JPS60261596A - Biological sewage treating apparatus - Google Patents

Abstract

PURPOSE:To improve the efficiency of treatment and denitrification by providing an intermittent aeration vessel and a separation vessel in parallel, and connecting the top part of the aeration vessel with a sludge downpipe through an overflow pipe. CONSTITUTION:An intermittent aeration vessel 12 and a separation vessel 13 are provided in parallel, and an organic sludge introducing means 14 and an intermittent air introducing means 16 are furnished to the aeration vessel 12. The middle part of the separation vessel 13 is communicated with the lower part of the aeration vessel 12 by a sludge circulating line 15, and the top part of the aeration vessel 12 is connected to a sludge downpipe 22 by an overflow pipe 21 to send the sludge in the aeration vessel 12 into the sludge downpipe 22 of the separation vessel 13. Consequently, the equipment is made compact, and the efficiency of treatment and denitrification is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a treatment device for organic sewage containing ammonia nitrogen, and more specifically to a biological sewage treatment device that has compact equipment but has high nitrogen removal efficiency. .

Biological denitrification methods are widely used to remove ammonia nitrogen contained in organic wastewater. Biological denitrification method converts ammonia nitrogen (NHa-N) into nitrate nitrogen (NO) in an aerobic atmosphere by the action of nitrifying bacteria.
The nitrate nitrogen produced at the same time as being oxidized to In order to allow the reaction to proceed, it was considered that the aeration conditions had to be cut off and a hydrogen donor (such as methanol) had to be added instead. Therefore, as a system to solve this uneconomical problem and economically implement the biological denitrification method, a method using the BOD component in organic wastewater (sometimes called raw water) as a hydrogen donor has been proposed and put into practical use. has been made into FIG. 1 is a flow diagram showing an example of such a sewage treatment system, in which a denitrification tank 1 is provided on the upstream side and a nitrification tank 2 is provided on the downstream side, and the two are connected by a downflow line 3 and a return line 4. By doing so, we are trying to more completely denitrify the nitrified material. To explain the logistics in this flow, let Q be the amount of organic sewage flowing into denitrification tank 1, and if you want to increase the most effective treatment efficiency (balance between total treatment amount and purification rate), About 4 times the amount (4Q) of wastewater is sent from the denitrification tank 1 to the nitrification tank 2 through the downflow line 3, while about 3 times the amount (3Q) of wastewater is sent from the nitrification tank 2 to the denitrification tank 1 through the return line 4.
At the same time, treated water in an amount (Q) approximately equivalent to the inflow amount is discharged from the nitrification tank 2 and introduced into the sedimentation separation tank 6, where it is separated into sludge M and supernatant liquid W, and a part of the former is sent to the denitrification tank. The remaining portion is incinerated or otherwise disposed of, and the latter is discharged.

That is, organic sewage is nitrified in nitrification tank 2 while circulating between nitrification tank 2 and denitrification tank 1, and is returned to denitrification tank 1 where it is denitrified using the BOD component in the organic sewage as a hydrogen source. After undergoing the reaction, the water is further returned to the nitrification tank 2 via the downstream line 3 and discharged as treated water.

1 However, in the above system, it is necessary to maintain the dissolved oxygen (D O) in the nitrification tank at 2 rng/Jlj or more in order to advance the nitrification reaction in the nitrification tank.
DO will inevitably be present in the circulating fluid. Therefore, if you try to increase the nitrogen removal rate by increasing the circulation ratio, a large amount of DO will flow into the denitrification tank, and this will consume some of the organic matter that should be used as a hydrogen donor. Since the reaction rate in the denitrification tank is reduced accordingly, and the presence of Do impairs the anaerobic function, there are restrictions on increasing the circulation ratio. The normal circulation ratio is about 3, and the nitrogen removal rate in such cases is at most 75 to 80%, which leaves much room for improvement.

On the other hand, there is an idea that sewage generated in a small-scale specific area can be treated at a nearby small-scale treatment plant without having to send it to a large-scale treatment plant far away. There is a demand for something that is small and easy to maintain. From this point of view, research is progressing on devices that can perform nitrification and denitrification reactions in a single tank.
A continuous inflow batch type sewage treatment apparatus as shown in Utility Model Application No. 58-171300 has been proposed. In other words, this device divides the reaction tank into an organic sewage introduction part and a reaction part (however, the communication state is maintained), and the reaction part is equipped with a plurality of aeration pipes and rotating drainage pipes, and air is discharged from the aeration pipe. Nitrification and denitrification are carried out in the same reaction section by intermittent blowing.

When such a sewage treatment device is used, there is no need to return organic sewage or sludge, so a pump or the like for this purpose is unnecessary, and the maintenance of the device is easy. Furthermore, since aeration, denitrification and sedimentation separation are carried out in one tank, it has the advantage that the equipment is partially more compact than the conventional apparatus shown in FIG. However, in the above-mentioned treatment apparatus, aeration and precipitation are performed while the introduction of organic wastewater into the reaction tank is continued without interruption, so the amount of liquid in the reaction tank continues to increase until the precipitation is completed. On the other hand, if you try to fully aerate the organic sewage in the reaction tank and then settle the sludge, it will take a considerable amount of time, and the time required for the treatment cycle consisting of aeration, sedimentation, and discharge of supernatant water will be considerably longer. It also extends. Therefore, the reaction tank must have a volume that can accommodate the amount of organic sewage introduced for at least 3 to 4 hours. In addition, the denitrification reaction that takes place during the precipitation process is difficult to separate into nitrified liquid and BOD# because organic wastewater (BOD component), which is the hydrogen source, flows only from one side of the tank and the tank is left standing. insufficient contact.

The present invention has been made focusing on these circumstances,
It is an object of the present invention to provide a biological sewage treatment device that can make the equipment compact and improve the treatment efficiency, particularly the denitrification rate.

The sewage treatment equipment of the present invention, which has achieved the above object, has the following features:
An intermittent aeration tank and a separation tank are installed together, and the intermittent aeration tank is provided with means for introducing organic sewage and a means for intermittently introducing air, while the separation tank is provided with a sludge downpipe and an upper pipe at the top. A clear liquid discharge line, a circulation means for drawing out a sludge circulation line from the intermediate part via a sludge inlet and reintroducing the sludge circulation line to the lower part of the intermittent aeration tank, and furthermore, The gist is that the sludge descending pipes are connected by an overflow pipe, and the sludge from the intermittent aeration tank flows into the sludge descending pipe of the separation tank.

The configuration and effects of the present invention will be explained below with reference to the drawings, but the device shown in the drawings is not intended to limit the present invention, and any design changes that may be made as appropriate in keeping with the spirit of the preceding and following statements are within the scope of the present invention. included in the technical scope of

FIG. 2 is a cross-sectional explanatory diagram showing the sewage treatment equipment according to the present invention, in which 12 is a nitrification-denitrification tank (intermittent aeration tank), 13 is a separation tank, 14 is an organic sewage introduction line, and 15 is a circulating sludge introduction line. , 16 is an air introduction line, 17 is a first sludge descending pipe,
Reference numeral 18 indicates a supernatant liquid discharge line, 19 indicates a sludge inlet, 20 indicates a sludge discharge pipe, 21 indicates an overflow pipe, and 22 indicates a second sludge descending pipe, and the present structure will be described in more detail below.

The sewage treatment equipment S is configured with a nitrification/denitrification tank 12 and a separation tank 13, and the nitrification/denitrification tank 12 has circulating sludge at the introduction side end of a first sludge downpipe 17 whose lower end is enlarged in diameter and opened. Adjacent to the introduction line 15, the circulating sludge introduction line 15
An organic sewage introduction line 14 is connected to the introduction line 15, and an air introduction line 16 is connected to the ejector 23 interposed in the introduction line 15. Furthermore, sewage introduction line 14. Part or all of the circulating sludge introduction line 15 and the air introduction line 16 may be directly connected to the bottom of the tank. Also, approximately in the center of the separation tank 13 is a second tank which is open at the top and expanded in diameter at the bottom.
A sludge descending pipe 22 is disposed, and a gutter-shaped sludge inlet 19 is provided in the middle part of the separation tank 13 in the height direction so as to surround the second sludge descending pipe 22. The sludge circulation line 15a is connected to the circulation sludge introduction line 15 via a circulation pump P2. And separation tank 13
Since a treated supernatant layer is formed at the top of the tank, an overflow tank 24 is provided to overflow and discharge the supernatant layer, and
An overflow pipe 21 connects the top of the nitrification O denitrification tank 12 and a portion higher than the overflow water level of the separation tank 13 to the second sludge descending pipe 22 . Further, the separation tank 13 is provided with a sludge extraction pipe 20 at a position lower than the sludge inflow section 19. The reason why the second sludge descending pipe 22 is provided to pass through the supernatant layer and reach the bottom of the tank is to prevent the supernatant layer from being disturbed by the overflow sludge from the nitrification/denitrification tank 12. The sludge downcomer pipe 22 may be communicated with the tank bottom along the tank wall or through the outside of the tank.

When removing nitrogen from organic sewage using the sewage treatment equipment S as described above, first operate the pump P1 while the circulation pump P2 is stopped, and then operate the nitrification/denitrification tank 1.
Organic sewage is introduced into 2, and the sewage overflowing the same type 12 enters a separation tank 13 through an overflow pipe 21. Next, when the pump P1 is stopped and the solenoid valve 25 is opened by the timer 10 and the circulation pump P2 is started, the sludge extracted from the sludge inlet 19 (untreated sewage at the beginning of operation) is transferred to the circulation pump P2. through the inlet line 15 and the first ejector 23 while drawing in air.
The sludge descends through the downcomer pipe 17 and is introduced into the nitrification φ denitrification tank 12 . Then, by introducing circulating sludge, nitrification/denitrification tank 1
As the sludge level in 2 increases, the overflowing sludge passes through the overflow pipe 21 and enters the second sludge downcomer pipe 22, descends inside the second sludge downcomer pipe 22 by the siphon action, and is introduced into the separation tank 13 from the bottom, and the following is how it is. This cycle will be repeated, but the continuous introduction of sewage will not be carried out. By circulating the sludge in the sewage treatment apparatus S in this manner, the inside of the nitrification Φ denitrification tank 12 is brought into an aerated state (aerobic atmosphere), and the nitrification reaction progresses due to the action of nitrifying bacteria. Furthermore, as the amount of dissolved oxygen in the nitrification/denitrification tank 12 increases, the amount of dissolved oxygen in the separation tank 13 also increases, so that a slight nitrification reaction proceeds here as well. If the nitrification/denitrification tank is deep, the aeration effect will be increased and the nitrification efficiency will be improved.

When the nitrification reaction progresses to some extent through repeated sludge circulation,
The solenoid valve 25 is closed by the timer 10 to stop air entrainment, and the pump P1 is operated to introduce new organic sewage. That is, as the aeration in the nitrification and denitrification is stopped, the BOD component begins to increase, an anaerobic atmosphere is formed, and the denitrification reaction proceeds using the BOD component in the organic wastewater as a hydrogen donor. In other words, the nitrogen content in nitrified sludge is N2
At the same time as it was decomposed into gas and removed, the sewage in the separation tank 13 was separated into sludge and supernatant liquid, which overflowed the top of the separation tank 13.
The clear liquid enters the overflow tank 24 and is discharged out of the system. The sludge separated from the supernatant liquid forms a sludge level structure and flows into the sludge inflow section 19.
A portion of the sludge is circulated through the sludge and discharged from the sludge extraction pipe 20 to the outside of the system.

Since the sludge inflow section 19 is formed, the sludge level exhibits a stable height during operation, and there is no fear of disturbing the supernatant liquid layer. Thereafter, while circulating the sludge in the tank using the circulation pump P2, the opening of the solenoid valve 25 and the operation of the pump P1 are alternately repeated at regular intervals to nitrify the organic sewage.
Denitrification treatments are carried out alternately. In addition, in the device of the present invention, organic sewage is repeatedly subjected to denitrification treatment (nitrification/denitrification cycle), so treated water with an extremely high denitrification rate can be obtained.
″<-6z6″’fLMi, @+=w′″hjf95%
I am getting ``Go+yJl*''. Therefore, even if the introduction of organic sewage is not interrupted during nitrification operation, sewage treatment can be carried out without significantly reducing the denitrification rate. In the apparatus of the embodiment, since the ejector 23 is used during aeration, there is no need to provide an aeration blower, which can further contribute to reducing equipment costs.

In aerobic conditions, dissolved oxygen (D O) is 2 mg/l due to aeration.
The amount of air blown in should be set so that the amount of air is blown in at or below the same level as the above, and the amount of raw water inflow, etc., should be set so that the DO will disappear quickly after the aeration stops in the anaerobic state. One aeration time is usually 5 to 60 minutes, and the stop time is 10 to 60 minutes.
Although it operates for 20 minutes, if the total time of aeration and aeration stop time is considered to be one cycle time, the maximum number of cycles performed in one day is about 96 times in 7 days.

The above number of cycles corresponds to the circulation ratio in the conventional nitrification liquid circulation method described above, and considering that the conventional circulation ratio is about 3, the number of cycles according to the present invention is much larger than that. In the present invention, for example, 95
This is the reason for achieving a high nitrogen removal rate of over %.

The basic configuration of the present invention is as described above. It is recommended to mix blast furnace slag, converter slag (hg)N. That is, when the above-mentioned solid component is mixed, this forms a nucleus around which microorganisms adhere and grow at a high concentration, so that the nitrification-denitrification reaction proceeds rapidly. Along with this, the settling properties of activated sludge are also greatly improved. In addition, when Ca-containing substances such as lime, blast furnace slag, and converter slag are used as the solid component, free Ca reacts with phosphorus components (POa-P) contained in organic wastewater, and is captured as Ca salt (calcium phosphate).・Nitrogen and phosphorus can be removed stably at the same time by appropriately replenishing the solid components that are removed from the tank as surplus sludge and adjusting the tank internal pH to about 8.

The present invention is configured as described above, and since the MLSS can be increased by adding solid components, the apparatus can be made compact. In addition, since the denitrification reaction is carried out in the sludge circulation state, the contact efficiency between the hydrogen donor and the nitrified sludge is high, and the denitrification reaction efficiency is also excellent.2 In other words, the amount of sewage treated per unit time is large, and the device is compact. It is possible to treat a large amount of wastewater. In addition, the sludge obtained through treatment has good dewatering properties,
It can be used as fertilizer by composting.

Examples of the present invention will be described below.

Example Sewage was introduced into the apparatus of the present invention and nitrified and sewage was carried out under the conditions shown in Table 1.
When the denitrification treatment was carried out, treated water shown in Table 2 was obtained.

Table 1 Table 2 Table 5 As shown in Table 1.2, in the example, an excellent denitrification rate of 97.4% was obtained, and phosphorus was also removed by adding converter slag. . In addition, since the reaction proceeded quickly, the wastewater could be treated in a short time as shown by the wastewater residence time (4 poems). In addition, in the present invention, the short residence time of sewage means that the scale of the treatment equipment can be small to treat a certain amount of sewage, and conversely, if the scale is the same, the amount of treatment will increase. It means that.

By the way, when comparing the examples shown in Tables 1 and 2 with the conventional nitrification liquid circulation system, it is found that in the conventional system (the volume ratio of the first denitrification tank, nitrification tank, second denitrification tank, and re-aeration tank is 1. : 1.3
3: 0.88: 0.33, the total residence time is 1
5.284), circulation ratio 4. When the same sewage as in the example was treated at a water temperature of 16 to 22°C), the total nitrogen removal rate of the treated water was 74% on average, and the maximum was about 86% (the volume load is the total volume of the first denitrification tank and nitrification tank). against 0.030 kg BO
About n/m3・day, 0.0 for the total volume of all tanks.
021 kg BOD/m3・day).

By increasing the volume load of the present invention, the apparatus can be made smaller, and a high nitrogen removal rate can be obtained even though the addition of methanol is not necessary. Furthermore, it has advantages such as easy maintenance and management of the device.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing a conventional sewage treatment device, and FIG. 2 is a cross-sectional explanatory diagram showing a sewage treatment device according to the present invention. l... Denitrification tank 2... Nitrification tank 3... Downflow line 4... Return line 5... Discharge line 6... Sedimentation separation tank 12... Nitrification/denitrification tank
13... Separation tank 14... Organic sewage introduction line 15... Circulating sludge introduction line 18... Air introduction line 17... First sludge descending pipe 1st... Supernatant discharge line 18... ...Sludge inflow section 2o...Sludge extraction pipe 21...
・Overflow pipe 22...Second sludge descending pipe Applicant: Kobe Steel, Ltd. U9 Figure 1

Claims (1)

[Claims] An intermittent aeration tank and a separation tank are installed together, and the intermittent aeration tank is provided with means for introducing organic sewage and a means for intermittently introducing air, while the separation tank is provided with a sludge downpipe and an upper pipe at the top. A clear liquid discharge line, a circulation means for drawing out a sludge circulation line from the intermediate part via a sludge inlet and reintroducing the sludge circulation line to the lower part of the intermittent aeration tank, and furthermore, 1. A biological sewage treatment device characterized by having a structure in which sludge downcomers are connected by an overflow pipe and sludge from one intermittent aeration tank flows into the sludge downcomer of a separation tank.