JP5981799B2 - Wastewater treatment method - Google Patents
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- JP5981799B2 JP5981799B2 JP2012172493A JP2012172493A JP5981799B2 JP 5981799 B2 JP5981799 B2 JP 5981799B2 JP 2012172493 A JP2012172493 A JP 2012172493A JP 2012172493 A JP2012172493 A JP 2012172493A JP 5981799 B2 JP5981799 B2 JP 5981799B2
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- 238000004065 wastewater treatment Methods 0.000 title claims description 44
- QGZKDVFQNNGYKY-UHFFFAOYSA-N Ammonia Chemical compound N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 claims description 112
- 239000007864 aqueous solution Substances 0.000 claims description 57
- 229910021529 ammonia Inorganic materials 0.000 claims description 56
- 239000011941 photocatalyst Substances 0.000 claims description 54
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 51
- IOVCWXUNBOPUCH-UHFFFAOYSA-N Nitrous acid Chemical compound ON=O IOVCWXUNBOPUCH-UHFFFAOYSA-N 0.000 claims description 39
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 claims description 34
- 229910017604 nitric acid Inorganic materials 0.000 claims description 34
- 229910052757 nitrogen Inorganic materials 0.000 claims description 22
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical group O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 claims description 11
- 239000003795 chemical substances by application Substances 0.000 claims description 7
- 238000006243 chemical reaction Methods 0.000 description 60
- HEMHJVSKTPXQMS-UHFFFAOYSA-M Sodium hydroxide Chemical compound [OH-].[Na+] HEMHJVSKTPXQMS-UHFFFAOYSA-M 0.000 description 30
- 229910010413 TiO 2 Inorganic materials 0.000 description 30
- 238000000034 method Methods 0.000 description 27
- 230000000694 effects Effects 0.000 description 26
- 230000001678 irradiating effect Effects 0.000 description 19
- 238000006552 photochemical reaction Methods 0.000 description 15
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 14
- 239000000126 substance Substances 0.000 description 13
- 238000013032 photocatalytic reaction Methods 0.000 description 12
- CAMXVZOXBADHNJ-UHFFFAOYSA-N ammonium nitrite Chemical compound [NH4+].[O-]N=O CAMXVZOXBADHNJ-UHFFFAOYSA-N 0.000 description 11
- 239000003054 catalyst Substances 0.000 description 11
- JVMRPSJZNHXORP-UHFFFAOYSA-N ON=O.ON=O.ON=O.N Chemical compound ON=O.ON=O.ON=O.N JVMRPSJZNHXORP-UHFFFAOYSA-N 0.000 description 10
- 239000000758 substrate Substances 0.000 description 10
- 230000007423 decrease Effects 0.000 description 8
- QSHDDOUJBYECFT-UHFFFAOYSA-N mercury Chemical compound [Hg] QSHDDOUJBYECFT-UHFFFAOYSA-N 0.000 description 8
- 229910052753 mercury Inorganic materials 0.000 description 8
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 7
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Substances [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 7
- 239000002351 wastewater Substances 0.000 description 7
- 239000006227 byproduct Substances 0.000 description 6
- 238000010586 diagram Methods 0.000 description 6
- 239000007788 liquid Substances 0.000 description 6
- 238000004519 manufacturing process Methods 0.000 description 6
- 239000000243 solution Substances 0.000 description 6
- 238000009281 ultraviolet germicidal irradiation Methods 0.000 description 6
- 239000002699 waste material Substances 0.000 description 6
- MMDJDBSEMBIJBB-UHFFFAOYSA-N [O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[NH6+3] Chemical compound [O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[NH6+3] MMDJDBSEMBIJBB-UHFFFAOYSA-N 0.000 description 5
- 238000010521 absorption reaction Methods 0.000 description 5
- 230000003197 catalytic effect Effects 0.000 description 5
- 239000010949 copper Substances 0.000 description 5
- 230000003247 decreasing effect Effects 0.000 description 5
- -1 nitrate ions Chemical class 0.000 description 5
- OGIDPMRJRNCKJF-UHFFFAOYSA-N titanium oxide Inorganic materials [Ti]=O OGIDPMRJRNCKJF-UHFFFAOYSA-N 0.000 description 5
- 238000000354 decomposition reaction Methods 0.000 description 4
- 229910017464 nitrogen compound Inorganic materials 0.000 description 4
- 150000002830 nitrogen compounds Chemical class 0.000 description 4
- KDLHZDBZIXYQEI-UHFFFAOYSA-N palladium Substances [Pd] KDLHZDBZIXYQEI-UHFFFAOYSA-N 0.000 description 4
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- 239000004065 semiconductor Substances 0.000 description 4
- 239000010802 sludge Substances 0.000 description 4
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- WSFSSNUMVMOOMR-UHFFFAOYSA-N Formaldehyde Chemical compound O=C WSFSSNUMVMOOMR-UHFFFAOYSA-N 0.000 description 3
- MUBZPKHOEPUJKR-UHFFFAOYSA-N Oxalic acid Chemical compound OC(=O)C(O)=O MUBZPKHOEPUJKR-UHFFFAOYSA-N 0.000 description 3
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 3
- XKMRRTOUMJRJIA-UHFFFAOYSA-N ammonia nh3 Chemical compound N.N XKMRRTOUMJRJIA-UHFFFAOYSA-N 0.000 description 3
- 238000010170 biological method Methods 0.000 description 3
- 230000007613 environmental effect Effects 0.000 description 3
- 229910021645 metal ion Inorganic materials 0.000 description 3
- QJGQUHMNIGDVPM-UHFFFAOYSA-N nitrogen group Chemical group [N] QJGQUHMNIGDVPM-UHFFFAOYSA-N 0.000 description 3
- 230000003647 oxidation Effects 0.000 description 3
- 238000007254 oxidation reaction Methods 0.000 description 3
- 238000006479 redox reaction Methods 0.000 description 3
- 238000006722 reduction reaction Methods 0.000 description 3
- 230000007704 transition Effects 0.000 description 3
- IKHGUXGNUITLKF-UHFFFAOYSA-N Acetaldehyde Chemical compound CC=O IKHGUXGNUITLKF-UHFFFAOYSA-N 0.000 description 2
- RZVAJINKPMORJF-UHFFFAOYSA-N Acetaminophen Chemical compound CC(=O)NC1=CC=C(O)C=C1 RZVAJINKPMORJF-UHFFFAOYSA-N 0.000 description 2
- CIWBSHSKHKDKBQ-JLAZNSOCSA-N Ascorbic acid Chemical compound OC[C@H](O)[C@H]1OC(=O)C(O)=C1O CIWBSHSKHKDKBQ-JLAZNSOCSA-N 0.000 description 2
- 241000894006 Bacteria Species 0.000 description 2
- 239000002028 Biomass Substances 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 2
- UFHFLCQGNIYNRP-UHFFFAOYSA-N Hydrogen Chemical compound [H][H] UFHFLCQGNIYNRP-UHFFFAOYSA-N 0.000 description 2
- LRHPLDYGYMQRHN-UHFFFAOYSA-N N-Butanol Chemical compound CCCCO LRHPLDYGYMQRHN-UHFFFAOYSA-N 0.000 description 2
- 229910002651 NO3 Inorganic materials 0.000 description 2
- IOVCWXUNBOPUCH-UHFFFAOYSA-M Nitrite anion Chemical compound [O-]N=O IOVCWXUNBOPUCH-UHFFFAOYSA-M 0.000 description 2
- 230000002378 acidificating effect Effects 0.000 description 2
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- 239000011575 calcium Substances 0.000 description 2
- 150000001875 compounds Chemical class 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- XBDQKXXYIPTUBI-UHFFFAOYSA-N dimethylselenoniopropionate Natural products CCC(O)=O XBDQKXXYIPTUBI-UHFFFAOYSA-N 0.000 description 2
- 238000002848 electrochemical method Methods 0.000 description 2
- 239000003344 environmental pollutant Substances 0.000 description 2
- 239000005383 fluoride glass Substances 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 229910052742 iron Inorganic materials 0.000 description 2
- 230000007246 mechanism Effects 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- BDAGIHXWWSANSR-UHFFFAOYSA-N methanoic acid Natural products OC=O BDAGIHXWWSANSR-UHFFFAOYSA-N 0.000 description 2
- 239000000203 mixture Substances 0.000 description 2
- 230000001590 oxidative effect Effects 0.000 description 2
- 229910052760 oxygen Inorganic materials 0.000 description 2
- 230000001699 photocatalysis Effects 0.000 description 2
- 238000006303 photolysis reaction Methods 0.000 description 2
- 238000011197 physicochemical method Methods 0.000 description 2
- 229910052697 platinum Inorganic materials 0.000 description 2
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- BDERNNFJNOPAEC-UHFFFAOYSA-N propan-1-ol Chemical compound CCCO BDERNNFJNOPAEC-UHFFFAOYSA-N 0.000 description 2
- 239000005297 pyrex Substances 0.000 description 2
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- 238000002371 ultraviolet--visible spectrum Methods 0.000 description 2
- OSWFIVFLDKOXQC-UHFFFAOYSA-N 4-(3-methoxyphenyl)aniline Chemical compound COC1=CC=CC(C=2C=CC(N)=CC=2)=C1 OSWFIVFLDKOXQC-UHFFFAOYSA-N 0.000 description 1
- GMVPRGQOIOIIMI-DODZYUBVSA-N 7-[(1R,2R,3R)-3-hydroxy-2-[(3S)-3-hydroxyoct-1-enyl]-5-oxocyclopentyl]heptanoic acid Chemical compound CCCCC[C@H](O)C=C[C@H]1[C@H](O)CC(=O)[C@@H]1CCCCCCC(O)=O GMVPRGQOIOIIMI-DODZYUBVSA-N 0.000 description 1
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 1
- QGZKDVFQNNGYKY-UHFFFAOYSA-O Ammonium Chemical compound [NH4+] QGZKDVFQNNGYKY-UHFFFAOYSA-O 0.000 description 1
- NLXLAEXVIDQMFP-UHFFFAOYSA-N Ammonium chloride Substances [NH4+].[Cl-] NLXLAEXVIDQMFP-UHFFFAOYSA-N 0.000 description 1
- 229910004613 CdTe Inorganic materials 0.000 description 1
- 229910020599 Co 3 O 4 Inorganic materials 0.000 description 1
- 229910002515 CoAl Inorganic materials 0.000 description 1
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 1
- 229910002528 Cu-Pd Inorganic materials 0.000 description 1
- MHAJPDPJQMAIIY-UHFFFAOYSA-N Hydrogen peroxide Chemical compound OO MHAJPDPJQMAIIY-UHFFFAOYSA-N 0.000 description 1
- DGAQECJNVWCQMB-PUAWFVPOSA-M Ilexoside XXIX Chemical compound C[C@@H]1CC[C@@]2(CC[C@@]3(C(=CC[C@H]4[C@]3(CC[C@@H]5[C@@]4(CC[C@@H](C5(C)C)OS(=O)(=O)[O-])C)C)[C@@H]2[C@]1(C)O)C)C(=O)O[C@H]6[C@@H]([C@H]([C@@H]([C@H](O6)CO)O)O)O.[Na+] DGAQECJNVWCQMB-PUAWFVPOSA-M 0.000 description 1
- 229910001030 Iron–nickel alloy Inorganic materials 0.000 description 1
- 229910020068 MgAl Inorganic materials 0.000 description 1
- 229910000943 NiAl Inorganic materials 0.000 description 1
- NPXOKRUENSOPAO-UHFFFAOYSA-N Raney nickel Chemical compound [Al].[Ni] NPXOKRUENSOPAO-UHFFFAOYSA-N 0.000 description 1
- 229910004298 SiO 2 Inorganic materials 0.000 description 1
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 1
- 229910006404 SnO 2 Inorganic materials 0.000 description 1
- 235000011054 acetic acid Nutrition 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 150000001298 alcohols Chemical class 0.000 description 1
- 150000001299 aldehydes Chemical class 0.000 description 1
- 229910001413 alkali metal ion Inorganic materials 0.000 description 1
- 235000010323 ascorbic acid Nutrition 0.000 description 1
- 229960005070 ascorbic acid Drugs 0.000 description 1
- 239000011668 ascorbic acid Substances 0.000 description 1
- 230000001651 autotrophic effect Effects 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 230000015572 biosynthetic process Effects 0.000 description 1
- CXKCTMHTOKXKQT-UHFFFAOYSA-N cadmium oxide Inorganic materials [Cd]=O CXKCTMHTOKXKQT-UHFFFAOYSA-N 0.000 description 1
- UHYPYGJEEGLRJD-UHFFFAOYSA-N cadmium(2+);selenium(2-) Chemical compound [Se-2].[Cd+2] UHYPYGJEEGLRJD-UHFFFAOYSA-N 0.000 description 1
- WUKWITHWXAAZEY-UHFFFAOYSA-L calcium difluoride Chemical compound [F-].[F-].[Ca+2] WUKWITHWXAAZEY-UHFFFAOYSA-L 0.000 description 1
- 229910001634 calcium fluoride Inorganic materials 0.000 description 1
- 150000001735 carboxylic acids Chemical class 0.000 description 1
- 239000003153 chemical reaction reagent Substances 0.000 description 1
- 239000003426 co-catalyst Substances 0.000 description 1
- 239000003245 coal Substances 0.000 description 1
- 239000000356 contaminant Substances 0.000 description 1
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- 229910001873 dinitrogen Inorganic materials 0.000 description 1
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- 230000005593 dissociations Effects 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- KTWOOEGAPBSYNW-UHFFFAOYSA-N ferrocene Chemical compound [Fe+2].C=1C=C[CH-]C=1.C=1C=C[CH-]C=1 KTWOOEGAPBSYNW-UHFFFAOYSA-N 0.000 description 1
- 235000019253 formic acid Nutrition 0.000 description 1
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 description 1
- 229910052737 gold Inorganic materials 0.000 description 1
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- 229910052736 halogen Inorganic materials 0.000 description 1
- 150000002367 halogens Chemical class 0.000 description 1
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- XMBWDFGMSWQBCA-UHFFFAOYSA-M iodide Chemical compound [I-] XMBWDFGMSWQBCA-UHFFFAOYSA-M 0.000 description 1
- 238000005342 ion exchange Methods 0.000 description 1
- YEXPOXQUZXUXJW-UHFFFAOYSA-N lead(II) oxide Inorganic materials [Pb]=O YEXPOXQUZXUXJW-UHFFFAOYSA-N 0.000 description 1
- ORUIBWPALBXDOA-UHFFFAOYSA-L magnesium fluoride Chemical compound [F-].[F-].[Mg+2] ORUIBWPALBXDOA-UHFFFAOYSA-L 0.000 description 1
- 229910001635 magnesium fluoride Inorganic materials 0.000 description 1
- 229910000510 noble metal Inorganic materials 0.000 description 1
- 239000013307 optical fiber Substances 0.000 description 1
- 235000006408 oxalic acid Nutrition 0.000 description 1
- SOQBVABWOPYFQZ-UHFFFAOYSA-N oxygen(2-);titanium(4+) Chemical class [O-2].[O-2].[Ti+4] SOQBVABWOPYFQZ-UHFFFAOYSA-N 0.000 description 1
- 238000010979 pH adjustment Methods 0.000 description 1
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- IUVKMZGDUIUOCP-BTNSXGMBSA-N quinbolone Chemical compound O([C@H]1CC[C@H]2[C@H]3[C@@H]([C@]4(C=CC(=O)C=C4CC3)C)CC[C@@]21C)C1=CCCC1 IUVKMZGDUIUOCP-BTNSXGMBSA-N 0.000 description 1
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- 238000001223 reverse osmosis Methods 0.000 description 1
- 239000010948 rhodium Substances 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- MHOVAHRLVXNVSD-UHFFFAOYSA-N rhodium atom Chemical compound [Rh] MHOVAHRLVXNVSD-UHFFFAOYSA-N 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
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- 239000000725 suspension Substances 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- 229910001428 transition metal ion Inorganic materials 0.000 description 1
- 238000003911 water pollution Methods 0.000 description 1
- 229910052724 xenon Inorganic materials 0.000 description 1
- FHNFHKCVQCLJFQ-UHFFFAOYSA-N xenon atom Chemical compound [Xe] FHNFHKCVQCLJFQ-UHFFFAOYSA-N 0.000 description 1
- XLOMVQKBTHCTTD-UHFFFAOYSA-N zinc oxide Inorganic materials [Zn]=O XLOMVQKBTHCTTD-UHFFFAOYSA-N 0.000 description 1
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Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02W—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
- Y02W10/00—Technologies for wastewater treatment
- Y02W10/30—Wastewater or sewage treatment systems using renewable energies
- Y02W10/37—Wastewater or sewage treatment systems using renewable energies using solar energy
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- Physical Water Treatments (AREA)
- Treatment Of Water By Oxidation Or Reduction (AREA)
Description
本発明は、排水処理法に関する。 The present invention relates to a wastewater treatment method.
近年、貴金属産業をはじめとする様々な製造業では、大量の窒素含有廃液が発生している。窒素含有廃液に含まれる硝酸（ＮＯ３ −）、亜硝酸（ＮＯ２ −）、アンモニア（ＮＨ３）は、水質汚濁防止法により排出基準が定められているほか、今後の規制強化も見込まれている。そのため、これらの無機窒素化合物を低濃度化する技術が求められている。 In recent years, a large amount of nitrogen-containing waste liquid has been generated in various manufacturing industries including the precious metal industry. Emission standards for nitric acid (NO 3 − ), nitrous acid (NO 2 − ), and ammonia (NH 3 ) contained in the nitrogen-containing waste liquid are set by the Water Pollution Control Law, and regulations are expected to be strengthened in the future. Yes. Therefore, a technique for reducing the concentration of these inorganic nitrogen compounds is required.
水中無機窒素化合物（ＮＯ３ −、ＮＯ２ −、ＮＨ３）の除去方法として、イオン交換、逆浸透若しくは電気化学透析などの物理化学的な方法、生物学的な方法、電気還元法などの電気学的な方法または触媒法などがある。 As a method for removing inorganic nitrogen compounds (NO 3 − , NO 2 − , NH 3 ) in water, physicochemical methods such as ion exchange, reverse osmosis or electrochemical dialysis, biological methods, electroreduction methods, etc. Such as a chemical method or a catalytic method.
生物学的な方法としては、アンモニア含有排水に含まれるアンモニア性窒素を生物処理により亜硝酸性窒素に酸化した後、亜硝酸性窒素に耐性のある独立栄養細菌を用いた生物学的脱窒素法により亜硝酸性窒素を窒素ガスに還元して排水から除去し、アンモニア性窒素を高濃度に含有する排水を処理する際に発生する亜硝酸性窒素による処理効率低下を防止する方法が知られている（特許文献２）。 Biological denitrification method using autotrophic bacteria resistant to nitrite nitrogen after oxidizing ammonia nitrogen in ammonia-containing wastewater to nitrite nitrogen by biological treatment. Is known to reduce nitrite nitrogen to nitrogen gas and remove it from wastewater, and to prevent reduction in treatment efficiency due to nitrite nitrogen generated when treating wastewater containing high concentrations of ammonia nitrogen. (Patent Document 2).
また、亜硝酸性窒素含有化合物を直接アンモニア性窒素含有化合物とともに処理する方法として、亜硝酸イオン（ＮＯ２ −）とアンモニウムイオン（ＮＨ４ ＋）の細菌による反応を利用するＡｎａｍｍｏｘ反応（法）が知られている（非特許文献１）。 Further, as a method of directly treating a nitrite nitrogen-containing compound together with an ammonia nitrogen-containing compound, there is an Anammox reaction (method) that uses a nitrite ion (NO 2 − ) and ammonium ion (NH 4 + ) reaction by bacteria. It is known (Non-Patent Document 1).
電気化学的方法としては、Ｇｅ／Ｐｄ電極またはＣｕ／Ｐｄ電極を用いて硝酸イオンを除去する方法が報告されている（非特許文献２〜４）。この方法は常温常圧下で動作し安全性が高いが、窒素（Ｎ２）への選択性が低く環境汚染物質の除去という観点から不十分である。
As an electrochemical method, a method of removing nitrate ions using a Ge / Pd electrode or a Cu / Pd electrode has been reported (
触媒法としては、非特許文献５および６に、熱触媒法（Ｃｕ−Ｐｄ／活性炭）が実用化されている。また、触媒法として、非処理水中に含まれるアンモニアを光触媒により酸化しながら、生成する亜硝酸イオン、硝酸イオンをイオン除去手段によって除去することにより、アンモニア性窒素の酸化を促進させる水中アンモニアの除去方法が開示されている（特許文献１）
As the catalyst method,
酸化チタン（ＴｉＯ２）などの光触媒はバンドギャップに相当する光を吸収し、正孔と励起電子を生成することによって、汚染物質を分解除去することができる。この酸化還元反応は、常温常圧で進行する安全かつクリーンな反応である。ＮＯ３ −およびＮＯ２ −の分解反応は、シュウ酸などの正孔捕捉剤の存在下、金属担持ＴｉＯ２により光触媒的に進行する。 A photocatalyst such as titanium oxide (TiO 2 ) absorbs light corresponding to the band gap and generates holes and excited electrons, thereby decomposing and removing contaminants. This redox reaction is a safe and clean reaction that proceeds at normal temperature and pressure. The decomposition reaction of NO 3 — and NO 2 — proceeds photocatalytically with metal-supported TiO 2 in the presence of a hole scavenger such as oxalic acid.
物理化学的な方法は選択的に反応させることができ、コスト面では有利とされているが、非選択的なプロセスであるため反応条件を厳密に規定する必要があること、および余剰汚泥が発生し分離後に処理を必要とするなどの問題がある。 Although the physicochemical method can be selectively reacted and is advantageous in terms of cost, it is a non-selective process, and it is necessary to strictly define the reaction conditions, and excess sludge is generated. However, there are problems such as requiring treatment after separation.
生物学的な方法は選択的に反応させることができるが、反応条件を厳密に規定する必要があり、廃棄処理が必要な余剰汚泥が発生するなどの問題がある。非特許文献１に記載のＡｎａｍｍｏｘ反応（法）は、直接亜硝酸イオン（ＮＯ２ −）とアンモニウムイオン（ＮＨ４ ＋）を処理することはできるが、バイオマスが副生し、余剰汚泥が発生する。
Biological methods can be reacted selectively, but there are problems such as the need to strictly define reaction conditions and generation of excess sludge that requires disposal. The Anammox reaction (method) described in
非特許文献２〜４に記載の電気化学的方法は、常温常圧下で動作し安全性が高いが、窒素（Ｎ２）への選択性が低く環境汚染物質の除去という観点から見れば不十分である。
The electrochemical methods described in
非特許文献５および６に記載の触媒法は、水素ガス（Ｈ２）を必要とし、副生成物が多く生成するなどの問題点がある。
The catalytic methods described in
したがって、本発明は、効率的かつ高い安全性で水中無機窒素化合物を除去するとともに、有害な副生成物の発生を抑制して環境負荷を十分に低減することができる排水処理法を提供することを目的としている。 Therefore, the present invention provides a wastewater treatment method that can remove inorganic nitrogen compounds in water efficiently and with high safety, and can sufficiently reduce environmental burden by suppressing generation of harmful by-products. It is an object.
本発明者らは、硝酸および亜硝酸の少なくとも一方とアンモニアとを含有する水溶液に波長２００〜３００ｎｍの紫外光を照射することにより、光化学反応により硝酸および亜硝酸の少なくとも一方とアンモニアを窒素（Ｎ２）へと転換し、硝酸および亜硝酸の少なくとも一方とアンモニアを同時に該水溶液から除去できることを見出し、本発明を完成させた。 The inventors of the present invention irradiate an aqueous solution containing at least one of nitric acid and nitrous acid and ammonia with ultraviolet light having a wavelength of 200 to 300 nm, thereby converting at least one of nitric acid and nitrous acid and ammonia to nitrogen (N 2 ), it was found that at least one of nitric acid and nitrous acid and ammonia could be simultaneously removed from the aqueous solution, and the present invention was completed.
すなわち、本発明は以下の通りである。
（１）硝酸および亜硝酸の少なくとも一方とアンモニアとを含有する水溶液に波長２００〜３００ｎｍの紫外光を照射して、硝酸または亜硝酸とアンモニアとを窒素へ分解する排水処理法。
（２）光触媒を用いずに硝酸または亜硝酸とアンモニアとを窒素へ分解する前記（１）に記載の排水処理法。
（３）光触媒を用いて硝酸または亜硝酸とアンモニアとを窒素へ分解する前記（１）に記載の排水処理法。
（４）光触媒を用い、且つ正孔捕捉剤を用いずに亜硝酸とアンモニアとを窒素へ分解する前記（３）に記載の排水処理法。
（５）光触媒がチタニア光触媒である前記（３）または（４）に記載の排水処理法。
（６）光触媒を水溶液全量に対して０．０２〜２０質量％用いる前記（３）〜（５）のいずれか１に記載の排水処理法。
（７）水溶液をｐＨ６〜９に調整して硝酸または亜硝酸とアンモニアとを窒素へ分解する前記（１）〜（６）のいずれか１に記載の排水処理法。
That is, the present invention is as follows.
(1) A wastewater treatment method in which an aqueous solution containing at least one of nitric acid and nitrous acid and ammonia is irradiated with ultraviolet light having a wavelength of 200 to 300 nm to decompose nitric acid or nitrous acid and ammonia into nitrogen.
(2) The wastewater treatment method according to (1), wherein nitric acid or nitrous acid and ammonia are decomposed into nitrogen without using a photocatalyst.
(3) The wastewater treatment method according to (1), wherein nitric acid or nitrous acid and ammonia are decomposed into nitrogen using a photocatalyst.
(4) The wastewater treatment method according to (3), wherein nitrous acid and ammonia are decomposed into nitrogen without using a photocatalyst and without using a hole trapping agent.
(5) The waste water treatment method according to (3) or (4), wherein the photocatalyst is a titania photocatalyst.
(6) The waste water treatment method according to any one of (3) to (5), wherein the photocatalyst is used in an amount of 0.02 to 20% by mass based on the total amount of the aqueous solution.
(7) The wastewater treatment method according to any one of (1) to (6), wherein the aqueous solution is adjusted to
本発明の排水処理法によれば、水溶液中の硝酸および亜硝酸の少なくとも一方とアンモニアを同時に除去することが可能であり、水溶液中の硝酸性窒素および亜硝酸性窒素の少なくとも一方とアンモニアとを高効率で低濃度化することができる。 According to the wastewater treatment method of the present invention, it is possible to simultaneously remove ammonia and at least one of nitric acid and nitrous acid in an aqueous solution, and to remove at least one of nitrate nitrogen and nitrite nitrogen in an aqueous solution and ammonia. The concentration can be reduced with high efficiency.
本発明の排水処理法は、高濃度の硝酸性窒素および亜硝酸性窒素の少なくとも一方とアンモニアとを含む水溶液への適用が可能であり、装置コストを低減でき、環境負荷が十分に低減され、有害な副生成物の発生を抑制でき、安全性が高いので、工業的スケールへの適用が可能である。 The wastewater treatment method of the present invention can be applied to an aqueous solution containing at least one of high-concentration nitrate nitrogen and nitrite nitrogen and ammonia, can reduce the apparatus cost, and the environmental load is sufficiently reduced. Generation of harmful by-products can be suppressed and safety is high, so application to an industrial scale is possible.
以下に、本発明を実施するための最良の形態を説明する。 The best mode for carrying out the present invention will be described below.
本発明は、硝酸および亜硝酸の少なくとも一方とアンモニアとを含有する水溶液に波長２００〜３００ｎｍの紫外光を照射して、硝酸および亜硝酸の少なくとも一方とアンモニアとを窒素へ分解する排水処理法である。 The present invention is a wastewater treatment method in which an aqueous solution containing at least one of nitric acid and nitrous acid and ammonia is irradiated with ultraviolet light having a wavelength of 200 to 300 nm to decompose at least one of nitric acid and nitrous acid and ammonia into nitrogen. is there.
（水溶液）
本発明の排水処理法を適用できる水溶液中の硝酸、亜硝酸またはアンモニアの濃度としては、低濃度（例えば、１００μｍｏｌ／Ｌ以下）から高濃度（例えば、１０ｍｏｌ／Ｌ以上）に至るまで、任意の適切な濃度を採用し得る。
(Aqueous solution)
The concentration of nitric acid, nitrous acid, or ammonia in the aqueous solution to which the wastewater treatment method of the present invention can be applied is arbitrary from low concentration (for example, 100 μmol / L or less) to high concentration (for example, 10 mol / L or more). Appropriate concentrations can be employed.
水溶液における硝酸および亜硝酸の合計とアンモニアとの物質量比は、１０：１〜１：１０であることが好ましく、３：１〜１：３であることがより好ましい。物質量比を当該範囲とすることにより、硝酸および亜硝酸の少なくとも一方とアンモニアを同時に効率よく除去することができる。 The mass ratio of nitric acid and nitrous acid in the aqueous solution to ammonia is preferably 10: 1 to 1:10, and more preferably 3: 1 to 1: 3. By setting the substance amount ratio in this range, at least one of nitric acid and nitrous acid and ammonia can be efficiently removed simultaneously.
本発明の排水処理法においては、硝酸および亜硝酸の少なくとも一方とアンモニアとを含有する水溶液のｐＨは６〜９であることが好ましく、ｐＨ８〜９であることがより好ましい。該水溶液のｐＨを６〜９に調整することによって、より高い転化率で硝酸および亜硝酸の少なくとも一方とアンモニアを窒素へ分解する反応を進行させることができる。
In the wastewater treatment method of the present invention, the pH of the aqueous solution containing at least one of nitric acid and nitrous acid and ammonia is preferably 6 to 9, and more preferably
前記水溶液のｐＨを６〜９に調整する手段としては、任意の適切な手段を採用し得る。具体的には、例えば、本発明の排水処理法が貴金属製造・再生業などの各種産業において排出された廃液中の硝酸性窒素または亜硝酸性窒素およびアンモニアの浄化に適用される場合、水酸化ナトリウムをｐＨ調整のために用いることができる。 Any appropriate means can be adopted as means for adjusting the pH of the aqueous solution to 6-9. Specifically, for example, when the wastewater treatment method of the present invention is applied to purification of nitrate nitrogen or nitrite nitrogen and ammonia in waste liquid discharged in various industries such as precious metal manufacturing / regeneration industry, Sodium can be used for pH adjustment.
（紫外光）
本発明の排水処理法において、硝酸および亜硝酸の少なくとも一方とアンモニアとを含有する水溶液に照射する紫外光の波長は２００〜３００ｎｍであり、好ましくは２２０〜２８０ｎｍである。紫外光の波長が２００ｎｍ未満であると、大気雰囲気下で照射することは困難になる。また、紫外光の波長が３００ｎｍを超えると効率よく反応が進行しなくなる。特に亜硝酸とアンモニアの反応速度が著しく低下する。排水に照射する紫外光の一部又は全部が２００〜３００ｎｍの波長であれば本発明の排水処理を効率良く行うことができる。
(Ultraviolet light)
In the wastewater treatment method of the present invention, the wavelength of ultraviolet light applied to the aqueous solution containing at least one of nitric acid and nitrous acid and ammonia is 200 to 300 nm, preferably 220 to 280 nm. When the wavelength of the ultraviolet light is less than 200 nm, it is difficult to irradiate in an air atmosphere. Further, when the wavelength of ultraviolet light exceeds 300 nm, the reaction does not proceed efficiently. In particular, the reaction rate between nitrous acid and ammonia is significantly reduced. If part or all of the ultraviolet light irradiated to the wastewater has a wavelength of 200 to 300 nm, the wastewater treatment of the present invention can be performed efficiently.
本発明の排水処理法で使用する紫外光の光源としては、例えば、太陽光などの自然光、並びに蛍光灯、ブラックライト、キセノンランプ、低圧水銀ランプ、高圧水銀ランプ、超高圧水銀ランプ、ハロゲンランプ、殺菌ランプおよびＬＥＤなどの人工光（紫外光など）が挙げられる。 Examples of the ultraviolet light source used in the wastewater treatment method of the present invention include natural light such as sunlight, fluorescent lamps, black lights, xenon lamps, low-pressure mercury lamps, high-pressure mercury lamps, ultrahigh-pressure mercury lamps, halogen lamps, Artificial light (such as ultraviolet light) such as sterilizing lamps and LEDs can be used.
本発明の排水処理法において、波長が２００ｎｍ付近の光源を使用する場合、光源として、低圧水銀ランプ、高圧水銀ランプ、超高圧水銀ランプ、殺菌ランプ、またはＬＥＤが好ましい。光源は波長２００〜３００ｎｍの紫外光を発光することが好ましく、波長特性として、吸収ピークが一つでもよく、二つ以上あってもかまわない。２００〜３００ｎｍの波長の吸収ピークが１以上含まれればよい。 In the wastewater treatment method of the present invention, when a light source having a wavelength of about 200 nm is used, the light source is preferably a low pressure mercury lamp, a high pressure mercury lamp, an ultrahigh pressure mercury lamp, a sterilization lamp, or an LED. The light source preferably emits ultraviolet light having a wavelength of 200 to 300 nm, and the wavelength characteristic may be one absorption peak or two or more. It is sufficient that at least one absorption peak having a wavelength of 200 to 300 nm is included.
紫外光を照射する水溶液の温度としては、任意の適切な温度を採用し得る。しかしながら、本発明の排水処理法においては、紫外光照射中の水溶液の温度を常温付近で行うことが可能である。 Any appropriate temperature can be adopted as the temperature of the aqueous solution irradiated with ultraviolet light. However, in the wastewater treatment method of the present invention, it is possible to perform the temperature of the aqueous solution during irradiation with ultraviolet light at around room temperature.
すなわち、紫外光を照射する水溶液の温度は、好ましくは５０℃以下であり、より好ましくは０〜４５℃であり、さらに好ましくは２〜４０℃以下であり、特に好ましくは５〜３０℃である。 That is, the temperature of the aqueous solution irradiated with ultraviolet light is preferably 50 ° C. or lower, more preferably 0 to 45 ° C., still more preferably 2 to 40 ° C., and particularly preferably 5 to 30 ° C. .
本発明の排水処理法において、紫外光を照射する水溶液の温度を常温付近で行うことが可能であれば、排水処理に費やすエネルギーを低減できるだけでなく、該水溶液が有毒な揮発性物質を含む廃液である場合には、該有毒な揮発性物質の揮散を抑制することが可能となり、また、水溶液温度上昇による副反応の発生に起因する安全性低下の問題も回避可能となる。 In the wastewater treatment method of the present invention, if it is possible to perform the temperature of the aqueous solution irradiated with ultraviolet light at around room temperature, not only can the energy consumed for wastewater treatment be reduced, but the aqueous solution contains a toxic volatile substance. In this case, it is possible to suppress the volatilization of the toxic volatile substance, and it is also possible to avoid the problem of a decrease in safety due to the occurrence of a side reaction due to an increase in aqueous solution temperature.
紫外光の照射形態としては、例えば、排水面に直接照射する方法、排水を噴霧状にして照射する方法、および光ファイバースコープで排水液中に直接照射する方法等が挙げられるが、限定されない。 Examples of the irradiation form of the ultraviolet light include, but are not limited to, a method of directly irradiating the drainage surface, a method of irradiating the wastewater in a spray state, and a method of directly irradiating the wastewater with an optical fiber scope.
以下、波長２００〜３００ｎｍの紫外光を照射することによる、亜硝酸およびアンモニアの同時除去、硝酸およびアンモニアの同時除去の機構を説明する。 Hereinafter, the mechanism of simultaneous removal of nitrous acid and ammonia and simultaneous removal of nitric acid and ammonia by irradiating with ultraviolet light having a wavelength of 200 to 300 nm will be described.
（亜硝酸およびアンモニアの同時除去）
水中ＮＯ２ −とＮＨ４ ＋は高温高圧条件下で反応してＮ２を放出する。亜硝酸とアンモニアの反応式を下記式１に示す。
ＮＯ２ −＋ＮＨ４ ＋→Ｎ２＋２Ｈ２Ｏ （式１）
(Simultaneous removal of nitrous acid and ammonia)
Underwater NO 2 − and NH 4 + react under high temperature and high pressure conditions to release N 2 . The reaction formula of nitrous acid and ammonia is shown in the following
NO 2 − + NH 4 + → N 2 + 2H 2 O (Formula 1)
前記反応を利用する脱窒法としては、生物法であるＡｎａｍｍｏｘ法（嫌気性アンモニア酸化法）、および熱触媒としてＰｔ／ＴｉＯ２を用いる方法などが実用化されている。しかし、Ａｎａｍｍｏｘ法はＮＯ３ −およびバイオマスが副生すること（式２）や、廃棄処理が必要な余剰汚泥が発生するなどの問題がある。Ｐｔ／ＴｉＯ２による熱触媒法は、４２０Ｋ以上の加熱と水素ガス（Ｈ２）、過酸化水素（Ｈ２Ｏ２）、気密性の高い反応容器および高価な白金（Ｐｔ）を必要とする。 As the denitrification method using the above reaction, an biological method such as Anammox method (anaerobic ammonia oxidation method) and a method using Pt / TiO 2 as a thermal catalyst have been put into practical use. However, the Anammox method has problems such as generation of NO 3 − and biomass as a by-product (Formula 2), and generation of excess sludge that requires disposal. The thermal catalyst method using Pt / TiO 2 requires heating of 420 K or more, hydrogen gas (H 2 ), hydrogen peroxide (H 2 O 2 ), a highly airtight reaction vessel, and expensive platinum (Pt).
ＮＨ４ ＋＋１．３２ＮＯ２ −＋０．０６６ＨＣＯ３ −＋０．１３Ｈ＋→
１．０２Ｎ２＋０．２６ＮＯ３ −＋２．０３Ｈ２Ｏ＋０．０６６ＣＨ２Ｏ０．５Ｎ０．１５ （式２）
NH 4 + +1.32 NO 2 − +0.066 HCO 3 − + 0.13H + →
1.02N 2 + 0.26NO 3 − + 2.03H 2 O + 0.066CH 2 O 0.5 N 0.15 (Formula 2)
一方、光触媒による酸化還元反応は常温常圧で進行するクリーンな反応である。ＴｉＯ２（Ｐ２５）光触媒に紫外光（λ＞３００ｎｍ）を照射することにより、ＮＯ２ −とＮＨ４ ＋から選択的にＮ２が生成する（図１）。 On the other hand, the redox reaction by the photocatalyst is a clean reaction that proceeds at normal temperature and pressure. By irradiating the TiO 2 (P25) photocatalyst with ultraviolet light (λ> 300 nm), N 2 is selectively generated from NO 2 − and NH 4 + (FIG. 1).
前記反応をより効率的に進行させるため本発明者が反応条件を検討した結果、以下の機構により、波長２００〜３００ｎｍの紫外光を照射することで水溶液中の亜硝酸およびアンモニアを同時除去できることが分かった。 As a result of studying the reaction conditions by the present inventor in order to make the reaction proceed more efficiently, it is possible to simultaneously remove nitrous acid and ammonia in an aqueous solution by irradiating ultraviolet light having a wavelength of 200 to 300 nm by the following mechanism. I understood.
半導体は伝導帯（Ｃｏｎｄｕｃｔｉｏｎ ｂａｎｄ，Ｃ．Ｂ．）と価電子帯（Ｖａｌｅｎｃｅ ｂａｎｄ，Ｖ．Ｂ．）とが適当な幅の禁制帯（Ｂａｎｄ ｇａｐ，Ｂ．Ｇ．）で隔てられたバンド構造を有する。そして、バンドギャップ以上のエネルギーを照射すると、価電子帯の電子が伝導帯に励起され、その結果として価電子帯に正孔（ホール）、伝導帯に電子が生じる。そして、これらの正孔または電子が酸化または還元反応を引き起こす。 A semiconductor has a band structure in which a conduction band (C.B.) and a valence band (Valence band, V.B.) are separated by a forbidden band (Band gap, B.G.) having an appropriate width. Have. When energy of a band gap or more is irradiated, electrons in the valence band are excited to the conduction band, and as a result, holes are generated in the valence band and electrons are generated in the conduction band. These holes or electrons cause an oxidation or reduction reaction.
式（ｂ１）に亜硝酸―アンモニア反応の化学量論式を示す。亜硝酸―アンモニア溶液にλ＞２００ｎｍの紫外光が照射されると光化学反応が起こり、ＮＯ２ −が励起されて光解離し、ＯＨラジカルとＮＯラジカルが生じる（ｂ２）。このとき生じたＯＨラジカルがＮＨ３からＨラジカルを引き抜くことでＮＨ２ラジカルが生成し（ｂ３）、ＮＨ２ラジカルとＮＯラジカルがカップリングすることによってＮＨ２ＮＯ中間体が生成し（ｂ４）、これが分解してＮ２とＨ２Ｏが生じる（ｂ５）。 Formula (b1) shows the stoichiometric formula of the nitrous acid-ammonia reaction. When the nitrous acid-ammonia solution is irradiated with ultraviolet light with λ> 200 nm, a photochemical reaction occurs, and NO 2 − is excited and photodissociated to generate OH radicals and NO radicals (b2). The generated OH radicals extract H radicals from NH 3 to generate NH 2 radicals (b3), and NH 2 radicals and NO radicals are coupled to generate NH 2 NO intermediates (b4). This decomposes to produce N 2 and H 2 O (b5).
ＮＯ２ −＋ＮＨ４ ＋→Ｎ２＋２Ｈ２Ｏ （ｂ１）
ＮＯ２ −＋Ｈ２Ｏ→（ＮＯ２ −）＊＋Ｈ２Ｏ→・ＯＨ＋・ＮＯ＋ＯＨ−（ｂ２）
ＮＨ３＋・ＯＨ→・ＮＨ２＋Ｈ２Ｏ （ｂ３）
Ｈ２Ｎ・＋・ＮＯ→ＮＨ２−Ｎ＝Ｏ （ｂ４）
ＮＨ２−Ｎ＝Ｏ（ａｄｓ）→Ｎ２＋Ｈ２Ｏ （ｂ５）
NO 2 − + NH 4 + → N 2 + 2H 2 O (b1)
NO 2 − + H 2 O → (NO 2 − ) * + H 2 O → OH + NO + OH− (b2)
NH 3 + .OH → .NH 2 + H 2 O (b3)
H 2 N · + · NO → NH 2 —N═O (b4)
NH 2 —N═O (ads) → N 2 + H 2 O (b5)
亜硝酸とアンモニアの場合は光触媒を使用しなくても窒素に転化することができるが、光触媒を使用する場合は光量が少なくても亜硝酸とアンモニアの分解が進行する。光触媒表面に紫外光が照射されると、価電子帯の電子が伝導帯に励起される。生成した励起電子によりＮＯ２ −が還元され、正孔によりＮＨ４ ＋が酸化されることによりＮＨ２ＮＯが生じ（ａ１）、これが分解されてＮ２とＨ２Ｏが生成する（ａ２）。λ＞２００ｎｍの紫外光を用いると光触媒反応と光化学反応が同時に進行する。 Nitrous acid and ammonia can be converted to nitrogen without using a photocatalyst. However, when using a photocatalyst, decomposition of nitrous acid and ammonia proceeds even if the amount of light is small. When the photocatalyst surface is irradiated with ultraviolet light, electrons in the valence band are excited to the conduction band. NO 2 − is reduced by the generated excited electrons, and NH 4 + is oxidized by holes to generate NH 2 NO (a1), which is decomposed to generate N 2 and H 2 O (a2). When ultraviolet light with λ> 200 nm is used, the photocatalytic reaction and the photochemical reaction proceed simultaneously.
ＮＯ２ −（ａｄｓ）＋ＮＨ４ ＋（ａｄｓ）→ＮＨ２−Ｎ＝Ｏ（ａｄｓ）＋Ｈ２Ｏ （ａ１）
ＮＨ２−Ｎ＝Ｏ（ａｄｓ）→Ｎ２＋Ｈ２Ｏ （ａ２）
NO 2 − (ads) + NH 4 + (ads) → NH 2 —N═O (ads) + H 2 O (a1)
NH 2 —N═O (ads) → N 2 + H 2 O (a2)
（硝酸およびアンモニアの同時除去）
水中ＮＯ３ −をλ＞２００ｎｍの紫外光を用いて光化学的に分解すると、下記式３に示すように、ＮＯ２ −およびＯ２が生成する。
ＮＯ３ −→ＮＯ２ −＋１／２Ｏ２（式３）
(Simultaneous removal of nitric acid and ammonia)
When the photochemically decomposed using ultraviolet light of lambda> 200 nm, as shown in the following
NO 3 − → NO 2 − + 1 / 2O 2 (Formula 3)
そこで、ＮＯ３ −からＮＯ２ −への光分解反応と、ＮＯ２ −―ＮＨ４＋反応を組み合わせることにより、水中ＮＯ３ −およびＮＨ４ ＋を同時除去することを目的として検討したところ、波長２００〜３００ｎｍの紫外光を照射することで水溶液中の硝酸およびアンモニアを同時除去できることが分かった。 Therefore, when a study was conducted for the purpose of simultaneously removing NO 3 − and NH 4 + in water by combining a photolysis reaction from NO 3 − to NO 2 − and a NO 2 − —NH 4 + reaction, It was found that nitric acid and ammonia in the aqueous solution can be removed simultaneously by irradiating ultraviolet light of 200 to 300 nm.
硝酸およびアンモニアを含む水溶液にλ＞２００ｎｍの紫外光を照射すると、光化学反応により以下の式４−６により定義されるＴｏｔａｌ−ＮＢ（全窒素バランス）、ＮＯ３ −−ＮＢ（ＮＯ３−バランス）、ＮＨ４ ＋−ＮＢ（ＮＨ４ ＋バランス）において、ＮＯ３ −−ＮＢが若干増加してＮＨ４ ＋−ＮＢが若干減少するが、ほぼ量論的に硝酸およびアンモニアが分解すると考えられる。 When an aqueous solution containing nitric acid and ammonia is irradiated with ultraviolet light of λ> 200 nm, Total-NB (total nitrogen balance) and NO 3 − −NB (NO 3 −balance) defined by the following formula 4-6 by photochemical reaction In NH 4 + -NB (NH 4 + balance), NO 3 -- NB slightly increases and NH 4 + -NB slightly decreases, but it is considered that nitric acid and ammonia are decomposed almost stoichiometrically.
前記式４〜６において、ｎ０は反応開始前の物質量であり、ｎは反応後の物質量である。なお、硝酸とアンモニアの同時除去の場合は光触媒のない方がよい場合があり、光触媒を添加すると硝酸およびアンモニアの分解が遅くなることがある。
In the
（光触媒）
本発明の排水処理法においては、光触媒の存在下で硝酸および亜硝酸の少なくとも一方とアンモニアとを窒素に分解してもよい。本発明の排水処理法においては、水溶液に光触媒を添加して紫外光を照射してもよいし、または光触媒を添加しないで紫外光を照射した後に光触媒を添加して紫外光を照射してもよい。
(photocatalyst)
In the wastewater treatment method of the present invention, at least one of nitric acid and nitrous acid and ammonia may be decomposed into nitrogen in the presence of a photocatalyst. In the wastewater treatment method of the present invention, the photocatalyst may be added to the aqueous solution and irradiated with ultraviolet light, or the ultraviolet light may be irradiated without adding the photocatalyst and then the photocatalyst may be added and irradiated with ultraviolet light. Good.
前記光触媒としては、任意の適切な光触媒を採用し得る。このような光触媒としては、好ましくは、酸化物半導体型光触媒である。酸化物半導体型光触媒としては、例えば、ＢｅＯ、ＭｇＯ、ＣａＯ、ＳｒＯ、ＢａＯ、ＣｅＯ２、ＴｈＯ２、ＵＯ３、Ｕ３Ｏ８、ＴｉＯ２、ＺｒＯ２、Ｖ２Ｏ５、Ｙ２Ｏ３、Ｙ２Ｏ２Ｓ、Ｎｂ２Ｏ５、Ｔａ２Ｏ５、ＭｏＯ３、ＷＯ３、ＭｎＯ２、Ｆｅ２Ｏ３、ＭｇＦｅ２Ｏ４、ＮｉＦｅ２Ｏ４、ＺｎＦｅ２Ｏ４、ＺｎＣｏ２Ｏ４、ＺｎＯ、ＣｄＯ、Ａｌ２Ｏ３、ＭｇＡｌ２Ｏ４、ＺｎＡｌ２Ｏ４、Ｔｌ２Ｏ３、Ｉｎ２Ｏ３、ＳｉＯ２、ＳｎＯ２、ＰｂＯ２、ＵＯ２、Ｃｒ２Ｏ３、ＭｇＣｒ２Ｏ４、ＦｅＣｒＯ４、ＣｏＣｒＯ４、ＺｎＣｒ２Ｏ４、ＷＯ２、ＭｎＯ、Ｍｎ３Ｏ４、Ｍｎ２Ｏ３、ＦｅＯ、ＮｉＯ、ＣｏＯ、Ｃｏ３Ｏ４、ＰｄＯ、ＣｕＯ、Ｃｕ２Ｏ、Ａｇ２Ｏ、ＣｏＡｌ２Ｏ４、ＮｉＡｌ２Ｏ４、Ｔｌ２Ｏ、ＧｅＯ、ＰｂＯ、ＴｉＯ、Ｔｉ２Ｏ３、ＶＯ、ＭｏＯ２、ＩｒＯ２、ＲｕＯ２、ＣｄＳ、ＣｄＳｅおよびＣｄＴｅなどが挙げられる。
Any appropriate photocatalyst can be adopted as the photocatalyst. Such a photocatalyst is preferably an oxide semiconductor type photocatalyst. Examples of the oxide semiconductor type photocatalyst include BeO, MgO, CaO, SrO, BaO, CeO 2 , ThO 2 , UO 3 , U 3 O 8 , TiO 2 , ZrO 2 , V 2 O 5 , Y 2 O 3 , Y 2 O 2 S, Nb 2 O 5, Ta 2 O 5 , MoO 3 , WO 3 , MnO 2 , Fe 2 O 3 , MgFe 2 O 4 , NiFe 2 O 4, ZnFe 2 O 4, ZnCo 2 O 4 , ZnO, CdO, Al 2 O 3 , MgAl 2 O 4 , ZnAl 2 O 4 , Tl 2 O 3 , In 2 O 3 , SiO 2 , SnO 2 , PbO 2 , UO 2 , Cr 2 O 3 , MgCr 2 O 4 , FeCrO 4, CoCrO 4, ZnCr 2
これらの酸化物半導体型光触媒の中でも、触媒活性の高さおよび入手のし易さなどの点からは、ＴｉＯ２が好ましい。特に、亜硝酸およびアンモニアを同時除去する場合、光触媒としてＡｎａｔａｓｅ／Ｒｕｔｉｌｅ混合型の酸化チタンが好ましい。前記光触媒は、１種のみを用いてもよいし、２種以上を併用してもよい。 Among these oxide semiconductor photocatalysts, TiO 2 is preferable from the viewpoint of high catalytic activity and availability. In particular, when removing nitrous acid and ammonia simultaneously, a photocatalyst is preferably mixed with an Natase / Rutile type titanium oxide. Only 1 type may be used for the said photocatalyst and it may use 2 or more types together.
水溶液中の光触媒の量としては、光触媒反応が起こり得る量であれば、任意の適切な量を採用し得る。このような光触媒の量としては、水溶液全量に対して、好ましくは０．０２〜２０質量％であり、より好ましくは０．２〜２．０質量％である。基質の量に対する光触媒の量としては、基質０．１Ｍのときの光触媒の量は０．１２５ｍｇ／ｍｇ〜１．２５ｍｇ／ｍｇとすることが好ましく、０．２５ｍｇ／ｍｇ〜０．６２５ｍｇ／ｍｇとすることがより好ましい。 As the amount of the photocatalyst in the aqueous solution, any appropriate amount can be adopted as long as the photocatalytic reaction can occur. The amount of such a photocatalyst is preferably 0.02 to 20% by mass and more preferably 0.2 to 2.0% by mass with respect to the total amount of the aqueous solution. As the amount of the photocatalyst with respect to the amount of the substrate, the amount of the photocatalyst when the substrate is 0.1 M is preferably 0.125 mg / mg to 1.25 mg / mg, and 0.25 mg / mg to 0.625 mg / mg. More preferably.
光触媒反応中の水溶液の温度としては、任意の適切な温度を採用し得る。前記光触媒反応中の水溶液の温度は、好ましくは５０℃以下であり、より好ましくは０〜４５℃であり、さらに好ましくは２〜４０℃以下であり、特に好ましくは５〜３０℃である。 Any appropriate temperature can be adopted as the temperature of the aqueous solution during the photocatalytic reaction. The temperature of the aqueous solution during the photocatalytic reaction is preferably 50 ° C. or less, more preferably 0 to 45 ° C., still more preferably 2 to 40 ° C., and particularly preferably 5 to 30 ° C.
光触媒には、助触媒が併用されてもよい。このような助触媒としては、例えば、金、白金、パラジウム、銀、銅およびロジウムなど、任意の適切な貴金属系助触媒が挙げられる。助触媒の量としては、任意の適切な量を採用し得る。このような助触媒は、１種のみを用いてもよいし、２種以上を併用してもよい。 A cocatalyst may be used in combination with the photocatalyst. Examples of such promoters include any appropriate noble metal promoters such as gold, platinum, palladium, silver, copper and rhodium. Any appropriate amount can be adopted as the amount of the cocatalyst. Only 1 type may be used for such a co-catalyst and it may use 2 or more types together.
また、光触媒とともに正孔捕捉剤を用いてもよい。正孔捕捉剤としては、具体的には、例えば、アスコルビン酸；エタノール、ブタノールおよびプロピルアルコール等のアルコール類；ホルムアルデヒド、アセトアルデヒド等のアルデヒド類；ギ酸、酢酸およびプロピオン酸等のカルボン酸類；臭素イオン、ヨウ素イオン、鉄イオン（Ｆｅ２＋）およびフェロセン等のレドックス試薬；等が挙げられるが、特に限定されるものではない。正孔捕捉剤の量としては、任意の適切な量を採用し得る。 Moreover, you may use a hole-trapping agent with a photocatalyst. Specific examples of the hole trapping agent include ascorbic acid; alcohols such as ethanol, butanol and propyl alcohol; aldehydes such as formaldehyde and acetaldehyde; carboxylic acids such as formic acid, acetic acid and propionic acid; Redox reagents such as iodine ion, iron ion (Fe 2+ ) and ferrocene; and the like are mentioned, but are not particularly limited. Any appropriate amount can be adopted as the amount of the hole trapping agent.
なお、光触媒を用いて硝酸とアンモニアとを窒素へ分解する場合は、反応効率の観点から、正孔捕捉剤を用いることが好ましい。また、光触媒を用いて亜硝酸とアンモニアを窒素へ分解する場合は、反応効率の観点から、正孔捕捉剤を用いないことが好ましい。 In addition, when decomposing | disassembling nitric acid and ammonia into nitrogen using a photocatalyst, it is preferable to use a hole-trapping agent from a viewpoint of reaction efficiency. Moreover, when decomposing | disassembling nitrous acid and ammonia into nitrogen using a photocatalyst, it is preferable not to use a hole-trapping agent from a viewpoint of reaction efficiency.
本発明の排水処理法で使用する排水処理装置は、紫外光照射ランプを設置出来れば、室内型排水処理装置であっても屋外型排水処理装置であってもよい。 The wastewater treatment device used in the wastewater treatment method of the present invention may be an indoor wastewater treatment device or an outdoor wastewater treatment device as long as an ultraviolet light irradiation lamp can be installed.
また、本発明の排水処理法で使用する排水処理装置において、硝酸および亜硝酸の少なくとも一方とアンモニアとを含有する水溶液を収容する容器は、光源を直接水溶液に入れ場合は限定されないが、容器を挟んで水溶液に紫外光を照射する場合は、波長２００〜３００ｎｍの紫外光を透過する容器であることが好ましい。このような容器としては、例えば、石英ガラス、フッ化マグネシウムガラスおよびフッ化カルシウムガラス等が挙げられる。 Further, in the wastewater treatment apparatus used in the wastewater treatment method of the present invention, the container containing the aqueous solution containing at least one of nitric acid and nitrous acid and ammonia is not limited when the light source is directly put into the aqueous solution, In the case of irradiating the aqueous solution with ultraviolet light, the container is preferably a container that transmits ultraviolet light having a wavelength of 200 to 300 nm. Examples of such containers include quartz glass, magnesium fluoride glass, and calcium fluoride glass.
本発明の排水処理法は、高濃度（例えば、１０ｍｏｌ／Ｌ以上）の硝酸および亜硝酸の少なくとも一方とアンモニアとを含む水溶液に適用できるので、貴金属製造・再生業などの各種産業において排出された廃液中の硝酸性窒素および亜硝酸性窒素の少なくとも一方とアンモニアとを含む排水処理に適用できる。 Since the wastewater treatment method of the present invention can be applied to an aqueous solution containing at least one of nitric acid and nitrous acid having a high concentration (for example, 10 mol / L or more) and ammonia, the wastewater treatment method has been discharged in various industries such as precious metal manufacturing and recycling industries. The present invention can be applied to wastewater treatment containing at least one of nitrate nitrogen and nitrite nitrogen in the waste liquid and ammonia.
以下、実施例により本発明を説明するが、本発明はそれに限定されるものではない。尚、実施例で用いた評価方法は以下の通りである。 EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to it. The evaluation methods used in the examples are as follows.
〔実験方法〕
（１）水中ＮＯ２ −およびＮＨ４ ＋の光触媒反応
パイレックス（登録商標）または石英試験管中、水（５ｃｍ３）にＴｉＯ２（５０．０ｍｇ）を懸濁させ、ＮａＮＯ２（５００μｍｏｌ 和光純薬）と（ＮＨ４）２ＳＯ４（ＮＨ４ ＋として５００μｍｏｌ，関東化学）を加えた。系内をＡｒ雰囲気（バブリング：３０ｍｉｎ）にし、４００Ｗ高圧水銀灯の紫外光（λ＞２００ｎｍ）を照射した。このときのＮＯ２ −の初期濃度は０．１ｍｏｌＬ−１であり、窒素濃度に換算するとＮＨ４ ＋と合わせて２８００ｍｇ−ＮＬ−１であった。
〔experimental method〕
(1) Photocatalytic reaction of NO 2 - and NH 4 + in water TiO 2 (50.0 mg) was suspended in water (5 cm 3 ) in Pyrex (registered trademark) or a quartz test tube, and NaNO 2 (500 μmol Wako Pure Chemical Industries, Ltd.). ) And (NH 4 ) 2 SO 4 (NH 4 + as 500 μmol, Kanto Chemical) were added. The system was placed in an Ar atmosphere (bubbling: 30 min) and irradiated with ultraviolet light (λ> 200 nm) from a 400 W high-pressure mercury lamp. The initial concentration of NO 2 − at this time was 0.1 mol L −1 , which was 2800 mg-NL −1 when combined with NH 4 + when converted to a nitrogen concentration.
（２）水中ＮＯ３ −およびＮＨ４ ＋の光化学反応
パイレックス（登録商標）または石英試験管中、水（５ｃｍ３）にＮａＮＯ３（５００μｍｏｌ 関東化学）と（ＮＨ４）２ＳＯ４（ＮＨ４ ＋として５００μｍｏｌ 関東化学）を加えた。系内をＡｒ雰囲気（バブリング：３０ｍｉｎ）にし、４００Ｗ高圧水銀灯の紫外光（λ＞２００ｎｍ）を照射した。
(2) Photochemical reaction of NO 3 − and NH 4 + in water In a Pyrex (registered trademark) or quartz test tube, NaNO 3 (500 μmol Kanto Chemical) and (NH 4 ) 2 SO 4 (NH 4 + in water (5 cm 3 )) As 500 μmol Kanto Chemical). The system was placed in an Ar atmosphere (bubbling: 30 min) and irradiated with ultraviolet light (λ> 200 nm) from a 400 W high-pressure mercury lamp.
＜実施例１＞
〔水中ＮＯ２ −およびＮＨ４ ＋の同時除去〕
光触媒による酸化還元反応は常温常圧で進行する反応である。ＴｉＯ２（Ｐ２５）光触媒に紫外光（λ＞３００ｎｍ）を照射することにより、ＮＯ２ −とＮＨ４ ＋から選択的にＮ２が生成する（図１）。この反応をより効率的に進行させるため、反応条件を検討した。また、超高濃度域における反応を検討した。
<Example 1>
[Simultaneous removal of NO 2 − and NH 4 + in water]
The redox reaction by a photocatalyst is a reaction that proceeds at normal temperature and pressure. By irradiating the TiO 2 (P25) photocatalyst with ultraviolet light (λ> 300 nm), N 2 is selectively generated from NO 2 − and NH 4 + (FIG. 1). In order to make this reaction proceed more efficiently, reaction conditions were examined. In addition, the reaction in the ultrahigh concentration range was examined.
（１）酸化チタン光触媒の種類の影響
各種酸化チタンを用いて亜硝酸−アンモニア反応を行った結果を表１に示す。
(1) Effect of type of titanium oxide photocatalyst Table 1 shows the results of nitrite-ammonia reaction using various titanium oxides.
表１に示すように、Ａｎａｔａｓｅ／Ｒｕｔｉｌｅ混合型のＰ２５が最も活性が高かった。一方、ＳＴ−０１（Ａｎａｔａｓｅ）の活性は低く、ＭＴ−１５０Ａ（Ｒｕｔｉｌｅ）は全く活性を示さなかった。よって、以降の反応は最も活性の高かったＰ２５を用いて行った。 As shown in Table 1, the activity / Putyl mixed type P25 had the highest activity. On the other hand, the activity of ST-01 (Anatase) was low, and MT-150A (Rutile) showed no activity at all. Therefore, subsequent reaction was performed using P25 having the highest activity.
（２）各種光触媒の検討
各種の光触媒を用いて亜硝酸−アンモニア反応を行った結果を表２に示す。
(2) Examination of various photocatalysts Table 2 shows the results of nitrite-ammonia reaction using various photocatalysts.
表２に示すように、酸化チタン以外の光触媒はほとんど活性を示さなかった。 As shown in Table 2, photocatalysts other than titanium oxide showed almost no activity.
（３）紫外光波長の影響
（３−１）光触媒反応における紫外光波長の影響
ＮａＮＯ２と（ＮＨ４）２ＳＯ４の水溶液にＴｉＯ２（Ｐ２５）を懸濁し、λ＞３００ｎｍの紫外光を照射した結果を図２（ａ）に、λ＞２００ｎｍの紫外光を照射した結果を図２（ｂ）に示す。図２（ａ）および（ｂ）に示す結果から、λ＞２００ｎｍの紫外光を用いることで、反応速度が大幅に増加することが明らかになった。
(3) Influence of ultraviolet light wavelength (3-1) Influence of ultraviolet light wavelength in photocatalytic reaction TiO 2 (P25) is suspended in an aqueous solution of NaNO 2 and (NH 4 ) 2 SO 4 , and ultraviolet light with λ> 300 nm is applied. The result of irradiation is shown in FIG. 2A, and the result of irradiation with ultraviolet light with λ> 200 nm is shown in FIG. From the results shown in FIGS. 2 (a) and 2 (b), it has been clarified that the reaction rate is greatly increased by using ultraviolet light with λ> 200 nm.
（３−２）光化学反応における紫外光波長の影響
ＮａＮＯ２と（ＮＨ４）２ＳＯ４の水溶液に無触媒でλ＞３００ｎｍの紫外光を照射した結果を図３（ａ）に、λ＞２００ｎｍの紫外光を照射した結果を図３（ｂ）に示す。λ＞２００ｎｍの紫外光を用いることにより、無触媒で光化学反応が高速に進行することが明らかになった。
(3-2) Effect of UV Light Wavelength on Photochemical Reaction FIG. 3A shows the result of irradiating an aqueous solution of NaNO 2 and (NH 4 ) 2 SO 4 with UV light having a wavelength of λ> 300 nm. FIG. 3B shows the result of irradiation with ultraviolet light. It was revealed that the photochemical reaction proceeds at high speed without using a catalyst by using ultraviolet light with λ> 200 nm.
図４にＮａＮＯ２および（ＮＨ４）２ＳＯ４のＵＶ−Ｖｉｓスペクトルを示す。図４に示すように、ＮＯ２ −は３００または３５０ｎｍの弱い吸収（ｎ→ｐ＊，対称禁制遷移）と２２０ｎｍ付近の強い吸収（ｐ→ｐ＊，許容遷移）をもつ。よって、２２０ｎｍ付近の遷移確率の高い吸収を利用することにより活性が増大したと考えられた。 FIG. 4 shows UV-Vis spectra of NaNO 2 and (NH 4 ) 2 SO 4 . As shown in FIG. 4, NO 2 − has a weak absorption at 300 or 350 nm (n → p * , symmetrical forbidden transition) and a strong absorption at around 220 nm (p → p * , allowable transition). Therefore, it was considered that the activity was increased by utilizing absorption with a high transition probability around 220 nm.
（４）ｐＨの影響
ＮａＮＯ２と（ＮＨ４）２ＳＯ４の水溶液にＴｉＯ２（Ｐ２５）を懸濁し、ＮａＯＨ水溶液またはＨＣｌ水溶液で各種ｐＨに調整して反応を行った結果を図５に示す。
(4) Effect of pH FIG. 5 shows the results obtained by suspending TiO 2 (P25) in an aqueous solution of NaNO 2 and (NH 4 ) 2 SO 4 and adjusting the pH to various pH with an aqueous NaOH solution or an aqueous HCl solution. .
図５に示すように、酸性条件ではＮＯ２ −がＮＯ３ −およびＮ２Ｏへ不均化するために反応が進行しなかった。一方、塩基性条件では解離平衡により反応性の高いＮＨ３が増加するために反応速度が増加するが、強塩基性条件ではＮＨ３の溶解度が低下するために反応速度が低下した。また、強酸性および強塩基性条件では、ＴｉＯ２界面のζポテンシャルの絶対値が大きいためにイオンの吸着速度が低下することも活性低下に寄与している。 As shown in FIG. 5, the reaction did not proceed under acidic conditions because NO 2 − disproportionated to NO 3 − and N 2 O. On the other hand, under basic conditions, NH 3 with high reactivity increases due to dissociation equilibrium, and thus the reaction rate increases. However, under strong basic conditions, the solubility of NH 3 decreases and the reaction rate decreases. Moreover, under strong acidity and strong basic conditions, since the absolute value of the ζ potential at the TiO 2 interface is large, a decrease in the adsorption rate of ions also contributes to a decrease in activity.
以上の結果から、亜硝酸―アンモニア反応の最適ｐＨは、弱塩基性条件である８〜９であることが分かった。 From the above results, it was found that the optimum pH of the nitrous acid-ammonia reaction was 8 to 9 which is a weak basic condition.
（５）超高濃度ＮＯ２ −およびＮＨ４ ＋の同時除去
基質濃度を５倍（２５００μｍｏｌ，０．５Ｍ）に増加させ、ＴｉＯ２（Ｐ２５，５０ｍｇ）を懸濁させ、Ａｑ．ＮａＯＨを加えて最適ｐＨであるｐＨ８に調整し、紫外光（λ＞２００ｎｍ）を照射した結果を図６に示す。
(5) Simultaneous removal of ultra-high concentrations of NO 2 − and NH 4 + The substrate concentration was increased 5-fold (2500 μmol, 0.5 M), TiO 2 (P25, 50 mg) was suspended, and Aq. FIG. 6 shows the result of adjusting to
図６に示すように、亜硝酸―アンモニア反応が超高濃度域においても進行し、８時間で９９％以上のＮＯ２ −およびＮＨ４ ＋を除去することができた。 As shown in FIG. 6, the nitrite-ammonia reaction proceeded even in the ultrahigh concentration region, and 99% or more of NO 2 − and NH 4 + could be removed in 8 hours.
次に、高濃度条件で光触媒を用いた場合と用いない場合を比較した結果を図７に示す。図７に示すように、無触媒の場合、濃度が増加してもＮ２生成量はほとんど増加しなかった。これは、高濃度条件では光量が不足すると考えられる。 Next, FIG. 7 shows a result of comparison between the case where the photocatalyst is used and the case where it is not used under the high concentration condition. As shown in FIG. 7, in the case of no catalyst, the N 2 production amount hardly increased even when the concentration increased. This is considered that the amount of light is insufficient under high density conditions.
一方、ＴｉＯ２（Ｐ２５）を用いた場合は、基質濃度の増加に対してＮ２生成量はほぼ直線的に増大した。これは２００〜３００ｎｍの波長を含む紫外光を照射することで、光化学反応と光触媒反応が効率良く進行し反応速度が増加したと考えられ、高濃度条件にも適用できることが明らかとなった。 On the other hand, when TiO 2 (P25) was used, the amount of N 2 produced increased almost linearly with increasing substrate concentration. This is considered to be due to the fact that the photochemical reaction and the photocatalytic reaction proceeded efficiently and the reaction rate was increased by irradiating with ultraviolet light having a wavelength of 200 to 300 nm.
以上より、超高濃度ＮＯ２ −およびＮＨ４ ＋の同時除去においては、ＴｉＯ２（Ｐ２５）を用いて光化学反応と光触媒反応を併用することにより効率的に反応が進行することが明らかになった。 From the above, it has been clarified that in the simultaneous removal of ultra-high concentrations of NO 2 − and NH 4 + , the reaction proceeds efficiently by using a photochemical reaction and a photocatalytic reaction in combination with TiO 2 (P25). .
（６）触媒量の影響
ＮａＮＯ２と（ＮＨ４）２ＳＯ４の水溶液に懸濁させるＴｉＯ２の量を変化させて亜硝酸―アンモニア反応を行った結果を図８に示す。
(6) Influence of catalyst amount FIG. 8 shows the result of the nitrite-ammonia reaction performed by changing the amount of TiO 2 suspended in an aqueous solution of NaNO 2 and (NH 4 ) 2 SO 4 .
図８に示すように、基質０．１Ｍのときの最適量は１０ｍｇ、０．５Ｍのときの最適量は５０ｍｇであった。よって、５００μｍｏｌの基質を５ｍＬのＨ２Ｏに溶解させる場合、触媒量は従来の５０ｍｇから１０ｍｇに削減できることが明らかになった。 As shown in FIG. 8, the optimum amount when the substrate was 0.1 M was 10 mg, and the optimum amount when the substrate was 0.5 M was 50 mg. Therefore, it was revealed that when 500 μmol of the substrate was dissolved in 5 mL of H 2 O, the amount of the catalyst could be reduced from the conventional 50 mg to 10 mg.
（８）共存金属イオンの影響
貴金属産業等の業界において発生する窒素含有廃液には、Ｃａ２＋などのアルカリ金属イオン、またはＦｅ２＋、Ｆｅ３＋若しくはＣｕ２＋などの遷移金属イオンが含まれている。そこで、亜硝酸とアンモニアの溶液に各種金属イオンを加えて亜硝酸―アンモニア反応を行った。その結果を図９に示す。
(8) Influence of coexisting metal ions Nitrogen-containing waste liquids generated in industries such as the precious metal industry contain alkali metal ions such as Ca 2+ or transition metal ions such as Fe 2+ , Fe 3+ or Cu 2+ . Therefore, nitrite-ammonia reaction was carried out by adding various metal ions to a solution of nitrous acid and ammonia. The result is shown in FIG.
図９に示すように、ＦｅおよびＣｕが強い妨害作用を示した一方、Ｃａはほとんど妨害しなかった。また、Ｆｅを５ｐｐｍおよび５０ｐｐｍ加えた場合、溶解せずＦｅＯ（ＯＨ）の沈殿が生成した。 As shown in FIG. 9, while Fe and Cu showed a strong disturbing action, Ca hardly disturbed. Further, when Fe was added at 5 ppm and 50 ppm, it was not dissolved and a precipitate of FeO (OH) was formed.
（９）亜硝酸−アンモニア比の影響
亜硝酸−アンモニア反応においてＮＯ２ −とＮＨ４ ＋は１：１の等量で反応するが、工業排水の組成は必ずしもそのような理想的な状態にはなっていない。そこで、ＮＯ２ −とＮＨ４ ＋の比を１：３および３：１にして、ＴｉＯ２（Ｐ２５，２５ｍｇ）を懸濁させ、Ａｑ．ＮａＯＨを加えてｐＨ７に調整し、紫外光（λ＞２００ｎｍ）を照射した結果を図１０に示す。
(9) Effect of nitrous acid-ammonia ratio In the nitrous acid-ammonia reaction, NO 2 - and NH 4 + react in an equal amount of 1: 1, but the composition of industrial wastewater is not necessarily in such an ideal state. is not. Therefore, TiO 2 (P25, 25 mg) was suspended at a ratio of NO 2 − to NH 4 + of 1: 3 and 3: 1, and Aq. The result of adjusting the pH to 7 by adding NaOH and irradiating with ultraviolet light (λ> 200 nm) is shown in FIG.
図１０に示すように、いずれの場合も亜硝酸―アンモニア反応が高速かつ高選択的に進行したことから、当反応は広範な組成比の排水に適用できることが明らかになった。 As shown in FIG. 10, since the nitrous acid-ammonia reaction proceeded at high speed and with high selectivity in any case, it became clear that this reaction can be applied to wastewater with a wide composition ratio.
＜実施例２＞
〔水中ＮＯ３ −およびＮＨ４ ＋の同時除去〕
水中ＮＯ３ −をλ＞２００ｎｍの紫外光を用いて光化学的に分解すると、ＮＯ２ −およびＯ２が生成する（式３）。
ＮＯ３ −→ＮＯ２ −＋１／２Ｏ２（式３）
<Example 2>
[Simultaneous removal of NO 3 − and NH 4 + in water]
When the photochemically decomposed using ultraviolet light of λ> 200nm, NO 2 - - water NO 3 and O 2 is produced (Equation 3).
NO 3 − → NO 2 − + 1 / 2O 2 (Formula 3)
そこで、ＮＯ３ −からＮＯ２ −への光分解反応と、ＮＯ２ −―ＮＨ４ ＋反応を組み合わせることにより、水中ＮＯ３ −およびＮＨ４ ＋を同時除去することを目的として検討を行った。 Therefore, studies were conducted for the purpose of simultaneous removal of NO 3 − and NH 4 + in water by combining a photolysis reaction from NO 3 − to NO 2 − and a NO 2 − —NH 4 + reaction.
（１）熱反応
ＮａＮＯ３および（ＮＨ４）２ＳＯ４の水溶液にＮａＯＨ水溶液を加えてｐＨ９に調製し、暗所下３５８Ｋで反応させた結果を図１１に示す。
(1) Thermal Reaction FIG. 11 shows the result of adjusting the pH to 9 by adding an aqueous NaOH solution to an aqueous solution of NaNO 3 and (NH 4 ) 2 SO 4 and reacting at 358 K in the dark.
図１１に示すように、加熱による揮発のためＮＨ４ ＋濃度が低下したが、反応はほとんど進行しなかった。このことから、常温常圧で光化学反応を行った場合、熱反応の影響はほとんど無視できることが明らかになった。 As shown in FIG. 11, the NH 4 + concentration decreased due to volatilization by heating, but the reaction hardly proceeded. From this, it was clarified that the effect of the thermal reaction can be neglected when the photochemical reaction is carried out at normal temperature and pressure.
（２）光化学反応
ＮａＮＯ３および（ＮＨ４）２ＳＯ４の水溶液にＮａＯＨ水溶液を加えてｐＨ８．５に調製し、λ＞２００ｎｍの紫外光を照射して反応を行った結果を図１２に示す。この反応において、Ｔｏｔａｌ−ＮＢ（全窒素バランス）、ＮＯ３ −−ＮＢ（ＮＯ３−バランス）、ＮＨ４ ＋−ＮＢ（ＮＨ４ ＋バランス）は下記式４〜６により定義される：
(2) Photochemical reaction The aqueous solution of NaNO 3 and (NH 4 ) 2 SO 4 was adjusted to pH 8.5 by adding NaOH aqueous solution, and the result of reaction by irradiating ultraviolet light with λ> 200 nm is shown in FIG. . In this reaction, Total-NB (total nitrogen balance), NO 3 - -NB (NO 3 - Balance), NH 4 + -NB (NH 4 + balance) is defined by the following formula 4-6:
前記式４〜６において、ｎ０は反応開始前の物質量であり、ｎは反応後の物質量である。
In the
図１２に示すように、７時間の光照射により、約５５％のＮＯ３ −およびＮＨ４ ＋を分解することができた。この結果から、ＮＯ３ −およびＮＨ４ ＋を光化学的に同時除去できることが分かった。 As shown in FIG. 12, about 55% of NO 3 − and NH 4 + could be decomposed by light irradiation for 7 hours. From this result, it was found that NO 3 − and NH 4 + can be simultaneously removed photochemically.
しかし、時間経過とともにｐＨが減少し、それに伴って反応速度が低下した。また、Ｔｏｔａｌ−ＮＢは９８％程度に保たれている一方、ＮＯ３ −−ＮＢが増加してＮＨ４ ＋−ＮＢが減少する傾向を示したことから、ＮＨ４ ＋の光酸化反応が生じていると考えられる。 However, the pH decreased with time, and the reaction rate decreased accordingly. In addition, while Total-NB was maintained at about 98%, NO 3 − -NB increased and NH 4 + -NB tended to decrease, so that NH 4 + photooxidation reaction occurred. It is thought that there is.
次に、基質濃度を５倍（２５００μｍｏｌ，０．５Ｍ）に増加させ、Ａｑ．ＮａＯＨを加えてｐＨ８．５に調整し、紫外光（λ＞２００ｎｍ）を照射した結果を図１３に示す。 Next, the substrate concentration was increased 5 times (2500 μmol, 0.5 M), and Aq. The result of adjusting the pH to 8.5 by adding NaOH and irradiating with ultraviolet light (λ> 200 nm) is shown in FIG.
図１３に示すように、０．１Ｍの系と比較すると、ｐＨがより急速に減少し、反応速度の低下も速く生じた。ＮＢ（ＮＯ３ −）およびＮＢ（ＮＨ４ ＋）からは明確な傾向は見られなかったが、一度減少したＴｏｔａｌ−ＮＢが回復していることから、未同定の窒素化合物（ＮＯ、Ｎ２ＯまたはＮＯ２など）が生成した可能性が示唆される。 As shown in FIG. 13, compared to the 0.1M system, the pH decreased more rapidly and the reaction rate decreased faster. Although a clear tendency was not seen from NB (NO 3 − ) and NB (NH 4 + ), since the once-reduced Total-NB was recovered, unidentified nitrogen compounds (NO, N 2 O Or NO 2 etc.) may be generated.
（３）光化学反応におけるｐＨの影響
ＮａＮＯ３および（ＮＨ４）２ＳＯ４の水溶液にＮａＯＨ水溶液を加えて各種ｐＨに調製し、λ＞２００ｎｍの紫外光を照射して反応を行った結果を図１４に示す。
(3) Effect of pH in photochemical reaction The NaOH aqueous solution was added to the aqueous solution of NaNO 3 and (NH 4 ) 2 SO 4 to prepare various pH values, and the results of the reaction by irradiating ultraviolet light with λ> 200 nm are shown in FIG. 14 shows.
図１４に示すように、酸性条件下では反応はほとんど進行せず、弱塩基性条件において最高の活性を示した。また、ｐＨ上昇とともに窒素バランスも低下する傾向を示したが、これはＮＨ３の溶解度が低下するためであると考えられる。 As shown in FIG. 14, the reaction hardly proceeded under acidic conditions, and showed the highest activity under weakly basic conditions. Further, although the tendency to decrease even nitrogen balance with pH increase, which is the solubility of the NH 3 is believed to be due to reduction.
（４）ＴｉＯ２による光触媒反応
ＮａＮＯ３および（ＮＨ４）２ＳＯ４の水溶液にＰ２５を懸濁し、ＮａＯＨ水溶液を加えてｐＨ８．２に調製し、λ＞２００ｎｍの紫外光を照射して反応を行った結果を図１５に示す。
(4) Photocatalytic reaction with TiO 2 P25 is suspended in an aqueous solution of NaNO 3 and (NH 4 ) 2 SO 4 , adjusted to pH 8.2 by adding an aqueous NaOH solution, and reacted by irradiating ultraviolet light with λ> 200 nm. The results are shown in FIG.
図１５に示すように、光化学反応（無触媒）と比較すると、反応速度は非常に遅かった。これは、中間生成物であるＮＯ２ −が光触媒によりＮＯ３ −へ酸化されるためであると考えられる（スキーム２）。 As shown in FIG. 15, the reaction rate was very slow compared to the photochemical reaction (no catalyst). This is thought to be because the intermediate product NO 2 − is oxidized to NO 3 − by the photocatalyst (Scheme 2).
また、Ｐ２５に代えて各種の光触媒を用い、同様にｐＨ８．２に調製して反応を行った結果を表３に示す。 In addition, Table 3 shows the results of performing the reaction by using various photocatalysts instead of P25 and similarly adjusting the pH to 8.2.
表３に示すように、いずれの光触媒も光化学反応よりも低い活性を示した。 As shown in Table 3, all the photocatalysts showed lower activity than the photochemical reaction.
ＮａＮＯ３および（ＮＨ４）２ＳＯ４の水溶液に金属担持ＴｉＯ２（１質量％ Ｍｅｔａｌ−ｌｏａｄｅｄ Ｐ２５）を懸濁し、ＮａＯＨ水溶液を加えてｐＨ８．５に調整し、紫外光を照射して反応を行った結果を図１６に示す。 Metal-supported TiO 2 (1 mass% Metal-loaded P25) is suspended in an aqueous solution of NaNO 3 and (NH 4 ) 2 SO 4 , adjusted to pH 8.5 by adding an aqueous NaOH solution, and irradiated with ultraviolet light to react. The results obtained are shown in FIG.
図１６に示すように、Ａｇ／Ｐ２５は無触媒系と同程度のＮＯ２ −生成活性を示したがＮ２生成活性は低かった。その他の金属担持ＴｉＯ２はほとんど活性を示さなかった。 As shown in FIG. 16, Ag / P25 are comparable to the absence of a catalyst system NO 2 - showed production activity N 2 formation activity was low. Other metal-supported TiO 2 showed little activity.
本発明の排水処理法は、高濃度の硝酸性窒素または亜硝酸性窒素およびアンモニアを含む水溶液への適用が可能であり、装置コストを低減でき、環境負荷が十分に低減され、有害な副生成物の発生を抑制でき、安全性が高いので水溶液が廃液である場合に適用できる。また、本発明の排水処理法で用いる光触媒は、再利用することも可能である。 The wastewater treatment method of the present invention can be applied to an aqueous solution containing high-concentration nitrate nitrogen or nitrite nitrogen and ammonia, can reduce the cost of the apparatus, sufficiently reduce the environmental burden, and generate harmful by-products. Since the generation of substances can be suppressed and the safety is high, it can be applied when the aqueous solution is waste liquid. The photocatalyst used in the wastewater treatment method of the present invention can be reused.
Claims (7)
The wastewater treatment method according to any one of claims 1 to 6, wherein the aqueous solution is adjusted to pH 6 to 9 to decompose nitric acid or nitrous acid and ammonia into nitrogen.
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