JP2001047051A - Water treatment device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a water treatment device capable of assuring eluation of iron ions and preventing phosphorus-removing capacity from being lowered due to the iron oxide layer formed on the surfaces of electrodes. SOLUTION: A septic tank 1 is provided with a dephosphorization treating apparatus P having an electrolytic cell 30, iron electrodes 31, 32 and a power source 33. In the electrolytic cell 30, an aeration tube 34 and a blower 35 are installed. Iron ions which react with phosphoric acid in water are eluted from electrodes 31, 32 by electrolysis. The electrodes 31, 32, both of positive and negative electrodes, are made of carbon steel having the carbon content of 0.2-0.9 wt.%. A controlling section 20 controls the amount of eluted iron ions by controlling the electric current fed to the electrodes 31, 32, and controls a polarity-switching device 21 to switch the polarity of the electrodes 31, 32.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a water treatment apparatus,
More specifically, the present invention relates to a water treatment apparatus incorporated in a septic tank for treating human wastewater or domestic wastewater or a water tank for breeding organisms, and for removing phosphoric acid from water to be treated.

[0002]

2. Description of the Related Art Conventionally, as this type of water treatment apparatus, there is known an apparatus provided with an iron electrode for eluting iron ions by electrolysis for removing phosphoric acid in water.

[0003]

In such a water treatment apparatus, no particular attention is paid to the type and composition of the iron material used for the iron electrode.

[0004] During the electrolysis, the iron electrode may be affected by phosphate ions, nitrate ions, nitrite ions and the like in the water, and an iron oxide layer may be formed on the electrode surface.

[0005] In this case, the iron oxide layer on the electrode surface may inhibit the elution of iron ions from the iron electrode (passivation), and the phosphorus removal capability of the water treatment apparatus may be significantly reduced.

The present invention has been made in view of such circumstances, and can stably elute iron ions, and the phosphorus removing ability is reduced by the iron oxide layer formed on the electrode surface. It is an object of the present invention to provide a water treatment device capable of preventing the fear.

[0007]

According to the present invention, there is provided an electrolytic cell containing water to be treated, and iron ions disposed in the electrolytic cell for removing phosphoric acid in water are electrolyzed. At least a pair of electrodes, a power supply for supplying an electrolytic current to these electrodes, and a control unit connected to the electrodes and the power supply for controlling electrolysis, At least one of 0.2 to
A water treatment apparatus is provided, which is made of a steel material containing 0.9% by weight of carbon.

[0008] The pair of electrodes, for example, both comprise iron electrodes, or one comprises an iron electrode and the other comprises an insoluble metal electrode. In the former case, it is possible to prevent the formation of an iron oxide layer on the electrode surface, which may obstruct the elution of ions from the electrode, by the control unit inverting the polarity of the electrode as desired. In the latter case, the iron electrode is used as an anode and the insoluble metal electrode is used as a cathode. Examples of the insoluble metal electrode include an electrode made of silver, platinum, or the like. Note that the water treatment apparatus according to the present invention further includes an electrode holder for holding the electrode, in order to perform the electrode replacement work in a shorter time, and the electrode is configured to be detachable from the electrode holder, The electrode and the electrode holder may be configured to be electrically connectable.

The iron electrode used in the water treatment apparatus according to the present invention is made of a steel material containing 0.2 to 0.9% by weight of carbon.

The lower limit of the carbon content of the iron electrode is 0.2% by weight.
It is based on the following facts.

[0011] That is, the present inventor has proposed using a variety of iron electrodes having different carbon contents in a liquid to be treated containing a phosphate ion and a nitrite ion (an ion which is likely to cause passivation). A phosphorus removal test was conducted in which electrolysis was performed under electrolysis conditions such that the iron ion concentration with respect to the ion concentration became 1.5 times the molar ratio. FIG. 3 shows the test results. From this test,
When a steel material having a carbon content of 0.2% by weight or more is used for the iron electrode, the molar ratio of the iron ion concentration eluted into the liquid to be treated from the iron electrode to the phosphate ion concentration is at least 1.0 on average. It turns out that it can be done.

[0012] The use of a steel material having a carbon content of 0.2% by weight or more has the effect of preventing the iron oxide layer formed on the electrode surface during electrolysis from sticking to the electrode surface.
It is considered that stable elution of iron ions became possible. Therefore, the lower limit of the carbon content of the steel material constituting the iron electrode was set to 0.2% by weight.

On the other hand, the upper limit of the carbon content of the iron electrode is set to 0.9.
The weight percentage is determined based on the following facts.

That is, in general, the structure of carbon steel is such that when the carbon content in the steel is less than 0.9%, ferrite, 0.9%
Is classified as pearlite, and above 0.9% is classified as cementite. The inventor conducted electrolysis under the same conditions using each of these three types of tissues as an iron electrode. As a result, it was found that iron ions easily eluted in the case of ferrite. Therefore, the upper limit of the carbon content of the steel material constituting the iron electrode was set to 0.9% by weight.

As described above, the carbon content of the steel constituting the iron electrode is in the range of 0.2 to 0.9% by weight, and more preferably in the range of 0.3 to 0.8% by weight. And most preferably in the range of 0.4-0.7% by weight.

The iron ions eluted from the iron electrode into the electrolytic cell are:
It reacts with phosphoric acid (orthophosphoric acid) in water to form a poorly soluble phosphorus compound (Fe (OH) _x (PO ₄ ) _y ) and aggregates and precipitates. The elution amount of iron ions in the electrolytic cell is adjusted by controlling the electrolytic current supplied from the power supply by the control unit.

[0017] In the water treatment apparatus according to the present invention, it is preferable that both the pair of electrodes are made of the above-mentioned steel material, and the control unit further reverses the polarity of the electrodes. In that case, formation or fixation of the iron oxide layer on the electrode surface can be prevented.

In the water treatment apparatus according to the present invention, an electrolytic tank is provided with an aeration pipe in the tank for aerating the electrodes and a blower outside the tank for supplying air to the aeration pipe. Is preferred. In this case, it is possible to prevent the iron oxide layer from being formed or fixed on the electrode surface by aerating the electrode.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to the drawings. Note that the present invention is not limited by this.

As shown in FIG. 1, a small-sized combined treatment / purification tank D incorporating a dephosphorization treatment device P as a water treatment device according to one embodiment of the present invention is a mixture of human wastewater and domestic wastewater. From the side of the inflow pipe 2 into which water flows, to the side of the discharge pipe 3 which discharges water treated water to the outside, a purification tank main body 1 in which a plurality of tanks are formed in accordance with the process order of the water purification treatment is provided. I have.

Reference numeral 4 denotes a first anaerobic filter bed tank formed at the forefront of the inflow pipe 2 side. The first anaerobic filter bed tank 4 is provided with an anaerobic filter bed 5 which is a filter bed for anaerobic microorganisms.
Anaerobic treatment is performed by inhabiting microorganisms in the anaerobic filter bed 5. The anaerobic filter bed 5 suppresses the load of the next tank by preventing the sediment from being lifted up by the water flow when the inflow water or backwash wastewater temporarily flows in and becoming a suspended substance and flowing out to the next tank. Can be lowered.

Reference numeral 6 denotes a next second anaerobic filter bed tank formed adjacent to the first anaerobic filter bed tank 4. In the second anaerobic filter bed tank 6, anaerobic microorganisms are made to inhabit the anaerobic filter bed 7 to perform anaerobic treatment.

Reference numeral 8 denotes a next biofilm filtration tank formed adjacent to the second anaerobic filter bed tank 6. The biofilm filtration tank 8 is provided with an aerobic filter bed 9 which is a filter bed for aerobic microorganisms. The aerobic microorganisms inhabit the aerobic filter bed 9 to perform aerobic treatment. ing.

Reference numeral 10 denotes a next treated water tank formed adjacent to the biofilm filtration tank 8. In the treated water tank 10, the treated water that has been subjected to aerobic treatment in the biofilm filtration tank 8 and that has been filtered and advected is stored.

Numeral 11 denotes a disinfecting tank formed above the treated water tank 10. This disinfection tank 11 is usually
The supernatant water after the treatment is sterilized and discharged from the discharge pipe 3 to the outside.

The first anaerobic filter tank 4 and the second anaerobic filter tank 6 are separated by a vertical partition 12. At the upper part of the partition wall 12, an advection port 13 penetrating the partition wall 12 is formed. A rectangular or cylindrical advection tube 14 is fitted in the advection port 13. The lower end of the advection tube 14 is located below the anaerobic filter bed 5 of the first anaerobic filter bed tank 4 and also serves as a cleaning port.

The second anaerobic filter bed tank 6 and the next biofilm filtration tank 8 are separated by an intermediate partition wall 15. An upflow passage 16 is fixedly provided on the second anaerobic filter bed tank 6 side of the intermediate partition wall 15. The water that has flowed from the first anaerobic filter bed tank 4 to the second anaerobic filter bed tank 6 through the convection tube 14 passes through the anaerobic filter bed 7 in a downward flow, and then rises through the upflow passage 16.

A metering pump 17 is provided above the upflow passage 16.
Is provided. The metering pump 17 is the second
A certain amount of water is transferred from the anaerobic filter tank 6 to the biofilm filter tank 8. That is, water is taken into the metering pump 17 from the water intake port 18 and sent to the next biofilm filtration tank 8 in a fixed amount.

In the anaerobic filter bed 7 in the second anaerobic filter bed tank 6,
Some suspended solids (SS) are captured. The trapped SS is gradually anaerobically decomposed and becomes soluble, or is stored as sludge at the bottom of the second anaerobic filter bed tank 6. In the anaerobic filter bed 7, organic nitrogen is anaerobically decomposed into ammonia nitrogen.

Near the bottom of the biofilm filtration tank 8,
2 are arranged in a horizontal state. The air diffuser tube 22 is connected to a blower (not shown), and blows out the air supplied by the blower, thereby forming the aerobic filter bed 9 of the biofilm filtration tank 8.
It functions to supply oxygen to aerobic microorganisms living in the sea.

A filter medium is disposed on the aerobic filter bed 9 in the biofilm filtration tank 8, and microorganisms adhering to the filter medium are used to remove BO.
The D component and the like are decomposed or made into SS, and captured in the filter medium. The biofilm filtration tank 8 also has a physical filtration action,
Here, SS is also captured. In the biofilm filtration tank 8,
The action of nitric acid bacteria and nitrites that convert nitrogen to nitric acid converts ammoniacal nitrogen to nitrate nitrogen.

A partition 23 is provided between the biofilm filtration tank 8 and the next treatment water tank 10. And this partition 23
A U-shaped pipe 24 is provided to connect the biofilm filtration tank 8 and the treatment water tank 10 through the water. The U-shaped tube 24 is bent at the upper part of the partition wall 23, and opens at a position near the bottom of the biofilm filtration tank 8 and a position near the bottom of the treated water tank 10.

From the upper part of the treated water tank 10, the first anaerobic filter bed tank 4
A circulation path 26 for constantly returning the supernatant water of the treated water is provided over the upper part of the water. An air lift pump 27 is connected to an end of the circulation path 26 above the treatment water tank 10. The air lift pump 27 has a treatment water tank 1
An air lift pipe 28 that pumps up the treated water of No. 0 is connected.

An end of the circulation path 26 above the first anaerobic filter tank 4 is formed as an inlet 29 to the first anaerobic filter tank 4. And near the inflow port 29 of the circulation path 26,
The phosphorus removal device P is connected to the circulation path 26.

As shown in FIG.
An electrolytic cell 30, three sets of rectangular plate-shaped iron electrodes 31 and 32 disposed in the electrolytic cell 30, a DC power supply 33 for supplying a current between the electrodes 31 and 32, and polarities of the electrodes 31 and 32. Switching device 21 for switching between
And The electrodes 31 and 32 elute iron ions that react with phosphoric acid by electrolysis. The control unit 20 controls the elution amount of the ions in the electrolytic cell 30 by controlling the current supplied between the iron electrodes 31 and 32.

For the electrodes 31 and 32, both the anode and the cathode are made of steel. The steel material constituting the electrodes 31 and 32 is as follows:
It consists of carbon steel with a carbon content of 0.45% by weight.

The reason why such carbon steel is used as the steel material constituting the electrodes 31 and 32 is as follows.

That is, before the dephosphorization treatment apparatus P is constructed, the above-mentioned phosphorus removal test is performed in advance, and the results of the graph in FIG. 3 show the average molar ratio of the iron ion concentration to the phosphate ion concentration. = A steel material having a carbon content of 0.45% by weight capable of securing about 1.2 was used.

The electrolytic tank 30 has an aeration tube 34 at the bottom of the tank for aerating the electrodes 31 and 32, and the aeration tube 34.
And a blower 35 outside the tank for supplying air.
The treated water flowing from the circulation path 26 is stored in the electrolytic cell 30.

The current flowing between the electrodes 31 and 32 is proportional to the concentration that dissolves the amount of iron one to three times the molar concentration of phosphorus flowing into the electrolytic cell 30. Usually, the operation is performed at a molar ratio of Fe / P = 1.5. The immersion electrode area is adjusted so that the current density at this time is 0.1 mA / cm ² or more, but the operation is usually performed at a current density of about 0.3 mA / cm ² . Also,
Aeration volume by the aeration tube 35 is usually 10 liter / m
The operation is performed after adjusting to be in. Further, the control unit 20 controls the polarity switching device 21 to invert the polarities of the electrodes 31 and 32 at predetermined time intervals.

In the dephosphorization treatment apparatus P, when the control unit 20 starts electrolysis, the electrode 31
Iron ions Fe ²⁺ are eluted from 32, and oxygen is supplied into the treated water by the aeration tube 34.

Fe²⁺Is oxidized by dissolved oxygen
Fe³⁺While being sent to the first anaerobic filter bed tank 4
Phosphoric acid PO_Four ^3-And the hardly soluble iron phosphate Fe (O
H)_x (PO_Four)_yBecomes And this iron phosphate salt F
e (OH)_x(PO_Four)_yExists in the first anaerobic filter bed tank 4.
Aggregates around the SS component to become a large floc,
Settles and deposits on the bottom of the tank.

The dephosphorized sludge deposited on the bottom of the first anaerobic filter tank 4 is periodically removed from the portion of the first anaerobic filter tank 4 where the anaerobic filter bed 5 is not provided by a vacuum car (usually for one year). About once per day).

In the dephosphorization treatment apparatus P, the electrodes 31 and 32 are affected by phosphate ions, nitrate ions, nitrite ions and the like in the treated water during the electrolysis, and
It was confirmed that even when an iron oxide layer was formed on the surface of No. 32, stable elution of iron ions Fe ²⁺ could be ensured, and the possibility of reducing the phosphorus removal ability could be prevented.

This is because the steel material constituting the electrodes 31 and 32 is made of carbon steel having a carbon content of 0.45% by weight, so that the average molar ratio of iron to phosphorus is about 1.2. It is presumed that the effect of preventing the adhesion of the iron oxide layer formed on the surfaces of the electrodes 31 and 32 to the surfaces of the electrodes 31 and 32 was obtained.

[0046]

In the water treatment apparatus according to the first aspect of the present invention, there is provided an electrolytic cell for storing water to be treated, and an iron for disposing phosphoric acid in the water provided in the electrolytic cell. At least one pair of electrodes for eluting ions by electrolysis, a power supply for supplying an electrolytic current to these electrodes, and a control unit connected to the electrodes and the power supply for controlling electrolysis. And at least one of the pair of electrodes is made of a steel material containing 0.2 to 0.9% by weight of carbon. Therefore, even when the electrode is affected by phosphate ions, nitrate ions, nitrite ions, and the like in the treated water during the electrolysis and the iron oxide layer is formed on the electrode surface, the iron oxide layer is not fixed. In particular, stable elution of iron ions can be ensured, and the possibility of reducing the phosphorus removal ability can be prevented.

[0047] In the water treatment apparatus according to the second aspect of the present invention, both the pair of electrodes are formed of the steel material, and the control unit is further configured to invert the polarity of the electrodes. Therefore, by performing the polarity reversal of the electrode, it is possible to reliably prevent the iron oxide layer from being formed or fixed on the electrode surface, and to ensure the above-mentioned effect achieved by the invention of claim 1 reliably and easily. can do.

[0048] In the water treatment apparatus according to the third aspect of the present invention, the electrolytic cell has an aeration pipe in the tank for aeration of the electrode, and an aeration pipe outside the tank for supplying air to the aeration pipe. Blowers and are arranged. Therefore, by performing the aeration of the electrode, it is possible to more reliably prevent the iron oxide layer from being formed or fixed on the surface of the electrode, and to reliably and surely achieve the effect of the invention according to claim 1 or 2. It can be easily secured.

[Brief description of the drawings]

FIG. 1 is a vertical longitudinal sectional view of a small-sized combined treatment septic tank according to one embodiment of the present invention.

FIG. 2 is a configuration explanatory view of a dephosphorization treatment device incorporated in the merged treatment septic tank of FIG.

3 is a graph showing a correlation between a carbon content of a steel plate electrode and a molar ratio of an iron ion concentration to a phosphate ion concentration, which was tested by the dephosphorization treatment apparatus of FIG.

[Explanation of symbols]

 Reference Signs List 20 control unit 21 polarity switching device 30 electrolytic cell 31 electrode 32 electrode 33 power supply 34 aeration tube 35 blower

Continued on front page F-term (reference) 4D027 AB07 BA04 BA07 BA13 4D061 DA08 DB05 DC09 EA06 EB01 EB05 EB14 EB20 EB28 EB29 EB30 EB31 EB39 ED06 FA15 GC16

Claims (3)

[Claims] 1. An electrolytic cell containing water to be treated, at least one pair of electrodes disposed in the electrolytic cell and eluting iron ions by electrolysis for removing phosphoric acid in water, and these electrodes. And a control unit connected to the electrodes and the power supply for controlling the electrolysis, wherein at least one of the pair of electrodes has a power of 0.2 to 0. .9
A water treatment apparatus comprising a steel material containing carbon by weight. 2. The water treatment apparatus according to claim 1, wherein both the pair of electrodes are made of the steel material, and the control unit further performs polarity reversal of the electrodes. 3. The electrolytic cell according to claim 1, wherein an aeration pipe in the tank for aerating the electrode and a blower outside the tank for supplying air to the aeration pipe are arranged in the electrolytic cell. Water treatment equipment.