JP3676392B2 - Dephosphorization method in oxidation ditch - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a dephosphorization method in oxidation ditch treatment of organic wastewater such as small-scale sewage.
[0002]
[Prior art]
In small-scale sewage treatment plants, the time variation of the influent water volume is large, and since there are few engineers managing the sewage treatment plant, the oxidation ditch method, which is easy to maintain and resists load fluctuations, is becoming popular in recent years. . Compared to the standard activated sludge method used in large-scale sewage treatment plants, the treatment time and sludge retention time are longer, which makes denitrification easier.
[0003]
[Problems to be solved by the invention]
However, for dephosphorization, which is another indicator of eutrophication, methods such as anaerobic aerobic operation in an aeration tank have been tried, but there was a disadvantage that stable dephosphorization performance could not be obtained. .
[0004]
An object of the present invention is to provide a method for obtaining stable dephosphorization performance in an oxidation ditch.
[0005]
[Means for Solving the Problems]
The present invention has been made to solve the above-mentioned object, and in the oxidation ditch treatment of organic waste water, a flow rate adjusting tank is provided in front of the aeration tank, and sludge precipitated in the settling tank is returned to the flow rate adjusting tank. After mixing with inflowing sewage and making sludge completely anaerobic for 1 to 4 hours, dephosphorization is performed by flowing into an aeration tank and making it aerobic to contain phosphorus The sludge is extracted as excess sludge from the aeration tank or the sedimentation tank and led to the sludge concentration storage tank. In the sludge concentration storage tank, the sludge is precipitated by aeration for 2 to 6 hours, standing for 6 to 12 hours, and standing. increasing the storage amount of concentrated sludge with concentrating sludge while repeating the flow of excess sludge in it are conditions characterized by Rukoto.
[0006]
[Action]
After the flow adjustment tank is provided in the front stage of the aeration tank, the sludge precipitated in the settling tank is returned to the flow adjustment layer and mixed with the inflowing sewage to make the sludge completely anaerobic for 1 to 4 hours and then dephosphorized. Then, let it flow into the aeration tank to make it aerobic. As a result, the phosphoric acid in the sewage is absorbed by the sludge microorganisms, and the sludge containing phosphorus is extracted from the aeration tank or the sedimentation tank into the sludge concentration storage tank, and then aerated for 2 to 6 hours. The sludge is concentrated while repeating the inflow of excess sludge in a state where the sludge is settled by standing, and the storage amount of the concentrated sludge is increased. As a result, it is possible to prevent phosphorus from being released from the sludge into the separated water at the time of sludge concentration and return to the flow rate adjustment tank, and a stable dephosphorization performance can be obtained.
[0007]
【Example】
Hereinafter, an embodiment of the dephosphorization method in the oxidation ditch of the present invention will be described with reference to the drawings.
FIG. 1 shows the processing flow of the present invention. Inflow sewage a flows into a pump well 1 that is usually provided deep underground. Sewage is pumped up by the raw water pump 2 provided in the pump well 1, and after removing sand and screen residue in the sewage in the sand settling tank 3, it flows into the flow rate adjusting tank 4. The pretreatment method and position for removing sand and screen residue are appropriately selected depending on the scale of the treatment and the location conditions.
[0008]
The flow rate adjusting tank 4 is provided with a stirrer 5 and a flow control pump 6. From the flow rate adjusting tank 4, the sewage is fed to the aeration tank 7 by the flow control pump 6, intermittently aerated by the mechanical aeration tank 8, overflowed from the aeration tank 7 as a sludge mixed liquid, and returned to the sedimentation tank 9. Let it flow.
[0009]
The shape of the aeration tank 7 is not limited to an oval shape as shown in FIG. 1, and the aeration machine 8 is not limited to the screw shape shown in FIG. 1, and various types can be used.
[0010]
The supernatant water separated from the solid and liquid in the sedimentation tank 9 is discharged as treated water b, and the precipitated sludge c is returned d to the adjustment tank 4 via the sludge mass 11 by the return sludge pump 10. A part of the sludge is transferred to the sludge concentration storage tank 12 through the sludge mass 11 as surplus sludge e. The method of extracting excess sludge e is a method of directly extracting the mixed liquid of the aeration tank 4 with a sludge pump or the like provided in the tank and guiding it to the sludge concentration storage tank 12 in addition to the method of extracting a part of the precipitated sludge as described above. Can also be used.
[0011]
Next, an example of the structure of the sludge concentration storage tank 12 is shown in FIG. In FIG. 2, 24 is a sludge inflow pipe, and 21 is a screw-type aerator similar to the aeration tank 7. The screw-type aerator is fixed to the float 22, and has a structure that moves up and down following a water level fluctuation by a support 23. The aeration method is not limited to such a mechanical type, and a method using a blower and an air diffuser can also be applied. However, since aeration is performed intermittently, the air diffuser port is not easily blocked when aeration is stopped. It needs to be structured.
[0012]
When excess sludge is allowed to stand and concentrate, most of the sludge settles, but some of the sludge floats and scums due to bubbles adhering to it. This produces intermediate water. Therefore, the separated water drain pipe 25 is arranged so as to be pulled out from the lower part of the floating sludge as shown in FIG. As a result, the intermediate water flows out into the overflow mass 26 as the separated water f and is returned to the flow rate adjustment tank 4.
[0013]
Next, the operation and action of the present invention will be described.
In the method of the present invention, the sludge precipitated in the settling tank is returned to the flow rate adjusting tank 4 and mixed with the inflow 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 releasing phosphorus from such microorganisms is important, and in order to perform dephosphorization effectively, the minimum of the adjustment tank is set so that the complete anaerobic state is 1 to 4 hours. Set the volume at the water level. Next, the phosphorus released sludge is fed to the aeration tank 7 by the flow control pump 6, and when the aeration tank 8 is in an aerobic state during operation, the phosphoric acid in the water is taken into the sludge microorganisms and accumulates as polyphosphorus. However, the amount of phosphorus taken up at this time is larger than the amount released in the adjustment tank, and thus the phosphoric acid present in the inflowing sewage is taken up by the sludge microorganisms.
[0014]
The aeration tank may be continuously operated by controlling the number of aerators operated and the number of revolutions, but it is more preferable to promote nitrification and denitrification by intermittent aeration. At the time of aeration stop, it becomes anaerobic, but at this time it is oxygen-free as in the adjustment tank, but there is oxygen chemically bound like nitrate nitrogen due to nitrification reaction during aerobic, and it does not become completely anaerobic Therefore, phosphorus release from sludge does not occur.
[0015]
Next, the excess sludge extracted from the sedimentation tank or the aeration tank is guided to the sludge concentration storage tank 12. Aeration is performed for 2 to 6 hours after surplus sludge inflow. Thereafter, the sludge is allowed to settle for 6 to 12 hours to settle and concentrate the sludge. If the standing time is too short, the sludge concentration will be insufficient, but if it is too long, the sludge will become completely anaerobic, and the phosphorus absorbed in the sludge will be released outside the sludge microorganisms, releasing phosphorus. It must be allowed to stand for as long as possible within the limits not allowed.
[0016]
The surplus sludge is allowed to flow from the sludge inflow pipe 24 in a state where the sludge is concentrated, and the separated water f is discharged. At this time, from the bottom of the sludge concentration storage tank, the sludge settled is prevented from rolling up as much as possible. It is necessary to flow in at a low flow rate. In this way, the sludge concentration storage tank gradually increases the storage amount of concentrated sludge while preventing the phosphorus absorbed in the sludge from being released by repeatedly performing aeration, standing, and surplus sludge inflow. .
[0017]
In small-scale sewage treatment plants, there are many cases where dewatering facilities and incineration facilities are not installed in the treatment plant, and when sludge stored for about one week is carried out by a vacuum vehicle, etc., and processing such as dehydration is performed at another treatment plant However, if the time until the dehydration process is 24 hours or more, there is a risk that the sludge will release phosphorus into the desorbed water. Therefore, it is desirable to perform the dehydration process as soon as possible after the sludge is carried out. A mobile dewatering vehicle can be used as a method suitable for this. In addition, even when dewatering facilities are provided in the treatment plant, if dewatering treatment is not performed every day, biological dephosphorization is performed using the method of the present invention, and sludge is concentrated and stored while preventing phosphorus release from the sludge. In addition, it is preferable to perform the dehydration treatment as soon as possible after the aeration treatment.
[0018]
【The invention's effect】
According to the present invention, in the oxidation ditch process, which has conventionally been difficult to obtain stable dephosphorization performance, a flow rate adjusting tank is provided in front of the aeration tank, and sludge precipitated in the settling tank is returned to the flow rate adjusting layer. After mixing with the inflowing sewage and making the sludge completely anaerobic for 1 to 4 hours and dephosphorizing it, the phosphoric acid in the sewage is put into the body of the sludge microorganisms by flowing into the aeration tank and making it aerobic. Absorb and remove the sludge containing phosphorus from the aeration tank or sedimentation tank into the sludge concentration storage tank , and surplus in the state where the sludge is precipitated by aeration for 2 to 6 hours, standing for 6 to 12 hours and standing Concentrate sludge and increase the amount of concentrated sludge while repeatedly injecting sludge. Thereby, it can prevent that phosphorus is discharge | released from sludge to the separation water at the time of sludge concentration , and it returns to a flow control tank, and has the effect that stable dephosphorization performance can be obtained.
[Brief description of the drawings]
FIG. 1 is a process flow showing one embodiment of a dephosphorization method in the oxidation ditch of the present invention.
FIG. 2 is a sectional view showing a sludge concentration storage tank according to the present invention.
[Explanation of symbols]
a inflow sludge b treated water c sludge d surplus sludge 1 pump well 2 raw water pump 3 sand settling tank 4 flow rate adjustment tank 5 stirrer 6 flow control pump 7 aeration tank 8 aeration machine 9 sedimentation tank 10 return sludge pump 11 sludge mass 12 sludge concentration Storage tank

Claims (1)

In the oxidation ditch treatment of organic wastewater, a flow rate adjustment tank is provided in front of the aeration tank, the sludge settled in the settling tank is returned to the flow rate adjustment tank, and mixed with the inflowing sewage to completely anaerobize the sludge for 1 to 4 hours. After dephosphorization in a state, it is biologically dephosphorized by flowing into an aeration tank to make it aerobic, and the sludge containing phosphorus is extracted from the aeration tank or the precipitation tank as excess sludge, Lead to the sludge concentration storage tank, and in the sludge concentration storage tank, the sludge is removed while repeating the inflow of excess sludge in the state where the sludge has settled by aeration for 2 to 6 hours, standing for 6 to 12 hours, and standing still. dephosphorization method in oxidation ditch, characterized in Rukoto increase the storage amount of concentrated sludge with concentrated.

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