JP2012239947A - Water treatment method and water treatment apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treatment method and a water treatment apparatus reducing the cost of chemicals and attaining the stable operation of solid-liquid separation in the water treatment method of carrying out solid-liquid separation after flocculating raw water by injecting an oxidizing agent and a flocculant into the raw water that contains ferrous ions.SOLUTION: The water treatment method of flocculating raw water by injecting the oxidizing agent and the flocculant into the raw water that contains ferrous ions and then carrying out solid-liquid separation to obtain clarified water includes measuring the ferrous ion concentration of the raw water, computing the injection amount of the oxidizing agent for oxidizing the ferrous ions, and the produced amount of iron hydroxide (III) produced by the reaction between the ferrous ions and the oxidizing agent, and computing the required injection amount of the flocculant by subtracting the produced amount of the iron hydroxide (III) from the appropriate injection amount of the flocculant for flocculating the raw water, to control the injection amount of the oxidizing agent and the required injection amount of the flocculant.

Description

  The present invention relates to a water treatment method and a water treatment apparatus for solid-liquid separation of raw water containing turbidity components, chromaticity components, and ferrous ions.

  In water treatment such as water and sewage and wastewater treatment, it is necessary to remove turbidity components and chromaticity components in raw water, and to treat them until they are below the specified turbidity and chromaticity. In many cases, solid-liquid separation treatment such as filtration and membrane filtration is performed. Usually, after a flocculant is first poured into raw water and thoroughly mixed with a stirrer or the like to form flocs, the coarse flocs are settled and separated in a sedimentation basin. The remaining minute floc is solid-liquid separated by sand filtration or membrane filtration, and finally treated water having a predetermined turbidity and chromaticity is obtained.

  In any method, by adding a flocculating agent such as PAC (polyaluminum chloride) or ferric chloride into raw water and incorporating turbidity components and chromaticity components in the raw water into the coagulation floc, filtration is performed. In addition to improving the quality of filtered water, the rise in filtration differential pressure is suppressed. The flocculant injection rate is determined by measuring the turbidity of the raw water taken with a turbidimeter, and using a turbidity proportional injection control that injects an amount of flocculant proportional to the turbidity, or a jar test using a container, beaker, etc. From the results of the above, it is common to artificially control (Patent Document 1, Non-Patent Document 1).

  On the other hand, when ferrous ions are contained in the raw water, the ferrous ions are oxidized to ferric ions by an oxidizing agent, and the pH is adjusted by injecting a neutralizing agent, whereby iron hydroxide (III ) A method for generating and agglomerating main particles has been proposed (Patent Document 2). Thereby, ferrous ions can also be removed by the solid-liquid separation means at the subsequent stage.

  In solid-liquid separation means, especially membrane filtration, it is important to control the amount of flocculant injected appropriately. If the amount of flocculant injected is insufficient, turbidity components and chromaticity components can be incorporated into the flocs. Is not performed sufficiently, the membrane filtration water quality decreases and the filtration differential pressure increases. On the other hand, if the injection amount of the flocculant is too large, excessive flocs are formed and the membrane is rapidly blocked, and the membrane differential pressure rises in a short period of time, resulting in inability to process. Moreover, since the water quality of river water and lake water fluctuates depending on the season and weather, it is an important management item to control the injection amount of the flocculant according to the water quality change.

  However, if the turbidity proportional injection control or chromaticity proportional injection control of the flocculant alone is directly applied to the pretreatment in the membrane filtration method while oxidizing the ferrous ion by injecting the oxidizing agent, the turbidity and color of the raw water It was found that there was a problem when the degree was low and ferrous ions were elevated. In other words, when the turbidity and chromaticity of the raw water are low, the injection amount of the flocculant is small, but a large amount of iron hydroxide (III) is generated by the injection of the oxidant, and as a result, the aggregation is derived from iron (III) hydroxide. It has been found that flocs can be generated excessively, resulting in membrane clogging. When the oxidant injection amount is reduced in order to prevent a large amount of iron hydroxide (III) from being generated by the oxidant injection, ferrous ions pass through the membrane and the quality of the treated water deteriorates. was there.

  Thus, the flocculant and ferrous ions necessary to agglomerate the turbidity component and chromaticity component of the raw water are oxidized against the raw water whose turbidity, chromaticity, and ferrous ion concentration frequently change. It was very difficult to determine the amount of oxidant injection required to do this.

JP-A-5-146608 JP 2005-296866 A

“Water Supply Facility Design Guidelines 2000”, Japan Waterworks Association, p175-p177

  The present invention relates to a water treatment method for obtaining clear water by solid-liquid separation after injecting and agglomerating an oxidizing agent and a flocculant to raw water in which turbidity components, chromaticity components and ferrous ions vary. Optimize the amount of oxidant injected to oxidize ferrous ions to iron (III) hydroxide and the amount of flocculant injected to flocculate turbidity and chromaticity components of raw water, It is an object of the present invention to provide a water treatment method and a water treatment apparatus capable of stable operation of solid-liquid separation that optimizes the amount of reducing agent to be injected in order to prevent the reverse osmosis membrane in the latter stage from being deteriorated by the oxidizing agent. To do.

  In order to solve the above problems, a water treatment method and a water treatment apparatus of the present invention have the following characteristics.

  (1) In a water treatment method in which an oxidant and a flocculant are injected into raw water containing ferrous ions and agglomerated to obtain a clarified water by solid-liquid separation, the ferrous ion concentration of the raw water is measured, Calculate the amount of oxidant injected to oxidize 1 iron ion and the amount of iron (III) hydroxide produced by the reaction between ferrous ions and oxidant, and the appropriate amount of coagulant injected to agglomerate raw water A water treatment method characterized by controlling the oxidant injection amount and the necessary flocculant injection amount by calculating the required flocculant injection amount by subtracting the iron (III) hydroxide production amount from

  (2) In a water treatment method in which an oxidant and an aggregating agent are injected into raw water containing ferrous ions and agglomerated to aggregate, then solid-liquid separation is performed to measure the ferrous ion concentration of the clarified water. Calculate the amount of oxidant injected to oxidize ferrous ions and the amount of iron (III) hydroxide produced by the reaction between ferrous ions and oxidants, and inject appropriate coagulant for agglomerating raw water A water treatment method characterized by controlling the oxidant injection amount and the necessary coagulant injection amount by calculating the required coagulant injection amount by subtracting the iron (III) hydroxide production amount from the amount.

  (3) The water treatment method according to (1) or (2), wherein the solid-liquid separation means is one of sand filtration, microfiltration membrane, and ultrafiltration membrane.

  (4) The water treatment method according to any one of (1) to (3), wherein the turbidity or chromaticity of the raw water is measured, and the proper amount of the flocculant injected is proportionally calculated by the turbidity or chromaticity of the raw water.

  (5) The water treatment method according to any one of (1) to (4), wherein the flocculant includes an iron-based flocculant or an aluminum-based flocculant.

  (6) The water treatment method according to any one of (1) to (5), wherein the oxidizing agent includes a chlorine-based oxidizing agent.

  (7) The water treatment method according to any one of (1) to (6), wherein the clear water is treated with a reverse osmosis membrane.

  (8) The water treatment method according to (7), wherein a reducing agent is injected into the clear water before treatment with the reverse osmosis membrane.

  (9) Solid-liquid separation means for separating raw water containing ferrous ions to obtain clarified water, means for measuring the ferrous ion concentration of raw water, means for supplying an oxidizing agent to the raw water, and raw water A means for supplying a flocculant to the gas, and a means for calculating an oxidant injection amount for oxidizing ferrous ions and an iron (III) hydroxide production amount produced by a reaction between the ferrous ions and the oxidant; Means for calculating an appropriate flocculant injection amount; means for calculating an injection amount of the necessary flocculant by subtracting the iron (III) hydroxide generation amount from the appropriate flocculant injection amount; and raw water, flocculant, and oxidizing agent A water treatment apparatus comprising means for stirring the water and means for supplying raw water to the primary side of the solid-liquid separation means.

  (10) Solid-liquid separation means for obtaining clear water by solid-liquid separation of raw water containing ferrous ions, means for measuring the ferrous ion concentration of clear water, means for supplying an oxidizing agent to the raw water, Means for supplying flocculant to raw water, means for calculating oxidant injection amount for oxidizing ferrous ions and iron (III) hydroxide produced by reaction of ferrous ions and oxidant Means for calculating an appropriate flocculant injection amount, means for calculating an injection amount of the necessary flocculant by subtracting the iron (III) hydroxide production amount from the appropriate flocculant injection amount, raw water, flocculant, and oxidation A water treatment apparatus comprising means for stirring the agent and means for supplying raw water to the primary side of the solid-liquid separation means.

  (11) The water treatment apparatus according to (9) or (10), wherein the solid-liquid separation means is any one of sand filtration, microfiltration membrane, and ultrafiltration membrane.

  (12) It is provided with means for measuring the turbidity or chromaticity of the raw water, and the means for calculating the appropriate flocculant injection amount is a proportional calculation of the turbidity or chromaticity of the raw water, (9) to (11) The water treatment apparatus in any one.

  (13) The water treatment apparatus according to any one of (9) to (12), comprising a reverse osmosis membrane for treating the clarified water with a reverse osmosis membrane.

  (14) The water treatment apparatus according to (13), comprising means for injecting a reducing agent before treating the clarified water with a reverse osmosis membrane.

  According to the water treatment method of the present invention, in the water treatment method for obtaining clear water by injecting an oxidant and a flocculant into raw water containing ferrous ions and then aggregating and solid-liquid separation, The amount of oxidant to be injected to oxidize to iron (III) hydroxide can be minimized, and ferrous ions can be oxidized to iron (III) hydroxide, so that the turbidity and chromaticity of raw water The amount of flocculant injected to flocculate the components is minimal. Furthermore, since the amount of reducing agent to be injected to prevent the downstream reverse osmosis membrane from being deteriorated by the oxidizing agent can be minimized, the chemical cost can be reduced and stable operation of solid-liquid separation becomes possible.

It is an apparatus schematic flowchart which shows an example of the water treatment apparatus to which this invention is applied. It is an apparatus schematic flowchart which shows another example of the water treatment apparatus to which this invention is applied.

  Hereinafter, the present invention will be described in more detail based on embodiments shown in the drawings. In addition, this invention is not limited to the following embodiments.

  As shown in FIG. 1, for example, the water treatment apparatus of the present invention includes an oxidant storage tank 1 that stores an oxidant, an oxidant supply pump 2 that injects an oxidant into raw water, and a flocculant that stores a flocculant. A storage tank 3, a flocculant supply pump 4 for injecting a flocculant into raw water, a ferrous ion measuring device 5 for measuring ferrous ion concentration of raw water, and turbidity for measuring turbidity / chromaticity of raw water Oxidation that calculates the amount of iron (III) hydroxide produced by the reaction between the luminometer / chromatometer 6 and the oxidant injection amount necessary for oxidizing ferrous ions and the reaction between ferrous ions and oxidants The required amount of coagulant is calculated by subtracting the iron (III) hydroxide generation amount from the appropriate coagulant injection amount proportional to the raw water turbidity or raw water color and the theoretical coagulant injection amount. A coagulant calculator 8; a stirrer 9 for mixing and stirring the raw water, the oxidizing agent, and the coagulant; A flocculated water supply pump 11 for injecting the flocculated water in the reaction tank 10 into the microfiltration membrane / ultrafiltration membrane 13, a flocculated water supply valve 12 that is opened when the flocculated water is supplied, and a microfiltration membrane for filtering the flocculated water / An ultrafiltration membrane 13, an air vent valve 14 that is opened when performing reverse pressure washing or air washing, a filtrate water valve 15 that is opened during membrane filtration, and a filtrate storage tank 16 that stores membrane filtrate. , Backwash pump 17 that operates when backwashing microfiltration membrane / ultrafiltration membrane 13 with membrane filtrate, backwash valve 18 that opens when backwashing, microfiltration membrane / ultrafiltration membrane A blower 19 as an air supply source of air cleaning 13, an empty flush valve 20 that is opened when air is supplied to the lower part of the microfiltration membrane / ultrafiltration membrane 13 and air cleaning, and a microfiltration membrane / ultrafiltration A drain valve 21 that opens when draining water on the primary side of the filtration membrane 13, a reverse osmosis membrane 22, A high pressure pump 23 for supplying filtrate to the reverse osmosis membrane 22, a reverse osmosis membrane permeated water storage tank 24 for storing reverse osmosis membrane permeated water, and a reverse osmosis membrane concentrated water storage tank 25 for storing reverse osmosis membrane concentrated water; A reducing agent supply pump 26 for injecting the reducing agent into the membrane filtrate and a reducing agent storage tank 27 for storing the reducing agent are provided.

In the above-described water treatment apparatus, the ferrous ion concentration (α) [mg-Fe / L] of raw water is measured by the ferrous ion measuring device 5, and the turbidity or chromaticity (β) [degree] of the raw water is measured. Is measured with a turbidimeter / colorimeter 6. The measured value of ferrous ions is input to the oxidant calculator 7, and the oxidant calculator 7 converts the ferrous ion concentration (α) [mg-Fe / L] and the raw water flow rate (γ) [L / min]. ], The oxidant injection amount (A) [mg-Cl ₂ / min] necessary for oxidizing ferrous ions in the raw water per unit time is calculated, and the discharge flow rate of the oxidant supply pump 2 is calculated. And the iron hydroxide (III) concentration (B) [mg-Fe / L] generated by the reaction between ferrous ions and the oxidizing agent is calculated and input to the flocculant calculator 8. The turbidity or chromaticity (β) [degree] of the raw water is also input to the coagulant calculator 8, and the coagulant injection concentration (C) [mg−Fe / mg] appropriate for aggregating the turbidity or chromaticity in the raw water. L], and then the iron (III) hydroxide concentration (B) [mg] produced by the reaction between ferrous ions and the oxidizing agent from the appropriate flocculant injection concentration (C) [mg-Fe / L]. Based on the required flocculant injection concentration (D) [mg-Fe / L] and the raw water flow rate (γ) [L / min] calculated by subtracting -Fe / L], the turbidity component in raw water per unit time or The flocculant injection amount (E) [mg-Fe / min] necessary for oxidizing the chromaticity component is calculated, and the discharge flow rate of the flocculant supply pump 4 is controlled. The ferrous ion measuring device 5 generally uses a colorimetric analysis method using a color former such as dipyridyl or o-phenanthroline. Considering sensitivity, specificity, solubility, etc., bathophenanthroline, 2-nitroso-5- (N-propyl-N-sulfopropylamino) -phenol (nitroso PSAP), 3- (2-pyridyl) -5,6 -Coloring agents such as bis [2- (5-furylsulfonic acid)] 1,2,4-triazine disodium salt, tripyridyltriazine, and ferrozine are often used, and regular manual measurement or automatic online measurement may be used. Absent.

  The turbidimeter / colorimeter 6 generally uses a transmitted light absorbance method. In the transmitted light absorbance method, when light of a certain intensity is incident on a water layer containing turbidity components or chromaticity components, the light is reflected or scattered by turbidity component particles or chromaticity component particles. Therefore, the ratio of the intensity of the incident light to the intensity of the transmitted light is taken, and the principle (Lambert-Beer's law) in which the logarithm (absorbance) is proportional to the water layer thickness and turbidity or chromaticity is used. Thus, the turbidity or chromaticity is measured by measuring the absorbance. In order to avoid interference due to chromaticity, the turbidity measurement wavelength often measures absorbance near 660 nm, and the chromaticity measurement wavelength often measures absorbance near 390 nm. As the turbidimeter, in addition to the transmitted light absorbance method described above, a scattered light measurement method that measures the intensity of light generated by reflection or scattering of incident light may be used.

  The oxidant stored in the oxidant storage tank 1 may be sodium hypochlorite, chlorine dioxide, potassium permanganate, ozone, or the like. For example, when the oxidizing agent is sodium hypochlorite, the reaction formula with ferrous ions is as follows.

2Fe ²⁺ + 4OH ⁻ + NaOCl + H ₂ O → 2Fe (OH) ₃ + NaCl
Theoretically, 0.63 mg of chlorine Cl ₂ is required to oxidize 1 mg of Fe ²⁺ (A) = 0.63 × (α) × (γ)
(B) = (α)
In practice, however, the oxidizing agent can be consumed to oxidize substances other than ferrous ions, so it is preferable to make the coefficient appropriately larger than 0.63 depending on the raw aqueous state.

Further, as a method for calculating the oxidizing agent injection flow rate (A) [mg-Cl ₂ / min] required for oxidizing ferrous ions in the raw water, ferrous iron as shown in FIG. The ion measuring device 5 may be installed on the membrane filtrate side, and the discharge amount of the oxidant supply pump 2 may be feedback controlled based on the measured value of the ferrous ion concentration in the obtained membrane filtrate. As specific control means, (1) means to convert the measured value of ferrous ion concentration to analog value (voltage, current, etc.) or digital value (signal converter etc.) and the converted value is above a certain value Then, means for operating the oxidant supply pump 2 (adjustment switch + electromagnetic relay, etc.), (2) means for converting the measured value of ferrous ion concentration, and further controlling the oxidant supply pump 2 with the converted value Means for converting to a signal (signal converter for current, voltage, pulse, etc.) and means for operating the oxidant supply pump 2 by a control signal; (3) means for converting the measured value of ferrous ion concentration; Based on the calculated value, the appropriate oxidant injection amount is calculated, and based on this, a means for outputting a signal for controlling the oxidant supply pump 2 (PID controller, etc.), a means for operating the oxidant supply pump 2 by the control signal, etc. Be mentioned However, the control means is not limited to those listed here. In the feedback control of the present invention, when the measured value of the ferrous ion concentration in the membrane filtrate exceeds a predetermined upper limit set value, a signal for increasing the oxidant injection amount is transmitted from the oxidant calculator 7. Then, when the measured value of the ferrous ion concentration falls below a predetermined lower limit set value, the oxidant calculator 7 performs control such as transmitting a signal for reducing the injection amount of the oxidant, whereby the oxidant Therefore, stable and efficient treatment can be performed by preventing excessive injection.

The coagulant injection concentration (C) [mg-Fe / L] appropriate for aggregating the turbidity component or chromaticity component in the raw water is proportional to the turbidity or chromaticity (β) [degree] of the raw water. Yes,
(C) = (K) × (β)
It becomes. The coefficient (K) [mg-Fe / (L · degree)] is appropriately set according to the raw aqueous state and the solid-liquid separation means. As a method of calculating the coefficient (K), for example, the raw water in several beakers with different agglomeration conditions is agglomerated by a multiple stirrer called a jar tester to agglomerate the relatively best agglomeration floc. It is obtained by performing a jar test to find the aggregation conditions to be formed. Measure aggregated floc particle size by dynamic light scattering method, laser diffraction scattering method, electrical detector method, etc., measure sedimentation rate of aggregated floc, measure zeta potential of aggregated floc The coagulant injection concentration [mg-Fe / L] for obtaining a numerical value of is obtained, and the coefficient (K) can be calculated by dividing by the turbidity or chromaticity [degree] of the raw water used during the jar test. When the solid-liquid separation means is a microfiltration membrane / ultrafiltration membrane 13, the predetermined value of the zeta potential of the aggregation floc is preferably −10 mV or more and less than 0 mV.

  The calculation formula of the necessary flocculant injection concentration (D) [mg-Fe / L] and the flocculant injection amount (E) [mg-Fe / min] necessary for oxidizing the turbidity or chromaticity in the raw water is as follows. It is as follows.

(D) = (C) − (B) = (K) × (β) − (α)
(E) = (D) × (γ) = (K) × (β) × (γ) − (α) × (γ)
As the coagulant stored in the coagulant storage tank 3, the above calculation formula can be applied as it is as long as it is an iron-based coagulant such as ferric chloride, ferric sulfate, polysilica iron, etc. When using an aluminum-based aggregating agent such as aluminum, 1 mol of Fe and 1 mol of Al have the same aggregating effect,
(C ｀) [mg-Al / L] = 0.48 × (C)
(D ｀) [mg-Al / L] = 0.48 × (D)
(E ｀) [mg-Al / min] = 0.48 × (E)
Can be converted and calculated. When (D) is negative, no flocculant injection is required.

  The raw water whose ferrous ion concentration and turbidity or chromaticity are measured in the raw water flows into the agglomeration reaction tank 10, and the oxidant and the flocculant supply pump discharged from the oxidant supply pump 2 controlled based on the calculation. The flocculant discharged from 4 is mixed and stirred by a stirrer, whereby ferrous ions in the raw water are oxidized and agglomeration is performed. Thereafter, the aggregated water supply valve 12 is opened, the aggregated water supply pump 11 is operated, and the aggregated water stored in the aggregation reaction tank 10 is supplied to the primary side of the microfiltration membrane / ultrafiltration membrane 13 for filtration. By opening the water valve 15, pressure filtration of the microfiltration membrane / ultrafiltration membrane 13 is performed. The filtration time is preferably set as appropriate according to the raw water quality and the membrane permeation flux, but the filtration time may be continued until a predetermined membrane filtration differential pressure is reached.

  The membrane filtrate obtained by filtering the raw water through the microfiltration membrane / ultrafiltration membrane 13 is temporarily stored in the filtrate storage tank 16 and then reduced in order to eliminate residual oxidant in the membrane filtration water. The agent supply pump 26 is operated, and the reducing agent in the reducing agent storage tank 27 is injected. Thereafter, the pressure is increased by the high-pressure pump 23 and supplied to the reverse osmosis membrane 22. The supplied membrane filtrate is separated into reverse osmosis membrane permeated water from which salt and organic matter have been removed and reverse osmosis membrane concentrated water from which salt and organic matter have been concentrated, and then stored in reverse osmosis membrane permeated water, respectively. It is stored in the tank 24 and the reverse osmosis membrane concentrated water storage tank 25.

  As the reducing agent stored in the reducing agent storage tank 27, any of sodium bisulfite, sodium sulfite, sodium thiosulfate, and the like may be used.

  The condensed water supply pump 11 is stopped, the condensed water supply valve 12 and the filtration water valve 15 are closed, the filtration process of the microfiltration membrane / ultrafiltration membrane 13 is stopped, and then the backwash valve 18 and the air vent valve 14 are turned on. Back pressure cleaning is performed by opening and operating the backwash pump 17.

  The time for back pressure washing is not particularly limited, and the flow rate for back pressure washing is not particularly limited. However, it is better to perform back pressure washing at a pressure higher than the filtration pressure to prevent contamination on the membrane surface and membrane pores. Since it is easy to exfoliate a substance, it is preferably 1 or more times the filtration flow rate in the filtration step, and is set appropriately within a range that does not cause damage such as breakage of the membrane module container and cracking of the membrane.

  Further, when a large amount of pollutant adheres to the microfiltration membrane / ultrafiltration membrane 13, the flush valve 20 is opened, the blower 19 is operated, and the lower portion of the microfiltration membrane / ultrafiltration membrane 13 is operated. It is also preferable to perform air cleaning for supplying air to the microfiltration membrane / ultrafiltration membrane 13 simultaneously with the above-described back pressure cleaning. The cleaning effect is improved by the combined use of back pressure cleaning and air cleaning. A larger air flow rate is preferable because the cleaning effect becomes higher, but the air flow rate is appropriately set within a range that does not cause damage such as film abrasion or cracking.

  The back flush valve 18 and the air flush valve 20 are closed, the back flush pump 17 and the blower 19 are stopped, the above reverse pressure washing and air washing are finished, and then the drain valve 21 is opened, whereby the membrane surface In addition, a drainage process is performed in which the fouling substances that are separated from the pores of the membrane and are suspended in the module are discharged out of the system. After the drainage process is completed, the drainage valve 21 is closed, the aggregated water supply valve 12 is opened, the aggregated water supply pump 11 is operated, the water supply process is performed, and the module is filled with the aggregated water. 14 is closed and the filtered water valve 15 is opened to return to the filtration step and repeat the above steps.

  The microfiltration membrane / ultrafiltration membrane 13 in the present invention is attached to a storage container for actual use. Depending on the type of the raw water inflow part, filtered water take-out part and module, the concentrated water discharge part, physical A pressure-type membrane module equipped with a cleaning discharge unit or the like, or a submerged membrane module that is immersed in a membrane immersion tank containing raw water and sucked and filtered with a pump, siphon, or the like may be used. In the case of a pressure-type membrane module, an external pressure type or an internal pressure type may be used, but an external pressure type is preferable from the viewpoint of simplicity of pretreatment.

  Further, the pore size of the separation membrane constituting the module is not particularly limited as long as it is porous, but depending on the desired quality and quantity of treated water, an MF membrane (microfiltration membrane) or a UF membrane (ultrafiltration) is used. Film) or a combination of both. For example, when removing turbid components, Escherichia coli, Cryptosporidium, etc., either the MF membrane or the UF membrane may be used. However, when removing viruses or high molecular organic substances, it is preferable to use the UF membrane. .

  Examples of the shape of the separation membrane include a hollow fiber membrane, a flat membrane, a tubular membrane, and a monolith membrane, and any of them may be used.

  The material of the separation membrane is not particularly limited, but polyethylene, polypropylene, polyacrylonitrile, ethylene-tetrafluoroethylene copolymer, polychlorotrifluoroethylene, polytetrafluoroethylene, polyvinyl fluoride, tetrafluoroethylene-hexafluoropropylene Copolymers, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers and chlorotrifluoroethylene-ethylene copolymers, polyvinylidene fluoride, polysulfone, cellulose acetate, polyvinyl alcohol, and polyether sulfone, ceramics, and other inorganic materials It is preferable to contain at least one selected from the group consisting of polyvinylidene fluoride (PVDF) from the viewpoint of film strength and chemical resistance, and has high hydrophilicity and high resistance. Polyacrylonitrile is more preferable from the viewpoint of strong stain resistance.

  The filtration method may be either a full-volume filtration method or a cross-flow filtration method, but a full-volume filtration module is preferred from the viewpoint of low energy consumption.

  The filtration flux control method may be constant flux filtration or constant pressure filtration, but constant flux filtration is used because a constant amount of treated water is obtained and the overall control is easy. Some are preferred.

  In the present invention, the reverse osmosis membrane used for the reverse osmosis membrane 22 is a semi-pervious separation capable of substantially reverse osmosis separation that does not allow other components to permeate through some components in the liquid mixture to be separated. It is a permeable membrane, and a high molecular weight material such as cellulose acetate polymer, polyamide, polyester, polyimide, vinyl polymer is often used as the material. In addition, the membrane structure has a dense layer on at least one side of the membrane, an asymmetric membrane having fine pores gradually increasing from the dense layer to the inside of the membrane or the other side, and another layer on the dense layer of the asymmetric membrane. There are composite membranes having a very thin separation functional layer formed of a material. The membrane form includes hollow fiber and flat membrane. The present invention can be carried out regardless of the film material, film structure and film form, and any of them is effective, but as typical films, for example, cellulose acetate-based or polyamide-based asymmetric membranes and polyamide-based, There are composite membranes having a urea-based separation functional layer, and it is preferable to use a cellulose acetate-based asymmetric membrane and a polyamide-based composite membrane from the viewpoint of water production, durability, and salt rejection.

  In the present invention, the reverse osmosis membrane used for the reverse osmosis membrane 22 has a performance of a salt rejection rate of 99% or more when a saline solution having a pH of 7 and a concentration of 32,000 mg / L is supplied at 5.5 MPa. It is preferable. When the raw water is seawater, if the salt rejection rate is less than 99%, the amount of chlorine ions in the permeate increases, and it is difficult to use the filtered water as it is as drinking water.

  A reverse osmosis membrane having such performance is incorporated into an element such as spiral, tubular, plate and frame for practical use, and hollow fibers are bundled and incorporated into the element. However, the present invention does not depend on the form of these reverse osmosis membrane elements.

  In the present invention, the reverse osmosis membrane 22 includes not only a module in which the reverse osmosis membrane element is housed in one to several pressure vessels, but also includes a plurality of modules arranged in parallel. . Combination, number, and arrangement can be arbitrarily performed according to the purpose.

Example 1
As shown in FIG. 1, sodium hypochlorite is used as the oxidant in the oxidant storage tank 1, and ferric chloride is used as the flocculating agent in the flocculant storage tank 3. The filtration membrane 13 is a pressure-sensitive membrane module made of polyvinylidene fluoride, a hollow fiber UF membrane with a molecular weight cut off of 150,000 Da, manufactured by Toray Industries, Inc. and having a membrane area of 72 m ^2. The valve 15 was opened, the condensed water supply pump 11 was operated, and the whole well water was filtered at a membrane filtration flux of 2.5 m ³ / m ² / d (filtration flow rate 125 L / min). In addition, the reverse osmosis membrane 22 to operate the high-pressure pump 23 with four reverse osmosis membrane elements manufactured by Toray Industries (Inc.) (TM820S-400), film membrane filtration water in the filtered water reservoir 16 filtration flow rate 60 m ³ / D, cross flow filtration was performed at a flow rate of concentrated water of 120 m ³ / d (recovery rate 33%). Sodium thiosulfate was used as the reducing agent in the reducing agent storage tank 27, and 1 mg / L was injected into the membrane filtrate. The ferrous ion measuring instrument 5 is measured manually using a digital pack test multi from Kyoritsu Riken Co., Ltd. The chromaticity meter 6 is CZ402G manufactured by Yokogawa Electric Co., Ltd. did.

  After 30 minutes of filtration through the microfiltration membrane / ultrafiltration membrane 13, the condensed water supply valve 12 and the filtered water valve 15 are closed and the condensed water supply pump 11 is stopped, and at the same time, the air vent valve 14, the backwash valve 18, and the empty The flush valve 20 is opened, the backwash pump 17 and the blower 19 are operated, and backwashing with a flow rate of 3.0 m / d and air washing at 100 L / min for supplying air from below the membrane module are simultaneously performed for 1 min. did. Thereafter, the backwash valve 18 and the air wash valve 20 are closed, the backwash pump 17 and the blower 19 are stopped, and after the above-described back pressure washing and air washing are finished, the drain valve 21 is opened, and the draining process is performed. 1 min. After the drainage process is completed, the drainage valve 21 is closed, the aggregated water supply valve 12 is opened, the aggregated water supply pump 11 is operated, the water supply process is performed, and the module is filled with the aggregated water. 14 was closed and the filtered water valve 15 was opened to return to the filtration step, and the above steps were repeated.

  As a result of measurement with a ferrous ion measuring device 5 and a chromaticity meter 6 on March 1, 2011, the ferrous ion concentration (α) of raw water = 6 [mg−Fe / L], the chromaticity of raw water (β ) = 9 [degrees].

  The ferrous ion concentration (α) = 6 [mg-Fe / L] and the raw water flow rate (γ) = 125 [L / min] are input to the oxidant calculator 7 and then the oxidant injection amount (A). The iron hydroxide (III) concentration (B) produced by the reaction between ferrous ions and the oxidizing agent was calculated, and the discharge amount of the oxidizing agent supply pump 2 was adjusted.

(A) = 0.63 × 6 × 125 = 472.5 [mg-Cl ₂ / min]
(B) = 6 [mg-Fe / L]
Next, the coefficient (K) = 0.6 [mg−Fe / (L · degree)], the chromaticity (β) = 9 [degree] of raw water, and produced by the reaction between ferrous ions and an oxidizing agent. The iron hydroxide (III) concentration (B) = 6 [mg-Fe / L] is input to the flocculant calculator 8 and the appropriate flocculant injection concentration (C) for aggregating the turbidity or chromaticity in the raw water. ) And the necessary flocculant injection concentration (D) [mg-Fe / L].

(C) = 0.6 × 9 = 5.4 [mg-Fe / L]
(D) = 5.4-6 = −0.6 [mg-Fe / L]
Since (D) was negative, the flocculant supply pump 4 did not operate.

As a result of operation for one month from March 1 in the above manner, as shown in Table 1, the average injection amount of the oxidizing agent was 323 [mg-Cl ₂ / min], and the average injection amount of the flocculant was 144 [mg-Fe / min]. The filtration differential pressure of the microfiltration membrane / ultrafiltration membrane 13 was stable at 35 kPa even after one month with respect to 30 kPa immediately after the start of operation. Further, the filtration differential pressure of the reverse osmosis membrane 22 was stable at 5.9 MPa after 2 months with respect to 5.5 MPa immediately after the start of operation, and the desalination rate was 1 month with respect to 99.7% immediately after the start of operation. After that, it was stable at 99.7%.

(Comparative Example 1)
Without using the ferrous ion measuring instrument 5 and the chromaticity meter 6, the oxidant supply pump 2 constantly injects the oxidant at 320 [mg-Cl ₂ / min], and the coagulant supply pump 4 supplies the coagulant to 150 [ [mg-Fe / min] Same as Example 1 except that constant injection was always performed.

  As a result, the filtration differential pressure of the microfiltration membrane / ultrafiltration membrane 13 was increased to 98 kPa after one month with respect to 30 kPa immediately after the start of operation. Stable operation was possible. Further, the filtration differential pressure of the reverse osmosis membrane 22 increased to 8.7 MPa after 1 month with respect to 5.5 MPa immediately after the start of operation, and the desalination rate was 29.7 months after 99.7% immediately after the start of operation. Decreased to 96.1%.

1: Oxidant storage tank 2: Oxidant supply pump 3: Flocculant storage tank 4: Flocculant supply pump 5: Ferrous ion measuring instrument 6: Turbidimeter / colorimeter 7: Oxidant calculator 8: Aggregation Agent calculator 9: Stirrer 10: Coagulation reaction tank 11: Coagulated water supply pump 12: Coagulated water supply valve 13: Microfiltration membrane / ultrafiltration membrane 14: Air vent valve 15: Filtration water valve 16: Filtration water storage tank 17 : Backwash pump 18: Backwash valve 19: Blower 20: Air wash valve 21: Drain valve 22: Reverse osmosis membrane 23: High pressure pump 24: Reverse osmosis membrane permeated water storage tank 25: Reverse osmosis membrane concentrated water storage tank 26: Reducing agent supply pump 27: Reducing agent storage tank

Claims (14)

In a water treatment method in which an oxidant and a flocculant are injected into raw water containing ferrous ions and agglomerated to obtain clarified water by solid-liquid separation, the ferrous ion concentration of raw water is measured and ferrous ions The amount of oxidant injected to oxidize and the amount of iron (III) hydroxide produced by the reaction between ferrous ions and oxidant is calculated, and the water is calculated from the appropriate amount of flocculant injected for agglomerating raw water. A water treatment method, wherein the oxidant injection amount and the necessary flocculating agent injection amount are controlled by calculating a necessary flocculating agent injection amount by subtracting an iron (III) oxide production amount. In a water treatment method in which an oxidant and an aggregating agent are injected into raw water containing ferrous ions and agglomerated to obtain solid water by solid-liquid separation, the ferrous ion concentration of the clear water is measured and ferrous iron is obtained. The oxidant injection amount for oxidizing the ions and the iron (III) hydroxide production amount produced by the reaction between ferrous ions and the oxidant are calculated, and the above-mentioned from the appropriate coagulant injection amount for aggregating the raw water A water treatment method characterized by controlling the oxidant injection amount and the necessary flocculant injection amount by calculating the required flocculant injection amount by subtracting the iron hydroxide (III) production amount. The water treatment method according to claim 1 or 2, wherein the solid-liquid separation means is sand filtration, microfiltration membrane, or ultrafiltration membrane. The water treatment method according to any one of claims 1 to 3, wherein the turbidity or chromaticity of the raw water is measured, and the appropriate amount of the flocculant is proportionally calculated by the turbidity or chromaticity of the raw water. The water treatment method according to claim 1, wherein the flocculant contains an iron-based flocculant or an aluminum-based flocculant. The water treatment method according to claim 1, wherein the oxidizing agent contains a chlorine-based oxidizing agent. The water treatment method according to claim 1, wherein the clarified water is treated with a reverse osmosis membrane. The water treatment method according to claim 7, wherein a reducing agent is injected into the clear water before the treatment with the reverse osmosis membrane. Solid-liquid separation means for obtaining clear water by solid-liquid separation of raw water containing ferrous ions, means for measuring the ferrous ion concentration of raw water, means for supplying an oxidizing agent to raw water, and flocculant for raw water , A means for calculating the amount of oxidant injected for oxidizing ferrous ions and the amount of iron (III) hydroxide produced by the reaction of ferrous ions and oxidant, and proper aggregation Means for calculating the injection amount of the agent, means for calculating the injection amount of the necessary coagulant by subtracting the iron (III) hydroxide production amount from the appropriate injection amount of the coagulant, and stirring the raw water, the coagulant and the oxidizing agent And a means for supplying raw water to the primary side of the solid-liquid separation means. Solid-liquid separation means for obtaining clear water by solid-liquid separation of raw water containing ferrous ions, means for measuring the ferrous ion concentration of the clear water, means for supplying an oxidizing agent to the raw water, and aggregation in the raw water Means for supplying an agent, means for calculating the amount of oxidant injected for oxidizing ferrous ions and the amount of iron (III) hydroxide produced by the reaction of ferrous ions and oxidant, Means for calculating the coagulant injection amount, means for calculating the injection amount of the necessary coagulant by subtracting the iron (III) hydroxide production amount from the appropriate coagulant injection amount, and stirring the raw water, the coagulant and the oxidant And a means for supplying raw water to the primary side of the solid-liquid separation means. The water treatment apparatus according to claim 9 or 10, wherein the solid-liquid separation means is one of sand filtration, microfiltration membrane, and ultrafiltration membrane. The means for measuring turbidity or chromaticity of raw water is provided, and the means for calculating an appropriate flocculant injection amount is a proportional calculation of turbidity or chromaticity of raw water. Water treatment equipment. The water treatment apparatus according to any one of claims 9 to 12, further comprising a reverse osmosis membrane for treating the clarified water with a reverse osmosis membrane. The water treatment apparatus according to claim 13, comprising means for injecting a reducing agent before treating the clarified water with a reverse osmosis membrane.

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