JPH0813355B2 - Reverse osmosis membrane treatment method for organic acid cleaning wastewater - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for treating reverse osmosis membrane of organic acid cleaning wastewater, and particularly to oxide scales attached to the metal surface of boilers, heat exchangers and other plants. Reverse osmosis membrane treatment of organic acid cleaning wastewater that can efficiently treat organic acid cleaning wastewater generated when chemically cleaning organic acid or its water-soluble salt with an organic acid cleaning agent that is a main component at low cost Concerning the law.

[Prior Art] Oxide scales and the like adhering to metal surfaces of boilers, heat exchangers and other plants are generally removed by chemical cleaning with an organic acid cleaner mainly containing an organic acid or a water-soluble salt thereof. I have. Organic acids used in this chemical cleaning include citric acid, hydroxy acetic acid, malic acid and other oxycarboxylic acids, formic acid, oxalic acid, saturated carboxylic acids such as malonic acid, and aminopolycarboxylic acids such as ethylenediaminetetraacetic acid (EDTA). Is used. In addition to such organic acid, a reducing agent and a corrosion inhibitor are added to the organic acid detergent.

The cleaning wastewater discharged by organic acid cleaning is generally
It consists of 1 volume of acid washing solution, 4 volumes of washing water, 1 volume of neutralized rust preventive solution to which citric acid and hydrazine are added, and 1 volume of others, for a total of 7 volumes. In some cases, citric acid is not added in the neutralized rust preventive liquid. Such cleaning wastewater cannot be discharged directly because it contains a large amount of organic acids, reducing agents, corrosion inhibitors, COD components derived from hydrazine, and iron eluted from the scale due to cleaning.

Therefore, conventionally, the total amount of cleaning wastewater is decomposed with an oxidizing agent such as hydrogen peroxide, or by incineration of 1.5 to 2 volumes of acid cleaning liquid with high COD concentration and initial washing water, washing water with low COD concentration, medium Wastewater treatment is performed by a split method in which 5 to 5.5 volumes of Japanese rust preventive solution and others are decomposed with an oxidizing agent such as hydrogen peroxide. Also, recently, for the purpose of reducing the volume of treated wastewater, the washing wastewater is treated with a reverse osmosis membrane to separate it into a concentrate and a permeate, and the concentrate is incinerated and the permeate is treated with an oxidizing agent. Decomposition method is adopted (see
No. 63-123491).

[Problems to be Solved by the Invention] In the above-mentioned splitting method and the method disclosed in JP-A-63-123491, the permeate of the reverse osmosis membrane treatment or the rinsing water having a low COD concentration is chemically treated with an oxidizing agent. There are disadvantages in that the chemical cost is high and sludge is generated, so that the treatment is required. That is, in the above-mentioned conventional techniques, in any case, an oxidizing agent such as hydrogen peroxide, an iron salt as an oxidation catalyst is used to finally neutralize with slaked lime, an alkaline agent such as caustic soda,
It requires the use of large amounts of chemicals. Further, since sludge such as iron hydroxide and calcium hydroxide is generated, it is necessary to carry out a dehydration work and a dehydration cake treatment.

The present invention solves the above-mentioned conventional problems, does not use chemicals such as oxidizers, and does not accompany the generation of sludge, is safe, inexpensive, and has high treatment efficiency. An object is to provide a membrane treatment method.

[Means for Solving the Problems] The reverse osmosis membrane treatment method for organic acid cleaning wastewater of the present invention, when performing organic acid cleaning wastewater reverse osmosis membrane treatment, transforms the organic acid cleaning wastewater into high COD wastewater and low COD wastewater. Separation and high COD drainage first
In the reverse osmosis membrane separation step, the concentrated water and the permeated water are separated, and the permeated water is mixed with the low COD waste water and treated in the second reverse osmosis membrane separation step.

 Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 is a system diagram showing one embodiment of a method for treating a reverse osmosis membrane of organic acid washing wastewater of the present invention.

In the method of the present invention, first, the organic acid cleaning wastewater to be treated is separated into high COD wastewater having a high COD concentration and low COD wastewater having a low COD concentration. That is, as described above, wastewater of various water qualities is discharged from the washing step, the washing step, and the like in the organic acid washing wastewater in a capacity corresponding to each step. In general, the capacity and quality of wastewater discharged in each step in chemical cleaning with an organic acid or a salt thereof are as shown in Table 1 below.

In the present invention, among the wastewater of each of such processes, for example, the wastewater of the organic acid washing process having a high COD concentration and the wastewater of the first washing process, preferably the initial discharge water of the first washing process is defined as the high COD wastewater. In addition, the wastewater of the second washing step, which has a relatively low COD concentration, the wastewater of the neutralization and rust prevention step, and other wastewater (preferably the rest of the first washing step) are separately treated as low-COD wastewater and treated. .

First, high COD wastewater is introduced into the drainage tank 1 through the pipe 11, and if necessary, an alkaline agent is added to adjust the pH.
The first RO device (reverse osmosis membrane separation device; hereinafter referred to as "RO device")
Is abbreviated. ) No. 2 and perform reverse osmosis membrane separation treatment. (Hereinafter, the membrane separation treatment by such an RO device may be referred to as a reverse osmosis membrane treatment.) Then, the first RO device 2
The concentrated water is extracted from the pipe 13 and circulated in the drain tank 1. In addition, if necessary, this concentrated water is extracted from the system,
Dispose by off-site treatment (incineration). On the other hand, the first
The permeated water of the RO device 2 is sent to the drainage tank 3 through the pipe 14.

The type of the first RO device 2 is not particularly limited,
RO devices such as a spiral type, a hollow fiber type, and a tube type can be used. In this first RO device 2,
The pH of the inflowing wastewater is optimally around 7, but it may be in the range of pH 4-9. As the alkaline agent used for adjusting the pH, caustic soda, ammonia or the like can be used. In addition, the operating pressure of the first RO device 2 varies depending on the type of reverse osmosis membrane used, but is generally 30 to 65 kg / cm ²
The range is preferably By the first reverse osmosis membrane treatment in the first RO device 2, the permeated water in which COD is preferably separated and removed by 99% or more and the concentrated water in which the COD is concentrated to about 80,000 mg / (acid concentration about 14% by weight) %). If the acid concentration of the concentrated water becomes excessively high, the osmotic pressure of the liquid increases, and the flow rate of the treated water decreases.

The permeated water of the first RO device 2 supplied from the pipe 14 to the drainage tank 3 is mixed with the low COD wastewater supplied from the pipe 15, and the pH is adjusted by adding an acid or alkali agent if necessary. Then, it is introduced into the second RO device 4 through the pipe 16, and the second reverse osmosis membrane treatment is performed. Then, the concentrated water of the second RO device 4 is extracted from the pipe 17 and circulated in the drain tank 3. The concentrated water may be circulated in the drainage tank 1. On the other hand, the permeated water of the second RO device 4 is sent to the drain tank 5 through the pipe 18.

The permeated water of the second RO device 4 sent to the drainage tank 5 is
Since COD concentration and acid concentration are sufficiently low and discharge is possible, it is sent to the discharge system through the pipe 19. The permeated water of the second RO device may also be circulated to the drainage tank 1 or 3 if necessary.

The type of the second RO device 4 is not particularly limited, but it is preferable to use the spiral type. This second RO
In the apparatus 4, the pH of the inflowing wastewater is optimally around 7, but it may be in the range of pH 4-9. As the alkaline agent used for the pH adjustment, caustic soda, ammonia, etc. can be used, and as the acid, hydrochloric acid, sulfuric acid, etc. can be used. Although the operating pressure of the second RO device 4 varies depending on the type of reverse osmosis membrane used, it is generally preferable to set it in the range of 30 to 50 kg / cm ² . By the second reverse osmosis membrane treatment in the second RO device 4, preferably 90% or more of COD is separated and removed, and the permeated water having a COD concentration of 10 mg / or less and COD of 3 or more are removed.
Obtain concentrated water concentrated to about 000-5000 mg /.

The example shown in FIG. 1 is an embodiment of the present invention,
The invention is not limited in any way to the illustrated method. For example, the concentrated water of the first RO device 2 or the second RO device 4 may be incinerated without being circulated in the drain tanks 1 or 3, etc., respectively. Further, it is not always necessary to use two RO devices, and one RO device may be used, and low COD wastewater may be mixed with RO device permeated water having high COD wastewater for further reverse osmosis membrane treatment.

[Operation] In the reverse osmosis membrane treatment method of the organic acid cleaning wastewater of the present invention, high COD wastewater of the organic acid cleaning wastewater is subjected to reverse osmosis membrane treatment to concentrate and reduce the permeated water to be further reversed together with the low COD wastewater. By the osmotic membrane treatment, treated water that can discharge the entire amount of the organic acid washing wastewater and concentrated water that is separately treated (incineration treatment) without the need for chemicals and without the generation of sludge. Can be processed separately. Moreover, the organic acid cleaning wastewater has high COD wastewater and low C
Since it is separated into OD wastewater and the high-COD wastewater is treated with a two-stage reverse osmosis membrane only, it is possible to obtain high-quality treated water with high treatment efficiency.

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. In addition, below, "%" shows "weight%."

Example 1 Organic acid cleaning wastewater generated when a boiler was cleaned with an acid solution containing 3% citric acid and 3% hydroxyacetic acid as main components 1590 m ³
High COD for medium, acid solution and initial effluent 442m ³ of the first washing process
Wastewater, the rest of the first washing step, other washing water, neutralization and rust prevention step wastewater, heated steam drain water, etc. were treated as low COD wastewater according to the method of the present invention.

First, the high COD wastewater is 342 permeated from the first reverse osmosis membrane treatment.
It was separated into m ³ and concentrated water 100 m ³ (concentration factor 4.4).

Subsequently, the permeate and the low COD wastewater 1490M ³ obtained was thoroughly stirred air, and reverse osmosis membrane treatment (second reverse osmosis membrane treatment) for the 0.89 m ^3, the permeate 869 concentrated water 21
(Concentration factor 42). Based on this value, the water balance was calculated when the total amount of 1490 m ³ was subjected to reverse osmosis membrane treatment, and it was found that the organic acid cleaning wastewater was separated into 92% of water that could be discharged and 8% of concentrated water that was treated off-site. Was confirmed.

The quality of the raw water, treated water (permeate) and concentrated water of each reverse osmosis membrane treatment was as shown in Table 2.

From Table 2, according to the method of the present invention, in addition to COD, BOD
It is clear that TN, Fe and TN are also removed, and treated water of high quality is obtained.

In addition, the conventional chemical method (COD decomposition treatment with hydrogen peroxide and studder dehydration treatment) which has been conventionally carried out, or JP-A-63-1
One-stage reverse osmosis membrane treatment method disclosed in No. 23491 (high COD wastewater is treated by reverse osmosis membrane, concentrated water is treated by external incineration, permeated water and other low COD wastewater is treated by hydrogen peroxide for COD decomposition treatment and sludge dewatering treatment) And the two-stage reverse osmosis membrane treatment method according to the present invention, as a result of comparison of cost and construction period, as shown in Table 3,
According to the method of the present invention, it was confirmed that the cost and the construction period were significantly reduced.

[Effects of the Invention] As described in detail above, according to the method for treating reverse osmosis membrane of organic acid cleaning wastewater of the present invention, two-stage reverse osmosis is applied in which concentration of organic acid cleaning wastewater by reverse osmosis membrane and removal of COD and the like are applied. By the membrane treatment method, it is possible to efficiently separate the entire amount of the organic acid washing wastewater into high-quality treated water that can be discharged and concentrated water that undergoes off-site treatment (incineration). Thus, in the present invention, chemicals such as an oxidizing agent are not required unlike the conventional method, and since there is no precipitation of iron hydroxide, the studging process is also unnecessary. Therefore, it is possible to reduce the processing cost and the construction period.

[Brief description of drawings]

FIG. 1 is a system diagram showing one embodiment of a method for treating a reverse osmosis membrane of organic acid washing wastewater of the present invention. 1,3,5 ... Drainage tank, 2 ... First RO device, 4 ... Second RO device.

Claims (1)

[Claims] 1. When treating organic acid washing wastewater with a reverse osmosis membrane, the organic acid washing wastewater is separated into high COD wastewater and low COD wastewater, and the high COD wastewater is treated in the first reverse osmosis membrane separation step. A method for reverse osmosis membrane treatment of organic acid-washed waste water, comprising separating concentrated water and permeated water, mixing the permeated water with the low COD waste water, and treating the mixture in the second reverse osmosis membrane separation step.