JP2013236983A - Device and method for treating waste water - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a waste water treatment device capable of preventing waste water containing heavy metal from being discharged by preventing discharge of the heavy metal to the downstream side of an insolubilization tank when the metal waste water treatment device is stopped.SOLUTION: A waste water treatment device 1 includes a pump P1, an oxidization tank 21 for oxidizing a complex formation compound contained in waste water W, an insolubilization tank 31 disposed on the downstream side of the oxidization tank 21 and insolubilizing heavy metal contained in the waste water Wflowing from the oxidizing tank 21, a membrane separation tank 42 disposed on the downstream side of the insolubilization tank 31 and subjecting waste water flowing from the insolubilization tank 31 to membrane separation treatment, and a stirrer 34 for stirring the waste water in the insolubilization tank 31. The oxidizing tank 21 and the insolubilization tank 31, and the insolubilization tank 31 and the membrane separation tank 42 are respectively connected by an overflow mechanism, and the stirrer 34 is stopped after a predetermined lapse of time from stopping of the pump.

Description

  The present invention relates to a wastewater treatment apparatus and a treatment method, and more particularly, to a wastewater treatment apparatus and method for treating wastewater containing heavy metals.

  Conventionally, as a method for removing heavy metals from waste water containing heavy metals such as plating waste water discharged from an electrolytic plating process, the following methods are generally used.

  First, the waste water once stored in the storage tank is insolubilized in the insolubilization tank. Specifically, an insolubilizing agent such as a hydroxylating agent (alkaline agent) or a sulfiding agent is added to the waste water, and the heavy metal is made into an insolubilized material such as a hydroxide or sulfide that is hardly soluble in water. Since the insolubilized material has a small particle size, an inorganic flocculant (such as polyaluminum chloride (PAC)) or a polymer flocculant is added to the wastewater insolubilized in the coagulation tank, and Aggregate. Next, the insoluble material agglomerated in the settling tank is settled and separated, and the supernatant is filtered through a filter such as a sand filter as necessary, and the filtered water is neutralized in a pH adjusting tank and then treated. Discharge as water.

  In recent years, electroless plating such as electroless nickel plating has been widely performed. Electroless plating is characterized by using a reducing agent, and deposits a metal using the electrons of the reducing agent. According to this method, it is possible to plate even a non-conductive substance. However, when treating the wastewater discharged from this electroless plating step, it is difficult to sufficiently treat the conventional method described above, and it is difficult to reduce the heavy metal concentration in the wastewater.

  In electroless plating such as electroless nickel plating, this may be due to the fact that the plating solution contains a compound (for example, a chelating agent) that forms a metal complex by coordination with heavy metal. . As described above, when treating plating wastewater, insolubilization treatment is performed by adding an insolubilizing agent to the wastewater, but a compound that forms a metal complex such as a chelating agent in the wastewater (hereinafter referred to as “complex forming compound”) )), A heavy metal such as nickel forms a metal complex with the complex-forming compound, and it is considered that this metal complex leaks from the filter and lowers the processing efficiency. Further, even when acidic zinc plating is performed, it is considered that the treatment efficiency is lowered because a large amount of ammonia is contained in the bath and the heavy metal forms ammonia and an ammine complex.

  Therefore, as a method of treating wastewater containing heavy metals, heavy metal complexes of heavy metals and chelating agents, etc., after adding an insolubilizer to the wastewater to produce insolubilized material, solid-liquid separation is performed by supplying it to a membrane separator Have been proposed (see, for example, Patent Documents 1 and 2).

Japanese Patent No. 3111508 JP-A-2-157090

  However, even in the methods described in Patent Documents 1 and 2, when a complex-forming compound is contained in the wastewater, the heavy metal to be removed forms a metal complex with the complex-forming compound, so insolubilization with an insolubilizing agent The reaction was easily inhibited, and it was difficult to obtain a sufficient treatment effect.

  In order to solve this problem, a wastewater treatment apparatus has been proposed that can treat wastewater containing compounds that form heavy metals and metal complexes to a high degree without adding a flocculant and sufficiently reduce the concentration of heavy metals. Yes. The proposed wastewater treatment equipment performs membrane separation of oxidation treatment tanks that oxidize compounds that form metal complexes in wastewater, insolubilization tanks that insolubilize heavy metals in oxidized wastewater, and insolubilized wastewater And a membrane tank. And between each processing tank, it is made to move to a downstream processing tank by overflowing processing water.

  However, since the proposed wastewater treatment apparatus adopts the overflow method, even if the pump and the stirrer are stopped to stop the water treatment, the oxidation treatment tank is changed to the insolubilization tank for a predetermined time, and Wastewater flows from the insolubilization tank to the membrane separation tank. And if the stirrer of an insolubilization tank stops, stirring of the wastewater in an insolubilization tank will be stopped. When the wastewater containing heavy metal overflowing from the oxidation treatment tank flows into the insolubilization tank in a state where the stirring of the wastewater in the insolubilization tank is stopped, the heavy metal stays without being sufficiently insolubilized. If the wastewater overflows from the insolubilization tank to the membrane treatment tank while the heavy metal that has not been insolubilized remains in the insolubilization tank, the wastewater containing the heavy metal that has not been insolubilized flows into the membrane treatment tank. As a result, the heavy metal may be discharged as it is without being sufficiently treated.

  Accordingly, the present invention has been made to solve the above-described problems, and prevents wastewater containing heavy metals from flowing downstream from the insolubilization tank when the metal wastewater treatment apparatus is stopped. An object of the present invention is to provide a wastewater treatment apparatus that can prevent discharge of water.

  In order to solve the above-described problems, the present invention provides a pump for flowing a wastewater containing a heavy metal and a complex-forming compound that forms a metal complex with the heavy metal toward a downstream side, and a complex contained in the wastewater flowing from the pump. An oxidation treatment tank for oxidizing the forming compound, an insolubilization tank provided on the downstream side of the oxidation treatment tank, for insolubilizing heavy metals contained in waste water flowing from the oxidation treatment tank, and the insolubilization tank Provided with a membrane separation tank for membrane separation treatment of waste water flowing from the insolubilization tank, and a stirrer for stirring the waste water in the insolubilization tank, an oxidation treatment tank and an insolubilization tank, and The insolubilization tank and the membrane treatment tank are respectively connected by an overflow mechanism, and the stirrer is stopped after a predetermined time has elapsed since the pump stopped.

  According to this invention comprised in this way, the stirrer of an insolubilization tank can be stopped after predetermined time progress, after a pump stops. Thereby, the inside of the insolubilization tank can be stirred by the stirrer for a predetermined time after the pump is stopped, and the heavy metal contained in the waste water in the insolubilization tank can be insolubilized. Further, by stopping the pump after a predetermined time has elapsed, it is possible to prevent the insoluble matter floc formed in the insolubilization tank from being destroyed.

  In the present invention, preferably, the predetermined time is determined according to the amount of waste water flowing into the metal waste water treatment apparatus. In the present invention, the predetermined time is preferably determined according to the volumes of the oxidation treatment tank and the insolubilization tank. In the present invention, it is preferable that the predetermined time is 30 seconds to 3 minutes.

  Moreover, in order to solve the above-described problem, the present invention is a wastewater treatment method for treating wastewater containing a heavy metal and a complex-forming compound that forms a metal complex with the heavy metal by a wastewater treatment apparatus, toward the downstream side. The waste water is caused to flow into the oxidation treatment tank by a flowing pump, the complex-forming compound contained in the waste water is oxidized in the oxidation treatment tank, and the waste water is caused to flow into the insolubilization tank provided on the downstream side of the oxidation treatment tank. The insoluble heavy metals are insolubilized and wastewater is passed through a membrane separation tank provided downstream of the insolubilization tank, and the wastewater is subjected to membrane separation treatment in the membrane separation tank. The wastewater is stirred in the insolubilization tank. The oxidation treatment tank and the insolubilization tank, and the insolubilization tank and the membrane treatment tank are arranged to be fed by an overflow mechanism, respectively, and stop the wastewater treatment apparatus. Come, the pump is adapted to stop the stirring gas from the stop after a predetermined period of time, characterized in that.

  According to this invention comprised in this way, the stirrer of an insolubilization tank can be stopped after predetermined time progress, after a pump stops. Thereby, the inside of the insolubilization tank can be stirred by the stirrer for a predetermined time after the pump is stopped, and the heavy metal contained in the waste water in the insolubilization tank can be insolubilized. Further, by stopping the pump after a predetermined time has elapsed, it is possible to prevent the insoluble matter floc formed in the insolubilization tank from being destroyed.

  As described above, according to the wastewater treatment apparatus and the treatment method of the present invention, when the metal wastewater treatment apparatus is stopped, the wastewater containing heavy metals is prevented from flowing to the downstream side of the insolubilization tank. It can be prevented from being discharged.

1 is a schematic configuration diagram showing a wastewater treatment apparatus according to an embodiment of the present invention.

  Hereinafter, a wastewater treatment apparatus and a treatment method according to embodiments of the present invention will be described with reference to the drawings.

The wastewater treatment apparatus of the present invention is an apparatus for treating wastewater W ₀ containing heavy metals and complex-forming compounds, and is particularly suitable for treating wastewater discharged from an electroless plating process such as electroless nickel plating. .

FIG. 1 is a schematic configuration diagram showing an example of a wastewater treatment apparatus of the present invention. Wastewater treatment apparatus 1 of this embodiment includes, in order from the upstream side, a pump P1 to flow wastewater W ₀ toward the downstream side, a storage unit 10 for temporarily storing waste water W ₀ flowing from pump P1, oxidation means 20 And an insolubilizing means 30, a membrane separating means 40, and a pH adjusting means 50.

The waste water W ₀ to be treated in the present invention is a waste liquid (treated water) generated from a metal surface treatment factory such as a plating factory, and is a compound that forms a metal complex by coordination with heavy metals and heavy metals. (Hereinafter referred to as “complex-forming compound”). Examples of heavy metals include chromium, copper, zinc, cadmium, nickel, mercury, lead, and iron. These heavy metals may be contained alone, but are usually contained in a state where a plurality of heavy metals are mixed. On the other hand, a complex-forming compound is a compound that forms a metal complex centered on a heavy metal atom by coordination with any of heavy metals. Examples of complex-forming compounds include acidic cleaning components such as citric acid, gluconic acid, oxalic acid, tartaric acid, succinic acid, cyanide and salts thereof; EDTA, ethylenediamine, triethanolamine, ammonia (including ammonium salts), etc. Examples include amines. In addition, since a chelate complex is also contained in a metal complex, chelating agents, such as tartaric acid and EDTA, naturally correspond to a complex formation compound.
In addition to the heavy metal and the complex-forming compound, the waste water W ₀ may contain a washing component, a surfactant as a pH adjusting component, a Lewis acid other than the complex-forming compound, and the like.

The pump P1 flows waste water W ₀ generated from a metal surface treatment factory or the like toward the downstream side. The pump P1 generates power for flowing the waste water W ₀ in the waste water treatment apparatus.

The storage means 10 is provided on the downstream side of the pump P1, and is a means for temporarily storing the waste water W ₀ flowing from the pump P1. The storage means 10 includes a storage tank 11. The storage tank 11 is not particularly limited as long as it can store the waste water W _0.

The oxidation treatment means 20 is adapted to oxidize the complex-forming compound in the waste water W ₀ . The oxidation treatment means 20 in this example includes an oxidation tank 21 for storing waste water W ₀ sent from the storage means 10, an oxidant addition means 22 for adding an oxidant to the waste water W ₀ in the oxidation tank 21, and an oxidation tank 21. and water gauge 23 for inspecting the water quality of waste water W _0, and a stirring blade 24 for stirring the waste water W ₀ in the oxidation vessel 21.

The oxidation tank 21 is not particularly limited as long as it can store the waste water W ₀ , but is preferably made of a material that is not easily deteriorated by the oxidizing agent. The oxidizing agent adding means 22 is not particularly limited as long as an oxidizing agent can be added.

The water quality meter 23 inspects the water quality of the waste water W _{0 in} the oxidation tank 21. By examining the water quality, it is possible to grasp the excess and deficiency of the added amount of the oxidant, and in particular, it is effective for suppressing the excessive addition of the oxidant. Examples of the water quality meter 23 include an oxidation-reduction potentiometer and an oxidant concentration meter. Moreover, it is also possible to use a densitometer for measuring the concentration of the complex-forming compound instead of or in combination with these electrometers and densitometers. However, the densitometer for measuring the concentration of the complex-forming compound is used when treating the waste water W ₀ containing the complex-forming compound capable of measuring the concentration such as ammonia.
In addition, although the oxidation treatment means 20 of this example is provided with one water quality meter 23, it may be provided with a plurality of types of water quality meters according to the water quality inspection method.

The insolubilizing means 30 insolubilizes heavy metals in the waste water W ₀ oxidized by the oxidizing means 20. The insolubilization means that heavy metals floating in the waste water W ₀ are precipitated by using a hardly soluble compound (insolubilized material). The insolubilizing means 30 includes an insolubilizing tank 31 for storing the waste water W ₀ sent from the oxidizing means 20, an insolubilizing agent adding means 32 for adding an insolubilizing agent to the waste water W ₀ in the insolubilizing tank 31, and the insolubilizing tank 31. It includes a water meter 33 for inspecting the water quality of waste water W _0, and a stirring blade 34 for stirring the waste water W ₀ in the insolubilized 31.

The insolubilizing tank 31 is not particularly limited as long as it can store the waste water W ₀ , but is preferably made of a material that is not easily deteriorated by the insolubilizing agent. The insolubilizing agent adding means 32 is not particularly limited as long as an insolubilizing agent can be added.

The water quality meter 33 inspects the water quality of W ₀ in the insolubilization tank 31. By examining the water quality, it is possible to grasp the excess or deficiency of the amount of the insolubilizing agent added, and it is particularly effective for suppressing the excessive addition of the insolubilizing agent. Examples of the water quality meter 33 include a pH meter. Although the insolubilization processing means 30 of this example includes one water quality meter 33, a plurality of types of water quality meters may be provided depending on the water quality inspection method.

The agitating blade 34 agitates the waste water W ₀ in the insolubilizing tank 31 so that the insolubilizing agent is evenly distributed in the insolubilizing tank 31. The stirring blade 34 is configured to be driven according to the driving of the pump P1.

The membrane separation means 40 is means for membrane separation of the waste water W ₀ insolubilized by the insolubilization treatment means 30 into filtered water W ₁ and membrane separation concentrated water W ₂ . The membrane separation means 40 includes a membrane separation tank 42 for storing the waste water W ₀ sent from the insolubilization treatment means 30, a membrane module 43 provided in the membrane separation tank 42, and an aeration means 44 for membrane cleaning. . A suction pump P <b> 2 is connected to the membrane module 43, and a blower B is connected to the air diffuser 44.

Examples of the membrane module 43 include a normal membrane module used for a separation operation such as water treatment. In the membrane module 43, filtered water W ₁ and the membrane separation concentrated water W waste water W ₀ by suction filtration through pores of the filtration membrane of the waste water W ₀ of the membrane in the separation tank 42 by the suction pump P2 membrane module 43 Separated into _two . On the other hand, the air diffuser 44 is provided below the membrane module 43 and discharges the air supplied from the blower B into the membrane separation tank 42. Thereby, the air bubbles continuously or intermittently diffused from the air diffuser 44 reach the membrane module 43 through the liquid of the waste water W ₀ , and are then released from the water surface. At this time, the filtration membrane is washed. A part of the membrane separation concentrated water W ₂ separated by the membrane separation means 40 may be returned to the insolubilization tank 31, the oxidation tank 21, and the storage tank 11.

The insolubilization tank 31 and the membrane separation tank 42 are connected by an overflow method, and waste water W ₀ is allowed to flow from the insolubilization tank 31 to the membrane separation tank 42 using an overflow mechanism. Here, the overflow mechanism is the waste water W in the tank when the amount of liquid stored in the insolubilization tank 31 disposed on the upstream side exceeds a threshold value determined in advance according to the volume or depth of the insolubilization tank 31. _This is a mechanism that automatically flows ₀ to the membrane separation tank 42 disposed on the downstream side. As such an overflow mechanism, for example, a mechanism in which the tanks are connected by an overflow pipe, a hole is provided in the upper side of the upstream tank, and when the water level reaches the height of the hole, waste water is discharged downstream through the hole. There is a mechanism that flows into the tank, or a mechanism in which an overflow weir is provided at the upper end of either side wall of the upstream tank.

The pH adjusting unit 50 is a unit that adjusts the pH of the filtered water W ₁ membrane-separated by the membrane separating unit 40 to a pH suitable for discharge to a river or the like. The pH-adjusted filtered water W ₁ is treated. It is discharged as water W _3. In addition, since the insolubilized material is sufficiently removed by the membrane separation means 40, there is no possibility that the heavy metal is re-dissolved even if the pH of the filtered water W ₁ is neutralized.

The pH adjusting means 50 includes a pH adjusting tank 51, a pH meter (not shown), an acid addition device, and an alkali addition device (both not shown). The pH adjustment tank 51 is not particularly limited as long as the filtered water W ₁ can be stored. Further, the pH meter, the acid addition device, and the alkali addition device are not particularly limited as long as they are used for pH adjustment.

Hereinafter, the operation of the above-described wastewater treatment apparatus 1 will be described.
By driving the wastewater treatment apparatus 1 and driving the pump P1, the wastewater W ₀ flows into the storage tank 11 of the storage means 10 from the upstream side. When the reservoir 11 is filled with waste water W _0, wastewater W ₀ is overflowing from the reservoir 11, it flows into the oxidation vessel 21 for oxidation treatment unit 20 in the downstream side of the reservoir 11. In the oxidation tank 21, an oxidizing agent is added to the wastewater W ₀ while driving the stirring blade 24, whereby the complex-forming compound in the wastewater W ₀ is oxidized.

Examples of the oxidizing agent used in the oxidation treatment include hypochlorous acid, chlorous acid, perchloric acid or salts thereof, and hydrogen peroxide. Among these, hypochlorous acid, chlorous acid, perchloric acid or a salt thereof, or a mixed solution thereof is preferable, and a sodium hypochlorite solution is particularly preferable from the viewpoints of handleability and availability. If hypochlorous acid, chlorous acid, perchloric acid or a salt thereof, or a mixed solution thereof is used as an oxidizing agent, the oxidation reaction can easily proceed quickly, and the overall processing speed can be increased. Moreover, since these have high decomposition efficiency of complex-forming compounds having a chelating action such as EDTA and tartaric acid, they can prevent the inhibition of aggregation of insolubilized products by the complex-forming compounds in the insolubilization treatment step described later, and more insolubilization treatment Can be done efficiently. In particular, when sodium hypochlorite or a solution thereof is used as the oxidizing agent, the particle size of the heavy metal insolubilized product produced in the subsequent insolubilizing treatment step tends to increase. When the particle size of the insolubilized material is larger, it is possible to suppress clogging of the pores of the filtration membrane in the membrane separation step described later, and the membrane flux can be maintained high. Further, when the waste water W ₀ is waste water containing nickel as a heavy metal, such as electroless nickel plating waste water, dissolved nickel ions are converted into nickel oxyhydroxide (NiO (OH) by adding an oxidizing agent such as sodium hypochlorite. Oxidized to)). Nickel oxyhydroxide generally has a lower solubility than nickel hydroxide (Ni (OH) 2), so sodium chlorite or a solution thereof is an oxidizing agent for advanced wastewater treatment. Is particularly preferred.

The addition of the oxidizing agent to the waste water W ₀ is a purpose to be oxidizing the complex forming compound contained in the wastewater W _0, adding an excess oxidizing agent becomes excessive consumption of chemicals. Moreover, when an oxidizing agent is added excessively, there exists a possibility that the filtration membrane used at the membrane separation process mentioned later may be oxidized with the remaining oxidizing agent. In addition, when an oxidizing agent is excessively added, the amount of sludge that is finally generated tends to increase.

By the above, when the oxidation treatment process that all oxidized complex forming compound contained in the wastewater W _0, it is desirable to stop the addition of the oxidizing agent to the waste water W _0, to control the excessive addition Good. Examples of the method for detecting the end point of addition of the oxidant include a method of monitoring the oxidation-reduction potential using the water quality meter 23, monitoring the concentration of the oxidant, and monitoring the concentration of the complex-forming compound.

Since the pump P1 is driven during the oxidation treatment in the oxidation tank 21, the waste water W ₀ is continuously poured from the pump P1 to the storage tank 11 and from the storage tank 11 to the oxidation tank 21 during this time. It is. When the oxidation tank 21 is filled with waste water W _0, wastewater W ₀ is out overflowing from the oxidation tank 21, flows into the insolubilization tank 31 of insolubilization means 30 located downstream of the oxidation vessel 21.

Within insolubilized tank 31, while driving the stirring blade 34 is doped with insoluble agents to the waste water W _0, which heavy metals in waste water W ₀ is insolubilization treatment by. When the insolubilization tank 31 is filled with waste water W _0, wastewater W ₀ flow into the membrane separation tank 42 of the insolubilized tank 31 overflowing out by membrane separation means 40.

In the insolubilization treatment means 30, the oxidized waste water W ₀ is transferred to the insolubilization tank 31 of the insolubilization treatment means 30, and an insolubilizing agent is added to insolubilize the heavy metals in the waste water W ₀ . As the insolubilization method, there are a hydroxide method using a hydroxylating agent and a sulfide method using a sulfiding agent. In the case of the sulfide method, hydrogen sulfide may be generated, and therefore the hydroxide method is preferable as the insolubilization treatment.

  The hydroxide method is a method in which a hydroxylating agent (hydroxide ion) and a target metal are reacted to precipitate a metal hydroxide with low solubility. As the hydroxylating agent, sodium hydroxide, sodium carbonate, calcium hydroxide, magnesium hydroxide or the like is used. Sodium hydroxide is more preferable because sludge generation is reduced.

  On the other hand, the sulfide method is a method in which a sulfiding agent (sulfide ion) and a target metal are reacted and precipitated as a metal sulfide having low solubility. As the sulfiding agent, sodium sulfide, hydrogen sulfide, or the like is used.

When insolubilization is performed by a hydroxide method, heavy metals have different pH ranges where the solubility is lowest depending on each metal species. Therefore, in order to increase the removal rate of heavy metals, an insolubilizing agent (hydroxylating agent) is added until the pH reaches the lowest solubility. At that time, the addition amount of the insolubilizing agent is controlled by measuring the pH of the waste water W ₀ in the insolubilizing tank 31 by the water quality meter 33.
However, when it is known that the composition and concentration of heavy metal in the waste water W ₀ supplied to the waste water treatment apparatus are always constant, it can be controlled by injecting a certain amount of insolubilizing agent.

Moreover, even if it is the same heavy metal, the pH area | region where solubility becomes the lowest may differ with the other components to coexist. Therefore, in practice, it is desirable to conduct a preliminary test using the waste water W ₀ to be treated and control it to be in the most suitable pH range.

The membrane separation unit within 40, the waste water W ₀ of the membrane in the separation tank 42 by suction filtration through a pore of a filtration membrane of the membrane module 43 by wastewater suction pump P2, filtered water W ₁ and the membrane wastewater W ₀ Separated into separated concentrated water W ₂ . The filtered water W ₁ flows to the pH adjusting means 50, and the membrane separation concentrated water W ₂ is dehydrated by a dehydrating means (not shown) and processed as industrial waste such as a dehydrated cake.

The filtered water W ₁ flowing to the pH adjusting means 50 is discharged as treated water W ₃ after the hydrogen ion concentration is adjusted in the pH adjusting means 50. In the pH adjusting step, the filtered water W ₁ is transferred to the pH adjusting tank 51 of the pH adjusting means 50, and the pH of the filtered water W ₁ is adjusted to a pH suitable for discharge into a river or the like. In particular, when the hydroxide method is used in the insolubilization treatment step, the filtered water W ₁ is usually alkaline, so it is preferable to neutralize it. The filtered water W ₁ whose pH is adjusted is discharged as treated water W ₃ .
In the pH adjustment step, an acid such as hydrochloric acid, sulfuric acid, carbon dioxide is used as a pH adjuster for neutralization. When an excessive amount of acid is added in the pH adjustment process, an alkali such as sodium hydroxide, sodium carbonate, calcium hydroxide, magnesium hydroxide or the like is added as a pH adjuster, and the pH is adjusted again to be in a neutral region. adjust. In addition, since the insolubilized substances are sufficiently removed by the membrane separation step, there is no possibility that heavy metals are redissolved even if the pH of the filtered water W ₁ is neutralized.

  Moreover, when stopping the waste water treatment apparatus 1, the following control is performed.

When stopping the waste water treatment apparatus 1, first, the pump P1, the pump P2, and the stirring blade 24 of the oxidation treatment means 30 are stopped. This stops the wastewater W ₀ from flowing into the storage tank 11. Then, 30 seconds to 3 minutes after the pump P1 is stopped, the stirring blade 34 of the insolubilizing means 30 is stopped.

The time for stopping the stirring blade 24 after the pump P1 is stopped, that is, the driving time t of the stirring blade 24 after the pump P1 is stopped is the volume of the insolubilization tank 31 and the flow rate of the waste water W ₀ flowing into the insolubilization tank 31. In this case, it is preferable to set in the range of time t = (HRT / 20) to (HRT / 2.5). Here, HRT (hydraulic residence time) is determined based on the capacity of the insolubilization tank 31 / the amount of waste water W ₀ flowing into the insolubilization tank 31.

Table 1 below illustrates the relationship between the amount of water flowing into the insolubilization tank 31, the capacity of the insolubilization tank 31, and the stirring time. The stirring time in the table is calculated by introducing the amount of water and the volume of the insolubilization tank into the above formula.

After this way a new waste water W ₀ in the pump P1 is stopped is stopped from flowing into the storage tank 11, 3 min stirring blades 34 from 30 seconds, by continuously driven, new waste water W ₀ even after stopping that flow into the storage tank 11 continues to stir the waste water W ₀ in the insolubilization tank 31.

That is, the wastewater treatment apparatus 1 according to the present embodiment is configured to flow the wastewater W ₀ to the downstream side using the overflow method. In such a wastewater treatment apparatus 1, the inflow of the wastewater W ₀ is stopped. Even so, the transfer of the downstream wastewater W ₀ does not stop immediately. Accordingly, even after the pump P1 is stopped, the waste water W ₀ flows from the oxidation treatment tank 21 into the insolubilization tank 31. Then, by driving the stirring blade 34 for a predetermined time after the pump P1 is stopped, the waste water W ₀ that has flowed into the insolubilization tank 31 from the oxidation treatment tank 21 after the pump P1 is stopped, and the insolubilization tank 31 already exists when the pump P1 stops. Waste water W ₀ is agitated. Thereby, heavy metals can be sufficiently insolubilized included from the oxidation treatment tank 21 after the stop of the pump P1 to the waste water W in ₀ that has flowed into the insoluble tank 31. This prevents heavy metals contained in the waste water W ₀ flowing from the oxidation treatment tank 21 into the insolubilization tank 31 after the pump P1 is stopped from flowing into the membrane separation means 40 on the downstream side of the insolubilization tank 31 without being insolubilized. can do.

The time for which the stirrer 34 is continuously driven after the pump P1 is stopped is determined according to the amount of waste water W ₀ flowing into the waste water treatment apparatus 1 and / or the volumes of the oxidation treatment tank 21 and the insolubilization tank 31. Is done. When this time is too short, insolubilization of heavy metals in the insolubilization tank 31 is not sufficient, and overflows from the insolubilization tank 31 and flows into the membrane separation means 40 as it is. On the other hand, if this time is too long, the flocs of the insolubilized material formed in the insolubilizing tank 31 are destroyed, which is not preferable.

  In addition, this invention is not limited to the above-mentioned embodiment, The structure of the above-mentioned embodiment can be suitably changed in the range which does not deviate from the meaning of this invention.

For example, in the method described above, the pH adjustment step is performed after the membrane separation step, but the pH adjustment step may not be performed if the pH of the filtered water W ₁ is suitable for discharge into a river or the like.

Further, in the above-described method, the oxidant addition method is exemplified as the oxidation treatment method in the oxidation treatment step. However, from the viewpoint of simplicity of control and reaction rate, an oxidizing agent addition method is preferable as the oxidation treatment method.
In addition, when an oxidizing agent addition method using a chlorine-based oxidizing agent is adopted as an oxidation treatment method, odorous components such as chlorine gas or chloramine due to ammonia oxidation are generated, so gas recovery can be performed according to the generated concentration. It is desirable to do it.

The following examples and comparative examples of the present invention will be described in detail.
In Examples and Comparative Examples, wastewater containing Ni concentration of 10 mg / L was treated using the metal wastewater treatment apparatus having the above-described configuration. The inflow of raw water was 1.5 m ³ / hr, and the volume of the oxidation treatment tank and insolubilization tank was 0.2 m ³ respectively. Under these conditions, the metal wastewater treatment device was continuously operated for 30 minutes, and then repeatedly stopped after being stopped for 10 minutes. Then, the pH in the insolubilization tank is monitored by a pH meter, and during operation of the metal wastewater treatment device, a 32% sodium hydroxide solution is automatically placed in the insolubilization tank so that the environment in the insolubilization tank becomes pH 10-11. Added.

  In Example 1, after the pump on the upstream side of the storage tank was stopped, the stirring blade of the insolubilization tank was driven for 30 seconds, and in Example 2, the stirring blade of the insolubilization tank was driven for 3 minutes. On the other hand, in Comparative Example 1, after the pump on the upstream side of the storage tank was stopped, the stirring blade of the insolubilization tank was driven for 20 seconds, and in Comparative Example 2, the stirring blade of the insolubilization tank was driven for 4 minutes. As a result, the results shown in Table 2 below were obtained.

  As described above, after stopping the pump on the upstream side of the storage tank, by driving the stirring blade of the insolubilization tank for 30 seconds to 3 minutes, while keeping the pH in the insolubilization tank uniform, the flocs of the insolubilized material Was prevented from being destroyed.

1 Wastewater treatment device 21 Oxidation treatment tank 31 Insolubilization tank 34 Stirring blade 42 Membrane separation tank

Claims (5)

A pump for flowing downstream wastewater containing a heavy metal and a complex-forming compound that forms a metal complex with the heavy metal;
An oxidation treatment tank for oxidizing the complex-forming compound contained in the wastewater flowing from the pump;
An insolubilization tank for insolubilizing heavy metals contained in waste water flowing from the oxidation treatment tank, provided downstream of the oxidation treatment tank;
A membrane separation tank for downstream of the insolubilization tank, for membrane separation treatment of waste water flowing from the insolubilization tank,
A stirrer for stirring the waste water in the insolubilization tank,
The oxidation treatment tank and the insolubilization tank, and the insolubilization tank and the membrane treatment tank are arranged to be fed by an overflow mechanism, respectively.
The agitator is a wastewater treatment apparatus configured to stop after a predetermined time has elapsed since the pump stopped.   The wastewater treatment apparatus according to claim 1, wherein the predetermined time is determined according to an amount of wastewater flowing into the metal wastewater treatment apparatus.   The wastewater treatment apparatus according to claim 1, wherein the predetermined time is determined according to a volume of the oxidation treatment tank and the insolubilization tank.   The wastewater treatment apparatus according to claim 1, wherein the predetermined time is 30 seconds to 3 minutes. A wastewater treatment method for treating wastewater containing a heavy metal and a complex-forming compound that forms a metal complex with the heavy metal by a wastewater treatment apparatus,
The waste water is caused to flow into the oxidation tank by a pump that flows toward the downstream side,
Oxidizing the complex-forming compound contained in the wastewater in the oxidation treatment tank and flowing the wastewater to an insolubilization tank provided on the downstream side of the oxidation treatment tank,
Insolubilize heavy metals in wastewater in the insolubilization tank, and flow wastewater to a membrane separation tank provided on the downstream side of the insolubilization tank,
In the membrane separation tank, wastewater is subjected to membrane separation treatment,
In the insolubilization tank, a stirrer for stirring waste water is provided, and the oxidation treatment tank and the insolubilization tank, and the insolubilization tank and the membrane treatment tank are respectively fed by an overflow mechanism. Has been placed,
A wastewater treatment method, wherein when the wastewater treatment apparatus is stopped, the stirring air is stopped after a predetermined time has elapsed since the pump was stopped.

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