JPH0515878A - Treatment of waste slicing water - Google Patents

Abstract

PURPOSE:To improve the quality of filtered water and to reuse it as the cutting water by removing the coarse grain in a waste slicing water with a filter, suppressing the propagation of bacteria with aeration and discharging the sludge consisting of bacteria and fine particles outside the system by backwashing and blowing. CONSTITUTION:A waste slicing water sent by a feed pump 9 is filtered by a cartridge filter 1, and then aerated in the circulating tank 2 provided with a polyolefin diffuser cylinder 3. The waste slicing water in the tank 2 is supplied by a circulating pump 4 to the ultrafilter membrane module 5 of polyolefin hollow fiber type having 13,000 fractional mol.wt. The filtrate is stored in a tank 6, discharged outside the system as the filtrate and reused as cutting water. The sludge consisting of bacteria and fine particles accumulated at the module inlet is backwashed and blown once a day and discharged outside the system.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a method for treating slicing wastewater. More specifically, the present invention relates to a method for treating slicing wastewater, which is obtained by filtering slicing wastewater discharged in the electronics industry with a filtration membrane and reusing the filtered water as cutting water.

[0002]

Silicon is the most commonly used semiconductor material. The processing of semiconductors using silicon includes cutting of silicon ingots. The cut crystal plate is called a wafer. A disk-shaped blade coated with diamond abrasive grains or a wire saw is used for cutting. Cutting water is used for the purpose of imparting lubricity and cooling during cutting, extending the life of the blade or wire saw, and increasing the yield of wafers. Water containing 1 to 5% of water-soluble cutting oil is used as cutting water. Since the water-soluble cutting oil is expensive and the amount of cutting water used is large, the slicing waste water containing the silicon fine particles and the water-soluble cutting oil is used again after separating the silicon fine particles. For separating fine particles and cutting water,
Filter membranes pre-coated with diatomaceous earth, microfiltration membranes and ultrafiltration membranes are used.

[0003]

However, the method of using a filter membrane in which diatomaceous earth is pre-coated on the filter cloth is not recommended.
Silicon microparticles of 5 microns or less leak, and since the filtered water is repeatedly used, bacteria propagate and the performance as cutting water deteriorates. In addition, there is a problem that the filter cloth is clogged and the processing ability is lowered, and it is difficult to wash the filter cloth when the throughput is lowered. In addition, the method that uses microfiltration membranes and ultrafiltration membranes is called sludge consisting of bacteria and silicon fine particles that have propagated, resulting in a decrease in treatment capacity due to clogging of the inlet of the membrane module and a decrease in treatment capacity due to clogging of the membrane surface. There was a problem.

[0004]

Means for Solving the Problems As a result of intensive studies for solving the above-mentioned problems, the present inventors found that most of the clogging of the entrance of the membrane module by the metabolic products of bacteria is due to the metabolism of anaerobic bacteria. Found to be by product, significantly improved by aeration, and the inlet of the membrane module is pre-filtered to remove coarse particles, while the backwash blow and / or the reverse circulation blow causes the membrane to The inventors have found that the problem can be solved by discharging sludge consisting of bacteria and fine particles clogging the module inlet to the outside of the system of a slicing drainage filtration device, and completed the present invention.

That is, according to the present invention, in a treatment method in which slicing waste water is filtered with a filtration membrane and the filtered water is reused as cutting water, (1) removing coarse particles in advance with a filter, and (2) bacterial growth. It is a method for treating slicing wastewater, which is characterized by suppressing by aeration, and (3) discharging sludge consisting of bacteria and fine particles to the outside of the system of a slicing wastewater filtering apparatus by backwash blow and / or reverse circulation blow.

The present invention will be described in detail below. First, a specific example will be described of a method for treating slicing wastewater containing coarse particles and fine particles of silicon and water-soluble cutting oil discharged by cutting a silicon ingot. The filter used for removing coarse particles in advance in the present invention may be any as long as it cuts silicon and other coarse particles,
Cartridge filters or bag filters with pores of short diameter 25-200 microns are suitable. The filter should be replaced when the pressure gauge attached to the filter reaches a certain pressure.

Aerobic bacteria, anaerobic bacteria, sulfate-reducing bacteria and the like propagate in the slicing wastewater, but the aeration suppresses the growth of anaerobic bacteria and sulfate-reducing bacteria. The location and method of aeration are not particularly limited as long as they are in the slicing wastewater treatment system, but a pit or tank for storing the slicing wastewater and a pipe having a flow of the slicing wastewater of 0.1 micron to a commercially available cylinder or cylinder are used It is advisable to install a dispersion cylinder with 5 mm holes at the bottom of the container. Air is preferably supplied at 100 to 2000 liters / hour per 1000 liters of slicing waste water.

Bacteria and silicon fine particles in the circulation tank are periodically removed from the inside of the filtration device to the outside of the device by means such as backwash blow by a valve and piping for removing the bacteria and silicon fine particles. That is, the sludge made up of bacteria and fine particles clogging the inlet of the filtration membrane is backwashed with filtered water or the slicing wastewater is subjected to reverse circulation blowing. Alternatively, by using both of them together, sludge-forming bacteria and silicon fine particles at the inlet of the membrane module can be discharged out of the apparatus together with the concentrated slicing waste water.

Since the size of the silicon fine particles is 15 microns or less, an ultrafiltration membrane or a microfiltration membrane having a pore size of the filtration membrane of the membrane module used in the present invention of 10 angstrom to 2 microns is suitable. The material of the film is not particularly limited, and organic films such as polysulfone resin, polyether sulfone resin, polyolefin resin, fluorine resin, polytetrafluoroethylene resin, acetyl cellulose resin, polyvinyl chloride resin, nylon resin, and alumina, zirconia. Inorganic membranes such as can be used.

The above-mentioned filtration membrane, which has been deteriorated in filtration ability after being used for a long time, can be regenerated by bringing it into contact with a strongly basic aqueous solution.
For example, if it is treated with 0.2 to 1N sodium hydroxide, the filtration capacity is restored. 100 sodium hypochlorite
The recovery effect can be further enhanced by using together up to 1000 ppm.

[0011]

EXAMPLES Hereinafter, examples and comparative examples of the present invention will be specifically described.

[0012]

Example 1 As shown in FIG. 1, the slicing wastewater sent by a supply pump (9) was filtered by a 25-micron cartridge filter (1) and then a circulation tank (2).
Accepted to. The circulation tank was provided with a 0.2-micron polyolefin dispersion cylinder (3), and aeration was performed at twice the amount of liquid in the circulation tank / hour.

Normal filtration is performed by valves V-1, V-2, V
-3 is opened, V-4, V-5 and V-6 are closed, and the slicing wastewater in the circulation tank is circulated by the circulation pump (4).
Membrane module (5) via valve V-1 (fraction molecular weight 1
3000, a polyacrylic hollow fiber type ultrafiltration membrane), and the circulating liquid is returned to the circulating tank (2) via the valve V-2. The filtrate is stored in the filtrate tank (6),
It is discharged as a filtrate out of the system and reused as cutting water (the above-mentioned route is indicated by a white arrow). In order to keep the concentration of the slicing wastewater in the circulation tank (2) constant,
Operate the liquid feed pump (7) at a frequency of 10 seconds every 10 minutes,
Open V-6 and drain the concentrate.

The sludge consisting of bacteria and fine particles clogging the entrance of the module is subjected to backwash blow and reverse circulation blow once a day. First, in the backwash blow, the circulation pump (4) is stopped, the valves V-3 and V-4 are opened, and V-1, V-2, V-5, and V-6 are closed, and the backwash pump is used. (8) is operated, and the filtrate in the filtrate tank (6) is discharged from the system V-4 to the outside of the system.

Next, in the reverse circulation blow, the backwash pump (8) is stopped, the valve V-5 is opened, and V-3 is closed,
The circulation pump (4) is operated, and the circulating liquid is discharged to the outside of the system through the valve V-4 (the routes of the backwash blow and the reverse circulation blow are indicated by →). Finally, valves V-1, V-2, V
-3 was opened, V-4 and V-5 were closed, the circulation pump (4) was operated, and normal filtration was performed.

The transparency of the obtained filtered water (JIS.K10
10) was 50 cm or more, and no bacteria were measured. The filtration capacity retained the initial 80% for 3 weeks. There was no clogging of the filtration membrane at the inlet of the membrane module due to sludge. 1
About 100,000 bacteria were measured from the 0-fold concentrated slicing wastewater.

[0017]

Comparative Example 1 Filtration was carried out in the same manner as in Example 1, but when aeration was not carried out in the circulation tank (2), the filtration capacity decreased to 40% of the initial value after 3 weeks. About 300,000 bacteria were measured from the 10 times concentrated slicing wastewater.

[0018]

[Comparative Example 2] Filtration was carried out in the same manner as in Example 1, but neither backwash blow nor reverse circulation blow was performed, and the filtration capacity was 3
It decreased to 50% of the initial value after a week.

[0019]

[Comparative Example 3] The slicing waste water was filtered using a filter membrane prepared by pre-coating diatomaceous earth on a filter cloth. Permeability of filtered water is 1
At 0 cm, about 2000 bacteria / ml were measured. The filtration capacity decreased to 30% of the initial value after one week.

[0020]

As is apparent from the above, according to the present invention, the filtered water obtained by treating the slicing wastewater has improved water quality and can be reused as cutting water. Further, since the processing capacity is stable, it is possible to automatically save labor, which is extremely useful in industry.

[Brief description of drawings]

FIG. 1 is a slicing drainage filtration device used in Example 1.

[Explanation of symbols]

 P Pressure gauge V Valve 1 Cartridge filter 2 Circulation tank 3 Dispersion cylinder 4 Circulation pump 5 Membrane module 6 Filtrate tank 7 Liquid feed pump 8 Backwash pump 9 Supply pump

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location C02F 3/02 Z 6647-4D // C02F 9/00 A 6647-4D (72) Inventor Takashi Ogawa Asahi Kasei Kogyo Co., Ltd. 1 No. 2 Samejima, Fuji City, Shizuoka Prefecture

Claims (1)

Claim: What is claimed is: 1. A treatment method in which slicing wastewater is filtered through a filtration membrane and the filtered water is reused as cutting water (1).
Remove coarse particles with a filter in advance, (2)
Suppressing the growth of bacteria by aeration,
(3) A method for treating slicing wastewater, which comprises discharging sludge composed of bacteria and fine particles to the outside of a slicing wastewater filtering device by backwashing blow and / or reverse circulation blow.