Water treatment method and water treatment apparatus

Abstract

To provide a water treatment method and water treatment apparatus that are less prone to calcium scale formation while also being compact in design. [Solution] A water treatment method for removing calcium components contained in water to be treated, comprising: a reaction step of adding a calcium insolubilizing agent to the water to be treated to insolubilize the calcium components; a mixing step of adding an inorganic coagulant to the water to be treated after the reaction step to coagulate the calcium insolubilized material; a coagulation step of adding a coagulation aid to the water to be treated after the mixing step to further coagulate the calcium insolubilized material; and a sedimentation separation step of separating the calcium insolubilized material from the water to be treated after the coagulation step by sedimentation, wherein the hydraulic residence time (HRT) of the water to be treated in the reaction step is 1 minute or more and 5 minutes or less.

Description

【Technical Field】 【0001】 The present invention relates to a water treatment method and a water treatment apparatus for removing calcium components contained in treated water. 【Background Art】 【0002】 Since high-concentration calcium components are dissolved in the leachate of the final disposal site, calcium scale may form on the pipes and equipment in the water treatment facilities that treat the leachate, resulting in inconvenient situations such as pipe blockage. To prevent this, a pretreatment is performed to remove the calcium components in the leachate by adding sodium carbonate, which is a calcium insolubilizing agent, to the leachate and precipitating and separating it as calcium carbonate. 【Prior Art Documents】 【Patent Documents】 【0003】 【Patent Document 1】 Japanese Patent Application Laid-Open No. 2023-106900 【Summary of the Invention】 【Problems to be Solved by the Invention】 【0004】 As a conventional water treatment apparatus, for example, as shown in Patent Document 1 and the like, a reaction tank in which a chemical that reacts with calcium components contained in treated water to insolubilize them and the treated water are mixed, a mixing tank in which an inorganic flocculant is further mixed, a flocculation tank in which a flocculation aid is further added to flocculate and precipitate calcium insolubles generated in the treated water, and a neutralization tank that neutralizes the treated water after removing the calcium insolubles are generally known. 【0005】 In a conventional water treatment apparatus, in order to sufficiently insolubilize the calcium components in the treated water in the reaction tank, a relatively large reaction tank is used, and the residence time of the treated water is set to 10 minutes or more. 【0006】 However, as reaction vessels become larger, cleaning becomes more burdensome and maintenance costs increase. Furthermore, calcium scale tends to accumulate more easily on the walls of the reaction vessels and on the agitators. 【0007】 This invention has been made in view of the above circumstances, and its purpose is to provide a water treatment method and water treatment apparatus that are less prone to calcium scale formation while making the apparatus more compact. [Means for solving the problem] 【0008】 The water treatment method according to the present invention is a water treatment method for removing calcium components contained in water to be treated, comprising: a reaction step of adding a calcium insolubilizing agent to the water to be treated to insolubilize the calcium components; a mixing step of adding an inorganic coagulant to the water to be treated after the reaction step to coagulate the calcium insolubilized material; a coagulation step of adding a coagulation aid to the water to be treated after the mixing step to further coagulate the calcium insolubilized material; and a sedimentation separation step of separating the calcium insolubilized material from the water to be treated after the coagulation step by sedimentation, wherein the hydraulic residence time (HRT) of the water to be treated in the reaction step is 1 minute or more and 5 minutes or less. 【0009】 The water treatment method according to the present invention is a water treatment method for removing calcium components contained in water to be treated, comprising: a reaction mixing step of adding a calcium insolubilizing agent and an inorganic coagulant to the water to be treated to insolubilize the calcium components; a coagulation step of adding a coagulation aid to the water to be treated after the reaction mixing step to coagulate the calcium insolubilized material; and a sedimentation separation step of separating the calcium insolubilized material from the water to be treated after the coagulation step by sedimentation, wherein the hydraulic residence time (HRT) of the water to be treated in the reaction mixing step is 1 minute or more and 5 minutes or less. 【0010】 The water treatment apparatus according to the present invention is a water treatment apparatus capable of carrying out the first water treatment method described above, wherein the reaction step, the mixing step, the coagulation step, and the sedimentation separation step are carried out in a single tank, and the area in which the reaction step is carried out and the area in which the mixing step is carried out are separated by a partition member via a connecting part so that the water to be treated can flow through them. 【0011】 The water treatment apparatus according to the present invention is a water treatment apparatus capable of carrying out the second water treatment method described above, wherein the reaction mixing step, the coagulation step, and the sedimentation separation step are carried out in a single tank, and the area in which the reaction mixing step is carried out and the area in which the coagulation step is carried out are separated by a partition member via a connecting section, allowing the water to be treated to flow through them. 【0012】 In the water treatment apparatus according to the present invention, it is preferable that the reaction mixing step is carried out in a cylindrical body that is vertically arranged in a single tank and has an opening at its lower end. [Effects of the Invention] 【0013】 The calcium scale is formed by the reaction of calcium components with carbonates, but according to the classical interpretation, its formation process is divided into several stages. The first stage is the reaction of calcium ions (Ca 2+ ) and carbonate ions (CO3 2- The first stage involves repeated aggregation of crystals, the second stage involves the clusters exceeding the critical radius during repeated aggregation to form crystal nuclei, and the third stage involves the crystal nuclei gradually growing to form a crystalline state of a certain size. Generally, the state before crystallization is called the amorphous state (ACC state). The final stage is the growth of calcium carbonate crystals. 【0014】 The inventors of this invention have discovered that calcium carbonate in an unstable, amorphous state during the relatively early stages of calcium scale formation, specifically from the first to the third stages, is most likely to adhere to walls and other surfaces, and that its adhesion decreases in subsequent stages. Further diligent research has revealed that scale adhesion occurs significantly within 5 minutes of the start of the reaction, and therefore, a reaction time of 5 minutes is sufficient for calcium insolubilization (calcium carbonate formation). Thus, it is possible to set the hydraulic residence time (HRT) to within 5 minutes, leading to the completion of this invention. 【0015】 According to the present invention, the processing time in the reaction process can be significantly reduced, allowing the reaction vessel to be designed to be smaller and more compact. As a result, in addition to the miniaturization of the reaction vessel, the amount of calcium scale generated is also greatly reduced, which significantly reduces the cleaning area, cleaning frequency, and cleaning time of the reaction vessel walls and other surfaces that need to be cleaned, thereby improving the maintainability of the water treatment equipment. [Brief explanation of the drawing] 【0016】 [Figure 1] This is a schematic diagram showing the longitudinal cross-section of a water treatment device. [Modes for carrying out the invention] 【0017】 (Water treatment equipment) In the following, embodiments of the present invention will be described with reference to drawings, using as an example an application of the water treatment apparatus 1 according to the present invention to a calcium removal apparatus that removes calcium components from leachate (an example of water to be treated) discharged from a final disposal site for waste. In this embodiment, the water treatment apparatus 1 is functionally integrated and comprises a reaction tank in which a chemical agent that reacts with and insolubilizes the calcium components contained in the leachate is mixed with the leachate, a mixing tank in which an inorganic coagulant is further mixed, and a coagulation tank in which a coagulation aid is further added to coagulate and precipitate the calcium insoluble matter generated in the leachate. 【0018】 As shown in FIG. 1, the water treatment apparatus 1 according to the present embodiment includes a main body 2 for storing leachate, a cylindrical body 3 disposed vertically in the main body 2 and having an opening 30 (an example of a communication part) at the lower end, a stirring device 4 disposed in the cylindrical body 3 for stirring the leachate in the cylindrical body 3, a treated water supply device 5 for supplying the leachate into the cylindrical body 3, a chemical supply device 6 for supplying a chemical that reacts with the calcium component contained in the leachate to insolubilize it into the cylindrical body 3, a flocculation aid supply device 7 for supplying a flocculation aid for flocculating and sedimenting the calcium-insoluble product generated in the leachate, a take-out part 8 for taking out the leachate after the calcium component is removed, a discharge part 9 for discharging the flocculated sediment of the calcium-insoluble product, and a control device (not shown). 【0019】 The main body 2 includes a first main body part 20 having a straight cylindrical shape with a constant cross-sectional area in the vertical direction, and a second main body part 21 having a tapered shape with a smaller cross-sectional area toward the lower side. The second main body part 21 is disposed adjacent to the lower side of the first main body part 20. In the present embodiment, the cross-sectional shape of the first main body part 20 is substantially square, and the second main body part 21 has a substantially inverted square pyramid-shaped hopper structure. Note that the inclination angle of the second main body part 21 does not need to be constant, and for example, it may be configured to be different at the top and bottom. For example, the upper inclination angle may be set to about 60 degrees and the lower inclination angle may be set to about 45 degrees. 【0020】 The cylindrical body 3 in the present embodiment has a cylindrical shape, but is not limited to this shape. In the present embodiment, the cylindrical body 3 is disposed at a substantially central portion of the main body 2 in a plan view, and the opening 30 of the cylindrical body 3 is disposed in the second main body part 21. Regarding the size of the cylindrical body 3 of the water treatment apparatus 1, it is desirable that the hydraulic retention time (HRT) is designed to be in the range of 1 minute or more and 5 minutes or less. 【0021】 The stirring device 4 in this embodiment includes a stirring shaft 40, stirring blades 41, a motor drive unit 42, and the like. The stirring blades 41 are arranged inside the cylindrical body 3, and their stirring speed and timing are adjusted by a control device. The stirring device 4 is preferably configured to generate swirling flows both inside and outside the cylindrical body 3, but it is particularly desirable to configure it to generate an upward flow in the leachate water inside the cylindrical body 3. Also, regarding the stirring intensity of the stirring device, it is desirable to adjust it so that the sludge interface A of the calcium-insoluble matter, which will be described later, is at a height equal to or higher than the height of the opening 30 of the cylindrical body 3. 【0022】 The treated water supply device 5 in this embodiment includes a storage tank (not shown) for storing leachate water, a liquid delivery pump, and the like. The liquid delivery pump is provided in a pipe connecting the leachate water storage tank and the upper end portion of the cylindrical body 3. The control device controls the liquid delivery pump to adjust the supply amount of the leachate water supplied to the main body 2. Note that the supply of the leachate water may be configured to be supplied by natural flow through a pipe instead of by the treated water supply device 5 described above. 【0023】 The chemical supply device 6 in this embodiment includes an insolubilizing agent supply device 60 for supplying an insolubilizing agent containing a carbonate such as sodium carbonate, and a flocculant supply device 61 for supplying an inorganic flocculant such as ferric chloride. 【0024】 The insolubilizing agent supply device 60 includes a storage tank for storing the insolubilizing agent, a liquid delivery pump, and the like. The liquid delivery pump is provided in a pipe connecting the insolubilizing agent storage tank and the upper end portion of the cylindrical body 3. The control device controls the liquid delivery pump to adjust the supply amount of the insolubilizing agent supplied to the cylindrical body 3. Examples of the insolubilizing agent include, but are not limited to, an aqueous sodium carbonate solution. 【0025】 The coagulant supply device 61 includes a storage tank for storing inorganic coagulant and a liquid transfer pump, etc., and the liquid transfer pump is installed in the piping connecting the coagulant storage tank and the upper end portion of the cylindrical body 3. The control device adjusts the amount of inorganic coagulant supplied to the cylindrical body 3 by controlling the liquid transfer pump. Examples of inorganic coagulants include, but are not limited to, iron-based coagulants such as ferric chloride and polyferric sulfate, and aluminum sulfate. 【0026】 The flocculation aid supply device 7 includes a storage tank for storing the flocculation aid and a liquid transfer pump, etc., and the liquid transfer pump is installed in the piping connecting the flocculation aid storage tank and the main body 2. The control device controls the liquid transfer pump to adjust the amount of flocculation aid supplied to the main body 2. The flocculation aid supply device 7 is configured to supply the flocculation aid downstream of the agitator 4. It is desirable, but not limited to, that the flocculation aid be supplied near the opening 30 of the cylindrical body 3, and it is preferable to configure it to be supplied below the interface of the sludge containing calcium insoluble matter that is formed inside the main body 2. Examples of flocculation aids include, but are not limited to, polymer flocculants such as acrylamide polymers. 【0027】 The control device is a device that controls the operation of each part of the water treatment device 1 based on measurement values ​​from instruments installed in each part of the water treatment device 1, and a known computing device can be used. The control device may also have a storage device for storing various data, an input device for use by the user, an output device for presenting information to the user, etc. The control device can communicate with at least the stirring device 4, the water to be treated supply device 5, the immobilizer supply device 60, the coagulant supply device 61, and the coagulation aid supply device 7, and controls the operation and stopping of these devices. 【0028】 The discharge section 9 is located at the deepest part of the second main body section 21. In this embodiment, the discharge section 9 is provided with a valve member 90 such as an electric valve, and by opening the valve member 90, the sludge containing calcium insoluble matter that has flocculated and settled by gravity is discharged into a sludge storage tank or the like. 【0029】 The outlet section 8 is provided at the upper end portion of the first main body section 20 of the main body 2. In this embodiment, the outlet section 8 includes an overflow weir 80. 【0030】 (Water treatment method) The water treatment method in this embodiment includes a reaction mixing step in which a calcium insolubilizing agent and an inorganic coagulant are added to the leachate to insolubilize the calcium component; a coagulation step in which a coagulation aid is added to the leachate after the reaction mixing step to coagulate the calcium insolubilized material; and a sedimentation separation step in which the calcium insolubilized material is separated by sedimentation from the leachate after the coagulation step. In this embodiment, the area in which the reaction mixing step is performed and the area in which the coagulation step is performed are separated by a cylindrical body 3 (an example of a partition member) that allows leachate to flow through an opening 30 (an example of a communication part). 【0031】 (1) Reaction and mixing step In the water treatment apparatus 1, when leachate flows into the cylindrical body 3 of the main body 2 from above by the water to be treated supply device 5, it is mixed with the insolubilizing agent supplied by the insolubilizing agent supply device 60 by the stirring action of the agitator device 4. When the insolubilizing agent is an aqueous sodium carbonate solution, calcium ions Ca in the leachate 2+ The reaction between the leaching agent and sodium carbonate (Na2CO3) is represented by the following equation (1), and calcium carbonate (CaCO3, an example of calcium insoluble material) precipitates. In other words, a region is formed inside the cylindrical body 3 where the insolubilizing agent, which reacts with and insolubilizes the calcium components contained in the leaching water, and the leaching water are mixed. Ca 2+ +Na2CO3→CaCO3↓+2Na + (1) 【0032】 Furthermore, the leachate containing calcium carbonate precipitated by the reaction in equation (1) is mixed with an inorganic coagulant supplied by the coagulant supply device 61, causing the calcium carbonate precipitate to coagulate. It is desirable to set the hydrological residence time (HRT) of the leachate in the reaction mixing step to 1 minute or more and 5 minutes or less. That is, by setting the hydrological residence time (HRT) of the leachate in the reaction mixing step to be shorter than conventionally, the calcium scale in the initial formation stage can move to the next coagulation step more easily before it adheres to the walls of the cylindrical body 3, and as a result, the adhesion and growth of calcium scale on the cylindrical body 3 can be suppressed. In addition, the calcium scale in the initial formation stage can rapidly crystallize while suspended during the subsequent coagulation step, making it less likely to adhere to the walls. 【0033】 (2) Agglomeration process After the leachate containing calcium carbonate precipitates is released from the opening 30 of the cylindrical body 3, the coagulation aid supplied by the coagulation aid supply device 7 promotes the coagulation and precipitation of the calcium carbonate precipitates. At this time, near the opening 30 of the cylindrical body 3, the cross-sectional shape of the second main body 21 is approximately square, so the swirling flow originating from the agitator 4 is more easily disturbed and turbulence is generated compared to when the cross-sectional shape of the second main body 21 is circular or the like. This promotes the mixing of the coagulation aid, further advancing the coagulation and precipitation of the calcium carbonate precipitates. 【0034】 Furthermore, the configuration that promotes the generation of turbulence in the leachate near the opening 30 of the cylindrical body 3 is not limited to the above configuration. It is also possible to promote the generation of turbulence by making the cross-sectional shape of the main body 2 corresponding to the height position of the opening 30 of the cylindrical body 3 a shape other than a perfect circle, for example, a rectangle, or by providing a baffle plate member that disrupts the flow of leachate at a position corresponding to the height position of the opening 30 of the cylindrical body 3, or even if the cross-sectional shape of the main body 2 corresponding to the height position of the opening 30 of the cylindrical body 3 is a perfect circle, by configuring the cylindrical body 3 to be eccentrically positioned in the cross-section of the main body 2. 【0035】 (3) Sedimentation separation process The region where calcium carbonate precipitates formed in the leachate are coagulated and precipitated is mainly formed inside the second main body 21, and sludge containing calcium carbonate precipitates is generated. At this time, a sludge interface A is formed at a height near the upper end of the second main body 21. It is desirable that the stirring strength of the stirring device be adjusted so that the sludge interface A of calcium-insoluble matter is at or above the height of the opening 30 of the cylindrical body 3. 【0036】 The leachate containing aggregated calcium carbonate precipitates is separated into solid and liquid components in the second main body section 21, and the settled solid portion of calcium carbonate precipitates is discharged as sludge from the discharge section 9. Meanwhile, the liquid portion, after the solid portion has been removed, rises up the main body 2 and flows out by overflow from the overflow weir 80 of the outlet section 8 located at the upper end of the first main body section 20, and is sent to a subsequent process (not shown). 【0037】 [Other Embodiments] 1. In the above-described embodiment, the water treatment method includes a reaction mixing step in which a calcium insolubilizing agent and an inorganic coagulant are added to the water to be treated to insolubilize the calcium component; a coagulation step in which a coagulation aid is added to the water to be treated after the reaction mixing step to coagulate the calcium insolubilized material; and a sedimentation separation step in which the calcium insolubilized material is separated by sedimentation from the water to be treated after the coagulation step. In this water treatment method, the hydrological residence time (HRT) of the leachate in the reaction mixing step is set to 1 minute or more and 5 minutes or less, but the method is not limited to this configuration. In addition, for example, in a water treatment method that includes a reaction step of adding a calcium insolubilizing agent to the water to be treated to insolubilize the calcium component, a mixing step of adding an inorganic coagulant to the water to be treated after the reaction step to coagulate the calcium insolubilized material, a coagulation step of adding a coagulation aid to the water to be treated after the mixing step to further coagulate the calcium insolubilized material, and a sedimentation separation step of separating the calcium insolubilized material from the water to be treated after the coagulation step by sedimentation, the hydrological residence time (HRT) of the leachate in the reaction step may be set to 1 minute or more and 5 minutes or less. 【0038】 2. In the above-described embodiment, the water treatment method is shown in which a reaction mixing step of adding a calcium insolubilizing agent and an inorganic coagulant to the water to be treated to insolubilize the calcium component, a coagulation step of adding a coagulation aid to the water that has gone through the reaction mixing step to coagulate the calcium insolubilized material, and a sedimentation separation step of separating the calcium insolubilized material from the water that has gone through the coagulation step are performed in a single tank, but the method is not limited to this configuration. For example, the reaction mixing step, the coagulation step, and the sedimentation separation step may each be performed in separate treatment tanks. Furthermore, in a water treatment method that includes a reaction step of adding a calcium insolubilizing agent to the water to be treated to insolubilize the calcium component, a mixing step of adding an inorganic coagulant to the water to be treated after the reaction step to coagulate the calcium insolubilized material, a coagulation step of adding a coagulation aid to the water to be treated after the mixing step to further coagulate the calcium insolubilized material, and a sedimentation separation step of separating the calcium insolubilized material from the water to be treated after the coagulation step, the process may be carried out in a single tank, or these steps may be carried out in separate treatment tanks. When carried out in a single tank, it is desirable that the area in which the reaction step is carried out and the area in which the mixing step is carried out are separated by a partition member so that the water to be treated can flow through a connecting section. 【0039】 3. In the above embodiment, the overflow weir 80 of the outlet section 8 is provided on the inner circumferential wall of the first main body section 20, but the configuration is not limited to this. For example, the overflow weir 80 of the outlet section 8 may also be provided on the outer circumferential wall of the cylindrical body 3, or it may be provided between the inner circumferential wall of the first main body section 20 and the outer circumferential wall of the cylindrical body 3. 【0040】 Although the present invention has been described above with reference to the drawings, the present invention is not limited to the configuration shown in the drawings, and can be implemented in various forms without departing from the spirit of the invention. [Industrial applicability] 【0041】 This invention can be used, for example, in a calcium removal device that removes calcium from leachate discharged from a final disposal site for waste. [Explanation of symbols] 【0042】 1: Water treatment equipment 2: Main unit 20: First main body 21: Second main body 3: Cylindrical body 30: Opening 4: Stirring device 40: Stirring shaft 41: Stirring blade 42: Motor drive unit 5: Water supply device for treated water 6: Drug supply device 60: Insolubilizing agent supply device 61: Coagulant supply device 7: Coagulation aid supply device 8: Removal section 80:Overflow weir 9: Discharge section 90: Valve component A: Sludge interlo

Claims

[Claim 1] A water treatment method for removing calcium components contained in water to be treated, A reaction step in which a calcium-insolubilizing agent is added to the water to be treated to insolubilize the calcium component, A mixing step is performed in which an inorganic coagulant is added to the water to be treated after the above reaction step to coagulate calcium insoluble matter. A coagulation step is performed in which a coagulation aid is added to the water to be treated after the mixing step to further coagulate the calcium insoluble matter, The process includes a sedimentation separation step for separating the calcium-insoluble material from the treated water after the coagulation step, A water treatment method wherein the hydraulic residence time (HRT) of the water to be treated in the reaction step is 1 minute or more and 5 minutes or less. [Claim 2] A water treatment method for removing calcium components contained in water to be treated, A reaction mixing step in which a calcium-insolubilizing agent and an inorganic coagulant are added to the water to be treated to insolubilize the calcium component, A coagulation step is performed in which a coagulation aid is added to the water to be treated after the reaction mixing step to coagulate calcium insoluble matter, The process includes a sedimentation separation step for separating the calcium-insoluble material from the treated water after the coagulation step, A water treatment method wherein the hydraulic residence time (HRT) of the water to be treated in the reaction mixing step is 1 minute or more and 5 minutes or less. [Claim 3] A water treatment apparatus capable of carrying out the water treatment method described in claim 1, The reaction step, the mixing step, the coagulation step, and the sedimentation separation step are carried out in a single tank. A water treatment apparatus in which a region where the reaction step is performed and a region where the mixing step is performed are separated by a partition member via a communication portion, allowing the water to be treated to flow through them. [Claim 4] A water treatment apparatus capable of carrying out the water treatment method described in claim 2, The reaction mixing step, the coagulation step, and the sedimentation separation step are carried out in a single tank. A water treatment apparatus in which a region where the reaction mixing step is performed and a region where the coagulation step is performed are separated by a partition member via a communication portion, allowing the water to be treated to flow through them. [Claim 5] The water treatment apparatus according to claim 4, wherein the reaction mixing step is carried out in a cylindrical body that is vertically arranged in the single tank and has an opening at its lower end.