JP6735830B2 - Membrane filtration method and membrane filtration system - Google Patents

Description

TECHNICAL FIELD The present invention relates to a technique of a membrane filtration method and a membrane filtration system.

Conventionally, wastewater treatment is known in which an organic flocculant is added to water to be treated to perform flocculation and sedimentation treatment or pressure floating treatment (see, for example, Patent Document 1).

JP, 11-57313, A

By the way, if ultrafiltration membranes or microfiltration membranes are used for treated water obtained by coagulation sedimentation treatment using an organic coagulant or pressure flotation treatment, the surface of the membrane is contaminated and pores are blocked. A phenomenon of fouling (fouling) may occur. Therefore, an object of the present disclosure is to suppress the fouling of the ultrafiltration membrane or the microfiltration membrane with respect to the treated water obtained by the flocculation-precipitation treatment or the pressure flotation treatment using an organic flocculant, and perform stable operation. It is to provide a membrane filtration method and a membrane filtration system that enable the above.

(1) One aspect of the present embodiment is to add an inorganic coagulant to treated water obtained by adding an organic coagulant to the water to be treated to perform coagulation sedimentation treatment or coagulation pressurization floating treatment, and then use an ultrafiltration membrane. A membrane filtration method for performing at least one of membrane treatment and microfiltration membrane treatment , wherein the organic flocculant is a polyacrylamide flocculant, a polysulfonic acid flocculant, or a polyacrylic acid flocculant. At least one of a polyacrylic acid ester-based coagulant, a polyamine-based coagulant, and a polymethacrylic acid coagulant .

(2) In the membrane filtration method described in the above (1), during the membrane filtration process, or to impart a shearing force by stirring at a stirring speed 200~1000rpm using a stirrer to pair with the treated water It is preferable that at least one of adding an oxidant to the treated water is performed so that the average molecular weight of the organic coagulant in the treated water is not more than the molecular weight cutoff of the membrane used in the membrane filtration treatment. ..

(3) In the membrane filtration method according to (1) or (2), the amount of the inorganic flocculant added is 0 with respect to the concentration (mg/L) of the organic flocculant in the water to be treated. It is preferably in the range of 0.5 to 75 times.

(4) In the membrane filtration method according to any one of (1) to (3) above, an addition amount of the inorganic coagulant in treated water subjected to the coagulation sedimentation treatment or the coagulation pressurization floating treatment is LC- It is preferable to control according to the concentration of the high molecular weight organic substance detected by OCD.

(5) In the membrane filtration method according to any one of (1) to (4) above, after the membrane-treated water is treated with at least one of activated carbon treatment and reverse osmosis membrane treatment. Treatment is preferred.

(6) In the membrane filtration method according to any one of (1) to (5) above, the Langerlia index (LSI) of the treated water is set to be less than 0 during the membrane filtration treatment. It is preferable to adjust the pH of the treated water.

(7) One aspect of the present embodiment is an inorganic coagulant adding means for adding an inorganic coagulant to the treated water obtained by adding an organic coagulant to the water to be treated to perform coagulation sedimentation treatment or coagulation pressurization floating treatment. , Having at least one of an ultrafiltration membrane and a microfiltration membrane, comprising a membrane filtration treatment means for subjecting the treated water to which the inorganic flocculant has been added to a membrane filtration treatment, to the organic flocculant, Membrane filtration system which is at least one of polyacrylamide type coagulant, polysulfonic acid type coagulant, polyacrylic acid type coagulant, polyacrylic acid ester type coagulant, polyamine type coagulant, polymethacrylic acid coagulant Is.

(8) In the membrane filtration system according to the above (7), a shearing force imparting means for agitating the treated water at a stirring speed of 200 to 1000 rpm to impart a shearing force to the treated water, and the treatment. An average molecular weight of the organic coagulant in the treated water is provided by at least one of oxidant addition means for adding an oxidant to water, and by at least one of imparting the shearing force and adding the oxidant. Is preferably not more than the molecular weight cutoff of the membrane used in the membrane filtration treatment.

(9) In the membrane filtration system according to (7) or (8), the amount of the inorganic flocculant added is 0 with respect to the concentration (mg/L) of the organic flocculant in the water to be treated. It is preferably in the range of 0.5 to 75 times.

(10) In the membrane filtration system according to any one of (7) to (9) above, there is a post-treatment means for performing a post-treatment on the treated water subjected to the membrane filtration treatment, and the post-treatment means is It is preferable to provide at least one of the activated carbon treatment means and the reverse osmosis membrane treatment means.

(11) In the membrane filtration system according to any one of (7) to (10), during the membrane filtration treatment, the Langeria index (LSI) of the treated water may be less than 0. It is preferable to provide a pH adjusting means for adjusting the pH of the treated water.

According to the membrane filtration method and the membrane filtration system according to the present embodiment, fouling of the ultrafiltration membrane or the microfiltration membrane with respect to the treated water obtained by the coagulation sedimentation treatment using the organic coagulant or the pressure floating treatment. It suppresses the noise and enables stable operation.

It is a schematic diagram which shows an example of a structure of the processing system which concerns on this embodiment. It is a schematic diagram which shows an example of a structure of the processing system which concerns on other embodiment. It is a schematic diagram which shows an example of a structure of the processing system which concerns on other embodiment. It is a schematic diagram which shows an example of a structure of the processing system which concerns on other embodiment. It is a schematic diagram which shows an example of a structure of the processing system which concerns on other embodiment. It is a schematic diagram which shows the structure of the processing system in a reference example. Is a graph showing the results of filtration resistance to filtration rate of the membrane filtration apparatus in Examples 1-2, and Comparative Examples ^{1~2 (m 3 / m 2)} (1 / m). Is a graph showing the results of filtration resistance to filtration rate of the membrane filtration apparatus in Embodiment 3 and Comparative Example ^{3 (m 3 / m 2)} (1 / m). It is a figure which shows the result of the filtration resistance (1/m) with respect to the filtration amount (m< ³ >/m< ² >) of the membrane filtration apparatus in Example 4 and Comparative Example 4.

Hereinafter, embodiments of the present invention will be described. The present embodiment is an example for carrying out the present invention, and the present invention is not limited to this embodiment.

FIG. 1 is a schematic diagram showing an example of the configuration of a processing system according to this embodiment. The processing system 1 shown in FIG. 1 includes a coagulating sedimentation system and a membrane filtration system. The coagulation sedimentation system includes a first coagulation reaction tank 10, an organic coagulant addition line 12, and a coagulation sedimentation tank 14. The membrane filtration system includes an inorganic flocculant addition device 15 as an example of an inorganic flocculant addition means, an inorganic flocculant addition line 16, a second flocculation reaction tank 18, and a membrane filtration device 20 as an example of a membrane filtration treatment means. Equipped with.

A treated water pipe 22 is connected to the inlet of the first flocculation reaction tank 10. Further, one end of the connection pipe 24a is connected to the outlet of the first coagulation reaction tank 10, the other end is connected to the inlet of the coagulation sedimentation tank 14, one end of the connection pipe 24b is connected to the exit of the coagulation sedimentation tank 14, and the like. The end is connected to the inlet of the second flocculation reaction tank 18, one end of the connection pipe 24c is connected to the outlet of the second flocculation reaction tank 18, and the other end is connected to the inlet of the membrane filtration device 20. A treated water pipe 26 is connected to the outlet of the membrane filtration device 20. The organic flocculant addition line 12 is connected to the first flocculation reaction tank 10. Further, one end of the inorganic coagulant addition line 16 is connected to the inorganic coagulant addition device 15, and the other end is connected to the second coagulation reaction tank 18.

The inorganic coagulant addition device 15 is composed of, for example, a tank that stores the inorganic coagulant, a pump that discharges the inorganic coagulant, a valve, and the like. The inorganic coagulant supplied from the inorganic coagulant addition device 15 is supplied to the second coagulation reaction tank 18 through the inorganic coagulant addition line 16. Examples of the inorganic flocculant used in the present embodiment include polyaluminum chloride (PAC), sulfuric acid band, ferric chloride, ferric sulfate, aluminum chloride, aluminum sulfate and the like.

The organic coagulant used in the present embodiment includes polyacrylamide coagulant, polysulfonic acid coagulant, polyacrylic acid coagulant, polyacrylic acid ester coagulant, polyamine coagulant, polymethacrylic acid coagulant, etc. Examples thereof include high-molecular coagulants, low-molecular coagulants (coagulants) such as surfactants, and the like. The organic flocculant is supplied to the first flocculation reaction tank 10 through an organic flocculant addition line 12 from, for example, an organic flocculant addition device (not shown).

The membrane filtration device 20 may include at least one of a UF membrane device including an ultrafiltration membrane and an MF membrane device including a microfiltration membrane. The UF membrane device and the MF membrane device are composed of, for example, at least one module in which an ultrafiltration membrane or a microfiltration membrane is housed in a sealable container. The shape of the ultrafiltration membrane or the microfiltration membrane is not particularly limited, and examples thereof include a hollow fiber membrane, a tubular membrane, a flat membrane, and a spiral. As the water-passing method of the membrane filtration device 20, any water-passing method such as an internal pressure type or an external pressure type can be applied, and any filtering method such as cross-flow filtration or dead end filtration can be applied.

The material of the ultrafiltration membrane or the microfiltration membrane is, for example, an organic membrane such as polyvinylidene fluoride (PVDF), polyvinyl chloride (PVC), polyether sulfone (PES), cellulose acetate (CA), or an inorganic ceramic material. Examples include membranes.

The molecular weight cutoff of the ultrafiltration membrane is, for example, in the range of 5,000 to 360,000, preferably in the range of 10,000 to 360,000. The pore size of the ultrafiltration membrane is, for example, in the range of 0.01 to 0.1, preferably 0.01 to 0.03. The pore size of the microfiltration membrane is, for example, in the range of 0.1 to 0.5, preferably 0.1 to 0.2.

The water to be treated in the treatment system 1 is not particularly limited and is, for example, raw water containing impurities such as suspended substances and scale components such as calcium. Specifically, industrial wastewater (for example, Plating system drainage, etc.), tap water, ground water (eg, well water, spring water, underground water, etc.), surface water (eg, river water, lake water, etc.), etc.

An example of the operation of the processing system 1 of this embodiment will be described.

The water to be treated is supplied to the first coagulation reaction tank 10 through the water to be treated 22 and the organic coagulant is supplied to the first coagulation reaction tank 10 from the organic coagulant addition line 12. In the first flocculation reaction tank 10, the stirrer 28a stirs the water to be treated and the organic coagulant to flocculate impurities such as suspended substances in the water to be treated. Then, the water to be treated containing the organic flocculant is supplied to the flocculation sedimentation tank 14 through the connection pipe 24a, and impurities such as flocculated suspended substances are precipitated as sludge.

The supernatant liquid is supplied to the second agglutination reaction tank 18 as the treated water subjected to the agglomeration and sedimentation treatment through the connection pipe 24b. Further, the inorganic coagulant is supplied from the inorganic coagulant addition device 15 to the second coagulation reaction tank 18 through the inorganic coagulant addition line 16. In the second flocculation reaction tank 18, the treated water and the inorganic flocculant are stirred by the stirrer 28b to bring the organic flocculant and the inorganic flocculant remaining in the treated water into contact with each other. The treated water to which the inorganic coagulant has been added is introduced into the membrane filtration device 20 through the connection pipe 24c. The impurities in the treated water are captured by the ultrafiltration membrane or the microfiltration membrane in the membrane filtration device 20, and the treated water from which the impurities have been removed is discharged from the treated water pipe 26. The treated water thus obtained is used, for example, as cleaning water for food processing factories, chemical factories, semiconductor factories, machine factories and the like.

The membrane filtration device 20 is regularly backwashed with treated water or the like obtained by the membrane filtration treatment, and the impurities accumulated on the membrane surface are discharged out of the system together with the backwash drainage, or the coagulating sedimentation tank 14 Is sent to. The backwash wastewater is aggregated because of the fact that suspended substances in the backwash wastewater can be separated by sedimentation and the water recovery rate (treated water quantity/supply water quantity, which reduces the water recovery rate when discharged outside the system). The liquid is preferably sent to the settling tank 14.

Usually, when treated water containing an organic flocculant is subjected to a membrane filtration treatment with an ultrafiltration membrane, a microfiltration membrane, or the like, the organic flocculant is deposited on the membrane surface, and fouling of the membrane is easily caused. However, in the present embodiment, by bringing the inorganic flocculant into contact with the organic flocculant, the inorganic flocculant is attached on the organic flocculant, and the organic flocculant is a form that is difficult to attach to the film surface, Alternatively, it is considered that the film has changed to a form that is easily peeled off from the film surface by backwashing or the like. Therefore, by performing the membrane filtration treatment with the addition of the inorganic flocculant, the fouling of the membrane can be suppressed and the stable operation can be performed, as compared with the case of performing the membrane filtration treatment without adding the inorganic flocculant. By the way, in the coagulation-sedimentation treatment using an organic coagulant, it is possible to coagulate and sediment by adding an inorganic coagulant together with an organic coagulant. Since a certain amount of the organic flocculant (for example, the organic flocculant to which the inorganic flocculant is not attached) remains, the inorganic flocculant is added to the treated water that has been subjected to the coagulation sedimentation treatment as in this embodiment. It is difficult to sufficiently suppress fouling of the membrane, and it is difficult to perform stable treatment, as compared with the method of performing membrane filtration treatment.

The addition amount of the inorganic coagulant is not particularly limited as long as it can suppress the fouling of the film, but for example, the concentration of the organic coagulant in the water to be treated (mg/L) It is preferably in the range of 0.5 times to 75 times, and more preferably in the range of 0.5 times to 2.5 times from the viewpoint of economy. When the amount of the inorganic flocculant added is less than 0.5 times, it is considered that the fouling of the membrane cannot be suppressed, and when it exceeds 75 times, the filtration resistance due to the flocs derived from the inorganic flocculant is considered to increase. Therefore, when the above range is satisfied, the fouling of the film can be effectively suppressed as compared with the case where the above range is not satisfied.

In the present embodiment, the treated water obtained by the coagulating sedimentation treatment using the organic coagulant has been described as an example, but the same effect can be obtained even by the treated water obtained by the coagulating pressure flotation treatment using the organic coagulant. To be The aggregation pressure floating process is, for example, a conventionally known pressure floating process (see, for example, Japanese Patent No. 5239653).

From the viewpoint of increasing the contact rate between the organic coagulant and the inorganic coagulant, it is desirable to provide a coagulation reaction tank (second coagulation reaction tank 18 shown in FIG. 1), but from the viewpoint of reducing the installation space, etc. As in the processing system 2 shown in FIG. 2, the aggregation reaction tank may not be installed, and the inorganic coagulant addition line 16 may be installed in the connection pipe 24b so that the inorganic coagulant is line-injected. ..

FIG. 3 is a schematic diagram showing an example of the configuration of a processing system according to another embodiment. In the processing system 3 shown in FIG. 3, the same components as those in the processing system 1 shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted. The treatment system 3 shown in FIG. 3 is configured such that an oxidant is added to the treated water that has been subjected to the coagulation sedimentation treatment (or the coagulation pressurization floating treatment) during the membrane filtration treatment. Specifically, the processing system 3 shown in FIG. 3 includes an oxidant addition device 29 as an oxidant addition means and an oxidant addition line 30, and the oxidant passes from the oxidant addition device 29 through the oxidant addition line 30. , To the second agglutination reaction tank 18. The oxidant may be added by the line injection shown in FIG.

When a polymer flocculant such as a polyacrylamide flocculant is used as the organic flocculant, the average molecular weight (weight average molecular weight or number average molecular weight) of the organic flocculant is usually the ultrafiltration in the latter stage. It is larger than the molecular weight cut-off of the membrane or microfiltration membrane. Therefore, if the organic coagulant having a molecular weight larger than the cut-off molecular weight of the membrane remains in the treated water, it will affect the fouling of the membrane. The molecular weight cutoff is determined from the molecular weight corresponding to a rejection of 90% by allowing a standard substance having a known molecular weight to permeate. For example, for an ultrafiltration membrane or a microfiltration membrane with a molecular weight cutoff of 5,000. Then, if treated water containing a polymer coagulant having a molecular weight of more than 5,000 is passed, 90% or more of the polymer coagulant is captured.

Therefore, in the treatment system 3 shown in FIG. 3, during the membrane filtration treatment, an oxidizing agent is added to the treated water to break the molecular chains of the organic coagulant, and the molecular weight of the organic coagulant is ultrafiltered. The molecular weight is less than or equal to the molecular weight cut-off of the membrane or microfiltration membrane, preferably smaller than the molecular weight cut-off. As a result, a part of the organic coagulant is not captured by the membrane and passes through the membrane together with the treated water, so that it is possible to further suppress the fouling of the membrane as compared with the addition of only the inorganic coagulant. ..

The oxidizing agent is, for example, sodium hypochlorite, an alkali metal hypochlorite such as potassium hypochlorite, calcium hypochlorite, an alkaline earth metal hypochlorite such as barium hypochlorite, Other lithium chlorite, sodium chlorite, potassium chlorite, etc., alkali metal chlorite, calcium chlorite, barium chlorite, etc., alkaline earth metal chlorite, nickel chlorite, etc. And chlorite alkali metal salts such as ammonium chlorate and sodium chlorate, and alkaline earth metal chlorates such as calcium chlorate.

The addition amount of the oxidizing agent is not particularly limited as long as the molecular weight of the organic coagulant can be made equal to or less than the molecular weight cutoff of the membrane, for example, the organic system in the water to be treated before coagulation and precipitation. The concentration (mg/L) of the aggregating agent is preferably 0.5 to 75 times, more preferably 0.5 to 2.5 times.

Moreover, it is preferable to control the addition amount of the inorganic coagulant according to the concentration of the high molecular weight organic substance detected by LC-OCD in the treated water subjected to the coagulation sedimentation treatment or the coagulation pressurization floatation treatment. With LC-OCD, organic substances are fractionated by molecular weight, and peaks of high molecular weight organic substances, humic substances, humic decomposition products, low molecular weight organic acids, low molecular weight organic substances, etc. are displayed for each retention time, and the respective concentrations are quantified. It is possible.

Since it is considered that the high molecular weight organic matter contributes to the clogging of the membrane, by knowing the concentration of the high molecular weight organic matter in detail from the organic matter in the treated water that has been subjected to the coagulation sedimentation treatment or the coagulation pressurization floatation process, the inorganic coagulation added The addition amount of the agent can be determined to be a more appropriate amount. Then, the running amount can be reduced because the addition amount of the inorganic coagulant can be increased or decreased depending on the height of the peak of the high molecular weight organic substance detected by LC-OCD.

As a method of reducing the molecular weight of the organic coagulant, a method of imparting a shearing force to the treated water may be mentioned in addition to the addition of the oxidizing agent. As the shearing force imparting means, for example, a stirrer 28b installed in the second aggregating reaction tank 18 is used to stir the treated water to impart a shearing force to break the chains of the molecules of the organic coagulant. The molecular weight of the coagulant is set to be equal to or lower than the molecular weight cut-off of the ultrafiltration membrane or the microfiltration membrane. For example, the molecular weight of the organic coagulant can be made equal to or lower than the molecular weight cut-off of the ultrafiltration membrane or the microfiltration membrane by adjusting the stirring speed, stirring time, and the like. The stirring speed set to reduce the molecular weight of the organic flocculant is, for example, in the range of 200 rpm to 1,000 rpm, and preferably in the range of 700 rpm to 1,000 rpm. The stirring time set to reduce the molecular weight of the organic coagulant is, for example, in the range of 5 minutes to 1 hour, preferably 30 minutes to 1 hour.

FIG. 4 is a schematic diagram showing an example of the configuration of a processing system according to another embodiment. In the processing system 4 of FIG. 4, the same components as those of the processing system 1 shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted. The treatment system 4 shown in FIG. 4 is provided with an activated carbon device 32 filled with activated carbon and a reverse osmosis membrane device 34 including a reverse osmosis membrane in a subsequent stage of the membrane filtration device 20. One end of the treated water pipe 26a is connected to the outlet of the membrane filtration device 20, and the other end is connected to the inlet of the activated carbon device 32. Further, one end of the treated water pipe 26b is connected to the outlet of the activated carbon device 32, and the other end is connected to the inlet of the reverse osmosis membrane device 34. A permeated water pipe 36 is connected to the permeated water outlet of the reverse osmosis membrane device 34, and a concentrated water pipe 38 is connected to the concentrated water outlet.

The reverse osmosis membrane used in the present embodiment is, for example, a membrane capable of removing ionic components in treated water, and also includes a nanofiltration membrane (NF membrane). The shape of the reverse osmosis membrane is not particularly limited, and examples thereof include hollow fiber membranes, tubular membranes, flat membranes and spirals. Examples of the material of the reverse osmosis membrane include polyamide type, piperazine amide type, and cellulose acetate type.

In the treatment system 4 shown in FIG. 4, the treated water discharged from the membrane filtration device 20 is supplied to the activated carbon device 32 through the treated water pipe 26a. After the impurities in the treated water are removed by the activated carbon device 32, they are supplied to the reverse osmosis membrane device 34 from the treated water pipe 26b and separated into permeated water and concentrated water. The permeated water (treated water) obtained by the reverse osmosis membrane device 34 is discharged from the permeated water pipe 36. The obtained permeated water is not only used as washing water for food processing plants, chemical plants, semiconductor factories, machine factories, etc., but also, for example, dilution water, drinking water, intermediate water, air conditioning water, pure water, pure water, rinser raw water, It can also be used as steam water. The concentrated water obtained by the reverse osmosis membrane device 34 is discharged from the concentrated water pipe 38 and stored in, for example, a storage tank (not shown).

The treatment system 4 shown in FIG. 4 includes both the activated carbon device 32 and the reverse osmosis membrane device 34, but for example, depending on the target water quality of the treated water finally obtained, etc., only the activated carbon device 32 is installed, Installation of only the reverse osmosis membrane device 34 or installation of both the activated carbon device 32 and the reverse osmosis membrane device 34 may be selected. Although not described in the drawings, the activated carbon device 32 and the reverse osmosis membrane device 34 may be installed in the treatment system shown in FIGS. 2 and 3.

FIG. 5 is a schematic diagram showing an example of the configuration of a processing system according to another embodiment. In the processing system 5 of FIG. 5, the same components as those of the processing system 1 shown in FIG. 1 are designated by the same reference numerals, and the description thereof will be omitted. The processing system 5 shown in FIG. 5 includes a pH adjusting system as an example of pH adjusting means. The pH adjusting system includes a pH adjusting agent adding device 40, a pH adjusting agent adding pipe 42, a water quality detecting device 44, and a control unit 46.

The pH adjusting agent adding device 40 includes, for example, a tank that stores the pH adjusting agent, a pump that discharges the pH adjusting agent, a valve, and the like. One end of the pH adjusting agent adding pipe 42 is connected to the pH adjusting agent adding device 40, and the other end is connected to the second aggregation reaction tank 18.

The water quality detection device 44 has a pH value sensor, a temperature sensor, an electric conductivity sensor, a calcium hardness sensor, and a total alkalinity sensor, and has a pH value, a water temperature, and an electric conductivity of the treated water in the second coagulation reaction tank 18. Detects calcium hardness and total alkalinity.

The control unit 46 includes a processor and a memory, and includes a Langerian index calculation unit 48 and a pH adjusting agent amount control unit 50 as functional blocks. Each detection value detected by the water quality detection device 44 is input to the Langerian index calculation unit 48. The pH adjusting agent amount control unit 50 calculates the addition amount of the pH adjusting agent on the basis of the Langeria index calculated by the Langeria index calculating unit 48, and controls the addition amount of the pH adjusting agent by the pH adjusting agent adding device 40. ..

The processor of the control unit 46 executes various processes such as a process for calculating the Langerian index and a process for controlling the addition amount of the pH adjusting agent, for example, according to the processing program stored in the memory. An example of the operation of the control unit 46 will be described below.

The Langeria index calculating unit 48 calculates the Langeria index of the treated water based on the detection value detected by the water quality detection device 44. The Langeria index (LSI) is usually obtained by the following equation (1).
LSI=pH-pHs (1)

In Formula (1), pH is a pH value of treated water. Further, pHs is a theoretical pH value when the treated water is in an equilibrium state in which calcium carbonate is neither dissolved nor precipitated, and is calculated by the following equation (2).
pHs=9.3+A value+B value-C value-D value (2)

In Expression (2), the A value is a correction value determined by the concentration of the evaporation residue. Since the concentration of the evaporation residue has a correlation with the electric conductivity, the concentration of the evaporation residue can be obtained from the electric conductivity using a predetermined conversion formula. The B value is a correction value determined by the water temperature. The C value is a correction value determined by the calcium hardness. The D value is a correction value determined by the total alkalinity. The A to D values can be obtained from the detection values of the water quality detection device 44 using a relational expression or by referring to a numerical table.

The Langeria index is a general index for evaluating the tendency of scale generation in water systems, and a positive value indicates that calcium carbonate is more likely to precipitate, and a negative value indicates a larger absolute value. It indicates that calcium carbonate is less likely to precipitate. When the Langeria index is 0, calcium carbonate is in an equilibrium state in which neither precipitation nor dissolution occurs. From this, when the Lageria index of the treated water is less than 0, it is difficult to generate scales due to calcium carbonate on the membrane surface of the ultrafiltration membrane or microfiltration membrane, and conversely, when it exceeds 0, the membrane is On the surface, scales due to calcium carbonate are easily generated.

Therefore, the pH adjusting agent amount control unit 50 sets the addition amount of the pH adjusting agent such that the Langereria index of the treated water becomes less than 0 when the calculated Langerian index of the treated water is 0 or more. Then, the pH adjusting agent adding device 40 adds the pH adjusting agent to the treated water based on the set addition amount of the pH adjusting agent, and makes the Langeria index of the treated water less than 0. As is clear from the formula (1), the Langeria index of the treated water decreases as the pH of the treated water decreases and increases as the pH increases. Therefore, the Langeria index of the treated water can be controlled by adjusting the pH of the treated water.

The treatment system 5 of the present embodiment is effective, for example, as a system for treating wastewater containing fluorine. In the coagulation sedimentation treatment or the pressure floating treatment for the wastewater containing fluorine (water to be treated), a calcium agent may be added to the water to be treated together with the organic flocculant in order to recover the fluorine. The treated water obtained by such coagulating sedimentation treatment or pressure floating treatment may contain calcium, and the Langerian index of the treated water tends to be 0 or more. As a result, scale may be generated on the surface of the ultrafiltration membrane or the microfiltration membrane. However, in the present embodiment, as described above, the pH of the treated water is adjusted so that the Langeria index of the treated water is less than 0 (so that it has a negative value), so that generation of scale is suppressed. Therefore, fouling of the membrane can be further suppressed, and more stable operation can be performed. Although not shown in the drawings, a pH adjusting system may be installed in the processing system shown in FIGS.

(Reference example)
FIG. 6 is a schematic diagram showing the configuration of the processing system in the reference example. In the processing system 6 shown in FIG. 6, the same components as those of the processing system 1 shown in FIG. 1 are designated by the same reference numerals, and their description will be omitted. In the treatment system 6 shown in FIG. 6, during the membrane filtration treatment, the inorganic flocculant is not added to the treated water subjected to the flocculation sedimentation treatment (or the flocculation pressurization floating treatment), and the oxidizing agent is added from the oxidizing agent adding device 29. It is configured to be added into the second aggregation reaction tank 18 through the oxidant addition line 30. The oxidant may be added by the line injection shown in FIG.

In the treatment system 6 shown in FIG. 6, during the membrane filtration treatment, an oxidizing agent is added to the treated water to break the chains of the molecules of the organic flocculant, thereby reducing the molecular weight of the organic flocculant to an ultrafiltration membrane or The molecular weight is less than or equal to the molecular weight cut-off of the microfiltration membrane, preferably smaller than the molecular weight cut-off. As a result, a part of the organic coagulant is not captured by the membrane and passes through the membrane together with the treated water, so that it is possible to further suppress the fouling of the membrane as compared with the addition of only the inorganic coagulant. ..

The addition amount of the oxidant is not particularly limited as long as the molecular weight of the organic coagulant can be equal to or less than the molecular weight cutoff of the membrane, for example, the concentration of the organic coagulant in the water to be treated It is preferably 2.5 times to 100 times, more preferably 20 times to 50 times (mg/L).

As a method of reducing the molecular weight of the organic coagulant, a method of imparting a shearing force to the treated water may be mentioned in addition to the addition of the oxidizing agent. As the shearing force imparting means, for example, a stirrer 28b installed in the second aggregating reaction tank 18 is used to stir the treated water to impart a shearing force to break the chains of the molecules of the organic coagulant. The molecular weight of the coagulant is set to be equal to or lower than the molecular weight cut-off of the ultrafiltration membrane or the microfiltration membrane. The stirring speed set to reduce the molecular weight of the organic flocculant is, for example, in the range of 200 rpm to 1,000 rpm, and preferably in the range of 700 rpm to 1,000 rpm. The stirring time set to reduce the molecular weight of the organic coagulant is, for example, in the range of 5 minutes to 1 hour, preferably 30 minutes to 1 hour. Although not described in the figure, the processing system shown in FIG. 6 can be applied to the processing systems shown in FIGS.

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

(Example 1)
The treatment system shown in FIG. 1 was used to treat the plating-based wastewater having the water quality shown in Table 1.

A UF membrane device was used as the membrane filtration device of Example 1. Details of the UF membrane device are as follows.
Dimensions: 230 mm outer diameter x 2400 mm height
Filtration area (membrane area): 77 m ²
Ultrafiltration membrane: Hollow fiber membrane, PVDF, nominal pore size 0.01 μm (nominal molecular weight cutoff 360,000 Da)
Filtration method: External pressure type dead end filtration Treatment flow rate: 9.6 m ³ /h

After adding 1.0 ppm of a polyacrylamide polymer as an organic flocculant to the water-based plating wastewater having the water quality shown in Table 1 and performing a flocculation-precipitation treatment, supernatant water was supplied to the second flocculation reaction tank. After adding 75 ppm of iron chloride as an inorganic flocculant to the second flocculation reaction tank, water was passed through a membrane filtration device (UF membrane device) for membrane filtration treatment.

(Example 2)
The same process as in Example 1 was performed except that the inorganic flocculant (iron chloride) was changed from 75 ppm to 10 ppm.

(Comparative Example 1)
The same treatment as in Example 1 was performed except that the inorganic flocculant (iron chloride) was not added.

(Comparative example 2)
The same treatment as in Example 1 was performed except that the organic flocculant (polyacrylamide polymer) was changed from 1.0 ppm to 0.5 ppm and the inorganic flocculant (iron chloride) was not added.

Table 2 shows the water quality results of the treated water obtained by the membrane filtration treatments of Examples 1 and 2 and Comparative Examples 1 and 2. Further, FIG. 7 shows the results of the filtration resistance to filtration rate of the membrane filtration apparatus in Examples 1-2, and Comparative Examples ^{1~2 (m 3 / m 2)} (1 / m).

As shown in FIG. 7, in Examples 1 and 2 in which an inorganic coagulant was added to the treated water obtained by the coagulation sedimentation treatment using an organic coagulant, the inorganic water was added to the treated water. Compared to Comparative Examples 1 and 2 in which the membrane filtration treatment was carried out without adding a coagulant, the increase in filtration resistance was suppressed even if the filtration amount increased. The rate of increase in filtration resistance with respect to the increase in filtration amount indicates a decrease in filtration performance due to fouling of the membrane. Therefore, the treatment methods of Examples 1 and 2 show that fouling of the membrane is suppressed and stable operation is possible. Considering that Comparative Example 1 in which the addition amount of the organic coagulant is larger than Comparative Example 2 has a higher rate of increase in filtration resistance than Comparative Example 2, the fouling of the membrane remains in the treated water. It can be said that the organic coagulant contributes. On the other hand, in Examples 1 and 2, the same amount of the organic coagulant as in Comparative Example 1 was added, but the filtration resistance hardly increased even when the filtration amount increased, and the fouling of the membrane was suppressed. There is. It is considered that this is because the addition of the inorganic coagulant changed the organic coagulant in the treated water into a form in which the organic coagulant was less likely to adhere to the film surface.

Further, as shown in Table 2, in Examples 1 and 2, the TOC of the treated water was reduced, and it was confirmed that the residual organic coagulant was treated.

(Example 3)
The same treatment as in Example 1 except that the organic flocculant (polyacrylamide polymer) was changed from 1.0 ppm to 5.0 ppm and the inorganic flocculant (iron chloride) was changed from 75 ppm to 2.5 ppm. I went.

(Comparative example 3)
After adding 5.0 ppm of (polyacrylamide polymer) as an organic flocculant and 1 ppm of iron chloride as an inorganic flocculant to the plating effluent of the water quality shown in Table 1, after performing coagulating sedimentation treatment The supernatant water was directly passed through the membrane filtration device (UF membrane device described above) for membrane filtration treatment.

Table 3 shows the water quality results of the treated water obtained by the membrane filtration treatment of Example 3 and Comparative Example 3.

FIG. 8 shows the results of filtration resistance (1/m) with respect to the filtration amount (m ³ /m ² ) of the membrane filtration devices in Example 3 and Comparative Example 3. The rate of increase in filtration resistance in Example 3 was similar to those in Examples 1 and 2. On the other hand, the rate of increase in filtration resistance of Comparative Example 3 was higher than that of Example 3 in which the addition amount of the inorganic coagulant was the same, but Comparative Examples 1 and 2 in which the inorganic coagulant was not added. The result was lower than that of From these results, it can be said that in order to suppress the fouling of the membrane, it is necessary to add the inorganic coagulant to the treated water obtained by the coagulation sedimentation treatment using the organic coagulant.

(Example 4)
The same treatment as in Example 1 was performed except that the inorganic coagulant was changed from iron chloride to polyaluminum chloride (PAC) and the addition amount was changed from 75 ppm to 50 ppm.

(Comparative Example 4)
The same treatment as in Comparative Example 1 was performed except that the sampling date and time of the raw water was changed.

FIG. 9 shows the results of filtration resistance (1/m) with respect to the filtration amount (m ³ /m ² ) of the membrane filtration devices in Example 4 and Comparative Example 4. In Example 4, in which PAC was used as the inorganic flocculant, the filtration resistance hardly increased even when the filtration amount increased, and the fouling of the membrane was suppressed, as in Examples 1 to 3. On the other hand, in Comparative Example 4 in which the inorganic coagulant was not added, the filtration resistance increased as the filtration amount increased.

(Examples 5 to 10)
Simulated wastewater was treated using the treatment system shown in FIG. The simulated waste water is obtained by dispersing bentonite 10 mg/L in tap water. The membrane filtration device is the same UF membrane device as in the first embodiment.

In Example 5, 1.0 ppm of a polyacrylic acid polymer (OX-304 (cationic polymer) manufactured by Organo Co.) as an organic flocculant was added to the simulated wastewater, and after performing coagulation sedimentation treatment, the supernatant was obtained. Water was supplied to the second flocculation reaction tank. After adding 10 ppm of PAC as an inorganic flocculant to the second flocculation reaction tank, water was passed through a membrane filtration device (UF membrane device) for membrane filtration treatment.

In Example 6, the organic coagulant was changed from a polyacrylic acid-based polymer (Organo, OX-304 (cationic polymer)) to an acrylamide-based polymer (Organo, AP-1 (anionic polymer)). Membrane filtration treatment was performed in the same manner as in Example 5 except for the above.

In Example 7, the organic coagulant was changed from a polyacrylic acid-based polymer (Organo, OX-304 (cationic polymer)) to a polyacrylamide-based polymer (Organo, ON-1H (nonionic polymer)). Membrane filtration treatment was performed in the same manner as in Example 5 except for the above.

In Example 8, the membrane filtration treatment was performed in the same manner as in Example 5 except that the inorganic coagulant was changed from PAC to iron chloride (FeCl ₃ ).

In Example 9, the membrane filtration treatment was performed in the same manner as in Example 6 except that the inorganic coagulant was changed from PAC to iron chloride (FeCl ₃ ).

In Example 10, the membrane filtration treatment was performed in the same manner as in Example 7 except that the inorganic coagulant was changed from PAC to iron chloride (FeCl ₃ ).

(Comparative Examples 5-7)
In Comparative Example 5, the membrane filtration treatment was performed in the same manner as in Example 5 except that the inorganic coagulant was not added.

In Comparative Example 6, the membrane filtration treatment was performed in the same manner as in Example 6 except that the inorganic coagulant was not added.

In Comparative Example 7, the membrane filtration treatment was performed in the same manner as in Example 7 except that the inorganic coagulant was not added.

In Examples 5 to 10 and Comparative Examples 5 to 7, the time (filtering time) from passing water through the membrane filtration device to obtaining 200 ml of filtrate was measured. The results are shown in Table 4. The longer the filtration time, the faster the filtration resistance increases.

In each of Examples 5 to 10 in which the organic coagulant and the inorganic coagulant were added, the filtration time was shortened as compared with Comparative Examples 5 to 7 in which only the organic coagulant was added. That is, it can be said that Examples 5 to 10 suppressed the increase in filtration resistance as compared with Comparative Examples 5 to 7.

1 to 6 treatment system, 10 first coagulation reaction tank, 12 organic coagulant addition line, 14 coagulation sedimentation tank, 15 inorganic coagulant addition device, 16 inorganic coagulant addition line, 18 second coagulation reaction tank, 20 Membrane filtration device, 22 treated water pipe, 24a to 24c connection pipe, 26, 26a, 26b treated water pipe, 28a, 28b stirrer, 29 oxidant addition device, 30 oxidant addition line, 32 activated carbon device, 34 reverse osmosis Membrane device, 36 permeate water pipe, 38 concentrated water pipe, 40 pH adjusting agent adding device, 42 pH adjusting agent adding pipe, 44 water quality detecting device, 46 control unit, 48 Langerian index calculating unit, 50 pH adjusting agent amount control unit.

Claims (9)

At least one of ultrafiltration membrane treatment and microfiltration membrane treatment by adding an inorganic flocculant to treated water obtained by adding an organic flocculant to treated water A membrane filtration method for performing one membrane filtration process,
The organic coagulant is at least one of a polyacrylamide coagulant, a polysulfonic acid coagulant, a polyacrylic acid coagulant, a polyacrylic acid ester coagulant, a polyamine coagulant, and a polymethacrylic acid coagulant. One,
At the time of the membrane filtration treatment, at least one of applying a shearing force to the treated water by stirring with a stirrer at a stirring speed of 200 to 1000 rpm, or adding an oxidant to the treated water. One is performed, and the average molecular weight of the organic coagulant in the treated water is set to be equal to or less than the molecular weight cutoff of the membrane used in the membrane filtration treatment. The amount of the inorganic flocculant added is in the range of 0.5 times to 75 times the concentration ( mg / L ) of the organic flocculant in the water to be treated. The membrane filtration method described in. The addition amount of the inorganic coagulant is controlled according to the concentration of a high molecular weight organic substance detected by LC-OCD in the treated water that has been subjected to the coagulation sedimentation treatment or the coagulation pressurization floatation treatment. The membrane filtration method according to any one of 2 above. The membrane filtration method according to any one of claims 1 to 3, wherein at least one of activated carbon treatment and reverse osmosis membrane treatment is performed on the treated water subjected to the membrane filtration treatment. .. The pH of the treated water is adjusted so that the Langerian index (LSI) of the treated water is less than 0 during the membrane filtration treatment. Membrane filtration method. An inorganic coagulant addition means for adding an inorganic coagulant to the treated water that has been subjected to coagulation sedimentation treatment or coagulation pressure floating treatment by adding an organic coagulant to the water to be treated,
Membrane filtration treatment means having at least one of an ultrafiltration membrane and a microfiltration membrane, performing membrane filtration treatment of the treated water to which the inorganic coagulant is added,
At least one of a shearing force applying means for applying a shearing force to the treated water by stirring at a stirring speed of 200 to 1000 rpm and an oxidizing agent adding means for adding an oxidizing agent to the treated water during the membrane filtration treatment. With one side,
The organic coagulant is at least one of a polyacrylamide coagulant, a polysulfonic acid coagulant, a polyacrylic acid coagulant, a polyacrylic acid ester coagulant, a polyamine coagulant, and a polymethacrylic acid coagulant. One,
By applying at least one of the application of the shearing force and the addition of the oxidizing agent, the average molecular weight of the organic coagulant in the treated water is set to be not more than the molecular weight cutoff of the membrane used in the membrane filtration treatment. Membrane filtration system. 7. The amount of the inorganic flocculant added is in the range of 0.5 to 75 times the concentration ( mg / L ) of the organic flocculant in the water to be treated. The membrane filtration system according to. Having a post-treatment means for performing a post-treatment on the treated water subjected to the membrane filtration treatment,
8. The membrane filtration system according to claim 6, wherein the post-treatment means includes at least one of activated carbon treatment means and reverse osmosis membrane treatment means. 9. A pH adjusting unit for adjusting the pH of the treated water so that the Langerian index (LSI) of the treated water becomes less than 0 during the membrane filtration treatment. The membrane filtration system according to item 1.

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