JPS60893A - Biological treatment of organic waste water - Google Patents

Abstract

PURPOSE:To improve rate of absorption of oxygen and to supply necessary quantity of oxygen with a small quantity of air by allowing bubbles contg. oxygen to stick to the surface of particles of microorganisms in the sludge to be returned and distributing oxygen throughout an aerobic biological treatment system under mixed phase flow condition of org. waste water. CONSTITUTION:Org. waste water 11 such as sewage or nightsoil, etc. is separated into microorganism flock 14 and biologically treated water 15 in a solid/liquid separation stage 13 after it is treated biologically by passing through an aerobic biological treatment reactor 12. Major part of the separated microorganism flock 14 is used for microorganism slurry for recycling 16 and a part of the microorganism flock 14 is disposed as excess sludge 17. And air (or oxygen) bubbles are attached to the surface of microorganism flock which constitutes the microorganism slurry 16 for recycling by supplying air (or gaseous oxygen) 18 to a contacting stage 19. BOD component is removed biologically in a reactor 12 by the mixed phase flow of the microorganism flock 20 having oxygen-contg. bubbles on the surface with the org. waste water 11.

Description

[Detailed Description of the Invention] The present invention relates to a method for biological treatment of organic wastewater, and an object of the present invention is to provide a new method that can significantly reduce the aeration power required for aerobic biological treatment such as an activated sludge process. .

The aeration process consumes the most energy in aerobic biological treatment of organic wastewater. Therefore, energy saving in the aeration process is extremely important, and effective solutions are strongly desired.

The present invention provides a process based on a new idea that provides one answer to this problem.

The conventional aerobic biological treatment method uses an aeration tank 1 as shown in Figure 1.
However, due to poor oxygen absorption efficiency, a large amount of aeration power was required. The reason why the oxygen absorption efficiency of conventional aeration methods is poor is that most of the supplied air is not utilized at all and dissipates into the atmosphere from the water surface of the aeration tank. In addition, 2 in Figure 1 is raw water,
3 is air, 4 is treated water, 5 is water surface, and 6 is air bubbles.

The inventor of the present invention strongly recognizes that as long as the conventional aeration method is followed, no matter how much the aerator is improved, the limits of the technology cannot be broken.As a result of the study, the inventor found that the oxygen absorption efficiency was approximately 100%. %, and also did not require aeration in an aerobic biological reaction tank.

That is, in the conventional method, as shown in Figure 1, oxygen is dissolved in the aqueous phase in the aeration tank 1 by air region, and this dissolved oxygen is used for respiration of aerobic microorganisms, so that the supplied air is Most of it is never used and dissipates into the atmosphere.

On the other hand, the present inventor has found that if oxygen-containing bubbles are attached to the surface of microorganism flocs containing water as shown in Fig. 2, and this microorganism-bubble complex is brought into contact with the wastewater to be treated, it is sufficiently efficient. It was discovered that a gaseous biological reaction progresses.

What is extremely important here is the fact that the air bubbles attached to and captured on the surface of the microbial flocs are in contact with the wastewater to be treated for a long time without dissipating into the atmosphere. This is a completely different phenomenon than the phenomenon in which approximately 100 of these particles instantly reach the water surface and dissipate into the atmosphere. Therefore, in the method of the present invention, the oxygen absorption efficiency is significantly improved, so that the oxygen required for respiration of aerobic microorganisms can be sufficiently supplied with an extremely small amount of air.

The present invention was completed based on the above considerations, and includes an aerobic biological treatment process followed by a solid-liquid separation process, and organic wastewater is treated with sludge returned from the solid-liquid separation process. The method for biological treatment is characterized in that oxygen-containing bubbles are attached to the surface of microbial particles in the returned sludge, and the bubbles are allowed to flow through the aerobic biological treatment process in a multiphase flow state with organic wastewater. This is a biological treatment method for organic wastewater.

Next, one embodiment of the present invention will be described with reference to FIG.

Organic wastewater 11 such as sewage and human waste is fed to an aerobic biological reactor 1
2 and is subjected to biological treatment, solid-liquid separation step 13
The water is separated into microbial flocs 14 and biologically treated water 15. Most of the separated microbial flocs 14 are used as microbial slurry 16 for recycling, and a portion is disposed of as surplus sludge 17. Therefore, air 18 (or oxygen gas)
is supplied to the contacting step 19 to cause air bubbles to adhere to the surface of the microbial flocs constituting the microbial slurry 16 for recycling.

In this way, as shown in FIG.
1 and flowing through the reactor 12 in a multiphase flow state, BOD components and the like in the liquid to be treated are biologically removed.

The flow conditions in the reactor 12 are an important factor, and are preferably set so that the microbial flocs 2o to which oxygen-containing bubbles are attached are in sufficient contact with the liquid to be treated without being separated. If the flow rate in the reactor 12 is too slow, the microbial flocs 20
As shown in the figure, it floats to the top of the reactor 12 and does not effectively come into contact with the liquid to be treated, which is not preferable. For this purpose, a tubular type reactor 12 is suitable. It is also good to provide a baffle in the reactor 12 in order to bring the microbial flocs 20 with air bubbles into sufficient contact with the liquid to be treated.

Furthermore, in order to effectively attach oxygen-containing bubbles to the microbial flocs, it is extremely important to add a polymer flocculant 21 (cationic type is effective), a foaming agent (for example, saponin), etc. to the flocs. It is valid.

Note that the reactor 12 may be either an open type or a closed type.

In this way, in the present invention, aerobic microorganisms can reduce the BOD,
Since the oxygen necessary for oxidizing NH3--N etc. is supplied, there is no need for aeration as in the conventional method shown in FIG. 1, which is an industrially advantageous effect.

Oxygen in the bubbles attached to the surface of microbial flocs is removed from reactor 1.
Since the oxygen-containing gas is sufficiently absorbed by increasing the residence time in 2, a very small amount of oxygen-containing gas is sufficient to be supplied to the contacting step 19, and as a result, the power of the near compressor can be reduced.

According to the experiments of the present invention, sewage (BOD 150 mfA
) is treated with activated sludge by the conventional method using an aeration tank while supplying air with an aeration pipe from the bottom of the aeration tank (at a depth of 4 m), the aeration power of the blower is used to remove BOD 1.
kg at. ! 70.9~1. OKWH was required, whereas in the method of the present invention, the power of the near compressor was only 0.2 to 0.4 KWH per kg of removed BOD.

According to the present invention as described above, the following industrially important effects can be obtained.

■ Airage thinning is not required in the microbial reaction process.

■ Therefore, the scattering of droplets from the aeration tank, the generation of odors,
Since problems such as foaming do not occur, maintenance management is greatly streamlined.

■ The power required to supply oxygen to aerobic microorganisms is significantly less than in conventional processes, resulting in energy savings.

[Brief explanation of the drawing]

Figure 1 is a flow sheet of the conventional aerobic biological treatment method;
FIG. 3 is a flow sheet showing an embodiment of the present invention, and FIG. 4 is a sectional view showing the floating state of microbial flocs in the reactor in this embodiment. 11...Organic wastewater, 12...Reactor, 13...
Solid-liquid separation step, 14, 20... Microbial floc, 1
5... Biologically treated water, 16... Microbial slurry for recycling, 17... Excess sludge, 18... Air, 19...
... Contact step, 21... Polymer flocculant. Patent applicant: Patent attorney representing Ebara Infilco Co., Ltd.
1,000 1) Twisting Takao Maruyama

Claims (1)

[Scope of Claims] 1. A method in which an aerobic biological treatment step and a solid-liquid separation step are disposed subsequent thereto, and organic wastewater is biologically treated by adding return sludge from the solid-liquid separation step, A method for biological treatment of organic wastewater, which comprises attaching oxygen-containing bubbles to the surface of microbial particles in sludge and causing the bubbles to flow through the aerobic biological treatment process in a multiphase flow state with the organic wastewater. 2. The biological treatment method according to claim 1, wherein the aerobic biological treatment step is performed using a tubular reactor. 3. The biological treatment method according to claim 1 or 2, wherein the treatment for adhering the oxygen-containing bubbles is performed after adding a foaming agent to the returned sludge in advance.