KR20180100011A - A method for physical washing using osmotic pressure back washing in FO-RO process - Google Patents

Abstract

The present invention relates to a forward osmosis-backward osmosis treatment process comprising: (a) a step in which raw water pre-treated by an inflow water pretreatment unit (110) is introduced into one side of an FO treatment unit (100); (b) a step in which a high concentration induction solution from an induction solution supply unit (120) is introduced to the other side around a separation membrane in the FO treatment unit (100); (c) a step in which a part of the raw water introduced in step (a) flows through a separation membrane by a forward osmosis principle due to the high concentration induction solution introduced in step (c) while the raw water introduced in step (a) flows to the separation membrane in the FO treatment unit (100); (d) a step in which raw water is filtered while passing through the separation membrane and discharged from the other side of the FO treatment unit (100) as treated water; and (e) a step in which another part which does not pass through the separation membrane is discharged from one side of the FO treatment unit (100) as concentrated water. In the physical cleaning using osmotic pressure backwashing, the raw water pretreated in step (a) is introduced to the other side of the FO treatment unit (100), and the induction solution is introduced into the one side of the FO treatment unit (100) in step (b).

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a physical washing method using osmotic pressure back washing in a forward osmosis-reverse osmosis treatment process,

Field of the Invention [0002] The present invention relates to the field of water treatment technology, and more particularly, to a physical cleaning method using osmotic backwash in a forward osmosis-reverse osmosis treatment process.

In general, the membrane filtration process refers to a physical filtration method that separates and removes impurities in raw water by passing water through a membrane as a filter medium to obtain clean filtered water.

Recently, research on commercialization of forward osmosis (FO) filtration and direct osmosis (DO) filtration has been actively conducted as opposed to reverse osmosis (RO) filtration.

As shown in FIG. 1, when the raw water and the inducing solution, which are solutions having different concentrations, are injected into the FO processing unit 100, the positive osmosis process is performed in such a manner that a membrane having a selective permeability is sandwiched, To maintain this concentration of equilibrium, an osmosis principle is used, which is a physical phenomenon that moves through a separation membrane to a higher concentration. Here, the pressure generated by a relatively large amount of water moving toward the high concentration is called osmotic pressure. The driving force for the osmosis separation is an osmotic pressure gradient (hydraulic gradient), unlike the reverse osmosis process using hydraulic pressure )to be.

The positive osmosis process has many advantages. Membrane pollution is small and the concentration of salt content can be changed according to various kinds of influent water and energy consumption is much lower than reverse osmosis process when the recovery of the draw solution is not considered.

In addition, the permeability and salt removal rate of the purified osmosis membrane itself are high, and the recovery rate is relatively high. When the desalination plant is refurbished, the osmosis membrane can be replaced with a reverse osmosis membrane or a nanofiltration membrane and modules can be integrated.

However, there is a problem that high energy consumption required for regeneration such as separation and recovery and re-concentration of the draw solution diluted as described above with treated water is indispensable in order to be used as a sole process in the forward osmosis process. Therefore, at present, the cleansing technology can not be solely used as a desalination technology, and a reverse osmosis-positive osmosis treatment process fused with a separate RO treatment unit 200 as shown in FIG. 2, or a combination of a MBR- Process is mainly used. 2 shows that raw water and inductive solution supplied from the influent water preprocessing unit 110 and the induction solution supply unit 120 are injected into the FO processing unit 100 and then subjected to RO treatment in the RO treatment unit 200 to generate final treatment water.

On the other hand, membrane contamination necessarily occurs in the filtration process of the FO processing unit 100. Here, "membrane fouling" is a phenomenon in which various foreign substances present in the influent water flowing into the separation membrane are deposited on or adsorbed on the surface of the filtration membrane to reduce the permeation rate of the separation membrane. Based on the cause substance, the contamination of the particle material membrane by the colloid or the suspended solids, the contamination of the organic material film by the adsorption of the organic material such as natural organic material, the contamination of the biofilm by the adhesion or growth of the microorganism, And inorganic substance film contamination.

Membrane contamination in the desalination plant is the biggest problem in operation in the field because it reduces the performance of the membrane and lowers the recovery rate.

In order to solve this problem, a method of strengthening the pretreatment process to minimize membrane contamination in advance or a method of optimizing the operating condition of the main treatment process may be used. In general, when the membrane contamination is progressed to a certain level, A physical cleaning such as flushing or a chemical cleaning (CIP) through a chemical is performed in order to recover the permeation performance of the substrate.

The most effective is chemical cleaning (CIP). When performing frequent chemical cleaning (CIP), the production performance is greatly deteriorated due to the stoppage of the treated water, and the increase of the chemical cost and the waste treatment cost The maintenance performance deteriorates and deterioration of the rejection performance of the separation membrane used and the deformation and aging of the separation membrane ultimately lead to an increase in the total operation management cost.

Therefore, it is very important to carry out the cleaning at an appropriate point in time. For this purpose, the importance of effectively predicting and evaluating the degree of membrane contaminants is increasing day by day. Conventionally, various methods for this purpose have been proposed and used, and this will be examined in detail.

Currently, the most widely used method is the SDI (Silt Density Index) measurement method.

This means that the SDI index obtained by measuring the SDI of the influent source is a method for predicting the membrane contamination tendency of the influent source in the desalination process using the reverse osmosis membrane / the osmosis membrane and the nanofiltration membrane. In general, if the SDI index value is less than 2 to 3, membrane contamination is considered to be an insignificant inflow source. If the SDI index value is 5 or more, it is judged to be a serious inflow source.

However, the SDI index is only an indirect measure of the possibility of membrane fouling, especially when the permeate is measured at a pressure of 30 psi using a membrane with a diameter of 47 mm (in other words, 0.45 pore size) There is a big problem that the influence of colloid or organic matter smaller in size can not be evaluated.

In addition, since the desalination process mainly using the reverse osmosis membrane / the osmosis membrane and the nanofiltration membrane uses a cross-flow filtration mode in which the direction of flow of the inflow water and the direction of permeation of the filtration membrane are orthogonal to each other, There is a problem that the dead-end mode and filtration principle are different.

In order to overcome the limitations of the SDI index, a modified fouling index (MFI) measurement method, a modified fouling index by ultrafilter (MFI-UF) measurement method, and a modified fouling index by nanofilter (MFI- Since all of them use one separator and are measured in the same filtration mode in the same way, the problem of being different from the crossflow filtration mode in the actual desalination process is not solved.

In this regard, the patent literature will first be reviewed as follows.

Korean Patent Publication No. 10-2011-0089710, Korean Patent Publication No. 10-2014-0016417, Korean Patent Publication No. 10-2010-0057262, Korean Patent Publication No. 10-2013-0081436, Korean Patent Laid- 2014-0076197 uses a combination of various microfiltration (MF), ultrafiltration (UF) and nanofiltration (NF) membranes to quantify membrane contamination by particulate matter, colloidal material, organic material, etc. as a quantitative film contamination index And a method for predicting by film source is proposed.

It is advantageous in that it is possible to measure in parallel and in series manner with a plurality of membranes in order to enhance the portability of the measurement, increase the measurement accuracy of the membrane contamination index, and shorten the measuring time.

However, these methods do not solve the problem of using a membrane having a pore size of 0.45, which is the same as that of the SDI index, and the problem of being different from the cross flow filtration mode in the actual desalination process.

Korean Patent Laid-Open No. 10-2014-0054670 discloses a method of detecting a membrane contamination index in real time in a membrane filtration process operated at a low pressure of microfiltration (MF) and ultrafiltration (UF) (CIP) according to the calculated film contamination index by using the rate of change of the film contamination index, and to propose a device and a method for controlling the membrane contamination using the film contamination index capable of selectively performing the optimal chemical cleaning (CIP) according to the calculated film contamination index.

Similarly, the problem of using a 0.45-pore separation membrane in the same manner as the SDI index and the problem of being different from the cross-flow filtration mode in the actual desalination process can not be solved.

Korean Patent Laid-Open No. 10-2013-0085220 proposes a real-time monitoring apparatus for receiving measurement information from a sensor such as a flow meter and a pressure gauge of a seawater desalination plant to calculate the degree of membrane fouling of the reverse osmosis membrane and diagnose and control the same through a control unit.

However, it is limited to indirect measurement of membrane contamination through real-time measurement and information interpretation of sensors such as flow meter, pressure gauge, pH meter, and thermometer as a result.

Korean Patent No. 10-0811199, Korean Patent No. 10-1318578 and Korean Patent Publication No. 10-2011-0102750 disclose a flow field flow method useful for measuring molecular weight and particle size distribution such as chromatography, Fractionation method is used to calculate the area of the separation chromatogram of natural organic materials to evaluate the adsorption degree according to the characteristics of the membrane. Also, dynamic hysteresis of the reverse osmosis membrane and the nanofiltration membrane is measured to predict the membrane contamination of the membrane and to predict the chemical and physical non-uniformity simultaneously or individually.

However, this is limited to organic film contamination, the problem is that continuous measurement is impossible due to the limitation of the direct measurement pressure range, which is not applicable in practical desalination facilities.

Korean Patent Laid-Open No. 10-2014-0037357 points out that not only the degree of film contamination through the film contamination index is predicted but also it is very important to clean the contaminated membrane to normalize the water treatment process, This paper proposes a method for securing objective grounds such as selection of cleaning agent used in the process of cleaning membrane and guidelines on cleaning performance. That is, by supplying the cleaning agent to the surface of the separation membrane in the contaminated state, and by supplying the washing water to the separation membrane, the membrane washing index calculated by measuring the amount of the washing water passing through the separation membrane, A cleaning index measuring device is proposed.

However, since it is difficult to confirm membrane contamination below 0.45 pore size, and the type and amount of detergent are all based on the filtration mechanism of the pre-treatment microfiltration membrane (MF), nanofiltration (MF) and reverse osmosis (RO) separator is different from the cleaning condition of the RO separator.

The problem is that the nanofiltration membrane and the reverse osmosis membrane, which are operated at high pressure by solute and solvent diffusion movement principle, do not have a pore size. Therefore, a microfiltration membrane that operates at low pressure by pore- The filtration mechanism of the membrane is due to the difference.

In other words, unlike the microfiltration membrane and the ultrafiltration membrane, the nanofiltration membrane and the reverse osmosis membrane / positive osmosis membrane are generally composed of a particulate material, an organic substance, an inorganic substance (scaling) It is virtually impossible to apply the proposed technique to desalination facilities such as reverse osmosis / forward osmosis in that it is not possible to reverse-wash the biomembrane contamination.

Korean Patent Publication No. 10-2011-0089710 Korean Patent Publication No. 10-2014-0016417 Korean Patent Publication No. 10-2010-0057262 Korean Patent Publication No. 10-2013-0081436 Korean Patent Publication No. 10-2014-0076197 Korean Patent Publication No. 10-2014-0054670 Korean Patent Publication No. 10-2013-0085220 Korean Patent No. 10-0811199 Korean Patent No. 10-1318578 Korean Patent Publication No. 10-2011-0102750 Korean Patent Publication No. 10-2014-0037357

Accordingly, the present invention proposes a method capable of effectively reducing the level of film contamination by removing contaminants from the quasi-osmosis membrane, particularly in the process of treating the osmosis membrane as described above.

In addition, it is possible to apply environmentally friendly techniques without using a separate chemical, so as to improve the quality of the treated water and to propose a method that can ensure cost-effectiveness.

In order to solve the above-described problems, an embodiment of the present invention provides a method of controlling the osmosis-reverse osmosis process in which (a) raw water pretreated by the influent pre-treatment unit 110 is supplied to one side of the FO processing unit 100 An incoming step; (b) introducing the high concentration induction solution from the induction solution supply unit 120 into the other side of the FO processing unit 100 with the separation membrane as a center; (c) While the raw water flowing in the step (a) flows into the separation membrane in the FO processing unit 100, part of the raw water passes through the separation membrane due to the high concentration inducing solution introduced in the step (c) ; (d) the raw water is filtered and discharged from the other side of the FO processing unit 100 as process water while passing through the separation membrane; And (e) the other part that has not passed through the separation membrane is discharged from the one side of the FO processing unit 100 as concentrated water. In the physical cleaning using osmotic backwashing, the pre-treatment in step (a) Wherein the raw water flows into the other side of the FO processing unit 100 and the induction solution flows into the one side of the FO processing unit 100 in the step (b).

In addition, it is preferable that the flow direction of the raw water on the basis of the separation membrane of the FO processing unit 100 is reversed in accordance with the physical cleaning using the osmotic pressure backwash.

In the step (a), when the flux of the FO processing unit 100 is less than a predetermined standard, it is preferable that physical cleaning using osmotic backwashing is performed.

It is preferable that the inflow water pre-processing unit 110 and the inductive solution supply unit 120 are in fluid communication with one side and the other side of the FO processing unit 100, but are controlled as valves.

In addition, it is preferable that the step (e) further comprises: (f) the process water discharged in the step (d) flows into the RO processing unit 200 and is filtered by the reverse osmosis principle.

Through the present invention, the consolidation of the cake layer is relieved by the osmotic backwash, and the reversibly film-impregnated layer is cracked. Accordingly, in the forward osmosis-reverse osmosis treatment process, the efficiency of the FO process, which is a kind of pretreatment, is increased, and optimized pretreatment is possible.

Particularly, even during long-term continuous operation of the forward osmosis-reverse osmosis treatment process, the film contamination of the positive osmosis decreases and the efficiency of the whole process increases.

As a result, it is possible to minimize the cleaning time, the input power, the amount of the chemical used, and the amount of the washing waste generated in the cleansing process in the osmosis-reverse osmosis treatment process through the present invention, thereby stably operating the entire facility and economically Saving effect can be achieved.

Figure 1 shows a prior art osmotic osmotic device.
FIG. 2 is a conceptual diagram for explaining a process of a forward osmosis-reverse osmosis treatment according to the present invention.
FIG. 3 and FIG. 4 are conceptual diagrams for explaining a physical cleaning method using osmotic backwash in the forward osmosis-reverse osmosis treatment process according to the present invention.

Hereinafter, "raw water" means a fluid to be injected into the forward osmosis-reverse osmosis treatment process. Seawater, wastewater, sewage water, or water may be used.

Hereinafter, the term "inducing solution" refers to a high-concentration solution to be injected into the forward osmosis-reverse osmosis treatment process to perform positive osmosis. For example, if the raw water is sewage water, the inducing solution may be seawater, but it may be any fluid that can be applied for the positive osmosis treatment.

Hereinafter, the present invention will be described in detail with reference to the drawings.

Referring to FIG. 2, the system for describing the forward osmosis-reverse osmosis treatment process according to the present invention.

The system according to the present invention includes an FO processing unit 100 and an RO processing unit 200.

The raw water having passed through the influent pre-processing unit 110 flows into one end of the FO processing unit 100. The raw water may be any water to be subjected to filtration, as described above.

After the raw water flows into the FO processing unit 100, it passes through the separation membrane according to the principle of the positive osmosis due to the high concentration of the inductive solution flowing on the opposite side with respect to the separation membrane. In this process, the raw water is filtered. Here, the induction solution is supplied from a separate induction solution supply part 120.

The 'filtered water', which is filtered raw water, flows together with the induction solution, and the induction solution is separated by a separate treatment. The treated water from which the induction solution has been separated is discharged from the FO processing unit 100 and flows into the RO processing unit 200. In the RO treatment unit 200, the treatment water is once again subjected to reverse osmosis filtration to increase the treatment efficiency.

On the other hand, the raw water that has not passed through the separation membrane is discharged from the FO treatment unit 100 as concentrated water. Some of the contaminants that are not permeated by the separation membrane during the passage of raw water through the separation membrane are discharged together as concentrated water, And remains as contaminants in the separator.

The osmotic pressure backwashing physical cleaning method according to the present invention functions to remove contaminants remaining in the separation membrane.

3 and 4, a description will be given of a physical cleaning method using osmotic pressure backwashing according to the present invention.

The method for physically cleaning the osmotic pressure backwash according to the present invention is to remove contaminants on the separation membrane by reversing the concentration difference between the both ends of the separation membrane of the FO processing unit 100. [

Basically, in the FO processing unit 100, the fluid flows from the low concentration side to the high concentration side based on the separation membrane. In the present invention, contaminants are removed on the surface by periodically or non-periodically reversing the concentration.

For example, in the case of FIG. 2, the concentration of the raw water flows to the right toward the high concentration solution. Since the flow direction of the raw water is fixed in this process, contaminants that have not passed through the separation membrane are always accumulated on the side where the raw water flows.

When the contaminants are piled up, it is possible to reverse the direction of the fluid flow by reversing the concentration gradient periodically or aperiodically. In this case, it is possible to remove the contaminants from the film surface by cracking the membrane- (See FIG. 4).

In order to set the concentration gradient to the opposite, the source water with a relatively low concentration and the induction solution with a relatively high concentration should be supplied in reverse.

As shown in FIG. 3, a bypass line is provided between the influent pre-processing unit 110 and the induction solution supply unit 120 for this purpose. By opening and closing the valve, the raw water flows into the other side of the FO processing unit 100 to which the raw water flows normally, and the induction solution flows into the other side of the FO processing unit 100 into which the induction solution flows.

As a result, the concentration gradient is reversed so that the raw water does not flow to the right but to the left as shown in FIG. At this time, the membrane contaminant layer accumulated on the left side of the separation membrane is cracked by the raw water and relaxed in consolidation, so that it can be mixed with concentrated water and discharged.

In one embodiment of the invention, this concentration gradient inverse setting can be made at regular intervals. In this case, the filtration treatment of the raw water is temporarily stopped, and the osmotic pressure backwashing physical washing according to the present invention is performed. When the physical cleaning is completed, the raw water is filtered again.

In another embodiment of the present invention, a separate sensor (not shown) for sensing the flux of the FO processing unit 100 is further provided, and the concentration gradient inverse setting may be automatically performed according to the sensed value of the sensor.

That is, when the flux of the FO processing unit 100 is decreased to a predetermined reference value or less, this means that the film contamination of the FO processing unit 100 has progressed considerably, and the reverse of the concentration gradient is executed.

In this case, there is an advantage that the time for temporarily stopping the filtration process is reduced, and the reduction in the treatment efficiency can be minimized.

While the present invention has been described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims. It will be appreciated that embodiments are possible. Accordingly, the scope of protection of the present invention should be determined by the claims.

100: FO processor
110: Inflow water pre-
120: induction solution supply part
200: RO processor

Claims (5)

In the forward osmosis-reverse osmosis treatment process,
(a) the raw water pretreated by the influent pre-processing unit 110 flows into one side of the FO processing unit 100;
(b) introducing a high concentration induction solution from the induction solution supply unit 120 into the other side of the FO processing unit 100 with the separation membrane as a center;
(c) While the raw water flowing in the step (a) flows into the separation membrane in the FO processing unit 100, part of the raw water passes through the separation membrane due to the high concentration inducing solution introduced in the step (c) ;
(d) the raw water is filtered and discharged from the other side of the FO processing unit 100 as process water while passing through the separation membrane; And
(e) the other part that does not pass through the separation membrane is discharged from the one side of the FO processing part 100 as concentrated water,
During the physical cleaning using the osmotic pressure reverse cleaning,
The raw water pretreated in the step (a) flows into the other side of the FO processing unit 100, and the induction solution flows into the one side of the FO processing unit 100 in the step (b)
Physical cleaning method.
The method according to claim 1,
The flow direction of the raw water with respect to the separation membrane of the FO processing unit 100 is reversed according to the physical cleaning using the osmotic pressure reverse cleaning,
Physical cleaning method.
The method according to claim 1,
The step (a)
When the flux of the FO processing unit 100 is equal to or less than a preset reference value, physical cleaning using osmotic reverse cleaning is performed,
Physical cleaning method.
The method according to claim 1,
The inflow water pre-processing unit 110 and the inductive solution supply unit 120 are in fluid communication with one side and the other side of the FO processing unit 100,
Physical cleaning method.
5. The method according to any one of claims 1 to 4,
After the step (e)
(f) the treated water discharged in the step (d) flows into the RO treatment unit (200) and is filtered by the reverse osmosis principle.
Physical cleaning method.

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