Ozone reaction tower and wastewater treatment system based on ozone reaction tower

Abstract

The utility model provides an ozone reaction tower and a wastewater treatment system based on the ozone reaction tower, and relates to the technical field of wastewater treatment, the ozone reaction tower comprises a water inlet, a water outlet, an aeration device, a filler area and an ozone generator; the aeration device is arranged above the water outlet; the filler area is arranged above the aeration device; and the ozone generator is communicated with the aeration device. The electrochemical reaction of iron-carbon micro-electrolysis and the catalytic ozone reaction of zero-valent iron are utilized, and ozone is decomposed to generate OH, so that the oxidation capacity is improved, and the types of oxidized organic matters are increased. Meanwhile, ozone is dispersed into small bubbles through the aeration device, so that the ozone is further fully mixed with the filler and the wastewater, and the catalytic ozone reaction efficiency is improved. The technical problem of low oxidation efficiency of a catalytic ozonation method in the prior art is solved.

Description

Technical Field

[0001] The utility model relates to the technical field of wastewater treatment, in particular to an ozone reaction tower and a wastewater treatment system based on the ozone reaction tower. Background Art

[0002] Industrial wastewater has the characteristics of a wide variety, complex composition, and high concentration of toxic substances. It is difficult to treat industrial wastewater to the standard level by relying solely on basic physical and chemical or biochemical treatment technologies. Advanced oxidation methods are currently the conventional treatment methods for difficult-to-treat industrial wastewater, which can be divided into Fenton method and ozone catalytic oxidation method. The Fenton method has high treatment efficiency, but it has disadvantages such as large sludge production, high cost, and difficult to control dosing; although the ozone catalytic oxidation method has simple materials and no secondary pollution in the process, it also has problems such as low oxidation efficiency, low ozone utilization rate, and high equipment investment.

[0003] Bioactivated carbon technology originated in the 1970s. It utilizes the huge specific surface area, developed pore structure and excellent adsorption properties of activated carbon, and uses activated carbon as a carrier to construct a biofilm to form bioactivated carbon to degrade pollutants.

[0004] Iron-carbon micro-electrolysis utilizes the principle of metal corrosion, and is also known as internal electrolysis, iron filings filtration, etc.

[0005] Micro-electrolysis technology, also known as internal electrolysis, is a method of electrolyzing wastewater by using the 1.2V potential difference generated by the micro-electrolysis material filled in the wastewater without electricity, so as to achieve the purpose of degrading organic pollutants, but it is easy to cause the problem of "color reversion" of the effluent.

[0006] In view of this, the present utility model is proposed. Utility Model Content

[0007] One of the purposes of the utility model is to provide an ozone reaction tower to solve the technical problem that the ozone catalytic oxidation method in the prior art has simple materials and no secondary pollution, but also has low oxidation efficiency.

[0008] The second purpose of the utility model is to provide a wastewater treatment system to solve the technical problem in the prior art that it is difficult to treat industrial wastewater to a standard level using the ozone catalytic oxidation method due to low ozone utilization rate.

[0009] In order to achieve the above-mentioned purpose of the utility model, the following technical solutions are adopted:

[0010] In a first aspect, an ozone reaction tower is provided, comprising a water inlet, a water outlet, an aeration device, a packing area and an ozone generator;

[0011] The aeration device is arranged above the water outlet;

[0012] The packing area is arranged above the aeration device;

[0013] The ozone generator is communicated with the aeration device.

[0014] Furthermore, a filler expansion zone is provided at the upper end of the filler zone, and a partition layer is provided at the lower end of the filler zone.

[0015] Furthermore, a water distribution pipe is provided at the water inlet, the water distribution pipe is connected with the water inlet, an orifice plate water distributor is provided on the water distribution pipe, and the orifice plate water distributor is located above the packing area.

[0016] Furthermore, a lower perforated plate is provided between the aeration device and the water outlet.

[0017] Furthermore, it also includes an ozone inlet regulating valve arranged at the output end of the ozone generator;

[0018] The aeration device is a micro-nano aerator;

[0019] It also includes an ozone tail gas absorption tank connected to the ozone reaction tower and located above the water distribution pipe;

[0020] The input end of the ozone tail gas absorption tank is also provided with a regulating valve;

[0021] The height of the packing area is 600 mm to 1000 mm.

[0022] In a second aspect, a wastewater treatment system is also provided, comprising a pre-flocculation sedimentation tank, the above-mentioned ozone reaction tower, a secondary sedimentation tank and a clean water tank which are connected in sequence.

[0023] Furthermore, the output end of the pre-flocculation sedimentation tank is connected to the water inlet of the ozone reaction tower, and the water outlet of the ozone reaction tower is connected to the secondary sedimentation tank.

[0024] Furthermore, it also includes an intermediate water tank, the input end of the intermediate water tank is connected to the output end of the pre-flocculation sedimentation tank, and the output end of the intermediate water tank is connected to the water inlet of the ozone reaction tower.

[0025] Furthermore, a lifting pump is provided between the intermediate water tank and the ozone reaction tower.

[0026] Furthermore, it also includes a dosing device arranged between the secondary sedimentation tank and the clean water tank;

[0027] It also includes a dosing system, which is connected to the pre-flocculation sedimentation tank, the secondary sedimentation tank and the dosing device respectively.

[0028] The utility model provides an ozone reaction tower, which has a top-in and bottom-out water distribution mode. The ozone produced by the ozone generator enters the inside of the ozone reaction tower through an aeration device arranged below the packing area, mixes with the wastewater in countercurrent, and reacts with the packing in the packing area, realizing the electrochemical reaction of iron-carbon micro-electrolysis and the catalytic ozone reaction of zero-valent iron. The ozone decomposes to produce ·OH, improves the oxidation capacity, and increases the types of oxidized organic matter. At the same time, the ozone is dispersed into small bubbles through the aeration device, and the ozone is further fully mixed with the packing and wastewater, thereby improving the efficiency of the catalytic ozone reaction. The utility model solves the technical problem of low oxidation efficiency of the ozone catalytic oxidation method in the prior art.

[0029] On the other hand, he provided a wastewater treatment system, which uses a pre-flocculation sedimentation tank to remove settleable suspended solids in the wastewater, uses an ozone reaction tower to treat organic matter in the wastewater, sets up a secondary sedimentation tank, adds alkali and flocculants to precipitate flocs such as iron ions carried out from the ozone reaction tower, and avoids the wastewater from carrying flocs such as iron ions. After secondary flocculation and sedimentation, it enters a clean water tank to wait for the subsequent biochemical system or other deep treatment systems. The technical problem that the ozone catalytic oxidation method in the prior art is difficult to treat industrial wastewater to a standard level due to the low ozone utilization rate is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the specific implementation methods of the utility model or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the utility model. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 A schematic diagram of the overall structure of an ozone reaction tower provided in Example 1 of the utility model;

[0032] Figure 2 This is a schematic diagram of the overall structure of a wastewater treatment system provided in Example 2 of the utility model.

[0033] Icons: 1-pre-flocculation sedimentation tank; 2-intermediate water tank; 3-lifting pump; 4-ozone generator; 5-ozone air inlet regulating valve; 6-ozone reaction tower; 60-water inlet; 61-water distribution pipe; 62-orifice water distributor; 63-aeration device; 64-filling area; 65-filling expansion area; 66-water outlet; 67-regulating valve; 68-ozone tail gas absorption tank; 69-lower orifice plate; 610-partition layer; 7-secondary sedimentation tank; 8-dosing device; 9-clean water tank. DETAILED DESCRIPTION

[0034] Unless otherwise defined herein, scientific and technical terms used in conjunction with the present invention shall have the meanings commonly understood by those of ordinary skill in the art. The meaning and scope of the terms should be clear, however, in the case of any potential ambiguity, the definitions provided herein take precedence over any dictionary or external definitions. In this application, unless otherwise stated, the use of "or" means "and / or". In addition, the use of the term "including" and other forms is non-limiting.

[0035] The technical solution of the utility model will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the utility model, not all of the embodiments. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0036] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the present invention to be protected, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0038] In the description of the present utility model, it should be noted that the terms "proximal end", "distal end", "front end", "rear end", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the utility model product is usually placed when in use, which are only for the convenience of describing the present utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific position, be constructed and operated in a specific position, and therefore cannot be understood as a limitation on the present utility model. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0039] The terms "horizontal", "vertical" and the like do not mean that the components must be absolutely horizontal or suspended, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", and does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0040] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be a communication between the two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0041] On one hand, the utility model provides an ozone reaction tower, including a water inlet 60, a water outlet 66, an aeration device 63, a packing area 64 and an ozone generator 4;

[0042] The aeration device 63 is arranged above the water outlet;

[0043] The packing area 64 is arranged above the aeration device 63;

[0044] The ozone generator 4 is communicated with the aeration device 63 .

[0045] The ozone reaction tower adopts a top-in-bottom-out water distribution method. The packing area 64 is used to place iron-based biological activated carbon packing. The ozone generated by the ozone generator 4 enters the inside of the ozone reaction tower through the aeration device 63 arranged below the packing area 64, mixes with the wastewater in countercurrent, and reacts with the packing in the packing area, realizing the electrochemical reaction of iron-carbon micro-electrolysis and the catalytic ozone reaction of zero-valent iron. Ozone decomposes to produce ·OH, improves the oxidation capacity, and increases the types of oxidized organic matter. At the same time, the aeration device 63 is used to disperse the ozone into small bubbles, further fully mix the ozone with the packing and wastewater, and improve the efficiency of the catalytic ozone reaction. The technical problem of low oxidation efficiency of the ozone catalytic oxidation method in the prior art is solved.

[0046] Since pollutants are easily left in the packing after use, affecting the wastewater treatment capacity of the packing and the working efficiency of the ozone reaction tower, regular backwashing is required.

[0047] In some specific embodiments, a filler expansion area 65 is provided at the upper end of the filler area 64 .

[0048] When backwashing is performed, the filler in the filler area 64 will float up, and the filler expansion area 65 provides space for the backwashing filler, thereby facilitating the backwashing of the filler.

[0049] In some specific embodiments, a partition layer 610 is disposed at the lower end of the filler area 64 .

[0050] Specifically, the partition layer 610 is a water cap partition layer, so that the partition layer 610 is divided into two compartments up and down to prevent the filler in the filler area 64 from being lost.

[0051] In some specific embodiments, a water distribution pipe 61 is provided at the water inlet 60 , and a perforated plate water distributor 62 is provided on the water distribution pipe 61 . The perforated plate water distributor 62 is located above the filling area 64 .

[0052] The waste water is distributed through the water distribution pipe 61 and the orifice plate water distributor 62 and evenly sprinkled onto the fillers in the filler area to fully contact with the fillers.

[0053] In some specific embodiments, a lower perforated plate 69 is provided between the aeration device 63 and the water outlet 66 .

[0054] The aperture of the lower perforated plate 69 is smaller than the particle size of the biological activated carbon particles, so as to prevent the biological activated carbon from being lost through the lower perforated plate 69 .

[0055] In order to avoid excessive ozone in the ozone reaction tower 6 and incomplete reaction.

[0056] In some specific embodiments, it also includes an ozone inlet regulating valve 5 arranged at the output end of the ozone generator 4;

[0057] The ozone intake amount is controlled by the ozone intake regulating valve. In order to keep the pressure in the ozone reaction tower 6 balanced, it is necessary to collect the excess ozone.

[0058] Preferably, the aeration device 63 is a micro-nano aerator.

[0059] Ozone is dispersed into micro-nano bubbles through the micro-nano aerator to improve the efficiency of catalytic ozone reaction.

[0060] Preferably, it also includes an ozone tail gas absorption tank 68 connected to the ozone reaction tower 6 and located above the water distribution pipe 61;

[0061] Excess ozone is absorbed by the ozone tail gas absorption tank 68. In order to control the amount of ozone absorbed by the ozone tail gas absorption tank 68, preferably, a regulating valve 67 is further provided at the input end of the ozone tail gas absorption tank 68;

[0062] Specifically, the regulating valve 67 can be a self-operated pressure regulating valve. When the pressure in the ozone reaction tower 6 rises due to excessive ozone, the regulating valve 67 opens to collect excess ozone. When the pressures on both sides of the regulating valve 67 are equal, the regulating valve closes to stop collecting ozone.

[0063] In order to ensure that the wastewater is in full contact with the filler in the filler area and to ensure that the filler can fully treat the wastewater, it is necessary to avoid reducing the treatment efficiency due to excessive filler affecting the flow of wastewater.

[0064] Preferably, the height of the filling area 64 is 600 mm to 1000 mm.

[0065] The height of the filling area 64 may be, but is not limited to, 600 mm, 650 mm, 700 mm, 750 mm, 800 mm, 850 mm, 900 mm, 950 mm or 1000 mm, and may also be any value between 600 mm and 1000 mm.

[0066] Preferably, the height of the filling area 64 is 800 mm.

[0067] On the other hand, the utility model provides a wastewater treatment system, comprising a pre-flocculation sedimentation tank 1, the above-mentioned ozone reaction tower 6, a secondary sedimentation tank 7 and a clean water tank 9 which are connected in sequence.

[0068] The settleable suspended solids in the wastewater are removed by the pre-flocculation sedimentation tank, the organic matter in the wastewater is treated by the ozone reaction tower 6, and a secondary sedimentation tank 7 is set up to add alkali and flocculants to precipitate the flocculants such as iron ions carried out from the ozone reaction tower 6, so as to avoid the flocculants such as iron ions being carried in the wastewater. After the secondary flocculation sedimentation, the wastewater enters the clean water tank 9 to wait for the subsequent biochemical system or other deep treatment system. The technical problem that the ozone catalytic oxidation method is difficult to treat industrial wastewater to the standard level due to the low ozone utilization rate in the prior art is solved.

[0069] In some specific embodiments, the output end of the pre-flocculation sedimentation tank 1 is connected to the water inlet 60 of the ozone reaction tower 6 , and the water outlet 66 of the ozone reaction tower 6 is connected to the secondary sedimentation tank 7 .

[0070] In order to ensure that the wastewater output from the pre-flocculation sedimentation tank 1 enters the ozone reaction tower 6 smoothly.

[0071] In some specific embodiments, an intermediate water tank 2 is further included, wherein the input end of the intermediate water tank 2 is connected to the output end of the pre-flocculation sedimentation tank 1 , and the output end of the intermediate water tank 2 is connected to the water inlet 60 of the ozone reaction tower 6 .

[0072] The water in the pre-flocculation sedimentation tank 1 is collected through the intermediate water tank 2 , so that the wastewater can enter the ozone reaction tower 6 .

[0073] In some specific embodiments, a lift pump 3 is provided between the intermediate water tank 2 and the ozone reaction tower 6 .

[0074] By lifting the pump 3 , the problem that the intermediate water tank 2 is set too high in order to allow the waste water to enter the ozone reaction tower 6 can be solved.

[0075] In order to make the treated wastewater convenient for subsequent biochemical systems or other deep treatment systems.

[0076] In some specific embodiments, it further includes a dosing device 8 disposed between the secondary sedimentation tank 7 and the clean water tank 9;

[0077] The specific dosing device 8 is a pipeline dosing mixer, which adjusts the pH to neutral by adding acid.

[0078] Preferably, it also includes a dosing system, which is connected to the pre-flocculation sedimentation tank 1, the secondary sedimentation tank 7 and the dosing device 8 respectively.

[0079] The dosing system is connected to the pre-flocculation sedimentation tank 1, and is used to control the addition of flocculants or coagulants in the pre-flocculation sedimentation tank 1; the dosing system is connected to the secondary sedimentation tank 7, and is used to control the addition of flocculants, alkali or coagulants in the secondary sedimentation tank 7; the dosing system is connected to the dosing device 8, and is used to control the addition of acid in the dosing device 8 to adjust the pH.

[0080] The technical solution of the utility model will be described clearly and completely through specific embodiments below. Based on the embodiments of the utility model, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the utility model.

[0081] Example 1

[0082] Combination Figure 1 To illustrate, an ozone reaction tower includes a water inlet 60, a water outlet 66, a micro-nano aerator arranged above the water outlet 66, a packing area 64 arranged above the micro-nano aerator, and an ozone generator 4 connected to the micro-nano aerator, and an ozone inlet regulating valve 5 is provided at the output end of the ozone generator 4.

[0083] Among them, the filler area 64 is filled with iron-based biological activated carbon filler, and the height of the filler area 64 is 800 mm. The iron-based biological activated carbon filler is a filler in which metal substances such as zero-valent iron are loaded on biological activated carbon. Specifically, the activated carbon is acidified, distilled, and dried to obtain modified activated carbon, and then metal oxides such as iron powder and iron oxide are reacted with activated carbon under acidic conditions for 24 hours, and the composite solid is taken out and carbonized in a nitrogen-sealed muffle furnace for 2 hours. After cooling to room temperature, it is taken out, washed to neutrality, and dried to obtain an iron-based loaded biological activated carbon filler, and the filler particle size is 1 to 2 mm.

[0084] A filler expansion zone 65 is provided at the upper end of the filler zone 64 , and a water cap partition layer is provided at the lower end of the filler zone 64 .

[0085] The water inlet 60 is communicated with a water distribution pipe 61 , and a perforated plate water distributor 62 is provided on the water distribution pipe 61 . A lower perforated plate 69 is provided between the aeration device 63 and the water outlet 66 .

[0086] It also includes an ozone tail gas absorption tank 68 which is connected to the ozone reaction tower 6 and is located above the water distribution pipe 61 ; a self-operated pressure regulating valve is also provided at the input end of the ozone tail gas absorption tank 68 .

[0087] Working principle of ozone reaction tower:

[0088] The wastewater enters the water distribution pipe 61 through the water inlet 60, passes through the orifice water distributor 62, and is poured into the filler area 64 to fully contact with the iron-based multi-loaded biological activated carbon filler; at the same time, the ozone produced by the ozone generator 4 is dispersed into tiny bubbles by the micro-nano aerator, and flows upstream with the wastewater, so that the ozone is fully mixed with the filler and the wastewater; by utilizing the electrochemical reaction of iron-carbon micro-electrolysis and the catalytic ozone reaction of zero-valent iron, ozone is decomposed to produce ·OH, thereby improving the oxidation capacity, increasing the types of oxidized organic matter, and improving the efficiency of the catalytic ozone reaction, and the treated wastewater flows out through the outlet 66.

[0089] When backwashing is performed, water flows in from the water outlet 66 to backwash the filler in the filler area, and the filler floats up to the filler expansion area 65 along with the water flow.

[0090] Example 2

[0091] Combination Figure 2 To illustrate, a wastewater treatment system includes a pre-flocculation sedimentation tank 1, an intermediate water tank 2, a lift pump 3, an ozone reaction tower 6 provided in Example 1, a secondary sedimentation tank 7, a dosing device 8 and a clean water tank 9 which are arranged in sequence.

[0092] Among them, the pre-flocculation sedimentation tank 1 is a high-density sedimentation tank, which is equipped with a sludge discharge system. The output end of the pre-flocculation sedimentation tank 1 is connected to the input end of the intermediate water tank 2, and the output end of the intermediate water tank 2 is connected to the water inlet 60 of the ozone reaction tower 6. The lifting pump 3 is arranged between the intermediate water tank 2 and the ozone reaction tower 6. The water outlet 66 of the ozone reaction tower 6 is connected to the input end of the secondary sedimentation tank 7, and the output end of the secondary sedimentation tank 7 is connected to the clean water tank 9. The dosing device 8 is arranged between the secondary sedimentation tank 7 and the clean water tank 9.

[0093] How wastewater treatment systems work:

[0094] The wastewater passes through the pre-flocculation sedimentation tank 1 to remove the settleable suspended solids in the wastewater, enters the intermediate water tank 2, and enters the ozone reaction tower 6 through the lifting pump 3. The ozone reaction tower 6 is used to remove organic matter in the wastewater. A secondary sedimentation tank 7 is set up to add alkali and flocculants to precipitate the flocculants such as iron ions carried out from the ozone reaction tower 6 to avoid the wastewater from carrying flocculants such as iron ions. After the secondary flocculation sedimentation, acid is added through the pipeline dosing mixer to adjust the pH to neutral, and then enters the clean water tank 9 to wait for entering the subsequent biochemical system or other deep treatment systems.

[0095] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the utility model, rather than to limit it. Although the utility model has been described in detail with reference to the aforementioned embodiments, ordinary technicians in this field should understand that they can still modify the technical solutions recorded in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solution of the embodiments of the utility model.

Claims

1. An ozone reaction tower, characterized in that: It includes a water inlet (60), a water outlet (66), an aeration device (63), a filler area (64) and an ozone generator (4); The aeration device (63) is arranged above the water outlet (66); The packing area (64) is arranged above the aeration device (63); The ozone generator (4) is in communication with the aeration device (63); A filler expansion zone (65) is provided at the upper end of the filler zone (64), and a partition layer (610) is provided at the lower end of the filler zone (64); A water distribution pipe (61) is provided at the water inlet (60), and a perforated plate water distributor (62) is provided on the water distribution pipe (61), and the perforated plate water distributor (62) is located above the filler area (64).

2. The ozone reaction tower according to claim 1, characterized in that: A lower perforated plate (69) is provided between the aeration device (63) and the water outlet (66).

3. The ozone reaction tower according to claim 1 or 2, characterized in that: It also includes an ozone inlet regulating valve (5) arranged at the output end of the ozone generator (4); The aeration device (63) is a micro-nano aerator; It also includes an ozone tail gas absorption tank (68) which is in communication with the ozone reaction tower (6) and is located above the water distribution pipe (61); The input end of the ozone tail gas absorption tank (68) is also provided with a regulating valve (67); The height of the filling area (64) is 600 mm to 1000 mm.

4. A wastewater treatment system, characterized in that: It comprises a pre-flocculation sedimentation tank (1), an ozone reaction tower (6) as claimed in any one of claims 1 to 3, a secondary sedimentation tank (7) and a clean water tank (9) which are connected in sequence.

5. The wastewater treatment system according to claim 4, characterized in that: The output end of the pre-flocculation sedimentation tank (1) is connected to the water inlet (60) of the ozone reaction tower (6), and the water outlet (66) of the ozone reaction tower (6) is connected to the secondary sedimentation tank (7).

6. The wastewater treatment system according to claim 4, characterized in that: It also comprises an intermediate water tank (2), the input end of the intermediate water tank (2) being connected to the output end of the pre-flocculation sedimentation tank (1), and the output end of the intermediate water tank (2) being connected to the water inlet (60) of the ozone reaction tower (6).

7. The wastewater treatment system according to claim 6, characterized in that: A lifting pump (3) is provided between the intermediate water tank (2) and the ozone reaction tower (6).

8. The wastewater treatment system according to any one of claims 4 to 7, characterized in that: It also includes a dosing device (8) disposed between the secondary sedimentation tank (7) and the clean water tank (9); It also comprises a dosing system, which is respectively connected to the pre-flocculation sedimentation tank (1), the secondary sedimentation tank (7) and the dosing device (8).

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