JPS60255199A - Biological treating device for organic waste water - Google Patents

Abstract

PURPOSE:To remove simultaneously, efficiently and biologically nitrogen and phosphorus in org. waste water to be admitted into aeration tanks by communicating and disposing the plural aeration tanks in such a way that the org. waste water therein moves in the state of plug flow. CONSTITUTION:The aeration tank 9 is segmented by a partition wall 10 having a notched bottom to the 1st layer 9a and the 2nd layer 9b. Both layers are communicated in the bottom. An air diffusing pipe 12 connected to a blower 5 is disposed in the bottom of the tank 9 and a settling and separating tank 6 is provided on the down stream side of the tank 9 to return part of the separated sludge to the waste water inlet of the tank 9. Simultaneous removal of nitrogen and phosphorus is efficiently executed by such compact device.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an organic wastewater treatment apparatus capable of biologically simultaneously and efficiently removing nitrogen and phosphorus from organic wastewater.

A nitrifying solution circulation system has been put to practical use as a method for removing ammonia nitrogen (NH, -N) contained in organic wastewater (hereinafter simply referred to as wastewater).

In this method, as shown in Figure 1, the NH in the wastewater that has passed through the denitrification tank 2 and flowed into the nitrification tank 2 is returned to the denitrification tank 1.
4-N is nitrified to NOx-N by aeration from the blower 5, and the generated nitrified liquid 3 is returned to the denitrification tank 1 where it is decomposed into nitrogen and removed using the B01) component in the wastewater 4 as a hydrogen donor. Ru.

In such a nitrification liquid circulation system, since the BOD component in the waste water 4 is used as a hydrogen donor, there is no need to purchase and input a hydrogen donor such as methanol, and there is an advantage that there is no need for chemical costs. However, in the nitrification liquid circulation system, in order for the nitrification reaction of NH4-H to proceed in nitrification tank 2, the dissolved oxygen ('D O) in the tank must be reduced to 2 my/1l.
Since it is necessary to retain F, DO is inevitably present in the circulating nitrification liquid 3 as well. Therefore, if an attempt is made to increase the circulation ratio to improve the nitrogen removal rate, i amount of DO will flow into the denitrification tank. As a result, the reaction rate in the denitrification tank is reduced accordingly, and furthermore, the presence of DO in the anaerobic tank impairs the anaerobic function itself. Therefore, it is not possible to unnecessarily increase the amount of nitrifying fluid circulated, and although the aforementioned range of 3 to 6 times is considered a suitable index, in general, nitrifying fluid 3
The actual situation is that the amount of circulating water is kept to about three times the amount of wastewater 4 introduced, and the nitrogen removal rate at this time is only as low as 75 to 80 inches. Therefore, in the conventional nitrification liquid circulation system, it is common to add a second denitrification tank that uses methanol, etc. after the nitrification tank 2, and a re-aeration tank following this to improve the nitrogen removal rate. be. In other words, the nitrification liquid circulation method has the disadvantages of (1) low nitrogen removal rate, or (2) the cost of installing a second denitrification tank and the cost of chemicals such as methanol. Eutrophication of rivers has become a problem, and in order to prevent eutrophication, in addition to removing nitrogen components, phosphorus components (PO, -
It is necessary to remove P, etc.), and an oxidation/coagulation-sedimentation method by adding lime or sulfuric acid is used to remove the phosphorus component.

However, in 1975, Barnard of the Federation of South Africa reported that even with the above-mentioned nitrifying solution circulation method, the removal of phosphorus components sometimes progressed well at the same time, and based on this knowledge, simultaneous removal of nitrogen and phosphorus was reported. Various methods have been proposed (for example, Proceedings of the Japan Society of Civil Engineers, No. 324, 198
(August 2016). The dephosphorization mechanism in the nitrification liquid circulation system is considered as follows. That is, in FIG. 1, the dewinging tank 1 is in an anaerobic state, but under this condition, the phosphoric acid polymer inside the microorganism is decomposed and released as PO and -P outside the microorganism. Therefore, PO in the wastewater introduced into denitrification tank 1,
-P concentration becomes higher than before introduction, and is transferred to the nitrification tank as it is. As described above, the nitrification tank 2 is kept in an aerobic state, where the PO4-PfrE microorganisms in the wastewater ingest it and convert it into phosphoric acid polymer in the body. This amount of intake exceeds the amount released under anaerobic conditions, and the microorganisms are in a state where they have taken in too much phosphorus, and from the perspective of the wastewater, the po and -p concentrations decrease. The treated wastewater is then introduced into a sedimentation separation tank 6 together with activated sludge containing an excess of PO4-P, where it is separated into treated water 7 and settled sludge 8.
The treated water 7 is discharged to the outside of the system, a part of the settled sludge 8 is returned to the denitrification tank 1, and the rest is discharged to the outside of the system as surplus sludge. In this way, the phosphorus component (PO, -
Removal of P) is carried out in parallel with nitrification and denitrification.

However, upon further investigation, it was found that the above-mentioned nitrogen/phosphorous removal type apparatus has a drawback in that if it is attempted to perform sufficient dephosphorization, nitrogen removal becomes insufficient. This means that the BOD load when the dephosphorization reaction progresses smoothly is 0.3 to 0.4 kg B OD/l<g
The BOD load when the denitrification reaction progresses smoothly is 0.16 kg, whereas the BOD load is 0.16 kg when the denitrification reaction progresses smoothly.
BOD/kg ML S S・day (Nitrogen load: 0.02
The BOD load under proper dephosphorization conditions is excessive for the denitrification reaction because it is as low as 4 kg N7 kg ML SS day).

Therefore, if the BOD load is set under appropriate dephosphorization conditions, non-nitrogen will be discharged from the denitrification tank 1 without being denitrified, which will eventually increase the NH4-N concentration in the treated water discharged to the outside of the system. On the other hand, if the BOD load is set according to the denitrification treatment, the dephosphorization treatment efficiency will be significantly reduced. In addition, practically BOD
In many cases, a method is adopted in which the load is set to the dephosphorization processing conditions and the unremoved nitrogen is removed in a second denitrification tank installed as a post-process, but in this case, the installation cost of the second denitrification tank is and drug costs will rise further.

The present invention has been made with attention to this situation, and is a method that simultaneously and efficiently removes both nitrogen and phosphorus from organic wastewater and reduces processing costs such as equipment costs. The present invention aims to provide a treatment device for organic wastewater.

The treatment apparatus of the present invention, which has achieved the above object, connects a plurality of aeration tanks in which microorganism-attached carriers are arranged so that the organic wastewater flowing into the aeration tanks moves in a plug flow state. An intermittent aeration means is provided at the bottom of each aeration tank, a sedimentation separation tank for sludge in the aerated water is provided downstream of the aeration tank, and a sludge return means is provided for returning the separated sludge to the aeration tank. The main point lies in the following points.

That is, the aeration tank of the treatment device according to the present invention does not have two types of tanks with different functions, such as an aerobic tank (nitrification tank) and an anaerobic tank (denitrification tank) in known devices, but rather By providing an intermittent aeration means in the tank, the same tank can be configured to function as an aerobic tank during aeration and as an anaerobic tank when aeration is fixed. Examples include placing the trachea and operating the blower intermittently using a timer. In addition, the aeration tank according to the present invention is one in which a microorganism-adhering carrier is arranged in the aeration tank, and for example, a compartment partitioned by a porous shelf is provided in the middle part of the aeration tank, and the microorganism-adhering carrier such as Raschig ring is placed in the aeration tank. For example, an aeration tank may be used, such as an aeration tank in which a large number of shelves are arranged in the form of a baffle plate, or an aeration tank in which a honeycomb body is installed. In addition, in the case of Raschig rings, by using a material with a lower specific gravity than water, such as polypropylene, the microorganism-attached carrier can be floated without requiring downward support. In addition, when Raschig rings or honeycomb bodies are used as carriers, they also play a role in allowing the wastewater moving in the reaction tank to pass through in a plug flow state, and also have a disturbance prevention function so that the wastewater in the aeration tank is not disturbed during aeration. do. Note that the means for obtaining a plug flow state is not limited to the use of Raschig rings or honeycombs, and it is sufficient to gradually introduce and discharge wastewater.

Further, a sludge settling tank is provided downstream of the aeration tank, and the two are connected so that the treated water and sludge discharged from the aeration tank flow into the sludge settling tank, and the sludge separated by sedimentation in the sludge settling tank is A line with a sludge return means, such as a sludge feed pump, is provided so that the sludge is returned to the reaction tank, and the bottom of the sludge settling tank is connected to the wastewater inlet of the aeration tank.

FIG. 2 is a schematic diagram showing an example of a wastewater treatment device that satisfies the above requirements. The aeration tank 9 is divided into a first layer 9a and a second layer 9b by a partition wall 10 with a cutout at the bottom, and both layers are divided into a first layer 9a and a second layer 9b. The six tanks are connected to each other at the bottom, and at an intermediate position in the height direction of the six tanks, both ends are partitioned by a porous shelf 11 to form a microorganism support section filled with Raschig rings 16. Further, an aeration pipe 12 connected to the blower 5 is arranged at the bottom of the aeration tank 9, and a timer 13 is connected to the blower 5. Furthermore, aeration tank 9
A sedimentation separation tank 6 is provided on the downstream side of the sedimentation separation tank 6, and the discharged treated water from the aeration tank 9 is introduced, and the sludge separated in the sedimentation separation tank 6 is discharged from the extraction pipe 14, and some of the separated sludge is transferred to the sludge feeder. The wastewater is returned to the wastewater inlet of the aeration tank 9 by the pump 15 . Further, the supernatant liquid in the sedimentation separation tank 6 is discharged to the outside of the system as treated water 7.

In the treatment apparatus of the present invention having the above configuration, the organic wastewater containing NH4-N, PO, and -P introduced into the inlet of the aeration tank descends through the first layer 9a while forming a plug flow state, and passes through the bottom communication section. The liquid then enters the second layer 9b, where it also rises in a plug flow state and is discharged to the sedimentation separation tank 6. During this time, the timer 13 operates the sieve blower 5 intermittently to create an aerobic state and an anaerobic state in the aeration tank 9 alternately. As a result, when the atmosphere becomes aerobic, the nitrification reaction and the excessive intake reaction of PO4-P proceed, while when the atmosphere becomes anaerobic, the denitrification reaction and the release reaction of PO4-P proceed.

Treated water from which nitrogen and phosphorus have been sufficiently removed can be obtained.

Next, the above intermittent aeration situation will be schematically explained using FIGS. 3 to 9 (schematic diagrams). Assuming that the wastewater in the aeration tank 9 is completely replaced by repeating the aeration/non-aeration cycle six times, the wastewater in the first layer 9a and the second layer 9b is equally divided into three layers A to F. However, for ease of understanding, the introduction of waste water and the discharge of treated water will be explained intermittently. First, when the aeration tank 9 at the water level shown in Figure 3 is maintained in a non-aerated state for a certain period of time while only introducing waste water without discharging treated water, the amount of waste water increases by P as shown in Figure 4. The state is obtained. Next, the introduction of wastewater is stopped and aeration is carried out for a certain period of time while only discharging the treated water. As shown in Figure 5, F of the treated water is discharged and the water level decreases (however, in reality, the introduction of wastewater and the treated water In some cases, the water level is kept constant and the changes shown in Figs. When the aeration is repeated, treated water from E to A is sequentially discharged, and the state shown in FIG. 8 is obtained after passing through the states shown in FIGS. 6 and 7. As described above, the wastewater in the aeration tank moves in a plug flow state and then repeats the non-aerated and aerated states, so that denitrification and dephosphorization treatments are performed to a high degree during that time.

The aeration/non-aeration cycle described above is carried out by, for example, continuing the aeration state for 5 to 60 minutes and then continuing the non-aeration state for 10 to 120 minutes, and the time required for one cycle is set to the shortest 15 minutes. Then, the number of cycles performed per day can be 96 times/day. This number of cycles corresponds to the circulation ratio in the nitrification liquid circulation system, and is significantly higher than the circulation ratio of 3 to 6 times, so the nitrogen removal rate can be reduced to 9 times.
It can be increased to 5φ or more. The ratio (aeration time/aeration stop time) is preferably 1 to 5, and particularly 1 to 3 to give better results. Also, during aeration, it is preferable to set the aeration amount so that Do is 2 my/l or less, and the DO during aeration is 2 my/l or less.
/l, it becomes difficult to quickly reduce DO when aeration is stopped.

Other examples in Figure 2 show the aeration tank 9 divided into two tanks, but as shown in Figure 9, it is divided into three tanks and the discharged treated water is extracted from the bottom of the rightmost tank in the figure. As shown in FIG. 10, it may be divided into 4 tanks, and of course it is also possible to partition into 5 or more tanks.

In that case, in order to keep the final stage of the treatment process aerobic and prevent the release of phosphorus from the sludge, a continuous aeration means may be provided at the bottom without disposing a sludge supporting member in the final stage tank. Alternatively, as shown in FIG. 11, the lower portions of independent reaction vessels 9 may be connected through a communication pipe 17.

In the present invention, the denitrification reaction with a low appropriate BOD load can proceed simultaneously with the dephosphorization reaction with a high appropriate BOD load by arranging a microorganism support member in the aeration tank and by controlling the wastewater in a plug flow state. The reason for this effect is not clear, but
For example, in order to improve the contact efficiency between wastewater and sludge, a stirrer is provided in each column to completely mix the inside of the tank, but the desired dephosphorization effect cannot be obtained. In addition, due to the arrangement of the two microorganisms, the sludge does not settle, so the contact area between the sludge and wastewater is wide, and the contact condition is also very good, so that new water and sludge are always in contact with each other. Therefore, there was no need to perform mechanical stirring to improve the contact state, and the nitrification and denitrification ability was improved, contributing to a reduction in the unit power consumption.

The present invention is constructed as described above, and can efficiently remove nitrogen and phosphorus simultaneously with a compact device. In particular, it is possible to obtain a high nitrogen removal rate without using a secondary denitrification device while sufficiently carrying out the dephosphorization reaction.

Furthermore, since it is necessary to circulate the nitrifying solution, there is no need to install or operate a pump, and the running cost is particularly low, which is a significant economic effect.

Examples of the present invention will be described below.

In the treatment apparatus shown in FIG. 12, wastewater having the quality shown in Table 1 below was treated at a rate of 601 days.

The reaction tanks 9 have a total volume of 14/9A and 9B.

It is divided into 9C and 9D with a volume of 41, 9A and 9B.

In 9C and 9D, 31 polypropylene sludge supporting members (Raschig rings) each with an apparent volume were arranged, and an intermittent aeration means 12 was installed at the bottom.

Further, on the downstream side of the reaction tank 9, a ``sedimentation separation tank 6'' was arranged.

While introducing wastewater during the aeration stoppage of the intermittent aeration tanks 9A, 9B, and 9C, the DO of the intermittent aeration tanks is 1 to 1.5 fnti/
Adjust the amount of air blown from the blower 5a so that it becomes 1.
When the cycle of aeration for 0 minutes and then stopping aeration for 30 minutes was repeated, treated water having the quality shown in Table 2 was obtained from the settling tank 6.

Table 2 □ At 9D during operation, continuous aeration was omitted and the air supply amount was adjusted so that the DO was 1.5 to 12 to 1/2.

Additionally, excess sludge was periodically extracted so that the MLSS in the reaction tank was 40,0004.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram showing a nitrification liquid circulation type processing equipment, Figure 2
The figure is an explanatory diagram of the processing apparatus according to the present invention, FIGS. 3 to 8 are schematic diagrams showing a plug flow state, and FIGS. 9 to 12 are explanatory diagrams showing other embodiments. 4...Wastewater 9...Reaction tank 16...Sludge holding member Applicant Kobe Steel, Ltd. Figure 3 Figure 4 Figure 6A 7th bolt 17i7/ Figure 5 Figure 8 ν

Claims (1)

[Claims] A plurality of aeration tanks arranged in a microbial adhesion carrier tank are arranged in communication with each other so that organic wastewater flowing into the aeration tank moves in a plug flow state, and an intermittent aeration means is provided at the bottom of each aeration tank,
A sedimentation separation tank for sludge in the aerated water is provided downstream of the aeration tank, and a sludge return means for returning the separated sludge to the aeration tank is provided. Biological treatment equipment for wastewater.