JP2023143332A - Method for acclimatizing active sludge, method for treating organic wastewater, and device for treating organic wastewater in nitrification and denitrification treatment - Google Patents

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

The present invention relates to a method for acclimating activated sludge in nitrification and denitrification treatment, a method for treating organic wastewater, and an apparatus for treating organic wastewater.

Nitrification and denitrification using activated sludge is widely used to treat organic wastewater containing ammonia nitrogen. Among these, standard denitrification methods have been widely used in human waste treatment plants, in which the removed human waste is treated with activated sludge. On the other hand, the pre-dehydration method is the mainstream of current human waste treatment methods, and the number of cases of upgrading from the standard denitrification method to the pre-dehydration method is increasing.

The dehydrated separated liquid generated by the pre-dehydration method has a lower BOD concentration than the filtered human urine, and the ratio of nitrogen concentration to BOD concentration is greatly increased. Therefore, in the denitrification treatment, BOD may be insufficient and the treatment may not be carried out satisfactorily. Therefore, a BOD source is added to the denitrification process to supplement the BOD required for the denitrification process using activated sludge.

However, depending on the type of BOD source input, it may be difficult to use it for denitrification, and activated sludge may need to be acclimatized. For example, there are reports that it takes about two weeks for activated sludge to be able to denitrify using methanol as BOD, and it takes about a month for it to show high denitrification ability (for example, , see Non-Patent Document 1).

At human waste treatment plants, for example, when upgrading from a standard denitrification method to a pre-dehydration method, the amount of methanol added is increased to compensate for the lack of BOD source for denitrification due to a decrease in the BOD concentration of raw water. However, denitrification treatment using activated sludge may become temporarily insufficient as the water is not acclimatized to methanol, making it difficult to comply with water quality standards. Furthermore, if the methanol added by the denitrification reaction of activated sludge immediately after renovation work is not fully utilized, methanol may remain in the treated water and flow out of the human waste treatment plant, causing a pollution load to the discharge destination. .

Such a phenomenon can occur not only when updating to a pre-dehydration method but also when applying methane fermentation. That is, in methane fermentation, a BOD source is removed, but ammonia nitrogen is not removed. Therefore, in the subsequent nitrification and denitrification treatment, it is necessary to add a BOD source from the outside for denitrification of ammonia nitrogen.

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

In view of the above problems, the present invention provides a method for acclimatizing activated sludge in nitrification and denitrification treatment, which can suppress the decline in nitrification and denitrification performance due to changes in the properties of inflow raw water, and can suppress the deterioration of the water quality of treated water, and a method for acclimating organic wastewater. A treatment method and an organic wastewater treatment device are provided.

In order to solve the above problems, the inventors of the present invention conducted extensive studies and found that new organic wastewater is supplied into the treatment tank under the conditions in which the organic wastewater being treated is subjected to nitrification and denitrification treatment, which may result in insufficient denitrification treatment. It has been found that it is effective to supply a BOD source from the outside into the processing tank in advance.

One aspect of the present disclosure, which was completed based on the above knowledge, includes a nitrification-denitrification treatment step of nitrification-denitrification treatment of a first organic wastewater containing ammonia nitrogen in a treatment tank containing activated sludge. In the nitrification and denitrification treatment process, before the second organic wastewater is supplied into the treatment tank, the denitrification treatment may be insufficient under the conditions in which the first organic wastewater is nitrified and denitrified. This is a method for acclimatizing activated sludge in nitrification and denitrification treatment, which includes a step of acclimating activated sludge by supplying a BOD source from the outside.

In one embodiment of the method for acclimating activated sludge in nitrification-denitrification treatment according to the present invention, methanol is supplied as a BOD source.

In another embodiment of the method for acclimating activated sludge in nitrification and denitrification treatment according to the present invention, in the nitrification and denitrification treatment process, the second organic wastewater is treated from 2 to 6 weeks before being supplied into the treatment tank. A BOD source is supplied into the tank.

In another embodiment of the activated sludge acclimatization method in nitrification and denitrification treatment according to the present invention, before a BOD source is supplied into the treatment tank, the MLSS concentration in the treatment tank is lowered than during steady operation. include.

In yet another embodiment of the activated sludge acclimatization method in the nitrification-denitrification treatment according to the present invention, the nitrification-denitrification treatment step denitrifies the first organic wastewater and the second organic wastewater. The method includes a treatment step and a nitrification treatment step of nitrifying denitrification treated water obtained in the denitrification treatment step, and includes supplying a BOD source in the denitrification treatment step.

In yet another embodiment of the activated sludge acclimatization method in nitrification-denitrification treatment according to the present invention, the nitrification-denitrification treatment step includes a first-stage nitrification-denitrification treatment step and a second-stage nitrification-denitrification treatment step; Before the second organic wastewater is supplied to the denitrification treatment process, a BOD source is supplied from the outside in advance in the latter nitrification and denitrification treatment process to acclimatize the activated sludge, and the nitrification treatment in the latter nitrification and denitrification treatment process is performed. It has a step of returning the treated sludge from which water has been separated into solid and liquid to the previous nitrification and denitrification treatment step.

In another aspect, the present invention provides a first nitrification-denitrification treatment step of nitrification-denitrification treatment of a first organic wastewater containing ammonia nitrogen in a treatment tank containing activated sludge; After the denitrification treatment step, a second organic wastewater is supplied into the treatment tank, and the second organic wastewater is nitrified. a second nitrification and denitrification treatment step for denitrification treatment, and in the first nitrification and denitrification treatment step, the first organic wastewater is nitrified and denitrified, and a BOD source is introduced from the outside into the treatment tank. This is a method for treating organic wastewater, which includes a step of supplying activated sludge that can be subjected to nitrification and denitrification treatment of the second organic wastewater.

In still another aspect, the present invention provides a denitrification tank for denitrifying first organic wastewater containing ammonia nitrogen, a nitrification tank for nitrifying denitrification treated water in the denitrification tank, and a nitrification tank for nitrifying the denitrification treated water in the denitrification tank. A solid-liquid separation tank that separates treated water into solid and liquid, a return means that returns the sludge separated into solid and liquid in the solid-liquid separation tank to the previous stage of the denitrification tank, and a BOD source supply means that supplies a BOD source to the denitrification tank from the outside. Based on the information on the timing at which the second organic wastewater is supplied to the denitrification tank, under the conditions in which the first organic wastewater is subjected to nitrification and denitrification treatment, insufficient denitrification treatment may occur. Before being supplied to the nitrification tank, the BOD source supply means is controlled to increase the BOD source supplied to the denitrification tank compared to the steady state, and the second organic wastewater is converted into activated sludge that can be nitrified and denitrified. This is an organic wastewater treatment device equipped with a BOD control means that promotes acclimatization.

In still another aspect, the present invention provides a first denitrification tank that denitrifies first organic wastewater containing ammonia nitrogen, and a first nitrification tank that nitrifies denitrification treated water of the first denitrification tank. a second denitrification tank that denitrifies the nitrified water in the first nitrification tank; a BOD source supply means that supplies a BOD source to the second denitrification tank from the outside; and aerates the denitrified water in the second denitrification tank. a solid-liquid separation tank for separating solid-liquid treated water obtained in the aeration tank; a return means for returning the sludge separated into solid-liquid in the solid-liquid separation tank to a stage before the first denitrification tank; The BOD source supplied to the second denitrification tank is based on the information on the timing at which the second organic wastewater is supplied to the first denitrification tank, which may result in insufficient denitrification under the conditions in which organic wastewater is subjected to nitrification and denitrification treatment. BOD control means for controlling the addition rate of the BOD source added to the second denitrification tank so as to increase the amount of activated sludge that can be treated with nitrification and denitrification of the second organic wastewater by increasing This is an organic wastewater treatment device comprising:

In one embodiment of the organic wastewater treatment device according to the present invention, before the second organic wastewater is supplied to the first denitrification tank, the amount of returned sludge supplied to the first denitrification tank is lower than a steady value. The apparatus further includes return sludge control means for controlling the return means to increase the amount of sludge.

In another embodiment, the organic wastewater treatment apparatus according to the present invention includes a circulation means for circulating a part of the nitrified water in the first nitrification tank to the first denitrification tank, and the second organic wastewater is supplied to the first denitrification tank. A circulating water control means for controlling the circulating means so as to reduce the amount of circulating water of the nitrified water that is circulated to the first denitrifying tank via the circulating means to be less than a steady value before being supplied to the first denitrifying tank. Be prepared.

According to the present invention, a method for acclimating activated sludge in nitrification-denitrification treatment, a method for treating organic wastewater, and a method for acclimating activated sludge in nitrification-denitrification treatment that can suppress a decline in nitrification-denitrification performance due to changes in the properties of inflow raw water and suppress deterioration of the water quality of treated water; Organic wastewater treatment equipment can be provided.

1 is a schematic diagram showing an example of an organic wastewater treatment apparatus according to a first embodiment using a standard denitrification treatment method. FIG. 1 is a schematic diagram showing an example of an organic wastewater treatment apparatus according to a first embodiment using a pre-dehydration method. FIG. 2 is a schematic diagram showing an example of an organic wastewater treatment apparatus according to a second embodiment using a standard denitrification treatment method. It is a schematic diagram showing an example of an organic wastewater treatment device concerning a 2nd embodiment incorporating anaerobic digestion treatment as a pretreatment tank. It is a schematic diagram showing a human waste processing plant of an example. It is a graph showing an example of the transition of the effluent TN concentration when switching the treatment method from the standard denitrification method to the pre-dehydration method. 2 is a graph showing an example of simulation results of changes in the amount of methanol denitrifying bacteria present in the tank in the denitrification treatments of Example 1 and Comparative Example. 3 is a graph showing an example of a simulation result of changes in the amount of methanol denitrifying bacteria present in the tank in the denitrification treatment of Example 2.

Embodiments of the present invention will be described below with reference to the drawings. In the description of the drawings below, the same or similar parts are denoted by the same or similar symbols. The embodiments shown below are illustrative of devices and methods for embodying the technical idea of this invention. It is not something specific.

(First embodiment)
Figure 1 shows an example of an organic wastewater treatment system using a standard denitrification treatment method. The organic wastewater treatment apparatus according to the first embodiment of the present invention includes a denitrification tank 1 that denitrifies organic wastewater, a nitrification tank 2 that nitrifies the denitrified water of the denitrification tank 1, and a nitrification tank 2 that nitrifies the denitrified water of the denitrification tank 1. A solid-liquid separation tank 3 that separates the nitrified water in the tank 2 into solid and liquid; a return means 4 that returns the sludge separated into solid and liquid in the solid-liquid separation tank 3 to the previous stage of the denitrification tank 1; It includes a BOD source supply means 6 that supplies a BOD source, and a control device 7.

As the organic wastewater, organic wastewater containing ammonia nitrogen and solid content is used. For example, human waste, septic tank sludge, organic sludge, food waste, etc. are used as organic wastewater, and typically a mixture of human waste and septic tank sludge is used.

Organic wastewater is fed into drum screen 8. By rotating the cylindrical filter body included in the drum screen 8, solid content in the organic wastewater is removed. Although FIG. 1 shows an example in which a drum screen 8 is installed, the present invention is not limited to this as long as the device is capable of removing solid content from organic wastewater. For example, instead of the drum screen 8, a bar type screen, a scraping type screen, an inclined wire type screen, etc. may be provided.

The organic wastewater (removed human waste) from which the solid content has been removed by the drum screen 8 is supplied into the adjustment tank 5 and mixed with the return sludge returned from the solid-liquid separation tank 3. The organic wastewater contained in the adjustment tank 5 is supplied into a treatment tank 10 that includes a denitrification tank 1 and a nitrification tank 2 for subjecting the organic wastewater to nitrification and denitrification processing. The nitrification tank 2 contains activated sludge containing nitrifying bacteria for nitrifying organic wastewater, and the nitrification process using the activated sludge is performed within the nitrification tank 2. The nitrified water that has undergone the nitrification process is supplied to the denitrification tank 1 by the 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 infuse nitrate nitrogen in the nitrification treatment water. Denitrification treatment is performed using BOD in raw water. The denitrified water that has been denitrified in the denitrification tank 1 is supplied to the nitrification tank 2.

The nitrified water obtained in the nitrification tank 2 is supplied to the solid-liquid separation tank 3, where it is separated into solid-liquid water and treated sludge. As the solid-liquid separation tank 3, for example, a settling tank is used. The treated sludge is returned to the adjustment tank 5 via a return means 4 equipped with a drawing pump, etc., mixed with organic wastewater supplied from a drum screen 8, and then returned to the denitrification tank 1. A circulation means 13 is provided between the nitrification tank 2 and the denitrification tank 1 for circulating nitrified water from the nitrification tank 2 to the denitrification tank 1 as circulating water. Normally, the amount of circulating water is often about 10 to 30 times the inflow raw water.

The BOD source supply means 6 adds a BOD source into the denitrification tank 1 from the outside. It is preferable to use methanol as the BOD source. Methanol is highly biodegradable and is quickly utilized by microorganisms in the denitrification reaction, so by using methanol as a BOD source, nitrogen can be removed more efficiently in the denitrification process. Furthermore, it is superior in cost and versatility compared to other organic substances that can be used as a BOD source.

The control device 7 is connected to the BOD source supply means 6, the circulation means 13, and the return means 4, respectively. The control device 7 outputs control signals to the BOD source supply means 6, circulation means 13, and return means 4, respectively, thereby controlling the BOD source addition rate, addition start, and addition stop by the BOD source supply means 6. , control of the circulation flow rate of circulating water and supply or stop of circulating water by the circulation means 13, control of the amount of return sludge returned by the return means 4, control of return or stop of return, etc.

FIG. 2 shows an example of a pre-dehydration type organic wastewater treatment apparatus in which a dehydration device is arranged as a pre-treatment tank 9 instead of the drum screen 8 of FIG. When switching the equipment from the standard denitrification treatment method shown in FIG. 1 to the pre-dehydration method shown in FIG. 2, the properties of the organic wastewater flowing into the denitrification tank 1 change greatly as the equipment is switched.

For example, in a human waste treatment plant using the standard denitrification treatment method shown in FIG. SS is 1,000-30,000mg/L, biological oxygen demand (BOD) is 2,000-20,000mg/L, total nitrogen (TN) is 300-3,500mg/L, BOD and The total nitrogen ratio (BOD/TN) is about 3.0 to 5.0.

On the other hand, when the equipment is switched to the pre-dehydration method as shown in FIG. Since a large amount of SS, BOD, etc. are removed by the method, the BOD concentration is typically low, and the ratio of the nitrogen concentration to the BOD concentration increases greatly. Although not limited to the following, for example, when a dehydrator is used as the pretreatment tank 9, the properties of the dehydrated liquid are, for example, SS 700 to 20,000 mg/L and BOD 600 to 6,000 mg/L. /L, total nitrogen (TN) is 200 to 2,000 mg/L, and the ratio of BOD to total nitrogen (BOD/TN) is about 1.0 to 3.0.

As a result, in the denitrification tank 1, 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. . As a result, the denitrification treatment by activated sludge is temporarily insufficient, and the denitrification treated water flows into the nitrification tank 2 with a high nitrate nitrogen (NOx-N) concentration. Since denitrification treatment is not performed in the nitrification tank 2 and beyond, a situation may arise in which the NOx-N concentration of the treated water remains high and does not satisfy the TN water quality standards at the time of discharge.

According to the organic wastewater treatment apparatus according to the embodiment of the present invention, the BOD control means 71 controls the second organic wastewater, which may cause insufficient denitrification treatment under the conditions for nitrification and denitrification treatment of the first organic wastewater. Based on the information on the timing at which wastewater is supplied to the denitrification tank 1, the BOD source supplied to the denitrification tank 1 is determined in advance during a predetermined period before this second organic wastewater is supplied to the denitrification tank 1. The BOD source supply means 6 is controlled so as to increase the BOD source more than in the steady state. For example, the BOD control means 71 switches the equipment from the drum screen 8 in FIG. 1 to the pretreatment tank 9 configured with the dehydration device in FIG. If information on the date and time of inflow is known, the BOD source supply means 6 is controlled so that more BOD source is supplied into the denitrification tank 1 than in the steady state from a predetermined period before that date and time. .

As a result, it is possible to promote the acclimatization of activated sludge that can be treated with nitrification and denitrification of the second organic wastewater with a low BOD concentration that flows in immediately after the equipment is switched, as well as to promote the deactivation of the activated sludge. The denitrification tank 1 can be supplemented with a BOD source so that the BOD source necessary for the nitrification process does not run out. As a result, even if organic wastewater with a low BOD concentration flows into the denitrification tank 1 immediately after the equipment is switched, denitrification treatment using the added BOD source can be performed sufficiently by the activated sludge that has been acclimatized in advance. This suppresses temporary deterioration in the quality of treated water due to equipment switching.

The BOD control means 71 is configured to control the BOD control means 71 from 2 to 6 weeks before the reference time when the second organic wastewater flows in, which has a lower BOD concentration than the organic wastewater and may cause insufficient denitrification treatment. In one embodiment, it is preferable to control the BOD source supply means 6 so as to increase the amount of BOD source supplied to the denitrification tank 1 from 2 to 4 weeks in advance, and in a further embodiment from 2 to 3 weeks in advance. Thereby, even if a large change in the properties of the inflow raw water occurs, the denitrification process in the denitrification tank 1 can be performed more stably.

It is preferable that the BOD control means 71 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 stepwise. For example, the BOD control means 71 gradually increases the BOD source by 0.5 times, 1 times, and 2 times the steady state (rated value) after switching the equipment, and supplies it for about 4 weeks. The activated sludge in the denitrification tank 1 can be acclimated more smoothly.

Furthermore, before supplying a BOD source to the denitrification tank 1 from the outside to promote acclimatization of activated sludge, the MLSS concentration in the denitrification tank 1 should be adjusted to be lower than during steady operation (steady value). is preferred. As a result, the generation ratio of denitrifying bacteria that can utilize the BOD source added from the outside to the activated sludge in the denitrification tank 1 can be increased, so that the activated sludge is acclimated, which is suitable for the second organic wastewater treatment. can be carried out more smoothly. The MLSS concentration must be adjusted to a level that does not deteriorate the quality of the denitrified water treated in the denitrification tank 1. Although not limited to the following, the MLSS concentration in the denitrification tank 1 is adjusted to be 80% or less, typically about 50 to 80%, more preferably about 60 to 70% of the MLSS concentration in the steady state. It is preferable to do so.

For example, when denitrifying treated human urine in the denitrification tank 1, the MLSS concentration is typically about 4000 to 7000 mg/L, but when a BOD source is supplied to the denitrification tank 1 from the 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.

As a method for adjusting the MLSS concentration, for example, based on the measurement results of an MLSS meter installed in the denitrification tank 1, the return sludge control means 72 adjusts the return sludge so that the MLSS concentration in the denitrification tank 1 is lowered. There is a method to temporarily reduce the return ratio. Alternatively, it is also possible to arrange one or more backup tanks for adjusting the MLSS concentration and perform adjustment using the backup tanks.

On the other hand, a culture tank (not shown) is provided separately, and the returned sludge is used to acclimate the BOD source supplied from the outside under suitable conditions, and the obtained sludge is added to the adjustment tank 5 or the denitrification tank 1. It is also preferable that For example, when methanol is supplied as a BOD source, the pH of the culture tank should be around 7.0 to 8.5, preferably around pH 8.0, and the temperature should be around 15 to 30°C, more preferably around 25°C to acclimate the activated sludge. It is preferable to do this.

(Acclimatization method for activated sludge in nitrification and denitrification treatment)
The activated sludge acclimatization method in the nitrification and denitrification treatment according to the first embodiment of the present invention can be carried out using, for example, the organic wastewater treatment apparatus shown in FIG. This acclimatization method includes a nitrification-denitrification treatment step of nitrification-denitrification treatment of first organic wastewater containing ammonia nitrogen in a treatment tank 10 containing activated sludge. In this nitrification-denitrification treatment process, the first organic wastewater is nitrified and denitrified, and the second organic wastewater is treated with the second organic wastewater, which may be insufficiently denitrified under the conditions of nitrification-denitrification treatment of the first organic wastewater. Before being supplied into the treatment tank 10, there is a step of supplying a BOD source into the treatment tank 10 from the outside to acclimatize the activated sludge.

As mentioned above, "second organic wastewater in which denitrification treatment may be insufficient under the conditions in which the first organic wastewater is subjected to nitrification and denitrification treatment" means, for example, that organic wastewater is Refers to wastewater in which the concentration of a BOD source for denitrification derived from organic wastewater is different from that of the first organic wastewater by subjecting the wastewater to a predetermined pretreatment that reduces SS, BOD, etc. .

Although not limited to the following, the first organic wastewater when using the organic wastewater treatment apparatus shown in FIG. However, when the second organic wastewater is pretreated using the pretreatment tank 9 in FIG. ~2,000mg/L.

While the first organic wastewater is being nitrified and denitrified in the treatment tank 10, a BOD source is supplied from the outside into the treatment tank 10 during the treatment of the first organic wastewater. Before the industrial wastewater is supplied, a sufficient amount of activated sludge that has been acclimatized to the BOD source added from the outside can be stored in the treatment tank 10 in advance. In addition, even immediately after the second organic wastewater flows into the treatment tank 10, the BOD source necessary for denitrification treatment is supplemented in the denitrification tank 1, so that the water quality of the treated water due to temporary insufficient treatment due to activated sludge can be reduced. Deterioration can be suppressed.

The nitrification and denitrification treatment process includes a denitrification treatment process in which first organic wastewater and second organic wastewater are denitrified in a denitrification tank 1, and denitrification treated water obtained in the denitrification treatment process is denitrified in a nitrification tank 2. It is preferable that the BOD source is supplied to the denitrification tank 1 in the denitrification treatment process. In the denitrification process, a BOD source is supplied from the outside to the denitrification tank 1, so that the BOD source necessary for denitrification can be sufficiently supplemented, so that the denitrification process can proceed stably.

(Organic wastewater treatment method)
The organic wastewater treatment method according to the first embodiment of the present invention includes a first method for nitrifying and denitrifying a first organic wastewater containing ammonia nitrogen in a treatment tank 10 containing activated sludge. After the nitrification and denitrification treatment process and the first nitrification and denitrification treatment process, a second nitrification and denitrification process is performed in which a second organic wastewater is supplied into the treatment tank 10 and the second organic wastewater is nitrified and denitrified. and a nitrification process.

For example, in the first nitrification and denitrification treatment step, using the organic wastewater treatment apparatus shown in FIG. Nitrification and denitrification treatment. Thereafter, the drum screen 8 is replaced with the pretreatment tank 9 shown in FIG. 2, and the organic wastewater is pretreated in the pretreatment tank 9 to remove BOD, SS, etc. A second organic wastewater with a low BOD concentration is obtained. Next, the second organic wastewater is supplied to the treatment tank 10 and subjected to nitrification and denitrification treatment.

In the first nitrification and denitrification treatment step, the first organic wastewater is nitrified and denitrified, and a BOD source is supplied from the outside into the treatment tank 10 to nitrify and denitrify the first organic wastewater. It is preferable to have a step of acclimatizing activated sludge that can be subjected to nitrification and denitrification treatment to the second organic wastewater, which may cause insufficient denitrification treatment under certain conditions.

According to the activated sludge acclimatization method, organic wastewater treatment method, and organic wastewater treatment apparatus in nitrification and denitrification treatment according to the first embodiment of the present invention, the BOD source of inflow raw water accompanying equipment switching, etc. Since good denitrification performance can be exhibited even after the composition of the treated water changes, deterioration of the quality of the treated water can be suppressed and safer effluent water that can satisfy water quality standards can be obtained.

(Second embodiment)
As shown in FIG. 3, the organic wastewater treatment device according to the second embodiment of the present invention denitrifies the first organic wastewater and the second organic wastewater containing ammonia nitrogen. A first denitrification tank 11, a first nitrification tank 12 that nitrifies the denitrified water of the first denitrification tank 11, a second denitrification tank 21 that denitrifies the nitrified water of the first nitrification tank 12, and A BOD source supply means 6a that supplies a BOD source to the second denitrification tank 21 from the outside, an aeration tank 22 that aerates the denitrified water in the second denitrification tank 21, and solid-liquid separation of the treated water obtained in the aeration tank 22. A solid-liquid separation tank 3, a return means 4 for returning the sludge separated into solid and liquid in the solid-liquid separation tank 3 to the previous stage of the first denitrification tank 11, and a Based on the information on the timing at which the second organic wastewater is supplied to the first denitrification tank 11, where insufficient nitrogen treatment may occur, the BOD source supplied to the second denitrification tank 21 is increased compared to the steady state. BOD control means 71 is provided for controlling the addition rate of the BOD source added to the second denitrification tank 21 so as to acclimatize the activated sludge that can nitrify and denitrify the second organic wastewater. A BOD source supply means 6b for supplying a BOD source from the outside is connected to the first denitrification tank 11. Others are the same as the organic wastewater treatment apparatus shown in FIG.

In the organic wastewater treatment apparatus according to the second embodiment, the first denitrification tank 11 and the first nitrification tank 12 perform the first stage nitrification and denitrification process, and the second denitrification tank 21 and the aeration tank 22 perform the second stage nitrification and denitrification process. Perform processing. According to the organic wastewater treatment apparatus according to the second embodiment, since two or more denitrification tanks are provided, for example, while the normal nitrification and denitrification treatment operation is continued in the first denitrification tank 11 in the former stage, By acclimating the activated sludge in the second denitrification tank 21, the nitrification-denitrification process and the acclimatization of the activated sludge can be performed slowly in parallel.

FIG. 4 shows an example of an organic wastewater treatment apparatus in which an anaerobic digestion tank for anaerobically digesting organic wastewater is arranged as a pretreatment tank 9 for nitrification and denitrification treatment. Compared to the residual human waste obtained in the drum screen 8 in FIG. 3, the anaerobic digested liquid obtained in the pretreatment tank 9 in FIG. 4 has a lower concentration of SS, BOD, etc. With the switching of the device from the anaerobic digestion tank shown in FIG. 9 to the anaerobic digestion tank shown in FIG. 9, the properties of the organic wastewater flowing into the first denitrification tank 11 change greatly.

Therefore, in the second embodiment, the BOD control means 71 in FIG. 3 causes the anaerobic digestive fluid treated in the pretreatment tank 9 in FIG. For example, four weeks before the point in time, start supplying the BOD source from the outside to the second denitrification tank 21 via the BOD source supply means 6a, and control the supply amount of the BOD source so as to gradually increase the supply of the BOD source. do. As a result, while the first denitrification tank 11 and the first nitrification tank 12 perform normal nitrification and denitrification processing, the second denitrification tank 21 and the aeration tank 22 acclimatize activated sludge for treating anaerobic digestive fluid. can be completed slowly.

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, so that the treated water obtained in the solid-liquid separation tank can be The remaining BOD can also be suppressed, and deterioration of water quality can be prevented. After the activated sludge has been acclimatized in the second denitrification tank 21, a BOD source is added from the outside to the first denitrification tank 11 at the front stage, which is approximately one times the rated value, via the BOD source supply means 6b. Acclimatization will be completed in about two weeks. Note that it is also possible to shorten the acclimatization period by making the amount of BOD source added in the second denitrification tank 21 about twice the rated value.

When the anaerobic digestive fluid is supplied to the first denitrification tank 11 and denitrification treatment may be insufficient under the conventional conditions in the first denitrification tank 11, the BOD control means 71 controls the BOD source. It is also possible to additionally supply a BOD source such as methanol to the first denitrification tank 11 via the supply means 6b. As a result, even if the treatment equipment before the first denitrification tank 11 is switched, the organic wastewater after switching can be efficiently treated, and the quality of the treated water will not deteriorate due to changes in the properties of the organic wastewater. Problems can be contained.

The return sludge control means 72 returns more of the activated sludge acclimatized in the second denitrification tank 21 to the adjustment tank 5 before the anaerobic digestive fluid starts flowing into the first denitrification tank 11. In order to promote the acclimatization of activated sludge in step 11, the amount of returned sludge (amount of returned sludge) is set to be higher than the steady state (steady value) for a certain period of time before the inflow of anaerobic digestive fluid begins. It is preferable to control the return means 4 to. For example, if the steady-state return volume is Q (m ³ /d), the volume of returned sludge during the period in which BOD source is added and acclimatization is performed in the second denitrification tank 21 will not affect the water quality. For example, it can be set to 1.1 to 1.5Q, or even 1.2 to 1.4Q.

Before supplying a BOD source from the outside to the second denitrification tank 21 to promote acclimatization of activated sludge, the MLSS concentration in the first denitrification tank 11 is set to a steady state so that the treatment performance of the first denitrification tank 11 does not deteriorate. It is preferable to adjust it so that it is lower than the current value. Similarly to the first embodiment, also in the second embodiment, the MLSS concentration in the first denitrification tank 11 is 80% or less, typically 50 to 80%, of the MLSS concentration during steady operation. It is preferable to adjust the amount to be about 60 to 70%, more preferably about 60 to 70%.

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, the circulating water control means 73 reduces the circulation flow rate of the circulating water from a steady value, and transfers the nitrified and denitrified water in which nitrogen content remains to the second denitrification tank. It is preferable to control the circulation means 13 so as to supply activated sludge to the activated sludge tank 21 and to promote adaptation of the activated sludge in the second denitrification tank 21. For example, when the return amount in a steady state is Q (m ³ /d), the amount of circulating water during the period in which the BOD source is added and acclimatized in the second denitrification tank 21 is 0.5 to 0. 9Q, preferably 0.6 to 0.8Q, more preferably 0.7 to 0.8Q. By setting it to 0.5Q or more, it is possible to perform the treatment in the second denitrification tank 21, so that the water quality is not further deteriorated. Furthermore, by setting the temperature to 0.9Q or less, the amount of denitrification in the first denitrification tank 11 can be limited, and a sufficient amount of nitrate nitrogen can be supplied to the second denitrification tank 21 for acclimatization.

(Acclimatization method for activated sludge in nitrification and denitrification treatment)
In the activated sludge acclimatization method in the nitrification-denitrification treatment according to the second embodiment, the nitrification-denitrification treatment step includes a first-stage nitrification-denitrification treatment step and a second-stage nitrification-denitrification treatment step; Before the second organic wastewater is supplied to the process, a BOD source is supplied from the outside in advance in the latter nitrification and denitrification treatment process to acclimatize the activated sludge, and the treated sludge obtained in the latter nitrification and denitrification treatment process is This method differs from the activated sludge acclimatization method in the nitrification and denitrification treatment according to the first embodiment in that it includes a step of returning the activated sludge to the first stage nitrification and denitrification treatment step.

According to the acclimatization method according to the second embodiment, since there are two or more denitrification tanks, by lowering the amount of circulating water and increasing the nitrogen load in the second denitrification tank 21 in the latter stage, the first denitrification tank 11 is Activated sludge can be gradually acclimatized while continuing normal operation.

Examples of the present invention are shown 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.

(Change in TN concentration of effluent water when device switching processing is performed)
FIG. 6 shows an example of the change in TN concentration in the effluent when the treatment method is switched from the standard denitrification method to the pre-dehydration method in the human waste treatment plant shown in FIG. 5. Here, in order to reduce the effect of switching the treatment method on the denitrification treatment, the inflow load was reduced to half of the normal load until the fourth day, and then the treatment was performed with the inflow load returned to the normal load. Note that methanol was used as a BOD source for denitrification. The required amount of methanol was calculated and added according to the increase in TN concentration. However, because there were not enough bacteria in the treatment system to denitrify using methanol, the TN concentration continued to rise for about two weeks, reaching a maximum around the discharge standard value (10 mg/L) 12 days after switching. It rose to Thereafter, the TN concentration began to decrease as the number of methanol denitrifying bacteria increased, and the treatment became stable after 3 weeks.

(simulation result)
In the human waste treatment plant shown in FIG. 5, a simulation was conducted regarding 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. Tables 1 and 2 show the processing conditions. In both embodiments, the BOD required for TN removal was set to be three times the amount of TN removed, and the amount of methanol required for the treatment was calculated to compensate for the BOD insufficient for the treatment. In the steady state (normal state after switching to the pre-dehydration method), the inflow BOD load decreases, so the amount of methanol is increased, and the second denitrification tank denitrifies all the TN that could not be treated in the previous stages. I set it to do so. Further, in Comparative Example and Example 1, 97% of the TN inflow load was removed up to the first nitrification tank, and in Example 2, 94% in the acclimatization stage and 97% in the steady state. In Table 1, the TN removed by human waste-derived BOD is assumed to be 1/3 of the human waste-derived BOD, and the TN removed by methanol is calculated from the TN inflow load by the T-N removed by human waste-derived BOD. The value was obtained by subtracting N. The inflow load of TN into the second denitrification tank is set to be 3 to 6% of the inflow load of raw water TN, and the required amount in the second denitrification tank is T that is removed with methanol during acclimatization. -N, and 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. Further, each yield in Table 2 indicates how many bacterial cells are generated when various types of bacteria contained in the activated sludge treat the inflow load.

(Comparative example and Example 1)
In the human waste treatment plant shown in Figure 5, the case where methanol addition was started immediately after switching the processing method without acclimatization was used as a comparative example, and the case where acclimatization was carried out while performing nitrification and denitrification treatment before switching the processing method was used as a comparative example. FIG. 7 shows the changes in the amount of each methanol denitrifying bacteria present in the tank in the case of Example 1. In the comparative example in which acclimatization was not performed in advance, it was found that the methanol denitrifying bacteria increased to the required amount only 10 days after switching the BOD source. However, this result is an overestimation because methanol is added every day at the maximum amount that can be processed by the sludge in the system, and in reality, at least 2 to 3 weeks are required as shown in the example in Figure 6. It is thought that it will become.

In Example 1, in which acclimatization was performed, it was found that methanol denitrifying bacteria increased to the required amount 20 days after the start of acclimatization. The amount of methanol added during acclimatization was increased by 0.5 times, 1 times, and 2 times the amount added after switching (steady state) in order to give more margin to the methanol utilization capacity of activated sludge. I was able to do that. In addition, in Comparative Example and Example 1, in order to determine the amount of methanol to be added, it is necessary to evaluate the abundance of methanol denitrifying bacteria and methanol denitrification activity, and be careful that the amount added does not exceed the decomposition ability of sludge. There is.

(Example 2)
FIG. 8 shows simulation results of changes in the amount of methanol denitrifying bacteria present in the tank when the amount of denitrification was increased in the second denitrification tank and methanol was then added to the first denitrification tank. As a result of increasing the amount of denitrification in the second denitrification tank, it is possible to increase the amount of methanol denitrifying bacteria in the system by approximately 1.6 times in 28 days without adding methanol to the first denitrification tank. . Thereafter, by adding methanol twice as much as in the steady state in the first denitrification tank in the previous stage, the required amount of denitrifying bacteria can be secured in 11 days. Since this method does not require detailed adjustment of the amount of methanol added, various operations related to adjusting the amount of methanol added can be omitted, and it can be seen that activated sludge can be acclimatized easily.

1...Denitrification tank 2...Nitrification tank 3...Solid-liquid separation tank 4...Return means 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 means 72…Return sludge control means 73…Circulating water control means

Claims (11)

a nitrification-denitrification treatment step of nitrification-denitrification treatment of a first organic wastewater containing ammonia nitrogen in a treatment tank containing activated sludge;
In the nitrification-denitrification treatment step, before the second organic wastewater is supplied into the treatment tank, the denitrification treatment may be insufficient under the conditions for nitrification-denitrification treatment of the first organic wastewater. A method for acclimating activated sludge in nitrification and denitrification treatment, comprising a step of acclimating activated sludge by supplying a BOD source into a tank from the outside. The method for acclimating activated sludge in nitrification and denitrification treatment according to claim 1, characterized in that methanol is supplied as the BOD source. Claim 1, wherein in the nitrification and denitrification treatment step, the BOD source is supplied into the treatment tank from 2 to 6 weeks before the second organic wastewater is supplied into the treatment tank. Or the method for acclimating activated sludge in nitrification-denitrification treatment according to 2. Nitrification and denitrification according to any one of claims 1 to 3, characterized in that before supplying the BOD source into the treatment tank, the MLSS concentration in the treatment tank is lowered than during steady operation. Method for acclimating activated sludge in treatment. The nitrification and denitrification treatment step is
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;
has
The method for acclimating activated sludge in nitrification and denitrification treatment according to any one of claims 1 to 4, wherein the BOD source is supplied in the denitrification treatment step. The nitrification and denitrification treatment step is
It has a first stage nitrification denitrification treatment process and a second stage nitrification denitrification treatment process,
Before the second organic wastewater is supplied to the first stage nitrification and denitrification treatment process, the activated sludge is acclimatized by supplying the BOD source from the outside in advance in the second stage nitrification and denitrification treatment process, and the activated sludge is The nitrification and denitrification process according to any one of claims 1 to 5, further comprising a step of returning the treated sludge obtained by solid-liquid separation of the nitrification treated water in the denitrification treatment process to the preceding nitrification and denitrification treatment process. Method for acclimating activated sludge in treatment. a first nitrification-denitrification treatment step of nitrification-denitrification treatment of a first organic wastewater containing ammonia nitrogen in a treatment tank containing activated sludge;
After the first nitrification and denitrification treatment step, a second organic wastewater in which denitrification may be insufficient under the conditions for nitrification and denitrification of the first organic wastewater is supplied into the treatment tank, and the a second nitrification-denitrification treatment step of nitrification-denitrification treatment of the second organic wastewater;
In the first nitrification and denitrification treatment step, the first organic wastewater is nitrified and denitrified, and a BOD source is supplied from the outside into the treatment tank, and the second organic wastewater is nitrified and denitrified. A method for treating organic wastewater, comprising the step of acclimating treatable activated sludge. a denitrification tank that denitrifies first organic wastewater containing ammonia nitrogen;
a nitrification tank for nitrifying the denitrification treated water in the denitrification tank;
a solid-liquid separation tank that separates the nitrified water of the nitrification tank into solid-liquid;
a return means for returning the sludge separated into solid and liquid in the solid-liquid separation tank to the previous stage of the denitrification tank;
BOD source supply means for supplying a BOD source to the denitrification tank from the outside;
Based on the information on the timing at which the second organic wastewater is supplied to the denitrification tank, under the conditions in which the first organic wastewater is subjected to nitrification and denitrification treatment, insufficient denitrification treatment may occur. Before being supplied to the denitrification tank, the BOD source supply means is controlled to increase the BOD source supplied to the denitrification tank compared to the steady state, and the second organic wastewater is nitrified and denitrified. An organic wastewater treatment device comprising: BOD control means for promoting acclimatization of treatable activated sludge. a first denitrification tank that denitrifies first organic wastewater containing ammonia nitrogen;
a first nitrification tank that nitrifies the denitrified water of the first denitrification tank;
a second denitrification tank that denitrifies the nitrified water of the first nitrification tank;
BOD source supply means for supplying a BOD source to the second denitrification tank from the outside;
an aeration tank for aerating the denitrified water of the second denitrification tank;
a solid-liquid separation tank that separates the treated water obtained in the aeration tank into solid-liquid;
a return means for returning the sludge separated into solid and liquid in the solid-liquid separation tank to a stage before the first denitrification tank;
Based on the information on the timing at which the second organic wastewater is supplied to the first denitrification tank, the denitrification treatment may be insufficient under the conditions for nitrification and denitrification treatment of the first organic wastewater. The BOD source added to the second denitrification tank so as to increase the BOD source supplied to the second denitrification tank so that the second organic wastewater is acclimated with activated sludge that can be nitrified and denitrified by increasing the BOD source supplied compared to the steady state. A BOD control means for controlling the addition rate of organic wastewater. Before the second organic wastewater is supplied to the first denitrification tank, the return sludge is controlled to increase the amount of return sludge supplied to the first denitrification tank from a steady value. The organic wastewater treatment apparatus according to claim 9, further comprising a control means. comprising a circulation means for circulating a part of the nitrified water in the first nitrification tank to the first denitrification tank,
Before the second organic wastewater is supplied to the first denitrification tank, the circulating amount of the nitrified water that is circulated to the first denitrification tank via the circulation means is reduced from a steady value. 10. The organic wastewater treatment apparatus according to claim 9, further comprising circulating water control means for controlling said circulation means.