JP2008221168A - Membrane filtration method and membrane filtration apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a membrane filtration method and a membrane filtration apparatus by which good membrane filtration water quality can be maintained and membrane differential pressure rising rate can be reduced and further consumption of a flocculant can be suppressed. <P>SOLUTION: In the membrane filtration method in which a flocculation process of pouring the flocculant into water to be treated to cause flocculation is carried out before a membrane filtration process of the water to be treated, pH of flocculation liquid is variably controlled so that pH becomes a value corresponding to raw water quality in the water to be treated, filtered water quality after the filtration process and the membrane differential pressure rising rate based on at least one among raw water quality in the water to be treated, filtered water quality after the filtration process and the membrane differential pressure rising rate. Since desired flocculation characteristic can be obtained thereby, good membrane filtration water quality can be maintained and membrane differential pressure rising rate can be reduced and further consumption of the flocculant can be suppressed to attain efficient membrane filtration treatment. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a membrane filtration method and a membrane filtration device for injecting and aggregating a flocculant into water to be treated before filtration of the water to be treated by a membrane.

  In recent years, introduction of a membrane filtration method using a membrane having fine pores has been promoted as a turbidity treatment technique for river water, lake water, ground water, water supply, sewerage, industrial water or wastewater. The membrane filtration method using this membrane has been mainly adopted in water purification plants that use groundwater as raw water, but is also being adopted in treatment plants that use river water as raw water. Here, when processing raw water that contains a lot of contaminants such as river water, the flocculant is injected into the water to be treated as a pretreatment for membrane filtration, and the flocculant is treated to stabilize the membrane filtration treatment and the range of applicable raw water The expansion of

  In the agglomeration treatment, the turbidity component in the raw water and the chromaticity component, which is a soluble substance that is not larger than the pore diameter of the membrane, cannot be removed by the membrane as it is, are incorporated into the agglomeration floc by the aggregating agent and insolubilized. . If the amount of the flocculant injected is insufficient, the chromaticity component or the like is not sufficiently taken into the floc flocs, resulting in clogging of the membrane, resulting in a decrease in filtered water quality and an increase in the membrane differential pressure. May end up. Further, when the amount of the flocculant injected is excessive, the flocculent flocs are generated excessively, the membrane is blocked, and the membrane differential pressure rises in a short time, making it impossible to perform the filtration process. Therefore, conventionally, a membrane filtration method for controlling the injection amount of the flocculant based on the chromaticity and turbidity measurement results of the raw water, a measurement result of the floc particle size after the flocculant injection, and the pore diameter of the membrane Based on the above, the agglomeration process is controlled by a membrane filtration method for controlling the injection amount of the aggregating agent, and the formation of agglomerated floc having high peelability from the membrane surface (for example, Patent Document 1 and Patent Document 2). reference).

JP 2002-336871 A Japanese Patent Laid-Open No. 11-577739

  By the way, the turbidity component and the chromaticity component in the raw water are charged on the surface of the particles, and repel each other to maintain a stable dispersion state in the raw water. For this reason, the flocculant first aggregates the dispersed turbidity component and chromaticity component by neutralizing the charge on the particle surface. However, since the chromaticity component generally has a smaller particle size than the turbidity component, the total amount of charge to be neutralized by the flocculant is larger than that of the turbidity component. The amount needs to be increased. Therefore, conventionally, in order to generate an agglomeration floc sufficiently incorporating the chromaticity component, it is necessary to inject a large amount of the aggregating agent, and there is a problem that it is difficult to suppress the consumption of the aggregating agent. .

  According to the present invention, in view of the above, it is possible to maintain good membrane filtration water quality and reduce the rate of increase in the membrane differential pressure, and to suppress the consumption of the flocculant. An object is to provide a filtration method and a membrane filtration device.

  In order to solve the above-described problems and achieve the object, the membrane filtration method according to the present invention performs a coagulation step of injecting a coagulant into the water to be treated and aggregating it before the water to be treated is filtered by the membrane. In the membrane filtration method, based on at least one of the quality of the raw water in the treated water, the quality of the filtered water after the filtration step, and the rate of increase in the membrane differential pressure, the quality of the raw water in the treated water, the filtration step The pH of the flocculated liquid is variably controlled so that the pH depends on the value of the quality of the subsequent filtrate water or the rate of increase in the membrane differential pressure.

  In the membrane filtration method according to the present invention, when the quality of the filtered water is within a predetermined setting range, the pH of the flocculated liquid is controlled to be within the first pH range, When the water quality is outside a predetermined set range, the pH of the flocculated liquid that has been controlled within the first pH range is changed to a second pH range.

  The membrane filtration method according to the present invention is characterized in that the quality of the filtered water is determined based on the chromaticity of the filtered water or the absorbance of the filtered water.

  Further, the membrane filtration method according to the present invention is such that when the quality of the raw water is within a predetermined set range and / or the membrane differential pressure increase rate in the membrane is within a predetermined set range, When the pH of the liquid is controlled to be within the first pH range, and the water quality of the raw water is outside the predetermined setting range, and / or the membrane differential pressure increase rate in the membrane is outside the predetermined setting range In some cases, the pH of the flocculated liquid, which has been controlled within the first pH range, is changed within the second pH range.

  The membrane filtration method according to the present invention is characterized in that the quality of the raw water is obtained based on the chromaticity of the raw water or the absorbance of the raw water.

  The membrane filtration method according to the present invention is characterized in that the first pH range and the second pH range are set according to a pH-dependent aggregation property of the flocculant with respect to the water to be treated. .

  In the membrane filtration method according to the present invention, the flocculant is polyaluminum chloride, the first pH range is a neutral to weakly alkaline range, and the second pH range is weakly acidic. It is a region.

  The membrane filtration method according to the present invention is characterized in that the pore diameter of the membrane is 0.5 μm or less.

  The membrane filtration device according to the present invention measures the pH of the flocculated liquid in a membrane filtration device that performs a flocculation process for injecting a flocculating agent into the water to be treated and aggregating it before the water to be treated is filtered by the membrane. pH measuring means, charging means for introducing a pH adjusting agent into the flocculated liquid, water quality measuring means for measuring the quality of filtered water after the filtration treatment, and pH of the flocculated liquid measured by the pH measuring means. In addition, when the quality of the filtered water is within a predetermined setting range, the amount of the pH adjusting agent supplied by the charging means is controlled so that the pH of the flocculated liquid is within the first pH range. And when the water quality of the filtered water is outside a predetermined setting range, the amount of the pH adjusting agent supplied by the charging means is controlled to control the aggregated liquid that has been controlled within the first pH range. pH changed to within second pH range And pH control means that, characterized by comprising a.

  The membrane filtration device according to the present invention is characterized in that the quality of the filtered water is determined based on the chromaticity of the filtered water or the absorbance of the filtered water.

  Further, the membrane filtration device according to the present invention is a membrane filtration device that performs a coagulation treatment by injecting a coagulant into the water to be treated and aggregating it before the water to be treated is filtered by the membrane, and measuring the pH of the coagulated liquid. PH measuring means, a charging means for feeding a pH adjusting agent into the flocculated liquid, a water quality measuring means for measuring the quality of raw water in the treated water, and a pressure measuring means for measuring a membrane differential pressure in the membrane Based on the pH of the coagulated liquid measured by the pH measuring means, when the quality of the raw water is within a predetermined setting range, and / or the rate of increase in the differential pressure in the membrane is within the predetermined setting range If so, the amount of the pH adjusting agent supplied by the charging means is controlled to control the pH of the flocculated liquid to be within the first pH range, and the quality of the raw water is outside the predetermined setting range. If there is, and Alternatively, when the rate of increase in the membrane differential pressure in the membrane is out of a predetermined setting range, the agglomeration was controlled within the first pH range by controlling the amount of the pH adjusting agent introduced by the introduction means. PH control means for changing the pH of the liquid within the second pH range.

  The membrane filtration apparatus according to the present invention is characterized in that the quality of the raw water is determined based on the chromaticity of the raw water or the absorbance of the raw water.

  In the membrane filtration device according to the present invention, the first pH range and the second pH range are set according to a pH-dependent aggregation property of the flocculant with respect to the water to be treated. .

  In the membrane filtration device according to the present invention, the flocculant is polyaluminum chloride, the first pH range is a neutral to weak alkaline range, and the second pH range is weakly acidic. It is a region.

  In the membrane filtration device according to the present invention, the membrane has a pore size of 0.5 μm or less.

  In the flocculation treatment, the present invention variably controls the pH of the flocculation liquid so that the pH of the raw water in the water to be treated, the quality of the filtered water after the filtration step, or the pH of the membrane differential pressure increase are adjusted to the respective values. Therefore, it is possible to maintain desired membrane filtration water quality and reduce the rate of increase in the membrane differential pressure, while suppressing the consumption of the flocculant and efficiently performing membrane filtration treatment. Can be performed.

  Embodiments of the present invention will be described below with reference to the drawings. Note that the present invention is not limited to the embodiments. In the description of the drawings, the same parts are denoted by the same reference numerals.

(Embodiment 1)
First, the first embodiment will be described. In Embodiment 1, the flocculating agent consumption is controlled by variably controlling the pH of the flocculating liquid so as to have a pH according to the quality of the filtered water after the filtering step, thereby controlling the flocculating specification of the flocculating liquid. The stabilization of the filtration process is aimed at with the suppression of the above.

  FIG. 1 is a schematic diagram illustrating the configuration of the membrane filtration device according to the first embodiment. As shown in FIG. 1, the membrane filtration apparatus 1 according to the first embodiment includes a raw water tank 2, a mixing tank 3, a flocculant container 4, a flocculant injection pump 5, a stirring mechanism 6, a pH meter 7, and a pH adjuster container. 81, 82, adjusting agent injection pumps 91, 92, raw water pump 10, membrane 11, filtered water tank 12, backwash pump 13, chromaticity meter 14, control unit 20, input unit 22, and output unit 23. The membrane filtration device 1 performs a filtration process on raw water mixed with impurities.

  The raw water tank 2 can receive raw water such as river water and lake water, and can store the raw water. The raw water stored in the raw water tank 2 is sent to the mixing tank 3. In the mixing tank 3, a flocculant is injected into the raw water sent from the raw water tank 2, and a flocculation reaction is performed to form a flocculation flock incorporating the turbidity component and chromaticity component in the raw water. The mixing tank 3 retains the aggregating agent and raw water mixed and stirred for at least the agglomeration reaction time. The flocculant container 4 contains polyaluminum chloride (PAC) as a flocculant injected into the mixing tank 3. The flocculant injection pump 5 injects a predetermined amount of the flocculant in the flocculant container 4 into the mixing tank 3 under the control of the control unit 20. The agitation mechanism 6 mixes the raw water fed into the mixing tank 3 and the flocculant injected into the mixing tank 3 to form an agglomeration floc due to an agglomeration reaction.

  The pH meter 7 measures the pH of the liquid in the mixing tank 3 and outputs the measured pH to the control unit 20. In addition, the measurement of pH is not limited to the mixing tank 3 and may be performed on filtered water or the like, and the control unit 20 performs pH control processing using the input measured pH value.

  The pH adjuster container 81 contains sulfuric acid as a pH adjuster that is injected into the mixing tank 3 and adjusts the pH of the liquid in the mixing tank 3. The pH adjuster container 82 contains sodium hydrogen carbonate as a pH adjuster that is injected into the mixing tank 3 and adjusts the pH of the liquid in the mixing tank 3. In addition, what is necessary is just to install alkaline agents, such as sodium hydrogencarbonate, according to the quality of raw | natural water.

  The adjusting agent injection pump 91 injects sulfuric acid in the pH adjusting agent container 81 into the mixing tank 3 under the control of the pH control unit 21. The adjusting agent injection pump 92 injects sodium hydrogen carbonate in the pH adjusting agent container 82 into the mixing tank 3 under the control of the pH control unit 21. The adjusting agent injection pumps 91 and 92 function as input means for supplying the pH adjusting agent into the aggregation liquid in the claims. The adjusting agent injection pump 91 injects a predetermined amount of sulfuric acid in the pH adjusting agent container 81 into the mixing tank 3 under the control of the pH control unit 21. The adjusting agent injection pump 92 injects a predetermined amount of sodium hydrogen carbonate in the pH adjusting agent container 82 into the mixing tank 3 under the control of the pH control unit 21. In addition, the raw water pump 10 pressure-feeds the floc-containing water in the mixing tank 3 to the membrane 11.

  The membrane 11 has micropores, separates the aggregated floc from the floc-containing water sent by the raw water pump 10, and sends the filtrate to the filtrate tank 12. The pore diameter of this membrane is 0.5 μm or less in order to remove aggregated floc that has not been agglomerated. The filtered water tank 12 stores the filtered water filtered by the membrane 11. The backwash pump 13 performs a backwash process in which air or filtered water is made to flow backward after the filtration process for a predetermined time in the film 11 to remove the detained substances in the pores of the film 11 and the surface of the film 11. The chromaticity meter 14 measures the chromaticity of filtered water stored in the filtered water tank 12 and outputs the measured chromaticity of filtered water to the control unit 20.

  The control unit 20 controls each constituent part constituting the membrane filtration device 1. The control unit 20 has a pH control unit 21. The input unit 22 inputs information related to the processing operation of the membrane filtration device 1 to the control unit 20. The output unit 23 outputs information related to the processing operation of the membrane filtration device 1.

  Based on the pH of the liquid in the mixing tank 3 measured by the pH meter 7, the pH control unit 21 uses sulfuric acid from the adjusting agent injection pumps 91 and 92 when the water quality of the filtered water is within a predetermined setting range. Alternatively, the input amount of sodium hydrogen carbonate is controlled so that the pH of the flocculated liquid is controlled to be in the neutral to weakly alkaline range which is the first pH range. Then, the pH control unit 21 adjusts the infusion pumps 91 and 92 when the water quality of the filtered water is out of a predetermined setting range based on the pH of the liquid in the mixing tank 3 measured by the pH meter 7. By controlling the amount of sulfuric acid or sodium hydrogen carbonate to be added, the pH of the flocculated liquid that has been controlled within the neutral to weakly alkaline range is changed to the weakly acidic range that is the second pH range.

  Here, the first pH range and the second pH range for the pH control of the flocculating liquid that is the liquid in the mixing tank 3 are set according to the flocculating characteristics of the flocculating agent with respect to the raw water. When the flocculant is PAC, the first pH range is set to a neutral to weakly alkaline range, and the second pH range is a weakly acidic region having a pH of 5.0 to 6.8. It is set in a certain weak acid range. In order to explain each pH range, the aggregation characteristics in PAC will be described with reference to FIG.

FIG. 2 is a diagram showing the morphological change of PAC as a flocculant depending on pH. As shown in FIG. 2, PAC becomes soluble Al ³⁺ when injected into a liquid having a pH of 1 to 3 in a strongly acidic region S1. Then, PAC, if the pH is injected into the liquid is an acidic region S2 of 2.5 to 5.5, mainly of the Al ₈ (OH) ₂₀ ⁴⁺ is soluble. Since this Al ₈ (OH) ₂₀ ⁴⁺ has the highest positive charge among the forms of PAC, the charge neutralization power capable of neutralizing the charged state of the particles in the raw water is greater than that of other forms. It becomes. In addition, when PAC is injected into a liquid having a pH in the neutral neighborhood S3 of 4.5 to 9.5, the main one is insoluble Al (OH) ₃ . Since this Al (OH) ₃ has a strong cross-linking action, it can form a strong aggregated floc. Then, PAC, if the pH is injected into the liquid is an alkali region S4 is 7.5 or more, a soluble Al (OH) ₄ ^- and becomes.

  The turbidity component and the chromaticity component in the raw water are repelled from each other because the particle surface is negatively charged and are not easily precipitated, and are kept dispersed in the raw water. The turbidity component and chromaticity component in the raw water are neutralized on the particle surface by the action of the PAC having a form having a charge neutralizing power, and the repulsive force between the particles is reduced. As a result, the dispersed turbidity component and chromaticity component are aggregated, and due to the action of the PAC having a strong crosslinking action, the aggregation of the turbidity component and the chromaticity component is increased, and an aggregated floc is formed.

  The conventional membrane filtration device uses the strong cross-linking action of PAC to control the pH of the liquid in the mixing tank so that it is always within a certain range from neutral to weakly alkaline. A flock was formed. Generally, when a flocculant is added, the alkalinity is consumed and the pH of the liquid in the mixing tank is lowered. Therefore, conventionally, an alkali agent such as sodium hydrogen carbonate is injected in accordance with the pH of the liquid in the mixing tank so that the pH of the liquid in the mixing tank is always within a certain range of neutral to weakly alkaline. Was. In particular, in sand filtration devices with a large pore size compared to membranes that filter contaminants, it is necessary to reliably grow large agglomerated flocs with high strength so that there is no precipitation failure after aggregation and filtration failure due to membranes. Therefore, the pH of the liquid in the mixing tank was always strictly controlled so as to be within a certain range from neutral to weakly alkaline.

However, when the pH of the liquid in the mixing tank is always controlled to be within a certain range of neutral to weakly alkaline as in the past, most of the PAC is Al (OH) _{3 having} a strong crosslinking action, There is little Al ₈ (OH) ₂₀ ⁴⁺ with strong power. For this reason, when the pH of the liquid in the mixing tank is always controlled to be within a certain range of neutral to weakly alkaline, the pH of the liquid in the mixing tank is higher than that in the acidic range. The progress of charge neutralization of the turbidity component and chromaticity component in the sent raw water is delayed. Furthermore, the chromaticity component generally has a smaller particle size than the turbidity component, and the total amount of charge to be neutralized by the flocculant is larger than that of the turbidity component. For this reason, when controlling the pH of the liquid in the mixing tank to be always within a certain range of neutral to weakly alkaline as in the past, in order to proceed with charge neutralization of the turbidity component and the chromaticity component, It was necessary to inject excessive flocculant. Therefore, it has been difficult to suppress the consumption of the flocculant.

  On the other hand, the membrane 11 in the membrane filtration device 1 has a pore diameter of 0.5 μm or less in order to remove aggregated floc that has not been agglomerated. That is, the film 11 can be removed if it has a particle size equal to or greater than the turbidity component. For this reason, the membrane filtration apparatus 1 can appropriately filter the water to be treated without always forming a large flocculated floc. In other words, in the membrane filtration device 1, it is not always necessary to form a large flocculated floc. Therefore, the membrane filtration device 1 efficiently promotes charge neutralization of the chromaticity component by changing the pH of the liquid in the mixing tank 3 to the acidic range only when necessary.

Next, the reason why the second pH range for pH control of the flocculated liquid that is the liquid in the mixing tank 3 is set to a weakly acidic range will be described. In the acidic region S2 shown in FIG. 2, the charge on the particle surface of the turbidity component and the chromaticity component can be most strongly neutralized by Al ₈ (OH) ₂₀ ⁴⁺ . For this reason, when the PAC is injected when the state of the raw water is in the acidic region S2, the amount of the flocculant is smaller than that when the raw water is in the neutral vicinity region S3, compared with the case where the flocculating agent is injected. Charge neutralization of the turbidity component and the chromaticity component becomes possible, and aggregation can be started. In particular, even when the chromaticity component having a smaller particle size than the turbidity component and having a large total charge to be neutralized by the flocculant occupies the raw water, the state of the raw water is in the acidic region S2. By injecting PAC, charge neutralization in the chromaticity component is enabled without increasing the injection amount of PAC.

However, when PAC is injected into raw water having a relatively strong acidity in the acidic region S2, PAC mainly has the form of Al ₈ (OH) ₂₀ ⁴⁺ , so that the crosslinking action by Al (OH) ₃ is exerted. Instead, an agglomerated floc having a low strength is formed and introduced into the film 11. The weakly flocculated flocs are easily broken by the pressurized water supply of the raw water pump 10, and the membrane 11 is clogged due to the breakage of the flocculent flocs, which may cause an excessive load exceeding the allowable range. There is.

Weak Therefore, in the membrane filtration device 1 according to the first embodiment, pH controller 21 can exhibit both crosslinking action due to Al ₈ (OH) ₂₀ ⁴⁺ by charge neutralization forces and Al (OH) ₃ The acidic range Sp (pH is 5.0 to 6.8) is set as the second pH range. The pH control range in the pH control treatment is set according to the pH-dependent aggregation characteristics of PAC with respect to raw water. The pH control unit 21 controls the pH of the liquid in the mixing tank 3 within the weakly acidic range Sp when the chromaticity component is not sufficiently aggregated. As a result, in the membrane filtration device 1, the neutralization of the surface of the turbidity component and the chromaticity component can be promoted while suppressing a rapid decrease in strength in the coagulation floc, so that the liquid in the mixing tank 3 is neutral. The amount of the flocculant injected can be reduced as compared with the case of weak alkalinity, and the generation of the flocculent floc can be performed.

In this weakly acidic range Sp, a part of PAC has a form of soluble Al ₈ (OH) ₂₀ ⁴⁺ . Therefore, when injected a PAC in raw water in the state of the weakly acidic region Sp, there is a possibility that the floc-containing water including soluble Al ₈ (OH) ₂₀ ⁴⁺ is pumped to the membrane 11 from the mixing vessel 3 . However, the film 11 cannot remove soluble Al ₈ (OH) ₂₀ ⁴⁺ . As a result, Al ₈ (OH) ₂₀ ⁴⁺ may remain in the filtered water in the filtered water tank 12.

  Therefore, the pH control unit 21 does not always perform the pH control process in which the pH of the liquid in the mixing tank 3 is in the weakly acidic range Sp, and the pH of the liquid in the mixing tank 3 is weak only when necessary. By performing the pH control treatment that is in the acidic range Sp, the PAC component is prevented from remaining in the filtered water.

  Specifically, the pH control unit 21 normally controls the introduction of the pH adjusting agent so that the pH of the liquid in the mixing tank 3 falls within the first pH range from neutral to weak alkaline. Then, the pH control unit 21 is configured to reduce the pH of the liquid in the mixing tank 3 to the second pH range when the chromaticity component remains in the filtered water more than an allowable amount and the quality of the filtered water is deteriorated. A pH control process is performed within Sp. In other words, the pH control unit 21 adjusts the pH of the liquid in the mixing tank 3 within the weakly acidic region Sp only when the chromaticity of the filtered water exceeds a predetermined set value based on the water quality required for the filtered water. The pH control process is started. As a result of controlling the pH of the raw water within the weakly acidic region Sp by this pH control treatment, among the turbidity component and chromaticity component, charge neutralization and aggregation floc formation on the surface of the chromaticity component are particularly promoted. Even in the state where the injection amount of the flocculant is reduced, the formation of the flocculent floc can proceed. And the separation of the turbidity component and the chromaticity component by the membrane 11 is promoted, the quality of the filtrate water is recovered, and the chromaticity of the filtrate water is lowered. When the chromaticity of the filtrate falls below a predetermined set value indicating the water quality required for the filtered water, the pH control unit 21 recovers the quality of the filtered water and can maintain a stable water quality. The pH control process for setting the pH of the liquid in the weakly acidic region Sp to be stopped, and the injection amount of sodium hydrogen carbonate and sulfuric acid are controlled so that the pH of the liquid in the mixing tank 3 becomes neutral to weakly alkaline. .

  With reference to FIG. 3, the process sequence of the pH control process in the membrane filtration apparatus 1 is demonstrated in detail. FIG. 3 is a flowchart showing a processing procedure of pH control processing in the membrane filtration device 1 shown in FIG.

  As shown in FIG. 3, first, the pH control unit 21 starts a first pH control process in which the liquid in the mixing tank 3 is in a first pH range that is neutral to weakly alkaline (step S1). Next, the pH control unit 21 determines whether or not chromaticity information including the chromaticity measured by the chromaticity meter 14 has been received (step S2). The chromaticity meter 14 periodically measures the chromaticity of the filtered water in the filtered water tank 12 and transmits the chromaticity information to the pH control unit 21, and also filters the filtered water tank 12 when instructed by the pH control unit 21. The chromaticity information of water may be measured and chromaticity information may be transmitted to the pH control unit 21. The pH control unit 21 repeats the determination process in step S2 until determining that the chromaticity information has been received.

  And when the pH control part 21 judges that chromaticity information was received (step S2: Yes), it processes the received chromaticity information, and whether the chromaticity of filtered water is within a predetermined setting value. Is determined (step S4). This set value is set based on the water quality required for filtered water, and is, for example, 1 degree. This is because when the chromaticity of the filtered water measured by the chromaticity meter 14 exceeds 1 degree, it can be determined that the quality of the filtered water has deteriorated.

  When the pH control unit 21 determines that the chromaticity of the filtered water is within the predetermined set value (step S4: Yes), the pH control unit 21 determines that the quality of the filtered water satisfies the required water quality, and the first pH control is performed as it is. The process is continued, and the process returns to step S2 to determine whether or not chromaticity information has been received again. On the other hand, when the pH control unit 21 determines that the chromaticity of the filtered water is not within the set value (step S4: No), the pH control unit 21 determines that the quality of the filtered water is deteriorated, and the liquid in the mixing tank 3 is reduced. In order to perform the second pH control process in which the pH is within the weakly acidic range Sp, it is determined whether or not the back washing process is performed on the film 11 (step S6). When the pH control unit 21 determines that the backwash process is performed (step S6: Yes), the filtration process in the membrane 11 is stopped, so the first pH control process is stopped and the process returns to step S6 again. Then, the determination process in step S6 is repeated until the backwash process is completed.

  On the other hand, when the pH control unit 21 determines that the backwashing process is not performed or when it is determined that the backwashing process is completed (step S6: No), the first pH control process is continued. Stops the first pH control process (step S7), and controls the introduction of the pH adjusting agent in the adjusting agent injection pumps 91 and 92, thereby setting the pH of the liquid in the mixing tank 3 to the weakly acidic range Sp. The control process is started (step S8). Then, the pH control unit 21 adjusts the injection pumps 91 and 92 so that the pH in the mixing tank 3 is in the range of 5.0 to 6.8 based on the pH measured by the pH meter 7. The pH control process is performed by changing the injection output.

  Next, the pH control unit 21 determines whether or not the backwash process is performed (step S10), and when it is determined that the backwash process is performed (step S10: Yes), the second pH control process is stopped (step S10). Step S16). On the other hand, when it is determined that the backwash process is not performed (step S10: No), the pH control unit 21 determines whether the chromaticity information transmitted from the chromaticity meter 14 is received (step S10). S12). If it is determined that the chromaticity information has not been received (step S12: No), the pH control unit 21 continues the second pH control process as it is. And the pH control part 21 progresses to step S10, and performs the judgment process of step S10.

  On the other hand, when the pH control unit 21 determines that the chromaticity information has been received (step S12: Yes), the received chromaticity information is processed, and whether the chromaticity of the filtrate is within a predetermined set value. It is determined whether or not (step S14). The set value after the start of the second pH control process is set based on the water quality required for filtered water, and is, for example, 0.5 degrees. This is because when the chromaticity of the filtered water measured by the chromaticity meter 14 is less than 0.5 degrees, it can be determined that the quality of the filtered water is sufficiently recovered and a stable water quality can be maintained. If the pH control unit 21 determines that the chromaticity of the filtered water is not within the predetermined set value (step S14: No), the pH control unit 21 can determine that the quality of the filtered water has not recovered, so the second pH control process is continued as it is. To do. And the pH control part 21 progresses to step S10, and performs the judgment process of step S10.

  On the other hand, when the pH control unit 21 determines that the chromaticity of the filtered water is within the predetermined set value (step S14: Yes), the pH control unit 21 can determine that the quality of the filtered water has been recovered, and thus stops the second pH control process. In step S16, the first pH control process is started in order to stably generate a large aggregate floc having a high strength (step S17). In addition, when backwashing processing is performed, after this backwashing processing is complete | finished, 1st pH control processing is started. And the pH control part 21 judges whether the filtration process in the membrane filtration apparatus 1 is complete | finished based on the instruction information input from the input part 22 (step S18). When the pH control unit 21 determines that the filtration process is finished (step S18: Yes), the control process is finished as it is. On the other hand, when the pH control unit 21 determines that the filtration process is not completed (step S18: No), the pH control unit 21 returns to step S2 and determines whether or not the chromaticity information from the chromaticity meter 14 has been received.

  Specifically, the pH control unit 21 first starts the first pH control process. And the pH control part 21 is the setting value whose chromaticity of filtered water is a criterion of a 2nd pH control start at time t1, as it exists in the curve 11 which shows the time change of the chromaticity of filtered water of FIG. If it is determined that T1 (for example, 1 degree) has been exceeded, it is determined that the quality of the filtered water has deteriorated. Then, after stopping the first pH treatment in the OFF state, the pH control unit 21 changes the pH of the liquid in the mixing tank 3 to a weakly acidic range as shown in a curve l2 showing a timing chart for the second pH control treatment in FIG. The second pH control process is started while the second pH control process in the Sp is turned on. Then, the pH control unit 21 adjusts the injection pumps 91 and 92 so that the pH in the mixing tank 3 is in the range of 5.0 to 6.8 based on the pH measured by the pH meter 7. The second pH control process is performed in which the pH of the liquid in the mixing tank 3 is set to be in the weakly acidic region Sp by changing the injection output of. Here, when the backwash process is performed by driving the backwash pump 13, the filtration process by the membrane 11 is stopped, so the pH control process is also stopped. For this reason, the pH controller 21 turns off the second pH control process from the time t2 to the time t3 when the backwash process is performed. Then, when the chromaticity of the filtered water remains above the set value T1, the pH control unit 21 sets the second pH control process to the ON state again from the time t3 when the backwash process is completed. Start processing. At time t4, when it is determined that the chromaticity of the filtrate falls below the set value T2 (for example, 0.5 degrees), which is the criterion for stopping the second pH control process, the quality of the filtrate is stably recovered. The second pH control process is turned off, the second pH control process is stopped, and the first pH control process is started. In order to prevent chattering, the set value relating to the second pH control process condition is set to different values of T1 and T2. However, of course, one set value may be provided and the second pH control process may be performed when the set value is outside the set value.

  As described above, in Embodiment 1, the pH of the liquid in the mixing tank 3 is changed from the first pH range that is neutral to weakly alkaline only when the chromaticity of the filtered water is increased, and in the weakly acidic range. By performing the second pH control process for controlling to be within a certain second pH range, the aggregation operation is performed by appropriately utilizing the charge neutralization force and the cross-linking action of the aggregating agent. For this reason, according to Embodiment 1, while suppressing the injection amount of the flocculant, it is possible to efficiently form the flocs flocs in which the chromaticity components that cause clogging of the film 11 are captured in the flocs flocs. it can. Therefore, according to the first embodiment, it is possible to maintain good filtered water quality and reduce the rate of increase in the membrane differential pressure, so it is possible to realize an efficient and stable operation of the membrane filtration device for a long time, and to collect filtrate water. It is possible to improve the rate. In addition, according to the first embodiment, since the second pH control process in which the pH of the liquid in the mixing tank 3 is set in the weakly acidic region Sp is performed in a timely manner, it is not necessary to always inject an alkaline agent, and the pH is adjusted together with the flocculant. The injection amount of the alkaline agent as the agent can also be reduced, and the power cost of the coagulant injection pump for injecting the coagulant and the adjustment agent injection pump for injecting the pH adjuster can be reduced.

  In the first embodiment, the chromaticity of the filtered water is measured to obtain the quality of the filtered water. However, the present invention is not limited to this, and as shown in the membrane filtration device 1a in FIG. Instead of 14, an absorbance meter 14 a that measures the absorbance of the filtrate water in the filtration water tank 12 may be provided, and the absorbance of the filtrate water in the filtration water tank 14 may be measured to obtain the quality of the filtrate water. In this case, the pH controller 21 stops the first pH control process and executes the second pH control process when the absorbance of the filtered water measured by the absorbance meter 14a is outside the predetermined setting range.

(Embodiment 2)
Next, a second embodiment will be described. In the second embodiment, the pH of the flocculated liquid is variably controlled so that the pH corresponds to the chromaticity of the raw water and the value of the rate of increase in the membrane differential pressure in the membrane. FIG. 6 is a schematic diagram illustrating the configuration of the membrane filtration device according to the second embodiment. As shown in FIG. 6, the membrane filtration device 201 according to the second embodiment includes a chromaticity meter 214 and a pressure gauge 215 instead of the chromaticity meter 14 in the membrane filtration device 1 shown in FIG. The membrane filtration device 201 includes a control unit 220 having a pH control unit 221 instead of the control unit 20 in the membrane filtration device 1.

  The chromaticity meter 214 measures the chromaticity of the raw water stored in the raw water tank 2 and outputs the measured chromaticity of the raw water to the control unit 220. In other words, the chromaticity meter 214 measures the chromaticity of the raw water before the aggregation treatment in the mixing tank 3. The pressure gauge 215 measures the membrane differential pressure in the membrane 11 and outputs the measured membrane differential pressure to the control unit 220. The control unit 220 has the same function as the control unit 20 shown in FIG.

  The pH control unit 221 performs the first pH control process and the second pH control process in the same manner as the pH control unit 21 shown in FIG. The pH control unit 221 performs the second pH control process only when the chromaticity of the raw water in the raw water tank 2 is increased and when the membrane differential pressure is increased in the membrane 11, and otherwise performs the first pH control process. When the chromaticity of the raw water becomes higher than the filtration performance by the membrane 11, there is a possibility that the chromaticity component is clogged by the membrane 11 and the filtered water quality is deteriorated due to the remaining chromaticity component. For this reason, the pH control unit 221 performs the second pH control process when the chromaticity of the raw water in the raw water tank 2 rises, thereby sufficiently incorporating the chromaticity component in the raw water into the coagulation floc, and reducing the burden on the membrane 11. Maintain the quality of filtered water. Moreover, when the membrane differential pressure rises abruptly due to the progression of pore blockage in the membrane 11, there is a possibility that the filtration process becomes impossible. For this reason, the pH control unit 221 performs the second pH control process when the membrane differential pressure in the membrane 11 is increased, thereby sending floc-containing water in which dispersion of chromaticity components is sufficiently suppressed to the membrane 11. Reduce the membrane differential pressure. The pH control unit 221 also controls the membrane differential pressure of the membrane 11 measured by the pressure gauge 215 when the chromaticity of the raw water in the raw water tank 2 measured by the chromaticity meter 214 is within a predetermined setting range. In the case where the rate of increase in the membrane differential pressure determined in the above is within a predetermined setting range, the injection amount and adjustment of sulfuric acid by the adjusting agent injection pump 91 based on the pH of the liquid in the mixing tank 3 measured by the pH meter 7 The amount of sodium hydrogen carbonate injected by the agent injection pump 92 is controlled so that the pH of the liquid in the mixing tank 3 is controlled to be within a first pH range that is a neutral to weakly alkaline range. When the chromaticity of the raw water in the raw water tank 2 measured by the chromaticity meter 214 is outside the predetermined setting range, the pH control unit 221 also controls the membrane differential pressure of the membrane 11 measured by the pressure gauge 215. In the case where the rate of increase in the membrane differential pressure determined in step 2 is outside the predetermined setting range, the pH of the liquid in the mixing tank 3 is weakly acidic based on the pH of the liquid in the mixing tank 3 measured by the pH meter 7. The mixing tank was controlled within the first pH range by controlling the sulfuric acid injection amount by the adjusting agent injection pump 91 and the sodium hydrogen carbonate injection amount by the adjusting agent injection pump 92 so as to be within the predetermined range. The pH of the liquid in 3 is changed to the second pH range.

  Next, with reference to FIG. 7, a processing procedure of pH control processing in the membrane filtration device 201 will be described. FIG. 7 is a flowchart showing a processing procedure of pH control processing in the membrane filtration device 201 shown in FIG.

  As shown in FIG. 7, the pH control unit 221 starts the first pH control process in which the liquid in the mixing tank 3 is in the first pH range that is neutral to weakly alkaline (step S21). Next, the pH control unit 221 determines whether the information output from the chromaticity meter 214 and the pressure gauge 215 has been received (step S22). The chromaticity meter 214 periodically measures the chromaticity of the raw water in the raw water tank 2 and transmits the chromaticity information to the pH control unit 221, and when instructed by the pH control unit 221, the raw water in the raw water tank 2. The chromaticity may be measured and chromaticity information may be transmitted to the pH control unit 221. Further, the pressure gauge 215 periodically measures the membrane differential pressure of the membrane 11 and transmits the membrane differential pressure information to the pH control unit 221, and when instructed by the pH control unit 221, the pressure differential of the membrane 11 May be measured and the film differential pressure information may be transmitted to the pH controller 221. The pH control unit 221 repeats the determination process in step S22 until it is determined that the chromaticity information and the film differential pressure information have been received.

  And when the pH control part 221 judges that the information output from the chromaticity meter 214 and the pressure gauge 215 was received (step S22: Yes), the received information is processed and chromaticity of raw | natural water is set to predetermined | prescribed It is determined whether the value is within the value (step S24). This set value is set based on the water quality required for the filtered water and the filtration performance of the membrane 11. If the chromaticity of the raw water measured by the chromaticity meter 214 exceeds the set value, it is required for the filtered water. It can be judged that there is a risk that the quality of water is not maintained.

  When the pH control unit 221 determines that the chromaticity of the raw water is not within the predetermined set value (step S24: No), the pH control unit 221 determines that it is difficult to maintain the water quality required for filtered water, In order to perform the second pH control process in which the pH of the liquid is within the weakly acidic range Sp, it is determined whether or not the backwash process is performed on the film 11 (step S26).

  On the other hand, when the pH control unit 221 determines that the chromaticity of the raw water is within the predetermined set value (step S24: Yes), it determines that the water quality of the filtered water can maintain the required water quality. Then, the pH control unit 221 calculates the membrane differential pressure increase rate in the membrane 11 based on the membrane differential pressure output from the pressure gauge 215, and determines whether or not the membrane differential pressure increase rate is within a predetermined set value. Is determined (step S25). This set value is set based on the membrane differential pressure at which the membrane 11 cannot be filtered and the filtration processing duration, and when the calculated membrane differential pressure increase rate exceeds the set value, the membrane 11 performs the filtration treatment. It can be judged that there is a possibility that it cannot be performed stably.

  For this reason, the pH control unit 221 determines that the membrane 11 can stably perform the filtration process when it is determined that the rate of increase in the membrane differential pressure is within a predetermined set value (step S25: Yes). And it returns to step S22 and the pH control part 221 judges whether the information was received again.

  On the other hand, when the pH controller 221 determines that the rate of increase in the membrane differential pressure is not within the predetermined set value (step S25: No), the pH controller 221 determines that it is difficult to perform a stable filtration process on the membrane 11 and mixes them. In order to perform the second pH control process in which the pH of the liquid in the tank 3 is set in the weakly acidic range Sp, it is determined whether or not the backwash process is performed in the film 11 (step S26).

  When the pH control unit 221 determines that the backwash process is performed (step S26: Yes), the filtration process in the membrane 11 is stopped, so the first pH control process is stopped and the process returns to step S26 again. Then, the determination process in step S26 is repeated until the backwash process is completed.

  On the other hand, when the pH control unit 221 determines that the backwashing process is not performed or when it is determined that the backwashing process is completed (step S26: No), the first pH control process is continued. Stops the first pH control process (step S27), and starts the injection of the pH adjusting agent to the adjusting agent injection pumps 91 and 92, thereby setting the pH of the liquid in the mixing tank 3 within the weakly acidic region Sp. The second pH control process is started (step S28). The pH control unit 221 then adjusts the injection pumps 91 and 92 so that the pH in the mixing tank 3 is in the range of 5.0 to 6.8 based on the pH measured by the pH meter 7. The second pH control process is performed in which the pH of the liquid in the mixing tank 3 is set to be in the weakly acidic region Sp by changing the injection output of.

  Next, the pH control unit 221 determines whether or not the backwashing process is performed (step S30). When it is determined that the backwashing process is performed (step S30: Yes), the second pH control process is stopped (step S30). Step S36). On the other hand, when it is determined that the backwash process is not performed (step S30: No), the pH control unit 221 determines whether information transmitted from the chromaticity meter 214 and the pressure gauge 215 has been received. (Step S32). If the pH control unit 221 determines that the information has not been received (step S32: No), the second pH control process is continued as it is. Then, the pH control unit 221 proceeds to step S30 and performs the determination process of step S30.

  On the other hand, when the pH control unit 221 determines that the information transmitted from the chromaticity meter 214 and the pressure gauge 215 is received (step S32: Yes), the received information is processed, and the chromaticity of the raw water is set to a predetermined value. It is determined whether the value is within the value (step S34). The set value after the start of the pH control process is set based on the performance of the membrane 11 and the water quality required for filtered water, and when the chromaticity of the raw water measured by the chromaticity meter 14 falls below the set value. It can be judged that the filtration treatment can be stably performed in the membrane 11 and that the quality of the filtered water is recovered and the stable water quality can be maintained. If the pH control unit 221 determines that the chromaticity of the raw water is not within the predetermined set value (step S34: No), the pH control unit 221 can determine that the quality of the filtered water cannot be maintained, and thus continues the second pH control process. Then, the pH control unit 221 proceeds to step S30 and performs the determination process of step S30.

  On the other hand, when the pH control unit 221 determines that the chromaticity of the raw water is within the predetermined set value (step S34: Yes), the membrane 11 is then based on the membrane differential pressure output from the pressure gauge 215. Is calculated, and it is determined whether or not the film differential pressure increase rate is within a predetermined setting (step S35). This set value is set based on the membrane differential pressure at which the membrane 11 cannot be filtered and the filtration processing duration, and when the calculated membrane differential pressure increase rate falls below the set value, stable filtration processing is continued. It can be judged that it can be done.

  If the pH control unit 221 determines that the rate of increase in the membrane differential pressure is not within the set value (step S35: No), it can be determined that it is difficult to perform a stable filtration process, and thus the second pH control process is continued as it is. Then, the pH control unit 221 proceeds to step S30 and performs the determination process of step S30.

  On the other hand, when the pH control unit 221 determines that the membrane differential pressure increase rate is within the set value (step S35: Yes), the chromaticity of the raw water and the membrane differential pressure increase rate of the membrane 11 are subjected to stable filtration. It is considered that the value has fallen to a value that can be continued. For this reason, the pH controller 221 stops the second pH control process (step S36) and starts the first pH control process (step S37). In addition, when backwashing processing is performed, after this backwashing processing is complete | finished, 1st pH control processing is started. And the pH control part 221 judges whether the filtration process in the membrane filtration apparatus 201 is complete | finished based on the instruction information input from the input part 22 (step S38), and judged that the filtration process is complete | finished. In the case (step S38: Yes), the control process is terminated as it is. On the other hand, when the pH control unit 221 determines that the filtration process is not completed (step S38: No), the pH control unit 221 returns to step S22 and determines whether or not the information output from the chromaticity meter 214 and the pressure gauge 215 has been received. To do.

  Next, the second pH control process in the pH control unit 221 will be specifically described with reference to FIG. FIG. 8 is a diagram illustrating the start and stop of the second pH control process in the pH control unit 221. A curve l21 in FIG. 8 shows the time change of the chromaticity of the raw water, a curve l31 in FIG. 8 shows a time change in the membrane differential pressure increase rate of the membrane 11, and a curve l41 in the lower part of FIG. 8 shows the second pH control process. It is a timing chart which shows an ON state and an OFF state.

  First, the pH control unit 221 starts the first pH control process. When the pH control unit 221 determines that the chromaticity of the raw water has exceeded the set value T21, which is a determination criterion for starting pH control, at time t11, as shown by a curve l21 in FIG. 8, the first pH process is turned off. After stopping as a state, as shown by a curve l41, the second pH control process is turned on and the pH control process is started. Based on the pH measured by the pH meter 7, the pH controller 221 injects the adjusting agent injection pumps 91 and 92 so that the pH in the mixing tank 3 is in the range of 5.0 to 6.8. A second pH control process is performed by changing the output so that the pH of the liquid in the mixing tank 3 is within the weakly acidic range Sp. Then, the pH control unit 221 sets the second pH control process to the OFF state from the time t12 when the backwash process is performed to the time t13. Then, when the chromaticity of the raw water or the rate of increase in the membrane differential pressure remains above a predetermined set value, the pH control unit 221 turns on the second pH control process again from the time t13 when the backwash process is completed. As a result, the second pH control process is started in which the pH of the liquid in the mixing tank 3 is set within the weakly acidic range Sp. Then, at time t14 when the chromaticity of the raw water falls below the set value T22, which is the judgment criterion for stopping the pH control process, and further, the membrane differential pressure increase rate falls below the set value T32, which is the judgment standard for stopping the pH control process. The control unit 221 turns off the second pH control process and starts the first pH control process. In order to prevent chattering, the set values for the second pH control treatment conditions are different values for T21, T22 and T31, T32. However, of course, one set value is provided for each of the raw water chromaticity and the membrane differential pressure increase rate. If it is outside the set value, the second pH control process may be performed.

  As described above, in the second embodiment, the pH of the liquid in the mixing tank 3 is controlled within the weakly acidic region only when the chromaticity of the raw water in the raw water tank 2 is increased and only when the differential pressure in the membrane 11 is increased. Since the 2pH control treatment is performed, as in the first embodiment, it is possible to maintain good membrane filtered water quality and reduce the rate of increase in the membrane differential pressure, and to suppress the consumption of the flocculant.

  In the second embodiment, when either the chromaticity of raw water or the rate of increase in the membrane differential pressure of the membrane 11 is outside a predetermined set value, the second pH control process is started to ensure stable filtration. The case where it tried to make it easy was explained. In the second embodiment, the pH control unit 221 is not limited to this, and the pH control unit 221 starts the second pH control process when both the chromaticity of the raw water and the rate of increase in the membrane differential pressure are outside the predetermined set values, and performs filtration. You may further suppress the residue of the soluble substance in water.

  Specifically, the pH control unit 221 has the chromaticity of the raw water exceeding the set value T21 as shown by a curve l21 in FIG. 9, and the membrane differential pressure increasing rate exceeds the set value T31 as shown by a curve l31. At time t21, the first pH control process is stopped, and the second pH control process is started with the pH control process turned on as indicated by a curve l42 showing a timing chart of the second pH control process. In this case, the pH control unit 221 performs the second pH control process by performing the processing procedure shown in FIG. As shown in FIG. 10, the pH controller 221 performs the first pH control start process (step S41) and the information reception determination process (step S42) in the same manner as step S22 shown in FIG. Is determined to be within the set value (step S44). If it is determined that the chromaticity of the raw water is within the set value (step S44: Yes), the process returns to step S42. In addition, when the pH control unit 221 determines that the chromaticity of the raw water is not within the set value (step S44: No), the pH control unit 221 determines whether the membrane differential pressure increase rate is within the set value (step S45), When it is determined that the film differential pressure increase rate is within the set value (step S45: Yes), the process returns to step S42. When the pH control unit 221 determines that the rate of increase in the membrane differential pressure is not within the set value (step S45: No), the pH control unit 221 performs a backwash process in order to perform the second pH control process. If it is determined whether or not the backwashing process is performed (step S46: Yes), the determination process of step S46 is repeated to determine that the backwashing process is not performed (step S46: No), the first pH control is stopped (step S47), and the second pH control process is started (step S48).

  And the pH control part 221 is the backwashing process determination process (step S50), the information reception determination process (step S52), and the determination process with respect to the chromaticity of raw | natural water (step S54) similarly to step S30-step S38 in FIG. The determination process for the differential pressure increase rate (step S55), the second pH control stop process (step S56), the first pH control start process (step S57), the filtration process end determination process (step S58), and the color of the raw water When it is determined that both the temperature and the membrane differential pressure increase rate are within the predetermined set values, the second pH control process is stopped.

  In the second embodiment, the chromaticity of the filtrate water is measured to obtain the quality of the filtrate water. However, the present invention is not limited to this, and as shown in the membrane filtration device 201a in FIG. Instead of 214, an absorbance meter 214a that measures the absorbance of the raw water in the raw water tank 2 may be provided, and the water quality of the raw water may be acquired by measuring the absorbance of the raw water in the raw water tank 2. In this case, the pH controller 221 stops the first pH control process and executes the second pH control process when the absorbance of the raw water measured by the chromaticity meter 214 is outside the predetermined setting range.

  Further, as shown in the membrane filtration device 301 of FIG. 12, the first embodiment and the second embodiment are combined, and based on the chromaticity of the filtrate water, the chromaticity of the raw water tank, and the rate of increase in the membrane differential pressure, You may perform 2pH control processing. As shown in FIG. 12, the membrane filtration device 301 includes a chromaticity meter 14 that measures the chromaticity of the filtered water in the filtered water tank 12, a chromaticity meter 214 that measures the chromaticity of the raw water in the raw water tank 2, and the membrane 11. A pressure gauge 215 for measuring the membrane differential pressure is provided. And the pH control part 321 which the control part 320 has stops the 1st pH control process based on the chromaticity of filtrate water, the chromaticity of a raw water tank, and a membrane differential pressure rise speed, and performs 2nd pH control timely. . In this case, the pH controller 321 may execute the second pH control process when any one of the chromaticity of the filtered water, the chromaticity of the raw water, or the rate of increase in the membrane differential pressure is outside the predetermined setting ranges. The second pH control process may be performed when the chromaticity of the filtered water, the chromaticity of the raw water, and the rate of increase in the membrane differential pressure are all outside the predetermined setting ranges. Further, the membrane filtration device 301 shown in FIG. 12 may include the absorptiometer 14a shown in FIG. 5 and the absorptiometer 214a shown in FIG. In this case, the pH control unit 321 may perform the second pH control process when any one of the absorbance of the filtered water, the absorbance of the raw water, or the rate of increase in the membrane differential pressure is outside the predetermined setting ranges. The second pH control process may be performed when all of the absorbance of the water, the absorbance of the raw water, and the rate of increase in the membrane differential pressure are outside the predetermined setting ranges.

  In the first embodiment and the second embodiment, the case where the first pH control process and the second pH control process are performed on the liquid in the mixing tank 3 to be aggregated has been described. Of course, a mixing tank is provided. Even when the flocculant is injected into the line, the consumption of the flocculant may be suppressed by performing the first pH control process and the second pH control process.

  In the first and second embodiments, the case where the pH in the mixing tank 3 is measured and the first pH control process and the second pH control process are performed based on the measurement result has been described. However, the present invention is not limited to this, and a pH meter that measures the pH of the filtered water that has been filtered by the membrane 11 may be provided, and the first pH control process and the second pH control process may be performed based on the measurement result of the pH meter. .

It is a schematic diagram which shows the structure of the membrane filtration apparatus concerning Embodiment 1. FIG. It is a figure which shows the form change by pH of PAC which is a coagulant | flocculant. It is a flowchart which shows the process sequence of the pH control process in the membrane filtration apparatus shown in FIG. It is a figure explaining the pH control process in the pH control part shown in FIG. It is a schematic diagram which shows the other structure of the membrane filtration apparatus concerning Embodiment 1. FIG. It is a schematic diagram which shows the structure of the membrane filtration apparatus concerning Embodiment 2. FIG. It is a flowchart which shows the process sequence of the pH control process in the membrane filtration apparatus shown in FIG. It is a figure explaining the pH control process in the pH control part shown in FIG. It is a figure explaining the other example of the pH control process in the pH control part shown in FIG. It is a flowchart which shows the other example of the process sequence of the pH control process in the membrane filtration apparatus shown in FIG. It is a schematic diagram which shows the other structure of the membrane filtration apparatus concerning Embodiment 2. It is a schematic diagram which shows the other structure of the membrane filtration apparatus concerning Embodiment 2.

Explanation of symbols

1, 1a, 201, 201a, 301 Membrane filtration device 2 Raw water tank 3 Mixing tank 4 Coagulant container 5 Coagulant injection pump 6 Stirring mechanism 7 pH meter 81, 82 pH adjusting agent container 91, 92 Adjusting agent injection pump 10 Raw water pump DESCRIPTION OF SYMBOLS 11 Membrane 12 Filtration water tank 13 Backwash pump 14,214 Chromaticity meter 14a, 214a Absorbance meter 20,220,320 Control part 21,221,321 pH control part 22 Input part 23 Output part 215 Pressure gauge

Claims (15)

In the membrane filtration method for performing a coagulation step of injecting and coagulating a flocculant into the water to be treated before the step of filtering the water to be treated by the membrane,
Based on at least one of the quality of the raw water in the treated water, the quality of the filtered water after the filtration step and the rate of increase in membrane differential pressure, the quality of the raw water in the treated water, the filtered water after the filtration step A membrane filtration method characterized by variably controlling the pH of the flocculated liquid so that the pH corresponds to each value of the water quality or the rate of increase in the membrane differential pressure.   When the water quality of the filtered water is within a predetermined setting range, the pH of the flocculated liquid is controlled to be within the first pH range, and the water quality of the filtered water is outside the predetermined setting range. The membrane filtration method according to claim 1, wherein the pH of the flocculated liquid, which has been controlled within the first pH range, is changed within the second pH range.   The membrane filtration method according to claim 1 or 2, wherein the quality of the filtered water is obtained based on the chromaticity of the filtered water or the absorbance of the filtered water.   When the water quality of the raw water is within a predetermined setting range and / or when the rate of increase in the differential pressure in the membrane is within the predetermined setting range, the pH of the flocculated liquid is set within the first pH range. If the water quality of the raw water is outside the predetermined setting range, and / or if the rate of increase in the membrane differential pressure in the membrane is outside the predetermined setting range, the raw water is within the first pH range. The membrane filtration method according to claim 1, wherein the pH of the flocculated liquid that has been controlled to be changed to a second pH range.   The membrane filtration method according to claim 1 or 4, wherein the quality of the raw water is determined based on the chromaticity of the raw water or the absorbance of the raw water.   The first pH range and the second pH range are set according to a pH-dependent aggregation property of the flocculant with respect to the water to be treated. The membrane filtration method described. The flocculant is polyaluminum chloride;
The first pH range is a neutral to weakly alkaline range;
The membrane filtration method according to any one of claims 2 to 6, wherein the second pH range is a weakly acidic range.   The membrane filtration method according to claim 1, wherein the pore size of the membrane is 0.5 μm or less. In the membrane filtration apparatus for performing a flocculation process for injecting and aggregating a flocculant into the water to be treated before the filtration of the water to be treated by the membrane,
PH measuring means for measuring the pH of the flocculated liquid;
Charging means for charging the pH adjusting agent into the flocculated liquid;
Water quality measuring means for measuring the quality of filtered water after the filtration treatment;
Based on the pH of the flocculated liquid measured by the pH measuring means, when the quality of the filtered water is within a predetermined setting range, the amount of the pH adjusting agent by the charging means is controlled to control the flocculation. The pH of the liquid is controlled to be within the first pH range, and when the water quality of the filtered water is outside a predetermined setting range, the amount of the pH adjusting agent supplied by the charging means is controlled to control the first pH range. PH control means for changing the pH of the agglomerated liquid that has been controlled within the pH range of 1 to a second pH range;
A membrane filtration apparatus comprising:   The membrane filtration device according to claim 9, wherein the quality of the filtered water is obtained based on the chromaticity of the filtered water or the absorbance of the filtered water. In the membrane filtration apparatus that performs the agglomeration treatment for injecting and aggregating the flocculant into the water to be treated before the filtration treatment of the water to be treated by the membrane,
PH measuring means for measuring the pH of the aggregate liquid;
Charging means for charging a pH adjusting agent into the agglomerated liquid;
Water quality measuring means for measuring the quality of raw water in the treated water;
Pressure measuring means for measuring a membrane differential pressure in the membrane;
Based on the pH of the flocculated liquid measured by the pH measuring means, when the quality of the raw water is within a predetermined setting range, and / or when the rate of increase in the membrane differential pressure in the membrane is within the predetermined setting range In some cases, the amount of the pH adjusting agent supplied by the charging means is controlled to control the pH of the flocculated liquid to be within the first pH range, and the quality of the raw water is outside a predetermined set range. In this case, and / or when the rate of increase in the differential pressure in the membrane is outside a predetermined setting range, the amount of the pH adjusting agent supplied by the charging means is controlled to be controlled within the first pH range. PH control means for changing the pH of the flocculated liquid that has been within a second pH range;
A membrane filtration apparatus comprising:   The membrane filtration device according to claim 11, wherein the quality of the raw water is obtained based on the chromaticity of the raw water or the absorbance of the raw water.   The first pH range and the second pH range are set according to a pH-dependent aggregation property of the flocculant with respect to the water to be treated. The membrane filtration apparatus described. The flocculant is polyaluminum chloride;
The first pH range is a neutral to weakly alkaline range;
The membrane filtration device according to any one of claims 9 to 13, wherein the second pH range is a weakly acidic region.   The membrane filtration device according to any one of claims 9 to 14, wherein the pore diameter of the membrane is 0.5 µm or less.

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