JP2013013846A - Wastewater treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wastewater treatment method which can be practised inexpensively in a simplified manner and by which organic compounds, ammonia nitrogen or the like in the wastewater can be oxidatively decomposed without being accompanied by production of secondary pollutants and with high efficiency.SOLUTION: Limonite obtained by bringing hydrogen sulfide into contact with limonite or the like which is used as a desulfurizing agent and then is recovered, is used as a solid catalyst directly or after pelletized or sintered. The solid catalyst is brought into contact with the wastewater to which a compound such as a peroxide producing active oxygen species by reaction with the solid catalyst is added, and as a result, hydroxyl radicals are produced by a Fenton-like reaction. The organic compounds, ammonia nitrogen or the like in the wastewater can be oxidatively decomposed by utilizing the hydroxyl radicals.

Description

  The present invention relates to a wastewater treatment method capable of quickly and efficiently oxidizing and decomposing organic compounds and ammonia nitrogen in wastewater.

  Examples of treatment methods for purifying wastewater containing various organic compounds to the extent that they can be released to the environment include biological treatment methods, activated carbon adsorption methods, and coagulation precipitation methods. In any of these methods, secondary treatment of sludge generated in large quantities becomes a problem. Further, in the conventional method, the organic compounds that can be treated are limited, and there is a possibility that the organic compounds that could not be treated remain in the waste water. These persistent organic compounds are rather problematic when released into the environment.

  For example, biological treatment methods such as the activated sludge method cannot decompose biologically degradable organic compounds such as trihalomethanes and dioxins, and the activity of microorganisms is inhibited. There is also a problem that it is difficult to apply biological treatment methods to treatment and wastewater treatment containing high concentrations of organic compounds.

  In recent years, in order to solve the problems of these conventional methods, a chemical oxidation treatment method, an electrochemical treatment method, and the like have been proposed as a method for decomposing and removing organic compounds contained in waste water. However, it is possible to reduce the molecular weight by oxidizing and decomposing the organic compound contained in the wastewater or to discharge it as carbon dioxide out of the system.

  The electrochemical treatment method includes an electrochemical synthesis of an oxidant, an oxidative decomposition of the organic compound contained in the wastewater by the synthesized oxidant, and a method of direct oxidative decomposition of the organic compound by an electrochemical reaction. Two types have been proposed.

  As the former method, for example, Patent Document 1 discloses a method of electrolytically treating ethanolamine-containing water under water quality conditions containing chloride ions, specifically hypochlorous acid produced by anodization of chloride ions. A method for decomposing ethanolamine with an acid is disclosed.

  As the latter method, for example, in Patent Document 2, raw water containing an electrolyte made of a chloride is electrolyzed using a first electrolytic cell and a second electrolytic cell to generate hydroxy radicals, and oxidation of the hydroxy radicals is performed. A method for decomposing organic compounds by force is disclosed.

  On the other hand, as a chemical oxidation method, for example, as disclosed in Patent Document 3, a method of oxidizing an organic compound by adding hypochlorous acid to wastewater is widely used.

  A method using ozone as an oxidizing agent other than hypochlorous acid has been proposed. For example, Patent Document 4 discloses a method of continuously decolorizing wastewater by ozone-oxidizing the wastewater by blowing and mixing ozone-oxidized oxygen in an amount of 10 to 200 mg with respect to 1 liter of wastewater. Is disclosed.

  In addition, a method of oxidizing and decomposing organic compounds and the like in wastewater using hydroxyl radicals generated by the reaction between iron salt and hydrogen peroxide (Fenton reaction) has been studied. For example, Patent Document 5 discloses an iron salt reaction means for adding and reacting a trivalent iron salt to wastewater containing an organic substance and a reducing agent, and peroxidizing the wastewater after the iron salt is added and mixed. There is disclosed a wastewater treatment apparatus characterized by having a hydrogen peroxide reaction means for adding hydrogen and reacting, and a biological treatment means for biologically treating the wastewater after the hydrogen peroxide is added and mixed.

JP-A-11-216473 JP 2000-79394 A JP-A-9-192679 Japanese Unexamined Patent Publication No. 7-31990 JP 2002-282874 A

  However, the method described in Patent Document 1 points out the possibility of secondary contamination by harmful organic chlorine compounds such as trihalomethanes generated in the reaction process of hypochlorous acid and ethanolamine. In the method described in Patent Document 2, hypochlorous acid is not used as an oxidant, but hypochlorous acid is involved in the process of synthesizing a hydroxy radical. Therefore, as in the method described in Patent Document 1, trihalomethane or the like is used. May produce harmful organochlorine compounds. Moreover, since the production | generation efficiency of a hydroxyl radical is low, there exists a problem in economical efficiency.

  The method described in Patent Document 3 has a safety problem regarding transportation and storage of harmful and dangerous hypochlorous acid to the processing site. Further, this method cannot solve the above-mentioned problem that harmful organic chlorine compounds such as trihalomethane are generated by the reaction of hypochlorous acid with an organic compound.

  The method described in Patent Document 4 has a problem that a large apparatus is required for generating ozone and running cost such as electricity bill is high. In addition, the wastewater treatment apparatus described in Patent Document 5 and the wastewater treatment method using the wastewater treatment apparatus have strict drainage standards (in the uniform drainage standards established by the Ministry of the Environment, the allowable limit of soluble iron is set to a low value of 10 mg / L. ) Since iron ions are used as a catalyst, a post-treatment step for removing iron content may be required.

  The present invention has been made in view of such problems, and can be carried out easily and at low cost, and oxidatively decomposes organic compounds, ammonia nitrogen, and the like in wastewater with high efficiency without accompanying by-products of secondary pollutants. It aims at providing the processing method of waste water which can be done.

As a result of intensive studies, the present inventor produced limonite (limonite) contacted and reacted with inorganic and organic compounds such as hydrogen sulfide with hydrogen peroxide and the like to generate oxidizing radicals such as hydroxyl radicals. In addition, the present inventors have found that organic compounds contained in waste water can be efficiently oxidized and decomposed by using this.
That is, the present invention provides the wastewater treatment method according to the following [1] to [4].
[1] Drainage obtained by adding a compound that generates active oxygen species by reaction with the solid catalyst to a solid catalyst containing limonite brought into contact with any of hydrogen sulfide, sulfide ions, hydrosulfide ions, thiols and sulfides Wastewater treatment method for contact.
[2] The method for treating waste water according to the above [1], wherein the solid catalyst is limonite recovered after use as a desulfurizing agent.
[3] The wastewater treatment method according to the above [1] or [2], wherein the peroxide is hydrogen peroxide.
[4] The wastewater treatment method according to the above [4], wherein the peroxide is hydrogen peroxide.

  The wastewater treatment method of the present invention does not require large-scale facilities such as an ozone generator and an electrolyzer. Therefore, there is no large power consumption and the running cost is low. Further, unlike the precipitation method or the like, there is no need to control the pH of the drainage. Furthermore, in the waste liquid treatment method of the present invention, since hydroxyl radicals having high activity are used as an oxidizing agent, the treatment speed for decolorization and the like is extremely fast, and waste water treatment that is more efficient than conventional methods becomes possible. In addition, since a solid catalyst containing limonite after contact with hydrogen sulfide is used as a catalyst for generating hydroxy radicals, iron ions are not easily eluted into the waste water. Therefore, the wastewater after the treatment using the wastewater treatment method of the present invention can be directly released to the environment without removing iron ions.

  In particular, in the wastewater treatment method of the present invention, the waste material of limonite used as an exhaust gas desulfurization agent can be used as it is for wastewater treatment. Limonite having a part of its surface sulfided can be used for wastewater treatment to be regenerated to its original state upon reaction with hydrogen peroxide and used again for exhaust gas treatment after molding. Therefore, when the recovered limonite is used as a solid catalyst after being used as a desulfurizing agent, it is expected that not only the cost required for the disposal becomes unnecessary, but also the limonite can be recycled semipermanently.

It is a graph which shows the effect of limonite on the time-dependent change of the methylene blue density | concentration in a methylene blue aqueous solution, (A) shows the result in hydrogen peroxide absence, (B) shows the result in hydrogen peroxide presence, respectively. It is a graph which shows a time-dependent change of the hydroxy salicylic acid density | concentration at the time of making hydrogen peroxide and a salicylic acid aqueous solution contact the limonite used as a sulfurizing agent.

Hereinafter, embodiments of the present invention will be described.
In the wastewater treatment method according to an embodiment of the present invention (hereinafter sometimes abbreviated as “wastewater treatment method” or “treatment method”), a solid catalyst containing limonite in contact with hydrogen sulfide is used. The wastewater to which the peroxide is added is brought into contact, and the organic compounds and ammonia nitrogen in the wastewater are oxidatively decomposed using hydroxyl radicals generated by the Fenton-like reaction.

  Limonite (limonite) is an aggregate of one or both of goethite (goethite, α-FeOOH) and spheroite (repidocrocite, γ-FeOOH), dark brown or black nodules, soil-like Is produced as Limonite has long been used as an iron ore and pigment, but it can be used in feed additives, sewage, exhaust gas, etc. to reduce the body odor and excrement odor of pets by utilizing its property of reacting with hydrogen sulfide. It is also used as a removal agent (desulfurization agent) for contained hydrogen sulfide. The removal of hydrogen sulfide by limonite is thought to be due to the reaction between hydrogen sulfide and iron present on the surface of limonite to produce iron sulfide.

  In the wastewater treatment method according to the present embodiment, limonite after contact with hydrogen sulfide is generated very rapidly by contacting with hydrogen peroxide (an example of a compound that generates active oxygen species by reaction with a solid catalyst). Hydroxy radicals to be used for decomposition of organic compounds in waste water. The generation of hydroxyl radicals is thought to be due to the Fenton-like reaction shown in the following formula.

  By this reaction, it is thought that the limonite containing trivalent iron is regenerated by oxidizing iron (II) sulfide generated on the surface of limonite. In fact, the surface of limonite after contact with hydrogen sulfide has a blackish brown color that is thought to be due to iron sulfide, but the limonite after use for wastewater treatment has a yellowish brown color. Therefore, limonite after use in the wastewater treatment method can be used as it is as a desulfurization agent, and can be used as a desulfurization agent and a solid catalyst for wastewater treatment.

  Conventionally, limonite after being used as a desulfurizing agent has been disposed of as industrial waste, but by making it possible to use the cycle as described above, the processing cost of limonite after desulfurization can be reduced and the environmental load can be reduced. It is also expected to have an effect such as reduction of

  Limonite after contact with hydrogen sulfide, for example, may be used as it is as a desulfurization agent, but only limonite after contact with hydrogen sulfide alone, or a granulated or sintered mixture of binder May be used as a solid catalyst. Granulation or sintering can be performed using any known method and apparatus, and any known binder can be appropriately selected and used for the binder used as needed during granulation or sintering. Can do.

  In the present embodiment, an example of limonite after being brought into contact with hydrogen sulfide has been described. However, the sulfur-containing compound or chemical species to be brought into contact with limonite is not limited as long as it reacts with limonite to produce iron sulfide. It may be a thing. Specific examples of such sulfur-containing compounds or chemical species include hydrogen sulfide, sulfide ions, hydrosulfide ions, thiols, sulfides and the like.

  The wastewater to be treated is not particularly limited, and may be any of household wastewater, business wastewater, middle water or sewage, and human waste. These wastewaters may be subjected to direct treatment, but if necessary, the solid content can be removed using a known solid-liquid separation method such as agglomeration method, precipitation separation method, flotation separation method, filtration method, and centrifugal separation method. It is preferable to remove it.

  The amount of the solid catalyst brought into contact with the wastewater is appropriately determined according to the content of limonite in the solid catalyst, the particle size of the solid catalyst, the type of wastewater, the degree of contamination, etc., but recovered after use as a desulfurizing agent. When using limonite, it is 0.1-50g per 1L of waste_water | drain, Preferably it is 5-25g.

  The amount of hydrogen peroxide added to the wastewater is appropriately determined according to the content of limonite in the solid catalyst, the particle size of the solid catalyst, the type of wastewater, the degree of contamination, and the like. It is preferable that it is 01-100 mmol / L. In addition to hydrogen peroxide, peroxides such as percarbonate, persulfate, and peracetic acid can be used, but hydrogen peroxide is preferred from the viewpoint of cost and ease of handling.

  There is no particular limitation on the method of bringing the wastewater containing peroxide into contact with the solid catalyst, for example, a batch method in which the solid catalyst is added to the mixed solution of wastewater and peroxide, and stirring is performed as necessary. Any of continuous methods in which a mixed solution of waste water and peroxide is passed through a column packed with a solid catalyst may be used.

Examples carried out to study the effects of the present invention will be described.
(1) Decolorization experiment of methylene blue aqueous solution Take 70 mL each of 16 μM methylene blue aqueous solution into a beaker, collect 2 blanks (Blank), recover limonite used as desulfurization agent (desulfurization agent), untreated limonite ( Untreated), limonite sintered body (sintered), and two beakers each containing 2.2 g each of sodium carbonate added and sintered (NaHCO ₃ ) were prepared. Only in one of these five sets of beakers, 100 μL of 30% hydrogen peroxide was added, and the change with time in absorbance at 665 nm was measured while stirring with a magnetic stirrer. FIG. 1A shows the measurement results in the group to which hydrogen peroxide was not added, and FIG. 1B shows the measurement results in the group to which hydrogen peroxide was added. The absorbance is indicated as a percentage (C / C ₀ (%)) with respect to the absorbance immediately before the start of stirring.

  As shown in FIG. 1 (A), when hydrogen peroxide is not added, the absorbance hardly changes for the sample in which the solid catalyst is not present, whereas for the sample to which the solid catalyst is added, time elapses. A slight decrease in absorbance associated with was observed.

  As shown in FIG. 1B, when hydrogen peroxide was added, a rapid decrease in absorbance was observed for the sample to which the recovered limonite used as the desulfurizing agent was added. It shows that methylene blue was almost completely oxidatively decomposed within 1 minute after the addition of hydrogen oxide. On the other hand, for the other samples, results similar to those shown in FIG. From these results, limonite has the ability to remove a part of methylene blue in the aqueous solution from the aqueous solution by physical adsorption, but has little ability to catalyze the generation of hydroxyl radical by Fenton-like reaction. It can be seen that limonite in contact with hydrogen sulfide has a high ability to catalyze the production of hydroxyl radicals by Fenton-like reaction and can oxidize and decompose organic compounds in aqueous solution very rapidly.

  In limonite, iron exists mainly in a trivalent (Fe (III)) state, so that hydroxyl radicals can hardly be generated by the above reaction, whereas the surface of limonite after contact with hydrogen sulfide. Has iron sulfide (II), and this divalent iron is considered to cause a Fenton-like reaction to rapidly generate hydroxyl radicals.

(2) Decolorization experiment of bilirubin aqueous solution and manure The decomposition experiment was performed in the same procedure as the above (1) using the hardly degradable bilirubin aqueous solution and the manure sample collected from barns, and the absorbance of the absorption band derived from bilirubin Was observed over time. Similar to the experiment using the methylene blue aqueous solution, in the sample added with the recovered limonite used as the desulfurizing agent, a rapid decrease in absorbance was observed in both the bilirubin aqueous solution and the manure.

(3) Confirmation of hydroxyl radical generation Using salicylic acid that reacts with hydroxyl radical to produce 2,3- or 2,5-dihydroxybenzoic acid (DHBA) as a trapping agent, hydroxyl radical generation was investigated. .

  After contacting the recovered salmonylic acid aqueous solution (350 μM, 100 mL) with the recovered limonite used as the desulfurizing agent (2 g), hydrogen peroxide was added while stirring with a magnetic stirrer. The time course of the concentration of DHBA was determined using a calibration curve method from the time course of the UV-visible absorption spectrum and the time course of the peak intensity in high performance liquid chromatography (HPLC). The results are shown in FIG.

It can be seen that the concentration of DHBA reaches a maximum within a few minutes after the addition of hydrogen peroxide. Note that the DHBA concentration slightly decreases after reaching the maximum, which is considered to be due to oxidative decomposition of DHBA by hydroxyl radicals.
From this result, it was confirmed that when the recovered limonite used as a desulfurizing agent was used as a solid catalyst, the concentration of hydroxyl radicals rapidly increased and reached a maximum within a few minutes when hydrogen peroxide was added. It was.

Claims (4)

  Contacting a solid catalyst containing limonite in contact with any of hydrogen sulfide, sulfide ions, hydrosulfide ions, thiols and sulfides with wastewater to which a compound that generates active oxygen species by reaction with the solid catalyst is added. A method for treating wastewater.   The wastewater treatment method according to claim 1, wherein the solid catalyst is limonite recovered after use as a desulfurization agent.   The wastewater treatment method according to claim 1 or 2, wherein the compound that generates active oxygen species by reaction with the solid catalyst is a peroxide.   The wastewater treatment method according to claim 3, wherein the peroxide is hydrogen peroxide.

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