JP2008161798A - Nitrogen-containing waste liquid treatment method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nitrogen-containing waste liquid treatment method which prevents aerobic decomposition of organic matter in an anaerobic process during treatment of nitrogen-containing waste liquid with intermittent aeration to effectively utilize the organic matter as a hydrogen donor required in the anaerobic process. <P>SOLUTION: In the nitrogen-containing waste liquid treatment method where ammonia nitrogen-containing waste liquid is supplied to an intermittent aeration tank 20, and intermittent aeration treatment alternately repeating an aerobic process due to aeration of the waste liquid in the intermittent aeration tank 20 and the anaerobic process due to stop of the aeration is carried out to convert the ammonia nitrogen in the waste liquid into nitrogen gas to remove the ammonia nitrogen, supply of the waste liquid to the intermittent aeration tank 20 in each cycle is started at a predetermined time after the start of the anaerobic process, determined from the reduction time of dissolved oxygen concentration in the waste liquid, and is completed by the end of the anaerobic process. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for treating a nitrogen-containing waste liquid in which waste liquid containing ammoniacal nitrogen is treated biochemically and removed as nitrogen gas.

  Organic waste such as garbage and sewage surplus sludge (hereinafter referred to as “organic matter”) is treated with methane fermentation in the presence of methane bacteria to recover energy as methane gas. It is adopted as part of the formation of a type society.

  In the methane fermentation treatment, the organic matter can be decomposed into methane and carbon dioxide gas, but the organic matter cannot be decomposed 100%, and the organic matter remains in the fermentation waste liquid after the methane fermentation treatment. The methane fermentation waste liquid also contains sludge containing fermentation residues or bacterial cells grown in a methane fermentation tank, and ammonia, which is a decomposition product of organic matter. Therefore, the fermentation waste liquid cannot be discharged as it is into the sewer or the river, and it is necessary to decompose and remove organic substances and nitrogen components to reduce them to below the discharge level.

  For the treatment of methane fermentation waste liquid, intermittent aeration activated sludge treatment (hereinafter referred to as “intermittent aeration treatment”), which is one of activated sludge treatment methods, is widely used.

  Intermittent aeration treatment refers to a waste liquid containing ammoniacal nitrogen such as the above methane fermentation waste liquid (hereinafter referred to as “nitrogen-containing waste liquid”), in which air aeration and aeration stop are repeated alternately to remove ammonia and organic matter. This is a treatment method for decomposing and removing microorganisms cultivated in activated sludge. That is, the nitrification reaction (aerobic process) that oxidizes ammonia nitrogen to nitrite nitrogen and nitrate nitrogen by nitrifying bacteria in an aerobic state and the nitrite nitrogen and nitrate nitrogen obtained by the nitrification reaction are anaerobic. In this state, ammonia in the nitrogen-containing waste liquid is removed as nitrogen gas by a two-stage biological reaction consisting of a denitrification reaction (anaerobic process) that is reduced by the action of denitrifying bacteria and decomposed to nitrogen gas.

  This intermittent aeration treatment includes, for example, a method in which aerobic conditions and anaerobic conditions are repeated in a single activated sludge tank as disclosed in Patent Document 1 below, and the treatment is divided in terms of time. Are known.

  Various attempts have been made to improve the processing efficiency. For example, in Patent Document 2 below, the operation temperature of the intermittent aeration tank is controlled to 25 to 35 ° C. to detect the time when the oxidation of ammonia ends. A method for treating a nitrogen-containing waste liquid by controlling the nitrification reaction with a nitrite type by setting the aeration time to 1 to 1.5 times that the oxidation of ammonia is completed is disclosed.

In Patent Document 3 below, a liquid to be treated is supplied to an intermittent aeration tank, and aeration is intermittently performed in the presence of activated sludge to repeat an aerobic process and an anaerobic process. It is disclosed that nitrogen nitrification is performed, and in the anaerobic process, the amount of hydrogen donor necessary for denitrification is separately injected over a period of 1/2 or more of the anaerobic process for denitrification.
JP-A-4-104896 JP 2005-144306 A JP-A-11-216493

  In the denitrification reaction in the anaerobic process, a hydrogen donor is required for the reaction. For this reason, since it is necessary to add hydrogen donors, such as organic substance from the outside of a system, effective utilization of the organic substance in an anaerobic process leads to the reduction of processing cost.

  Here, oxygen is dissolved in the waste liquid in the intermittent aeration tank immediately after switching from the aerobic process to the anaerobic process. For this reason, when the organic substance is supplied to the intermittent aeration tank at the same time as switching to the anaerobic process, the intermittent aeration tank continues to be in an aerobic state for a while. Sometimes it could not be used for the nitrogen reaction.

  As a result, there is a problem that the supply amount of organic matter increases, processing costs increase, and processing efficiency of the nitrogen-containing waste liquid is inferior. In particular, when the concentration of activated sludge in the intermittent aeration tank is low, or when the activity of aerobic microorganisms is reduced, such a problem is likely to occur because the rate of decrease in dissolved oxygen is slow.

  Therefore, the object of the present invention is to prevent the aerobic decomposition of organic substances in the anaerobic process when the nitrogen-containing waste liquid is processed by intermittent aeration treatment, and the organic substance is effective as a hydrogen donor required in the anaerobic process. The object is to provide a method for treating a nitrogen-containing waste liquid to be used.

  In order to solve the above-described problems, the nitrogen-containing waste liquid treatment method of the present invention supplies ammonia liquid containing ammonia nitrogen to an intermittent aeration tank, and the waste liquid is favorably obtained by air aeration in the intermittent aeration tank. In the method for treating a nitrogen-containing waste liquid in which an intermittent aeration process that alternately repeats an air process and an anaerobic process by stopping aeration is performed and ammonia nitrogen in the waste liquid is converted to nitrogen gas and removed, the waste liquid in each cycle The supply to the intermittent aeration tank is started after a predetermined time determined by a decrease time of the dissolved oxygen concentration in the waste liquid from the start of the anaerobic process, and is completed by the completion of the anaerobic process. And

  According to the present invention, when the nitrogen-containing waste liquid is processed by the intermittent aeration process, the supply of the waste liquid to the intermittent aeration tank in each cycle is performed according to the decrease time of the dissolved oxygen concentration in the waste liquid from the start of the anaerobic process. By starting after a predetermined time and completing by the end of the anaerobic process, it is possible to prevent the organic matter in the supplied nitrogen-containing waste liquid from being aerobically decomposed and necessary in the anaerobic process Therefore, it is not necessary to add resources such as methyl alcohol, or the amount of addition can be reduced, so that the processing cost of the nitrogen-containing waste liquid can be reduced.

  In one of the preferable embodiments of the present invention, a dissolved oxygen meter is installed in the intermittent aeration tank, and the dissolved oxygen in the treatment liquid after the start of the anaerobic process is measured, and the dissolved oxygen concentration becomes a predetermined value or less. The supply of the waste liquid is started. According to this, the dissolved oxygen in the treatment liquid after the start of the anaerobic process is measured, and after the dissolved oxygen concentration becomes a predetermined value or less, the supply of the waste liquid is started to sufficiently reduce the remaining oxygen. Since it becomes possible to supply waste liquid at the time of having carried out, it can prevent more reliably that the organic substance in waste liquid is decomposed aerobically.

  In another preferred embodiment of the present invention, based on the time required for the denitrification reaction of nitrous acid or nitric acid produced in the aerobic process, the limit from the start of the anaerobic process to the start of the supply of the waste liquid Set a delay time, install a dissolved oxygen meter in the intermittent aeration tank, measure the dissolved oxygen in the treatment liquid after the start of the anaerobic process, and the dissolved oxygen concentration is below a predetermined value within the limit delay time In this case, the supply of the waste liquid is started at that time, and when the dissolved oxygen concentration does not become a predetermined value or less within the limit delay time, the waste liquid is discharged when the limit delay time has elapsed. Start supplying. According to this, when the dissolved oxygen in the treatment liquid after the start of the anaerobic process is measured and the dissolved oxygen concentration becomes a predetermined value or less within the limit delay time, the supply of the waste liquid is started at that time. In the case where the dissolved oxygen concentration does not become a predetermined value or less within the limit delay time, by starting the supply of the waste liquid when the limit delay time has elapsed, the organic matter in the waste liquid is removed in the anaerobic process. It can be used as effectively as possible, and a sufficient denitrification reaction of nitrous acid or nitric acid produced in the aerobic process can be performed.

  In still another preferred embodiment of the present invention, a dissolved oxygen meter is installed in the intermittent aeration tank, and the dissolved oxygen concentration in the treatment liquid after the start of the anaerobic process is measured every predetermined number of cycles, so that the dissolved oxygen concentration is predetermined. The time required to be equal to or less than the value is set, and the supply of the waste liquid is started when the predetermined time defined above has elapsed since the start of the anaerobic process. According to this, for every predetermined number of cycles, the dissolved oxygen in the treatment liquid after the start of the anaerobic process is measured, the time required for the dissolved oxygen concentration to become a predetermined value or less is set, and after the start of the anaerobic process By starting the supply of the waste liquid when the predetermined time defined above has elapsed, it becomes possible to supply the waste liquid when the remaining oxygen is sufficiently reduced, so the organic matter in the waste liquid is aerobic. It is possible to effectively prevent the decomposition, and it is not necessary to measure the dissolved oxygen concentration every cycle, so that the operation can be simplified.

  According to the present invention, when a nitrogen-containing waste liquid is treated by intermittent aeration treatment, organic substances in the supplied nitrogen-containing waste liquid can be prevented from being aerobically decomposed, and a hydrogen donor required in an anaerobic process. Can be used effectively. For this reason, it is not necessary to add resources such as methyl alcohol, or the addition amount thereof can be reduced, and the processing cost of the nitrogen-containing waste liquid can be reduced.

  Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 shows a schematic configuration diagram of an embodiment of a processing apparatus used for processing the nitrogen-containing waste liquid of the present invention.

  The nitrogen-containing waste liquid to be treated in the present invention is not particularly limited as long as it contains water containing ammoniacal nitrogen, and is discharged when methane fermentation treatment of organic waste such as manure, raw garbage, food processing residue, etc. An example is methane fermentation treatment waste liquid.

  This processing apparatus includes an intermittent aeration tank 20 that nitrifies and denitrifies a nitrogen-containing waste liquid by an intermittent aeration method.

  An air ejection device 21 is disposed at the bottom of the intermittent aeration tank 20, and a gas (normal air) containing oxygen is supplied into the intermittent aeration tank 20 by operating a blower 22 installed outside. It is configured so that the waste liquid inside can be aerated.

  A stirrer including a motor 23, a stirring shaft 24, and a stirring blade 25 is provided on the upper part or the side wall of the intermittent aeration tank 20, and the waste liquid in the intermittent aeration tank 20 can be stirred by the stirring blade 25. Has been.

  A dissolved oxygen meter 26 and a thermometer 27 are arranged on the upper part of the intermittent aeration tank 20 so that the dissolved oxygen and temperature of the treatment liquid in the tank can be measured over time.

  A temperature control device 28 is provided at the lower part or the side part of the intermittent aeration tank 20, and the temperature control device 28 is operated based on the measured value by the thermometer 27 to set the temperature in the intermittent aeration tank 3 to a predetermined value. It is configured to be adjustable to temperature.

  The intermittent aeration tank 20 is connected to a pipe L <b> 1 extending from the waste liquid storage tank 10. A supply pump P1 is disposed in the middle of the pipe L1.

  The waste liquid storage tank 10 is not particularly limited, and may be a storage tank, or a methane fermentation treatment tank or the like for treating organic waste with methane bacteria or the like.

  Further, the pipe L2 extending from the intermittent aeration tank 20 is connected to a next process (not shown).

  Next, a first embodiment of the method for treating nitrogen-containing waste liquid of the present invention using this waste liquid treatment apparatus will be described.

  First, the supply pump P <b> 1 is operated to supply the nitrogen-containing waste liquid from the waste liquid storage tank 10 to the intermittent aeration tank 20.

  In the intermittent aeration tank 20, first, the blower 22 is operated and air is supplied from the nozzle of the air ejection device 21 to the waste liquid in the intermittent aeration tank 20 to perform an aeration process (aerobic process). In this state, ammonia nitrogen in the waste liquid is oxidized into nitrite nitrogen or nitrate nitrogen (nitrification reaction) by the action of nitrifying bacteria (ammonia oxidizing bacteria, nitrite oxidizing bacteria).

  It is preferable to adjust the air aeration amount so that the dissolved oxygen concentration of the waste liquid in the intermittent aeration tank 20 is 0.5 to 3 mg / L, and the air aeration amount is 1.5 to 2.5 mg / L. It is more preferable to adjust. If the dissolved oxygen concentration of the waste liquid is within the above range, the activity of nitrifying bacteria can be improved.

  Microorganisms related to the nitrification reaction are ammonia-oxidizing bacteria and nitrite-oxidizing bacteria, but there are differences in the growth rates of ammonia-oxidizing bacteria and nitrite-oxidizing bacteria. It is known that the growth rate of ammonia-oxidizing bacteria is faster than that of nitrate-oxidizing bacteria, and that the difference increases with increasing temperature.

  And, it is known that the nitrous acid type intermittent aeration treatment can reduce the processing cost because it can reduce the air aeration amount in the aerobic process and the consumption amount of organic matter in the anaerobic process compared with the nitric acid type intermittent aeration treatment. Yes.

  Therefore, the temperature of the waste liquid in the intermittent aeration tank 20 during the aerobic process is preferably 25 to 35 ° C. In the aerobic process, by setting the temperature of the waste liquid within the above range, only the nitrite oxidizing bacteria can be selectively reduced without impairing the activity of the ammonia oxidizing bacteria. You can drive.

  Further, the aerobic process time, that is, the air aeration time is preferably 1 to 1.5 times as long as the reaction time for converting ammoniacal nitrogen to nitrite nitrogen is completed. When the air aeration is less than the time (less than 1 time) when the reaction for converting ammonia nitrogen to nitrite nitrogen is completed (less than 1 time), the amount of ammonia oxidizing bacteria that die and flows out of the system is better than the growth. Therefore, ammonia oxidizing bacteria may gradually decrease, and ammonia oxidation may not proceed. In addition, when the time of air aeration exceeds 1.5 times the time for completing the reaction for converting ammonia nitrogen to nitrite nitrogen, it becomes a condition that nitrite-oxidizing bacteria can also grow, and nitrite is converted to nitric acid. Since the reaction proceeds, it becomes difficult to operate with a nitrous acid type intermittent aeration treatment.

  And after predetermined time progress, the blower 22 is stopped and air aeration is stopped (anaerobic process).

  Here, as described above, oxygen remains in the nitrogen-containing waste liquid in the intermittent aeration tank 20 immediately after the blower 22 is stopped and switched from the aerobic process to the anaerobic process.

  In the present invention, after the blower 22 is stopped, the supply pump P1 is operated after a predetermined time determined by the decrease time of the dissolved oxygen concentration of the waste liquid in the intermittent aeration tank 20, and the waste liquid is stored in the intermittent aeration tank 20. A certain amount of nitrogen-containing waste liquid is supplied from the tank 10, the motor 23 is operated, and the waste liquid in the intermittent aeration tank 20 is stirred by the stirring blade 25.

  Specifically, in this embodiment, the dissolved oxygen concentration of the waste liquid in the intermittent aeration tank 20 is measured by the dissolved oxygen meter 26, and the dissolved oxygen of the waste liquid is not more than a predetermined value, preferably 0 mg / L. Later, the supply pump P <b> 1 is operated to supply the nitrogen-containing waste liquid from the waste liquid storage tank 10 to the intermittent aeration tank 20.

  In this way, when the dissolved oxygen concentration of the waste liquid in the intermittent aeration tank 20 falls below a predetermined value, the nitrogen-containing waste liquid is supplied to the intermittent aeration tank 20 so that the organic matter in the nitrogen-containing waste liquid is exposed to an aerobic state. It becomes difficult to be aerobically decomposed and the organic matter in the nitrogen-containing waste can be effectively used in the denitrification reaction. As a result, it is not necessary to add resources such as methyl alcohol, or the amount added can be reduced, so that the processing cost of the nitrogen-containing waste liquid can be reduced.

  The supply of the nitrogen-containing waste liquid from the waste liquid storage tank 10 in the anaerobic process may be performed at the initial stage of the supply start so that the supply of the nitrogen-containing waste liquid required in the cycle is completed. May be supplied. By introducing the organic matter necessary for the denitrification reaction at the initial stage of the anaerobic process, the denitrification reaction can be performed stably without running out of organic matter in the cycle.

  The total of the aerobic process time and the anaerobic process time is preferably set to 1 to 4 hours by a timer or the like. In this case, the aerobic process time is determined in consideration of the time required for all ammonia nitrogen in the nitrogen-containing waste liquid supplied in one cycle to be converted into nitrous acid or nitrate nitrogen, and the anaerobic process time. Is determined in consideration of the time required for denitrification of all nitrous acid and nitrate nitrogen present in the waste liquid that has undergone the aerobic process.

  Next, a second embodiment of the nitrogen-containing waste liquid treatment method of the present invention using the treatment apparatus of FIG. 1 will be described.

  Basically, the treatment of the nitrogen-containing waste liquid is performed in the same manner as in the first embodiment.

  In this embodiment, the supply of nitrogen-containing waste liquid from the waste liquid storage tank 10 after the blower 22 is stopped (anaerobic process) and the inside of the intermittent aeration tank 20 is switched from the aerobic process to the anaerobic process is as follows. This is a difference from the first embodiment.

  That is, in this embodiment, considering the time required to denitrify all nitrous acid and nitrate nitrogen present in the waste liquid that has undergone the aerobic process, the nitrogen-containing waste liquid after the start of the anaerobic process. Set the limit delay time until the start of supply. Then, from the start of the anaerobic process, the dissolved oxygen concentration of the waste liquid in the intermittent aeration tank 20 is measured by the dissolved oxygen meter 26, and the dissolved oxygen concentration of the waste liquid is within a predetermined delay time, and the dissolved oxygen concentration is not more than a predetermined value, preferably 0 mg / When it becomes L, the supply pump P1 is operated at that time and supply of the nitrogen-containing waste liquid from the waste liquid storage tank 10 is started. On the other hand, if the dissolved oxygen concentration does not fall below the predetermined value within the limit delay time, the supply pump P1 is operated when the limit delay time has elapsed to supply the nitrogen-containing waste liquid from the waste liquid storage tank 10. Start.

  Here, the limit delay time is preferably set as shown in the following formula (1), for example. That is, the time required for denitrification during normal load operation (denitrification time) is measured in advance, and the denitrification time is set so as to be secured within the time set in the anaerobic process.

Time required for anaerobic process-denitrification time = limit delay time (1)
According to this aspect, when the dissolved oxygen concentration of the waste liquid in the intermittent aeration tank 20 becomes a predetermined value or less within the limit delay time, the supply of the nitrogen-containing waste liquid from the waste liquid storage tank 10 is performed at that time. By starting, the organic matter in the nitrogen-containing waste liquid supplied to the intermittent aeration tank 20 becomes difficult to be exposed to the aerobic state, so that it is difficult to be aerobically decomposed and the organic matter can be effectively used for the denitrification reaction.

  Further, when the activated sludge concentration in the intermittent aeration tank 20 is low or the activity of aerobic microorganisms such as nitrifying bacteria is reduced, the rate of decrease of dissolved oxygen is slow, and the dissolved oxygen concentration is within the anaerobic process time. May not fall below a predetermined value. For this reason, when the dissolved oxygen concentration does not become a predetermined value or less within the limit delay time, the supply of the nitrogen-containing waste liquid from the waste liquid storage tank 10 is started when the limit delay time has elapsed. The activity of the aerobic microorganisms having decreased is increased by using the organic matter in the waste liquid as a nutrient source. As a result, since the decrease in dissolved oxygen concentration is promoted, the aerobic decomposition of the organic substance in the nitrogen-containing waste liquid supplied during the anaerobic process can be suppressed to the minimum, and the organic substance can be effectively used in the denitrification reaction.

  Next, a third embodiment of the method for treating a nitrogen-containing waste liquid of the present invention using the treatment apparatus of FIG. 1 will be described.

  Basically, the treatment of the nitrogen-containing waste liquid is performed in the same manner as in the first embodiment.

  In this embodiment, the supply of nitrogen-containing waste liquid from the waste liquid storage tank 10 after the blower 22 is stopped (anaerobic process) and the inside of the intermittent aeration tank 20 is switched from the aerobic process to the anaerobic process is a predetermined number of cycles. Every time, the dissolved oxygen concentration of the nitrogen-containing waste liquid in the intermittent aeration tank 20 is measured to set the time required for the dissolved oxygen of the nitrogen-containing waste liquid to be a predetermined value or less, and determined above after the start of the anaerobic process. The difference from the first embodiment is that the supply of the nitrogen-containing waste liquid from the waste liquid storage tank 10 is started when the predetermined time has elapsed.

  For example, in the case where the water quality of the nitrogen-containing waste liquid is stable and the properties and the like are not particularly likely to fluctuate, the nitrogen content from the waste liquid storage tank 10 is reached when the predetermined time has elapsed since the start of the anaerobic process. By starting the supply of the waste liquid, it becomes possible to supply the nitrogen-containing waste liquid from the waste liquid storage tank 10 when the remaining oxygen is sufficiently reduced, so that the organic matter in the waste liquid is aerobically decomposed. It can be effectively prevented, and the operation can be simplified because it is not necessary to measure the dissolved oxygen concentration every cycle.

It is a schematic block diagram of one Embodiment of the processing apparatus used for a process of the nitrogen-containing waste liquid of this invention.

Explanation of symbols

10: Waste liquid storage tank 20: Intermittent aeration tank 21: Air ejection device 22: Blower 23: Motor 24: Stirrer shaft 25: Stirrer blade 26: Dissolved oxygen meter 27: Thermometer 28: Temperature controller P1: Supply pump

Claims (4)

Supplying a waste liquid containing ammonia nitrogen to the intermittent aeration tank, and performing an intermittent aeration process that alternately repeats an aerobic process by air aeration and an anaerobic process by aeration stop for the waste liquid in the intermittent aeration tank, In the method for treating a nitrogen-containing waste liquid in which ammonia nitrogen in the waste liquid is converted to nitrogen gas and removed,
The supply of the waste liquid to the intermittent aeration tank in each cycle is started after a predetermined time determined by the decrease time of the dissolved oxygen concentration in the waste liquid from the start of the anaerobic process, and is completed by the end of the anaerobic process. A method for treating a nitrogen-containing waste liquid, which is characterized by the above.   The dissolved oxygen meter is installed in the intermittent aeration tank, the dissolved oxygen in the treatment liquid after the start of the anaerobic process is measured, and the supply of the waste liquid is started after the dissolved oxygen concentration becomes a predetermined value or less. The processing method of the nitrogen-containing waste liquid as described.   Based on the time required for the denitrification reaction of nitrous acid or nitric acid generated in the aerobic process, a limit delay time from the start of the anaerobic process to the start of the supply of the waste liquid is set, and the intermittent Install a dissolved oxygen meter in the aeration tank, measure the dissolved oxygen in the treatment liquid after the start of the anaerobic process, and if the dissolved oxygen concentration falls below the predetermined value within the limit delay time, 2. The nitrogen according to claim 1, wherein the supply of the waste liquid is started, and when the dissolved oxygen concentration does not become a predetermined value or less within the limit delay time, the supply of the waste liquid is started when the limit delay time has elapsed. Treatment method for waste liquid.   Install the dissolved oxygen meter in the intermittent aeration tank, measure the dissolved oxygen in the treatment liquid after the start of the anaerobic process every predetermined number of cycles, and set the time required for the dissolved oxygen concentration to be less than the predetermined value The method for treating a nitrogen-containing waste liquid according to claim 1, wherein the supply of the waste liquid is started when the predetermined time defined above has elapsed after the start of the anaerobic process.