JP2019150795A - Aeration amount control method and facility for aerobic tank in sewage treatment facility - Google Patents

Abstract

To provide a method and facility that can accurately determine the NH-N concentration at an outlet of an aerobic tank without providing an ammonia meter at the outlet and determine the appropriate aeration amount in the aerobic tank.SOLUTION: In a sewage treatment facility having an aerobic tank that oxidizes ammonia nitrogen to generate nitrate nitrogen, the above-mentioned problem can be solved by a method and facility for measuring ammonia nitrogen concentration and nitrate nitrogen concentration at the aerobic tank inlet and nitrate nitrogen concentration at the aerobic tank outlet, determining the ammonia nitrogen concentration at the aerobic tank outlet from these concentrations, and using the ammonia nitrogen concentration at the aerobic tank outlet to control the amount of aeration air blown into sewage in the aerobic tank.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method and facility for controlling the amount of aeration air in an aerobic tank provided in a sewage treatment facility.

In the aerobic tank of the sewage treatment plant, the blower for aeration consumes a large amount of power. Therefore, measure the NH ₄ -N (ammonia nitrogen) concentration in the sewage or sludge and minimize the blast volume. Attempts have been made to control. As a system, a system (Patent Documents 1 and 2) that feedback-controls the air volume based on an indication value of an NH ₄ -N meter installed in the aerobic tank, and an NH ₄ -N concentration of the aerobic tank inflow water. There is known a method (Patent Documents 2 and 3), etc., in which the air volume is measured with an NH ₄ -N meter and the air volume is feedforward controlled based on the indicated value.

The invention of Patent Document 1 is an aeration air volume control device for a sewage treatment plant including an aeration apparatus that supplies air to the aerobic tank according to a target aeration air volume when performing water treatment using a biological reaction tank having an aerobic tank. ,
An NH ₄ -N meter for measuring the NH ₄ -N concentration in the aerobic tank;
Control target setting means for setting a NH ₄ -N concentration target value of the effluent water of the aerobic tank;
And _NH 4 -N controller for calculating the aeration amount target value to approach the measured _NH 4 -N concentration is set _NH 4 -N concentration target,
The NH ₄ -N meter is installed at a position 25 to 35% upstream from the outlet portion with respect to the total length of the aerobic tank, and the control target value of the NH ₄ -N concentration is set The present invention relates to an aeration flow control device for a sewage treatment plant, which is characterized by being set to 1 mg / L to 3 mg / L. As shown in FIG. 4, the NH ₄ -N meter and the dissolved oxygen concentration meter are provided apart from the outlet of the aerobic tank.

In the invention of Patent Document 2, the water quality value estimated by the water quality value estimation unit in the aerobic tank that estimates the water quality value other than the dissolved oxygen concentration in the aerobic tank that oxidizes the water to be treated is that oxygen is blown from the blower. The blower air volume calculation unit that calculates the blower air volume is the target value of the dissolved oxygen concentration in the aerobic tank and the dissolved oxygen concentration estimation unit that estimates the dissolved oxygen concentration in the aerobic tank. The blower air volume calculated based on the estimated value of dissolved oxygen concentration, the target value of the water quality value other than the dissolved oxygen concentration in the aerobic tank, and the estimated value of the water quality value in the aerobic tank by the aerobic tank water quality estimation unit Of the blower airflows calculated based on this, a larger blower airflow is output. As shown in FIG. 5, an NH ₄ -N meter and a dissolved oxygen concentration meter are provided in the aerobic tank, but the NH ₄ -N meter is provided apart from the outlet. An NH ₄ -N meter is also provided in the anoxic tank.

The invention of Patent Document 3 is an aeration control device that controls the amount of air supplied to biological treatment of non-treated water,
The water quality data of the water to be treated and the reaction tank for biologically treating the water to be treated are subjected to a biological reaction model for estimating the nitrification rate to estimate the nitrification rate of the water to be treated, and the target treated water quality based on the nitrification rate is obtained. A set value calculation unit for determining a set value of a control factor of air supply to the reaction tank based on a necessary nitrification rate for satisfying,
A set value determination unit that generates the control signal for the air supply based on the determination of the suitability of the determined set value;
The present invention relates to an aeration control device including a control unit that controls a flow rate of air supplied to the reaction tank based on the control signal. As shown in FIG. 6, only the dissolved oxygen concentration meter is provided in the aerobic tank, and the NH ₄ -N meter is provided so as to measure the inflow water sent from the anoxic tank.

Japanese Patent No. 4509579 JP 2017-100092 A JP 2017-109170 A

In order to properly oxidize NH ₄ -N in the aerobic tank, it is necessary to know the residual concentration of NH ₄ -N at the outlet of the aerobic tank, but an electrode-type NH ₄ -N meter is provided at the aerobic tank outlet. The problem is that it cannot be installed. This is because when the electrode-type NH ₄ -N meter is used in a low NH ₄ -N concentration solution, problems such as a large error and a short electrode life occur. Therefore, since air volume control is performed without monitoring the water quality at the aerobic tank outlet, it is necessary to sufficiently control the safety side so as not to exceed the water quality standard. Therefore, there exists a problem that energy saving property is small.

Therefore, as shown in Patent Documents 1 and 2, is provided away NH 4 _-N meter from the outlet of the aerobic tank, when performing feedback control based on the measured value, on principle, influent NH ₄ - Even if the N concentration rapidly rises, it is not reflected in the control until the NH ₄ -N meter is reached. In other words, there is a risk of processing failures due to fluctuations in the influent water quality.

On the other hand, the feedforward control shown in Patent Documents 2 and 3 measures the NH ₄ -N concentration in the aerobic tank inflow water, estimates the necessary air volume based on the measured NH ₄ -N concentration, and reduces the necessary minimum air diffusion. How to do it. However, it is generally difficult to accurately estimate the required air volume from the NH ₄ —N concentration, and in Patent Document 2, the feedforward control is only used supplementarily. In addition, a method for predicting the required air volume using an activated sludge model (ASM) or the like as in Patent Document 3 is also conceivable, but in order to make an accurate prediction, the actual state of the process is grasped, and parameters are adjusted accordingly. It is necessary to correct from time to time. The parameter calibration needs to be performed based on the actual value of the aerobic tank outlet NH ₄ -N concentration. However, as described above, there is a problem that the aerobic tank outlet NH ₄ —N concentration is difficult to continuously measure.

An object of the present invention is to provide a method and equipment capable of accurately determining the NH ₄ —N concentration at the outlet and determining the appropriate air aeration amount in the aerobic tank without providing an ammonia meter at the outlet of the aerobic tank. It is to provide.

The present inventors have utilized extensive studying, low NH 4 _-N concentration can also be used in a NO 3 _-N (nitrate nitrogen) such as aerobic tank outlet gauge to develop a means for solving the above problems Thought to do. And, if the NH ₄ -N concentration and NO ₃ -N concentration at the aerobic tank inlet and the NO ₃ -N concentration at the outlet of the good tank are measured, the NH ₄ -N concentration at the aerobic tank outlet can be accurately obtained. The headline and the present invention have been completed.

That is, the present invention
In a sewage treatment facility having an aerobic tank that oxidizes NH ₄ -N to generate NO ₃ -N, the NH ₄ -N concentration and NO ₃ -N concentration at the aerobic tank inlet and the NO _{3-at the} aerobic tank outlet the N concentration was measured to obtain the NH 4 _-N concentration of aerobic tank outlet from these concentrations, control the air volume blown into the sewage aerobic tank with NH 4 _-N concentration of aerobic tank outlet and the estimated A method of controlling the amount of aeration air sent to the aerobic tank in the sewage treatment facility,
In a sewage treatment facility having an aerobic tank that oxidizes NH ₄ -N to generate NO ₃ -N, an NH ₄ -N meter that measures the NH ₄ -N concentration at the aerobic tank inlet and an NO ₃ -N concentration and NO 3 _-N meter for measuring, there is provided a sewage treatment facility, characterized in that the NO 3 _-N meter for measuring the NO 3 _-N concentration in the aerobic tank outlet is provided.

According to the present invention, it is possible to continuously and accurately estimate the NH ₄ -N concentration at the aerobic tank outlet in a sewage treatment facility that has been difficult in the past. In addition, the method of the present invention can cope with fluctuations in the inflow NH ₄ -N concentration for feedforward control, and the feedforward control parameters are based on the aerobic tank outlet (treated water) NH ₄ -N concentration. Correction is possible, and the prediction accuracy can be improved. According to the present invention, the amount of power used by the blower can be reduced by appropriately controlling the amount of aeration, and the operation of the aerobic tank can be stabilized to prevent processing failures.

It is the figure which showed one embodiment of this invention typically. It is a graph showing the time course of NH 4 _-N concentration and NO 3 _-N concentration obtained in Example of the present invention in actual measurement values and estimated values. Is a graph showing the time course of NH 4 _-N concentration and NO 3 _-N concentration resulting aeration amount as a fixed amount in actual measurement value and the estimated value. It is a figure which shows typically the aeration air volume control method of patent document 1. FIG. It is a figure which shows typically the aeration air volume control method of patent document 2. FIG. It is a figure which shows typically the aeration air volume control method of patent document 3. FIG.

Treatment of NH ₄ -N contained in sewage in a sewage treatment facility is generally performed using an aerobic tank, and in the aerobic tank, NH ₄ -N is oxidized to NO ₃ -N by nitrifying bacteria. . When an oxygen-free tank is combined, NO ₃ is reduced to N ₂ because microorganisms use NO _X oxygen in the oxygen-free tank without dissolved oxygen. The liquid in the aerobic tank is returned to the anoxic tank, but a part is extracted and sent to the final sedimentation basin. There is also a sewage treatment facility that does not provide an oxygen-free tank and performs only the nitrification treatment of the aerobic tank.

  The aerobic tank is usually box-shaped or cylindrical, and is provided with a diffuser mechanism such as air in order to make the inside of the tank aerobic. The air diffusion mechanism may be any of an air diffuser plate, an air diffuser cylinder, a flexible tube, a disk diffuser, a perforated tube, and the like, and a blower for sending air or the like to these is also installed.

In the present invention, the NH ₄ -N meter for measuring the NH ₄ -N concentration at the inlet of the aerobic tank, the NO ₃ -N meter for measuring the NO ₃ -N concentration, and the outlet of the aerobic tank. A NO ₃ -N meter is provided for measuring the NO ₃ -N concentration. _NO 3 -N meter for measuring the _NH 4 -N meter and _NO 3 -N concentration measuring _NH 4 -N concentration at the inlet of the aerobic tank is outside provided in the vicinity of the entrance of the aerobic tank, the flow of aerobic tank You may provide in the flow path of water. Further, usually, an initial sedimentation tank and an anaerobic tank are provided on the upstream side of the aerobic tank, and NH ₄ -N is not decomposed in the first sedimentation tank or the anaerobic tank, so the NH ₄ -N meter is an aerobic tank. The NH ₄ —N concentration in the preceding tank may be measured. On the other hand, since NO ₃ -N is reduced to N ₂ in the anaerobic tank, the NO ₃ -N meter should be close to the outlet when the preceding tank of the aerobic layer is an anoxic tank. The NO ₃ -N meter for measuring the NO ₃ -N concentration at the outlet of the aerobic tank may be provided in the flow path of the effluent water from the aerobic tank in addition to being provided near the outlet of the aerobic tank. It may be provided in a final sedimentation basin where water is collected. These may be anything as long as they can continuously measure NH ₄ -N concentration and NO ₃ -N concentration, respectively, and their names are not limited.

In the case of municipal sewage, the NH ₄ —N concentration of the inflow water to the sewage treatment facility depends on the properties of the sewage that is the treated water, and often fluctuates greatly, but is usually about 10 to 100 mg / L, especially It is about 20-50 mg / L. Further, the NO ₃ —N concentration is about 10 mg / L or less, and is often below the detection limit. The NH ₄ -N concentration and the NO ₃ -N concentration of the aerobic tank inflow water largely depend on the treatment method, but are about 3 to 50 mg / L and about 10 mg / L or less, respectively. In particular, in a sewage treatment facility in which an anaerobic tank is provided in front of the aerobic tank, the NO ₃ —N concentration of the aerobic tank inflow water is usually below the detection limit.

The NH ₄ —N concentration at the aerobic tank outlet in the present invention is determined as follows.

That is, the NH ₄ -N concentration at the aerobic tank inlet is C _{NH 4 in} , the NO ₃ -N concentration is C _{NO 3 in} , and the aerobic tank outlet NO ₃ -N concentration is C _{NO 3 out} . _Assuming that the ratio of the Kj-N (Kjeldahl nitrogen) concentration C _{Kj, in} to C _{NH4, in} at the aerobic tank inlet is constant, β = C _{NH4, in} / C _{kj, in} . It is widely accepted that this ratio β is constant, and it has been adopted in the following publication of the Japan Sewerage Association: “Sewerage Construction Plan / Design Guidelines and Explanations”. Then, α = _{CNO3, out} (t) / _{Ckj, in} (t−Δt), assuming that the ratio of Kj−N that changes to NO ₃ −N is constant under the aerobic condition. C _{NO3, out} (t) represents the NO ₃ -N concentration at the aerobic tank outlet at time t, and C _{kj, in} (t-Δt) represents the Kj-N concentration at the aerobic tank inlet at time t-Δt. ing. Δt represents the residence time of the aerobic tank. Therefore, α represents the ratio of the Kj-N concentration of the water flowing into the aerobic tank at t-Δt and the NO ₃ -N concentration when the water flows out.

Generally, since the TN (total nitrogen) concentration contained in the inflow water at the aerobic tank inlet is the sum of the Kj-N concentration and the NO ₃ -N concentration, the TN concentration at the aerobic tank inlet is

で表わされ、完全硝化を仮定した場合の好気槽出口におけるＮＯ_３−Ｎ濃度を
Ｃ´_{ＮＯ３，ｏｕｔ}とすると、

And the NO ₃ —N concentration at the aerobic tank outlet when assuming complete nitrification is C ′ _{NO 3, out} ,

となる。ただし、一般に無酸素槽出口においてＮＯ_３−Ｎは完全脱窒しており、ほとんどの場合Ｃ_{ＮＯ３．ｉｎ}は１未満である。故に好気槽入口におけるＮＨ_４−Ｎ計の設置を省略し、Ｃ_{ＮＯ３．ｉｎ}＝０としても大きな誤差は生じえない。
好気槽出口におけるＮＨ_４−Ｎ濃度の推定値Ｃ´_{ＮＨ４，ｏｕｔ}は、

It becomes. However, NO ₃ -N is generally completely denitrified at the oxygen-free tank outlet, and in most cases C _{NO 3. in} is less than 1. Therefore, the installation of the NH ₄ -N meter at the aerobic tank inlet is omitted, and _{CNO3. Even if in} = 0, no large error can occur.
Estimated value C ′ _{NH4 out} of NH ₄ -N concentration at the aerobic tank outlet is

となる。

It becomes.

The Kj-N concentration (C _{kj, in} ) at the aerobic tank inlet is the Kjeldahl concentration of the influent water measured for the NH ₄ -N concentration (C _{NH4, in} ) and the NO ₃ -N concentration (C _{NO3, in} ). Is determined by Kjeldahl analysis. Then, β of this influent can be obtained by C _{NH4, in} / C _{kj, in} , but may change due to seasonal fluctuations. Therefore, it is desirable to perform analysis of TN and NH ₄ -N (for example, a method according to JIS K 0102) of the aerobic tank inflow water once a month to correct β.

Next, α is C _{NO3, out} (t) / C _{kj, in} (t−Δt), and Δt is the residence time in the aerobic tank, which is the amount of water in the aerobic tank. Divided by speed. Accordingly, α is a ratio of C _{kj, in} and C _{NO3, out} of the effluent after Δt time when it is measured. α may also change due to seasonal variations. Therefore, the analysis of NH ₄ -N of aerobic tank effluent (eg JIS K) is performed about once a month.
[0102] It is desirable to correct α so that NH ₄ -N can be correctly predicted by performing a method in accordance with [0102].

In the present invention, thus, NH 4 _-N concentration and NO 3 _-N concentration in the aerobic tank inlet, and the NO 3 _-N concentration in the aerobic tank outlet continuously measured, from their values aerobic tank outlet The aerobic tank can be operated with an appropriate air flow by calculating the NH ₄ -N concentration and instructing the required oxygen amount to the blower control device. However, as described above, in urban sewage and the like, the NO ₃ —N concentration of inflow water is often higher than the detection limit, and in this case, it is not necessary to measure the NO ₃ —N concentration at the aerobic tank inlet.

  In the present invention, since feedforward control is performed, this will be described using the calculation method of the required oxygen amount based on “Sewerage Facility Planning / Facility Guidelines and Explanation, Part 1994”, Japan Sewerage Association, p69-73.

(1) Based on the indicated value C _{NH4, in} of the aerobic tank inlet NH ₄ -N meter, the Kjeldahl nitrogen concentration С _{Kj-N, in} = C _{NH4, in} / β is estimated.

(2) The proportion of Kj-N that changes to NO ₃ -N is α (1-α) is used for microbial growth and is used for assimilation metabolism as activated sludge). Also, let the aerobic tank inflow water amount be Q (m ³ / day). The oxygen necessary for the breakdown per Kj-N1kg is a _{4.57kg-O 2 / kg-Kj} -N, required amount of oxygen _{O D} per unit water amount is as follows.
O _D = 4.57 [kg-O ₂ / kg-Kj-N] · α [−] · C _{Kj-N, in} [kg-Kj-N / m ³ ] · Q [m ³ / day]
= 4.57 QC _{Kj-N, in} α [kg-O ₂ / day]
= 4.57 QC _{NH4, in} α / β [kg-O ₂ / day]
* Square brackets in the formula represent units.

(3) The required amount of oxygen is commanded to the blower control device, and the blower control device determines the blowing rate based on the water temperature and oxygen dissolution efficiency.

Thus, the NH 4 _-N concentration of aerobic tank outlet obtained, it is possible to determine the air volume calculated required amount of oxygen O _D.

An experiment was conducted using municipal sewage by installing an NH ₄ -N meter and an NO ₃ -N meter in an experimental apparatus employing a circulation type nitrification denitrification method in the arrangement shown in FIG.

This device consists of an anaerobic tank on the left side of the drawing and an aerobic tank on the right side, and sewage flows into the anoxic tank, where NO ₃ -N is reduced by denitrifying bacteria to become N ₂ gas. Released from the tank. The sewage discharged from the anaerobic tank flows into the aerobic tank in which air is sent from the blower and is aerated from the aeration tank, where NH ₄ -N contained in the sewage is oxidized by nitrifying bacteria, and NO _3. Change to -N. And most of the sewage in the aerobic tank is returned to the anoxic tank through the return line, and a part is extracted out of the system. An NH ₄ -N meter is installed near the center of the anaerobic tank, a NO ₃ -N meter is installed near the outlet, and a NO ₃ -N meter is installed near the outlet of the aerobic tank. The signals detected by these are sent to the NH ₄ -N feedforward controller, where the required oxygen amount is calculated and sent to the blower controller, and the blower blow rate is controlled by its administration.

The NH ₄ -N concentration of sewage flowing into the anoxic tank is 10 to 35 mg / L, the NO ₃ -N concentration is less than 1 to 5 mg / L, Kj-N is 10 to 40 mg / L, and the flow rate is 10 m ³ / L. day. The Kj-N at the aerobic tank inlet was 3 to 15 mg / L, and a large variation was observed. The amount of water in the aerobic tank is 2 m ³ , and therefore the residence time is 4.8 hr.

The NH ₄ -N concentration and NO ₃ -N concentration at the aerobic tank inlet and the NO ₃ -N concentration at the aerobic tank outlet are continuously measured, and the NO at the aerobic tank outlet obtained by controlling the air volume is operated. FIG. 2 shows changes with time of the _3- N concentration (mg / L) and the NH ₄ -N concentration (mg / L) every 3 hours. In the figure, the NO ₃ -N concentration indicates the measured value of the NO ₃ -N meter, and the ● indicates the estimated value obtained by assuming complete nitrification, and it can be seen from the drawing that both agree well. . Regarding the NH ₄ -N concentration, □ indicates the analytical value analyzed based on JIS K 0102 by the indophenol blue absorptiometry, and ● indicates the estimated value in the method of the present invention, and it can be seen that both agree well.

On the other hand, the amount of aeration air was obtained by dividing the required oxygen amount 4.57QC _{NH4, in} α / β (kg-O ₂ / day) by the oxygen dissolution efficiency.

FIG. 3 shows time-dependent changes of the NO ₃ —N concentration and the NH ₄ —N concentration at the aerobic tank outlet obtained by performing the operation at a constant rate every 3 hours. It can be seen that the NO ₃ —N concentration in the figure does not match the estimated value (●) and the measured value (□) in the time zone of poor nitrification. On the other hand, the NH ₄ -N concentration almost coincided with the estimated value (●) and the manual analysis value (□).
α and β are not values that fluctuate in a short time, but may be treated as almost constants. A calibration frequency of about once a month is sufficient.

  The method of the present invention can accurately estimate the amount of aeration in an aerobic tank of a sewage treatment plant, thereby eliminating unnecessary aeration, and thus can be widely used in each sewage treatment plant.

Claims (6)

  In a sewage treatment facility with an aerobic tank that oxidizes ammonia nitrogen to produce nitrate nitrogen, the ammonia nitrogen concentration and nitrate nitrogen concentration at the aerobic tank inlet and the nitrate nitrogen concentration at the aerobic tank outlet are measured. The concentration of ammonia nitrogen at the outlet of the aerobic tank is determined from these concentrations, and the amount of air blown into the sewage in the aerobic tank is controlled using the ammonia nitrogen concentration at the outlet of the aerobic tank. A method for controlling the amount of aeration air sent to the aerobic tank in the facility.   The method for controlling the aeration air volume according to claim 1, wherein the nitrate nitrogen concentration of the aerobic tank inflow water is 3 mg / L or less, and the nitrate nitrogen concentration is not measured at the inlet of the aerobic tank. In a sewage treatment facility having an aerobic tank that oxidizes ammonia nitrogen to generate nitrate nitrogen, an NH ₄ -N meter that measures the ammonia nitrogen concentration at the inlet of the aerobic tank and NO ₃ that measures the nitrate nitrogen concentration sewage treatment facility, wherein the -N meter, that NO 3 _-N meter for measuring the concentration of nitrate nitrogen aerobic tank outlet is provided. Nitrate concentrations of aerobic tank influent is less 3 mg / L, sewage treatment facility according to claim 3, NO 3 _-N meter for measuring the nitrate concentration in the aerobic tank inlet is not provided. An anaerobic tank is provided for returning the effluent from the aerobic tank, reducing nitrate nitrogen contained in the effluent, generating nitrogen, and flowing the effluent into the aerobic tank. The sewage treatment facility according to claim 3 or 4, wherein an NH ₄ -N meter for measuring the ammonia nitrogen concentration at the tank inlet and a NO ₃ -N meter for measuring the nitrate nitrogen concentration are provided in the oxygen-free tank. An NH ₄ -N meter that measures the ammonia nitrogen concentration at the aerobic tank inlet, an NO ₃ -N meter that measures the nitrate nitrogen concentration, and an NO ₃ -N meter that measures the nitrate nitrogen concentration at the outlet of the aerobic tank The sewage treatment facility according to any one of claims 3 to 5, further comprising a control mechanism for controlling the amount of air sent to the aerobic tank from the indicated values of the three meters.

Images