JP3637819B2 - Waste water nitrification method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a nitrification method for wastewater, and in particular, wastewater is continuously introduced from the inlet of the nitrification tank and out of the outlet, and the mixed solution of the wastewater and microorganisms is aerobic in the nitrification tank. The present invention relates to a nitrification method for wastewater in which ammonia nitrogen in the wastewater is nitrified by the action of microorganisms by aeration.
[0002]
[Prior art]
In this type of wastewater nitrification method, nitrification is performed in a nitrification tank to oxidize ammonia nitrogen in waste water mainly to nitrate nitrogen by the action of microorganisms represented by nitrifying bacteria. In nitrification treatment, it is important to complete the nitrification reaction in the nitrification tank almost completely in response to the ammonia nitrogen load of the wastewater and the daily and annual fluctuations of the water temperature. For this reason, in actual wastewater treatment such as sewage, the amount of aeration air necessary for nitrification and the nitrification time are designed according to the maximum ammoniacal nitrogen load in the low water temperature period when the treatment efficiency decreases.
[0003]
[Problems to be solved by the invention]
However, if the aeration air volume is set according to the maximum ammonia nitrogen load as described above, the nitrification performance has more margin than necessary when the load decreases or during high water temperature periods, and the power for aeration is wasted. . Furthermore, if aeration is excessive, the microorganisms in the nitrification tank, that is, activated sludge is disassembled by self-decomposition, and the sedimentation property is lowered, resulting in an adverse effect that the transparency of treated water deteriorates in the subsequent sedimentation basin.
[0004]
The present invention provides a nitrification method for wastewater that improves the above-mentioned problems of the prior art, prevents excessive aeration in a nitrification tank, and allows a nitrification reaction to be almost completely achieved with a minimum amount of aeration air. Objective.
[0005]
[Means for Solving the Problems]
The present invention allows the waste water to continuously flow in from the inflow port of the nitrification tank, to flow out of the outflow port, and to aerate the mixed solution of waste water and microorganisms in the nitrification tank so as to be in an aerobic condition. In the nitrification method of wastewater in which ammonia nitrogen in wastewater is nitrified by the action of the microorganism, the mixed solution collected from the nitrification tank is batch-treated under aerobic conditions, and several minutes from the start of batch reaction of the mixed solution time the difference between the oxygen consumption rate was measured by defining the time reduction of the oxygen consumption rate of oxygen consumption rate and time T ₁ in T ₁ at time T _2, after a predetermined time, the time reduction is set after When the value is larger than the value, the aeration air volume is increased. When the amount of decrease over time is smaller than the set value, the aeration air volume is decreased.
[0006]
Further, the present invention is characterized in that the set value is set so that a value converted per minute is 1 to 3 mg-O ₂ / L · h.
[0007]
In addition, the present invention is characterized in that the increase / decrease amount of the aeration air volume is controlled in accordance with a difference between a measured value of a decrease amount with time of the oxygen consumption rate and a set value.
[0008]
Further, the present invention is characterized in that the collection position of the mixed solution for performing the batch reaction of the mixed solution is in the vicinity of the waste water outlet of the nitrification tank.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an apparatus configuration diagram for explaining an embodiment of the present invention. The waste water continuously supplied from the inflow pipe 10 to the denitrification tank 12 stays in the denitrification tank 12 for a predetermined time and is denitrified, and then continuously into the nitrification tank 14 from the inlet 16 of the nitrification tank 14. Inflow. In the nitrification tank 14, the mixed solution of waste water and microorganisms is supplied with oxygen by aeration from the blower 18 and is maintained under aerobic conditions. Ammonia nitrogen in the wastewater is nitrified by the action of microorganisms to mainly become nitrate nitrogen. Part of the nitrified waste water (nitrification liquid) is sent to the denitrification tank 12 via the circulation path 20 and denitrified, and the nitrogen component is released to the atmosphere as nitrogen gas. The remaining nitrification liquid is mixed with microorganisms and sent from the flow outlet 22 of the nitrification tank 14 to the settling basin 24, where the treated water from which the sludge has been settled is discharged from the outflow passage 26. The sludge precipitated in the sedimentation basin 24 is mainly an aggregate of active microorganisms, a part thereof is returned to the denitrification tank 12 via the return path 28, and the remainder is discharged from the extraction pipe 30 as surplus sludge. The above apparatus configuration is the same in the prior art.
[0010]
In the present embodiment, a sampling tube 32 for sampling a mixed solution of waste water and microorganisms in the tank is inserted in the vicinity of the outlet 22 of the nitrification tank 14, and sampling provided in the middle of the sampling pipe 32. The liquid mixture is collected in a small batch tank 36 by the pump 34. An air pump 38 for supplying air and a sensor 40 capable of detecting the oxygen consumption rate of the collected mixed solution are connected to the batch tank 36. The detection result of the sensor 40 is transmitted to the calculator 42, and the controller 44 controls the rotational speed of the blower 18 based on the calculation result of the calculator 42.
[0011]
FIG. 2 is a model diagram for explaining the behavior of the oxygen consumption rate of the mixed liquid in the nitrification reaction. That is, curve 1 in FIG. 2 shows the time-dependent change in the oxygen consumption rate when a microorganism having a nitrification function is mixed with wastewater containing ammonia nitrogen at a predetermined concentration and batch-treated under aerobic conditions. In the first stage where the concentration of ammoniacal nitrogen is relatively high, since the nitrification reaction is active, the oxygen consumption rate K1 is high. Thereafter, by continuing batch processing, the concentration of ammonia nitrogen gradually decreases and the nitrification reaction becomes inactive, so the oxygen consumption rate also gradually decreases, finally reaches the lower limit K2, and thereafter aeration is continued. Even so, the value of K2 is almost maintained.
[0012]
Point a on curve 1 is a stage where a considerable amount of ammonia nitrogen remains in the wastewater and there is room for nitrification reaction to proceed, point b is the stage when nitrification reaction is almost complete, and point c is the stage where nitrification reaction is completed. This is the stage of excessive aeration after completion. The reason why the oxygen consumption rate does not become zero and maintains the lower limit K2 even in this excessive aeration stage is that the microorganisms mixed in the wastewater consume oxygen mainly in a state where nutrient sources (BOD components and ammonia nitrogen) are depleted. However, the self-decomposition causes a problem that the sedimentation property of the microorganism (sludge) is lowered as described above, and the treated water after the precipitation treatment becomes cloudy and the transparency is deteriorated.
[0013]
The tendency of curve 1 in batch processing varies greatly depending on the properties of the wastewater, the water temperature, the activity and concentration of the mixed microorganisms, and the like. Even when the initial load of ammonia nitrogen is almost the same, the curve 2 is obtained under conditions where the nitrification reaction is active such as a high water temperature, and conversely, the curve 3 is obtained under conditions where the nitrification reaction is inactive.
[0014]
On the other hand, in the continuous inflow type nitrification tank according to the present invention, the influent wastewater stays in the nitrification for several hours and immediately mixes with the existing wastewater that has undergone nitrification treatment. A constant oxygen consumption rate is exhibited in the mixed state.
[0015]
When the oxygen consumption rate of this mixed solution is applied to the curve 1 in the batch process of FIG. 2, when the oxygen consumption rate is the same as the point a, a considerable amount of ammonia nitrogen remains in the mixed solution and the nitrification reaction proceeds. It is assumed that the nitrification reaction is almost complete when it is the same as point b, and that it is in the state of excessive aeration after completion of the nitrification reaction when it is the same as point c. Is done.
[0016]
In addition, various factors affecting the nitrification reaction in this continuous inflow type nitrification tank, such as the amount of influent wastewater and the concentration of ammoniacal nitrogen, the temperature of the mixture, the microorganism concentration (MLSS) of the mixture, the amount of aeration air, Focusing on the aeration air volume that can be controlled most easily, the region A in which the oxygen consumption rate of the mixed solution includes the point a is a state in which the aeration air amount is insufficient, and the region B including the point b has an aeration air amount. It can be estimated that the region C which is in an appropriate state and includes the point c is in a state where the aeration air volume is excessive.
[0017]
From the above viewpoint, it has been proposed in the prior art to detect the oxygen consumption rate of the mixed liquid and to control the amount of aeration air according to the detected value. However, in such a method, for example, the oxygen consumption rate values are approximated at points b and c shown in FIG. 2, and it is not possible to determine whether the aeration air volume is appropriate or excessive. is there. Based on such a background, the present invention has been made paying attention to the rate of change of the oxygen consumption rate.
[0018]
That is, paying attention to the fact that the rate of change of the oxygen consumption rate when the mixed solution is processed in batches is relatively large in the region A, small in the region B, and almost zero in the region C, it is aerated by the magnitude of the rate of change. The air volume is adjusted.
[0019]
Specifically, the sampling pump 34 is operated once every 10 minutes to 2 hours, and the mixed solution in the nitrification tank 14 is collected from the sampling tube 32 into the batch tank 36. Next, the air pump 38 is operated to supply a sufficient amount of air to the batch tank 36, and the oxygen consumption rate of the mixed solution is detected by the sensor 40 while the nitrification reaction is progressed with the collected mixed solution. The detection result is transmitted to the computing unit 42, and the computing unit 42 obtains, for example, the difference between the oxygen consumption rate after 5 minutes from the start of the batch reaction and the oxygen consumption rate after 8 minutes. As shown in FIG. 2, since the oxygen consumption rate in the batch reaction usually decreases with time, the difference in the oxygen consumption rate is obtained as a decrease with time.
[0020]
The calculator 42 is preset with a preferable range as the amount of decrease in oxygen consumption rate, and the amount of decrease with time is smaller than the set range by comparing this set range with the amount of decrease with time based on the measurement result. The controller 44 sends a signal to increase the aeration air volume when it is large, maintain the current aeration air volume when the temporal decrease amount is within the set range, and decrease the aeration air volume when the temporal decrease amount is smaller than the set range. Send to. The controller 44 adjusts the aeration air volume by controlling the rotational speed of the blower 18 based on the signal from the computing unit 42.
[0021]
Figure 3 is a relationship diagram showing time reduction of oxygen consumption rate in the batch processing of the mixed solution mentioned above collected, batch oxygen consumption rate K ₁₁ and after a predetermined time Δt has elapsed at time T ₁ starts after a few minutes of the reaction The difference from the oxygen consumption rate K ₁₂ at time T ₂ is calculated as the decrease amount ΔK of the oxygen consumption rate with time. The predetermined time Δt is preferably 3 minutes or more, and if it is less than this, the amount of decrease ΔK of the oxygen consumption rate calculated with time becomes small, and the measurement accuracy of the oxygen consumption rate of the sensor 40 and the influence of disturbance are affected. Since it becomes large, it is not preferable. The oxygen consumption rate decrease ΔK at this time is compared with a set range ΔKs as an appropriate value set in the calculator 42. According to the experiment results of the present inventor, when the predetermined time Δt is 3 to 5 minutes as the setting range ΔKs, the setting range ΔKs is about 1 to 3 mg-O ₂ / L · h converted per minute. It has been found to be preferable. The reason for starting the measurement of the oxygen consumption rate from time T _{1 a} few minutes after the start of the batch reaction is that the reaction is unstable immediately after the start of the batch reaction, and the measured value of the oxygen consumption rate varies greatly. This is because it takes about 4 to 6 minutes for the reaction to stabilize.
[0022]
FIG. 4 is a diagram illustrating the relationship between the time-dependent decrease amount ΔK of the oxygen consumption rate and the amount of aeration air in the nitrification tank 14. In FIG. 4, the setting range ΔKs has ΔKs1 as a lower limit value and ΔKs2 as an upper limit value. When the amount of decrease with time ΔK is in this range, it is assumed that the nitrification reaction in the nitrification tank 14 is almost completed, Since it can be determined that the aeration air volume is also appropriate, the current aeration air volume Qs is maintained. When the amount of decrease with time ΔK is smaller than the lower limit value ΔKs1, it is assumed that the nitrification reaction is in the state of excessive aeration, so the amount of aeration air is reduced according to the difference from the lower limit value ΔKs1. On the other hand, when the amount of decrease with time ΔK is larger than the upper limit value ΔKs2, there is a considerable amount of ammonia nitrogen remaining in the mixed solution, and there is room for the nitrification reaction to proceed, and the amount of aeration air is insufficient. Since the determination can be made, the aeration air volume is increased according to the difference from the upper limit value ΔKs2. However, if the time-dependent decrease amount ΔK is larger than the predetermined value ΔKa, it is estimated that the cause is other than a shortage of aeration air volume, for example, a decrease in microbial activity or a decrease in microbial concentration due to low water temperature, and the aeration air volume is the upper limit. Qa is maintained. The upper limit of the aeration air volume is naturally limited by the capacity of the installed blower 18.
[0023]
The liquid mixture collected in the batch tank 36 is returned to the nitrification tank 14 with the above-described control based on the amount of decrease in oxygen consumption with time as a unit of operation, and the batch tank 36 is emptied. . Hereinafter, the proper operation in the nitrification tank 14 is maintained by repeating the control by batch reaction once every 10 minutes to 2 hours as described above. As for the frequency of this repeated operation, the interval is shortened when the load variation of ammonia nitrogen in the influent wastewater is large, and the interval is lengthened when the load variation is small.
[0024]
FIG. 5 is a view showing a preferred example of the sampling position of the mixed solution. There is a case where the nitrification tank 14 is formed in a horizontally long shape and the inflow port 16 and the outflow port 22 of the waste water are largely separated. In such a case, the waste water forms a kind of plug flow in the nitrification tank 14, and a concentration difference occurs between the inflow side and the outflow side of the waste water. That is, since the nitrification reaction does not proceed sufficiently on the inflow side, the concentration of ammonia nitrogen is relatively high and the concentration of nitrate nitrogen is relatively low. On the other hand, since the nitrification reaction has sufficiently progressed on the outflow side, the ammonia nitrogen concentration is relatively low and the nitrate nitrogen concentration is relatively high. The object of the present invention is to achieve the nitrification reaction in the nitrification tank almost completely. Therefore, it is preferable that the sampling position of the mixed solution is in the vicinity of the outlet 22. This collection position may be the wastewater outflow passage 23 from the nitrification tank 14.
[0025]
According to the embodiment of the present invention, the progress of the nitrification reaction in the nitrification tank 14 can be grasped in a timely and accurate manner by measuring the amount of decrease in oxygen consumption rate over time in the batch reaction of the mixed solution. it can. And since the aeration air volume in the nitrification tank 14 is controlled based on this measurement result, the nitrification reaction can be achieved almost completely with the minimum necessary aeration air volume, and excessive aeration can be prevented.
[0026]
In the above embodiment, the case where the aeration air volume is automatically controlled using the controller 44 has been described. However, the present invention is not limited to this. For example, the liquid mixture in the nitrification tank is manually sampled, and the oxygen consumption rate in the batch reaction of the sampling liquid is quickly measured in the analysis chamber or the like. Based on this, the aeration air volume in the nitrification tank may be manually adjusted.
[0027]
In the above embodiment, as shown in FIG. 5, the case where the increase / decrease amount of the aeration air volume is controlled linearly according to the difference between the measured value of the decrease amount of oxygen consumption with time and the set value has been described. The aeration air volume may be increased or decreased in stages. Further, although the above description has been made with a predetermined range having a lower limit value and an upper limit value as the set value, the present invention is not limited to this, and the set value can be controlled at one point.
[0028]
【The invention's effect】
As described above, according to the present invention, excessive aeration in the nitrification tank can be prevented, and the nitrification reaction can be almost completely achieved with the minimum necessary amount of aeration air.
[Brief description of the drawings]
FIG. 1 is an apparatus configuration diagram for explaining an embodiment of the present invention. FIG. 2 is a model diagram illustrating the behavior of the oxygen consumption rate of a mixed solution in a nitrification reaction. FIG. 3 is an oxygen consumption in a batch treatment of the mixed solution. Fig. 4 is a graph illustrating the relationship between the amount of decrease in oxygen consumption rate with time and the amount of aeration air in the nitrification tank. Fig. 5 is a diagram illustrating a preferred example of the sampling position of the mixed solution. Explanation of]
DESCRIPTION OF SYMBOLS 10 ... Inflow pipe 12 ... Denitrification tank 14 ... Nitrification tank 16 ... Inlet 18 ... Blower 22 ... Outlet 32 ... Sampling pipe 36 ... Batch tank 40 ... (Oxygen consumption rate) sensor 42 …… Calculator 44 …… Controller

Claims (4)

Ammonia in the wastewater is introduced by continuously inflowing the wastewater from the inlet of the nitrification tank and outflowing from the outlet, and aerating the mixed solution of the wastewater and microorganisms in the nitrification tank so as to be in an aerobic condition. In the nitrification method of wastewater in which nitrous acid is nitrified by the action of the microorganism, the mixed solution collected from the nitrification tank is batch-treated under aerobic conditions, and a time T several minutes after the start of batch reaction of the mixed solution the difference between the oxygen consumption rate of oxygen consumption rate and time T ₁ at time T _2, after a predetermined time in _one measure is defined as time reduction of oxygen consumption rate, if the time reduction is larger than the set value A method for nitrification of wastewater, characterized in that the aeration air volume is increased and the aeration air volume is decreased when the decrease over time is smaller than a set value. _2. The nitrification method for wastewater according to claim 1, wherein the set value is set so that a value converted per minute is 1 to 3 mg-O ₂ / L · h.     The method for nitrification of wastewater according to claim 1, wherein an increase / decrease amount of the aeration air volume is controlled in accordance with a difference between a measurement value of the oxygen consumption rate decrease with time and a set value.     The wastewater nitrification method according to claim 1, wherein a sampling position of the mixed solution for performing batch reaction of the mixed solution is set in the vicinity of the wastewater outlet of the nitrification tank.

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