JP2004074107A - Treatment method and treatment apparatus for nitrate nitrogen - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a decomposition treatment method and decomposition treatment apparatus for nitrate nitrogen, which method and apparatus are compact, are highly efficient and can reduce the environmental load by lowering the concentration of nitrogen components, such as nitrate nitrogen, nitrite nitrogen and ammonia nitrogen, remaining in post-treatment water. <P>SOLUTION: An aqueous solution containing the nitrate nitrogen is treated by using a nitrite nitrogen forming means 1 to reduce the nitrate nitrogen in the aqueous solution and to convert the same to the nitrite nitrogen. More specifically, means such as electrolysis or irradiation with UV rays, are employed for the nitrite nitrogen forming means. In succession, the aqueous solution treated in the previous step is treated by using a nitrite nitrogen decomposing means to reduce the nitrite nitrogen and to convert the same to gaseous nitrogen. More specifically, means of supplying a reducing agent such as hydrogen or formic acid to the aqueous solution of mixing the same and of bringing the mixture into contact with a hydrogenation catalyst are employed as the nitrite nitrogen decomposing means. <P>COPYRIGHT: (C)2004,JPO

Description

【００６９】
何れにおいても、約１０Ｌの被処理物を電解槽１と触媒反応器７に導入した後、循環処理を開始した。被処理物の液温は２０℃に保った。電解は定電流で行った。実施例２を除いては、ステンレス繊維焼結体を陰極２の多孔質基材として用い、全ての場合において陽極３の基材としてチタン繊維焼結体を用いた。触媒反応器７は何れも固定床型である。ここに導入する水素ガス量は、電解槽１の陰極室４出口における亜硝酸性窒素濃度をモニタリングして算出した、亜硝酸性窒素の流量に基づいて決定した。その量を示す表１の水素ガス等量比とは、（水素ガスのモル流量／亜硝酸性窒素のモル流量）の、亜硝酸性窒素１モルを窒素ガスに転換するために必要な水素ガスのモル数である１．５に対する比のことである。陰極室４出口においては、陰極２において生成したガスの流量と水素ガス濃度も併せてモニタリングし、算出した水素ガス流量が必要量を下回った場合に限り、水素ガスボンベから不足分を補った。この循環処理を、表１に示す循環処理時間だけ行った後に全量をタンクに回収し、それを分析した結果を表２に示す。
【００７０】
【表２】

【００７１】
上記表２に見られるように、いずれの場合も、硝酸性窒素が良好に除去されていると共に、全窒素量に示される窒素化合物全体としての残存量は少量であった。
【００７２】
（比較例１〜４）
図９に示す処理装置を用い、実施例１〜４で処理したのと同じ被処理物を、表３に記載の実施例１〜４と同じ条件で処理した。触媒反応器７は用いなかった。
【００７３】
【表３】

【００７４】
循環処理を、実施例１〜４と同じ循環処理時間だけ行った後に全量をタンクに回収し、それを分析した結果を表４に示す。
【００７５】
【表４】

【００７６】
表４から明らかなように、上記比較例のいずれの場合でも、実施例１〜４の結果を大きく上回る濃度の硝酸性窒素、亜硝酸性窒素、全窒素が検出され、分解効率が低いことが明らかになった。
【００７７】
（実施例５〜８）
図２に示す処理装置を用い、実施例１〜４で処理したのと同じ被処理物を、表５に記載の条件で処理した。
【００７８】
【表５】

【００７９】
処理条件は循環処理時間を除いて実施例１〜４と同じとしたが、第２触媒反応器９を追加設置し、陽極室５から流出する被処理物中に含まれる亜硝酸性窒素も分解した。第１触媒反応器８と第２触媒反応器９は同一の形状を有し、同じ触媒を同じ量だけ充填している。両触媒反応器に導入する水素ガス量は、陰極室４出口と陽極室５出口における亜硝酸性窒素濃度をモニタリングして算出した、亜硝酸性窒素の流量の和に基づいて決定した。その量を示す表５の水素ガス等量比とは、（水素ガスのモル流量／亜硝酸性窒素のモル流量）の、亜硝酸性窒素１モルを窒素ガスに転換するために必要な水素ガスのモル数である１．５に対する比のことである。陰極室４出口においては、陰極２において生成したガスの流量と水素ガス濃度も併せてモニタリングし、算出した水素ガス流量が必要量を下回った場合に限り、水素ガスボンベから不足分を補った。この循環処理を、表５に示す循環処理時間だけ行った後に全量をタンクに回収し、それを分析した結果を表６に示す。
【００８０】
【表６】

【００８１】
表６の結果から明らかなように、実施例５〜８においては、処理時間は何れも実施例１〜４より短いにも関わらず、処理後の水質はほぼ同等であった。
【００８２】
（実施例９〜１２）
図３に示す処理装置を用い、実施例１〜４で処理したのと同じ被処理物を、表７に記載の条件で処理した。ただし、１つの電解槽と２つの触媒反応器から構成されるモジュールを、５つ直列に設置した。
【００８３】
【表７】

【００８４】
いずれにおいても、被処理物の液温は３０℃に保った。全ての場合において、チタン繊維焼結体を陰極２および陽極３の多孔質基材として用いた。電解は定電流で行った。第１触媒反応器８と第２触媒反応器９は同一の形状を有し、同じ触媒を同じ量だけ充填している固定床型の触媒反応器である。両触媒反応器に導入する水素ガス量は、陰極室４出口と陽極室５出口における亜硝酸性窒素濃度をモニタリングして算出した、亜硝酸性窒素の流量の和に基づいて決定した。その量を示す表７の水素ガス等量比とは、（水素ガスのモル流量／亜硝酸性窒素のモル流量）の、亜硝酸性窒素１モルを窒素ガスに転換するために必要な水素ガスのモル数である１．５に対する比のことである。陰極室４出口においては、陰極２において生成したガスの流量と水素ガス濃度も併せてモニタリングし、算出した水素ガス流量が必要量を下回った場合に限り、水素ガスボンベから不足分を補った。この処理を２４時間連続して行った時の結果を表８に示す。なお、結果は５つめのモジュールの出口で１時間毎にサンプリングした値の平均値である。
【００８５】
【表８】

【００８６】
表８から明らかなように、いずれの場合も、硝酸性窒素が良好に除去されていると共に、全窒素量に示される窒素化合物全体としての残存量は少量であった。
【００８７】
（実施例１３〜１６）
図４に示す処理装置を用い、実施例１〜４で処理したのと同じ被処理物を、表９に記載の条件で処理した。
【００８８】
【表９】

【００８９】
上記実施例１３〜１６のいずれにおいても、約５Ｌの被処理物を電解槽１の陰極室４と触媒反応器７に導入した後、循環処理を開始した。被処理物の液温は２０℃に保った。電解は定電流で行った。全ての場合において、ステンレス繊維焼結体を陰極２の多孔質基材として用い、チタン繊維焼結体を陽極３の基材として用いた。触媒反応器７は何れも固定床型である。ここに導入する水素ガス量は、電解槽１の陰極室４出口における亜硝酸性窒素濃度をモニタリングして算出した、亜硝酸性窒素の流量に基づいて決定した。その量を示す表９の水素ガス等量比とは、（水素ガスのモル流量／亜硝酸性窒素のモル流量）の、亜硝酸性窒素１モルを窒素ガスに転換するために必要な水素ガスのモル数である１．５に対する比のことである。陰極室４出口においては、陰極２において生成したガスの流量と水素ガス濃度も併せてモニタリングし、算出した水素ガス流量が必要量を下回った場合に限り、水素ガスボンベから不足分を補った。この循環処理を、表９に示す循環処理時間だけ行った後に全量をタンクに回収し、それを分析した結果を表１０に示す。
【００９０】
【表１０】

【００９１】
表１０の結果から明らかなように、本実施例のいずれの場合も、硝酸性窒素が良好に除去されていると共に、全窒素量に示される窒素化合物全体としての残存量は少量であった。アンモニア性窒素は殆ど検出されなかった。
【００９２】
（実施例１７〜２０）
図５に示す処理装置を用い、実施例１〜４で処理したのと同じ被処理物を、表１１に記載の条件で処理した。
【００９３】
【表１１】

【００９４】
本発明の実施例１７〜２０のいずれにおいても、約５Ｌの被処理物を電解槽１の陰極室４と触媒反応器７に導入した後、循環処理を開始した。被処理物の液温は２０℃に保った。電解は定電流で行った。全ての場合において、チタン繊維焼結体を陰極２および陽極３の多孔質基材として用いた。電解は定電流で行った。電解処理の後に、水溶液の全量をいったんバッファータンク１２に移送し、水素ガスホルダー１１に貯蔵された水素ガス含有ガスと混合して、触媒反応器７に少量ずつ導入した。ここに導入する水素ガス量は、バッファータンク１２内の亜硝酸性窒素濃度を分析して算出した、亜硝酸性窒素の流量に基づいて決定した。その量を示す表１１の水素ガス等量比とは、（水素ガスのモル流量／亜硝酸性窒素のモル流量）の、亜硝酸性窒素１モルを窒素ガスに転換するために必要な水素ガスのモル数である１．５に対する比のことである。水素ガスホルダー１１からの水素ガス流量が必要量を下回った場合に限り、水素ガスボンベから不足分を補った。一連の処理終了後の被処理物をタンクに全量回収し、それを分析した結果を表１２に示す。
【００９５】
【表１２】

【００９６】
上記表１２の結果から明らかなように、いずれの場合も、硝酸性窒素が良好に除去されていると共に、全窒素量に示される窒素化合物全体としての残存量は少量であった。アンモニア性窒素は殆ど検出されなかった。
【００９７】
（実施例２１〜２４）
図６に示す処理装置を用い、実施例１〜４で処理したのと同じ被処理物を、表１３に記載の条件で処理した。
【００９８】
【表１３】

【００９９】
被処理物を、陰極室４に連続的に導入して電解処理した。何れにおいても、被処理物の液温は３０℃に保った。電解は定電流で行った。全ての場合において、ステンレス繊維焼結体を陰極２の多孔質基材として用い、チタン繊維焼結体を陽極３の基材として用いた。触媒反応器７は何れも固定床型である。ここに導入する水素ガス量は、電解槽１の陰極室４出口における亜硝酸性窒素濃度をモニタリングして算出した、亜硝酸性窒素の流量に基づいて決定した。その量を示す表１３の水素ガス等量比とは、（水素ガスのモル流量／亜硝酸性窒素のモル流量）の、亜硝酸性窒素１モルを窒素ガスに転換するために必要な水素ガスのモル数である１．５に対する比のことである。陰極室４出口においては、陰極２において生成したガスの流量と水素ガス濃度も併せてモニタリングし、算出した水素ガス流量が必要量を下回った場合に限り、水素ガスボンベから不足分を補った。この処理を２４時間連続して行った時の結果を表１４に示す。なお、結果は触媒反応器７の出口で１時間毎にサンプリングした値の平均値である。
【０１００】
【表１４】

【０１０１】
表１４から明らかなように、いずれの場合も、硝酸性窒素が良好に除去されていると共に、全窒素量に示される窒素化合物全体としての残存量は少量であった。アンモニア性窒素は殆ど検出されなかった。
【０１０２】
（実施例２５〜２８）
図７に示す処理装置を用い、実施例１〜４で処理したのと同じ被処理物を、表１５に記載の条件で処理した。
【０１０３】
【表１５】

【０１０４】
これらを紫外線照射反応器１３と触媒反応器７に導入した後、循環処理を開始した。被処理物の液温は４０℃に保った。紫外線照射反応器１３の光源には総出力６０Ｗの低圧水銀灯を用いた。また、触媒反応器７は何れも固定床型である。水素ガスは、触媒反応器７の手前から連続的に供給し、触媒反応器７の出口からは、還元反応で消費されなかった水素ガスと、生成した窒素ガスを外部に排出した。水溶液は紫外線照射反応器１３の入口に還流した。供給する水素ガスの量は、紫外線照射反応器１３出口における亜硝酸性窒素濃度をモニタリングし、それから算出される亜硝酸性窒素のモル流量に対して１５倍のモル流量とした。つまり、水素ガス等量比を常に１０になるように制御した。この循環処理を、表１５に示す循環処理時間だけ行った後に全量をタンクに回収し、それを分析した結果を表１６に示す。
【０１０５】
【表１６】

【０１０６】
何れの場合も、硝酸性窒素が良好に除去されていると共に、全窒素量に示される窒素化合物全体としての残存量は少量であった。アンモニア性窒素は殆ど検出されなかった。
【０１０７】
（実施例２９〜３２）
図８に示す処理装置を用い、実施例１〜４で処理したのと同じ被処理物を、表１７に記載の条件で処理した。ただし、２つの紫外線照射反応器と２つの触媒反応器から構成されるモジュールを、５つ直列に設置した。
【０１０８】
【表１７】

【０１０９】
何れにおいても、被処理物の液温は３０℃に保った。第１紫外線照射反応器１４と第２紫外線照射反応器１５は同一の形状であり、かつ同じ材質である。その光源には共に出力６Ｗの低圧水銀灯を用いた。また、第１触媒反応器８と第２触媒反応器９は同一の形状を有し、同じ触媒を同じ量だけ充填している固定床型の触媒反応器である。水素ガスは、第１触媒反応器８の手前から連続的に供給し、第２触媒反応器９の出口からは、還元反応で消費されなかった水素ガスと、生成した窒素ガスを外部に排出した。水溶液は次のモジュールの紫外線照射反応器の入口に導入した。供給する水素ガスの量は、第１紫外線照射反応器１４出口と第２紫外線照射反応器１５出口における亜硝酸性窒素濃度をモニタリングして算出した、亜硝酸性窒素のモル流量の和に対して１５倍のモル流量とした。つまり、水素ガス等量比を常に１０になるように制御した。この処理を２４時間連続して行った時の結果を表１８に示す。なお、結果は５つめのモジュールの出口で１時間毎にサンプリングした値の平均値である。
【０１１０】
【表１８】

【０１１１】
表１８から明らかなように、いずれの場合も、硝酸性窒素が良好に除去されていると共に、全窒素量に示される窒素化合物全体としての残存量は少量であった。アンモニア性窒素は殆ど検出されなかった。
【０１１２】
【発明の効果】
本発明によれば、従来の硝酸性窒素の分解処理方法の欠点を解消し、コンパクトで高効率であり、かつ、処理後、水中に残存する硝酸性窒素、亜硝酸性窒素、アンモニア性窒素といった窒素化合物の濃度を極力低減することによって環境に対する負荷を低下させることが可能な、硝酸性窒素の分解処理方法および分解処理装置を提供することが出来る。
【図面の簡単な説明】
【図１】本発明の第１の実施形態の硝酸性窒素の処理装置を示す図である。
【図２】本発明の第２の実施形態の硝酸性窒素の処理装置を示す図である。
【図３】本発明の第３の実施形態の硝酸性窒素の処理装置を示す図である。
【図４】本発明の第４の実施形態の硝酸性窒素の処理装置を示す図である。
【図５】本発明の第５の実施形態の硝酸性窒素の処理装置を示す図である。
【図６】本発明の第６の実施形態の硝酸性窒素の処理装置を示す図である。
【図７】本発明の第７の実施形態の硝酸性窒素の処理装置を示す図である。
【図８】本発明の第８の実施形態の硝酸性窒素の処理装置を示す図である。
【図９】本発明の第１の実施形態の比較例を示す図である。
【符号の説明】
１…電解槽
２…陰極
３…陽極
４…陰極室
５…陽極室
６…陽イオン交換膜（水素イオン選択透過膜）
７…触媒反応器
８…水性溶液供給容器
９…還元剤供給容器
１０…気液分離器
１１…水素ガスホルダー
１２…バッファータンク
１３…バルブ
１４…陰極室処理水性溶液供給口
１５…陰極室環流供給口
１６…陰極室処理水性溶液排出口
１７…陽極室処理水性溶液供給口
１８…陽極室処理水性溶液排出口
１９…陰極室排ガス排出口
２０…陽極室排ガス排出口
２１…紫外線照射反応器
２２…紫外線発生装置
２３…水性溶液流通配管
２４…処理水性溶液供給口
２５…処理水性溶液排出口[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for treating nitrate nitrogen, which converts nitrate nitrogen contained in drinking water, raw water thereof, wastewater, used chemical liquids and the like into harmless gas such as nitrogen gas and removes the same, and an apparatus therefor.
[0002]
[Prior art]
BACKGROUND ART In recent years, contamination of raw drinking water such as river water and groundwater by nitrate nitrogen has become apparent. Nitrate nitrogen cannot be completely removed by water purification treatment, and the concentration of nitrate nitrogen in drinking water is also increasing with increasing raw water pollution. Nitrate nitrogen is a harmful substance that can cause cyanosis and become a precursor of carcinogenic substances when taken into the human body. There is a need for an effective treatment method for industrial and agricultural wastewater.
[0003]
On the other hand, many pure water and fluorine-based chemicals are used in semiconductor manufacturing plants, and the nitric acid contained in these is used to treat wastewater from the pure water manufacturing process and to recycle used pure water and chemicals. It is desired to establish a technology for removing volatile nitrogen.
[0004]
As a conventional method for decomposing nitrate nitrogen, there is a biological treatment using microorganisms. However, there is a problem that maintenance and management are difficult, the scale of the apparatus is large, and a large amount of excess sludge is generated.
[0005]
As a compact method of decomposing nitrate nitrogen instead of biological treatment, a reduction method using a hydrogenation catalyst supporting a noble metal has been proposed. However, although this catalyst has the activity of converting nitrite nitrogen to nitrogen gas, it is necessary to add copper, tin, etc. to the catalyst in addition to precious metals in order to reduce nitrate nitrogen. There is a problem that these are eluted depending on the properties.
[0006]
Also, a reduction method for reducing nitrate nitrogen using electrolysis is known. That is, Japanese Patent Application Laid-Open No. 11-347558 discloses a method for electrolytically treating oxidized nitrogen using a cathode carrying a conductive catalyst having an ability to reduce oxidized nitrogen. In this method, carriers such as zirconia, titania, alumina, and silica that are preferably used for supporting the active material are insulators, and therefore, when these are used as carriers, they function as electrodes of an electrolytic cell. It is impossible to combine For this reason, in the examples of this document, copper expanded metal is used, and since it is a conductor, it certainly has the function of an electrode, but the performance as a hydrogenation catalyst is extremely low due to its small specific surface area. turn into. As described above, although nitrate nitrogen can be converted to nitrogen gas by this known method, there is a problem that its efficiency is low.
[0007]
[Problems to be solved by the invention]
The present invention solves the drawbacks of the conventional nitrate nitrogen decomposition treatment method, is compact and highly efficient, and is capable of removing nitrogen compounds such as nitrate nitrogen, nitrite nitrogen, and ammonia nitrogen remaining in water after the treatment. An object of the present invention is to provide a method and an apparatus for decomposing nitrate nitrogen, which can reduce the load on the environment by reducing the concentration as much as possible.
[0008]
[Means for Solving the Problems]
A first step of the present invention is to electrolyze an aqueous solution containing nitrate nitrogen supplied to a cathode chamber of an electrolytic cell to reduce nitrate nitrogen contained in the aqueous solution, and
At least a second step of adding a reducing agent to the aqueous solution treated in the first step and bringing the aqueous solution into contact with a reducing catalyst to reduce acidic nitrogen oxides contained in the aqueous solution is provided. This is a method for treating nitrate nitrogen.
[0009]
In the first aspect of the present invention, the aqueous solution treated in the second step is supplied to an anode chamber of the electrolytic cell, and an anode disposed in the anode chamber is supplied with a cathode of the electrolytic cell in the first step. Converting the by-produced nitrogen compound to nitrate nitrogen, and then supplying this aqueous solution to the cathode compartment of the electrolytic cell suppresses the production of by-product ammoniacal nitrogen compound and efficiently converts nitrate nitrogen. It is preferable because it can be converted to harmless gas such as nitrogen gas.
[0010]
Further, in the first aspect of the present invention, it is preferable that the cathode of the electrolytic cell is made of zinc or a compound thereof because the formation of an ammoniacal nitrogen compound by the electrolytic treatment can be suppressed.
[0011]
Further, in the first aspect of the present invention, the reduction catalyst used in the second step may be at least one selected from palladium, ruthenium, rhodium, osmium, iridium, platinum, nickel, and compounds thereof. It is preferable because the nitrogen can be efficiently reduced.
[0012]
In the first aspect of the present invention, it is preferable to use hydrogen or formic acid as the reducing agent used in the second step, since good reduction efficiency can be obtained. Further, in the second step, it is preferable to use, as the reducing agent, hydrogen generated at the cathode of the electrolytic cell in the first step, since the processing apparatus can be reduced in size and small-scale equipment can be used.
[0013]
The second invention is a first step of reducing nitrate nitrogen by irradiating an aqueous solution containing nitrate nitrogen with ultraviolet rays,
A nitric acid comprising at least a second step of adding a reducing agent to the aqueous solution treated in the first step and bringing the aqueous solution into contact with a reducing catalyst to reduce acidic nitrogen oxides contained in the aqueous solution. This is a method for treating nitrogen.
[0014]
In the second aspect of the present invention, the reduction catalyst used in the second step may be at least one selected from palladium, ruthenium, rhodium, osmium, iridium, platinum, nickel, and compounds thereof. Is preferred because it can be efficiently reduced.
[0015]
In the second aspect of the present invention, it is preferable that the reducing agent used in the second step is hydrogen or formic acid in order to obtain good reduction efficiency.
[0016]
According to a third aspect of the present invention, there is provided an electrolytic cell having an anode and a cathode, and a diaphragm for separating the anode and the cathode, and a reduction catalyst for supplying an electrolytic product generated in a cathode portion of the electrolytic cell and performing a contact treatment. A nitrate nitrogen treatment device, comprising at least a catalytic reactor filled with a nitrogen gas.
[0017]
According to a fourth aspect of the present invention, there is provided an ultraviolet ray irradiation device comprising an ultraviolet ray generating device, an ultraviolet ray transmitting pipe disposed around the ultraviolet ray generating device, and a reduction catalyst for supplying a reactant generated in the ultraviolet ray irradiation reactor and performing a contact treatment. And a catalyst reactor comprising at least a catalytic reactor described above.
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the principle and operation of the present invention will be described.
In the first and second aspects of the present invention, which are methods for treating nitrate nitrogen, first, in the first step, a nitrite nitrogen generator is used to reduce nitrate nitrogen dissolved in an aqueous solution to be treated. To convert to nitrite nitrogen. Specifically, nitrate nitrogen is mainly reduced to nitrite nitrogen by electrolysis or ultraviolet irradiation. Subsequently, in a second step, the nitrite nitrogen generated in the step is reduced and converted into nitrogen gas. Specifically, a reducing agent such as hydrogen gas or formic acid is supplied to and mixed with the aqueous solution, and the mixture is brought into contact with a reducing catalyst such as a hydrogenation catalyst to be reduced and converted into nitrogen gas. In the present invention, the aqueous solution to be treated is a solution containing nitrate nitrogen and containing water as a main solvent, but reduces the electric conductivity of the solution or adversely affects the reduction reaction of the nitrate nitrogen. , An organic solvent or another inorganic compound or an organic compound component may be added. A suitable concentration range of the nitrate nitrogen compound suitable for treatment in the present invention is 1 to 2000 mg / L as the total amount of nitrogen. If this concentration range is not within this range, the processing efficiency is reduced and is not practical.
[0019]
(First step: electrolytic treatment)
When the electrolytic process is used as the first step, nitrate nitrogen in the object to be treated is reductively decomposed at the cathode of the electrolytic cell mainly according to the following formula.
NO₃ ⁻+ 2H⁺+ 2e⁻→ NO₂ ⁻+ H₂O
NO₃ ⁻+ 9H⁺+ 8e⁻→ NH₃+ 3H₂O
2NO₃ ⁻+ 12H⁺+ 10e⁻→ N₂+ 6H₂O
The case where nitrite nitrogen is reduced is as follows.
NO₂ ⁻+ 7H⁺+ 6e⁻→ NH₃+ 2H₂O
2NO₂ ⁻+ 8H⁺+ 6e⁻→ N₂+ 4H₂O
[0020]
The current density applied in this electrolytic treatment is 10 to 1000 mA / cm.²Is preferable. If the current density falls below this range, sufficient reduction reaction does not proceed and the conversion to nitrite nitrogen decreases, while if the current density exceeds this range, a large-capacity power source is used. Needs things and is not economical. The applied voltage is set so that the current density falls within this range. The treatment temperature is not particularly limited, but if necessary, is adjusted to at least the boiling point of the aqueous solution using a known cooling device. In addition, the time for the electrolytic treatment varies depending on conditions such as applied voltage, current, liquid temperature, and electric conductivity, and it is difficult to determine the range in a straightforward manner, but a range of about 10 to 600 minutes is sufficient. . If the electrolytic treatment time falls below the above range, a sufficient reduction reaction does not proceed, and the conversion rate to nitrite nitrogen decreases. On the other hand, when the electrolytic treatment time is longer than the above range, the conversion rate is not improved and the cost is long, and the cost is uneconomical.
[0021]
In the first step of the present invention, as an electrode material of the electrolytic cell, a plate-like body, a sintered body, a porous body, or a net-like material such as carbon, copper, stainless steel, or titanium used in a general electrolytic apparatus is used. Alternatively, a material obtained by plating these surfaces with palladium, ruthenium, platinum, or the like can be used. When zinc or a compound thereof is used for the cathode of the electrolytic cell, depending on the processing conditions, the reduction potential at which nitrite nitrogen or nitrate nitrogen is converted to ammonia nitrogen is lower than the hydrogen generation potential. Almost no ammoniacal nitrogen can be produced. In that case, a process is adopted in which an aqueous solution to be treated, which is an object to be treated, which has flowed out of the catalytic reactor, is first introduced into the anode chamber of the electrolytic cell, and ammonia nitrogen is converted into nitrate nitrogen or the like and then introduced into the cathode chamber. There is no necessity, and the aqueous solution to be treated taken out of the catalytic reactor may be directly introduced into the cathode chamber. Alternatively, it may be circulated through the cathode chamber of the electrolytic cell until the concentration of nitrate nitrogen is sufficiently reduced, and then introduced into the catalytic reactor. Further, it is also possible to adopt a flow-type apparatus configuration in which the residence time in the cathode chamber of the electrolytic cell is sufficiently long. In any case, the configuration of the processing device is simplified.
[0022]
(2nd process)
In this method, unreacted nitrate nitrogen and the generated nitrite nitrogen and ammonia nitrogen are dissolved in the aqueous solution which is subjected to the electrolytic treatment and flows out of the cathode chamber of the electrolytic cell. Subsequently, the object to be treated containing these is introduced into the catalytic reactor in the second step. In the catalytic reactor in the second step, a reducing agent such as hydrogen gas or formic acid is added to and mixed with the aqueous solution to be treated, and the mixture is brought into contact with the reducing catalyst, whereby most of the nitrite nitrogen is removed. Is reduced to nitrogen gas. The reaction formulas when the reducing agent is hydrogen gas and formic acid are respectively as follows.
2NO₂ ⁻+ 3H₂→ N₂+ 2H₂O + 2OH⁻
2NO₂ ⁻+ 3HCOOH → N₂+ 2H₂O + CO₂+ 2HCO₃ ⁻
[0023]
In the contact reaction with the reduction catalyst in the second step, the temperature of the catalyst reactor is preferably in the range of 5 ° C. or higher and the boiling point of the aqueous solution at the processing pressure or lower. When the temperature falls below this range, the reduction reaction rate is low, and the processing efficiency is low, which is not economical. On the other hand, when the temperature exceeds this range, the water of the aqueous solution evaporates and the input energy is wasted. Further, the total contact reaction time is preferably in the range of 1 to 60 minutes. If the total contact reaction time falls below the above range, a sufficient reaction does not occur, and the treatment efficiency is reduced. On the other hand, if the reaction time exceeds the above range, the reaction no longer proceeds for the time required for the treatment, which is uneconomical.
[0024]
In the second step, 1.5 moles of hydrogen gas or formic acid are required with respect to nitrous acid per mole, and a sufficient amount is required to minimize the amount of nitrite remaining in the second step. Need to be added. For this purpose, the amount of nitrite nitrogen generated by reduction from the nitrate nitrogen charged in the first step is measured sequentially by a method such as ion chromatography, and the amount of the reducing agent to be charged is controlled. Can be. Alternatively, based on the conversion rate of nitrate nitrogen to nitrite nitrogen by electrolytic treatment required experimentally, estimate the amount of nitrite nitrogen generated from the amount of input nitrate nitrogen and determine the amount of reducing agent to be charged You can also.
[0025]
As the reduction catalyst used in the second step, a catalyst known as a hydrogenation catalyst can be used. Specifically, the catalyst is a catalyst in which at least one selected from palladium, ruthenium, rhodium, osmium, iridium, platinum, nickel and these compounds is supported as an active material. These catalysts are known as substances to which hydrogen molecules are easily dissociated and adsorbed, and have a high ability to reductively decompose by adding hydrogen to nitrite nitrogen. In this reduction catalyst, in order to ensure high decomposition efficiency, it is preferable to support these on a porous carrier by using a known method such as an impregnation method or a coprecipitation method. As the carrier, various commonly used shapes such as zirconia, titania, activated carbon, alumina, silica, and solid or porous powders, spheres, pellets, and honeycombs of these compounds may be used. It is possible. When hydrogen gas is used as the reducing agent, hydrogen gas is generated at the cathode of the electrolytic cell. Therefore, an object to be treated containing the hydrogen gas can be introduced into a catalytic reactor, and the hydrogen gas can be subjected to a reduction reaction. By using a hydrogen gas generated by electrolysis from the cathode as a reducing agent as described above, processing can be performed with a small and small-sized apparatus, which is economical.
[0026]
At the outlet of the catalyst reactor in the second step, a gas containing hydrogen gas and generated nitrogen gas is separated from an aqueous solution to be processed using a gas-liquid separator. This gas-liquid separator introduces an aqueous solution in which a gas and a liquid are mixed into a container having a sufficient volume having a gas outlet and a liquid outlet, and separates the gas-liquid by allowing the aqueous solution to stand still. Alternatively, gas-liquid can be separated using a gas-liquid separation membrane such as a gas-permeable, liquid-impermeable polymer membrane. As described above, a conventionally known gas-liquid separator can be used. Since the separated gas sometimes contains a small amount of NOx derived from the electrolytic cell, if necessary, the gas is converted to nitrogen gas using a known abatement equipment.
[0027]
The gaseous component discharged from the catalytic reactor is separated, that is, in the aqueous solution, ammonia nitrogen and nitrate nitrogen, which have not reacted at all in the catalytic reactor, are mainly dissolved. Is introduced into the anode chamber of the electrolytic cell and anodized, the following reaction mainly occurs at the anode, and ammonia nitrogen is converted to nitrate nitrogen or the like. The nitrate nitrogen does not react any further.
NH₃+ 3H₂O → NO₃ ⁻+ 9H⁺+ 8e⁻
NH₃+ 2H₂O → NO₂ ⁻+ 7H⁺+ 6e⁻
2NH₃→ N₂+ 6H⁺+ 6e⁻
[0028]
Subsequent to the oxidation treatment step by the anodic reaction, the treatment is performed by repeating a cycle of introducing a treatment object flowing out of the anode chamber into the cathode chamber and causing a conversion reaction to nitrite nitrogen, ammonia nitrogen, and the like. Efficiency can be improved. At this time, a plurality of electrolyzers are connected, and the aqueous solution processed in one electrolyzer is introduced into the cathode chamber of another electrolyzer to complete the process. A flow-type processing method for performing the processing may be used. At this time, before introducing the object to be treated into the cathode chamber of the second electrolytic cell, the gas containing the generated nitrogen gas may be separated from the object to be treated. Alternatively, a catalytic reactor may be provided here to reduce nitrite nitrogen generated in the anode chamber and convert it to nitrogen gas. Since the separated gas sometimes contains a small amount of NOx, if necessary, the gas is converted to nitrogen gas using a known abatement equipment. As described above, not only the components gasified in the electrolytic cell but also the components converted into nitrite nitrogen in the electrolytic cell are gasified using the catalytic reactor, so that the object to be treated is simply converted into the cathode chamber and the anode chamber. It is possible to remove the dissolved nitrogen component much more efficiently than alternately introducing the nitrogen component.
[0029]
(First step: UV irradiation)
When the ultraviolet irradiation method is used as the first step of the second invention, the nitrate nitrogen is converted into nitrite nitrogen by irradiating the aqueous solution containing nitrate nitrogen with ultraviolet rays using a low-pressure mercury lamp. Convert. In this conversion reaction, ultraviolet rays having a wavelength of about 185 nm emitted from a low-pressure mercury lamp act, so that it is difficult to apply a commercially available black light or high-pressure mercury lamp. Further, the total irradiation time of the ultraviolet rays cannot be unconditionally determined by the content, the concentration, the liquid amount, the temperature, the energy amount of the irradiation ultraviolet rays, and the like of the nitrate nitrogen contained in the aqueous solution as the object to be treated. A range of ６００600 minutes is sufficient.
[0030]
Here, the reaction of converting nitrate nitrogen to nitrite nitrogen is a reversible reaction as described below, and the conversion rate to nitrite nitrogen does not become 100%. The nitrate nitrogen remains in the object to be treated introduced into the vessel.
NO₃ ⁻⇔NO₂ ⁻+ 0.5O₂
[0031]
Since the nitrate nitrogen is not decomposed and removed in the catalyst reactor for introducing the aqueous solution to be treated which has been treated in the first step, the object to be treated after passing through the catalyst reactor is subjected to the ultraviolet irradiation reactor in the first step. The conversion rate can be improved by repeating a cycle in which a part of the nitrate nitrogen is converted into nitrite nitrogen by irradiating ultraviolet rays again and then introduced into the catalytic reactor. At the outlet of the catalytic reactor, the gas containing the generated nitrogen gas may be separated from the object to be treated, similarly to the first embodiment of the present invention. Alternatively, the system may be introduced into another ultraviolet irradiation reactor without reflux, and a flow-type treatment system may be employed.
[0032]
Incidentally, a method of irradiating a sample solution containing nitrate nitrogen with ultraviolet light, reducing nitrate nitrogen to nitrite nitrogen, and then adding a coloring reagent to detect the nitrate nitrogen is disclosed in JP-A-7-151767. At this time, it is described that the conversion rate to nitrite nitrogen is increased by adding ethylenediaminetetraacetic acid or a phosphate. Also in the present invention, by adding these substances and irradiating with ultraviolet rays, the conversion rate to nitrite nitrogen is improved, and therefore, it is expected that the efficiency of removing nitrogen compounds from the object to be treated is also improved. . However, since the additive remains in the solution after the treatment, there is a problem that the environmental load is increased. Therefore, sufficient consideration must be given to its use.
[0033]
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited to these embodiments.
[0034]
(1st Embodiment)
A first embodiment of the present invention will be described with reference to FIG. FIG. 1 relates to the first embodiment of the present invention, and shows a basic configuration of a nitrate nitrogen treatment apparatus when an electrolytic method is used as a first step. In FIG. 1, reference numeral 1 denotes an electrolytic cell that is a nitrite-nitrogen generator. After a certain amount of a nitrate-nitrogen-containing aqueous solution to be treated is introduced into a pipe connecting the electrolytic cell 1 and the catalytic reactor 7 and between these device elements, the circulation of the aqueous solution is started. Note that a pump is used to circulate the aqueous solution that is the object to be treated, but is omitted in the drawings after FIG.
[0035]
At the cathode 2, a reaction occurs in which nitrate nitrogen is reductively converted to nitrite nitrogen, ammonia nitrogen, or the like, and hydrogen gas is generated from water. The cathode chamber 4 and the anode chamber 5 are separated by a cation exchange membrane 6 to suppress the generated nitrite nitrogen from reaching the anode 3 and being oxidized to nitrate nitrogen.
[0036]
Next, the object to be treated flowing out from the cathode chamber 4 through the cathode chamber treated aqueous solution outlet 16 is transferred to the catalytic reactor 7 containing a reducing catalyst such as a hydrogenation catalyst which is a nitrite-nitrogen decomposing device. Is introduced, where the nitrite nitrogen is converted to nitrogen gas. In this reaction, a reducing agent such as hydrogen gas is required. However, hydrogen gas is generated from the cathode 2 by electrolysis, and hydrogen gas is mixed in the aqueous solution. The reduction reaction can be advanced using hydrogen gas. When the amount of hydrogen gas necessary for the reaction is insufficient with only the hydrogen gas generated at the cathode, a reducing agent may be separately supplied from the reducing agent supply container 9. The amount of generated hydrogen gas can be calculated from the gas flow rate and the concentration of hydrogen gas sequentially measured by a gas chromatograph or the like. Conversely, when the amount of hydrogen gas generated at the cathode 2 is excessive than the required amount in the catalytic reactor 7, a gas flow control valve (not shown) is provided at the cathode chamber exhaust gas discharge port 19 to discharge the surplus. Is possible. A gas permeable membrane having a function of allowing gas to permeate but not allowing liquid to permeate may be used for the exhaust gas outlet of the cathode chamber.
[0037]
The reduction catalyst filled in the catalyst reactor 7 can take both a fixed bed type and a suspension bed type. When the reduction catalyst has a honeycomb shape, a fixed bed is preferably used, and when the reduction catalyst is in a powder shape, a suspension bed is preferably used. In the case of a sphere or a pellet, either may be used. At the outlet of the catalytic reactor 7, a gas containing hydrogen gas, nitrogen gas or the like is separated from the aqueous solution by the gas-liquid separator 10, and the aqueous solution mainly containing ammonia nitrogen and nitrate nitrogen is supplied to the electrolytic cell 1. The aqueous solution is introduced into the anode chamber 5 through the anode chamber treatment aqueous solution supply port 17, and the ammoniacal nitrogen contained in the aqueous solution is anodized and converted into nitrate nitrogen, nitrite nitrogen, and the like at the anode 3. The aqueous solution flowing out of the anode chamber 5 via the anode chamber treated aqueous solution discharge port 18 is then returned to the cathode chamber 4 via the cathode chamber reflux supply port 15 and reduced at the cathode 2 to be treated with nitrous acid. A conversion reaction to nitrogen and ammonia nitrogen occurs. By repeating this series of circulation cycles until the concentration of nitrate nitrogen, other nitrite nitrogen and ammonia nitrogen contained in the material to be treated falls below the set value, nitrate nitrogen is removed from the wastewater. Can be removed.
[0038]
(Second embodiment)
A second embodiment of the present invention will be described with reference to FIG. FIG. 2 relates to a second embodiment of the present invention and shows a modification of the first embodiment. In FIG. 2, reference numeral 1 denotes an electrolytic cell which is a nitrite-nitrogen generator. After a certain amount of an aqueous solution containing nitrate nitrogen, which is an object to be treated, is introduced into the electrolytic cell 1, the first catalytic reactor 8, the second catalytic reactor 9, and the piping, the circulation of the aqueous solution is started. In the cathode 2, a reaction occurs in which nitrate nitrogen is converted into nitrite nitrogen, ammonia nitrogen, and the like, and hydrogen gas is generated from water. The cathode chamber 4 and the anode chamber 5 are separated by a cation exchange membrane 6 to suppress the generated nitrite nitrogen from reaching the anode 3 and being oxidized to nitrate nitrogen.
[0039]
Next, the aqueous solution flowing out of the cathode chamber 4 through the cathode chamber treatment aqueous solution outlet 16 is introduced into a first catalytic reactor 7a containing a hydrogenation catalyst, which is a nitrite-nitrogen decomposing device. This converts nitrite nitrogen into nitrogen gas. In the gas-liquid separator 10 installed at the outlet of the first catalytic reactor 7a, the aqueous solution to be treated is separated into a gas containing hydrogen gas, nitrogen gas or the like and an aqueous solution. An aqueous solution mainly containing ammonia nitrogen and nitrate nitrogen is introduced into the anode chamber 5 of the electrolytic cell 1, where it is anodized at the anode 3, and the ammonia nitrogen is converted into nitrate nitrogen, nitrite nitrogen, or the like. The aqueous solution flowing out of the anode chamber 5 via the anode chamber treated aqueous solution outlet 18 is mixed with the gas from the gas-liquid separator 10 and introduced into the second catalytic reactor 7b, where the nitrite nitrogen Is converted to nitrogen gas.
[0040]
At the outlet of the second catalytic reactor 7b, a gas containing hydrogen gas, nitrogen gas or the like is separated from the aqueous solution to be treated, and the aqueous solution mainly containing nitrate nitrogen and ammonia nitrogen is supplied to the electrolytic cell 1 It is introduced into the cathode chamber 4 via the cathode reflux supply port 15, and a conversion reaction to nitrite nitrogen, ammonia nitrogen and the like occurs. This series of circulation cycles is repeated until the concentrations of nitrite nitrogen, other nitrite nitrogen, and ammonia nitrogen contained in the object to be treated fall below the set value.
[0041]
According to this embodiment, two catalytic reactors are provided, and the conversion reaction of nitrite nitrogen into nitrogen gas is performed not only from the aqueous solution that is the substance to be treated flowing out from the cathode chamber 4 but also from the anode chamber 5. By applying the treatment to the outflow target, the efficiency of removing nitrogen compounds from the aqueous solution can be improved.
[0042]
(Third embodiment)
A third embodiment of the present invention will be described with reference to FIG. FIG. 3 relates to a third embodiment of the present invention, and shows a configuration of a flow-through type nitrate nitrogen treatment apparatus which is a modified example of the second embodiment. The basic configuration of this embodiment is almost the same as that of the above-described second embodiment, except that it has two electrolytic cells and four catalytic reactors, and has a flow-through device configuration. The aqueous solution separated from the aqueous solution to be treated at the outlet of the 2-catalyst reactor 7b is introduced into the cathode chamber 4b of the second electrolytic cell 1b, and the treatment is completed in one treatment step without circulating the material to be treated. It is configured to be.
[0043]
According to this embodiment, continuous processing is possible, so that it is not necessary to install a tank for temporarily storing an object to be processed in front of the processing apparatus, so that space can be saved. In addition, the concentration of the aqueous solution as an object to be treated introduced into the respective cathode compartments of the first electrolytic cell 1a and the second electrolytic cell 1b is different. Can be performed under different conditions, for example, by adjusting the applied voltage, etc., so that the processing efficiency can be improved.
[0044]
Further, if necessary, a module composed of one electrolytic cell and two catalytic reactors can be added to the subsequent stage of the second electrolytic cell 1b shown in FIG. The conversion rate of neutral nitrogen to nitrogen gas can be further improved.
[0045]
(Fourth embodiment)
A fourth embodiment of the present invention will be described with reference to FIG. FIG. 4 relates to a fourth embodiment of the present invention, in which zinc is used as a cathode of an electrolytic cell when an electrolytic method is used as a first step, and nitrate nitrogen is treated when almost no ammoniacal nitrogen is generated at the cathode. 1 shows the configuration of the device.
[0046]
In FIG. 4, reference numeral 1 denotes an electrolytic cell which is a nitrite-nitrogen generator. After a certain amount of the nitrate-nitrogen-containing aqueous solution to be treated is introduced into the electrolytic cell 1, the catalytic reactor 7 and the piping, the circulation of the aqueous solution is started. At the cathode 2, a reaction occurs in which nitrate nitrogen is converted to nitrite nitrogen and the like, and hydrogen gas is generated from water. The cathode chamber 4 and the anode chamber 5 are separated by a cation exchange membrane 6 to suppress the generated nitrite nitrogen from reaching the anode 3 and being oxidized to nitrate nitrogen. When the inside of the anode chamber 5 is filled with an aqueous electrolyte solution such as nitric acid, the efficiency of electrolysis is improved. When the aqueous electrolyte solution filled in the anode chamber 5 contains a salt such as sodium nitrate, it is preferable to use a hydrogen ion selective permeable membrane instead of the cation exchange membrane 6.
[0047]
Next, the aqueous solution, which is an object to be processed, flowing out of the cathode chamber 4 through the cathode chamber treated aqueous solution outlet 16 is supplied to the catalytic reactor 7 containing a hydrogenation catalyst, which is a nitrite-nitrogen decomposing device. Is introduced, where the nitrite nitrogen is converted to nitrogen gas. As in the above embodiment, hydrogen gas generated at the cathode 2 can be used as the reducing agent. If the amount of hydrogen gas required for the reaction is insufficient, the reducing agent is separately supplied from the reducing agent supply container 9. Supply. Conversely, when the amount of hydrogen gas generated in the cathode 2 is excessive than the amount required in the catalytic reactor 7, a gas (not shown) connected to a cathode chamber exhaust gas outlet 19 provided in the cathode chamber 4 of the electrolytic cell 1 It is possible to discharge the surplus via the flow control valve. A gas permeable membrane having a function of transmitting gas but not liquid can be used.
[0048]
In FIG. 4, the catalyst reactor 7 can take both a fixed bed type and a suspension bed type. When the catalyst has a honeycomb shape, a fixed bed is used. When the catalyst is a powder, a suspension bed is used. In the case of a sphere or a pellet, either may be used. At the outlet of the catalytic reactor 7, a gas containing hydrogen gas, nitrogen gas, or the like is separated from the aqueous solution to be treated, and the aqueous solution mainly containing unreacted nitrate nitrogen in the electrolytic cell 1 is subjected to electrolysis. It is introduced into the cathode chamber 4 of the cell 1, and a conversion reaction to nitrite nitrogen occurs. This series of circulation cycle is repeated using the apparatus of FIG. 4 until the concentration of nitrate nitrogen or nitrite nitrogen contained in the aqueous solution falls to a set value or less.
[0049]
In the present embodiment, by adopting zinc or a compound thereof as the electrode material of the cathode, nitrate nitrogen can be converted to nitrite nitrogen at the cathode without generating ammoniacal nitrogen. Highly efficient conversion can be performed by the device.
[0050]
(Fifth embodiment)
A fifth embodiment of the present invention will be described with reference to FIG. FIG. 5 relates to a fifth embodiment of the present invention and shows a modification of the fourth embodiment.
[0051]
In FIG. 5, reference numeral 1 denotes an electrolytic cell which is a nitrite-nitrogen generator. After a certain amount of an aqueous solution containing nitrate nitrogen as an object to be treated is introduced into the cathode chamber 4, an electrolytic treatment is performed. The aqueous solution treated in the cathode chamber 4 is connected between the cathode chamber treated aqueous solution discharge port 16 provided in the cathode chamber 4 and the cathode chamber reflux supply port 15 by a pipe, and circulated by a pump (not shown). . In the cathode 2, a reaction in which nitrate nitrogen is converted to nitrite nitrogen or the like and a hydrogen gas is generated from water occurs, and a gas containing the hydrogen gas or the like is provided above the cathode chamber 4. From the cathode chamber exhaust gas outlet 19, it is led to the hydrogen gas holder 11 and stored there. The cathode chamber 4 and the anode chamber 5 are separated by a cation exchange membrane 6 to suppress the generated nitrite nitrogen from reaching the anode 3 and being oxidized to nitrate nitrogen. When the inside of the anode chamber 5 is filled with an aqueous electrolyte solution such as nitric acid, the efficiency of electrolysis is improved. When the aqueous electrolyte solution filled in the anode chamber 5 contains a salt such as sodium nitrate, it is preferable to use a hydrogen ion selective permeable membrane instead of the cation exchange membrane 6.
[0052]
After the completion of the reduction treatment in the electrolytic cell 1, the entire amount of the aqueous solution, which is an object to be treated in which nitrate nitrogen contained in the initial stage is almost completely decomposed, is transferred to the buffer tank 12. A fresh aqueous solution is introduced into the emptied cathode chamber 4, and subjected to electrolytic treatment. The aqueous solution temporarily stored in the buffer tank 12 is mixed with the hydrogen gas-containing gas from the hydrogen gas holder 11 and then introduced into the catalytic reactor 7 containing a hydrogenation catalyst, which is a nitrite-nitrogen decomposing device. Here, nitrite nitrogen is converted to nitrogen gas. If the amount of hydrogen gas required for the reaction is insufficient, it is supplied separately.
[0053]
According to the present embodiment, the hydrogen gas and the aqueous solution generated in the electrolytic cell 1 are accumulated in the hydrogen gas holder 11 and the buffer tank 12, respectively, and then reduced by the reduction catalyst filled in the catalyst reactor 7. Therefore, it is not necessary to calculate the amount of hydrogen gas generated in the electrolytic cell 1 by sequential measurement, and the amount of gas in the hydrogen gas holder 11 and the concentration of hydrogen gas may be measured after the electrolysis is completed. Therefore, the system for measuring the amount of generated hydrogen gas and the system for controlling the amount of hydrogen gas separately supplied can be simplified.
[0054]
(Sixth embodiment)
A sixth embodiment of the present invention will be described with reference to FIG. FIG. 6 relates to a sixth embodiment of the present invention, and shows a configuration of a flow-through type nitrate nitrogen treatment apparatus which is a modified example of the fourth embodiment.
[0055]
In FIG. 6, reference numeral 1 denotes an electrolytic cell that is a nitrite-nitrogen generator. A nitrate-nitrogen-containing aqueous solution as an object to be treated is continuously introduced into the cathode chamber 4. At the cathode 2, a reaction occurs in which nitrate nitrogen is converted to nitrite nitrogen and the like, and hydrogen gas is generated from water. The cathode chamber 4 and the anode chamber 5 are separated by a cation exchange membrane 6 to suppress the generated nitrite nitrogen from reaching the anode 3 and being oxidized to nitrate nitrogen. When the inside of the anode chamber 5 is filled with an aqueous electrolyte solution such as nitric acid, the efficiency of electrolysis is improved. When the electrolyte aqueous solution filled in the anode chamber 5 contains a salt such as sodium nitrate, it is preferable to use a hydrogen ion selective permeable membrane for 6.
[0056]
In the electrolytic cell 1 of FIG. 6, the reduction treatment is sufficiently completed in the course of the flow of the aqueous solution to be treated, and the nitrate nitrogen contained in the initial stage is almost completely decomposed. Next, the aqueous solution is introduced into a catalytic reactor 7 containing a hydrogenation catalyst, which is a nitrite-nitrogen decomposing device, where the nitrite nitrogen is converted into nitrogen gas.
[0057]
According to this embodiment, continuous processing is possible, so that it is not necessary to install a tank for temporarily storing an object to be processed in front of the processing apparatus, so that space can be saved. Further, by using zinc or a compound thereof as a cathode, production of ammonia nitrogen can be suppressed, and efficient treatment can be performed.
[0058]
(Seventh embodiment)
A seventh embodiment of the present invention will be described with reference to FIG. FIG. 7 relates to the second embodiment of the present invention, and shows the configuration of a nitrate nitrogen treatment apparatus when an ultraviolet irradiation method is used as the first step. As shown in FIG. 7, the processing apparatus according to this embodiment includes at least an ultraviolet irradiation reactor 21 that is a nitrite-nitrogen generator, and a catalyst reactor 7 that is a nitrite-nitrogen decomposer. . The ultraviolet reactor 13 has a structure in which an aqueous solution flowing pipe 23 as an object to be processed, for example, an amorphous fluororesin tube or a quartz glass tube coil is wound around an ultraviolet generator 22 such as a low-pressure mercury lamp. I can do it. When the aqueous solution flow pipe 23 is made of quartz glass, the conversion rate of nitrate nitrogen to nitrite nitrogen can be further improved by using synthetic quartz having a high transmittance of ultraviolet rays having a wavelength of about 185 nm.
[0059]
In order to treat nitrate nitrogen using this apparatus, first, the nitrate nitrogen-containing aqueous solution to be treated is placed in the ultraviolet irradiation reactor 21, the catalyst reactor 7, and the piping connecting these device elements. After a certain amount of introduction, circulation is started. In the ultraviolet irradiation reactor 13, a part of the nitrate nitrogen in the object to be treated is converted into nitrite nitrogen, and the catalyst reactor 7 containing the hydrogenation catalyst together with the hydrogen gas supplied from the reducing agent supply container 9. To convert the nitrite nitrogen into nitrogen gas. Hydrogen gas is continuously supplied, for example, in the process up to the supply port of the catalytic reactor 7, and at the outlet of the catalytic reactor 7, a mixed gas of hydrogen gas not consumed in the reduction reaction and nitrogen gas generated is used. It is possible to discharge separately. This gas can of course be refluxed before the catalytic reactor 7.
[0060]
Subsequently, the aqueous solution, which is an object to be treated, which has been treated in the catalytic reactor 7 is separated from a product gas such as nitrogen gas by the gas-liquid separator 10 and is returned to the inlet of the ultraviolet irradiation reactor 13. As described above, in the ultraviolet irradiation reactor 21, the conversion rate to nitrite nitrogen does not become 100%, so that the nitrate nitrogen remains in the treatment object flowing out of the catalyst reactor 7. I have. The object to be treated is again irradiated with ultraviolet rays, and a part of the remaining nitrate nitrogen is converted into nitrite nitrogen. This series of circulation cycle is repeated until the concentration of nitrate nitrogen or nitrite nitrogen contained in the object to be treated falls below a set value, and then discharged to the outside, and the ultraviolet irradiation reactor 13 and the catalyst reactor 7 are discharged. And a new object to be treated is introduced into the pipe.
[0061]
The catalyst reactor 7 can take both a fixed bed type and a suspension bed type as in the embodiment employing the above-described electrolytic treatment. When the catalyst has a honeycomb shape, a fixed bed is used. When the catalyst is a powder, a suspension bed is used. In the case of a sphere or a pellet, either may be used.
[0062]
According to this embodiment, the reduction treatment of nitrate nitrogen can be performed by irradiation with ultraviolet rays, and thus the treatment can be performed without requiring a large-scale apparatus such as an electrolytic treatment apparatus. Device can be realized.
[0063]
(Eighth embodiment)
An eighth embodiment of the present invention will be described with reference to FIG. FIG. 8 relates to an eighth embodiment of the present invention, and shows a configuration of a flow-through type nitrate nitrogen treatment apparatus which is a modification of the seventh embodiment.
[0064]
The configuration of this embodiment is almost the same as the seventh embodiment. However, instead of the circulation type processing in the above-described embodiment, the flow type apparatus is configured to perform the processing in one pass from the introduction to the discharge of the aqueous solution as the object to be processed.
[0065]
In the gas-liquid separator 10 installed at the outlet of the first catalytic reactor 8, the object to be treated is separated into a gas containing hydrogen gas and an aqueous solution. The aqueous solution is introduced into the inlet of the second ultraviolet irradiation reactor 21b. Here, nitrate nitrogen is converted to nitrite nitrogen, and subsequently introduced into the second catalytic reactor 7b together with the gas from the gas-liquid separator 10 to convert nitrite nitrogen to nitrogen gas. If necessary, not only one module consisting of two ultraviolet irradiation reactors and two catalytic reactors as shown in FIG. 8 but also nitrate nitrogen or nitrite nitrogen contained in the object to be treated. Are arranged in series as necessary to reduce the concentration of the solution below the set value.
[0066]
According to the present embodiment, continuous processing is possible, so that it is not necessary to install a tank for temporarily storing the object to be processed in front of the processing apparatus, so that space can be saved.
[0067]
【Example】
(Examples 1 to 4)
Using the treatment apparatus shown in FIG. 1, the nitrate-nitrogen-containing aqueous solution shown in Table 1 was treated under the conditions shown in the same table. In Example 1, simulated wastewater in which the nitrate nitrogen concentration was adjusted to 100 mg / L was treated. In Example 2, groundwater immediately before being introduced into the water treatment plant was treated. In Example 3, as a part of the process of treating semiconductor factory wastewater containing about 1000 mg / L of fluorine as a main component and recycling it as a high-concentration fluorine-containing chemical solution, nitrate nitrogen as an impurity was removed. Was. In Example 4, wastewater from a plating plant containing a high concentration of nitrate nitrogen was treated.
[0068]
[Table 1]

[0069]
In each case, the circulation treatment was started after about 10 L of the object to be treated was introduced into the electrolytic cell 1 and the catalytic reactor 7. The liquid temperature of the object was kept at 20 ° C. Electrolysis was performed at a constant current. Except for Example 2, a stainless fiber sintered body was used as a porous base material of the cathode 2, and a titanium fiber sintered body was used as a base material of the anode 3 in all cases. Each of the catalytic reactors 7 is of a fixed bed type. The amount of hydrogen gas introduced here was determined based on the flow rate of nitrite nitrogen calculated by monitoring the concentration of nitrite nitrogen at the outlet of the cathode chamber 4 of the electrolytic cell 1. The hydrogen gas equivalent ratio in Table 1 showing the amount is the hydrogen gas necessary to convert 1 mol of nitrite nitrogen to nitrogen gas in (mol flow rate of hydrogen gas / mol flow rate of nitrite nitrogen). Is the ratio to the number of moles of 1.5. At the outlet of the cathode chamber 4, the flow rate of the gas generated at the cathode 2 and the hydrogen gas concentration were also monitored, and only when the calculated flow rate of the hydrogen gas was lower than the required amount, the shortage was supplemented from the hydrogen gas cylinder. After this circulation treatment was performed for the circulation treatment time shown in Table 1, the entire amount was collected in a tank, and the result of analysis was shown in Table 2.
[0070]
[Table 2]

[0071]
As can be seen from Table 2 above, in each case, the nitrate nitrogen was successfully removed, and the amount of the residual nitrogen compound represented by the total nitrogen amount was small.
[0072]
(Comparative Examples 1-4)
Using the processing apparatus shown in FIG. 9, the same processing target as in Examples 1 to 4 was processed under the same conditions as in Examples 1 to 4 described in Table 3. No catalytic reactor 7 was used.
[0073]
[Table 3]

[0074]
After the circulation treatment was performed for the same circulation treatment time as in Examples 1 to 4, the entire amount was collected in a tank, and the result of the analysis is shown in Table 4.
[0075]
[Table 4]

[0076]
As is clear from Table 4, in any of the above comparative examples, nitrate nitrogen, nitrite nitrogen, and total nitrogen were detected at concentrations much higher than the results of Examples 1 to 4, indicating that the decomposition efficiency was low. It was revealed.
[0077]
(Examples 5 to 8)
Using the processing apparatus shown in FIG. 2, the same workpieces as those processed in Examples 1 to 4 were processed under the conditions shown in Table 5.
[0078]
[Table 5]

[0079]
The treatment conditions were the same as in Examples 1 to 4 except for the circulating treatment time. However, a second catalytic reactor 9 was additionally installed to decompose nitrite nitrogen contained in the treatment object flowing out of the anode chamber 5. did. The first catalytic reactor 8 and the second catalytic reactor 9 have the same shape and are filled with the same amount of the same catalyst. The amount of hydrogen gas introduced into both catalyst reactors was determined based on the sum of the flow rates of nitrite nitrogen, which was calculated by monitoring the concentration of nitrite nitrogen at the outlet of the cathode chamber 4 and the outlet of the anode chamber 5. The hydrogen gas equivalent ratio in Table 5 showing the amount is the hydrogen gas necessary to convert 1 mol of nitrite nitrogen to nitrogen gas in (mol flow rate of hydrogen gas / mol flow rate of nitrite nitrogen). Is the ratio to the number of moles of 1.5. At the outlet of the cathode chamber 4, the flow rate of the gas generated at the cathode 2 and the hydrogen gas concentration were also monitored, and only when the calculated flow rate of the hydrogen gas was lower than the required amount, the shortage was supplemented from the hydrogen gas cylinder. After this circulation treatment was performed for the circulation treatment time shown in Table 5, the entire amount was collected in a tank, and the result of analysis was shown in Table 6.
[0080]
[Table 6]

[0081]
As is clear from the results in Table 6, in Examples 5 to 8, although the treatment time was shorter than Examples 1 to 4, the water quality after the treatment was almost the same.
[0082]
(Examples 9 to 12)
Using the processing apparatus shown in FIG. 3, the same processing target as in Examples 1 to 4 was processed under the conditions shown in Table 7. However, five modules composed of one electrolytic cell and two catalytic reactors were installed in series.
[0083]
[Table 7]

[0084]
In each case, the liquid temperature of the object was kept at 30 ° C. In all cases, a titanium fiber sintered body was used as a porous substrate of the cathode 2 and the anode 3. Electrolysis was performed at a constant current. The first catalytic reactor 8 and the second catalytic reactor 9 have the same shape and are fixed-bed catalytic reactors filled with the same amount of the same catalyst. The amount of hydrogen gas introduced into both catalyst reactors was determined based on the sum of the flow rates of nitrite nitrogen, which was calculated by monitoring the concentration of nitrite nitrogen at the outlet of the cathode chamber 4 and the outlet of the anode chamber 5. The hydrogen gas equivalent ratio in Table 7 indicating the amount is the hydrogen gas necessary to convert 1 mol of nitrite nitrogen to nitrogen gas in (mol flow rate of hydrogen gas / mol flow rate of nitrite nitrogen). Is the ratio to the number of moles of 1.5. At the outlet of the cathode chamber 4, the flow rate of the gas generated at the cathode 2 and the hydrogen gas concentration were also monitored, and only when the calculated flow rate of the hydrogen gas was lower than the required amount, the shortage was supplemented from the hydrogen gas cylinder. Table 8 shows the results when this process was performed continuously for 24 hours. The result is the average of the values sampled hourly at the exit of the fifth module.
[0085]
[Table 8]

[0086]
As is clear from Table 8, in each case, the nitrate nitrogen was successfully removed, and the amount of the residual nitrogen compound represented by the total nitrogen amount was small.
[0087]
(Examples 13 to 16)
Using the processing apparatus shown in FIG. 4, the same workpieces as those processed in Examples 1 to 4 were processed under the conditions shown in Table 9.
[0088]
[Table 9]

[0089]
In all of Examples 13 to 16, after about 5 L of the material to be treated was introduced into the cathode chamber 4 of the electrolytic cell 1 and the catalyst reactor 7, the circulation treatment was started. The liquid temperature of the object was kept at 20 ° C. Electrolysis was performed at a constant current. In all cases, a sintered stainless steel fiber was used as a porous base material of the cathode 2 and a titanium fiber sintered body was used as a base material of the anode 3. Each of the catalytic reactors 7 is of a fixed bed type. The amount of hydrogen gas introduced here was determined based on the flow rate of nitrite nitrogen calculated by monitoring the concentration of nitrite nitrogen at the outlet of the cathode chamber 4 of the electrolytic cell 1. The hydrogen gas equivalent ratio in Table 9 showing the amount is the hydrogen gas necessary to convert 1 mol of nitrite nitrogen to nitrogen gas in (mol flow rate of hydrogen gas / mol flow rate of nitrite nitrogen). Is the ratio to the number of moles of 1.5. At the outlet of the cathode chamber 4, the flow rate of the gas generated at the cathode 2 and the hydrogen gas concentration were also monitored, and only when the calculated flow rate of the hydrogen gas was lower than the required amount, the shortage was supplemented from the hydrogen gas cylinder. After this circulation treatment was performed for the circulation treatment time shown in Table 9, the entire amount was collected in a tank, and the result of analysis was shown in Table 10.
[0090]
[Table 10]

[0091]
As is clear from the results in Table 10, in each case of this example, nitrate nitrogen was well removed, and the residual amount of the entire nitrogen compound indicated by the total nitrogen amount was small. Almost no ammoniacal nitrogen was detected.
[0092]
(Examples 17 to 20)
Using the processing apparatus shown in FIG. 5, the same processing target as in Examples 1 to 4 was processed under the conditions shown in Table 11.
[0093]
[Table 11]

[0094]
In each of Examples 17 to 20 of the present invention, after about 5 L of the material to be treated was introduced into the cathode chamber 4 of the electrolytic cell 1 and the catalytic reactor 7, the circulation treatment was started. The liquid temperature of the object was kept at 20 ° C. Electrolysis was performed at a constant current. In all cases, a titanium fiber sintered body was used as a porous substrate of the cathode 2 and the anode 3. Electrolysis was performed at a constant current. After the electrolytic treatment, the entire amount of the aqueous solution was once transferred to the buffer tank 12, mixed with the hydrogen gas-containing gas stored in the hydrogen gas holder 11, and introduced into the catalyst reactor 7 little by little. The amount of hydrogen gas introduced here was determined based on the flow rate of nitrite nitrogen, which was calculated by analyzing the concentration of nitrite nitrogen in the buffer tank 12. The hydrogen gas equivalent ratio in Table 11 indicating the amount is the hydrogen gas required to convert 1 mol of nitrite nitrogen to nitrogen gas in (mol flow rate of hydrogen gas / mol flow rate of nitrite nitrogen). Is the ratio to the number of moles of 1.5. Only when the flow rate of the hydrogen gas from the hydrogen gas holder 11 was lower than the required amount, the shortage was compensated from the hydrogen gas cylinder. Table 12 shows the results obtained by collecting the entire amount of the object to be processed after completion of the series of processing in the tank and analyzing it.
[0095]
[Table 12]

[0096]
As is clear from the results in Table 12, in each case, nitrate nitrogen was successfully removed, and the residual amount of the entire nitrogen compound represented by the total nitrogen amount was small. Almost no ammoniacal nitrogen was detected.
[0097]
(Examples 21 to 24)
Using the processing apparatus shown in FIG. 6, the same processing target as in Examples 1 to 4 was processed under the conditions described in Table 13.
[0098]
[Table 13]

[0099]
The object to be treated was continuously introduced into the cathode chamber 4 and subjected to electrolytic treatment. In each case, the liquid temperature of the object was kept at 30 ° C. Electrolysis was performed at a constant current. In all cases, a sintered stainless steel fiber was used as a porous base material of the cathode 2 and a titanium fiber sintered body was used as a base material of the anode 3. Each of the catalytic reactors 7 is of a fixed bed type. The amount of hydrogen gas introduced here was determined based on the flow rate of nitrite nitrogen calculated by monitoring the concentration of nitrite nitrogen at the outlet of the cathode chamber 4 of the electrolytic cell 1. The hydrogen gas equivalent ratio in Table 13 showing the amount is the hydrogen gas necessary to convert 1 mol of nitrite nitrogen to nitrogen gas in (mol flow rate of hydrogen gas / mol flow rate of nitrite nitrogen). Is the ratio to the number of moles of 1.5. At the outlet of the cathode chamber 4, the flow rate of the gas generated at the cathode 2 and the hydrogen gas concentration were also monitored, and only when the calculated flow rate of the hydrogen gas was lower than the required amount, the shortage was supplemented from the hydrogen gas cylinder. Table 14 shows the results obtained when this process was performed continuously for 24 hours. The result is the average of the values sampled every hour at the outlet of the catalytic reactor 7.
[0100]
[Table 14]

[0101]
As is clear from Table 14, in each case, nitrate nitrogen was successfully removed, and the residual amount of the entire nitrogen compound represented by the total nitrogen amount was small. Almost no ammoniacal nitrogen was detected.
[0102]
(Examples 25 to 28)
Using the processing apparatus shown in FIG. 7, the same processing target as in Examples 1 to 4 was processed under the conditions shown in Table 15.
[0103]
[Table 15]

[0104]
After introducing these into the ultraviolet irradiation reactor 13 and the catalyst reactor 7, the circulation treatment was started. The liquid temperature of the object was kept at 40 ° C. A low-pressure mercury lamp having a total output of 60 W was used as a light source of the ultraviolet irradiation reactor 13. Each of the catalyst reactors 7 is of a fixed bed type. Hydrogen gas was continuously supplied from just before the catalyst reactor 7, and hydrogen gas not consumed in the reduction reaction and nitrogen gas generated were discharged from the outlet of the catalyst reactor 7 to the outside. The aqueous solution was refluxed at the inlet of the ultraviolet irradiation reactor 13. The amount of the supplied hydrogen gas was determined by monitoring the nitrite nitrogen concentration at the outlet of the ultraviolet irradiation reactor 13 and was set to a molar flow rate 15 times the molar flow rate of the nitrite nitrogen calculated from the concentration. That is, the hydrogen gas equivalent ratio was controlled to always be 10. After this circulation treatment was performed for the circulation treatment time shown in Table 15, the entire amount was collected in a tank, and the result of analysis was shown in Table 16.
[0105]
[Table 16]

[0106]
In each case, the nitrate nitrogen was successfully removed, and the amount of the residual nitrogen compound indicated by the total nitrogen amount was small. Almost no ammoniacal nitrogen was detected.
[0107]
(Examples 29 to 32)
Using the processing apparatus shown in FIG. 8, the same processing target as in Examples 1 to 4 was processed under the conditions shown in Table 17. However, five modules composed of two ultraviolet irradiation reactors and two catalyst reactors were installed in series.
[0108]
[Table 17]

[0109]
In each case, the liquid temperature of the object was kept at 30 ° C. The first ultraviolet irradiation reactor 14 and the second ultraviolet irradiation reactor 15 have the same shape and are made of the same material. A low-pressure mercury lamp with an output of 6 W was used as the light source. Further, the first catalyst reactor 8 and the second catalyst reactor 9 have the same shape, and are fixed-bed catalyst reactors filled with the same amount of the same catalyst. Hydrogen gas was continuously supplied before the first catalytic reactor 8, and hydrogen gas not consumed in the reduction reaction and nitrogen gas generated were discharged from the outlet of the second catalytic reactor 9 to the outside. . The aqueous solution was introduced into the inlet of the ultraviolet irradiation reactor of the next module. The amount of the supplied hydrogen gas was calculated based on the nitrite nitrogen concentration at the outlet of the first ultraviolet irradiation reactor 14 and the outlet of the second ultraviolet irradiation reactor 15, and was calculated with respect to the sum of the molar flow rates of nitrite nitrogen. The molar flow rate was 15 times. That is, the hydrogen gas equivalent ratio was controlled to always be 10. Table 18 shows the results when this process was performed continuously for 24 hours. The result is the average of the values sampled hourly at the exit of the fifth module.
[0110]
[Table 18]

[0111]
As is clear from Table 18, in each case, nitrate nitrogen was successfully removed, and the residual amount of the nitrogen compound as a whole indicated by the total nitrogen amount was small. Almost no ammoniacal nitrogen was detected.
[0112]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the disadvantage of the conventional nitric-nitrogen decomposition processing method is eliminated, it is compact and highly efficient, and after processing, nitrate nitrogen, nitrite nitrogen, ammonia nitrogen, etc. which remain in water after treatment. It is possible to provide a method and an apparatus for decomposing nitrate nitrogen, which can reduce the load on the environment by minimizing the concentration of nitrogen compounds.
[Brief description of the drawings]
FIG. 1 is a view showing an apparatus for treating nitrate nitrogen according to a first embodiment of the present invention.
FIG. 2 is a diagram showing a nitrate nitrogen treatment apparatus according to a second embodiment of the present invention.
FIG. 3 is a diagram showing a nitrate nitrogen treatment apparatus according to a third embodiment of the present invention.
FIG. 4 is a view showing a nitrate nitrogen treatment apparatus according to a fourth embodiment of the present invention.
FIG. 5 is a diagram showing a nitrate nitrogen treatment apparatus according to a fifth embodiment of the present invention.
FIG. 6 is a view showing a nitrate nitrogen treating apparatus according to a sixth embodiment of the present invention.
FIG. 7 is a diagram illustrating a nitrate nitrogen treatment apparatus according to a seventh embodiment of the present invention.
FIG. 8 is a view showing an apparatus for treating nitrate nitrogen according to an eighth embodiment of the present invention.
FIG. 9 is a diagram showing a comparative example of the first embodiment of the present invention.
[Explanation of symbols]
1 .... electrolyzer
2 ... Cathode
3… Anode
4: Cathode room
5. Anode chamber
6 ... Cation exchange membrane (hydrogen ion selective permeable membrane)
7 ... Catalyst reactor
8. Aqueous solution supply container
9 ... Reducing agent supply container
10 gas-liquid separator
11 ... Hydrogen gas holder
12 ... Buffer tank
13 ... Valve
14. Cathode chamber treatment aqueous solution supply port
15 ... Cathode room reflux supply port
16: Cathode chamber treatment aqueous solution outlet
17 ... Anode chamber treatment aqueous solution supply port
18: Aqueous solution outlet for anode chamber treatment
19: Cathode chamber exhaust gas outlet
20… Anode exhaust gas outlet
21 ... UV irradiation reactor
22 ... Ultraviolet generator
23… Aqueous solution flow piping
24: Treatment aqueous solution supply port
25: Treatment aqueous solution outlet

Claims (5)

A first step of electrolyzing an aqueous solution containing nitrate nitrogen supplied to a cathode chamber of an electrolytic cell to reduce at least nitrate nitrogen contained in the aqueous solution to produce at least acidic nitrogen oxides;
A method for treating nitrate nitrogen, comprising at least a second step of adding a reducing agent to the aqueous solution reduced in the first step and bringing the aqueous solution into contact with a reduction catalyst to reduce acidic nitrogen oxides. The aqueous solution subjected to the reduction treatment in the second step is supplied to an anode chamber of the electrolytic cell, and a nitrogen compound by-produced in the first step is converted into nitrate nitrogen.
The method for treating nitrate nitrogen according to claim 1, wherein the aqueous solution containing the converted nitrate nitrogen is supplied to a cathode chamber of the electrolytic cell. A first step of reducing nitrate nitrogen to generate at least nitrate nitrogen oxide by irradiating the aqueous solution containing nitrate nitrogen with ultraviolet light;
A method for treating nitrate nitrogen, comprising at least a second step of adding a reducing agent to the aqueous solution reduced in the first step and bringing the aqueous solution into contact with a reduction catalyst to reduce the acidic nitrogen oxides. An anode and a cathode, and an electrolytic cell provided with a diaphragm for separating the anode and the cathode,
An apparatus for treating nitrate nitrogen, comprising at least a catalytic reactor filled with a reduction catalyst for supplying an electrolytic product generated at a cathode portion of the electrolytic cell and performing a contact treatment. An ultraviolet irradiation device, an ultraviolet irradiation reactor comprising an ultraviolet-permeable pipe disposed around the ultraviolet generator,
And a catalyst reactor filled with a reduction catalyst for supplying a reactant generated in the ultraviolet irradiation reactor and performing contact treatment.

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