JP2020069448A - Water purification treatment method and water purification treatment device - Google Patents

Abstract

To provide a water purification treatment method and a water purification treatment device capable of improving operation stability in coagulation settling treatment by improving settleability of a coarse floc and obtaining filtration treatment water having good quality even when a thickness of filter layer in filtration treatment after the coagulation settling treatment is made small.SOLUTION: The water purification treatment method for obtaining filtration treatment water includes: adding a flocculant to water to be treated to form a fine floc; adding an organic polymer coagulant to the water to be treated containing the fine floc; growing the fine floc and forming a coarse floc; separating the water to be treated containing the coarse floc by solid liquid separation to a slurry containing the coarse floc and a supernatant; blending the slurry with the water to be treated containing the coarse floc for acceleration of growth of the coarse floc; and filtering the supernatant by using a particulate filter material having an effective diameter capable of capturing the coarse floc.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a water purification treatment method and a water purification treatment device for producing tap water, industrial water, and the like.

  In tap water (purified water) treatment for producing tap water, industrial water, etc., solid-liquid separation technology such as coagulation sedimentation treatment and sand filtration treatment of turbidity components that are insoluble components in raw water and pollutants such as algae Is being processed in. Of these, the coagulation-sedimentation treatment is an effective treatment method for removing not only insoluble components but also contaminants such as soluble chromaticity and soluble organic substances, and is widely used.

  This coagulation-sedimentation method involves the inclusion of pollutants after a step of adding pollutants in raw water by adding an inorganic flocculating agent or a pH adjusting agent, a step of adsorbing pollutants to flocs generated from the inorganic flocculating agent, and the like. This is a treatment method in which flocs are separated by sedimentation from raw water.

  On the other hand, in the sand filtration process, the water to be treated is supplied from above into a tank filled with sand as a filter layer. When the water to be treated passes through the gaps between the sands, some of the flocs flowing out of the sedimentation tank in the coagulation-sedimentation process are adsorbed to the sands or trapped in the gaps between the sands, so that clear filtered water can be obtained. Obtainable.

  In order to carry out the above process at the water purification plant, a mixing tank (mixing pond), a floc forming tank, a sedimentation tank, and a sand filtration layer are continuously installed. This method is an excellent system that can separate and remove various pollutants, but it has a sufficient thickness to obtain a clear filtered water because a large sedimentation tank is required due to the slow sedimentation speed of flocs. There were problems such as the need for a fine and uniform sand layer.

  The settling basin occupies a huge area in the water treatment plant, so if the settling basin can be reduced, it is possible to reduce the land for the whole treatment plant, and secure the amount of treated water even in urban water purification plants where there is not enough land. It becomes possible to do. Further, if the thickness of the sand layer can be reduced and a filter medium having a low specific gravity can be used, the structure of the sand filter layer can be simplified.

  On the other hand, although the turbidity of river water, which is raw water in recent years, has tended to decrease, when coagulating sedimentation treatment of raw water with low turbidity, the flocculation reaction is difficult to proceed and the sedimentation of flocs deteriorates, affecting the quality of treated water. Known to give. Even in high-speed coagulation-sedimentation processing, the technique uses high-quality flocs in the tank to react efficiently with the turbidity derived from raw water to perform efficient coagulation, so the processing becomes unstable when the turbidity of raw water is low. ..

  In Patent Document 1 (Japanese Patent Laid-Open No. 2006-7086), it is extremely important to stably hold the slurry blanket in high-speed coagulation sedimentation, and the blanket is not formed well, and flocs in the slurry leak to the treated water. It is described that the quality of treated water then deteriorates. In such a case, a method of adding an insoluble granular coagulation aid such as sand has been proposed for the purpose of stabilizing the treatment.

  In Patent Document 2 (Japanese Patent No. 4004854), a combined use of an inorganic coagulant and an organic polymer coagulant is proposed in order to improve the cohesive sedimentation property. If the organic polymer coagulant is added excessively, it may promote clogging of sand filtration or membrane filtration. Therefore, in Patent Document 2, the streaming current of the floc after the injection of the organic polymer coagulant is measured, and the measurement is performed. The injection amount of the polymer coagulant is controlled based on the result. In the method of Patent Document 2, the charge state of flocs is measured, and the amount of charge insufficient for neutralization is supplemented with an organic polymer flocculant according to the charge state, so that electrically neutral flocs can be formed. Becomes

  In Patent Document 3 (Japanese Patent No. 3854471), in order to improve floc cohesiveness, a coagulation-sedimentation treatment facility using an organic polymer coagulant together with an inorganic coagulant is provided. In addition, in order to increase the filtration resistance in the sand filtration section due to the addition of polymer, a fiber filter is installed in front of the sand filtration section, and the coagulation-sedimentation-treated water is once fiber-filtered to remove fine flocs and then sand. It has been proposed to suppress the filtration resistance in the sand filtration section by supplying it to the filtration section.

JP, 2006-7086, A Japanese Patent No. 4004854 Japanese Patent No. 3854471

  In the method of Patent Document 1, when the flocculating property of the floc in the high-speed coagulation-sedimentation section is deteriorated due to low turbidity or the like, a substance having a large specific gravity such as sand is added as a precipitation promoting agent and mixed with the floc. This has the advantage of increasing the sedimentation rate and stabilizing the solid-liquid separation. However, the pouring equipment becomes a problem, and the pouring equipment is abraded by the sand, which deteriorates the maintainability. Further, since the sedimentation accelerator is a consumable item, it is difficult to reuse it, and the amount of sludge generated increases, which causes a problem that the treatment cost increases.

  In Patent Document 2, it is necessary to prepare an electrode for measuring the charged state, and in order to always perform stable measurement, it is necessary to keep the electrode in a usable state. Further, Patent Document 2 proposes a method for facilitating the formation of flocs by mixing a slurry containing flocs in the flocculation-precipitation portion with raw water, but the returned flocs react with the inorganic coagulant, and In some cases, the reaction between the turbidity component in water and the inorganic coagulant is hindered, and good flocculating property cannot be obtained.

  In Patent Document 3, it is possible to improve the flocculating property by using an organic polymer coagulant together with the inorganic coagulant, but it is possible to increase the filtration resistance due to the combined use of the organic polymer coagulant. On the other hand, since the fiber filter needs to be additionally installed, the device becomes complicated. Further, in addition to the sand filter, it is necessary to clean the fiber filter, which causes problems in terms of operation management and a decrease in the water recovery rate due to an increase in the amount of cleaning water.

  In view of the above problems, the present invention can improve the settling property of coarse flocs to improve the operational stability in the coagulation-sedimentation treatment, and it is of good quality even if the thickness of the filter layer in the filtration treatment after the coagulation-sedimentation treatment is reduced. Provided are a water purification treatment method and a water purification treatment device capable of obtaining filtered water.

  In order to solve the above problems, the inventors of the present invention have made diligent studies and found that coarse flocs are formed by adding a coagulant and an organic polymer flocculant to the water to be treated, and the coarse flocs are obtained by solid-liquid separation. It was found that returning the obtained slurry to the coarse floc forming step is one of the effective means.

  The water purification method according to the embodiment of the present invention completed on the basis of the above findings is, in one aspect, adding a coagulant to the water to be treated to form fine flocs, and to the water to be treated containing the fine flocs to be organic. A polymer flocculant is added, fine flocs are grown to form coarse flocs, and water to be treated containing coarse flocs is solid-liquid separated into a slurry containing coarse flocs and a supernatant liquid, and the slurry contains coarse flocs. A water purification process that involves mixing with water to be treated to promote the growth of coarse flocs, and filtering the supernatant liquid using a particulate filter medium with an effective diameter that can capture coarse flocs to obtain filtered water. Is the way.

  In one embodiment of the water purification treatment method according to the embodiment of the present invention, the effective diameter of the particulate filter medium is 1.2 to 2.0 mm.

  In another embodiment of the water purification treatment method according to the embodiment of the present invention, the slurry is subjected to solid-liquid separation so as to be 0.2 to 2.0 times the inflow amount of the water to be treated. Mix with water to be treated.

  In still another embodiment of the water purification method according to the embodiment of the present invention, an organic polymer coagulant is added to the water to be treated in an amount of 0.2 to 0.8 mg / L.

  In still another embodiment of the water purification treatment method according to the embodiment of the present invention, filtered treatment water is subjected to sterilization treatment including ultraviolet irradiation.

  In still another embodiment of the water purification treatment method according to the embodiment of the present invention, the turbidity of the filtered treatment water is measured, and when the turbidity exceeds a predetermined value, sterilization treatment is performed.

  In one aspect, a water purification apparatus according to an embodiment of the present invention includes a fine floc forming unit that forms a fine floc by adding a coagulant to the water to be treated, and an organic polymer coagulant for the water to be treated containing the fine flocs. , Coarse floc forming means for forming coarse flocs by growing fine flocs, and water to be treated containing coarse flocs, solid-liquid separation means for performing solid-liquid separation into a slurry containing coarse flocs and a supernatant liquid, Returning means for returning the slurry to the water to be treated containing coarse flocs, and the supernatant liquid is filtered by passing water through a filter layer composed of a particulate filter medium having an effective diameter capable of capturing coarse flocs. It is a water purification apparatus provided with a filtration means for obtaining water.

  In one embodiment, the water purification device according to the embodiment of the present invention has an effective diameter of the particulate filter medium of 1.2 to 2.0 mm and a thickness of the filter layer of 550 mm or less.

  In another embodiment of the water purification apparatus according to the embodiment of the present invention, a coarse flock deposit layer having a maximum thickness of 5 mm is provided on the filter medium.

  ADVANTAGE OF THE INVENTION According to this invention, the settling property of coarse flocs can be improved and the operation stability in coagulation sedimentation processing can be improved, and even if the thickness of the filter layer in the filtration processing after coagulation sedimentation processing is made small, it is good quality filtered water. A water purification method and a water purification apparatus that can obtain

It is the schematic which shows an example of the water purification apparatus which concerns on embodiment of this invention. It is the schematic which shows an example of the water purification apparatus which concerns on the 1st modification of embodiment of this invention. It is the schematic which shows an example of the water purification apparatus which concerns on the 2nd modification of embodiment of this invention. It is the schematic which shows an example of the water purification apparatus which concerns on the 3rd modification of embodiment of this invention. It is the schematic which shows an example of the water purification apparatus which concerns on the modification of the 3rd modification of embodiment of this invention. It is explanatory drawing showing the height of the filter layer with which the filtration apparatus of Example 1 is equipped. It is explanatory drawing showing the height of the filter layer with which the filtration apparatus of the comparative example 1 is equipped. 3 is a graph showing the turbidity of coagulation-sedimentation-treated water (supernatant solution) of Example 1 and Comparative Example 1. 3 is a graph showing pressure changes of sensors 1 and 2 included in the filtration device of Example 1. 7 is a graph showing pressure changes of sensors 1 to 3 included in the filtration device of Comparative Example 1. It is the schematic showing an example of the purified water treatment water apparatus which concerns on the comparative example 3 showing the conventional coagulation sedimentation treatment. 9 is a graph showing pressure changes of sensors 1 and 2 included in the filtering device of Example 3. It is a graph showing the relationship between the addition rate of an organic polymer coagulant and the turbidity of filtered water. It is a graph showing the turbidity of the coagulation sedimentation treated water of the reference example 1 and the comparative example 4.

  An embodiment of the present invention will be described below with reference to the drawings. The embodiments described below exemplify devices and methods for embodying the technical idea of the present invention, and the technical idea of the present invention is that the structure, arrangement, etc. of constituent parts are specified as follows. Not something to do.

<Water to be treated>
Water to be treated (raw water) of the water purification method according to the embodiment of the present invention includes river water, rainwater, water containing fine suspended substances such as factory wastewater. In Japan, river water, lake water, and ground water free from soluble organic substances and metals are used as raw water for water purification plants, and any water is treated as the subject water of the present invention. However, in general, groundwater is less contaminated with suspended solids, so that coagulation-sedimentation treatment is omitted, and sand filtration and sterilization are often performed. Therefore, in the present embodiment, river water and lake water are the main targets of the water to be treated.

<Water purification method>
In the water purification method according to the embodiment of the present invention, (1) a coagulant is added to treated water to form fine flocs, and (2) an organic polymer coagulant is added to treated water containing fine flocs. Then, fine flocs are grown to form coarse flocs, and (3) the water to be treated containing the coarse flocs is subjected to solid-liquid separation into a slurry containing the coarse flocs and a supernatant liquid, and (4) the slurry is treated with the coarse flocs. Mixing with treated water to promote the growth of coarse flocs, and (5) filtering the supernatant with a particulate filter medium having an effective diameter capable of capturing coarse flocs to obtain filtered treated water. ..

(1) Fine floc forming step As a coagulant for forming fine flocs in the water to be treated, an inorganic coagulant (inorganic coagulant) is typically added. Any inorganic coagulant can be used as long as it forms a hydroxide with a pollutant and precipitates. Water treatment plants for water supply often use polyaluminum chloride (hereinafter referred to as PAC), sulphate, and polysilica iron. Among them, PAC is suitable as an inorganic coagulant for water purification plants because of little change in pH during addition, high coagulation efficiency, and little coloring.

  Depending on the use of the water to be treated, commonly used organic coagulants can be used in place of the inorganic coagulant. Condensation polyamines, dicyandiamide / formalin condensates, polyethyleneimine, polyvinylimidazoline, polyvinylpyridine, diallylamine salts. -Sulfur dioxide copolymer, polydimethyldiallylammonium salt, polydimethyldiallylammonium salt-Sulfur dioxide copolymer, polydimethyldiallylammonium salt-acrylamide copolymer, polydimethyldiallylammonium salt-diallylamine hydrochloride derivative copolymer, Examples thereof include allylamine salt polymers.

  Specific examples of the condensed polyamine include a condensate of alkylene dichloride and alkylene polyamine, a condensate of aniline and formalin, a condensate of alkylene diamine and epichlorohydrin, a condensate of ammonia and epichlorohydrin, and the like. Examples of the alkylenediamine that is condensed with epichlorohydrin include dimethylamine, diethylamine, methylpropylamine, methylbutylamine, dibutylamine and the like.

  The above-mentioned inorganic coagulant and organic coagulant may be used alone or in the form of a mixture at the time of use, but such a mixture may be used in the state of an aqueous solution which is previously diluted with water. When it is used as a mixture, it may be necessary to be careful because a precipitate may be deposited depending on the combination. The order of adding the inorganic coagulant and the organic coagulant to the raw water is not particularly limited.

  Since the coagulant addition rate varies depending on the water to be treated, it is desirable to determine an appropriate addition rate in advance by a small-scale treatment test. For example, in the case of PAC, the amount of PAC stock solution added per 1 L of water to be treated is preferably about 20 to 150 mg.

  When only an inorganic coagulant is used as a coagulant, it is necessary to change the addition rate in a small-scale treatment test and find out the conditions for forming fine flocs for sufficiently forming coarse flocs described later. In the present embodiment, since an organic polymer flocculant is used in combination in order to more reliably form coarse flocs in the treatment described later, it may be possible to treat even if the floc growth due to the addition of the inorganic coagulant is insufficient. .. However, the role of the inorganic coagulant is to neutralize the charge state of the pollutants in the water to be treated, to condense them, and to form fine flocs.Therefore, the inorganic coagulant must be in an appropriate state suitable for the water to be treated. It is desirable to determine the coagulant addition rate.

  After adding the inorganic coagulant, it is necessary to sufficiently mix it with the coagulant in order to neutralize the charge of the pollutants in the water to be treated. For this reason, it is preferable to provide a facility capable of stirring for a predetermined time after the addition of the inorganic coagulant. For example, providing the mixing tank 10 as in the water purification apparatus shown in FIG. 1 has an advantage of facilitating the management of the stirring state because the hydraulic retention time of the mixing tank 10 becomes the stirring time.

  The residence time in the mixing tank 10 is generally about 1 to 5 minutes. Further, as the stirring device in the mixing tank 10, a mechanical stirring device such as a flash mixer or a pump stirring device can be applied. Depending on the water purification plant, a plurality of solid-liquid separation tanks 30 may be provided and the water to be treated may be distributed and supplied. In the case of such equipment, it is possible to add an inorganic coagulant before the distribution tank (not shown) and use the distribution tank as a substitute for the mixing tank 10.

  On the other hand, if the water to be treated and the inorganic coagulant can be sufficiently stirred, it is possible to stir them in the pipe without providing the independent mixing tank 10. In this case, after adding the inorganic coagulant, it is necessary to secure a pipe length according to the amount of water so that the residence time is constant. Further, in order to promote stirring, it is also preferable to provide a device such as a line mixer that disturbs the flow in the pipe in the middle of the pipe.

  In the fine floc forming step, fine flocs having a particle size of less than 1 mm are typically formed in the water to be treated. The particle diameter of the floc diameter is comprehensively determined by those skilled in the art as described in the Water Supply Maintenance and Management Guideline of the Japan Water Works Association, and in the present embodiment, it is determined by visually observing the water to be treated. The production amount of fine flocs depends on the concentration of the raw water in the turbid chamber, but cannot be generally stated. For example, when the inorganic coagulant is added according to the present embodiment at a turbidity of 10 degrees, the fine floc concentration is the concentration of suspended solids. It is 12 to 13 mg / L.

(2) Coarse floc formation process The charge of the pollutants in the water to be treated is neutralized by the addition of the coagulant, and the water to be treated after formation of fine flocs is supplied to the floc formation tank 20 shown in FIG. It In the floc formation tank 20, the organic polymer coagulant and the slurry circulated from the solid-liquid separation facility to be described later are supplied to the water to be treated and stirred to grow fine flocs in the water to be treated to form coarse flocs. Form.

  As the organic polymer flocculant, a cationic, anionic or nonionic one can be used depending on the charge state, and may be appropriately selected according to the water to be treated. Anionic or nonionic organic polymer flocculants are particularly suitable when the process is applied in water purification plants.

  As the anionic polymer flocculant, Polyacrylamide partial hydrolyzate, A copolymer of anionic monomers, Examples thereof include copolymers of anionic monomers and nonionic monomers such as acrylamide. Acrylic acid as the anionic monomer, Methacrylic acid, Itaconic acid, Maleic acid, Fumaric acid, Vinyl sulfonic acid, Allyl sulfonic acid, Methallyl sulfonic acid, Styrene sulfonic acid, 2-allylamidoethanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-methallylamide ethanesulfonic acid, 2-methacrylamido-2-methylpropanesulfonic acid, 2-acryloyloxyethanesulfonic acid, 3-acryloyloxypropane sulfonic acid, 4-acryloyloxybutane sulfonic acid, 2-methacryloyloxyethanesulfonic acid, 3-methacryloyloxypropane sulfonic acid, 4-methacryloyloxybutane sulfonic acid, And these alkali metals, Examples thereof include metal salts such as alkaline earth metals or ammonium salts.

  The anionic monomers may be used alone or in combination of two or more. Examples of the nonionic monomer include acrylamide, methacrylamide, methacrylonitrile, vinyl acetate and the like. These nonionic monomers may be used alone or in combination of two or more. Preferred copolymers are acrylamide / acrylic acid salt copolymers and acrylamide / 2-acrylamido-2-methylpropanesulfonic acid copolymers.

  The nonionic polymer flocculant is a polymer or copolymer of the above nonionic monomers, but polyacrylamide can be preferably used.

  The cationic polymer flocculant has a cationic monomer as an essential component, and a copolymer of a cationic monomer or a copolymer of a cationic monomer and the above nonionic monomer can be used. Examples of the cationic monomer include dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, their neutralization salts, and quaternary salts. Further, a cationic polymer flocculant containing an amidine unit in the molecule can also be used.

  If the turbidity of the water to be treated is high, adding a cationic polymer flocculant in the previous stage and adding an anionic or nonionic polymer flocculant in the latter stage will increase the turbidity-eliminating effect The effect of reducing the turbidity can be expected. The organic polymer flocculants may be used alone or in combination of two or more. Generally, the organic polymer flocculant is used as an aqueous solution, and its dissolution concentration is about 0.01 to 0.5% by mass.

  By adding the organic polymer coagulant, in the floc forming tank 20, fine flocs of the pollutants in the water to be treated are mixed with the organic polymer coagulant and the flocs in the circulated slurry to form coarser flocs. .. Since the organic polymer coagulant has a large molecular weight, its cross-linking action entangles fine flocs to coarsen them.

  It is possible to form coarse flocs only with fine flocs and organic polymer flocculants, but in this embodiment, the flocs forming tank is mixed with the slurry obtained by solid-liquid separation to be described later, and coarse flocs in the slurry are mixed. Since the flocs can also contribute to the formation of coarse flocs having a larger particle size, coarse flocs having a larger coarseness and a favorable sedimentation property are formed.

  Further, since the slurry is circulated in the floc formation tank 20 and the floc concentration in the system is increased, the frequency with which the fine flocs come into contact with the existing flocs is also increased, and the effect of increasing the fine floc trapping ability is also expected. it can.

  Also in the floc forming tank 20, it is preferable to stir in order to promote the contact with the fine flocs, the organic polymer coagulant, and the coarse flocs in the slurry. However, unlike the mixing tank 10, it is preferable that the stirring speed be slower than that of the mixing tank 10 in order to suppress the miniaturization of flocs. The residence time in the floc forming tank 20 may be about 20 to 40 minutes, which is the residence time in a general floc forming tank, but it can be shortened if the treatment conditions are confirmed and good flocs are formed. ..

  The amount of the organic polymer coagulant added can be appropriately adjusted according to the properties of the water to be treated, but if the amount of the organic polymer coagulant added is too small, the organic polymer coagulant does not sufficiently contribute to the growth of coarse flocs. In some cases, the treatment may not be stable, and when the amount is too large, the treatment cost may increase due to the cost of the liquid chemicals. In the present embodiment, the organic polymer coagulant is added to the water to be treated in an amount of 0.2 to 0.8 mg / L, preferably 0.2 to 0.5 mg / L to improve the sedimentation property of coarse flocs. be able to.

(3) Solid-Liquid Separation Step The water to be treated flowing out of the floc formation tank is supplied to the solid-liquid separation tank 30. The solid-liquid separation tank 30 may have any structure as long as it is possible to perform solid-liquid separation of flocs and a supernatant liquid from the water to be treated containing coarse flocs by sedimentation separation (coagulation sedimentation treatment) using a difference in specific gravity.

  For example, in the example of FIG. 1, as the solid-liquid separation tank 30, an example in which an upflow sedimentation tank (upflow sedimentation column) that forms an upflow is used is shown. In the upflow sedimentation tank, the inflow water is discharged to the central part of the column. The coarse flocs contained in the inflow water settle down by gravity and accumulate in the lower part, and the supernatant liquid flows out from the upper part by overflow. At this time, if the inflow water is made to flow downward as shown by the arrow in FIG. 1, the coarse flocs have a downward velocity from the beginning, so that the sedimentation of the coarse flocs can be improved.

  Furthermore, if the discharge port of the inflow water is installed at a position where it is discharged into the floc layer accumulated in the column, the inflowing floc is directly mixed with the floc layer in the column, so that the floc layer in the column is mixed. Acts as a slurry blanket and is effective in reducing the turbidity of the supernatant.

(4) Slurry circulation step A return pipe 32 for pulling out the accumulated coarse flocs is provided in the lower part of the upward flow sedimentation tank, and the slurry containing the coarse flocs is circulated to the flocculation tank 20. It should be noted that the purpose of slurry circulation is to more reliably form coarse flocs that are likely to settle in the solid-liquid separation tank 30, so in the present embodiment, it means that a slurry containing coarse flocs is circulated to the floc formation tank 20. Is circulated in the return pipe 32 arranged downstream of the flock formation tank 20 and upstream of the solid-liquid separation tank 30, or in the pipe 12 connecting the mixing tank 10 and the flock formation tank 20. It also includes.

  Here, the slurry is used in an amount of 0.2 to 2.0 times, preferably 0.4 to 0.8 times, and in one embodiment, 0.5 times the amount of inflow water to be treated. It is preferable to mix with water to be treated for solid-liquid separation. As a result, the sedimentation property of the coarse flocs can be improved and the operational stability in the coagulation sedimentation treatment can be maintained for a long time.

  The slurry circulated in the floc forming tank 20 is mixed with water to be treated containing coarse flocs. The coarse flocs grown from the fine flocs in the floc formation tank 20 are further mixed and contacted with the slurry in the floc formation tank 20, so that the growth of the coarse flocs is further promoted and coarse flocs having a better sedimentation property can be obtained.

  Due to this circulation of slurry, in the water to be treated before the solid-liquid separation treatment, when a typical floc diameter is visually measured, the particle diameter is about 2.0 to 5.0 mm, and more typically, the particle diameter is 2.0. Coarse flocs with good sedimentation of ~ 4.0 mm are formed.

(5) Filtration Treatment Step As shown in FIG. 1, the water to be treated flowing out from the solid-liquid separation tank 30 is temporarily stored in the adjustment tank 50 and then supplied to the filtration device 40. A filter layer 41 made of a particulate filter medium is disposed in the filtration device, and the water to be treated is passed through the filter layer 41 to be filtered, and thus is not separated / removed in the solid-liquid separation tank 30. Fine and coarse flocs in water (collectively referred to as "flocs") are separated.

  The thickness of the general filter layer 41 is set to 60 to 70 cm according to the water supply facility design guidelines. The effective diameter of the filter medium is 0.6 to 0.7 mm. In the filter layer 41, the flocs flowing out from the solid-liquid separation tank 30 are captured by the filter layer 41, so that clear filtered water is obtained.

  The flocs captured by the sand filter of a general water purification plant are captured not only on the surface of the filter layer but also in the gaps inside the sand filter layer. Therefore, in the conventional sand filter, it is necessary to secure a sufficient thickness in consideration of the fact that the flocs penetrate into the sand filter layer. Further, if the particle size of the sand filtration layer is large, the gap becomes large, so that the filtration resistance becomes small, but at the same time, it becomes difficult to capture fine flocs, and therefore it cannot be made so large.

Multi-layer filtration has also been devised, in which two or more types of filter sand with different densities and effective diameters are filled. In the example using sand and anthracite, sand (density about 2.6 g / cm ³ ; effective diameter 0.45 to 0.6 mm) and anthracite (density about 1.5 g / cm ³ ; effective diameter 0.9 to 1) 0.4 mm) as a filter layer into the column. The sand layer has a thickness of about 300 to 400 mm, the anthracite has a thickness of 200 to 300 mm, and the total layer thickness is 600 mm.

  Since anthracite has a lower density than sand, the sand layer and the anthracite layer are stacked in this order from the bottom. In filtration, the water to be treated is supplied from above, but since the anthracite layer has a large effective diameter, relatively large flocs are captured and small flocs pass. Since small flocs are captured by the next sand layer, the amount of trapped flocs in the entire filter layer is large and the filtration duration is long.

  On the other hand, according to the water purification method according to the embodiment of the present invention, an organic polymer coagulant is added to the water to be treated to form coarse flocs, and a slurry containing coarse flocs obtained by solid-liquid separation is treated as coarse flocs. By returning to the forming process, the floc coarsening is promoted. As a result, the particle size of the flocs flowing out of the solid-liquid separation tank 30 is also larger than that of the flocs in the conventional method in which only the inorganic coagulant is added, so that the flocs contained in the supernatant liquid are captured by the filter layer. It will be easier.

  In addition, in the embodiment of the present invention, when the trapped state of the flocs in the filter layer 41 and the pressure increase in the tower due to the flocs trapped were also confirmed, unlike the filtration treatment using the conventional sand filtration method, It was found that most of the flocs were captured in the vicinity of the surface of the upper part of the filter layer 41 without the invasion of the flock from the surface of the filter layer 41 toward the lower part.

  According to the present embodiment, a deposition layer of flock having a thickness of 0.5 mm or more and 1.0 mm or more, typically a maximum thickness of about 5 mm is formed in the filtration device 40 in which the treatment is stable. When the accumulated layer of flocs is formed, the fine flocs contained in the supernatant can be captured by cake filtration using the cake layer. Therefore, it is considered that clear filtered water can be obtained even if the thickness of the filter layer is reduced as compared with the conventional sand filtration method. As a result, the structure of the filtering device 40 can be further simplified and downsized.

  For example, while the thickness of the conventional sand filtration layer is 600 mm, the thickness of the filtration layer 41 in the present embodiment can be typically 550 mm or less, and in one embodiment, 400 mm or less, and further 300 mm. Hereafter, it may be 250 mm or less. On the other hand, if the thickness of the filter layer 41 is too small, sufficient filtration performance may not be obtained. Therefore, the thickness of the filter layer 41 can be 150 mm or more, further 200 mm or more.

As the filter medium used as the filter layer 41, a particulate filter medium having an effective diameter capable of capturing coarse flocs, typically 1.2 mm or more, further 1.5 mm or more, further 1.7 mm or more can be used. Is. If the effective diameter of the filter medium used as the filter layer 41 is too large, it may be difficult to form a deposition layer of flocs on the upper surface of the filter layer 41. Therefore, the effective diameter is 2.0 mm or less. It is preferable to use a filter medium, more preferably a filter medium having a diameter of 1.8 mm or less. For example, conventional materials were used by using anthracite (density 1.5 g / cm ³ ; effective diameter 0.9 to 1.4 mm) and filter sand (silica sand) that are currently widely available for water purification treatment. A highly versatile filtering device 40 can be obtained.

  According to the water purification method according to the embodiment of the present invention, an organic polymer coagulant is added to water to be treated to form coarse flocs, and a slurry containing coarse flocs obtained by solid-liquid separation is formed into coarse flocs. By returning to the process, the particle size of flocs can be coarsened and stable treatment can be performed. Therefore, even if a material having a large effective diameter of the filter layer 41, for example, a filter material such as anthracite is used alone, it is of good quality. Filtered water can be obtained.

  Further, by using a material having a density higher than that of silica sand or the like, such as anthracite, as the filter medium, the amount of filtered water (the rising speed of the washing water) when backwashing the filtering device 40 is smaller than that of the conventional one. Even if it is possible to sufficiently flow the filter layer 41, the amount of washing water can be saved, and the effect of increasing the final recovery rate of purified water can be expected.

<Water purification device>
Water purification apparatus according to an embodiment of the present invention, fine floc forming means for forming a fine floc by adding a coagulant to the water to be treated, and an organic polymer flocculant is added to the water to be treated containing the fine flocs. A coarse floc forming means for growing fine flocs to form coarse flocs; a solid-liquid separation means for separating liquid to be treated containing coarse flocs into a slurry containing coarse flocs and a supernatant liquid; and a coarse slurry. Return means for returning to the water to be treated containing flocs, and the supernatant liquid is filtered by passing water through a filter layer composed of a particulate filter medium having an effective diameter capable of capturing coarse flocs to obtain filtered water. And a filtering means.

  Specifically, a water purification apparatus as shown in FIGS. 1 to 5 can be used. The water purification apparatus shown in FIG. 1 includes a mixing tank 10, a flock forming tank 20, a solid-liquid separation tank 30, an adjusting tank 50, and a filtering device 40. The mixing tank 10 is not particularly limited in specific configuration as long as it has a configuration for adding a coagulant to the water to be treated to form fine flocs. The mixing tank 10 is provided with a stirring means 11 for stirring the coagulant and the water to be treated, and the water to be treated and the coagulant are contained and allowed to stay while being stirred for a certain period of time so that the particle diameter is less than 1 mm. Allows flock to form. The water to be treated containing the fine flocs obtained in the mixing tank 10 is supplied to the floc forming tank 20 through the pipe 12.

  The floc formation tank 20 is not particularly limited as long as it has a configuration capable of adding an organic polymer coagulant to water to be treated containing fine flocs to grow fine flocs to form coarse flocs. The flock forming tank 20 is equipped with a stirring means 21 for stirring the organic polymer coagulant and the water to be treated containing fine flocs, and the organic polymer flocculant and the water to be treated containing fine flocs are stirred for a certain period of time. While staying, coarse flocs are formed.

  The flock formation tank 20 is provided with a return pipe 32 for returning the slurry obtained by the solid-liquid separation in the solid-liquid separation tank 30 into the flock formation tank 20, and is pulled from the bottom of the solid-liquid separation tank 30. A part of the extracted slurry is circulated to the flock forming tank 20 via the return pipe 32. By supplying a predetermined amount of coarse flocs contained in this slurry to the floc formation tank 20, the sedimentation of the coarse flocs in the floc formation tank 20 is improved and the coarse flocs are promoted to be coarse. The return pipe 32 can also be connected to the pipe 12 connected to the upstream side of the flock formation tank 20 or the pipe 23 connected to the downstream side of the flock formation tank 20.

  By mixing the water to be treated in the floc formation tank 20 with the slurry deposited in the solid-liquid separation tank 30, coarse flocs having a particle size of about 2.0 to 5.0 mm or more are formed. The water to be treated containing coarse flocs obtained in the floc formation tank 20 is supplied to the solid-liquid separation tank 30 via a pipe 23.

  The solid-liquid separation tank 30 is a device for performing solid-liquid separation of the water to be treated containing coarse flocs into a slurry containing coarse flocs and a supernatant liquid by sedimentation separation. For example, as shown in FIG. A countercurrent sedimentation tank can be preferably used. The pipe 23 for supplying the treated water containing the coarse flocs is arranged near the center of the upward flow sedimentation basin so that the treated water can flow in the downward flow. It deposits at the bottom of an upflow sedimentation tank. The supernatant liquid is supplied to the adjusting tank 50 via the pipe 31 connected to the upper part of the upward flow sedimentation tank, is temporarily stored in the adjusting tank 50, and is then supplied to the filtering device 40.

  The filtering device 40 is not particularly limited as long as it is a device for filtering the supernatant with a particulate filter medium having an effective diameter capable of capturing coarse flocs to obtain filtered water. For example, the filtration device 40 is a filter layer in which a particulate filter medium such as anthracite having an effective diameter of 1.2 to 2.0 mm is deposited in a tower to a thickness of 150 to 550 mm, more typically about 200 to 350 mm. 41, and the supernatant liquid is filtered by passing water downward from the upper part of the column. It is preferable that a flock deposit layer is formed on the surface of the filter layer 41. However, if the flock deposit layer becomes thicker, the filter resistance becomes too high, so it is desirable to suppress it to about 5 mm at maximum. Since the deposition layer of this floc functions as a cake layer, the deposition layer can capture fine flocs having a particle size of less than 1.2 to 2.0 mm to obtain higher quality filtered water.

  In the example of FIG. 1, an example in which an upflow sedimentation tank is used as the solid-liquid separation tank 30 is shown, but the present embodiment is not limited to this, and high-speed aggregation such as slurry circulation type, sludge blanket type, or composite type is performed. Besides the settling device, a cross-flow type settling tank or the like can also be used. From the viewpoint of space saving, it is preferable to use the upflow sedimentation tank shown in FIG. 1 or the high-speed coagulation sedimentation apparatus 300 shown in FIG.

(First modification)
As shown in FIG. 2, the purified water treatment apparatus according to the first modified example of the present invention differs from the purified water treatment apparatus of FIG. 1 in that a high-speed coagulating sedimentation apparatus 300 is applied as the solid-liquid separation tank 30. The other configurations are substantially the same as those of the water purification apparatus of FIG.

  The high-speed coagulation-sedimentation apparatus 300 includes a tank-shaped apparatus body 301 and a cylindrical outer draft tube 302 arranged in the center of the apparatus body 301. Inside the outer draft tube 302, the upper end of a cylindrical inner draft tube 303 having a smaller diameter than the outer draft tube 302 is inserted.

  The lower end of the inner draft tube 303 is projected from the outer draft tube 302, and the projected portion is conically expanded toward the bottom surface of the apparatus body 301. In this high-speed coagulation-sedimentation apparatus 300, a conical inner space of the inner draft tube 303 serves as a stirring section 304, and a stirring apparatus 305 that stirs the fluid by the stirring section 304 is installed. The stirring device 305 is not particularly limited, but has, for example, a stirring blade driven by a stirring motor.

  When the water to be treated on which the coarse flocs are formed is supplied from the floc forming tank 20 to the stirring unit 304, the stirring blade is rotated to stir and mix with the slurry flowing out from the precipitation unit 306 outside the stirring unit 304. .. As a result of the stirring at this time, an upward flow is generated, and the slurry mixed with the water to be treated rises in the inner draft tube 303 while being swirled rapidly so that the flocs do not settle.

  At this time, the flocs come into contact with each other and coalesce to grow further. Therefore, in this high-speed coagulation-sedimentation apparatus 300, the space surrounded by the inner draft tube 303 above the stirring section 304 becomes the floc forming section 307 in which flocs are formed. The flocs grown in the floc forming unit 307 overflow from the upper end of the inner draft tube 303 into the space surrounded by the outer draft tube 302 by the flocs that sequentially rise from the stirring unit 304, and become an overflow slurry flow, and the outer draft tube 302 The gap between the inner draft tube 303 and the inner draft tube 303 is lowered.

  Even while passing through this gap, the flocs grow in contact with each other. The grown flocs flow out to the precipitation unit 306. In the settling unit 306, flocs having a terminal velocity that balances with the rising velocity of the treatment liquid form a slurry blanket, and the water clarified through the slurry blanket passes through the interface of the slurry to become a supernatant liquid, and the supernatant liquid is piped. It is discharged to the outside of the high speed coagulation-sedimentation apparatus 300 via 308. On the other hand, the slurry that settles in the settling unit 306 becomes a slurry that flows from the settling unit 306 into the stirring unit 304 and returns to the stirring unit 304.

  The amount of water flowing from the stirring unit 304 to the floc forming unit 307 is larger than the amount of water to be treated flowing into the stirring unit, but this is due to the jetting action of water by the stirring blade. Therefore, a part of the amount of water flowing from the floc forming unit 307 to the sedimentation unit 306 is sucked into the stirring unit 304 at the bottom of the sedimentation unit 306. The flow to the stirring section 304 at the bottom of the settling section 306 is an inflow slurry flow, and the slurry at the bottom of the settling section 306 is returned to the stirring section 304 without using a fluid transfer means such as a pump. The flocs of the returned slurry contribute to the flocs growth in the flocs forming portion 307.

  Also in this high-speed coagulation-sedimentation apparatus 300, since the obtained slurry contains coarse flocs in a high concentration, by circulating the slurry back to the floc formation tank 20 via the return pipe 32, the growth of flocs is further promoted, The quality of treated water is improved. Although not shown, the extracted slurry can be further returned to the floc forming tank 20 even in the high-speed coagulation-sedimentation apparatus 300 of FIG.

(Second modified example)
The water purification apparatus according to the second modified example of the present invention is different from the first modified example shown in FIG. 2 in that it does not include the flock formation tank 20. Other configurations are substantially the same as those of the water purification apparatus of FIG.

  In the example of FIG. 3, the organic polymer coagulant is a pipe 12 connected to one of the dotted lines in FIG. 3, that is, the mixing tank 10 on the upstream side of the solid-liquid separation tank 30 (high-speed coagulating sedimentation apparatus 300). , And is supplied to at least one of the stirring unit 304 and the flock forming unit 307. In the example of FIG. 3, the floc forming tank 20 is not arranged, but as described in the first modification, the high speed coagulating sedimentation device 300 of FIG. The contact of the above and the mixing of the organic polymer coagulant and the floc can be promoted similarly to the example of FIG. 2, and the object of the present embodiment can be achieved.

(Third modification)
As shown in FIG. 4, the purified water treatment apparatus and the purified water treatment method according to the third modified example of the present invention are applied to the filtered water obtained by the filtering apparatus 40 after the filtering apparatus 40 of the water purification apparatus of FIG. It is the same as the water purification apparatus of FIG. 1 except that the water purification apparatus shown in FIG. 1 is further provided with a sterilization means 60 for performing sterilization processing including ultraviolet irradiation.

  According to the purified water treatment apparatus and the purified water treatment method according to the third modification, the filtered treated water can be irradiated with ultraviolet rays to be sterilized, so that higher quality purified water can be obtained. Needless to say, it is also possible to add a sterilizing agent such as chlorine in place of the irradiation of ultraviolet rays for sterilization treatment.

  As shown in FIG. 5, a measuring unit 70 for measuring the turbidity of the filtered treated water obtained by the filtering unit 40 and a measuring unit 70 are provided after the filtering unit 40 of the purified water treating unit of FIG. The control means 80 for controlling the sterilizing means 60 when the turbidity of the filtered water exceeds a predetermined value may be provided. As a result, the sterilization treatment can be performed as needed, so that the power of the sterilization unit 60 or the amount of the chemical used for the sterilization treatment can be reduced, and more efficient water purification treatment can be performed.

  Hereinafter, examples of the present invention will be shown together with comparative examples, but these examples are provided for better understanding of the present invention and its advantages, and are not intended to limit the present invention.

(Example 1)
In Example 1, a treatment test was carried out by combining a solid-liquid separation tank having an upflow sedimentation tank as shown in FIG. The treated water was assumed to be river water, and kaolin was added to tap water to adjust the turbidity to 3 degrees. This treated water was supplied to the mixing tank at a rate of 3.2 L / min. In the mixing tank, polyaluminum chloride (Taki Kagaku 250A, hereinafter abbreviated as "PAC") was added to 20 mg / L and stirred. The residence time of the mixing tank in Example 1 was set to 2 minutes. The stirring speed was set to 0.5 m / sec as the peripheral speed of the stirring blade.

  After the flocs condensed in the mixing tank were produced, the water to be treated was supplied to the floc forming tank having a volume of 16 L. In addition, in order to adjust the amount of inflow into the upflow column, a part of the water to be treated flowing out of the mixing tank was discharged out of the system as waste water for flow rate adjustment. In the floc formation tank, the organic polymer coagulant was added to the inflowing water to be treated. In Example 1, Eggrose WA-542 (anionic organic polymer flocculant, manufactured by Mizu Ing Co., Ltd., hereinafter simply referred to as “WA-542”) was added as an organic polymer flocculant. The addition rate of the organic polymer coagulant was set to 0.2 mg / L with respect to the water to be treated. The residence time in the floc forming tank was set to about 9 minutes (upflow 150 mm / min). The stirring speed was set to 0.14 m / sec as the peripheral speed of the stirring blade.

  In the floc formation tank, fine flocs and an organic polymer coagulant were sufficiently mixed to form coarse flocs, and then the water to be treated was supplied to the upflow sedimentation tank. The treated water was supplied from the upper part of the upward flow sedimentation tank, and the treated water was caused to flow downward through the center well in the column. The inner diameter of the column was 120 mm, and the height of the entire column was 1200 mm. The opening of the center well was installed at a height of 380 mm from the bottom of the column. A pipe for extracting the slurry was installed at the bottom of the column, and a pipe for circulating the slurry extracted by the roller pump to the floc forming tank was provided. The ratio of the amount of circulating water to the water to be treated was set to 0.5Q (volume flow rate ratio).

  The coagulation-sedimentation-treated water that overflowed from the upflow sedimentation tank was once stored in the adjustment tank and then supplied to the filtration device. The structure of the filtration device of Example 1 is shown in FIG. The sensor 1 and the sensor 2 inserted in the filtration device of FIG. 6 are pressure sensors. In Example 1, only anthracite (Japan Raw Materials Co., Ltd., nominal particle size 1.2 mm) was filled as a filter layer at a height (thickness) of 300 mm.

(Comparative Example 1)
Comparative Example 1 in an experimental apparatus configuration equivalent to that of Example 1, in which only PAC was added in the mixing tank and no organic polymer flocculant was added in the floc forming tank, and a conventional sand filter was used as the filter. Show as. In Comparative Example 1, the upflow in the upflow sedimentation tank was set to 75 mm / min. In Comparative Example 1, a general multi-layer filtration basin is assumed as the filter layer of the sand filtration tower, and as shown in FIG. 7, an anthracite (Nippon Raw Materials Co., Ltd. nominal particle size 1.2 mm) is in the upper 200 mm and a lower 400 mm. It was filled with filtered sand (Japan Raw Materials Co., Ltd., nominal particle size 0.6 mm). Sensor 1, sensor 2, and sensor 3 are pressure sensors, respectively.

  FIG. 8 shows the turbidity of the coagulation-sedimentation-treated water (supernatant solution) in Example 1 in which the organic polymer coagulant was added at 0.2 mg / L and in Comparative example 1 in which only PAC was added. In Comparative Example 1, the average turbidity of the treated water was about 0.6 degree at an upflow of 75 mm / min. On the other hand, in Example 1, the average turbidity was 0.2 degrees even at an upflow of 150 mm / min, and good water quality was obtained by adding the organic polymer coagulant.

  Comparing the turbidity of the filtered water obtained by the filtering treatment, both of Example 1 and Comparative Example 1 were less than 0.05 degree, which sufficiently satisfied the tap water quality standard value of 2 degrees. In addition, the turbidity of filtered water, which is stipulated in the guidelines for countermeasures against cryptosporidium and the like in water supply, is 0.1 degree or less, which is also satisfied. In Comparative Example 1, the average turbidity of the treated water was about 0.6 degree at an upflow of 75 mm / min. On the other hand, in Example 1, the average turbidity was 0.2 degrees even at an upflow of 150 mm / min, and good water quality was obtained by adding the organic polymer coagulant.

Although it is desirable to determine the thickness of the filter layer and the filter medium particle size by experiment, the following formula (1) is proposed as a guide for the filter layer thickness and the filter medium particle size in the water supply facility design guidelines (2012 version). If the calculated value is 800 or more, it is considered to be almost safe.

L / D ≧ 800 ・ ・ ・ (1)

Here, L is the filter layer thickness (m), and D is the harmonic mean diameter (m) of the filter medium.

  Comparative Example 1 was in accordance with the standard thickness of the filter layer described in the water supply facility design guide (2012), and the value of the formula 1 was also about 830, which exceeded the standard 800. On the other hand, in Example 1, the thickness of the filter layer was 300 mm, which is half of that in Comparative Example 1. Moreover, the value of Formula 1 was about 250, and it was expected that the sand filtration treatment water turbidity would be high originally. However, in Example 1, since the organic polymer coagulant was added in the floc formation step to promote the growth of coarse flocs, the floc sedimentation was improved and the upflow in the solid-liquid separation tank was doubled. Nevertheless, the water quality of the coagulated sedimentation treated water was improved as compared with Comparative Example 1.

  Further, in Example 1, since the flocs generated were coarsened due to the effect of the organic polymer flocculant, the particle size of the filter medium was large and the thickness of the filter layer was also small, but good filtered water quality could be obtained. It was Comparing the turbidity of the filtered treated water, both Example 1 and Comparative Example 1 were less than 0.05 degree, which sufficiently satisfied the tap water quality standard value of 2 degrees. In addition, the turbidity of filtered water, which is stipulated in the guidelines for countermeasures against cryptosporidium and the like in water supply, is 0.1 degree or less, which is also satisfied.

  The course of pressure of each sensor of Example 1 is shown in FIG. 9, and the course of pressure of each sensor of Comparative Example 1 is shown in FIG. Here, the pressure is expressed as the head height at each sensor position. In the filter in this test, when the supernatant liquid flowing out of the solid-liquid separation tank is supplied from the upper part of the filter layer, the flocs contained in the supernatant liquid flowing out of the solid-liquid separation tank are also supplied to the upper part of the filter layer together with water. Therefore, as the filtration continues, the filter layer is blocked by the flocs. When the filter layer is clogged, filtered water is less likely to flow out and water is stored in the upper part of the filtration tank, so that the pressure applied to the filter layer is increased. This phenomenon was evaluated using each sensor.

  In Example 1, the head of the sensor 2 gradually increased as the filtration operation continued. On the other hand, the water head of the sensor 1 hardly changed during the filtration operation. From this, it can be seen that in Example 1, since the flocs contained in the supernatant liquid were deposited on the upper part of the filter medium, the pressure of the sensor 1 located inside the filter layer did not become high. At this time, when the filtration section was observed, it was observed that flocs were deposited on the surface of the anthracite layer by about several mm.

  On the other hand, in Comparative Example 1, the head of the sensor 3 gradually increased at the beginning of the filtration operation, but then the heads of the sensors 2 and 3 also increased. That is, in Comparative Example 1, it can be seen that the flocs were blocked in the entire filter layer. In Example 1, since the flocs were coarsened to a particle size of about 2 to 5 mm by adding the organic polymer coagulant, the flocs were captured near the surface even in the filter layer due to anthracite having a relatively large particle size, and the filter layer height was increased. It is considered that good filtered water was obtained even when the value was lower than Comparative Example 1. On the other hand, in Comparative Example 1, since only PAC was added, the particle size of the flocs was as small as about 2 mm or less visually, and it is considered that sufficient flocculation layer height was necessary because the flocs also entered the inside of the filtration layer.

(Comparative example 2)
In Comparative Example 2, as in Comparative Example 1, the same experimental apparatus configuration was used, and the operation was performed under the condition that the organic polymer coagulant was not added and only the inorganic coagulant was added. The upflow in the upflow column was set to 75 mm / min. In Comparative Example 2, the coagulation-sedimentation-treated water was supplied to a filtration tower in which 600 mm of anthracite (Japan Raw Materials Co., Ltd., nominal particle size 1.2 mm) was packed as the filter layer as in Example 1.

  The average turbidity of the filtered water from the filtration tower was 0.23 degrees, which was worse than in Example 1. In Comparative Example 2, the floc was not coarsened because no organic polymer flocculant was added, and fine flocs could not be captured in the same filter layer containing anthracite as in Example 1, so it is considered that the quality of filtered water deteriorated. Was given.

(Comparative example 3)
In Comparative Example 3, as a solid-liquid separation system for the coagulation-sedimentation section, a conventional general cross-flow type sedimentation tank as shown in FIG. 11 was used. The surface loading rate of the sedimentation tank was set to 15 mm / min. In addition, the sand filtration section was filled with filtered sand having an effective diameter of 0.6 mm to a height of 600 mm to perform single-phase filtration using only sand. The average turbidity of the overflow water of the settling basin in Comparative Example 3 was 0.4 degrees, which was slightly higher than that in Example 1, and an example using the slurry circulation method due to the difference in the solid-liquid separation method in the coagulating sedimentation treatment. It was confirmed that the water quality of No. 1 was better than that of Comparative Example 3 of the lateral flow type sedimentation tank.

  Comparing the filtration resistance in the sand filtration section, in Example 1, the filtration resistance increase rate was about 340 mm per 24 hours. On the other hand, in Comparative Example 3, the filtration resistance increase rate was about 600 mm per hour, and in Comparative Example 3, the filtration resistance increase rate was significantly increased as compared with Example 1, and the addition of the organic polymer coagulant was used. It was shown that the filter sand was easily blocked.

  From these results, it was shown that it is necessary to use a filter medium having a relatively large particle size such as anthracite when applying the organic polymer coagulant. The turbidity of the sand-filtered water of Comparative Example 3 was less than 0.05, and there was no problem in terms of water quality.

(Example 2)
In Example 2, an experimental apparatus having the same configuration as in Example 1 was used, and anthracite having a nominal pore diameter of 1.2 mm was filled to a height of 510 mm as a filter layer in the filtration section. When the coagulation-sedimentation-treated water was operated under the same coagulation-sedimentation conditions as in Example 1 and the coagulation-sedimentation-treated water was supplied to the filtration tower, the turbidity of the filtration-treated water was less than 0.01 degree as in Example 1. It was confirmed that good filtered water quality was obtained even with filtration under conditions close to the standard filter layer thickness.

(Example 3) WA-542 addition concentration In Example 3, the same apparatus as in Example 1 was used, except that only the WA-542 addition rate was changed to 0.1 mg / L. As in Example 1, the filtration part was also filled with 300 mm of anthracite having an effective diameter of 1.2 mm. The turbidity of the coagulation-sedimentation-treated water was about 0.01 degree or less, but sometimes increased to about 0.2 degree.

  FIG. 12 shows the pressure curve of each sensor of the third embodiment. The head of sensor 2 gradually increased as the operation continued. The operation time was about 38 hours, which was slightly shorter than that of Example 1. In Example 3, compared with Example 1, the turbidity of the coagulation-sedimentation-treated water was slightly unstable and the filtration duration was shortened, so that the addition rate of WA-542 was insufficient at 0.1 mg /. Therefore, in this example, 0.2 mg / L or more was considered appropriate.

(Example 4)
In Example 4, the aggregation-precipitation part of Example 1 was used, and the aggregation-precipitation treatment was performed while changing the WA-542 addition rate from 0.2 to 0.8 mg / L. Other operating conditions are the same as in the first embodiment. FIG. 13 shows the results of the turbidity of the coagulated sediment treated water. Here, comparison was made in a short period of 1 to 2 operating hours. The turbidity of the coagulated sediment-treated water was slightly higher than that in Example 1, but the turbidity of the coagulated sediment-treated water did not change significantly up to the WA-542 addition rate of 0.8 mg / L. From these results, it is considered appropriate that the WA-542 addition rate in this test is 0.2 to 0.8 mg / L.

(Reference example 1)
In Reference Example 1, as shown in FIG. 1, when a treatment test was carried out by combining a solid-liquid separation tank having an upward flow column, the slurry separated by the solid-liquid separation tank was not circulated. The treated water was assumed to be river water, and kaolin was added to tap water to adjust the turbidity to 3 degrees. This treated water was supplied to the mixing pond at a rate of 3.2 L / min. In the mixing tank 10, PAC was added to 20 mg / L and stirred. The residence time in the mixing tank was set to 2 minutes. The stirring speed was set to 0.5 m / sec as the peripheral speed of the stirring blade.

  After the flocs condensed in the mixing tank were produced, the water to be treated was supplied to the floc forming tank having a volume of 16 L. In addition, in order to adjust the amount of inflow into the upflow column, a part of the water to be treated flowing out of the mixing tank was discharged out of the system as waste water for flow rate adjustment. In the floc formation tank, the organic polymer coagulant was added to the inflowing water to be treated. In this example, WA-542 was added. The addition rate of WA-542 was set to 0.2 mg / L with respect to the water to be treated. The residence time in the floc forming tank was set to about 9 minutes (upflow 150 mm / min). The stirring speed was set to 0.14 m / sec as the peripheral speed of the stirring blade. In the floc formation tank, fine flocs and WA-542 were mixed to form coarse flocs, and then the water to be treated was supplied to the upward flow sedimentation tank (solid-liquid separation tank). The treated water was supplied from the lower part of the upflow sedimentation tank, and the coagulated sedimented water was overflowed from the upper part of the column. The inner diameter of the column was 120 mm, and the height of the entire column was 1200 mm.

  The coagulation-sedimentation-treated water that overflowed from the upflow sedimentation tank was once stored in the adjusting tank and then supplied to the filtration tower. In Reference Example 1, as in the case of Example 1, only anthracite (Nippon Raw Materials Co., Ltd., nominal particle size 1.2 mm) was filled into the filtration tower at a height of 300 mm.

(Comparative example 4)
Comparative Example 4 with respect to Reference Example 1 was operated under the same experimental apparatus configuration as that in which WA-542 was not added and only PAC was added. The upflow in the upflow column was set to 75 mm / min. Further, in Comparative Example 4, assuming a general multi-layer filtration basin as a filter layer of the sand filtration tower, anthracite (Japan Raw Materials Co., Ltd. nominal particle size 1.2 mm) is in the upper 200 mm and filter sand (Japan Raw Materials Co., Ltd.) is in the lower part. (Nominal particle size 0.6 mm).

  FIG. 14 shows the turbidity of the coagulated sedimentation treated water of Reference Example 1 and Comparative Example 4. In Reference Example 1 to which WA-542 was added, although the upflow was twice that of Comparative Example 4, the water turbidity was equivalent to the coagulation-sedimentation treatment, and the sedimentation property was improved by the addition of the organic polymer coagulant, The turbidity was lower than that of the filtered water of FIG. 1 and was not always stable, and the processing stability was slightly lower than that of Example 1.

10 ... Mixing tank 11 ... Stirring means 12 ... Piping 20 ... Flock forming tank 21 ... Stirring means 23 ... Piping 30 ... Solid-liquid separation tank 31 ... Piping 32 ... Returning pipe 33 ... Piping 40 ... Filtration device 41 ... Filter layer 50 ... Adjustment Tank 60 ... Sterilizing means 70 ... Measuring means 80 ... Control means 300 ... High-speed coagulating sedimentation device 301 ... Device body 302 ... Outer draft tube 303 ... Inner draft tube 304 ... Stirring unit 305 ... Stirring device 306 ... Sedimentation unit 307 ... Flock forming unit 308 ... Piping

Claims (9)

Add a coagulant to the water to be treated to form fine flocs,
An organic polymer flocculant is added to the water to be treated containing the fine flocs to grow the fine flocs to form coarse flocs,
Solid-liquid separation of the treated water containing the coarse flocs into a slurry containing the coarse flocs and a supernatant liquid,
The slurry is mixed with the water to be treated containing the coarse flocs to promote the growth of the coarse flocs,
A method for purifying water, comprising: filtering the supernatant liquid with a particulate filter medium having an effective diameter capable of capturing the coarse flocs to obtain filtered water.   The purified water treatment method according to claim 1, wherein an effective diameter of the particulate filter medium is 1.2 to 2.0 mm.   The said slurry is mixed with the said to-be-processed water which carries out said solid-liquid separation so that it may become 0.2 to 2.0 times the inflow amount of the said to-be-treated water. Purified water treatment method described in.   The water purification method according to any one of claims 1 to 3, wherein the organic polymer coagulant is added to the water to be treated in an amount of 0.2 to 0.8 mg / L.   The water purification treatment method according to any one of claims 1 to 4, wherein the filtered water is subjected to a sterilization treatment including ultraviolet irradiation.   The turbidity of the filtered treated water is measured, and when the turbidity exceeds a predetermined value, the sterilization treatment is performed, and the purified water treatment method according to claim 5. A fine floc forming means for forming a fine floc by adding a coagulant to the water to be treated,
A coarse floc forming means for forming coarse flocs by adding an organic polymer coagulant to the water to be treated containing the fine flocs, and growing the fine flocs.
Solid-liquid separation means for solid-liquid separating the water to be treated containing the coarse flocs into a slurry containing the coarse flocs and a supernatant liquid,
Returning means for returning the slurry into the water to be treated containing the coarse flocs,
And a filtration means for obtaining filtered water by passing the supernatant liquid through a filter layer composed of a particulate filter medium having an effective diameter capable of capturing the coarse flocs to obtain filtered water. Processing equipment.   The water purification apparatus according to claim 7, wherein the effective diameter of the particulate filter medium is 1.2 to 2.0 mm, and the thickness of the filter layer is 550 mm or less.   The purified water treatment apparatus according to claim 7 or 8, further comprising a deposition layer of the coarse flocs having a maximum thickness of 5 mm on the filter medium.