JP2003033779A - Wastewater treatment system and wastewater treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wastewater treatment system and a wastewater treatment method capable of decreasing running cost and installation cost by minimizing the quantity of excess sludge to zero or at least decreasing its quantity to downsize the system. SOLUTION: This wastewater treatment system which treats organic wastewater biologically is characterized by comprising a primary biological treatment tank for aerobic treatment of organic wastewater, a solid-liquid separation device for separation of sludge from the liquid having been exposed to the biological treatment, a secondary biological treatment tank for aerobic biological treatment of the separated sludge, a sludge treatment tank, connected to the secondary biological treatment tank via a circulating channel, for aerobic treatment of the sludge at a high temperature, and a channel that returns the sludge having been treated in the secondary treatment tank to the primary logical treatment tank.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wastewater treatment apparatus for aerobically treating organic wastewater and a wastewater treatment method therefor, and more specifically, an amount of surplus sludge produced in the step of aerobically treating organic wastewater. The present invention relates to a wastewater treatment device and a wastewater treatment method using the device, which can reduce the number of wastewater treatment devices as compared with the conventional wastewater treatment device.

[0002]

2. Description of the Related Art Conventionally, as an apparatus for treating organic wastewater (hereinafter sometimes referred to as raw water) such as sewage, food wastewater, kitchen wastewater or septic tank sludge, an activated sludge treatment apparatus, a fixed bed biological treatment apparatus or A fluidized bed type processing device is used.

In the above activated sludge treatment device, waste water is supplied into a treatment tank in which sludge, which is an aerobic microorganism, floats.
By aeration with air, it is a device that biologically oxidizes and decomposes organic matter in the raw water by the biological action of sludge. It is a device that provides a fixed bed and causes the microorganisms to adhere and grow on the surface of the carrier by aerating with air, and biologically oxidatively decomposes the organic matter in the raw water by the biological action of the adhered microorganisms. The biological treatment device is a biological carrier of microorganisms attached and proliferated on the surface of the fluidizing biological carrier by filling the liquid in the aerobic biological treatment tank with the biological carrier so that it can be fluidized and supplying raw water and aerating with air. It is a device that biologically oxidizes and decomposes organic matter in raw water by biological action.

In each of the above-mentioned biological treatment devices, a large amount of grown microorganisms are generated as sludge as the organic matter is biologically decomposed. The generated sludge is separated and concentrated in a sedimentation tank, etc., and part of it is recycled to the biological treatment process, but the rest is discharged outside the system as excess sludge.The excess sludge is concentrated and dehydrated and then disposed of by incineration or landfill. Or
Or the volume has been reduced by anaerobic digestion treatment. The excess sludge amount is said to be 20 to 50% of the amount of organic matter (BOD) in the raw water introduced into the biological treatment process.

Further, as a method for reducing the volume of generated sludge as much as possible, Japanese Patent Publication No. 6-509986 discloses a combination of a mesophilic biological treatment tank and a thermophilic biological treatment tank in which sludge generated from the mesophilic biological treatment tank is combined. After solubilization in a thermophilic biological treatment tank, it is returned to the mesophilic biological treatment tank and the solubilized sludge is treated with raw water to disclose a method for reducing the volume of sludge, and Japanese Patent No. 2973761 discloses aeration. A method for reducing the volume of sludge is disclosed, in which sludge in the tank is extracted, solubilized by ozone treatment, and then returned to the aeration tank for processing. In addition, the solubilization of sludge means that the microorganisms that compose the sludge are decomposed into an organic substance having a low molecular weight, and the volume reduction of the sludge means
It means reducing the volume of sludge discharged as excess sludge. Further, the sludge in the present invention, after treating the organic wastewater such as sewage, food wastewater, kitchen wastewater or septic tank sludge, concentrated and discharged in a sedimentation tank, a membrane separator, a centrifuge or a combination thereof It refers to excess sludge that is treated, returned sludge that is returned to the biological treatment tank, and other organic wastes that are fluid and that have fluidity, such as slurry or liquefied organic waste.

[0006]

In the conventional method for disposing of excess sludge, the method of condensing and dewatering sludge and then incinerating or landfilling the sludge has a water content of 70 to 70 even after sludge concentration and dewatering. Since it is as high as 90 wt%, it is bulky,
Currently, when a waste company is requested to dispose of the waste, the cost of collection is high, and it currently accounts for most of the cost of wastewater treatment. Furthermore, in the case of landfill disposal, the remaining years of the industrial waste landfill disposal site are decreasing, and the cost of collection is also increasing year by year. In addition, in the case of incineration, the fuel content is high due to the high water content, the fuel cost is high, and it is necessary to treat exhaust gas and incineration ash.In recent years, the incineration process itself has become difficult due to the dioxin problem. It is a situation that is getting worse.

Further, in the method of volume reduction treatment by anaerobic digestion method, sludge is supplied into a treatment tank in which anaerobic microorganisms such as methane bacteria are suspended and aerated and stirred by anaerobic gas, It is a method of decomposing organic matter in sludge into methane gas, carbon dioxide gas, etc. by the biological action of anaerobic microorganisms, and although it has the advantage that methane gas can be effectively used as fuel, etc. The equipment is too large, and the amount of sludge finally generated is large, and the above problems cannot be solved by disposing of it.

Further, in the sludge volume reduction method disclosed in Japanese Patent Publication No. 6-509986, since the treatment is carried out in a plurality of cycle operations, there are problems that the treatment process is complicated and the treatment time is long. Furthermore, in the solubilization treatment in the thermophilic biological treatment tank, since aeration with a large amount of air,
An extremely large amount of heat is lost due to the discharge of air, and since the sludge itself has a strong odor, an extremely strong odor is released by aeration. The method disclosed in Japanese Patent No. 2973761 has a problem that the equipment cost of the ozone production apparatus is expensive and that the oxygen in the ozone-containing gas is not effectively used, so that the equipment cost and the operating cost increase. .

The present invention has been made in view of the problems in the above-mentioned conventional sludge disposal and volume reduction treatment, and a wastewater treatment apparatus capable of reducing the amount of surplus sludge to zero or at least reducing the volume thereof. Also, the present invention has been made for the purpose of providing a wastewater treatment apparatus and a wastewater treatment method, which can reduce the equipment size in the wastewater treatment method and can reduce the operating costs and equipment costs.

[0010]

The gist of the present invention for achieving the above-mentioned object is, in the invention described in claim 1, a wastewater treatment apparatus for biologically treating organic wastewater,
A first biological treatment tank that treats organic wastewater aerobically, a solid-liquid separation device that solid-liquid separates the sludge in the biologically treated mixture, and a second biological treatment that processes the separated sludge aerobically. A tank and a sludge treatment tank that communicates with the second biological treatment tank through a circulation channel for aerobic biological treatment of sludge under high temperature conditions, and the sludge treated in the second biological treatment tank is treated as the first biological treatment tank. The wastewater treatment device is characterized in that a circulation flow path that circulates is provided.

According to the structure of claim 1, in the solubilization treatment of sludge in the sludge treatment tank by the biological action of the thermophilic microorganisms, the sludge is allowed to stay in the sedimentation tank for a long time for solid-liquid separation. Since the sludge is depleted of easily decomposable organic matter and microbial intracellular nutrients by re-aeration, not sludge that is about to decompose, it can be solubilized without consuming oxygen for decomposing easily decomposable organic matter. Therefore, the amount of oxygen consumption can be reduced, and thereby the amount of heat lost by aeration can also be reduced.

Further, in the invention described in claim 2, the first biological treatment tank in the wastewater treatment equipment according to claim 1 is divided into a plurality of communicating tanks, and the tank at the front stage is the second biological treatment. It is a wastewater treatment device characterized by being used as a tank.

According to the structure of claim 2, since it is not necessary to separately install the second biological treatment tank, the equipment area can be reduced, and it is not necessary to transfer sludge by a pump. The cost can be low.

According to the third aspect of the invention, in a wastewater treatment device for biologically treating organic wastewater,
Aeration of the supplied organic wastewater for aerobic biological treatment, a first biological treatment step, a solid-liquid separation step for solid-liquid separation of sludge in the biologically treated mixture, and aeration of the separated sludge A second aerobic treatment step by which aerobic biological treatment is performed, and aerobic biological treatment is performed by aeration under a high temperature condition of a temperature of 40 to 100 ° C. while circulating sludge in the second biological treatment tank through a circulation flow path. A sludge treatment step is provided, and the sludge treated in the second biological treatment step is circulated to the first biological treatment step through a circulation flow path.

Further, in the invention described in claim 4, in the wastewater treatment method according to claim 3, the MLSS concentration in the second biological treatment tank is 5000 to 20000 mg /
1 and the dissolved oxygen concentration is 0.5 to 6 mg / l for treatment.

According to the above-mentioned constitution of claim 3 or 4, in the solubilization treatment of sludge in the sludge treatment tank by the biological action of thermophilic microorganisms, the sludge is allowed to stay in the sedimentation tank for a long time and solidified. It is not a liquid-separated sludge that is about to decompose, but a sludge depleted of easily decomposable organic matter and microbial intracellular nutrients by re-aeration, so solubilization is performed without consuming oxygen to decompose easily decomposable organic matter. be able to. Therefore, the amount of oxygen consumption can be reduced, and thereby the amount of heat lost by aeration can also be reduced. Further, the temperature in the sludge treatment tank is preferably 40 to 100 ° C. at which the biological treatment action and the heat treatment action exhibit a synergistic effect, and more preferably 55 to 75 ° C.
S concentration is 5000 to 60,000 mg / l, preferably 1
0000 to 40,000 mg / l, and the residence time is 1
It is 0 to 100 hours, preferably 18 to 50 hours. M
When the LSS concentration is lower than 5000 mg / l, a large amount of heat is required for heating, and when it is higher than 60,000 mg / l, the sludge has less fluidity and it is difficult to supply oxygen. Further, if the residence time is shorter than 10 hours, the thermophilic microorganisms are difficult to reproduce and easily flow out of the treatment tank. If the residence time is longer than 100 hours, the sludge decomposition is almost stopped and the activity of the thermophilic microorganisms is reduced. .

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system diagram of a wastewater treatment device which is an embodiment of the present invention, and FIG. 2 is a system diagram of a wastewater treatment device which is another embodiment of the present invention. In both figures, the same reference numerals are given to members having corresponding functions.

Reference numeral 1 is an adjusting tank for adjusting the supply amount and pH value of raw water such as sewage, food wastewater, kitchen wastewater or septic tank sludge, and 2 is a raw water supplied with an aeration means 6 installed at the bottom. The first biological treatment tank for biologically treating organic matter in raw water by biological action of aerobic microorganisms by aeration of oxygen with an oxygen-containing gas such as air. 3 sediments and separates sludge in the biologically treated mixture. A settling tank 4 of the solid-liquid separator has a diffusing means 6 provided at the bottom thereof, and aeration sludge is aerated with an oxygen-containing gas such as air to remove organic matter forming sludge from aerobic microorganisms. The second biological treatment tank 5, which biologically treats by biological action, has an air diffuser 6 provided at the bottom thereof, and communicates with the second biological treatment tank 4 through the circulation channels 18 and 19. The sludge in 4 is circulated through the flow paths 18, 19
A sludge treatment tank that solubilizes organic matter that forms sludge by aeration with an oxygen-containing gas such as air under a high temperature condition of 40 to 100 ° C while circulating through the sludge by the biological action of thermophilic microorganisms. Is. The sludge treatment tank 5 is provided with a heating means (not shown) such as steam for heating the sludge in the treatment tank.

In FIG. 1, the first biological treatment tank 2 and the second biological treatment tank 4 are arranged separately, but as shown in FIG. 2, the first biological treatment tank 2 is partitioned by partition walls. A plurality of tanks 4 communicating at the upper ends 12a, 12b, 12c of the partition walls,
6a, 6b, 6c may be provided, and the tank 4 at the frontmost stage may be a second biological treatment tank, and the first biological treatment tank 2, the second biological treatment tank 4 and the sludge treatment tank 5 may be A fixed bed type treatment tank in which a biological carrier such as a synthetic resin or a fibrous material is fixed and filled, or a fluidized bed type biological treatment tank in which a biological carrier is fluidly filled may be used.

Further, in the above description, the settling tank 3 is provided as the solid-liquid separation device, but a membrane separation device or the like can be used in addition to the settling tank 3, and the sludge is further concentrated in the circulation channel 18. A sludge concentrator such as a centrifuge, a membrane separator or a filter may be provided, and further, if necessary,
A heat exchanger for exchanging heat between the sludge flowing through the circulation channel 18 and the concentrated concentrated sludge and the sludge solubilized in the sludge treatment tank 5 may be provided.

A method of treating organic wastewater with the wastewater treatment apparatus having the above-mentioned structure will be described in detail below. In FIG. 1, raw water is supplied from the raw water supply channel 10 to the adjusting tank 1 and once stored, and the pH value and the like are adjusted. Biological treatment of sludge, which is aerobic microorganisms suspended by being aerated with an oxygen-containing gas such as air supplied from the aeration means 6, is supplied to the first biological treatment tank 2 in which one biological treatment step is performed. By the action, organic matter in the raw water is efficiently oxidatively decomposed. The treatment temperature in the first biological treatment tank 2 is preferably 10 to 45 ° C.

In FIG. 2, the adjusted raw water whose pH value and the like have been adjusted in the adjusting tank 1 is supplied from the adjusted raw water supply passage 11 to the tanks 2a and 2b in the preceding stage of the first biological treatment tank 2 for each tank. Is adjusted and supplied, and is aerated with an oxygen-containing gas such as air supplied from the air diffusers 6a and 6b, whereby the biological action of sludge, which is an aerobic microorganism floating in the raw water, causes It is efficiently oxidatively decomposed. In addition,
The adjusted raw water may be supplied only to the first-stage tank 2a or may also be supplied to the second biological treatment tank 4, and may be appropriately supplied depending on the shape of the first biological treatment tank 2 and the division status. it can.

The mixed liquid in which the sludge grown in the first biological treatment tank 2 is mixed is introduced from the mixed liquid discharge channel 13 into the settling tank 3 where the solid-liquid separation step is performed, and the sludge is naturally settled by standing. The separated and purified treated water is discharged out of the system through the treated water discharge passage 14. The sludge that has been separated by settling is extracted from the sludge withdrawal channel 15 of the settling tank 3, and a part of it is discharged as excess sludge from the sludge discharge channel 17 to the outside of the system and treated with a sludge treatment device (not shown) or the like. It The remaining sludge is supplied to the second biological treatment tank 4 in which the sludge treatment process is performed, from the sludge return passage 16 for volume reduction processing.

The sludge supplied to the second biological treatment tank 4 is aerated with an oxygen-containing gas such as air supplied from the aeration means 7, whereby the sludge which is an aerobic microorganism is biologically self-digested. At that time, it is efficiently oxidatively decomposed, and easily degradable organic matter and microbial intracellular nutrients are depleted. The treatment temperature in the second biological treatment tank 4 is preferably 10 to 45 ° C, and the MLSS concentration is 5000 to 20000 m.
It is preferable to carry out g / l and the dissolved oxygen concentration at 0.5 to 6 mg / l because oxygen can be efficiently supplied and biological autolysis can be promoted.

The sludge in the second biological treatment tank 4 is self-extinguished, and is circulated between the sludge treatment tank 5 in which the sludge treatment process is performed through the circulation flow paths 18 and 19 to obtain the sludge treatment tank. 5, aeration is performed with an oxygen-containing gas such as air supplied from the aeration means 8 under a high temperature condition of 40 to 100 ° C., and the microorganisms in the sludge are efficiently killed by the biological action of the thermophilic microorganisms.・ Decomposes and becomes a low molecular weight organic substance and is solubilized. The sludge supplied to the sludge treatment tank 5 is a sludge depleted of easily decomposable organic substances and microbial intracellular nutrients by re-aeration, and thus solubilized without consuming oxygen for decomposing easily decomposable organic substances. Can be processed. In addition, it is preferable to use a high-concentration oxygen-containing gas in the sludge treatment tank 1 because the dissolution efficiency of oxygen becomes extremely high.

The sludge self-digested and solubilized in the second biological treatment tank 4 and the sludge treatment tank 5 is circulated and supplied from the sludge circulation channel 12 to the first biological treatment tank 2, and floats together with the organic matter in the raw water. By efficiently oxidizing and decomposing sludge, which is an aerobic microorganism, the volume of generated sludge can be reduced, and the volume of excess sludge generated can be reduced to zero or at least. You can In addition, in FIG. 2, the sludge self-digested and solubilized in the second biological treatment tank 4 and the sludge treatment tank 5 is supplied from the upper end portion 12a of the partition wall to the adjacent biological treatment tank 2a for processing, Biological treatment tanks 2b, 2 through the upper ends 12b, 12c of the partition walls
air diffusers 6a, 6 provided in the respective tanks.
It is aerated with an oxygen-containing gas by b, and introduced into the settling tank 3 through the mixed solution discharge flow path 13.

Since the sludge circulated from the second biological treatment tank 4 to the first biological treatment tank 2 has been re-aerated and the organic matter concentration has been reduced, the organic matter load in the first biological treatment tank 2 should be reduced. Therefore, the quality of the treated water discharged from the treated water discharge channel 14 can be kept good.

[0028]

INDUSTRIAL APPLICABILITY The present invention provides a wastewater treatment equipment and a wastewater treatment method which are capable of highly efficient treatment of organic wastewater and can reduce the amount of excess sludge generated or at least reduce the volume thereof. The size can be reduced, and the operating expenses and equipment costs can be reduced.

[Brief description of drawings]

FIG. 1 is a system diagram of a wastewater treatment device that is an embodiment of the present invention.

FIG. 2 is a system diagram of a wastewater treatment device which is another embodiment of the present invention.

[Explanation of symbols]

1: Adjustment tank 2: First biological treatment tank 3: Solid-liquid separator (sedimentation tank) 4: Second biological treatment tank 5: Sludge treatment tank 6, 7, 8: Aeration means

Claims (4)

[Claims] 1. A wastewater treatment apparatus for biologically treating organic wastewater, wherein a first biological treatment tank for treating aerobic biological wastewater and a solid-liquid separation for solid-liquid separation of sludge in the biologically treated mixed liquid. An apparatus, a second biological treatment tank for treating the separated sludge with aerobic organisms, and a sludge treatment tank for communicating the sludge with the aerobic organisms under high temperature conditions through a circulation channel are provided. A wastewater treatment device comprising a circulation flow path for circulating sludge treated in the second biological treatment tank to the first biological treatment tank. 2. The wastewater treatment equipment according to claim 1, wherein the first biological treatment tank is divided into a plurality of communicating tanks, and the frontmost tank is used as the second biological treatment tank. 3. A wastewater treatment apparatus for biologically treating organic wastewater, wherein a first biological treatment step of aerobic biological treatment by aeration of the supplied organic wastewater and sludge in the biologically treated mixed liquid are carried out. Solid-liquid separation process for solid-liquid separation, second biological treatment process for aerobic biological treatment by aeration of the separated sludge, and temperature while circulating the sludge in the second biological treatment tank through the circulation channel. A sludge treatment process for treating aerobic organisms by aeration under a high temperature condition of 40 to 100 ° C., and circulating the sludge treated in the second organism treatment process to the first organism treatment process through a circulation channel. Wastewater treatment method characterized by. 4. The MLSS concentration in the second biological treatment tank is 500.
0 to 20000 mg / l, dissolved oxygen concentration 0.5 to 6 m
The waste water treatment method according to claim 3, wherein the waste water is treated as g / l.