KR101153772B1 - Water treatment process using direct filtration technique and membrane separation technique - Google Patents

Abstract

PURPOSE: A method for treating water using a direct filtering technique and a membrane separation technique is provided to save costs required for the construction and the operation of a post process according to the required quality of water. CONSTITUTION: A method for treating water includes the following: an inorganic coagulating agent is introduced into feed water, and the agent and the water are rapidly mixed in a rapid mixing unit(10); coagulated floc is enlarged in a coagulation and aging unit(20); coagulated aged water is filtered in a fiber filtering unit(30); and the filtered water is further filtered through a membrane unit(40). The fiber filtering unit includes a strainer as a support, one or more fiber filtering media layers, and an actuator. Fine holes are formed at the strainer.

Description

Water treatment method using direct filtration and membrane separation technology {WATER TREATMENT PROCESS USING DIRECT FILTRATION TECHNIQUE AND MEMBRANE SEPARATION TECHNIQUE}

The present invention relates to a water treatment method using a direct filtration technique and a membrane separation technique, and more particularly, a rapid mixing step of rapidly mixing in a rapid mixing apparatus after adding an inorganic coagulant to the raw water to be purified, and agglomerated in the rapid mixing process. A coagulation aging process that increases the size of the flocs, a direct filtration process for directly filtering the coagulated aging water passed through the coagulation aging step in a fiber filtration device, and further filtering the treated water filtered in the fiber filtration device in a membrane device. The present invention relates to a water treatment process including a membrane separation process.

Generally, it is used to remove impurities such as suspended matter, colloidal substances such as suspended substances in floating water, sewage, groundwater, seawater, sewage, wastewater, etc., and microorganisms of some size such as algae and protozoa. Techniques include sand filtration after chemical flocculation, mechanical filtration after chemical flocculation, and direct mechanical filtration by omission of a precipitation tank after chemical flocculation.

After chemical flocculation sedimentation, sand filtration treatment technology uses a chemical flocculant to flocculate the impurities as described above by flocculation and then flows into the settling tank, and the supernatant from which the flocs are first removed from the settling tank is introduced into the rear sand filter. This is the most common technique for removing residual turbidity causing substances. The advantage of this technology is that it is a textbook method that is familiar to the general driver, and the operating conditions due to changes in the surrounding environment such as raw water quality are most established so far. Is that it is. However, because the size is very large compared to the treatment capacity, that is, the construction cost is high because it takes up a lot of installation sites, and the size must be large to settle most of the flocculated flocs. Will result. There is also a limit to the quality of the treated water in a typical properly sized device.

The mechanical coagulation and precipitation process from the raw water is the same as that of the sand filtration after the chemical coagulation, but the overall size is slightly smaller by using a mechanical filter which is generally 1/4 of the size of the sand filter. Although it can be reduced, there is still a large site for the construction of the whole process, since there is a sedimentation tank that occupies most of the required site. On the other hand, in the removal of turbidity-causing substances, the sand filter is generally about 50%, whereas the non-membrane general mechanical filter is more than 85% than the sand filter.

Direct chemical filtration treatment by omitting the settling tank after chemical coagulation is the same as the two conventional methods from raw water to chemical coagulation, but removes turbidity-causing substances by applying a direct mechanical filtration technology without passing through the settling tank. Therefore, the site required for the construction of the treatment process is reduced to 1/10 to 1/50 compared to the existing treatment process, which can greatly reduce the construction cost, and the size may be smaller than that of using the sedimentation tank because there is no need to precipitate the chemical flocculation flocs. In general, the amount of flocculant used can be reduced. In addition, the coagulation aging time is also required 20-40 minutes when using the existing sedimentation tank, but in the case of a mechanical filter 2 to 3 minutes is sufficient, the agitation power is reduced as the volume of the coagulation aging tank is reduced, thereby reducing the operating cost.

However, the first stage treatment of the mechanical filter has a problem that the treated water quality is about 1 NTU, which is much higher than 0.5 NTU, which is the general standard of drinking water quality, when high-purity raw water inflow of several tens of NTU or more is applied. In case of use, there is a problem that the amount of backwash due to frequent backwashing is greatly increased due to the deepening of the filtration pores. In addition, when only the membrane process is applied, turbidity of influent raw water is limited to 10 NTU or less.

In particular, the technology for removing inorganic salts or ions for pure water production is a general technique, and since the standardization is not a problem in utilizing the technology, it is essential to remove components that cause membrane fouling. For example, when using reverse osmosis technology, SDI values of 5.0 or less are generally recommended. For the stable reverse osmosis membrane operation, conventionally, precision or ultrafiltration membranes are usually used as pretreatment, and the above-described precipitation tank, sand filter, Pretreatment processes, such as a mechanical filter, have been normally used. However, as described above, the prior art is the removal of the turbidity-causing substances, which is the first step of the process of removing contaminants contained in the water, thus excessively increasing the required size of the subsequent high-treatment process, leading to an increase in construction cost and operation cost. This resulted in an increase in the cost of producing and reusing drinking water.

The present invention is to solve the problems of the prior art as described above, one object of the present invention is about 1/4 of the size of the conventional sand filter that can be used up to 5 mg / ℓ of 17% PAC, It is to provide a water treatment method that can significantly reduce the installation site because no settling tank is used.

Another object of the present invention can be used up to 30mg / ℓ of inorganic coagulant based on 17% PAC, the turbidity of the treated water is maintained below 0.3 NTU, SDI below 5.0 by the fiber filtration device and Membrane even when high turbidity raw water inflow By providing a water treatment method that can significantly reduce the construction cost and operating costs of expensive subsequent processes.

Aspects of the present invention for achieving the above object is a rapid mixing step of rapidly mixing in a rapid mixing apparatus after the inorganic coagulant is added to the raw water to be purified, coagulation aging to increase the size of the flocculated flocculation in the rapid mixing process Water treatment method comprising a process, a direct filtration step of filtering the coagulated aging water passed through the coagulation aging process directly in a fiber filtration device, and a membrane filtration step of further filtering the treated water filtered in the fiber filtration device in a membrane device. It is about.

The water treatment method according to an embodiment of the present invention is characterized in that the membrane filtration step of filtering in the membrane device when the heavy turbidity inflow is omitted.

The water treatment method according to an embodiment of the present invention is characterized in that a direct filtration step of filtering directly in a fiber filtration device when low turbidity is introduced is omitted.

The water treatment method according to an embodiment of the present invention is characterized in that it further comprises a high-treatment process for removing a small amount of turbidity-induced substances or dissolved inorganic salts in the advanced treatment apparatus.

In the water treatment method according to an embodiment of the present invention, the rapid mixing device comprises a line mixer, the membrane device is made of a microfiltration membrane (MF) or ultrafiltration membrane (UF), the advanced treatment apparatus The microfiltration membrane device or ultrafiltration membrane device or reverse osmosis membrane device is characterized in that it is made.

According to the water treatment method according to the present invention as described above, by adding the inorganic coagulant 17% PAC up to 30mg / ℓ to the raw water to remove the flocculated turbidity causing material with a fiber filtration device and membrane to turbidity 0.5 NTU of water purification requirements In order to meet the requirements of the water quality, or to reduce the construction cost and operating cost of the subsequent process to be installed according to the requirements of the water quality more than 30%, in the case of the process that requires pure water removed even dissolved salt pretreatment of reverse osmosis membrane that requires inflow water of SDI 5.0 or less By using the process, it is possible to lower the cost of the reverse osmosis membrane production water by stably preventing the reverse osmosis membrane fouling at a much lower construction cost and operation cost than the conventional membrane pretreatment process.

1 is a block diagram of a water treatment method using a direct filtration technology according to an embodiment of the present invention.
Figure 2 is a block diagram showing the operation mode of the water treatment method according to Figure 1 when heavy turbidity inflow.
3 is a block diagram showing the operation mode of the water treatment method according to FIG.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings, examples, and the like. In the following description of the present invention, a detailed description of known general functions or configurations will be omitted.

1 is a block diagram of a water treatment method using a direct filtration technique and a membrane separation technique according to an embodiment of the present invention. Referring to FIG. 1, the water treatment method according to the present invention includes a rapid mixing step of rapidly mixing in the rapid mixing apparatus 10 after adding an inorganic coagulant to the raw water to be purified, and greatly increasing the size of the flocculated floc in the rapid mixing step. The coagulation aging process 20, the direct filtration process for directly filtering the coagulated aging water passed through the coagulation aging process in the fiber filtration device 30 and the treated water filtered in the fiber filtration device 30 membrane device 40 It relates to a water treatment method comprising a membrane separation step of further filtering.

According to one embodiment of the present invention, the water treatment method further removes traces of turbidity causing substances remaining in the treated water through the fiber filtration device 30 and / or the membrane device 40 according to the treated water quality requirements. To this end, it is preferable to further include an advanced processing device 50, which is composed of a reverse osmosis membrane device which connects a microfiltration membrane or an ultrafiltration membrane device or removes dissolved inorganic salts in a subsequent process.

Figure 2 is a block diagram showing the operation mode of the water treatment process according to Figure 1 when heavy turbidity inflow. Referring to FIG. 2, in the same configuration as in FIG. 1, it is preferable to minimize the energy consumption while satisfying the subsequent process feed water quality by omitting the membrane device 40 which is a subsequent process of the fiber filtration device 30 when the heavy turbidity raw water is introduced. . Since the membrane device 40 consumes more energy than the fiber filtration device 30, the heavy turbidity raw water inflow period, which has the most time to operate, can be satisfied with only the fiber filtration device 30, thereby eliminating the membrane device 40. It is preferable.

3 is a block diagram showing an operation mode of the water treatment process according to FIG. 1 when low turbidity is introduced. Referring to FIG. 3, in the same configuration as in FIG. 1, when the low turbidity inflow is omitted, the fiber filtration device 30 is omitted in the process of FIG. 1, and only the membrane device 40 is applied to satisfy the subsequent process water supply while minimizing energy consumption. It is preferable. Since the membrane device 40 can be used at low turbidity without a pretreatment step, it is preferable to omit the fiber filtration device 30.

Although not shown in the drawings, the raw water flowing in is preferably introduced in a state in which foreign matters such as suspended solids having a relatively large size are filtered out by a screen forming a fine mesh of about 1 mm.

The purpose of the inorganic coagulant is to facilitate the removal of contaminants such as suspended solids, including algae, polymers, and the like, and turbidity causing substances in the form of colloids. However, the use of such an inorganic coagulant may increase the operating cost due to the increase of the cost and the amount of sludge generated, so it is desirable to properly control the use and the amount of use according to the quality of raw water. The inorganic coagulant may be a general poly aluminum chloride (PAC). Depending on the amount of the inorganic coagulant administered, the turbidity of the raw water and the removal rate of suspended solids may be changed, which will be described later.

According to one embodiment of the water treatment method according to the invention, the raw water and the flocculant are first instantaneously mixed by the rapid mixing device 10 made of a line mixer and then transferred to the coagulation aging device 20.

Coagulation aging device 20 may be provided in the form of a coagulation tank having a constant volume. Therefore, the raw water mixed with the inorganic coagulant and rapidly mixed is introduced into the membrane device 40 in a state in which a large portion of the turbidity-inducing substance is removed from the fiber filtration device 30 after coagulation aging in the coagulation aging device 20.

The fiber filtration device 30 is composed of a plurality of unit filters connected in parallel. The unit filter comprises a strainer, which is a support in which micropores are densely formed, one or more fibrous media layers composed of microflexible yarn bundles fixed between upper and lower stems of the strainer, and the upper stem when filtering water. It may include an actuator to lift or rotate. The fiber media layer may have a fine pore of 5 to 10 micrometers.

The purpose of the filtration of the membrane device 40 is to filter the turbidity causing substances contained in the water as in the fiber filtration device 30. However, since the influent of the membrane device 40 is the first filtered filtrate in the fiber filtration device 30, the concentration of the turbidity inducing material in the influent is low, so the role of the membrane device 40 causes a slight amount of turbidity. To filter the material.

The membrane device 40 is formed by connecting a plurality of known membrane modules in parallel, the membrane may be made of a microfiltration membrane (MF) or an ultrafiltration membrane (UF, Ultrafiltration membrane).

In the water treatment method according to the embodiment of the present invention, when the high turbidity is introduced, the final stage of the fiber filtration device 30 is processed using the process of treating the filtrate treated in the first stage by the fiber filtration device 30 with the membrane device 40 again. It is preferable to make treated water average turbidity into 0.3 NTU or less. Therefore, when the raw water of medium turbidity is introduced, only one stage filtration is performed by the fiber filtration device 30 to be used in the present invention after coagulation aging, and when the raw water of high turbidity is introduced, the fiber filtration device 30 and the membrane device 40 Treatment may be possible to supply drinking water or agricultural water.

On the other hand, when using a microfiltration membrane or an ultrafiltration membrane with a membrane thickness of 1.0 μm or less, which is not a conventional mechanical filter, an excellent turbidity removal efficiency of nearly 100% and an immersion type membrane can be operated for a high turbidity influent. As the scale increases to 1.0 m / day, which is 1/50 to 1/100 of the fiber filtration system, the construction cost is more than six times higher than that of the mechanical filter, and the excessive use of backwash air and backwash to reduce membrane contamination As a result, the driving cost is generally three times higher. Therefore, in order to solve this problem, it is common to use the above-described pretreatment device before membrane filtration to remove turbidity-causing substances contained in raw water. Even if the best existing pretreatment device is used in one stage, it is more than 10 NTU. It is known that the feed linear velocity does not exceed 1.5 m / day when raw water is introduced.

However, when the fiber filtration device 30 according to the present invention is used as a pretreatment, the treated water turbidity of the fiber filtration device 30 and the membrane device 40 is maintained not more than 0.3 NTU even when a high turbidity of 100 NTU or more is introduced. Since it is treated under SDI (Silt Density Index) 3.0, which is an influent condition to avoid membrane fouling, the efficiency of subsequent processes can be improved, so the construction cost per filtration amount is 6 times more expensive than the pretreatment facility. Can be reduced. This improved pretreatment method can also be greatly seen as a pretreatment process for advanced treatment such as reverse osmosis membrane method or ion exchange resin method used to remove dissolved inorganic salts.

Hereinafter, embodiments of the present invention will be described in detail based on the empirical data obtained using the water treatment process according to the present invention described so far. In the demonstration experiment of the present invention, both the case consisting of the fiber filtration device and the membrane device and the case of using only the fiber filtration device were examined. In addition, by controlling the amount of inorganic coagulant 17% PAC injected into each fiber filtration device, it was possible to confirm the correlation between the concentration of the inorganic coagulant and the filtration efficiency.

The fiber filtration device used in the experiment for the embodiment of the present invention is a pressure fiber filtration device, the specifications of the unit filter and the membrane of the fiber filtration device used in the experiment are shown in Tables 1 and 2 below.

<Unit filter specification of fiber filtration device> Item Specifications Size (mm) 390 (Ø) × 1,745 (H) Filtration area (m ² ) 0.66 Capacity (m ³ / day) 75 Textile Media material Polypropylene importance 0.91 Tensile force (N) 7,000

<Microfiltration Membrane Specification> Item Specifications Pore size (㎛) 0.025 to 20 Filtration pressure (kgf / cm ² ) 1 to 2 Capacity (m ³ / day) 75 Membrane Material Polyamide

Table 3 below shows the turbidity and suspended solids concentration of the raw water used in this experiment.

Item unit at least maximum Average Turbidity NTU 15.0 547.0 126.0 Suspended solids (SS) mg / ℓ 23.0 900.0 204.5

Example  One

Low turbidity raw water (about 15 NTU) was filtered using only a fiber filtration apparatus. Table 4 below shows the appropriate amount of inorganic coagulant input for this case.

Item
Flocculant Treated Water Turbidity (NTU) Filtration duration
(minute) at least maximum Average Average removal rate (%) 0 mg / ℓ 7.0 9.0 7.68 48.8 180 10 mg / ℓ 1.9 6.1 2.39 84.1 85 20 mg / ℓ 0.18 4.3 0.30 98.0 50 30 mg / ℓ 0.32 4.2 0.66 95.6 30

According to the above analysis, removal rate of inorganic coagulant was 48.8% when no inorganic coagulant was added, but 98% when 20 mg / l of inorganic coagulant was added and 95.6% when 30 mg / l of inorganic coagulant was added (minimum turbidity 0.32). NTU) can be seen. Therefore, the water quality of the filtered water is proportional to the proper amount of the inorganic coagulant, but it can be seen that there is no proportion above. As a result, it can be confirmed that the addition of a large amount of inorganic coagulant may lower the processing performance of the filtration apparatus.

On the other hand, the filtration duration was inversely proportional to the amount of inorganic coagulant, but the filtration duration, which lasted more than 3 hours, was reduced to about 30 minutes when the inorganic coagulant was injected. This is because as the amount of inorganic coagulant is increased, the amount of suspended solids (SS) Al (OH) ₃ induced by the inorganic coagulant increases, and as the amount of the remaining inorganic coagulant increases, the pore closing action proceeds quickly.

Example  2

High turbidity raw water (about 300 NTU) was filtered using only a fiber filtration apparatus. Table 5 below is a result of measuring the treated water quality and duration while adding an inorganic coagulant in the range of 10-25 mg / ℓ to determine the proper amount of flocculant for high turbidity raw water of 300NTU or more.

Item
Amount of flocculant Treated Water Turbidity (NTU) Filtration duration
(minute) at least maximum Average Average removal rate (%) 10 mg / ℓ 10 43 21.9 92.7 55 15 mg / ℓ 12 32 14.4 95.2 45 20 mg / ℓ 6.9 21 7.5 97.5 35 25 mg / ℓ 10 25.2 12.3 95.9 20

Experimental results showed that the average turbidity of 7.5 NTU (removal rate of 97.5%) was obtained at 20 mg / ℓ of inorganic coagulant, and the filtration duration was around 35 minutes. This result is similar to that of low turbidity.

Example  3

The fiber filtration device and the membrane device were operated for a long time (about 1 month). Table 6 below shows the treatment results in each of the fiber filtration device and the membrane device.

Item
sample Turbidity (NTU) Average turbidity removal rate
(%) at least maximum Average enemy 23 900 204.5 - Filtration Filtration 0.2 19.2 6.4 95.3 Membrane Filtrate 0.2 0.32 0.26 99.4

As can be seen from Table 6, the water treatment system according to the invention was continuously operated for one month under the experimental conditions in which the raw water of high turbidity was introduced. As a result, the filtrate of the fiber filtration device was increased to 20 NTU according to the turbidity of the raw water, but the membrane Filtration water of the filtration device was stable around 0.3NTU. It was confirmed that there is much better treatment effect than the case of using one by connecting two filtration devices with turbidity of the degree suitable for drinking water standard.

Example  4

Changes in the turbidity-inducing agent removal rate and SDI values of the fiber filtration device and the membrane device were measured and shown in Table 7 below.

17% PAC input concentration
(mg / ℓ) Turbidity (NTU) SDI Influent fiber
filtrate UF
filtrate Kinds fiber
filtrate UF
filtrate 20 100 3.50 0.35 SDI ₁₅ 2.9 1.9

The SDI value is an indicator that turbidity-inducing substance contained in the reverse osmosis membrane influent causes membrane fouling on the reverse osmosis membrane, and it refers to the degree of sugar blockage for 1 minute of the membrane of nominal pore 0.14㎛ by the suspended solids contained in the water, and is supplied to the reverse osmosis membrane. It is an index index for quantifying small amount of suspended solids in water to determine the appropriate pretreatment.

Reverse osmosis membrane manufacturers generally order pretreatment to be less than SDI 5.0 for spiral wound osmosis membranes. The method of measurement is in accordance with ASTM D4189-95.

According to the water treatment process using a combination of direct filtration and membrane separation after coagulation using the fiber filtration device according to the embodiment of the present invention described above, the turbidity removal efficiency is much higher than that of the conventional sand filter, and the fiber is applicable to high turbidity raw water. The use of a filtration device reduces the installation area and filtration power costs, and removes more than 98% of the turbidity-inducing material in advance. The construction and operating costs of the filtration process can be reduced by more than 30%. In addition, the filtered water can be used according to its use or processed in duplicate with a process such as a reverse osmosis membrane to remove dissolved salts, so that it can be reused as not only drinking water but also seawater desalination, river maintenance water, and agricultural industry water.

Although the present invention has been described in detail with reference to preferred embodiments of the present invention, the present invention is not limited to the above-described embodiments, and many modifications are made by those skilled in the art to which the present invention pertains within the scope of the technical idea of the present invention. This possibility will be self-evident.

10: rapid mixing device
20: coagulation aging device
30: fiber filtration device
40: membrane device
50: altitude processor

Claims (8)

A rapid mixing step of rapidly mixing in a rapid mixing apparatus after adding an inorganic coagulant to the raw water to be purified; An agglomeration aging step of increasing the size of the flocculated floc in the rapid mixing process; A direct filtration process of directly filtering the coagulated aging water having undergone the coagulation aging process in a fiber filtration apparatus; And a membrane separation process of further filtering the treated water filtered in the fiber filtration device in a membrane device.
The fiber filtration device is composed of a strainer that is a support in which micropores are densely formed, and a bundle of microflexible yarns fixed between upper and lower stems of the strainer, and at least one fibrous media layer having fine pores of 5 to 10 micrometers. And an actuator for elevating or rotating the upper stem when filtering the water to be treated. The water treatment method according to claim 1, wherein the water treatment method omits the membrane separation step of filtering in the membrane apparatus when a heavy turbidity inflow of 15 NTU or more and less than 300 NTU is performed. The water treatment method according to claim 1, wherein the water treatment method omits a direct filtration process which is directly filtered by a fiber filtration apparatus when a low turbidity inflow of less than 15 NTU is introduced. The water treatment method according to any one of claims 1 to 3, wherein the water treatment method further comprises an advanced treatment step of removing trace amounts of turbidity-inducing substances or dissolved inorganic salts in the advanced treatment apparatus. The water treatment method according to claim 1, wherein the rapid mixing device comprises a line mixer. The method of claim 1, wherein the fiber filtration device is characterized in that a plurality of unit filters are connected in parallel. The water treatment method according to claim 1, wherein the membrane of the membrane device is made of a microfiltration membrane (MF) or an ultrafiltration membrane (UF). The water treatment process according to claim 4, wherein the advanced treatment device is made of a microfiltration membrane device, an ultrafiltration membrane device, or a reverse osmosis membrane device.

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