KR100734035B1 - Method for reducing nitrogen in nitrate solution - Google Patents

Abstract

The present invention relates to a method for reducing nitrogen in an aqueous nitrate solution. More specifically, the present invention provides a method for reducing nitrogen in an aqueous solution of nitrate, which comprises reducing and denitrifying nitrate nitrogen by treating metal and amide in an aqueous solution of nitrate, wherein the aqueous solution obtained in the step is treated with a halogen group oxidant to The present invention relates to a method for reducing nitrogen in an aqueous solution of nitrate comprising oxidative denitrification of ammonia nitrogen and amid organic nitrogen. The method of the present invention has the effect of reducing the total nitrogen present in the nitrate aqueous solution by oxidative denitrification of ammonia nitrogen and amide organic nitrogen generated in the reduction and denitrification process of nitrate nitrogen.

Nitrate Reduction Method, Oxidative Denitrification, Break Point Chlorine Injection Method

Description

Method for reducing nitrogen in nitrate solution             

1 is a schematic diagram schematically showing a process of a nitrogen reduction method according to the present invention.

The present invention relates to a method for reducing nitrogen in an aqueous nitrate solution. More specifically, the present invention provides a method for reducing nitrogen in an aqueous solution of nitrate, which comprises reducing and denitrifying nitrate nitrogen by treating metal and amide in an aqueous solution of nitrate, wherein the aqueous solution obtained in the step is treated with a halogen group oxidant to The present invention relates to a method for reducing nitrogen in an aqueous solution of nitrate comprising oxidative denitrification of ammonia nitrogen and amid organic nitrogen.

Water quality is deteriorating as high concentrations of nitrogen, such as fertilizer, steel, plating, livestock, gunpowder, dyestuff, leather, and caprolactam, enter the lakes, reservoirs and rivers. . Nitrogen in water is largely composed of organic nitrogen (organic nitrogen), ammonia nitrogen (NH ₃ -N), nitrite nitrogen (NO ₂ -N) and nitrate nitrogen (NO ₃ -N). When these nitrogen enters the water system, the eutrophication of water is promoted, and algae are generated. If the algae concentration is too high, the ecosystem is destroyed, such as the death of fish due to lack of oxygen and the release of toxic substances. For example, annual red tide occurs on the southern and eastern coasts, causing millions of farmed fish to die, causing enormous damage to property. Nitrogen is also contaminated with drinking water sources such as Paldang Lake and Daecheong Dam. . Therefore, various methods have been developed to remove nitrogen in water.

The removal of ammonia nitrogen from water is biological treatment, air stripping, advanced oxidation treatment, break point chlorination, etc. The removal of organic nitrogen is biological treatment, advanced oxidation. Treatment and the like. The removal of nitrous and nitrate nitrogen, which is the most problematic problem in water pollution, has relied mainly on biological denitrification. However, this method did not effectively remove nitrous and nitrate nitrogen in high concentration industrial wastewater. Accordingly, a nitrate reduction method (ChemDen method), which is a method for effectively and simply treating nitrite nitrogen and nitrate nitrogen, has been developed (Korean Patent Application No. 1997-7009760 and US Patent No. 6,436,275).                         

The nitrate reduction method uses metal and amide for denitrification. The denitrification process uses a metal such as zinc, copper, or cadmium to reduce nitric acid to nitrous acid (a) and to convert the reduced nitrous acid into a form of nitrogen gas by contacting an amide such as sulfamic acid or urea. It consists of the process (b), the effect of removing the nitrate nitrogen by performing the above two processes sequentially or simultaneously. However, due to the limitation of the yield of the reduction reaction in step (a), the nitrate nitrogen may be converted to ammonia nitrogen in which only the oxidation state (or oxidation state) is changed, and in addition, the amide introduced in step (b). Since the self-containing nitrogen (N) component does not consume all of the amide added to the reaction in the denitrification process, the remaining amide may be converted into organic nitrogen. That is, in the case of the theoretical complete mixing tank, the complete reaction without ammonia generation or amide residue may occur during the above (a) and (b) processes, but the actual reaction may be reduced due to the limitation of the yield of the chemical reaction. Subsequent reactions in which nitrous acid nitrogen is converted to ammonia nitrogen occur by continuously reacting with a metal reducing agent rather than an amide reducing agent. In addition, the residual ratio of amide also increases in proportion to the conversion of ammonia generated by side reaction.

Increasing the amide input rate in order to reduce the production rate of ammonia, the reaction rate of step (b) increases as the probability of reduced nitrite nitrogen reacted with the amide through (a) increases the reaction rate is suppressed And the denitrification efficiency can be increased. However, there is a problem in that the nitrogen component of the amide not consumed through the reaction is converted into organic nitrogen.                         

Conversely, if the amide input rate is lowered to reduce the residual ratio of amide, the nitrite nitrogen generated in step (a) is less likely to react with the amide. The reaction rate for denitrification is reduced. In addition, after all of the amides are exhausted by the denitrification reaction, nitrate or nitrite nitrogen, which cannot be denitrated, continuously undergoes a reduction reaction with the metal, so that only the oxidation value is converted into ammonia nitrogen. In this case, therefore, the conversion to ammonia nitrogen becomes higher than if amide is sufficiently present.

As a result, the conventional nitrate reduction method can remove nitrate nitrogen through the denitrification process using metals and amides, but ammonia nitrogen is inevitably generated by the side reaction of the process, and organic nitrogen increases due to the remaining amides. There is a problem. Therefore, the conventional nitrate reduction method is limited in the reduction of total nitrogen by the reduction of the yield of the reduction reaction and the characteristics of the reducing agent used in the reduction reaction. Therefore, in order to reduce total nitrogen, a process for simultaneously removing both ammonia nitrogen and amide organic nitrogen generated as a by-product of the nitrate reduction process is required.

Accordingly, the present inventors have been studying to solve the problems of the conventional nitrate reduction method, ammonia nitrogen and amide organic nitrogen produced by the by-product of the reduction reaction of nitrate by a combination process of the nitrate reduction method and the breakdown point chlorine injection method The present invention has been completed by confirming that can be effectively removed.

Accordingly, it is an object of the present invention to provide a method for effectively and simultaneously removing nitrate nitrogen as well as amide organic nitrogen produced from ammonia nitrogen and residual amides produced as a side reaction of the nitrate reduction and denitrification process.

In order to achieve the above object, the present invention

In the method for reducing nitrogen in the nitrate aqueous solution comprising the step of reducing and denitrifying nitrate nitrogen by treating the nitrate aqueous solution with metal and amide,

It provides a method for reducing nitrogen in the aqueous solution of nitrate, comprising the step of oxidatively denitrifying the ammonia nitrogen and the amide organic nitrogen contained in the aqueous solution by treating a halogen group oxidant to the aqueous solution obtained in the step.

In the present invention, "nitrate aqueous solution" refers to all aqueous solutions in which nitrate is dissolved, and various industrial wastewater, sewage and sewage such as livestock wastewater, steel wastewater, aluminum pickling wastewater, dye wastewater, fertilizer wastewater, gunpowder wastewater, leather wastewater, plating wastewater, etc. Include all of them.

Hereinafter, the present invention will be described in detail.                     

In order to solve the problem of the nitrate reduction method known as the conventional nitrate reduction method, the present invention is characterized in that it provides a new nitrogen removal process combining the break point chlorine injection method.

The present inventors have combined the general ammonia nitrogen removal methods into the nitrate reduction method in order to identify a method that can be combined with the nitrate reduction method in a subsequent step to effectively remove the ammonia nitrogen and the amid organic nitrogen produced by the method. Let's find out the effect.

 First, air-stripping, ion-exchange, electrodialysis, reverse osmosis, and distillation, which separate and concentrate ammonia nitrogen and remove it, are performed with nitrate reduction. In combination to investigate the effect. As a result, in the case of combining deaeration, the treatment ability for ammonia nitrogen was high, but the remaining amide could not be treated. In addition, the method requires a high reaction pH, so excessive chemical costs are not economical. When the ion exchange method was combined, the treatment ability for the low concentration ammonia nitrogen was high, but the treatment ability for the high concentration ammonia nitrogen was very low, and the residual amide could not be treated. On the other hand, in the case of the combination of electrodialysis, there was a problem in that the processing cost increases when the low concentration of ammonia nitrogen is treated, and the remaining amides cannot be treated like the above two methods. In the case of reverse osmosis, the separation and backwashing of ammonia nitrogen was difficult because most of the amides were polymers. In addition, the combination of distillation method was effective to remove high concentration of nitrogen, but there was a problem that lack of economic efficiency because of low energy efficiency. In this way, among the methods of separating and concentrating ammonia nitrogen, there was no method that could obtain a satisfactory effect in combination with the nitrate reduction method.

Therefore, the present inventors know the effects of combining the nitrate reduction method with the biological nitridation / denitrification method, the electrochemical treatment, and the breakdown point chlorine injection method, respectively, which are methods for decomposing ammonia nitrogen into a safe form such as nitrogen gas. saw. Among them, in the case of combining the biological nitriding / denitrification method, it is difficult to combine the method as a subsequent step of the nitrate reduction method due to the nature of the process to be preceded by the nitriding process. In particular, since the denitrification medium is a microorganism, the denitrification rate is low, and when the microorganism does not work properly when applied to high concentration ammonia nitrogen, the concentration of ammonia nitrogen in the applicable solution is limited. Had a problem. In addition, in the case of combining the electrochemical treatment method, it was possible to remove both ammonia nitrogen and residual amide, but it was confirmed that nitrogen oxide was caused by side reaction. In particular, in a low concentration solution, there is a problem in that the current efficiency (current efficiency) falls. On the other hand, when the breakdown point chlorine injection method was combined, it was confirmed that ammonia nitrogen was converted to stable nitrogen gas, and the remaining amide was also converted to nitrogen gas. In addition, no additional problems occurred. As described above, the present invention has found that the breaking point chlorine injection method is most suitable as a subsequent step of the nitrate reduction method among various ammonia nitrogen removal methods.

The ammonia nitrogen and the amide organic nitrogen produced by the reduction denitrification reaction are denitrated to nitrogen gas by reacting with the oxidizing agent OCl ⁻ through the break point chlorine injection method. In this process, OCl ⁻ may be imparted from the outside into the denitrification reactor in the form of NaOCl, and may be imparted either directly in the reactor in an electrochemical manner in the presence of Cl ⁻ or in an external producer. have.

In the present invention, the optimum reaction conditions for the most effective removal of the ammonia nitrogen and the amide organic nitrogen produced by the nitrate reduction method are identified by combining the breakdown point chlorine injection method with the nitrate reduction method.

The method for reducing total nitrogen in an aqueous solution of nitrate according to the present invention comprises the steps of reducing and denitrifying nitrate nitrogen by treating metal and amide in an aqueous solution of nitrate, and ammonia nitrogen and amide organic nitrogen contained in the aqueous solution obtained in the step. Oxidation and denitrification step (see Figure 1 ).

Reductive denitrification of nitrate nitrogen may be performed according to a conventional nitrate reduction method. Preferred reduced denitrification can be carried out by the following method. First, amide is added to an aqueous solution of nitrate (water to be treated) to remove nitrogen. The amide may be sulfamic acid, urea, formic acid, acetamide, etc., but preferably sulfamic acid may be used. Since sulfamic acid is hydrolyzed slowly under normal temperature and pressure conditions, it has the best efficiency in terms of reaction rate with nitrous acid and economical efficiency of chemicals. The dosage of amide is preferably 80-300%, more preferably 100-150% of the theoretical amount (calculated amount of amide compared to nitric acid concentration).

Then, after adjusting the pH of the aqueous solution to which the amide was added to 2.5, metal powder was added while stirring. pH adjustment can be made using concentrated sulfuric acid. Magnesium (Mg), manganese (Mn), zinc (Zn), chromium (Cr), iron (Fe), cadmium (Cd), tin (Sn), aluminum (AI), and lead (Pb) may be used as the metal. Can be. Preferably zinc can be used which is the most suitable metal for environmental and commercial reasons. After the metal powder was added, the pH of the aqueous solution was adjusted to 2.5 again, followed by stirring. It is preferable that the stirring strength is imparted to the extent that the metal powder is suspended in the aqueous solution and sufficiently in contact with the reactant upon stirring. When stirring, the rotational speed is preferably not exceeding 240rpm unless a simple vortex (a phenomenon in which the rotational force transmitted through the stirring blades does not contribute to the mixing and merely moves the water body in the rotational direction) does not occur. If a simple vortex occurs, it can be prevented by installing a collision plate that is perpendicular or inclined to the direction of the water flow rotation. In addition, in order to increase the mixing strength, an aeration facility, an injection facility, or a circulation pump circulating to the upper or lower portion of the reactor may be used. When the reaction is performed for about 1 hour under these conditions, the denitrification of nitrate nitrogen is completed. At this time, the reaction time may vary depending on the concentration of nitrate nitrogen, pH, the amide input rate, the strength of the stirring, the metal input rate and the input speed.                     

The reduction denitrification step of nitrate nitrogen is preferably performed using a stirred tank reactor. More preferably, it can be carried out using a metal reactor, a sulfuric acid feeder, an amide feeder, a pH meter and controller, a caustic soda feeder, a stirring blade, a stirring motor and a circular reactor with impingement plates. The ammonia conversion rate and nitrogen gas conversion rate in the reduction and denitrification reaction of nitrate nitrogen using a stirred tank reactor are determined by the rate of metal input. In batch reactions, the proper loading rate of metal is (total metal required for reaction) / (total reaction time). In addition, the total input of metal is preferably 100-300% of the theoretical metal consumption, more preferably 200%. At this time, if less than 100%, the reaction time is long, on the contrary, if more than 300%, the metal powder is simply reacted with acid ions and converted into hydrogen gas, thereby increasing metal consumption. Here, the theoretical metal consumption can be estimated based on the ammonia nitrogen conversion determined through repeated experiments.

As described above, after the reduction and denitrification of the nitrate nitrogen is completed, the step of removing or recovering the metal salt generated in the reduction and denitrification reaction may be further performed. Removal of the metal salt may be performed through neutralized flocculation precipitation, in which the metal salt is precipitated in the form of hydroxide using caustic soda (NaOH), and the recovery of the metal salt may be performed through an electrochemical treatment.

Thereafter, an oxidative denitrification step is performed. The oxidative denitrification step is also preferably carried out using a stirred tank reactor. More preferably, it can be carried out using a circular reactor with halogen oxidant feeder, sulfuric acid feeder, caustic soda feeder, pH meter and controller, oxygen reduction potential (ORP) meter and controller, stir vane, stir motor and impingement plate. have. Preferred oxidative denitrification can be carried out by the following method.

First, a halogen group oxidant is added and stirred to the aqueous solution (or the aqueous solution obtained by removing or recovering a metal salt) in which denitrification is completed. It is preferable to adjust the initial pH of the aqueous solution to 7.3 before adding the halogen group oxidant. Moreover, 6.5-11 are preferable and, as for the operation pH after injecting a halogen group oxidant, 7.0-8.0 is more preferable. It is preferable to avoid the reaction under acidic conditions, since irritant gases may occur when the reaction is under acidic conditions. The halogen oxidant used in the present invention may be a chlorine or bromine oxidant. As the chlorine-based oxidant, any one selected from the group consisting of sodium hypochlorite (NaOCl), chlorine (Cl ₂ ) and calcium hypochlorite (Ca (OCl) ₂ ) may be used, and sodium hypochlorite is more preferable. .

The total reaction time of the oxidative denitrification step may be determined according to the nitrogen concentration and characteristics of the water to be treated. The total reaction time is preferably 30-360 minutes, more preferably 30-90 minutes. In addition, the dose of halogenated oxidant is determined through ORP meters and eliminators. In particular, the oxidative denitrification step is preferably divided into primary oxidation and secondary oxidation. That is, it is preferable to first add a halogen oxidant in an amount maintained by ORP450 and to oxidize it first, and then to add a halogen oxidant in an amount maintained in ORP850 to secondary oxidize. When an excess halogen group oxidant is introduced at the beginning of the oxidative denitrification reaction, the pH of the reaction solution changes rapidly and ammonia nitrogen is oxidized to nitrate nitrogen rather than nitrogen gas. Therefore, it is preferable to perform the oxidation reaction first and second by changing the amount of halogen group oxidizing agent. The fraction of time between the primary and secondary oxidations, like the total reaction time, can also depend on the concentration and nature of the water to be treated. The primary oxidation time is preferably 5-30% of the total reaction time, more preferably 20%. In addition, the secondary oxidation time is preferably 70-95% of the total reaction time, more preferably 80%. The total amount of halogen group oxidant is preferably 90-100% of the theoretical amount, more preferably 100-150%.

Through this oxidative denitrification step, ammonia nitrogen and amide organic nitrogen can be oxidized to nitrogen gas. In addition, after the oxidative denitrification step, an oxygen oxidation process of the halogen anion may be further performed through the electrochemical treatment to convert the halogen element into a halogen group oxygen acid.

As a reactor for the reduction and denitrification of nitrate nitrogen and the oxidative denitrification of ammonia nitrogen and amide organic nitrogen according to the present invention, a general tubular reactor or an electrolysis reactor may be used in addition to the stirred tank reactor. Can be used individually or in combination in order to increase the efficiency.

In addition, the reduction denitrification and oxidative denitrification steps according to the present invention may be repeated as necessary to complete the reduction of total nitrogen present in the nitrate aqueous solution, and may be performed alone or continuously in each step in the same reactor or in separate reactors. The total nitrogen removal efficiency may be further improved through a neutralization flocculation process or a metal salt recovery process (electrochemical treatment) following the reduction denitrification process, or an oxygen oxidation process of a halogen group anion following the oxidation denitrification process.

Most preferred method for reducing nitrogen in nitrate aqueous solution according to the present invention,

a) reducing and denitrifying nitrate nitrogen by adding a metal and an amide to an aqueous solution of nitrate to be removed (water to be treated);

b) treating the aqueous solution obtained in step a) with caustic soda or electrochemical treatment to remove metal salts;

c) oxidizing and denitrifying ammonia nitrogen and amide organic nitrogen by adding a halogen group oxidant to the aqueous solution from which the metal salt is removed; And

d) electrochemical treatment of the solution obtained in step c) to convert the halogen element into a halogen group oxygen acid.

Hereinafter, the present invention will be described in detail by way of examples.

However, the following examples are merely to illustrate the invention, but the content of the present invention is not limited to the following examples.                     

<Example>

Potassium nitrate was dissolved in deionized water to prepare an aqueous 1000 mg / L potassium nitrate solution. 5 L of the prepared aqueous solution was added to a circular stirred reactor, and 45.036 g of sulfamic acid (130% of theory) was added and dissolved. Concentrated sulfuric acid was added to adjust the pH to 2.5. Thereafter, while passing the # 200 sieve powder zinc powder through the zinc feeder while rotating the stirrer of the circular stirring reactor. At the same time, sulfuric acid was supplied through a pH controller and a sulfuric acid feeder to maintain a pH of the reaction solution at 2.5. At this time, the zinc powder was charged at a constant speed at a feed rate of 26.861 g / hr. Thereafter, the mixture was stirred for 1 hour.

After the reduction and denitrification was completed, 33.490 g of caustic soda and a small amount of polymer were added to the aqueous solution. Thereafter, the precipitated metal salt precipitate in the form of hydroxide was removed. The concentrations of ammonia nitrogen and organic nitrogen in the aqueous solution from which the metal salt precipitate was removed were measured. As a result, the concentration of ammonia nitrogen was 50 mg / l, and the concentration of organic nitrogen due to amide (sulfamic acid) was 350 mg / l.

Thereafter, 5 L of the aqueous solution was added to a circular stirred reactor, and the initial pH was adjusted to 7.3 and stirred. Then, sodium hypochlorite was added to the aqueous solution for oxidation reaction. At this time, sodium hypochlorite was added in the amount of OPR450 maintained in the first half reaction time (20% of the total reaction time) and ORP850 was maintained in the second half reaction time (80% of the total reaction time). Charged (secondary oxidation). Total reaction time was 30-90 minutes. The total dose of sodium hypochlorite was 15.964 g, 120% of the theoretical amount. After the oxidative denitrification reaction was completed, the amounts of nitrate nitrogen, ammonia nitrogen and amide organic nitrogen in the aqueous solution obtained were measured and described in Table 1 below.

division Total nitrogen Nitrate nitrogen Ammonia nitrogen Amide Organic Nitrogen Water to be treated (Aqueous Potassium Nitrate Solution) 1000 1000 0 0 Reduced denitrification 405 5 50 350 Reduction Denitrification + Oxidative Denitrification 15 5 5 5

As shown in Table 1, when only the denitrification step of nitrate nitrogen was carried out according to the conventional nitrate reduction method (reduced denitrification treatment water), the nitrate nitrogen was significantly reduced compared to before treatment, but was not present before treatment. It was confirmed that a large amount of nitrogen and amide organic nitrogen. On the other hand, when the oxidative denitrification step is performed using a halogen group oxidant after the reduction denitrification step (reduction denitrification + oxidative denitrification treated water) according to the method according to the present invention, ammonia nitrogen and amid organic nitrogen are generated as by-products of the reduction denitrification reaction. It was confirmed that a large amount was removed. From this, it can be seen that the method according to the present invention has the effect of effectively removing the total nitrogen in the nitrate aqueous solution.

As described above, the present invention solves the problem of the conventional nitrate reduction method by combining the breakdown point chlorine injection method in the method. Therefore, the method of the present invention has the effect of reducing the total nitrogen present in the nitrate aqueous solution by oxidative denitrification of ammonia nitrogen and amide organic nitrogen generated in the reduction and denitrification process of nitrate nitrogen. Therefore, the method according to the present invention can be very usefully used to remove nitrogen from various industrial wastewater, sewage and sewage such as livestock wastewater, plating wastewater and the like.

Claims (8)

delete delete delete In the method for reducing nitrogen in the nitrate aqueous solution comprising the step of reducing and denitrifying nitrate nitrogen by treating the nitrate aqueous solution with metal and amide, A method for reducing nitrogen in an aqueous nitrate solution, comprising treating the aqueous solution obtained in the step with a halogen group oxidant to oxidatively denitrify the ammonia nitrogen and the amide organic nitrogen contained in the aqueous solution for 30 to 360 minutes. 5. The method according to claim 4, wherein 5-30% of the total reaction time is added to a halogen group oxidant to maintain an oxidation reduction potential (ORP) of 450, and then 70-95% of the total reaction time is used for the ORP 850. Adding so that it is retained and subjecting it to secondary oxidation. In the method for reducing nitrogen in the nitrate aqueous solution comprising the step of reducing and denitrifying nitrate nitrogen by treating the nitrate aqueous solution with metal and amide, Neutralizing agglomerated precipitation or electrochemical treatment of the aqueous solution obtained in the above step and treating a halogen group oxidant to oxidatively denitrify the ammonia nitrogen and the amid organic nitrogen contained in the aqueous solution. Nitrogen abatement method. 7. The method of claim 6, wherein the neutralizing flocculation precipitation step comprises treating caustic soda in the aqueous solution obtained in the reduction and denitrification step to precipitate metal salts in the form of hydroxides. In the method for reducing nitrogen in the nitrate aqueous solution comprising the step of reducing and denitrifying nitrate nitrogen by treating the nitrate aqueous solution with metal and amide, A method of reducing nitrogen in an aqueous solution of nitrate, comprising the step of oxidatively denitrifying ammonia nitrogen and amide organic nitrogen contained in the aqueous solution by treating a halogen group oxidant to the aqueous solution obtained in the above step. .

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