JP2002254080A - Waste water treatment process and waste water treatment system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an effective treatment process capable of treating untreated water containing nitrogen compounds and phosphorus compounds. SOLUTION: In an electrochemical treatment process for untreated water containing nitrogen compounds and phosphorus compounds, a cathode 6 whose metal material is composed of electric conductor and an anode 5 whose metal material is composed of insoluble metal or carbon, and untreated water contains calcium chloride.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for treating wastewater containing phosphoric acid, phosphorus compounds, phosphate ions, organic nitrogen, nitrite nitrogen, nitrate nitrogen, and ammonia nitrogen.

[0002]

2. Description of the Related Art Conventionally, one of the causes of eutrophication of rivers and lakes.
It is well known that there are nitrogen compounds and phosphorus compounds. Further, these phosphorus compounds and nitrogen compounds are abundant in domestic household wastewater and industrial wastewater, but are difficult to purify, and no effective measures can be taken at present. Generally, biological treatment is performed to treat nitrogen compounds. First, a nitrification step of converting ammonia nitrogen to nitrate nitrogen and a denitrification step of converting nitrate nitrogen to nitrogen gas are performed. Is being done.

[0003] On the other hand, various methods for treating a phosphorus compound have been proposed. For domestic wastewater, a lime coagulation sedimentation method is known. This technology is a technology in which phosphate ions in the water to be treated are reacted with calcium ions to be condensed and precipitated as a water-insoluble salt, calcium hydroxyapatite, and removed.

[0004]

However, in the conventional biological treatment, two reaction tanks are required, and the treatment time is slow, so that the treatment efficiency is reduced.
Further, in the above-mentioned conventional method, since the water to be treated containing the nitrogen compound and the phosphorus compound is not simultaneously treated, there is a problem that the apparatus becomes large.

[0005] In the biological treatment, large-capacity aerobic tanks and anaerobic tanks are required to hold nitrifying bacteria and denitrifying bacteria, which causes a rise in equipment construction costs and an increase in equipment installation area. was there. Furthermore, since the denitrifying bacteria are significantly affected by the surrounding temperature environment and other components contained in the water to be treated, the activity is reduced particularly in winter when the temperature is lowered, and the denitrifying action is reduced. There has been a problem that the processing efficiency is reduced and the processing efficiency becomes unstable.

Furthermore, in the above-mentioned method for treating a phosphorus compound, since the pH in the formation of condensation precipitate is high, it is necessary to treat the phosphorus compound from alkaline to neutral. Further, there is a problem that the amount of lime used is large and maintenance is difficult.

Accordingly, the present invention has been made to solve the conventional technical problem, and proposes a wastewater treatment method capable of efficiently treating water to be treated containing a nitrogen compound and a phosphorus compound. I do.

[0008]

SUMMARY OF THE INVENTION The present invention is a method for treating a nitrogen compound and a phosphorus compound in water to be treated by an electrochemical method, wherein the metal material constituting the cathode is a conductor, and The conductive material is an insoluble material or carbon, and calcium chloride is added to the water to be treated.

According to the present invention, in the method for treating a nitrogen compound and a phosphorus compound in water to be treated by an electrochemical method, the metal material forming the cathode is a conductor, and the conductive material forming the anode is In addition to the insoluble material or carbon, the water to be treated is added with calcium chloride.
Ammonia in the water to be treated undergoes a denitrification reaction with a substance such as hypochlorous acid, thereby effectively removing nitrogen components such as nitrate nitrogen, ammonia nitrogen and nitrogen compounds by a synergistic effect. Become like

Further, phosphate ions can be condensed and precipitated by making use of the fact that the pH near the cathode becomes alkaline, so that there is no need to adjust the water to be treated to neutral after the treatment.

[0011] This makes it possible to efficiently remove nitrogen compounds and phosphorus compounds from the water to be treated containing nitrogen compounds and phosphorus compounds discharged from general households and factories, thereby improving the wastewater treatment capacity. You.

Further, it is possible to perform the treatment of the phosphorus compound and the nitrogen compound in the same tank without providing a specially separate processing tank, so that the processing apparatus for realizing the present invention can be downsized. become able to.

According to a second aspect of the present invention, in addition to the first aspect, the metal material forming the cathode may be a conductor containing Group Ib or Group IIb of the periodic table or a homologous conductor. It is characterized by using a material covered with a conductor.

According to the invention of claim 2, in addition to the invention of claim 1, the metal material forming the cathode is a conductor containing Group Ib or Group IIb of the periodic table or a conductor containing the same group. 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 reduced. .

According to a third aspect of the present invention, the amount of calcium ions contained in the water to be treated is at least 5/3 times the molar amount of the phosphate ions contained in the water to be treated. It is characterized by.

According to the invention of claim 3, in addition to the invention of claim 2, the amount of calcium ions contained in the water to be treated is 5 times the molar ratio of the amount of phosphate ions contained in the water to be treated. / 3 times or more, phosphorus can be effectively coagulated and precipitated by allowing sufficient calcium ions to coagulate and precipitate phosphate ions in the water to be treated, thereby improving the phosphorus treatment efficiency. Will be able to do it.

According to a fourth aspect of the present invention, in addition to the first, second, or third aspect of the present invention, the water to be treated is water treated by a biological treatment septic tank. Features.

According to the fourth aspect of the present invention, in addition to the first, second, or third aspect of the present invention, the water to be treated is water that has been treated by a biological treatment septic tank. CO2 and B in an activated sludge treatment tank such as an activated sludge treatment tank
After removing OD etc. to a high degree, after sterilizing bacteria generated in the activated sludge treatment tank with hypochlorous acid or active oxygen,
Wastewater can be treated.

According to a fifth aspect of the present invention, there is provided a wastewater treatment system comprising a nitrogen and phosphorus treatment apparatus for treating a nitrogen compound and a phosphorus compound in water to be treated by the wastewater treatment method according to the first, second or third aspect. A wastewater treatment system, which is disposed at the latter stage of a wastewater treatment septic tank.

According to a fifth aspect of the present invention, there is provided a wastewater treatment system for treating a nitrogen compound and a phosphorus compound in water to be treated by the wastewater treatment method according to the first, second, or third aspect. Is disposed downstream of the biological treatment septic tank, so that COD and BOD can be highly removed in a biological treatment septic tank, for example, an activated sludge treatment tank, and bacteria generated in the activated sludge treatment tank can be treated with hypochlorous acid or After sterilization with active oxygen, the wastewater can be treated.

[0021]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing an outline of a wastewater treatment apparatus 1 for realizing the nitrogen and phosphorus treatment method of the present invention. The wastewater treatment apparatus 1 according to the present embodiment has a treatment tank 2 that constitutes a treatment chamber 4 having an inlet and an outlet for wastewater (not shown), and at least a part of the treatment tank 2 is immersed in the water to be treated in the treatment chamber 4. A pair of electrodes, ie, an anode 5, a cathode 6, and the electrodes 5, 6
And a control device (not shown) for controlling the electrodes 7. In addition, 1 in the figure
Reference numeral 0 denotes a stirrer as stirring means for stirring the inside of the processing tank 2.

The cathode 6 is made of a conductor containing Group Ib or Group IIb of the periodic table, or a material obtained by coating the same with a conductor.
It is composed of an insoluble electrode containing an insoluble metal, for example, platinum, iridium, palladium or an oxide thereof, or carbon.

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, for example, a non-conductive member such as a glass fiber or a plastic mesh, whereby oxygen bubbles generated from the anode 5 are removed from the cathode 6.
To the side. At this time,
Ions existing on the anode 5 side can pass through the shielding member 9 and move to the cathode 6 side.

With the above configuration, the processing chamber 4 in the processing tank 2
To store treated water containing nitrate nitrogen and phosphorus compounds
The power supply 7 is turned on by the control device, and the cathode 6 and the anode 5 are energized. Thus, 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, the nitrite ions generated by the reduction reaction of the nitrate ions are further converted to ammonia by the reduction reaction (reaction B). At this time, the vicinity of the cathode 6 becomes alkaline. The reaction A and the 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) +7
OH ^-

On the other hand, on the anode 5 side, active oxygen and hypochlorous acid are generated from the surface of the anode 5, whereby nitrogen gas is generated by denitrification of ammonia in the water to be treated (reaction C). The reaction C is shown below. Reaction C NH ₃ (aq) +3 (O) → N ₂ ↑ + 3H ₂ O

This makes it possible to effectively treat nitrogen compounds such as nitrate nitrogen, nitrite nitrogen and ammonia nitrogen in the water to be treated.

Further, calcium chloride is added to the water to be treated in order to treat the phosphorus compound in the water to be treated, that is, phosphate ions. As a result, the calcium ions of the 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, and the water-insoluble calcium ions Produce hydroxyapatite (reaction D). The reaction D is shown below. Reaction D 10Ca ²⁺ + 2OH ⁻ + 6PO ₄ ^3- → Ca ₁₀ (O
H) ₂ (PO ₄ ) ₆

As shown in Reaction Formula D, the molar ratio of calcium ions required to coagulate and precipitate 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 at least 5/3 times the molar amount of phosphate ions contained in the water to be treated.
When calcium ions are present in the water to be treated in advance, the molar ratio of the calcium ions, including the amount of the calcium ions, to the amount of the phosphate ions contained in the water to be treated is 5/3.
More than twice the amount of calcium chloride may be added.

[0029] In this way, by allowing sufficient calcium ions to coagulate and precipitate phosphate ions in the water to be treated, phosphorus can be coagulated and precipitated effectively, and the phosphorus treatment efficiency can be improved. become able to.

Usually, in order to cause the above-mentioned dephosphorization reaction D, it is necessary to add a special chemical in order to make the solution alkaline, but in the present invention, the vicinity of the cathode is alkaline, No need. Further, the solution made alkaline by chemicals or the like must be neutralized with a pH adjuster at the time of drainage. However, in the present invention, the adjustment of the pH is not necessary.

On the other hand, chloride ions of calcium chloride added to the water to be treated are oxidized at the anode 5 to produce chlorine (reaction E), and the produced chlorine reacts with water in the water to be treated. To produce hypochlorous acid (reaction F). The generated hypochlorous acid reacts with ammonia present in the water to be treated, undergoes a plurality of chemical changes, and is converted into nitrogen gas (reaction G). Hereinafter, Reactions E to 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

Here, the experimental results shown in FIG. 3 show that the anode 5 and the cathode 6 were made of platinum and iridium-based electrodes, and phosphoric acid and calcium chloride were added.
The graph shows changes in the concentration of each ion with time when 300 ml of potassium nitrate is electrolyzed.

According to FIG. 3, at the cathode 6, nitrate ions are gradually changed to ammonia ions.
It decreases with the passage of time.
After a lapse of 70 minutes, it hardly exists in the water to be treated.
On the other hand, at the cathode 6, the ammonia ions generated gradually increase, and after a certain period of time, react with the chloride ions of calcium chloride added to the water to be treated, gradually decrease, and the nitrate ions are reduced. Due to the decrease, almost no water is present in the water to be treated 170 minutes after the start of electrolysis.

In the vicinity of the anode 5, phosphate ions undergo a dephosphorization reaction with calcium ions of calcium chloride, and as a result, 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 in the dephosphorization reaction of phosphate ions gradually decrease with time, and after 300 minutes from the start of electrolysis, phosphate ions are treated. Almost non-existent in water.

Thus, by adding calcium chloride to the water to be treated as described above, calcium ions are subjected to a dephosphorization reaction, and the dephosphorization reaction of phosphate ions in the water to be treated can be promoted. Same treatment tank 2
Within, 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.

Therefore, the phosphorus compound and the nitrogen compound can be treated in the same tank without providing a separate treatment tank, and the size of the wastewater treatment apparatus 1 can be reduced.

The ammonia generated from the cathode 6 undergoes a denitrification reaction with a substance of hypochlorous acid, thereby effectively removing nitrogen components such as nitrate nitrogen, ammonia nitrogen and nitrogen compounds by a synergistic effect. Will be able to

Furthermore, since phosphate ions can be condensed and precipitated by utilizing the fact that the pH in the vicinity of the cathode 6 becomes alkaline, there is no need to adjust the water to be treated to neutral after the treatment.

This makes it possible to efficiently remove the nitrogen compound and the phosphorus compound from the water to be treated containing the nitrogen compound and the phosphorus compound discharged from general households, factories and the like. Processing capacity is improved.

As a first concrete application example of the present invention, as shown in FIG. 4, a 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 is carried out. After removing COD and BOD in the tank 11, the CO
The treated water subjected to the D and BOD treatments 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.

Thus, the water to be treated is supplied to the activated sludge treatment tank 1
After once treating COD and BOD in step 1, the wastewater treatment apparatus 1 can further treat nitrogen compounds and phosphorus compounds, so that the water to be treated can be treated effectively. become. The activated sludge treatment tank 11
The water to be treated, which is treated in the wastewater treatment apparatus 11, contains bacteria generated in the activated sludge treatment tank 11, but is sterilized by the wastewater treatment apparatus 1 with hypochlorous acid or active oxygen as described above. The treated water can be drained in a state suitable for the environment.

Further, 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.

Further, as a third specific application example of the present invention, as shown in FIG. 6, the present invention can be used for removing nitrogen compounds and phosphorus compounds in water in a water tank 12 for inhabiting fish in a fish cage or an aquarium. it can. The water in which a fish inhabits is remarkably contaminated by nitrogen compounds such as ammonia discharged from the fish, so that it is necessary to periodically replace the water in the water tank. Therefore, the water tank 1 containing a nitrogen compound
The water in 2 is treated with a nitrogen compound by the wastewater treatment device 1, and then the treated water discharged from the wastewater treatment device 1 is treated with hypochlorous acid in the treated water by the hypochlorous acid removing device 13. Is removed and returned into the water tank 12.

Accordingly, it is not necessary to periodically change the water in the water tank 12, and the maintenance workability of the water tank 12 can be improved. In addition, since the water to be treated stored in the wastewater treatment device 1 from the water tank 12 is sterilized by hypochlorous acid, the water to be treated is returned to the water tank 12 and the survival rate of the fish in the water tank 12 is returned. Can be improved.

In addition, 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 a bath, purification of well water or groundwater, and the like.

[0046]

As described in detail above, according to the present invention, in a method for treating a nitrogen compound and a phosphorus compound in water to be treated by an electrochemical method, the metal material constituting the cathode is a conductor, Since the conductive material constituting is an insoluble material or carbon, and calcium chloride is added to the water to be treated, ammonia in the water to be treated is changed by chlorine ions of calcium chloride, such as hypochlorous acid. By performing a denitrification reaction with the substance, a nitrogen component such as nitrate nitrogen, ammonia nitrogen and a nitrogen compound can be effectively removed by a synergistic effect.

Furthermore, phosphate ions can be condensed and precipitated by utilizing the fact that the pH in the vicinity of the cathode becomes alkaline, so that there is no need to adjust the water to be treated to neutral after the treatment.

As a result, the nitrogen compound and the phosphorus compound can be efficiently removed from the treated water containing the nitrogen compound and the phosphorus compound discharged from general households and factories, and the nitrogen compound and the phosphorus compound can be efficiently removed. Processing capacity is improved.

Further, it is possible to perform the treatment of the phosphorus compound and the nitrogen compound in the same tank without providing a specially separate processing tank, so that the processing apparatus for realizing the present invention can be downsized. become able to.

According to the invention of claim 2, in addition to the invention of claim 1, the metal material forming the cathode is a conductor containing Group Ib or Group IIb of the periodic table or a conductor containing the same group. 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 reduced. .

According to the invention of claim 3, in addition to the invention of claim 2, the amount of calcium ions contained in the water to be treated is 5 times the molar ratio of the amount of phosphate ions contained in the water to be treated. / 3 times or more, phosphorus can be effectively coagulated and precipitated by allowing sufficient calcium ions to coagulate and precipitate phosphate ions in the water to be treated, thereby improving the phosphorus treatment efficiency. Will be able to do it.

According to the fourth aspect of the present invention, in addition to the first, second or third aspect of the present invention, since the water to be treated is water that has been treated by a biological treatment septic tank, CO2 and B in an activated sludge treatment tank such as an activated sludge treatment tank
After removing OD etc. to a high degree, after sterilizing bacteria generated in the activated sludge treatment tank with hypochlorous acid or active oxygen,
Wastewater can be treated.

According to the wastewater treatment system of the fifth aspect, the wastewater treatment apparatus for treating nitrogen compounds and phosphorus compounds in the water to be treated by the wastewater treatment method according to the first, second or third aspect is a biological wastewater treatment system. Since it is arranged at the latter stage of the treatment septic tank, the biological treatment septic tank, for example, activated sludge treatment tank
OD and BOD can be removed to a high degree, and bacteria generated in the activated sludge treatment tank can be sterilized with hypochlorous acid or active oxygen and then subjected to wastewater treatment.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an outline of a wastewater treatment apparatus for realizing a wastewater treatment method of the present invention.

FIG. 2 is a diagram illustrating the structure of an anode.

FIG. 3 is a diagram showing a change 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 illustrating a third specific application example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wastewater treatment apparatus 2 Treatment tank 4 Wastewater treatment chamber 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

Continued on front page F-term (reference) 4D028 AB00 AC01 AC03 4D038 AA08 AB45 BA02 BB10 BB13 4D061 DA08 DB01 DB10 DB19 DC14 EA02 EA03 EB01 EB04 EB11 EB29 EB31 FA15

Claims (5)

[Claims] 1. A wastewater treatment method for treating a nitrogen compound and a phosphorus compound in water to be treated by an electrochemical method, wherein the metal material forming the cathode is a conductor, and the conductive material forming the anode is: A wastewater treatment method, wherein the treatment target water is calcium chloride added to the water to be treated. 2. The metal material forming the cathode is a conductor containing Group Ib or Group IIb of the periodic table, or a material obtained by coating the same with a conductor. Wastewater treatment method. 3. 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. Wastewater treatment method. 4. The wastewater treatment method according to claim 1, wherein the water to be treated is water treated by a biological treatment septic tank. 5. A wastewater treatment apparatus for treating a nitrogen compound and a phosphorus compound in water to be treated according to the wastewater treatment method according to claim 1, 2, 3 or 4, which is disposed downstream of the biological treatment septic tank. And wastewater treatment system.