Method for treating water contaminated with heavy metals and / or phosphates, and associated filter unit

Abstract

The invention relates to a method for treating water contaminated with heavy metals and / or phosphates, which water, for the purpose of adsorption of the heavy metals and / or phosphates, flows through an adsorber bed (6) containing iron hydroxide. Before flowing through the adsorber bed (6), the water is mixed with air enriched with CO2, the proportion of CO2 in the air being ≥0.120%.

Description

[0001] Description

[0002] Process for the treatment of water contaminated with heavy metals and / or phosphates and associated filter unit

[0003] The invention relates to a process for treating water contaminated with heavy metals and / or phosphates, which flows through an adsorbent bed containing iron hydroxide to adsorb the heavy metals and / or phosphates. The invention further relates to a filter unit for carrying out the process.

[0004] In known processes for the treatment of water containing heavy metals, such as wastewater from the mining industry, groundwater and mineral water, other industrial and process wastewater, roof water, contaminated groundwater, or for the treatment of phosphate-containing water from bathing facilities such as swimming ponds or pools, it is known, sometimes with the interposition of various pre-treatment stages, to pass the water through an adsorbent bed containing iron hydroxide (FeO(OH)). Such an adsorbent bed binds heavy metal anions such as arsenic, lead, cadmium, illin, mercury, copper, and zinc ions, as well as phosphates (PO4), in the case of water from bathing facilities such as swimming pools or ponds.

[0005] Regarding the purification and biological treatment of water from bathing facilities, such as swimming pools and ponds, it is known, for example, from WO 2009 / 124899 A1, to mechanically purify near-surface pool water in a first water circuit and, in a second water circuit, to initially retain turbidity in the pool water in a biological filter. Organic substances contained in the pool water, such as algae or detritus, are mineralized by the activity of bacteria. The phosphorus contained in the organic and inorganic substances is broken down into dissolved reactive phosphorus, which is then adsorbed in an anion exchanger.EP 0 928 776 A2 discloses a method for reducing algae growth in natural or artificial bodies of water, such as lakes, ponds or swimming pools, by introducing CO2 into the water, which originates from the air or from the soil or from air from compost heaps, whereby this air is mixed with the water to be treated, for example by direct introduction into the body of water.

[0006] JP 2020032321 A discloses a method for removing metal ions from hard water. This known method uses an ion removal system that includes a degasser for degassing carbon dioxide dissolved in hard water and a hard water tank for storing hard water, in which carbon dioxide is degassed by the degasser. A microgas generator is used, which feeds microgases into the hard water tank. In the hard water tank, the metal ions from the hard water are adsorbed onto the microbubbles and thus removed from the hard water.

[0007] CN 109 205 928 B relates to a process for leachate treatment, in particular a process and system for the deep treatment of leachate, in particular landfill leachate. Leachate from a landfill contains many types of inorganic and organic pollutants, including persistent toxic and harmful pollutants and heavy metals. The leachate treatment system comprises an electrolytic cell, a sedimentation tank, and a wetland treatment device for subjecting the leachate to electro-oxidation, electro-flocculation, and advanced wetland treatment, thereby effectively reducing or removing the pollutant content in the leachate. A mixture of gas and water vapor in the form of microbubbles with a size of 100 pm to 500 pm is introduced into the electrolytic cell, through which the leachate flows, by means of a nozzle and under high pressure.The microbubbles contain a high proportion of dissolved oxygen and, when they burst, form a strong oxidizing agent that accelerates the mineralization of the pollutants.

[0008] It is known that the sorption of unwanted ions in an iron hydroxide-based adsorber bed depends on the pH value of the water flowing through the adsorber bed. Most anions bind to iron hydroxide in the range of pH 6.50 to pH 8.40. Within this range, a lower pH value results in increased sorption compared to a higher pH value. Furthermore, a sufficient oxygen supply must be ensured in an iron hydroxide adsorber bed. This is often achieved by aerating the water to be purified with atmospheric air upstream of the adsorber stage, which usually leads to simultaneous CO2 degassing. If oxygen deficiency nevertheless occurs, for example, due to the degradation of organic compounds in the adsorber bed or in a pre-purification stage, microorganisms, particularly sulfate- and iron-reducing bacteria, develop. SO4 and Fe 3+If the adsorber medium is partially decomposed by Fe 3+ to Fe 2+ reduced, the binding capacity of the adsorption medium is greatly reduced and already bound unwanted ions partially re-dissolve. In addition, Fe 3+ react with hydrogen sulfide (H2S from the SCM reduction) to form FeS. The solid FeS has no binding capacity for anions, so the adsorbent medium's function for binding anions is permanently lost. In this chemical reaction, Fe 2+ bound, unwanted ions are released into the water flowing out of the filter stage.

[0009] The invention is therefore based on the object of increasing the sorptivity of the adsorber medium containing iron hydroxide, in particular granulated iron hydroxide, in a process of the type mentioned above and effectively preventing the formation of reducing conditions. The aim is to permanently prevent the partial or complete reduction of the adsorber medium, the chemical conversion of the adsorber material, for example, by H2S, as well as the undesired redissolution of ions from the adsorber bed.

[0010] According to the invention, the stated object is achieved by mixing the water with CO2-enriched air, the CO2 content of which is > 0.1200%, before flowing through the adsorber bed.

[0011] By introducing air enriched with CO2 to a proportion of > 0.1200% into the water fed to the adsorber bed, a supersaturation with regard to CO2 compared to the atmospheric equilibrium is achieved and thus a noticeable reduction in the pH of the water, whereby the pH value drops by approximately 0.40 to 1.00 units. This increases the sorptivity of the adsorber medium in the adsorber bed by approximately 30% to 150%, whereby a reduction below a pH of 7 due to CC enrichment of the air is excluded or largely excluded. As a result of the significantly improved sorptivity of the adsorber medium, the filter surface of the adsorber bed can be made relatively small, which enables a smaller design of the adsorber bed. Furthermore, the amount of undesirable anions that can be bound in the adsorber medium is significantly increased, so that saturation of the adsorber medium occurs much more slowly.This significantly extends the adsorption medium replacement interval. The introduction of CO2-enriched air also increases the oxygen supply within the adsorption medium. This prevents the development of anoxic conditions in the adsorption medium and thus the resulting reducing conditions that can otherwise cause undesired ions to be released from the adsorption bed.

[0012] In a preferred embodiment, the water is mixed with air containing a CO2 content of < 1,000%. An optimum sorptivity of the adsorber medium in the adsorber bed can be expected in the range of 0.120% to 1,000% CO2 content in the air.

[0013] The process is particularly advantageous if the CO2-enriched air is introduced into the water in bubble form, as this results in a particularly good distribution of the CO2-enriched air in the water.

[0014] In a simple implementation of the process, the CO2-enriched air is introduced into the water in bubble form using a nozzle, such as a Venturi nozzle.

[0015] However, a particularly advantageous variant of the process involves introducing the CO2-enriched air into the water in the form of microbubbles with a diameter of < 100 pm. Such microbubbles ensure particularly high solubility of the CO2 in the water. This is achieved in particular by the fact that some of the generated microbubbles collapse in the water body, thereby achieving complete dissolution of the gases and thus a high supersaturation of the water in the adsorber bed according to Henry's law.

[0016] A particularly advantageous feature of this design is when the CO2-enriched air is introduced into the water in the form of microbubbles with a diameter of > 10 pm and, as mentioned, < 100 pm. This ensures that, at a given filter speed, the majority of the bubbles remain in the adsorber bed until they have completely dissolved. As the gas bubbles continue to dissolve in the water, the bubbles become increasingly smaller until they are completely dissolved. This creates a very high gas partial pressure within the gas bubbles, which forces the entire gas to dissolve. This means that the gases contained in the supplied CO2-enriched air, which also contains O2 in addition to CO2, can be completely added to the water to be purified. The water supersaturated with CO2 is therefore acidic, and the pH value is reduced by approximately 0.40 to 1.00 units compared to atmospheric equilibrium.In addition, a good oxygen supply can be achieved through O2 supersaturation.

[0017] In this context, another positive aspect of the process is that the high partial pressure at the moment of microbubble collapse creates small amounts of OH' radicals. These radicals have a strong oxidizing effect and can therefore convert already reduced iron hydroxide back into the form of trivalent iron or iron hydroxide (FeO(OH)). When the process is used to treat water from swimming pools, the oxidizing effect of OH' radicals has another positive property. OH' radicals have a disinfecting effect because they oxidize and thereby destroy organic compounds of all kinds, especially the cell membranes of microorganisms.

[0018] Microbubbles with a diameter in the aforementioned preferred diameter range can be generated by the method according to the invention in such a way that the CO2-enriched air is fed to a microbubble generator. This microbubble generator can be a conventional microbubble generator, for example a CARMIN type generator, manufactured by YLEC Consultants, Saint-Martin-d'Heres, France. In one possible embodiment, the CO2-enriched air can be generated by means of a technical device. In an alternative embodiment, the CO2-enriched air is soil air supplied from a soil air collection system. Soil air from a living soil is particularly advantageous because it naturally contains a CO2 content in the range of 0.120% to 1.000%.

[0019] In one variant of the process, the water enriched with CO2-enriched air can be fed directly into the adsorber bed. This process variant is particularly suitable when the goal is to bind primarily heavy metal ions from the water in the adsorber bed.

[0020] In a further variant of the process, the CO2-enriched, aerated water passes through at least one mechanical and / or at least one biological filter layer before entering the adsorbent bed. This method allows the removal of suspended solids and dissolved organic substances from the water. This process variant is therefore also, or especially, suitable for water from swimming pools, ponds, and the like, for subsequent adsorption of phosphate anions in the adsorbent bed.

[0021] A filter unit according to the invention which is particularly suitable for carrying out the method has the following components:

[0022] - a tank with an inlet for supplying the water contaminated with heavy metals and / or phosphates and with a return for discharging the purified / filtered water,

[0023] - an adsorber bed located inside the container, in particular containing granulated iron hydroxide,

[0024] - a microbubble generator located in the water during operation of the filter unit and arranged upstream of the adsorber bed to generate microbubbles,

[0025] - a pressure pump connected to a pressure line to supply the microbubble generator with water contained in the filter unit or a component of the filter unit that conducts the water, a supply line to supply CO2-enriched air to the microbubble generator and a pump to pass the water through the filter unit.

[0026] A filter unit equipped with these components can be constructed in a compact design and can ensure optimal sorption of heavy metals and / or phosphates in the adsorber bed in a particularly effective manner.

[0027] In one embodiment, the container is designed such that it has two container parts separated from each other by an intermediate wall, so that a passage for water to flow from one container part into the second container part is present in the lower container area. One container part contains at least one biological filter, optionally at least one mechanical filter, and the second container part contains the adsorbent bed. Such a container has an advantageous "separation" between the biological and optionally mechanical filters and the adsorbent bed, allowing the filter materials or filter media to be exchanged separately from one another.

[0028] Depending on the space available in the tank, the microbubble generator can be positioned before or after the biological filter, relative to the direction of water flow.

[0029] In one possible embodiment, the container is an open-topped container, particularly the two container parts mentioned above. In another, very compact embodiment, the container is a closed pressure vessel.

[0030] Further features, advantages and details of the invention will now be described in more detail with reference to the schematic drawing, which illustrates exemplary embodiments.

[0031] Fig. 1 to Fig. 3 each show a view of a variant of a filter unit. The filter units shown in the figures are shown in their usual upright position, so terms used in the description, such as vertical, top, and bottom, refer to this position. The arrows in the figures symbolize the direction of water flow.

[0032] The embodiments of a filter unit shown in Fig. 1 to 3 comprise a cuboid-shaped container 1 (Fig. 1, Fig. 2), 1' (Fig. 3), which in a preferred embodiment is made of polypropylene and has a container bottom 1b, 1'b and outer container walls 1a, 1'a.

[0033] The container 1 according to Fig. 1 and Fig. 2 has an intermediate wall 1d parallel to the container walls 1a, which divides the container 1 into a container part 4a with a larger volume and a container part 4b with a smaller volume. In the upper area of ​​the container part 4a, an inlet 2 is led through one of the container walls 1a, via which inlet 2 the interior of the container part 4a is supplied with the water to be filtered. The water level present inside the container part 4a during operation of the filter unit, which is located above the inlet 2, is designated by w. The water level present inside the container part 4b during operation of the filter unit is designated by w'. The interior of the container part 4a contains layers of a biological filter 3 on an intermediate floor 1c which is attached in the lower area and through which water can flow.The water to be filtered flows through the biological filter 3 from top to bottom and flows below the intermediate floor 1 ci , as will be described.

[0034] In the tank section 4b, parallel to the base 1b, there is another, water-permeable intermediate base 1c2, on which a layer 5 of supporting gravel and, on this, an adsorber bed 6—a layer of a filter medium in which undesirable anions are bound—are applied. The filter medium of the adsorber bed 6 is thus an anion exchange medium, and in particular the applicant's filter medium known under the trademark PHOSTEC, protected as a European Union trademark, and based on iron hydroxide (FeO(OH)). In both the embodiments shown in Fig. 1 and Fig. 2, the water to be filtered is enriched with microbubbles 7a by means of a microbubble generator 7.

[0035] In the embodiment shown in Fig. 1, the microbubble generator 7 is located in the housing part 4b below the intermediate floor 1c2 and within the water to be filtered and therefore, with respect to the flow direction of the water, after the biological filter 3. In the embodiment shown in Fig. 2, the microbubble generator 7 is located in the housing part 4a above the biological filter 3 and within the supplied water to be filtered, thus, with respect to the flow direction of the water, before the biological filter 3.

[0036] In the embodiment shown in Fig. 1, a pressure pump 8 is attached to the upper area of ​​the container part 4b, and in the embodiment shown in Fig. 2, to the upper area of ​​the container part 4a, in the examples on the intermediate wall 1d, which sucks water out of the filter unit through a suction line 8a. In the embodiment shown in Fig. 1, the water is sucked in from above the adsorber bed 6, and in the embodiment shown in Fig. 2, from below the intermediate floor 1ci. The pressure pump 8 supplies the water at a pressure > 5 bar through a pressure line 8b to the microbubble generator 7, which, when the filter unit is in operation, independently sucks in air enriched with CO2 through an air line 9 from outside, above the water level w in the container 1 or from outside the container 1 in order to generate microbubbles 7a.

[0037] In the embodiment shown in Fig. 1, the CO2-enriched microbubbles 7a pass through the layer of supporting gravel 5 and then reach the adsorber bed 6; in the embodiment shown in Fig. 2, the CO2-enriched microbubbles 7a first pass through the biological filter 3 and then the two layers 5, 6. By means of a filter pump 10, which is mounted inside the water on an outer wall 1a of the container part 4b and is connected to a return 11, the purified water is returned through this container wall 1a to the system to be purified.In the embodiment shown in Figure 3, a filter unit is positioned within the container 1' on the container bottom 1'b, said filter unit comprising a pressure vessel 12 having, in the lower region of its interior, a water-permeable intermediate floor 12a on which is located the layer 5 of supporting gravel and, on this, the adsorber bed 6 made of the aforementioned filter medium. Reference w denotes the water level present inside the pressure vessel 12 during operation of the filter unit. A microbubble generator 7 is located above the adsorber bed 6 and within the water to be filtered. The water to be filtered is supplied from the outside via an inlet 2' and a pipe 2'a, in particular such that the open end of the pipe 2'a is approximately at the level of the microbubble generator 7.In the embodiment shown, there is no biological filter stage in the pressure vessel 12, i.e., no biological filter; however, this can be applied to the adsorber bed 6. In the embodiment shown, the water enriched with microbubbles 7a flows through the layer 5 and the adsorber bed 6 and is collected below the intermediate floor 12a and returned to the outside via a further pipe 11'a belonging to an outlet 11' through the wall of the pressure vessel 14 and the wall of the container 1'. Water is supplied to the microbubble generator 7 by means of a pressure pump 8' positioned outside the pressure vessel 12 via a suction line 8'a from the pipe 11'a. During operation of the filter unit, the microbubble generator 7 independently sucks in CO2-enriched air through an air line 9 from outside, here from above the pressure vessel 12, in order to generate microbubbles 7a.The flow through the pressure vessel 12 is accomplished by a filter pump (not shown), which is located upstream of the inlet 2' or downstream of the outlet 11'. A flushing line 13 is located in the lower area of ​​the pressure vessel 12.

[0038] By generating air microbubbles enriched with CO2, the water becomes supersaturated with CO2 compared to atmospheric equilibrium, thereby lowering the pH of the water. The pH drops by approximately 0.40 to 1.00 units, increasing the sorptivity of the adsorber medium in the adsorber bed 6 by approximately 30% to approximately 150%. A reduction in the pH below pH 7 due to CO2 enrichment is largely ruled out. The microbubbles 7a generated in the microbubble generator 7 have an average size of < 100 pm, in particular 90% have a size of 50 pm to 100 pm. In the illustrated embodiments, microbubbles are generated from CO2-enriched air; in another embodiment not shown separately, CO2-enriched air is introduced directly into the water, for example by means of a nozzle.

[0039] The CO2-enriched air can come either from a CO2 source (technical device) that enriches atmospheric air with a CO2 content of approximately 0.040% to a CO2 content of > 0.120% (1,200 ppm) using additional CO2, or from CO2 from soil air. Soil air supplied from green, overgrown soils typically has a CO2 content in the range of 0.120% to 1,000% and is therefore particularly suitable.

[0040] To minimize the energy required to operate the filter unit, it can also be fed with CO2-enriched air only at intervals, for example, 3 to 5 minutes of enrichment during a 30-minute operating period. This reduces or minimizes the amount of energy required to operate the microbubble generator or its pump, as well as the amount of enriched air required, while the high solubility of the microbubbles ensures a lasting positive effect on sorption in the adsorber bed.

[0041] List of reference symbols

[0042] 1 container

[0043] 1' filter unit la, 1'a tank wall lb, 1 'b tank bottom

[0044] 1ci, 1c2 intermediate floor

[0045] 1d partition wall

[0046] 2, 2' inlet

[0047] 2'a pipeline

[0048] 3 biological filters

[0049] 4a, 4b container part

[0050] 5 supporting gravel layer

[0051] 6 adsorber bed

[0052] 7 Microbubble Generator

[0053] 7a Microbubbles

[0054] 8, 8' pressure pump

[0055] 8a, 8'a suction line

[0056] 8b, 8'b pressure line

[0057] 9 Air line

[0058] 10 filter pump

[0059] 11 , 11 ' Return

[0060] 11'a pipeline

[0061] 12 pressure vessels

[0062] 12a intermediate floor

[0063] 13 Flushing line w, w' water level

Claims

Patent claims 1. A process for the treatment of water contaminated with heavy metals and / or phosphates, which water flows through an adsorber bed (6) containing iron hydroxide for adsorption of the heavy metals and / or phosphates, characterized in that the water is mixed with CO2-enriched air, the CO2 content of which is > 0.120%, before flowing through the adsorber bed (6).

2. Process according to claim 1, characterized in that the air with which the water is mixed has a CO2 content of < 1,000%.

3. Method according to claim 1 or 2, characterized in that the air enriched with CO2 is introduced into the water in the form of bubbles.

4. Method according to one of claims 1 to 3, characterized in that the air enriched with CO2 is introduced into the water in the form of bubbles by means of a nozzle, for example a Venturi nozzle.

5. Method according to one of claims 1 to 3, characterized in that the air enriched with CO2 is introduced into the water in the form of microbubbles (7a) with a diameter < 100 pm.

6. Method according to one of claims 1 to 3 or 4, characterized in that the air enriched with CO2 is introduced into the water in the form of microbubbles (7a) with a diameter > 10 pm and < 100 pm.

7. Method according to one of claims 1 to 3, 5 or 6, characterized in that the air enriched with CO2 is fed to a microbubble generator (7) which generates microbubbles (7a) directly in the water.

8. Method according to one of claims 1 to 7, characterized in that the air enriched with CO2 is produced by means of a technical device.

9. Method according to one of claims 1 to 7, characterized in that the air enriched with CO2 is soil air which is supplied from a soil air collection system.

10. Process according to one of claims 1 to 9, characterized in that the water enriched with CO2-enriched air is fed directly to the adsorber bed (6).

11. Method according to one of claims 1 to 9, characterized in that the water enriched with CO2-enriched air passes through at least one mechanical and / or at least one biological filter layer (3) before entering the adsorber bed (6).

12. Filter unit for carrying out the method according to one or more of claims 1 to 11, with the following components: a container (1, 12) with an inlet for supplying the water contaminated with heavy metals and / or phosphates and with a return line for discharging the purified / filtered water, an adsorber bed (6) located inside the container (1, 12), in particular containing granulated iron hydroxide, a microbubble generator (7) located in the water during operation of the filter unit and arranged upstream of the adsorber bed (6) for generating microbubbles (7a), a pressure pump (8, 8') connected to a pressure line (8b, 8'b) for supplying the microbubble generator (7) with water located in the filter unit or a component of the filter unit conducting the water, a supply line for supplying CO2-enriched air to the microbubble generator (7), a pump (10) for passing the water through the filter unit.

13. Filter unit according to claim 12, characterized in that the container (1) has two container parts (4a, 4b) which are separated from one another by an intermediate wall (1d) in such a way that a passage for water to flow through from one container part (4a) into the second container part (4b) is present in the lower container region, wherein the one container part (4a) contains at least one biological and / or mechanical filter and the adsorber bed (6) is contained in the second container part (4b).

14. Device according to claim 12 or 13, characterized in that the microbubble generator (7) is positioned before or after the biological filter (3), with respect to the flow direction of the water.

15. Device according to one of claims 12 to 14, characterized in that the container is a closed pressure container (12).

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