JP2018134625A - Waste water treatment system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To appropriately perform a coagulation treatment without using water for dissolution when an emulsion type polymer flocculant is used for wastewater. A wastewater treatment system includes a water channel through which wastewater flows, a stirring tank 30 in which a part of the wastewater flowing through the water channel is introduced, and agglomeration in which an emulsion-type polymer flocculant P is added to the wastewater in the stirring tank 30. The agent addition section 32, the stirring section 34 that stirs the wastewater in the stirring tank 30 to disperse the polymer flocculant P, and the wastewater other than a part of the wastewater flowing through the water channel that is introduced into the stirring tank 30. The wastewater in which the polymer flocculant P is dispersed flows into the stirring tank 30, and the polymer flocculant P generates flocs from the wastewater to precipitate and separate the flocs. [Selection diagram] Fig. 6

Description

  The present invention relates to a wastewater treatment system.

  When treating wastewater such as sewage, there is a case where a treatment for removing solid components (floating solids, colloids, etc.) in the wastewater is performed. In general, this solid component can be removed efficiently by adding a coagulation treatment. In the flocculation treatment, a flocculant is added to the wastewater to be treated, and the solid components in the wastewater are coarsened with the components in the flocculant to form flocks. Since the solid component has a high sedimentation property by flocking, it is separated and removed from the wastewater by precipitating the floc.

  When the flocculation treatment is added, the waste water to which the flocculating agent is added is stirred, and the flocculating agent is mixed with the waste water. For example, Patent Literature 1 describes a technique in which a flocculant is added to sewage in an agglomeration reaction tank and stirred and mixed. There are various kinds of flocculants, and one of them is an emulsion type polymer flocculant. The emulsion type polymer flocculant has a form in which a polymer for aggregating a suspended substance is dispersed in a liquid (oil). When using an emulsion type polymer flocculant, the polymer flocculant is usually added to the dissolution water containing no solid component and stirred for about 10 minutes before being added to the treatment target. It is necessary to dissolve and dilute the polymer flocculant in the dissolving water. And the water for melt | dissolution which melt | dissolved the polymer flocculent is added to a process target, and the aggregation process is performed by stirring. That is, conventionally, the polymer flocculant is dissolved in a solvent other than wastewater (dissolution water) and then added to the wastewater to be treated. Conventionally, tap water and sewage secondary treated water are used as dissolution water, for example.

JP 2007-229658 A

  By the way, wastewater may be generated in large quantities. Therefore, when an emulsion type polymer flocculant is used for waste water, if the treatment with the dissolving water is performed first, a large amount of the dissolving water is required, which may increase the scale of equipment for preparing the dissolving water. There is. Therefore, there is a demand for coagulation treatment of wastewater with an emulsion type polymer flocculant without using water for dissolution. On the other hand, when an emulsion type polymer flocculant is added to wastewater without mixing with water for dissolution, it is also required to disperse the polymer flocculant (polymer) appropriately in the wastewater. For example, if the agglomeration reaction between the polymer and the solid component proceeds in a state where the polymer is not dispersed in the sewage, the polymer may agglomerate only the nearby solid component and the solid component other than the near may not be appropriately aggregated. . In this case, a large amount of unagglomerated solid components remain, or the flocs are not sufficiently coarsened, and the agglomeration treatment is not performed appropriately. Patent Document 1 only describes that a flocculant is added to sewage and stirred and mixed, and there is no description that an emulsion type polymer flocculant is appropriately dispersed in waste water. Accordingly, there is a need for a technique for appropriately dispersing the polymer flocculant in the waste water without using the dissolving water when the emulsion type polymer flocculant is used in the waste water.

  The present invention has been made in view of the above, and when an emulsion type polymer flocculant is used in wastewater, the polymer flocculant is appropriately dispersed in the wastewater without using dissolution water. The purpose is to provide a wastewater treatment system.

  In order to solve the above-described problems and achieve the object, a wastewater treatment system according to the present disclosure includes a water channel through which waste water flows, a stirring tank into which a part of waste water flowing through the water channel is introduced, and waste water in the stirring tank. A flocculant addition part for adding an emulsion-type polymer flocculant to, an agitation part for agitating waste water in the agitation tank to disperse the polymer flocculant, and the agitation of the waste water flowing through the water channel Waste water other than a part of the waste water introduced into the tank and waste water in which the polymer flocculant is dispersed in the agitation tank flow to generate flocs from the waste water by the polymer flocculant. And a separation tank for separating the precipitate.

  The waste water treatment system is connected to the agitation tank, leads waste water in which the polymer flocculant is dispersed in the agitation tank to the water channel, and flows the waste water in which the polymer flocculant is dispersed through the water channel. It is preferable that a discharge path for joining the wastewater is further provided, and the wastewater joined with the wastewater in which the polymer flocculant is dispersed flows into the separation tank.

  It is preferable that the residence time in the stirring tank of the wastewater that has flowed into the stirring tank is 5 minutes or less.

  The polymer flocculant preferably has a viscosity of 40 mPa · s or more and 120 mPa · s or less when contained in 4% by mass of saline at a concentration of 0.5% by mass.

  The wastewater treatment system preferably includes an electrolyte addition unit that adds an electrolyte to the wastewater in the stirring tank.

  The wastewater treatment system is connected to the waterway, and introduces a wastewater flowing through the waterway into the stirring tank, and is provided in the introduction path, and a collection unit that collects solid components in the wastewater; It is preferable to have.

  Preferably, the wastewater treatment system further includes a biological reaction tank in which wastewater from which flocs are separated in the separation tank is introduced, biological treatment is performed on the introduced wastewater, and the wastewater is purified.

  The wastewater treatment system includes: a flow rate measuring unit that measures a flow rate of wastewater flowing through the water channel; and a wastewater from which flocs are separated in the separation tank when the flow rate of wastewater flowing through the water channel is equal to or greater than a predetermined threshold. It is preferable to further include a control unit that causes the part to flow out without passing through the biological reaction tank.

  According to the present invention, when using an emulsion type polymer flocculant in wastewater, the polymer flocculant can be appropriately dispersed in the wastewater without using water for dissolution.

FIG. 1 is a schematic diagram of a wastewater treatment system according to this embodiment. FIG. 2 is a schematic diagram for explaining the principle of aggregation of solid components by the polymer flocculant. FIG. 3 is a schematic diagram illustrating the principle of aggregation of solid components by the polymer flocculant. FIG. 4 is a schematic diagram illustrating the principle of aggregation of solid components by the polymer flocculant. FIG. 5 is a schematic diagram for explaining the principle of aggregation of solid components by the polymer flocculant. FIG. 6 is a schematic diagram showing the configuration of the stirring tank unit according to the present embodiment. FIG. 7 is a schematic diagram of a wastewater treatment system according to a modification. FIG. 8 is a table showing measurement results of turbidity and SS removal rate. FIG. 9 is a table showing measurement results of turbidity and SS removal rate.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the embodiments described below.

(About wastewater treatment system)
FIG. 1 is a schematic diagram of a wastewater treatment system according to this embodiment. As shown in FIG. 1, the wastewater treatment system 1 according to this embodiment includes a water channel 10, an introduction channel 12, an agitation tank unit 14, a lead-out channel 16, a separation tank 18, a biological reaction tank 20, and a final A settling tank 22, a discharge path 24, a bypass path 25, a flow rate measurement unit 26, a bypass valve 27, and a control unit 28 are included. The wastewater treatment system 1 is a system for treating the wastewater W, purifies the raw water W0 flowing from the water channel 10 by performing the processing described below, and discharges the raw water W6 to the external environment as treated water W6. In the following, the raw water W0, the raw water W1, the dispersed water W2, the mixed water W3, the supernatant water W4, the treated water W5, and the treated water W6 will be described in the process of passing through the wastewater treatment system 1, but these are not distinguished. This is described as waste water W.

  The water channel 10 is a water conduit, and raw water W0 flowing from the outside flows. The raw water W0 is waste water, and more specifically, sewage. The raw water W0 is a mixture of sewage and rainwater, for example, in rainy weather. The raw water W0 contains a solid component S. In addition, the water channel 10 is normally not filled with the raw water W0 even when the raw water W0 flows therein, and the inside is not completely filled with the raw water W0. That is, the water surface of the raw water W 0 inside the water channel 10 is located below the upper surface of the water channel 10. However, the water channel 10 may be filled with the raw water W0 (may be full).

  The introduction channel 12 is a water channel connected to the water channel 10, here, a pipe. The introduction channel 12 is a water channel branched from the water channel 10, and one end 12 a is connected to the water channel 10. The introduction channel 12 introduces a part of the raw water W0 flowing through the water channel 10 from one end 12a as the raw water W1. The other end 12b of the introduction path 12 is provided above the stirring tank unit 14 in the vertical direction, and the introduced raw water W1 is introduced into the stirring tank unit 14 from the other end 12b.

  The agitation tank unit 14 adds the polymer flocculant P to the raw water W1 introduced from the introduction path 12 and stirs to generate dispersed water W2 in which the polymer flocculant P is dispersed. In the present embodiment, the polymer flocculant P is an emulsion type polymer flocculant. Further, the polymer flocculant P is a cationic flocculant, that is, the polymer to be contained has a positively charged ionic group. The detailed structure and processing of the stirring tank unit 14 will be described later.

  The lead-out channel 16 is a water channel, here a pipe, connected to the stirring tank unit 14 and the water channel 10. One end 16 a of the lead-out path 16 is connected to the stirring tank unit 14. The lead-out path 16 introduces the dispersed water W2 generated in the stirring tank unit 14 into the inside from one end 16a. The other end 16 b of the lead-out channel 16 is connected to the water channel 10. The lead-out path 16 guides the dispersed water W <b> 2 derived from the stirring tank unit 14 into the water path 10. Thereby, the raw water W0 flowing in the water channel 10 merges with the dispersed water W2 in the water channel 10 and is mixed with the dispersed water W2. Hereinafter, raw water W0 mixed with dispersed water W2 is referred to as mixed water W3.

  In addition, as for the water channel 10, the connection location with the other edge part 16b of the outlet channel 16 is located in the downstream of the flow of the raw | natural water W0 rather than the connection location with the one edge part 12a of the introduction channel 12. FIG. Accordingly, in the water channel 10, among the raw water W0 introduced into the water channel 10, raw water W0 other than a part of the raw water W1 introduced into the introduction channel 12 joins and is mixed with the dispersed water W2 to become the mixed water W3. . In the water channel 10, a water flow is generated by the mixed water W3, and the polymer flocculant P contained in the dispersed water W2 is dispersed in the mixed water W3 by this water flow.

  The separation tank 18 is connected to the water channel 10. The connection location of the water channel 10 with the separation tank 18 is on the downstream side of the flow of the raw water W0 (mixed water W3) relative to the connection location with the other end 16b of the outlet channel 16. Therefore, the mixed water W <b> 3 is introduced into the separation tank 18. A connection point between the separation tank 18 and the water channel 10 is usually provided with a gate (not shown) for adjusting the flow rate, and the mixed water W3 is placed in a turbulent state when passing through the gate. . Thereby, the polymer flocculant P in the mixed water W3 is further dispersed and dissolved in the mixed water W3. In the separation tank 18, the solid component S in the mixed water W <b> 3 is grown and coarsened by the polymer flocculant P dispersed in the mixed water W <b> 3 to form a floc F. In the separation tank 18, the formed floc F is precipitated to separate the liquid component (supernatant water W 4) and the floc F in the mixed water W 3. In the separation tank 18, forced stirring by the stirrer is not performed, and a gentle water flow is generated due to the inflow of the mixed water W3.

  The biological reaction tank 20 is connected to the separation tank 18 by a water channel 19. In the biological reaction tank 20, the supernatant water W <b> 4 generated in the separation tank 18 flows through the water channel 19. The biological reaction tank 20 stores activated sludge Sl inside. The biological reaction tank 20 performs biological treatment on the supernatant water W4 using the activated sludge Sl, purifies the supernatant water W4, and generates treated water W5. In addition, the biological reaction tank 20 can perform a nitrification process and a denitrification process as an example of the biological process with respect to the supernatant water W4. In the example of FIG. 1, there is one biological reaction tank 20, but for example, a plurality of tanks including a nitrification tank that performs nitrification and a denitrification tank that performs denitrification may be provided.

  The final sedimentation tank 22 is connected to the biological reaction tank 20 by a water channel 21. In the final sedimentation tank 22, the treated water W <b> 5 generated in the biological reaction tank 20 flows through the water channel 21. The final sedimentation tank 22 settles the solid component in the treated water W5 by gravity sedimentation, and separates the liquid component (treated water W6) and the solid component in the treated water W5. A discharge path 24 is connected to the final sedimentation tank 22. The treated water W6 separated in the final sedimentation tank 22 is discharged to the outside from the discharge path 24 as waste water W after purification.

  As described above, rainwater also flows into the water channel 10 as the raw water W0. When the amount of rainwater is large, the flow rate of the raw water W0 flowing into the water channel 10 increases. In this case, the biological treatment in the biological reaction tank 20 and the separation treatment in the final sedimentation tank 22 may not be in time for all the raw water W0 that flows in. In preparation for this case, the wastewater treatment system 1 is provided with a bypass 25.

  The bypass path 25 has one end 25 a connected to the separation tank 18 and the other end 25 b connected to the discharge path 24. In the bypass passage 25, the supernatant water W4 in the separation tank 18 flows from one end portion 25a, and the introduced supernatant water W4 is led out to the discharge passage 24 from the other end portion 25b. The supernatant water W4 joins the treated water W6 in the discharge passage 24 and is discharged to the outside. That is, the bypass path 25 discharges the supernatant water W4 to the discharge path 24 without passing through the biological reaction tank 20 and the final sedimentation tank 22. However, if the bypass path 25 is configured to discharge the supernatant water W4 to the outside without passing through the biological reaction tank 20 and the final sedimentation tank 22, the other end 25b may not be connected to the discharge path 24. Good.

  More specifically, the water channel 10 is provided with a flow rate measuring unit 26, and the bypass channel 25 is provided with a bypass valve 27. In the water channel 10, the flow rate measuring unit 26 is disposed on the upstream side of the flow of the raw water W 0 with respect to the connection portion with the one end 12 a of the introduction channel 12. The flow rate measuring unit 26 measures the flow rate of the raw water W0 flowing into the water channel 10. The control unit 28 acquires the value of the flow rate of the raw water W0 measured by the flow rate measurement unit 26. The control unit 28 keeps the bypass valve 27 closed when the value of the flow rate of the raw water W0 is smaller than a predetermined threshold value. Therefore, at the normal time when the flow rate of the raw water W0 in the water channel 10 is smaller than the threshold value, the supernatant water W4 does not flow out of the bypass channel 25, and the entire amount of the supernatant water W4 flows out to the biological reaction tank 20.

  On the other hand, the control part 28 opens the bypass valve 27, when the flow volume of the raw | natural water W0 which flows in into the water channel 10 is more than a predetermined threshold value. Thereby, a part of the supernatant water W4 in the separation tank 18 is discharged to the outside via the bypass 25 without passing through the biological reaction tank 20 and the final sedimentation tank 22. In addition, the supernatant water W4 other than flowing out to the bypass passage 25 flows into the biological reaction tank 20. In this way, in an emergency (such as during heavy rain) when the flow rate of the raw water W0 in the water channel 10 is greater than or equal to the threshold value, a part of the supernatant water W4 passes from the bypass channel 25 to the outside without passing through the biological reaction tank 20. leak. Therefore, even when the flow rate of the raw water W0 becomes excessive, the raw water W0 that exceeds the processing capacity of the biological reaction tank 20 is restricted from flowing into the biological reaction tank 20, thereby suppressing the processing failure. Also in this case, the entire amount of the raw water W0 flowing into the water channel 10 is introduced into the separation tank 18, and most of the solid component S is removed as floc F. Therefore, also in this case, even if the supernatant water W4 after the floc F is separated in the separation tank 18 is bypassed and discharged, the deterioration of the water quality of the surrounding environment due to the discharged water can be more suitably suppressed.

(Aggregating with polymer flocculant)
Hereinafter, the principle of aggregation of the solid component S by the polymer flocculant P will be described. 2 to 5 are schematic diagrams for explaining the principle of aggregation of solid components by the polymer flocculant. First, the case where the water L1 for melt | dissolution which is a prior art is used is demonstrated. The dissolution water L1 is water that does not contain the solid component S, and is, for example, tap water. FIG. 2 shows the state of the polymer flocculant P in the state before addition before the polymer flocculant P is added to the dissolving water L1. In the state before addition, the polymer flocculant P has a plurality of water P2 phases dispersed in the oil P1 as a solvent. In the phase of water P2, a plurality of polymers P3 that are polymers are included. In addition, a surfactant P4 is present around the water P2 phase.

  When the polymer flocculant P in the state shown in FIG. 2 is added to the dissolving water L1 and appropriately stirred, the polymer flocculant P is dispersed in the dissolving water L1 and the dispersion state shown in FIG. 3 is obtained. As shown in FIG. 3, when the polymer flocculant P is added to the dissolving water L1, the surfactant P4 undergoes phase inversion (the direction of the hydrophilic group and hydrophobic group changes), and the oil P1 and the water P2 are switched. The polymer P3 is released into the aqueous phase around the surfactant P4, ie, the dissolving water L1. The dispersed state refers to a state in which the polymer P3 is released into the dissolving water L1 and dispersed throughout the dissolving water L1.

  After that, the polymer P3 released into the dissolving water L1 moves over time to a dissolved state in which the molecular chain extends, as shown in FIG. To do. Further, in the polymer P3, the positively charged ionic groups of the other polymer P3 repel each other, so that the extension of the molecular chain is suppressed to a certain degree and the viscosity of the dissolving water L1 is increased. That is, the dispersed state is a state before the polymer P3 is released into the dissolving water L1, but before the molecular chain is extended, and the dissolved state is a state where the molecular chain of the polymer P3 is extended.

  After the polymer flocculant P is dissolved in the dissolving water L1 over a sufficient time (the dissolved state has sufficiently progressed), that is, for example, after all the polymers P3 are in a dissolved state, the polymer flocculant P Dissolving water L1 in which is dissolved is added to waste water L2. The waste water L2 is water containing the solid component S like the raw water W1. In this case, as shown in FIG. 5, the extended polymer P3 attracts (bonds) the negatively charged solid component S in the wastewater L2, and the solid component S is aggregated via the polymer P3 (aggregated state). . As the solid component S is aggregated in this way, the solid component S is coarsened to form the floc F. In addition, it is also possible to make the floc F coarser by attracting the polymers P3 through the solid component S.

  Next, as shown in the present embodiment, a mechanism when the polymer flocculant P is added to the raw water W1 will be described. The state before addition in FIG. 2 shows the state of the polymer flocculant P, and the same applies to this embodiment.

  In the present embodiment, in the stirring tank unit 14, the polymer flocculant P is added to the raw water W1 instead of the dissolving water L1. Even if the polymer flocculant P is added to the raw water W1, the polymer P3 is released into the raw water W1. And in this embodiment, although mentioned later in detail, this raw | natural water W1 is stirred by the stirring tank unit 14. FIG. Thereby, as shown in FIG. 3, it will be in the dispersion state which the polymer P3 disperse | distributed to the whole raw | natural water W1, and the dispersion water W2 is produced | generated. The dispersion of the polymer flocculant P can be achieved as long as appropriate stirring is performed as in the prior art. Further, since the phase inversion of the surfactant P4 can be achieved immediately upon dispersion, there is no influence of the raw water W1, and the same effect as that obtained when the dispersion is performed in the dissolving water L1 can be obtained. In this embodiment, the polymer P3 can be appropriately dispersed when the dispersed water W2 is first generated as described above, and is later mixed again with the raw water W0.

  Thereafter, the polymer flocculant P shifts to the dissolved state shown in FIG. 4 over time. In the dissolved state, the molecular chain of the polymer P3 extends with time, but at the same time, the solid component S in the raw water W1 can be attracted and the solid component S can be aggregated via the polymer P3. Becomes prominent. In other words, the longer the dissolution time (transition from the dispersed state to the dissolved state) in the raw water W1, the more the polymer P3 is consumed by the solid component S in the raw water W1. In this case, even if the raw water W1 in which the polymer flocculant P is dispersed, that is, the dispersed water W2 is mixed with the raw water W0, the polymer P3 is already consumed, so the agglomeration reaction effect after mixing with the raw water W0 is reduced. There is a risk. Therefore, the residence time in the stirring vessel unit 14, that is, the time for maintaining the dissolved state, affects the subsequent aggregation effect. The residence time in the agitation tank unit 14 can be rephrased as the time from the addition of the polymer flocculant P to the raw water W1 to the remixing of the dispersed water W2 into the raw water W0.

  Further, as described above, the viscosity increases with time when the polymer P3 shown in FIG. 4 is stretched. That is, the viscosity of the dispersed water W2 increases as the dissolved state is kept longer. In general, it is difficult to mix a high-viscosity solution and a low-viscosity solution. If the viscosity of the dispersion water W2 is excessively increased, mixing with the raw water W0 becomes difficult. In particular, as in the wastewater treatment system 1 according to the present embodiment, the raw water W0 and the dispersed water W2 are mixed at the water channel 10 or the junction between the water channel 10 and the separation tank 18, that is, only mixed by the water flow generated by the flow of water. In this case, mixing of the dispersed water W2 and the raw water W0 becomes extremely difficult. In this case, the aggregation of the solid component S starts as shown in FIG. 5 at the location where the raw water W0 and the dispersed water W2 are mixed and the polymer P3 is concentrated, but it is difficult to aggregate the solid component S at other locations. It becomes. That is, when the polymer P3 is not sufficiently dispersed in the raw water W1, the growth of the floc F may be inhibited, and the agglomeration process may not be performed appropriately. Therefore, in the present embodiment, the dispersion water W2 is added to the raw water W0 before the molecular chain of the polymer P3 is sufficiently advanced and the viscosity of the dispersion water W2 is increased.

  In the wastewater treatment system 1 according to the present embodiment, the polymer flocculant P (polymer P3) is dispersed in the raw water W1 by the stirring tank unit 14 to generate the dispersed water W2, and the dispersed water W2 is mixed with the raw water W0. By doing so, the polymer flocculant P (polymer P3) is dispersed in the entire mixed water W3. That is, the polymer flocculant P is dispersed (dispersed) in the dispersion water W2, but the polymer P3 is not completely dissolved (all the polymers P3 are not dissolved). ). Therefore, the dispersion water W2 is mixed with the raw water W0 in a state where the aggregation reaction between the polymer P3 and the solid component S is suppressed and the increase in the viscosity of the dispersion water W2 is suppressed. In the mixed water W3, the dissolution of the polymer P3 further proceeds, and the aggregation reaction with the solid component S in the mixed water W3 proceeds. Thereby, the wastewater treatment system 1 which concerns on this embodiment is performing the aggregation process appropriately. Hereinafter, the stirring tank unit 14 will be described in detail.

(About stirring tank unit)
FIG. 6 is a schematic diagram showing the configuration of the stirring tank unit according to the present embodiment. As shown in FIG. 6, the stirring tank unit 14 includes a stirring tank 30, a flocculant adding unit 32, a stirring unit 34, an electrolyte adding unit 36, and a control unit 38.

  The stirring tank 30 is a tank into which raw water W1 is introduced. The upper part of the stirring tank 30 is open, and the other end 12b of the introduction path 12 is provided above. In the stirring tank 30, raw water W <b> 1 is introduced from the other end 12 b of the introduction path 12. In addition, one end portion 16 a of the outlet path 16 is connected to the stirring tank 30. The stirring tank 30 discharges the dispersed water W2 in which the raw water W1 and the polymer flocculant P are mixed from one end portion 16a of the outlet path 16. However, as long as the stirring tank 30 is configured so that the raw water W1 is introduced from the other end 12b of the introduction path 12, the other end 12b of the introduction path 12 may not be disposed above. . For example, the other end 12b of the introduction path 12 may be connected to the stirring tank 30. Similarly, as long as the stirring tank 30 has a structure capable of discharging the dispersed water W2 from one end portion 16a of the outlet path 16, the connection position with the outlet path 16 is arbitrary.

  The flocculant addition unit 32 is an apparatus that adds the polymer flocculant P into the stirring tank 30. The flocculant addition unit 32 is provided, for example, above the stirring tank 30 and injects the polymer flocculant P into the raw water W1 in the stirring tank 30. However, the arrangement and structure of the flocculant addition unit 32 are arbitrary as long as the polymer flocculant P can be added to the raw water W1 in the stirring tank 30.

  In the present embodiment, the polymer flocculant P has a viscosity of 40 mPa · s (pascal · second) or more and 120 mPa · s or less when contained in 4% by weight saline at a concentration of 0.5% by mass. Is preferred. A 4 mass% salt solution refers to the salt solution in which the mass of salt is 4% with respect to the total mass of the saline solution. In addition, the content of 0.5% by mass in 4% by mass saline means that the mass of the polymer flocculant P added relative to the total mass when the polymer flocculant P is added to this saline. Indicates 0.5%. The polymer flocculant P specified by such a viscosity has an estimated molecular weight of the polymer P3 of about 3 million or more and about 10 million or less. In addition, the polymer flocculant P is preferably 10% or more and 60% or less in the concentration of the polymer P3, that is, the mass of the polymer P3 with respect to the total mass before being added to the raw water W1. % Or less is more preferable. However, the viscosity, molecular weight, and concentration of the polymer P3 of the polymer P3 are not limited to these ranges, and may be arbitrarily set. Examples of the type of the polymer P3 include acrylate-based, methacrylate-based, acrylate-based or methacrylate-based and acrylic acid and acrylamide copolymer systems, and acrylic acid and acrylic copolymer systems.

  The stirring unit 34 is a device that stirs the raw water W1 in the stirring tank 30. In the present embodiment, the stirring unit 34 includes a shaft portion 34A and a stirring blade 34B. The shaft portion 34A is a shaft-like member, and can rotate in the direction R with the extending axial direction as a rotation axis. The stirring blade 34B is a wing-like member provided at the tip of the shaft portion 34A, and rotates as the shaft portion 34A rotates. In the stirring unit 34, the stirring blade 34 </ b> B is located in the stirring tank 30 and is submerged in the raw water W <b> 1 in the stirring tank 30. The stirring unit 34 stirs the raw water W1 with the stirring blade 34B by the rotation of the shaft portion 34A. The raw water W1 in the stirring tank 30 is added with the polymer flocculant P by the flocculant addition unit 32. Therefore, the stirring unit 34 disperses the polymer flocculant P in the raw water W1 in the stirring tank 30 by stirring the raw water W1 with the stirring blade 34B.

  The electrolyte addition unit 36 is a device that adds the electrolyte E into the stirring tank 30. The electrolyte addition unit 36 is provided, for example, above the stirring tank 30, and adds the electrolyte E to the raw water W <b> 1 in the stirring tank 30. The electrolyte E is dissolved in the raw water W1 and ionized into cations and anions. However, if the electrolyte addition part 36 can add the electrolyte E with respect to the raw | natural water W1 in the stirring tank 30, the arrangement | positioning and structure are arbitrary. However, the agitation tank unit 14 does not necessarily have the electrolyte addition part 36, and the electrolyte E does not have to be added to the raw water W1 in the agitation tank 30.

  In the present embodiment, the electrolyte E is a chloride, and is preferably sodium chloride or calcium chloride, for example. However, the electrolyte E is not limited to these substances as long as it dissolves in the raw water W1 and ionizes into cations and anions.

  The control unit 38 controls the operations of the introduction control unit 12A, the flocculant addition unit 32, the stirring unit 34, and the electrolyte addition unit 36. The introduction control unit 12A is provided in the introduction path 12. The introduction control unit 12A is an on-off valve in the present embodiment, and is controlled to be opened and closed by the control unit 38. The control unit 38 controls the flow rate of the raw water W1 flowing into the agitation tank 30 by opening / closing the introduction control unit 12A. The introduction control unit 12A is not limited to the on-off valve as long as it controls the flow rate of the raw water W1 flowing into the stirring tank 30 by the control unit 38, and may be a pump, for example.

  In the present embodiment, the control unit 38 keeps the flow rate of the raw water W1 flowing into the stirring tank 30 constant. More specifically, the control unit 38 controls the residence time of the raw water W1 flowing into the stirring tank 30 in the stirring tank 30 by controlling the flow rate of the raw water W1 flowing into the stirring tank 30. That is, the residence time is the time that the raw water W1 stays in the stirring tank 30. This residence time is preferably 5 minutes or less (that is, greater than 0 seconds and 5 minutes or less), more preferably 10 seconds or more and 5 minutes or less, and further preferably 30 seconds or more and 1 minute or less. . In addition, the control part 38 is controlling the flow volume of the raw | natural water W1 which flows in so that a residence time is maintained at the fixed time within the range of this time. The raw water W1 in the stirring tank 30 is stirred by the stirring unit 34 while the polymer flocculant P is added. Therefore, the residence time can also be said to be the time during which the raw water W1 to which the polymer flocculant P has been added is being stirred by the stirring unit 34 in the stirring tank 30. The residence time is longer than the time required for the polymer flocculant P to be dispersed in the raw water W1, and is shorter than the time during which the solid component S and the polymer flocculant P in the raw water W1 react excessively. If it is time (or time shorter than the time when all the polymers P3 are in a dissolved state), it is not limited to the above numerical range.

  In the present embodiment, the residence time is controlled by controlling the flow rate of the raw water W1 flowing into the agitation tank 30 under the control of the introduction control unit 12A. However, the control of the residence time is not limited to this. For example, the stirring tank unit 14 may be set (controlled) so that the inflow amount of the raw water W1 is set to the above-described time by the structure such as the pipe diameter of the introduction path 12. Further, for example, a derivation control unit that controls the discharge amount of the dispersed water W2 from the derivation channel 16 may be provided in the derivation channel 16, and the derivation control unit may be controlled by the control unit 38 to control the residence time. The control unit 38 may control both the introduction control unit 12A and the derivation control unit.

  The control unit 38 controls addition of the polymer flocculant P by the flocculant adding unit 32. The control unit 38 continues to add a predetermined amount of the polymer flocculant P to the flocculant addition unit 32. Here, the amount (predetermined amount) of the polymer flocculant P to be added is the amount and quality of the raw water W0 flowing from the outside, that is, the flow rate measuring unit 26 of the raw water W0 and the water quality measuring device (not shown). Based on the measurement result, it is determined (controlled) by the control unit 38. Further, the control unit 38 determines that the concentration of the polymer P3 after the polymer flocculant P is added to the raw water W1, that is, the mass of the polymer P3 with respect to the total mass of the raw water W and the polymer flocculant P in the stirring tank 30. The addition amount of the polymer flocculant P is set so as to be 0.01% or more and 1.0% or less. The concentration of the polymer P3 is more preferably 0.1% or more and 0.5% or less.

  Further, the control unit 38 controls the addition of the electrolyte E by the electrolyte addition unit 36. The control unit 38 continues to add a predetermined amount of electrolyte E to the electrolyte addition unit 36. Here, the amount (predetermined amount) of the electrolyte E to be added is controlled according to the amount of the polymer flocculant P added by the control unit 38. After the electrolyte E is added to the raw water W1, the control unit 38 is configured so that the concentration of the electrolyte E, that is, the mass of the electrolyte E with respect to the total mass of the raw water W1 and the electrolyte E in the stirring tank 30 is 0.05% or more 1 The amount of electrolyte E added is set so as to be 0.0% or less. The concentration of the electrolyte E is more preferably 0.05% or more and 0.2% or less.

  As described above, when the solid component S is aggregated by the polymer flocculant P to generate the floc F, the polymer P3 is dispersed in the raw water W1 and mixed with the raw water W0 before the aggregation reaction becomes active. The effect of the aggregation reaction is further improved. In the present embodiment, the raw water W1 is taken into the agitation tank 30, and the polymer flocculant P is appropriately added to the raw water W1 by stirring the raw water W1 while adding the polymer flocculant P to the raw water W1. Dispersing water W2 is generated by dissolving polymer flocculant P in raw water W0 while being dispersed. And before the aggregation by the polymer P3 becomes active in the dispersion water W2, the dispersion water W2 is discharged from the outlet path 16.

  The dispersed water W2 discharged from the outlet channel 16 is introduced into the water channel 10 and merges with the raw water W0 flowing through the water channel 10. The dispersed water W2 is appropriately mixed with the raw water W0 by the flow of the raw water W0 flowing through the water channel 10, and the polymer flocculant P (polymer P3) is dispersed in the mixed raw water W0. The raw water W0 mixed with the dispersed water W2 flows into the separation tank 18 as mixed water W3. The mixed water W3 is in a state where the polymer flocculant P (polymer P3) is dispersed in the raw water W0 (W1). That is, in this embodiment, before the aggregation becomes active, the dispersed water W2 is mixed with the raw water W0. Therefore, the polymer flocculant P (polymer P3) in the dispersion water W2 is appropriately dispersed throughout the raw water W0. Therefore, the polymer P3 in the mixed water W3 can appropriately collect the solid component S in the mixed water W3 in the separation tank 18 and generate floc F.

  The dispersed water W2 discharged from the outlet channel 16 is introduced into the water channel 10, but may be introduced into a connection portion between the water channel 10 and the separation tank 18. In other words, the dispersed water W2 is mixed with the raw water W0 upstream of the separation tank 18. That is, the raw water W0 other than the raw water W1 introduced into the stirring tank 30 and the dispersed water W2 flow into the separation tank 18 in a mixed state. Even in this case, the polymer flocculant P (polymer P3) in the dispersed water W2 is dispersed in the raw water W0 in the separation tank 18, and the floc F can be generated appropriately.

  In the stirring tank 30, the electrolyte E is added to the raw water W1. In the electrolyte E, the negatively charged ionic group is attracted to the positively charged ionic group of the stretched polymer P3. Therefore, the addition of the electrolyte E suppresses the repulsion of the polymers P3 in the extended state, thereby suppressing the increase in viscosity. Thereby, the polymer flocculant P can be more appropriately dispersed in the raw water W1. Further, the ionic group of the electrolyte E is attracted to the positively charged ionic group of the polymer P3, thereby suppressing the solid component S from being attracted to the polymer P3, and suppressing the start of aggregation in the stirring tank 30, A decrease in the efficiency of the agglomeration process in the subsequent separation tank 18 is suppressed. The raw water W1 to which the electrolyte E has been added is diluted by mixing with the raw water W0 in the subsequent stage, so that the suppression of the aggregation treatment in the separation tank 18 is eliminated.

  As described above, the wastewater treatment system 1 according to this embodiment includes the water channel 10, the agitation tank 30, the flocculant addition part 32, the agitation part 34, and the separation tank 18. The water channel 10 is a water channel through which the waste water W (raw water W0) flows. A part of the waste water W flowing through the water channel 10 (raw water W1) is introduced into the stirring tank 30. The flocculant addition unit 32 adds the polymer flocculant P to the waste water (raw water W1) in the stirring tank 30. The polymer flocculant P is an emulsion type polymer flocculant. The agitation unit 34 agitates the waste water (raw water W1) in the agitation tank 30 to disperse the polymer flocculant P. In the separation tank 18, the waste water W (raw water W 0) other than a part of the waste water W (raw water W 0) flowing through the water channel 10 and the polymer flocculant P are dispersed in the stirring tank 30. Waste water W (dispersed water W2) flows in and flocs are generated from the waste water W (mixed water W3) by the polymer flocculant P, and flocs are precipitated and separated.

  The wastewater treatment system 1 takes a part of the raw water W0 into the stirring tank 30, and adds and stirs the polymer flocculant P to the part of the raw water W1. Thereby, the dispersion water W2 in which the polymer flocculant P is dispersed in a part of the raw water W0 is generated. Thereafter, the dispersed water W2 is mixed with the raw water W0 flowing through the water channel 10, and the polymer flocculant P is dispersed in the mixed raw water W0. In the separation tank 18, the solid component S is grown from the mixed raw water W <b> 0 by the polymer flocculant P to form the floc F. That is, the wastewater treatment system 1 uses a part of the raw water W0 to once dilute and disperse the polymer flocculant P in the stirring tank 30, and mix the dispersed water W2 with the raw water W0. The polymer flocculant P can be appropriately dispersed throughout the raw water W0. Therefore, according to the wastewater treatment system 1, when the emulsion-type polymer flocculant P is used for the wastewater W, the polymer flocculant is appropriately added to the wastewater without using water for dissolution. It can be dispersed.

  Further, the wastewater treatment system 1 further includes a lead-out path 16. The lead-out path 16 is connected to the stirring tank 30, and the waste water W (dispersed water W <b> 2) in which the polymer flocculant P is dispersed in the stirring tank 30 is led to the water path 10, and waste water in which the polymer flocculant P is dispersed W (dispersed water W2) is joined to waste water W (W0) flowing through the water channel 10. This waste water treatment system 1 returns the dispersed water W2 in which the polymer flocculant P is dispersed to the water channel 10, so that the polymer flocculant P is appropriately applied to the entire waste water W by the water flow of the waste water W in the water channel 10. It can be dispersed. Therefore, according to the wastewater treatment system 1, the polymer flocculant P can be appropriately dispersed in the wastewater.

  Moreover, in this wastewater treatment system 1, the residence time in the stirring tank 30 of the waste water W (raw water W1) which flowed into the stirring tank 30 is 5 minutes or less. In this wastewater treatment system 1, the residence time in the stirring tank 30, that is, the time in which the raw water W1 to which the polymer flocculant P has been added stays in the stirring tank 30 is shortened in this way. Thereby, the wastewater treatment system 1 can quickly mix the dispersed water W2 in which the polymer flocculant P is dispersed with the raw water W0. Therefore, according to this wastewater treatment system 1, it suppresses that agglomeration reaction becomes active before the polymer flocculant P disperse | distributes to the whole raw | natural water W0, and suppresses the efficiency reduction of agglomeration process.

  Moreover, in this wastewater treatment system 1, the polymer flocculant P has a viscosity of 40 mPa · s or more and 120 mPa · s or less when contained in 4% by mass of saline at a concentration of 0.5% by mass. In this case, the polymer flocculant P has an estimated molecular weight of the polymer P3 of about 3 million or more and about 10 million or less. By using the polymer flocculant P having a high molecular weight of the polymer P3 as described above, the wastewater treatment system 1 can promote the generation of floc F and perform the flocculation process more appropriately.

  In addition, the wastewater treatment system 1 includes an electrolyte addition unit 36 that adds the electrolyte E to the wastewater W (raw water W1) in the stirring tank 30. This wastewater treatment system 1 is able to suppress the increase in viscosity or active aggregation reaction before the dispersed water W2 is mixed with the raw water W0 by adding the electrolyte E to the raw water W1. Suppresses deterioration of state and efficiency of aggregation treatment.

  The wastewater treatment system 1 further includes a biological reaction tank 20. In the biological reaction tank 20, the waste water W (supernatant water W4) from which the floc F has been separated in the separation tank 18 is introduced, and the introduced waste water W (supernatant water W4) is subjected to biological treatment to produce the waste water W (supernatant water W4). To purify. The wastewater treatment system 1 can appropriately purify the wastewater W by purifying the wastewater W after removing the floc F by biological treatment.

  In addition, the wastewater treatment system 1 includes a flow rate measurement unit 26 and a control unit 28. The flow rate measuring unit 26 measures the flow rate of the waste water W (raw water W0) flowing through the water channel 10. When the flow rate of the waste water W flowing through the water channel 10 is equal to or greater than a predetermined threshold value, the control unit 28 uses the biological reaction tank 20 as a part of the waste water W (supernatant water W4) from which the floc F has been separated in the separation tank 18. Let go outside without going through. For example, when the amount of waste water W increases during heavy rain, the waste water treatment system 1 bypasses a part of the waste water W and discharges it to the outside, thereby discharging the biological reaction tank 20 to the outside. Can be suppressed. Further, in this case, since the waste water W from which more flocs F have been removed is discharged, deterioration of the water quality of the surrounding environment due to the discharged waste water W can be reduced.

(Modification)
Next, a modification of this embodiment will be described. The wastewater treatment system 1 according to the modification is the same as the wastewater treatment system 1 according to the first embodiment except that the collection unit 13 is included.

  FIG. 7 is a schematic diagram of a wastewater treatment system according to a modification. As shown in FIG. 7, in the wastewater treatment system 1 according to the modification, a collection unit 13 is provided in the introduction path 12. In the introduction path 12, the collection part 13 is provided between one end part 12a and the other end part 12b, and is provided closer to the one end part 12a than the introduction control part 12A. The collection unit 13 is a filter that collects solid components contained in the waste water W (raw water W1) flowing through the introduction path 12, and is, for example, a strainer or a screen. When the concentration of the solid matter of the waste water W (raw water W1) is large, when the polymer flocculant P is added to the solid matter, the agglomeration process proceeds too quickly and the polymer flocculant P may not be properly dispersed. is there. In the modification, by collecting a certain amount of solids in advance, the concentration of the solids in the wastewater W (raw water W1) is prevented from becoming too high, and the polymer flocculant P is appropriately dispersed. Is possible. In addition, as shown in FIG. 7, a derivation control unit 16A that controls the derivation amount of the dispersed water W2 may be provided in the derivation path 16. The derivation control unit 16A may have the same configuration as the introduction control unit 12A. The derivation control unit 16A may be provided in the wastewater treatment system according to the above-described embodiment, or may not necessarily be provided.

(Example)
Next, examples will be described. In the examples, the polymer flocculant P is added and stirred using a plurality of samples, and after flocculation treatment is performed and floc F is removed, the turbidity (NTU) of the supernatant water and SS (Suspended Solid suspension) ) The removal rate was measured. In the comparative example, an emulsion type polymer flocculant P having a polymer concentration of 50% was added to ion exchange water (dissolution water) and stirred for 10 minutes to generate dispersed water. The polymer concentration in this dispersed water is 0.3%. Thereafter, this dispersed water was mixed with sewage and stirred to produce mixed water having a polymer concentration of 1 ppm. And after leaving this mixed water for 5 minutes, supernatant water was extract | collected and the turbidity and SS removal rate of the supernatant water were measured.

  In Example 1, an emulsion type polymer flocculant P having a polymer concentration of 50% was added to sewage and stirred for 30 seconds to produce dispersed water. The polymer concentration in this dispersed water is 0.3%. Subsequent processing is the same as in the comparative example. Moreover, Example 2 is the same as Example 1 except that sodium chloride (electrolyte E) is added to the dispersed water so that the concentration becomes 0.1%. Moreover, Example 3 is the same as Example 1 except that calcium chloride (electrolyte E) is added to the dispersed water so that the concentration becomes 0.1%. Moreover, Example 4 is the same as Example 1 except that sodium chloride (electrolyte E) is added to the dispersed water so that the concentration becomes 0.2%.

  FIG. 8 is a table showing measurement results of turbidity and SS removal rate. As shown in FIG. 8, in the comparative example, the turbidity (NTU) was 71 and the SS removal rate was 84%. In Example 1, the turbidity (NTU) was 69, and the SS removal rate was 86%. In Example 2, the turbidity (NTU) was 73, and the SS removal rate was 86%. In Example 3, the turbidity (NTU) was 78, and the SS removal rate was 86%. In Example 4, the turbidity (NTU) was 86, and the SS removal rate was 83%. From the above, as shown in each example, even when dispersed water is generated using sewage (waste water), compared to the case where dispersed water is generated using clean water as in the past, the agglomeration treatment is performed. It turns out that processing performance does not fall.

  In the following, experimental results using polymer flocculants PA, PB, and PC having different molecular weights of the polymer P3 will be described. Example 5 is a result using the polymer flocculant PA, Example 6 is a result using the polymer flocculant PB, and Example 7 is a result using the polymer flocculant PC. . In Examples 5, 6, and 7, experiments were performed using the same method as in Example 1 except that the polymer flocculants PA, PB, and PC were used as the polymer flocculent P, respectively. The polymer flocculants PA and PB have a polymer P3 molecular weight of several hundred thousand, and the polymer flocculant PC has a polymer P3 molecular weight of several million. Among the polymer flocculants PA, PB, and PC, the polymer flocculant PC has the highest molecular weight of the polymer P3, and the polymer flocculant PB has the second highest molecular weight of the polymer P3.

  FIG. 9 is a table showing measurement results of turbidity and SS removal rate. As shown in FIG. 9, in Example 5, the turbidity (NTU) was 85, and the SS removal rate was 64.3%. In Example 6, the turbidity (NTU) was 72, and the SS removal rate was 74.2%. In Example 7, the turbidity (NTU) was 44, and the SS removal rate was 88.5%. From the above, according to Example 5-7, it can be seen that the larger the molecular weight of the polymer P3, the better the treatment performance of the aggregation treatment. Therefore, as in this embodiment, the viscosity when the polymer flocculant P is contained in 4% by weight saline at a concentration of 0.5% by weight is 40 mPa · s or more and 120 mPa · s or less, that is, When the polymer P3 having an estimated molecular weight of about 3 million or more and about 10 million or less is used, it is possible to improve the processing performance of the aggregation treatment.

  As mentioned above, although embodiment of this invention was described, embodiment is not limited by the content of these embodiment etc. In addition, the above-described constituent elements include those that can be easily assumed by those skilled in the art, those that are substantially the same, and those in a so-called equivalent range. Furthermore, the above-described components can be appropriately combined. Furthermore, various omissions, substitutions, or changes of the constituent elements can be made without departing from the spirit of the above-described embodiments and the like.

DESCRIPTION OF SYMBOLS 1 Wastewater treatment system 10 Water path 12 Introductory path 14 Stirring tank unit 16 Outlet path 18 Separation tank 20 Biological reaction tank 22 Final sedimentation tank 24 Discharge path 30 Stirring tank 32 Coagulant addition part 34 Stirring part 36 Electrolyte addition part W Waste water W0, W1 Raw water W2 Dispersed water W3 Mixed water

Claims (8)

A channel through which wastewater flows,
A stirring tank into which a part of the wastewater flowing through the water channel is introduced;
A flocculant addition part for adding an emulsion type polymer flocculant to the waste water in the stirring tank;
Stirring the waste water in the stirring tank to disperse the polymer flocculant;
Of the waste water flowing through the water channel, waste water other than a part introduced into the stirring tank and waste water in which the polymer flocculant is dispersed in the stirring tank flow in, and the polymer flocculant causes the A separation tank for generating flocs from waste water and precipitating and separating the flocs;
Having a wastewater treatment system. A lead-out path connected to the agitation tank and leading the waste water in which the polymer flocculant is dispersed in the agitation tank to the water channel, and joining the waste water in which the polymer flocculant is dispersed to the waste water flowing through the water channel Further comprising
The wastewater treatment system according to claim 1, wherein wastewater combined with wastewater in which the polymer flocculant is dispersed flows into the separation tank.   The wastewater treatment system according to claim 1 or 2, wherein a residence time of the wastewater flowing into the stirring tank in the stirring tank is 5 minutes or less.   4. The viscosity according to claim 1, wherein the polymer flocculant has a viscosity of 40 mPa · s or more and 120 mPa · s or less when contained in 4 mass% saline at a concentration of 0.5 mass%. The wastewater treatment system according to item 1.   The wastewater treatment system according to any one of claims 1 to 4, further comprising an electrolyte addition unit that adds an electrolyte to the wastewater in the stirring tank. An introduction path connected to the water channel and for introducing waste water flowing through the water channel into the stirring tank;
The wastewater treatment system according to any one of claims 1 to 5, further comprising a collection unit that is provided in the introduction path and collects a solid component in the wastewater.   The waste water from which the floc was separated in the separation tank is introduced, and the introduced waste water is subjected to biological treatment to further purify the waste water. 7. The described wastewater treatment system. A flow rate measuring unit for measuring a flow rate of waste water flowing through the water channel,
A control unit for causing a part of the waste water from which flocs have been separated in the separation tank to flow outside without passing through the biological reaction tank when the flow rate of the waste water flowing through the water channel is a predetermined threshold value or more. The wastewater treatment system according to claim 7.

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