JPH0710390B2 - Method for forming microbial flocs - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming microbial flocs for treating sewage in a short period of time in an apparatus for biologically treating sewage. It is related to the technology.

[0002]

As a method for biologically removing pollutants such as organic substances and inorganic substances contained in sewage and industrial wastewater, aerobic biological treatment methods such as activated sludge method and contact aeration method, and methane Anaerobic biological treatment methods such as fermentation, digestion and acid fermentation are known.

[0003] The activated sludge method is a method which is generally widespread because it can aerobically and efficiently remove organic pollutants from wastewater. Further, the methane fermentation method is a method that is widely used in the fields of human waste treatment and food processing wastewater treatment because it can anaerobically remove high-concentration organic pollutants.

In these biological treatment methods, the microorganisms are present as microbial flocs, and it is basically necessary to rapidly settle and separate the pollutants after decomposing and removing the pollutants to release the treated supernatant water.

Therefore, the microorganisms in the treatment equipment have a particle size of 10
The point is to form microbial flocs of 0 to 500 μm and have sufficient sedimentation properties.

As a method of expressing the function of the treatment apparatus (so-called startup), a method of transplanting biological sludge from another biological treatment apparatus, a method of using a microbial preparation, etc. are generally performed.

However, the process until the proliferated microorganisms form flocs naturally waits for the formation of floc-forming bacteria, which requires a very long period of time.

In addition, depending on the type of pollutant, the growth of floc-forming bacteria may be hindered and floc formation may not be possible, and in reality, there are many devices in which the propagated microorganisms are operated without forming microbial flocs.

As a method for shaping the grown useful microorganisms into particles, an entrapping immobilization method has been proposed in recent years. (Japanese Patent Publication No. 63-52556, Japanese Patent Publication Nos. 1-8599 and 1-37987)

In these methods, the useful microorganisms that have proliferated are taken out of the wastewater treatment equipment by using a flocculating agent, a centrifugal separation method, etc., and a fixing agent that gels by a chemical reaction with the proliferating agent is added to the microorganisms in the gel body. It is a method of fixing it comprehensively on the device and then returning it to the processing device.

However, in these methods, since it is necessary to take out useful microorganisms from the treatment apparatus once by using a physicochemical method, the operation is complicated and the microorganisms are caused to gel by using a chemical reaction harmful to the microorganisms. There was a problem that the damage given to the

[0012]

In the method of the present invention, in the formation of microbial flocs, which is an important point in the biological treatment of pollutants, in view of the fact that waiting for the formation of the flocs naturally, the microbial flocs are removed at an early stage. It is intended to provide a method of forming.

[0013]

The present inventors have conducted various tests in order to solve such problems, and as a result, have found that the biological treatment apparatus for sewage has a carboxymethyl group substitution degree of 0.2.
The intended purpose by adding a mixed composition of carboxymethyl cellulose (hereinafter abbreviated as low DS-CMC) in the range of 0.5 to 0.5 and clay mineral powder and a metal salt which dissolves in water and hydrolyzes to generate a positive charge. The inventors have found that the above can be achieved, and have completed the present invention.

Low DS- used in the practice of the invention
CMC is synthesized by a solvent method, a water medium method, or another carboxymethyl cellulose synthesis method. Generally, carboxymethyl cellulose is synthesized using cellulose, sodium hydroxide, and monochloroacetic acid as raw materials, but carboxymethyl cellulose having an arbitrary degree of substitution can be synthesized by adjusting the molar ratio of these raw materials in the reaction.

The substitution degree used in the present invention is from 0.2 to
A low DS-CMC of 0.5 has a molar ratio of cellulose: sodium hydroxide: monochloroacetic acid of 1: 0.7 to 1.2: 0.25 to 0.
Set arbitrarily within the range of 7, reaction temperature 70 ℃ reaction time 3
It is obtained by reacting under the conditions of time, neutralizing excess sodium hydroxide after completion of the reaction, separating from the solvent and drying.

The clay mineral powder used in the practice of the present invention includes kaolin, activated clay, bentonite, diatomaceous earth, perlite, talc, silt, dolomite, magnesite, vermiculite having a particle size of 10 μm to 100 μm. , Limestone, natural zeolite and the like, and among these, perlite, diatomaceous earth, and kaolin are suitable because the particle surface has many irregularities and microorganisms are easily attached.

Low DS-C used in the practice of the invention
A mixed composition of MC and a clay mineral can be obtained by a method of dry mixing these two components, a method of adding a small amount of water with stirring and granulating, or the like, but the clay mineral is contained in a partially hydrous sol of low DS-CMC. In order to form a structure in which particles are present, a method in which a small amount of water is added while mixing and stirring these two components and granulation is preferable.

The weight blending ratio of the low DS-CMC and the clay mineral powder is preferably in the range of 8: 2 to 3: 7, and the addition amount of these mixed compositions to the biological treatment equipment depends on the tank volume of the equipment. On the other hand, 100 to 1,000 ppm is preferable.

As the metal salt used in the practice of the present invention, any metal salt can be used as long as it is soluble in water and hydrolyzed to form a positively charged metal hydroxide. Considering the properties, aluminum sulfate, aluminum chloride, ferrous sulfate or ferric sulfate, ferrous chloride or ferric chloride are preferable. The amount of these metal salts added to the biological treatment device is 20 to 20 relative to the tank volume of the device.
0 ppm is preferred.

In the embodiment of the present invention, when seeding a biological treatment apparatus and at the same time adding a composition of low DS-CMC and clay mineral powder and a metal salt to a biological treatment tank, seeding has already been carried out and microorganisms are It may be added in the state where it is proliferating but microbial flocs are not formed.
In either case, microbial flocs can be formed in a short period of time.

[0021]

It is known that carboxylmethyl cellulose behaves differently in water depending on the substitution degree of carboxymethyl group. When DS is 0.2 or less, the characteristics are the same as cellulose, and it is hardly dissolved in water. Substitution degree is 0.2 ~
In the range of 0.5, a partially water-soluble state is produced, and an insoluble portion and a hydrous sol portion coexist. When the degree of substitution is 0.5 or more, it becomes completely water-soluble and the aqueous solution becomes viscous.

Since the microorganisms used in the biological treatment apparatus are negatively charged, the grown microorganisms are less likely to aggregate,
Microorganism flocs are not formed unless the bacteria that produce sticky organic substances called floc-forming bacteria grow.

The method of the present invention electrically neutralizes the negative charge of the microorganisms grown in the biological treatment tank to facilitate the aggregation, while the microorganisms are added to the partially sol-like substance of low DS-CMC containing clay mineral particles. By attaching them, microbial flocs are formed without waiting for the generation of floc-forming bacteria. Here, the clay mineral particles act as an attachment nucleus for microorganisms and as a weight agent for maintaining the sedimentation of the formed microbial flocs.

Since the low DS-CMC has biodegradability, it is gradually decomposed in the formed microbial flocs, and transferred to the microbial flocs with the clay mineral as the nucleus while maintaining the floc shape.

[0025]

Example 1 40 g of sodium hydroxide, 2000 g of isopropyl alcohol and 300 g of water were charged into a reaction vessel and stirred at room temperature for 1 hour to dissolve sodium hydroxide, and then 180 g of crushed pulp of softwood was added for 15 minutes. Stir.
Next, add 52 g of monochloroacetic acid and stir for 15 minutes.
Heat to ℃ and react for 3 hours.

After the reaction, excess sodium hydroxide is neutralized with sulfuric acid, the reaction product is collected by centrifugation and dried at a temperature of 100 ° C. for 2 hours. Low DS-C thus obtained
The substitution degree of MC was 0.41.

40 g of the low DS-CMC, 60 g of an average particle diameter of 24 μm as a clay mineral and 10 g of water were charged in a high-speed mixer and mixed and stirred for 20 minutes to obtain a granulated mixed composition.

In an aerobic biological treatment apparatus having an aeration tank volume of 10 liters and a sedimentation tank volume of 4 liters, a treatment system was set up in which sewage BOD of 250 mg / 1 was used and operated at a volume load of 0.7 kg BOD / m ³ · day. The activated sludge of the sewage treatment plant was seeded as an inoculum, and at the same time, 5 g of the composition and 1 g of aluminum sulfate crystals were added and the operation was continued.

The results of the test are shown in Table 1,
When the size of microbial flocs was measured with a microscope micrometer, it was 200 μm or more from the third day of operation, and the treated water had a BOD of 15 ppm or less and SS10
We were able to maintain ppm or less and transparency of 15 cm or more.

[0030]

[Table 1]

[0031]

Examples 2-11 Specific low DS-Cs shown in Table 2
The same treatment method and operation as in Example 1 were repeated using MC, clay mineral and metal salt in the predetermined proportions.

[0032]

[Table 2]

These test methods are as shown in Table 3, and in each case, microbial flocs were formed in a short period of time, and BOD, SS and transparency of the treated water were good. .

[0034]

[Table 3]

[0035]

Comparative Example 1 In Example 1, the aerobic biological treatment apparatus was operated in exactly the same operation without adding the mixed composition of low DS-CMC and clay mineral and the metal salt. The results of this test are shown in Table 4, and the size of the microbial flocs was 10 even at the time of 2 to 3 weeks after the start of operation.
It was 0 μm or less, and the treated water contained a large amount of many free cells, and it took a long time to stabilize the transparency and BOD of the treated water slowly.

[0036]

[Table 4]

[0037]

[Example 12] Batting tank volume 400 m ³ settling tank volume 14
In 0 m ^3, it was field tested using apparatus of certain meat processing centers that drainage average BOD450mg / l volume loading 0.9kgBOD / m ³ · day. Despite the fact that 2 months have passed since the seed sludge seeding, the average particle size of microbial flocs is 50-60.
μm, many free cells, treated water BOD178mg /
1, SS430 mg / l, transparency 6 cm, and the processing condition was very bad.

200 kg of a mixed composition of the same low DS-CMC and perlite powder as in Example 1 and aluminum sulfate crystals 4
The operation was continued by adding 0 kg. As a result of the treatment, the average particle size of microbial flocs was 200-250μ on the 7th day.
m and the amount of free cells was drastically reduced. B of treated water
The OD was 62 mg / l, the SS was 24 mg / l, the transparency was 21 cm, and the processing function was good. Further, the test was continued for 2 months, and the average particle size of the microbial flocs and the treated water quality were measured on the 14th, 30th and 60th days, and the good treating function measured on the 7th day was maintained. .

[0039]

[Embodiment 13] In an upflow anaerobic sludge bed treatment apparatus having a reaction tank volume of 6 liters, a volume load of 20 kg COD / m ³ · using artificial starch drainage of COD 20,000 mg / l.
A treatment system was set up at a liquid temperature of 37 ° C. daily. At the same time as inoculating the digestion sludge of the urine treatment plant as an inoculum into the above-mentioned treatment equipment, 2.2 g of CMC of DS0.35 and an average particle size of 24
Table 5 shows the test results when 5 g of the mixed composition of 2.8 g of pearlite having a size of μm and 0.6 g of aluminum sulfate crystals were added and the operation was continued.

[0040]

[Table 5]

As a result, the size of the microbial flocs became 200 μm or more from the second week after the start of operation, and the granules became about 1 mm after 1.5 months. C of treated water
OD is 3,400 mg / l in 2 weeks (removal rate 83%)
It became 1,200 mg / l (removal rate 94%) after 1.5 months.

[0042]

Comparative Example 2 The anaerobic treatment apparatus was operated in the same manner as in Example 13 without adding the mixed composition of low DS-CMC and clay mineral and the metal salt in Example 13. The results of this test are as shown in Table 6, and the size of the microbial flocs was 200 μm or less until 2 months after the start of operation.
It was estimated that it would take more than 6 months to make granules of about mm.

[0043]

[Table 6]

[0044]

According to the present invention, microbial flocs necessary for biological treatment of wastewater can be formed in a short period of time, and the function of the biological treatment unit can be expressed in a short period of time. Is effective at startup. Further, the method of the present invention can form good microbial flocs even when treating wastewater in which microbial flocs are difficult to form, so that treated water with good water quality can always be obtained.

Claims (3)

[Claims] 1. A biological treatment tank for sewage is added with a mixed composition of carboxymethyl cellulose having a carboxymethyl group substitution degree of 0.2 to 0.5 and a clay mineral powder, and a metal salt which dissolves in water to generate a positive charge. A method for forming microbial flocs, which is characterized by the above. 2. A clay mineral powder having a particle size of 10 to 10
The method according to claim 1, which is 0 μm. 3. The method according to claim 1, wherein any one of aluminum sulfate, aluminum chloride, iron sulfate and iron chloride is used as the metal salt.