Methods for cleaning polluted water

Abstract

A purification process for cleaning polluted water, comprising at least one biological purification path and one filtration purification path, wherein the filtration purification path is operated at least partially in parallel to the biological purification path with a partial stream taken from the biological purification path, wherein the purification in the filtration purification path comprises the following steps: - Feeding a partial flow of the biological purification pathway into a purification basin, - Filtering the contaminated water through a membrane module, the membrane module being located in the purification basin, - Adding the adsorbent to the raw side of the membrane module, wherein the membrane module is located in the cleaning basin with the contaminated water and wherein the adsorbent comprises powdered activated carbon, - Ventilation of the membrane module by an airflow from below, preferably with air bubbles, the steps can be performed in parallel and / or sequentially, wherein the purification process is used as a preferably final stage of a purification process in a wastewater treatment plant before the purified water is discharged into a river, lake or the sea and wherein the partial flow supplied to the filtration purification path is taken downstream of an aeration basin of the biological purification path.

Description

Technical field

[0001] The present invention relates to a method for purifying contaminated water, which includes a filtration stage in the partial flow and at least partially parallel to a conventional biological purification stage. The method is used for purifying contaminated water, such as rainwater or surface water, e.g., as an additive to biological purification stages, parallel to a sedimentation stage. State of the art

[0002] Contaminated water intended for reintroduction into the water cycle requires increasingly intensive purification before being released. On the one hand, regulatory requirements for water discharged into rivers, lakes, or the sea are rising. On the other hand, technical requirements are also increasing, for example, due to contaminants such as bacteria, including multi-resistant germs, growing problems with plastics, including microplastics, or mineral impurities or trace substances such as phosphate, which can originate from industrial or agricultural runoff.

[0003] An overview of the state of the art is provided in "Use of Membrane Processes for Water / Wastewater Treatment: Overview of Manufacturers of Membrane Modules and Systems," Competence Center for Micropollutants, North Rhine-Westphalia, 2018. This publication describes the elimination of micropollutants using oxidative, adsorptive, and physical processes. Adsorptive processes can be carried out with powdered or granular activated carbon. When using a membrane bioreactor, the activated carbon can, for example, be dosed directly into the aeration tank. The membrane is used to separate the activated sludge from the biologically treated wastewater, thus eliminating the need for a secondary clarifier. The membrane filtration also retains the activated carbon.

[0004] The demands placed on wastewater treatment have steadily increased in recent years and will continue to intensify in the future. More complex technologies are being used more frequently. According to current knowledge, membrane technology, in combination with other applications, achieves the highest purification effect for various contaminants.

[0005] Many (municipal) wastewater treatment plants still operate exclusively using conventional technology, meaning they rely solely on biological treatment. Furthermore, existing plants, particularly in densely populated areas, are increasingly reaching their capacity limits, necessitating upgrades. Retrofitting these plants is complex and expensive, and therefore often avoided.

[0006] Methods for cleaning polluted water can also be found in EP 1 313 669 B1, EP 2 840 070 A1, CN 107 892 400 A and the subsequently published DE 10 2019 128 677 A1. Disclosure of the invention

[0007] Against this background, the present invention aims to provide a method for cleaning polluted water, which allows for the economically and technically improved removal of impurities from water and simultaneously increases the capacity of existing treatment plants.

[0008] The purification method according to the invention for purifying contaminated water comprises at least one biological purification path and one filtration purification path, wherein the filtration purification path is operated at least partially parallel to the biological purification path with a partial stream taken from the biological purification path.

[0009] The cleaning process in the filtration cleaning path includes the following steps: - Feeding a partial flow of the biological purification pathway into a purification basin, - Filtering the contaminated water through a membrane module, the membrane module being located in the purification basin, - Adding the adsorbent to the raw side of the membrane module, wherein the membrane module is located in the cleaning basin with the contaminated water, aerating the membrane module by flowing air from below, preferably with air bubbles, wherein the adsorbent comprises powdered activated carbon (PAC) and wherein the steps can be carried out in parallel and / or sequentially.

[0010] The purification process according to the invention is preferably used as the final stage of a wastewater treatment plant's purification process before the treated water is discharged into a river, lake, or the sea. The feature that the process according to the invention is used as the "final stage" before discharge into a river, lake, or the sea is explicitly optional. In some embodiments, it is expressly possible to combine the process downstream with further purification stages, such as ozonation and / or sand filtration.

[0011] The inventive method does not completely replace the existing plant technology in the form of a biological treatment pathway with filtration, but advantageously combines it with the latter. This allows for both capacity expansion for peak loads and optimization of wastewater treatment quality with low investment costs.

[0012] The installation of a filtration stage and any necessary recirculation flows allows for an increase in the dry solids content in the upstream biological treatment stage, thereby increasing the plant capacity while simultaneously improving treatment performance. This capacity increase results from the independence from a secondary clarifier, as the sludge-water mixture (so-called excess sludge) generated in the biological treatment stage is no longer solely limited by the sedimentation rate of the sludge flocs, but rather undergoes (pressure-driven) sludge-water separation through filtration with the membrane module. The increased dry solids content frees up capacity in the aeration tank volumes of the biological treatment pathway. The separation efficiency of the membrane filtration also reduces the load on the parallel secondary clarifier, thus creating additional free capacity.

[0013] The addition of the adsorbent to the cleaning basin of the filtration cleaning path is preferably carried out directly, i.e. directly into the cleaning basin, or indirectly, in particular into certain steps of the biological cleaning path and / or in the area of ​​a process interface between the filtration cleaning path and the biological cleaning path.

[0014] The ventilation can primarily serve to clean the membrane module for filter cake removal.

[0015] The purification process according to the invention, which can also be referred to as a "membrane hybrid process" due to the use of a biological purification path and a filtration purification path, can be advantageously used for the technically and structurally simple capacity expansion of existing plants.

[0016] The purification process or membrane hybrid process according to the invention makes it possible to flexibly adapt the membrane operation to existing requirements by combining different process applications. Thus, depending on the water flow rate, the capacity of existing purification stages can be increased or the elimination of micropollutants can be optimized by reducing PAC consumption. The creation of different operating modes makes it possible to combine the expansion of a plant as a membrane hybrid process with other planned investment measures (expansion of the secondary clarifier or activated sludge) and thus utilize economic synergies, making the process technology more economical compared to competing processes.

[0017] Furthermore, the filtration stage can be combined with downstream ozonation, which is a particularly interesting technical approach for installations with limited space, allowing for the integration of an additional treatment stage in municipal wastewater treatment plants while simultaneously increasing the plant's biological performance. This approach offers the possibility of reducing the formation of environmentally harmful oxidation byproducts through the upstream membrane. The mobilization of antibiotic-resistant bacteria during ozonation is also significantly reduced by the upstream membrane. Moreover, the separation of solid-bound organic compounds through filtration allows for a lower ozone dosage, thus achieving energy and economic optimization of the ozone-based process.

[0018] The partial flow fed to the filtration treatment path is taken downstream of an aeration tank of the biological treatment path. Preferably, the partial flow fed to the filtration treatment path is also taken upstream of a secondary clarifier of the biological treatment path. In other words, the partial flow fed to the filtration treatment path is taken flow-wise between the aeration tank and the secondary clarifier.

[0019] The adsorbent comprises powdered activated carbon, preferably produced from organic material such as wood and / or peat. The steps can be carried out in parallel and / or sequentially. The process can be used temporarily (depending on the prevailing hydraulic conditions), preferably as the final stage of the wastewater treatment process in a wastewater treatment plant, before the treated water is discharged into a river, lake, or the sea. Such a process could also be used for the treatment of surface water, rainwater, or other polluted water.

[0020] Surprisingly, it has been found that powdered activated carbon made from wood or peat is less abrasive than, for example, activated carbon made from minerals.

[0021] In this purification process, preferably only one membrane module in the purification tank is permeated by the contaminated water. The contaminated water is fed to the membrane module from a sedimentation stage, particularly from a secondary clarifier of the sedimentation stage, without passing through a second membrane module, and is then discharged from the purification tank into a river, lake, or the sea without passing through any further membrane modules. Obviously, several membrane modules can be connected in parallel in the purification tank to increase the flow rate.

[0022] The nominal particle size of the powdered activated carbon is preferably between 10 and 150 µm, more preferably between 10 and 50 µm. Within this range, the activated carbon can be kept in suspension in the cleaning tank with the blown-in air, sufficient cleaning can be achieved, and the abrasive effect on the membrane is not yet too great.

[0023] Preferably, the iodine number of the powdered activated carbon used in the purification process is greater than 900 mg / g, and more preferably greater than 1000 mg / g.

[0024] The internal surface area of ​​the powdered activated carbon is preferably greater than 800 m². 2 / g determined according to the BET method.

[0025] The adsorbent can be mixed or suspended in water before being added, with various components of the adsorbent being present in suspended, mixed, or dissolved form. This allows for more precise dosing, as the activated carbon concentration is adjusted independently of the cleaning tank in a separate device outside of it.

[0026] The adsorbent can be added in the purification basin at the membrane bioreactor without a pre-existing contact zone or without a contact reactor.

[0027] During the purification process, precipitating and / or flocculant agents can be added. These can be used, for example, to reduce the phosphorus content. In particular, iron or aluminum salts, especially FeCl3 or (Fe,Al)Cl3, are added.

[0028] Membrane filtration uses either a microfiltration stage or, preferably, an ultrafiltration stage.

[0029] The membrane module can be designed as a flat membrane module, a pocket module, or a hollow fiber membrane module.

[0030] A concrete basin or a standard container, possibly modified, can serve as a cleaning basin.

[0031] In another embodiment, in addition to the polluted water from the biological purification path, a volume flow of clarified water from a secondary clarifier can be supplied to the cleaning basin of the filtration purification path.

[0032] This has the advantage that, depending on the hydraulic load scenario of the entire system, the entire water flow can be routed through the filtration purification path, thus resulting in a higher purification effect. Furthermore, the recirculation dilutes the contaminated water from the biological purification path, thereby increasing the filtration efficiency of the membrane.

[0033] In this case, in particular, the dosage of the adsorbent can be carried out in the cleaning basin of the filtration cleaning path in the volume flow of clarified water returned from the secondary clarifier.

[0034] The dosage of the adsorbent in the volume flow returned from the secondary clarifier can, for example, be carried out in an intermediate contact / equalization basin.

[0035] This has the further positive effect of ensuring sufficient contact time between the recirculated volume flow and the adsorbent. Furthermore, optimal mixing of the adsorbent into the partial volume flow is guaranteed.

[0036] Alternatively or additionally, the dosage of the adsorbent can be added to the cleaning basin of the filtration cleaning path or to an aeration basin of the biological cleaning path, in particular to a flow-wise rear part of the aeration basin, especially to an area of ​​the last third of the total length of the aeration basin.

[0037] This is particularly advantageous from a technical standpoint when space is limited in a plant, as no construction work is required. To prevent the powdered activated carbon (PAC) adsorption sites from being occupied by dissolved organic carbon (DOC), it is dosed in the rear section of the aeration tank, where many organic substances have already been removed. In addition to secondary clarification, further filtration is advantageously employed in biological treatment stages with activated sludge for the efficient separation of the PAC. Suitable options include, for example, cloth filters or sand filters. Since no contact reactor or sedimentation is required, the investment costs are relatively low, and the space requirement is also minimal.

[0038] The required specific dosage of powdered activated carbon (PAC) depends on the chosen injection point. This can vary between 5 and 30 mg PAC / L. For processes with (multiple) recirculation of the PAC, a dosage between 5 and 10 mg PAC / L is usually chosen. PAC dosages up to 30 mg PAC / L are typically used when dosing into a separate contact tank. The PAC dosage also depends on the type of PAC used.

[0039] Finally, according to another embodiment, a return volume flow from the cleaning basin of the filtration cleaning path can be returned to the biological cleaning path, thereby concentrating the adsorbent in the polluted water in particular.

[0040] This has the further positive effect of creating additional contact with the sludge-water mixture and maximizing the utilization of the available adsorption sites on the PAC. This reuse / recycling of the PAC can result in a reduction of the PAC dosage. Brief description of the drawings

[0041] It shows: Fig. 1 Schematic of a system for the cleaning process in a first embodiment; Fig. 2 Schematic of a system for the cleaning process in a second embodiment; Fig. 3 Schematic of a system for the cleaning process in a third embodiment; Fig. 4 Schematic diagram of a system for the cleaning process in a fourth embodiment. embodiment(s) of the invention

[0042] To clarify the invention, the method will be explained using exemplary embodiments.

[0043] The purification process according to the invention is used for the treatment of wastewater, which may be contaminated with various substances, for example in a (municipal) wastewater treatment plant. A schematic diagram of a plant for carrying out the process is shown in Fig. 1 shown. The system includes a "conventional" biological purification pathway, which is depicted in the illustration of the Fig. 1 shown above (Q zul to Q Abl,dir ), and one with a partial flow of the biological purification pathway (Q zul,MBR ) operated filtration purification path, comprising a membrane bioreactor (MBR). Both the flow outlet of the biological purification path (Q Abl,dir ) as well as the flow outlet of the filtration cleaning path (Q Abl,MBR ) flow into a surface water body, which is in Fig. 1 is shown on the far right.

[0044] The volume flow passing through the biological purification pathway is measured as Q before being discharged into the surface water. Abl,dir further cleaned by a cloth filter TF to reduce suspended substances that were not removed in the secondary clarification.

[0045] The partial stream Q supplied to the filtration cleaning path zul,MBR The biological treatment pathway branches off downstream of the aeration tank BB, but upstream of the secondary clarifier NK (sedimentation stage). From this point onward, the filtration treatment pathway operates at least partially in parallel with the process steps of the biological treatment pathway downstream of the aeration tank BB. The volume flow rate supplied to the further biological treatment stage is Q. zul,NK .

[0046] The supply of contaminated water to the cleaning basin of the filtration cleaning path, in which the MBR is immersed, can be done, for example, via a feed pump or by gravity.

[0047] In the filtration purification pathway, an ultrafiltration membrane technology with powdered activated carbon dosing is used as an additional purification stage. The purification of the contaminated water takes place in the filtration purification pathway with at least one submerged membrane module, in particular a flat-plate membrane module, which includes at least one ultrafiltration membrane.

[0048] The powdered activated carbon (PAC) adsorbent can be added directly to the cleaning tank of the MBR in the filtration treatment pathway. Alternatively or additionally, the PAC can also be added to a volume flow of clarified water Q returned from the secondary clarifier NK. Rück to take place, which in Fig. 2 is shown.

[0049] The membrane module retains suspended solids, dirt particles, viruses, bacteria, and powdered activated carbon, among other substances. The added powdered activated carbon acts as an adsorption medium for removing contaminants from the polluted water, such as micropollutants, especially microplastics, dissolved pharmaceuticals, and corrosion inhibitors. The addition of precipitating and flocculants (FHMs) converts dissolved substances like phosphates into insoluble substances, which are then also separated from the wastewater as solids by the ultrafiltration membrane.

[0050] The combination of process elements – ultrafiltration technology with filtration and sedimentation, dosing of powdered activated carbon for adsorption and, if necessary, the dosing of precipitating and flocculant agents for chemical precipitation – makes up this very efficient process.

[0051] The ultrafiltration membrane of the membrane module immersed in the purification basin, in particular a flat membrane module, comprises a membrane with a nominal pore size of 0.01 to <0.1 µm.

[0052] The membrane preferably consists of polyethersulfone, polysulfone, polyacrylonitrile, polyvinylidene fluoride, polyamide, polyetherimide, cellulose acetate, regenerated cellulose, polyolefins, or fluoropolymers and can be produced, for example, by coating nonwovens or fabrics with a polymer solution and creating the pores in a subsequent phase inversion step, or by stretching polymer films in a suitable manner to form the desired pores. Many of these filtration membranes are commercially available, e.g., under the name NADIR. ® Membranes (NADIR Filtration GmbH, Wiesbaden) or Celgard ® Flat Sheet Membranes (Celgard Inc., Charlotte, NC, USA).

[0053] The contaminated water is purified by pumping it through the membrane to the so-called permeate side. A vacuum is created for this purpose using a pump. The flow rate of the process is preferably 4-31 LMH (L / m³) net. 2 h).

[0054] A ventilation system is installed beneath the membrane module, through which air generated by a compressor is distributed. Specific air volume flows of 60-115 m³ / h, depending on the rising surface area, are required for the operation of the process. 3 / h (0.125 m 3 / m 2 -0.239 m 3 / m 2 ) used.

[0055] The membrane module can be operated in the following filtration cycles: filtration, relaxation, backwash, relaxation. During the relaxation phase, the membrane unit will be purged with air without filtration operation.

[0056] Depending on the degree of soiling, the membrane module is cleaned with sodium hypochlorite, hydrogen peroxide, and / or citric acid. Other acids, alkalis, or oxidizing agents can also be used.

[0057] Powdered activated carbon with a nominal particle size of 1-50 µm is dosed directly from a reservoir into the MBR cleaning tank. The target concentration of powdered activated carbon in the cleaning tank is 5-40 mg / l.

[0058] The powdered activated carbon used is made from wood and / or peat.

[0059] The dry solids content in the purification tank, which is adjusted by adding powdered activated carbon, is between 2 and 15 g / l, but can also range from 1 to 10 g / l. To monitor the total solids content in the purification tank, a portion of the activated carbon is removed discontinuously.

[0060] By using it as a membrane-based process for the treatment of biologically treated polluted water and adding powdered activated carbon, the dry matter content in the conventional biological treatment stage can be increased, thus expanding the plant capacity and relieving the secondary clarifier (sedimentation stage) by separating the resulting sludge.

[0061] Furthermore, the process can be extended by adding precipitating and / or flocculant (iron or aluminum salts). The precipitating and / or flocculant is added from a reservoir via pumps directly into the purification tank (see Fig. 1) or the volume flow Q returned from the secondary clarifier NK Rück (see Fig. 2) The dosage depends on the composition of the medium to be treated and its phosphorus content. Dissolved phosphorus (orthophosphate) can be removed from the medium by chemically precipitation into a solid, insoluble form. Due to its nominal pore size, the ultrafiltration membrane retains both particulate, solid-bound phosphorus and the chemically precipitated phosphorus. This process component achieves total phosphorus concentrations in the permeate, the water purified by the membrane module, of ≤ 0.2 mg / l.

[0062] In addition to micropollutants through powdered activated carbon dosing and phosphorus elimination through precipitating and flocculant dosing, bacteria and germs are also separated from the medium using this combined process.

[0063] In the further education of Fig. 3. Additionally, a return volume flow Q is added. RS,MBRfrom the MBR cleaning basin back into the BB aeration basin of the biological treatment stage, thereby concentrating the adsorbent in the polluted water.

[0064] This allows the adsorbent, in the form of powdered activated carbon (PAC), to remain in contact with the sludge-water mixture for a longer period, thus optimizing the use of the PAC's adsorption capacity. This optimized use of the PAC can significantly reduce the overall PAC consumption.

[0065] Finally, in Fig. 4 another embodiment is shown, which differs from the embodiment of Fig. 3 differs in that in the biological purification pathway a volume flow return secondary clarification Q RS,NKThe sludge is intended to be returned from the secondary clarifier NK to the aeration tank BB. This is advantageous because it allows the biologically active sludge to be removed from the sludge-water mixture Q fed into the secondary clarifier. Zul, NK can be separated and remain in the system.

[0066] In addition, the TF cloth filter carries a volume flow of cloth filter rinse water Q. TF, SPW taken from the volume flow of clarified water Q returned from the secondary clarifier NK Rück is added and indirectly fed to the MBR cleaning basin. The volume flow rate of the cloth filter rinse water Q TF, SPW is taken in particular from the retentate side of the cloth filter.

[0067] This ensures that the volume flow Q Abl,dirAny remaining activated carbon particles that were not removed by the secondary clarifier (for example, because the particle size is too small) are retained by the cloth filter and remain in the system due to recirculation. This further reduces activated carbon consumption. Reference symbol list Q Zul Flow rate / dirty water inlet BB aeration basin (biological treatment) VBW distribution structure Q RS, NK Volume flow rate return secondary clarification (sedimentation stage) Q RS, MBR Volume flow rate return flow Membrane Bioreactor (MBR) Q Zul, MBR Volume flow rate inlet MBR Q Zul, NK Volume flow rate inlet secondary clarification NK Secondary Clarification (Sedimentation Stage) MBR Membrane Bioreactor Q Rück Return flow rate PAC powdered activated carbon Q ABI, dir Direct volume flow to the receiving water body Q TF, SPWVolume flow rate cloth filter rinse water TF Cloth Filter

Claims

[1] A purification process for purifying contaminated water, comprising at least one biological purification path and a filtration purification path, wherein the filtration purification path is operated at least partially parallel to the biological purification path with a partial flow taken from the biological purification path, wherein the purification in the filtration purification path comprises the following steps: - feeding a partial flow of the biological treatment path into a treatment tank, - Filtering the contaminated water through a membrane module, the membrane module being located in the cleaning tank, - Dosing of the adsorbent on the raw side of the membrane module, wherein the membrane module is located in the purification tank containing the contaminated water and wherein the adsorbent comprises powdered activated carbon, - Ventilation of the membrane module by flowing air from below, preferably with air bubbles, where the steps can be carried out in parallel and / or sequentially, wherein the purification process is used as a preferably final stage of a purification process of a sewage treatment plant before the discharge of the purified water into a river, lake or the sea and wherein the partial flow fed to the filtration purification path is taken downstream of an aeration tank of the biological purification path. [2] Purification process according to claim 1, wherein the partial flow to be fed to the filtration purification path is taken upstream of a secondary clarifier of the biological purification path. [3] Cleaning method according to claim 1 or 2, wherein during the cleaning in the filtration cleaning path, the contaminated water flows through exactly one membrane module in the cleaning tank, wherein the contaminated water from a sedimentation stage, in particular from a secondary clarifier of the sedimentation stage, is fed to this membrane module without flowing through a second membrane module and is discharged from the cleaning tank into a river, lake or the sea without flowing through a further membrane module. [4] Purification method according to one of claims 1 to 3, wherein the adsorbent added in the filtration purification path comprises powdered activated carbon made from wood and / or peat. [5] Cleaning process according to one of claims 1 to 4, wherein the nominal grain size of the powdered activated carbon added in the filtration cleaning path is between 5 and 150 µm, preferably between 10 and 50 µm. [6] Purification process according to one of claims 1 to 5, wherein the iodine number of the powdered activated carbon used in the filtration purification path is greater than 900 mg / g, preferably greater than 1000 mg / g. [7] A purification method according to any one of claims 1 to 6, wherein the inner surface area of ​​the powdered activated carbon used in the filtration purification path is greater than 800 m 2 / g determined according to the BET method. [8] Purification process according to one of claims 1 to 7, wherein the adsorbent used in the filtration purification path is mixed or suspended in water before metering, wherein various components of the adsorbent may be present in suspended, mixed or dissolved form. [9] Cleaning process according to one of claims 1 to 8, wherein precipitants and / or flocculants are added in the filtration cleaning path. [10] Purification process according to claim 9, wherein iron or aluminum salts, in particular FeCl3 or (Fe,Al)Cl3, are added in the filtration purification path. [11] Purification method according to one of claims 1 to 10, wherein the filtration in the filtration purification path through the membrane module is a microfiltration or preferably an ultrafiltration. [12] A purification method according to any one of claims 1 to 11, wherein the membrane module used in the filtration purification path is a flat membrane module or a hollow fiber membrane module. [13] A cleaning method according to any one of claims 1 to 12, wherein the cleaning basin of the filtration cleaning path comprises a concrete basin or a standard container. [14] Cleaning method according to one of claims 1 to 13, wherein, in addition to the contaminated water from the biological cleaning path, a volume flow of clarified water recycled from a secondary settling tank is supplied to the cleaning tank of the filtration cleaning path. [15] Cleaning method according to claim 14, wherein the dosage of the adsorbent into the cleaning tank of the filtration cleaning path takes place in the volume flow of clarified water returned from the secondary clarification tank. [16] Cleaning method according to one of claims 1 to 15, wherein the dosing of the adsorbent into the cleaning tank of the filtration cleaning path takes place in an aeration tank of the biological cleaning path, in particular in a rear part of the aeration tank in terms of flow, in particular in a region of the last third of the total length of the aeration tank. [17] Cleaning method according to one of claims 1 to 16, wherein a return volume flow is returned from the cleaning basin of the filtration cleaning path into the biological cleaning path, whereby in particular the adsorbent is concentrated in the polluted water.

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