JP7008007B2 - Step-inflow multi-stage nitrification denitrification method and system - Google Patents

Description

The present invention relates to a step-inflow multi-stage nitrification denitrification method and system for biologically nitrifying and denitrifying organic wastewater containing nitrogen such as sewage, urine, and other industrial wastewater, and sewage having a particularly large fluctuation in inflow. It relates to a step-inflow type multi-stage nitrification denitrification method and a system suitable for use in treatment and the like.

Conventionally, the biological nitrification denitrification method has been widely used for the treatment of wastewater containing a nitrogen component. In the biological nitrification denitrification method, an anaerobic tank is provided on the upstream side and an aerobic tank is provided on the downstream side. It is denitrified in an anaerobic tank as a carbon source.

In addition, the step inflow type multi-stage nitrification denitrification method was developed for the purpose of improving the efficiency of nitrogen removal in this biological nitrification denitrification method. In this step inflow type multi-stage nitrification denitrification method, the anaerobic tank and the aerobic tank are regarded as one unit, and these units are arranged in series in multiple stages, and the inflow water is separately injected into the anaerobic tank of each unit to improve the efficiency of nitrogen removal. It is intended. In the step inflow type nitrification denitrification method, the nitrogen removal rate improves as the number of units of the anaerobic tank and the aerobic tank arranged in series increases, but in reality, there are many examples of operation in two or three stages. In the design concept of the conventional step inflow type multi-stage nitrification denitrification method, the dispensing rate of the inflow water flowing into each anaerobic tank is fixed to a certain ratio, and usually it is divided into equal parts for operation.

Japanese Unexamined Patent Publication No. 01-242198 Japanese Unexamined Patent Publication No. 11-244891

Kazumasa Kamoike and 2 others, "Optimization of Air Volume Control Operation Using Ammonia Sensor by Activated Sludge Model", Journal of Environmental System Measurement and Control Society, 2015, Vol. 20, Volume 2, 3 Merger, p. 3-10 Ryo Yabushina, 2 others, "Flower structure considering uniform inflow in multi-step inflow nitrification denitrification method", 2015, Proceedings of the 52nd Sewerage Research Presentation, p.593-595 "Frequently seen sewerage terms", [online], 2014/7/11, JS Technology Development Information Email No. 152, Japan Sewage Works Agency, [Search on September 25, 2018], Internet <URL: https://www.jswa.go.jp/g/g5/g5m/mb/pdf/152-1 .pdf>

In the above step inflow type multi-stage vitrification denitrification method, the design concept is to distribute the inflow water to the anaerobic tank of each unit in equal amounts and equalize the load in each stage, but it is very difficult to actually distribute evenly. It is difficult, for example, even if the inflow weir is set so that the inflow becomes even at a certain time, there is a problem that the inflow ratio changes if the flow rate changes (see, for example, Non-Patent Document 3).

In addition, there are cases where sewage does not flow as expected in actual facilities, and it is known that the flow of inflow water is biased at the site, but the specific amount cannot be grasped. When the flow rate is significantly different from that in normal times, the flow rate distribution is greatly biased, which may affect the processing. For these reasons, it was difficult to actually distribute and adjust the inflow water to an appropriate amount to perform stable treatment (see, for example, Non-Patent Document 2).

The present invention has been made in view of the above points, and an object thereof is a step inflow type capable of performing a stable step inflow type multi-stage nitrification denitrification treatment and further reducing the nitrogen concentration of the treated water. To provide a multi-stage nitrification denitrification method and system.

The present invention is a step inflow type multi-stage nitrification denitrification method in which an anaerobic tank and an aerobic tank are regarded as one unit, a plurality of the units are connected in series, and inflow water having a fluctuating amount of water is distributed and injected into the anaerobic tank of each unit. , The inflow amount of the inflow water distributed and injected into the anaerobic tank of the final unit is fixed at a predetermined constant flow rate , while the remaining fluctuating inflow water is the anaerobic tank of the remaining units on the front stage side of the final unit. It is characterized in that it is distributed and injected according to the fluctuation .
The inventor of the present application sets the inflow amount of the inflow water to be distributed and injected (divided water supply) into the anaerobic tank of the final unit to a constant flow rate (fixed flow rate), so that the step ratio constant operation (inflow water is each) which is the conventional method. It was found that the treated water quality equivalent to that of the operation of distributing and supplying to the anaerobic tank of the unit at a constant ratio can be obtained.
That is, according to the present invention, stable step inflow type multi-stage nitrification denitrification treatment can be easily performed without accurately adjusting the distribution of the inflow water to the anaerobic tank of each unit.
Further, according to the method of the present application, it is possible to improve the deterioration of water quality due to the large bias in the flow rate distribution during the time period when the inflow water amount fluctuates greatly.

Further, in addition to the above-mentioned characteristics, the present invention is characterized in that the inflow amount of the inflow water into the anaerobic tank of the final unit is 20 to 60% of the daily inflow amount.
This makes it possible to perform a stable step inflow type multi-stage nitrification denitrification treatment.

Further, the present invention is the final unit in the step inflow type multi-stage nitrification denitrification method in which the anaerobic tank and the aerobic tank are regarded as one unit, the units are connected in series, and the inflow water is distributed and injected into the anaerobic tank of each unit. The inflow rate of the inflow water distributed and injected into the anaerobic tank is set to a constant flow rate, the aerobic tank of the final unit is divided into two tanks, and the DO value of the upstream side of the divided two tanks is predetermined. By controlling the value to be less than or equal to the value, the nitrification reaction and the denitrification reaction are simultaneously promoted in the aerobic tank on the upstream side.
If the DO value of the aerobic tank is set to a predetermined value or less, the nitrogen concentration of the treated water will be reduced due to the simultaneous progress of nitrification and denitrification, but the inflow amount of the inflow water to the anaerobic tank of the final unit will be a constant flow rate. In the present invention, it is important to divide the aerobic tank of the final unit into two tanks and control the DO value of the aerobic tank on the upstream side to a predetermined value or less in order to reduce the nitrogen concentration. I found it. Thereby, the nitrogen concentration of the treated water can be further reduced.
The aerobic tank of the final unit is divided by the tank wall or partition, as well as when the tank is partitioned by the tank wall or structurally by a partition to give the tank structural strength. Even if it is not structurally divided, it may be functionally divided by forming zones having different DO concentrations by adjusting the amount of air or changing the model of the air diffuser. In short, at least the aerobic tank may be functionally divided.

Further, in addition to the above features, the present invention sets the NH ₄ -N set value of the upstream aerobic tank so that the DO value of the upstream aerobic tank is equal to or less than a predetermined value, and the set value thereof. It is characterized in that the amount of air supplied to the aerobic tank on the upstream side is controlled so as to be.
Thereby, the DO value of the aerobic tank on the upstream side can be controlled to a predetermined value or less.

Further, in addition to the above-mentioned features, the present invention is characterized in that the amount of air supplied to the aerobic tank on the upstream side is controlled by using an ammonia sensor.
Thereby, the amount of air supplied to the aerobic tank on the upstream side can be appropriately controlled.

Further, in the present invention, an anaerobic tank and an aerobic tank are regarded as one unit, and a plurality of the units are connected in series, and inflow water having a fluctuating amount of water is distributed and injected into the anaerobic tank of each unit. In the system, a constant flow rate supply means is provided to fix the inflow amount of the inflow water distributed and injected into the anaerobic tank of the final unit to a predetermined constant flow rate , while the remaining fluctuating inflow water is previously set to the stage before the final unit. It is characterized by dispensing and injecting into the anaerobic tank of the remaining units on the side according to the fluctuation .
According to the present invention, a stable step inflow type multi-stage nitrification denitrification treatment can be easily performed without accurately adjusting the distribution of the inflow water to the anaerobic tank of each unit.
In addition, it is possible to improve the deterioration of water quality due to the large bias in the flow rate distribution during the time when the inflow water volume fluctuates greatly.

According to the present invention, a stable step inflow type multi-stage nitrification denitrification treatment can be performed, and further, the nitrogen concentration of the treated water can be reduced.

It is a figure which shows the step inflow type multi-stage nitrification denitrification system 1-1. It is a figure which shows the step inflow type multi-stage nitrification denitrification system 1-2. It is a figure which shows the step inflow type multi-stage nitrification denitrification system 1-3. It is a figure which shows the step inflow type multi-stage nitrification denitrification system 1-4. It is a figure which shows the measurement result of the treated water N concentration operated by various operation methods. It is a figure which shows the measurement result of the treated water N concentration operated by various operation methods. It is a figure which shows the measurement result of the 5th tank DO value and the treated water N concentration operated by various operation methods. It is a figure which shows the measurement result of the 5th tank NH ₄ -N value and the treated water N concentration operated by various operation methods.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto. FIG. 1 is a diagram showing a step inflow type multi-stage nitrification denitrification system (treatment flow) 1-1 according to the first embodiment of the present invention. The step inflow type multi-stage nitrification denitrification system 1-1 includes an anaerobic tank A-1 and an aerobic tank O-1 unit N-1, and an anaerobic tank A-2 and an aerobic tank O-2 unit N-2. Is connected in series, and the inflow water (sewage) is distributed and injected into the anaerobic tanks A-1 and A-2 of each unit N-1 and N-2, respectively, in a two-stage step treatment system. Further, a settling basin S is installed after the aerobic tank O-2, and the sludge settled in the settling basin S is returned to the anaerobic tank A-1.

In the step inflow type multi-stage nitrification denitrification system 1-1 configured as described above, the inflow water is separately injected into the first-stage anaerobic tank A-1 and the second-stage anaerobic tank A-2. .. Then, in this embodiment, only a predetermined constant flow rate of the inflow water flowing into the step inflow type multi-stage nitrification denitrification system 1-1 is dividedly injected into the second stage anaerobic tank A-2. The inflow water other than the above is configured to be separately injected into the anaerobic tank A-1 of the first stage. In order to inject a constant flow rate of inflow water into the anaerobic tank A-2 of the second stage, a constant flow rate supply means R is installed in the flow path. A pump is preferable as the constant flow rate supply means R, but other various means such as various weir type flow meters can also be used as long as the inflow at a constant flow rate is possible.

In the step-inflow type multi-stage nitrification denitrification system 1-1 configured as described above, the nitrogen component mainly composed of ammoniacal nitrogen (NH ₄ -N) flowing into the first-stage anaerobic tank A-1 is one-stage. It flows into the aerobic tank O-1 of the eye and is converted to nitrate nitrogen and nitrite nitrogen (NO _X- N) by the nitrification reaction in this aerobic tank O-1. The outflow water from the aerobic tank O-1 containing nitrate nitrogen and nitrite nitrogen (NO _X -N) flows directly into the anaerobic tank A-2 of the second stage and is separately injected into the anaerobic tank A-2. By the denitrification reaction that utilizes the organic matter in the inflow water as a carbon source, it is converted to nitrogen gas and nitrogen is removed from the water. The nitrogen component mainly composed of ammoniacal nitrogen (NH ₄ -N) that has flowed into the anaerobic tank A-2 flows into the second-stage aerobic tank O-2, and nitrification occurs in this aerobic tank O-2 due to the nitrification reaction. Convert to sex nitrogen and nitrite nitrogen (NO _X -N). The effluent from the aerobic tank O-2 is solid-liquid separated in the settling pond S, and part of the nitrate nitrogen and nitrite nitrogen (NO _X- N) generated in the aerobic tank O-2 is used as return sludge. Nitrogen is removed by denitrification reaction that uses the organic matter in the inflow water that flows into the anaerobic tank A-1 of the first stage and is separately injected into the anaerobic tank A-1 as a carbon source. ..

Conventionally, the flow rate of inflow water (sewage) has been adjusted by adjusting the opening of the gate or adjusting the inflow weir to fix the inflow water distribution rate to a certain ratio or divide it into equal parts. Even if the amount of inflow water fluctuated, the gate opening and the height of the weir were adjusted by hand in order to maintain the inflow water distribution rate. However, in these conventional methods, the inflow water injection rate differs from the set conditions, which may cause instability in nitrogen removal. For example, when the amount of inflow water into the anaerobic tank A-2 in the second stage is small, the carbon source required for the denitrification treatment in the anaerobic tank A-2 is insufficient, and nitrate nitrogen and nitrate nitrogen and Causes residual nitrite nitrogen (NO _X -N). Further, when the inflow amount of the inflow water into the anaerobic tank A-2 becomes large, the shortage of the carbon source required for the denitrification treatment in the anaerobic tank A-2 can be avoided, but the aerobic tank O-2 Increased organic and nitrogen loadings cause residual ammoniacal nitrogen (NH ₄ -N).

On the other hand, in the present invention, the inflow amount of the inflow water into the anaerobic tank A-2 of the second stage unit N-2, which is the final unit, that is, the inflow amount Q2 of the inflow water in the final step inflow step is constant. The amount of water is maintained, and the remaining inflow water is configured to flow into the anaerobic tank A-1 of the first stage as Q1. According to the present invention, it is possible to avoid a shortage of carbon sources required for denitrification treatment in the second-stage anaerobic tank A-2, and the organic matter load and nitrogen in the second-stage aerobic tank O-2. Since the load can be kept in an appropriate range, stable step inflow type multi-stage nitrification denitrification treatment can be achieved. The inflow amount Q2 of the inflow water into the anaerobic tank A-2 of the second stage is preferably 20 to 60% (0.2 to 0.6Q) of the average daily treated water amount (Q). The optimum amount of water to be sent to the anaerobic tank A-2 in the second stage (water supply ratio) differs depending on the DO set value of the aerobic tank-2.

FIG. 2 is a diagram showing a step inflow type multi-stage nitrification denitrification system (treatment flow) 1-2 according to the second embodiment of the present invention. The step inflow type multi-stage nitrification denitrification system 1-2 includes the anaerobic tank A3 and the aerobic tank O3 in addition to the unit N-1 and the unit N-2 similar to the step inflow type multi-stage nitrification denitrification system 1-1. Units N-3 are further connected in series, and inflow water (sewage) is distributed and injected into the anaerobic tanks A-1, A-2, and A-3 of each unit N-1, N-2, and N-3, respectively. It is a step-step processing system. A settling basin S is installed after the aerobic tank O-3, and the sludge settled in the settling basin S is returned to the anaerobic tank A-1. In the case of the treatment method of this step inflow type multi-stage nitrification denitrification system 1-2, the principle of nitrogen removal is the same as described above.

In the step inflow type multi-stage nitrification denitrification system 1-2 configured as described above, the inflow water amount Q3 of the inflow water to the final stage anaerobic tank A-3 is set to a constant amount, and the remaining anaerobic tanks A-1 and Let the inflow amount of the inflow water to A-2 be Q1 and Q2, respectively. The inflow water amount Q2 to the anaerobic tank A-2 in the second stage (the stage immediately before the final stage, the middle stage) may be a constant flow rate, but the inflow water amount Q3 in the anaerobic tank A-3 in the final stage is kept constant. In this state, even if the amount of water Q2 flowing into the anaerobic tank A-2 fluctuates, the effect on the nitrogen concentration of the treated water is small. By keeping the inflow amount of the inflow water in the final step step constant, it is possible to avoid a shortage of carbon sources required for denitrification treatment, and to keep the organic matter load and nitrogen load of the aerobic tank O-3 within an appropriate range. From these facts, stable step inflow type multi-stage nitrification denitrification treatment can be achieved. As described above, it is extremely effective to set the inflow rate of the final step inflow step to a constant flow rate.

By the way, as disclosed in Patent Document 1, when the DO value of the aerobic tank is kept at 1 mg / L or less and the nitrification reaction is promoted, the denitrification reaction also proceeds at the same time in the aerobic tank, and the treated water is treated. It is possible to reduce the nitrogen concentration in the water. Also in the present invention, a method for reducing the nitrogen concentration of treated water can be applied by keeping the DO value of the aerobic tank O at 1 mg / L or less and promoting the simultaneous progress of nitrification and denitrification in the aerobic tank O.

Then, when applying the above method to the step inflow type multi-stage nitrification denitrification system 1-1, 1-2, the inventor of the present application found that the DO setting of the aerobic tank O in the final step inflow step was to reduce the nitrogen concentration of the treated water. We found that the effect was great.

FIG. 3 is a diagram showing a step-inflow type multi-stage nitrification denitrification system 1-3 according to a third embodiment in consideration of reducing the nitrogen concentration of treated water by setting a DO value. In the case of this embodiment, the final step inflow step, that is, the aerobic tank O-2 of the final unit N-2 is divided into two tanks O (1) and O (2), and the upstream side of the divided two tanks. By controlling the DO value of the aerobic tank O (1) to be equal to or less than a predetermined value (1 mg / L or less in this example), the nitrification reaction and denitrification are performed in the aerobic tank O (1) on the upstream side. It is configured to allow the reaction to proceed simultaneously. Hereinafter, a specific description will be given.

The nitrogen component mainly composed of ammoniacal nitrogen (NH ₄ -N) that has flowed into the first-stage anaerobic tank A-1 is nitrate nitrogen and nitrite nitrogen due to the nitrification reaction in the first-stage aerobic tank O-1. Convert to (NO _X -N). In this case as well, by keeping the DO value at 1 mg / L or less, the reaction of nitrogen removal by the simultaneous progress of nitrification and denitrification occurs. Since the nitrate nitrogen and nitrite nitrogen (NO _X -N) components are removed by the denitrification reaction using the organic matter in the inflow water separately injected into the anaerobic tank A-2 of the second stage as a carbon source, In the situation where the organic matter supplied to the second-stage anaerobic tank A-2 is not insufficient even if there is no nitrogen concentration reduction effect due to the simultaneous progress of nitrification and denitrification in the first-stage aerobic tank O-1, 1 Since the nitrogen component mainly composed of ammoniacal nitrogen (NH ₄ -N) flowing into the anaerobic tank A-1 of the second stage is removed by the anaerobic tank A-2 of the second stage, the aerobic tank O- of the first stage The effect of reducing nitrogen concentration by simultaneous progress of nitrification and denitrification when proceeding with nitrification in a state where the DO value is reduced to 1 mg / L or less in 1 is relatively small. In addition, if the nitrification reaction becomes insufficient and ammoniacal nitrogen (NH ₄ -N) remains due to the reduction of the DO value in the first-stage aerobic tank O-1, the residual ammoniacal nitrogen (NH 4-N) remains. NH ₄ -N) flows into the aerobic tank O-2 of the second stage as it is without changing in the anaerobic tank A-2 of the second stage, which causes an increase in the nitrogen concentration of the treated water. Therefore, in the first-stage aerobic tank O-1, it is necessary to set the DO setting value at which the nitrification reaction proceeds sufficiently. In a situation where the ammoniacal nitrogen (NH ₄ -N) in the first-stage aerobic tank O-1 cannot be monitored, avoid excessively lowering the DO value of the first-stage aerobic tank O-1 and use the second stage. It is preferable to set the DO value at which nitrification sufficiently proceeds in the aerobic tank O-2.

The nitrogen component mainly composed of ammoniacal nitrogen (NH ₄ -N) that has flowed into the second-stage anaerobic tank A-2 flows into the second-stage aerobic tank O-2 (O (1) + O (2)). , It is converted to nitrate nitrogen and nitrite nitrogen (NO _X- N) by nitrification reaction in this aerobic tank O-2. This aerobic tank O-2 runoff water is solid-liquid separated in the settling basin S, and nitrogen components mainly composed of nitrate nitrogen and nitrite nitrogen (NO _X- N) flow out as the supernatant water of the settling basin S. This is the nitrogen concentration of the treated water. Therefore, the nitrogen concentration reduction effect due to the simultaneous progress of nitrification and denitrification when the DO value in the second stage aerobic tank O-2 is reduced to 1 mg / L or less is the effect of reducing the nitrogen concentration of the treated water. growing. By keeping the inflow amount of the inflow water in the final step step constant, it is possible to avoid a shortage of carbon source required for denitrification treatment, and the organic matter load of the second stage aerobic tank O-2 and This is due to the effect of the present invention that stable step inflow type multi-stage nitrification denitrification treatment can be achieved because the nitrogen load can be kept in an appropriate range.

The DO value setting in the second-stage aerobic tank O-2 is not to set the DO value to 1 mg / L or less in the entire aerobic tank O-2, but to set the DO value in the upstream split aerobic tank O (1). Set the DO value to 1 mg / L or less, and set the DO value to 1 to 2 mg / L so that ammoniacal nitrogen (NH ₄ -N) does not remain in the split aerobic tank O (2) on the downstream side. Is preferable.

The division of the divided aerobic tank O (1) and the divided aerobic tank O (2) is structurally divided when the tank is partitioned by the tank wall and by a partition for giving the structural strength of the tank. Even if it is not structurally divided by the tank wall or partition, it may be functionally divided by forming zones with different DO concentrations by adjusting the air volume or changing the model of the air diffuser. .. In short, at least the aerobic tank may be functionally divided.

The tank capacities of the split aerobic tank O (1) and the split aerobic tank O (2) can exert the effect of reducing the nitrogen concentration even when O (1) <O (2), but O (1) ≧ O (2). This has the effect of reducing the (NH ₄ -N + NO _X- N) concentration of the outflow of the split aerobic tank O (1) due to the simultaneous progress of the nitrification reaction and the denitrification reaction in the split aerobic tank O (1). Is preferable, and the split aerobic tank O (2) is more preferably one-third or less of the split aerobic tank O (1).

The DO setting value of the split aerobic tank O (1) is preferably 1 mg / L or less, and the DO set value of the split aerobic tank O (1) that minimizes the nitrogen concentration of the treated water is 0.5 mg / L. More preferably, it is 0.3 mg / L or less. When a DO sensor is used, accurate control of the amount of air becomes difficult because the influence of the sensor measurement error becomes large at such a low DO. In addition, if the air volume is controlled at a low DO value by the DO sensor, there is a risk of residual ammoniacal nitrogen (NH ₄ -N) in the aerobic tank O-2, which may lead to deterioration of the water quality of the treated water. ..

In such low DO air volume control, it is effective to apply an ammonia sensor instead of the DO sensor. When an ammonia sensor is used to control the air volume of the split aerobic tank O (1) on the upstream side, stable air volume control is possible and the ammonia concentration can be continuously monitored, so ammonia nitrogen in the treated water. (NH ₄ -N) It is also an effective means to avoid residue. The ammonia sensor is preferably installed at the end of the split aerobic tank O (1).

First, the sedimentation pond overflow water was used as raw water for treatment using the step inflow type multi-stage nitrification denitrification system (treatment flow) 1-4 shown in FIG. In the system 1-4 of FIG. 4, the water tanks are divided into 6 tanks, and the capacities of the water tanks are the same. Ammonia nitrogen (NH ₄ -N) in the raw water is 30 mg / L per day on average, 18 to 24 mg / L per day on average, and the water temperature in the aeration tank is 20 to 23 ° C. The MLSS of the tank was set to 2,000 mg / L and the results were examined. Evaluation of nitrogen removal performance is based on the concentration of runoff water (NH ₄ -N + NO _X -N) from the 6th tank (hereinafter also referred to as "treated water N concentration") and the nitrogen removal rate (raw water NH ₄ -N: daily average value). And NH ₄ -N + NO _X -N of the 6th tank runoff water: calculated from the daily average value).

<Example 1>
Under the operating conditions of the two-stage step processing in which the inflow of raw water (inflow water) is divided and injected into the first tank and the fourth tank, the conventional method 1 in which the opening of the step inflow gate is fixed and the step inflow opening are set to the amount of inflow water. A comparative study was carried out between the conventional method 2 in which the amount of raw water inflow in the fourth tank was adjusted to a constant amount by pumping water, and the method according to the present invention, which was empirically adjusted manually according to the fluctuation, and the following comparative example. The amount of raw water inflow in the first tank is also referred to as Q1, and the amount of raw water inflow in the fourth tank is also referred to as Q4. The 1st and 4th tanks were designated as anaerobic tanks, and the 2nd, 3rd, 5th and 6th tanks were designated as aerobic tanks. The DO value of each aerobic tank was set to 1 mg / L, and the amount of air was controlled.

In the comparative example, the inflow of raw water into the 4th tank was eliminated, and the total amount of the raw water flowed into the 1st tank.
In the conventional method 1, the gate opening is empirically adjusted so that Q1: Q4 = 60: 40, and the gate opening is fixed regardless of the fluctuation of the raw water amount. In the conventional method 1, it was visually confirmed that there was a time zone in which Q4 was clearly reduced, and the step inflow ratio fluctuated with time due to the fluctuation of the raw water flow rate.
In the conventional method 2, the opening degree of the gate is empirically appropriately adjusted so that Q1: Q4 = 60: 40 according to the fluctuation of the raw water flow rate.
In Example 1 according to the present invention, Q4 was kept at a constant flow rate by pumping water, and the remaining raw water was used as Q1 and flowed into the first tank. Q4 was set to 40% of the average daily inflow of water.

FIG. 5 is a diagram showing the operation results of each of the above operation methods. Table 1 below shows the daily average value of the treated water N concentration and the nitrogen removal rate. As shown in FIGS. 5 and 1, the N concentration of the treated water was lower in the conventional method 1 and the conventional method 2 than in the comparative method, and the effect of the step inflow type multi-stage nitrification denitrification method was confirmed. Further, in Example 1 of the present invention, the concentration of treated water N was lower and the nitrogen removal rate was higher than that of the conventional method 1 and the conventional method 2. From this result, it is possible to avoid the shortage of carbon source required for denitrification treatment by keeping the amount of raw water flowing into the anaerobic tank in the final step step constant, and it is possible to avoid the shortage of carbon sources in the 5th and 6th tanks. Since it is possible to keep the organic matter load and the nitrogen load within an appropriate range, the effectiveness of the present invention that can achieve a stable step inflow type multi-stage nitrification denitrification treatment has been confirmed.

<Example 2>
Under the operating conditions of the three-stage step processing in which the inflow of raw water (inflow water) is dividedly injected into the first, third, and fifth tanks, the conventional method 3 and the fifth tank in which the opening of the step inflow gate is fixed are fixed. A comparative study was carried out with the method according to the present invention (Examples 2-1 and 2-2) in which the inflow of raw water was set to a constant amount by pumping water. The inflow amount of raw water in the first tank is also referred to as Q1, the inflow amount of raw water in the third tank is referred to as Q3, and the inflow amount of raw water in the fifth tank is also referred to as Q5. The first, third, and fifth tanks were anaerobic tanks, and the second, fourth, and sixth tanks were aerobic tanks. The DO value of each aerobic tank was set to 1 mg / L, and the amount of air was controlled.

In the conventional method 3, the gate opening is empirically adjusted so that Q1: Q3: Q5 = 1: 1: 1 (equal inflow), and the gate opening is fixed regardless of the fluctuation of the raw water amount. In the conventional method 3, it was visually confirmed that there was a time zone in which Q3 and Q5 were clearly reduced, and the step inflow ratio fluctuated with time due to the fluctuation of the raw water flow rate.
In Example 2-1 according to the present invention, Q5 is kept at a constant flow rate of 33% of the average daily inflow rate by pumping water, and the remaining raw water flows into the first and third tanks with Q1: Q3 = 1: 1. The driving method used was used. The inflow amount of Q1 and Q3 was adjusted by adjusting the gate opening degree, and the gate opening degree was fixed regardless of the fluctuation of the raw water amount. In Example 2-1 it was visually confirmed that there was a time zone in which Q3 was clearly low, and the inflow ratio of Q1 and Q3 fluctuated with time due to the fluctuation of the raw water flow rate.
In Example 2-2 according to the present invention, an operation method was used in which Q3 and Q5 were kept at a constant flow rate of 33% of the average daily inflow rate by pumping water, and the remaining raw water was used as Q1 and flowed into the first tank.

FIG. 6 is a diagram showing the operation results of each of the above operation methods. Table 2 below shows the daily average value of the treated water N concentration and the nitrogen removal rate. As shown in FIGS. 6 and 2, in Examples 2-1 and 2-2 of the present invention, the treated water N concentration was lower and the nitrogen removal rate was higher than that of the conventional method 3. From this result, it is possible to avoid the shortage of carbon source required for denitrification treatment by keeping the inflow amount in the final step step constant even in the three-step step treatment method, and the organic matter load in the sixth tank. And since it is possible to keep the nitrogen load within an appropriate range, the effectiveness of the present invention that can achieve stable step inflow type multi-stage nitrification denitrification treatment was confirmed.

Further, in Example 2-1 and Example 2-2 of the present invention, the treated water N concentration and the nitrogen removal rate were almost the same values. When the present invention is applied to the three-stage step processing method, Q3 may be set to a constant flow rate as long as the flow rate of Q5 is kept constant, but the flow rate of Q3 and the step ratio of Q1 and Q3 fluctuate. However, the effect on the N concentration of treated water is small. This result shows that it is extremely effective to set the inflow rate of the final step inflow step to a constant flow rate in order to achieve stable nitrogen removal.

<Example 3>
Under the operating conditions of the two-stage step processing in which the inflow of raw water is divided into the first and fourth tanks, the effect of reducing the N concentration of treated water by the DO set value when the air volume control in the fifth tank is DO control by the DO meter. Was examined.

The inflow amount of raw water in the 4th tank is set to a constant amount Q2 by pumping water, and the remaining raw water is set to Q1 and flows into the 1st tank. The first and fourth tanks were anaerobic tanks, the second tank, the third tank, the fifth tank, and the sixth tank were aerobic tanks. The DO value of the 2nd, 3rd, and 6th tanks was set to 1 mg / L, and the DO value of the 5th tank was set to 0.3 to 1.5 mg / L, and the amount of air was controlled. Q2 was set to 50% of the average daily inflow of water.

FIG. 7 is a diagram showing the operation results of each of the above operation methods. The N concentration of the treated water in FIG. 7 is a daily average value. From FIG. 7, it was confirmed that the N concentration of the treated water was reduced by setting the DO value in the fifth tank to 1 mg / L or less. This is due to the nitrogen concentration reduction effect due to the simultaneous progress of nitrification and denitrification when nitrification is promoted in a state where the DO value in the fifth tank is reduced to 1 mg / L or less. By keeping the inflow amount in the final step of the present invention constant, it is possible to avoid a shortage of carbon sources required for denitrification treatment, and the organic matter load and nitrogen load in the 5th and 6th tanks are appropriate. Since it is possible to keep the range, it is possible to realize simultaneous progress of nitrification and denitrification when proceeding with nitrification with the DO value reduced to 1 mg / L or less in the 5th tank, and further treated water nitrogen. Concentration reduction has become achievable.

<Example 4>
NH ₄ -N set value when the air volume control in the 5th tank is NH ₄ -N concentration control by the ammonia sensor under the operating conditions of the 2-step step processing in which the inflow of raw water is divided into the 1st tank and the 4th tank. The effect of reducing the N concentration of treated water was examined. The ammonia sensor was installed at the end of the 5th tank.

The inflow amount of raw water in the 4th tank is set to a constant amount Q2 by pumping water, and the remaining raw water is set to Q1 and flows into the 1st tank. The first and fourth tanks were anaerobic tanks, the second tank, the third tank, the fifth tank, and the sixth tank were aerobic tanks. The DO value of the 2nd, 3rd, and 6th tanks was set to 1 mg / L, and the NH ₄ -N of the 5th tank was set to 1 to 4 mg / L, and the amount of air was controlled. Q2 was set to 50% of the average daily inflow of water.

FIG. 8 is a diagram showing the operation results of each of the above operation methods. The treated water N concentration in FIG. 8 is a daily average value. From FIG. 8, by controlling the air volume in the 5th tank with the NH ₄ -N concentration control by the ammonia sensor, the treated water nitrogen concentration is 2 to 4 mg / L when the NH ₄ -N concentration setting in the 5th tank is 2 to 4 mg / L. The concentration was 6 mg / L or less, and it was possible to reduce the nitrogen concentration of the treated water as compared with the case of controlling the air volume by the DO meter of Example 3. In addition, there was an NH ₄ -N set value of 3 mg / L in the fifth tank, which minimized the nitrogen concentration in the treated water.

In Example 4, as in Example 3, the nitrogen concentration of the treated water is increased due to the effect of reducing the nitrogen concentration by the simultaneous progress of nitrification and denitrification when the nitrification is promoted in the state where the DO value in the fifth tank is reduced to 1 mg / L or less. It was possible to reduce it. When the NH ₄ -N setting value of the 5th tank is 2 to 4 mg / L, the DO measurement value of the 5th tank is 0.05 to 0.2 mg / L, and at such a low DO, the influence of the DO sensor measurement error Therefore, it is difficult to accurately control the air volume by the DO sensor. Therefore, it was effective to apply the ammonia sensor instead of the DO sensor in the air volume control in the low DO range of the fifth tank. When the ammonia sensor is used to control the air volume in the low DO range of the present invention, stable air volume control is possible and the ammonia concentration can be continuously monitored, so that NH ₄ -N residue in the treated water remains. It is also an effective means of avoiding it.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications may be made within the scope of claims and the technical ideas described in the specification and drawings. It is possible. It should be noted that any configuration not directly described in the specification and drawings is within the scope of the technical idea of the present invention as long as the action and effect of the present invention are exhibited. For example, the number of units connected in series may be a plurality of units of 3 or more. In addition, the above description and the embodiments shown in each figure can be combined with each other as long as there is no contradiction in the purpose, configuration, and the like. Further, the above description and the description contents of each figure can be independent embodiments even if they are a part thereof, and the embodiment of the present invention is one embodiment in which the above description and each figure are combined. Not limited to.

1-1, 1-2, 1-3, 1-4 Step inflow type multi-stage nitrification denitrification system N-1, N-2, N-3 Unit A-1, A-2, A-3 Anaerobic tank O- 1, O-2, O-3 Aerobic tank O (1) Upstream split aerobic tank O (2) Downstream split aerobic tank R Constant flow supply means S Settling basin

Claims (6)

In the step inflow type multi-stage nitrification denitrification method, in which an anaerobic tank and an aerobic tank are regarded as one unit, a plurality of the units are connected in series, and inflow water having a variable amount of water is distributed and injected into the anaerobic tank of each unit.
The inflow amount of the inflow water distributed and injected into the anaerobic tank of the final unit is fixed at a predetermined constant flow rate , while the remaining fluctuating inflow water is sent to the anaerobic tank of the remaining units on the front stage side of the final unit. A step inflow type multi-stage nitrification denitrification method characterized by being dispensed and injected according to the fluctuation . The step inflow type multi-stage nitrification denitrification method according to claim 1, wherein the inflow amount of the inflow water into the anaerobic tank of the final unit is 20 to 60% of the daily inflow amount. In the step inflow type multi-stage nitrification denitrification method in which an anaerobic tank and an aerobic tank are regarded as one unit, a plurality of the units are connected in series, and the inflow water is distributed and injected into the anaerobic tank of each unit.
The inflow rate of the inflow water distributed and injected into the anaerobic tank of the final unit is set to a constant flow rate.
By dividing the aerobic tank of the final unit into two tanks and controlling the DO value of the aerobic tank on the upstream side of the divided two tanks to be equal to or less than a predetermined value, the aerobic tank on the upstream side is controlled. A step -inflow multi-stage nitrification denitrification method characterized in that the nitrification reaction and the denitrification reaction proceed simultaneously. The NH ₄ -N setting value of the aerobic tank on the upstream side is set so that the DO value of the aerobic tank on the upstream side is equal to or less than a predetermined value, and the favorable value of the upstream side is set so as to be the set value. The step inflow type multi-stage nitrification denitrification method according to claim 3, wherein the amount of air supplied to the air tank is controlled. The step inflow type multi-stage nitrification denitrification method according to claim 4, wherein the amount of air supplied to the aerobic tank on the upstream side is controlled by using an ammonia sensor. In a step inflow type multi-stage nitrification denitrification system in which an anaerobic tank and an aerobic tank are regarded as one unit, a plurality of the units are connected in series, and inflow water having a variable amount of water is distributed and injected into the anaerobic tank of each unit.
A constant flow rate supply means is provided to fix the inflow amount of the inflow water distributed and injected into the anaerobic tank of the final unit to a predetermined constant flow rate , while the remaining fluctuating inflow water is the rest on the front stage side of the final unit. A step-inflow multi-stage nitrification denitrification system characterized by dispensing and injecting into the anaerobic tank of the unit according to the fluctuation .

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