JPH0688031B2 - Biological treatment method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a biological treatment method used for treating activated sludge of sewage / industrial wastewater.

(Prior Art) Generally, sewage and industrial wastewater (hereinafter abbreviated as sewage)
The activated sludge treatment is carried out as follows.

First, after removing most of the sediment, coarse suspended solids, etc. from the sewage, the sludge of the sewage is decomposed by performing activated sludge treatment in the aeration tank of the activated sludge treatment equipment, and the next sludge sediment tank. In step 1, the activated sludge is separated by sedimentation and the supernatant water is discharged as treated water. On the other hand, the activated sludge settled in the sludge settling tank is returned to the aeration tank as return sludge, and part of it is withdrawn as excess sludge for digestion, dehydration and incineration and disposal.

Conventionally, studies have been made to efficiently perform such wastewater treatment and save space. For example, one of them is the high-concentration activated sludge method. This increases the concentration of activated sludge, shortens the time required for purification, and makes the aeration tank capacity compact. However, this high-concentration activated sludge method also has a limited solid-liquid separation function in the final settling basin, so it is not possible to conserve space as much as desired. That is, since the method using the existing floating flocks is light in weight, it is impossible to drastically improve the processing efficiency per volume.

Therefore, research on a fluidized bed biofilm method in which a biofilm is formed on a carrier and microorganisms are grown has been conducted (for example, Water Pollution Research Vol.9 No.11 1986), and 0.3 to 0.6 mm of sand as a carrier, Activated carbon or anthracite is used.

By using this fluidized bed biofilm method, it is possible to increase the concentration of activated sludge in the aeration tank and easily perform solid-liquid separation of the carrier to which the biofilm is attached. However, this fluidized bed biofilm method also has a large flow energy for floating the carrier, sludge that has separated from the carrier easily flows out to the outside, and it is necessary to install another sedimentation tank in the latter stage. There are drawbacks such as a long time required for forming a biofilm having a strong binding force on the carrier.

(Problems to be Solved by the Invention) The present invention aims to save space by biologically treating the sludge flocs by increasing the specific gravity of the activated sludge flocs, rather than forming a biofilm on the carrier. Provide a processing method.

(Means for Solving the Problems) The present invention relates to a biological treatment method of incorporating particulate solid matter into activated sludge flocs in an aeration tank, in which glass-shaped oxides are covalently bonded and modified oxides are ionicly bonded. Particle size
Granulated blast furnace slag of 100μ or less is added to the activated sludge flocs to elute the metal ions of the modified oxide and ion-exchange with hydrogen ions in the water, thereby separating the hydroxyl groups separated in the water and the wastewater / activated sludge. It is characterized in that a hydroxide is generated by the presence of existing metal ions. Further, it is effective to use a high-speed aeration sedimentation basin as a biological treatment device. In this case, it is preferable to form a blanket zone in the sedimentation part in the high-speed aeration sedimentation basin.

(Function) The present invention provides a total amount by incorporating the granulated blast furnace slag having a particle size of 100 μ or less in which the glass-forming oxide is covalently bonded and the decorative oxide is ionically bonded in the activated sludge floe in the aeration tank. Enables space saving. Conventionally, as a measure for preventing bulking, a weighting agent such as clay, activated carbon or incineration ash, or a sulfuric acid band, a synthetic polymer coagulant, or an iron salt or other coagulant has been temporarily added. However, the present invention is not a preventive / therapeutic means for such bulking, but rather the particulate solid matter (carrier) of the granulated blast furnace slag described above is permanently incorporated into a large number of floating flocs to obtain a specific gravity of the flocs. By increasing (anchor effect), solid-liquid separation is promoted and the concentration of activated sludge in the aeration section is increased. If the activated sludge concentration in the aeration section is high, the time required for purification can be shortened, and the aeration section can be made compact. Further, the size of the final sedimentation basin, which was conventionally limited, can be made compact by promoting the solid-liquid separation function because of its large floc specific gravity. As a result, total space saving of both the aeration part and the precipitation part is possible.

According to the present invention, a carrier of finely granulated blast furnace slab is mixed with floating flocs, and the carrier is easily taken into the floating flocs and exhibits an effect in a short time. Therefore, unlike the conventional fluidized bed biofilm method, there is no need to ripen a biofilm having a strong binding force, a period for that is also unnecessary, and the biofilm does not peel from the carrier and flow out of the system. Also, no special flow energy is required to float the carrier. The carrier once taken does not separate from the floc unless a strong shearing force is applied, and therefore, there is no concern that the carrier / floc may separate and flow out during ordinary aeration mixing and mechanical stirring.

In general, activated sludge organisms secrete polymeric substances such as polysaccharides involved in floc formation, and since this is an anionic polymeric substance, activated sludge is negatively charged. Therefore, it is better to be positively charged in order to be taken into the activated sludge flocs. However, in the natural world, there are very few particles that are positively charged, have a uniform fine particle system, and are inexpensive and easily available. For example,
JP-A-1-207194 discloses silica sand, cristobalite,
Although a method of charging an inorganic carrier called zeolite using a cationic polymer flocculant has been disclosed, it cannot be said to be inexpensive because it requires a charging operation with the polymer flocculant.

Then, as a result of various studies by the present inventors, it became clear that fine powder of granulated blast furnace slag is very good. Granulated blast furnace slag is produced by rapidly cooling slag generated as a by-product from a blast furnace in an iron mill with high pressure water, and has a composition of Ca.
O, SiO ₂ , and Al ₂ O ₃ are the main components, and the vitrification rate is about 90% or more.

It is necessary to make the size fine so that the particle size is 100 μm or less so that it can be easily incorporated into the activated sludge flocs, and 40 μm or less and a relatively large specific gravity are preferable.

Granulated blast furnace slag is usually negatively charged, but it is taken into the activated sludge floc by the following mechanism. That is, the granulated blast furnace slag is vitrified due to rapid cooling with high-pressure water, and glass forming oxides SiO ₂ and Al ₂ O ₃ are covalently bonded with a strong bonding force. Modified oxides such as CaO and MgO are ionically bonded to the pores of the glass-forming oxide network. Granulated blast furnace slag like this can
Ca ^2+, etc. elutes slowly and undergoes ion exchange with H ⁺ in water. At the same time, an equal amount of OH ^- is separated into water and metal ions present in the inflowing wastewater and activated sludge, such as Fe ²⁺ , AI.
Make ³⁺ and hydroxide. This phenomenon can be confirmed by an increase in pH and a decrease in redox potential when adding granulated blast furnace slag. This hydroxide serves as a bridging agent between the granulated blast furnace slag and the activated sludge flocs, and takes in the granulated blast furnace slag into the activated sludge flocs.

In this way, it is easily incorporated into the activated sludge flocs. Granulated blast furnace slag also has a relatively large specific gravity of 2.9 and has a sufficient anchor effect. Moreover, since it is generated as a by-product from steelworks, etc., it is a solid substance that is inexpensive and easily available.

The method of the present invention can be sufficiently used for various biological treatment methods which have been practically used in the past, for example, standard activated sludge method, batch method, oxidation ditch method, etc., but is applied to the following high-speed aeration sedimentation basins. Is preferred.

FIG. 1 shows a longitudinal section to clarify the internal mechanism of the high-speed aeration sedimentation basin. The aquarium body 1 is an inner cylinder 4
The outer cylinder 8 is divided into an aeration section 5, a circulation section 9 and a precipitation section 10.

The inflow water W flows into the aeration unit 5 from the inflow port 2 near the bottom of the water tank body 1, and is circulated in the aeration unit 5 by the air AO and the agitation device 12 ejected from the air diffuser 3 for biological treatment. Is given. The inflow may be performed by inserting a pipe into the aeration unit 5 from the upper part of the water tank body 1. The temporary treated water W ₁ and the activated sludge 6 overflowing from the upper part of the inner cylinder 4 flow down the circulation part 9 surrounded by the inner cylinder 4 and the outer cylinder 8. In this process, biological treatment further progresses and sludge Are sedimented and separated. The secondary treated water W ₂ overflowing from the lower part of the outer cylinder 8 to the outside through the circulation part 9 flows upward in the precipitation part 10. Here, activated sludge is settled and separated by the same principle as that of a general upward flow type sedimentation basin.
The separated sludge D separated from the treated water in the circulation part 9 and the precipitation part 10 flows down between the inner cylinder 4 and the outer cylinder 8 and the water tank body 1, and returns to the aeration part 5 again. Excess sludge D ₁ is the sludge discharge port 7
More discharged and processed separately.

Conventionally, the high-speed aeration sedimentation basin was designed for the purpose of highly efficient treatment, but the solid-liquid separation in the sedimentation part 10 was not stable, so that it was not sufficiently effective.

When the present invention is applied to this high-speed aeration sedimentation basin, that is, when fine granulated blast furnace slag is added, this granulated blast furnace slag is easily incorporated into the activated sludge flocs by generating hydroxides, and the floc specific gravity is increased. Enlarge and accelerate solid-liquid separation function. As a result, solid-liquid separation, which has been a problem in the past, is stabilized, and highly efficient processing becomes possible.

In addition to adding granulated blast furnace slag into the aeration section 5,
As shown in FIG. 2, when the blanket zone 14 is formed in the settling portion 10, flocs having a large specific gravity form a stable blanket zone, further promoting solid-liquid separation.
As a result, the concentration of activated sludge in the aeration unit 5 is increased and the time required for purification is shortened. Further, the blanket zone has an adsorption / filtration function in addition to promoting and stabilizing solid-liquid separation, so that more stable treatment can be performed. In addition, a large amount of sludge will be retained in this blanket zone, but since the sludge at the bottom of the blanket is drawn in by the circulation flow that flows down between the inner and outer cylinders (entrainment phenomenon), slow convection occurs in the blanket zone, Sludge does not stay for several days and become anaerobic.

Therefore, the addition of granulated blast furnace slag and the formation of blanket zones make the high-speed aeration sedimentation basin more functional than before. That is, since highly efficient treatment can be stably performed in both the aeration section and the precipitation section, the apparatus becomes very compact and the equipment space can be saved.

(Example) A water tank body (capacity 2.5 m ³ ) is divided into an aeration part (1 m ³ ) and a sedimentation part (1.5 m ³ ) by an inner cylinder and an outer cylinder, and the aeration part has a particle size of 1
Fines granulated blast furnace slag of ~50μ 5kg (approximately per aeration tank 1 m ³
Equivalent to 5 kg), raw water BOD concentration average 200 mg / l, raw water COD
Aggregate groundwater with an average concentration of 150 mg / l and raw water SS concentration of 200 mg / l was supplied.

A stable blanket zone was formed in the precipitation section, and continuous treatment was carried out for 1 year with a residence time of 2 hours for the aeration section and 3 hours for the precipitation section. As a result, stable treatment comes out and treated water BOD
Concentration is 10-20 mg / l, COD concentration is 10-15 mg / l, SS concentration is 10
It was ~ 15 mg / l. At this time, the aeration part MLVSS concentration is about 6,000.
It was mg / l.

An example of the processing result by the conventional method for the above-described embodiment of the present invention is shown below.

Aeration unit by the inner cylinder and the outer cylinder of the aquarium body (capacity 2.5m ²⁾ (1m ^3), partition the precipitation unit (1.5 m ^3), raw BOD concentration average 200 mg / l, raw COD concentration average 150 mg / l, raw water SS Concentration average 2
A group groundwater of 00 mg / l was supplied. As a result, the treated water BOD concentration was 20% at the residence time of 2 hours for the aeration section and 3 hours for the precipitation section.
〜30mg / l, COD concentration was 15〜30mg / l, which resulted in unstable treated water quality. Further, in order to obtain the same treated water quality as the treatment result of the example of the present invention, the residence time in the aeration section was required to be 4 hours, which required twice the apparatus capacity of the example of the present invention. In the precipitation area, it is difficult to form a stable blanket zone, and SS
Does not carry over, and the MLVSS concentration in the aeration part is 200
It could only be maintained at 0 to 3000 mg / l.

(Effect of the Invention) According to the present invention, in the activated sludge treatment of the sewage, the sewage can be treated efficiently, stably, and inexpensively. That is, solid-liquid separation is promoted by the anchor effect of the granulated blast furnace slau, the concentration of activated sludge in the aeration section can be maintained at a high concentration, the time required for purification can be shortened, and both the aeration section and the final sedimentation section can be made compact. Therefore, total space saving can be achieved at low cost.

[Brief description of drawings]

FIG. 1 is a diagram showing a high-speed aeration sedimentation basin, and FIG. 2 is a diagram showing a high-speed aeration sedimentation basin in which a blanket zone is formed. 1 ... Water tank body, 2 ... Inlet, 3 ... Air diffuser, 4 ...
… Inner cylinder, 5 …… Aeration section, 6 …… Activated sludge, 7 …… Sludge discharge port, 8 …… Outer cylinder, 9 …… Circulation section, 10 …… Settling section, 11…
… Outflow groove, 12 …… Stirring device, 13 …… Inner cylinder umbrella part, 14 …… Blanket zone, W …… Influent water, W ₁ …… Temporary treated water,
W ₂ …… Secondary treated water, W ₃ …… Clear water, AO, A …… Air, D
...... Separated sludge, D ₁ …… Excess sludge.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Riki Miki 1-1-1 Edamitsu, Hachimanto-ku, Kitakyushu, Fukuoka Prefecture, Nippon Steel Corporation Third Technical Research Institute (56) Reference JP-A-55-152593 ( JP, A) JP 62-294496 (JP, A) JP 53-111658 (JP, A) JP 61-129095 (JP, A)

Claims (3)

[Claims] 1. A blast furnace having a particle size of 100 μ or less in which a glass-forming oxide is covalently bonded and a modified oxide is ionic-bonded in a biological treatment method of incorporating a particulate solid substance into an activated sludge floc in an aeration tank. Granulated slag is added to the activated sludge flocs to elute the metal ions of the modified oxide and exchange with the hydrogen ions in the water, resulting in the hydroxyl groups separated in the water and the metal ions present in the wastewater and activated sludge. A biological treatment method characterized in that a hydroxide is produced by 2. The biological treatment method according to claim 1, wherein a high-speed aeration sedimentation basin is used as the biological treatment device. 3. The biological treatment method according to claim 2, wherein a blanket zone is formed in the sedimentation portion in the high-speed aeration sedimentation basin.