JPH0338299A - Fluidized-bed type waste water treatment apparatus - Google Patents

Abstract

PURPOSE:To realize a scale-down and energy-saving and to separate SS from an effluence waste water through rapid filtration by using carriers made of polypropylene, by installing a screen at a treated water outlet side of a tank and by attaching a multilayer type filtration equipment to the tank. CONSTITUTION:An air dispersion equipment 11 is installed at whole bottom part of a tank 11, and carriers 3, which are made of polypropylene and whose specific gravity are in a range between 1.00 to 1.02, are used. A screen 12 for separating the carriers is installed at an outlet side of treated water and communicated to a multilayer type filtration equipment 15 with a discharge pipe 9. A small-scale and energy-saving fluidized-bed type waste water treatment apparatus is obtained by applying an overall aeration system and using polypropylene carriers of a specified specific gravity. As the multilayer type filtration equipment is composed of layers packed by a fiber filter medium suitable for large SS and a granular one for fine SS, SS concentration in the effluent waste water is remarkably reduced and it is possible to increase a filtration speed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to improvements in fluidized bed wastewater treatment equipment.

[Conventional technology] Activated sludge method, fluidized bed method, etc. are used as wastewater treatment methods for urban sewage, industrial wastewater, etc. However, activated sludge method generally requires large-sized treatment equipment, so it is difficult to make it more compact. There are some drawbacks from this point of view. For this reason, fluidized bed methods, which have fewer such drawbacks, have recently been increasingly used.

FIG. 6 is a conceptual diagram showing the configuration of a draft tube type reactor used in the conventional fluidized bed method.
1 is an outer cylinder, 2 is an inner cylinder disposed coaxially within the outer cylinder 1, and 3 is a particle (hereinafter referred to as a carrier) for attaching microorganisms that is placed inside the actor. , activated carbon, plastic, etc. Reference numeral 4 denotes a partition plate forming the carrier weight separation section 5 in the enlarged upper part of the outer cylinder 1; 6, the raw water supply pipe; 7, an air diffuser disposed on the bottom of the outer cylinder 1 below the inner cylinder 2; 8 is a compressor or blower for supplying oxygen-containing gas (air, etc.) to the diffuser 7; 9 is a drain pipe;
10 is a bubble.

In the draft tube type reactor configured as described above, when wastewater to be treated is supplied into the reactor from the raw water supply pipe 6 and then gas is blown from the aeration device 7, the inside of the inner cylinder 2 rises. A downward flow occurs outside the inner cylinder 2. As the carrier 3 flows along with these flows, microorganisms involved in wastewater treatment adhere to and grow on the surface of the carrier 3, forming a biofilm on the surface. The pollutants in the wastewater are then decomposed by these microorganisms. The gas blown by the aeration device 7 is an oxygen-containing gas (air, etc.), and the blowing of this gas supplies oxygen to the microorganisms, causes the carrier 3 to flow, and stirs the water. Since gas, liquid, and solid are present in the reactor, it becomes a three-phase fluidized bed. The treated water and part of the carrier 3 enter the carrier gravity separation unit 5, and the carrier gravity separation unit 5 is designed so that the sedimentation rate of the carrier 3 is greater than the rising rate of the water.
The carrier 3 returns to the reactor again, and the treated water is taken out through the drain pipe 9.

[Problems to be Solved by the Invention] However, the following problems have been pointed out also in this fluidized bed reactor.

■Lower oxygen dissolution efficiency. In other words, in a liquid where a carrier exists, the coalescence of the bubbles emitted from the air diffuser is promoted by the presence of the carrier, and fine bubbles change into coarse bubbles, which reduces the gas-liquid contact area and reduces oxygen dissolution. Efficiency decreases. In addition, since the liquid flow rate is upward in the area where bubbles exist,
The bubbles reach the water surface in a short time. In other words, the gas-liquid contact time is short.

Therefore, the oxygen dissolution efficiency further decreases. therefore,
Same amount! The amount of gas blown to move the 12 elements to the liquid side is larger than when no carrier is used, and the energy consumption of gas blowing equipment such as a blower compressor becomes large (increase in running costs).

Further, a large-sized device such as a blower compressor is required (initial cost increases).

■Poor liquidity. When using a carrier with a large specific gravity such as sand or activated carbon, small particles of about 0.05 mmφ to 0.3 mmφ have been used because large particles have extremely low fluidity.

The sedimentation velocity of a single particle, which can be said to be an index of fluidity, is the following arene (A
It is expressed by the formula L L E N).

However, ')F: fluid density (g/cl13) μF=fluid viscosity (g/al・5eC) DP2 particle diameter (
(To) g: Gravitational acceleration (cm/see 2) From this equation, it can be seen that it is certainly advantageous to use particles with a small diameter. However, equation (1) shows that when a biofilm attaches, D and ρ change, and the fluidity of s changes.

In actual processes, the flow rate and concentration vary greatly over time, and the biofilm thickness changes accordingly, resulting in large changes in the fluidity of the carrier. Furthermore, it is extremely difficult to control biofilm thickness. For this reason, if the amount of blown gas is insufficient, the carriers will be deposited, whereas if it is excessive, troubles such as the carriers flying out of the reactor will occur.

■Floating or suspended solids (hereinafter referred to as Ss)
It has almost no removal ability. Almost no suspended solids are incorporated into the biofilm of the carrier and flow out together with the treated water. Furthermore, biofilm fragments detached from the carrier are also mixed into the treated water.

■Low sedimentation (separation) of SS components contained in treated water.

SS in the treated water hardly forms flocs. In addition, since it is made fine by rubbing against the carrier, it has low sedimentation properties. For this reason, conventional sand filtration equipment does not contain SS in raw water.
When the concentration is high, filtration resistance increases rapidly, causing clogging of the filter tank, requiring frequent backwashing of the filter tank.

Therefore, the conventional fluidized bed wastewater treatment apparatus still has various problems in achieving miniaturization and energy saving, and also has the problem that it is difficult to separate SS from the treated water.

The present invention was made in order to solve the above problems, and aims to provide a fluidized bed wastewater treatment device that is downsized and energy-saving, and that can separate SS in treated water by rapid filtration. do.

[Means for Solving the Problems] The fluidized bed wastewater treatment device according to the present invention is provided with an aeration device throughout the bottom of a tank for supplying raw water, and a carrier placed in the tank is made of polypropylene and has a specific gravity. 1.00
~1.02 is used, and a screen for carrier separation is installed on the treatment and water discharge side of the tank, and SS in the treated water is
A multilayer filtration device is attached to the tank to separate the

Preferably, a bubble generator is provided near the screen to prevent clogging of the screen due to adhesion of the carrier.

Further, it is more convenient to provide a screen on the raw water supply side of the tank to remove fibrous impurities such as hair and fibrous dirt in advance.

A multilayer filtration device is equipped with at least two upper and lower filter layers within the device body, and the two filter layers serve as the initial filter layers through which the treated water (wastewater) from the tank passes through, and are equipped with a large number of filter layers. One is filled with a fibrous filter material made of non-woven water-resistant fibers and whose porosity does not substantially change during water flow, and the other is filled with a granular filter material as a filter layer at the final stage of filtration through which wastewater passes. It is composed of

[Function] The main reason why the present invention is limited to polypropylene carriers is that, as a result of experiments, the amount of adhered sludge is larger than that of other plastic carriers.

Performances generally required of carriers include the following.

■ Good fluidity (specific gravity 1.00 to 1.02) ■ Good adhesion of living organisms ■ Inexpensive ■ Long life As a carrier that satisfies these conditions, plastic-based carriers are excellent. ing. However, for those with specific gravity of 1 or more,
The specific gravity is 1. It is difficult to control the specific gravity to OO~1.02, and even if it is possible to control the specific gravity to 1.00~1.02 by foaming, after long-term use, water will penetrate into the air bubbles inside the carrier and the specific gravity will decrease. This is not desirable because it changes the For this reason, it is preferable to use a plastic having a specific gravity of 1 or less to which a specific gravity adjusting agent such as talc, calcium carbonate, or barium sulfate is added. Therefore, as a result of conducting an experiment to confirm the bioadhesion of plastics with a specific gravity of 1.0 or less using actual wastewater (see Table 1), we came to the conclusion that polypropylene is optimal.

Table 1 The polypropylene carrier thus obtained has good fluidity because its specific gravity is equal to or slightly greater than that of water. Furthermore, since the entire surface is aerated, the gas-liquid contact time is long and the oxygen dissolution efficiency is improved.

The carrier is separated from the treated water by a screen provided on the treatment and treated water discharge sides of the tank, and is not discharged outside the tank. Furthermore, the carrier is prevented from adhering to the screen due to air bubbles generated by the air bubble generator.

Furthermore, since fibrous impurities contained in the raw water are removed in advance by the screen on the raw water supply side, the carrier separation screen is prevented from being clogged with these impurities.

The wastewater discharged from the tank is led to a multilayer filtration device and filtered. This multilayer filtration device includes at least two filter layers with different functions. That is, the filter layer is mainly composed of a combination of a filter layer filled with a fibrous filter medium suitable for removing large SS and a filter layer filled with a granular filter medium suitable for removing fine SS. For this reason,
Since rough filtration of wastewater is performed in a filter layer filled with fiber filter media, SS in the wastewater that passes through the next filter layer filled with granular filter media is
concentration is significantly reduced, and the load on the filter bed filled with granular filter media is reduced. Therefore, even with a filter bed filled with granular filter media, filtration can be continued for a long time and the filtration rate can be increased.

Since the above-mentioned fibrous filter medium is made of non-woven water-resistant fibers, it has a very large porosity, and therefore has very low resistance to water flow and is less likely to become clogged. For this reason, it is a filter medium suitable for filling the filter bed in the rough filtration stage, which mainly removes large SS.

The above-mentioned granular filter media is determined by the particle size distribution of SS in the wastewater to be filtered, the expected value of water flow resistance, the expected value of the SS concentration in the filtrate water, etc., but it is necessary to ensure that the SSa degree in the filtrate water is at the expected value. It is desirable to use particles with as large a particle size as possible. 5 in normal case
The preferred particle size is about +n to 1 city. Particle size is 1 m
If it is less than 1, the removal rate of fine SS is good, but it is not preferable because the degree of clogging of the layer where the pressure loss is large is large. starts to decrease.

[Example] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

FIG. 1 is a conceptual diagram showing an embodiment of the present invention, and the same reference numerals as in FIG. 6 indicate the same or corresponding parts.

In this embodiment, an air diffuser 7 is installed at the entire bottom of the tank 11 to adopt a full-surface aeration system, and the carrier 3 is made of polypropylene and has a specific gravity within the range of 1.00 to 1.02. use. Further, a screen 12 for carrier separation is provided on the discharge side of the treated water, and preferably the screen 12
In order to prevent the carrier 3 from adhering to the screen and causing clogging, it is preferable to install the bubble generator 13 near and below the screen 12.

Further, the raw water may be directly supplied to the tank 11 from the supply pipe 6, but a screen 14 is used to remove in advance fibrous impurities such as hair and fibrous dust contained in the raw water.
It is best to supply it via .

If the carrier separation screen 12 becomes clogged with these fibrous contaminants, it will be difficult to clean them, so clogging is prevented by removing them on the raw water supply side. Also,
Cleaning of the screen 14 on the raw water supply side can be done relatively easily since the mesh is coarser than that of the screen 12.

The carrier 3 placed in the tank 11 is made of polypropylene and has a specific gravity of 1.00 to 1.02 as described above. For example, 1 as shown in FIGS.
It is a shaped particle having more than one through hole. Molded particles 3a
is a polypropylene thermoplastic resin to which inorganic materials such as talc, calcium carbonate, and barium sulfate are added as lumber with a specific gravity of A. Also, its outer diameter is 3.0 to 20
It is appropriate that the inner diameter of the through-hole 3b at position 9 is approximately 1.0 to 18III11, and the ratio of length to outer diameter is approximately 0.8 to 1.2. The shape of the shaped particles 3a is generally cylindrical, but may be freely determined to be spherical, ellipsoidal, quadrangular prism, polygonal prism, triangular pyramid, etc. Moreover, the surface of the molded particles 3a can be made uneven by foaming treatment during molding.

If the specific gravity of the carrier 3 is less than 1.00, the carrier will aggregate in the upper layer due to full-surface aeration, making it difficult to fluidize, and if the specific gravity exceeds 1.02, a large amount of gas will have to be blown for fluidization. This increases the energy consumption of the compressor or blower 8.

The flow rate on the screen 12 is 1 m/hr.
It is used at ~120 m/hr, and the material should have sufficient strength, excellent corrosion resistance, and be resistant to the attachment of living things. - Stainless steel is used inside the membrane.

The drain side of the tank 11 is connected to a multilayer filtration device 1 by a drain pipe 9.
5 has been contacted. This multilayer filtration device 15, as shown in detail in FIG. 3, is provided with at least two upper and lower filter layers 17 and 18 in the device body 16.

The upper filter layer 17 is a filter layer at the initial stage of filtration (hereinafter referred to as the initial filter layer) through which wastewater first passes, and is made of a large number of water-resistant fibers formed into a non-woven structure and has a porosity that is substantially reduced during water passage. It is filled with fiber filter media that does not change. Lower filter layer 18
is the filter layer at the final stage of filtration (hereinafter referred to as the final filter layer) through which wastewater passes last, and is filled with granular filter media. The initial filter layer 17 is supported by a filter layer holding material 20 that has virtually no water flow resistance, and its upper end is fixed by a filtering fixing member 21 so as not to float up. The final filter layer 18 is held by a perforated plate 22. Initial filter layer 1
The diameter and porosity of the fibrous filter media to be filled in the filter layer 7 and the diameter of the granular filter media to be filled in the initial filter layer 17 are determined based on the SS concentration and particle size distribution in the wastewater to be treated and the required water quality of the filtrate water.

Further, the filling heights of the initial filter layer 17 and the final filter layer 18 are also determined as appropriate based on the above conditions. 24 is a filtered water discharge pipe that also serves as a backwash water supply pipe, 25 is an air blowing pipe used during backwashing, 26 is a distributor that disperses the air blown in in step 1 over the entire surface of the filter layer during backwashing, and 27 is a reverse Wash water discharge pipe, 28
is the backwash water collecting pipe.

The above-mentioned fiber filter medium is made by bending water-resistant fibers such as curling them into an elastic body, and forming the bent fibers into a non-woven material. Plastic fibers, metal fibers, etc. are used as the water-resistant fibers forming this fiber filter medium.

As the above-mentioned granular filter medium, sand, anthracite, synthetic resin particles, activated carbon, zeolite, various ceramics (preferably those with low bulk density such as hollow ones), or a combination thereof are used.

FIG. 4 is an explanatory diagram schematically showing the fiber filter medium used in the present invention. This fiber filter medium 30 was discovered through many filter medium selection experiments, and is made by coating and bonding a large number of bent plastic fibers 31, which are water-resistant fibers, with a binder to form a three-dimensional mesh-like structure. It is formed into a non-woven material.

The fiber 31 constituting the fiber filter medium 30 has a diameter of 100 denier (approximately 0.091 mm) to 10,000 denier (approximately 0.91 mm)
mm). The porosity of the mff1 filter medium 30 is selected within the range of 70% to 99.5%.

Diameter of fibers 31 constituting fiber filter medium 30 and fiber filter medium 30
The porosity of was determined as follows based on the results of a filter medium selection experiment.

Regarding the diameter of the fibers 31, if the filled fiber filter medium 30 is compressed and reduced in volume during water passage, the porosity will decrease and the filtration performance will change, which is not preferable. For this reason, the fibers 31 need to have enough strength to prevent the fiber filter medium 30 from being substantially compressed during water passage, and the diameter of the fibers 31 that meets this condition needs to be about 100 deniers or more. However, if the fibers 31 become too thick, the effective surface area per unit volume of the filter medium decreases, and the filtration efficiency deteriorates. Thus, in consideration of the relationship with filtration efficiency, it is desirable that the diameter of the fibers 31 be 10,000 deniers or less.

The porosity of the fiber filter medium 30 is such that the water flow resistance does not suddenly increase in a short period of time during water flow, and the SS removal rate is good.

The decision was made with that in mind. The porosity of the fiber filter medium 30 is 7
If the porosity is less than 0%, water flow resistance will increase rapidly after a few hours of water flow, which is undesirable.If the porosity exceeds 99.5%, S
The removal rate of S becomes insufficient, and the function as a filter medium becomes insufficient. Therefore, the preferred porosity of the fiber filter medium 30 is 70%.
~99.5%.

This embodiment is configured as described above, and the air diffuser 7
Oxygen dissolution efficiency is improved by full-scale aeration. The degree was about 1.25 times that of the conventional draft tube type reactor shown in FIG. The reason for this is that in the draft tube method, the flow of water in the bubble-existing area is upward (the upward velocity of this water is V).
Further, since the bubble has a floating velocity (v) relative to water, the rising velocity of the bubble is v10v, and the contact time of the gas S with the liquid is shortened. This provides an energy saving effect.

Further, since the carrier 3 has good fluidity, a stable fluid state can be achieved by blowing in a small amount of gas necessary for biological reaction.

FIG. 5 shows the results of carrier fluidization experiments conducted using cylindrical (4 mm-X4+n) carriers of various specific gravity. The experiment was 3m wide and 1m deep.

The experiment was conducted using a water tank with a height of 5 m. Aeration was carried out using a disk-type diffuser and a full-surface aeration method. The apparent filling rate of the carrier was 44%.

From FIG. 5, it can be seen that a very slight increase in specific gravity causes an extreme decrease in fluidity. This is because the fluidity is strongly influenced by the "difference in specific gravity between the carrier and water" as shown in the above formula (1).

Here, the carrier with a specific gravity of 1.04 is blown with 3
3- Amount (speed) 5. At about 3Nm-Air/m reactor/hr, 90% or more of the carrier will flow. However, - high-load treatment of sewage with a membrane composition (retention time in the reactor of 2 hours... standard activated sludge method 3~
4 times the load), and the volume ratio of the amount of blown air (aeration ratio) to the treated water is increased to 7 times (in the standard activated sludge method, the
7 times), the amount of air included is 3. 5Nm-Air/m reactor/hr. Therefore, for a carrier with a specific gravity of 1.04, (blow air jl required for biological reaction) (blow air amount required for fluidization)...
...(2) Therefore, extra energy is consumed for carrier fluidization.

On the other hand, carrier 3 with specific gravity 1.005 and 1.02
3- The body is like this 1. With a blown air amount of about 3 Nm -Alr/m reactor/hr, more than 90% of the carrier becomes fluidized, the inequality sign in equation 2) is reversed, and high energy efficiency is obtained.

In addition, the rate of decomposition of organic matter by microorganisms generally increases as the concentration of organic matter increases, so making the flow of wastewater from the reactor closer to a plug flow (for example, connecting multiple reactors in series) is an effective way to downsize the reactor. Although it is effective, in this case, the amount of blown air required for the biological reaction near the exit (later stage) is considerably smaller.

Furthermore, when ammonia nitrogen in wastewater is nitrified into nitrite and nitrate nitrogen, the load is low, so the amount of blown air required for biological reactions is small. In these cases, the energy saving effect of using a carrier with a specific gravity of about 1.00 to 1.02 becomes even clearer.

Furthermore, since the carrier 3 is separated from the treated water by the screen 12, there is almost no loss of the carrier 3. Further, the carrier 3 does not jump out of the tank 11.

When this example is compared with the conventional activated sludge method, 100
While the conventional example requires a capacity of 25 m3 to obtain a processing capacity of m3/day, this embodiment only requires a capacity of 4 m3, making it possible to downsize to approximately 176 m3.

Tank wastewater contains SS, which is difficult to separate from water. Therefore, in the present invention, the tank waste water is led to the multilayer filtration device 15 through the drain pipe 9 and treated by rapid filtration.

As mentioned above, this multilayer filtration device 15 has at least two
It has two filter layers, namely an initial filter layer 17 and a final filter layer 18. The initial filter layer 17 is composed of a large number of water-resistant fibers formed in a non-woven manner and filled with a fiber filter medium 30 whose porosity does not substantially change when water passes through it, so it is mainly used to remove large SS. useful for. In addition, initial filter layer 1
7 has much lower water flow resistance than the final filter layer 18,
Since most of the SS is removed by the initial filter layer 17, the SS concentration on the final filter layer 18 is reduced, and the load on the final filter layer 18 is reduced. The final filter layer 18 removes fine SS that could not be removed by the initial filter layer 17.

With the above configuration, the backwash interval of the present multilayer filtration device 15 has been significantly extended, approximately five times longer than that of a conventional sand filtration device.

Table 3 shows the results of a filtration experiment conducted using the apparatus shown in FIG. 3 under the conditions shown in Table 2.

Table 2 Filtration conditions Anthracite has an effective diameter of 4 yam Table 3 Filtration experiment results [Effects of the invention As described above, according to the present invention, the entire surface aeration system is adopted and a polypropylene carrier having a specific specific gravity is used. As a result, a compact, energy-saving fluidized bed wastewater treatment device can be obtained. In addition, the carrier is separated by a screen provided on the treated water discharge side to prevent loss.

Further, the air bubbles generated by the air bubble generator prevent the carrier from adhering to the screen, thereby preventing the screen from clogging.

By providing a screen that removes fibrous impurities in the raw water in advance, clogging of the carrier separation screen can be further prevented.

By passing tank wastewater through a multilayer filtration device, SS in the wastewater can be separated by rapid filtration, and effects such as filter layer clogging and backwashing operations can be reduced.

[Brief explanation of drawings]

Figure 1 is a conceptual diagram showing one embodiment of the present invention, Figure 2 (a)
~(b) is a perspective view showing an example of the carrier used in the device of FIG. 1, FIG. 3 is a detailed view of the multilayer filtration device of FIG. 1, and FIG. 4 is a diagram of the initial filter in the multilayer filtration device. Schematic diagram of the layers,
FIG. 5 is a diagram showing the results of a fluidization experiment for each specific gravity of the carrier, and FIG. 6 is a conceptual diagram showing a conventional draft tube type reactor. 3...Carrier 6...Raw water supply pipe 7...Diffuser 8...Compressor or blower 9...Drain pipe 11...Tank 12...Screen for carrier separation 13... Bubble generator 14...Screen for removing fibrous impurities 15...Multilayer filtration device 16...Device main body 17...Initial filter layer 18...Final filter layer

Claims (4)

[Claims] (1) A tank to which raw water is supplied, an aeration device provided on the entire bottom of the tank, a carrier made of polypropylene having a specific gravity of 1.00 to 1.02 placed in the tank, and the A fluidized bed wastewater treatment device comprising: a screen for separating the carrier provided on the drainage side of the tank; and a multilayer filtration device attached to the tank for wastewater treatment. (2) The fluidized bed wastewater treatment apparatus according to claim 1, further comprising a bubble generator provided in the vicinity of the carrier separation screen. (3) The fluidized bed wastewater treatment apparatus according to claim 1, further comprising a screen provided on the raw water supply side of the tank for removing fibrous impurities in the raw water. (4) The multilayer filtration device has at least two filter layers, and the filter layer at the initial stage of filtration through which wastewater first passes has a large number of water-resistant fibers formed in a non-woven manner, and the porosity during water flow is substantially reduced. 2. The fluidized bed wastewater treatment apparatus according to claim 1, wherein the filter layer at the final stage of filtration through which the wastewater passes last is filled with granular filter media.