JPH0679275A - Treatment of waste water - Google Patents

Abstract

PURPOSE:To discharge permeated water in a sewerage and to reduce raw water by cleaning off the solder flux residue of a mounted printed circuit board with a specified detergent, washing the board and then concentrating the waste washing water with a water permselective oil-water separation semipermeable membrane. CONSTITUTION:The solder flux residue of a mounted printed circuit board is cleaned off with a petroleum hydrocarbonic detergent, that is a substitute for fluorocarbon, and then the board passes successively through the first, second and third washing tanks 1, 2 and 3 and cleaned. Pure water 10 is supplied to the third washing tank 3, the overflow washing water flows toward the first washing tank 1, and the first washing tank has the highest concn. of detergent. The waste cleaning water passes through a prefilter 5 and an oil-water separation semipermeable membrane 6 to be concentrated. The concentrated water is discharged outside the system from a line 8, and the permeated water is discharged into sewerage from a line 7. The TCC concn. of the treated water is reduced by a half at the line 7 and concentrated about 25 times at the line 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wastewater treatment method for a CFC substitute cleaning system for printed wiring boards, and more particularly to cleaning solder flux residue of a mounted printed wiring board using a CFC substitute cleaning agent containing a surfactant. The present invention relates to a method of concentrating the wastewater from the water washing step performed after the removal by a selective water-permeable oil-water separation semipermeable membrane.

[0002]

2. Description of the Related Art As an oil-water separation membrane having selective water permeability, for example, a membrane made of an acrylonitrile copolymer has been proposed in Japanese Patent Publication No. 58-14804. On the other hand, in order to clean the rosin-based solder flux remaining after the electronic component is mounted on the printed wiring board by soldering, a CFC-based cleaning agent has been conventionally used. However, due to environmental issues, alternative cleaning agents are being sought, and CFC alternative cleaning agents consisting of a combination of terpene-based hydrocarbons that dissolve rosin, petroleum-based hydrocarbons and non-halogen oily solvents such as higher alcohols and surfactants have been developed. Is being considered.

[0003]

When the CFC substitute cleaning agent as described above is used, a large amount of waste water is discharged from the cleaning step, which causes a problem of waste water treatment. Biological treatment and coagulation / sedimentation are effective in solving this problem, but both of them cause new problems such as difficulty in maintenance and restrictions on installation space. Therefore, a wastewater treatment technology that does not cause such a problem and that can be efficiently treated is required.

[0004]

Means for Solving the Problems As a result of earnest studies on a wastewater treatment method in a CFC substitute cleaning system for printed wiring boards, the present inventor has found that the above-mentioned problems can be solved by performing a treatment operation with a specific membrane. The present invention has been completed based on the knowledge obtained.

That is, the first aspect of the present invention is that the waste water from the water washing step, which is performed after the solder flux residue of the mounted printed wiring board is washed and removed by using a CFC substitute detergent containing a surfactant, has a water selective permeability. The wastewater treatment method is characterized by concentrating treatment with an oil-water separation semipermeable membrane. A second aspect of the present invention relates to a method for recovering the performance of an oil / water separation semipermeable membrane whose performance has deteriorated in such wastewater treatment.

The wastewater treated in the present invention includes:
This is the drainage from the water cleaning step performed after the solder flux residue of the mounted printed wiring board is cleaned and removed using a CFC substitute cleaning agent containing a surfactant. A system for cleaning and removing the solder flux residue of the mounted printed wiring board using the CFC substitute cleaning agent usually includes a cleaning process using a CFC substitute cleaning agent, a water cleaning process, and a drying process. The wastewater to be treated is the wastewater from the intermediate water washing process in this washing system. Further, the preferred TOC (total organic carbon) concentration of the wastewater that can be treated by the present invention is 1000 m.
It is preferably g / liter or less, and particularly preferably 100 mg / liter or less.

The water-selective oil-water separating semipermeable membrane used in the present invention is a hydrophilic semipermeable membrane which selectively allows water to permeate while hardly permeating an oily substance, and has a magnification of 10,000 times. It is preferable that the pores are not substantially confirmed in the active layer of the film even by observation with an electron microscope, and that the film is made of a film material having a hydroxyl group. The membrane material is preferably a cellulose-based material such as regenerated cellulose or a saponified product of cellulose acetate, and β-polyglucose formed by binding glucose by β-glucoside bonds can be exemplified as a particularly preferable one. Further, the membrane may be a composite membrane as long as the active layer is a cellulose type. The type of module using the above-mentioned membrane is not particularly limited, and is flat type,
Various types such as cylindrical type, spiral type, and hollow fiber type can be used. Among these, the hollow fiber type is preferable, and as a cellulosic hollow fiber, an inner diameter of 300 to 1000 is particularly preferable.
μm, outer diameter is 500-1500 μm, molecular weight cutoff is 2
It is preferable to use an internal pressure type by using a cross flow method of 30,000 to 100,000 and a circulation flow rate of 1/5 to 1/10 of that of a normal ultrafiltration membrane.

The permeated water treated by the method of the present invention usually has a BOD (biochemical oxygen demand) of 600 mg / liter or less, and may be discharged as it is to sewage, but it may be further treated with a reverse osmosis membrane or activated carbon. By treatment, it can be recycled to the water washing tank in the water washing step and reused.

Further, if the wastewater treatment is continuously continued for a long time, the performance of the oil-water separating semipermeable membrane is gradually lowered and the amount of permeated water is lowered. In that case, for example, in the case of a hollow fiber type module, the performance of the membrane can be restored by backwashing from the permeation side of the membrane. The backwash can be usually performed from the backwash line using clean pressurized water such as pressurized tap water.

Further, as another method of cleaning the membrane for recovering the performance of the oil-water separating semipermeable membrane, it is preferable to use an aqueous solution of a lower alcohol such as methanol, ethanol or isopropyl alcohol, particularly an isopropyl alcohol aqueous solution from the viewpoint of operability and economy. , The concentration of the aqueous solution is 5
It is preferably in the range of 40% by weight.

[0011]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

(Embodiment 1) According to the process chart shown in FIG. 1, the waste water from the water cleaning process performed after the solder flux residue is cleaned and removed from the mounted printed wiring board using a petroleum hydrocarbon-based CFC substitute cleaning agent is treated. did. In FIG. 1, the mounted printed wiring board (not shown) that has been cleaned with the CFC substitute cleaning agent is cleaned in the order of the first washing tank 1, the second washing tank 2, and the third washing tank 3 as a washing process. Pure water 10 is supplied to the third water washing tank 3, and the wash water overflowing from the third water washing tank 3 sequentially flows toward the first water washing tank 1. Therefore, the first water washing tank 1 has the highest concentration of the CFC substitute cleaning agent. The washing waste water stored in the first water washing tank 1 was sent to the oil / water separation semipermeable membrane 6 through the prefilter 5 by the water feed pump 4 to be concentrated. The concentrated water was discharged to the outside of the system through the concentration line 8, while the permeated water was discharged to the sewer through the permeated water discharge line 7.

As the oil-water separating semipermeable membrane 6, a hollow fiber type module having a filtration area of 4 m ² was used. The module is made of cellulosic material and has an inner diameter of 400 μm and outer diameter of 65
It is a hollow fiber type with an internal pressure of 0 μm and a molecular weight cutoff of 60,000
0, filtration method is cross-flow method, working pH range 6-9,
A temperature range of 5 to 65 ° C. was used. As the prefilter 5, a microfiltration membrane having a pore size of 20 μm was used. The TOC concentration in the cleaning wastewater of the treated first washing tank 1 is 1000 mg / liter, and the flow rate is 61.5 m ³ / h.
It was sent to the oil-water separation semipermeable membrane 6 at r. As a result, in the steady state, the flow rate of the permeated water discharge line 7 was 60 m ³ / hr and its TOC concentration was 450 mg / liter.
The TOC concentration in the concentration line 8 was 25,000 mg / liter, and the concentration was about 25 times.

(Example 2) Instead of the first washing tank washing drainage treated in Example 1, a washing drainage 11 having a TOC concentration of 1000 mg / liter was used, and the treatment was performed according to the flow schematically shown in FIG. 2 that are the same as those in FIG. 1 are the same. The TOC concentration of permeated water obtained by treating with the oil-water separation semipermeable membrane 6 was 435 mg / liter. The change with time of the permeation flux of the oil-water separation semipermeable membrane in this case is shown by ◯ in FIG. The horizontal axis of Fig. 3 shows the cumulative operating time (h
r), the vertical axis is the permeation flux at 40 ° C. (liter / m
² · hr) is shown. The permeation flux gradually decreases,
By performing a backwash (indicated by a thin arrow in the figure),
Performance has recovered to some extent. For backwashing, a backwashing line 9 was used, and pressurized tap water having a pressure of ^{2 to 3} kg / cm ² was used to feed water from the permeate side. After 170 hours of drainage treatment under the same conditions, the membrane was chemically washed from the inside with a 30% by weight aqueous solution of isopropyl alcohol, and the performance was extremely recovered as shown by the thick arrow in FIG.

(Comparative Example 1) In Example 2, the result when backwashing was not carried out is shown by ● in FIG. From FIG. 3, it can be seen that the permeation flux gradually decreases if the treatment is continued without backwashing periodically.

[0016]

EFFECTS OF THE INVENTION According to the present invention, wastewater from a water washing step performed after the solder flux residue of a mounted printed wiring board is washed and removed by using a CFC substitute cleaning agent containing a surfactant, is selectively separated into oil and water. By using the semipermeable membrane, the TOC concentration of the permeated water could be reduced by about 50%, and it became possible to discharge it into the sewer. Also, the water discharged from the concentration line will be 1 / 50th the raw water by concentrating it about 50 times.
It can be reduced to 50.

[Brief description of drawings]

FIG. 1 is a schematic process diagram illustrating a first embodiment of a wastewater treatment method of the present invention.

FIG. 2 is a schematic process diagram illustrating a method for cleaning a membrane of the present invention (Example 2) using a backwash line.

FIG. 3 is a diagram showing changes with time of permeation flow rates obtained in Example 2 and Comparative Example 1.

[Explanation of symbols]

 1 1st water washing tank 2 2nd water washing tank 3 3rd water washing tank 4 Water pump 5 Prefilter 6 Oil-water separation semipermeable membrane 7 Permeate discharge line 8 Concentration line 9 Backwash line 10 Pure water 11 Raw water

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[Procedure amendment]

[Submission date] September 1, 1993

[Procedure Amendment 2]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

4. The waste water from the water washing step performed after the solder flux residue of the mounted printed wiring board is removed by washing with a CFC substitute cleaning agent containing a surfactant, is concentrated by a water-selective oil-water separating semipermeable membrane. A method for recovering the performance of an oil / water separation semipermeable membrane, which comprises backwashing an oil / water separation semipermeable membrane whose concentration treatment performance has decreased due to treatment from the permeation side of the membrane.

5. The waste water from the water washing step performed after the solder flux residue of the mounted printed wiring board is washed and removed using a CFC substitute cleaning agent containing a surfactant, is concentrated by a water-selective oil-water separation semipermeable membrane. A method for recovering the performance of an oil / water separation semipermeable membrane by washing an oil / water separation semipermeable membrane whose concentration treatment performance has deteriorated by treatment with isopropyl alcohol.

Claims (1)

Claim: What is claimed is: 1. The waste water from the water washing step, which is performed after the solder flux residue of the mounted printed wiring board is removed by washing with a CFC substitute cleaning agent containing a surfactant, is selected as a water selective permeation agent. A wastewater treatment method, characterized by concentrating with an oil-water separation semipermeable membrane. 2. The oil-water separating semipermeable membrane having selective water permeability is a cellulosic hollow fiber type semipermeable membrane in which substantially no pores can be confirmed by observing with an electron microscope at a magnification of 10,000 times. Wastewater treatment method described in 1. 3. The total organic carbon concentration (TOC) is 1000 m.
The wastewater treatment method according to claim 1, wherein the wastewater treatment method is applied to wastewater of g / liter or less. 5. Waste water from a water washing step performed after the solder flux residue of a mounted printed wiring board is removed by washing with a CFC substitute cleaning agent containing a surfactant is concentrated by a water-selective oil-water separating semipermeable membrane. A method for recovering the performance of an oil / water separation semipermeable membrane, which comprises backwashing an oil / water separation semipermeable membrane whose concentration treatment performance has decreased due to treatment from the permeation side of the membrane. 6. The waste water from a water washing step performed after the solder flux residue of a mounted printed wiring board is removed by washing with a CFC substitute cleaning agent containing a surfactant, is concentrated by an oil-water separating semipermeable membrane having selective water permeability. A method for recovering the performance of an oil / water separation semipermeable membrane by washing an oil / water separation semipermeable membrane whose concentration treatment performance has deteriorated by treatment with isopropyl alcohol.