Method for treating water by adsorption on activated carbon combined with the addition of ozone, and equipment for carrying out said method

Abstract

The present invention relates to a water treatment method comprising the steps of injecting ozone into water to be treated by the Venturi effect, followed immediately by saturating said water with ozone, conveying the ozone-treated water to be treated in a reactor comprising a fluidized bed of activated carbon particles, placing the ozone-treated water to be treated in contact with the activated carbon particles according to the flow of water ascending in the reactor, and discharging the treated water as is.The present invention also relates to an installation comprising an activated carbon reactor, means for conveying the water to be treated into the reactor, means for discharging the treated water, and means for injecting ozone into the water by the Venturi effect and means for saturating the water with ozone, mounted directly on the means for conveying water into the reactor or as a bypass.

Description

Detailed Description of the Invention

[0001] [Technical Field of the Invention] The present invention relates to the technical field of water treatment, in particular to methods for obtaining drinking water and for purifying wastewater, and more particularly to a method for treating water to remove dissolved organic pollutants by flowing it up through a reactor containing activated carbon in combination with the addition of ozone, and to an installation making it possible to carry out such a method.

[0002] [Prior Art] There are several methods that allow the removal of dissolved organic pollutants in effluent water. The main methods used in drinking water production systems to treat municipal wastewater and residual effluents are biological, coagulation / flocculation / sedimentation, oxidation, and adsorption.

[0003] Biological and coagulation / flocculation / sedimentation methods have the disadvantage of generating sludge. Sludge management is becoming increasingly problematic and costly. Additionally, coagulation / flocculation / sedimentation methods are based on the supply and consumption of chemicals (coagulants, flocculants), which cannot be extracted from the generated sludge prior to the same process to allow their reuse. Oxidation methods for some of them have the disadvantage of generating oxidation by-products (partial oxidation of dissolved organic compounds without achieving complete mineralization). These by-products can be as toxic and / or ecotoxic as the initial organic compounds. Additionally, some of these oxidation methods are based on homogeneous catalytic reaction mechanisms (e.g., Fenton reaction), which result in the generation of additional sludge.

[0004] Adsorption techniques, particularly on activated carbon, are well known and commonly used in drinking water production systems to remove dissolved organic pollutants (pesticides, industrial residues, pharmaceutical residues, etc.) and to treat municipal and industrial wastewater. However, this technique has the drawback of generating a significant amount of spent activated carbon, which must be removed from the reactor and replaced with an equal amount of fresh activated carbon.

[0005] The combined use of ozonation and activated carbon adsorption is also known, particularly in drinking water systems. The interest of this technology lies not only in the combination of the strong oxidizing power of ozone and the significant adsorption capacity of activated carbon, but also in the accelerated decomposition of ozone into hydroxyl radicals by activated carbon. The two processes are carried out consecutively in their respective dedicated compartments: first, the process of placing water in contact with ozone, followed by the adsorption process. The adsorption process can be carried out in a granular activated carbon filter. Ozone is typically injected into the ozonation reactor through a porous diffuser, typically for a contact time of approximately 20 minutes. However, because ozone transfer into the water is not complete, ozone can remain in the gas space within the ozonation reactor. Therefore, to protect the health of workers, the ozonation reactor must be covered and an ozone destroyer must be installed in the vent. Furthermore, a reducing agent, such as sodium bisulfite, must be added to reduce the ozone molecules remaining in the water exiting the ozonation reactor. Another drawback of this technology is that the ozonation and adsorption steps are physically separated, resulting in a long contact time between the water being treated and ozone, which creates conditions favorable for the formation of ozonation by-products (e.g., bromate, which begins to form after 2–3 minutes of contact) as well as by-products derived from organic substances present in the water (e.g., N-nitrosodimethylamine (NDMA)). These by-products are not necessarily adsorbable onto activated carbon particles and can accumulate in the water exiting the adsorption step. Therefore, it is important to prevent their formation.

[0006] [Object of the Invention] One object of the present invention is to propose a water treatment technology that does not result in the formation of by-products or solid residues.

[0007] Another object of the present invention is to propose a water treatment technique that does not result in the formation of bubbles and / or gas clouds above the compartment where the adsorption takes place, so that the use of chemicals such as reducing agents is prevented or at least limited, which also involves a reduction in the risk to the health of workers.

[0008] Another object of the present invention is to propose a technique for treating water by adsorption onto activated carbon, which delays the saturation of the activated carbon or allows its in situ regeneration, with a view to reducing the amount of new adsorbent introduced to replace used adsorbent.

[0009] Another object of the present invention is to propose a water treatment technology that consumes less ozone compared to existing methods of advanced oxidation type.

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

[0011] Another object of the present invention is to propose a water treatment technology that allows the elimination of bacteria and viruses present in the water to be treated without the need for steps specifically implemented for this purpose.

[0012] Summary of the Invention These objectives, as well as others that will become apparent hereinafter, are achieved by the present invention.

[0013] A first aspect of the present invention relates to a water treatment method, in particular, the method of the present invention comprises: injecting ozone into the water to be treated; conveying the ozonated water to be treated into a reactor containing a fluidized bed of activated carbon particles; placing the ozone-treated water in contact with the activated carbon particles according to the upward flow of the water in the reactor; Discharging the treated water as is; wherein the step of injecting ozone into the water to be treated is performed by the Venturi effect, and the step of injecting is immediately followed by a step of saturating the water to be treated with ozone.

[0014] This method allows ozone to be introduced into water and then dissolved therein for the purpose of removing bubbles while regenerating the activated carbon particles present in the reactor. This method can reduce the amount of ozone used and the amount of new activated carbon introduced as a replacement for used activated carbon compared to existing methods while maintaining good water treatment performance, as demonstrated in the examples.

[0015] Alternatively, the amount of ozone and the amount of activated carbon may be similar to those used in existing methods, in which case the water treatment performance will be improved over that achieved by these existing methods.

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

[0017] The use of saturated cones is advantageous because the installation of the device is simple, effective, and quick, and the installation area can be selected depending on the configuration of the equipment and the desired performance. Therefore, saturated cones can be easily incorporated into existing equipment containing fluidized bed reactors of activated carbon particles in order to improve their performance or reduce the consumption of new activated carbon to be replenished. Saturation may also be performed in the degassing column.

[0018] According to a preferred embodiment, said steps of injecting and saturating said water with ozone have a total duration of less than 1 minute, preferably between 10 and 30 seconds.

[0019] Indeed, the method of the present invention allows improving the performance of water treatment or reducing the consumption of ozone and new activated carbon without slowing down the water treatment process. The injection of ozone and its dissolution into the water takes only a few seconds, which is particularly interesting in situations where existing installations are being retrofitted.

[0020] According to a particular embodiment, the steps of injecting ozone and saturating the water with ozone are implemented in the means for conveying the water to be treated into the reactor, or alternatively, these steps may be implemented in a pipe attached as a bypass on the means for conveying the water to be treated into the reactor.

[0021] This choice in configuration allows the method to be cleverly adapted as best as possible to existing installations, in particular depending on the available floor space.

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

[0023] Activated carbon agglomerates having these characteristics are particularly advantageous because they allow for optimal expansion of the fluidized bed of activated carbon particles to be achieved, thereby improving the adsorption capacity of the activated carbon particles for contaminants.

[0024] According to one embodiment, the fluidized bed reactor according to the present method comprises at least one means for diverting the water, located in the upper part. Such diverting means is intended to reduce the velocity of the upward flow of water so that a tranquil area is formed above the bed of activated carbon particles. Such a tranquil area is an area of ​​low hydrodynamic turbulence, making it possible to prevent activated carbon particles, especially the finest particles, from being carried away by the upward flow of water and escaping from the reactor, which would increase the consumption of new activated carbon replenishment. This is particularly advantageous when ozone coalescence on the surface of activated carbon particles causes the release of gas bubbles and carbon loss.

[0025] According to one variant, at least one of said deflection means consists of a set of blades parallel to one another and inclined relative to the vertical by an angle θ between 50° and 60°, preferably close to 60°.

[0026] According to one embodiment, when at least one of the diverting means is present in the reactor, the reactor further comprises means for recovering the water arranged downstream of the stabilization zone, preferably consisting of a prism-shaped chute having a number of sides forming an angle α of 45° to 70° with respect to the horizontal, each of which comprises a first fluid spout and a deflector acting as a baffle as a diverting means.

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

[0028] Because air bubbles are incompatible with the operation of a fluidized bed reactor due to the hydraulic disturbances they cause, it is essential that there are no air bubbles (in this case, ozone) present in the ozonated water. This is achieved by dissolving the ozone in the water at the saturation cone before it enters the activated carbon reactor. The absence of ozone bubbles in the water reduces turbulence in the bed of activated carbon particles. This has the effect of further reducing the amount of activated carbon that tends to escape from the reactor.

[0029] Another aspect of the invention relates to an installation for treating water according to the method of the invention.

[0030] In particular, the installation according to the invention an activated carbon reactor comprising a fluidized bed of activated carbon particles; means for conveying the water to be treated into the reactor; means for discharging the treated water; Equipped with means for injecting ozone into the water by the Venturi effect and means for saturating the water with ozone, mounted directly on the means for conveying the water into the reactor or on a pipe mounted as a bypass on the means for conveying the water to be treated into the reactor; Further provided are:

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

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

[0033] Such activated carbon agglomerates are particularly adapted for the installation according to the invention, as their particular properties make it possible to achieve an optimal expansion of the activated carbon bed even when high velocities are applied to the ascending water flow.

[0034] According to a particular embodiment, the reactor of the installation comprises at least one deflection means arranged in the upper part of the reactor.

[0035] By this means, a stable zone can be created in the upper part of the reactor, which prevents the escape of activated carbon particles, especially the finest particles.

[0036] According to one variant, at least one of said deflection means consists of a set of blades parallel to one another and inclined relative to the vertical by an angle θ between 50° and 60°, preferably close to 60°.

[0037] According to one embodiment, when the reactor comprises a diverting means, the reactor further comprises a means for recovering the water arranged downstream of the stabilization area, and the recovering means preferably comprises a prism-shaped chute having a plurality of sides forming an angle α of 45° to 70° with respect to the horizontal plane, each of which comprises a first fluid spout and a diverter acting as a baffle as the diverting means.

[0038] BRIEF DESCRIPTION OF THE DRAWINGS [Figure 1]: Figure 1 shows a schematic diagram of the installation in which the Venturi system and the means for saturating the water with ozone are mounted on the pipe that carries the water to the reactor.

[0039] [Figure 2]: Figure 2 shows a schematic diagram of an installation according to the invention, in which the Venturi system and the means for saturating water with ozone are installed on a pipe attached as a bypass to the pipe that carries the water to be treated to the reactor.

[0040] [Figure 3]: Figure 3 shows the effect of activated carbon particles (10 g / m) in the presence or absence of ozone. 3 Figure 1 shows the removal rate of various trace pollutant compounds in a bed reactor of activated carbon particles (white: no ozone, black: 2 g / m). 3 A list of compounds is given in Table 2.

[0041] [Mode for Carrying Out the Invention] The present invention aims to improve existing water treatment methods and installations. In particular, the present invention aims to improve the technology for treating wastewater and / or drinking water. Indeed, this water is particularly suitable for treatment by ozonation and adsorption on activated carbon. Therefore, the technology according to the present invention is particularly useful for treating such water.

[0042] The method and installation according to the invention essentially involve the combination of a means for injecting ozone by the Venturi effect and a means for saturating water with ozone, immediately upstream of a reactor dedicated to the adsorption of pollutants through a fluidized bed of activated carbon particles.

[0043] Within the meaning (intent) of the present invention, "pollutants" refers to organic substances and chemicals that adversely affect water quality, including those present in very low concentrations (micropollutants).

[0044] In the first step of the method of the present invention, ozone is injected into the water to be treated. The ozonated water is then directed to a reactor containing a fluidized bed of activated carbon particles. As the water progresses (develops) by flowing upward through the bed of activated carbon particles, the water's contaminants are adsorbed onto the activated carbon particles, and the treated water is then discharged from the reactor.

[0045] Ozone injection is performed by suction created by the Venturi effect, which has the advantage of preventing ozone from escaping into the air. This allows the ozone to mix with the water. The Venturi effect is a suction effect created by a moving fluid under negative pressure. As a result, through the Venturi effect, the water to be treated is subjected to negative pressure, which allows the ozone to be drawn up into the water. This method ensures that all of the injected ozone is incorporated and mixed into the water to be treated. Therefore, the amount of ozone used can be reduced compared to methods known in the prior art. The amount of ozone injected into the water is preferably 0.5 to 3.0 mg per liter of water to be treated. The Venturi effect can be generated by any means known in the art. In particular, it can be achieved by a Venturi system.

[0046] The water to be treated, mixed with ozone, is then immediately subjected to an ozone saturation step. The ozone molecules then dissolve in the water, significantly preventing the formation of ozone bubbles in the water. In fact, these bubbles promote turbulence in the layer of activated carbon particles, thereby facilitating their removal from the reactor. In addition, ozone in the form of bubbles is not captured very well on the surface of the activated carbon particles. Furthermore, activated carbon has the ability to reduce ozone molecules. Therefore, reducing the ozone-capturing capacity of the activated carbon particles would result in the formation of harmful gas spaces above the reactor. Finally, the very short time of a few seconds required to inject ozone and saturate the water to be treated with ozone also has the advantage of preventing the formation of by-products due to reactions between ozone and chemical species contained in the water to be treated. The saturation of water with ozone can be carried out by any known means. In particular, it is carried out using a saturation cone, which allows for the achievement of transfer efficiencies of the order of 95-99%. Alternatively, the ozone saturation of water can be carried out by a degassing column. Such columns have the advantage of being simple in construction, but are quite tall, which can prevent the column from being implemented in existing operations.

[0047] Without wishing to be bound by any theory, it is believed that the improvement obtained by the method of the present invention is due in part to the ability of dissolved ozone molecules to react with the surface of activated carbon particles and create new surface functional groups. Indeed, activated carbon captures pollutant molecules not only due to the presence of adsorption sites, but also due to the presence of functional groups that can bind to pollutants (especially organic compounds). Ozone, due to its strong oxidizing power, can create new functional groups on the surface of activated carbon particles. Thus, the adsorption capacity of activated carbon particles is significantly improved, especially with respect to organic pollutants (e.g., pesticides, pharmaceutical residues, and natural organic matter). This results in a significant improvement in water treatment performance for the same amount of activated carbon used. A 25% improvement in pollutant adsorption capacity is accompanied by a 25% increase in the adsorption capacity of ozone per m3 of treated water. 3 A reduction in carbon exchange of up to 10 g per 1000 g of activated carbon has been observed. Alternatively, the method of the present invention can significantly reduce the amount of activated carbon required to treat water while maintaining the same performance. Furthermore, advantageously, ozone can be reduced by reaction on the surface of the activated carbon, thereby preventing ozone from being found in the treated water and / or in the gas space above the reactor.

[0048] As demonstrated in the experimental section, the method of the present invention makes it possible to avoid the formation of by-products such as bromate, even when high concentrations of bromide are present in the water to be treated. In addition, the method of the present invention makes it possible to reduce the vast majority of trace pollutants by more than 90%. Finally, the present invention allows for better water purification, in particular by reducing bacteria and viruses in the water through the action of ozone.

[0049] Another advantage of the method of the present invention is that the total duration of the steps of injecting ozone and saturating the water to be treated with ozone is very short. According to certain embodiments, the total duration of the steps of injecting ozone and saturating the water with ozone is less than 60 seconds, preferably less than 30 seconds, and more preferably 10 to 20 seconds. In this case, it takes only a few seconds for the water to be treated to be saturated with ozone. This results in a significant improvement in water treatment performance or, for comparable performance, a significant reduction in the amount of activated carbon particles that must be replaced. Advantageously, the shortened contact time can avoid or at least reduce the formation of by-products.

[0050] According to one embodiment, the steps of injecting ozone and saturating the water with ozone are implemented in a means (e.g., a pipe) for transporting the water to be treated to the reactor. In fact, the method according to the invention gives better results when these two steps are carried out near the reactor containing the fluidized bed of activated carbon particles. The increased transport time of the water saturated with ozone favors the appearance of by-products such as bromate.

[0051] However, the method according to the invention allows these injection and saturation steps to be carried out at different levels, which makes it possible to adapt its implementation to different configurations of water treatment plants.

[0052] According to another embodiment, these steps are carried out in a pipe attached as a bypass of the means for conveying the water to be treated to the reactor. Thus, it is possible to add a preliminary step of conveying the water to be treated to a pipe attached as a bypass of the main pipe. In this pipe attached as a bypass, the steps of injecting ozone and saturating the water with ozone are carried out. An additional step can then be provided of conveying the resulting ozone-saturated water to the main pipe.

[0053] Once the water to be treated is saturated with ozone, it is conveyed into a reactor containing a fluidized bed of activated carbon particles. This step is carried out by a means (e.g., a main pipe) for conveying the water to be treated into the reactor, optionally preceded by a step of conveying the ozone-saturated water through a pipe attached as a bypass to the means for conveying the water to be treated into the reactor.

[0054] In the reactor, the ozone-saturated water evolves as it flows upward through a fluidized bed of activated carbon particles. As previously mentioned, the ozone contained in the water creates new functional groups on the surface of the activated carbon particles. As a result, contaminants in the water being treated are adsorbed by both the adsorption sites of the activated carbon particles and the functional groups created on the surface of the activated carbon particles. At the same time, the ozone is depleted by reaction with the surface of the activated carbon particles. As a result, little or no ozone is present in the interstitial water.

[0055] In a preferred embodiment, the step of placing the ozone-saturated water in contact with activated carbon particles in the form of agglomerates, which differ from powdered activated carbon, particularly with respect to particle size, specific surface area, and density.

[0056] Preferably, the agglomerates of activated carbon particles are in the form of granules. The activated carbon granules used in the method according to the invention have an average particle size of 300 μm to 1500 μm, preferably 400 μm to 800 μm. The proportion of particles smaller than 400 μm is strictly less than 5%. It should be noted that the particle size of powdered activated carbon is significantly smaller, generally 5 μm to 50 μm, in particular 10 μm to 25 μm.

[0057] According to one embodiment, the density of the activated carbon granules is greater than 0.45, preferably greater than 0.5 (dry product).

[0058] 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.

[0059] The speed of the upward water flow applied in the reactor is adjusted depending on the particle size of the activated carbon particles in the particle bed. In fact, it should not result in under-expansion or over-expansion of the particle bed. If the bed expands too little, the carbon particles will not be completely separated from each other, which will reduce the adsorption performance of the particle bed. Conversely, if the expansion is too great, there is a risk that more activated carbon particles will be carried away by the ascending water flow and leave the reactor, which will increase the amount of new activated carbon that needs to be added to compensate for these losses. Therefore, in practice, the upward flow speed can be preferably selected so that an expansion zone of the activated carbon particle bed and a transition zone above it are formed, with the particle concentration being lower in the transition zone than in the expansion zone.

[0060] According to one embodiment, the speed of the water flowing upward in the reactor is 8 m / h to 50 m / h, preferably 20 m / h to 40 m / h.

[0061] This embodiment is particularly suitable when the activated carbon particles forming the reactor layer are fine particles as described above.

[0062] According to a particular embodiment, means for diverting water are arranged in the upper part of the reactor. Such diverting means are described, for example, in International Patent Application Publication WO2019224258A1. The diverting means contribute to the formation of a stable region in the upper part of the reactor.

[0063] This allows for the utilization of high velocity upward flow of the water being treated while preventing the escape of activated carbon particles, and further allows for the elimination of the use of ballasting polymers, even when the upward flow of the water being treated is relatively high velocity.

[0064] Preferably, the deflecting means consist of a set of parallel blades inclined to the vertical, the blades being preferably inclined at an angle θ between 50° and 60° to the vertical, and advantageously the blades may be inclined at an angle θ close to 60° to the vertical.

[0065] The blades may be spaced apart from one another by a distance of 25 mm to 100 mm. In particular, the blades may be spaced apart from one another by a distance of 36 mm to 42 mm. This spacing is particularly suitable for adsorbent media particles (especially activated carbon grains or micrograins) with a particle size of 300 μm to 1500 μm. The velocity of the water decreases within the blades as it passes into the diverting means. This allows for the creation of a stability zone (an area where the particles can settle).

[0066] According to a particular embodiment, if a deflection means is present, the reactor of the installation further comprises a means for recovering water, arranged downstream of the stabilization zone. Such a means may consist, for example, of a prismatic chute having several sides that form an angle α of 45° to 70° with the horizontal, each of which comprises a first fluid spout and a deflector acting as a baffle as a deflection means. The angle α may in particular have a value close to 60°. Such a chute has already been described in French Patent Application Publication No. FR 2 694 209 A1.

[0067] The invention also relates to an installation for treating water, in particular wastewater or drinking water, adapted to carry out the method according to the invention as described above. This installation will be described with reference to Figures 1 and 2. Figures 1 and 2 are used solely for illustrative purposes and do not constitute a limitation on the detailed description given below.

[0068] The equipment 10 according to the present invention comprises: an activated carbon reactor 1 containing a fluidized bed of activated carbon particles 2; means 3 for conveying the water to be treated into the reactor 1; means 7 for discharging the treated water; The equipment 10 according to the present invention comprises: - further comprising means for injecting ozone into the water to be treated by the Venturi effect (in this case a Venturi system 4) and means for saturating the water with ozone (in this case a saturation cone 5), either arranged directly on the means 3 or on a means 3' attached as a bypass of the means 3;

[0069] A reactor 1 suitable for the method according to the invention further comprises a fluidized bed of activated carbon particles 2. The reactor may be cylindrical or square in shape. Preferably, the reactor has a height of between 3 m and 10 m. In its lower part, the reactor comprises means for injecting and distributing the water to be treated so that an ascending flow of water is formed in the reactor.

[0070] The activated carbon particles constituting layer 2 of reactor 1 are the activated carbon particles as described above. Preferably, the layer of activated carbon particles in the reactor has a height of 1.5 m to 3 m when at rest and a height of 2 m to 5 m when expanding.

[0071] The water supply means 3 and the optional bypass means 3' of the water supply means 3 may be pipes. If bypass means 3' are implemented, the means 3 and the means 3' are connected to each other by known means such as a tee fitting. In a variant of this particular embodiment, means 6 for conveying the water to be treated may be provided so that part of the water to be treated is led from the means 3 to the means 3'. This relates in particular to pumps, preferably jet pumps.

[0072] A suitable venturi system 4 within the meaning of the present invention may be any known venturi system, and particular mention may be made of the venturi injector sold by Stubbe (u with an umlaut) or its equivalent.

[0073] The saturation cone in the sense of the present invention may be selected from known cones suitable for saturating water with ozone. It may further be selected according to various criteria, in particular the space required and the flow rate of the water to be treated. For example, saturation cones sold by Pentair or Linde-Gas, or their equivalents, are known. Of course, other means for saturating water with ozone (e.g., degassing columns, etc.) may also be implemented.

[0074] According to a particular embodiment, the reactor of the installation according to the invention comprises a diverting means (not shown). Suitable diverting means for the installation according to the invention are as described above. Advantageously, the installation is equipped with a diverting means, which makes it possible to avoid the need to increase the height of the reactor in order to avoid losses of activated carbon particles. This allows a more compact installation to be obtained. Advantageously, the diverting means are complemented by a water recovery means, as described above.

[0075] Advantageously, the installation comprises means 7 (for example a pipe) for discharging the treated water so that it is directed towards a collection tank or an auxiliary treatment reactor.

[0076] [Example] Other features and advantages of the present invention will become more apparent from the following examples, given by way of illustration and not by way of limitation.

[0077] Example 1: Formation of functional groups on activated carbon particles Laboratory tests were conducted to verify the effectiveness of ozone treatment on the activation of functional groups on the surface of powdered activated carbon and granular activated carbon. The surface of activated carbon was treated with ozone at pH 7.0, which is the "point of zero charge" pH. PZC If the pH is higher than pH 5, it will be negatively charged and PZC It is known that when the charge is lower than 0.05, the activated carbon will be positively charged. In the latter case, the activated carbon will have a strong affinity for anionic compounds.

[0078] In these tests, the pH of the water containing the tested activated carbon was between 7.4 and 7.9. Therefore, the activated carbon was adapted to the negatively charged organic matter. The amount of ozone injected was 1000 s / m of water to be treated. 3 The concentration of activated carbon particles was 1.2 g / L. The test was performed for 10 minutes.

[0079] The identification of surface functional groups was carried out according to the Boehm method. The iodine number values ​​were obtained according to the method ASTM D4607-94(2006). pH PZC (point of zero charge) was obtained according to the method of Noh and Schwarz (1989).

[0080] The results obtained are shown in Table 1.

[0081] [Table 1]

[0082] pH of water containing activated carbon PZCwas 8.05 without ozone and 8.28 after 10 minutes of ozone treatment (degassing of CO2 present in the sample). The in situ ozone treatment of activated carbon particles acts directly on the surface of the material by generating or increasing surface functional groups. As a result, an increase in surface groups was observed.

[0083] The surface acid-base properties of activated carbon are very high and appear to dominate over its porous nature when adsorbing organic compounds in aqueous phases. The surface chemistry of carbon results from the presence of heteroatoms such as oxygen, nitrogen, hydrogen, chlorine, sulfur, and phosphorus. These heteroatoms form pendant organic functional groups such as ketones (group I), ethers (group II), amines (group III), and phosphates (group IV) located at the periphery of the carbon crystallites. Their content, which depends on the origin of the carbon and its activation method, determines the acidity or basicity of the material. Their presence has only a minor effect on the adsorption of polar molecules.

[0084] The results above show that Group I changes from 2.58 meq / g to 4.30 meq / g (indicating a significant increase in strong carboxylic functionality), Group III decreases from 2.36 meq / g to 0 meq / g (explained by the oxidation of hydroxyl and phenolic groups to carbonyl and carboxylic groups), and Group IV changes 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 matter, particularly through CO and OH interactions (organic matter-surface functional groups).

[0085] The iodine number increases, changing from 910 mg / g to 930 mg / g. This increase in iodine number, and the overall increase in surface functional groups, indicates an optimization of the adsorption performance of the activated carbon subjected to ozone.

[0086] Example 2: In-situ Contaminant Removal An existing fluidized bed reactor of activated carbon micrograin, with activated carbon concentrations of 100-300 g / L, was modified to allow ozone injection and saturation of the water before it entered the reactor. The water used came from two factories: one producing drinking water and the other wastewater undergoing tertiary treatment.

[0087] For each of these plants, the amount of ozone injected was 1 g / m 3 ~2.5g / m 3 The rate of renewal of the activated carbon granules was 10 mg / L to 20 mg / L. The water flow rate ascending through the reactor was 20 m / h to 40 m / h. The contact time of the ozone-saturated water to be treated in the fluidized reactor was approximately 10 minutes.

[0088] The contents of various compounds listed in Table 2 below were measured to assess their removal rate in response to treatment.

[0089] [Table 2]

[0090] The results obtained are shown in FIG.

[0091] These results confirm that the method according to the invention brings about a significant improvement in the quality of water treatment. An improvement of the order of 20% to 25% in the average performance for removing various micropollutants was recorded at one of these sites, resulting in removal efficiencies of 85% to 92%. At the other site, with the exception of benzotriazole (77.6%), all other molecules were removed at a rate of 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, 98% removal).

[0092] Example 3: Formation of By-Products In the prior art, the ozone concentration used is 8-10 g / m 3 Such concentrations and long water / ozone contact times are known to favor the appearance of by-products due to the oxidation of pollutants by ozone. In particular, it is well known that ozonation of water containing bromide leads to the formation of bromate.

[0093] Tests were conducted to determine whether the low doses of ozone implemented in accordance with the present invention also resulted in the formation of harmful by-products. These tests used tertiary wastewater containing approximately 6.5-7 mg / L bromide. The concentration of injected ozone was approximately 2 g / m. 3 The concentration of activated carbon particles in the fluidized bed reactor was 100-300 g / L. The contact time in the fluidized bed was longer than 8 minutes. This result was confirmed by carrying out ozonation in different compartments as known in the prior art, with a contact time of 3 minutes and a concentration of 3 g / m 3 These were compared with those obtained in a fluidized bed reactor without ozone injection.

[0094] Table 3 shows the results of the bromate concentration in the water.

[0095] [Table 3]

[0096] 3g / m 3 The injected ozone concentration of less than 1000 ppm was low enough to avoid oxidation of contaminants, especially trace contaminants, thereby preventing the formation of by-products in the water.

[0097] Furthermore, due to the method of the present invention, ozone was injected almost directly into the reactor containing activated carbon. This resulted in a direct reaction between the oxidizing agent (ozone) and the reducing agent (activated carbon), which was much faster than the reaction between ozone and pollutants (e.g., organic matter and trace pollutants). This is why trace pollutants were not modified by the ozonation reaction. Furthermore, there was no residual ozone in the pore water.

[0098] Example 4: Bactericidal effect Coliform bacteria were enumerated in the raw water being treated and then in the water exiting the reactor containing activated carbon. A reduction of approximately 1-2 logs of total coliform counts was observed. These results confirm the bactericidal action of ozone.

[0099] Ozone is also known for its virucidal properties, so comparable results were expected with respect to viruses present in the water being treated.

[0100] [References] 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. [Brief explanation of the drawings]

[0101] [Figure 1] 1 shows a schematic diagram of an installation in which a venturi system and a means for saturating water with ozone are mounted on the pipe that carries the water to the reactor. [Figure 2]1 shows a schematic diagram of an installation according to the invention, in which the Venturi system and the means for saturating water with ozone are installed on a pipe attached as a bypass to the pipe that carries the water to be treated to the reactor. [Figure 3] Figure 1 shows the removal rate of various trace pollutant compounds in a bed reactor of activated carbon particles (10 g / m3 activated carbon particles) in the presence or absence of ozone (white: no ozone, black: 2 g / m3 ozone). The list of compounds is given in Table 2.

Claims

1. injecting ozone into the water to be treated; conveying the ozonated water to be treated into a reactor containing a fluidized bed of activated carbon particles; placing the ozone-treated water to be treated in contact with the activated carbon particles according to the flow of water ascending in the reactor; Discharging the treated water as is; A water treatment method comprising: the step of injecting ozone into the water to be treated is carried out by the Venturi effect; the injecting step is immediately followed by a step of saturating the water to be treated with ozone; 1. A method for treating water, characterized in that the steps of injecting ozone and saturating the water with ozone are performed (i) in a means for conveying the water to be treated into the reactor, or (ii) in a pipe attached as a bypass on the means for conveying the water to be treated into the reactor.

2. 2. The method of claim 1, wherein the saturation step is carried out using a saturation cone or a degassing column.

3. 3. The method of claim 1, wherein the steps of injecting and saturating the water with ozone have a total duration of less than 1 minute.

4. The method of claim 3, wherein the steps of injecting and saturating the water with ozone have a total duration of 10 seconds to 30 seconds.

5. The method according to any one of claims 1 to 4, characterized in that the activated carbon particles are agglomerates having a particle size of 300 μm to 1500 μm and a true density of greater than 0.

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6. The method described in claim 5, characterized in that the activated carbon particles are agglomerates having a particle size of 400 μm to 800 μm.

7. 7. The method according to any one of claims 1 to 6, characterized in that the speed of the flow of rising water is between 8 m / h and 50 m / h.

8. The method described in claim 7, characterized in that the flow speed of the rising water is 20 m / h to 40 m / h.

9. an activated carbon reactor (1) containing a fluidized bed of activated carbon particles (2); a means (3) for conveying the water to be treated into the reactor; means (7) for discharging the treated water; An installation (10) for carrying out the method according to any one of claims 1 to 8, comprising: means (4) for injecting ozone into the water by the Venturi effect and means (5) for saturating the water with ozone, mounted either directly on the means (3) for conveying the water into the reactor or on a pipe (3') mounted as a bypass on the means (3) for conveying the water to be treated into the reactor; The installation (10) further comprises:

10. The installation (10) according to claim 9, characterized in that the activated carbon particles (2) are agglomerates having a particle size of 300 μm to 1500 μm and a true density of greater than 0.

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11. The equipment (10) described in claim 10, characterized in that the activated carbon particles (2) are agglomerates having a particle size of 400 μm to 800 μm.

12. The reactor (1) is equipped with a set of parallel blades arranged in the upper part of the reactor, The installation (10) according to any one of claims 9 to 11, characterized in that the set of blades is inclined at an angle θ of between 50° and 60° to the vertical.

13. The equipment (10) described in claim 12, characterized in that the angle θ is close to 60°.

14. the reactor is provided with a recovery means for recovering the water; The installation (10) according to any one of claims 9 to 11, characterized in that the recovery means consist of a prismatic chute.

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