• 0₃ + Ti0₂

• 0₃ + Ti0₂ + H₂0₂

• H₂0₂ + UV

• Ti0₂ + UV

Some of the processes referred to above exploit the mechanism that consists in generation of ·0Η radicals via photolysis with UV radiation of conventional oxidants such as O3 and H2O2, either dispensed individually or simultaneously. The common factor consists in the fact that chemical agents will be used that are already in themselves oxidants and that, if subject to UV radiation, react so as to give rise to compounds provided with an oxidizing power that is far higher than the starting ones, such as ·0Η radicals.

0₃ + UV PROCESS

The O3 + UV process in water produces H2O2, which is in turn subjected to photolysis, converting into hydroxyl radicals. The coefficient of molar extinction of O3 is much higher than in the H2O2 + UV process; hence the O3 + UV technique requires a low dose of ozone and a time of exposure to UV radiation shorter than does the method that uses hydrogen peroxide directly (see, H2O2 + UV process) .

0₃ + H2O2 PROCESS

The O3 + H2O2 process is used for those compounds that are unable to absorb UV radiation (such as TCE and PCE) , and ozone-based and hydrogen-peroxide based processes of chemical oxidation hence prove more effective.

H₂0₂ + 20₃ → ΌΗ + ^"OH + 30₂

H2O2 + UV PROCESS

The H2O2 + UV process produces hydroxyl radicals according to the following relation:

H₂0₂ + hv → ^"OH + ^"OH

This represents one of the most promising techniques, backed up and encouraged by the results so far obtained in the literature. It should, however, be pointed out that, in some cases, the application of said process of chemical oxidation is not possible on account of the fact that hydrogen peroxide is characterized by a low coefficient of molar extinction; consequently, high concentrations of H₂O₂ are necessary, and in any case there is a poorly efficient exploitation of the energy associated to UV radiation.

Ti0₂ + UV PROCESS

Another technique, once again provided by way of example, is T1O₂ + UV advanced oxidation. Photocatalysis is the natural phenomenon whereby a substance, referred to as photocatalyst , through the action of light (natural light or light produced by special lamps) modifies the rate of a chemical reaction. In the presence of air and light, a marked oxidizing process is activated, which leads to decomposition of pollutant organic and inorganic substances that enter into contact with said surfaces. Photocatalysis is hence based upon the use of a photocatalyst (this is a semiconductor that, once activated by UV radiation, enables the mechanism of action that is clarified hereinafter) . Generally, photochemical degradation in heterogeneous catalysis (i.e., with catalysts that are not soluble in water) of a pollutant in aqueous phase envisages the following stages:

a) activation of the catalyst by light;

b) transfer of the pollutant from the aqueous phase to the surface of the catalyst;

c) adsorption of the pollutant on the surface of the catalyst;

d) photocatalyt ic reaction in the adsorbed phase; and

e) desorption of the product of degradation from the surface of the catalyst.

Ti0₂ + hv → Ti0₂ (e^", h⁺)

A characteristic of the oxides of the semiconductor metals is the marked oxidizing power of their holes h⁺, which can react with the water absorbed on their surface.

The following reactions show how the electrons of the conduction band can reduce the oxygen that acts as electron acceptor for formation of the super-oxide ion (1), whereas the holes can oxidize the molecules of the donor, which in the case in point may be an organic contaminant (2) .

Ti0₂ (el + 0₂ → Ti0₂ + ^"0R^~ ₂ (D

H₂0 + Ti0₂ (h⁺) → ^"OH + Ti0₂ + H⁺ (2)

The water absorbed on the titanium-oxide surfaces is oxidized by the holes and gives rise to hydroxyl radicals (^"OH) . Next, this radical reacts with the organic matter. If oxygen is present in this reactive process, the radicals, which are present between the organic compounds and the oxygen molecules start a chain reaction that ideally leads the organic materials to decompose into carbon dioxide and water.

T1O₂ possesses a series of requisites that enable practical and convenient use thereof: it is readily available, inexpensive, chemically stable in the reaction environment, has an extensive surface area, and its absorption spectrum comprises radiation in the near UV and in the visible.

Known from US 2006/000785 are a (radial) filtering apparatus and an ascending-flow deep filter of the continuous-backwash type that envisage the use of the so-called "moving bed" principle, the use of air for lifting the filtering medium, as well as the use of ozone. In the systems described in US 2006/000785, the action of mechanical cleaning on the filtering particles occurs only during transfer along the duct towards the top of the filter. Basically, these are common filters to which particular arrangements have been applied for use of reagents in the treatment of waters with solvents. Unlike the present invention, in US 2006/000785 administration of the reagents occurs in the water to be treated in a pre-reactor external to the filter. These reagents are moreover administered in modalities such as to cause flocculation of the contaminants dissolved in water. The floes thus produced can thus be separated by the traditional filters described in the same document US 2006/000785. The action of mechanical cleaning on the filtering particles occurs during transfer along a duct towards the top of the filter and, in a way not clearly specified, in a separator.

US 2009/178980 describes a filter with a structure very similar to the ones already known, present in which are solutions for optimizing disinfection of the waters already filtered using UV rays. Also in this case there is described the use of various reagents to be administered in the waters to be treated outside the filter. The action of mechanical cleaning on the filtering particles occurs during transfer along a conduit towards the top of the filter, as well as in a washbox.

Moreover known from W02007 / 134064 is a wide range of combinations of technologies of treatment of waters that use sand filters, which do not envisage any washing chamber or contacting reactor at the base of the filter itself.

Finally, US 5681472 describes a filter presenting specific solutions for separating the air introduced into it to obtain nitrification. These are basically modifications that concentrate at the top of the filter except for injection of diffused air at the base of the filter bed. No modification is present to the well-known air-lift system .

One of the purposes of the present invention is to provide an altogether innovative continuously self-regenerating filter, which presents high efficiency and reliability as compared to the known technical solutions referred to above.

It should also be noted that, according to the prior art mentioned, in the cases where a perfectly conical geometry is used at the base of the airlift, this shape has been chosen with the sole purpose of optimizing lifting of the filtering medium .

Unlike the technical teachings present in the documents referred to, according to the present invention the function that this component has to perform is different. The effectiveness of the lifting phase is reduced in order to favour the efficiency of the cleaning and/or contacting step: this is obtained - according to the present invention - by envisaging a dome shape that increases the stay time of the particles in the bottom area of the airlift where swirling motion is present .

More specifically, according to the invention, a filter is envisaged, the base of which has been modified so that one of the components present therein, in particular the vault (or cap or bell), can perform a number of functions simultaneously:

- distributor: the filter bed rests thereon and little by little is captured by the airlift ;

- chamber for washing the filtering medium: it is not envisaged in any of the aforementioned patents;

- contacting reactor: in the case where reagents are administered, it is present elsewhere outside the filter; and

- manifold for the airlift. A better understanding of the invention will be obtained from the ensuing detailed description and with reference to the attached drawings, which represent, purely by way of non-limiting example, a preferred embodiment and some variants thereof.

In the drawings:

Figure 1 is a diagram of a deep ascending-flow filter with continuous backwash of a known type;

Figure 2 is a vertical schematic cross- sectional view of a filter according to a preferred embodiment of the present invention;

Figure 3 shows a detail regarding the bottom part of the example of embodiment of Figure 2;

Figures 4 and 5 show constructional details regarding the top part of the example of embodiment of Figure 2;

Figure 6 illustrates the displacement of the height of the weir for overflow of the washing water;

Figure 7, which is similar to Figure 3, shows a variant that envisages adoption of an active granular material;

Figure 8 represents an example of embodiment in which O3, and/or H2O2 are/is administrated also in the separator reactor through specific inlet points ;

Figure 9 regards a further embodiment in which substrates coated with T1O₂ are provided;

Figure 10 is a variant of Figure 9, in which regeneration is provided by means of advanced oxidation techniques by administering fluid oxidizing agents through specific injection points;

Figure 11 is a variant of the regeneration of Figure 10, which can be used in the case where solids trapped in the granules that constitute the filter bed were to be present and that this were to create problems of absorption of UV radiation: in this case, the UV + T1O₂ block can be shifted onto the top of the filter, together with the means for administration of oxidizing agents; and

Figure 12 shows a variant in which the UV lamps are positioned outside the bell of the washing section of the separator reactor in order to extend the benefits of advanced oxidation also to the effluent that has been filtered by positioning, above the filter bed, lamellar packs having a complex geometry.

The present invention substantially relates to an innovative filtering apparatus, provided with particular constructional stratagems to implement regeneration of the granular media in ascending- flow deep filters of the continuous-backwash type. According to the invention, the aforesaid stratagems enable a longer duration of the capacity of removal of the dissolved substances of the filter bed constituted by active materials, as well as a greater efficiency of washing of the filter bed constituted by inert sands.

Currently known ascending-flow deep filters of the continuous-backwash type act with a moderate mechanical action to remove the suspended solids from the filter bed, or else with the simple capture of the dissolved substances by active filtering media. In the latter case, continuous backwash prevents only mechanical clogging of the filter, and it is envisaged that regeneration of the media will occur offline, hence requiring replacement of the filtering charge, with consequent interruptions in the service.

The particular constructional stratagems forming the subject of the present invention, applied to filters of the type described above, not only improve substantially the levels of performance of washing of the inert filtering media, but enable introduction into said filters of new functions, such as oxidation of the contaminating substances within the filter itself. Advantageously, application of oxidation techniques within filters of the continuous-backwash type makes it possible to improve considerably the quality of the wastewater and to obtain a continuity of operation that is clearly superior as compared to systems that envisage the use of an active filter, which tends to get saturated with use .

Hence, the present invention envisages constructional stratagems that enable regeneration of the granular media:

- both in the case where they are active, as in the filtering carried out for removal of the dissolved pollutant substances, since via the oxidation and/or advanced-oxidation processes the sequestering or adsorbent characteristics of the active filter bed are restored,

- and in the case where they are inert, as in normal bulk filtering with sand bed (or with filtering media constituted by any inert granular particle) , since in this way there are obtained better levels of performance of washing of the surfaces of the particles that constitute the filter bed.

As will be seen in greater detail in what follows, the invention substantially regards:

• arrangements for improving removal of the impurities that adhere to the granular particles (creation of a washing chamber with turbulent flows, new design of the top washing compartment) ;

• administration of oxidizing agents into the washing chamber with turbulent flows, and into the top washing compartment;

• arrangements for increasing the contacting time between the particles and the oxidizing fluids ;

• application of photolysis or of photocatalysis (advanced-oxidation processes) in the washing sections by adoption of lamellar packs coated with T1O₂ and of UV lamps;

• application of photolysis or photocatalysis (advanced-oxidation processes) as finishing treatment of the effluent by adoption of lamellar packs coated with T1O₂ and of UV lamps above the filter bed; and

• conditioning of the filter bed with purposely provided photocatalyst s (T1O2) .

According to the present invention, the choice of the most appropriate method of advanced chemical oxidation, such as application from among, or a combination of, strong oxidizing agents (for example, O3 and H₂O₂) , catalysts (transition-metal ions or photocatalyst s such as TiC>₂) , and UV radiation, must take into account the following considerations:

- the nature, physico-chemical properties, and concentration of the pollutant that is to be removed;

- the biodegradability of the pollutant;

- the presence of scavengers of ·0Η radicals, i.e., of substances that are able to transform the radicals of the oxygen into non-radical compounds, and of compounds that absorb UV radiation;

- the appropriateness of the discharge waters to be treated: the pH of the solutions must be carefully regulated on account of the sensitive equilibria that govern the processes of formation of the ^'OH radical; and

- the presence of possible components in the waters, which could interfere with the reaction intermediates .

DETAILED DESCRIPTION OF THE INVENTION

In what follows, there are first illustrated the constructional stratagems that improve washing of the surfaces of the granular particles and that at the same time increase the contacting times between the particles and the oxidizing agents, and then the constructional and functional modalities of application of the oxidation techniques will be described .

With reference to Figure 2, the apparatus is constituted by a vertical cylindrical tank (1), supported by supports (2), with the bottom part that narrows in the form of an upturned truncated cone (3a) having the final part with a plane end plate (3b) or else with the bottom part of the vertical cylindrical tank that is directly closed with a crowned end plate. The end plate (3b) is flanged in a removable way to the conical bottom (3a) of the tank (1) to enable removal from beneath of the granular filling. Connected to the end plate (3b) is the bottom drain (3c) for enabling, during maintenance operations, emptying of the liquids. The drain may be protected by a grill appropriately sized for withholding the granular filling.

The influent to be filtered is fed through the inlet (4) and evenly distributed over the filter bed from the bottom of the unit through a circular distributor (5) with holes in the underlying part to prevent clogging. The delivery pipe feeds the circular distributor through thin radial branches (7) and is located at the centre of the filter (6) so as not to alter the flow of the granular media. The liquid flows upwards within the filtering medium (8) and is discharged by the filter through an outlet overflow (9), regulated by a weir, which determines the static level (10) of liquid present in the filter.

At the same time, the granular particles that constitute the filter bed and the possible solids trapped therein are drawn downwards into the washing and contacting chamber (22), or contacting reactor, by the airlift device (11) present in the proximity of the bottom of the tank (1) . In this way, a backflow filtering is obtained: the influent, containing suspended solids and/or dissolved substances, in its ascending motion encounters in the first filtering steps the granular filtering medium, which prepares, with descending motion, for undergoing the cleaning step. Advantageously, in this way most of the pollutant charge is immediately removed from the filter bed.

The washing and contacting chamber (22), or contacting reactor, is characterized in that it has the top part designed to exerting most of the action of cleaning of the surfaces of the particles, whether this action is mechanical or chemical. The impurities that have adhered and are trapped are separated from the granular particles as a result of an action of abrasion against the surfaces of the chamber and of the shear actions in the turbulent motion of the fluids also during ascent along the intake duct (12) of the airlift system .

In the example described (Figure 3), the washing and contacting chamber (22) set at the base of the tank (1) of the filter, which hereinafter will be also referred to as "contacting reactor", may be shaped like a vault, cap, or bell (19) and is connected in its top part to the intake duct (12) of the airlift system. Located in the bottom part of the contacting reactor is the nozzle for delivery of the compressed air (13) necessary for supplying the airlift. The contacting reactor (22) extends downwards so as to let through the granular particles and the discharge water a little at a time, from the top downwards, through the annulus that is created between the bottom base of said cap (19) and the upturned cone (3a) , or crowned end plate, set at the base of the container that constitutes the filter. Underneath the vault (19) of the contacting reactor (22), the granular particles are free to move and be agitated under the action of the compressed air introduced, thus releasing the trapped impurities. The cap, or vault, or bell shape (19) is such as to enable creation in the contacting reactor (22) of convective motion with a high degree of turbulence that produces excellent performance as regards washing of the surface of the granular particles that constitute the filter bed. Moreover, thanks to said turbulent motion, it is possible to optimize the action of the oxidizing agents on the contaminants present, increasing the stay time in the reactor (22) of the granular particles themselves .

The airlift device (11) present on the bottom of the tank is completed by an intake duct (12) connected to the top part of the cap (19) of the contacting reactor (22) and positioned at the centre of the filter. With a purposely provided duct (13) small amounts of air are introduced into the bottom part of the contacting reactor. This entails, in addition to the turbulent motion underneath the cap (19), an action of return of the granular particles that constitute the filter bed and of the solids trapped therein, and lifting thereof. Once the top of the airlift intake duct (12) has been reached, the suspension containing the impurities overflows (14) into the central discharge device (15), which separates the flows of the granular particles from the air and from the water that has ascended together with them. The granular particles, which are heavier, drop towards the top washing compartment (18), the air is discharged into the atmosphere, and the water rich in suspended solids is discharged into a purposely provided conduit (Figure 4) .

The ensemble constituted by the central discharge device (15) and by the top washing compartment (18) will be referred to in what follows as "separator reactor".

The granular particles undergo in the top washing compartment (18) of the separator reactor a further cleaning stage that releases new suspended solids (or pollutant substances) . To remove the latter it is possible to generate an ascending flow of filtered water, which traverses the top washing compartment (18), when the weir (16) is positioned so that it is located below the weir for the effluent (9) . This flow entrains upwards the suspended solids, which are freed from the granular particles as they traverse the top washing compartment (18) of the separator reactor. The ascending flow, rich in suspended solids characterized by a low sedimentation rate, is discharged through the overflow on the weir (16) into a collection basin (17) and then discharged into a purposely provided conduit. The granular particles, after traversing the top washing compartment (18), drop back onto the filter bed (8) thus reconstituting it.

It should also be noted that, advantageously, unlike what occurs in the contacting reactor (22), washing in the top washing compartment (18) of the separator reactor is performed with clean water, already filtered, and hence suitable for finishing the washing process.

In the preferred embodiment that is described, the top washing compartment (18) of the separator reactor will be described hereinafter with reference to Figure 5. The current constituted by air, washing water, granular particles, and suspended solids, climbs with turbulent motion up the airlift pipe (12) . In the top stretch, before reaching the central discharge compartment (15), the airlift pipe has openings (holes or eyelets) (20) through which part of the granular particles at a higher sedimentation rate can exit from the pipe itself and directly enter the washing compartment (18) of the separator reactor. This washing section is constituted by various cap- shaped chambers (21) set on top of one another where a turbulent motion is set up caused by propagation through the holes (20) made in the pipe of the turbulence of the ascending the airlift flow. In these chambers, which have the shape represented in the drawings, the granular particles encounter one another in turbulent regime, and the water that has been filtered climbs up the washing section. The washing and abrading action on the walls of the chamber frees any possible solids that still adhere to the surface of the filtering material. According to a peculiar characteristic of the invention, the holes or eyelets (20) are located in the top part of each chamber (21) so that the air will not accumulate above the caps that constitute the chambers (21) themselves.

In the example of embodiment that is described, the ascending flow of the effluent that has been filtered and cleaned, which traverses the washing section of the separator, can be regulated by controlling the height of the weir (16) in the central discharge compartment (15) of the separator reactor. By acting in this way, it is also possible to modify certain parameters that regulate the modalities of cleaning of the granular particles. Thanks to this stratagem, it is in fact possible to adjust more finely the ascent of the granular particles, automatically compensating for the flow rate of clean washing water. By so doing a differentiated action is performed on the flow rates of the three phases present in the airlift pipe, and the composition of the flow itself, which is made up of water, more or less fine suspended solids, and air can be hence modified. For example, as may be seen in Figure 6, given the same amount of air supplied in the airlift, it will be possible to adjust, by varying the height of the weir, the ratio between the flow rate of the granular particles that are subjected to the washing action and the water containing suspended solids that climbs up pushed by the airlift action. By increasing the overflow there will be a reduction both in the flow rate of the granular particles and in the flow rate of the washing water ascending along the airlift pipe (12) , but the flow rate of granular particles will be reduced to a proportionally greater extent. This occurs since said flow rate depends upon the entraining forces caused by viscosity of the fluid in which the particles are suspended, which, as is known, is a function of the square of the relative velocity between the fluid and the particles. Application of this solution in the case of adoption of oxidation techniques in the filter is of particular importance since it is possible to separate the flow rate of air blown into the contacting reactor and the flow rate of recirculation of the granular particles, it thus being possible to lengthen the times of stay in the reactor, without thereby reducing the turbulence induced by the flow of air and removal of the contaminants.

In the example illustrated, in the case where dissolved substances were to be present in the influent, it is possible to carry out a targeted treatment by adopting a deep ascending-flow filter of the continuous-backwash type with the constructional stratagems described above, charged with a specific active material. In this way, it is possible to withhold the dissolved substances, prevent clogging of the filter bed, remove possible suspended solids, and clean the surface of the active granular particles, thus guaranteeing a high quality of the effluent and excellent levels of performance. It is moreover possible to use an inert filtering material in the case where only suspended solids were to be present in the influent .

Advantageously, even adopting a different type of material that constitutes the filter bed, it is not necessary to make structural modifications to the filter described above, but it is sufficient only to regulate appropriately the operating parameters of the filter itself. For example, following upon the choice of the material of which the granular particles are constituted, it is possible to adopt more or less intense, continuous or discontinuous, washing operations.

With reference to Figure 7, which shows a preferred variant that envisages adoption of an active granular material, in order to delay exhaustion of the charge of the filter, it is possible to carry out administration of a mixture of oxidizing fluids in given points of the filter. For example, it is possible to administer O3, and/or H2O2 directly into the contacting reactor (22), so that it becomes an oxidizing reactor, through specific inlet points (25) . In this way, during the step of initial washing, the filtering medium is subjected to the action of the oxidizing agents, which free the surface of the granules from the pollutant substances by oxidizing them. Administration of O3 and/or H2O2 occurs through specific inlet points (25) so as to optimize diffusion of the oxidizing agents in water (e.g., fine-bubble diffusers) . The contacting reactor (22) and the separator reactor (18) are specifically designed to increase exposure of the granular particles that constitute the filter bed to the oxidizing agents (it is, precisely, designed as described previously) . In particular, by adopting said system in the contacting reactor (22), the chemical reactions of oxidation are optimized. Consequently, it becomes the reactor in which regeneration of the filtering medium occurs according to the modalities set forth above.

It is moreover possible, for example, to administer O3 and/or H2O2 also in the separator reactor (18) through specific inlet points (25) (Figure 8) .

According to the type of treatment and the type of service required, it is possible to evaluate whether to introduce the oxidizing agents during filtration or only in a purposely provided regeneration step envisaged upon periodic arrest of delivery of the influent.

In a further variant, it is moreover possible to envisage techniques of advanced chemical oxidation by combining to O3 and/or H₂O₂ catalysts (T1O₂) and/or UV radiation.

In a further embodiment (Figure 9) substrates coated with T1O₂ are envisaged both as building materials for the contacting reactor (22), and as purposely provided fillers of complex geometry with an extensive specific surface, as well as granules to be added to the active filtering material, along with lamps located in suitable points.

An example is the case of use of a substrate with a large specific surface coated with T1O₂ (24) combined with UV lamps (23) applied directly in the washing and contacting chamber (22) . Said solution is possible in the case where the influent does not present significant amounts of suspended solids, which would prevent diffusion of UV radiation.

In the example referred to in the previous point, it is also possible to adopt regeneration by means of advanced oxidation techniques by administering fluid oxidizing agents through specific injection points (25) (Figure 10) . In this way, the oxidizing fluids introduced from the bottom of the filter are immediately exposed to the combined action of radiation and of the catalyst, which optimizes generation of ·ΟΗ radicals.

A further example is provided in Figure 11: in the case where solids were to be present trapped in the granules that constitute the filter bed, and this were to create problems of absorption of UV radiation in the contacting reactor (22), the UV + T1O₂ block can be shifted onto the top of the filter together with the means for administration of oxidizing agents. In this case, the separator reactor (18) is modified in such a way as to house the UV lamps (23), the systems for injection of the oxidizing agents (25) and the catalyst pack (24) . By so doing, a strong oxidizing power is supplied to the ascending flow, which eliminates the pollutant substances from the granules and from the washing water itself (N.B. the lamps can be inserted inside the bell, and/or outside, in this case adopting a transparent bell) . A further example is represented in Figure 12. By locating the lamps outside the bell of the washing section (18) of the separator reactor, it would be possible to extend the benefits of advanced oxidation also to the effluent that has been filtered by positioning above the filter bed, in combination with the UV lamps, lamellar packs with complex geometry, in order to increase the specific surface, which are coated with T1O₂.

Claims

1. A filtering apparatus for liquids, based upon the structure and technology of ascending-flow deep filters of the continuous-backwash type, equipped with means for continuous self-regeneration of the filter bed, whether this be constituted by active material or inert material, of the type comprising a vertical cylindrical tank (1) having the bottom part that narrows in the form of an upturned truncated cone (3a) or that narrows by means of a crowned end plate, in which a supply inlet (4) is provided for the liquid to be filtered, referred to as "influent", connected to a distributor (5) set in the proximity of the bottom of the unit in which the liquid is provided with upward motion, traversing the filter bed (8), and present in the top part of the filtering apparatus is an overflow (9) for outlet of the effluent, regulated by a weir, which determines the static level (10) of liquid present in the filter; where the granular particles that constitute the filter bed and the possible solids trapped therein are designed to descend and then be sent towards the top of the filter by a purposely provided airlift device referred to as "airlift" (11) present in the proximity of the bottom of the tank (1) and positioned at the centre of the filter; where the granular particles are designed to be drawn back downwards and to be lifted by the airlift together with the suspended solids that were trapped among them; and where the granular particles with a high sedimentation rate are designed to fall back onto the filter bed (8), in order to reconstitute it, whereas the particles with a low sedimentation rate, i.e., the suspended solids, are designed to be discharged into a purposely provided conduit (26), thus obtaining a backflow filtering: the influent, rich in suspended solids and/or dissolved substances, has an ascending motion, in order to traverse first the dirtiest granular filtering medium, which is present in the lowest part of the filter bed (8) and has a descending motion, to undergo the cleaning step so that in this way a large part of the pollutant charge is immediately removed from the filter bed, said filtering apparatus being characterized in that to apply regeneration of the filter bed in the filter itself, provided at the intake mouth of the airlift device (11) is a purposely designed washing and contacting chamber (22), referred to as "contacting reactor", and in that provided at the other end of the airlift device (11) is a separation and finishing section (15 and 18), referred to as "separator reactor"; wherein said contacting reactor (22), set at the base of the tank (1) of the filter, is in the form of a vault, or cap, or bell (19) and is connected in its top part to an intake duct (12) of the airlift device, whereas set in the bottom part is a nozzle for delivery of the compressed air (13) necessary for supplying the airlift itself; and wherein said contacting reactor (22) extends downwards so as to create an annular through which the granular particles and the discharge water pass a little at a time, from the top downwards, said annulus being created between the bottom base of said vault (19) and the upturned cone (3a) set at the base of the container that constitutes the filter; where, underneath the vault (19) of the contacting reactor (22), the granular particles are free to move and are agitated under the effect of the compressed air introduced, thus releasing the trapped impurities; in the contacting reactor (22) there being created convective motion with a high degree of turbulence - caused by the shape of the cap, or vault, or bell (19) -, which ensures excellent performance as regards washing of the surface of the granular particles that constitute the filter bed.

2. The filtering apparatus according to the preceding claim, characterized in that said contacting reactor (22) is designed to carry out the major part of the action of cleaning of the surfaces of the particles, wherein the impurities that have adhered and have been trapped are separated from the granular particles as a result of an action of abrasion against the surfaces of the chamber (19) and as a result of the actions of shear in the turbulent motion of the fluids also during the ascent along an intake duct (12) of the airlift device.

3. The filtering apparatus according to Claim 2, characterized in that, once the top of the airlift has been reached, the suspension containing the impurities overflows (14) into the central discharge device (15) of the separation and finishing section, or separator reactor, which separates the granular particles from the suspension at a high sedimentation rate; said granular particles, which are heavier, dropping towards the washing section (18) of the separator reactor, and falling back onto the filter bed (8), thus reconstituting it, whereas air is discharged into the atmosphere, and the water rich in suspended solids is discharged into a purposely provided discharge conduit (26) .

4. The filtering apparatus according to the preceding claim, characterized in that in the washing section (18) of the separator reactor, the granular particles undergo a further cleaning stage that releases new suspended solids or pollutant substances; to remove the latter it being envisaged to generate an ascending flow of filtered water, which traverses the top compartment (18) for washing the granular particles, a weir (16) being positioned so that it is set below the effluent weir (9) ; said ascending flow, rich in suspended solids that are characterized by a low sedimentation rate, being discharged by overflowing over the weir (16) into a collection basin (17) and then being discharged into a purposely provided conduit (26) .

5. The filtering apparatus according to either Claim 3 or Claim 4, characterized in that in the separator reactor, the current constituted by air, washing water, granular particles, and suspended solids that climbs in turbulent motion up the airlift pipe (12), before reaching the central discharge compartment (15), encounters openings (20) made in the airlift pipe (12), such as for example holes or eyelets, through which part of the granular particles at a higher sedimentation rate can exit from the duct itself and directly enter the washing section (18) of the separator reactor.

6. The filtering apparatus according to the preceding claim, characterized in that said washing section (18) of the separator reactor is constituted by various cap-shaped chambers (21) set on top of one another, where a turbulent motion is set up caused by propagation, through the holes (20) made in the duct, of the turbulence of the ascending flow brought about by the airlift; wherein, within said chambers (21) set on top of one another the granular particles collide, in turbulent regime, with one another and with the surfaces of the chambers themselves, thus creating a marked abrasive action, so releasing possible solids that still adhere to the surface of the granular filtering material, whereas the water that has been filtered rises up the washing section (18) itself, removing the suspended solids freed by the washing action .

7. The filtering apparatus according to either Claim 5 or Claim 6, characterized in that the ascending flow of the effluent that has been filtered and cleaned, which traverses the washing section (18) of the separator reactor, can be adjusted by controlling the height of the weir (16) in the central discharge compartment (15); wherein, by adjusting the height of said weir (16), it is also possible to modify certain parameters that regulate the modalities of cleaning of the granular particles; thanks to this stratagem, it is in fact possible to adjust more finely the ascent of the granular particles, automatically compensating the flow rate of clean washing water; it being thus possible to act in a differentiated way also on the flow rates of the three phases present in the airlift ascending duct, thereby modifying the composition of the flow itself, which is made up of water, more or less fine suspended solids, and air.

8. The filtering apparatus according to any one of Claims 3 to 7, characterized in that, to obtain regeneration of the filter bed, it envisages adding to the action of mechanical cleaning in the contacting reactor (22) and/or in the separator reactor, further actions of a chemical nature by administering oxidizing agents, such as O3 and/or H2O2, given that the turbulent motion that is created lengthens the stay time of the granular particles in the reactors, thus optimizing the chemical reactions of oxidation with which regeneration of the filter bed occurs.

9. The filtering apparatus according to Claims 7 and 8, characterized in that, in the case where oxidation techniques are adopted in the filter, the use of said means for adjusting the height of the weir (16) is of particular importance since it is possible to render the flow rate of compressed air blown into the contacting reactor independent of the flow rate of recirculation of the granular particles, it thus being possible to lengthen the times of stay in the reactor itself without thereby reducing the turbulence induced by the flow of air and the removal of contaminants.

10. The filtering apparatus according to the preceding claim, characterized in that, in the case where there is envisaged adoption of an active granular material, in order to delay exhaustion of the charge of the filter it is envisaged either:

- to carry out administration of a mixture of oxidizing fluids during filtering in given points of the filter: for example, it is possible to administer O3, and/or H2O2 directly in the contacting reactor (22), so that it becomes an oxidizing reactor, through specific inlet points (25), which are designed to optimize diffusion of the oxidizing agents in water, for example with fine-bubble diffusers; thus obtaining that, in this way, during the step of first washing, the filtering medium is subjected to the action of the oxidizing agents that free the surface of the granules from the pollutant substances by oxidizing them; or

- to introduce the oxidizing agents only in a purposely provided step of regeneration envisaged upon periodic arrest of the filtering operations.

11. The filtering apparatus according to the preceding claim, characterized in that also in the washing section (18) of the separator reactor specific inlet points (25) are provided for administering O3, and/or H₂O₂, which can be used to introduce the oxidizing agents during filtering or else only in a purposely provided step of regeneration envisaged upon periodic arrest of the filtering operations.

12. The filtering apparatus according to either Claim 10 or Claim 11, characterized in that, to apply techniques of advanced chemical oxidation, in addition to the means for administration of O3 and/or H₂O₂, catalysing means (T1O₂) and/or means for emission of UV radiation are also provided.

13. The filtering apparatus according to at least one of Claims 10 onwards, characterized in that there are provided: substrates coated with T1O₂, used both as building materials for the contacting reactor (22) and as purposely designed fillers of complex geometry with large specific surface, and also as granules to be added to the active filtering material; and lamps located in suitable points.

14. The filtering apparatus according to the preceding claim, characterized in that a substrate with large specific surface (24), coated with T1O₂, is provided, combined with UV lamps (23) applied directly in the contacting reactor (22) .

15. The filtering apparatus according to the preceding claim, characterized in that to apply techniques of advanced oxidation there are provided means for administration of fluid oxidizing agents through specific injection points (25) and means for emission of UV radiation so that the oxidizing fluids introduced from the bottom of the filter are immediately exposed to the combined action of radiation and of the catalyst, thus optimizing generation of ^'OH radicals .

16. The filtering apparatus according to the preceding claim, characterized in that, in the case where solids are present trapped in the granules that constitute the filter bed and this creates problems of absorption of UV radiation in the contacting reactor

(22) , said means for administration/emission of UV+T1O₂ may be set on the top of the filter, together with the means for administration of oxidizing agents; in this case, the washing section (18) of the separator reactor being appropriately modified for housing the UV lamps

(23) , the systems for injection of the oxidizing agents (25) , and the catalyst pack (24) ; thus obtaining an ascending flow having a marked oxidizing power that eliminates the pollutant substances from the granules and from the washing water itself.

17. The filtering apparatus according to the preceding claim, characterized in that the UV lamps (23) are inserted inside the top washing compartment (18) of the separator reactor, or else outside the latter, adopting a transparent compartment.

18. The filtering apparatus according to the preceding claim, characterized in that, by positioning the UV lamps (23) outside the transparent top washing compartment (18) of the separator reactor, it is possible to extend the benefits of advanced oxidation also to the filtered effluent, positioning above the filter bed further lamellar packs of complex geometry in order to increase the specific surface, which are coated with T1O₂, in combination with the UV lamps.

19. The filtering apparatus according to Claim 8, characterized in that the holes or eyelets (20) are located in the top part of each chamber (21) so that air will not accumulate above the caps that constitute the chambers (21) themselves.