JP4026920B2 - Sewage treatment equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sewage treatment apparatus, and more particularly, to a sewage treatment apparatus for removing phosphoric acid contained in sewage such as manure wastewater and domestic wastewater by reacting with metal ions eluted by electrolysis.
[0002]
[Prior art]
As this kind of sewage treatment apparatus, conventionally, the following is known.
[0003]
That is, a sewage storage tank for storing sewage to be treated is provided, and one or more sets of electrodes made of insoluble phosphate forming metal are arranged in the tank, and a voltage is applied between these electrodes to perform electrochemical This is an apparatus in which phosphoric acid is converted into a water-insoluble phosphate by precipitating the insoluble phosphate-forming metal ions into the sewage to remove the precipitate.
[0004]
[Problems to be solved by the invention]
In such a sewage treatment apparatus, as a result of forming a corrosion-resistant oxide film called a passive film on the surface of the electrode, elution of water-insoluble phosphate-forming metal ions is reduced or stopped. There is a risk (passivation). When such passivation occurs, it becomes difficult or impossible to remove phosphoric acid in wastewater as a water-insoluble phosphate.
[0005]
Further, when the phosphoric acid in the sewage flowing into the sewage storage tank decreases, the water-insoluble phosphate forming metal ions may be eluted excessively. If such excessive metal ion elution occurs, the amount of sludge that precipitates as water-insoluble phosphates and metal compounds increases, so the number of sludge removal operations increases, and the same metal is added to the water after sewage treatment. Since ions remain, there is a disadvantage that causes harmful effects.
[0006]
The present invention has been made in view of such circumstances, and prevents passivation when water-insoluble phosphate-forming metal ions are eluted electrochemically in sewage, thereby preventing phosphoric acid in sewage. It is an object of the present invention to provide a sewage treatment apparatus capable of stably removing water and preventing elution of excessive metal ions.
[0007]
[Means for Solving the Problems]
According to one aspect of the present invention, a sewage storage tank in which sewage flows in and is stored, and iron ions that are disposed in the sewage storage tank and precipitate and remove phosphoric acid in the sewage are eluted by electrolysis. At least one set of electrodes, a power source for supplying electrolysis current to the electrodes, and the ratio of the number of moles of phosphorus of sewage flowing into the sewage storage tank to the number of moles of iron to be eluted is a predetermined value. There is provided a sewage treatment apparatus comprising a control unit for controlling the current.
[0008]
The sewage storage tank stores sewage used for electrolysis. The electrodes are, for example, a set of two rectangular plates that are arranged in a set, and elute iron ions Fe ²⁺ into the sewage storage tank by electrolysis. The power supply supplies current for electrolysis to each set of electrodes.
[0009]
One set of electrodes, for example, are both iron electrodes, or one is an iron electrode and the other is an insoluble metal electrode. In the former case, it is possible to prevent electrode passivation by reversing the polarity of the electrode as desired. In the latter case, the iron electrode is the anode and the insoluble metal electrode is the cathode. Here, examples of the insoluble metal electrode include a silver electrode and a platinum electrode. Further, it is preferable that the pair of electrodes is fixed to, for example, an electrically insulating spacer having a handle portion, and the distance between them is kept constant.
[0010]
The iron ions eluted in the sewage storage tank react with phosphoric acid (orthophosphoric acid) in the sewage water to agglomerate as a water-insoluble phosphorus compound (Fe (OH) _x (PO ₄ ) _y ) and enter the sewage storage tank. Precipitate.
[0011]
The control unit controls the current so that the ratio (P / Fe) of the number of moles of phosphorus to the number of moles of iron to be eluted becomes a predetermined value. Here, the number of moles of phosphorus, for example, as shown in FIG. 6, if a sensor 70 for detecting the flow rate of sewage flowing into the small combined treatment septic tank incorporating the sewage storage tank according to the present invention is provided, Based on the output of the sensor 70, the number of users of the small merged treatment septic tank can be estimated, and the number of moles of phosphorus generated from the estimated number of persons can be calculated. In addition, since the number of moles of phosphorus can be grasped in advance in a home where the number of people used does not vary, the number of moles of iron can be determined when installing a small-size merger treatment septic tank.
[0012]
The control part controls the current in this way because the present inventors have studied (1) that there is a correlation between P / Fe during passivation and elution of excess iron ions and electrolysis, (2) It has been found that iron ions may be excessively eluted when P / Fe is smaller than a predetermined value, and (3) Passivation occurs when P / Fe is larger than a predetermined value. is there.
[0013]
According to another aspect of the present invention, instead of the control unit, a phosphate ion concentration detection unit, and the number of moles of phosphorus obtained from the phosphate ion concentration detected by the detection unit, of iron to be eluted. There is provided a sewage treatment apparatus provided with a control unit for controlling the current so that the ratio to the number of moles becomes a predetermined value. This ion concentration detection unit detects the concentration of phosphate ions PO ₄ ³⁻ in wastewater flowing into the wastewater storage tank for electrolysis. The phosphate ion concentration detection unit includes, for example, a detection tank for temporarily collecting sewage flowing into the sewage storage tank, and an ion concentration sensor disposed in the detection tank.
[0014]
As a sensor for detecting the phosphate ion concentration in sewage, for example, there is a known sensor having an ion sensitive film holding an ion sensitive substance made of a copper complex having a chain diamine as a ligand. Preferably used.
[0015]
Moreover, it was also found through experiments that the predetermined value of P / Fe is more preferably in the range of 0.3 to 1.0.
[0016]
In the sewage treatment apparatus according to the present invention, it is preferable that all the electrodes are made of iron, and the control unit further has a function of instructing the power supply to invert the polarity of the electrodes. This is because by performing polarity reversal, it is possible to prevent the passivation of the electrode more reliably by preventing the formation and growth of the passive film on the electrode surface.
[0017]
The sewage treatment apparatus according to the present invention is configured such that when the polarity reversal is performed, the control unit instructs the reversal at a rate of once every predetermined time within a range of 30 minutes to 15 days. preferable. This is because by performing the polarity reversal of the electrodes at regular intervals, the passivation of the electrodes can be prevented more reliably and the efficiency of electrolysis can be improved.
[0018]
Here, instructing the polarity reversal to be performed once every predetermined time within the range of 30 minutes to 15 days is when the polarity reversal is performed once every predetermined time of less than 30 minutes. This is because the elution of iron ions is not sufficient and the reaction with phosphate ions in sewage is too low. When the polarity is reversed once every predetermined time exceeding 15 days, Fe adhering to the electrode surface _This is because, as a result of the rapid growth of a passive film such as ₃ O ₄ , the reaction between the eluted iron ions and phosphate ions is significantly hindered. This is a fact that has been found by experiments of the present inventors.
[0019]
Such polarity reversal time is more preferably once per predetermined time within the range of 1 hour to 10 days, and most preferably once per predetermined time within the range of 1 hour to 5 days. The ratio was also found by the same experiment.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, one embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited thereby.
[0021]
As shown in FIG. 1, a sewage treatment apparatus D _{1 according} to one embodiment of the present invention includes a sewage storage tank 1, four sets of electrodes 2 and 3, and a current flowing through each set of electrodes 2 and 3. A DC power source (not shown) for supplying the power and four electrode holders 4 are provided.
[0022]
As shown in FIG. 2, the sewage storage tank 1 is a box having a substantially rectangular plane shape, and sewage to be treated such as urine wastewater and domestic wastewater is stored. A sewage inflow port 1 a and a sewage outflow port 1 b are formed at the upper part of the opposite side wall of the sewage storage tank 1. In addition, two bottom positioning rods 5 extending in the left-right direction are provided at the bottom of the sewage storage tank 1. A total of six right and left positioning rods 6 extending in the vertical direction are provided inside these bottom positioning rods 5.
[0023]
Each pair of electrodes 2 and 3 is made of iron in a rectangular plate shape, and iron ions for removing phosphoric acid in the sewage are eluted by electrolysis. As shown in enlarged views in FIG. 3 and FIG. 4, the pair of electrodes 2 and 3 is kept at a constant distance by an electrically insulating spacer 7 made of pinyl chloride resin attached to the upper ends thereof. Yes. The spacer 7 is provided with a handle portion 7a.
[0024]
A connection terminal 8 is provided at the upper ends of the electrodes 2 and 3. These terminals 8 are connected to a connector 10 via lead wires 9. The connector 10 is connected to the power source. For convenience of explanation, an assembly including a pair of electrodes 2 and 3, one spacer 7, two terminals 8, two lead wires 9, and one connector 10 is referred to as an electrode body 11.
[0025]
As shown in FIGS. 3 and 4 in an enlarged manner, the electrode holder 4 has a rectangular box shape in plan view and is made of polypropylene resin. The left and right side walls of the electrode holder 4 are electrically insulating partition plates 4 a for partitioning adjacent electrode holders 4. Both front and rear ends of the electrode holder 4 are rectangular sewage inlet 4b and sewage outlet 4c.
[0026]
Further, the upper and lower surfaces of the electrode holder 4 are cut out into a rectangular shape with the peripheral portion being left, thereby forming an electrode attaching / detaching port 4d and an aeration port 4e, respectively. Furthermore, the left-right width of the electrode holder 4 (the distance between the outer surfaces of the two partition plates 4a) is substantially equal to the distance between the two adjacent left and right positioning rods 6 in the sewage storage tank 1.
The two circular holes 4 f on the upper surface of the electrode holder 4 are for screwing the spacer 7 to the upper surface of the electrode holder 4.
[0027]
The electrode holder 4 configured in this way is arranged in the sewage storage tank 1 so that it can be taken out. That is, it is gently fixed at a fixed position by the bottom positioning rod 5 and the left and right positioning rods 6 provided in the tank.
[0028]
Further, the electrode body 11 is detachably held on the electrode holder 4 by being fitted into the electrode holder 4 from the electrode attaching / detaching port 4 d and the spacer 7 being screwed to the electrode holder 4. Accordingly, the inspection and replacement work of the electrodes 2 and 3 can be performed easily and in a short time. Further, the two partition plates 4a of the pair of electrodes 2 and 3 and the electrode holder 4 are parallel to each other. Therefore, the SS in the sewage in the electrode holder 4 flows without a stagnation from the sewage inlet 4a toward the sewage outlet 4b along the electrode surfaces of the electrodes 2 and 3.
[0029]
As shown in FIGS. 1 and 2, the center of the bottom surface of the electrode holder 4 is a concave groove 1 c extending in the left-right direction. One aeration tube 12 is fitted in the groove 1c.
[0030]
Aeration tube 12 is part of the aeration device provided in the sewage treatment apparatus D _1. That is, the aeration apparatus is connected to an air supply blower (not shown) provided outside the sewage storage tank 1, an air supply pipe (not shown) connected to the blower and extending into the tank, and the air supply pipe. And an aeration tube 12 disposed at the bottom of the tank.
[0031]
By performing aeration from the aeration tube 12 through the aeration port 4e of the electrode holder 4, the cleaning effect of the electrodes 2 and 3 and the partition plate 4a can be further enhanced.
[0032]
As shown in FIG. 5, the sewage treatment apparatus D ₁ is incorporated in a small merged treatment septic tank 101.
[0033]
The inside of the septic tank 101 is in accordance with the order of the sewage purification process from the side of the inflow pipe 102 into which sewage mixed with urine wastewater and domestic wastewater flows to the side of the discharge pipe 103 that discharges sewage-treated water to the outside. The tank structure is formed by partitioning a plurality of tanks.
[0034]
Reference numeral 104 denotes a first anaerobic filter bed tank formed in the foremost part on the inflow pipe 102 side. In the first anaerobic filter bed tank 104, impurities that cannot be purified by being mixed in manure wastewater or domestic wastewater are separated by precipitation and removed.
[0035]
The first anaerobic filter bed tank 104 is provided with a first anaerobic filter bed 105 which is a filter bed for anaerobic microorganisms, and anaerobic treatment is performed by causing the first anaerobic filter bed 105 to inhabit the microorganisms. Yes. The first anaerobic filter bed 105 suppresses the sediment from being rolled up by the water flow when the inflow water or backwash wastewater temporarily flows into the suspended tank and flowing out to the next tank. The load can be reduced.
[0036]
Reference numeral 106 denotes a second second anaerobic filter bed tank formed adjacent to the first anaerobic filter bed tank 104. In the second anaerobic filter bed tank 106, anaerobic treatment is performed by causing the second anaerobic filter bed 107 to inhabit anaerobic microorganisms.
[0037]
Reference numeral 108 denotes a next biofilm filtration tank that is partitioned adjacent to the second anaerobic filter bed tank 106.
[0038]
The first anaerobic filter bed tank 104 and the second anaerobic filter bed tank 106 are partitioned by a vertical partition wall 109. An advection port 110 penetrating the partition wall 109 is formed in an upper part of the partition wall 109. A convection tube 111 is fitted in the convection port 110.
[0039]
The second anaerobic filter bed tank 106 and the next biofilm filtration tank 108 are partitioned by a vertical partition 112. An advection port 113 penetrating the partition 112 is formed in an upper part of the partition 112. A convection tube 114 is fitted into the convection port 113. The sewage that has been transferred from the first anaerobic filter bed tank 104 to the second anaerobic filter bed tank 106 through the transfer pipe 111 passes through the second anaerobic filter bed 107 in a downward flow, and then passes through the transfer pipe 114 to the next. It is sent to the biofilm filtration tank 108.
[0040]
A certain amount of SS is captured by the second anaerobic filter bed 107 provided in the second anaerobic filter bed tank 106. The trapped SS is gradually anaerobically decomposed to become soluble, or stored as sludge at the bottom of the second anaerobic filter bed tank 106. In the second anaerobic filter bed 107, organic nitrogen is anaerobically decomposed into ammonia nitrogen.
[0041]
The biofilm filtration tank 108 is provided with an aerobic filter bed 115 which is a filter bed of aerobic microorganisms, and aerobic treatment is performed by causing the aerobic microorganisms to inhale in the aerobic filter bed 115. Yes. In the vicinity of the bottom of the biofilm filtration tank 108, an aeration pipe 116 of the aeration apparatus is arranged in a horizontal state. The aeration apparatus supplies oxygen to aerobic microorganisms that inhabit the aerobic filter bed 115 of the biofilm filtration tank 108 by blowing air from the aeration pipe 116.
[0042]
Reference numeral 117 denotes a next treated water tank that is formed adjacent to the biofilm filtration tank 108. In the treated water tank 117, the treated water that has been aerobically treated in the biofilm filtration tank 108, filtered and transferred is stored in a stationary manner.
[0043]
Reference numeral 118 denotes a disinfection tank that is partitioned on the upper part of the treated water tank 117. The disinfection tank 118 disinfects the supernatant water that has been treated in the treatment water tank 117 and discharges it from the discharge pipe 103 to the outside.
[0044]
The biofilm filtration tank 108 and the next treated water tank 117 are partitioned by a vertical partition wall 119. An advection port 120 penetrating the partition wall 119 is formed in the upper part of the partition wall 119. A convection tube 121 is fitted into the convection port 120. The sewage that has been transferred from the second anaerobic filter bed tank 106 to the biofilm filtration tank 108 through the transfer pipe 114 passes through the aerobic filter bed 115 in a downward flow, and then passes through the transfer pipe 121 to the next treated water tank 117. It is sent to.
[0045]
A return pipe 122 for returning the supernatant water of the treated water is disposed from the upper part of the treated water tank 117 to the upper part of the first anaerobic filter bed tank 104. Then, the supernatant water pumped up from the treated water tank 117 by the lift pipe 123 is sent to the sewage treatment apparatus D ₁ through the diversion meter 124 and the return pipe 122 and subjected to the phosphorus removal treatment, and then the first anaerobic filter. Returned to the floor tank 104.
[0046]
5, 125 a control unit which includes the sewage treatment apparatus D _1, 126 denotes a power respectively. The power supply 126 supplies a current for electrolysis to the electrodes 2 and 3 disposed inside the sewage storage tank 1. Reference numeral 127 denotes an air supply blower provided outside the sewage storage tank 1. The blower 127 is a part of an aeration apparatus for cleaning these surfaces by aeration of the electrodes 2 and 3 and the partition plate 4 a inside the sewage storage tank 1.
[0047]
The amount of sewage flowing into the septic tank 101 is 1200 liters per day, and the circulation flow rate in the septic tank 101 is 6000 liters. At this time, a current is allowed to flow through the electrodes 2 and 3 disposed inside the sewage storage tank 1 by a constant value within a range of 120 to 2400 mA. The distance between the electrodes of each electrode body 11 is set to 25 mm so that the voltage between the electrodes can always be monitored.
[0048]
The control unit 125 always performs constant current electrolysis while maintaining the current density at the time of electrolysis for elution of iron ions at a constant value within the range of 0.1 to 5.0 mA / cm ^2. Control to indicate one polarity reversal every minute to 15 days. When the current density is less than 0.1 mA / cm ² occurs passivating, power consumption interelectrode voltage becomes greater than or equal to about 25V is increased when it exceeds the 5.0 mA / cm ^2.
[0049]
Here, for three months from the start of operation of the septic tank 101, the current density is always maintained at 0.5 mA / cm ² by the control unit 125, and constant current electrolysis is performed with polarity reversal once every 6 hours. It was broken.
[0050]
As shown in FIG. 5, the sewage treatment apparatus D ₁ is further provided with a characteristic phosphate ion concentration detector 60.
[0051]
The phosphate ion concentration detection unit 60 includes a detection tank 61 provided in communication with the return pipe 122 on the upstream side of the sewage storage tank 1, and a phosphate ion concentration sensor 62 provided in the detection tank 61. . The detection tank 61 temporarily accumulates sewage before flowing into the sewage storage tank 1. The phosphate ion concentration sensor 62 includes an ion-sensitive film that holds an ion-sensitive substance made of a copper complex having one kind of chain diamine as a ligand, and is connected to the control unit 125. ing. The phosphate ion concentration sensor 62 is immersed in a certain amount of sewage stored in the detection tank 61, and detects the phosphate ion concentration in the sewage. Then, the control unit 125 calculates the number of moles of phosphorus from the detected phosphate ion concentration.
[0052]
In addition, as shown in FIG. 6, if the sensor 70 which detects the flow volume of the sewage which flows into the small merger processing septic tank in which the sewage storage tank 1 is incorporated is provided as shown in FIG. Based on this, it is possible to estimate the number of people using the combined treatment septic tank and calculate the number of moles of phosphorus generated from the estimated number of people.
[0053]
Next, the control unit 125 determines an appropriate number of moles of iron to be ion-eluting from the calculated number of moles of phosphorus. That is, the value of the ratio P / Fe of the number of moles of phosphorus to the number of moles of iron is determined to be a predetermined value within the range of 0.3 to 1.0 obtained from experiments as shown in FIGS. .
[0054]
First, the experiment shown in FIG. 7 will be described.
The phosphate ion concentration of the wastewater flowing into the wastewater storage tank 1 is 0.6 mg / liter (P / Fe = 0.3), 1.2 mg / liter (P / Fe = 0.6), 2.4 mg / liter ( P / Fe = 1.3), 6.0 mg / liter (P / Fe = 3.3), and 18.0 mg / liter (P / Fe = 10) for electrolysis, in each case per day The time course of phosphorus removal was measured. However, the elution amount of iron ions was kept constant (19 mA). In addition, the polarity reversal time was all 1 hour.
[0055]
From this experimental result, when the P / Fe is 1.3 or more, the amount of phosphorus removal decreases to half or less of the initial value after 35 days (due to passivation), whereas P / Fe In the case of less than 1.3, it can be seen that there is almost no decrease from the initial value after 35 days.
[0056]
Next, the experiment shown in FIG. 8 will be described.
The phosphorus removal rate (%) for each P / Fe was determined by varying P / Fe.
[0057]
From this experimental result, when P / Fe is less than 0.3, the phosphorus removal rate becomes 99% or more, and extra iron ions are eluted for phosphorus removal, whereas P / Fe is 0.3. It can be seen that an appropriate phosphorus removal rate of about 80 to 98% can be secured in the range of -1.0.
[0058]
Thus, the value of P / Fe is determined to be a predetermined value within the range of 0.3 to 1.0, and the control unit 125 controls the electrolytic current. An example thereof will be described with reference to FIG. The control unit 125 selects two sets of electrodes 2 and 3 from the four sets of electrodes 2 and 3 of A to D, and applies a DC constant current. That is, the electrodes A (2 · 3) and the electrode B (2 · 3) are set for the time a to b, and the electrodes B (2 · 3) and the electrode C (2 · 3) are set for the time c to d for the time b to c. Then, the electrodes C (2 · 3) and D (2 · 3) are applied to the electrodes D (2 · 3) and A (2 · 3) in the time d to e, and the electrodes A (2 · 3) are applied to the time e to f. 3) A DC constant current (about 1 to 1.2 A) is applied to the electrode B (2.3). Then, a predetermined amount of iron ions is eluted.
[0059]
In such a septic tank 101, sewage having a phosphate ion concentration of 1.2 mg / liter is caused to flow into the sewage storage tank 1 at a flow rate of 100 ml / min, and the electrolytic current is maintained at 19 mA (set to Fe / P = 1.5). Electrolytic operation was performed. The time-dependent change in phosphorus removal amount (mg / day) when the polarity reversal time of the electrodes 2 and 3—the time from the polarity reversal at one time point to the polarity reversal at the next time point—was obtained. A graph was obtained.
[0060]
According to the graph of FIG. 10, when polarity inversion is not performed, the phosphorus removal amount starts to greatly decrease from the 10th day onward of the electrolysis operation. The phosphorus removal amount is about 75% of the initial value on the 15th day of the electrolysis operation, and is about 50% of the initial value on the 18th day.
[0061]
From this result, it is considered that the polarity reversal needs to be performed once on the 15th day at maximum when the tolerance of the phosphorus removal amount reduction is set to 75%.
[0062]
Further, from the graph of FIG. 10, even when the polarity inversion time is 1 hour (1H), 1 day (24H), and 5 days (5day), stable phosphorus removal is possible for a long period (up to 3 months). I know that there is.
[0063]
Next, in order to make the iron ion elution efficiency-percentage of iron ions actually eluted with respect to iron ions theoretically eluted according to Faraday's law-when electrolysis is performed, to 95% or more, The experiment also confirmed that it was necessary to reverse the polarity once every 30 minutes or more.
[0064]
That is, (1) In order to ensure 95% iron ion elution efficiency, it is preferable to perform polarity reversal at a rate of once every fixed time within a range of 30 minutes to 15 days, and (2) In order to ensure the elution efficiency of 96% of iron ions, it is preferable to reverse the polarity at a rate of once every fixed time within a range of 1 hour to 10 days, and (3) 97% of iron ions. In order to ensure elution efficiency, it was also found that it is preferable to perform polarity reversal at a rate of once every fixed time within a range of 1 hour to 5 days.
[0065]
FIG. 11 shows the phosphate ion concentration (mg / liter) when the polarity reversal time is maintained at 1 day (1440 minutes) and the operation days are changed in 5 stages (0 to 90 days). The change over time from 0 minutes to 1440 minutes is shown. According to FIG. 11, it can be seen that the phosphate ion concentration increases as the number of operating days increases, and the degree of the increase is small.
[0066]
When such an experiment was performed with the polarity reversal time changed, the amount of sludge (metal oxide, phosphate compound, etc.) deposited in the sewage storage tank 1 was 20 g for 1 hour when the polarity reversal time was 30 minutes. Was 7.5 g for 1 day and 5.5 g for 1 day. From this, it can be seen that if the polarity reversal time is lengthened, the amount of sludge in the sewage storage tank 1 decreases. If the amount of sludge decreases, the sewage storage tank 1 can be made compact and the maintenance period can be extended.
[0067]
Generally, the ion concentration of phosphoric acid flowing into the combined septic tank is about 3 to 8 mg / liter. Assuming that the amount of sewage flowing into the small combined treatment septic tank 101 and the sewage circulation flow rate in the septic tank 101 are 1200 liter and 6000 liter, respectively, the ion concentration of phosphoric acid flowing into the sewage storage tank 1 is 0. 6-1.6 mg / liter.
[0068]
Therefore, when the molar ratio Fe / P = 1 to 3 at this time, the iron ion concentration to be eluted, that is, the iron elution amount = (phosphoric acid ion concentration / phosphorus atomic weight) × (molar ratio) × (iron From atomic weight), 0.6 ÷ 31 × 1 × 55.847 = 1.08 mg / liter to 1.6 ÷ 31 × 3 × 55.847 = 8.54 mg / liter. That is, elution of about 1 to 9 mg / liter of iron ions is required.
[0069]
If the ion concentration of phosphoric acid flowing into the sewage storage tank 1 exceeds 1.6 mg / liter, many passive films such as metal oxides are formed on the surfaces of the electrodes 2 and 3 and iron ions are eluted. Be disturbed.
[0070]
【The invention's effect】
According to the first aspect of the present invention, the sewage storage tank into which sewage flows and is stored, and the iron ions that are disposed in the sewage storage tank and precipitate and remove phosphoric acid in the sewage are eluted by electrolysis. At least one set of electrodes, a power source for supplying electrolysis current to the electrodes, and the ratio of the number of moles of phosphorus of sewage flowing into the sewage storage tank to the number of moles of iron to be eluted is a predetermined value. And a control unit for controlling the current. Therefore, by such a control unit, it is possible to stably remove the phosphoric acid in the sewage by preventing passivation when the water-insoluble phosphate-forming iron ions are eluted electrochemically in the sewage. Excessive iron ion elution can be prevented.
[0071]
According to the second aspect of the present invention, the sewage storage tank into which sewage flows and is stored, and the iron ions that are disposed in the sewage storage tank and precipitate and remove phosphoric acid in the sewage are eluted by electrolysis. At least one set of electrodes, a power source for supplying electrolysis current to the electrodes, a phosphate ion concentration detection unit for detecting the phosphate ion concentration of sewage flowing into the sewage storage tank, and detection by this detection unit A controller for controlling the current so that the ratio of the number of moles of phosphorus determined from the phosphate ion concentration to the number of moles of iron to be eluted becomes a predetermined value. Therefore, by such a control unit, it is possible to stably remove the phosphoric acid in the sewage by preventing passivation when the water-insoluble phosphate-forming iron ions are eluted electrochemically in the sewage. Excessive iron ion elution can be prevented.
[0072]
According to the third aspect of the present invention, the control unit maintains the predetermined value within the range of 0.3 to 1.0, and thus the effect according to the first or second aspect of the present invention is more reliably exhibited. be able to.
[0073]
According to the invention described in claim 4, all the electrodes are made of iron, and the control unit further has a function of instructing the power source to invert the polarity of the electrodes. Therefore, in addition to the above-described effect of the invention according to any one of claims 1 to 3, by performing polarity reversal, electrode passivation can be prevented more reliably and electrolysis efficiency can be improved. Can be achieved.
[0074]
According to the invention described in claim 5, the control unit is configured to instruct the polarity reversal to be performed at a rate of once every fixed time within a range of 30 minutes to 15 days. Therefore, by reversing the polarity of the electrodes at regular intervals, it is possible to more reliably prevent the passivation of the electrodes produced by the invention of claim 4 and increase the efficiency of electrolysis.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view of a sewage treatment apparatus according to one embodiment of the present invention.
FIG. 2 is a configuration explanatory view of a part of the sewage treatment apparatus of FIG. 1 as viewed from above.
FIG. 3 is a perspective view of an electrode body and an electrode holder that are constituent members of the sewage treatment apparatus of FIG. 1;
4 is an exploded perspective view of an electrode body and an electrode holder in FIG. 3;
5 is an explanatory diagram of an enlarged configuration of the inside of a combined treatment septic tank in which the sewage treatment apparatus of FIG. 1 is incorporated, as viewed from the front. FIG.
6 is a block diagram showing a control unit and a phosphate ion concentration detection unit in the septic tank of FIG. 5. FIG.
7 is a graph in which the electrolysis was performed while changing the phosphate ion concentration of sewage flowing into the sewage storage tank in the septic tank of FIG. 5 and the temporal transition of the phosphorus removal amount per day in each case was measured. .
8 is a graph in which phosphorus removal rates with respect to respective P / Fe are obtained by variously changing P / Fe in the sewage storage tank in the septic tank of FIG. 5;
FIG. 9 is an explanatory diagram when the electrolysis current is controlled based on a predetermined value of P / Fe determined within a range of 0.3 to 1.0.
10 is a graph showing the change over time in the amount of phosphorus removal when the polarity reversal time of the electrode in the sewage storage tank in the septic tank of FIG. 5 is changed.
11 is a diagram showing a case where the polarity reversal time of the electrode in the sewage storage tank in the septic tank of FIG. 5 is maintained at 1 day (1440 minutes) and the operation days are changed in 5 stages (0 to 90 days). It is a graph which shows a time-dependent change of an acid ion concentration.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Sewage storage tank 2 Electrode 3 Electrode D ₁ Sewage treatment apparatus 60 Phosphate ion concentration detection part 61 Detection tank 62 Phosphate ion concentration sensor 101 Small merge processing purification tank 125 Control part 126 Power supply

Claims (5)

A sewage storage tank in which sewage flows in and is stored, at least one set of electrodes disposed in the sewage storage tank and eluting iron ions for precipitation removal of phosphoric acid in the sewage by electrolysis, and electrolysis of the electrodes And a controller for controlling the current so that the ratio of the number of moles of phosphorus in the sewage flowing into the sewage storage tank to the number of moles of iron to be eluted becomes a predetermined value. A sewage treatment apparatus characterized by comprising A sewage storage tank in which sewage flows in and is stored, at least one set of electrodes disposed in the sewage storage tank and eluting iron ions for precipitation removal of phosphoric acid in the sewage by electrolysis, and electrolysis of the electrodes A power source for supplying electric current, a phosphate ion concentration detection unit for detecting the phosphate ion concentration of sewage flowing into the sewage storage tank, and a phosphorus ion determined from the phosphate ion concentration detected by the detection unit And a control unit that controls the current so that a ratio of the number of moles to the number of moles of iron to be eluted becomes a predetermined value. The sewage treatment apparatus according to claim 1 or 2, wherein the predetermined value is within a range of 0.3 to 1.0. The sewage treatment apparatus according to any one of claims 1 to 3, wherein all the electrodes are made of iron, and the control unit further has a function of instructing the power source to invert the polarity of the electrodes. The sewage treatment apparatus according to claim 4, wherein the control unit instructs the polarity reversal to be performed at a rate of once every fixed time within a range of 30 minutes to 15 days.

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