JPS6321554B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for aerobic microbial treatment of wastewater and an apparatus therefor. More specifically, microorganisms are attached to carrier particles that float on water and filled into a wastewater treatment tank, and the wastewater is introduced in a downward flow and brought into contact with the microorganisms attached to the carrier particles under aerobic conditions. A method of efficiently treating wastewater by dramatically increasing oxygen dissolution efficiency by aerating from the bottom or below the packed bed of carrier particles and bringing them into contact with the wastewater in a countercurrent manner. and its equipment. Wastewater treatment methods that utilize microorganisms have traditionally included floating treatment methods using individual microorganisms, as typified by activated sludge, and fixed microbial membrane treatment, in which microorganisms are attached to plastic plates, as seen in sprinkler beds, submerged beds, and rotating disk methods. It is well known that there are laws and regulations, and they are all widely used. Furthermore, recently, methods and devices have been proposed in which particles that float on water are used as carriers for microorganisms, and wastewater is treated aerobically by passing the water through it in a downward direction. In this case, methods and devices are known in which a portion of the treated water is pumped up and circulated to form a downward flow together with the wastewater for continuous treatment.The pumping means includes a draft tube installed in the treatment tank, etc. The main methods are to use an air lift effect by ventilating the pumping part of the water from an aeration mechanism, and to use a pump installed outside the treatment tank. For example, as an example of the former,
53-69171, JP-A-54-85542, and JP-A-56-76295. The common feature of the technologies in ~ is that the aeration section that supplies oxygen and the aerobic microbial reaction section where floating carrier particles are present are separated, and the two communicate with each other so that the oxygen supplied in the aeration section, that is, the dissolved oxygen, is absorbed by microorganisms. It moves to the reaction section and reacts in a downward flow, and for this purpose the aeration section has two functions: one to circulate water through an air lift effect, and the other to dissolve oxygen. Another feature of the process is that air or the like is blown directly from the bottom of the carrier particle packed bed in the processing tank to generate a convection-like circulating flow. Further, as an example of the latter, there is JP-A-54-142863. Aerobic microbial treatment of wastewater using carrier particles that float on water can increase the amount of microorganisms retained compared to conventional activated sludge methods and biological catalytic oxidation methods.
It has the advantage of high reaction rate. For example, in conventional technologies such as the activated sludge method, the BOD reaction rate is approximately 1KgBOD/ ^m3・day, whereas
Reaction rates of BOD/m ³ ·day or more can be achieved. In order to take full advantage of these advantages, it is necessary to be able to supply a sufficient amount of oxygen necessary for the reaction. However, as mentioned above, in the conventional method of increasing dissolved oxygen and transferring it to the microbial reaction zone using the air lift type aeration method, the saturated dissolved oxygen concentration is constant, so when a large amount of oxygen is required, The amount of circulating water must be increased. However, the oxygen dissolution efficiency of the airlift aeration method when gas is blown from a depth of 3 m is about 4 to 12%, and if a large amount of air is blown in to increase the amount of circulating water, the oxygen will dissolve. Efficiency will actually decrease. An object of the present invention is to provide a method for aerobic microbial treatment of wastewater and an apparatus therefor, which eliminates such problems. The present invention firstly provides carrier particles (hereinafter referred to as
Sometimes they are simply called carrier particles. ), wastewater is introduced in a downward flow through a wastewater distributor into a packed bed, and the wastewater is treated by contacting with microorganisms under aerobic conditions as it passes through the bed. In an aerobic microbial treatment method for wastewater, which comprises pumping and circulating a portion of the water to form a downward flow together with the wastewater to continuously treat the wastewater and recovering the treated water, the filling of the carrier particles Air, pure oxygen gas, or oxygen-containing gas is blown from the bottom or below the bed at a rate of 1 to 50 Nm ³ /m ² ·hr per unit cross-sectional area of the packed bed to bring it into countercurrent contact with the waste water, and the said waste water An aerobic system for wastewater, characterized in that air bubbles accumulated below the distributor are removed through an air vent port, and carrier particles flowing out from the packed bed of carrier particles are returned through a carrier particle return port. This is a microbial treatment method. The second aspect of the present invention is a wastewater inlet at the top of the treatment tank, a perforated plate type wastewater distributor at the top,
A treatment for wastewater that is equipped with a middle part filled with carrier particles with apparent specific gravity of 1.0 or less that have microorganisms attached to them and float on water, a treated water outlet in the bottom part, and a means for pumping up a part of the treated water. In the tank, an aeration means for air, pure oxygen gas, or oxygen-containing gas is provided at the bottom or the entire lower surface of the part filled with the carrier particles, and the distributor is provided with an air vent port and the carrier particle return port. This is an aerobic microbial treatment device for wastewater that is characterized by: The lower part of the packed bed in the present invention means the lower part within the packed bed, and usually refers to a position within about 30% of the bottom end of the packed bed. Further, the term "below the packed bed" means the lower part outside the packed bed, and usually means within about 1 m from the lower end of the packed bed. Direct aeration to a packed bed of carrier particles to which microorganisms are attached promotes the detachment of microorganisms and inevitably reduces the reaction rate, and furthermore, aeration to the microbial reaction area where the carrier particles are present may cause coalescence of air bubbles. It was thought that this would promote coalescence and reduce the aeration effect, but as a result of repeated experiments, the inventors found that this expected phenomenon did not occur, and rather the effect of the present invention was remarkable. I have confirmed that there is. That is, the present invention is based on the process of attaching microorganisms to floating carrier particles and introducing wastewater into a bed filled with carrier particles in a downward flow for treatment. Perform more aeration,
When brought into contact with the downward flowing wastewater in a countercurrent manner, the floating bubbles are suppressed from rising by the downward flow, prolonging the residence time and contact time, resulting in efficient oxygen dissolution. It becomes possible. Furthermore, it has been observed that the air bubbles adhere to the surface of the carrier particles (microorganisms) and stop there, and as a result, oxygen is efficiently dissolved without promoting coalescence or aggregation of the air bubbles. In this case, since dissolved oxygen is actively consumed by microorganisms, the dissolved oxygen concentration never reaches saturation, and a high oxygen dissolution rate can always be maintained. On the other hand, regarding the removal of microorganisms, it is necessary to use carrier particles made of synthetic resin with fine irregularities on the surface to which microorganisms can easily adhere, and because the present invention has a very high oxygen dissolution efficiency, it is necessary to use a carrier particle packed layer. Since only a small amount of air is supplied from the lower part or below, no trouble occurs. When carrying out the method of the present invention, the downward flow rate per unit cross-sectional area of the packed bed of microorganism-adhered carrier particles is 1 to 1.
720 m/hr, preferably 1 to 150 m/hr, and the amount of blown gas per unit cross-sectional area of the packed bed to 1 to 50 N.
m ³ /m ² ·hr, preferably 1 to 30Nm ³ /m ² ·hr, to maintain oxygen dissolution efficiency at a high value,
Wastewater can be treated at a high reaction rate. The above numerical range is necessary for improving oxygen dissolution without destroying the flow pattern of countercurrent contact, and is an aeration condition that does not cause significant detachment of microorganisms attached to the surface of carrier particles. Moreover, the amount of air, etc. blown, power consumption, etc. can be reduced. By introducing the wastewater in a downward flow, the packed bed of carrier particles expands at a predetermined downward flow velocity or higher to form a fluidized bed, but the expansion coefficient at this time is adjusted to be 1.0 to 2.5. It is desirable to do so. The carrier particles used in the present invention are suitably particles with an apparent specific gravity of 1.0 or less and which do not absorb water and settle when present in water. In general, foamed synthetic resin is granulated by adding an inorganic substance, or foamed synthetic resin particles have one or more substances selected from inorganic and organic substances adhered to the surface. etc. can be mentioned. The synthetic resins used in this case include polyethylene,
Examples include polypropylene, polystyrene, and polyvinyl chloride, and the particles can have any shape such as spherical, prismatic, or cylindrical. Inorganic substances include sand, natural crushed stone, activated carbon, perlite, shirasu balloons, gypsum, alumina, zeolite, ceramics, etc., and organic substances include anthracite,
Coal, coke, pitch, waste ion exchange resin, rubber, etc. Since many fine irregularities are formed on the surface of these carrier particles, microorganisms can easily adhere to them.
It also has the characteristic of being difficult to peel off. Next, embodiments of the apparatus of the present invention will be described with reference to the drawings. FIG. 1 shows the basic principle of the invention. That is, the wastewater a flows downward through the carrier particle packed bed 2 from the wastewater introduction pipe 5 through the wastewater distributor 3 provided at the top of the treatment tank 1, and flows downward through the carrier particle packed bed 2 provided at the bottom of the treatment tank 1. The treated water is recovered from the treated water extraction pipe 6 as treated water b. At this time, the particles are purified by coming into contact with microorganisms in the carrier particle packed bed 2. Oxygen required for aerobic microbial treatment during this purification is supplied by blowing gas (air, pure oxygen gas or oxygen-containing gas) c from the aeration means 4 provided at the bottom of the treatment tank 1. be done. As the aeration means 4, a defuser or the like is used. In addition, 7 in the figure is a gas blowing pipe. Figures 2a, b and 3 show a case where a pumping section such as a draft tube 8 and an aeration mechanism 9 are provided as a means for pumping a part of the treated water; This is an example in which the perforated plate type wastewater distributor 3 is used only for dispersing wastewater, and FIG. 3 shows an example in which it is used both to prevent floating of carrier particles and to disperse wastewater. Since air bubbles accumulate below this drainage distributor 3, an air bubble vent 10 is provided, and the carrier particles flow out from the draft tube or the like and the air bubble vent to the upper part of the drainage distributor. A carrier particle return port 11 is provided for returning the carrier particles to the carrier particle packed bed. The air bubble removal port 10 has an upper opening located above the water surface in the upper part of the drainage distributor, and the upper opening of the carrier particle return port 11 is located at the same level as or slightly below the water surface. In addition, the lower opening of the carrier particle return port is located below the drainage distributor, and a buttful plate is installed below the opening to prevent air bubbles rising from below from flowing in. It is desirable to have one. 4a, b and 5 show the case where the pump 12 is used as a means for pumping a part of the treated water, and FIGS. 4a, b show that the perforated plate type drainage distributor 3 is floating. Figure 5 shows a type in which the drainage distributor is immersed. In the figure, 13 and 14 are piping. Note that the draft tube 8 is provided for circulating some of the carrier particles. In the present invention, a portion of the treated water pumped by the above-described means is transferred to the waste water distributor 3.
It is introduced into the treatment tank 1 as a downward flow along with the waste water, and comes into contact with air etc. supplied from the lower part or the entire lower surface of the carrier particle packed bed 2 in a countercurrent manner. In the present invention, when pure oxygen gas or oxygen-containing gas is used as the gas supplied from the lower part or the entire lower surface of the carrier particle packed bed 2, the processing tank is designed to have a closed structure in order to effectively utilize these gases. From the gas circulation port provided in the tank, gas can be sucked through piping by a blower or the like and flowed into the processing tank again. 6a and 6b are plan views of an embodiment of the perforated plate type drainage distributor 3. FIG. In the figure, 15 is a hole. Further, FIG. 7 is a plan view showing an example of the arrangement of a differential user, which is an aeration means. FIGS. 8 and 9 are detailed explanatory diagrams of the carrier particle return port. As is clear from the figure, the upper opening of the carrier particle return port is located at or slightly below the water level 17. In the figure, 16 is a carrier particle, and 18 is a baffle plate. Next, the present invention will be explained in detail using experimental examples and examples. Experimental example (countercurrent aeration test using tap water) A polyvinyl chloride diameter 100 mm x treatment tank
An apparatus with a height of 5000 mm was used, and a diffuser plate (BP-23 manufactured by Daicel Chemical Industries, Ltd.) was used as an aeration means. Additionally, the gas injection position inside the treatment tank is 1.6m below the water surface.
or 3.2m, and air was used as the gas.
Inorganic material (talc)-containing foamed polypropylene particles having a width of 3.0 mm, a height of 2.5 mm, and a length of 3.0 mm and a specific gravity of 0.56 were used as carrier particles and filled into a treatment tank. The experimental results are shown in Table 1.

【table】

[Table] Examples and Comparative Examples A polyvinyl chloride device (effective volume: 785 mm) with a diameter of 500 mm and a height of 5000 mm as shown in Figure 1 was used as the treatment tank, and a draft tube (diameter
100cm x length 4000cm) was installed. The aeration means used were the same as in the experimental example. In addition, talc-containing foamed polypropylene particles (diameter 3.5 mm x
4.0 mm in length), and organic artificial waste water (BOD 73-210 mg/substrate: mixture of glucose, sodium citrate, and fish meat extract) was used as waste water. The treatment conditions and results are shown in Table 2. On the other hand, Table 3 shows the results when a conventional air lift type device was used for comparison. The dimensions of the equipment and processing conditions were the same.

[Table] *2 Calculated assuming air is introduced using a blower.

[Table] *1 Same as total air volume As is clear from the table, in the present invention, the oxygen dissolution efficiency of the aeration air is extremely high compared to the conventional method, so regardless of whether the BOD load is low or high, It shows a stable and high BOD removal rate. Similar results were confirmed when the gas was blown into the lower part of the packed bed. On the other hand, in the case of the comparative example, dissolved oxygen is rate-determining, and when the BOD load becomes high, the BOD removal rate decreases extremely. In the present invention, it is desirable that the aeration means installed at or below the carrier particle packed bed be installed at appropriate intervals so as to diffuse air over the entire surface of the packed bed. As a result, countercurrent contact between the blown gas and the liquid is effectively carried out, increasing oxygen dissolution efficiency, and as a result, the amount of gas blown can be reduced, and power consumption can be reduced accordingly. According to the inventors' calculations, the power consumption is approximately 1/2 to 1/5 in the case of the standard activated sludge method.
becomes. Furthermore, in the present invention, the surface area of the carrier per unit volume of the carrier particle packed bed is 10 to 20 times larger than that of the conventional fixed microbial membrane method equipment, so the amount of microorganisms retained per unit volume is increased, and the reaction rate is lower than that of standard activated sludge. It is more than five times larger than the law. Therefore, it is possible to downsize the treatment tank and reduce the amount of construction land. Further, in the present invention, since the amount of oxygen dissolved is approximately proportional to the amount of gas blown, it is very easy to deal with load fluctuations. Moreover, since there is no need to vary the flow velocity of the downward flow even with load variations, the amount of microorganisms retained in the carrier particle packed bed can always be kept constant. Furthermore, according to the present invention, the gas blown from the lower part or below of the carrier particle packed bed rises in the form of bubbles through the packed bed by countercurrent contact with the liquid.
The driving force causing oxygen dissolution is always large throughout the packed bed. Moreover, the amount of gas blown can be adjusted according to the amount of oxygen required for microbial reactions, and even in that case, the oxygen dissolution efficiency remains almost constant, so energy savings can be achieved by blowing the appropriate amount of gas depending on the load. can.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the basic principle of the apparatus of the present invention, FIGS. 2 to 5 are explanatory diagrams of embodiments of the apparatus of the present invention,
6a and 6b are plan views of one embodiment of the drainage distributor, and FIG. 7 is a plan view of one embodiment of the aeration means. FIGS. 8 and 9 are detailed explanatory diagrams of the carrier particle return port. a... Waste water, b... Treated water, c... Gas, 1... Treatment tank, 2... Carrier particle packed bed, 3... Waste water distributor, 4... Aeration means, 5... Waste water introduction pipe, 6...
Treated water extraction pipe, 7... Gas blowing pipe, 8... Draft tube, 10... Air bubble removal port, 11... Carrier particle return port, 12... Pump.

Claims (1)

[Scope of Claims] 1. When wastewater is introduced in a downward flow through a wastewater distributor into a packed bed of carrier particles having an apparent specific gravity of 1.0 or less and floating on water, and passing through the bed. Treating wastewater by contacting it with microorganisms under aerobic conditions, and pumping and circulating a portion of the resulting treated water to form a downward flow together with the wastewater to continuously treat the wastewater, In an aerobic microbial treatment method for wastewater that involves recovering treated water, air, pure oxygen gas, or oxygen-containing gas is introduced from below or below the packed bed of carrier particles at 1 to 50 Nm per unit cross-sectional area of the packed bed. ³ /m ² ·hr to contact the wastewater in a countercurrent manner, and remove the air bubbles that have accumulated below the waste water distributor from the air vent port, and flow out from the packed bed of carrier particles. An aerobic microbial treatment method for wastewater, characterized in that the carrier particles are returned through a carrier particle return port. 2. The method according to claim 1, in which a portion of the treated water is pumped up using an air lift. 3. The method according to claim 1, in which a part of the treated water is pumped up using a pump. 4 A wastewater inlet at the top of the treatment tank, a perforated plate-type wastewater distributor at the top, a part filled with carrier particles with an apparent specific gravity of 1.0 or less that has microorganisms attached to it in the middle, and which floats on water, and a treatment at the bottom. In a wastewater treatment tank equipped with a water outlet and a means for pumping a part of the treated water, an aeration means for aerating air, pure oxygen gas or oxygen-containing gas to the lower part or the entire lower surface of the part filled with carrier particles. An aerobic microbial treatment device for wastewater, characterized in that the distributor is provided with an air bubble outlet and the carrier particle return port. 5. The device according to claim 4, wherein the means for pumping up a portion of the treated water is a pumping section and an aeration mechanism provided in the wastewater treatment tank. 6. The device according to claim 4, wherein the means for pumping up a portion of the treated water is a pipe that communicates the lower part and the upper part of the wastewater treatment tank, and a pump provided in the middle of the pipe.