EP2043956A1

EP2043956A1 - Method for the removal of pollutants from liquids and device for carrying out said method

Info

Publication number: EP2043956A1
Application number: EP07802398A
Authority: EP
Inventors: Alexander Hahn; Klaus Strätz; Manfred Waidhas
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2006-07-25
Filing date: 2007-07-24
Publication date: 2009-04-08
Also published as: DE102006034895A1; CN101516785A; WO2008012303A1

Abstract

There are known methods for the removal of pollutants from aqueous media, particularly for the removal of organic pollutants from water, wherein the desired effect is achieved by mainly introducing ozone (O3) into the liquid to be cleaned. The ozone forms (H2O)-radicals in the water, wherein the radicals have an oxidation effect. According to the invention, the OH-radicals are directly produced electrochemically and the electrochemically produced OH-radicals are used for the removal of organic pollutants, for rendering the pollutants ineffective and/or for the reduction of the effectiveness thereof. The associated device comprises an electrode arrangement (10, 20) with positive and negative electrodes (10i, 21), forming an electron array, and an inlet- and outlet (35, 26) for the liquid to be cleaned.

Description

description

Process for the removal of pollutants from liquids and apparatus for carrying out the process

The invention relates to a method for removing pollutants from liquids, in particular for removing organic pollutants from aqueous media. In addition, the invention also relates to an apparatus for carrying out the method.

Known methods for removing in particular organic pollutants from water, for example waste water, groundwater and / or process water, are usually based on the oxidation of the corresponding substances. For example, it is known that a corresponding effect is achieved by introducing ozone into a liquid to be purified. Particularly in the context of papermaking, in which the effluents from remaining organic constituents or humic substances have a high COD value (COD = chemical oxygen demand) and therefore can not be discharged untreated into the municipal water system, cleaning systems with ozonizers are proposed. However, this process is complicated and costly, since the devices are usually fed with pure oxygen, a high voltage power supply 10 to 40 kV need and also the efficiency for generating the ozone (O3) is relatively poor.

From US 2003/0 196 983 Al a method is known, with which dissolved in liquids metals are removed by a so-called. E- lektrokoagulation. For the purpose of removing organic contaminants of the liquids, reference is made in this connection to the use of microorganisms. An associated device for carrying out this method is realized as a plate assembly with bipolar electrodes. Further arrangements for the treatment of liquids are described in WO 99/11 577 A1 and DE 196 02 369 A1 described.

In the process known from US 2003/0 196 983 A1, the ozone (O ₃ ) is electrically split into OH radicals which have the actual oxidation action before or during introduction into water.

The object of the invention, in contrast, is to provide a method which operates without the separate use of ozone and which is inexpensive. In addition, a suitable device for carrying out the method is to be created.

The object is achieved by the sequence of process steps according to claim 1. A related device is the subject of claim 24. Further developments of the method, in particular also suitable applications, and the associated device are specified in the respective subclaims.

In the process according to the invention, the OH radicals, which have the actual oxidation action, are generated directly electrochemically, a considerably higher overall efficiency being achieved than via the path of introduction of ozone. Advantageously, a voltage of <5 V is usually required, the voltage being dependent on the electrode material. Overall, the apparatus for carrying out the method according to the invention is made compact and includes a closed liquid circuit for a continuous operation, which can be harmless in particular organic pollutants in liquids.

For the treatment of wastewater especially in the paper and textile industry, however, with the US 2002/125 180 Al a pollutant oxidation proposed in such a way that in a

Treatment tank catalytically produced hydroxide peroxide and reacts with the organic substances. In principle, therefore, the suitability of OH radicals for the purification of wastewater previously known. However, the described methods and associated devices are consistently complex in construction and have therefore not yet prevailed technically. On the other hand, the electrochemical process for purifying water according to the invention can be carried out with a simply constructed device. Such a device essentially requires only an arrangement of alternating positive and negative electrodes, which are arranged plane-parallel to one another, wherein an inlet and a drain is present, via which the liquid to be purified or led away and continuously guided along the electrodes.

From the paper industry is still a process known specifically for the electrochemical degradation of lignin. For this purpose, devices are used in which in particular so-called 'diamond' electrodes are used.

Further details and advantages of the invention will become apparent from the following description of exemplary embodiments play with reference to the drawing in conjunction with the claims.

Show it

Figures 1 and 2 show two alternative working schemes for water treatment and

Figure 3 shows the concrete structure of a cell operating according to the electrochemical principle as part of a device for wastewater treatment.

From Figures 1 and 2, the workflow in the water treatment can be seen. In each case, a working area A designed as an electrolytic cell, a liquid feed area B, a liquid discharge area C and an electrochemical processing area D with electrodes are present. It is essential that one for the interaction of the areas A to D a self-contained liquid circuit of continuously supplied liquid and steadily away feasible liquid is realized, wherein in the work area between the electrodes only the liquid to be processed in each case. This is advantageously a continuous operation possible.

In the container of the working area A, the individual electrodes of the processing area D are arranged plane-parallel, wherein the electrodes are respectively poled alternately positive and negative. In the area B, alternative feeds B1, B2 can be present for the water to be treated, wherein in particular the water in the tank A can be returned to a shower-like distributor B2 above the electrode arrangement in the processing area D via a circulating pump not shown in the figures. In order for a proper use of the system thus formed is considered essential uniform coverage of the electrodes guaranteed. The drainage area C is substantially realized as a drainage channel Cl for collecting the purified water and a drain C2 as a subsequent liquid discharge line.

Since foaming may occur when working in aqueous media, suitable means are provided especially in the alternative to FIG. 2, in order to control the formation of foam S. For this purpose is in the container in area A a

Overflow edge Cl for foam separation is present, wherein in the electrode container downstream collecting container of the liquid path leading region C, a circuit with a circulating pump and a shower-type C2 distributor according to Figure 1 is present. Into the liquid feed and the

Flüssigkeitsswegführleitungen the areas B and C valves V can be arranged.

The diagrams of FIGS. 1 and 2 therefore show suitable procedures by the coordinated interaction of the individual regions in the treatment of water, the electrochemical principle being the same in both cases. Specifically, it is about having organic pollutants in the water be made harmless by oxidation, including an oxidizing agent must be provided. It is proposed to use for this purpose OH radicals, which OH radicals are generated electrochemically, which is electrolytic according to the reaction equation

H ₂ OH ⁺ + (OH) + e ^" (equation i: occurs.

The OH radicals are known to have an oxidizing effect. They can be produced electrochemically with a high overall efficiency in accordance with Equation 1, for which purpose a voltage of <5 V is generally sufficient. In this case, the exact structure of the electrode arrangement, the formation of the electrodes themselves and the electrode material plays a role.

Specific use in the pulp and paper industry is to remove residual lignin or humic matter in the liquid from paper waste effluents. Under lignin (Latin lignum =

Wood) is understood to mean a phenolic macromolecule of various monomer units. It is a solid, colorless substance, which is stored in the plant cell wall and thus causes the lignification of the cell (so-called lignification). Humic substances are weakly brown to black-colored, usually formed in soils, organic substances without reproducible chemical structure and with very different properties and compositions.

The lignin and humic substances are both organic

Substances and are understood in the context of the present invention as the main pollutants in wastewater in papermaking. Such pollutants can be influenced by oxidation in their effect.

The latter organic substances have a high COD (chemical oxygen demand), which reduces the demand for (OH ^" ) radicals. FIG. 3 shows a suitable concrete structure 1 of a single cell for this purpose. The structure consists essentially of a base plate 2 with vertical struts for holding two electrode systems. Several cells can be connected in parallel.

The cell 1 contains a first electrode system 10 with individual planar electrodes 11, 11 ', 11 ",..., The electrodes 11, 11', 11"... Being arranged parallel to one another. The individual electrodes 11, 11 ', H''',... Are connected via an electrical supply line 15, which likewise serves as a distributor for the individual electrodes H ₁ , to a voltage source (not shown in the figure). Furthermore, a second electrode system 20 with electrodes 21, 21 ', 21'', ... is present, wherein an electrical supply line 25 is present, which serves as a distributor for the individual electrodes 2I ₁ . Overall, the first electrode system 10 and the second electrode system 20 are interleaved with the respective electrodes H ₁ and 2I ₁ such that in each case one electrode H _{1 of} the electrode system 10 two electrodes 2I ₁ and 21 ₁₊ i of the electrode system 20 (and vice versa ) is adjacent. Thus, a comb structure is formed with plane-parallel electrode surfaces of opposite polarity.

The liquid to be purified is supplied via a line system 30 with an inlet 35 and a drain 36 and led away and continuously into the spaces between the individual NEN electrodes 11, 11 ', 11 ", ... and 21, 21', 21 ", ... introduced.

The electrode system shown in FIG. 3 can be operated with direct current or alternating current. In particular, the system is galvanostatically operated, for example, with a current density of 2 to 500 mA per cm ² electrode area. The current can also be fed pulsed or it can be a reversal of the current direction. The system can also be operated with alternating current, wherein the alternating current is advantageously designed as a triangular, sinusoidal or plateau flow. The frequency is in particular in the range of 10 ^-3 to 1 Hz.

From Figure 3 it can be seen that the electrode systems 10 and 20 with the flat individual electrodes H ₁ and 2I _{1 in} parallel nested form the comb electrode system. Instead, the electrodes may also be formed radially symmetric or cylindrically symmetrical, wherein they are then also nested. Alternatively, the electrodes may also each form symmetrically distributed wire bundles.

Between the electrodes H ₁ and 2I ₁ separators for

Separation of the electrode spaces be introduced. This is not shown in detail in the figures.

The electrodes are made of suitable materials known from the prior art and may be surface-structured. Advantageously, suitable materials have been found to be so-called MMO ("mixed metal oxides"), but other materials are also possible, such as, for example, diamond, platinum (Pt), silicon carbide (SiC), tungsten carbide (WC), titanium carbide (TiC). , Titanium nitride (TiN) or titanium carbon nitride (TiCN).

The positive electrodes can also consist of consumable electrode materials, such as iron (Fe), stainless steel alloys, aluminum (Al) or carbon (C). The negative electrodes in this case are made of material such as iron (Fe), stainless steel alloys, carbon (C) or aluminum (Al).

The structure of the device according to FIG. 3 can be developed by providing means for cleaning the electrodes. The cleaning can be done by mechanical wipers / scrapers, by ultrasound, by self-cleaning Surfaces or materials or even by adding appropriate floats in the liquid circulation done. The device described may have a foam separator according to the diagram of FIG. 2, which is formed, for example, by an overflow edge, by showering in the liquid flow or liquid drain or by mechanical separation. In addition, the device may have a separation device for oxygen (O ₂ ) or hydrogen (H ₂ ). In particular, the oxygen (O2) produced during the process can be used further and used, for example, for the activation of biological clarification tanks.

The device described above makes it possible to economically remove organic pollutants from water with process engineering simple and safe means. This process has been tested in wastewater treatment in the paper industry and is particularly suitable for reducing the COD value caused by lignin in the processing of cellulose.

In addition to the specific use in the paper or pulp industry, the device described and the method operated therewith can always be used where it comes to the reduction of COD values. This can be done both for the degradation of non-biodegradable COD, but also in particular for

Converted into biodegradable COD. The process can also be used to treat concentrates from filtration processes. In this case, a mechanical pre-crushing of solid components in or before the feed to the cell can be carried out in particular by a disperser. Such a dispersant is, for example, a so-called thorax stirrer.

The method described above may further be carried out in combination with UV activation of the liquid medium by one or more corresponding UV lamps. This serves to improve both reductive and oxidative degradation of the pollutants. It is particularly advantageous that the process can be operated in the circulation with a biological stage, where - as already mentioned - the oxygen is used for the activation of biological clarifiers.

The new process has been described above specifically for the elimination of pollutants in aqueous media, with particular regard to lignin and humic substances in papermaking as pollutants. These are the main pollutants there. It is important to reduce the effect of organic pollutants in a conventional manner by oxidation, with both a suitable process control and a reductive influence is detected. For this purpose, the device can be adjusted accordingly.

The method described can also be used for degradation of organic dyes in liquids. Such organic dyes are used, for example, in the printing industry and / or in the textile industry. For printing and / or coloring, natural or synthetic dyes are suitable as colorants. These colorants can generally be dissolved in liquid solvents, with particular preference currently being given to aqueous solvents.

The remaining in the aqueous solvents organic dyes are considered in the disposal of pollutants in the context of the present invention, the effect of which is to be eliminated or at least reduced. In this respect, the same problem exists as in the case of the water treatment described above with reference to the process diagrams, and a device as shown in detail in FIG. 3 can be used.

With the device described with reference to FIG. 3, it is possible to achieve a reductive degradation of the dyes, but also an oxidative degradation of the dyes. Both a reductive and an oxidative degradation of the dyes can be used in terms of process technology. In addition to the industrial applications of decolorization especially of the printing industry and the textile industry, but also in the pulp and paper industry, in general, even in the wastewater, groundwater or service water existing organic dyes and pollutants can be effectively removed.

Overall, the invention provides a broad application potential by reducing the COD value (COD = chemical oxygen demand). It can be used for the mining of non-biodegradable COD, but also for the generation of biodegradable COD. For use in environmental technology, the oxygen (O 2) produced in the process described can be separated off and used for the activation of biological clarification tanks or the like. environmentally friendly facilities. It is also possible that the pollutant degradation is operated as a process in the cycle with a biological stage.

Further possibilities for the application of the invention can be seen in the treatment of concentrates from filtration processes. It can be done before an electrochemical treatment, a mechanical pre-crushing of solids. Possibly. In this case, the aqueous medium or the liquid associated therewith is also UV-activated.

Claims

claims

1. A process for the removal and / or degradation of pollutants from liquids, in particular for the removal of organic pollutants from aqueous media, wherein the desired effect is achieved by oxidizing OH radicals in the liquid to be purified, with the following measures: - It is carried out continuously Processing of the liquid,

an arrangement of alternating positive and negative electrodes is used,

- Wherein the electrodes are formed areally and corresponding electrodes are arranged plane-parallel to each other and

- The liquid is continuously supplied to the electrodes and led away, including an inlet and outlet (and possibly a distributor) are used, - The OH radicals are generated directly electrochemically in the liquid at the electrodes,

- The directly electrochemically generated OH radicals are used to remove the pollutants, to inactivate the pollutants and / or to reduce their effect.

2. The method according to claim 1, characterized in that for the electrochemical generation of the OH radicals electrode assemblies are used which require a voltage of <5 V ter.

3. The method according to claim 2, characterized in that the electrodes are applied alternately in the electrode assembly with positive or negative voltage.

4. The method according to any one of the preceding claims, characterized by the use in the paper or pulp industry.

5. The method according to any one of claims 1 to 4, wherein the chemical oxygen demand is defined as a criterion for the presence of pollutants, characterized by the reduction of the COD value (COD = chemical oxygen demand).

6. The method according to claim 5, characterized for the degradation of non-biodegradable COD.

7. The method according to claim 5, characterized for generating biodegradable COD.

8. The method according to any one of the preceding claims, characterized for the treatment of concentrates from Filtrationspro-.

9. The method according to claim 8, characterized in that prior to the electrochemical treatment, a mechanical pre-crushing of solid components takes place.

10. The method according to claim 8, characterized in that the liquid or the relevant medium is UV-activated.

11. The method according to claim 3, characterized in that for use in the paper or pulp industry, the reductive degradation of pollutants, in particular lignin or humic substances, is used in terms of technology.

12. The method according to claim 11, characterized in that both a reductive and an oxidative degradation of the pollutants takes place and that the degradation is used in terms of process technology.

13. The method according to any one of the preceding claims, characterized in that the resulting oxygen (O2) separated and od for the activation of biological treatment tanks. Like. environmentally friendly facilities.

14. The method according to any one of the preceding claims, characterized in that the pollutant degradation is operated as a process in the circulation with a biological stage.

15. The method according to any one of the preceding claims, characterized in that the process is operated with direct current.

16. The method according to any one of the preceding claims, characterized in that the process is galvanostatically operated and that a current density of about 2 to 500 mA / cm ² electrode surface is used.

17. The method according to any one of the preceding claims, characterized in that the direct current is pulsed fed.

18. The method according to any one of the preceding claims, character- ized in that the liquid treatment process is operated with alternating current, in particular triangular, sinusoidal and / or plateau, wherein the frequency of the alternating current is in the range of 10 ^{~ 3} to 1 Hz.

19. The method according to any one of the preceding claims, characterized in that the pollutants are organic dyes.

20. The method according to any one of the preceding claims, characterized in that the organic dyes are natural dyes,

21. The method according to any one of the preceding claims, characterized in that the organic dyes are synthetic dyes.

22. The method according to any one of the preceding claims characterized by a use in the printing industry

23. The method according to any one of the preceding claims characterized by a use in the textile industry.

24. An apparatus for carrying out the method according to claim 1 or one of claims 2 to 23 with means for the electrochemical generation of OH radicals, characterized in that an arrangement of alternating positive and negative electrodes are present, that corresponding electrodes (Hi, 21i) are arranged plane-parallel to each other and that an inlet and a drain (35, 36) is present, via which the liquid to be purified on or led away and is passed continuously past the electrodes.

25. The device according to claim 24, characterized in that the electrodes (Hi, 2I ₁ ) are formed radially symmetrically.

26. The device according to claim 24, characterized in that the electrodes (II _{i (} 21i) are formed cylindrically symmetrical.

27. The device according to claim 26, characterized in that the electrodes (Hi, 2I ₄ ) are nested.

28. The device according to claim 24, characterized in that the electrodes (Hi, 21χ) form a wire bundle.

29. The device according to claim 23, characterized in that the electrodes (Hi, 2Ii) are surface-structured.

30. Device after. Claim 24, characterized in that the electrodes (H ₄ , 2I ₁ ) of so-called MMO (mixed metal oxide) material are formed.

31. The device according to claim 30, characterized in that dieβ the MMO material diamond, platinum (Pt), silicon carbide (SiC), tungsten carbide (WC), titanium carbide (TiC), titanium nitride (TiN) and / or titanium carbon nitride (TiCN).

32. Device according to claim 24, characterized in that as positive electrodes (H ₁ ) consumable electrode materials, in particular iron (Fe), stainless steel alloys, aluminum (Al), aluminum alloys or carbon (C) are used.

33. Apparatus according to claim 24, characterized in that as negative electrode (2I ₁ ) electrode materials such as

Iron (Fe), stainless steel alloys, carbon (C) and / or aluminum (Al) are used.

34. Device according to one of claims 24 to 33, characterized in that between the electrodes (H ₁ , 2I ₁ ) separators for the separation of the electrode spaces are introduced.

35. Device according to one of claims 24 to 33, characterized in that means for an electrode cleaning are present.

36. Apparatus according to claim 35, characterized in that the means for cleaning the electrode are mechanical wipers / scrapers, ultrasound, and additives of corresponding floats in the liquid circuit.

37. Device according to one of claims 24 to 36, characterized in that a foam separator and / or a distributor is present.

38. Device according to one of claims 24 to 37, characterized in that a separation device for oxygen

(O2) and / or hydrogen (H ₂ ) is present.