JP2876831B2 - Wastewater treatment method and apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for treating fluorine-containing organic wastewater.

[0002]

2. Description of the Related Art In recent years, in the field of electronics industry, organic wastewater containing hydrofluoric acid, methanol and the like is discharged with the advance of industrial technology. In particular, in the semiconductor manufacturing industry, a large amount of wastewater containing hydrofluoric acid and a solvent such as methanol or isopropanol used in the process is discharged.

Heretofore, for this type of wastewater, a method has been used in which hydrofluoric acid is subjected to coagulation and sedimentation treatment, and organic matter is biologically treated. In the flocculation and precipitation treatment of hydrofluoric acid, slaked lime was used and calcium fluoride was precipitated and removed by the following formula. _{^{2F - + Ca (OH) 2}} → CaF 2 ↓

Activated sludge method, catalytic oxidation method and the like have been used for biological treatment of organic substances. However, these methods cannot increase the BOD removal rate very much. Therefore, it is conceivable that high-speed processing can be performed by using immobilized microorganisms. However, combining calcium precipitation and aeration using immobilized microorganisms,
There is a drawback that the activity of the immobilized microorganism pellet gradually decreases, and the BOD removal rate decreases.

[0005]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks of the prior art and provides a fluorine-containing organic material capable of achieving a high fluorine removal rate and a high BOD removal rate without reducing the activity of the immobilized microorganism pellet. It is an object of the present invention to provide a method and an apparatus for treating wastewater.

[0006]

The inventor of the present invention has found that, after the fluorine is precipitated and removed by the calcium precipitation method, an excess of calcium ions is present in the supernatant, which is hardly soluble in calcium carbonate or the like in the aeration tank. When a calcium compound is formed and adheres to the pores of the immobilized microorganism pellet, clogging occurs and the BOD removal activity decreases. However, when calcium carbonate adheres, the color tone of the pellet changes from brown to white or the pellet diameter increases. Of calcium carbonate is determined based on the color tone and / or size of the pellet, and calcium carbonate can be dissolved and exfoliated by adjusting the pH of the solution to 6 to 7. Was.
The present invention has been completed based on such findings.

That is, in the method for treating wastewater according to the present invention, a water-soluble calcium compound is added to wastewater containing fluorine to cause coagulation and sedimentation of generated calcium fluoride, and then contacted with immobilized microorganism pellets in an aeration tank to obtain a BOD. In a method for treating wastewater comprising removing components, the presence or absence of adhesion of a poorly soluble calcium compound to a pellet of immobilized microorganisms in an aeration tank is determined based on a change in color and / or size of the pellet. The pH of the solution
-7.

Further, the wastewater treatment apparatus of the present invention is a wastewater treatment apparatus comprising a flocculation settling tank of calcium fluoride and an aeration tank through which immobilized microorganism pellets flow, and judges the color and / or size of the pellet. An image processing apparatus is provided.

In the present invention, first, fluorine contained in wastewater is removed by a calcium precipitation method. As the water-soluble calcium compound, any water-soluble calcium compound usually used in a calcium precipitation method can be used, and examples thereof include calcium hydroxide and calcium chloride. The amount of the calcium compound to be added varies depending on the concentration of fluorine contained in the wastewater. However, when calcium hydroxide is used, generally, the calcium hydroxide is added so that the pH of the wastewater becomes 9 to 12. Thereby, calcium fluoride is coagulated and precipitated. Here, if necessary,
A flocculant can be added. As the coagulant, for example, an inorganic coagulant such as aluminum sulfate, ferric sulfate, ferrous sulfate, sodium aluminate, ammonium alum or the like, or an organic coagulant composed of various polymer substances can be used.

The supernatant after the coagulation and precipitation contains a large amount of excess calcium compounds, and generally contains calcium ions at a concentration of 200 to 500 mg / l. Form soluble calcium compounds. When such a supernatant is directly contacted with the immobilized microorganism pellet and subjected to biological treatment, calcium adheres to the pores of the immobilized microorganism pellet, and clogging occurs.
Organic substances do not permeate, and the activity of removing BOD decreases.

[0011] However, this kind of deposit has a pH of 6 to
When adjusted to 7, the calcium carbonate dissolves and separates from the pellet. If the pH is out of this range, calcium carbonate does not dissolve, and the deposits on the surface of the pellet cannot be dissolved and removed. Therefore, in the present invention, in order to automatically add an acid for adjusting the pH, the presence or absence of adhesion is determined based on the color tone and / or size of the pellet.
The color tone and / or size of the pellet can be easily determined by using an image processing device connected to an underwater camera or by sampling the pellet and performing image processing.

The type of microorganism used is not particularly limited, and can be appropriately selected according to the nature of the wastewater to be treated. For example, when treating wastewater containing hydrofluoric acid and a solvent such as methanol or isopropanol discharged in the electronics industry, a large amount of an enzyme such as dehydrogenase having a molecular weight of 100,000 or more that decomposes a lower alcohol as a main component is used. Secreting microorganisms, for example, Methylomonas sp.
ylomonas sp.), Saccharomycetaceae (Saccharomycetace
ae), Sporobolomycetacea
e), yeasts such as Cryptococcaceae are suitable, and activated sludge containing a large amount of these microorganisms is most suitable.

In the present invention, the above-mentioned microorganisms are used by being immobilized and immobilized on an immobilizing material. The immobilizing material is not particularly limited, but has pores having a molecular weight cut-off of 67,000 or less and can hold enzymes such as dehydrogenase involved in the decomposition of the BOD component inside the pellet. It is preferable to use polyurethane, polyvinyl alcohol, polyethylene glycol, polyacrylamide or the like which does not elute.

As described above, when aeration treatment is performed by bringing the microorganisms into contact with the immobilized microorganism pellets, the leakage of the microorganisms is extremely small. However, in order to coprecipitate the leaked microorganisms and residual fluorine, a coagulant is added. I do. Here, as the coagulant, various inorganic or organic coagulants as described above can be used.

[0015]

FIG. 1 is a system diagram showing an embodiment of the apparatus of the present invention. When treating wastewater with the apparatus shown in FIG. 1, the wastewater is first mixed with a water-soluble calcium compound, for example, slaked lime, in the coagulation sedimentation tank 1, and hydrofluoric acid in the wastewater is precipitated and removed in the form of calcium fluoride. Next, in order to remove the BOD component by contacting the immobilized microorganism pellets flowing in the aeration tank 2 and to coprecipitate the microorganisms leaked from the immobilized microorganism pellets and the residual hydrofluoric acid in the coagulation sedimentation tank 3, a coagulant is used. Is added.

A camera 4 connected to an image processing device 5 is installed in the aeration tank 2, and the immobilized microorganism pellet is photographed by the camera 4, and the color tone and / or the size of the pellet is determined by the image processing device 5. It is analyzed and determined. When calcium carbonate adheres to the immobilized microbial pellet, the pellet changes from brown to white and the pellet diameter increases. This makes it possible to determine whether calcium carbonate has adhered to the pellets. In order to accurately determine the color and / or size of the pellet, the camera 4 is preferably placed submerged in the aeration tank 2. Therefore, the camera is preferably an underwater camera.

When it is determined that the image processing device 5 has adhered to the pellets, the acid supply device 6 is operated online, the acid is added to the aeration tank 2, the pH of the solution is adjusted to 6 to 7, and the adhered calcium carbonate is adjusted. Is dissolved and peeled off. As the acid supply device, an acid injection pump or the like is preferably used. Also,
As the acid, an inorganic acid such as hydrochloric acid or phosphoric acid is preferable. By this treatment, the activity of the immobilized microorganism pellet is improved,
It is possible to efficiently remove the BOD component.

Example 1 In this example, wastewater having a BOD of 240 to 310 mg / l of Company T was used as the water to be treated. Activated sludge containing a large amount of Methylomonas bacteria 2% by weight, polyethylene glycol dimethacrylate 8% by weight, acrylamide 5% by weight, N,
A gel was prepared using 0.5% by weight of N, N ', N'-tetramethylethylenediamine and 0.25% by weight of potassium persulfate to obtain a 3 mm square cubic immobilized microorganism pellet.

Slaked lime is added to the wastewater to perform coagulation and sedimentation.
Fluorine concentration 8-37 mg / l, BOD 240-310 mg /
of the immobilized microorganism pellets described above,
It was placed in the aeration tank 2 charged with 0% and subjected to biological treatment. As the image processing apparatus 5, HIDIC / IP-200 manufactured by Hitachi, Ltd.
Was used. It was controlled so that hydrochloric acid was added when the color of the pellet became white. The aerated water was further sent to the coagulation sedimentation tank 3 and aluminum alum was added to coprecipitate the microorganisms leaking from the pellets and residual fluorine. The BOD value of the obtained treated water was measured and is shown in Table 1 below. In addition, the composition and activity of the pellets after the treatment were measured and are shown in Table 1.

As a conventional method, the quality of the treated water, the composition and the activity of the pellets when operated without adding the hydrochloric acid and without performing the image processing were measured, and the results are shown in Table 1.

[0021]

[Table 1]

According to the present invention, it can be seen that the BOD removal rate is clearly higher and the pellet activity is higher than in the conventional method.

[0023]

According to the present invention, since a hardly soluble calcium compound such as calcium carbonate does not adhere to the immobilized microorganism pellet, the activity of the pellet does not decrease and a high BOD removal rate can be achieved for a long time.

[Brief description of the drawings]

FIG. 1 is a system diagram showing one embodiment of the apparatus of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Coagulation sedimentation tank 2 Aeration tank 4 Camera 5 Image processing device 6 Acid supply device

Claims (3)

(57) [Claims] A wastewater comprising adding a water-soluble calcium compound to a fluorine-containing wastewater, coagulating and sedimenting the generated calcium fluoride, and then contacting the immobilized microorganism pellets in an aeration tank to remove BOD components. In the treatment method, the color tone of the immobilized microorganism pellets in the aeration tank and / or
Or to determine the presence or absence of adhesion of the poorly soluble calcium compound to the pellet by the change in size, when the adhesion occurs,
A method for treating wastewater, wherein the pH of the liquid is adjusted to 6 to 7. 2. A wastewater treatment apparatus comprising a flocculation settling tank for calcium fluoride and an aeration tank for flowing immobilized microorganism pellets, wherein an image processing apparatus for judging the color tone and / or size of the pellets is provided. Wastewater treatment equipment. 3. The wastewater treatment device according to claim 2, wherein an acid supply device is connected to the image processing device.