KR101692789B1

KR101692789B1 - Water-treatment apparatus using membrane unit and Method thereof

Info

Publication number: KR101692789B1
Application number: KR1020150126719A
Authority: KR
Inventors: 박연종; 주정돈; 권혁; 구본성; 김진만
Original assignee: 에스케이건설 주식회사; (주)티에스케이워터; 서울특별시(상수도사업본부장)
Priority date: 2015-09-08
Filing date: 2015-09-08
Publication date: 2017-01-04

Abstract

In an embodiment, a water treatment method comprising an aggregation pretreatment step and a cleaning step, wherein the flocculation pre-treatment step comprises: calculating a plurality of flocculant injection amounts according to predetermined conditions; Measuring membrane permeability and membrane contamination rate index; And comparing the measured membrane permeability and the membrane fouling index with a preset reference value to determine a coagulant injection amount.

Description

[0001] The present invention relates to a water treatment apparatus using a membrane unit and a water treatment method using the membrane unit,

Embodiments relate to a water treatment apparatus and a water treatment method using a membrane unit.

As the pollution of the water source becomes more intense and the water shortage becomes serious, the need for advanced water treatment is increasing. Recently, microfiltration or ultrafiltration process has attracted attention in water treatment field among various advanced water treatment techniques.

However, membrane contamination is an obstacle to the field application of microfiltration or ultrafiltration. Membrane contamination is a phenomenon that various foreign substances present in the influent water are deposited on the surface of the membrane or adsorbed on the surface of the membrane to reduce the water permeability of the membrane. There are various kinds of foreign substances causing pollution, such as floating particles, colloids, organic matter, and microorganisms. Therefore, it is difficult to anticipate the membrane contamination by these various contaminants in advance.

Recently, a method of diagnosing the progress of membrane contamination by collecting and analyzing operation data in microfiltration or ultrafiltration process in real time has been proposed. This method is known as a method for directly monitoring and controlling the film contamination phenomenon in an actual process. However, since membrane fouling is analyzed based on the operation state of the process, it has a function to diagnose only the membrane fouling which is currently in progress without predicting the membrane fouling that will appear in the future. Therefore, if the membrane contamination actually occurs, it is disadvantageous because it can not cope with the contamination beforehand.

The embodiment provides a water treatment apparatus and method for controlling the operation condition of the membrane filtration process in real time and controlling the coagulation pre-treatment condition, the recovery rate of the treatment water, the maintenance interval and method, and the recovery interval and method.

The water treatment method according to the embodiment is a water treatment method in which a coagulant is injected into inflow water and filtration is performed using a membrane unit, the coagulation pretreatment step of determining the injection amount of the coagulant, the step of filtering the influent water using the membrane unit, And a cleaning step of cleaning the membrane unit when it is determined that the membrane unit is contaminated, wherein the flocculation preprocessing step comprises: calculating a plurality of flocculant injection volumes; Measuring membrane permeability using membrane permeation rate and transmembrane pressure, and measuring membrane contamination rate index (f _{a, j} ) using Equation 4; And determining the coagulant injection amount by comparing the measured membrane permeability and the membrane fouling index with a preset reference value,
Wherein the step of calculating the plurality of coagulant injected quantities comprises: calculating a first coagulant injected amount by Equation 1; When the algae measuring apparatus disposed in the water source determines that algae are not generated, the amount of the flocculant injected is calculated according to Equation 2-1, and when it is determined that the algae has occurred, the second flocculant Calculating an injection amount; And calculating a third coagulant injection amount by which the amount of coagulant injected is controlled to 1.0 ppm when the turbidity is less than or equal to a predetermined value, in the case where the turbidity of the inflow water is a predetermined value or more and,
The determining of the amount of the coagulant injected may be performed by selecting the smallest value among the first to third coagulant injection amounts when the membrane permeability is larger than the reference value and the film contamination rate index is smaller than the reference value, Wherein the membrane permeability index is less than a reference value and the film contamination rate index is less than a reference value or the membrane permeability is less than a reference value, And when the film contamination rate index is greater than or equal to the reference value, an intermediate value among the first to third coagulant injection volumes is selected.

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According to the embodiment, it is possible to optimize the amount of coagulant used and improve the quality of the treated water by varying the amount of the coagulant injected according to various conditions such as the turbidity of the influent water.

In addition, the load of the membrane can be appropriately maintained by changing the recovery rate of the membrane filtration process depending on the operation state of the influent water quality and membrane filtration process.

In addition, the cycle and method of membrane cleaning can be optimized according to the operating conditions of the incoming water quality and the membrane filtration process.

The various and advantageous advantages and effects of the present invention are not limited to the above description, and can be more easily understood in the course of describing a specific embodiment of the present invention.

1 is a conceptual diagram of a water treatment apparatus according to an embodiment of the present invention,
FIG. 2 is a flowchart of an aggregation preprocessing process according to an embodiment of the present invention,
3 is a flowchart of a maintenance cleaning process according to an embodiment of the present invention,
Figure 4 is a flow chart of the recovery cleaning process in accordance with one embodiment of the present invention.

The present invention is capable of various modifications and various embodiments, and specific embodiments are illustrated and described in the drawings. It is to be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

Terms including ordinals, such as first, second, etc., may be used to describe various elements, but the elements are not limited to these terms. The terms are used only for the purpose of distinguishing one component from another. For example, without departing from the scope of the present invention, the second component may be referred to as a first component, and similarly, the first component may also be referred to as a second component. And / or < / RTI > includes any combination of a plurality of related listed items or any of a plurality of related listed items.

It is to be understood that when an element is referred to as being "connected" or "connected" to another element, it may be directly connected or connected to the other element, . On the other hand, when an element is referred to as being "directly connected" or "directly connected" to another element, it should be understood that there are no other elements in between.

The terminology used in this application is used only to describe a specific embodiment and is not intended to limit the invention. The singular expressions include plural expressions unless the context clearly dictates otherwise. In the present application, the terms "comprises" or "having" and the like are used to specify that there is a feature, a number, a step, an operation, an element, a component or a combination thereof described in the specification, But do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, or combinations thereof.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings, wherein like or corresponding elements are denoted by the same reference numerals, and redundant description thereof will be omitted.

1, the water treatment apparatus according to the embodiment mainly includes a water treatment unit for filtering the influent water 1, a flocculant supply unit for mixing the flocculant to the influent water 1, a cleaning unit for washing the membrane unit, . &Lt; / RTI >

The water treatment section includes a membrane filtration tank 2 and a membrane unit 3 which is immersed in the membrane filtration tank 2 and filters the influent water 1. The purified water filtered can be discharged to the water pipe 5 through the pump 4. The water treatment section can be modified in various ways according to the configuration of a general advanced treatment apparatus. The inflow water 1 can be introduced into the water treatment section through the inflow pipe 1. Therefore, there is a difference in structure from the membrane filtration module including the conventional sedimentation tank.

The flocculant supply part includes a flocculant reservoir (8) and a first pump (12). The first pump 12 can inject an appropriate amount of the flocculant into the influent 1. [ Therefore, the influent 1 can be mixed with the flocculant to form flocs. The agglomerated flocs can be removed from the membrane unit 3. In this process, flocs are deposited on the membrane surface, and the inter-membrane pressure difference increases with time. The coagulant may be, but is not limited to, a PAC. The inline mixer 6 may serve to mix the flocculant into the influent 1. [

The cleaning section can supply the membrane filtration tank 2 with chemicals for cleaning the membrane unit 3. The wash station may include an acidic chemical reservoir 9, an alkaline chemical reservoir 10, and a second pump 13 for injecting the drug.

The main controller 11 controls the membrane filtration operation using the membrane unit 3 and can control the cleaning process in consideration of the contamination state of the membrane.

In the water treatment process, the main controller 11 can calculate the appropriate amount of the flocculant based on the turbidity, PH, temperature, alkalinity, and occurrence of algae or the like of the influent water 1. For example, turbidity, PH, temperature, alkalinity, etc. can be measured using a sensor disposed in the influent supply pipe. However, at least one of the turbidity, pH, temperature, and alkalinity may be an off-line detected value. The occurrence of algae can receive information from the algae measuring device disposed at the water source.

The membrane cleaning process can be roughly divided into backwash, maintenance cleaning, and recovery cleaning. The backwashing may be performed in a direction opposite to the inflow direction of the inflow water 1 to remove foreign matters from the membrane.

Maintenance and recovery Cleaning is a chemical cleaning method. The maintenance cleaning is a method of cleaning without stopping the membrane filtration process, and the recovery cleaning is a method of cleaning after stopping the membrane filtration process because the contamination of the membrane is relatively serious.

From the viewpoint of the membrane cleaning process, the main controller 11 can determine whether or not to maintain the membrane filtration rate, the membrane permeability, the membrane contamination rate index, and the turbidity, etc., according to whether they satisfy predetermined reference values. An output signal may be applied to the second pump 13 during maintenance and cleaning to introduce a suitable amount of chemical into the membrane filtration tank 2. [

2, the flocculation pre-treatment process according to the embodiment includes a step of calculating a plurality of coagulant injected amounts in accordance with predetermined conditions, a step of measuring a membrane permeability and a membrane contamination rate index, And comparing the exponent with a predetermined reference value to determine the coagulant injection amount.

The step of calculating a plurality of coagulant injected amounts may include calculating (S102) a first coagulant injected amount using at least one of alkalinity, turbidity, pH, and temperature information of influent water (S102) Calculating the injection amount (S104, S105), and calculating the third flocculant injection amount (S106).

The step S102 of calculating the first flocculant injection amount can be calculated by first measuring the alkalinity, turbidity, pH, and temperature of the influent water (S101) and using the value. At this time, some values may be input values measured by offline measurement. Then, the first coagulant injection amount can be calculated using the following equation (1).

[Formula 1]

Where T is the turbidity (NTU), P is the pH, A is the alkalinity (mg / L) and t is the temperature (C).

In the step (S104, S105) of calculating the second flocculant injection amount, the injection amount can be adjusted depending on whether algae are generated or not. When algae are generated in the water source, even if the same amount of coagulant is administered, the flocculation may not be performed well and the problem of film contamination may occur. Therefore, when no algae is generated, the injection amount is calculated using Equation 2-1 (S104), and when the algae is generated, the injection amount can be calculated using Equation 2-2 (S105).

[Formula 2-1]

[Formula 2-2]

Where T is the turbidity of the influent (NTU).

The step (S106) of calculating the third flocculant injection amount can be derived using the following equations (3-1) and (3-2). Equation 3-1 is applied when the turbidity of the influent water is 3.2 NTU or more, and Equation 3-2 is applicable when the turbidity is less than 3.2 NTU.

[Formula 3-1]

[Formula 3-2]

Does = 1

That is, when the turbidity is less than 3.2 NTU, the amount of the third flocculant injected can be adjusted to 1.0 ppm.

For example, if a tide occurs and the turbidity of the influent water is 4.0 NTU, the main controller 11 may calculate three flocculant adjustments using Equation 1, Equation 2-2, and Equation 3-1.

In the steps (S107 and S108) of measuring the membrane permeability and the membrane contamination rate index, the membrane contamination rate index (fa _{, j} ) can be calculated using the following equation (4).

[Formula 4]

J is the first measured inter-membrane pressure difference in the same filtration period, η is the centipoise of the influent water, and J Is the membrane permeation rate (L / m2-hr). Since the inter-membrane pressure difference is measured n times in one filtration period, ΔPn, j is actually the last measured intermembrane pressure within the filtration period, and ΔP1, j is the first measured intermembrane pressure difference.

The membrane permeation rate can be measured using a flow meter. Membrane permeability can be obtained by membrane permeation rate / intermembrane pressure difference. The membrane permeability is better as the membrane permeability is higher than the reference value, and the membrane contamination rate index is better as it is lower than the reference value.

The step of determining the amount of coagulant injected may include (1) when the membrane permeability is larger than the reference value (S109), and when the membrane contamination rate index is smaller than the predetermined reference value (S110), the contamination of the membrane is relatively small and the permeability is good. The minimum value can be selected (S112).

(2) If the membrane permeability is less than the reference value and the membrane contamination rate index is equal to or greater than the reference value (S111), the membrane is rapidly contaminated and the permeability is decreased.

(3) If the membrane permeability is less than the reference value and the membrane contamination rate index is smaller than the reference value, or if the membrane permeability is larger than the reference value and the membrane contamination rate index is greater than or equal to the reference value, the middle value among the calculated injections can be selected (S113).

Here, the reference value of the film contamination rate index may be 0.20 to 0.40. In one example, the membrane contamination rate index may be 0.25. The reference value of the membrane permeability may be 250 L / m ² -hr-bar.

When the film contamination rate is slower (smaller) than the reference value, and when the film permeability is faster (larger) than the reference value, it can be determined that the reference value is satisfied.

3, the maintenance cleaning method includes steps (S202 to S206) of measuring membrane permeation rate, backwash efficiency evaluation index, membrane permeability, and turbidity (S202 to S206), and evaluating the membrane permeation rate and turbidity product, membrane permeability, And performing a maintenance cleaning process when two or more of the indexes do not satisfy the preset reference value.

Measuring (S202 to S206) is the after performing the membrane filtration operation for a predetermined cycle, membrane permeation rate (flux, jv), backwash efficiency rating scale (F _b), film permeability (Pe), and turbidity (Tu) . The membrane permeation rate (jv), membrane permeability (Pe) and turbidity (Tu) can be measured by the method described above.

During the membrane filtration operation, several backwash processes are performed. Therefore, in the measuring step, the backwash efficiency evaluation index (f _b ) is measured using the following equation (5) (S203).

[Formula 5]

Where ΣΔPi, j + 1 / n is the average intermembrane pressure in the j + 1th filtration period, ΣΔPi, j / n is the mean intermembrane pressure in the jth filtration period, ΣΔPi, 1 / n Where n is the number of times the inter-membrane pressure difference is measured within a filtration period, η is the centipoise of the influent and J is the membrane permeation rate (L / m2-hr).

Determining step of performing a maintenance cleaning process, the base film satisfy the transmission rate (jv) and the product, the film transmission rate (Pe), and backwash efficiency rating scale (F _b) 2 gaji reference value more than a pre-set of the turbidity (Tu) If not, the maintenance cleaning process is performed. Although three index factors are illustrated in the present embodiment, the present invention is not limited thereto and various index factors may be determined.

The first indicator factor may be the product of the turbidity (Tu) of the influent and the membrane permeation rate (jv). If the first index factor is smaller than the reference value AC, it is determined that the reference value is satisfied (S206). For example, the reference value may be 250 L-NTU / m ² -hr, but is not limited thereto.

The second indicator parameter may be the membrane permeability (Pe). If the film permeability is larger than the reference value Pe, C2, it is determined that the reference value is satisfied (S207). For example, the reference value may be 150 L / m ² -hr-bar, but is not limited thereto.

The third indicator factor may be the backwash efficiency rating index (F _b ). Since the backwash efficiency evaluation index is inversely proportional to the backwash efficiency, it can be determined that the backwash efficiency calculated by Equation 5 is smaller than the reference value (Fb, c) (S209). For example, the reference value may be 0.2, but is not limited thereto.

For example, when the product of the turbidity of the influent water and the membrane permeation rate is smaller than the reference value and the membrane permeability is larger than the reference value (S206, S208), the product of the turbidity of the influent water and the membrane permeation rate is smaller than the reference value and the backwash efficiency evaluation index is smaller than the reference value The membrane filtration operation can be resumed.

If at least two of the above-mentioned first to third index factors do not satisfy the reference value, it is determined that the film is contaminated and MC is performed (S212). However, when two or more of the three index factors satisfy the reference value, it is determined that the degree of membrane contamination is not serious and the membrane filtration operation can be resumed.

In this case, however, it can be determined whether or not the predetermined maintenance cycle (MC time) has passed (S211). If the period has already elapsed, the maintenance cleaning may be performed (S212). The maintenance cycle can be set by the operator according to the experimental or empirical rules. The maintenance cycle may be set to once a week or once a month, but not limited to this.

After the maintenance cleaning, the maintenance cleaning evaluation index Fc is calculated using the following equation (6) (S213).

[Formula 6]

Where ΣΔPi and m + 1 / n are the average transmembrane pressure in the initial filtration step after the maintenance cleaning, and ΣΔPi and m / n are the average transmembrane pressure in the final filtration step before maintenance cleaning, n is the number of times the inter-membrane pressure difference was measured within one filtration period, m is the number of filtration cycles at the time of maintenance retention, and? is the viscosity of the influent water (centipoise), and J is the membrane permeation rate (L / m2-hr).

Since the maintenance cleaning evaluation index Fc is inversely related to the maintenance cleaning efficiency, it can be interpreted that the larger the value is, the lower the efficiency is. Therefore, when the maintenance cleaning evaluation index is larger than the reference value Fc, c, a warning signal can be output to the display. The reference value may be 0.5, but is not limited thereto. Thereafter, it can be determined whether maintenance cleaning should be performed again (S217).

The re-execution of maintenance cleaning may depend on the operator's choice or on the value of the evaluation index. For example, in the case where the maintenance cleaning evaluation index is 0.7 or more, the maintenance cleaning may be set again.

When the maintenance evaluation index is less than or equal to the reference value, the membrane permeability is measured again. If the membrane permeability is smaller than the reference value, the warning signal is output again. If the membrane filtration rate is larger than the reference value, membrane filtration operation can be resumed.

Referring to FIG. 4, in the recovery cleaning step, the membrane filtration process is first operated for a predetermined period (for example, one cycle), and then the membrane-to-membrane pressure immediately before membrane cleaning is measured (S301, S302). Thereafter, the transmittance immediately before the film is cleaned is calculated (S303). Then, the target cleaning efficiency is determined (S304).

The concentration of NaOCl and citric acid for achieving the target cleaning efficiency at the membrane permeability immediately before the present recovery cleaning can be calculated using the following equation (7) (S305).

[Equation 7]

x0 is the membrane permeability immediately before the recovery, x1 is the concentration of NaOCl, x2 is the concentration of citric acid, and A1, A2, B1 and B2 C1 are constants.

Thereafter, the calculated chemical NaOCl and citric acid may be injected to perform chemical cleaning (S306).

Thereafter, the inter-membrane pressure difference after the membrane washing is measured (S307), and the actual cleaning efficiency Ye can be calculated using the following equation (8) (S308).

[Equation 8]

Where P2 is the transmembrane pressure immediately before membrane cleaning, P1 is the transmembrane pressure difference after membrane washing, eta is the viscosity of the influent water (centipoise), and J is the membrane permeation rate (L / m ² -hr).

Thereafter, when the actual cleaning efficiency Ye is larger than the target cleaning efficiency Y, the recovery cleaning is terminated. When the actual cleaning efficiency is smaller than the target cleaning efficiency, a warning signal is output to the display, .

Claims

A method for treating water by injecting a coagulant into an influent and filtering the same using a membrane unit, comprising the steps of: an aggregation pretreatment step of determining the amount of the coagulant to be injected; a step of filtering the influent water using the membrane unit; And a cleaning step of cleaning the membrane unit when the membrane unit is cleaned,
The coagulation pre-
Calculating a plurality of flocculant injected quantities;
Measuring membrane permeability using membrane permeation rate and transmembrane pressure, and measuring membrane contamination rate index (f _{a, j} ) using equation (4); And
Determining a coagulant injection amount by comparing the measured membrane permeability and the membrane fouling index with a preset reference value,
Wherein the step of calculating the plurality of coagulant injected amounts comprises:
Calculating a first coagulant injection amount by the following formula 1;
When the algae measuring apparatus disposed in the water source determines that algae are not generated, the amount of the flocculant injected is calculated by the following equation (2-1), and when it is determined that algae has occurred, the amount of the flocculant injected by the equation 2 flocculant injection amount; And
If the turbidity of the influent water is equal to or greater than a predetermined value, calculating the amount of the coagulant injected by the following formula 3-1 and calculating the amount of the third coagulant injected amount controlling the coagulant injection amount to 1.0 ppm when the turbidity is not more than the predetermined value and,
The step of determining the coagulant injection amount may include:
When the membrane permeability is higher than the reference value and the film contamination rate index is smaller than the reference value, the lowest value among the first to third coagulant injection volumes is selected,
When the membrane permeability is not more than a reference value and the film contamination rate index is not less than a reference value, the largest value among the first to third coagulant injection volumes is selected,
When the film permeability is less than a reference value and the membrane contamination rate index is less than a reference value, the membrane permeability is greater than a reference value, and the membrane contamination rate index is equal to or greater than a reference value, Way.
[Formula 1]

Where T is the turbidity (NTU), P is the pH, A is the alkalinity (mg / L) and t is the temperature (C).
[Formula 2-1]

[Formula 2-2]

[Formula 3-1]

Where T is the turbidity of the influent (NTU).
[Formula 4]

Where ΔPn, j is the nth measured inter-membrane pressure difference within the jth filtration period, ΔP1, j is the first measured inter-membrane pressure difference within the jth filtration period, η is the centipoise of the influent water, J is the membrane permeation rate (L / m2-hr).

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The method according to claim 1,
Wherein the cleaning step includes a maintenance cleaning step of cleaning the membrane unit without stopping the filtration step, and a recovery cleaning step of stopping the filtration step and cleaning the membrane unit.

The method according to claim 6,
In the maintenance cleaning step,
Measuring permeation rate, backwash efficiency evaluation index, membrane permeability, and turbidity; And
And performing a maintenance cleaning process when two or more index factors of the product of membrane permeation rate and turbidity, membrane permeability, and backwash efficiency evaluation index do not satisfy predetermined reference values,
The backwash efficiency evaluation index (f _{b, j} ) is measured by the following equation (5).
[Formula 5]

8. The method of claim 7,
Wherein,
Wherein the retentive cleaning is performed when at least two of the product of the membrane permeation rate and the turbidity, the membrane permeability, and the backwash efficiency evaluation index satisfies a predetermined reference value, but the predetermined maintenance period has passed.