JP2001255319A - Test method for wastewater treatment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a test method for controlling the operation state of an activated sludge method and a biological denitrification method. SOLUTION: The general mass transfer coefficient of the oxygen dissolving speed of an aeration device at the time of aeration of an activated sludge mixed waste liquid is set to Kabs and the waste liquid is sufficiently aerated to obtain a value at a point of time when the concentration of dissolved oxygen becomes almost constant and the area S1 which is surrounded by a dissolved oxygen concentration change curve, which is obtained when the waste liquid to which a set amount of an easily decomposable BOD substance is added is aerated until the concentration D01 of dissolved oxygen at the start time of aeration becomes the obtained value, and an imaginary dissolved oxygen concentration change curve, which is calculated from a formula when aeration is started from the initial value D01 at the start time of aeration, is multiplied by Kabs to obtain a value BOD1 while the mixed liquid is brought to an anaerobic state for a definite time after a set amount of the easily decomposable BOD substance is added and, thereafter, aeration is started from the concentration D02 of dissolved oxygen at the start time of aeration to obtain a dissolved oxygen change curve and a value BOD2 is calculated from the formula corresponding to the initial value D02 by the same technique and, from the difference between BOD1 and BOD2, the concentration of nitrite ions or nitrite ions in the mixed waste liquid and the reaction quantity of denitrification reaction are measured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a test method for controlling operating conditions of an activated sludge treatment method and a biological denitrification method.

[0002]

2. Description of the Related Art As a wastewater treatment method, a biological treatment method using an aerobic microorganism is a widely used wastewater treatment method. A typical process is an activated sludge treatment method. The treatment principle is that aerobic microorganisms capture the pollutants in the wastewater and obtain oxygen supply to decompose and obtain energy for biological activity, or decompose and synthesize the pollutants in the wastewater to produce their own. Purifying wastewater by highly concentrating the biological activities of the natural world that maintain and proliferate the living body.

[0003] An activated sludge treatment apparatus generally comprises an aeration tank for supplying oxygen to microorganisms to decompose pollutants, and a sedimentation tank for separating treated liquid from microorganisms. In operating the actual activated sludge treatment apparatus stably, the trouble of sludge flowing out together with the treated water due to poor sedimentation of the sludge in the sedimentation tank is a very serious problem in the operation of the activated sludge treatment apparatus. The causes of poor sedimentation of sludge are roughly classified into the following three. Activated sludge is predominant in filamentous fungi, and sludge sedimentation is poor. Nitrate ions and nitrite ions in the treated water are reduced to nitrogen gas by denitrifying bacteria in the sedimentation tank, and sludge floats by the generated nitrogen gas and the like. Due to lack of oxygen in the sedimentation tank, the sludge rises due to the methane gas generated by the sludge being putrefied. The causes of these occurrences vary depending on the operating conditions of the activated sludge, but they are serious troubles in which the operation of the activated sludge treatment device becomes impossible when the degree of floating increases.

[0004] Among the above, countermeasures are relatively easy because the causes such as insufficient amount of aerated air and defective sludge scraper in the sedimentation tank are simple, but depending on the operating conditions such as the amount of aerated air, Fundamental countermeasures are not easy because the factors caused by the pollutants in the raw water are large and it is difficult to remove the cause. The mechanism of the generation has been elucidated as described below, and the biological denitrification method uses this mechanism to remove nitrogen from wastewater. In operation management, there is no simple method for predicting the occurrence, and a different phenomenon occurs rapidly. Therefore, in the activated sludge method, countermeasures are delayed, and the damage tends to be enormous.
The activated sludge treatment method can be applied to various waste liquids, and compared with other waste water treatment methods such as treatment capacity, treatment performance, treatment cost,
Although it is a very useful method, the biggest difficulty is that sludge floating prevention management is difficult.

The mechanism of occurrence is as follows. Microorganisms require nitrogen and phosphorus to work. Generally, the composition ratio in wastewater is BOD: N: P = 100:
5: 1 is said to be good, and if the raw water does not contain N, replenish the N source. N in raw water is contained in various forms in its molecular structure, but in simple terms, microorganisms convert N to ammonia nitrogen during the BOD degradation process. Further, ammoniacal nitrogen is converted into nitrate ions and nitrite ions by nitrifying bacteria in an aerobic state as shown in the following formula. Equations (1) and (2) are called a nitrification reaction. Nitrate ions and nitrite ions are further reduced in an anaerobic state by a denitrifying bacterium to nitrogen gas as in the following formula. (3) Equation (4) is called a denitrification reaction. Nitrogen in wastewater is BO
If D: N: P = 100: 5: 1, it will be taken into the living body, so the reaction of formulas (3) and (4) is small, but there is excess nitrogen,
If the other conditions are satisfied, the reactions of equations (3) and (4) proceed. (3)
In the activated sludge method, equation (4) usually occurs in the sedimentation tank, and the generated nitrogen gas or carbon dioxide gas causes sludge to float.

[0006] The conditions under which the nitrification reaction proceeds proceed with BOD treatment if nitrifying bacteria are present in the activated sludge and there is a dissolved oxygen concentration in the wastewater, but especially at the end of the BOD treatment. I do. This is because the growth rate of nitrifying bacteria is lower than that of general BOD-degrading bacteria, and in order to convert ammoniacal nitrogen to nitrate nitrogen, nitrogen in the waste liquid must first be converted to B
This is because it is necessary to change to ammonia nitrogen in the OD treatment.

In the denitrification reaction, denitrifying bacteria are present in the activated sludge, and reduce nitric acid in an anaerobic condition. Therefore, an organic substance which can be easily decomposed and an acid for maintaining an appropriate pH are required. Equations (3) and (4) are reaction equations when methanol is used as an organic substance. The reaction rate varies depending on the dissolved oxygen concentration, temperature and pH conditions, the type of organic substance, the ratio of organic substance to nitrogen, the activity and concentration of denitrifying bacteria, and the like.

[0008] Sludge floating problems due to nitrification and denitrification are common phenomena when treating wastewater containing a large amount of nitrogen in the wastewater, and may occur whenever the above conditions are met. In a typical case, wastewater with a high nitrogen content flows in, the inside of the aeration tank is kept at a sufficiently high dissolved oxygen concentration, the BOD treatment is maintained well, and the nitrogen content in the wastewater is oxidized to nitrate ions. After accumulated in the aeration tank and the sedimentation tank, wastewater with a high BOD concentration flows into the aeration tank and cannot be treated in the aeration tank. The sludge rises with the generated gas. In severe cases, the sludge flows out of the overflow weir of the sedimentation tank, and the surface of the sedimentation tank is thickly covered with the sludge that floats, making it impossible to operate at all. Wastewater containing nitrogen in wastewater includes many wastewaters, including food wastewater containing amino acids.

[0009] The biological denitrification method is a method of removing the nitrogen content in the wastewater by positively adopting the equations (1) to (4).
The activated sludge method consists of an aeration tank for BOD treatment and a sedimentation tank for solid-liquid separation. And a sedimentation tank for sedimenting and separating sludge and treated water. The apparatus configuration is generally anaerobic tank → nitrification tank → anaerobic tank → re-aeration tank → sedimentation tank, but there are various variations mainly due to differences in the method of supplying organic substances necessary for the denitrification reaction and the method of controlling pH. In the biological denitrification method, nitrogen is removed in an anaerobic tank before going to a settling tank, and bubbles are removed in a re-aeration tank to prevent sludge from floating.

[0010] The nitrification denitrification reaction is a problem in activated sludge, and the purpose of the biological denitrification method is to cause the reaction. However, in both cases, it is necessary to control the likelihood of the nitrification denitrification reaction. is there. However, the activated sludge method usually only measures SV30, which measures the sedimentation of sludge in a cylinder. Even wastewater with a high risk of sludge floating trouble is sometimes analyzed for nitrogen in raw water, It is only necessary to measure the nitrate ion of the inflowing treated water and the nitrate ion of the treated water flowing out of the precipitation tank. Biological denitrification is similar. This is because the analysis of nitrogen content, ammonia nitrogen, and nitrate ion in wastewater is very expensive and time-consuming to maintain, and there is a problem with accuracy in simple measurement. This is because data cannot be obtained unless the measurement frequency is increased, so that it cannot be managed very much. Although there is a need as described above, the nitrification denitrification reaction is not very well controlled.

[0011]

The present invention predicts the danger of sludge floating trouble due to nitrification denitrification in activated sludge, and determines whether nitrogen removal is normally performed in biological denitrification. As a means for judging, an object of the present invention is to provide a wastewater treatment test method in which the concentration of nitrate ions or nitrite ions in a mixed solution is measured or the reaction amount of a denitrification reaction is evaluated.

[0012]

In a treatment test method for wastewater treatment using aerobic microorganisms, the rate at which oxygen dissolves in a mixed liquid containing activated sludge and waste liquid when the mixed liquid is aerated with an aeration device. The total mass transfer coefficient when the difference between the saturated dissolved oxygen concentration of the mixture and the dissolved oxygen concentration of the mixture at that time is defined as the driving force is represented by the symbol of Kabs,
The mixture is aerated for a sufficiently long time to obtain a value of highfinalDO when the dissolved oxygen concentration becomes substantially constant, a set amount of easily decomposable BOD substance is added to the mixture, and the aeration apparatus starts aeration at the time of aeration. When the aeration is started from the same initial value DO ₁ at the same time as the aeration start time, the change curve of the dissolved oxygen concentration DO according to the aeration elapsed time t obtained when the aeration is performed from the dissolved oxygen concentration DO ₁ to the high-final DO DO = highfinalDO -(highfinalDO-DO ₁ ) exp (-Kabs ・ t) The value BOD ₁ obtained by multiplying the area S ₁ surrounded by the virtual dissolved oxygen concentration change curve by Kabs and the easily decomposable BOD substance After the addition of the set amount, the supply of oxygen from the outside was stopped for a certain period of time to make the mixture anaerobic, and then the dissolved oxygen concentration curve at the start of aeration and the aeration from the dissolved oxygen concentration DO ₂ were obtained. Aeration started from the same initial value DO ₂ at time DO = highfinalDO- (highfinalDO-DO ₂ ) exp (−Kabs · t) The value BOD ₂ is obtained by multiplying Kas by the area S ₂ surrounded by the virtual dissolved oxygen concentration change curve calculated by the formula: , BOD
_From the difference between ₁ and BOD _2, the concentration of nitrate ions or nitrite ions in the mixture is measured, or the reaction amount of the denitrification reaction is measured.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the principle of the present method will be briefly described. When the mixed solution in the aeration tank is sampled and aerated by the aeration device of the present method, the dissolved oxygen concentration DO in the wastewater increases with the aeration elapsed time t, and the change is expressed by equation (5). You. Where DOsat is the saturated oxygen concentration [mg / l], DO is the oxygen concentration in the aeration tank [mg / l], Kabs is the overall mass transfer coefficient [1 / min], and ASact is the oxygen consumption rate used by activated sludge for breathing [ mg / l / min], BODac
t is the oxygen consumption rate used by activated sludge to decompose the BOD component [mg
/ l / min]. The first term on the right side of the equation (5) is the oxygen supply rate from the aeration device, and the second term is the oxygen consumption rate used by the activated sludge for respiration and BOD decomposition.

ASact is the rate of consumption of oxygen by the basic respiration of sludge. Since it is basal respiration, it is not directly related to the BOD component and is almost constant within a short time. It is known that ASact is constant regardless of the DO value if the DO value is approximately 0.5 mg / l or more, and this means that the mixture containing almost 0 mg / l of BOD component can be supplied with oxygen. When the change of DO is measured from a state where the dissolved oxygen concentration is high in a state where it is turned off, it can be easily proved by a linear decrease.

BODact is the consumption rate of oxygen used when sludge is decomposing BOD components. BODact determines whether the sludge is acclimated to the substance, the condition of the sludge, the water temperature,
It changes with habitat such as H and salt concentration. The microorganism is BO
When decomposing the D component, the reaction is carried out by an enzyme or the like corresponding to the BOD component, and each component has a specific reaction rate. Generally, in the process in which an organic substance is finally decomposed into water and carbon dioxide by a microorganism, it passes through several intermediate products, and the decomposition of each intermediate product has its own reaction rate. For this reason, when various BOD components are contained, such as raw water in wastewater treatment, the reaction processes are complicatedly overlapped, and it is difficult to specify one-to-one with the BOD components. And a step-like decomposition curve corresponding to the decomposition rate of the BOD component can be easily specified one-to-one with the BOD component.

When BODact changes during the aeration process (5)
The equation cannot be easily integrated, but the BOD component is almost 0mg / l
In the case of the mixed solution of formula (5), the BODact in equation (5) is almost 0, and equation (5) is as follows ASact is constant regardless of DO at approximately DO> 0.5 mg / l, as described above. Therefore, equation (6) can be easily integrated in the range of DO> 0.5 mg / l and expressed by equation (7). DO = α− (α−DO ₀ ) exp (−Kabs · t) (7) where α = DOsat−ASact / Kabs DO ₀ is an initial value when aeration is started. In equation (7), the second term on the right-hand side can be neglected if the aeration elapsed time t becomes sufficiently large, so DO = α = DOsat−ASact / Kabs (8) becomes constant, and this value is calculated by highfinalDO. Expressed as hig
hfinalDO If BOD component has little aerated a mixture of 0 mg / l, and finally can DO value and definition to arrive, (8) the _{DO = highfinalDO- (highfinalDO-DO 0} ) exp (-Kabs · t) (9) can be rewritten as The change of DO according to equation (9) is a curve as shown by the dotted line 1 in FIG.

On the other hand, when the BOD component is present in the mixture, the BODact has a non-negligible value, and the value of BODact changes from a large value to a small value with the aeration elapsed time t, mainly because the BOD component to be decomposed changes. However, when the BOD component that can be decomposed finally disappears, BODact changes to almost zero. For this reason, equation (5) cannot be simply integrated as in equation (9), but the change in DO is a curve as shown by the solid curve 2 in FIG. This curve shows that for simple BOD components such as methanol and acetic acid, the DO is constant at a low level that is balanced by the oxygen supply rate and the oxygen consumption rate of ASact + BODact during decomposition, and when decomposition is complete, It becomes a typical two-step curve like a constant line in FIG.

Now, an initial value DO ₀ of DO when aeration is started.
And the DO change curve represented by the equation (9) when the BOD component in the mixture was almost 0 mg / l was aerated.
When the DO change curve when the mixture is aerated when the BOD component is present in the mixture is represented by the solid line in FIG. 1, the dotted line and the solid line at each aeration elapsed time The difference between the values represents the difference due to the oxygen consumption rate used to decompose the BOD at that time, and the value obtained by integrating this difference with the elapsed aeration time t corresponds to the area S enclosed by both curves. Multiplied by Kabs corresponds to the amount of oxygen used by the microorganism to decompose the BOD component. This value is JI
Although different from the BOD measurement method defined by the S method, the measurement principle itself of measuring the amount of oxygen required for microorganisms to decompose is the same. The BOD measurement method of the JIS method requires a long time of 5 days, but this measurement method uses sludge that has already been sufficiently acclimated and uses a sludge with a high concentration of several thousand mg / l, so it takes about several tens of minutes. A value highly correlated with the BOD of the JIS method can be measured in a short time. This measurement principle itself is described in Japanese Patent Application Nos. 9-342261, 10-119919, and 200.
As already described in detail in U.S. Pat. No. 4,064,412, the present invention is a method utilizing the above principle from another angle.

A specific operation method will be described below. BOD of the mixed liquid sampled from the aeration tank is almost 0 mg / l, or even if BOD components remain at the beginning of the sampling, the BOD is sufficiently aerated in the measuring device and the BOD is almost 0 m
To the g / l mixed solution, a solution containing a specified concentration of an easily decomposable organic substance (hereinafter referred to as a BOD standard solution) was added to the mixed solution in a set amount, and then mixed with the mixed solution. The mixed solution is kept in an anaerobic state by aeration, and then the mixed solution is aerated by an aeration device of a measuring device, and a change curve of DO during that time is measured. If nitric acid ions are present in the mixed solution and there is an environment in which the denitrifying bacteria can be active in the activated sludge, the denitrifying bacteria will react with nitric acid Nitrate ions are reduced to nitrogen using organic matter in the BOD standard solution.
For this reason, the value obtained by measuring the BOD amount by the calculation based on the above-described principle from the DO change curve that rises by aeration after the anaerobic period is calculated as BOD
_The BOD amount calculated from the DO change curve in which aeration was started immediately after the addition of the BOD standard solution without an anaerobic period was defined as B.
When OD _1, BOD ₂ becomes a value smaller than the BOD _1. BOD ₁ -BOD ₂ corresponds to the amount used for reducing nitrate ions and nitrite ions and the amount used for growing denitrifying bacteria. Further, the amount of the organic matter consumed depends on the amount of nitrate ions and the vitality and concentration of the denitrifying bacteria, provided that the components and the concentration of the BOD standard solution are fixed. Thus by comparing the BOD ₁ and BOD _2, a nitrate ion and nitrite ion concentration in the mixed liquor can be metered, it can be evaluated and the reaction amount of denitrification.

Here, the mixed solution having a BOD of almost 0 means BODa
This means that the waste liquid has a small value of ct and hardly changes within the measurement time, and when measured over a long period of time such as the BOD of the JIS method, there is a BOD component having a very small decomposition rate that decomposes slowly over a long period of time. Even BOD ₁ and B
Since it affects both OD ₂ equally, the calculation error is small and almost does not hinder.

As the organic substance of the BOD standard solution, the most easily decomposable organic substance contained in raw water, to which the activated sludge used for the test has been sufficiently acclimated, can be used. Generally, methanol represented by the formulas (3) and (4) is used. Or ethanol or acetic acid.

Next, an example of a specific measuring method based on the above measuring principle will be described. This measurement method is intended to be used as an operation management device installed in a running activated sludge device or biological denitrification device, and is hereinafter referred to as measurement method 1. FIG. 2 is a diagram showing this state. Measurement method is Step
Step 1 consists of two steps, Step 3 and Step 3
It consists of three sub-steps: 1, Step 3-2 and Step 3-3. Step1
And Step 3 are defined as one cycle, and this cycle is repeated. St
ep1 is a process of pumping the mixed solution in the aeration tank into the device by a sampling pump and sufficiently replacing the inside of the device with a new sample solution. In Step 3, the sampled mixture is first aerated with an aeration device as Step 3-1 and the BOD in the mixture is
Aeration is continued until the dissolved oxygen concentration becomes highfinalDO by decomposing the components. When the dissolved oxygen concentration becomes highfinalDO, the process proceeds to Step 3-2. The solid line 3 in FIG. 2 shows the dissolved oxygen concentration change curve at this time. In Step 3-2, a set amount of a BOD reference solution is first added to the mixed solution and aerated.
The dissolved oxygen concentration starts from highfinalDO and decomposes the BOD component in the BOD standard solution by using highfinalDO-BODact /
The value decreases toward the value corresponding to Kabs. When the BOD component in the BOD standard solution is completely decomposed, the value increases toward highfinalDO. When the value becomes constant at highfinalDO, the process proceeds to Step 3-3. The solid line 5 in FIG. 2 shows the dissolved oxygen concentration change curve at this time. In Step3-3, BOD is first added to the mixture at the beginning
The aeration is stopped by adding the same amount of the reference solution as in Step 3-2.
Since a readily decomposable BOD component is added and there is no supply of oxygen from the outside, the dissolved oxygen concentration drops sharply to almost 0 mg / l and becomes anaerobic. In this state, aeration is started again after a certain period of time, and when the remaining BOD component in the mixed solution is decomposed and the dissolved oxygen concentration becomes highfinal DO, Step 3-3 is terminated, and St.
The entire ep3 ends. The solid line 7 in FIG. 2 shows the dissolved oxygen concentration change curve at this time. Step 3-1 is a step of previously decomposing the BOD component in the mixed solution by aeration. The solid line of FIG. 2 and the BOD are mixed from the area S surrounded by the virtual dissolved oxygen concentration curve 4 of almost 0 mg / l. The BOD of the liquid can be calculated.
Step3-2 aerated by the addition of BOD standard solution of step the dissolved oxygen concentration variation curves 5 and BOD is Motomari value of BOD ₁ from the virtual dissolved oxygen concentration curve area S ₁ surrounded by 6 most 0 mg / l, Step3 -3 Process BOD standard solution is added to create an anaerobic state and then aeration is performed.
from the area S ₂ surrounded by the virtual dissolved oxygen concentration curve 8 of g / l to B
The value of OD ₂ is obtained. More precisely, the value of BOD ₂ is Step
3-3 The difference in dissolved oxygen concentration from highfinalDO to anaerobic state at the start of the process is also added as a slight correction to the value obtained from the dissolved oxygen change curve after aeration as the amount of BOD aerobic microorganisms decomposed by oxygen. . If the difference between BOD _{1 and} BOD ₂ is large, the reactions of equations (3) and (4) are actively performed, and if the difference is small, the reaction is slow.

In the above example, the BO of the sampled mixture is
Decomposing D component, subsequently when the dissolved oxygen concentration became HighfinalDO, because of the transition to the measurement to determine the BOD _1, DO ₁ is to become equal to the HighfinalDO, virtual dissolved oxygen concentration curve 6 in HighfinalDO It becomes a constant straight line.
In the step of obtaining BOD ₂ , aeration starts from an anaerobic state, so that DO ₂ is usually 0 mg / l. Therefore, the equation (9) for calculating the hypothetical dissolved oxygen concentration curve 8 does not hold strictly. However, in the case of a waste liquid having a BOD of almost 0 mg / l, the ASact becomes constant in a very short time, approximately 0.5 mg / l or more. Since the DO rises, the BOD becomes almost 0mg / l virtual waste liquid from the beginning.
Applying equation (9) has a small error and does not hinder practical use.

Step 3-1 is an operation for previously bringing the BOD in the mixture to almost 0 mg / l. However, when the BOD in the mixture is already almost 0 mg / l, or when the BOD value is determined by another method, If the degree of change during the measurement period is known, it can be obtained by subtraction from the above measured value and can be omitted. In addition, the object can be similarly achieved by reversing Step 3-2 and Step 3-3.

The measuring method 1 includes a Step 3-2 step of measuring the BOD of the BOD standard solution added every cycle, but when the activity of the activated sludge is stable, the same value is obtained every time. Not every cycle to reduce
It is possible to omit at once every 2-3 cycles. However, when activated sludge changes its activity, it is difficult to predict when the activity of sludge changes. Therefore, it is not preferable to continuously omit Step 3-2 for many cycles.

Next, an example of an apparatus for implementing the above-mentioned measuring method 1 will be described. FIG. 3 shows a specific example when the apparatus according to the present invention is installed in an activated sludge treatment apparatus. 9 is an aeration tank and 10 is a sedimentation tank. 11 is a control unit of the device according to the present invention. The main device of the control unit is a personal computer. Reference numeral 12 denotes a measuring unit of the device according to the present invention. A sampling pump 13 is a part of the inspection device. The apparatus according to the present invention pumps the mixed solution from the aeration tank with a sampling pump according to a command from the control unit, performs the inspection from Step 1 to Step 3 of the embodiment in the measurement unit, and transmits the DO change data to the control unit for control. Analyzed by the part. In the case of standard activated sludge, a sampling pump is usually installed near the outlet of the aeration tank. Since the BOD in the waste liquid has already been treated near the outlet of the aeration tank, Step3-1
This is because the measurement process can be shortened because the process is short. Since the nitrification reaction proceeds actively at the end of the BOD treatment, the vicinity of the outlet of the aeration tank is appropriate. In the biological denitrification method, the vicinity of the outlet of the nitrification tank is appropriate for the same reason. Next, an example of an apparatus for realizing the above-described measurement method 1 will be described.

FIG. 4 is a flow sheet showing an example of an apparatus embodying the present invention. 14 is a dissolved oxygen meter. Reference numeral 15 denotes a measuring vessel, in which a sensor of a dissolved oxygen meter is immersed in a mixed solution in the vessel. The shape of the container is such that the arrangement of the inlet and outlet of the liquid and the accumulation of air do not occur so that the measurement error does not occur due to the dissolution of oxygen from the liquid surface. 13 is a sampling pump. Reference numeral 16 denotes a stirring pump, and 17 denotes an aeration container. 18 is an aeration solenoid valve, 19 is an aspirator, 20 is an air flow control valve, and 21 is an overflow pipe. In Step1, 1
The sampling pump of No. 3 operates and is discharged from the overflow pipe of No. 21 via Nos. 17 and 15. 17-2
Numeral 0 denotes a system used when re-aeration in Step 3 is performed. The aeration solenoid valve 18 is opened to suck and agitate air from an aspirator 19 to dissolve oxygen and separate bubbles in an aeration container. Reference numeral 22 denotes a BOD reference liquid tank, and 23 denotes a BOD reference liquid addition pump. 22 to 23 are set amount B in Step 3
Used when adding OD material. The 16 stirring pumps
It is used to always maintain the flow velocity near the sensor of the dissolved oxygen meter and to obtain the circulating water flow to the aspirator when the aeration solenoid valve is open in Step 3. Numeral 24 is a thermometer and the measured value is connected to the control unit 11 via a controller. During the measurement time, the temperature of the mixed liquid at the time of sampling is controlled by the heater 25 and the cooling pipe 26 so that the inside of the apparatus becomes constant. Is done. The operation of the inspection operation, the analysis of the measurement data, the instruction of the operating condition, the alarm, and the like of the present invention are all centrally managed by the computer of the 11 control units. An ordinary personal computer can be used as the computer used in the present invention. In this embodiment, IBM Corporation's Optiva is used, and the extended I / O is used.
IBX-3133 manufactured by Interface Co., Ltd. as an analog-to-digital or digital-to-analog conversion board in the O slot.
IBX-3325 was used, and IBX-2727 manufactured by Interface Co., Ltd. was used as a digital output board for driving commands such as pumps. 27 and 28 are a control section and a measurement section terminal board. The drive of the pump and the solenoid valve operates the relay by the signal from the computer via the digital output board.
ON-OF the equipment at the required timing from 1 to Step 3
F. Incidentally, the Step 1 step is about 3 minutes, and the Step 3-1 step is variable depending on the BOD amount in the mixture, but is usually about 10 minutes to 60 minutes since the mixture is near the outlet of the aeration tank. St
The ep3-2 step is usually about 20 minutes, and the anaerobic state of the Step3-3 step is 10 minutes.
It is appropriate that the aeration time is about 15 minutes with a total of about 25 to 35 minutes. 29 is a converter of the dissolved oxygen meter. 1
The signal of the dissolved oxygen meter 4 is converted into an analog current signal of 4-20 mA by the converter 28, converted by the analog-to-digital conversion board of the computer 11 and taken into the computer. The computer calculates BOD ₁ and B
The comparison results of OD ₂ displays output on a computer screen as a reaction amount of nitrate ion concentration or denitrification. The hardware for realizing the present invention is basically the same as that shown in Japanese Patent Application No. 8-205359, "Wastewater treatment control method and apparatus" and Japanese Patent Application No. 10-119919, "Wastewater treatment control method". The present invention realizes, by computer software, a measurement method for controlling the hardware and calculation analysis display of the obtained dissolved oxygen concentration change data by the above-described method.

An example of the result measured by the above-mentioned apparatus example is shown below. A BOD standard solution containing 4.5 cc / l methanol as a component with respect to the volume of the mixed solution in the device of 2300 cc
Add 14cc each at the beginning of tep3-3, and the aeration time of Step3-2 is 2
2 minutes, Step 3-3 was performed under the conditions of anaerobic time 15 minutes and re-aeration time 15 minutes, and Kabs = 0.6 [1 / min] and highfinalDO = 6.0 [mg / l]. As a result, BOD ₁ = 20 mg / l. On the other hand, BOD ₂ = 5 mg / l, and the amount of BOD decomposed by the denitrification reaction was 15 mg / l. This BOD amount was 16.4 mg / l in terms of methanol, and assuming that this reaction was all carried out by the reaction of formula (4), 38 mg / l of nitrate ion was reduced to nitrogen gas by denitrification in 15 minutes. Will be. This result indicates that the activated sludge treatment apparatus has a great risk of sludge floating and is at a warning alert level, and is judged to be normal in the biological denitrification method.

HighfinalDO and ASact used for operations and calculations
And Kabs values are stored in advance in a storage device of a computer, but these values slightly change depending on conditions such as the properties and temperature of the activated sludge. Ask for. FIG. 5 is a diagram showing this state. If sampling is performed in Step 1 and aeration is performed without adding anything in Step 3, and the aeration time is sufficiently long, the dissolved oxygen concentration becomes constant at a high level. The value at that time is highfi
nalDO. This state is shown in the Step 3 aeration period in FIG.
At that time, the aeration is stopped, the supply of oxygen from outside is stopped, and the rate of decrease of the dissolved oxygen concentration is measured. This state is shown in Step 3 of the aeration stop period in FIG. As time further elapses and the rate of decrease decreases linearly
Aeration is resumed when the dissolved oxygen concentration becomes sufficiently lower than that of highfinalDO, and the rise curve of the dissolved oxygen concentration is measured.
The result 30 in FIG. 5 is the result. The Kabs is changed by the equation (9) with the dissolved oxygen concentration at the time of restarting the aeration as the initial value DO ₀ , and the value that can best approximate the 30 measurement curves is Kabs.
This is shown in the Step 3 re-aeration period in FIG.

In the above example of the apparatus, the operation control apparatus has been shown to be installed in the activated activated sludge apparatus or the biological denitrification apparatus. However, the experiment can be carried out by simply replacing the Step 1 step with the operation of putting the mixture in the sampling vessel. Needless to say, it can also be used as a laboratory analysis instrument.

The method of the present invention can be sufficiently effective as an apparatus for evaluating the reaction amount of denitrification as an example of the above-described apparatus or an analytical and analytical instrument in a laboratory. If this function is incorporated into the 3StepDO control method described in 205359 and Japanese Patent Application No. 10-119919, the BOD of the treated water of the activated sludge method and the biological denitrification method and the sludge activity can be simultaneously displayed on the computer screen in a short time. Become a powerful operation management device. 3S
In the tepDO control method, the mixed liquid is sampled from the aeration tank in Step 1, the sampling is stopped in Step 2, the supply of oxygen from the outside is stopped, and the decreasing rate β of the dissolved oxygen concentration is measured, and when β is larger than a preset value. In step 3, aeration is performed without any addition, and the BOD of the mixed solution is calculated from the rising curve of the dissolved oxygen concentration based on the same principle as in the present invention. If β is smaller than a preset value, a set amount of a BOD standard solution containing a BOD component that can be easily decomposed is added, and aeration is performed to measure the sludge activity from the rising curve of the dissolved oxygen concentration.

FIG. 6 shows one pattern of the 3 Step DO control method, St.
It is a figure which shows the DO change when this invention is incorporated when it becomes an ep3 (BOD addition) process. Step1 of 3StepDO control method
Is the same operation as Step 1 of the measuring method 1 of the present invention. Also 3
Since the BOD standard solution used in the StepDO control method is made of a BOD component that can be easily decomposed, it can be used as the BOD standard solution of the measuring method 1 of the present invention. Fig. 6
The magnitude β of the slope is measured from the 31 DO change curve, and the measurement method of Step 3 is selected according to the magnitude. That is, when β is smaller than the set value, the process is the Step 3 (BOD addition) step of adding the BOD reference solution and performing aeration. This operation is the same as the Step 3-2 step of the measuring method 1 of the present invention.
BOD ₁ can be calculated from the area S ₁ surrounded by the measurement curve of _No. 33 and the virtual dissolved oxygen concentration curve of 33. Therefore, if the sludge activity is determined to be normal in the Step 3 (BOD addition) step of the 3Step DO control method, the Step 3-3 of the measurement method 1 of the present invention is continued.
When the process is performed, the sludge activity and the nitrification denitrification reactivity can be simultaneously measured without wasting the measurement time, which is convenient. β is the rate of decrease of DO during the aeration stop period, so β = A from equation (5).
Sact + BODact, and the set value for BOD addition is B
ODact because a state that a slight but BOD of the waste liquid in a small amount in the BOD ₁ described above is plus, BODact the measuring method 1 of continuing the present invention since the change amount in the measuring time for a small value smaller Step3- BOD ₂ measured in three steps is similarly added, and is canceled in the subtraction of BOD ₁ and BOD ₂ , so that the error is small and is at a level that does not hinder practical use.

If β is large in the 3 Step DO control method, it is evidence that the undecomposed BOD component in the mixture is large, so that the BOD in the mixture is measured by aeration without adding anything. Since this operation corresponds to Step 3-1 of the measuring method 1 of the present invention, if the dissolved oxygen concentration becomes highfinal DO and the Step 3-2 and Step 3-3 steps of the measuring method 1 of the present invention are performed, β
The nitrification denitrification reactivity can be evaluated even in the case of a large value. However, when β is large, it may take a long time until the dissolved oxygen concentration becomes highfinal DO, and if this operation is performed every time, it may be difficult to grasp changes in the BOD processing state. It is more practical to carry out the measurement method 1 of the present invention even when β is large only when there is a high risk of sludge floating in the denitrification reaction in the measurement when β is small, or to make it selectable with the option button on the computer. It is. In the biological denitrification method, the purpose is to treat BOD and remove nitrogen simultaneously. One of the important factors affecting the nitrogen removal rate is to convert the nitrogen content in the waste liquid to nitrate nitrogen via ammonia nitrogen. This is a fogging nitrification process.
It is necessary to decompose the OD component. Therefore, when β is large, the removal rate of nitrogen is naturally reduced by the evidence that BOD treatment is insufficient. When β is large, emphasis is placed on grasping changes in the BOD treatment state as described above, and β is increased. When the method of the present invention is focused on a small case, the efficiency of the whole measurement is improved.

[0034]

The present invention can be applied to an activated sludge treatment apparatus and a biological denitrification method, and in the activated sludge method, quantitatively predicts the risk of trouble of sludge floating due to denitrification in a sedimentation tank. In the biological denitrification method, the determination of whether or not the denitrification reaction is normally performed can be quantitatively expressed, which is useful for each operation management. In addition, if this function is incorporated in the 3StepDO control method shown in Japanese Patent Application Nos. 8-205359 and 10-119919, the BOD of the treated water of the activated sludge method and the physical denitrification method, and the health condition of the sludge Can be simultaneously displayed on a computer screen in a short time, which is more effective for operation management.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating the principle of the present method.

FIG. 2 is a diagram illustrating a measurement method of the present invention.

FIG. 3 is a diagram showing the relationship between the apparatus according to the present invention and an activated sludge treatment apparatus.

FIG. 4 is a flow sheet for explaining an example of the apparatus of the present invention.

FIG. 5 is a diagram illustrating a method for measuring Kabs and highfinalDO.

FIG. 6 is a diagram illustrating an example in which the method according to the present invention is incorporated in a 3Step DO control method.

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Claims (1)

[Claims] Claims: 1. Treatment in wastewater treatment using aerobic microorganisms
In the test method, a mixture containing activated sludge and waste liquid is aerated.
The rate at which oxygen dissolves in the mixture when aerated with the device
Is the saturated dissolved oxygen concentration of the mixture and the
Overall substance based on the difference in dissolved oxygen concentration as the driving force
When the transfer coefficient is represented by the symbol of Kabs, the mixture
Value when dissolved oxygen concentration becomes almost constant
(Hereinafter referred to as highfinalDO), and
Add a set amount of easy-to-dissolve BOD substance and aerate with the aerator
Dissolved oxygen concentration at the start (hereinafter DO₁Abbreviated to) highfin
Elapsed aeration time obtained when aeration is performed to alDO
Dissolved oxygen concentration (hereinafter referred to as DO)
The same initial value DO at the same time as the change curve
₁DO = highfinalDO- (highfinalDO-DO₁) Exp (-Kabs ・ t)
Area S₁Multiplied by Kabs (hereinafter BOD₁Is called)
At a certain time after adding a set amount of easily decomposable BOD substance
The supply of oxygen from outside is cut off to make the mixture anaerobic.
Dissolved oxygen concentration at the start of aeration (hereinafter DO_TwoAbbreviated)
Curve of dissolved oxygen and aeration obtained by starting aeration
Same initial value DO at the same start time_TwoStart aeration from
DO = highfinalDO- (highfinalDO-DO_Two) Exp (-Kabs ・ t)
Area S_TwoMultiplied by Kabs (hereinafter BOD_TwoIs called)
And BOD₁And BOD_TwoFrom the difference in
Measurement of nitrogen and nitrite ion concentration or denitrification reaction
A test method for measuring quantities.