JP2013233483A - Wastewater treatment device and wastewater treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wastewater treatment device capable of sufficiently cleaning a hollow fiber membrane filter while preventing clogging of the hollow fiber membrane filter by insolubilized materials.SOLUTION: A wastewater treatment device 1 includes: an insolubilization-treating unit 30 for insolubilizatio-treating heavy metals contained in wastewater; and a membrane separation unit 40 provided at the downstream side of the insolubilization-treating unit 30 and filtering a wastewater Wflowing from the unit 30. A membrane module 43 for filtering the wastewater, and an air diffuser 44 for cleaning the membrane module 43 by blowing the air to the membrane module 43 are provided to the membrane separation unit 40. The air diffuser 44 blows air to the membrane module 43 only when the wastewater Wis not filtered by the membrane module 43.

Description

  The present invention relates to a wastewater treatment apparatus and a wastewater 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, for example, a waste water treatment method described in Patent Document 1 is known.

Japanese Patent Laid-Open No. 10-15551

  In the wastewater treatment method described in Patent Document 1, wastewater once stored in a storage tank is insolubilized in an insolubilization tank. Specifically, an insolubilizing agent such as a hydroxylating agent (alkali agent) or a sulfiding agent is added to the waste water to make the heavy metal insoluble material such as a hydroxide or sulfide that is hardly soluble in water. Since this insolubilized material has a small particle size, a flocculant such as an inorganic flocculant (for example, aluminum sulfate) is added to the wastewater that has been insolubilized in the aggregating tank, and the insolubilized material is aggregated to generate a floc of the insolubilized material. . Next, the waste water containing the flocs of aggregated insolubilized material is filtered through a hollow fiber membrane filter, and the filtered water is neutralized in a pH adjustment tank and then discharged as treated water. Further, an aeration tube is provided below the hollow fiber membrane filter, and the hollow fiber membrane filter is washed by so-called aeration by bubbling air from the aeration tube.

  By the way, when aeration is performed using the air discharged from the air diffuser, the air discharged from the air diffuser is applied to the surface of the membrane filter, the membrane filter is shaken, and the vibration causes the floc to fall off from the surface of the membrane filter. However, if air is continuously discharged for a long time, the air hits the flocs of the insolubilized material in the wastewater and the flocs are destroyed, and the membrane filter is clogged by the finely divided insolubilized material. On the other hand, if the aeration time is shortened in order to prevent the destruction of the floc, there arises a problem that the membrane filter cannot be sufficiently cleaned.

  Accordingly, the present invention has been made to solve the above-described problems, and is a wastewater treatment capable of sufficiently washing a hollow fiber membrane filter while preventing the hollow fiber membrane filter from being clogged with an insolubilized material. An object is to provide an apparatus and a wastewater treatment method.

  According to the experiment of the inventors of the present invention, only when the wastewater is not filtered by the hollow fiber membrane filter, by performing intermittent aeration of blowing air to the hollow fiber membrane filter, without destroying the floc, It was found that the hollow fiber membrane filter can be cleaned.

  Therefore, in order to solve the above-mentioned problems, the present invention provides an insolubilization treatment means for insolubilizing heavy metals contained in wastewater, and wastewater flowing from the insolubilization treatment means provided downstream of the insolubilization treatment means. A membrane separation means for filtering, the membrane separation means comprising: a membrane module for filtering waste water; and a washing means for washing the membrane module by blowing air to the membrane module. The cleaning means is provided so that air is blown onto the membrane module only when the wastewater is not filtered by the membrane module.

  Further, in order to solve the above-described problems, the present invention has been provided with an insolubilization treatment means for insolubilizing heavy metals contained in waste water, and downstream from the insolubilization treatment means, and has flowed from the insolubilization treatment means. A membrane separation means for filtering waste water, and the membrane separation means is provided at least one membrane module for filtering waste water, and provided below each of the at least one membrane module. At least two aeration units for blowing air to clean the membrane module, a plurality of valves coupled to each of the at least two aeration units, and a source of air coupled to the plurality of valves And at least two aeration units are only activated when the wastewater is not filtered by each membrane module That.

  According to the present invention configured as described above, it is possible to perform aeration by blowing air to the membrane module only when the wastewater is not filtered by the membrane module, and thereby the flocs generated by the insolubilization processing means. The membrane module can be cleaned without destroying. Further, by suppressing the breakage of the floc, it is possible to prevent the membrane module from being clogged by the insolubilized material that has been atomized.

  In the present invention, preferably, the membrane module is washed for 30 seconds to 300 seconds after the membrane separation means is continuously driven for 5 minutes to 20 minutes.

  Moreover, in this invention, Preferably, it has a control means which controls not to operate all the air diffusing units of at least two air diffusing units at the same time. In the present invention, it is preferable that the control means is configured to control the plurality of valves so as not to open the plurality of valves simultaneously.

  According to the present invention configured as described above, the plurality of valves are configured not to be opened at the same time so that the aeration units of the at least two aeration units are not operated at the same time. The unit can be operated intermittently. Thereby, two aeration units provided at different positions can be operated intermittently, the fixation of the water flow path caused by air is prevented, and the membrane surface cleaning effect by air is improved. In addition, the membrane module can be sufficiently cleaned even if the amount of air supplied to the entire air diffusion unit is halved due to the above effect.

  Further, in order to solve the above-described problems, the present invention has been provided with an insolubilization treatment means for insolubilizing heavy metals contained in waste water, and downstream from the insolubilization treatment means, and has flowed from the insolubilization treatment means. A membrane separation means for filtering waste water, a membrane module provided in the membrane separation means for filtering waste water, and a cleaning means for cleaning the membrane module by blowing air to the membrane module The wastewater treatment method using the wastewater treatment apparatus is characterized in that air is blown onto the membrane module by the cleaning means only when the wastewater is not filtered by the membrane module.

  In order to solve the above-described problems, the present invention provides an insolubilization process for insolubilizing heavy metals contained in wastewater, at least one membrane module for filtering wastewater, and at least one of these membrane modules. Each of the at least two air diffusion units for blowing the air to the membrane module to clean the membrane module, a plurality of valves coupled to each of the at least two air diffusion units, and the plurality of the plurality of air diffusion units. Filtering wastewater containing insolubilized material by means of membrane separation means having a supply source of air connected to a valve, wherein at least two aeration units filter wastewater through each membrane module It works only when not.

  According to the present invention configured as described above, it is possible to perform aeration by blowing air to the membrane module only when the wastewater is not filtered by the membrane module, and thereby the flocs generated by the insolubilization processing means. The membrane module can be cleaned without destroying. Further, by suppressing the breakage of the floc, it is possible to prevent the membrane module from being clogged by the insolubilized material that has been atomized.

  In the present invention, preferably, the membrane module is washed for 30 seconds to 300 seconds after the membrane separation means is continuously driven for 5 minutes to 20 minutes.

  In the present invention, it is preferable that the waste water treatment apparatus includes a control unit that controls the air diffuser units of at least two air diffuser units not to be operated simultaneously. In the present invention, it is preferable that the control means is configured to control the plurality of valves so as not to open the plurality of valves simultaneously.

According to the present invention configured as described above, the plurality of valves are configured not to be opened at the same time so that the aeration units of the at least two aeration units are not operated at the same time. The unit can be operated intermittently.
Thereby, two aeration units provided at different positions can be operated intermittently, fixing of the water flow path caused by air is prevented, and the membrane surface cleaning effect by air is improved. In addition, the membrane module can be sufficiently cleaned even if the amount of air supplied to the entire air diffusion unit is halved due to the above effect.

  As described above, according to the wastewater treatment apparatus of the present invention, the hollow fiber membrane filter can be sufficiently washed while preventing the hollow fiber membrane filter from being clogged with the insolubilized material.

1 is a schematic configuration diagram illustrating a wastewater treatment apparatus according to a first embodiment of the present invention. It is a time chart for demonstrating operation | movement of the wastewater treatment apparatus by the 1st Embodiment of this invention. It is the schematic which shows the membrane separation means of the wastewater treatment apparatus by the 2nd Embodiment of this invention. It is a perspective view which shows the diffuser of the waste water treatment apparatus by the 2nd Embodiment of this invention. It is a top view which shows a part of diffuser of the waste water treatment apparatus by the 2nd Embodiment of this invention. It is a side view which shows a part of diffuser of the waste water treatment apparatus by the 2nd Embodiment of this invention. It is a perspective view which shows the waste water treatment apparatus by the 2nd Embodiment of this invention. It is a time chart for demonstrating operation | movement of the wastewater treatment apparatus by the 2nd Embodiment of this invention. It is a time chart for demonstrating operation | movement of the wastewater treatment apparatus by the 2nd Embodiment of this 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 a wastewater treatment apparatus according to a first embodiment of the present invention. The wastewater treatment apparatus 1 of this example includes a pump P1 for flowing the wastewater W ₀ toward the downstream side in order from the upstream side, a storage unit 10 for temporarily storing the wastewater W ₀ flowing from the pump P1, and an oxidation treatment unit 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 the heavy metal in the waste water W ₀ that has been oxidized by the oxidizing means 20 to generate a floc of insolubilized material. 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 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 device 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. The membrane separation means 40 further includes a control device 46 for controlling the suction pump P2 and the blower B.

  Examples of the types of filtration membranes constituting the membrane module 43 include hollow fiber membranes, flat membranes, tubular membranes, monolithic membranes and the like used for separation operations such as water treatment. A membrane is preferred. When a hollow fiber membrane is used as the filtration membrane, examples of the material include cellulose, polyolefin, polysulfone, polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE). When a flat membrane or a monolith type membrane is used as the filtration membrane, a ceramic membrane can be used. The average pore size of the micropores formed in the filtration membrane is generally an average pore size of 0.001 to 0.1 μm for a membrane called an ultrafiltration membrane, and an average pore size of 0.1 to 1 μm for a membrane commonly called a microfiltration membrane. In the present invention, these films are preferably used. In addition, since the particle diameter of the insolubilized material produced by insolubilizing the heavy metal is generally 0.1 to 100 μm, the average pore diameter of the fine pores of the filtration membrane is preferably 0.03 μm or more. When the average pore diameter is less than 0.03 μm, the pressure required for membrane separation increases, and the operating energy becomes excessive. On the other hand, the average pore diameter of the fine pores of the filtration membrane 41 is preferably 3 μm or less. When the average pore diameter exceeds 3 μm, the ratio of heavy metal insolubilized particles leaking to the secondary side (filtered water) of the filtration membrane increases, and the metal concentration in the filtered water tends to increase.

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 diffused from the 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 rising bubbles hit the filtration membrane and shake the filtration membrane, so that the insolubilized material adhering to the filtration membrane is detached from the filtration membrane, so that the filtration membrane of the membrane module 43 can be 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 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)). Since nickel oxyhydroxide generally has a lower solubility than nickel hydroxide (Ni (OH) ₂ ), sodium hypochlorite or a solution thereof is an oxidizing agent when performing 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 processing means 30, the oxidized waste water W ₀ is transferred to the insolubilization tank 31 of the insolubilization processing means 30, and an insolubilizing agent is added to insolubilize heavy metals in the waste water W ₀ , and insolubilized heavy metal flocs are insolubilized. It produces | generates in the tank 31. FIG. 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.

In the membrane separation means 40, the waste water W ₀ in the membrane separation tank 42 is suction filtered through the pores of the filtration membrane of the membrane module 43 by the waste water suction pump P2, so that the waste water W ₀ is filtered with the filtered water W ₁ . Separated into membrane-separated concentrated water W ₂ containing insoluble matter floc. 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.

  Next, the operation of the wastewater treatment apparatus when cleaning the membrane module 43 will be described in detail.

FIG. 2 is a time chart for explaining the operation of the wastewater treatment apparatus.
As shown in FIG. 2, in the membrane separation means 40, when the waste water W ₀ is being filtered, that is, when the pump P2 is operating and the waste water W ₀ in the membrane separation tank 42 is being suction filtered, B is stopped and aeration is not performed. Then, when the waste water W ₀ is suction filtered for a predetermined time t ₁ and the floc is captured on the surface of the membrane module 43, the control device 46 once suctions and filters the waste water W ₀ by stopping the pump P2. At the same time, the blower B is operated to start aeration. As a result, air is released from the diffuser 44 toward the membrane module 43. The flocs captured on the surface of the membrane module 43 by the air from the air diffuser 44 are released from the surface of the membrane module 43. After aeration for a predetermined time t ₂ , the controller 46 stops the aeration by stopping the blower B, and at the same time, operates the pump P2 to resume the suction filtration of the waste water W ₀ .

If the time t ₁ for performing the suction filtration is too short, the filtration time of the waste water W ₀ is shortened and the treatment efficiency of the waste water treatment apparatus 1 is lowered. The filtration efficiency of module 43 will fall. According to experiments by the inventors, the time t ₁ for performing suction filtration is preferably about 5 to 20 minutes. Further, if the time t _{2 for} aeration is too short, the membrane module 43 cannot be sufficiently washed. If it is too long, the flocs captured by the membrane module 43 are destroyed by air, so that the insolubilized material that has been atomized As a result, the membrane module 43 is easily clogged. According to experiments by the inventors, the time t _{2 for} aeration is preferably about 30 seconds to 300 seconds. The time t ₁ for performing suction filtration and the time t ₂ for performing aeration are preferably proportional to each other within the above-described range. If the time t ₁ for performing suction filtration is short, the time t ₂ for performing aeration is shortened. On the other hand, if the time t ₁ for performing suction filtration is long, it is preferable to lengthen the time t ₂ for performing aeration.

As described above, membranes in separation means 40, by the range time t ₂ of a given aeration for washing the membrane module 43, while thoroughly washed membrane module 43, floc insolubles air It can be prevented from being destroyed by. By preventing the flocs of the insolubilized material from being destroyed, the insolubilized material can be prevented from becoming fine particles in the membrane separation tank 42, thereby preventing the membrane module 43 from being clogged. Can do. In the case of using a hollow fiber membrane module as a membrane module 43, can be hollow fiber membranes in contact with the hollow fiber membranes to each other by a time t ₂ the aeration within a predetermined range is prevented from being damaged . Further, by limiting the time t ₂ of the aeration, it is possible to suppress energy used during aeration.

  Next, a wastewater treatment apparatus according to the second embodiment of the present invention will be described in detail. Since the wastewater treatment apparatus according to the second embodiment has the same configuration as that of the wastewater treatment apparatus according to the first embodiment, in the following description, configurations that are mainly different will be described in detail. Specifically, the wastewater treatment apparatus according to the first embodiment and the wastewater treatment apparatus according to the second embodiment mainly differ in the configuration of the membrane separation means and the operation when washing the membrane module.

  FIG. 3 is a schematic view showing membrane separation means of the wastewater treatment apparatus according to the second embodiment, FIG. 4 is a perspective view showing the air diffuser, and FIG. 5 shows a part of the air diffuser. FIG. 6 is a top view, and FIG. 6 is a side view showing a part of the air diffuser.

  As shown in FIGS. 3 and 4, the air diffuser is connected to the air diffuser 44 and the blower B, and is provided with a first air supply pipe 61 and a second air supply that are provided one by one along the vertical direction. A pipe 62 and a first air branch pipe 63 in the form of a square pipe connected along the horizontal direction and connected to the end of the first air supply pipe 61 and a lower end of the second air supply pipe 62 and connected in the horizontal direction And a second air branch pipe 64 in the form of a square pipe. The air diffuser 44 is connected to the first air diffuser 65 having two or more linear first air diffusers 65 a connected to the first air branch 63 and the second air branch 64. A second air diffusion unit 66 having two or more linear second air diffusion tubes 66a.

  5 and 6, the first air diffuser 65a of the air diffuser 44 extends horizontally from the first air branch pipe 63 toward the second air branch pipe 64, and the second air diffuser 66a is The second air branch pipe 64 extends horizontally toward the first air branch pipe 63. The first air diffuser 65a and the second air diffuser 66a are alternately arranged in parallel at regular intervals, and a gap A is formed between the first air diffuser 65a and the second air diffuser 66a. The first air diffusion pipe 65a is fixed to the first air branch pipe 63 and the second air branch pipe 64 and communicates with the inside of the first air branch pipe 63. There is no communication with the inside. The second air diffusion pipe 66a is fixed to the first air branch pipe 63 and the second air branch pipe 64 and communicates with the inside of the second air branch pipe 64. There is no communication with the inside. Further, the first air diffuser 65a and the second air diffuser 66a are respectively formed with air diffuser holes 65b and 66b that open upward. The diameter and number of the diffuser holes 65b and 66b may be appropriately selected so as to be sufficiently washed according to the size, type, etc. of the module constituting the membrane unit 43.

  The air diffuser having such a structure supplies the air supplied from the blower B to the first air diffuser 65a through the first air supply pipe 61 and the first air branch pipe 63, or the second. The air is supplied to the second air diffuser 66a through the air supply pipe 62 and the second air branch pipe 64.

  A switching valve 71 is provided between the first air branch pipe 63 and the second air branch pipe 64 and the blower B. The switching valve 71 includes a valve 71 a provided in the first air supply pipe 61 and a valve 71 b provided in the second air supply pipe 62. The switching valve 71 (71a and 71b) is composed of, for example, a rotary valve or a reciprocating valve, and the air from the blower B and the first air supply pipe 61 are controlled by control by a control means (not shown). Switching is performed so that only one of the second air supply pipes 62 is supplied. Thereby, the air from the blower B is supplied from only one of the first air diffuser 65a and the second air diffuser 66a. The switching valve 78 may be constituted by two valves 71a and 71b, or may be constituted by one valve.

FIG. 7 is a perspective view showing the membrane unit 43. As shown in FIG. 7, the membrane unit 43 includes a large number of flat membrane modules 71, and a water collection header pipe 72 that is connected to the membrane module 71 and collects water that has passed through the membrane module 71. Yes. The membrane modules 71 are arranged in parallel at regular intervals so that the membrane surfaces adjacent to each other face each other. Each membrane module 71 includes a plurality of membrane sheets 71a having membrane surfaces 71a ₁ extending in the vertical direction, a membrane sheet upper end fixing portion 71b that fixes the upper end of the membrane sheet 71a, and a membrane sheet lower end that fixes the lower end of the membrane sheet 71a. and a fixing portion 71c, in which the film surface 71a ₁ of each membrane sheet 71a is arranged so as to be flush. The membrane sheet 71a in the present embodiment is formed by arranging a large number of hollow fiber membranes having a large number of fine holes formed on the surface thereof in parallel with each other. Examples of the material of the hollow fiber include cellulose, polyolefin, polysulfone, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), and ceramics. Each membrane module 71 is positioned with respect to the air diffuser 44 so as to cross over the gap A of the air diffuser 44, and the number of the membrane modules 71 is the same as that of the first air diffuser 65a and the second air diffuser 66a. It is less than the total number.

  The inside of the water collection header pipe 72 of the membrane unit 43 and the inside of the membrane sheet upper end fixing portion 71b are hollow and communicate with the hollow portion of each hollow fiber membrane. Therefore, the filtered water that has been filtered and entered the hollow portion of the hollow fiber membrane is collected in the water collection header pipe 72 through the inside of the membrane sheet upper end fixing portion 71b.

  Next, the operation of the wastewater treatment apparatus when cleaning the membrane module 43 will be described in detail.

8 and 9 are time charts for explaining the operation of the wastewater treatment apparatus.
As shown in FIG. 8, in the membrane separation means 40, when the waste water W ₀ is being filtered, that is, when the pump P2 is operating and the waste water W ₀ in the membrane separation tank 42 is being suction filtered, B is stopped and aeration is not performed. Then, when the waste water W ₀ is suction filtered for a predetermined time t ₁ and the floc is captured on the surface of the membrane module 43, the control device 46 of the waste water treatment apparatus 1 once sucks the waste water W ₀ by stopping the pump P 2. Filtration is stopped, and the blower B is started almost simultaneously with this, and the aeration device 44 performs aeration for a predetermined time t ₂ . Thereby, air is discharged from the diffuser 44 toward the membrane module 43.

When aeration is performed, the control means opens one of the valves 71a or 71b and closes the other so that air is supplied from one of the first air supply pipe 61 and the second air supply pipe 62. To. In this control, as shown in FIG. 8, for example, closing the valve 71a after the air has been supplied from the time by opening the valve 71a t ₂ by a first air supply pipe 61, filtered by the predetermined time t ₁ is carried out, Thereafter, air is supplied from the time t ₂ by a second air supply pipe 62 by opening the valve 71b. Further, as shown in FIG. 9, the control means switching the bubble 71a, and 71b during time t _2, by supplying air from the first air supply pipe 61 by half the time t2, only the remaining half second air Air may be supplied from the supply pipe 73. The flocs captured on the surface of the membrane module 43 by the air from the air diffuser 44 are released from the surface of the membrane module 43. Then, after aeration for a predetermined time t ₂ , the wastewater treatment apparatus 1 stops the aeration by stopping the blower B, and at the same time, operates the pump P2 to resume the suction filtration of the wastewater W ₀ .

Further, in the example of FIG. 8 and FIG. 9, although the filtration time t ₁ and aeration time t ₂ is adjusted so as not to overlap, if necessary, with overlapping and filtration time t ₁ and aeration time t ₂ Further, filtration and aeration may be performed simultaneously.

If the time t ₁ for performing the suction filtration is too short, the filtration time of the waste water W ₀ is shortened and the treatment efficiency of the waste water treatment apparatus 1 is lowered. The filtration efficiency of module 43 will fall. According to experiments by the inventors, the time t ₁ for performing suction filtration is preferably about 5 to 20 minutes. Further, if the time t _{2 for} aeration is too short, the membrane module 43 cannot be sufficiently washed. If it is too long, the flocs captured by the membrane module 43 are destroyed by the air, and the insolubilized material that has been atomized As a result, the membrane module 43 is easily clogged. According to experiments by the inventors, the time t _{2 for} aeration is preferably about 30 seconds to 300 seconds. The time t ₁ for performing suction filtration and the time t ₂ for performing aeration are preferably proportional to each other within the above-described range. If the time t ₁ for performing suction filtration is short, the time t ₂ for performing aeration is shortened. On the other hand, if the time t ₁ for performing suction filtration is long, it is preferable to lengthen the time t ₂ for performing aeration.

  As described above, in the membrane separation means 40, the aeration unit used for aeration can be switched by switching the valve 71, so that each aeration unit can be operated intermittently.

In addition, by setting the aeration time t ₂ for cleaning the membrane module 43 within a predetermined range, it is possible to prevent the flocs of the insolubilized material from being destroyed by air while sufficiently cleaning the membrane module 43. Can do. By preventing the flocs of the insolubilized material from being destroyed, the insolubilized material can be prevented from becoming fine particles in the membrane separation tank 42, thereby preventing the membrane module 43 from being clogged. Can do. In the case of using a hollow fiber membrane module as a membrane module 43, can be hollow fiber membranes in contact with the hollow fiber membranes to each other by a time t ₂ the aeration within a predetermined range is prevented from being damaged . Further, by limiting the time t ₂ of the aeration, it is possible to suppress energy used during aeration.

  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.

Further, the membrane sheet 21a in the wastewater treatment apparatus according to the second embodiment is not limited to one in which the hollow fiber membranes are arranged in parallel to each other, and if the membrane sheet 21a is provided with a filtration membrane having a large number of fine holes, for example Various known separation membranes such as flat membrane type, tubular membrane type, and bag-like membrane type can be applied. Moreover, the air diffusion holes 65b and 66b of the first air diffusion pipe 65a and the second air diffusion pipe 66a may be formed so as to open downward. In the above-described embodiment, the first air diffuser 65a of the first air diffuser unit 65 and the second air diffuser 66a of the second air diffuser 66 are alternately arranged. However, the present invention is not limited to this arrangement. For example, some of the bubbles ejected from the outermost to the arranged diffusing pipe in the air diffuser apparatus will be away from the membrane module 71, the outermost cleaning of the membrane surface 71a ₁ of the membrane module 71 that is insufficient is there. Therefore, the air diffuser pipe disposed on the outermost side in the air diffuser 44 may be a different air diffuser unit from the first air diffuser unit 65 and the second air diffuser unit 66 so as to continuously eject bubbles. . If continuously jetting bubbles, even if some bubbles away from the membrane module 71, most cleaning of outer membrane surface 71a ₁ of the membrane module is less likely to decrease.
Further, the second diffuser 66a (or first diffuser 65a) may be disposed adjacent to the outermost first diffuser 65a (or second diffuser 66a). In this case, the outermost membrane surface 71a ₁ of the membrane module 71 comes in contact with the air bubbles ejected from the first air diffuser 65a and the air bubbles ejected from the second air diffuser 66a alternately. Therefore, an effect similar to that of continuously ejecting bubbles from the outermost diffuser tube is obtained.

  In the air diffuser 44, the number of the first air supply pipes 61 and the number of the second air supply pipes 62 may be two each. In that case, a first air branch pipe 63 is connected to each of the two first air supply pipes 61, and a second air branch pipe 64 is connected to each of the two second air supply pipes 62. Further, both ends of each first air diffusion pipe 65a are connected to two first air branch pipes 63, and the inside of each first air diffusion pipe 65a and each first air branch pipe 63 communicates with each other. The first air diffusion pipe 65a does not communicate with the second air branch pipe 66 inside. Both ends of each second air diffuser 66a are connected to two second air branch pipes 64, and each second air diffuser 66a and each second air branch pipe 64 communicate with each other. The second air diffusing pipe 66a does not communicate with the first air branch pipe 63 inside. In the air diffuser 44, the air supplied from the first air supply pipe 61 passes through each first air branch pipe 63 and is supplied to the first air diffuser pipe 65a from both ends thereof. The air supplied from the second air supply pipe 62 passes through each second air branch pipe 64 and is supplied to the second air diffusion pipe 66a from both ends thereof.

  Further, the first air branch pipe 63 and the second air branch pipe 64 may not be a square pipe shape, but may be a cylindrical shape or the like. The air diffusing device 44 has two air diffusing units, but may have three or more air diffusing units. Further, the air diffuser is not linear, and may be curved, bent, or serpentine, for example. Further, the diffuser tubes may not be arranged in parallel to each other. Furthermore, the air diffuser does not necessarily have to be arranged horizontally. Moreover, the diffuser tube adjacent to each other may be the same diffuser unit.

Hereinafter, examples and comparative examples of the wastewater treatment apparatus according to the first embodiment of the present invention will be described.
In the following Examples 1 and 2 and Comparative Examples 1 to 5, an aqueous sodium hydroxide solution adjusted to 0.1 mol / l as an insolubilizing agent was added to waste water containing 10 mg / l Ni, so that the pH of the waste water was 10 Adjusted. Ten hollow fiber membranes made of polyvinylidene fluoride ("Sterapore SADF" (nominal pore diameter 0.4 µm, membrane area 10 m ² ) manufactured by Mitsubishi Rayon Co., Ltd.) were prepared. The above waste water was subjected to membrane separation treatment at 4 m ³ / m ² / day, an aeration tube was placed below the hollow fiber membrane, air was flowed at a flow rate of 45 m ³ / hr, and aeration was performed. When t ₁ and aeration time t ₂ were adjusted and continuous operation was performed for 10 days, the results shown in Table 1 were obtained.

  In Example 1 and Example 2, the increase rate of the differential pressure between the hollow fiber membranes was 0.03 kPa / day or less, and a stable operation could be performed.

On the other hand, in Comparative Examples 1 to 3, the increase rate of the differential pressure between the hollow fiber membranes was 0.5 kPa / day or more, and clogging of the hollow fiber membranes was noticeable. In Comparative Example 4, the rate of increase in the differential pressure between the hollow fiber membranes was 0.03 kPa / day or less, but the ratio between the filtration time t ₁ and the aeration time t ₂ was 1: 1. The amount of wastewater filtered has decreased. In Comparative Example 5, filtration was continued for 7 minutes and filtration was stopped for 1 minute in Comparative Example 5, but aeration was continuously performed (that is, aeration was performed during filtration and during filtration stop). As a result, although the rate of increase in the differential pressure was 0.03 kPa or less, the electrical cost of the aeration blower increased, and the contact between the hollow fiber membranes became excessive, resulting in increased membrane damage. .

Next, examples and comparative examples of the wastewater treatment apparatus according to the second embodiment will be described.
In the following examples and comparative examples, the pH of the wastewater was adjusted to 10 by adding an aqueous sodium hydroxide solution adjusted to 0.1 mol / l as an insolubilizer to wastewater containing 10 mg / l of Ni. Ten hollow fiber membranes made of polyvinylidene fluoride ("Sterapore SADF" (nominal pore diameter 0.4 µm, membrane area 10 m ² ) manufactured by Mitsubishi Rayon Co., Ltd.) were prepared. The above-mentioned waste water was subjected to membrane separation treatment at 4 m ³ / m ² / day, and two sets of air diffusion units (first air supply pipe and second air supply pipe) were arranged below the hollow fiber membrane, 22. 5 m ³ / hr flow rate flowing air in a, was aerated. aeration cycle was carried out aeration in cycle shown in FIG. that is the air in the first air supply pipe by the time the first half half of aeration time t ₂ The air was supplied to the second air supply pipe during the second half of t ₂ , and the filtration time t ₁ and the aeration time t ₂ were adjusted to perform continuous operation for 10 days. The second embodiment was obtained. By using the waste water treatment apparatus according to, it was possible to continue the filtration operation was stable and an air volume of to half compared with the case of the "first embodiment wastewater treatment device according to."

DESCRIPTION OF SYMBOLS 1 Waste water treatment apparatus 21 Oxidation treatment tank 31 Insolubilization tank 34 Stirring blade 42 Membrane separation tank 44 Aeration apparatus B Blower

Claims (10)

Insolubilization means for insolubilizing heavy metals contained in wastewater;
Provided on the downstream side of the insolubilization treatment means, and a membrane separation means for filtering waste water flowing from the insolubilization treatment means,
The membrane separation means is provided with a membrane module for filtering waste water, and a cleaning means for cleaning the membrane module by blowing air to the membrane module,
The waste water treatment apparatus, wherein the cleaning means blows air to the membrane module only when waste water is not filtered by the membrane module. Insolubilization means for insolubilizing heavy metals contained in wastewater;
A membrane separation means provided on the downstream side of the insolubilization treatment means for filtering waste water flowing from the insolubilization treatment means,
The membrane separation means comprises at least one membrane module for filtering waste water,
At least two aeration units each provided below the at least one membrane module, for blowing the air to the membrane module to clean the membrane module;
A plurality of valves coupled to each of the at least two aeration units;
An air supply connected to the plurality of valves,
A wastewater treatment device, wherein at least two aeration units are adapted to operate only when the wastewater is not filtered by each membrane module.   The wastewater treatment apparatus according to claim 1 or 2, wherein the membrane module is washed for 30 seconds to 300 seconds after the membrane separation means is continuously driven for 5 minutes to 20 minutes.   The wastewater treatment apparatus according to claim 2, further comprising control means for controlling not to operate all the air diffuser units of at least two air diffuser units at the same time.   The waste water treatment apparatus according to claim 4, wherein the control means is configured to control the plurality of valves so as not to open the plurality of valves simultaneously. An insolubilization treatment means for insolubilizing heavy metals contained in wastewater, a membrane separation means provided on the downstream side of the insolubilization treatment means for filtering wastewater flowing from the insolubilization treatment means, and provided in the membrane separation means A wastewater treatment method using a wastewater treatment apparatus comprising: a membrane module for filtering wastewater; and a cleaning means for spraying air to the membrane module to wash the membrane module,
A wastewater treatment method, wherein air is blown onto the membrane module by the cleaning means only when the wastewater is not filtered by the membrane module. An insolubilization process for insolubilizing heavy metals contained in wastewater;
At least one membrane module for filtering waste water, at least two aeration units each provided below the at least one membrane module, for blowing the air to the membrane module to wash the membrane module, at least two of these A wastewater treatment method comprising: a plurality of valves coupled to each of the two aeration units; and a step of filtering wastewater containing insolubilized matter by a membrane separation means having an air supply source coupled to the plurality of valves. There,
The wastewater treatment method, wherein at least two aeration units are adapted to operate only when the wastewater is not filtered by each membrane module.   The wastewater treatment method according to claim 6 or 7, wherein the membrane module is washed for 30 seconds to 300 seconds after the membrane separation means is continuously driven for 5 minutes to 20 minutes.   The wastewater treatment method according to claim 7, wherein the wastewater treatment apparatus includes a control unit that performs control so that all of the aeration units of at least two aeration units are not simultaneously operated.   The waste water treatment apparatus according to claim 4, wherein the control means is configured to control the plurality of valves so as not to open the plurality of valves simultaneously.

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