JP6949770B2 - Coagulation sedimentation device and coagulation sedimentation method - Google Patents

Description

The present invention relates to a treatment method using a coagulation sedimentation device that can be used in a water purification treatment for producing tap water, industrial water, and the like.

In tap water (purified water) treatment for producing tap water and industrial water, turbidity components, which are insoluble components contained in raw water, and pollutants such as algae are separated by solid-liquid separation technology such as coagulation sedimentation treatment and sand filtration. Processing. Of these, the coagulation-precipitation treatment is an effective treatment method for removing not only insoluble components but also pollutants such as soluble chromaticity and soluble organic substances, and is widely used.

This coagulation-precipitation method includes a pollutant after a step of adding an inorganic coagulant or a pH adjuster to precipitate a pollutant in the raw water, a step of adsorbing the pollutant on the flocs generated from the inorganic coagulant, and the like. This is a treatment method for separating flocs from raw water.

In the water purification plant, a mixing tank (mixing pond), a floc forming tank, and a settling tank are continuously installed in order to carry out the above process. It has been practiced to form flocs in the sedimentation basin and segregate the flocs in the sedimentation basin. This method is an excellent system that can separate and remove various pollutants, but it has the disadvantage of requiring a large sedimentation basin due to the slow sedimentation rate of flocs.

Since the area occupied by the sedimentation basin in the water purification plant is huge, it is possible to reduce the land of the entire treatment plant if the sedimentation basin can be reduced, and the amount of treated water can be secured even in water purification plants in urban areas where there is not enough land. It becomes possible to do.

Various methods have been proposed as methods for reducing the sedimentation basin. For example, in Patent Documents 1 and 2 (Japanese Patent Laid-Open No. 2014-237122, Japanese Patent Application Laid-Open No. 2014-237123), a sedimentation accelerator having a high specific density (for example, sand) is added to form a floc containing the sedimentation accelerator. Flock containing a sedimentation accelerator increases the sedimentation rate and can increase the water area load in the sedimentation basin, so that the sedimentation basin area can be reduced.

On the other hand, since the sedimentation accelerator is discharged as it is together with the flocs, it has been proposed to recover and reuse the sedimentation accelerator with a cyclone. The methods of Patent Documents 1 and 2 can increase the settling speed of flocs and have the advantage of stabilizing solid-liquid separation, but increase the stirring power and promote settling to mix the settling accelerator well with the pollutant. Since the agent is separated by a cyclone, there is a problem that the number of auxiliary equipment such as pumps increases, and it is necessary to add a depleted sedimentation accelerator, and the piping etc. wears due to the circulation of the sedimentation accelerator in the system. There is also.

In Patent Document 3 (Japanese Patent Laid-Open No. 2009-247957), in order to increase the sedimentation rate, a slurry is stored in a solid-liquid separation tank, and water to be treated is introduced therein. The water to be treated mixed with the inorganic coagulant is introduced in the presence of existing flocs and forms flocs together with the existing flocs, so that the efficiency of coagulation sedimentation can be increased and the solid-liquid separation equipment can be miniaturized. It will be possible.

Further, the method of Patent Document 3 has a feature that by adding fine solid particles, flocs containing the solid particles are formed, the sedimentation rate of the flocs is improved, and stable treatment is possible even with water having less turbidity. be. On the other hand, since this method requires the addition of solid particles, it has the same problems as those in Patent Documents 1 and 2. That is, there are problems such as an increase in auxiliary equipment such as a pump for separating the sedimentation accelerator with a cyclone, the need to add a worn sedimentation accelerator, and wear of pipes and the like due to the circulation of the sedimentation accelerator in the system.

On the other hand, in recent years, the turbidity of river water, which is the raw water, has been decreasing. Known to give.

Even in the high-speed coagulation-sedimentation treatment, the high-quality flocs in the tank react with the turbidity derived from the raw water to perform efficient coagulation, so that the treatment becomes unstable when the turbidity of the raw water is low. In high-speed coagulation precipitation, it is extremely important to stably hold the slurry blanket, and if the blanket is not formed well and the flocs in the slurry leak into the treated water, the quality of the treated water deteriorates.
In such a case, a method of adding an insoluble granular coagulation aid such as sand (Patent Document 4, Japanese Patent Application Laid-Open No. 2006-7086) has been proposed for the purpose of stabilizing the treatment.

In addition, although slurry management is usually performed by draining mud, an interface meter or an SV meter is used for the control (Patent Documents 5 and 6, Japanese Patent Application Laid-Open No. 3-174205, Japanese Patent Application Laid-Open No. 2009-241045). However, when the slurry expands and its properties deteriorate, the slurry interface does not deteriorate even if mud is drained, and excessive mud drainage promotes a decrease in the slurry concentration, which significantly reduces the processability of high-speed coagulation sedimentation. was there.

Further, the addition of the coagulation aid (precipitation accelerator) is effective in improving the sedimentation property, but the injection equipment is excessive and the injection equipment is worn and deteriorated by sand, so that the maintainability is lowered. Furthermore, since foreign matter is added from outside the system, there is a problem that the amount of sludge generated increases. In addition, the SV meter was simply used to measure the concentration of slurry and required complicated control in combination with an interface meter (Claim 1, paragraph 0008 of Patent Document 6).

Patent Document 7 (Patent 4008454) proposes a combined use of an inorganic coagulant and an organic polymer coagulant in order to improve coagulation and sedimentation. If an organic polymer flocculant is added excessively, blockage of sand filtration or membrane filtration may be promoted. Therefore, in Patent Document 7, the flow current of agglomerated flocs after injection of the organic polymer flocculant is measured and measured. The injection amount of the polymer flocculant is controlled based on the result. In the method of Patent Document 7, the charged state of the flocs is measured, and the amount of electrification insufficient for neutralization is supplemented by the organic polymer flocculant according to the charged state, so that an electrically neutral floc can be formed. It becomes.

On the other hand, it is necessary to prepare an electrode for measuring the charged state, and in order to perform stable measurement at all times, it is necessary to keep the electrode in a usable state at all times. In addition, a method has been proposed in which a slurry containing flocs in the coagulated sedimentation portion is mixed with raw water to facilitate floc formation, but the returned flocs react with the inorganic coagulant, and the turbidity component in the raw water. And may inhibit the reaction of the inorganic coagulant.

JP 2014-237122 JP 2014-237123 JP-A-2009-247957 JP 2006-7086 Japanese Patent Application Laid-Open No. 3-174205 Japanese Patent Application Laid-Open No. 2009-24145 Patent 4008454 Japanese Patent Application Laid-Open No. 2002-11472 JP 2006-35221 JP-A-2007-7601

The water purification plant facilities constructed during the high-growth period have deteriorated in recent years and are about to be renewed. In particular, since water purification plants in urban areas have little land, equipment with a small installation area is required for renewal.

In terms of water quality, large changes in water quality are expected in recent years, such as sudden heavy rains and local heavy rains increasing due to climate change, and the turbidity of river water, which is the raw water of water purification plants, increases sharply. Therefore, highly stable processing equipment is required. In terms of management, the number of staff who manage water purification plant facilities is decreasing, and treatment facilities that are easier to maintain are required.

Furthermore, if the turbidity of the raw water suddenly increases in a short time at a water purification plant that uses river water as the raw water due to the sudden and local heavy rain as described above, the amount of the coagulant to be used should be the amount of the turbidity component. It is necessary to adjust according to the increase, but for adjustment, it is necessary to carry out a coagulation sedimentation treatment test on a small scale and determine an appropriate chemical injection rate, which imposes a heavy burden on maintenance.

In addition, there is a difference in the water temperature in the settling pond, especially when the temperature rises in summer, and the water flow in the settling pond is disturbed by the density current. Although the absolute value of the flow velocity of the density current is not large, the density of the flocs precipitated inside is not large, so that the sedimentation of the flocs is hindered by the density current, which may hinder the solid-liquid separation. This is especially significant in high-speed coagulation sedimentation basins that are operated at high loads.

In order to solve the above problems, the present invention can have the following configuration.

(1) A step of adding at least one of an inorganic coagulant and an organic coagulant to the water to be treated, stirring and mixing to form fine flocs, and an organic polymer flocculant to the water to be treated in which the fine flocs are formed. Is added, and the mixture is further stirred and mixed to grow fine flocs to form coarse flocs, and the coarse flocs are settled to separate the coarse flocs into a solid-liquid separation into a slurry and a supernatant. Further, at least a part of the slurry is returned to one or more of the place where the organic polymer flocculant is added and the place downstream from the place where the organic polymer flocculant is added (solid-liquid separation side) to form a floc. It relates to a method of circulating and improving flock sedimentation.

(2) In addition to the floc circulation, the floc sedimentation property can be improved by the addition control treatment that controls the addition of the organic polymer flocculant according to the interfacial height of the slurry.
The "addition control" of the organic polymer flocculant means, for example, an increase or decrease in the amount of addition. Here, the increase in the addition amount includes not only the case where the addition amount of the organic polymer flocculant per unit time increases but also the case where the addition amount changes from zero to plus (addition start), and the addition amount decreases. This includes not only the case where the amount of the organic polymer flocculant added per unit time decreases, but also the case where the amount changes from plus to zero (addition stop).

The present invention may have the following aspects.

(3) As the organic polymer flocculant, it is preferable to use at least one of an anionic organic polymer flocculant and a nonionic organic polymer flocculant.

(4) The interface height can be indirectly measured by measuring at least one of the sludge volume (SV) and the turbidity of the water to be treated.

(5) Further, it is possible to control the addition of the organic polymer flocculant based on the measurement result of the temperature of the slurry before returning.

(6) The present invention is particularly suitable for a method of treating raw water for purification as water to be treated.

(7) The present invention also relates to a coagulation and settling apparatus, which comprises a coagulant supplying means for adding at least one of an organic coagulant and an inorganic coagulant to the water to be treated, and the organic coagulant. A coagulant supply means for supplying an organic polymer coagulant to the water to be treated to which at least one of the inorganic coagulants has been added, and a floc forming tank for stirring the water to be treated to which the organic polymer coagulant has been added. It is installed on the downstream side of the flock forming tank and has a solid-liquid separating device for separating the water to be treated into a slurry and a supernatant liquid, and further, the slurry of the solid-liquid separating device is solidified with the flock forming tank. A liquid separating device and a returning means for circulating the flocs by returning the liquid to any one or more of the flow paths between the solid-liquid separating device and the flock forming tank are provided.

(8) In addition to the return means, it is preferable to install a control unit that directly or indirectly measures the slurry interface of the solid-liquid separation device and controls the coagulant supply means based on the measurement result.

(9) As the measuring means connected to the control unit, an interface meter installed in the solid-liquid separation device, a thermometer installed in the solid-liquid separation device, and a turbidity meter for measuring the turbidity of the water to be treated. and so on.

(10) The solid-liquid separation device can be selected from, for example, a solid-liquid separation device provided with an upward flow column and a high-speed coagulation / precipitation device.

According to the present invention, by using an inorganic (organic) coagulant and an organic polymer flocculant in combination, it is possible to enhance the cohesiveness of flocs and improve the sedimentation property of flocs. Therefore, it is possible to reduce the size of the equipment by increasing the water area load of the solid-liquid separation device. In addition, since the floc cohesiveness is enhanced by the combined use of the organic polymer coagulant, it is possible to ensure the stability of operation even in the case of high turbidity. Further, the floc cohesiveness is enhanced and the sedimentation property is improved, so that the operation management becomes easy.

Flow chart showing the outline of the present invention The figure which shows typically the 1st Embodiment of this invention. The figure which shows typically the 2nd Embodiment of this invention. The figure which shows typically the 3rd Embodiment of this invention. The figure which shows typically the 4th Embodiment of this invention. The figure explaining the control using the high-speed coagulation-precipitation type solid-liquid separation apparatus. The figure explaining the control using the upward flow column type solid-liquid separator The figure which shows typically the 5th Embodiment of this invention. The figure which shows typically the 6th Embodiment of this invention. Graph showing treated water turbidity (control system) with PAC alone (without addition of organic polymer flocculant) Graph showing treated water turbidity with PAC alone (without addition of organic polymer flocculant) The figure explaining the apparatus used in Example A2. Graph showing the effect of PAC addition position Graph showing the effect of slurry circulation Graph showing the effect of the amount of organic polymer flocculant added Graph showing slurry interface height under each condition Graph showing turbidity of column treated water with respect to upward flux

Hereinafter, the present invention will be specifically described, but the present invention is not limited to a specific specific example.

FIG. 1 is a flow chart showing an outline of the present invention. In the method and apparatus of the present invention, first, at least one of an inorganic coagulant and an organic coagulant (abbreviated as an inorganic (organic) coagulant) is added to the water to be treated. Add, stir and mix to form fine flocs. Next, an organic polymer flocculant is added to the water to be treated on which fine flocs are formed, and the mixture is stirred and mixed to grow fine flocs to form coarse flocs.

In the water to be treated on which coarse flocs are formed, the supernatant is separated from the flocs by solid-liquid separation, and the supernatant is discharged as treated water to the outside of the system or subjected to another post-treatment, and is subjected to solid-liquid separation. The concentrated floc slurry (sludge) is returned and circulated in a step of growing coarse flocs, that is, at the place where the organic polymer flocculant is added or on the downstream side thereof.

Since the solid-liquid separation ability is affected by the sedimentation state of the slurry, it is possible to control the addition of the organic polymer flocculant using the slurry interface as an index, but at least the solid-liquid separation is performed by returning the slurry. The resolvability is improved, resulting in good quality of treated water. The details will be described below.

[Water to be treated]
The water to be treated includes water containing fine suspended solids such as river water (including dam water), rainwater, lake water, groundwater, and factory effluent. The present invention is more suitable for treating raw water for purified water (clean water, irrigation water) than wastewater (wastewater). In Japan, river water and groundwater that are not contaminated with soluble organic substances and metals are used as raw water for water purification plants, but any water is the subject of the present invention. However, since groundwater is generally less contaminated with suspended solids and the like, it is often the case that the coagulation sedimentation treatment is omitted, sand filtration and sterilization are performed. Therefore, when this process is applied to water purification, river water and lake water, especially river water, are more suitable as the water to be treated.

[Inorganic (organic) coagulant]
In the present invention, one or more coagulants selected from an inorganic coagulant and an organic coagulant are used. Hereinafter, the inorganic coagulant and the organic coagulant will be described.

-Inorganic coagulant Inorganic coagulant can be applied as long as it forms and precipitates hydroxide with pollutants, for example, aluminum sulfate (sulfuric acid band), polyaluminum chloride, polysilica iron, polyferrous sulfate. One or more of (poly iron) and ferric chloride can be selected and used. Polyaluminum chloride (hereinafter referred to as PAC), sulfated soil, polysilica iron and the like can be preferably used in water purification plants for water services. Among these, PAC is particularly suitable as an inorganic coagulant for water purification plants because it has a small pH change at the time of addition, a high aggregation efficiency, and a small amount of coloring.

Depending on the type and water quality of the water to be treated, the above-mentioned inorganic coagulant may be replaced with, or an organic coagulant may be used together with the above-mentioned inorganic coagulant. The organic coagulant is classified as a polymer flocculant in a broad sense, but is a small molecule as compared with a drug classified as a polymer flocculant. That is, in the present invention, an organic coagulant having a smaller molecule than the organic polymer flocculant described later can be defined as an organic coagulant.

Specifically, the molecular weight of the organic coagulant is several million or less, more specifically, the molecular weight is 1.5 million or less, preferably 1 million or less, more preferably 500,000 or less, and particularly preferably the molecular weight. It is 100,000 or less. The lower limit of the molecular weight is, for example, 1000 or more, preferably 5000 or more, more preferably 10,000 or more, still more preferably 20,000 or more, and particularly preferably 30,000 or more.

The molecular weight here is obtained by converting from the intrinsic viscosity (measured value at 25 ° C. in 0.2N-NaCl aqueous solution, unit is dl / g), and the viscosity formula of the polyacrylamide polymer: [η]. = 3.02 × 10 ^-4 × (Mw) ^0.68 [Polymer coagulant, published by Tokyo Metropolitan Sewerage Service Co., Ltd., p. 113], the molecular weight (Mw) can be obtained for convenience.

The type of the organic coagulant is not particularly limited, and one or more known ones can be used. For example, a condensing polymer, a dicyandiamide-formalin condensate, polyethyleneimine, polyvinylimidarin, polyvinylpyridine, etc. Dialylamine salt / sulfur dioxide copolymer, polydimethyldialylammonium salt, polydimethyldialylammonium salt / sulfur dioxide copolymer, polydimethyldialylammonium salt / acrylamide copolymer, polydimethyldialylammonium salt / diallylamine hydrochloride derivative co-weight There are coalescence, allylamine salt polymer, etc.

Specific examples of the condensation polyamine include a condensate of alkylene dichloride and alkylene polyamine, a condensate of aniline and formarin, a condensate of alkylenediamine and epichlorohydrin, and a condensate of ammonia and epichlorohydrin. Examples of the alkylenediamine that condenses with epichlorohydrin include dimethylamine, diethylamine, methylpropylamine, methylbutylamine, and dibutylamine.

The above-mentioned inorganic coagulant and organic coagulant may be used alone or in the form of a mixture, respectively, or the mixture may be used in the form of an aqueous solution diluted with water in advance. When used as a mixture, care must be taken as a precipitate may precipitate depending on the combination. If necessary, one or more additives such as a dispersant, a pH adjuster, and a pH buffer can be added to the aqueous solution of these coagulants. When the inorganic coagulant and the organic coagulant are added separately to the water to be treated, the order of addition is not particularly limited.

In either case, the role of the inorganic (organic) coagulant is to neutralize the charged state of the pollutant in the water to be treated and condense to form fine flocs, so that the coagulation state is appropriate for the water to be treated. It is desirable to determine the addition rate so that Therefore, it is desirable to determine an appropriate addition rate in advance in a small-scale treatment test, but in general, the amount of the inorganic coagulant added per 1 L of water to be treated is about 10 mg to 1000 mg, preferably about 20 mg to 200 mg. Yes, the amount of the organic coagulant added is about 1 mg to 100 mg. The amount of these additions is the amount excluding the diluting solvent (water).

[Organic polymer flocculant]
The organic polymer flocculant may be cationic, anionic, nonionic, or amphoteric depending on the charged state, and may be appropriately selected according to the water to be treated. In particular, when the present invention is used for water purification, one or more of anionic organic polymer flocculants and nonionic organic polymer flocculants are preferably selected and used.

Examples of the anionic polymer flocculant include a polyacrylamide partial hydrolyzate, a homopolymer or copolymer of an anionic monomer, and a copolymer of an anionic monomer and a nonionic monomer such as acrylamide. Anionic monomers include acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, vinyl sulfonic acid, allyl sulfonic acid, metharyl sulfonic acid, styrene sulfonic acid, 2-allylamide ethane sulfonic acid, 2-acrylamide-2. -Methylpropanesulfonic acid, 2-Metalylamide ethanesulfonic acid, 2-methacrylamide-2-methylpropanesulfonic acid, 2-acryloyloxyethanesulfonic acid, 3-acryloyloxypropanesulfonic acid, 4-acryloyloxybutanesulfonic acid , 2-methacryloyloxyethanesulfonic acid, 3-methacryloyloxypropanesulfonic acid, 4-methacryloyloxybutanesulfonic acid, and metal salts or ammonium salts of these alkali metals, alkaline earth metals and the like. Preferable homopolymers are acrylic acid polymers and sodium acrylate polymers.

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

Next, the nonionic polymer flocculant is a homopolymer or copolymer of the nonionic monomer described above, and is preferably polyacrylamide.

One type of organic polymer flocculant may be used alone, or two or more types may be used in combination. The organic polymer flocculant can be used by any method, but since it usually takes time to dissolve, the polymer flocculant is generally used after being prepared as a solution (aqueous solution). The dissolved concentration is about 0.01% by mass to 0.5% by mass, for example, 0.1% by mass. However, the concentration of the organic polymer flocculant can be set to, for example, 0.01% by mass or less in consideration of the improvement of the solubility in the diluent (water) and the improvement of the dispersibility during use. The amount of the organic polymer flocculant added may be in the range of 0.1 to 1 mg / L, which is the amount added in the usual coagulation-precipitation treatment.

When the turbidity of the water to be treated is high, the turbidity effect is enhanced by adding a cationic polymer flocculant in the first stage and adding an anion-based or nonionic polymer flocculant in the second stage. The effect of reducing the turbidity of the treated water can be expected. In this case, the cationic polymer flocculant is one having a cationic monomer as an essential component, and is a copolymer of a cationic monomer or a copolymer of a cationic monomer and the above-mentioned nonionic monomer. Examples of the cationic monomer include dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, a neutralized salt thereof, and a quaternary salt. Further, a cationic polymer flocculant containing an amidine unit in the molecule can also be used.

Further, examples of the cationic polymer flocculant of the present invention include so-called amphoteric polymer flocculants obtained by copolymerizing a cationic monomer unit, an anionic monomer unit and a nonionic monomer unit.

As described above, the type of the organic polymer flocculant used in the present invention is not particularly limited, but in the present invention, the solid-liquid separability is improved by the circulation of flocs and the addition control of the organic polymer flocculant, as will be described later. Therefore, the step of adding the cationic or amphoteric organic polymer flocculant can be omitted, and as a result, the treatment step is simplified. Moreover, since the total amount of the organic polymer flocculant used can be suppressed, it is particularly effective in water purification applications where the use of the organic polymer flocculant is restricted.

[Other treatment agents]
The use of treatment agents other than inorganic (organic) coagulants and organic polymer flocculants is not restricted at all, and treatment agents used for water purification treatment and wastewater treatment can be widely used. For example, one or more known treatment agents such as a precipitation accelerator, a pH adjuster (for example, an alkaline agent), and a chlorinating agent (for example, sodium hypochlorite) can be used.

Among these, the sedimentation accelerator is a treatment agent that is often used when the turbidity of the raw water (water to be treated) is high, but the sedimentation accelerator is generally mainly composed of an inorganic material such as _{SiO 2 or its salt mineral.} Insoluble particles (for example, sand) as a component are contained in the slurry together with flocs due to solid-liquid separation, so that the amount of slurry (sludge) generated is significantly increased. A method of separating the sedimentation accelerator from the slurry and reusing it is also known, but the treatment is complicated.

Moreover, since the slurry containing the insoluble particles has a high viscosity, it may cause clogging of the pipes and valves for transportation, and the hard insoluble particles may damage the pipes and the like during transportation. Therefore, it is necessary to reduce the amount of the sedimentation accelerator used. In the present invention, since the solid-liquid separability of flocs is high even if the amount of the sedimentation accelerator used is small, the amount of the sedimentation accelerator used can be suppressed, and the water quality is sufficient even when the sedimentation accelerator is not used at all. It is possible to obtain the treated water of.

Next, the method of the present invention will be specifically described together with the apparatus.

[First Embodiment]
Reference numeral 1a in FIG. 2 indicates a coagulation / precipitation device according to the first embodiment, and the coagulation / sedimentation device 1a includes a coagulant supply means 12 for supplying an inorganic (organic) coagulant to water to be treated, and an inorganic (coagulation / sedimentation device 1a). A coagulant supply means 14 that supplies an organic polymer coagulant to the water to be treated to which an organic) coagulant is added, and a solid-liquid separator 31 that solid-liquid separates the water to be treated to which the organic polymer coagulant is added. have.

The connection location of these supply means 12 and 14 is not particularly limited, but in order to neutralize the charge of the pollutant in the water to be treated, it is necessary to sufficiently mix the inorganic (organic) coagulant after adding it to the water to be treated. .. Therefore, it is preferable to provide equipment capable of stirring for a predetermined time after adding the inorganic (organic) coagulant.

Specifically, the coagulant supply means 12 is connected to a mixing tank 22 capable of storing water to be treated, and a mechanical stirring device such as a flash mixer or a pump stirring device such as a stirring pump is installed in the mixing tank 22. If the water to be treated and the inorganic (organic) coagulant are stirred and mixed, the hydraulic residence time in the mixing tank 22 becomes the stirring time, so that there is an advantage that the stirring state can be easily controlled. The residence time of the mixing tank 22 is generally about 1 to 5 minutes.

The number of mixing tanks 22 and the connection method with the solid-liquid separation device 31 are not particularly limited. For example, when water to be treated is distributed from one distribution tank to a plurality of solid-liquid separation devices 31, this distribution tank is set as a mixing tank 22, and an inorganic (organic) coagulant is added in the distribution tank or its predecessor. It is also possible to stir and mix in the distribution tank.

If the water to be treated and the inorganic (organic) coagulant can be sufficiently stirred and mixed, the water to be treated such as pipes and valves is not an independent device that retains the water to be treated like the mixing tank 22 and the distribution tank. The coagulant supply means 12 can also be connected to the flow path. In this case, it is necessary to secure the pipe length according to the amount of water so that the residence time becomes constant after the addition of the inorganic (organic) coagulant.

Further, even if a turbulent flow generator such as a line mixer or a bent pipe is installed in the place where the inorganic (organic) coagulant is added or in the pipe on the downstream side thereof, stirring is promoted. Even when the coagulant supply means 12 is connected to a flow path such as a pipe, the connection location is on the upstream side of the mixing tank 22 provided with the stirring device, and the inorganic (organic) coagulant is connected. If is sufficiently agitated, it is possible to omit the installation of the turbulent flow generator and the bent pipe and the securing of the pipe length. That is, the length and type of the pipe (bent pipe) and the stirring device (turbulent flow generator) so that the inorganic (organic) coagulant is sufficiently stirred and mixed with the water to be treated before the organic polymer flocculant is added. ) And one or more stirring conditions may be set.

When coagulating and precipitating with only an inorganic (organic) coagulant, it is necessary to change the addition rate in a small-scale treatment test to find the conditions for producing sufficiently coarse flocs. In the present invention, since the organic polymer flocculant is used in combination, the floc coagulability can be supplemented by the organic polymer flocculant even if the floc growth due to the addition of the inorganic (organic) coagulant is insufficient, and the organic polymer flocculant can be supplemented. It is not necessary to set the addition amount strictly as compared with the case where the agent is not used, but it is preferable to set an appropriate addition amount to some extent according to the water to be treated.

When an appropriate amount of an inorganic (organic) coagulant is added to the water to be treated and stirred and mixed, the charge of the pollutant in the water to be treated is neutralized and fine flocs are formed. The inorganic (organic) coagulant is sufficiently mixed with the water to be treated, and the water to be treated in a state where fine flocs are formed is organically heightened from the coagulant supply means 14 before being solid-liquid separated by the solid-liquid separation device 31. Add a molecular flocculant.

Similar to the inorganic (organic) coagulant, the organic polymer flocculant may be supplied to the flow path of the water to be treated for mixing and stirring, but here, the pipe is connected between the mixing tank 22 and the solid-liquid separating device 31. A floc forming tank 24 is provided via a small-diameter flow path such as, and the flocculant supplying means 14 is connected to the floc forming tank 24 or its upstream side (however, downstream of the mixing tank 22) to form an organic polymer flocculant. Preferably, an aqueous solution of an organic polymer flocculant is supplied. The method of adding the organic polymer flocculant is not particularly limited, and in order to promote the dispersion of the solution, the addition portion of the flocculant supply means 14 can be branched into a plurality of points and injected at multiple points.

Preferably, the floc forming tank 24 is provided with a stirring device in the same manner as the mixing tank 22, and the water to be treated to which the organic polymer flocculant is added is stirred. The stirring speed at this time is not particularly limited, but if the stirring speed is too fast, the flocs are destroyed. Therefore, the stirring speed is slower than that at the time of forming the fine flocs (weak stirring intensity).

Since the organic polymer flocculant has a large molecular weight, when the organic polymer flocculant is stirred and mixed with the water to be treated by slow stirring, the organic polymer flocculant entangles fine flocs due to the cross-linking action and coarsens the flocs. Let me. As described above, since the organic polymer coagulant improves the cohesiveness of the flocs, the cohesiveness of the coagulant can be complemented even when the raw water turbidity increases sharply due to heavy rain or the like.

Although it is possible to coarsen the flocs only by adding an organic polymer flocculant, it is preferable to add a slurry described later together with the organic polymer flocculant or separately from the organic polymer flocculant. Stir the treated water slowly. Since this slurry contains a large amount of coarse flocs, the frequency of flocs collision increases and the aggregation rate increases. Then, since the fine flocs also aggregate with the coarse flocs, coarser flocs with good sedimentation property are formed.

The residence time of the flock forming tank 24 may be about 10 to 40 minutes, preferably about 20 to 40 minutes in a general flock forming tank, but if the treatment status is confirmed and good flock is formed, it is sufficient. It can also be shortened. In the present invention, the aggregation rate can be increased by using the organic polymer flocculant and the slurry is returned, so that the residence time can be further shortened.

The water to be treated on which the coarse flocs are formed is sent from the flocs forming tank 24 to the solid-liquid separation device 31. The solid-liquid separation device 31 is not particularly limited as long as it separates the water to be treated into solid-liquid by utilizing the difference in specific gravity. Here, the solid-liquid separation device 31 is an upward flow column type, and has a column 32 and a cylindrical center well 33 erected in the column 32.

The center well 33 has a discharge port communicating with the internal space of the column 32 on the lower end side thereof, and when the water to be treated on which the coarse flocs are formed is introduced into the center well 33, the inside of the center well 33 is moved downward. It moves and flows downward into the column 32 from the discharge port.

At this time, since the coarse flocs contained in the water to be treated have a downward vector, the flocs flowing into the column 32 are promoted by gravity sedimentation, and the water to be treated is solid-liquid separated into the flocs and the supernatant liquid (treated water). , Flock is accumulated under the column 32 as a slurry 35, and the treated water is discharged to the outside of the solid-liquid separation device 31 by overflow.

When the discharge port of the center well 33 is arranged below the interface between the slurry 35 and the treated water and the water to be treated flows into the slurry 35, the flocs of the water to be treated are directly mixed with the flocs in the slurry 35 and flocs. Grow, and the growth of flocs separates the water. Water rises through the slurry 35 in the column 32, and the slurry 35 acts as a so-called slurry blanket, and the effect of reducing the turbidity of the treated water is further improved.

In order to obtain a high slurry blanket effect, it is necessary to appropriately control the interface height and the floc concentration of the slurry 35. Therefore, a pipe for pulling out the accumulated flocs (slurry 35) is connected to the lower part of the column 32.

The extracted slurry 35 can be discharged to the outside of the coagulation sedimentation device 1a as it is, but a return means 25 is installed and a part or all of the extracted slurry 35 is returned to an apparatus (process) for forming coarse flocs. And circulate the flocs. The return means 25 is not particularly limited, but has a pipe through which the slurry 35 passes, and if necessary, a liquid feed means such as a pump and a check valve are also installed.

The return destination of the return means 25 is not particularly limited, but since the returned flocs contribute to the growth of coarse flocs, one of the same locations as the place where the organic polymer flocculant is added and one on the downstream side of the addition location. That is all. Here, the "same place" also means that the addition places are close to each other, and specifically, it is the same as the device (including the flow path such as piping in addition to the tank) to which the organic polymer flocculant is added. Means a device. The “downstream side” means a side close to the solid-liquid separation device 31, and is a concept including the solid-liquid separation device 31. In either case, the slurry 35 is returned to the water to be treated in a slow stirring state in which fine flocs grow into coarse flocs. Here, the slurry 35 is returned to the floc forming tank 24.

The return amount (circulation ratio) at this time is not particularly limited and can be arbitrarily set according to the interface height of the slurry 35. For example, the return amount (circulation ratio) is 0. It can be operated at 2 to 0.8 times, for example, about 0.5 times (volume ratio).

Since the returned slurry 35 contains a high concentration of flocs, the formation of coarse flocs is promoted as described above. The flocs grown by taking in the flocs in the slurry 35 are sent to the solid-liquid separation device 31, and are returned to the slow stirring step again after the solid-liquid separation, so that the flocs circulate. As a result, the floc concentration in the system of the coagulation sedimentation apparatus 1a becomes high, and the coagulation rate of fine flocs is further improved.

The above has described the case where an upward flow column is used for the solid-liquid separation device 31, but the present invention is not limited to this, and the present invention is not limited to this, and in addition to high-speed coagulation and precipitation devices such as slurry circulation type, sludge / blanket type, and composite type, A cross-flow type solid-liquid separator (cross-flow type sedimentation pond) or the like can also be used. From the viewpoint of space saving, the upward flow column of FIG. 2 and the high-speed coagulation sedimentation device are preferable. Hereinafter, a specific example using the high-speed coagulation sedimentation device will be described.

[Second Embodiment]
Reference numeral 1b in FIG. 3 indicates a coagulation / precipitation device using a solid-liquid separation device 41 composed of a high-speed coagulation / precipitation device (slurry circulation type), and the same members as those in FIG. 2 are designated by the same reference numerals and description thereof will be omitted. ..

The solid-liquid separation device 41 has a tank-shaped device main body 42, and a cylindrical outer draft tube 43 is erected inside the device main body 42, and the outer draft tube 43 has an outer draft tube. The upper end of the inner draft tube 44 having a smaller diameter than 43 is inserted.

The lower end of the inner draft tube 44 protrudes from the outer draft tube 43, and the protruding portion extends in a conical shape toward the bottom surface of the apparatus main body 42. In the solid-liquid separation device 41, the conical internal space of the inner draft tube 44 becomes the stirring unit 47, and the stirring device 45 for stirring the fluid by the stirring unit 47 is installed. The stirring device 45 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 24 to the stirring section 47, it is stirred and mixed with the slurry 35 flowing in from the settling section 49 outside the stirring section 47 by the rotation of the stirring blade. .. An upward flow is generated by the stirring at this time, and the slurry 35 mixed with the water to be treated rises in the inner draft tube 44 while being gently stirred by the water flow so that the flocs do not settle.

At this time, the flocs come into contact with each other and coalesce, and further grow. Therefore, in this solid-liquid separation device 41, the space surrounded by the inner draft tube 44 above the stirring portion 47 becomes the forming portion 48 on which the flocs grow. The stirring of the forming unit 48 is usually weaker than the stirring in the stirring unit 47, and the stirring method is not particularly limited. For example, stirring by a water stream ejected from the stirring unit 47 by the stirring blade may be used, and another stirring blade may be used. (Agitator) may be provided to stir.

The upper end of the outer draft tube 43 protrudes above the upper end of the inner draft tube 44, and the flock grown in the forming portion 48 is formed from the upper end of the inner draft tube 44 by the flock gradually rising from the stirring portion 47. It overflows into the space surrounded by 43 and becomes an overflowing slurry flow, and descends the gap between the outer draft tube 43 and the inner draft tube 44.

The flocs come into contact with each other and coalesce while passing through this gap. Therefore, in this solid-liquid separation device 41, flocs grow between the stirring portion 47 and the settling portion 49, that is, while passing through the gap between the forming portion 48 and the tubes 43 and 44. The grown flocs flow out to the settling portion 49, which is the outer space of the tubes 43 and 44.

In the settling section 49, flocks having a terminal velocity that is commensurate with the rising flow velocity of the treatment liquid form a slurry blanket, and the water that has passed through the slurry blanket and is clarified becomes a supernatant liquid through the interface of the slurry 35. It is discharged from the solid-liquid separation device 41 as treated water. That is, in this solid-liquid separation device 41, at least the precipitation portion 49 functions as a solid-liquid separation means.

The amount of water flowing from the stirring unit 47 to the forming unit 48 is larger than the amount of water flowing into the stirring unit 47 from the outside of the solid-liquid separation device 41, which is due to the water ejection action of the stirring device 45. Therefore, a part of the amount of water flowing from the forming portion 48 to the settling portion 49 is sucked into the stirring portion 47 at the bottom of the settling portion 49. The flow to the stirring section 47 at the bottom of the settling section is the inflow slurry flow, and the slurry 35 at the bottom of the settling section is returned to the stirring section 47 without using a fluid transfer means such as a pump. The flocs of the slurry 35 produced contribute to the flocs growth at the forming portion 48.

Even in this solid-liquid separation device 41, since the slurry 35 contains coarse flocs at a high concentration, the growth of flocs is further promoted by returning the slurry 35 to the flocs forming tank 24 and circulating the slurry 35, and the water quality of the treated water is improved. improves.

In any of the embodiments, sludge (flock) derived from the pollutant contained in the water to be treated is accumulated in the slurry 35 circulating between the floc forming tank 24 and the solid-liquid separation devices 31 and 41. The sludge concentration of the slurry 35 gradually increases. As the sludge concentration increases, the interface between the slurry 35 and the supernatant water in the solid-liquid separation devices 31 and 41 gradually increases, so that adjustment by wastewater and waste water, particularly wastewater, is required.

For sludge drainage, a part of the slurry may be pulled out of the system, but it is desirable to pull out the slurry having a high sludge concentration in order to suppress the sludge treatment amount. Therefore, it is preferable to pull out the lower part of the solid-liquid separation devices 31 and 41 and a part of the circulating slurry 35.

The drawing of the slurry 35 may be carried out according to the interface height in the solid-liquid separator, but if it is difficult to directly measure the interface height, it may be measured indirectly, for example, of the circulating slurry. The sludge volume (SV) can be measured and replaced. Specifically, the slurry is separated into a measuring cylinder, allowed to stand for a predetermined time (for example, 5 minutes), and the sludge volume after 5 minutes is evaluated as a percentage. The SV value in the present invention is maintained at about 10 to 15% for the slurry (water to be treated) of the floc forming tank 24 and about 40 to 60% for the circulating slurry 35 of the solid-liquid separation devices 31 and 41. Is preferable.

The above has described the case where the floc forming tank 24 is installed between the solid-liquid separating devices 31 and 41 and the mixing tank 22, but the present invention is not limited thereto.

[Third Embodiment]
Reference numeral 1c in FIG. 4 indicates a coagulation / precipitation apparatus according to a third embodiment, and the same members as those in FIGS. 2 and 3 are designated by the same reference numerals and the description thereof will be omitted. The floc forming tank 24 is not always necessary in this coagulation sedimentation device 1a.

The water to be treated is mixed by adding an inorganic (organic) coagulant in the device before the solid-liquid separation device 41 such as the mixing tank 22, and then passing through a small-diameter flow path such as a pipe to the solid-liquid separation device 41. It flows into the stirring unit 47. In this solid-liquid separation device 41, a flow path (for example, a flow path between the mixing tank 22 and the solid-liquid separation device 41) which is downstream of the mixing tank 22 and upstream of the settling portion 49 which exerts a slurry blanket effect, for example. The flocculant supply means 14 is connected to at least one location selected from the stirring unit 47, the stirring unit 47, and the forming unit 48, more preferably at least one of the flow path and the stirring unit 47.

In the solid-liquid separation device 41 of FIG. 4, the slurry 35 circulates through the stirring section 47, the forming section 48, and the settling section 49, as in the device of FIG. Since the organic polymer flocculant is added in the pipe), when the slurry 35 rises while gently stirring the forming portion 48 with a water flow, the slurry 35 supplied from the sedimentation portion 49 and the organic polymer flocculant The action promotes the coarsening of flocs.

That is, in this solid-liquid separation device 41, the stirring unit 47 and its downstream side (forming unit 48) function as a floc forming tank in which coarse flocs grow due to the addition of the organic polymer flocculant, and the sedimentation unit 49 to the stirring unit 47 The flow path to the floc functions as a means for returning the flocs, and the slurry 35 is returned from the settling section 49 to the same place as the organic polymer flocculant or to the downstream side thereof (stirring section 47, forming section 48).

In the coagulation sedimentation device 1c of FIG. 4, it is important to mix the organic polymer coagulant and the fine floc well. Therefore, when injecting the organic polymer coagulant into the pipe, a line mixer or a bent pipe is provided after the injection to make it organic. It is desirable to disperse the polymer flocculant well in the water to be treated.

When the organic polymer flocculant is added in the stirring unit 47, the mixing of the organic polymer flocculant and the floc is promoted by the stirring of the stirring device 45, but in order to further promote the mixing, the organic polymer flocculant is injected. It is also possible to divide the part into a plurality of parts and inject the organic polymer flocculant at multiple points of the stirring part 47. When the organic polymer flocculant is added in the forming portion 48, not only the water jet from the stirring portion 47 but also another stirring device (stirring blade) is installed to stir the forming portion 48 in order to improve the dispersion thereof. It is also possible.

In addition, if the unreacted inorganic (organic) coagulant reacts directly with the organic polymer coagulant, the turbidity of the treated water deteriorates. Prevent the water to be treated from flowing back. For example, another device (tank) in which the place where the inorganic (organic) coagulant is added (mixing tank) and the place where the organic (inorganic) coagulant is added is completely separated, and the place where they are added is via a small-diameter pipe or the like. Backflow is prevented by connecting them together. Alternatively, a check valve (valve) or the like may be installed between the addition locations.

More preferably, in any of the embodiments, the inorganic (organic) coagulant and the water to be treated are stirred and mixed in the apparatus (tank) before the place where the organic polymer flocculant is added, and the unreacted inorganic (organic) is mixed. ) Prevent the coagulant from flowing into the place where the organic polymer flocculant is added. For example, the residence time (that is, stirring time) in the mixing tank 22 is lengthened (for example, 1 minute or more, preferably 2 minutes or more), and the unreacted inorganic (organic) coagulant to the place where the organic polymer flocculant is added. It is also possible to prevent the inflow of In particular, when the organic polymer flocculant is injected by piping, the organic polymer flocculant is added at a position sufficiently distant from the mixing tank 22, and the inorganic (organic) coagulant and the water to be treated are sufficiently mixed.

The coagulation sedimentation device and the coagulation sedimentation method of the present invention are not particularly limited, and a solid-liquid separation device other than the above can be used, and other tanks and devices can be incorporated into the coagulation sedimentation devices 1a, 1b, and 1c. It is possible. Examples of such a tank (device) include a landing well, a biological treatment tank, an activated carbon tank, a filtration membrane, and a chlorine treatment tank.

In either case, the floc growth is promoted by circulating the slurry 35 of the solid-liquid separation devices 31 and 41, and finally the sedimentation state of the slurry 35 in the solid-liquid separation devices 31 and 41 is appropriately maintained. The solid-liquid separability as a slurry blanket is improved. Therefore, the slurry 35 does not need to be constantly circulated as long as the sedimentation state of the slurry 35 is properly maintained.

However, the sedimentation state of the slurry 35 may fluctuate depending on the state of raw water and changes in the environment. For example, when the properties of the water to be treated that flows into the coagulation sedimentation devices 1a to 1c change drastically, more specifically, when the load of pollutants in the water to be treated suddenly increases due to heavy rain or the like, the inorganic (inorganic) Due to insufficient injection rate of the organic) coagulant, the coagulation state is deteriorated and the water flow in the solid-liquid separator 31 is disturbed.

Further, when the temperature of the water to be treated is suddenly fluctuated or the temperature is high such as in summer, a density current is generated when the distribution width of the water temperature becomes large in the solid-liquid separation devices 31 and 41. Since the specific gravity of the flock is small, the flock rises even in the density current. As described above, when the sedimentation state of the slurry 35 fluctuates, the slurry 35 interface rises (falls) and the slurry 35 interface is disturbed, which affects the solid-liquid separation ability and the agglutination ability of fine flocs.

Limit the inflow of water to be treated into the solid-liquid separation devices 31 and 41 with waste water or the like, or change the amount of mud discharged (returned) from the solid-liquid separation devices 31 and 41 to increase the interface height of the slurry 35. Although it is possible to control it, it is difficult to improve the sedimentation state of the slurry 35 only by discarding water or draining mud.

The floc cohesiveness is supplemented by the combined use of the above-mentioned organic polymer flocculant and the returned slurry, but in order to make the sedimentation state more stable, the organic polymer is returned together with the slurry 35 or separately from the return of the slurry 35. The amount of the flocculant added can be controlled to stabilize the flocculation, and the sedimentation property of the slurry 35 in the solid-liquid separator 31 can be improved. This will be described in detail below.

[Fourth Embodiment]
FIG. 5 shows an example of the coagulation sedimentation device 2a, and the same members as those in FIGS. 2 to 4 are designated by the same reference numerals and the description thereof will be omitted. The solid-liquid separation device is not particularly limited, but here, a case where a cross-flow type solid-liquid separation device 51 (cross-flow type sedimentation pond) is used will be described.

The solid-liquid separation device 51 has a settling tank 52, and the water to be treated on which flocs are formed is introduced into the settling tank 52 from a tank or device in the previous stage such as the floc forming tank 24, and the flocs are formed due to the difference in specific gravity. It settles in the settling tank 52 and is separated into solid and liquid.

Even in the cross-flow type solid-liquid separation device 51, if the sedimentation state of the slurry 35 deteriorates, the solid-liquid separation property deteriorates. Therefore, in order to improve the sedimentation state of the slurry 35, a control unit 55 is installed. The control unit 55 is not particularly limited, but is installed inside or outside the coagulation sedimentation device 2a, and the sedimentation state of the slurry 35 is input as information.

The information indicating the sedimentation state of the slurry 35 is not particularly limited, but usually, when the sedimentation state is disturbed, an abnormality or fluctuation appears at the interface 59 between the slurry 35 and the supernatant (treatment liquid). It is acquired as information and input to the control unit 55.

More specifically, in order to measure the interface 59 itself, the sludge volume (SV) of the solid-liquid separation device 51 (sedimentation tank 52) is measured, and when this rapidly increases, an organic polymer flocculant is added. A control method can be mentioned. For the SV value, the slurry 35 of the solid-liquid separation device 51 is separated into a measuring cylinder, allowed to stand for a predetermined time (for example, 5 minutes), and the sludge volume after 5 minutes is evaluated as a percentage. Since the SV value of the solid-liquid separation device 51 is affected by the SV value on the upstream side, the SV value on the upstream side (for example, the SV value of the floc forming tank 24) is measured, and the interface 59 state is measured from the measured value. Can also be grasped.

The timing of measuring SV is not particularly limited, and it may be measured periodically, when an abnormal factor such as the inflow amount of water to be treated or the air temperature occurs, or when an abnormality is actually detected. May be good. By setting SV as an item for daily inspection and increasing the number of measurement data, it is possible to make it easier to judge when there is an abnormal value.

The actually measured SV value and the past SV value are input to the control unit 55 individually or in combination. Based on these SV values, the control unit 55 can use the temperature (eg, air temperature, water temperature), water amount (eg, inflow, outflow), treatment conditions (eg, stirring speed, type of inorganic (organic) coagulant). The information on the addition of the organic polymer flocculant is determined by associating one or more factor data such as (or amount) with the SV value.

This addition information is added, for example, when the start / end of addition of the organic polymer flocculant, the addition amount / addition rate / addition concentration of the organic polymer flocculant, or two or more kinds of organic polymer flocculants are used. Contains one or more types of information, such as the type of organic polymer flocculant to be used.

The coagulant supply means 14 has a flow rate control means such as a pump, a valve, and a mass flow meter, and the flow rate control means starts, ends, or ends the addition of the organic polymer coagulant according to the addition information from the control unit 55. Increase or decrease the amount added.

Therefore, even when the turbidity of the raw water rapidly increases and the injection rate of the inorganic (organic) coagulant is insufficient, an appropriate amount of the organic polymer coagulant is added to the treated water to make the flocs cohesive. Is supplemented, and the flocs with improved cohesiveness are sent to the solid-liquid separation device 51. As a result, the sedimentation property of the slurry 35 in the solid-liquid separation device 51 is improved, and the solid-liquid separation ability is improved, so that treated water having stable water quality can be obtained. Further, since the organic polymer flocculant is not excessively added, it is excellent in economy and is particularly suitable for water purification applications in which the amount of the organic polymer flocculant added is limited.

Although the case where the sedimentation state is determined by the SV value has been described above, the present invention is not limited to this. As a similar method, a measuring means for directly measuring the interface 59 such as the interface meter 58 can be installed in the solid-liquid separation device 51, and the indicated value of the interface meter 58 can be referred to. In this case, the control unit 55 adds an organic polymer flocculant, for example, when the interface 59 of the slurry 35 rises. The interface meter 58 is not particularly limited, but as an example thereof, a sensor capable of moving up and down is provided in the solid-liquid separation device 51.

This sensor is provided with a light emitter and a light receiver so that the light intensity at the light receiver can be detected. For example, when this sensor moves from the top to the bottom of the solid-liquid separation device 51 (sedimentation tank 52), it first passes through the supernatant having a small turbidity component, so that the light intensity at the receiver is high. When the sensor reaches the interface 59 of the slurry 35, the light is absorbed due to the influence of the flocs in the slurry 35, and the light intensity at the receiver is lowered. The sensor position where this decrease in light intensity is detected is the interface position.

As another method for simply observing the interface 59 of the slurry 35, there is also a method in which a sensor installed with the light emitter and the receiver facing each other is provided, and a decrease in light intensity at the receiver is detected to measure the interface position. Be done. Even in this method, it is preferable that the sensor can be moved up and down so that it can measure at an arbitrary height.

In either case, the interface position information is measured when a periodic or abnormality (factor) is detected, as in the case of the SV value, and the control unit 55 positively increases the amount of change in the interface position per hour. Is particularly suitable for control in which the addition of the organic polymer flocculant is started (or the amount is increased), and when the interface position is detected to decrease, the addition of the organic polymer flocculant is terminated (or the amount is decreased). ing.

When controlling the addition of the organic polymer flocculant, the solid-liquid separation device 51 is not limited to the cross-flow type, and may be a coagulation-sedimentation device 2b using a high-speed coagulation-precipitation type solid-liquid separation device 41 as in FIG. (FIG. 6), a coagulation / precipitation apparatus 2c using an upward flow column type solid-liquid separation apparatus 31 similar to FIG. 2 may be used (FIG. 7). In the upward flow column type, the position of the interface 59 in the column 32 instead of the center well 33 is measured, and in the high-speed coagulation sedimentation type, the position of the interface 59 of the sedimentation portion 49 is measured instead of the forming portion 48.

The position of addition of the organic polymer flocculant is not particularly limited, and in addition to being added to the floc forming tank 24, it may be added to the stirring part 47 and the forming part 48 of the solid-liquid separation device 41, as shown in FIG. In addition, it may be added to the flow path (piping) in the previous stage of the solid-liquid separation device 41. Since it is important that the fine flocs generated in the mixing tank 22 and the organic polymer flocculant are sufficiently mixed, when injecting the organic polymer flocculant into the piping, install a line mixer or bending piping after the injection. It is desirable to sufficiently disperse the organic polymer flocculant. In addition, if the unreacted inorganic (organic) coagulant reacts directly with the organic polymer flocculant, the turbidity of the treated water deteriorates. Inject at a position sufficiently separated from the tank 22.

It is also possible to return and circulate the slurry 35 while controlling the addition of the organic polymer flocculant, and the coarse flocs circulate in the presence of an appropriate amount of the organic polymer flocculant to grow the flocs. Is promoted more.

It is not necessary to circulate the slurry 35 all the time, and if an abnormality occurs in the solid-liquid separation devices 31, 41, 51, it can be performed as a means for improving the sedimentation property of the flocs. As an abnormality of the solid-liquid separation devices 31, 41, 51, there is an interface position of the slurry 35. Therefore, the control unit 55 can control the return of the slurry 35 together with the addition of the organic polymer flocculant or separately from the addition of the organic polymer flocculant, and can maintain the sedimentation state of the slurry 35 normally. ..

Here, the return control of the slurry 35 is based on, for example, the start and end of the return, the increase / decrease in the return amount, and the interface position (interface state) of the slurry 35 measured directly or indirectly and the water temperature described later. It can be controlled by the control unit 55.

The case where the state of the slurry 35 is directly measured by the interface meter 58 or the like has been described above, but the present invention is not limited to this. When a factor that deteriorates the sedimentation state of the slurry 35 is detected, it can be indirectly determined that an abnormality has occurred in the sedimentation state. Hereinafter, the fifth and sixth embodiments will be described.

[Fifth Embodiment]
The coagulation-precipitation device 2d of FIG. 8 includes a turbidity meter 56 as a means for indirectly measuring the interface state of the slurry 35. The turbidity meter 56 is installed at a place where the turbidity of the water to be treated (raw water) can be measured, for example, on the upstream side of the mixing tank 22. The turbidity of the water to be treated should be measured constantly or regularly, and if preferred, it should be measured constantly, and data on the turbidity should be collected.

A reference value for turbidity (eg, turbidity in a normal state) is set in the control unit 55, and the measured turbidity V _m is a reference value (reference value upper limit V _U ) in the control unit 55. If it exceeds, the addition of the organic polymer flocculant is started (or the amount is increased), and if the measured turbidity is lower _{than the reference value (reference value lower limit VL} ), it is judged that the turbidity has increased rapidly. Then, the addition of the organic polymer flocculant is terminated (or the amount is reduced). The control method is not particularly limited, and it can be determined that the turbidity has increased rapidly when _{the turbidity fluctuation amount δ m} per hour exceeds the set fluctuation amount (positive value) δ _s.

When the turbidity changes abruptly, the sedimentation state of the slurry 35 is disturbed, the interface 59 fluctuates, and the solid-liquid separability decreases. Therefore, by controlling the amount of the organic polymer flocculant added, the slurry 35 The sedimentation property of flocs can be improved and the solid-liquid separability can be improved.

[Sixth Embodiment]
The coagulation sedimentation device 2e of FIG. 9 is provided with a thermometer 57 as a means for indirectly measuring the interface state of the slurry 35. The thermometer 57 is installed so that the temperature of the solid-liquid separation device 41 can be measured. The installation location and method of installing the thermometer 57 are not particularly limited, but preferably, the slurry temperature (water temperature) is measured, and particularly in the high-speed coagulation-sedimentation type solid-liquid separation device 41, the interface 59 of the precipitation portion 49 which exerts a slurry blanket effect. The water temperature (slurry temperature) at the settling section 49 is preferably measured in order to detect the fluctuation of the above.

The water temperature is measured constantly or regularly, preferably constantly. When the water temperature changes abruptly, a density current is generated and the sedimentation state of flocs is disturbed. Therefore, for example, when the temperature change per hour exceeds a certain amount, an organic polymer flocculant can be added (or increased). ..

Even if there is no fluctuation in water temperature, when the temperature rises such as in summer, a water temperature difference may occur between the part near the wall surface of the solid-liquid separation device 41 and the central part of the device, and this water temperature difference is also in a sedimentation state due to the density current. It leads to the disorder of. Therefore, the water temperature is measured at a plurality of locations, for example, locations where the distance from the wall surface of the apparatus main body 42 is different with the thermometer 57, and when the temperature difference δ _tp depending on the location exceeds a certain value δ _ts , the organic polymer flocculant is applied. It can also be added (or increased).

Furthermore, when the density current is generated on a daily basis only during a certain period such as summer, the organic polymer flocculant is added only during the period when the density current is generated, and the amount of the organic polymer flocculant is added during the other period. It is also possible to continuously add a fixed amount without control, or to not add an organic polymer flocculant.

Factors that worsen the sedimentation state are not limited to temperature (water temperature) and turbidity. Abnormality of sedimentation state is determined by detecting abnormalities of other factors such as inflow amount of water to be treated to coagulation sedimentation devices 2a to 2e, outside temperature, return (mud drainage) amount of slurry 35, and outflow amount of treated water. However, the interface 59 can be measured indirectly. Further, the combination of the interface meter 58 or other detection means (turbidity meter 56, thermometer 57) and the solid-liquid separation devices 31, 41, 51 is not limited to the one shown in the figure.

Next, examples of the present invention will be described, but the present invention is not limited to the following examples.

First, a specific example A in the case of circulating the slurry 35 will be described.

<Example A1: Effect of adding organic polymer flocculant on upward flow column>
In this example, as shown in FIG. 2, a treatment test was carried out in combination with a solid-liquid separator 31 having an upward flow column. Assuming river water as the water to be treated, kaolin was added to tap water to adjust the turbidity to 10 degrees. This water to be treated was supplied to the mixing pond (mixing tank 22) at a ratio of 3.2 L / min.

In the mixing tank 22, PAC was added so as to be 20 mg / L, and the mixture was stirred. The residence time of the mixing tank in Example A1 was set to 2 minutes. The stirring speed was set to 0.5 m / sec at the peripheral speed of the stirring blade.

After forming condensed flocs in the mixing tank 22, water to be treated was supplied to the flocs forming tank 24 having a volume of 16 L. In order to adjust the amount of inflow to the upward flow column, a part of the water to be treated that flowed out from the mixing tank 22 was discharged to the outside of the system as waste water for adjusting the flow rate.

In the floc forming tank 24, an organic polymer flocculant was added to the inflowing water to be treated. In this example, Ebagulose WA-542 (anionic organic polymer flocculant, manufactured by Swing Corporation, hereinafter simply referred to as WA-542) was added as an organic polymer flocculant. The addition rate of the organic polymer flocculant was set to 0.2 mg / L with respect to the water to be treated. The residence time in the flock forming tank 24 is set to about 7 minutes (upflow 200 mm / min), about 9 minutes (upflow 150 mm / min), and about 28 minutes (upflow 50 mm / min) depending on the upflow in the column 32. bottom. The stirring speed was set to 0.14 m / sec at the peripheral speed of the stirring blade.

In the floc forming tank 24, fine flocs and an organic polymer flocculant were mixed to form coarse flocs, and then water to be treated was supplied to an upward flow sedimentation pond (solid-liquid separation device 31). The upward flow sedimentation pond supplied the water to be treated from the upper part, and the water to be treated was flowed downward at the center well 33 in the column 32. The inner diameter of the column 32 was 120 mm, and the height of the entire column 32 was 1200 mm. The opening of the center well 33 was installed at a height of 580 mm from the bottom of the column 32. At the bottom of the column 32, a pipe for drawing out the slurry was installed, and a pipe for circulating the slurry drawn out by the roller pump to the floc forming tank 24 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).

FIG. 10 shows the turbidity of the treated water when the same experimental device was operated as a control system under the condition that no organic polymer flocculant was added. The upflow in the upward flow column was set to 50 mm / min and 100 mm / min.

In the system to which only the inorganic coagulant PAC was added, the average was 2.2 degrees at an upflow of 50 mm / min, 6.2 degrees at an upflow of 100 mm / min, and about the water turbidity to be treated at an upflow of 50 mm / min. Although 80% could be removed, only 40% was removed at 100 mm / min.

FIG. 11 shows the treated water turbidity in the system in which 0.2 mg / L of the organic polymer flocculant (WA-542) was added. Compared with the result without the organic polymer flocculant, the average turbidity of the treated water decreased to 0.5 degrees at the same upflow of 100 mm / min, and the quality of the treated water was significantly improved. Further, even at an upflow of 150 mm / min, the average turbidity was 1.2 degrees, although the variation in turbidity was large, and good water quality was obtained. On the other hand, when the upflow is 200 mm / min, the average turbidity increases to 3.1 ° C and the slurry interface in the column rises remarkably. Therefore, the upflow that can be tolerated under the conditions of Example A1 is 150 mm / min. It was about.

From the results of Example A1 above, by combining the step of adding the organic polymer flocculant after adding and stirring the inorganic coagulant and the slurry circulation step, sufficient treatment is possible even at a high speed of upflow of 150 mm / min. This proved that it was possible to reduce the size of the column (solid-liquid separation device) and tank, that is, the size of the entire coagulation sedimentation device.

<Example A2: Position where organic polymer flocculant is added>
In Example A2, the effect of changing the addition position of the inorganic coagulant (PAC) was investigated. The treated water turbidity when PAC was added to the floc forming tank 24 instead of the mixing tank 22 was compared with the result (addition of the mixing pond) at the upflow of 100 mm / min in Example A1.

In Example A2, as shown in FIG. 12, two flock forming tanks 24a and 24b are arranged side by side, a water tank having an opening at the lower part of the tank is used, and an inorganic coagulant (PAC) is used in the flock forming tank 24a on the upstream side. An organic polymer flocculant was added to the slurry and the floc forming tank 24b on the downstream side. The stirring speed in the upstream flock forming tank 24a was adjusted so as to be the same as the stirring speed for the inorganic coagulant of Example A1, and there was no significant difference in the stirring state.

The turbidity of the treated water is shown in FIG. The average turbidity of Example A1 in which PAC was added to the mixing tank 22 was 0.5 degrees, but the average turbidity of Example A2 in which PAC and circulating slurry were added to the upstream floc forming tank 24 was 2.4 degrees. The water quality deteriorated. In the structure of the water tank of Example A2, since the two tanks 24a and 24b are connected by an opening having a diameter much larger than that of the pipe or the like, the organic polymer flocculant added to the downstream floc forming tank 24b and the like. Since the flocs containing the organic polymer flocculant flow back into the upstream floc forming tank 24a and the circulating slurry itself is also supplied, the unreacted PAC reacts with the organic polymer flocculant or the circulating slurry, which is effective. It was considered that the PAC had decreased. For this reason, it was considered that fine flocs were not sufficiently formed, and uncondensed kaolin particles flowed out into the treated water as they were, resulting in an increase in turbidity.

On the other hand, in Example A1, the mixing tank 22 and the flock forming tank 24 are connected by a pipe, and the slurry of the flock forming tank does not flow back to the mixing tank 22 side. Therefore, it is considered that all the PACs added in the mixing tank are used for forming fine flocs, and the outflow of uncondensed kaolin particles is suppressed. Based on the above results, the PAC addition position and organic polymer agglomeration can be achieved by adding the inorganic (organic) coagulant and the organic polymer coagulant in a separate tank (device) separated by piping, etc., or by installing a backflow prevention means. It was shown that the position of addition of the agent is necessary for obtaining good water quality to be completely separated.

<Example A3: Example in which no slurry circulation is provided>
Example A3 had the same equipment configuration as Example A1 (FIG. 2), but compared with Example A1, the treatment test was carried out by eliminating the slurry circulation from the upward flow sedimentation pond (column). Other operating conditions are the same as in Example A1.

In Example A3, since the slurry was not circulated, the floc forming tank 24 had almost no flocs.

The average turbidity of the treated water when the upflow is 150 mm / min is shown in FIG. In Example A3 without slurry circulation, the average turbidity increased to 1.4 and the turbidity fluctuation became large. Therefore, compared with Example A1 in which circulation was performed, the water quality was more stable when slurry circulation was used in combination. It was shown to do.

When the floc forming tank 24 of Example A3 was observed, it was confirmed that the addition of the organic polymer flocculant had flocs, but the effect of colliding with each other and coarsening could not be expected. Therefore, when the flocs cannot be coarsened and the upflow is large, it is considered that the sedimentation speed of the flocs in the column 32 is lower than the upflow and the water quality deteriorates due to the outflow.
From this result, it was considered that by circulating the slurry to increase the floc concentration in the floc forming tank, coarsening of the flocs could be expected, leading to improvement in the sedimentation rate.

<Example A4: Amount of organic polymer flocculant added>
In Example A4, the effect of changing the amount of the organic polymer flocculant added was examined. In this test, Ebagulose WA-142 (anionic organic polymer flocculant, manufactured by Swing Corporation, hereinafter simply referred to as WA-142) was used as the organic polymer flocculant. Using the same equipment as in Example A1, the amount of WA-142 added was varied from 0.4 mg / L to 0.8 mg / L. The upflow in the upward flow column was set to 150 mm / min.

The turbidity of the treated water is shown in FIG. Under all the conditions of this example, the average turbidity was about 1 degree, and it was confirmed that good treated water quality could be obtained. It was shown that good water quality can be obtained within the range of the amount of the organic polymer flocculant added in this example. It was also confirmed that good treated water quality can be obtained even if the type of the organic polymer flocculant is changed from that of Example A1.

Next, a specific example B for controlling the addition of the organic polymer flocculant will be described.

<Example B1: Effect of improving sedimentation rate by adding organic polymer flocculant>
In Example B1, the effect of improving the sedimentation property of flocs by using an organic polymer flocculant in combination with the coagulation sedimentation treatment was compared and examined. As shown in FIG. 2, a test apparatus provided with an agglomeration portion provided with a mixing tank 22 and a floc forming tank 24 and a sedimentation portion using an upward flow column type solid-liquid separation device 31 was used, and the upper part of the sedimentation portion was used. The degree of expansion of the slurry interface was compared by changing the flow velocity. However, in this Example B1, the slurry 35 was not returned.

Assuming river water, simulated raw water in which kaolin was added to tap water so as to have a turbidity of 10 degrees was supplied to the test apparatus as water to be treated. In the mixing tank 22, simulated raw water was supplied at a flow rate of 3.2 L / min, and the inorganic coagulant PAC (250A manufactured by Taki Chemical Co., Ltd.) was added at a rate of 20 mg / L. A part of the outflow water from the mixing tank 22 was discarded according to the upward flux and supplied to the floc forming tank 24. As the organic polymer flocculant, an anionic organic polymer flocculant (WA-542 manufactured by Swing Corporation) was added at a predetermined ratio, mixed in the floc forming tank 24, and then supplied to the column 32. The inner diameter of the column 32 was 120 mm.

The column 32 is filled with the slurry 35 adjusted in advance under each addition condition so that the amount of kaolin is the same, and the upward flux is set to two types, 50 mm / min and 100 mm / min, in a stable state. The height of the slurry interface in the column 32 was measured.

FIG. 16 shows the slurry interface height under each condition together with the addition amount (0.2 mg / L, 0.4 mg / L) of the organic polymer flocculant. When the organic polymer flocculant was added, the interface height was about 800 to 900 mm for both the upward flux of 50 mm / min and 100 mm / min under the "PAC alone" condition in which only PAC was added. The interface height remained below about 300 mm. From this result, it was confirmed that the sedimentation rate of the flocs increased and the interface decreased when the organic polymer flocculant was used in combination.

<Example B2: Effect of improving sedimentation rate by adding organic polymer flocculant>
In Example B2, the sedimentation state of the flocs was compared by changing the upward flux with the apparatus shown in FIG. Assuming river water, simulated raw water in which kaolin was added to tap water so as to have a turbidity of 10 degrees was supplied to the test apparatus as water to be treated. In the mixing tank 22, simulated raw water was supplied at a flow rate of 3.2 L / min, and the inorganic coagulant PAC (250A manufactured by Taki Chemical Co., Ltd.) was added at a rate of 20 mg / L.

A part of the outflow water from the mixing tank 22 was discarded according to the upward flux and supplied to the floc forming tank 24. An anionic organic polymer flocculant (WA-542 manufactured by Swing Corporation) was added in a predetermined ratio, mixed in the floc forming tank 24, and then supplied to a column 32 having an inner diameter of 120 mm. In Example B2, the column was not filled with slurry in advance, and water to be treated was supplied. In addition, the slurry 35 was not returned. The results are shown in FIG.

With the addition of PAC alone, the turbidity of the treated water increased with the increase in the upward flux, indicating that the sedimentation rate of flocs was small. Further, at a WA-542 addition rate of 0.1 mg / L, the treated water turbidity increased as the upward flux increased, indicating that the floc sedimentation rate was small at this addition rate.

On the other hand, when the WA-542 addition rate is 0.2 mg / L, the upward flux is 150 mm / min, and when the WA-542 addition rate is 0.4 mg / L, the treated water turbidity is stable up to 200 mm / min. At these addition rates, it was shown that the floc settling rate was improved by the addition of the organic polymer flocculant, and that the floc settled despite the high upward flux. Therefore, it is presumed that the sedimentation state of flocs is improved when the organic polymer flocculant is used in a certain amount (eg, 0.2 mg / L or more).

<Example B3: Effect of improving sedimentation rate by adding an organic polymer flocculant in highly turbid raw water>
In Example B3, assuming a case where the turbidity increases in river water, kaolin is added to tap water for which the effect of adding an organic polymer flocculant has been examined, and the water to be treated is adjusted so that the turbidity becomes about 100 degrees. Was used.
PAC (250A manufactured by Taki Chemical Co., Ltd.) was added to 500 mL of the water to be treated at a ratio of 60 mg / L, and the mixture was stirred at a speed of 150 rpm for 3 minutes using a paddle blade stirrer having a diameter of 80 mm. After stirring for 3 minutes, an anionic organic polymer flocculant (WA-542 manufactured by Mizuing), which is an organic polymer flocculant, was added at a ratio of 0.2 mg / L and 0.4 mg / L, and the speed was 150 rpm. Was stirred for 1 minute.

After the completion of stirring at 150 rpm for 1 minute, all the systems were stirred at 50 rpm for 10 minutes to form flocs, and then the sedimentation rates of flocs were compared. The results are shown in Table 1. It was confirmed that the sedimentation rate was increased by the addition of the organic polymer flocculant even in water with high turbidity.

From Examples B1 to B3, it was confirmed that the sedimentation state was improved by adding an appropriate amount of the organic polymer flocculant. It is presumed that the interface position will be stable due to the improvement of this sedimentation state.

1a to 1c, 2a to 2e: Coagulation and precipitation devices 31, 41, 51: Solid-liquid separation device 12: Coagulant supply means 14: Coagulant supply means 22: Mixing tanks 24, 24a, 24b: Flock forming tank 25: Return means 32: Column 33: Center well 35: Slurry 42: Device main body 43: Outer draft tube 44: Inner draft tube 45: Stirrer 47: Stirrer 48: Forming section 49: Sedimentation section 52: Sedimentation tank 55: Control section 56: Turbidity meter 57: Thermometer 58: Interface meter 59: Interface

Claims (6)

At least one of an inorganic coagulant and an organic coagulant is added to the water to be treated, and the mixture is stirred and mixed to form fine flocs.
An organic polymer flocculant is added to the water to be treated on which fine flocs are formed, and the mixture is further stirred and mixed to grow fine flocs to form coarse flocs.
In the coagulation sedimentation method in which the coarse flocs are precipitated and solid-liquid separated into a slurry and a supernatant.
At least a part of the slurry is returned to one or more of the place where the organic polymer flocculant is added and one place downstream of the place where the organic polymer flocculant is added to circulate the coarse flocs.
The amount of the organic polymer flocculant added is controlled according to the interface height of the slurry in which the coarse flocs have settled, and the volume ratio of the returned amount to 0.2 to 0.8 times the inflow amount of the water to be treated. A coagulation sedimentation method characterized by promoting the formation of the coarse flocs and improving the sedimentation property of the flocs. At least one of an inorganic coagulant and an organic coagulant is added to the water to be treated, and the mixture is stirred and mixed to form fine flocs.
An organic polymer flocculant is added to the water to be treated on which fine flocs are formed, and the mixture is further stirred and mixed to grow fine flocs to form coarse flocs.
In the coagulation sedimentation method in which the coarse flocs are precipitated and solid-liquid separated into a slurry and a supernatant.
At least a part of the slurry is returned to one or more of the place where the organic polymer flocculant is added and one place downstream of the place where the organic polymer flocculant is added to circulate the coarse flocs.
The sludge volume due to the circulation of the slurry is measured, and the measured value is maintained at 10 to 15% in the case of the coarse floc-forming slurry and 40 to 60% in the case of the solid-liquid separation circulation slurry. Indirectly, the interface height of the slurry was measured.
A coagulation-sedimentation method, which comprises controlling the amount of the organic polymer flocculant added to improve the sedimentation property of the flocs. At least one of an inorganic coagulant and an organic coagulant is added to the water to be treated, and the mixture is stirred and mixed to form fine flocs.
An organic polymer flocculant is added to the water to be treated on which fine flocs are formed, and the mixture is further stirred and mixed to grow fine flocs to form coarse flocs.
In the coagulation sedimentation method in which the coarse flocs are precipitated and solid-liquid separated into a slurry and a supernatant.
At least a part of the slurry is returned to one or more of the place where the organic polymer flocculant is added and one place downstream of the place where the organic polymer flocculant is added to circulate the coarse flocs.
A coagulation-sedimentation method characterized by controlling the amount of the organic polymer flocculant added based on the measurement results of the interface height of the slurry and the temperature of the slurry before return to improve the sedimentation property of the flocs. A coagulant supply means for adding at least one of an organic coagulant and an inorganic coagulant to the water to be treated,
A coagulant supply means for supplying an organic polymer coagulant to water to be treated to which at least one of the organic coagulant and the inorganic coagulant has been added.
A floc forming tank that agitates the water to be treated to which the organic polymer flocculant is added, and
A solid-liquid separator installed on the downstream side of the floc forming tank to separate the water to be treated into a slurry and a supernatant.
The slurry of the solid-liquid separation device is returned to one or more of the flow paths between the flock forming tank, the solid-liquid separating device, and the solid-liquid separating device and the flock forming tank to generate flocs. Circulating return means and
A control unit that directly or indirectly measures the slurry interface and slurry temperature of the solid-liquid separator and controls the coagulant supply means based on the measurement results.
A coagulation sedimentation device characterized by having . The solid-liquid and a thermometer installed in the separation device, and any one or more of the selected solid-liquid interface meter installed in the separation apparatus and the or turbidimeter to measure the turbidity of the water to be treated, et al, The coagulation / sedimentation apparatus according to claim 4 , wherein the control unit is connected to the coagulation / sedimentation apparatus. The coagulation / precipitation device according to claim 4 or 5, wherein the solid-liquid separation device is selected from a solid-liquid separation device including an upward flow column and a high-speed coagulation / precipitation device.

Images