JP2001179074A - Treatment method and apparatus of organic substance containing nitrogen and phosphorus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an efficient treatment method and apparatus with a long- term durability for removing organic substances containing nitrogen and phosphorus by supercritical water treatment. SOLUTION: In a treatment method provided with supercritical water treatment systems for treating organic substances containing nitrogen and phosphorus, the supercritical water treatment systems are a first treatment system for treatment of decomposing and removing the organic substances in a supercritical water region of at lowest the supercritical pressure and at a supercritical water temperature within a region in which nitrogen or nitrogen compounds are difficult to be decomposed and a second treatment system for separating either one of or both of nitrogen and phosphorus components remaining in the treated water discharged out the first treatment system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to solid matter, microorganisms,
Organic compounds dissolved in aqueous solutions as well as organic compounds,
An aqueous solution containing a solute substance such as a phosphorus-based substance or a nitrogen-based substance is removed or separated by a treatment system including a decomposition removal treatment of the organic substance in a supercritical water region. The present invention relates to a method and an apparatus for treating an organic substance containing nitrogen and phosphorus capable of removing the organic substance contained in factory wastewater or the like from wastewater or a solid aqueous solution and separating and recovering valuable substances.

[0002]

2. Description of the Related Art Conventionally, sewage sludge containing organic substances has been treated by landfill or incineration. However, wastewater containing harmful substances discharged from incineration facilities due to the problem of landfill shortage and the like. Due to problems such as an increase in the treatment load of wastewater, an efficient sewage sludge treatment method with a small final disposal amount is desired. Therefore, organic matter completely decomposed, and nitrogen, can be removed in the phosphorus content, as a treatment of an organic material that does not generate harmful substances such as NO _X and SO _X, supercritical water treatment has been proposed.

[0003] Supercritical water is high-temperature, high-pressure water at a temperature and pressure higher than the critical point (temperature: 374 ° C, pressure: 22 MPa), which has intermediate properties between liquid and gas. It has the following characteristics in a fluid having both characteristics. Since it has a dielectric constant substantially equal to that of hydrocarbons, it dissolves hydrocarbons. Dissolve gases such as oxygen and nitrogen to behave similarly to gases. In the presence of supercritical water, the organic matter and the oxidizing agent are sufficiently mixed, so that conditions suitable for oxidation are formed. It has good fluidity and does not become diffusion-controlled in reactions in supercritical water. Due to these characteristics, supercritical water oxidation is considered to increase the reaction rate and increase the decomposition rate.

[0004] Supercritical Water Treatment Unlike incineration, organic substances and nitrogen content is completely decomposed, the flue gas does not contain harmful substances such as NO _X, SO _X, further processing nitrogen in water, decomposed and removed even phosphorus content, etc. It is possible to Therefore, the supercritical water treatment does not require further treatment of the generated gas or liquid, and may possibly reduce the size of the treatment system.

FIG. 4 is a schematic view of an apparatus for oxidizing organic matter by supercritical water treatment proposed in Japanese Patent Application Laid-Open No. 57-4225. In FIG. 4, the feed of the organic material and the conditioning water are supplied to a feed slurry tank 011, and the mixed conditioning water and the organic material are supplied to an extractor 017 and an oxidation reactor 019 via a feed pump 013. Oxygen or air from the raw material source 020 is supplied to the feed pump 01
The mixture is mixed with the organic material supplied from Step 3 and the conditioning water, and enters the oxidation reactor 019 via the oxidant compressor 022 to form a reaction mixture. The effluent after the oxidation reaction is subjected to removal of ash and inorganic salts by an ash separator 025, and a part of the effluent reaches an expander turbine 028, and an outlet 0
At 30 it is extracted as useful energy in the form of high pressure steam or water.

[0006] In such a treatment apparatus, under the supercritical condition of water, organic chain bonds in an aqueous solution are destroyed to modify toxic organic materials, thereby converting them into harmless low-molecular-weight materials. It has been proposed that it can be disposed of by conventional means. Also, the organic material is oxidized, thereby recovering useful energy. The temperature in the oxidation reactor 019 is 374 ° C. or higher, and the pressure is at least 22MP.
a, preferably at a high rate in a relatively uncomplicated apparatus, by finally raising the temperature to a temperature substantially above the critical temperature and configuring it to substantially completely oxidize the organic toxic waste. Processing can be performed.

[0007]

However, nitrogen or nitrogen compounds contained in organic substances such as sewage sludge are very difficult to decompose. Decomposes almost completely at 400 ° C. or higher, whereas the reaction temperature is 60
The reaction must be carried out at 0 ° C. or higher and at a reaction pressure of 25 MPa, which is quite severe in the supercritical water region. At present, Inconel 625, a nickel alloy that can withstand high temperature and high pressure, is used as a material that satisfies the above conditions. However, since it is very expensive and corrodes severely, it stays at a laboratory scale apparatus and aims at realization. Long-term durability becomes a problem. Further, under the above conditions, there still remains a problem that running costs such as fuel cost for maintaining the temperature in the reaction tank increase.

[0008] The present invention is in view of such technical problems, in the process using supercritical water treatment, nitrogen, phosphorus can organic substance removal including, in harmful substances do not remain processing such as NO _X and SO _X, It is another object of the present invention to provide a method and an apparatus for treating an organic substance capable of solving the problems of running cost and durability.

[0009]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a processing method including a supercritical water treatment system for treating an organic substance containing nitrogen and phosphorus in a supercritical water region. A first processing system that decomposes and removes the organic substance in a supercritical water region in a supercritical water temperature region above a critical pressure and in which nitrogen or a nitrogen compound is difficult to decompose, and discharged from the first processing system. A second treatment system for separating one or both of nitrogen and phosphorus remaining in the treated water, and a method for treating an organic substance containing nitrogen and phosphorus.

[0010] According to the present invention, the supercritical water region is set to a supercritical water temperature region above the critical pressure and in which nitrogen or nitrogen compounds are difficult to decompose. , The conditions of the reaction field can be relaxed,
In addition, the durability of the device can be improved by minimizing the corrosion of the device used, and the running costs such as fuel cost and power cost can be reduced.

Preferably, the first processing system has a temperature range of about 380 to 450 ° C.
When the pressure is set in a supercritical water region of approximately 23 to 30 MPa, the treatment can be performed under better conditions. However,
Since organic substances except nitrogen and phosphorus are almost completely decomposed at about 400 ° C., it is possible to efficiently perform supercritical water treatment by setting the supercritical water region to the above temperature range. .

According to the third or fourth aspect of the present invention, the treated water discharged from the first treatment system by biological treatment or catalytic decomposition depends on the properties of the substance to be treated and the installation conditions. By appropriately combining the separation and removal of nitrogen or nitrogen compounds remaining in the treated water or the separation and removal of phosphorus or phosphorus compounds remaining in the treated water by coagulation and precipitation treatment, not only organic substances but also nitrogen and phosphorus components can be removed. It can be almost completely removed.

[0013] As another method of the second treatment system, the treated water discharged from the first treatment system is adjusted to pH so as to be substantially neutral, and then magnesium ions are added to the treated water. It is also possible to react the phosphate ion with the ammonium ion and the magnesium ion to precipitate and recover as magnesium ammonium phosphate hexahydrate.

This is an efficient treatment method capable of simultaneously removing nitrogen and phosphorus remaining in the treated water discharged from the first treatment system.
Further, by reacting with the added magnesium ions to generate stratite, which is a magnesium phosphate ion, nitrogen and phosphorus can be separated from the treated water, and the generated stravite can be reused as fertilizer. Processing method.

Further, the method for treating an organic substance according to claim 5, wherein the molar ratio in the treated water is adjusted so that the phosphate ion, ammonium ion or magnesium ion reacts in an equimolar amount. The reaction of generation is performed efficiently, and the treatment can be carried out such that almost no nitrogen or phosphorus remains in the treated water.

When the organic substance contains a small amount of inorganic substance, an insoluble salt may be formed in the supercritical water region in the first treatment system. Therefore, the invention according to claim 7 is characterized in that an insoluble salt contained in the treated water is separated before the second treatment system. According to the invention, the inorganic salts contained in the treated water are likely to deteriorate the water quality due to the concentration of the inorganic salts at the time of rational use of water such as water reuse and circulation. By providing a step of separating and removing inorganic salts, water can be repeatedly used.

As described above, the treatment method according to the present invention can remove organic substances containing nitrogen and phosphorus almost completely and efficiently, and also eliminate the conventional cost problem. Therefore, by applying to the treatment method of sewage sludge and industrial wastewater, etc., more reasonable treatment can be expected.
The present invention can be applied not only to such a sludge and sewage treatment method but also to other fields as long as the treatment is an organic substance.

According to a ninth aspect of the present invention, there is provided a processing apparatus for effectively achieving the invention according to the processing method, wherein the organic substance containing nitrogen and phosphorus is decomposed and removed in a supercritical water region. In the treatment apparatus provided with the first, a first step of decomposing and removing the organic substance heated at a temperature above a critical pressure in a supercritical water region in a temperature region where nitrogen or a nitrogen compound is difficult to decompose and heated by a heat exchanger. Means, and second means for separating nitrogen and phosphorus remaining in the treated water discharged from the first treatment system.

In order to carry out the above-mentioned invention effectively, the above-mentioned first means requires that the temperature is about 380-450 ° C. and the pressure is about 2 ° C.
It is preferably a reactor of 3 to 30 MPa. By maintaining the reactor at the lowest temperature at which organic substances excluding nitrogen are decomposed, the durability of the reactor can be improved and running costs such as fuel costs can be reduced. The second means may include a reaction means for decomposing nitrogen by biological treatment or catalytic decomposition, and a reaction means for separating phosphorus by coagulation and precipitation. preferable.

Further, as another embodiment of the second means, the invention according to claim 13 is characterized in that the second means adjusts the discharged treated water of the first means to pH 7 to 9. A regulating tank, and a struvite sedimentation tank for recovering after generating and precipitating magnesium ammonium phosphate hexahydrate by adding magnesium ions to the treated water adjusted to be almost neutral, An apparatus for treating an organic substance containing nitrogen and phosphorus according to claim 9 is proposed. Thereby, the nitrogen content and the phosphorus content in the treated water can be simultaneously removed, and the wastewater can be reused as fertilizer. In addition, by providing a desalination device in front of the adjustment tank,
Insoluble inorganic salts in the treated water can be separated.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention unless otherwise specified, and are merely illustrative examples. Only. FIG. 1 is an overall schematic configuration diagram of a supercritical water treatment apparatus according to a first embodiment of the present invention, and FIG.
FIG. 3 is a partial configuration diagram showing a configuration of a facility for removing phosphorus or these compounds, and FIG. 3 is an overall schematic configuration diagram of a supercritical processing apparatus according to a second embodiment of the present invention.

In FIG. 1, reference numeral 10 denotes a concentrated aqueous solution containing nitrogen, phosphorus, or an organic substance, such as sewage sludge or industrial wastewater, which is concentrated by a solid-liquid separation means (not shown) to a water content of about 98%. Sludge (a slurry-like substance having a water content of about 80% may be charged, and water may be appropriately added in a reactor)
Then, the concentrated sludge 10 is supplied to the heat exchanger 12 by the press-fitting piston 11, and after being heated in the heat exchanger 12, is guided to the reactor 13. Further, the oxidizing agent 15 such as hydrogen peroxide and oxygen introduced into the heat exchanger 14 is supplied to the reactor 13 through the heat exchanger 14 similarly to the concentrated sludge, and promotes the reaction in the reactor 13. Let it.

The reactor 13 is maintained in a supercritical water region, preferably at a pressure of about 25 MPa and at a temperature of about 400 to 450 ° C., and contains nitrogen, phosphorus, or nitrogen contained in the concentrated sludge 10 led to the reactor 13. Organic substances excluding these compounds are almost completely separated by the oxidation reaction in the reactor 13. In the reactor 13, the organic substance is decomposed into carbon dioxide, water, and the like, and the nitrogen component produces ammonium ions, and the phosphorus component produces phosphate ions and the like,
In addition, the inorganic substances in the concentrated sludge that are insolubilized in the supercritical water region are discharged as insoluble inorganic salts together with the treated water.

Since the treated water is discharged at a high temperature and a high pressure, the concentrated sludge 1 is discharged from the heat exchangers 12 and 14.
0, the temperature is reduced by heat exchange with the oxidizing agent 15, and after the pressure is reduced by the gas-liquid separator 16 such as a high-pressure separator, a low-pressure separator, the exhaust gas 19 is discharged as it is. The poorly soluble harmful substances such as NO _x , SO _x , and organic chlorine compounds contained in the organic substances are decomposed in the supercritical water region in the reactor to make them harmless, so that the exhaust gas 19 is discharged as a clean gas. Therefore, there is no problem if it is discharged out of the system.

The treated water separated by the gas-liquid separator 16 contains nitrogen and phosphorus such as ammonium ions and phosphate ions, and these substances are factors of the eutrophication phenomenon and need to be removed from the treated water. Therefore, the treated water is separated from the treated water by the nitrogen removing equipment 17 or the phosphorus removing equipment 18 in the next step, removed, and then discharged out of the system as detoxified treated water 20 or reused.

As an example of the equipment for removing nitrogen and phosphorus,
2 (a) and 2 (b) show a partial configuration diagram. First, FIG.
In order to explain the removal treatment by the combination of the biological treatment and the coagulation precipitation treatment in (a), the treated water separated by the gas-liquid separator 16 in FIG. 1 first removes nitrogen such as ammonium ions. The nitric acid is introduced into the nitrification tank 17a, and is changed into nitric acid by the action of nitrite bacteria, nitric acid bacteria, etc., and then is changed into nitrogen molecules by denitrification bacteria and the like in the denitrification tank 17b. Next, the treated water containing nitrogen which has not been treated in the sedimentation basin 17c is returned to 17a to be reprocessed. After almost all the nitrogen is removed, the treated water is supplied to the phosphorus removing equipment 18. Further, the treated water is subjected to a coagulating sedimentation device 18 to which a coagulant is added in order to remove a phosphorus content in a phosphorus removing device 18.
The treated water 20 which has been introduced into a and precipitates and removes flocs generated by agglomeration, and from which nitrogen and phosphorus are almost removed, is discharged out of the system and reused, circulated, or discharged.

FIG. 2 (b) shows a combination of a catalyst separation treatment and a coagulation / precipitation treatment. The treated water containing nitrogen and phosphorus is introduced into a reaction tank 17d containing a catalyst to decompose nitrogen. , And settled and separated in the next settling basin 17e. Next, in order to remove the phosphorus content in the phosphorus removal equipment 18, the phosphorus content is separated by the coagulation / sedimentation apparatus 18a in the same manner as described above, and the treated water 20 which has been removed and made harmless is discharged.
By appropriately combining these devices according to conditions such as the installation location and cost, a low-cost, efficient, and durable processing device can be realized.

FIG. 3 is a schematic structural view of a processing apparatus using a stravite method as a second embodiment of the present invention for removing nitrogen, phosphorus or these compounds contained in the treated water. . First, similarly to the first embodiment, the concentrated sludge 10 heated by the heat exchangers 12 and 14 is used.
And the oxidizing agent 15 are supplied to the reactor 13 held in the supercritical water region, and nitrogen,
Decompose and remove organic substances excluding phosphorus.

The treated water discharged from the reactor passes through the heat exchangers 12 and 14 and is separated into exhaust gas 19 and treated water by a gas-liquid separator. The insoluble inorganic salt in the water is separated, and the treated water containing nitrogen and phosphorus is adjusted to pH 7 to 9 in which strabite is easily formed in the adjusting tank 22, and the treated water maintained almost neutral is treated with stravite. It is supplied to the sedimentation tank 23.

Magnesium ions are added to the strabite sedimentation tank 23, and orthophosphate ions and ammonium ions contained in the treated water are reacted with the added magnesium ions to form a sparingly soluble magnesium ammonium phosphate hexahydrate. A stravitite crystal 24 of a Japanese product is generated. Magnesium ions are used for smoke washing in the sludge incineration process of a treatment plant, and the wastewater can be easily used. Therefore, it is preferable to reuse the wastewater to reduce the cost of additives.

The struvite crystal 24 precipitated and separated from the treated water contains phosphate ions, magnesium ions and ammonium ions which are important as fertilizers, and is a high-quality chemical fertilizer with a long-acting effect. Not only can nitrogen and phosphorus be removed from the treated water, but also it can be used as fertilizer, which enables environmentally and economically reasonable treatment. Incidentally, in order to generate and recover stravite from the treated water, a high recovery rate can be obtained by setting appropriate pH, temperature and contact time. As conditions for high recovery, a pH of 7 to 9 and a temperature of about 25 ° C. are preferable.

[0032]

As described above, according to the present invention, in a supercritical water treatment of an organic substance containing nitrogen and phosphorus, the reaction field in the supercritical water treatment is made lower than before so that the reactor and the like can be used. Corrosion can be suppressed, durability can be improved, and running costs such as fuel costs can be reduced. In addition, the supercritical water treatment has a high reaction rate and a high decomposition rate, so that dissolved substances other than nitrogen can be almost completely removed, and nitrogen, phosphorus removing means, or desalting means is appropriately provided, whereby the supercritical water treatment is performed. Nitrogen, phosphorus, inorganic salts, and the like, which cannot be removed by the critical water treatment, can be removed from the substance to be treated, almost all polluting substances in the substance to be treated can be removed, and the treated water can be recycled.

As the means for removing nitrogen and phosphorus, magnesium ions are added to separate and collect from the treated water as stramite, which is magnesium ammonium phosphate hexahydrate, so that nitrogen and phosphorus can be removed. Since it can be separated from the treated water and effectively used as a high-quality fertilizer with a long-lasting effect, it is possible to provide a reasonable treatment that is environmentally and economically suitable. Furthermore, since the supercritical water treatment is a treatment at a high temperature, harmful hard-to-decompose waste such as SO _X , NO _X or organic chlorine-based compounds contained in the substance to be treated such as the sewage sludge and factory effluent is removed. Can be safely and completely disassembled.

[Brief description of the drawings]

FIG. 1 is an overall schematic configuration diagram of a supercritical water treatment apparatus according to a first embodiment of the present invention.

FIG. 2 is a partial configuration diagram showing a configuration of a facility for removing nitrogen, phosphorus, or a compound thereof in the first embodiment.

FIG. 3 is an overall schematic configuration diagram of a supercritical water treatment apparatus according to a second embodiment of the present invention.

FIG. 4 is an overall schematic configuration diagram of a conventional supercritical water treatment apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Condensed sludge 12, 14 Heat exchanger 13 Reactor 16 Gas-liquid separator 17 Nitrogen removal equipment 18 Phosphorus removal equipment 20 Treated water 21 Desalination equipment 22 Adjustment tank 23 Stravite sedimentation tank

 ────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Jun Sato 1-8-1 Koura, Kanazawa-ku, Yokohama-shi F-term in Yokohama Research Laboratory, Mitsubishi Heavy Industries, Ltd. 4D038 AA08 AB12 AB15 BA02 BB01 BB13 BB16 BB18 BB20 4D050 AA13 AA15 AB17 AB20 BB01 BC04 BC06 BD03 CA13 CA16 4G075 AA34 AA37 BA05 BD16 CA02 CA05 CA65

Claims (14)

[Claims] A supercritical water treatment system for treating an organic substance containing nitrogen and phosphorus in a supercritical water region, wherein the temperature of the supercritical water is higher than a critical pressure and nitrogen or a nitrogen compound is difficult to decompose. A first treatment system for decomposing and removing the organic substance in the supercritical water region of the region, and one or both of nitrogen and phosphorus remaining in the treated water discharged from the first treatment system A method for treating an organic substance containing nitrogen and phosphorus, comprising a second treatment system. 2. The method according to claim 1, wherein the first processing system has a temperature range of about 380.
2. The method for treating an organic substance containing nitrogen and phosphorus according to claim 1, wherein the treatment is performed in a supercritical water region at a temperature of about 450 [deg.] C. and a pressure of about 23 to 30 MPa. 3. The second treatment system includes a treatment system for separating nitrogen or a nitrogen compound remaining in treated water discharged from the first treatment system from the treated water by biological treatment or catalytic decomposition treatment. The nitrogen according to claim 1, wherein
A method for treating an organic substance containing phosphorus. 4. The method according to claim 1, wherein the second treatment system includes a treatment system for separating the phosphorus or the phosphorus compound remaining in the treated water discharged from the first treatment system from the treated water by coagulation and precipitation. The method for treating an organic substance containing nitrogen and phosphorus according to claim 1. 5. The second treatment system adjusts the pH of the treated water discharged from the first treatment system to approximately neutral, and then adds magnesium ions to the treated water to form phosphate ions in the treated water. 2. The organic substance containing nitrogen and phosphorus according to claim 1, further comprising a treatment system for reacting the ammonium ion with the magnesium ion to precipitate and recover as magnesium ammonium phosphate hexahydrate. Processing method. 6. The organic substance containing nitrogen and phosphorus according to claim 5, wherein the molar ratio in the treated water is adjusted so that the phosphate ions, ammonium ions or magnesium ions react in an equimolar manner. Processing method. 7. The method for treating an organic substance containing nitrogen and phosphorus according to claim 1, wherein an insoluble salt contained in the treated water is separated at a stage prior to the second treatment system. 8. The treatment of an organic substance containing nitrogen and phosphorus according to claim 1, wherein the substance to be treated is an organic substance containing nitrogen and phosphorus contained in sewage sludge and factory wastewater. Method. 9. A processing apparatus comprising means for decomposing and removing an organic substance containing nitrogen and phosphorus in a supercritical water region, comprising: a supercritical water in a temperature range of a critical pressure or higher and in which nitrogen or a nitrogen compound is difficult to decompose. A first means for decomposing and removing the organic substance held in the region and heated by a heat exchanger; and a second means for separating nitrogen and phosphorus remaining in the treated water discharged from the first treatment system. An apparatus for treating an organic substance containing nitrogen and phosphorus, comprising: 10. The method according to claim 1, wherein the first means has a temperature of about 380 to 380.
The apparatus for treating an organic substance containing nitrogen and phosphorus according to claim 9, wherein the reactor is a reactor at 450 ° C. and a pressure of about 23 to 30 MPa. 11. The apparatus for treating an organic substance containing nitrogen and phosphorus according to claim 9, wherein said second means comprises a reaction means for decomposing nitrogen by biological treatment or catalytic decomposition. . 12. The apparatus for treating an organic substance containing nitrogen and phosphorus according to claim 9, wherein said second means comprises a reaction means for separating phosphorus by coagulation sedimentation. 13. The second means comprises: an adjusting tank for adjusting the pH of the treated water discharged from the first means to pH 7 to 9; and adding magnesium ions to the substantially neutralized treated water to add phosphorus. The apparatus for treating an organic substance containing nitrogen and phosphorus according to claim 9, comprising a struvite precipitation tank for recovering after generating and precipitating magnesium ammonium phosphate hexahydrate. 14. The apparatus for treating an organic substance containing nitrogen and phosphorus according to claim 13, wherein a desalination apparatus is provided in a stage preceding the adjustment tank.