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Water Treatment Patent

Water treatment apparatus that can reduce water treatment time

Water treatment abstract


In a water treatment apparatus, the time for treatment after water to be treated is introduced into an electrolytic bath is reduced. The water to be treated in a reservoir is subjected to electrolysis at a first electrolytic bath. Electrolysis is carried out at respective first and second electrolytic baths. By the electrolysis at the second electrolytic bath, hypochlorous acid is generated from chloride ions at the anode side. The solution subjected to electrolysis at the second electrolytic bath is mixed at a predetermined site of the pipe connected between the reservoir and the first electrolytic bath with the water output from the reservoir via a pipe prior to introduction into the first electrolytic bath. Accordingly, the water subjected to electrolysis at the first electrolytic bath can be sterilized in advance by the hypochlorous acid generated by electrolysis at the second electrolytic bath.

Water treatment claims


What is claimed is:

1. A water treatment apparatus comprising: a first electrolytic bath into which water to be treated is introduced from a predetermined vessel, a first pair of electrodes stored in said first electrolytic bath, a first pipe connecting said predetermined vessel with said first electrolytic bath, and through which the water to be treated passes, a second electrolytic bath storing a solution, a second pair of electrodes stored in said second electrolytic bath, and a second pipe connecting said second electrolytic bath with said first pipe, and through which the solution of said second electrolytic bath passes.

2. The water treatment apparatus according to claim 1, wherein said second pipe is connected to said first pipe at a predetermined site of said first pipe, and said predetermined site is located where the water to be treated of said predetermined vessel to be introduced into said first electrolytic bath can react with a compound included in the water to be treated from said second electrolytic bath via said second tube, during passage from said predetermined site of said first pipe and prior to introduction into said first electrolytic bath.

3. A water treatment apparatus comprising: a buffer tank into which water to be treated is introduced from a predetermined vessel, a chemical agent introduction unit to introduce a chemical agent into said buffer tank, a pair of electrodes, and an electrolytic bath storing said pair of electrodes and the water to be treated of said buffer tank.

4. The water treatment apparatus according to claim 3, wherein the chemical agent to be introduced by said chemical agent introduction unit includes a chemical agent supplying chloride ions into the water to be treated in said buffer tank.

5. The water treatment apparatus according to claim 4, wherein the chemical agent to be introduced by said chemical agent introduction unit includes sodium chloride.

6. The water treatment apparatus according to claim 4, further comprising: a chloride ion concentration detection unit detecting a concentration of chloride ions in said buffer tank, and a first ion concentration control unit controlling an operation of introducing a chemical agent by said chemical agent introduction unit based on a detected output from said chloride ion concentration detection unit.

7. The water treatment apparatus according to claim 4, further comprising: an electric conductivity detection unit detecting an electric conductivity of water to be treated that is introduced into said buffer tank, and a second ion concentration control unit controlling an operation of introducing a chemical agent by said chemical agent introduction unit based on a detected output from said conductivity detection unit.

8. The water treatment apparatus according to claim 3, wherein the chemical agent to be introduced by said chemical agent introduction unit includes a chemical agent to adjust a pH of the water to be treated in said buffer tank.

9. The water treatment apparatus according to claim 8, wherein the chemical agent to adjust the pH includes concentrated sulfuric acid and/or sodium hydroxide.

10. The water treatment apparatus according to claim 8, wherein said chemical agent to adjust the pH includes hydrochloric acid.

11. The water treatment apparatus according to claim 8, further comprising: a pH detection unit detecting a pH in said buffer tank, and a pH control unit to control an operation of introducing a chemical agent by said chemical agent introduction unit based on a detected output from said pH detection unit.

Water treatment description


BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to water treatment apparatuses, and more particularly, to a water treatment apparatus having a pair of electrodes immersed in water to be treated for causing a chemical agent generated by electrolytic reaction through the pair of electrodes to act on the water to be treated.

[0003] 2. Description of the Background Art

[0004] A conventional technique of treating water electrochemically is known. For example, Japanese Patent Laying-Open No. 2003-225672 discloses a water treatment apparatus reducing nitric acid ions and nitric acid ions in the water to be treated by electrochemical reaction to produce ammonia, and then converting the ammonia into nitrogen gas which is to be removed from the water to be treated.

[0005] In such a water treatment apparatus, reduction reaction of nitric ion represented by the following formula (1) occurs at the cathode side, and the reaction represented by formulas (2) and (3) occurs at the anode side. 1

[0006] Then, the ammonia generated at the cathode side and the hypochlorous acid generated at the anode side react as represented by the following formula (4) to become nitrogen gas, which is removed from the water to be treated. 2

[0007] The chloride ions reacting in accordance with the above formula (2) are originally contained in the water to be treated. When the amount of hypochlorous acid generated by such chloride ions is insufficient for the reaction with the nitrogen compound in formula (3) and formula (4), a chemical agent such as sodium chloride to supply chloride ions into the water to be treated was introduced into the electrolytic bath.

[0008] The hypochlorous acid generated by the above formula (3) is also used for purification and sterilization of water to be treated, in addition to the aforementioned reaction with ammonia.

[0009] In the above-described conventional water treatment apparatus, the water to be treated is introduced into an electrolytic bath, and then a chemical agent for supply of chloride ions into the water was introduced in accordance with the amount of nitric acid ions in the water to be treated. In other words, electrolysis is initiated only after, the chemical agent for supply of chloride ions is introduced into the water to be treated in the electrolytic bath.

[0010] The pH of the water to be treated in the electrolytic bath must be adjusted for electrolysis. It was sometimes necessary to incorporate a chemical agent for adjusting the pH into the water to be treated in the electrolytic bath.

[0011] There is the need for minimizing the time require to introduce a chemical agent for supply of chloride ions and for pH adjustment from the standpoint of shortening the processing time after water to be treated is introduced into the electrolytic bath.

SUMMARY OF THE INVENTION

[0012] In view of the foregoing, an object of the present invention is to provide a water treatment apparatus that can reduce the time required for treatment after the water to be treated is introduced into an electrolytic bath.

[0013] According to an aspect of the present invention, a water treatment apparatus includes a first electrolytic bath into which water to be treated is introduced from a predetermined vessel, a first pair of electrodes placed in the first electrolytic bath, a first pipe connecting the predetermined vessel with the first electrolytic bath, and through which the water to be treated passes, a second electrolytic bath storing a solution, a second pair of electrodes placed in the second electrolytic bath, and a second pipe connecting the second electrolytic bath with the first pipe, and through which the solution stored in the second electrolytic bath passes.

[0014] In accordance with the present invention, hypochlorous acid generated by the electrolysis in the second electrolytic bath is introduced into the first electrolytic bath via the second and first pipes simultaneous to the water to be treated. In other words, hypochlorous acid is added to the water to be treated prior to introduction into the first electrolytic bath.

[0015] Preferably in the water treatment apparatus of the present invention, the second pipe is connected to the first pipe at a predetermined site of the first pipe, and said predetermined site is located where the water to be treated and to be introduced into the first electrolytic bath from the predetermined vessel can react with the compound included in the water to be treated introduced from the second electrolytic bath via the second pipe, during passage from said predetermined site at the first pipe prior to introduction into the first electrolytic bath.

[0016] The first and second pipes are connected at a site in the first pipe where the chemical agent generated by electrolysis in the second electrolytic bath can react with the water to be treated that is introduced from the predetermined vessel, prior to introduction into the first electrolytic bath.

[0017] According to another aspect of the present invention, a water treatment apparatus includes a buffer tank into which water to be treated is introduced from a predetermined vessel, a chemical agent introduction unit to introduce a chemical agent into the buffer tank, a pair of electrodes, and an electrolytic bath storing the pair of electrodes and the water to be treated from the buffer tank.

[0018] In accordance with the present invention, in the case where the water to be treated is subjected to electrolysis in the electrolytic bath in batches, a chemical agent can be added to the water to be treated in the buffer tank during treatment of the previous batch in the electrolytic bath.

[0019] Preferably in the water treatment apparatus of the present invention, the chemical agent to be introduced by the chemical agent introduction unit is a chemical agent supplying chloride ions into the water to be treated in the buffer tank.

[0020] In the water treatment apparatus of the present invention, the chemical to be introduced by the chemical agent introduction unit is preferably sodium chloride.

[0021] Preferably, the water treatment apparatus of the present invention further includes a chloride ion concentration detection unit detecting the concentration of chloride ions in the buffer tank, and a first ion concentration control unit controlling the operation of introducing the chemical agent by the chemical agent introduction unit based on the detected output from the chloride ion concentration detection unit.

[0022] Further preferably, the water treatment apparatus of the present invention includes an electric conductivity detection unit detecting the electric conductivity of the water to be treated that is introduced into the buffer tank, and a second ion concentration control unit controlling the operation of introducing a chemical agent by the chemical agent introduction unit based on the detected output of the electric conductivity detection unit.

[0023] In the water treatment apparatus of the present invention, the chemical to be introduced by the chemical agent introduction unit is preferably a chemical agent to adjust the pH of the water to be treated in the buffer tank.

[0024] In the water treatment apparatus of the present invention, the chemical agent to adjust the pH is preferably concentrated sulfuric acid and/or sodium hydroxide.

[0025] In the water treatment apparatus of the present invention, the chemical agent to adjust the pH is preferably hydrochloric acid.

[0026] Further preferably, the water treatment apparatus of the present invention further includes a pH detection unit detecting the pH in the buffer tank, and a pH control unit controlling the operation of introducing a chemical agent by the chemical agent introduction unit based on the detected output from the pH detection unit.

[0027] In accordance with the present invention, the addition of hypochlorous acid in advance into the water to be treated to be introduced into the first electrolytic bath allows suppressing the amount of hypochlorous acid that is required to be generated for removal of nitric acid ions and the like in the first electrolytic bath. Accordingly, the amount of chloride ions to be added into the water to be treated in the first electrolytic bath can also be suppressed. Therefore, the time required to add a chemical agent for supply of chloride ions into the water to be treated can be reduced after the water to be treated is introduced into the first electrolytic bath. In other words, the processing time after introduction of water to be treated into the electrolytic bath can be reduced in the water treatment apparatus.

[0028] In accordance with the present invention, the water to be treated that is introduced into the first electrolytic bath has hypochlorous acid added prior to introduction into the first electrolytic bath, whereby the water to be treated is introduced into the first electrolytic bath under a status subjected to sterilization by the hypochlorous acid. Therefore, even if the hypochlorous acid is converted into chloride ions by sterilization and the like, more of the chloride ions will be converted into hypochlorous acid again by the electrolysis of the first electrolytic bath for usage. Thus, the chloride ion can be employed efficiently in the treatment of water, and the amount of chloride ions remaining in the under-treating water after treatment at the first electrolytic bath can be suppressed.

[0029] According to the present invention, the hypochlorous acid generated in the second electrolytic bath is introduced, not into the predetermined vessel where the water to be treated is stored for introduction into the first electrolytic bath, but into the first pipe where the water output from the predetermined vessel is located. Accordingly, the amount of hypochlorous acid to be generated in the second electrolytic bath can be suppressed. Furthermore, since sterilization and the like of the water to be treated by the hypochlorous acid generated at the second electrolytic tank is not conducted in the predetermined vessel, the amount of chloride ions in the water to be treated in the predetermined vessel will not increase. The event of restriction in the application of the water to be treated in the predetermined vessel can be avoided.

[0030] In accordance with the present invention, a chemical agent can be added in the buffer tank to the water to be treated that is to be introduced into the electrolytic bath, prior to introduction of the water to be treated into the electrolytic bath. Therefore, the time required for introducing a chemical agent such as chloride ions into the water to be treated can be reduced after the water to be treated is introduced into the electrolytic bath. In other words, the treatment time after the water to be treated is introduced into the electrolytic bath can be reduced in the water treatment apparatus.

[0031] The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 is a schematic diagram of a configuration of a water treatment apparatus according to a first embodiment of the present invention.

[0033] FIG. 2 is a flow chart of a process executed by a control device in the water treatment apparatus of FIG. 1.

[0034] FIG. 3 schematically shows a configuration of a water treatment apparatus according to a second embodiment of the present invention.

[0035] FIG. 4 is a control block diagram of the water treatment apparatus of FIG. 3.

[0036] FIG. 5 schematically shows a configuration of a water treatment apparatus according to a third embodiment of the present invention.

[0037] FIG. 6 is a control block diagram of the water treatment apparatus of FIG. 4.

[0038] FIGS. 7 and 8 schematically show stored contents in the memory of FIG. 4.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0039] Embodiments of the present invention will be described hereinafter with reference to the drawings.

[0040] First Embodiment

[0041] Referring to FIG. 1, a water treatment apparatus according to a first embodiment of the present invention treats water stored in a reservoir 7, and includes a first water treatment unit 1 and a second water treatment unit 4.

[0042] First and second water treatment units 1 and 4 include a first electrolytic bath 2 and a second electrolytic bath 5, and chemical agent supply units 3 and 6, respectively. Each of first and second electrolytic baths 2 and 5 is provided so as to accommodate a pair of electrodes not shown for electrolysis.

[0043] Chemical agent supply units 3 and 6 are provided to appropriately supply a chemical agent to first electrolytic bath 2 and second electrolytic bath 5, respectively. Specifically, chemical agent supply units 3 and 6 appropriately supply a compound to supply chloride ions into a solution such as sodium chloride, or supply appropriately a chemical agent to adjust the pH into first electrolytic bath 2 and second electrolytic bath 5, respectively, to promote the aforementioned reaction in accordance with formula (2) and formula (3). The chemical agent for supplying chloride ions into the solution is preferably, but not limited to, sodium chloride from the standpoint of cost, distributability, facile handling and the like. As to the chemical agent to adjust the pH, concentrated sulfuric acid and/or sodium hydroxide can be cited taking into consideration the cost, distributability, the ease of handling, and the like. Further, hydrochloric acid can be cited since first and second electrolytic baths 2 and 5 often require supply of chloride ions.

[0044] The water to be treated in reservoir 7 is delivered to first electrolytic bath 2 via pipe 8. A pipe 9 is connected to pipe 8 at a site P. In the water treatment apparatus of FIG. 1, the solution subjected to electrolysis in second electrolytic bath 5 is delivered to first electrolytic bath 2 via pipes 9 and 8. Second electrolytic bath 5 may have the water to be treated in reservoir 7 introduced, or a solution from a tank other than reservoir 7 introduced via a channel not shown.

[0045] Although not shown in FIG. 1, pipes 8 and 9 in the water treatment apparatus are provided with a pump and a solenoid valve to adjust the flow of the solution at respective pipes 8 and 9.

[0046] Furthermore, the water treatment apparatus includes the aforementioned pump and solenoid valve, a control device to control the operation of the pump and solenoid valve, and a control device to control power supply towards the pair of electrodes provided. These elements are not shown in FIG. 1.

[0047] The electrolysis process on the water to be treated carried out in the water treatment apparatus will be described hereinafter with reference to FIG. 2.

[0048] In the electrolysis process of the water to be treated in reservoir 7 in the water treatment apparatus of FIG. 1, water is supplied appropriately to second electrolytic bath 5 through a channel not shown from reservoir 7 or another tank, and then power is supplied to the pair of electrodes in second electrolytic bath 5 for electrolysis at step (step abbreviated as S hereinafter) 1. Accordingly, hypochlorous acid is generated in the solution in second electrolytic bath 5.

[0049] At S2, water supply from reservoir 7 to first electrolytic bath 2 is initiated.

[0050] At S3, the solution subjected to electrolysis at second electrolytic bath 5 is provided to first electrolytic bath 2. Accordingly, the solution in second electrolytic bath 5 passes through pipe 9 to be carried into pipe 8 at site P to be mixed with the water to be treated of reservoir 7.

[0051] By S2 and S3, the water to be treated of reservoir 7 and the solution of second electrolytic bath 5 are supplied to first electrolytic bath 2. The processes of S2 and S3 may be carried out in opposite order, or concurrently.

[0052] At S4, determination is made as to whether first electrolytic bath 2 is full or not. The processes of S2 and S3 are continued until determination of a full level is made. When determination is made that first electrolytic bath 2 is full, the processes of S5 and S8 are executed.

[0053] At S5, power is applied to the pair of electrodes in first electrolytic bath 2 to initiate electrolysis. The electrolysis of S5 continues until determination is made that a predetermined processing time has expired at S6. When determination is made that the processing time has expired, control proceeds to S7 where the under-treating water in first electrolytic bath 2 is output. Then, control returns to S2.

[0054] At S8, electrolysis is conducted after water is supplied to second electrolytic bath 5. During the electrolysis process at second electrolytic bath 5, water supply from second electrolytic bath 5 to first electrolytic bath 2 may be inhibited, or conducted appropriately such as in the case where addition of chloride ions into first electrolytic bath 2 is required. The electrolysis at second electrolytic bath 5 is conducted for a predetermined time. Then, the electrolysis ends, and control returns to S2.

[0055] Although the electrolysis at the first electrolytic bath 2 and the second electrolytic bath 5 is both carried out for a predetermined time in the process set forth above with reference to FIG. 2, the present invention is not limited thereto. A sensor detecting the concentration of nitric acid ions or chloride ions can be installed for each electrolytic bath to terminate electrolysis under the condition that the relevant sensor detects a predetermined value.

[0056] In the present embodiment, the solution subjected to electrolysis in the second electrolytic bath 5 is mixed at site P with the water to be treated from reservoir 7 directed to the first electrolytic bath 2, prior to introduction into first electrolytic bath 2. Accordingly, the water to be treated that will be subjected to electrolysis in first electrolytic bath 2 can be sterilized in advance by the hypochlorous acid generated by the electrolysis in the second electrolytic bath 5. Therefore, even if the hypochlorous acid is converted into chloride ions by sterilization, such chloride ions are consumed in the electrolysis at the first electrolytic bath 2.

[0057] Site P is preferably set at a location distant from the site of introduction into first electrolytic bath 2 (for example, the inlet of first electrolytic bath 2) such that the water to be treated of reservoir 7 is sterilized by the hypochlorous acid in the solution subjected to electrolysis at second electrolytic bath 5 during passage from site P prior to introduction into first electrolytic bath 2. Thus, the solution to be supplied to first electrolytic bath 2 from second electrolytic bath 5 can be mixed reliably with the water to be treated from reservoir 7, prior to introduction into first electrolytic bath 2.

[0058] Second Embodiment

[0059] Referring to FIG. 3, a water treatment apparatus according to a second embodiment of the present invention is directed to treating the water stored in a reservoir 50.

[0060] The water treatment apparatus of the second embodiment is mainly constituted of an electrolytic bath 10, a buffer tank 20, a chloride ion tank 31 and a pH adjuster tank 32.

[0061] A water level sensor 11 and a pH sensor 12 are installed in electrolytic bath 10. A water level sensor 21, a chloride ion concentration sensor 22, and a pH sensor 23 are installed in buffer tank 20.

[0062] Buffer tank 20 and reservoir 50 are connected through a pipe. On this pipe are provided a pump 61 to deliver the water to be treated in reservoir 50 to buffer tank 20, and a solenoid valve 71 to open/close this pipe.

[0063] Chloride ion tank 31 stores the chemical agent for supplying chloride ions into the solution, and is connected with buffer tank 20 through a pipe to supply the chemical agent to buffer tank 20. On this pipe are provided a pump 62 to deliver the chemical agent in chloride ion tank 31 into buffer tank 20, and a solenoid valve 72 to open/close this pipe.

[0064] pH adjuster tank 32 stores the chemical agent to adjust the pH of the solution, and is connected to buffer tank 20 through a pipe to supply the chemical agent to buffer tank 20. On this pipe are provided a pump 63 to deliver the chemical agent in pH adjuster tank 32 into buffer tank 20, and a solenoid valve 73 to open/close this pipe.

[0065] pH adjuster tank 32 is connected to electrolytic bath 10 to supply the aforementioned chemical agent through a pipe. On this pipe are provided a pump 65 to deliver the chemical agent in pH adjuster tank 32 to electrolytic bath 10, and a solenoid valve 75 to open/close this pipe. In the water treatment apparatus of the present embodiment, the pH of the water to be treated can be adjusted even if an electrolysis process is conducted currently at electrolytic bath 10.

[0066] Buffer tank 20 temporarily stores the water to be supplied to electrolytic bath 10. Prior to supply into electrolytic bath 10, the water to be treated in reservoir 50 is supplied with chloride ions at buffer tank 20 to have the pH adjusted. Buffer tank 20 is connected with electrolytic bath 10 through a pipe. On this pipe are provide a pump 64 to deliver the water in buffer tank 20 to electrolytic bath 10, and a solenoid valve 74 to open/close this pipe.

[0067] Electrolytic bath 10 accommodates a pair of electrodes (electrode pair 15 described afterwards). The electrode pair is immersed in the water supplied from buffer tank 20. Power is supplied to this electrode pair, whereby electrolysis is applied on the water to be treated. In electrolytic bath 10, a predetermined amount of water to be treated is stored and subjected to electrolysis. When the electrolysis process ends, the current water is output, and water to be processed is newly introduced to be subjected to electrolysis. In other words, electrolysis is applied in batches in electrolytic bath 10.

[0068] Referring to FIG. 4, the water treatment apparatus also includes a control unit 40 that controls the overall operation of the water treatment apparatus. A memory 41 in which various operation parameters and the like are recorded is provided in control unit 40.

[0069] Control unit 40 receives the detection outputs from water level sensors 11 and 21, chloride ion concentration sensor 22, and pH sensors 12 and 23. Control unit 40 controls the operation of pumps 61-65 and solenoid valves 71-76 based on relevant detected outputs, and controls power supply to electrode pair 15.

[0070] When the water of reservoir 50 is subjected to electrolysis at electrolytic bath 10 in the water treatment apparatus of the present embodiment, the water of reservoir 50 has chloride ions added at buffer tank 20, and then delivered to electrolytic bath 10 to be subjected to electrolysis. In the water treatment apparatus of the present embodiment, addition of chloride ions into the water to be treated at buffer tank 20, and the electrolysis process on the water to be treated at electrolytic bath 10 are carried out concurrently.

[0071] Addition of chloride ions into the water to be treated at buffer tank 20 is specifically set forth below.

[0072] Solenoid valve 71 attains an open status, and pump 61 is driven, whereby water to be treated is supplied from reservoir 50 into buffer tank 20. When a predetermined amount of water to be treated is supplied into buffer tank 20, the drive of pump 21 is inhibited, and solenoid valve 71 is closed. Thus, supply of water to be treated is stopped. The amount of water to be treated in buffer tank 20 is determined based on the detection output of water level sensor 21.

[0073] At buffer tank 20, chloride ions are added into the water to be treated based on the detection output of chloride ion concentration sensor 22, and a pH adjuster is added based on the detection output of electrolytic bath 23. As a result, a solution appropriate for electrolysis is obtained. The chloride ion concentration suitable for electrolysis (the added amount of chloride ions) may be prestored in memory 41, or the nitric acid ion concentration or the like in the water to be treated in buffer tank 20 may be detected to calculate the amount based on the relation stored in memory 41 using the detected output.

[0074] Then, solenoid valve 74 is opened, and pump 64 is driven, whereby the water in buffer tank 20 is delivered to electrolytic bath 10. As set forth above, another batch of water to be processed is stored in electrolytic bath 10 and subjected to electrolysis parallel to the supply of (a compound providing) chloride ions to the water to be treated in buffer tank 20. The supply of water from buffer tank 20 to electrolytic bath 10 is conducted after the batch of water subjected to electrolysis in electrolytic bath 10 is output.

[0075] In the electrolysis process at electrolytic bath 10 in the present embodiment, water to be processed is supplied to electrolytic bath 10 attaining a state where chloride ions are added to the water at buffer tank 20 in advance. Such addition of chloride ions is carried out concurrent with the electrolysis process carried out on the water of another batch at electrolytic bath 10. Accordingly, the electrolysis process can be initiated simultaneous to the supply of water to be treated at electrolytic bath 10. Thus, the time required for the series of processes in association with the electrolysis can be reduced by the time required to add chloride ions.

[0076] Since water having the pH adjusted in advance at buffer tank 20 is introduced into electrolytic bath 10 in the present embodiment, the pH of the water is of a level suitable for electrolysis from the beginning of the electrolysis process. Accordingly, degradation in the efficiency of removing nitride compound in the electrolysis process due to the effect of pH can be avoided.

[0077] Possible chemical agents for supplying chloride ions into the solution preferably include, but is not limited to, sodium chloride from the standpoint of cost, distributability, facile handling and the like. Further, possible chemical agents to adjust the pH applied to pH adjuster tank 32 include, but are not limited to, concentrated sulfuric acid and/or sodium hydroxide from the standpoint of cost, distributability, facile handling and the like. Furthermore, hydrochloric acid can be cited since supply of chloride ions is required in the water to be treated in buffer tank 20.

[0078] The usage of hydrochloric acid as a pH adjuster is allowed by the configuration specific to the water treatment apparatus of the present embodiment. In the water treatment apparatus of the present embodiment, addition of the pH adjuster into the water to be treated is carried out concurrent with the electrolysis at electrolytic bath 10. Therefore, even if addition of the pH adjuster is relatively time consuming, initiation of the electrolysis process at electrolytic bath 10 will not be deferred by the addition of the pH adjuster. Therefore, the pH adjuster can be added in relatively small amounts into the water to be treated. By adding hydrochloric acid on a relatively small amount basis, this configuration of the water treatment apparatus minimizes the generation of fumes generally encountered when hydrochloric acid is added into water. Thus, hydrochloric acid can be used as the pH adjuster.

[0079] Third Embodiment

[0080] Referring to FIG. 5, a water treatment apparatus according to a third embodiment of the present invention is similar to the water treatment apparatus of the second embodiment, provided that a conductivity meter detecting the electric conductivity of the water to be introduced into buffer tank 20 is installed instead of the chloride ion concentration sensor in buffer tank 20.

[0081] Referring to FIG. 6, the water treatment apparatus of the present embodiment includes the elements such as a control unit 40, likewise the water treatment apparatus of the second embodiment. The water treatment apparatus of the third embodiment includes a conductivity meter 33 instead of chloride ion concentration sensor 22, as compared to the water treatment apparatus of the second embodiment. The detected output of conductivity meter 33 is applied to control unit 40.

[0082] In the water treatment apparatus of the present embodiment, the amount of chloride ions to be added at buffer tank 20 is determined based on the detection output of conductivity meter 33, as compared to the determination based on the detected output of chloride ion concentration sensor 22 in the water treatment apparatus of the second embodiment.

[0083] Specifically, memory 41 stores the relationship between the detected output from conductivity meter 33 (electric conductivity) and the concentration of nitrogen compound expected to be included in the water to be treated (expected nitrogen compound concentration), as schematically shown in FIG. 7, and the relationship between the expected nitrogen compound concentration and the amount of chloride ions to be added to buffer tank 20, as schematically shown in FIG. 8. In FIG. 7, the expected nitrogen compound concentration becomes higher substantially proportional to a higher electric conductivity. FIG. 8 represents that the amount of chloride ions to be added increases in accordance with a higher expected nitrogen compound concentration. Control unit 40 refers to memory 41 to calculate the expected nitrogen compound concentration based on the electric conductivity detected by conductivity meter 33, and also to calculate the amount of chloride ions to be added from the calculated expected nitrogen compound concentration, and takes the calculated result as the amount of chloride ions to be added.

[0084] In the present embodiment, a conductivity meter is employed instead of the chloride ion concentration sensor of a second embodiment. Determination of the nitride compound concentration through a conductivity meter requires that the component of the water to be treated introduced into buffer tank 20 is relatively constant. Since a conductivity meter is more economic than a chloride ion concentration sensor, the usage of a conductivity meter such as in the present embodiment is advantageous from the standpoint of cost when the water treatment apparatus is installed to process water that satisfies the constant requirement.

[0085] Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.


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