Patent Publication Number: US-2013228500-A1

Title: Apparatus for water treatment using filtration or a membrane separation method

Description:
The invention concerns an apparatus for water treatment by means of filtration or membrane separation method. 
     For treating raw water, process water or wastewater, different methods in separate processing stages are used. Known is mechanical cleaning by filtration or a membrane separation method. In filters that are used in dead-end operation but also on membranes that are operated in so-called cross flow, a cover layer is formed over time. This cover layer impairs the functionality of the filter or membrane and must be removed with high energetic and apparatus-technological expenditure. Partially, the cover layer formations are irreversible so that a removal is not possible and the entire membrane must be exchanged. Moreover, the membranes or filters tend to experience microbial contamination by microorganisms such as algae or bacteria so that chemicals that form undesirable by-products must be used for disinfection. 
     As a further processing stage a chemical treatment of the raw water, process water or wastewater by electrolytic oxidation is carried out. In this context, by electrochemical processes substances that act as disinfectant are generated from the water itself or from its natural ingredients. By electrolysis, water is split into the elements oxygen and hydrogen. In side reactions, disinfectant substances such as ozone (O 3 ) and OH radicals are formed at the anode and hydrogen peroxide (H 2 O 2 ) at the cathode. In addition, disinfectant components are formed by conversion of the chloride ions (Cl − ) that are contained naturally in the drinking water to hypochloric acid (HOCl) or hypochlorite ions (ClO − ). 
     The invention has the object to provide an improved method for treatment of drinking water and process water. 
     The invention is based on the idea of producing a membrane of an inert conductive material so that it can be used for mechanical separation methods as well as an anode for formation of hydroxyl radicals and reactive oxygen by electrolytic oxidation. In this way, in accordance with the invention an advantageous possibility is provided to combine membrane separation methods and chemical purification methods in water treatment. In this way, facilities and apparatus can be designed more compact, more energy-efficient and more cost-efficient. 
     It is particularly beneficial when the membrane is produced of ceramic, polymeric or metallic materials. Ceramic or polymeric materials are in general chemically inert and can be made conducting, for example, by admixture of conducting components to the starting material in a simple way. The invention can be realized even more simply when the membrane is produced, for example, of metallic materials, for example, foils. They are inherently conducting. 
     An advantageous embodiment of the invention provides that an anode is arranged at a permeate side. In this way, the oxidation agents which are formed preferably at the anode, for example, hypochlorite ions, ozone or hydroxide radicals, are directly formed in the medium to be oxidized and the two process steps of the mechanical separation, on the one hand, and of the electrolytic oxidation, on the other hand, are combined in an advantageous way. Accordingly, the apparatus of water treatment can be constructed to be more compact, more energy-efficient and more cost-efficient. 
     Moreover, it is proposed that the cathode is arranged on a retentate side. Accordingly, the oxidation agents are preferably formed in the feed stream and act thus on the membrane surface. Because of the oxidizing and thus also disinfecting action, microbiological activities on or in the membrane are prevented. Back-flushing for removal of a microbial cover layer, combined with high flow velocities that require an appropriately high energetic and apparatus expenditure are not required. In particular, an irreversible blocking of ceramic membranes with algae, for example, in seawater desalination is reduced. Irreversible means in this context that the a cover layer is formed by the algae growth on the membrane surface that cannot be removed by back-flushing or by addition of appropriate chemicals and therefore forces the premature exchange of the membrane. Accordingly, with the arrangement according to the invention the membrane becomes utilizable for a longer period of time. 
     A further advantageous embodiment resides in that the cathode is arranged at the feed or retentate side and a second cathode at the permeate side. In this way, electrical fields for generating disinfectant substances can be formed without great constructive or financial expenditure simultaneously at the retentate side and the permeate side. With the arrangement according to the invention, the retentate the permeate, and the membrane are simultaneously disinfected. Accordingly, the costs for a separate apparatus for disinfection of permeate or retentate are saved 
     Moreover, it is proposed to design an apparatus for water treatment comprising a filter surface, operated in as dead-end filtration in such a way that the filter surface is embodied as an anode. In this way, the filter surface combines two essential functions for the water treatment. On the one hand, it serves as a filter medium during filtration; on the other hand, it can be used as an anode for electrolytic disinfection. Accordingly, the mechanical purification of the wastewater by filtration and a chemical treatment by electrolytic oxidation can be combined advantageously in one apparatus so that the facilities for water treatment become more compact and cost-efficient. 
     A manufacturing-technologically simple solution is provided when the filter surface is produced of paper or fabric. Paper or fabric of natural fibers or synthetic fibers are in general inert and the introduction of conductive fibers can be effected in a simple way. 
     An advantageous embodiment of the invention provides that a cathode is arranged on a filtrate side. Accordingly, the oxidizing substances required for disinfection are formed by electrolysis directly in the medium to be disinfected and from the medium. Accordingly, the addition of dangerous chemicals that possibly may form poisonous by-products can be eliminated. Moreover, a complex facility technology as it is required, for example, for ozone treatment of drinking water is also not needed. 
     A further advantageous embodiment of the apparatus according to the invention provides that the cathode is arranged on a feed side. Accordingly, the oxidizing substances that are formed by electrolysis act on in the filter surface or in the filter cake and can immediately destroy thereat hazardous substances or microorganisms so that the danger of filter passage is minimized. 
     Moreover, it is proposed that the cathode is arranged on the feed side and a second cathode at the filtrate side. In this way, electrical fields for generating disinfectant substances can be formed without great constructive or financial expenditure simultaneously at the feed side and the filtrate side. With the arrangement according to the invention, the filter cake, the filtrate and the filter are simultaneously disinfected. In this way, the costs for a separate apparatus for disinfection of filtrate or filter cake are saved. 
     It is particularly beneficial when the anode is embodied to be inert with a surface of platinum or diamond. In the electrolysis of water anodes with such surfaces are characterized in that a particularly large quantity of oxidizing substances is formed on them. In particular, on diamond surfaces preferably hydroxide radicals (OH) are formed. These hydroxide radicals are extremely reactive and represent therefore a very good disinfectant agent. 
     It is moreover beneficial when a sacrificial anode is arranged in the flow direction upstream or downstream of the membrane or the filter surface and is constructively connected therewith. By using non-inert materials for the anode, for example, iron or aluminum, hydroxide flakes can be formed by electrolysis in a targeted fashion. These chemicals are suitable for targeted water treatment. For example, iron hydroxide has a decomposition-inhibiting action while aluminum hydroxide acts as a phosphate binder. 
     Further advantages and advantageous embodiments can be taken from the following drawings, their description, and the claims. All features disclosed in the drawings, their description, and the claims can be important for the invention individually as well as in combination with each other. 
    
    
     
       The drawings show in schematic illustration in: 
         FIG. 1  an embodiment of the invention in a first arrangement for membrane separation methods, 
         FIG. 2  a second arrangement for membrane separation methods, 
         FIG. 3  a third arrangement for membrane separation methods 
         FIG. 4  a second embodiment of the invention in a first arrangement for filtration methods, 
         FIG. 5  a second arrangement for filtration methods, and 
         FIG. 6  a third arrangement for filtration methods. 
     
    
    
       FIG. 1  shows a first example of application of the invention for a membrane separation method. Illustrated is in a schematic illustration a housing  10  of an apparatus for water treatment. Arranged therein is a membrane  12  embodied as an anode and separating a feed or retentate  14  of the apparatus from an outflow side  16 . At the outflow side  16  a cathode  18  is arranged. 
     The liquid that is supplied as feed  20  passes through the membrane  12 . In doing so, the substances to be separated are retained at the feed side  14  and are concentrated thereat and removed as a retentate  22 . At the same time, an electrical direct current or alternating current applied between the cathode  18  and anode leads to the formation of oxidizing or disinfectant substances on the basis of oxygen or chlorine. In the process, water is split by electrochemical reaction into the elements oxygen and hydrogen. As by-products, ozone (O 3 ) and OH radicals are generated at the anode  18 ; at the cathode  12  hydrogen peroxide (H 2 O 2 ). These substances have a disinfectant action. Native chloride ions (Cl − ) that are contained in the water react with direct current to hypochloric acid (HOCl) or hypochlorite ions (ClO − ) which also act disinfectantly. 
     The substances that are formed in this way pass directly into the water to be treated at the feed side  14  and purified water  24  exits the apparatus at the outflow side  16 . 
     The kind and quantity of oxidizing or disinfectant substances depend inter alia on the employed anode material and the ingredients of the water. 
       FIG. 2  shows a second arrangement according to the invention for membrane separation methods wherein the cathode  18  is arranged at the feed side  14 . In this connection, the oxidizing or disinfectant substances are formed at the feed side  14  and effect thereat oxidation or disinfection of the retentate  22  and the surface of the cathode  12 . 
     In  FIG. 3 , a third arrangement according to the invention for membrane separation methods is illustrated. In this context, a cathode  18  is arranged at the feed side or retentate side  14  and a second cathode  25  at the permeate side  16 . Between them, the membrane  12  that is embodied as an anode is arranged. By applying an electrical direct current or alternating current, between the cathodes  18  and  25  and the anode  12  an electrical field is generated and under its effect the disinfectant substances are formed. With the arrangement according to the invention the substances are formed at the permeate side  16  as well as at the retentate side  14 . In this way, the disinfection and oxidation of retentate  22 , membrane surface and permeate  24  are performed simultaneously. 
     In  FIG. 4 , an example of application of the invention for filtration methods is illustrated. In this context, a filter surface  26  is embodied as an anode. The filter surface  26  separates in the housing  10  the feed side  14  from the outflow side  16 . The cathode  18  is arranged at the feed side  14 . The liquid that is supplied as feed  20  passes through the filter surface  26 . The substances that are entrained in the feed  20  are separated at the filter surface  26  and form successively a filter cake (not illustrated). A filtrate  28  exits the housing  10  at the outflow side  16 . Between cathode  18  and the filter surface  26  embodied as an anode, disinfectant and oxidizing substances are formed by application of a direct current in accordance with the identical mechanism as in the previously described membrane separation methods. 
     They inhibit biological activities in the filter cake and decompose harmful substances in the filter surface  26  or the filter cake. 
       FIG. 5  shows a second arrangement according to the invention for filtration methods. The anode  18  is arranged on the outflow side  16 . The oxidizing and disinfectant substances are formed in the filtrate  28  and act thereat such that disinfected, oxidized filtrate  28  is discharged. 
     In  FIG. 6 , a third arrangement of the invention for filtration methods is illustrated. A cathode  18  is arranged at the feed side  14  and a second cathode  25  at the filtrate side  16 . Between them, the filter surface  26  is arranged that is embodied as an anode. By applying an electrical direct current or alternating current between the cathode  18  and  25  and the anode  26 , an electrical field is generated and under its effect the disinfectant substances are formed. With the arrangement according to the invention, the substances are formed at the filtrate side  16  as well as at the feed side  14 . Accordingly, the disinfection and oxidation of filter cake, filter surface  26  and filtrate is carried out simultaneously