JP3127776B2 - Apparatus and method for monitoring nitrogen removal performance of wastewater - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus and a method for monitoring nitrogen removal performance when biologically treating BOD and nitrogen components in wastewater at the same time.

[0002]

2. Description of the Related Art In a nitrogen removal method utilizing a nitrification and denitrification reaction by activated sludge microorganisms, nitrogen components such as ammonia nitrogen (hereinafter referred to as ammonia) are first activated in a nitrification tank by the action of nitrifying bacteria in the activated sludge. Nitric acid, which is oxidized mainly into nitric nitrogen (hereinafter referred to as nitric acid), and then a mixture of microorganisms containing nitric acid flows into the denitrification tank, and the nitric acid is reduced to nitrogen gas by the action of denitrifying bacteria to remove it. It is. As a typical process, there is a process in which a nitrification mixed solution in a subsequent nitrification tank is circulated as a circulating liquid to a preceding denitrification tank in order to utilize organic matter in wastewater as an organic carbon source required for a denitrification reaction. In this process, although the removal amount of nitric acid depends on the amount of circulating liquid, and the portion not circulated to the denitrification tank flows out as treated water as it is, there is a limit to the nitrogen removal rate, but nitrogen removal up to approximately 70 to 80% is possible. It is possible. In order to obtain stable nitrogen removal performance in this process, the first condition is to perform near-complete nitrification in a nitrification tank. It is also important to maintain an adequate amount of organic substances to maintain high denitrification capacity in the denitrification tank, and to maintain an appropriate amount of circulating liquid to circulate an appropriate amount of nitric acid from the nitrification tank to the denitrification tank. It is. For this reason, in order to perform operation management to obtain stable nitrogen removal performance, it is necessary to measure ammonia remaining in the nitrification tank or treated water and monitor the nitrification / denitrification rate performance. is important.

For monitoring the performance of the nitrogen removal process, Japanese Patent Application Laid-Open No. 1-143693 has proposed an apparatus and a method for measuring the oxygen consumption rate of a microorganism mixture in a reaction vessel. Oxygen consumption rate ATU-R related to carbon-based substrate with Nit-Rr or nitrification inhibitor added
r has been measured. The nitrification rate of the microorganism mixture can be converted from the oxygen consumption rate Nit-Rr, and the nitrogen load and the ammonia concentration of the treated water can be estimated from the values. However, in this case, there are the following problems. (I) Factors that affect the nitrification rate include a large number of factors such as nitrogen load, water temperature, dissolved oxygen concentration, and sludge residence time in addition to the ammonia concentration of the treated water. It can only be estimated from the equation and cannot be directly detected. (Ii) The nitrification inhibitor must be separately added from the outside, and the operation is complicated, such as repeating aeration and mechanical stirring for the two types of addition and non-addition of the nitrification inhibitor. (Iii) About the method of measuring the oxygen consumption rate itself,
In some cases, it is necessary to aerate the mixed microorganism solution taken into the container once, and to start the measurement after increasing the dissolved oxygen concentration.In the meantime, the ammonia concentration and the oxygen consumption rate accompanying nitrification decrease every moment, In some cases, the actual oxygen consumption rate in the reaction tank cannot be measured.

Japanese Patent Application Laid-Open No. 61-100657 discloses a device for measuring the concentration of ammonia in a reaction tank.
A method has been proposed in which a part of the activated sludge is introduced into a small aeration tank, and the difference between the oxygen consumption when the nitrification inhibitor is not injected and the oxygen consumption when the nitrification inhibitor is injected is calculated as an integrated value. However, even in this method, it is necessary to separately add a nitrification inhibitor from the outside, and there is a problem that there is a slight time delay until the suppression effect fully appears, and an error occurs in an integrated value during the time. Furthermore, it is necessary to perform two types of measurements on the sample at the same time, with and without the addition of a nitrification inhibitor, and the operation of adjusting the amount of air supplied to each using two small aeration tanks was complicated. .

[0005]

SUMMARY OF THE INVENTION The present invention provides a simple apparatus for measuring the concentration of ammonia remaining in a nitrification tank and monitoring the nitrification / denitrification rate performance with high accuracy in biological treatment of wastewater. The aim is to provide a method.

[0006]

According to the present invention, a container capable of continuous aeration is immersed in a nitrification tank, a sufficient amount of the nitrification mixture is allowed to flow into the container in a short time, and the dissolved oxygen concentration of the nitrification mixture is reduced. It has been found that by measuring the nitrogen concentration, the nitrogen removal performance can be monitored with a simple and accurate device.
That is, the monitoring device for nitrogen removal performance of wastewater of the present invention is:
It is immersed in a nitrification tank with at least one openable water sampling port.
That the container consists of an air supply tube connected to the bottom of the vessel, and dissolved oxygen concentration meter provided on said container, said adoption
Before the nitrification mixed solution in the nitrification tank that was flowed into the container from the water port
Air is continuously supplied from the air supply pipe, and the dissolved oxygen
Change of dissolved oxygen concentration of nitrification mixture measured by densitometer
Monitoring the microbial activity in the nitrification tank based on
And it said that there was Unishi.

The container having one or more openable water sampling ports which can be used in the monitoring device of the present invention may be of various structures. An outer cylinder having one or more water sampling ports, The inner cylinder is provided with a water intake that can be matched with the water intake of the outer cylinder by rotating the inner cylinder, and the water intake can be opened and closed by rotating the inner cylinder. Or a container in which the container can be separated vertically and the water sampling port is opened by the separation.
In the monitoring device of the present invention, it is desirable that the dissolved oxygen concentration of the nitrification mixed solution in the container at the time of water sampling and immediately after water sampling (immediately after closing the water sampling port) be the same as that outside the container. It is preferable to make the water port as large as possible so as to allow the nitrification mixed solution to flow in and out of the container.

Further, the method for monitoring the nitrogen removal performance of wastewater according to the present invention is characterized in that the above-described apparatus for monitoring the nitrogen removal performance of wastewater is immersed in a nitrification tank, and a nitrification mixed solution is introduced from a water collection port. Is closed, and while the air is continuously supplied from the air supply pipe, the time-dependent change of the dissolved oxygen concentration is measured by the dissolved oxygen concentration meter in the container, and the change rate of the dissolved oxygen concentration and the overall oxygen transfer capacity of the continuously supplied air are measured. It is characterized in that the change of the oxygen consumption rate of the nitrification mixed solution with time is obtained from the coefficient and the microbial activity is monitored by this.

[0009] Specifically, the time when the water intake is closed after the nitrification mixed solution flows into the inner cylinder is set to time 0, and the oxygen consumption rate is set to a substantially constant value lower than the value near time 0. Is defined as T, and the nitrification rate and denitrification rate of the nitrification mixture are converted from the oxygen consumption rate Rr0 near time 0 and the oxygen consumption rate RrT near time T, thereby monitoring the nitrogen removal performance of the wastewater. can do. The product dt (Rrt-RrT) of the difference between the oxygen consumption rate Rrt at time t and the oxygen consumption rate RrT near time T and the short time dt is calculated from t = 0 to t = T
By converting the ammonia nitrogen concentration remaining in the nitrification tank from the value integrated up to the above, the nitrogen removal performance of the wastewater can be monitored.

Next, the method of the present invention will be described in more detail. In the nitrification tank of the nitrogen removal process, the following reactions are mainly performed simultaneously. Nitrification reaction of ammonia component in solution by nitrifying bacteria Oxidation reaction of soluble organic matter by BOD oxidizing bacteria Ammonium elution and reaction derived from the oxidation reaction of accumulated organic matter in sludge by BOD oxidizing bacteria With the reaction, the mixture of microorganisms consumes oxygen.

In the case of general sewage and the like, the ammonia to be nitrified is usually oxidized not only to nitrous acid but also to nitric acid, with an oxygen consumption rate proportional to the nitrification rate. In addition, the rate decreases rapidly when the ammonia nitrogen in the solution disappears. This is because the above-mentioned reaction proceeds in almost zero-order reaction with respect to the ammonia concentration in the solution, and the above-mentioned reaction rate is extremely low. By taking advantage of this fact, if the microbial mixture in the nitrification tank is collected in the container and the reaction is continued by supplying only air, the end point of the nitrification reaction where ammonia is no longer present in the solution will be marked by a sharp decrease in the oxygen consumption rate. Can be detected. At this time, since it is difficult to directly determine the amount of oxygen used only for the above reaction before reaching the end point, there is a possibility that a method of subtracting the amount of oxygen used for other reactions from the total reaction amount of the above ~ is possible. However, there was a problem how to easily and accurately measure the difference.

The method of measuring the rate of oxygen consumption in a state in which a nitrification inhibitor such as allylthiourea is added to a mixed solution of microorganisms involves the above reaction, and the above reaction is very slight but strict. Does not include this, and its disadvantages are as described in the description of the prior art.

[0013] In the nitrogen removal process, the nitrification reaction usually proceeds in a nitrification tank, and thus the operation is performed with a sufficiently long residence time of the microorganisms in the tank so that the nitrifying bacteria can be retained in the system. Therefore, in the nitrogen removal process for sewage, the microorganism mixture in the nitrification tank is collected in a container, and when aeration is continued, ammonia is contained in the nitrification tank.
Even when ｍｇ3 mg / l remained, it was found that the above reaction was completed within 30 minutes to 1 hour at most.

Further, as a result of a detailed study of the amount of accumulated BOD in the activated sludge and its oxidation rate, the following became clear. That is, the concentration of the soluble BOD in the nitrification tank is several meters.
g / l, whereas the accumulated BOD concentration is usually 100-3
When the mixture of microorganisms is collected in a container and aeration is continued, 90% or more of the accumulated BOD concentration remains even after 1 hour, and there is almost no change in the oxidation reaction rate. . During this period, it was found that the pH did not change significantly, and that the reaction rates other than those described above remained almost constant.

From the above, it has been found that the value of the oxygen consumption rate accompanying the reaction other than the above during the progress of the reaction can be substituted with the value after the completion of the reaction.
Therefore, in the present invention, a container that can be immersed in a nitrification tank, can easily collect a nitrification mixed solution, and can continuously supply air is used, and a dissolved oxygen concentration meter is installed in the container. The oxygen consumption rate can be determined from the change over time in the concentration, and the nitrification rate, the ammonia nitrogen concentration, and the denitrification rate can be determined, making it possible to easily monitor the nitrogen removal performance.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described based on embodiments with reference to the drawings. FIG. 1 is a schematic vertical sectional view of a monitoring apparatus for nitrogen removal performance showing a first embodiment of the present invention, FIG. 2 is an exploded view of a container portion thereof, and FIG. FIG. 4 is a cross-sectional view of the container when the water sampling port is closed. In the monitoring device shown in FIGS. 1 to 4, the container is composed of an outer cylinder 1 having a water sampling port 2a and an inner cylinder 3 having a water sampling port 2b, and an air supply pipe 4 is provided at the bottom of the outer cylinder 1. A dissolved oxygen concentration meter 6 is installed in the inner cylinder 3. Air is supplied to the air supply pipe 4 by an air pump 5, and the amount of air is measured by an air flow meter 7. 8 is an exhaust valve. The inner cylinder 3 is rotatable by a motor 9 and automatically opens and closes the water sampling port 2.

This monitoring device is immersed in a nitrification tank, and the inner cylinder 3 is rotated by the motor 9 so that the water sampling port 2a of the outer cylinder 1 and the water sampling port 2b of the inner cylinder 3 coincide with each other, as shown in FIG. When the water sampling port is opened, the mixed liquid of microorganisms in the nitrification tank freely enters and exits the outer cylinder 1. A predetermined amount of air is supplied from the air supply pipe 4, and the dissolved oxygen concentration C is constantly measured by the dissolved oxygen concentration meter 6. After the mixture of microorganisms in the nitrification tank and the container 1 becomes uniform, the water sampling port is closed as shown in FIG. The measurement of the dissolved oxygen concentration C is continued, and the measured C, its change rate dC / dt, and the saturated dissolved oxygen concentration C
Using s and the overall oxygen transfer capacity coefficient K _La , the oxygen consumption rate Rr is calculated from the following equation. Rr = K _La (Cs−C) −dC / dt (1) In addition, the overall oxygen transfer capacity coefficient K _La is calculated based on each water temperature, air amount,
Use the value determined in advance for the sludge concentration. The amount of air is detected by the air flow meter 7 and adjusted by opening and closing the exhaust valve 8.

If the time when the water sampling port is closed is set to time 0 and aeration is continued, the oxygen consumption rate eventually becomes substantially constant at a value lower than the value near time 0 for the above-described reason. This time is defined as T. The oxygen consumption rate near time 0 is Rr0, that at time t is Rrt, and that near time T is RrT. It is considered that the above reaction is completed at time T, and RrT is defined as the oxygen consumption rate for the other reactions.
Furthermore, Rr0 represents the total oxygen consumption rate due to the reaction of the actual-taking place in the nitrification tank, using oxygen emgO ₂ / mgN is this consumption per unit nitrification amount,
The reaction rate in the nitrification tank, that is, the nitrification rate K _N can be calculated from the following equation. K _N = (Rr0−RrT) / e (2)

Dissolved oxygen concentration measured every 10 seconds when the monitoring device of the present invention is applied to a microorganism mixture in a nitrification tank in a nitrogen removal process (activated sludge circulation modified method) comprising a denitrification tank and a nitrification tank. Is shown in FIG. 5, and the change over time of the oxygen consumption rate calculated by the above equation (1) is shown in FIG. Water temperature is 23
° C and K _La were 13.3 (l / h). In each of the examples a) and b) having different operating conditions of the nitrogen removal process, the time T was about 30 minutes. The value obtained by integrating dT (Rrt−RrT) from time 0 to T with the minute time dT being 1 minute is further expressed as an oxygen amount emg consumed per unit nitrification amount.
The remaining ammonia concentration was determined by dividing by O ₂ / mgN. Further, the nitrification rate K _N was obtained from the equation (2). Table 1 shows the results under each of the operating conditions a) and b).
Here, as the value of e, a theoretical value of 4.57 when the amount of ammonia used for cell synthesis was ignored was used.

Further, in the nitrification tank mixture, Table 1 shows, as actual values, the actual ammonia concentration and the nitrification rate calculated from the difference between the nitric acid concentrations in the denitrification tank and the nitrification tank, based on the analysis of the filtrate of the 5A filter paper according to the sewage test method. From the results shown in Table 1, it can be seen that according to the present invention, the ammonia concentration and the nitrification rate in the nitrification tank can be accurately calculated.

[0021]

[Table 1]

The oxygen consumption rate and the nitrification rate at the actual dissolved oxygen concentration in the nitrification tank can be calculated more accurately as the change rate of the dissolved oxygen concentration near the time 0 is smaller. Is desirably determined so that K _La in the container is equal to K _La in the actual air flow rate of the nitrification tank. In this case, the dissolved oxygen concentration shows a higher value at time T than at time 0,
The rate of the organic substance oxidation reaction (the above and the above reactions) is hardly affected by the dissolved oxygen concentration as long as the dissolved oxygen concentration is about 1 mg / l or more.

Next, the relationship between RrT and the denitrification rate is shown in FIG. FIG. 7 summarizes the data at a water temperature of 12 to 27 ° C., and it was found that the denitrification rate was almost proportional to RrT regardless of the water temperature. From this, R
It was found that the denitrification rate of the nitrogen removal process could be monitored by multiplying rT by the residence time of the wastewater in the denitrification tank.

FIGS. 8 and 9 show a second embodiment of the monitoring apparatus according to the present invention. In this monitoring device, the container comprises an outer cylinder 11 and an inner cylinder 12 which can be separated vertically, and an inner cylinder 1
Numeral 2 is installed so as to be able to move up and down by a cylinder 15 provided on the upper part of the support 10, and the outer cylinder 11 and the inner cylinder 12 are separated by moving the inner cylinder 12 upward by reducing the pressure of the cylinder 15. Then, a water sampling port 13 is generated. FIG. 8 shows a case where the water sampling port 13 is in the open state, and FIG. 9 shows a case where the water sampling port 13 is in the closed state. The outer cylinder 11 is supported by the support body 10, and an air supply pipe 14 is connected to the bottom. Further, a dissolved oxygen concentration meter 16 is provided in the inner cylinder 12, and the dissolved oxygen concentration is measured as in the first embodiment, and the nitrogen removal performance is monitored efficiently.

[0025]

The apparatus for monitoring nitrogen removal performance of the present invention can accurately measure the dissolved oxygen concentration with a simple structure, and according to the method of the present invention using this apparatus, the apparatus remains accurately in the reaction tank. Measure the ammonia concentration
It is possible to monitor the nitrification / denitrification speed performance, and it is possible to always perform stable and efficient wastewater treatment.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a monitoring device according to a first embodiment of the present invention.

FIG. 2 is an exploded view of a container portion of the monitoring device shown in FIG.

FIG. 3 is a cross-sectional view of the monitoring device shown in FIG. 1 when a water sampling port is in an open state.

4 is a cross-sectional view of the monitoring device shown in FIG. 1 when a water sampling port is in a closed state.

FIG. 5 is a graph showing the change over time of the concentration of dissolved oxygen in a container measured in the first embodiment of the present invention.

FIG. 6 is a graph showing the change over time of the oxygen consumption rate measured in the first embodiment of the present invention.

FIG. 7 is a graph showing the relationship between the oxygen consumption rate and the denitrification rate after the end of the nitrification reaction measured in the first embodiment of the present invention.

FIG. 8 is an explanatory diagram of a monitoring device according to a second embodiment of the present invention, in which a water sampling port is open.

FIG. 9 is an explanatory view of a monitoring device with a water sampling port closed according to a second embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Container 2 Sampling port 2a Sampling port 2b Sampling port 3 Inner cylinder 4 Air supply pipe 5 Air pump 6 Dissolved oxygen concentration meter 7 Air flow meter 8 Exhaust valve 9 Motor 10 Support 11 Outer cylinder 12 Inner cylinder 13 Sampling port 14 Air supply pipe 15 Cylinder 16 Dissolved oxygen concentration meter

Claims (6)

(57) [Claims] 1. A nitrification tank having at least one openable water sampling port.
A container immersed in the container and air connected to the bottom of the container
A supply pipe, and a dissolved oxygen concentration meter installed in the container, and a nitrification tank in the nitrification tank that flows into the container from the water sampling port.
Continuously supplying air from the air supply pipe to the chemical mixture,
The dissolved oxygen of the nitrification mixture measured by the dissolved oxygen concentration meter
Microbial activity in the nitrification tank based on changes in concentration over time
Monitoring apparatus of the nitrogen removal performance of the waste water, characterized in that so as to monitor. 2. An outer cylinder, wherein the container has at least one water sampling port,
An inner cylinder fitted in the outer cylinder, and the inner cylinder is provided with a water sampling port that can be matched with a water sampling port of the outer cylinder by rotating the inner cylinder. The monitoring apparatus for nitrogen removal performance of wastewater according to claim 1, wherein the monitoring apparatus is capable of being opened and closed. 3. The monitoring device for nitrogen removal performance of wastewater according to claim 1, wherein the container is vertically separable, and the water sampling port is opened by the separation. 4. The apparatus for monitoring the nitrogen removal performance of wastewater according to claim 1 is immersed in a nitrification tank, and after the nitrification mixed solution flows from the water intake, the water intake is closed and air is supplied from the air supply pipe. Measure the change over time of the dissolved oxygen concentration with a dissolved oxygen concentration meter in the vessel while continuously supplying the oxygen, and determine the oxygen consumption rate of the nitrification mixture from the change rate of the dissolved oxygen concentration and the overall oxygen transfer capacity coefficient of the continuously supplied air. A method for monitoring the nitrogen removal performance of wastewater, wherein a time-dependent change of the water is determined, and thereby the microbial activity is monitored. 5. The time when the water sampling port is closed after the nitrification mixed solution has flowed into the container is defined as time 0, and the time at which the oxygen consumption rate becomes a substantially constant value lower than the value near time 0 is defined as T. The method for monitoring the nitrogen removal performance of wastewater according to claim 4, wherein the nitrification rate and the denitrification rate of the nitrification mixture are converted from the oxygen consumption rate Rr0 near time 0 and the oxygen consumption rate RrT near time T. 6. A product d of a difference between the oxygen consumption rate Rrt at time t and the oxygen consumption rate RrT near time T and a minute time dt.
The method for monitoring the nitrogen removal performance of wastewater according to claim 4, wherein the concentration of ammonia nitrogen remaining in the nitrification tank is converted from a value obtained by integrating t (Rrt-RrT) from t = 0 to t = T.