KR101019092B1 - Advanced water-treating apparatus and method for removing phosphorus - Google Patents

Abstract

PURPOSE: An advanced water treatment apparatus of wastewater for removing phosphorus, and a method thereof are provided to reduce the concentration of the phosphorus from effluent discharged from the apparatus. CONSTITUTION: An advanced water treatment apparatus of wastewater for removing phosphorus comprises the following: an anoxic tank(20) for removing nitrate nitrogen from processed water inserted from a flow control tank(10); an anaerobic tank(30) discharging the phosphorus from the processed water using microorganisms; a contact aeration tank(40) nitrifying nitrogen inside the processed water by contacting with a carrier including the microorganisms; a film separation tank(50) separating solid portions and liquid portions from the processed water; and a phosphorus remover.

Description

Advanced water-treating apparatus and method for removing phosphorus

The present invention relates to an apparatus and method for advanced wastewater treatment of wastewater for phosphorus removal, and more particularly, to solve problems such as total nitrogen, total phosphorus, bulking, etc., which are difficult to treat biologically, and in particular, the concentration of phosphorus in effluent finally discharged. It relates to an apparatus and method for advanced water treatment that can be reduced as much as possible.

Advanced water treatment refers to an improved water treatment method that simultaneously removes nitrogen and phosphorus as well as organics from sewage / wastewater containing nitrogen and phosphorus. Nitrogen is removed through a nitrification process that converts nitrogen compounds in wastewater into nitrate nitrogen under an aerobic atmosphere and a denitrification process that reduces nitrate nitrogen to nitrogen gas under an oxygen-free atmosphere. Phosphorus is released by the metabolic activity of microorganisms, and the aerobic state causes microorganisms to ingest excess phosphorus and removes it with sludge.

Recently, water quality standards have been gradually strengthened as a measure of water quality improvement in public waters that are rapidly polluted. In order to improve the quality of the final discharged water, the removal of nutrients (nitrogen, phosphorus, etc.) as well as organic matters is very important. In particular, nitrogen and phosphorus compounds in the water itself is a contaminant and cause a loss of water resources value, but is used as a nutrient necessary for algae growth, causing further deterioration of water quality.

As such, there is an urgent need for the proper removal of nitrogen and phosphorus, which cause eutrophication of lakes and offshore waters. As a result, it is very difficult to treat nitrogen and phosphorus together, while maintaining high levels of discharged water is often required. However, most small and medium-sized wastewater treatment plants focus on organic and suspended solids. There is very little treatment for the nutrients of nitrogen and phosphorus.

In the large-scale activated sludge process using suspended microorganisms, the microbial flocs collected in the sedimentation tank are returned to the aeration tank to keep the concentration of microorganisms in the aeration tank as high as desired to maintain proper treatment, but in small and medium-sized facilities with high fluctuations in inflow water quality and flow rate. If the microbial floc formation is not good, it is difficult to process nitrogen and phosphorus because it is difficult to maintain a high enough concentration of microorganisms in the reaction tank, it is necessary to operate the facility through a very difficult control process to maintain an appropriate microbial amount.

Furthermore, the denitrification and nitrification process for the removal of nitrogen has its associated microorganisms separately, but under the prior art in which the two processes are continuous, all microorganisms related to each process are present and provide favorable conditions for the microorganisms in each reactor. As a result, denitrification or nitrification is achieved, and therefore, it is very difficult to maintain an appropriate amount of microorganisms of autotrophic microorganisms, which are relatively nitrifying microorganisms, which are slower in growth rate and environmentally sensitive than other heterotrophic microorganisms involved in general organic matter removal and denitrification.

On the other hand, the removal of phosphorus is highly dependent on the biological treatment method in the high-level treatment, but in the case of small and medium-sized facilities, the operation is complicated and the fluctuation of the influent load is difficult to process the phosphorous stable.

Therefore, there is an urgent need for a breakthrough process development that satisfies the enhanced water quality standards and can make the most of existing facilities without additional facilities.

The present invention was created to improve the above problems, by filling a carrier in the contact aeration tank to aeration, a variety of microorganisms such as aerobic microorganisms, random microorganisms, anaerobic microorganisms such as survival and activation is achieved high altitude excellent decomposition It is an object to provide a water treatment apparatus and method.

Another object of the present invention is to provide a high-water treatment apparatus and method that aggregates and precipitates phosphorus which has not been biologically treated by chemical flocculation to reduce the concentration of phosphorus in the effluent as much as possible and is not affected by external change factors.

Advanced wastewater treatment apparatus for sewage water of the present invention for achieving the above object is an oxygen-free tank for removing nitrate nitrogen in the treated water flowing from the flow rate adjustment tank; An anaerobic tank for releasing phosphorus by using microorganisms in the treatment target water flowing from the anoxic tank; A contact aeration tank for nitrifying nitrogen by contacting the treated water flowing in from the anaerobic tank with a carrier on which microorganisms are fixed under aeration conditions; A membrane separation tank for solid-liquid separation of the water to be treated introduced from the contact aeration tank through a separation membrane; And phosphorus removal means for removing phosphorus from the discharged water separated from the sludge by the separator.

The phosphorus removing means is connected to the separation membrane and the effluent flow inlet, a coagulant supply unit is connected to the agitator to supply the coagulant to the agitator, and the inclined plate is installed inside the aggregates in the effluent flowing out from the agitator It is settled and the supernatant is provided with a settling tank for discharging to the outside, wherein the stirring unit is formed in the outer circumference of the stirring shaft and the rotating shaft installed in the inside of the stirring tank, and the discharge water is introduced into the rotating shaft and It characterized in that it comprises a stirring blade for ejecting the flocculant supplied from the flocculant supply unit into the stirring tank.

The rotating shaft is formed with a first flow path through which a liquid coagulant flows, and the stirring blade has a second flow path connected to the first flow path formed therein, and communicates with the second flow path on an outer circumferential surface of the coagulation agent. Is formed with a plurality of ejection holes are ejected, the coagulant supply unit is a storage tank in which the liquid coagulant is stored, a coagulant supply pipe connected to the storage tank, is installed at the end of the rotary shaft is connected to the coagulant supply pipe and through the coagulant supply pipe And a connecting member for introducing the supplied flocculant into the first flow path of the rotating shaft.

And an advanced water treatment method of the present invention for achieving the above object comprises an anoxic treatment step of removing nitrate nitrogen in the incoming water to be treated; An anaerobic treatment step of releasing phosphorus using microorganisms in the denitrification treatment water in the anoxic treatment step; A catalytic oxidation step of contacting the anaerobic treated water in the anaerobic treatment step with the carrier fixed with the microorganisms under aeration conditions to nitrify; A membrane separation step of solid-liquid separation of the discharged water and the sludge by the separation membrane subjected to the catalytic oxidation step; And a post-treatment step for removing phosphorus in the effluent separated by the separator.

The post-treatment step includes a stirring step of introducing the effluent water and the flocculant into a stirring tank in which a rotating shaft having a stirring blade is formed therein is rotatable therein, and flowing the discharged water discharged from the stirring tank into a settling tank in which the aggregate is precipitated. And a precipitation step of releasing the supernatant to the outside.

The stirring step is characterized in that the effluent and the flocculant is stirred while blowing the flocculant into the effluent water through a jet hole formed in the stirring blade to rotate with the rotary shaft.

In the stirring step, the flocculant supplied from the flocculant supply unit connected by the rotating shaft and the connecting member is sequentially introduced into the first flow path formed in the rotating shaft and the second flow path formed in the stirring blade. It characterized in that for blowing the flocculant to the blowing hole communicated.

As described above, according to the present invention, by filling a carrier in the contact aeration tank and aeration, various microorganisms such as aerobic microorganisms, random microorganisms, anaerobic microorganisms, etc. can survive and activate, and thus have excellent decomposition ability of various organic substances.

In addition, in the present invention, a process for reducing phosphorus by a physicochemical reaction is additionally performed to remove phosphorus that has not been biologically treated, so that the concentration of phosphorus in the effluent is kept constant according to the water quality standard without being affected by external change factors. Can be.

1 is a block diagram showing the configuration of an advanced waste water treatment system (KAPHO SYSTEM) for phosphorus removal according to an embodiment of the present invention,
2 is a cross-sectional view schematically showing FIG.
3 is a cross-sectional view showing the inside of the stirring unit applied to another embodiment of the present invention.

Hereinafter, with reference to the accompanying drawings will be described in detail with respect to the advanced waste water treatment apparatus according to a preferred embodiment of the present invention.

1 and 2, the altitude water treatment apparatus according to an embodiment of the present invention is largely the flow rate adjustment tank 10, the anaerobic tank 20, the anaerobic tank 30, the contact aeration tank 50, the membrane Separation tank 50 and phosphorus removal means are provided.

Waste water or sewage that is the water to be treated is introduced into the flow rate adjusting tank 10 through a pretreatment device, that is, a screen, a immersion tank, etc., although not shown. The flow rate adjustment tank 10 serves to evenly regulate the inflow and contamination load of the water to be treated. The water to be treated is introduced into the anaerobic tank 20 by the pump 13 installed inside the flow rate adjusting tank 10.

The oxygen-free tank 20 is installed at the rear end of the flow control tank 10, that is, the biological process front end. As described above, the present invention can efficiently use the organic carbon source of the water to be treated by arranging the oxygen-free tank 20 at the front end of the biological process. The anoxic tank 20 is operated under anoxic conditions to change the nitrate nitrogen in the water to be treated flowing from the flow adjusting tank into nitrogen gas and release it to the atmosphere to remove it. This denitrification is carried out by denitrification microorganisms such as Pseudomonas, Micrococcus, Bacillus and the like.

The oxygen-free tank 20 is provided with a stirring device for even distribution. For example, the stirring device is connected to a driving motor (not shown) installed on the upper portion of the anaerobic tank 20, and includes a rotating shaft 21 extending into the anaerobic tank 20 and a screw 23 installed below the rotating shaft 21. Is made of. The supernatant of the sludge storage tank 70 to be described later may be introduced into the acid-free tank 20.

The anaerobic tank 30 is installed at the rear end of the anaerobic tank 20. An outlet hole 27 is formed in an upper portion of the partition wall formed between the anaerobic tank 20 and the anaerobic tank 30. Therefore, the treated water denitrified in the anaerobic tank 20 is introduced into the anaerobic tank 30 through the outflow hole 27. Anaerobic tank 30 is operated under anaerobic conditions, and releases phosphorus up to 3 to 4 times the inflow concentration using microorganisms. The anaerobic tank 30 is provided with a driving motor (not shown), a rotating shaft 31, and a screw 33 as a stirring device for equal distribution, such as the anaerobic tank 20.

The contact aeration tank 40 is installed at the rear end of the anaerobic tank 30. The water to be treated flows from the anaerobic tank 30 into the contact aeration tank 40 through the outlet hole 37 formed in the upper portion of the partition wall formed between the anaerobic tank 30 and the contact aeration tank 40.

The contact aeration tank 40 contacts the treated water flowing in from the anaerobic tank 30 with the carrier 45 on which the microorganisms are fixed under aeration conditions, thereby nitrifying ammonia nitrogen. In addition, the excessive intake of phosphorus by the microorganism and the oxidation of organic matter occurs.

The upper porous panel 43 and the lower porous panel 41 spaced vertically are provided inside the contact aeration tank 40, respectively. Each of the porous panels 41 and 43 is installed to horizontally cross the inner space of the contact aeration tank 41. The carrier 45 is filled in the reaction space formed between the upper porous panel 43 and the lower porous panel 41. Preferably, the total volume occupied by the carrier 45 to the reaction space volume is filled to 60 to 70%. The upper and lower porous panels 43 and 41 are provided with a plurality of through holes having a size that allows the water to be treated but blocks the passage of the carrier 45. Therefore, the carrier 45 is brought into contact with the water to be treated while flowing in the reaction space by the water flow formed by the aeration means. Thus, by forming the carrier 45 in the fluidized bed, the contact efficiency can be improved.

Microorganisms may be immobilized with a carrier 45 applicable to the present invention, and known carriers having a specific gravity of about 0.6 to 0.9 may be used. Preferably, the carrier 45 is formed of a polyethylene material, it may be made of a hollow cylindrical shape. In this case, the microorganisms are fixed to the inner and outer surfaces of the carrier 45. Therefore, aerobic conditions are formed on the outer surface of the carrier 45, and anaerobic conditions are formed inside the carrier 45, so that a variety of microorganisms, such as aerobic microorganisms, random microorganisms, and anaerobic microorganisms, can survive and be activated in the carrier. This can improve the decomposition ability of various organic materials by various microorganisms.

Meanwhile, in addition to the above-described porous panels 43 and 41, a mesh of synthetic resin material having a rectangular cylindrical shape may be used. In this case, the carrier is filled in the network to a volume of about 60 to 70%.

Aeration means for giving up inside the contact aeration tank 40 is provided. A blower 47 and an air diffuser 49 connected to the blower 47 and installed under the contact aeration tank 40 are provided as a means for giving up aeration condition. By aeration means by filling the carrier 45 in the contact aeration tank 40, the nitrification and oxidation of organic matters by aerobic microorganisms, random microorganisms, anaerobic microorganisms and the like proceeds.

The water to be treated is introduced into the membrane separation tank 50 installed at the rear end of the contact aeration tank 40 through the outlet hole 46. In the membrane separation tank 50, residual organic substances are removed, and the sludge and the discharged water are solid-liquid separated by the separation membrane 51.

The separation membrane 51 is preferably an immersion type flat membrane. In addition, the membrane separation tank 51 may further include a separator cleaner (not shown) for cleaning the surface of the separator 51 to prevent the membrane 51 from being blocked. As an example, the separator scrubber may include a cleaning liquid storage tank in which a cleaning liquid is stored for cleaning the separation membrane, a suction pump for supplying the cleaning liquid stored in the cleaning liquid storage tank to the separation membrane by suction force to remove sludge adhered to the surface, and a suction pump. It consists of a cleaning liquid conveying line for delivering the cleaning liquid from the cleaning liquid reservoir to the separator by suction force, and a differential pressure gauge provided on the cleaning liquid conveying line to sense the differential pressure generated by the water passing through the separation membrane. In this case, the cleaning solution may be used by diluting sodium hypochlorite or citric acid in water to dilute to a certain concentration for cleaning the drug, and use the treated effluent water for physical cleaning.

In order to discharge the discharged water separated through the separation membrane 51, the suction pump 81 for sucking the discharged water by suction power, and the suction pump 81 and the separation membrane 51 are connected to the suction power of the suction pump 81. It consists of a suction line 83 to be delivered to the separation membrane (51).

The blower 53 is connected to the blower 53 as an aeration means for operating the membrane separation tank 50 under an aerobic condition, and the diffuser 55 is provided below the separation membrane 51. By the aeration means, the membrane separation tank 50 is operated under the aeration condition, nitrification is performed, and air bubbles generated from the diffuser 55 are attached to the separation membrane 51 by a shear force that strikes the separation membrane 51. The sludge is detached from the separator 51.

Activated sludge, that is, mixed liquor suspended solids (MLSS) of the membrane separation tank 50, is preferably maintained at a concentration of 10,000 to 20,000 mg / l of microorganisms.

Phosphorus removal means for removing phosphorus in the effluent discharged from the membrane separation tank 50 is connected to the separation membrane by the suction line and the stirrer 90 to which the effluent flows, and the stirrer 90 is connected to the Coagulant supply unit 100 for supplying the coagulant to the stirring unit 90, and the inclined plate 61 is installed inside the settling tank 60 to precipitate the aggregates in the effluent flowing out from the stirring unit 90 and discharge the supernatant to the outside (60) ).

The stirring unit 90 applied to the present embodiment may be applied to any structure as long as the structure can mix the flocculant and the discharged water. For example, the stirring unit 90 includes a stirring tank into which the effluent water and the coagulant flow into the inside, a rotating shaft installed inside the stirring tank, and a stirring blade formed on the outer circumference of the rotating shaft to stir the discharged water and the coagulant.

The coagulant supply unit 100 for supplying the coagulant to the stirring unit 90 includes a coagulant storage tank 101, a coagulant supply pipe 105 connecting the coagulant storage tank 101 and the stirring unit 90, and a coagulant supply pipe ( It is installed in the 105 is made of a metering pump 107 for pumping the flocculant to the stirring unit (90). As the flocculant, a conventional inorganic polymer flocculant can be used. For example, poly aluminum chloride may be used.

The settling tank 60 is provided with a plurality of inclined plate 61 at the top. When the outflow water flows from the stirring unit 90 and the water level of the settling tank 60 rises, the sludge or floc that is agglomerated on the inclined plate 61 collides and settles to the bottom of the settling tank 60 by gravity along the inclined plate 61, and the sludge After the final discharged water is removed to the upper side of the inclined plate 61 is discharged to the outside through the discharge line (63). The precipitated sludge or floc is pumped into the sludge storage tank 70 and stored. The upper water of the sludge storage tank 70 is conveyed to the flow rate adjustment tank 10 by a fixed amount as mentioned above.

On the other hand, Figure 3 shows a stirring unit 110 applied to another embodiment of the present invention. The illustrated stirring portion 110 can greatly increase the contact efficiency of the effluent and the flocculant.

Referring to FIG. 3, a rotating shaft 113 is installed horizontally across an inner space of the stirring vessel 111 into which the discharge water flows from the separation membrane through the suction line 83. The rotating shaft 113 is supported to be rotatable by a bearing unit installed in the stirring vessel 111. One end of the rotary shaft 113 is connected to the drive shaft of the electric motor 120 installed outside the stirring tank 111 to rotate.

A spiral screw 115 is formed on the outer circumference of the rotating shaft 113. In addition, a plurality of stirring blades 130 are installed at a predetermined interval on the rotation shaft in a position where the screw 115 does not overlap. A first flow passage 114 through which the liquid coagulant flows is formed inside the rotary shaft 113 to eject the coagulant into the stirring tank 111 through the stirring blade 130. In addition, each stirring blade 130 has a second flow passage 131 connected to the first flow passage 114 is formed therein. In addition, the outer peripheral surface of the stirring blade 130 is formed with a plurality of ejection holes 135 for ejecting the flocculant.

And a connecting member is installed on one side of the rotating shaft in order to introduce the coagulant supplied through the coagulant supply pipe 105 to the first flow path 114 of the rotary shaft 113. The connecting member serves to continuously supply the flocculant to the rotating shaft 113. As an example of the connecting member, a rotary joint 140 is used. The inner side of the rotary joint 140 is provided with a bearing and a sealing member in contact with the outer circumferential surface of the rotary shaft 113 to allow the rotary shaft 113 to rotate while maintaining watertightness. In this case, an inlet hole 117 is formed at the side surface of the rotary shaft 113 located inside the rotary joint 140 so that the coagulant supplied to the rotary joint 140 may enter the first flow passage 114 of the rotary shaft 140. Although not shown, a fixing device may be installed to fix the rotary joint 140 coupled to the rotating shaft 113 to rotate, thereby fixing the rotary joint 140.

Coagulant introduced into the stirring blade 130 by the stirring unit having the above configuration is injected into the stirring tank 111 through the ejection hole 135, the coagulant is injected into the stirring tank 111 With mixed effluent. At this time, the stirring blade 130 rotates to form a vortex in the effluent and at the same time the flocculant is ejected through the ejection hole 135 can greatly improve the contact efficiency of the flocculant and the effluent. In addition, the effluent mixed with the effluent and the flocculant is easily transferred to the settling tank through the outlet pipe 119 by the screw 115.

Hereinafter, the advanced water treatment method of the present invention using the above-described advanced water treatment apparatus will be described with reference to FIGS. 1 and 2.

In the advanced water treatment method according to an embodiment, first, water to be treated is introduced into the anaerobic tank 20 through the flow adjusting tank 10 in the anaerobic treatment step. The treated water introduced into the anaerobic tank 20 is removed with nitrate nitrogen in the treated water by the action of microorganisms.

Next, the water treated through the anaerobic tank 20 in the anaerobic treatment step is introduced into the anaerobic tank 30. In the anaerobic tank 30 operated under anaerobic conditions, microorganisms release a large amount of phosphorus.

In addition, the treated water that has passed through the anaerobic tank 30 in the contact oxidation step is introduced into the contact aeration tank 40. In the contact aeration tank 40, the anaerobic treated water is brought into contact with the carrier 45 on which microorganisms are fixed under aeration conditions to nitrify ammonia nitrogen to nitrate nitrogen. In addition, the excessive intake of phosphorus by the microorganism and the oxidation of organic matter occurs. In addition, since the microorganisms are fixed to the inner and outer surfaces of the carrier 45, aerobic conditions are formed on the outer surface of the carrier 45 by aeration, and anaerobic conditions are formed inside the carrier 45 to form aerobic microorganisms and random microorganisms. Many microorganisms, such as anaerobic and anaerobic microorganisms, can survive and be activated in a carrier. The present invention by the various microorganisms can improve the decomposition ability of various organic matter.

Next, the discharged water and sludge are solid-liquid separated by the separation membrane 51 from the water to be treated introduced into the membrane separation tank 50 in the membrane separation step. And the solid-liquid separated effluent is subjected to a post-treatment step to remove phosphorus in the effluent before finally discharged.

The post-treatment step is a stirring step of stirring the effluent and the flocculant in the stirring unit 90, and the effluent water discharged from the stirring unit is introduced into the settling tank 60 in which the inclined plate 61 is installed to precipitate the aggregate and discharge the supernatant to the outside. A precipitation step is provided.

On the other hand, the stirring step applied to another embodiment of the present invention uses the stirring unit 110 shown in FIG. Therefore, the effluent and the flocculant are introduced into the stirring tank 111, and the effluent and the flocculant are stirred by the stirring blade 130. Preferably, the stirring step effectively stirs the effluent and the flocculant while ejecting the flocculant into the effluent through the jet hole 135 formed in the stirring vane 130.

That is, in the stirring step, the flocculant supplied from the flocculant supply unit connected by the rotation shaft and the connecting member is sequentially introduced into the first flow path formed inside the rotation shaft and the second flow path formed inside the stirring blade, thereby allowing the second flow path. The flocculant may be ejected into the jet hole communicating with the mixture to effectively stir the effluent and the flocculant.

In the above, the present invention has been described with reference to one embodiment, which is merely exemplary, and it will be understood by those skilled in the art that various modifications and equivalent embodiments are possible.

Therefore, the true scope of protection of the present invention should be defined only by the appended claims.

10: flow adjusting tank 20: anoxic tank
30: anaerobic tank 40: contact aeration tank
50: membrane separation tank 60: sedimentation tank
70: sludge storage tank 90: stirring section

Claims (7)

delete An anoxic tank for removing nitrate nitrogen in the water to be treated introduced from the flow rate adjusting tank;
An anaerobic tank for releasing phosphorus by using microorganisms in the treatment target water flowing from the anoxic tank;
A contact aeration tank for nitrifying nitrogen by contacting the treated water flowing in from the anaerobic tank with a carrier on which microorganisms are fixed under aeration conditions;
A membrane separation tank for solid-liquid separation of the water to be treated introduced from the contact aeration tank through a separation membrane;
And phosphorus removing means for removing phosphorus from the discharged water separated from the sludge by the separator;
The phosphorus removing means is connected to the separation membrane and the effluent flow inlet, a coagulant supply unit is connected to the agitator to supply the coagulant to the agitator, and the inclined plate is installed inside the aggregates in the effluent flowing out from the agitator Is precipitated and the supernatant is discharged to the outside,
The stirring unit ejects the stirring tank into which the discharge water flows into the inside, the rotating shaft installed inside the stirring tank, and the coagulant supplied from the flocculant supply unit while rotating together with the rotating shaft formed on the outer circumference of the rotating shaft. Advanced water treatment apparatus comprising a stirring blade to. According to claim 2, The rotating shaft is formed with a first flow path through which a liquid flocculant flows,
The stirring vane has a second passage connected to the first passage formed therein, and a plurality of ejection holes are formed on the outer circumferential surface to communicate with the second passage to eject the flocculant.
The coagulant supplying unit includes a storage tank in which a liquid coagulant is stored, a coagulant supply pipe connected to the storage tank, and a coagulant installed at an end of the rotary shaft and connected to the coagulant supply pipe and supplied through the coagulant supply pipe. An advanced water treatment apparatus, comprising a connecting member flowing into the flow path. delete An anoxic treatment step of removing nitrate nitrogen from the treated water;
An anaerobic treatment step of releasing phosphorus using microorganisms in the denitrification treatment water in the anoxic treatment step;
A catalytic oxidation step of contacting the anaerobic treated water in the anaerobic treatment step with the carrier fixed with the microorganisms under aeration conditions to nitrify;
A membrane separation step of solid-liquid separation of the discharged water and the sludge by the separation membrane subjected to the catalytic oxidation step;
And a post-treatment step for removing phosphorus in the effluent separated by the separation membrane.
The post-treatment step includes a stirring step of introducing the effluent water and the flocculant into a stirring tank in which a rotating shaft having a stirring blade is formed therein is rotatable therein, and flowing the discharged water discharged from the stirring tank into a settling tank in which the aggregate is precipitated. And a precipitation step of releasing the supernatant to the outside. The method of claim 5, wherein the stirring step comprises stirring the discharged water and the flocculant while ejecting the flocculant into the discharged water through a jet hole formed in the stirring blade that rotates together with the rotary shaft. The method of claim 6, wherein the stirring step sequentially flows the coagulant supplied from the coagulant supply unit connected by the rotating shaft and the connecting member into a first flow path formed inside the rotating shaft and a second flow path formed inside the stirring blade. And ejecting the flocculant into the ejection hole in communication with the second flow path.

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