JP4581551B2 - Biological treatment method for organic wastewater - Google Patents

Description

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

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

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

  In Japanese Patent Laid-Open No. 55-20649, organic wastewater is first treated with bacteria in a first treatment tank to oxidize and decompose organic matter contained in the wastewater, and convert it into non-aggregable bacterial cells. There is a description that excess sludge can be reduced by precipitating and removing the sticking protozoa in the treatment tank. Furthermore, the above method enables high-load operation and improves the treatment efficiency of the activated sludge method.

  In this way, many wastewater treatment methods have been devised that use the predation of protozoa and metazoans located at high levels of bacteria. Japanese Patent Application Laid-Open No. 2000-210692 proposes a countermeasure for deterioration in processing performance due to fluctuations in the quality of raw water, which is a problem in the processing method of Japanese Patent Application Laid-Open No. 55-20649. As specific methods, “adjust BOD fluctuation of treated water to within 50% from median average concentration”, “measure water quality in first treatment tank and first treated water over time”, A method such as “adding a microbial preparation or seed sludge to the first treatment tank when the quality of the first treated water deteriorates” is proposed. In Japanese Examined Patent Publication No. 60-23832, when protozoa and metazoans prey on bacteria, yeast, actinomycetes, algae, molds and wastewater treatment primary sludge or surplus sludge, ultrasonic treatment or mechanical stirring, We propose a method to reduce the size of the food flock in the animal.

Japanese Patent No. 3410699 discloses a multi-stage treatment of fluidized bed and activated sludge process. In this method, the latter activated sludge method is operated at a low load of BOD sludge load 0.1 kg-BOD / kg-MLSS / d, so that the sludge can be self-oxidized and the amount of sludge extraction can be greatly reduced.
Japanese Patent Laid-Open No. 55-20649 JP 2000-210692 A Japanese Patent Publication No. 60-23832 Japanese Patent No. 3410699

  The multistage activated sludge method using the above-mentioned predatory action of micro animals and self-digestion of bacteria itself is actually used for organic wastewater treatment. Depending on the target wastewater, the treatment efficiency is improved and the amount of generated sludge is reduced. Is possible. For example, when the predation of micro animals is used, the sludge reduction effect varies depending on the treatment conditions and the quality of the wastewater, but the amount of sludge generated by the standard activated sludge method can be reduced by about 30 to 70%. However, the sludge reduction effect depends on the number of micro-animals in the tank, and the current situation is that stable sludge reduction cannot be maintained over a long period of time. This is because the micro-animals involved in sludge reduction are higher animals than bacteria, and the demand for nutrition is high, and the generation of non-aggregating bacteria (dispersed bacteria) that are easy to prey in the biological treatment tank in the previous stage. This is because it is difficult to perform stably.

  On the other hand, in the multistage activated sludge method using self-digestion of bacteria, the amount of sludge generated can be reduced by about 50% compared to the standard activated sludge method regardless of the state of bacteria (dispersed state, flock, filamentous). However, in order to obtain a sludge reduction rate of 50%, it is necessary to set a longer sludge retention time in a biological treatment tank that performs self-digestion. For this reason, if a membrane separator is installed, running costs due to sludge reduction due to membrane maintenance costs Will offset the reduction.

  Therefore, in order to achieve a sludge reduction rate of 50% or more at a low running cost using an existing aeration tank, the use of micro-animals is effective. It is necessary to stably produce bacteria that are easily preyed on by minute animals in the tank.

  The present invention relates to a biological treatment method for organic wastewater which aims to further improve the treatment efficiency and reduce the amount of surplus sludge while maintaining a stable treated water quality in the multistage activated sludge method utilizing the predatory action of micro animals. The purpose is to provide.

  The biological treatment method for organic wastewater according to claim 1 is a first biological treatment step for converting BOD in organic wastewater into a microbial cell by subjecting the BOD in the organic wastewater to a high load, and prey on the microbial cell after the conversion. In a biological treatment method for organic wastewater having a second biological treatment process in which microanimals coexist, it is necessary for 70% or more and less than 100% of BOD in the organic wastewater serving as a reference to be converted into cells. The hydraulic residence time (HRT) in the first biological treatment step is determined, and this value is set as a reference HRT, and the HRT in the first biological treatment step is 0.75 to 1.5 times the reference HRT. A liquid is added to the organic waste water introduced into the first biological treatment step so as to be within a range.

  The organic wastewater biological treatment method according to claim 2 is the organic wastewater biological treatment method according to claim 1, wherein the liquid is treated water that has undergone the second biological treatment step. .

  The biological treatment method for organic wastewater according to claim 3 is a first biological treatment step for converting BOD in organic wastewater into a microbial cell by subjecting the BOD in the organic wastewater to a high load, and prey on the microbial cell after the conversion. In a biological treatment method for organic wastewater having a second biological treatment process in which microanimals coexist, it is necessary for 70% or more and less than 100% of BOD in the organic wastewater serving as a reference to be converted into cells. The hydraulic residence time (HRT) in the first biological treatment step is determined, and this value is set as a reference HRT, and the HRT in the first biological treatment step is 0.75 to 1.5 times the reference HRT. The amount of water in the treatment tank in which the first biological treatment process is performed is varied so as to be within a range.

  The biological treatment method for organic wastewater according to claim 4 is the biological treatment method for organic wastewater according to any one of claims 1 to 3, wherein the first biological treatment step adds a carrier to the treatment tank. It is a fluidized bed biological treatment process.

In the present invention, the “standard organic wastewater” means the organic wastewater that is biologically treated according to the present invention, that is, the organic wastewater whose flow rate, temperature, and BOD concentration vary with time, Refers to organic wastewater with BOD concentration. The reference temperature and BOD concentration are as follows.
Reference temperature: The lowest temperature of the year, including when heating.
Reference BOD concentration: The maximum BOD concentration of the wastewater flowing into the first biological treatment process.

  According to the organic wastewater biological treatment method of the present invention, in the multi-stage activated sludge method utilizing the predatory action of micro-animals based on the following effects, while maintaining stable treated water quality, The treatment efficiency can be improved and the amount of excess sludge generated can be reduced.

  Among the bacterial states produced in the first biological treatment process for removing organic matter, the ones that are most likely to be preyed on by minute animals are the dispersed bacteria. Even if the bacteria are flocked, they can be predated sufficiently if aggregate predation type micro-animals are present in addition to the filtration predation type micro-animals during the second biological treatment step. However, in order for a micro animal to rapidly prey on bacteria, it is advantageous that a single bacterial individual is smaller than the diameter of the micro animal, regardless of whether the bacteria are in a dispersed state or a flock state. In the case where is threaded, although it is predatory depending on the minute animal, the predation speed is reduced and the sludge reduction effect is also reduced.

  In order to solve the above problems, the present invention is characterized in that it is operated under conditions that do not cause the bacteria produced in the first biological treatment step to become filamentous.

  That is, in the present invention (Claims 1 and 3), 70% or more and less than 100% of the organic component (BOD) in the organic waste water used as a reference is 0.75 to 1. The HRT of the first biological treatment process is controlled so as to be 5 times the range.

  Here, the BOD oxidative degradation rate of the standard HRT is less than 100% and the BOD is not completely oxidatively decomposed. Non-aggregating bacteria tend to form filaments and flocs under the condition that no BOD exists in the system. This is to prevent this. The reason why the BOD oxidative degradation rate of the reference HRT is set to 70% is to prevent BOD exceeding 30% from moving to the second biological treatment process. When BOD exceeding 30% shifts to the second biological treatment process, it is not possible to enjoy a sufficient sludge reduction effect. This is because in the second biological treatment step, non-aggregating bacteria break down while forming more than 30% of the BOD in filamentous form, making it difficult for the micro-animals to prey, resulting in a sufficient sludge reduction effect. Because there is no.

  Although the organic wastewater amount varies with time, HRT is the treatment tank volume (L) divided by the treated water flow rate (L / h). Bacterial flocculation and filamentation occur, the predation rate in the second biological treatment process is reduced, and the sludge reduction effect is also reduced.

  Therefore, in claim 1, when the amount of organic wastewater is reduced, the amount of water to be treated flowing into the first biological treatment step is made constant by adding a liquid to the organic wastewater supplied to the first biological treatment step. To stabilize the HRT. As this liquid, the treated water which passed through the 2nd biological treatment process like Claim 2 can be used conveniently.

  Moreover, in Claim 3, HRT of a 1st biological treatment process is stabilized by fluctuating the amount of water in the processing tank which performs a 1st biological treatment process according to the fluctuation | variation of the amount of organic waste water.

  As described above, according to the present invention, it is within the range of 0.75 to 1.5 times the standard HRT that achieves the BOD oxidative decomposition rate of 30% or more and less than 100% of the standard organic wastewater. By controlling the HRT of the first biological treatment step, the non-aggregating bacteria produced in the first biological treatment step can be fed to the second biological treatment step without forming filaments or flocs. In the biological treatment process, the fine animal concentration can be stabilized at a high concentration, and a good sludge reduction effect can be obtained.

  The HRT in the first biological treatment process is preferably optimally controlled to be the reference HRT, but generally, within a range of 0.75 to 1.5 times the reference HRT, The effect by this invention can fully be acquired. However, it is preferable that the HRT of the first biological treatment process is controlled within a range of 0.9 to 1.2 times, particularly 0.95 to 1.05 times the reference HRT.

  By the way, when the BOD concentration of the organic waste water greatly fluctuates, according to the present invention, the first biological treatment process is performed within the range of 0.75 to 1.5 times the standard HRT determined for the standard organic waste water. Even if the HRT is controlled, the following problems may occur. That is, when the BOD concentration of the organic wastewater is reduced to 50% or less of the BOD concentration of the reference organic wastewater and then returned to the reference BOD concentration again, in the first biological treatment process, The fluctuation cannot follow, and the remaining BOD that cannot be decomposed in the first biological treatment process flows into the second biological treatment process. The BOD that has flowed into the second biological treatment process is oxidatively decomposed in the second biological treatment process. However, if oxidative decomposition of BOD by bacteria occurs in the second biological treatment process in which a large amount of micro-animals are present, Is known to proliferate in a form that is difficult to prey, as a measure to escape from predation of micro-animals, and bacteria that proliferate in this way are not preyed on by micro-animals, and their degradation relies solely on autolysis As a result, the effect of reducing sludge generation is impaired.

  Therefore, as shown in claim 4, the first biological treatment process is a fluidized bed biological treatment process in which a carrier is added to the treatment tank, whereby the biofilm attached to the carrier is reduced when the load is reduced. It becomes a source of bacteria in the biological treatment process, and when the load returns again, the bacteria can quickly grow and stabilize the BOD removal rate in the first biological treatment process. The above problem due to concentration fluctuation can be solved.

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

  1-4 is a systematic diagram showing an embodiment of a biological treatment method for organic wastewater of the present invention. 1-4, 1 is a first biological treatment tank, 2 is a second biological treatment tank, 3 is a sedimentation tank, 4 is a flow meter, 5 is a regulating tank, 5A is a raw water storage tank, 5B is a treated water tank, and 6 is raw water. A pump, 7 is a water level adjusting pump, 8 is a carrier separation screen, and 9 is a carrier.

In any of the methods, raw water (organic wastewater) is first introduced into the first biological treatment tank (dispersed bacteria tank) 1, and 70% or more, preferably 80%, of BOD (organic component) due to non-aggregating bacteria. More preferably, 90% or more is oxidatively decomposed. The pH of the first biological treatment tank 1 is 6 or more, preferably pH 6-8. Moreover, the BOD volumetric load to the 1st biological treatment tank 1 is 1 kg / m < ³ > / d or more, for example, 1-20 kg / m < ³ > / d, HRT (raw water residence time) is 24 h or less, for example, the range of 0.5-24 h Thus, by setting it within the range of 0.75 to 1.5 times the standard HRT determined in advance by the method described later, it is possible to obtain treated water in which non-aggregating bacteria predominate, and shorten the HRT. By doing so, wastewater having a low BOD concentration can be treated with a high load, which is preferable.

  The treated water in the first biological treatment tank 1 is introduced into the second biological treatment tank (micro animal tank) 2 where the remaining organic components are oxidatively decomposed, self-degraded by non-aggregating bacteria, and by the micro animals. Sludge reduction by predation is performed. The second biological treatment tank 2 performs the treatment under the condition of pH 6 or more, preferably pH 6-8.

  The treated water in the second biological treatment tank 2 is solid-liquid separated in the precipitation tank 3, and the separated water is discharged out of the system as treated water. A part of the separated sludge is discharged out of the system as surplus sludge, and the remaining part is returned to the second biological treatment tank 2. In addition, this sludge return is performed in order to maintain the amount of sludge in each biological treatment tank. For example, the first biological treatment tank 1 and / or the second biological treatment tank 2 is loaded with a carrier as described later. In the case of an added fluidized bed type, sludge return may not be necessary. When the BOD volumetric load of the first biological treatment tank 1 is low, the sludge return may be only the second biological treatment tank 2 as shown in the figure, but the sludge return may be performed in the first biological treatment tank 1, You may go to both the 1st biological treatment tank 1 and the 2nd biological treatment tank 2. Moreover, a 3rd biological treatment tank may be provided, the sludge extracted from the 2nd biological treatment tank or the sedimentation tank may be processed, and it may reduce further. The sludge extracted from here may be returned to the first and / or second biological treatment tank as it is, or may be solid-liquid separated and treated as surplus sludge. In that case, part or all of the desorbed liquid may be returned to the first and / or second biological treatment tank. Moreover, a part or all of the solid content may be returned to the first and / or second biological treatment tank, or may be treated as dehydrated sludge. The biological treatment method may be an anaerobic treatment or an aerobic treatment.

  In the present invention, the reference HRT is obtained in advance by a desktop 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 reference HRT.

  As a method of the desktop test for obtaining the standard HRT, the organic waste water to be supplied to the culture tank is continuously supplied and withdrawn at the same speed, and the growth of the bacteria and the dilution of the bacteria by the supply of the organic waste water are balanced. In some cases, the optimum residence time (HRT) is obtained from the wastewater supply speed so that the wastewater BOD remaining at that time is 30% or less, preferably 20% or less, of the initial BOD of the wastewater. In addition to the continuous experiment described above, the decomposition rate of the target wastewater may be obtained from a batch experiment, and the optimum HRT may be obtained from the result. Also, if the wastewater contains many difficult-to-decompose components and the optimum HRT is long or contains many components that have a difference in decomposition speed, the target wastewater is treated in some way, It is desirable to promote the decomposition of HRT so that the organic components in the wastewater can be decomposed by 70% or more, desirably 80% or more in HRT 24h or less, desirably 12h or less. As a method for promoting the decomposition of the hardly decomposable component, any of chemical treatment using chemicals such as acid and alkali, biological treatment using specific bacteria or enzymes, and physical treatment may be used.

  In the present invention, the standard HRT is an HRT required for 70% or more and less than 100% of the BOD of the organic waste water used as a standard to be converted into cells, but preferably 75% or more, particularly 80% of the BOD. It is preferable to set as HRT required for conversion of ˜95% into cells.

  Further, as described above, the HRT of the first biological treatment tank 1 is preferably controlled within a range of 0.9 to 1.2 times, particularly 0.95 to 1.05 times the reference HRT.

  In the method of FIG. 1, the treated water in the sedimentation tank 3 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.

  That is, when the flow rate of raw water is measured with the flow meter 4 and the amount of raw water is insufficient to ensure a predetermined HRT, the shortage is compensated with treated water, and the total amount of raw water and return treated water is The HRT of the first biological treatment tank 1 is controlled within a predetermined range.

  The method shown in FIG. 2 controls the amount of liquid flowing into the first biological treatment tank 1 by the treated water as in the method shown in FIG. 1, but in FIG. 2, the raw water storage tank 5A and the treated water tank 5B Is provided adjacent thereto, and water to be treated is supplied from the adjustment tank 5 to the first biological treatment tank 1 by a raw water pump 6 with a predetermined amount of water. This adjustment tank 5 is provided with a partition wall having a liquid circulation part between both tanks so that the treated water in the treated water tank 5B flows into the raw water storage tank 5A according to the water level of the raw water storage tank 5A. The adjustment tank 5 absorbs the increase / decrease in the amount of water, and feeds raw water or raw water and treated water to the first biological treatment tank 1 with a constant amount of water, thereby maintaining the HRT of the first biological treatment tank 1 within a predetermined range. can do. In the method of FIG. 2, by providing the adjustment tank 5, the flow meter 4 and the treated water return pump (not shown in FIG. 1) in FIG. 1 can be omitted, and the control of the HRT can be simplified.

  In the method shown in FIG. 3, the first biological treatment tank 1 is provided with a water level adjusting pump 7, 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 be long. In this case, the water in the first biological treatment tank 1 is forcibly transferred to the second biological treatment tank 2 by the water level adjusting pump 7 to reduce the apparent water retention amount of the first biological treatment tank 1. Thus, the HRT of the first biological treatment tank 1 is maintained in a predetermined range.

  The method shown in FIG. 4 is the same as the method shown in FIG. 3 except that a carrier separating screen 8 is provided in the first biological treatment tank 1 and a carrier 9 is introduced into the raw water introduction side of the screen 8 and the treated water is discharged from the screen 8 A water level adjustment pump 7 is provided on the side, and the water in the first biological treatment tank 1 is forcibly transferred to the second biological treatment tank 2 by this water level adjustment pump 7 in the same manner as the method shown in FIG. By reducing the apparent water retention amount of the first biological treatment tank 1, the HRT of the first biological treatment tank 1 is maintained within a predetermined range.

  In the method shown in FIG. 4, by introducing the carrier 9 into the first biological treatment tank 1, as described above, the BOD removal rate in the first biological treatment tank 1 is stabilized against fluctuations in the raw water BOD concentration. Can do.

  The addition rate to the first biological treatment tank 1 (hereinafter referred to as “filling ratio in the tank”) is 0.1 to 20%, particularly 1 to 10%, based on the effective volume of the first biological treatment tank 1. In particular, 2 to 5% is preferable. The shape of the carrier to be added is arbitrary such as a spherical shape, a pellet shape, a hollow cylindrical shape, a thread shape, and the size may be about 0.1 to 10 mm. The material of the carrier is arbitrary such as a natural material, an inorganic material, or a polymer material, and a gel material may be used.

  It goes without saying that the carrier may be added to the first biological treatment tank 1 in the method shown in FIGS. When adopting a configuration in which the water in the first biological treatment tank 1 is transferred to the second biological treatment tank 2 by the water level adjusting pump 7, the water reaches the bottom of the first biological treatment tank 1 as shown in FIG. It is necessary to provide a carrier separating screen 8. In this case, the biofilm peeled off from the carrier is the screen 8, that is, the SS is prevented from flowing out, and the sludge residence time is prevented from becoming long. The carrier 9 to be added preferably has a diameter of 5 mm or more.

  The method shown in FIGS. 1 to 4 is an example of an embodiment of the present invention, and the present invention is not limited to the illustrated method unless it exceeds the gist. For example, as the liquid added to the raw water for HRT control, industrial water, well water, city water, river water, and the like may be used in addition to the treated water, but preferably treated water is used.

  Further, the carrier may be added not only to the first biological treatment tank 1 but also to the second biological treatment tank 2. Moreover, the 1st biological treatment tank 1 and the 2nd biological treatment tank 2 are good also as a multistage process which has arrange | positioned the biological treatment tank of 2 or more tanks in series, and is as membrane separation type | formula activated sludge process which immersed the separation membrane in the tank. Also good.

  By the way, the activity of bacteria, that is, the BOD resolution, increases as the temperature increases and decreases as the temperature decreases. That is, the HRT of the first biological treatment tank required to obtain a predetermined BOD oxidative degradation rate becomes shorter when the temperature becomes higher and becomes longer when the temperature becomes lower. Therefore, for raw water that has a temperature change of 5 ° C or higher with respect to the temperature at which the temperature of the raw water is the reference, the optimal HRT change due to the temperature is confirmed in advance from a desktop test. Is set in advance, and the HRT of the first biological treatment tank is within a range of 0.75 to 1.5 times, particularly 0.9 to 1.2 times, especially 0.95 to the reference HRT with respect to the reference HRT. It is preferable to control within a range of 1.05 times.

  Similarly, when the BOD concentration change of the raw water greatly fluctuates with respect to the reference BOD concentration, a reference HRT based on the BOD concentration fluctuation is set in advance, and the first biological treatment tank is set with respect to the reference HRT. Is preferably controlled within a range of 0.75 to 1.5 times, particularly 0.9 to 1.2 times, particularly 0.95 to 1.05 times the reference HRT.

  Thus, according to the biological wastewater treatment method of the present invention for controlling the HRT of the first biological treatment tank 1 within a predetermined range, the density of micro animals in the second biological treatment tank 2 is increased, The proportion of minute animals occupying the inner SS is maintained at 10% or more, and as is clear from the results of Examples described later, a sludge reduction effect of 50% or more can be stably obtained as compared with the standard activated sludge method.

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

Example 1
Using an experimental apparatus in which an activated sludge tank with a capacity of 3.6 L (no sludge return) is connected as the first biological treatment tank 1 and an activated sludge tank with a capacity of 15 L is connected as the second biological treatment tank 2, the book shown in FIG. The organic wastewater was treated by the method of the invention. The pH of the first biological treatment tank 1 was adjusted to 6.8, and the pH of the second biological treatment tank 2 was adjusted to 6.8. The soluble BOD volumetric load on the first biological treatment tank 1 is 3.85 kg-BOD / m ³ / d, HRT4h, and the soluble BOD sludge load on the second biological treatment tank 2 is 0.022 kg-BOD / kg-SS / d, HRT17h, overall BOD volumetric load 0.75kg-BOD / m ³ / d, HRT21h. The experiment was conducted in a constant temperature room at 20 ° C. As a result, the sludge conversion rate was 0.18 kg-SS / kg-BOD. In addition, HRT of the 1st biological treatment tank 1 required in order to oxidatively decompose 75% of BOD in raw | natural water previously calculated | required by the desktop test is 4 h.

  1 month after the start of operation, the operation is continued for 12 hours under the same conditions as above, and thereafter the substrate flow rate is reduced to half and the reduced amount of water is supplemented with treated water (BOD volumetric load is halved during this time) alternately for 12 hours. As a result of repeated tests (load fluctuation operation), the HRT of the first biological treatment tank 1 was maintained at about 4 h, and the bacteria in the first biological treatment tank 1 were also maintained in a dispersed state. However, the concentration of the dispersal bacteria decreased when the load was reduced to half, the re-growth of the dispersal bacteria was not in time when the load was recovered, and the organic matter in the wastewater was not decomposed, which sometimes flowed into the second biological treatment tank 2. Therefore, the sludge conversion rate slightly increased to 0.28 kg-SS / kg-BOD.

  In the second biological treatment tank 2 during the operation period, the rotifer predominates, the number of micro-animals before the load fluctuation operation was 55,000-70000 / ml, and the proportion of SS in the tank was 20%. After the start of operation, the number of micro animals remained at about 30,000 / ml.

Example 2
The same conditions as in Example 1 except that a sponge having a particle size of 5 mm was added to the first biological treatment tank 1 at a filling rate of 5% in the tank, and the fluidized bed activated sludge treatment was performed in the first biological treatment tank. I drove in.

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

  During the operation period, both before and after the high load fluctuation, the stag beetle predominates in the second biological treatment tank 2, the number of micro-animals is 55000-70000 / ml, and the proportion of SS in the tank is 20%. .

Comparative Example 1
In Example 1, the 1st biological treatment tank was abbreviate | omitted and it processed using the experimental apparatus which consists only of a 15L capacity | capacitance 2nd biological treatment tank. The experiment was conducted in a constant temperature room at 20 ° C., and the continuous load operation was performed for 1 month under the conditions of soluble BOD volume load of 0.76 kg-BOD / m ³ / d and HRT20h. It became 0.40 kg-SS / kg-BOD.

  Further, in the same manner as in Example 1, every 12 h, the operation in which the substrate flow rate was reduced to half (the BOD volumetric load was halved during this time) was repeated alternately for 12 h. It was 0.40 kg-SS / kg-BOD. During the operation period, in the activated sludge tank, stag beetles were observed at 3000 / ml and vertebrate beetles were observed at 10,000 / ml, but the proportion of micro animals in the SS was always 5% or less.

Comparative Example 2
After the load fluctuation operation, the operation was performed under the same conditions as in Example 1 except that the treated water was not returned when the substrate flow rate was reduced to half.

  As a result, the sludge conversion rate was 0.18 kg-SS / kg-BOD as in Example 1 before the load fluctuation operation, but in the first biological treatment tank 1 after the load fluctuation operation was started, the dispersion state was reached. Of the filamentous bacteria (length: 50 to 1000 μm), and in the second biological treatment tank 2, the rotifer that prevailed before the load was varied decreased from 50000 / ml to 0 / ml, The sludge conversion rate also increased to 0.34 kg-SS / kg-BOD.

  In the above Examples 1 and 2 and Comparative Examples 1 and 2, the relationship between the surplus sludge generation amount (generated VSS: sludge conversion rate) with respect to the input BOD amount before the load fluctuation operation is shown in FIG. FIG. 6 shows the relationship between the excess sludge generation amount (generated VSS: sludge conversion rate) with respect to the input BOD amount.

  5 and 6, the multistage activated sludge method using the predation action of micro animals can obtain a higher sludge reduction effect regardless of before and after the load fluctuation, but in the treatment by the multistage activated sludge method, the present invention In accordance with the above, by maintaining the HRT of the first biological treatment tank within a predetermined range, and further by adding the carrier to the first biological treatment tank and performing the fluidized bed type activated sludge treatment, it is stable despite fluctuations in load. It can be seen that a sludge reduction effect can be obtained.

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

It is a systematic diagram which shows embodiment of the biological treatment method of the organic waste water of this invention. It is a systematic diagram which shows other embodiment of the biological treatment method of the organic waste water of this invention. It is a systematic diagram which shows another embodiment of the biological treatment method of the organic waste water of this invention. It is a systematic diagram which shows different embodiment of the biological treatment method of the organic waste water of this invention. It is a graph which shows the relationship (before load fluctuation) of the amount of input BOD and the amount of surplus sludge generation in Examples 1 and 2 and Comparative Examples 1 and 2. It is a graph which shows the relationship (after load fluctuation) between the amount of input BOD and the amount of surplus sludge generation in Examples 1 and 2 and Comparative Examples 1 and 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st biological treatment tank 2 2nd biological treatment tank 3 Precipitation tank 4 Flowmeter 5 Adjustment tank 5A Raw water storage tank 5B Treated water tank 6 Raw water pump 7 Pump for adjusting water level 8 Screen for carrier separation 9 Carrier

Claims (4)

A first biological treatment process for converting BOD in organic wastewater into cells by high-load treatment;
In a biological treatment method for organic wastewater, comprising a second biological treatment step in which the transformed bacterial cells coexist with microanimals that prey on the bacterial cells,
The hydraulic residence time (HRT) in the first biological treatment process required to convert 70% or more and less than 100% of the BOD in the organic waste water serving as a reference to cells is obtained, and this value is used as a reference. HRT,
Adding a liquid to the organic wastewater introduced into the first biological treatment step so that the HRT in the first biological treatment step is in the range of 0.75 to 1.5 times the reference HRT. A biological treatment method for organic wastewater.   2. The organic wastewater biological treatment method according to claim 1, wherein the liquid is treated water that has undergone the second biological treatment step. A first biological treatment process for converting BOD in organic wastewater into cells by high-load treatment;
In a biological treatment method for organic wastewater, comprising a second biological treatment step in which the transformed bacterial cells coexist with a micro animal that prey on the bacterial cells,
The hydraulic residence time (HRT) in the first biological treatment process required to convert 70% or more and less than 100% of the BOD in the organic waste water serving as a reference to cells is obtained, and this value is used as a reference. HRT,
The amount of water in the treatment tank in which the first biological treatment process is performed is varied so that the HRT in the first biological treatment process is in a range of 0.75 to 1.5 times the reference HRT. Biological treatment method for organic wastewater.   The biological treatment method for organic wastewater according to any one of claims 1 to 3, wherein the first biological treatment step is a fluidized bed biological treatment step in which a carrier is added to a treatment tank. Biological treatment method for organic wastewater.

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