JPS646837B2 - - Google Patents

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 method that can significantly reduce the aeration power required for biological treatment.

The aeration process is the process that consumes the most energy in aerobic biological treatment of organic wastewater.
For this reason, great efforts have been made to develop aerators with good power efficiency, but no aerator that can be evaluated satisfactorily from the standpoint of energy saving has yet appeared. Biological treatment of wastewater containing highly concentrated pollutant components such as human waste requires a particularly large amount of aeration power, so energy saving in the aeration process is an extremely important and urgent issue.

The present invention provides a process based on a new idea that is completely different from conventional methods, which satisfactorily answers this problem.

In the past, it was common for human waste to be biologically treated by adding 10 to 20 times as much dilution water, but recently, with the main purpose of saving water resources, no dilution or low dilution treatment has started to be performed. It's here.

However, when biologically treating foaming organic wastewater such as human waste or livestock sewage by reducing the dilution ratio, intense foaming occurs in the aeration tank, and unless antifoaming measures are taken, the foam will overflow, causing serious problems. .
For this reason, in the past, the process could not function stably unless a defoaming machine 1 or defoaming agent 2 was added as shown in FIG. Furthermore, since the oxygen absorption efficiency of the air 4 supplied from the bottom of the aeration tank 3 in Figure 1 is as low as about 8%, the amount of air required to biologically nitrify and denitrify, for example, 100Kl/day of human waste is This was a huge value of approximately 1 million m ³ /day, and the power required for the aeration blower 5 was inevitably enormous. Furthermore, the power of the defoaming machine mentioned above,
The cost of injecting antifoaming agents cannot be ignored. In FIG. 1, 6 is raw water, 7 is an aeration pipe, 8 is an aqueous phase, 9 is foam, and 10 is treated water.

The inventor of the present invention closely observed the bubbling phenomenon in the aeration tank during experiments on the non-dilution treatment of human waste, and as a result, was able to arrive at the following extremely important idea.

That is, in the case of a liquid that does not foam, the air bubbles supplied to the bottom of the aeration tank rise within the aeration tank at high speed, instantly reach the water surface, and are dissipated into the atmosphere. Therefore, the opportunity for oxygen to dissolve from air bubbles into water is extremely short, only a few seconds.
As a result, the oxygen absorption efficiency is extremely low. The inventor believed that if the air bubbles that would otherwise escape into the atmosphere from the aeration tank water surface could be captured without being dissipated into the atmosphere, the oxygen absorption efficiency would improve, and while conducting various studies, he discovered the following important phenomena. I found out.

In other words, in the case of foaming organic wastewater, the bubbles that reach the water surface of the aeration tank form foam and become trapped inside the foam without dissipating directly into the atmosphere. Furthermore, as shown in Figure 2, it was discovered that a large amount of aerobic bacteria B such as activated sludge adhered to the interface of air bubbles A in the foam in a wet state.

The essential requirement for an aerobic biological reaction to proceed is the coexistence of microorganisms, oxygen, and water containing a substrate, so the foam in Figure 2 provides the conditions for an aerobic biological reaction to proceed. I have come to an important realization. The most important industrial fact derived from this recognition is that the oxygen-containing bubbles are trapped inside the foam, so the oxygen necessary for bacteria to breathe is automatically supplied from the bubbles within the foam without any aeration. The point is that

In other words, in order for the conventional biological treatment method shown in Figure 1 to supply the oxygen essential to the bacteria in the aeration tank, continuous aeration is an absolute prerequisite; if aeration is stopped, the dissolved Whereas oxygen is consumed and aerobic biological reactions stop, in the method of the present invention, once bubbles are formed, there is no need to continue the explosion, and the oxygen necessary for aerobic bacteria to respire is trapped within the bubbles. It is supplied sufficiently from the air bubbles. This is the reason why the present invention enables significant savings in aeration power, and is a new concept that has not been considered before.

As described above, the present invention reverses the foam formation effect caused by foaming, which was conventionally recognized as an extremely undesirable phenomenon in biological treatment, and turns it into an extremely favorable phenomenon from the viewpoint of saving aeration power. It was completed based on the novel idea of actively utilizing the foam itself as a place for aerobic microbial reactions to proceed.

The reason that conventional technical thinking was unable to reach the idea of using foam is thought to be because it could only take a narrow view that foaming would immediately cause problems.

The effect of the present invention, which utilizes foam, can be said to be amazing, with the aeration power required being 1/5 to 1/10 of that of conventional methods.

Moreover, when the generated foam enters a packed bed made of granular fillers such as Raschig rings and TELLARETZ, or materials frequently used in the sprinkled bed method such as corrugated plates and honeycomb tubes, microorganisms attached to the foam interface and the surface of the filler It was observed that the biological reaction proceeded more effectively due to both the microorganisms attached to the .

More interestingly, the biological reaction progresses more favorably, probably because the foam undergoes deformation during the process of passing through the packed bed and the bubble interface of the foam is renewed.

That is, the present invention involves bringing a liquid to be biologically treated into gas-liquid contact with an oxygen-containing gas in the presence of aerobic bacteria at a foaming generation part to form foam, and filling the foam with a medium for attachment of aerobic bacteria. Organic wastewater is introduced into the formed packed bed, and contaminant components in the biological treatment target liquid are removed by aerobic bacteria adhering to the interface of the foam and the surface of the adhesion medium. It is a biological treatment method.

Here, in the present invention, the "foaming part" means:
This refers to the area where the liquid to be treated is aerated with oxygen-containing gas in the presence of aerobic microorganisms, and the microorganisms generate foam that adheres to the interface of the oxygen-containing gas bubbles. Note that the liquid phase portion may not exist in the foaming portion. In other words, if aeration is performed strongly, the liquid phase part disappears and the entire foaming part becomes only foam.

Next, one embodiment of the present invention will be described using human waste treatment as an example. In FIG. 3, human waste 11 is allowed to flow into the foaming part 12 (liquid phase part) without adding dilution water, and is aerated with air 12' in the coexistence of activated sludge.
Foam vigorously. As aeration methods, in addition to aeration, methods that mechanically stir the water surface, and methods that combine aeration and mechanical agitation can be adopted.In short, the liquid to be treated, aerobic bacteria, and oxygen-containing gas are brought into gas-liquid contact. Any method that produces foaming is fine.

The dilution ratio of human waste is an important factor that affects foaming, and non-dilution treatment is the best as it is easiest to foam.On the other hand, if the dilution ratio exceeds 5 (if the amount of dilution water exceeds 5 times the amount of human waste) It should be avoided as it will make it difficult to foam. Note that a foaming agent may be added to promote foaming.

Further, the concentration of microorganisms in the foaming part 12 is also a factor that greatly affects foaming, and a higher concentration is preferable because foaming becomes easier.

As a result, foam 13 to which microorganisms are attached is formed in the foaming portion 12 and enters the packed bed 14.

In the process of the foam 13 entering the packed bed 14, contaminant components (BOD, NH ₃ -N, etc.) in human waste are
It is removed by both the microorganisms attached to the foam and the microorganisms attached to the particulate solid surface, as well as the air within the foam.

Note that since the foam 13 itself has a rising force, it automatically enters the packed bed 14, so no pump power is required.

In the packed bed 14, the oxygen necessary for respiration of microorganisms is supplied from the air bubbles trapped inside the foam, so there is a remarkable effect that there is no need to continue forced aeration as in the conventional process (Fig. 1). be.

The foam generated during undiluted or lightly diluted human waste treatment is highly stable, and even if left for several days, the foam will hardly break down and the air bubbles will remain in stable contact with aerobic bacteria. Therefore, there is no shortage of oxygen supply.

The foaming generating section 12 in the present invention does not supply dissolved oxygen to the liquid phase to proceed with most of the aerobic biological treatment, but merely generates foaming, and the water depth may be shallow. . Therefore, the power of the aeration blower 15 may be significantly less than in conventional processes.

Therefore, the contaminated components in the human waste 11 are biologically treated in the packed bed 14 filled with foam, and the foam 16 flowing out from the upper part of the packed bed 14 is processed to contain the contaminated components in a solid-liquid separation section 17 such as flotation or centrifugation. is separated into biologically treated water 18 and thickened sludge 19.

The thickened sludge 19 is recycled to the foaming section 12. Reference numeral 20 indicates surplus activated sludge, which may be extracted from pipe 20'. The biologically treated water 18 may be subjected to advanced treatment in various advanced treatment steps depending on the target water quality.

Although this embodiment shows a type in which the filling layer 14 is located above the foaming part 12, it is also possible to provide separate tanks for each.

According to the present invention as described above, the following industrially important effects can be obtained and the organic wastewater treatment process can be revolutionized.

In aerobic biological treatment, the forced aeration operation to supply dissolved oxygen to the aqueous phase, which was an essential requirement in the past, is no longer necessary, and only a small amount of air is required to cause foaming, resulting in significant aeration power. can be saved.

In other words, the power required for the present invention is the same as that of the conventional process (the type shown in Figure 1 in which aeration is performed in an aeration tank).
It is reduced to 1/5 to 1/10 compared to the previous year.

Both the microorganisms attached to the foam and the biofilm attached to the surface of the filler remove organic contaminants, thereby accelerating the reaction rate.

When the foam flows through the packed bed, the bubbles within the foam undergo deformation, resulting in renewal of the bubble interface, which promotes the diffusion of oxygen within the bubbles to the microorganisms.

In conventional processes, defoaming measures are essential to prevent foaming, and for this purpose, defoaming machine power,
Although the cost of adding an antifoaming agent was high, in the present invention, since foaming is rather carried out intentionally, such problems are completely solved.

The present invention is applicable not only to human waste but also to various highly concentrated organic wastewaters such as livestock sewage, and is also applicable to fermentation industries that utilize aerobic bacteria.

[Brief explanation of the drawing]

FIG. 1 is a flow sheet of the conventional method, FIG. 2 is a sectional view showing the structure of foam, and FIG. 3 is a flow sheet showing one embodiment of the present invention. 11... Human waste, 12... Foaming area, 12'...
...Air, 13,16...Foam, 14...Filled layer,
15...Aeration blower, 17...Solid-liquid separation section, 1
8... Biologically treated water, 19... Thickened sludge, 20...
Surplus activated sludge, 20'... pipe.

Claims (1)

[Claims] 1. A packed bed formed by bringing the liquid to be treated biologically into gas-liquid contact with an oxygen-containing gas in the presence of aerobic bacteria at a foaming generation part to form foam, and filling the foam with a medium for attachment of aerobic bacteria. A method for biological treatment of organic wastewater, characterized in that contaminant components in the liquid to be biologically treated are removed by aerobic bacteria adhering to the interface of the foam and the surface of the adhesion medium.