JP2015181975A - Flocculation and sedimentation tank and flocculation and sedimentation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flocculation and sedimentation tank and a flocculation and sedimentation system capable of obtaining superior treated water quality without increasing the size of the flocculation and sedimentation tank.SOLUTION: A flocculation and sedimentation tank 30A provided with a sludge blanket portion S having a floc growth zone Z1 formed with a fluid bed by at least the upward flow of inflow water and a separation zone Z2 separating solid matter formed above the floc growth zone Z1 and treated water includes a drawing-out line 35 drawing sludge from a portion lower than the separation zone Z2 and a discharge line L2 discharging sludge overflowing from a portion higher than the separation zone Z2.

Description

  The present invention relates to a coagulation sedimentation tank and a coagulation sedimentation system.

  2. Description of the Related Art Conventionally, as one of the effective means for wastewater treatment, a coagulation-precipitation method is known, as disclosed in Patent Document 1, in which an organic substance is coagulated and separated by adding a coagulant to wastewater. In this coagulation sedimentation method, sludge concentrated in the coagulation sedimentation tank is drawn out and a part of the sludge is circulated to the previous reaction tank in order to enhance the precipitation effect of organic matter and the like.

  For example, a sludge blanket type coagulation sedimentation tank as disclosed in Patent Document 2 can be applied as the above coagulation sedimentation tank. These sludge blanket type coagulation sedimentation tanks are divided into a sludge blanket part having a flock growth zone in which flocs grow as inflow water to which a flocculant is added rises, and the sludge blanket part. A sludge settling portion for sinking the sludge flowing in from, and a sludge concentration portion provided at a lower portion of the sludge settling portion for concentrating the sludge.

  In the above coagulation sedimentation method, a part of the concentrated sludge extracted from the sludge concentration section of the coagulation sedimentation tank is returned to the previous reaction tank and circulated, so that raw water and sludge are fed into the coagulation sedimentation tank. It is introduced into the sludge blanket section. The inflow water flowing into the coagulation sedimentation tank is separated into treated water and sludge by raising the sludge blanket part.

Japanese Patent Laid-Open No. 10-479 Japanese Patent No. 5085609

  However, when the coagulation sedimentation tank described in Patent Document 2 is applied to the configuration in which the sludge concentrated in the sludge concentration section is returned to the previous stage, the sludge blanket section is introduced in accordance with the introduction of the sludge into the sludge blanket section of the coagulation sedimentation tank. The ascending flow velocity at becomes faster. In this case, since the residence time in the sludge blanket portion of the introduced influent water is shortened, floc growth / separation is not sufficiently performed, and the quality of treated water after separation may be deteriorated. Here, as measures to prevent floc growth and separation failure due to shortening of stay time in the sludge blanket part of the influent water and increase of the rising speed, for example, the sludge blanket part is enlarged or a separate coagulation tank is provided, etc. However, there is a concern that the equipment will become larger and the cost will increase.

  Then, an object of this invention is to provide the coagulation sedimentation tank and coagulation sedimentation system which can obtain a favorable treated water quality without enlarging.

  In order to achieve the above object, a coagulation sedimentation tank according to an embodiment of the present invention includes a floc growth zone in which a fluidized bed is formed at least by an upward flow of inflow water, solids formed above the growth zone, and treated water. A coagulation sedimentation tank having a sludge blanket section having a separation zone for separating the wastewater, a drawing line for drawing sludge from below the separation zone, and a discharge line for discharging sludge overflowing from above the separation zone It is characterized by providing.

  According to the agglomeration sedimentation tank, the sludge can be extracted from the sludge blanket portion by providing the extraction line for extracting the sludge from below the separation zone. When sludge is extracted from the sludge concentration part of a conventional coagulation sedimentation tank, the flow rate for raising the sludge blanket part is only the raw water amount (flow rate for raising the sludge blanket part = raw water amount). On the other hand, when sludge is extracted from the sludge blanket part, the flow rate of raising the sludge blanket part is the amount of raw water minus the drawn sludge (the flow rate of raising the sludge blanket part = raw water amount-drawn sludge amount. is there). Therefore, compared with the case where sludge is extracted from the sludge concentration section of the conventional coagulation sedimentation tank, when sludge is extracted from the sludge blanket section, the increase in the rising speed in the sludge blanket section is suppressed, and the effect of separating solids and water is reduced. It is possible to increase. Therefore, the separation effect of solids and water can be improved without increasing the size of the coagulation sedimentation tank, and good treated water quality can be obtained.

  Moreover, in said coagulation sedimentation tank, a drawing line may be connected to the lower part of a sludge blanket part. According to this configuration, by adopting a configuration in which sludge is extracted at the lower part of the sludge blanket part, it is possible to suppress an increase in the rising speed and to suppress a decrease in HRT and SRT above the extraction line. In addition, by providing a drawing line further downward, an area where the increase in the rising speed can be suppressed and the decrease in the hydraulic residence time (hereinafter referred to as HRT) and sludge residence time (hereinafter referred to as SRT) can be suppressed. Can be wide. Therefore, without increasing the size of the coagulation sedimentation tank, the effect of growing flocs and the effect of separating solids and water are further improved, and a better quality of treated water can be obtained.

  In the above coagulation sedimentation tank, a sludge storage section may be provided at the bottom of the sludge blanket section, and the drawing line may be connected to the sludge storage section. According to this configuration, by extracting the sludge for circulation from the sludge storage section provided at the bottom of the sludge blanket section, the sludge is concentrated in the sludge storage section, and the sludge with a high SS concentration can be extracted.

  In the coagulation sedimentation tank, the drawing line may be provided through the separation zone. According to this configuration, the drawing line is connected to the outside of the coagulation sedimentation tank above the sludge blanket part, so that the coagulation sedimentation tank can have a simpler structure.

  Moreover, in said coagulation sedimentation tank, the extraction line may be provided so that a sludge extraction position can be changed. According to this configuration, since the sludge can be drawn uniformly from the sludge blanket part by adopting a variable structure such as the top and bottom, horizontal, etc., it is possible to operate so as not to affect the rectification of the sludge blanket part. It becomes possible. Therefore, the rectification | straightening property of a sludge blanket part can be improved, and more favorable treated water quality can be obtained, without enlarging a coagulation sedimentation tank.

  Moreover, the coagulation precipitation system which concerns on one form of this invention is a coagulation precipitation system provided with the coagulation reaction tank which makes a coagulant and raw | natural water react, and said coagulation precipitation tank which carries out solid-liquid separation of the inflow water from an aggregation reaction tank. The drawing line is connected to the agglomeration reaction vessel.

  According to this coagulation sedimentation system, the sludge can be extracted from the extraction line provided below the separation zone of the sludge blanket section, and returned to the preceding aggregation reaction tank for circulation. At this time, the increment of the inflow water to the sludge blanket portion with respect to the raw water becomes substantially equal to the amount of sludge extracted from the extraction line. Therefore, compared with the case where the sludge extracted from the sludge concentration part of the conventional coagulation sedimentation tank is returned to the front | former stage, it is possible to reduce the rising speed of the inflow water in a sludge blanket part. In addition, by suppressing the reduction of SRT in the HRT and sludge blanket sections, the residence time for capturing fine particles is maintained, the reaction time necessary for floc growth is maintained, and flow diffusion and particle collisions are maintained. Thus, it is possible to enhance the effect of making the flow in the sludge blanket uniform, and to suppress the deterioration of the solid-liquid separation performance due to the disturbance of the flow, such as a single flow in the sludge blanket. Therefore, it is possible to obtain good treated water quality without increasing the size of the coagulation sedimentation tank.

  ADVANTAGE OF THE INVENTION According to this invention, the coagulation sedimentation tank and the coagulation sedimentation system which can obtain favorable treated water quality without enlarging a coagulation sedimentation tank are provided.

It is a block diagram which shows the coagulation sedimentation system which concerns on one Embodiment of this invention. It is sectional drawing which shows the coagulation sedimentation tank of the coagulation sedimentation system which concerns on one Embodiment of this invention. It is sectional drawing which shows the example of a change of a coagulation sedimentation tank. It is sectional drawing which shows the example of a change of a coagulation sedimentation tank. (A) And (b) is a block diagram which shows the example of a change of a coagulation sedimentation system.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and redundant description is omitted.

  FIG. 1 is a configuration diagram showing a coagulation sedimentation system employing a coagulation sedimentation tank according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a coagulation sedimentation tank of the coagulation sedimentation system according to an embodiment of the present invention. The coagulation sedimentation system according to the present embodiment has a coagulation sedimentation tank called a “sludge blanket type”. The sludge blanket type coagulation sedimentation tank forms a fluidized bed of coagulated flocs by the rising water flow in the tank and allows newly generated flocs to pass through the fluidized bed. At this time, the small flocs are captured by the large flocs in the fluidized bed and become large, and the sedimentation speed increases. Thereby, the inflow water to the sludge blanket type coagulation sedimentation tank is separated into treated water and sludge, and each is discharged out of the tank. Hereinafter, the floc is sometimes referred to as agglomerated floc, sludge, or solid matter.

  As shown in FIG. 1, the coagulation sedimentation system 100A includes a first reaction tank 10, a second reaction tank 20, and a coagulation sedimentation tank 30A connected in this order, and from the sludge blanket part S of the coagulation sedimentation tank 30A. A return line L1 for returning the extracted sludge to the first reaction tank 10, a discharge line L2 for discharging sludge from the coagulation sedimentation tank 30, a storage tank 50 connected to the discharge line L2, and a rear stage of the storage tank The dehydrator 60 is provided.

  In the first reaction tank 10, the raw water is introduced and the inorganic flocculant is added by the inorganic flocculant adding means 11. Moreover, the sludge returned by the return line L1 flows into the 1st reaction tank 10, and these are mixed, for example by stirring with a stirrer.

Here, as the inorganic flocculant, Al-based inorganic flocculants such as sulfuric acid band and PAC, and Fe-based inorganic flocculants such as polyiron sulfate may be used. Alternatively, crystals are precipitated by adjusting the pH with an alkali such as NaOH or Ca (OH) ₂ or an acid such as H ₂ SO ₄ or HCL, adding a Ca, Al or Fe compound, or adding an oxidizing agent or a reducing agent. You may let them. Here, the crystal grows using the sludge returned from the coagulation sedimentation tank 30 as the nucleus of the crystal.

  The second reaction tank 20 introduces treated water from the first reaction tank 10, and a polymer flocculant is added from the polymer flocculant addition means 21, thereby causing an agglomeration reaction to form an aggregate floc.

  Here, as the polymer flocculant, for example, anionic to cationic polyacrylamide can be used.

  The coagulation sedimentation tank 30A introduces the treated water containing the coagulated floc from the second reaction tank 20, and after the coagulated floc is grown in the sludge blanket part S, the coagulated floc as a solid is separated from the treated water. . The separated treated water is discharged out of the tank at the upper part of the coagulation sedimentation tank 30A. Part of the aggregated floc is returned to the preceding stage via the return line L1, and the rest overflows from the sludge blanket part and is discharged from the sludge concentrating part to the storage tank 50 through the discharge line L2 as concentrated sludge.

  The storage tank 50 stores the sludge discharged from the coagulation sedimentation tank 30A via the discharge line L2. The sludge stored in the storage tank 50 is transported to the dehydrator 60, dehydrated, and then transported out of the system.

  Next, the coagulation sedimentation tank 30A of this embodiment will be described. As shown in FIG. 2, the coagulation sedimentation tank 30 </ b> A includes a bottomed cylindrical outer wall portion 31, and further, a bottomed bottom erected so as to be concentric with the outer wall portion 31 inside the outer wall portion 31. A cylindrical inner wall portion 32 is provided. The inner wall portion 32 has a smaller diameter and a smaller height than the outer wall portion 31. The inner wall portion 32 is supported on the outer wall portion 31 by a gantry (not shown).

  A center shaft 40 is disposed on the axis L of the outer wall portion 31. A feed pipe 41 is provided outside the center shaft 40 so as to surround the center shaft 40. The feed pipe 41 is connected to the inflow water distribution pipe 39. The inflow water distribution pipe 39 penetrates the outer wall portion 31 and protrudes to the outside of the outer wall portion 31, and is connected to the second reaction tank 20. The inside of the inflow water distribution pipe 39 communicates with the inside of the feed pipe 41. In the present embodiment, the outer walls 31, the inner wall 32, the center shaft 40, and the axis of the feed pipe 41 are all the common axis L.

  The feed pipe 41 is divided into an upper part 41a and a lower part 41b in the vertical direction, and the upper part 41a and the lower part 41b are connected by a rotary joint 42 such as a labyrinth structure. The feed pipe 41 is connected to the inflow water distribution pipe 39 at the side surface of the upper part 41a, and the dispersion pipe 33 is provided at the lower part 41b of the feed pipe 41. The dispersion pipe 33 is disposed below the inner wall portion 32, and a plurality of inflow water discharge ports 33 a are formed in the dispersion pipe 33. The dispersion pipe 33 rotates together with the center shaft 40 with the inflow water discharge port 33a facing the bottom 32c side of the inner wall part 32. At this time, the lower part 41 b of the feed pipe 41 rotates together with the dispersion pipe 33. In addition, although the upper end part of the feed pipe 41 is closed, you may open | release upwards.

  The center shaft 40 is connected to the bottom portion 32 c by a rotary joint 43. A concentrated sludge scraper 34 is provided at the lower end of the center shaft 40. As the center shaft 40 rotates, the concentrated sludge scraper 34 also rotates. The concentrated sludge scraping machine 34 is provided on the bottom 31c of the outer wall 31, and scrapes the concentrated sludge accumulated on the bottom 31c of the outer wall 31 to the central portion where the discharge line L2 is provided.

  In the present embodiment, the inner region of the inner wall portion 32 functions as the sludge blanket portion S, and the cross-sectional donut-shaped region of the outer region of the inner wall portion 32 surrounded by the outer wall portion 31 functions as a sedimentation zone Z3 that settles sludge. . The sludge blanket portion S has a flock growth zone Z1 and a separation zone Z2 formed above the flock growth zone Z1. In the floc growth zone Z1, a fluidized bed of coagulated flocs is formed by the upward flow of inflow water flowing into the coagulation sedimentation tank 30A. The separation zone Z2 performs solid-liquid separation of the aggregated floc (solid matter) and the treated water. The area where the concentrated sludge scraper 34 is provided functions as the sludge concentration unit Z4.

  A pull-out line 35 that can pull out sludge from the sludge blanket portion S is connected to the inner wall portion 32. In the extraction line 35, an extraction port 35 a provided at an end of the extraction line 35 is connected to the bottom portion 32 c of the inner wall portion 32 so that sludge containing aggregated floc and water is drawn from below the separation zone in the sludge blanket portion S. Has been. Further, the drawing line 35 penetrates the outer wall portion 31 and the inner wall portion 32 and protrudes to the outside, and is connected to the return line L1 via the pump P. The return line L1 is connected to the first reaction tank 10. As a result, the sludge drawn from the lower side of the separation zone in the sludge blanket part S is returned to the previous stage, and then agglomerates again via the first reaction tank 10 and the second reaction tank 20 via the drawing line 35 and the return line L1. It flows into the settling tank 30A.

  Next, a coagulation sedimentation method using the coagulation sedimentation tank 30A will be described. The treated water containing flocs from the second reaction tank 20 is introduced into the feed pipe 41 via the inflow water distribution pipe 39. The inflow water introduced into the feed pipe 41 flows downward in the feed pipe 41, is divided by the dispersion pipe 33, and is ejected from the inflow water discharge port 33a. The inflow water supplied into the flock growth zone Z1 is supplied almost uniformly over the entire surface of the flock growth zone Z1, and a fluidized bed is formed by the upward flow of the inflow water. Small flocs contained in the inflowing water are collected in contact with the aggregated flocs in the process of rising in the fluidized bed, and grow with a large particle size. In this way, the inflowing water grows flocs while ascending the floc growth zone Z1.

Here, since the specific gravity of flocs is greater than that of water, the flocs tend to accumulate at the bottom of the floc growth zone Z1, but rise due to continuous supply of influent water. In the process of rising, the influent water floc grows and becomes heavier and does not rise when it gets heavier to some extent. Therefore, as shown in FIG. 2, larger and heavier flocs gather on the upper portion of the inner wall portion 32, and the floc concentration changes discontinuously by balancing with the ascending force due to the rising flow of the inflowing water. A thin virtual boundary layer K (near the interface of the sludge blanket portion S) is formed. That is, the virtual boundary layer K is formed at the boundary between the clarification part Q and the sludge blanket part S above the outer wall part 31. Here, in the present embodiment, the virtual boundary layer K and the vicinity thereof are referred to as a separation zone Z2. In the separation zone Z2, flocs are held at a high concentration. Further, part of the flocs gathered in the separation zone Z2 moves to the peripheral edge of the inner wall portion 32 by the fluidized bed due to the inflowing water, and flows into the sedimentation zone Z3 by overflowing from the inner wall portion 32 along the F1 direction. Here, overflow means that a large and heavy floc overflows from the separation zone Z2 to the settling zone Z3 over the inner wall portion 32.

  The treated water that has passed through the sludge blanket part S rises due to the rising flow of the inflowing water, and is discharged from the upper part of the outer wall part 31 to the outside. The aggregated floc that has overflowed from the peripheral edge of the inner wall portion 32 along the direction F1 flows into the sedimentation zone Z3 and settles.

  The sedimentation zone Z3 sediments the aggregated floc (sludge) that has flowed in from the inside of the peripheral edge of the inner wall portion 32. Here, since the specific gravity of the aggregated floc flowing in from the sludge blanket portion S is larger than that of water, it naturally settles toward the bottom portion 31 c of the outer wall portion 31. The aggregated floc that settles and accumulates on the bottom 31c of the outer wall portion 31 is concentrated to become concentrated sludge, which is scraped to the central portion by the rotation of the concentrated sludge scraper 34 provided in the sludge concentration portion Z4 and discharged. It is carried to the storage tank 50 by the line L2.

  Here, in the coagulation sedimentation system of the prior art, a part of the sludge discharged from the discharge line L2 connected to the sludge concentration unit Z4 is returned to the preceding agglomeration reaction tank and circulated. The purpose is to supply seed crystals as nuclei for crystal growth to the agglomeration reactor. When seed crystals are supplied to the agglomeration reaction tank, crystals grow using the seed crystals as nuclei, and large particles are generated. Therefore, the solid-liquid separation property between the solid matter and the treated water in the coagulating sedimentation tank is improved.

  However, if a configuration is adopted in which the sludge discharged from the discharge line L2 connected to the sludge concentration unit Z4 is returned to the previous stage as in the prior art coagulation sedimentation system, the sludge is introduced into the sludge blanket section S of the coagulation sedimentation tank. As a result, the rising flow velocity in the sludge blanket portion S becomes faster. In this case, the residence time of the introduced influent water in the sludge blanket portion S is shortened and the rising speed is increased, so that floc growth / separation is not sufficiently performed, and the quality of treated water after separation may be deteriorated. is there.

  On the other hand, in this embodiment, in the sludge blanket part S, the mixture (sludge) containing floc and water is drawn from the lower side of the separation zone Z2, and returned to the first reaction tank in the previous stage.

At this time, the amount of water flowing into the sludge blanket part S and the amount of sludge drawn from the sludge blanket part S by the drawing line 35 satisfy the following formula.
Total amount of inflow water to sludge blanket part = (Amount of inflow water to sludge blanket part S) − (Amount of sludge withdrawn from sludge blanket part S) = Amount of raw water

  When the raw water amount is constant, the ascending flow rate of the sludge blanket part S is constant regardless of the presence or absence of sludge circulation and the amount of sludge circulation. That is, without increasing the capacity of the sludge blanket part S, it is possible to grow a good coagulation floc and maintain an appropriate residence time and ascending flow rate for sedimentation separation, and to obtain clear treated water. Become. Moreover, in the sludge blanket part S, the residence time required for flocking can be secured, and the flow rate can be made uniform without increasing the ascending flow velocity, so that the quality of the treated water discharged from the sludge blanket part S is maintained well. It is possible. As a result, it is not necessary to enlarge the sludge blanket part S as compared with the case where the sludge extracted from the sludge concentrating part Z4 is returned to the previous stage, so that a better treatment can be performed without increasing the size of the coagulation sedimentation tank 30. Water quality can be obtained.

Furthermore, in the case of this embodiment, by extracting sludge from the sludge blanket part S, returning it to the previous stage and circulating it,
(Amount of SS flowing into the sludge blanket portion S) − (amount of SS extracted from the sludge blanket portion S) = constant.
That is, the flow rate of the flocs flocs from the sludge blanket part S to the sedimentation zone Z3 is constant, and it does not depend on the presence or absence of sludge circulation or the amount of sludge circulation. Therefore, in order to circulate sludge, for example, it is not necessary to increase the capacities of the sedimentation zone Z3 and the sludge concentration part Z4.

  As described above, according to the present embodiment, the extraction line 35 extracts sludge from the sludge blanket portion S, returns it to the previous stage, and circulates it, so that the coagulation sedimentation tank 30 is not enlarged and the processing is improved. Water quality can be obtained.

  Moreover, in this embodiment, since sludge is extracted from the bottom 32c side of the sludge blanket part S, in the sludge blanket part S, the region where the flow velocity of the upward flow of the sludge blanket part S increases due to sludge return is minimized. It is possible.

  As mentioned above, although this invention was demonstrated based on the embodiment, this invention is not limited to said embodiment, A various change can be made. For example, in the above embodiment, a double-structured coagulation sedimentation tank having a bottomed cylindrical outer wall portion 31 and an inner wall portion 32 is used, but the coagulation sedimentation tank of the present invention has such a double-structure formula. It does not specifically limit, You may change in the range provided with the structure which the flocs floc of a sludge blanket part overflows and can flow in into a sedimentation zone. Examples of such a modification include a configuration in which one or more settling tanks functioning as a settling zone are provided along a part of the outer periphery of the sludge blanket tank that forms the sludge blanket section. Thus, the shape of the sludge blanket tank as a sludge blanket part and the shape of the sedimentation tank as a sedimentation zone can be changed suitably.

  Moreover, in the said embodiment, although the drawing line 35 is connected to the bottom part 32c of the inner wall part 32 which forms the sludge blanket part S of 30 A of coagulation sedimentation tanks, you may be attached to the side surface of the inner wall part 32, It suffices that it is attached at least below the separation zone Z2 of the sludge blanket portion S. In this case, it is possible to reduce the rising speed of the inflowing water in the sludge blanket part S as described in the above embodiment above the position where the drawing line 35 is attached. Therefore, since it can suppress that the speed | rate of the inflow water which passes especially the separation zone Z2 rises, the separation of the solid substance and water in the separation zone Z2 can be performed suitably, and the coagulation sedimentation tank 30 is enlarged. Better quality of treated water can be obtained.

  In addition, when the drawing line 35 is attached to the side surface of the sludge blanket portion S, it is only necessary to provide a nozzle on the side plate of the sludge blanket portion S, so that the device structure can be simplified. On the other hand, when the drawing line 35 is connected to the bottom 32c of the sludge blanket part S, the nozzle is provided on the bottom surface of the sludge blanket part S, so the drawing line 35 is provided in the sludge concentration part Z4, and the apparatus structure becomes complicated. There is a case. However, the configuration in which the drawing line 35 is connected to the bottom portion 32c of the sludge blanket portion S can reduce the ascending speed of the entire sludge blanket portion S in the entire sludge blanket portion S, and the sludge blanket portion S is raised by returning sludge. This is preferable because it is possible to minimize the region in which the flow velocity increases.

  In addition, the pull line 35 is connected to the lower part of the sludge blanket part S from the lower part of the sludge blanket part S in terms of promoting the growth of flocs by suppressing the rising flow velocity inside the sludge blanket part S. It can be set as the structure which pulls out sludge. Here, the lower part of the sludge blanket part S refers to the lower half of the sludge blanket part S in the vertical direction. In this case, the drawing line 35 may be provided on the bottom surface or side surface of the lower half of the sludge blanket portion S. By adopting a configuration in which the sludge is extracted at the lower portion of the sludge blanket portion S, the influence on the rectifying property of the fluidized bed above the extraction line 35 can be reduced, so that good treated water quality can be obtained. In the sludge blanket part S, it is possible to minimize the region where the flow velocity of the upward flow of the sludge blanket part S increases due to sludge return.

  Furthermore, when the drawing line 35 is attached below the inflowing water dispersion pipe 33 as in the above-described embodiment, it becomes easy to favorably maintain the rectification property of the fluidized bed formed above the dispersion pipe 33. Therefore, it becomes easy to obtain good treated water quality.

  In the above-described embodiment, the drawing line 35 in which one drawing port 35a is connected to the bottom 32c of the inner wall portion 32 is shown. However, a drawing line 35 having a plurality of drawing ports 35a may be used. In this case, for example, the plurality of extraction openings 35a may be arranged so as to surround the axis L and be uniform. Further, for example, the drawing openings 35 a can be arranged so as to be uniformly distributed on the bottom 32 c of the inner wall portion 32. In this case, since the places where the sludge is drawn out are uniformly distributed, the influence on the fluidized bed formed by the inflowing water can be suppressed.

  As mentioned above, the structure of the drawing line provided in the sludge blanket part of a coagulation sedimentation tank can be changed suitably. Here, a coagulation sedimentation tank 30B shown in FIG. 3 will be described as a first modification of the coagulation sedimentation tank. The coagulation sedimentation tank 30 </ b> B has a sludge reservoir 46 provided so as to be recessed downward at the bottom 32 c of the inner wall portion 32, and the drawing line 35 is connected to the sludge reservoir 46. In this case, by drawing sludge from the sludge reservoir 46 provided on the bottom 32c of the inner wall 32, the range that affects the rectification of the fluidized bed by providing the extraction line may be the vicinity of the sludge reservoir 46. In addition, the sludge is concentrated in the sludge reservoir 46, and sludge having a high SS concentration can be returned to the previous stage. In addition, the sludge storage part 46 may be formed, for example so that the axis line L may be enclosed, and the some sludge storage part 46 may be disperse | distributed uniformly. With such a configuration, the places where the sludge is drawn out are uniformly distributed, so that the influence on the fluidized bed formed by the inflowing water can be suppressed. Therefore, the effect of growing flocs and the effect of separating solids and water are further improved.

  In FIG. 4, the sludge storage part 46 is provided so that a part of the bottom part 32 c is recessed downward. For example, the sludge storage part 46 is provided outside the coagulation sedimentation tank 30 </ b> B via a pipe, and the extraction line 35 is provided. The sludge storage section outside the coagulation sedimentation tank 30B may be connected. According to this configuration, the sludge is concentrated in the sludge reservoir, and the sludge having a high SS concentration can be returned to the previous stage.

  Further, a coagulation sedimentation tank 30C as shown in FIG. 4 can be used as a second modification. In the coagulation sedimentation tank 30C, the extraction line 45 has an extraction port 45a that is inserted from the upper surface of the sludge blanket portion S without penetrating the wall of the inner wall portion 32 and is positioned below the separation zone Z2 of the sludge blanket portion S. . At this time, the drawing line 45 penetrates the separation zone Z2 in a substantially vertical direction, protrudes to the outside of the outer wall portion 31 above the inner wall portion 32, and is connected to the return line L1. Here, since the extraction line 45 penetrates the outer wall portion 31 at the upper part and protrudes outside, the water pressure in the vicinity of the penetration part is lower than that when the extraction line penetrates the outer wall part 31 at the lower part. The structure for sealing the penetration part of the part 31 becomes simple.

  Furthermore, in the coagulation sedimentation tank 30 </ b> C of the second modified example, the drawing line 45 can protrude outside the outer wall portion 31 by penetrating only the outer wall portion 31. Therefore, compared with the case where the drawing line does not penetrate the separation zone Z2 in the vertical direction and penetrates the inner wall portion 32 and the outer wall portion 31 and protrudes to the outside of the outer wall portion 31, the number of walls to be penetrated is reduced. Can be easier.

  The drawing line 45 penetrates the outer wall 31 above the inner wall 32 and protrudes outward. For example, like the drawing line 47, the drawing line 45 penetrates the water surface of the upper open type coagulation sedimentation tank and protrudes outward. May be. At this time, since the drawing line 47 does not penetrate the outer wall portion 31, the configuration is simplified. Moreover, it can be set as the structure which changes the vertical position of the extraction opening 45a, and changes the extraction position of sludge.

  Here, the extraction ports 45a may be uniformly distributed around the axis L, for example, so that the influence of extracting the sludge on the rectification of the fluidized bed in the floc growth zone Z1 can be controlled. For example, the extraction line 45 connected to the extraction port 45 a may be connected to a single line and protrude to the outside of the outer wall portion 31.

  Moreover, the extraction line 45 may be provided so that the position of the extraction port 45a can be changed. According to this configuration, the sludge extraction position can be adjusted so as not to affect the rectification of the sludge blanket portion S by providing the extraction line 45 so as to change the sludge extraction position depending on the position of the extraction port 45a. It is. Therefore, the rectification | straightening property of the sludge blanket part S can be improved, and more favorable treated water quality can be obtained. In this configuration, for example, extraction ports 45a may be provided at a plurality of locations, and control may be performed so that the sludge extraction position is changed at regular intervals by automatic valve switching or the like.

  Moreover, in the said embodiment, although the two dispersion pipes 33 of inflow water were used, you may make it provide three or more dispersion pipes extended radially with respect to a drive shaft pipe. Further, the dispersion pipe 33 is not limited to a mode orthogonal to the axis of the drive shaft pipe, and may be inclined corresponding to the shape of the bottom of the coagulation sedimentation tank.

  Moreover, it can change suitably also about the structure of a coagulation sedimentation system. Here, two modified examples of the coagulation sedimentation system will be described with reference to FIGS.

  As shown in FIG. 5 (a), the coagulation sedimentation system 100B has a line mixer 22 instead of the second reaction tank 20 of the first embodiment. The line mixer 22 adds the polymer flocculant from the polymer flocculant addition means 21 to the treated water from the first reaction tank 10 and mixes the treated water and the polymer flocculant. Thereafter, the treated water mixed with the polymer flocculant flows as inflow water of the coagulation sedimentation tank 30, and the coagulation sedimentation process is performed in the coagulation sedimentation tank 30.

  Here, since the line mixer 22 mixes the polymer flocculant and the treated water, the reaction for forming the flocs flocs is basically performed in the sludge blanket part S of the flocs sedimentation tank 30, and the flocs flocs are removed. Form.

  Further, as shown in FIG. 5 (b), the polymer flocculant adding means 21 does not use the second reaction tank of the first embodiment, and the polymer flocculant adding means 21 enters the polymer in the influent water distribution pipe immediately before the coagulation sedimentation tank 30. The flocculant may be line injected. In this case, the aggregation flocs are mainly formed in the sludge blanket portion S of the aggregation sedimentation tank 30.

  Further, as shown in FIG. 5B, the coagulation sedimentation system 100 </ b> C may have an activated sludge treatment tank 70 before the first reaction tank 10. In this case, all of the sludge extracted from the coagulation sedimentation tank 30 may be returned to the activated sludge treatment tank 70 and circulated, with some sludge in the activated sludge treatment tank 70 and the other sludge in the first reaction. You may circulate by returning to the tank 10.

  Here, by supplying sludge to the activated sludge treatment tank 70, the sludge concentration in the activated sludge treatment tank can be maintained at an appropriate concentration, and the number of bacteria in the activated sludge treatment tank can be maintained. Therefore, the activated sludge treatment tank 70 can be efficiently treated with a high treatment load.

  DESCRIPTION OF SYMBOLS 10 ... 1st reaction tank, 20 ... 2nd reaction tank, 30A, 30B, 30C ... Coagulation sedimentation tank, 35, 45 ... Extraction line, 46 ... Sludge storage part, 100A, 100B, 100C ... Coagulation sedimentation system, S ... Sludge Blanket section, L1 ... return line, L2 ... discharge line, Z1 ... flock growth zone, Z2 ... separation zone, Z3 ... sedimentation zone, Z4 ... sludge concentration section.

  As shown in FIG. 1, the coagulation sedimentation system 100A includes a first reaction tank 10, a second reaction tank 20, and a coagulation sedimentation tank 30A connected in this order, and from the sludge blanket part S of the coagulation sedimentation tank 30A. A return line L1 for returning the extracted sludge to the first reaction tank 10, a discharge line L2 for discharging sludge from the coagulation sedimentation tank 30A, a storage tank 50 connected to the discharge line L2, and a rear stage of the storage tank The dehydrator 60 is provided.

Here, as the inorganic flocculant, Al-based inorganic flocculants such as sulfuric acid band and PAC, and Fe-based inorganic flocculants such as polyiron sulfate may be used. Alternatively, crystals are precipitated by adjusting the pH with an alkali such as NaOH or Ca (OH) ₂ or an acid such as H ₂ SO ₄ or HCL, adding a Ca, Al or Fe compound, or adding an oxidizing agent or a reducing agent. You may let them. Here, the crystal grows using the sludge returned from the coagulation sedimentation tank 30A as the nucleus of the crystal.

  The coagulation sedimentation tank 30A introduces the treated water containing the coagulated floc from the second reaction tank 20, and after the coagulated floc is grown in the sludge blanket part S, the coagulated floc as a solid is separated from the treated water. . The separated treated water is discharged out of the tank at the upper part of the coagulation sedimentation tank 30A. A part of the aggregated floc is returned to the preceding stage via the return line L1, and the rest overflows from the sludge blanket part S and is discharged from the sludge concentrating part Z4 to the storage tank 50 through the discharge line L2 as concentrated sludge.

  A pull-out line 35 that can pull out sludge from the sludge blanket portion S is connected to the inner wall portion 32. The extraction line 35 has an extraction port 35a provided at the end of the extraction line 35 at the bottom 32c of the inner wall 32 so that sludge containing aggregated floc and water is extracted from below the separation zone Z2 in the sludge blanket portion S. It is connected. Further, the drawing line 35 penetrates the outer wall portion 31 and the inner wall portion 32 and protrudes to the outside, and is connected to the return line L1 via the pump P. The return line L1 is connected to the first reaction tank 10. As a result, the sludge drawn from below the separation zone Z2 in the sludge blanket part S is returned to the previous stage, passes through the first reaction tank 10 and the second reaction tank 20 via the drawing line 35 and the return line L1, and again. It flows into the coagulation sedimentation tank 30A.

  On the other hand, in this embodiment, in the sludge blanket part S, the mixture (sludge) containing flock and water is drawn from the lower side of the separation zone Z2, and returned to the first reaction tank 10 in the previous stage.

At this time, the amount of water flowing into the sludge blanket part S and the amount of sludge drawn from the sludge blanket part S by the drawing line 35 satisfy the following formula.
Total amount of inflow water to sludge blanket part S = (Amount of inflow water to sludge blanket part S) − (Amount of sludge withdrawn from sludge blanket part S) = Amount of raw water

  When the raw water amount is constant, the ascending flow rate of the sludge blanket part S is constant regardless of the presence or absence of sludge circulation and the amount of sludge circulation. That is, without increasing the capacity of the sludge blanket part S, it is possible to grow a good coagulation floc and maintain an appropriate residence time and ascending flow rate for sedimentation separation, and to obtain clear treated water. Become. Moreover, in the sludge blanket part S, the residence time required for flocking can be secured, and the flow rate can be made uniform without increasing the ascending flow velocity, so that the quality of the treated water discharged from the sludge blanket part S is maintained well. It is possible. As a result, it is not necessary to enlarge the sludge blanket part S as compared with the case where the sludge extracted from the sludge concentrating part Z4 is returned to the previous stage, and thus a better treatment without increasing the size of the coagulation sedimentation tank 30A. Water quality can be obtained.

  As described above, according to the present embodiment, the extraction line 35 extracts sludge from the sludge blanket part S, returns it to the previous stage, and circulates it, so that the coagulation sedimentation tank 30A can be processed more smoothly without increasing the size. Water quality can be obtained.

  Moreover, in the said embodiment, although the drawing line 35 is connected to the bottom part 32c of the inner wall part 32 which forms the sludge blanket part S of 30 A of coagulation sedimentation tanks, you may be attached to the side surface of the inner wall part 32, It suffices that it is attached at least below the separation zone Z2 of the sludge blanket portion S. In this case, it is possible to reduce the rising speed of the inflowing water in the sludge blanket part S as described in the above embodiment above the position where the drawing line 35 is attached. Therefore, since it can suppress that the speed | rate of the inflow water which passes especially the separation zone Z2 raises, the separation of the solid substance and water in the separation zone Z2 can be performed suitably, and the coagulation sedimentation tank 30A is enlarged. Better quality of treated water can be obtained.

  In FIG. 3, the sludge storage part 46 is provided so that a part of the bottom part 32 c is recessed downward. For example, the sludge storage part 46 is provided outside the coagulation sedimentation tank 30 </ b> B via a pipe, and the drawing line 35 is provided. The sludge storage section outside the coagulation sedimentation tank 30B may be connected. According to this configuration, the sludge is concentrated in the sludge reservoir, and the sludge having a high SS concentration can be returned to the previous stage.

  As shown in FIG. 5A, the coagulation sedimentation system 100B has a line mixer 22 instead of the second reaction tank 20 of the first embodiment. The line mixer 22 adds the polymer flocculant from the polymer flocculant addition means 21 to the treated water from the first reaction tank 10 and mixes the treated water and the polymer flocculant. Thereafter, the treated water mixed with the polymer flocculant flows as inflow water of the coagulation sedimentation tank 30A, and the coagulation sedimentation process is performed in the coagulation sedimentation tank 30A.

  Here, since the line mixer 22 mixes the polymer flocculant and the treated water, the reaction for forming the flocculation floc is basically performed in the sludge blanket part S of the flocculation settling tank 30A, and the flocculation floc is removed. Form.

  Further, as shown in FIG. 5 (b), the polymer flocculant addition means 21 does not use the second reaction tank of the first embodiment and the polymer flocculant addition means 21 enters the polymer in the influent water distribution pipe immediately before the coagulation sedimentation tank 30A. The flocculant may be line injected. In this case, the aggregation floc is mainly formed in the sludge blanket part S of the aggregation sedimentation tank 30A.

  5B, the coagulation sedimentation system 100C may have an activated sludge treatment tank 70 before the first reaction tank 10. In this case, all the sludge extracted from the coagulation sedimentation tank 30A may be returned to the activated sludge treatment tank 70 and circulated, with some sludge in the activated sludge treatment tank 70 and other sludge in the first reaction. You may circulate by returning to the tank 10.

Claims (6)

Coagulation sedimentation provided with sludge blanket part which has a floc growth zone where a fluidized bed is formed at least by the rising flow of inflow water, and a separation zone which separates solids and treated water which are formed above the growth zone A tank,
An extraction line provided by extracting sludge from below the separation zone;
A discharge line for discharging sludge overflowed from above the separation zone;
A coagulating sedimentation tank characterized by comprising:   The coagulation sedimentation tank according to claim 1, wherein the drawing line is connected to a lower portion of the sludge blanket portion.   The coagulation sedimentation tank according to claim 1 or 2, wherein a sludge storage section is provided at the bottom of the sludge blanket section, and the drawing line is connected to the sludge storage section.   The coagulation sedimentation tank according to claim 1, wherein the drawing line is provided so as to penetrate the separation zone.   The coagulation sedimentation tank according to claim 4, wherein the extraction line is provided so that a sludge extraction position can be changed. A coagulation reaction tank for reacting the coagulant with raw water;
The coagulation sedimentation tank according to any one of claims 1 to 5, wherein the influent water from the aggregation reaction tank is subjected to solid-liquid separation,
A coagulation sedimentation system comprising:
The coagulation sedimentation system, wherein the drawing line is connected to the coagulation reaction tank.

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