Patent Application
20110017610
The invention relates to a device, a process and the use of such a device for breaking down pollutants in a liquid, in particular for breaking down pollutants in an aqueous medium.
The pollutants are broken down substantially through the oxidizing action of OH radicals. In order to break down the pollutants, the liquid is treated in a device which has an arrangement of positively and negatively charged electrodes, which are arranged in a container through which the liquid flows. The electrodes are separated from one another, in each case forming a working space. For the purpose of continuous treatment of the liquid, the latter is supplied to the working space by means of a feed and discharge. A device of this type and a process for operating such a device are proposed, for example, in the not previously published application: DE 10 2006 034 895.8 bearing the title: Process for removing pollutants from liquids and device for carrying out the process, dated Jul. 25, 2006.
In the effluents from the paper or pulp industry and also in the printing or textile industry, lignin, resins and humic substances are found. Lignin (Latin: lignum=wood) is understood to mean a phenolic macromolecule. Lignin in wood is a solid, colorless substance which is incorporated in the vegetable cell wall and thus effects the lignification of the cell. Humic substances are generally understood to be weakly brown to black organic substances which are generally formed in humic soils, have no reproducible chemical structure and have different properties and compositions. Lignin and humic substances in the sense of the present invention are understood to be the substantial pollutants in the effluent from the aforementioned industrial sectors.
Industrial effluents of this type have a high COD value (COD=Chemical Oxygen Demand). Such effluents need to be purified before their introduction into the general effluent system.
One possible process for purifying such effluents is the oxidation of the corresponding lignin or humic substances. The oxidation is carried out by introducing ozone (O3) into the effluent. Following introduction into water, ozone breaks down into OH radicals, which have an oxidizing action.
For the purpose of purifying effluents with ozone, what are known as ozonizers are used. Ozonizers use pure oxygen as starting material and generate ozone by means of a high voltage between 10 kV and 40 kV. Ozonizers have a poor efficiency.
On account of the poor efficiency and the fact that, for industrial processes, pure oxygen is normally used as starting material, the production of ozone with an ozonizer is expensive.
As an alternative to an ozonizer, electrochemical processes exist. By means of such processes, OH radicals are produced directly by an electrochemical route in the liquid to be purified. Electrochemical processes have a considerably higher overall efficiency as compared with ozonizers.
With the not previously published German patent application AZ 10 2006 034 895 from the applicant, bearing the title: “Process for removing pollutants from liquids and device for carrying out the process”, a process for the electrochemical production of OH radicals for the purification of industrial effluents, in particular for purifying the effluents from the paper industry, is proposed. In this process, the liquid to be purified is led through a chamber-like arrangement of alternating positively and negatively charged electrodes. The liquid to be purified is thus in direct contact with the electrodes.
In order to produce OH radicals, a specific quantity of charge is needed, which depends on the type of reaction. In addition, parasitic secondary reactions take place, which limit the efficiency. The power needed for the production of OH radicals is determined as the product of current (A) and voltage (V); the necessary energy in a corresponding way from the product of charge (A·s) and voltage (V).
In the following text, only an examination with respect to the energy is to be carried out.
Of the two parameters current (A) and voltage (V) which determine the energy needed for the OH radical production, only the voltage term can be influenced directly by means of an apparatus structure, since the current term (A), as mentioned above, is predefined by the chemical reaction of the OH radical formation.
The voltage term (V) is determined firstly by the half-reactions taking place at the electrodes. According to Ohm's Law V=RI, the voltage term (V) is, however, also determined by the resistance between the electrodes. The resistance present between the electrodes is in turn dependent on the electrolyte present between the electrodes and the spacing of the electrodes from one another.
The amount of energy for the electrochemical production of OH radicals decreases as the spacing of the electrodes from one another decreases. On account of recombination effects, which counteract the OH radical formation, the spacing of the electrodes cannot be reduced arbitrarily.
Taking this as a starting point, according to various embodiments, a device and a process for breaking down pollutants in a liquid can be specified which are improved with regard to the technical problems present in the prior art. In particular, the device and the process are intended to have an improved yield in relation to the electrochemical production of OH radicals.
According to an embodiment, a device for breaking down pollutants in a liquid, in particular for breaking down organic pollutants in an aqueous medium, by means of oxidizing OH radicals, may have—an arrangement of positively and negatively charged electrodes, which are separated from one another, forming a working space and—a feed and discharge, by means of which the working space is accessible to the liquid for the purpose of continuous processing of the latter, wherein—at least one of the positively or negatively charged electrodes, at least in the contact region between the liquid and the electrode, being surrounded by a separator, forming an electrode chamber, which reduces the working space between the electrodes, and wherein—the electrode chamber being filled with a conductive electrolyte.
According to a further embodiment, at least one negatively charged electrode can be surrounded by a separator and the electrode chamber is filled with an alkaline conductive electrolyte. According to a further embodiment, at least one positive electrode can be surrounded by a separator and the electrode chamber is filled with an acid conductive electrolyte. According to a further embodiment, all the positively or all the negatively charged electrodes can be in each case surrounded by a separator. According to a further embodiment, the separator can be fabricated from a microporous material. According to a further embodiment, the electrodes can be formed as plane-parallel surfaces. According to a further embodiment, one of the electrodes and the separator can be formed as hollow cylinders arranged substantially concentrically with respect to each other, and the further electrode is arranged in the center of the hollow cylinders. According to a further embodiment, the electrodes can be surface-structured. According to a further embodiment, the positive electrodes can be formed from MMO (Mixed Metal Oxide) material. According to a further embodiment, the positive electrode can be selected from at least one material from the material group comprising diamond, platinum, silicon carbide, tungsten carbide, titanium carbide, titanium nitrite, titanium carbon nitrite. According to a further embodiment, as the material for a positively charged electrode, consumable material is selected from at least one material from the material group comprising iron, stainless steel alloys, aluminum, aluminum alloys, carbon. According to a further embodiment, the material for a negatively charged electrode can be selected from at least one material from the material group comprising iron, stainless steel alloys, carbon, aluminum. According to a further embodiment, there can be means for electrode cleaning. According to a further embodiment, the means for electrode cleaning can be mechanical wipers/scrapers, ultrasound and/or additions of floating elements in the liquid. According to a further embodiment, there can be a foam separator. According to a further embodiment, a separating device for oxygen and/or hydrogen can be provided.
According to another embodiment, a process for breaking down pollutants in a liquid, in particular for breaking down organic pollutants in an aqueous medium, may comprises the following steps: —continuous feeding of the liquid by means of a feed and discharge into a working space, which is formed between mutually separated, positively and negatively charged electrodes of an arrangement, —electrochemical production of OH radicals in the liquid, at least one of the positively or negatively charged electrodes, at least in the contact region between the liquid and the electrode, being surrounded by a separator, forming an electrode chamber, and the separator reducing the working space between the electrodes, the electrode chamber being filled with a conductive electrolyte, —breaking down pollutants in the liquid by means of OH radicals.
According to a further embodiment, the electrochemical production of the OH radicals can be carried out with a voltage of <5 V. According to a further embodiment, the voltage can be a DC voltage. According to a further embodiment, the process may comprise galvanostatic performance, the current density on the electrode surfaces being between 2 mA/cm2 and 500 mA/cm2. According to a further embodiment, the DC voltage can be pulsed. According to a further embodiment, the electrochemical production of the OH radicals can be carried out with an alternating current, in particular with an alternating current in the form of a triangular, sinusoidal and/or plateau oscillation, the frequency of the alternating current lying between 10−3 Hz and 1 Hz. According to a further embodiment, a COD (Chemical Oxygen Demand) value can be used as a measure of the pollutant concentration and breakdown of the pollutants is measured by using a decline in the COD value. According to a further embodiment, the process may comprise the breaking down of non-biodegradable COD. According to a further embodiment, the process may comprise the generation of biodegradable COD. According to a further embodiment, before the electrochemical treatment of the liquid, mechanical pre-disintegration of solid constituents present in the liquid can be carried out. According to a further embodiment, the liquid can be UV-activated. According to a further embodiment, the process may comprise separation of oxygen arising in the process and use of the oxygen for the activation of biological settling tanks. According to a further embodiment, the pollutants can be primarily organic dyes. According to a further embodiment, the organic dyes can be natural dyes. According to a further embodiment, the organic dyes can be synthetic dyes.
According to yet another embodiments, a device as described above can be used in the paper or pulp industry, the printing or textile industry, to break down lignin or humin in the effluents from the respective industry.
Further possible configurations of the device according to various embodiments for breaking down pollutants and also of the process according to various embodiments for breaking down pollutants emerge from the description and also in particular from the highly schematic drawing, in which:
In the drawing, corresponding components are provided with the same designations. Parts not explained specifically are generally known prior art.
According to various embodiments: During the electrochemical production of OH radicals in an aqueous environment, the amount of energy needed decreases as the spacing of the electrodes from one another becomes smaller. Recombination effects prevent it from being possible for the plate spacing to be reduced as desired in order to increase the electrochemical chemical yield of OH radicals further. By means of a separator, which can be arranged between the electrodes, recombination effects can be reduced. The electrode reactions themselves, across which a certain voltage term drops, cannot be reduced by a separator, however. In order to reduce the effective electrode spacing, one of the two electrodes, that is to say the positively or negatively charged electrode, is surrounded by a separator in such a way that direct contact of the liquid to be purified with the corresponding electrode is no longer possible. The chamber between the corresponding electrode and the barrier surrounding it is filled with a highly conductive liquid. As a result, the non-reactive voltage drop between the electrode and separator is reduced greatly. In this way, the distance across which the voltage applied between the electrodes drops, i.e. the effective electrode spacing, is able to be reduced to the distance between a separator and the electrode respectively not surrounded by the separator, it being possible for recombination effects to be suppressed at the same time. The electrodes not surrounded by the separator are generally also designated as working electrode.
In the latter connection, a separator is understood to be a body made of a porous or microporous material, it being possible to use as material a hydrophilic polymer or one hydrophilized by means of appropriate surface treatment, such as polypropylene, polytetrafluoroethylene. Furthermore, the separator can consist of glass, glass mesh or nonwoven. The separator can have a pore volume between 25% and 95%, pores not accessible from the surface of the separator (closed porosity) not being taken into account.
According to the various embodiments, with reference to the device, the object is achieved with the following measures. A device for breaking down pollutants in a liquid, in particular for breaking down organic pollutants in an aqueous medium, through the oxidizing action of OH radicals is specified, this device comprising an arrangement of positively and negatively charged electrodes, which are separated from one another, forming a working space. The device further comprises a feed and discharge, by means of which the liquid is fed to the working space for the purpose of continuous processing of the former. At least one of the positively or negatively charged electrodes, in the contact region between the liquid and the electrode, is surrounded by a separator, forming an electrode chamber, the electrode chamber reducing the working space between the electrodes. The electrode chamber is also filled with a conductive electrolyte.
With the aid of the aforementioned measures according to various embodiments, it is possible to achieve an improved efficiency by an electrochemical route, which means that more effective purification of the liquid, in particular the breakdown of pollutants in a liquid, can be achieved. The device thus permits the more cost-effective breaking down of pollutants in the liquid.
Accordingly, the device according to other various embodiments can also have the following features:
With reference to the process, the object is achieved with the following measures: For breaking down pollutants in a liquid, in particular for breaking down organic pollutants in an aqueous medium, the process according to various embodiments may comprise the following steps. The liquid is fed continuously by means of a feed and discharge to a working space, which is formed between the mutually spaced positively and negatively charged electrodes of an arrangement. OH radicals are produced electrochemically in the liquid, at least one of the positively or negatively charged electrodes, in the contact region between the liquid and the electrode, being surrounded by a separator, forming an electrode chamber. The separator reduces the working space between the electrodes; the electrode chamber is filled with a conductive electrolyte. Pollutants which are present in the liquid are broken down by oxidation by means of OH radicals at the positive electrode or by reduction at the negative electrode.
According to various further embodiments, the process can be combined with various features. Accordingly, the process according to various embodiments can additionally have the following features:
The device according to various embodiments can be used in particular in the paper or pulp industry, the printing or textile industry, to break down lignin or humin in the industrial effluents.
In the aforementioned industries, lignin or humin constitutes an essential constituent part of the effluent contamination. Use of the device according to various embodiments or one of its developments is therefore particularly advantageous.
At least one negatively charged electrode 105, preferably some of the negatively charged electrodes 105 or, furthermore, preferably all the negatively charged electrodes 105a . . . c are surrounded in the same way by a separator 107. The separator 107 surrounds the negative electrodes 105a . . . c completely in such a way that no direct contact is possible between the liquid F to be purified present in the container 103 and the actual electrode 105a . . . c. The separator 107 surrounds the electrodes 105a . . . c, in particular in a contact region predefined by the height L of the liquid F in the container 103.
The separator 107, which can in particular be fabricated from a microporous material, reduces the size of the working space (A) between the electrodes 104a . . . 104c and 105a . . . 105c as a result of the fact that the electrode spacing 106 is reduced to an effective electrode spacing 108. The separator 107 surrounds the electrodes 105a . . . 105c, forming an electrode chamber 109. The electrode chamber 109 is filled with a highly conductive electrolyte E. According to the embodiment shown in
Within the liquid F to be purified which is located within the container 103, water is decomposed electrolytically at the positive electrode in accordance with the equation
H2O→H++OH*+e− (1)
At the positively charged electrodes 104a . . . 104c, the electrolytic decomposition of water with the production of OH radicals takes place in accordance with the above equation 1. The electrons (e−) are transported away via the positively charged electrodes 104a . . . 104c.
The H+ ions are transported away by means of ion conduction. In the process, the H+ ions pass the microporous separator 107 unhindered, and reach the negatively charged electrodes 105a . . . 105c.
The microporous separator 107, according to the exemplary embodiment shown in
The electric conductivity of a liquid F to be purified is generally of the order of magnitude of a few mS (e.g. between 1 and 10 mS) and is typically 4 mS. The electrode chamber 109 is filled with a highly conductive electrolyte E, which typically has an electric conductivity higher by several orders of magnitude, for example of 1000 mS. The drop in the voltage applied to the electrodes 104a . . . 104c and 105a . . . 105c of typically less than 5 V consequently takes place not across the electrode spacing 106 but across the effective electrode spacing 108, which is determined by the spacing of the separator 107 from the positively charged electrode 104a . . . 104c.
As a result of the processes described above, an increased concentration of OH radicals builds up in the region of the positively charged electrodes 105a . . . 105c. The OH radicals develop an oxidizing action on the pollutants present in the liquid F and in this way promote their breakdown. Those electrodes, specifically the positively charged electrodes 105a . . . c in the exemplary embodiment illustrated in
As an alternative to the exemplary embodiment shown in
The above-described process is designated reductive conversion.
In this case, there are no OH radicals and there is no oxidative conversion. The breaking down is carried out reductively, which means:
In the aforementioned processes of the oxidative or reductive conversion of pollutants which are present in the liquid F, it is possible for foam formation to occur in a device 100. For this purpose, a device of this type, as shown in
All the aforementioned exemplary embodiments can be developed subsequently with the measures cited below.
For instance, the electrodes can be surface-structured in order to enlarge their surface. Furthermore, the electrodes can be formed from an MMO material (Mixed Metal Oxide). Furthermore, for example, diamond, platinum, silicon carbide, tungsten carbide, titanium carbide, titanium nitrite and/or titanium carbon nitrite can be used for the construction of the positively charged electrodes 104a . . . 104c. In particular, positively charged electrodes 104a . . . 104c can be formed of consumable material such as in particular iron, stainless steel alloys, aluminum, aluminum alloys and/or carbon. The negatively charged electrodes 105a . . . 105c can be fabricated in particular from iron, stainless steel alloys, carbon and/or aluminum.
A device 100 for breaking down pollutants according to one of the exemplary embodiments shown in
In the following text, further possible configurations of a process for breaking down pollutants in a liquid F in accordance with various exemplary embodiments will be explained. For instance, the electrochemical production of the OH radicals can be carried out with a voltage of less than 5 V. Furthermore, the voltage for the production of the OH radicals can be a DC voltage. Furthermore, this DC voltage can be pulsed. Alternatively, the electrochemical production of OH radicals can be carried out with an alternating voltage. This alternating voltage can in particular have the form of a triangular, sinusoidal and/or plateau oscillation having a frequency between 10−3 Hz and 1 Hz. In general terms, the process for OH radical production can be carried out galvanostatically, it being possible for the current density on the electrode surfaces to be between 2 mA/cm2 and 500 mA/cm2.
The breakdown of pollutants can be measured by using the COD value (Chemical Oxygen Demand) as a measure of the pollutant concentration. Furthermore, it is possible to carry out in particular the breakdown of non-biodegradable COD and the generation of biodegradable COD.
Before electrochemical treatment of the liquid F to be purified, mechanical pre-disintegration of solid constituents possibly present in the liquid F can be carried out. Furthermore, the liquid F can be UV-activated. Oxygen and/or hydrogen arising during the process can be used for further processes. For instance, by means of the oxygen arising, which can be separated off from the process, a biological settling tank can be activated. The pollutants present in the liquid F to be purified can be, in particular, organic dyes. These organic dyes can be natural or synthetic dyes.
The aforementioned process according to one of the exemplary embodiments and the aforementioned device according to one of the exemplary embodiments can be used in particular in the paper or pulp industry and/or the printing or textile industry to break down lignin or humin in the industrial effluents.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2007 041 828.2 | Sep 2007 | DE | national |
This application is a U.S. National Stage Application of International Application No. PCT/EP2008/061501 filed Sep. 1, 2008, which designates the United States of America, and claims priority to German Application No. 10 2007 041 828.2 filed Sep. 3, 2007, the contents of which are hereby incorporated by reference in their entirety.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/061501 | 9/1/2008 | WO | 00 | 9/16/2010 |
