Method for acclimatizing activated sludge in nitrification-denitrification treatment, method for treating organic wastewater, and apparatus for treating organic wastewater

Abstract

To provide a method for acclimatizing active sludge, a method for treating organic wastewater, and a device for treating organic wastewater, in nitrification and denitrification treatment which can suppress a decline in nitrification and denitrification performance due to changes in the properties of inflow raw water and suppress a deterioration of a quality of treated water.SOLUTION: There is provided a method for acclimatizing active sludge in nitrification and denitrification treatment having a nitrification and denitrification treatment process of nitrifying and denitrifying first organic wastewater containing ammonia nitrogen in a treatment tank 10 housing active sludge. The method for acclimatizing active sludge further has a process of acclimatizing active sludge by supplying a BOD source from outside into the treatment tank 10 before second organic wastewater where insufficient denitrification treatment may occur under conditions where the first organic wastewater is subjected to the nitrification and denitrification treatment is supplied into the treatment tank 10, in the nitrification and denitrification treatment process.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for acclimating activated sludge in nitrification / denitrification treatment, a method for treating organic wastewater, and an apparatus for treating organic wastewater. [Background technology]

[0002] Nitrification and denitrification using activated sludge is widely used to treat organic wastewater containing ammonia nitrogen. Among these, standard denitrification methods, which treat sludge-free human waste, have been widely used in night soil treatment plants. However, the pre-dehydration method has become the mainstream method for night soil treatment, and there are increasing cases of replacing the standard denitrification method with the pre-dehydration method.

[0003] The separated liquid from the pre-dehydration method has a lower BOD concentration than the sludge-removed sewage, and the ratio of nitrogen concentration to BOD concentration is significantly higher. As a result, there is a BOD deficiency in the denitrification process, and the treatment cannot be carried out sufficiently. Therefore, a BOD source is added to the denitrification process to supplement the BOD required for denitrification using activated sludge.

[0004] However, depending on the type of BOD source added, it may be difficult to use it for denitrification, and activated sludge may need to be acclimatized. For example, it has been reported that it takes about two weeks for activated sludge to be able to use methanol as a BOD for denitrification, and about one month for it to exhibit high denitrification capacity (see, for example, Non-Patent Document 1).

[0005] In sewage treatment plants, for example, when upgrading from a standard denitrification method to a pre-dehydration method, the amount of methanol added may be increased to compensate for a lack of BOD sources for denitrification due to a decrease in the BOD concentration of the raw water, but the denitrification process using activated sludge may temporarily be insufficient because the activated sludge has not been acclimatized to methanol, making it difficult to comply with water quality standards. Furthermore, if the added methanol is not fully utilized by the denitrification reaction of the activated sludge immediately after the upgrade work, the methanol may remain in the treated water and flow out of the sewage treatment plant, potentially causing a pollution load at the discharge destination.

[0006] This phenomenon can occur when upgrading to a pre-dehydration method or when applying methane fermentation. In other words, methane fermentation removes BOD sources but not ammonia nitrogen, so in the subsequent nitrification / denitrification treatment, an external BOD source must be added to denitrify the ammonia nitrogen. [Prior art documents] [Non-patent literature]

[0007] [Non-Patent Document 1] Hallin S., Rothman M. and Pell M. (1996) Adaptation of denitrifying bacteria to acetate and methanol in activated sludge. Water Research Vol. 30 No. 6 pp.1445-1450 Summary of the Invention [Problem to be solved by the invention]

[0008] In view of the above problems, the present invention provides a method for acclimating activated sludge in a nitrification / denitrification treatment, a method for treating organic wastewater, and an apparatus for treating organic wastewater, which can suppress a decrease in nitrification / denitrification performance due to changes in the properties of influent raw water and suppress deterioration of the water quality of the treated water. [Means for solving the problem]

[0009] As a result of extensive research conducted by the present inventors to solve the above problems, they found that it is effective to supply a BOD source from outside into the treatment tank before new organic wastewater, which may cause insufficient denitrification under the conditions of nitrification-denitrification treatment of the organic wastewater being treated, is supplied to the treatment tank.

[0010] One aspect of the present disclosure, which has been completed based on the above findings, is a method for acclimatizing activated sludge in nitrification / denitrification treatment, which includes a nitrification / denitrification treatment step of nitrifying / denitrifying a first organic wastewater containing ammonia nitrogen in a treatment tank containing activated sludge, and a step of supplying a BOD source from outside into the treatment tank to acclimate the activated sludge in the nitrification / denitrification treatment step before supplying into the treatment tank a second organic wastewater that may be insufficiently denitrified under the conditions for nitrification / denitrification of the first organic wastewater.

[0011] In one embodiment of the method for acclimatizing activated sludge in nitrification / denitrification treatment according to the present invention, methanol is supplied as a BOD source.

[0012] In another embodiment of the activated sludge acclimation method for nitrification-denitrification treatment according to the present invention, a BOD source is supplied into the treatment tank 2 to 6 weeks before the second organic wastewater is supplied into the treatment tank in the nitrification-denitrification treatment step.

[0013] In another embodiment, the method for acclimatizing activated sludge in nitrification / denitrification treatment according to the present invention includes lowering the MLSS concentration in the treatment tank below that during steady operation before supplying a BOD source to the treatment tank.

[0014] In yet another embodiment of the method for acclimatizing activated sludge in nitrification-denitrification treatment according to the present invention, the nitrification-denitrification treatment step comprises a denitrification treatment step of denitrifying the first organic wastewater and the second organic wastewater, and a nitrification treatment step of nitrifying the denitrification-treated water obtained in the denitrification treatment step, and a BOD source is supplied in the denitrification treatment step.

[0015] In yet another embodiment of the method for acclimatizing activated sludge in nitrification-denitrification treatment according to the present invention, the nitrification-denitrification treatment step comprises an upstream nitrification-denitrification treatment step and a downstream nitrification-denitrification treatment step, and includes a step of supplying a BOD source from outside in advance in the downstream nitrification-denitrification treatment step to acclimate the activated sludge before the second organic wastewater is supplied to the upstream nitrification-denitrification treatment step, and returning the treated sludge obtained by solid-liquid separation of the nitrification-treated water from the downstream nitrification-denitrification treatment step to the upstream nitrification-denitrification treatment step.

[0016] In another aspect, the present invention provides a method for treating organic wastewater, comprising: a first nitrification-denitrification treatment step of nitrifying and denitrifying a first organic wastewater containing ammonia nitrogen in a treatment tank containing activated sludge; and a second nitrification-denitrification treatment step of supplying, after the first nitrification-denitrification treatment step, into the treatment tank second organic wastewater that may be insufficiently denitrified under the conditions for nitrification-denitrification treatment of the first organic wastewater, and nitrifying and denitrifying the second organic wastewater, wherein the first nitrification-denitrification treatment step nitrifies and denitrifies the first organic wastewater, and the method further comprises a step of supplying a BOD source from outside into the treatment tank and acclimating activated sludge that can nitrify and denitrify the second organic wastewater.

[0017] In yet another aspect, the present invention provides an organic wastewater treatment apparatus comprising: a denitrification tank for denitrifying first organic wastewater containing ammonia nitrogen; a nitrification tank for nitrifying the denitrified water from the denitrification tank; a solid-liquid separation tank for performing solid-liquid separation on the nitrified water from the nitrification tank; return means for returning sludge separated in the solid-liquid separation tank to a stage upstream of the denitrification tank; BOD source supply means for supplying a BOD source from an external source to the denitrification tank; and BOD control means for controlling the BOD source supply means to increase the BOD source supplied to the denitrification tank from that in a steady state before the second organic wastewater is supplied to the denitrification tank, based on information about the timing at which second organic wastewater, which may be insufficiently denitrified under conditions for nitrification and denitrification of the first organic wastewater, is supplied to the denitrification tank, thereby promoting acclimatization of activated sludge capable of nitrifying and denitrifying the second organic wastewater.

[0018] In yet another aspect, the present invention provides a first denitrification tank for denitrifying first organic wastewater containing ammonia nitrogen, a first nitrification tank for nitrifying the denitrified water from the first denitrification tank, a second denitrification tank for denitrifying the nitrified water from the first nitrification tank, a BOD source supply means for supplying a BOD source from an external source to the second denitrification tank, an aeration tank for aerating the denitrified water from the second denitrification tank, a solid-liquid separation tank for performing solid-liquid separation on the treated water obtained in the aeration tank, and a sludge separated in the solid-liquid separation tank. The organic wastewater treatment device is equipped with a return means for returning the wastewater to the stage preceding the first denitrification tank, and a BOD control means for controlling the rate of addition of the BOD source to the second denitrification tank based on information on the timing at which second organic wastewater, which may be insufficiently denitrified under the conditions for nitrification / denitrification treatment of the first organic wastewater, is supplied to the first denitrification tank, so as to increase the BOD source supplied to the second denitrification tank from that in a steady state and acclimate the second organic wastewater to activated sludge capable of nitrification / denitrification treatment.

[0019] In one embodiment, the organic wastewater treatment device according to the present invention further comprises a return sludge control means for controlling the return means so as to increase the amount of return sludge supplied to the first denitrification tank above a steady-state value before the second organic wastewater is supplied to the first denitrification tank.

[0020] In another embodiment, the organic wastewater treatment device according to the present invention comprises a circulation means for circulating a portion of the nitrification-treated water from the first nitrification tank to the first denitrification tank, and further comprises a circulating water control means for controlling the circulation means so as to reduce the amount of nitrification-treated water circulated to the first denitrification tank via the circulation means below a steady-state value before the second organic wastewater is supplied to the first denitrification tank. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a method for acclimating activated sludge in a nitrification / denitrification treatment, a method for treating organic wastewater, and an apparatus for treating organic wastewater, which can suppress a decrease in nitrification / denitrification performance due to changes in the properties of influent raw water and suppress deterioration of the water quality of the treated water. [Brief explanation of the drawings]

[0022] [Figure 1]1 is a schematic diagram showing an example of an organic wastewater treatment device according to a first embodiment, which utilizes a standard denitrification treatment method. [Figure 2] 1 is a schematic diagram showing an example of an organic wastewater treatment device according to a first embodiment that utilizes a pre-dehydration method. [Figure 3] FIG. 10 is a schematic diagram showing an example of an organic wastewater treatment device according to a second embodiment, which utilizes a standard denitrification treatment method. [Figure 4] FIG. 10 is a schematic diagram showing an example of an organic wastewater treatment device according to a second embodiment, in which an anaerobic digestion treatment is incorporated as a pretreatment tank. [Figure 5] 1 is a schematic diagram showing a sewage treatment plant according to an embodiment of the present invention. [Figure 6] 1 is a graph showing an example of the change in effluent TN concentration when the treatment method is switched from a standard denitrification method to a pre-dehydration method. [Figure 7] 1 is a graph showing an example of the simulation results of the transition of the amount of methanol-denitrifying bacteria present in the tank in the denitrification treatments of Example 1 and Comparative Example. [Figure 8] 10 is a graph showing an example of the simulation results of the transition of the amount of methanol-denitrifying bacteria present in the tank in the denitrification treatment of Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0023] Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, identical or similar parts are designated by identical or similar reference numerals. Note that the embodiments shown below are merely examples of devices and methods for embodying the technical concept of the present invention, and the technical concept of the present invention does not limit the structure, arrangement, etc. of component parts to those described below.

[0024] (First embodiment) An example of an organic wastewater treatment apparatus using the standard denitrification treatment method is shown in Figure 1. The organic wastewater treatment apparatus according to the first embodiment of the present invention comprises a denitrification tank 1 for denitrifying organic wastewater, a nitrification tank 2 for nitrifying the denitrified water from the denitrification tank 1, a solid-liquid separation tank 3 for performing solid-liquid separation on the nitrification water from the nitrification tank 2, a return means 4 for returning the sludge separated in the solid-liquid separation tank 3 to the upstream stage of the denitrification tank 1, a BOD source supply means 6 for supplying a BOD source from an external source to the denitrification tank 1, and a control device 7.

[0025] The organic wastewater used is organic wastewater containing ammonia nitrogen and solids. For example, human waste, septic tank sludge, organic sludge, food waste, etc. are used as the organic wastewater, and typically a mixture of human waste and septic tank sludge is used.

[0026] Organic wastewater is supplied into the drum screen 8. Solids in the organic wastewater are removed by rotating the cylindrical filter body provided in the drum screen 8. While FIG. 1 shows an example in which a drum screen 8 is installed, the device is not limited to this as long as it is capable of removing solids in the organic wastewater. For example, a bar screen, a scraper screen, an inclined wire screen, or the like may be installed instead of the drum screen 8.

[0027] The organic wastewater (sewage with residue removed) from which solids have been removed by the drum screen 8 is supplied to an adjustment tank 5 and mixed with the returned sludge returned from the solid-liquid separation tank 3. The organic wastewater contained in the adjustment tank 5 is supplied to a treatment tank 10, which includes a denitrification tank 1 and a nitrification tank 2, for nitrifying and denitrifying the organic wastewater. The nitrification tank 2 contains activated sludge containing nitrifying bacteria for nitrifying the organic wastewater, and nitrification treatment using the activated sludge takes place in the nitrification tank 2. The nitrification-treated water that has undergone nitrification treatment is supplied to a denitrification tank 1 by a circulation means 13. The denitrification tank 1 contains activated sludge containing heterotrophic bacteria for denitrifying the supplied nitrification-treated water, and the activated sludge is used in the denitrification tank 1 to denitrify the nitrate nitrogen in the nitrification-treated water by utilizing the BOD of the influent raw water. The denitrification-treated water that has been denitrified in the denitrification tank 1 is supplied to a nitrification tank 2.

[0028] The nitrified water obtained in the nitrification tank 2 is supplied to a solid-liquid separation tank 3, where it is separated into treated water and treated sludge. A settling tank, for example, is used as the solid-liquid separation tank 3. The treated sludge is returned to the adjustment tank 5 via a return means 4 equipped with a withdrawal pump or the like, and after being mixed with organic wastewater supplied from a drum screen 8, is returned to the denitrification tank 1. A circulation means 13 is provided between the nitrification tank 2 and the denitrification tank 1, for circulating the nitrified water from the nitrification tank 2 to the denitrification tank 1 as circulated water. The amount of circulated water is usually about 10 to 30 times the amount of influent raw water.

[0029] The BOD source supply means 6 adds a BOD source from outside to the denitrification tank 1. Methanol is preferably used as the BOD source. Methanol is highly biodegradable and is quickly utilized by microorganisms in the denitrification reaction. Therefore, by using methanol as a BOD source, nitrogen removal can be performed more efficiently in the denitrification process. Furthermore, methanol is more cost-effective and versatile than other organic substances that can be used as BOD sources.

[0030] The control device 7 is connected to the BOD source supply means 6, the circulation means 13, and the return means 4. By outputting control signals to the BOD source supply means 6, the circulation means 13, and the return means 4, the control device 7 controls the addition rate of the BOD source by the BOD source supply means 6, the start and stop of addition, the circulation flow rate of the circulating water by the circulation means 13, and the supply or stop of the circulating water, and the amount of returned sludge by the return means 4, and the return or stop of return, etc.

[0031] Figure 2 shows an example of a pre-dehydration type organic wastewater treatment device in which a dehydration device is provided as a pre-treatment tank 9 instead of the drum screen 8 in Figure 1. When switching from the standard denitrification treatment method shown in Figure 1 to the pre-dehydration method shown in Figure 2, the properties of the organic wastewater flowing into the denitrification tank 1 change significantly as a result of the equipment switch.

[0032] For example, in a sewage treatment plant using the standard denitrification treatment method of Figure 1, the properties of the residue-removed sewage (also referred to in this specification as "first organic wastewater") treated in the drum screen 8 are, for example, SS of 1,000 to 30,000 mg / L, biological oxygen demand (BOD) of 2,000 to 20,000 mg / L, total nitrogen (TN) of 300 to 3,500 mg / L, and the ratio of BOD to total nitrogen (BOD / TN) of about 3.0 to 5.0.

[0033] On the other hand, when the equipment is switched to a pre-dehydration system as shown in Figure 2, the dehydrated liquid treated in the pretreatment tank 9 (also referred to as "second organic wastewater" in this specification) typically has a low BOD concentration and a significantly increased ratio of nitrogen concentration to BOD concentration because many SS, BOD, etc. are removed by the dehydration treatment. For example, when a dehydration device is used as the pretreatment tank 9, the properties of the dehydrated liquid are, for example, SS of 700 to 20,000 mg / L, BOD of 600 to 6,000 mg / L, total nitrogen (TN) of 200 to 2,000 mg / L, and the ratio of BOD to total nitrogen (BOD / TN) of about 1.0 to 3.0, although this is not limited thereto.

[0034] As a result, immediately after the equipment is replaced from the drum screen 8 to the pretreatment tank 9, the BOD consumed by the activated sludge to remove nitrogen from the organic wastewater flowing into the denitrification tank 1 becomes insufficient. This temporarily results in insufficient denitrification treatment by the activated sludge, and the denitrification-treated water flows into the nitrification tank 2 with a high concentration of nitrate nitrogen (NOx-N). Because no denitrification treatment is performed in the nitrification tank 2 and beyond, the treated water may remain with a high NOx-N concentration and fail to meet the TN water quality standards at the time of discharge.

[0035] In the organic wastewater treatment apparatus according to the embodiment of the present invention, the BOD control means 71 controls the BOD source supply means 6 to increase the BOD source supplied to the denitrification tank 1 in advance compared to the steady state during a predetermined period before the second organic wastewater is supplied to the denitrification tank 1, based on information about the timing of supply of the second organic wastewater, which may result in insufficient denitrification under the conditions for nitrification / denitrification treatment of the first organic wastewater. For example, when the BOD control means 71 switches the equipment from the drum screen 8 of FIG. 1 to the pretreatment tank 9 composed of the dehydration apparatus of FIG. 2 and knows the date and time when the organic wastewater treated in the pretreatment tank 9 will flow into the denitrification tank 1, the BOD control means 71 controls the BOD source supply means 6 to supply a larger amount of BOD source to the denitrification tank 1 than the steady state during a predetermined period before that date and time.

[0036] This allows for the acclimation of activated sludge capable of nitrifying and denitrifying the second organic wastewater with a low BOD concentration that will flow in immediately after the equipment switchover to be promoted in advance, and also allows for the BOD source necessary for denitrification by the activated sludge to be supplied to the denitrification tank 1 so that it does not run short of the BOD source.As a result, even if organic wastewater with a low BOD concentration flows into the denitrification tank 1 immediately after the equipment switchover, the pre-acclimated activated sludge can fully perform denitrification using the added BOD source, and temporary deterioration in the quality of the treated water due to the equipment switchover is suppressed.

[0037] The BOD control means 71 preferably controls the BOD source supply means 6 so as to increase the supply amount of the BOD source to the denitrification tank 1 from 2 to 6 weeks, in one embodiment 2 to 4 weeks, and in another embodiment 2 to 3 weeks prior to the reference time, when the time at which the second organic wastewater, which has a lower BOD concentration than the organic wastewater and may cause insufficient denitrification treatment, is introduced. This allows the denitrification treatment in the denitrification tank 1 to be carried out more stably, even if there is a significant change in the properties of the influent raw water.

[0038] The BOD control means 71 preferably controls the BOD source supply means 6 so as to gradually increase the amount of BOD source supplied to the denitrification tank 1 continuously or in stages. For example, the BOD control means 71 gradually increases the BOD source to 0.5, 1, and 2 times the steady state (rated value) after equipment switching, and supplies the BOD source for about four weeks, thereby enabling the activated sludge in the denitrification tank 1 to acclimate more smoothly.

[0039] Furthermore, before supplying an external BOD source to the denitrification tank 1 to promote acclimation of the activated sludge, it is preferable to adjust the MLSS concentration in the denitrification tank 1 so that it is lower than that during steady-state operation (steady-state value). This increases the proportion of denitrifying bacteria capable of utilizing the externally added BOD source relative to the activated sludge in the denitrification tank 1, thereby more smoothly acclimating the activated sludge suitable for treating the second organic wastewater. The MLSS concentration must be adjusted to a level that does not deteriorate the quality of the denitrification-treated water treated in the denitrification tank 1. Although not limited to the following, it is preferable to adjust the MLSS concentration in the denitrification tank 1 so that it is 80% or less, typically about 50 to 80%, and more preferably about 60 to 70% of the MLSS concentration during steady state.

[0040] For example, when denitrifying residue-removed night soil in the denitrification tank 1, the MLSS concentration is typically about 4000 to 7000 mg / L. However, when a BOD source is supplied to the denitrification tank 1 from outside, it is preferable to lower the MLSS concentration in the denitrification tank 1 to, for example, about 3000 to 5000 mg / L before supplying the BOD source.

[0041] One method for adjusting the MLSS concentration is to have the return sludge control means 72 temporarily reduce the return ratio of returned sludge so as to lower the MLSS concentration in the denitrification tank 1, based on the measurement results of an MLSS meter provided in the denitrification tank 1. Alternatively, one or more backup tanks may be provided to adjust the MLSS concentration, and adjustment may be performed using the backup tanks.

[0042] Alternatively, it is also preferable to provide a separate culture tank (not shown), use the returned sludge to acclimate the activated sludge to an externally supplied BOD source under suitable conditions, and then add the resulting sludge to the adjustment tank 5 or denitrification tank 1. For example, when methanol is supplied as the BOD source, it is preferable to acclimate the activated sludge in the culture tank at a pH of about 7.0 to 8.5, more preferably about 8.0, and at a temperature of 15 to 30°C, more preferably about 25°C.

[0043] (Acclimation method of activated sludge in nitrification / denitrification treatment) The method for acclimating activated sludge in a nitrification-denitrification treatment according to the first embodiment of the present invention can be carried out, for example, by an organic wastewater treatment apparatus shown in Fig. 1. This acclimation method includes a nitrification-denitrification treatment step in which a first organic wastewater containing ammonia nitrogen is nitrified and denitrified in a treatment tank 10 containing activated sludge. This nitrification-denitrification treatment step includes a step of nitrifying and denitrifying the first organic wastewater and supplying a BOD source from outside into the treatment tank 10 to acclimate the activated sludge before a second organic wastewater, which may be insufficiently denitrified under the conditions for nitrification-denitrification of the first organic wastewater, is supplied to the treatment tank 10.

[0044] The "second organic wastewater that may be denitrified insufficiently under the conditions for nitrification-denitrification treatment of the first organic wastewater" refers to wastewater in which the concentration of the BOD source for denitrification derived from the organic wastewater is different from that of the first organic wastewater, as a result of performing a predetermined pretreatment such as reducing SS, BOD, etc. on the organic wastewater using, for example, the pretreatment tank 9 in Figure 2, as described above.

[0045] Although not limited to the following, when the organic wastewater treatment device of Figure 1 is used, the first organic wastewater has a BOD of about 2,000 to 20,000 mg / L and a TN of about 300 to 3,500 mg / L, while when pretreatment is performed using the pretreatment tank 9 of Figure 2, the second organic wastewater has a BOD of about 600 to 6,000 mg / L and a TN of about 200 to 2,000 mg / L.

[0046] By supplying a BOD source from an external source into the treatment tank 10 while the first organic wastewater is being treated by nitrification and denitrification in the treatment tank 10, a sufficient amount of activated sludge that has been acclimatized to the externally added BOD source can be stored in the treatment tank 10 before the second organic wastewater is supplied. Furthermore, immediately after the second organic wastewater flows into the treatment tank 10, the BOD source necessary for denitrification treatment is replenished in the denitrification tank 1, thereby preventing deterioration in the quality of the treated water due to temporary insufficient treatment by the activated sludge.

[0047] The nitrification-denitrification treatment process comprises a denitrification treatment step in which the first organic wastewater and the second organic wastewater are denitrified in a denitrification tank 1, and a nitrification treatment step in which the denitrification-treated water obtained in the denitrification treatment step is nitrified in a nitrification tank 2. It is preferable that a BOD source is supplied to the denitrification tank 1 in the denitrification treatment step. By supplying a BOD source from outside to the denitrification tank 1 in the denitrification treatment step, the BOD source necessary for denitrification can be sufficiently supplied, allowing the denitrification treatment to proceed stably.

[0048] (Method for treating organic wastewater) The method for treating organic wastewater according to the first embodiment of the present invention includes a first nitrification-denitrification treatment step in which first organic wastewater containing ammonia nitrogen is nitrified and denitrified in a treatment tank 10 containing activated sludge, and a second nitrification-denitrification treatment step in which, after the first nitrification-denitrification treatment step, second organic wastewater is supplied into the treatment tank 10 and the second organic wastewater is nitrified and denitrified.

[0049] For example, in the first nitrification-denitrification treatment step, using the organic wastewater treatment device shown in Figure 1, the organic wastewater after removing solids using a drum screen 8 is supplied to a treatment tank 10 for nitrification-denitrification treatment. Thereafter, the drum screen 8 is replaced with a pretreatment tank 9 shown in Figure 2, and the organic wastewater is pretreated in the pretreatment tank 9 to remove BOD, SS, etc., thereby obtaining a second organic wastewater having a lower BOD concentration than the first organic wastewater. Next, the second organic wastewater is supplied to the treatment tank 10 for nitrification-denitrification treatment.

[0050] In the first nitrification-denitrification treatment step, it is preferable to have a step of supplying a BOD source from outside into the treatment tank 10 while nitrifying and denitrifying the first organic wastewater, and acclimating activated sludge capable of nitrifying and denitrifying the second organic wastewater, which may be insufficiently denitrified under the conditions for nitrifying and denitrifying the first organic wastewater.

[0051] According to the method for acclimatizing activated sludge in nitrification-denitrification treatment, the method for treating organic wastewater, and the apparatus for treating organic wastewater, which are the first embodiment of the present invention, good denitrification performance can be exhibited even after the composition of the BOD source of the influent raw water changes due to equipment switching or the like, thereby suppressing deterioration in the water quality of the treated water and producing safer effluent that can satisfy water quality standards.

[0052] (Second embodiment) As shown in FIG. 3, the organic wastewater treatment apparatus according to the second embodiment of the present invention comprises a first denitrification tank 11 for denitrifying first and second organic wastewater containing ammonia nitrogen, a first nitrification tank 12 for nitrifying the denitrified water from the first denitrification tank 11, a second denitrification tank 21 for denitrifying the nitrified water from the first nitrification tank 12, a BOD source supplying means 6a for supplying a BOD source from an external source to the second denitrification tank 21, an aeration tank 22 for aerating the denitrified water from the second denitrification tank 21, and a means for separating the treated water from the aeration tank 22 into solid and liquid. The system includes a solid-liquid separation tank 3, a return means 4 for returning the sludge separated in the solid-liquid separation tank 3 to a stage upstream of the first denitrification tank 11, and a BOD control means 71 for controlling the rate of addition of the BOD source to the second denitrification tank 21 based on information about the timing at which the second organic wastewater, which may be insufficiently denitrified under the conditions for nitrification and denitrification treatment of the first organic wastewater, is supplied to the first denitrification tank 11. The BOD source supply means 6b for supplying the BOD source from an external source is connected to the first denitrification tank 11. The other features of the system are the same as those of the organic wastewater treatment system shown in FIG. 1.

[0053] In the organic wastewater treatment device according to the second embodiment, a first-stage nitrification / denitrification treatment is carried out in the first denitrification tank 11 and the first nitrification tank 12, and a second-stage nitrification / denitrification treatment is carried out in the second denitrification tank 21 and the aeration tank 22. Since the organic wastewater treatment device according to the second embodiment has two or more denitrification tanks, for example, by continuing normal nitrification / denitrification treatment operation in the first denitrification tank 11 in the first stage while carrying out activated sludge acclimatization in the second denitrification tank 21 in the second stage, the nitrification / denitrification treatment and activated sludge acclimatization can be carried out gently in parallel.

[0054] Figure 4 shows an example of an organic wastewater treatment system in which an anaerobic digester that anaerobically digests organic wastewater is installed as the pretreatment tank 9 for nitrification / denitrification. Compared to the residual human waste obtained in the drum screen 8 of Figure 3, the anaerobically digested liquid obtained in the pretreatment tank 9 of Figure 4 has lower concentrations of SS, BOD, etc., so when the system is switched from the drum screen 8 of Figure 3 to the anaerobic digester of Figure 9, the properties of the organic wastewater flowing into the first denitrification tank 11 change significantly.

[0055] Therefore, in the second embodiment, in response to an apparatus changeover or the like, the BOD control means 71 in Fig. 3 starts supplying a BOD source from outside to the second denitrification tank 21 via the BOD source supply means 6a, for example, four weeks before the anaerobic digestion liquid treated in the pretreatment tank 9 in Fig. 4 flows into the first denitrification tank 11, and controls the supply amount of the BOD source so as to gradually increase the supply of the BOD source. As a result, while normal nitrification and denitrification treatment is carried out in the first denitrification tank 11 and the first nitrification tank 12, the acclimatization of activated sludge for treating the anaerobic digestion liquid can be gradually completed in the second denitrification tank 21 and the aeration tank 22.

[0056] Even if an excess BOD source is supplied to the second denitrification tank 21, the BOD source can be decomposed by sufficient aeration in the subsequent aeration tank 22, thereby suppressing the BOD remaining in the treated water obtained in the solid-liquid separation tank and preventing deterioration of water quality. After the activated sludge has been acclimated in the second denitrification tank 21, a BOD source is added from the outside to the preceding first denitrification tank 11 via the BOD source supply means 6b at approximately one time the rated value, completing the acclimation in approximately two weeks. Note that the amount of BOD source added to the second denitrification tank 21 can also be reduced by approximately twice the rated value to shorten the acclimation period.

[0057] When the anaerobic digestion liquid is supplied to the first denitrification tank 11 and the denitrification treatment may be insufficient under the conventional conditions in the first denitrification tank 11, the BOD control means 71 can additionally supply a BOD source such as methanol to the first denitrification tank 11 via the BOD source supply means 6b. This allows efficient treatment of the organic wastewater after the switchover, even when the treatment device upstream of the first denitrification tank 11 is switched, and prevents deterioration of the quality of the treated water due to changes in the properties of the organic wastewater.

[0058] The returned sludge control means 72 preferably controls the return means 4 so that the amount of returned sludge (returned sludge amount) is greater than that in a steady state (steady state value) for a certain period before the inflow of the anaerobic digestion liquid into the first denitrification tank 11 begins, in order to return a larger amount of activated sludge that has been acclimatized in the second denitrification tank 21 to the adjustment tank 5 and promote the acclimatization of the activated sludge in the first denitrification tank 11. For example, the steady state return amount is set to Q(m 3 / d), the amount of returned sludge during the period in which a BOD source is added to the second denitrification tank 21 and acclimatization is performed can be set to, for example, 1.1 to 1.5 Q, or even 1.2 to 1.4 Q, to an extent that does not affect the water quality.

[0059] Before supplying an external BOD source to the second denitrification tank 21 to promote acclimatization of the activated sludge, it is preferable to adjust the MLSS concentration in the first denitrification tank 11 to be lower than that during steady operation, to an extent that does not deteriorate the treatment performance of the first denitrification tank 11. As in the first embodiment, in the second embodiment, it is preferable to adjust the MLSS concentration in the first denitrification tank 11 to be 80% or less, typically about 50 to 80%, and more preferably about 60 to 70% of the MLSS concentration during steady operation.

[0060] The circulating water control means 73 controls the circulation flow rate of the circulation means 13 that circulates the nitrified and denitrified water from the first nitrification tank 12 to the first denitrification tank 11. For example, when acclimating activated sludge in the second denitrification tank 21, it is preferable that the circulating water control means 73 controls the circulation flow rate of the circulating water to be less than the steady value, supply the nitrified and denitrified water containing residual nitrogen to the second denitrification tank 21, and control the circulation means 13 so as to promote acclimation of activated sludge in the second denitrification tank 21. For example, the return amount in the steady state is set to Q(m 3 / d), the amount of circulating water during the period in which a BOD source is added and acclimatization is performed in the second denitrification tank 21 is 0.5 to 0.9Q, preferably 0.6 to 0.8Q, and more preferably 0.7 to 0.8Q. By setting the amount to 0.5Q or more, treatment in the second denitrification tank 21 is possible, and the water quality is less likely to deteriorate. Furthermore, by setting the amount to 0.9Q or less, the amount of denitrification in the first denitrification tank 11 is limited, and a sufficient amount of nitrate nitrogen can be supplied to the second denitrification tank 21 for acclimatization.

[0061] (Acclimation method of activated sludge in nitrification / denitrification treatment) The method for acclimatizing activated sludge in nitrification-denitrification treatment according to the second embodiment differs from the method for acclimatizing activated sludge in nitrification-denitrification treatment according to the first embodiment in that the nitrification-denitrification treatment process comprises an upstream nitrification-denitrification treatment process and a downstream nitrification-denitrification treatment process, and includes a process in which, before the second organic wastewater is supplied to the upstream nitrification-denitrification treatment process, a BOD source is supplied from outside in advance in the downstream nitrification-denitrification treatment process to acclimate the activated sludge, and the treated sludge obtained in the downstream nitrification-denitrification treatment process is returned to the upstream nitrification-denitrification treatment process.

[0062] According to the acclimatization method of the second embodiment, since there are two or more denitrification tanks, by reducing the amount of circulating water and increasing the nitrogen load in the downstream second denitrification tank 21, it is possible to gradually acclimate the activated sludge while continuing normal operation in the first denitrification tank 11. [Example]

[0063] Examples of the present invention are given below, but these examples are provided for a better understanding of the present invention and its advantages, and are not intended to limit the invention.

[0064] (Changes in TN concentration in effluent water when equipment switching treatment is performed) Figure 6 shows an example of the change in effluent TN concentration when the treatment method was switched from the standard denitrification method to the pre-dehydration method at the sewage treatment plant shown in Figure 5. To minimize the impact of the switch on denitrification, the influent load was reduced to half of the normal load until the fourth day, after which the normal load was restored. Methanol was used as the BOD source for denitrification. The amount of methanol required was calculated and added in accordance with the increase in TN concentration. However, because there were insufficient bacteria capable of denitrifying using methanol in the treatment system, the TN concentration continued to rise for approximately two weeks, reaching a maximum of nearly the effluent standard value (10 mg / L) 12 days after the switch. Subsequently, the TN concentration began to decrease as the number of methanol-denitrifying bacteria increased, and the treatment stabilized after three weeks.

[0065] (Simulation results) A simulation was performed on the transition of the amount of methanol-denitrifying bacteria in the first denitrification tank when the treatment method was switched from the standard denitrification method to the pre-dehydration method at the night soil treatment plant shown in Figure 5. Tables 1 and 2 show the treatment conditions. In both cases, the BOD required for TN removal was set to three times the TN removal amount, and the amount of methanol required for treatment was calculated to compensate for the BOD deficiency. Because the influent BOD load decreases in the steady state (normal state after switching to the pre-dehydration method), the amount of methanol was increased, and the second denitrification tank was set to denitrify all TN that was not completely removed in the previous treatment stages. In the comparative example and Example 1, 97% of the TN influent load was removed by the first nitrification tank, and in Example 2, 94% was removed during the acclimation stage and 97% was removed in the steady state. In Table 1, the TN removed by the night soil-derived BOD was set to one-third of the night soil-derived BOD, and the TN removed by methanol was calculated by subtracting the TN removed by the night soil-derived BOD from the TN influent load. The TN inflow load to the second denitrification tank was set to 3-6% of the raw water TN inflow load, and the amount required in the second denitrification tank was set to be equivalent to the TN removed by methanol during acclimation. The amount required in the first denitrification tank was calculated by subtracting the amount required in the second denitrification tank from the amount of methanol required for treatment. Furthermore, each yield in Table 2 indicates the amount of bacterial cells generated when various types of bacteria contained in activated sludge treat the inflow load.

[0066] [Table 1]

[0067] [Table 2]

[0068] (Comparative Example and Example 1) Figure 7 shows the transition of the amount of methanol denitrifying bacteria present in the tank for the two sewage treatment plants shown in Figure 5: Comparative Example (where methanol addition was started immediately after switching the treatment method without acclimation), and Example 1 (where acclimation was carried out while nitrification / denitrification treatment was being carried out before switching the treatment method). It can be seen that in the Comparative Example, where no prior acclimation was carried out, the amount of methanol denitrifying bacteria finally increased to the required amount 10 days after switching the BOD source. However, this result is an overestimate because the maximum amount of methanol added daily was the maximum amount that could be used to treat the sludge in the system. In reality, it is thought that at least 2 to 3 weeks would be required, as in the example of Figure 6.

[0069] In Example 1, where acclimation was performed, it was found that the number of methanol-denitrifying bacteria increased to the required amount 20 days after the start of acclimation. By increasing the amount of methanol added during acclimation by 0.5 times, 1 time, and 2 times the amount added after switching (steady state), it was possible to provide a margin for the activated sludge's methanol utilization capacity. In the Comparative Example and Example 1, the amount of methanol added was determined by evaluating the abundance of methanol-denitrifying bacteria and methanol denitrification activity, and care was taken to ensure that the amount added did not exceed the decomposition capacity of the sludge.

[0070] Example 2 Figure 8 shows the results of a simulation of the change in the amount of methanol-denitrifying bacteria present in the tank when the amount of denitrification in the second denitrification tank is increased and then methanol is also added to the first denitrification tank. By increasing the amount of denitrification in the second denitrification tank, it is possible to increase the amount of methanol-denitrifying bacteria present in the system by approximately 1.6 times over 28 days without adding methanol to the first denitrification tank. Then, by adding 1x the amount of methanol at steady state in the first denitrification tank, which is the preceding stage, it is possible to secure the required amount of denitrifying bacteria in 11 days. With this method, fine adjustment of the amount of methanol added is not necessary, so the various tasks related to adjusting the amount can be omitted, and it is clear that activated sludge can be acclimatized easily. [Explanation of symbols]

[0071] 1...Denitrification tank 2…Nitrification tank 3…Solid-liquid separation tank 4. Return method 5…Adjustment tank 6, 6a, 6b...BOD source supply means 7...Control device 8...Drum screen 9...Pretreatment device 10...Treatment tank 11...First denitrification tank 12…Second nitrification tank 13…Circulation means 21…Second denitrification tank 22...Aeration tank 71...BOD control measures 72... Return sludge control means 73...Circulating water control means

Claims

1. a nitrification / denitrification treatment step of nitrifying / denitrifying the first organic wastewater containing ammonia nitrogen in a treatment tank containing activated sludge; In the nitrification / denitrification treatment step, a step of supplying a BOD source from outside into the treatment tank to acclimate activated sludge before second organic wastewater, which has a lower BOD to total nitrogen ratio than the first organic wastewater, is supplied into the treatment tank, and the second organic wastewater may be insufficient in denitrification treatment due to a lack of BOD under the conditions for nitrification / denitrification treatment of the first organic wastewater. A method for acclimatizing activated sludge in a nitrification / denitrification treatment, comprising:

2. 2. The method for acclimatizing activated sludge in a nitrification-denitrification treatment according to claim 1, wherein the ratio of the BOD to the total nitrogen is 3.0 or less.

3. 3. The method for acclimatizing activated sludge in a nitrification-denitrification treatment according to claim 1, wherein methanol is supplied as the BOD source.

4. The method for acclimatizing activated sludge in nitrification-denitrification treatment according to any one of claims 1 to 3, characterized in that in the nitrification-denitrification treatment step, the BOD source is supplied into the treatment tank 2 to 6 weeks before the second organic wastewater is supplied into the treatment tank.

5. The method for acclimatizing activated sludge in nitrification / denitrification treatment according to any one of claims 1 to 4, characterized in that, before the BOD source is supplied to the treatment tank, the MLSS concentration in the treatment tank is reduced to a value lower than a steady-state value determined for subjecting the first organic wastewater to the nitrification / denitrification treatment.

6. The nitrification / denitrification treatment step a denitrification treatment step of denitrifying the first organic wastewater and the second organic wastewater; a nitrification treatment step of nitrifying the denitrification-treated water obtained in the denitrification treatment step; and 6. The method for acclimatizing activated sludge in nitrification-denitrification treatment according to claim 1, wherein the BOD source is supplied in the denitrification treatment step.

7. The nitrification / denitrification treatment step It has a front-stage nitrification / denitrification treatment step and a rear-stage nitrification / denitrification treatment step, a step of supplying the BOD source from an external source in advance to the downstream nitrification / denitrification treatment step to acclimate activated sludge before the second organic wastewater is supplied to the upstream nitrification / denitrification treatment step, and returning the treated sludge obtained by solid-liquid separation of the nitrification-treated water from the downstream nitrification / denitrification treatment step to the upstream nitrification / denitrification treatment step. The method for acclimatizing activated sludge in a nitrification / denitrification treatment according to any one of claims 1 to 6, comprising:

8. a first nitrification / denitrification treatment step of nitrifying and denitrifying a first organic wastewater containing ammonia nitrogen in a treatment tank containing activated sludge; a second nitrification / denitrification treatment step of supplying, into the treatment tank, second organic wastewater having a lower ratio of BOD to total nitrogen than the first organic wastewater, which may cause insufficient denitrification due to a lack of BOD under conditions for nitrification / denitrification of the first organic wastewater, and nitrifying / denitrifying the second organic wastewater after the first nitrification / denitrification treatment step; and A method for treating organic wastewater, characterized in that in the first nitrification-denitrification treatment step, the first organic wastewater is subjected to nitrification-denitrification treatment, and a step of supplying a BOD source from outside into the treatment tank and acclimating the second organic wastewater to activated sludge capable of nitrification-denitrification treatment is also included.

9. 9. The method for treating organic wastewater according to claim 8, wherein the ratio of the BOD to the total nitrogen is 3.0 or less.

10. a denitrification tank for denitrifying the first organic wastewater containing ammonia nitrogen; a nitrification tank for nitrifying the denitrification-treated water from the denitrification tank; a solid-liquid separation tank for separating the nitrification-treated water from the nitrification tank into solid and liquid; a return means for returning the sludge separated into solid and liquid in the solid-liquid separation tank to a stage upstream of the denitrification tank; a BOD source supply means for supplying a BOD source from an external source to the denitrification tank; a BOD control means for controlling the BOD source supply means to increase the supply amount of the BOD source to be supplied to the denitrification tank before the second organic wastewater is supplied to the denitrification tank, based on information about the timing at which second organic wastewater, which has a smaller BOD to total nitrogen ratio than the first organic wastewater and which may cause insufficient denitrification treatment due to a lack of BOD under conditions for nitrification / denitrification treatment of the first organic wastewater, is supplied to the denitrification tank above a rated value set for the denitrification tank to perform the denitrification treatment of the second organic wastewater, and for promoting the acclimatization of activated sludge capable of nitrification / denitrification treatment of the second organic wastewater; An organic wastewater treatment device comprising:

11. a first denitrification tank for denitrifying the first organic wastewater containing ammonia nitrogen; a first nitrification tank for nitrifying the denitrification-treated water from the first denitrification tank; a second denitrification tank for denitrifying the nitrification-treated water from the first nitrification tank; a BOD source supply means for supplying a BOD source from an external source to the second denitrification tank; an aeration tank for aerating the denitrification treated water from the second denitrification tank; a solid-liquid separation tank for separating the treated water obtained in the aeration tank into solid and liquid; a return means for returning the sludge separated into solid and liquid in the solid-liquid separation tank to a stage upstream of the first denitrification tank; a BOD control means for controlling the addition rate of the BOD source to be added to the second denitrification tank based on information on the timing at which second organic wastewater, which has a smaller BOD to total nitrogen ratio than the first organic wastewater and which may cause insufficient denitrification due to a lack of BOD under conditions for nitrification / denitrification treatment of the first organic wastewater, is supplied to the first denitrification tank, by increasing the supply amount of the BOD source to be supplied to the second denitrification tank above a rated value set for denitrifying the nitrified water of the second organic wastewater, so as to acclimate activated sludge capable of nitrification / denitrification treatment of the second organic wastewater; An organic wastewater treatment device comprising:

12. 12. The organic wastewater treatment device according to claim 10, wherein the ratio of the BOD to the total nitrogen is 3.0 or less.

13. 12. The organic wastewater treatment device according to claim 11, further comprising a return sludge control means for controlling the return means so that an amount of return sludge supplied to the first denitrification tank is increased to be greater than a steady-state value set for returning the sludge of the first organic wastewater before the second organic wastewater is supplied to the first denitrification tank.

14. a circulation means for circulating a portion of the nitrification-treated water in the first nitrification tank to the first denitrification tank, 12. The organic wastewater treatment device according to claim 11, further comprising a circulating water control means for controlling the circulation means so that the amount of the nitrification-treated water circulated to the first denitrification tank via the circulation means is reduced below a steady-state value determined for the denitrification treatment of the first organic wastewater before the second organic wastewater is supplied to the first denitrification tank.

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