JPH06236B2 - Organic wastewater treatment method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for treating organic wastewater which can efficiently treat sewage and the like at low cost.

(Prior Art) As a method of treating organic wastewater such as sewage containing a nitrogen component, a nitrification solution circulation method, an A ₂ O method, a batch activated sludge method and the like have been conventionally known.

As shown in Fig. 6, the nitrification solution circulation method of
It is a method to circulate a part of the liquid nitrified in 1) to the denitrification tank (12) and use the organic matter in the raw water (organic wastewater) as a hydrogen donor to remove nitrogen. There is a drawback that the denitrification tank (12) must be increased in volume if the circulation rate is increased and the nitrogen remaining in the treated water is increased due to insufficient denitrification.

As shown in Fig. 7, the A ₂ ○ method is to remove nitrogen using organic matter in raw water, and further add methanol to completely remove nitrogen in the second denitrification tank (13). However, there is a drawback that the running cost is increased due to the addition of methanol and an extra power for re-aeration is required for removing the residual methanol by the re-aeration tank (14).

The batch activated sludge method is a method of performing nitrification and denitrification in one tank.The operation method is to stop the aeration in the tank after nitrification and to separate the treated water after solid-liquid separation. Part, and anaerobically stirring while supplying raw water commensurate with the amount discharged to perform denitrification using organic matter in the raw water, then aeration and nitrification, and the same cycle is repeated. Is. However, similarly to this method, not only the amount of nitrogen remaining in the treated water changes depending on the withdrawal rate of the treated water, but it is difficult to apply this method when the amount of raw water to be treated such as sewage is large.

Each of the above-mentioned methods (1) to (4) is a method belonging to the external respiration type denitrification method using organic matter in raw water or added methanol as a hydrogen donor necessary for denitrification. There is also proposed a method of performing denitrification without using methanol by an internal respiration type denitrification method utilizing internal constituent components of the surplus denitrifying bacterium itself as described in Japanese Patent Publication No. 44400. However, even in this method, it is difficult to compete with the denitrifying bacteria alive in the denitrifying tank in a short period of time to feed on them, and it is difficult to control the amount of bacteria to be killed, so avoid the disadvantage that the removal of nitrogen becomes unstable. I can't.

In this way, the conventional treatment method of organic wastewater becomes unstable when the organic matter in the raw water is used as a hydrogen donor to perform denitrification, and conversely, when a hydrogen donor is added from the outside, the treatment becomes unstable. Is stable but the running cost is high, and if 100% of the organic matter in the raw water is not used, the organic matter needs to be decomposed and extra power cost is required. In addition, there was a defect that the denitrification tank was enlarged by that amount.

(Problems to be Solved by the Invention) The present invention solves the above-mentioned conventional drawbacks and enables stable denitrification to be performed at low running cost using only organic substances in raw water, and The present invention has been completed in order to provide a method for treating organic wastewater which can achieve downsizing of a treatment apparatus and reduction of treatment time.

(Means for Solving the Problem) The above problem is that after adding return sludge to raw water containing organic matter and ammonia nitrogen and / or organic nitrogen, after adsorbing soluble organic matter in raw water in a mixing tank, The sludge and the separated liquid are separated in the first settling tank, and the separated liquid is nitrified by the biofilm filtration method, and then the sludge and the nitrified solution in the first settling tank are supplied again to the denitrification tank for denitrification, and further denitrified liquid. Aeration in the re-aeration tank, solid-liquid separation in the second precipitation tank, and returning part of the sludge in the second precipitation tank to the mixing tank. You can

Further, the above-mentioned problem is that after returning sludge is added to the raw water containing organic matter and ammonia nitrogen and / or organic nitrogen, the soluble organic matter in the raw water is adsorbed in the mixing tank and then separated from the sludge in the first settling tank. Liquid, and the separated liquid is nitrified by the biofilm filtration method, and then the sludge in the first settling tank and the nitrifying solution are again supplied to the denitrification tank for denitrification, and the denitrified solution is solid-liquid separated in the second settling tank. However, this can be solved by a method for treating organic wastewater, which comprises aeration of a part of the sludge in the second settling tank in the re-aeration tank and then returning it to the mixing tank.

(Operation) According to the present invention, since denitrification is performed using only organic substances in raw water, it is not necessary to add a hydrogen donor such as methanol, and the running cost can be reduced. Further, according to the present invention, the power used for decomposing the organic matter may be used only for decomposing the remaining portion of the organic matter in the raw water that has been used for denitrification, so that the power cost can be kept low. Further, according to the present invention, since the treatment is carried out by a one-pass method in which the nitrification liquid is not circulated, it is not necessary to increase the volume of the denitrification tank, and since the nitrification tank only oxidizes nitrogen, the residence time is reduced. And the nitrification tank can be downsized. Hereinafter, the present invention will be described in more detail with reference to the illustrated embodiments.

(Example) In the flow sheet of the example shown in FIG. 1, (1) is a mixing tank, (2) is a first precipitation tank, (3) is a nitrification tank, (4) is a denitrification tank,
(5) is a re-aeration tank, and (6) is a second precipitation tank.

First, a mixing tank of organic substances such as BOD and raw water (organic wastewater) containing ammonia nitrogen and / or organic nitrogen
Part of the sludge supplied to (1), activated with the re-aeration tank (5) and settled and separated in the second precipitation tank (6) is supplied to the mixing tank (1) as return sludge and mixed. . Soluble organic matter such as BOD of raw water in the mixing tank (1) is adsorbed to the sludge by the contact stabilization method, and settled and separated in the first precipitation tank (2). The residence time of the mixing tank (1) at this time is about 15 to 60 minutes. If the residence time is shorter than 15 minutes, the adsorption of BOD is insufficient, but as shown in FIG. 3, even if the retention time is longer than 60 minutes, the adsorption rate is hardly improved. In order to keep the adsorption rate of BOD stable, 30 to 60 minutes is preferable.

The separated liquid separated in the first settling tank (2) is then supplied to the nitrification tank (3), and organic nitrogen and ammoniacal nitrogen are converted to nitrite nitrogen or nitrate nitrogen by the action of nitrite bacteria and nitrifying bacteria. Is oxidized to. Most of the BOD was removed in advance in the mixing tank (1), so some of the BO that could not be removed.
D, Oxygen required for the oxidation of organic nitrogen and ammonia nitrogen, and oxygen required for the maintenance of organisms (nitrite and nitrate) are sufficient. As this nitrification tank (3), an ordinary activated sludge treatment tank may be used, but in this case, a sedimentation tank for sludge separation is further required, so a treatment tank using a biofilm, particularly a biofilm filtration tank, is suitable. There is.

The nitrification solution nitrified in the nitrification tank (3) is mixed with the sludge separated in the first precipitation tank (2) and enters the denitrification tank (4). Denitrification tank
In (4), nitrite nitrogen and / or nitrate nitrogen in the nitrification solution is denitrified by using an organic substance such as BOD adsorbed in sludge as a hydrogen donor. The residence time in the denitrification tank (4) is 0.5 to 3 hours, preferably 1.5 to 3 hours.
As shown in FIG. 4, when the residence time is shorter than 0.5 hours, the denitrification rate decreases, and even when it exceeds 3 hours, the denitrification rate is hardly improved.

After denitrification in this way, the mixture of liquid and sludge is sent to the re-aeration tank (5) and re-aerated. This leaves the residual B
The oxidative decomposition of organic matter such as OD, and the subsequent second
After solid-liquid separation in the settling tank (6), part of the sludge is mixed in the mixing tank (1)
When it is returned as sludge, it is given the activity to sufficiently adsorb soluble organic substances such as BOD in raw water. The residence time in the re-aeration tank (5) is 1.5 to 3 hours, preferably 2 to 3 hours. As shown in Fig. 5, if the retention time is less than 1.5 hours, the residual BOD will not be sufficiently adsorbed to the sludge returned to the mixing tank (1) even if it has been treated, and conversely, it will exceed 3 hours. However, the BOD removal rate in the re-aeration tank (5) and the adsorbability of organic substances in the mixing tank (1) are not improved. The mixed solution treated by the re-aeration tank (5) is the second precipitation tank.
It is sent to (6) and separated into sludge and supernatant water, and the supernatant water is discharged as treated water, while the sludge is returned to the mixing tank (1).

Tables 1 and 2 show 1 m ³ according to the method of the present invention and the conventional method.
It shows the result of treating sewage at a treatment scale of / Hr.

Of the processing equipment, the volume of the denitrification tank present invention is 2.7 m ^3, the conventional method is first denitrification tank, 6.9 m ³ der therefor; sum of the second denitrification tank, about conventional according to the present invention 40% It has been made compact. Further, the total tank volume is 9.25 m ^{3 in the} present invention when the biofilm filtration method is adopted in the nitrification tank, and 24.15 m in the conventional method.
It is ^3, which is still about 40% of the conventional size.

Further, while 68 g / m ^{3 of} raw water methanol was conventionally required for denitrification, the present invention does not require any addition. Further, compared with the conventional case where 300 g oxygen / m ³ raw water oxygen was required in the nitrification tank, 180 g oxygen / m ³ raw water was sufficient in the present invention, and the aeration power reduction of about 40% was achieved.

The organic wastewater contains a lot of SS organic nitrogen, and the nitrogen adsorbed and separated in the sludge in the first settling tank (2) moves to the sludge side and is then nitrified in the re-aeration tank (5) to become treated water. When nitrogen is mixed in, the portion after the denitrification tank (4) in FIG. 1 is changed so that it is as shown in FIG.

In the flow of FIG. 2, the denitrification liquid containing sewage discharged from the denitrification tank (4) is subjected to solid-liquid separation in the second precipitation tank (6), and the separated liquid is biofilm in the reprocessing tank (7). Remaining B according to law
OD is removed and discharged as treated water, while sludge is re-aeration tank
After giving activity in (5), return to mixing tank (1). This is more preferable because there is no possibility that the nitrogen component transferred to the sludge side in the first settling tank (2) will be mixed into the treated water.

(Effects of the Invention) As described above, the present invention can downsize the denitrification tank and the entire processing apparatus to about 40% as compared with the conventional method. In addition, since organic substances such as BOD in raw water are used as hydrogen donors necessary for denitrification, it is not necessary to add methanol or the like, and the running cost can be kept low. Further, according to the present invention, most of the organic substances in the raw water are treated by denitrification, so that the portion that needs to be removed by the aeration treatment is reduced, and the aeration power can be largely eliminated. There is also an advantage that dephosphorization can be performed at the same time by re-aeration after denitrification.

Therefore, the present invention is extremely large in that it contributes to the development of industry as a method for treating organic wastewater that eliminates the conventional problems.

[Brief description of drawings]

FIG. 1 is a flow sheet showing the first embodiment of the present invention, FIG. 2 is a flow sheet showing the second embodiment, and FIG. 3 is a graph showing the relationship between the mixing tank residence time and the BOD removal rate. FIG. 4 is a graph showing the relationship between the residence time of the denitrification tank and the denitrification rate.
Figure is a graph showing the relationship between residence time in the re-aeration tank and BOD removal rate. Figure 6 is a flow sheet showing the conventional nitrification solution circulation method.
FIG. 7 is a flow sheet showing the conventional A ₂ O method. (1): Mixing tank, (2): First precipitation tank, (3): Nitrification tank, (4): Denitrification tank, (5): Re-aeration tank, (6): Second precipitation tank, (7) : Reprocessing tank.

Claims (2)

[Claims] 1. A recycled sludge is added to raw water containing organic matter and ammoniacal nitrogen and / or organic nitrogen, and after dissolving organic matter in the raw water is adsorbed in a mixing tank, the sludge and the separated liquid are placed in a first settling tank. After the separated liquid is nitrified by the biofilm filtration method, the sludge in the first settling tank and the nitrification liquid are again supplied to the denitrification tank for denitrification, and the denitrification liquid is further aerated in the re-aeration tank, A method for treating organic wastewater, comprising solid-liquid separation in a second settling tank and returning a part of sludge in the second settling tank to a mixing tank. 2. After returning sludge to raw water containing organic matter and ammonia nitrogen and / or organic nitrogen and adsorbing soluble organic matter in the raw water in a mixing tank, the sludge and the separated liquid in the first settling tank. And nitrifying the separated liquid by the biofilm filtration method, the sludge and nitrification liquid in the first precipitation tank are again supplied to the denitrification tank for denitrification, and the denitrification liquid is subjected to solid-liquid separation in the second precipitation tank. ,
A method for treating organic wastewater, which comprises aerating a part of the sludge in the second settling tank in a re-aeration tank and then returning it to the mixing tank.