JP3780407B2 - Sludge volume reduction method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for reducing the volume of excess sludge generated due to organic matter removal in organic matter removal for biological treatment of organic wastewater such as sewage, industrial wastewater, and domestic wastewater.
[0002]
[Prior art]
In the biological treatment of organic wastewater, the organic matter in the wastewater is decomposed, and at the same time, part of it is used for the growth of microorganisms involved in wastewater treatment. Microorganisms that have grown in excess of the amount required for wastewater treatment are treated as excess sludge.
[0003]
As a method for treating surplus sludge, conventional methods such as landfill, incineration, or anaerobic digestion have been implemented after concentration and dehydration. An example in which surplus sludge is landfilled by a conventional method will be described later as Comparative Example 1 based on the flowchart of FIG.
[0004]
[Problems to be solved by the invention]
In the conventional method, in addition to the complicated operation of sludge concentration and dehydration, it is necessary to secure a landfill site for landfilling, and a large amount of energy is required for incineration. there were. In addition, when anaerobic digestion is performed, a long treatment period of about 30 days is required, and the sludge volume reduction rate is as low as about 50%.
[0005]
[Means for Solving the Problems]
The present invention introduces a sludge mixture from an aerobic treatment tank that aerobically biotreats organic wastewater to a sludge heating tank, where the sludge mixture is heated to aerobically biodegrade easily. It is a method of changing the form and then returning the same mixture to the aerobic treatment tank, where the sludge is subjected to aerobic biological treatment to reduce the volume, and the heating temperature in the sludge heating tank is 65 to 65. 95 ° C., the heating time was set to 2 to 8 hours, after which the pH of the sludge mixture which leads to the sludge heating tank and 7-10, to adjust the pH of the discharged sludge mixture from the sludge heating tank 5-8 It is a method characterized by returning to an aerobic treatment tank.
[0006]
By heating the sludge mixed solution in the sludge heating tank, the sludge can be aerobically changed to a form that is easily biodegradable. The reason why sludge is generally difficult to biodegrade aerobically is because sludge is surrounded by a hard cell wall, and the cell wall is difficult to aerobically biodegrade. Therefore, by changing the aerobically biodegradable easily form the cell wall by heating, by return sludge mixture again to aerobic treatment tank, aerobic biological treatment sludge aerobic treatment tank To reduce the volume.
[0007]
The "heating time" in here, in the case of continuous treatment means the residence time of the sludge mixture in the sludge heating tank.
[0008]
It is preferable to provide a heat exchanger between the aerobic treatment tank and the sludge heating tank. By installing this heat exchanger, heating of the sludge mixture when introducing the sludge mixture to the sludge heating tank and cooling of the sludge mixture when returning the sludge mixture from the sludge heating tank to the aerobic treatment tank are efficient. As a result, the heat input to the sludge heating tank from the outside can be reduced.
[0009]
The pH of the sludge mixed liquid led to the sludge heating tank is adjusted to 7-10. Since the main component of sludge is an organic substance, heating the sludge mixture in a neutral to alkaline pH range can effectively change the sludge into an aerobic and biodegradable form.
[0010]
The sludge mixed liquid discharged from the sludge heating tank is returned to the aerobic treatment tank after the pH is adjusted to 5-8. This pH adjustment is for adjusting to the normal pH condition of the aerobic treatment tank.
[0011]
The amount of the sludge mixed liquid introduced from the aerobic treatment tank to the sludge heating tank is calculated by converting the surplus sludge generation amount derived from the raw water of the wastewater treatment into the BOD dry weight, and the amount containing BOD corresponding to 1 to 10 times that amount. It is preferable to do this.
[0013]
Inside the aerobic treatment tank, a membrane separation device for separating treated water obtained by decomposing organic matter in the wastewater is disposed. This makes it possible to maintain a high sludge concentration in the sludge mixture in the aerobic treatment tank. When a membrane separator is used, SRT (sludge retention time) becomes long, which is extremely advantageous for reducing sludge volume.
[0014]
【The invention's effect】
As described above, according to the present invention, the sludge settling tank, the excess sludge extraction device, the sludge return pump, the sludge concentration equipment, and the sludge treatment equipment, which have been conventionally required, become unnecessary, and the surplus sludge treatment process is simplified and the organic matter is removed. The removal device can achieve the effect of allowing simultaneous treatment of waste water and sludge.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the examples unless it exceeds the gist.
[0016]
Example 1
FIG. 1 is a flowchart showing an example of a sludge volume reduction method according to the present invention.
[0017]
Wastewater is supplied to the organic matter removal tank (2) by the wastewater supply pump (1), and the organic matter in the wastewater is decomposed by aeration treatment. A membrane separation device (3) is disposed in the organic matter removal tank (2) and is immersed in the waste water. A diffuser (4) is disposed under the membrane separator (3), and a blower (5) for feeding air into the diffuser is provided outside the tank.
[0018]
Part of the sludge mixture in the organic matter removal tank (2) is drawn from the bottom of the organic substance removal tank (2) by the sludge mixture extraction pump (6), heated by the heat exchanger (7), and adjusted to pH After pH adjustment in (8), heat treatment is performed in the sludge heating tank (9). By this heat treatment, the sludge is changed into a biologically easily degradable form. The sludge mixture discharged from the sludge heating tank (9) is pH adjusted by the pH adjuster (10), cooled by the heat exchanger (7), returned to the organic matter removal tank (2), and sludge Organic substances in the mixed solution are decomposed.
[0019]
Next, a specific operation example performed using the apparatus shown in FIG. 1 will be described.
[0020]
Wastewater having a BOD concentration of 200 mg / liter was supplied to a 3 liter organic substance removal tank (2) at a flow rate of 6 liters / day. The sludge mixed liquid was drawn from the organic matter removing tank (2) by the sludge mixed liquid drawing pump (6) and led to the sludge heating tank (9) having a volume of 45 ml. The heating temperature in the sludge heating tank (9) was 90 ° C., the heating time was 5 hours, and the pH of the sludge mixed solution was 7. Thereafter, the sludge mixed liquid discharged from the sludge heating tank (9) was returned to the organic matter removing tank (2).
[0021]
Comparative Example 1
The same operation as in Example 1 was performed except that the sludge heating tank was not installed and therefore the sludge mixed liquid was not drawn from the organic matter removing tank (2) to the sludge heating tank.
[0022]
Comparative Example 2
An example in which surplus sludge is landfilled by a conventional method is shown in FIG.
[0023]
The wastewater is supplied to the aeration tank (22) by the wastewater supply pump (21), and the organic matter in the wastewater is decomposed by the aeration treatment. An aeration device (23) for aeration is disposed in the lower part of the aeration tank, and a blower (24) for sending air to the aeration device (23) is provided outside the tank.
[0024]
Next, the treated water containing sludge is transferred from the aeration tank (22) to the sludge settling tank (25), where the sludge is precipitated. The supernatant of the tank is withdrawn as treated water by a treated water extraction pump (26). A part of the sludge settled in the sludge settling tank (25) is returned to the aeration tank (22) by the sludge return pump (27).
[0025]
The excess sludge in the sludge settling tank (25) is sent to the sludge concentration tank (29) by the excess sludge extraction pump (28), and the concentrated sludge is sent to the sludge dewatering machine (31) by the mud feed pump (30). Sent. In the sludge dewatering machine (31), the concentrated sludge is separated into dehydrated sludge and dehydrated filtrate. The dehydrated sludge is landfilled at the landfill, the dehydrated filtrate is returned to the aeration tank (22) by the dehydrated filtrate return pump (32), and the organic matter in the dehydrated filtrate is decomposed by the aeration process.
[0026]
In performance evaluation example 1 and comparative example 1, the time-dependent change of MLSS (sludge density) in an organic substance removal tank (2) was measured, respectively. The obtained measurement results are shown in FIG. In both Example 1 and Comparative Example 1, the excess sludge was not drawn out of the system. As is apparent from FIG. 2, the sludge concentration is increased in Comparative Example 1, whereas it is decreased in Example 1, and a significant volume reduction effect of sludge is recognized.
[0027]
In Example 1 and Comparative Example 1, the change over time in the organic matter content of the sludge in the organic matter removing tank was measured. The obtained measurement results are shown in FIG.
[0028]
The organic matter content in the tank slightly increased in Comparative Example 1, but decreased in Example 1. This is because the sludge, which is an organic substance, is reduced in volume, and as a result, the organic substance content of the sludge is reduced.
[Brief description of the drawings]
FIG. 1 is a flowchart showing a sludge volume reduction method according to an embodiment of the present invention.
FIG. 2 is a graph showing a change with time of MLSS (sludge concentration) in an organic substance removal tank.
FIG. 3 is a graph showing the change over time in the organic content of sludge in the organic matter removal tank.
FIG. 4 is a flow chart showing an example in which surplus sludge is landfilled by a conventional method.
[Explanation of symbols]
(1): Wastewater supply pump
(2): Organic matter removal tank
(3): Membrane separator
(4): Air diffuser
(5): Blower
(6): Sludge mixture pump
(7): Heat exchanger
(8): pH adjuster
(9): Sludge heating tank
(10): pH adjuster

Claims (4)

The sludge mixture is introduced from the aerobic treatment tank that aerobically biotreats organic wastewater to the sludge heating tank, where the sludge mixture is heated to change the sludge into an aerobic and biodegradable form. Then, the mixed solution is returned to the aerobic treatment tank, where the sludge is aerobically biologically treated to reduce the volume,
The heating temperature in the sludge heating bath 65 to 95 ° C., the heating time was set to 2 to 8 hours, the pH of the sludge mixture which leads to the sludge heating tank and 7-10, the sludge mixture discharged from the sludge heating tank A method for reducing the volume of sludge, wherein the pH is adjusted to 5 to 8 and then returned to the aerobic treatment tank.   The method according to claim 1, wherein a heat exchanger is provided between the aerobic treatment tank and the sludge heating tank.   The method according to claim 1 or 2, wherein the amount of surplus sludge generated is converted into a BOD dry weight, and a sludge mixed liquid containing BOD corresponding to 1 to 10 times thereof is led to a sludge heating tank. .   The method according to claim 1, wherein a membrane separation device is immersed in the aerobic treatment tank.

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