EP2855364A1

EP2855364A1 - Process and device for purification treatment of liquid effluents, in particular aqueous liquid effluents, by photocatalysis

Info

Publication number: EP2855364A1
Application number: EP13729996.2A
Authority: EP
Inventors: Pascal Rousseaux; Jacques Breysse; Eric Puzenat; Chantal Guillard; Jean-Marie Herrmann; Christos SARANTOPOULOS
Original assignee: Centre National de la Recherche Scientifique CNRS; Universite Claude Bernard Lyon 1 UCBL; Processium SA
Current assignee: Centre National de la Recherche Scientifique CNRS; Universite Claude Bernard Lyon 1 UCBL; Processium SA
Priority date: 2012-05-25
Filing date: 2013-05-27
Publication date: 2015-04-08
Also published as: CN104507872B; FR2990935A1; WO2013175150A1; FR2990935B1; CN104507872A

Abstract

The invention relates to an improved process/device for purification treatment, by photocatalysis, of aqueous liquid effluents comprising at least one pollutant. In this process: (a) a suspension consisting of the effluent to be treated and loaded with particles of a photocatalyst is used and/or prepared; (b) the suspension of effluent to be treated, loaded with photocatalyst particles, is circulated in a reactor which has an inlet and an outlet and which comprises at least two zones; (c) a stream of air bubbles is diffused within the suspension circulated; (d) a photoactivation is carried out using irradiation means placed in the reactor; (e) the liquid phase is separated from the solid phase of the treated effluent by filtration; (f) then this liquid phase of the treated effluent is recovered. This process is characterized in that (i) the reactor used comprises at least two zones; (ii) it is seen to that the stream of gas bubbles is diffused within only one of the two zones: the aerated zone, and generates a gas lift which makes it possible to obtain recirculation between the two zones and hydrodynamic behaviour of perfectly stirred reactor (PSR) type.

Description

METHOD AND DEVICE FOR PROCESSING THE PURIFICATION OF LIQUID EFFLUENTS, ESPECIALLY AQUEOUS BY PHOTOCATALYSIS

Technical area

The technical field of the invention is that of the purification treatment of polluted effluents, in particular aqueous effluents.

It relates more specifically to the continuous photocatalytic treatment of an effluent or fluid, in particular aqueous, polluted by organic and / or inorganic components, treatment in which the effluent is brought into contact with a suspension of solid catalyst, in the presence of UV radiation.

This heterogeneous photocatalysis is preferably coupled to a separation treatment (advantageously by filtration) of the liquid phase and of the solid phase of the treated effluent.

The polluted effluents considered may be of industrial or domestic origin.

The invention also relates to a treatment device for the purification of liquid effluents, in particular aqueous effluents, by photocatalysis.

Technological background

The purification treatment of effluents or polluted liquid discharges, in particular effluents or aqueous effluents, is a major environmental issue.

Water is vital for humans and animals. It is also essential for agricultural, industrial and domestic activities without forgetting the functioning of terrestrial ecosystems.

The sources of water pollution are increasingly numerous and diverse: pharmaceutical industries, iron and steel, automotive, petroleum, consumer products ... More particularly, urban waste water or from industrial activity are increasingly contaminated persistent organic substances that are toxic and / or dangerous to human health (eg medicines, pesticides, detergents, phthalates, polychlorinated biphenyls.

All these pollutants are only partially destroyed in the treatment plants and require specific and effective treatments, in order to prevent their spread in the environment. It is therefore crucial to develop effective and inexpensive treatment treatments for liquid effluents, domestic and industrial, and more particularly aqueous effluents or discharges aqueous contaminated with organic compounds. For this purpose, photocatalysis has emerged as a suitable chemical treatment. Thus, have we known and studied for many years the depollution by photocatalytic oxidation using a photocatalyst based on TiO ₂ titanium oxide, heterogeneous phase (TiO ₂ deposited on a support or particles TiO ₂ , suspended in the liquid effluent to be treated), activated by near UV radiation, either solar or artificial (UV lamp).

This technology is very effective in mineralizing organic substances in C0 ₂ and H ₂ 0 and does not transfer pollution from one phase to another, such as physico-chemical treatment methods, including absorption on activated carbon. The heterogeneous photocatalysis is particularly well adapted to the cases of toxic pollutants present in low concentration (from a few ppb to several ppm) in the waters to be treated. Therefore, it is an advantageous complement to biological treatment, widely used today.

If the photocatalysis depollution treatments (TiO ₂ deposited on a support) have some applications on an industrial scale, especially with gaseous effluents, this technique currently suffers from a certain handicap in economic terms, even in terms of depolluting efficiency. , for liquid effluents.

Heterogeneous photocatalysis with a TiO ₂ photocatalyst in suspension may not have this handicap, provided that it is possible to overcome the technical difficulties of implementation, particularly related to the irradiation of the photocatalyst and the suspension of the photocatalyst.

In vain attempts have been made to achieve this goal.

Thus, Japanese patent application JP-2003-010653-A describes a water treatment equipment comprising, on the one hand, a reactor 12 containing the water to be treated which is fed into the reactor 12 through an inlet disposed in the upper part thereof, and, on the other hand, a filtration membrane 11 which is immersed in the water to be treated, mixed with a powder photocatalyst (Ti0 ₂ , ZnO, etc.). This reactor 12 is also equipped with UV radiation lamps 17 which are arranged in the upper part of the reactor 12 and which are only partially immersed in the suspension formed by the water to be cleaned and the photocatalyst particles. An aeration system 18 is provided in the bottom of the reactor 12 to deliver air bubbles which in particular have the effect of removing the organic material adhering to the filtration membrane 11, thus avoiding clogging. The water treated by photocatalysis, under the effect of the UV lamps 17 and in the presence of air bubbles, diffuses from the inlet 13 to the filtration membranes 11 to be evacuated via the duct 16 with the aid of a pump 15. This reactor 11 comprises only one compartment and the treatment process does not provide for loop circulation of the suspension consisting of the effluent to be treated in the reactor, which is the seat at the same time photocatalysis and filtration separating the TiO ₂ particles from the treated liquid effluent.

This process and this device for the purification by heterogeneous photocatalysis, are perfectible (weak and hydrodynamic irradiation poorly controlled) and did not give rise, to the knowledge of the applicant, to concrete and effective industrial applications.

The PCT patent application WO2006 / 079837-A1 discloses a process and a photocatalytic reactor TiO ₂ in suspension, comprising a reactor 2 consisting of a vessel containing the aqueous effluent to be treated, loaded with TiO ₂ particles in suspension and a vertical multitubular membrane filtration apparatus 18, for separating the treated effluent from the pulverulent TiO ₂ catalyst. Two UV lamps 3 are totally immersed in the effluent to be treated contained in the reactor 2, in the bottom of which is disposed a bubbler 14. The filtration system 18 disposed downstream of the reactor 2 is also equipped with a bubbler 32 allowing the diffusion of air bubbles within the filter. The effluent treated and filtered downstream of the filtration system 18 can be recirculated in the reactor 2. The latter comprises only one compartment and the method of implementation in the device according to the PCT patent application WO2006 / 079837 -A1 does not provide stirring within the reactor effluent suspension to be treated / TiO ₂ particles.

The external multitubular membrane micro filtration system with bubbling according to the PCT patent application WO2006 / 079837-A1 can be subject, despite everything, to a pressure drop due to the clogging phenomenon, that is to say to the deposition of particles photocatalyst or other impurities on the inner walls. This phenomenon can limit the flow of (re) circulation, hence:

insufficient flow rates at the filtration membranes (increased risk of clogging, transfer performance through degraded membranes);

a low recirculation in the reactor 2 which generates risks of little renewed zones (suspension photocatalyst / stagnant effluent in the reactor and not subjected to filtration for the recovery of the treated effluent), and loss of efficiency in terms of material transfer. This random flow can also cause deposits of photocatalyst particles at the bottom of the reactor.

The fact of being able to feed the reactor with air through the bubbler 14 to improve the mixing within the reactor, aggravates the clogging phenomenon mentioned above for the filtration system 18, besides bubbling in the reactor 2 and bubbling. of a filtration system 18 mutually antagonize each other. In addition, the method and the device according to the PCT patent application WO2006 / 079837-A1 are not controllable since they are exclusively dependent on the natural hydrodynamics they generate, which is not controllable and which can degrade in time.

Japanese patent application JP-2001-070935-A discloses a method and a photocatalytic treatment device in which the liquid effluents to be treated are mixed with a photo catalyst P based on TiO ₂ powder, this mixture being introduced into the bottom of a reactor (1), by a lateral port (la). This reactor (1) of circular right cross section is divided into two central zones Kt and peripheral Kg by a cylindrical septum wall (3), equipped with internal plates for rotating the liquid in one direction and external rotation plates liquid in another direction. UV activation lamps (5) are arranged in Kg only (Fig. 2 or 3) or in Kt and Kg (Fig. 1). The bottom of the reactor (1) comprises an injection port (1c) of an air jet which generates an upward flow in Kt and a downward flow in Kg. A central filter (8) for recovering the treated liquid without the particles of TiO 2 is provided in the embodiment of Figure 2. The flow of injected gas is not disclosed in JP-2001-070935-A and there is no indication that the composition of the reaction medium is homogeneous. The injection of gas is not uniform over the section of the central zone Kt and it does not appear that a flow of gas bubbles is diffused homogeneously in this central zone Kt. This reactor does not have a Hydrodynamic behavior of the Reactionally Agitated Reactor (RPA) type. In addition, this Japanese patent application JP-2001-070935-A gives no example illustrating the feasibility of photocatalytic treatment.

All these methods and non-optimized prior art devices have never been developed on an industrial and commercial scale. Technical problem - Objectives of the invention

In this context, the technical problem underlying the present invention is to satisfy at least one of the objectives set out below. (i) providing a method and a treatment device for the purification of liquid effluents, in particular aqueous effluents, by photocatalysis for optimizing the operating parameters such as the irradiation of the photocatalyst or the homogenous suspension of the photocatalyst or the photocatalyst; stirring, and thus significantly improve the chemical detoxification performance; (ii) providing a method and a device for the treatment of liquid effluents, in particular aqueous effluents, by photocatalysis, which are economically viable;

(iii) providing a process and a device for treatment of purification of liquid effluents, in particular aqueous effluents, by photocatalysis, allowing operation in a "perfectly stirred continuous reactor" with a homogeneous composition (especially with regard to the concentrations of pollutant (s) and / or catalyst) at each point of the reactor during operation;

(iv) providing a method and a device for treating liquid effluents, in particular aqueous effluents, which are improvements over the methods and devices described in the prior art and, in particular, in the patent application Japanese JP-2003-010653-A and PCT Patent Application WO2006 / 079837-A1;

(v) providing a process and a treatment device for the purification of liquid effluents, in particular aqueous effluents, by heterogeneous photocatalysis, in which the means for separating the photocatalyst particles in suspension after treatment of the polluted effluent, have an efficiency improved, in particular are less subject to the clogging phenomenon while being more efficient;

(vi) providing a process and a treatment device for the purification of liquid effluents, in particular aqueous effluents, by heterogeneous photocatalysis, which make it possible to control the hydrodynamics of the flow in the reactor.

(vii) providing a method and a treatment device for the purification of liquid effluents, in particular aqueous effluents, by heterogeneous photocatalysis, which make it possible to dispense with mechanical agitation which has the drawbacks of being complex and expensive. Brief description of the invention

The above-mentioned problem is solved by the invention which proposes, in the first place, a treatment process for treating liquid effluents, in particular aqueous effluents, comprising at least one pollutant, by heterogeneous photocatalysis, in which:

(a) using and / or preparing a suspension constituted by the effluent to be treated charged with particles of a photocatalyst; (b) circulating the suspension of effluent to be treated charged with particles of a photocatalyst, in at least one reactor:

^■ provided with at least one inlet and at least one liquid outlet,

^■ and comprising at least two zones. (c) a flow of gas bubbles is diffused within the circulating suspension;

(d) photoactivation is carried out using irradiation means to reduce the pollutant content (s) - to eliminate the pollutant (s);

(e) separating the liquid phase from the solid phase of the treated effluent;

(f) then this liquid phase is recovered from the treated effluent; characterized in that

i. it is arranged that the flow of gas bubbles is diffused within one of the two zones only: the aerated zone;

ii. the flow of gas bubbles is made to generate a gasosiphon which makes it possible to obtain an internal circulation between the two zones and a hydrodynamic behavior of the Perfectly Agitated Reactor type.

(RPA).

The technology according to the invention is based on the combination of an activation radiation, for example ultraviolet radiation emitted by lamps or LEDs and a photo-catalyst powder, for example Ti0 ₂ . The photocatalyst is suspended in the aqueous medium by the flow of gas bubbles (for example air), which allows optimized solid / liquid transfer. The adsorption of pollutants on the photocatalyst particles is thus favored, so that these pollutants are on the surface of the particles. This contributes to an effective and rapid degradation of pollutants after activation by the irradiation means.

Step (b) is implemented using external circulation means (e.g. pump). This allows the suspension to pass through the reactor (from inlet to outlet).

In step (c), the gas bubbles allow internal circulation between the two zones, with a very high number of cycles per unit of time. This internal loop circulation of the effluent suspension to be treated, between the two zones, under a stream of gas bubbles and with irradiation means within at least one of the two zones, has a cooling effect. agitation and leads to improved performance in terms of speed and degradation performance. The economy of the process is thus optimal. Secondly, the invention relates to a liquid effluent treatment treatment device, in particular aqueous, by heterogeneous photocatalysis, especially for the implementation of the method according to the invention as defined above. This device comprises:

^■ a reactor,

^■ irradiation means,

^■ means for circulating a suspension constituted by an effluent to be treated charged with particles of a photocatalyst (P),

^■ means of diffusion of a gas bubble flow (preferably air) within the suspension circulated,

^■ separating means (preferably by filtration) from the liquid phase and the solid phase (PI) of the treated effluent,

^■ optionally means for preparing the suspension of the effluent to be treated charged with particles of a photocatalyst (P),

^■ possibly means of recycling:

o the effluent treated and charged with particles of the photocatalyst, upstream of the separation means, preferably between the reactor and the separation means, preferably by filtration,

o the effluent treated and charged with particles of the photocatalyst, upstream of the reactor,

and / or the treated effluent charged with particles of the photocatalyst, in the means for preparing said suspension, characterized in that:

/. the reactor comprises at least two zones,

2. the irradiation means are disposed within at least one of the zones,

3. the diffusion means are designed and are arranged in such a way that the flow of gas bubbles (preferably air) is diffused within one of the two zones only, and generates a gasosiphon which makes it possible to obtain a recirculation between the two zones and a hydrodynamic behavior of the Perfectly Agitated Reactor (RPA) type

This device is advantageous in that it allows the implementation of the method referred to above with the associated advantages. In addition, this device has a simple structure. It is easy to manufacture, at a reasonable cost and is perfectly adapted on the industrial level. Because of the control of hydrodynamics (RPA), the method and the device according to the invention are easy to extrapolate on an industrial scale. From the acquisition of kinetic data in the laboratory, it is indeed possible, thanks to the invention, to model the performance of an industrial reactor.

Pleasures

Process :

According to a preferred characteristic, the suspension of effluent to be treated charged with particles of the photocatalyst circulates in the reactor at a speed such that the circulation time Te of an element of the suspension is less than the characteristic photocatalytic oxidation degradation time Td of said element, preferably Te <(Td / 10), and more preferably still Te <(Td / 100).

Even more preferably, the ratio (Tm / Td) or number of Damkholer is less than or equal to-in order of increasing preferably-: 1.0; 0.5; 0.1; 0.05; 0.01; Tm corresponding to 4Tc, Te being the circulation time of an element of the suspension and Td the characteristic photocatalytic oxidation degradation time of said element.

The parameters Te, Tm & Td are parameters known to those skilled in the art (see for example Albright's Chemical Engineering Handbook, p.620, 637 & 643, 2009).

The degradation time Td is defined as the measured reaction rate divided by the initial pollutant concentration.

The circulation time Te or Tm / 4 is a quantity measurable by the reference protocol P ^refl according to:

1. At the inlet of the reactor in operation, a defined quantity of a tracer is injected into the suspension of the effluent to be treated charged with photocatalyst and, 2. At the exit of the reactor in operation, it is measured at using a suitable measuring device the tracer concentration,

3. The curve C multi peaks of the tracer concentration measured at the outlet of the reactor as a function of time is plotted (Albright's Chemical Engineering Handbook, p.637),

4. On this curve C is determined the time interval between two peaks of the curve C, this interval corresponding to Te.

Applicable tracers are known to those skilled in the art and will be chosen according to the measuring apparatus available. If, for example, a conductivity measuring apparatus is available, the tracer will for example be sodium chloride.

The amount of tracer injected will depend on the sensitivity of the measuring instrument available. The circulation time Te or Tm / 4 is also a quantity that can be calculated by the following reference protocol P ^ref2 (the correlations used are found in the work of P. Trambouze and JP Euzen, "The chemical reactors, from design to implementation "at page 238-239-240, 2002):

1. The gas velocity in the aerated zone is calculated by dividing the injected gas flow by the free section of the aerated zone (ie the total section of the riser zone minus the section of the installed lamps). there is).

2. The rate of aeration of the liquid in the aerated section (defined as the volume percentage of the liquid itself occupied by the gas) is then calculated using the correlation 4.45 of the above mentioned work. The gas velocity calculated previously, the viscosity of the water and the interfacial tension between the water and the gas are the input data of this correlation.

3. The velocity of the liquid in the aerated zone is then calculated using the correlation 4.49 of the above mentioned work. The geometrical data of the reactor are the input data of this correlation and in more detail:

at. The height H of the liquid in the reactor in operation

b. Am section available to the aerated liquid from the aerated (or rising) zone (ie the total section of the rising zone minus the installed lamps section if any)

vs. The Ad section available to the descending zone liquid (ie the total section of the descending zone minus the section of the installed lamps, if any)

d. Ab passage area available at the base of the gasosiphon, under the cylinder that separates the reactor into two zones

4. The flow rate of the liquid in the aerated part of the reactor is then calculated by multiplying the value of the speed of the liquid calculated previously by the section Am available to the aerated liquid of the zone. The flow rate of the liquid flow will be the same in the descending part and therefore throughout the reactor by the law of conservation of the mass known by those skilled in the art.

5. The circulation time Te is finally calculated by dividing the flow rate of the liquid calculated previously by the volume of liquid present in the reactor in operation.

Td is determined as follows:

1. The reactor is operated in closed mode.

2. A suspension to be treated charged with photocatalyst and pollutant is injected into the operating reactor. The initial pollutant concentration is C0. The suspension is taken from time to time in the reactor and the concentration of pollutant C is measured.

The evolution of the concentration C is followed over time t, as shown in FIG.

The values of C and t for the first two points of this curve are measured. From these values, the initial reaction rate, rO, which is defined as the ratio between the concentration difference and the time difference, is calculated.

The characteristic degradation time Td is calculated as the ratio between C0 and rO.

The term "suspension element" refers for example to a volume unit of suspension.

These characteristics peculiar to the process according to the invention ensure a controlled hydrodynamic behavior of the reactor and thus a homogeneous concentration of the species present throughout the reactor. Moreover, these characteristics make it possible to envisage an adaptation of the process on an industrial scale.

Advantageously, it is arranged that the flow of gas bubbles determines a homogeneous composition within the reactor, that is to say a substantially identical composition at any point in the liquid phase, preferably a homogeneous concentration of photocatalyst and / or or polluting (s) within the liquid phase. This is partly achieved by the fact that the concentration variation due to the reaction in the irradiated zone is much slower than the effect of homogenization of the concentration due to the circulation of the fluid between the irradiated zone and the non-irradiated zone.

According to a remarkable characteristic of the invention, the flow of gas bubbles is diffused at least partly in the zone (s) comprising the irradiation means and / or in the zone (s) exposed (s) irradiation means, this diffusion is preferably carried out homogeneously through perforations also distributed homogeneously over the entire section of the ventilated area.

These features of the invention allow, on the one hand, a perfect irradiation of the photocatalyst particles on which the pollutants of the effluent are adsorbed, and, on the other hand, a good hydrodynamics conducive to a stable suspension of the particles. with stirring. All this contributes to photocatalytic degradation performance, in terms of speed and quantity. In addition, this flow and this circulation contribute to the agitation of said suspension and to the suspension suspension of the photocatalyst particles. The gasosiphon or "air lift" reactors, commonly used in the chemical and biochemical industry, are composed of two zones: the "riser" and the "downcomer". These gazosiphon reactors are two-phase (liquid-gas) or three-phase (liquid-gas-solid) reactors. The injection of gas inside the "riser" compartment causes a circulation of liquid passing through this compartment, while the second compartment "downcomer" allows the liquid to return to the bottom of the reactor. The introduction of the gas into one of the two zones of the reactor causes a difference in gaseous retention between the two zones ventilated and unventilated. A driving force is then created, inducing the circulation of the liquid in the reactor. When the flow of gas entering the "riser" is important, the speed of the liquid is then high.

According to a remarkable characteristic of the invention, the method comprises at least one of the following modalities:

^■ the irradiation means are arranged, preferably evenly, within at least one of the two zones, preferably the aerated zone;

several reactors are used, in series or in parallel, and that each reactor is made to be associated with at least one irradiation means;

^■ the treated effluent loaded photocatalyst is partially recycled in step (d) of photocatalytic treatment and / or in step (e) solid / liquid separation;

^■ at least a portion of the suspension of the treated effluent charged with particles of a photocatalyst is recycled in step (a) for the preparation of said suspension.

According to another conceivable possibility, the irradiation means extend over at least half the height of the suspension to be treated intended to be contained in the reactor - and more preferably still - over at least 80% of this height.

Advantageously, the photoactivation according to step (d) is carried out using irradiation means arranged regularly in at least one of the zones.

The irradiation means advantageously comprise UV sources and / or visible UV sources.

According to a particularly preferred embodiment of the process according to the invention, a tubular reactor is used in which the two zones (in practice eg contiguous) are separated by a tubular partition, which thus defines two cylindrical annular zones, respectively interior and outdoor.

In a first variation of this preferred mode of implementation, the photoactivation according to step (d) is carried out using irradiation means (preferably a plurality of UV sources) distributed within the zone. outer ring. These irradiation means are preferably distributed in a regular manner, and more preferably in radial directions, for example in a triangular or square pitch. According to an advantageous variant of this first variation of the preferred mode of implementation, the method according to the invention comprises:

- a circulation (b) loop of the suspension to be treated in an upward movement in the outer zone and in a downward movement in the inner zone, and / or;

- diffusion (c) of a flow of gas bubbles (preferably air) within the circulation suspension, at least partly in the outer zone.

In a second variation of the preferred mode of implementation, the photoactivation, according to step (d), is carried out using irradiation means, distributed within the inner (central) cylindrical annular zone, preferably in a regular manner, and even more preferably in radial directions.

Advantageously, the photocatalyst is chosen from the group comprising, or better still consisting of: ΤΊ02; ZnO; ZrO2; Ce02; SnO2; CdS; Mo03; W03 V205; MoS2; ZnS and mixtures thereof.

Advantageously, the gas diffused in steps (b) and (ii) comprises an oxidant (eg O ₃ ; H ₂ 0 ₂ ).

As regards pollutants degraded by the process according to the invention, they are chosen from organic molecules in general or from inorganic molecules and preferably nitrite ions, cyanide ions. The book D.M. Blake ,. National Renewable Energy Laboratory Technical ReportNREL / TP - 510 - 31319, 2001 mentions examples of pollutants. Without this being limiting, they may be chosen substances:

In the group comprising or consisting of alkanes, and more preferably still, in the subgroup comprising or consisting of isobutane, pentane, heptane, cyclohexane, paraffins;

In the group comprising or consisting of haloalkanes, and more preferably still, in the subgroup comprising or consisting of mono-, di-, tri- and tetrachloromethane, tribromoethane, 1,1,1-trifluoro-2 2,2-trichloroethane;

In the group comprising or consisting of alcohols and more preferably still, in the subgroup comprising or consisting of methanol, ethanol, propanol, glucose; in the group comprising or consisting of aliphatic carboxylic acids, and more preferably still, in the subgroup comprising or consisting of formic, ethanoic, propenoic, oxalic, butyric and malic acids; in the group comprising or consisting of alkenes, and more preferably still, in the subgroup comprising or consisting of propene, cyclohexene;

in the group comprising or consisting of haloalkenes, and more preferably still, in the subgroup comprising or consisting of 1,2-dichloroethylene, 1,1,2-trichoroethylene;

in the group comprising or consisting of the aromatics, and more preferably still, in the subgroup comprising or consisting of benzene, naphthalene;

in the group comprising or consisting of haloaromatic, and more preferably still, in the subgroup comprising or consisting of chlorobenzene, 1,2-dichlorobenzene;

in the group comprising or constituted by nitrohaloaromatiques, and more preferably still, in the subgroup comprising or consisting of dichloronitrobenzene;

in the group comprising or consisting of phenolic compounds, and more preferably still, in the subgroup comprising or consisting of phenol, hydroquinone, catechol, methylcatechol, resorcinol, o-m-, p- cresol, nitrophenols;

in the group consisting of or consisting of halophenols, and more preferably still, in the subgroup comprising or consisting of 2-, 3-, 4-chlorophenol, pentachlorophenol, 4-fluorophenol;

in the group comprising or consisting of amides, and more preferably still, in the subgroup comprising or consisting of benzamide;

in the group comprising or consisting of aromatic carboxylic acids, and more preferably still, in the subgroup comprising or consisting of benzoic acid, 4-aminobenzoic acid, phthalic acid, salicylic acid, m- and p-hydroxybenzoic acid, chlorohydroxybenzoic acid and chlorobenzoic acid;

in the group comprising or consisting of surfactants, and more preferably still, in the subgroup comprising or consisting of sodium dodecyl sulphate, polyethylene glycol, sodium dodecyl benzene sulphonate, trimethyl phosphate, tetrabutylammonium phosphate; In the group comprising or constituted by the herbicides, and more preferably still, in the subgroup comprising or consisting of atrazine, prometrou, propétryne, bentazon, 2-4 D, monuron;

In the group comprising or consisting of pesticides, and more preferably still, in the subgroup comprising or constituted by the

DDT, parathione, lindane, tetrachlorvinphos, phenitrothione;

In the group comprising or consisting of the dyes, and more preferably still, in the subgroup comprising or consisting of methylene blue, rhodamine B, methyl orange, fluorescein;

· And mixtures thereof

Device:

In its preferred embodiment, the device according to the invention is characterized in that the reactor comprises two cylindrical annular zones, respectively internal and external, and in that the irradiation means are distributed within the outer cylindrical annular compartment, preferably in a regular manner, and more preferably in radial directions, for example in a triangular or square pitch.

According to an alternative embodiment, the irradiation means extend over at least half the height of the suspension to be treated intended to be contained in the reactor - and more preferably still - over at least 80% of this height.

According to a remarkable feature, the reactor is tubular and comprises two cylindrical annular zones, respectively inner and outer, and in that the irradiation means are distributed within the outer cylindrical annular zone, preferably in a regular manner, and, more preferably in radial directions.

Advantageously, the device according to the invention is characterized by at least one of the following characteristics:

the irradiation means are tabular UV lamps and / or UV LEDs;

the separating means comprise a filter provided with filtering surface (s), preferably sintered (s), and / or a multitubular membrane system and / or a tangential microfiltration system provided with a membrane, preferably ceramic and, more preferably, having a cut-off threshold at least once (advantageously twice) lower than the D50 of the photocatalyst particles. According to one variant, the device comprises several reactors, in series or in parallel, and each reactor is associated with at least one irradiation means.

According to a remarkable possibility, the means for diffusing the flow of gas bubbles (gas injection) are designed so that the gas bubbles can be distributed homogeneously, preferably through perforations, over the entire section of the aerated area. These means may be in particular a multi-perforation injector, such as a perforated disc, a sintered, a perforated torus. Definitions

Throughout this presentation, any singular denotes indifferently a singular or a plural.

The definitions given below as examples may be used to interpret this presentation:

- "Perfectly Agitated Reactor (RPA)" means a reactor as defined on page 65 of the work "Chemical reaction engineering - 2nd edition -JACQUES VILLERMAUX-1993" and / or in "H. SCOTT FOGLER - Elements of chemical reaction engineering - 3rd ed. - p.10 ". "Gazosiphon" means a reactor as defined on page 389 of the book "Chemical reaction engineering- 2nd edition - JACQUES VILLERMAUX -1993" also called "Air-lift Reactor" (see for example in biochemistry MERCHUK / GLUZ - Encyclopedia of bioprocess technology / Bioreactors, Air-lift Reactors) ".

"substantially": +/- (in% by weight and in increasing order of preference) 10; 5; 1; 0.5; 0.1; 0.01.

Detailed description of the invention

Description of the figures

Examples of the device and method according to the invention are described below with reference to the figures in which:

FIG. 1 represents a diagram of an exemplary embodiment of the treatment device for purifying aqueous liquid effluents by heterogeneous photocatalysis according to the invention, at the laboratory scale,

FIG. 2 represents a perspective view of a preferred industrial embodiment of the reactor which forms an integral part of the invention,

FIG. 3 is a view from above of FIG. 2,

FIG. 4 is a non-industrial variant embodiment (laboratory) of the reactor at the heart of the invention,

FIG. 5A illustrates a control configuration of a known bubble column type reactor in which an upward flow of gas bubbles is diffused,

FIG. 5B is a configuration of a reactor according to the invention, with supply of the gas diffused inside the inner annular zone of the reactor, FIG. 6 is a curve showing the evolution of the concentration of formic acid as a function of time in the context of an exemplary embodiment of the process according to the invention,

FIG. 7 is a graph showing the rates of degradation of formic acid in the reactor as a function of the TiO ₂ photocatalyst concentration obtained in the context of an exemplary implementation for the configurations of FIGS. 5A, 5B of the reactor.

The device represented in FIG. 1 allows the purification treatment of liquid effluents, in particular aqueous effluents, by heterogeneous photocatalysis. This device comprises a reactor 2, means 8 for preparing the suspension 5 of the effluent 1 to be treated, irradiation means 3, means 4 for circulating a suspension 5 constituted by an effluent 1 to be treated charged particles of a photocatalyst, means 6 for diffusing a flow of gas bubbles within the suspension 5 circulated, means 7 for separating the liquid phase and the solid phase of the treated effluent , recycling means 9 of the treated effluent and separated from the solid phase (upstream of the separation means 7 and downstream of the reactor 2), recycling means 10 of the treated effluent 1 'and separated from the phase solid, upstream of the reactor 2, and recycling means 11 of the effluent 1 in the means 8 for preparing the suspension 5.

The suspension 5 constituted by the effluent 1 to be treated, charged with particles of a photocatalyst P, is prepared upstream in a vessel 8 equipped with stirring means.

12 and fed, on the one hand, with liquid effluent 1 to be treated (for example water polluted with one or more organic components) and, on the other hand, with photocatalyst particles P consisting, for example, of Ti0 ₂ , for example crystalline anatase particle size (D50) mainly comprised between 0.1 and 10 μιη. The suspension 5 is circulated using a pump 4 which conveys it from the container

8 to the reactor 2, via pipes equipped with valves 9,10,11,13 to control the flow of liquids in these pipes.

The container 8 has for example a total volume of 401 and the pump 4.1 for conveying the suspension 5 of the container 8 to the reactor 2 is for example a magnetic pump with a flow rate of 7 to 11 liters per minute.

The agitation system 12 of the container 8 is a mechanical system with rotating blades

(for example 600 rpm).

At the outlet of the reactor 2, the suspension 5 'of treated effluents is fed into a buffer tank 22, and then conveyed by means of the pump 4.2 (for example a peristaltic pump with a flow rate of 500 liters per hour to the control system. filtration 7. The container 22 is a filtration tank with a capacity of, for example, 4 liters. The entry of the suspension 5 'of treated effluents into the filtration system 7 takes place in the lower part of the latter.

Permeate 1 is recovered at the outlet of the filtration system 7.

The device of FIG. 1 comprises, downstream of the reactor 2 or the reactor 2 ', tangential microfiltration means 7 capable of separating the liquid phase from the solid phase P' constituted by the TiO ₂ catalyst. These microfiltration means comprise a membrane whose cutoff threshold is between 0.1 and 10 μιη. It may be for example, a ceramic membrane of the type marketed under the name M9 by the company CARBOSEP ^® . The size of this membrane is of the order of 0.14 μιη. This size is two times smaller than the diameter of the TiO ₂ catalyst particles of particle size D 50 = 0.30 μιη. The parameters of this M9 ceramic membrane are as follows:

Recycling / recycling

This permeate 1 is the effluent treated by photo-catalysis and depolluted. Part of the retentate can be recycled upstream of the filtration system 7 and downstream of the reactor 2 and / or upstream of the reactor 2. These recycling or recirculation loops allow homogenization. The recycling or recirculation ducts are equipped with valves 9, 10, 11 constituting the corresponding recycling or recirculation means and making it possible to control the flow rates and the flows of treated effluents or of permeate 1.

The reactor 2

With respect to reactor 2, FIGS. 2 and 3 show a first preferred embodiment of the reactor operating continuously, while FIG. 4 shows a second reactor embodiment more suitable for use at the laboratory scale. in batch. First favorite year of directed

The reactor 2 according to Figures 2 and 3 operating continuously is of tabular form and comprises an inner cylindrical annular compartment 14 and an outer cylindrical annular compartment 15, delimited by an inner tabular partition 16 and a tabular outer wall 17.

The irradiation means 3 equipping this reactor 2 are constituted by UV lamps 3 immersed in the suspension 5 and distributed within the outer cylindrical annular compartment 15 in a homogeneous manner. These UV lamps 3 have a length L3 greater than or equal to half the height H5 of the suspension, itself equal to the length L15 of the outer cylindrical annular compartment 15. Preferably L3> 0.8.H5 or 0.8X15 . In the example shown in the figures, L3 = H5 and = L15.

The arrangement of the UV lamps 3 in the outer cylindrical annular compartment 15 is of radial geometry in a suitable pitch, for example triangular, with a distance between the lamps 3 sufficient to guarantee the good hydrodynamics of the gasosiphon. A reaction zone 18 is thus defined around each UV lamp 3.

The UV lamps emit UVC photons of wavelength lambda between 200 and 300 nm with an electric power of between 20 and 50 Watts. Their length L3 can vary between 5 and 100 cm.

The reactor 2 is equipped at its base with means 6 for diffusing a stream of gas bubbles, preferably air, within the suspension, for example, in the outer cylindrical annular compartment 15 comprising the UV lamps 3.

The means 6 for diffusing a flow of bubbles define an internal gasosiphon or air-lift. The inlet of the air providing agitation and air-lift is in the lower part of the reactor 2. With Γ air-lift, the suspension 5 has an upward movement in the outer cylindrical annular compartment 15 and a movement descending into the inner cylindrical annular compartment 14, so that a circulation loop of the suspension 5 between the two internal compartments 14 and outside 15 of the reactor 2 occurs. Second embodiment of the reactor

The reactor 2 'shown in FIG. 4 is also a tabular reactor comprising an inner cylindrical annular compartment 14', an outer cylindrical annular compartment 15 'delimited by an inner partition 16' and an outer tubular wall 17 '. The inner cylindrical annular compartment 14 'is also delimited by a tabular inner wall 19 defining a compartment 20 in which is housed a UV irradiation lamp 3'. In this second embodiment L3 '= H5' = L15 '. The entry of the suspension 5 of the effluent 1 to be treated takes place through the opening 20 disposed in the lower part of the reactor 2 ', while the outlet of the suspension 5' of the treated effluent is effected by conduit 21. The outer tubular wall 17 'is a hollow wall for containing a coolant or a coolant to control the reaction temperature. The reactor 2 'is equipped with means 6' for diffusing a stream of gas bubbles preferably of air disposed in the lower part of said reactor 2 '.

The central UV lamp 3 'is, for example, a Philips TUV 254 nm UV lamp of 36 Watts and 18 cm in height.

The inner tubular wall 19 is for example quartz transparent to radiation

UV and the outer wall 17 'is hollow and for example Pyrex. The tubular partition 16 'for separating the inner cylindrical annular compartment 14' from the outer cylindrical annular compartment 15 'is for example made of stainless steel.

The total volume of the reactor 2 'is 11 with a useful volume of 0.81. The diameter of the tubular partition 16 'is 57 mm.

FIGS. 5A and 5B show two possible configurations of the reactor 2 'of FIG. 4, respectively:

5A: control bubble column without inner and outer cylindrical annular compartment 14'-15 ';

- 5B: gazosiphon according to the invention with supply of gas in the inner cylindrical annular compartment 14 'defined by the tubular partition 16'.

Process

The method according to the invention consists in implementing the steps a, b, c, d, e, f as defined above.

According to a preferred arrangement, it is arranged that the circulation of the slurry 5 of effluents 1 to be treated charged with photocatalyst particles P is looped between the two zones of the reactor.

This loop circulation is preferably provided according to a gasosiphon mechanism, using the diffusion means 6 in one or other of the inner cylindrical annular zones 14-14 'or outer 15-15', preferably in the zone 14 comprising the irradiation means or UV lamps 3.

Once treated by heterogeneous photo-catalysis, the suspension 5 'of treated effluents is fed out of the reactor 2-2' to the filtering means 7 which make it possible to collect

2 '

a treated effluent 1 or permeate freed of the photocatalyst particles P '. Part of the permeate 1 is optionally recycled upstream between the reactor 2 and the means filtration 7 and / or upstream of the reactor 2 (in the preparation tank 8 or between the preparation vessel 8 or preparation vessel 8 and the reactor 2).

With this method of continuous operation and economically, it is possible to carry out a rapid and effective depollution of a liquid effluent, for example aqueous, significantly improving the speed and the degradation yields of pollutants.

The following examples illustrate the performance of the process according to the invention.

EXAMPLES

The following examples were made using the device shown in Figures 1,4,5A, 5B and defined in the above detailed description by way of example.

The example made with the device of Figure 5 A is a comparative example.

The tests carried out in these examples are tests for the degradation of formic acid in aqueous solution at an initial concentration of 90 mg / l.

Powdered photocatalyst P used in the tests is P25 titanium dioxide at a concentration of 1.5 g / l.

The suspension 5 of effluents 1 to be treated was prepared with stirring in the vessel 8 under the conditions specified above.

The average rate of diffusion of air bubbles in the lower part of the reactor 2 'is 2L / min.

The concentration of formic acid during photocatalytic degradation tests was determined by HPLC analysis.

For this, regular samples of the suspension 5 'at the outlet of the reactor 2' and of the permeate 1 at the outlet of the filtration means 7 were made. Tests were carried out batchwise and continuously.

1. Batch tests

The results are shown in Figure 6.

The formic acid is completely degraded by the photo-catalytic process of the invention in 50 min.

2. Continuous tests

Continuous tests were performed in the reactor 2 'configurations shown in Figures 5A and 5B.

Figure 7 shows the results obtained. These results demonstrate that the photo-catalysis process alloyed with the suspended photocatalyst makes it possible to obtain a very good degradation rate for the configuration B of the reactor 2 'according to the invention, which is greater than that of the configuration 5 A of the reactor 2 according to the prior art, TiO ₂ concentrations greater than or equal to 0.5 g per liter.

3. Determination of the RPP scheme (calculation of Tm / Td)

The reference protocol P ^ref2 for calculating Te on the reactor of FIG. 4 is used. The protocol for measuring Td is applied to the data shown in Figure 6. The number of Damkholer largely respects the constraints.

The following table gives Te, Tm, Td & Tm / Td.

Claims

1. A treatment process for the purification of liquid effluents, in particular aqueous effluents, comprising at least one pollutant, by heterogeneous photocatalysis, in which:

(a) using and / or preparing a suspension constituted by the effluent to be treated charged with particles of a photocatalyst;

(b) circulating the suspension of effluent to be treated charged with particles of a photocatalyst, in at least one reactor:

^■ provided with at least one inlet and at least one liquid outlet,

(e) separating the liquid phase from the solid phase of the treated effluent;

(f) then this liquid phase is recovered from the treated effluent. characterized in that

ii. it is arranged that the flow of gas bubbles generates a gasosiphon making it possible to obtain an internal circulation between the two zones and a hydrodynamic behavior of the Perfectly Agitated Reactor (RPA) type.

2. Method according to claim 1, characterized in that the suspension of the effluent to be treated charged with particles of the photocatalyst circulates in the reactor at a speed such that the circulation time Te of an element of the suspension is less than the time Td photocatalytic oxidation degradation characteristic of said element, preferably Te <(Td / 10), and, more preferably still Te <(Td / 100).

3. Method according to claim 1 or 2, characterized in that the ratio (Tm / Td) or number of Damkholer is less than or equal to -in order of increasing preferably: -1.0; 0.5; 0.1; 0.05; 0.01;

Tm corresponding to 4Tc, Te being the circulation time of a suspension element on a circuit and Td the characteristic photocatalytic oxidation degradation time of said element.

4. Method according to claim 1 or 2, characterized in that it is arranged that the flow of gas bubbles determines a homogeneous composition within the reactor, that is to say a substantially identical composition in every respect the liquid phase, preferably a homogeneous concentration of photocatalyst and / or pollutant (s) in the liquid phase.

5. Method according to claim 1 or 2, characterized in that the flow of gas bubbles is diffused at least partly in the (or) zone (s) comprising the irradiation means and / or in the (or the) zone (s) exposed (s) irradiation means, this diffusion is preferably carried out homogeneously through perforations also distributed homogeneously over the entire section of the ventilated area.

6. Method according to at least one of the preceding claims, characterized in that it comprises at least one of the following modes: "the irradiation means are arranged, preferably regularly, within at least one of the two zones, preferably the aerated zone;

^■ is implemented more reactors in series or in parallel, and in that one causes each reactor to be associated with at least one irradiation means;

^■ the treated effluent loaded photocatalyst particles is in part recycled to step (d) of photocatalytic treatment and / or in step (e) solid / liquid separation;

^■ at least a portion of the suspension of the treated effluent loaded photocatalyst particles is recycled in step (a) for the preparation of said suspension.

7. Method according to at least one of the preceding claims, characterized in that it implements a tubular reactor in which the two zones are separated by a tubular partition, which thus defines two cylindrical annular zones, respectively inner and outer .

8. A method according to claim 7, characterized in that the photoactivation according to step (d) is carried out using irradiation means distributed within the outer cylindrical annular zone in radial directions.

9. Method according to claim 8 characterized in that one implements in step (b), a loop circulation of the suspension to be treated in an upward movement in the outer zone and in a downward movement in the inner zone, and / or,

in step (c), a diffusion of a flow of gas bubbles within the circulated suspension, at least partly in the outer zone.

10. Treatment device for the purification of liquid effluents, in particular aqueous effluents, by photocatalysis, especially for the implementation of the method according to at least one of the preceding claims, characterized in that it comprises:

^■ a reactor (2),

Irradiation means (3),

^■ means (4) for circulating a suspension (5) constituted by an effluent (1) to be processed charged particles of a photocatalyst (P),

^■ means (6) for diffusing a flow of gas bubbles (preferably air) in the suspension (5) circulating,

Means (7) for separating (preferably by filtration) the liquid phase (1 ") and the solid phase (PI) from the treated effluent (1 '),

^■ possibly means (8) for the preparation of the suspension (5) of the effluent (1) to be processed charged particles of a photocatalyst (P),

^■ possibly means (9) of recycling:

o the treated effluent () charged with particles of the photocatalyst upstream of the separation means, preferably between the reactor (2) and the separation means (7), preferably by filtration,

o the treated effluent () treated with particles of the photocatalyst upstream of the reactor (2),

o and / or treated effluent (1) charged particles of photocatalyst (P), in the means (8) for preparing said suspension (5), characterized in that. the reactor (2) comprises at least two zones,

2. the irradiation means (3) are arranged within at least one of the zones, 3. the diffusion means (6) are designed and are arranged in such a way that the flow of gas bubbles is diffused in one of the two zones only, and generates a gasosiphon making it possible to obtain recirculation between the two zones and a Hydrodynamic behavior of the Reactionally Agitated Reactor (RPA) type.