Wastewater treatment facility and wastewater treatment method

Abstract

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 an amount of chemical solution used for pH adjustment in water treatment when reusing treated water of wastewater containing heavy metals.SOLUTION: There is provided a wastewater treatment facility 1 including: a first pH adjustment facility 3A that adds an alkaline agent to wastewater containing heavy metals to adjust pH to 10 to 12; a filtration facility 3B that separates and removes precipitates precipitated as a result of the pH adjustment in the first pH adjustment facility 3A by using a filtration device; a second pH adjustment facility 5 that adds an acid to the filtered treated water discharged from the filtration facility 3B to adjust the pH to 9.5 to 11; and a reverse osmosis membrane treatment device 7 that subjects the treated water whose pH has been adjusted in the second pH adjustment facility 5 to reverse osmosis membrane treatment by using a reverse osmosis membrane.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a wastewater treatment facility and a wastewater treatment method. [Background technology]

[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 cause the heavy metals contained in the wastewater to precipitate and coagulate as hydroxides, and then the wastewater is treated by going through 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 water for facilities such as cooling towers (hereinafter referred to as CT). In this case, it is necessary to perform desalination or filtration using reverse osmosis membranes or other microfiltration membranes depending on the quality of the effluent. However, if the organic matter concentration of the effluent is high, supplying it directly to the reverse osmosis membrane or microfiltration membrane may reduce the permeation flux due to biofouling, so 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] 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 an alkali treatment and a 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. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-137540 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the wastewater treatment method described in Patent Document 1, when the water recovered in the salt separation step is circulated to the flue gas desulfurization equipment for reuse, the pH of the water needs to be readjusted. That is, the pH needs to be adjusted at both the step of removing heavy metals and the step of desalination or filtration of the treated water after the heavy metals have been removed. This increases the number of pH adjustment steps and increases the amount of chemicals used for pH adjustment, which is a problem in conventional wastewater treatment methods.

[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 which are capable of preventing 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. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention employs the following configuration. [1] A first pH adjustment facility that adds an alkaline agent to wastewater containing heavy metals to adjust the pH to 10 to 12; A filtration facility that separates and removes a precipitate formed by the pH adjustment in the first pH adjustment facility using a filtration device; A second pH adjustment facility that adds an acid to the filtered treated water discharged from the filtration facility to adjust the pH to 9.5 to 11; A reverse osmosis membrane treatment device that performs reverse osmosis membrane treatment on the treated water whose pH has been adjusted in the second pH adjustment device using a reverse osmosis membrane; Equipped with wastewater treatment facilities. [2] The wastewater treatment facility according to [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 [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 backwashing facility for backwashing the filtration device provided in the filtration facility; A coagulation and sedimentation facility for performing coagulation and sedimentation treatment on the cleaning wastewater discharged from the backwashing facility; The wastewater treatment facility according to any one of [1] to [3], further comprising a first return flow path that supplies treated water discharged from the coagulation sedimentation facility to the first pH adjustment facility. [5] A dehydration treatment facility for dehydrating the sludge generated in the coagulation and sedimentation facility; The wastewater treatment facility according to [4], further comprising a second return flow path that returns dehydrated water separated from the sludge in the dewatering treatment facility to the coagulation and sedimentation facility.

[0009] [6] 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 the precipitate formed 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; a reverse osmosis membrane treatment step of subjecting the treated water after the second pH adjustment step to a reverse osmosis membrane treatment using a reverse osmosis membrane; The wastewater treatment method is provided with: [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] A backwashing process for backwashing the filtration device used in the filtration process; A coagulation and sedimentation process for subjecting the cleaning wastewater after the backwashing process to a coagulation and sedimentation process; The wastewater treatment method according to any one of [6] to [8], further comprising a first return step of supplying the treated water after the coagulation and sedimentation step to the first pH adjustment step.

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

[0010] According to the wastewater treatment facility of the present invention, the second pH adjustment facility for adjusting the pH of the treated water from which heavy metals have been removed by the first pH adjustment facility and the filtration facility to 9.5 to 11 is disposed in the upstream of the reverse osmosis membrane treatment device, so that biofouling of the reverse osmosis membrane caused by the treated water after heavy metal removal can be prevented. Furthermore, in the present invention, the neutralization process for adjusting the pH of the treated water after filtration to a range in which it can be discharged is omitted, and the pH of the treated water after filtration is adjusted to a pH range in which biofouling can be suppressed, so that the number of pH adjustments can be reduced and an increase in the amount of chemicals used for pH adjustment can be prevented. Furthermore, by adjusting the pH of the treated water by the second pH adjustment facility, the durability of the reverse osmosis membrane treatment device in the downstream can be improved.

[0011] In addition, according to the wastewater treatment equipment of the present invention, a third pH adjustment equipment is provided downstream of the reverse osmosis membrane treatment equipment, 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.

[0012] Furthermore, according to the wastewater treatment facility of the present invention, the supply flow path is provided for supplying treated water, the pH of which has been adjusted by the third pH adjustment facility, as facility water, so that the water can be reused.

[0013] Furthermore, according to the wastewater treatment facility of the present invention, the washing wastewater generated during backwashing of the filtration device is subjected to coagulation and sedimentation treatment before being supplied to the first pH adjustment facility, so that the washing wastewater after backwashing can be reused.

[0014] In addition, according to the wastewater treatment equipment of the present invention, the dehydrated sludge treatment water (separated water) generated when the cleaning wastewater is subjected to the coagulation and sedimentation treatment is returned to the coagulation and sedimentation equipment, thereby improving the recovery rate of sludge.

[0015] Next, according to the wastewater treatment method of the present invention, the treated water from which heavy metals have been removed by the first pH adjustment step and the filtration step is subjected to a second pH adjustment step for adjusting the pH of the treated water to 9.5 to 11, and then the reverse osmosis membrane treatment step is performed, so that biofouling of the reverse osmosis membrane caused by the treated water after the heavy metals have been removed can be prevented. Furthermore, in the present invention, the neutralization process for adjusting the pH of the treated water after the filtration step to a range in which it can be discharged is omitted, and the pH of the treated water after the filtration step is adjusted to a pH range in which biofouling can be suppressed, so that the number of pH adjustments can be reduced and an increase in the amount of chemical solution used for pH adjustment can be prevented. Furthermore, by adjusting the pH of the treated water by the second pH adjustment step, the durability of the reverse osmosis membrane treatment device used in the subsequent reverse osmosis membrane treatment step can be improved.

[0016] In addition, according to the wastewater treatment method of the present invention, a third pH adjustment step is provided in which an acid is added to the permeate 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 use in facilities.

[0017] Furthermore, according to the wastewater treatment method of the present invention, the treated water after the third pH adjustment step is supplied to the facility water supply flow path, so that the water can be reused.

[0018] Furthermore, according to the wastewater treatment method of the present invention, the washing wastewater generated during backwashing of the filtration device is subjected to coagulation and sedimentation treatment and then supplied to the first pH adjustment step, so that the washing wastewater after backwashing can be reused.

[0019] In addition, according to the wastewater treatment method of the present invention, the dehydrated sludge water (separated water) generated when the washing wastewater is subjected to the coagulation and sedimentation process is returned to the coagulation and sedimentation step, thereby improving the recovery rate of the sludge. [Brief description of the drawings]

[0020] [Figure 1] 1 is a schematic diagram showing a configuration of a wastewater treatment facility according to an embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] 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.

[0022] 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. In addition, the filtration facility 3B is provided with a backwash facility (not shown), and a backwash wastewater tank 12 is connected to the filtration facility 3B.

[0023] Moreover, the wastewater treatment facility 1 shown in Fig. 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 facility 3. The filtered water tank 4 is disposed between the heavy metal treatment facility 3 and a second pH adjustment facility 5. The RO water tank 6 is disposed between the second pH adjustment facility 5 and a reverse osmosis membrane treatment device 7.

[0024] In addition, in the wastewater treatment facility 1 shown in FIG. 1, a third pH adjustment facility 8 and a recovery treatment tank 9 are arranged downstream of the reverse osmosis membrane treatment device 7. A supply flow path L1 is connected to the recovery treatment 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. In addition, the third pH adjustment facility 8 is configured so that permeated water of the treated water treated by the reverse osmosis membrane treatment device 7 flows into it.

[0025] In addition, a fourth pH adjustment equipment 10 and a discharge water tank 11 are arranged downstream of the reverse osmosis membrane treatment device 7. The fourth pH adjustment equipment 10 is configured so that concentrated water separated by the reverse osmosis membrane treatment device 7 flows into it.

[0026] 1 includes a coagulation-sedimentation equipment 13 and a relay tank 14 downstream of the backwash drainage tank 12. A first return flow path L2 that returns the separated water (supernatant water) from the coagulation-sedimentation equipment 13 to the raw water tank 2 is connected to the relay tank 14.

[0027] A sludge storage tank 15 and a dehydration treatment facility 16 are provided on the path for discharging the sludge separated in the coagulation sedimentation facility 13. A second return flow path L3 for returning dehydrated separated water generated when the sludge is dehydrated to the backwash drainage tank 12 is connected to the dehydration treatment facility 16.

[0028] Furthermore, in the wastewater treatment facility 1 of this embodiment, in addition to the above-mentioned flow paths L1 to L3, a flow path L for flowing water between adjacent tanks or devices is arranged. The wastewater stored in the raw water tank is configured to flow 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.

[0029] The permeated water treated by the reverse osmosis membrane treatment device 7 flows through a flow path L to a third pH adjustment device 8 and a recovery treatment water tank 9 in that order. Furthermore, the concentrated water separated from the permeated water by the reverse osmosis membrane treatment device 7 flows through a fourth pH adjustment device 10 and a discharge water tank 11 in that order.

[0030] Furthermore, washing wastewater generated in the backwashing equipment attached to the filtration equipment 3B flows through a flow path L to the coagulation sedimentation equipment 13 and the relay tank 14 in this order.

[0031] The sludge generated in the coagulation sedimentation equipment 13 is transported by a flow path L to a sludge storage tank 15 and a dewatering treatment equipment 16 in that order.

[0032] Next, the facilities and devices provided in the wastewater treatment facility 1 will be described in order. 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 level. Examples of such heavy metals include Cd, Cr, Cu, Fe, Mn, Ni, and Zn.

[0033] The heavy metal treatment equipment 3 is composed of a first pH adjustment equipment 3A and a filtration equipment 3B. The first pH adjustment equipment 3A adds an alkaline agent to wastewater containing heavy metals to adjust the pH to 10 to 12. For example, sodium hydroxide is used as the alkaline agent. The filtration equipment 3B has a function of storing the wastewater whose pH has been adjusted to 10 to 12, sufficiently precipitating the heavy metals, and then performing a solid-liquid separation process using a filtration device to separate and remove the heavy metals in the wastewater. The filtration device provided in the filtration equipment 3B is preferably 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 devices may also be used.

[0034] The filtration equipment 3B is also equipped with a backwashing equipment (not shown). The backwashing equipment backwashes the filtration medium of the filtration device on whose surface deposits (mainly heavy metal deposits) have accumulated. This restores the filtration performance of the filtration device, specifically the permeation flux. Backwashing generates washing wastewater.

[0035] The filtered water tank 4 temporarily stores the treated water that flows out from the filtration equipment 3B.

[0036] The second pH adjustment equipment 5 adds an acid to the treated water that has passed through the filtration equipment 3B via the filtration water tank 4, thereby adjusting the pH of the treated water to 9.5 to 11, preferably 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.

[0037] If the TOC (total organic carbon) of the treated water after filtration is 5 ppm or more, 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 an alkaline region. Therefore, by adjusting the pH of the treated water supplied to the reverse osmosis membrane treatment device 7 to 9.5 or more by the second pH adjustment equipment 5, it is possible to create an environment in which the growth of microorganisms is inhibited in the reverse osmosis membrane treatment device 7, and biofouling can be inhibited. In addition, it is known that nonionic surfactants and other organic substances that may reduce flux are desorbed from the membrane surface in an alkaline region, and by setting the pH of the treated water to 9.5 or more, it is possible to inhibit the adhesion of these components to the membrane surface of the reverse osmosis membrane.

[0038] 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 lower.

[0039] The RO water tank 6 temporarily stores treated water whose pH has been adjusted by the second pH adjustment equipment 5.

[0040] The reverse osmosis membrane treatment device 7 includes 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 permeated water and concentrated water.

[0041] The third pH adjustment equipment 8 adjusts the pH to 5.8 to 8.6 by adding an acid to the permeate treated in the reverse osmosis membrane treatment device 7. Sulfuric acid is used as the acid. Moreover, the fourth pH adjustment equipment 10 adjusts the pH to 5.8 to 8.6 by adding an acid to the concentrated water treated in the reverse osmosis membrane treatment device 7. For example, sulfuric acid is used as the acid.

[0042] The recovered and treated water tank 9 temporarily stores the treated water whose pH has been adjusted by the third pH adjustment equipment 8. Furthermore, the discharge water tank 11 temporarily stores the treated water whose pH has been adjusted by the fourth pH adjustment equipment 10.

[0043] The backwash drain tank 12 temporarily stores the washing drainage discharged from the filtration equipment 3B by the backwash equipment.

[0044] The coagulation sedimentation equipment 13 performs a coagulation sedimentation process on the washing wastewater after the backwashing, thereby separating the washing wastewater into solid-liquid separation into sludge and treated water.

[0045] The relay tank 14 temporarily stores the treated water discharged from the coagulation and sedimentation equipment 13. The sludge storage tank 15 temporarily stores the sludge discharged from the coagulation and sedimentation equipment 13.

[0046] The dehydration treatment equipment 16 dehydrates the sludge generated in the coagulation and sedimentation equipment 13.

[0047] 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 carried out in this order. Each step will be described below.

[0048] First, wastewater containing heavy metals stored in a raw water tank 2 is supplied to a 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 equipment 3A of the heavy metal treatment equipment 3 to adjust the pH 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.

[0049] Next, in the filtration process, after the heavy metal precipitates are sufficiently precipitated from the wastewater in the filtration equipment 3B, a solid-liquid separation process is performed using a filtration membrane to separate and remove the heavy metals in the wastewater. In this embodiment, since the heavy metal precipitates are separated from the wastewater by filtration, it is not necessary to aggregate the precipitates, and it is not necessary to add a coagulant. By omitting the coagulation process using a coagulant, the addition of a coagulant is not required, and there is no risk of generating coagulants (pin flocs) having a shape that adversely affects the filtration performance, and the risk of clogging the downstream reverse osmosis membrane treatment device due to leakage of pin flocs can be reduced. The filtered treated water is stored in the filtration water tank 4. However, in order to improve the filtration performance in the filtration equipment 3B, it is also possible to add a coagulant and perform coagulation process as necessary.

[0050] Next, in the second pH adjustment step, the filtered treated water is adjusted to a pH of 9.5 to 11 by adding acid in second pH adjustment equipment 5. By adjusting the pH of the filtered treated water to 9.5 to 11, it becomes possible to prevent biofouling of the reverse osmosis membrane. The pH-adjusted treated water is stored in RO water supply tank 6.

[0051] Next, in the reverse osmosis membrane treatment step, the treated water adjusted to a pH of 9.5 to 11 is separated into permeate and concentrated water 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 the reverse osmosis membrane treatment can be performed without causing biofouling in the reverse osmosis membrane.

[0052] Next, the third pH adjustment step will be described. The permeated water generated 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 can be used as water for facilities. The treated water after the third pH adjustment step is sent to a recovery treatment water tank 9. The treated water sent to the recovery treatment water tank 9 is supplied by a supply flow path L1 to a cooling tower, boiler, cleaning facility, or the like, where the treated water can be reused.

[0053] 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 water tank 11. The treated water sent to the discharge water tank 11 is discharged into public water areas such as rivers or public sewerage systems.

[0054] 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 the backwashing of the filtration device of the filtration equipment 3B, thereby enabling the reuse of the water. In the backwashing process, the backwashing equipment installed 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 recovers the filtration performance of the filtration equipment 3B and generates washing wastewater. The washing wastewater contains the deposits removed from the filtration membrane. The washing wastewater is sent to the coagulation sedimentation equipment 13 via the backwashing wastewater tank 12.

[0055] Next, in the coagulation sedimentation step, the washing wastewater is subjected to a coagulation sedimentation treatment by the coagulation 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 precipitation treatment is performed on the treated water to which the coagulant has been added, so that the sludge containing the deposits is separated into solid and liquid. The treated water that has been subjected to the coagulation sedimentation step is sent to the relay tank 14. The sludge is sent to the sludge storage tank 15.

[0056] 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 to the first pH adjustment step as wastewater. This makes it possible to reuse the washing wastewater.

[0057] 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 a dehydration facility 16. The sludge separated by the dehydration process is finally disposed of by incineration or landfill.

[0058] In the second return process, the dehydrated water (separated water) generated 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 and sedimentation process. Then, a part of it is sent to the first pH adjustment process by the first return process. This makes it possible to reuse the washing drain water.

[0059] As described above, according to the wastewater treatment equipment 1 of this embodiment, the second pH adjustment equipment 5, which adjusts the pH of the 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 disposed in the upstream of the reverse osmosis membrane treatment device 7, so that biofouling of the reverse osmosis membrane caused by the treated water from which heavy metals have been separated and removed can be prevented. Furthermore, in this embodiment, the neutralization process for adjusting the pH of the treated water after filtration to a range in which it can be discharged is omitted, and the pH of the treated water after filtration is adjusted to a pH range in which biofouling can be suppressed, so that the number of pH adjustments can be reduced and an increase in the amount of chemicals used for pH adjustment can be prevented. Furthermore, by adjusting the pH of the treated water by the second pH adjustment equipment 5, the durability of the reverse osmosis membrane treatment device 7 in the downstream can be improved.

[0060] 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.

[0061] Furthermore, according to the wastewater treatment facility 1 of this embodiment, the supply flow path L1 is provided for supplying treated water, the pH of which has been adjusted by the third pH adjustment facility 8, as facility water, so that the water can be reused.

[0062] 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, and then supply it to the first pH adjustment equipment 3A, thereby making it possible to reuse the cleaning wastewater after the backwashing.

[0063] 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.

[0064] Furthermore, according to the wastewater treatment equipment 1 of this embodiment, the capacity 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 capacity, thereby making it possible to reduce the installation area of ​​the equipment.

[0065] 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 the filtration step is subjected to a second pH adjustment step for adjusting the pH of the treated water to 9.5 to 11, and then the reverse osmosis membrane treatment step is performed, so that biofouling of the reverse osmosis membrane caused by the treated water from which heavy metals have been separated and removed can be prevented. Furthermore, in this embodiment, the neutralization process for adjusting the pH of the treated water after the filtration step to a range in which it can be discharged is omitted, and the pH of the treated water after the filtration step is adjusted to a pH range in which biofouling can be suppressed, so that the number of pH adjustments can be reduced and an increase in the amount of chemical solution used for pH adjustment can be prevented. Furthermore, by adjusting the pH of the treated water by the second pH adjustment step, the durability of the reverse osmosis membrane treatment device 7 used in the subsequent reverse osmosis membrane treatment step can be improved.

[0066] In addition, according to the wastewater treatment method of this embodiment, a third pH adjustment step is provided in which an acid is added to the permeate 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 use in facilities.

[0067] Furthermore, according to the wastewater treatment method of the present embodiment, the treated water after the third pH adjustment step is supplied to the facility water supply flow path, so that the water can be reused.

[0068] Furthermore, according to the wastewater treatment method of the present embodiment, the washing wastewater generated during backwashing of the filtration device is coagulated and precipitated before being supplied to the first pH adjustment step, so that the washing wastewater after backwashing can be reused.

[0069] Furthermore, according to the wastewater treatment method of this embodiment, the dehydrated treated water (separated water) generated when the washing wastewater is subjected to the coagulation and sedimentation process is returned to the coagulation and sedimentation process, thereby improving the recovery rate of sludge. [Explanation of symbols]

[0070] 1...wastewater treatment equipment, 2...raw water tank, 3...heavy metal treatment equipment, 3A...first pH adjustment equipment, 3B...filtration equipment, 4...filtration 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 first pH adjustment facility for adding an alkaline agent to wastewater containing heavy metals to adjust the pH to 10 to 12; a filtration facility for separating and removing a precipitate formed by the pH adjustment in the first pH adjustment facility using a filtration device; A second pH adjustment facility that adds an acid to the filtered treated water discharged from the filtration facility to adjust the pH to 9.5 to 11; a reverse osmosis membrane treatment device that performs reverse osmosis membrane treatment on the treated water whose pH has been adjusted in the second pH adjustment device, using a reverse osmosis membrane; Equipped with wastewater treatment facilities.

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 backwashing facility for backwashing the filtration device provided in the filtration facility; A coagulation and sedimentation facility for performing coagulation and sedimentation treatment on the cleaning wastewater discharged from the backwashing facility; The wastewater treatment facility according to claim 1 , further comprising a first return flow path that supplies treated water discharged from the coagulation sedimentation facility to the first pH adjustment facility.

5. A dehydration treatment facility for dehydrating the sludge generated in the coagulation sedimentation facility; The wastewater treatment facility according to claim 4 , further comprising a second return flow path that returns dehydrated water separated from the sludge in the dewatering treatment facility to the coagulation sedimentation facility.

6. 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 the precipitate formed 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; a reverse osmosis membrane treatment step of subjecting the treated water after the second pH adjustment step to a reverse osmosis membrane treatment using a reverse osmosis membrane; The wastewater treatment method is provided with:

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. A backwashing process for backwashing the filtration device used in the filtration process; A coagulation and sedimentation process for subjecting the cleaning wastewater after the backwashing process to a coagulation and sedimentation process; The wastewater treatment method according to claim 6 , further comprising a first return step of supplying the treated water after the coagulation and sedimentation step to the first pH adjustment step.

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

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