1. A complex flocculant water-treating solution that removes impurities from feed water, the complex flocculant water-treating solution essentially consisting of: at least two types of flocculants, at least one of the flocculants is an inorganic flocculant and at least one of the flocculants is an organic flocculant.

2. The complex flocculant water-treating solution according to Claim 1, wherein the inorganic flocculant includes trivalent metal ions, and the organic flocculant includes an anionic polymer.

3. The complex flocculant water-treating solution according to Claim 1 or 2, wherein a pH is 3 or lower.

4. A water treatment apparatus comprising: a water intake section that introduces feed water including impurities; a flocculating section that adds a complex flocculant water-treating solution stored in a flocculant tank to the feed water to obtain a mixed solution; and a flocculate removing section that removes flocculate including the impurities that is formed in the feed water due to addition of the complex flocculant water-treating solution, wherein the complex flocculant water-treating solution essentially consists of at least two types of flocculants, at least one of the flocculants being an inorganic flocculant and at least one of the flocculants being an organic flocculant.

5. The water treatment apparatus according to Claim 4, wherein the flocculating section includes a flocculation basin into which the water intake section introduces the feed water, and the flocculation basin is connected to the flocculant tank such that the complex flocculant water-treating solution in the flocculant tank is supplied to the flocculation basin.

6. The water treatment apparatus according to Claim 4, wherein the flocculant tank is connected to a pipe through which the feed water flows.

7. The water treatment apparatus according to any one of Claims 4 to 6, further comprising a pH adjusting section that adds an alkaline solution or an acidic solution to the mixed solution of the feed water and the complex flocculant water-treating solution and thereby adjusts a pH of the mixed solution.

8. The water treatment apparatus according to any one of Claims 4 to 7, further comprising a desalinating section that removes salts from the feed water from which the flocculate has been removed.

9. The water treatment apparatus according to any one of Claims 4 to 8, wherein the number of flocculant tank included is one.

10. The water treatment apparatus according to any one of Claims 7 to 9, wherein the pH adjusting section neutralizes a pH of the mixed solution.

11. The water treatment apparatus according to any one of Claims 4 to 10, wherein the feed water is seawater.

12. A water treatment method comprising: introducing feed water including impurities; adding a complex flocculant water-treating solution to the feed water to obtain a mixed solution; and removing flocculate including the impurities that is formed in the feed water due to addition of the complex flocculant water-treating solution, wherein the complex flocculant water-treating solution essentially consists of at least two types of flocculants, at least one of the flocculants being an inorganic flocculant and at least one of the flocculants being an organic flocculant.

13. The water treatment method according to Claim 12, Wherein the introducing includes introducing the feed water into a flocculation basin, and the adding includes adding the complex flocculant water-treating solution to the flocculation basin.

14. The water treatment method according to Claim 12, wherein the adding includes adding the complex flocculant water-treating solution to the feed water that is flowing through a pipe.

15. The water treatment method according to any one of Claims 12 to 14, further comprising adjusting a pH of the mixed solution of the feed water and the complex flocculant water-treating solution by adding an alkaline solution or an acidic solution to the mixed solution.

16. The water treatment method according to any one of Claims 12 to 15, further comprising desalinating by removing salts from the feed water from which the flocculate has been removed.

17. The water treatment method according to Claim 15 or 16, wherein the adjusting includes neutralizing a pH of the mixed solution.

18. The water treatment method according to any one of Claims 12 to 17, wherein the feed water is seawater.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a complex flocculant solution that is added to raw water containing organic and inorganic impurities so as to remove the impurities by causing the impurities to flocculate and settle, and also to an apparatus and a method for treating water by using this solution.

2. Description of the Related Art

Conventionally, water purification technology for producing potable water and public use water from natural water such as river water includes chemical treatment such as flocculation settlement and physical treatment such as sand filtration.

Microfiltration (MF) membranes and ultrafiltration (UF) membranes are also used in the filtration process to remove finer impurities. By adopting a flocculant in the filtration process, the particle size of the impurity particles that pass through the filtration membrane can be increased leading to higher performance.

Recently, water shortage has caused a great challenge all over the world, especially in Middle Eastern and Asian countries. To address this challenge, a technology for desalinating seawater to produce potable water and public use water has become a focus of attention and is now being put into practical use. In this technology, an evaporation method is used to obtain fresh water. In the evaporation method, seawater is heated to evaporate the water and obtain steam, and then the steam is cooled to obtain fresh water. This method is advantageous in its unaffectedness by salt concentration or organic matter concentration in seawater, and therefore has been mainstream.

The evaporation method, however, has drawbacks of low energy efficiency and high costs. Therefore, there has been a need for a more efficient method. Nowadays, reverse osmosis method is becoming mainstream. In the reverse osmosis method, seawater is desalinated by filtration through a reverse osmosis membrane (RO membrane) to obtain fresh water.

In the reverse osmosis method, however, organic and inorganic impurities in the seawater contaminate the RO membrane and reduce its filtering capacity. This necessitates frequent replacement of the RO membrane and leads to an increase in the cost of producing fresh water in the apparatus.

To prevent the RO membrane from being contaminated, suitable pretreatment needs to be performed on the seawater before filtering the seawater through the RO membrane to remove turbid matters, organic matters, and the like. As the pretreatment method, UF or MF membrane filtration, use of an absorbent such as activated carbon, and use of a flocculant have been considered, in the same manner as in the water purification method.

In general, the efficiency of the sand-filtration or membrane-filtration water treatment processes can be enhanced by adding a flocculant.

Typical flocculants adopted in wastewater treatment and water purification include inorganic flocculants using polyvalent metal ions (cations) such as polyaluminum chloride (PAC) and iron chloride, and organic flocculants {polymer flocculants) using water soluble polymers that have polyvalent ions. Such flocculants remove electrically-charged impurities from the water through flocculation settlement. If a sufficient effect cannot be obtained by using one of the organic and inorganic flocculants, both the flocculants are used to enhance the flocculation effect.

As discussed above, the flocculants can be divided mainly into an inorganic type and an organic type. Inorganic flocculants include PAC and iron chloride, while organic flocculants include cationic, anionic, or non-ionic polymers. Recently, hundreds of types of flocculants are commercially available for treatment of water of various qualities.

Which flocculant to use is decided based on the quality of the water that is to be treated, and in most cases, any of the inorganic type and the organic type can be used. In some cases, however, both the types are used. Generally, if an inorganic flocculant alone does not produce a sufficient flocculant settlement effect, both the types of flocculants are used to enhance the effect.

Japanese Patent Application Laid-open No. 2005-324148 discloses combined use of inorganic and organic flocculants. This patent document teaches flocculation treatment in which an inorganic flocculant such as PAC, aluminum sulfate, ferrous sulfate, ferric sulfate, and ferric chloride, a cationic, anionic, or non-ionic polymer flocculant, an agent such as activated carbon that gives some weight to suspended solids that have become floe in order to help them settle, and, if necessary, a pH adjuster are added to raw water.

Japanese Patent Application Laid-open No. 2008-264723 discloses an impurity flocculation method, with which two types of flocculants are added into raw water in two different flocculation basins, and flocculation conditions are controlled in accordance with different water quality indices.

Japanese Patent Application Laid-open No. Hll-104696 discloses a pure water production method that includes a flocculation step of adding an inorganic flocculant into raw water in a single neutralization and flocculation basin and also adding a return sludge containing a polymer flocculant thereto to bring about flocculating reaction.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a complex flocculant water-treating solution that can be easily stored even if it is obtained by combining different flocculants into one solution, and also a water treatment apparatus that has a simple structure and low water producing costs (running costs).

According to an aspect of the present invention, a complex flocculant water-treating solution essentially consists of at least two types of flocculants. At least one of the flocculants is an inorganic flocculant, and at least one of the flocculants is an organic flocculant.

According to another aspect of the present invention, a water treatment apparatus includes a water intake section that introduces feed water including impurities; a flocculating section that adds a complex flocculant water-treating solution stored in a flocculant tank to the feed water to obtain a mixed solution; and a flocculate removing section that removes flocculate including the impurities that is formed in the feed water due to addition of the complex flocculant water-treating solution. The complex flocculant water-treating solution essentially consists of at least two types of flocculants. At least one of the flocculants is an inorganic flocculant, and at least one of the flocculants is an organic flocculant.

According to another aspect of the present invention, a water treatment method includes introducing feed water including impurities; adding a complex flocculant water-treating solution to the feed water to obtain a mixed solution; and removing flocculate including the impurities that is formed in the feed water due to addition of the complex flocculant water-treating solution. The complex flocculant water-treating solution essentially consists of at least two types of flocculants. At least one of the flocculants is an inorganic flocculant, and at least one of the flocculants is an organic flocculant.

The above and other objects, features, advantages and the technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic diagram of a water treatment apparatus according to an embodiment of the present invention;

FIG. 1B is a schematic diagram of a modification of the water treatment apparatus shown in FIG. 1A;

FIG. 1C is a schematic diagram of another modification of the water treatment apparatus shown in FIG. 1A;

FIG. 2A is a schematic diagram of a flocculating section having a flocculation basin;

FIG. 2B is a schematic diagram of pipe arrangement for the flocculating section;

FIG. 2C is a schematic diagram of a modification of the flocculating section shown in FIG. 2A;

FIG. 3 is a schematic diagram of a pH adjusting section;

FIG. 4A is a schematic diagram for explaining a treatment process performed by the flocculating section that has the flocculation basin;

FIG. 4B is a schematic diagram for explaining a treatment process performed in a pipe of the flocculating section;

FIG. 5A is a schematic diagram for explaining the action of a flocculant when a pH value is high; and

FIG. 5B is a schematic diagram for explaining the action of the flocculant when a pH value is low.

DETAILED DESCRIPTION

The present invention relates to a flocculant solution (complex flocculant water-treating solution} that is added to raw water containing organic and inorganic impurities to remove the impurities by causing the impurities to flocculate and settle, and a water treatment apparatus and a water treatment method that use this solution to treat water. More specifically, the present invention relates to a complex flocculant solution that is prepared from both an inorganic flocculant and a polymer flocculant (organic flocculant) and exhibits a high impurity removal rate, and also to water treatment that uses this solution. With the complex flocculant solution, treated water can be obtained at low cost.

The complex flocculant solution (complex flocculant water-treating solution) indicates a solution obtained by mixing an inorganic flocculant and an organic flocculant such as a cationic, anionic, non-ionic polymer flocculant of an ionic polymer material and a bipolar polymer flocculant. Two kinds or more of inorganic flocculants or organic flocculants can be selected and mixed from the same type or different types.

Exemplary embodiments of the complex flocculant water-treating solution, and the water treatment apparatus and the water treatment method that adopt this solution to treat water are now explained in detail below with reference to accompanying drawings.

The complex flocculant water-treating solution that removes impurities from feed water essentially consists of at least two types of flocculants, at least one of the flocculants is an inorganic flocculant and at least one of the flocculants is an organic flocculant. The inorganic flocculant and the organic flocculant are preferably dissolved in water. A solution can be such that the inorganic flocculant and the organic flocculant in solid state are dispersed into an already saturated solution of the inorganic flocculant and the organic flocculant. When such a solution is added to the feed water, the feed water serves as a solvent and dissolves the solid-state flocculants. Alternatively, the inorganic flocculant and the organic flocculant can be encapsulated in such a manner as to be soluble in water or seawater. The inorganic flocculant and the organic flocculant can be encapsulated in separate capsules.

In the complex flocculant water-treating solution, it is preferable that the inorganic flocculant includes trivalent metal ions and that the organic flocculant includes an anionic polymer.

In the complex flocculant water-treating solution, it is preferable that a pH is 3 or lower.

The water treatment apparatus includes a water intake section that introduces feed water including impurities; a flocculating section that adds a complex flocculant water-treating solution stored in a flocculant tank to the feed water to obtain a mixed solution; and a flocculate removing section that removes flocculate including the impurities that is formed in the feed water due to addition of the complex flocculant water-treating solution, wherein the complex flocculant water-treating solution essentially consists of at least two types of flocculants, at least one of the flocculants being an inorganic flocculant and at least one of the flocculants being an organic flocculant.

In the water treatment apparatus, it is preferable that the flocculating section includes a flocculation basin into which the water intake section introduces the feed water and that the flocculation basin is connected to the flocculant tank such that the complex flocculant water-treating solution in the flocculant tank is supplied to the flocculation basin.

In the water treatment apparatus, it is preferable that the flocculant tank is connected to a pipe through which the feed water flows.

It is preferable that the water treatment apparatus further includes a pH adjusting section that adds an alkaline solution or an acidic solution to the mixed solution of the feed water and the complex flocculant water-treating solution and thereby adjusts a pH of the mixed solution.

It is preferable that the water treatment apparatus further includes a desalinating section that removes salts from the feed water from which the flocculate has been removed.

In the water treatment apparatus, it is preferable that the number of flocculant tank included is one.

In the water treatment apparatus, it is preferable that the pH adjusting section neutralizes the mixed solution.

For the water treatment apparatus, the feed water can be any water that can be fed to reverse osmosis (RO), such as seawater, river water, groundwater, and sewage water. Seawater is the most preferable.

The water treatment method includes introducing feed water including impurities; adding a complex flocculant water-treating solution to the feed water to obtain a mixed solution; and removing flocculate including the impurities that is formed in the feed water due to addition of the complex flocculant water-treating solution, wherein the complex flocculant water-treating solution essentially consists of at least two types of flocculants, at least one of the flocculants being an inorganic flocculant and at least one of the flocculants being an organic flocculant.

In the water treatment method, it is preferable that the introducing includes introducing the feed water into a flocculation basin, and the adding includes adding the complex flocculant water-treating solution to the flocculation basin.

In the water treatment method, it is preferable that the adding includes adding the complex flocculant water-treating solution to the feed water that is flowing through a pipe.

The water treatment method further includes adjusting a pH of the mixed solution of the feed water and the complex flocculant water-treating solution by adding an alkaline solution or an acidic solution to the mixed solution.

The water treatment method further includes desalinating by removing salts from the feed water from which the flocculate has been removed.

In the water treatment method, it is preferable that the adjusting includes neutralizing the mixed solution.

In the water treatment method, it is preferable that the feed water is seawater.

The water treatment apparatus that adopts the complex flocculant water-treating solution is explained in detail below with reference to the accompanying drawings.

FIGS. 1A to1c are schematic diagrams of the water treatment apparatus according to an embodiment of the present invention.

The simplest structure, which is meant for treatment of fresh water such as river water, is shown in FIG. 1A.

As shown in FIG. 1A, a water treatment apparatus 100 includes a water intake section 101, a flocculating section 102, and a flocculate removing section 103. Impurities are removed from the feed water 1 when the feed water 1 passes sequentially through the water intake section 101, the flocculating section 102, and the flocculate removing section 103. Consequently, the feed water 1 becomes clean water.

In the structure shown in FIG.1B, a desalinating section is provided so that salt-containing water such as seawater can be treated.

The water treatment apparatus 100 shown in FIG. IB includes the water intake section 101, the flocculating section 102, the flocculate removing section 103, and a desalinating section 104. Feed water 51 is seawater. Impurities are removed from the feed water 51 when the feed water 51 passes sequentially through the water intake section 101, the flocculating section 102, the flocculate removing section 103, and the desalinating section 104. Consequently, the feed water 51 becomes fresh water.

In the structure shown in FIG. 1C, a pH adjusting section is added to the structure shown in FIG.1B.

The water treatment apparatus 100 shown in FIG. 1C includes a pH adjusting section 105 between the flocculating section 102 and the flocculate removing section 103. The feed water 51 is seawater. Impurities are removed from the feed water 51 when the feed water 51 passes sequentially through the water intake section 101, the flocculating section 102, the pH adjusting section 105, the flocculate removing section 103, and the desalinating section 104. Consequently, the feed water 51 becomes fresh water.

The sections of the water treatment apparatus 100 are explained in detail below.

Water Intake Section

The water intake section 101 shown in FIGS. 1A to 1C pumps the feed water 1, or 51, into the water treatment apparatus 100. The type of a pump is not particularly limited, and a velocity (turbo) pump, a positive displacement pump, or other special pumps can be adopted. More specifically, examples of the pumps include a magnetic pump, a plunger pump, a screw pump, a diaphragm pump, a diffuser pump, a gear pump, a piston pump, a rotary pump, a tube pump, and a submersible pump. Other pumps that are not mentioned here are also applicable.

Flocculating Section

Two types of the flocculating section 102 can be used in FIGS. 1A to 1C. One that has a flocculation basin and the other that injects and adds a flocculant directly into the pipe into which the feed water flows.

The flocculating section 102 shown in FIG. 2A is a type that has the flocculation basin.

As shown in FIG. 2A, the flocculating section 102 includes a complex flocculant storage basin 3 (flocculant tank) and a flocculation basin 5. A complex flocculant 9 prepared from two types or more of flocculants (by either mixing or dispersing them into one solution) is stored in the complex flocculant storage basin 3. The flocculation basin 5 includes an agitation mechanism 6 and a submersible pump 7. The feed water 1 is introduced into the flocculation basin 5 through a feed water introduction pipe 4, and the complex flocculant 9 is injected into the flocculation basin 5 through a drip nozzle 10. The agitation mechanism 6 sufficiently mixes the feed water 1 and the complex flocculant 9 and makes the concentration uniform in the flocculation basin 5. A propeller type of the agitation mechanism 6 is shown in FIG. 2A; however, a mechanism that uses a water stream from the pump, a stream of water intake, or the like can be adopted. Alternatively, a static mixer can be adopted to perform inline processing.

The feed water 1 that includes flocculate is supplied to the flocculate removing section 103 through a pipe 8. The submersible pump 7 adopted here is a mere example. That is, a pump that has a power unit such as a motor arranged outside the flocculation basin 5 can be adopted instead.

In the flocculating section 102 shown in FIG. 2A, a controller manages and automatically controls a dripping speed of the complex flocculant 9 and the volume of the complex flocculant 9 stored in the complex flocculant storage basin 3. The complex flocculant 9 can be continuously injected, or can be intermittently injected by opening and closing a cock 11. The injection volume can be varied by adjusting the opening of the cock 11. When the complex flocculant 9 is intermittently injected, it is preferable that the feed water 1 is quickly agitated by the agitation mechanism 6 after dripping so that the complex flocculant 9 is sufficiently dispersed. Thereafter, it is preferable that the complex flocculant 9 is gently agitated to promote effective flocculate formation.

The flocculant is usually in the form of a solution; however, solid flocculants can be used. When the flocculant is in a solid state, it is added to the water in the complex flocculant storage basin 3 and dissolved. If a solid flocculant is to be used, a water supply pipe, a feeder that supplies different flocculants, and an agitation mechanism that agitates the complex flocculant 9 need to be provided in the complex flocculant storage basin 3. Such an agitation mechanism can be used also for mixing two or more flocculants.

In addition, regardless of presence/absence of the agitation mechanism 6, it is effective and preferable to arrange multiple drip nozzles 10 in order to readily disperse the complex flocculant 9 throughout the feed water 1.

It is preferable that the complex flocculant 9 is acidic, and that the complex flocculant storage basin 3 and the drip nozzle 10 are formed of acid-resistant materials. Examples of the acid-resistant materials include acid-resistant stainless steel and acid-resistant resins. Besides these materials, any material that has acid resistance sufficient to store the complex flocculant 9 can be used.

FIG. 2C is a schematic diagram of a modification of the flocculating section shown in FIG. 2A.

In the drip nozzle 10 shown in FIG. 2C, a pump 211 is arranged in place of the cock 11 shown in FIG. 2A. The rest of the structure is the same as that of FIG. 2A.

The injection of the complex flocculant 9 can be controlled by turning the pump 211 on/off. The pumping rate of the pump 211 can be adjusted by controlling the number of revolutions of its motor.

The flocculation basin 5 need not necessarily be provided in the flocculating section 102. When the flocculation basin 5 is absent, the complex flocculant 9 is added directly to the feed water 1 that is flowing through a pipe.

FIG. 2B is a schematic diagram of the pipe arrangement in the flocculating section 102.

The flocculating section 102 shown in FIG. 2B is arranged such that the complex flocculant 9 is injected from the complex flocculant storage basin 3 through the drip nozzle 10 directly to a pipe 14 through which the feed water 1 flows. The injection volume of the complex flocculant 9 can be adjusted by the cock 11.

The pipe 14 or the like is preferably ingeniously designed so as to assist formation of flocculate. One approach is to form projections on an inner wall of the pipe 14. Another approach is to use a tapering pipe whose inner diameter increases in steps in the downstream direction.

pH Adjusting Section

The pH adjusting section 105 shown in FIG. 1C adjusts the hydrogen ion concentration (pH) of the feed water 51 (mixed solution) into which the complex flocculant 9 has been added.

FIG. 3 is a schematic diagram of the pH adjusting section 105.

The pH adjusting section 105 shown in FIG. 3 includes a pH adjusting liquid storage basin 16 in which an acidic or alkaline pH adjusting liquid 17 is stored, an injection nozzle 18 connected to a pipe 114, and a cock 19. With this structure, the pH adjusting liquid 17 can be injected into feed water 131 flowing through the pipe 114. It is preferable, from a view point of preventing acids and alkalis from spattering, that the injection nozzle 18 is connected directly to the pipe 114 through which the feed water 131 flows. It is also preferable that multiple injection nozzles 18 are provided so that the pH adjusting liquid 17 can be injected and distributed from multiple positions.

Because the complex flocculant 9 that is strongly acidic is preferably used, the feed water 131 after adding the complex flocculant 9 often becomes acidic, and therefore an alkaline solution is usually used as the pH adjusting liquid 17. More specifically, the pH adjusting liquid 17 is, for example, aqueous sodium hydroxide.

It is also possible that the feed water 131 becomes alkaline after addition of the complex flocculant 9, depending on the volume of complex flocculant 9 added and the acidity/alkalinity of the feed water 131. In such a situation, an acidic solution can be stored in the pH adjusting liquid storage basin 16. More specifically, the pH adjusting liquid 17 is, for example, a hydrochloric acid solution.

One more storage basin can be provided in the pH adjusting section 105 so that both alkaline and acidic solutions can be prepared simultaneously. Furthermore, the pH adjusting section 105 can be given functions of detecting the acidity/alkalinity of the feed water 131 and automatically injecting a suitable volume of acidic solution or alkaline solution to adjust the pH level to neutral. The neutral level here indicates the pH being between 6 and 8.

It is further preferable that the pH adjusting section 105 is arranged adjacent to the flocculating section 102 on the downstream side thereof as shown in FIG. 1C and that the pH adjustment is performed immediately after adding and uniformly dispersing the complex flocculant 9.

In addition, the pH adjusting section 105 can be incorporated within the flocculating section 102. This structure can improve the accuracy of the pH level adjustment and facilitate suitable adjustment of the supply volume of flocculant.

Flocculate Removing Section

The flocculate formed due to addition of the complex flocculant 9 is removed in the flocculate removing section 103 shown in FIGS. 1A to 1C The removal is performed mainly by filtration, which can be sand filtration, multimedia filtration, microfiltration, or ultrafiltration. A suitable filtration method can be selected depending on the shape and strength of the flocculate. Any other removal method can be adopted for the flocculate removing section 103, such as decantation for collecting supernatant liquid and magnetic separation.

Desalinating Section

The desalinating section 104 shown in FIGS. IB and 1C removes salts from the feed water 51 to produce fresh water. Desalination is usually performed by using a semipermeable membrane such as a reverse osmosis (RO) membrane and a forward osmosis (FO) membrane. Membranes of various materials and shapes have been contrived; however, the membrane is not limited to any specific material or shape, and any membrane that has a desalinating function can be adopted for the desalinating section 104.

Complex flocculant

The complex flocculant 9 contains at least two types among an inorganic flocculant, a polymer flocculant, a low-molecular organic flocculant, and other flocculants. It is preferable that those flocculants, when they are mixed, do not produce any flocculate and form a clear and uniform liquid.

Specific examples of the flocculants are given below.

An inorganic flocculant can be polyaluminum chloride (PAC), aluminum sulfate, ferric chloride, ferric sulfate, and aluminum chloride. A polymer flocculant can be a polyacrylamide type, a polysulfonate type, a polyacrylic acid, a polyacrylate ester, a polyamine type, and a polymethacrylate type. A low-molecular organic flocculant (coagulant) and the like can also be used for a complex flocculant.

The above are typical examples of flocculants, and the present invention is not limited thereto. Any substance that can serve as a flocculant, such as metal ions, ionic polymer, and an ionic organic compound, can be used.

The molar weight of the polymer flocculant is also not limited to any specific molar weight. The complex flocculant 9 of a cationic flocculant and an anionic flocculant, in particular, is preferable from a viewpoint of its capability of flocculating and removing both a negative charge and a positive charge in the water. The optimal flocculation effect can be achieved in accordance with the type of water by changing the proportion of the cationic flocculant and the anionic flocculant.

When a cationic flocculant and an anionic polymer are used, their solution should be kept acidic so that hydrogen ions can be prevented from being dissociated from the acidic group and the anionic polymer can be prevented from being ionized. In this manner, the cationic flocculant and the anionic polymer can be stably preserved as a solution without producing any flocculate. The acidity here denotes the pH being lower than 6. Preferably, the pH of the complex flocculant 9 is 3 or lower from the viewpoint of its stability, and 2 or lower from the viewpoint of its effectiveness.

The order of preparing the complex flocculant 9 is not limited to any specific order; however, to suppress the interaction of the anionic polymer and the inorganic flocculant, it is preferable that the inorganic flocculant is added after a solution of the anionic polymer flocculant is acidified with a hydrochloric acid solution or the like.

Flocculation Method

FIG. 4A is a diagram for explaining the process performed by the flocculating section 102 that includes the flocculation basin 5.

As shown in FIG. 4A, first, (a) a certain volume of feed water 1 is introduced to the flocculation basin 5 through the feed water introduction pipe 4. Next, (b) a suitable volume of complex flocculant 9 is added from the complex flocculant storage basin 3 to the flocculation basin 5 containing the feed water 1, and the feed water 1 is quickly agitated by the agitation mechanism 6 so that the complex flocculant 9 can be uniformly distributed. Thereafter, the agitation is slowed down to form flocculate 20. Then, (c) the agitation is stopped to allow the flocculate 20 to settle, and the treated water is collected through the pipe 8.

FIG. 4B is a diagram for explaining the process performed in the pipe 14 of the flocculating section 102.

As shown in FIG. 4B, first, (a) the feed water 1 is supplied to the pipe 14 at a constant rate. Next, (b) the complex flocculant 9 is injected from the complex flocculant storage basin 3 directly to the pipe 14 through the drip nozzle 10 so that (c) the flocculate 20 is formed. The structure of the pipe 14, or the inner wall of the pipe 14, can be ingeniously designed so as to assist formation of the flocculate 20. For example, projections can be formed on the inner wall of the pipe 14, or a tapered pipe whose inner diameter increases in steps toward the downstream side can be adopted as the pipe 14.

The action of the flocculant is explained below with reference to the drawings.

In the following example, the inorganic flocculant and the organic flocculant used in the complex flocculant 9 are trivalent iron chloride and polyaerylie acid, respectively.

FIG. 5A is a diagram for explaining the action of the flocculant whose pH is 5 or higher.

When the pH is high as shown in {a} of FIG. 5A, polyacrylic acid 61 tends to be ionized in the solution. That is, hydrogen ions are dissociated from the carboxyl group of the polyacrylic acid 61, which increases ionized functional groups. On the other hand, the iron chloride is dissolved, from which chloride ions and iron ions are dissociated. Consequently, the ionized carboxyl groups and the iron ions tend to be bound through electrostatic interaction 62. In addition, iron ions tend to form sediment of ferric hydroxide because the pH is high.

As shown in (b) of FIG. 5A, even when seawater or the like that contains organic matters such as acidic sugars 63 as impurities is mixed with the complex flocculant solution, bonding of the carboxyl groups of the acidic sugars 63 and the iron ions tends not to occur because there are few free iron ions. This makes it difficult to flocculate the impurities.

FIG. 5B is a schematic diagram for explaining the action of the flocculant whose pH is 3 or lower.

When the pH is low as shown in (a) of FIG. 5B, the polyacrylic acid 61 tends not to be ionized in the solution. That is, hydrogen ions tend not to be dissociated from the carboxyl groups of the polyacrylic acid 61, and therefore there are few ionized functional groups. On the other hand, the iron chloride is dissolved, from which chloride ions and iron ions are dissociated. Even so, because the polyacrylic acid 61 tends not to be ionized, bonding with the iron ions through the electrostatic interaction 62 hardly occurs. In addition, the iron ions tend not to form ferric hydroxide because the pH is low.

As shown in (b) of FIG. 5B, there are many free iron ions, but the electrostatic interaction 62 between the polyacrylic acid 61 and the iron ions is weak. Thus, when seawater or the like that contains organic matters such as the acidic sugars 63 as impurities is mixed with the complex flocculant solution, the carboxyl groups of the acidic sugars 63 and the iron ions tend to bind each other, which makes it easy to form insoluble sediment.

As shown in (c) of FIG. 5B, when the pH is adjusted and brought approximately to 7, the carboxyl groups of the polyacrylic acid 61 are ionized to bring about the electrostatic interaction 62 with the iron ions, which increases the flocculation and sedimentation.

Next, specific explanation is given by way of examples and comparative examples.

Examples 1 to 18 and Comparative Examples 1 to 8

The water intake section 101 shown in FIG. 1C introduces the feed water 51 into the flocculating section 102, into which the complex flocculant 9 is added. Thereafter, the pH adjusting section 105 adjusts the pH of the feed water 51 to 6 to 8 to form the flocculate. Then, the flocculate removing section 103 removes the flocculate. Finally, the desalinating section 104 removes salts from the feed water 51 to obtain fresh water.

The complex flocculant is prepared by adding a polymer flocculant such as polyacrylic acid (PAA) and polystyrene sulfonate (PSS) into water that is stored in advance and agitating the water for about an hour to dissolve the flocculant. Then, an acidic solution is added thereto and agitated for five minutes. Finally, an inorganic flocculant such as ferric chloride and aluminum chloride is added and agitated for about ten minutes. The pH adjusting section 105 adopts aqueous sodium hydroxide that has been adjusted to 1 molarity (M), the flocculate removing section 103 adopts the ultrafiltration membrane (UF membrane), and the desalinating section 104 adopts the reverse osmosis membrane (RO membrane).

Tables 1 and 2 show evaluation results of complex flocculants that are prepared by different combinations of inorganic flocculants and polymer flocculants.

The tables list the concentration of inorganic flocculant in the solution, the pH of the complex flocculant solution, the type of feed water, presence/absence of sediment after adjusting the complex flocculant solution, and the total organic carbon concentration (TOC) removal rate of the feed water sampled before filtering through the RO membrane. In addition, in the Tables, when the feed water is sewage water, the suspended solid (SS) concentration removal rate is listed, while, when the feed water is seawater, the acidic sugar concentration removal rate is listed. The sewage water here indicates domestic wastewater, which includes organic matters such as food, detergents, and human waste, and also metals. Specific examples of the acidic sugars include polysaccharides contained in the seawater such as alginic acid.

Structural formulae and molecular weights of the polymer flocculants included in the Tables are shown below.

The structural formula of polyacrylic acid (PAA) is indicated in Chemical Structure (1), and its molecular weight is 250000.

[Chemical Structure 1]


The structural formula of polystyrene sulfonate (PSS) is indicated in Chemical Structure (2), and its molecular weight is 300000.

[Chemical Structure 2]

The structural formula of polyacrylamide is indicated in Chemical Structure (3), and its molecular weight is 10000000.

[Chemical Structure 3]

For each removal rate, 70% or higher is denoted as >70%, and 80% or higher is denoted as >80%. In this manner/ the effects of the complex flocculants are evaluated. When the TOC removal rate is 50% or higher and also when the SS or acidic sugar removal rate is 70% or higher, "satisfactory" is entered. When either one of these conditions is satisfied, "not bad" is entered, and when neither of the conditions is satisfied, "bad" is entered. If the complex flocculant solution contains impurities, "bad" is entered regardless of the removal rates.

Besides the type and concentration of the complex flocculant, the pH of the complex flocculant after the pH adjustment, and the type of feed water, the examples and the comparative examples are subjected to the experiment under the same conditions. The volume of anionic polymer flocculant added is determined to be sufficient to neutralize the electric charge of the inorganic flocculant, and for other polymer flocculants, the same amount as the anionic polymer flocculant is added.

Comparative Examples 9 to 12

In the same apparatus as the one used for Examples 1 to 24, the pH of the flocculant-added feed water is adjusted to 5 or 9 by the pH adjusting section 105. Besides this adjustment, the water treatment is performed in the same manner as Examples 1 to 24 and evaluated. The evaluation results are given in Table 2.

The Table 2 shows that the TOC removal rate is lower than 50% and that the SS or acidic sugar removal rate is lower than 70% for Comparative Examples 9 to 12.

According to the present invention, a complex flocculant solution prepared with two or more different types of flocculants is adopted in the water treatment apparatus. This simplifies the structure of the apparatus, and reduces both initial costs and running costs.

Although the invention has been described with respect to specific embodiments for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching of the claims.

We claim:

1. A complex flocculant water-treating solution that removes impurities from feed water, the complex flocculant water-treating solution essentially consisting of:

at least two types of flocculants, at least one of the flocculants is an inorganic flocculant and at least one of the flocculants is an organic flocculant.

2. The complex flocculant water-treating solution according to Claim 1, wherein the inorganic flocculant includes trivalent metal ions, and

the organic flocculant includes an anionic polymer.

3. The complex flocculant water-treating solution according to Claim 1 or 2, wherein a pH is 3 or lower.

4. A water treatment apparatus comprising:

a water intake section that introduces feed water including impurities;

a flocculating section that adds a complex flocculant water-treating solution stored in a flocculant tank to the feed water to obtain a mixed solution; and

a flocculate removing section that removes

flocculate including the impurities that is formed in the feed water due to addition of the complex flocculant water-treating solution,

wherein the complex flocculant water-treating solution essentially consists of at least two types of flocculants, at least one of the flocculants being an inorganic flocculant and at least one of the flocculants being an organic flocculant.

5. The water treatment apparatus according to Claim 4, wherein the flocculating section includes a flocculation basin into which the water intake section introduces the feed water, and

the flocculation basin is connected to the flocculant tank such that the complex flocculant water-treating solution in the flocculant tank is supplied to the flocculation basin.

6. The water treatment apparatus according to Claim 4, wherein the flocculant tank is connected to a pipe through which the feed water flows.

7. The water treatment apparatus according to any one of Claims 4 to 6, further comprising a pH adjusting section that adds an alkaline solution or an acidic solution to the mixed solution of the feed water and the complex flocculant water-treating solution and thereby adjusts a pH of the mixed solution.

8. The water treatment apparatus according to any one of Claims 4 to 7, further comprising a desalinating section that removes salts from the feed water from which the flocculate has been removed.

9. The water treatment apparatus according to any one of Claims 4 to 8, wherein the number of flocculant tank included is one.

10. The water treatment apparatus according to any one of Claims 7 to 9, wherein the pH adjusting section neutralizes a pH of the mixed solution.

11. The water treatment apparatus according to any one of Claims 4 to 10, wherein the feed water is seawater.

12. A water treatment method comprising:

introducing feed water including impurities;

adding a complex flocculant water-treating solution to the feed water to obtain a mixed solution; and

removing flocculate including the impurities that is formed in the feed water due to addition of the complex flocculant water-treating solution,

wherein the complex flocculant water-treating solution essentially consists of at least two types of flocculants, at least one of the flocculants being an inorganic flocculant and at least one of the flocculants being an organic flocculant.

13. The water treatment method according to Claim 12,

Wherein the introducing includes introducing the feed water into a flocculation basin, and the adding includes adding the complex flocculant water-treating solution to the flocculation basin.

14. The water treatment method according to Claim 12, wherein the adding includes adding the complex flocculant water-treating solution to the feed water that is flowing through a pipe.

15. The water treatment method according to any one of Claims 12 to 14, further comprising adjusting a pH of the mixed solution of the feed water and the complex flocculant water-treating solution by adding an alkaline solution or an acidic solution to the mixed solution.

16. The water treatment method according to any one of Claims 12 to 15, further comprising desalinating by removing salts from the feed water from which the flocculate has been removed.

17. The water treatment method according to Claim 15 or 16, wherein the adjusting includes neutralizing a pH of the mixed solution.

18. The water treatment method according to any one of Claims 12 to 17, wherein the feed water is seawater.