Water treatment apparatus and water treatment system

Abstract

A water treatment apparatus equipped with a pH-adjusting agent addition means for adding an acidic or alkaline pH-adjusting agent aqueous solution to water to be treated, said water treatment apparatus being characterized in that a plurality of the pH-adjusting agent additions means are provided, and at least one pH-adjusting agent addition means differs from the other pH-adjusting agent addition means in terms of the concentration of the pH-adjusting agent aqueous solution to be added thereby.

Description

Water treatment apparatus and water treatment system

[0001] The present invention relates to a water treatment apparatus having a pH adjuster adding means, and particularly to a water treatment apparatus that can appropriately control pH even when the wastewater concentration is dilute or concentrated. The present invention also relates to a water treatment system provided with this water treatment apparatus.

[0002] In water treatment such as wastewater treatment, a step of adjusting the pH of water to be treated by adding an aqueous solution of a pH adjuster (pH adjusting chemical) from a pH adjuster adding means is often performed.

[0003] In conventional pH adjustment methods, different concentrations of pH adjusting chemicals are not used in response to changes in wastewater concentration, and pH adjustment is always performed with a pH adjuster aqueous solution of a constant concentration.

[0004] When the concentration of the entire wastewater is dilute, and in particular contains no buffering components such as carbonic acid and ammonia, or the buffering component is dilute, if the concentration of the pH adjusting chemical is relatively high for such wastewater, the responsiveness of pH adjustment is too fast, causing hunting, and there is a problem that the pH deviates from the set pH adjustment range.

[0005] Conversely, in the case of wastewater with a high buffering component concentration, if the concentration of the pH adjusting chemical is relatively dilute for such wastewater, the responsiveness of pH adjustment is too slow, and the pH may not reach the set pH adjustment range.

[0006] In order to address such problems, at the initial design stage, the concentration of the pH adjusting chemical is set to an optimal value in consideration of the expected quality of the wastewater. However, actual wastewater does not necessarily conform to design values, and wastewater quality often fluctuates, so it is not possible to properly follow such changes, which may cause the aforementioned problems.

[0007] In particular, when the water treatment apparatus is a water treatment apparatus in a wastewater recovery facility, and a reverse osmosis membrane device is installed downstream of the pH adjustment step, even a slight deviation in pH adjustment causes the water to deviate from the standard as raw water for the reverse osmosis membrane device, thereby creating a risk of causing clogging of the reverse osmosis membrane.

[0008] Japanese Patent Application Laid-Open No. 2022-174973 Japanese Patent Application Laid-Open No. 2001-290542

[0009] As described above, conventional pH adjustment methods do not vary the concentration of pH adjusting chemicals according to the characteristics and concentration changes of the discharged wastewater; instead, a constant concentration of pH adjusting chemical (aqueous solution) is always used. Therefore, when the wastewater concentration is low or the wastewater does not contain many buffering components, the pH can change sensitively upon addition of pH adjusting chemicals, sometimes causing the pH adjustment target to overshoot. Conversely, when the wastewater concentration is high or it contains many buffering components, the pH may not reach the target value even after adding pH adjusting chemicals.

[0010] The present invention aims to provide a water treatment device that can appropriately control the pH even when the wastewater concentration is dilute or concentrated, and a water treatment system equipped with this water treatment device.

[0011] The present invention relates to a water treatment apparatus equipped with a pH adjusting agent adding means for adding an acidic or alkaline pH adjusting agent aqueous solution to water to be treated, wherein a plurality of pH adjusting agent adding means are provided, and at least one pH adjusting agent adding means is characterized in that the concentration of the pH adjusting agent aqueous solution added by at least one pH adjusting agent adding means is different from that of the other pH adjusting agent adding means.

[0012] In one aspect of the present invention, the pH adjusting agent adding means comprises at least: a low-concentration acidic pH adjusting agent aqueous solution adding means for adding a low-concentration acidic pH adjusting agent aqueous solution; a high-concentration acidic pH adjusting agent aqueous solution adding means for adding a higher-concentration acidic pH adjusting agent aqueous solution; a low-concentration alkaline pH adjusting agent aqueous solution adding means for adding a low-concentration alkaline pH adjusting agent aqueous solution; and a high-concentration alkaline pH adjusting agent aqueous solution adding means for adding a higher-concentration alkaline pH adjusting agent aqueous solution.

[0013] In one aspect of the present invention, there is a switching means for switching a pH adjusting agent aqueous solution addition means for adding a pH adjusting agent aqueous solution to the water to be treated.

[0014] In one aspect of the present invention, a water quality detection means for detecting the water quality of the water to be treated is provided, and the switching means switches the pH adjusting agent aqueous solution addition means based on the detection result of the water quality detection means.

[0015] In one aspect of the present invention, the water quality detection means detects at least the pH of the water to be treated.

[0016] In one aspect of the present invention, the pH adjusting agent aqueous solution is injected, and if the reaction rate is fast, the injection is switched to an aqueous solution with a lower concentration than the injected pH adjusting agent aqueous solution, and if the reaction rate is slow, the injection is switched to an aqueous solution with a higher concentration than the injected pH adjusting agent aqueous solution.

[0017] One embodiment of the present invention is a water treatment system comprising a water pretreatment device for water to be treated and a reverse osmosis membrane device installed downstream of the pretreatment device, wherein the pretreatment device is equipped with the water treatment device of the present invention.

[0018] In one aspect of the present invention, an aqueous pH adjusting agent solution of an appropriate concentration can be selected and added according to the concentration and characteristics of the water to be treated. By switching to an aqueous pH adjusting agent solution of an appropriate concentration in response to changes in the water quality of the incoming water to be treated, hunting and other issues can be prevented, and the responsiveness of pH adjustment is improved.

[0019] Furthermore, as mentioned above, in wastewater recovery equipment having a coagulation separation means and a subsequent reverse osmosis membrane device, when responding to changes in wastewater properties by controlling the amount of coagulant injected, conventional methods sometimes fail to keep up with these fluctuations in pH control, causing the water supply to the reverse osmosis membrane device to deviate from the appropriate standard range. In contrast, in one aspect of the present invention, it is possible to control the pH within a predetermined range using a water treatment device installed in the pretreatment device, thereby keeping the water quality of the water supply to the subsequent reverse osmosis membrane device within the appropriate standard range and maintaining stable operation of the osmosis membrane device.

[0020] This is a diagram showing the configuration of a water treatment system according to an embodiment. This is a diagram showing the configuration of a pH adjusting agent aqueous solution preparation device used in the embodiment.

[0021] The present invention will be described in more detail below with reference to the drawings. Figure 1 shows one embodiment of the water treatment system of the present invention, and Figures 2(a) and 2(b) are configuration diagrams of the pH adjusting agent aqueous solution preparation device used in this water treatment system.

[0022] As described above, the water treatment apparatus of the present invention is a water treatment apparatus equipped with a pH adjusting agent adding means for adding an acidic or alkaline pH adjusting agent aqueous solution to water to be treated, wherein a plurality of pH adjusting agent adding means are provided, and at least one pH adjusting agent adding means is characterized in that the concentration of the pH adjusting agent aqueous solution added is different from that of the other pH adjusting agent adding means.

[0023] In the embodiments described below, as shown in Figures 2(a) and 2(b), the pH adjusting agent addition means includes an acidic pH adjusting agent aqueous solution preparation device 10 and an alkaline pH adjusting agent aqueous solution preparation device 20.

[0024] The apparatus 10 for preparing an acidic pH adjusting agent aqueous solution includes a stock solution tank 15 for storing a high-concentration acid solution (stock solution), a first dilution tank 11 for preparing a dilute acid aqueous solution, a second dilution tank 12 for preparing a concentrated acid aqueous solution, and a dilution water tank (not shown) for supplying dilution water to each of the dilution tanks 11 and 12. Hydrochloric acid (HCl) is preferred as the acid.

[0025] By supplying specified amounts of concentrated acid solution (e.g., 35% HCl aqueous solution) and dilution water from the stock solution tank 15 and the dilution water tank, respectively, a specified low-concentration acid aqueous solution (e.g., 0.5% to less than 5% HCl aqueous solution) is prepared in the first dilution tank 11, and a specified high-concentration acid aqueous solution (e.g., 5-10% HCl aqueous solution) is prepared in the second dilution tank 12.

[0026] A circulation liquid supply line 13 is connected to dilution tank 11, and a circulation liquid supply line 14 is connected to dilution tank 12. Each circulation liquid supply line 13 and 14 is equipped with a liquid supply pump (not shown), and acidic aqueous solution is circulated through each of the dilution tanks 11 and 12.

[0027] One end of each of the liquid supply pipes a1, a2, and a3 is connected to the dilute acid solution circulation line 13 in order to supply the dilute acid solution to each of the facilities shown in Figure 1, which will be described later. One end of each of the liquid supply pipes A1, A2, and A3 is connected to the concentrated acid solution circulation line 14 in order to supply the concentrated acid solution to each of the facilities shown in Figure 1, which will be described later.

[0028] The alkaline pH adjusting agent aqueous solution preparation apparatus 20 includes a stock solution tank 25 for storing a high-concentration alkaline aqueous solution (stock solution), a first dilution tank 21 for preparing a dilute alkaline aqueous solution, a second dilution tank 22 for preparing a concentrated alkaline aqueous solution, and a dilution water tank (not shown) for supplying dilution water to each of the dilution tanks 21 and 22. This dilution water tank is shared with the aforementioned dilution water tank. Sodium hydroxide (NaOH) is preferred as the alkali.

[0029] By supplying a specified amount of alkaline stock solution (e.g., 25% NaOH aqueous solution) and dilution water from the stock solution tank 25 and the dilution water tank, respectively, a specified low-concentration alkaline aqueous solution (e.g., 0.5% to less than 5% NaOH aqueous solution) is prepared in the first dilution tank 21, and a specified high-concentration alkaline aqueous solution (e.g., 5-10% NaOH aqueous solution) is prepared in the second dilution tank 22.

[0030] A circulation liquid supply line 23 is connected to dilution tank 21, and a circulation liquid supply line 24 is connected to dilution tank 22. Each circulation liquid supply line 23 and 24 is equipped with a liquid supply pump (not shown), and alkaline aqueous solution is circulated through each of the dilution tanks 21 and 22.

[0031] One end of the liquid supply pipes b1, b2, and b3 are connected to the alkaline aqueous solution circulation liquid supply line 23 in order to supply dilute alkaline aqueous solution to each of the facilities shown in Figure 1, which will be described later. One end of the liquid supply pipes B1, B2, and B3 are connected to the concentrated alkaline aqueous solution circulation liquid supply line 24 in order to supply concentrated alkaline aqueous solution to each of the facilities shown in Figure 1, which will be described later.

[0032] An embodiment of the water treatment apparatus shown in Figure 1 will be described below. This water treatment apparatus has three types of wastewater treatment lines 40, 60, and 80 for dilute wastewater, medium-concentrated wastewater, and concentrated wastewater. Two or more types of treatment lines may be provided. Examples of dilute wastewater include final rinse wastewater from washing processes requiring ultrapure water in factory production facilities, and mainly inorganic wastewater containing fluorine, ammonia, and other acids and alkalis. Other examples include air washer wastewater and pollution-treated wastewater. Examples of medium-concentrated wastewater include wastewater from washing processes in factory production facilities that contains organic matter, fluorine, and ammonia at a certain concentration and requires biological treatment including nitrification and denitrification or fluorine treatment equipment. Other examples include cooling tower concentrated blowdown wastewater. Examples of concentrated wastewater include BHF (buffered hydrofluoric acid) wastewater, IPA wastewater, TMAH wastewater, and wastewater containing surfactants and other organic matter in amounts of several hundred to several thousand ppm or several percent.

[0033] In the dilute wastewater treatment line 40, dilute wastewater is sent from the dilute wastewater raw water tank 41 to the pretreatment equipment 42 for treatment. The pretreatment equipment 42 is equipped with a reaction tank (not shown) that performs neutralization or coagulation, and a filter (not shown) such as a UF membrane device that filters the liquid from the reaction tank. Dilute acid aqueous solution, concentrated acid aqueous solution, dilute alkaline aqueous solution, and concentrated alkaline aqueous solution can be added to this reaction tank. Dilute acid aqueous solution and concentrated acid aqueous solution are added to the reaction tank via liquid supply pipe a1, liquid supply pipe A1, and automatic valve 51. Dilute alkaline aqueous solution and concentrated alkaline aqueous solution are added to the reaction tank via liquid supply pipe b1, liquid supply pipe B1, and automatic valve 52. The automatic valve 51 can switch between adding dilute acid aqueous solution from liquid supply pipe a1 to the reaction tank, adding concentrated acid aqueous solution from liquid supply pipe A1 to the reaction tank, and no addition of either dilute acid aqueous solution or concentrated acid aqueous solution to the reaction solution. The same applies to automatic valve 52 and the automatic valves 71, 72, 91, and 92 described later.

[0034] The treated water (filtered water) from the filter of the pretreatment equipment 42 is introduced into the desalination equipment 44 via the filtration tank 43, where it is desalinized by a reverse osmosis membrane device (not shown). The desalination treated water is then used as equipment water after passing through the desalination tank 45.

[0035] The concentrated water from this reverse osmosis membrane device is sent via the concentration tank 47 to the medium-concentration wastewater raw water tank 61 of the medium-concentration wastewater treatment line 60. The backwash wastewater from the filter of the pretreatment equipment 42 is sent to the medium-concentration wastewater raw water tank 61 via the backwash wastewater tank 46.

[0036] In the Chuno wastewater treatment line 60, the Chuno wastewater from the Chuno wastewater raw water tank 61 is introduced into the wastewater treatment facility 62. The wastewater treatment facility 62 is equipped with a pH adjustment tank and a coagulation tank (neither of which are shown), and a sedimentation tank (not shown) for settling the liquid from the coagulation tank.

[0037] Dilute acid solution, concentrated acid solution, dilute alkaline solution, and concentrated alkaline solution can be added to this pH adjustment tank. The dilute acid solution and concentrated acid solution are added to the pH adjustment tank via liquid supply pipe a2, liquid supply pipe A2, and automatic valve 71. The dilute alkaline solution and concentrated alkaline solution are added to the pH adjustment tank via liquid supply pipe b2, liquid supply pipe B2, and automatic valve 72. The treated water (supernatant) from the sedimentation tank is discharged through the monitoring tank 63.

[0038] The sludge from the sedimentation tank is discharged after passing through the sludge storage tank 64 and the dewatering machine 65.

[0039] In the concentrated wastewater treatment line 80, concentrated wastewater from the concentrated wastewater raw water tank 81 is introduced into the wastewater concentration equipment 82. The wastewater treatment equipment 82 is equipped with an evaporator (evaporator / concentrator), a pH adjustment tank (not shown), etc. Dilute acid solution, concentrated acid solution, dilute alkaline solution, and concentrated alkaline solution can be added to this pH adjustment tank. The dilute acid solution and concentrated acid solution are added to the pH adjustment tank via liquid supply pipe a3, liquid supply pipe A3 and automatic valve 91. The dilute alkaline solution and concentrated alkaline solution are added to the pH adjustment tank via liquid supply pipe b3, liquid supply pipe B3 and automatic valve 92. The concentrated water (concentrated liquid) from the evaporator (evaporator / concentrator) is discharged via the concentration storage tank 83 and collected as industrial waste. The condensed water (dilute liquid) from the evaporator (evaporator / concentrator) is sent to the wastewater treatment equipment.

[0040] Thus, in this water treatment system, dilute acid solution, concentrated acid solution, dilute alkaline solution, and concentrated alkaline solution can be added to the reaction tank and pH adjustment tank via automatic valves 51, 52, 71, 72, 91, and 92. Therefore, an appropriate concentration of pH adjusting agent solution (dilute acid solution, concentrated acid solution, dilute alkaline solution, or concentrated alkaline solution) is added according to the concentration and characteristics of the wastewater. As a result, it is possible to switch to adding an appropriate concentration of pH adjusting agent solution in response to changes in the wastewater quality, improving the responsiveness of pH adjustment and preventing hunting and other issues.

[0041] Furthermore, in the dilute wastewater treatment line 40 equipped with a reverse osmosis membrane device in the desalination equipment 44, it is possible to control the pH of the treated water from the pretreatment equipment 42 within a set range even if there are changes in the properties of the wastewater, thereby keeping the water quality supplied to the reverse osmosis membrane device within an appropriate standard range and maintaining stable operation of the reverse osmosis membrane device.

[0042] In this invention, the automatic valves 51, 52, 71, 72, 91, and 92 may be manual valves.

[0043] When using automatic valves 51, 52, 71, 72, 91, and 92, a pH meter may be installed in the wastewater raw tanks 41, 61, and 81 or the water supply piping from them, and a valve control device may be installed to switch the automatic valves 51, 52, 71, 72, 91, and 92 based on the detection results.

[0044] Other switching means include the following means. First, the automatic valves 51, 71, 91 are opened for a certain period of time, and either a dilute aqueous acid solution or a concentrated aqueous acid solution is injected. Next, if the pH is not within the set range, the injection is switched to a solution having a lower or higher concentration than the injected aqueous solution. Specifically, when hunting occurs because the reaction rate is too fast, there are fewer buffer components relative to the concentration of the injected aqueous solution, so switching is performed to an aqueous solution having a lower concentration than the injected aqueous solution. Conversely, when the reaction rate is too slow and does not converge within a certain period of time, there are more buffer components relative to the concentration of the injected aqueous solution, so switching is performed to an aqueous solution having a higher concentration than the injected aqueous solution. The above switching may be performed manually depending on the situation, or may be automatically switched depending on whether the convergence time is earlier or later than a threshold value by additionally providing a timer. The same applies to the case of an alkaline aqueous solution.

[0045] In the above embodiment, four dilution tanks 11, 12, 21, 22 are provided to prepare acid and alkaline aqueous solutions of two concentrations, but more dilution tanks may be provided to prepare acid and alkaline aqueous solutions of three or more concentrations, and the addition may be sequentially switched according to the properties of wastewater. This makes it possible to respond to finer pH adjustment.

[0046] Although the present invention has been described in detail using specific embodiments, it is obvious to those skilled in the art that various modifications can be made within the scope where the effects of the invention are exhibited. This application is based on Japanese Patent Application No. 2025-052045 filed on March 26, 2025, the entire content of which is incorporated by reference.

[0047] 10 Apparatus for preparing acidic pH adjuster aqueous solution 20 Apparatus for preparing alkaline pH adjuster aqueous solution 40 Dilute wastewater treatment line 60 Medium-concentration wastewater treatment line 80 Concentrated wastewater treatment line 51, 52, 71, 72, 91, 92 Automatic valve

Claims

1. A water treatment apparatus equipped with a pH adjusting agent adding means for adding an acidic or alkaline pH adjusting agent aqueous solution to water to be treated, wherein a plurality of pH adjusting agent adding means are provided, and at least one pH adjusting agent adding means has a different concentration of pH adjusting agent aqueous solution added from the other pH adjusting agent adding means.

2. The water treatment apparatus according to claim 1, comprising, as the pH adjusting agent adding means, at least: a low-concentration acidic pH adjusting agent aqueous solution adding means for adding a low-concentration acidic pH adjusting agent aqueous solution; a high-concentration acidic pH adjusting agent aqueous solution adding means for adding a higher-concentration acidic pH adjusting agent aqueous solution; a low-concentration alkaline pH adjusting agent aqueous solution adding means for adding a low-concentration alkaline pH adjusting agent aqueous solution; and a high-concentration alkaline pH adjusting agent aqueous solution adding means for adding a higher-concentration alkaline pH adjusting agent aqueous solution.

3. The water treatment apparatus according to claim 2, further comprising a switching means for switching a means for adding an aqueous solution of a pH adjusting agent to water to be treated.

4. The water treatment apparatus according to claim 3, wherein a water quality detection means is provided for detecting the water quality of the water to be treated, and the switching means switches the pH adjusting agent aqueous solution addition means based on the detection result of the water quality detection means.

5. The water treatment apparatus according to claim 4, wherein the water quality detection means detects at least the pH of the water to be treated.

6. The water treatment apparatus according to claim 3, wherein a switching means for switching the pH adjusting agent aqueous solution addition means is used to inject the pH adjusting agent aqueous solution, and if the reaction rate is fast, the method is switched to injecting an aqueous solution with a lower concentration than the injected pH adjusting agent aqueous solution, and if the reaction rate is slow, the method is switched to injecting an aqueous solution with a higher concentration than the injected pH adjusting agent aqueous solution.

7. A water treatment system comprising a pretreatment device for water to be treated and a reverse osmosis membrane device installed downstream of the pretreatment device, wherein the pretreatment device comprises the water treatment device described in any one of claims 1 to 6.

8. The water treatment system comprises at least a first treatment line having a first raw wastewater tank, a first pretreatment device, and a first reverse osmosis membrane device installed downstream of the first pretreatment device; and a second treatment line having a second raw wastewater tank, a second pretreatment device, and a second reverse osmosis membrane device installed downstream of the second pretreatment device, wherein the first pretreatment device comprises a reaction tank for neutralization or coagulation and a filter for filtering the liquid from the reaction tank, the reaction tank can be supplied with an aqueous pH adjusting agent solution from each of the pH adjusting agent adding means, filtered water from the filter is supplied to the first reverse osmosis membrane device, and backwash wastewater from the filter is supplied to the second raw wastewater tank, the water treatment system according to claim 7.

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