Title of Invention

AN ELECTROCHEMICAL DEVICE TO REMOVE ARSENIC FROM GROUND WATER AND SURFACE WATERS

Abstract

In the present invention there is provided an electrochemical device for removing arsenic from water which consists of a three stage electrochemical reactor equipped with a plurality of both stable and soluble electrodes. The combination of electrodes can simultaneously oxidize the arsenite present in the contaminated water and generate an adsorbent in-situ on which arsenic is adsorbed and removed from water. Stable electrodes such as titanium metal coated with oxides of Ru/Tn/lr are fitted in the first chamber, whereas both stable and soluble electrodes are placed in the second chamber and the third chamber is fitted with only soluble electrodes. The treated water can be further passed through known filter, activated carbon and UV-lighting to remove suspended solids, dissolved organics and pathogenic bacteria.

Full Text

The present invention relates to an electrochemical device to remove arsenic from ground and surface waters. This invention is particularly useful for the remediation of arsenic from ground water and the effluents containing arsenic. Arsenic is a toxic element that naturally occurs in a variety of forms in the earth. Under normal conditions, arsenic is found dissolved in aqueous systems in trivalent arsenite and pentavalent arsenate oxidation states. Arsenic in natural water may originate, for example, from geo-chemical reactions, industrial waste discharges and arsenic containing pesticides. Ground water for human consumption should be free from arsenic since it is toxin. The ground water bodies in West Bengal, Bangaladesh and part of USA are contaminated with arsenic. In West Bengal, India, an estimated 2,00,000 people currently suffer from arsenic induced skin lesions, some of which have advanced to pre-cancerous hyperkeratoses. The effective removal of arsenic by coagulation technique requires the arsenic to be in the arsenate form. Arsenite, in which the arsenic exists in the +3 oxidation state, is only partially removed by adsorption and coagulation techniques. Various technologies have been used in the past to remove arsenic from aqueous systems. The common methods involving adsorbents such as alumina and activated carbon, ion- exchange resins and electro dialysis are reported. An US patent number 6461535 dated 2002-10-08 filed by De Esparza Maria Luisa revealed a process involving (a) contacting with clay, a coagulant and an oxidizer with water containing arsenic to form a coagulated colloidal mixture (b) adsorbing the arsenic onto the coagulated colloidal mixture and (c) separating the water from the coagulated colloidal mixture for removing arsenic from ground water. The invention also provides a composition ready for use in removing arsenic from ground water to be used in remote areas. The composition includes activated clay, a coagulant and an oxidizer in pre-determined proportions for efficient removal of arsenic from ground water. A patent CA2327065 dated 2001-05-29 by Miyamoto Henry described an in-situ removal of arsenic from well water contaminated by arsenic. A reactive adsorptive barrier consisting of iron containing material and filter media surrounding the screened casing of the well was described. An another method (patent number US20030196961 dated 2003-10-23) wherein finely divided metallic iron in the presence of powdered elemental sulfur or other sulfur compounds such as manganese sulfide, followed by an oxidation step was provided to remove arsenic and TOC from drinking water or waste waters. A method (patent number US2004222162 dated 2004-11-11) for removing arsenic from water by using a reactor that is provided with a fluidized bed of carriers is disclosed. An arsenic containing influent is mixed in the reactor with a sulfide aqueous solution or metallic salt aqueous solution at a predetermined pH, thereby arsenic is converted to arsenic sulfide or arsenic acid metal salts. The arsenic contained in the influent is later removed by crystallization. An effluent with a reduced arsenic content in discharged from the reactor. The carriers, on which the crystals are formed, are periodically removed from the reactor, which is replenished with fresh carriers. An invention (patent number US2004262225 dated 2004-12-30) comprising a method and composition using akaganeite, an iron oxide, as an ion adsorption medium for the removal of arsenic from water and affixing it onto carrier media was disclosed. A system (patent number US6821434 dated 2004-11-23) for removing arsenic from water by addition of inexpensive and commonly available magnesium oxide, magnesium hydroxide and calcium oxide to the water was disclosed. A process for the separation of pentavalent arsenic from an aqueous solution using an N- alkyl pyridinium containing adsorption medium is disclosed in a patent CN1262665 dated 2000-08-09. An oxidizing medium and process for the oxidation of trivalent arsenic to pentavalent arsenic with removal of pentavalent arsenic so formed is also disclosed. A method for the treatment of wastewaters containing heavy metals and/or arsenic and/or non-organic anions was disclosed in a patent WO0234676 dated 2002-05-02. The said treatment is carried out in the galvanic cell, which consists of a mixture of metallic materials with various carbon-containing materials in the presence of a chemical resistant filter. A heat-treated carbon containing material, an acid/alkali resistant metallic material is used as a chemical resistant filter.A process for removing arsenic aqueous streams by (1) treating the feed with a compound containing cerium in the +4 oxidation state, preferably cerium dioxide, to oxidize arsenic in the +3 oxidation state to arsenic in the +5 oxidation state and (2) removing the arsenic in the +5 oxidation state from the aqueous phase, normally by contacting the treated feed with alumina or other precipitating agent containing cations in the +3 oxidation state was described in a patent WO 2004067452 dated 2004-08-12. A process for the preparation of arsenic free water, apparatus therefore, method for the manufacture of porous ceramics for use in pressure filtration to produce arsenic free water was described in a patent US20030183579 dated 2003-10-02. In all the above methods/processes either chemicals, or fine powders, which in turn are hazardous, were used to remove arsenic from water. A better process was disclosed in a patent RU2214968 dated 2003-10-27 wherein electrochemical processes for purifying natural and sewage waters containing arsenic compounds. Method comprises steps of electric coagulation in diaphragm-free electrolyzer having steel consumable anodes and placed in autoclave while supplying oxygent at a pressure 0.2 MPa. Another electrochemical invention (US20020036172 dated 2002-03-28) describes a process and apparatus for the removal of arsenic from water. The process consists in promoting the circulation of the water to be treated in an electrolytic cell equipped with iron or iron alloy electrodes while the contemporary insufflation into the cell of a gas, partially or totally, composed of oxygen. A device (US2003183516 dated 2003-10-02) for the decontamination of water, particularly of heavy metals and/or arsenic by means of electrolysis wherein the water to be purified is fed through a receptacle and passes by electrodes of different polarities. According to the invention, a combination of electrodes made from iron, aluminium and graphite or from aluminium and graphite is used. The drawbacks of the above inventions are: 1. The chemicals used for oxidation and adsorption may continue to remain in water if the dosage is excess. Generally the level of arsenic contamination will vary from source to source and also from time to time. Under such conditions it is difficult to arrive at exact dosage required for arsenic decontamination. If the dosage is less, the removal of arsenic is incomplete. In electrochemical processes, carbon-containing materials was used. Most of the carbon electrodes will disintegrate and very frequently these electrodes are to be replaced for better performance. 2. In certain cases, ion exchange membranes are used to adsorb arsenic compounds. The performance of the membrane will gradually decrease and when the surface sites are saturated, a separate process is required to regenerate the original surface. The membrane is to be replaced after certain period. The main object of the present invention is to provide an electrochemical device to remove arsenic from ground and surface waters, which obviates the drawbacks as detailed herein above. Another object of the present invention is to provide a device by which effective removal of both arsenite and arsenate can be achieved. Yet another object of the present invention is to provide a device by which power can be reduced and economic operation is assured. Still another object of the present invention is to provide an electrochemical device by which pollutant waters containing arsenic are effectively removed by oxidation, adsorption and coagulation. Still yet another object of the present invention is to provide a single and compact electrochemical device wherein arsenite can be converted to arsenate. A further object of the present invention is to provide an electrochemical device wherein fresh adsorbent can be generated in-situ, that too continuously. A still further object of the present invention is to provide an electrochemical device wherein oxygen can be generated in-situ. A yet further object of the present invention is to provide an electrochemical device wherein ferrous can be oxidized to ferric state. Another object of the present invention is to provide an electrochemical device with stable electrodes that can withstand corrosion. Yet another object of the present invention is to provide an electrochemical device with electrodes of long life. Still another object of the present invention is to provide an electrochemical device that can be operated continuously for the removal of arsenic from aqueous solutions. Still yet another object of the present invention is to provide an electrochemical device that can be retrofitted to any of the existing domestic water purifier systems. A further object of the present invention is to provide an electrochemical device wherein the entire spectrum of pathogenic bacteria present in the water source can be inactivated and eliminated. In the present invention there is provided an electrochemical device for removing arsenic from water which consists of a three stage electrochemical reactor equipped with a plurality of both stable and soluble electrodes. The combination of electrodes can simultaneously oxidize the arsenite present in the contaminated water and generate an adsorbent in-situ on which arsenic is adsorbed and removed from water. Stable electrodes such as titanium metal coated with oxides of Ru/Tn/Ir are fitted in the first chamber, whereas both stable and soluble electrodes are placed in the second chamber and the third chamber is fitted with only soluble electrodes. The arsenite present in water is oxidized to arsenate in the first stage with the help of stable electrodes. Subsequently, in the second stage the water is passed through a set of both soluble and stable electrodes arranged in proximity, wherein soluble iron electrodes release ferrous ions which in turn are oxidized to ferric with the help of stable electrodes arranged adjacent to the said iron electrodes. Finally, in the third stage the water is passed through a set of iron electrodes that aid coagulation of suspended solids. This treated water can be further passed through known filter, activated carbon and UV-lighting to remove suspended solids, dissolved organics and pathogenic bacteria. In the drawings accompanying this specification, figure-1 shows a schematic flow diagram and layout of components including the electrochemical device of the present invention and figure-2 depicts an embodiment of the electrochemical device of the present invention for the purification of contaminated water. The detailed flow diagram and layout of components including the electrochemical device of the present invention is shown in figure-1. Ground water or water contaminated with arsenic is transferred to a storage tank marked as (1). From the storage tank (1), the water is allowed to flow into the electrochemical device of the present invention marked as (3) through a control valve marked as (2) for control of the water flow rate. Power is supplied to the electrochemical device by a DC power source marked as (10). The treated water containing iron oxy-hydroxide (in-situ generated adsorbant) is subjected to filtration by a known filter device marked as (4). The clean water free from suspended solids is sucked out from the filter device with the help of the known suction pump marked as (5), and allowed to pass through a known cartridge filter marked as (6) filled with activated carbon. The clean and transparent water is further passed through a container marked as (7) containing ultraviolet lamp. Power is supplied to the suction pump (5) and ultraviolet lamp by a power source marked as (9). The water free from arsenic, suspended solids, dissolved organics and pathogenic bacteria that come out from (7) is collected in a clean tank marked as (8). In figure-2 is shown an embodiment of the electrochemical device of the present invention for the purification of contaminated water. The electrochemical device of the present invention as shown in figure-2 is fitted with both stable and soluble electrodes marked as (13). Stable electrodes such as titanium metal coated with oxides of Ru/Tn/lr are fitted in the inner chamber marked as (14), whereas both stable and soluble electrodes are placed in the middle chamber marked as (15). The outer chamber marked as (16) is fitted with only soluble electrodes. The contaminated water is initially directed into the inner chamber fitted only with stable electrodes through an inlet marked as (11). In this chamber, the arsenite present in water is oxidized to arsenate form. The oxidized water subsequently flows in to the middle chamber by gravity. While soluble electrodes generate metal oxy-hydroxy species, the stable electrodes oxidize the Fe2+ ions to Fe3+ ions. The wastewater from the middle chamber automatically enters in to the outer chamber where the colloidal iron oxy-hydroxide is coagulated. The processed water along with suspended solids is taken out from the electrochemical device through an outlet marked as (12) and further processed by conventional methods to remove solids. The electrochemical device is provided with DC power supply (10) and support legs marked as (17). Accordingly, the present invention provides an electrochemical device for removing arsenic from ground and surface waters, which comprises a three stage electrochemical reactor consisting in combination a plurality of both stable and soluble electrodes arranged in parallel in close proximity without short-circuiting; wherein the first stage chamber has a plurality of stable electrodes such as titanium metal coated with oxides of Ru/Tn/lr; whereas the second stage chamber being provided with a plurality of both stable and soluble electrodes and the third stage chamber having only soluble electrodes. In an embodiment of the present invention, the anodes are dimensionally stable electrodes such as iron, aluminium, platinum, platinized titanium, sub-stoichiometric titanium oxide metal, electro catalytic and isomorphous metal oxides such as lrO2, TaO2, RuO2 and titanium coated with oxides of Ir/Ru/Ta. Considering the factors such as cost, stability and nature of duty to be performed makes the selection of appropriate anode material. In another embodiment of the present invention, the cathode materials include iron, platinized titanium, titanium coated with oxides of Ir/Ru/Ta, platinum and aluminium. In still another embodiment of the present invention, the electrodes are arranged in alignments capable of providing improved efficiency such as vertical to the bottom of the reactor or horizontal. In yet another embodiment of present invention, the number and quantity of anodes and cathodes is dependent on the nature and extent of arsenic contamination. In still yet another embodiment of the present invention, the anodes and cathodes are arranged in parallel in close proximity with a minimum gap of the order of 2 mm and separated by non-conducting spacers. In a further embodiment of the present invention, the geometry of the electrodes are either in the form of rods of cylindrical, square, rectangular and other shapes or plates of different geometry or mesh or screen of any geometry. In a yet further embodiment of the present invention, the anode and cathodes are connected to the respective positive and negative leads of a variable DC power source. In a still further embodiment of the present invention, the three stage set-up consisting of a plurality of both stable and soluble electrodes directs the flow of the arsenic contaminated water into the first stage where it comes in contact with only stable electrodes such as titanium coated with oxides of Ta/Ru/lr and in the second stage, the water comes in contact with electrodes where titanium coated with oxides of Ta/Ru/lr and iron are connected to anode and iron connected to cathode; and finally in the third stage the water comes in contact with anodes and cathodes where both are iron electrodes. In another embodiment of the present invention, the electrochemical reactor is left open to atmospheric pressure and the flow is maintained by gravity. In a still another embodiment of the present invention, the electrochemical device to remove arsenic from ground water and surface waters comprises a rigid non conducting container (3) divided into multiple compartments (14, 15 & 16) open to atmosphere and each compartment being equipped with atleast one anode and one cathode (13) separated by a minimum distance of 2 mm and positioned in an electrolyzer zone ensuring connection of anodes and cathodes to respective leads of a DC power source (10); wherein the inner compartment (14) having a water inlet (11) being provided with only stable electrodes such as titanium metal coated with oxides of Ru/Tn/lr; the middle compartment (15) having both stable and soluble electrodes (13) and the outer compartment (16) being fitted with only soluble electrodes and having a water outlet (12). In a further embodiment of the present invention, the inlet (11) of electrochemical device (3) is connected through a control valve (2) to an arsenic contaminated water supply source (1) and the outlet (12) of the said the electrochemical device (3) being connected in tandem to a clean tank marked as (8) through a known water filter device (4), a known suction pump (5), a known cartridge filter (6) filled with activated carbon and a container (7) containing ultraviolet lamp; the said electrochemical device (3) being connected to a DC power source (10) and the suction pump (5) and ultraviolet lamp being connected to a power source (9). Initially the water containing arsenic from tank (1) is allowed to flow through an inlet (11) in to the first compartment (14) where the stable electrode like titanium coated with oxides of Ru/Ta/lr was used as anode and cathode, water flows in to the second compartment (15) where the titanium coated with oxides of Ru/Ta/lr and Fe as anodes and Fe as cathodes and finally the water flows through the third compartment (16) where Fe electrodes are used as anodes and cathodes. The water from the outlet (12) of the electrochemical device is further subjected to filtration (4), UV radiation (7) and passed through a cartridge containing activated carbon (6). The water flow is controlled by using suitable gadgets such as control valve (2) and pump (5). The electrochemical device of the present invention for removing arsenic from water comprises of an electrochemical device equipped with electrodes of both stable and soluble arranged in such a way that the arsenite is oxidized to arsenate in the first stage with the help of stable electrodes and subsequently passed through a set of iron electrodes which release ferrous ions which in turn are oxidized to ferric with the help of stable electrodes arranged adjacent to iron electrodes and finally through a set of iron electrodes that aid coagulation of suspended solids and thus treated water can be allowed to pass through a filter, activated carbon and UV-lighting to remove suspended solids, dissolved organics and pathogenic bacteria. The important features of the invention have thus been rather broadly outlined. There are additional features of the invention that will be described hereinafter forming the subject matter of the claims appended hereto. It should be appreciated by those skilled in the art that the disclosed specific methods and structures might be used as a basis for modifying or designing other methods and structures for carrying out the same purpose of the present invention. Such similar equivalent devices and structures do not depart from that spirit and scope of the invention as set forth in the suspended claims. It is to be understood that the invention is not limited in its application to the details of construction and arrangement of the components. The invention is capable of other embodiments and of being practiced and carried out in various ways. Novelty of the invention is that the oxidation of arsenite, ferrous iron is instantaneous and the oxidation, adsorption and coagulation are achieved in a single electrochemical reactor. This has been made possible by the no-obvious inventive steps of providing in combination a three stage electrochemical reactor consisting of a plurality of both stable and soluble electrodes; wherein the first stage chamber consists of a plurality of stable electrodes; whereas the second stage chamber has a plurality of both stable and soluble electrodes and the third stage chamber is provided with only soluble electrodes. This enables in situ generation of the adsorbent and varying the current can produce the quantity of the adsorbent required. Above all, electrodes that can resist corrosion are incorporated in the electrochemical reactor. The life of the electrodes used for oxidation purpose is long, of the order of 5 -10 years, and free from maintenance. There is no disintegration of electrodes as observed in the case of carbon/graphite electrodes. Thus sludge generation can be avoided. There is no need for pH adjustment. A further novelty of the invention is that there is no need to add oxidizing chemicals for the oxidation of arsenite and ferrous iron. It can be achieved by direct anodic oxidation or indirectly by the oxidizing agents generated from the electrodes. Similarly, the adsorbent also can be generated in-situ by anodic oxidation of iron. Thus both adsorbent and oxidation processes could be achieved in the electrochemical device. Yet another novelty of this process is the electrodes. Titanium coated with oxides of Ru/Tu/lr, which are very effective and durable, was used. Still another novelty is the compactness of the electrochemical device. The following examples are given by way of illustration of the electrochemical device of the present invention for removing arsenic from water in actual practice and therefore should not be construed to limit the scope of the present invention in any way. Example -1 Water samples containing 1 ppm of arsenite were processed as per the flow chart shown in figure-1 of the drawings. Separate test bypassing the electrochemical device was also conducted to demonstrate the effectiveness of electrochemical device. The initial concentration of arsenic and the final concentration of arsenic after processing was analyzed and shown in the table given below. The electrochemical device with other accessories was taken to the field and field tests were conducted by drawing ground water from bore wells. Ground water contaminated with arsenic was processed and the results obtained are given below. (Table Removed) The above results clearly demonstrate the effectiveness of the electrochemical device of the present invention irrespective of the source and the level of arsenic contamination in the ground water. Example - 3 Water containing arsenic was continuously passed through the electrochemical device of the present invention over a period of 40 minutes and the water was analyzed under steady state conditions and the results obtained are as presented below. (Table Removed) The main advantages of the present invention are: 1. The electrochemical device is simple and effective. 2. The adsorbent is generated in-situ. 3. The arsenite and ferrous ions is instantaneously oxidized without the addition of oxidizing agents. 4. The coagulation of the suspension is ensured. 5. The energy consumption is low. 6. The life of the electrodes is long. We claim: 1. An electrochemical device for removing arsenic from ground and surface waters, which comprises a three stage electrochemical reactor consisting in combination a plurality of both stable and soluble electrodes arranged in parallel in close proximity without short-circuiting; wherein the first stage chamber has a plurality of stable electrodes such as titanium metal coated with oxides of Ru/Tn/lr; whereas the second stage chamber being provided with a plurality of both stable and soluble electrodes and the third stage chamber having only soluble electrodes. 2. An electrochemical device as claimed in claim 1, wherein the anodes are dimensionally stable electrodes such as iron, aluminium, platinum, platinized titanium, sub-stoichiometric titanium oxide metal, electro catalytic and isomorphous metal oxides such as lrO2, TaO2, RuO2 and titanium coated with oxides of Ir/Ru/Ta. Considering the factors such as cost, stability and nature of duty to be performed makes the selection of appropriate anode material. 3. An electrochemical device as claimed in claim 1-2, wherein the cathode materials include iron, platinized titanium, titanium coated with oxides of Ir/Ru/Ta, platinum and aluminium. 4. An electrochemical device as claimed in claim 1-3, wherein the electrodes are arranged in alignments capable of providing improved efficiency such as vertical to the bottom of the reactor or horizontal. 5. An electrochemical device as claimed in claim 1-4, wherein the number and quantity of anodes and cathodes is dependent on the nature and extent of arsenic contamination. 6. An electrochemical device as claimed in claim 1-5, wherein the anodes and cathodes are arranged in parallel in close proximity with a minimum gap of the order of 2 mm and separated by non-conducting spacers. 7. An electrochemical device as claimed in claim 1-6, wherein the geometry of the electrodes are either in the form of rods of cylindrical, square, rectangular and other shapes or plates of different geometry or mesh or screen of any geometry. 8. An electrochemical device as claimed in claim 1-7, wherein the anode and cathodes are connected to the respective positive and negative leads of a variable DC power source. 9. An electrochemical device as claimed in claim 1-8, wherein the three stage set-up consisting of a plurality of both stable and soluble electrodes directs the flow of the arsenic contaminated water into the first stage where it comes in contact with only stable electrodes such as titanium coated with oxides of Ta/Ru/Ir and in the second stage, the water comes in contact with electrodes where titanium coated with oxides of Ta/Ru/Ir and iron are connected to anode and iron connected to cathode; and finally in the third stage the water comes in contact with anodes and cathodes where both are iron electrodes. 10. An electrochemical device as claimed in claim 1-9, wherein the electrochemical reactor is left open to atmospheric pressure and the flow is maintained by gravity. 11. An electrochemical device as claimed in claim 1-10, wherein the electrochemical device consists of a rigid non conducting container (3) divided into multiple compartments (14, 15 & 16) open to atmosphere and each compartment being equipped with atleast one anode and one cathode (13) separated by a minimum distance of 2 mm and positioned in an electrolyzer zone ensuring connection of anodes and cathodes to respective leads of a DC power source (10); wherein the inner compartment (14) having a water inlet (11) being provided with only stable electrodes such as titanium metal coated with oxides of Ru/Tn/lr; the middle compartment (15) having both stable and soluble electrodes (13) and the outer compartment (16) being fitted with only soluble electrodes and having a water outlet (12). 16 12. An electrochemical device as claimed in claim 1-11, wherein the inlet (11) of electrochemical device (3) is connected through a control valve (2) to an arsenic contaminated water supply source (1) and the outlet (12) of the said the electrochemical device (3) being connected in tandem to a clean tank marked as (8) through a known water filter device (4), a known suction pump (5), a known cartridge filter (6) filled with activated carbon and a container (7) containing ultraviolet lamp; the said electrochemical device (3) being connected to a DC power source (10) and the suction pump (5) and ultraviolet lamp being connected to a power source (9). 13. An electrochemical device for removing arsenic from ground and surface waters, substantially as herein described with reference to the examples and drawings accompanying this specification.

Documents:

642-del-2006-Abstract-(13-01-2014).pdf

642-del-2006-abstract.pdf

642-del-2006-Claims-(13-01-2014).pdf

642-del-2006-claims.pdf

642-del-2006-Correspondence Others-(13-01-2014).pdf

642-del-2006-correspondence-others 1.pdf

642-del-2006-correspondence-others.pdf

642-del-2006-description (complete).pdf

642-del-2006-drawings.pdf

642-del-2006-form-1.pdf

642-del-2006-form-18.pdf

642-del-2006-form-2.pdf

642-del-2006-form-3.pdf

642-del-2006-form-5.pdf