JP2017225924A - Wastewater treatment method and wastewater treatment equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To optimize an operation condition in a wastewater treatment method in which a photochemical reaction is used.SOLUTION: The wastewater treatment method is provided that comprises: an aqueous solution supply step of supplying aqueous solution containing at least nitrate ion from a buffer tank 100 where the aqueous solution is stored to a reaction tank 200; a reductant supply step of supplying a reductant for use in a reduction reaction of the nitrate ion to the aqueous solution; a nitrate ion reducing step of progressing a reduction reaction of the nitrate ion by irradiating the aqueous solution in the reaction tank 200 with ultraviolet in the presence of the reductant after or before completion of supply of the aqueous solution to the reaction tank 200; and an aqueous solution discharge step of discharging the aqueous solution from the reaction tank 200 after nitrate ion concentration of the aqueous solution is reduced by the reduction reaction of the nitrate ion. The aqueous solution supply step, the reductant supply, the nitrate ion reducing step and the aqueous solution discharge step can be conducted repeatedly.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a wastewater treatment method and wastewater treatment apparatus for nitrogen-containing wastewater containing nitrate nitrogen.

In recent years, the outflow and accumulation of nitrogen into the environment has become a global problem, and there are concerns about adverse effects on animals and plants. Ammonia nitrogen (ammonium ion: NH ₄ ⁺ ), nitrate nitrogen (nitrate ion: NO ₃ ⁻ ), and nitrite nitrogen (nitrite ion: NO ₂ ⁻ ) contained in nitrogen-containing wastewater are treated by the Water Pollution Control Law. Emission standards are established. From the viewpoint of environmental protection, these nitrogen compounds have a possibility of stricter regulations, and a technique for reducing the concentration of nitrogen compounds is required. As means for removing nitrate nitrogen composed of nitrate nitrogen and nitrite nitrogen, physicochemical methods (for example, ion exchange, reverse osmosis, electrochemical dialysis, electroreduction, etc.), biological methods, catalysts Alternatively, a method using a photocatalyst and a method using a photochemical reaction are known.

  For example, Patent Document 1 describes a method for reducing nitrate ion concentration in wastewater by irradiating ultraviolet light in the presence of methanol or ethanol in a potassium nitrate aqueous solution as a wastewater treatment method using a photochemical reaction.

JP 2014-30803 A

  However, the wastewater treatment method using the photochemical reaction described in Patent Document 1 is not optimized in terms of operating conditions, and is impractical from the viewpoint of wastewater treatment effort, cost, maintenance, and the like.

  In view of the above points, an object of the present invention is to optimize operating conditions in a wastewater treatment method using a photochemical reaction.

  In order to achieve the above object, in the invention of the wastewater treatment method according to claim 1, an aqueous solution supplying step of supplying an aqueous solution containing at least nitrate ions to the reaction vessel (200), and at the time of supplying the aqueous solution to the reaction vessel, Alternatively, a reducing agent supplying step for supplying the reducing agent used for the reduction reaction of nitrate ions to the aqueous solution once or a plurality of times at least after supply of the aqueous solution to the reaction vessel, and the aqueous solution to the reaction vessel After the supply is completed or before the supply is completed, a nitrate ion reduction process in which the aqueous solution in the reaction vessel is irradiated with ultraviolet rays in the presence of a reducing agent to promote the reduction reaction of nitrate ions, and the nitrate ions in the aqueous solution by the reduction reaction of nitrate ions An aqueous solution discharge step for discharging the aqueous solution from the reaction tank after the concentration is reduced, and an aqueous solution supply step, a reducing agent supply step, a nitrate ion reduction step, and an aqueous solution discharge step. It is characterized in that it is possible to carry out returns Ri.

  According to the present invention, the operation conditions can be optimized, and the wastewater supply process, the reducing agent supply process, the nitrate ion reduction process, and the wastewater discharge process can be continuously executed by automatic operation.

  In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.

It is explanatory drawing which shows the structure of the waste water treatment equipment of 1st Embodiment to which this invention is applied. It is a figure which shows the structure of an ultraviolet irradiation device. It is a figure which shows the structure of a control apparatus. It is a figure which shows the coexistence component contained in waste water. It is a graph which shows the time-dependent change of the nitrate ion in a reaction tank. It is a figure which shows the modification of an ultraviolet irradiation device. It is a figure which shows the modification of an ultraviolet irradiation device.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, the waste water treatment apparatus of the present embodiment includes a first buffer tank 100, a reaction tank 200, a reducing agent tank 300, and a second buffer tank 400. Moreover, the waste water treatment apparatus includes pipes 10, 20, 30, 40, and 50 through which waste water and a reducing agent flow. The pipes 10, 20, 30, 40, and 50 are preferably made of a material that is not corroded by the liquid flowing therethrough, such as a resin such as stainless steel or Teflon (registered trademark).

  The 1st buffer tank 100 is a container which stores the waste_water | drain before performing the purification process (namely, reduction process of nitrate ion) which reduces nitrate ion. Waste water is supplied to the first buffer tank 100 from the outside through the first pipe 10. The first pipe 10 is provided with a first pump 11 for sending waste water to the first pipe 10.

The waste water of the first embodiment is a nitrogen compound-containing waste water and may be an aqueous solution containing at least nitrate ions (NO ₃ ⁻ ) as the nitrogen compound. Furthermore, the wastewater is selected from ammonium ions, alkali metal ions, alkaline earth metal ions, transition metal ions, borate ions, fluoride ions, silicate ions, phosphate ions, sulfate ions, chloride ions as coexisting components. One or more kinds of ions may be contained.

  Although the capacity | capacitance of the 1st buffer tank 100 is not specifically limited, Since there exists a possibility of overflowing depending on the waste_water | drain amount which flows in into the buffer tank 100, it is preferable to set it as the capacity | capacitance of about several dozen L-several hundred L thru | or several thousand L. Moreover, although the material of the 1st buffer tank 100 is not specifically limited, Since it is necessary to endure a large capacity | capacitance, it is preferable to set it as the material which is hard to crack, such as stainless steel and resin.

  The first buffer 100 includes a liquid level sensor 101 for detecting the liquid level of the waste water, a temperature sensor 102 for detecting the temperature of the waste water, a pH sensor 103 for detecting the pH of the waste water, and the electrical conductivity (EC: Electric Conductivity). ) And a nitrate ion concentration sensor 105 for detecting nitrate ion concentration in the waste water. The EC sensor 104 can detect the electrolyte concentration in the waste water based on the electrical conductivity, and can indirectly detect the nitrate ion concentration. Sensor signals output from these sensors 101, 102, 103, 104, and 105 are input to a control device 500 described later.

  Waste water is supplied from the first buffer tank 100 to the reaction tank 200 via the second pipe 20. The second pipe 20 is provided with a second pump 21 for sending waste water to the second pipe 20.

  The second pipe 20 is provided with a filter 22 for filtering out fine solids contained in the drainage. The filter 22 may be provided before the wastewater flows into the first buffer tank 100 or before the wastewater that flows out of the first buffer tank 100 flows into the reaction tank 200. The filter 22 can be replaced.

Further, when there is a possibility that viruses and microorganisms are contained in the waste water, it is desirable to use a filter 22 that can filter out viruses and microorganisms. Further, when the waste water is agricultural waste liquid, an ion exchange membrane may be provided on the filter 22 in order to reduce the concentration of potassium (K) and phosphorus (PO ₄ ³⁻ ), which are essential elements as fertilizer components.

  The reaction tank 200 is a container that accommodates waste water. In the reaction tank 200, purification treatment for reducing the nitrate ion concentration in the waste water is performed. The purification treatment of nitrate ions is performed by irradiating the waste water with ultraviolet rays in the presence of a reducing agent to advance the reduction reaction of nitrate ions.

  One or a plurality of reaction vessels 200 can be provided. When a plurality of reaction tanks 200 are provided, reaction tanks 200 having the same structure or a structure equivalent thereto may be provided in series, and the same purification process may be repeatedly performed in order from the reaction tank 200 on the upstream side. Alternatively, a plurality of reaction vessels 200 may be provided in parallel, and the same purification process may be performed simultaneously.

  The size of the reaction vessel 200 is not particularly limited, but is preferably several to several tens of liters or several hundreds of liters in consideration of practicality.

  The material of the reaction vessel 200 is not particularly limited as long as it does not transmit light, but at least a portion irradiated with ultraviolet rays is preferably made of metal or glass in order to prevent deterioration due to ultraviolet rays. Alternatively, a resin having excellent ultraviolet resistance such as PTFE may be used for the reaction vessel 200.

In order not to leak the ultraviolet rays emitted from the ultraviolet irradiation unit 207 to the outside, it is desirable to arrange a material that reflects ultraviolet rays on the inner wall of the reaction vessel 200 or to make the inner wall of the reaction vessel 200 reflect ultraviolet rays. . As a material that reflects ultraviolet rays, for example, aluminum or the like can be used. In addition, as a structure that reflects ultraviolet rays, a structure subjected to geometric processing can be used.
The reaction tank 200 includes a liquid level sensor 201 for detecting the liquid level of the waste water, a temperature sensor 202 for detecting the temperature of the waste water, a pH sensor 203 for detecting the pH of the waste water, and an EC sensor 204 for detecting the electrical conductivity of the waste water. A nitrate ion concentration sensor 205 for detecting the nitrate ion concentration in the waste water and a reducing agent concentration sensor 206 for detecting the reducing agent concentration are provided. Sensor signals output from these sensors 201, 202, 203, 204, 205, 206 are input to the control device 500 described later.

  The reaction tank 200 is provided with an ultraviolet irradiation device 207 for irradiating the waste water with ultraviolet rays. In this embodiment, a high pressure mercury lamp is used as the ultraviolet irradiation device 207. The output of the high-pressure mercury lamp is not particularly limited, but the output of the high-pressure mercury lamp can be determined based on the number of required photons determined by the number of moles of nitrate ion nitrate (nitrate ion concentration × drainage amount) that can be stored in the reaction vessel 200.

  By using a high-pressure mercury lamp as the ultraviolet irradiation device 207, the rate of reduction of nitrate ions in the wastewater can be made faster than when a low-pressure mercury lamp is used. Further, by using a high-pressure mercury lamp as the ultraviolet irradiation device 207, it is possible to suppress nitrite ions from remaining in the waste water.

  When the wavelength of the ultraviolet ray irradiated from the ultraviolet irradiation device 207 is 300 nm or less, the ultraviolet ray is absorbed by the coexisting component of the waste water described above, and the nitrate ion reduction reaction is not sufficiently performed. For this reason, in this embodiment, ultraviolet rays with a wavelength longer than 300 nm are emitted from the ultraviolet irradiation device 207. Note that the ultraviolet rays irradiated from the ultraviolet irradiation device 207 include a trace amount of ultraviolet rays having a wavelength of 300 nm or less.

  One or a plurality of high-pressure mercury lamps constituting the ultraviolet irradiation device 207 may be used. From the viewpoint of maintenance, it is desirable to use a plurality of medium-pressure high-pressure mercury lamps rather than a single high-power high-pressure mercury lamp.

  The ultraviolet irradiation device 207 is desirably arranged as follows in the reaction vessel 200 in order to uniformly irradiate the entire reaction vessel 200 with ultraviolet rays from the ultraviolet irradiation device 207. When the ultraviolet irradiation device 207 is composed of a single lamp, it is desirable to arrange the lamp near the geometric gravity center position of the cross section of either the vertical direction or the horizontal direction of the reaction vessel 200. When the ultraviolet irradiation device 207 is composed of a plurality of lamps, it is desirable that the numerical value obtained by dividing the distance between the lamp centers by the distance between the lamp center and the inner wall of the reaction vessel 200 is about 1-2. Further, the distance between the lamp and the inner wall surface of the reaction vessel 200 depends on the size of the reaction vessel 200, but is preferably about 100 to 300 mm in consideration of practicality.

  The mercury lamp used in the ultraviolet irradiation device 207 needs to be replaced every predetermined usage time. For this reason, it is desirable to manage the lamp usage time with a timer and to notify the user of lamp replacement when the lamp replacement time has come.

  The mercury lamp constituting the ultraviolet irradiation device 207 needs to be cooled. The mercury lamp can be cooled by a water cooling method or an air cooling method. In this embodiment, the mercury lamp is a water cooling method.

  As shown in FIG. 2, the ultraviolet irradiation device 207 includes a lamp unit 207a formed of a mercury lamp and a case unit 207b that houses the lamp unit 207a. The case portion 207b is made of quartz glass. The case portion 207b has a hollow structure. Cooling water circulates inside the case 207b so that the heat of the lamp portion 207a does not affect the drainage. In the example shown in FIG. 2, the cooling water flows in from the upper part of the case part 207 and flows out from the upper part of the case part 207b. The medium used for cooling the lamp unit 207a is not limited to water as long as the medium does not absorb ultraviolet rays that contribute to the reaction.

  The case 207b is provided with a lid portion 207c at a portion where the lamp portion 207a is inserted. The lid 207c may be made of a material and a structure that prevents ultraviolet rays from leaking outside.

  The reaction vessel 200 is provided with a stirring device 208 for stirring the internal waste water. The agitation device 208 can agitate the waste water by rotating the agitation element 209 provided in the reaction vessel 200 by a magnetic force. The stirrer 209 is preferably made of a material excellent in chemical resistance and ultraviolet resistance, and for example, stainless steel, Teflon (registered trademark), glass, or the like can be used. The stirring speed by the stirring device 208 is not particularly limited, but is preferably several tens of rpm or more.

  The reaction tank 200 is provided with a vent hole 210 that is a vent for communicating the inside and the outside of the reaction tank 200. When nitrogen gas or the like is generated inside the reaction tank 200 along with the waste water purification process, the generated gas is discharged to the outside through the vent hole 210.

  A reducing agent used for the reduction reaction of nitrate ions is added to the waste water of the reaction tank 200. The reducing agent is preferably an organic substance having 6 or less carbon atoms in the molecule. Examples of the organic substance having 1 to 6 carbon atoms include formic acid, ethanol, glycolic acid, tartaric acid, and citric acid. In addition, since the reducing agent having 1 or 2 carbon atoms (ie, formic acid or ethanol) has a high nitrate ion reduction rate, the reducing agent is more preferably an organic substance having 2 or less carbon atoms. These organic substances may be dissolved in water or diluted with water.

  The reducing agent tank 300 is a container that contains a reducing agent. The reducing agent is supplied from the reducing agent tank 300 to the reaction tank 200 via the third pipe 30. The third pipe 30 is provided with a third pump 31 for sending the reducing agent to the third pipe 30. When the reducing agent in the reducing agent tank 300 decreases, the reducing agent may be replenished from the outside as necessary.

  The reducing agent tank 300 is provided with a liquid level sensor 301 for detecting the liquid level of the reducing agent and a temperature sensor 302 for detecting the temperature of the reducing agent. Further, depending on the type of the reducing agent, it may be sensitive to the influence of the environmental temperature, so it is desirable to control the temperature of the reducing agent by the temperature sensor 302. Sensor signals output from these sensors 301 and 302 are input to a control device 500 described later.

  Although the size of the reducing agent tank 300 is not particularly limited, it is desirable that the reducing agent tank 300 be several hundred mL to several tens L so that the reducing agent is not replenished frequently from the outside. The material of the reducing agent tank 300 is not particularly limited as long as it is not attacked by the reducing agent. For example, a resin such as glass, stainless steel, or polypropylene can be used.

  The reducing agent tank 300 is provided with a vent hole 303 which is a vent for communicating the inside and outside of the reducing agent tank 300. The reducing agent is often an organic substance, and when the organic substance is gasified inside the reducing agent tank 300, the generated gas is discharged to the outside from the vent hole 303. Furthermore, it is desirable to provide a canister in the vent hole 303 for collecting the gasified organic matter and returning it to the reducing agent tank 300.

  In the reaction tank 200, in order to reliably reduce nitrate ions in the waste water, the molar ratio of the reducing agent to the nitrate ions before the purification treatment with ultraviolet irradiation is set to 1 or more per one carbon number in the reducing agent molecule. It is desirable to make it.

  In the reaction tank 200, the reducing agent gradually decreases as the nitrate ion reduction reaction proceeds. At this time, if the reducing agent is consumed before the nitrate ions, the nitrate ions in the waste water cannot be sufficiently reduced. For this reason, it is desirable to maintain the molar ratio of the reducing agent with respect to nitrate ions to 1 or more per one carbon number in the reducing agent molecule even during the purification treatment with ultraviolet irradiation.

  For this purpose, it is more desirable to add a sufficient amount of reducing agent to the wastewater in advance for the nitrate ions in the wastewater. In the first embodiment, the molar ratio of the reducing agent to nitrate ions before performing the purification treatment with ultraviolet irradiation is set to about 5 per carbon number in the reducing agent molecule. As the amount of the reducing agent increases, nitrate ions in the wastewater can be reliably reduced, but more reducing agent than necessary remains in the wastewater after the purification treatment. For this reason, it is desirable that the amount of the reducing agent with respect to the nitrate ions before the purification treatment is 6 or less in terms of the molar ratio per carbon number in the reducing agent molecule. Furthermore, it is more desirable that the molar ratio of the reducing agent to nitrate ions is within the range of 3 to 5 per carbon number in the reducing agent molecule.

  Moreover, in order to maintain the molar ratio of the reducing agent to nitrate ions at 1 or more per carbon number in the reducing agent molecule during the purification treatment, the reducing agent is replenished to the waste water during the purification treatment. Also good. When the reducing agent is replenished to the wastewater during the purification treatment, the concentration of the reducing agent in the wastewater is measured during the purification treatment by the nitrate ion concentration sensor 205 of the reaction tank 200. What is necessary is just to replenish the reaction tank 200 with the reducing agent from the reducing agent tank 300. Or you may make it replenish a reducing agent to the waste_water | drain of the reaction tank 200 from the reducing agent tank 300 for every predetermined time progress.

  The waste water that has been purified in the reaction tank 200 is transferred to the second buffer tank 400 through the fourth pipe 40. The fourth pipe 40 is provided with a fourth pump 41 for sending waste water to the fourth pipe 40.

  The second buffer tank 400 is a container for temporarily storing the drained water that has been subjected to the purification treatment before being discharged to the outside. Although the capacity | capacitance of the 2nd buffer tank 400 is not specifically limited, Since there exists a possibility that it may overflow depending on the waste_water | drain amount which flows into the 2nd buffer tank 400, it is preferable to set it as the capacity | capacitance of about several dozen L-several hundred L thru | or several thousand L. The material of the second buffer tank 400 is not particularly limited. However, since it is necessary to withstand a large capacity, it is preferable to use a material that is difficult to break, such as stainless steel or resin.

  The waste water in the second buffer tank 400 is discharged to the outside through the fifth pipe 50. The fifth pipe 50 is provided with a fifth pump 51 for sending waste water to the fifth pipe 40.

  The second buffer layer 400 includes a liquid level sensor 401 that detects the level of the waste water, a temperature sensor 402 that detects the temperature of the waste water, a pH sensor 403 that detects the pH of the waste water, and an EC that detects the electrical conductivity of the waste water. A sensor 404 and a nitrate ion concentration sensor 405 for detecting the nitrate ion concentration in the waste water are provided. Sensor signals output from these sensors 401, 402, 403, 404, and 405 are input to the control device 500 described later.

  As shown in FIG. 3, the waste water treatment apparatus is provided with a control device 500. The control device 500 includes a known microcomputer including a CPU, a ROM, a RAM, and the like and peripheral circuits thereof. The control device 500 performs various arithmetic processes based on a control program stored in the ROM, controls operations of various devices connected to the output side, and enables automatic operation of the wastewater treatment apparatus.

  Various sensors provided in the first buffer tank 100, the reaction tank 200, the reducing agent tank 300, and the second buffer tank 400 are connected to the input side of the control device 500. The control apparatus 500 can monitor the state of each tank 100, 200, 300, 400 based on the measured values of various sensors. The above-described pumps 11, 21, 31, 41, 51, the ultraviolet irradiation device 207, the stirring device 208, and the like are connected to the output side of the control device 500.

  A display device 501 is connected to the output side of the control device 500. The display device 501 can display various information. The display device 501 includes numerical values detected by various sensors provided in the first buffer tank 100, the reaction tank 200, the reducing agent tank 300, and the second buffer tank 400 (for example, the liquid level of the waste water, the waste water temperature, the waste water temperature). pH, drainage electrical conductivity, drainage nitrate ion concentration, etc.), a message to the user (for example, a message notifying the occurrence of an abnormality), and the like can be displayed.

  A lamp 502 capable of outputting light and a speaker 503 capable of outputting sound are connected to the output side of the control device 500. By outputting light from the lamp 502 or outputting sound from the speaker 503, for example, a user can be notified that an abnormal state has occurred in the wastewater treatment apparatus.

  Next, the operation of the wastewater treatment apparatus of this embodiment will be described. The following processes are executed by the control device 500 controlling the operation of various devices.

[Drainage supply process]
First, a wastewater supply process for supplying wastewater from the first buffer tank 100 to the reaction tank 200 is performed. In the waste water supply process, the liquid level sensor 101 determines whether or not a predetermined amount of waste water is stored in the first buffer tank 100. The predetermined amount can be set to be equal to or greater than the capacity of the drain tank 200, for example.

  When it is determined that the amount of wastewater stored in the first buffer tank 100 is less than a predetermined amount, the second pump 21 is not operated. On the other hand, when it is determined that the amount of wastewater stored in the first buffer tank 100 is greater than or equal to a predetermined amount, the second pump 21 is operated to supply wastewater from the first buffer tank 100 to the reaction tank 200.

  Moreover, when it determines with the liquid level of the waste_water | drain of the 1st buffer tank 100 measured with the liquid level sensor 101 exceeding the upper limit, it can be judged that the waste_water | drain of the 1st buffer tank 100 may overflow. . Therefore, at least one of the display device 501, the lamp 502, and the speaker 503 is used to notify the user that there is a possibility that the drainage of the first buffer tank 100 may overflow. The determination of the possibility of overflow of the first buffer tank 100 may take into account the purification rate of the wastewater in the reaction tank 200.

  Further, by measuring the nitrate ion concentration in the waste water of the first buffer tank 100 with the nitrate ion concentration sensor 105, the supply amount of the reducing agent supplied from the reducing agent tank 300 to the reaction tank 200 is determined in advance. Can do. The nitrate concentration may be indirectly detected by detecting the electrolyte concentration with the EC sensor 104.

  If it is determined that the temperature of the waste water in the first buffer tank 100 measured by the temperature sensor 102 exceeds a predetermined temperature, it can be determined that the waste water temperature in the first buffer tank 100 is abnormal. Therefore, at least one of the display device 501, the lamp 502, and the speaker 503 is used to notify the user that the drain temperature of the first buffer tank 100 is abnormal.

  When it is determined that a predetermined amount of supply has been supplied from the first buffer tank 100 to the reaction tank 200, the second pump 21 is stopped and supply of waste water from the first buffer tank 100 to the reaction tank 200 is stopped. . Whether or not a predetermined amount of wastewater is supplied to the reaction tank 200 can be determined based on the liquid level of the wastewater in the reaction tank 201 measured by the liquid level sensor 201, or the liquid feeding speed and the feeding speed by the second pump 21. Judgment can be made based on the liquid time.

[Reducing agent supply process]
After the end of the wastewater supply process or simultaneously with the wastewater supply process, a reducing agent supply process for supplying a reducing agent from the reducing agent tank 300 to the reaction tank 200 is performed. In the reducing agent supply process, the reducing agent is supplied from the reducing agent tank 300 to the reaction tank 200 by operating the third pump 31.

  When a predetermined amount of reducing agent is supplied from the reducing agent tank 300 to the reaction tank 200, the third pump 31 is stopped, and supply of the reducing agent from the reducing agent tank 300 to the reaction tank 200 is stopped. Whether or not a predetermined amount of the reducing agent has been supplied to the reaction tank 200 can be determined based on the liquid feeding speed and the liquid feeding time by the third pump 31. Supply of the reducing agent from the reducing agent tank 300 to the reaction tank 200 may be performed once or may be intermittently performed a plurality of times.

  In the reducing agent tank 300, when the liquid level of the reducing agent measured by the liquid level sensor 301 falls below a predetermined value, the reducing agent tank 300 is reduced using at least one of the display device 501, the lamp 502, and the speaker 503. The user is informed that the amount of the agent is low, and prompts the user to replenish the reducing agent.

  Further, when it is determined that the temperature of the reducing agent in the reducing agent tank 300 measured by the temperature sensor 302 exceeds a predetermined temperature, it can be determined that the reducing agent temperature in the reducing agent tank 300 is abnormal. For this reason, at least one of the display device 501, the lamp 502, and the speaker 503 is used to notify the user that the reducing agent temperature in the reducing agent tank 300 is abnormal.

[Nitrate ion reduction process]
After completion of the reducing agent supply process, a nitrate ion reduction process for reducing the nitrate ion concentration of the wastewater is performed in the reaction tank 200. In the nitrate ion reduction step, the wastewater is irradiated with ultraviolet rays by the ultraviolet irradiation device 207 in the presence of the reducing agent, and the wastewater is stirred by the stirring device 208. Thereby, the reduction process of a nitrate ion can be advanced and the purification process which reduces the nitrate ion in waste_water | drain can be performed.

  The irradiation of ultraviolet rays by the ultraviolet irradiation device 207 and the stirring of the waste water by the stirring device 208 may be performed before the supply of the reducing agent to the reaction vessel 200 or after the supply of the reducing agent to the reaction vessel 200. However, in the ultraviolet irradiation device 207, the circulation of the cooling water is started before the lamp unit 207a is turned on.

  In the reaction tank 200, the nitrate ion concentration sensor 205 measures the nitrate ion concentration in the waste water and further measures the elapsed time since the start of the nitrate ion reduction process in order to grasp the progress of the nitrate ion reduction reaction. . When the nitrate ion concentration in the wastewater measured by the nitrate ion concentration sensor 205 falls below a predetermined value, or when the elapsed time since the start of the nitrate ion reduction process exceeds a predetermined time, the nitric acid in the reaction tank 200 It can be determined that it is the end timing of the ion reduction process.

  When it is determined that it is the end timing of the nitrate ion reduction process, the ultraviolet irradiation by the ultraviolet irradiation device 207 and the stirring by the stirring device 208 may be continued as they are, or may be stopped. However, in the case where a mercury lamp is used as the ultraviolet irradiation device 207, it is desirable to continue the lighting state because the life may be shortened as lighting and extinguishing are repeated.

  When the reducing agent concentration in the waste water of the reaction tank 200 is measured by the reducing agent concentration sensor 206 and the reducing agent concentration falls below a predetermined value, the reducing agent may be replenished from the reducing agent tank 300 to the reaction tank 200.

  If the nitrate ion concentration does not fall below the reference concentration even after the predetermined upper limit time has elapsed in the reaction vessel 200, it can be determined that some abnormality has occurred in the nitrate ion reduction step. Therefore, at least one of the display device 501, the lamp 502, and the speaker 503 is used to notify the user that an abnormal state has occurred in the reaction tank 200.

  The “upper limit time” for determining that an abnormal state has occurred in the nitrate ion reduction step can be arbitrarily set, and can be set to 8, 12, 24 hours, for example. Alternatively, when the nitrate ion concentration is measured at regular intervals (for example, every hour) and the nitrate ion concentration does not change continuously for a predetermined number of times (for example, 3 times or more), an abnormal state has occurred in the nitrate ion reduction process. You may judge.

  When it is determined that the liquid level of the waste water in the reaction tank 200 measured by the liquid level sensor 201 exceeds the upper limit value, it can be determined that there is a possibility that the waste water in the reaction tank 200 overflows. Therefore, at least one of the display device 501, the lamp 502, and the speaker 503 is used to notify the user that there is a possibility that the waste water in the reaction tank 200 may overflow.

  Further, when it is determined that the temperature of the wastewater in the reaction tank 200 measured by the temperature sensor 202 exceeds a predetermined temperature, it can be determined that the wastewater temperature in the reaction tank 200 is abnormal. Therefore, at least one of the display device 501, the lamp 502, and the speaker 503 is used to notify the user that the waste water temperature in the reaction tank 200 is abnormal.

[Drainage discharge process]
After completion of the nitrate ion reduction process, a drainage discharge process for discharging the wastewater that has been subjected to the purification treatment from the reaction tank 200 is performed. The drainage process is performed by operating the fourth pump 41.

  When the end timing of the drainage discharge process arrives, the fourth pump 41 is stopped. When the liquid level of the waste water in the reaction tank 200 measured by the liquid level sensor 201 falls below a predetermined value, or when the elapsed time from the start of the waste water discharge process exceeds a predetermined time, the waste water discharge process It can be determined that the end timing has arrived.

  The waste water that has been subjected to the purification treatment is temporarily stored in the second buffer tank 400. In the second buffer tank 400, when the liquid level of the wastewater measured by the liquid level sensor 401 exceeds a predetermined value, the fifth pump 51 is operated to discharge the wastewater in the second buffer tank 400 to the outside. Good.

  In addition, when the temperature of the drainage water in the second buffer tank 400 is measured by the temperature sensor 402 and the drainage temperature is equal to or higher than a predetermined temperature, the drainage temperature is lowered and discharged to the outside in consideration of the environmental load. That's fine.

  By repeatedly performing the wastewater supply process, the reducing agent supply process, the nitrate ion reduction process, and the wastewater discharge process described above, the purification treatment for reducing nitrate ions in the wastewater can be continuously performed.

  Next, the result of purifying wastewater using the wastewater treatment apparatus 1 of the first embodiment will be described. The capacity of the first buffer tank 100 was 30 L, the capacity of the reaction tank 200 was 10 L, the capacity of the reducing agent tank 300 was 1 L, and the capacity of the second buffer tank 200 was 30 L. A 450 W high-pressure mercury lamp was used as the ultraviolet irradiation device 207.

  In the waste water treatment, a total of 30 L of waste water was used. The waste water has a nitrate ion concentration of 120 mg / L. The waste water contains the substances shown in FIG. 4 as coexisting components. Further, formic acid having a concentration of 90% was used as a reducing agent. The amount of formic acid added is such that the molar ratio to nitrate ions in the wastewater is 5 per carbon number in the formic acid molecule.

  As shown in FIG. 5, according to the wastewater treatment apparatus of this embodiment using a high-pressure mercury lamp, the rate of decrease in the nitrate ion concentration with the lapse of the reaction time is fast, and the nitrate ions disappear after 4 hours. Yes. Then, the purification process of nitrate ions in the wastewater can be continuously performed by repeating the above-described liquid supply process, reducing agent supply process, purification process, and discharge process.

  According to this 1st Embodiment demonstrated above, the various sensors which monitor the state of each tank 100, 200, 300, 400 are provided, and various apparatuses are controlled by the control apparatus 500 based on the measured value of various sensors. The operation conditions can be optimized, and each process of the wastewater supply process, the reducing agent supply process, the nitrate ion reduction process, and the drainage discharge process can be executed continuously by automatic operation.

  In this embodiment, when any abnormal state occurs in any of the tanks 100, 200, 300, and 400 based on the measurement values of various sensors, at least one of the display device 501, the lamp 502, and the speaker 503 is used. Is used to notify the user that an abnormal condition has occurred in the wastewater treatment apparatus. Thereby, the user can recognize the occurrence of abnormality in the wastewater treatment apparatus, and can return the wastewater treatment apparatus to an appropriate state at an early stage.

  In this embodiment, a high-pressure mercury lamp is used as the ultraviolet irradiation device 207. Thereby, compared with the case where a low pressure mercury lamp is used, the rate of decrease of nitrate ions in the wastewater can be increased, and nitrite ions can be prevented from remaining in the wastewater. Furthermore, in this embodiment, ultraviolet rays with a wavelength longer than 300 nm are emitted from the ultraviolet irradiation device 207. Thereby, it can suppress that an ultraviolet-ray is absorbed by the coexistence component shown in FIG. 4, and can reduce the density | concentration of nitrate ion effectively.

(Other embodiments)
As mentioned above, although the Example of this invention was described, this invention is not limited to this, Unless it deviates from the range described in each claim, it is not limited to the description word of each claim, and those skilled in the art Improvements based on the knowledge that a person skilled in the art normally has can be added as appropriate to the extent that they can be easily replaced.

  (1) In the above-described embodiment, liquid feeding in the first buffer tank 100, the reaction tank 200, the reducing agent tank 300, and the second buffer tank 400 is performed using the pumps 11, 21, 31, 41, and 51. However, liquid feeding may be performed using a height difference or the like without using power such as a pump. In this case, a valve may be provided for each of the pipes 10, 20, 30, 40, 50, and the flow of fluid in the pipes 10, 20, 30, 40, 50 may be controlled by opening and closing the valves.

  (2) In the above embodiment, the second buffer tank 400 for temporarily storing the waste water after the purification treatment of nitrate ions in the reaction tank 200 is provided, but the reaction is performed without providing the second buffer tank 400. You may make it discharge the waste_water | drain after performing the purification process of nitrate ion with the tank 200 from the reaction tank 200 outside.

  (3) In the above embodiment, the reducing agent is supplied from the reducing agent tank 300 to the reaction tank 200, and the reducing agent is added to the waste water inside the reaction tank 200. The third pipe 30 may be joined in the middle of the pipe 20, and the reducing agent may be supplied to the waste water flowing through the second pipe 20 via the third pipe 30.

  (3) In the above embodiment, the reaction tank 200 is configured to stir the wastewater by the stirring device 208 and the stirrer 209. However, the present invention is not limited thereto, Stirring may be performed by taking other means capable of stirring, or the nitrate ions may be reduced without stirring the waste water.

  (4) In the above embodiment, the waste water that has been subjected to the purification treatment of nitrate ions in the reaction tank 200 is stored in the second buffer tank 400, and then the waste water is discharged to the outside. The nitrate ion concentration of the waste water in the second buffer tank 400 is measured, and when the nitrate ion concentration exceeds a predetermined value, the waste water may be returned from the second buffer tank 400 to the reaction tank 200. In the reaction tank 200 to which the drainage has been returned, the purification treatment of nitrate ions may be performed again.

  (5) In the above embodiment, the ultraviolet irradiation unit 207 is configured as shown in FIG. 2, but the configuration is not limited thereto, and a different configuration may be used. For example, the ultraviolet irradiation unit 207 can be configured as shown in FIG. 6 or FIG.

  The example shown in FIG. 6 is a water-cooled mercury lamp, in which a case 207b is provided from the upper side to the lower side of the reaction tank 200, and a lid part 207d is also provided below the case part 207b. In the configuration of FIG. 6, the flow direction of the cooling water in the case portion 207b may be from the top to the bottom or from the bottom to the top, but is preferably a flow from the top to the bottom.

  The example shown in FIG. 7 is an air-cooled mercury lamp, in which a case 207b is provided from the upper side to the lower side of the reaction tank 200, and a lid part 207d is also provided below the case part 207b. In the example shown in FIG. 7, the case 207b does not have a hollow structure, and through holes are formed in the lid portions 207c and 207d. Air can flow through the case 207b through the through holes of the lid portions 207c and 207d, and the lamp portion 207a is air-cooled. The direction of air flow in the case portion 207b may be from the top to the bottom or from the bottom to the top. The through holes of the lid portions 207c and 207d are preferably formed to be inclined with respect to the plate surfaces of the lid portions 207c and 207d so that the ultraviolet rays emitted from the lamp portion 207a do not leak outside.

  (8) In the above embodiment, when it is determined that an abnormal state has occurred in at least one of the drainage supply process, the reducing agent supply process, the nitrate ion reduction process, and the drainage discharge process (for example, the amount of liquid is When the amount exceeds the appropriate amount, or when the temperature of the liquid exceeds the appropriate temperature, etc., the occurrence of an abnormality is notified using the display device 501 or the like. As described above, when any abnormal state occurs in the wastewater treatment apparatus, it is desirable to stop at least one of the processes in addition to the notification of the occurrence of the abnormality or instead of the notification of the occurrence of the abnormality. The step of stopping may be a step in which an abnormal state has occurred, a step in which no abnormal state has occurred, or all steps. Specifically, the discharge of waste water by the pumps 11, 21, 41, the supply of reducing agent by the pump 31, the irradiation of ultraviolet rays by the ultraviolet irradiation unit 207, the agitation of waste water by the stirring device 208 may be stopped.

  In addition, after stopping at least one of the above-described wastewater supply process, reducing agent supply process, nitrate ion reduction process, and drainage discharge process, the abnormal state that caused the process to stop is resolved ( For example, when the amount of liquid has decreased to an appropriate amount, or when the temperature of the liquid has decreased to an appropriate temperature, etc., a recovery process for restarting the stopped process may be performed.

DESCRIPTION OF SYMBOLS 100 1st buffer tank 200 Reaction tank 207 Ultraviolet irradiation apparatus 208 Stirrer 300 Reducing agent tank 400 2nd buffer tank 101, 201, 301, 401 Liquid level sensor 102, 202, 302, 402 Temperature sensor 103, 203, 403 pH sensor 104, 204, 404 EC sensor 105, 205, 405 Nitrate ion concentration sensor

Claims (8)

An aqueous solution supplying step of supplying an aqueous solution containing at least nitrate ions to the reaction vessel (200);
At least one of the reducing agent used for the reduction reaction of nitrate ions at the time of supplying the aqueous solution to the reaction vessel or after the supply of the aqueous solution to the reaction vessel is divided into the aqueous solution once or plural times. A reducing agent supply step to supply,
A nitrate ion reduction step in which the aqueous solution in the reaction tank is irradiated with ultraviolet rays in the presence of the reducing agent to advance the reduction reaction of nitrate ions after the supply of the aqueous solution to the reaction tank is completed or before the supply is completed; ,
An aqueous solution discharge step of discharging the aqueous solution from the reaction tank after the nitrate ion concentration of the aqueous solution is reduced by the reduction reaction of the nitrate ions,
A wastewater treatment method capable of repeatedly performing the aqueous solution supply step, the reducing agent supply step, the nitrate ion reduction step, and the aqueous solution discharge step.   When at least one of the amount of the aqueous solution, the temperature of the aqueous solution, and the nitrate ion concentration of the aqueous solution is measured and it is determined that an abnormal state has occurred based on the measured value, the fact that the abnormal state has occurred The waste water treatment method according to claim 1, wherein the user is notified of this.   When measuring at least one of the amount of the aqueous solution, the temperature of the aqueous solution, and the nitrate ion concentration of the aqueous solution, and determining that an abnormal state has occurred based on the measured value, the aqueous solution supplying step, The wastewater treatment method according to claim 1 or 2, wherein at least one of a reducing agent supply step, the nitrate ion reduction step, and the aqueous solution discharge step is stopped.   When it is determined that the abnormal state has been resolved based on the measured value after stopping at least one of the aqueous solution supply step, the reducing agent supply step, the nitrate ion reduction step, and the aqueous solution discharge step. The wastewater treatment method according to claim 3, wherein the stopped process is resumed.   In the nitrate ion reduction step, the nitrate ion concentration of the aqueous solution does not fall below a predetermined concentration when a predetermined time has elapsed since the start of irradiation of the aqueous solution supplied to the reaction vessel. The waste water treatment method according to any one of claims 2 to 4, wherein it is determined that the abnormal state has occurred.   The wastewater treatment method according to any one of claims 2 to 4, wherein in the reaction tank, when the amount of the aqueous solution exceeds a predetermined amount set in advance, it is determined that the abnormal state has occurred. .   The wastewater treatment method according to any one of claims 2 to 4, wherein when the temperature of the aqueous solution is higher than a predetermined temperature set in advance, it is determined that the abnormal state has occurred. A buffer tank (100) for storing an aqueous solution containing at least nitrate ions;
A reducing agent tank (300) for storing a reducing agent used for the reduction reaction of the nitrate ions;
The aqueous solution is supplied from the buffer tank, the reducing agent is supplied from the reducing agent tank, and includes an ultraviolet irradiation unit (206) for irradiating the aqueous solution with ultraviolet light in the presence of the reducing agent. A reaction vessel (200) for proceeding a reduction reaction of ions;
Sensors (101 to 105, 201 to 205, 301, 302) for measuring at least one of the amount of the aqueous solution, the temperature of the aqueous solution, and the nitrate ion concentration of the aqueous solution;
An error notification unit (501, 502, 503) for notifying the user that an abnormal state has occurred;
A wastewater treatment apparatus comprising: a control unit (500) for notifying the abnormal state by the error notification unit when it is determined that the abnormal state has occurred based on a measured value by the sensor.

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