JPH0421559B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for treating nitrogen components in organic wastewater in a single tank, and particularly to a method for treating organic wastewater with high nitrogen removal efficiency. [Prior Art] Biological denitrification methods are widely used to remove ammonia nitrogen contained in organic wastewater. Biological denitrification is a process in which ammonia nitrogen ( _NH4 -N) is oxidized to nitrate nitrogen ( _NOx -N) by the action of nitrifying bacteria in an aerobic atmosphere. It is reduced to N ₂ gas in an anaerobic atmosphere by the action of denitrifying bacteria, and it is known that organic matter as a hydrogen donor is essential for this reaction to proceed. Methanol is a typical hydrogen donor, but problems remain in terms of operating costs. 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 was proposed and put into practical use. has been done. FIG. 2 is a flow diagram showing an example of such a sewage treatment system. The system includes a denitrification tank 11 on the upstream side and a nitrification tank 12 on the downstream side, and both are connected by a downstream line 13 and a return line 14. By connecting it, we are trying to more completely denitrify the nitrified material. To explain the logistics in this flow, if the amount of organic sewage L flowing into the denitrification tank 11 is Q, if we want to increase the effective treatment efficiency (balance between the total amount of treatment and the purification rate), 3 to 6 times the amount, e.g. 4 times the amount (4Q)
About 3Q of wastewater is sent from the denitrification tank 11 to the nitrification tank 12 through the downflow line 13, while about 3 times the amount (3Q) of wastewater is returned from the nitrification tank 12 to the denitrification tank 11 through the return line 14, and the inflow amount is approximately At the same time, an equal amount (Q) of treated water is discharged from the nitrification tank 12 and introduced into the sedimentation separation tank 16, where it is separated into sludge M and supernatant liquid W. A part of the former is returned to the denitrification tank 11, and the remainder is The latter is treated by incineration, etc., and then released.
That is, the organic wastewater L is nitrified in the nitrification tank 12 while circulating between the nitrification tank 12 and the denitrification tank 11, and is returned to the denitrification tank 11, where the organic wastewater L is nitrified.
It undergoes a denitrification reaction using the BOD component as a hydrogen source, and then returns to the nitrification tank 12 via a downstream line 13 and is discharged as treated water. However, in the above system, in order to advance the nitrification reaction in the nitrification tank, it is necessary to maintain the dissolved oxygen (DO) in the tank at 2 mg/or more.
DO will inevitably exist in the circulating fluid from the nitrification tank 12. Therefore, if an attempt is made to increase the nitrogen removal rate by increasing the circulation ratio, a large amount will be generated in the denitrification tank 11.
Since DO flows in and consumes some of the organic matter that should be used as hydrogen donors, the reaction rate in the denitrification tank decreases, and furthermore, the presence of DO impairs the anaerobic function. Therefore, even if we want to increase the circulation ratio, there are naturally restrictions. For this reason, the circulation ratio is usually set at around 3Q as described above, and the nitrogen removal rate in such cases is at most 60%, which is insufficient. Therefore, in the nitrification liquid circulation method, in order to improve the nitrogen removal rate, it is common practice to install a second denitrification tank and a reaeration tank after the nitrification tank (for example, Japanese Patent Application Laid-Open No. 58-210898). However, since the second denitrification tank uses methanol or the like as a hydrogen donor, the treatment cost increases, and since multiple treatment tanks and sedimentation separation tanks are provided, the equipment cost also increases, and it is difficult to achieve a sufficiently satisfactory nitrogen removal rate. I never got close to getting it. [Problems to be Solved by the Invention] The present invention has been made in view of these circumstances, and is capable of reducing processing costs and equipment costs, and improving nitrogen removal efficiency and nitrogen removal rate. The aim is to provide a biological treatment method for organic wastewater. By the way, recently, organic wastewater is introduced into a treatment tank filled with granular carriers, air is sent into the tank from the bottom of the carrier filling part to aerobically decompose the organic matter in the wastewater, and the treated wastewater is discharged from the bottom of the tank. In other words, research is being conducted on a treatment method that can be called an aerobic biological method (for example, Japanese Patent Application Laid-Open No. 1983-
No. 51986). This method has the advantage of being able to obtain clear treated wastewater from the bottom of the tank because the sludge is taken up in the carrier filling section, and has the advantage of not requiring a sludge sedimentation separation tank and having a high ability to remove organic matter. are doing. Since this method involves aerobic decomposition, nitrogen components cannot be removed at all. Therefore, the present inventors have conducted research in an attempt to provide a method that can eliminate the drawbacks of the nitrification liquid circulation method and the aerobic biological filtration method, that is, a method that can obtain high nitrogen removal efficiency at low cost. As a result, the present invention was completed. [Means for Solving the Problems] The present invention provides biological treatment for organic sewage using a treatment tank in which microorganism-attached carriers are arranged and an intermittent aeration means is provided at the bottom of the treatment tank. The gist of this method is that when aeration is stopped, organic sewage is introduced into the tank from the top of the tank and allowed to descend inside the tank, while aeration is performed intermittently, and the treated wastewater is discharged from the bottom of the tank. It is something. [Function] The treatment tank itself used in the present invention has roughly the same configuration as that applied to the biological filtration method, but
The aeration means provided in the treatment tank is operated intermittently, unlike the biological filtration system. That is, in the present invention, by aeration, an aerobic atmosphere is formed in the tank to allow the nitrification reaction to proceed, while by stopping aeration, an anaerobic atmosphere is created in the tank to allow the denitrification reaction to proceed. By repeating intermittent aeration, the nitrification reaction and denitrification reaction are allowed to proceed alternately within a single tank. When the aeration is stopped, the BOD component contained in the organic wastewater introduced into the tank from the top is used as a hydrogen donor for the denitrification reaction. In addition, in the present invention, the microorganism-attached carrier 3 is housed in the treatment tank 1, and the organic wastewater is introduced from above and discharged from the bottom, so the organic wastewater moves within the treatment tank 1 in a plug flow state. The wastewater is then repeatedly subjected to nitrification and denitrification treatments during transportation, yielding highly treated wastewater. In addition, sludge generated as a result of nitrification and denitrification is
Clear treated water can be obtained from the bottom of the treatment tank 1 because it adheres to the carriers or is taken up in the gaps between the carriers.
In the present invention, when forming an aerobic atmosphere, the dissolved oxygen concentration (DO) in the tank should be 1 to 2 mg/
It is desirable to carry out aeration to such a degree that the DO will drop to almost zero in about 2 minutes after the aeration stops, creating an anaerobic atmosphere, which is particularly inconvenient when carrying out continuous operation. Nor. Although it depends on the properties of the raw water, the aeration time is generally 2 to 60 minutes.
It is generally desirable that the aeration stop time be 5 to 60 minutes. By the way, the total of one aeration and aeration stop time is one cycle time, for example, if aeration is 3 minutes,
Assuming that the stoppage is 7 minutes and that the organic sewage introduced from the top of the tank reaches the bottom of the tank and is discharged out of the tank once every day, the number of cycles per day is 144. This number of cycles corresponds to the circulation ratio in the nitrification liquid circulation system, and is much higher than the circulation ratio of 3, so that in the present invention, a high nitrogen removal rate of 95% or more can be obtained. In addition, examples of microorganism-attached carriers in the present invention include plastics, bricks, crushed stone, coke, blast furnace slag, etc. Among these, porous inorganic materials such as coke, blast furnace slag, and lightweight aggregates are particularly recommended in terms of performance and cost. be done. Also, the carrier has a particle size of 2 to 8 mm.
Particularly desirable is one with a diameter of 3 to 6 mm.
It is preferable to fill the tank at a height of 1.5 to 2.5 m. [Example] Next, one embodiment of the present invention will be described with reference to FIG. The treatment tank 1 stores microorganism-attached carriers 3 on a perforated plate 2 arranged at the bottom of the tank, and has an aeration pipe 4 at the lower part of the carrier storage part, and an aeration pipe 4a for backwashing below the perforated plate 2. are installed respectively. The air diffuser pipe 4 is connected to the blower B through the electromagnetic valve V1, and the backwash air diffuser pipe 4a is connected to the blower B through the valve V2. Further, a discharge pipe 5 for discharging treated water is connected to the bottom of the treatment tank 1, and the discharge side is led to a treated water storage tank 6, and a pump P1 is connected to the top of the treatment tank 1.
An organic sewage inlet pipe 8 is provided so as to face the inside of the tank. Further, the pump P1, the blower B, the solenoid valve V1, and the control unit 7 are configured so that when the pump P1 is operated, the solenoid valve V1 is closed and the blower B is also stopped, while when the pump P1 is stopped, the solenoid valve V1 is closed. They are connected by an intermittent operating circuit that opens and blower B operates. In the above system, organic sewage L is placed in treatment tank 1.
After putting in a predetermined amount of , the pump P1 is stopped, while the solenoid valve V1 is opened, and at the same time, the blower B is operated to send air into the tank from the diffuser pipe 4. This creates an aerobic atmosphere inside the tank and allows the nitrification reaction to proceed. After aeration for a predetermined period of time, the solenoid valve V1 is closed, the blower B is stopped, and the pump P1 is operated to introduce organic wastewater L into the tank. A short time after the aeration stops, the inside of the tank becomes an anaerobic atmosphere, and the denitrification reaction proceeds using the BOD component in the organic wastewater as a hydrogen supply source. Furthermore, the valve V3 of the discharge pipe 5
is opened as appropriate while the aeration is stopped, and clear treated water generated at the bottom of the tank is drawn out to the storage tank 6. Thereafter, the organic wastewater L is treated by repeating the same operation. Next, when the organic sewage L is continuously treated for 1 to 2 days and sludge adheres to and accumulates on the carrier in the tank, the flow resistance of the organic sewage L increases according to the accumulated amount, so the valve V3 Even if the tank is opened, the liquid level in the processing tank 1 will not drop. When such a state occurs, the operation of the pump P1 and the blower B is stopped, the control by the control unit 7 is released, the electromagnetic valve V1 is closed, and the valve V3 is also closed. Next, the valve V4 is opened and the pump P2 is activated to send the treated water in the storage tank 6 to the bottom of the tank as backwash water. At the same time, the valve V3 is opened and the blower B is operated to introduce air into the tank from the aeration pipe 4a. By the above operation, the sludge accumulated on the surface of the carriers or in the gaps between the carriers 3 is lifted up, washed away by the backwash water, and moved to the upper side of the treatment tank 1. Then, it overflows from the upper end of the treatment tank 1 and enters the overflow groove 9, where it is discharged outside the system, for example, to the initial settling tank of a sewage treatment plant. Note that by automatically detecting the water level in the treatment tank, the backwashing operation can be automated. Example A treatment tank of the type shown in FIG. 1 having an inner diameter of 25 cm and a height of 400 cm was filled with blast furnace slag having a particle size of 4 to 6 mm to a bed height of 170 cm. The treatment was carried out by charging 442 times a day of overflow sewage from the primary sedimentation tank having the water quality shown in Table 1 below to the treatment tank (water temperature: 15-18°C). Aeration time is 5 minutes,
The aeration stop time was set to 10 minutes, and when the aeration stopped, pump P1 was operated to introduce wastewater. Also, aeration
The amount of air was adjusted so that the DO was 1.5 to 2.5 mg/. The quality of the treated water is also listed in Table 1.

【table】

〔Effect of the invention〕

The present invention is configured as described above, and can obtain the effects summarized below. (1) By performing intermittent aeration in the treatment tank, nitrification, denitrification, and denitrification reactions can be performed in a single tank. (2) Microbial-attached carriers were placed in the treatment tank, and sewage was introduced from above and treated water was extracted from below, so the sludge produced as a result of nitrification and denitrification reactions was captured in the carrier layer and removed from the system. It is not discharged to. Therefore, there is no need to provide a settling tank for sludge separation. (3) As a result of (1) and (2) above, equipment costs can be reduced. Furthermore, since the processing capacity per unit volume/time indicated by the volumetric load value is large,
It is possible to obtain processing capacity equivalent to or higher than conventional methods with small processing equipment. (4) Since the number of cycles corresponding to the circulation ratio in the nitrification liquid circulation system can be set to a large value, the nitrogen removal rate can be improved. (5) Since there is no need to add a hydrogen donor such as methanol, processing costs can be reduced.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example of an apparatus for carrying out the method of the present invention, and FIG. 2 is a schematic diagram showing an apparatus of a nitrification liquid circulation type. 1: Processing tank, 2: Perforated plate, 3: Carrier, 4, 4
a: aeration pipe, 5: discharge pipe, 6: storage tank, 7: control section, 8: sewage introduction pipe, L: organic sewage, 9: overflow ditch.

Claims (1)

[Claims] 1 A method of biologically treating organic wastewater using a treatment tank in which microorganism-attached carriers are placed in the treatment tank and an intermittent aeration means is provided at the bottom of the treatment tank, and when the aeration is stopped, the A biological treatment method for organic sewage characterized by introducing organic sewage into a tank, allowing it to descend through the tank, aerating the tank intermittently, and discharging the treated wastewater from the bottom of the tank.