JPH07290083A - Denitrification and dephosphorization method in oxidation ditch - Google Patents

Abstract

PURPOSE:To provide a treating method small in installation space than conventional oxidation ditch and capable of providing stable denitrificaton and dephosphorization performance. CONSTITUTION:In the oxidation ditch method for treating sewage with a high concn. activated sludge by providing a mechanical aeration machine 8 to a circulation water passage type aeration tank 7, a flow rate control tank 4 is provided at a preceding stage of the aeration tank 7. Then, a sludge settled at a sedimentation tank 9 is returned to the flow rate control tank 4 and mixed with an influent sewage to make sludge in completely anaerobic state, then returned to the aeration tank 7.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for appropriately treating denitrification and dephosphorization in an oxidation ditch method which is a treatment method for small-scale sewage.

[0002]

2. Description of the Related Art Small-scale sewage has large fluctuations in the amount of inflowing water over time, and few engineers manage sewage treatment plants.
Oxidation ditch method, which is easy to maintain and resistant to load fluctuation, is becoming popular in recent years. In addition, compared to the standard activated sludge method used in large-scale sewage treatment plants, the treatment time and sludge convection time are longer, so denitrification is easier to proceed.

[0003]

FIG. 2 shows a flow of a conventional oxidation ditch. Inflowing sewage a flows into a pump well 1 and is then directly aerated by a raw water pump 2 through a settling tank 3 through an aeration tank 7. Flows into. Since the capacity of the pump well 1 is small, the load fluctuation of the inflow sewage a is directly transmitted to the aeration tank 7 and further to the precipitation tank 9. In general small-scale sewage, the maximum hourly water volume fluctuates 2-3 times as much as the hourly average water volume. Therefore, in the sedimentation tank, the water area load of about 20 to 30 cubic meters per square meter per day is compared with the standard activated sludge method per day by the conventional oxidation ditch method. In addition, the aeration tank residence time is 24 to 3
Since it was 6 hours long, it required a large space. Further, in the aeration tank, nitrification and denitrification are promoted by forming an aerobic zone and an anaerobic zone along the flow, but the fluctuation of the load is large and stable zone formation is difficult. Therefore, in order to obtain high denitrification performance and to cope with this load fluctuation, the water area of the sedimentation tank is 8 per square meter per day.
Since it is necessary to take a large water area so that the value is as small as a cubic meter, there is a problem that the space of the entire treatment plant becomes large. In addition, the conventional oxidation ditch method does not have a significant dephosphorization effect on phosphorus, which is another indicator of eutrophication, and the aeration amount is also considered for the denitrification performance by considering the fluctuation of the inflow load. There is a drawback that stable denitrification performance cannot be obtained unless it is properly controlled.

An object of the present invention is to provide a treatment method which requires a smaller installation space than the conventional oxidation ditch and can obtain stable denitrification and dephosphorization performance.

[0005]

The present invention has been made to solve the above-mentioned object, and an oxygenator for treating sewage with a high-concentration activated sludge is provided by providing a mechanical aerator in an aeration tank in the form of a circulating water channel. In the foundation ditch method, a flow control tank is installed in front of the aeration tank, and the sludge settled in the settling tank is returned to the flow control tank, mixed with the inflowing sewage to make the sludge completely anaerobic, and then flowed into the aeration tank. The main point is to do. Further, if necessary, an agitator is provided in the flow rate adjusting tank to sufficiently stir and mix the inflowing sewage and the returned sludge, and intermittent aeration is performed in the aeration tank to alternately repeat aerobic and anaerobic.

[0006]

The present invention is provided with a flow rate adjusting tank in front of the aeration tank of the oxidation ditch to absorb the inflow load fluctuation, and from the adjusting tank to a settling tank which naturally flows down by supplying sewage to the aeration tank at a constant flow rate. On the contrary, the load is constant. The aeration tank is operated alternately with anaerobic and aerobic, and the sludge in the settling tank is returned to the adjusting tank and mixed with the inflow sewage to make the sludge completely anaerobic, and then sent to the aeration tank. As a result, since the returned sludge is completely anaerobicized in the adjustment tank and then sent to the aeration tank to be aerobic, phosphorus can be removed by the biological dephosphorization action, and the aeration tank is also favorable. Since sewage is supplied from the adjustment tank at a constant flow rate while performing alternate operation of air and anaerobic, more stable denitrification performance than conventional oxidation ditch can be obtained, and the capacity of the aeration tank and sedimentation tank can be reduced. .

[0007]

EXAMPLE An example of a denitrification / dephosphorization method in the oxidation ditch of the present invention will be described below with reference to FIG. FIG. 1 shows a processing flow of the present invention. Inflow sewage a generally flows into a pump well 1 deep underground. Sewage is pumped up by a raw water pump 2 provided in a pump well 1 and sent to a sand settling tank 3 to remove sand components and screen debris in the sewage, and then to flow into a flow rate adjusting tank 4. The method and position of the pretreatment for removing sand and screen residue in the sewage are appropriately selected depending on the scale of the treatment and site conditions.

The flow rate adjusting tank 4 has an agitator 5 and a flow adjusting pump 6
The sewage water is sent from the flow rate adjusting tank 4 to the aeration tank 7 by the flow control pump 6, the aeration process is intermittently performed by the mechanical aerator 8, and the sludge mixed liquid is overflowed from the aeration tank 7 to precipitate. It is made to flow into the tank 9. This aeration tank 7
The shape of is not limited to the elliptical shape shown in FIG. 1, and the aerator 8 is not limited to the screw shape shown in FIG. Aerator 8
Is preferably a method in which aeration and anaerobic stirring can be alternately performed, but when anaerobic stirring cannot be performed, a method of intermittently operating the aerator may be used.

The supernatant water that has been solid-liquid separated in the settling tank 9 is discharged as treated water b, and sludge c that has settled in the settling tank 9 is discharged.
Is returned to the adjusting tank 4 through the sludge mass 11 by the sludge pipe and the sludge return pump 10. Further, a part of the sludge is transferred to the sludge treatment facility 12 as excess sludge e via the sludge mass 11. The sludge treatment facility 12 uses mechanical concentration, or performs gravity concentration in a short time to perform dehydration treatment in order to prevent phosphorus from being re-released from the sludge that has taken in phosphorus.
A treatment facility suitable for phosphorus-containing sludge shall be provided.

Next, the operation and action of the present invention will be described. According to the method of the present invention, the amount of water flowing into the aeration tank 7 from the adjusting tank 4 is made constant, and aeration is performed at a predetermined interval in the aeration tank, thereby forming a time distribution of aerobic and anaerobic to form nitrification. Advance denitrification. In contrast to the conventional oxidation ditch method that promotes nitrification and denitrification by forming aerobic zones and anaerobic zones while performing continuous aeration, the method that promotes nitrification and denitrification by intermittent aeration in this way is 1. Since a nitrification rate and denitrification rate about 5 times higher can be obtained,
Nitrification and denitrification can be promoted more efficiently.

In the method of the present invention, the sludge settled in the settling tank is returned to the flow rate adjusting tank 4 and mixed with the inflowing sewage by the stirrer 5 to keep the sludge in a completely anaerobic state.
At this time, polyphosphorus accumulated in the microorganism body of the returned sludge is discharged out of the body in the form of soluble phosphoric acid, and the phosphorus concentration in the water temporarily rises. In the mechanism of biological dephosphorization, the process of phosphorus release from such microorganisms is important, and in order to perform effective dephosphorization, the minimum water level in the adjusting tank should be set so that the completely anaerobic state is 1 to 4 hours. Set the capacity at. Next, the sludge that has released phosphorus is sent to the aeration tank 7 by the flow control pump 6, and when the aerator 8 is in an aerobic state, the phosphoric acid in the water is taken into the body of the sludge microorganisms and accumulated as polyphosphorus. However, the amount of phosphorus taken in at this time is larger than the amount released in the adjusting tank, and thus the phosphoric acid present in the inflowing sewage is taken in by the sludge microorganisms.

[0012] In the aeration tank, intermittent aeration is performed to alternately repeat aerobic and anaerobic. In the aerobic state of the aeration tank, which is anoxic as in the adjusting tank, nitric acid is generated by nitrification reaction during aerobic conditions. Since nitrogen oxides such as nitrogen are present and a complete anaerobic condition is not achieved, phosphorus is not released from sludge. Since the intake rate of phosphoric acid by sludge microorganisms is higher than that of nitrification and denitrification, the required residence time in the aeration tank depends on the nitrification and denitrification rate. As described above, in intermittent aeration, the nitrification / denitrification rate is faster than in the continuous aeration method that forms aerobic and anaerobic zones like the conventional oxidation ditch. Since organic matter is always supplied to the aeration tank in the form of inflowing sewage at a constant flow rate, nitrification denitrification can be performed in about 12 to 20 hours.

On the other hand, in order to effectively promote nitrification and denitrification, it is necessary to keep the nitrifying bacteria and denitrifying bacteria at a high concentration. Therefore, the retention time of sludge is lengthened and MLSS of the aeration tank is set to 1
It is necessary to operate at a high concentration of 2500 mg or more per liter, but under such conditions, bulking and foaming by actinomycetes are likely to occur. Since filamentous fungi and actinomycetes, which are the causative organisms of bulking, are aerobic bacteria, they lose their activity when kept in an anaerobic state, and eventually die.

According to the method of the present invention, a flow rate adjusting tank is provided in front of the aeration tank and the returned sludge is kept under a completely anaerobic condition for several hours. Therefore, the growth of filamentous fungi and actinomycetes can be suppressed, and nitrification can be performed. The operation suitable for denitrification can be maintained.

[0015]

EFFECTS OF THE INVENTION The denitrification / dephosphorization method in the oxidation ditch according to the present invention is provided with a flow rate adjusting tank in front of the aeration tank, the sludge precipitated in the settling tank is returned to the flow rate adjusting tank, and mixed with inflowing sewage. After the sludge has been completely anaerobicized, the sludge is allowed to flow into the aeration tank.If necessary, a stirrer is installed in the flow rate adjustment tank to mix the inflowing sewage and the returned sludge with sufficient agitation, and the aeration tank is operated intermittently. Since aeration is performed to alternate between aerobic and anaerobic, (1) Nitrification / compared to conventional oxidation ditch
Since denitrification can be performed efficiently, the capacity of each tank can be reduced and the installation space can be reduced. (2) While the conventional oxidation ditch has a dephosphorization performance of 50% or less, a high dephosphorization performance of 80% or more can be obtained. (3) Solid-liquid separation defects such as foaming scum due to bulking and actinomycetes are less likely to occur than in the conventional oxidation ditch. And so on.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a processing flow of a denitrification / dephosphorization method in the oxidation ditch of the present invention.

FIG. 2 is an explanatory diagram showing a processing flow of a conventional oxidation ditch.

[Explanation of symbols]

 1 Pump well 2 Raw water pump 3 Sand setter 4 Flow rate control tank 5 Stirrer 6 Flow control pump 7 Aeration tank 8 Mechanical aerator 9 Sedimentation tank 10 Sludge return pump 11 Sludge mass 12 Sludge treatment facility a Influent sewage b Treated water c Sludge d Return sludge e Excess sludge

Claims (2)

[Claims] 1. In an oxidation ditch method in which a mechanical aerator is installed in an aeration tank in the form of a circulating water channel to treat sewage with high-concentration activated sludge, a flow rate adjusting tank is provided in the preceding stage of the aeration tank, and a sedimentation tank is used. After returning the precipitated sludge to the flow rate adjustment tank and mixing it with the inflowing sewage to make the sludge completely anaerobic,
A denitrification and dephosphorization method in an oxidation ditch, which is characterized by flowing into an aeration tank. 2. The flow control tank is equipped with a stirrer to sufficiently stir and mix the inflowing sewage and the returned sludge, and the aeration tank performs intermittent aeration to alternately repeat aerobic and anaerobic. Method for denitrification and dephosphorization in the described oxidation ditch.