JP2006116480A - Method and apparatus for treating and measuring waste water - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for carrying out the quantitative measurement of nitrification activity of a mixture liquid and a degree of inhibition of the nitrification activity of raw water in a short time, automatically and precisely as an on-line instrument by sampling the mixture liquid containing a microbe and a waste liquid from an aeration tank to analyze the measured data of DO (dissolved oxygen) acquired by aerating with a measurement device by a computer, and its apparatus. <P>SOLUTION: After a value when a concentration of dissolved oxygen is roughly fixed by aerating the mixture liquid sampled from the aeration tank for a sufficiently long time is set as high finalDO and an overall mass transfer coefficient Kabs of an aerator is determined from a variation curve of the dissolved oxygen concentration determined by repeatedly aerating from a low dissolved oxygen concentration, a standard liquid is loaded and a decomposition rate of the standard liquid is calculated from a DO variation to evaluate the nitrification activity. If the nitrification activity is not less than a set value, next, the raw water is loaded to treat BOD (biological oxygen demand) of the raw water, then the standard liquid is further loaded to calculate the decomposition rate of the standard liquid, and a degree of inhibition of the nitrification activity of the raw water is evaluated from a decomposition rate variation of the standard liquid before and after the raw water is loaded. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a measurement method and apparatus for operation management of wastewater treatment such as activated sludge using microorganisms and biological nitrification denitrification.

Nitrogen in wastewater needs to be treated to prevent eutrophication. There are several treatment methods, but the activated sludge method and biological nitrification denitrification method using microorganisms are the most general treatment methods.
In the activated sludge method, nitrogen compounds in the wastewater are fixed and removed as excess sludge by the growth of the cells, and some of them are oxidized to nitrite ions and nitrate ions by the action of nitrifying bacteria in the activated sludge, and the action of denitrifying bacteria It is removed as nitrogen gas from an aeration tank or a precipitation tank that is partially anaerobic. When the removal rate is insufficient with activated sludge, a biological nitrification denitrification method, which is an extension of the activated sludge method, is applied.
The biological nitrification denitrification method has various variations in the construction method of its unit. Basically, under the aerobic condition, the BOD component in wastewater is oxidatively decomposed, and the nitrogen compound is produced by the action of nitrifying bacteria (5) As shown by the formula (6), the BOD oxidation / nitrification step for oxidizing to nitrite ions and nitrate ions via ammonia ions and the action of denitrifying bacteria under anaerobic conditions, the formula (7), (8) As shown by the formula, this is a combination of a denitrification step of reducing nitrite ions and nitrate ions to nitrogen gas in the presence of a hydrogen donor. The hydrogen donor is added with methanol, acetic acid or raw water.
2NH ₄ ⁻ + 3O ₂ → 2NO ₂ ⁻ + H ₂ O + 4H ⁺ (5) Formula 2NO ₂ ⁻ + O ₂ → 2NO ₃ ⁻ (6) Formula 2NO ₂ ⁻ + CH ₃ OH → N ₂ ↑ + CO ₂ ⁻ ↑ + H ₂ O + 2OH ⁻ (7 ) formula ^{_{6NO 3 - + 5CH 3 OH →}} 3N 2 ↑ + 5CO 2 - ↑ + 7H 2 O + 6OH - (8) formula

FIG. 3 is a flow sheet showing an example of an apparatus for biological nitrification denitrification.
The center of this process is the BOD oxidation / nitrification step, which is basically the same process as activated sludge. A mixture of activated sludge and wastewater containing BOD-oxidizing bacteria and nitrifying bacteria at high concentrations is aerated, and microorganisms oxidize and decompose BOD in the wastewater by dissolved oxygen in the mixture, and oxidize ammonia ions to nitrate ions. Is. The nitrification liquid mixture is returned to the first denitrification tank, and nitrite ions and nitrate ions are reduced to nitrogen gas by nitrifying bacteria using the BOD component in the raw water as a hydrogen donor under anaerobic conditions in the denitrification tank. Nitrite ions and nitrate ions contained in the treatment liquid flowing out of the BOD oxidation / nitrification process are added to a hydrogen donor such as methanol in an anaerobic condition in the subsequent denitrification tank. Reduce to nitrogen gas. Finally, the anaerobic mixed liquid is re-aerated to treat the remaining BOD, and solid-liquid separation is performed in a sedimentation tank to obtain supernatant water as treated water.

  In order to properly manage the biological nitrification / denitrification process, it is necessary to properly manage the BOD oxidation / nitrification process and the denitrification process, and management of the nitrification process is particularly important. . The nitrifying bacteria that are responsible for the nitrification process have a slower growth rate and weak chemical resistance than BOD oxidizing bacteria and denitrifying bacteria. This is because the action of converting to nitrate ions or nitrate ions varies. Therefore, it is important for the operation management of the biological nitrification denitrification process to manage the function of nitrifying bacteria in addition to the usual management of activated sludge.

However, at present, there is no instrument that can easily measure the function of nitrifying bacteria directly on-line. For example, an instrument that automatically measures total nitrogen and nitrate ions is installed before and after each process, and its concentration is measured. Operation management can be performed from the data. However, these instruments are expensive, and oxidation from total nitrogen to nitrite ions and nitrate ions involves the degradability of nitrogen-containing substances, the operating conditions of BOD oxidation / nitrification tanks, the activity of BOD oxidation bacteria, the activity of nitrification bacteria, etc. It is a comprehensive result, and when there is a change in water quality, it is not sufficient to reflect it in an appropriate operation.

  If the activity of nitrifying bacteria and the inhibition of nitrifying bacteria can be quantified during operation management of the biological nitrification denitrification process and reflected in the operation, the optimal operation of the biological nitrification denitrification process becomes possible. Thus, great effects such as improvement of nitrogen removal rate and treatment can be obtained.

  The inventor measures the behavior of oxygen consumption rate of microorganisms using a dissolved oxygen concentration meter, and analyzes this with a computer, thereby measuring the BOD required for activated sludge treatment in a short time and in the raw water. A method for calculating the degradation rate of BOD components and quantifying the activity of microorganisms has been disclosed. Specifically, a method for acquiring measurement data of dissolved oxygen concentration, a calculation method for calculating BOD from the acquired data, and a method for analyzing the decomposition rate of BOD are described in detail from the calculation principle (see Patent Document 1). .

  In addition, based on the same calculation principle, by installing the activated sludge device in operation on the aeration tank, by repeating the sampling of the mixed liquid in the aeration tank and the activity measurement of BOD and sludge in the mixed liquid, A method and apparatus capable of collecting data necessary for operation management of activated sludge with a frequency close to continuous measurement in practice is disclosed (see Patent Document 2).

However, if the methods described in Patent Documents 1 and 2 are used, the data necessary for the operation management of activated sludge can be collected, but this alone will enable the nitrification activity and nitrification necessary for the operation management of the biological nitrification denitrification process. Inhibitory properties cannot be assessed.
JP2001-235462 JP 10-28992 A

  As described above, an apparatus for automatically measuring the nitrification activity and nitrification inhibitory activity of nitrifying bacteria that can be used for operation management of a biological nitrification denitrification process has not been put into practical use. The present invention modifies and expands the function of the automatic measurement method and apparatus for activated sludge described in [Patent Document 2], and is a nitrifying bacterium inherently essential for operation management of a biological nitrification denitrification process. It is intended to provide a method and apparatus capable of accurately and quantitatively measuring nitrification activity and nitrification inhibitory activity on-line.

In order to solve the above problems, the present invention is summarized as follows. That is,
Sampling the mixed solution from the aeration tank, charging the mixed solution to the measuring device, aeration with the aeration device, decomposing the BOD in the mixed solution by aeration, the oxygen supply rate of the aeration device and the mixing after decomposition After obtaining the dissolved oxygen concentration (this concentration is referred to as highfinalDO) at the point where the oxygen consumption rate of the liquid balances, after stopping the aeration apparatus and lowering the dissolved oxygen concentration decreased by the oxygen consumption of the mixed solution, Reactivate the aeration device, obtain the mass transfer coefficient (hereinafter referred to as Kabs) of the aeration device by calculation from the rising DO change, add the reference solution, and change the DO by the decomposition of the components by the sludge in the mixture Calculate the decomposition rate of the reference solution from the change, evaluate the nitrification activity from the magnitude of the decomposition rate, and if the decomposition rate of the reference solution is larger than the preset value stored in the computer, after the decomposition of the reference solution, original After decomposing the raw water BOD, add the reference solution again, calculate the decomposition rate of the reference solution from the DO change that changes with decomposition, and nitrification activity of the raw water from the change in the decomposition rate of the reference solution before and after the addition of the raw water To evaluate the inhibitory properties. If it is smaller than the set value, the measurement is terminated without adding raw water. By repeating this sampling-measurement operation, the nitrification activity of the mixed solution and the nitrification activity inhibition of the mixed solution of raw water are measured with a frequency close to that of continuous measurement in practice.

  According to the measurement method of the present invention, the nitrification activity of sludge and the nitrification inhibition of raw water can be quantitatively measured with high accuracy in a short time of about 2-3 hours. And by repeating measurement-sampling, automatic measurement can be performed with a frequency close to practical continuous measurement. As a result, it becomes possible to quantitatively handle the behavior of nitrogen removal rate and biological nitrification denitrification process in activated sludge, which could only be handled qualitatively in the past, and contribute to optimum operation and stable operation.

Since it is necessary for the description of the present invention, first, the basic principle of calculation will be briefly described.
When the mixed liquid containing activated sludge and waste liquid is aerated with an aeration device, the dissolved oxygen concentration in the waste water increases with the aeration time, and the change is expressed by equation (1).

  Where DOsat is the saturated dissolved oxygen concentration [mg / l], DO is the dissolved oxygen concentration in the aeration tank [mg / l], Kabs is the overall mass transfer coefficient [1 / min], ASact is the oxygen used by activated sludge for respiration Consumption rate [mg / l / min], BODact is the oxygen consumption rate [mg / l / min] used by activated sludge to decompose BOD components.

The first term on the right side of equation (1) is the oxygen supply rate from the aeration apparatus, and the second term is the oxygen consumption rate used by activated sludge for respiration and decomposition of BOD. ASact is the rate of oxygen consumption by basic sludge respiration. Since it is a basal respiration, it is not directly related to the BOD component and is almost constant within a short time. ASact is known to be constant regardless of the DO value if the DO value is approximately 0.5 mg / l or more. This can be easily verified from the fact that DO decreases linearly from a state in which the dissolved oxygen concentration is high in a state where the supply of oxygen is cut off in a mixed solution in which the BOD component is almost 0 mg / l.

  BODact is the consumption rate of oxygen used when sludge is oxidizing BOD components and ammonia ions to nitrate ions. BODact changes depending on whether the sludge is acclimatized to the substance, the state of the sludge, water temperature, pH, habitat environment such as salt concentration. When microorganisms oxidize BOD components or ammonia ions to nitrate ions, the reaction is carried out by microorganisms corresponding to the BOD component, nitrifying bacteria, etc., and each component shows a specific reaction rate.

  When BODact changes during the aeration process, equation (1) cannot be easily integrated. However, in the case of a mixed solution with almost 0 mg / l of BOD components and ammonia ions, BODact of equation (1) is almost zero. It is shown by the formula (2).

As described above, ASact is constant regardless of DO when DO> 0.5 mg / l. Therefore, equation (2) can be easily integrated in this range and expressed by equation (3).
DO = α− (α−DO ₀ ) exp (−Kabs · t) (3) where α = DOsat−ASact / Kabs
DO ₀ is an initial value when aeration is started. Also, in equation (3), if the aeration elapsed time t is sufficiently large, the second term on the right side can be ignored.
DO = α = DOsat−ASact / Kabs
The value is constant. If this value is expressed as highfinalDO, highfinalDO can be defined as the DO value that is finally reached when a mixed liquid having a BOD component of almost 0 mg / l is aerated.
Therefore, Equation (3) is
DO = highfinalDO− (highfinalDO−DO ₀ ) exp (−Kabs · t) (4) can be rewritten. In the equation (4), the change in DO becomes a curve indicated by a dotted line 1 in FIG.
On the other hand, when a BOD component and ammonia ions are present in the mixed solution, BODact has a value that cannot be ignored. Furthermore, the value of BODact changes from a large value to a small value with the aeration elapsed time t mainly due to a change in the BOD component to be decomposed. If there is no BOD component that can be finally decomposed, BODact becomes almost zero. Therefore, equation (1) cannot be simply integrated like equation (3), but the change in DO becomes a two-stage curve as shown by the curve of solid line 2 in FIG. That is, in the case of a simple BOD component such as methanol or acetic acid, during decomposition, DO becomes constant at a low level that balances the oxygen supply rate and the oxygen consumption rate of ASact + BODact. It rises and becomes constant at highfinalDO.

Now, the initial DO value DO ₀ when aeration is started is assumed to be the same, and the DO change curve (expressed by equation (4)) when a mixture of BOD components and ammonia ions is almost 0 mg / l is aerated. It is represented by a dotted line 1 in FIG. 2, and a DO change curve when a mixed liquid containing a BOD component and ammonia ions is aerated is represented by a solid line 2 in FIG. 2. In this case, the value obtained by multiplying the difference between the dotted line and the solid line at each aeration elapsed time by Kabs represents the oxygen consumption rate at which the BOD component or ammonia ion is used for oxidation at that time = the reaction rate. A value obtained by integrating this difference by the aeration elapsed time t corresponds to an area S surrounded by both curves. Further, the value obtained by multiplying this value by Kabs corresponds to the amount of oxygen used by microorganisms to oxidize BOD components and ammonia ions. The principle of this measurement itself is described in detail in Patent Document 1. Patent Document 1 further shows an operation procedure and a calculation procedure for specifically acquiring highfinalDO of the equation (4) and Kabs of the equation (1) in the measuring apparatus.

Next, an apparatus embodying the present invention will be described. FIG. 4 shows a processing apparatus 1 according to an embodiment of the present invention.
The processing device 1 includes a sampling device unit 2a and a measuring device unit 2b. The measuring device unit 2b is provided with an aeration container 3 for aeration with a mixed liquid of activated sludge, and a measurement container 4 connected to the aeration container 3 by piping at the bottom. The cooling pump 5, the aspirator type aeration device 6, the air flow meter 7, the air solenoid valve 8, the dissolved oxygen meter electrode 9, the circulation pump 5, the heater 10, and the cooling water flow inside. A heat exchange pipe 11, a reference liquid addition pump 12, a raw water addition pump 13, a drain electromagnetic valve 14, a dissolved oxygen meter 15, a control panel 16, and a computer 17 are provided. The sampling device unit 2a includes a measuring container 18, a vacuum pump 19, a vacuum electromagnetic valve 20, an atmosphere opening electromagnetic valve 21, a sampling electromagnetic valve 22, a measuring container 18, and a drain electromagnetic valve 23. ing.
In addition, although the aspirator system is employ | adopted as the aeration apparatus 6 in the example of a device, you may use a compressor and a diffuser tube.
By the circulation pump 5, the mixed liquid in the apparatus is circulated in the flow of the measurement container 4 → the aspirator of the aeration apparatus 6 → the aeration container 3 → the measurement container 4, the air is sucked by the aspirator of the aeration apparatus 6 and aeration is performed in the aeration container 3. The bubbles are separated by transferring the liquid from the bottom to the measurement container 4, and the flow velocity of the sensor surface of the dissolved oxygen meter electrode 9 installed in the vicinity of the inlet nozzle in the measurement container 4 is ensured.
The computer 17 has a digital output / analog-digital conversion PC card attached to a PCMCIA adapter and is connected to a control panel, and controls a pump, a solenoid valve, and the like of the measuring device according to a command from the computer 17. The computer 17 takes in the measured value of the dissolved oxygen meter electrode 9 through the serial port. The control panel 16 is equipped with a temperature controller, and the temperature of the mixed liquid is kept constant by controlling the heater 10. In addition to this, a sampling device for sampling the mixed solution from the aeration tank is necessary. In this device example, a system using a vacuum pump is employed in connection with the block 3 described later. A system using a meter can also be configured.
The measuring container 18 of the sampling device unit 2a is equipped with a temperature sensor 25 and a pressure gauge sensor 26, and each measured value is taken into the computer 17 via a PC card.
The sampling device unit 2 a and the measuring device unit 2 b are connected via a communication electromagnetic valve 24.

  The operation method will be described below. FIG. 5 is an operation flowchart of the apparatus 1 according to the present embodiment. In the figure, block 1 refers to a range excluding block 2 in the following description. FIG. 1 is a diagram conceptually showing a DO change by the measurement method of the present embodiment.

  First, the block 1 portion will be described first. The first step (hereinafter referred to as Step 1) is a step of sampling the mixed solution from the aeration tank, and opens the drain electromagnetic valve 14 to drain the measured mixed solution in the measuring device. Flow charts S1. And S2. Correspond to this. Next, the operation of step S2. Is performed. The mixed solution is sampled from the aeration tank to the measuring device using the sampling device unit 2a. Specifically, from the state where the electromagnetic valves 20, 21, 22, 23, 24 are closed, the vacuum electromagnetic valve 20 is opened and the vacuum pump 19 is operated to depressurize the measuring container 18 to p1 KPa. Next, the sampling electromagnetic valve 22 is opened, and the mixed solution in the aeration tank is sucked into the measuring container 18. When the pressure in the measuring container 18 reaches p2 KPa, the sampling solenoid valve 20 is closed. The amount of the liquid mixture sucked into the measuring container 18 can be calculated from the total space volume V0, p1, and p2 of the measuring container 18. By operating the electromagnetic valve from the computer 17 so that p1 and p2 become a predetermined suction amount, an arbitrary mixed liquid amount can be sampled. Next, the air release solenoid valve 21 and the communication solenoid valve 24 are opened, and the liquid mixture in the measuring container 18 is transferred to the measuring device by the drop between the measuring container 18 and the measuring container 4.

  Regarding Step 1, in the present embodiment, the mixed liquid at the outlet of the aeration tank is mainly sampled from the viewpoint of shortening the measurement time. However, the shape of the aeration tank is such that the inlet / outlet is not clear, such as a complete mixing tank type, and the case where the next to the nitrification tank is not necessarily a sedimentation tank, as in the case of biological denitrification, or like batch activated sludge. However, the sampling position is not limited to the above position because the sampling position differs depending on the form of the aeration tank, the purpose of measurement, and the like.

The next step (hereinafter referred to as Step 2) is a step of obtaining the values of highfinalDO and Kabs (parts of flowcharts S3. To S10.). Steps 2-1 to 2-3 in FIG. 1 show the DO change measurement pattern in this step. The measurement / calculation method in this step is performed by the method shown in Patent Document 1. That is, when the circulating DO 5 is operated by setting the initial DO value of the sampled mixed liquid to DO ₀ , the air electromagnetic valve 8 is opened, and aeration by the aspirator is started, the BOD of the mixed liquid is eventually processed. The oxygen consumption rate is only ASact, and the DO value is balanced at a high position that balances the oxygen supply rate by aeration. The dissolved oxygen concentration during this period shows a change like the DO curve 2-1 in FIG. A point at which equilibrium is reached at the end of the DO curve 2-1 is defined as highfinalDO. The process so far is referred to as Step 2-1.
After obtaining highfinalDO, the air solenoid valve 8 is closed to stop aeration, and when DO is reduced by the consumption of dissolved oxygen by the ASact of the mixed solution, the dissolved oxygen concentration changes as shown in the DO curve 2-2 in FIG. Show. This process is referred to as Step 2-2.
When the air solenoid valve 8 is opened and aeration is restarted from the point of DO ₁ at which the DO is sufficiently lowered, and a change in DO is measured, a change as shown by the DO curve 2-3 in FIG. 1 is shown. The process so far is referred to as Step2-3.
The Kabs value is calculated from the measured value of the DO curve 2-3. The calculation method is to change DO ₀ in equation (4) to DO ₁ and obtain highfinalDO obtained from DO curve 2-1.
Using the Kabs assumed to be, the calculation is repeated while changing the Kabs value until the calculated value calculated from the equation (4) matches the measured value of the DO curve 2-3. Determined as Kabs. Flow charts S7 and S9. The set value 1 and the set value 2 are provided to reduce the error by taking a sufficiently large DO calculation width when calculating the equation (4).

The next step (hereinafter referred to as Step 3-1) is a step of adding the reference solution and measuring the nitrification activity from the decomposition rate of the reference solution, and this corresponds to the portions of the flowcharts S11. To S14. A DO curve 3-1 in FIG. 1 is an example of a measurement pattern of DO change in this step. After calculating Kabs in Step 2-3, after the equilibrium is completely reached, the reference solution addition pump 12 is operated in accordance with a command from the computer 17 to add the reference solution to the measuring apparatus 1.
The change in DO when the activated sludge in the mixed solution decomposes the reference solution is measured. The decomposition rate of the reference solution is measured based on the measurement data, and the nitrification activity of the nitrifying bacteria is quantified from the magnitude of the decomposition rate. The above is the description of the portion corresponding to the first aspect.

  Next, the part corresponding to claim 2 will be described. In the flowchart of FIG. 5, the S16. To S21. Portions of the block 2 will be described. This process is referred to as Step 3-2 and Step 3-3. A DO curve 3-2 and a DO curve 3-3 in FIG. 1 are measurement pattern examples of DO change in this step.

  After adding and measuring the reference solution in Step3-1 and evaluating the nitrification activity of the sludge, it is next determined whether or not Step3-2 is performed based on the activity value. Step 3-2 is originally a process for adding raw water to decompose the BOD of raw water, and is for evaluating the nitrification inhibitory activity of raw water. However, in Step 3-1, the nitrification activity is already inhibited and the decomposition rate is low. In this case, it is not necessary to evaluate the nitrification inhibitory property of the raw water. For this reason, if the nitrification activity falls below the set value 3, measurement of the raw water BOD is omitted. The set value 3 as a determination criterion is input to the computer 17 in advance, but a specific numerical value can be arbitrarily selected based on the need for information on nitrification activity inhibition. By incorporating such a treatment, the overall measurement time can be shortened.

As a result of addition and measurement of the reference solution in Step 3-1, if the nitrification activity is 3 or more, the raw water addition pump 13 is actuated by a command from the computer 17 in Step 3-2, and the raw water is added to the measuring device 1. To do.
The change in DO when the activated sludge in the mixed liquid decomposes the BOD component of the raw water is measured, and when the decomposition is completed, the reference liquid addition pump 12 is actuated by a command from the computer 17 and again the reference liquid Is added, and the decomposition rate of the reference solution is measured based on the measurement data, and the degree of nitrification activity inhibition by the raw water is quantified from the change in the decomposition rate of the reference solution before and after the addition of the raw water.

  If the raw water is toxic to nitrifying bacteria, the degradation rate of the addition and measurement of the reference solution after the addition of the raw water is necessarily reduced compared to that before the addition of the raw water. The degree of reduction increases with the degree of toxicity. The measurement pattern of DO curve 3-1 and DO curve 3-3 in FIG. 1 is an example in the case where raw water shows strong toxicity. The DO change of DO curve 3-3 is the same as the DO change of DO curve 3-1. Compared to this, the DO reduction width is small, and the flat shape as shown in FIG.

  After the measurement in Step 3-3, if the automatic measurement mode is set, the process returns to the flowchart S1. That is, the measured mixed solution is drained, the mixed solution is newly sampled from the aeration tank, and the above measurement is repeated. In the case of normal activated sludge, if the treatment is good, the time required for the above operation is about 50 minutes for Step1, 35 minutes for Step2, about 20 minutes for Step3-1, about 55 minutes for Step3-2, Step3-3 Is about 20 minutes, about 3 hours in total. That is, it is possible to obtain quantitative information about the activity of nitrifying bacteria and the degree of nitrification inhibition of raw water nitrifying bacteria, which are extremely important operation indices for the biological nitrification and denitrification process about every 3 hours.

Next, matters relating to the components of the reference solution will be described.
The reference solution added in Step 3-1 or Step 3-3 is an additive solution that serves as a reference for evaluating the activity of nitrifying bacteria, and is an additive solution having a constant component composition. Requirements that can be used as a reference solution are:
(1) The component of the reference solution has a sufficiently high decomposition rate enough to discriminate changes in the appropriate concentration and activity state of nitrifying bacteria.
(2) The components of the reference solution have a sufficiently large difference in oxygen consumption by BOD oxidizing bacteria and oxygen consumption by oxidation to nitrate ions by nitrifying bacteria.
(3) The components of the reference solution have a sufficiently large difference between the oxygen consumption rate by BOD oxidizing bacteria and the oxygen consumption rate by oxidation to nitrate ions by nitrifying bacteria.
Substances satisfying the above conditions (1) to (3) include substances that dissolve in water such as ammonium sulfate and ammonium chloride to generate ammonium ions, and urea, nitrile amide, hydroxylamine, and formamide. The reference solution contains at least one of these substances.
Always use the same reference solution after selection.

  The oxidation reaction rate of the components of the reference solution by nitrifying bacteria is not always constant. Therefore, in order to compare changes in activity, it is necessary to define at what time the decomposition rate is to be compared. In many cases, the DO change pattern due to the addition of the reference solution changes stepwise in the process of progressing at a constant oxidation rate due only to the activity of the nitrifying bacteria. To do. Finally, when nitrification is complete, the oxygen consumption rate by ASact of activated sludge and the oxygen supply rate by aeration converge to the highfinalDO value.

FIG. 6 shows an example of a DO change pattern in this process. DO measurement curve of FIG. 6, but differs from the solid curve 2 in FIG. 2, this is because the initial value DO ₀ is started from a high highfinalDO value. When the activity of nitrifying bacteria changes, the decomposition rate of all components of the reference solution does not always change evenly. For this reason, a macro way of grasping is practical. For example, an average decomposition rate until 50% of the entire BOD is decomposed is used as an index. The larger this value is, the more reasonable it is as an index for evaluating the resolution, but the larger the measurement error. In addition, since the measurement end time is greatly influenced by a small fluctuation of a small amount of a component having a slow decomposability, the variation due to the fluctuation of the component becomes unnecessarily large, and the measurement error also increases. On the other hand, the maximum decomposition rate immediately after the addition can be sensitive to changes, but the contribution of the fastest decomposable component in the reference liquid component is very large. For this reason, there is a risk of evaluating the activity of only microorganisms that selectively nitrify the component. On the other hand, the average activity of microorganisms that nitrify various components in the reference solution contributes to nitrification of about 50%. Therefore, it is generally appropriate to use the average oxidation rate until decomposition of about 50% as an index. Of course, when the reference solution is a single component, the maximum decomposition rate is used as an index when the decomposition rate is simple, and when the nitrification rate in the nitrification tank is important, an average oxidation rate with a large nitrification rate is used. Sometimes used as an indicator.

The average oxidation rate up to a certain nitrification rate can be determined as follows using DO measurement data.
Total oxygen consumption by nitrification (hereinafter referred to as BODt), in FIG. 6, the DO change curve from the start of addition up to the decomposition was finished, the DO ₀ as the initial value, (4) curve which is calculated by the formula (hereinafter, virtual It is indicated by a value obtained by multiplying the area surrounded by the DO curve 1) by Kabs. When the initial value DO ₀ is a highfinalDO value, the virtual DO curve is a constant (highfinalDO value) straight line.
Next, the amount of oxygen consumed that has been nitrified by a certain time (hereinafter referred to as BOD) can be determined as follows. That is, if the BOD becomes 0 mg / l at that time, the DO change curve is a curve calculated by the equation (4) using the high DO value and Kabs, with the DO measurement value at that time as the initial value DO _2. Hereinafter, it is referred to as a virtual DO curve 2). Therefore, the value obtained by multiplying the area surrounded by the DO change curve from the start of addition to the time point and the virtual DO curve 1 and the virtual DO curve 2 by Kabs becomes the BOD up to that point (hereinafter referred to as BODp).
Furthermore, if the time point at which BODp / BODt × 100 (%) reaches the target decomposition rate is tp, the average decomposition rate obtained by BODp / tp is obtained.

Next, a method for determining whether or not the decomposition reaction has ended will be described. In the flowchart of FIG. 5 as well, it is necessary to determine whether or not the decomposition reaction has been completed in S4, S13, S17, and S21. This determination uses the characteristics of the microbial reaction of activated sludge. Normally, when waste liquid is added, as shown in FIG. 6, the DO measurement curve undergoes a step-like change as the main components in the waste liquid decompose. And when it is near the end of the reaction, it rises on the slope and finally changes almost constant near highfinalDO. Therefore, if the DO value becomes almost constant around highfinalDO, it can be determined that the reaction has ended. A method for realizing this on the computer 17 is, for example, as follows. The slope β of the regression line is calculated from several DO measurement values from several minutes before the measurement. Since β is the DO change rate, it is compared with the set value 5 (previously stored in the computer 17), which is the minimum allowable value of β and DO increase rate,
β <set value 5 and DO ≒ highfinalDO
It is determined that the reaction is completed under the conditions of

Here, DO≈highfinalDO is taken into consideration that the state of activated sludge at the end of the reaction is not necessarily the same as when highfinalDO was acquired. For example, the BOD of the mixed solution is 0 mg / l at the time when highfinalDO is acquired in Step 2-1, but strictly speaking, there is also a BOD component having a slow decomposition rate below the measurement accuracy. Moreover, the property of sludge may change with the addition of waste liquid. When Kabs = 0.3 [1 / min] and highfinalDO = 6.0 [mg / l], the decomposition reaction is generally higher than highfinalDO-0.5, the increase of DO becomes a slope in most cases. If the value indicating the points DO _L in FIG. 6, practically, it can be determined by setting such as beta <setpoint 5 and DO> DO _L.

  The present invention is not limited to biological nitrification and denitrification methods and activated sludge, as long as it uses floating microorganisms partially, contact oxidation method, biological filtration method, fluidized bed method for holding carrier microorganisms, etc. The wastewater treatment method using other aerobic microorganisms can also be applied when nitrification activity needs to be evaluated.

It is an example of a pattern showing basic operation of measurement and DO change by the present invention. It is a figure explaining the calculation principle used as the foundation of the present invention. It is a flow sheet which shows the example of an apparatus of biological nitrification denitrification method. It is a flow sheet which shows the example of a measuring device. It is a flowchart explaining the action | operation of a measuring apparatus. It is an example of DO measurement pattern by the measuring apparatus of a present Example.

Explanation of symbols

3 Aeration vessel 4 Measurement vessel 5, 12, 13 Pump 6 Aeration device 7 Air flow meter 8, 14, 20-24 Solenoid valve
9 Dissolved oxygen meter electrode 10 Heater 11 Heat exchange pipe 15 for cooling 15 Dissolved oxygen meter 16 Control panel 17 Computer 18 Measuring container 19 Vacuum pump 25 Temperature sensor 26 Pressure gauge sensor

Claims (3)

It is an operation evaluation method in wastewater treatment such as activated sludge using microorganisms or biological nitrification denitrification method,
The mixed solution containing the wastewater and activated sludge sampled from the aeration tank is aerated, the change curve of dissolved oxygen concentration in the mixed solution (hereinafter referred to as DO curve 2-1) and the oxygen supply rate after BOD decomposition in the mixed solution Measure the dissolved oxygen concentration (hereinafter referred to as highfinalDO) at the balance point between the oxygen consumption rate of the liquid mixture and
Next, after aeration is stopped and the dissolved oxygen concentration is lowered, a dissolved oxygen concentration change curve (hereinafter referred to as DO curve 2-3) when aeration is resumed is measured.
Based on the DO curve 2-3 and highfinalDO, the mass transfer coefficient (hereinafter referred to as Kabs) in the oxygen supply means is calculated,
Next, a standard solution containing at least one of urea, nitrile amide, hydroxylamine, formamide and a constant component composition is added to the mixture. Then, the nitrification activity of the activated sludge in the mixed solution is evaluated by determining the decomposition rate of the reference solution based on the subsequent dissolved oxygen concentration change and highfinalDO and Kabs.
A wastewater treatment operation evaluation method characterized by that. In claim 1, when the nitrification activity is larger than a predetermined set value, raw water is added after the decomposition of the reference liquid, and the reference liquid is added again after the decomposition of the BOD component of the raw water. Then, by determining the decomposition rate of the reference solution based on the change in dissolved oxygen concentration and highfinal DO and Kabs, and comparing the decomposition rate of the reference solution before and after the addition of raw water, the degree of inhibition of nitrification activity on the activated sludge of the raw water can be reduced. evaluate,
A wastewater treatment operation evaluation method characterized by that. It is an operation evaluation device in wastewater treatment such as activated sludge using microorganisms and biological nitrification denitrification method,
Mixing the sampled wastewater and the activated sludge mixed solution, aeration curve of dissolved oxygen concentration in the mixed solution (hereinafter referred to as DO curve 2-1) and oxygen supply rate and mixing after decomposition of BOD in the mixed solution Means for measuring the dissolved oxygen concentration (hereinafter referred to as highfinalDO) at a balance point with the oxygen consumption rate of the liquid;
Means for measuring a dissolved oxygen concentration change curve (hereinafter referred to as DO curve 2-3) when aeration is resumed after stopping aeration and reducing the dissolved oxygen concentration;
Means for calculating a mass transfer coefficient (hereinafter referred to as Kabs) in the oxygen supply means based on the DO curve 2-3 and highfinalDO;
Evaluate the nitrification activity of activated sludge in the mixed solution by adding a reference solution with a constant component composition to the mixed solution and then determining the decomposition rate of the reference solution based on the change in dissolved oxygen concentration and highfinalDO and Kabs. Means to
When the nitrification activity is larger than a preset value, the raw water is added after the decomposition of the reference solution, and the BOD component of the raw water is added after the decomposition, and then the dissolved oxygen concentration change and means for calculating the decomposition rate of the reference solution based on highfinalDO and Kabs;
Means for evaluating the degree of inhibition of nitrification activity against activated sludge of raw water by comparing the decomposition rate of the reference solution before and after addition of raw water;
A device for evaluating operation in wastewater treatment, comprising:

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