JPH0994584A - Treatment of waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To treat waste water with high purifying capacity, in wet oxidation treatment of waste water under pressure holding a liquid phase while heating waste water and supplying oxygen-containing gas, by respectively specifying the content of the scale product in waste water and heating temp. and supplying the oxygen-containing gas to the rear part of a heating side. SOLUTION: The waste water sent from a waste water supply line 8 is fed by a waste water supply pump 3 while raised in pressure and the pressurized waste water is heated to 140-370 deg.C by a heat exchanger 2 to be supplied to the lower part of a wet oxidation reaction tower 1. Air supplied from an oxygen-containing gas supply line 9 is raised in pressure by a compressor 5 and supplied to a reaction column 1 through an oxygen-containing gas insertion line 10 to be mixed with waste water. When waste water is subjected to wet oxidation treatment under pressure holding a liquid phase while air is supplied, waste water contains a scale product in an amt. of 50mg/l or more and air is supplied to the flow of waste water from the rear side of the heating part of the heat exchanger 2.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention purifies wastewater discharged from various industrial plants such as chemical plants, food processing equipment, metal processing equipment, metal plating equipment, printing plate making equipment, and photoprocessing equipment by a wet oxidation treatment method. Regarding how to handle. More specifically, it relates to a method for purifying waste water having a high chemical oxygen demand (hereinafter, also referred to as “COD”) discharged from various industrial plants by a wet oxidation treatment method. In particular, the wastewater relates to a method for purifying wastewater containing heavy metals, aluminum, phosphorus, silicon, calcium, magnesium or the like by a wet oxidation treatment method, and further, sulfur and / or a sulfur compound having a lower oxidation number ( The present invention also relates to a method for purifying the wastewater containing also a "sulfur compound etc." by a wet oxidation treatment method.

[0002]

2. Description of the Related Art Conventionally, when wastewater is treated by a wet oxidation method, if the wastewater produces solid matter, scale is attached to a heater, a heat exchanger, a reaction tower, a packing and a catalyst. There was a problem to do. In particular, in the heater and the heat exchanger, even if a small amount of scale adheres, the heat exchange rate significantly decreases, and the scale adherence has a significant effect. Further, since the heater and the heat exchanger have small tube diameters, if the scale adheres further, the problem of clogging may occur and the treatment may not be possible. Therefore, a method of suppressing scale formation in the heater and heat exchanger is important.

The scale-forming substance is a substance that produces a solid matter when the wastewater is treated by the wet oxidation treatment method. For example, scales such as heavy metals, aluminum, phosphorus, silicon, calcium or magnesium are easily produced. Refers to ingredients.

When the waste water also contains sulfur and / or a sulfur compound having a lower oxidation number, the adhesion of scale is particularly remarkable. Therefore, when containing sulfur etc.,
The problem of scale adhesion is often more pronounced with conventional methods.

As a method for suppressing the scale adhesion, various methods are available, for example, (i) a method of adding an additive or the like to waste water to make it difficult to generate scale, and (ii) a cleaning method for the adhered scale. Methods to be used and removed, (iii) methods to remove scale-forming substances in wastewater by pretreatment to prevent scale generation, and (iv) methods to improve the system such as equipment to make scales less likely to adhere have been implemented or proposed. There is.

However, these conventional methods are not sufficiently satisfactory. For example, the method of adding the additive (i) is effective for a specific scale-forming substance but is not widely effective for various scale-forming substances.
In addition, as described above, no particular effect can be expected for wastewater containing sulfur or the like. (ii) In the method of removing the scale by using a cleaning agent, the wastewater treatment must be stopped and washed every time the scale adheres, which causes problems in maintenance and operation of the wastewater treatment. (iii) In the method of removing the scale-forming substance by pretreatment, a large amount of pretreatment is required to remove all the various scale-forming substances, and it is difficult to remove it sufficiently. Therefore, the merit of treating the wastewater by the wet oxidation treatment method is reduced. (i
v) It was difficult to solve the problem by improving the system such as the conventional device.

[0007]

Therefore, an object of the present invention is to provide a novel wastewater treatment method in wet oxidation treatment which can solve the above problems.
That is, it is an object of the present invention to provide a novel method for treating wastewater which does not cause scale to adhere to the heater and the heat exchanger when the wastewater which produces solid matter by the wet oxidation treatment is treated by the treatment method. More specifically, it is to stably wet-oxidize wastewater containing components such as heavy metals, aluminum, phosphorus, silicon, calcium and magnesium that easily form scales, and treat the wastewater with high purifying properties. . Further, when the waste water further contains sulfur and / or a sulfur compound having a lower oxidation number, the wet oxidation treatment is stably performed, and the waste water is treated with high purifying properties.
That is, it is an object of the present invention to provide a novel wastewater treatment method that suppresses scale adhesion, performs stable wet oxidation treatment, treats wastewater with high purifying properties, and is economically excellent.

[0008]

As a result of earnest research for solving the above-mentioned problems, the present inventor has found that when the waste water is subjected to wet oxidation treatment, an oxygen-containing gas is supplied to a heater or a heating side of a heat exchanger. The present invention has been completed by finding a method for purifying the wastewater which is easy to operate and excellent in practicability and economy by supplying it later. That is, in order to treat the wastewater that produces solid matter by the wet oxidation treatment, a method of supplying the oxygen-containing gas after the heating side of the heater or the heat exchanger is adopted. That is, it was found that by not supplying the entire amount of the oxygen-containing gas supplied to the reaction tower to the heating side of the heater or the heat exchanger, it is possible to obtain the effect of suppressing scale adhesion to the heat exchanger.

The present invention thus provides a method for treating wastewater as follows.

(1) The waste water is heated to 140 ° C. to 370 ° C. by a heater or a heat exchanger, and the waste water is subjected to a wet oxidation treatment under a pressure at which the waste water maintains a liquid phase while supplying an oxygen-containing gas. The wastewater contains 50 m of scale-producing material.
A method for treating wastewater, comprising g / liter or more, and supplying the oxygen-containing gas from behind the heating side of the heater or heat exchanger with respect to the flow of the wastewater.

(2) The scale forming material is a heavy metal,
2. The method for treating wastewater according to the above 1, which is at least one selected from the group consisting of aluminum, phosphorus, silicon, calcium and magnesium.

(3) The above-mentioned 2 characterized in that the wastewater contains sulfur and / or a sulfur compound having a lower oxidation number.
The wastewater treatment method described.

(4) When the oxygen-containing gas is supplied after the heating side of the heater or the heat exchanger, the temperature of the heated liquid or gas-liquid at the oxygen-containing gas supply is 140 ° C. to 230 ° C. 1 above, which is characterized in that
The wastewater treatment method described.

(5) The amount of the oxygen-containing gas is 1 time or more and 10 times or less of a theoretical oxygen demand amount (hereinafter, also referred to as ThOD) in the waste water, and the above 1 or 4
The wastewater treatment method described.

(6) The above-mentioned (1), wherein the amount of the oxygen-containing gas supplied from the front side of the heating side of the heater or the heat exchanger is equal to or less than the theoretical oxygen demand amount in the wastewater. The wastewater treatment method described.

(7) In the method (6), the oxygen-containing gas is not supplied from before the heating side of the heater or the heat exchanger, and the wastewater treatment method described in the above (6).

(8) The method for treating wastewater according to the above (1) or (3), wherein the wastewater contains wastewater discharged from a photographic processing facility.

Hereinafter, the present invention will be described in detail.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION According to the present invention, waste water is heated to 140 ° C. to 370 ° C. by a heater or a heat exchanger, and the waste water is supplied under a pressure at which it holds a liquid phase and is supplied with an oxygen-containing gas. When the waste water produces a solid matter by the wet oxidation treatment in the wet oxidation treatment, the oxygen-containing gas is supplied after the heating side of the heater or the heat exchanger. That is, by not supplying the entire amount of the oxygen-containing gas supplied to the reaction tower to the heating side of the heater or the heat exchanger, the effect of suppressing scale adhesion to the heater or the heat exchanger is obtained.

Further, the wastewater according to the present invention is a component (scale-forming substance) that easily produces scale by wet oxidation treatment.
It is not particularly limited as long as it is a wastewater containing 50 mg / liter or more of. The reason is that if the amount of the scale-generating substance is less than 50 mg / liter, it can often be treated by the conventional method.

Further, the scale-forming substance according to the present invention means a component which can be a scale in the wet oxidation treatment. For example, when the wastewater is heated not only in the wet oxidation reactor but also in the heater, a solid substance is produced. It is a component that can be a substance, and is specifically at least one element selected from the group consisting of heavy metals, aluminum, phosphorus, silicon, calcium and magnesium. These elements may be in any state of various insoluble or sparingly soluble compounds such as oxides and salts, as long as they exist as solids.

The problem of these substances in the treatment of waste water is particularly in a treatment requiring heating such as a wet oxidation treatment. When these substances are heated, they often adhere as scales to heat exchangers, reaction towers, etc., which reduces the heat exchange rate even if a small amount of scale adheres, especially when they adhere to heat exchangers. Appears significantly, and the effect of scale adhesion is significant. Further, since the heat exchanger has a small tube diameter, if the scale further adheres, the problem of blockage may occur and the treatment may not be possible, which is a particular problem. INDUSTRIAL APPLICABILITY The present invention is an effective method for preventing scale from adhering to a portion having a small tube diameter such as a heat exchanger.

[0023] Conventionally, even in the case of wastewater containing such a scale-forming substance, in the case of performing wet oxidation treatment, generally, the oxygen-containing gas is entirely supplied from the front side of the heating side of the heater or heat exchanger. Was being supplied. This was because the linear velocity of the fluid was increased by causing the oxygen-containing gas to flow through the heat exchanger as much as possible, and the scale did not adhere. Further, as measures for preventing scale, various studies have been made such as adjusting the pH of the liquid and improving the shape of the apparatus. However, in these methods, especially the scale prevention in the heat exchanger is not sufficient, and further scale prevention method is desired, but the present invention provides an effective means for preventing scale adhesion. It will be.

The wastewater to which the present invention is applied contains scale-forming substances, specifically, heavy metals, aluminum,
It contains at least one element selected from the group consisting of phosphorus, silicon, calcium and magnesium. These elements may be ionized and dissolved in the waste water, but generally they are often chelated and dissolved by organic substances and the like. These scale formers are often easily removable by conventional techniques if they are only ionized and dissolved in the wastewater. However, when it is chelated with an organic substance and dissolved, it is often difficult to remove these scale-forming substances from the waste water by conventional techniques. This is because when wastewater containing these substances is treated by a wet oxidation treatment method, chelating organic substances (hereinafter also referred to as chelating agents) and / or scale-generating substances are decomposed and adhered to heat exchangers and the like as scales. This is because it is difficult to remove.

Therefore, in the present invention, the wet oxidation reaction state does not occur in the heat exchanger or the like, or even if the wet oxidation reaction occurs, the reaction is very gradual.
It has been found that the scale formation can be suppressed by not decomposing the chelating agent and / or the scale forming substance. That is, in the present invention, it was found that the above results can be obtained by not supplying the oxygen-containing gas to the heating side of the heater or the heat exchanger, or by keeping the amount of the oxygen-containing gas to be small.

The scale-forming substance in the wastewater according to the present invention contains at least one selected from the group consisting of heavy metals, aluminum, phosphorus, silicon, calcium and magnesium in the wastewater in a total amount of 50 mg / liter (each element conversion). ) It is effective to contain more than 100 mg / l, more preferably more than 100 mg / l. If the amount is less than 50 mg / liter, the adhesion of scale does not often become a problem, and if the amount is less than 100 mg / liter, it may be possible to perform the treatment to some extent even by the conventional technique. When the total amount of scale-forming substances exceeds 200 g / liter, it is more effective to treat the wastewater by a method other than the wet oxidation treatment, preferably less than 100 g / liter, and more preferably 10 g / liter. It is less than liter. When the amount of the scale-generating substance is very large, it is necessary to remove not only the method according to the present invention but also a separate removing means in advance, for example, the scale-generating substance such as a precipitation treatment in which a precipitating agent is added. .

The wastewater targeted by the present invention is a wastewater which produces solid matter by a wet oxidation treatment, and in many cases,
At least one selected from the group consisting of heavy metals, aluminum, phosphorus, silicon, calcium and magnesium
A wastewater containing certain elements, wherein sulfur and / or a sulfur compound having a lower oxidation number is further added to the wastewater.
It is effective even if the waste water contains more than 00 mg / liter (calculated as sulfur element). Conventionally, when the wastewater containing the scale-forming substance further contains sulfur and / or a sulfur compound having a lower oxidation number, there is a tendency that the scale adheres very much. The wastewater treatment method according to the present invention is very effective even in such wastewater.
Conventionally, it is considered that since the wet oxidation treatment of the sulfur and / or the sulfur compound having a lower oxidation number was carried out in the heat exchanger, the scale adherence increased. However, in the method for treating wastewater according to the present invention, it is considered that scale adhesion is suppressed because the wet oxidation treatment is not performed or the wet oxidation treatment is not performed in the heat exchanger as much as possible.

The heavy metals according to the present invention are not particularly limited and include all heavy metals, for example, cadmium (Cd), nickel (Ni), cobalt (C).
o), manganese (Mn), copper (Cu), zinc (Zn),
Silver (Ag), iron (Fe), tin (Sn), antimony (Sb), lead (Pb), thallium (Tl), mercury (H
g), arsenic (As), chromium (Cr), bismuth (B
i).

Further, as the state of the scale generating substance,
It is not particularly limited, and for example, it may be in the form of various ions or organometallic compounds, etc., and particularly effectively, it is in a state of being chelated by an organic substance.

The amount of the sulfur compound etc. according to the present invention is not particularly limited, but it is effective when the total amount of the sulfur compound etc. in the waste water is 100 mg / liter (calculated as elemental sulfur) or more. Yes, more effective is 1g /
This is the case when more than one liter (as converted to sulfur element) is contained. 1
If it is less than 00 mg / liter, the sulfur compound is less likely to cause a problem. Conversely, the larger the amount, the more likely it is to cause scale generation, and the effect of the processing method according to the present invention becomes remarkable. However, when the amount exceeds 70 g / liter (calculated as elemental sulfur), the wet oxidation reaction is rate-determined by the dissolution of oxygen and the treatment efficiency often decreases, and preferably 35 g / liter (calculated as elemental sulfur) or less.

Further, the sulfur and / or the sulfur compound having a lower oxidation number according to the present invention is not particularly limited as long as it is a sulfur compound other than a sulfate ion. For example, in addition to sulfur itself, a sulfur compound having a lower oxidation number. As the compound, various thiosulfates such as sodium thiosulfate and potassium thiosulfate, or various sulfide inorganic salts such as sodium sulfide, potassium sulfide and sodium hydrogen sulfide, hydrogen sulfide, or sulfur such as various alkyl sulfides and mercaptans. It is an organic substance to be contained.

Further, the wastewater containing both the scale-forming substance and the sulfur compound includes various wastewaters, and is not particularly limited, but preferably, the wastewater including the wastewater discharged from the photographic processing equipment. Is. The wastewater discharged from the photographic processing equipment has a large amount of both scale-forming substances and sulfur compounds, and it has been very difficult to treat with conventional wastewater treatment methods. This is because it is possible to process efficiently over the entire range.

Further, in the present invention, when the oxygen-containing gas is supplied from the rear of the heating side of the heater or the heat exchanger to the wastewater flow, the heated liquid or gas-liquid at the place where the oxygen-containing gas is supplied. Temperature of 140 ℃ ~ 2
Preference is given to working at 30 ° C. That is, the temperature of the liquid or gas-liquid heated by the heater or heat exchanger is set to 140 ° C. to 230 ° C. and supplied to the reaction tower. If the heating temperature of the heater or the heat exchanger is set to a temperature within this temperature range, scale adhesion can be suppressed. In conventional heaters or heat exchangers, gas-liquid was often heated to a temperature higher than 230 ° C. However, at such a temperature, many of the chelating organic substances, that is, the chelating agents, are decomposed or partially modified even under a short-time heating condition in the heat exchanger of the wet oxidation treatment, By releasing the chelated element, it became easy to adhere as a scale. On the contrary, if the temperature is lower than 230 ° C., it is considered that the chelating ability is less inactivated, and the scale adhesion is suppressed. When supplying the oxygen-containing gas from behind the heating side of the heater or the heat exchanger, the temperature of the heated liquid or gas-liquid at the oxygen-containing gas supply is preferably 160 ° C to 210 ° C. Is effective,
More preferably, it is 170 ° C to 200 ° C. When the temperature was high, some scales might adhere depending on the type of wastewater or treatment conditions. On the contrary, when the temperature is low, a heat source for the wet oxidation treatment may be separately required in the reaction tower, or the treatment efficiency may decrease.

In the present invention, when the oxygen-containing gas is supplied from the front of the heating side of the heater or the heat exchanger with respect to the flow of the wastewater, the amount of the oxygen-containing gas is the theoretical oxygen demand of the wastewater. It is effective that the amount is less than the equivalent amount. That is, when the amount of the oxygen-containing gas is large, the chelating agent is wet-oxidized in the heater or the heat exchanger, the chelating ability is deactivated, and the scale is often attached. Therefore, the amount of the oxygen-containing gas is effectively 0.5 times or less of the theoretical oxygen demand of the waste water, and preferably 0.2 times or less of the theoretical oxygen demand of the waste water. Target. Most preferably, the oxygen-containing gas is not supplied from the front of the heating side of the heater or heat exchanger. In this case, since a general wet oxidation reaction does not occur, the chelating agent is very rarely oxidized and / or oxidatively decomposed and deactivated. Therefore, adhesion of scale can be suppressed very much. However, even in this case, it is effective that the temperature of the liquid (or gas-liquid) heated on the heating side of the heater or the heat exchanger is 140 to 230 ° C. If it is higher than 230 ° C, the chelating agent may be thermally decomposed. Even if the chelating agent is not thermally decomposed, the chelating ability is inactivated by heat and the scale-forming substance is insolubilized in many cases, so that the scale easily adheres.

In the present invention, it is effective that the amount of the oxygen-containing gas supplied from the rear of the heating side of the heater or the heat exchanger is 1 to 10 times the theoretical oxygen demand of the waste water. Is. When it is less than 1 time of the theoretical oxygen demand in the wastewater, the purification performance of the wastewater is often deteriorated.
On the other hand, if it exceeds 10 times, the supply amount is excessive, and the treatment efficiency is lowered and the treatment cost is increased due to the lowering of the wet oxidation treatment temperature. Further, it is preferable that 5 times or less of the theoretical oxygen demand is effective, and more preferably 2 times or less of the theoretical oxygen demand is effective.

In the method for treating wastewater according to the present invention, a solid catalyst usually used for wet oxidation can be used, but it is preferably effective in wet oxidation treatment without using a solid catalyst. In the wastewater treatment method, solid matter is often produced, and therefore, when a reaction tower filled with a solid catalyst is used, it may be clogged with a catalyst layer. Therefore, in order to carry out the wet oxidation treatment using the solid catalyst, it is preferable to carry out the method for treating wastewater according to the present invention without using the solid catalyst, and thereafter to carry out after removing the solid matter.

The heater according to the present invention is a heater that heats waste water by using an external heat source such as an electric heater, a heat medium heater, or a steam heater, and is not particularly limited.

The heat exchanger according to the present invention is one which uses heat exchange to heat the wastewater according to the present invention and to cool the treatment liquid, and is not particularly limited and is not particularly limited. As for the shape, various types such as a double-tube type and a multi-tube type can be used.

In the wastewater treatment method according to the present invention, the reaction tower is generally treated in an adiabatic state, but it may be reheated in the reaction tower by using steam, an electric heater or the like. It is not something that will be done.

In the method for treating wastewater according to the present invention, the addition position of the oxygen-containing gas supplied after the heating side of the heater or the heat exchanger is after the heating side of the heater or the heat exchanger. Although not particularly limited, it is preferably between immediately after the heating side of the heater or the heat exchanger and the lower part of the reaction column, and more preferably at the lower part of the reaction column. The addition position may be several, and the addition amount can be appropriately divided for each nozzle.

The heater and / or heat exchanger according to the present invention can use a plurality of heaters and / or heat exchangers and is not particularly limited. In this case, the addition position of the oxygen-containing gas supplied after the heating side of the heater or the heat exchanger in the wastewater treatment method according to the present invention is one even if the heater or the heat exchanger is upstream of the wastewater. I wish I had it. In particular, the start-up heater or heat exchanger is often further behind the addition position of the oxygen-containing gas, which would be after the heating side of the heater or heat exchanger according to the invention. However, start-up heaters or heat exchangers are usually shut down during wastewater treatment, so there are often no problems with scale formation.

In the case of the present invention, the COD concentration of wastewater is 1
It is effective when it is contained in the range of g / liter to 200 g / liter, and more effective is in the range of 5 g / liter to 150 g / liter. COD concentration is 200
When it exceeds g / liter, the heat of oxidation of COD becomes very large, which makes it difficult to control the processing apparatus, and 1 g / l
When it is less than 1 liter, the effect of treating the wastewater by using the treatment method of the present invention is small, and it is possible to treat by using other conventional techniques. If it is less than 5 g / liter, the heat of oxidation of COD is small, and in such a case,
Even if heat is recovered by using a heat exchange device as an auxiliary equipment, it becomes difficult to operate the wet oxidation treatment device by this heat independently. Further, in such a case, although there is no problem in the wet oxidation itself, a separate heat supply device is required for the treatment, which is relatively disadvantageous in terms of energy consumption.

As the wet oxidation treatment apparatus used in the present invention, a commonly used one is used, and the wet oxidation reaction tower may be of a single-tube type or a multi-tube type.

The treatment pressure of the wet oxidation treatment according to the present invention is
The pressure is selected as appropriate depending on the correlation with the processing temperature, and is determined by the pressure at which the liquid holds the liquid phase.

The treatment temperature of the wet oxidation treatment according to the present invention, that is, the maximum temperature in the reaction tower is 140 ° C. or higher 37
It is lower than 0 ° C, and preferably 160 ° C or higher and lower than 300 ° C. When the temperature is 370 ° C. or higher, the liquid cannot hold the liquid phase. On the other hand, when the temperature is lower than 140 ° C., the treatment efficiency is remarkably reduced and waste water cannot be purified in many cases.

The oxygen-containing gas used in the present invention is a gas containing oxygen, air, and ozone. When a gas such as ozone or oxygen is used, it should be appropriately diluted with an inert gas before use. I can. Oxygen-enriched gas can also be used, and in addition to these gases, oxygen-containing exhaust gas generated from other plants can also be appropriately used. However, most preferred is cheap air.

As the space velocity of the waste water of the wet oxidation treatment according to the present invention, 0.1 hr-1 to 10 hr-1 is effective. If the space velocity is less than 0.1 hr -1, the amount of wastewater treated will be reduced and the equipment will be oversized, and conversely 10 hr -1
When it exceeds, the treatment efficiency is lowered, which is not preferable.

In the method for treating wastewater according to the present invention, it is also possible to appropriately perform solid-liquid separation and removal of insoluble matter and the like by using various solid-liquid separation treatment equipment after subjecting the wastewater to wet oxidation treatment.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

[0050]

【Example】

(Example 1) The wet oxidation treatment apparatus shown in FIG. 1 was used, and the wet oxidation reaction tower was not filled with anything. Then, the treatment was continuously performed for 500 hours under the following wet oxidation treatment conditions. After 500 hours, the heat exchanger was disassembled and the inside of the heating side tube was observed. The detailed experimental methods and results are described below.

The detailed method of the wet oxidation treatment apparatus is as follows. Waste water sent from the waste water supply line 8 is pressure-fed by the waste water supply pump 3 at a flow rate of 1 liter / hr to 90 kg / cm 2 G, and then the heat exchanger 2 is operated at 190. The mixture was heated to 0 ° C. and supplied to the reaction tower 1 from below. On the other hand, as for air, the air supplied from the oxygen-containing gas supply line 9 is pressurized by the compressor 5, and the oxygen-containing gas insertion line is supplied at a ratio of O2 / ThOD (oxygen amount in air / theoretical oxygen demand amount) = 1.5. It was supplied from the lower part of the reaction tower 1 via 10 and mixed into the waste water.
At this time, the oxygen-containing gas insertion line 11 was not used. In the reaction tower 1, heating is performed using an electric heater 15,
The wet oxidation treatment was performed at the maximum treatment temperature of 255 ° C., and the liquid to be treated was cooled in the heat exchanger 2 and the cooler 18 via the treatment liquid line 12, and then flowed to the gas-liquid separator 4. The space velocity of the waste water in the whole amount of this reaction tower was 1 hr-1. In the gas-liquid separator 4, the liquid level controller (LC) detects the liquid level to operate the liquid level control valve 6 to maintain a constant liquid level, and the pressure controller (PC) detects the pressure. Then, the pressure control valve 7 is operated to maintain a constant pressure. Then, the processing liquid is discharged from the processing liquid discharge line 14. Further, a 25 wt% sodium hydroxide aqueous solution was supplied from the alkali supply line 17, and was supplied from the front of the heat exchanger 2 at a flow rate of 20 ml / hr using the alkali supply pump 16.

The waste water used for the treatment was the waste water discharged from the photographic processing equipment. The wastewater has a ThOD of 4
2 g / liter, COD (Cr) 35 g / liter, pH
Was 8.5, and contained 700 mg / liter of iron, 320 mg / liter of aluminum, and 80 mg / liter of phosphorus. Further, the sulfur compound was contained in the form of sulfide, thiosulfate ion, and sulfite ion in a total amount of 2700 mg / liter (calculated as elemental sulfur).

The results of the treatment solutions obtained after 500 hours are:
COD (Cr) was 9.5 g / liter and pH was 7.3.
After that, the treatment was stopped, the heat exchanger was disassembled, and the inside of the heating side was inspected, but no particular scale was observed.
Further, the treatment liquid after the wet oxidation treatment of the wastewater contained 2 g / liter of solid matter.

COMPARATIVE EXAMPLE 1 In Example 1, air was added from before the heat exchanger 2 through the oxygen-containing gas insertion line 11 without using the oxygen-containing gas insertion line 10 and mixed into the waste water. . And the heating temperature in the heat exchanger 2 is 2
The same wastewater as in Example 1 was treated by the same operation method except that the temperature was 40 ° C.

As a result, after about 70 hours, the inside of the heat exchanger 2 on the heating side was blocked and the treatment could not be performed.

(Comparative Example 2) In Example 1, air was added from before the heat exchanger 2 through the oxygen-containing gas insertion line 11 without using the oxygen-containing gas insertion line 10 and mixed into the wastewater. . Except for this, the same wastewater as in Example 1 was treated by the same operation method.

The result is that after about 320 hours, the heat exchanger 2
The inside of the heating side of was clogged and processing could not be performed.

Example 2 The following wastewater was used in place of the wastewater treated in Example 1, heated to 170 ° C. in the heat exchanger 2, treated at the maximum treatment temperature of 240 ° C., and further 25% by weight. 7 ml / h of sodium hydroxide aqueous solution
The treatment was performed by the same operation method as in Example 1 except that the flow rate was r. And after 500 hours, disassemble the heat exchanger,
The inside of the tube on the heating side was observed.

The wastewater used for the treatment had a ThOD of 3
9 g / liter, COD (Cr) 28 g / liter, pH
Was 2.4 and contained 240 mg / liter of copper, 45 mg / liter of calcium and 10 mg / liter of magnesium.

The results of the treatment solutions obtained after 500 hours are:
COD (Cr) was 6.1 g / liter and pH was 8.5.
After that, the treatment was stopped, the heat exchanger was disassembled, and the inside of the heating side was inspected, but no particular scale was observed.
The treatment liquid after the wet oxidation treatment of the wastewater is 400 m
It contained g / l of solids.

(Comparative Example 3) In Example 2, air was added from before the heat exchanger 2 through the oxygen-containing gas insertion line 11 without using the oxygen-containing gas insertion line 10 and mixed into the waste water. .

The heating temperature in the heat exchanger 2 is 240
Waste water similar to that of Example 2 was treated in the same manner except that the temperature was changed to 0 ° C.

The result shows that after about 190 hours, the heat exchanger 2
The inside of the heating side of was clogged and processing could not be performed.

[Brief description of drawings]

FIG. 1 is one of embodiments of a processing apparatus according to the present invention.

[Explanation of symbols]

 1. Wet oxidation reaction tower 2. Heat exchanger 3. Waste water supply pump 4. Gas-liquid separator 5. Compressor 6. Liquid level control valve 7. Pressure control valve 8. Waste water supply line 9. Oxygen-containing gas supply line 10. Oxygen-containing gas insertion line 11. Oxygen-containing gas insertion line 12. Processing liquid line 13. Treatment liquid discharge line 14. Gas discharge line 15. Electric heater 16. Aqueous NaOH supply pump 17. NaOH aqueous solution supply line 18. Cooler

Claims (8)

[Claims] 1. The waste water is heated by a heater or a heat exchanger.
When the wastewater is subjected to wet oxidation treatment by heating at 0 ° C to 370 ° C and supplying the oxygen-containing gas under a pressure at which the wastewater maintains a liquid phase, the wastewater contains 50 mg / scale of the scale forming substance.
A method for treating waste water, comprising at least 1 liter, and supplying the oxygen-containing gas to the flow of the waste water from behind the heating side of the heater or the heat exchanger. 2. The method for treating wastewater according to claim 1, wherein the scale-forming substance is at least one selected from the group consisting of heavy metals, aluminum, phosphorus, silicon, calcium and magnesium. 3. The method for treating wastewater according to claim 2, wherein the wastewater contains sulfur and / or a sulfur compound having a lower oxidation number. 4. When the oxygen-containing gas is supplied after the heating side of the heater or heat exchanger, the temperature of the heated liquid or gas-liquid at the oxygen-containing gas supply is
The method for treating wastewater according to claim 1, wherein the temperature is 140 ° C to 230 ° C. 5. The amount of the oxygen-containing gas is 1 time or more and 10 times or less of a theoretical oxygen demand amount (hereinafter, also referred to as ThOD) in the waste water, according to claim 1 or 4. Waste water treatment method. 6. The method according to claim 1, wherein the amount of the oxygen-containing gas supplied from the front side of the heating side of the heater or the heat exchanger is equal to or less than the theoretical oxygen demand amount in the waste water. Waste water treatment method. 7. The method for treating wastewater according to claim 6, wherein the oxygen-containing gas is not supplied before the heating side of the heater or the heat exchanger. 8. The waste water contains waste water discharged from a photographic processing facility, according to claim 1 or 3.
The wastewater treatment method described.