Process for purifying aqueous effluent containing micropollutants and aqueous effluent purifier

Abstract

Process for purifying an aqueous effluent containing micropollutants, the process comprising: The introduction (D.) of a micro-grain adsorbent (210) into the aqueous effluent (420), The agitation (E.) of the micro-grain adsorbent (210) and the aqueous effluent (420) so as to adsorb at least a part of the micropollutants onto the micro-grain adsorbent (210), to produce a used adsorbent (310) and a purified effluent (320), The separation (F.) by filtration with a rotary filter (300) of the used adsorbent (310) and the purified effluent (320).

Description

Title of the invention: Process for purifying an aqueous effluent containing micropollutants and aqueous effluent purifier

[0001] The present invention relates to a method for purifying an aqueous effluent containing micropollutants and a purifier for purifying such an aqueous effluent. Prior art

[0002] The integrity of water resources is increasingly compromised by the presence of micropollutants. These are often discharged in wastewater into natural environments, which they then contaminate.

[0003] Document US20090032471A1 describes an innovative treatment technology for recycled water. This technology is based on a complex process involving hydrogen peroxide and microfiltration, resulting in high operating costs and an environmental impact incompatible with the treatment of large water flows. Summary

[0004] The present invention proposes a method for purifying an aqueous effluent containing micropollutants. This method aims to improve the efficiency of micropollutant removal while being compatible with existing water treatment infrastructure.

[0005] To this end, a first aspect of the invention relates to a process for purifying an aqueous effluent containing micropollutants, the process comprising the following steps: • The introduction of a micro-granular adsorbent into the aqueous effluent, • Agitation of the adsorbent and the aqueous effluent in such a way as to adsorb at least some of the micropollutants onto the adsorbent, to produce a used adsorbent and a purified effluent, • Separation by filtration with a rotary filter such as a drum or disc filter of the used adsorbent and the purified effluent.

[0006] Such a process, and in particular the use of a micro-granular adsorbent separated after contact by a rotary filter, allows for the efficient removal of micropollutants in a confined space, without high operating costs. Furthermore, avoiding contact by fluidized bed in favor of simple agitation helps to reduce operating costs and environmental impact.

[0007] Advantageously, the process includes prior coagulation and / or flocculation and decantation comprising the introduction of a flocculating agent and optionally a coagulation agent into the aqueous effluent, to allow the The process involves creating flocs and then settling them. These steps allow for better removal of micropollutants and limit clogging of the drum or disc filter.

[0008] Advantageously, coagulation and / or flocculation include introducing at least a portion of the used adsorbent from the filtration separation into the aqueous effluent. The used adsorbent can therefore be reused to contribute to coagulation and / or flocculation, thereby facilitating the formation of heavier and denser flocs, which increases the treatment efficiency.

[0009] Advantageously, the rotary filter includes a catalyst arranged to produce hydroxyl radicals and / or ozone by UV illumination, the process further comprising UV illumination of the rotary filter. The process can therefore include disinfection of the aqueous effluent simultaneously or immediately after filtration.

[0010] The catalyst can be integrated into the filter body and / or arranged on a filter wall in the form of elements fixed to the filter, preferably on an external filter wall, i.e., facing an outlet of the purified effluent. Alternatively, the catalyst can simply be placed in a tank housing the rotary filter, for example, near the rotary filter.

[0011] Advantageously, the process includes measuring the quantity or concentration of micropollutants in the aqueous effluent and, during the introduction of the micro-granular adsorbent into the aqueous effluent, dosing the micro-granular adsorbent according to the measured quantity or concentration of micropollutants. Alternatively or in combination, the adsorbent is introduced according to a predetermined weight or mass flow rate, for example, as a function of the flow rate of the aqueous effluent.

[0012] Advantageously, the micro-grain adsorbent has a grain size of 100 pm to 1000 pm, preferably from 300 pm to 800 pm.

[0013] Advantageously, the micro-grain adsorbent is a carbon adsorbent such as activated carbon.

[0014] Another aspect of the invention relates to an aqueous effluent purifier comprising: • introduction means configured to introduce a micro-granular adsorbent into the aqueous effluent, • a stirred tank configured to agitate the adsorbent and the aqueous effluent in order to adsorb at least some of the micropollutants onto the adsorbent, to produce a used adsorbent and a purified effluent, • a rotary filter such as a drum or disc filter hydraulically connected to the agitated tank and configured to achieve separation of the used adsorbent and the purified effluent.

[0015] Advantageously, the rotary filter includes a catalyst arranged to produce hydroxyl radicals and / or ozone by UV illumination, the aqueous effluent purifier comprising at least one UV source arranged to illuminate the rotary filter. Alternatively or in combination, the aqueous effluent purifier comprises a tank housing the rotary filter and at least one catalytic element fixed in the tank, for example near the rotary filter and so as to be illuminated by the UV source or lamp.

[0016] Advantageously, said aqueous effluent purifier includes means for measuring the quantity or concentration of micropollutants in the aqueous effluent, the introduction means including dosing means configured to allow dosing of the adsorbent according to the quantity or concentration of micropollutants measured. These measuring means may include a UV absorbance sensor, for example at 254 nm.

[0017] Advantageously, said aqueous effluent purifier comprises upstream of the agitated tank: • Optionally, coagulation means allowing the introduction of a coagulation agent into the aqueous effluent, • Flocculation methods allowing the introduction of a flocculating agent into the aqueous effluent to form flocs, • means of reuse allowing the introduction of used adsorbent into the aqueous effluent, within the flocculation and / or coagulation means • settling means arranged to separate flocs from aqueous effluent. Presentation of the figures

[0018] Other features and advantages of the present invention will become more apparent upon reading the following detailed description of an embodiment of the invention given by way of non-limiting example and illustrated by the accompanying drawings, in which:

[0019] [Fig. 1] represents a schematic diagram of a process for treating an aqueous effluent according to the present invention.

[0020] [Fig.2] represents a schematic diagram of an aqueous effluent purifier according to the present invention. Detailed description

[0021] The present invention relates to a method for treating an aqueous effluent, such as water from the natural environment or wastewater that may originate from a domestic wastewater collection network, an industrial installation, or from an agricultural installation, the aqueous effluent to be treated may be water intended for human or industrial consumption or may be intended to be discharged into the natural environment.

[0022] The aqueous effluent contains micropollutants, which are chemical substances present at very low concentrations, generally on the order of micrograms per liter or less.

[0023] Micropollutants include a wide range of compounds such as pesticides, pharmaceuticals, BTEX, hormones, heavy metals, industrial residues and personal care products.

[0024] BTEX are a group of chemical compounds that include benzene, toluene, ethylbenzene, and xylenes. They are volatile aromatic hydrocarbons (VAHs) commonly found in crude oil and refined petroleum products such as gasoline.

[0025] Despite their minute concentrations, micropollutants can have significant effects on the environment and human health. They can disrupt aquatic ecosystems by affecting the reproduction and development of living organisms, and can also pose a health risk when they accumulate in the food chain or contaminate drinking water sources.

[0026] The process detailed below and the corresponding device can be integrated into a more general aqueous effluent purification process including pretreatment steps and / or posttreatment steps as known to those skilled in the art.

[0027] The present process relies on the use of a micro-granular adsorbent for adsorbing micropollutants. For example, the adsorbent has a size in micrometers, such as 30 to 1000 pm or preferably 300 to 800 pm, representing at least 80% and preferably at least 90% by weight of the adsorbent. A nano-granular or superfine adsorbent, having, for example, a grain size of less than 30 pm, is therefore excluded by the present process.

[0028] A micro-grain size can be measured by a measurement technique known as a sieving technique (ISO 10752 standard) or preferably by laser diffraction (ISO 13320 standard).

[0029] The adsorbent is, for example, a carbonaceous material such as activated carbon and / or graphene. Alternatively or in combination, the adsorbent may be a zeolite, a clay, a mesoporous silica, and / or chitosan. Preferably, the adsorbent is microgranular activated carbon. Even more preferably, the activated carbon has a low moisture content, for example, less than 19%. The specific surface area of ​​the activated carbon may be from 750 to 1100 m² / g, for example, from 850 to 950 m² / g. Examples of usable activated carbons include Chemviron CycleCarb 305 and Norit GAC 3040 AW.

[0030] The adsorbent is brought into contact, i.e. mixed with the aqueous effluent and agitated for a predetermined time. This time may vary, for example, according to the quantity or concentration of micropollutants in the aqueous effluent and / or in relation to an aqueous effluent flow rate.

[0031] Finally, the used adsorbent, i.e., the adsorbent loaded with micropollutants adsorbed onto its surface, is separated from the purified effluent, i.e., the water freed from micropollutants. This separation is achieved by filtration, preferably using a rotary filter such as a disc or drum filter, with the drum filter being preferable.

[0032] Optionally, the used adsorbent can be reused, for example in a coagulation step prior to the adsorption of micropollutants.

[0033] Figure 1 presents a schematic view of such a process. Steps A to C are optional and include a coagulation step, i.e., the formation of particles by the introduction of a coagulation agent. Step B includes a flocculation step, i.e., the agglomeration of the flocs of agglomerated particles by the introduction of a flocculating agent. Step C includes the settling of the flocs and / or particles generated in steps A and B. Only one of these steps or a selection of two of these steps may be used depending on the quality of the aqueous effluent and / or the requirements that the purified effluent must meet.

[0034] In a step D according to the present process, the micro-granular adsorbent is introduced into the aqueous effluent to be treated, for example, according to a predetermined weight or flow rate, and / or according to a dosage of a quantity or concentration of micropollutants contained in the aqueous effluent to be treated, measured, for example, by the UV absorbance or transmittance of the aqueous effluent. For example, the micro-granular adsorbent is introduced at a concentration of 5 to 25 mg / L, preferably 11 to 19 mg / L, for example 15 mg / L, relative to a volume of aqueous effluent in the agitated tank carrying out the adsorption step and / or relative to a flow rate of aqueous effluent.

[0035] In step E, the micropollutants are adsorbed onto the surface of the micro-grains. This step E is carried out, for example, under agitation, for a time determined by information from a sensor or processor, or predetermined. The contact time, i.e., the time it takes for the adsorbent in micro-grains to come into contact with the aqueous effluent under agitation, can be, for example, 5 to 15 minutes, or 6 to 12 minutes. Preferably, this step E is not carried out in a fluidized bed, which is more expensive.

[0036] In a step F, the used adsorbent is separated by a technique for separating the treated aqueous effluent. Preferably, the separation technique is a filtration technique, such as rotary filtration by disc filter, or preferably by drum filter.

[0037] This step F may optionally include disinfection of the treated effluent, for example by ozone treatment, by UV illumination and / or by ozone generation with UV illumination of a catalyst such as titanium oxide or zinc oxide.

[0038] In a step G., the used adsorbent from the separation step F. can be reused, for example in another step of the purification process, such as the coagulation step A. and / or the flocculation step B.

[0039] An aqueous effluent purifier 100 capable of implementing the process described above is shown schematically in [Fig. 2]. This aqueous effluent purifier 100 comprises an agitated tank 200 and a rotary filter 300.

[0040] The agitated tank 200 allows, by means of introduction, the micro-granular adsorbent 210 to be introduced into the aqueous effluent and, by means of agitation and contact time, the adsorption of micropollutants onto the adsorbent to be achieved (steps D and E). These introduction means may include a hopper and a screw conveyor, a hopper including an automatic weighing system, a compressed air injector, a piston injector, and / or a rotary injector using centrifugal force. Alternatively, the adsorbent introduction step is carried out in a first tank and the adsorption step is carried out in a second tank (not shown).

[0041] The agitated tank can be made of any type of material, in particular thermoplastic, concrete and / or stainless steel and the agitator it contains can be a standard mechanical agitator including an electric motor and blades connected to the electric motor by a drive shaft, or any other type of mechanical agitator known to a person skilled in the art.

[0042] The rotary filter 300 can be a drum filter consisting of a rotating drum covered with a fine mesh or filter fabric, having, for example, a filtration size of less than 100 µm, preferably less than 50 µm, such as 40 µm. The aqueous effluent containing the adsorbent is introduced into the drum, and the solid particles of the adsorbent are retained on the surface of the filter while the filtered effluent passes through. The drum is rotated at a reduced speed, and the retained adsorbent particles can be removed by scrapers or water jets, thus ensuring continuous cleaning of the filter.

[0043] Alternatively or in combination, the rotary filter 300 can be a disc filter (or PCMS filter) consisting of several filter discs mounted on a central shaft. Each disc is covered with a filter material, such as fabric or fine mesh. The aqueous effluent is directed to the discs, and the solid particles of the adsorbent are retained on the surface of the discs as the filtered effluent passes through. The discs rotate slowly, and the retained adsorbent particles are removed by scrapers, water jets, or suction, thus ensuring continuous cleaning of the filter.

[0044] The rotary filter 300 may further include at least one catalyst element and UV lighting means. The catalyst elements may include titanium dioxide and / or zinc oxide, and, under UV illumination, may generate ozone and / or hydroxide radicals in the water being filtered. For example, these catalyst elements are placed in the tank of the rotary filter 300 and / or on the drum or on the discs (not shown). Such a rotary filter 300 thus makes it possible to disinfect the purified effluent and / or to at least partially clean the rotary filter 300.

[0045] Alternatively or in combination, an ozone injection can be carried out, for example in the filtration tank upstream of the rotary filter, preferably in close proximity to the rotary filter.

[0046] At the outlet of the rotary filter 300, purified effluent 320 is recovered and can be conveyed to a drinking water distribution system, to a natural environment, to an agricultural environment and / or to an industrial process by known means.

[0047] The used adsorbent 310 recovered in the separation step E can be reused, for example in the coagulation step A and / or in the flocculation step B, in order to aid coagulation and / or flocculation by weighting the flocs or micro-flocs and reducing the amount of coagulation and / or flocculation agent required 410. For example, means of reuse, including for example a gravity flow, a pump, an airlift, a juice elevator or a screw conveyor (not shown), can convey the used adsorbent from the rotary filter 300 to a coagulation 400 and / or flocculation tank 500.

[0048] The coagulation tank is part of the coagulation means and can receive aqueous effluent 420 to perform the optional coagulation step A. A coagulation agent 410 can be introduced into the tank to carry out coagulation, i.e., the agglomeration of the organic matter in the effluent to be treated into particles or microflocs. The coagulation agent can be dosed according to the flow rate of aqueous effluent, the amount of organic matter contained in the aqueous effluent 410 (for example, according to a chemical oxygen demand (COD) or a transmittance measurement), and / or the amount of used adsorbent 310 introduced into the coagulation tank 400. The coagulation tank 400 can be subjected to rapid agitation as is known to those skilled in the art.

[0049] The coagulation agent 410 includes any known coagulation agent, and for example one or more of the following: A12(SO4)3, FeC13, Fe2(SO4)3, A1C13, A1(OH)3, Fe(OH)2, Na2SiO3, CaC12, CaSO4, MgC12, MgSO4, ZnC12, ZnSO4, CuC12.

[0050] The aqueous effluent containing the micro-flocs and the coagulation agent and / or the used adsorbent is then directed to a flocculation tank 500, which is part of an optional flocculation means. A flocculating agent 510 can then be added to the aqueous effluent to perform flocculation. This refers to the agglomeration of micro-flocs into flocs. The flocculating agent can be any type of flocculating agent, and for example, one or more polymers chosen from among polyacrylamide, polyethyleneimine, polyamine, polyquatemium, polyvinylpyrrolidinone, polyvinyl alcohols, or sodium alginate. Coagulation and flocculation agents can be combined.

[0051] Once the flocs have formed, the aqueous effluent is introduced into a sedimentation tank or decanter 600, so as to carry out step C. of decanting the solid elements (flocs, micro-flocs, used adsorbent...) into sludge 610 and transfer the clarified, i.e. pre-purified, aqueous effluent to the agitated tank 200. The decanter 600 can be made of stainless steel, concrete or composite materials or thermoplastics resistant to corrosion and chemical attack, in order to guarantee its durability over time.

[0052] The settling tank 600 is part of a settling device and can be in the form of a circular or rectangular basin, equipped with a piping system for the inlet of aqueous effluents and a weir for the discharge of clarified effluents. A bottom scraper mechanism for collecting sludge and / or a surface scraper for removing floating matter may be provided.

[0053] Finally, the aqueous effluent purifier 100 can include any type of necessary sensor, such as temperature, effluent level, flow rate, pH, micropollutant concentration sensors, etc. Standard safety devices and valves can be integrated to isolate or bypass certain elements, for example, the coagulation tank 400, the flocculation tank 500 and / or the settling tank 600.

[0054] Pretreatment such as screening can be carried out, for example, before coagulation step A. Furthermore, posttreatment such as a finishing or polishing step can be carried out after separation step F on the purified effluent, for example, involving sand filtration, a reverse osmosis step, or membrane filtration. In addition, the process implemented by the aqueous effluent purifier 100 can also include treatment by biofilm on a fluidized bed (MBBR), for example, placed upstream of the coagulation and / or flocculation means.

[0055] In one test, an absorption step F was carried out with activated carbon having a grain size of 300 µm to 800 µm at a concentration of 15 g / m³ of aqueous effluent. This resulted in the removal of 80% of the micropollutants.

[0056] It will be understood that various modifications and / or improvements obvious to a person skilled in the art can be made to the different embodiments of the invention described in this description without departing from the scope of the invention as defined by the attached claims.

Claims

Demands

1. A process for purifying an aqueous effluent containing micropollutants, the process comprising: • Introducing (D.) a micro-grain adsorbent (210) into the aqueous effluent (420), • Agitation (E.) of the micro-grain adsorbent (210) and the aqueous effluent (420) so as to adsorb at least a portion of the micropollutants onto the micro-grain adsorbent (210), to produce a used adsorbent (310) and a purified effluent (320), • Separating (F.) by filtration with a rotary filter (300) the used adsorbent (310) and the purified effluent (320).

2. A water purification process according to the preceding claim, comprising prior coagulation (A.) and / or flocculation (B.) and decantation (C.) and comprising the introduction of a flocculating agent (510) and optionally the introduction of a coagulation agent (410) into the aqueous effluent (420), to enable the creation of flocs and then the decantation of the flocs.

3. A water purification process according to the preceding claim, wherein the coagulation (A.) and / or flocculation (B.) comprise an introduction into the aqueous effluent (420) of at least a portion of the used adsorbent (310) from the separation (F.) by filtration.

4. A water purification process according to any one of the preceding claims, the rotary filter (300) comprising a catalyst arranged to produce hydroxyl radicals and / or ozone by UV illumination, the process further comprising UV light illumination of the rotary filter (300).

5. A water purification process according to any one of the preceding claims, comprising a measurement of a quantity or concentration of micropollutants in the aqueous effluent (420) and, during the introduction (D.) of the micro-grain adsorbent (210) into the aqueous effluent (420), a dosage of the micro-grain adsorbent (210) according to the quantity or concentration of micropollutants measured.

6. A water purification process according to any one of the preceding claims, wherein the micro-grain adsorbent (210) has a grain size of 100 pm to 1000 pm, preferably 300 pm to 800 pm.

7. A water purification process according to any one of the preceding claims, wherein the micro-grain adsorbent (210) is a carbonaceous adsorbent such as activated carbon.

8. Aqueous effluent purifier (100) comprising: • introduction means configured to introduce a micro-grain adsorbent (210) into the aqueous effluent (420), • an agitated tank (200) configured to agitate the micro-grain adsorbent (210) and the aqueous effluent (420) so as to adsorb at least a portion of the micropollutants onto the micro-grain adsorbent (210), to produce a used adsorbent (310) and a purified effluent (320), • a rotary filter (300) hydraulically connected to the agitated tank (200) and configured to separate the used adsorbent (310) and the purified effluent (320).

9. Aqueous effluent purifier (100) according to the preceding claim, wherein the rotary filter includes a catalyst arranged to produce hydroxyl radicals and / or ozone by UV illumination, the aqueous effluent purifier (100) comprising at least one UV source arranged to illuminate the rotary filter (300).

10. Aqueous effluent purifier (100) according to any one of claims 8 and 9, comprising means for measuring a quantity or concentration of micropollutants in the aqueous effluent (420), the introduction means comprising dosing means configured to allow dosing of the micro-grain adsorbent (210) according to the quantity of micropollutants measured.

11. Aqueous effluent purifier (100) according to any one of claims 8 to 10, comprising, upstream of the agitated tank: • Optionally, coagulation means for introducing a coagulation agent into the aqueous effluent, • flocculation means for introducing a flocculating agent (510) into the aqueous effluent (420) to form flocs, means of reuse allowing the introduction of used adsorbent (310) into the aqueous effluent (420), means of settling arranged to separate flocs from the aqueous effluent (410).

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