JP2000254644A - Treatment of waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain highly purified treated-water by separating the obtained treated liquid to water not-transmitting through a reverse osmosis membrane and water transmitting through the reverse osmosis membrane by using the reverse osmosis membrane having a high desalting ratio, when waste water containing a >=2C organic compound and/or a nitrogen compound is treated with an oxidation treating process. SOLUTION: Waste water containing the >=2C organic compound and/or the nitrogen compound fed from a waste water supply source is fed to a waste water tank 18 through a waste water feed line 6 and is fed to a heating device 3 through a waste water feed pump 5. The waste water fed to the heating device 3 is preliminarily heated, then is fed to a reaction tower 1. The waste water oxidized and decomposed at the reaction tower 1 is taken out through a treated liquid line 12 and is cooled with a cooling device 4 as necessary, and then is separated to gas and liquid with a gas liquid separator 13. The separated liquid is treated by using the reverse osmosis membrane having a high desalting ratio, thus the liquid is separated to the non-transmitted liquid containing an oxidized product and the transmitted liquid hardly containing the oxidized product.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a method for purifying waste water. More specifically, the present invention relates to a method for efficiently treating wastewater containing an organic compound having 2 or more carbon atoms and / or a nitrogen compound by combining an oxidation treatment step and a reverse osmosis membrane treatment step.

[0002]

2. Description of the Related Art Conventionally, as one means for treating wastewater,
Although a method of oxidizing and decomposing organic substances and nitrogen compounds in wastewater by oxidizing treatment has been implemented, hardly decomposable organic substances and nitrogen compounds could not be sufficiently oxidized and decomposed. For example, when wet oxidation treatment is used, a method has been proposed in which wastewater subjected to wet oxidation treatment is concentrated using a reverse osmosis membrane, and the concentrated liquid is subjected to wet oxidation treatment again to improve the purification action. As such a method, for example, Japanese Patent Application Laid-Open No. 1-26993 discloses a method in which wastewater is subjected to wet oxidation treatment for the purpose of suppressing NOx-N generation in a reaction tower, and the acid component in the treated wastewater is treated using a reverse osmosis membrane. A method has been proposed in which the concentrated liquid (non-permeated liquid) is mixed with wastewater to be further subjected to an oxidation step, so that the pH of the wastewater is adjusted to 7. However, in the reverse osmosis membrane used in this method for concentrating an acid component, although the acid component having a pH of 1 to 3 can be concentrated by the reverse osmosis membrane, acetic acid almost permeates the reverse osmosis membrane. For this reason, the permeated liquid contains oxides such as acetic acid, and the wastewater has not been sufficiently purified.

[0003] "Development of wastewater recycling technology by wet oxidation method using a catalyst" (Desertification Technology, Vol. 16, N.
o. 3, P13-24 (1990)) describes a method of treating treated water obtained by subjecting waste water to wet oxidation treatment using a polyether-based or polyvinyl alcohol-based reverse osmosis membrane. Reverse osmosis membranes such as polyethylene, cellulose acetate, polyvinyl alcohol, and polyether, including polyethylene oxide and polyethyleneimine, have high separation performance (exclusion rate) for acid components having a molecular weight of 100 or more. However, it has a low exclusion rate for an acid component having a molecular weight of less than 100, and cannot sufficiently capture an organic acid such as acetic acid having a small molecular weight. for that reason,
It was necessary to further subject the permeate to a purification step such as methane fermentation to treat acetic acid and the like.

[0004]

SUMMARY OF THE INVENTION The present invention has been made in view of such a situation, and an object of the present invention is to treat a wastewater by subjecting the wastewater to an oxidation treatment step to oxidize and / or decompose the wastewater. It is an object of the present invention to provide a wastewater treatment method that enables a liquid to be separated into a treatment solution containing an oxide such as an organic substance and a treatment solution containing almost no oxide by a reverse osmosis membrane.

[0005]

The wastewater treatment method of the present invention which has solved the above-mentioned problems is an oxidation treatment for oxidizing and / or decomposing wastewater containing an organic compound having at least 2 carbon atoms and / or a nitrogen compound. In the method of performing the treatment in the step, the treatment liquid obtained through the oxidation treatment step is separated into a reverse osmosis membrane non-permeate and a reverse osmosis membrane permeate using a reverse osmosis membrane having a high desalination rate. It has a gist.

[0006] At this time, all or a part of the non-permeate may be subjected to an oxidation treatment step together with the wastewater, or all or a part of the non-permeate may be subjected to a recovery step of an organic acid and / or ammonia. You may. At this time, it is recommended that the pH of the treatment liquid treated with the reverse osmosis membrane be 4 or more.

In the present invention, it is recommended to use a polyamide composite membrane as the reverse osmosis membrane.

In the present invention, it is preferable to employ a wet oxidation treatment as the oxidation treatment step, and it is desirable that the wet oxidation treatment is performed under heat and pressure.

The non-permeate obtained by the method of the present invention contains at least one of organic acids and ammonia.
These active components contained in the non-permeate can be subjected to a recovery step.

Further, it is also effective to subject a part of the treatment liquid obtained through the oxidation treatment step and / or part or all of the permeate to the oxidation treatment step together with the wastewater.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have conducted various studies on a method for purifying waste water, and as a result, it has been found that organic acids (acetic acid and the like) and oxides such as ammonia contained in the treatment liquid after the oxidation treatment step are not removed. When treated using a reverse osmosis membrane having a high desalination rate, it can be concentrated and contained in a non-permeate, and the permeate becomes highly purified treated water containing almost no oxides. I found that.

That is, in the treatment method of the present invention, wastewater, particularly wastewater containing an organic compound and / or nitrogen compound having 2 or more carbon atoms, is subjected to oxidation treatment and / or decomposition treatment (hereinafter abbreviated as “oxidation / decomposition treatment”). The treatment liquid obtained through the oxidation treatment step and the oxidation treatment step is treated with a reverse osmosis membrane having a high desalination rate, and the organic acid and / or ammonia is contained in the non-permeate liquid. It has one feature in the place where it is concentrated.

The type of wastewater to be treated in the present invention is not particularly limited. For example, various industrial plants such as chemical plants, electronic parts manufacturing equipment, food processing equipment, metal processing equipment, metal plating equipment, printing and plate making equipment, photographic equipment, etc. Wastewater or wastewater from power generation facilities such as thermal power generation and nuclear power generation. In other words, any wastewater containing an organic compound having at least 2 carbon atoms and / or a nitrogen compound is included. Specifically, wastewater from EOG production equipment, alcohol production equipment such as methanol, ethanol, and higher alcohols, particularly aliphatic carboxylic acids and esters thereof such as acrylic acid, acrylic acid ester, methacrylic acid and methacrylic acid ester, or terephthalic acid And organic-containing wastewater discharged from a process for producing an aromatic carboxylic acid or an aromatic carboxylic acid ester such as terephthalic acid ester. Also, waste water containing nitrogen compounds such as amine, imine, ammonia, hydrazine and the like may be used. It may also be domestic wastewater such as sewage or human waste. Or dioxins, fluorocarbons, diethylhexyl phthalate,
Wastewater containing harmful substances such as organic halogen compounds such as nonylphenol and environmental hormone compounds may be used.

The oxidation treatment steps employed in the present invention include, for example, wet oxidation treatment, supercritical oxidation treatment, ozone oxidation treatment, oxidation treatment using hydrogen peroxide, oxidation treatment using perchlorate, etc. An oxidation treatment using nitrous acid, an oxidation treatment using ultraviolet light, an oxidation treatment using electrolysis, and a biological treatment or a combustion treatment are also included. In particular, it is recommended to use a wet oxidation treatment.

Hereinafter, a method of treating wastewater using the treatment apparatus of FIG. 1 will be described. FIG. 1 is a schematic view showing an embodiment of a processing apparatus in a case where wet oxidation processing is employed as one of the oxidation processing steps, but the apparatus used in the present invention is not limited to this.

The wastewater containing an organic compound having at least 2 carbon atoms and / or a nitrogen compound supplied from a wastewater supply source is supplied to a wastewater tank 18 through a wastewater supply line 6. In addition, a non-permeate described later may be supplied to the drainage tank 18 through the concentrate return line 19, but the non-permeate may be supplied to the drainage at an arbitrary position and mixed therewith.
Further, the drain tank 18 need not be provided.

In the wastewater to be subjected to the oxidation treatment step, an organic compound and / or a nitrogen compound having 2 or more carbon atoms contained in the wastewater may be previously concentrated and contained in a non-permeate using a reverse osmosis membrane. At this time, a reverse osmosis membrane having a high desalting rate used after the wet oxidation treatment described later can be used.

The waste water is sent from the drain tank 18 to the heater 3 from the drain pump 5. The space velocity at this time is not particularly limited, and may be appropriately determined depending on the treatment capacity of the reaction tower. Usually, the space velocity per reaction tower is 0.1 hr ^-1.
10 hr ^-1 , more preferably 0.2 hr ^{-1 to 5} h
It is recommended to adjust so as to be r ^-1 , more preferably 0.3 hr ^{-1 to 3} hr ^-1 . Space velocity is 0.1hr
If it is less than ^-1 , the amount of wastewater to be treated decreases, and excessive equipment is required. If it exceeds 10 hr- ¹ , on the other hand, the oxidation and decomposition treatment of the wastewater in the reaction tower becomes insufficient.

The wet oxidation treatment that can be used in the present invention can be carried out in the presence or absence of an oxygen-containing gas. However, when the oxygen concentration in the wastewater is increased, the wastewater in the reaction tower is increased. It is desirable to mix an oxygen-containing gas into the wastewater since the oxidation / decomposition efficiency of the oxide to be contained therein can be improved.

When the treatment is carried out in the presence of an oxygen-containing gas, the oxygen-containing gas is introduced from an oxygen-containing gas supply line 10 and pressurized by a compressor 9.
It is desirable to mix in the wastewater before it is supplied to the wastewater.

The oxygen-containing gas that can be used in the present invention is not particularly limited as long as it contains oxygen molecules and / or ozone, and may be pure oxygen, oxygen-enriched gas, air, or the like. Hydrogen water or oxygen-containing gas generated in other plants may be used. Among them, the use of air is recommended from an economic viewpoint.

The supply amount when supplying the oxygen-containing gas is not particularly limited, and it is sufficient to supply an effective amount for enhancing the ability to oxidize and decompose the oxide in the wastewater. The supply amount of the oxygen-containing gas can be appropriately adjusted by, for example, providing the oxygen-containing gas flow control valve 11. The supply amount of the oxygen-containing gas is preferably 0.5 to 5.0 times, more preferably 0.7 to 3.0 times the theoretical oxygen demand of the oxide to be discharged from the wastewater. Recommended. When the supply amount of the oxygen-containing gas is less than 0.5 times, the oxide target is not sufficiently oxidized and decomposed and remains in the treatment liquid obtained through the wet oxidation treatment in a relatively large amount, and the reverse osmosis membrane is used. The burden on the reverse osmosis membrane in the processing step increases. Even if oxygen is supplied more than 5.0 times, the oxidation / decomposition treatment capacity is saturated.

In the present invention, the term "theoretical oxygen demand" refers to the amount of oxygen required to oxidize and / or decompose oxides in wastewater to nitrogen, carbon dioxide, water and ash. .

In many cases, the theoretical oxygen demand of the oxide in the wastewater can also be obtained from the chemical oxygen demand (COD (Cr)).

Next, the wastewater sent to the heater 3 is supplied to the reaction tower 1 after being preheated. The temperature of the effluent in the reaction column is affected by other conditions, but when heated to a temperature exceeding 370 ° C., high pressure must be applied to keep the effluent in a liquid phase, and Therefore, the heating temperature is preferably 270 ° C. or lower, more preferably 230 ° C. or lower, and further preferably 170 ° C. or lower. On the other hand, if the temperature of the waste water is less than 80 ° C., it becomes difficult to efficiently perform the oxidation / decomposition treatment of the oxides in the waste water, so it is preferable to heat the waste water to 100 ° C. or more, more preferably 110 ° C. or more. desirable.

The timing of heating the wastewater is not particularly limited, and the previously heated wastewater may be supplied into the reaction tower as described above, or the wastewater may be heated after being supplied into the reaction tower. Alternatively, a heat source such as steam may be supplied to the wastewater.

In the wet oxidation method used in the present invention, the number, type, shape, and the like of the reaction towers are not particularly limited, and one or a combination of a plurality of reaction towers used for ordinary wet oxidation treatment can be used. For example, a single-tube reaction tower or a multi-tube reaction tower can be used. When a plurality of reaction towers are installed, they may be arranged arbitrarily, for example, in series or in parallel according to the purpose.

As a method of supplying the wastewater to the reaction tower, various forms such as a gas-liquid upward co-current, a gas-liquid downward co-current, and a gas-liquid countercurrent can be used. They may be combined.

When a solid catalyst is used for the treatment in the reaction tower,
It is desirable because the efficiency of oxidation and decomposition treatment of organic compounds and nitrogen compounds contained in the wastewater can be improved, and the treatment temperature in the reaction tower can be reduced as compared with the case where a solid catalyst is not used. The solid catalyst that can be used in the present invention is not particularly limited. For example, manganese, cobalt, nickel, copper, cerium, silver, platinum, palladium,
A solid catalyst containing at least one selected from the group consisting of rhodium, gold, iridium and ruthenium is recommended. The content of these elements is not particularly limited, but is desirably contained in the solid catalyst at a ratio of preferably 0.01 to 25% by mass, more preferably 0.05 to 10% by mass. In addition, solid catalysts include titanium,
It is desirable to contain at least one selected from zirconium, aluminum, silicon, iron and activated carbon.

The shape of the solid catalyst is not particularly limited, and may be any shape such as a pellet, a sphere, a granule, a ring and a honeycomb.

When the wet oxidation treatment is used, several kinds of the above solid catalysts may be used. When a plurality of reaction towers are used, a reaction tower using the solid catalyst and a reaction tower not using the solid catalyst are combined. The method of using the solid catalyst is not particularly limited.

Further, in addition to these solid catalysts, various packings, in-plant products and the like may be incorporated into the reaction tower in order to stir gas-liquid, improve contact efficiency, reduce gas-liquid drift, and the like. .

On the other hand, if the temperature of the waste water is too high, the waste water is in a gaseous state in the reaction tower, so that organic substances, inorganic substances, etc. adhere to the surface of the catalyst, and the activity of the catalyst may be deteriorated. Therefore, it is recommended to apply pressure to the inside of the reaction tower so that the wastewater can maintain a liquid phase even at a high temperature. It is also desirable to provide a pressure regulating valve on the exhaust gas outlet side of the wet oxidation treatment apparatus, and to appropriately adjust the pressure according to the treatment temperature so that the wastewater can maintain a liquid phase in the reaction tower. For example, if the processing temperature is 80 ° C or higher,
When the temperature is lower than 95 ° C., the wastewater is in a liquid phase even at atmospheric pressure, and may be at atmospheric pressure from the viewpoint of economy. However, it is preferable to increase the pressure in order to improve the processing efficiency.
When the treatment temperature is 95 ° C. or higher, the wastewater often evaporates under the atmospheric pressure.
When the temperature is lower than 0 ° C., the pressure is about 0.2 to 1 MPa (Gauge). When the processing temperature is 170 ° C. or higher and lower than 230 ° C., the pressure is about 1 to 5 MPa (Gauge), and when the processing temperature is 230 ° C. or higher. It is desirable to apply a pressure exceeding 5 MPa (Gauge) and control the pressure so that the wastewater can maintain a liquid phase.

The oxide to be oxidized in the wastewater is oxidized and decomposed in the reaction tower. In the present invention, the term "oxidation and decomposition" means oxidative decomposition of acetic acid into water and carbon dioxide, Decomposition treatment to convert urea to ammonia and carbon dioxide, oxidative decomposition treatment to convert ammonia and hydrazine to nitrogen gas and water, and dimethyl sulfoxide to ash such as carbon dioxide, water and sulfate ions Oxidation and oxidative decomposition treatment, oxidation treatment of converting dimethyl sulfoxide to dimethyl sulfone or methane sulfonic acid, and the like are exemplified.
Various oxidation and / or oxidation treatments such as a treatment to decompose carbon dioxide, water, ash, etc., a decomposition treatment to reduce the molecular weight of hardly decomposable organic compounds and nitrogen compounds, or an oxidation treatment to oxidize
Or the meaning including decomposition.

In the treatment solution obtained through the wet oxidation treatment, the organic compound which is hardly decomposable among the oxides often remains in the form of low-molecular-weight compounds. In many cases, a low molecular weight organic acid, particularly acetic acid, remains as a compound. Also, when the wastewater contains a large amount of nitrogen compounds as an oxide, ammonia often remains in the processing solution obtained through the wet oxidation treatment, and especially when the wet oxidation treatment is performed without using a solid catalyst. In addition, a large amount of ammonia can be left in the treatment liquid after the wet oxidation treatment.

The wastewater oxidized and decomposed in the reaction tower is taken out of the treatment liquid line 12 and, if necessary, cooled by the cooler 4.
After being cooled appropriately, the gas and liquid are separated by the gas-liquid separator 13 into gas and liquid. At this time, it is desirable to detect the liquid level using the liquid level controller LC and control the liquid level in the gas-liquid separator by the liquid level control valve 15 to be constant. Or, without cooling the oxidized and decomposed wastewater,
Alternatively, after being cooled to some extent by the cooler 34 as shown in FIG. 3, the gas may be discharged through the pressure control valve 44, and then separated into gas and liquid by the gas-liquid separator 43.

Here, the temperature in the gas-liquid separator is not particularly limited, but since the wastewater oxidized and decomposed in the reaction tower contains carbon dioxide, for example, the temperature in the gas-liquid separator To release carbon dioxide in wastewater,
Alternatively, it is desirable that the liquid separated by the gas-liquid separator be subjected to bubbling treatment with a gas such as air to release carbon dioxide in the liquid.

The liquid (treatment liquid) obtained by separation in the gas-liquid separator 13 is then treated with a reverse osmosis membrane having a high desalination rate to thereby remove the liquid (non-permeate) containing oxides. It is separated into a permeate containing almost no oxide. The temperature of the treatment liquid supplied to the reverse osmosis membrane is preferably 40 ° C. or lower in order to maintain the durability of the reverse osmosis membrane. For controlling the temperature of the processing liquid, the processing liquid may be cooled by providing a cooler 4 before applying the processing liquid to the gas-liquid separator 13, or a heat exchanger (not shown) or a cooler (not shown) after the gas-liquid separation. ) May be provided to cool the processing liquid.

In performing the wet oxidation treatment used in the present invention, a heat exchanger may be used for the heater and the cooler, and these may be used in an appropriate combination.

Further, the processing solution provided for the reverse osmosis membrane is an MF membrane,
The solid-liquid separation treatment may be performed in advance using various filtration equipment such as a UF membrane, and then the treatment may be performed with the reverse osmosis membrane.

In the method for treating wastewater according to the present invention, when the treatment liquid obtained through such a wet oxidation treatment or another oxidation treatment is treated using a reverse osmosis membrane having a high desalination ratio, Organic acid (acetic acid and the like) and / or nitrogen compound (ammonia and the like) and the like contained in the non-permeate can be captured and concentrated.

The oxide to be contained in the treatment liquid obtained through the oxidation treatment step is preferably mainly an organic acid and / or ammonia, preferably 30% by mass or more, more preferably 50% by mass or more. More preferably, it is desirably contained in the processing liquid at a ratio of 70% by mass or more.

The amount of the oxide contained in the processing solution is, for example, TOD, ThOD, COD (Cr), COD (M
n), TOC, BOD, total nitrogen, or can be calculated from measured values of specific components.

In the present invention, "a reverse osmosis membrane having a high desalination rate" means a pressure of 1.47 MPa (Gauge), pH
6.5, the desalting rate (exclusion rate) with respect to a 0.15% NaCl aqueous solution at a temperature of 25 ° C. is 98.0% or more, more preferably 99.0% or more, and still more preferably 99.5%. The reverse osmosis membrane having the above-described properties and having a high separation performance (an exclusion rate of 60%) for an organic acid having a molecular weight of less than 100, for example, acetic acid.
(Preferably 70% or more, more preferably 80% or more). Examples of such a reverse osmosis membrane include polyamides including cross-linked polyamides and aromatic polyamides, and aliphatics. Examples include amine condensate-based and heterocyclic polymer-based reverse osmosis membranes. In particular, a polyamide-based reverse osmosis membrane such as a crosslinked polyamide-based or aromatic polyamide-based membrane is recommended because of its high separability to organic acids and / or ammonia.

Incidentally, cellulose acetate-based, polyethylene-based,
Reverse osmosis membranes having a low separation performance (exclusion rate of less than 60%) for organic acids having a molecular weight of less than 100, for example, acetic acid, such as reverse osmosis membranes such as polyvinyl alcohol and polyether, have a high desalination rate. Is not preferred.

As the membrane form of the reverse osmosis membrane, various membrane forms such as an asymmetric membrane and a composite membrane can be used. Among them, a composite membrane is particularly recommended. In the present invention, a polyamide-based composite membrane is used as the reverse osmosis membrane. It is recommended to use

The reverse osmosis membrane module used in the present invention is not particularly limited, and may be any of a flat membrane module, a hollow fiber module, a spiral module, a cylindrical module, a pleated module, and the like. In particular, a spiral type module which has a large membrane area and is suitable for downsizing of the apparatus is desirable.

The amount of the treatment liquid supplied to the reverse osmosis membrane is not particularly limited, and the whole or a part of the treatment liquid obtained through the wet oxidation treatment can be applied to the reverse osmosis membrane.

When the treatment liquid obtained through the oxidation treatment step is separated (treated) by a reverse osmosis membrane into a non-permeate liquid and a permeate liquid, the organic acids and / or ammonia contained in the treatment liquid are converted into organic acids, respectively. If the salt or ammonium salt is used, the separation performance of the reverse osmosis membrane is improved, and the non-permeate can contain more oxidizable substances such as organic acid salts and ammonium salts. And is highly purified.

As a method for converting an organic acid into a salt, it is desirable to add an alkali metal ion and / or an ammonium ion.

The added alkali metal ion and / or ammonium ion ionically bond with the organic acid contained in the processing solution to form an organic acid salt, and the molecular size increases. The separation performance (rejection rate) for is improved. In addition, the organic acid becomes negatively charged by the addition of the alkali metal ion and / or ammonium ion, causing electrostatic repulsion with the negatively charged reverse osmosis membrane, thereby improving the separation performance of the reverse osmosis membrane.

In FIG. 1, although an alkali supply line 8 is provided and added to waste water, alkali metal ions and / or
Alternatively, the position at which ammonium ions are added is not particularly limited, and alkali metal ions and / or ammonium ions may be added to the treatment liquid after the oxidation treatment step, provided that it is added to the treatment liquid supplied to the reverse osmosis membrane. Good. At this time, the content of alkali metal ions and / or ammonium ions is 5 to the total amount of organic acids contained in the treatment liquid.
Addition of 0 mol% or more is desirable because the separation performance of the reverse osmosis membrane can be further enhanced.

As a method for converting ammonia into a salt,
It is preferable to add an organic acid and / or an inorganic acid. However, since an organic acid deteriorates the purification of wastewater, it is preferable to add an inorganic acid such as sulfuric acid.

The added organic acid and / or inorganic acid ionically bond with ammonia contained in the processing solution to form an ammonium salt, and the molecular size becomes large. Is improved.

The position at which the organic acid and / or the inorganic acid are added is not particularly limited, as in the case where the organic acid is converted into a salt.
At this time, the separation performance of the reverse osmosis membrane can be further enhanced by adding the organic acid and / or the inorganic acid so that the content of the organic acid and / or the inorganic acid is 50 mol% or more with respect to the total amount of the alkali components contained in the treatment liquid.

If an organic substance is contained in the nitrogen compound oxidation treatment step, a carbonate is generated by the oxidation / decomposition treatment, and ammonia can be converted to an ammonium salt.

The pH of the processing solution used for the treatment with the reverse osmosis membrane
Is 4 or more, the separation performance of the reverse osmosis membrane is further improved,
The rejection rate of the reverse osmosis membrane with respect to the oxide to be oxidized is increased, and the purifying property of the obtained permeate can be remarkably improved.

When the content of the organic acid in the treatment liquid is high, it is desirable to adjust the pH to preferably 4 or more, more preferably 5 or more, and still more preferably 6 or more. When the pH exceeds 9, the separation performance of the reverse osmosis membrane often deteriorates. Therefore, the upper limit of the pH of the treatment solution is preferably pH 9, more preferably pH 8, and even more preferably p.
H7.5.

When the ammonia content in the treatment liquid is high, it is desirable to adjust the pH to preferably 4 or more, more preferably 5 or more, and still more preferably 6 or more. Since the separation performance of the permeable membrane decreases, it is recommended to set the pH to preferably 9 or less, more preferably 8 or less.

The organic acid (and / or organic acid salt) and / or ammonia (and / or ammonium salt) are trapped in the non-permeate by the method for treating wastewater of the present invention. Part or all of the non-permeate liquid may be returned directly or indirectly to any position in the wastewater oxidation treatment step. For example, the wastewater may be directly returned to the wastewater before being subjected to the oxidation treatment step, or supplied to the wastewater from an arbitrary position and subjected to the oxidation treatment step.

It is preferable that the non-permeated liquid is circulated to the oxidizing step and oxidized and decomposed again, since the circulated oxide can be almost completely oxidized and decomposed.
At this time, part or all of the non-permeated liquid may be subjected to biological treatment such as methane fermentation, or may be subjected to other wastewater treatment such as combustion treatment or chemical treatment. They can be combined freely. The amount of the non-permeated liquid to be subjected to such treatment is higher in concentration of the oxide as compared with the case where the reverse osmosis membrane is not used, and the treatment can be performed with higher efficiency and at lower cost.

A part or the whole of the non-permeate may be subjected to a step of recovering an effective ingredient contained in the non-permeate, such as an organic acid or an organic acid salt and / or an ammonia or an ammonium salt. The recovery method at this time is not particularly limited, for example, a method of recovering by direct distillation, a method of extracting an organic acid using an organic solvent, and then dehydrating and removing the solvent by distillation of the extract to recover the organic acid. For example, a known collection method can be used.

When the wastewater is treated using the wastewater treatment method according to the present invention, it can be separated into a non-permeate containing an oxide and a permeate containing almost no oxide by a reverse osmosis membrane. In addition, the permeated liquid contains almost no oxides and is highly treated purified water, so that industrial water and domestic water can be used without performing a conventional acetic acid treatment step such as biological treatment. Can be reused as Further, the treated water obtained by further subjecting the permeated liquid to a high purification treatment can also be used as pure water.

Further, in the method according to the present invention, part of the treatment liquid obtained through the oxidation treatment step and / or part or all of the permeated liquid of the reverse osmosis membrane is directly returned to the wastewater before being subjected to the oxidation treatment step. Alternatively, the wastewater may be supplied to wastewater from an arbitrary position in the wastewater supply line and subjected to the oxidation treatment step. For example, when a treatment liquid and / or a permeate obtained through the oxidation treatment step are used as dilution water for wastewater, the TOD concentration and COD concentration of the wastewater can be reduced. Alternatively, the permeate can be used as salt concentration dilution water in wastewater.

Hereinafter, the present invention will be described in more detail by way of examples. However, the following examples are not intended to limit the present invention, and all modifications and alterations may be made without departing from the spirit of the present invention. Included in the scope.

[0066]

Example 1 The apparatus shown in FIGS. 1 and 2 was used, and a wet oxidation treatment was employed for the oxidation treatment step, and the treatment was carried out for 500 hours under the following conditions. 26mm in diameter and 300 in length for wet oxidation
A cylindrical reaction tower 1 of 0 mm was used. Titania and platinum were the main components as a solid catalyst inside, and the platinum content was 0.1%.
0.8 liter of the catalyst by mass was charged. The wastewater used for treatment is the wastewater discharged from the aliphatic carboxylic acid and aliphatic carboxylic acid ester production process, and alcohol,
It contained many organic compounds having 2 or more carbon atoms such as aldehydes and carboxylic acids. The COD (Cr) of the wastewater is 35
g / liter and pH was 2.8. The wastewater did not contain alkali metal ions, ammonium ions, and inorganic salts.

(Oxidation treatment step) The waste water supplied through the waste water supply line 6 and a non-permeate liquid described later are mixed in the waste water tank 18 and the waste water is supplied to the waste water supply pump 5 at a flow rate of 2.4 liter / h. After the pressurized feed, the heater 3
Waste water heated to 00 ° C. was supplied from the bottom of the reaction tower 1. Also, after air is supplied from the oxygen-containing gas supply line 10 and pressurized by the compressor 9, O ₂ / COD (Cr) (oxygen amount in supply gas / chemical oxygen demand of wastewater) = 1.1.
Thus, the flow rate was controlled by the oxygen-containing gas flow rate control valve 11 and mixed into the wastewater before the heater 3. In the reaction tower 1, the treatment was performed in a gas-liquid upward parallel flow. In the reaction tower 1, the wastewater is kept at a temperature of 200 ° C. by using the electric heater 2 to perform oxidation and decomposition treatments.
, And sent to the gas-liquid separator 13 for gas-liquid separation. In the gas-liquid separator 13, the liquid level was detected by the liquid level controller LC, and the liquid was discharged from the liquid level control valve 15 so as to maintain a constant liquid level. The pressure control valve 14 detects the pressure with a pressure controller PC and controls the pressure to maintain a pressure of 2.45 MPa (Gauge). The COD (Cr) of the treatment liquid obtained through the wet oxidation treatment is 2.6 g / liter, pH 3.0.
And 92% of the total TOC component was acetic acid.

(Reverse Osmosis Membrane Treatment Step) This treatment solution was further applied to a reverse osmosis membrane treatment apparatus 20 as shown in FIG.
a), and the amount of the non-permeate was controlled to be about 1/5 of the amount of the treatment liquid treated by the reverse osmosis membrane. As the reverse osmosis membrane, a polyamide-based composite membrane (desalting rate (exclusion rate) with respect to a 0.15% NaCl aqueous solution)
99.5%). The COD (Cr) of the permeate obtained by treatment with the reverse osmosis membrane was 1.1 g / liter, and the COD (Cr) of the non-permeate was 8.4 g / liter. Then, 95% of the non-permeate was supplied to the drain tank 18 from the concentrate return line 19. In addition, the treatment solution obtained by adding sodium hydroxide to the treatment solution obtained through the wet oxidation treatment and changing the pH of the treatment solution is subjected to a reverse osmosis membrane treatment step, and the COD (Cr) concentration of the obtained permeate is obtained. Was examined. FIG. 5 shows the results.

Comparative Example 1 (Reverse osmosis membrane treatment step) The treatment solution (COD (Cr) 2.6 g / liter) obtained in Example 1 after the wet oxidation treatment was subjected to a reverse osmosis membrane treatment. The reverse osmosis membrane treatment process was performed in the same manner as in Example 1 except that a cellulose acetate-based membrane (desalting rate (rejection rate: 95% with respect to a 0.15% NaCl aqueous solution) of 95%) was used as the reverse osmosis membrane. . Organic substances can hardly be separated by this reverse osmosis membrane.
D (Cr) was 2.3 g / liter, and sufficient separation results could not be obtained.

Example 2 (Oxidation treatment step) A wet oxidation treatment was performed in the same manner as in Example 1 except that an aqueous solution of sodium hydroxide was supplied from the alkali supply line 8. The supply amount of the aqueous sodium hydroxide solution was controlled so that the pH of the treatment liquid after the wet oxidation treatment was about 6. The COD (Cr) of the obtained treatment liquid was 3.0 g / liter, and 93% of the total TOC component was acetic acid. Further, Na was contained in an amount of about 1.5 mol times with respect to acetic acid.

(Reverse osmosis membrane treatment step) The obtained treatment solution was subjected to the same reverse osmosis membrane treatment step as in Example 1. COD (Cr) of the obtained permeate is less than 0.1 g / liter,
The COD (Cr) of the non-permeate was 15 g / liter. Then, 95% of the non-permeate was mixed into the wastewater from the concentrate return line 19.

Comparative Example 2 (Reverse osmosis membrane treatment step) The treatment solution (CO
D (Cr) 3.0 g / liter) was treated with a reverse osmosis membrane using a polyvinyl alcohol-based membrane (demineralization rate (exclusion rate: 93% with respect to 0.15% NaCl aqueous solution: 93%)) as the reverse osmosis membrane. The same reverse osmosis membrane process as in Example 1 was performed except that the pressure was 1.96 MPa (Gauge). The obtained permeate had a COD (Cr) of 2.6 g / liter, and this reverse osmosis membrane could hardly eliminate organic substances.

Example 3 Using the same reaction tower as in Example 1, a wet oxidation treatment was performed for 500 hours. 0.8 liter of a catalyst containing titania and platinum as main components as a solid catalyst and having a platinum content of 0.5% by mass was filled in the reaction tower 1. The wastewater subjected to the treatment was wastewater discharged from the power generation equipment, and was wastewater containing ammonium sulfate, sodium ions and carbonate ions. The concentration of ammonia in the wastewater was 2.2 g / liter, and the pH was 7.8. The amount of solids evaporated from the wastewater was 15 g / liter.

(Oxidation treatment step) This waste water and a non-permeate liquid to be described later are mixed in a waste water tank 18 and fed to the waste water supply pump 5 at a flow rate of 0.8 liter / h. And supplied from the bottom of the reaction tower 1.
Air was introduced from the oxygen-containing gas supply line 10 and pressurized by the compressor 9, and then supplied to the drainage before the heater 3 so that O ₂ /COD=2.0. In the reaction tower 1, the temperature of the wastewater was kept at 160 ° C. by using the electric heater 2, and after oxidizing and decomposing, cooled to 30 ° C. in the cooler 4 and sent to the gas-liquid separator 13 for gas-liquid separation. At this time, the pressure is detected by a pressure controller (PC),
(Gauge) pressure was controlled in the same manner as in Example 1. The ammonia concentration of the obtained processing solution is 0.5
3 g / liter, pH 7.1.

(Reverse Osmosis Membrane Treatment Step) This treatment liquid was supplied to the reverse osmosis membrane treatment device 20 so as to maintain a pressure of 4.9 MPa (Gauge). The amount of the non-permeate was controlled to be about 1/3 of the amount of the treatment liquid applied to the reverse osmosis membrane. The reverse osmosis membrane includes a polyamide-based composite membrane (0.15% N) according to the present invention.
A desalting rate (exclusion rate: 99.5%) was used for the aCl aqueous solution. The ammonia concentration of the obtained permeate is 0.01 g.
/ L, and the ammonia concentration of the non-permeate was 1.6 g / l. 80% of the non-permeate was mixed into the wastewater from the concentrate return line 19.

Example 4 Using the apparatus shown in FIGS. 3 and 4, a wet oxidation treatment was performed under the following conditions for 500 hours. The reaction tower 31 has a diameter of 2
A cylindrical catalyst having a length of 6 mm and a length of 3000 mm was used, and 1.3 liters of a catalyst containing activated carbon and platinum as main components and having a platinum content of 0.2 mass% were filled therein.
The wastewater used for the treatment was a solvent wastewater containing a large amount of alcohols such as ethyl alcohol and propyl alcohol. The COD (Cr) of the wastewater was 30 g / liter, and the pH was 7.1. The wastewater did not contain alkali metal ions, ammonium ions, and inorganic salts.

(Oxidation Treatment Step) The waste water sent from the waste water supply line 36 was mixed with a non-permeate liquid described later in a waste water tank 48. The waste water was fed under pressure at a flow rate of 1.3 liter / h by a waste water supply pump 35, heated to 120 ° C. by a heater 33, and supplied from above the reaction tower 31. Further, an aqueous solution of sodium hydroxide was mixed into the waste water using an alkali supply pump 37 from an alkali supply line 38. The supply amount of sodium hydroxide was controlled so that the pH of the treatment solution after the wet oxidation treatment was about 6.5. After air is supplied from the oxygen-containing gas supply line 40 and pressurized by the compressor 39, O ₂ / COD (Cr) =
The flow rate was controlled by the oxygen-containing gas flow control valve 41 so as to be 0.7, and the water was supplied to the wastewater before the heater 33. In the reaction tower 31, the treatment was performed in a gas-liquid downward co-current flow. Reaction tower 3
In the case of 1, the temperature of the waste water is set to 120 by using the electric heater 32.
Oxidation / decomposition treatment was performed while maintaining the temperature. The waste water after the treatment was cooled to 80 ° C. in the cooler 34 through the treatment liquid line 42, and was discharged from the pressure control valve 44 under pressure. The discharged gas-liquid was sent to a gas-liquid separator 43 and gas-liquid separated. The pressure control valve 44 detects the pressure with the pressure controller PC,
Control was performed so as to maintain a pressure of 9 MPa (Gauge).
The COD (Cr) of the obtained treatment liquid was 9.1 g / liter, and 95% of the total TOC component was acetic acid.

(Reverse osmosis membrane treatment step) The obtained treatment liquid was supplied to the reverse osmosis membrane treatment step 50 so as to maintain a pressure of 2.9 MPa (Gauge). In addition, the treatment was performed so that the amount of the non-permeated liquid was about 1/3 of the amount of the treatment liquid supplied. The reverse osmosis membrane used was a polyamide composite membrane (desalting rate (exclusion rate: 99.7% with respect to 0.15% NaCl aqueous solution)).
The resulting permeate is less than 0.1 g / L COD (Cr) and the non-permeate is 28 g / COD (Cr).
Liters. The entire amount of the non-permeate was supplied to a drain tank 48 through a concentrate return line 49, and was mixed with the waste water.

Example 5 A wet oxidation treatment was performed in the same manner as in Example 1 except for the following conditions. The inside of the reaction tower 1 was not filled with the catalyst and was made an empty tower. The wastewater used was sewage sludge containing various organic substances. The COD (Cr) of the wastewater was 9.7 g / liter, and the pH was 2.8.

(Oxidation treatment step) The waste water and a non-permeate liquid to be described later are mixed in a waste water tank 18 and fed to the waste water supply pump 5 at a flow rate of 1.6 liter / h, and then heated at 230 ° C. And supplied from the bottom of the reaction tower 1. An aqueous solution of sodium hydroxide was supplied from an alkali supply line 8 to drainage using an alkali supply pump 7 so that the pH of the treatment solution after the wet oxidation treatment was about 6.5.
Air was supplied in the same manner as in Example 1 so that the ratio of O _{2 /} COD (Cr) was 1.5. In the reaction tower 1, the oxidizing and decomposing treatment was performed while keeping the waste water at 230 ° C. using the electric heater 2. The obtained processing liquid was cooled to 30 ° C. in the cooler 4 through the processing liquid line 12 and then sent to the gas-liquid separator 13 for gas-liquid separation. At this time, the pressure is 4.
Control was performed to maintain 9 MPa (Gauge). The COD (Cr) of the obtained treatment liquid was 3.3 g / liter, and 89% of the total TOC component was acetic acid. Further, the ammonia concentration was 0.14 g / liter.

(Reverse Osmosis Membrane Treatment Step) After the obtained treatment liquid was filtered using a filter having a filtration accuracy of 1 μm, it was supplied to a reverse osmosis membrane treatment device 20 so as to maintain a pressure of 2.9 MPa (Gauge). The amount of the non-permeate was controlled to be about 1/3 of the amount of the treatment liquid applied to the reverse osmosis membrane. As the reverse osmosis membrane, a polyamide composite membrane (desalting rate (exclusion rate) 99.5)
%)It was used. The permeate obtained has a COD (Cr) of less than 0.1 g / l and an ammonia concentration of 0.01 g.
/ Liter. In addition, COD (C
r) is 9.8 g / l, and the ammonia concentration is 0.39
g / liter. And 70% of this non-permeate
Was supplied to a drain tank 18 through a concentrate return line 19 and mixed with the waste water.

Example 6 The same wet oxidation treatment as in Example 4 was performed except for the following conditions.
As a solid catalyst, 1.3 liters of a catalyst containing activated carbon, ruthenium and palladium as main components, and having a ruthenium content of 0.4% by mass and a palladium content of 0.1% by mass are filled in the reaction tower 31. did. As the wastewater, wastewater containing a long-chain alcohol or a solvent and having a COD (Cr) of 76 g / liter and a pH of 8.5 was used.

(Oxidation Treatment Step) The waste water and the entire amount of a non-permeate liquid described later and a part of the wet oxidation treatment liquid are transferred to a drain tank 4.
The mixture was mixed at 8 and controlled so that the COD (Cr) of the wastewater became 35 g / liter. The drainage is supplied to the drainage pump 35
And then heated to 140 ° C. by the heater 33, supplied from the upper part of the reaction tower 31, and controlled to a processing pressure of 0.9 MPa (Gauge). . After supplying air from the oxygen-containing gas supply line 40 and increasing the pressure by the compressor 39,
The flow rate was controlled by the oxygen gas flow rate control valve 41 so that the ratio of O ₂ /COD(Cr)=0.82 was supplied to the wastewater before the heater 33. In the reaction tower 31, the treatment was performed in a gas-liquid downward co-current flow. In the reaction tower 31, the temperature of the waste water was kept at 140 ° C. by using the electric heater 32, and the oxidation and decomposition treatment was performed. The obtained processing solution had a COD (Cr) of 6.5 g / liter and a pH of 2.8, and accounted for 80% of the total TOC component.
These are organic acids such as succinic acid, acetic acid and propionic acid. Also, 50% of the organic acid was acetic acid.

(Reverse Osmosis Membrane Treatment Step) 25% of the obtained treatment liquid after the wet oxidation treatment is returned from the concentrated liquid return line 49 to the drainage tank 48, and the remainder is subjected to the reverse osmosis membrane treatment step by 1.5%.
The processing was performed such that the pressure was supplied to maintain the pressure of MPa (Gauge), and the amount of the non-permeated liquid was about の of the supply amount. At this time, the treatment liquid after the wet oxidation treatment was subjected to an air bubbling treatment in advance to release carbon dioxide in the liquid, and an aqueous ammonia solution was further added to control the pH of the treatment liquid to about 6. As the reverse osmosis membrane, a polyamide-based composite membrane (desalting rate (exclusion rate) 99.5%) was used. COD (Cr) of the obtained permeate is less than 0.1 g / liter,
The ammonia concentration was less than 0.1 g / l, and the COD (Cr) of the non-permeate was 13 g / l. Then, the entire amount of the non-permeate is returned to the concentrate return line 49.
Was returned to the drainage tank 48.

Example 7 (Oxidation treatment step) A wet oxidation treatment was performed using the same waste water as in Example 1. The wet oxidation treatment was performed in the same manner as in Example 1 except that the non-permeated liquid was not supplied to the drain tank 18. The obtained treatment liquid had a COD (Cr) of 2.9 g / l and a pH of 3.0, and 90% of the total TOC component was acetic acid.

(Reverse osmosis membrane treatment step (first time)) A non-permeate obtained in the second reverse osmosis membrane treatment step described later is mixed with the obtained treatment liquid, and the same reverse osmosis membrane treatment as in Example 1 is performed. Process attached. The processing liquid was supplied so as to maintain a pressure of 4.9 MPa (Gauge). Using the same reverse osmosis membrane as in Example 1, the amount of non-permeate was about 1% of the processing liquid applied to the reverse osmosis membrane.
/ 5. This reverse osmosis membrane treatment step (1)
COD (Cr) of the permeate obtained in the second round) was 1.
It was 2 g / l, and the COD (Cr) of the non-permeate was 9.6 g / l.

(Reverse osmosis membrane treatment step (second time)) The permeate obtained in the first reverse osmosis membrane treatment step is supplied to the same reverse osmosis membrane treatment step as in the first time, and the treatment is performed with the reverse osmosis membrane. did. At this time, control was performed so that the obtained non-permeate liquid amount (second time) was about 1/3 of the supplied liquid amount. Then, the second non-permeate was supplied to the treatment liquid obtained through the wet oxidation treatment. COD (Cr) of the second reverse osmosis membrane non-permeate
Is 2.9 g / liter, COD (C
r) was 0.5 g / l.

(Acetic Acid Recovery Step) The first non-permeate was subjected to an acetic acid recovery step. Note that a solvent extraction method and a distillation method were used in the acetic acid recovery step. In the solvent extraction method, extraction was performed three times using a separating funnel having a volume of 1 liter and using ethyl acetate as an extractant. The obtained extractant phases were mixed three times and subjected to a distillation treatment with a distillation apparatus to collect acetic acid. 85% of the acetic acid in the processing solution subjected to the recovery step could be recovered.

Comparative Example 3 (Acetic Acid Recovery Step) The treatment liquid obtained in Example 7 was subjected to the same acetic acid recovery step as in Example 7 without being subjected to the reverse osmosis membrane treatment step. 7 of acetic acid in the processing solution subjected to the acetic acid recovery process
8% was recovered.

Example 8 (Oxidation treatment step) The same wet oxidation treatment as in Example 7 was performed except that the aqueous solution of sodium hydroxide was supplied from the alkali supply line 8. The supply amount of the aqueous sodium hydroxide solution was controlled so that the solution pH after the wet oxidation treatment was about 6. The COD (Cr) of the obtained processing solution is 3.3 g.
/ L and 92% of the total TOC component was acetic acid. Also, sodium ion was contained in about 1.5 mole times with respect to acetic acid.

(Reverse Osmosis Membrane Treatment Step) The obtained treatment solution was subjected to the same reverse osmosis membrane treatment step as in Example 1. 4.9
The supply was performed so as to maintain the pressure of MPa (Gauge), and the amount of the non-permeated liquid was controlled to be about １ ／ of the supplied liquid amount.
The resulting permeate has a COD (Cr) of less than 0.1 g / liter and the non-permeate has a COD (Cr) of 16.5 g / liter.
Liters.

(Acetic acid recovery step)
Acetic acid was recovered by subjecting it to the same acetic acid recovery step. 97% of the acetic acid in the treatment solution subjected to the acetic acid recovery step could be recovered.

Comparative Example 4 (Acetic Acid Recovery Step) The treatment liquid obtained by the wet oxidation treatment of Example 8 was subjected to an acetic acid recovery step, and acetic acid was directly extracted with a solvent.
81% of the acetic acid in the processing solution subjected to the acetic acid recovery step could be recovered.

Example 9 (Oxidation treatment step) A wet oxidation treatment was carried out under the same conditions and under the same conditions as in Example 3, except that the non-permeated liquid was not supplied to the drainage tank 18. The resulting treatment solution had an ammonia concentration of 0.59 g / liter and a pH of 7.2.

(Reverse osmosis membrane treatment step) As a result of performing the same reverse osmosis membrane treatment step as in Example 3, the obtained permeate had an ammonia concentration of less than 0.01 g / liter, and the non-permeate had an ammonia concentration of less than 0.01 g / liter. Was 1.8 g / liter.

(Ammonia Recovery Step) The obtained non-permeate was subjected to an ammonia recovery step using a distillation method to recover ammonia. 95% of the ammonia in the processing solution subjected to the ammonia recovery step could be recovered.

Comparative Example 5 (Ammonia Recovery Step) Ammonia was recovered from the treatment liquid obtained in the wet oxidation treatment of Example 9 by using the same ammonia recovery step as in Example 9. 83% of the ammonia in the processing solution subjected to the ammonia recovery step could be recovered.

[0098]

The wastewater is subjected to an oxidation treatment step, and the oxides such as organic acids (acetic acid, etc.) and ammonia contained in the obtained treatment liquid are removed by using a reverse osmosis membrane having a high desalination rate. By processing, it can be concentrated and contained in the non-permeate liquid,
In addition, highly purified treated water containing almost no oxide was obtained as the permeate. Further, when the pH of the treatment liquid when treating with the reverse osmosis membrane was set to 4 or more, the separation performance of the reverse osmosis membrane could be significantly improved.

[Brief description of the drawings]

FIG. 1 is an embodiment of a wet oxidation treatment apparatus according to the present invention.

FIG. 2 is an outline of a wastewater treatment method according to the present invention.

FIG. 3 shows an embodiment of a wet oxidation treatment apparatus according to the present invention.

FIG. 4 is an outline of a method for treating wastewater according to the present invention.

FIG. 5 is a diagram showing a change in COD (Cr) concentration of a permeate obtained in Example 1.

[Explanation of symbols]

 1,31 Reaction tower 2,32 Electric heater 3,33 Heater 4,34 Cooler 5,35 Drainage supply pump 6,36 Drainage supply line 7,37 Alkaline supply pump 8,38 Alkaline supply line 9,39 Compressor 10, 40 oxygen-containing gas supply line 11,41 oxygen-containing gas flow control valve 12,42 treatment liquid line 13,43 gas-liquid separator 14,44 pressure control valve 15 liquid level control valve 16,46 gas discharge line 17,47 treatment liquid Discharge line 18,48 Drainage tank 19,49 Concentrate return line 20,50 Reverse osmosis membrane treatment unit LC Liquid level controller PC Pressure controller

Claims (8)

[Claims] 1. A method for treating wastewater containing an organic compound having at least 2 carbon atoms and / or a nitrogen compound by subjecting the wastewater to an oxidation treatment step, wherein the treatment liquid obtained through the oxidation treatment step is subjected to high removal. A method for treating wastewater, comprising separating a non-permeated liquid and a permeated liquid using a reverse osmosis membrane having a salt ratio. 2. The method according to claim 1, wherein all or a part of the non-permeate is subjected to an oxidation treatment step together with the wastewater. 3. The method according to claim 1, wherein all or a part of the non-permeate is subjected to a step of recovering an organic acid and / or ammonia. 4. The pH of a treatment solution treated by the reverse osmosis membrane.
Is 4 or more. 5. The method according to claim 1, wherein the reverse osmosis membrane is a polyamide-based composite membrane. 6. The method according to claim 1, wherein the oxidation treatment step is a wet oxidation treatment performed under heating and pressure. 7. The method according to claim 1, wherein the non-permeate is an organic acid and / or ammonia-containing liquid. 8. A part of the treatment liquid obtained through the oxidation treatment step and / or a part or all of the permeate is
The method according to claim 1, wherein the wastewater is subjected to an oxidation treatment step together with the wastewater.