JP5149728B2 - Denitrification treatment method and denitrification treatment apparatus - Google Patents

Denitrification treatment method and denitrification treatment apparatus Download PDF

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JP5149728B2
JP5149728B2 JP2008192239A JP2008192239A JP5149728B2 JP 5149728 B2 JP5149728 B2 JP 5149728B2 JP 2008192239 A JP2008192239 A JP 2008192239A JP 2008192239 A JP2008192239 A JP 2008192239A JP 5149728 B2 JP5149728 B2 JP 5149728B2
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denitrification
hydrogen donor
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JP2010029749A (en
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吉昭 長谷部
正浩 江口
裕章 目黒
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オルガノ株式会社
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02WCLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO WASTEWATER TREATMENT OR WASTE MANAGEMENT
    • Y02W10/00Technologies for wastewater treatment
    • Y02W10/10Biological treatment of water, waste water, or sewage
    • Y02W10/15Aerobic processes

Description

  The present invention relates to a denitrification treatment method and a denitrification treatment apparatus for reducing nitrate ions and nitrite ions contained in water to be treated into nitrogen by denitrifying bacteria.

  In recent years, in the field of water treatment, particularly wastewater treatment, biochemical water treatment is often used in which the pollutant in the wastewater is changed to a harmless substance by utilizing the physiological activity of microorganisms. The activated sludge method is the mainstream as a general biological treatment method. However, in the normal activated sludge method, it is difficult to increase the concentration of microorganisms in the tank and the load cannot be increased. It has been regarded as a problem that it is necessary, the management of organisms is difficult and processing performance such as bulking is likely to deteriorate, the need for large-scale sedimentation facilities, and the generation of waste such as excess sludge . As a technique for solving these problems, a method of performing solid-liquid separation of activated sludge with a membrane, a method of performing treatment by attaching microorganisms such as sponges and polymer carriers, a mass with a high specific gravity, which is self-granulated microorganisms, so-called A method for performing processing using granules has been developed. Among them, the method using granules has been attracting attention because it can retain a large amount of microorganisms in the tank, and thus has a high reaction rate per unit volume and easy solid-liquid separation.

  Similarly, biochemical water treatment is applied to treatment of wastewater containing nitrogen. For example, in the treatment of wastewater containing ammonia nitrogen, anaerobic conditions and hydrogen donors are obtained after nitrifying ammonium ions to nitrite ions and nitrate ions by ammonia oxidizing bacteria and nitrite oxidizing bacteria under aerobic conditions. In the presence of nitrite, there is a method of reducing nitrite ions and nitrate ions to nitrogen gas by denitrifying bacteria. At this time, an organic substance or the like contained in the waste water can be used as the hydrogen donor, but when the hydrogen donor is insufficient, it is necessary to supply it from the outside. At this time, the supply amount of the hydrogen donor is determined based on the nitrogen concentration in the waste water, and the hydrogen donor is continuously added based on the supply amount.

  Among these, in the denitrification treatment that reduces nitrite ions and nitrate ions to nitrogen gas by denitrifying bacteria, in addition to the activated sludge method, in order to increase the concentration of denitrifying bacteria and facilitate solid-liquid separation, There is a method in which a denitrification treatment is performed by adding a sponge or a gel-like carrier. There is also a method in which denitrifying bacteria are self-granulated to form a lump with high specific gravity, that is, granules, and the concentration of denitrifying bacteria in the tank is dramatically increased to perform denitrification treatment. In the treatment method using granulated denitrifying bacteria, a high concentration of denitrifying bacteria can be retained in the tank, so the processing speed per tank is faster than the treatment method with the addition of the carrier. Can be reduced in cost. Furthermore, since the specific gravity of the granule is high and the sedimentation speed is fast, it has advantages such as easy solid-liquid separation. Formation of such granules has been confirmed in anaerobic methane fermentation, an upflow sludge blanket reactor (USB), and a semi-batch reactor (SBR) (see, for example, Patent Documents 1 to 3).

JP 63-258695 A JP-A-1-262996 JP 2000-51893 A

  In the semi-batch reactor, the denitrification tank is a complete mixing type. In one denitrification tank, inflow of treated water, oxygen supply and contact between treated water and denitrifying bacteria, sedimentation of denitrifying bacteria, treated water The process is performed through four steps such as discharging. However, since both the inflow of treated water and the discharge of treated water are performed in a short time, the variation of the treatment flow rate becomes large, and the apparatus requires a large flow rate adjustment tank. Therefore, although it can be a simple and advantageous device in a small-scale device, it is difficult to apply to a medium-to-large device. In addition, when an upward flow type sludge blanket reactor is used, although a very high processing speed can be obtained, the equipment cost increases because a specially shaped denitrification tank is used. In addition, due to the configuration of the equipment, the inside of the denitrification tank cannot be sufficiently stirred, making it difficult to control the pH of the water to be treated. In the water to be treated containing calcium, etc., the generation of scales and inorganic substances in the granule Have problems such as accumulation.

  In order to solve these problems, it is desirable to use a completely mixed type denitrification tank that has been used in many devices in the past, and to have a device configuration that continuously inflows (and continuously discharges) the water to be treated. There has never been a report on the formation of granules of denitrifying bacteria in such a device configuration.

  Therefore, in the denitrification treatment in which nitrate ions and nitrite ions contained in the water to be treated are reduced to nitrogen by the denitrifying bacteria, the present invention continuously removes the denitrifying bacteria while allowing the water to be treated to continuously flow into the complete denitrification tank. The purpose is to granulate.

  The present invention provides a denitrification treatment in which treated water is continuously supplied to a complete mixing type denitrification tank, a hydrogen donor is supplied, and nitrate ions and nitrite ions contained in the treated water are reduced to nitrogen by denitrifying bacteria. In this method, as the denitrification tank, a first denitrification unit and a second denitrification unit are installed after the first denitrification unit, and the water to be treated in the second denitrification unit is hydraulic The concentration of the hydrogen donor in the first denitrification part during the residence time, and the concentration of the hydrogen donor in the second denitrification part during the hydraulic residence time of the water to be treated in the second denitrification part The hydrogen donor is supplied to at least the first denitrification unit so that the difference in concentration is a concentration difference that induces self-granulation of the denitrifying bacteria.

  In the denitrification method, the maximum concentration of the hydrogen donor in the first denitrification unit during the hydraulic residence time of the water to be treated in the second denitrification unit, and the second denitrification unit Supply the hydrogen donor to at least the first denitrification unit so that the difference from the minimum concentration of the hydrogen donor in the second denitrification unit in the hydraulic residence time of the treated water is 50 mg TOC / L or more. It is preferable to do.

  In the denitrification method, the volume of the first denitrification unit is preferably 1/30 to 1/3 of the volume of the second denitrification unit.

  In the denitrification treatment method, it is preferable that a hydrogen donor is intermittently supplied to the first denitrification unit.

  Further, in the denitrification treatment method, with respect to the concentration of nitrate ion and nitrite ion, the supply amount of hydrogen donor necessary for the denitrification treatment is used as a reference, and an amount of hydrogen donor less than the reference value is added to the first value. A combination of a first supply step for supplying to the first denitrification unit and a second supply step for supplying a hydrogen donor in an amount greater than the reference value to the second denitrification unit, It is preferred to supply a donor.

  In the denitrification method, the first denitrification unit is preferably a plurality of tanks.

  In the denitrification method, the second denitrification unit is preferably a plurality of tanks.

  The present invention also includes a complete mixing type denitrification tank, treated water supply means for continuously supplying treated water to the denitrification tank, and hydrogen donor supply means for supplying a hydrogen donor to the denitrification tank. And a denitrification apparatus for reducing nitrate ions and nitrite ions contained in the water to be treated in the denitrification tank to nitrogen by denitrifying bacteria, wherein the denitrification tank includes the first denitrification unit and the first denitrification unit. A second denitrification unit installed at a subsequent stage of the denitrification unit, wherein the hydrogen donor supply means includes the first denitrification during the hydraulic residence time of the water to be treated in the second denitrification unit. The difference between the concentration of the hydrogen donor in the section and the concentration of the hydrogen donor in the second denitrification section in the hydraulic residence time of the treated water in the second denitrification section is A hydrogen donor is supplied to at least the first denitrification unit so as to achieve a concentration difference that induces self-granulation.

  According to the present invention, denitrifying bacteria can be granulated while allowing the water to be treated to flow continuously into a complete mixing type denitrification tank, and the apparatus can be downsized or reduced in cost.

  Embodiments of the present invention will be described below. This embodiment is an example for carrying out the present invention, and the present invention is not limited to this embodiment.

  FIG. 1 is a schematic configuration diagram illustrating an example of a water treatment apparatus according to the present embodiment. As shown in FIG. 1, the water treatment device 1 includes a fluorine treatment device 10, a nitrification device 12, and a denitrification device 14. The present embodiment relates to a method and a denitrification apparatus for treating water containing nitrate ions and nitrite ions. For example, fluorine and ammonia are used for electronic industrial wastewater such as semiconductor factory wastewater. In such a case, it is necessary to remove fluorine by the fluorine treatment device 10 and nitrify ammonia nitrogen to nitric acid or nitrous acid by the nitrification device 12 as described above. is there.

  Ammonia nitrogen originates from organic nitrogen compounds such as ammonia, ammonium compounds, and amine compounds such as tetramethylammonium hydroxide, monoethanolamine, and other amino acids. Fluorine is caused by hydrofluoric acid, a fluorine compound, or the like. In addition, although the example is demonstrated below about the structure of the fluorine processing apparatus 10, the fluorine removal method, the structure of the nitrification apparatus 12, and the nitrification method, an apparatus structure and a method are not restrict | limited to this.

  The fluorine treatment apparatus 10 includes a water tank to be treated, a reaction tank, and a precipitation tank. The outlet of the water tank to be treated and the inlet of the reaction tank, and the outlet of the reaction tank and the inlet of the precipitation tank are connected by piping.

  The nitrification device 12 includes a water tank to be treated and a nitrification tank. The outlet of the precipitation tank of the fluorine treatment apparatus 10 and the inlet of the water tank to be treated of the nitrification apparatus 12, and the outlet of the water tank to be treated of the nitrification apparatus 12 and the inlet of the nitrification tank are connected by piping.

  FIG. 2 is a schematic diagram illustrating an example of the configuration of the denitrification apparatus according to the present embodiment. As shown in FIG. 2, the denitrification device 14 includes a denitrification tank (first denitrification section 16 a and second denitrification section 16 b), an oxidation tank 18, a precipitation tank 20, and a first water treatment pipe 22 for treated water. , To-be-treated water second inflow pipe 23, sludge return pipe 24, treated water take-out pipes 26a, 26b, and 26c, hydrogen donor supply device 28, and pH adjusting device 30. A denitrification tank has the 1st denitrification part 16a and the 2nd denitrification part 16b installed in the back | latter stage of the 1st denitrification part 16a. The outlet of the nitrification tank of the nitrification device 12 shown in FIG. 1 and the treated water supply port of the first denitrification unit 16 a shown in FIG. 2 are connected by a first treated water inflow pipe 22. The treated water discharge port of the first denitrification unit 16 a and the treated water supply port of the second denitrification unit 16 b are connected by the second treated water inflow pipe 23. The treated water outlet of the second denitrification unit 16b and the inlet of the oxidation tank 18 are connected by a treated water take-out pipe 26a, and the outlet of the oxidation tank 18 and the inlet of the settling tank 20 are connected by a treated water take-out pipe 26b to cause precipitation. A treated water outlet pipe 26 c is connected to the treated water outlet of the tank 20. The sludge discharge port of the sedimentation tank 20 and the sludge inlet of the first denitrification unit 16 a are connected by a sludge return pipe 24 via a pump 25. In the 1st denitrification part 16a and the 2nd denitrification part 16b, the stirring apparatuses 32a and 32b which stir the water in a tank are provided.

  The hydrogen donor supply device 28 supplies a hydrogen donor to at least the first denitrification unit 16a, a hydrogen donor tank 34 in which the hydrogen donor is accommodated, and the hydrogen donor to the first denitrification unit 16a. A pump 36 for feeding water, a hydrogen donor inflow pipe 38 serving as a flow path for the hydrogen donor, and a controller 40 for controlling the drive of the pump 36 and controlling the supply amount of the hydrogen donor are provided. The outlet of the hydrogen donor tank 34 and the hydrogen donor supply port of the first denitrification unit 16 a are connected by a hydrogen donor inflow pipe 38 via a pump 36. The pump 36 and the control device 40 are electrically connected. In addition, when supplying a hydrogen donor also to the 2nd denitrification part 16b, the pump which supplies a hydrogen donor to the 2nd denitrification part 16b, the hydrogen donor inflow pipe used as the flow path of a hydrogen donor, a pump A control device for controlling the driving of the hydrogen donor and controlling the supply amount of the hydrogen donor may be provided separately.

  The pH adjuster 30 adjusts the pH of the water to be treated in the first denitrification unit 16a and the second denitrification unit 16b, and adjusts the pH of an acid agent such as hydrochloric acid or an alkali agent such as sodium hydroxide. PH adjusting agent tank 42 in which the agent is accommodated, pumps 44a and 44b for feeding the pH adjusting agent to the first denitrifying unit 16a and the second denitrifying unit 16b, and the pH adjusting agent inflow serving as a channel for the pH adjusting agent The pipes 46a and 46b, pH sensors 48a and 48b for measuring the pH values of the water to be treated in the first denitrification unit 16a and the second denitrification unit 16b, and the drive of the pump 44a are controlled, and the first denitrification unit 16a And a control device 50b for controlling the supply amount of the pH adjusting agent supplied to the second denitrification unit 16b by controlling the drive of the pump 44b. The first outlet of the pH adjuster tank 42 and the pH adjuster supply port of the first denitrification unit 16a are connected by a pH adjuster inflow pipe 46a via a pump 44a. Further, the second outlet of the pH adjuster tank 42 and the pH adjuster supply port of the second denitrification unit 16b are connected by a pH adjuster inflow pipe 46b via a pump 44b. The pH sensor 48a and the control device 50a, the control device 50a and the pump 44a, the pH sensor 48b and the control device 50b, and the control device 50b and the pump 44b are electrically connected.

Next, the operation of the water treatment method and the water treatment apparatus 1 according to this embodiment will be described. First, the water to be treated containing fluorine and ammonia nitrogen is fed to the water tank to be treated of the fluorine treatment apparatus 10 shown in FIG. After the flow rate and concentration of the water to be treated are averaged in the water tank to be treated and the pH is adjusted, the water to be treated is sent to the reaction tank of the fluorine treatment apparatus 10. In addition, a calcium compound is supplied to the reaction vessel. Then, in a reaction vessel of the fluorine treatment unit 10 is reacted with fluorine and calcium compounds in the for-treatment water, to form calcium fluoride (CaF 2). Here, in order to increase the treatment efficiency of fluorine in the water to be treated, together with the calcium compound, a flocculant may be supplied to the reaction tank of the fluorine treatment apparatus 10 to flock the generated calcium fluoride. Then, individual liquid separation of water to be treated containing calcium fluoride (flocculated) is performed in the precipitation tank of the fluorine treatment apparatus 10 to remove fluorine (and calcium fluoride) from the water to be treated.

  Moreover, the fluorine processing apparatus 10 may include a plurality of reaction vessels. For example, a first reaction tank and a second reaction tank are provided, and in the first reaction tank, treated water containing fluorine and ammonia nitrogen and a calcium compound are reacted to generate calcium fluoride, and the second reaction tank The flocculant may be flocked by adding a flocculant. In addition, the reaction tank may be provided with a stirring mechanism for stirring water in the tank.

The calcium compound supplied to the reaction tank of the fluorine treatment apparatus 10 is not particularly limited as long as fluorine can be extracted as calcium fluoride. For example, calcium hydroxide (Ca (OH) 2 ), calcium chloride (CaCl 2 ), calcium sulfate (CaSO 4 ) and the like. Examples of the flocculant include inorganic flocculants such as polyaluminum chloride and aluminum sulfate, and organic polymer flocculants such as an anionic polymer.

  Next, the water to be treated containing ammonia nitrogen from which fluorine has been removed is fed to the water tank to be treated of the nitrification apparatus 12 shown in FIG. After the flow rate and concentration of the water to be treated are averaged in the water tank to be treated and the pH is adjusted, the water to be treated is sent to the nitrification tank. The nitrification tank is filled with a microorganism-supporting carrier formed by supporting a microorganism film containing nitrifying bacteria on a carrier. In addition, an air introduction pipe (not shown) is connected to the nitrification tank so that air can be supplied to the water to be treated in the nitrification tank. Then, in the nitrification tank, ammonia nitrogen in the water to be treated is nitrified into nitrate nitrogen and nitrite nitrogen by the action of nitrifying bacteria of the microorganism-supporting carrier. Here, nitrifying bacteria are ammonia-oxidizing bacteria, which are auxotrophic bacteria that nitrify ammonia nitrogen contained in treated water to nitrite nitrogen, and sub-types of autotrophic bacteria that nitrify nitrite nitrogen to nitrate nitrogen. Such as nitrate-oxidizing bacteria.

  The carrier on which nitrifying bacteria are supported is not particularly limited, and for example, sponges, gels, plastic molded products, and the like can be used. Specifically, it is preferable to use hydrophilic polyurethane sponge, polyvinyl alcohol gel, or the like.

  Next, the nitrification liquid subjected to nitrification, that is, the water to be treated containing nitrate nitrogen and nitrite nitrogen is supplied to the first denitrification unit 16a of the denitrification device 14 through the water to be treated first inflow pipe 22. To liquid. Here, the 1st denitrification part 16a is a complete mixing type tank, and in the case of a denitrification process, to-be-processed water is continuously supplied to the 1st denitrification part 16a. Further, the pump 36 is operated to supply the hydrogen donor in the hydrogen donor tank 34 to the first denitrification unit 16a through the hydrogen donor inflow pipe 38. In the 1st denitrification part 16a (and the 2nd denitrification part 16b), the sludge containing denitrification bacteria is accommodated in the state suspended in water. After the nitrate ion and nitrite ion in the treated water are brought into contact with the denitrifying bacterium in the first denitrification unit 16a, the treated water, the denitrifying bacterium, and the hydrogen donor are secondly passed through the treated water second inflow pipe 23. The liquid is sent to the denitrification unit 16b. Moreover, the 2nd denitrification part 16b is also a complete mixing type tank, and the to-be-processed water discharged | emitted from the 1st denitrification part 16a is continuously supplied to the 2nd denitrification part 16b.

  In the first denitrification unit 16a and the second denitrification unit 16b, nitrate ions and nitrite ions in the water to be treated are reduced to nitrogen gas by the action of the denitrifying bacteria. When methanol is used as the hydrogen donor, nitrate ions and nitrite ions in the water to be treated are reduced to nitrogen gas by the reaction shown in the following reaction formula.

2NO 2 + CH 3 OH → N 2 + CO 2 + H 2 O + 2OH
6NO 3 - + 5CH 3 OH → 3N 2 + 5CO 2 + 7H 2 O + 6OH -

  Next, the treated water from which nitrate ions and nitrite ions have been removed by the denitrification treatment is sent to the oxidation tank 18 through the treated water extraction pipe 26a, and the hydrogen donor remaining in the treated water in the oxidation tank 18 Oxidize organic matter such as. Next, the treated water from which the hydrogen donor has been removed is sent to the sedimentation tank 20 through the treated water take-out pipe 26b. Then, denitrifying bacteria contained in the water to be treated (self-granulated in this embodiment) accumulate as sludge in the lower part of the sedimentation tank 20, and the supernatant water of the upper part of the precipitation tank 20 is taken out from the treated water extraction pipe 26c. . Further, the pump 25 is operated, and the sludge accumulated in the lower part of the settling tank 20 is returned again from the sludge return pipe 24 into the first denitrification unit 16a. In addition, when performing the nitrification process performed with the nitrification apparatus 12 also with a floating sludge, you may return sludge to a nitrification tank.

  FIG. 3 is a schematic diagram showing an example of the configuration of a denitrification apparatus according to another embodiment of the present invention. In the denitrification apparatus 14, it is not always necessary to provide the precipitation tank 20 independently of the denitrification tank. As shown in FIG. 3, a partition wall 52 having a lower opening is provided in the second denitrification section 16b, and a denitrification chamber is provided. 54 and settling chamber 56 may be formed. Further, the individual liquid separation may be performed by any means such as a gas solid separator (GSS), a membrane separation device, etc., without using the precipitation tank 20 shown in FIG. 2 and the precipitation chamber 56 shown in FIG.

  The oxidation tank 18 is for oxidizing and decomposing organic substances such as a hydrogen donor contained in the water to be treated by the action of microorganisms. As shown in FIG. 2, the oxidation tank 18 may be installed on the upstream side of the precipitation tank 20, or may be installed on the downstream side of the precipitation tank 20.

  Next, a method for supplying a hydrogen donor will be described in detail. Normally, the hydrogen donor calculates the supply amount of the hydrogen donor required for the denitrification treatment from the concentration of nitrate ion and nitrite ion in the water to be treated supplied to the denitrification tank, and without changing the amount. Continuously supply to the denitrification tank. Therefore, the concentration of the hydrogen donor in the denitrification tank is almost constant at a low concentration. In addition, in order to efficiently perform the denitrification treatment, about 1.2 times the supply amount of hydrogen donor (necessary theoretical amount of hydrogen donor) necessary for the denitrification treatment of nitrate ion and nitrite ion in the denitrification tank Is supplied to the denitrification tank.

  However, in this embodiment, the concentration of the hydrogen donor in the first denitrification unit 16a during the hydraulic residence time (HRT) of the water to be treated in the second denitrification unit 16b and the second denitrification unit The difference between the concentration of the hydrogen donor in the second denitrification unit 16b in the hydraulic retention time of the water to be treated in 16b and the concentration that induces (granulates) self-granulation of the denitrifying bacteria A hydrogen donor is supplied to at least the first denitrification unit 16a so as to make a difference. Specifically, the control device 40 is made to record in advance a concentration variation map of the hydrogen donor in the first denitrification unit 16a and the second denitrification unit 16b during the hydraulic residence time. Based on this, the difference between the concentration of the hydrogen donor in the first denitrification unit 16a and the concentration in the second denitrification unit 16b is a concentration difference that induces self-granulation of the denitrifying bacteria. The operation of the pump 36 is controlled and the supply amount of the hydrogen donor is adjusted.

  The volume of the first denitrification unit 16a is preferably in the range of 1/30 to 1/3 of the volume of the second denitrification unit 16b, and 1/20 to 1/5 of the volume of the second denitrification unit 16b. It is preferable that it is the range of these. When the volume of the first denitrification unit 16a is more than 1/3 of the volume of the second denitrification unit 16b, the concentration of the hydrogen donor in the first denitrification unit 16a and the second denitrification unit 16b It may be difficult to make the difference from the hydrogen donor concentration a concentration difference that induces self-granulation of denitrifying bacteria. In addition, if the volume of the first denitrification unit 16a is less than 1/30 of the volume of the second denitrification unit 16b, the HRT in the first denitrification unit 16a becomes too short, so The dissolved oxygen consumption cannot catch up, and the first denitrification unit 16a becomes an aerobic condition, and the denitrification treatment may not be performed efficiently. Although it depends on the nitrate ion, nitrite ion concentration, and dissolved oxygen concentration in the water to be treated, the first denitrification unit 16a has a size that can secure an HRT of several minutes or more (the volume of the second denitrification unit 16b). 1/30 or more).

  Here, the maximum concentration of the hydrogen donor in the first denitrification unit 16a in the hydraulic retention time (HRT) of the water to be treated in the second denitrification unit 16b, and the target concentration in the second denitrification unit 16b. At least the hydrogen donor in the first denitrification unit 16a so that the difference from the minimum concentration of the hydrogen donor in the second denitrification unit 16b in the hydraulic residence time of the treated water is 50 mg TOC / L or more. It is preferable to supply the hydrogen donor, and it is more preferable to supply the hydrogen donor into at least the first denitrification unit 16a so as to be 100 mg TOC / L or more. If the difference between the maximum concentration of the hydrogen donor in the first denitrification unit 16a and the minimum concentration of the hydrogen donor in the second denitrification unit 16b is less than 50 mg TOC / L, self-granulation of the denitrifying bacteria May not be sufficiently induced.

  In the present embodiment, the hydrogen donor may be continuously supplied to the first denitrification unit 16a (may also be supplied to the second denitrification unit 16b), but nitrate ions and nitrite ions in the water to be treated. When the concentration of hydrogen is low, the concentration of the hydrogen donor necessary for the denitrification process is also low, so that a concentration difference of the hydrogen donor is formed between the first denitrification unit 16a and the second denitrification unit 16b. Difficult to do. Therefore, it is preferable to intermittently supply the hydrogen donor to the first denitrification unit 16a. That is, when the hydrogen donor is supplied, the concentration of the hydrogen donor in the first denitrification unit 16a is increased, and when the supply of the hydrogen donor is stopped, the hydrogen donor in the second denitrification unit 16b at the latter stage is increased. Since the concentration can be reduced (because the hydrogen donor is consumed by the denitrification treatment), the difference in concentration of the hydrogen donor between the first denitrification unit 16a and the second denitrification unit 16b can be easily achieved. Can be formed. However, the supply and stop time of the hydrogen donor and the supply amount of the hydrogen donor are the maximum concentration of the hydrogen donor in the first denitrification unit 16a and the minimum concentration of the hydrogen donor in the second denitrification unit 16b. Is preferably set so as to be, for example, 50 mg TOC / L or more.

  When a plurality of hydrogen donor supply and stop cycles are performed in the first denitrification unit 16a, the concentration of the hydrogen donor in the second denitrification unit 16b in the subsequent stage can be averaged. The (supply-stop) time is shorter than 50% of the hydraulic retention time of the treated water in the second denitrification unit 16b, that is, the hydraulics of the treated water in the second denitrification unit 16b. It is preferable to carry out 2 cycles or more with respect to the general residence time.

  Further, in the present embodiment, with respect to the concentration of nitrate ions and nitrite ions supplied to the denitrification tank, the supply amount of hydrogen donor required for the denitrification treatment (the required theoretical amount of hydrogen donor) is used as a reference. A first supply step of supplying a hydrogen donor in an amount less than the value to the first denitrification unit 16a, and a second supply step of supplying a hydrogen donor in an amount greater than the reference value to the first denitrification unit 16a. By combining and supplying a hydrogen donor to the first denitrification unit 16a, a concentration difference of the hydrogen donor can be easily formed between the first denitrification unit 16a and the second denitrification unit 16b. Can do. However, the supply and stop time of the hydrogen donor and the supply amount of the hydrogen donor are the maximum concentration of the hydrogen donor in the first denitrification unit 16a and the minimum concentration of the hydrogen donor in the second denitrification unit 16b. Is preferably set so as to be, for example, 50 mg TOC / L or more.

  When performing a plurality of cycles of the first supply step and the second supply step in the first denitrification unit 16a, the concentration of the hydrogen donor in the second denitrification unit 16b in the subsequent stage can be averaged. The time of one cycle (first supply step-second supply step) is shorter than 50% of the hydraulic retention time of the water to be treated in the second denitrification unit 16b, that is, in the second denitrification unit 16b. It is preferable to carry out 2 cycles or more with respect to the hydraulic residence time of the water to be treated.

  In the present embodiment, it is sufficient to supply a hydrogen donor to at least the first denitrification unit 16a, but in the first denitrification unit 16a during the hydraulic residence time of the water to be treated in the second denitrification unit 16b. The difference between the hydrogen donor concentration in the second denitrification part 16b and the hydrogen donor concentration in the second denitrification part 16b during the hydraulic residence time of the treated water in the second denitrification part 16b If the concentration difference induces granulation (granulates), the second denitrification unit 16b is also supplied with a hydrogen donor (including supply-stop intermittent supply, large amount supply-small amount supply, etc.). Good. However, when the hydrogen donor is supplied to the second denitrification unit 16b, it is necessary to increase the supply amount of the hydrogen donor in the first denitrification unit 16a in order to ensure the above concentration difference. There are cases where the amount of use of the body increases and the running cost of the device increases. Therefore, it is preferable to supply the hydrogen donor only to the first denitrification unit 16a.

  In this embodiment, although the 1st denitrification part 16a and the 2nd denitrification part 16b were illustrated as a single tank, it is not restrict | limited to this. That is, if a hydrogen donor concentration difference that induces (granulates) self-granulation of denitrifying bacteria can be formed between the first denitrifying unit 16a and the second denitrifying unit 16b, The first denitrification unit 16a may be a plurality of tanks, and the second denitrification unit 16b may be a plurality of tanks. For example, the first denitrification unit 16a may include tubs A and B, and the second denitrification unit 16b may include tubs C and D. In this case, the difference between the concentration of the tub A of the first denitrification unit 16a and the concentration of the tub B in the hydraulic retention time of the water to be treated in the second denitrification unit 16b causes self-granulation. Not the concentration difference of the hydrogen donor to be induced (granulated) but the concentration in the small tank A of the first denitrification unit 16a and the first concentration in the hydraulic residence time of the treated water in the second denitrification unit 16b. 2 The difference between the concentration in the small tank C of the denitrification unit 16b or the concentration of the small tank B in the first denitrification unit 16a and the second desorption in the hydraulic retention time of the water to be treated in the second denitrification unit 16b The difference from the concentration in the small tank C of the nitrogen part 16b may be a concentration difference in the hydrogen donor that induces (granulates) self-granulation of denitrifying bacteria. At this time, the hydrogen donor may be supplied to at least the small tank A of the first denitrification unit 16a or the small tank A and the small tank B of the first denitrification unit 16a. In addition, when there are a plurality of denitrification units, for example, when the second denitrification unit 16b includes small tanks C and D, the hydraulic retention time of the water to be treated in the second denitrification unit 16b is It is the sum of the hydraulic residence time of water to be treated in the tubs C and D. The volume of the 1st denitrification part 16a and the volume of the 2nd denitrification part 16b are the same, for example, the 1st denitrification part 16a is equipped with the small tanks A and B, and the 2nd denitrification part 16b is the small tank C, When D is provided, the sum of the volumes of the small tanks A and B (volume of the first denitrification unit 16a) is 1/30 to the sum of the volumes of the small tanks C and D (volume of the second denitrification unit 16b). A range of 1/3 is preferable, and a range of 1/20 to 1/5 of the sum of the volumes of the small tanks C and D (the volume of the second denitrification unit 16b) is preferable.

  In the present embodiment, all the water to be treated is allowed to flow into the first denitrification unit 16a, but is not limited thereto. For example, when it is desired to control the hydraulic residence time of the water to be treated in the first denitrification unit 16a, the water to be treated is caused to flow into both the first denitrification unit 16a and the second denitrification unit 16b. Alternatively, the inflow of water to be treated into the first denitrification unit 16a and the inflow of water to be treated into the second denitrification unit 16b may be switched according to time.

  In addition, when granulating denitrifying bacteria, addition of some metals may give a favorable result. These are generally positioned as granulation accelerators, and examples of ions include calcium ions and iron ions, examples of compounds include fly ash, iron oxide, and calcium carbonate. Among these, ions are preferably added continuously or intermittently over the denitrification treatment period or at the start-up period of the apparatus. Further, regarding the compounds, it is preferable to add them together with the addition of sludge when the apparatus is started up.

  Examples of the hydrogen donor used in the present embodiment include methanol, ethanol, isopropanol, acetic acid, hydrogen gas, acetone, glucose, ethyl methyl ketone, and the like. Any conventionally known one can be used.

  The reduction reaction from nitrate ion and nitrite ion to nitrogen gas is slightly different depending on the type of hydrogen donor, but in any case, nitrate ion and nitrite ion and equimolar hydroxide ions are generated. The pH of the water to be treated increases. In general, it is preferable to adjust the pH of water to be treated in the denitrification treatment to a range of 8-9. However, when the concentration of carbonate ions derived from the hydrogen donor is high and there is a concern about the generation of scale due to calcium ions or the like contained in the water to be treated, the pH of the water to be treated in the tank is in the range of 6 to 7.5. It is preferable to adjust to 6.3, and it is more preferable to adjust to the range of 7.3-7.0. Specifically, the pH sensors 48a and 48b of the pH adjusting device 30 detect the pH of the water to be treated in the first denitrification unit 16a and the second denitrification unit 16b, and the first denitrification is performed based on the detected pH. The pumps 44a and 44b are operated by the control devices 50a and 50b so that the pH of the water to be treated in the unit 16a and the second denitrification unit 16b is in the above pH range, and the pH adjuster is first supplied from the pH adjuster tank 42. It supplies in the denitrification part 16a and the 2nd denitrification part 16b, and adjusts the pH of the to-be-processed water in a tank.

  Although it does not restrict | limit especially as MLSS density | concentration in a denitrification tank (1st denitrification part 16a, 2nd denitrification part 16b), In order to achieve sufficient denitrification processing speed, about 5000-100000 mgMLSS / L It is preferable that

  As described above, the concentration of the hydrogen donor in the first denitrification unit 16a during the hydraulic residence time (HRT) of the water to be treated in the second denitrification unit 16b and the second denitrification unit 16b The difference between the hydrogen donor concentration in the second denitrification part 16b in the hydraulic residence time of the treated water in the water and the concentration difference that induces the self-granulation (granulation) of the denitrifying bacteria Preferably, the difference between the maximum hydrogen donor concentration in the first denitrification section 16a and the minimum hydrogen donor concentration in the second denitrification section 16b is 50 mg TOC / L or more. The denitrifying bacteria can be granulated by supplying a hydrogen donor to at least the first denitrifying unit 16a. By granulating the denitrifying bacteria, the microorganism concentration (sludge concentration) in the denitrifying tank can be increased, so that the processing speed of the denitrification treatment can be improved, and the apparatus can be reduced in size or cost.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

Example 1
In Example 1, water to be treated shown in Table 1 below was continuously passed through a denitrification tank using an apparatus similar to that shown in FIG. The volume of the 1st denitrification part was 4L, and the volume of the 2nd denitrification part was 40L. Using methanol as the hydrogen donor, the maximum concentration of methanol in the first denitrification unit in the HRT of the water to be treated in the second denitrification unit, and the second concentration in the HRT of the water to be treated in the second denitrification unit. The methanol was continuously supplied to the first denitrification unit so that the difference from the minimum concentration of methanol in the denitrification unit was 50 mg TOC / L or more. The supply amount of methanol was 3 kg methanol / kg nitrogen with respect to the treated nitrogen amount. Moreover, the activated sludge which is performing denitrification so that it may become about 500 mgMLSS / L at the time of a test start was supplied to the 1st denitrification part and the 2nd denitrification part. Moreover, the pH of the to-be-processed water of the 1st denitrification part and the 2nd denitrification part was adjusted using hydrochloric acid so that it might be set to 6.5. Moreover, the sludge collected in the settling tank installed in the latter stage of the denitrification tank was returned to the first denitrification section. The test was conducted for 33 days.

(Comparative Example 1)
In Comparative Example 1, the first denitrification unit was not installed, and the difference between the maximum concentration and the minimum concentration of methanol in the HRT of the water to be treated in the second denitrification unit was maintained below 50 mg TOC / L. The test was performed under the same conditions as in Example 1.

FIG. 4 is a diagram showing a change in MLSS concentration with respect to the number of days elapsed in the test of Example 1. FIG. 5 is a diagram illustrating a change in the processing speed of the denitrification process with respect to the elapsed test days of Example 1. FIG. 6 is a graph showing the transition of the nitrate ion concentration of the treated water with respect to the test elapsed days in Example 1. FIG. 7 is a diagram showing changes in SVI with respect to the number of days elapsed in the test of Example 1. As shown in FIG. 4, in Example 1, the MLSS concentration increased with the passage of days, and the MLSS concentration reached 8000 mg MLSS / L on the 33rd day from the start of the test. Further, as shown in FIG. 5, with the increase of the MLSS concentration, the processing speed of the denitrification process also increases, reaching about 2 kgN / m 3 / day on the 33rd day from the start of the test, and a high processing speed is obtained. It was confirmed. Moreover, as shown in FIG. 6, it was confirmed that the nitrate ion concentration in the treated water was low, and a stable treatment was performed during the test period. Further, as shown in FIG. 7, it was confirmed that SVI as an index of sludge settling properties decreased with the passage of days, and granules having a very small SVI value (good settling properties) were formed. In addition, SVI of general activated sludge is 120-150 mL / g. On the other hand, in Comparative Example 1, on the 33rd day from the start of the test, the MLSS concentration reached only 2000 mgMLSS / L, and the treatment speed of the denitrification treatment was 0.4 kgN / m 3 / day.

(Example 2)
In Example 2, the test was performed under the same conditions as in Example 1 except that the volume of the first denitrification unit was 20L, 12L, 4L, 2L, and 1L. Then, 25 days after the start of the test, whether or not the sludge containing denitrifying bacteria in the denitrifying tank is granulated was evaluated according to the following criteria and summarized in Table 2.
○: The whole sludge containing the vaginal bacteria was granulated △: A part of the sludge containing the vaginal bacteria was granulated ×: The sludge containing the vaginal bacteria was not granulated

  As can be seen from Table 2, when the first denitrification part was not installed (the above comparative example), granulation of devaginal bacteria did not occur even after 33 days from the start of the test. Further, by setting the volume of the first denitrification part / volume of the second denitrification part to 3/10, 1/10, 1/20, the entire sludge containing devaginal bacteria after 33 days from the start of the test. Can be granulated and good results have been obtained.

(Example 3)
In Example 3, water to be treated shown in Table 3 below was continuously passed through a denitrification tank using an apparatus similar to that shown in FIG. Using methanol as the hydrogen donor, the maximum concentration of methanol in the first denitrification unit in the HRT of the water to be treated in the second denitrification unit, and the second concentration in the HRT of the water to be treated in the second denitrification unit. The methanol was intermittently supplied to the first denitrification unit so that the difference from the minimum concentration of methanol in the denitrification unit was 50 mg TOC / L or more. The ratio of the hydrogen donor stop time to the feed time was fixed at 1: 4, and the cycle time was changed by the inflowing nitrogen load with the feed-stop 1 cycle time being 1/5 of the HRT. Otherwise, the test was performed under the same conditions as in Example 1. The test was conducted for 50 days.

(Comparative Example 2)
In Comparative Example 2, methanol was continuously supplied to the first denitrification unit. The maximum concentration of methanol in the first denitrification part in the HRT of the water to be treated in the second denitrification part and the minimum concentration of methanol in the second denitrification part in the HRT of the water to be treated in the second denitrification part And the difference was maintained below 50 mg TOC / L. Otherwise, the test was performed under the same conditions as in Example 3.

FIG. 8 is a diagram showing changes in MLSS concentration with respect to the number of days elapsed in the test of Example 3. FIG. 9 is a diagram illustrating a change in the processing speed of the denitrification process with respect to the test elapsed days of Example 3. FIG. 10 is a graph showing the transition of the nitrate ion concentration of the treated water with respect to the test elapsed days of Example 3. FIG. 11 is a diagram illustrating a change in SVI with respect to the elapsed test days of Example 3. As shown in FIG. 8, in Example 3, the MLSS concentration increased with the passage of days, and the MLSS concentration reached 8000 mg MLSS / L on the 50th day from the start of the test. Further, as shown in FIG. 9, the treatment speed of the denitrification treatment also increased, and reached about 2 kgN / m 3 / day on the 50th day from the start of the test, and it was confirmed that a high treatment speed was obtained. Moreover, as shown in FIG. 10, the nitrate ion density | concentration in process water was low, and it confirmed that the process stabilized during the test period was performed. Moreover, as shown in FIG. 11, it confirmed that SVI as a sludge sedimentation parameter | index decreased with progress of days, and the granule with the very small value of SVI (good sedimentation) was formed. On the other hand, in Comparative Example 2, on the 50th day from the start of the test, the MLSS concentration reached only about 1000 mgMLSS / L, and the treatment rate of the denitrification treatment was also 0.25 kgN / m 3 / day. Further, the TOC concentration in the first denitrification section at this time was 30 to 40 mg TOC / L, and in the second denitrification section was 15 mg TOC / L or less, which was a similar value throughout the entire period.

It is a schematic block diagram which shows an example of the water treatment apparatus which concerns on this embodiment. It is a schematic diagram which shows an example of a structure of the denitrification apparatus which concerns on this embodiment. It is a schematic diagram which shows an example of a structure of the denitrification apparatus which concerns on other embodiment of this invention. It is a figure which shows the change of the MLSS density | concentration with respect to the test elapsed days of Example 1. FIG. It is a figure which shows the change of the processing speed of the denitrification process with respect to the test elapsed days of Example 1. FIG. It is a figure which shows transition of the nitrate ion density | concentration of the treated water with respect to the test elapsed days of Example 1. FIG. It is a figure which shows the change of SVI with respect to the test elapsed days of Example 1. FIG. It is a figure which shows the change of the MLSS density | concentration with respect to the test elapsed days of Example 3. FIG. It is a figure which shows the change of the processing speed of the denitrification process with respect to the test elapsed days of Example 3. FIG. It is a figure which shows transition of the nitrate ion density | concentration of the treated water with respect to the test elapsed days of Example 3. FIG. It is a figure which shows the change of SVI with respect to the test elapsed days of Example 3. FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Water treatment apparatus, 10 Fluorine treatment apparatus, 12 Nitrification apparatus, 14 Denitrification apparatus, 16a 1st denitrification part, 16b 2nd denitrification part, 18 Oxidation tank, 20 Precipitation tank, 22 First treated water inflow pipe, 23 treated water second inflow pipe, 24 sludge return pipe, 25, 36, 44a, 44b pump, 26a, 26b, 26c treated water take-out pipe, 28 hydrogen donor supply device, 30 pH adjusting device, 32a, 32b stirring device 34 Hydrogen donor tank, 38 Hydrogen donor inflow pipe, 40, 50a, 50b Controller, 42 pH adjuster tank, 46a, 46b pH adjuster inflow pipe, 48a, 48b pH sensor, 52 partition, 54 Denitrification chamber 56 Precipitation chamber.

Claims (7)

  1. A denitrification method in which water to be treated is continuously supplied to a complete mixing type denitrification tank, a hydrogen donor is supplied, and nitrate ions and nitrite ions contained in the water to be treated are reduced to nitrogen by denitrifying bacteria. ,
    As the denitrification tank, a first denitrification unit and a second denitrification unit are installed downstream of the first denitrification unit,
    The maximum concentration of the hydrogen donor in the first denitrification unit during the hydraulic residence time of the treated water in the second denitrification unit, and the hydraulic retention of the treated water in the second denitrification unit The hydrogen donor is supplied to at least the first denitrification part so that the difference from the minimum concentration of the hydrogen donor in the second denitrification part over time is 50 mg TOC / L or more. Nitrogen treatment method.
  2.   2. The denitrification method according to claim 1, wherein the volume of the first denitrification unit is 1/30 to 1/3 of the volume of the second denitrification unit.
  3. The denitrification method according to claim 1 , wherein a hydrogen donor is intermittently supplied to the first denitrification unit.
  4. 2. The denitrification treatment method according to claim 1 , wherein the amount of hydrogen donation is smaller than the reference value with respect to the concentration of nitrate ion and nitrite ion based on the supply amount of hydrogen donor necessary for the denitrification treatment. A first supply step for supplying the first denitrification unit to the first denitrification unit and a second supply step for supplying a hydrogen donor in an amount greater than the reference value to the first denitrification unit, A denitrification method characterized by supplying a hydrogen donor to the nitrogen part.
  5.   The denitrification method according to claim 1, wherein the first denitrification unit is a plurality of tanks.
  6.   The denitrification method according to claim 1, wherein the second denitrification unit is a plurality of tanks.
  7. A demixing tank having a complete mixing type, a treated water supply means for continuously supplying treated water to the denitrification tank, and a hydrogen donor supply means for supplying a hydrogen donor to the denitrification tank, A denitrification apparatus that reduces nitrate ions and nitrite ions contained in the water to be treated into nitrogen by denitrifying bacteria,
    The denitrification tank has a first denitrification unit and a second denitrification unit installed at a subsequent stage of the first denitrification unit,
    The hydrogen donor supply means includes a maximum concentration of the hydrogen donor in the first denitrification unit during a hydraulic residence time of water to be treated in the second denitrification unit, A hydrogen donor is provided in at least the first denitrification part so that the difference from the minimum concentration of the hydrogen donor in the second denitrification part in the hydraulic residence time of the water to be treated is 50 mg TOC / L or more. A denitrification processing apparatus characterized by being supplied.
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