KR101144580B1 - Apparatus and method for membrane filtration with automatic coagulating control using screaming current - Google Patents

Abstract

PURPOSE: Membrane filtration-based water treating apparatus and method for automatically controlling coagulation pre-treatment using streaming current are provided to maximize the efficiency of membrane filtration-based water treatment and to prevent the contamination of a separating membrane. CONSTITUTION: A membrane filtration-based water treating apparatus includes a raw water bath(110), a mixing and coagulating bath(120), a membrane filtration unit(130), a streaming current meter(140), and a coagulant injecting amount controlling unit(150). The mixing and coagulating bath mixes raw water and coagulant. The streaming current meter measures the streaming current value of the mixed water. The coagulant injecting amount controlling unit compares the streaming current value and a reference value. Based on the comparison result, the injecting amount of coagulant is determined and the reference value is corrected.

Description

Apparatus and method for membrane filtration with automatic coagulating control using screaming current}

The present invention relates to a coagulation pretreatment automatic control membrane filtration water treatment apparatus and method using a flow current, and more specifically, to determine the coagulant injection amount by using the flow current value (SCV, stream current value), IRRsop) is periodically checked and reflected to calibrate the SOP (streaming current optimum set point) to automatically set the flocculant injection amount and minimize the fouling. A water treatment apparatus and method.

In recent years, as the pollution of the water source becomes serious, interest in purified water quality has increased and the demand for advanced purified water treatment has increased. Therefore, supplementation of existing water treatment facilities or introduction of new processes have been attempted. However, in order to supplement existing water purification facilities or to introduce new advanced water treatment facilities, many difficulties are involved, including securing the site. Therefore, not only stable water quality but also advanced water treatment process using membrane filtration that is easy to operate and maintain is proposed. It is becoming. Membrane filtration is a method of separating contaminants in raw water using a membrane having a selective permeation function, which has the advantage of reliably removing suspended substances of a predetermined size or more contained in raw water.

In this membrane filtration process, the pre-agglomeration process is essential for preventing membrane fouling, and it is suitable for membrane filtration process because it can directly affect the treatment performance of membrane filtration process due to the efficiency of the membrane pretreatment process. The selection of the coagulation pretreatment process is very important.

In the conventional water treatment process, the method used to control and control the amount of flocculant injection can be largely divided into a jar-test method and a turbidity proportional control method. The first jar-test method performs jar-test periodically to change raw water properties. The flocculant injection rate is selected by measuring the flocculation floc formation rate, sedimentation efficiency, turbidity removal efficiency, etc. and calculating the empirical judgment and empirical equation of the operator, and the second turbidity proportional control method measures the turbidity of raw water flowing into the water treatment process. Therefore, the coagulant injection amount is selected in a proportional way to the turbidity through the arithmetic equation calculated based on Jar-test or the operator's empirical judgment. Turbidity proportional control method is disclosed in Korean Patent Laid-Open No. 2005-17306. However, such a conventional flocculation pretreatment process is mainly performed to increase the size of the flocculation floc in order to improve the precipitation efficiency of the precipitation process, and a high amount of flocculant injection is likely to be added to maintain stable precipitation efficiency.

Therefore, in the conventional method, it is difficult to determine the membrane fouling effect, which is the most important factor in the operation of the membrane filtration process, and it is difficult to automatically control the pre-aggregation treatment according to the membrane fouling and the membrane pressure difference. In particular, when the coagulant is excessively added for the precipitation efficiency as in the conventional method, the membrane fouling is aggravated by the unreacted coagulant, which makes it difficult to operate the membrane filtration device. It is necessary to automatically control the flocculant injection amount in consideration of the effect of the flocculant itself on the contamination of the filtration membrane.

On the other hand, even when the conventional automatic flocculation control technique is applied, membrane fouling control is not effectively performed, and thus there is a limitation in improving membrane filtration process performance such as recovery rate and filtration flow rate.

KR 2005-17306 A

The present invention has been made to solve the above problems, it is determined by the flow current value (SCV, stream current value) to determine the amount of coagulant injection and mean the differential pressure rise that is not recovered by physical cleaning due to membrane contamination By checking and reflecting the IRRsop periodically, the flow current value is corrected to correct the streaming current optimum set point (SOP) to set the coagulant injection amount optimally and to minimize the membrane contamination. It is an object of the present invention to provide a pretreatment automatic control membrane filtration water treatment apparatus and method.

In order to achieve the above object, the coagulation pretreatment type automatic membrane filtration water treatment device using the flow current according to the present invention includes a raw water tank in which raw water is stored, a mixing coagulation tank in which raw water and a coagulant are mixed, and raw water in which coagulant is mixed. Membrane filtration device for membrane filtration using a separation membrane, a flow current meter for measuring the flow current value of raw water mixed with the flocculant, and a flocculant injection amount for determining a flocculant injection amount by comparing the flow current value with a reference value. The reference value is corrected by the flocculant injection amount control device, and the reference value is corrected when the membrane differential pressure rising speed of the membrane filter device satisfies the condition that the set value is higher than the set value and the electric conductivity change value is higher than the predetermined value. It is characterized by.

The coagulant injection amount control device determines that the change rate of the electrical conductivity of the current electrical conductivity is higher or lower than a predetermined range (Δz) when the membrane differential pressure rising speed of the membrane filter is greater than or equal to the set value (x). The reference value may be corrected upward when the electric conductivity change value is increased by more than a predetermined range Δz, and may be corrected by decreasing the reference value when the electric conductivity change value is reduced by more than a predetermined range Δz.

The flocculant injection amount control device determines whether the turbidity value of the raw water is less than or equal to the set value (y NTU) before judging whether the electric conductivity change value is increased or decreased by a predetermined range (Δz) or more, and the turbidity value of the raw water is set to the set value ( y NTU) or less, it may be determined whether the electric conductivity change value is increased or decreased by more than a predetermined range Δz.

The flocculant injection amount control device may control the flocculant injection amount by controlling the rotation speed or the stroke of the flocculant injection pump.

The membrane pressure rise rate is calculated by the following equation.

(IRRsop: membrane differential pressure increase rate, TMP _i : initial membrane differential pressure, TMP _t : thick film differential pressure after t time, μ: viscosity of water, μ _i : viscosity of water at initial membrane pressure measurement, μ _t : viscosity of water at t time, μ ₂₅ : viscosity of water at 25 ° C.)

Agglomeration pretreatment using a flow current in accordance with the present invention automatically controlled membrane filtration water treatment method is a raw water tank in which raw water is stored; A mixing flocculation tank for mixing raw water and flocculant; Membrane filtration device for membrane filtration using a separator for the raw water mixed with the flocculant; Flow current meter for measuring the flow current value of the raw water mixed with the flocculant; And a flocculant injection amount control device for determining a flocculant injection amount by comparing the flow current value with a reference value and correcting the reference value, wherein the flocculant injection amount control device includes the flow current. The flocculant is injected as much as the difference value by comparing the flow current value measured by the measuring device with the reference value (SOP), and the reference value (SOP) is corrected in consideration of the differential pressure rise rate, turbidity value, and electrical conductivity, and the membrane. Determining whether the differential pressure rising speed is greater than or equal to the set value (x); if the differential pressure rising speed is greater than or equal to the set value (x), determining whether the turbidity value is less than or equal to the set value (y NTU); y NTU) or less, determining whether the current electric conductivity EC _p has risen or decreased by a predetermined range Δz compared to the existing electric conductivity EC _i , and the current electric conductivity E If C _p ) has risen above a certain range (Δz) compared to the existing conductivity (EC _i ), the reference value (SOP) is adjusted upward, and the current conductivity (EC _p ) is a certain range (compared to the existing conductivity (EC _i ). Δz) or more, the method may include adjusting the reference value SOP downward.

Apparatus and method for pre-aggregation auto-controlled membrane filtration water treatment method using flow current according to the present invention has the following effects.

Injecting the flocculant using the flow current value, the optimal flocculant injection amount can be corrected in real time according to the properties of the raw water, that is, the film differential pressure rise rate, turbidity value, and electrical conductivity. Can be controlled. This can prevent the membrane from being contaminated and maximize the membrane filtration water treatment efficiency.

1 is a block diagram of a coagulation pre-treatment automatic control membrane filtration water treatment apparatus using a flow current according to an embodiment of the present invention.
Figure 2 is a flow chart for explaining the flocculant injection process according to the flow current measurement.
3 is a flowchart for explaining a reference value correction method.
4 is a graph showing a change in flocculant injection amount for maintaining the SOP value when the electrical conductivity of raw water changes.
5 is a graph showing the results of the experiment for selecting the optimum aggregation concentration through the flux test (Flux Test) for each electrical conductivity.
6 is a schematic diagram of SOP variation according to IRRsop, turbidity, and electrical conductivity change.
Figure 7 is a graph comparing the results of the membrane pressure difference according to the aggregation control method.

The present invention is basically characterized by measuring the flow current value of the raw water and comparing it with a reference value (SOP, streaming current optimum set point) to inject a certain amount of flocculant accordingly. In addition, the present invention determines the optimum flocculant injection amount by checking the membrane differential pressure increase rate of the membrane and correcting the reference value (SOP), which is a reference value of the flocculant injection amount, when the membrane differential pressure increase rate is above a certain level. It is characterized by preventing deepening.

In addition, when the rate of increase in the membrane pressure is more than a certain level, as a detailed step, the electrical conductivity and turbidity of the raw water are measured, and the corresponding electrical conductivity and turbidity value are verified to verify whether the conditions are satisfied. If satisfied, the reference value SOP may be corrected. Hereinafter, with reference to the drawings will be described in detail a coagulation pre-treatment automatic control membrane filtration water treatment apparatus and method using a flow current according to an embodiment of the present invention.

Referring to Figure 1, the coagulation pre-treatment automatic control membrane filtration water treatment apparatus using a flow current according to an embodiment of the present invention is a raw water tank 110, a mixed flocculation tank 120, a membrane filtration device 130, a flow current measuring instrument 140, a streaming current detector (SCD) and a flocculant injection amount controller 150 are configured.

The raw water tank 110 is a space in which raw water taken from a river or a lake is stored, and the mixed agglomeration tank 120 mixes the raw water and the flocculant of the raw water tank 110 to aggregate the solids in the raw water. In addition, the membrane filtration device 130 serves to separate the raw water into the treated water and sludge by filtering the raw water mixed with the flocculant through the separation membrane.

The flow current measuring unit 140 (SCD) serves to measure the flow current for the raw water flowing into the membrane filter device 130 from the mixing coagulation tank 120, the flocculant injection amount control device 150 The amount of coagulant injected into the mixed agglomeration tank 120 is controlled by comparing the flow current value (SCV) measured by the flow current meter 140 (SCD) with a reference value (SOP, streaming current optimum set point). It also serves to calibrate the reference value.

The present invention is basically based on measuring the flow current of raw water as described above and comparing it with the reference value (SOP) to determine the coagulant injection amount accordingly, and in addition to the comparison value of the measured flow current value (SCV) Phosphorus reference value (SOP) is characterized in that it is possible to determine the optimal amount of flocculant injection according to the properties of the raw water by applying the correction in real time according to the properties of the raw water. The characteristics of raw water applied to the reference value correction are the film differential pressure rising speed, the electric conductivity and the turbidity value. Hereinafter, the flocculant injection process and the reference value correction method according to the flow current measurement will be described. The flocculant injection process and the reference value correction method according to the flow current measurement are performed under the control of the flocculant injection amount controller 150. 2 is a flowchart illustrating a flocculant injection process according to flow current measurement, and FIG. 3 is a flowchart illustrating a reference value correction method.

Referring to the flocculant injection process according to the flow current measurement as follows. Referring to FIG. 2, first, a reference value SOP is set (S201). The reference value SOP is a value that is compared with a flow current value measured by the flow current meter 140 (SCD), and the reference value is corrected according to the membrane differential pressure rising speed, electrical conductivity, and turbidity value measured in real time. The correction will be described later in detail.

With the reference value SOP set, the flocculant injection amount is determined. At the time of initial coagulant injection, an arbitrary amount of coagulant is determined, and the amount of the coagulant is injected into the mixing flocculation tank 120 (S202) (S203). Injection of the coagulant is made through the coagulant injection pump 160, and the determination of the coagulant injection amount is performed by the coagulant injection amount controller 150.

After the first predetermined amount of flocculant is injected into the mixing flocculation tank 120, the flow current is measured by using a dielectric current meter (SCD) targeting raw water supplied to the membrane filtration apparatus in the mixing flocculation tank 120 (S204). . Subsequently, by comparing the measured current value and the reference value (SOP) to determine whether the match (S205).

As a result of the comparison between the flow current value and the reference value, if the two values coincide with each other, the injected amount of the coagulant injected is maintained as it is (S206), and if the two values are different, the coagulant injection amount is reduced to the determination step (S202). As much flocculant is determined to be injected. For example, if the reference value is -50 and the measured flow current value (SCV) is -1000, the flocculant injection pump 160 causes the flocculant to form the flocculating agent 120 until the flow current value is -50. To be added. At this time, the comparison of the flow current value (SCV) and the reference value (SOP) and the determination of the amount of flocculant injection amount proceeds by the flocculant injection amount control device 150, through the rotation speed or the stroke control of the flocculant injection pump 160 The amount of flocculant injection can be controlled.

Next, a reference value correction method will be described. In FIG. 2, the flow current value and the reference value are compared, and accordingly, the addition of the coagulant is injected and the amount of coagulant is injected. Since the properties of the raw water are not always constant, when a constant reference value is applied regardless of the properties of the raw water, the coagulant is used. Too much or too little may cause contamination of the membrane of the membrane filtration device. In order to prevent this, the present invention is applied by correcting the reference value according to the properties of the raw water.

The process of correcting the reference value is performed in the same order as in FIG. 3. Specifically, first, the irreversible membrane pressure rise rate (IRRsop) is measured. Membrane pressure difference refers to the pressure difference between the input end and the discharge end of the membrane filtration device, and the irreversible rise rate of the pressure difference refers to the rate of increase between the initial pressure difference and the pressure difference after a certain period of time. Is calculated through.

<Equation 1>

IRRsop: irreversible rate of increase in pressure (hereinafter referred to as rate of increase in pressure)

TMP _i : Initial membrane pressure

TMP _t : T time-lapse thick film differential pressure

μ: viscosity of water

μ _i : Viscosity of water at initial membrane pressure measurement

μ _t : viscosity of water at time t

μ ₂₅ : viscosity of water at 25 ° C

If the last pressure difference rising speed is equal to or higher than the set value x (S301), it is determined whether or not the turbidity value of the raw water exceeds the set value y NTU (S302). Since the sudden increase in turbidity value is often caused by rainfall, in the present invention, when the turbidity value rises above the set value (y NTU), it is determined that it is caused by rainfall so that the reference value does not change. On the other hand, if the turbidity value is less than the set value (y NTU), it is determined whether there is a change in the conductivity of the raw water (S303). If the measured electrical conductivity EC _p is above or below a predetermined range Δz above the existing electrical conductivity EC _i , the reference value SOP is corrected by determining that the properties of the raw water have changed. For example, if the measured electrical conductivity (EC _p ) is greater than a predetermined range (Δz) than the existing electrical conductivity (EC _i ), it means that ions and contaminants in the raw water have increased, and accordingly, the reference value is increased to further add a flocculant. (SOP _{n + 1} = SOP _n + n) (S304). On the other hand, if the measured electrical conductivity (EC _p ) is less than a certain range (Δz) than the existing electrical conductivity (EC _i ) (S311), it means that the ions and contaminants in the raw water are reduced and the reference value is adjusted downward to reduce the amount of coagulant injection. (SOP _{n + 1} = SOP _n -n) (S312). In FIG. 3, when the measured electric conductivity EC _p is greater than or equal to a predetermined range Δz or less than the initial electric conductivity EC _i , the reference value is adjusted by an arbitrary value n or −n. The turbidity value and the value (n) (x) (y NTU) (z), which are the standards of conductivity, may also be selectively applied.

On the other hand, in the reference value correction method of Figure 3, there is a step of first determining whether the turbidity value is greater than or equal to the set value before determining whether the electrical conductivity changes, but the determination step for the turbidity value may be omitted.

The coagulant injection process and the reference value correction method according to the flow current measurement described above with reference to FIGS. 2 and 3, as described above, the coagulant injection process and the reference value correction method are the coagulant injection amount control device 150. Controlled by Therefore, the flocculant injection amount control unit 150 performs a flocculant injection amount control function and a reference value correction function according to the flow current value.

With respect to the flocculant injection amount control function according to the flow current value, the flocculant injection amount control device 150 is inputted when the flow current value (SCV) measured by the flow current meter 140 (SCD) is inputted, the measured flow current value and the reference value ( SOP) is compared and the coagulant injection pump is controlled to maintain the set coagulant injection amount if the two values match, and to add an additional amount of coagulant corresponding to the difference between the two values. Implemented through stroke control.

In addition, with respect to the reference value correction function, the flocculant injection amount control unit 150 receives the membrane differential pressure increase rate, the turbidity value of the raw water, and the electrical conductivity information of the raw water in real time, and the turbidity is increased if the membrane differential pressure increase rate is equal to or higher than the set value (x). It is determined whether the value is less than or equal to the set value (y NTU), and if the turbidity value is less than or equal to the set value (y NTU), the change value of the conductivity is judged, and if the change value of the conductivity is above or below a certain range (Δz), the reference value is determined. It increases or decreases to increase or decrease the amount of flocculant injection.

On the other hand, Figure 4 shows the correlation between the electrical conductivity, the flocculant injection amount, the flow current value, the coagulant injection concentration is reduced when the electrical conductivity of the target water increases under the condition of maintaining a constant SOP value. However, in the membrane permeability efficiency test results shown in FIG. 5, when the electrical conductivity increases, the actual optimum cohesive concentration increases. Therefore, when the electrical conductivity increases, the concentration of coagulant is increased by increasing the SOP value, and when the electrical conductivity is decreased, it is appropriate to proceed in the direction of decreasing the coagulation concentration by decreasing the SOP value. The validity of this proved.

6 is a schematic diagram illustrating a process of changing the SOP for each condition (membrane pressure increase rate, electrical conductivity, turbidity, reference value) according to the logic of FIG. 3. In FIG. 6, in case 1, the IRRsop value and the turbidity value were satisfied with the SOP fluctuation standard, but the SOP value was unchanged because the change in the conductivity was below a certain range. In case 2, the IRRsop value and the turbidity were satisfied with the SOP fluctuation standard. At the same time, the change in conductivity increased over a certain range and the SOP value increased. On the other hand, in case 3, the IRRsop value and turbidity met the SOP fluctuation criteria, and at the same time, the SOP value was decreased due to the decrease in the conductivity change over a certain range. Case 4 is the same as Case 1. In Case 5, the IRRsop value and the conductivity value fluctuated more than the SOP fluctuation reference value, but the turbidity was higher than the reference value.

7 is a result of measuring the change in membrane pressure after applying the conventional Jar-test method, the turbidity proportional control method and the method according to the present invention to the membrane filtration process, respectively. In this case, the membrane differential pressure rapidly increases after a certain time, whereas when the coagulation pretreatment auto-controlled membrane filtration water treatment method using the flow current according to the present invention is applied (see 'automatic control' in FIG. 6), the membrane differential pressure is kept constant. It can be seen that the membrane filtration device can be stably operated.

110: raw water tank 120: mixed flocculation tank
130 membrane filter 140 flow current meter
150: flocculant injection amount control device 160: flocculant injection pump

Claims (7)

A raw water tank in which raw water is stored;
A mixing flocculation tank for mixing raw water and flocculant;
Membrane filtration device for membrane filtration using a separator for the raw water mixed with the flocculant;
Flow current meter for measuring the flow current value of the raw water mixed with the flocculant; And
It includes a flocculant injection amount control device to determine the flocculant injection amount by comparing the flow current value with the reference value and to correct the reference value,
The reference value correction by the flocculant injection amount control device is corrected when the membrane differential pressure rise rate of the membrane filter device satisfies a condition that the set value is higher than the set value and the electric conductivity change value is higher than the predetermined value.
The flocculant injection amount control device,
If the membrane differential pressure increase speed of the membrane filter device is greater than or equal to the set value (x), it is determined whether the electric conductivity change value of the current electric conductivity compared to the existing electric conductivity is increased or decreased by a predetermined range (Δz).
If the change in conductivity changes above a certain range (Δz), the reference value is corrected upward.If the change in conductivity changes over a certain range (Δz), the reference value is corrected downward.
The flocculant injection amount control device,
Before judging whether the change in conductivity has increased or decreased by a certain range (Δz),
Determining whether the turbidity value of the raw water is less than or equal to the set value (y NTU). Coagulation pretreatment automatic control type membrane filtration water treatment device using a flow current.
delete delete The flocculant injection pump is further provided, and the flocculant injection amount control device controls the flocculant injection amount by controlling the rotation speed or the stroke of the flocculant injection pump. Membrane filtration water treatment device.
2. The membrane coagulation water treatment device according to claim 1, wherein the membrane differential pressure rising speed is calculated by the following equation.

(IRRsop: membrane differential pressure increase rate, TMP _i : initial membrane differential pressure, TMP _t : thick film differential pressure after t time, μ: viscosity of water, μ _i : viscosity of water at initial membrane pressure measurement, μ _t : viscosity of water at t time, μ ₂₅ : viscosity of water at 25 ° C.)
A raw water tank in which raw water is stored;
A mixing flocculation tank for mixing raw water and flocculant; Membrane filtration device for membrane filtration using a separator for the raw water mixed with the flocculant; Flow current meter for measuring the flow current value of the raw water mixed with the flocculant; In the membrane filtration water treatment method using a membrane filtration water treatment device comprising a flocculant injection amount control device for correcting the reference value while determining a flocculant injection amount by comparing the flow current value with the reference value,
The flocculant injection amount control device injects the flocculant as much as the difference value by comparing the flow current value measured by the flow current meter with the reference value (SOP),
The reference value (SOP) is corrected in consideration of the pressure difference rising speed, turbidity value and electrical conductivity,
Determining whether the pressure difference rising speed is equal to or greater than a set value (x);
Determining whether or not the turbidity value is less than or equal to the set value y NTU when the rate of increase in the pressure difference is greater than or equal to the set value x;
Determining whether the current conductivity EC _p rises or exceeds a predetermined range Δz relative to the existing conductivity EC _i when the turbidity value is less than or equal to the set value y NTU;
If the current conductivity (EC _p ) has risen above a certain range (Δz) compared to the existing conductivity (EC _i ), the reference value (SOP) is adjusted upward, and the current conductivity (EC _p ) is compared with the existing conductivity (EC _i ). If the predetermined range (Δz) is reduced by more than the step of adjusting the reference value (SOP), characterized in that it comprises a step of the pre-coagulation automatic control type membrane filtration water treatment method using a flow current.
7. The method according to claim 6, wherein the membrane differential pressure rising speed is calculated by the following equation.

(IRRsop: membrane differential pressure increase rate, TMP _i : initial membrane differential pressure, TMP _t : thick film differential pressure after t time, μ: viscosity of water, μ _i : viscosity of water at initial membrane pressure measurement, μ _t : viscosity of water at t time, μ ₂₅ : viscosity of water at 25 ° C.)

Images