JP2009078253A - Method for treating waste water containing inorganic sulfur compound - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a treatment method for waste water where treating performance for waste water containing an inorganic sulfur compound is further improved, and also, equipment investment and driving cost can be reduced. <P>SOLUTION: Disclosed is a method for treating waste water where waste water containing an inorganic sulfur compound is subjected to wet oxidation treatment using a solid catalyst under temperature and pressure at which the waste water holds a liquid phase, and the solid catalyst comprises at least one kind selected from the group consisting of platinum, palladium, ruthenium, iridium, rhodium and gold and at least one kind selected from the group consisting of cerium, lanthanum, yttrium, praseodymium, neodymium, indium, copper and manganese. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to petrochemicals such as wood cooking wastewater and wood kettle wastewater, fiber washing wastewater, iron and steel industry coke oven wastewater, photographic development wastewater, metal processing wastewater, sulfurous acid gas-absorbing alkaline wastewater, ethylene / BTX, etc. Contains wastewater from product production plants and compounds containing inorganic sulfur emitted from various industrial factories such as coal gasification plants, oil refineries, rayon manufacturing plants, dyeing and arranging plants, meat processing plants, and chemical manufacturing plants. The present invention relates to a method for effectively purifying wastewater.

  Conventionally, biological treatment methods, combustion treatment methods, wet oxidation treatment methods and the like have been widely used as methods for treating wastewater. Of these, in biological treatment methods, surplus sludge and other by-products are generated, so the treatment is often a problem, and there are also problems such as the presence of many wastewaters that are difficult to treat with biological treatment methods. . In particular, when inorganic sulfur compounds are contained in the waste water, biological treatment is often impossible. Further, in the combustion treatment method, since fossil fuel is often used as a fuel, resources are wasted, and there is often a problem as an emission source of exhaust gas such as carbon dioxide.

  On the other hand, it is said that the wet oxidation method in which the wastewater is purified by oxidative decomposition while maintaining the liquid phase at a high temperature and high pressure is excellent without causing the above-described problems. There are various forms in this wet oxidation treatment method, in addition to the method of processing in the gas-liquid upward cocurrent flow, the method of processing in the gas-liquid downward cocurrent flow, the method of processing in the gas-liquid countercurrent flow in the reaction tower, There are a method in which a catalyst is used in combination and a method in which a treatment is performed without a catalyst.

  In order to obtain and demonstrate high processing performance in the non-catalytic wet oxidation method, it is necessary to use harsh processing conditions of high temperature and high pressure, or to increase the reaction time. It has been pointed out that the operating cost becomes high.

  Therefore, a catalytic wet oxidation method has been proposed in which the treatment performance is improved by using a solid catalyst. By using a solid catalyst, the reaction temperature and pressure can be reduced, and the reaction time can be shortened. However, even in such catalytic wet oxidation treatment methods, depending on the type and concentration of wastewater to be treated, a large amount of catalyst is required and equipment costs and operating costs increase, and durability and treatment performance of solid catalysts. There was a problem.

JP 2003-236567 A

  This invention is made paying attention to the above situations, and the objective can further improve the treatment performance with respect to the wastewater containing an inorganic sulfur compound, and can reduce capital investment and operation cost. The object is to provide a useful wastewater treatment method.

  As a result of intensive studies to solve the above problems, the present inventors have completed the invention shown below. A method in which wastewater containing an inorganic sulfur compound is subjected to a wet oxidation treatment using a solid catalyst under a temperature and pressure at which the wastewater maintains a liquid phase, wherein the solid catalyst is platinum, palladium, ruthenium, iridium At least one elemental metal and / or compound (catalyst A component) selected from the group consisting of rhodium and gold, and at least selected from the group consisting of cerium, lanthanum, yttrium, praseodymium, neodymium, indium, copper and manganese A wastewater treatment method containing an inorganic sulfur compound, characterized by containing an oxide of one element (catalyst B component). In the solid catalyst, the ratio of the mass of the catalyst A component to the total mass of the catalyst A component and the catalyst B component is preferably 0.1 to 0.5. The solid catalyst further contains an oxide containing titanium as a carrier component, and the catalyst A component is 0.05 to 5% by mass and the catalyst B component is 0.5 to 10% by mass with respect to the solid catalyst. You can also. In the wastewater treatment, it is preferable to perform wet oxidation treatment in a state in which sodium is contained so that the molar ratio (Na / S) of sodium and sulfur contained in the wastewater is larger than 2. A biological treatment can be further performed after the wet oxidation treatment.

  According to the method of the present invention, it is possible to efficiently oxidatively decompose and decompose inorganic sulfur compounds into inorganic sulfates, carbon dioxide, water, ash and the like. In addition, since inorganic sulfur compounds that adversely affect living organisms can be highly processed, further advanced processing can be stably performed by combining biological processing in the subsequent stage. As a result, it was possible to realize a simple and compact treatment process as compared with the conventional treatment technology, and to provide a wastewater treatment method that is advantageous in terms of capital investment and running cost.

The waste water according to the present invention contains an inorganic sulfur compound, and the inorganic sulfur compound is an inorganic compound other than sulfuric acid (SO ₄ ²⁻ ) containing at least one sulfur atom, such as hydrogen sulfide, sodium sulfide, Sulfides such as potassium sulfide, sodium hydrosulfide and sodium polysulfide; thiosulfates and salts thereof such as sodium thiosulfate and potassium thiosulfate; sulfites and salts thereof such as sodium sulfite; trithionic acids such as sodium trithionate , Tetrathioic acid and its salts. The amount of the inorganic sulfur compound is 1 to 50 g / liter, preferably 5 to 40 g / liter in terms of the theoretical oxygen demand, and if it is less than 1 g / liter, the reaction caused by the wet oxidation reaction Since there is little heat, the amount of heat recovered by the heat exchanger is insufficient, the gas and liquid supplied to the reaction tower must be constantly heated, and if it exceeds 50 g / liter, too much reaction heat is generated in the wet oxidation reaction. This is because the temperature difference between the reaction tower inlet side and the outlet side becomes too large. The theoretical oxygen demand here refers to the amount of oxygen required to oxidatively decompose inorganic sulfur compounds in wastewater to sulfuric acid (SO ₄ ²⁻ ). When the concentration of the waste water deviates from the above range, it can be adjusted to an appropriate concentration by appropriately diluting or concentrating.

Inorganic sulfur in wastewater is converted to sulfuric acid (SO ₄ ^2- ) when oxidation and / or decomposition is completely advanced by wet oxidation treatment. However, in the case of catalytic wet oxidation treatment using a conventional catalyst, the treatment performance is sufficient. However, in order to obtain high processing performance, a large amount of catalyst is required, which is not preferable.

  On the other hand, the present invention uses a novel solid catalyst containing the catalyst A component and the catalyst B component to perform catalytic wet oxidation treatment of wastewater containing inorganic sulfur compounds at a significantly higher efficiency than the prior art. Made possible.

  In addition, it is possible to stably perform advanced treatment by performing wet oxidation treatment in a state in which a sodium amount in which the molar ratio (Na / S) of sodium and sulfur contained in the wastewater is greater than 2 is included. did. The inclusion of sodium may be wastewater containing the amount of sodium, and also indicates that sodium is added to the wastewater when the amount of sodium is not included, and preferably sodium is added to the wastewater. To do. This is because there is little waste water containing this amount of sodium, and the applicable range of waste water becomes narrow.

  Furthermore, in the present invention, by performing the catalytic wet oxidation treatment, it is possible to decompose inorganic sulfur compounds that are toxic to living organisms, thus enabling biological treatment of wastewater containing inorganic sulfur compounds, which has been difficult in the past. I was able to.

  The waste water treatment method according to the present invention will be described. In the wastewater treatment method according to the present invention, wastewater containing an inorganic sulfur compound is introduced into a reactor filled with the catalyst. Prior to the catalyst treatment, solid suspended solids contained in the waste water can be removed. A commonly used filter can be used as the means for removing the solid suspended solids. In addition, the wastewater treatment can be performed in advance by a wet oxidation treatment without a catalyst and then by a wet oxidation treatment using a catalyst. By performing a wet oxidation process without a catalyst in advance, it is possible to reduce the load applied to the solid catalyst or to decompose in advance a substance that adversely affects the processing performance and durability of the solid catalyst.

  In the treatment according to the present invention, it is preferable to add a predetermined amount of sodium to the wastewater, and the method for adding sodium may be any time before the wastewater is wet-oxidized with a catalyst, and is used in combination with a non-catalytic wet oxidation treatment. When doing so, it is preferable to add sodium before the non-catalytic wet oxidation treatment.

  Hereinafter, the processing method of the present invention will be described with reference to the drawings. However, these drawings are merely examples of embodiments of the present invention, and the apparatus used in the present invention is not limited to the illustrated configuration. .

  FIG. 1 is a schematic explanatory diagram showing an apparatus configuration example for carrying out the method of the present invention. First, the wastewater to be treated is boosted from the drainage supply line 1 by the pump 2 and sent to the heat exchanger 5 (pressurized feed). At this time, the oxygen source introduced from the oxygen source supply line 3 is pressurized by the compressor 4 and then mixed into the waste water to be in a gas-liquid mixed phase state. The gas-liquid mixed phase waste water obtained here is preheated by the heat exchanger 5, further heated by the heater 6, and then introduced into the lower portion of the reaction tower 7, where it moves upward from below (upper). Counterflow) Wet oxidation treatment. In the present invention, although not particularly limited, the reaction tower 7 performs a catalyst-free wet oxidation treatment as a first treatment step, and then further performs a wet oxidation treatment using a solid catalyst as a second treatment step. Is preferred.

The space velocity (hereinafter referred to as LHSV) when the wastewater is pressure-feeded with the pump 2 is not particularly limited, and may be appropriately set depending on the wet oxidation treatment capability. In particular, the LHSV in the second treatment step is 0.1 hr ^−1. may preferably be higher, more preferably 0.5 hr ^-1 or more, more preferably may be adjusted so as to 1hr ^-1 or more. Further, preferably 10 hr ^-1 or less the upper limit of the LHSV in the second process step, more preferably 7Hr ^-1 or less, may be adjusted so as to become more and 5 hr ^-1 or less. When LHSV in the second treatment step is less than 0.1 hr ⁻¹ , the amount of treatment may be reduced, and excessive equipment may be required. Further, when the LHSV in the second processing step exceeds 10 hr ⁻¹ , the processing may not be performed sufficiently. Note that the LHSV in the first processing step is obtained from the volume ratio of the first processing step and the second processing step described later.

  The oxygen source introduced from the oxygen source supply line 3 is not particularly limited. For example, pure oxygen, oxygen-enriched gas, air, ozone, hydrogen peroxide, or the like can be used. It is also possible to use oxygen-containing gas or the like generated in step 1. Among these, the use of air is particularly recommended from an economic viewpoint.

  Further, the supply amount of the oxygen source is not particularly limited, and an amount necessary for decomposing the harmful substances in the wastewater may be supplied. A preferable supply amount is 0.5 times or more, more preferably 1 time or more, and further preferably 1.5 times or more the theoretical oxygen demand of the waste water. The upper limit of the supply amount is preferably 5.0 times or less, more preferably 4.0 times or less, and still more preferably 3.0 times or less. When the supply amount of the oxygen source is less than 0.5 times the theoretical oxygen demand, harmful substances in the wastewater cannot be sufficiently decomposed. Moreover, even if it supplies exceeding 5.0 times, a processing performance is not improved only by an enlargement of an installation. The theoretical oxygen demand here refers to the amount of oxygen required to decompose the oxidizable substance in the wastewater into ash such as nitrogen, carbon dioxide, water, and sulfate.

  The gas-liquid mixed phase wastewater is sent to the heat exchanger 5 and preheated, and further heated by the heater 6 and supplied to the reaction tower 7, but the heating method at this time is particularly limited. Instead, it may be heated by the heat exchanger 5 and / or the heater 6, and the reaction tower 7 may be provided with heating means such as a heater (not shown) for heating. These heating means may be used alone or in any combination. Furthermore, in the present invention, the heating may be performed by injecting steam. Usually, when heating is performed by injecting steam, if the inside of the reaction tower 7 is only a catalyst, the catalyst near the entrance is easily worn and damaged by the impact of the steam. However, in the present invention, since the non-catalytic layer is provided as the first treatment step in the reaction tower, the impact due to steam can be buffered and such a problem does not occur. Moreover, since the heat exchanger 5 becomes unnecessary by heating with steam, the equipment cost and the maintenance cost can be reduced.

  In addition, the gas-liquid mixed phase wastewater supplied to the heat exchanger 5 may be heat-exchanged by a high-temperature treatment liquid treated in the reaction tower 7 or heated by a high-temperature liquid discharged from another plant. It may be exchanged. Thus, the heat medium for heating the waste water is not particularly limited.

  In the configuration shown in FIG. 1, the case where the wastewater is made into a gas-liquid mixed phase state and then supplied to the reaction tower 7 and processed in an upward flow is shown. Not only the form, but also a method of processing in a gas-liquid mixed phase downward flow, a method of separately introducing gas and liquid into the reaction tower 7 and processing in a counterflow, etc. may be adopted. Among these, by making the continuous phase in the reaction tower 7 into a liquid phase, the contact efficiency between the inorganic sulfur compound in the water and the catalyst is increased, and the sulfate produced by oxidizing the inorganic sulfur compound, etc. Since precipitation of the salt resulting from it can be suppressed, it is preferable to set it as the gas-liquid upward flow from which a continuous phase turns into a liquid phase. In addition, the continuous phase in the reaction tower is a liquid phase even in the countercurrent type in which the liquid (drainage) is supplied from the bottom and the gas is supplied from the top. In this case, the gas directly hits the catalyst layer on the treatment liquid discharge port side to deteriorate the catalyst. This is not preferable because it may cause

  In the region where the first treatment step in the reaction tower 7 is performed, in order to improve the agitation and contact efficiency of the gas and liquid, and to reduce the drift of the gas and liquid, it is filled with a packing, a gas and liquid dispersion plate, etc. Various domestic crops can be used.

  There are no particular limitations on the material, type, size, and the like of such a filler as long as it increases the gas-liquid contact efficiency, and various fillers can be used. Those that are inert are preferred. For example, a metal, ceramic, glass, resin, etc. are mentioned. Examples of the shape of the filler include pellets, spheres, granules, rings (such as Raschig rings, Lessing rings, and ball rings), honeycombs, nets, and nets or plates made of a woven structure. The size of these fillers is not particularly limited, but in the case of pellets, spheres, granules, or rings, those having a diameter (outer diameter) or major axis of 3 to 5 mm are preferable. In addition, when using a gas-liquid dispersion plate, the material, type, size and the like are not particularly limited as long as the gas-liquid contact efficiency can be increased. For example, a single-hole plate, a porous plate, Various gas-liquid dispersion plates such as a single hole plate with a collision plate and a perforated plate with a collision plate can be used. These fillers and gas-liquid dispersion plates may be used in combination.

  In the present invention, a solid catalyst is installed as a second treatment step in the reaction tower 7 to improve the ability to oxidize and / or decompose harmful substances. In the wastewater treatment method of the present invention, the solid catalyst that can be used in the second treatment step is a solid that is generally used for wet oxidation treatment that combines activity and durability under the conditions of liquid phase oxidation. A catalyst can be used. Specifically, a metal and / or compound (catalyst A component) of at least one element selected from the group consisting of platinum, palladium, ruthenium, iridium, rhodium, and gold, cerium, lanthanum, yttrium, praseodymium, neodymium, A catalyst containing an oxide (catalyst B component) of at least one element selected from the group consisting of indium, copper, and manganese can be given.

  The catalyst component A may be either a metal or an oxide, and the metal and oxide may coexist.

  The ratio of the mass of the catalyst A component to the total mass of the catalyst A component and the catalyst B component is preferably 0.1 to 0.5, and more preferably 0.1 to 0.3.

  The solid catalyst used in the present invention preferably contains an oxide containing titanium as a carrier component. The oxide containing titanium is not particularly limited. In addition to titanium oxide, binary or multi-component oxides such as titanium-zirconium, titanium-silicon, titanium-aluminum, and titanium-iron (composite oxidation). And a mixture thereof.

  As the composition ratio when the solid catalyst includes a carrier, the ratio of the catalyst A component in the solid catalyst is preferably 0.05 to 5% by mass, more preferably 0.07 to 3% by mass. Preferably, the content is 0.1 to 1% by mass. By setting the ratio of the catalyst A component to 0.05% by mass or more, it becomes possible to sufficiently oxidize and / or decompose the harmful substances in the waste water. Even if the amount of the catalyst A component used exceeds 5% by mass, the processing performance corresponding to the amount used cannot be obtained, and since the raw material of the catalyst A component is expensive, the cost of the solid catalyst is increased. Disadvantageous. Among the components of the catalyst A, when it contains a metal and / or compound of at least one element selected from the group consisting of platinum, palladium, ruthenium and iridium, the catalytic activity is particularly high, which is preferable.

  Specific examples of the catalyst B component include oxides of the above elements. The ratio of the catalyst B component in the solid catalyst is preferably 0.5 to 10% by mass with respect to the mass of the solid catalyst by converting the catalyst B component as an oxide, and 0.7 to 5% by mass. More preferably, it is more preferably 0.1 to 3% by mass. The mass of the catalyst B component in the present invention refers to the mass in terms of oxide unless otherwise specified. By setting the ratio of the catalyst B component (as oxide) to 0.5% by mass or more, it becomes possible to sufficiently oxidize and / or decompose the harmful substances in the waste water. Moreover, even if the usage-amount of a catalyst B component exceeds 10 mass% (oxide conversion), the processing performance according to the usage-amount cannot be obtained in many cases. Among the components of the catalyst B, when an oxide of at least one element selected from the group consisting of cerium, lanthanum, yttrium, indium, and manganese is contained, the catalytic activity is particularly high, and cerium and lanthanum are more preferable. And an oxide of at least one element selected from the group consisting of indium.

  The shape of the catalyst is not particularly limited, and may be any of granular, spherical, pellet, crushed, saddle, honeycomb, and ring shapes, for example. In the case of a pellet shape, an arbitrary shape such as an elliptical shape, a polygonal shape, a trilobal shape, and a quadrilateral shape can be used in addition to a circular cross section. Among these, those molded into a spherical shape or a pellet shape are preferable.

  In order to reduce the vibration of the solid catalyst, a pressing material layer made of metal, ceramic, glass or the like may be provided on the upper portion (treated water discharge side) of the solid catalyst layer used in the treatment method of the present invention. preferable. The pressing material layer preferably has a shape that follows the deformation and movement of the solid catalyst layer, and does not interfere with the pressing effect even if it moves or deforms. Specifically, there are molded products such as SUS metal balls and pellets, or titania pellets, and granular glass.

  The lower part of the solid catalyst layer (drainage supply side) reduces wear of the solid catalyst due to gas-liquid collision, supports the solid catalyst, prevents clogging of the lower grid due to the solid catalyst, and prevents pressure loss. It is also preferable to provide a support layer of a solid catalyst for preventing the rise. Specifically, in addition to molded products such as SUS metal balls and pellets or titania pellets, granular glass, and the like, wire mesh and various packings can be used.

  In the second treatment step, in addition to the solid catalyst, various fillers and internal crops may be installed in order to improve gas-liquid stirring and contact efficiency and reduce gas-liquid drift. In particular, when the packed bed of the solid catalyst is long, it is effective to divide the solid catalyst layer into a plurality of layers. Specifically, it is effective when the catalyst layer length is 1000 mm or more, and more effective when the catalyst layer length is 1500 mm or more. It is preferable to install a dispersion device for reducing gas-liquid drift at the beginning of the second treatment step or at the bottom of each of the divided layers. This dispersion apparatus can be used in various shapes and materials, for example, a dispersion apparatus used in a reaction tower, distillation tower, stripping tower, etc. of a chemical plant.

  In the configuration shown in FIG. 1, the case where the first processing step and the second processing step are installed in one unit is shown, but these steps may be provided in separate reaction towers. When using separate reaction towers, a gas-liquid conducting pipe is provided and connected from the upper part of the reaction tower of the first treatment step to the lower part of the reaction tower of the second treatment step. However, when a plurality of reaction towers are used, the equipment cost rises and the maintenance cost becomes high. Therefore, one reaction tower should be used. That is, the first treatment step and the second treatment step are preferably present in the same reaction tower. In this case, a non-catalytic wet processing step that is a first processing step and a catalytic wet processing step that is a second processing step are provided from the waste water supply line side of the reaction tower.

  Moreover, when the reaction tower of a 1st processing process and the reaction tower of a 2nd processing process are different, gas-liquid separation can also be performed between both. In the case of gas-liquid separation, the gas-liquid conducting tube connecting the reaction tower in the first treatment step and the reaction tower in the second treatment step can be independent of the gas-phase conducting tube and the liquid-phase conducting tube. The phase can also be discharged out of the system to provide only a liquid phase conducting tube. It is also possible to improve the processing performance by newly adding an oxygen source to the second processing step.

  The volume ratio of the wet oxidation treatment region of the first treatment step and the second treatment step in the reaction tower 7 is preferably 0.5: 1 to 20: 1 in the first treatment step: second treatment step, more Preferably it is 0.5: 1-15: 1, More preferably, it is 0.5: 1-10: 1. When wastewater containing inorganic sulfur compounds is treated in the first treatment step, thiosulfuric acids and salts thereof are often produced as intermediate products or by-products. In order to further oxidize these intermediate products or by-products, it is effective to perform a catalytic wet oxidation treatment using a solid catalyst as the second treatment step. The volume ratio between the first treatment process and the second treatment process is preferably determined in consideration of the reactivity of the substance to be treated. That is, it is preferable that the volume of the second treatment step is larger than that of the first treatment step when the treatment target material is hardly decomposable, and the second treatment is performed when the treatment subject material is easily decomposable. It is preferable to make the volume of the first treatment process larger than the process.

  The reaction temperature of the wet oxidation reaction in the reaction tower 7 is affected by other conditions, but if it exceeds 370 ° C., the wastewater cannot be maintained in a liquid phase, and the equipment becomes large or the running cost increases. Therefore, the reaction temperature is preferably 370 ° C. or less, more preferably 280 ° C. or less, and further preferably less than 180 ° C. On the other hand, since it is difficult to perform the wet oxidation reaction efficiently at less than 80 ° C., it is preferably 80 ° C. or more, more preferably 100 ° C. or more, and further preferably 110 ° C. or more.

  In the wet oxidation reaction of the present invention, it is desirable to appropriately adjust the pressure so that the wastewater can maintain the liquid phase, and the pressure is appropriately selected depending on the correlation with the reaction temperature. In particular, when the reaction temperature is less than 180 ° C., it is preferable that the reaction temperature is less than 1 MPa (gauge pressure) in view of costs such as capital investment and operation costs.

  The kind and shape of the reaction tower used in the present invention are not particularly limited. The reaction tower may be either a single tube type or a multi-tube type, and a plurality of these may be used in combination. However, a single single tube type reaction tower is used, and the first treatment step is performed inside the reaction tube. It is preferable to perform the processing of the second processing step.

  The treatment liquid treated in the reaction tower 7 is appropriately cooled by the heat exchanger 5 or the cooler 8 as necessary, and then separated into gas and liquid by the gas-liquid separator 9. At this time, the heat exchanger 5 and the cooler 8 can be used alone or in combination.

  In the gas-liquid separator 9, it is desirable to detect the liquid level using a liquid level controller (LC) and control the liquid level in the gas-liquid separator 9 to be constant by the liquid level control valve 10. Here, “constant” means that the liquid level is within a certain value or within a certain range.

  Further, after the treated water is cooled, it is discharged through a pressure regulating valve (not shown), and then separated into gas and liquid by the gas-liquid separator 9.

  The liquid separated by the gas-liquid separator 9 is discharged through the treated water discharge line 11. In the present invention, it is preferable to further perform biological treatment after wet oxidation treatment. Specifically, although not particularly limited, the liquid discharged from the treated water discharge line 11 is sent to a biological treatment facility, where biological treatment is performed. The biological treatment here is not particularly limited, and various methods such as aerobic treatment and anaerobic treatment can be used. Among these, it is preferable to perform an aerobic biological treatment. Since many inorganic sulfur compounds are biologically toxic, it is difficult to biologically treat them with ordinary biological treatment equipment. In particular, when sulfide ions, hydrosulfide ions, and the like are contained in the wastewater, it is very difficult to perform biological treatment as it is. On the other hand, in the wet oxidation treatment of the present invention, the inorganic sulfur compound in the waste water can be easily oxidized. Biologically toxic sulfide ions, hydrosulfide ions, and the like are oxidized to thiosulfate ions, sulfate ions, and the like having low biotoxicity by the wet oxidation treatment of the present invention, so that biological treatment can be easily performed. . When factories or factories with plants that are the source of wastewater containing inorganic sulfur compounds have biological treatment facilities as equipment for comprehensively treating various wastewater discharged from various plants There are many. In such factories and factories, conventionally, wastewater containing inorganic sulfur compounds had to be treated separately, but this became unnecessary by applying the treatment method of the present invention, and wastewater was treated economically. Is possible.

  The pressure is preferably detected by a pressure controller (PC) and the pressure control valve 12 is operated to maintain the pressure at a predetermined value, that is, less than 1 MPa (gauge pressure) in the present invention. The gas separated by the gas-liquid separator 9 may be released into the atmosphere through the exhaust gas discharge line 13, or may be further processed by a known method.

Further, it is preferable to adjust the pH by supplying an alkaline component before or during the treatment so that the pH after treatment of the waste water containing the inorganic sulfur compound is in the neutral to alkaline range. Specifically, it is preferable to perform wet oxidation treatment by adjusting the pH by adding sodium so that the molar ratio (Na / S) of sodium and sulfur contained in the waste water is larger than 2. This is also because the oxidation reaction of the inorganic sulfur compound present in the wastewater by the solid catalyst is accelerated from neutral to alkaline. In particular, in the case of conditions lower than 180 ° C., the effect is remarkable. In addition, wet oxidation treatment under acidic conditions in which sulfuric acid or the like is present is because corrosion of the wet oxidation treatment apparatus material becomes severe and the durability of the apparatus may be significantly impaired.
The position where sodium is added to the wastewater is not particularly limited. In the treatment method of the present invention, it may be added to the raw water of the waste water, may be added before or after the first treatment step, or may be added at the first treatment step, and before or after the second treatment step, or the second treatment step. May be added. The addition amount may be controlled by always adding a certain amount, or by measuring the pH or ion amount of the liquid. It is also possible to dilute the waste water as appropriate.

  The effects of the present invention will be specifically described below with reference to examples, but the technical scope of the present invention is not limited to these examples.

Example 1
When treating the inorganic sulfur compound in the waste water, wet oxidation treatment was performed for 1,500 hours using the apparatus having the configuration shown in FIG. The undiluted | stock solution used for the process was the waste_water | drain of the composition shown in Table 1 discharged | emitted from the chemical plant. Since this stock solution has a Na / S (molar ratio) of less than 2 as shown in Table 1, a solution to which 12 g of NaOH was added per liter of the stock solution was used as a feed solution. The Na / S (molar ratio) of this feed liquid was 2.24.

The reaction tower 7 was made of cylindrical SUS316 having a diameter of 400 mm and a length of 4,000 mm. In the lower part of the reaction tower 7, gas-liquid dispersion plates (perforated plates) are installed at intervals of 450 mm so that the non-catalytic layer length is 3,150 mm, and 57 liters of catalyst is installed in the upper part of the catalyst layer. The length was set to 450 mm. The catalyst of titanium - Using supported on oxides of zirconium and palladium (0.3 wt% as Pd) lanthanum (1.5 wt% as _La 2 _{O 3)} catalyst. The shape of the catalyst was a pellet having a diameter of 5 mm and a length of 7 mm.

Wastewater is pumped from the drainage supply line 1 at a flow rate of 160 liters / hr, and air is supplied from the oxygen source supply line 3 as an oxygen source at a flow rate of 27 Nm ³ / hr (equivalent to twice the theoretical oxygen demand). After being introduced and increased in pressure by the compressor 4, it was mixed into the waste water. The gas-liquid mixed phase waste water obtained here was heated with the heat exchanger 5 and further heated with the heater 6, then supplied to the reaction tower 7 and subjected to wet oxidation at a treatment temperature of 160 ° C. The treatment liquid treated in the reaction tower 7 was cooled by the heat exchanger 5 and the cooler 8 and then introduced into the gas-liquid separator 9. In the gas-liquid separator 9, the liquid level controller (LC) detects the liquid level and operates the liquid level control valve 10 to maintain a constant liquid level, and the pressure controller (PC) detects the pressure and detects the pressure. The control valve 12 was operated so as to maintain a pressure of 0.9 MPa (gauge pressure). The treatment liquid was discharged from the treated water discharge line 11.

  As a result, the COD (Cr) concentration measured value of treated water was 1,500 mg / liter, and the COD (Cr) treatment efficiency calculated from this value was 94%. In addition, sulfide ions were not detected in the treated water, and the treatment performance was not particularly deteriorated in the treatment for 1,500 hours. Further, no abnormality such as corrosion was observed in the reaction tower 7 opened after the completion.

(Examples 2 to 6)
Except for changing the catalyst, wet oxidation treatment of the inorganic sulfur compound-containing wastewater was performed under the same conditions as in Example 1. These results are shown in Table 2.

(Example 2)
As a solid catalyst (pellet-like), a catalyst in which ruthenium (0.3% by mass as Ru) and cerium (1.0% by mass as CeO ₂ ) were supported on a titanium-iron oxide was used.

(Example 3)
As the solid catalyst (pellet form), a catalyst in which ruthenium (0.4% by mass as Ru) and indium (1.5% by mass as In ₂ O ₃ ) were supported on an oxide of titanium was used.

Example 4
As the solid catalyst (pellet form), a catalyst in which ruthenium (0.2% by mass as Ru) and manganese (2.0% by mass as MnO ₂ ) were supported on an oxide of titanium-zirconium was used.

(Example 5)
As a solid catalyst (pellet form), a catalyst in which platinum (0.2 mass% as Pt) and yttrium (1.5 mass% as Y ₂ O ₃ ) were supported on a titanium-iron oxide was used.

(Example 6)
As the solid catalyst (pellet form), a catalyst in which iridium (0.5 mass% as Ir) and lanthanum (2.0 mass% as La ₂ O ₃ ) were supported on an oxide of titanium was used.

(Comparative Examples 1-9)
Except for changing the catalyst, wet oxidation treatment of the inorganic sulfur compound-containing wastewater was performed under the same conditions as in Example 1. These results are shown in Table 2.

(Comparative Example 1)
As a solid catalyst (pellet form), a catalyst in which platinum (0.2 mass% as Pt) was supported on a titanium-iron oxide was used.

(Comparative Example 2)
As the solid catalyst (pellet form), a catalyst in which palladium (0.3 mass% as Pd) was supported on an oxide of titanium-zirconium was used.

(Comparative Example 3)
As the solid catalyst (pellet form), a catalyst in which ruthenium (0.3% by mass as Ru) was supported on an oxide of titanium was used.

(Comparative Example 4)
As a solid catalyst (pellet form), a catalyst in which iridium (0.5 mass% as Ir) was supported on an oxide of titanium was used.

(Comparative Example 5)
As the solid catalyst (pellet form), a catalyst in which cerium (1.0 mass% as CeO ₂ ) was supported on a titanium-iron oxide was used.

(Comparative Example 6)
As the solid catalyst (pellet form), a catalyst in which lanthanum (1.5% by mass as La ₂ O ₃ ) was supported on an oxide of titanium-zirconium was used.

(Comparative Example 7)
As the solid catalyst (pellet form), a catalyst in which yttrium (1.5% by mass as Y ₂ O ₃ ) was supported on a titanium-iron oxide was used.

(Comparative Example 8)
As the solid catalyst (pellet form), a catalyst in which indium (1.5% by mass as In ₂ O ₃ ) was supported on an oxide of titanium was used.

(Comparative Example 9)
As the solid catalyst (pellet form), a catalyst in which manganese (2.0% by mass as MnO ₂ ) was supported on a titanium-zirconium oxide was used.

(Comparative Example 10)
As a liquid used for the wet oxidation treatment, wastewater having a composition shown in Table 1 (without adding NaOH) was used. Otherwise, the wet oxidation treatment of the inorganic sulfur compound-containing wastewater was performed under the same conditions as in Example 1. As a result, the measured COD (Cr) concentration of the treated water was 6,200 mg / liter, and the COD (Cr) treatment efficiency calculated from this value was 75%. The sulfide ion concentration in the treated water was 120 mg / liter. When the reaction tower 7 was opened after 1,500 hours of treatment, the entire inner wall was thin and rough, and it was confirmed that the reactor was corroded.

(Example 7)
The treated water obtained by the wet oxidation treatment of Example 1 was stored, and this liquid was further biologically treated.
When biological treatment was carried out under aerobic conditions with an MLSS concentration of 2,000 mg / liter and a residence time of 15 hours, it was confirmed that it could be treated stably with water quality with a treated water COD (Cr) concentration of 13 mg / liter for about 500 hours. It was.

(Comparative Example 11)
Biological treatment similar to that in Example 7 was performed using wastewater (no addition of NaOH) having the composition shown in Table 1 as a liquid to be treated. As a result, the activated sludge began to die immediately after the start, and the treatment could not be continued.

  The present invention relates to wastewater treatment, and particularly provides a novel treatment method for wastewater containing inorganic sulfur compounds.

It is the schematic which shows the example of an apparatus structure for enforcing the method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Wastewater supply line 2 Pump 3 Oxygen source supply line 4 Compressor 5 Heat exchanger 6 Heater 7 Reaction tower 8 Cooler 9 Gas-liquid separator 10 Liquid level control valve 11 Treated water discharge line 12 Pressure control valve 13 Exhaust gas discharge line 14 First treatment step (non-catalytic layer)
15 Second treatment step (catalyst layer)

Claims (5)

A method in which wastewater containing an inorganic sulfur compound is subjected to a wet oxidation treatment using a solid catalyst under a temperature and pressure at which the wastewater maintains a liquid phase, wherein the solid catalyst is platinum, palladium, ruthenium, iridium At least one elemental metal and / or compound (catalyst A component) selected from the group consisting of rhodium and gold, and at least selected from the group consisting of cerium, lanthanum, yttrium, praseodymium, neodymium, indium, copper and manganese A method for treating wastewater containing an inorganic sulfur compound, characterized by containing an oxide of one element (catalyst B component). The wastewater treatment method according to claim 1, wherein the ratio of the mass of the catalyst A component to the total mass of the catalyst A component and the catalyst B component is 0.1 to 0.5. The solid catalyst further comprises an oxide containing titanium as a carrier component, and the catalyst A component is 0.05 to 5% by mass and the catalyst B component is 0.5 to 10% by mass with respect to the solid catalyst. The method for treating waste water according to claim 1, wherein: 4. The method of treating waste water according to claim 1, wherein wet oxidation is performed in a state in which sodium is contained so that a molar ratio (Na / S) of sodium and sulfur contained in the waste water is greater than 2. . A method for treating wastewater containing an inorganic sulfur compound, wherein the biological treatment is further performed after the wet oxidation treatment according to any one of claims 1 to 5.

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