JP2004313902A - Sewage purifying tank equipped with electrolytic cell - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sewage purifying tank equipped with an electrolytic cell capable of more stably removing BOD than before and capable of also efficiently removing nitrogen. <P>SOLUTION: In the sewage purifying tank 1 having an anaerobic biological treatment tank (2 or 3), an aerobic biological treatment tank 6 and a treated water tank 7 successively provided thereto from an upstream side, the electrolytic cell 5 having a nitrogen removing function is provided between the anaerobic biological treatment tank (2 or 3) and the aerobic biological treatment tank 6. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a sewage treatment tank for physically and biochemically purifying human waste, other domestic wastewater, or a combined wastewater thereof (hereinafter also referred to as wastewater).
[0002]
[Prior art]
2. Description of the Related Art Various types of sewage purification tanks used in homes and the like are conventionally known. FIG. 3 shows one of the conventional sewage purification tanks in which an anaerobic treatment tank and an aerobic treatment tank are combined. From the upstream side, an anaerobic filter tank first chamber 51, an anaerobic filter tank second chamber 52, and a biological filtration tank are shown. 53, a treatment water tank 54 and a disinfection tank 55 are arranged. The anaerobic filter bed first chamber 51 and the anaerobic filter tank second chamber 52 in the tanks are provided with a water amount fluctuation absorbing portion 56 to alleviate a large amount of wastewater flowing in a short time. A transfer air lift pump 58 is provided to supply the liquid flowing into the pump tank 57 after passing through the chamber 52 by the downward flow to the biological filtration tank 53 at the subsequent stage at a constant flow rate. In the treated water tank 54, an air lift pipe 59 for circulating the liquid (part) treated in the biological filtration tank 53 and the sludge settling at the bottom to the anaerobic filter bed first chamber 51 is provided. (For example, see Patent Document 1).
[0003]
In this sewage purification tank, in the first chamber 51 of the anaerobic filter bed tank, the solid matter in the inflowing sewage precipitates in the lower part of the tank, or floats to the upper part of the tank by scumming, and separation of the solid matter in the sewage occurs. . In addition, anaerobic biodegradation of organic matter proceeds in the filter bed. At this time, the nitrogen component is converted to ammonia nitrogen. In the anaerobic filter tank second chamber 52, the separation of solids and the anaerobic biodegradation of organic substances proceed further as in the anaerobic filter tank first chamber 51. In the biological filtration tank 53, aerobic biodegradation of the remaining organic matter further proceeds, and nitrification of ammonia nitrogen (nitrate nitration) proceeds. In the treated water tank 54, the circulation air lift pipe 59 is operated to return a part of the treated liquid in the biological filtration tank 53 to the first anaerobic filter bed tank 51. Thereby, in the first anaerobic filter bed tank 51, biological nitrogen removal (nitrogen gasification) of nitrate nitrogen contained in the treated liquid proceeds. By the above treatment, the treated water from which BOD (biochemical oxygen demand) and TN (total nitrogen) have been removed is discharged outside the sewage treatment tank.
[0004]
Separately, a nitrogen treatment method or a nitrogen treatment system for efficiently removing low-concentration nitrogen compounds by electrolysis has recently been proposed (see Patent Document 2). In one example, the effluent after being treated in the activated sludge treatment tank is guided to a nitrogen treatment system for treatment. Here, in the activated sludge treatment tank, aerobic biodegradation of organic matter proceeds, and nitrification of ammonia nitrogen (nitrate nitration) also proceeds. In the nitrogen treatment system, nitrate nitrogen is converted to ammonia nitrogen by electrolysis, and the ammonia nitrogen is gasified with hypochlorous acid, which is simultaneously generated, to remove nitrogen. At this time, sterilization is also performed with hypochlorous acid.
[0005]
[Patent Document 1]
JP 2001-96285 A [Patent Document 2]
Japanese Patent Application Laid-Open No. 2002-248473
[Problems to be solved by the invention]
In the above-mentioned conventional sewage treatment tank, since it is a system utilizing microorganisms, it is easily affected by load fluctuations, treatment water temperature, etc., and in particular, nitrification of ammonia nitrogen and denitrification (nitrogen removal) of nitrate nitrogen are sufficiently performed. It tends not to be achieved. Further, in order to highly remove TN (total nitrogen) (for example, 20 mg / L or less), the capacity of the sewage purification tank must be increased. However, in a cold region or the like, a liquid temperature (for example, 13 ° C.) at which the microbial activity is almost stopped is obtained. Therefore, even if the capacity of the sewage purification tank is increased, it is difficult to obtain an effect corresponding thereto.
[0007]
In the case where the effluent of the activated sludge tank is electrolyzed to remove nitrogen, the nitrate nitrogen that has been nitrified in the activated sludge tank is reduced again by electrolysis to remove ammonia-nitrogen, which is efficient. I don't think
[0008]
The present invention compensates for the weak points of the conventional sewage treatment tank provided with an anaerobic biological treatment tank, an aerobic biological treatment tank, and a treated water tank, and can remove BOD more efficiently and more stably than before, and furthermore, nitrogen is also efficiently used. It is an object of the present invention to provide a sewage purification tank that can be efficiently removed.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention has the following configuration.
That is, the present invention is a sewage purification tank 1 including an anaerobic biological treatment tank (2 or 3), an aerobic biological treatment tank 6 and a treated water tank 7 in order from the upstream, and the anaerobic biological treatment tank (2 or 3). ) And an aerobic biological treatment tank 6, the sewage purification tank 1 having an electrolysis tank 5 having a nitrogen removing function.
[0010]
Here, the return pump 18 (the suction port) for returning a part of the liquid treated in the aerobic biological treatment tank 6 to the anaerobic biological treatment tank (2 or 3) is connected to the lower part of the treatment water tank 7 or aerobic. It is preferable to provide the lower part of the biological treatment tank 6.
[0011]
[Action]
When sewage is anaerobically treated in the anaerobic biological treatment tank, the nitrogen content in the organic matter of the sewage is reduced (decomposed) to ammonia nitrogen. Next, when this solution is electrolyzed in an electrolysis tank provided with a cathode (cathode) and an anode (anode) (having a nitrogen removing function), chlorine ions contained in the sewage are oxidized at the anode to form hypochlorite. It becomes an acid (formulas (1) and (2)), and this hypochlorous acid directly reacts with ammonia nitrogen to remove nitrogen (formula (3)).
2Cl ⁻ → Cl ₂ + 2e (1)
Cl ₂ + H ₂ O → HClO + HCl (2)
2NH ₄ ⁺ + 4HClO → N ₂ ↑ + 4HCl + 4H ₂ O (3)
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described more specifically with reference to the drawings.
FIG. 1 is an example of a sewage purification tank of the present invention, in which (a) is a schematic plan view and (b) is a schematic cross-sectional view taken along the line AA of (a). The sewage purification tank 1 includes, from the upstream side, a first anaerobic treatment tank 2 and a second anaerobic treatment tank 3 as anaerobic biological treatment tanks. And an electrolysis tank 5 having a nitrogen removing function is provided at the upper part of the advection pipe 4, and an aerobic biological treatment tank 6 and a treatment communicating with a lower part of the aerobic biological treatment tank 6 are connected to the subsequent stream. A water tank 7 is provided, and a disinfection tank 8 is provided above the treated water tank 7.
[0013]
More specifically, the first anaerobic treatment tank 2 is provided with a sewage inflow pipe 9, and below the sewage inflow pipe 9 is provided a box-shaped inflow baffle 10 having upper and lower openings. An advection pipe 11 is provided on the partition wall opposite to the inflow pipe 2. In the first anaerobic treatment tank 2, sediment that tends to settle out of the inflowing sewage is separated and separated and concentrated and stored at the bottom of the tank. At this time, part of the sludge stored at the bottom of the tank becomes scum due to an anaerobic biological reaction, floats and is stored at the top of the tank. In the filter bed 22, the anaerobic biological reaction proceeds.
The second anaerobic treatment tank 3 has a treatment function similar to that of the first anaerobic treatment tank 2, and stores sludge at the top of the tank by scumming, decomposes organic matter in the filter bed 23, and sludge at the bottom due to sedimentation. To store. In the above anaerobic biological treatment tanks (the first anaerobic treatment tank 2 and the second anaerobic treatment tank 3), most of the nitrogen contained therein is converted to ammonia nitrogen with the decomposition of organic substances. In addition, the filter beds 22 and 23 can be omitted.
[0014]
At the upper part of each of the first anaerobic treatment tank 2 and the second anaerobic treatment tank 3, the liquid level is the highest water level (HWL) in order to alleviate the fluctuation of the inflowing sewage and transfer it to the next tank. And a flow rate adjusting unit 12 that can be varied between a minimum water level (LWL). In addition, the L.F. of the advection tube 4 disposed in the second anaerobic treatment tank 3 W. L is provided with a suction port 14 of a transfer pump 13 for transferring the liquid to the electrolysis tank 5 at a constant flow rate. In this case, the water level in the first anaerobic treatment tank 2 and the second anaerobic treatment tank 3 depends on whether the inflow of sewage is larger or smaller than the amount of liquid sent from the transfer pump 13. W. L and H. W. L. By doing so, the inflow of sewage is averaged, and in the anaerobic biological treatment tanks (the first anaerobic treatment tank 2 and the second anaerobic treatment tank 3), the functions of the respective tanks are exhibited well. You. Although the transfer pump 13 is an air lift pump using air supplied from the blower 15 in FIG. 1, an intermittent fixed-quantity pump for pumping air into a closed container or an electrically driven submersible pump may be used.
[0015]
The electrolysis tank 5 electrolyzes the liquid sent from the transfer pump 13 and gasifies the existing ammonia nitrogen to denitrify the nitrogen. The electrode is composed of an anode and a cathode. A direct current is supplied from the box 16. When the solution subjected to anaerobic treatment is electrolyzed, chloride ions contained in the solution are oxidized at the cathode to generate hypochlorous acid, and the hypochlorous acid and ammonia nitrogen react to form nitrogen gas.
[0016]
For the electrode material of the anode of the electrolysis, platinum, iridium, ruthenium, palladium, titanium coated with at least one kind of noble metal or noble metal oxide such as rhodium, lead dioxide, ferrite, carbon and the like can be used. Of these, non-elutable electrodes are preferred. As the cathode electrode material, zinc, copper, silver, brass, gold, stainless steel, iron, aluminum, zirconium, nickel alloy, titanium coated with platinum, copper coated with palladium, or the like can be used.
[0017]
In the electrolysis, not only the reaction shown in the above formula (3) but also a slight oxidation of ammonia nitrogen to generate nitrate nitrogen may occur. Since the load of nitrogen is eliminated, it is advantageous in decomposing organic substances. In addition, although hypochlorous acid may remain, it is consumed for oxidation of the organic substance due to the high concentration of the organic substance, and the adverse effect on the microorganisms in the aerobic biological treatment tank 6 at the subsequent stage is reduced and acts rather advantageously. .
[0018]
In the aerobic biological treatment tank 6, a diffuser tube 17 for aeration is disposed at the bottom, and air from the blower 15 is blown out. In the aerobic biological treatment tank 6, a bed filled with a microorganism-adhering material (also referred to as a carrier, a microorganism carrier, a contact material, and a contact filter material) is formed. Here, the bed filled with the microorganism-adhering material may be a fluidized bed in which the microorganism-adhering material flows together with the liquid by the air ejected, a fixed bed in which only the liquid moves, or both a fluidized bed and a fixed bed. May be incorporated. When both the fluidized bed and the fixed bed are incorporated, the fluidized bed is arranged on the upper side and the fixed bed is arranged on the lower side in the vertical direction. Or you can. In the aerobic biological treatment tank 6, aeration is performed so that the microorganism-attached material (to which microorganisms are attached) and the liquid are sufficiently mixed, or the microorganism-attached material and the liquid are positively contacted. As a result, organic substances are oxidized and decomposed, and nitrification proceeds when ammonia nitrogen remains.
[0019]
The shape of the microorganism adhering material to be used can be various such as plate, mesh plate, loofah, porous, cylindrical, rod, skeleton spherical, string, and even granular, irregular mass, cube, fiber mass, etc. Can be used. Among these microorganism adhering materials, those having a relatively small and easy-to-flow shape are preferably used for the fluidized bed, and those having a relatively large and easy-to-fix shape are preferably used for the fixed bed. Examples of the material of the microorganism adhering material include synthetic resin products such as vinylidene chloride, polyvinyl formal, polyurethane, and melamine resin, inorganic products such as ceramics and silica sand, fossil products such as anthracite, and activated carbon. Can be used, and any of polyolefin resins such as polyethylene and polypropylene, polystyrene and the like having a specific gravity of about 1 or 1 or less can be used.
[0020]
The lower part (bottom part) of the boundary between the aerobic biological treatment tank 6 and the next treatment water tank 7 is communicated with each other, and the liquid flowing from the aerobic biological treatment tank 6 to the treatment water tank 7 is transferred to the upper part of the treatment water tank 7. Overflow to the disinfection tank 8 provided in one area. The treatment water tank 7 also has a function to precipitate and separate SS in the liquid.
[0021]
In the treated water tank 7, a return pump 18 for returning a part of the liquid treated in the aerobic biological treatment tank 6 to the first anaerobic treatment tank 2 is provided. By returning the aerobic biologically treated liquid, sludge settled at the bottom of the treated water tank 7 can be pulled out. This is because denitrification can be achieved. The return of the liquid from the return pump 18 may be continuous or intermittent. Although the return pump 18 is an air lift pump that supplies air from the blower 15 in FIG. 1, an intermittent fixed-quantity pump or an electric pump that pumps air into a closed container can be used.
[0022]
In the disinfecting tank 8, the advection liquid from the treatment water tank 7 is brought into contact with the medicine cartridge 19 to disinfect or sterilize. In addition, a manhole is provided above each tank (each room) of the sewage purification tank so that maintenance such as inspection and cleaning can be easily performed, and a manhole cover 21 is usually attached thereto.
[0023]
Next, a method for treating sewage in a sewage treatment tank will be described.
The sewage (raw water) enters the first anaerobic treatment tank 2 via the inflow baffle 10 from the sewage inflow port 9, and the sedimentation separation of solids and anaerobic biodegradation are performed. In the first anaerobic treatment tank 2, concentrated sludge (solid matter) is stored at the bottom of the tank, and scum generated by anaerobic treatment is stored at the top of the tank. The advection liquid from the first anaerobic treatment tank 2 passes through the advection pipe 11 and enters the second anaerobic treatment tank 3, where sedimentation and separation of solids, anaerobic treatment, and scumification of sludge further proceed. The transfer from the second anaerobic treatment tank 3 to the electrolysis tank 5 is performed by the transfer pump 13. That is, the advection liquid is L.P. W. L is sucked through the suction port 14, and a predetermined amount (almost constant amount) is transferred to the electrolysis tank 5 from above the transfer pump 13. At this time, when the amount of inflowing sewage is larger than the transfer amount of the transfer pump 13, the water levels of the first anaerobic treatment tank 2 and the second anaerobic treatment tank 3 are set to L.P. W. L, but the capacity of the flow rate adjusting unit 12 is H. W. L is usually designed so as not to exceed L. W. Does not rise above L. By doing so, the respective processing functions of the first anaerobic treatment tank 2 and the second anaerobic treatment tank 3 are kept good.
[0024]
In the liquid supplied from the transfer pump 13 to the electrolysis tank 5, ammonia nitrogen is gasified into nitrogen by electrolysis and denitrified. In the aerobic biological treatment tank 6, it comes into contact with the microorganism-adhering material and the air from the diffuser tube 17, and oxidative decomposition of organic substances and nitrification of remaining ammonia nitrogen proceed. The treated liquid enters the treatment water tank 7 from the lower part (or bottom) of the aerobic biological treatment tank 6 and then flows to the disinfection tank 8. The liquid to be disinfected in the disinfection tank 8 is discharged from the discharge port 20 to the outside of the sewage purification tank. In addition, a part of the aerobic biologically treated liquid is returned from the lower part (or bottom part) of the treated water tank 7 to the first anaerobic treatment tank 2 by the return pump 18. At this time, if there is settled sludge or floating SS, these are also returned, and if nitrate nitrogen is present, they are denitrified in the first anaerobic treatment tank 2.
[0025]
(Experimental example)
A denitrification test for electrolysis using artificial wastewater containing ammonia nitrogen was performed.
Artificial wastewater is prepared by dissolving 0.25 mmol of sodium hydrogen carbonate, 0.25 mmol of calcium chloride, 0.25 mmol of magnesium sulfate, 0.025 mmol of potassium hydrogen carbonate, and 2.86 mmol of ammonium chloride in distilled water to make 1 liter. 0.5 liter of this aqueous solution was used for the test.
As the electrode material, a platinum plate and iridium coated on a titanium plate were used for the anode, and brass was used for the cathode. The current was a constant current and the current density was set to 0.015 A / cm ² .
FIG. 2 shows the results of tests performed up to 60 minutes of electrolysis. After 35 minutes, the ammonia nitrogen 35 mg / L was reduced to 3 mg / L after 60 minutes, and 32 mg / L could be removed. Incidentally, nitrate nitrogen was produced at 2 mg / L, but the total nitrogen was reduced to 5 mg / L.
[0026]
【The invention's effect】
The sewage purification tank of the present invention is provided with an electrolysis tank having a nitrogen removing function between the anaerobic biological treatment tank and the aerobic biological treatment tank, so that nitrogen can be efficiently and stably removed in addition to BOD. it can. Further, in the aerobic biological treatment tank, nitrification of ammonia-nitrogen, which is controlled by nitrification, is not required. Therefore, the capacity of the aerobic biological treatment can be reduced by that much, and the size of the sewage purification tank can be further reduced than before. Also, by returning the aerobic biologically treated liquid to the anaerobic biological treatment tank, nitrogen in the effluent can be significantly reduced.
[Brief description of the drawings]
FIG. 1 is an example of a sewage purification tank of the present invention, in which (a) is a schematic plan view, and (b) is a schematic cross-sectional view taken along the line AA of (a).
FIG. 2 is a graph showing the results of a denitrification test by electrolysis.
FIG. 3 is a schematic sectional view of an example of a conventional sewage purification tank.
[Explanation of symbols]
1: Sewage purification tank 2: First anaerobic treatment tank 3: Second anaerobic treatment tank 4: Advection tube 5: Electrolytic tank 6 (having nitrogen removal function) 6: Aerobic biological treatment tank 7: Treatment water tank 8: Disinfection tank 9: Sewage inlet 10: Baffle 11: Advection tube 12: Flow control unit 13: Transfer pump 14: Suction port 15: Blower 16: Electrical box 17: Diffusion tube 18: Return pump 19: Medicine tube 20: Discharge port 21: Manhole cover 22: Filter bed 23: Filter bed 51: Anaerobic filter bed tank first room 52: Anaerobic filter bed tank second chamber 53: Biological filtration tank 54: Treatment water tank 55: Disinfection tank 56: Water volume fluctuation absorption unit 57 : Pump tank 58: Air lift pump for transfer 59: Air lift pipe for circulation

Claims (2)

In order from the upstream, an anaerobic biological treatment tank, an aerobic biological treatment tank, and a sewage purification tank including a treatment water tank, wherein a nitrogen removal function is provided between the anaerobic biological treatment tank and the aerobic biological treatment tank. A sewage treatment tank equipped with an electrolysis tank. A return pump for returning a part of the liquid processed in the aerobic biological treatment tank to the anaerobic biological treatment tank is provided at a lower part of the treatment water tank or a lower part of the aerobic biological treatment tank. 1 sewage septic tank.

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