JP5257591B2 - Water treatment method - Google Patents

Description

  The present invention relates to a water treatment method for removing trace components in water such as oxidizable components, silica and inorganic harmful substances contained in raw water such as surface water, lake water, dam water, spring water, and groundwater.

  Drinking water (tap water) that treats raw water such as surface water, lake water, dam water, spring water, groundwater, etc., and meets water quality standards (hereinafter also referred to as “tap water quality standards”, “water quality standards”) So-called water purification technology has a history of more than 100 years, but the basis of water purification technology is still coagulation, sedimentation and sand filtration.

  In recent years, with the advancement of analytical technology, the detection accuracy of trace harmful components has been improved, the need for construction of water supply facilities in underdeveloped countries where raw water contamination is serious, and the need to deal with water pollution due to the deterioration of the global environment. Along with this, there is a growing need for further removal of components (trace components in water) such as iron, manganese, silica, and arsenic contained in raw tap water.

  Many methods have been proposed for removing such trace elements in water. For example, as a method for removing iron and manganese, a method is known in which iron and manganese are oxidized to produce oxide microcrystals and filtered. However, since this method uses sand filtration, there is a dislike for requiring a large installation area.

As a method for removing silica, a method using a reverse osmosis membrane (RO membrane) capable of removing silica at an ion level has been proposed. However, this method tends to cause clogging of the RO membrane, and as a focus of recent technological development, many methods for preventing clogging by using a dispersing agent are used in combination, but the processing becomes complicated in practice. On the other hand, as a single treatment by membrane separation (membrane filtration) of silica, membrane filtration by an ultrafiltration membrane (UF membrane) is also being studied. In this case, the treatment efficiency by fouling (so-called membrane clogging) is considered. Because of a sharp drop, it is difficult to adopt as a silica removal measure except in special cases.
Further, as another method for removing silica, a method is used in which the colloidal silica is coarsened with a flocculant such as polyaluminum chloride or aluminum sulfate and then agglomerated and separated. However, even with this method, the removal target is limited to silica, the working range is narrow, and because aggregation and separation are performed in separate processes, the construction cost of the processing apparatus increases, and the installation area also increases. Problems have been pointed out.

  As for the removal method of arsenic, adsorption removal by iron compound, iron clathrate compound or low crystalline iron compound has been proposed, but this method requires a special adsorbent, and adsorption The separation operation is also complicated and is not preferable (see, for example, Patent Document 3).

  As described above, many methods for individually removing trace components due to adsorption and aggregation have been proposed, but many problems remain in either method. In addition, in the above-described method, except for the simultaneous removal of iron and manganese, all of the trace components in the water are individually targeted for removal, and therefore separate processing steps (treatment devices) are required for the removal of each trace component in the water. To do. Therefore, the construction cost and operation cost required for the entire water treatment system are increased, resulting in a large installation area, which has been an obstacle to plant construction.

  On the other hand, chemicals that can be used for drinking water are often restricted by the condition that they finally meet the water quality standards (hereinafter also referred to as tap water quality standards) based on the Water Supply Law, and are further restricted in consideration of costs and other factors. The problem also occurs.

In tap water treatment, flocculants and coagulant aids are widely used and have many achievements. Originally, flocculants and coagulant aids are mainly used for turbid components, organic substances, odors of chromaticity, etc. Was the main process. Accordingly, the treatment of silica, arsenic and the like with a flocculant, a coagulant aid, etc. has not been sufficiently studied, and the need for advanced treatment techniques according to each trace component in water is desired. By the way.
Japanese Patent No. 3672855 JP 2003-225680 A JP 2008-43921 A

  As described above, the removal of trace components in water in tap water is generally carried out individually except for the simultaneous removal of iron and manganese, and there are many cases where the process is complicated and the cost is excessive. Therefore, when drinking raw water such as groundwater to obtain drinking water that meets tap water quality standards, the emergence of technology that easily and inexpensively removes trace water components such as iron, manganese, silica, and arsenic contained in raw water is expected. ing.

  The present invention has been intensively studied in view of such circumstances, and the object of the present invention is to minimize the use of chemicals, and in a simple process, a plurality of iron, manganese, silica, arsenic, and the like. An object of the present invention is to provide a water treatment method capable of removing trace components in water at once.

In order to solve the above-mentioned problems, the present inventors have conducted research. As a result, aluminum sulfate and an oxidizing agent were introduced into raw water to be treated containing an oxidizable component, silica and an inorganic harmful component, and a separation membrane filter It has been found that by performing a membrane filtration treatment with the above, it is possible to simultaneously remove oxidizable components, silica and inorganic harmful components, and the present invention has been completed.
That is, as a flocculant generally used as a flocculant for water purification, for example, aluminum sulfate (also referred to as a sulfate band, general formula: Al ₂ (SO ₄ ) ₃ .nH ₂ O), PAC (polyaluminum chloride) , General formula: Aln (OH) _m Cl _3n-m ), polysilica iron, sodium alginate, organic polymer flocculant, etc., and as agglomeration aid, sodium alginate, bentonite, powdered activated carbon, active Silicic acid or the like can be used.

  However, with flocculating agents and / or flocculating aids other than aluminum sulfate, even if PAC (polyaluminum chloride), which is the same aluminum-based flocculant as aluminum sulfate, is used, the above oxidizable components, silica and inorganic harmful substances are used. It was not possible to obtain an excellent effect that the components could be removed at a high removal rate as in the case of using a combination of aluminum sulfate and an oxidizing agent. Of course, such an effect could not be obtained with an oxidizing agent alone or a flocculant alone.

Accordingly, the gist of the present invention is that after treating raw water containing 0.5 mg / L or more of iron as an oxidizable component, silica and arsenic as an inorganic harmful component , with an oxidizing agent and aluminum sulfate, An object of the present invention is to provide a water treatment method for removing the oxidizable component, silica and inorganic harmful components at a time by solid-liquid separation of the generated solid matter with a separation membrane filter.

Specifically, the water treatment method according to the embodiment of the present invention performs membrane filtration with a separation membrane filter immersed in a tank in which raw water to be treated containing oxidizable components, silica and inorganic harmful components is stored, A water treatment method to be obtained, wherein iron is contained as the oxidizable component in an amount of 0.5 mg / L or more in the treated raw water, the inorganic harmful component is arsenic, and the treated raw water is treated with an oxidizing agent and aluminum sulfate. After the treatment, the resulting solid matter is subjected to solid-liquid separation by the separation membrane filter in the tank, so that the oxidizable component, silica and inorganic harmful components are collectively removed.

It is preferable that 0.5 mg / L or more of manganese is contained in the raw water to be treated as the oxidizable component.

It is preferable that manganese is contained as the oxidizable component, and the concentration of iron, manganese, and arsenic in the treated water meets the water quality standards of the Waterworks Law. That is, the iron concentration in the treated water is preferably 0.3 mg / L or less, the manganese concentration is 0.05 mg / L or less, and the arsenic concentration is 0.01 mg / L or less.

It is preferable that sodium hypochlorite is used as the oxidant and the residual chlorine concentration in the tank is 0.1 mg / L or more and 1.0 mg / L or less.
It is preferable that sodium hypochlorite and air are used in combination as the oxidizing agent, and air is supplied from an air diffuser installed below the separation membrane filter.
The HRT of the raw water to be treated in the tank is preferably 5 minutes or more.

The water treatment method according to another aspect of the present invention includes an arsenic as an inorganic harmful component , iron, and silica, in a tank in which raw water to be treated having an iron concentration of 0.5 mg / L or more is stored. Is a water treatment method for obtaining treated water by injecting sodium hypochlorite and aluminum sulfate and then separating the resulting solids with a separation membrane filter immersed in the tank, wherein residual chlorine in the tank The injection amount of sodium hypochlorite is controlled so that the concentration becomes 0.1 mg / L or more and 1.0 mg / L or less, and the oxidizing gas is removed by the aeration means provided below the separation membrane filter. By aeration, when the oxidizing gas is diffused, it assists the oxidation reaction in the tank, and at the same time generates an upward flow that rises along the membrane surface of the separation membrane filter, and the membrane surface of the separation membrane filter were washed, and, iron The iron oxide produced by reaction with sodium hypochlorite and / or the oxidizing gas are allowed to be present almost uniformly in a bath, the oxidation of the bath, crystallization, and / or to promote aggregation, oxidizing gas At the time of stoppage, it is promoted that at least a part of the solid matter generated in the tank settles on the bottom of the tank, and the amount of the solid substance floating in the tank is adjusted so that inorganic harmful components and iron And silica are collectively removed.

According to the present invention, it is not necessary to provide a processing apparatus for each trace component to be removed. In addition, when injecting the oxidizing agent and aluminum sulfate into the tank in which the separation membrane filter is immersed, since the membrane separation process is performed in the same tank, a chemical processing tank for injecting and reacting separately with the oxidizing agent, There is no need to provide a treatment tank such as a precipitation separation tank for injecting aluminum sulfate and performing solid-liquid separation. Therefore, it is possible to reduce the size of the apparatus used in the water treatment method of the present invention, reduce the installation area, and reduce the construction cost and the power cost for driving the apparatus.
Further, by combining membrane filtration treatment, the chemicals used are kept to the minimum necessary chemicals such as an oxidizing agent and aluminum sulfate.

  Therefore, according to the present invention, an inorganic harmful component of arsenic and silica contained in a trace amount at an ionic level in raw water supply can be safely and inexpensively used in a simple water supply without using many chemicals. It can be removed together with oxidizable components such as iron and manganese.

  Hereinafter, the present invention will be described in detail.

  The water treatment method of the present invention performs membrane filtration with a separation membrane filter in a tank (also referred to as a treatment tank or a reaction tank) in which raw water to be treated is stored, and supplies oxidant into the treatment tank when obtaining treated water. Then, the inside of the treatment tank is made an oxidizing atmosphere, and after supplying the aluminum sulfate and treating the raw water to be treated, the solid matter such as precipitates and agglomerates produced is filtered through a membrane to obtain an oxidizable component, Remove silica and inorganic harmful components at once.

  The treated raw water (raw water for water supply) used in the present invention is not particularly limited as long as it contains an oxidizable component, silica and an inorganic harmful component as a separation target component (removal target component). Surface water, lake water, dam reservoir water, spring water, groundwater, and the like can be the targets of the water treatment of the present invention.

Examples of the oxidizable component to be separated include iron, an oxidizable metal component such as manganese, and particularly an oxidizable transition metal component. The oxidizable component only needs to contain at least iron in the raw water to be treated, but may also contain one or more other components . Oxidizing metal components are oxidized to form metal oxides (eg, iron oxide, manganese oxide, etc.). For example, new catalysts for oxidation reaction of oxidizable components such as iron and manganese, silica, etc. It is considered to act as a precipitation accelerator (seeds [seed] during silica precipitation) and promote reactions such as oxidation, precipitation, and / or aggregation (sedimentation) in the treatment tank.

As oxidizable metal component in the processed raw water, the iron content is set to 0.5 mg / L or more. In addition, when two or more kinds of oxidizable metal components are included, at least 0.5 mg / L or more of iron may be included, but each oxidizable metal component includes 0.5 mg / L or more of each. It is preferable that When the amount of the oxidizable metal component contained in the raw water is less than 0.5 mg / L, silica and inorganic harmful components cannot be removed effectively, and the oxidizable metal component is added. However, if it is 0.5 mg / L or more, it is necessary to add a minimum amount of drugs (for example, sodium hypochlorite and aluminum sulfate) in water without adding a new drug. Trace components (for example, iron, manganese, silica, arsenic) can be removed all at once.

In addition, as the oxidizable metal component in the raw water, the amount of iron is less than 0.5 mg / L, while the content of arsenic inorganic harmful component and silica is large and needs to be removed. A metal component that is relatively easily oxidized is added to the raw water so that the amount of iron is 0.5 mg / L or more . As such a metal component that is easily oxidized, iron ions are most preferable in terms of handling. Specifically, for example, ferric chloride can be added to the raw water to be treated.

  Moreover, after discharging | emitting the solid substance containing the oxide of the oxidizable metal component settled in the tank from the bottom part in a tank, you may return in a processing tank again. By circulating solids containing oxides of oxidizable metal components, metal oxides such as iron oxide and manganese oxide contained in the solids act as an oxidation catalyst, and further iron, manganese, etc. It becomes possible to promote the oxidation of the oxidizing metal component.

Is an inorganic toxic components include components defined in tap water quality standards for arsenic. One or more inorganic harmful components may be contained.

  The component to be separated contained in the raw water to be treated may be present in any state such as ions or compounds. Therefore, it may be dissolved in water in an ionic state, or may exist as a soluble or insoluble compound. For example, in the case of iron, it may exist as iron ions in the raw water to be treated, or may exist in the state of a compound such as iron oxide or iron hydroxide. The same applies to other components such as manganese, silica, and arsenic. In addition, iron and manganese are usually present in tap water in the form of iron ions and manganese ions.

  Examples of the oxidizing agent used in the present invention include chlorine-based oxidizing agents such as chlorine, sodium hypochlorite, and chlorine dioxide, ozone gases, hydrogen peroxide, oxygen-based oxidizing agents such as air and oxygen, and potassium permanganate. And any material such as sodium permanganate. Further, the oxidizing agent may be any of solid, liquid, and gas (oxidizing gas). An oxidizing agent may be used individually by 1 type, and may be used in combination of 2 or more type. Among these oxidizing agents, sodium hypochlorite is used from the viewpoints of ease of handling, economy, and the ability to make iron a trivalent oxide and manganese a tetravalent oxide. It is preferable.

  The amount of oxidant introduced is the concentration of the oxidizable component in the raw water, the type of oxidant, the concentration of the oxidant when the oxidant is a solution, HRT (hydraulic residence time), and the size of the treatment tank. Since an appropriate amount is determined by, for example, it is not particularly limited.

  For example, when sodium hypochlorite is used as an oxidizing agent and iron and manganese are oxidized as oxidizable components, the residual chlorine concentration in the tank is 0.05 mg / L or more and 5.0 mg / L or less, preferably It is preferable to determine the amount of sodium hypochlorite introduced so that is 0.1 mg / L or more and 1.0 mg / L or less.

If the residual chlorine concentration is less than the lower limit value, the progress of the oxidation is delayed regardless of the concentration of the oxidizable component, and the oxidation treatment tends to take a long time (HRT must be lengthened). In addition, when the residual chlorine concentration is less than the lower limit value, metal components such as oxidizable iron and manganese are in the form of hydroxides such as ferric hydroxide Fe (OH) ₃ and manganese hydroxide Mn (OH) _2. It tends to be in the form of a fouling that adheres to the separation membrane. However, by setting the residual salt concentration to be equal to or higher than the above lower limit value, metal components such as oxidizable iron and manganese can be completely converted into, for example, ferric oxide Fe ₂ O ₃ .nH ₂ O and manganese dioxide MnO _2. Since it becomes possible to be in an oxidized state (oxide state), fouling is difficult to occur. On the other hand, if the residual chlorine concentration exceeds the above upper limit, the HRT can be reduced, but environmental management of the treatment tank tends to be difficult.

  When using a combination of a liquid or solid oxidant and an oxidizing gas as the oxidant, the optimum amount of liquid or solid oxidant added is determined in consideration of the gas blowing method and amount. decide. For example, when sodium hypochlorite and air blowing are used in combination, the amount of sodium hypochlorite to be added can be reduced according to the method and amount of air blowing.

In the present invention, a submerged membrane is used as a separation membrane filter. From the viewpoint of improving membrane separation efficiency, an aeration tube (aeration means) is installed below the separation membrane filter, and the separation membrane filter is shaken. Bubbling (aeration) may be performed so that it moves.
Moreover, this bubbling can stir the raw water to be treated in the treatment tank without newly providing a stirrer, and can spread the chemicals such as the oxidizing agent and aluminum sulfate introduced into the tank almost uniformly. It is possible to disperse solid substances containing metal oxides generated by introducing these chemicals in the raw water to be treated, and the oxidation, precipitation and agglomeration reactions can be carried out substantially uniformly in the treatment tank. It becomes. At this time, if a gas having an oxidizing action such as air (oxidizing gas) is blown as a bubbling gas, it becomes possible to assist the oxidation reaction in the treatment tank, and when other oxidizing agents are used, This is preferable because the amount of the oxidizing agent added can be reduced.

In the diffuser, the upward flow (gas-liquid mixed upward flow), which is a mixture of gas and liquid generated by the gas generated from the diffuser, passes evenly between the separation membranes and rises along the surface of the separation membrane filter. It is desirable to arrange it so that the deposits can be cleaned. Bubbling may be performed continuously or intermittently. However, if bubbling is performed intermittently, the solids produced in the treatment tank due to oxidation, precipitation, and / or agglomeration, etc. when the bubbling is suspended At least a part can be settled and separated in the lower part of the treatment tank without using membrane filtration, and the burden on the membrane can be reduced, which is preferable.
In addition, by adjusting the bubbling interval, the floating amount of oxides such as iron and manganese in the treatment tank can be adjusted. The interval of bubbling is determined by the amount of solids in the treatment tank, the degree of recovery of the film differential pressure, etc., and is not particularly limited. For example, from the standpoint that the balance between the effect of preventing membrane clogging and the amount of floating oxide that promotes the reaction in the treatment tank is good, the air diffuses for 5 to 60 minutes, the interval between the stops for 10 minutes, In other words, it is preferably performed at intervals of aeration for 8 to 10 minutes and stop for 1 to 2 minutes. Further, the suction filtration is preferably performed by adjusting the suction-stop interval to the bubbling interval, but this does not particularly limit the present invention.

  Furthermore, if an inclined plate is provided below the diffuser tube, it is effective because it is possible to promote the sedimentation of the solid matter to the lower part of the treatment tank and to prevent the solid matter that has once settled from rising. .

  The HRT of the raw water to be treated in the treatment tank is desirably 5 minutes or more from the viewpoint of sufficiently promoting a reaction such as oxidation. Further, from the viewpoint of processing efficiency, economy, etc., the HRT is desirably 30 minutes or less.

  The method for controlling the amount of oxidant introduced is not particularly limited, and any method may be used. For example, when sodium hypochlorite is used as an oxidant, a residual chlorine meter (residual chlorine sensor) is installed in the treatment tank, and the residual chlorine concentration is continuously detected and detected. The amount of sodium hypochlorite injected may be controlled according to the residual salt concentration. In addition, a residual chlorine meter is installed in the secondary side (treated water side) pipe of the separation membrane filter, and control is performed so as to inject a predetermined amount of sodium hypochlorite according to the detected residual salt concentration. Good.

As the aluminum sulfate used in the present invention, those generally used as a flocculant for tap water can be used. The amount of aluminum sulfate added is adjusted not only by the concentration of oxidizable components contained in the raw water, but also by the content of inorganic harmful components such as arsenic and silica. The relationship between the concentration of the separation target component and the amount of aluminum sulfate added is not particularly limited. For example, the value obtained by converting aluminum sulfate to Al ₂ O ₃ with respect to the concentration of the separation target component of 10 to 70 mg / L (hereinafter, It is effective to add 5 to 100 mg / L, preferably 10 to 50 mg / L in terms of Al ₂ O ₃ .
Here, the concentration of components to be separated is the total concentration of all trace components in water to be removed (for example, the total of these components when oxidizable components, silica and arsenic are to be removed). Say.

  As a method for controlling the amount of aluminum sulfate added, for example, proportional control in which aluminum sulfate is injected in proportion to the amount of raw water to be treated (injection amount is controlled at a predetermined injection rate), or the amount of raw water to be treated is treated. However, the latter is preferable because the equipment cost is low and the latter is preferable.

In the present invention, treated water (filtrated water) is obtained by allowing the treated water supplied to the primary side of the separation membrane filter to pass through the separation membrane filter to the secondary side. Specifically, a submerged membrane filter is used in which the separation membrane filter is immersed in a treatment tank on the primary side of the separation membrane filter, and the treatment water outlet on the secondary side of the separation membrane filter is subjected to filtration treatment under reduced pressure. Based on separation membrane immersion type filtration), membrane separation is performed when water to be treated passes from the outside (primary side) to the inside (secondary side) of the membrane wall.
The pore size (membrane pore size) of the separation membrane filter is not particularly limited, but the particle size of the oxide fine particles produced by oxidation of the oxidizable component and the aggregate containing the oxide fine particles or other trace components in water. In consideration of the size of the aggregate, it is desirable that it is 0.0001 μm or more and 1.0 μm or less, preferably 0.005 μm or more and 0.5 μm or less. When the membrane pore diameter is within the above range, the balance of water permeability, treatment efficiency, and aggregate permeation prevention tends to be excellent.

The material of the separation membrane filter may be an organic material or an inorganic material, and is not particularly limited.
Examples of separation membrane filters using organic materials include, for example, hollow fiber membranes, flat membranes or tubular membranes made of organic materials such as polysulfone, polyethylene, polypropylene, polyacrylonitrile, polyvinyl chloride, PTFE, or PVDF Is used.
Moreover, as an example of the separation membrane filter using an inorganic material, for example, a tubular membrane or a monolith membrane made of an inorganic material such as ceramic can be used. As the shape of the submerged membrane module including a single or a plurality of separation membrane filters, a shape in which all of the openings of the separation membrane filter are directly connected to the water collecting pipe is used.

  The membrane filtration differential pressure necessary for the filtration may be obtained by any method, for example, obtained by natural flow using the water head pressure resulting from the water level difference, by suction by a pump such as a vacuum pump, or these Combined use is mentioned. In the case of suction, for example, the other end of the water collecting pipe connected to the opening of the separation membrane filter serves as a treated water outlet. It can be performed.

  Next, the water treatment apparatus used in the present invention will be described with reference to FIG. The apparatus shown in FIG. 1 is a typical example, and the present invention is not limited to this. Accordingly, among the components of the apparatus shown in FIG. 1, components that are not essential parts of the present invention can be replaced or omitted.

  FIG. 1 is a schematic view showing an embodiment of a water treatment apparatus used in the water treatment method of the present invention. As shown in FIG. 1, the water treatment apparatus of the present embodiment diffuses a bubbling gas sent from a treatment tank 1 storing raw water to be treated, a submerged membrane module 2 disposed in the treatment tank 1, and a blower 3. The trachea 4, the raw water to be treated to be introduced into the treatment tank 1, the oxidant introduction means for introducing the oxidant into the treatment tank 1, the aluminum sulfate introduction means for introducing aluminum sulfate into the treatment tank 1, and the immersion membrane It is mainly composed of a treated water pump 10 as a suction means for sucking treated water from the module 2. The oxidant introduction means mainly includes an oxidant tank (not shown), an oxidant introduction pipe 7 connecting the oxidant tank and the processing tank 1, and a metering pump. The aluminum sulfate introduction means is mainly composed of an aluminum sulfate tank (not shown), an aluminum sulfate introduction pipe 8 connecting the aluminum sulfate tank and the treatment tank 1, and a metering pump.

In the present embodiment, raw water containing inorganic harmful components such as arsenic, iron, manganese, and silica and having an iron component concentration of 0.5 mg / L or more is used as the raw water to be treated. An example in which an aqueous solution of sodium hypochlorite is used, air is used as the bubbling gas, and the raw water to be treated is continuously treated will be described.
The raw water to be treated containing iron, manganese, silica and inorganic harmful components is introduced into the treatment tank 1 by a metering pump (not shown) through the raw water introduction pipe 6 to be treated as means for introducing the raw water to be treated.

  In the present embodiment, the processing tank 1 also serves as a raw water storage tank (raw water tank). Thus, it becomes possible to reduce the area concerning the installation of a raw | natural water tank, expense, etc., when the processing tank 1 serves as a raw | natural water tank. Here, the raw water tank refers to a water tank (tank) for temporarily storing raw water before treatment, for example, when processing groundwater or when processing surface water at a water purification plant, A so-called raw water tank for storing raw water (for example, groundwater or surface water) before treatment.

  In the treatment tank 1, an immersion membrane module 2 composed of a plurality of separation membrane filters is installed. A diffuser tube 4 is arranged below the submerged membrane module 2, and air sent continuously or intermittently from the blower 3 is released as bubbles 5 from the diffuser tube 4 and rises through the separation membrane filter. To do. At this time, a gas-liquid mixed upward flow is generated by the bubbles 5 and the submerged membrane module 2 is swung, so that solids (precipitates and aggregates) 13 floating in the raw water to be treated are retained between the separation membrane filters. Further, it is possible to suppress the solid matter 13 from adhering to the surface of the separation membrane filter and to remove the attached solid matter 13, so that the membrane separation efficiency can be improved.

Next, sodium hypochlorite and aluminum sulfate are introduced into the treatment tank 1 by a metering pump through an oxidant introduction pipe 7 and an aluminum sulfate introduction pipe 8, respectively. In the processing tank 1, as described above, a gas-liquid mixed upward flow is generated by the air supplied from the diffuser pipe 4, and the inside of the processing tank 1 is stirred by this upward flow, so that it is introduced into the processing tank 1. Further, sodium hypochlorite and aluminum sulfate can be distributed throughout the treatment tank 1. For this reason, the oxidation reaction of iron and manganese is performed substantially uniformly in the treatment tank 1.
Moreover, since it becomes possible to disperse | distribute the oxide of iron and manganese which can act as a catalyst and / or precipitation promoter, etc. which arises by this oxidation reaction in the processing tank 1 substantially uniformly, processing Various reactions such as oxidation, precipitation, and / or aggregation occurring in the tank 1 can be performed substantially uniformly. Therefore, it is considered possible to further promote the oxidation reaction or further promote the aggregation (precipitation) of trace components such as silica.

The amount of sodium hypochlorite introduced is adjusted so that the residual chlorine concentration in the treatment tank is 0.05 mg / L or more and 5.0 mg / L or less, preferably 0.1 mg / L or more and 1.0 mg / L or less. Is done. Specifically, a residual chlorine sensor 15 is installed in the processing tank 1 and the residual chlorine concentration in the processing tank 1 is measured. The measured value of the residual chlorine concentration is sent to a control unit (not shown) and compared with a preset range set in the control unit.
When the control unit determines that the measured value of the residual chlorine concentration is lower than the lower limit value of the residual chlorine concentration setting range, the amount of sodium hypochlorite introduced is increased so as to be greater than the amount currently supplied. An instruction is given to a metering pump constituting the oxidant introduction means, and an instruction is sent to fix the amount of sodium hypochlorite introduced as it is when the measured value of residual chlorine concentration falls within the set range.
If the control unit determines that the measured value of residual chlorine concentration is higher than the upper limit of the residual chlorine concentration setting range, it instructs the metering pump to reduce the amount currently supplied, and the residual chlorine concentration When the measured value falls within the set range, an instruction is sent to fix the amount of sodium hypochlorite introduced as it is. These controls are performed continuously.

The aluminum sulfate, to measure the concentration of the separation target substances contained in the processed raw water, to a concentration 10 to 70 mg / L to be separated component, the value obtained by converting the aluminum sulphate Al ₂ O ₃ (hereinafter, Al ₂ O ₃ as converted value) 5 to 100 mg / L, preferably such that 10 to 50 mg / L, is introduced into the treatment vessel 1.

In addition, you may provide the metal component addition means (metal component addition apparatus) in the water treatment apparatus of this embodiment as needed. The metal component addition means is mainly composed of a metal component tank (not shown), a metal component introduction pipe 9 connecting the metal component and the processing tank 1, and a metering pump. As oxidizable metal component contained in the raw water, if the amount of iron is less than 0.5 mg / L, as the amount of iron is 0.5 mg / L or more, relatively oxidation of iron ions, etc. The metal component that is easily treated is added to the raw water to be treated in the treatment tank 1 by the metering pump through the metal component introduction pipe 9.

  An inclined plate 12 is disposed below the diffuser tube 4. At least a part of the solid material 13 generated in the processing tank 1 by the introduction of the oxidizing agent and aluminum sulfate is accumulated in the lower part of the processing tank 1 through the inclined plate 12. The inclined plate 12 serves to prevent the solid matter 13 from sinking to the lower portion of the processing tank 1 and to prevent it from rising again. The accumulated solid matter 13 is appropriately discharged to the outside by opening and closing the valve 14 disposed at the lower part of the processing tank 1. This makes it possible to prevent membrane clogging caused by excessive solids floating in the raw water to be treated.

  The raw water to be treated that has been treated with the oxidizing agent and aluminum sulfate in the treatment tank 1 is sucked by the treated water pump 10 through the separation membrane filter, so that solids are filtered out and clear treated water is taken out, It is sent to a water storage tank (not shown) through the treated water pipe 11.

  In the present embodiment, the treated water obtained is within the range of values determined by the water quality standard based on the Water Supply Law, that is, the iron concentration is 0.3 mg / L or less, the manganese concentration is 0.05 mg / L or less, The concentration of arsenic is aimed at 0.01 mg / L or less, but it is more preferable that each concentration is about half or less of each concentration.

  In the embodiment described above, the solid matter 13 discharged from the lower part of the processing tank 1 is discharged to the outside. However, at least a part of the solid matter 13 is processed via a return line (pipe) (not shown). You may return it within. Moreover, although the said embodiment demonstrated the example which carries out the continuous process of to-be-processed raw water, it does not prevent making it a batch process. Moreover, in the said embodiment, although the processing tank 1 demonstrated the example which serves as a raw | natural water tank, you may provide a raw | natural water tank separately before the processing tank 1. FIG.

Groundwater was flowed into the raw water tank as raw water, and sodium hypochlorite as an oxidant was injected in a controlled manner so that the residual chlorine concentration in the raw water tank was 0.2 mg / L. Separately, aluminum sulfate was added such that the concentration in the raw water tank was 20 mg / L (Al ₂ O ₃ equivalent value). An immersion UF hollow fiber membrane filter module made of PVDF with a fraction of 0.01 μm is placed in the raw water tank, and the suction pump pumps out for 10 minutes under a differential pressure of 30 KPa with an OUT-IN method at intervals of 10 minutes. The membrane was continuously filtered at a flow rate of about 1 m ³ / m ² / day. HRT was 30 minutes.
A diffuser tube was placed below the submerged membrane module, and air bubbling was performed at ²⁰ Nm ³ / m ² / hour per bottom area of the filter module, both for assisting oxidation and preventing membrane fouling. There was an inclined plate below the air diffuser, and oxidation, precipitation, and aggregates were sequentially deposited on the bottom of the cone-shaped raw water tank.

  As a comparative example, a system in which aluminum sulfate was not added (Comparative Example 1) and a system in which PAC (polyaluminum chloride) was added instead of aluminum sulfate (Comparative Example 2) were used and the same conditions as in Example 1 were tried.

  The results of Example 1, Comparative Example 1, and Comparative Example 2 are shown in Table 1.

  As shown in Table 1, in any of Example 1, Comparative Example 1 and Comparative Example 2, the iron and manganese components were removed at a high removal rate of nearly 99% in any case. Therefore, it is considered that iron and manganese are removed at a high removal rate by treating raw water with an oxidizing agent and performing membrane separation. In contrast, when the raw water was treated with an oxidizing agent and aluminum sulfate, the removal rate of 90% or more was achieved for silica and arsenic components (Example 1), but no aluminum sulfate was added. In the system (Comparative Example 1) and the system (Comparative Example 2) to which the same aluminum-based flocculant PAC was added, silica and arsenic components were hardly removed.

The groundwater with a low content of iron and manganese components flows into the raw water tank as raw water, and an aqueous ferric chloride solution is injected into the raw water tank as an iron component so that the iron content becomes 0.6 mg / L. It was adjusted. Residual chlorine concentration in the raw water tank was controlled to 0.2 mg / L as an oxidizing agent, and sodium hypochlorite was injected.
Separately, aluminum sulfate was added so that the concentration in the raw water tank would be 20 mg / L (Al ₂ O ₃ equivalent value). An immersion UF hollow fiber membrane filter module made of PVDF with a fraction of 0.01 μm is placed in the raw water tank, and the suction pump pumps out for 10 minutes under a differential pressure of 30 KPa with an OUT-IN method at intervals of 10 minutes. The membrane was continuously filtered at a flow rate of about 1 m ³ / m ² / day. HRT was 30 minutes.
A diffuser tube was placed below the submerged membrane module, and air bubbling was performed at ²⁰ Nm ³ / m ² / hour per bottom area of the filter module, both for assisting oxidation and preventing membrane filtration fouling. An inclined plate was placed below the air diffuser, and oxidation, precipitation, and aggregates were sequentially deposited on the bottom of the cone-shaped raw water tank.

  As a comparative example, a system in which an aqueous ferric chloride solution was injected into the raw water tank so that the iron content was 0.4 mg / L (Comparative Example 3) and a system in which an aqueous ferric chloride solution was not injected into the raw water tank (comparison) Using Example 4), the experiment was conducted under the same conditions as in Example 2.

  The results of Example 2, Comparative Example 3, and Comparative Example 4 are shown in Table 2.

  As shown in Table 2, in the system in which iron as an oxidizable component is contained in raw water of 0.5 mg / L or more, 90% or more of silica and arsenic components as well as iron by treatment with an oxidizing agent and aluminum sulfate. In contrast to the removal (Example 2), silica and arsenic components were hardly removed in the system (Comparative Examples 3 and 4) in which the oxidizable component iron contained in the raw water was less than 0.5 mg / L. .

  In recent years, it has become necessary to innovate water purification technology to cope with the progress of raw water pollution due to the deterioration of the global environment, to achieve rapid increases in demand for construction of water supply facilities in less developed countries, and to save energy and resources. ing. The present invention can efficiently remove a plurality of trace water components simultaneously with simple equipment and can be suitably applied to the production of drinking water (tap water) in a small-scale facility or the like.

FIG. 1 is a schematic view showing an embodiment of a water treatment apparatus used in the water treatment method of the present invention.

1 treatment tank (raw water tank)
2 Submerged membrane module 3 Blower 4 Aeration pipe 5 Air bubbles 6 Raw water introduction pipe 7 Oxidant introduction pipe 8 Aluminum sulfate introduction pipe 9 Metal component introduction pipe 10 Treated water pump 11 Treated water pipe 12 Inclined plate 13 Solid 14 Valve 15 Residual Chlorine sensor

Claims (8)

A water treatment method for obtaining treated water by performing membrane filtration with a separation membrane filter immersed in a tank storing raw water to be treated containing oxidizable components, silica and inorganic harmful components,
Iron is contained in the raw water to be treated as 0.5 mg / L or more as the oxidizable component, and the inorganic harmful component is arsenic,
After the raw water to be treated is treated with an oxidant and aluminum sulfate, the resulting solid matter is solid-liquid separated by the separation membrane filter in the tank, so that the oxidizable component, silica and inorganic harmful components are collected at once. A water treatment method comprising removing the water. The water treatment method according to claim 1, wherein manganese is contained in the raw water to be treated in an amount of 0.5 mg / L or more as the oxidizable component. Manganese is included as the oxidizable component , the iron concentration in the treated water is 0.3 mg / L or less, the manganese concentration is 0.05 mg / L or less, and the arsenic concentration is 0.01 mg / L or less. The water treatment method according to claim 1 or 2 . 4. The water treatment method according to claim 1 , wherein sodium hypochlorite is used as the oxidizing agent, and the residual chlorine concentration in the tank is 0.1 mg / L or more and 1.0 mg / L or less. . As the oxidizing agent, a combination of sodium hypochlorite and air, air of any of claims 1 to 4, characterized in that to supply the gas diffusing means installed below said separation membrane filter Water treatment method. The water treatment method according to any one of claims 1 to 5 , wherein the raw water to be treated in the tank has an HRT of 5 minutes or more. Sodium hypochlorite and aluminum sulfate were injected into a tank containing raw water to be treated containing arsenic , iron, and silica as inorganic harmful components and having an iron concentration of 0.5 mg / L or more. Then, the generated solid matter is separated by a separation membrane filter immersed in the tank, and a water treatment method for obtaining treated water,
Aeration means provided below the separation membrane filter while controlling the injection amount of sodium hypochlorite so that the residual chlorine concentration in the tank is 0.1 mg / L or more and 1.0 mg / L or less. By diffusing the oxidizing gas, when the oxidizing gas is diffused, the oxidation reaction in the tank is assisted, and at the same time, an upward flow rising along the membrane surface of the separation membrane filter is generated, The membrane surface of the separation membrane filter is washed, and iron oxide generated by the reaction of iron with sodium hypochlorite and / or the oxidizing gas is present almost uniformly in the tank, and the oxidation in the tank is performed. It promotes crystal precipitation and / or agglomeration, and at the time of stopping the oxidizing gas, it promotes that at least a part of the solid matter generated in the tank settles on the bottom of the tank, and the solid matter floating in the tank By adjusting the amount, inorganic Water treatment wherein the component, and iron, that collectively remove the silica. 8. The water treatment method according to claim 7, wherein the raw water to be treated contains 0.5 mg / L or more of manganese.

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