Water treatment apparatus and water treatment method

Abstract

The present invention provides a water treatment device that suppresses the formation of scale derived from calcium carbonate and facilitates the control of sodium carbonate addition. [Solution] A water treatment device 1 is employed, comprising: a reaction tank 102 that reacts calcium in the water to be treated with sodium carbonate in the presence of CaCO3-containing sludge to precipitate it as calcium carbonate; a mixing tank 103 that adds an inorganic coagulant to the water to be treated; a coagulation tank 104 that adds a polymer flocculant to the water to be treated; a sedimentation tank 105 that separates the CaCO3-containing sludge from the water to be treated by sedimentation; a first return channel L1 that returns a portion of the separated CaCO3-containing sludge to the chemical reaction tank 106; a first sodium carbonate addition device 107; a chemical reaction tank 106 that adds sodium carbonate to the returned CaCO3-containing sludge; a second return channel L2 that returns the CaCO3-containing sludge with added sodium carbonate to the reaction tank; a calcium ion meter 108; and a control unit 109.

Description

Technical Field

[0001] The present invention relates to a water treatment apparatus and a water treatment method for treating water to be treated containing calcium.

Background Art

[0002] Environmental pollution problems caused by final disposal sites of waste were mainly organic pollution due to high-concentration BOD or eutrophication due to high-concentration nitrogen in the era when garbage was disposed of.

[0003] Today, when incineration ash and incombustibles are the main components of landfill materials, leachate contains high-concentration inorganic salts, resulting in problems caused by high-concentration calcium and salt damage caused by high-concentration chlorine. Therefore, technologies for dealing with inorganic salts have been developed and put into practical use (see Patent Document 1 and Non-Patent Document 1).

[0004] Among them, calcium not only precipitates on the detection parts such as pH meters of subsequent treatment equipment and the inner wall of pipes, but also adheres scale to the membrane surface of reverse osmosis membrane (RO membrane) treatment equipment for removing inorganic salts and the heat exchanger of vacuum distillation equipment, inhibiting stable operation. Therefore, it is necessary to always remove the Ca ion concentration to 100 mg-Ca / L or less by pretreatment (such as the lime soda method described later).

[0005] As a method for pretreating calcium, a method is generally used in which an aqueous sodium carbonate solution is added to adjust the pH to 8.0 - 10.5 to insolubilize Ca ions as calcium carbonate, and flocculation is carried out with an iron-based inorganic coagulant and a polymer flocculant (hereinafter referred to as polymer), followed by solid-liquid separation for removal (lime soda method).

[0006] Since the calcium ion concentration of raw water fluctuates, it was necessary to analyze the calcium ions in the raw water and treated water several times a day and adjust the injection amount of the aqueous sodium carbonate solution to the theoretical required amount. In addition, if an excessive amount leaks to the subsequent stage even temporarily, it will directly lead to troubles in the desalination equipment. As a result, the aqueous sodium carbonate solution is usually added in excess at a setting more than twice the theoretical amount.

[0007] Conventionally, attempts have been made to adjust the amount of sodium carbonate injected by periodically analyzing the calcium ion concentration of raw or treated water. However, due to the time lag required to obtain analysis results and limitations on the frequency of analysis, the amount of sodium carbonate injected had to be set excessively.

[0008] Furthermore, attempts have been made to optimize the amount of sodium carbonate injected by installing a calcium ion meter to measure the calcium contained in the raw or treated water. However, the accumulation of calcium carbonate-derived scale on the detection unit of the calcium ion meter hinders stable measurement, requiring acid cleaning of the detection unit several times a day, which has made it impractical. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2016-16341 [Non-patent literature]

[0010] [Non-Patent Document 1] Calcium removal from leachate, Takayuki Hashimoto, Kobe Steel Pantech Technical Report, Vol. 41, No. 2, 1998, pp. 83-89. [Overview of the project] [Problems that the invention aims to solve]

[0011] The present invention has been made in view of the above circumstances, and aims to provide a water treatment apparatus and a water treatment method that suppress the generation of scale derived from calcium carbonate and facilitate the control of sodium carbonate addition. [Means for solving the problem]

[0012] To solve the above problems, the present invention adopts the following configuration.

[0013] [1] A water treatment apparatus for treating water containing calcium, A reaction tank in which calcium contained in the water to be treated reacts with sodium carbonate in the presence of CaCO3-containing sludge containing calcium carbonate to precipitate the calcium as calcium carbonate, A mixing tank for adding an inorganic coagulant to the water to be treated, which contains the CaCO3-containing sludge and the precipitated calcium carbonate, A flocculant tank to which a polymer flocculant is added to the water to be treated to which the inorganic coagulant has been added, A sedimentation tank for separating the CaCO3-containing sludge from the treated water to which the polymer flocculant has been added, A first return channel for returning a portion of the CaCO3-containing sludge separated by sedimentation in the sedimentation tank to the chemical reaction tank, A first sodium carbonate addition device provided in the chemical reaction vessel, The chemical reaction tank, which adds the sodium carbonate to the CaCO3-containing sludge returned by the first return channel using the first addition device, A second return channel for returning the CaCO3-containing sludge to the reaction tank, to which the sodium carbonate has been added, A calcium ion meter installed in the mixing tank, A water treatment apparatus comprising: a control unit having a function to control the amount of sodium carbonate added by the first additive device based on the measurement value of the calcium ion meter. [2] The reaction vessel is equipped with a second additive device for adding the sodium carbonate to the water to be treated, The water treatment apparatus according to [1], wherein the control unit further has a function to control the amount of sodium carbonate added by the first additive device and the second additive device based on the measurement value of the calcium ion meter. [3] The coagulation tank is equipped with a coagulation sensor for measuring the turbidity of uncoagulated particles in the water to be treated, The water treatment apparatus according to [1], wherein the control unit further has a function of controlling the addition amount of the inorganic coagulant to the mixing tank based on the measurement value of the aggregation sensor. [4] A water treatment method for treating water to be treated containing calcium, comprising: a reaction step of reacting calcium contained in the water to be treated with sodium carbonate in the presence of CaCO3-containing sludge containing calcium carbonate; a coagulation step of adding an inorganic coagulant to the water to be treated containing the CaCO3-containing sludge and precipitated calcium carbonate; a flocculation step of adding a polymer flocculant to the water to be treated to which the inorganic coagulant has been added; a sedimentation separation step of sedimentation-separating the CaCO3-containing sludge from the water to be treated to which the polymer flocculant has been added; a first return step of returning a part of the CaCO3-containing sludge sedimentation-separated in the sedimentation separation step to the chemical reaction step; the chemical reaction step of adding sodium carbonate to the CaCO3-containing sludge returned by the first return step; and a second return step of returning the CaCO3-containing sludge to which sodium carbonate has been added in the chemical reaction step to the reaction step. In the coagulation step, the amount of calcium ions in the water to be treated is measured, and the addition amount of sodium carbonate in the chemical reaction step is controlled based on the measured value of the amount of calcium ions. A water treatment method. [5] In the reaction step, while further adding the sodium carbonate to the water to be treated, The total amount of the addition amount of sodium carbonate in the chemical reaction step and the reaction step is controlled based on the measured value of the amount of calcium ions. The water treatment method according to [4]. [6] In the second return step, The return amount of the CaCO3-containing sludge is adjusted so that calcium carbonate four times or more the precipitation amount of calcium carbonate precipitated in the reaction step is returned. The water treatment method according to [4]. [Advantages of the Invention]

[0014] According to the present invention, it is possible to provide a water treatment apparatus and a water treatment method that can suppress the generation of scale derived from calcium carbonate and facilitate the control of the addition of sodium carbonate.

Brief Description of the Drawings

[0015] [Figure 1] Schematic diagram showing a water treatment apparatus according to an embodiment of the present invention. [Figure 2] Configuration diagram showing a schematic configuration of a coagulation sensor used in a water treatment apparatus according to an embodiment of the present invention. [Figure 3] Enlarged view showing the configuration of the laser light irradiation unit and the scattered light receiving unit of the coagulation sensor shown in FIG. 2. [Figure 4] Enlarged view showing the configuration of the shielding member of the coagulation sensor shown in FIG. 2.

Embodiments for Carrying Out the Invention

[0016] Conventionally, when treating raw water by the lime-soda method, when the amount of calcium ions contained in the raw water (hereinafter sometimes referred to as calcium ion concentration) is high and in a supersaturated state, scale derived from calcium is generated and adheres to various sensors such as pH meters and calcium ion meters, making stable measurement difficult. Therefore, the optimization of the dosage of chemicals such as sodium carbonate has been carried out by manually analyzing the calcium ion concentration of the raw water before water treatment and the treated water after water treatment several times a day.

[0017] However, it has been difficult to automatically control chemical injection using a calcium ion meter or the like because the calcium ion concentration cannot be measured at night or on holidays when unmanned operation is performed, and if calcium ion leakage occurs even for a short time, there is concern about the adverse effects on the subsequent desalination treatment equipment.

[0018] Therefore, after diligent research by the inventors, they discovered that when treating water to be treated using the lime-soda method, by returning the sludge containing coagulated and settled calcium carbonate (hereinafter sometimes referred to as CaCO3-containing sludge) to the water to be treated, it is possible to preferentially cause scale derived from calcium carbonate to adhere to the surface of the CaCO3-containing sludge, thereby reducing the calcium ion concentration of the water to be treated from a supersaturated state to a saturated state, and significantly reducing the degree of scale adhesion derived from calcium carbonate.

[0019] Furthermore, regarding the iron hydroxide and iron oxide scales derived from Fe that adhere to various sensors such as pH meters and calcium ion meters in conjunction with the calcium carbonate scale, we found that by using a flocculation sensor capable of measuring turbidity between flocs and optimally controlling the amount of inorganic coagulant (e.g., ferric chloride solution) added so that the turbidity between flocs approaches the target value, we were able to reduce the excess iron concentration remaining in the treated water. As a result, it became unnecessary to frequently acid-clean the various sensors, enabling stable measurements by the various sensors, and thus allowing for the optimization of the amount of inorganic coagulant added.

[0020] Hereinafter, embodiments of the present invention, namely a water treatment apparatus and a water treatment method, will be described with reference to the drawings.

[0021] The water treatment apparatus 1 of this embodiment, shown in Figure 1, includes a raw water tank 101, a reaction tank 102, a mixing tank 103, a coagulation tank 104, a sedimentation tank 105, a first return channel L1, a chemical reaction tank 106, a first sodium carbonate addition device 107 provided in the chemical reaction tank 106, a second return channel L2, a calcium ion meter 108 installed in the mixing tank 103, and a control unit 109. The water treatment apparatus 1 is also equipped with channels L11 to L15.

[0022] The raw water tank 101 stores the treated water containing calcium. The treated water stored in the raw water tank 101 can be exemplified by leachate leaking from final disposal sites for incinerated ash and non-combustible materials. Such leachate contains high concentrations of calcium. A flow path L11 is connected to the raw water tank 101.

[0023] The flow path L11 is provided for transferring the water to be treated from the raw water tank 101 to the reaction tank 102.

[0024] The reaction tank 102 is provided to react calcium contained in the water to be treated with sodium carbonate in the presence of CaCO3-containing sludge containing calcium carbonate, thereby precipitating calcium as calcium carbonate.

[0025] Specifically, the reaction tank 102 is connected to channels L11 and L12 and a second return channel L2. The water to be treated is sent to the reaction tank 102 via channel L11. CaCO3-containing sludge is also sent to the reaction tank 102 via the second return channel L2. Sodium carbonate is added to this CaCO3-containing sludge in the chemical reaction tank 106.

[0026] Furthermore, the reaction tank 102 is equipped with a stirrer 102a and a second adding device 112 for adding sodium carbonate to the water to be treated as needed. The second adding device 112 receives control signals from the control unit 109, and the amount of sodium carbonate added is controlled based on the commands from the control unit 109.

[0027] Furthermore, the reaction vessel 102 is equipped with a pH adjustment means (not shown). The pH adjustment means includes a pH meter. The pH of the water to be treated is adjusted by adding an alkali or acid to the water to be treated. Suitable alkalis or acids include, for example, NaOH, KOH, Ca(OH)2, H2SO4, and HCl.

[0028] The flow path L12 is provided for transferring the treated water containing CaCO3-containing sludge from the reaction tank 102 to the mixing tank 103.

[0029] The mixing tank 103 is provided for adding an inorganic coagulant to the water to be treated, which contains calcium carbonate precipitated in the reaction tank 102 and CaCO3-containing sludge.

[0030] Specifically, the mixing tank 103 is equipped with a stirrer 103a, an additive device 103b for adding an inorganic coagulant to the water to be treated, and a calcium ion meter 108. Furthermore, flow paths L12 and L13 are connected to the mixing tank 103.

[0031] The inorganic coagulant addition device 103b adds an inorganic coagulant to the water to be treated. For example, ferric chloride is used as the inorganic coagulant. The addition device 103b receives control signals from the control unit 109, and the amount of inorganic coagulant added is controlled based on the commands from the control unit 109.

[0032] The calcium ion meter 108 is configured to measure the calcium ion concentration of the water to be treated in the mixing tank 103 and send the measurement result to the control unit 109.

[0033] The flow path L13 is provided for transferring the treated water containing CaCO3-containing sludge from the mixing tank 103 to the coagulation tank 104.

[0034] The coagulation tank 104 is provided for adding a polymer coagulant to the water to be treated, to which an inorganic coagulant has been added.

[0035] Specifically, the coagulation tank 104 is equipped with a stirrer 104a, an additive device 104b for adding a high-molecular-weight coagulant, and a coagulation sensor 114. Furthermore, flow paths L13 and L14 are connected to the coagulation tank 104.

[0036] The polymer flocculant addition device 104b adds a polymer flocculant to the water to be treated. The polymer flocculant used is one commonly used in the lime-soda process.

[0037] The coagulation sensor 114 uses a sensor capable of measuring the turbidity (turbidity between flocs) of uncoagulated particles in the water to be treated. The coagulation sensor 114 is configured to measure the turbidity of uncoagulated particles in the water to be treated in the coagulation tank 104 and send the measurement result to the control unit 109.

[0038] The flow path L14 is provided for transferring treated water containing CaCO3-containing sludge from the coagulation tank 104 to the sedimentation tank 105.

[0039] The sedimentation tank 105 is provided to separate CaCO3-containing sludge, which contains calcium carbonate, from the treated water to which a polymer flocculant has been added.

[0040] In other words, a general coagulation-sedimentation tank can be used as the sedimentation tank 105. The sedimentation tank 105 is also connected to channels L14 and L15 and the first return channel L1.

[0041] The flow path L15 is provided for transferring the treated water (clarified water) after sedimentation separation in the sedimentation tank 105 to the outside of the water treatment device 1.

[0042] The first return channel L1 is provided to transfer a portion of the CaCO3-containing sludge that has settled and separated in the settling tank 105 to the chemical reaction tank 106.

[0043] The chemical reaction tank 106 is provided for adding sodium carbonate to the CaCO3-containing sludge returned by the first return channel L1.

[0044] Specifically, the chemical reaction tank 106 is equipped with a stirrer 106a and a first adding device 107 for adding sodium carbonate to the CaCO3-containing sludge. The first adding device 107 receives control signals from the control unit 109, and the amount of sodium carbonate added is controlled based on the commands from the control unit 109. The chemical reaction tank 106 is also connected to a first return channel L1 and a second return channel L2.

[0045] The second return channel L2 is provided to transfer CaCO3-containing sludge, to which sodium carbonate has been added in the chemical reaction tank 106, from the chemical reaction tank 106 to the reaction tank 102.

[0046] The control unit 109 is equipped with a function to control the amount of sodium carbonate added by the first dosing device 107 based on the measurement value of the calcium ion meter 108.

[0047] Furthermore, the control unit 109 may be equipped with a function to control the amount of sodium carbonate added by the first additive device 107 and the second additive device 112 based on the measurement value of the calcium ion meter 108. In addition, the control unit 109 may be equipped with a function to control the amount of inorganic coagulant added in the mixing tank 103 based on the measurement value of the coagulation sensor 114. The functions and operation of the control unit 109 will be described later.

[0048] Next, a water treatment method using the water treatment apparatus 1 shown in Figure 1 will be described. The water treatment method of this embodiment includes a reaction stage, a condensation stage, a coagulation stage, a sedimentation separation stage, a first return stage, a chemical reaction stage, and a second return stage. Each stage will be described below.

[0049] In the reaction stage, in reaction tank 102, calcium contained in the water to be treated is reacted with sodium carbonate in the presence of CaCO3-containing sludge that includes calcium carbonate.

[0050] Specifically, first, the water to be treated stored in the raw water tank 101 is transferred to the reaction tank 102. Preferably, the water to be treated is adjusted to a pH range of 8 to 10.5 using the pH adjustment means provided in the reaction tank 102.

[0051] Furthermore, CaCO3-containing sludge to which sodium carbonate has been added is returned through the second return channel L2 and stored in the reaction tank 102. The addition of sodium carbonate to the CaCO3-containing sludge is carried out during the chemical reaction stage by the first addition device 107 provided in the chemical reaction tank 106, as will be described later.

[0052] In reaction tank 102, calcium contained in the treated water, which has been adjusted to a pH of 8 to 10.5, is reacted with sodium carbonate in the presence of CaCO3-containing sludge that includes calcium carbonate. As a result, the calcium contained in the treated water precipitates as calcium carbonate.

[0053] In the presence of CaCO3-containing sludge, calcium carbonate precipitates more readily on the surface of the CaCO3-containing sludge than on the pH meter attached to the pH adjustment means, the inner wall of the reaction tank 102, the inner wall of the flow path L12, or the calcium ion meter 108 provided in the mixing tank 103. The precipitated calcium carbonate is insoluble in the water to be treated and exists in the water to be treated as fine particles in the reaction tank 102, with some of it adhering to the surface of the CaCO3-containing sludge.

[0054] The average residence time of the water to be treated during the reaction stage is preferably in the range of 0.1 to 0.3 hours (6 to 18 minutes). The average residence time is calculated by the flow rate of the water to be treated X1 (m³) of the water flowing into the reaction tank 102. 3 ( / h) and the volume Z(m³) of reaction vessel 102 3 ) and the amount of CaCO3-containing sludge returned to the reaction tank 102 by the second return channel L2 X2 (m³ 3 Based on the formula ( / h), the average residence time can be calculated as Z / (X1+X2). If the average residence time is 0.1 hours (6 minutes) or more, sufficient precipitation of calcium carbonate can be achieved, and the concentration of calcium ions in the treated water can be reduced. Furthermore, if the average residence time is 0.3 hours (18 minutes) or less, the delay time of the feedback control can be shortened, and the tendency for the output of the chemical injection control and the concentration of calcium ions to hunt can be suppressed.

[0055] As previously mentioned, the addition of sodium carbonate to CaCO3-containing sludge is carried out during the chemical reaction stage, so it is not necessary to add sodium carbonate to the treated water during the reaction stage. However, the present invention is not limited to this, and sodium carbonate may be further added to the treated water by the second adding device 112 during the reaction stage in the reaction tank 102. In this case, the amount of sodium carbonate added should be the sum of the amounts added by the first adding device 107 and the second adding device 112, which corresponds to the theoretically required amount for the reaction between calcium and sodium carbonate (the required amount in reaction equation (1) below). The method for adjusting the amount of sodium carbonate added will be described later.

[0056] Ca 2+ +Na2CO3→CaCO3+2Na + …(1)

[0057] The treated water, containing CaCO3-containing sludge and precipitated calcium carbonate, is sent to the mixing tank 103 via the flow path L12.

[0058] Next, in the setting stage, an inorganic coagulant is added to the treated water containing CaCO3-containing sludge and precipitated calcium carbonate in the mixing tank 103. The inorganic coagulant is added using the addition device 103b. The method for adjusting the amount of inorganic coagulant added will be described later.

[0059] By adding an inorganic coagulant, particulate calcium carbonate present in the water to be treated is coagulated, generating fine flocs containing calcium carbonate.

[0060] Furthermore, a small amount of calcium ions may remain in the treated water during the condensation stage. The concentration of these calcium ions is measured by the calcium ion meter 108, and the measured value is sent to the control unit 109. The calcium ion concentration is referenced when adjusting the amount of sodium carbonate added.

[0061] The water to be treated, to which an inorganic coagulant has been added, is sent to the coagulation tank 104 via the channel L13.

[0062] Next, in the coagulation stage, a polymer coagulant is added to the treated water to which an inorganic coagulant has been added in the coagulation tank 104. The polymer coagulant is added by the addition device 104b. The method for adjusting the amount of polymer coagulant added will be described later.

[0063] By adding a polymer flocculant, fine flocs in the treated water aggregate, generating coarse flocs containing calcium carbonate.

[0064] Furthermore, in the treated water during the coagulation stage, fine flocs may remain as turbidity. In addition, uncoagulated calcium carbonate particles may remain. The concentration of these calcium carbonate particles and fine flocs (hereinafter referred to as inter-floc turbidity) is measured by the coagulation sensor 114, and the measured value is sent to the control unit 109. The inter-floc turbidity is referenced when adjusting the amount of inorganic coagulant added.

[0065] The treated water to which the polymer flocculant has been added is sent to the sedimentation tank 105 via channel L14.

[0066] Next, in the sedimentation separation stage, CaCO3-containing sludge is separated by sedimentation from the treated water to which a polymer flocculant has been added in the sedimentation tank 105. The treated water supplied to the sedimentation tank 105 contains coarse flocs containing calcium carbonate. By allowing these coarse flocs to settle, CaCO3-containing sludge is deposited at the bottom of the sedimentation tank 105. Meanwhile, the treated water after the coarse flocs have settled becomes clarified water. The clarified water is transferred to the outside of the water treatment device 1 via the flow path L15.

[0067] Next, in the first return stage, a portion of the CaCO3-containing sludge separated by sedimentation in the sedimentation separation stage is returned to the chemical reaction tank 106 via the first return channel L1. Meanwhile, the remaining CaCO3-containing sludge that is not returned is disposed of by dewatering, incineration, or other means.

[0068] Next, in the chemical reaction stage, sodium carbonate is added to the CaCO3-containing sludge returned in the first return flow stage in the chemical reaction tank 106. The addition of sodium carbonate is carried out by the first addition device 107. The method for adjusting the amount of sodium carbonate added will be described later.

[0069] Next, in the second return stage, the CaCO3-containing sludge to which sodium carbonate was added during the chemical reaction stage is returned to the reaction tank 102 via the second return channel L2.

[0070] It is preferable to adjust the amount of CaCO3-containing sludge returned to the reaction tank 102 so that at least four times the amount of calcium carbonate precipitated during the reaction stage is returned, as this prevents the adhesion of calcium carbonate-derived scale to various sensors (pH meter, calcium ion meter 108).

[0071] Specifically, the amount of CaCO3-containing sludge returned to the reaction tank 102, X2, should be adjusted so that the following equation (2) holds true.

[0072] (X2·Y2) / (X1·Y1)≧4 …(2)

[0073] In equation (2), X1 is the flow rate (m³ / h) of the water to be treated flowing from the raw water tank 101 to the reaction tank 102, Y1 is the calcium carbonate equivalent concentration (mg-CaCO3 / L) of the water to be treated flowing into the reaction tank 102, and X2 is the amount of CaCO3-containing sludge returned to the reaction tank 102 by the second return channel L2 (m³ / h). 3 Y2 is the concentration of calcium carbonate (mg-CaCO3 / L) in the CaCO3-containing sludge returned to the reaction tank 102 by the second return channel L2.

[0074] The calcium carbonate equivalent concentration Y1 of the treated water can be determined by measuring the calcium ion concentration in the treated water. Since the calcium ion concentration in the treated water does not fluctuate significantly in the short term, it is sufficient to measure it once every few days or weeks, for example.

[0075] Furthermore, while the calcium carbonate concentration Y2 in CaCO3-containing sludge can be determined by measuring the amount of CaCO3 in the sludge, a simpler method is to use the concentration of suspended solids (SS) in the sludge. The SS concentration can be measured online using an SS meter or similar device for the CaCO3-containing sludge flowing through the second return channel L2, or it can be measured offline by taking a sample of the sludge. Since the amount of CaCO3 and the SS concentration in CaCO3-containing sludge do not fluctuate significantly in the short term, it is sufficient to measure them once every few days or weeks, for example.

[0076] Next, we will explain how to adjust the amount of sodium carbonate added during the chemical reaction.

[0077] First, the calcium ion meter 108 installed in the mixing tank 103 measures the calcium ion concentration in the water to be treated, and sends the measured value to the control unit 109. Based on the measured value from the calcium ion meter 108, the control unit 109 determines the amount of sodium carbonate to be added and sends the result to the first adding device 107. Based on the command from the control unit 109, the first adding device 107 adds sodium carbonate to the CaCO3-containing sludge. The amount of sodium carbonate to be added should be equivalent to the theoretically required amount for the reaction between calcium and sodium carbonate (the required amount in the above reaction equation (1)).

[0078] In this case, if the measurement value from the calcium ion meter 108 is relatively high, it indicates that a relatively large amount of calcium ions remain in the treated water, and the amount of sodium carbonate added is insufficient. In this case, it is preferable for the control unit 109 to control the first additive device 107 to increase the amount of calcium carbonate added.

[0079] On the other hand, if the measurement value from the calcium ion meter 108 is relatively low, it may indicate that the amount of residual calcium ions in the treated water is low, and that the amount of sodium carbonate added is either sufficient or excessive. In this case, it is preferable to control the first addition device 107 to maintain a constant amount of calcium carbonate added or to reduce the amount added.

[0080] In this way, the amount of sodium carbonate added should be controlled so that the measurement values ​​obtained by the calcium ion meter 108 fall within a certain range.

[0081] In this embodiment, since the calcium in the treated water and sodium carbonate are reacted in the presence of CaCO3-containing sludge during the reaction stage, the calcium ion concentration in the treated water after the reaction stage is kept low. This suppresses the amount of scale generated from calcium carbonate and significantly reduces its adhesion to the calcium ion meter 108. As a result, the maintenance frequency of the calcium ion meter 108 is greatly reduced, and the amount of sodium carbonate added can be stably controlled over a long period of time.

[0082] Furthermore, the addition of sodium carbonate is not limited to the first adding device 107; it may also be added using both the first adding device 107 and the second adding device 112. In this case, the amount of sodium carbonate added should be the sum of the amounts added by the first adding device 107 and the second adding device 112, as described above, which corresponds to the theoretically required amount for the reaction between calcium and sodium carbonate (the required amount in reaction equation (1) above).

[0083] Furthermore, it is preferable to install the calcium ion meter 108 in the mixing tank 103 rather than the reaction tank 102. This is because if the calcium ion meter 108 is installed in the reaction tank 102, it will be difficult to stably measure the calcium ion concentration due to the presence of unreacted calcium ions and carbonate ions in the reaction tank 102, and it will also be difficult to prevent calcium carbonate from adhering to the detection part of the calcium ion meter 108.

[0084] Next, we will explain how to adjust the amount of inorganic coagulant added during the setting stage.

[0085] First, a coagulation sensor 114 installed in the coagulation tank 104 measures the turbidity between flocs in the water to be treated and sends the measured value to the control unit 109. Based on the measured value from the coagulation sensor 114, the control unit 109 determines the amount of inorganic coagulant to be added and sends the result to the inorganic coagulant addition device 103b. The inorganic coagulant addition device 103b adds the inorganic coagulant to the water to be treated based on the command from the control unit 109.

[0086] If the amount of inorganic coagulant added is insufficient, a relatively large amount of uncoagulated calcium carbonate particles and fine flocs will remain in the treated water, resulting in a relatively high measurement value from the coagulation sensor 114.

[0087] On the other hand, if the amount of inorganic coagulant added is excessive, the amount of calcium carbonate particles and fine flocs remaining in the treated water will decrease, but a large amount of iron-based scale derived from the metal (e.g., iron) contained in the inorganic coagulant may precipitate and adhere to the inner walls of the mixing tank 103 or coagulation tank 104, or to the coagulation sensor 114, etc.

[0088] Therefore, it is preferable to control the addition device 103b to adjust the amount of inorganic coagulant added to a certain range so that the measurement value from the coagulation sensor 114 falls below a certain standard value, specifically, for example, so that the turbidity is in the range of 0 to 50 ntu.

[0089] In this way, by controlling the amount of inorganic coagulant added, the generation of scale (e.g., iron-based scale) originating from the components of the inorganic coagulant is reduced, and the amount of scale adhering to the inner walls of the mixing tank 103 or coagulation tank 104, as well as the coagulation sensor 114, is significantly suppressed. As a result, the maintenance frequency of the coagulation sensor 114 is greatly reduced, and the control of the amount of inorganic coagulant added can be stably maintained over a long period of time.

[0090] As described above, according to this embodiment, the generation of scale derived from calcium carbonate can be suppressed, and the addition of sodium carbonate can be easily controlled.

[0091] Furthermore, according to this embodiment, the amount of sodium carbonate and inorganic coagulants (e.g., ferric chloride solution), which are the main chemicals used in the decalcification coagulation and sedimentation equipment (lime-soda process) of the leachate treatment facility at the final landfill site, can be efficiently optimized.

[0092] Furthermore, according to this embodiment, in order to optimize the amount of sodium carbonate injected using the calcium ion meter 108, the optimal amount of CaCO3-containing sludge is returned to the optimal location, and the calcium ion meter 108 is installed in the optimal location. This suppresses the adhesion of scale to the detection unit of the calcium ion meter 108, enabling stable automatic drug injection control.

[0093] Furthermore, according to this embodiment, by optimizing the injection amount of inorganic coagulant (e.g., ferric chloride solution) using the coagulation sensor 114 that measures turbidity between flocs, scale formation derived from iron hydroxide (iron oxide) can be suppressed, and stable automated drug injection control can be performed.

[0094] In this embodiment, the aggregation sensor 114 is not particularly limited as long as it is capable of measuring turbidity between flocs, but as an example, the device described below can be used.

[0095] As the coagulation sensor 114, a preferred method is one that irradiates the treated water with laser light, receives scattered light from particles contained in the treated water, and detects the turbidity of the treated water.

[0096] For example, the following device can be used as the agglutination sensor 114. Figure 2 is a schematic diagram showing the general configuration of the agglomeration sensor 114 used in this embodiment. Figure 3 is an enlarged view showing the configuration of the laser light irradiation unit and the scattered light receiving unit of the agglomeration sensor 114 shown in Figure 2. Figure 4 is an enlarged view showing the configuration of the shielding member of the agglomeration sensor 114 shown in Figure 2.

[0097] As shown in Figure 2, the aggregation sensor 114 includes a laser oscillator 201, a first optical fiber 202, a laser light irradiation unit 203, a scattered light receiving unit 204, a second optical fiber 205, a photoelectric conversion circuit 206, a detection circuit 207, and a minimum value detection circuit 208.

[0098] The treated water 221 in the coagulation tank 104 is immersed in a laser beam irradiation unit 203 and a scattered light receiving unit 204, which are located at the bottom of a shielding member 222. The shielding member 222 blocks natural light from above from reaching the measurement area 223 between the laser beam irradiation unit 203 and the scattered light receiving unit 204.

[0099] In other words, as shown in Figure 4, the shielding member 222 is a pentagonal prism with a bottom surface that protrudes downward and grooves 224 formed on both protruding sides. The first optical fiber 202 and the second optical fiber 205 are fixed to the grooves 224. The laser light irradiation part 203, which is one end of the first optical fiber 202, and the scattered light receiving part 204, which is one end of the second optical fiber 205, are arranged symmetrically (line symmetrically) in Figure 3. Furthermore, it is preferable that the centerlines of the laser light irradiation part 203 of the first optical fiber 202 and the scattered light receiving part 204 of the second optical fiber 205 intersect each other at a 90-degree angle.

[0100] Furthermore, it is generally preferable to modulate the intensity of the laser light emitted from the laser oscillator 201 in order to distinguish it from natural light. In order to convert the scattered light intensity received by the photoelectric conversion circuit 206 back into the original electrical signal, it is preferable to modulate the intensity of the laser light emitted from the laser oscillator 201 to a frequency of approximately 70 kHz to 150 kHz. Therefore, in this embodiment, the laser oscillator 201 consists of a function generator 211 and a laser diode 212, and the laser light, which is amplitude-modulated (AM) with an electrical signal of a predetermined frequency, for example, 95 kHz, generated from the function generator 211, is emitted from the laser diode 212 to one end of the first optical fiber 202. This laser light is emitted from the other end of the optical fiber 202, which is the laser light irradiation unit 203, through the first optical fiber 202 into the water to be treated. Note that the laser oscillator 201 is not limited to consisting of a function generator 211 and a laser diode 212, and it is also possible to use, for example, a light-emitting diode.

[0101] As previously described, the treated water contains fine particles and fine flocs of calcium carbonate (hereinafter referred to as fine colloidal particles). The laser light irradiated from the laser light irradiation unit 203 onto the fine colloidal particles in the treated water 221 is scattered into scattered light, which enters the second optical fiber 205 from one end of the second optical fiber 205, which is a scattered light receiving unit 204. In this embodiment, the measurement area 223 for fine colloidal particles is an overlapping area between the area irradiated by the laser light emitted from the laser light irradiation unit 203 and the area where the scattered light receiving unit 204 can receive the scattered light. The scattered light receiving unit 204 receives scattered light scattered in the direction of 90 degrees (the center line of the second optical fiber 205) from the measurement area 223.

[0102] The photoelectric conversion circuit 206 consists of a photodetector 261, a bandpass filter 262, and an amplifier 263. The photodetector 261 is connected to the other end of the second optical fiber 205 and converts the optical signal of scattered light incident on the second optical fiber 205 into an electrical signal. The bandpass filter 262 extracts the modulation frequency component signal from the electrical signal converted by the photodetector 261 in order to distinguish it from natural light. Amplifier 263 amplifies the modulation frequency component signal extracted by the bandpass filter 262 and outputs it to the detection circuit 207.

[0103] The photoelectric conversion circuit 206 is not limited to the above configuration, as long as it converts an optical signal into an electrical signal. For example, a photodiode may be used instead of a photodetector, or a low-pass filter may be used instead of a bandpass filter.

[0104] The modulated frequency component signal is subjected to AM detection by the detection circuit 207 to measure the change in scattered light intensity, and the detected signal is output to the minimum value detection circuit 208. The signal output by the detection circuit 207 undergoes the same signal processing as a signal passing through a low-pass filter. Therefore, by appropriately selecting the cutoff frequency of the bandpass filter 262, the detection circuit 207 can detect the DC component of the output waveform signal, with the fluctuation of this cutoff frequency removed, and output it to the minimum value detection circuit 208. In this way, the optical signal detected by the photodetector 261, with the modulated frequency component extracted by the bandpass filter 262 and amplified by the amplifier 263, is subjected to AM detection, allowing the change in light intensity associated with the scattering of minute colloidal particles to be measured as a change in signal intensity.

[0105] The minimum value detection circuit 208 detects the lowest signal intensity from the DC component signal input from the detection circuit 207. This minimum value detection, in terms of the signal waveform output from the amplifier 263, means measuring the constricted portion of the waveform. The portion outside the constricted area indicates the presence of aggregated coarse flocs and unaggregated minute colloidal particles in the measurement region 223. The constricted portion indicates the point where aggregated coarse flocs have left the measurement area. Therefore, by detecting the lowest value of the signal intensity with the minimum value detection circuit 208, it becomes possible to measure the scattered light intensity, i.e., the number of minute colloidal particles, when only minute colloidal particles are present. A decrease in this minimum value indicates a decrease in the number of minute colloidal particles in the measurement area. Conversely, an increase in the minimum value indicates an increase in the number of minute colloidal particles. This allows for the measurement of the turbidity of the minute colloidal particles.

[0106] Furthermore, the agglomeration sensor 114 does not require a separate special measurement unit; the laser light irradiation unit 203 and the scattered light receiving unit 204 attached to the shielding member 222 are placed in the agglomeration tank 104 to measure the scattered light. Therefore, the agglomeration sensor 114 can have a simple device configuration. [Examples]

[0107] The present invention will be described in more detail below with reference to examples.

[0108] (Example 1) Using the water treatment apparatus shown in Figure 1, water containing approximately 2,000 mg / L of calcium ions was treated. During this process, the amount of CaCO3-containing sludge returned to the reaction tank via the chemical reaction tank was adjusted to a return ratio of 4:1. This water treatment was continued for approximately 3 months. The amount of sodium carbonate used during these 3 months was then divided by the calcium content of the treated water to determine the required sodium carbonate quantity. The results are shown in Table 1.

[0109] (Comparative example) Except for not returning the CaCO3-containing sludge to the reaction tank and extending the water treatment period to one year, the water treatment was carried out in the same manner as in Example 1 above. The amount of sodium carbonate used during the year was then divided by the amount of calcium in the treated water to determine the required sodium carbonate count. The results are shown in Table 1.

[0110] [Table 1]

[0111] As shown in Table 1, Example 1 significantly reduced the amount of sodium carbonate used compared to the comparative example. This is because, in Example 1, the CaCO3-containing sludge was returned, allowing for calcium removal using the lime-soda method without excessive sodium carbonate addition.

[0112] (Example 2) Using the water treatment apparatus shown in Figure 1, water containing approximately 2,000 mg / L of calcium ions was treated. During this process, the amount of CaCO3-containing sludge returned to the reaction tank via the chemical reaction tank was varied. The test was conducted under seven different conditions, as shown in Table 2, with return ratios of 20, 16, 12, 8, 4, 2, and 1 for each condition. Water treatment was continued for 30 days under each condition. After the period, the detection unit of the calcium ion meter installed in the mixing tank was checked for the presence of calcium carbonate-derived scale. The results are shown in Table 2.

[0113] [Table 2]

[0114] As shown in Table 2, it was confirmed that controlling the return ratio to be 4 times or more effectively suppresses scale buildup. [Explanation of symbols]

[0115] 1…Water treatment equipment 101... Raw water tank 102…Reaction vessel 102a, 103a, 104a, 106a... Agitator 103…Mixing tank 103b, 104b...addition device 104…Flocculation tank 105...Sedimentation tank 106...Chemical reaction vessel 107...First addition device 108...Calcium ion meter 109... Control Unit 112…Second addition device 114... Aggregation sensor L1...First return channel L2...Second return channel L11~L15...flow channel

Claims

1. A water treatment apparatus for treating water containing calcium, CaCO3, which contains calcium carbonate ３ A reaction tank in which calcium contained in the water to be treated reacts with sodium carbonate in the presence of sludge to precipitate the calcium as calcium carbonate, The aforementioned CaCO ３ A mixing tank for adding an inorganic coagulant to the water to be treated, which contains the contained sludge and the precipitated calcium carbonate, A flocculant tank to which a polymer flocculant is added to the water to be treated to which the inorganic coagulant has been added, From the treated water to which the polymer flocculant has been added, the CaCO3 ３ A sedimentation tank for settling and separating the contained sludge, The CaCO3 that was sedimented and separated in the sedimentation tank ３ A first return channel that returns a portion of the contained sludge to the chemical reaction tank, A first sodium carbonate addition device provided in the chemical reaction vessel, The CaCO2 returned by the first return channel ３ The chemical reaction tank for adding sodium carbonate to the contained sludge using the first additive device, The CaCO3 to which sodium carbonate is added ３ A second return channel for returning the contained sludge to the reaction tank, A calcium ion meter installed in the mixing tank, A water treatment apparatus comprising: a control unit having a function to control the amount of sodium carbonate added by the first additive device based on the measurement value of the calcium ion meter.

2. The reaction tank is equipped with a second additive device for adding the sodium carbonate to the water to be treated. The water treatment apparatus according to claim 1, wherein the control unit further has a function of controlling the amount of sodium carbonate added by the first additive device and the second additive device based on the measurement value of the calcium ion meter.

3. The coagulation tank is equipped with a coagulation sensor that measures the turbidity of uncoagulated particles in the water to be treated. The water treatment apparatus according to claim 1, further comprising a control unit that controls the amount of inorganic coagulant added to the mixing tank based on the measurement value of the coagulation sensor.

4. A water treatment method for treating water containing calcium, CaCO3, which contains calcium carbonate ３ A reaction step in which calcium contained in the water to be treated reacts with sodium carbonate in the presence of sludge, The aforementioned CaCO ３ A coagulation step in which an inorganic coagulant is added to the treated water containing the sludge and the precipitated calcium carbonate, A coagulation step in which a polymer coagulant is added to the water to be treated to which the inorganic coagulant has been added, From the water to be treated to which the polymer flocculant has been added, the CaCO ３ A sedimentation separation step of sedimentation-separating the contained sludge; The CaCO3 separated by sedimentation in the aforementioned sedimentation separation step ３ The first return stage involves returning a portion of the contained sludge to the chemical reaction stage, The CaCO that was returned in the first return step ３ The chemical reaction step involves adding sodium carbonate to the sludge containing it, In the aforementioned chemical reaction step, the sodium carbonate is added to the CaCO3 ３ The process includes a second return step in which the contained sludge is returned to the reaction step, A water treatment method comprising measuring the amount of calcium ions in the water to be treated during the coagulation stage, and controlling the amount of sodium carbonate added during the chemical reaction stage based on the measured amount of calcium ions.

5. In the reaction step described above, sodium carbonate is further added to the water to be treated, The water treatment method according to claim 4, wherein the total amount of the chemical reaction step and the amount of sodium carbonate added in the reaction step are controlled based on the measured amount of calcium ions.

6. In the second return stage, In the aforementioned reaction step, the amount of calcium carbonate returned is four times or more than the amount of calcium carbonate precipitated, as described above. ３ The water treatment method according to claim 4, which adjusts the amount of sludge contained and returned.

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