JP5149736B2 - Denitrification treatment method and denitrification treatment apparatus - Google Patents

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 carried out through four processes 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 denitrification in which water to be treated is continuously supplied to a completely mixed type denitrification unit, 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. In the treatment method, a first denitrification unit and a second denitrification unit are installed as the denitrification unit, and a part of the reaction liquid in the second denitrification unit is supplied to the first denitrification unit. Above, the 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 hydraulics of the treated water in the second denitrification unit The hydrogen donation to at least the first denitrification unit so that the difference from the concentration of the hydrogen donor in the second denitrification unit in the general residence time is a concentration difference that induces self-granulation of the denitrifying bacteria. The body is supplied and returned to the second denitrification unit.

  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 in the second denitrification unit It is preferable 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.

  In the denitrification method, the water to be treated is supplied to the second denitrification unit, a hydrogen donor is supplied to the first denitrification unit, and nitrate ions and nitrite ions are supplied. It is preferable to supply water containing.

  In the denitrification method, the water containing nitrate ions and nitrite ions is preferably branched water to be treated supplied to the second denitrification unit.

  In the denitrification method, the supply of the hydrogen donor to the first denitrification unit is preferably intermittent.

  In the denitrification method, the supply of the hydrogen donor to the first denitrification unit is based on the supply amount of the hydrogen donor necessary for the denitrification treatment with respect to the concentration of nitrate ions and nitrite ions. The first supply step for supplying a hydrogen donor in an amount smaller than the reference value and the second supply step for supplying a hydrogen donor in an amount larger than the reference value are preferably performed.

  The present invention also provides a complete mixing type denitrification unit, treated water supply means for continuously supplying treated water to the denitrification part, and hydrogen donor supply means for supplying a hydrogen donor to the denitrification part. A denitrification apparatus for reducing nitrate ions and nitrite ions contained in the water to be treated in the denitrification part to nitrogen by denitrifying bacteria, wherein the denitrification part is a first denitrification part And a second denitrification part, a reaction liquid supply means for supplying a part of the reaction liquid in the second denitrification part to the first denitrification part, and a reaction liquid in the first denitrification part A reaction liquid returning means for returning the reaction liquid to the second denitrification section, and supplying a part of the reaction liquid in the second denitrification section to the first denitrification section by the reaction liquid supply means. 2 The concentration of the hydrogen donor in the first denitrification unit during the hydraulic residence time of the water to be treated in the denitrification unit, and the water to be treated in the second denitrification unit At least the hydrogen donor supply means causes the difference in concentration of the hydrogen donor in the second denitrification part in the physical residence time to be a concentration difference that induces self-granulation of the denitrifying bacteria. It is preferable that a hydrogen donor is supplied to the first denitrification unit, and the reaction solution in the first denitrification unit is returned to the second denitrification unit by the reaction solution returning unit.

  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 unit (first denitrification unit 16 a and second denitrification unit 16 b), an oxidation tank 18, a precipitation tank 20, a treated water inflow pipe 22, a reaction. A liquid return pipe 23, a sludge return pipe 24, treated water take-out pipes 26a, 26b and 26c, a reaction liquid supply pipe 27 and a pump 29 as a reaction liquid supply means, a hydrogen donor supply apparatus 28, and a pH adjusting apparatus 30 are provided. . The denitrification unit is a complete mixing type, and includes a first denitrification unit 16a and a second denitrification unit 16b. The outlet of the nitrification tank of the nitrification apparatus 12 shown in FIG. 1 and the treated water supply port of the second denitrification unit 16 b shown in FIG. 2 are connected by a treated water inflow pipe 22. The reaction liquid discharge port of the first denitrification unit 16 a and the reaction liquid supply port of the second denitrification unit 16 b are connected by a reaction liquid return 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 second denitrification unit 16 b 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 reaction solution supply means is for extracting the reaction solution in the second denitrification unit 16b and supplying it to the first denitrification unit 16a, and one end of the reaction solution supply pipe 27 is placed in the second denitrification unit 16b. The other end is connected to the reaction liquid supply port of the first denitrification unit 16a. A pump 29 is installed in the reaction liquid supply pipe 27.

  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 the nitrification treatment, that is, the water to be treated containing nitrate nitrogen and nitrite nitrogen is continuously supplied to the second denitrification unit 16b of the denitrification apparatus 14 through the water to be treated inflow pipe 22. To do. Then, the pump 29 of the reaction liquid supply means is operated, and a part of the reaction liquid (the treated water and denitrifying bacteria in the second denitrification part 16b, etc.) in the second denitrification part 16b is removed from the reaction liquid supply pipe 27. While supplying to the 1st denitrification part 16a, the pump 36 of the hydrogen donor supply apparatus 28 is operated, and the hydrogen donor in the hydrogen donor tank 34 is made into the 1st denitrification part 16a via the hydrogen donor inflow pipe 38. To supply. Thereafter, the reaction solution in the first denitrification unit 16 a is supplied to the second denitrification unit 16 b through the reaction solution return pipe 23. Thereby, the denitrifying bacteria in the reaction solution in the first denitrifying unit 16a are temporarily exposed to a high concentration hydrogen donor. Further, since the reaction solution in the first denitrification unit 16a is supplied to the second denitrification unit 16b, the denitrifying bacteria in the reaction solution in the second denitrification unit 16b are exposed to an environment with a low hydrogen donor concentration. Will be. In this way, it is possible to induce granulation of the denitrifying bacteria by varying the hydrogen donor concentration with respect to the denitrifying bacteria. The pump 29 of the reaction solution supply means may be continuously operated so that a part of the reaction solution in the second denitrification unit 16b is continuously supplied into the first denitrification unit 16a. You may operate the pump 29 of a reaction liquid supply means intermittently so that a part of reaction liquid in the 2nd denitrification part 16b may be intermittently supplied in the 1st denitrification part 16a.

  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. . Moreover, the pump 25 is operated, and the sludge accumulated in the lower part of the sedimentation tank 20 is returned again from the sludge return pipe 24 into the second denitrification unit 16b (or 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 unit. As shown in FIG. 3, a partition wall 52 having a lower opening is provided in the second denitrification unit 16 b, and denitrification is performed. The chamber 54 and the sedimentation 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 section, and changes the amount. Continuously supplied to the denitrification section. Therefore, the concentration of the hydrogen donor in the denitrification part is almost constant at a low concentration. In order to efficiently perform the denitrification treatment, about 1.2 times the supply amount of hydrogen donor (necessary theoretical amount of hydrogen donor) required for the denitrification treatment of nitrate and nitrite ions in the denitrification section Is supplied to the denitrification section.

  However, in this embodiment, after supplying the reaction liquid in the 2nd denitrification part 16b to the 1st denitrification part 16a, the hydraulic residence time (HRT) of the to-be-processed water in the 2nd denitrification part 16b ) Of the hydrogen donor in the first denitrification unit 16a and the hydraulic donor residence time in the second denitrification unit 16b during the hydraulic residence time of the treated water in the second denitrification unit 16b. The hydrogen donor is supplied to at least the first denitrification unit 16a and the second denitrification unit 16b so that the difference from the concentration is a concentration difference that induces (granulates) self-granulation of the denitrifying bacteria. Return to 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. Then, the reaction solution is returned from the reaction solution return pipe 23 to the second denitrification unit 16b.

  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. 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 preferably 50 mg TOC / L or more, and more preferably 100 mg TOC / L or more. preferable. 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. Further, the minimum concentration of the hydrogen donor in the second denitrification unit 16b is ½ or less of the maximum concentration of the hydrogen donor in the first denitrification unit 16a (greater than 0, with respect to the maximum concentration). And a range of 1/2 or less). If the minimum concentration exceeds 1/2 with respect to the maximum concentration, it may be difficult to induce self-granulation of denitrifying bacteria.

  In this embodiment, when the concentration of nitrate ions and nitrite ions in the reaction solution passing through the reaction solution supply pipe 27 from the second denitrification unit 16b is low, the first denitrification unit 16a after supplying the hydrogen donor is used. In order to enhance the denitrification activity inside, it is preferable to supply water containing nitrate ions and nitrite ions to the first denitrification unit 16a. Specifically, a tank for containing water containing nitrate ions and nitrite ions, a pump for feeding the water from the tank to the first denitrification unit 16a, and a liquid feed pipe are provided, and the water is first supplied. It supplies to the denitrification part 16a. However, because the configuration of the apparatus can be simplified, the treated water inflow pipe 22 is branched, and the branched pipe is connected to the first denitrification unit 16a, so that the treated water is mixed with nitrate ions and nitrous acid. It is preferable to supply the first denitrification unit 16a as water containing ions.

  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 is low, it becomes difficult to form a concentration difference of the hydrogen donor between the first denitrification unit 16a and the second denitrification unit 16b. Therefore, the hydrogen donor is intermittently formed between the first denitrification unit 16a and the second denitrification unit 16b so that the hydrogen donor is intermittently formed. It is preferable to supply to. 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.

  In this embodiment, the concentration of nitrate ions and nitrite ions supplied to the denitrification unit is based on the supply amount of hydrogen donor necessary for the denitrification treatment (the theoretical amount of hydrogen donor required), A first supply step for supplying a hydrogen donor in an amount less than a reference value to the first denitrification unit 16a; a second supply step for supplying a hydrogen donor in an amount greater than the reference value to the first denitrification unit 16a; In combination, the hydrogen donor is supplied to the first denitrification unit 16a, so that a concentration difference of the hydrogen donor is easily formed between the first denitrification unit 16a and the second denitrification unit 16b. be able to. 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, The 1st denitrification part 16a is a several tank, 2nd denitrification part 16b may be a plurality of tanks. Moreover, the 1st denitrification part 16a does not necessarily need to be a tank. FIG. 4 is a schematic diagram showing an example of the configuration of a denitrification apparatus according to another embodiment of the present invention. As shown in FIG. 4, the 1st denitrification part 16a may be a pipe | tube which has predetermined length. That is, an integral line is formed by the reaction liquid supply pipe 27, the tubular denitrification unit 16 a, and the reaction liquid return pipe 23. In addition, when the 1st denitrification part 16a is a pipe type like this embodiment, it is not necessarily required to provide the reaction liquid return pipe | tube 23. FIG.

  Then, a hydrogen donor is supplied from the hydrogen donor supply device 28 into the tube-type denitrification unit 16a, and the reaction solution and hydrogen donated from the second denitrification unit 16b in the tube-type denitrification unit 16a. The body comes into contact, flows through the first denitrification section 16a and the reaction liquid return pipe 23 having a predetermined length, and is returned to the second denitrification section 16b. Here, the predetermined length of the first denitrification unit 16a varies depending on the flow rate of the reaction solution, but may be set as appropriate so as to ensure sufficient contact between the reaction solution and the hydrogen donor. .

  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 part (1st denitrification part 16a, 2nd denitrification part 16b), In order to achieve sufficient denitrification processing speed, 5000-100000 mgMLSS / L It is preferable to set the degree.

  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.

  In the examples, the same apparatus as shown in FIG. 2 was used, and the water to be treated shown in Table 1 below was continuously passed through the second denitrification section having a volume of 40 L. Further, the reaction liquid in the second denitrification unit was continuously supplied to the 4 L first denitrification unit (HRT 6 minutes to 144 minutes of the first denitrification unit). 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 is fixed at 1:19, and the addition-stop cycle time is changed according to the inflow rate of the water to be treated, and is 1/5 of the HRT of the second denitrification unit. It was. The supply amount of methanol at this time was 2.7 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 a 1st denitrification part and a 2nd denitrification part was adjusted so that it might become 6.5-7.0 using hydrochloric acid. Moreover, the sludge collected in the settling tank installed in the latter stage of the denitrification unit was returned to the first denitrification unit. The test was conducted for 33 days.

  In the comparative example, 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 conducted under the same conditions as in the examples.

FIG. 5 is a diagram showing a change in MLSS concentration with respect to the number of days elapsed in the test of the example. FIG. 6 is a diagram illustrating a change in the processing speed of the denitrification process with respect to the elapsed test days of the example. FIG. 7 is a graph showing the transition of the nitrate ion concentration of the treated water with respect to the test elapsed days of the example. FIG. 8 is a diagram illustrating a change in SVI with respect to the number of days elapsed in the test of the example. As shown in FIG. 5, in the example, the MLSS concentration increased with the passage of days, and the MLSS concentration reached 5000 mg MLSS / L on the 33rd day from the start of the test. Further, as shown in FIG. 6, with the increase of the MLSS concentration, the processing speed of the denitrification process also increased, and reached about 2.5 kgN / m ³ / day on the 33rd day from the start of the test, and the high processing speed was high. It was confirmed that it was obtained. Moreover, as shown in FIG. 7, 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. 8, it confirmed that SVI as a sludge sedimentation parameter | index decreased with progress of the number of days, and the granule with the very small value of SVI (good sedimentation) was formed. In addition, SVI of general activated sludge is 120-150 mL / g. On the other hand, in the comparative example, on the 33rd day from the start of the test, the MLSS concentration reached only 2000 mgMLSS / L, and the treatment rate of the denitrification treatment was 0.4 kgN / m ³ / day.

  In the examples, the sludge containing denitrifying bacteria, which was initially floating, changed to a granular shape after about 2 weeks from the start of the test, and after about 3 weeks, the sludge was almost entirely granulated sludge having a diameter of about 0.3 mm. changed. Moreover, it became granule sludge of about 0.5 mm in diameter after 30 days.

  Moreover, FIG. 9 is a figure which shows the TOC density | concentration change of methanol in a 1st denitrification part and a 2nd denitrification part. As shown in FIG. 9, the TOC concentration of methanol changes with time in the first denitrification unit, but it is confirmed that the TOC concentration of methanol is low and almost constant in the second denitrification unit. did. In addition, the TOC concentration of methanol in the treated water obtained in the examples was 0.362 g TOC / g methanol.

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 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 an Example. It is a figure which shows the change of the processing speed of the denitrification process with respect to the test elapsed days of an Example. 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 an Example. It is a figure which shows the change of SVI with respect to the test elapsed days of an Example. It is a figure which shows the TOC density | concentration change of methanol in a 1st denitrification part and a 2nd denitrification part.

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 To-be-processed water inflow pipe, 23 Reaction liquid Return pipe, 24 sludge return pipe, 26a, 26b, 26c treated water take-out pipe, 27 reaction liquid supply pipe, 28 hydrogen donor supply apparatus, 25, 29, 36, 44a, 44b pump, 30 pH adjuster, 32a, 32b Stirring device, 34 Hydrogen donor tank, 38 Hydrogen donor inflow pipe, 40, 50a, 50b Control device, 42 pH adjuster tank, 46a, 46b pH adjuster inflow pipe, 48a, 48b pH sensor, 52 Bulkhead, 54 Desorption Nitrogen chamber, 56 sedimentation chamber.

Claims (6)

This is a denitrification treatment method in which water to be treated is continuously supplied to a completely mixed type denitrification section, 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. And
As the denitrification unit, a first denitrification unit and a second denitrification unit are installed,
After supplying a part of the reaction liquid in the second denitrification unit to 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 Supplying 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 over time is 50 mg TOC / L or more , A denitrification method characterized by returning to the department.   The denitrification method according to claim 1, wherein the water to be treated is supplied to the second denitrification unit, a hydrogen donor is supplied to the first denitrification unit, and nitrate ions, A denitrification method characterized by supplying water containing nitrite ions. 3. The denitrification method according to claim 2 , wherein the water containing nitrate ions and nitrite ions is obtained by branching water to be treated supplied to the second denitrification unit. Nitrogen treatment method. The denitrification method according to claim 1 , wherein the supply of the hydrogen donor to the first denitrification unit is intermittent. 2. The denitrification treatment method according to claim 1 , wherein the supply of the hydrogen donor to the first denitrification unit is performed by supplying the hydrogen donor necessary for the denitrification treatment with respect to the concentration of nitrate ions and nitrite ions. Based on the supply amount, the first supply step for supplying a hydrogen donor in an amount less than the reference value is combined with the second supply step for supplying a hydrogen donor in an amount greater than the reference value. A denitrification method characterized by the above. A complete mixing type denitrification unit, treated water supply means for continuously supplying treated water to the denitrification unit, and hydrogen donor supply means for supplying a hydrogen donor to the denitrification unit, A denitrification apparatus for reducing nitrate ions and nitrite ions contained in water to be treated in the denitrification unit to nitrogen by denitrifying bacteria,
The denitrification unit has a first denitrification unit and a second denitrification unit,
Reaction liquid supply means for supplying a part of the reaction liquid in the second denitrification part to the first denitrification part, and reaction liquid return for returning the reaction liquid in the first denitrification part to the second denitrification part Means,
After supplying a part of the reaction liquid in the second denitrification part to the first denitrification part by the reaction liquid supply means,
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 by the hydrogen donor supply means 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. The denitrification processing apparatus is characterized in that the reaction liquid in the first denitrification part is returned to the second denitrification part by the reaction liquid return means.

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