JP2873968B2 - Wastewater treatment method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a wastewater treatment method, and more particularly, to a wastewater treatment method in a short-time and small-scale facility while preventing membrane clogging. It relates to the method of processing.

Therefore, according to the present invention, so-called annoying facilities in conventional local governments such as human waste treatment facilities and sewage facilities can be converted and improved into amenity facilities, and therefore the present invention is very useful in fields such as pollution prevention technology or environmental improvement technology. This is an important weight.

(Prior art) The physicochemical treatment method and the biological treatment method are conventionally known for the treatment of wastewater, but the biological treatment method in which microorganisms play a leading role is a self-cleaning action performed in nature. Is efficiently controlled and controlled in a specific facility, and because of its high removal rate of pollutants and low running cost, it is widely used as a method for treating organic wastewater, making a significant contribution to environmental purification. I have. It is also known that the biological treatment includes an aerobic treatment represented by the activated sludge method and an anaerobic treatment represented by the methane fermentation. (Hiroshi Iizuka, “Bio-industry and patents,” Chalk Shobo, June 9, 1989, pp. 73-84).

A fluidized bed capable of performing aerobic treatment and anaerobic treatment in one tank and directly treating, for example, human waste without diluting the same has been already developed by the present inventors (Japanese Patent Application Laid-Open No. Sho. 58-166994).

On the other hand, there is also known a wastewater treatment system characterized by treating treated water subjected to activated sludge treatment with an ultrafiltration membrane.

That is, as shown in FIG. 2, the material 1 to be treated, such as human waste and septic tank sludge, flows into the receiving facility 2 and is crushed, after which the impurities are removed by the impurity removing device 3 and stored. The removed impurities are incinerated4.

The treatment object sent from the storage tank 5 is treated in the reaction tank 6-1 and then treated with activated sludge in the circulation 6-2.
A part of the activated sludge is taken out and treated in the sludge treatment equipment 10, and the effluent from the circulation tank 6-2 is separated by an ultrafiltration membrane (hereinafter, referred to as an ultrafiltration membrane).
The solid-liquid separation treatment is performed by the separation device 13.

The concentrated liquid is returned to the reaction tank 6-1 and the above processing is repeated again. On the other hand, the permeated liquid is temporarily stored in the storage tank 13-1 and then subjected to the coagulation processing in the coagulation equipment 13-2 to generate the resulting processing. The water is sent to the activated carbon adsorption equipment 14 and then discharged 15.

(Problems to be Solved by the Invention) In such a conventional method, first, in the former method using a fluidized bed, it is necessary to coagulate and settle the treated water. Not only is equipment required, but even if a flocculant is used, it takes a long time to settle and precipitate SS components and the like.

In the latter method using a UF membrane, clogging of the membrane occurs in a short period of time as the processing is started, not only greatly reducing the operation rate but also causing the apparatus itself to stop operating. In addition, there is no definitive industrial solution as a pretreatment for preventing clogging, and the disadvantage that the UF membrane treatment itself requires a long time is inevitable.

(Means for Solving the Problems) The present invention has been made to solve the above-mentioned disadvantages all at once, and does not save a settling tank which requires a long treatment time and extensive equipment in wastewater treatment. To omit
From the viewpoint that UF membrane treatment is suitable.

Therefore, as a result of studying various aspects to develop technology to prevent clogging, which is a major drawback in UF membrane treatment, as a result of adding a flocculant to the treated water from the biological treatment process, the sludge was mechanically separated and removed. When the water separation was sent to the UF membrane separator by a pump via the circulation tank and processed, not only clogging of the membrane did not occur, but also the concentrated water was returned to the circulation tank and the UF membrane separation processing was possible again. In addition, we have obtained new and useful knowledge that this cycle can be performed at high speed.

The present invention has been based on this new finding, and as a result of further research, has found that it is suitable as a biological treatment method for implementing a fluidized bed, and has completed the present invention.

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

FIG. 1 is a block diagram illustrating an example of a system for implementing the present invention. In the drawing, first, water to be treated (for example, human waste, septic tank sludge, etc.) 1 is removed into a receiving facility 2 after removing a substance having a large specific gravity, such as sand, and then crushed. And quantitatively sent to the primary processing step. The contaminant removal device 3 is a combination of a drum screen and a screw press, and has two stages, a coarse screen and a fine screen, to remove the fiber content. The contaminants removed by the contaminant removal device 3 are disposed of by an appropriate method such as incineration 4.

The human waste and the septic tank sludge sent from the storage tank 5 are subjected to primary treatment. That is, the fluidized bed 6 decomposes BOD / COD (organic matter) and nitrogen components by high and low circulating flow by the air lift function.

The treated water from the fluidized bed 6 flows down to the finishing tank 7, where remaining organic matter and nitrogen components are removed. Other finishing tank 7
Then, sludge dewatering separation liquid, plant wastewater, etc. are treated to complete the biological treatment. Next, in the solid-liquid separation device 8,
A flocculant is added to the effluent of the finishing tank, and the sludge is separated and concentrated effectively by the screen. As the flocculant, a polymer or the like commonly used in the art can be appropriately used, and examples thereof include: ferric chloride, ferrous chloride,
Chlorinated wire van, sodium aluminate, aluminum sulfate, lime, sodium polyacrylate and other commonly used polymer flocculants.

Here, the fluidized bed is, as disclosed in JP-A-58-166994, a tower-like water tank, and a draft tube is installed in the center of the tank, and is injected into the draft tube. Due to the air lift effect of the air, high vertical circulating flow occurs in the tank, and at the same time, oxygen necessary for the microbial reaction is supplied.

The inside of the tank is 12,000mg with microorganism-immobilized carrier and suspended sludge.
A sludge concentration of about / is preserved and consists of an upper part where DO (dissolved oxygen) is abundant and a lower part where DO is not present. Such microbial environmental conditions enhance the nitrification denitrification reaction.

Supported by high circulation (about 1,000 times / day) and high activity / high sludge age, stable treatment of BOD99% and T-N95% removal continues, and it is an excellent fluid bed that is resistant to load fluctuations. Demonstrate the processing effect. The treated water flows down to the finishing tank together with the suspended sludge, and the immobilized carrier is separated by the carrier separating device and stays in the tank.

Therefore, in the fluidized bed, high-concentration sludge can be secured without returning sludge, and there is no need for membrane concentration.

According to the fluidized bed, most of the microorganisms remain in the tank because they are immobilized. Therefore, the amount of sludge flowing out of the tank is small. Is separated and removed, so that the stock solution to be subjected to the UF membrane treatment has already substantially removed the cause of clogging at this point in comparison with the conventional system. Therefore, any system other than a fluidized bed can be freely used in the present invention as long as the system does not allow a large amount of clogging substances such as activated sludge to flow out of the tank.

The sludge separated by the solid-liquid separation device 8 is dewatered by a sludge dewatering machine 9 and then sent to a sludge treatment facility 10 where it is finally treated according to incineration and composting methods. When the separated sludge is incinerated, the sludge treatment facility 10 can be substituted by the incineration facility 4.

In the solid-liquid separation (separation of sludge), according to the present method, the biologically treated excess sludge is fresh, and thus has a very good dehydration property.

The sludge separated water (primary treated water) after separation and removal of the sludge by the solid-liquid separation device 8 is purified as SS when the raw waste liquid is, for example, raw manure, down to 100 mg / or less. In this method, further purification treatment is performed.

That is, the sludge separation water is sufficiently mixed with the flocculant in the mixing tank 11 by a commonly used stirring means such as mechanical stirring. As the flocculant, those well-known in the industry, including those described above, are appropriately used. When ferric chloride is used as a flocculant, the pH in the tank drops to about 2.5,
Such iron cannot be directly processed in the next step, since iron is also considerably reduced. This is because, for example, activated carbon or the like is significantly damaged, and its effect is rapidly reduced.

Therefore, the conventional method required extensive precipitation equipment, and further required other post-treatments. Therefore, as described above, reducing or completely omitting such processing is one of the important objects of the present invention.

Therefore, in the present invention, in order to further purify the primary treated water without providing a settling facility such as a settling tank or a settling tank,
The following system was newly adopted.

That is, the sludge separated water treated with the flocculant is immediately sent to the circulation tank or the storage tank 12 as the flocculated mixed water without performing the precipitation treatment as in the conventional method. Add an oxidizing agent while aerating here, and add an alkali if necessary.
The pH rises to about 5.5 to 7, and iron and / or other solids also form flocs with or alone with iron and separate and precipitate in slurry.

Since the chemically oxidized and aggregated flocs formed in this way have a sufficient size, the UF membrane separation treatment is directly performed as aggregated mixed water while containing these flocs without separating them. Also, it was confirmed that clogging of the film did not occur. Here, for the first time, the present invention enables industrial separation treatment of high-concentration wastewater using a UF membrane.

In the circulation tank, aeration is not sufficient just as described above, and an oxidizing agent is also added. The amount is 0 ₂ as normal 10 to 1000 mg /, but preferably a 50 to 100 mg /,
It is appropriately selected according to the type and concentration of the wastewater to be treated.
Oxidizing agents include hydrogen peroxide, potassium permanganate, potassium periodate, chromic acid, potassium chromate, potassium dichromate, sodium peroxide, barium peroxide and other permanganates (salts), chromate compounds Conventional oxidizing agents such as peroxides, peroxides, oxyacids, and oxides can be used as appropriate. The oxidizing agent may be added in the mixing tank or upstream thereof.

As the alkali, hydroxides of alkali (±) metals and other commonly used alkali agents are appropriately used, and usually, caustic soda or caustic potash is used in solid and / or liquid form.

Further, the amount of the coagulant used varies depending on its type, the type and amount of wastewater to be treated, but in the case of ferric chloride, usually 50 to 4000 mg / Fe, preferably 100 ~ 1500mg /, particularly preferably 200 ~ 900mg /
It is about.

The coagulated mixed water in the circulation tank 12 may be sent to the UF membrane separation device 13 or at least a part thereof may be returned to the solid-liquid separation device 8 as necessary, and this cycle may be repeated.

The coagulated mixed water is taken out of the circulation tank 12 and is removed from the UF membrane separation device.
Process at 13. As the UF membrane separation device, a polyacrylonitrile-based or polyethersulfonate-based known separation device using a known UF membrane can be appropriately used. There is no particular limitation on the module type, too, such as tubular, hollow, pleated,
Various modules such as a spiral can be used as appropriate.

The permeate treated in the separation device 13 is sent to the next step as secondary treated water, while the concentrated solution is returned to the circulation tank 12,
Repeat this cycle. In the present invention, as described above, clogging does not occur in the UF membrane due to the specific pretreatment, so that if necessary, the pump P is further operated to perform high-speed circulation of liquid, high-speed processing, Processing can be performed.

Therefore, according to the present invention, since the following effects are particularly exhibited, it has become possible to industrially effectively use the UF membrane separation device, which could not be effectively used in the past, for the first time. : (1) No clogging occurs because there is no fibrous or activated sludge.

(2) The permeate flow rate (Flux) is large.

(3) The film process is simple in one place.

(4) It is less susceptible to fluctuations in biological processes.

In this way, by performing solid-liquid separation of the coagulated water by the UF membrane separation device, COD, phosphorus, chromaticity, and the like are efficiently removed, and good treated water can be stably obtained.

The permeate (secondarily treated water) from the UF membrane separation device 13 is discharged 15 after performing the advanced treatment 14. For the advanced treatment, a conventionally used method such as activated carbon adsorption treatment is appropriately used. As described above, the secondary treatment water is subjected to the activated carbon adsorption treatment, and the remaining chromaticity, COD, and the like are highly removed.

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

Example 1 Collected raw manure (BOD13,500mg /, COD7000mg /, SS
21,000 mg /, TN 5000 mg /, TP 400 mg /) were processed by the system shown in FIG.

As the fluidized bed, the same type as in JP-A-58-166994 was used, aeration was performed at 420 m ³ / h, and the sludge concentration in the tank was maintained at about 12,000 mg / h.

In the solid-liquid separator, a polymer (cationic) was added at 100 mg / coagulant to separate sludge and liquid. The properties of the liquid part (primary treated water) are described in the first section below.
It was as shown in the table.

Hydrogen peroxide was used as an oxidizing agent, and was added so that the O ₂ concentration in the mixing tank was in the range of 50 to 100 mg /. Ferric chloride is used as a coagulant, and 600 mg / Fe
It was added to maintain the degree. The pH of the mixing tank was 2.5.

In the circulation tank, use aeration at 6 m ³ / h, NaO
H was added to adjust the pH to 6.

As the UF membrane separation device, a DUY-LOOO tubular module (trade name of Daicel Chemical Industries, Ltd.) was used, and the liquid sending flow rate was 1.
Operation was performed at 2 m ³ / h and pressure <20 mg / cm ³ . The properties of the obtained permeate (secondarily treated water) were as shown in Table 1.

The permeate was subjected to advanced treatment by activated carbon treatment.
The properties of the obtained highly treated water are as shown in Table 1, and it was confirmed that the raw sewage was almost completely treated and could be discharged directly to rivers.

(Effects of the Invention) According to the present invention, since the main reaction tank is of a fluidized bed type using a microorganism-immobilized carrier, a generally provided membrane separation device mainly for returning sludge is not required.

In addition, since this system incorporates a membrane separation device in the coagulation process, as a final overall finish after biological treatment and coagulation treatment, the system is passed through a membrane to ensure processing reliability and simplify the system. It is possible to obtain good results such as stable processing and easy management.

In the weakly acidic agglomeration + UF membrane separation method according to the present invention, since the colloidal substance is aggregated and flocculated,
Even if a membrane having a relatively high molecular weight cut-off is used, formation of a gel layer and clogging of pores are unlikely to occur, and the quality of permeated water does not change, so that a membrane having a molecular weight cut-off of 40,000 or more can be used. The water has a clear water quality without any E. coli as well as SS, and advanced processing with reduced space and processing time has become possible.

[Brief description of the drawings]

FIG. 1 shows an example of an apparatus for carrying out the present invention, and FIG. 2 shows a conventional apparatus.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI C02F 9/00 501 C02F 9/00 501B 502 502P 502R 502G 503 503D 504 504A 504E (58) Fields surveyed (Int. Cl. ⁶ , (DB name) C02F 1/44 C02F 1/52 C02F 1/72 C02F 3/08 C02F 9/00-9/00 504 B01D 65/08

Claims (2)

(57) [Claims] 1. A method for separating sludge by treating a pretreated wastewater by passing it through a fluidized bed while passing through a fluidized bed, and then treating the wastewater with a flocculant in a solid-liquid separator provided with a screen without passing through a sedimentation tank. The sludge separated water is treated with a flocculant in a mixing tank, and the flocculated mixed water obtained is brought into contact with an oxidizing agent while being aerated in a circulation tank without settling, to form flocs, and then directly To the ultrafiltration device, and the permeate is sent to the next step, while the concentrate is returned and sent back to the ultrafiltration device, and if necessary, the cycle is repeated, and thus the ultrafiltration device A method for treating wastewater, comprising subjecting the separated permeate to an advanced treatment according to a conventional method. 2. The method according to claim 1, wherein the wastewater is human waste and / or septic tank sludge.