JP4501496B2 - Biological treatment method for organic wastewater - Google Patents

Description

  The present invention relates to a biological treatment method for organic wastewater that can be used for treatment of organic wastewater in a wide concentration range including domestic wastewater, sewage, food factories and pulp factories. The present invention relates to a biological treatment method for organic wastewater that can improve the treatment efficiency and reduce the amount of excess sludge generation without deteriorating.

The activated sludge method used when biologically treating organic wastewater is widely used for sewage treatment, industrial wastewater treatment, and the like because of its advantages such as good treated water quality and easy maintenance. However, since the BOD volumetric load in the activated sludge method is about 0.5 to 0.8 kg / m ³ / d, a large site area is required. Moreover, since 20% of the decomposed BOD is converted into microbial cells, that is, sludge, a large amount of excess sludge treatment also becomes a problem.

For high load treatment of organic waste water, a fluidized bed method with a carrier added is known. When this method is used, it is possible to operate with a BOD volume load of ³ kg / m ³ / d or more. However, this method has a disadvantage that the amount of generated sludge is about 30% of the decomposed BOD, which is higher than the normal activated sludge method.

  In Japanese Patent Application Laid-Open No. 55-20649, organic wastewater is first treated with bacteria in a first treatment tank, and organic matter contained in the wastewater is oxidatively decomposed and converted into non-aggregating bacterial cells. It is said that the amount of excess sludge can be reduced by precipitating and removing the sticking protozoa in the treatment tank. Furthermore, this method enables high-load operation and improves the treatment efficiency of the activated sludge method.

  Many wastewater treatment methods using protozoa and metazoan predation located at a high level of bacteria have been devised. For example, Japanese Patent Laid-Open No. 2000-210692 discloses Japanese Patent Laid-Open No. 55-20649. Proposals are made for countermeasures against deterioration in treatment performance due to fluctuations in the quality of raw water, which is a problem in the treatment method. As a specific method, “adjust BOD fluctuation of treated water within 50% from the median average concentration”, “measure water quality in first treatment tank and first treated water over time”, The method includes “adding a microbial preparation or seed sludge to the first treatment tank when the quality of the first treated water is deteriorated”.

  In Japanese Patent Publication No. 60-23832, when protozoa and metazoans prey on bacteria, yeast, actinomycetes, algae, molds and wastewater treatment primary sediment sludge and surplus sludge, ultrasonic treatment or mechanical stirring, A method for reducing the above-mentioned flock size of the food from the mouth of the animal is proposed.

In addition, a technique related to multistage treatment of a fluidized bed and an activated sludge method is proposed in Japanese Patent No. 3410699. In this method, the biological treatment in the former stage is a carrier fluidized bed type, and the biological treatment in the latter stage is a multistage activated sludge treatment. By doing so, it is said that the amount of surplus sludge generation is further reduced. In this method, the activated sludge treatment at the latter stage is operated at a low load of BOD sludge load 0.1 kg-BOD / kg-MLSS / d, so that the sludge is self-oxidized and the amount of sludge extraction can be greatly reduced.
Japanese Patent Laid-Open No. 55-20649 JP 2000-210692 A Japanese Patent Publication No. 60-23832 Japanese Patent No. 3410699

  The multi-stage activated sludge method using the predatory action of micro animals as described above has already been put into practical use for organic wastewater treatment, and depending on the target wastewater, it is possible to improve treatment efficiency and reduce the amount of generated sludge. is there.

  However, although the sludge reduction effect varies depending on the treatment conditions and the water quality of the wastewater, it is only enough to halve the amount of sludge generated by the single tank activated sludge method, and it is not possible to maintain a stable sludge reduction over a long period of time. is there. This is due to the fact that most of the sludge remains without being predated in the subsequent microanimal tank for precipitating bacteria-based sludge, or the microanimals involved in predation cannot be maintained at a high concentration. In addition, predatory micro-animals are higher organisms than bacteria and thus have a long life (slow self-degradation rate), which makes it more difficult to reduce sludge.

  Therefore, the present invention is an organic wastewater organism that aims to further improve the treatment efficiency and reduce the amount of surplus sludge while maintaining a stable treated water quality in the multistage activated sludge method utilizing the predatory action of minute animals. An object is to provide a processing method.

The first aspect of the organic wastewater biological treatment method of the present invention is the organic wastewater introduced into the first biological treatment step, biologically treated with non-aggregating bacteria, and non-aggregable from the first biological treatment step. In the biological treatment method for treating activated sludge by introducing treated water containing bacteria into the second biological treatment step, in the first biological treatment step, a BOD volume load of 1 kg / m ³ / d or more, HRT (raw water retention) Time) performing biological treatment with non-aggregating bacteria under a condition of 24 hours or less, and at least a part of the sludge obtained by solid-liquid separation of the sludge of the second biological treatment step or the sludge of the second biological treatment step Introducing into the anaerobic treatment process, anaerobic treatment, solid-liquid separation of the processed product of the anaerobic treatment process, returning the separated liquid to the first biological treatment process and returning the separated sludge to the second biological treatment process It is characterized by that.

According to a second aspect of the organic wastewater biological treatment method of the present invention, the organic wastewater is introduced into the first biological treatment step and biologically treated with non-aggregating bacteria, and the non-aggregable nature from the first biological treatment step. In the biological treatment method for treating activated sludge by introducing treated water containing bacteria into the second biological treatment step, in the first biological treatment step, a BOD volume load of 1 kg / m ³ / d or more, HRT (raw water retention) Time) performing biological treatment with non-aggregating bacteria under a condition of 24 hours or less, and at least a part of the sludge obtained by solid-liquid separation of the sludge of the second biological treatment step or the sludge of the second biological treatment step Introduced into the aerobic treatment step and digested aerobically under the condition of pH 5 to 5.5 , introduced at least a part of the processed product of the aerobic treatment step into the anaerobic treatment step, anaerobic treatment, The treated product is solid-liquid separated, and the separated liquid is It sends back the object processing step, characterized by returning the separated sludge as in the second biological treatment Engineering.

  In the first aspect of the present invention, the sludge from the second biological treatment process (microanimal tank) that preys on the dispersal bacteria from the first biological treatment process (dispersion bacteria tank) that removes organic substances is subjected to anaerobic conditions. By solubilization, organic oxidation, and denaturation by the action of anaerobic bacteria, it is again used for dispersal bacteria and / or predation on micro-animals, thereby improving processing efficiency and reducing the amount of excess sludge generated.

  In the second aspect of the present invention, by passing through the aerobic treatment step prior to the anaerobic treatment step, the proportion of minute animals occupying in the sludge increases, and solubilization of the sludge in the subsequent anaerobic treatment step is facilitated. Become.

  According to the organic wastewater biological treatment method of the present invention, in the multistage activated sludge method utilizing the predatory action of micro-animals, while maintaining a stable treated water quality, further improvement in treatment efficiency and surplus sludge generation amount Reduction can be achieved.

  Embodiments of a biological treatment method for organic wastewater according to the present invention will be described below in detail with reference to the drawings.

  1, 2 and 4 are system diagrams showing a biological treatment method for organic wastewater according to a reference example, and FIG. 3 shows an embodiment of the biological treatment method for organic wastewater according to the first aspect of the present invention. FIG. 5 is a system diagram showing an embodiment of the organic wastewater biological treatment method according to the second aspect of the present invention. 1 to 5, members having the same function are denoted by the same reference numerals.

In the method of FIG. 1, raw water (organic wastewater) is first introduced into a first biological treatment tank (dispersed bacteria tank) 1 and is 70% or more, preferably 80% of BOD (organic component) due to non-aggregating bacteria. More preferably, 90% or more is oxidatively decomposed. The pH of the first biological treatment tank 1 is 6 or more, preferably pH 6-8. Moreover, the BOD volumetric load to the 1st biological treatment tank 1 shall be 1 kg / m < ³ > / d or more, for example, 1-20 kg / m < ³ > / d, HRT (raw water residence time) shall be 24 h or less, for example, 0.5-24 h. Thus, it is possible to obtain treated water in which non-aggregating bacteria predominate, and by shortening the HRT, wastewater having a low BOD concentration can be treated with a high load, which is preferable. Further, by adding a carrier, it becomes possible to reduce a high load and a residence time.

  The treated water in the first biological treatment tank 1 is introduced into a second biological treatment tank (micro animal tank) 2 that is controlled to have a pH of 6 or more, preferably in the range of pH 6-8, where the remaining organic components are removed. Sludge is reduced by oxidative degradation, self-degradation of non-aggregating bacteria and predation by micro animals.

  Since the second biological treatment tank 2 utilizes the action of micro-animals that have a slower growth rate than bacteria and the self-degradation of bacteria, operating conditions and treatment equipment that allow micro-animals and bacteria to remain in the system must be used. . Therefore, it is desirable to use an activated sludge method or a membrane-separated activated sludge method for returning the sludge to the second biological treatment tank 2. More desirably, the amount of micro-animal retained in the tank can be increased by adding a carrier to the aeration tank.

  In addition, as shown in FIG. 2, in the method of FIG. 1, the second biological treatment tank 2 is multi-staged, and two or more biological treatment tanks 2A and 2B are provided in series. The treatment may be performed under the condition of pH 5 to 5.5, and the treatment may be performed under the condition of pH 6 or more, preferably pH 6 to 8 in the post-treatment tank 2B. By such multi-stage treatment, sludge is produced in the pre-treatment tank 2A. In this way, it is possible to improve the solid-liquid separation property of the sludge and the quality of the treated water in the post-treatment tank 2B. The method shown in FIG. 2 is different from that shown in FIG. 1 only in that the second biological treatment tank 2 is multistaged, and the other configuration is the same. In order to reduce the amount of sludge generated in the second biological treatment tank 2, the partition is not made as shown in FIG. 2, and the pH of the second biological treatment tank 2 is set to 6 or less in a single tank as shown in FIG. In this case, however, neutralization is required before the treated water is discharged.

  The treated water in the second biological treatment tank 2 is solid-liquid separated in the precipitation tank 3, and the separated water is discharged out of the system as treated water. A part of the separated sludge is discharged out of the system as surplus sludge, a part is returned to the second biological treatment tank 2, and the remaining part is fed to the anaerobic digestion tank 4. The sludge return ratio of the separated sludge to the second biological treatment tank 2 and the anaerobic digestion tank 4 is only required to maintain the sludge residence time in the following anaerobic digestion tank 4, and can be arbitrarily changed according to the amount of generated sludge. Can do.

  That is, in the first aspect of the present invention, at least a part of the sludge in the second biological treatment tank 2 where the microanimals prey on the dispersal bacteria or the sludge obtained by solid-liquid separation of the sludge is anaerobic digester. Introduced into No. 4, sludge solubilization, organic oxidation to lower organic acids and lower alcohols, or modification under anaerobic conditions. Therefore, sludge extracted from the second biological treatment tank 2 may be introduced into the anaerobic digestion tank 4 instead of the separated sludge in the sedimentation tank 3.

  The sludge in the second biological treatment tank 2 has a high proportion of micro-animals, and at least 10% or more of SS and 30% or more depending on the operating conditions. Microanimals easily die under anaerobic conditions compared to bacteria, solubilized, and organically oxidized by acid-producing bacteria, so that the sludge residence time (SRT) in the anaerobic digester 4 is 0.5 days or more, for example, 0.5-5 days is sufficient. In addition, in order to prevent the organic acid and alcohol generated in the anaerobic digestion tank 4 from being converted to methane by the action of the methanogenic bacteria, the pH in the anaerobic digestion tank 4 is 6.0 or less, preferably 5.5. Hereinafter, it is desirable to set it to, for example, 5 to 5.5, or to set the temperature to 30 ° C. or lower, desirably 25 ° C. or lower, for example 20 to 25 ° C. However, when the organic substance converted into the organic acid or alcohol is converted into methane and recovered or disposed as energy, the anaerobic digester 4 may have a pH of 6.0 or higher or a temperature of 30 ° C. or higher. By the anaerobic digestion in the anaerobic digestion tank 4, the minute animals in the second biological treatment tank 2 and the bacteria remaining without being predated are converted into organic acids and alcohols. In addition, components that are not reduced in the second biological treatment tank 2, such as micro animal feces, carcasses, and bacteria, which are other SS components, are denatured or subdivided in the anaerobic digestion tank 4, and the cells of the anaerobic bacteria are also present. Therefore, it becomes predatory by micro animals.

  In FIG. 1, 2, the processed material of this anaerobic digestion tank 4 is returned to the 1st biological treatment tank 1 and / or the 2nd biological treatment tank 2 as it is.

  As shown in FIG. 3, the processed product in the anaerobic digestion tank 4 is subjected to solid-liquid separation by a solid-liquid separation device 5 such as a concentrator or a dehydrator, and separated water containing an organic acid or alcohol (anaerobic treated water) is first added. It is possible to reduce sludge further by returning it to the biological treatment tank 1 and converting it again into dispersal bacteria, and returning the solid content (sludge) to the second biological treatment tank 2 so that it can be eaten by micro animals. It becomes. In this case, extraction of excess sludge may be performed from the sedimentation tank 3, or may be performed from the solid-liquid separation device 5 subsequent to the anaerobic digestion tank 4. In addition, in the anaerobic digestion tank 4, the high-concentration anaerobic condition is obtained by not returning all the solid content separated by the solid-liquid separation device 5 to the second biological treatment tank 2 but returning it to the anaerobic digestion tank 4 again. Sexual digestion is possible, SRT can be lengthened, and solubilization can be promoted. Moreover, solid-liquid separation or high-concentration digestion can also be performed by providing an immersion membrane in the anaerobic digestion tank 4 or adding a carrier without providing a solid-liquid separation device such as a concentrator.

  The method shown in FIG. 4 is different from the method shown in FIG. 1 in that an aerobic digester 6 is provided in front of the anaerobic digester 4, and the first biological treatment tank 1, the second biological treatment tank 2, and the precipitation tank 3. And the process in the anaerobic digester 4 is performed similarly.

That is, in the second aspect of the present invention, by introducing at least a portion of the sludge obtained by solid-liquid separation sludge or this second biological treatment tank 2 to the aerobic digestion tank 6, p H5~5. The aerobic digestion is performed under the condition 5 and at least a part of the treated sludge and the treated water is supplied to the anaerobic digestion tank 4 so as to be solubilized, organically oxidized or denatured under the anaerobic condition. Even in this case, the ratio of the sludge returned to the aerobic digester 6 and the second biological treatment tank 2 can be adjusted to the amount of generated sludge if the sludge retention time in the aerobic digester 6 shown below can be maintained. It can be changed arbitrarily.

  In FIG. 4, the aerobic digestion tank 6 not only has a sludge reduction effect, but also passes through this aerobic digestion tank 6, so that the proportion of minute animals occupying the sludge is further increased. It is excellent in that sludge can be solubilized easily. The sludge residence time in the aerobic digestion tank 6 is 12 hours or more, desirably 24 hours or more, for example, 24 to 240 hours. However, the aerobic treatment method in which the sludge is returned by providing a solid-liquid separation device or the flow added with the carrier By using a bed or membrane separation type aerobic treatment method, the sludge residence time can be further increased. A part of the sludge from the aerobic digestion tank 6 may be returned directly to the second biological treatment tank 2 without going through the anaerobic digestion tank 4, thereby replenishing the minute animals in the second biological treatment tank 2. Also useful.

  The method shown in FIG. 5 differs from the method shown in FIG. 4 in that a solid-liquid separation device 5 is provided after the anaerobic digester 4 as shown in FIG. Solid-liquid separation of the treated product, separation water and separation sludge are returned. Here, the separated sludge of the solid-liquid separator 5 may be further returned to the aerobic digester 6.

  The method of FIGS. 3 and 5 shows an example of an embodiment of the present invention, and the present invention is not limited to the illustrated method unless it exceeds the gist of the present invention.

For example, the first biological treatment tank is a fluidized bed system with a carrier added in addition to returning a part of the separated sludge from the subsequent sedimentation tank for high load treatment, or two or more biological treatment tanks in series. It is also possible to perform multi-stage processing by providing them. In particular, the addition of a carrier is preferable because a high load treatment with a BOD volume load of 5 kg / m ³ / d or more is possible. In this case, the shape of the carrier to be added is arbitrary such as a spherical shape, a pellet shape, a hollow cylindrical shape, and a thread shape, and the size may be about 0.1 to 10 mm. The material of the carrier is arbitrary such as a natural material, an inorganic material, or a polymer material, and a gel material may be used. Further, in the second biological treatment tank 2, in order to utilize the action of the microanimal whose growth rate is slower than that of the bacterium and the self-degradation of the bacterium, the operating conditions and the treatment apparatus are adopted so that the tiny animal and the bacterium stay in the system. For this reason, as shown in FIGS. 3 and 5, the second biological treatment tank performs sludge return biological treatment for returning sludge and immerses a separation membrane in the tank. It is also desirable to perform a separate activated sludge treatment. More desirably, the amount of micro-animal retained in the tank can be increased by adding a carrier to the aeration tank. As the carrier in this case, the same carrier as described above as the carrier added to the first biological treatment tank can be used.

  By the way, in the wastewater treatment, sludge is generated from the initial sedimentation basin, the pressurized flotation tank and the like in addition to the sludge derived from the biological treatment. When these are anaerobically treated, they are more easily decomposed than sludge derived from biological treatment, so that they can be solubilized by 50% or more and converted into organic acids. In addition, components that are not solubilized are also subdivided and can be preyed on by minute animals. Therefore, in the present invention, initial sedimentation sludge and pressurized floating sludge are added to the anaerobic treatment process (anaerobic digestion tank) in which the sludge of the second biological treatment tank is introduced, and the minute animal is preyed on the SS component that is not solubilized. This makes it possible to reduce the amount of excess sludge discharged from the entire factory.

  Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

Reference example 1
As shown in FIG. 1, a first biological treatment tank (activated sludge tank (no sludge return)) 1 having a capacity of 3.6 L, a second biological treatment tank (active sludge tank) 2 and a sedimentation tank 3 having a capacity of 15 L, Using an experimental apparatus connected with an anaerobic digester 4 having a capacity of 1 L, the organic waste water (BOD 630 mg / L) according to the present invention was treated. The pH of the first biological treatment tank 1 was adjusted to 6.8, the pH of the second biological treatment tank 2 was adjusted to 6.8, and the pH of the anaerobic digestion tank 4 was adjusted to 6.0. The soluble BOD volumetric load on the first biological treatment tank 1 is 3.85 kg-BOD / m ³ / d and HRT4h, and the soluble BOD sludge load on the second biological treatment tank 2 is 0.022 kg-BOD / kg-MLSS / It was operated under the conditions of HRT17h for d, and BRT volume load of 0.75 kg-BOD / m ³ / d for HRT21h.

  The SS in the first and second biological treatment tanks 1 and 2 was 5000 mg / L, and the drawn sludge from the settling tank 3 was concentrated to 10,000 mg / L. This concentrated sludge was extracted at a rate of 250 ml / d and added to the anaerobic digester 4. Moreover, 250 ml / d was discharged out of the system as surplus sludge, and all the remaining sludge was returned to the second biological treatment tank 2. The HRT and SRT of the anaerobic digestion tank 4 were set on the 4th, and the treated sludge of the anaerobic digestion tank 4 was returned to the second biological treatment tank 2.

  When continuously operated for 4 months under these conditions, the soluble BOD concentration in the treated water of the anaerobic digester 4 was 4000 mg-BOD / L, and acetic acid accounted for 55% and propionic acid accounted for 40%. The sludge conversion rate calculated from the amount of sludge extracted from the second biological treatment tank 2 was 0.12 kg-MLSS / kg-BOD.

Reference example 2
As shown in FIG. 2, the second biological treatment tank 2 is the same as in Reference Example 1 except that the second-stage activated sludge tank (5L + 10L) is composed of a front-stage treatment tank 2A having a capacity of 5L and a rear-stage treatment tank 2B having a capacity of 10L. The organic waste water (BOD 630 mg / L) was treated in the same manner as in Reference Example 1 using an experimental apparatus. In addition, pH of the front-stage treatment tank was adjusted to 5.0, and pH of the rear-stage treatment tank was adjusted to 6.8. Other conditions are the same as in Reference Example 1.

  The SS in the first and second biological treatment tanks 1 and 2 was 5000 mg / L, and the drawn sludge from the settling tank 3 was concentrated to 10,000 mg / L. Of this concentrated sludge, 250 ml / d was withdrawn and added to the anaerobic digester 4. Moreover, 208 ml / d was discharged out of the system as surplus sludge, and all the remaining sludge was returned to the second biological treatment tank 2. The HRT and SRT of the anaerobic digestion tank 4 were set on the 4th, and the treated sludge of the anaerobic digestion tank 4 was returned to the second biological treatment tank 2.

  When continuously operated for 4 months under these conditions, the soluble BOD concentration in the treated water of the anaerobic digester 4 was 6500 mg-BOD / L, and acetic acid accounted for 55% and propionic acid accounted for 35%. The sludge conversion rate calculated from the amount of sludge extracted from the second biological treatment tank 2 was 0.10 kg-MLSS / kg-BOD.

Reference example 3
As shown in FIG. 4, organic waste water (BOD 630 mg) was used in the same manner as in Reference Example 1 using the same experimental apparatus as in Reference Example 1 except that an aerobic digester 6 having a capacity of 2 L was provided in front of the anaerobic digester 4. / L). The pH of the aerobic treatment tank was adjusted to 5.0. Other conditions are the same as in Reference Example 1.

  The SS in the first and second biological treatment tanks 1 and 2 was 5000 mg / L, and the drawn sludge from the settling tank 3 was concentrated to 10,000 mg / L. 250 ml / d of this concentrated sludge is added to the aerobic digester 6, the same amount is extracted from the aerobic digester 6, added to the anaerobic digester 4, and all the remaining concentrated sludge is returned to the second biological treatment tank 2. did. The HRT and SRT of the aerobic digester 6 were 8 days. The HRT and SRT of the anaerobic digestion tank 4 were set to 4 days, and the treated sludge of the anaerobic digestion tank 4 was returned to the second biological treatment tank 2.

  When continuously operated for 4 months under these conditions, the soluble BOD concentration in the treated water of the anaerobic digester 4 was 6500 mg-BOD / L, and acetic acid accounted for 55% and propionic acid accounted for 35%. The sludge conversion rate calculated from the amount of sludge extracted from the second biological treatment tank 2 (185 ml / d) was 0.09 kg-MLSS / kg-BOD.

Example 1
As shown in FIG. 3, the organic waste water (BOD 630 mg / L) of the organic waste water (BOD 630 mg / L) was used in the same manner as in Reference Example 1 using the same experimental apparatus as in Reference Example 1 except that a solid-liquid separation device 5 was provided at the subsequent stage of the anaerobic digester 4. Processed. The pH conditions and load conditions of each tank are the same as in Reference Example 1.

  The SS in the first and second biological treatment tanks 1 and 2 was 5000 mg / L, and the drawn sludge from the settling tank 3 was concentrated to 10,000 mg / L. By adding 250 ml / d of this concentrated sludge to the anaerobic digestion tank 4 and returning all the remaining concentrated sludge to the second biological treatment tank 2, the sludge is extracted from the first and second biological treatment tanks 1 and 2. The SS in the tank could be kept constant. The HRT of the anaerobic digestion tank 4 is 4 days, the treated product of the anaerobic digestion tank 4 is solid-liquid separated by the solid-liquid separation device 5, the treated water is in the first biological treatment tank 1, and half of the separated sludge is second. A quarter amount was returned to the anaerobic digestion tank 4 to the biological treatment tank 2, and a quarter amount was extracted as excess sludge.

  When continuously operated for 4 months under these conditions, the soluble BOD concentration in the treated water of the anaerobic digester 4 was 4000 mg-BOD / L, and acetic acid accounted for 55% and propionic acid accounted for 40%. The sludge conversion rate calculated from the amount of sludge extracted from the anaerobic digester 4 was 0.10 kg-MLSS / kg-BOD.

Example 2
As shown in FIG. 5, similarly organic waste water as in Example 1 using the same experimental apparatus except that in front of the anaerobic digestion tank 4 provided with aerobic digester 6 capacity 2L to Example 1 (BOD630mg / L). The pH of the aerobic digester 6 was adjusted to 5.0. Other conditions are the same as those in the first embodiment .

  The SS in the first and second biological treatment tanks 1 and 2 was 5000 mg / L, and the drawn sludge from the settling tank 3 was concentrated to 10,000 mg / L. 250 ml / d of this concentrated sludge is added to the aerobic digester 6, the same amount is extracted from the aerobic digester 6 and added to the anaerobic digester 4, and all the remaining concentrated sludge is added to the second biological treatment tank 2. By returning to the tank, the SS in the tank could be kept constant without extracting sludge from the first and second biological treatment tanks 1 and 2. The HRT and SRT of the aerobic digester 6 were 8 days. The HRT of the anaerobic digestion tank 4 is 4 days, the treated sludge of the anaerobic digestion tank 4 is solid-liquid separated by the solid-liquid separator 5, the treated water is supplied to the first biological treatment tank 1, and half of the solid content is The remaining 3/8 amount was returned to the second biological treatment tank 2 to the anaerobic digestion tank 4, and the remaining 1/8 amount was extracted as excess sludge.

  When operated continuously for 4 months under these conditions, the soluble BOD concentration in the treated water in the anaerobic treatment tank 4 was 6500 mg-BOD / L, and acetic acid accounted for 55% and propionic acid accounted for 35%. The sludge conversion rate calculated from the amount of sludge extracted from the anaerobic digester 4 was 0.07 kg-MLSS / kg-BOD.

Comparative Example 1
As shown in FIG. 6, the organic waste water (BOD 630 mg / L) was treated using an experimental apparatus composed of a biological treatment tank (activated sludge tank) 2 ′ having a capacity of 15 L and a sedimentation tank 3. Biological treatment tank 2 ′ has a soluble BOD volumetric load of 0.76 kg-BOD / m ³ / d and was continuously operated for 4 months under the conditions of HRT20h and pH 6.8. The rate was 0.40 kg-MLSS / kg-BOD.

Comparative Example 2
As shown in FIG. 7, the organic waste water (BOD 630 mg / L) was treated in the same manner as in Reference Example 1 using the same experimental apparatus as in Reference Example 1 except that the anaerobic digester 4 was omitted. The pH conditions and load conditions of each tank are the same as in Reference Example 1.

  When continuously operating for 4 months under these conditions, the treated water was good, but the sludge conversion rate calculated from the amount of sludge extracted from the second biological treatment tank 2 was 0.20 kg-MLSS / kg-BOD. In addition, the proportion of micro animals in the VSS of the second biological treatment tank 2 was about 25% (w / w).

Reference Example 1, the excess sludge generation quantity versus charged BOD in the real施例1 and 2 and Comparative Examples 1 and 2 (sludge conversion ratio) shown in FIG. 8. Also, the operating conditions after the start of the experiment 4 months Comparative Examples 1 and 2 with the actual施例1 and 2 are shown in Table 1.

  The following can be understood from the above results.

  Comparative Example 1 is a conventional activated sludge method, and Comparative Example 2 is a conventional two-stage biological treatment method. In the conventional activated sludge method (Comparative Example 1), the sludge conversion rate was 0.40 kg-MLSS / kg-BOD, but by introducing multistage biological treatment as in Comparative Example 2, the sludge conversion rate was 0. It became 20 kg-MLSS / kg-BOD, and the sludge generation amount could be reduced to ½. This sludge reduction effect is similar to the two-stage biological treatment methods reported so far.

On the other hand, in Example 2 where the anaerobic digestion process was introduced as in the present invention and the sludge reduction effect was particularly remarkable, the sludge conversion rate was 0.07 kg-MLSS / kg-BOD, respectively, and the conventional method The amount of generated sludge could be reduced to 1/6. In Example 2, sludge weight loss is markedly caused by microanimal predation in the aerobic digestion tank set to pH 5 so that the proportion of fine animals in the sludge VSS is 32% (w / w) in the second biological treatment tank 2. On the other hand, this aerobic digester reached 60% at the maximum. It is easy to solubilize sludge of a high minute animal ratio, the solubilization rate in the anaerobic digester 4 of Example 2 reaches 65%, and the maximum solubilization rate is 40% (in the anaerobic digester 4). animalcule ratio of input to the sludge VSS: 30% (w / w )) did not reach only up to reference example 1, compared with example 1 led to a higher sludge reduction effect. Furthermore, the anaerobic digested sludge is separated into solid and liquid, and the soluble COD component is converted again to the dispersal bacteria in the first biological treatment tank 1, so that in Example 2, 1/6 of the sludge reduction effect of the conventional method is achieved. We were able to.

  The organic wastewater biological treatment method of the present invention can be used to treat organic wastewater in a wide concentration range including domestic wastewater, sewage, food factories and pulp factories.

It is a systematic diagram which shows embodiment of the biological treatment method of the organic waste_water | drain which concerns on a reference example. It is a systematic diagram which shows other embodiment of the biological treatment method of the organic waste_water | drain which concerns on a reference example. It is a systematic diagram which shows another embodiment of the biological treatment method of the organic waste_water | drain which concerns on the 1st aspect of this invention. It is a systematic diagram which shows embodiment of the biological treatment method of the organic waste_water | drain which concerns on a reference example. It is a systematic diagram which shows other embodiment of the biological treatment method of the organic waste_water | drain which concerns on the 2nd aspect of this invention. 4 is a system diagram showing an experimental apparatus used in Comparative Example 1. FIG. 10 is a system diagram showing an experimental apparatus used in Comparative Example 2. FIG. Reference Example 1 is a graph showing the relationship between the charged BOD volume and excess sludge generation amount in the real施例1 and 2 and Comparative Examples 1 and 2.

DESCRIPTION OF SYMBOLS 1 1st biological treatment tank 2 2nd biological treatment tank 3 Precipitation tank 4 Anaerobic digestion tank 5 Solid-liquid separator 6 Aerobic digestion tank

Claims (4)

Organic wastewater is introduced into the first biological treatment process and biologically treated with non-aggregating bacteria, and treated water containing non-aggregable bacteria from the first biological treatment process is introduced into the second biological treatment process to activate activated sludge. In the biological treatment method to be treated,
In the first biological treatment step, biological treatment with non-aggregating bacteria is performed under conditions of pH 6 or more, BOD volumetric load 1 kg / m ³ / d or more, HRT (raw water retention time) 24 h or less,
Introducing at least a part of the sludge of the second biological treatment step or the sludge obtained by solid-liquid separation of the sludge of the second biological treatment step into the anaerobic treatment step, and treating the anaerobic treatment step A method for biological treatment of organic wastewater, comprising separating a solid into a liquid, returning the separated liquid to the first biological treatment step, and returning separated sludge to the second biological treatment step.   In Claim 1, pH of said 2nd biological treatment process shall be 6 or more, The biological treatment method of the organic waste water characterized by the above-mentioned.   2. The biological treatment method for organic wastewater according to claim 1, wherein the second biological treatment step is a multistage treatment of two or more stages, and biological treatment of pH 6 or more is performed after biological treatment of pH 5.5 or less. Organic wastewater is introduced into the first biological treatment process and biologically treated with non-aggregating bacteria, and treated water containing non-aggregable bacteria from the first biological treatment process is introduced into the second biological treatment process to activate activated sludge. In the biological treatment method to be treated,
In the first biological treatment step, biological treatment with non-aggregating bacteria is performed under conditions of pH 6 or more, BOD volumetric load 1 kg / m ³ / d or more, HRT (raw water retention time) 24 h or less,
The sludge of the second biological treatment process or at least a part of the sludge obtained by solid-liquid separation of the sludge of the second biological treatment process is introduced into the aerobic treatment process and is favorably used at a pH of 5 to 5.5. Aerobic digestion , anaerobic treatment step of introducing at least a part of the treatment product of the aerobic treatment step, solid-liquid separation of the treatment product of the anaerobic treatment step, and separation liquid into the first biological treatment step biological treatment method of organic waste water, characterized in that sends back, returning the separated sludge as in the second biological treatment Engineering in.

Images