JP2016093789A - Water treatment method and water treatment system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treatment method and a water treatment system capable of effectively performing water treatment without loading special energy and without excessively raising pH, and continuously and stably supplying a large amount of clean water at a low cost.SOLUTION: A water treatment method uses a gravity force filtration method using a membrane module so as to treat water. The water treatment method includes: a raw water supply step of supplying raw water; a specific component aggregation step of treating the supplied raw water under a condition of pH 7-9.5, using an oxidant, and generating an aggregate having Mn main component; and a filtration step of supplying the raw water subjected to the specific component aggregation step to the membrane module followed by treating. A water treatment system includes: raw water supply means 10; specific component aggregation means 20 of treating the supplied raw water under a condition of pH 7-9.5, using an oxidant, and generating an aggregate having Mn main component; and filtration means 30 of treating the raw water subjected to the specific component aggregation means 20.SELECTED DRAWING: Figure 1

Description

  The present disclosure relates to a water treatment method and a water treatment system.

Due to water pollution of rivers in the suburbs due to urban population concentration or groundwater pollution due to the progress of environmental pollution, water pollution accidents caused by chlorine-resistant protozoa such as Cryptosporidium that are difficult to remove by existing water purification treatment processes It has occurred.
On the other hand, in order to prevent this, the water purification technology by membrane filtration is spreading. However, in particular, groundwater contains a large amount of manganese, and even if membrane treatment is performed as it is, it is not suitable as drinking water.

Under such circumstances, there is an enthusiasm for a technique for efficiently purifying a large amount of water through membrane treatment while reducing soluble manganese in raw water below the water quality standard.
Conventional soluble manganese treatment technologies include sand filtration technology using manganese sand and ozone oxidation treatment technology using ozone (for example, Patent Documents 1 and 2), and this is generally combined with membrane filtration. is there. However, in the former method, the filtration flux is low, and large-scale equipment is required when producing a large amount of purified water. The latter method has a problem that the equipment cost and / or the running cost becomes very expensive. On the other hand, as a method for treating soluble manganese, it has been proposed to micronize manganese with sodium hypochlorite.

Japanese Patent Application Laid-Open No. 07-1000049 Japanese Patent Laid-Open No. 08-080489

Usually, manganese exists as divalent ions in water, but these divalent manganese ions have a high oxidation-reduction potential, so they are not oxidized at a neutral pH, and the pH may be 10 or more. is necessary. On the other hand, if the pH of the treated water is 10 or more in the water purification plant, heavy metals other than manganese will also be deposited, leading to contamination of the water purification equipment.
The present disclosure has been made in view of the above problems, and efficiently performs water treatment while reducing soluble manganese to below the water quality standard without excessively increasing pH without loading special energy. It is an object of the present invention to provide a water treatment method and a water treatment system that can continuously and stably supply a large amount of clean water at a low cost.

The water treatment method of the present disclosure includes:
A water treatment method for treating water by a gravity filtration method using a membrane module,
Raw water supply process for supplying raw water,
A specific component agglomeration step of treating the raw water supplied by the raw water supply step with an oxidizing agent under conditions of pH 7 to 9.5 to generate an agglomerate mainly composed of manganese;
And a filtration step of supplying the raw water subjected to the specific component agglomeration step to the membrane module for processing.
The water treatment device of the present disclosure is
A water treatment system for treating water by gravity filtration using a membrane module,
Raw water supply means for supplying raw water;
Specific component agglomeration means for treating the raw water supplied from the raw water supply means with an oxidizing agent under conditions of pH 7 to 9.5 to generate an agglomerate mainly composed of manganese;
And a filtering means for treating the raw water attached to the specific component aggregating means.

  According to the present disclosure, water treatment can be performed efficiently while reducing soluble manganese to below the water quality standard without excessively increasing the pH without applying special energy, and continuously stable. Thus, it is possible to provide a water treatment method and a water treatment system that can supply a large amount of clean water at low cost.

It is a conceptual diagram of the water treatment system utilized for the water treatment method of this indication. It is a schematic sectional drawing of the hollow fiber membrane module of this indication. It is a conceptual diagram of another water treatment system utilized for the water treatment method of this indication. It is a conceptual diagram of another water treatment system utilized for the water treatment method of this indication.

  The water treatment method of the present disclosure mainly includes a raw water supply step, a specific component agglomeration step, and a filtration step. And the water treatment method of this indication can perform water treatment efficiently and effectively by using the water treatment system of this indication.

[Water treatment system]
The water treatment system of this indication can be used in order to realize the water treatment method of this indication. As shown in FIG. 1, one embodiment of such a water treatment system mainly includes raw water supply means 10, specific component aggregation means 20, and filtration means 30.
In another embodiment, the specific component reducing means 25 may be provided upstream or downstream of the specific component aggregation means 20. For example, as shown in FIG. 4, a specific component reducing unit 25 may be provided between the specific component aggregating unit 20 and the filtering unit 30.
Each of these means is connected in this order via a flow path.

This water treatment system is configured so that water can be treated by gravity filtration. With such a configuration, the water head pressure due to gravity can be efficiently used, and the cost for energy consumption such as electric power energy can be minimized. If the water head pressure to be used is large, the water treatment efficiency can be promoted. On the other hand, in the filtration means, it is necessary to improve the performance of the membrane, the filtration efficiency, the antifouling and the like. In the present disclosure, in order to further improve the performance of the filtering means while making the best use of gravity in each means, each means is provided with a height difference, and a specific component aggregating means is provided upstream of the filtering means. Yes.
Further, in particular, by making the membrane constituting the membrane module in the filtration means, for example, a large-diameter hollow fiber membrane, the filtration efficiency can be effectively improved in a large area, so that the water head pressure is relatively small. However, it is possible to efficiently perform a large amount of water treatment, and it is possible to further improve the performance of the filtering means by the specific component aggregating means described above.

<Raw water supply means 10>
The raw water supply means 10 mainly includes a raw water tank that stores raw water. It is preferable that a flow path (for example, a distribution path) is connected to the raw water tank in order to supply the raw water to the specific component aggregating means described later.
Raw water includes wastewater containing activated sludge at sewage treatment plants, urban sewage such as household wastewater, wastewater from various facilities such as factory wastewater, agricultural wastewater, biologically treated water, wastewater containing suspended solids, city water, well water, It means water to be treated such as water such as rivers or lakes and seawater. In order to concentrate liquid food by membrane separation, fruit juice, milk, and the like may be used. The raw water may have any value for turbidity and SS (floating matter). For example, turbidity is 20000 or less, 5000 or less, and 10-4000. A liquid having an SS (floating substance) of about 20000 or less, about 5000 or less, for example, about 10 to 4000 is given. The raw water (ground water, river water, etc.) normally shows a pH of about 6 to 8 in measurement with a commercially available pH meter, for example.

  The flow path may be equipped with a pump, but is preferably not. When the pump is not equipped, raw water can be supplied to the flow path or the specific component aggregating means 20 as will be described later using a head difference or overflow. When equipped with a pump, any pump can be used without particular limitation as long as it can feed raw water. For example, various pumps, such as a vortex pump, a diffuser pump, a vortex mixed flow pump, a mixed flow pump, a piston pump, a plunger pump, a diaphragm pump, a gear pump, a screw pump, a vane pump, a cascade pump, and a jet pump, can be mentioned. The pump can be used to absorb raw water, pump water, pump out, etc., for specific component coagulation means described later.

  Moreover, as shown in FIGS. 1, 3, and 4, it is preferable that the raw | natural water tank is connected with the flow path which draws in the raw | natural water X from the outside. Furthermore, as will be described later, it is preferable that a flow path for recovering recovered water Y, which is a supernatant of concentrated water discharged from the spout 36, is connected to the filtering means 30. This flow path may be connected to a flow path for drawing the raw water X from the outside.

<Specific component aggregation means 20>
The specific component aggregating means 20 is a means for aggregating a specific component among the components contained in the raw water supplied in the raw water supply step. Here, the specific component refers to an ion containing a manganese element (divalent manganese ion) and / or a water-soluble compound (such as manganese bicarbonate).

Agglomeration refers to generating aggregates (water-insoluble substances such as MnO ₂ and MnCO ₃ ) containing manganese element from raw water supplied in the raw water supply step. As a result, it is only necessary to reduce the concentration of specific components, that is, divalent manganese ions and / or water-soluble compounds in the raw water, and these specific components are reduced to 80% or less of the raw water by the filtration step described later. Preferably, it is reduced to 60% or less and 50% or less. In some cases, it may be reduced to 40% or less.

  The specific component aggregating means mainly includes a treatment tank for treating raw water. The treatment tank has a flow path for introducing the raw water X from the raw water tank. Furthermore, it is preferable that the treatment tank is equipped with stirring means such as a stirrer and a baffle plate. Further, as the specific component aggregating means, an aggregating agent adding means, and if necessary, a pH adjusting agent or a pH adjusting means may be used. Moreover, it is preferable that the specific component aggregating means is connected with a flow path for supplying water to be treated in which the specific component is agglomerated to the filtering means described later. This flow path may be equipped with a pump, but is preferably not. When the pump is not equipped, the water to be treated can be supplied to the flow path using a water head difference or an overflow. A pump similar to that described above can be used. For this reason, for example, the treatment tank (especially the water level) is preferably disposed at a lower position than the raw water tank (particularly the water level).

<Specific component reducing means 25>
In the water treatment system of the present disclosure, when the specific component reducing unit 25 is further provided, as shown in FIG. 4, for example, the specific component reducing unit is provided between the specific component aggregating unit 20 and the filtering unit 30. 25 is arranged.

  The specific component reducing unit 25 is a unit that reduces specific particle components among the particle components contained in the raw water supplied from the specific component aggregating unit 20. Here, the specific particle component mainly refers to a particle component having a specific particle size. The specific particle size can be appropriately set depending on the pore size of the porous membrane provided in the membrane module used in the filtration step described later. For example, the particle component having a specific particle size is preferably a particle component having a particle size 0.1 to 50 times the pore size of the porous membrane, 0.1 to 40 times, 0.1 to 30 times 0.1 to 25 times, 0.1 to 20 times, 0.1 to 15 times, 0.1 to 10 times, 0.1 to 1 times, 0.5 to 30 times, 0.5 to 25 times, A particle component having a particle size of 0.5 to 20 times, 0.5 to 15 times, 0.5 to 10 times, or 0.5 to 1 times is more preferable. Specific examples include particle components having a particle size of 0.001 to 5 μm, 0.001 to 4 μm, 0.001 to 3 μm, 0.001 to 2.5 μm, or 0.005 to 2.5 μm. A particle component having a particle size of 0.01 to 1 μm, 0.01 to 0.5 μm, or 0.01 to 0.15 μm is preferable, and a particle component having a particle size of 0.01 to 0.1 μm is more preferable.

  The reduction means that the particle component having a specific particle size is less than that of the raw water supplied in the raw water supply step, and the particle component having the specific particle size is preferably reduced to 40% or less, and 20% or less. It is more preferable to reduce it to 15% or less or 10% or less.

  From another viewpoint, the particle weight of a specific particle component is calculated from the correction as described in the reference example, that is, the ratio of the specific particle component to be reduced in the particle size distribution and the total particle weight after drying. By doing so, the weight of the specific particle component is preferably reduced to 40% or less, more preferably 20% or less, and further preferably 15% or less or 10% or less.

  The specific component reducing means mainly includes a second treatment tank for treating the water to be treated. The second treatment tank has a flow path for introducing the water to be treated from the specific component aggregating means 20. Furthermore, it is preferable that the second treatment tank is equipped with a stirrer. Further, as the specific component reducing means 25, a flocculant, a flocculant adding means, and a pH adjusting agent and a pH adjusting means as required may be used. Alternatively, a filtration module may optionally be used. These may be used in combination. Moreover, it is preferable that the flow path for supplying the to-be-processed water which reduced the specific component is connected with the filtration means mentioned later of the specific component reduction means 25. FIG. This flow path may be equipped with a pump, but is preferably not. When the pump is not equipped, the water to be treated can be supplied to the flow path using a water head difference or an overflow. A pump similar to that described above can be used. For this reason, for example, the second treatment tank (particularly, the water level) is preferably disposed at a lower position than the raw water tank (particularly, the water level).

Examples of the flocculant include inorganic flocculants and polymer flocculants used in the field. Examples of the inorganic flocculant include aluminum salts such as aluminum sulfate (sulfuric acid band) and polyaluminum chloride (PAC), ferric chloride (FeCl ₃ ), ferrous sulfide, polyferric sulfate, and iron-silica inorganic. Examples thereof include iron salts such as polymer (PSI).

  Examples of the polymer flocculant include a cationic polymer, an anionic polymer, and a nonionic polymer. Examples of cationic polymers include primary amines, secondary amines, tertiary amines and their acid salts, and homopolymers of cationic monomers or allyl monomers having functional groups such as quaternary ammonium groups. Examples thereof include copolymers with various vinyl monomers and the like. Specific examples include acid salts such as dimethylaminoethyl (meth) acrylate and dimethylaminopropyl (meth) acrylamide or quaternary ammonium salts thereof, diallyldimethylammonium chloride, vinylaniline and the like. Examples of the anionic polymer include (meth) acrylic acid, itaconic acid, homopolymers of their alkali metal salts, and copolymers with copolymerizable monomers. Nonionic polymers include, for example, homopolymers such as (meth) acrylamide and N-isopropylacrylamide, copolymers with copolymerizable monomers, etc., novolak resins using phenol, catechol, etc., and polyvinyl acetate. Saponified polyvinyl alcohol, polyvinyl phenol, polyvinyl pyrrolidone, etc. are mentioned. These may be used alone or in combination of two or more.

  The amount of the flocculant to be used can be appropriately adjusted according to the contamination state of the raw water, the treatment amount and the like. It has also been confirmed that the particle size distribution of the particle component can be controlled by adjusting the amount of the flocculant, the stirring conditions, and the like. Therefore, agglomeration of the specific particle size component can be performed very effectively by selecting an appropriate amount. For example, on the basis of the injection amount, about several ppm to about 200 ppm or about 1 to 200 ppm can be mentioned. By setting such an amount, the amount of the flocculant added can be remarkably reduced as compared with the amount of the flocculant used to reduce turbidity.

Examples of the pH adjuster include inorganic acids such as sulfuric acid, nitric acid, perchloric acid and hydrochloric acid, bases such as sodium hydroxide, calcium hydroxide and barium hydroxide.
Examples of the flocculant adding means and the pH adjusting means include a pump.
As the stirrer, any of those known in the art can be used depending on the size of the treatment tank.
The flocculant is usually added to the second treatment tank, and the specific component can be reduced by stirring with a stirrer or the like.

  Any known filtration module can be used as the filtration module as long as the specific component to be aggregated or reduced can be reduced. For example, a membrane module provided with a large-diameter hollow fiber membrane or a flat membrane can be used. Especially, it is preferable to use the membrane module provided with the hollow fiber membrane of a large diameter comparable as the membrane module mentioned later.

  In order to effectively use the gravity filtration method, when using a filtration module, the height of the filtration module and the permeate outlet of the filtration module is set to the raw water tank, the specific component aggregating means 20 or the specific component reducing means 25. It is preferable to arrange at a position where a water head difference can be generated with respect to the water level, that is, a position lower than the water level of the raw water tank, the specific component aggregating means 20 or the specific component reducing means 25.

<Filtration means 30>
The filtering means 30 mainly includes a membrane module 31.
The membrane module 31 may be any membrane module known in the art used for water treatment. In particular, the membrane used in the membrane module is preferably a porous membrane, more preferably a hollow fiber membrane, and even more preferably a single layer structure. Examples thereof include those described in JP-A-62-140607, JP-A-6-319961, JP-A-2009-183822, International Publications 2011/004786 and 2011/108579.

As shown in FIG. 2, the membrane module 31 has a hollow fiber membrane 32 that filters the water to be treated, a holding member 33 that holds the hollow fiber membrane 32, and a fixing that fixes the hollow fiber membrane 32 and the holding member 33. Member 34.
The membrane module 31 includes, for example, an inlet 35 and a spout 36 that communicate with the inside of the hollow fiber membrane 32 and a permeate outlet 37 that communicates with the outside of the hollow fiber membrane, by the holding member 33 and the fixing member 34. The injection port 35 is connected to the flow path connected to the above-described specific component aggregating means 20, and treated water whose specific components are reduced by the specific component aggregating means 20 is supplied. The concentrated water Z in which the water to be treated is concentrated, the residue remaining without being filtered, and the like are discharged from the spout 36. Therefore, it is preferable that a flow path connected to the concentrated water tank 42 containing the concentrated water Z and / or the residue is connected to the spout 36 as described later. As will be described later, the permeate outlet 37 is preferably connected to a flow path that is connected to a permeate tank 40 containing permeate. However, the specific component reducing means 20 and the spout 36 of the filtering means 30 may be connected, and the inlet 35 of the filtering means 30 and the concentrated water tank 42 may be connected.

  The hollow fiber membrane is preferably composed of a resin membrane having pores of 0.01 to 0.1 μm. The density of the holes can be adjusted as appropriate according to the inner diameter, film thickness, outer diameter, characteristics to be obtained, etc. of the hollow fiber membrane, which will be described later, and such fine holes serve as a water treatment membrane. Depending on the density or the like, for example, the fractionation property of the ultrafiltration membrane or the microfiltration membrane can be adjusted. In general, it is known that an ultrafiltration membrane is a membrane having a pore size of about 2 to 200 nm, and a microfiltration membrane is a membrane of about 50 nm to 10 μm. The inner diameter is preferably 2 to 10 mm. The film thickness is preferably 0.1 to 1.7 mm. The outer diameter is preferably 2.1 to 11.7 mm. The membrane filling rate in the membrane module is preferably 40 to 70%.

  The hollow fiber membrane may be formed of any material. Among these, those containing a structural unit derived from a vinyl chloride monomer are preferable. For example, the structural unit derived from the vinyl chloride monomer is 40% by mass or more (preferably 50% by mass or 60% by mass or more, more preferably 70% by mass or more, 80% by mass) in the total resin constituting the hollow fiber membrane. More preferably, the material occupies 85% by mass or more).

  It is preferable that the hollow fiber membrane further includes a hygroscopic resin or a copolymer containing such a resin as a structural unit. The “resin having hygroscopicity” means a resin having a weight increase rate (water content) of 0.1 to 6% after being left for 24 hours at 23 ° C. and 50% relative humidity. The moisture content of the hygroscopic resin is preferably 1 to 5%, more preferably 2 to 3%. By adjusting the humidity by the method defined in JISP8111, the hygroscopicity of the resin, that is, the water content can be evaluated.

  Examples of the hygroscopic resin include a polymer having a molecular side chain containing a hydroxyl group and the like. For example, one or more resins selected from the group consisting of polyalkylene glycol, polyvinyl acetate, polyvinyl formal, polyacetal, polyvinyl butyral, and polyvinyl alcohol, or a copolymer containing two or more of these resins as structural units (for example, Block copolymer) and the like. This copolymer may be one containing a structural unit derived from a vinyl chloride monomer (for example, a block copolymer or a random copolymer). By using such a resin, it becomes difficult for contaminants to adhere to the hollow fiber membrane. Even if temporarily attached, contaminants can be easily removed by a cleaning process such as backwashing. In order to prevent the adhesion of contaminants, it is effective to use a hollow fiber membrane having a relatively large diameter as described above in addition to such material selection. As a result, the in-membrane flow rate can be easily controlled, and contaminants attached to the hollow fiber membrane can be easily removed. Furthermore, even when using the limited pressure of gravity filtration, the use of a hygroscopic resin as the membrane material increases the hydrophilicity between the membrane and water, so efficient filtration is possible. More useful to do.

  The hollow fiber membrane includes (a) a blend resin of polyvinyl chloride and a hygroscopic resin, and (b) a copolymer of a vinyl chloride monomer and a monomer constituting the hygroscopic resin (for example, a graft copolymer). ), (C) copolymers of polyvinyl chloride and hygroscopic resins (for example, block copolymers), (d) blend resins of polyvinyl chloride and (b) or (c), etc. It can be a film made of morphological material. Especially, the film | membrane by (a), (c) and (d) is preferable, and the film | membrane by (d) is more preferable. By making hollow fiber membranes using such materials, it is possible to ensure antifouling properties, and in addition to reducing specific components, prolong the period until the next membrane module cleaning. Can do. On the other hand, if the amount of the turbidity component having a volume larger than that of the specific component increases in the membrane, a high load may be applied to the membrane during cleaning. However, the strength is ensured by using the above-described materials. Therefore, it is possible to suppress damage to the membrane during cleaning due to an increase in the amount of turbidity components having a large volume. As a result, the cost merit and strength increase of the membrane module act synergistically to ensure long-term reliability.

The holding member may be any member that can hold the hollow fiber membrane, and can be formed of, for example, an acrylic resin, a polystyrene resin, an ABS resin, an AS resin, a polycarbonate resin, a vinyl chloride resin, or the like.
The fixing member can be formed of an epoxy resin, a urethane resin, or the like.
A membrane module may be used independently and may be used in combination of 2 or more. Two or more membrane modules can be combined in various forms such as series, parallel, series-parallel, and parallel-series.

<Other means>
As shown in FIGS. 1, 3, and 4, the water treatment system of the present disclosure further includes a permeated water tank 40 that stores permeated water filtered by the filtering means 30 downstream of the filtering means 30. Further, in order to wash the membrane module in the filtration means 30, it is preferable that a backwash water tank 41 is provided downstream of the filtration means 30. The permeated water tank and the backwash water tank may be used in combination.

  Further, a concentrated water tank 42 is preferably provided downstream of the filtering means 30. As described above, the concentrated water tank 42 is preferably connected to the flow path for introducing the concentrated water Z from the filtration means 30 and the flow path for introducing the supernatant Y to the raw water tank. In general, the closer the amount of the raw water tank and the permeated water tank 40 are to the same amount, the ideal water treatment, that is, the recovery rate of filtered water from the raw water is increased, and the amount of energy used is reduced and the cost is reduced. Water treatment can be realized. Therefore, it is preferable to provide a flow path for collecting the supernatant Y from the concentrated water tank 42 into the raw water tank.

The permeated water tank 40, the backwash water tank 41, and the concentrated water tank 42 are connected to the filtering means 30 by a flow path, respectively. Between the permeated water tank 40 and / or the backwash water tank 41 and the filtering means 30, liquid feeding and / or return pumps 43 and 44 may be provided. These pumps 43 and 44 can use the thing similar to what was mentioned above.
However, as shown in FIG. 3, when the backwash water tank 41 is installed at a higher position than the outlet on the permeate side of the membrane module, the water head pressure can be used more effectively. It is not necessary to provide a pump.
The concentrated water tank 42 is preferably connected to the raw water supply means 10 by a flow path. In this case, the return pump 44 may be provided between the concentrated water tank 42 and the raw water supply means 10. Moreover, you may make the raw | natural water supply means 10 function as the concentrated water tank 42, without providing the concentrated water tank 42. FIG.

  Furthermore, the flow path may be provided with an on-off valve, a gas supply device, an ultrasonic generator, a chemical tank, and the like that are generally used in the field of water treatment.

<Relationship between various means>
When gravity (or water head pressure) is used for filtration, at least the specific component agglomeration means 20 (the highest pressure release position), optionally the water level of the specific component reduction means 25, is set to the outlet on the permeate side of the membrane module (permeate water). It is preferable that the flow path on the side is installed at a higher position than the position of the outlet 50 of the permeate when the water is full, the lowest pressure release position.
Further, in order to suppress the use of energy consumption, the water level of the raw water tank of the raw water supply means 10 is set at a higher water level than the water level in the specific component aggregation means 20 and optionally the specific component reduction means 25. It is preferable. In particular, the water level of the raw water tank of the specific component aggregating means 20 or the specific component reducing means 25 and the raw water supply means 10 is set higher than the position of the outlet 37 on the permeate side of the membrane module. It is preferable.

Although the water head difference due to the height difference of these means is better, energy is required for water supply to the raw water tank or the like of the raw water supply means 10. Therefore, these height differences are not particularly limited, and can be set as appropriate according to the processing performance of the filtration means, the intended water permeability, and the like. Specifically, about 1 to 100 m, about 1 to several tens of meters, and about 4 m are mentioned.
Actually, by using the specific component aggregating means and / or the specific component reducing means 25, it is possible to ensure an appropriate water permeability even with a head difference of about 4 m before and after the filtering means in a general water purification plant. Have confirmed. Therefore, existing facilities can be used almost as they are or simply by changing a rapid filtration facility or the like to specific component agglomeration means and / or filtration means, and economically and stably perform high-performance water treatment. Can be performed.

In addition, the position of the membrane module is close to the water level of the raw water tank and / or the treated water tank, and there is a large difference in level with respect to the water level of the permeated water tank 40 that stores the permeated water. When the path is full of water, the water pulls the water in the membrane module, and suction pressure is applied to the permeate-side outlet at the transmembrane differential pressure applied to the membrane module. When this suction pressure is larger than the pressure applied to the membrane module from the raw water tank and / or the treated water tank (suction pressure> pressurization), the siphon effect works and the membrane module is less likely to foul (clog). Sometimes useful. However, maintaining the siphon effect may be cumbersome, and attention must be paid to the siphon running out due to air entering the permeate channel.
On the other hand, when the position of the membrane module is close to the water level of the permeated water tank and far from the water level of the raw water tank and / or the treated water tank, and the head pressure difference increases, the membrane pressure from the treated water tank to the membrane is increased. The pressure applied to the module increases. If the suction pressure is smaller than the pressure applied to the membrane module from the treated water tank (suction pressure <pressurization), there is no siphon effect and no siphon breakage occurs. is there.

[Water treatment method]
The water treatment method of the present disclosure may use any method / method as long as the gravity filtration method can be realized. In the following, a method for performing water treatment mainly using the water treatment system shown in FIG. 1 or FIG. 4 will be described. In the water treatment method of the present disclosure, in particular, a simple method of combining a specific component agglomeration step and a filtration step allows water treatment to be performed stably at a low cost and in a large amount without excessively increasing the pH. It can be done continuously.
<Raw water supply process>
First, raw water is supplied to the specific component aggregating means 20. The supply of raw water here is preferably performed using the head pressure difference with the raw water supply means 10 as described above. The feed rate of the raw water is preferably adjusted as appropriate in consideration of the type of the specific component agglomeration means 20, its size, the thickness of the flow path, the specific component agglomeration method, the speed of the subsequent filtration step, and the like. For example, the flow rate in the flow path of the raw water is about 0.001 to 10 m / s, and preferably about 0.001 to 5 m / s. That is, it is preferable that the flow rate is the same as that of the membrane module. As the flow velocity in the flow path, a value calculated based on the volume of raw water to be circulated per unit time is adopted.
And

<Specific component agglomeration process>
Aggregates (water-insoluble substances such as MnO ₂ , MnCO _3, etc.) containing manganese element are generated from the raw water supplied in the raw water supply step by the specific component agglomeration. By such agglomeration, the agglomerate can be removed by a filtration step described later. As a result, the specific component can be reduced to 80% or less of the raw water. Preferably, it can be reduced to 60% or less and 50% or less. In some cases, it may be reduced to 40% or less.

First, the pH of the raw water is adjusted to 7 to 9.5 for specific component aggregation. The method for adjusting the pH is not particularly limited, and can be appropriately selected depending on the state of raw water to be treated. For example, an alkalizing agent may be added while monitoring with a commercially available pH meter. Examples of the alkalizing agent include NaOH, CaO, Ca (OH) ₂ , MgO, Mg (OH) ₂ , steel products slag, recycled products such as waste concrete, and the like. Steelmaking slag contains about 1 to 2% by mass of soluble CaO and / or Ca (OH) ₂ and supplies OH ions when these substances come into contact with water. Further, steelmaking slag, dicalcium silicate (2CaO · _SiO 2), for calcium silicate compounds such as tricalcium silicate (3CaO · SiO ₂₎ is mainly dissolves gradually and is possible to supply the OH ion for a long time it can.

  In particular, when the alkalizing agent is used in water purification treatment, it is preferable to use NaOH in the form of an aqueous solution because the addition amount can be easily adjusted. The amount of the alkalizing agent used can be appropriately adjusted depending on the raw water supplied.

Then, the pH-adjusted raw water is treated with an oxidizing agent.
As an oxidizing agent, what is used in the said field | area is mentioned. For example, ozone, a peroxide, a metal salt compound, a chlorine compound, etc. are mentioned. Particularly preferred are chlorine compounds, and specific examples include sodium hypochlorite and calcium hypochlorite. Particularly when used in water purification treatment, an aqueous sodium hypochlorite solution is preferred.

The amount of the oxidizing agent to be used can be appropriately adjusted depending on the manganese concentration of raw water, the amount of treated water, and the like. For example, it is preferable that the chloride ion concentration in the oxidizer is 1.0 to 5 times, 2.0 to 4 times, or 2.0 to 2.5 times the manganese concentration of the raw water. Such an amount can be determined by collecting a certain amount of raw water in advance and measuring the manganese concentration.
When using sodium hypochlorite, it is preferable that the free chlorine concentration in sodium hypochlorite is about 1.3 times the manganese concentration. In addition, since free chlorine is consumed by the organic substance in raw | natural water, more chlorine quantity may be needed with respect to the above-mentioned quantity.
By setting the oxidizing agent to such an amount, manganese ions or soluble compounds contained in the raw water can be changed into insoluble manganese compounds, and can effectively be aggregated as flocs.
Therefore, when the raw water is treated with the oxidizing agent, it is preferable to stir in order to uniformly disperse the oxidizing agent in the raw water, and it is preferable to rapidly stir after the injection of the oxidizing agent. Thereafter, the agglomerates may be precipitated by standing arbitrarily.
Or in order to be able to remove an aggregate by the filtration process mentioned later and the specific component reduction process, you may attach to the next process as it is after stirring.

<Specific component reduction process>
As shown in FIG. 4, in the water to be treated that has been subjected to the specific component aggregating step, a step of reducing specific particle components among the particle components contained in the water to be treated may be performed. The specific particle component is preferably a particle component having a particle size of 0.1 to 50 times the pore size of the porous membrane used in the membrane module used in the filtration step. 1 to 30 times, 0.1 to 25 times, 0.1 to 20 times, 0.1 to 15 times, 0.1 to 10 times, 0.1 to 1 times, 0.5 to 30 times, 0.5 Particle components having a particle size of ˜25 times, 0.5 to 20 times, 0.5 to 15 times or 0.5 to 10 times, 0.5 to 1 times are reduced. Especially, it is preferable to reduce the particle component having a particle size of 0.1 to 20 times. Specific examples include particle components having a particle size of 0.001 to 5 μm, 0.001 to 4 μm, 0.001 to 3 μm, 0.001 to 2.5 μm, or 0.005 to 2.5 μm. It is preferable to reduce the particle component having a particle size of 0.01 to 1 μm, 0.01 to 0.5 μm, 0.01 to 0.15 μm, and a particle component having a particle size of 0.01 to 0.1 μm. More preferably, it is reduced.
Therefore, as described above, a flocculant is added to the water to be treated in the second treatment tank. In this case, it is preferable to stir so that the flocculant acts uniformly on the treatment. As described above, the agitation may be performed by using a stirrer or by using a flow rate at the time of supply of the treatment to the second treatment tank (for example, bypass-type agitation) to add the flocculant to the treatment. It may be added / mixed.

  The particle component having a specific particle size in the above-described range can be effectively reduced by adjusting the addition amount according to the type and / or addition amount of the flocculant to be used, stirring conditions, and the like. Moreover, the particle component having a specific particle diameter can be effectively reduced to 40% or less, 20% or less, 15% or less, or 10% or less of raw water by adjusting the addition amount.

The inventor of the present application confirmed that the particle component having a specific particle size could be reduced without reducing the turbidity by performing the specific component agglomeration step on the raw water having a predetermined turbidity. doing.
In order to reduce the particle component having a specific particle size, the type, amount, stirring speed, stirring / contact time, etc. of the flocculant may be appropriately changed. For example, it has been confirmed that smaller particles increase by changing the stirring speed or shortening the stirring time. Therefore, in order to ensure reduction of the particle component having a specific particle size, it is preferable to perform a preliminary experiment by changing the type, amount, stirring speed, stirring / contact time, etc. of the flocculant.

The time required to reduce the particle component having a specific particle size can be adjusted by, for example, stirring or contact time after the addition of the flocculant. For example, the water to be treated may be brought into contact with the flocculant for several minutes to several hours. At this time, the degree of stirring may be changed, or may be constant, or stirring may be stopped and allowed to stand.
Before and after the addition of the flocculant (preferably, before), it is preferable to adjust the pH to about pH 7, for example, with a pH adjuster.

Moreover, the particle | grain component which has the specific particle size mentioned above is realizable also by rough filtration. In this case, the filtration can be appropriately set such as using a filtration membrane having an appropriate pore diameter and applying an appropriate transmembrane pressure difference.
The inventor of the present application was able to reduce the particle component having a specific particle size without changing the turbidity by performing a specific component agglomeration step by filtration on the raw water having a predetermined turbidity. Have confirmed.

<Filtration process>
Various methods can be adopted in the filtration process using the filtration means, particularly the membrane module. The membrane surface of the membrane module and the flow direction of the water to be treated are substantially parallel, and either a cross-flow method or a dead-end method in which suspended matter or the like attached to the membrane surface is separated and circulated may be used.
The pressurization method in the membrane module may be either an internal pressure type or an external pressure type. However, particularly when the hollow fiber membrane having a relatively large pore diameter as described above is used, the internal pressure type, that is, the hollow fiber membrane type is used. A method of supplying water to be treated on the inside and taking out permeated water on the outside of the hollow fiber membrane is preferable. Moreover, any of constant pressure filtration, constant flow filtration, these combinations, etc. may be sufficient.
For the membrane module, a method of repeatedly performing water treatment and backwashing may be employed, or flushing or draining may be performed after or during water treatment or backwashing.

  The flow rate of the water to be treated in which the particle component is agglomerated supplied to the membrane module varies depending on the water head difference in the water treatment system described above, but is preferably about 0.001 to 10 m / second, for example. More preferably, it is about 0.005 to 6 m / sec, about 0.005 to 3 m / sec, or about 0.01 to 1 m / sec. By supplying raw water to the hollow fiber membrane at such a flow rate, it becomes difficult for contaminants to adhere to the hollow fiber membrane, so that it is possible to continue to treat the raw water efficiently. Here, the flow rate of the water to be treated supplied to the hollow fiber membrane can be a value measured by an electromagnetic flow meter for wastewater treatment (manufactured by Endless Hauser).

  In the membrane module, the water to be treated is preferably loaded with a transmembrane pressure difference of about 5 to 200 kPa, more preferably about 5 to 150 kPa, about 5 to 100 kPa, or about 5 to 50 kPa. In the case of such a transmembrane pressure difference, the water permeation performance required in practice can be maintained. Moreover, it is possible to effectively prevent the contaminants from adhering to the membrane module.

Example 1
Manganese sulfate pentahydrate was dissolved in purified water to prepare a solution containing 50 μg / L of manganese, which was used as a stock solution.
After adjusting the pH of the stock solution to pH 8 with an aqueous sodium hydroxide solution, an appropriate amount of an aqueous sodium hypochlorite solution was added as an oxidizing agent. At this time, the chloride ion concentration in sodium hypochlorite was set to be twice the manganese concentration in the stock solution. Then, it stirred at 300 rpm for 1 hour using the stirrer, and filtered the whole quantity with the membrane module provided with the hollow fiber membrane with a hole diameter of 0.1 micrometer. The manganese concentration of the filtrate was measured. The results are shown in Table 1. The filtration was performed at a transmembrane pressure difference of 30 kPa and a flow rate of 0.01 m / s.
In addition, an experiment was also conducted in which sulfuric acid was added to the stock solution and the pH was returned to 7 before the filtration. As a result, it was the same as above.

As shown in FIG. 2, the membrane module used here has a hollow fiber membrane accommodated in a holding member and fixed by a fixing member. The hollow fiber membrane was formed by using a vinylpyrrolidone-vinyl chloride copolymer and a vinyl chloride resin (polymerization degree 800) as materials, hygroscopicity 1.6%, inner diameter 4 mm, film thickness 1.5 mm, long The membrane area in the membrane module was 1 m ² . For the hygroscopicity, a value measured by the weight increase rate (water content) of the resin after being left for 24 hours at 23 ° C. and 50% relative humidity was adopted.

Example 2
As in Example 1, a stock solution was prepared and filtered in the same manner as in Example 1 except that the pH of the stock solution was adjusted to 9. The manganese concentration of the filtrate was measured. The results are shown in Table 1.

Example 3
As in Example 1, a stock solution was prepared and filtered in the same manner as in Example 1 except that the pH of the stock solution was adjusted to 9. The manganese concentration of the filtrate was measured. The results are shown in Table 1. The filtration was performed at a transmembrane differential pressure of 150 kPa and a flow rate of 0.8 m / s.

Comparative Example 1
As in Example 1, a stock solution was prepared and filtered in the same manner as in Example 1. The manganese concentration of the filtrate was measured. The results are shown in Table 1. In addition, filtration was implemented with the membrane module provided with the hollow fiber membrane with the hole diameter of 2 micrometers.

Comparative Example 2
As in Example 1, a stock solution was prepared and filtered in the same manner as in Example 1 except that the pH of the stock solution was adjusted to 6. The manganese concentration of the filtrate was measured. The results are shown in Table 1.

In Table 1, the manganese removal rate of the filtered water is 50% or more.
A removal rate of 80% or more was rated as ◎.

  In Example 1, after adding sodium hypochlorite and stirring, sulfuric acid was added to the water to be treated to adjust the pH to 7, so that polyaluminum chloride was 80 ppm based on the injection amount. And stirred at 120 rpm for 5 minutes, followed by 30 rpm for 10 minutes. Then, when it filtered with the membrane module provided with the hollow fiber membrane, the manganese density | concentration of a filtrate is comparable as Example 1, Furthermore, it has confirmed that a lot of filtration is realizable over a long term.

Reference Example As raw water, a kaolin turbidity standard solution in which turbidity measuring kaolin was adjusted to turbidity of 2000 degrees was used. To this raw water, polyaluminum chloride was added to 80 ppm on the basis of the injection amount, and the mixture was stirred at 120 rpm for 5 minutes and then at 30 rpm for 10 minutes. Thereafter, a small amount of the suspension was collected, and the entire remaining amount was filtered through a membrane module having a hollow fiber membrane having a pore diameter of 0.02 μm. As shown in FIG. 2, the membrane module used here has a hollow fiber membrane accommodated in a holding member and fixed by a fixing member. The hollow fiber membrane was formed by using a vinylpyrrolidone-vinyl chloride copolymer and a vinyl chloride resin (polymerization degree 800) as materials, hygroscopicity 1.6%, inner diameter 4 mm, film thickness 1.5 mm, long The membrane area in the membrane module was 1 m ² . For the hygroscopicity, a value measured by the weight increase rate (water content) of the resin after being left for 24 hours at 23 ° C. and 50% relative humidity was adopted.
The transmembrane pressure difference during filtration with the membrane module was 30 kPa, and the flow rate was 0.01 m / s.

About the fractionated suspension, the particle size distribution of the particle component contained therein was measured with a particle size distribution meter by a laser diffraction method.
The particle size distribution was measured after filtering the collected suspension with a filter having a pore size of 0.5 μm (= pretreatment before measuring the particle size distribution). As a result, the number of particles having a particle size of 0.2 μm or less was 10% (cumulative particle number) of the whole.

More specifically, the cumulative number of particles having a particle size of 0.2 μm or less is calculated as follows.
First, raw water is filtered through a filter having a predetermined pore size (for example, 0.5 μm pore size as described above), and a portion of the obtained filtrate is collected and measured with a particle size distribution analyzer by laser diffraction method. To do.
Similarly, the raw water subjected to the reduction treatment is similarly filtered through a filter having a predetermined pore size, for example, a pore size of 0.5 μm, and a part of the obtained filtrate is fractionated, and the particle size distribution is measured.

Part of raw water and reduced treated water not used for particle size distribution measurement is dried and the total weight of particles after drying is measured. This measures the absolute amount of turbidity in the 0.5 μm passage liquid.
And the ratio with respect to the particle existing amount and the particle size distribution of the part to be reduced in the reduced treated water is obtained. At this time, by performing the reduction process, as the particle diameter becomes larger as it is captured by a predetermined pore diameter, for example, a 0.5 μm filter, particles that are not measured by the above-described particle size distribution measurement may appear. In that case, the particle size distribution of the reduced treated water is corrected by the following method.
In other words, the weight difference between the reduced treated water and the raw water measured above is a predetermined pore size, for example, the weight of particles that have become so large that they are captured by a 0.5 μm filter (if using a flocculant, (Including a flocculant). This weight difference is added to the weight of the reduced treated water. Thereafter, the particle size distribution of the reduced treated water is calculated again.

  Specifically, when the total particle weight of reduced treated water is 1 g, the amount of particles present in the target portion in the reduced treated water is 20%, and the total weight of raw water particles is 2 g, the amount of particles present in the reduced treated water is It is corrected to 10%.

  This disclosure is widely used as a water treatment method or water treatment system used for water purification such as river water and groundwater clarification, clarification of industrial water, drainage and sewage treatment, seawater desalination pretreatment, etc. Therefore, economical and efficient water treatment can be performed.

DESCRIPTION OF SYMBOLS 10 Raw water supply means 20 Specific component aggregation means 25 Specific component reduction means 30 Filtration means 31 Membrane module 32 Hollow fiber membrane 33 Holding member 34 Fixing member 35 Inlet 36 Water inlet 37 Permeate outlet 40 Permeated water tank 41 Backwash water tank 42 Concentrated water tank 43, 44 Pump 50 Permeated water outlet X Raw water Y Recovered water Z Concentrated water

Claims (10)

A water treatment method for treating water by a gravity filtration method using a membrane module,
Raw water supply process for supplying raw water,
A specific component agglomeration step of treating the raw water supplied by the raw water supply step with an oxidizing agent under conditions of pH 7 to 9.5 to generate an agglomerate mainly composed of manganese;
A filtration step of supplying the raw water subjected to the specific component agglomeration step to the membrane module for processing;
A water treatment method comprising:   The water treatment method according to claim 1, wherein the oxidizing agent is selected from chlorine-based compounds.   The water treatment method according to claim 1 or 2, wherein the oxidizing agent is sodium hypochlorite.   The water treatment method according to any one of claims 1 to 3, wherein the porous membrane used in the membrane module is composed of a resin membrane having pores of 0.01 to 0.1 µm.   The water treatment method according to any one of claims 1 to 3, wherein a porous membrane is used in the membrane module, and the porous membrane is constituted by a hollow fiber membrane having an inner diameter of 2 to 10 mm.   The water treatment method according to claim 5, wherein the porous membrane used in the membrane module has a thickness of 0.1 to 1.7 mm.   The porous membrane used in the membrane module is one or more resins selected from the group consisting of polyvinyl chloride, polyvinyl acetate, polyvinyl formal, polyacetal, polyvinyl butyral, and polyvinyl alcohol, or structural units derived from these resins. The water treatment method as described in any one of Claims 1-5 comprised including this.   The water treatment method according to any one of claims 1 to 7, wherein in the filtration step, the raw water subjected to the specific component agglomeration step is filtered with a transmembrane differential pressure of 5 to 500 kPa.   In the said filtration process, the water treatment method as described in any one of Claims 1-8 which supplies the raw | natural water attached | subjected to the said specific component aggregation process to the said membrane module with the flow rate of 0.01-1 m / sec. . A water treatment system for treating water by gravity filtration using a membrane module,
Raw water supply means for supplying raw water;
Specific component agglomeration means for treating the raw water supplied from the raw water supply means with an oxidizing agent under conditions of pH 7 to 9.5 to generate an agglomerate mainly composed of manganese;
A water treatment system comprising: filtration means for treating raw water attached to the specific component aggregation means.