JP2017006902A - Water treatment system, water treatment method, and method for managing water treatment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treatment system that can sufficiently remove impurity components from water, and is low in equipment cost, treatment cost and management cost.SOLUTION: Provided is a water treatment system and method including: a raw water tank for diluting a heavy metal-containing raw water with a treated water or a fresh water; a means for adding an inorganic coagulant and a chelator installed after the raw water tank; a pH adjustment means disposed in the inorganic coagulant and chelator addition means, or downstream of the inorganic coagulant and chelator addition means; a membrane filtration unit capable of treating a high turbidity wastewater at high permeation flow rate, in which hollow fibers made of PVDF having an unused fresh water permeation flow rate of 50 m/m/ day or more on a single fiber base under an operation pressure of 100 kPa, are bundled with one end free, downstream of the pH adjustment means as a means for carrying out a physical treatment; and a means for sending the treated water from the membrane filtration unit to the raw water tank.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a water treatment system and a water treatment method. Specifically, the present invention relates to a system and a processing method for performing a treatment for removing heavy metals from wastewater containing heavy metals, and a water treatment system and a water treatment that can be applied to wastewater containing COD components or turbidity components other than heavy metals. Regarding the method.

  In order to protect water resources, there is a demand for water treatment that removes impurity components from various waters such as tap water, waste water, waste water, and sewage to obtain purified water. For example, like cadmium which is a causative agent of Itai-itai disease, it is used for wastewater of the metal industry, non-ferrous metal primary smelting / refining industry, non-ferrous metal secondary smelting / refining industry, hot-dip plating industry, fishery food manufacturing industry. Contained heavy metal components can affect human health. For this reason, environmental standards and emission standards for heavy metals have been established in each country, including UN agencies and Japan. Cadmium has been set tolerable intake by the United Nations organization, and the water pollution standard of the Water Pollution Control Law has been strengthened to 0.03 mg / L or less (Non-patent Document 1).

JP 2014-61506 A Special table 2009-509737 gazette

Ministry of the Environment “About review of allowable limits of items related to regulations such as discharge of discharged water and penetration of underground seepage water based on Water Pollution Control Law (Draft Report)”

As a method for removing cadmium from wastewater, a method of separating as sludge by adding coagulant and inorganic flocculant after coagulating sedimentation or pressurized flotation, or a method of separating it as cadmium hydroxide sludge by coagulation sedimentation with alkalinity of about pH 12 Physicochemical processing such as is known. However, when the present inventor examined the physicochemical treatment, it was found that the sludge separation rate (removal rate) during coagulation sedimentation or pressurized flotation was not 100%, and the impurity components could not be sufficiently removed from water. For example, it was difficult to purify water to the extent that it satisfies the legal regulation value (less than 0.03 mg / L) only by physicochemical treatment of wastewater with a high cadmium content.
That is, conventionally, in the treatment of wastewater, it was not necessary to reduce the cadmium content to a new legal regulation value (less than 0.03 mg / L), and thus biological treatment and / or physicochemical treatment was sufficient. However, it has been found that the desire to fully remove cadmium that has not been removed by biological and / or physicochemical treatment has arisen due to changes in legal standards.

  On the other hand, as a method of removing impurity components from water, a method of performing physical treatment such as filtration membrane is known. However, if high-precision physical treatment is performed using an ultrafiltration membrane or the like in an attempt to bring the ratio of impurity components removed from water close to 100%, a sufficient amount of treated water ( The equipment cost increases because the water flow rate cannot be maintained. Moreover, if physical processing with high accuracy is performed, the frequency of backwashing of the filtration membrane must be increased, which increases processing costs and management costs.

On the other hand, a method is known in which physical treatment is possible by adding cleaning using ozone or the like, and the solid concentration in the treated water is further reduced (see Patent Documents 1 and 2).
Patent Document 1 discloses a primary treatment means for performing solid-liquid separation after at least one of sewage and wastewater containing organic substances flows in and biologically treated, and primary treated water generated by the treatment by the primary treatment means. Secondary processing means for filtering with an ultrafiltration membrane, backwashing means for backwashing the secondary treatment means with secondary treated water generated by the secondary treatment means, and backwashed by the secondary treatment means A backwash drainage channel for guiding the generated backwash wastewater to the primary treatment means, and a sludge extraction channel for discarding the sludge withdrawn from the primary treatment means, the secondary treatment means being treated by the secondary treatment means A liquid treatment facility having a circulation means for circulating water is described. According to Patent Document 1, it is said that a secondary ultrafiltration membrane treatment is possible by periodically performing cleaning with ozone.
Patent Document 2 discloses a water treatment method including a liquid-solid separation step and at least one filtration step following the step, wherein the liquid-solid separation step is performed at a speed exceeding 15 m / h. A water treatment method is described, wherein the filtration step is carried out directly by at least one microfiltration membrane or ultrafiltration membrane. According to Patent Document 2, a treatment method that enables better control of the clogging index (or SDI) of treated water by performing cleaning with ozone, that is, an index obtained by a known technique. Is intended to reduce this index.

  The first feature of the present invention is that a physical treatment is possible by appropriately combining an inorganic flocculant and a chelating agent without performing cleaning with ozone as described in Patent Documents 1 and 2 and the like. . Furthermore, by using the chelating agent, a turbid component dissolved in water such as cadmium, which is impossible by the method described in Patent Documents 1 and 2, which simply combines physicochemical treatment and physical treatment, is regulated by law (0.03 mg). / L) can be purified to such a degree as to satisfy.

  The second feature of the present invention is that the raw water is diluted with physically treated treated water or fresh water so that the COD or turbidity of the raw water is not more than a certain concentration, and it is difficult to apply advanced treatment such as a conventional hollow fiber membrane. This is the point that it is possible to treat the raw water with high COD or high turbidity. Furthermore, unlike the cross-flow method, which is widely used as a means of mixing treated water with raw water, the pollutant components separated by the hollow fiber membrane are not accumulated as concentrated water on the raw water side, and are contaminated by regular physical cleaning. It is in the point that a thing can be periodically discharged out of the system. However, as the dilution rate of raw water increases, the amount of wastewater that passes through physical treatment increases, and there is a disadvantage that the equipment becomes excessive, so a hollow fiber membrane that can treat raw water with high turbidity and has a high permeate flow rate is adopted for physical treatment. And the above-mentioned drawbacks were overcome.

  The problem to be solved by the present invention is to provide a water treatment system that can sufficiently remove impurity components including dissolved components from water and has low equipment cost, treatment cost, and management cost.

In order to solve the above problems, intensive studies were conducted. It has been found that by adding an inorganic flocculant and a chelating agent prior to physical treatment, a heavy metal component can be sufficiently removed from water, and a water treatment system with low equipment cost, treatment cost and management cost can be provided. However, when COD or turbidity of raw water is high, the effect of the chelating agent or inorganic flocculant is reduced, and the removal of heavy metals is insufficient. Therefore, it was found that sufficient heavy metals can be removed by diluting raw water with a part of physical treated water or with fresh water to make COD or turbidity below a certain concentration.
The present invention, which is a specific means for solving the above problems, and preferred embodiments of the present invention have the following configurations.

[1] Arranged in the means for adding the inorganic flocculant and chelating agent to the raw water containing heavy metal and the means for adding the inorganic flocculant and chelating agent, or downstream of the means for adding the inorganic flocculant and chelating agent One end of a PVDF hollow fiber with a pH adjustment means and a fresh water permeation flow rate of 50 m3 / m2 / day or more on a single yarn base under an operating pressure of 100 kPa as a means for performing physical treatment downstream of the pH adjustment means. A water treatment system equipped with a membrane filtration device that can treat high-turbidity wastewater bundled as free at a high permeation flow rate.
[2] The water treatment system according to [1], further comprising means for diluting the raw water containing the heavy metal with treated water or fresh water that has been physically treated.
[3] A method for treating raw water containing heavy metal, wherein the raw water containing heavy metal is diluted with the physically treated treated water or fresh water, and the COD or turbidity of the raw water is adjusted to be less than a certain concentration.

  ADVANTAGE OF THE INVENTION According to this invention, a heavy metal can fully be removed from the waste_water | drain with COD or turbidity pollution, and the water treatment system with low installation cost, processing cost, and management cost can be provided.

FIG. 1 is a schematic diagram showing an example of the configuration of the water treatment system of the present invention.

  Hereinafter, the present invention will be described in detail. The description of the constituent elements described below may be made based on representative embodiments and specific examples, but the present invention is not limited to such embodiments. In the present specification, a numerical range expressed using “to” means a range including numerical values described before and after “to” as a lower limit value and an upper limit value.

[Water treatment system, water treatment method]
The water treatment system of the present invention adjusts the pH with a means for adding an inorganic flocculant and a chelating agent to raw water, a means for adjusting the pH disposed in or downstream of the means for adding an inorganic flocculant and a chelating agent. Means for performing physical processing installed downstream of the means for performing the processing. Furthermore, it has means for diluting the COD or turbidity of raw water to below a certain value using treated water or fresh water that has been physically treated.
With these configurations, the water treatment system and the water treatment method of the present invention can sufficiently remove heavy metal components from water, and the equipment cost, treatment cost, and management cost are low. Furthermore, by adjusting the dilution of raw water with treated water, heavy metals can be sufficiently removed even with raw water having high COD or high turbidity.
According to the water treatment system and the water treatment method of the present invention, the concentration of the impurity component in the physically treated treated water can be lowered. Since the impurities in the early stage include bacteria such as E. coli, the treated water is aseptic water from which the bacteria have been completely removed.
According to the water treatment system and water treatment method of the present invention, heavy metals can be sufficiently removed even with raw water having high COD or high turbidity, so that conventionally required physicochemical treatment and biological treatment can be omitted. Therefore, equipment cost, processing cost, and management cost can be reduced.
In JP 2014-61506 A, JP 2009-509737 A, etc., physical treatment such as ultrafiltration is performed on the treated water that has passed through the primary treatment means without adding an inorganic flocculant before the physical treatment. For this reason, the problem of fouling that occurs when the fine suspension is clogged in the pores of the physical processing apparatus has a big problem in economy and processability. According to the present invention, it has been found that the problem is that the flocculant coarsens the suspension, does not cause pore clogging, and fouling trouble is less likely to occur. Furthermore, in the present invention, by adopting management that makes the COD and / or ultraviolet absorption amount of the primary treated water less than the set value, fouling in the physical treatment is suppressed, the backwash interval is extended and the treatment flow rate is increased. It was possible.
Treated water treated by physicochemical treatment to separate solids and liquids after adding a flocculant to water described in JP-A-2014-61506 and JP-T-2009-509737, using a filtration membrane or the like to perform treatment Although it is a method of further reducing the concentration of solids in water, there was no effect of removing dissolved heavy metal components from waste water. The present invention is excellent in that a heavy metal such as cadmium that is dissolved can be removed to a level equal to or lower than the drainage regulation value by using an appropriate amount of a chelating agent that changes heavy metal into a state insoluble in water as a part of the flocculant.

In the water treatment system and the water treatment method of the present invention, even if the raw water has high COD or high turbidity, the heavy metal concentration of the finally obtained purified water can be very low. In particular, even when raw water containing a high concentration (0.1 mg / L or more) of cadmium is used, purified water with a cadmium concentration that is surely less than the release regulation value (0.03 mg / L) of the Water Pollution Control Law is used. can get.
The purified water finally obtained after physical treatment by the water treatment system and the water treatment method of the present invention is clear water that does not contain fungi such as Escherichia coli. Therefore, in the fishery processing field where tap water is used instead of seawater from the viewpoint of hygiene, a merit that the obtained purified water can be used instead of tap water can be expected.
Hereinafter, preferred embodiments of the water treatment system and the water treatment method of the present invention will be described.

<Configuration of water treatment system>
The preferable aspect of the structure of the water treatment system of this invention is demonstrated based on drawing. The present invention is not limited to the specific configuration shown in the drawings.
FIG. 1 is a schematic diagram showing an example of the configuration of the water treatment system of the present invention. The water treatment system shown in FIG. 1 receives the raw water 1 and dilutes the raw water 1 with the treated water 5 and fresh water treated by the physical treatment device 14 so that the COD or turbidity of the raw water 1 is less than a certain concentration, Means 12 for adding an inorganic flocculant and a chelating agent to the treated water 2 whose COD or turbidity is adjusted to be less than a certain concentration in the water tank 11; means 13 for adjusting the pH of the treated water 3 that has passed the means 12; A means 14 for physically treating the treated water 4 whose pH is adjusted by the means 13 and a means 15 for returning the treated water 5 that has passed the means 14 to the raw water tank are provided. The chelating agent added by means 12 is adjusted according to the concentration of heavy metal contained in the raw water, and the inorganic flocculant is adjusted according to the COD or turbidity contained in the raw water. The order of addition of the chelating agent and the inorganic flocculant may be simultaneous addition, but it is preferable to add the inorganic flocculant after the addition of the chelating agent.
As shown in FIG. 1, the water treatment system of the present invention desirably includes a cleaning device 16 that periodically discharges the suspension accumulated on the surface of the hollow fiber in the physical treatment means 14.
Next, the preferable aspect of each means which comprises the water treatment system of this invention is demonstrated.

<Raw water tank>
The water treatment system of this invention contains the raw | natural water tank which adjusts COD or turbidity of raw | natural water to less than a fixed density | concentration.

Examples of the raw water include public sewage that receives sewage from fishery processing wastewater and fishery processing plant wastewater.
When removing components dissolved in the raw water, such as heavy metals such as cadmium, the mixture is thoroughly reacted with an aggregating agent suitable for the dissolved component to be removed, such as a chelating agent, and then changed to a water-insoluble suspension, then hollow. The suspension can be separated from the raw water by physical treatment such as a thread membrane to obtain water that does not contain the contaminating component. In the intensive study of the treatment method, organic substances in raw water, especially proteins and fats and oils that are abundantly contained in fishery processing wastewater, inhibit the reaction with aggregating agents such as chelating agents added before the previous physical treatment, In addition, the organic matter adheres to the hollow fiber membrane surface and impedes filtration, or increases the viscosity of the raw water to increase the passage resistance of the pre-deadline membrane and increases the frequency of backwashing of the membrane. Or COD (manganese) of raw water in the raw water tank is 160 mg / L or less, preferably 120 mg / L or less, most preferably 80 mg / L. It has been found that the substances dissolved in water such as cadmium can be reliably removed without increasing the aggregating agent and membrane area in the previous period. The index of dilution treatment in the raw water tank can be replaced by turbidity, and the turbidity of the raw water after passing through the raw water tank is 50 degrees or less, desirably 30 degrees or less, and most desirably 20 degrees or less. The set value of the UV absorption amount is affected by turbidity or chromaticity, and is set after confirming the correlation with COD.

Examples of raw water that is heavy metal-containing water include fishery processing wastewater. Fishery processing wastewater is wastewater discharged from a fishery processing establishment, and is mainly wastewater containing fish, shellfish, fish egg-derived organic matter and heavy metals. In particular, cadmium is contained in the midgut gland of the scallop, the liver of the squid, and the internal organs of the crabs. Therefore, wastewater containing cadmium is discharged from the fishery processing plant that processes these molluscs and crustaceans. For this reason, this invention can be preferably used for fishery processing waste water. Marine processed wastewater usually has a BOD concentration of 10 to 5000 mg / L, a COD concentration of 30 to 3000 mg / L, a salinity concentration of 0 to 20%, a cadmium concentration of 0 to 3 mg / L, and a zinc concentration of 0 to 30 mg / L. The iron concentration is 0-30 mg / L.
In addition, although this invention has a remarkable effect in the treatment of heavy metal containing wastewater discharged from a fishery processing plant, it contains heavy metals discharged from other raw water such as non-ferrous metal industry, plating factory, semiconductor factory, etc. It can also be applied to wastewater treatment.

The amount of raw water that can be treated in the present invention is not particularly limited, but a large amount of raw water can be treated in the present invention. Specifically, it is possible to treat raw water of 500 m ³ or more per day. The present invention can efficiently treat a large amount of raw water. In particular, when a large amount of raw water is treated, the present invention that can treat high-turbidity raw water with a high permeated water amount is advantageous from the viewpoint of equipment cost and equipment area. ,

  The means for adding the flocculant is to add the chelating agent and the inorganic flocculant to the treated water 1 whose concentration has been adjusted in the raw water tank, then mix well with an appropriate mixing time, adjust the pH, and supply it to the subsequent physical treatment To do. As a chelating agent, it is necessary to add Oji Flock L-1 etc. according to content depending on the kind of dissolved heavy metals to remove, such as cadmium. Although it is possible to use sodium sulfide instead of the chelating agent, hydrogen sulfide safety measures and corrosion measures are required. As the inorganic flocculant, an appropriate amount of either PAC (polyaluminum chloride) or sulfuric acid band aluminum flocculant or polyiron or ferrous chloride or ferric chloride iron flocculant is added. The amount of the inorganic flocculant added is desirably less than 100 mg / L in terms of the solid oxide content of the inorganic flocculant with respect to the treated water 1. When the amount of the inorganic flocculant added is less than this, the cost required for the inorganic flocculant can be further reduced. Moreover, when the added amount of the inorganic flocculant is less than this, the amount of sludge generated as a by-product can be further reduced, and therefore the disposal cost of the sludge can be further reduced. Furthermore, since the amount of sludge generated is reduced, the frequency of backwashing in the means 14 (hollow fiber membrane treatment equipment) is reduced, the operation is increased, the treatment flow rate per bottle is increased, and the equipment cost can be suppressed.

  The chelating agent also reacts with components other than the heavy metal to be removed, such as zinc, aluminum, and iron. Therefore, when zinc, aluminum, and iron are contained in the dissolved component, it is necessary to add 2 to 5 times the amount of the chelating agent. Even if the primary treatment is insufficient and the COD or BOD of raw water is higher than specified, the required amount of chelating agent increases. In this case, addition of 2 to 10 times is required, but COD or turbidity is significantly higher than the specified concentration. In this case, even if the chelating agent is increased, dissolved components such as cadmium cannot be removed to the target level. The addition amount of the chelating agent is desirably less than 10 mg / L with respect to the treated water 1 diluted with raw water. When the addition amount of the chelating agent is less than this, the cost required for the chelating agent can be further reduced.

  The pH of the raw water when subjected to physical treatment is preferably 4 to 10, more preferably 5 to 9, and most preferably 6 to 8. When the pH is higher than the above range, it causes a scale trouble that the calcium carbonate adheres to the physical processing device, and when it is lower than the above range, the effect of the aggregating agent such as a chelating agent cannot be sufficiently exhibited. The generation of flocs of aluminum-based or iron-based flocculants is impossible or hindered, resulting in a problem that the performance of removing dissolved components such as heavy metals is deteriorated and the physical processing apparatus is contaminated. Examples of the pH adjuster include sodium hydroxide and calcium hydroxide.

As a physical treatment, high turbidity drainage of high-turbidity wastewater bundled with PVDF hollow fibers with a free end at 50 m3 / m2 / day or more on a single yarn base under an operating pressure of 100 kPa is used for physical treatment. Use a membrane filtration device that can be treated with In the present invention, high turbidity drainage means the permeate flow rate of fresh water after treatment of 0.5 m ³ / m ² of kaolin suspension water with an SS concentration of 20 mg / L at an operating pressure of 100 kPa. It means that it is 40% or more. This high turbidity drainage is desirably 50% or more, and most desirably 60% or more. In the present invention, the high permeate flow rate means that the fresh water permeate flow rate is 50 m ³ / m ² · day or more on a single yarn base under an operating pressure of 100 kPa. This high permeation flow rate is desirably 70 m ³ / m ² · day or more, and most desirably 80 m ³ / m ² · day or more. It is desirable to clean the membrane surface once every 5 to 120 minutes, more preferably once every 10 to 60 minutes and most preferably once every 20 to 40 minutes.

  Physical treatment potentially has the problem of biofouling where microorganisms grow and accumulate on the surface of the device. By managing the amount of COD or UV absorption in the primary treatment, the progress rate of biofouling can be suppressed, and the cleaning frequency of biofouling can be reduced. The biofouling wash is preferably performed once every 1 to 48 hours with sodium hypochlorite, more preferably once every 6 to 36 hours, and 12 to 24 hours. It is most desirable to carry out once.

  By adopting an ultrafiltration membrane or a microfiltration membrane for physical treatment, bacteria such as Escherichia coli can be completely removed from the raw water and aseptic water can be obtained. The physical treated water can be treated as it is with a nanofiltration membrane (NF membrane) or a reverse osmosis membrane (RO membrane), and demineralized water can be easily obtained.

  Examples of the heavy metal contained in the heavy metal-containing water include copper (Cu), zinc (Zn), tin (Sn), nickel (Ni), lead (Pb), and cadmium (Cd). Cadmium has been set tolerable intake by the United Nations organization, and the water pollution standard of the Water Pollution Control Act has been strengthened to 0.03 mg / L or less (the Ministry of the Environment's discharge of discharged water based on the Water Pollution Control Act, underground seepage water) Review of permissible limits for items related to regulations such as penetration of reports (draft report) ”).

  The water treatment system and water treatment method of the present invention can be particularly preferably used when the heavy metal component contained in the raw water is cadmium or cadmium ions. In particular, according to the water treatment system and the water treatment method of the present invention, by adjusting the pH by adding a chelating agent and a flocculant to the diluted water having COD or turbidity within the above range in the raw water tank, Purified water having a cadmium content of 0.03 mg / L or less can be produced. Therefore, the water treatment system and the water treatment method of the present invention is an epoch-making method that allows the cadmium concentration in the wastewater to be equal to or lower than the above-mentioned reference value, in order to treat wastewater containing cadmium discharged from the fishery processing establishment. Particularly preferably used.

  The features of the present invention will be described more specifically with reference to examples and comparative examples. The chemicals, amounts used, ratios, processing details, processing procedures, and the like shown in the following examples can be changed as appropriate without departing from the spirit of the present invention. Therefore, the scope of the present invention should not be construed as being limited by the specific examples shown below.

Example 1
The following treatment was performed using the wastewater from the fishery processing plant as raw water (treated water). First, activated sludge treatment was performed on the wastewater from the fishery processing plant. The COD concentration converted from the ultraviolet absorption amount of the obtained treated water was 42 to 76 mg / L. Moreover, the cadmium density | concentration of this treated water changed with 0.02 mg / L-0.09 mg / L. To this treated water, 1 mg / L of chelating agent and 50 mg / L of 10% PAC were added. After adjusting the pH to 7.0 with sodium hydroxide, PVDF hollow fiber with a fresh water permeation flow rate of 80 m3 / m2 / day on a single yarn base under an operating pressure of 100 kPa was attached to one end. High turbidity waste water bundled as free was treated with a membrane filtration device capable of treating with high permeate flow rate. The cadmium concentration of purified water obtained by this method was always less than 0.03 mg / L. E. coli was not detected from the purified water obtained by this method. By performing backwashing once every 30 minutes and washing with sodium hypochlorite solution once a day, this ultrafiltration membrane becomes 1. The permeation flow rate of m3 / m2 / · day could be maintained.

(Example 2)
The activated sludge raw water of the fishery processing plant with a COD concentration of 380 mg / L is diluted with the treated water of the hollow fiber membrane filtration device so that the COD concentration is 120 mg / L in the raw water tank, and the chelating agent 1 mg / L And 10% PAC 50 mg / L was added. After adjusting the pH to 7.0 with sodium hydroxide, PVDF hollow fiber with a fresh water permeate flow rate of 80 m3 / m2 / day on a single yarn base under an operating pressure of 100 kPa is free at one end. The high turbidity waste water bundled as was treated with a membrane filtration device capable of treating with high permeate flow rate. The cadmium concentration of purified water obtained by this method was always less than 0.03 mg / L. E. coli was not detected from the purified water obtained by this method. The number of hollow fiber modules required for processing was estimated to be 30.

(Comparative Example 1)
The raw raw water (treated water) was used as the activated sludge raw water from a fishery processing plant with a COD concentration of 380 mg / L. The cadmium concentration of this treated water was 0.12 mg / L. 2 mg / L of chelating agent and 3000 mg / L of 10% PAC were added to this treated water. After adjusting the pH to 7.0 with sodium hydroxide, PVDF hollow fiber with a fresh water permeate flow rate of 80 m3 / m2 / day on a single yarn base under an operating pressure of 100 kPa is free at one end. The high turbidity waste water bundled as was treated with a membrane filtration device capable of treating with high permeate flow rate. The cadmium concentration of the water obtained by this treatment was 0.027 mg / L. The permeation flow rate of the ultrafiltration membrane was 0.3 m ³ / m ² · day, but it was necessary to remove biofouling with sodium hypochlorite solution every 2 hours, and it did not lead to actual operation It was.

(Comparative Example 2)
Same as Example 2, except that the activated sludge raw water of a fishery processing plant with a COD concentration of 380 mg / L is 20 m3 / m2 / day on a single yarn basis with a fresh water permeate flow rate of 100 kPa under an operating pressure. Processed with conditions. The cadmium concentration of purified water obtained by this method was always less than 0.03 mg / L. E. coli was not detected from the purified water obtained by this method. The number of hollow fiber modules required for the treatment was estimated to be 240.

DESCRIPTION OF SYMBOLS 1 Raw water 2 Diluted raw water 3 Chelating agent and inorganic flocculant treated water 4 pH adjusted treated water 5 Physically treated water 11 Raw water tank 12 Means for adding chelating agent and inorganic flocculant 13 Means for adjusting pH 14 Physically treated means 15 Treatment Means 16 for sending water 5 to raw water tank Means for periodically discharging sludge adhering to hollow fiber

Claims (3)

Means for adding inorganic flocculant and chelating agent to raw water containing heavy metal, means for adding inorganic flocculant and chelating agent, or pH adjusting means disposed downstream of means for adding inorganic flocculant and chelating agent As a means for performing physical treatment downstream of the pH adjusting means, a fresh water permeate flow rate of 50 m3 / m2 / day or more on a single yarn base under an operating pressure of 100 kPa is bundled with PVDF hollow fibers free at one end. Water treatment system equipped with a membrane filtration device that can treat high turbidity wastewater with high permeate flow rate. The water treatment system of Claim 1 which has a means to dilute the raw | natural water containing the said heavy metal with the treated water or the fresh water which carried out the physical treatment. A method for treating a raw water containing heavy metal, comprising diluting the raw water containing the heavy metal with the physically treated treated water or fresh water, and adjusting the COD or turbidity of the raw water to be less than a certain concentration.

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