Water treatment apparatus and water treatment method

Abstract

To provide a water treatment apparatus capable of reducing the use amount of an adsorbent.SOLUTION: A water treatment apparatus 1 includes a mixing tank 12 that mixes raw water and an adsorbent, a settling tank 16 that settles and separates sludge containing the adsorbent from treated water discharged from the mixing tank 12, and a sludge returning device (50,52) that returns the sludge in the settling tank 16 to the mixing tank, in which a return amount of the sludge by the sludge returning device (50,52) is controlled based on a concentration of the adsorbent in the sludge in the settling tank 16.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a water treatment device and a water treatment method. [Background technology]

[0002] To remove suspended solids from raw water such as river water or lake water, a coagulant is added to the raw water to coagulate the suspended solids, forming flocs, which are then removed by settling to obtain clarified water. This method, known as coagulation and sedimentation, is widely used in a wide variety of systems. High-speed coagulation and sedimentation systems, which combine the flocculation and sedimentation processes in the same tank, are particularly popular due to their compact installation area. One type of high-speed coagulation and sedimentation system is the sludge blanket coagulation and sedimentation system. In this system, for example, raw water containing a coagulant is introduced into a vacuum tower, and a vacuum pump is used to repeatedly evacuate and de-evacuate the vacuum tower, thereby raising and lowering the water level within the vacuum tower and creating a pulsating flow in the raw water. The pulsated raw water is then introduced into a settling tank through a raw water piping system. The suspended solids in the raw water are coagulated to form flocs, and the sludge blanket layer is passed through the settling tank to remove the flocs (suspended solids) and obtain clarified water from which the suspended solids have been removed. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 03-174204 Summary of the Invention [Problem to be solved by the invention]

[0004] When raw water contains high concentrations of color components, TOC, odorous substances, etc., it is common to add an adsorbent such as powdered activated carbon before the settling tank to remove these substances. The amount of adsorbent to be added is typically determined by conducting an equilibrium adsorption test, but because such tests require time, actual treatment plants often add an amount of adsorbent that exceeds the amount required by the equilibrium adsorption test. Furthermore, once adsorbent addition begins, it is often continued until the color components, TOC, odorous substances, etc. in the raw water return to their predetermined values. In these cases, the amount of adsorbent used is greater than necessary, resulting in increased costs.

[0005] Therefore, an object of the present disclosure is to provide a water treatment device and a water treatment method that can reduce the amount of adsorbent used. [Means for solving the problem]

[0006] A water treatment device according to one aspect of the present disclosure comprises a mixing tank for mixing raw water with an adsorbent, a settling tank for settling and separating sludge containing the adsorbent from treated water discharged from the mixing tank, and a return means for returning the sludge in the settling tank to the mixing tank, and is characterized in that the amount of sludge returned by the return means is controlled based on the concentration of the adsorbent in the sludge in the settling tank.

[0007] In the above water treatment apparatus, the settling tank is preferably a sludge blanket type coagulation and settling tank partitioned by a partition plate, the upper end of which is located below the water surface, into a coagulation and settling chamber for coagulating and settling flocs and a concentration chamber for storing, concentrating and discharging the flocs.

[0008] Furthermore, the water treatment device preferably includes a flocculant adding means for adding an Al-based inorganic flocculant to the raw water, and an acid adding means for adding acid to the sludge returned from the settling tank to the mixing tank.

[0009] The water treatment device preferably further comprises a heat treatment means for heat treating the sludge returned from the settling tank to the mixing tank.

[0010] In the water treatment device, the adsorbent preferably includes any one of activated carbon, zeolite, activated alumina, powdered ion exchange resin, silica-based adsorbent, and polymer-based adsorbent.

[0011] Furthermore, a water treatment method according to one aspect of the present disclosure includes a mixing process for mixing raw water with an adsorbent, a precipitation process for settling and separating sludge containing the adsorbent from treated water discharged from the mixing process, and a return process for returning the sludge in the precipitation process to the mixing process, and in the return process, it is preferable to control the amount of sludge returned based on the concentration of the adsorbent in the sludge in the precipitation process.

[0012] In the above-mentioned water treatment method, the settling step is preferably carried out in a sludge blanket type coagulation and settling tank which is partitioned by a partition plate, the upper end of which is located below the water surface, into a coagulation and settling chamber for coagulating and settling flocs and a concentration chamber for storing, concentrating and discharging the flocs.

[0013] Furthermore, the above water treatment method preferably includes a flocculant addition step of adding an Al-based inorganic flocculant to the raw water, and an acid addition step of adding acid to the sludge returned from the precipitation step to the mixing step.

[0014] The water treatment method preferably further comprises a heat treatment step of heat treating the sludge returned from the settling step to the mixing step.

[0015] In the water treatment method, the adsorbent preferably includes at least one of activated carbon, zeolite, activated alumina, powdered ion exchange resin, silica-based adsorbent, and polymer-based adsorbent. [Effects of the Invention]

[0016] According to the present disclosure, it is possible to provide a water treatment device and a water treatment method that can reduce the amount of adsorbent used. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic configuration diagram illustrating an example of a water treatment device according to an embodiment of the present invention. [Figure 2] FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to the present embodiment. [Figure 3] FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to the present embodiment. [Figure 4] FIG. 4 is a schematic configuration diagram showing another example of a water treatment device according to the present embodiment. [Figure 5] FIG. 1 is a graph showing the relationship between raw water turbidity and PAC injection rate. [Figure 6] FIG. 10 is a graph showing the relationship between raw water turbidity and blanket concentration for each water flow velocity (LV). DETAILED DESCRIPTION OF THE INVENTION

[0018] An embodiment of the present disclosure will be described below. The embodiment is an example of implementing the present disclosure, and the present disclosure is not limited to the embodiment.

[0019] Fig. 1 is a schematic diagram showing an example of a water treatment device according to this embodiment. The water treatment device 1 in Fig. 1 includes a raw water tank 10, a mixing tank 12 for mixing raw water with an adsorbent, a storage tank 14 for storing treated water treated in the mixing tank 12, and a settling tank 16 for settling and separating sludge containing the adsorbent from the treated water treated in the mixing tank 12.

[0020] An agitator 18 that agitates the raw water and the adsorbent is installed in the mixing tank 12. In addition, an adsorbent addition pipe 20 for adding the adsorbent to the raw water and a flocculant addition pipe 22 for adding a flocculant to the raw water are connected to the mixing tank 12. In addition, in the water treatment device 1 of Figure 1, one end of pipe 24a is connected to the raw water outlet of the raw water tank 10, and the other end of pipe 24a is connected to the raw water inlet of the mixing tank 12.

[0021] Storage tank 14 may be equipped with a pulsation generator that imparts pulsation to the treated water supplied to settling tank 16. The pulsation generator shown in Fig. 1 includes vacuum pump 26, which is a vacuum generating means, and vacuum breaker 28, which is a vacuum release means. In addition, in water treatment device 1 in Fig. 1, one end of pipe 24b is connected to a treated water outlet of storage tank 14, and the other end of pipe 24b is connected to a treated water inlet at the bottom of settling tank 16.

[0022] The settling tank 16 shown in Figure 1 is a sludge blanket type settling tank that is divided by a partition plate 30, the upper end of which is located below the water surface, into a settling chamber 32 for coagulating and settling flocs, and a thickening chamber 34 for storing, thickening, and discharging flocs. A sludge discharge pipe 36 is connected to the sludge outlet of the thickening chamber 34 of the settling tank 16, and a treated water discharge pipe 38 is connected to the treated water outlet at the top of the settling tank 16.

[0023] At least one baffle plate 40, whose longitudinal cross section is, for example, V-shaped, is installed in the coagulation and sedimentation chamber 32. The baffle plate 40 is located higher than the treated water inlet to which the pipe 24b is connected. By installing the baffle plate 40, the treated water (treated water treated in the mixing tank 12) that flows into the coagulation and sedimentation chamber 32 hits the baffle plate 40 and is agitated, which has the effect of facilitating the formation of flocs. Above the coagulation and sedimentation chamber 32 in Figure 1 is a sludge blanket layer 42, and below the sludge blanket layer 42 is an agitation zone 44.

[0024] The water treatment device 1 shown in FIG. 1 also includes a sludge return device that returns the sludge in the settling tank 16 to the mixing tank 12, a sludge concentration meter that detects the sludge concentration in the settling tank 16, and a control device .

[0025] 1 has a sludge return pipe 50 and a sludge return pump 52. One end of the sludge return pipe 50 is connected to the sludge discharge pipe 36, and the other end of the sludge return pipe 50 is connected to the sludge inlet of the mixing tank 12.

[0026] 1 is installed in the sludge blanket layer 42 and measures the sludge concentration of the sludge blanket layer 42. The sludge concentration meter 46 may be any meter that detects the sludge concentration in the settling tank 16, and may be, for example, installed in the concentration chamber 34 and detects the sludge concentration in the concentration chamber 34.

[0027] The control device 48 is composed of, for example, a microcomputer and electronic circuitry, which is composed of a CPU that executes a predetermined program, and ROM and RAM that store the program, calculation results, etc. The control device 48 is electrically connected, for example, by wire or wirelessly, to the sludge concentration meter 46 and the sludge return pump 52. As will be described later, the control device 48 adjusts the output of the sludge return pump 52 based on the adsorbent concentration in the sludge in the settling tank 16, thereby controlling the amount of sludge returned to the mixing tank 12. Note that the control of the sludge return amount by the control device 48 is not limited to adjusting the output of the pump, and may also be, for example, by adjusting the opening / closing degree of a valve installed in the sludge return pipe 50.

[0028] The operation of the water treatment device 1 according to this embodiment will be described.

[0029] The raw water in the raw water tank 10 is sent to the mixing tank 12 through piping 24a. An adsorbent is supplied to the mixing tank 12 through adsorbent addition piping 20, and a flocculant is supplied to the mixing tank 12 through flocculant addition piping 22. In the mixing tank 12, the raw water, adsorbent, and flocculant are mixed by an agitator 18 (mixing process). Color components, TOC, odorous substances, and the like in the raw water are adsorbed by the adsorbent. While the addition of a flocculant is not essential, adding a flocculant promotes the aggregation and flocculation of suspended solids in the raw water. The treated water discharged from the mixing tank 12 after the mixing process (hereinafter referred to as the first treated water) is stored in a storage tank 14. The storage tank 14 is repeatedly evacuated and de-evacuated by driving a vacuum pump 26 and opening and closing a vacuum breaker 28. As a result, the first treated water in the storage tank 14 repeatedly falls and rises in level, causing the water level to rise and fall and imparting a pulsating motion to the first treated water. The pulsating first treated water is sent from the treated water inlet through pipe 24b to the stirring zone 44 of the coagulation and sedimentation chamber 32. The pulsation caused by the first treated water being sent to the coagulation and sedimentation chamber 32 stirs the water in the coagulation and sedimentation chamber 32, causing suspended matter in the first treated water to coagulate and form flocs. Above the stirring zone 44 of the coagulation and sedimentation chamber 32, a sludge blanket layer 42 is formed, in which flocs are suspended in equilibrium at a high concentration. This sludge blanket layer 42 gradually increases in height until its upper surface reaches the height of the partition plate 30. As the first treated water passes upward through the sludge blanket layer 42, flocs formed at the bottom come into contact with and are absorbed by existing flocs in the sludge blanket layer 42, producing clarified water from which the flocs have been removed. The decontaminated water is discharged as second treated water from treated water discharge pipe 38. Because there is almost no upward flow within the concentration chamber 34 and above the concentration chamber 34, which are separated by partition plate 30, excess flocs on the upper surface of the sludge blanket layer 42 flow over the upper end of partition plate 30, are stored in the concentration chamber 34, are thickened, and accumulate as sludge. The sludge contains the adsorbent added in the previous stage. In this way, the sludge containing the adsorbent is settled and separated from the first treated water in settling tank 16 (settling step). The sludge containing the adsorbent stored in the concentration chamber 34 may be discharged to the outside of the system through sludge discharge pipe 36 at appropriate intervals, for example, periodically.

[0030] 1, the sludge containing the adsorbent in the concentration chamber 34 is returned to the mixing tank 12 through the sludge return pipe 50 (return process). When the sludge containing the adsorbent is returned to the mixing tank 12, the amount of sludge returned through the sludge return pipe 50 to the mixing tank 12 is controlled based on the adsorbent concentration in the sludge in the settling tank 16. A specific example of controlling the amount of sludge returned will be described below.

[0031] The concentration of the adsorbent in the sludge in the settling tank 16 can be determined, for example, from the sludge concentration in the sludge blanket layer 42 measured by the sludge concentration meter 46. Specifically, when the turbidity of the raw water, the amount of coagulant added, and the flow rate of the first treated water flowing through the coagulation and sedimentation chamber 32 are constant, the control device 48 determines the difference (absolute value) between the sludge concentration in the sludge blanket layer 42 measured by the sludge concentration meter 46 before the addition of the adsorbent begins and the sludge concentration in the sludge blanket layer 42 measured by the sludge concentration meter 46 after the addition of the adsorbent begins. This difference is the concentration of the adsorbent in the sludge in the settling tank 16 (effectively, the concentration of the adsorbent in the sludge blanket layer 42). The control device 48 then, for example, calculates the difference as needed and controls the amount of sludge containing the adsorbent to be returned by PID control of the output of the sludge return pump 52 so that the calculated difference falls within a preset range.

[0032] Furthermore, when the turbidity of the raw water, the amount of coagulant added, or the flow rate of the first treated water flowing through the coagulation and sedimentation chamber 32 fluctuates, the control device 48 determines the difference (absolute value) between the blanket concentration of the sludge blanket layer 42 calculated from the turbidity of the raw water, the amount of coagulant added, and the flow rate of the first treated water flowing through the coagulation and sedimentation chamber 32, and the sludge concentration of the sludge blanket layer 42 measured by the sludge concentration meter 46 after the start of adsorbent addition. Using this difference as the concentration of the adsorbent in the sludge in the settling tank 16 (effectively, the concentration of the adsorbent in the sludge blanket layer 42), the control device 48 controls the amount of sludge containing the adsorbent to be returned in the same manner as described above.

[0033] An example of calculating the blanket concentration of the sludge blanket layer 42 from the turbidity of raw water, the amount of coagulant added, and the flow rate of the first treated water flowing through the coagulation and settling chamber 32 will be described below. FIG. 5 is a diagram showing the relationship between the raw water turbidity and the PAC injection rate, and FIG. 6 is a diagram showing the relationship between the raw water turbidity and the blanket concentration for each flow rate (LV). When calculating the blanket concentration, the relationships shown in FIGS. 5 and 6 are investigated in advance by preliminary experiments. Then, the relationships in FIGS. 5 and 6 are used to derive the blanket concentration according to the raw water turbidity, the PAC injection rate (i.e., the amount of coagulant added), and the flow rate.

[0034] The amount of sludge containing the adsorbent returned may be controlled by an operator. For example, the operator may determine the difference and adjust the output of the sludge return pump 52 in accordance with the difference, thereby controlling the amount of sludge containing the adsorbent returned.

[0035] The adsorbent contained in the sludge sedimented and separated in the settling tank 16 still retains sufficient adsorption capacity. Therefore, by returning the sludge sedimented and separated in the settling tank 16 to the mixing tank 12, chromaticity components, TOC, odorous substances, and the like can be removed without the need for continuous addition of adsorbent, thereby reducing the amount of adsorbent used. Furthermore, the reduction in the amount of adsorbent used also reduces the amount of sludge generated, thereby reducing sludge disposal costs. Furthermore, as in this embodiment, by controlling the amount of sludge returned based on the adsorbent concentration in the sludge in the settling tank 16, the amount of adsorbent in the settling tank 16 can be maintained at an appropriate level, thereby stabilizing the quality of the treated water. If the amount of adsorbent in the settling tank 16 is too high, the treated water discharged from the settling tank 16 may contain adsorbent. If the amount of adsorbent in the settling tank 16 is too low, the removal rates of chromaticity components, TOC, and odorous substances may be reduced. Furthermore, when the raw water has low turbidity, the returned sludge acts as a nucleus for coagulation and promotes floc formation, making it possible to further improve the turbidity of the treated water by sedimentation treatment.

[0036] The sludge concentration meter 46 may measure, for example, the sludge concentration in the concentration chamber 34. In this case, the control device 48 may calculate the difference (absolute value) between the sludge concentration in the concentration chamber 34 measured by the sludge concentration meter 46 before the addition of the adsorbent begins and the sludge concentration in the concentration chamber 34 measured by the sludge concentration meter 46 after the addition of the adsorbent begins, and use this difference as the concentration of the adsorbent in the sludge in the settling tank 16 to control the amount of sludge returned containing the adsorbent in the same manner as described above. Alternatively, the control device 48 may calculate the difference (absolute value) between the sludge concentration in the concentration chamber 34 calculated from the turbidity of the raw water, the amount of coagulant added, and the flow rate of the first treated water flowing through the coagulation and sedimentation chamber 32 and the sludge concentration in the concentration chamber 34 measured by the sludge concentration meter 46 after the addition of the adsorbent begins, and use this difference as the concentration of the adsorbent in the sludge in the settling tank 16 to control the amount of sludge returned containing the adsorbent in the same manner as described above.

[0037] The sludge concentration meter 46 may be, for example, a near-infrared scattered light type, a transmitted light type, an ultrasonic type, a microwave type, or the like.

[0038] The raw water in this embodiment is, for example, clean water such as tap water, service water such as industrial water, river water, lake water, dam water, well water, various types of wastewater, etc. The turbidity of the raw water is not particularly limited, but is, for example, in the range of 1 to 5000 degrees. The water treatment device according to this embodiment can reduce the turbidity of the treated water to, for example, less than 1 degree.

[0039] The adsorbent is not particularly limited as long as it can adsorb at least one of chromaticity components, TOC, and odorous substances, but examples that can be used include activated carbon (e.g., powdered activated carbon with a particle size of 10 μm to 150 μm, finely powdered activated carbon with a particle size of 1 μm to 10 μm), zeolite, activated alumina, powdered ion exchange resin, silica-based adsorbents, and polymer-based adsorbents. Of these, activated carbon is preferred from the standpoint of cost.

[0040] Examples of flocculants include inorganic flocculants and polymer flocculants. Examples of inorganic flocculants include Al-based inorganic flocculants such as polyaluminum chloride (PAC) and aluminum sulfate, and Fe-based inorganic flocculants such as ferric chloride, polyiron, and polysilica iron (PSI). Examples of polymer flocculants include nonionic polymer flocculants, anionic polymer flocculants, and cationic polymer flocculants. Specific examples include polyacrylamide, sodium polyacrylate, acrylamide-acrylate copolymer, sodium acrylamidopropanesulfonate, chitosan, dimethylaminoethyl methacrylate, dimethylaminoethyl acrylate, and polyamidine.

[0041] The concentration of the returned sludge may be, for example, about 200 to 20,000 mg / L, and preferably about 500 to 10,000 mg / L. If the concentration of the returned sludge is too low, a large-capacity sludge return pump 52 is required, and if the concentration of the returned sludge is too high, the sludge return pump 52 may become clogged.

[0042] The pulsation generating device may be any device capable of imparting pulsation to the treated water sent to the settling tank 16. For example, in addition to the system using the vacuum pump 26 shown in FIG. 1, a system using a siphon or a rotary valve may also be used.

[0043] The baffle plate 40 is not particularly limited as long as it has a structure that allows the treated water sent to the settling tank 16 to hit and agitate it. The baffle plate 40 may be, for example, a mountain-shaped baffle plate (having a V-shaped cross section) as shown in FIG. 1 , or a flat baffle plate. The baffle plate 40 may also be a straightening plate with a plurality of straightening holes formed therein to allow the raw water to pass through, i.e., a baffle plate with a straightening mechanism. For example, the baffle plate may have an opening ratio (the ratio of the opening area of ​​the straightening holes to the area of ​​the baffle plate) of 3 to 30%, preferably 5 to 20%.

[0044] FIG. 2 is a schematic diagram showing another example of a water treatment device according to the present embodiment. In the water treatment device 2 shown in FIG. 2, the same components as those in the water treatment device 1 of FIG. 1 are designated by the same reference numerals, and their description will be omitted. The water treatment device 2 shown in FIG. 2 includes an acid addition pipe 54 as an acid addition means. The acid addition pipe 54 is connected to the sludge return pipe 50. In the water treatment device 2 shown in FIG. 2, it is preferable to add an Al-based inorganic flocculant to the mixing tank 12 (flocculant addition step). Then, acid is added from the acid addition pipe 54 to the sludge passing through the sludge return pipe 50 (acid addition step). This ionizes aluminum oxide in the sludge and allows it to be regenerated as an Al-based inorganic flocculant, thereby reducing the amount of flocculant used and further reducing the amount of sludge generated.

[0045] Figure 3 is a schematic diagram showing another example of a water treatment device according to the present embodiment. In the water treatment device 3 shown in Figure 3, the same components as those in the water treatment device 1 shown in Figure 1 are assigned the same reference numerals, and their description will be omitted. The water treatment device 3 shown in Figure 3 includes a heating device 56 such as a heat exchanger as a heat treatment means. The heating device 56 is installed on the sludge return pipe 50. In the water treatment device 3 shown in Figure 3, the sludge passing through the sludge return pipe 50 is heat-treated by the heating device 56. The heat treatment by the heating device 56 heats and sterilizes the sludge passing through the sludge return pipe 50 (for example, at 60°C to 80°C), thereby killing Cryptosporidium in the sludge.

[0046] Although not shown in the drawings, the water treatment device according to this embodiment may also include an ultraviolet treatment device. The ultraviolet treatment device is installed on the sludge return pipe 50 and irradiates ultraviolet rays onto the sludge passing through the sludge return pipe 50. This makes it possible to inactivate Cryptosporidium in the sludge.

[0047] Although not shown in the drawings, the water treatment device according to this embodiment may also include a cyclone. The cyclone separates and recovers the adsorbent from the sludge passing through the sludge return pipe 50. The recovered adsorbent is then returned to the mixing tank 12. This reduces the amount of sludge returned to the mixing tank 12, and reduces the risk of increasing the amount of coagulant added as the amount of sludge increases.

[0048] The settling tank 16 may be of any type (for example, a horizontal flow settling tank, a slurry circulation type coagulating and settling tank, a sludge blanket type coagulating and settling tank, a combined type coagulating and settling tank, etc.), but in the case of a sludge blanket type coagulating and settling tank, the adsorbent can be retained in the sludge blanket layer 42, allowing for more effective use of the adsorbent than in a horizontal flow settling tank. As a result, it is possible to further reduce the amount of adsorbent used and the amount of sludge.

[0049] Fig. 4 is a schematic diagram showing another example of a water treatment device according to this embodiment. The water treatment device 4 shown in Fig. 4 includes a raw water tank 10, a first mixing tank 12a, a second mixing tank 12b, a third mixing tank 12c, and a settling tank 16.

[0050] Each mixing tank is equipped with an agitator 18. An adsorbent addition pipe 20 for adding an adsorbent to the raw water is connected to the first mixing tank 12a, and a flocculant addition pipe 22 for adding a flocculant to the raw water is connected to the second mixing tank 12b. One end of pipe 24a is connected to the raw water outlet of the raw water tank 10, and the other end of pipe 24a is connected to the inlet of the first mixing tank 12a. One end of pipe 24b is connected to the outlet of the first mixing tank 12a, and the other end of pipe 24b is connected to the inlet of the second mixing tank 12b. One end of pipe 24c is connected to the outlet of the second mixing tank 12b, and the other end of pipe 24c is connected to the inlet of the third mixing tank 12c. One end of pipe 24d is connected to the outlet of the third mixing tank 12c, and the other end of pipe 24d is connected to the treated water inlet of the settling tank 16.

[0051] The settling tank 16 is a cross-flow type settling tank. A pit (thickening chamber) 58 in which sludge accumulates is provided at the bottom of the settling tank 16. A sludge discharge pipe 36 is connected to the sludge outlet of the pit 58 of the settling tank 16, and a treated water discharge pipe 38 is connected to the treated water outlet of the settling tank 16.

[0052] The water treatment device 4 shown in FIG. 4 also includes a sludge return device that returns the sludge in the settling tank 16 to the mixing tank 12, a sludge concentration meter 46 that detects the sludge concentration in the settling tank 16, and a control device 48.

[0053] The sludge return device has a sludge return pipe 50 and a sludge return pump 52. One end of the sludge return pipe 50 is connected to the sludge discharge pipe 36, and the other end of the sludge return pipe 50 is connected to the sludge inlet of the first mixing tank 12a. The other end of the sludge return pipe 50 may be connected to the sludge inlet of the second mixing tank 12b or the sludge inlet of the third mixing tank 12c. In other words, it is sufficient that the other end of the sludge return pipe 50 is connected to at least one of the sludge inlets of the first to third mixing tanks.

[0054] The sludge concentration meter 46 is installed in the pit 58 and measures the sludge concentration in the pit. The sludge concentration meter 46 measures the sludge concentration in the settling tank 16. Therefore, the sludge concentration meter 46 may be installed anywhere in the settling tank 16 as long as it can measure the sludge concentration in the settling tank 16.

[0055] The control device 48 adjusts the output of the sludge return pump 52 based on the adsorbent concentration in the sludge in the settling tank 16, thereby controlling the amount of sludge returned to the mixing tank 12.

[0056] The operation of the water treatment device 4 according to this embodiment will be described.

[0057] The raw water in the raw water tank 10 is sent to the first mixing tank 12a through pipe 24a. The adsorbent is supplied to the first mixing tank 12a through adsorbent addition pipe 20. In the first mixing tank 12a, the raw water and the adsorbent are mixed by the agitator 18 (first mixing step). The first treated water discharged from the first mixing tank 12a is sent to the second mixing tank 12b through pipe 24b. The flocculant is supplied to the second mixing tank 12b through flocculant addition pipe 22. In the second mixing tank 12b, the raw water, the adsorbent, and the flocculant are mixed by the agitator 18 (second mixing step). The second treated water discharged from the second mixing tank 12b is supplied to the third mixing tank 12c through pipe 24c. In the third mixing tank 12c, the raw water, adsorbent, and coagulant are further mixed by the agitator 18, promoting the coagulation and flocculation of suspended solids in the raw water (third mixing step). Furthermore, the mixing of the raw water with the adsorbent in each mixing tank causes the chromaticity components, TOC, odorous substances, and the like in the raw water to be adsorbed by the adsorbent. The treated water discharged from the third mixing tank 12c after the mixing step (hereinafter referred to as the third treated water) is supplied to the horizontal flow settling tank 16 via pipe 24d. In the settling tank 16, sludge containing the adsorbent is separated by settling (settling step). The adsorbent-containing sludge is collected in the pit 58. The adsorbent-containing sludge stored in the pit 58 may be discharged to the system at appropriate intervals, for example, periodically, through the sludge discharge pipe 36. The clarified water from which the sludge has been removed is discharged as the fourth treated water from the treated water discharge pipe 38.

[0058] In the water treatment device 4 shown in FIG. 4 , the sludge containing the adsorbent in the pit 58 is returned to the first mixing tank 12a through the sludge return pipe 50 (return process). Here, when the raw water turbidity is constant, the control device 48 calculates the difference (absolute value) between the sludge concentration in the pit 58 measured by the sludge concentration meter 46 before the start of adsorbent addition and the sludge concentration in the pit 58 measured by the sludge concentration meter 46 after the start of adsorbent addition. When the raw water turbidity fluctuates, the control device 48 calculates the difference (absolute value) between the assumed sludge concentration corresponding to a predetermined raw water turbidity and the sludge concentration in the pit 58 measured by the sludge concentration meter 46 after the start of adsorbent addition. This difference represents the concentration of the adsorbent in the sludge in the settling tank 16. The control device 48 then, for example, calculates the difference as needed, and PID-controls the output of the sludge return pump 52 so that the calculated difference falls within a preset range of values, thereby controlling the amount of sludge containing the adsorbent returned from the sludge return pipe 50 to the first mixing tank 12a. Note that the sludge containing the adsorbent is not limited to being returned to the first mixing tank 12a, and may be returned to at least one of the first to third mixing tanks.

[0059] In this way, by controlling the amount of sludge returned based on the concentration of adsorbent in the sludge in the settling tank 16, the amount of adsorbent used can be reduced and the amount of adsorbent in the settling tank 16 can be maintained at an appropriate level, thereby stabilizing the water quality of the treated water.

[0060] One or more devices selected from the group consisting of a sand filtration device, a membrane filtration device (e.g., a microfiltration (MF) membrane, an ultrafiltration (UF) membrane, an organic hollow fiber membrane, an inorganic membrane, etc.), an activated carbon device, etc. may be installed downstream of the water treatment device according to this embodiment, and one or more processes selected from the group consisting of sand filtration, membrane filtration, activated carbon treatment, etc. may be performed. [Example]

[0061] Hereinafter, the present disclosure will be described more specifically and in detail with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0062] <Example> Raw water was treated using the water treatment equipment shown in Figure 1. Powdered activated carbon was used as the adsorbent. The specifications of the sludge blanket type coagulation sedimentation tank used in the water treatment equipment and the raw water conditions are as follows:

[0063] <Specifications of sludge blanket type coagulation sedimentation tank> Sedimentation tank dimensions: 800mm x 900mm x 4000mm Sedimentation tank residence time: 80min Water flow rate: 2.2m 3 / h Water flow rate: 3.6m / h Concentration chamber height: 1000mm Sludge concentration meter: SSD-1620 (manufactured by Toa DKK)

[0064] <Raw water conditions> Raw water: Lake water Flocculant: PCA 25 mg / L Agglutination pH:7 Raw water turbidity: 1 degree Raw water temperature: 13 degrees 2-MIB concentration: 100ng / L (added as a standard substance to raw water) Geosmin concentration: 100ng / L (added as a standard substance in raw water)

[0065] In this example, the addition of powdered activated carbon was started while monitoring the fluctuation of the powdered activated carbon concentration in the sludge blanket layer so that the powdered activated carbon concentration in the sludge blanket layer was 250 mg / L, and the amount of sludge returned to the mixing tank from the sludge return pipe was also controlled. Table 1 shows the results of the water quality of the treated water and the amount of powdered activated carbon added.

[0066] <Comparative Example> In the comparative example, the same treatment as in the example was carried out except that sludge was not returned to the mixing tank from the sludge return pipe. That is, while monitoring the fluctuation of the powdered activated carbon concentration in the sludge blanket layer, powdered activated carbon was added so that the powdered activated carbon concentration in the sludge blanket layer was 250 mg / L. Table 1 shows the results of the water quality of the treated water and the amount of powdered activated carbon added.

[0067] [Table 1]

[0068] In the Comparative Example, the amount of powdered activated carbon added was 12.5 mg / L, but in the Example, the amount was 9.0 mg / L, a 24% reduction compared to the Comparative Example. The geosmin and 2-MIB concentrations in the treated water were the same in both the Example and Comparative Example, but the Example showed better results in terms of turbidity.

[0069] [Note] The present disclosure has the following configuration. (1) a mixing tank for mixing raw water and an adsorbent; a settling tank for settling and separating sludge containing the adsorbent from the treated water discharged from the mixing tank; a return means for returning the sludge in the settling tank to the mixing tank, A water treatment device comprising: a return means for returning the sludge; a return amount of the sludge controlled based on the concentration of the adsorbent in the sludge in the settling tank; (2) The water treatment device according to (1) above, wherein the settling tank is a sludge blanket type coagulation and sedimentation tank, which is partitioned by a partition plate whose upper end is located below the water surface into a coagulation and sedimentation chamber for coagulating and settling flocs and a concentration chamber for storing, thickening and discharging flocs. (3) a flocculant adding means for adding an Al-based inorganic flocculant to the raw water; The water treatment device according to (1) or (2) above, further comprising an acid adding means for adding acid to the sludge returned from the settling tank to the mixing tank. (4) The water treatment device according to any one of (1) to (3) above, further comprising a heat treatment means for heat treating the sludge returned from the settling tank to the mixing tank. (5) The water treatment device according to any one of (1) to (4) above, characterized in that the adsorbent includes at least one of activated carbon, zeolite, activated alumina, powdered ion exchange resin, silica-based adsorbent, and polymer-based adsorbent. (6) a mixing step of mixing raw water with an adsorbent; a settling step of settling and separating sludge containing the adsorbent from the treated water discharged from the mixing step; A returning step of returning the sludge in the settling step to the mixing step, A water treatment method, characterized in that in the returning step, the amount of the sludge returned is controlled based on the concentration of the adsorbent in the sludge in the settling step. (7) The water treatment method according to (6) above, wherein the settling step is carried out in a sludge blanket type coagulation and settling tank which is partitioned by a partition plate whose upper end is located below the water surface into a coagulation and settling chamber for coagulating and settling flocs and a concentration chamber for storing, concentrating and discharging the flocs. (8) a flocculant addition step of adding an Al-based inorganic flocculant to the raw water; The water treatment method according to claim 6 or 7, further comprising an acid addition step of adding acid to the sludge returned from the settling step to the mixing step. (9) The water treatment method according to any one of (6) to (8) above, further comprising a heat treatment step of heat treating the sludge returned from the precipitation step to the mixing step. (10) The water treatment method according to any one of (6) to (9), wherein the adsorbent includes at least one of activated carbon, zeolite, activated alumina, powdered ion exchange resin, silica-based adsorbent, and polymer-based adsorbent. [Explanation of symbols]

[0070] 1-4 water treatment device, 10 raw water tank, 12 mixing tank, 12a first mixing tank, 12b second mixing tank, 12c third mixing tank, 14 storage tank, 16 settling tank, 18 agitator, 20 adsorbent addition piping, 22 coagulant addition piping, 24a-24d piping, 26 vacuum pump, 28 vacuum breaker, 30 partition plate, 32 coagulation and settling chamber, 34 concentration chamber, 36 sludge discharge pipe, 38 treated water discharge pipe, 40 baffle plate, 42 sludge blanket layer, 44 mixing zone, 46 sludge concentration meter, 48 control device, 50 sludge return pipe, 52 sludge return pump, 54 acid addition piping, 56 heating device, 58 pit.

Claims

1. a mixing tank for mixing raw water and an adsorbent; a settling tank for settling and separating sludge containing the adsorbent from the treated water discharged from the mixing tank; and a return means for returning at least a portion of the sludge in the settling tank to the mixing tank, A water treatment device comprising: a return means for returning the sludge; a return amount of the sludge controlled based on the concentration of the adsorbent in the sludge in the settling tank;

2. 2. The water treatment device according to claim 1, wherein the settling tank is a sludge blanket type coagulation and settling tank partitioned by a partition plate, the upper end of which is located below the water surface, into a coagulation and settling chamber for coagulating and settling flocs and a concentration chamber for storing, concentrating and discharging flocs.

3. a flocculant adding means for adding an Al-based inorganic flocculant to the raw water; 3. The water treatment device according to claim 1, further comprising an acid adding means for adding acid to the sludge returned from the settling tank to the mixing tank.

4. 3. The water treatment device according to claim 1, further comprising a heat treatment means for heat treating the sludge returned from the settling tank to the mixing tank.

5. 3. The water treatment device according to claim 1, wherein the adsorbent material includes at least one of activated carbon, zeolite, activated alumina, powdered ion exchange resin, silica-based adsorbent, and polymer-based adsorbent.

6. a mixing step of mixing raw water with an adsorbent; a settling step of settling and separating sludge containing the adsorbent from the treated water discharged from the mixing step; A returning step of returning at least a portion of the sludge in the settling step to the mixing step, A water treatment method, characterized in that in the returning step, the amount of the sludge returned is controlled based on the concentration of the adsorbent in the sludge in the settling step.

7. 7. The water treatment method according to claim 6, wherein the settling step is carried out in a sludge blanket type coagulation and settling tank which is partitioned by a partition plate, the upper end of which is located below the water surface, into a coagulation and settling chamber for coagulating and settling flocs and a concentration chamber for storing, concentrating and discharging the flocs.

8. a flocculant addition step of adding an Al-based inorganic flocculant to the raw water; 8. The water treatment method according to claim 6, further comprising an acid addition step of adding acid to the sludge returned from the settling step to the mixing step.

9. 8. The water treatment method according to claim 6, further comprising a heat treatment step of heat-treating the sludge returned from the settling step to the mixing step.

10. 8. The water treatment method according to claim 6, wherein the adsorbent includes at least one of activated carbon, zeolite, activated alumina, powdered ion exchange resin, silica-based adsorbent, and polymer-based adsorbent.

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