JP2012020225A - Method for evaluating denitrification strength of sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for controlling denitrification strength of a liquid mixture containing activated sludge in an activated sludge or biological denitrification process.SOLUTION: A precipitation test method using a cylinder includes, when the ratio of the liquid level of the liquid mixture containing the activated sludge to the liquid level of a sludge layer in the cylinder after allowing the cylinder to stand is referred to as SV, comparing SV2 with SV1, where an SV value measured after a longer standing time is S2 and an SV value measured after a shorter standing time is SV1, to thereby evaluate the denitrification level of the liquid mixture containing the activated sludge. A method includes preliminarily adding a BOD solution to the liquid mixture containing the activated sludge in the cylinder which is to be allowed to stand over a longer time and mixing them, then measuring SV2s after standing and comparing the SV2s with SV1 to thereby evaluate the denitrification strength versus the amount of nitrate nitrogen in the liquid mixture containing the activated sludge.

Description

  The present invention relates to an operation control method for a wastewater purification apparatus, and more particularly to a method for managing the strength of denitrification of sludge in wastewater treatment using aerobic microorganisms.

  Engineering fields using microorganisms are diverse, but representative fields include wastewater treatment. Among them, activated sludge treatment is the most general wastewater treatment method. The basic process of the activated sludge treatment method is as follows. That is, waste water is put into an activated sludge mixed solution containing aerobic microorganisms at a high concentration, and dissolved oxygen dissolved in the mixed solution by aeration is used to decompose and purify contaminants in the waste water. Furthermore, it isolate | separates into sludge and supernatant water in a sedimentation tank, the sedimented sludge is returned to an aeration tank as return sludge, and supernatant water is discharged | emitted as treated water.

As a solid-liquid separation method for the activated sludge mixed liquid, precipitation treatment by gravity is often used, and in this case, sludge sedimentation management is extremely important for operation control.
Sludge sedimentation varies depending on various factors, but as a typical factor that develops into trouble, nitrate ions cause a denitrification reaction in the sedimentation tank, and the fine nitrogen gas produced causes sludge to become poorly settled. There are cases where sludge emerges.

  Similarly to activated sludge, in a biological denitrification process that simultaneously removes BOD and nitrogen by combining aerobic treatment and anaerobic treatment using microorganisms, nitrate ions in raw water or nitrifying bacteria in a nitrification tank for aerobic treatment are used. The nitrate ions produced by the action are reduced to nitrogen gas by the action of denitrifying bacteria in the presence of a BOD source in an anaerobic state.

  In terms of operational management, a common requirement for both is how to evaluate the denitrification reaction of the mixture. In principle, it is sufficient to measure the nitrate ion and nitrite ion in the mixed solution before and after the denitrification reaction and evaluate the difference between before and after. However, it is not easy to accurately measure nitrate ions and nitrite ions in an activated sludge mixed liquid containing various interfering substances. For example, in the ion electrode method, the measurement in activated sludge is actually difficult. Moreover, the instrument which automated the official method has a problem that it is expensive and difficult to handle.

For this reason, conventionally, a method for evaluating the denitrification reaction by a simple method has been proposed (for example, Patent Documents 1 to 3).
In Patent Document 1, the oxygen utilization rate (Nt-Rr) associated with the denitrification reaction in the activated sludge mixture and the value obtained by subtracting Nt-Rr from the total oxygen utilization rate in the mixture (ATU-Rr) are measured. , Nt-Rr and ATU-Rr, a method for determining whether or not the mixed liquid in the sedimentation tank is in a state where sludge floating phenomenon is likely to occur is disclosed.

In Patent Document 2, the liquid mixture before entering the settling tank is quantitatively collected in a cylinder, allowed to stand for a set time, and then the position of the sludge phase is measured to detect whether the sludge has floated. A method for evaluating the risk of denitrification and floating of sludge is disclosed.
Further, in Patent Document 3, in a reaction system using a microorganism in which carbon dioxide gas and a gas having low solubility in water such as nitrogen gas or methane gas are simultaneously generated, the measurement target liquid is charged in a sealed container, The liquid to be measured in the container is deaerated under reduced pressure, left for a predetermined time after deaeration, the amount of pressure change in the container due to the gas generated during the standing is measured, and the increase in the space volume of the container A method for evaluating the reactivity by calculating the amount of generated gas based on the pressure change amount is disclosed.

JP-A-6-304581 JP 2006-175357 A JP-A-2005-238089

  Any of the above methods is a detection method that assumes a denitrification reaction strength that is large enough to cause sludge levitation, and is not appropriate as a method for evaluating a relatively small denitrification reaction strength that affects the sedimentation property of sludge. At present, no method has been found to evaluate the denitrification reaction intensity over a wide range at low cost and with high accuracy.

As a result of diligent research, the present inventor has found a method capable of easily and accurately measuring the denitrification reaction intensity over a wide range, and has completed the following invention.
That is, the first invention is
A method for evaluating the degree of denitrification reactivity of an activated sludge mixture in an activated sludge or biological denitrification process,
The activated sludge mixed solution is allowed to stand in a cylinder, and SV1 and SV2, which are SV values after standing for a short time (t1) and standing for a long time (t2) (where t2> t1), are measured.
It is characterized by evaluating the degree of denitrification reactivity by comparing SV1 and SV2.
Here, the SV value refers to the ratio (h2 / h1 × 100 (%)) of the sludge layer liquid surface height (h2) after standing with respect to the liquid surface height (h1) of the activated sludge mixed liquid.

The second invention is a method for evaluating the degree of denitrification reactivity of the activated sludge mixed solution in the activated sludge treatment or biological denitrification process, wherein the activated sludge mixed solution is left in the first cylinder. The SV value (SV1) after standing for a short time (t1) was measured, and the BOD solution was added in advance to the second cylinder containing the activated sludge mixed solution, and then left standing for a long time. The later SV value (SV2s) is measured, and the magnitude of denitrification reactivity is evaluated by comparing SV1 and SV2s.
The first cylinder and the second cylinder are not necessarily separate cylinders. For example, the mixture is discarded after the SV1 measurement, and the SV2s measurement is performed by the above procedure using the same cylinder. It may be.
The third invention is characterized in that, in each of the above inventions, the short-time standing (t1) is 20 minutes to 40 minutes, and the long-time standing (t2) is 60 minutes to 150 minutes.

The operation of the first invention is as follows. When the activated sludge mixed liquid is put in the cylinder and left to stand, the sludge and the supernatant liquid are separated with time as shown in FIG. Here, the SV value (hereinafter referred to as a short time SV value) at a short standing time (t1 minutes) is designated as SV1, and the SV value (hereinafter referred to as a long time SV value) at a long standing time (t2 minutes) is designated as SV2. To do. If there is no action due to denitrification, as shown in (a) of the figure, sedimentation proceeds with time and the SV value decreases and SV2 <SV1.
However, when nitrate ions or nitrite ions are present in the liquid mixture and the BOD component is present as a carbon source, the sludge layer of the cylinder becomes an anaerobic environment during the standing time, and the action of denitrifying bacteria The nitrate ions are reduced to nitrogen gas. As a result, fine nitrogen gas is generated in the sludge and adheres to the sludge to generate buoyancy, so that SV2> SV1 as shown in FIG. When a large amount of denitrification reaction occurs, sludge rises as shown in (c) of the figure, and SV2 cannot be measured.
From the above, it is possible to evaluate the denitrification reaction strength of the activated sludge mixture by comparing the short time SV value (SV1) and the long time SV value (SV2).

Next, the operation of the second invention is as follows. The denitrification reaction requires the presence of nitrate ions and a BOD source in an anaerobic state. When the BOD treatment of the activated sludge mixture is good and the residual BOD is low, the denitrification reaction is unlikely to occur even if nitrate ions are present, and the denitrification reaction intensity is not necessarily the amount of residual nitrate nitrogen in the activated sludge mixture Is not proportional.
When evaluating sedimentation in an activated sludge sedimentation tank, the sedimentation in the sedimentation tank and the risk of sludge levitation are evaluated, so there is no problem in the evaluation including the effect of residual BOD. Since the purpose of the denitrification process is to determine whether denitrification is normal, it is inconvenient for the result to change depending on the amount of residual BOD. For this reason, in order to prevent the shortage of the BOD source, a sufficient amount of BOD source (such as methanol) is added in advance for the denitrification reaction, and the mixture is stirred and allowed to stand. Thereafter, SV2s is measured, and the denitrification reaction intensity is further evaluated by (SV2s / SV1). Since this strength is proportional to the amount of nitrate nitrogen in the mixed solution, it becomes a management index for determining whether the denitrification step of the biological denitrification process is normally performed.

Next, the operation of the third invention is as follows.
The first and second inventions compare SV1 which is a short-time SV value and SV2 which is a long-time SV value, and evaluate denitrification reactivity. It is necessary to set the time appropriately.
t1 is preferably a standing time with less error and less influence by the denitrification reaction after transferring to compaction than the rapid sedimentation process.
It is about 15 minutes to 45 minutes after standing that the sludge sedimentation moves from rapid sedimentation to consolidation.
In addition, the activated sludge in which aerobic microorganisms are the main treatment and the denitrification reaction in the biological denitrification process are due to the action of denitrifying bacteria that are facultative anaerobic bacteria. Sampled into a cylinder, consuming dissolved oxygen and becoming anaerobic, until denitrifying bacteria change from taking up dissolved oxygen to taking in oxygen from nitrate ions, and further generating nitrogen gas to affect sludge settling In general, it usually takes about 1 hour or more. When the standing time is about 30 minutes as shown in (b) of FIG. 1, the difference from the SV value of the mixed solution that does not cause the denitrification reaction shown in (a) is slight.
Of course, in the case of a mixed solution that causes a large denitrification reaction that causes sludge levitation, even if it is left at rest for about 30 minutes, as shown in FIG. In the case of SV for a long time, since sludge floats up, it is possible to evaluate the denitrification reaction strength without comparing SV2 / SV1.

Therefore, if the short standing time is set to about 15 to 45 minutes, the error is in a range where there is little error in practical use, and in that range, about 20 to 40 minutes as short as possible is reasonable, and the past activated sludge In view of the fact that the SV value when the standing time is 30 minutes is SV30 and has been used as an important index for driving operation, it is most preferably 30 minutes.
Further, the long standing time t2 should be set in a range in which a denitrification reaction that affects the sedimentation property of the sludge can be detected and a decay reaction due to anaerobic does not occur. The denitrification reaction that affects the sedimentation property of the sludge can be sufficiently detected when about 1 hour or more has passed since the start of standing. In addition, there is a wide range of spoilage depending on the properties of the activated sludge mixed liquid and the accompanying BOD. In general, considering that the residence time of the sludge phase in the activated sludge settling tank is about 180 minutes, t2 is suitably from 50 minutes to 180 minutes, preferably from 60 minutes to 150 minutes.

  FIG. 2 shows the relationship between the amount of residual nitrate nitrogen in the mixed solution and the denitrification reaction intensity (SV2 / SV1) under the condition that the BOD source is sufficiently present in the mixed solution. Although it varies depending on the properties of the activated sludge mixture and MLSS, etc., the amount of residual nitrate nitrogen and the denitrification reaction intensity are generally proportional to each other in the range where the amount of residual nitrate nitrogen in the mixture is relatively small (see the figure). Proportional area). When the amount of residual nitrate nitrogen is large and sludge floats up, SV cannot be measured in the first place, so it cannot be evaluated by (SV2 / SV1) (sludge floating region in the figure).

  According to the present invention, in activated sludge, the denitrification reaction strength of the activated sludge mixed liquid, which is important for managing sludge settling in the settling tank, managing the reaction state of the denitrification step in the biological denitrification process, and the like, It becomes possible to evaluate by a simple method.

It is a figure which shows the relationship between the denitrification reaction intensity | strength of a liquid mixture, and SV value time change. It is a figure explaining the relationship between the quantity of residual nitrate nitrogen in activated sludge liquid mixture, and denitrification reactive strength. It is a figure which shows the denitrification reaction measuring apparatus 10 which concerns on embodiment of this invention. It is a figure which shows the sedimentation state of the sludge in the cylindrical SV tank in embodiment. It is a figure which shows the relationship between the sludge sedimentation state in the case of FIG. 4, and an absorbance change.

Hereinafter, embodiments of the present invention will be described in more detail. Needless to say, the scope of the present invention is described in the claims and is not limited to the following embodiments.
FIG. 3 is a diagram showing a denitrification reaction measuring apparatus 10 for evaluating a denitrification reaction according to the present invention.
The sampling sludge 1 samples the activated sludge mixed liquid from the vicinity of the outlet of the aeration tank (not shown), and charges the SV measuring tank 2 (hereinafter referred to as the SV tank) having an actual volume of 1 liter with a certain amount. A predetermined amount of the additive solution in the additive solution tank 3 is added to the charged mixture solution by the addition pump 4, and the mixture is stirred and mixed by the stirring pump 5. Here, the additive solution supplies a carbon source necessary for denitrifying bacteria to reduce nitrate ions. For example, a methanol solution or an acetic acid solution can be used. Whether it is actually added depends on the purpose of use. That is, the additive liquid is not used for the purpose of managing the settling / rising risk of sludge in the activated sludge settling tank. On the other hand, for the purpose of managing the denitrification reaction in the biological denitrification process, an additive solution is added.
The measurement is performed in two stages. In the first stage, the sampled mixed solution is allowed to stand in a SV tank for a preset time (for example, about 30 minutes) without adding the additive solution, and the volume SV1 of the settled sludge phase after standing is measured.
After the measurement, the mixed solution is discarded, and a new activated sludge mixed solution is sampled by the sampling pump 1, and an additive solution is added as necessary in accordance with the above purpose. After stirring, the mixture is allowed to stand for a preset time (for example, about 90 minutes), and the volume SV2 of the settled sludge phase after standing is measured. If sludge rises during standing, mark the measurement data as being in a floating state and set SV2 = 100.

The volume or height of the sedimentation sludge phase in the SV tank can be measured by measuring the sludge concentration while moving the MLSS meter sensor in the depth direction of the SV tank and obtaining the sludge concentration distribution in the SV tank. is there. In addition, as in the apparatus of FIG. 3, an absorptiometer 6 is provided at the lower outlet of the SV tank, and a discharge metering pump 7 or the like is used to adjust the absorptiometer at a flow rate that does not disturb the sludge interface in the SV tank. While discharging between the cells, the change in absorbance can be measured, and the position of the sludge phase and the concentration of the sludge phase can be specified from the change in the discharge flow rate and the absorbance. FIG. 4 and FIG. 5 are diagrams showing the sedimentation state and absorbance change of the sludge in the SV tank by this method, respectively. The computer 8 manages the measurement data of the operation and absorbance of all the devices including the pump.
FIG. 4 (a) shows a state in which sludge does not float and settles normally in the absence of nitrate ions, and FIG. 4 (b) shows a case in which sludge does not float completely when there is a little more nitrate ions. FIG. 4 (c) shows a state in which the sludge is completely levitated when a large amount of nitrate ions are present.
Fig.5 (a) is a figure which shows the intensity | strength change of the transmitted light when the liquid mixture of the SV tank of Fig.4 (a) is discharged | emitted. Since there is a large change in the transmitted light when passing through the sludge phase and the transmitted light when passing through the supernatant phase, the position and state of the sludge phase can be easily identified by computer analysis.

In this embodiment, SV1 and SV2 were measured using one cylindrical SV tank. The sludge measured for SV1 and the sludge measured for SV2 are not the same, but if SV2 sludge is sampled after measuring SV1, the time delay is about 30 minutes, so it is possible to evaluate it as the same sludge.
Of course, two cylindrical SV tanks may be used and measurement may be performed with completely the same sludge.
Further, in the measurement method according to the first invention, after measuring SV1 without disturbing the stationary state of the sludge phase using one cylindrical SV tank, the stationary state may be continued and SV2 may be measured. .

1 ... Sampling pump 2 ... SV measuring tank (SV tank)
3 .... Additive solution tank 4 .... Addition pump 5 ... Stirring pump 6 ... Absorbance meter 7 ... Discharge metering pump 8 ... Computer 10 ... Denitrification Reaction measuring device

Claims (3)

A method for evaluating the degree of denitrification reactivity of an activated sludge mixture in activated sludge treatment and biological denitrification processes,
The activated sludge mixed solution is allowed to stand in a cylinder, and SV1 and SV2, which are SV values after standing for a short time (t1) and standing for a long time (t2) (where t2> t1), are measured.
A denitrification reaction strength evaluation method for an activated sludge mixed liquid, characterized in that the magnitude of denitrification reactivity is evaluated by comparing SV1 and SV2. A method for evaluating the degree of denitrification reactivity of an activated sludge mixture in activated sludge treatment and biological denitrification processes,
The activated sludge mixed solution is allowed to stand in the first cylinder, and the SV value (SV1) after standing for a short time (t1) is measured.
Into the second cylinder containing the activated sludge mixed solution, the BOD solution was added in advance and left standing, and the SV value after standing for a long time (SV2s) was measured.
A method for evaluating the denitrification reaction strength of an activated sludge mixed liquid, wherein the magnitude of denitrification reactivity is evaluated by comparing SV1 and SV2s. 3. The activated sludge mixed liquid according to claim 1 or 2, wherein the short-time standing (t1) is 20 minutes to 40 minutes and the long-time standing (t2) is 60 minutes to 150 minutes. Denitrification reaction strength evaluation method.

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