JP2011189287A - Monitoring control system for water purification membrane filtration - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively design and operate an entire system by simulating a designing specification and an operating condition beforehand. <P>SOLUTION: A monitoring control system for water purification membrane filtration which separates and removes a muddy content in water includes: a supply water tank 1 for supplying raw water; a coagulant injection device for injecting a coagulant into the supply water tank; an activated carbon injection device 8 for injecting an activated carbon into the supply water tank; a membrane module 11 arranged in downstream side of the supply tank for filtering the pretreatment water; a treated water tank arranged in downstream side of the membrane module; a heated water supply device 14 for supplying heated water to the membrane module; an absorption spectrometer 5 for measuring the absorbancy of the raw water; a current measure 9 for measuring the current of the raw water which is supplied from the supply water tank to the membrane module; and a control part 19 for controlling the coagulant injection ratio from the coagulant injection device using an online streaming current value which is electrically connected to a liquid measure and the coagulant injection device and measured by the current measure as an index. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention provides a membrane filtration technology that separates turbid components in raw water such as fresh water such as river water, groundwater, rainwater storage, lake water, sewage such as rainwater storage, industrial wastewater and sewage, and seawater such as ballast water. It is related with the used water purification membrane filtration monitoring control system.

  As is well known, the membrane filtration method can efficiently remove sterilization and sterilization, and is easy to manage. Therefore, it has been introduced into water purification plants. Depending on the object, fouling (clogging) may occur. Therefore, it is necessary to operate the membrane while repeating cleaning, and there are generally two types of cleaning methods. These are physical cleaning and backwashing with chemicals as representative examples of back-pressure cleaning in which filtered water flows from the permeate side (secondary side).

  The physical cleaning is automatically performed regularly (about once every 30 minutes to 1 hour), and reversible substances on the film surface or inside can be removed. However, the physical cleaning cannot completely remove the fouling substances adhering to the membrane pores and the pressure difference between the membranes continues to increase. Therefore, the chemical cleaning must be performed if the membrane pressure difference increases to some extent. And even if chemical cleaning is performed, it is impossible to remove deposits such as the membrane surface and inside, and recovery of the membrane differential pressure is not recognized, or when the usage period of the membrane exceeds a certain period, The membrane is replaced when it is judged that it has reached the end of its life.

  As described above, if the frequency of chemical cleaning is high, the environmental load and cost of chemical cleaning wastewater treatment increase, and the membrane filtration processing must be stopped each time chemical cleaning, filtration membrane replacement, etc. are performed. If there are too many physical cleaning intervals, the frequency of chemical cleaning and the replacement frequency of filtration membranes will be reduced as much as possible from the viewpoint of draining unnecessary treated water (reducing the recovery rate), and the operating rate of the membrane filtration system It is necessary to reduce the cost required for chemical cleaning and membrane replacement.

The following are known as techniques for reducing the frequency of chemical cleaning.
(1) Introduction of warm water cleaning (Patent Document 1)
Period of chemical cleaning as much as possible by using a process of cleaning with warm water (once a day) between physical cleaning (once every 30 minutes to once per hour) and chemical cleaning (once every six months to once a year) Is extended. It is known that fouling substances clogged in membrane pores and the like are separated to some extent by washing with warm water. In addition, warm water is produced | generated by heating a membrane filtration process water to 25 to 60 degreeC with a heat pump.

(2) Coagulant injection as pretreatment
There has been known a method for carrying out a membrane treatment after a fine suspended substance having a high stickiness is made to have a certain size (micro floc) before the membrane treatment. The purpose of this method is to facilitate flaking by physical cleaning by growing flocs to a size that does not easily clog the pores of the membrane.

(3) Activated carbon injection as pretreatment
Powdered activated carbon is injected for the purpose of reducing organic substances that are components that do not peel off by physical cleaning. However, in this case, since the activated carbon itself may become a fouling component of the membrane, the combined use with the flocculant injection of the above (2) is essential.

JP-A-2005-324151

  For each of the above (1) to (3), the effect is sufficiently known. However, the increase in membrane differential pressure in the future varies greatly depending not only on the performance of the membrane module but also on the quality of the target raw water, the surrounding processes such as pretreatment, and the operating method such as hot water cleaning. Appropriate pretreatment operation and cleaning conditions need to be determined. In general, an appropriate operation indicates that an increase in membrane differential pressure can be suppressed. When the flocculant injection or the activated carbon injection is performed in the pretreatment, a substance that is easily peeled off by physical cleaning can be generated. However, in the case of constant-speed filtration, the pump power required until the physical cleaning tends to increase. Therefore, total system design / evaluation technology is required, including pump power costs required for the entire period during membrane filtration.

  The present invention has been made in consideration of such circumstances, and in a membrane filtration apparatus for separating turbid components in water used in water purification treatment, a fau that causes an increase in the differential pressure of the membrane deposited on the membrane by pretreatment. It is an object of the present invention to provide a water purification membrane filtration monitoring and control system that makes it easy to remove ring components and simulates design specifications and operating conditions in advance to efficiently design and operate the entire system.

  The water purification membrane filtration monitoring control system according to the present invention is a water purification membrane filtration monitoring control system for separating and removing turbid components in water, a feed water tank to which raw water is supplied, and a flocculant injection for injecting a flocculant into the feed water tank An apparatus, an activated carbon injection device for injecting activated carbon into the supply water tank, a membrane module for filtering pretreatment water, disposed downstream of the supply water tank, and a treatment water tank disposed downstream of the membrane module; A hot water supply device for supplying hot water to the membrane module, an absorbance meter for measuring the absorbance of raw water supplied to the supply water tank, and a current measuring meter for measuring the current of raw water supplied from the supply water tank to the membrane module And the flocculant injection device from the flocculant injection device using the on-line flow current value measured by the current meter as an index. Characterized by comprising a control unit for controlling.

  According to the present invention, it is easy to remove fouling components that cause an increase in the differential pressure of the film deposited on the film by pretreatment, and the entire system is designed efficiently by simulating design specifications and operating conditions in advance.・ Provide a clean water membrane filtration monitoring and control system.

BRIEF DESCRIPTION OF THE DRAWINGS Schematic explanatory drawing of the water purification membrane filtration monitoring control system which concerns on one Example of this invention. The characteristic view which shows the relationship between the coagulant | flocculant injection rate, a flow electric current value, and a sediment supernatant turbidity in the monitoring control system of FIG. The characteristic view which shows the relationship between the membrane filtrate water flow rate and the transmembrane differential pressure | voltage rise in the monitoring control system of FIG. In the monitoring control system of FIG. 1, explanatory drawing for showing the change of the resistance before and behind the cake layer by flocculant injection. FIG. 2 is a characteristic diagram for obtaining parameters α and β when there is no operation record data as in the introduction of the membrane filtration equipment in the monitoring control system of FIG. 1. FIG. 2 is a characteristic diagram showing a relationship between a backwash flow rate and a cumulative turbidity removal rate when an adjustment parameter that is an index of the cumulative turbid mass removal rate is a predetermined value in the monitoring control system of FIG. 1.

Below, the water purification membrane filtration monitoring control system which concerns on embodiment of this invention is demonstrated with reference to FIG.
Reference numeral 1 in the figure indicates a supply water tank to which raw water is supplied. A raw water pump 3, a strainer 4, and a raw water absorbance meter 5 are interposed in a pipe 2 a that supplies raw water to the supply water tank 1. Here, the strainer 4 has a function of removing impurities in the raw water, and the raw water absorbance meter 5 has a function of continuously measuring the absorbance of the raw water. A pH adjusting agent injection facility 6, a flocculant injection facility 7, and an activated carbon injection facility 8 are connected to the supply water tank 1, so that a pH adjusting agent, a flocculant, and activated carbon can be injected, respectively.

  A plurality of series of membrane modules 11 are connected to the feed water tank 1 via a pipe 2b having a flow ammeter 9 and a pretreatment pump 10 interposed therebetween. Here, the flow ammeter 9 uses the characteristic that the negatively charged raw water particles are neutralized by the addition of the flocculant and aggregated by van der Waals force, and the charged state of the suspended particle surface is determined. It is a measuring instrument that indirectly measures, and serves as an index for judging the excess or deficiency of the flocculant injection.

  The pretreatment pump 10 has a function of filtering the pretreated water to the membrane module 11 by a pressurized total amount filtration method. In the pretreatment pump 10, a constant treatment flow rate control is performed by inverter control of the pump rotation speed. The membrane module 11 has a function of performing reverse pressure water cleaning (physical cleaning). In this reverse pressure water cleaning, a regular reverse pressure water system (with air scrubbing) that supplies treated water from the secondary side of the membrane, and hot water that warms the treated water from the secondary side of the membrane are supplied at a low frequency. Use both counter pressure water cleaning of the counter pressure water method. A heat pump type hot water supply device to be described later is used for generating hot water.

  The membrane module 11 contains a large number of membranes having pores of a predetermined diameter, and supplements substances larger than the pores by the sieving action of the membrane. A treated water tank 12 is connected to the membrane module 11 via a pipe 2c. A hot water supply device (hot water supply device) 14 including a compressor 13 and a heat pump 14 a is connected to the membrane module 11. The compressor 13 sends compressed air from the raw water side to the membrane module 11 to perform physical cleaning. The branch pipe 15 connecting the middle of the pipe 2c and the treated water tank 12 is provided with a pump 16 used for cleaning the membrane, and the pipe 2d connecting the treated water tank 12 and the hot water supply device 14 is used for cleaning the film. A pump 17 is connected. A downstream side of the treated water tank 12 is connected to a pipe 2e that includes a treated water absorbance meter 18 for measuring the absorbance of treated water.

  A controller 19 is electrically connected to the flocculant injection device 7 and the flow ammeter 9.

Although not shown, the control unit 19 is also electrically connected to the pH adjuster injection device 6, the activated carbon injection device 8, the raw water absorbance meter 5, the flow current meter 9, the treated water absorbance meter 18, the hot water supply device 14, and the like. ing. Further, although not shown, the control unit 19 includes a membrane differential pressure predicting unit for obtaining a predicted value ΔP of a future increase in the membrane differential pressure in the membrane module 11. Here, the means for predicting the membrane differential pressure is the operation of physical washing conditions (such as backwash flow rate and backwash time), hot water washing conditions (such as hot water washing temperature), filtration flux, and coagulant injection rate at the system design stage. This is a concept necessary for determining conditions.

  The predicted value is expressed as a value obtained by adding the second predicted value in the case of hot water cleaning to the first predicted value in the case of physical cleaning. Here, the first predicted value is a value based on the viscosity coefficient of the raw water, the filtration flow rate, the turbidity of the raw water, the amount of material separation due to cleaning, and the amount of cake resistance accumulated by a flocculant or activated carbon. The second predicted value is a value based on the viscosity coefficient of raw water, filtration flow rate, turbidity, amount of material stripped by hot water, accumulated amount of cake resistance by flocculant or activated carbon, concentration of organic matter, membrane resistance by flocculant or activated carbon It is.

The operation of the water purification membrane filtration monitoring control system during filtration and washing is as follows.
(When filtering)
The raw water is guided to the supply water tank 1 by the raw water pump 3. In the pipe 2 a on the way to the supply water tank 1, impurities in the raw water are removed by the strainer 4, and the absorbance of the raw water is measured by the raw water absorptiometer 5. A flocculant is injected into the feed water tank 1 from the flocculant injection facility 7, and activated carbon is injected from the activated carbon injection facility 8. The raw water is introduced into the membrane module 11 by the pretreatment pump 10, and the treated water that has passed through the membrane module 11 flows into the treated water tank 12. In the pipe 2b on the downstream side of the feed water tank 1, the flow current value of the raw water is measured by the flow current meter 9, and in the pipe 2e on the downstream side of the treated water tank 12, the absorbance of the treated water is continuously measured by the treated water absorbance meter 18. The

(When washing)
By continuously passing the raw water, fouling substances in the raw water are deposited on the membrane surface of the membrane module 11, the filtration resistance is increased, and the membrane differential pressure is increased. Therefore, when the membrane differential pressure shows a predetermined value, reverse pressure water cleaning is performed to supply treated water filtered from the secondary side of the membrane, or compressed air from the compressor 13 is sent from the raw water side. Further, hot water obtained by heating the treated water from the secondary side of the membrane is supplied by the hot water supply device 14 at a low frequency. The hot water from the hot water supply device 14 is set to 40 to 80 ° C., for example.

Next, specific examples will be described.
Example 1
Please refer to FIG. The present Example 1 is operated while constantly changing the coagulant injection rate from the coagulant injection device 7 arranged on the upstream side of the membrane module 11 using the online flowing current value measured by the current meter 9 as an index. It is characterized by doing.

  The coagulant injection rate is set to an optimum value as shown in FIG. Here, FIG. 2 shows the relationship between the flocculant injection rate, the flowing current value (no unit), and the sediment supernatant turbidity (degree). That is, in the case of a water purification plant that performs normal coagulation sedimentation, the coagulant injection rate with a flow current value of 0 (here, about 60 mg / L) is the optimum coagulant injection rate. However, if there is a membrane filtration process after the feed water tank as in the process targeted in the present application, a smaller coagulant injection rate (about 30 mg / L in this case) may be optimal. . Here, “optimum” means that the increase in the membrane differential pressure after physical cleaning and hot water cleaning is the smallest. Therefore, since the method of determining the target value of the flowing current value is related to the increase in the membrane differential pressure, the optimum flowing current value target value is set to, for example, -2.0 to -3.5 by obtaining the test result shown in FIG. Can be set to Note that FIG. 3 differs depending on whether the hot water cleaning is performed or not. Here, the case where the hot water cleaning is performed is shown.

  According to the first embodiment, the flocculant injection rate from the flocculant injection device 7 arranged on the upstream side of the membrane module 11 is constantly changed using the online flow current value measured by the current meter 9 as an index. By operating while operating, membrane fouling can be suppressed, and total system design and operation including pump power costs becomes possible.

(Example 2)
Please refer to FIG. The present Example 2 shows an example in which the flocculant is supplied from the flocculant injection facility 7 to the supply water tank 1 and the activated carbon is supplied from the activated carbon injection equipment 8 to the supply water tank 1 before the membrane module 11. In this embodiment, the on-line flow current value measured by the flow ammeter 9 is used as an index to operate while constantly changing the flocculant injection rate from the flocculant injection facility 7 and based on the absorbance of the raw water absorptiometer 5. The activated carbon injection rate is controlled. That is, it is difficult to flock only by injecting the flocculant, and after microscopic organic substances are adsorbed by activated carbon, the flocculant is added to form a micro floc, which is changed to a fouling component that can be peeled off by physical cleaning.

The activated carbon injection rate is performed based on the following injection rate formula, for example.
Activated carbon injection rate = a × raw water absorbance + b
Here, the symbols a and b are parameters, and can be adjusted based on the indicated value by the treated water absorbance meter 18 after membrane filtration and the results of experiments conducted in the past.
According to Example 2, by supplying the flocculant and activated carbon to the supply water tank 1, an increase in the membrane differential pressure can be further suppressed as compared with Supply Example 1.

(Example 3)
When pretreatment is not carried out (when neither flocculant nor activated carbon is injected), there is a concern that the fouling component peeling rate by physical cleaning is increased, but the increase in the differential pressure until physical cleaning is increased. The A large increase in the membrane differential pressure until the physical cleaning results in an increase in pump power. Therefore, it is desirable to determine the chemical injection rate in consideration of these factors.

  Since this Example 3 is required to predict the membrane differential pressure when the operation is continued under the conventional cleaning conditions and chemical injection rate, the predicted value ΔP of the membrane differential pressure increase due to fouling accumulation during filtration. Therefore, the chemical cleaning time is predicted, and the chemical cleaning cost, pump power cost, and chemical cost are evaluated in total.

The predicted value ΔP for the increase in the membrane differential pressure is obtained as follows.
First, the predicted value ΔP [Pa] is expressed by the following [Equation 1]. Here, Rr in one item of [Formula 1] is represented by the following [Formula 2], and Rir in two items of [Formula 1] is represented by the following [Formula 3].

Formula 1

Formula 2

Formula 3

(ａ) ろ過中におけるファウリングの蓄積による膜差圧上昇の予測値ΔＰ[Ｐａ]は、上記式（１）で表される。即ち、膜差圧上昇は、抵抗Ｒr（物理洗浄で低減可能）と抵抗Ｒir（温水洗浄である程度低減可能）によるものと定義でき、ケーク抵抗Ｒrと膜モジュールの細孔の閉塞による抵抗Ｒirとも定義できる。模式的に示せば、図４の符号Ｐ１から符号Ｐ２までの抵抗がＲr、符号Ｐ２から符号Ｐ３までの抵抗がＲirとなる。なお、図４中、符番２１はファウリング物質が蓄積されたケーキ層を、符番２２は膜モジュール１１の膜を示す。

(a) The predicted value ΔP [Pa] of the increase in membrane differential pressure due to accumulation of fouling during filtration is expressed by the above formula (1). That is, the increase in the differential pressure of the membrane can be defined as a resistance Rr (which can be reduced by physical cleaning) and a resistance Rir (which can be reduced to some extent by hot water cleaning), and is also defined as a resistance Rir due to clogging of the cake resistance Rr and the pores of the membrane module. it can. If it shows typically, the resistance from the code | symbol P1 of FIG. 4 to the code | symbol P2 will be Rr, and the resistance from the code | symbol P2 to the code | symbol P3 will be Rir. In FIG. 4, reference numeral 21 indicates a cake layer in which fouling substances are accumulated, and reference numeral 22 indicates a membrane of the membrane module 11.

(b) Rr in the above formula (1) is a function of turbidity accumulation x (integrated value), physical cleaning, and flocculant / activated carbon injection, and is represented by the above formula (1). Further, Rir is expressed by the above equation (3) on the assumption that the organic substance deposition y (integrated value) is a function of hot water cleaning / flocculating agent / activated carbon injection.
The parameters α, β, K, n, and y in the equation can be identified by, for example, the least square method when there is past operation record data. Further, when there is no operation record data such as introduction of membrane filtration equipment, it can be determined by the experimental results shown in FIGS. 5 (A) and 5 (B), for example. Here, FIG. 5A is a characteristic diagram showing the relationship between the deposition amount of the fouling material and the film differential pressure when the parameter n according to the equation (4) is 2. FIG. 5B is a characteristic diagram showing the relationship between time and membrane differential pressure. For example, the slope α in FIG. 5B is a filtration resistance, the slope β is a macro view of the slope α, and a constant pressure filtration test that tests the filtration pressure, filtration amount, filtration differential pressure, etc. of a given raw water. Obtained from the results.

Further, according to the definition of Rr, Rr = 0 should be set at the time of physical cleaning, but it needs to be a model expression that can express a case where sufficient cleaning cannot be performed depending on the physical cleaning flow rate and the cleaning cycle. That is, the peeling amount wa substances by physical washing is defined as follows using the coefficients k _1. That is, the cleaning effect at the time of backwashing was regarded as a decrease in accumulated turbid mass, and was defined by the following formula (6).
Pr (n) = (1-k ₁ ) Rr (n-1) (6)
However, _{k 1} represents a cumulative turbidity mass removal rate is 0.0 ≦ _{k 1} ≦ 1.0. This removal rate k ₁ is expressed by the following equations (7) and (8).
k ₁ = exp (−h ₁ / Qb) (however, flag = 1) (7)
k ₁ = 0 (however, flag = 0) (8)
The flag (determination flag) “1” indicates that physical cleaning is being performed, and the flag “0” indicates that the cleaning is not being performed. In addition, the symbol Qb in the equation (7) indicates a physical cleaning flow rate [m ³ / h], and h ₁ indicates an adjustment parameter. FIG. 6 is a characteristic diagram showing the backwash flow rate and cumulative turbidity removal rate when h ₁ = 0.001. FIG. 6 shows that the cumulative turbidity removal rate becomes 1 when the backwash flow rate exceeds a certain value (about 2 m ³ / h).

Further, the basic idea at the time of hot water cleaning is the same as that of reversible fouling peeling by physical cleaning. However, the peeling is the resistance Rir due to the blockage of the membrane pores, and the removal rate is determined by the hot water cleaning flow rate, the hot water cleaning cycle, and the hot water temperature.
As described above, Rr and Rir are obtained from the equations (2) to (5), and these values are introduced into the equation (1) to obtain the predicted value ΔP of the increase in the membrane differential pressure.

  According to Example 3, since it is possible to predict the chemical cleaning time by obtaining the predicted value ΔP of the increase in the membrane differential pressure due to the accumulation of fouling during filtration, it is possible to estimate the chemical cleaning cost, the pump power cost, and the chemical cost in total. can do.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Further, various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, you may combine suitably the component covering different embodiment. Specifically, for example, by controlling the flocculant injection rate using the removal rate of the membrane fouling component obtained by carrying out warm water cleaning at a predetermined timing in addition to the flow current value index, the film etc. The clogged fouling material can be further peeled off. Moreover, you may make it connect the pH adjuster injection | pouring equipment for inject | pouring a pH adjuster into a supply water tank, and adjust pH in raw | natural water.

  DESCRIPTION OF SYMBOLS 1 ... Supply tank, 2a-2e ... Piping, 3 ... Raw water pump, 4 ... Strainer, 5 ... Raw water absorptiometer, 6 ... pH adjuster injection equipment, 7 ... Flocculant injection equipment, 8 ... Activated carbon injection equipment, 9 ... Flow Ammeter, 10 ... pretreatment pump, 11 ... membrane module, 12 ... treated water tank, 13 ... compressor, 14 ... hot water supply device (hot water supply device), 18 ... treated water absorbance meter, 19 ... control unit.

Claims (3)

In a water purification membrane filtration monitoring and control system that separates and removes turbid components in water,
A supply tank to which raw water is supplied;
A flocculant injecting device for injecting the flocculant into the supply water tank;
An activated carbon injection device for injecting activated carbon into the supply water tank;
A membrane module that is disposed downstream of the feed water tank and filters pretreated water;
A treated water tank disposed downstream of the membrane module;
A hot water supply device for supplying hot water to the membrane module;
An absorptiometer for measuring the absorbance of the raw water supplied to the feed water tank;
A current meter for measuring the current of raw water supplied to the membrane module from the supply water tank;
A controller that is electrically connected to each of the flow meter and the flocculant injection device, and that controls the flocculant injection rate from the flocculant injection device using an on-line flow current value measured by the current meter as an index; A water purification membrane filtration monitoring control system characterized by comprising:   2. The water purification membrane according to claim 1, wherein the flocculant injection rate is controlled using the removal rate of the membrane fouling component obtained by performing warm water cleaning at a predetermined timing in addition to the index of the flowing current value. Filtration monitoring and control system.   The water purification membrane filtration monitoring control system according to claim 1 or 2, further comprising a pH adjusting agent injection facility for injecting a pH adjusting agent into the water supply tank.

Images