Wastewater treatment facility and wastewater treatment method

Abstract

This wastewater treatment facility comprises: a first pH adjustment facility for adjusting the pH of wastewater containing heavy metals to 10-12 by adding an alkali agent thereto; a filtration facility for separating and removing, by means of a filtration device, precipitates precipitated by pH adjustment in the first pH adjustment facility; a second pH adjustment facility for adjusting the pH of the treated water that has flowed out from the filtration facility to 9.5-11 by adding an acid thereto; and a reverse osmosis membrane treatment device for subjecting the treated water having undergone pH adjustment in the second pH adjustment facility to a reverse osmosis membrane treatment using a reverse osmosis membrane.

Description

Wastewater treatment equipment and wastewater treatment method

[0001] This application claims priority to Japanese Patent Application No. 2023-148051, filed on September 13, 2023, the contents of which are incorporated herein by reference.

[0002] When treating wastewater containing heavy metals such as Ni and Cu, the pH of the wastewater is generally adjusted to about 10 to 12 to precipitate and coagulate the heavy metals contained in the wastewater as hydroxides, and then the wastewater is treated by undergoing a precipitation or filtration process. The treated water after filtration is neutralized before being discharged.

[0003] Incidentally, some or all of this effluent may be reused as facility water for, for example, a cooling tower (hereinafter referred to as CT). In this case, the effluent must be desalinated or filtered using a reverse osmosis membrane or other microfiltration membrane depending on the water quality of the effluent. However, if the organic matter concentration of the effluent is high, supplying it directly to a reverse osmosis membrane or microfiltration membrane may induce biofouling and reduce the permeation flux of the reverse osmosis membrane or microfiltration membrane. Therefore, it is necessary to readjust the pH of the effluent to, for example, about 9 to 11 to suppress biofouling before supplying it to the reverse osmosis membrane or microfiltration membrane.

[0004] Furthermore, Patent Document 1 describes a method for treating wastewater from a wet flue gas desulfurization system, the method comprising: a reaction step in which wastewater from a wet flue gas desulfurization system is subjected to alkali treatment and softening treatment to precipitate heavy metals, fluorine, calcium, magnesium, and the like as solids; a first solid-liquid separation step in which the solids produced in the reaction step are separated from the wastewater; a second solid-liquid separation step in which the pH of the wastewater treated in the first solid-liquid separation step is adjusted and fine solids contained in the wastewater are separated using a microfiltration membrane; and a salts separation step in which salts dissolved in the wastewater treated in the second solid-liquid separation step are separated using a reverse osmosis membrane, and the water recovered in the salts separation step is circulated to the flue gas desulfurization system for reuse.

[0005] Japanese Patent Application Publication No. 10-137540

[0006] However, in the wastewater treatment method described in Patent Document 1, when the water recovered in the salt separation step is circulated to a flue gas desulfurization system for reuse, the pH of the water needs to be readjusted. That is, pH adjustment needs to be performed both in the step of removing heavy metals and in the step of desalination or filtration of the treated water after heavy metal treatment. As a result, conventional wastewater treatment methods have had problems in that the number of pH adjustment steps increases and the amount of chemical solution used for pH adjustment increases.

[0007] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a wastewater treatment facility and a wastewater treatment method that can prevent an increase in the number of pH adjustment steps and an increase in the amount of chemical solution used for pH adjustment in water treatment when treated wastewater containing heavy metals is reused.

[0008] In order to solve the above problems, the present invention employs the following configurations. [1] A wastewater treatment system comprising: a first pH adjustment system that adds an alkaline agent to wastewater containing heavy metals to adjust the pH to 10 to 12; a filtration system that separates and removes precipitates precipitated as a result of the pH adjustment in the first pH adjustment system using a filtration system; a second pH adjustment system that adds an acid to filtered treated water discharged from the filtration system to adjust the pH to 9.5 to 11; and a reverse osmosis membrane treatment system that treats the treated water whose pH has been adjusted in the second pH adjustment system using a reverse osmosis membrane. [2] The wastewater treatment system according to [1], further comprising a third pH adjustment system that adds an acid to permeate discharged from the reverse osmosis membrane treatment system to adjust the pH to 5.8 to 8.6. [3] The wastewater treatment system according to [2], further comprising a supply flow path that supplies the treated water whose pH has been adjusted in the third pH adjustment system as facility water. [4] The wastewater treatment facility according to any one of [1] to [3], further comprising: a backwashing facility that backwashes the filtration device provided in the filtration facility; a coagulation and sedimentation facility that performs coagulation and sedimentation treatment on the cleaning wastewater discharged from the backwashing facility; and a first return flow path that supplies the treated water flowing out from the coagulation and sedimentation facility to the first pH adjustment facility. [5] The wastewater treatment facility according to [4], further comprising: a dehydration treatment facility that dehydrates sludge produced in the coagulation and sedimentation facility; and a second return flow path that returns the dehydrated treated water separated from the sludge in the dehydration treatment facility to the coagulation and sedimentation facility.

[0009] [6] A wastewater treatment method comprising: a first pH adjustment step of adding an alkaline agent to wastewater containing heavy metals to adjust the pH to 10 to 12; a filtration step of separating and removing precipitates precipitated in the first pH adjustment step using a filtration device; a second pH adjustment step of adding an acid to the treated water after the filtration step to adjust the pH to 9.5 to 11; and a reverse osmosis membrane treatment step of treating the treated water after the second pH adjustment step using a reverse osmosis membrane. [7] The wastewater treatment method according to [6], further comprising a third pH adjustment step of adding an acid to the permeate after the reverse osmosis membrane treatment step to adjust the pH to 5.8 to 8.6. [8] The wastewater treatment method according to [7], wherein the treated water after the third pH adjustment step is supplied to a supply line for facility water. [9] The wastewater treatment method according to any one of [6] to [8], further comprising: a backwashing step of backwashing the filtration device used in the filtration step; a coagulation and sedimentation step of coagulating and sedimenting the washing wastewater after the backwashing step; and a first return step of supplying the treated water after the coagulation and sedimentation step to the first pH adjustment step.

[10] The wastewater treatment method according to [9], further comprising: a dehydration step of dehydrating sludge produced in the coagulation and sedimentation step; and a second return step of returning dehydrated water separated from the sludge in the dehydration step to the coagulation and sedimentation step.

[0010] According to the present invention, it is possible to provide a wastewater treatment facility and a wastewater treatment method that can prevent an increase in the number of pH adjustment steps and an increase in the amount of chemical solution used for pH adjustment in water treatment when treating wastewater containing heavy metals and reusing the treated water.

[0011] 1 is a schematic diagram showing the configuration of a wastewater treatment facility according to an embodiment of the present invention.

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A wastewater treatment facility and a wastewater treatment method according to an embodiment of the present invention will now be described. Fig. 1 is a schematic diagram showing the configuration of a wastewater treatment facility according to an embodiment of the present invention.

[0013] As shown in Fig. 1, the wastewater treatment facility 1 of this embodiment is equipped with at least a heavy metal treatment facility 3, a second pH adjustment facility 5, and a reverse osmosis membrane treatment device 7. The heavy metal treatment facility 3 is composed of a first pH adjustment facility 3A and a filtration facility 3B. The filtration facility 3B is also provided with a backwash facility 3B2. A backwash wastewater tank 12 is connected to the filtration facility 3B.

[0014] 1 includes a raw water tank 2, a filtered water tank 4, and an RO water tank 6. The raw water tank 2 is installed upstream of the heavy metal treatment equipment 3. The filtered water tank 4 is disposed between the heavy metal treatment equipment 3 and the second pH adjustment equipment 5. The RO water tank 6 is disposed between the second pH adjustment equipment 5 and the reverse osmosis membrane treatment device 7.

[0015] The wastewater treatment facility 1 shown in Figure 1 also includes a third pH adjustment facility 8 and a recovered treated water tank 9 disposed downstream of the reverse osmosis membrane treatment device 7. A supply flow path L1 is connected to the recovered treated water tank 9. The supply flow path L1 is connected to various facilities and equipment that can reuse the treated water. Examples of such facilities and equipment include a cooling tower, a boiler, and a cleaning facility. The third pH adjustment facility 8 is configured to receive permeated water from the treated water treated by the reverse osmosis membrane treatment device 7.

[0016] In addition, a fourth pH adjustment facility 10 and a discharge water tank 11 are arranged downstream of the reverse osmosis membrane treatment device 7. The fourth pH adjustment facility 10 is configured so that the concentrated water separated by the reverse osmosis membrane treatment device 7 flows into it.

[0017] 1 is provided with a coagulation-sedimentation facility 13 and a relay tank 14 downstream of the backwash wastewater tank 12. A first return flow path L2 is connected to the relay tank 14, which returns the separated water (supernatant water) from the coagulation-sedimentation facility 13 to the first pH adjustment facility 3A via the raw water tank 2.

[0018] The path for discharging the sludge separated in the coagulation sedimentation equipment 13 is equipped with a sludge storage tank 15 and a dehydration treatment equipment 16. The dehydration treatment equipment 16 is connected to a second return flow path L3 for returning dehydrated separated water obtained when the sludge is dehydrated to the coagulation sedimentation equipment 13 via the backwash drainage tank 12.

[0019] Furthermore, in the wastewater treatment facility 1 of this embodiment, in addition to the above-described flow paths L1 to L3, a flow path L for flowing water or sludge between adjacent tanks or devices is arranged. The wastewater stored in the raw water tank 2 flows through the flow path L to the heavy metal treatment facility 3, the filtered water tank 4, the second pH adjustment facility 5, the RO water supply tank 6, and the reverse osmosis membrane treatment device 7 in this order.

[0020] The permeated water treated by the reverse osmosis membrane treatment device 7 flows through a flow path L to a third pH adjustment facility 8 and a recovery treatment water tank 9. Furthermore, the concentrated water separated from the permeated water by the reverse osmosis membrane treatment device 7 flows through a fourth pH adjustment facility 10 and a discharge water tank 11 in this order.

[0021] Furthermore, the washing wastewater generated in the backwashing equipment 3B2 attached to the filtration equipment 3B flows through a flow path L to the coagulation settling equipment 13 and the relay tank 14 in this order.

[0022] The sludge produced in the coagulation and sedimentation equipment 13 is transported by a flow path L to a sludge storage tank 15 and then to a dewatering treatment equipment 16 .

[0023] Next, we will explain the facilities and devices provided in the wastewater treatment facility 1. Wastewater containing heavy metals is stored in the raw water tank 2. Heavy metals contained in the wastewater include heavy metals that can be removed by adjusting the pH. Examples include Cd, Cr, Cu, Fe, Mn, Ni, and Zn.

[0024] The heavy metal treatment facility 3 is composed of a first pH adjustment facility 3A and a filtration facility 3B. The first pH adjustment facility 3A adds an alkaline agent to wastewater containing heavy metals to adjust the pH to 10 to 12. The alkaline agent may be, for example, sodium hydroxide. The filtration facility 3B includes a filtration device 3B1 that stores the wastewater whose pH has been adjusted to 10 to 12, thoroughly precipitates the heavy metals, and then performs solid-liquid separation to separate and remove the heavy metals from the wastewater. The filtration device 3B1 included in the filtration facility 3B preferably includes a microfiltration membrane (MF membrane) or an ultrafiltration membrane (UF membrane), but is not limited thereto, and a two-layer filtration device or other filtration device may also be used.

[0025] The filtration equipment 3B is also equipped with backwashing equipment 3B2. The backwashing equipment 3B2 backwashes the filtration media of the filtration device 3B1, on whose surface deposits (mainly heavy metal precipitates) have accumulated. This restores the filtration performance of the filtration device 3B1, specifically the permeation flux. Backwashing generates washing wastewater.

[0026] The filtered water tank 4 temporarily stores the treated water that flows out from the filtration equipment 3B.

[0027] The second pH adjustment equipment 5 adds an acid to the treated water that has passed through the filtered water tank 4 and flowed out of the filtration equipment 3B, adjusting the pH of the treated water to 9.5 to 11. Preferably, the pH is adjusted to a range of 10 to 10.5. For example, sulfuric acid is used as the acid. This prevents biofouling of the reverse osmosis membrane by the treated water after filtration.

[0028] If the TOC (total organic carbon) of the filtered treated water is 5 ppm or higher, biofouling may occur even if a slime inhibitor is added to the treated water. On the other hand, microorganisms that cause biofouling are inhibited from living in alkaline regions. Therefore, by adjusting the pH of the treated water supplied to the reverse osmosis membrane treatment device 7 to 9.5 or higher using the second pH adjustment equipment 5, an environment in which microbial growth is inhibited can be created within the reverse osmosis membrane treatment device 7, thereby suppressing biofouling. Furthermore, nonionic surfactants and other organic substances that may reduce flux are known to desorb from the membrane surface in alkaline regions. Therefore, by adjusting the pH of the treated water to 9.5 or higher, it is possible to suppress the adhesion of these components to the reverse osmosis membrane surface.

[0029] Furthermore, if the pH of the treated water remains high, the reverse osmosis membrane of the downstream reverse osmosis membrane treatment device 7 may deteriorate. Therefore, the second pH adjustment equipment 5 needs to adjust the pH of the treated water to 11 or less.

[0030] The RO water supply tank 6 temporarily stores the treated water whose pH has been adjusted by the second pH adjustment equipment 5 .

[0031] The reverse osmosis membrane treatment device 7 is equipped with a reverse osmosis membrane. The reverse osmosis membrane separates the treated water, the pH of which has been adjusted to 9.5 to 11 by the second pH adjustment equipment 5, into permeate and concentrated water.

[0032] The third pH adjustment equipment 8 adds an acid to the permeate treated in the reverse osmosis membrane treatment device 7 to adjust the pH to 5.8 to 8.6. Sulfuric acid is used as the acid. The fourth pH adjustment equipment 10 adds an acid to the concentrated water treated in the reverse osmosis membrane treatment device 7 to adjust the pH to 5.8 to 8.6. For example, sulfuric acid is used as the acid.

[0033] The recovered and treated water tank 9 temporarily stores the treated water whose pH has been adjusted by the third pH adjustment equipment 8. The discharge water tank 11 temporarily stores the treated water whose pH has been adjusted by the fourth pH adjustment equipment 10.

[0034] The backwash drain tank 12 temporarily stores the cleaning drainage water discharged from the filtration equipment 3B by the backwash equipment 3B2.

[0035] The coagulation sedimentation equipment 13 performs coagulation sedimentation treatment on the washing wastewater after backwashing, thereby separating the washing wastewater into solid and liquid into sludge and treated water.

[0036] The relay tank 14 temporarily stores the treated water discharged from the coagulation sedimentation equipment 13. The sludge storage tank 15 temporarily stores the sludge discharged from the coagulation sedimentation equipment 13.

[0037] The dehydration treatment equipment 16 dehydrates the sludge generated in the coagulation and sedimentation equipment 13 .

[0038] Next, the water treatment method of this embodiment will be described. In the water treatment method of this embodiment, a first pH adjustment step, a filtration step, a second pH adjustment step, and a reverse osmosis membrane treatment step are performed in this order. Each step will be described below.

[0039] First, the wastewater containing heavy metals stored in the raw water tank 2 is supplied to the heavy metal treatment facility 3, where a first pH adjustment step and a filtration step are carried out. In the first pH adjustment step, an alkaline agent is added to the wastewater in the first pH adjustment facility 3A of the heavy metal treatment facility 3, and the pH is adjusted to 10 to 12. The pH adjustment should be set to an optimum pH depending on the type of heavy metal. As a result, the heavy metals contained in the wastewater are precipitated mainly as hydroxides.

[0040] Next, in the filtration process, after the heavy metal precipitates are sufficiently precipitated from the wastewater in the filtration equipment 3B, solid-liquid separation is performed using the filtration membrane of the filtration device 3B1 to separate and remove the heavy metal precipitates from the wastewater. In this embodiment, since the heavy metal precipitates are separated from the wastewater by filtration, there is no need to flocculate the precipitates, and therefore no need to add a flocculant. By omitting the flocculation treatment using a flocculant, not only is there no need to add a flocculant, but there is also no risk of forming flocs (pin flocs) with a shape that adversely affects filtration performance, reducing the risk of clogging the downstream reverse osmosis membrane treatment device 7 due to pin floc leakage. The filtered treated water is stored in the filtration tank 4. However, to improve the filtration performance of the filtration equipment 3B, it is possible to add a flocculant to perform flocculation treatment as needed.

[0041] Next, in the second pH adjustment step, acid is added to the filtered treated water in second pH adjustment equipment 5 to adjust the pH to 9.5 to 11. Adjusting the pH of the filtered treated water to 9.5 to 11 makes it possible to prevent biofouling of the reverse osmosis membrane. The pH-adjusted treated water is stored in RO water supply tank 6.

[0042] Next, in the reverse osmosis membrane treatment step, the treated water, which has been adjusted to a pH of 9.5 to 11, is separated into permeate and concentrate by the reverse osmosis membrane of the reverse osmosis membrane treatment device 7. As described above, the pH of the water supplied to the reverse osmosis membrane treatment device 7 is adjusted to 9.5 to 11, so that reverse osmosis membrane treatment can be carried out without causing biofouling in the reverse osmosis membrane.

[0043] Next, the third pH adjustment step will be described. The permeated water produced by the reverse osmosis membrane treatment step is sent to a third pH adjustment facility 8. In the third pH adjustment step, an acid is added to the permeated water after the reverse osmosis membrane treatment step to adjust the pH to a neutral range of 5.8 to 8.6. This allows the quality of the permeated water to be adjusted to a quality that is usable as facility water. The treated water after the third pH adjustment step is sent to a recovered and treated water tank 9. The treated water sent to the recovered and treated water tank 9 is supplied via a supply flow path L1 to a cooling tower, boiler, cleaning equipment, or the like, where the treated water can be reused as facility water.

[0044] Next, the fourth pH adjustment step will be described. The concentrated water produced by the reverse osmosis membrane treatment step is sent to a fourth pH adjustment facility 10. In the fourth pH adjustment step, an acid is added to the concentrated water after the reverse osmosis membrane treatment step to adjust the pH to a neutral range of 5.8 to 8.6. This allows the quality of the concentrated water to be adjusted to a quality suitable for discharge. The treated water after the fourth pH adjustment step is sent to a discharge tank 11. The treated water sent to the discharge tank 11 is discharged into public waters such as rivers or public sewerage systems.

[0045] Next, the backwashing process, the coagulation and sedimentation process, and the first return process will be described. These processes treat the backwashing water generated by backwashing the filtration device 3B1 of the filtration equipment 3B, thereby enabling the water to be reused. In the backwashing process, the backwashing equipment 3B2 provided in the filtration equipment 3B backwashes the filtration media, such as the filtration membrane, on whose surface deposits (mainly heavy metal precipitates) have accumulated. This restores the filtration performance of the filtration equipment 3B, and generates cleaning wastewater. The cleaning wastewater contains the deposits removed from the filtration membrane. The cleaning wastewater is sent to the coagulation and sedimentation equipment 13 via the backwash wastewater tank 12.

[0046] Next, in the coagulation and sedimentation step, the washing wastewater is subjected to a coagulation and sedimentation treatment by the coagulation and sedimentation equipment 13. Specifically, a coagulant is added to the washing wastewater to coagulate the deposits removed from the filtration membrane in the backwashing step. Furthermore, a sedimentation treatment is performed on the treated water to which the coagulant has been added, thereby separating the sludge containing the deposits into solid and liquid. The treated water that has been subjected to the coagulation and sedimentation step is sent to the relay tank 14. The sludge is sent to the sludge storage tank 15.

[0047] Next, in the first return step, the treated water sent to the relay tank 14 is returned to the raw water tank 2 via the first return flow path L2. The treated water returned to the raw water tank 2 is sent as wastewater to the first pH adjustment step. This makes it possible to reuse the washing wastewater.

[0048] Next, the dehydration process and the second return process will be described. These processes aim to reuse water. In the dehydration process, the sludge sent to the sludge storage tank 15 is dehydrated by the dehydration equipment 16. The sludge separated by the dehydration process is finally disposed of by incineration or landfill.

[0049] In the second return step, the dehydrated water (separated water) produced by the dehydration process is sent to the backwash drain tank 12 via the second return flow path L3. The dehydrated water (separated water) returned to the backwash drain tank 12 is sent again to the coagulation sedimentation step in the coagulation sedimentation equipment 13. A portion of the dehydrated water is then sent to the first pH adjustment step by the first return step. This makes it possible to reuse the washing drain water.

[0050] As described above, according to the wastewater treatment system 1 of this embodiment, the second pH adjustment equipment 5, which adjusts the pH of treated water from which heavy metals have been separated and removed by the first pH adjustment equipment 3A and the filtration equipment 3B to 9.5 to 11, is located upstream of the reverse osmosis membrane treatment device 7, thereby preventing biofouling of the reverse osmosis membrane caused by the treated water from which heavy metals have been separated and removed. Furthermore, this embodiment omits the neutralization process for adjusting the pH of the filtered treated water to a range that allows discharge, and instead adjusts the pH of the filtered treated water to a pH range that suppresses biofouling. This reduces the number of pH adjustments and prevents an increase in the amount of chemical solution used for pH adjustment. Furthermore, adjusting the pH of the treated water using the second pH adjustment equipment 5 improves the durability of the downstream reverse osmosis membrane treatment device 7.

[0051] Furthermore, according to the wastewater treatment equipment 1 of this embodiment, a third pH adjustment equipment 8 is provided downstream of the reverse osmosis membrane treatment equipment 7, which adds acid to the permeate to adjust the pH to 5.8 to 8.6, so that the treated water can be adjusted to a water quality suitable for use in the equipment.

[0052] Furthermore, according to the wastewater treatment equipment 1 of this embodiment, a supply flow path L1 is provided that supplies treated water whose pH has been adjusted by the third pH adjustment equipment 8 as water for the equipment, thereby enabling the reuse of water.

[0053] Furthermore, according to the wastewater treatment equipment 1 of this embodiment, the backwashing equipment, the coagulation and sedimentation equipment 13, and the first return flow path L2 can coagulate and sediment the cleaning wastewater generated during the backwashing of the filtration equipment 3B before supplying it to the first pH adjustment equipment 3A, thereby enabling the reuse of the cleaning wastewater after backwashing.

[0054] Furthermore, according to the wastewater treatment equipment 1 of this embodiment, the dehydration treatment equipment 16 and the second return flow path L2 supply the dehydrated treated water (separated water) generated when the cleaning wastewater is coagulated and sedimented back to the coagulation and sedimentation equipment 13, thereby improving the sludge recovery rate.

[0055] Furthermore, according to the wastewater treatment equipment 1 of this embodiment, the capacities of the first pH adjustment equipment 3A, the filtration equipment 3B, the second pH adjustment equipment 5, and the coagulation and sedimentation equipment 13 can be reduced to 10 to 50% of the conventional capacities, thereby reducing the installation area of ​​the equipment.

[0056] Next, according to the wastewater treatment method of this embodiment, the treated water from which heavy metals have been separated and removed by the first pH adjustment step and filtration step is subjected to a second pH adjustment step in which the pH of the treated water is adjusted to 9.5 to 11, and then the reverse osmosis membrane treatment step is performed. This prevents biofouling of the reverse osmosis membrane by the treated water from which heavy metals have been separated and removed. Furthermore, this embodiment omits the neutralization treatment for adjusting the pH of the treated water after the filtration step to a range that allows discharge, and instead adjusts the pH of the treated water after filtration to a pH range that suppresses biofouling. This reduces the number of pH adjustments and prevents an increase in the amount of chemical solution used for pH adjustment. Furthermore, adjusting the pH of the treated water by the second pH adjustment step improves the durability of the reverse osmosis membrane treatment device 7 used in the subsequent reverse osmosis membrane treatment step.

[0057] Furthermore, according to the wastewater treatment method of this embodiment, a third pH adjustment step is provided in which an acid is added to the permeated water after the reverse osmosis membrane treatment step to adjust the pH to 5.8 to 8.6, so that the treated water can be adjusted to a water quality suitable for facility use.

[0058] Furthermore, according to the wastewater treatment method of this embodiment, the treated water after the third pH adjustment step is supplied to a cooling tower or the like as facility water, so that the water can be reused.

[0059] Furthermore, according to the wastewater treatment method of this embodiment, the cleaning wastewater generated during the backwashing of the filtration device 3B1 is coagulated and precipitated before being supplied to the first pH adjustment step, so that the cleaning wastewater after the backwashing can be reused.

[0060] Furthermore, according to the wastewater treatment method of this embodiment, the dehydrated treated water (separated water) generated when the cleaning wastewater is subjected to the coagulation and sedimentation process is returned to the coagulation and sedimentation process, thereby improving the sludge recovery rate.

[0061] According to the wastewater treatment facility and the wastewater treatment method of the present invention, it is possible to prevent an increase in the number of pH adjustment steps and an increase in the amount of chemical solution used for pH adjustment in water treatment when treating wastewater containing heavy metals and reusing the treated water, and therefore the wastewater treatment facility and the wastewater treatment method of the present invention have industrial applicability.

[0062] 1...wastewater treatment equipment, 2...raw water tank, 3...heavy metal treatment equipment, 3A...first pH adjustment equipment, 3B...filtration equipment, 3B1...filtration device, 3B2...backwashing equipment, 4...filtered water tank, 5...second pH adjustment equipment, 6...RO water supply tank, 7...reverse osmosis membrane treatment device, 8...third pH adjustment equipment, 9...recovery treatment water tank, 10...fourth pH adjustment equipment, 11...discharge water tank, 12...backwash wastewater tank, 13...coagulation sedimentation equipment, 14...relay tank, 15...sludge storage tank, 16...dehydration treatment equipment, L...flow path, L1...supply flow path, L2...first return flow path, L3...second return flow path.

Claims

1. A wastewater treatment facility comprising: a first pH adjustment facility which adds an alkaline agent to wastewater containing heavy metals to adjust the pH to 10-12; a filtration facility which separates and removes precipitates produced by the pH adjustment in the first pH adjustment facility using a filtration device; a second pH adjustment facility which adds an acid to the filtered treated water discharged from the filtration facility to adjust the pH to 9.5-11; and a reverse osmosis membrane treatment device which treats the treated water whose pH has been adjusted in the second pH adjustment facility using a reverse osmosis membrane.

2. The wastewater treatment facility according to claim 1, further comprising a third pH adjustment facility for adding an acid to the permeate discharged from the reverse osmosis membrane treatment device to adjust the pH to 5.8 to 8.

6.

3. The wastewater treatment facility according to claim 2, further comprising a supply flow path for supplying treated water whose pH has been adjusted in the third pH adjustment facility as facility water.

4. A wastewater treatment facility as described in any one of claims 1 to 3, further comprising: a backwashing facility for backwashing the filtration device provided in the filtration facility; a coagulation and sedimentation facility for coagulating and sedimenting the cleaning wastewater discharged from the backwashing facility; and a first return flow path for supplying the treated water discharged from the coagulation and sedimentation facility to the first pH adjustment facility.

5. The wastewater treatment facility according to claim 4, further comprising: a dehydration treatment facility for dehydrating the sludge produced in the coagulation and sedimentation facility; and a second return flow path for returning dehydrated water separated from the sludge in the dehydration treatment facility to the coagulation and sedimentation facility.

6. A wastewater treatment method comprising: a first pH adjustment step of adding an alkaline agent to wastewater containing heavy metals to adjust the pH to 10 to 12; a filtration step of separating and removing precipitates precipitated by the first pH adjustment step using a filtration device; a second pH adjustment step of adding an acid to the treated water after the filtration step to adjust the pH to 9.5 to 11; and a reverse osmosis membrane treatment step of treating the treated water after the second pH adjustment step using a reverse osmosis membrane.

7. The wastewater treatment method according to claim 6, further comprising a third pH adjustment step of adding an acid to the permeated water after the reverse osmosis membrane treatment step to adjust the pH to 5.8 to 8.

6.

8. The wastewater treatment method according to claim 7, wherein the treated water after the third pH adjustment step is supplied to a supply line for facility water.

9. The wastewater treatment method according to any one of claims 6 to 8, further comprising: a backwashing step for backwashing the filtration device used in the filtration step; a coagulation and sedimentation step for coagulating and sedimenting the cleaning wastewater after the backwashing step; and a first return step for supplying the treated water after the coagulation and sedimentation step to the first pH adjustment step.

10. The wastewater treatment method according to claim 9, further comprising: a dehydration treatment step for dehydrating the sludge produced by the coagulation and sedimentation step; and a second return step for returning the dehydrated water separated from the sludge in the dehydration treatment step to the coagulation and sedimentation step.

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