METHOD FOR WATER TREATMENT BY ADSORPTION ON ACTIVATED CARBON IN COMBINATION WITH THE ADDITION OF OZONE, AND PLANT FOR IMPLEMENTING THIS METHOD

Description

Technical field of the invention

[0001] The invention relates to the technical field of water treatment, and in particular to processes for obtaining drinking water and wastewater treatment processes. More specifically, the invention relates to water treatment processes for removing dissolved organic pollution by upward flow through a reactor containing activated carbon coupled with the addition of ozone, as well as the installations enabling the implementation of such processes. Previous art

[0002] Several types of processes exist for removing dissolved organic pollution from aqueous effluents. The main processes used in drinking water production, municipal wastewater treatment, and residual effluent treatment are biological processes, coagulation / flocculation / sedimentation processes, oxidation processes, and adsorption processes.

[0003] Biological processes and coagulation / flocculation / sedimentation processes have the drawback of producing sludge whose management is increasingly problematic and costly. Furthermore, coagulation / flocculation / sedimentation processes rely on the supply and consumption of chemicals (coagulants, flocculating agents) that cannot be extracted from the sludge produced for reuse upstream in the same process. Oxidation processes, for their part, have the disadvantage of generating oxidation byproducts (partial oxidation of dissolved organic compounds that does not lead to complete mineralization). These byproducts can have toxicity and / or ecotoxicity as high as the initial organic compounds. Moreover, some of these oxidation processes rely on homogeneous catalysis mechanisms (such as the Fenton reaction), which also result in sludge production.

[0004] Adsorption, particularly with activated carbon, is a well-known and commonly used technique for removing dissolved organic pollutants (pesticides, industrial residues, pharmaceutical residues, etc.) from both drinking water production systems and the treatment of municipal and industrial wastewater. However, this technique has the drawback of producing a significant quantity of used activated carbon that must be removed from the reactor and replaced with an equal amount of new activated carbon.

[0005] The combined use of an ozonation step and an adsorption step on activated carbon is also known, particularly in drinking water treatment processes. The advantage of such a technique lies not only in the combination of ozone's strong oxidizing power with the high adsorption capacity of activated carbon, but also in the accelerated decomposition of ozone into hydroxyl radicals by the activated carbon. The two steps are carried out consecutively, each in its own dedicated compartment. This means that the water and ozone are first brought into contact, followed by an adsorption step, which can be performed in a granular activated carbon filter. Ozone injection is generally carried out using porous diffusers installed in the ozonation reactor for a contact time of approximately 20 minutes.However, since ozone transfer into water is not complete, some ozone may remain in the vapor space within the ozonation reactor. To protect the health of operators, it is therefore necessary to cover the ozonation reactor and add an ozone destroyer to the vent. Furthermore, to reduce residual ozone molecules in the water exiting the ozonation reactor, a reducing agent, such as sodium bisulfite, must be added. Another drawback of this technique is that the physical separation of the ozonation and adsorption stages, combined with a long contact time between the treated water and the ozone, creates conditions favorable to the formation of ozonation byproducts, such as bromates, which begin to form after 2 to 3 minutes of contact, as well as byproducts from organic matter present in the water, such as N-nitrosodimethylamine (NDMA).These by-products are not always adsorbable onto activated carbon particles and can accumulate in the water exiting the adsorption step. It is therefore important to prevent their formation. CN 205 061 675 U discloses a water treatment process comprising a step of injecting ozone into the water to be treated and a step of treating the ozonated water in a reactor comprising a fluidized bed of activated carbon particles. Objectives of the invention

[0006] One objective of the present invention is to propose a water treatment technique that does not lead to the formation of by-products or solid residues.

[0007] Another objective of the present invention is to provide a water treatment technique that does not lead to the formation of bubbles and / or a gas cloud above the compartment in which adsorption takes place, in order to avoid or at least limit the use of chemicals such as a reducing agent. Such a technique also contributes to reducing health risks for operators.

[0008] Another objective of the present invention is to propose a water treatment technique by adsorption on activated carbon that saturates the activated carbon less quickly, or even allows its regeneration in situ, in order to reduce the quantities of new adsorbent to be introduced to replace the used adsorbent.

[0009] Another objective of the present invention is to propose a water treatment technique that consumes less ozone compared to existing advanced oxidation processes.

[0010] Another objective of the present invention is to propose a technique which makes it possible to achieve these objectives while reducing the contact time between the ozone and the water to be treated.

[0011] Another objective of the present invention is to propose a water treatment technique which allows the elimination of bacteria and viruses present in the water to be treated, without requiring any steps specifically implemented for this purpose. Summary of the invention

[0012] These objectives, as well as others that will appear later, are achieved thanks to the invention.

[0013] A first object according to the invention relates to a water treatment process according to claim 1. In particular, the process according to the invention comprises: an ozone injection step into the water to be treated, a step of bringing the ozonated water to be treated into a reactor comprising a fluidized bed of activated carbon particles, a step of bringing the ozonated water to be treated into contact with the activated carbon particles according to an upward flow of water in the reactor, a step of evacuating the treated water, in which the ozone injection step into the water to be treated is carried out by a Venturi effect, and in which the injection step is immediately followed by a step of saturating the water to be treated with ozone.

[0014] This process incorporates ozone into the water and then dissolves it to eliminate bubbles while regenerating the activated carbon particles in the reactor. Thanks to this process, and as will be demonstrated in the examples, it is possible to reduce the amount of ozone used and the amount of new activated carbon required to replace the spent activated carbon, compared to existing processes, while maintaining good water treatment performance.

[0015] Alternatively, the quantities of ozone and activated carbon can be equivalent to those used in existing processes, and then the water treatment performance is increased compared to that obtained by these existing processes.

[0016] According to a preferred embodiment, the water saturation step with ozone is carried out using a saturation cone or a degassing column.

[0017] The use of a saturation cone is advantageous because it is a simple, efficient, and quick-to-install device, and its footprint can be chosen according to the installation configuration and desired performance. Thus, saturation cones can easily be integrated into existing installations containing a fluidized bed reactor for activated carbon particles, either to improve its performance or to reduce the consumption of additional fresh activated carbon. Saturation can also be carried out in a degassing column.

[0018] According to a preferred embodiment, the injection step and the water saturation step with ozone have an overall duration of less than 1 minute, preferably between 10 and 30 seconds.

[0019] The process according to the invention makes it possible to improve the performance of water treatment or to reduce the consumption of ozone and new activated carbon without slowing down the water treatment process. The injection of ozone and its dissolution in the water takes only a few seconds, which is particularly advantageous when modifying an existing installation.

[0020] According to the invention, the ozone injection and ozone saturation steps are carried out in means for supplying the water to be treated to said reactor. Alternatively, these steps can be carried out in a bypass pipe connected to means for supplying the water to be treated to said reactor.

[0021] This choice of configurations cleverly allows the process to be adapted to existing installations, depending in particular on the available floor space.

[0022] According to one embodiment, the activated carbon particles used according to the process are agglomerates having a particle size between 300 µm and 1500 µm, preferably between 400 µm and 800 µm, and an actual density greater than 0.45.

[0023] Activated carbon agglomerates meeting these characteristics are particularly advantageous, as they allow for optimal expansion of the fluidized bed of activated carbon particles, which improves the adsorption capacity of pollutants onto them.

[0024] In one embodiment, the fluidized bed reactor of the process is equipped with at least one water deflection device located at its upper end. This deflection device is designed to reduce the velocity of the upward water flow to create a calm zone above the bed of activated carbon particles. This calm zone is an area of ​​low hydrodynamic turbulence that prevents activated carbon particles, particularly the finest particles, from being carried away by the upward water flow and escaping from the reactor, which would increase the consumption of additional activated carbon. This is particularly advantageous in cases where ozone coalescence on the surface of the activated carbon particles would cause bubble formation and carbon losses.

[0025] According to one variant, at least one deflection means consists of a set of slats inclined with respect to the vertical and parallel to each other, inclined with respect to the vertical at an angle θ between 50° and 60°, preferably at an angle θ close to 60°.

[0026] According to one embodiment, when at least one deflection means is present in the reactor, the reactor further includes water recovery means disposed downstream of the quiet zone, such recovery means preferably consisting of a prismatic-shaped chute with lateral faces forming an angle α of 45° to 70° with respect to the horizontal and which are each provided with a first fluid overflow and a deflector acting as a baffle as a deflection means.

[0027] According to one embodiment, the velocity of the upward water flow in the fluidized bed reactor is between 8 m / h and 50 m / h, preferably between 20 m / h and 40 m / h.

[0028] Since gas bubbles are incompatible with the operation of a fluidized bed reactor because they cause hydraulic disturbances, it is imperative that there be no gas bubbles (in this case, ozone) in the ozonated water. This is achieved by dissolving the ozone in the water within the saturation cone before it enters the activated carbon reactor. The absence of ozone bubbles in the water reduces the turbulence of the activated carbon bed. This further reduces the amount of activated carbon that is likely to escape from the reactor.

[0029] Another object according to the invention relates to an installation for water treatment according to the process of the invention.

[0030] In particular, the installation according to the invention comprises: an activated carbon reactor comprising a fluidized bed of activated carbon particles, means for supplying the water to be treated into the reactor, and means for removing the treated water, and further includes a means for injecting ozone into the water by a Venturi effect and a means for saturating the water with ozone mounted directly on the means for supplying the water into the reactor, or on a pipe mounted in bypass on the means for supplying the water to be treated into the reactor.

[0031] Such an installation has the advantage of not significantly increasing the footprint of existing structures, which can easily be modified to incorporate the additional technical features according to the invention.

[0032] According to a preferred embodiment, the activated carbon particles in the installation are agglomerates having a particle size between 300 µm and 1500 µm, preferably between 400 µm and 800 µm, and an actual density greater than 0.45.

[0033] Such activated carbon agglomerates are particularly well-suited to the installation according to the invention. Their specific properties allow for optimal expansion of the activated carbon bed, even when high velocities are applied to the upward water flow.

[0034] According to a particular embodiment, the reactor of the installation is equipped with at least one deflection means disposed in the upper part of said reactor.

[0035] Such methods cleverly generate a zone of tranquility in the upper part of the reactor, which helps to prevent the leakage of activated carbon particles, especially the finest ones.

[0036] According to one variant, said at least one deflection means consists of a set of slats inclined with respect to the vertical and parallel to each other, inclined with respect to the vertical at an angle θ between 50° and 60°, preferably at an angle θ close to 60°.

[0037] According to one embodiment, and where the reactor includes deflection means, the reactor further includes water recovery means disposed downstream of the quiet zone, the recovery means preferably consisting of a prismatic-shaped chute with lateral faces forming an angle α of 45° to 70° with respect to the horizontal and which are each equipped with a first fluid spillway and a deflector acting as a baffle as a deflection means. Brief description of the figures

[0038] [ Fig.1 ] : there [ Fig.1[ ] presents a schematic view of the installation in which the Venturi system and the ozone water saturation device are mounted on the water supply pipe to the reactor. Fig. 2 ] : there [ Fig. 2 ] presents a schematic view of an installation according to the invention in which the Venturi system and the means for saturating the water with ozone are installed on a pipe mounted in parallel with a pipe supplying the water to be treated to the reactor. Fig.3 ] : there [ Fig.3 [Figure ] is a diagram showing the percentage removal of various micropollutant compounds in a particle bed reactor with activated carbon (10 g / m³ of activated carbon particles) in the presence and absence of ozone. White indicates the absence of ozone; black indicates ozone at 2 g / m³. The list of compounds is given in Table 2. Detailed description of the invention

[0039] The invention aims to improve existing water treatment processes and installations. In particular, the invention aims to improve wastewater and / or drinking water treatment techniques. Indeed, these waters are particularly suitable for treatment by ozonation and adsorption on activated carbon. Thus, the techniques according to the invention are particularly effective for treating such water.

[0040] The processes and installations according to the invention involve in an original way the association of a means of injecting ozone by a venturi effect with a means of saturating water with ozone, just upstream of a reactor dedicated to the adsorption of polluting substances through a fluidized bed of activated carbon particles.

[0041] For the purposes of this invention, "polluting substances" means organic and chemical materials that impair water quality, including those present in very low concentrations (micropollutants).

[0042] In a first step of the process according to the invention, ozone is injected into the water to be treated. The ozonated water is then conveyed to a reactor comprising a fluidized bed of activated carbon particles. As it flows upwards through the activated carbon bed, the pollutants in the water are adsorbed onto the activated carbon particles, and the treated water is then discharged from the reactor.

[0043] Ozone injection is achieved through suction generated by the Venturi effect, which has the advantage of preventing any ozone leakage into the atmosphere and allowing it to be mixed with the water. The Venturi effect is a suction effect generated by a moving fluid experiencing a vacuum. Thus, through the Venturi effect, the water to be treated experiences a vacuum that allows the ozone to be drawn into the water. Thanks to this technique, all of the injected ozone is incorporated and mixed into the water being treated. It is therefore possible to use reduced quantities of ozone compared to prior art techniques. Preferably, the quantity of ozone injected into the water is between 0.5 and 3.0 mg per liter of water to be treated. The generation of a Venturi effect is achieved by any means known in the art. In particular, it is achieved using a Venturi system.

[0044] The water to be treated, once mixed with ozone, immediately undergoes an ozone saturation step. The ozone molecules dissolve in the water, significantly reducing the formation of ozone bubbles. Such bubbles promote turbulence within the activated carbon bed, hindering their escape from the reactor. Furthermore, ozone in bubble form is less effectively captured on the surface of the activated carbon particles. Activated carbon is capable of reducing ozone molecules. Therefore, a decreased ozone-capturing capacity by the activated carbon particles would contribute to the formation of a harmful gaseous haze above the reactor. Finally, the very short timeframe of just a few seconds for ozone injection and saturation of the water also prevents the formation of byproducts through reactions between ozone and other substances present in the water.Water saturation with ozone is achieved by any known method. In particular, it is carried out using a saturation cone, which achieves a transfer efficiency of approximately 95 to 99%. Alternatively, the water saturation step can be performed using a degassing column. Such a column has the advantage of being simple to construct, but its considerable height can hinder its implementation in an existing facility.

[0045] Without being bound to any particular theory, it can be assumed that the improvements obtained through the process according to the invention are partly based on the ability of dissolved ozone molecules to react on the surface of activated carbon particles to create new surface functional groups. Indeed, activated carbon captures polluting molecules not only through the presence of adsorption sites but also through the presence of functional groups capable of binding to pollutants, particularly organic substances. Ozone, due to its strong oxidizing power, enables the creation of new functional groups on the surface of the activated carbon particles. The adsorption capacity of the activated carbon particles is therefore significantly improved, especially with regard to organic pollutants such as pesticides, pharmaceutical residues, and natural organic substances.Thus, for the same quantity of activated carbon used, water treatment performance is significantly improved. A reduction in carbon renewal to 10 g / m³ of water treated has been observed, associated with a 25% increase in pollutant adsorption performance. Alternatively, the process according to the invention maintains identical performance while significantly reducing the amount of activated carbon required for water treatment. Furthermore, the reaction of ozone on the surface of the activated carbon advantageously reduces ozone, thereby preventing ozone from being found in the treated water and / or in the vapor cloud above the reactor.

[0046] As demonstrated in the experimental section, the process according to the invention prevents the formation of by-products such as bromates, even in the presence of high bromide concentrations in the water being treated. Furthermore, the process according to the invention achieves the removal of the vast majority of micropollutants at rates exceeding 90%. Finally, the invention provides improved water sanitation, notably by reducing bacteria and viruses in the water through the action of ozone.

[0047] Another advantage of the process according to the invention is that the total duration of the ozone injection and ozone saturation steps is very short. In a particular embodiment, the ozone injection step and the ozone saturation step have a total duration of less than 60 seconds, preferably less than 30 seconds, and more preferably between 10 and 20 seconds. It then only takes a few seconds for the water to be saturated with ozone, thus significantly improving the water treatment performance, or, for equivalent performance, significantly reducing the amount of activated carbon particles that need to be replaced. Reducing the contact time advantageously prevents, or at least reduces, the formation of by-products.

[0048] In one embodiment, the ozone injection and ozone water saturation steps are carried out at the point where the water to be treated is conveyed to the reactor, such as a pipeline. Indeed, the process according to the invention yields better results when these two steps are conducted close to the reactor containing the fluidized bed of activated carbon particles. Increasing the duration of the ozone-saturated water supply promotes the formation of byproducts such as bromates.

[0049] However, the process according to the invention also allows these injection and saturation steps to be carried out at another level, which makes it possible to adapt its implementation to different configurations of water treatment installations.

[0050] Thus, according to another embodiment, these steps are carried out in a pipeline connected to the main supply line for the water to be treated. It is therefore possible to add a preliminary step of supplying the water to be treated to a pipeline connected to the main supply line, where the ozone injection and ozone saturation steps will be conducted. A further step of supplying the ozone-saturated water to the main supply line can then be included.

[0051] Once the water to be treated is saturated with ozone, it is conveyed to a reactor containing a fluidized bed of activated carbon particles. This step is carried out by the means of conveying the water to be treated to the reactor, such as a main pipeline, possibly preceded by a step of conveying the ozone-saturated water from the bypass pipeline to the means of conveying the water to be treated to the reactor.

[0052] In the reactor, ozone-saturated water flows upwards through the fluidized bed of activated carbon particles. As previously mentioned, the ozone in the water allows the formation of new functional groups on the surface of the activated carbon particles. The pollutants in the water being treated are then adsorbed both by the adsorption sites of the activated carbon particles and by the functional groups created on their surface. Simultaneously, the reaction of the ozone on the surface of the activated carbon particles leads to its reduction, resulting in little to no ozone remaining in the interstitial water.

[0053] In a preferred embodiment, the step of contacting the ozone-saturated water to be treated is carried out on activated carbon particles in the form of agglomerates. Agglomerates of activated carbon particles differ from powdered activated carbon in particular by their particle size, specific surface area, and density.

[0054] Preferably, the agglomerates of activated carbon particles are in the form of micrograins. The activated carbon micrograins used in the process according to the invention have an average particle size between 300 µm and 1500 µm, preferably between 400 µm and 800 µm, with a proportion strictly less than 5% of particles smaller than 400 µm. It should be noted that the particle size of powdered activated carbon is significantly smaller, generally between 5 µm and 50 µm, and in particular between 10 µm and 25 µm.

[0055] According to one embodiment, the density of the activated carbon micrograins is greater than 0.45, preferably greater than 0.5 (dry product).

[0056] According to one embodiment, the concentration of activated carbon particles in the reactor is between 100 g / L and 400 g / L, preferably between 150 g / L and 300 g / L.

[0057] The velocity of the upward water flow applied in the reactor is adjusted according to the particle size of the activated carbon in the particle bed. It is important to avoid excessive or insufficient expansion of the particle bed. When the bed expansion is too small, the carbon particles are not completely separated from each other, reducing the adsorption performance of the particle bed. Conversely, when the expansion is too large, the activated carbon particles are more likely to be carried away by the upward water flow and leave the reactor, increasing the amount of new activated carbon that must be added to compensate for these losses.In practice, the upward flow velocity can thus be preferentially chosen to form an expansion zone of the activated carbon particle bed and a transition zone above it, the particle concentration being less dense in the transition zone than in the expansion zone.

[0058] According to one embodiment, the upward flow velocity of water in the reactor is between 8 m / h and 50 m / h, preferably between 20 m / h and 40 m / h.

[0059] This embodiment is particularly suitable when the activated carbon particles forming the reactor bed are micrograins as described above.

[0060] In one particular embodiment, water deflection means are positioned in the upper part of the reactor. Such deflection means are described, for example, in international patent application WO2019224258A1. They contribute to the formation of a calm zone in the upper part of the reactor.

[0061] This allows for the use of high upward flow velocities of the treated water while preventing any leakage of activated carbon particles. Furthermore, it eliminates the need for ballast polymers even at relatively high upward flow velocities of the treated water.

[0062] Preferably, the deflection means consist of a set of slats inclined with respect to the vertical and parallel to each other. Preferably, these slats are inclined with respect to the vertical at an angle θ between 50° and 60°. Advantageously, the slats can, in particular, be inclined with respect to the vertical at an angle θ close to 60°.

[0063] The blades can be spaced between 25 mm and 100 mm apart. Specifically, they can be spaced between 36 mm and 42 mm apart. This spacing is particularly suitable for adsorbent media particles, especially activated carbon grains or micrograins, with a particle size between 300 µm and 1500 µm. The water velocity decreases within the blades as it passes through the deflection devices, creating a settling zone where the particles can settle.

[0064] In one particular embodiment, when deflection means are present, the reactor of the installation further includes water recovery means located downstream of the containment zone. Such means may, for example, consist of a prismatic chute with lateral faces forming an angle α of 45° to 70° with respect to the horizontal, each face equipped with a first fluid overflow and a deflector acting as a baffle for deflection. The angle α may, in particular, have a value close to 60°. Such a chute has already been described in patent application published under number FR2694209A1.

[0065] The invention also relates to a water treatment plant, particularly for wastewater or drinking water, adapted for implementing the process according to the invention described above. This plant is now described with reference to Figures 1 And 2 , which are used for illustrative purposes only and do not constitute a limitation of the detailed description given below.

[0066] Installation 10 according to the invention comprises: an activated carbon reactor 1 comprising a fluidized bed of activated carbon particles 2, means 3 for bringing the water to be treated into the reactor 1, means for removing the treated water 7, as well as a means for injecting ozone into the water to be treated by a Venturi effect, here a Venturi system 4, and a means for saturating the water with ozone, here a saturation cone 5, located either directly on the means 3, or on a means 3' mounted in parallel with the means 3.

[0067] The reactor 1 suitable for the process according to the invention comprises a fluidized bed of activated carbon particles 2. The reactor may be cylindrical or square in shape. Preferably, the reactor has a height between 3 m and 10 m. It is equipped with a means for injecting and distributing the water to be treated in the lower part of the reactor, in order to create an upward flow of water within the reactor.

[0068] The activated carbon particles constituting bed 2 of reactor 1 are as described above. The bed of activated carbon particles in the reactor preferentially has a height of between 1.5 m and 3 m at rest, and a height during expansion of between 2 m and 5 m.

[0069] The water supply means 3 and the optional means 3' for diverting the water supply means 3 may be pipes. When diverting means 3' are used, means 3 and 3' are connected to each other by known means, in particular tees. In a variant of this particular embodiment, means 6 for supplying the water to be treated may then be provided to convey a portion of the water to be treated from means 3 to means 3'. This may include a pump, preferably an accelerating pump.

[0070] A Venturi 4 system suitable for the purposes of the invention can be any known Venturi system. Examples include Venturi injectors marketed by the Stübbe brand or equivalent.

[0071] A saturation cone as defined in the invention can be selected from among known cones suitable for saturating water with ozone. It can also be chosen according to various criteria, particularly the space occupied and the flow rate of the water to be treated. For example, saturation cones marketed by Pentair or Linde-Gas, or equivalent brands, are known. Of course, other methods of saturating water with ozone can be used, such as a degassing column.

[0072] According to a particular embodiment, the reactor of the installation according to the invention is equipped with deflection means (not shown). The deflection means suitable for the installation according to the invention are those described above. Their implementation in the installation advantageously avoids the need to increase the reactor height to prevent losses of activated carbon particles, thus resulting in a more compact installation. Advantageously, the deflection means are complemented by water recovery means as described previously.

[0073] Advantageously, the installation includes means of 7 for evacuating the treated water, for example a pipeline, in order to convey the treated water to a collection tank or to an additional treatment reactor. Examples

[0074] Other features and advantages of the invention will become clearer from the following examples, which are given by way of illustration and not limitation. Example 1: Formation of functional groups on activated carbon particles

[0075] Laboratory tests were conducted to validate the effects of ozonation on the activation of functional groups on the surface of powdered and microgranular activated carbon. It is known that the surface of activated carbon is negatively charged when the pH is above the "zero charge point" (pH PZC), and positively charged when the pH is below the pH PZC. In the latter case, the activated carbon will have a high affinity for anionic compounds.

[0076] In these tests, the pH of the water containing the tested activated carbon ranged from 7.4 to 7.9. The activated carbon was therefore suitable for negatively charged organic substances. The amount of ozone injected was either 2 g / m³ of water to be treated or zero. The activated carbon particles were present at a concentration of 1.2 g / L. The tests were conducted for 10 minutes.

[0077] Surface function identification was performed using Boehm's method. The iodine value was obtained according to ASTM D4607-94 (2006). The pH PZC ( Point of Zero Charge ) was obtained according to the method of Noh and Schwarz (1989).

[0078] Table 1 presents the results obtained. [Tables 1] Ozone dosage g / m³ Group I meq / g Group II meq / g Group III meq / g Group IV meq / g Total groups meq / g Iodine value mg / g pH PZC 0 2,58 0,66 2,36 3,24 8,84 910 8,05 2,0 4,30 0 0 9,28 13,58 930 8,28

[0079] The pH of the water containing activated carbon (PZC) was 8.05 without ozone and 8.28 after ten minutes of ozonation (degassing of CO2 present in the sample). Ozonation in situ Activated carbon particles acted directly on the material's surface by creating or increasing surface functional groups. This resulted in an increase in surface groupings.

[0080] The acid-base properties of activated carbon are very important and even appear to outweigh its porosity characteristics in the case of aqueous organic compound adsorption. The surface chemistry of carbon results from the presence of heteroatoms such as oxygen, nitrogen, hydrogen, chlorine, sulfur, and phosphorus. These heteroatoms form functional organic groups (pendulous groups), such as ketones (Group I), ethers (Group II), amines (Group III), and phosphates (Group IV), located on the periphery of the carbon crystallites. Their content depends on the origin of the carbon and its activation method, and determines the acidity or alkalinity of the material. Their presence has a significant effect on the adsorption of polar molecules.

[0081] The results presented above show that Group I increases from 2.58 meq / g to 4.30 meq / g, indicating a significant increase in strong carboxyl groups; Group III decreases from 2.36 meq / g to 0 meq / g, which is explained by the oxidation of hydroxyl and phenol groups to carbonyl and carboxyl groups; and Group IV increases from 3.24 meq / g to 9.28 meq / g. This is particularly interesting because Groups I and IV are involved in the adsorption of organic substances, notably through CO and OH interactions (organic substance – surface functional groups).

[0082] The iodine value increases from 910 to 930 mg / g. This increase in the iodine value and the overall increase in surface functions demonstrate the optimization of the adsorption performance of the activated carbon treated with ozone. Example 2: Removal of polluting substances in situ

[0083] Existing microgranule activated carbon fluidized bed reactors with an activated carbon concentration of 100 to 300 g / L were modified to allow ozone injection and saturation of the water with ozone prior to its entry into the reactor. The water used came from two plants, one producing drinking water and the other wastewater undergoing tertiary treatment.

[0084] For each of these plants, the amount of ozone injected was between 1 g / m³ and 2.5 g / m³. The activated carbon microgranule replacement rate was between 10 mg / L and 20 mg / L. The upward water flow velocity in the reactor was between 20 m / h and 40 m / h. The contact time of the ozone-saturated water to be treated in the fluidization reactor was approximately 10 minutes.

[0085] The content of different compounds listed in Table 2 below was measured in order to evaluate the percentage of their elimination according to the treatment. [Tableaux2] Number Name CAS NO. 1 Carbamazepine 298-46-4 2 Gabapentine 60142-96-3 3 Primidon 125-33-7 4 Clarithromycin 81103-11-9 5 Sulfamethoxazole 723-46-6 6 Trimethoprim 738-70-5 7 Diclofenac 15307-86-5 8 Mefenamic acid 61-68-7 9 Venlafaxine 93413-69-5 10 Atenolol 29122-68-7 11 Atenolol acid 56392-14-4 12 Metoprolol 51384-51-1 13 Hydrochlorothiazide 51384-51-1 14 Valsartan 137862-53-4 15 Bezafibrate 41859-67-0 16 Benzotriazole 95-14-7 17 Methylchloroisothiazolone 26172-55-4

[0086] The results obtained are presented in [ Fig.3 ].

[0087] They confirm that the process according to the invention results in a marked improvement in the quality of water treatment. A gain of approximately 20% to 25% in the average removal performance of various micropollutants is recorded at one of the sites, bringing the removal efficiency to between 85% and 92%. At the other site, where apart from benzotriazole (77.6%), all other molecules are removed at more than 80%, with efficiencies reaching 99% for carbamazepine (compound no. 1), diclofenac (compound no. 7), hydrochlorothiazide (compound no. 13) and sulfamethoxazole (compound no. 5, removal at 98%). Example 3: Formation of by-products

[0088] In prior art techniques, ozone concentrations used ranged from 8 to 10 g / m³. It is known that such concentrations and long water / ozone contact times promote the formation of byproducts through the oxidation of pollutants by ozone. In particular, it is well known that ozonation of water containing bromides leads to the formation of bromates.

[0089] Tests were conducted to verify whether the low doses of ozone implemented using the invention also resulted in the detrimental formation of by-products. Tertiary wastewater containing approximately 6.5 to 7 mg / L of bromides was used for these tests. The injected ozone concentration was approximately 2 g / m³, and the concentration of activated carbon particles in the fluidized bed reactor was 100 to 300 g / L. The contact time in the fluidized bed was greater than 8 minutes. The results were compared to those obtained by performing ozonation in a separate compartment, as known in the prior art, with a contact time of 3 minutes and an ozone injection of 3 g / m³. They were also compared to those obtained in the fluidized bed reactor without ozone injection.

[0090] Table 3 presents the results of bromate concentrations in water. [Tables 3] Ozonated tertiary water Non-ozonated tertiary water treated on a fluidized bed of activated carbon microgranules Water saturated with ozone and then treated on a fluidized bed of activated carbon particles according to the invention Bromates (µg / L) 137 <10 <10

[0091] The injected ozone concentrations, below 3 g / m³, were too low to oxidize pollutants, particularly micropollutants. This prevented the production of byproducts in the water.

[0092] Furthermore, thanks to the process of the invention, ozone was injected almost directly into the reactor containing the activated carbon. This resulted in a direct reaction between the oxidant (ozone) and the reductant (activated carbon), which is much faster than the reaction between ozone and pollutants such as organic matter and micropollutants. This is why the ozonation reaction did not alter the micropollutants. In addition, the interstitial water was free of residual ozone. Example 4: bactericidal action

[0093] Coliform bacteria were enumerated in the raw water to be treated, and then in the water exiting the reactor containing activated carbon. A reduction in the total coliform count of approximately one to two logs was observed. These results confirm the bactericidal action of ozone.

[0094] Since ozone is also known for its virucidal action, comparable results are expected regarding viruses present in the water to be treated. References

[0095] Joong S Noh, James A Schwarz, 1989. Estimation of the point of zero charge of simple oxides by mass titration. Journal of Colloid and Interface Science 130(1): 157-164. ISSN 0021-9797, https: / / doi.org / 10.1016 / 0021-9797(89)90086-6.

Claims

1. Water treatment method comprising: - a step of injecting ozone into the water to be treated, - a step of bringing the ozonated water to be treated into a reactor comprising a fluidised bed of activated carbon particles, - a step of placing the ozonated water to be treated in contact with the activated carbon particles according to a flow of water ascending in the reactor, - a step of discharging the water treated in this way, characterised in that - the step of injecting ozone into the water to be treated is carried out by a Venturi effect, - the injection step is immediately followed by a step of ozone saturation of the water to be treated, said steps of injecting ozone and of saturating the water with ozone are implemented in means for bringing the water to be treated into said reactor, or in a pipe mounted as a bypass on means for bringing the water to be treated into said reactor.

2. Method according to claim 1, characterised in that said saturation step is performed with the aid of a saturation cone or of a degassing column.

3. Method according to claim 1 or 2, characterised in that said step of injecting and said step of saturating the water with ozone have an overall duration less than 1 minute, preferably between 10 and 30 seconds.

4. Method according to any one of the preceding claims, characterised in that said activated carbon particles are agglomerates having a particle size between 300 and 1500 µm, preferably between 400 and 800 µm, and a true density greater than 0,45.

5. Method according to any one of the preceding claims, characterised in that said reactor is equipped with at least one means for deflecting the water disposed in the upper portion, intended to reduce the speed of the ascending flow of water to arrange a tranquil area above the bed of activated carbon particles.

6. Method according to claim 5, characterised in that said at least one deflection means consists of a set of blades inclined in relation to the vertical and mutually parallel, inclined in relation to the vertical by an angle θ between 50° and 60°, preferably by an angle θ close to 60°.

7. Method according to claim 5 or 6, characterised in that the reactor further comprises means for recovering the water disposed downstream of the tranquil area, the recovery means preferably consisting of a prism-shaped chute with side faces forming an angle α of 45° to 70° in relation to the horizontal and that are each equipped with a first fluid spout and with a deflector acting as a baffle as a deflection means.

8. Method according to any one of the preceding claims, characterised in that the speed of the flow of ascending water is between 8 and 50 m / h, preferably between 20 and 40 m / h.

9. Facility (10) for implementing the method according to any one of the preceding claims, comprising: - an activated carbon reactor (1) comprising a fluidised bed of activated carbon particles (2) - means (3) for bringing the water to be treated into the reactor, - means (7) for discharging the treated water, characterised in that the facility (10) further comprises a means (4) for injecting ozone into the water by a Venturi effect and a means (5) for saturating the water with ozone mounted directly on the means (3) for bringing the water into the reactor, or on a pipe (3') mounted as a bypass on the means (3) for bringing the water to be treated into the reactor.

10. Facility (10) according to claim 9, characterised in that said activated carbon particles (2) are agglomerates having a particle size between 300 and 1500 µm, preferably between 400 and 800 µm, and a true density greater than 0,45.

11. Facility (10) according to claim 9 or 10, characterised in that said reactor (1) is equipped with at least one deflection means disposed in the upper portion of said reactor.

12. Facility (10) according to claim 11, characterised in that said at least one deflection means consists of a set of blades inclined in relation to the vertical and mutually parallel, inclined in relation to the vertical by an angle θ between 50° and 60°, preferably by an angle θ close to 60°.

13. Facility (10) according to claim 11or 12, characterised in that the reactor further comprises means for recovering the water disposed downstream of the tranquil area, the recovery means preferably consisting of a prism-shaped chute with side faces forming an angle α of 45° to 70° in relation to the horizontal and that are each equipped with a first fluid spout and with a deflector acting as a baffle as a deflection means.