JPH0338298A - Fluidized-bed type waste water treatment apparatus - Google Patents

Abstract

PURPOSE:To realize a scale-down and energy-saving by arranging carriers, whose specific gravity are 1.00 to 1.02 and which are made of polypropylene, in a tank and also by installing a separation screen at an outlet for treated water. CONSTITUTION:An overall aeration system is applied by installing a gas dispersion equipment 7 at whole bottom part of a tank 11, and carriers 3, which are made of polypropylene and whose specific gravity is 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 a bubbling equipment 13 is arranged in the vicinity below the screen 12. As fibrous impurities included in the original water has already been removed with a supply side screen 14, the screen 12 for separating carriers is prevented from clogging due to those impurities. A small-scale and energy-saving fluidized-bed type waste water treatment apparatus is obtained by applying the overall aeration system and using the carriers having the specified specific gravity and made of polypropylene.

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a fluidized bed wastewater treatment apparatus, and particularly to a reactor thereof. [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 and requires a large amount of water due to aeration. Since it requires a huge amount of energy, it is difficult to make it compact and save energy. For this reason, fluidized bed methods, which have fewer such drawbacks, have recently been increasingly used. FIG. 4 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 aeration device 7; 9 is a treated water drain pipe; and 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 from the treated water distribution 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. Moreover, since the liquid flux is upward in the bubble existing portion, the bubbles reach the water surface in a short time. In other words, the gas-liquid contact time is short. This further reduces the oxygen dissolution efficiency. Therefore, the amount of gas blown to transfer the same amount of oxygen to the liquid side is larger than when no carrier is used, and the energy consumption of gas blowing devices such as blowers and compressors becomes large (increasing 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 m+sφ to 0.3 mmφ have been used, since large-diameter 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 (AL) when the Raynozzle number is in the range of 1 to 500 (most carriers used in the fluidized bed method are within this range).
LEN). DP... (1) However, ρF=fluid density (g/as3) μF=fluid viscosity (g/3・see) DP: particle diameter (
am ) g: Gravitational acceleration (am/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. Therefore, the conventional fluidized bed wastewater treatment apparatus still has various problems in achieving miniaturization and energy saving. The present invention was made in order to solve the above problems, and an object of the present invention is to obtain a fluidized bed type wastewater treatment device that can realize downsizing and energy saving. [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 the carrier placed in this tank is made of polypropylene and has a specific gravity of 1.00
~1.02 was used, and a screen for carrier separation was provided on the treated water discharge side of the tank. Preferably, a bubble generator is provided near the screen to prevent clogging of the screen due to adhesion of the carrier. Further, it is preferable 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. [Function] In the present invention, the main reason for limiting the use 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,
It is difficult to control the specific gravity to 1.00 to 1.02, and even if it is possible to control the specific gravity to 1.00 to 1.02 by foaming, water will accumulate in the air bubbles inside the carrier after long-term use. This is not desirable because it will penetrate and change the specific gravity. 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 treated water discharge side of the tank, and is not discharged outside the tank. Furthermore, the carrier is prevented from adhering to the screen due to bubbles generated by the 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.

[Example] Hereinafter, an example 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. 4 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. In addition, a screen 12 for carrier separation is provided on the discharge side of the treated water, 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 as described above and has a specific gravity of 1. Consists of OO~1°02. 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 specific gravity adjusting agents. Also, its outer diameter is 3.0 to 20-
The inner diameter of the first through hole 3b is suitably about 1.0 to 18 mm, and the ratio of length to outer diameter is suitably about 0.8 to 1.2. Molded particles 3
The shape of a is generally cylindrical, but it can also be spherical, ellipsoidal,
It can be freely defined as a quadrangular prism, a polygonal prism, a 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-scale aeration, making it difficult to fluidize; 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. 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 speed (vS) of the bubble relative to water, the rising speed of the bubble is v 10v , and the contact time of the gas S with the acid 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. 3 shows the results of carrier fluidization experiments conducted using cylindrical (4 mmφX4+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 performed using a full-surface aeration method using a disc-type diffuser. The apparent filling rate of the carrier was 44%. From FIG. 3, it can be seen that a very small 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. If it is about 3Nm-A1r/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 blown air is 3.5 Nm −
Alt/m3-reactor/hr. Therefore, for a carrier with a specific gravity of 1.04, (blow air ff1 required for biological reaction)
(amount of blown air required for fluidization)...
・(2) As a result, extra energy is consumed for carrier fluidization. On the other hand, carrier 3 with a specific gravity of 1.005.1.02
3- The body is like this 1. At a blowing air amount of about 3Nm-Air/m reactor/hr, more than 90% of the carrier becomes fluidized, and the inequality sign in equation 2) is reversed, resulting in high energy efficiency. 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 outlet (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 reduce the size to about 1/6. [Effects of the Invention] As described above, according to the present invention, a compact and energy-saving fluidized bed wastewater treatment apparatus can be obtained by employing a full-surface aeration system and using a polypropylene carrier having a specific specific gravity. 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 to remove fibrous impurities in the raw water in advance, effects such as further prevention of clogging of the carrier separation screen can be obtained.

[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 apparatus shown in Figure 1, Figure 3 is a diagram showing the results of a fluidization experiment for each specific gravity of the carrier, and Figure 4 is a conventional draft tube reactor. FIG. 3... Carrier 6... Raw water supply pipe 7... Aeration device 8... Compressor or blower 9... Treated water drain pipe 11... Tank 12... Carrier separation screen 13.・Bubble generator

Claims (3)

[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 treated water discharge side of a tank. (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.