JP3738187B2 - Waste water treatment method and waste water treatment system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a wastewater treatment method containing phosphoric acid, a phosphorus compound, phosphate ions, organic nitrogen, nitrite nitrogen, nitrate nitrogen, and ammonia nitrogen.
[0002]
[Prior art]
Conventionally, it is well known that the presence of nitrogen compounds and phosphorus compounds is one of the causes of eutrophication of rivers and lakes. In addition, there are many phosphorus compounds and nitrogen compounds in domestic household wastewater and factory wastewater, but purification is difficult, and effective measures cannot be taken. In general, the treatment of nitrogen compounds is carried out by biological treatment. First, the nitrification step for converting ammonia nitrogen to nitrate nitrogen and the denitrification step for converting nitrate nitrogen to nitrogen gas are performed. Has been done.
[0003]
On the other hand, various treatment methods for phosphorus compounds have been proposed, but a lime coagulation precipitation method is known for domestic wastewater. This technique is a technique in which phosphate ions in water to be treated are reacted with calcium ions to be condensed and precipitated as a water-insoluble salt, calcium hydroxyapatite.
[0004]
[Problems to be solved by the invention]
However, the conventional biological treatment requires two reaction tanks and has a problem in that the treatment efficiency is lowered because the treatment time is slow. Moreover, in the said conventional method, since the to-be-processed water containing a nitrogen compound and a phosphorus compound is not processed simultaneously, there existed a problem which an apparatus enlarged.
[0005]
In addition, the biological treatment requires a large-capacity aerobic tank and anaerobic tank in order to retain nitrifying bacteria and denitrifying bacteria, and there is a problem in that the equipment construction cost increases and the installation area of the apparatus increases. . Furthermore, since the denitrifying bacteria are significantly affected by the ambient temperature environment and other components contained in the water to be treated, the activity decreases and the denitrifying action is reduced particularly in winter when the temperature is low. There has been a problem that the processing efficiency becomes unstable.
[0006]
Furthermore, in the processing method of the phosphorus compound, since the pH in the formation of the condensed precipitate is high, it is necessary to perform the processing from alkaline to neutral after the processing of the phosphorus compound. In addition, there is a problem that the amount of lime used is large and maintenance is difficult.
[0007]
Therefore, the present invention has been made to solve the conventional technical problems, and proposes a wastewater treatment method capable of efficiently treating water to be treated containing a nitrogen compound and a phosphorus compound.
[0008]
[Means for Solving the Problems]
The present invention is a method for treating nitrogen compounds and phosphorus compounds in water to be treated by an electrochemical method, wherein the metal material constituting the cathode is a conductor, and the conductive material constituting the anode is an insoluble material. Alternatively, it is carbon and calcium chloride is added to the water to be treated.
[0009]
According to the present invention, in the method for treating nitrogen compounds and phosphorus compounds in water to be treated by an electrochemical method, the metal material constituting the cathode is a conductor, and the conductive material constituting the anode is an insoluble material. In addition, since calcium chloride is added to the water to be treated while being carbon, ammonia in the water to be treated is denitrified with a substance such as hypochlorous acid by the chloride ions of calcium chloride, thereby synergistically. According to the effect, nitrogen components such as nitrate nitrogen, ammonia nitrogen and nitrogen compounds can be effectively removed.
[0010]
Furthermore, since the phosphate ions can be condensed and precipitated by utilizing the fact that the pH in the vicinity of the cathode becomes alkaline, it is not necessary to adjust the water to be treated to neutral after the treatment.
[0011]
As a result, the nitrogen compound and the phosphorus compound can be efficiently removed from the water to be treated containing the nitrogen compound and the phosphorus compound discharged from a general household or a factory, and the wastewater treatment capacity is improved.
[0012]
Moreover, it becomes possible to perform the treatment of the phosphorus compound and the nitrogen compound in the same tank without providing a special separate treatment tank, so that the processing apparatus for realizing the present invention can be miniaturized. Become.
[0013]
In the wastewater treatment method of the invention of claim 2, in addition to the invention of claim 1, the metal material constituting the cathode is a conductor containing Group Ib or Group IIb of the periodic table, or the same group as a conductor. It is characterized by using a coated one.
[0014]
According to the invention of claim 2, in addition to the invention of claim 1, the metal material constituting the cathode is a conductor containing the group Ib or IIb of the periodic table, or a conductor coated with the same group. Since one is used, the reduction reaction of nitrate nitrogen and nitrite nitrogen in the water to be treated to ammonia can be further promoted, and the time required for the reduction reaction can be further shortened.
[0015]
The waste water treatment method of the invention of claim 3 is characterized in that the amount of calcium ions contained in the water to be treated is at least 5/3 times the molar ratio of the amount of phosphate ions contained in the water to be treated. To do.
[0016]
According to the invention of claim 3, in addition to the invention of claim 2, the amount of calcium ions contained in the for-treatment water is 5/3 times the molar ratio of phosphate ions contained in the for-treatment water. As described above, by allowing calcium ions sufficient to coagulate and precipitate phosphate ions in the water to be treated, it is possible to effectively coagulate and precipitate phosphorus and improve the treatment efficiency of phosphorus. It becomes like this.
[0017]
The wastewater treatment method of the invention of claim 4 is characterized in that, in addition to the invention of claim 1, claim 2 or claim 3, the water to be treated is water after being treated by a biological treatment septic tank. .
[0018]
According to the invention of claim 4, in addition to the invention of claim 1, claim 2 or claim 3, the treated water is water after being treated by the biological treatment septic tank. For example, COD and BOD are highly removed in an activated sludge treatment tank or the like, and bacteria generated in the activated sludge treatment tank can be sterilized with hypochlorous acid or active oxygen, and then discharged. .
[0019]
The waste water treatment system of the invention of claim 5 is a biological treatment septic tank for treating a nitrogen and phosphorus treatment apparatus for treating nitrogen compounds and phosphorus compounds in water to be treated by the waste water treatment method of claim 1, claim 2 or claim 3. A wastewater treatment system characterized by being arranged in the subsequent stage.
[0020]
According to the waste water treatment system of the invention of claim 5, the nitrogen and phosphorus treatment apparatus for treating the nitrogen compound and phosphorus compound in the water to be treated by the waste water treatment method of claim 1, claim 2 or claim 3 is biological. Since it is placed after the treatment septic tank, COD and BOD are highly removed in biological treatment septic tanks such as activated sludge treatment tanks, and bacteria generated in the activated sludge treatment tanks are removed by hypochlorous acid and active oxygen. After sterilization, the waste water can be treated.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory view showing an outline of a wastewater treatment apparatus 1 for realizing the nitrogen and phosphorus treatment method of the present invention. The waste water treatment apparatus 1 in the present embodiment is at least partially immersed in the treatment tank 2 that constitutes a treatment chamber 4 having a waste water inlet and outlet (not shown) therein, and the water to be treated in the treatment chamber 4. A pair of electrodes, that is, an anode 5, a cathode 6, a power source 7 for energizing the electrodes 5 and 6, and a control device (not shown) for controlling the electrodes 7. It is configured. In addition, 10 is a stirring element as a stirring means for stirring the inside of the processing tank 2 in the figure.
[0022]
The cathode 6 is made of a conductor containing Group Ib or Group IIb of the periodic table, or a conductor coated with the same group, and the anode 5 is made of an insoluble metal such as platinum, iridium, or palladium. Or it is comprised from the insoluble electrode or carbon containing the oxide.
[0023]
Further, a shielding member 9 formed in a cylindrical shape as shown in FIG. 2 is provided between the anode 5 and the cathode 6 so as to surround the anode 5. The shielding member 9 is made of a non-conductive member such as glass fiber or plastic mesh, for example, thereby preventing oxygen bubbles generated from the anode 5 from passing to the cathode 6 side. it can. At this time, ions existing on the anode 5 side can pass through the shielding member 9 and move to the cathode 6 side.
[0024]
With the above configuration, water to be treated containing nitrate nitrogen and phosphorus compound is stored in the treatment chamber 4 in the treatment tank 2, the power supply 7 is turned on by the control device, and the cathode 6 and the anode 5 are energized. Thereby, on the cathode 6 side, nitrate ions contained in the water to be treated are converted into nitrite ions by a reduction reaction (reaction A). Further, nitrite ions generated by the reduction reaction of nitrate ions are further converted to ammonia by a reduction reaction (reaction B). At this time, the vicinity of the cathode 6 becomes alkaline. Reaction A and reaction B are shown below.
Reaction A NO ₃ ⁻ + H ₂ O + 2e ⁻ → NO ₂ ⁻ + 2OH ⁻
Reaction B NO ₂ ⁻ + 5H ₂ O + 6e ⁻ → NH ₃ (aq) + 7OH ⁻
[0025]
On the other hand, on the anode 5 side, active oxygen and hypochlorous acid are generated from the surface of the anode 5, thereby generating nitrogen gas by denitrification of ammonia in the water to be treated (reaction C). Reaction C is shown below.
Reaction C NH ₃ (aq) +3 (O) → N ₂ ↑ + 3H ₂ O
[0026]
This makes it possible to effectively treat nitrogen compounds such as nitrate nitrogen, nitrite nitrogen, and ammonia nitrogen in the water to be treated.
[0027]
Further, calcium chloride is added to the water to be treated in order to treat phosphorus compounds in the water to be treated, that is, phosphate ions. As a result, the calcium ions of calcium chloride added to the water to be treated coagulate and precipitate with the phosphate ions in the water to be treated by the dephosphorization reaction because the vicinity of the cathode 6 is alkaline as described above. Hydroxyapatite is produced (Reaction D). Reaction D is shown below.
Reaction D 10Ca ²⁺ + 2OH ⁻ + 6PO ₄ ^3- → Ca ₁₀ (OH) ₂ (PO ₄ ) ₆
[0028]
As shown in Reaction Formula D, the molar ratio of calcium ions required for coagulating and precipitating the phosphate ions is 10 with respect to the molar ratio of phosphate ions of 6. Therefore, the amount of calcium ions of calcium chloride added to the water to be treated is 5/3 times or more in molar ratio with respect to the amount of phosphate ions contained in the water to be treated. In addition, when calcium ions are present in the treated water in advance, including the amount of the calcium ions, the molar ratio is 5/3 times or more with respect to the amount of phosphate ions contained in the treated water. Calcium chloride may be added.
[0029]
Thereby, phosphorus can be effectively coagulated and precipitated by making calcium ions sufficient for coagulating and precipitating phosphate ions in the water to be treated, so that the processing efficiency of phosphorus can be improved. Become.
[0030]
Normally, in order to cause the dephosphorization reaction D, it is necessary to add a special chemical to make the solution alkaline, but in the present invention, the vicinity of the cathode is alkaline, so that is not necessary. . Further, the solution made alkaline by chemicals or the like needs to be neutralized by a pH adjuster during drainage, but in the present invention, adjustment of the pH is not necessary.
[0031]
On the other hand, the chlorine ions of calcium chloride added to the water to be treated are oxidized at the anode 5 to produce chlorine (reaction E). The produced chlorine reacts with water in the water to be treated, and the hypochlorite. Chloric acid is produced (reaction F). And the produced | generated hypochlorous acid reacts with the ammonia which exists in to-be-processed water, and after passing through several chemical changes, it is converted into nitrogen gas (reaction G). Hereinafter, Reaction E to Reaction G are shown.
Reaction ^{_{E CaCl 2 → Ca 2+ + 2Cl}} -2Cl - → Cl 2 + 2e - reaction _{F Cl 2 + H 2 O →} HClO + HCl Reaction _{G 2NH 4 + 4HClO → N 2} ↑ + 4HCl + 4H 2 O
[0032]
Here, the experimental results shown in FIG. 3 show that time elapsed when platinum and iridium electrodes were used for the anode 5 and the cathode 6 and 300 ml of 0.001M potassium nitrate was electrolyzed by adding phosphoric acid and calcium chloride. The accompanying concentration change of each ion is shown.
[0033]
According to FIG. 3, since nitrate ions are gradually changed to ammonia ions at the cathode 6, they decrease with the passage of time, and are almost present in the water to be treated after 170 minutes from the start of electrolysis. Not done. On the other hand, the ammonia ion generated at the cathode 6 gradually increases and then reacts with the chlorine ions of calcium chloride added to the water to be treated after a certain period of time. Along with the decrease, 170 minutes after the start of electrolysis, it is hardly present in the water to be treated.
[0034]
Further, in the vicinity of the anode 5, phosphate ions undergo a dephosphorylation reaction with calcium ions of calcium chloride, whereby precipitates are formed on the bottom surface of the treatment tank 2 in the form of calcium hydroxyapatite. Therefore, phosphate ions and calcium ions used for the dephosphorization reaction of phosphate ions gradually decrease with time, and after 300 minutes from the start of electrolysis, phosphate ions are treated. Almost no in the water.
[0035]
Thus, by adding calcium chloride to the water to be treated as described above, calcium ions are subjected to a dephosphorylation reaction, and the phosphorous ion dephosphorization reaction in the water to be treated can be promoted and the same treatment tank. 2, the reduction reaction of nitrate nitrogen and nitrite nitrogen to ammonia can be promoted, and the time required for the reduction reaction can be shortened.
[0036]
Therefore, the phosphorus compound and the nitrogen compound can be processed in the same tank without providing a special separate processing tank, and the wastewater treatment apparatus 1 can be downsized.
[0037]
In addition, the ammonia generated from the cathode 6 can effectively remove nitrogen components such as nitrate nitrogen, ammonia nitrogen, and nitrogen compounds by a synergistic effect by performing a denitrification reaction with the hypochlorous acid substance. become able to.
[0038]
Furthermore, since the phosphate ions can be condensed and precipitated by utilizing the fact that the pH in the vicinity of the cathode 6 becomes alkaline, it is not necessary to adjust the water to be treated to neutral after the treatment.
[0039]
As a result, nitrogen compounds and phosphorus compounds can be efficiently removed from the water to be treated containing nitrogen compounds and phosphorus compounds discharged from ordinary households and factories, and the treatment capacity of nitrogen compounds and phosphorus compounds is improved. Be improved.
[0040]
Further, as a first specific application example of the present invention, as shown in FIG. 4, water to be treated is stored in a biological treatment septic tank, in this embodiment a so-called activated sludge treatment tank 11, and the activated sludge treatment tank 11 is stored. After removing COD and BOD, the treated water that has been subjected to the COD and BOD treatment is treated with a nitrogen compound and a phosphorus compound in the treatment tank 2 of the wastewater treatment apparatus 1 to which the present invention is applied.
[0041]
As a result, after the COD and BOD are once treated in the activated sludge treatment tank 11, the wastewater treatment apparatus 1 can further treat the nitrogen compound and the phosphorus compound. It becomes possible to treat water effectively. Further, the water to be treated treated in the activated sludge treatment tank 11 contains bacteria generated in the activated sludge treatment tank 11, but hypochlorite and active in the wastewater treatment apparatus 1 as described above. Since it is sterilized by oxygen, the water to be treated can be drained in a state suitable for the environment.
[0042]
Furthermore, as a second specific application example of the present invention, as shown in FIG. 5, suspended substances in the water to be treated can be removed by so-called electrolytic levitation.
[0043]
Furthermore, as a third specific application example of the present invention, as shown in FIG. 6, it can be used for removing nitrogen compounds and phosphorus compounds of water in the aquarium 12 inhabiting fish in a cage or an aquarium. In the aquarium inhabiting fish, water is significantly polluted by nitrogen compounds such as ammonia discharged from the fish. Therefore, it is necessary to periodically exchange the water in the aquarium. Therefore, the water in the water tank 12 containing the nitrogen compound is treated with the nitrogen compound in the waste water treatment device 1, and then the treated water drained from the waste water treatment device 1 is treated with the hypochlorous acid removal device 13. Hypochlorous acid in the treated water is removed and returned to the water tank 12.
[0044]
Thereby, it becomes unnecessary to exchange the water in the water tank 12 regularly, and the maintenance workability | operativity of the water tank 12 can be improved. Moreover, since the to-be-processed water stored in the waste water treatment apparatus 1 from the water tank 12 is sterilized by hypochlorous acid, the to-be-processed water is returned to the water tank 12 after that, and the survival rate of the fish in the water tank 12 Can be improved.
[0045]
In addition to this, the wastewater treatment method to which the present invention is applied can be applied to purification of water to be treated in a pool or bathhouse, purification of well water or ground water, and the like.
[0046]
【The invention's effect】
As described above in detail, according to the present invention, in the method for treating nitrogen compounds and phosphorus compounds in water to be treated by an electrochemical method, the metal material constituting the cathode is a conductor, and the conductivity constituting the anode. The material is an insoluble material or carbon, and calcium chloride is added to the water to be treated. Therefore, ammonia in the water to be treated is denitrified with substances such as hypochlorous acid by the chlorine ions of calcium chloride. By doing so, nitrogen components such as nitrate nitrogen, ammonia nitrogen and nitrogen compounds can be effectively removed by a synergistic effect.
[0047]
Furthermore, since the phosphate ions can be condensed and precipitated by utilizing the fact that the pH in the vicinity of the cathode becomes alkaline, it is not necessary to adjust the water to be treated to neutral after the treatment.
[0048]
As a result, nitrogen compounds and phosphorus compounds can be efficiently removed from the water to be treated containing nitrogen compounds and phosphorus compounds discharged from ordinary households and factories, and the treatment capacity of nitrogen compounds and phosphorus compounds is improved. Be improved.
[0049]
Moreover, it becomes possible to perform the treatment of the phosphorus compound and the nitrogen compound in the same tank without providing a special separate treatment tank, so that the processing apparatus for realizing the present invention can be miniaturized. Become.
[0050]
According to the invention of claim 2, in addition to the invention of claim 1, the metal material constituting the cathode is a conductor containing the group Ib or IIb of the periodic table, or a conductor coated with the same group. Since one is used, the reduction reaction of nitrate nitrogen and nitrite nitrogen in the water to be treated to ammonia can be further promoted, and the time required for the reduction reaction can be further shortened.
[0051]
According to the invention of claim 3, in addition to the invention of claim 2, the amount of calcium ions contained in the for-treatment water is 5/3 times the molar ratio of phosphate ions contained in the for-treatment water. As described above, by allowing calcium ions sufficient to coagulate and precipitate phosphate ions in the water to be treated, it is possible to effectively coagulate and precipitate phosphorus and improve the treatment efficiency of phosphorus. It becomes like this.
[0052]
According to the invention of claim 4, in addition to the invention of claim 1, claim 2 or claim 3, the treated water is water after being treated by the biological treatment septic tank. For example, COD and BOD are highly removed in an activated sludge treatment tank or the like, and bacteria generated in the activated sludge treatment tank can be sterilized with hypochlorous acid or active oxygen, and then discharged. .
[0053]
According to the waste water treatment system of the invention of claim 5, the waste water treatment apparatus for treating nitrogen compounds and phosphorus compounds in the water to be treated by the waste water treatment method of claim 1, claim 2 or claim 3 Since it is placed in the latter stage, after removing COD and BOD in biological treatment septic tanks, such as activated sludge treatment tanks, and sterilizing bacteria generated in activated sludge treatment tanks with hypochlorous acid and active oxygen It will be possible to treat waste water.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing an outline of a wastewater treatment apparatus for realizing a wastewater treatment method of the present invention.
FIG. 2 is an explanatory diagram of the structure of an anode.
FIG. 3 is a diagram showing changes in each ion concentration.
FIG. 4 is a diagram illustrating a first specific application example of the present invention.
FIG. 5 is a diagram illustrating a second specific application example of the present invention.
FIG. 6 is a diagram for explaining a third specific application example of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Waste water treatment apparatus 2 Treatment tank 4 Waste water treatment room 5 Anode 6 Cathode 7 Power supply 9 Shielding member 10 Stirrer 11 Activated sludge treatment tank 12 Water tank 13 Hypochlorous acid removal apparatus

Claims (5)

Any or all of phosphoric acid, phosphorus compound and phosphate ion in the water to be treated by electrochemical technique , and any of organic nitrogen, nitrite nitrogen, nitrate nitrogen and ammonia nitrogen or A wastewater treatment method for treating everything ,
The metal material constituting the cathode is a conductor, and the conductive material constituting the anode is an insoluble material or carbon,
A treatment of adding calcium chloride to the water to be treated;
A process of oxidizing hypochlorite in the anode by oxidizing chlorine ions of the calcium chloride;
After reducing the nitrite nitrogen or nitrate nitrogen at the cathode, oxidizing the hypochlorous acid to remove the nitrogen component;
A treatment of aggregating and precipitating the phosphorus compound with calcium ions of the calcium chloride;
A wastewater treatment method comprising:   The wastewater treatment method according to claim 1, wherein the metal material constituting the cathode is a conductor containing Group Ib or Group IIb of the periodic table, or a conductor coated with the same group. Any or all of phosphoric acid, phosphorus compound and phosphate ion in the water to be treated by electrochemical technique , and any of organic nitrogen, nitrite nitrogen, nitrate nitrogen and ammonia nitrogen or A wastewater treatment method for treating everything ,
The metal material constituting the cathode is a conductor containing Group Ib or Group IIb of the periodic table, or a conductor coated with the same group.
The conductive material constituting the anode is an insoluble material or carbon,
In the wastewater treatment method in which calcium chloride is added to the treated water,
The wastewater treatment method characterized in that the amount of calcium ions contained in the water to be treated is at least 5/3 times the molar ratio of the amount of phosphate ions contained in the water to be treated.   The wastewater treatment method according to claim 1, wherein the treated water is water after being treated in a biological treatment septic tank. Any or all of phosphoric acid, phosphorus compound and phosphate ion in water to be treated by the waste water treatment method of claim 1, claim 2 or claim 3 , and organic nitrogen, nitrite nitrogen and nitric acid A wastewater treatment system in which a wastewater treatment apparatus for treating any or all of nitrogen and ammonia nitrogen is disposed in a subsequent stage of a biological treatment septic tank.

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