JP4622958B2 - Nitrogen-containing waste liquid treatment method - Google Patents

Description

  The present invention relates to a method for treating a nitrogen-containing waste liquid in which a nitrogen-containing waste liquid containing ammoniacal nitrogen or the like 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. Moreover, this fermentation waste liquid also contains fermentation residue or sludge as 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 process (aerobic process) in which ammonia nitrogen is oxidized to nitrite and nitrate nitrogen by nitrifying bacteria in an aerobic state, and the nitrite nitrogen and nitrate nitrogen obtained in the nitrification process 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 step (anaerobic step) 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.

  Although this intermittent aeration process using a single activated sludge tank has the advantage that the device can be downsized, advanced process management is required to continue operation under optimum conditions. It is necessary to grasp the processing state in the network in real time.

For example, in Patent Document 2 below, the pH of the nitrogen-containing waste liquid is sequentially stored in the storage means, and the pH change rate and the pH change width in the aerobic process and the anaerobic process are calculated by the calculation means from the temporal change of the stored pH value. Thus, it is disclosed that the progress of the nitrification reaction and the denitrification reaction is diagnosed based on the presence or absence of a point in time when the pH change rate reaches the standard rate and becomes virtually zero.
Japanese Patent Laid-Open No. 4-104896 JP-A-8-323394

  Nitrification / denitrification treatment by intermittent aeration treatment does not always maintain a stable state. For example, if the temperature of the nitrogen-containing waste liquid introduced into the activated sludge tank fluctuates, the activity of nitrification bacteria and denitrification bacteria decreases. There are things to do. In addition, the activity of nitrifying bacteria and denitrifying bacteria may decrease due to disturbances such as inadequate aerobic / anaerobic conditions, a decrease in microorganisms in the tank, and contamination with inhibitory substances. And if the continuous aeration process is continued in a state where the activity of nitrifying bacteria and denitrifying bacteria is reduced, the nitrogen in the nitrogen-containing waste liquid cannot be sufficiently treated, and the nitrogen concentration in the activated sludge tank gradually increases, Eventually, nitrification / denitrification will fail.

  Therefore, it is necessary to grasp the treatment state in the activated sludge tank. In Patent Document 2, the measured value of pH is subjected to various arithmetic processing, and the treatment state in the activated sludge tank is comprehensively determined from the calculation results. However, since the measured pH value is used for various calculations, there is a problem that the calculation process is complicated.

  In addition, when a decrease in the activity of nitrifying bacteria and denitrifying bacteria is observed, it is considered that some measures are required. However, Patent Documents 1 and 2 specifically describe means for preventing failure of nitrifying / denitrifying treatment. Is not disclosed.

  Accordingly, an object of the present invention is to provide a method for treating a nitrogen-containing waste liquid that can stably maintain nitrification / denitrification treatment of the nitrogen-containing waste liquid for a long period of time by relatively simple management.

  As a result of various studies on intermittent aeration treatment, the present inventor has found that when the activity of nitrifying bacteria and denitrifying bacteria decreases, the difference between the maximum and minimum pH values in one cycle of intermittent aeration treatment becomes small. The present inventors have found that it causes a failure of the nitrogen treatment, and have come to make the present invention based on this fact.

  That is, the nitrogen-containing waste liquid treatment method of the present invention supplies a waste liquid containing ammonia nitrogen to an activated sludge tank, and alternately repeats air aeration and aeration stop on the waste liquid to perform an aerobic process by air aeration. And a nitrogen-containing waste liquid treatment method for performing intermittent aeration treatment with one cycle as an anaerobic process by stopping aeration, measuring the pH in the activated sludge tank over time, and in one cycle of the intermittent aeration treatment. The difference between the maximum value and the minimum value of the pH is obtained, and when this difference falls below a predetermined value, the amount of waste liquid supplied to the activated sludge tank per cycle of the intermittent aeration treatment is reduced. Features.

  As the activity of nitrifying bacteria and denitrifying bacteria decreases, the difference between the maximum and minimum pH values in one cycle of intermittent aeration treatment tends to decrease, so the pH in the activated sludge tank during intermittent aeration treatment Can be measured over time, and the difference between the maximum and minimum pH values in one cycle of intermittent aeration treatment can be obtained, so that the active state of nitrifying bacteria and denitrifying bacteria can be easily achieved without any complicated processing. I can grasp. And when this pH difference falls below a predetermined value, the load on nitrifying bacteria and denitrifying bacteria is reduced by reducing the amount of nitrogen-containing waste liquid supplied to the activated sludge tank in one cycle of intermittent aeration treatment. Therefore, it is difficult to generate untreated ammonia nitrogen by intermittent aeration treatment, and nitrification / denitrification treatment of nitrogen-containing waste liquid does not break in the middle, and nitrogen-containing waste liquid can be treated stably for a long period of time. I can do it.

  According to the present invention, during the intermittent aeration treatment, the pH in the activated sludge tank is measured over time, and the difference between the maximum and minimum pH values in one cycle of the intermittent aeration treatment is obtained. When the value falls below a predetermined value, the load on nitrifying bacteria and denitrifying bacteria is reduced by reducing the supply amount of nitrogen-containing waste liquid to the activated sludge tank in one cycle of intermittent aeration treatment. Since it can prevent ammonia nitrogen from being generated and gradually accumulated, the nitrification / denitrification treatment of the nitrogen-containing waste liquid can be prevented from failing in the middle, and the nitrogen-containing waste liquid can be treated stably for a long period of time. I can do it.

  Hereinafter, the present invention will be described in more detail with reference to the drawings. FIG. 1 shows an example of a waste liquid treatment apparatus used in the method for treating a nitrogen-containing waste liquid of the present invention.

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

  This waste liquid treatment apparatus includes an activated sludge tank 20 that nitrifies and denitrifies a nitrogen-containing waste liquid by an intermittent aeration method. An air ejection device 21 is arranged at the bottom of the activated sludge tank 20, and a gas (normal air) containing oxygen is supplied into the activated sludge tank 20 by operating a blower 22 installed outside. It is configured so that the contained waste liquid can be aerated. In addition, a stirrer including a motor 23, a stirring shaft 24, and a stirring blade 25 is provided on the upper portion or side wall of the activated sludge tank 20, so that the waste liquid in the activated sludge tank 20 can be stirred by the stirring blade 25. It is configured. In addition, a pH meter 26 is disposed on the upper part of the activated sludge tank 20 so that the pH in the tank can be measured over time.

  The activated sludge tank 20 is connected to a pipe L1 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 L <b> 2 extending from the activated sludge tank 20 is connected to the final sedimentation tank 30. In the final sedimentation basin 30, the waste liquid nitrified and denitrified in the activated sludge tank 20 (hereinafter referred to as “treated waste liquid”) is separated into treated water and sludge by natural sedimentation, membrane separation, or the like. A pipe L3 is connected to the side wall of the final sedimentation basin 30 so that treated water obtained by separating the treated waste liquid can be discharged out of the system. A pipe L4 is connected to the bottom of the final sedimentation basin 30 so that the sludge accumulated on the bottom of the final sedimentation basin 30 can be discharged out of the system.

  Next, an embodiment of a method for treating a nitrogen-containing waste liquid according to 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 activated sludge tank 20.

  In the activated sludge tank 20, first, the blower 22 is operated, air is supplied from the nozzle of the air ejection device 21 to the nitrogen-containing waste liquid in the activated sludge tank 20, and aeration processing is performed (aerobic process). In this state, ammonia nitrogen in the nitrogen-containing waste liquid is oxidized (nitrification reaction) to nitrite nitrogen or nitrate nitrogen by the action of nitrifying bacteria.

  Then, after the predetermined time has elapsed, the operation of the blower 22 is stopped, the motor 23 is operated, and the nitrogen-containing waste liquid in the activated sludge tank 20 is stirred by the stirring blade 25. In this state, the nitrogen-containing waste liquid in the activated sludge tank 20 has no dissolved oxygen (anaerobic process), and nitrite nitrogen and nitrate nitrogen are reduced to nitrogen gas (denitrification) by the action of denitrifying bacteria. Reaction).

  In this manner, by repeating the aerobic process and the anaerobic process alternately, ammonia nitrogen contained in the nitrogen-containing waste liquid can be decomposed into nitrogen gas. In this case, in order to prevent nitrification and denitrification of all ammonia nitrogen contained in the nitrogen-containing waste liquid supplied to the activated sludge tank 20 per cycle, no untreated ammonia nitrogen remains per cycle. It is necessary to adjust the supply amount of the nitrogen-containing waste liquid and the time of one cycle. When untreated ammonia nitrogen remains, the pH gradually increases, the activity of nitrifying bacteria and denitrifying bacteria decreases, and eventually nitrification / denitrification treatment fails.

  However, even when the operation is performed by adjusting the time of one cycle so that untreated ammonia nitrogen does not remain, for example, the temperature variation of the nitrogen-containing waste liquid introduced into the activated sludge tank 20, aerobic / anaerobic, etc. The activity of nitrifying bacteria and denitrifying bacteria may decrease due to factors such as inadequate conditions, a decrease in microorganisms in the tank, and disturbances such as contamination with inhibitory substances. In such a case, if the intermittent aeration process is continued under the same conditions, the ammonia nitrogen in the nitrogen-containing waste liquid cannot be sufficiently treated, and the ammonia nitrogen remains and accumulates, and the pH gradually increases. Will fail in nitrification / denitrification treatment.

  FIG. 2 shows the results of measuring the pH over time when the nitrification / denitrification process fails in the waste liquid treatment method using the waste liquid treatment apparatus as shown in FIG. In this example, the activated sludge tank 20 has a capacity of 10,000 L, an inflow of nitrogen-containing waste liquid of 1000 L / Day, a residence time of 10 days (aerobic process 60 minutes, anaerobic process 60 minutes), and nitrogen-containing waste liquid intermittently under conditions of a water temperature of 28 ° C. It shows the situation that occurred when aeration processing was in progress.

  As shown in FIG. 2, when the difference between the maximum and minimum pH values in one cycle is ΔpH, ΔpH at about 100 minutes after the nitrification / denitrification treatment was stable was about 0.1. On the other hand, the ΔpH at about 600 minutes after the nitrification / denitrification treatment started to break was about 0.7, and the ΔpH at about 1400 minutes after the nitrification / denitrification treatment was completely broken was about 0. .5. At the same time, as the failure of nitrification / denitrification progresses, the pH in the activated sludge tank 20 gradually increases. This indicates that the ammonia nitrogen in the supplied nitrogen-containing waste liquid remains without being treated and is accumulated.

  Therefore, in the present invention, when the nitrogen-containing waste liquid is subjected to nitrification / denitrification treatment by intermittent aeration treatment, the pH in the activated sludge tank 20 is measured over time, and the maximum and minimum pH values in one cycle of the intermittent aeration treatment are measured. The difference from the value (hereinafter referred to as “ΔpH”) is calculated. Then, when the calculated ΔpH falls below a predetermined value, the supply amount of the nitrogen-containing waste liquid to the activated sludge tank 20 per cycle of the intermittent aeration treatment is reduced. The above ΔpH may be an average value of a plurality of cycles of intermittent aeration processing.

  In this way, by reducing the supply amount of the nitrogen-containing waste liquid supplied into the activated sludge tank 20 per cycle of intermittent aeration treatment, the nitrification reaction by nitrifying bacteria and the denitrification reaction by denitrifying bacteria can be advanced completely, Generation of ammonia nitrogen remaining without being treated can be prevented. As a result, an increase in pH in the activated sludge tank 20 can be prevented, and the nitrification / denitrification reaction can be maintained well. And by maintaining the nitrification / denitrification reaction well, the number and activity of nitrifying bacteria and denitrifying bacteria will gradually recover, so the nitrogen-containing waste liquid to the activated sludge tank 20 per cycle of intermittent aeration treatment The supply amount can be gradually increased to return to a steady operating state.

  In the present invention, when the supply amount of the nitrogen-containing waste liquid to the activated sludge tank 20 per cycle of the intermittent aeration treatment is reduced, the above ΔpH set values are the scale of the activated sludge tank 20, the properties of the nitrogen-containing waste liquid, the intermittent Although it is set as appropriate depending on the operating conditions of the aeration treatment, generally, the supply amount of the nitrogen-containing waste liquid to the activated sludge tank 20 is reduced when it falls below the lower limit value set between 0.1 and 1. Is preferred.

  In the present invention, it is preferable to continuously or stepwise reduce the supply amount of the nitrogen-containing waste liquid from the supply amount of the nitrogen-containing waste liquid during the steady operation until the decrease in ΔpH is not recognized. For example, a plurality of set values of ΔpH are provided, and the one-stage supply amount is reduced when the first set value of ΔpH is reached. Even so, if ΔpH further decreases and ΔpH reaches the next set value, an operation for further reducing the one-step inflow amount is performed.

  Then, when the decrease in ΔpH is no longer observed, the nitrification denitrification rate in the activated sludge tank 20 is changed to a conventionally known method, for example, the nitrification rate is changed to nitrate nitrogen in the activated sludge tank in the aerobic process, Nitrate nitrogen is measured and calculated as the rate of increase of the total amount, and the rate of denitrification is determined by measuring nitrate nitrogen and nitrite nitrogen in the activated sludge tank in the anaerobic process. Calculate as When the recovery of the nitrification / denitrification capability is recognized, it is preferable that the supply amount of the nitrogen-containing waste liquid is gradually increased to return to the waste liquid supply amount during the steady operation.

  Thus, according to the present invention, during intermittent aeration treatment, the pH in the activated sludge tank 20 is measured over time, ΔpH is calculated, and when this ΔpH falls below a predetermined value, Nitrogen-containing waste liquid nitrification / denitrification treatment can be stably performed for a long time without rupturing the nitrification / denitrification treatment of the nitrogen-containing waste liquid by reducing the supply amount of nitrogen-containing waste liquid to the activated sludge tank in one cycle of intermittent aeration treatment Can continue.

It is a schematic block diagram which shows an example of the waste liquid processing apparatus used for the processing method of the nitrogen-containing waste liquid of this invention. 2 is a chart showing the results of measuring the pH over time when the nitrification / denitrification treatment fails in the waste liquid treatment method using the waste liquid treatment apparatus as shown in FIG.

Explanation of symbols

10: Waste liquid storage tank 20: Activated sludge tank 21: Air ejection device 22: Blower 23: Motor 24: Stirrer shaft 25: Stirrer blade 26: pH meter 30: Final sedimentation tank

Claims (1)

A waste liquid containing ammonia nitrogen is supplied to the activated sludge tank, and air aeration and aeration stop are alternately repeated with respect to the waste liquid, and an aerobic process by air aeration and an anaerobic process by aeration stop are set as one cycle. A method for treating nitrogen-containing waste liquid that performs intermittent aeration treatment,
The pH in the activated sludge tank is measured over time, the difference between the maximum value and the minimum value of the pH in one cycle of the intermittent aeration treatment is obtained, and when this difference falls below a predetermined value, A method for treating a nitrogen-containing waste liquid, comprising reducing the amount of waste liquid supplied to the activated sludge tank per cycle of intermittent aeration treatment.