JP2001025789A - Treatment of organic waste liquid and device therefor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a treating method of an organic waste liquid and the device decreased in quantity of sludge discharged out of the system at low cost by reducing volume of the sludge without increasing capacity of an aeration tank and the quantity of oxygen to be supplied in an aerobic treating process, prevented in deterioration of quality of the treated liquid and capable of recovering resource and energy as a form of methane. SOLUTION: A mixed liquid aerobically biologically treated by activated sludge in the aeration tank 1 is solid-liquid separated in a settling tank 2, a part of the separated sludge 18 is taken out, the taken-out sludge 22 is brought into contact with ozone 25 in an ozone treating tank 3 to be reformed easily decomposable, the ozone treated sludge 26 is kept in an anaerobic state in an acid generating tank 4 to generate an organic acid. The acid generated liquid 28 is separated by a membrane separation device 5, the concentrated liquid 40 is returned to the acid generating tank 4 and the permeated liquid 39 is methane fermented in a methane fermentation tank 6 and after that, returned to the aeration tank 1 to be aerobically biologically treated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for biologically treating an organic effluent in the presence of activated sludge, and in particular, it is possible to reduce excess sludge in an activated sludge treatment system and to recover energy. Organic wastewater treatment method and apparatus.

[0002]

2. Description of the Related Art An aerobic biological treatment method, such as an activated sludge treatment method, in which an organic effluent is treated under aerobic conditions by utilizing the action of aerobic microorganisms has a low treatment cost and excellent treatment performance. Therefore, it is widely used in general, but generates a large amount of hardly dewaterable surplus sludge. For this reason, a treatment method for reducing the volume of sludge has attracted attention.

[0003] As a treatment method for reducing the volume of such sludge, sludge is extracted from an aeration tank or a sedimentation tank, and the extracted sludge is easily biodegraded by a reforming treatment such as ozone treatment, heat treatment, acid or alkali treatment. A method has been proposed in which the sludge is returned to an aeration tank and biodegraded by returning the sludge to an aeration tank (for example, JP-A-6-206088).

FIG. 2 is a flow sheet showing a method for treating an organic waste liquid described in Japanese Patent Application Laid-Open No. 6-2060888. Reference numeral 41 denotes an aeration tank, 42 denotes a sludge separation tank, and 43 denotes an ozone treatment tank. . In the treatment method of FIG. 2, the organic wastewater 44 and the return sludge 45 are introduced into the aeration tank 41, and the ozone-treated sludge 46 is introduced and mixed with the activated sludge in the aeration tank 41. Is sent from the air diffuser 48 to perform aerobic biological treatment.

[0005] The liquid in the aeration tank 41 is partly taken out and introduced into a sludge separation tank 42 to be separated into a separated liquid and a separated sludge 51. The separated liquid is discharged out of the system as a processing liquid 50, a part of the separated sludge 51 is returned to the aeration tank 41 as returned sludge 45, and the other part is introduced into the ozonation tank 43 as drawn sludge 53 to perform ozone treatment. Then, the remaining part is discharged out of the system as excess sludge 54. The extracted sludge 53 is introduced into the ozone treatment tank 43 and supplied with ozone from an ozone supply pipe 55 to be brought into contact with ozone to oxidize and decompose the sludge to convert it into a BOD component. The ozone exhaust gas is discharged from the discharge ozone pipe 56, and the ozone-treated sludge 46 is returned to the aeration tank 41 to perform the aerobic biological treatment as described above.

[0006] In the conventional method shown in FIG.
Is reformed into biodegradable and returned to the aeration tank 41, whereby the biodegradable modified sludge is assimilated to the microorganisms in the aeration tank 41, so that the amount of generated sludge decreases. .
In this case, if the amount of the extracted sludge 53 that is larger than the amount of the sludge generated from the BOD to be treated is reformed and returned, the excess sludge discharged out of the system can be substantially reduced to zero.

In the above-mentioned conventional method, all the sludge that has been subjected to the reforming treatment is returned to the aeration tank and decomposed under aerobic conditions. Therefore, the BOD load on the activated sludge treatment apparatus is greatly increased. It is necessary to increase the capacity according to the BOD load. Also, the capacity of the oxygen supply device needs to be increased in order to aerobically decompose the increased BOD. As described above, not only is it necessary to increase the facility capacity of the activated sludge treatment apparatus, but also the power for oxygen supply is greatly increased, so that an energy-consuming treatment system is obtained.
Further, energy cannot be recovered from sludge to be reformed. Furthermore, in the conventional method, in order to reduce the amount of excess sludge discharged to the outside of the system to zero, it is necessary to ozone-treat a large amount of sludge, which is about three times the normal amount of excess sludge, as drawn sludge. This is because 30 to 40% of the BOD generated by the ozone treatment is converted into sludge again in the process in which the sludge that has been converted into BOD by the ozone treatment is returned to the aeration tank and subjected to aerobic biological treatment. For this reason, ozone treatment requires a large amount of ozone, chemicals, energy, and the like, which increases costs. Further, when a large amount of sludge is subjected to ozone treatment as drawn sludge, there is a problem that the quality of treated water deteriorates because the amount of microorganisms required for treatment cannot be secured.

Japanese Patent Application Laid-Open No. 1-2224100 describes a method for treating organic sludge in which anaerobic digested sludge is heated at 100 to 180 ° C., and then this heat-treated sludge is returned to an anaerobic digestion tank. . However, this method relates to anaerobic treatment, and does not disclose the possibility of application in aerobic treatment.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to reduce sludge volume at a low cost without increasing the aeration tank capacity and supply oxygen amount in an aerobic biological treatment step, and to discharge sludge to the outside of the system. It is an object of the present invention to provide an organic wastewater treatment method and apparatus capable of reducing the amount and preventing deterioration of treated water quality and recovering resources and energy in the form of methane.

[0010]

SUMMARY OF THE INVENTION The present invention is a method and an apparatus for treating an organic effluent. (1) An aerobic biological treatment step in which an organic wastewater is introduced into an aeration tank and an aerobic biological treatment is performed in the presence of activated sludge. The mixed liquid in the aeration tank is solid-liquid separated, and the separated liquid is discharged as treated water. And a first solid-liquid separation step of returning at least a part of the separated sludge to the aeration tank, and extracting at least a part of the activated sludge from the separated sludge of the first solid-liquid separation step or the mixed liquid of the aeration tank. A reforming step of reforming the sludge to be easily biodegradable, an acid generating step of solubilizing the modified sludge while maintaining it in an anaerobic state in the presence of sludge containing acid-producing bacteria to generate an organic acid,
The mixed solution of the acid generation step is subjected to solid-liquid separation, the separated liquid is transferred to the methane fermentation step, and the separated liquid of the second solid-liquid separation step is returned to the acid generation step. A method for treating organic wastewater, comprising: a methane fermentation step of maintaining anaerobic conditions in the presence of sludge containing methane-producing bacteria for methane fermentation; and a transfer step of introducing a methane fermentation liquor to the aerobic biological treatment step. (2) An aerobic biological treatment device that introduces an organic wastewater into an aeration tank and performs aerobic biological treatment in the presence of activated sludge. The mixed liquid in the aeration tank is solid-liquid separated, and the separated liquid is discharged as treated water. A first solid-liquid separator for returning at least a part of the separated sludge to the aeration tank, at least a part of the activated sludge from the separated sludge of the first solid-liquid separator or the mixed liquid of the aeration tank, and the extraction. A reforming treatment apparatus for reforming sludge to be easily biodegradable, an acid generating tank for maintaining the reformed sludge in an anaerobic state in the presence of sludge containing acid-producing bacteria to solubilize and generate an organic acid, The liquid mixture in the acid generation tank is subjected to solid-liquid separation, the separated liquid is transferred to a methane fermentation tank, and the separated sludge is returned to the acid generation tank. A methane fermentation tank that maintains anaerobic conditions in the presence of sludge containing methanogens and performs methane fermentation. Organic effluent processing apparatus including a transfer device for introducing the finely methane fermentation liquid in the aerobic biological treatment apparatus.

The organic effluent to be treated in the present invention is an effluent containing an organic substance which is treated by a usual aerobic biological treatment method, but contains an organic substance or an inorganic substance which is hardly biodegradable. And ammonia nitrogen or the like may be contained. Such organic effluents include sewage, night soil, food factory effluents and other industrial effluents.

The aerobic biological treatment step in the present invention is configured to introduce an organic wastewater into an aeration tank and perform aerobic biological treatment in the presence of activated sludge. In the first solid-liquid separation step, the mixed liquid is guided from the aeration tank to the solid-liquid separation tank to perform solid-liquid separation, the separated liquid is discharged as treated water, and at least a part of the separated sludge is returned to the aeration tank. Be composed. As such a processing system and a processing apparatus, an organic effluent is mixed with activated sludge in an aeration tank and aerated, the mixed liquid is separated in a solid-liquid separation tank, and a part of the separated sludge is returned to the aeration tank. Aerobic biological treatment and treatment equipment in the standard activated sludge treatment method is generally used, but other modified forms of this may be used.
When treating the wastewater containing ammoniacal nitrogen, the treatment can be carried out by combining the nitrification and denitrification step.

The reforming treatment step is a step of extracting at least a part of the activated sludge (biological sludge) from the treatment system in the aerobic biological treatment and reforming the extracted sludge to be easily biodegradable. When extracting biological sludge, it is preferable to extract a part of the separated sludge separated in the solid-liquid separation tank, but it may be extracted in a mixed liquid state from the aeration tank. When extracting from the separated sludge, part or all of the part discharged as excess sludge can be extracted as extracted sludge,
In addition to excess sludge (corresponding to the amount of sludge multiplied by assimilation of BOD in the liquid to be treated), a part of the returned sludge returned to the aeration tank as returned sludge is further extracted and reformed, so that it is out of the system. The amount of excess sludge discharged to the wastewater can be reduced, and in some cases, reduced to zero. In order to reduce the amount of surplus sludge generated to zero, it was necessary to reform about three times the amount of multiplied sludge when returning the reformed sludge directly to the aeration tank. It is sufficient to perform 1.8 times the reforming treatment, and the amount of sludge drawn out for the reforming treatment is close to half of the conventional sludge amount.

[0014] As a reforming treatment method for reforming the drawn sludge into a property easily decomposed by living organisms, any method can be adopted. For example, reforming treatment by ozone treatment, reforming treatment by acid treatment, reforming treatment by alkali treatment, reforming treatment by heat treatment, high-pressure pulse discharge treatment, grinding by ball mill, colloid mill, etc. Modified treatment or the like can be employed. These processes can be performed using a known processing device. Among these, the reforming treatment by ozone treatment is preferable because the treatment operation is simple and the treatment efficiency is high.

In the ozone treatment as the reforming treatment, the sludge extracted from the aerobic biological treatment system may be brought into contact with ozone, and the sludge is reformed to be easily biodegradable by the oxidizing action of ozone. When the ozone treatment is performed in an acidic region having a pH of 5 or less, the oxidative decomposition efficiency increases. The pH adjustment at this time is as follows:
A method in which an inorganic acid such as sulfuric acid, hydrochloric acid or nitric acid is added as a pH adjuster to biological sludge can be adopted.
When adding a pH adjuster, it is preferable to adjust pH to 3-4.

The ozone treatment can be carried out by directly contacting the extracted sludge or, if necessary, concentrating it with a centrifugal separator or the like, and then contacting it with ozone. As a contact method, a method of introducing sludge into an ozone treatment tank and blowing ozone, a method of mechanical stirring, a method of using a packed bed, and the like can be adopted. As ozone, ozone-containing gas such as ozone-containing air and ozonized air can be used in addition to ozone gas. The amount of ozone used is 0.002-0.05 g-O ₃
/ G-VSS, preferably 0.005 to 0.03 g-O
₃ / g-VSS is desirable. The biological sludge is oxidatively decomposed and converted into a BOD component by the ozone treatment.

In the acid treatment as the reforming treatment, the extracted sludge extracted from the aerobic biological treatment system is guided to a reforming tank, and hydrochloric acid,
A mineral acid such as sulfuric acid is added, and pH 2.5 or less, preferably p
What is necessary is just to stay for a predetermined time under the acidic condition of H1-2. The residence time is, for example, about 5 to 24 hours. At this time, it is preferable to heat the sludge, for example, to 50 to 100 ° C., since the reforming is promoted.

In the alkali treatment as the sludge reforming treatment, the extracted sludge extracted from the aerobic biological treatment system is led to a reforming tank, and alkali such as sodium hydroxide and potassium hydroxide is added to the sludge at 0.1%. What is necessary is just to add 1 to 1% by weight and to stay for a predetermined time. The residence time is, for example, about 0.5 to 2 hours. At this time, the sludge is heated to, for example, 50 to 100.
Heating to ° C. is preferable because reforming is promoted.

The heat treatment as the reforming treatment can be performed alone, but is preferably performed in combination with an acid treatment or an alkali treatment. When heat treatment is performed alone, for example, the temperature may be 70 to 100 ° C., and the residence time may be 2 to 3 hours.

The high-voltage pulse discharge process is performed with an electrode spacing of 3 to
Sludge is present between a positive electrode of 10 mm, preferably 4 to 8 mm such as a tungsten / thorium alloy, and a negative electrode of stainless steel or the like, and an applied voltage of 10 to 50 kV, preferably 20 to 40 kV, and a pulse interval of 20 to 80 Hz, preferably Performs pulse discharge at 40 to 60 Hz, and can perform treatment while circulating sludge sequentially.

The acid generating step is a step of solubilizing the reformed sludge in an acid generating tank in the presence of sludge containing acid-producing bacteria in an anaerobic state to generate an organic acid. In the acid generation step, the separated sludge separated in the second solid-liquid separation step described later is also returned to the acid generation tank for processing. In such an acid generation step, an organic substance is converted into an organic acid which is easily decomposed by a methane-producing bacterium in a step of liquefaction → low molecular weight → organic acid generation by the action of an acid-producing bacterium. Since the organic acid becomes acidic due to its generation, the pH can be adjusted by adding an alkali such as sodium hydroxide.

As conditions for acid generation, either a medium-temperature acid-producing bacterium having an optimum temperature around 35 ° C. and a high-temperature acid-producing bacterium having an optimum temperature near 55 ° C. can be used. Processed at 45-60 ° C. The residence time (SRT) in the acid generator is 3 days or more, preferably 5 days.
About 10 to about 10 days. This residence time is set within a range where the methanogen does not substantially grow. The pH in the acid generation step is 5-7, preferably 5.8-6.
Preferably, it is 2.

In the second solid-liquid separation step, a liquid mixture (hereinafter, sometimes referred to as an acid generation liquid) is guided from the acid generation tank to a solid-liquid separation device to perform solid-liquid separation, and the separated liquid is sent to the methane fermentation step. The separated sludge is configured to return to the acid generation step. The solid-liquid separation device used in the second solid-liquid separation step is not particularly limited, and any solid-liquid separation device such as a membrane separation device, a decanter, and a filtration device can be used. When using membrane separation, various types of membrane such as hollow fiber, tubular, and flat membrane can be used. Since the purpose of membrane separation is to separate solids, a membrane having a relatively large pore size such as MF and UF is preferable.

The methane fermentation step is a step of performing methane fermentation while maintaining the separated liquid separated in the second solid-liquid separation step in an anaerobic state in the presence of sludge containing methanogens. The method of methane fermentation can employ any type of methane fermentation method such as UASB (upflow anaerobic sludge blanket) type, high load anaerobic treatment such as fixed bed type and fluidized bed type; and floating type. High load anaerobic treatment, especially UASB type, is preferred.

The UASB method is an anaerobic treatment method in which sludge blanket is formed by using sludge obtained by granulating methane-producing bacteria at high density and passing the solution in an upward flow. The fixed bed method is a method of performing anaerobic treatment using sludge in which methanogens are attached at a high density to the surface of a fixed bed type carrier. The fluidized bed method is a method in which biological sludge containing methanogens at a high density is supported on a granular carrier, and a fluidized bed is formed to perform anaerobic treatment. These are high-load anaerobic treatments, which are methods in which a soluble organic substance is passed at a high load and a high flow rate in a relatively short time.
The floating type is a method in which biological sludge in a floating state and a separated liquid are mixed and subjected to anaerobic treatment.

As conditions for the methane fermentation, either a medium-temperature methanogen having an optimum temperature around 35 ° C. or a high-temperature methanogen having an optimum temperature near 55 ° C. can be used. Processed at 45-60 ° C. Load in methane fermentation tank is 5-20kg-COD
/ M ³ · day, preferably 10 to 15 kg-COD /
m ³ · day, residence time ^{3 to} 48 hours, preferably 4
About 24 hours. The upward flow velocity in the case of the UASB type is 0.5 to 2 m / hr, preferably 1 to 2 m / hr.
It is desirable to set it to 1.5 m / hr.

The organic acid in the separated liquid is converted into methane gas and carbon dioxide by methane fermentation. Usually, methane gas accounts for 60-70% by volume of the generated gas. By recovering this methane gas, it can be effectively used as fuel. It can also generate methane gas and use it effectively in both electricity and heat (cogeneration).

The transfer step is a step of transferring the methane fermented liquid obtained by methane fermentation to the aerobic biological treatment step. The methane fermentation liquor introduced into the aeration tank is mixed with the organic wastewater and the activated sludge in the tank and is subjected to aerobic biological treatment. The methane fermentation liquor is more biodegradable than the modified sludge. ) Since the volume has decreased significantly, a new BOD
The amount of load is small, so there is no need to increase the capacity of the aeration tank, and it is not necessary to increase the amount of supplied oxygen. That is, in the present invention, since the BOD in the modified sludge is removed by acid generation and methane fermentation, even if the methane fermentation solution is introduced into the aeration tank, the activated sludge treatment capacity of the aerobic biological treatment step is increased. No need. In addition, deterioration of treated water quality is prevented.

By subjecting the methane fermentation liquor to aerobic biological treatment in an aeration tank, the methane-producing bacteria almost die by aeration and partially become BOD, so that the amount of sludge discharged to the outside of the system is further reduced. When the reforming treatment is ozone treatment, when the methane fermentation liquor is returned directly to the reforming treatment step, ozone is consumed wastefully because the methane fermentation liquor contains a reducing substance (such as H ₂ S). However, once introduced into the aeration tank and aerated, the reducing substance can be removed.

As described above, according to the present invention, it is possible to reduce the volume of sludge and reduce the amount of sludge discharged outside the system without increasing the aeration tank capacity and the amount of supplied oxygen in the aerobic biological treatment step. While sufficient sludge is retained in the aerobic treatment system, deterioration of treated water quality can be prevented, and resources and energy can be recovered in the form of methane.

Further, according to the present invention, the volume of sludge can be reduced efficiently at lower cost than in the conventional method. For example, when the same amount of extracted sludge is reformed as in the conventional case, the amount of sludge discharged to the outside of the system is smaller than in the conventional case. This is because, in the conventional method, 30 to 40% of the BOD generated by the reforming treatment is converted into sludge again in the aerobic biological treatment step, whereas in the present invention, the BOD in the acid generation step and the methane fermentation step is converted. This is because the sludge conversion rate is very small, about 5%, and the amount of sludge generated from the cells returned to the aeration tank can be almost ignored. Therefore, when achieving the same sludge volume reduction ratio as the conventional one, the amount of the extracted sludge to be reformed can be reduced, and the treatment can be performed at low cost.
For example, when the reforming treatment is ozone treatment, the amount of ozone used, chemicals, energy amount, etc. can be reduced,
Processing can be performed at low cost.

When methane fermentation is carried out by introducing the acid-generating solution produced in the acid-generating step into the methane-fermenting step without solid-liquid separation, the activity of the methane-fermenting bacteria decreases, and the methane fermentation takes a long time, and the sludge production amount also decreases. As a result, the load introduced into the aeration tank increases, and the sludge volume reduction rate also decreases.
On the other hand, as in the present invention, by solid-liquid separation of the acid generation liquid and returning the solid content to the acid generation step, only the soluble component can be transferred to the methane fermentation step, thereby improving the efficiency of the methane fermentation. By increasing the load, the load introduced into the aeration tank can be reduced, and the sludge volume reduction rate can be increased.

[0033]

According to the method for treating organic effluent of the present invention, the extracted sludge is subjected to a reforming treatment, followed by an acid generation treatment, and then the acid production liquid is subjected to solid-liquid separation. Introduced to the aerobic biological treatment process, and the separated sludge is returned to the acid generation process, so the sludge volume can be reduced at low cost without increasing the aeration tank capacity and supply oxygen amount in the aerobic biological treatment process. It can reduce the amount of sludge discharged to the outside, prevent the deterioration of treated water quality, and recover resources and energy in the form of methane.

The organic wastewater treatment apparatus of the present invention includes a reforming treatment apparatus, an acid generation tank, a second solid-liquid separation apparatus, a methane fermentation tank, and a transfer apparatus. The acid production solution is subjected to solid-liquid separation, and the separated solution is subjected to methane fermentation and then introduced into the aerobic biological treatment process, and the separated sludge is returned to the acid production process. In treating wastewater, the volume of sludge is reduced at low cost without increasing the aeration tank capacity and supply oxygen amount in the aerobic biological treatment process, and the amount of sludge discharged outside the system is reduced. And the recovery of resources and energy in the form of methane.

[0035]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a system diagram showing an organic wastewater biological treatment apparatus according to an embodiment of the present invention, and shows an example in which ozone treatment is performed as a reforming treatment. In FIG. 1, 1 is an aeration tank, 2 is a sedimentation tank, 3 is an ozone treatment tank, 4 is an acid generation tank, 5
Denotes a membrane separation device, and 6 denotes a UASB type methane fermentation tank.

The aeration tank 1 is connected to a raw water channel 11 and a return sludge channel 12, and a diffuser 15 is provided at the bottom, and an air supply channel 14 is connected. A communication path 16 communicates from the aeration tank 1 to the precipitation tank 2. The upper part of the settling tank 2 communicates with the treatment water channel 17, the lower part communicates with the sludge discharge channel 18, and communicates with the return sludge channel 12. 21 is an excess sludge discharge passage.

The ozone treatment tank 3 is connected to an upper part of a drawn sludge passage 22 and an exhaust ozone passage 23 branched from the sludge discharge passage 18. Further, an ozone supply passage 25 and an ozonized sludge passage 26 which are communicated from the ozone generator 24 communicate with the lower part. The acid generation tank 4 is connected to an ozone treatment sludge passage 26, an acid generation liquid passage 28 having a pump 27, and a concentrated liquid passage 29, and a stirrer 30 is provided therein.

The membrane separation apparatus 5 is connected to an acid generation liquid passage 28, a concentrated liquid passage 29, and a permeate passage 33 having a pump 32, and a separation membrane 34 is provided therein. The methane fermentation tank 6 is connected to a permeated liquid passage 33 at a lower portion, and a methane fermented liquid transfer passage 35 and a methane gas discharge passage 36 are connected to an upper portion. Inside the methane fermenter 6 is provided a permeate inlet 37 communicating from the permeate passage 33, and a sludge blanket 38 is formed by granule sludge on the upper part thereof. The methane fermentation liquid transfer passage 35 communicates with the raw water passage 11.

In order to treat organic effluent (raw water) by the biological treatment apparatus shown in FIG. 1, raw water is introduced into the aeration tank 1 from the raw water channel 11 and returned sludge and methane fermentation liquid returned from the returned sludge channel 12 The methane fermentation liquid transferred from the transfer path 35 and the activated sludge in the aeration tank 1 are mixed, and the air supplied from the air supply path 14 is diffused from the diffuser 15 to perform aerobic biological treatment.

The mixed liquid in the aeration tank 1 is partly taken out from the communication path 16 and introduced into the sedimentation tank 2 to be separated into a separated liquid and a separated sludge. The separated liquid is discharged as treatment water from the treatment water passage 17 to the outside of the system, the separated sludge is taken out from the sludge discharge passage 18, a part of which is returned to the aeration tank 1 from the return sludge passage 12 as return sludge, and the remaining portion is extracted as sludge. It is introduced into the ozone treatment tank 3 from the drawing sludge passage 22. If sludge to be discharged to the outside of the system is generated, the sludge is discharged to the outside of the system from the excess sludge discharge passage 21.

In the ozone treatment tank 3, ozone generated by the ozone generator 24 is supplied from an ozone supply passage 25, and is brought into contact with the extracted sludge to perform ozone treatment (reforming treatment). Thereby, the sludge in the extracted sludge is converted to BOD. The ozonized sludge is introduced into the acid generating tank 4 from the ozonized sludge passage 26.
The ozone exhaust gas is discharged from a discharge ozone passage 23.

In the acid generating tank 4, the ozone-treated sludge and the concentrated liquid 40 returned from the concentrated liquid passage 29 are mixed with the sludge containing the acid-producing bacteria in the acid generating tank 4, while being gently stirred by the stirrer 30. An acid is generated by anaerobic treatment. Thereby, the organic matter in the ozone-treated sludge is decomposed by the acid-producing bacteria to generate an organic acid.

A part of the mixed solution in the acid generating tank 4 is taken out from the acid generating liquid passage 28, and is pressurized by a pump 27 so that the membrane separation device 5
And the membrane is separated by the separation membrane 34. By this membrane separation, a permeate 39 and a concentrate 40 are separated. Permeate 39
Is sent from the permeate passage 33 to the methane fermentation tank 6. The concentrated liquid 40 is returned from the concentrated liquid passage 29 to the acid generation tank 4 to generate an acid as described above. When the concentrated SS 40 contains an inorganic SS component, it can be continuously or intermittently discharged from the sludge discharge passage 29a.

The permeated liquid 39 separated by the membrane separation device 5 is
The liquid is introduced into the lower part of the methane fermentation tank 6 from the permeate passage 33 by the pump 32, and passes through the sludge blanket 38 from the permeate inlet 37 in an upward flow. At this time, the permeated liquid 39 comes into contact with the granular sludge under anaerobic conditions, whereby the organic acid is anaerobically decomposed into methane and carbon dioxide by the action of methane-forming bacteria contained in the granular sludge. The methane fermentation liquid is taken out partly from the methane fermentation liquid transfer passage 35, transferred to the aeration tank 1 through the raw water passage 11, and subjected to the aerobic biological treatment as described above. The methane gas is recovered from a methane gas discharge path 36. The recovered methane gas can be used as an energy source.

Since most of the BOD in the methane fermentation liquor introduced into the aeration tank 1 has been decomposed by acid generation and methane fermentation, the BOD load in the aeration tank 1 is hardly increased, and thus the quality of the treated water is low. There is no deterioration and there is no need to increase the capacity of the aeration tank 1,
It is not necessary to increase the amount of oxygen supplied from the air supply path 14.

In the apparatus shown in FIG.
Although an SB type methane fermentation tank is employed, the methane fermentation can be performed by any type of methane fermentation method such as a fixed bed type, a fluidized bed type, and a floating type, and an apparatus according to the method can be employed.

[0047]

EXAMPLES Comparative Example 1 COD = 34 using peptone and yeast extract as organic sources
Aerobic biological treatment was performed on the 0 mg / l organic effluent without modification. That is, the aerobic biological treatment was performed in the apparatus of FIG. 2 omitting the ozone treatment. The operation conditions at this time were: aeration tank load = 1 kg-BOD / m ³ / day, sludge concentration in the aeration tank = about 4000 mg / l, SRT = 10
It was a day. In the case of Comparative Example 1 in which no volume reduction treatment was performed, the amount of excess sludge generated was 0.38 kg-SS / m ³ / da.
y, The treated water quality was 18 mg / l in COD.

Example 1 The same organic effluent as in Comparative Example 1 was subjected to aerobic biological treatment using the apparatus shown in FIG. However, a sedimentation tank was used instead of the membrane separation device. Ozone injection rate in the ozone treatment tank is 0.05 g
-O ₃ / g-SS, the SRT of the acid production tank was 5 days, and the residence time of the methane fermentation tank was 1 day. After the acid generation tank, a sedimentation treatment was performed, the supernatant was supplied to the UASB reactor, and the settled sludge was returned to the acid generation tank.

Table 1 shows the change in water quality in each step. After the ozone treatment, soluble organic components increased, were converted to organic acids by acid generation, and methane gas was efficiently generated in a methane fermenter (UASB). The methane fermentation liquor was returned to the aeration tank.

The amount of circulation of the extracted sludge to the ozone treatment tank in a 100% volume-reduced state in which no excess sludge was generated was about 1.8 times the amount of the generated sludge. Since the circulation amount in the conventional method of performing 100% volume reduction of the sludge by performing the ozone treatment alone is about three times, the circulation amount of the extracted sludge in Example 1 is about half the amount of the conventional method. The ozone requirement could be halved accordingly.

[0051]

[Table 1]

[Brief description of the drawings]

FIG. 1 is a system diagram illustrating an organic wastewater biological treatment apparatus according to an embodiment of the present invention.

FIG. 2 is a flow sheet showing a conventional method for treating organic wastewater.

[Explanation of symbols]

 1, 41 aeration tank 2 sedimentation tank 3, 43 ozone treatment tank 4 acid generation tank 5 membrane separation device 6 methane fermentation tank 11 raw water passage 12 return sludge passage 14 air supply passage 15, 48 air diffuser 16 communication passage 17 treatment water passage 18 Sludge discharge path 21 Excess sludge discharge path 22 Pull-out sludge path 23 Waste ozone path 24 Ozone generator 25 Ozone supply path 26 Ozonized sludge path 27, 32 Pump 28 Acid generation liquid path 29 Concentrated liquid path 29a Sludge discharge path 30 Stirrer 33 Permeate liquid path 34 Separation membrane 35 Methane fermentation liquid transfer path 36 Methane gas discharge path 37 Permeate liquid inflow section 38 Sludge blanket 39 Permeate liquid 40 Concentrate 42 Sludge separation tank 44 Organic waste liquid 45 Return sludge 46 Ozonized sludge 47 Air supply pipe 50 Treatment liquid 51 Separated sludge 53 Extracted sludge 54 Excess sludge 55 Ozone supply pipe 56 Waste ozone pipe

Claims (2)

[Claims] 1. An aerobic biological treatment step of introducing an organic wastewater into an aeration tank and performing an aerobic biological treatment in the presence of activated sludge, solid-liquid separation of the mixed liquid in the aeration tank, and separation of the separated liquid into treated water. As a first solid-liquid separation step of returning at least a part of the separated sludge to the aeration tank, extracting at least a part of the activated sludge from the separated sludge of the first solid-liquid separation step or the mixed liquid of the aeration tank, A reforming process for reforming the extracted sludge to be easily biodegradable; an acid generating process for solubilizing the reformed sludge in the presence of sludge containing acid-producing bacteria in an anaerobic state to generate an organic acid A solid-liquid separation of the mixture in the acid generation step, a separation liquid transfer to the methane fermentation step, and a return of the separated sludge to the acid generation step; a second solid-liquid separation step; a separation in the second solid-liquid separation step The liquor is maintained anaerobically in the presence of sludge containing methanogens and methane fermented. Methane fermentation step, and processing method of organic waste liquid containing a transfer step of introducing a methane fermentation liquid in the aerobic biological treatment process. 2. An aerobic biological treatment apparatus for introducing an organic effluent into an aeration tank to perform aerobic biological treatment in the presence of activated sludge. As a first solid-liquid separation device for returning at least a part of the separated sludge to the aeration tank, and extracting at least a part of the activated sludge from the separated sludge of the first solid-liquid separation device or the mixed solution of the aeration tank, A reforming treatment device that reforms the extracted sludge to be easily biodegradable. An acid generator that keeps the reformed sludge in an anaerobic state in the presence of sludge containing acid-producing bacteria, solubilizes it, and generates organic acids. A second solid-liquid separator, a second solid-liquid separator for returning the separated sludge to the acid generator, and a second solid-liquid separator. The liquid is maintained in an anaerobic state in the presence of sludge containing methanogens, and methane is fermented.酵槽, and organic drainage of the processing apparatus including a transfer device for introducing the methane fermentation liquid in the aerobic biological treatment apparatus.