JPH05247868A - Treatment of waste water in production of pulp - Google Patents

Abstract

PURPOSE:To facilitate treatment of waste water in production of pulp using a reverse osmosis membrane by enabling removal of clogged materials in the reverse osmosis membrane by a liquid generated in a process of pulp production or by a readily available chemical. CONSTITUTION:In treatment of waste water by fractionating polymer substances contained in a separated liquid in the processes of pulp production using a reverse osmosis membrane and condensing them, this invented method is carried out by washing the reverse osmosis membrane with an acid solution of <=pH4 generated in a process of pulp production and subsequently washing the membrane with an alkaline solution of >=pH10 used or generated in the subsequent process of pulp production.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing or preventing clogging of a reverse osmosis membrane used in a process for fractionating and concentrating a polymer substance in a liquid separated from a pulp manufacturing process.

[0002]

2. Description of the Related Art Conventionally, coagulation-sedimentation method, activated sludge method, etc. have been used as a method for treating pulp wastewater discharged from a paper pulp mill. However, these methods generate a large amount of sludge and dehydrate it. And incineration requires a lot of chemicals and energy, and the treatment cost is high. In recent years, as a method of treating pulp wastewater, a method of treating with a semipermeable membrane such as a microfiltration membrane, an ultrafiltration membrane, a reverse osmosis membrane has been proposed. For example,
In Japanese Patent Laid-Open No. 60-209089, high temperature waste water discharged from the pulp manufacturing process is contacted with one side of the hydrophobic polymer porous membrane to generate high temperature steam, and steam is generated from the waste water of the other side. A method of permeating the sample, cooling, and aggregating. Further, in Japanese Patent Laid-Open No. 62-171788, there is disclosed a method of removing not only a high molecular weight component but also a colored component of a relatively low molecular weight component by subjecting alkaline pulp wastewater to a semipermeable membrane treatment, and washing this membrane. It is described that an aqueous solution of hypochlorous acid is used for this.

As a conventional method for cleaning a membrane, for example, as a method for removing a deposit deposited on the membrane surface by a reverse osmosis membrane treatment of industrial wastewater, flushing with air or utilization of an enzyme-containing detergent precipitates. There is a report that it is effective for releasing substances. In addition, EDTA and sodium perborate are said to be effective for scale removal. Although silica is one of the precipitates that is difficult to remove, a method has been proposed in which sodium hexametaphosphate is added to the stock solution to prevent scale formation.

Further, as an example of cleaning other films, Japanese Patent Laid-Open No. 6-68242
Japanese Unexamined Patent Publication No. 0-220108 describes a method of washing the ultrafiltration membrane used for treating the water-soluble polymer dispersion with a solvent capable of dissolving the water-soluble polymer and an aqueous solution containing an acid or an alkali as a necessary component. JP-A-62-49906
The publication describes a method of washing an oil-containing wastewater with an aqueous solution of hydrochloric acid and a neutral detergent in the case of treating the membrane. Japanese Patent Application Laid-Open No. 61-78403 describes a method of washing an ultrafiltration membrane contaminated with an organic substance with a solution of an alkaline agent in multiple stages.

However, since pulp wastewater contains a large amount of lignin and other components, the membrane such as forming a gel layer on the membrane surface is apt to be clogged, and the stock solution is continuously pressurized to a high pressure for wastewater treatment. It is necessary, and as a result, the permeation performance of the membrane deteriorates significantly with time.

[0006] A semipermeable membrane made of cellulose acetate is generally considered to be weak against a high pH solution or a solution containing chlorine, and cannot be used for treating pulp wastewater such as chlorine white water or an alkali extraction stage. Further, a reverse osmosis membrane made of polysulfone having excellent pH resistance, chlorine resistance, heat resistance and the like has a large molecular weight cutoff, so that low molecular weight components cannot be efficiently removed.

When the reverse osmosis membrane is subjected to a treatment for fractionating and concentrating the polymer substance in the liquid separated from the pulp manufacturing process,
The turbidity in the stock solution gradually deposits on the membrane surface and causes the pores of the reverse osmosis membrane to be blocked, resulting in a decrease in the amount of permeation. As a result of analyzing this substance, lignin and compounds of lignin and saccharides, various fats and oils, resins and their oxides, microorganisms, various organic acids and their metal salts, iron, silicic acid, inorganic salts such as calcium and magnesium, etc. It turned out to be a substance.

In the conventional method, EDTA and sodium perborate were required to remove the metal salt.
Further, it was necessary to decompose organic substances by flushing with air or using a detergent containing an enzyme.

[0009]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems of the prior art, and relates to the removal and prevention of blockages in reverse osmosis membranes, without the use of any special chemicals, and is discharged from the pulp production process. The purpose is to enable the removal of blockages in the reverse osmosis membrane with a liquid or a readily available chemical. Further, the use of a large amount of the surfactant may cause foaming trouble in the treatment of the cleaning waste liquid on the membrane surface, and therefore the use of the surfactant should be made as small as possible.

[0010]

Means for Solving the Problems The present inventor has found that a large amount of iron, calcium, magnesium and silicic acid is contained in a plug of a reverse osmosis membrane obtained by treating pulp wastewater. I confirmed that it was salt. From this, it was clarified that most of these blockages were solubilized in the alkaline solution by the action of the acidic solution. Thus, the present invention has been completed. Further, even if it is not solubilized in an alkaline solution, the separation of the film surface is facilitated by mixing a small amount of a surfactant in the alkaline solution.

That is, the present invention provides a method for removing or preventing a closed matter of a reverse osmosis membrane used in a treatment for fractionating and concentrating a polymer substance in a liquid separated from a pulp manufacturing process. A method for treating wastewater from pulp production, which comprises solubilizing an alkaline solution with an acidic solution and then removing the blockages with the alkaline solution.

In the present invention, the acidic solution used is an acidic solution having a pH of 4 or less discharged from the pulp manufacturing process, and the white water in the chlorine bleaching stage, the white water in the chlorine dioxide bleaching stage, and the waste liquid generated during chlorine dioxide production. It means one or more acidic solutions selected from among others. In addition, these acids also include an acidic solution in which wastewater having a pH of more than 4 discharged from the pulp manufacturing process is adjusted to have a pH of 4 or less with hydrochloric acid, sulfuric acid, sulfamic acid or the like. With an acidic solution having a pH of more than 4, it is extremely difficult to easily solubilize the target clogging material and remove it from the membrane surface.

The alkaline solution used in the present invention easily forms a precipitate with calcium, magnesium, etc.,
Alternatively, it represents an alkaline solution having a pH of 10 or more excluding those that form scale. Further, the alkaline solution is, among various liquids discharged from the steps involved in pulp production, one containing the above-mentioned alkali, for example, white water in the alkali extraction stage, white water in the hypochlorous acid bleaching stage, and hydrogen peroxide bleaching stage. Produced from the white water and chemical solution recovery process
It is possible to substitute the above-mentioned alkaline solution for the cooking chemical liquid (white liquor) containing as a main component.

Further, in the alkaline solution, one or more kinds of cleaning aids selected from chelating agents such as EDTA, oxidizing agents such as sodium hypochlorite, surfactants, enzymes, etc., depending on the composition of the plugging material. Can also be added at a ratio of 1% or less with respect to the cleaning liquid.

The removal method of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic diagram of a fractionation processing device of the present invention.
First, the fractional concentration treatment of the treatment liquid will be described. The treatment liquid in the treatment liquid storage tank 3 is supplied to the membrane treatment apparatus 1 by the liquid feed pump 4 to fractionally concentrate the treatment liquid. Then valve 13,
14, 15 are closed, the throughput is adjusted by the treatment liquid supply adjusting valve 10, and the pressure applied to the membrane is adjusted by the membrane pressure adjusting valve 11. The membrane permeate is discharged from the permeate discharge line 9.

Next, the cleaning method will be described. The liquid supply pump 4 is stopped and the processing liquid supply control valves 10 and 12 are closed. The valves 13, 14, 15 are opened, and further the valve 16 is opened to supply the acidic cleaning liquid stored in the acidic cleaning liquid tank 5 into the membrane processing apparatus 1 to replace it with the processing liquid.
The membrane pressure control valve 11 and the valve 16 are closed. The cleaning liquid circulation pump 7 is operated, and the acidic cleaning liquid is circulated using the cleaning liquid circulation line 8 to clean the reverse osmosis membrane 2 in the membrane treatment apparatus 1 for a certain period of time.

After the acid cleaning treatment, the cleaning liquid circulation pump 7 is stopped, the membrane pressure adjusting valve 11 and the valve 17 are opened to replace the acidic cleaning liquid in the membrane processing apparatus 1 and the cleaning liquid circulation line 8 with an alkaline cleaning liquid, and the replacement is completed. After that, the valve 17 and the membrane pressure adjusting valve 11 are closed, the cleaning liquid circulation pump 7 is operated, and the alkaline cleaning liquid is circulated using the cleaning liquid circulation line 8 to clean the reverse osmosis membrane 2 in the membrane processing apparatus 1 for a certain period of time.

[0018]

The present invention divides the removal of the blockage into two steps and changes the pH of the cleaning solution from acidic to alkaline, so that the blockage of the reverse osmosis membrane can be removed by a readily available chemical or the like. Made possible. Further, in the fractional concentration treatment of pulp manufacturing wastewater, it is possible to reduce clogging of the reverse osmosis membrane by alternately treating alkaline wastewater and acidic wastewater.

[0019]

EXAMPLES Examples of the present invention will be described below together with comparative examples of the conventional method, but the present invention is not limited to these examples.

Example 1 A reverse osmosis membrane containing polysulfone as a main component and having a molecular weight cut-off of about 8,000, which was represented by the molecular weight of polyethylene glycol, was formed into a tubular shape, and the reverse osmosis membrane was bundled into a unit to produce pulp. About 5 kg of bleached white water in the alkaline extraction stage with oxygen addition discharged from the bleaching process of the manufacturing process
It is passed under a pressure of cm ² to fractionate and concentrate the polymer substance. Immediately after the start of this fractionation treatment, the pores of the reverse osmosis membrane begin to be blocked, and the amount of liquid permeation per unit area of the reverse osmosis membrane gradually decreases.

The amount of the permeated liquid of the reverse osmosis membrane is 7 after the fractionation treatment.
When it has dropped to about 50%, reverse osmosis membrane is adjusted to pH 2 to pH.
It is circulated in a tubular reverse osmosis membrane for 60 minutes at a flow rate of 1 m / sec or more under a pressure of about 2 kg / cm ² with a hydrochloric acid aqueous solution adjusted to a range of up to 4 and heated to 65 ° C. Then the pH
An aqueous solution of NaOH heated to 65 ° C adjusted to 11 or more and a flow rate of 1 m / sec or more under a pressure of about 2 kg / cm ²
It was circulated in the tube-shaped reverse osmosis membrane for 0 minutes to remove the blockage on the membrane surface. The removal results are shown in Table 1.

Example 2 Pulp production in which the reverse osmosis membrane was heated to 65 ° C. instead of the hydrochloric acid aqueous solution used in Example 1 when the amount of permeated liquid in the reverse osmosis membrane decreased to about 70% immediately after the fractionation treatment. About 2 kg of bleaching water in the chlorination stage discharged from the bleaching process
It is circulated in a tubular reverse osmosis membrane for 60 minutes at a flow rate of 1 m / sec or more under a pressure of 1 cm ² / cm ² . After that, about 2 kg / cm of the washing solution was added to the NaOH aqueous solution of pH 11 or more so that the surfactant was 0.1% or less and heated to 65 ° C.
^It was circulated in a tubular reverse osmosis membrane for 90 minutes under a pressure of ² at a flow rate of 1 m / sec or more to remove the clogging on the membrane surface.

Example 3 Pulp production in which the reverse osmosis membrane was heated to 65 ° C. instead of the hydrochloric acid aqueous solution in Example 1 when the amount of the permeated liquid in the reverse osmosis membrane decreased to about 70% immediately after the fractionation treatment. About 2 kg of bleaching water in the chlorination stage discharged from the bleaching process
It is circulated in a tubular reverse osmosis membrane for 60 minutes at a flow rate of 1 m / sec or more under a pressure of 1 cm ² / cm ² . Thereafter, the bleaching water in the hydrogen peroxide bleaching stage discharged from the bleaching step of the halp manufacturing process heated to 65 ° C. in place of the aqueous NaOH solution in Example 1 contained 0.1% or less of a surfactant. About 2 kg / cm with the cleaning solution added to
^It was circulated in a tubular reverse osmosis membrane for 90 minutes under a pressure of ² at a flow rate of 1 m / sec or more to remove the clogging on the membrane surface.

Comparative Example 1 When the amount of permeated liquid in the reverse osmosis membrane was reduced to about 70% immediately after the fractionation treatment, the reverse osmosis membrane was added to a NaOH aqueous solution having a pH of 12 or more so that the surfactant was 0.5%. 65 ℃
The washing liquid heated to a temperature of about 2 kg / cm ² and a flow rate of 1
It was circulated in a tubular reverse osmosis membrane at a rate of m / sec or more for 150 minutes to remove the blockage on the membrane surface.

Comparative Example 2 In Comparative Example 1, when the liquid permeation amount per unit area of the reverse osmosis membrane is not recovered, a surfactant is added to the NaOH aqueous solution having a pH of 12 or more so as to be 0.5%. About 2 kg / cm ^{2 of} cleaning solution is added with sodium hypochlorite so that available chlorine is less than 500ppm and heated to 65 ℃.
It was circulated in the tubular reverse osmosis membrane at a flow rate of 1 m / sec or more for 150 minutes under pressure to remove clogging on the membrane surface.

Comparative Example 3 In Comparative Example 2, when the permeation amount of the liquid per unit area of the reverse osmosis membrane is not recovered, the surfactant is added to the NaOH aqueous solution having a pH of 12 or more so as to be 0.5%. And then E
The washing liquid added with DTA to about 0.5% and heated to 65 ° C., the flow rate of 1 m / se under a pressure of about 2 kg / cm ^2.
The above procedure was circulated in the tubular reverse osmosis membrane for 150 minutes to remove blockages on the membrane surface.

Example 4 Bleaching in the pulp production process when the permeation amount immediately after the fractionation treatment of the bleaching white water in the alkali extraction stage accompanied by the addition of oxygen discharged from the bleaching process in the pulp production process decreased to about 80%. Bleached white water in the chlorine stage discharged from the process is passed under a pressure of about 5 kg / cm ² to fractionate and concentrate the polymer substance. Immediately after the start of this fractionation treatment, dissolution or alkali solubilization of the metal salt deposited on the membrane surface of the reverse osmosis membrane begins. On the contrary, the pores are clogged by the insoluble component in the acidic liquid, and the liquid permeation amount per unit area of the reverse osmosis membrane gradually decreases. Next, about 5 bleached white water in the alkali extraction stage with oxygen addition discharged from the bleaching step of the pulp manufacturing process.
It is passed under a pressure of kg / cm ² to fractionate and concentrate the polymer substance. Immediately after the start of the fractionation treatment, dissolution of the alkali-solubilized occluded substance due to the acid deposited on the membrane surface of the reverse osmosis membrane and separation from the membrane surface begin. On the contrary, the pores are closed by the insoluble component in the alkaline liquid, and the liquid permeation amount per unit area of the reverse osmosis membrane gradually decreases. In these series of treatments, the permeation amount of the liquid per unit area of the reverse osmosis membrane was around 70 to 80%.

[0028]

[Table 1]

The unit Flux value used in Table 1 is represented by the membrane permeate flow rate (1 / m ² · Hr) per unit area (m ² ). The Flux values shown in Table 1 are the values measured with water, and the measurement conditions at that time are an average pressure of 2.0 kg / cm ² (average of the membrane inlet and membrane outlet pressures) and a temperature of 25 ° C.

[0030]

INDUSTRIAL APPLICABILITY The present invention relates to the removal of a blockage of a reverse osmosis membrane, without using a special chemical, and by using a liquid or a readily available chemical discharged from a pulp manufacturing process, the reverse osmosis membrane is blocked. Made it possible to remove things. In addition, regarding the prevention of the blockage of the reverse osmosis membrane, it is possible to prevent the blockage of the reverse osmosis membrane by changing the liquid discharged from the pulp manufacturing process and the treatment process without using any special chemicals.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a fractionation processing device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Membrane treatment device 2 Reverse osmosis membrane 3 Treatment liquid storage tank 4 Liquid feed pump 5 Acid cleaning liquid tank 6 Alkaline cleaning liquid tank 7 Cleaning liquid circulation pump 8 Cleaning liquid circulation line 9 Permeate discharge line 10 Processing liquid supply control valve 11 Membrane pressure control valve 12 Valve 13 Valve 14 Valve 15 Valve 16 Valve 17 Valve

Front page continuation (72) Inventor Haruhiko Kawabata 3-4-3 Marunouchi, Chiyoda-ku, Tokyo Sanryo Paper Co., Ltd. (72) Inventor Yuji Numata 2-1, Okawamachi, Kawasaki-ku, Kawasaki-shi, Kanagawa Sanryo Kakoki Co., Ltd.

Claims (4)

[Claims] 1. In a wastewater treatment for fractionating and concentrating a polymer substance in a liquid separated from a pulp manufacturing process using a reverse osmosis membrane, the reverse osmosis membrane is discharged from the pulp manufacturing process.
A method of treating wastewater from pulp production, which comprises washing with an acidic solution of H4 or less and then washing with an alkaline solution having a pH of 10 or more, which is used or discharged in the pulp manufacturing process. 2. The method for treating wastewater from pulp production according to claim 1, wherein the acidic solution is one of white water in a chlorine bleaching stage, white water in a chlorine dioxide bleaching stage, and a waste liquid associated with chlorine dioxide production. 3. The alkaline solution is any one of white water in an alkali extraction stage, white water in a hypochlorous acid bleaching stage, white water in a hydrogen peroxide bleaching stage, and a cooking chemical liquid containing NaOH as a main component. 2. The method for treating wastewater from pulp production according to 2. 4. A pulp characterized by alternately treating acidic wastewater and alkaline wastewater in wastewater treatment in which a polymer substance in a liquid separated from a pulp manufacturing step is fractionated and concentrated using a reverse osmosis membrane. Manufacturing wastewater treatment method.