JP2005125170A - Method for restraining generation of excess sludge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for restraining the generation of excess sludge, which can be executed effectively at a low cost without causing such a problem of the conventional method when organic waste water is treated biologically that the quality of the treated water is deteriorated, the load to be imposed on a biological treatment tank is increased and the equipment cost is expensive. <P>SOLUTION: This method for restraining the generation of excess sludge comprises a step to bring a biodegradable plastic into contact with the sludge in an aerobic microbe treatment tank or a precipitation tank when organic waste water is treated in the aerobic microbe treatment tank. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for suppressing the generation of excess sludge in a method of biologically treating organic wastewater flowing out from sewage or a factory with activated sludge.

  Organic wastewater such as sewage and industrial wastewater is treated by biological treatment such as activated sludge, but surplus sludge mainly composed of microorganisms grown at that time is generated. This excess sludge is said to occupy about half of industrial waste, but it is an urgent task to reduce sludge because the landfill site is tight.

  In recent years, as a method of reducing excess sludge generated from biological treatment, sludge is solubilized by means of ozone, oxidant, ultrasonic, mechanical crushing, etc., and then returned to the biological treatment tank for mineralization. A technique for reducing the number has been put into practical use.

  However, in the method of mineralizing in the biological treatment tank after solubilization of the sludge, the sludge solubilization equipment cost is high and the running cost is high, and if the load of the existing biological treatment tank is not enough, the sludge reduction treatment equipment is introduced. The problem is that the quality of biologically treated water (COD, nitrogen, phosphorus, etc.) is deteriorated.

  On the other hand, recently, it has become clear that biodegradable solid materials can be used in place of methanol as a hydrogen donor for nitrogen-containing wastewater, and there are several examples of reports as hydrogen donors for denitrification of nitrogen-containing wastewater. There is. For example, Patent Document 1 describes that a biodegradable plastic can be used as a hydrogen donor when an organic wastewater containing nitrogen is denitrified by anaerobic treatment and aerobic treatment.

  Regarding denitrification treatment, Patent Document 2 describes that a solid denitrification accelerator mainly composed of a carboxylic acid having 6 or more carbon atoms can be used for aerobic biological treatment of organic wastewater.

However, Patent Document 1 and Patent Document 2 both describe techniques for denitrification treatment of nitrogen-containing wastewater. Conventionally, in a method of treating organic wastewater by aerobic biological treatment, it occurs in biological treatment by bringing biodegradable plastic into contact with sludge in an aerobic biological treatment tank or solid-liquid separated in a sedimentation tank. There are no reports that suggest controlling excess sludge.
JP 2000-153293 A Japanese Patent No. 3298562

  Therefore, the object of the present invention is to pay attention to the suppression of excess sludge in the biological treatment of organic wastewater, and in the conventional method in which the above sludge is solubilized and then mineralized in the biological treatment tank, An object of the present invention is to provide a surplus sludge generation suppression method that can be carried out effectively and inexpensively without problems such as an increase in load on the treatment tank, initial cost, and high running cost.

  The inventors of the present invention, when proceeding with the examination and experiment on the aerobic biological treatment, do not pay attention to denitrification treatment as in the conventional method, but pay attention to the reduction of excess sludge and activate the biodegradable plastic. As a result of advancing sludge experiments, it was found that the amount of sludge generated in a system charged with biodegradable plastic can be extremely reduced, and the present invention has been completed. As described above, conventionally, biodegradable plastics have been used as a hydrogen donor for denitrification, but there is no suggestion or report regarding the use of biodegradable plastics to reduce or suppress the generation of excess sludge. . Therefore, the present invention is very valuable as a new application of biodegradable plastics.

  That is, in order to solve the above-mentioned problem, the method for suppressing the generation of surplus sludge according to the present invention is a method for treating organic wastewater in an aerobic biological treatment tank, with respect to sludge present in the aerobic biological treatment tank. The method comprises contacting a biodegradable plastic.

  As the aerobic biological treatment, any of activated sludge, catalytic oxidation, fixed bed type and fluidized bed type biological treatment can be applied. At this time, it is preferable that the biodegradable plastic and the sludge are brought into contact with each other under an aerobic condition in which the dissolved oxygen concentration in the aerobic biological treatment tank is 3 mg / L or less, preferably 0.5 to 2.5 mg / L. Such aerobic conditions can be controlled by performing aeration.

  In addition, the biodegradable plastic and the sludge are brought into contact with the aerobic biological treatment tank as well as the aerobic biological treatment tank itself. A part of the sludge-containing organic waste water in the tank can be circulated in the reaction tank so that the biodegradable plastic and the sludge are brought into contact with each other in the reaction tank. In the latter case, the biodegradable plastic is preferably brought into contact with sludge under a condition where the dissolved oxygen concentration in the reaction tank is 1 mg / L or less. The conditions in the reaction tank are either aerobic or anaerobic. Is also possible. In general, an aerobic condition is assumed when the dissolved oxygen concentration is 0.1 mg / L or more.

  The surplus sludge generation suppressing method according to the present invention is a method of treating organic wastewater in an aerobic biological treatment tank and a sedimentation tank, wherein at least a part of the sludge separated into solid and liquid in the sedimentation tank is biodegradable plastic. The method characterized by making it contact with. In other words, it is possible to react sludge and biodegradable plastics under conditions where the dissolved oxygen concentration is lower when the biodegradable plastic is brought into contact with sludge that has been solid-liquid separated in the sedimentation tank. It becomes possible to suppress more efficiently.

  Also in this case, it is preferable to contact the biodegradable plastic and the sludge under a condition where the dissolved oxygen concentration is 1 mg / L or less, and the conditions for the contact reaction can be either aerobic or anaerobic.

  The biodegradable plastic and sludge can be brought into contact with the biodegradable plastic in the settling tank and at least one of the sludge solid-liquid separated in the settling tank itself. It is also possible to pull out the part into the reaction tank and bring the biodegradable plastic and sludge into contact in the reaction tank.

  In the surplus sludge generation suppression method according to the present invention as described above, the sludge that has come into contact with the biodegradable plastic can be returned to the aerobic biological treatment tank. Therefore, for example, in the embodiment in which the settling tank is provided, the sludge that has been contact-reacted with the biodegradable plastic in the settling tank is returned to the aerobic biological treatment tank or is solid-liquid separated in the return line in the settling tank. It is possible to provide a reaction tank for extracting at least a part of the sludge, and return the sludge contacted and reacted with the biodegradable plastic in the reaction tank to the aerobic biological treatment tank.

  Further, the pH in the tank where the biodegradable plastic and the sludge are contacted is preferably in the range of 6 to 9, and preferably in the range of 6.5 to 8. In particular, when the pH is 5 or less, there is a possibility that a remarkable effect may not be confirmed.

  In addition, the water temperature at the time of contact between the biodegradable plastic and the sludge is not particularly limited, but in order to more reliably obtain the effect of suppressing the generation of excess sludge, the water temperature is 15 to 40 ° C, preferably 20 to 30 ° C. It is desirable to make the contact between the functional plastic and sludge.

  The biodegradable plastic used in the present invention is not particularly limited, but from the viewpoint of cost and efficiency, as a raw material of the biodegradable plastic, polyhydroxybutyrate, a copolymer of polyhydroxybutyrate and polyhydroxyvalylate, It is preferable to use any one of polybutylene succinate, polycaprolactone, and polylactic acid.

  In such a method for suppressing the generation of excess sludge according to the present invention, the detailed mechanism for suppressing the generation of excess sludge is not yet elucidated, but the fungus having a low cell conversion rate due to the addition of biodegradable plastics. It is assumed that the effect will be obtained by the action of transitioning to the above, or by promoting catabolism or autooxidation accompanying the improvement of the denitrification rate.

  According to the surplus sludge generation suppression method according to the present invention, it is possible to suppress the generation of surplus sludge by simply putting biodegradable plastic into an appropriate place and bringing it into contact with the sludge under appropriate conditions. Sludge can be reduced simply by putting biodegradable plastic into existing biological treatment equipment, the introduction equipment cost (initial cost) and running cost in conventional sludge solubilization treatment are high, and the load on the biological treatment tank is high. Excess sludge effectively and inexpensively without problems such as the fact that the equipment cannot be introduced unless there is a margin in the load of the existing biological treatment tank due to the rise and the quality of biological treatment water (COD, nitrogen, etc.) deteriorates Can be suppressed. In particular, in relatively small factories, etc., when it is necessary to reduce sludge but the equipment cost is high and the equipment cannot be installed, there is a COD total amount regulation and the equipment cannot be introduced, and there is no allowance for the existing biological treatment BOD load. It is possible to provide an effective sludge reduction method for cases where the apparatus cannot be introduced, and the utility of the present invention is extremely high.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a schematic configuration of a sludge treatment system for carrying out a surplus sludge generation suppressing method according to an embodiment of the present invention. In the sludge treatment system 1 according to the present embodiment, organic waste water as raw water is sent to the aerobic biological treatment tank 3 by the pump 2, and the aerobic biological treatment tank 3 is aerated by supplying air from the blower 4. Aeration is performed using 5 and biological treatment is performed. The sludge-containing wastewater from the aerobic biological treatment tank 3 is sent to the precipitation tank 6 for solid-liquid separation, and the separated water is discharged as treated water or sent to a predetermined destination. The sludge subjected to solid-liquid separation is returned to the aerobic biological treatment tank 3 via the pump 7. Usually, the precipitated sludge separated into solid and liquid in the sedimentation tank 6 (concentration of activated sludge: about 6,000 to 15,000 mg / L as MLSS) is returned to the biological treatment tank 3, and the sludge concentration in the biological treatment tank 3 is The MLSS is maintained at about 2,000 to 6,000 mg / L. However, when the organic matter in the raw water is biologically treated, surplus sludge is generated due to the growth of the bacterial cells, and the concentration is adjusted to be constant while extracting the sludge. The configuration so far is not different from the conventional method. Therefore, the sludge treatment system 100 according to the conventional method is as shown in FIG.

  In the sludge treatment system 1 by the surplus sludge generation suppressing method according to an embodiment of the present invention, as shown in FIG. 1, at least a part of the precipitated sludge separated in the solid-liquid separation in the settling tank 6 is supplied via a pump 8. After being sent to the reaction tank 9 and in contact with the biodegradable plastic 10 (for example, polycaprolactan) in the reaction tank 9, it is returned to the aerobic biological treatment tank 3 as an aeration tank. The biodegradable plastic reaction tank 9 is provided with a stirrer 11 in order to promote contact between the sludge and the biodegradable plastic 10. The reaction time between the sludge and the biodegradable plastic 10 is 5 minutes or longer, preferably about 30 minutes to 6 hours. The reaction pH is 6 to 9, preferably 6.5 to 8.5. The dissolved oxygen concentration in the reaction tank 9 is 1 mg / L or less, preferably 0.5 mg / L or less. Further, the input amount of the biodegradable plastic 10 is preferably about 0.5 to 2 times the MLSS concentration in the reaction tank 9.

  The experimental data in the process in the sludge processing system 1 by this invention shown in FIG. 1 are shown. The conditions of the biological treatment tank 3 were as follows: MLSS was 3,000 mg / L, dissolved oxygen concentration was 1.5 mg / L, and pH was 7. Raw water consisting of organic wastewater having a BOD of 400 mg / L was supplied to the biological treatment tank 3 having a capacity of 25 L at a flow rate of 1.3 L / hr. In addition, the biodegradable plastic reaction vessel 9 was prepared under the conditions of a sludge concentration of 12 g / L, a polycaprolactan input amount of 24 g / L, a reaction time of 4 hours, a dissolved oxygen concentration of 0.5 mg / L, and a pH of 7 It was set to ~ 8. In order to confirm the denitrification reaction, FIG. 2 shows the change in nitric acid concentration in the biodegradable plastic reaction tank 9. After the start of this test, the denitrification activity was gradually recognized, and after 30 days, the nitric acid at the outlet of the reaction tank 9 became 0.5 mg / L or less, and the denitrification reaction was performed using the biodegradable plastic 10 as a carbon source. It can be seen that is progressing. However, the progress of the denitrification reaction and the progress of the sludge reduction focused in the present invention are out of timing. FIG. 3 shows changes in the amount of sludge generated when the present invention is carried out according to the conventional method and the above test. In the present invention, it was confirmed that the increase rate of sludge began to decrease after 3 weeks from the start of water flow, and after that about 50% of the sludge was reduced. Since this difference becomes a reduction amount of the excess sludge discharged outside the system, it was confirmed that the generation amount of the excess sludge was greatly suppressed by the present invention. Although the detailed mechanism regarding this inhibitory effect has not been elucidated, the addition of biodegradable plastics has shifted to a microflora with a low cell conversion rate, and the effect is enhanced by the catabolism reaction and autooxidation promotion effect accompanying the improvement of the denitrification rate. Estimated. However, as described above, the suppression of excess sludge generation according to the present invention is different from the denitrification reaction itself, and the generation suppression timing is considerably shifted (substantially delayed) from the denitrification reaction. . Therefore, even if the denitrification reaction contributes to the reduction of sludge generation, it is estimated that it is only one factor among the complex factors.

  In this invention, various aspects can be taken regarding the input place of biodegradable plastics. FIG. 4 shows another embodiment of the present invention. In the present embodiment, the biodegradable plastic 10 is suspended in the sedimentation tank 6 and the biodegradable plastic 10 is brought into contact with the concentrated sludge in the sedimentation tank 6 that has been subjected to solid-liquid separation. The structure to implement is shown.

  FIG. 5 shows still another embodiment of the present invention. The biodegradable plastic 10 is put into the aerobic biological treatment tank 3 as a tank, and the dissolved oxygen concentration is adjusted to 3 mg / L or less, preferably 0.5 to 1 mg / L, and the present invention is carried out. You can also.

  FIG. 6 shows still another embodiment of the present invention. A part of the sludge is pulled out from the aerobic biological treatment tank 3 as an aeration tank, introduced into the reaction tank 12 and reacted with the biodegradable plastic 10 introduced therein, and then returned to the aeration tank. Thus, the present invention can be implemented. At this time, it is preferable to adjust the dissolved oxygen concentration of the biodegradable plastic reaction tank 12 to 1 mg / L or less, preferably 0.5 mg / L or less, and to carry out the present invention.

  The method for suppressing the generation of excess sludge according to the present invention can be applied to all uses for biological treatment of organic wastewater, greatly reducing the amount of sludge discharged outside the system, and reducing the treatment cost as well as the environmental load. It can also contribute greatly to the reduction of

It is a schematic block diagram of the sludge processing system by the generation | occurrence | production suppression method of the excess sludge which concerns on one embodiment of this invention. It is a characteristic view which shows an example of nitric acid concentration change by the system of FIG. It is a comparative characteristic view of the sludge generation amount by the system of FIG. 1 and the sludge generation amount by the conventional method. It is a schematic block diagram of the sludge processing system by the generation | occurrence | production suppression method of the excess sludge which concerns on another embodiment of this invention. It is a schematic block diagram of the sludge treatment system by the generation | occurrence | production suppression method of the excess sludge which concerns on another embodiment of this invention. It is a schematic block diagram of the sludge treatment system by the generation | occurrence | production suppression method of the excess sludge which concerns on another embodiment of this invention. It is a schematic block diagram of the sludge processing system by the conventional method.

Explanation of symbols

1 Sludge treatment system 2, 7, 8 Pump 3 Aerobic biological treatment tank 4 Blower 5 Aeration means 6 Sedimentation tank 9, 12 Biodegradable plastic reaction tank 10 Biodegradable plastic 11 Stirrer

Claims (10)

  In a method for treating organic wastewater in an aerobic biological treatment tank, a method for suppressing the generation of surplus sludge, wherein biodegradable plastic is brought into contact with sludge present in the aerobic biological treatment tank.   The method for suppressing the generation of excess sludge according to claim 1, wherein the biodegradable plastic and sludge are brought into contact under aerobic conditions where the dissolved oxygen concentration in the aerobic biological treatment tank is 3 mg / L or less.   The surplus sludge generation suppression method according to claim 1, wherein a part of the sludge-containing organic waste water in the aerobic biological treatment tank is circulated to the reaction tank, and the biodegradable plastic and the sludge are contacted in the reaction tank.   The surplus sludge generation suppressing method according to claim 3, wherein the biodegradable plastic and the sludge are brought into contact with each other under a condition that the dissolved oxygen concentration in the reaction tank is 1 mg / L or less.   In a method of treating organic wastewater in an aerobic biological treatment tank and a sedimentation tank, a method for suppressing the generation of excess sludge, wherein at least a part of the sludge separated into solid and liquid in the precipitation tank is brought into contact with a biodegradable plastic .   The method for suppressing the generation of excess sludge according to claim 5, wherein the biodegradable plastic and the sludge are brought into contact under a condition where the dissolved oxygen concentration is 1 mg / L or less.   The method for suppressing the generation of excess sludge according to claim 5 or 6, wherein at least part of the sludge solid-liquid separated in the sedimentation tank is drawn into the reaction tank, and the biodegradable plastic and the sludge are contacted in the reaction tank.   The generation | occurrence | production suppression method of the excess sludge in any one of Claims 1-7 which returns the sludge contacted with the biodegradable plastic to the said aerobic biological treatment tank.   The generation | occurrence | production suppression method of the excess sludge in any one of Claims 1-8 which makes pH in the tank with which biodegradable plastic and sludge contact 6-9.   Any one of polyhydroxybutyrate, a copolymer of polyhydroxybutyrate and polyhydroxyvalylate, polybutylene succinate, polycaprolactone, and polylactic acid is used as a biodegradable plastic material. The surplus sludge generation | occurrence | production suppression method of crab.

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