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Electrochemical treatment of ammonia in waste-waterRelated Patent Categories: Chemistry: Electrical And Wave Energy, Apparatus, Electrolytic, Cells, With Feeding And/or Withdrawal Means, Gas WithdrawalElectrochemical treatment of ammonia in waste-water description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060131168, Electrochemical treatment of ammonia in waste-water. Brief Patent Description - Full Patent Description - Patent Application Claims
[0001] This invention relates to the breakdown of dissolved ammonia and ammonium, in waste-water, and to the desideratum of discharging the resulting nitrogen in the form of nitrogen gas. It is known that treatment of ammonium-water by electrolysis can release the nitrogen in the form of nitrogen gas, and the present invention aims to improve the cost-effectiveness of that electrolysis technology. BACKGROUND TO THE INVENTION [0002] The traditional non-electrolytic methods of breaking down and removing ammonia and ammonium from water have basically involved engineering a system which exposes the water to oxygen. The oxidation reactions are promoted, which usually have had a high aerobic micro-biological component. However, such oxidation reactions predominantly leave the nitrogen in the form of (dissolved) nitrate and of the various (gaseous) oxides of nitrogen. These nitrogen compounds themselves can be health hazards, and should not be simply discharged into the environment, at least not in the large quantities that arise from treating waste-water. [0003] Patent publication U.S. Pat. No. 6,083,377 (Lin+Shelp, July 2000) describes the use of electrolysis, in effecting the direct breakdown of ammonium to nitrogen gas. Effective though it can be, under many conditions, the disclosed electrolysis technology works best when the concentration of ammonium is high. When the concentration is low, the amount of electrical energy needed to drive current through the electrolytic cells can spoil the economics of the process. If the energy usage is kept economical, the ammonium content of the discharged water, though diminished, still might be too high. [0004] It is an aim of the present invention to provide (a) that the ammonium in waste-water is converted, by electrolysis, directly to nitrogen gas; (b) that the concentration level of ammonia and ammonium in the discharged water is acceptably low; and yet (c) that only an economic amount of electrical energy is required. [0005] Breaking down ammonium by electrolysis, when properly engineered and operated, avoids the formation of the unwanted and toxic oxidation products. Also, it is recognised that electrolytic treatment is much less dependent on ambient temperature than aerobic micro-biological oxidation. That is to say, electrolysis is a preferred method, especially in cold climates, for achieving the required diminishment of ammonium, if it could be done more economically. THE INVENTION IN RELATION TO THE PRIOR ART [0006] In the invention, preferably an ammonium-extraction-and-transfer station is provided, in which the ammonium is taken out of solution from the stream of waste-water. Preferably, the extracted ammonium is transferred back into solution, but now into a body of secondary-water. Preferably, the secondary-water does not mix with the waste-water. [0007] The body of secondary-water is provided as a vehicle for receiving the ammonium extracted from the waste-water. Now, the designer can engineer the system to ensure that the waste-water discharged from the apparatus has a low enough ammonium content that the treated waste-water can be discharged into the environment, while at the same time ensuring that the ammonium concentration in the secondary-water is considerably higher than was the concentration in the incoming waste-water. [0008] It is recognised that the designer can focus on engineering the ammonium treatment when the ammonium is in the secondary-water, whereas, when the ammonium is in the waste-water, it was all too possible that having to deal with the flow of waste-water could compromise the engineering of the ammonium treatment. The ammonium in the secondary-water, being more concentrated than the ammonium in the incoming waste-water, is easier to treat, in that the higher the concentration, the greater the rate at which the break-down reactions can take place. This would be true even if the ammonium were to be removed by the traditional aerobic microbial oxidation methods. However, it is recognised that the higher concentration of ammonium in the body of secondary-water makes it hugely more economical to extract the ammonium from the secondary-water by electrolysis, than it was to extract the ammonium from the waste-water itself, directly, by electrolysis. [0009] Preferably, the secondary-water is circulated through an electrolytic cell, whereby the ammonium in the secondary-water is broken down. Preferably, the cell is operated in such manner that the redox voltage of the secondary-water (the electrolyte comprising the secondary-water) and the pH of the secondary-water, are such that the ammonium breaks down in such manner that the nitrogen component of the ammonium takes the form of nitrogen gas. The said U.S. Pat. No. 6,083,377, to which attention is hereby directed, shows how to operate an electrolytic cell such that the desired conditions of Eh and pH can be realised, which will lead to the formation of nitrogen gas. [0010] It is recognised that the amount of electrical energy needed to break dissolved ammonium down to nitrogen gas is well within the limits of what is economically practical, under a wide range of conditions, when the electrolysis is done on the secondary-water. By contrast, when the electrolysis was done on the waste-water directly, only under a narrow range of conditions could the system be run economically. It is recognised in the invention that the conversion of dissolved ammonium directly to nitrogen gas can be engineered substantially more cost-effectively when the ammonium has been transferred out of the waste-water and into the secondary water, than when the ammonium was dissolved in the waste-water itself. [0011] The invention aims to provide a system in which the treated waste-water is discharged with only a negligibly-low ammonium content, yet which can be run economically under a wide range of conditions. [0012] In the systems as described herein, the ammonium is taken out of the stream of waste-water, and transferred to the body of secondary-water. This can be accomplished in a number of ways, of which two are described in detail. The electrolysis step, which is carried out on the secondary-water, and which converts the dissolved ammonium to nitrogen gas, can be carried out economically in the two cases. [0013] The two ways in which ammonium can be extracted from the waste-water stream and placed in solution in the secondary water are referred to in this specification as the ion-exchange system and the alkali-acid system. [0014] The ion-exchange system is preferred when dealing with large quantities of waste-water in which the ammonium concentration is medium to low. The alkali-acid system is more suitable when the ammonium concentration in the waste-water is higher. In many installations, it happens that, when a high-volume low-concentration stream is present, a low-volume high-concentration stream is also present, and both need to be treated. In those cases, it is economical to treat the high-concentration stream with the alkali-acid system; and then, the effluent discharged from that system would be added to the large-volume low-concentration stream entering the ion-exchange system. [0015] Other systems for extracting ammonium from a waste-water stream and transferring the extracted ammonium to the body of secondary-water, besides the two systems as described herein, may be utilised as required under different circumstances. In each case, the preference lies in the fact of electrolysing not the waste-water itself but the secondary water. [0016] With regard to the ion-exchange system as described herein, it is well known that dissolved ammonium can be removed from waste-water by ion-exchange. A solid body of sorbent medium is provided, and the waste-water containing the ammonium passes through the medium. The ammonium is sorbed out of solution in exchange for a cation (such as sodium), and the medium retains the ammonium ions on the material. [0017] When the ion-exchange medium becomes saturated with ammonium, now the ammonium has to be removed therefrom. The flow of waste-water is shut off, or diverted away from the sorbent body, and a volume of regenerant-water is flushed through the sorbent body. The regenerant-water contains a high concentration of dissolved sodium chloride, and the sodium ions displace the ammonium ions sorbed on the sorbent body. The ammonium ions then pass into solution in the regenerant-water. [0018] After the medium has been flushed, the waste-water flow can be fed therethrough and the medium will once again act to sorb ammonium out of the waste-water. The ammonium has now been transferred to the regenerant-water, which is now at a higher ammonium-concentration level than was the waste-water. The regenerant-water, in the ion-exchange system, comprises the secondary-water of the invention. [0019] The alkali-acid system as described herein makes use of the fact that the solubility of ammonium and the associated ammonia varies considerably as a function of the pH of the water in which it is dissolved. At high pH, ammonium has a very low solubility, whereby if ammonium is present in the water when the pH of the water is increased, under the right thermodynamic conditions ammonia will bubble out of the water as a gas. Equally, the solubility of ammonium in low-pH water is much higher; thus, low-pH water will readily take ammonia gas into solution. [0020] In the alkali-acid system, the pH of the waste-water stream is raised (e.g by the addition of sodium hydroxide to the stream), and the resulting gaseous ammonia is extracted in an air stream. Often, the effluent waste-water can be simply discharged, despite its having a high pH; where the elevated alkalinity is a problem, pH reduction measures would be needed. The air/ammonia stream now passes though a body of low-pH (acid) water, and the ammonia is taken into solution therein. This acid-water, in the alkali-acid system, comprises the secondary-water of the invention. [0021] The apparatus of the invention preferably includes an ammonium-extraction-and-transfer station and an electrolysis station. The body of secondary-water preferably is contained in a secondary-water circuit, which conducts the secondary-water from the ammonium-extraction-and-transfer station, where the secondary-water receives the ammonium, to the electrolysis station, where the dissolved ammonium is transformed into nitrogen gas. [0022] Preferably, the secondary-water, having been electrolysed in the electrolysis station, is circulated and recirculated back through the ammonium-transfer station. It would spoil the cost-effectiveness of the overall system considerably if the secondary-water were simply to be discharged after one single pass through the electrolysis station. Continue reading about Electrochemical treatment of ammonia in waste-water... Full patent description for Electrochemical treatment of ammonia in waste-water Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Electrochemical treatment of ammonia in waste-water patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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