JP2000005789A - Treatment of organic waste water and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the quality of treated water in an aeration tank provided with a membrane separator inside by aerobically treating and membrane- separating waste water and solubilizing a part of the liq. mixture in the aeration tank in a solubilization tank. SOLUTION: A membrane separator 2 is provided to an aeration tank 1. The solid-liq. separation of waste water by the membrane separator 2 and the biological digestion by aeration are performed in parallel, the liq. mixture contg. sludge and being aerated is appropriately withdrawn and introduced into the subsequent solubilization tank 3. The solid component of the sludge is converted to a water-soluble component in the solubilization tank 3, the solubilized liq. is returned again to the aeration tank 1, and the org. component is converted to the gas by biological digestion. Accordingly, the amts. of the soluble org. matter, gel component and fine solid component contained in the membrane-separated water discharged from the tank 1 are decreased, and the quality of the treated water is drastically improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a wastewater treatment process such as a sewage treatment plant and a human waste treatment plant, or a method of treating organic wastewater discharged from a food factory, a chemical factory, and the like.

[0002]

2. Description of the Related Art As a method for treating organic wastewater, wastewater is aerobically digested and decomposed in an aeration tank provided with an immersion type membrane separation device, and solid-liquid separated by a membrane separation device. A method for discharging the separated treated water has been proposed (Japanese Patent Application Laid-Open No. Hei 8-24597, Utility Model Registration No. 2555561, etc., and FIG. 2 shows an outline of this apparatus). In this method, aerobic digestion and decomposition of organic wastewater and isolation of treated water by membrane separation can be performed in parallel.
This is preferable in that the processing is not complicated. In addition, since the sludge concentration in the aeration tank can be maintained at a high concentration, there is an advantage that the sludge load is reduced and the amount of excess sludge generated is small. However, in this method, the quality of the treated water is often unfavorable unless the sludge is properly extracted, and may not be discarded without further treatment. The decrease in the quality of the treated water is caused by microscopic solids, gel-like substances, and the like, which are derived from dead sterilized bodies resulting from the growth of bacteria (especially aerobic microorganisms) in the sludge and an increase in the sludge concentration in the aeration tank. This is thought to be due to the fact that soluble organic substances and the like pass through the immersion membrane and enter the treated water, and the biological / chemical oxygen demand and the soluble / suspendable organic compound concentration of the treated water are high. It is. Thus, discarding both the sludge and the treated water generated by the above treatment into the ocean, rivers, lakes and marshes can cause environmental problems.

[0003]

SUMMARY OF THE INVENTION The present invention has been made in view of such problems of the prior art,
The purpose is to improve the quality of treated water generated in the above-mentioned organic wastewater treatment method, that is, to reduce the biological / chemical oxygen demand and the concentration of soluble / suspendable organic compounds in treated water. It is another object of the present invention to provide a treatment method capable of reducing the amount of generated excess sludge.

[0004]

In order to achieve the above object, the present invention provides a method for treating organic wastewater containing organic sludge, which comprises the following steps: Aerobic treatment and membrane separation of wastewater in an aeration tank disposed in the aeration tank, and (2) a step of solubilizing a part of the mixed solution in the aeration tank in a solubilization tank. A characteristic processing method (first invention of the present application) is provided. According to this method, a part of the mixed liquid containing the sludge containing the microorganisms grown in the aeration tank under aerobic conditions and the organic matter derived from the dead sterilized body after the growth is guided to the solubilization tank for solubilization. By doing so, the quality of the treated water discharged from the aeration tank is improved. That is, by extracting the mixed solution in the aeration tank to reduce the amount of sludge, especially the above-mentioned microorganisms, soluble organic matter derived from the dead sterilized body and the like, gel-like substances, fine solids and the like that are permeable to the membrane and the like can be obtained. In addition, the amount mixed into the discharged treated water can be reduced. The mixed liquid containing the sludge withdrawn from the aeration tank is solubilized, and the volume of the excess sludge is finally reduced.

[0005] Next, the solubilized solution after the step (2) is returned to the aeration tank and treated in the circulation system. In the second invention of the present application, the sludge is subjected to aerobic digestion and decomposition and solubilization. The amount can be further reduced, and the amount of the contaminants in the treated water as described above can be reduced, thereby improving the treated water quality.

[0006] In the third invention of the present application, the solubilizing step (2) is accomplished by digestion with a thermophilic bacterium.
Such thermophiles are generally contained in compost, excess sewage sludge, soil, and the like, and are preferable because they can solubilize sludge with high efficiency.

The fourth invention of the present application is an organic wastewater treatment apparatus for carrying out the above-mentioned treatment method, comprising an aeration tank provided with a submerged membrane separation device, a solubilization tank, An apparatus is provided that includes a path for introducing sludge from an aeration tank into a solubilization tank. With such a processing apparatus, the quality of the treated water can be improved with a device having a relatively simple configuration, and the above-described processing method can be performed in which the generation of excess sludge is small.

Further, the fifth invention of the present application further includes a route for returning the solubilized solution from the solubilization tank to the aeration tank of the treatment apparatus of the fourth invention, wherein the organic wastewater is circulated. Further, the present invention relates to an apparatus for further improving the quality of treated water and reducing the generation of excess sludge.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. First, in the aeration tank 1 provided with the membrane separation device 2, solid-liquid separation is performed by the membrane separation device 2 in parallel with biological digestion by aeration treatment. The mixed liquid during the aeration treatment including the sludge is appropriately extracted and introduced into the next solubilization tank 3. In the solubilization tank 3, the solid component of the sludge is converted to a water-soluble component, and the treated liquid after solubilization is returned to the aeration tank 1 again, and the organic component is converted to a gas as much as possible by biological digestion. Therefore, the amounts of soluble organic substances, gel components, and fine solid components contained in the treated water after membrane separation discharged from the aeration tank 1 are far reduced as compared with the conventional method shown in FIG. In addition, the quality of the treated water is remarkably improved.

In the present invention, the structure of each tank for performing aeration treatment, membrane separation, and solubilization, and the path connecting these tanks are not particularly limited, and essentially those conventionally used are used. (See Japanese Patent Application Laid-Open No. 9-10791 by the present applicant).

The aeration tank used in the apparatus of the present invention may be any one provided with aeration means and provided with a membrane separation device. The aeration treatment is preferably carried out at room temperature with an aeration of 0.1 to 0.5 vvm so as to allow aerobic digestion and decomposition. May be processed. The liquid to be treated is preferably adjusted to a pH of 5.0 to 8.0. Also,
The aeration tank contains microorganisms such as yeast to promote aerobic digestion and decomposition, and flocculants such as aluminum sulfate, polyaluminum chloride, ferric chloride, and ferrous sulfate to promote floc formation. May be added.

The membrane separation device provided in the aeration tank has, for example, a pore size of 0.1 to 2.5 μm, preferably 0.3 to 0.1 μm.
A membrane having a size of 5 μm may be used, and those formed from one or more membrane module structures are preferred. Preferred membrane separators include a submerged membrane separator equipped with a T-type filter element manufactured by Yuasa Corporation.

[0013] In the above membrane separation apparatus, preferably,
Cleaning means such as pressurization by water pressure, air pressure, or the like, or cleaning, vibration, vibration, or chemical injection is included or provided in parallel, and it is preferable to adopt a structure in which substances that do not pass through the membrane are prevented from adhering to the membrane surface as much as possible.

The mixture is withdrawn from the aeration tank in order to subject a part of the mixture to the next solubilization step. Preferably, the concentration of the mixture suspension (MLSS) in the aeration tank is maintained at a constant value. In order to smoothly carry out digestion and decomposition by aerobic treatment, the mixed solution may be withdrawn while controlling the amount intermittently or constantly, and then subjected to the next solubilization step.

In the solubilization step, a thermophilic bacterium (for example, a bacterium such as Bacillus stearothermophilus may be added).
Decomposition, ozone decomposition, electrolysis, thermal alkali decomposition,
The method may be selected from various conventionally known methods such as enzymatic degradation (for example, protease, lipase, glycosidase and the like are added alone or in combination).

At present, the solubilization step is preferably performed by a thermophilic bacterium treatment in terms of the solubilization rate to be achieved, maintainability, economy and the like. In this case, 50-9
The solubilization may be allowed to proceed at 0 ° C., preferably 60 to 70 ° C., under normal pressure, preferably at a pH in the range of about neutral to weakly alkaline. The solubilization by the thermophilic bacterium may be performed anaerobic or aerobic.

The wastewater treatment method of the present invention as described above may be performed in any of a batch system and a continuous system, and the treatment time is appropriately set in view of the physical properties of the wastewater and the scale and shape of each treatment tank. .

According to the treatment method of the present invention, the treated water finally obtained through the membrane separation device in the aeration tank is:
The water quality has been improved so that it can be generally disposed of.

[0019]

EXAMPLES Examples of the present invention will be described below, but the scope of the present invention should not be limited by these examples.

Example 1 An artificial wastewater prepared by diluting a mixture of peptone: glucose: yeast extract at a weight ratio of 4: 4: 1 with tap water to a BOD of about 1200 mg / L was prepared. Used as raw water.

The raw water is put into an aeration tank (square tank made of transparent vinyl chloride having a capacity of 40 L) in which an immersion type membrane separation device (T-type filter element manufactured by Yuasa Corporation) is installed. Charged at 4 kg-BOD / m ³ / day, and maintained at room temperature (25 ° C.) with a ventilation of 0.5 vvm. Then, the MLSS concentration in the aeration tank was increased to about 12,
A constant amount of the mixed solution was constantly drawn from the aeration tank so as to maintain the concentration at 300 mg / L, and was introduced into a solubilization tank (a cylindrical cylindrical tank having an internal volume of 2 L). Solubilization is through ventilation 0.5v
Performed at 65 ° C. at vm. In the solubilization tank, as a thermophilic bacterium at the start of operation, excess sewage sludge is used for 3 years or more under high temperature conditions (6
Seed sludge cultured at 5 ° C.) was added at 2% by volume. The treatment solution after solubilization was always returned to the aeration tank, and the treatment was continued in a circulation system for 100 days.

[Comparative Example 1] The same aeration treatment as in Example 1 was performed, except that drawing from the aeration tank, solubilization, and return were not performed. The MLSS concentration in the aeration tank was approximately 12,040 mg / L.

The amount of sludge generated by each of the above treatments was measured, and the quality of the treated water was examined for the following items. Table 1 shows the results.

BOD: 2 according to JIS K 0102
Biological oxygen consumption measurement based on the amount of dissolved oxygen consumed after leaving the diluted solution at 0 ° C. for 5 days. S-TOC: The filtrate filtered through a glass fiber filter paper having a pore size of 1 μm according to JIS K 0102 was also subjected to JIS K.
Determination of the amount of soluble total organic compounds by combustion oxidation-infrared TOC analysis method according to No. 0102 SS: A residue on the filter paper filtered through a glass fiber filter paper having a pore diameter of 1 μm according to JIS K 0102 is 105 to 110 ° C.
Dry and weigh suspended solids

[0025]

[Table 1]

From Table 1, it is clear that the treated water produced in Example 1 has a lower soluble organic matter and suspended solid content and improved water quality as compared with that of Comparative Example 1. It is. And the sludge amount was also zero.

[0027]

According to the present invention, it is possible to improve the quality of treated water obtained and generate excess sludge while maintaining the advantages of space saving and simplicity of organic wastewater treatment using an aeration tank provided with a membrane separation. The effect is achieved that the amount can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of an organic wastewater treatment apparatus of the present invention.

FIG. 2 is a schematic configuration diagram of a conventional organic wastewater treatment apparatus.

[Explanation of symbols]

 1 ... aeration tank 2 ... membrane separation device 3 ... solubilization tank

Claims (5)

[Claims] In the method for treating organic wastewater, the following steps are performed: (1) a step of aerobically treating wastewater and separating a membrane in an aeration tank provided with a membrane separation device in the tank; And (2) a step of solubilizing a part of the mixed solution in the aeration tank in the solubilization tank. 2. The solubilized solution after the step (2) is:
The treatment method according to claim 1, wherein the treatment method is returned to the aeration tank and treated in a circulation system. 3. The treatment method according to claim 1, wherein the solubilizing step (2) is achieved by digestion with a thermophilic bacterium. 4. An apparatus for treating organic wastewater, comprising: an aeration tank provided with a membrane separation device in a tank; a solubilization tank; and a path for introducing sludge from the aeration tank into the solubilization tank. A processing device comprising: 5. The processing apparatus according to claim 4, further comprising a path for returning the solubilized solution from the solubilizing tank to the aeration tank.