JP3534860B2 - Sewage treatment method - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating sewage containing organic matter such as sewage.

[0002]

2. Description of the Related Art Conventionally, as a sewage treatment method of this kind, sewage is introduced into an aeration tank to alternately perform aeration treatment and stirring treatment with aeration stopped, and organic matter is aerated under aerobic conditions. Oxidative decomposition of nitric acid, and nitrification of ammonia nitrogen by nitrifying bacteria, and decompose organic compounds into lower organic acids by spoilage bacteria under anaerobic conditions by stirring treatment after stopping aeration,
Furthermore, the methanogen is gasified into methane, carbon dioxide, etc., and the nitrifying nitrogen is gasified by denitrifying bacteria, and then sewage is precipitated in a settling tank, and the supernatant liquid is subjected to a subsequent treatment step such as filtration There is known one that is transferred to the same (see Japanese Patent Laid-Open No. 4-193399).

In this case, the sludge settled in the settling tank is returned to the aeration tank, but if all the settled sludge is returned, the sludge amount in the aeration tank becomes excessive, and the organic matter in the sludge is not decomposed and the settling tank is set up. Since the supernatant liquid of the settling tank becomes turbid when it flows into the tank, a part of the settling sludge is discarded as excess sludge.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention When excess sludge is generated as described above, disposal of the sludge becomes troublesome, and therefore it is desired to reduce the amount of excess sludge generated as much as possible.
An object of the present invention is to provide a sewage treatment method that meets such a demand.

[0005]

[Means for Solving the Problems] In order to achieve the above object,
In the present invention, after alternately performing aeration treatment and agitation treatment in a state where aeration is stopped on the wastewater in the aeration tank, the wastewater is subjected to a precipitation treatment in a settling tank, and a part of the precipitated sludge is left in the precipitation tank. In the sewage treatment method in which the wastewater is returned from the aeration tank to the aeration tank, the remaining sludge is sent from the settling tank to the mud storage tank and ORP
Rukoto is reserved in貯泥tank until the value falls below -190mV
In breaking the shell due to the oxidation of the surface of the sludge, characterized in that it returned to the aeration tank after it. In this case, it is desirable to reduce the ORP value to about -90 mV to -110 mV by the stirring process.

[0006]

[Function] Sludge is liable to form a shell due to oxidation on its surface, and when returned to the aeration tank, the sludge becomes difficult to disperse. However,
Sludge in the mud tank has an ORP value (oxidation-reduction potential) of -190 mV
If the sludge is stored until the amount becomes below, the sludge shell will be broken, and when returned to the aeration tank, the sludge will be well dispersed and organic matter in the sludge will be easily decomposed. Therefore, even if the whole amount of the settled sludge comes to be returned to the aeration tank by returning the remaining sludge that is not directly returned to the aeration tank to the aeration tank through the sludge storage tank, the organic matter in the sludge is efficiently decomposed. The generation of turbidity in the supernatant of the precipitation tank is suppressed. Further, if the ORP value is lowered to about -90 mV to -110 mV by stirring as described above, the sludge settling in the settling tank is less likely to have shells, and the sludge to be returned has a better dispersibility. The decomposition of the organic substance is promoted, and the generation of turbidity in the supernatant is prevented more effectively. In addition, if the ORP value is not lowered to -90 mV by stirring treatment, sludge shells are easily generated, and if the ORP value is lowered to less than -110 mV, the nitrification action in the aeration treatment is inhibited and the TN removal rate is reduced. Since it decreases, it is desirable to shift to the aeration process when the ORP value decreases to -90 mV to -110 mV.

[0007]

EXAMPLE FIG. 1 shows a wastewater treatment facility. A raw water tank 1, a flow rate adjusting tank 2, an aeration tank 3, a precipitation tank 4, and a filtration tank 5 are provided in this order from the upstream side. The wastewater is first introduced into the raw water tank 1, the SS in the wastewater is removed by the filter 1a, and then transferred to the flow rate adjusting tank 2 by the pump 1b, and then the pump 2
a is transferred to the aeration tank 3 via the measuring tank 2b.

In the aeration tank 3, the aeration process and the agitation process by the agitator 3a with the aeration stopped are alternately performed,
After that, the wastewater is transferred from the aeration tank 3 to the settling tank 4 by the pump 3b, and the supernatant of the settling tank 4 is transferred to the filtration tank 5 by the overflow method.

The sludge a that has settled in the settling tank 4 is returned to the aeration tank 3 by the pump 4a, leaving a part thereof, and the remaining sludge is transferred to the sludge storage tank 6 by the pump 4b. Then, the supernatant liquid of the sludge storage tank 6 is returned to the flow rate adjusting tank 2 by the overflow method, and the sludge b accumulated in the sludge storage tank 6 is returned to the aeration tank 3 via the flow rate adjusting tank 2 by the pump 6a. To do.

The inflow of sewage is 70 m ³ / day, the amount of sludge returned directly from the settling tank 4 to the aeration tank 3 is 24 m ³ / day, and the amount of sludge transferred to the sludge storage tank 6 is 630 l / day. O in the mud tank 6
When the sludge stored until the RP value became 190 mV to -210 mV was returned to the flow rate adjusting tank 2 as described above, the aeration tank 3
The component of sewage at the entrance of BOD is BOD59mg / l, TN
28 mg / l, was the NH ₄ -21mg / l, components of the supernatant from the precipitation tank 5 is _{T-N4.8mg / l, NH 4} -N2.1m
It became g / l, NO ₃ -N 0.64 mg / l, TP 1.1 mg / l, and it was proved that sewage could be sufficiently purified.

In the aeration tank 3, as shown in FIG.
The aeration treatment for 1 minute and the stirring treatment for 165 minutes were alternately performed, the DO value was raised to about 2 mg / l by the aeration treatment, and the ORP value was lowered to about -100 mV by the stirring treatment.

[0012] Under the above conditions, even if the sewage was treated for one year without discarding any sludge, the turbidity of the supernatant of the settling tank 4 did not occur. Incidentally, in the conventional method in which the sludge is not returned through the sludge tank 6, it was necessary to discard about 15 tons of sludge per year as excess sludge in order to prevent turbidity of the supernatant liquid. . In addition, the ORP value in the mud tank 6 is-
If sludge is returned when it reaches 180 mV, 0.4
Excess sludge of about t was generated, and when the sludge was returned at -160 mV, about 0.8 t of excess sludge was generated per month. On the other hand, even if sludge is returned when the ORP value drops to -190 mV or less, if the stirring process in the aeration tank 3 is stopped when the ORP value drops to about -80 mV, there will be an excess of about 0.5 t per month. When sludge is generated and the ORP value is lowered to about -120 mV by stirring treatment, the TN of the supernatant becomes 8.0 mg / l, and the nitrogen removal rate becomes poor.

[0013]

As is apparent from the above description, according to the present invention, it is possible to reduce the amount of excess sludge generated as much as possible and prevent the adverse effect on the environment due to the discard of excess sludge.

[Brief description of drawings]

FIG. 1 is a diagram showing an example of a wastewater treatment facility used for implementing the present invention.

FIG. 2 DO value and OR during treatment in an aeration tank
Shows changes in P value

[Explanation of symbols]

3 Aeration tank 4 Sedimentation tank 6 Mud storage tank

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Claims (2)

(57) [Claims] 1. The aeration tank is alternately subjected to aeration treatment and agitation treatment while aeration is stopped, and then the wastewater is subjected to a sedimentation treatment in a sedimentation tank to precipitate a settled sludge. In the sewage treatment method in which the tank is returned to the aeration tank, the remaining sludge is sent from the settling tank to the mud storage tank and OR
Turkey is reserved in貯泥bath until P value is less than -190mV
Breaking the shell by oxidation of the surface of the sludge in the sewage treatment process, characterized in that return to the aeration tank after it. 2. The ORP value in the stirring process is -90 mV to-
The sewage treatment method according to claim 1, wherein the sewage treatment method is reduced to about 110 mV.