JP2000084594A - Treatment of sewage and sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the amount of discharged excessive sludge by treating sewage utilizing decomposition capabilities of microorganisms for organic matters in a bioreactor, solubilizing the excessive sludge resulted from the treatment process by means of aerobic digestion and acid and alkali decompositions and returning the treated liquid to the bioreactor. SOLUTION: The sewage flowing into a sewerage treating place is introduced into the biological reactor 1, here air being fed into the sewage with an aeration device 11 to activate aerobic bacteria in the active sludge and to treat soluble organic matters in the contamination water. Next, the treated water containing the sludge after the biological treatment is introduced into a sedimentation tank 2, and here solid-liquid separation is performed to separate the sludge from the treated water. Next, the excessive sludge after the sedimentation separation is introduced into an aerobic digestion tank 3, and decomposition easy substance in the sludge is decomposed. The treated water with the aerobic digestion tank 3 is heated with a heat exchanger 4 and a heater 5, then undergoes acid decomposition and alkali decompositions at the acid and alkali decomposition tank 6, and finally neutralized to be fed to the biological reactor tank 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating sewage and sludge, and more particularly, to solid-liquid separation of sludge flowing out together with treated water from a biological reaction tank, and then returning the sludge to a biological reaction tank, thereby obtaining a sewage treatment plant. The present invention relates to a method for treating sewage and sludge, in which surplus sludge discharged from wastewater is reduced and biological treatment in a biological reaction tank can be performed stably.

[0002]

2. Description of the Related Art Conventionally, sewage flowing into a sewage treatment plant, etc.
It is treated by an activated sludge treatment method in which organic wastewater such as sewage is biologically treated with activated sludge using a biological reaction tank such as an aeration tank. In this activated sludge treatment method, after the sludge flowing out together with the treated water from the biological reaction tank is subjected to solid-liquid separation, part or all of the separated sludge is returned to the biological reaction tank as it is. In addition to reducing the amount of excess sludge discharged from such facilities, the biological treatment in the biological reaction tank can be stably performed.

[0003]

As described above, in the conventional activated sludge treatment method, after the sludge flowing out of the biological reaction tank together with the treated water is separated into solid and liquid, the separated sludge is returned to the biological reaction tank as it is. However, since the separated sludge contains a mixture of substances that are soluble in sewage and insoluble substances, even if it is returned to the biological reaction tank as it is, it is insoluble in sewage. The substance does not contribute to the biological treatment, flows out again from the biological reaction tank together with the treated water without being decomposed, and is eventually discarded as surplus sludge.

[0004] The excess sludge has a high moisture content,
Since the sludge concentration is about 1%, it cannot be directly incinerated or dumped in landfills. Usually, it is concentrated to make dehydrated cake, then incinerated or dumped in landfills. Therefore, there is a problem that not only is the treatment costly, but also the treatment itself is difficult due to the recent rise in environmental protection and the shortage of landfills.

The present invention has been made in consideration of the above-mentioned problems of the conventional activated sludge treatment method, and it has been found that surplus sludge discharged from a sewage treatment plant or the like can be significantly reduced, and the biological treatment in a biological reaction tank can be stably performed. It is an object of the present invention to provide a method for treating sewage and sludge.

[0006]

Means for Solving the Problems To achieve the above object, a method for treating sewage and sludge of the present invention utilizes the ability of microorganisms to decompose organic substances in a biological reaction tank, and treats sewage. After the excess sludge generated in the process is subjected to aerobic digestion and acid-alkali decomposition for solubilization, the treated liquid is returned to the biological reaction tank.

In this method for treating sewage and sludge, excess sludge generated in a treatment step in a biological reaction tank is subjected to aerobic digestion and acid-alkali decomposition to solubilize the treated sludge, and the treated liquid is returned to the biological reaction tank. Therefore, the biological treatment of the sludge is promoted, the excess sludge to be discharged can be significantly reduced or the excess sludge is not generated, and the biological reaction can be stably performed.

In this case, the sludge solubilization treatment is carried out by
After aerobic digestion, acid-alkali decomposition can be performed.

Thus, the sludge temperature raised to 40 ° C. to 50 ° C. by the aerobic digestion reaction by the thermophilic bacteria in the aerobic digestion tank is effectively used to efficiently convert the hardly decomposable organic matter into acid. Alkali can be decomposed.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the method for treating sewage and sludge of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of an activated sludge treatment facility installed in a sewage treatment plant or the like for carrying out the method for treating wastewater and sludge of the present invention, and an embodiment of the treatment flow. Sewage such as sewage that is drained from households into the sewage treatment plant is introduced into the biological reaction tank 1 such as an aeration tank by gravity or by means of pumping. An aeration device 11 such as a diffuser plate or a mechanical aerator is provided in the biological reaction tank 1, and air (oxygen) is supplied to the wastewater flowing into the aeration device 11 to improve the quality of the activated sludge. The aerobic microorganisms are activated to treat soluble organic matter in sewage.

A settling tank 2 is connected to the biological reaction tank 1, and treated water containing sludge after sewage is biologically treated in the biological reaction tank 1 is introduced into the settling tank 2.
Then, solid-liquid separation is performed by gravity sedimentation, etc., thereby separating sludge from treated water, and supernatant water is sterilized.
Discharge to rivers, etc.

On the other hand, part or all of the surplus sludge separated by settling is introduced into an aerobic digestion tank 3 connected to the settling tank 2. In this case, depending on the excess sludge concentration, the sludge can be concentrated by gravity or mechanically again before being introduced into the aerobic digestion tank 3.

The purpose of the aerobic digestion tank 3 is to decompose easily decomposable substances of the sludge, and to keep the sludge concentrated at a high concentration in an aerobic state, and to achieve the intended purpose by stirring the sludge. Can be When using the aerobic digestion reaction to decompose all organic substances in sludge, it takes an enormous amount of time, the power consumption of the aerobic digester that performs aerobic digestion increases, and sludge treatment cannot be performed efficiently. By decomposing only the easily decomposable substances of the sludge by the aerobic digestion reaction as in this case, the sludge can be efficiently treated in a short time. In addition, since the temperature in the aerobic digestion tank 3 has risen to 40 ° C. to 50 ° C. due to the action of thermophilic bacteria, an acid-alkali decomposition tank 6 is provided in the subsequent stage so that acid-alkali decomposition is performed. This makes it possible to efficiently utilize the temperature increased by the aerobic digestion reaction to efficiently decompose the hardly decomposable organic substances with acid and alkali.

By the way, the aerobic digestion in the aerobic digestion tank 3 is usually completed in about half a day to about one day,
Next, the treated water is introduced into the acid-alkali decomposition tank 6.
In this case, the temperature in the aerobic digestion tank 3 is raised to 40 ° C. to 50 ° C. due to the action of the thermophilic bacteria. Can not do. Therefore, here, aerobic digestion tank 3
Between the heat exchanger 4 and the heater 5
The temperature of the treated water from the aerobic digestion tank 3 is first raised by exchanging heat in the heat exchanger 4 and further heated by the heater 5 to a temperature suitable for acid-alkali decomposition,
For example, after heating to about 100 ° C., the heated treated water is caused to flow into the acid-alkali decomposition tank 6. In the present embodiment, the heater 5 is provided independently of the acid-alkali decomposition tank 6, but may be integrated into the acid-alkali decomposition tank 6.

Next, the acid-alkali decomposition of the treated water introduced into the acid-alkali decomposition tank 6 will be described. Usually, in the acid-alkali decomposition tank 6, the acid decomposition is carried out with sulfuric acid and the alkali decomposition is carried out with sodium hydroxide, but it is also possible to use similar acids and alkali agents. In this order, first, acid decomposition is performed in the acid decomposition tank 61, and then alkali decomposition is performed in the alkali decomposition tank 62.

The acid decomposition treatment temperature and the alkali decomposition treatment temperature are both performed at around 100 ° C. This is because the decomposition in the high temperature region is convenient for the decomposition of organic substances, and the processing time is respectively set. , Do about tens of minutes. And
Finally, the water to be treated is neutralized and introduced into the biological reaction tank 1. In this case, since the treated water after the acid decomposition treatment and the alkali decomposition treatment has a high temperature of about 100 ° C., it is necessary to introduce the treated water into the biological reaction tank 1 before introducing it into the biological reaction tank 1. Cool to a suitable temperature. Here, the heat exchanger 7 is interposed between the acid-alkali decomposition tank 6 and the biological reaction tank 1, and the treated water after the acid-alkali decomposition treatment is introduced into the biological reaction tank 1 in the process of being introduced into the biological reaction tank 1. Heat is recovered by the heat exchanger 7, and the heat exchanger 7 and the heat exchanger 4 at the preceding stage are connected by a pipe 8 to circulate the heat medium, thereby supplying heat to the heat exchanger 4 from the heat exchanger 7. To make effective use of heat energy.

As described above, the sludge that has been subjected to aerobic digestion and acid-alkali decomposition is solubilized in the organic component in a liquid, and is again in a state capable of being subjected to biological treatment, and is subjected to aerobic treatment in the biological reaction tank 1. In addition, the generated excess sludge can be remarkably reduced, and a water treatment system in which apparently no excess sludge is generated can be provided. In addition, this treatment method has an effect on land and disposal costs related to landfill disposal of sludge, and environmental problems such as dioxin during incineration. In the treatment step, aerobic digestion and acid-alkali decomposition method are used. By the combination of the above, acid-alkali decomposition is efficiently performed by utilizing the reaction heat of the aerobic digestion, so that it is several steps more efficient than using both alone. Furthermore, reduce the amount of chemicals used,
There is an advantage that a hardly decomposable organic substance can be decomposed and solubilized in a short time.

[0019]

According to the method for treating sewage and sludge of the present invention, the excess sludge generated in the treatment step in the biological reaction tank is subjected to aerobic digestion and acid-alkali decomposition to solubilize it, and then this treated liquid is treated. Since the sludge is returned to the biological reaction tank, biological treatment of sludge is promoted, surplus sludge discharged can be significantly reduced or surplus sludge is not generated, and land related to landfill disposal of sludge And disposal costs,
Environmental problems such as dioxin at the time of incineration can be solved, and biological reactions can be performed stably.

Further, the solubilization treatment of the sludge is carried out by aerobic digestion followed by acid-alkali decomposition, whereby the temperature is raised to 40 ° C. to 50 ° C. by an aerobic digestion reaction by thermophilic bacteria in an aerobic digestion tank. By effectively utilizing the temperature of the sludge, the hardly decomposable organic matter can be efficiently decomposed with acid and alkali.

[Brief description of the drawings]

FIG. 1 is a process flowchart showing one embodiment of a method for treating sewage and sludge of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Biological reaction tank 11 Aeration device 2 Sedimentation tank 3 Aerobic digestion tank 4 Heat exchanger 5 Heater 6 Acid-alkali decomposition tank 7 Heat exchanger 8 Piping

Claims (2)

[Claims] 1. A method for treating sewage by utilizing the ability of microorganisms to decompose organic substances in a biological reaction tank and subjecting excess sludge generated in this treatment step to aerobic digestion and acid-alkali decomposition for solubilization. And a method for treating sewage and sludge, wherein the treatment liquid is returned to the biological reaction tank. 2. The method for treating sewage and sludge according to claim 1, wherein the solubilization treatment of the sludge is performed by aerobic digestion and then acid-alkali decomposition.