CN1914122B - Biological Treatment of Organic Drainage - Google Patents

Abstract

The multistage activated sludge process utilizing the predation effect of microorganisms achieves further improvement in treatment efficiency and reduction in the amount of excess sludge produced while maintaining stable treatment water quality. The method comprises a 1 st biological treatment step of treating BOD in organic wastewater at a high load to convert the BOD into dispersed cells, and a 2 nd biological treatment step of flocculating the dispersed cells thus converted and allowing microorganisms to coexist. The 2 nd biological treatment step is carried out at a pH of 5-6. Or performing an excess sludge treatment step of separating the sludge of the 2 nd biological treatment step and/or the sludge of the 2 nd biological treatment step under a pH condition of 5 to 6, decomposing at least a part of the sludge obtained by the solid-liquid separation under an aerobic condition, and returning the treated sludge to the 1 st biological treatment step and/or the 2 nd biological treatment step.

Description

Biological Treatment of Organic Drainage

field of invention

The invention relates to a biological treatment method and device for organic drainage. the

Background technique

Currently, there is a demand for a biological treatment method for organic wastewater that can be used for the treatment of organic wastewater in a wide range of concentrations represented by domestic wastewater, sewage, food factories, and pulp factories. In particular, a biological treatment method for organic drainage that can improve treatment efficiency and reduce excess sludge production without deteriorating the treated water quality is desired. the

The activated sludge method used in the biological treatment of organic drainage is widely used in sewage treatment, industrial wastewater treatment, etc. due to its advantages of good water quality and easy maintenance. However, since the BOD volume load in the activated sludge method is about 0.5 to 0.8 kg/m ³ /d, a wide area of land is required. Since 20% of the decomposed BOD is transformed into bacteria, that is, sludge, a large amount of excess sludge is processed.

A fluidized bed method in which a carrier is added is known for high-load treatment of organic wastewater. When using this method, it is possible to operate with a BOD volume load of 3kg/m ³ /d or more. However, the amount of sludge generated in this method is about 30% of the decomposed BOD, which is more than the usual activated sludge method.

Japanese Patent Publication No. 56-48235 discloses the following method, that is, firstly, bacteria treat organic drainage in the first treatment tank, oxidatively decompose the organic matter contained in the drainage, and after being converted into non-aggregative bacterial cells, In the second treatment tank, the sessile protozoa were preyed on and removed. This method can reduce the amount of residual sludge. The same secondary biological treatment is also described in Japanese Patent Publication No. 62-54073. Using these methods, high-load operation is possible, and the efficiency of activated sludge treatment can also be improved. the

In Japanese Patent No. 3360076, the following method is described, that is, in this two-stage biological treatment method, the activated sludge containing protozoa is discharged from the biological treatment tank, and the sterilization and possible treatment are carried out in the reaction treatment tank. Melting treatment, and then return to the biological treatment tank, which can further reduce the amount of excess sludge produced. the

In Japanese Patent No. 3410699, the following method is described, that is, by making the previous stage biological treatment a carrier fluidized bed type and making the latter stage biological treatment a multistage activated sludge treatment, the residual sludge can be further reduced. Mud production. In this method, the sludge can be self-oxidized by the activated sludge treatment after the low-load operation with a BOD sludge load of 0.1kg-BOD/kg-MLSS/d, and the sludge discharge can be greatly reduced. the

Japanese Patent Publication No. 55-20649 discloses the following method, that is, firstly, bacteria treat the organic drainage in the first treatment tank, oxidize and decompose the organic matter contained in the drainage, and after being converted into non-aggregative bacterial cells, The second treatment tank is predated and removed by sessile protozoa, thereby reducing the amount of excess sludge. Using this method, it can also operate at a high load, and can also improve the efficiency of activated sludge treatment. the

For example, Japanese Patent Laid-Open No. 2000-210692 proposes a countermeasure against degradation of treatment performance due to the problem of fluctuations in raw water quality in the treatment method of Japanese Patent Application Publication No. 55-20649. Specifically, "adjust the BOD fluctuation of the treated water within 50% of the median value of the average concentration", "measure the water quality of the first treatment tank and the first treated water over time", "the water quality of the first treated water When it deteriorates, add microbial agents or inoculate sludge in the first treatment tank" and other methods. the

In Japanese Patent Publication No. 60-23832, the following method is proposed, that is, when protozoa and metazoans prey on bacteria, yeast, actinomycetes, algae, molds, or primary sludge or excess sludge from wastewater treatment , through ultrasonic treatment or mechanical stirring, the flocculation size of the above bait is smaller than the animal's mouth. the

The multi-stage activated sludge method using the predation of the above-mentioned tiny organisms has been applied to organic drainage treatment. For different drainage objects, it can improve the treatment efficiency and reduce the amount of sludge produced. the

For example, when microscopic animals are used for predation, the sludge reduction effect varies depending on the treatment conditions and the water quality of the effluent, but the amount of sludge generated by the standard activated sludge method can be reduced to about 30 to 70%. the

However, although the sludge reduction effect varies depending on the treatment conditions and the water quality of the effluent, the amount of sludge generated in the single-tank activated sludge process can be reduced to about half. This is because most of the sludge remains without predation in the microbiological tank of the subsequent stage of the sludge used to prey on the main body of bacteria, or the microscopic organisms involved in predation cannot be maintained at a high concentration. the

Furthermore, since microscopic organisms that prey are higher organisms than bacteria, they have a long lifespan (slow self-decomposition speed), which makes it difficult to further reduce the amount of sludge. the

Microscopic animals not only proliferate by division, but some also proliferate by eggs. Among such representative metazoans are rotifers. This tiny animal is considered to contribute to the reduction of sludge, but it is not always in a proliferating state (egg-laying state). It will not lay eggs after more than ten days after hatching, and it will reach its life span and die after more than ten days. When these microscopic animals predominate, even if eggs are laid, hatching may not be possible when a sufficient amount of adults exists or most of the sludge is feces and there are few bacteria used as bait, so sometimes the microscopic animals in the tank die together. Such metazoan characteristics make it difficult to stabilize and maintain low sludge production for a long period of time in the activated sludge process using microfauna. the

In the multi-stage activated sludge process using self-digestion of bacteria, regardless of the bacterial state (dispersed state, flocculation, filamentous), compared with the standard activated sludge process, the amount of sludge produced can be reduced by about 50%. However, in order to obtain a 50% reduction in sludge, it is necessary to set a longer sludge retention time in the self-digestion biological treatment tank. For this reason, if a membrane separation device is introduced, the maintenance cost of the membrane will offset the sludge. The reduction brings about the reduction of operating expenses. the

Therefore, in order to achieve a sludge reduction rate of more than 50% at low operating costs using the aeration tank already installed, the use of microscopic animals is effective, and in order to make it stable, in the previous biological treatment tank, it is necessary to Stably produces bacteria that are easily preyed on by microscopic animals. the

Contents of the invention

The object of the present invention is to provide a biological treatment method and device for organic drainage, wherein in the multi-stage activated sludge process utilizing the predation of micro organisms, further improvement of treatment efficiency and reduction of residual sewage can be achieved while maintaining stable treatment water quality. Reduced slime production. the

The first aspect relates to the biological treatment method and device of organic waste water, characterized in that the BOD in the organic waste water is treated with a high load so that it is converted into the first biological treatment process of dispersed bacteria, and the converted dispersed In the biological treatment method and apparatus of organic waste water in the second biological treatment step of allowing micro organisms to coexist while flocculating bacterial cells, the second biological treatment step is performed under the condition of pH 5-6. the

The second aspect relates to a biological treatment method and device for organic waste water, characterized in that the BOD in the organic waste water is treated with a high load so that it is converted into the first biological treatment process of dispersed bacteria, and the converted dispersed In the biological treatment method of organic waste water in the second biological treatment process in which bacteria are flocculated and micro organisms coexist, the sludge in the second biological treatment process and/or the sludge in the second biological treatment process are provided with solid-liquid separation , an excess sludge treatment process of decomposing at least a part of the sludge obtained under aerobic conditions, and returning the treated sludge of the excess sludge treatment process to the first biological treatment process and/or the second biological treatment process , the excess sludge treatment process is carried out under the condition of pH5-6. the

The third aspect relates to the biological treatment method and device of organic waste water, characterized in that, when the organic waste water is introduced into the first biological treatment process, the biological treatment is carried out by non-agglomerative bacteria, and the non- The treated water of agglutinating bacteria is introduced into the biological treatment method and device for activated sludge treatment in the second biological treatment process, and the sludge in the second biological treatment process is separated from solid and liquid, or the sludge in the second biological treatment process is In the anaerobic treatment step, at least a part of the sludge obtained by solid-liquid separation is introduced for anaerobic treatment, and the treated product of the anaerobic treatment step is returned to the first biological treatment step and/or the second biological treatment step. the

The fourth aspect relates to a biological treatment method and device for organic waste water, characterized in that, when the organic waste water is introduced into the first biological treatment process, biological treatment is carried out by non-agglomerative bacteria, and non- In the biological treatment method in which the treated water of agglutinating bacteria is introduced into the second biological treatment process for activated sludge treatment, the sludge in the second biological treatment process is separated from solid and liquid, or the sludge in the second biological treatment process is aerobically In the treatment process, at least a part of the sludge obtained by solid-liquid separation is introduced, and it is oxidized under aerobic conditions. The treated product of the treatment process is returned to one or more processes selected from the first biological treatment process, the second biological treatment process and the aerobic treatment process. the

A fifth aspect relates to a biological treatment method and device for organic waste water, characterized in that the organic waste water is introduced into the first biological treatment step, and bacteria are used for biological treatment, and the treatment solution containing bacteria from the first biological treatment step Introduce the second biological treatment process to conduct activated sludge treatment, solid-liquid separation of the treatment liquid from the second biological treatment process, separate it into sludge and treated water, and return a part of the sludge to the biological process of the second biological treatment process In the treatment method and device, in the third biological treatment process, a part of the sludge in the second biological treatment process, and/or the remaining part of the sludge after the solid-liquid separation treatment, is subjected to aerobic treatment, Dehydrating part or all of the aerobically treated sludge, separating it into solids and water, discharging the solids as excess sludge, and returning the water to the first biological treatment process and/or the second biological treatment process. the

A sixth aspect relates to a biological treatment method and device for organic waste water, characterized in that the organic waste water is introduced into a first biological treatment tank, and bacteria are used for biological treatment, and the treatment liquid containing bacteria from the first biological treatment tank Introduce the 2nd biological treatment tank to carry out in the biological treatment method and device of activated sludge treatment, the sludge residence time of this 2nd biological treatment tank is controlled at 5～40 days. the

The seventh aspect relates to a biological treatment method and device for organic waste water, characterized in that, in order to introduce the organic waste water into the first biological treatment tank, the biological treatment is carried out by using bacteria, and the non-aggregative bacteria contained in the first biological treatment tank The treatment liquid is introduced into the second biological treatment tank for activated sludge treatment, the solid-liquid separation comes from the sludge in the second biological treatment tank, and the sludge obtained from the solid-liquid separation is introduced into the third biological treatment tank under aerobic conditions. Oxidation treatment, the biological treatment method and device of returning part or all of the treated product of the third biological treatment tank to the second biological treatment tank, and retaining the sludge in the second biological treatment tank and the third biological treatment tank The time is controlled within 5-40 days respectively. the

The eighth aspect relates to a biological treatment method and device for organic waste water, characterized in that the BOD in the organic waste water is treated with a high load to convert it into a first biological treatment process of bacteria, and the transformed bacteria are combined with In the biological treatment method and device of the organic waste water in the second biological treatment process in which microscopic animals preying on the fungus coexist, it is determined that 70% or more and less than 100% of the BOD in the organic waste water is converted into bacteria as a standard The hydraulic retention time (HRT) in the first biological treatment process required by the body, with this value as the standard HRT, liquid is added to the organic waste water introduced in the first biological treatment process, so that all The HRT in the first biological treatment step is in the range of 0.75 to 1.5 times the standard HRT. the

A ninth aspect relates to a biological treatment method and device for organic wastewater, characterized in that the BOD in the organic wastewater is treated with a high load to convert it into a first biological treatment process of bacteria, and the transformed bacteria are combined with In the biological treatment method and device of the organic waste water in the second biological treatment process in which microscopic animals preying on the fungus coexist, it is determined that 70% or more and less than 100% of the BOD in the organic waste water is converted into bacteria as a standard The required hydraulic retention time (HRT) in the first biological treatment step, using this value as the standard HRT, changes the amount of water in the treatment tank for the first biological treatment step so that the first The HRT in the biological treatment process is within the range of 0.75 to 1.5 times the standard HRT. the

In aspects 8 and 9, "standard organic wastewater" refers to biologically treated organic wastewater, that is, the standard temperature and BOD concentration of organic wastewater whose flow rate, temperature, and BOD concentration fluctuate over time organic drainage. The meanings of the standard temperature and BOD concentration are as follows. the

Standard temperature: including the lowest temperature of the year when heating. the

Standard BOD concentration: The maximum BOD concentration of the wastewater flowing into the first biological treatment process. the

Description of drawings

[ Fig. 1 ] is a flow chart showing an embodiment of the biological treatment method of organic waste water according to the first aspect of the present invention. the

[ Fig. 2 ] is a flow chart showing another embodiment of the biological treatment method of organic wastewater according to the second aspect of the present invention. the

[ Fig. 3 ] It is a flow chart showing another embodiment of the excess sludge treatment step. the

[FIG. 4] FIG. 4a is a flowchart showing the experimental apparatus used in Example 1, and FIG. 4b is a flowchart showing the experimental apparatus used in Example 2. the

[ Fig. 5 ] is a graph showing the relationship between the amount of BOD charged and the amount of excess sludge produced in Examples 1, 2 and Comparative Examples 1, 2. the

[ Fig. 6 ] is a flow chart showing an embodiment of the biological treatment method of organic waste water according to the third aspect of the present invention. the

[ Fig. 7 ] is a flow chart showing another embodiment of the biological treatment method of organic waste water according to the third aspect of the present invention. the

[ Fig. 8 ] is a flow chart showing another embodiment of the biological treatment method of organic wastewater according to the third aspect of the present invention. the

[ Fig. 9 ] is a flow chart showing an embodiment of the biological treatment method of organic waste water according to the fourth aspect of the present invention. the

[ Fig. 10 ] is a flow chart showing another embodiment of the biological treatment method of organic wastewater according to the fourth aspect of the present invention. the

[ Fig. 11 ] is a flowchart showing the experimental apparatus used in Comparative Examples 3 and 5. the

[ FIG. 12 ] is a flow chart showing the experimental apparatus used in Comparative Examples 4 and 6. [ FIG. the

[ Fig. 13 ] is a graph showing the relationship between the amount of BOD charged and the amount of excess sludge produced in Examples 3, 6, and 7 and Comparative Examples 3 and 4. the

[ Fig. 14 ] is a flow chart showing an embodiment of the biological treatment method of organic waste water according to the fifth aspect of the present invention. the

[ Fig. 15 ] is a flow chart showing another embodiment of the biological treatment method of organic waste water according to the fifth aspect of the present invention. the

[ Fig. 16 ] is a graph showing the relationship between the amount of BOD charged and the amount of excess sludge produced in Examples 8 and 9 and Comparative Examples 5 and 6. the

[ Fig. 17 ] is a flow chart showing an embodiment of the biological treatment method of organic waste water according to the present invention. the

[ Fig. 18] Fig. 18 is a graph showing daily changes in the number of microscopic animals in the second biological treatment tank in Example 10 and Comparative Example 8. the

[ Fig. 19 ] is a graph showing daily changes in sludge conversion ratios in Example 10 and Comparative Example 8. the

[ Fig. 20 ] is a flow chart showing an embodiment of the biological treatment method of organic waste water according to the present invention. the

[ Fig. 21 ] is a flow chart showing another embodiment of the biological treatment method of organic waste water of the present invention. the

[ Fig. 22 ] is a flow chart showing another embodiment of the biological treatment method of organic waste water of the present invention. the

[ Fig. 23 ] is a flow chart showing a different embodiment of the biological treatment method of organic waste water according to the present invention. the

[ Fig. 24 ] is a graph showing the relationship between the amount of BOD charged and the amount of excess sludge produced in Examples 12 and 13 and Comparative Examples 9 and 10 (before load fluctuation). the

[ Fig. 25] Fig. 25 is a graph showing the relationship between the amount of BOD charged and the amount of excess sludge produced in Examples 12 and 13 and Comparative Examples 9 and 10 (after a load change). the

Detailed ways

[Aspects 1 and 2]

When aerobic treatment of organic wastewater is performed in an acidic region of pH 6 or less by the conventional single-tank activated sludge process, a large number of fungi will be produced, which will cause sludge bulking. However, like the method of the present invention, the first biological treatment process of converting BOD into dispersed bacteria is carried out in the neutral region of pH 6-8, and the second biological treatment process for reducing sludge is carried out in the acidic region of pH 5-6. Treatment process or excess sludge treatment process, which can greatly reduce the amount of sludge generated. The reason is as follows, that is, by making the pH of the second biological treatment process or the excess sludge treatment process in which micro organisms coexist to be 5 to 6, it is possible to efficiently prey on non-aggregated sludge and Coagulated sludge, on the other hand, is not affected by the pH if the proliferation of most of the micro organisms involved in predation is in the range of pH 5-8, so in the second biological treatment process or excess sludge treatment process, The proportion of tiny organisms in VSS can be increased to a high concentration of more than 10%. the

According to the first and second aspects, through the first biological treatment process for treating BOD and the second biological treatment process for sludge reduction or excess sludge treatment process, the environmental conditions are optimized according to their respective functions, thereby making the two By maximizing the function of the operator, the improvement of treatment efficiency and the reduction of excess sludge production can be realized. the

In the first aspect, the second biological treatment step includes a multi-stage treatment step of two or more stages, and in the second biological treatment step, the biological treatment at pH 6 or higher may be performed after the biological treatment at pH 5 to 6. the

In the second aspect, the excess sludge treatment process may be a sludge return type biological treatment process in which a solid-liquid separation device is installed in a subsequent stage of the biological treatment tank, and the sludge separated from the solid-liquid is returned to the biological treatment tank, A fluidized bed type biological treatment step in which a carrier is added to a biological treatment tank may also be used. the

No matter in the first or the second aspect, the second biological treatment step can be to install a solid-liquid separation device in the subsequent stage of the biological treatment tank, and return the sludge separated from the solid-liquid to the sludge return flow of the biological treatment tank Type biological treatment process, fluidized bed biological treatment process with carrier added in the biological treatment tank, any one of the membrane separation biological treatment process, can also be passed through the fluidized bed biological treatment process with carrier added in the biological treatment tank treatment, or multi-stage treatment of two or more stages to perform the first biological treatment step. the

Utilizing the biological treatment method and device of the organic waste water of the first and second aspects, in the multi-stage activated sludge process utilizing the predation of microscopic organisms, while maintaining a stable treatment water quality, it is possible to achieve high treatment efficiency Further improvement and reduction of excess sludge generation. the

Preferred embodiments of the first and second aspects will be described in detail below with reference to the drawings. the

Fig. 1 is a flow chart showing one embodiment of the biological treatment method of organic wastewater according to the first aspect of the present invention, and Fig. 2 is an embodiment of the biological treatment method of organic wastewater according to the second aspect of the present invention flow chart. the

In the method of Fig. 1, the raw water (organic drainage) is first introduced into the first biological treatment tank (dispersion bacteria tank) 1, and the BOD (organic component) is more than 70%, preferably more than 80%, more preferably more than 90% Oxidative decomposition by non-agglutinative bacteria. The pH of the first biological treatment tank 1 is controlled to be above 6, preferably at pH 6-8. By setting the BOD volume load in the first biological treatment tank 1 to 1 kg/m ³ /d or more, for example 1 to 20 kg/m ³ /d, and setting the HRT (raw water retention time) to 24 hours or less, for example 0.5 to 24 hours, it can be obtained Treated water in which non-coagulant bacteria predominate. By shortening the HRT, it is possible to treat wastewater with a low BOD concentration at a high load, so it is preferable. By adding a carrier, a high load can be achieved and the DC time can be shortened.

The treated water in the first biological treatment tank 1 is introduced into the second biological treatment tank (microbiological tank) 2 whose pH is controlled at 5-6, preferably in the range of 5-5.5, where the remaining organic components are oxidized Decomposition, self-decomposition of non-agglomerative bacteria and predation by microscopic organisms reduce sludge. the

In the method of Fig. 1, make the second biological treatment tank 2 be multi-stage, the biological treatment tank more than 2 tanks is set in series, in the biological treatment tank of one side of the previous stage, when pH is 5～6, hope pH is 5 to 5.5, or in the biological treatment tank on the next stage, at a pH of 6 or more, preferably at a pH of 6 to 6.8. Through this multi-stage treatment, the The predation of sludge is effectively carried out in the biological treatment tank on the side of the previous stage, and the solid-liquid separation of the sludge is improved in the biological treatment tank on the rear stage side, so as to improve the quality of treated water. the

The treated water in the second biological treatment tank 2 undergoes solid-liquid separation in the sedimentation tank 3, and the separated water is discharged out of the system as treated water. Part of the separated sludge is discharged out of the system as excess sludge, and the rest is returned to the first biological treatment tank 1 and the second biological treatment tank 2 . It should be noted that the backflow of the sludge is carried out in order to maintain the amount of sludge in each biological treatment tank, but there are also situations where there is no need to return the sludge, such as making the first biological treatment tank 1 and/or the second biological treatment tank 1 When the treatment tank 2 is a fluidized bed type in which a carrier described later is added, it is not necessary to return the sludge. When the BOD volumetric load of the first biological treatment tank 1 is low, the sludge can be returned only to the second biological treatment tank 2 . the

In the method of FIG. 2, the raw water (organic drainage) is sequentially introduced into the first biological treatment tank 1 and the second biological treatment tank 2, which are jointly controlled at a pH above 6 and pH 6-8. In the first biological treatment tank 1, more than 70%, preferably more than 80%, and more preferably 90% of the organic components are oxidatively decomposed by non-aggregative bacteria, and then the remaining organic components are oxidatively decomposed in the second biological treatment tank 2, Sludge is reduced by self-decomposition of non-aggregate bacteria and predation by microscopic organisms. The treated water in the second biological treatment tank 2 is solid-liquid separated in the sedimentation tank 3, and the separated water is discharged outside the system as treated water. At least a part of the generated sludge generated by the second biological treatment tank 2 (in FIG. 2 , a part of the separated sludge in the sedimentation tank 3 of the treated water introduced into the second biological treatment tank 2) is refluxed until the pH is controlled to be 5. ~6. The excess sludge treatment tank 4 within the range of preferably 5~5.5 is decomposed by aerobic digestion here. The treatment sludge of this excess sludge treatment tank 4 is returned to the first biological treatment tank 1 and/or the second biological treatment tank 2. In FIG. 2 , a part of the remainder of the separated sludge in the sedimentation tank 3 is discharged outside the system as excess sludge, and the remainder is returned to the second biological treatment tank 2 . the

In the separated sludge of the settling tank 3, the ratio of the amount of sludge sent to the excess sludge treatment tank 4 and the amount of sludge returned to the second biological treatment tank 2 is appropriately set according to the amount of sludge generated, so that it can The preferred excess sludge treatment tank residence time described later is maintained. The ratio of the amount of sludge returned to the first and second biological treatment tanks 1 and 2 among the treated sludge in the excess sludge treatment tank 4, or which biological treatment tank is returned to can be appropriately set so that each biological treatment can be maintained. The sludge holding capacity of the tank. the

In this excess sludge treatment tank 4, half of the total amount of generated sludge may be charged in the early stage of plant operation or when the amount of generated sludge is high. This excess sludge treatment tank 4 not only has the effect of reducing sludge, but also has the effect of supplying microscopic organisms in the second biological treatment tank 2 . the

The sludge residence time of the excess sludge treatment tank 4 is more than 6h, preferably more than 12h, such as 12 to 240h, but by implementing, for example, setting the sedimentation tank 4B as shown in Figure 3 and the sludge is returned to the excess sludge treatment tank The 4A aerobic treatment method, fluidized bed with added carrier, or membrane separation aerobic treatment method can further increase the sludge residence time. As the carrier of the excess sludge treatment tank 4, the carrier as the first biological treatment tank described later can be used. the

In any of the methods shown in FIGS. 1 and 2 , when a large amount of organic matter remains in the treated water introduced into the first biological treatment tank 1 of the second biological treatment tank 2 , its oxidative decomposition is carried out in the second biological treatment tank 2 . If the oxidative decomposition of organic matter by bacteria occurs in the second biological treatment tank 2 where microscopic organisms are present in large quantities, as a countermeasure to escape the predation of microscopic organisms, it is known that they proliferate in a manner that is difficult to be preyed on, and the bacterial group that proliferates in this way does not It will be preyed on by tiny organisms, and their decomposition only depends on self-digestion, which will reduce the effect of reducing sludge production. In the method of the present invention, the second biological treatment tank 2 or the excess sludge treatment tank 4 is set in an acidic region. When a large amount of organic matter remains, fungi and the like use the organic matter to proliferate and cause sludge bulking. the

Therefore, as mentioned above, in the first biological treatment tank 1, it is necessary to decompose most of the organic matter, that is, more than 70%, preferably more than 80%, and more preferably 90% of the BOD of the raw water, so as to be converted into bacteria. Therefore, the operation is preferably performed at 0.5 kg-BOD/kg-MLSS/d or less, eg, 0.01 to 0.1 kg-BOD/kg-MLSS/d, expressed by the dissolved BOD sludge load in the second biological treatment tank 2 . the

The methods in Figures 1 and 2 represent an example of the first and second aspects, and are not limited to any illustrated methods as long as the first and second aspects do not exceed their gist. the

For example, for high-load treatment, in addition to returning a part of the separated sludge in the sedimentation tank of the next stage, the first biological treatment tank can also use a fluidized bed method with added carriers, or install two or more biological treatment tanks in series. Do multi-level processing. In particular, by adding a carrier, it is possible to perform high-load treatment with a BOD volume load of 5 kg/m ³ /d or more, which is preferable. At this time, the shape of the carrier to be added may be any shape such as a spherical shape, a granular shape, a hollow cylindrical shape, or a filament shape, and the size may be about 0.1 to 10 mm in diameter. The material of the carrier is any material such as a natural material, an inorganic material, or a polymer material, and a gel-like material can also be used.

Since the second biological treatment tank 2 utilizes the action of micro organisms slower than the growth rate of bacteria and the self-decomposition of bacteria, it is important to adopt operating conditions and treatment devices in which micro organisms and bacteria remain in the system. For this reason, the first 2 Biological treatment tank As shown in Figures 1 and 2, in addition to the sludge return biological treatment of returning sludge, it is also desirable to dip a separation membrane in the tank to perform membrane separation active treatment as in the examples described later. the

By adding carrier in the aeration tank, the holding capacity of tiny organisms in the tank can be improved. As the carrier at this time, the same carrier as that added to the above-mentioned first biological treatment tank can be used. the

Examples and Comparative Examples of Aspects 1 and 2

The first and second aspects will be described more specifically below with reference to Examples and Comparative Examples. the

Example 1

As shown in Figure 4a, the activated sludge tank (non-reflux sludge) with a capacity of 3.6L connected as the first biological treatment tank 11 and the submerged membrane active sludge tank with a capacity of 15L as the second biological treatment tank 12 are used. The experimental device of the sludge tank is used for the treatment of organic drainage (BOD630mg/L). A submerged membrane 12a is provided in the second biological treatment tank 12, and permeated water from the submerged membrane 12a is taken out as treated water. the

Adjust the pH of the first biological treatment tank 11 to 6.8, and the pH of the second biological treatment tank 12 to 5.0, respectively. the

Table 1 shows the results 4 months after the start of the experiment. Figure 5 shows the excess sludge production (sludge conversion rate) relative to BOD input. the

In this embodiment, the operating conditions are: the soluble BOD volume load in the first biological treatment tank 11 is 3.5kg-BOD/m ³ /d, the HRT is 4h, and the soluble BOD sludge in the second biological treatment tank 12 The load is 0.022kg-BOD/kg-MLSS/d, HRT is 17h, the overall BOD volume load is 0.75kg-BOD/m ³ /d, HRT is 21h, and the sludge conversion rate is 0.1kg-MLSS/kg-BOD , the BOD of the treated water was below the detection limit.

Example 2

As shown in Figure 4b, use the activated sludge tank (non-reflux sludge) that is connected with the capacity as the first biological treatment tank 11 to be 3.6L, and the capacity as the second biological treatment tank 12 is a submerged membrane type activated sludge tank that is 15L. The sludge tank and the excess sludge treatment tank 13 with a capacity of 1 L are used for the treatment of organic drainage (BOD630 mg/L). As in Fig. 4a, a submerged membrane 12a is provided in the second biological treatment tank 12, and the permeated water of the submerged membrane 12a is taken out as treated water. the

Both the pH of the first biological treatment tank 11 and the second biological treatment tank 12 were adjusted to 6.8, and the pH of the excess sludge treatment tank 13 was adjusted to 5.0. Discharge the sludge in the tank with the ratio of 0.5L/d from the second biological treatment tank 12, import the excess sludge treatment tank 13, discharge the sludge in the tank with the ratio of 0.5L/d from this excess treatment tank 13, and It flows back to the second biological treatment tank 12 . The residence time of the excess sludge treatment tank 13 is SRT=HRT=10 days. the

Table 1 shows the results 4 months after the start of the experiment. Figure 5 shows the excess sludge production (sludge conversion rate) relative to BOD input. the

In this embodiment, the operating conditions are: the soluble BOD volume load in the first biological treatment tank 11 is 3.85kg-BOD/m ³ /d, the HRT is 4h, and the soluble BOD sludge in the second biological treatment tank 12 The load is 0.022kg-BOD/kg-MLSS/d, HRT is 17h, the overall BOD volume load is 0.75kg-BOD/m ³ /d, HRT is 21h, and the sludge conversion rate is 0.11kg-MLSS/kg-BOD , the BOD of the treated water was below the detection limit.

Comparative example 1

In Example 1, organic waste water (BOD630 mg/L) was treated by omitting the first biological treatment tank and using an experimental device including only the second biological treatment tank with a capacity of 15 L of submerged membrane activated sludge tank. Table 1 shows the results 4 months after the start of the experiment. Figure 5 shows the excess sludge production (sludge conversion rate) relative to BOD input. the

In this comparative example, the operating conditions are: the soluble BOD volume load is 0.76kg-BOD/m ³ /d, and the HRT is 20h. The results are shown in Table 1. Although the treated water quality is good, the sludge conversion rate is 0.40 kg-MLSS/kg-BOD.

Comparative example 2

The pH of the first biological treatment tank and the second biological treatment tank is all adjusted to 6.8, except that, other operations are identical with embodiment 1, carry out the processing of organic drainage (BOD630mg/L). Table 1 shows the results 4 months after the start of the experiment. Figure 5 shows the excess sludge production (sludge conversion rate) relative to BOD input. the

In this comparative example, the operating conditions are: the soluble BOD volume load in the first biological treatment tank 11 is 3.85kg-BOD/m ³ /d, the HRT is 4h, and the soluble BOD sludge in the second biological treatment tank 12 The load is 0.022kg-BOD/kg-MLSS/d, the HRT is 17h, the overall BOD volume load is 0.75kg-BOD/m ³ /d, and the HRT is 21h. The results are shown in Table 1. Although the treated water quality is good, but The sludge conversion rate is 0.2kg-MLSS/kg-BOD.

Table 1

The results of Examples 1 and 2 and Comparisons 1 and 2 are as follows. the

In Comparative Example 1, the conventional activated sludge method was implemented, and in Comparative Example 2, treatment by a multi-stage biological treatment method in which no biological treatment process in the acidic region was added was implemented. The sludge conversion rate in the conventional activated sludge process (Comparative Example 1) was 0.40kg-MLSS/kg-BOD, but as shown in Comparative Example 2, the sludge conversion rate became 0.20kg by introducing multi-stage biological treatment -MLSS/kg-BOD, can reduce sludge production by 1/2. This sludge reduction effect is to the same extent as reported so far for multi-stage biological treatment methods. the

On the other hand, in Examples 1 and 2 in which the biological treatment process in the acidic region was introduced like the present invention, the sludge conversion rate was 0.10 and 0.11kg-MLSS/kg-BOD, and compared with the conventional method, the sludge The amount of production can be reduced to 1/4, and the amount of sludge generated can be reduced to 1/2 compared with the previous multi-stage biological treatment method. the

[Aspects 3 and 4]

In the third aspect, the action of anaerobic bacteria is used to dissolve, organically oxidize, and denature the sludge from the second biological treatment process (micro animal tank) where the dispersed bacteria prey, and then disperse the bacteria again. and/or predation by tiny animals, thereby improving the treatment efficiency and reducing the amount of excess sludge produced, wherein the dispersed bacteria come from the first biological treatment process (dispersed bacteria tank) for organic matter removal. the

In the fourth aspect, since the aerobic treatment process is passed before the anaerobic treatment process, the proportion of microfauna in the sludge increases, and the sludge is solubilized in the subsequent anaerobic treatment process. the

Therefore, according to the biological treatment method of organic drainage according to the third and fourth aspects, in the multi-stage activated sludge method utilizing the predation of microscopic animals, further improvement of treatment efficiency and further improvement of treatment efficiency can be realized while maintaining stable treatment water quality. Reduction of excess sludge generation. the

Preferred embodiments of the third and fourth aspects will be described in detail below with reference to the drawings. the

6 to 8 are flow charts showing embodiments of the biological treatment method and apparatus for organic wastewater according to the third aspect of the present invention, and FIGS. 9 and 10 are diagrams showing the biological treatment of organic wastewater according to the fourth aspect of the present invention. Flowchart of an embodiment of the method. In FIGS. 6 to 10 , members that perform the same function are denoted by the same reference numerals. the

In the method and device of Fig. 6, raw water (organic drainage) is at first introduced into the first biological treatment tank (dispersion bacteria tank) 1, more than 70% of BOD (organic components), preferably more than 80%, more preferably 90% More than % is oxidized and decomposed by non-cohesive bacteria. Control the pH of the first biological treatment tank to be above 6, preferably at pH 6-8. By setting the BOD volume load in the first biological treatment tank 1 to 1 kg/m ³ /d or more, for example 1 to 20 kg/m ³ /d, and setting the HRT (raw water retention time) to 24 hours or less, for example 0.5 to 24 hours, it can be obtained Treated water in which non-coagulant bacteria predominate. By shortening the HRT, it is possible to treat wastewater with a low BOD concentration at a high load, so it is preferable. By adding a carrier, a high load can be achieved and the DC time can be shortened.

The treated water of the first biological treatment tank 1 is introduced into the second biological treatment tank (micro biological tank) 2 whose pH is controlled at 6, preferably in the range of 6 to 8, where the remaining organic components are oxidatively decomposed, Sludge is reduced by self-decomposition of non-aggregate bacteria and predation by microscopic organisms. the

In the second biological treatment tank 2 , the action of microscopic animals whose growth rate is slower than that of bacteria and the self-decomposition of bacteria are used, so the operating conditions and treatment equipment must be used so that microscopic animals and bacteria remain in the system. Therefore, it is desirable to use an activated sludge method or a membrane separation type activated sludge method in which sludge is returned to the second biological treatment tank 2 . It is more desirable to increase the retention of tiny animals in the tank by adding carriers in the aeration tank. the

As shown in Fig. 7, in Fig. 6 method, make the second biological treatment tank 2 be multi-stage, the biological treatment tank 2A, 2B that more than 2 tanks are arranged in series, in the previous stage treatment tank 2A, when pH is 5～ 6. It is desired that the pH be treated under the condition of 5 to 5.5, and it can also be processed under the condition that the pH is more than 6, preferably 6 to 8 in the subsequent treatment tank 2B. By this multi-stage treatment, Sludge predation can be effectively performed in the first-stage treatment tank 2A, and the improvement of the solid-liquid separation property of sludge and the improvement of the quality of treated water can be aimed at in the subsequent-stage treatment tank 2B. The method in FIG. 7 differs only in the point that the second biological treatment tank 2 is multi-staged in FIG. 6 , and the other configurations are the same. It should be noted that, in order to reduce the amount of sludge produced in the second biological treatment tank 2, it is also not possible to set the interval as shown in Figure 7, and set the pH of the second biological treatment tank 2 in a single tank as shown in Figure 6. Set it below 6, but at this time, it is necessary to neutralize before discharging the treated water. the

The treated water in the second biological treatment tank 2 undergoes solid-liquid separation in the sedimentation tank 3, and the separated water is discharged out of the system as treated water. A part of the separated sludge is discharged outside the system as excess sludge, a part is returned to the second biological treatment tank 2 , and the rest is sent to the anaerobic digestion tank 24 . The sludge return ratio between the second biological treatment tank 2 and the anaerobic digestion tank 24 for separating the sludge is sufficient as long as the sludge residence time in the anaerobic digestion tank 24 below can be maintained, and can be adjusted arbitrarily according to the amount of sludge produced. The change. the

In the third aspect, at least a part of the sludge in the second biological treatment tank 2 in which microscopic animals have been preyed on by dispersed bacteria or the sludge obtained by solid-liquid separation thereof is introduced into the anaerobic digestion tank 24, and Solubilization of sludge, organic oxidation to lower organic acids or lower alcohols, and denaturation of sludge are carried out under oxygen conditions. Therefore, instead of introducing the separated sludge of the settling tank 3 , the sludge discharged from the second biological treatment tank 2 may be introduced into the anaerobic digestion tank 24 . the

The proportion of tiny animals in the sludge in the second biological treatment tank 2 is high, accounting for at least 5% of SS, and can account for more than 30% according to operating conditions. Compared with bacteria, microscopic animals are more likely to die under anaerobic conditions, be solubilized, and be organically oxidized by acid-forming bacteria. Therefore, the sludge retention time (SRT) in the anaerobic digester 24 is 0.5 days or more, for example, 0.5 to 5 days. God, is enough. In order to prevent the organic acids and alcohols generated in the anaerobic digestion tank 24 from being converted into methane by the action of methane-forming bacteria, it is desirable to make the pH in the anaerobic digestion tank 24 6.0 or less, preferably 5.5 or less, such as 5-5. 5.5, or set the temperature below 30°C, preferably below 25°C, such as 20-25°C. However, when converting organic matter converted into organic acids and alcohols into methane and recovering or disposing of them as energy, the anaerobic digestion tank 24 may have a pH of 6.0 or higher or a temperature of 30° C. or higher. The anaerobic digestion in the anaerobic digestion tank 24 converts microscopic animals and bacteria remaining without predation in the second biological treatment tank 2 into organic acids and alcohols. As other SS components, the feces of micro animals, dead bodies, bacteria, etc. that have not been reduced in the second biological treatment tank 2 are also denatured or subdivided in the anaerobic digestion tank 24, or converted into anaerobic digestion tank 24. The bacterial cell thus becomes prey to tiny animals. the

In FIGS. 6 and 7 , the treated product of the anaerobic digestion tank 24 is directly returned to the first biological treatment tank 1 and/or the second biological treatment tank 2 . the

The treated product of this anaerobic digestion tank 24, also can be shown in Figure 8, solid-liquid separation in the solid-liquid separation device 25 such as concentrator or dehydrator, the separation water (anaerobic treatment water) that contains organic acid and alcohol ) back to the first biological treatment tank 1, converted into dispersed bacteria again, and the solid content (sludge) is returned to the second biological treatment tank 2 to be preyed on by tiny animals, thereby further reducing sludge. At this time, discharge of excess sludge may be performed from the sedimentation tank 3 or may be performed from the solid-liquid separation device 25 of the subsequent stage of the anaerobic digestion tank 24 . The solid content of the solid-liquid separation in the solid-liquid separation device 25 is not completely returned to the second biological treatment tank 2, but returned to the anaerobic digestion tank 24 again, thus in the anaerobic digestion tank 24, high concentration can be carried out. Anaerobic digestion, prolonging the SRT, may promote solubilization. It is also possible to perform solid-liquid separation or high-concentration digestion by installing a submerged membrane in the anaerobic digestion tank 24 or by adding a carrier without installing a solid-liquid separation device such as a concentrator. the

The method shown in FIG. 9 is different from the method shown in FIG. 6 on the point that the aerobic digestion tank 26 is arranged on the front stage of the anaerobic digestion tank 24. The first biological treatment tank 1, the second biological treatment tank 2. The treatment in the sedimentation tank 3 and the anaerobic digestion tank 24 is performed in the same manner. the

In the fourth aspect, at least a part of the sludge introduced into the second biological treatment tank 2 in the aerobic digestion tank 26 or the sludge obtained by separating its solid and liquid has a pH of 6 or less, preferably a pH of 5 to 5.5. Aerobic digestion is carried out under certain conditions, and at least a part of the treated sludge and treated water are sent to the anaerobic digestion tank 24, solubilized, organically oxidized, and denatured under anaerobic conditions. At this time, the sludge return ratio of the separated sludge to the aerobic digestion tank 26 and the second biological treatment tank 2 may be maintained as long as the sludge retention time in the aerobic digestion tank 26 shown below can be maintained. Arbitrary changes are made according to the amount of sludge generated. the

In Fig. 9, the aerobic digestion tank 26 not only has the effect of reducing sludge, but also has the following advantages, that is, after passing through the aerobic digestion tank 26, the proportion of microscopic animals in the sludge becomes higher, and in the Solubilization of the sludge in the anaerobic digestion tank 24 of the latter stage becomes easier. The sludge retention time of the aerobic digestion tank 26 is 12 hours or more, preferably 24 hours or more, for example, 24 to 240 hours, but the aerobic treatment method of returning sludge with a solid-liquid separation device or a fluidized bed with a carrier And the membrane separation aerobic treatment method can further increase the sludge residence time. A part of the sludge from the aerobic digestion tank 26 can also be directly returned to the second biological treatment tank 2 without passing through the anaerobic digestion tank 24 , which is also beneficial for the replenishment of microscopic animals in the second biological treatment tank 2 . the

The method shown in FIG. 10 is different from the method shown in FIG. 9 in that the solid-liquid separation device 25 is set at the rear stage of the anaerobic digestion tank 24 as shown in FIG. Solid-liquid separation, separated water and return of separated sludge. Here, the separated sludge of the solid-liquid separator 25 may further be returned to the aerobic digestion tank 26 . the

The methods in FIGS. 6 to 10 show an example of the third and fourth aspects, and are not limited to any of the illustrated methods as long as the third and fourth aspects do not exceed the gist thereof. the

For example, for high-load treatment, in addition to a part of the separated sludge that is returned to the subsequent settling tank, the first biological treatment tank may use a fluidized bed method with a carrier added, or two or more biological treatment tanks may be installed in series for multi-level processing. In particular, by adding a carrier, it is possible to perform high-load treatment with a BOD volume load of 5 kg/m ³ /d or more, which is preferable. At this time, the shape of the carrier to be added may be any shape such as a spherical shape, a granular shape, a hollow cylindrical shape, or a filament shape, and the size may be about 0.1 to 10 mm in diameter. The material of the carrier is any material such as a natural material, an inorganic material, or a polymer material, and a gel-like material can also be used. Since the second biological treatment tank 2 utilizes the action of microscopic animals whose growth rate is slower than that of bacteria and the self-decomposition of bacteria, it is important to adopt operating conditions and treatment devices in which microscopic animals and bacteria remain in the system. For this reason, No. 2 Biological treatment tank As shown in Figures 6 to 10, in addition to the sludge return type biological treatment of the return sludge, it is also desirable to impregnate the separation membrane in the tank for membrane separation type active treatment. It is more hoped that the amount of small animals held in the tank can be improved by adding a carrier in the aeration tank. As the carrier at this time, the same carrier as that added to the above-mentioned first biological treatment tank can be used.

In wastewater treatment, sludge is generated from a primary sedimentation tank, a pressurized flotation tank, and the like in addition to sludge derived from biological treatment. When they are anaerobically treated, they are easily decomposed compared with sludge from biological treatment, so more than 50% solubilization and conversion to organic acids are possible. Undissolved components are also subdivided and can be eaten by tiny animals. Therefore, in the third and fourth aspects, in the anaerobic treatment process (anaerobic digestion tank) of the sludge introduced into the second biological treatment tank, the primary sedimentation sludge and the pressurized floating sludge are added to allow microscopic animals to prey on the sludge. Undissolved SS components, thereby also reducing the amount of excess sludge discharged from the entire plant. the

Embodiments and comparative examples of the 3rd and 4th aspects

Next, examples and comparative examples will be given to describe the third and fourth aspects more specifically. the

Example 3

As shown in Figure 6, use the first biological treatment tank (activated sludge tank (non-reflux sludge)) 1 with a capacity of 3.6L, the second biological treatment tank (activated sludge tank) 2 with a capacity of 15L and sedimentation Tank 3 is an experimental device connected to an anaerobic digestion tank 24 with a capacity of 1 L, and the treatment of organic waste water (BOD630 mg/L) of the present invention is performed. Adjust the pH of the first biological treatment tank 1 to 6.8, the pH of the second biological treatment tank 2 to 6.8, and the pH of the anaerobic digestion tank 24 to 6.0, respectively. Operate under the following conditions: the soluble BOD volume load in the first biological treatment tank 1 is 3.85kg-BOD/m ³ /d, the HRT is 4h, and the soluble BOD sludge load in the second biological treatment tank 2 is 0.022 kg-BOD/kg-MLSS/d, HRT is 17h, overall BOD volume load is 0.75kg-BOD/m ³ /d, and HRT is 21h.

The SS in the second biological treatment tank 2 was 5000 mg/L, and the sludge discharged from the sedimentation tank 3 was concentrated to 10000 mg/L. This concentrated sludge was discharged at a rate of 250 ml/d, and added to the anaerobic digestion tank 24 . 250ml/d is discharged out of the system as excess sludge, and all excess sludge is returned to the second biological treatment tank 2 . The HRT and SRT of the anaerobic digestion tank 24 were set to 4 days, and the treated sludge in the anaerobic digestion tank 24 was returned to the second biological treatment tank 2 . the

After four months of continuous operation under this condition, the soluble BOD concentration in the treated water of the anaerobic digestion tank 24 was 4000 mg-BOD/L, acetic acid accounted for 55%, and propionic acid accounted for 40%. The sludge conversion rate calculated from the amount of sludge discharged from the second biological treatment tank 2 was 0.12 kg-MLSS/kg-BOD. the

Example 4

As shown in Figure 7, except that the second biological treatment tank 2 is a secondary activated sludge tank (5L+10L) with a capacity of 5L for the previous treatment tank 2A and a capacity for the subsequent treatment tank 2B of 10L , Using the same experimental device as in Example 3, the treatment of organic waste water (BOD630mg/L) was performed in the same manner as in Example 3. It should be noted that the pH of the first-stage treatment tank was adjusted to 5.0, and the pH of the subsequent-stage treatment tank was adjusted to 6.8. Other conditions are identical with embodiment 3. the

The SS in the second biological treatment tank 2 was 5000 mg/L, and the sludge discharged from the sedimentation tank 3 was concentrated to 10000 mg/L. 250 ml/d of this concentrated sludge was discharged and added to the anaerobic digestion tank 24 . 208ml/d is discharged out of the system as excess sludge, and all excess sludge is returned to the second biological treatment tank 2. The HRT and SRT of the anaerobic digestion tank 24 were set to 4 days, and the treated sludge in the anaerobic digestion tank 24 was returned to the second biological treatment tank 2 . the

After four months of continuous operation under this condition, the soluble BOD concentration in the treated water of the anaerobic digestion tank 24 was 6500 mg-BOD/L, acetic acid accounted for 55%, and propionic acid accounted for 35%. The sludge conversion rate calculated from the amount of sludge discharged from the second biological treatment tank 2 was 0.10 kg-MLSS/kg-BOD. the

Example 5

As shown in FIG. 9 , except that an aerobic digestion tank 26 with a capacity of 2 L was installed in the preceding stage of the anaerobic digestion tank 24 , organic drainage was performed in the same manner as in Example 3 using the same experimental device as in Example 3. (BOD630mg/L) treatment. In addition, the pH of an aerobic treatment tank was adjusted to 5.0. Other conditions are identical with embodiment 3. the

The SS in the second biological treatment tank 2 was 5000 mg/L, and the sludge discharged from the sedimentation tank 3 was concentrated to 10000 mg/L. 250ml/d of this concentrated sludge is added to the aerobic digester 26, an equivalent amount of sludge is discharged from the aerobic digester 26, added to the anaerobic digester 24, and all remaining concentrated sludge is returned to The second biological treatment tank 2. The HRT and SRT of the aerobic digester 26 were set to 8 days. The HRT and SRT of the anaerobic digestion tank 24 were set to 4 days, and the treated sludge in the anaerobic digestion tank 24 was returned to the second biological treatment tank 2 . the

After four months of continuous operation under this condition, the soluble BOD concentration in the treated water of the anaerobic digestion tank 24 was 6500 mg-BOD/L, acetic acid accounted for 55%, and propionic acid accounted for 35%. The sludge conversion rate calculated from the amount of sludge discharged from the second biological treatment tank 2 (185 ml/d) was 0.09 kg-MLSS/kg-BOD. the

Example 6

As shown in Figure 8, except that the solid-liquid separation device 25 is set in the rear stage of the anaerobic digestion tank 24, use the same experimental device as Example 3, and carry out organic drainage (BOD630mg/L) in the same way as Example 3 ) processing. The pH conditions, load conditions, etc. of each tank were the same as in Example 3. the

The SS in the second biological treatment tank 2 was 5000 mg/L, and the sludge discharged from the sedimentation tank 3 was concentrated to 10000 mg/L. 250ml/d of this concentrated sludge is added to the anaerobic digestion tank 24, and all remaining concentrated sludge is returned to the second biological treatment tank 2, so that it does not need to be discharged from the first and second biological treatment tanks 1 and 2 The sludge can keep the SS in the tank constant. The HRT of the anaerobic digestion tank 24 is set to 4 days, and the treated product of the anaerobic digestion tank 24 is separated by solid-liquid separation device 25, and the treated water is returned to the first biological treatment tank 1, and the separated sludge Half of the separated sludge is returned to the second biological treatment tank 2, 1/4 of the separated sludge is returned to the anaerobic digestion tank 24, and 1/4 of the separated sludge is discharged as excess sludge. the

After four months of continuous operation under this condition, the soluble BOD concentration in the treated water of the anaerobic digestion tank 24 was 4000 mg-BOD/L, acetic acid accounted for 55%, and propionic acid accounted for 40%. The sludge conversion rate calculated from the amount of sludge discharged from the anaerobic digestion tank 24 was 0.10 kg-MLSS/kg-BOD. the

Example 7

As shown in FIG. 10 , except that an aerobic digester 26 with a capacity of 2 L was installed in the previous stage of the anaerobic digester 24, the same experimental equipment as in Example 6 was used to carry out organic digestion in the same manner as in Example 6. Drainage (BOD630mg/L) treatment. In addition, the pH of the aerobic digestion tank 26 was adjusted to 5.0. Other conditions are identical with embodiment 6. the

The SS in the first and second biological treatment tanks 1 and 2 is 5000 mg/L, and the sludge discharged from the sedimentation tank 3 is concentrated to 10000 mg/L. 250ml/d of this concentrated sludge is added to the aerobic digester 26, an equivalent amount of sludge is discharged from the aerobic digester 26, added to the anaerobic digester 24, and all remaining concentrated sludge is returned to In the second biological treatment tank 2 , the SS in the tank can be kept constant without discharging sludge from the first and second biological treatment tanks 1 and 2 . The HRT and SRT of the aerobic digester 26 were set to 8 days. The HRT of the anaerobic digestion tank 24 was set as 4 days, and the treated sludge of the anaerobic digestion tank 24 was separated from the solid-liquid by the solid-liquid separation device 25, and the treated water was returned to the first biological treatment tank 1, and the solid content Half is returned to the second biological treatment tank 2, the remaining 3/8 is returned to the anaerobic digestion tank 24, and the remaining 1/8 is discharged as excess sludge. the

After four months of continuous operation under this condition, the soluble BOD concentration in the treated water of the anaerobic digestion tank 24 was 6500 mg-BOD/L, acetic acid accounted for 55%, and propionic acid accounted for 35%. The sludge conversion rate calculated from the amount of sludge discharged from the anaerobic digestion tank 24 was 0.07 kg-MLSS/kg-BOD. the

Comparative example 3

As shown in FIG. 11 , organic waste water (BOD 630 mg/L) was treated using an experimental device having a biological treatment tank (activated sludge tank) 2' with a capacity of 15 L and a sedimentation tank 3 . Continuous operation for 4 months under the following conditions: the volume load of soluble BOD in the biological treatment tank 2' is 0.76kg-BOD/m ³ /d, the HRT is 20h, and the pH is 6.8. As a result, although the treated water is good, the sludge is converted The rate is 0.40kg-MLSS/kg-BOD.

Comparative example 4

As shown in FIG. 12 , the treatment of organic waste water (BOD630 mg/L) was performed in the same manner as in Example 3 using the same experimental apparatus as in Example 3 except that the anaerobic digester 24 was omitted. The pH conditions, load conditions, etc. of each tank were the same as in Example 3. the

The operation continued for 4 months under this condition. As a result, although the treated water was good, the sludge conversion rate calculated from the amount of sludge discharged from the second biological treatment tank 2 was 0.20 kg-MLSS/kg-BOD. The proportion of tiny animals in the VSS of the second biological treatment tank 2 is about 25% (w/w). the

FIG. 13 shows the excess sludge production amount (sludge conversion ratio) with respect to the BOD charged in Examples 3, 6, 7 and Comparative Examples 3 and 4. FIG. See Table 2 for the operating conditions of Examples 6 and 7 and Comparative Examples 3 and 4 four months after the start of the experiment. the

Table 2

^＊ 1: The values in the parentheses are the values after the combined anaerobic digester treated water

^＊ 2: The values in the brackets are the values in the aerobic digester

The following conclusions can be drawn from the above results. the

In Comparative Example 3, the conventional activated sludge method was implemented, and in Comparative Example 4, treatment by the conventional secondary biological treatment method was implemented. The sludge conversion rate in the conventional activated sludge process (Comparative Example 1) was 0.40kg-MLSS/kg-BOD, but as shown in Comparative Example 2, the sludge conversion rate became 0.20kg by introducing multi-stage biological treatment -MLSS/kg-BOD, can reduce sludge production by 1/2. This sludge reduction effect is to the same extent as reported so far for secondary biological treatment methods. the

On the other hand, in Example 7, in which the anaerobic digestion process was introduced like the present invention, especially the sludge reduction effect was remarkable, the sludge conversion rate was 0.07kg-MLSS/kg-BOD, compared with the conventional method, the sludge Slime generation can be reduced to 1/6. The reason for the significant reduction in sludge in Example 7 is that the proportion of microscopic animals in the sludge VSS was lower than that of the second biological treatment tank 2 due to the predation of microscopic animals in the aerobic digestion tank with pH set at 5. 32% (w/w) in the aerobic digester and a maximum of 60% in the aerobic digester. The solubilization of the sludge of high microscopic animal ratio is easy, and the solubilization rate in the anaerobic digestion tank 24 of embodiment 3,4,5 can reach 65%, and the maximum solubilization rate can only reach 40% (put into Compared with Examples 3 and 4, the microfauna ratio of the sludge VSS of the anaerobic digestion tank 24: 30 (w/w)) has a high sludge reduction effect. By further solid-liquid separation of anaerobic digested sludge, the soluble COD components are converted into dispersed bacteria in the first biological treatment tank 1 again, and in Example 7, the sludge reduction effect of 1/6 of the conventional method can be achieved . the

[Aspect 5]

Utilizing the biological treatment method and device of the organic drainage of the fifth aspect, in the multi-stage activated sludge method utilizing the predation of micro organisms, while maintaining a stable treatment water quality, further improvement of treatment efficiency and Reduction in excess sludge generation. The organic waste water is introduced into the first biological treatment tank, and most of the organic components (for example, more than 70%) are oxidized and decomposed by bacteria or transformed into bacterial cells. The treatment liquid in the first biological treatment tank is introduced into the second biological treatment tank, and oxidative decomposition of remaining organic components, self-decomposition of bacteria, and predation of microscopic animals proceed, thereby reducing the amount of sludge. the

The treated liquid in the second biological treatment tank is separated into treated water and sludge through solid-liquid separation. Treated water is taken out of the system. A part of the sludge is returned to the second biological treatment tank. the

In the fifth aspect, the remainder of the solid-liquid separated sludge or a part of the sludge in the second biological treatment tank is introduced into the third treatment tank for aerobic treatment. Next, part or all of the aerobically treated sludge is dewatered and separated into solids and water. The solid content is discharged as excess sludge, and the water is returned to the first biological treatment tank and/or the second biological treatment tank. the

Sludge is reduced by the predation of microscopic animals in the third biological treatment tank. Sludge can be sufficiently reduced by controlling the pH of the third biological treatment tank to 6 or less, particularly 5 to 5.5. the

In the fifth aspect, the SRT of the second biological treatment tank and the third biological treatment tank is preferably 40 or less, for example, 10 to 40 days, particularly 15 to 30 days. Thereby, the microscopic organisms or metabolites in the tank are moderately reduced, and highly active microscopic animals can be maintained in the tank. the

Preferred embodiments of the fifth aspect will be described in detail below with reference to the drawings. the

14 and 15 are flow charts showing preferred modes of the fifth aspect, respectively. the

In the method of FIG. 14, raw water (organic drainage) is first introduced into the first biological treatment tank (bacteria tank) 1, and 70% or more of BOD (organic component), preferably 80% or more, and more preferably 90% or more, is introduced into the first biological treatment tank (bacteria tank) 1. Bacterial oxidative decomposition or transformation into bacterial cells. The pH of the first biological treatment tank 1 is controlled to be 6 or more, preferably pH 6-8. By setting the BOD volume load in the first biological treatment tank 1 to 1 kg/m ³ /d or more, for example 1 to 20 kg/m ³ /d, and setting the HRT (raw water retention time) to 24 hours or less, for example 0.5 to 24 hours, it can be obtained By shortening the HRT, it is possible to treat wastewater with a low BOD concentration at a high load while treating water in which non-cohesive bacteria are dominant.

The treated water in the first biological treatment tank 1 is introduced into the second biological treatment tank (microbiological tank) 2, where oxidative decomposition of residual organic components, self-decomposition of bacteria, and predation by microscopic organisms are carried out to reduce pollution. mud. the

The proportion of microscopic animals in the sludge in the second biological treatment tank 2 is high, accounting for at least 5% of SS, and microscopic animals can account for more than 30% according to operating conditions. the

Since the second biological treatment tank 2 uses the action of microscopic animals whose growth rate is slower than that of bacteria and the self-decomposition of bacteria, it is necessary to adopt operating conditions and treatment equipment in which microscopic animals and bacteria remain in the system. For this purpose, it is desirable to use an activated sludge method or a membrane separation type activated sludge method in which sludge is returned to the second biological treatment tank 2 . It is more desirable to make the second biological treatment tank an aeration tank to which a carrier is added in order to increase the holding amount of microscopic animals in the tank. the

In the second biological treatment tank 2 , by making pH 6 or less, for example, pH 5-6, preferably 5-5.5 acidity, predation of microbes on bacteria can be efficiently performed. the

When a large amount of organic matter remains in the treatment liquid from the first biological treatment tank 1 introduced into the second biological treatment tank 2 , the oxidative decomposition proceeds in the second biological treatment tank 2 . If the oxidative decomposition of organic matter caused by bacteria occurs in the second biological treatment tank 2 where microscopic organisms exist in large quantities, then as a countermeasure for escaping predation by microscopic organisms, it is known that they proliferate in a manner that is difficult to be preyed upon. In this way, the bacterial population that proliferates in a manner that is difficult to be prey will not be preyed on by tiny organisms, and their decomposition only depends on self-digestion, and the sludge becomes difficult to obtain in the 2nd biological treatment tank 2 and the 3rd biological treatment tank 34 described later. reduce. When the second biological treatment tank 2 is set in an acidic region with a pH of 6 or less, if a large amount of organic matter remains, fungi and the like will proliferate using the organic matter to cause sludge bulking. As mentioned above, in the first treatment tank 1, it is preferable to decompose most of the organic matter, that is, more than 70%, preferably more than 80% of the BOD of the raw water, so as to convert it into bacterial cells. It is preferable that the soluble BOD sludge load in the 2nd biological treatment tank 2 is 0.1 kg-BOD/kg-MLSS/d or less. the

The treatment liquid in the second biological treatment tank 2 undergoes solid-liquid separation in the sedimentation tank 3, and the separated water is discharged out of the system as treated water. Part of the separated sludge is returned to the second biological treatment tank 2 and the second biological treatment tank 2, and the rest is sent to the third biological treatment tank 34 to be reduced by aerobic treatment. the

The sludge return ratio of the second biological treatment tank 2 and the third biological treatment tank 34 of the separated sludge from the sedimentation tank 3 is sufficient as long as the sludge residence time in the third biological treatment tank 34 below can be maintained, and it can be determined according to the sludge The amount of mud produced can be changed arbitrarily. the

At the start of operation of the wastewater treatment device or when the amount of sludge generated in the first and second biological treatment tanks is high, more than half of the sludge separated in the sedimentation tank 3 may be supplied to the third biological treatment tank 34 . The sludge retention time (SRT) of the third biological treatment tank 34 is preferably 12 hours or more, particularly preferably 24 hours or more, for example, 24 to 960 hours. the

Like the second biological treatment tank, the sludge reduction effect in the third biological treatment tank 34 depends on predation by microscopic animals. Therefore, by maintaining the pH of the third biological treatment tank 34 at 6 or less, preferably in the range of 5 to 5.5, a higher sludge reduction effect can be obtained. However, when the pH of the third biological treatment tank 34 is set to this condition, since the sludge reduction effect is high, the sludge concentration in the third biological treatment tank 34 is excessively low, and the sewage that is carried out by the dehydrator 35 below may be reduced. Mud dehydration becomes difficult. At this time, the sludge concentration can also be increased by using an aerobic treatment tank equipped with a sedimentation tank for sludge return, a fluidized bed with a carrier added, or a membrane separation type aerobic treatment tank as the third biological treatment tank 34 . the

The sludge retention time (SRT) of the 3rd biological treatment tank 34 is more than 12 hours, preferably more than 24 hours, for example 24～960 hours, can be carried out the aerobic treatment method that will set up solid-liquid separation device and carry out sludge reflux, add Carrier fluidized bed or membrane separation aerobic treatment method to further increase the sludge residence time. the

The sludge reduced in the third biological treatment tank 34 is introduced into the dehydrator 35 and subjected to solid-liquid separation treatment. In addition, a part of sludge from the 3rd biological treatment tank 34 may be introduced into the 2nd biological treatment tank 2 instead of the dehydrator 35. The sludge (solid content) dehydrated by the dehydrator 35 is discharged outside the system as excess sludge. The dehydration filtrate (moisture content) is supplied to the first biological treatment tank 1 and/or the second biological treatment tank 2 . the

Thereby, the organic waste water can be efficiently treated by the biological treatment method of the organic waste water shown in FIG. 14 , and at the same time, the amount of excess sludge produced can be reduced. the

In this invention, as shown in FIG. 15, the 2nd biological treatment tank 2 is made into multiple stages. Specifically, two biological treatment tanks 2A and 2B are arranged in series. In the previous treatment tank 2A, the pH is 5 to 6, and the pH is preferably 5 to 5.5. In the treatment tank 2B, the treatment is performed at a pH of 6 or more, preferably at a pH of 6-8. Through this multi-stage treatment, the predation of sludge can be effectively performed in the first-stage treatment tank 2A, and the solid-liquid separation property of sludge can be improved and the quality of treated water can be improved in the subsequent-stage treatment tank 2B. The method in FIG. 15 differs only in that the second biological treatment tank 2 is multi-staged in FIG. 14 , and the other configurations are the same as those in FIG. 14 , and the same symbols denote the same parts. the

It should be noted that, in order to reduce the amount of sludge produced in the second biological treatment tank 2, it is also not possible to set the interval as shown in Figure 15, and the pH of the second biological treatment tank 2 will be adjusted in the single tank mode as shown in Figure 14. Set it below 6, in which case neutralization is required before the treated water is discharged. the

The methods shown in FIGS. 14 and 15 represent an example of the fifth aspect, and are not limited to any illustrated method as long as the fifth aspect does not exceed the gist thereof. the

The sludge discharged from the second biological treatment tank 2 may be introduced into the third biological treatment tank 34 instead of the separated sludge of the sedimentation tank 3 (or together with a part of the separated sludge of the sedimentation tank 3 ). the

Sludge reduction can be further stabilized by discharging 1/40, preferably 1/30 or more of the sludge in the tank from the second biological treatment tank and the third biological treatment tank every day. This decided to control the SRT to 40 days, and hope to operate it below 30 days. As an effect of operating under such conditions, microscopic organisms or metabolites in the tank are moderately reduced, and highly active microscopic animals can be maintained in the tank. the

In order to perform high-load treatment in the first biological treatment tank 1, a part of the separated sludge in the sedimentation tank 3 of the next stage can be returned to the first biological treatment tank 1, and the first biological treatment tank 1 can also be provided with two tanks in series The above biological treatment tanks are used for multi-stage treatment. the

The carrier may be added to the first biological treatment tank 1, or it may be a fluidized bed with the carrier added. This enables high-load treatment with a BOD volume load of 5 kg/m ³ /d or more.

In the second biological treatment tank 2, it is important to adopt operating conditions and treatment devices in which microscopic animals and bacteria remain in the system and to use the action of microscopic animals whose growth rate is slower than that of bacteria and the self-decomposition of bacteria. For this reason, No. 2 Biological treatment tank 2, as shown in Figures 14 and 15, preferably performs activated sludge treatment of return sludge or membrane separation activated sludge treatment. At this time, the amount of tiny animals held in the tank can be increased by adding a carrier in the aeration tank. the

The carrier added to the first biological treatment tank 1 and the second biological treatment tank 2 can be in any shape such as spherical shape, granular shape, hollow cylindrical shape, filament shape, etc., and the size can also be about 0.1 to 10 mm in diameter. The material of the carrier is any material such as a natural material, an inorganic material, or a polymer material, and a gel-like material can also be used. the

Examples and Comparative Examples of Aspect 5

The fifth aspect will be more specifically described below with reference to Examples and Comparative Examples. the

Example 8

As shown in Figure 14, the first biological treatment tank (activated sludge tank (non-reflux sludge)) 1 with a capacity of 3.6 L, the second biological treatment tank (activated sludge tank) 2 with a capacity of 15 L, and sedimentation The tank 3 is an experimental device connected to the third biological treatment tank 34 with a capacity of 4L, and the organic waste water (BOD630mg/L) of the present invention is treated at a rate of 22L/d. The pH of each biological treatment tank 1, 2, and 4 was adjusted to 6.8. Operate under the following conditions: the soluble BOD volume load in the first biological treatment tank 1 is 3.85kg-BOD/m ³ /d, HRT is 4h, and the soluble BOD sludge load in the second biological treatment tank 2 is 0.022 kg-BOD/kg-MLSS/d, HRT is 17h, overall BOD volume load is 0.75kg-BOD/m ³ /d, and HRT is 21h.

The SS in the second biological treatment tank 2 was 4000 mg/L, and the sludge settled in the sedimentation tank 3 was concentrated to 10000 mg/L. The concentrated sludge was discharged from the settling tank 3 , 250 ml/d of the discharged sludge was introduced into the third biological treatment tank 34 , and the remaining sludge was returned to the second biological treatment tank 2 . The HRT and SRT of the third biological treatment tank 34 were set to 16 days. The treated sludge in the third biological treatment tank 34 is dehydrated by the dehydrator 35 , the dewatered sludge is discharged as excess sludge, and the dewatered filtrate is returned to the second biological treatment tank 2 . the

After 4 months of continuous operation under this condition, the sludge conversion rate was 0.14kg-MLSS/kg-BOD. The BOD of the supernatant water flowing out from the sedimentation tank 3 was below the detection limit. the

Example 9

Use the experimental device identical with embodiment 8, carry out the processing of organic drainage (BOD630mg/L) similarly with embodiment 8. In addition, the pH of the biological treatment tank 1, 2 was adjusted to 6.8, and the pH of the 3rd biological treatment tank was adjusted to 5.0. The SS in the second biological treatment tank 2 was 5000 mg/L. Other conditions are identical with embodiment 8. the

As in Example 8, the sludge discharged from the sedimentation tank 3 was concentrated to 10000 mg/L. the

After operating continuously for 4 months under this condition, the sludge conversion rate calculated from the amount of sludge discharged from the second biological treatment tank 2 was 0.08 kg-MLSS/kg-BOD. the

Comparative example 5

As shown in FIG. 11 , organic waste water (BOD630 mg/L) was treated at a rate of 18 L/d using an experimental device having a biological treatment tank (activated sludge tank) 2' with a capacity of 15 L and a sedimentation tank 3 . The excess sludge discharge is 250mL/d, and the operating conditions are: the soluble BOD volume load of the biological treatment tank 2' is 0.76kg-BOD/m ³ /d, the HRT is 20h, and the pH is 6.8. Continuous operation under these conditions After 4 months, although the treated water was good, the sludge conversion rate was 0.40kg-MLSS/kg-BOD.

Comparative example 6

As shown in FIG. 12 , organic waste water (BOD630 mg/L) was treated in the same manner as in Example 1 at a rate of 22 L/d using the same experimental device as in Example 1 except that the third biological treatment tank 4 was omitted. The excess sludge discharge rate was 250mL/d, and the pH conditions and loading conditions of each tank were the same as in Example 1. the

After 4 months of continuous operation under these conditions, the treated water was good, but the sludge conversion rate calculated from the amount of sludge discharged from the second biological treatment tank 2 was 0.20 kg-MLSS/kg-BOD. The proportion of microscopic animals in the VSS of the second biological treatment tank 2 was about 25% (w/w). the

FIG. 16 shows the amount of excess sludge generation (sludge conversion ratio) with respect to the BOD charged in Examples 8 and 9 and Comparative Examples 5 and 6. FIG. See Table 3 for the operating conditions of Examples 8 and 9 and Comparative Examples 5 and 6 four months after the start of the experiment. the

table 3

The following conclusions can be drawn from the above results. the

In Comparative Example 5, the conventional activated sludge method was implemented, and in Comparative Example 6, treatment by the conventional secondary biological treatment method was implemented. The sludge conversion rate in the conventional activated sludge process (Comparative Example 5) was 0.40kg-MLSS/kg-BOD, but as shown in Comparative Example 6, the sludge conversion rate became 0.20kg by introducing multi-stage biological treatment -MLSS/kg-BOD, can reduce sludge production by 1/2. This sludge reduction effect is to the same extent as reported so far for secondary biological treatment methods. the

On the other hand, in Examples 8 and 9 in which the third biological treatment tank 34 was installed, the sludge conversion ratios were 0.14 and 0.08 kg-MLSS/kg-BOD, respectively, and the amount of sludge generated could be significantly increased compared with the conventional method. reduce. Especially in Example 2 in which the pH of the third biological treatment tank 34 was set to 5.0, sludge could be reduced to 1/5 of the conventional method. the

[Aspects 6 and 7]

Utilizing the biological treatment method and device for organic drainage according to aspects 6 and 7, in the multi-stage activated sludge process utilizing the predation of micro organisms, while maintaining stable treatment water quality, it is also possible to achieve high treatment efficiency. Further improvement and reduction of excess sludge generation. the

Organic waste water is introduced into the first biological treatment tank, and most of the organic components (for example, 70% or more) are oxidized and decomposed by non-agglomerative bacteria. The treatment solution in the first biological treatment tank is introduced into the second biological treatment tank, where oxidative decomposition of remaining organic components, self-decomposition of non-aggressive bacteria, and predation by microscopic animals proceed, thereby reducing the amount of sludge. the

In the sixth aspect, the sludge retention time (SRT) of the second biological treatment tank is controlled to 5 to 40 days. That is, to make the SRT of the second biological treatment tank 5 to 40 days, 1/5 to 1/40 of the sludge in the second biological treatment tank is discharged every day. By discharging the specified amount of sludge in the second biological treatment tank in this way, the microscopic animals and feces existing in the second biological treatment tank can be reduced, and a certain amount of productive sludge can be maintained in the second biological treatment tank at a relatively high rate. Small animals in the egg state can obtain good sludge reduction effect. the

In this way, compared with normal activated sludge, the sludge in the second biological treatment tank with a relatively high proportion of microscopic animals can be easily solubilized in any physical, chemical, or biological treatment. By solubilization, A further reduction in sludge can be achieved. the

In the seventh aspect of oxidizing the sludge in the second biological treatment tank in the third biological treatment tank under aerobic conditions, the SRT of the second biological treatment tank and the third biological treatment tank is 5 to 40 days. Sludge from each tank is discharged, and a large number of microscopic animals can be maintained in both tanks, achieving efficient sludge reduction. the

Preferred embodiments of the biological treatment methods of organic waste water according to aspects 6 and 7 will be described in detail below with reference to the drawings. the

Fig. 17 is a flow chart showing an embodiment of the biological treatment method of organic waste water according to the present invention. the

In the method of Fig. 17, the raw water (organic drainage) is first introduced into the first biological treatment tank (dispersion bacteria tank) 1D, and the BOD (organic component) is more than 70%, preferably more than 80%, more preferably more than 90%. Oxidative decomposition by non-agglutinative bacteria. The pH of the first biological treatment tank 1D is controlled to be 6 or more, preferably pH 6-8. By setting the BOD volume load in the first biological treatment tank 1D to 1 kg/m ³ /d or more, for example 1 to 20 kg/m ³ /d, and setting the HRT (raw water retention time) to 24 hours or less, for example 0.5 to 24 hours, it can be obtained Treated water in which non-agglomerative bacteria are dominant can treat wastewater with low BOD concentration at a high load by shortening the HRT.

The treated water in the first biological treatment tank 1D is introduced into the second biological treatment tank (microbiological tank) 2D, where oxidative decomposition of residual organic components, self-decomposition of non-agglutinative bacteria, and predation by microscopic organisms are carried out. Reduce sludge. the

Since the second biological treatment tank 2D utilizes the action of microscopic animals whose growth rate is slower than bacteria and the self-decomposition of bacteria, it is necessary to adopt operating conditions and treatment devices in which microscopic organisms and bacteria remain in the system. For this reason, it is desirable to use an activated sludge method or a membrane separation type active treatment in which sludge is refluxed in the second biological treatment tank 2D. It is more desirable to use the second biological treatment tank 2D as an aeration tank to which a carrier is added in order to increase the holding amount of microscopic animals in the tank. the

In this 2nd biological treatment tank 2D, by making pH 6 or less, for example pH 5-6, Preferably it is acidic 5-5.5, predation of bacteria by microscopic animals can be performed efficiently. the

As a result, the amount of sludge produced can be reduced to 50% of the usual amount. However, when reducing the amount of sludge discharged from the second biological treatment tank, that is, extending the SRT, as mentioned above, even if there is a sufficient amount of microscopic animals in the tank , It does not lay eggs, or most of the sludge is only dung, and the bacteria that become bait are also reduced, and sometimes the tiny animals in the tank die together when they reach the end of their life. In this way, if the microscopic animals in the second biological treatment tank 2D are greatly reduced, it will take more than one month to achieve the reduction. In order to avoid such a problem, it is necessary to periodically replace the sludge in the second biological treatment tank 2D, that is, to reduce microscopic animals and feces. Therefore, in the sixth aspect, in order to make the SRT of the second biological treatment tank 2D constant within the range of 5 to 40 days, preferably 10 to 30 days, and more preferably 20 to 30 days, discharge the second biological treatment tank 2D. Sludge in tank 2D. That is, the sludge in the second biological treatment tank 2D is discharged every day at a ratio of 1/40 to 1/5, preferably 1/30 to 1/10, and more preferably 1/20 to 1/30. By operating the second biological treatment tank 2D under such conditions, the proportion of microscopic animals in the SS in the tank can be maintained at 10% or more, preferably 15 to 30%, and thus, the amount of sludge produced can always be reduced. The status remains stable. the

Compared with the activated sludge during normal single-tank treatment, or the activated sludge when only increasing the sludge concentration of the second biological treatment tank in the multi-stage activated sludge process, since the second biological treatment tank 2D The discharged sludge has a high proportion of microscopic animals and can be easily solubilized by any physical, chemical or biological treatment, so it is preferable to solubilize by these treatments. As the solubilization treatment method, there are ultrasonic treatment, ozone treatment, cavitation, acid-base treatment, oxidant treatment, high temperature treatment, anaerobic digestion, etc., but any method can be easily processed with less energy and less treatment time. The discharged sludge of the second biological treatment tank 2D is solubilized. The solubilized sludge can be returned to the second biological treatment tank 2D, or the separated water can be returned to the first biological treatment tank 1D and/or the second biological treatment tank 2D through solid-liquid separation, and the solid content can be returned to the second biological treatment tank 2D. 2 Biological treatment tank 2D. Part or all of the solid content can also be discharged as excess sludge. When the solubilization device is a biological method such as anaerobic digestion, after solid-liquid separation, the sludge is returned to the anaerobic digestion sludge tank to prolong the SRT to further promote solubilization and inorganicization. the

In the present invention, when a large amount of organic matter remains in the treatment liquid from the first biological treatment tank 1D introduced into the second biological treatment tank 2D, this oxidative decomposition proceeds in the second biological treatment tank 2D. When oxidative decomposition of organic matter by bacteria occurs in the second biological treatment tank 2D where a large number of microscopic organisms exist, it is known that bacteria proliferate so as to be difficult to be preyed upon as a measure to escape predation by microscopic organisms. In this way, the bacterial population that proliferates in a way that is difficult to be prey will not be preyed on by tiny organisms, and the decomposition of these bacteria only depends on self-digestion, and the sludge becomes difficult to reduce. When the second biological treatment tank 2D is set in an acidic region with a pH of 6 or less, if a large amount of organic matter remains, fungi and the like will proliferate using the organic matter to cause sludge bulking. Therefore, as described above, in the first biological treatment tank 1D, it is preferable to decompose most of the organic matter, that is, 70% or more of raw water BOD, preferably 80% or more, so as to convert it into bacterial cells. It is preferable that the soluble BOD sludge load in the 2nd biological treatment tank 2D is 0.1 kg-BOD/kg-MLSS/d or less. the

The treated water in the second biological treatment tank 2D undergoes solid-liquid separation in the sedimentation tank 3D, and the separated water is discharged out of the system as treated water. Part of the separated sludge is discharged outside the system as excess sludge, and the remainder is returned to the second biological treatment tank 2D. the

In the present invention, it is also possible to set an aerobic digester which once again oxidizes the separated sludge (separated sludge of the settling tank 3D in FIG. 17 ) under aerobic conditions as the 3rd biological treatment tank (not shown in FIG. 17 ). The separated sludge is obtained by solid-liquid separation of the sludge discharged from the second biological treatment tank 2D or the sludge of the second biological treatment tank. In this case, also based on the same reason as in the second biological treatment tank, it is desirable not only for the second biological treatment tank but also for the third biological treatment tank, in 5 to 40 days, preferably in 10 to 30 days, more preferably in 10 days The SRT was controlled to be constant in the range of ~20 days. For this third biological treatment tank, while satisfying this SRT, the aerobic treatment method of setting up a sedimentation tank for sludge reflux, fluidized bed treatment with a carrier, or membrane separation type aerobic treatment method can be extended. SRT. Part or all of the treated sludge from the third biological treatment tank can be returned to the second biological treatment tank, or the solid-liquid separation can be performed to return the treated water to the first biological treatment tank and/or the second biological treatment tank , the solids return to the second biological treatment tank. Part or all of the solid content can also be discharged as excess sludge. the

The amount of sludge fed to the third biological treatment tank may be changed arbitrarily according to the amount of sludge generated as long as the SRT in the above-mentioned third biological treatment tank can be maintained. the

Like the second biological treatment tank, the sludge reduction effect in this third biological treatment tank depends on predation by microscopic animals. Therefore, by maintaining the pH of the third biological treatment tank at 6 or less, preferably in the range of 5 to 5.5, a higher sludge reduction effect can be obtained. However, when the pH of the third biological treatment tank is set to this condition, since the sludge reduction effect is high, the sludge concentration in the third biological treatment tank 34 may be excessively low. In this case, particularly as described above, it is preferable to increase the sludge concentration by using an aerobic treatment tank in which a sedimentation tank is installed to return sludge, a fluidized bed with a carrier added, or a membrane separation type aerobic treatment tank. the

According to the biological treatment method of the organic drainage according to the sixth and seventh aspects, the organic drainage can be efficiently treated, and at the same time, the amount of excess sludge produced can be stably reduced for a long time. the

It should be noted that the method in FIG. 17 shows an example of an embodiment of the sixth aspect, and is not limited to any illustrated method as long as the sixth and seventh aspects do not exceed the gist thereof. the

For example, the second biological treatment tank 2 may have multiple stages. Specifically, a biological treatment tank with 2 tanks is arranged in series, and in the previous treatment tank, the pH is 5 to 6, and the pH is expected to be 5 to 5.5. The pH is 6, and the treatment is carried out under the condition that the pH is preferably 6-8. Through this multi-stage treatment, the predation of sludge can be effectively carried out in the first-stage treatment tank, and the solid-liquid separation of the sludge can be improved in the latter-stage treatment tank, so as to improve the quality of treated water. the

In order to perform high-load treatment in the first biological treatment tank 1D, a part of the separated sludge in the subsequent settling tank 3D can be refluxed, or two or more biological treatment tanks can be installed in series as the first biological treatment tank 1D for multi-level processing. the

A carrier may be added to the first biological treatment tank 1D, or a carrier-added fluidized bed may be used. This enables high-load treatment with a BOD volume load of 5 kg/m ³ /d or more.

In the second biological treatment tank 2D, it is important to adopt operating conditions and treatment devices in which microscopic animals and bacteria remain in the system and to use the action of microscopic animals whose growth rate is slower than bacteria and the self-decomposition of bacteria. For this reason, No. 2. As shown in Figure 1, the biological treatment tank is preferably used for activated sludge treatment of return sludge or membrane separation activated sludge treatment. At this time, the amount of tiny animals held in the tank can be increased by adding a carrier in the aeration tank. the

The shape of the carrier added to the first biological treatment tank and the second biological treatment tank may be in any shape such as spherical shape, granular shape, hollow cylindrical shape, or filamentary shape, and the size may be about 0.1 to 10 mm in diameter. The material of the carrier is any material such as a natural material, an inorganic material, or a polymer material, and a gel-like material can also be used. the

Embodiments and comparative examples of the 6th and 7th aspects

Hereinafter, examples and comparative examples will be given to describe the sixth and seventh aspects more specifically. the

Example 10

As shown in Figure 17, the first biological treatment tank (activated sludge tank (non-reflux sludge)) 1D with a capacity of 3.6 L, the second biological treatment tank (activated sludge tank) 2D with a capacity of 15 L, and sedimentation In the experimental device connected to tank 3D, the organic waste water (BOD630mg/L) of the present invention was treated at a rate of 22L/d. The pH of each biological treatment tank 1D and 2D was adjusted to 6.8. Operate under the following conditions: the soluble BOD volume load in the first biological treatment tank 1D is 3.85kg-BOD/m ³ /d, HRT is 4h, and the soluble BOD sludge load in the second biological treatment tank 2D is 0.022 kg-BOD/kg-MLSS/d, HRT is 17h, overall BOD volume load is 0.75kg-BOD/m ³ /d, and HRT is 21h. From the second biological treatment tank 2D, 1/25 of the sludge in the tank was discharged every day so that the SRT was 25 days, and the discharged sludge was discharged outside the system.

FIG. 18 shows the diurnal change in the number of microscopic animals 2D in the second biological treatment tank at this time, and FIG. 19 shows the diurnal change in the sludge conversion rate. the

The SS in the second biological treatment tank 2D is 3500mg/L, and the dominant species of microscopic animals in the tank are rotifers and boid rotifers, which are about 30000/ml and about 35000/ml respectively. The proportion of tiny animals is about 50%, and this state can be maintained stably for more than 5 months. The sludge conversion rate was 0.15kg-MLSS/kg-BOD, while the sludge conversion rate in Comparative Example 7, which was carried out by single-tank treatment, was 0.37kg-MLSS/kg-BOD, which was stable compared with the latter. The sludge reduction effect was maintained at 60%. In addition, the BOD of the treated water obtained from the sedimentation tank 3D was below the detection limit. the

When the sludge discharged from the second biological treatment tank 2D is anaerobically digested under the condition of SRT of 15 days, 50% of COD can be converted into methane. Taking this effect into account, it can be said that sludge can be reduced by more than 75% compared with conventional methods. the

Comparative example 7

As shown in FIG. 11 , organic wastewater (BOD630 mg/L) was treated at a rate of 18 L/d using an experimental device including a biological treatment tank (activated sludge tank) 2' with a capacity of 15 L and a settling tank 3 . Continuous operation under the following conditions: the return sludge volume is 250mL/d, the excess sludge discharge volume is 250mL/d, the soluble BOD volume load of the biological treatment tank 2' is 0.76kg-BOD/m ³ /d, and the HRT is After 20 hours, the pH was 6.8. Although the quality of the treated water was good, the sludge conversion rate was 0.37kg-MLSS/kg-BOD.

Comparative example 8

Operation was performed under the same conditions as in Example 10 except that the amount of sludge discharged from the second biological treatment tank 2D was 1/45 of the sludge in the tank per day so that the SRT was 45 days. the

FIG. 18 shows the diurnal change in the number of microscopic animals 2D in the second biological treatment tank at this time, and FIG. 19 shows the diurnal change in the sludge conversion rate. the

In this Comparative Example 8, the amount of sludge discharged from the second biological treatment tank 2D is less than that of Example 10, so the SS in the second biological treatment tank 2D is as high as 5000 mg/L, and it is sludge that can be treated with activated sludge. mud concentration. The dominant species of tiny animals in the 2nd biological treatment tank 2D is bdellochora, and its amount is constantly changing, and it is 0-50000/ml. The proportion of tiny animals in the SS in the tank is about 0-25%. Under the conditions, a large number of micro-animals died about every 40 days, and the sludge conversion rate increased each time. Therefore, although the quality of the treated water was good, the average sludge conversion rate was 0.20 kg-MLSS/kg-BOD, and the sludge reduction effect remained at about 45% compared with Comparative Example 7. the

Even if the sludge discharged from the second biological treatment tank 2D is anaerobically digested under the condition of SRT of 15 days, the content of microscopic animals is low, so only 30% of COD can be converted into methane. Even considering this effect, Compared with the conventional method, the sludge reduction effect also remained at about 60%. the

From the above results, the following conclusions can be drawn. That is, by introducing the secondary biological treatment method, the amount of sludge generation can be reduced by about 45% on average. However, as shown in Comparative Example 8, if the SRT is too long to increase the sludge concentration in the second biological treatment tank, the second biological treatment tank cannot be reduced. 2 The number of microscopic animals in the biological treatment tank is stable, but the sludge conversion rate is still fluctuating, and as a result, a sufficient sludge reduction effect cannot be obtained. the

However, like Example 10, by regularly discharging the sludge in the second biological treatment tank according to the life cycle of microscopic animals that are intended to be maintained in the second biological treatment tank 2D, the sludge reduction rate is increased to 60%, and the remaining Sludge contains a large amount of metazoans called rotifers, so it is easier to reduce by anaerobic digestion than normal sludge, so that sludge can be further reduced. the

Example 11

A part of 600mL/d of the separated sludge in the sedimentation tank 3D is returned to the third biological treatment tank with a capacity of 6L, and the remaining part is returned to the second biological treatment tank 2D. In the third biological treatment tank, the solid-liquid separation is performed as needed. The oxygen digested sludge was treated in the same manner as in Example 10, except that the separated water was returned to the first biological treatment tank 1D, and the separated sludge was returned to the second biological treatment tank 2D. the

Make the pH of the third biological treatment tank 5.0, discharge 1/10 of the sludge in the tank every day so that the SRT is 10 days, and discharge the discharged sludge out of the system. As a result, the BOD of the treated water obtained from the settling tank was below the detection limit, and the sludge conversion rate was 0.7 kg-MLSS/kg-BOD. the

Reference example 1

1/45 of the sludge in the tank is discharged every day so that the SRT of the 3rd biological treatment tank is 45 days. In addition, it is operated under the same conditions as in Example 11. As a result, the quality of the treated water is the same as in Example 2, but the sludge The conversion rate was 0.11kg-MLSS/kg-BOD, and the sludge reduction effect by installing the third biological treatment tank was reduced. the

From Example 11 and Reference Example 1, it can be seen that further sludge reduction can be achieved by setting a third biological treatment tank for further aerobic digestion, but if the SRT in the third biological treatment tank is too long, the third biological treatment tank The sludge reduction effect by the treatment tank is reduced. the

[Aspects 8 and 9]

According to the biological treatment method of organic wastewater according to the eighth and ninth aspects, in the multi-stage activated sludge method using the predation of microscopic animals on the basis of the following effects, treatment can be realized while maintaining stable treatment water quality Further increase in efficiency and reduction in excess sludge generation. the

Among the states of bacteria generated in the first biological treatment step for removing organic matter, bacteria in a dispersed state are most likely to be preyed upon by microscopic animals. Even the flocculated bacteria can sufficiently prey on the presence of aggregated predatory microfauna in addition to filtering the predatory microfauna in the second biological treatment step. However, in order for bacteria to be preyed on by microscopic animals rapidly, it is advantageous for a single bacterium to be smaller than the caliber of microscopic animals. Regardless of whether the bacteria are in a dispersed state or in a flocculated state, when the bacteria are filamentous, although they can be preyed on by microscopic animals, the predation speed is low and pollution The slime reduction effect is also reduced. the

In order to solve the above problems, in the eighth and ninth aspects, the operation is performed under the condition that the bacteria produced in the first biological treatment step are not filamentous. the

That is, the HRT of the first biological treatment process is controlled so that the organic component (BOD) in the standard organic wastewater is 0.75 to 1.5 times the standard HRT required for oxidative decomposition, with a ratio of 70% or more and less than 100% . the

Here, the purpose of making the BOD oxidative decomposition rate of the standard HRT less than 100% and incompletely oxidatively decomposing BOD is to prevent non-aggregative bacteria from becoming filamentous and flocculating under the condition that BOD does not exist in the system. The purpose of making the BOD oxidative decomposition rate of standard HRT 70% is to prevent more than 30% of BOD from entering the second biological treatment process. When more than 30% of BOD enters the second biological treatment process, sufficient sludge reduction effect cannot be enjoyed. This is because in the second biological treatment step, non-agglutinating bacteria filamentize and decompose more than 30% of the BOD, which makes it difficult for microscopic animals to prey, resulting in insufficient sludge reduction effect. the

Although the amount of organic drainage fluctuates over time, since HRT is obtained by dividing the volume of the treatment tank (L) by the flow rate of treated water (L/h), the HRT becomes longer when the amount of organic drainage decreases, and flocculation or flocculation of non-agglomerative bacteria occurs. Filamentation reduces the predation rate in the second biological treatment process, and the sludge reduction effect is also low. the

Therefore, when the amount of organic waste water decreases in the eighth aspect, by adding liquid to the organic waste water supplied to the first biological treatment step, the amount of water to be treated flowing into the first biological treatment step is constant, and the first biological treatment step The HRT in is stable. As the liquid, as in claim 2, it is preferable to use treated water that has passed through the second biological treatment step. the

In the ninth aspect, the HRT of the first biological treatment process is stabilized by varying the water volume in the treatment tank in which the first biological treatment process is performed according to the fluctuation of the organic drainage volume. the

Thus, according to the eighth and ninth aspects, by controlling the HRT of the first biological treatment process to be within the range of 0.75 to 1.5 times the standard HRT, the BOD oxidative decomposition rate of the standard organic waste water is greater than or equal to 30% and less than 100%. , non-agglomerative bacteria generated in the first biological treatment process are not filamentous and flocculated, that is, they can be returned to the second biological treatment process, and in the second biological treatment process, the concentration of microscopic animals can be stabilized at a high concentration, A good sludge reduction effect is obtained. the

It should be noted that the HRT of the first biological treatment step is preferably controlled to the standard HRT, but generally within the range of 0.75 to 1.5 times the standard HRT, the effects of the present invention can be sufficiently obtained. However, it is preferable to control the HRT of the first biological treatment step within a range of 0.9 to 1.2 times, especially 0.95 to 1.05 times, the standard HRT. the

When the BOD concentration of organic wastewater fluctuates greatly, even if the HRT of the first biological treatment step is controlled within the range of 0.75 to 1.5 times the standard HRT established as a standard organic wastewater, the following problems may occur . That is, when the BOD concentration of the organic wastewater decreases to 50% or less of the standard organic wastewater BOD concentration, and then returns to the standard BOD concentration again, the change of BOD to bacteria can be tracked in the first biological treatment process, The remaining BOD that cannot be decomposed in the first biological treatment step will flow into the second biological treatment step. The BOD flowing into the second biological treatment process is oxidatively decomposed in the second biological treatment process, but if the oxidative decomposition of BOD by bacteria occurs in the second biological treatment process where a large number of microscopic animals exist, the microscopic organisms escape as bacteria Predation countermeasures are known to proliferate in a way that is difficult to be preyed. In this way, the proliferated bacterial population will not be preyed on by microscopic organisms, and their decomposition depends only on self-digestion, which will reduce the effect of reducing the amount of sludge produced. the

By using a fluidized bed biological treatment process in which a carrier is added to the treatment tank as the first biological treatment process, the biofilm attached to the carrier is used as a supply source of bacteria in the first biological treatment process that decreases when the load is low, and again When the load is restored, bacteria proliferate rapidly, and the BOD removal rate in the first biological treatment process can be stabilized, so the above-mentioned problems caused by fluctuations in the BOD concentration of organic wastewater can be solved. the

Preferred embodiments of the biological treatment methods of organic wastewater according to aspects 8 and 9 will be described in detail below with reference to the accompanying drawings. the

20 to 23 are flowcharts showing preferred embodiments of the biological treatment method of organic waste water according to the eighth and ninth aspects. In Figures 20-23, 1 is the first biological treatment tank, 2 is the second biological treatment tank, 3 is the sedimentation tank, 54 is the flow meter, 55 is the regulating tank, 55A is the raw water storage tank, 55B is the treatment water tank, 56 57 is a pump for water level regulation, 58 is a screen for carrier separation, and 59 is a carrier. the

In any method, the raw water (organic drainage) is first introduced into the first biological treatment tank (dispersion bacteria tank) 1, and the BOD (organic component) is more than 70%, preferably 80% or more, more preferably 90% or more Oxidative decomposition by non-agglutinative bacteria. The pH of the first biological treatment tank 1 is controlled to be 6 or more, preferably pH 6-8. The BOD volume load in the first biological treatment tank 1 is more than 1 kg/m ³ /d, for example, 1 to 20 kg/m ³ /d, and the HRT (raw water residence time) is less than 24 hours, for example, in the range of 0.5 to 24 hours. In the range of 0.75 to 1.5 times the standard HRT set in advance by the method described later, it is preferable to obtain treated water in which non-aggregative bacteria dominate, and by shortening the HRT, it is possible to treat wastewater with a low BOD concentration at a high load.

The treated water in the first biological treatment tank 1 is introduced into the second biological treatment tank (microbiological tank) 2, where oxidative decomposition of residual organic components, self-decomposition of non-agglutinative bacteria, and predation by microscopic organisms are carried out. Reduce sludge. The second biological treatment tank 2 is treated under conditions of pH 6 or higher, preferably pH 6-8. the

The treated water in the second biological treatment tank 2 undergoes solid-liquid separation in the sedimentation tank 3, and the separated water is discharged out of the system as treated water. Part of the separated sludge is discharged outside the system as excess sludge, and the rest is returned to the second biological treatment tank 2 . It should be noted that the return of the sludge is carried out in order to maintain the amount of sludge in each biological treatment tank, but there are also situations where it is not necessary to return the sludge, such as making the first biological treatment tank 1 and/or the second biological treatment tank 1 When the treatment tank 2 is a fluidized bed type in which a carrier described later is added, it is not necessary to return the sludge. When the BOD volume load of the first biological treatment tank 1 is low, as shown in the figure, the sludge can be returned only to the second biological treatment tank 2, or it can be returned to the first biological treatment tank 1, and it can also be returned to the first biological treatment tank Both the tank 1 and the second biological treatment tank 2. A third biological treatment tank may also be installed to treat the sludge discharged from the second biological treatment tank or sedimentation tank to further reduce sludge. The sludge discharged from here can be directly returned to the first and/or second biological treatment tank, or can be treated as excess sludge by solid-liquid separation. At this time, part or all of the detached liquid may be returned to the first and/or second biological treatment tank. In addition, part or all of the solid content may be returned to the first and/or second biological treatment tank, or may be treated as dewatered sludge. The biological treatment method may be any of anaerobic treatment and aerobic treatment. the

In aspects 8 and 9, the standard HRT is obtained in advance by a tabletop test or the like, and the HRT of the first biological treatment tank 1 is controlled so as to be in the range of 0.75 to 1.5 times the standard HRT. the

The tabletop test method for obtaining the standard HRT can be performed as follows. That is, the target organic waste water is continuously supplied and discharged from the culture tank at the same speed, and the proliferation of bacteria and the dilution of bacteria caused by the supply of organic waste water are in a balanced state, and the remaining waste water BOD at this time reaches the initial BOD of the waste water. Find the optimal residence time (HRT) at the supply rate of 30% or less of the water, preferably 20% or less. In addition to the above-mentioned continuous experiment, the decomposition rate of the target drainage can also be obtained by the fractional experiment, and the optimal HRT can be obtained from the result. When the wastewater contains a large amount of refractory components, the optimal HRT becomes longer, or a large amount of components with different decomposition speeds is contained, it is desirable to perform some treatment on the target wastewater to promote the decomposition of refractory components, and decompose 70 hours below HRT24h, preferably below 12h % or more, preferably more than 80% of the organic components in the wastewater. Any of chemical treatment with chemicals such as acids and alkalis, biological treatment with use of specific bacteria or enzymes, and physical treatment may be used as methods for promoting decomposition of refractory components. the

In aspects 8 and 9, the standard HRT is the HRT required to convert 70% or more and less than 100% of the BOD of the standard organic drainage into bacterial cells, but it is preferably set to 75% or more of the BOD, especially 80-95% is transformed into the HRT required by the bacteria. the

As described above, it is preferable to control the HRT of the first biological treatment tank 1 within a range of 0.9 to 1.2 times, particularly 0.95 to 1.05 times, the standard HRT. the

In the method of FIG. 20 , the treated water in the sedimentation tank 2 is returned to the raw water introduction side of the first biological treatment tank 1 so that the HRT of the first biological treatment tank 1 becomes a predetermined value. the

That is, the flow rate of the raw water is measured with the flowmeter 54, and when the raw water volume is insufficient to ensure the prescribed HRT, the insufficient part is supplemented with treated water, and the HRT of the first biological treatment tank 1 is controlled to a prescribed value by the sum of the raw water volume and the volume of returned treated water. scope. the

The amount of liquid flowing into the first biological treatment tank 1 can also be controlled by the method shown in FIG. 21 . In FIG. 21, a raw water storage tank 55A and a treatment water tank 55B are provided adjacent to a regulating tank 55, and the raw water pump 56 supplies a predetermined amount of treated water to the first biological treatment tank 1 from the regulating tank 55. According to the water level of the raw water storage tank 55A, the adjustment tank 55 is arranged on the partition wall with a liquid flow part between the two tanks, so that the treated water in the treatment water tank 55B flows into the raw water storage tank 55A, and the adjustment tank 55 absorbs the increase in the amount of raw water. The HRT of the first biological treatment tank 1 can be maintained within a specified range by returning the raw water, or the raw water and the treated water, to the first biological treatment tank 1 with a certain amount of water. In the method of FIG. 21 , by setting the regulating tank 55 , the flow meter 54 and the treated water return pump (not shown in FIG. 20 ) in FIG. 20 can be omitted, thereby simplifying the control of the HRT. the

In the method shown in FIG. 22, when the water level adjustment pump 57 is installed in the first biological treatment tank 1, the amount of raw water flowing into the first biological treatment tank 1 is small, and the HRT of the first biological treatment tank 1 tends to become longer , the water in the first biological treatment tank 1 is forcibly transferred to the second biological treatment tank 2 with the pump 57 for water level adjustment, so that the apparent water retention of the first biological treatment tank 1 is reduced, thus the first biological treatment tank 1 can be reduced. The HRT of the biological treatment tank 1 is maintained within a predetermined range. the

The method shown in FIG. 23 is that in the method shown in FIG. 22, a carrier separation screen 58 is set in the first biological treatment tank 1, and the carrier 59 is dropped into the raw water introduction side of the screen 58, and at the same time, the carrier is separated from the screen 58. The treated water discharge side of 58 is provided with a pump 57 for water level regulation, which is the same as the method shown in FIG. , by reducing the apparent water retention of the first biological treatment tank 1, the HRT of the first biological treatment tank 1 can be maintained within a predetermined range. the

In the method shown in FIG. 23, by injecting the carrier 59 into the first biological treatment tank 1, as described above, the BOD removal rate in the first biological treatment tank 1 can be stabilized with respect to the fluctuation of the raw water BOD concentration. the

The addition rate of the carrier in the first biological treatment tank 1 (hereinafter referred to as "tank filling rate") is preferably 0.1 to 20%, more preferably 1 to 10%, and particularly preferably 2 to 5%. The shape of the carrier to be added may be any shape such as spherical shape, granular shape, hollow cylindrical shape, or filamentary shape, and the size may be about 0.1 to 10 mm in diameter. The material of the carrier is any material such as a natural material, an inorganic material, or a polymer material, and a gel-like material can also be used. the

It goes without saying that, in the method of Fig. 20, 21, also can add carrier in the 1st biological treatment tank 1. When the water level adjustment pump 57 is used to transfer the water in the first biological treatment tank 1 to the second biological treatment tank 2, as shown in FIG. net58. At this time, in order to prevent the biofilm peeled off from the carrier from clogging the screen 58, hindering the outflow of SS, and preventing the sludge residence time from becoming longer, it is desirable that the opening of the screen 58 be more than 5 mm. In this case, it is desirable to add The diameter of the carrier 59 is more than 5 mm. the

It should be noted that the methods shown in FIGS. 20 to 23 are examples of the eighth and ninth aspects, and are not limited to any of the illustrated forms as long as the eighth and ninth aspects do not exceed the gist thereof. For example, as a liquid added to raw water for HRT control, industrial water, well water, city water, river water, etc. can be used other than treated water, and treated water is preferably used. the

The carrier may be added not only to the first biological treatment tank 1 but also to the second biological treatment tank 2 . The first biological treatment tank 1 and the second biological treatment tank 2 can adopt multi-stage treatment of biological treatment tanks with more than 2 tanks arranged in series, or can adopt membrane separation type activated sludge treatment in which a separation membrane is immersed in the tank. the

However, the activity of bacteria, that is, the BOD decomposition ability increases as the temperature increases and decreases as the temperature decreases. In short, the HRT of the first biological treatment tank required to obtain a predetermined oxidative decomposition rate of BOD shortens as the temperature becomes higher, and becomes longer as the temperature becomes lower. Therefore, for raw water whose temperature change is 5°C or more higher than the reference temperature, it is preferable to confirm the change of the optimal HRT caused by the temperature through a table test in advance, and to pre-set the standard HRT that considers the influence of temperature when the temperature changes. The HRT of the first biological treatment tank is controlled within a range of 0.75 to 1.5 times, more preferably 0.9 to 1.2 times, and particularly preferably 0.95 to 1.05 times the standard HRT. the

Similarly, when the BOD concentration of raw water fluctuates greatly relative to the reference BOD concentration, it is also preferable to preset a standard HRT based on the BOD concentration fluctuation, and control the HRT of the first biological treatment tank relative to the standard HRT. It is within the range of 0.75 to 1.5 times, more preferably 0.9 to 1.2 times, particularly preferably 0.95 to 1.05 times. the

Thus, according to the biological treatment method of organic wastewater of the present invention that controls the HRT of the first biological treatment tank 1 within a predetermined range, the density of microscopic animals in the second biological treatment tank 2 increases, and the microscopic animals in the SS in the tank The ratio is maintained at 10% or more, and it can be seen from the results of Examples described later that a sludge reduction effect of 50% or more can be stably obtained compared with the standard activated sludge method. the

Embodiments and comparative examples of the 8th and 9th aspects

Hereinafter, the eighth and ninth aspects will be described more specifically with reference to examples and comparative examples. the

Example 12

Using the experimental device connected with the activated sludge tank (non-reflux sludge) with a capacity of 3.6 L as the first biological treatment tank 1 and the activated sludge tank with a capacity of 15 L as the second biological treatment tank 1, use the diagram The method of the present invention shown in 1 implements the treatment of organic waste water. The pH of the first biological treatment tank 11 and the pH of the second biological treatment tank 12 were respectively adjusted to 6.8. Operate under the following conditions, that is, the soluble BOD volume load in the first biological treatment tank 1 is 3.85kg-BOD/m ³ /d, HRT is 4h, and the soluble BOD sludge load in the second biological treatment tank 2 is 0.022kg-BOD/kg-MLSS/d, HRT 17h, overall BOD volume load 0.75kg-BOD/m ³ /d, HRT 21h. The experiment was carried out in a constant temperature room at 20°C. Results The sludge conversion rate was 0.18kg-MLSS/kg-BOD. It should be noted that the HRT of the first biological treatment tank 1 required to oxidatively decompose 75% of the BOD in the raw water obtained in advance through a tabletop test is 4 hours.

One month after the start of operation, operate under the same conditions as above for 12 hours, and then perform an operation in which the matrix flow rate is reduced to half and the reduced water volume is supplemented with treated water (here, the BOD volume load is reduced by half), and repeated alternately for 12 hours As a result of the above operation test (load fluctuation operation), the HRT of the first biological treatment tank 1 can be maintained at about 4 hours, and the bacteria in the first biological treatment tank 1 are also maintained in a dispersed state. However, when the load is halved, the concentration of dispersed bacteria decreases, and when the load returns, it is too late for the re-growth of dispersed bacteria, and the organic matter in the wastewater may flow into the second biological treatment tank 2 without being decomposed. For this reason, the sludge conversion rate increased a little to 0.28kg-SS/kg-BOD. the

During the operation period, in the second biological treatment tank 2, the leech rotifers were dominant, and the number of microscopic animals before the load fluctuation operation was 55,000 to 70,000/ml, and the proportion of SS in the tank was 20%, but the load fluctuation operation started After that, the number of tiny animals stayed at around 30,000/ml. the

Example 13

In the first biological treatment tank 1, a sponge with a particle diameter of 5 mm was added at a filling rate of 5% in the tank, and in the first biological treatment tank, fluidized bed activated sludge treatment was performed. The operation was carried out under the same conditions as in Example 1. the

As a result, even after the start of the load fluctuation operation, the HRT of the first biological treatment tank 1 can be maintained at about 4 hours, and the bacteria in the first biological treatment tank 1 are also maintained in a dispersed state. Moreover, the sludge conversion rate can also be maintained at 0.18kg-SS/kg-BOD. the

During the operation period, before and after the high load fluctuation, the leech rotifers were dominant in the second biological treatment tank 2, the number of microscopic animals was 55,000-70,000/ml, and the proportion of SS in the tank was 20%. the

Comparative example 9

In Example 12, the first biological treatment tank was omitted, and the treatment was performed using an experimental device including only the second biological treatment tank with a capacity of 15 L. The experiment was carried out in a constant temperature room at 20°C. The volume load of soluble BOD was 0.76kg-BOD/m ³ /d, and the HRT was 20h. It is 0.40kg-SS/kg-BOD.

As in Example 12, the operation of reducing the substrate flow rate to half (half the BOD volume load here) was carried out for 12 hours, and the load variation operation test in which the above-mentioned operation was alternately repeated every 12 hours was carried out. As a result, the sludge conversion rate remained unchanged, reaching 0.40kg -SS/kg-BOD. During the operation period, in the activated sludge tank, 3,000/ml bdelloid rotifers and 10,000/ml rotifers were observed, and the proportion of microscopic animals in the SS in the tank was often 5% or less. the

Comparative Example 10

After the load fluctuation operation, operation was performed under the same conditions as in Example 12, except that the substrate flow rate was reduced to half and the treated water was not returned. the

As a result, before the load fluctuation operation, as in Example 1, the sludge conversion rate was 0.18kg-SS/kg-BOD, and after the load fluctuation operation started, in the first biological treatment tank 1, the filamentous bacteria (long 50～1000μm) is dominant, and in the second biological treatment tank 2, the dominant boidwheelworm before the load change is reduced from 50,000/ml to 0/ml, and the sludge conversion rate also rises to 0.34kg-SS/kg- BOD. the

Figure 24 shows the relationship between the amount of input BOD and the amount of excess sludge generated (VSS produced: sludge conversion rate) before the load fluctuation operation in the above Examples 12 and 13 and Comparative Examples 9 and 10, and Figure 25 shows the load The relationship between the amount of input BOD after the start of operation and the amount of excess sludge generated (generated VSS: sludge conversion rate) was varied. the

It can be seen from Figures 24 and 25 that the multi-stage activated sludge method using the predation of tiny animals can obtain a higher sludge reduction effect regardless of before and after the load change, but in the treatment using the multi-stage activated sludge method, according to this According to the invention, by maintaining the HRT of the first biological treatment tank within a specified range, and further adding carriers to the first biological treatment tank to perform fluidized bed activated sludge treatment, no matter how the load changes, stable Sludge reduction effect. the

Claims (4)

1. the bioremediation of organic drainage, this method has:

High loading handle in the organic drainage BOD so that the BOD 70% or more be converted into the dispersion thalline the 1st biological treating tank and

Make the 2nd biological treating tank of tiny organism coexistence in the dispersion thalline flocculating after will transforming,

The method is characterized in that: wherein said the 1st biological treating tank is handled under the condition of pH6～8, and said the 2nd biological treating tank is handled under the condition of pH5～6,

The BOD volumetric loading of the 1st biological treating tank is 1～20kg/m ³/ d,

The HRT of the 1st biological treating tank is 0.5～24h,

The solvability BOD sludge loading of the 2nd biological treating tank is 0.01～0.1kg-BOD/kg-MLSS/d.

2. the bioremediation of organic drainage as claimed in claim 1; It is characterized in that; Making the treatment process in said the 2nd biological treating tank is the multiple-stage treatment more than 2 grades, in the 2nd biological treating tank, after the biological treatment of pH5～6, carries out the biological treatment more than the pH6.

3. the bioremediation of organic drainage as claimed in claim 1; It is characterized in that; The processing mode of utilizing said the 2nd biological treating tank to carry out is that the back segment at biological treating tank is provided with equipment for separating liquid from solid, will be back to the sludge return type biological treatment mode of this biological treating tank through the mud of solid-liquid separation; In biological treating tank, added the fluidized bed type biological treatment mode of carrier, or membrane sepn formula biological treatment mode.

4. the bioremediation of organic drainage as claimed in claim 1; It is characterized in that; Be utilized in the fluidized bed type biological treatment mode or the multiple-stage treatment mode more than 2 grades of having added carrier in the biological treating tank, carry out the processing in said the 1st biological treating tank.

Images