KR20130115970A

KR20130115970A - Method for recovering raw water from the concentrate of a membrane water purification process using serially connected double stage filter

Info

Publication number: KR20130115970A
Application number: KR1020120090786A
Authority: KR
Inventors: 김규태; 윤창한; 배시열; 김충환; 권순범; 문용택; 이선주
Original assignee: 주식회사 생; 한국수자원공사
Priority date: 2012-04-13
Filing date: 2012-08-20
Publication date: 2013-10-22

Abstract

The present invention uses a two-stage filter connected in series to reduce the final external effluent quantity by recovering more than about 70% of the membrane backwash discharged to the purified water in the membrane purification method, to reduce the waste water treatment process site and to treat the membrane backwash discharged The present invention relates to a membrane purification method capable of recovering raw water from a membrane separation process from membrane apparatus backwashing water for improving economic efficiency.

Description

METHODS FOR RECOVERING RAW WATER FROM THE CONCENTRATE OF A MEMBRANE WATER PURIFICATION PROCESS USING SERIALLY CONNECTED DOUBLE STAGE FILTER}

The present invention relates to a membrane purification method that can recover the raw water from the membrane device backwashing water of the membrane separation process of water purification using a microfiltration membrane or an ultrafiltration membrane apparatus, and more particularly, using a membrane separation process in the field of water purification treatment. Membrane device discharged to the outside after water treatment to remove the turbidity by using two-stage filtration from the backwash effluent water to recover the purified water by reducing the quantity of effluent to reduce the size of the device for treatment of effluent, and to stabilize the water quality It is about membrane constant method.

When using surface water such as river water, valley water, lake water, or submerged water, or ground water as raw water for water purification, the concentrated water generated after water purification is usually equipped with a concentration tank to comply with environmental standards for discharge. It will be discharged after reduction. In particular, the water purification process using the membrane water purification method using a microfiltration membrane or an ultrafiltration membrane has a disadvantage in that the water recovery rate is low because the amount of backwash discharge is about 10%, which is about 5 times higher than the existing water purification process using sedimentation basins and sand filtration. A low water recovery rate not only increases the environmental burden due to the decrease in water use efficiency, but also increases the amount of water use due to the increase of raw water intake, and increases the energy cost of transferring raw water from the intake to the water purification plant and to comply with environmental standards when discharged. This leads to an increase in the investment cost of the equipment and an economical cost that is expensive to operate. In addition, since the backwater discharge is generated only at the time of the backwash, the turbidity change of the backwater discharge over time is so severe that an equalization tank must be overdesigned to evenly treat it, and the power cost of a large mixer to continuously mix Has the disadvantage (see FIG. 4).

1 is a flow chart schematically showing a conventional membrane water purification method using a membrane device. Filtrate filtered from membrane device is supplied to purified water after disinfection, but backwash discharged from membrane device is injected with backwashing effluent to settle and remove suspended solids after coagulation of suspended solids in order to satisfy effluent environmental regulations. And discharge through a concentration tank is a common process. At this time, the polymer coagulant is injected to improve floc sedimentation in the concentration tank by coagulating floc. Even though the turbidity of the effluent is lower than that of the purified water flowing into the water purification plant, the polymer coagulant, which is an organic substance, is mixed. Water cannot be recovered to raw water by tap water. As shown in FIG. 1, the use of a polymer flocculant for the condensation of suspended solids and suspended matter is inevitable for the operation of the concentration tank used in the existing effluent treatment process. Due to the organic matter, even if the effluent turbidity is lower than that of the purified water, it cannot be recovered. In addition, if the amount of discharged water is large, the size of the concentration tank, which is a wastewater treatment facility for treating this within the legal discharge standard, becomes large, and there is a disadvantage of using a lot of water purification plant sites. Severe. In other words, if the amount of discharged water is reduced, the burden is greatly reduced even if the wastewater treatment facility designed to comply with the stable discharged water standard is excessively designed and constructed.

In the water purification plant using the membrane water purification method, the membrane backwash discharged water can be recovered as raw water or purified water without using any chemicals used in the water purification process. Since investment and operating costs are high, there is a limit to economics in practical application.

The present invention is to overcome the problems of the prior art as described above, an object of the present invention is to remove the turbidity contained in the backwash discharge water generated in the water purification plant using the membrane device lower than the turbidity of the raw water of the purification plant, but the same A method of recovering purified water from backwash discharged from membrane backwater that prevents contaminated raw water recovered from backwashed water by using only chemicals such as inorganic coagulants and pH-controlling chemicals. It provides a membrane purification method with the addition of a process to discharge high concentration backwash water below the legal emission standard.

Another object of the present invention is to reduce the amount of external raw water flowing into the water purification plant using a membrane device by about 8% to reduce the energy and water resources consumed when transferring from the intake plant to the water purification plant, and to reduce the amount of discharged water discharged to the outside of the water purification plant about 80% Reduction of more than% reduces the size and investment cost of the wastewater treatment process to comply with environmental regulations, and reduces the operating cost, thereby improving the economics of the construction and operation of the water purification plant, and overdesigning the wastewater treatment facility for stable discharge. Since the quantity is reduced and there is no burden on the construction cost, it helps to stabilize the water quality of the discharged water.

In one aspect of the present invention for achieving the above object is a membrane water purification method for pre-treatment of raw water supplied from the outside of the water purification plant and filtering with a membrane device, the filtered purified water is supplied as a constant through the post-treatment,

It relates to a membrane purification method for recovering the raw water for purified water from the membrane device backwash discharge, characterized in that it comprises the step of filtering the backwash discharged water generated in the membrane device with a two-stage series filter after the mixed flocculation.

According to the method for recovering the raw water for purified water from the membrane apparatus backwash discharge water included in the present invention, using two filters connected in series, the membrane device backwash discharge water having high turbidity is not contaminated by dissolved organic substances such as polymer coagulant, and thus the raw water for purified water. By reducing the amount of wastewater discharged to the outside and reducing the energy costs associated with the transportation of raw water, the size of the wastewater treatment facility of the membrane purification method can be reduced. Not only can the initial investment and direct operating costs be significantly reduced, but it can also contribute greatly to the quality of the discharged water.

1 is a schematic flowchart of a membrane water purification method using a conventional membrane device.
2 is a schematic diagram of a membrane water purification method further comprising a step of recovering purified water from the membrane apparatus backwash discharged water to which an embodiment of the present invention is applied, and a discharge water treatment process for discharging the highly concentrated effluent according to the recovery below a legal standard. It is a flow chart.
3 is a schematic block diagram of a water purification recovery process for explaining a method for recovering purified water from membrane apparatus backwash discharge water according to one embodiment of the present invention.
Figure 4 shows the turbidity change of the membrane backwash effluent generated in the actual membrane water purification plant can be seen that the turbidity changes very rapidly over time.
FIG. 5 is a graph showing the change in turbidity removal rate of the membrane apparatus backwash discharge water according to the inorganic coagulant injection concentration obtained by the field test of the two stage filter during the recovery of purified raw water by the method of the present invention. A graph illustrating the optimal concentration of flocculant to be injected during filtration.
FIG. 6 is a graph showing the turbidity of the membrane apparatus backwash discharge obtained by field experiments and the filtered water turbidity change of the two-stage filter during the recovery of purified raw water by the method of the present invention.
Figure 7 is a graph showing the change in the recovery rate of purified water obtained by the field test of the two-stage filter during the recovery of purified water by the method of the present invention.

The above objects, features and other advantages of the present invention will become more apparent by referring to the preferred embodiments of the present invention with reference to the accompanying drawings. Hereinafter, with reference to the accompanying drawings will be described in detail a method for recovering the raw water for purification from the membrane device backwash discharge water according to an embodiment of the present invention. Embodiments of the present invention are shown by way of example, and are not limited to the configuration of the accompanying drawings. In order not to obscure the present invention, a detailed description of known configurations may be omitted or simplified.

In the embodiment of the present invention, the term “fiber filter” refers to a fibrous media comprising a bundle of fine flexible yarns fixed to a support and a microfiber including a fibrous mediator pore controller capable of squeezing the fibrous media upon filtration and relaxing the fibrous media upon backwashing. Means a filtration device using. The fibrous media may be composed of a polymer film having a fiber thickness of 1 to 1000 μm or a heat sealable composite fiber coated with another polymer material on the polymer fiber core. Such a fiber filter may be a single fiber filter or a plurality of fiber filters may be connected in parallel in multiple stages.

One embodiment of the present invention is a membrane water purification method in which the raw water supplied from the outside of the water purification plant is filtered through a membrane device, and the filtered purified water is supplied as a constant through post-treatment. It relates to a membrane purification method for recovering the raw water for purified water from the membrane apparatus backwash discharge, characterized in that it comprises the step of filtration with a two-stage serial filter.

Specifically, in the method of the present invention, in recovering purified water from the membrane backwashing water, the membrane backwashing water is first filtered using a primary fiber filter, and the secondary fibers connected in series with the primary fiber filter. The filtered water of the primary fiber filter is secondarily filtered using a filter to recover the raw water for purification of water lower than the turbidity of the raw water supplied to the membrane separation process.

In addition, the external discharge process of the conventional membrane device backwash discharged the supernatant water from which the suspended solids were removed using a concentration tank after the inorganic flocculant and the polymer flocculant were injected. At this time, the coagulant injection step may be performed by automatically adjusting the coagulant injection concentration by the three-point coagulant automatic control injection method according to the turbidity of the influent.

The backwash discharged water of the two-stage fiber filter of the present invention is more than three times higher concentration of suspended solids contained in the membrane device backwashed discharge water, so that the suspended solids must be removed within the legal discharge standard in order to discharge them externally within the legal discharge standard. For this purpose, an additional filtration process is required following the conventional concentration tank. In other words, an inorganic coagulant is injected into the front end of the pump to transfer the high concentration backwash discharged from the two-stage fiber filter, which is a recovery process, to the concentration tank, followed by rapid mixing. The sedimentation of the supernatant can lead to the removal of suspended solids from the suspended solids, and the concentration of suspended solids in these supernatants is likely to exceed legal discharge standards. At this time, the concentrated sludge collected by sedimentation at the bottom of the concentration tank is transferred to the dehydration process, solidified by dehydration, and then discharged to the outside, and the dewatered filtrate and the final filter backwashed. After being returned, the two-stage fiber filter is introduced again into the concentration tank together with the backwash discharged water.

Before the filtration by the primary fiber filter, a flocculant may be injected into the membrane apparatus backwashing water to increase the size of the floc floc by rapid mixing, and then the filtration may be performed by the fiber filter.

In the method for recovering purified raw water from the membrane apparatus backwash discharged water according to the embodiment of the present invention, the primary fiber filter first removes a relatively large size of suspended solids and turbidity in the membrane apparatus backwash discharged water to generate primary filtered water. The fiber filter removes suspended matter and turbidity remaining in the primary filtrate secondly to generate secondary filtrate turbidity lower than the turbidity of raw water introduced from the membrane water purification method, thereby allowing recovery to raw water for purification.

Here, the primary fiber filter serves to reduce the burden of the secondary fiber filter to remove microparticles by first removing most contaminants including large particles primarily by increasing the gap (pore) between the fibers. In addition, the secondary fiber filter serves to remove the remaining fine particles in the secondary by narrowing the pores for the production of the final filtered water to provide raw water for water purification below the turbidity of the raw water flowing from the water purification plant. Therefore, the fiber thickness of the fiber filter of the primary fiber filter is preferably used thicker than the fiber thickness of the fiber filter of the secondary fiber filter. For example, the thickness of the fiber filter of the primary fiber filter is 10 ~ 300㎛, the thickness of the fiber filter of the secondary fiber filter is used 10 ~ 100㎛ but the fiber thickness of the fiber filter of the primary fiber filter The same as the fiber thickness of the fiber filter medium of the secondary fiber filter is preferably about three times.

When the fibrous media is pressed onto the support, the size of the pore produced by the fibrous media pressed onto the support is preferably 1 to 100 µm. If the pore size of the fibrous media is less than 1 μm, the efficiency of removing suspended solids may be improved, but the quality of the treated water may be improved. Conversely, when the pore size of the fibrous media exceeds 100 μm, the filtration flow rate is increased to decrease the efficiency of removing the suspended solids.

The fiber filter is, for example, located on the outside of the support in which the fine pores are densely formed as a support, and made of a bundle of fine flexible yarns, and the fiber filter is fixed to the support, and the fiber filter is compressed when the water to be treated is filtered. And it may include a fiber pore controller for relaxing the fiber media when backwashing.

The support is a cylindrical body or a cylindrical body having a hole formed on the surface, or a structure of a filter plate provided with a plurality of fibrous media support rods at regular intervals, the fibrous media is a fiber filter media that is arranged densely on the outside of the support to form a filter layer , The gap of the fibrous media is controlled by applying a physical force such as rotational compression or pressing or pulling the fibrous media. To this end, an actuator is coupled to the outside to form an action stage in which rotation, pulling, or pressing motion occurs. An actuator is a drive, such as a motor or cylinder, that generates a rotational or elevating displacement. When filtering the raw water, the retraction of the actuator is used to pull the media claw located at the top of the media or to twist the media ledge at the top and bottom to narrow the gap between the fibrous media. Foreign materials in the raw water are efficiently filtered while flowing between the fibrous media.

The fibrous media is located outside of the support and the treated water filtered through the fibrous media moves into the interior of the support. The fiber filter may be a pressure or gravity fiber filter depending on the power to be treated to pass through the fiber filter. A pressure type fiber filter is a method of passing a fiber filter by directly applying pressure to the water to be treated by using a pump. A gravity fiber filter uses a head difference that is the difference between the height of the inlet and the outlet of the water to be treated to gravity. It is filtered by. Low-concentration raw water with low concentration of suspended solids has low pressure for filtration and gravity fiber filter which requires little filtration power has the advantage of low operating cost and manufacturing cost. It is more desirable for highly contaminated raw water where a degree of power is required.

In the method of the present invention, the backwash water used in the secondary filter can be reused as the backwash water of the primary filter, and the final injection concentration of the flocculant can be optimized through the three-point coagulant control method when the flocculant is administered.

FIG. 2 is a flowchart illustrating a membrane purification method further including a step of recovering raw water for purification of purified water from a membrane device backwash discharge and a discharge water treatment step for discharging discharged water below a legal discharge standard. In the method of the present invention, the backwash effluent discharged from the membrane device is treated with a two-stage fiber filter to recover the raw water for water purification and the discharge water quantity is reduced, and the filtrate is recovered as the raw water for the membrane separation process. Instead of reducing the size of the phosphorus concentration tank to less than one third, an additional filter was applied at the rear end.

3 is a block diagram of a recovery process for recovering raw water for purification from membrane treated backwash discharged water as an embodiment to which the method of the present invention is applied. Referring to FIG. 3, during the membrane separation process in the method of the present invention, the backwash discharge water generated in the membrane device 130 is stored in the membrane treated backwash discharge water storage tank 10 for storing the membrane treated backwash discharge water, and then the raw water from the reservoir. It is supplied to the primary fiber filter 70 through a pump. At this time, the inorganic coagulant may be mixed and aged by rapid mixing and maturing tank after the inorganic coagulant is injected before being filtered by the primary fiber filter 70 as necessary. At this time, the inorganic coagulant injection operation unit 30 includes an on-line turbidimeter 20 which automatically measures the turbidity of the supplied membrane treated backwash discharged water; The optimum inorganic coagulant injection amount is determined from the real-time turbidity information provided by the on-line turbidimeter 20 of the membrane treated backwash water and the on-line turbidimeter 90 of the two-stage filtrate filtrate. Accordingly, the inorganic coagulant injector 40 injects the coagulant into the supplied membrane treated backwash discharged water, and the rapid coagulation device 50 instantly mixes the injected coagulant with the membrane purified water backwashed discharged water. The size of the fine flocs produced by the rapid flocculator 50 is increased. The actual coagulant injection concentration is automatically adjusted by the three-point coagulant injection control method previously entered into the MMI according to the concentration of the membrane backwash water flowing into the two stage filter.

When the membrane treated backwash discharged water is supplied to the primary fiber filter 70 through the aging tank 60, the coarse flocculation floc is first removed to generate primary filtrate, and then the secondary fiber filter 80 is used as the primary filter water. Secondary removal of suspended solids and suspended solids in the primary filtrate. The secondary fiber filter 80 may be equipped with an online turbidity meter 90 for measuring the turbidity of the secondary filtrate in real time and transmitting it to the flocculant injection reminder device, and the secondary filtrate filtered by the secondary fiber filter 80. Is stored in the filtered water storage tank 100 and then transferred to the purified water tank of the membrane separation process. The backwash effluent in the two-stage fiber filtration process is concentrated in a high concentration of suspended solids, and the inorganic and polymer coagulants are injected into the backwash effluent in the two-stage fiber filtration process, and then filtered through a concentration tank and a filter.

If the filtration continues and the amount of particles trapped on the filtration surface of the primary fiber filter 70 increases and the filtration resistance increases beyond the limit, backwash water is supplied in the direction opposite to the filtration direction in the filter and air is supplied from the bottom of the filter. Implement backwashing supplies.

In the method of the present invention, backwashing water is supplied from the backwashing pump to the secondary fiber filter 80 for efficient backwashing, and backwashing air is supplied to the lower part of the filter by the backwashing air supply means 110. The backwash discharged water generated in the fiber filter may be stored in the fiber filter backwashing water storage tank 120. The backwash air supply means may comprise a blower and an diffuser.

In the method of the present invention, the primary or secondary fiber filter may be backwashed by the fiber filter treated water supplied from the filtrate storage tank for storing the secondary filtrate connected to the secondary fiber filter. In addition, when a plurality of fiber filters are connected in parallel in each fiber filtration step, instead of using the secondary filtration water stored in the filtrate reservoir as the backwash water, a part of the filtration water generated in the filter connected in parallel to the same filtration step is reversed. Can be used as a face wash.

In order to reduce the amount of backwash discharged water, the first backwashed water backwashed with a secondary filter having a lower pollution than the primary filter can be supplied to the primary filter as backwash water and reused. In this case, in order to smoothly supply the first backwash discharge water to the first filter backwash water, it may include a means for separating the air contained in the first backwash discharge water to discharge to the atmosphere.

According to the method for recovering purified water from the present invention using a two-stage filter in which two filters are connected in series, about 70% or more of the membrane treated backwash discharged water is recovered as raw water for purified water, and the backwash discharged from the filter having less than about 30% It is transferred to the wastewater treatment process consisting of a concentration tank and a filter, and treated under the discharge standard and discharged to the outside.

Hereinafter, the present invention will be described in more detail with reference to examples, but these are for illustrative purposes only and should not be construed as limiting the present invention.

Example

In order to verify the performance of the method for recovering the purified water from the membrane treated backwash discharged water of the present invention as a result of injecting different concentrations of flocculant injection in the raw water recovery process for purified water in the membrane treated backwash discharged water, as shown in Table 1 and As shown in FIG. 5, the optimal injection concentration of 17% PAC was about 20 ppm.

17% PAC injection concentration Turbidity average removal rate 15 ppm 94.09% 20 ppm 96.84% 25 ppm 95.58% 30 ppm 94.84%

Therefore, according to the result of long-term operation by the 3-point flocculant injection automatic control device based on 20 ppm of 17% PAC, the membrane purified water backwash discharged to about 63 NTU as shown in Table 2 and FIG. Water Purification Method It was confirmed that the raw water for purification may be recovered from the membrane treated backwash discharged water by the technology provided by the present invention because it can be filtered to 1.42 NTU, which is lower than the turbidity (about 6 NTU) of raw water flowing in from the water purification plant.

Item Water purification
enemy Membrane constant method
Backwash discharge Primary Fiber Filter
filtrate Secondary fiber filter
filtrate Turbidity (NTU) 6 63.2 27.4 1.42 Removal rate (%) - - 56.6 97.8

As a result of measuring the recovery in the same period showing the turbidity removal efficiency, a graph as shown in FIG. 7 was obtained, and the average recovery was 83.4%.

In the method of the present invention, in addition to the membrane treated backwash water, organic supernatant, such as a polymer coagulant, and a concentrated tank supernatant, a filtered backwash water, fiber filter backwash water, etc., which are used to reconcentrate the sedimentation tank sludge, are used as influent water in the recovery process. It can also be used to recover the raw water for purification.

While the invention has been shown and described with reference to preferred embodiments thereof, it will be appreciated that the invention can be variously modified and modified without departing from the spirit or scope of the invention as defined by the following claims. Those skilled in the art will readily understand. Therefore, the protection scope of the present invention will be defined by the claims and the equivalent scope to be described later.

10: membrane treated backwash discharge water storage tank
20: Membrane treated backwash water online turbidimeter
30: flocculant injection device 40: flocculant injection device
50: rapid mixing agglomeration device 60: aging tank
70: primary filter 80: secondary filter
90: filtered water online turbidimeter 100: secondary filtered water reservoir
110: backwash air supply means 120: two stage filter backwash discharge water storage tank
130: membrane device

Claims

In the membrane purification method in which the raw water supplied from the outside of the water purification plant is pretreated and filtered through a membrane device, and the filtered purified water is supplied as a constant through post-treatment.
Membrane water purification method for recovering the raw water for purified water from the membrane device backwash discharge, characterized in that it comprises the step of filtering the backwash discharged water generated in the membrane device with a two-stage serial filter after the mixed flocculation.

The membrane according to claim 1, further comprising the step of injecting a flocculant into the backwash effluent of the two-stage series filter, removing the suspended solids through a concentration tank and a subsequent filter, and then discharging the membrane to the outside. Membrane water purification method for recovering raw water for purified water from backwash discharged water.

According to claim 2, wherein the flocculant injection step is a step of automatically adjusting the flocculant injection concentration by the three-point coagulant automatic control injection method according to the turbidity of the influent water proceeds to the membrane device to recover the raw water for purified water from the backwash discharged Integer method.

According to claim 1, wherein the size of the filter medium of the primary filter of the two-stage series filter having the same to three times the thickness of the filter medium of the secondary filter membrane membrane for recovering the raw water for purified water from the backwash effluent of the membrane device Way.

The method of claim 1, wherein the two-stage series filter comprises a fibrous media consisting of a bundle of fine flexible yarn fixed to the outside of the support, and a fibrous median pore controller for controlling the size of the voids between the fibrous media Membrane purification method for recovering raw water for purification from membrane backwash discharged water.

2. The method of claim 1, wherein the method further comprises backwashing the primary or secondary filter with filter treated water supplied from a secondary serial filtration water reservoir. Membrane water purification method to recover.

The method according to claim 6, wherein in the case of a plurality of filters connected in parallel in each filtration step, instead of using the secondary filtration water stored in the filtrate reservoir as backwash water, A membrane purification method for recovering raw water for purified water from a membrane device backwash discharge, characterized in that a portion is used as backwash water.

The method of claim 6, wherein the method further comprises the step of reusing the backwash water used in the secondary filter to the backwash water of the primary filter, membrane purification method for recovering the raw water for purification from the membrane apparatus backwash discharged water. .

9. The method according to any one of claims 1 to 8, wherein the method is used for treatment of concentrated tank supernatant, filter paper backwash water, and filter backwash water without using organic compounds such as polymer coagulants and toxic substances. Membrane constant method.