JPS61192398A - Treatment of waste water - Google Patents

Abstract

PURPOSE:To enhance treatment efficiency by dividing a treatment tank into an anaerobic tank and an aerobic tank and changing treatment flow in the combination of the anaerobic tank and the aerobic tank at a definite time interval. CONSTITUTION:Raw water is introduced into a first fluidized bed type treatment tank 41 held to an anaerobic state to discharge phosphorus. This treated water is introduced into a second fluidized bed type treatment tank 42 always held to an anaerobic state to perform the denitrification of NO2 and NO3 recirculated and flowed in from a fourth fluidized bed type treatment tank 44. Subsequently, treated water in the second treatment tank 42 is introduced into a third fluidized bed type treatment tank 43 held to an aerobic state to perform the removal of BOD and the intake treatment of phosphorus. The treated water in the third treatment tank 43 is introduced into the fourth treatment tank 44 always held to an aerobic state to receive nitration treatment. As necessary, an alkali component is added to adjust the pH.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a method for treating wastewater, and in particular to a method for treating BOD in wastewater.
, relating to improvements in treatment methods for removing nitrogen and phosphorus.

[Technical background of the invention and its problems] Various techniques have been developed as methods for removing BOD and the like from wastewater. These will be explained with reference to FIGS. 2 to 7.

Figure 2 shows the flow of wastewater treatment using the activated sludge method installed in three stages in series: a first treatment tank 2 with a first settling tank 1;
Raw water is introduced into the tank, where BOD is removed, treated water is introduced into the sedimentation tank 1, and this treated water is introduced into the second treatment tank 4 having the second sedimentation tank 3, where nitrification is performed. , the treated water is introduced into the second sedimentation tank 3, this treated water is introduced into the third treatment tank 6 having the third sedimentation tank 5, denitrification is performed here, and the treated water is discharged through the third sedimentation tank 5. do. In addition, a part of the sludge in each sedimentation tank 1.3.5 is transferred to each treatment tank 2.4.6.
send it back to Further, the second treatment tank 4 is supplied with an alkaline component for pH adjustment, and the third treatment tank 6 is supplied with a carbon source such as methanol.

In the treatment of such wastewater, in the first treatment tank 2, BO
Since nitrifying bacteria are the priority species in the D removal removal box 2 treatment tank 4 and denitrifying bacteria are the priority species in the third treatment tank 6, the reaction rate per unit sludge amount of each can be increased, and the inflow water of the second treatment tank 4 is Since it has already been subjected to aerobic treatment, it has the advantage that there are few substances that interfere with nitrification flowing into the second treatment tank 4, and stable nitrification is possible. However, this method requires a sedimentation tank for each treatment tank, has almost no dephosphorization effect, and does not utilize BOD in raw water or alkalinity generated by denitrification reactions, so it is difficult to use as a carbon source. There are problems in that the amount of alkaline components used increases and that it is necessary to operate under conditions that do not cause sludge bulking.

FIG. 3 shows the flow of the activated sludge method called the nitrification liquid circulation method. A treatment tank 12 is divided by a partition wall 11, and raw water is introduced into the first treatment chamber 13a which is in an anaerobic state in the previous stage. The treated water (sludge mixture) is introduced into the aerobic second treatment chamber 13b in the latter stage, where nitrification and BOD removal are performed, and the treated water is discharged through the settling tank 14. In this case, a portion of the sludge mixture in the second treatment chamber 13b is circulated to the first treatment chamber 13a, and a portion of the sludge in the settling tank 14 is returned to the first treatment chamber 13a. In such wastewater treatment, the BOD components in the raw water are used as a carbon source during denitrification, so the amount of carbon sources such as methanol used can be reduced, and the alkalinity generated in the denitrification tank can be used in the nitrification tank. , it is possible to obtain the effect of reducing the amount of alkali used, and also to obtain the effect of reducing phosphorus. However, in this method, since BOD removal, nitrification, and denitrification are performed in a single sludge, BOD removal bacteria and denitrification bacteria coexist in the sludge, and the reaction rate per unit sludge of each is small. Because the reaction rate per sludge is low, the equipment becomes larger; NO2 and NO3 flow into the phosphorus release tank, which impedes phosphorus release; and it is necessary to operate under conditions where sludge backing does not occur. , S to maintain digestive bacteria in the system.
There is a problem in that RT adjustment is required.

Figure 4 shows the flow of the activated sludge method called the anaerobic-anaerobic-aerobic (A20) method, in which the treatment tanks 12 are divided by partition walls 111 and 112, and the first stage is placed in an anaerobic state.
Raw water is introduced into the treatment chamber 131, where phosphorus is released into the sludge, and the treated water (sludge mixture) is introduced into the second treatment chamber 132 in the middle stage, which is in an anaerobic state, where denitrification is performed. Furthermore, the treated water (sludge mixture) is introduced into the third treatment chamber 139 in an aerobic state at the latter stage, where it is nitrified, BOD removed, and phosphorous taken in, and then the treated water is discharged through the settling tank 14. In the treatment of such wastewater, BO in raw water is
Since component D is used as a carbon source during denitrification, the amount of carbon sources such as methanol used can be reduced, the dephosphorization effect can be obtained, and even if NO2 and NO3 are included in the circulation, phosphorus is not released. Since the phosphorus does not flow into the first processing chamber 131 where phosphorus is carried out, it has the advantage that the release of phosphorus is not hindered. However, in this method, a single sludge is used to
r) To perform removal, nitrification, and denitrification, BOD removal bacteria and denitrifying bacteria are mixed in the sludge, and the reaction rate per unit sludge of each is small; There are problems in that the equipment becomes larger, it needs to be operated under conditions where sludge backing does not occur, and SRT needs to be adjusted to maintain digestive bacteria in the system.

Figure 5 shows the flow when fluidized bed treatment 1121 to 23 is used instead of the activated sludge treatment tank and sedimentation tank shown in Figure 2, and raw water is introduced into the first fluidized bed treatment tank 21. Here, BOD is removed, the treated water is introduced into the second fluidized bed treatment tank 22, where nitrification is performed, and the treated water is introduced into the third fluidized bed treatment tank 23, where it is denitrified. After doing this, discharge it. Note that the second fluidized bed treatment tank 22 has a pH
1! An alkaline component for cleaning is supplied, and a carbon source such as methanol is supplied to the third fluidized bed treatment tank 23. In the treatment of such wastewater, the first fluidized bed treatment tank 21
Since nitrifying bacteria are the priority species in the BOD removal channel 2 fluidized bed treatment tank 22 and denitrification bacteria are the priority species in the third fluidized bed treatment tank 23, the reaction rate per unit sludge amount can be increased, and the reaction rate per unit volume can be increased. Because the reaction rate is high, it is possible to downsize the equipment, there is no need for sludge return or settling tanks61, and bacteria with low growth rates such as nitrifying bacteria can also adhere to the surface of the carrier. , it is difficult to flow out and its utilization can be improved, there is no need to worry about sludge backing, and the inflow water of the second fluidized bed treatment tank 22 has already undergone aerobic treatment, so the second fluidized bed treatment tank 22
Fewer substances that interfere with nitrification flow into the fluidized bed treatment tank 22,
This has the advantage that stable nitrification is possible.

However, this method has the following problems: there is almost no sharp phosphorus effect, and because it does not utilize the alkalinity generated by the BOD and 1112 nitrogen reactions in raw water, the amount of carbon sources and alkaline components used increases. be.

FIG. 6 shows the flow when fluidized bed type treatment tanks 31 and 32 are used instead of the activated sludge treatment tank shown in FIG. 3 described above. In this wastewater treatment method, BO in raw water
Since the D component is used as a denitrification carbon source, it is possible to reduce the amount of carbon sources used such as methanol, and because the alkalinity generated in the denitrification tank can be used in the nitrification tank, it is possible to reduce the amount of alkali used. The reaction rate per unit volume is high, making it possible to downsize the equipment, eliminating the need for sludge return or settling tanks, and allowing bacteria with low growth rates, such as nitrifying bacteria, to be grown on the surface of the carrier. It has the advantage that it adheres to the sludge and is difficult to flow out, improving its utilization, and there is no need to worry about sludge backing. However, this method has a problem in that it has almost no dephosphorizing effect.

FIG. 7 shows the flow using the two aerobic fluidized bed treatment tanks (321, 322) shown in FIG. 6 described above. In the treatment of such wastewater, ■ Denitrifying bacteria is used in the first fluidized bed treatment tank 31, and SO is added to the second fluidized bed treatment tank 321.
Since nitrifying bacteria are the priority species in the D removal removal box 3 fluidized bed treatment tank 322, the reaction rate per unit amount of sludge can be increased, and the BOD component in the raw water is used as a denitrification carbon source. Therefore, the effect of reducing the amount of carbon sources used such as methanol can be obtained; ■ The alkalinity generated in the denitrification tank can be used in the nitrification tank, resulting in the effect of reducing the amount of alkali used; ■ The reaction rate per unit volume is reduced. Because of its large size, it is possible to miniaturize the equipment; ■ Eliminates the need for sludge return and settling tanks; ■ Bacteria with low growth rates, such as nitrifying bacteria, adhere to the surface of the carrier and are difficult to flow out. The utilization rate can be improved, ■ There is no need to worry about sludge backing, ■
Since the water flowing into the third fluidized bed treatment tank 322 has already been subjected to aerobic treatment, there are few substances that interfere with nitrification flowing into the third fluidized bed treatment tank 322, and stable nitrification is possible. This method has various advantages over activated sludge methods such as the A20 method shown in FIG. 3 described above. However, the only problem with this method is that almost no dephosphorization effect is obtained. In other words, the principle of biological dephosphorization utilizes the property that sludge that releases phosphorus under anaerobic conditions absorbs more phosphorus than the released amount under aerobic conditions.
In the methods shown in FIGS. 7 to 7, the relative adhesion sludge is always kept under either aerobic or anaerobic conditions, so no dephosphorization effect can be obtained.

For this reason, a single fluidized bed treatment tank is aerobic (1
It is conceivable to perform a cycle operation of m gas)-anaerobic (II gas stop). In this method, the BOD component in the raw water is used as a carbon source for denitrification, so it is possible to achieve the effect of reducing the amount of carbon sources used such as methanol, the effect of dephosphorization, and the reduction of sludge return and sedimentation. On the other hand, it has the following characteristics: it eliminates the need for a pond, bacteria with low growth rates such as nitrifying bacteria adhere to the surface of the carrier, making it difficult for them to flow out and improving its utilization, and there is no need to worry about sludge backing. (b) Since BOD removal, nitrification, and denitrification are performed with a single sludge, BOD removal bacteria, nitrifying bacteria, and denitrifying bacteria are mixed in the sludge, and the reaction rate per unit of sludge is low; (b) Since the reaction rate per unit sludge is low, there are problems in that the size of the device increases, and (iii) the presence of NO2 and NO3 during phosphorus release hinders the release of phosphorus. In other words,
Although such a method has the characteristic that it can exhibit a phosphorus effect compared to the method shown in FIG.
The disadvantages of (b) and (c) are added.

[Purpose of the invention]

The present invention aims to provide a wastewater treatment method that can perform sufficient dephosphorization while taking advantage of the features of conventional methods.

(Summary of the invention) The present invention uses four fluidized bed biological treatment tanks, one of which is a constant aerobic tank, one of which is a constant anaerobic tank, and one of the two is an anaerobic tank. tank, the rest being an aerobic tank, raw water is introduced into the anaerobic tank, the treated water is treated in the constant anaerobic tank, further treated in the aerobic tank, and then treated in the constant aerobic tank, In treating wastewater in which a part of the treated water is constantly circulated to the anaerobic tank, the method is characterized in that the combination of the anaerobic tank and the aerobic tank and the flow of treatment are switched at fixed time intervals. .

Hereinafter, the present invention will be explained in detail with reference to FIG.

The wastewater treatment equipment shown in Fig. 1 consists of four fluidized bed treatment tanks 41 to 41.
It consists of 44. Wastewater treatment is first carried out according to the flow shown by the solid arrow. That is, raw water is introduced into the first fluidized bed treatment tank 41 in an anaerobic state, where phosphorus is released from the sludge. Next, this treated water is transferred to a second tank in a constant anaerobic state.
Introduced into the fluidized bed treatment tank 42, where the BOD component in the raw water is used (if insufficient, methanol etc. is added)
, NO2 and NO9 circulating and flowing from the fourth fluidized bed treatment tank 44 which is always in an aerobic state are denitrified. Subsequently, the treated water in the second treatment tank 42 is introduced into the third fluidized bed type treatment tank 43 in an aerobic state. In this third treatment tank 43, BO
Each 51!1yII of D removal and phosphorus intake is performed. The treated water in the third treatment tank 43 is introduced into the fourth treatment tank 44 which is always in an aerobic state. In this fourth treatment tank 44, nitrification treatment is performed, and if necessary, an alkaline component such as slaked lime is added to adjust the pH II. This fourth treatment tank 44
A part of the treated water is circulated to the second treatment tank 42.

Next, after operating under the above conditions for a certain period of time, the flow is switched to the flow indicated by the dashed arrow. That is, the first fluidized bed treatment tank 41
is in an aerobic state, and the third fluidized bed treatment tank 43 is in an anaerobic state,
Third treatment of raw water! 43, and the flow of the treated water is transferred from the third fluidized bed treatment slide 43 to the first fluidized bed treatment tank 42 to the third
The order is fluidized bed type treatment tank 43 → fourth fluidized bed type treatment tank 44 (part of the fourth treatment tank 44 is circulated to the second treatment tank 42). In this flow, denitrification is performed in the second treatment tank 42 and nitrification treatment is performed in the fourth treatment tank 44. In the first treatment tank 41, in the flow shown by the solid line, the sludge that has released phosphorus under anaerobic conditions is changed to aerobic conditions, thereby taking in more phosphorus than the released amount, and at the same time removing SOD components. In the third treatment tank 43, phosphorus is released. In such a method, phosphorus is incorporated into the sludge in both the first and third fluidized bed treatment tanks 41,43.

For this reason, the removal of phosphorus from within the processing system is as follows: (1) first and third steps;
(2) treatment of the sludge released from the carrier contained in the treated water (coagulation and sedimentation, etc.), or both.

In this way, the flow between the four fluidized bed treatment tanks 41 to 44 is switched at regular time intervals as shown by the solid line arrow and the broken line arrow, and the first fluidized bed treatment tank 41 is changed from an anaerobic state to an aerobic state. By changing the third fluidized bed treatment tank 43 from an aerobic state to an anaerobic state, the characteristics of the conventional method shown in FIG. Even if the phosphorus is removed, it does not flow into the phosphorus release tank (the first fluidized bed treatment tank 41 or the third fluidized bed treatment tank 43), so it has the advantage that the release of phosphorus is not hindered, and the dephosphorization effect can be exerted. Wastewater treatment can be achieved.

The configuration of the first and third fluidized bed treatment tanks 41 and 43 is as follows:
Mechanical stirring systems or water flow systems that can be used under both anaerobic and aerobic conditions are suitable. Since the fourth fluidized bed treatment tank 43 is always kept in an aerobic state, any of a mechanical stirring method, a water fluidization method, or an air lift method can be adopted.

Activated carbon, plastic, zeolite, sand, converter slag, blast furnace slag, coke powder, etc. can be used as the carrier loaded in each of the above fluidized bed treatment tanks.

It is desirable that the cycle time during operation, the volume of each fluidized bed treatment tank, the circulation amount of the sludge mixture, etc. be determined based on the quality of raw water, the amount of raw water to be treated, and the desired quality of treated water.

(Example of the invention) Examples of the present invention will be described in detail below.

The method of the present invention as shown in FIG. 1 and as shown in FIG.
When treating raw water (domestic wastewater) using the conventional methods shown in Figure 4 and Figure 7, the operation is performed under the conditions shown in Table 1 below to determine the amount of BODi, total nitrogen (T-N> amount, etc.) in the treated water. The amount of phosphorus (T-P), etc. was measured.The results are shown in Table 2 below.In addition, in the method of the present invention, the first fluidized bed treatment tank 4
Switching from anaerobic to aerobic, from aerobic to anaerobic, and switching of raw water in the first and third fluidized bed treatment tanks 43 were performed in cycles of one hour.

As is clear from Tables 1 and 2 above, the wastewater treatment method of this embodiment shown in Figure 1 has a volume that is about 1/4 of the conventional treatment method shown in Figure 4. It can be seen that it has the same dephosphorizing effect and the same nitrification and denitrification ability as the conventional treatment method shown in FIG.

〔Effect of the invention〕

As detailed above, according to the present invention, it is possible to reduce the amount of carbon sources such as methanol used, reduce the amount of alkaline components used, and downsize the device, and even if the circulating water contains NO2 and NO3, Since phosphorus does not flow into the release tank, phosphorus release is not hindered and it has sufficient nitrification and denitrification ability.
It is possible to provide a method for treating wastewater that can sufficiently remove phosphorus.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an apparatus used for wastewater treatment according to the present invention, and FIGS. 2 to 7 are schematic diagrams showing apparatuses used for conventional wastewater treatment. 41...First fluidized bed treatment tank, 42...Second fluidized bed treatment tank (continuously anaerobic tank), 43...Third fluidized bed treatment tank, 44...Fourth fluidized bed treatment tank Treatment tank (continuous aerobic tank). Figure 1 dumb 0 eyes
Tenken 5 He center D @ method A7ζ-

Claims (1)

[Claims] Four fluidized bed biological treatment tanks are used, one of which is a permanent aerobic tank, one is a permanent anaerobic tank, one of the other two is an anaerobic tank, and the rest are aerobic tanks. Raw water is introduced into the anaerobic tank, the treated water is treated in the continuous anaerobic tank, further treated in the aerobic tank, and then treated in the continuous aerobic tank, and a part of this treated water is treated in the continuous aerobic tank. A method for treating wastewater, which comprises switching the combination of the anaerobic tank and the aerobic tank and the flow of treatment at regular time intervals in treating the wastewater circulating in the anaerobic tank.